WorldWideScience

Sample records for titanite u-th-pb dating

  1. U-Th-Pb systematics in zircon and titanite

    International Nuclear Information System (INIS)

    Zartman, R.E.; Kwak, L.M.

    1990-01-01

    U-Th-Pb isotopic analyses of zircon and titanite were made for two core samples of granite from borehole ATK-1 drilled into the Eye-Dashwa Lakes pluton. One of the samples from near the bottom of the hole (990.97 to 996.78 m) yielded zircon and titanite that were slightly to severely disturbed isotopically. Eight fractions of zircon give an upper concordia intercept age of 2625 ± 16 Ma (MSWD = 34), which, based on an evaluation of the more concordant data points and on other geochronological results, is interpreted as being slightly too young. The time of crystallization is probably better approximated by the 207 Pb/ 206 Pb age of 2665 Ma determined on a slightly (∼8 percent) discordant titanite. The other sample from near the surface (3.85 to 9.61 m) generally revealed even more severely disturbed isotopic systematics for both zircon and titanite. The complex nature of the disturbances probably resulted from the penetration of meteoritic water into rock already modified by post-crystallization hydrothermal alteration. Nuclide migration occurred in both minerals -- during the Middle or Late Proterozoic for the zircon and during the modern weathering cycle for the titanite. Material balance calculations are used to demonstrate a recent relative gain of radiogenic Pb and/or loss of Th and U from the freshest-looking, least-altered titanite by exchange with altered, leucoxenite-bearing titanite

  2. Hydrothermal titanite from the Chengchao iron skarn deposit: temporal constraints on iron mineralization, and its potential as a reference material for titanite U-Pb dating

    Science.gov (United States)

    Hu, Hao; Li, Jian-Wei; McFarlane, Christopher R. M.

    2017-09-01

    Uranium-lead isotopes and trace elements of titanite from the Chengchao iron skarn deposit (Daye district, Eastern China), located along the contact zones between Triassic marine carbonates and an early Cretaceous intrusive complex consisting of granite and quartz diorite, were analyzed using laser ablation inductively coupled plasma mass spectrometry to provide temporal constraints on iron mineralization and to evaluate its potential as a reference material for titanite U-Pb geochronology. Titanite grains from mineralized endoskarn have simple growth zoning patterns, exhibit intergrowth with magnetite, diopside, K-feldspar, albite and actinolite, and typically contain abundant primary two-phase fluid inclusions. These paragenetic and textural features suggest that these titanite grains are of hydrothermal origin. Hydrothermal titanite is distinct from the magmatic variety from the ore-related granitic intrusion in that it contains unusually high concentrations of U (up to 2995 ppm), low levels of Th (12.5-453 ppm), and virtually no common Pb. The REE concentrations are much lower, as are the Th/U and Lu/Hf ratios. The hydrothermal titanite grains yield reproducible uncorrected U-Pb ages ranging from 129.7 ± 0.7 to 132.1 ± 2.7 Ma (2σ), with a weighted mean of 131.2 ± 0.2 Ma [mean standard weighted deviation (MSWD) = 1.7] that is interpreted as the timing of iron skarn mineralization. This age closely corresponds to the zircon U-Pb age of 130.9 ± 0.7 Ma (MSWD = 0.7) determined for the quartz diorite, and the U-Pb ages for zircon and titanite (130.1 ± 1.0 Ma and 131.3 ± 0.3 Ma) in the granite, confirming a close temporal and likely genetic relationship between granitic magmatism and iron mineralization. Different hydrothermal titanite grains have virtually identical uncorrected U-Pb ratios suggestive of negligible common Pb in the mineral. The homogeneous textures and U-Pb characteristics of Chengchao hydrothermal titanite suggest that the mineral might be a

  3. Integrated Laser Ablation U/Pb and (U-Th)/He Dating of Detrital Accessory Minerals from the Naryani River, Central Nepal

    Science.gov (United States)

    Horne, A.; Hodges, K. V.; Van Soest, M. C.

    2015-12-01

    The newly developed 'laser ablation double dating' (LADD) technique, an integrated laser microprobe U/Pb and (U-Th)/He dating method, could be an exceptionally valuable tool in detrital thermochronology for identifying sedimentary provenance and evaluating the exhumation history of a source region. A recent proof-of-concept study has used LADD to successfully date both zircon and titanite crystals from the well-characterized Fish Canyon tuff, but we also believe that another accessory mineral, rutile, could be amenable to dating via the LADD technique. To continue the development of the method, we present an application of LADD to detrital zircon, titanite, and rutile from a sample collected on the lower Naryani River of central Nepal. Preliminary analyses of the sample have yielded zircon U/Pb dates ranging from 31.4 to 2405 Ma; zircon (U-Th)/He from 1.8 to 15.4 Ma; titanite U/Pb between 18 and 110 Ma; titanite (U-Th)/He between 1 and 16 Ma; rutile U/Pb from 6 to 45 Ma; and rutile (U-Th)/He from 2 to 25 Ma. In addition to the initial data, we can use Ti-in-zircon, Zr-in-titanite, and Zr-in-rutile thermometers to determine the range of possible long-term cooling rates from grains with U/Pb ages younger than collision. Thus far our results from zircon analyses imply a cooling rate of approximately 15°C/Myr; titanite analyses imply between 10 and 67°C/Myr; and rutile between 9 and 267°C/Myr. This spread in potential cooling rates, especially in the order of magnitude differences of cooling rates calculated from the rutile grains, suggests that the hinterland source regions of the Naryani river experienced dramatically different exhumation histories during Himalayan orogenisis. Ongoing analyses will expand the dataset such that we can more adequately characterize the range of possibilities represented in the sample.

  4. Magmatic Longevity Constrained by ID-TIMS U-Pb Dating of Zircon and Titanite

    Science.gov (United States)

    Szymanowski, D.; Wotzlaw, J. F.; Ellis, B. S.; Bachmann, O.; Von Quadt, A.

    2016-12-01

    Clues about the timescales and thermal conditions associated with the growth and evacuation of large silicic magma reservoirs are frequently drawn from radiometric dating, diffusion modelling, or thermomechanical modelling. A growing amount of petrological and geochronological evidence, supported by thermal modelling, suggests that many silicic magma reservoirs may exist for some 104-106 years in the form of high-crystallinity mushes at relatively low temperatures ( 700-750°C; [1-3]). Geochronological studies addressing this issue typically utilise the U-Pb system in zircon capable of recording extended periods of crystallisation, particularly in evolved calc-alkaline systems that spend most of their lifetime zircon-saturated. In this study, we integrate U-Pb dating of zircon and titanite to investigate the longevity of the magma reservoir that produced the Kneeling Nun Tuff, a 35 Ma, >900 km3 crystal-rich rhyolitic super-eruption from the Mogollon-Datil volcanic field in New Mexico (USA). High-precision ID-TIMS U-Pb dates of single crystals of both zircon and titanite independently record a continuous crystallisation history over >400,000 years. We combine the dating of both accessory phases with textural, major, trace element and isotopic studies of single crystals, placing tight constraints on the thermal conditions of magma accumulation and storage while recording differentiation and rejuvenation processes within the magma reservoir. The results suggest a protracted `cool' upper-crustal storage of magma prior to the Kneeling Nun Tuff eruption followed by a melting event which reduced the magma crystallinity and conditioned it for eruption. [1] Bachmann & Bergantz (2004), J. Petrol. 45, 1565-1582. [2] Gelman et al. (2013), Geology 41, 759-762. [3] Cooper & Kent (2014), Nature 506, 480-483.

  5. Titanite chronology, thermometry, and speedometry of ultrahigh-temperature (UHT) calc-silicates from south Madagascar: U-Pb dates, Zr temperatures, and lengthscales of trace-element diffusion

    Science.gov (United States)

    Holder, R. M.; Hacker, B. R.

    2017-12-01

    Calc-silicate rocks are often overlooked as sources of pressure-temperature-time data in granulite-UHT metamorphic terranes due to the strong dependence of calc-silicate mineral assemblages on complex fluid compositions and a lack of thermodynamic data on common high-temperature calc-silicate minerals such as scapolite. In the Ediacaran-Cambrian UHT rocks of southern Madagascar, clinopyroxene-scapolite-feldspar-quartz-zircon-titanite calc-silicate rocks are wide-spread. U-Pb dates of 540-520 Ma from unaltered portions of titanite correspond to cooling of the rocks through upper-amphibolite facies and indicate UHT metamorphism occurred before 540 Ma. Zr concentrations in these domains preserve growth temperatures of 900-950 °C, consistent with peak temperatures calculated by pseudosection modeling of nearby osumilite-bearing gneisses. Younger U-Pb dates (510-490 Ma) correspond to fluid-mediated Pb loss from titanite grains, which occurred below their diffusive Pb-closure temperature, along fractures. The extent of fluid alteration is seen clearly in back-scattered electron images and Zr-, Al-, Fe-, Ce-, and Nb-concentration maps. Laser-ablation depth profiling of idioblastic titanite grains shows preserved Pb diffusion profiles at grain rims, but there is no evidence for Zr diffusion, indicating that it was effectively immobile even at UHT.

  6. Reply to Comment on "Zircon U-Th-Pb dating using LA-ICP-MS: Simultaneous U-Pb and U-Th dating on the 0.1 Ma Toya Tephra, Japan"

    Science.gov (United States)

    Ito, Hisatoshi

    2015-04-01

    Guillong et al. (2015) mentioned that corrections for abundance sensitivity for 232Th and molecular zirconium sesquioxide ions (Zr2O3+) are critical for reliable determination of 230Th abundances in zircon for LA-ICP-MS analyses. There is no denying that more rigorous treatments are necessary to obtain more reliable ages than those in Ito (2014). However, as shown in Fig. 2 in Guillong et al. (2015), the uncorrected (230Th)/(238U) for reference zircons except for Mud Tank are only 5-20% higher than unity. Since U abundance of Toya Tephra zircons that have U-Pb ages Ito (2014) obtained U-Th ages of the Toya Tephra by comparison with Fish Canyon Tuff (FCT) data. Because both the FCT and the Toya Tephra have similar trends of overestimation of 230Th, the effect of overestimation of 230Th to cause overestimation of U-Th age should be cancelled out or negligible. Therefore the pivotal conclusion in Ito (2014) that simultaneous U-Pb and U-Th dating using LA-ICP-MS is possible and useful for Quaternary zircons holds true.

  7. U-Pb systematics of zircon and titanite from the Gardnos impact structure, Norway: Evidence for impact at 546 Ma?

    Science.gov (United States)

    Kalleson, E.; Corfu, F.; Dypvik, H.

    2009-05-01

    Zircon and titanite were investigated in impactites of the Gardnos structure, a crater formed in Sveconorwegian (ca. 1 Ga) crust, which was then overridden in the Devonian by Caledonian nappes. Observed deformation features in zircons are granular texture, planar microstructures, and likely the incorporation of organic carbon during impact causing black staining of the zircon grains. The grains were studied by scanning electron microscopy (SEM) and cathode luminescence (CL) and dated by U-Pb isotope dilution - thermo-ionization mass spectrometry (ID-TIMS). Zircon grains without impact related features have U-Pb data showing moderate discordance (5-13%) and indicating formation ages mostly in the range of 1600-1000 Ma, except detrital zircon ages as old as >2481 Ma, reflecting the diversity of target rocks in the area. Titanite with concordant ages of 995-999 Ma dates metamorphism during final juxtaposition of the Telemarkia on the Idefjorden terrane to the east. Zircon grains with demonstrated or presumed shock features yield highly discordant (14-40%) U-Pb data, with a majority of them plotting along an array with a lower intercept of about 340 Ma reflecting the influence of the Caledonian orogeny and recent Pb-loss. One zircon grain was totally reset at 379 Ma during late Caledonian metamorphism, which also caused local growth of new titanite. A specific group of zircon grains yields data with relatively high discordance for moderate U contents, and five of these analyses, including that of a grain with proven granular or aggregate texture, fit a discordia line with an upper intercept of 546 ± 5 Ma. These features are interpreted as indicating zircon break-down to an amorphous state during impact, with subsequent recrystallization into microcrystalline aggregates causing extensive to complete Pb loss. We further suggest that their crystallinity prevented Pb loss during the Caledonian orogeny, while the small subgrain size and increasing metamictisation allowed

  8. Laser Ablation in situ (U-Th-Sm)/He and U-Pb Double-Dating of Apatite and Zircon: Techniques and Applications

    Science.gov (United States)

    McInnes, B.; Danišík, M.; Evans, N.; McDonald, B.; Becker, T.; Vermeesch, P.

    2015-12-01

    We present a new laser-based technique for rapid, quantitative and automated in situ microanalysis of U, Th, Sm, Pb and He for applications in geochronology, thermochronometry and geochemistry (Evans et al., 2015). This novel capability permits a detailed interrogation of the time-temperature history of rocks containing apatite, zircon and other accessory phases by providing both (U-Th-Sm)/He and U-Pb ages (+trace element analysis) on single crystals. In situ laser microanalysis offers several advantages over conventional bulk crystal methods in terms of safety, cost, productivity and spatial resolution. We developed and integrated a suite of analytical instruments including a 193 nm ArF excimer laser system (RESOlution M-50A-LR), a quadrupole ICP-MS (Agilent 7700s), an Alphachron helium mass spectrometry system and swappable flow-through and ultra-high vacuum analytical chambers. The analytical protocols include the following steps: mounting/polishing in PFA Teflon using methods similar to those adopted for fission track etching; laser He extraction and analysis using a 2 s ablation at 5 Hz and 2-3 J/cm2fluence; He pit volume measurement using atomic force microscopy, and U-Th-Sm-Pb (plus optional trace element) analysis using traditional laser ablation methods. The major analytical challenges for apatite include the low U, Th and He contents relative to zircon and the elevated common Pb content. On the other hand, apatite typically has less extreme and less complex zoning of parent isotopes (primarily U and Th). A freeware application has been developed for determining (U-Th-Sm)/He ages from the raw analytical data and Iolite software was used for U-Pb age and trace element determination. In situ double-dating has successfully replicated conventional U-Pb and (U-Th)/He age variations in xenocrystic zircon from the diamondiferous Ellendale lamproite pipe, Western Australia and increased zircon analytical throughput by a factor of 50 over conventional methods

  9. Zircon, titanite, and apatite (U-Th)/He ages and age-eU correlations from the Fennoscandian Shield, southern Sweden

    Science.gov (United States)

    Guenthner, William R.; Reiners, Peter W.; Drake, Henrik; Tillberg, Mikael

    2017-07-01

    Craton cores far from plate boundaries have traditionally been viewed as stable features that experience minimal vertical motion over 100-1000 Ma time scales. Here we show that the Fennoscandian Shield in southeastern Sweden experienced several episodes of burial and exhumation from 1800 Ma to the present. Apatite, titanite, and zircon (U-Th)/He ages from surface samples and drill cores constrain the long-term, low-temperature history of the Laxemar region. Single grain titanite and zircon (U-Th)/He ages are negatively correlated (104-838 Ma for zircon and 160-945 Ma for titanite) with effective uranium (eU = U + 0.235 × Th), a measurement proportional to radiation damage. Apatite ages are 102-258 Ma and are positively correlated with eU. These correlations are interpreted with damage-diffusivity models, and the modeled zircon He age-eU correlations constrain multiple episodes of heating and cooling from 1800 Ma to the present, which we interpret in the context of foreland basin systems related to the Neoproterozoic Sveconorwegian and Paleozoic Caledonian orogens. Inverse time-temperature models constrain an average burial temperature of 217°C during the Sveconorwegian, achieved between 944 Ma and 851 Ma, and 154°C during the Caledonian, achieved between 366 Ma and 224 Ma. Subsequent cooling to near-surface temperatures in both cases could be related to long-term exhumation caused by either postorogenic collapse or mantle dynamics related to the final assembly of Rodinia and Pangaea. Our titanite He age-eU correlations cannot currently be interpreted in the same fashion; however, this study represents one of the first examples of a damage-diffusivity relationship in this system, which deserves further research attention.

  10. Finding the "true" age: ways to read high-precision U-Pb zircon dates

    Science.gov (United States)

    Schaltegger, U.; Schoene, B.; Ovtcharova, M.; Sell, B. K.; Broderick, C. A.; Wotzlaw, J.

    2011-12-01

    Refined U-Pb dating techniques, applying an empirical chemical abrasion treatment prior to analysis [1], and using a precisely calibrated double isotope Pb, U EARTHTIME tracer solution, have led to an unprecedented two problems: (A) Post-crystallization Pb loss from decay damaged areas is considered to be mitigated by applying chemical abrasion techniques. The success of such treatment can, however, not be assumed a priori. The following examples demonstrate that youngest zircons are not biased by lead loss but represent close-to-youngest zircon growth: (i) coincidence of youngest zircon dates with co-magmatic titanite in tonalite; (ii) coincidence with statistically equivalent clusters of 206Pb/238U dates from zircon in residual melts of cogenetic mafic magmas; (iii) youngest zircons in ash beds of sedimentary sequences do not violate the stratigraphic superposition, whereas conventional statistical interpretation (mean or median values) does; (iv) results of published inter-laboratory cross-calibration tests using chemical abrasion on natural zircon crystals of the same sample arrive at the same 206Pb/238U result within case of single, significantly younger dates (>3 sigma), and are common in many pre-Triassic and hydrothermally altered rocks. (B) Pre-eruptive/pre-intrusive growth is found to be the main reason for scattered zircon ages in igneous rocks. Zircons crystallizing from the final magma batch are called autocrystic [3]. Autocrystic growth will happen in a moving or stagnant magma shortly before or after the rheological lockup by the crystals. Last crystallizing zircons in the interstitial melt may therefore postdate emplacement of the magma. The range of 206Pb/238U ages may yield a time frame for the cooling of a given magma batch, which could be added to quantitative thermal models of magma emplacement and cooling. Hf isotopes and trace elements of the dated zircon are used to trace the nature of the dated grains [4], specifically for identification of

  11. Ion microprobe U-Pb dating of a dinosaur tooth

    International Nuclear Information System (INIS)

    Sano, Yuji; Terada, Kentaro; Ly, Chi V.; Park, Eun Ju

    2006-01-01

    Ion microprobe U-Pb dating of apatite is applied to a fossil tooth of a Allosaurid derived from the Hasandong Formation in the Gyeongsang basin, southeastern Korea. Twelve spots on a single fragment of the fossil dentine yield a Tera-Wasserburg concordia intercept age of 115±10 Ma (2σ, MSWD=0.59) on a 238 U/ 206 Pb- 207 Pb/ 206 Pb- 204 Pb/ 206 Pb diagram. The age provides a constraint on the depositional age of the fossil in its host Hassandong Formation as Early Aptian. The success of the ion microprobe dating depends on the heterogeneities of diagenetically incorporated U and Pb at the few hundred μm scale, the consequent variations in Pb isotopic compositions due to radioactive decay and the closed-system behavior of U and Pb. There are at least three end-members to explain the variations of minor chemical components such as FeO, SiO 2 and Al 2 O 3 , and trace elements as Th, U and rare earth elements (REE) in the sample by a simple mixing model. They are (1) very low minor and REE, very high common Pb with variable U abundances, (2) low common Pb, high minor, REE, and U abundances, and (3) low minor, common Pb, and U with intermediate REE abundances, even though groups (2) and (3) may consist of a larger group. Various contributions of the three (and/or two) end-members during diagenetic processes may cause the elemental fractionation of U and Pb in a fossil tooth. (author)

  12. Characterization of titanite generations from Gameleira-I deposit (U-anomaly 35) Lagoa Real Uranium Province (LRUP), Bahia state, Brazil

    International Nuclear Information System (INIS)

    Santos, Camila M. dos; Rios, Francisco Javier; Amorim, Lucas E.D.; Palmieri, Helena E.

    2017-01-01

    The Lagoa Real Uranium Province (LRUP) is located in northwest of Bahia state and is the major uranium deposit of Brazil. Titanite is a common accessory mineral in rocks of LRUP and usually is part of uranium ore assemblage. Thirty three polished thin sections of F10 drill-hole located in Gameleira I deposit (anomaly 35) were petrographically studied and used for mineral chemistry study. Petrographically, titanite can be differentiated according to texture between granular and prismatic. Granular titanite is generally associated with magmatic assemblage (alkali feldspar hypersolvus granite) and it is present in some albitites (barren magnetite albitite). Prismatic titanite is restricted to albitite (garnet and mineralized magnetite albitite) and is associated with metamorphic assemblage. Microprobe analyses shows a trend from granites to mineralized albitites and do not cluster titanite by its texture, but by its host rocks. On the other hand, trace elements can distinguish titanite generation according to texture. Granular titanite is characterized by some highest high field strength elements (HFSE) values, like Hf, Pb, Th, U and HREE+Y, and the lowest V content. Vanadium has positive correlation with Zr/Hf ratio and inverse with U. Vanadium versus U relationship is inverse to the previously found by literature in LRUP what indicates that titanite was submitted to complexes processes of uranium loss after its crystallization. In addition, hafnium loss can be related to precipitation of hydrothermal zircon as it is strongly partitioned to this mineral. (author)

  13. Characterization of titanite generations from Gameleira-I deposit (U-anomaly 35) Lagoa Real Uranium Province (LRUP), Bahia state, Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Santos, Camila M. dos; Rios, Francisco Javier; Amorim, Lucas E.D.; Palmieri, Helena E., E-mail: cms@cdtn.br [Centro de Desenvolvimento da Tecnologia Nuclear (CDTN/CNEN-MG), Belo Horizonte, MG (Brazil)

    2017-11-01

    The Lagoa Real Uranium Province (LRUP) is located in northwest of Bahia state and is the major uranium deposit of Brazil. Titanite is a common accessory mineral in rocks of LRUP and usually is part of uranium ore assemblage. Thirty three polished thin sections of F10 drill-hole located in Gameleira I deposit (anomaly 35) were petrographically studied and used for mineral chemistry study. Petrographically, titanite can be differentiated according to texture between granular and prismatic. Granular titanite is generally associated with magmatic assemblage (alkali feldspar hypersolvus granite) and it is present in some albitites (barren magnetite albitite). Prismatic titanite is restricted to albitite (garnet and mineralized magnetite albitite) and is associated with metamorphic assemblage. Microprobe analyses shows a trend from granites to mineralized albitites and do not cluster titanite by its texture, but by its host rocks. On the other hand, trace elements can distinguish titanite generation according to texture. Granular titanite is characterized by some highest high field strength elements (HFSE) values, like Hf, Pb, Th, U and HREE+Y, and the lowest V content. Vanadium has positive correlation with Zr/Hf ratio and inverse with U. Vanadium versus U relationship is inverse to the previously found by literature in LRUP what indicates that titanite was submitted to complexes processes of uranium loss after its crystallization. In addition, hafnium loss can be related to precipitation of hydrothermal zircon as it is strongly partitioned to this mineral. (author)

  14. Enhanced provenance interpretation using combined U-Pb and (U-Th)/He double dating of detrital zircon grains from lower Miocene strata, proximal Gulf of Mexico Basin, North America

    Science.gov (United States)

    Xu, Jie; Stockli, Daniel F.; Snedden, John W.

    2017-10-01

    Detrital zircon U-Pb analysis is an effective approach for investigating sediment provenance by relating crystallization age to potential crystalline source terranes. Studies of large passive margin basins, such as the Gulf of Mexico Basin, that have received sediment from multiple terranes with non-unique crystallization ages or sedimentary strata, benefit from additional constraints to better elucidate provenance interpretation. In this study, U-Pb and (U-Th)/He double dating analyses on single zircons from the lower Miocene sandstones in the northern Gulf of Mexico Basin reveal a detailed history of sediment source evolution. U-Pb age data indicate that most zircon originated from five major crystalline provinces, including the Western Cordillera Arc (1800 Ma) terranes. Zircon (U-Th)/He ages record tectonic cooling and exhumation in the U.S. since the Mesoproterozoic related to the Grenville to Laramide Orogenies. The combined crystallization and cooling information from single zircon double dating can differentiate volcanic and plutonic zircons. Importantly, the U-Pb-He double dating approach allows for the differentiation between multiple possible crystallization-age sources on the basis of their subsequent tectonic evolution. In particular, for Grenville zircons that are present in all of lower Miocene samples, four distinct zircon U-Pb-He age combinations are recognizable that can be traced back to four different possible sources. The integrated U-Pb and (U-Th)/He data eliminate some ambiguities and improves the provenance interpretation for the lower Miocene strata in the northern Gulf of Mexico Basin and illustrate the applicability of this approach for other large-scale basins to reconstruct sediment provenance and dispersal patterns.

  15. Th-U-PbT dating by Electron Probe Microanalysis, Part I. Monazite: analytical procedures and data treatment

    International Nuclear Information System (INIS)

    Vlach, Silvio Roberto Farias

    2010-01-01

    Dating methodology by the electron probe microanalyser (EPMA) of (Th, U)-bearing minerals, highlighting monazite, acquired greater than ever importance in literature, particularly due to its superior spatial resolution, as well as versatility, which allow correlating petrological processes at times registered only in micro-scales in minerals and rocks with absolute ages. Although the accuracy is inferior to the one achieved with conventional isotopic methods in up to an order of magnitude, EPMA is the instrument that allows the best spatial resolution, reaching a few μm 3 in some conditions. Quantification of minor and trace elements with suitable precision and accuracy involves the own instrumental and analytical set-ups and data treatment strategies, significantly more rigorous when compared with those applied in conventional analyses. Th-U-Pb T dating is an example of these cases. Each EPMA is a unique machine as for its instrumental characteristics and respective automation system. In such a way, analytical procedures ought to be adjusted for laboratory specificities. The analytical strategies and data treatment adopted in the Electronic Microprobe Laboratory from Instituto de Geociencias of Universidade de Sao Paulo, Brazil, with a JEOL JXA8600S EPMA, and a ThermoNoran-Voyager 4.3 automation system, are presented and compared with the ones used in other laboratories. The influence of instrumental factors and spectral overlaps on Th, U, and Pb quantification is discussed. Applied procedures to interference correction, error propagation, data treatment, and fi nal chemical age presentation as well as to sampling and analyses are emphasized. Some typical applications are discussed, drawing attention to the most relevant aspects of electron microprobe dating. (author)

  16. New zircon (U-Th)/He and U/Pb eruption age for the Rockland tephra, western USA

    Science.gov (United States)

    Coble, Matthew A.; Burgess, Seth D.; Klemetti, Erik W.

    2017-09-01

    Eruption ages of a number of prominent Quaternary volcanic deposits remain inaccurately and/or imprecisely constrained, despite their importance as regional stratigraphic markers in paleo-environment reconstruction and as evidence of climate-altering eruptions. Accurately dating volcanic deposits presents challenging analytical considerations, including poor radiogenic yield, scarcity of datable minerals, and contamination of crystal populations by magma, eruption, and transport processes. One prominent example is the Rockland tephra, which erupted from the Lassen Volcanic Center in the southern Cascade arc. Despite a range in published eruption ages from 0.40 to 0.63 Ma, the Rockland tephra is extensively used as a marker bed across the western United States. To more accurately and precisely constrain the age of the Rockland tephra-producing eruption, we report U/Pb crystallization dates from the outermost ∼2 μm of zircon crystal faces (surfaces) using secondary ion mass spectrometry (SIMS). Our new weighted mean 238U/206Pb age for Rockland tephra zircon surfaces is 0.598 ± 0.013 Ma (2σ) and MSWD = 1.11 (mean square weighted deviation). As an independent test of the accuracy of this age, we obtained new (U-Th)/He dates from individual zircon grains from the Rockland tephra, which yielded a weighted mean age of 0.599 ± 0.012 Ma (2σ, MSWD = 5.13). We also obtained a (U-Th)/He age of 0.628 ± 0.014 Ma (MSWD = 1.19) for the Lava Creek Tuff member B, which was analyzed as a secondary standard to test the accuracy of the (U-Th)/He technique for Quaternary tephras, and to evaluate assumptions made in the model-age calculation. Concordance of new U/Pb and (U-Th)/He zircon ages reinforces the accuracy of our preferred Rockland tephra eruption age, and confirms that zircon surface dates sample zircon growth up to the time of eruption. We demonstrate the broad applicability of coupled U/Pb zircon-surface and single-grain zircon (U-Th)/He geochronology to accurate

  17. Th-U-Pb{sub T} dating by electron probe microanalysis, Part I. Monazite: analytical procedures and data treatment

    Energy Technology Data Exchange (ETDEWEB)

    Vlach, Silvio Roberto Farias [Universidade de Sao Paulo (USP), Sao Carlos, SP (Brazil). Inst. de Geociencias. Dept. de Mineralogia e Geotectonica], e-mail: srfvlach@usp.br

    2010-03-15

    Dating methodology by the electron probe microanalyser (EPMA) of (Th, U)-bearing minerals, highlighting monazite, acquired greater than ever importance in literature, particularly due to its superior spatial resolution, as well as versatility, which allow correlating petrological processes at times registered only in micro-scales in minerals and rocks with absolute ages. Although the accuracy is inferior to the one achieved with conventional isotopic methods in up to an order of magnitude, EPMA is the instrument that allows the best spatial resolution, reaching a few {mu}m{sup 3} in some conditions. Quantification of minor and trace elements with suitable precision and accuracy involves the own instrumental and analytical set-ups and data treatment strategies, significantly more rigorous when compared with those applied in conventional analyses. Th-U-Pb{sub T} dating is an example of these cases. Each EPMA is a unique machine as for its instrumental characteristics and respective automation system. In such a way, analytical procedures ought to be adjusted for laboratory specific cities. The analytical strategies and data treatment adopted in the Electronic Microprobe Laboratory from Instituto de Geociencias of Universidade de Sao Paulo, Brazil, with a JEOL JXA8600S EPMA, and a ThermoNoran-Voyager 4.3 automation system, are presented and compared with the ones used in other laboratories. The influence of instrumental factors and spectral overlaps on Th, U, and Pb quantification is discussed. Applied procedures to interference correction, error propagation, data treatment, and final chemical age presentation as well as to sampling and analyses are emphasized. Some typical applications are discussed, drawing attention to the most relevant aspects of electron microprobe dating. (author)

  18. Correcting for long-alpha stopping distances in (U-Th)/He dating

    Science.gov (United States)

    Glotzbach, Christoph; Lang, Karl; Avdievitch, Nikita; Flowers, Rebecca; Metcalf, James; Ehlers, Todd

    2017-04-01

    factors from photomicrographs taken at multiple perspectives that include images where the crystallographic c-axis of grains perpendicular to the field of view. This approach works on grains of any shape, as the 3D grain shape is numerically approximated directly from photomicrographs. A Monte Carlo simulation is then used to calculate the Ft correction factor. Preliminary applications of this new approach suggest that it is best applied to calculate Ft correction factors of broken grains and for those grains with abnormal shapes not well described by typical shapes used in the prior derivation of analytical solutions. In the latter case Ft values can be >10% different, largely exceeding the analytical error. Future MicroCT analyses may allow for quantitative evaluation of the accuracy of the numerical and traditional measurement approaches. References Dobson, K.J., Stuart, F.M., Dempster, T.J. 2008. U and Th zonation in Fish Canyon Tuff zircons: implications for a zircon (U-Th)/He standard. Geochim. Cosmochim. Acta 72, 4745-4755. Farley, K.A., Wolf, R.A., Silver, L.T. 1996.The effects of long alpha-stopping distances on (U-Th)/He ages. Geochim. Cosmochim. Acta 60, 4223-4229. Horne, A.M., van Soest, M.C., Hodges, K.V., Tripathy-Lang, A., Hourigan, J.K. 2016. Integrated single crystal laser ablation U/Pb and (U-Th)/He dating of detrital accessory minerals - Proof-of-concept studies of titanites and zircons from the Fish Canyon tuff. Geochim. Cosmochim. Acta 178, 106-123. Ketcham, R.A., Gautheron, C., Tassan-Got, L. 2011. Accounting for long alpha-particle stopping distances in (U-Th-Sm)/He geochronology: refinement of the baseline case. Geochim. Cosmochim. Acta 75, 7779-7791.

  19. U-Th Burial Dates on Ostrich Eggshell

    Science.gov (United States)

    Sharp, W. D.; Fylstra, N. D.; Tryon, C. A.; Faith, J. T.; Peppe, D. J.

    2015-12-01

    Obtaining precise and accurate dates at archaeological sites beyond the range of radiocarbon dating is challenging but essential for understanding human origins. Eggshells of ratites (large flightless birds including ostrich, emu and others) are common in many archaeological sequences in Africa, Australia and elsewhere. Ancient eggshells are geochemically suitable for the U-Th technique (1), which has about ten times the range of radiocarbon dating (>500 rather than 50 ka), making eggshells attractive dating targets. Moreover, C and N isotopic studies of eggshell provide insights into paleovegetation and paleoprecipitation central to assessing past human-environment interactions (2,3). But until now, U-Th dates on ratite eggshell have not accounted for the secondary origin of essentially all of their U. We report a novel approach to U-Th dating of eggshell that explicitly accounts for secondary U uptake that begins with burial. Using ostrich eggshell (OES) from Pleistocene-Holocene east African sites, we have measured U and 232Th concentration profiles across OES by laser ablation ICP-MS. U commonly peaks at 10s to 100s of ppb and varies 10-fold or more across the ~2 mm thickness of OES, with gradients modulated by the layered structure of the eggshell. Common Th is high near the shell surfaces, but low in the middle "pallisade" layer of OES, making it optimal for U-Th dating. We determine U-Th ages along the U concentration gradient by solution ICP-MS analyses of two or more fractions of the pallisade layer. We then estimate OES burial dates using a simple model for diffusive uptake of uranium. Comparing such "U-Th burial dates" with radiocarbon dates for OES calcite from the same shells, we find good agreement in 7 out of 9 cases, consistent with rapid burial and confirming the accuracy of the approach. The remaining 2 eggshells have anomalous patterns of apparent ages that reveal they are unsuitable for U-Th dating, thereby providing reliability criteria innate

  20. Th-U-PbT dating by Electron Probe Microanalysis, Part I. Monazite: analytical procedures and data treatment;Datacao Th-U-Pb{sub T} com microssonda eletronica, Parte I. Monazita: procedimentos analiticos e tratamento de dados

    Energy Technology Data Exchange (ETDEWEB)

    Vlach, Silvio Roberto Farias, E-mail: srfvlach@usp.b [Universidade de Sao Paulo (IG/USP), SP (Brazil). Inst. de Geociencias. Dept. de Mineralogia e Geotectonica

    2010-03-15

    Dating methodology by the electron probe microanalyser (EPMA) of (Th, U)-bearing minerals, highlighting monazite, acquired greater than ever importance in literature, particularly due to its superior spatial resolution, as well as versatility, which allow correlating petrological processes at times registered only in micro-scales in minerals and rocks with absolute ages. Although the accuracy is inferior to the one achieved with conventional isotopic methods in up to an order of magnitude, EPMA is the instrument that allows the best spatial resolution, reaching a few {mu}m{sup 3} in some conditions. Quantification of minor and trace elements with suitable precision and accuracy involves the own instrumental and analytical set-ups and data treatment strategies, significantly more rigorous when compared with those applied in conventional analyses. Th-U-Pb{sub T} dating is an example of these cases. Each EPMA is a unique machine as for its instrumental characteristics and respective automation system. In such a way, analytical procedures ought to be adjusted for laboratory specificities. The analytical strategies and data treatment adopted in the Electronic Microprobe Laboratory from Instituto de Geociencias of Universidade de Sao Paulo, Brazil, with a JEOL JXA8600S EPMA, and a ThermoNoran-Voyager 4.3 automation system, are presented and compared with the ones used in other laboratories. The influence of instrumental factors and spectral overlaps on Th, U, and Pb quantification is discussed. Applied procedures to interference correction, error propagation, data treatment, and fi nal chemical age presentation as well as to sampling and analyses are emphasized. Some typical applications are discussed, drawing attention to the most relevant aspects of electron microprobe dating. (author)

  1. The 230Th correction is the 1st priority for accurate dates of young zircons: U/Th partitioning experiments and measurements

    Science.gov (United States)

    Krawczynski, M.; McLean, N.

    2017-12-01

    One of the most accurate and useful ways of determining the age of rocks that formed more than about 500,000 years ago is uranium-lead (U-Pb) geochronology. Earth scientists use U-Pb geochronology to put together the geologic history of entire regions and of specific events, like the mass extinction of all non-avian dinosaurs about 66 million years ago or the catastrophic eruptions of supervolcanoes like the one currently centered at Yellowstone. The mineral zircon is often utilized because it is abundant, durable, and readily incorporates uranium into its crystal structure. But it excludes thorium, whose isotope 230Th is part of the naturally occurring isotopic decay chain from 238U to 206Pb. Calculating a date from the relative abundances of 206Pb and 238U therefore requires a correction for the missing 230Th. Existing experimental and observational constraints on the way U and Th behave when zircon crystallizes from a melt are not known precisely enough, and thus currently the uncertainty in dates introduced by they `Th correction' is one of the largest sources of systematic error in determining dates. Here we present preliminary results on our study of actinide partitioning between zircon and melt. Experiments have been conducted to grow zircon from melts doped with U and Th that mimic natural magmas at a range of temperatures, and compositions. Synthetic zircons are separated from their coexisting glass and using high precision and high-spatial-resolution techniques, the abundance and distribution of U and Th in each phase is determined. These preliminary experiments are the beginning of a study that will result in precise determination of the zircon/melt uranium and thorium partition coefficients under a wide variety of naturally occurring conditions. This data will be fit to a multidimensional surface using maximum likelihood regression techniques, so that the ratio of partition coefficients can be calculated for any set of known parameters. The results of

  2. Community-based Approaches to Improving Accuracy, Precision, and Reproducibility in U-Pb and U-Th Geochronology

    Science.gov (United States)

    McLean, N. M.; Condon, D. J.; Bowring, S. A.; Schoene, B.; Dutton, A.; Rubin, K. H.

    2015-12-01

    The last two decades have seen a grassroots effort by the international geochronology community to "calibrate Earth history through teamwork and cooperation," both as part of the EARTHTIME initiative and though several daughter projects with similar goals. Its mission originally challenged laboratories "to produce temporal constraints with uncertainties approaching 0.1% of the radioisotopic ages," but EARTHTIME has since exceeded its charge in many ways. Both the U-Pb and Ar-Ar chronometers first considered for high-precision timescale calibration now regularly produce dates at the sub-per mil level thanks to instrumentation, laboratory, and software advances. At the same time new isotope systems, including U-Th dating of carbonates, have developed comparable precision. But the larger, inter-related scientific challenges envisioned at EARTHTIME's inception remain - for instance, precisely calibrating the global geologic timescale, estimating rates of change around major climatic perturbations, and understanding evolutionary rates through time - and increasingly require that data from multiple geochronometers be combined. To solve these problems, the next two decades of uranium-daughter geochronology will require further advances in accuracy, precision, and reproducibility. The U-Th system has much in common with U-Pb, in that both parent and daughter isotopes are solids that can easily be weighed and dissolved in acid, and have well-characterized reference materials certified for isotopic composition and/or purity. For U-Pb, improving lab-to-lab reproducibility has entailed dissolving precisely weighed U and Pb metals of known purity and isotopic composition together to make gravimetric solutions, then using these to calibrate widely distributed tracers composed of artificial U and Pb isotopes. To mimic laboratory measurements, naturally occurring U and Pb isotopes were also mixed in proportions to mimic samples of three different ages, to be run as internal

  3. Textures, trace element compositions, and U-Pb ages of titanite from the Mangling granitoid pluton, East Qinling Orogen: Implications for magma mixing and destruction of the North China Craton

    Science.gov (United States)

    Hu, Hao; Li, Jian-Wei; McFarlane, Christopher R. M.; Luo, Yan; McCarron, Travis

    2017-07-01

    The Mangling granitoid pluton, located along the southern margin of the North China Craton, consists mainly of monzogranite with minor amounts of diorite. The monzogranite contains abundant mafic microgranular enclaves (MMEs) and is intruded by numerous mafic dikes, providing an opportunity to study magma mixing and its role in the formation of the granitioid pluton. In this paper, we present in situ analysis of U-Pb isotopes and trace element compositions of titanite from the MMEs and the host monzogranite using Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry to document the role of magma mixing in the formation of the Mangling granitoid pluton. Titanite grains from the MMEs (type 1) are euhedral with patchy zoning, whereas the varieties from the closely associated host monzogranite are euhedral and consist of two types (type 2 and type 3). Type 2 titanite is more abundant and has oscillatory zoning without Fe-Ti oxide inclusions, whereas type 3 grains commonly have Fe-Ti oxide inclusions in the core that is rimmed by inclusion-free overgrowths with weak oscillatory zoning. Titanite from monzogranite without MMEs (type 4) is euhedal and has weak oscillatory zoning, with rare ilmenite inclusions in the core. Titanite from a mafic dike intruding the monzogranite (type 5) is anhedral and has sector zoning. Titanite grains from MMEs and the monzogranite (type 1, 2 and 3) have U-Pb ages that are indistinguishable (149 ± 1 Ma, 148 ± 1 Ma and 148 ± 2 Ma, respectively). These ages agree well with zircon U-Pb ages of 150 ± 1 Ma, 150 ± 1 Ma and 149 ± 1 Ma for the MMEs, host monzogranite, and mafic dike, respectively. The age consistency thus confirms coeval formation of the MMEs, the host monzogranite, and the mafic dikes, demonstrating a mafic magmatic, rather than extraneous or restitic origin for the MMEs. Titanite grains from the MMEs (type 1) and mafic dike (type 5) have much lower Al2O3, REE, Nb/Zr, Y/Zr, and Lu/Hf, but higher (Ce + Nd)/Y and La

  4. Relics of continental lithosphere in the atlantic by data of (Th/U)th, (Th/U)pb, and K/Ti systematics

    International Nuclear Information System (INIS)

    Titayeva, N.A.; Mironov, Y.

    1996-01-01

    The problem of mantle heterogeneity of the Atlantic Ocean has been investigated. Th/U ratio is a sensitive geochemical tracer. This ratio can be calculated from 232Th/230Th or from 208Pb/206Pb since 230Th and 206Pb are decay product of 238U and 208Pb is a product of 232Th decay. The former way to get Th/U ratio is valid for quaternary volcanic rocks because of the relatively short 230Th half life (80000 years), the latter way gives an integral quantity characterizing the pre-oceanic history beginning from the onset of earth formation and ending about 150 million years ago. Clear distinctions between ''depleted oceanic'' and ''enriched continental'' reservoirs have been drawn from comparative analysis of rocks. (A.C.)

  5. Conventional U-Pb dating versus SHRIMP of the Santa Barbara Granite Massif, Rondonia, Brazil

    Science.gov (United States)

    Sparrenberger, I.; Bettencourt, Jorge S.; Tosdal, R.M.; Wooden, J.L.

    2002-01-01

    The Santa Ba??rbara Granite Massif is part of the Younger Granites of Rondo??nia (998 - 974 Ma) and is included in the Rondo??nia Tin Province (SW Amazonian Craton). It comprises three highly fractionated metaluminous to peraluminous within-plate A-type granite units emplaced in older medium-grade metamorphic rocks. Sn-mineralization is closely associated with the late-stage unit. U-Pb monazite conventional dating of the early-stage Serra do Cicero facies and late-stage Serra Azul facies yielded ages of 993 ?? 5 Ma and 989 ?? 13 Ma, respectively. Conventional multigrain U-Pb isotope analyses of zircon demonstrate isotopic disturbance (discordance) and the preservation of inherited older zircons of several different ages and thus yield little about the ages of Sn-granite magmatism. SHRIMP U-Pb ages for the Santa Ba??rbara facies association yielded a 207Pb/206Pb weighted-mean age of 978 ?? 13 Ma. The textural complexity of the zircon crystals of the Santa Ba??rbara facies association, the variable concentrations of U, Th and Pb, as well as the mixed inheritance of zircon populations are major obstacles to using conventional multigrain U-Pb isotopic analyses. Sm-Nd model ages and ??Nd (T) values reveal anomalous isotopic data, attesting to the complex isotopic behaviour within these highly fractionated granites. Thus, SHRIMP U-Pb zircon and conventional U-Pb monazite dating methods are the most appropriate to constrain the crystallization age of the Sn-bearing granite systems in the Rondo??nia Tin Province.

  6. Geologic evolution of the Paraiba do Sul complex, in the central part of the Ribeira belt, based on the geochemistry and U-Pb geochronology studies; Evolucao geologica do complexo Paraiba do Sul, no segmento central da faixa Ribeira, com base em estudos de geoquimica e geocronologia U-Pb

    Energy Technology Data Exchange (ETDEWEB)

    Valladares, Claudia Sayao

    1996-12-31

    Aiming the definition of the Complexo Paraiba do Sul evolution, the work presents a geochronological approach by the U-Pb method, considered appropriate to study polideformed terrains. The minerals used to the U-Pb dating (zircon, titanite and monazite) provides information about the ages of rock generation and the successive geological events the rocks were submitted. The U-Pb geochronological approach is pioneer in the investigated area and two questions referent to the Complexo Paraiba do Sul evolution in the central part of the Ribeira belt, were the aim of this approach. The first of them refers to the crystallization epoch and the gneisses metamorphism, interpreted here like orthogneisses, called Unidade Quirino of the Complexo Paraiba do Sul. The second refers to the metamorphism ages and meta sedimentary unit deformation. Looking for the contribution to the Complexo Paraiba do Sul evolution understanding, this work presents the data based on the geologic map of this area, comprising part of the Folha Volta Redonda (1:50.000), including petrographic, structural and microtectonic studies. It also presents and discusses the results of: 17 U-Pb analysis in zircon and titanite of the Complexo Paraiba do Sul orthogneisses collection; 24 geochemical analysis of major, minor, trace elements and ETR of the same collection; an U-Pb analysis in titanite of the Unidade Sao Joao, 5 U-Pb analysis in titanites and/or monazites of granites and granitoids; 12 geochemical analysis including major, minor and trace elements and ETR, in granites and sills of leucogranites. Finally, the data achieved were integrated with the objective to elaborate an evolutive view of the Complexo Paraiba do Sul 157 refs., 54 figs., 17 tabs.

  7. Geologic evolution of the Paraiba do Sul complex, in the central part of the Ribeira belt, based on the geochemistry and U-Pb geochronology studies; Evolucao geologica do complexo Paraiba do Sul, no segmento central da faixa Ribeira, com base em estudos de geoquimica e geocronologia U-Pb

    Energy Technology Data Exchange (ETDEWEB)

    Valladares, Claudia Sayao

    1997-12-31

    Aiming the definition of the Complexo Paraiba do Sul evolution, the work presents a geochronological approach by the U-Pb method, considered appropriate to study polideformed terrains. The minerals used to the U-Pb dating (zircon, titanite and monazite) provides information about the ages of rock generation and the successive geological events the rocks were submitted. The U-Pb geochronological approach is pioneer in the investigated area and two questions referent to the Complexo Paraiba do Sul evolution in the central part of the Ribeira belt, were the aim of this approach. The first of them refers to the crystallization epoch and the gneisses metamorphism, interpreted here like orthogneisses, called Unidade Quirino of the Complexo Paraiba do Sul. The second refers to the metamorphism ages and meta sedimentary unit deformation. Looking for the contribution to the Complexo Paraiba do Sul evolution understanding, this work presents the data based on the geologic map of this area, comprising part of the Folha Volta Redonda (1:50.000), including petrographic, structural and microtectonic studies. It also presents and discusses the results of: 17 U-Pb analysis in zircon and titanite of the Complexo Paraiba do Sul orthogneisses collection; 24 geochemical analysis of major, minor, trace elements and ETR of the same collection; an U-Pb analysis in titanite of the Unidade Sao Joao, 5 U-Pb analysis in titanites and/or monazites of granites and granitoids; 12 geochemical analysis including major, minor and trace elements and ETR, in granites and sills of leucogranites. Finally, the data achieved were integrated with the objective to elaborate an evolutive view of the Complexo Paraiba do Sul 157 refs., 54 figs., 17 tabs.

  8. U-Pb dating of deformed mafic dyke and host gneiss: implications for understanding reworking processes on the western margin of the Archaean U3o8 Block, NE Sao Francisco Craton, Brazil

    International Nuclear Information System (INIS)

    Oliveira, Elson Paiva

    2000-01-01

    U-Pb ages of deformed mafic dyke and host migmatitic grey gneiss from the transition zone between the Archaen Uaua Block and the Caldeirao Belt are presented. Titanites from the metamorphic dyke's margin and zircons from the gneiss were dated at 2,039 ± 2 Ma and 2,956 ± 39 Ma, respectively. The Sm-Nd data (T DM =2,965 Ma and ε Nd(t) =1.69) on the gneiss, coupled with the U-Pb data on both dyke and gneiss, suggest than an Archaen granodioritic batholith, probably originated at an andean-type continental margin, was intruded by mafic dykes, and subsequently was reworked during the Paleoproterozoic collisional event associated with the development of the Salvador-Curaca Orogen. (author)

  9. U-Th-Pb dating of the Brossasco ultrahigh-pressure metagranite, Dora-Maira massif, western Alps

    Energy Technology Data Exchange (ETDEWEB)

    Paquette, J.L.; Montel, J.M. [Centre National de la Recherche Scientifique, 63 - Clermont-Ferrand (France); Chopin, C. [Ecole Normale Superieure, 75 - Paris (France). Lab. de Geologie

    1999-01-01

    The Brossasco metagranite is part of the coherent ultrahigh-pressure metamorphic terrane in the Dora-Maira massif and, although it has reached Alpine peak metamorphic conditions of about 725 C/30 kbar, still locally preserves an undeformed magmatic texture. In order to obtain new chronological constraints on this key area of the western Alps, we studied the behaviour of the U-Th-Pb system in zircons and monazites from such an undeformed facies. Only zircon fractions containing very small needle-shaped inclusions are concordant at 304{+-}3 Ma. This result is interpreted as the emplacement age of the granite. All other zircons show an old inherited memory and the more U-rich of these crystals were affected by an episodic Pb loss with a poorly defined lower intercept at 60{+-}45 Ma. Both TIMS (thermo-ionisation mass spectrometry) and electron-microprobe analysis of monazites show that this last event has also disturbed their U-Pb and Th-Pb isotopic systems, without resetting them completely. Comparison with cofacial rock-types which have been completely reworked under these extreme P-T conditions shows that deformation and mass transfer as well as the nature of the protoliths and the characteristics of their zircons have a much more pronounced influence on the behaviour of isotopic systems than the temperature and/or pressure parameters. This evidence is an obvious limitation to the use of the blocking-temperature concept. (orig.)

  10. U-Th-Pb dating of the Brossasco ultrahigh-pressure metagranite, Dora-Maira massif, western Alps

    International Nuclear Information System (INIS)

    Paquette, J.L.; Montel, J.M.; Chopin, C.

    1999-01-01

    The Brossasco metagranite is part of the coherent ultrahigh-pressure metamorphic terrane in the Dora-Maira massif and, although it has reached Alpine peak metamorphic conditions of about 725 C/30 kbar, still locally preserves an undeformed magmatic texture. In order to obtain new chronological constraints on this key area of the western Alps, we studied the behaviour of the U-Th-Pb system in zircons and monazites from such an undeformed facies. Only zircon fractions containing very small needle-shaped inclusions are concordant at 304±3 Ma. This result is interpreted as the emplacement age of the granite. All other zircons show an old inherited memory and the more U-rich of these crystals were affected by an episodic Pb loss with a poorly defined lower intercept at 60±45 Ma. Both TIMS (thermo-ionisation mass spectrometry) and electron-microprobe analysis of monazites show that this last event has also disturbed their U-Pb and Th-Pb isotopic systems, without resetting them completely. Comparison with cofacial rock-types which have been completely reworked under these extreme P-T conditions shows that deformation and mass transfer as well as the nature of the protoliths and the characteristics of their zircons have a much more pronounced influence on the behaviour of isotopic systems than the temperature and/or pressure parameters. This evidence is an obvious limitation to the use of the blocking-temperature concept. (orig.)

  11. Chemical U-Th-Pb dating of monazite by 3D-Micro x-ray fluorescence analysis with synchrotron radiation

    DEFF Research Database (Denmark)

    Schmitz, Susanne; Möller, Andreas; Wilke, Max

    2009-01-01

    A confocal set-up for three-dimensional (3D) micro X-ray fluorescence (micro-XRF) was used at the mySpot beamline at BESSY II, which allows compositional depth profiling for various applications. We present results obtained with a confocal 3D micro-XRF set-up for chemical age dating using the U, Th...... and Pb concentrations of monazite within rock thin sections. The probing volume was determined to be approximately 21 × 21 × 24 µm3 for W-La using an excitation energy of 19 keV. The relative detection limits particularly for Pb are below 10 ppm (for counting times of 1000 s). Therefore, this 3D micro...... of ages, varying from 20 Ma to 1.82 Ga. Reference materials (GM3, F6, 3345) can be reproduced within error. The spread in the ages of all points determined by 3D micro-XRF is within 8 % of the isotopic reference value. The average 3D micro-XRF dates reproduce the reference ages with discrepancies between...

  12. Geologic evolution of the Paraiba do Sul complex, in the central part of the Ribeira belt, based on the geochemistry and U-Pb geochronology studies

    International Nuclear Information System (INIS)

    Valladares, Claudia Sayao

    1996-01-01

    Aiming the definition of the Complexo Paraiba do Sul evolution, the work presents a geochronological approach by the U-Pb method, considered appropriate to study polideformed terrains. The minerals used to the U-Pb dating (zircon, titanite and monazite) provides information about the ages of rock generation and the successive geological events the rocks were submitted. The U-Pb geochronological approach is pioneer in the investigated area and two questions referent to the Complexo Paraiba do Sul evolution in the central part of the Ribeira belt, were the aim of this approach. The first of them refers to the crystallization epoch and the gneisses metamorphism, interpreted here like orthogneisses, called Unidade Quirino of the Complexo Paraiba do Sul. The second refers to the metamorphism ages and meta sedimentary unit deformation. Looking for the contribution to the Complexo Paraiba do Sul evolution understanding, this work presents the data based on the geologic map of this area, comprising part of the Folha Volta Redonda (1:50.000), including petrographic, structural and microtectonic studies. It also presents and discusses the results of: 17 U-Pb analysis in zircon and titanite of the Complexo Paraiba do Sul orthogneisses collection; 24 geochemical analysis of major, minor, trace elements and ETR of the same collection; an U-Pb analysis in titanite of the Unidade Sao Joao, 5 U-Pb analysis in titanites and/or monazites of granites and granitoids; 12 geochemical analysis including major, minor and trace elements and ETR, in granites and sills of leucogranites. Finally, the data achieved were integrated with the objective to elaborate an evolutive view of the Complexo Paraiba do Sul

  13. The effects of radiation damage accumulation and annealing on fission-track dating of titanite

    International Nuclear Information System (INIS)

    Enkelmann, Eva; Jonckheere, Raymond; Ratschbacher, Lothar

    2005-01-01

    Fission-track dating of titanite is hindered by the fact that track etching is anisotropic in fresh titanites and becomes isotropic with increasing radiation damage. Independent age determinations with the population method are problematic due to different track counting efficiencies (Q) for ρ s in unannealed and ρ i in annealed titanite. Independent age determinations with the external detector method depend on correction factors for the track registration geometries (G = 0.5), counting efficiencies (Q) and range deficit (R = 1.38); however, Q is unaffected by annealing. It was attempted to determine GQR through calculation, direct experiment and on the basis of age standards. The direct experiment involves measurements of the ratio of the induced-track densities in titanite and a co-irradiated external detector. The track densities in the internal titanite surfaces could not be measured but the results for the external surfaces confirm that this approach leads to a significant overestimation of GQR, due to prior annealing. The GQR-values determined on the basis of age standards are consistent with that obtained by calculation assuming that Q ∼ 1, although there is no experimental confirmation for this fact apart from their isotropic etching characteristics. The fact that identical GQR-factors were obtained on standards of different age and uranium content suggests that a single GQR-value is appropriate for dating titanites within a broad range of radiation damage. In terms of the ζ-calibration this implies that a single ζ-factor is also suitable for dating different titanites. These findings suggest that other factors besides the accumulation of alpha-recoil damage, such as a phase transition, could be co-responsible for the different etching characteristics of annealed and unannealed titanites

  14. Air abrasion experiments in U-Pb dating of zircon

    Science.gov (United States)

    Goldich, S.S.; Fischer, L.B.

    1986-01-01

    Air abrasion of zircon grains can remove metamict material that has lost radiogenic Pb and zircon overgrowths that were added during younger events and thereby improve the precision of the age measurements and permit closer estimates of the original age. Age discordance that resulted from a single disturbance of the U-Pb isotopic decay systems, as had been demonstrated by T.E. Krogh, can be considerably reduced, and, under favorable conditions, the ages brought into concordancy. Two or more events complicate the U-Pb systematics, but a series of abrasion experiments can be helpful in deciphering the geologic history and in arriving at a useful interpretation of the probable times of origin and disturbances. In east-central Minnesota, U.S.A., Penokean tonalite gneiss is dated at 1869 ?? 5 Ma, and sheared granite gneiss is shown to have been a high-level granite intrusion at 1982 ?? 5 Ma in the McGrath Gneiss precursor. Tonalite gneiss and a mafic granodiorite in the Rainy Lake area, Ontario, Canada, are dated at 2736 ?? 16 and 2682 ?? 4 Ma, respectively. The tonalitic phase of the Morton Gneiss, southwestern Minnesota, is dated at 3662 ?? 42 Ma. ?? 1986.

  15. Chemical abrasion-SIMS (CA-SIMS) U-Pb dating of zircon from the late Eocene Caetano caldera, Nevada

    Science.gov (United States)

    Watts, Kathryn E.; Coble, Matthew A.; Vazquez, Jorge A.; Henry, Christopher D.; Colgan, Joseph P.; John, David A.

    2016-01-01

    Zircon geochronology is a critical tool for establishing geologic ages and time scales of processes in the Earth's crust. However, for zircons compromised by open system behavior, achieving robust dates can be difficult. Chemical abrasion (CA) is a routine step prior to thermal ionization mass spectrometry (TIMS) dating of zircon to remove radiation-damaged parts of grains that may have experienced open system behavior and loss of radiogenic Pb. While this technique has been shown to improve the accuracy and precision of TIMS dating, its application to high-spatial resolution dating methods, such as secondary ion mass spectrometry (SIMS), is relatively uncommon. In our efforts to U-Pb date zircons from the late Eocene Caetano caldera by SIMS (SHRIMP-RG: sensitive high resolution ion microprobe, reverse geometry), some grains yielded anomalously young U-Pb ages that implicated Pb-loss and motivated us to investigate with a comparative CA and non-CA dating study. We present CA and non-CA 206Pb/238U ages and trace elements determined by SHRIMP-RG for zircons from three Caetano samples (Caetano Tuff, Redrock Canyon porphyry, and a silicic ring-fracture intrusion) and for R33 and TEMORA-2 reference zircons. We find that non-CA Caetano zircons have weighted mean or bimodal U-Pb ages that are 2–4% younger than CA zircons for the same samples. CA Caetano zircons have mean U-Pb ages that are 0.4–0.6 Myr older than the 40Ar/39Ar sanidine eruption age (34.00 ± 0.03 Ma; error-weighted mean, 2σ), whereas non-CA zircons have ages that are 0.7–1.3 Myr younger. U-Pb ages do not correlate with U (~ 100–800 ppm), Th (~ 50–300 ppm) or any other measured zircon trace elements (Y, Hf, REE), and CA and non-CA Caetano zircons define identical trace element ranges. No statistically significant difference in U-Pb age is observed for CA versus non-CA R33 or TEMORA-2 zircons. Optical profiler measurements of ion microprobe pits demonstrate consistent depths of ~ 1.6

  16. Electron microprobe Th-U-Pb monazite dating and metamorphic evolution of the Acaiaca Granulite Complex, Minas Gerais, Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Medeiros Junior, Edgar Batista; Marques, Rodson Abreu, E-mail: edgarjr@ymail.com, E-mail: rodson.marques@ufes.br [Universidade Federal do Espirito Santo (UFES), Alegre, ES (Brazil). Departamento de Geologia; Jordt-Evangelista, Hanna; Queiroga, Glaucia Nascimento, E-mail: hanna@degeo.ufop.br, E-mail: glauciaqueiroga@yahoo.com.br [Universidade Federal de Ouro Preto (UFOP), Ouro Preto, MG (Brazil). Escola de Minas. Departamento de Geologia; Schulz, Bernhard, E-mail: bernhard.schulz@mineral.tu-freiberg.de [TU Bergakademie - Institute of Mineralogy, Freiberg - Saxony (Germany)

    2016-01-15

    The Acaiaca Complex (AC) is located in southeastern Minas Gerais state, and comprises felsic, mafic, ultramafic, and aluminous granulite as well as lower grade gneisses and mylonite. The complex is distributed over an area of ca. 36 km by 6 km, surrounded by amphibolite facies gneisses of the Mantiqueira Complex (MC). The discrepancy in the metamorphic grade between both complexes led to the present study aiming to understand the metamorphic history of the AC by means of geothermobarometry calculations and electron microprobe Th-U-Pb monazite dating. Estimates of the metamorphic conditions of the granulite based on conventional geothermobarometry and THERMOCALC resulted in temperatures around 800 deg C and pressures between of 5.0 and 9.9 kbar and a retro metamorphic path characterized by near-isobaric cooling. Part of the granulite was affected by anatexis. The melting of felsic granulite resulted in the generation of pegmatites and two aluminous lithotypes. These are: 1) garnet-sillimanite granulite with euhedral plagioclase and cordierite that show straight faces against quartz, and is the crystallization product of an anatectic melt, and 2) garnet-kyanite-cordierite granulite, which is probably the restite of anatexis, as indicated by textures and high magnesium contents. Th-U-Pb monazite geochronology of two granulite samples resulted in a metamorphic age around 2060 Ma, which is similar to the age of the MC registered in the literature. The similar Paleoproterozoic metamorphic ages of both complexes lead to the conclusion that the Acaiaca Complex may be the high grade metamorphic unit geochronological related to the lower grade Mantiqueira Complex. (author)

  17. Episodic growth and homogenization of plutonic roots in arc volcanoes from combined U-Th and (U-Th)/He zircon dating

    Science.gov (United States)

    Schmitt, Axel K.; Stockli, Daniel F.; Lindsay, Jan M.; Robertson, Richard; Lovera, Oscar M.; Kislitsyn, Roman

    2010-06-01

    Tracing the fate of unerupted magma is challenging because plutonic roots of young volcanoes are largely inaccessible. Here we develop the use of zircon age spectra to determine crystal provenance and source rocks for volcanic products, in analogy to detrital crystals in sediments. U-Th zircon crystallization ages for the Soufrière Volcanic Complex, Saint Lucia (Lesser Antilles) frequently predate their eruption as determined from combined U-Th and (U-Th)/He zircon dating. The oldest dated eruptions are 273 ± 15 ka and 264 ± 8 ka (1σ uncertainty) for Morne Bonin dacite and Bellevue pumice deposit, respectively. The most recent eruptions formed morphologically pristine domes in the center of the Qualibou depression (Belfond: 13.6 ± 0.4 ka; Terre Blanche: 15.3 ± 0.4 ka). U-Th (U-Pb) zircon crystallization ages determined for crystal rims and interiors range between near-eruption ages to ∼ 600 ka. Older xenocrysts are absent. Zircon crystallization age distributions are complex, yet systematic: crystal rim ages in the most recently erupted volcanic rocks match those of co-erupted plutonic inclusions, whereas crystal interiors are equivalent to the cumulative distribution of zircon ages from older eruptions. This is evidence that silicic lava domes and pyroclastic flows share a common source that is located underneath the Qualibou depression, where the intrusive roots of this long-lived arc volcanic system became homogenized through thermal and mechanical reprocessing of individual batches of unerupted magma from earlier volcanic episodes within timescales of < 100 ka.

  18. Detrital zircon U-Pb and (U-Th)/He double-dating of Upper Cretaceous-Cenozoic Zagros foreland basin strata in the Kurdistan Region of northern Iraq

    Science.gov (United States)

    Barber, D. E.; Stockli, D. F.; Koshnaw, R. I.; Horton, B. K.; Tamar-Agha, M. Y.; Kendall, J. J.

    2014-12-01

    The NW Zagros orogen is the result of the multistage collisional history associated with Late Cretaceous-Cenozoic convergence of the Arabian and Eurasian continents and final closure of Neotethys. Siliciclastic strata preserved within a ~400 km segment of the NW Zagros fold-thrust belt and foreland basin in the Iraqi Kurdistan Region (IKR) provide a widespread record of exhumation and sedimentation. As a means of assessing NW Zagros foreland basin evolution and chronostratigraphy, we present coupled detrital zircon (DZ) U-Pb and (U-Th)/He geo-thermochronometric data of Upper Cretaceous to Pliocene siliciclastic strata from the Duhok, Erbil, and Suleimaniyah provinces of IKR. LA-ICP-MS U-Pb age analyses reveal that the foreland basin fill in IKR in general was dominantly derived from Pan-African/Arabian-Nubian, Peri-Gondwandan, Eurasian, and Cretaceous volcanic arc terrenes. However, the provenance of these strata varies systematically along strike and through time, with an overall increase in complexity upsection. DZ age distribution of Paleocene-Eocene strata is dominated by a ~95 Ma grain age population, likely sourced from the Late Cretaceous Hassanbag-Bitlis volcanic arc complex along the northern margin of Arabia. In contrast, DZ U-Pb age distributions of Neogene strata show a major contribution derived from various Eurasian (e.g., Iranian, Tauride, Pontide; ~45, 150, 300 Ma) and Pan-African (~550, 950 Ma) sources. The introduction of Eurasian DZ ages at the Paleogene-Neogene transition likely records the onset of Arabian-Eurasian collision. Along strike to the southeast, the DZ U-Pb spectra of Neogene strata show a decreased percentage of Pan-African, Peri-Gondwandan, Tauride, and Ordovician ages, coupled with a dramatic increase in 40-50 Ma DZ ages that correspond to Urumieh-Dokhtar magmatic rocks in Iran. Combined with paleocurrent data, this suggests that Neogene sediments were transported longitudinally southeastward through an unbroken foreland basin

  19. U-Pb Dating of Zircons and Phosphates in Lunar Meteorites, Acapulcoites and Angrites

    Science.gov (United States)

    Zhou, Q.; Zeigler, R. A.; Yin, Q. Z.; Korotev, R. L.; Joliff, B. L.; Amelin, Y.; Marti, K.; Wu, F. Y.; Li, X. H.; Li, Q. L.; hide

    2012-01-01

    Zircon U-Pb geochronology has made a great contribution to the timing of magmatism in the early Solar System [1-3]. Ca phosphates are another group of common accessory minerals in meteorites with great potential for U-Pb geochronology. Compared to zircons, the lower closure temperatures of the U-Pb system for apatite and merrillite (the most common phosphates in achondrites) makes them susceptible to resetting during thermal metamorphism. The different closure temperatures of the U-Pb system for zircon and apatite provide us an opportunity to discover the evolutionary history of meteoritic parent bodies, such as the crystallization ages of magmatism, as well as later impact events and thermal metamorphism. We have developed techniques using the Cameca IMS-1280 ion microprobe to date both zircon and phosphate grains in meteorites. Here we report U-Pb dating results for zircons and phosphates from lunar meteorites Dhofar 1442 and SaU 169. To test and verify the reliability of the newly developed phosphate dating technique, two additional meteorites, Acapulco, obtained from Acapulco consortium, and angrite NWA 4590 were also selected for this study as both have precisely known phosphate U-Pb ages by TIMS [4,5]. Both meteorites are from very fast cooled parent bodies with no sign of resetting [4,5], satisfying a necessity for precise dating.

  20. Age relationships from U-Th-Pb isotope studies of uranium mineralization in Wernecke breccias, Yukon Territory

    International Nuclear Information System (INIS)

    Archer, A.

    1986-01-01

    Pb-U ± Th isotope analyses for 17 specimens of uraniferous breccia from the northeastern Wernecke Mountains reveal several apparent ages for mineralization. The oldest date, 1194 Ma, reflects either initial emplacement of the breccias or their modification by effects of the Rackla of Rapitan (Windermere) thick clastic wedges and iron formation. The 510 Ma date reflects mid-Cambrian mineralization roughly coincident with regional uplift (and attendant karstification) and development of thick clastic wedges. This was also an important period for Pb-Zn mineralization. Younger dates resulted from continuing remobilization, and all isotopic ages for mineralized breccia reflect movements associated with the Richardson Fault array

  1. A feasibility study of U-Pb and Pb-Pb dating of kimberlites using groundmass mineral fractions and whole-rock samples

    International Nuclear Information System (INIS)

    Kramers, J.D.; Smith, C.B.

    1983-01-01

    This paper describes partly successful attempts to determine emplacement ages of kimberlites by U-Pb and Pb-Pb methods involving groundmass minerals with high U content (notably perovskite) and whole-rock kimberlite samples. U/Pb ratios in perovskite in the matrix of kimberlites can be two orders of magnitude larger than in the rest of the kimberlite material, and with simple mineral separation techniques moderate success was achieved in U-Pb dating of fresh samples of younger kimberlites (around 100 Ma). The differences in U/Pb ratios between kimberlite samples from different parts of the same pipe have also been found to be large enough, in some cases, to allow reasonably accurate U-Pb age determination. In older kimberlites the U-Pb ages obtained were mostly imcompatible with geological constraints and results obtained by other methods. However, for such pipes use of Pb-Pb systematics yields realistic age limits in some cases

  2. LA-ICP-MS and SIMS U-Pb and U-Th zircon geochronological data of Late Pleistocene lava domes of the Ciomadul Volcanic Dome Complex (Eastern Carpathians

    Directory of Open Access Journals (Sweden)

    Réka Lukács

    2018-06-01

    Full Text Available This article provides laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS and secondary ionization mass spectrometry (SIMS U-Pb and U-Th zircon dates for crystals separated from Late Pleistocene dacitic lava dome rocks of the Ciomadul Volcanic Dome Complex (Eastern Carpathians, Romania. The analyses were performed on unpolished zircon prism faces (termed rim analyses and on crystal interiors exposed through mechanical grinding an polishing (interior analyses. 206Pb/238U ages are corrected for Th-disequilibrium based on published and calculated distribution coefficients for U and Th using average whole-rock and individually analyzed zircon compositions. The data presented in this article were used for the Th-disequilibrium correction of (U-Th/He zircon geochronology data in the research article entitled “The onset of the volcanism in the Ciomadul Volcanic Dome Complex (Eastern Carpathians: eruption chronology and magma type variation” (Molnár et al., 2018 [1].

  3. Geochemical features and U-Pb dating of trachyandesites of the Ktuts river basin

    International Nuclear Information System (INIS)

    Sahakyan, L.H.

    2015-01-01

    The article deals with the results on geochemical (including isotopes) and U-Pb dating on zircon minerals of trachyandesites from the r. Ktuts basin. Shoshonite series trachyandesites normalised by chondrites have mobile elements enrichment (Rb, Ba, and Th) together with negative HFSE (Nb, Ta) anomalies. The (La/Sm)CN ratio is 6.84 value but the (La/Yb)CN ratio is 38.17, suggesting the presence of residual material at the magmatic source from the deep parts. Neodymium and strontium isotopes have low εNd_(14.5Ma) and high 87"Sr/86"Sr(14.5Ma) ratios, respectively –0.4 and 0.7054. The trachyandesites age determined on the zircon minerals by the U-Pb method is 14,50,2 Ma, which coincides with the magmatism reactivation in the middle-upper Miocene after the collision of Arabic and European plates in the upper Eocene-Oligocene

  4. High temperature (>350 °C) thermal histories of the long lived (>500 Ma) active margin of Ecuador and Colombia: Apatite, titanite and rutile U-Pb thermochronology

    Science.gov (United States)

    Paul, Andre N.; Spikings, Richard A.; Ulianov, Alexey; Ovtcharova, Maria

    2018-05-01

    Quantitative reconstruction of thermal histories can be a powerful tool to study numerous natural processes such as tectonic plate interaction, cratonic stability and extra-terrestrial phenomena such as asteroid ejection. A majority of thermochronological studies have focused on temperatures lower than 300 °C. Few previous studies have demonstrated that U-Pb data from apatite and other accessory phases can be used to recover thermal history information at T > 350 °C. We present U-Pb data from apatite, to constrain the thermal histories of Triassic peralluminous anatectites from the Northern Andes between the temperatures of ∼350-550 °C. The accuracy of the thermal history models is assessed by comparisons with previous geological models, and comparisons with pre-existing and newly acquired U/Pb (titanite and rutile), 40Ar/39Ar (muscovite) and low temperature thermochronological data. This study also examines the feasibility of using a large, regionally dispersed apatite U-Pb data set to obtain continuous thermal history paths along a long-lived (>500 Ma) active margin. A second aim of this study is to further test the hypothesis that the dominant mechanism for Pb displacement through apatite is volume diffusion, as opposed to aqueous fluid interaction. The thermal history models derived from the Triassic anatectites exposed in the Andes of Colombia and Ecuador are entirely consistent with lower temperature thermochronological constraints, and previously established geochronological and geochemical constraints. They reveal and quantify trench parallel changes in the amount of Jurassic - Early Cretaceous extension, significantly bolstering and adding to previous tectonic interpretations. Confirmation of the utility of U-Pb thermochronology provides geologists with a powerful tool for investigating the high-temperature thermal evolution of accessory minerals.

  5. U, Th, and Pb isotopes in hot springs on the Juan de Fuca Ridge

    International Nuclear Information System (INIS)

    Chen, J.H.

    1987-01-01

    The concentrations and isotopic compositions of U, Th, and Pb in three hydrothermal fluids from the Juan de Fuca Ridge were determined. The samples consisted of 10.2--57.6% of the pure hydrothermal end-members based on Mg contents. The Pb contents of the samples ranged from 34 to 87 ng/g, U from 1.3 to 3.0 ng/g, and Th from 0.2 to 7.7 pg/g. These samples showed large enrichments of Pb and Th relative to deep-sea water and some depletion of U. They did not show coherent relationships with Mg, however, indicating nonideal mixings between the hot hydrothermal fluids and cold ambient seawater. Particles filtered from these hydrothermal fluids contained significant amounts of Th and Pb which may effectively increase the concentration of these elements in the fluids when acidified. The /sup 234/U//sup 238/U values in all samples show a /sup 234/U enrichment relative to the equilibrium value and have a seawater signature. The Pb isotopic composition of the Juan de Fuca hydrothermal fluids resembles that of 21 0 N East Pacific Rise and has a uniform mid-ocean ridge basalt signature. The hydrothermal systems at oceanic spreading ridges have circulated through a large volume of basalts. Therefore Pb in these fluids may represent the best average value of the local oceanic crust. From the effects of U deposition from seawater to the crust and Pb extraction from rock to the ocean, the U/Pb ratio in the hydrothermally altered oceanic crust may be increased significantly. copyright American Geophysical Union 1987

  6. Comment on "Zircon U-Th-Pb dating using LA-ICP-MS: Simultaneous U-Pb and U-Th dating on 0.1 Ma Toya Tephra, Japan" by Hisatoshi Ito

    Science.gov (United States)

    Guillong, M.; Schmitt, A. K.; Bachmann, O.

    2015-04-01

    Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) of eight zircon reference materials and synthetic zircon-hafnon end-members indicate that corrections for abundance sensitivity and molecular zirconium sesquioxide ions (Zr2O3+) are critical for reliable determination of 230Th abundances in zircon. Other polyatomic interferences in the mass range 223-233 amu are insignificant. When corrected for abundance sensitivity and interferences, activity ratios of (230Th)/(238U) for the zircon reference materials we used average 1.001 ± 0.010 (1σ error; mean square of weighted deviates MSWD = 1.45; n = 8). This includes the 91500 and Plešovice zircons, which were deemed unsuitable for calibration of (230Th)/(238U) by Ito (2014). Uranium series zircon ages generated by LA-ICP-MS without mitigating (e.g., by high mass resolution) or correcting for abundance sensitivity and molecular interferences on 230Th such as those presented by Ito (2014) are potentially unreliable.

  7. Two modes of orogenic collapse of the Pamir plateau recorded by titanite

    Science.gov (United States)

    Stearns, M. A.; Hacker, B. R.; Ratschbacher, L.; Rutte, D.; Kylander-Clark, A. R.

    2013-12-01

    Processes that operate in the mid- to lower crust during and following continent-continent collision are important for understanding how orogenic plateaux transition from thickening to collapse. In the central and southern Pamir, mid- to lower crustal rocks crop out in two belts of extensional domes. The central Pamir domes were exhumed by symmetrical N-S extension. In contrast, the southern Pamir domes were exhumed by asymmetrical top to the south (NNW-SSE) extension via a rolling-hinge detachment. To investigate the high-temperature exhumation history, titanites were dated using LASS (laser ablation split stream-ICP-MS). A multi-collector ICP was used to collect U-Pb isotopic ratios and a single collector ICP-MS was used to measure trace-element abundances. The data indicate that the central Pamir domes began exhumation synchronously at ~17 Ma. Titanite from the southern Pamir record two periods of protracted (re)crystallization: older metamorphic dates ranging from ~35-18 Ma and younger igneous and metamorphic dates from ~15-7 Ma. Samples with single populations of titanite dates are present throughout both groups. Samples with more-complex date populations typically have distinct trace-element (e.g., Sr, Y, Zr, and Nb) groups that can be used to distinguish different date populations (e.g., older dates may have higher Zr and younger dates lower Zr). The distinct early exhumation histories of the north and south Pamir require either a diachronous single process or two semi-independent processes. The N to S sequence of exhumation, ranges of dates, and overall extension directions may be related to two important plate-tectonic events inferred from seismic data: 1) breakoff of the northward subducting Indian slab around ~20 Ma, and 2) southward subduction and northwestward rollback of the Asian lithosphere between ~15-10 Ma based on geodetic convergence rates and Benioff zone length. We interpret these two lithospheric-detachment events to have driven the

  8. U-Pb dating of large zircons in low-temperature jadeitite from the Osayama serpentinite melange, southwest Japan: insights into the timing of serpentinization

    Science.gov (United States)

    Tsujimori, T.; Liou, J.G.; Wooden, J.; Miyamoto, T.

    2005-01-01

    Crystals of zircon up to 3 mm in length occur in jadeitite veins in the Osayama serpentinite mélange, Southwest Japan. The zircon porphyroblasts show pronounced zoning, and are characterized by both low Th/U ratios (0.2-0.8) and low Th and U abundances (Th = 1-81 ppm; U = 6-149 ppm). They contain inclusions of high-pressure minerals, including jadeite and rutile; such an occurrence indicates that the zircon crystallized during subduction-zone metamorphism. Phase equilibria and the existing fluid-inclusion data constrain P-T conditions to P > 1.2 GPa at T > 350°C for formation of the jadeitite. Most U/Pb ages obtained by SHRIMP-RG are concordant, with a weighted mean 206Pb/238U age of 472 ± 8.5 Ma (MSWD = 2.7, n = 25). Because zircon porphyroblasts contain inclusions of high-pressure minerals, the SHRIMP U-Pb age represents the timing of jadeitite formation, i.e., the timing of interaction between alkaline fluid and ultramafic rocks in a subduction zone. Although this dating does not provide a direct time constraint for serpentinization, U-Pb ages of zircon in jadeitite associated with serpentinite result in new insights into the timing of fluid-rock interaction of ultramafic rocks at a subduction zone and the minimum age for serpentinization.

  9. U,Th-21Ne dating and its applications

    International Nuclear Information System (INIS)

    Basu, Sudeshna; Murty, S.V.S.; Anil Kumar

    2003-01-01

    The potential of radiogenic and fissiogenic noble gas isotopes as dating tools has been well exploited. U, Th- 4 He , K- 40 Ar and U- fission Xe pairs as well as their variants like 39 Ar- 40 Ar and induced fission Xe- spontaneous fission Xe pairs have been extensively used as geochronological tools. A new dating method that utilizes the nucleogenic isotope 21 Ne and demonstrate its application for an apatite separate from a carbonatite is proposed

  10. U-Pb dating by zircon dissolution method using chemical abrasion

    Energy Technology Data Exchange (ETDEWEB)

    Takehara, Lucy, E-mail: lucytakehara@gmail.com.br [Servico Geologico do Brasil (CPRM), Brasilia, DF (Brazil); Chemale Junior, Farid [Universidade de Brasilia (UnB), Brasilia, DF (Brazil). Inst. de Geociencias. Lab. de Geocronologia; Hartmann, Leo A. [Universidade Federal do Rio Grande do Sul (UFRS), Porto Alegre, RS (Brazil). Inst. de Geociencias; Dussin, Ivo A.; Kawashita, Koji [Universidade de Sao Paulo (USP), SP, (Brazil). Centro de Pesquisa Geocronologicas

    2012-06-15

    Chemical abrasion was carried out on zircons grains of the Temora II standard for U-Pb dating prior to analyses using in situ Laser Ablation-Multi Collector Ion Coupled Plasma Mass Spectrometer (LA-ICPMS) followed by the Isotope Dissolution Thermal Ionization Mass Spectrometer (ID-TIMS) method. The proposed methodology was herein applied in order to reduce primarily the effects of secondary Pb loss, the presence of common lead and/or silicate impurities. Nine Temora II zircon grains were analyzed by the laser ablation method yielding an age of 418.3 +- 4.3 Ma. Zircon grains of a same population were separated for chemical abrasion before dissolution and mass spectrometry analyses. Six fractions of them were separated for isotope dissolution using {sup 235}U-{sup 205}Pb mixed spike after we have checked and assured the laboratory conditions of low blank values for total Pb of less than 2 pg/g. The obtained U-Pb zircon age by the ID-TIMS method was 415.7 +- 1.8 Ma (error 0.43 %) based on four successful determinations. The results are consistent with the published ages for the Temora diorite (Temora I - 416.75 +- 1.3 Ma; Temora II - 416.78 +- 0.33 Ma) and established as 416 +- 0.33 Ma. The technique is thus recommended for high precision U-Pb zircon analyses (error < 1 %), mainly for high resolution stratigraphic studies of Phanerozoic sequences. (author)

  11. U-Pb zircon in situ dating with LA-MC-ICP-MS using a mixed detector configuration

    Energy Technology Data Exchange (ETDEWEB)

    Chemale Junior, Farid, E-mail: fchemale@unb.br [Universidade de Brasilia (UnB), DF (Brazil). Inst. de Geociencias; Kawashita, Koji; Dussin, Ivo A. [Universidade de Sao Paulo (USP), SP (Brazil). Centro de Pesquisas Geocronologicas; Avila, Janaina N. [Australian National University, Canberra, (Australia). Research School of Earth Sciences; Justino, Dayvisson; Bertotti, Anelise [Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, RS (Brazil). Curso de Pos-Graduacao em Geociencias

    2012-06-15

    The LA-MC-ICP-MS method applied to U-Pb in situ dating is still rapidly evolving due to improvements in both lasers and ICP-MS. To test the validity and reproducibility of the method, 5 different zircon samples, including the standard Temora-2, ranging in age between 2.2 Ga and 246 Ma, were dated using both LA-MC-ICP-MS and SHRIMP. The selected zircons were dated by SHRIMP and, after gentle polishing, the laser spot was driven to the same site or on the same zircon phase with a 213 nm laser microprobe coupled to a multi-collector mixed system. The data were collected with a routine spot size of 25 {mu}m and, in some cases, of 15 and 40 {mu}m. A careful cross-calibration using a diluted U-Th-Pb solution to calculate the Faraday reading to counting rate conversion factors and the highly suitable GJ-1 standard zircon for external calibrations were of paramount importance for obtaining reliable results. All age results were concordant within the experimental errors. The assigned age errors using the LA-MC-ICP-MS technique were, in most cases, higher than those obtained by SHRIMP, but if we are not faced with a high resolution stratigraphy, the laser technique has certain advantages. (author)

  12. Preliminary Report on U-Th-Pb Isotope Systematics of the Olivine-Phyric Shergottite Tissint

    Science.gov (United States)

    Moriwaki, R.; Usui, T.; Yokoyama, T.; Simon, J. I.; Jones, J. H.

    2014-01-01

    Geochemical studies of shergottites suggest that their parental magmas reflect mixtures between at least two distinct geochemical source reservoirs, producing correlations between radiogenic isotope compositions, and trace element abundances.. These correlations have been interpreted as indicating the presence of a reduced, incompatible-element- depleted reservoir and an oxidized, incompatible-element-rich reservoir. The former is clearly a depleted mantle source, but there has been a long debate regarding the origin of the enriched reservoir. Two contrasting models have been proposed regarding the location and mixing process of the two geochemical source reservoirs: (1) assimilation of oxidized crust by mantle derived, reduced magmas, or (2) mixing of two distinct mantle reservoirs during melting. The former clearly requires the ancient martian crust to be the enriched source (crustal assimilation), whereas the latter requires a long-lived enriched mantle domain that probably originated from residual melts formed during solidification of a magma ocean (heterogeneous mantle model). This study conducts Pb isotope and U-Th-Pb concentration analyses of the olivine-phyric shergottite Tissint because U-Th-Pb isotope systematics have been intensively used as a powerful radiogenic tracer to characterize old crust/sediment components in mantle- derived, terrestrial oceanic island basalts. The U-Th-Pb analyses are applied to sequential acid leaching fractions obtained from Tissint whole-rock powder in order to search for Pb isotopic source components in Tissint magma. Here we report preliminary results of the U-Th-Pb analyses of acid leachates and a residue, and propose the possibility that Tissint would have experienced minor assimilation of old martian crust.

  13. LA-ICP-MS U-Th-Pb Dating and Trace Element Geochemistry of Allanite: Implications on the Different Skarn Metallogenesis between the Giant Beiya Au and Machangqing Cu-Mo-(Au Deposits in Yunnan, SW China

    Directory of Open Access Journals (Sweden)

    Yu Fu

    2017-12-01

    Full Text Available The giant Beiya Au skarn deposit and Machangqing porphyry Cu-Mo-(Au deposit are located in the middle part of the Jinshajiang–Ailaoshan alkaline porphyry metallogenic belt. The Beiya deposit is the largest Au skarn deposit in China, whilst the Machangqing deposit comprises a well-developed porphyry-skarn-epithermal Cu-Mo-(Au mineral system. In this paper, we present new allanite U-Th-Pb ages and trace element geochemical data from the two deposits and discuss their respective skarn metallogenesis. Based on the mineral assemblage, texture and Th/U ratio, the allanite from the Beiya and Machangqing deposits are likely hydrothermal rather than magmatic. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS allanite U-Th-Pb dating has yielded Th-Pb isochron ages of 33.4 ± 4.6 Ma (MSWD = 0.22 (Beiya and 35.4 ± 9.8 Ma (MSWD = 0.26 (Machangqing, representing the retrograde alteration and magnetite skarn mineralization age of the two deposits. The Beiya and Machangqing alkali porphyry-related mineralization are synchronous and genetically linked to the magmatic hydrothermal activities of the Himalayan orogenic event. Major and trace element compositions reveal that the Beiya allanite has higher Fe3+/(Fe3+ + Fe2+ ratios, U content and Th content than the Machangqing allanite, which indicate a higher oxygen fugacity and F content for the ore-forming fluids at Beiya. Such differences in the ore-forming fluids may have contributed to the different metallogenic scales and metal types in the Beiya and Machangqing deposit.

  14. Bioaccessibility of U, Th and Pb in particulate matter from an abandoned uranium mine

    Science.gov (United States)

    Millward, Geoffrey; Foulkes, Michael; Henderson, Sam; Blake, William

    2016-04-01

    Currently, there are approximately 150 uranium mines in Europe at various stages of either operation, development, decommissioning, restoration or abandonment (wise-uranium.com). The particulate matter comprising the mounds of waste rock and mill tailings poses a risk to human health through the inadvertent ingestion of particles contaminated with uranium and thorium, and their decay products, which exposes recipients to the dual toxicity of heavy elements and their radioactive emissions. We investigated the bioaccessibility of 238U, 232Th and 206,214,210Pb in particulate samples taken from a contaminated, abandoned uranium mine in South West England. Sampling included a mine shaft, dressing floor and waste heap, as well as soils from a field used for grazing. The contaminants were extracted using the in-vitro Unified Bioaccessibility Research Group of Europe Method (UBM) in order to mimic the digestion processes in the human stomach (STOM) and the combined stomach and gastrointestinal tract (STOM+INT). Analyses of concentrations of U, Th and Pb in the extracts were by ICP-MS and the activity concentrations of radionuclides were determined on the same particles, before and after extraction, using gamma spectroscopy. 'Total' concentrations of U, Th and Pb for all samples were in the range 57 to 16,200, 0.28 to 3.8 and 69 to 4750 mg kg-1, respectively. For U and Pb the concentrations in the STOM fraction were lower than the total and STOM+INT fractions were even lower. However, for Th the STOM+INT fractions were higher than the STOM due to the presence of Th carbonate species within the gastrointestinal fluid. Activity concentrations for 214Pb and 210Pb, including total, STOM and STOM+INT, were in the range 180 to samples were 39% and 8% in the STOM and STOM+INT, respectively, whereas the respective BAFs for 232Th were 3% and 9%. For stable 206Pb the STOM and STOM+INT BAFs were 16% and 3% for the most contaminated samples, whereas those from the field had 44% in the

  15. Extrapolation of tectonic boundaries across the Labrador shelf: U-Pb geochronology of well samples

    International Nuclear Information System (INIS)

    Wasteneys, H.A.; Krogh, T.E.

    1996-01-01

    Near Saglek Fiord, a northerly trending boundary between the early Archean Saglek block and the middle Archean Hopedale block extends between drill sites which, respectively, sampled Uivak amphibolite gneiss with U-Pb zircon intercept ages of 3742 ± 12 and 2752 ± 42 Ma, and migmatitic Lister gneiss with concordant ages of 3213 -4 +21 Ma for restite and 2552 -21 +4 Ma for leucosome. Titanite ages of ca. 2508 Ma are common to both rocks. A nearby metapsammitic gneiss has detrital zircon and monazite ages of 2681 ± 5, 2700 ± 4, ca. 2730, and 2750 ± 2 Ma representing high-grade metamorphism related to the Hopedale-Saglek collision and metamorphic monazite of ca. 2560 Ma age representing metamorphism of the sediment during reactivation of the Saglek-Hopedale suture. Two hundred kilometres southeast, a gneissic granite records a protolith age of 3170 Ma and Late Proterozoic Pb loss. Near the Nain-Makkovik boundary, 1269 ± 4 Ma zircons indicate a significant extension of the Nain Plutonic Suite. South of the Makkovik boundary, a foliated granite yielded an upper intercept age defining intrusion at 1895 ± 8 Ma and concordant 1872 ± 5 Ma titanite ages that date subsequent metamorphism. Discordant U-Pb ages from an alkali-feldspar granite also constrain crystallization to ca. 1890 Ma and together with the gneiss represent the previously defined Iggiuk event in the Kaipokok domain. Wells near the southerly end of the transect record 1801 ± 5, 1813 ± 3, and 1806 ± 8 Ma ages, respectively, that are typical of the synorogenic granitoid suite representing the Cape Harrison domain of southern Makkovik Province. (author). 46 refs., 1 tab., 5 figs

  16. Age constraints for Palaeolithic cave art by U-Th dating of thin carbonate crusts

    Science.gov (United States)

    Hoffmann, Dirk; Pike, Alistair; Garcia-Diez, Marcos; Pettitt, Paul; Zilhão, João

    2015-04-01

    U-series dating is an important geochronological tool which is widely applied for instance in speleothem based palaeoclimate research. It has also great potential to provide age constraints for Archaeology, especially for sites or artefacts in cave environments. We present our methods to conduct precise U-Th dating of calcite crusts that formed on top of cave paintings. Recent developments in multi-collector (MC) inductively coupled plasma mass spectrometry (ICPMS) U-series dating greatly improved the precision of this method, and sample sizes needed to obtain reliable results were significantly reduced. Based on these developments the U-series technique can be applied for accurate dating of thin calcite crusts covering cave art at many sites, while taking care not to harm the art underneath. The method provides minimum ages for the covered art and, where possible, also maximum ages by dating the flowstone layer the art is painted on. The U-Th method has been used in a number of recent projects to date calcite precipitates above and occasionally below cave paintings in Spain. Initial results from Cantabria have shown that the earliest dated paintings are older than 41.4 ± 0.6 ka, dating at least to the Early Aurignacian period and present a far longer chronology than that based so far on radiocarbon dating. Here we outline our methodology and the steps we take to demonstrate the reliability of U-Th dates, and present some recent results of our ongoing U-Th dating programme.

  17. Characterization of flux-grown Trace-element-doped titanite using the high-mass-resolution ion microprobe (SHRIMP-RG)

    Science.gov (United States)

    Mazdab, F.K.

    2009-01-01

    Crystals of titanite can be readily grown under ambient pressure from a mixture of CaO, TiO2 and SiO2 in the presence of molten sodium tetraborate. The crystals produced are euhedral and prismatic, lustrous and transparent, and up to 5 mm in length. Titanite obtained by this method contains approximately 4300 ppm Na and 220 ppm B contributed from the flux. In addition to dopant-free material, titanite containing trace alkali and alkaline earth metals (K, Sr, Ba), transition metals (Sc, Cr, Ni, Y, Zr, Nb, Hf and Ta), rare-earth elements (REE), actinides (Th, U) and p-block elements (F, S, Cl, Ge, Sn and Pb) have been prepared using the same procedure. Back-scattered electron (BSE) imaging accompanied by ion-microprobe (SHRIMP-RG) analysis confirms significant incorporation of selected trace-elements at structural sites. Regardless of some zonation, the large size of the crystals and broad regions of chemical homogeneity make these crystals useful as experimental starting material, and as matrix-matched trace-element standards for a variety of microbeam analytical techniques where amorphous titanite glass, heterogeneous natural titanite or a non-titanite standard may be less than satisfactory. Trace-element-doped synthetic crystals can also provide a convenient proxy for a better understanding of trace-element incorporation in natural titanite. Comparisons with igneous, authigenic and high-temperature metasomatic titanite are examined. The use of high-mass-resolution SIMS also demonstrates the analytical challenges inherent to any in situ mass-spectrometry-based analysis of titanite, owing to the production of difficult-to-resolve molecular interferences. These interferences are dominated by Ca-Ca, Ca-Ti and Ti-Ti dimers that are significant in the mass range of 80-100, affecting all isotopes of Sr and Zr, as well as 89Y and 93Nb. Methods do exist for the evaluation of interferences by these dimers and of polyatomic interferences on the LREE.

  18. U-series disequilibrium dating of Quaternary carbonates

    International Nuclear Information System (INIS)

    Stirling, C.

    2006-01-01

    One of the key dating methods used in paleoclimate research utilizes the natural radioactive decay of uranium to thorium in archives containing U-bearing minerals, such as the calcium carbonate forming the skeletons of fossil corals and speleothems. More specifically, this chronometer, commonly referred to as the U-series dating method, is based on the decay of 238 U to its longest-lived intermediate daughters, 234 U and 230 Th, and subsequent decay through to stable isotopes of Pb. It is the respective 250,000 and 75,000 year half-lives of these daughter isotopes, which make the U-series system particularly useful for dating Quaternary climate events spanning the last 600,000 years of Earth's history. The U-series thus bridges the gap between the ∼45,000 year upper limit of conventional radiocarbon dating and the ∼200,000 year lower limit of K-Ar and 40 Ar- 39 Ar dating. 2 refs., 5 figs

  19. Rb-Sr, Pb-Pb, U-Pb dating in the Bandja plutonic series of Western Cameroon. Donnees geochronologiques (Rb-Sr, Pb-Pb, U-Pb) sur le complexe plutonique de Bandja (Centre-Ouest Cameroun)

    Energy Technology Data Exchange (ETDEWEB)

    Tchankam, C N [Nancy-1 Univ., 54 (France); Vialette, Y [Clermont-Ferrand-2 Univ., 63 - Aubiere (France)

    1994-08-01

    The results of U-Pb zircon and Pb-Pb on minerals and whole rocks are reported on a charnockite syn-D1 from the Bandja series in the western Cameroon. Data are interpreted as representing a plutonic emplacement at 640 Ma. A syn- to post-tectonic pluton is dated at 557 [+-] 8 Ma (Rb-Sr whole rocks isochron). These results confirm the Pan-African age of the charnockitic intrusive body. Initial isotopic [sup 87]Sr/[sup 86]Sr ratios of charnockite (0.709) and granite (0.7089) show the importance of crustal imprint in the magma genesis. (authors).

  20. U-Th dating of speleothems to investigate the evolution of limestone caves in the Gunung Mulu National Park, Sarawak, Malaysia

    OpenAIRE

    Moseley, Gina E.; Richards, David A.; Smith, Christopher; Smart, Peter L.; Hoffmann, Dirk L.; Farrant, Andrew R.

    2013-01-01

    The Gunung Mulu National Park, Sarawak, Malaysia has been a focus of scientific research and exploration for several decades. Previous work investigated the relationship between fluvial incision into the limestone massif and the chronological evolution of the 500m-deep network of cave passages. This study involved analyses of newly available speleothem material using state-of-the-art U-Th dating methods and assessment of the potential for extension of the chronological record using U-Pb datin...

  1. In situ LA-ICPMS U–Pb dating of cassiterite without a known-age matrix-matched reference material: Examples from worldwide tin deposits spanning the Proterozoic to the Tertiary

    Science.gov (United States)

    Neymark, Leonid; Holm-Denoma, Christopher S.; Moscati, Richard J.

    2018-01-01

    Cassiterite (SnO2), a main ore mineral in tin deposits, is suitable for U–Pb isotopic dating because of its relatively high U/Pb ratios and typically low common Pb. We report a LA-ICPMS analytical procedure for U–Pb dating of this mineral with no need for an independently dated matrix-matched cassiterite standard. LA-ICPMS U-Th-Pb data were acquired while using NIST 612 glass as a primary non-matrix-matched standard. Raw data are reduced using a combination of Iolite™ and other off-line data reduction methods. Cassiterite is extremely difficult to digest, so traditional approaches in LA-ICPMS U-Pb geochronology that utilize well-characterized matrix-matched reference materials (e.g., age values determined by ID-TIMS) cannot be easily implemented. We propose a new approach for in situ LA-ICPMS dating of cassiterite, which benefits from the unique chemistry of cassiterite with extremely low Th concentrations (Th/U ratio of 10−4 or lower) in some cassiterite samples. Accordingly, it is assumed that 208Pb measured in cassiterite is mostly of non-radiogenic origin—it was initially incorporated in cassiterite during mineral formation, and can be used as a proxy for common Pb. Using 208Pb as a common Pb proxy instead of 204Pb is preferred as 204Pb is much less abundant and is also compromised by 204Hg interference during the LA-ICPMS analyses.Our procedure relies on 208Pb/206Pb vs 207Pb/206Pb (Pb-Pb) and Tera-Wasserburg 207Pb/206Pb vs 238U/206Pb (U-Pb) isochron dates that are calculated for a ~1.54 Ga low-Th cassiterite reference material with varying amounts of common Pb that we assume remained a closed U-Pb system. The difference between the NIST 612 glass normalized biased U-Pb date and the Pb-Pb age of the reference material is used to calculate a correction factor (F) for instrumental U-Pb fractionation. The correction factor (F) is then applied to measured U/Pb ratios and Tera-Wasserburg isochron dates are obtained for the unknown

  2. Magma Mixing, Mingling and Its Accompanying Isotopic and Elemental Partitioning: Records from Titanites in Guojialing-type Granodiorites and Dioritic Enclaves, Jiaodong, North China

    Science.gov (United States)

    Jiang, P.; Yang, K. F.; Fan, H. R.; Liu, X.

    2016-12-01

    The grain-scale textural and in-situ compositional analyses on accessory minerals (such as titanite, rutile, apatite, monazite, etc.) have recently been a hot topic for geologists, through which a detailed information on magmatic, metamorphic or hydrothermal process can be extracted. As an attempt to unravel the petrogenesis of Early Cretaceous Guojialing-type granodiorites and their bearing dioritic enclaves, we accomplished an integrated geochronological and geochemical study on titanites within these rocks. Three types of titanites, with distinguishable textural and geochemical features, are identified. G-type titanites (from granodiorites) and E-type-I titanites (from plagioclase-rich dioritic enclaves) yield identical U-Pb age of 130 Ma, but reveal distinct back-scattered electron (BSE) zonings. G-type titanites are characterized by oscillatory zonings whereas E-type-I titanites are marked by core-mantle-rim zonings, exhibiting drastic but contrary variation trends for several key elements (such as LREEs, Zr, Hf and F) among their transition BSE zones. These two types of titanites are interpreted to crystallize coevally, and record a notable temperature and compositional change of two corresponding melts, as a response to magma mixing. E-type-II titanites (from plagioclase-poor dioritic enclaves) yield a relatively younger U-Pb age at 128 Ma, and show typical interstitial growth with narrower and lower range of Zr, total REEs contents, but higher F content and Nb/Ta ratios. Such titanites are perceived to record late-stage mingling, during which F-rich and REE-poor hybrid granodioritic magma squeezed into the incompletely consolidated dioritic enclaves with accompanying fluid-rock interaction. Unlike the dramatic elemental changes in these differentiated titanites, in-situ Nd isotopic compositions are relatively homogeneous, which in our view is a good sign of showing that isotopic equilibrium among two magma systems was more easily reached compared to

  3. U-Pb thermochronology of the lower crust: producing a long-term record of craton thermal evolution

    Science.gov (United States)

    Blackburn, T.; Bowring, S. A.; Mahan, K. H.; Perron, T.; Schoene, B.; Dudas, F. O.

    2010-12-01

    The EarthScope initiative is focused on providing an enhanced view of the North American lithosphere and the present day stress field of the North American continent. Of key interest is the interaction between convecting asthenosphere and the conducting lithospheric mantle that underlie the continents, especially the cold ‘keels’ that underlie Archean domains. Cratonic regions are in general characterized by minimal erosion and or sediment accumulation. The Integration of seismic tomography, and mantle xenolith studies reveal a keel of seismically fast and relatively buoyant and viscous mantle; physical properties that are intimately linked with the long-term stability and topographic expression of the region. Missing from this model of the continental lithosphere is the 4th dimension--time--and along with it our understanding of the long-term evolution of these stable continental interiors. Here we present a thermal record from the North American craton using U-Pb thermochronology of lower crustal xenoliths. The use of temperature sensitive dates on lower crustal samples can produce a unique time-temperature record for a well-insulated and slowly cooling lithosphere. The base of the crust is insulated enough to remain unperturbed by any plausible changes to surface topography, yet unlike the subadjacent lithospheric mantle, contains accessory phases amenable to U-Pb dating (rutile, apatite, titanite). With near steady state temperatures in the lower crust between 400-600 °C, U-Pb thermochronometers with similar average closure temperatures for Pb are perfectly suited to record the long-term cooling of the lithosphere. Xenoliths from multiple depths, and across the craton yield time-temperature paths produced from U-Pb thermochronometers that record extremely slow cooling (<0.25 °C/Ma) over time scales of billions of years. Combining these data with numerical thermal modeling allow constraints to be placed on the dominant heat transfer mechanisms operating

  4. U-Th-He dating of apatite: A potential thermochronometer

    International Nuclear Information System (INIS)

    Zeitler, P.K.; Herczeg, A.L.; McDougall, I.; Honda, M.

    1987-01-01

    The authors found a gem quality crystal of Durango fluorapatite to have a 4 He content consistent with complete retention of radiogenic helium since its formation at about 31 Ma. Isothermal heating and step-heating analysis reveal 4 He loss to occur systematically by volume diffusion at low temperatures. The linear, low-temperature portion of the diffusion data yields an activation energy of 38.5 ± 8.1 kcal/mol and a frequency factor of 1n (D 0 /a 2 ) = 16.4 ± 2.8 sec -1 , corresponding to a closure temperature of 105 degree C ± 30 degree C (cooling rate 10 degree C/m.y.). It appears that U-Th-He dating of apatite might represent a useful new thermochronometer with a range similar to that of fission-track dating of apatite. From these results, they infer that a number of the too-young U-Th-He dates reported in the literature on minerals such as zircon and magnetite may in fact represent valuable records of the low-temperature thermal history of their host rocks

  5. Re-appraisal of the stratigraphy and determination of new U-Pb dates for the Sterkfontein hominin site, South Africa.

    Science.gov (United States)

    Pickering, Robyn; Kramers, Jan D

    2010-07-01

    Sterkfontein Caves is the single richest early hominin site in the world with deposits yielding one or more species of Australopithecus and possible early Homo, as well as an extensive faunal collection. The inability to date the southern African cave sites accurately or precisely has hindered attempts to integrate the hominin fossil evidence into pan-African scenarios about human evolutionary history, and especially hominin biogeography. We have used U-Pb and U-Th techniques to date sheets of calcium carbonate flowstone inter-bedded between the fossiliferous sediments. For the first time, absolute age ranges can be assigned to the fossil-bearing deposits: Member 2 is between 2.8 +/- 0.28 and 2.6 +/- 0.30 Ma and Member 4 between 2.65 +/- 0.30 and 2.01 +/- 0.05 Ma. The age of 2.01 +/- 0.05 Ma for the top of Member 4 constrains the last appearance of Australopithecus africanus to 2 Ma. In the Silberberg Grotto we have reproduced the U-Pb age of approximately 2.2 Ma of for the flowstones associated with StW573. We believe that these deposits, including the fossil and the flowstones, accumulated rapidly around 2.2 Ma. The stratigraphy of the site is complex as sediments are exposed both in the underground chambers and at surface. We present a new interpretation of the stratigraphy based on surface mapping, boreholes logs and U-Pb ages. Every effort was made to retain the Member system, however, only Members 2 and 4 are recognized in the boreholes. We propose that the deposits formally known as Member 3 are in fact the distal equivalents of Member 4. The sediments of Members 2 and 4 consisted of cone-like deposits and probably never filled up the cave. The U-Th ages show that there are substantial deposits younger than 400 ka in the underground cave, underlying the older deposits, highlighting again that these cave fills are not simple layer-cakes.

  6. Whole-rock U-Pb dating of the Shuijingtuo formation sedimentary rocks in the Yangtze Gorge

    International Nuclear Information System (INIS)

    Zheng, Y.F.; Huang, B.

    1990-01-01

    Black shale and enclosed limestone lenticule from Lower Cambrian Shuijingtuo Formation in the Yangtze Gorge is successfully dated by whole-rock U-Pb method. The results yield a concordant age of about 573±14 Ma, in excellent agreement with both stratigraphic and palaeontologic evidence. The whole-rock U-Pb method can provide a reliable approach for age determination of sedimentary stratum. (orig.) [de

  7. Determination of U, Th and K for optically stimulated luminescence dating by NAA

    International Nuclear Information System (INIS)

    Qin Yali; Chen Zhe; Wu Weiming

    2010-01-01

    Optically stimulated luminescence dating techniques have been widely used in northern Loess ancient soil series and recorded climate environment change, ancient earthquake, the ancients site and archaeology research. The determination of U, Th and K using neutron activation analysis (NAA) has been optimized for the samples related to OSL dating research. The procedure for determination of U, Th, K in loess have been fixed by using Miniature neutron source reactor. This procedure of NAA will provide a reliable data base for optically stimulated luminescence dating research. (authors)

  8. U-Pb zircon dating of the Bassies granite (Pyrenees): a syn-tectonic pluton of Westphalian age

    International Nuclear Information System (INIS)

    Paquette, J.L.

    1997-01-01

    A new U-Pb zircon age of 312 ± 2 Ma for the Bassies pluton (Pyrenees) contradicts the previous whole-rock Rb-Sr dating at 276 ± 16 Ma, which was considered as the age of emplacement, therefore regarded as post-tectonic. The new date is in agreement with recent structural studies which suggest a Hercynian syn-tectonic emplacement for the Bassies pluton. These results strengthen the few U-Pb ages already published for the Pyrenean granites and indicate that the Hercynian plutonism of the Pyrenees is essentially Carboniferous in age and syn-tectonic. (authors)

  9. U-series dating using thermal ionisation mass spectrometry (TIMS)

    International Nuclear Information System (INIS)

    McCulloch, M.T.

    1999-01-01

    U-series dating is based on the decay of the two long-lived isotopes 238 U(τ 1/2 =4.47 x 10 9 years) and 235 U (τ 1/2 0.7 x 10 9 years). 238 U and its intermediate daughter isotopes 234 U (τ 1/2 = 245.4 ka) and 230 Th (τ 1/2 = 75.4 ka) have been the main focus of recently developed mass spectrometric techniques (Edwards et al., 1987) while the other less frequently used decay chain is based on the decay 235 U to 231 Pa (τ 1/2 = 32.8 ka). Both the 238 U and 235 U decay chains terminate at the stable isotopes 206 Pb and 207 Pb respectively. Thermal ionization mass spectrometry (TIMS) has a number of inherent advantages, mainly the ability to measure isotopic ratios at high precision on relatively small samples. In spite of these now obvious advantages, it is only since the mid-1980's when Chen et al., (1986) made the first precise measurements of 234 U and 232 Th in seawater followed by Edwards et al., (1987) who made combined 234 U- 230 Th measurements, was the full potential of mass spectrometric methods first realised. Several examples are given to illustrate various aspects of TIMS U-series

  10. Chronology of fluid paleo-circulations in mesozoic formations on the site of Bure by U/Pb dating of secondary calcites

    International Nuclear Information System (INIS)

    Pisapia, C.; Deschamps, P.; Hamelin, B.; Pisapia, C.; Buschaert, S.

    2009-01-01

    The French national agency for the management of radioactive wastes (ANDRA, Agence nationale pour la gestion des dechets radioactifs) has developed an underground research laboratory in mesozoic formations of the eastern Parisian Basin in order to test the design of radioactive waste storage site in sedimentary formations. The authors report an investigation which aims at understanding the site paleo-hydrology. This investigation is based on the disintegration chain of uranium and on U/Th and U/Pb dating methods, and aims at giving a precise chronology of the different phases of precipitation of centimetric and millimetric secondary calcites sampled on this site

  11. Direct U-Pb dating of Cretaceous and Paleocene dinosaur bones, San Juan Basin, New Mexico: COMMENT

    Science.gov (United States)

    Koenig, Alan E.; Lucas, Spencer G.; Neymark, Leonid A.; Heckert, Andrew B.; Sullivan, Robert M.; Jasinski, Steven E.; Fowler, Denver W.

    2012-01-01

    Based on U-Pb dating of two dinosaur bones from the San Juan Basin of New Mexico (United States), Fassett et al. (2011) claim to provide the first successful direct dating of fossil bones and to establish the presence of Paleocene dinosaurs. Fassett et al. ignore previously published work that directly questions their stratigraphic interpretations (Lucas et al., 2009), and fail to provide sufficient descriptions of instrumental, geochronological, and statistical treatments of the data to allow evaluation of the potentially complex diagenetic and recrystallization history of bone. These shortcomings lead us to question the validity of the U-Pb dates published by Fassett et al. and their conclusions regarding the existence of Paleocene dinosaurs.

  12. U-Pb and K-Ar isotopic dating of Sinec (Rimavica) granites (Kohut zone of veporides)

    International Nuclear Information System (INIS)

    Bibikova, E.V.; Grachema, T.V.; Makarov, V.A.

    1988-01-01

    New results of radiometric dating of Sinec (Rimavica) granites by U-Pb and K-Ar method are presented. The K-Ar method (muscovite and biotite) gives the age of 94 m.y., which can be interpreted by tectonics. The U-Pb dating of zircons gave a concordant age of 350±5 m.y., which is a more reliable age than the one obtained from the same samples by Rb-Sr isochrone. The increased age of the Sinec (Rimavica) granites determined by the Sb-Sr method could be caused by the supply of radiogenic Sr from the surrounding older metamorphic rocks to the granites during retrograde metamorphism synchronous with granite autometasomatism. (author). 3 figs., 2 tabs., 15 refs

  13. Pleistocene apparent ages by U-Pb isotope and U-series methods for uranium ore in Dakota Sandstone near Gallup, New Mexico

    International Nuclear Information System (INIS)

    Ludwig, K.R.; Szabo, B.J.; Granger, H.C.

    1977-01-01

    Radiometric dates of a high-grade uranium ore from the Hogback No. 4 mine in Dakota Sandstone near Gallup, N. Mex., indicate a late Pleistocene age of mineralization. The 206 Pb/ 238 U and 207 Pb/ 235 U apparent ages of about 70,000 y and 100,000 y, respectively, are discordant, but are in broad agreement with the discordant 230 Th/ 238 U and 230 Pa/ 235 U apparent ages of 130,000 y and 78,000 y, respectively. Although it is not clear how the analyzed sample relates to the main period of mineralization at this mine, these dates are consistent with previous age limits suggested for Dakota Sandstone uranium ores

  14. 230Th/U-dating of a late Holocene low uranium speleothem from Cuba

    International Nuclear Information System (INIS)

    Fensterer, Claudia; Mangini, Augusta; Scholz, Denis; Hoffmann, Derik; Pajon, Jesus M

    2010-01-01

    We present 22 U-series ages for a stalagmite from north-western Cuba based on multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) and thermal ionisation mass spectrometry (TIMS). Our results reveal that the stalagmite continuously grew within the last ∼1400a. Low uranium content of the sample and thus, extremely low 230 Th concentrations limit the precision and accuracy of 230 Th/U-dating by TIMS. Samples measured by MC-ICPMS show a high variability of 232 Th content along the growth axis with some sections significantly affected by initial 230 Th from a detrital phase. An a-priori bulk earth ratio for ( 238 U/ 232 Th) cannot be used to accurately account for this initial 230 Th. Using an age model based on the 230 Th/U ages determined on samples with low or negligible 232 Th concentration, we find that the ( 238 U/ 232 Th) activity ratio of the detrital phase is an order of magnitude larger than the bulk earth value, indicating the importance of an accurately determined correction factor.

  15. U-series dating using thermal ionisation mass spectrometry (TIMS)

    Energy Technology Data Exchange (ETDEWEB)

    McCulloch, M.T. [Australian National University, Canberra, ACT (Australia). Research School of Earth Science

    1999-11-01

    U-series dating is based on the decay of the two long-lived isotopes{sup 238}U({tau}{sub 1/2}=4.47 x 10{sup 9} years) and {sup 235}U ({tau}{sub 1/2} 0.7 x 10{sup 9} years). {sup 238}U and its intermediate daughter isotopes {sup 234}U ({tau}{sub 1/2} = 245.4 ka) and {sup 230}Th ({tau}{sub 1/2} = 75.4 ka) have been the main focus of recently developed mass spectrometric techniques (Edwards et al., 1987) while the other less frequently used decay chain is based on the decay {sup 235}U to {sup 231}Pa ({tau}{sub 1/2} = 32.8 ka). Both the {sup 238}U and {sup 235}U decay chains terminate at the stable isotopes {sup 206}Pb and {sup 207}Pb respectively. Thermal ionization mass spectrometry (TIMS) has a number of inherent advantages, mainly the ability to measure isotopic ratios at high precision on relatively small samples. In spite of these now obvious advantages, it is only since the mid-1980`s when Chen et al., (1986) made the first precise measurements of {sup 234}U and {sup 232}Th in seawater followed by Edwards et al., (1987) who made combined {sup 234}U-{sup 230}Th measurements, was the full potential of mass spectrometric methods first realised. Several examples are given to illustrate various aspects of TIMS U-series 9 refs., 3 figs.

  16. In situ dating of the oldest morphological traces of life on Earth

    Science.gov (United States)

    Fliegel, D.; McLoughlin, N.; Simonetti, A.; de Wit, M.; Furnes, H.

    2008-12-01

    Sea floor pillow basalts contain tubular and granular bioalteration micro textures in their glassy margins1,2 created by microbes etching the rock3,4, hypothetically to get access to nutrients and electrons donors5. The etched pits in the rock can be regarded as trace fossils6 that later become mineralized by titanite (CaTiSiO5). Such trace fossils are known from recent oceanic crust to some of the oldest preserved Archean ocean floor, in the Barberton greenstone belt (BGB), in S-Africa7. However, the antiquity of BGB trace fossils has been questioned by some since only the host rock was dated until now8. Here, we report for the first time in situ U-Pb radiometric dating of titanite mineralizing the BGB trace fossils using LA-MC-ICPMS. An U-Pb date of of approx. 3.15 ± 0.05 Ga (95.4 % confidence) for the titanite demonstrates the antiquity of the BGB trace fossils. This result confirms the BGB trace fossils as the oldest directly dated morphological trace of life on Earth. We will present addition data to reveal the mineralization of trace fossils by titanite, comparing the BGB trace fossils to other similar tubular titanite mineralized textures from different locations and younger ages. Our data confirms that a sub-oceanic biosphere was already established in the early Archean by at least 3.2 Ga. Further the results highlight the importance of the sub-ocean habitats for the development and possibly refuge for life on (early) Earth. 1. Furnes, H. et al. Bioalteration of basaltic glass in the oceanic crust. Geochemistry Geophysics Geosystems 2, (2001). 2. Staudigel, H. et al. 3.5 billion years of glass bioalteration: vulcanic rocks as a basis for microbial life. Earth-Science Reviews 89, 156-176 (2008). 3. Furnes, H. et al. Links Between Geological Processes, Microbial Activeties and Evolution of Life. Dilek, Y., Furnes, H. and Muehlenbachs, K. (eds.), pp. 1-68 (Springer,2008). 4. McLoughlin, N. et al. Current Developments in Bioerosion (Erlangen Earth Conference

  17. Effect of 222Rn emanation from crystals on their 206Pb/238U age dating

    International Nuclear Information System (INIS)

    Barretto, Paulo M.C.

    2009-01-01

    The escape of radon from certain minerals with high uranium is of particular interest to those concerned with the determination of ages of rocks, minerals and tectonic events. To the extent that radon escapes, these minerals are not closed systems from the thermodynamic point of view and, more particularly, from the geochronological point of view. This investigation aimed to determine the radon escape from zircon crystals and how this fit into the severe isotopic constraints of the concordia dating model. To evaluate the consequences of radon loss on 238 U/ 206 Pb age dating methods, 20 zircon concentrates were analyzed. The observed range of relative percentage of radon loss was of 0.2-12 % and correlations with weathering of the crystals with natural alpha dose and with U-Pb age discordances were found. These correlations indicate relationships between the amount of lattice damage by radiation, the radon leakage out of the crystal and Pb mobility. Some of the stochastic complexities in specific age determinations are also discussed. (author)

  18. A comparison of U/Th and rapid-screen 14C dates from Line Island fossil corals

    Science.gov (United States)

    Grothe, Pamela R.; Cobb, Kim M.; Bush, Shari L.; Cheng, Hai; Santos, Guaciara M.; Southon, John R.; Lawrence Edwards, R.; Deocampo, Daniel M.; Sayani, Hussein R.

    2016-03-01

    Time-consuming and expensive radiometric dating techniques limit the number of dates available to construct absolute chronologies for high-resolution paleoclimate reconstructions. A recently developed rapid-screen 14C dating technique reduces sample preparation time and per sample costs by 90%, but its accuracy has not yet been tested on shallow-water corals. In this study, we test the rapid-screen 14C dating technique on shallow-water corals by comparing 44 rapid-screen 14C dates to both high-precision 14C dates and U/Th dates from mid- to late-Holocene fossil corals collected from the central tropical Pacific (2-4°N, 157-160°W). Our results show that 42 rapid-screen 14C and U/Th dates agree within uncertainties, confirming closed-system behavior and ensuring chronological accuracy. However, two samples that grew ˜6500 years ago have calibrated 14C ages ˜1000 years younger than the corresponding U/Th ages, consistent with diagenetic alteration as indicated by the presence of 15-23% calcite. Mass balance calculations confirm that the observed dating discrepancies are consistent with 14C addition and U removal, both of which occur during diagenetic calcite recrystallization. Under the assumption that aragonite-to-calcite replacement is linear through time, we estimate the samples' true ages using the measured 14C and U/Th dates and percent calcite values. Results illustrate that the rapid-screen 14C dates of Holocene-aged fossil corals are accurate for samples with less than 2% calcite. Application of this rapid-screen 14C method to the fossil coral rubble fields from Kiritimati Island reveal significant chronological clustering of fossil coral across the landscape, with older ages farther from the water's edge.

  19. Ediacaran ( 620 Ma) high grade regional metamorphism in the northern Arabian Nubian Shield: U/Th-Pb monazite ages of the Elat schist

    Science.gov (United States)

    Elisha, Bar; Katzir, Yaron; Kylander-Clark, Andrew

    2017-04-01

    Ediacaran times witnessed a hemisphere-scale orogenesis forming the extensive Pan-African mountain ranges and resulting in the final assembly of Gondwana supercontinent. The Elat metamorphic basement (S Israel) located at the northernmost tip of a major Pan-African orogenic suture, the Arabian Nubian Shield (ANS), comprises amphibolite facies schists and gneisses and was most likely shaped by this major continental collision. However the timing, number and duration of metamorphic events in Elat and elsewhere in the ANS are non-conclusive and a major emphasis was given to pre-Ediacaran island-arc related tectonics. This is mostly because U-Pb dating of zircon, widely used in Elat and elsewhere, is very successful in constraining the ages of the igneous and sedimentary protoliths, but is 'blind' to metamorphism at grades lower than granulite. Here U/Th-Pb dating of monazite, a precise chronometer of metamorphic mineral growth, is systematically applied to the Elat schist and unveils the tectono-metamorphic evolution of the Elat basement. Previous U-Pb dating of detrital zircon has shown that the sedimentary protoliths of the Elat schist are the oldest basement components (≥800 Ma), and detailed structural observations of the schists portrayed a complex deformation history including four successive phases (Shimron, 1972). The earliest three phases were defined as ductile and penetrative, but some of the available geochronological data apparently contradict field relations. In-situ analysis of metamorphic monazites by LASS (Laser Ablation Split Stream) involves simultaneous measurement of U/Th-Pb isotope ratios and REE contents in a single 10 μm sized grain or domain, thus allowing determining the age of specific texture and metamorphic assemblage. Monazite dating of the Elat schist yielded two concordant age clusters at 712±6 and 613±5 Ma. The corresponding REE patterns of the dated monazite grains indicate that porphyroblast growth, either garnet or staurolite

  20. Did the Kiruna iron ores form as a result of a metasomatic or igneous process? New U-Pb and Nd data for the iron oxide apatite ores and their host rocks in the Norrbotten region of northern Sweden

    Science.gov (United States)

    Westhues, A.; Hanchar, J. M.; Whitehouse, M. J.; Fisher, C. M.

    2012-12-01

    dating of zircon from both host rock and ore samples confirms a previously documented event around 1880 - 1900 Ma in the Norrbotten region. However, U-Pb in monazite from an ore sample suggests a further event at ca. 1650 Ma, a period of known activity in Fennoscandia. Further investigation and more U-Pb data are needed to confirm those dates and how the iron mineralization is related to those two events. The combination of U-Th-Pb ages, tracer isotopes and trace element abundances at mineral scale (e.g., Lu-Hf in zircon, and Sm-Nd in monazite, apatite, titanite), along with the O isotopic composition of zircon, will be used to decipher whether the Kiruna iron ore deposits are of metasomatic or igneous origin. Overall, the study also intends to develop a predictive model for exploration of similar iron oxide apatite deposits worldwide.

  1. Empirical constraints on the effects of radiation damage on helium diffusion in zircon

    Science.gov (United States)

    Anderson, Alyssa J.; Hodges, Kip V.; van Soest, Matthijs C.

    2017-12-01

    In this study, we empirically evaluate the impact of radiation damage on zircon (U-Th)/He closure temperatures for a suite of zircon crystals from the slowly cooled McClure Mountain syenite of south-central Colorado, USA. We present new zircon, titanite, and apatite conventional (U-Th)/He dates, zircon laser ablation (U-Th)/He and U-Pb dates, and zircon Raman spectra for crystals from the syenite. Titanite and apatite (U-Th)/He dates range from 447 to 523 Ma and 88.0 to 138.9 Ma, respectively, and display no clear correlation between (U-Th)/He date and effective uranium concentration. Conventional zircon (U-Th)/He dates range from 230.3 to 474 Ma, while laser ablation zircon (U-Th)/He dates show even greater dispersion, ranging from 5.31 to 520 Ma. Dates from both zircon (U-Th)/He datasets decrease with increasing alpha dose, indicating that most of the dispersion can be attributed to radiation damage. Alpha dose values for the dated zircon crystals range from effectively zero to 2.15 × 1019 α /g, spanning the complete damage spectrum. We use an independently constrained thermal model to empirically assign a closure temperature to each dated zircon grain. If we assume that this thermal model is robust, the zircon radiation damage accumulation and annealing model of Guenthner et al. (2013) does not accurately predict closure temperatures for many of the analyzed zircon crystals. Raman maps of the zircons dated by laser ablation document complex radiation damage zoning, sometimes revealing crystalline zones in grains with alpha dose values suggestive of amorphous material. Such zoning likely resulted in heterogeneous intra-crystalline helium diffusion and may help explain some of the discrepancies between our empirical findings and the Guenthner et al. (2013) model predictions. Because U-Th zoning is a common feature in zircon, radiation damage zoning is likely to be a concern for most ancient, slowly cooled zircon (U-Th)/He datasets. Whenever possible, multiple

  2. 238U-230Th dating of chevkinite in high-silica rhyolites from La Primavera and Yellowstone calderas

    Science.gov (United States)

    Vazquez, Jorge A.; Velasco, Noel O.; Schmitt, Axel K.; Bleick, Heather A.; Stelten, Mark E.

    2014-01-01

    Application of 238U-230Th disequilibrium dating of accessory minerals with contrasting stabilities and compositions can provide a unique perspective on magmatic evolution by placing the thermochemical evolution of magma within the framework of absolute time. Chevkinite, a Th-rich accessory mineral that occurs in peralkaline and metaluminous rhyolites, may be particularly useful as a chronometer of crystallization and differentiation because its composition may reflect the chemical changes of its host melt. Ion microprobe 128U-230Th dating of single chevkinite microphenocrysts from pre- and post-caldera La Primavera, Mexico, rhyolites yields model crystallization ages that are within 10's of k.y. of their corresponding K-Ar ages of ca. 125 ka to 85 ka, while chevkinite microphenocrysts from a post-caldera Yellowstone, USA, rhyolite yield a range of ages from ca. 110 ka to 250 ka, which is indistinguishable from the age distribution of coexisting zircon. Internal chevkinite-zircon isochrons from La Primavera yield Pleistocene ages with ~5% precision due to the nearly two order difference in Th/U between both minerals. Coupling chevkinite 238U-230Th ages and compositional analyses reveals a secular trend of Th/U and rare earth elements recorded in Yellowstone rhyolite, likely reflecting progressive compositional evolution of host magma. The relatively short timescale between chevkinite-zircon crystallization and eruption suggests that crystal-poor rhyolites at La Primavera were erupted shortly after differentiation and/or reheating. These results indicate that 238U-230Th dating of chevkinite via ion microprobe analysis may be used to date crystallization and chemical evolution of silicic magmas.

  3. Evaluation of potential of adsorption of U, Th, Pb, Zn and Ni by coconut fibers; Avaliacao do potencial de adsorcao de U, Th, Pb, Zn e Ni pelas fibras de coco

    Energy Technology Data Exchange (ETDEWEB)

    Monteiro, Raquel Almeida

    2009-07-01

    The residual biomass from agricultural activities has been evaluated as biosorbent for metals and organic composts from aqueous solutions, because of its adsorptive properties, low cost, abundance and to be a renewable resource. In this work, the efficiency of coir pith as biosorbent for the removal of U, Th, Pb, Zn e Ni ions from the aqueous solutions is presented. The coir pith is a by-product of the harvest of the coconut, a renewable natural source. The study was conducted by batch method. The influence of pH from 1 to 8, the dosage of the coir pith and the equilibrium time were studied. The adsorption of metal ions increased with the increase of pH and the dose. The Langmuir and Freundlich models were applied to describe the adsorption equilibrium isotherm. The kinetic process was studied using the pseudo-first order and pseudo-second order models. The Gibbs free energy was calculated. In the concentration range of 100 mg.L{sup -1} - 500 mg.L{sup -1}, the adsorption process was described better by the Langmuir equation for Pb{sup 2+} and Zn{sup 2+} ions and the Freundlich equation for UO{sub 2} 2{sup +}, Th{sup 4+} and Ni{sup 2+} ions, and represented by the pseudo-second order model. The biosorption process for removal of metal ions from the solutions was considered spontaneous. The results were promising, showing perspectives of application of coir pith as biosorbent of U, Th, Pb, Zn and Ni ions in wastewater treatment processes. (author)

  4. Advantages of conducting in-situ U-Pb age dating of multiple U-bearing minerals from a single complex: Case in point - the Oka Carbonatite Complex

    Science.gov (United States)

    Chen, W.; Simonetti, A.

    2012-12-01

    A detailed radiometric investigation is currently underway focusing on U-bearing accessory minerals apatite, perovskite, and niocalite from the Oka Carbonatite Complex (Canada). One of the main objectives is to obtain a comparative chronology of melt crystallization for the complex. Unlike other commonly adopted U-bearing minerals (e.g., zircon, monazite) for in-situ dating investigations, apatite, perovskite, and niocalite contain relatively high contents of common Pb. Hence, careful assessment of the proportion and composition of the common Pb, and usage of appropriate matrix-matched external standards are imperative. The Madagascar apatite was utilized as the external standard for apatite dating, and the Emerald Lake and Durango apatites were adopted as secondary standards; the latter yield ages of 92.6 ±1.8 and 32.2 ±1.1 Ma, respectively, and these are identical to their accepted ages. Pb/U ages for apatite from Oka were obtained for different rock types, including 8 carbonatites, 4 okaites, 3 ijolites and 3 alnoites, and these define a range of ages between ~105 and ~135 Ma; this result suggests a protracted crystallization history. In total, 266 individual analyses define two peaks at ~115 and ~125Ma. For perovskite dating, the Ice River perovskite standard was utilized as the external standard. The perovskites from one okaite sample yield an age of 112.2 ±1.9 Ma, and is much younger than the previously reported U-Pb perovskite age of 131 ±7 Ma. Hence, the combined U-Pb perovskite ages also suggest a rather prolonged time of melt crystallization. Niocalite is a rare, accessory silicate mineral that occurs within the carbonatites at Oka. The international zircon standard BR266 was selected for use as the external standard and rastering was employed to minimize the Pb-U fractionation. Two niocalite samples give young ages at 110.6 ±1.2 and 115.0 ±1.9 Ma, and are identical to their respective apatite ages (given associated uncertainties) from the same

  5. U/Pb dating: brioverian age of the Erquy series (Armorican massif, France)

    International Nuclear Information System (INIS)

    Cocherie, A.; Chantraine, J.; Egal, E.; Fanning, C.M.; Dabard, M.P.; Paris, F.; Le Herisse, A.

    2001-01-01

    New U/Pb analyses obtained with a high-resolution ion microprobe (SHRIMP) fix an age of 608 ± 7 Ma for spilites of the Erquy series, in Cadomian rocks of the Armorican massif, France. This Neo-proterozoic age re-integrates this unit into the Brioverian, the age it was initially assigned to. A Rb/sr whole-rock dating in the 1970's had undermined the regional Cadomian model, by suggesting an Ordovician age for these rocks; this was apparently further supported by the discovery of organic remains, interpreted as Paleozoic micro-fossils. The reassessment of this paleontologic attribution and the new isotope dating are a final confirmation of the age of this series. (authors)

  6. Measurement of L sub(III) subshell fluorescence yields in Pb, Th and U

    Energy Technology Data Exchange (ETDEWEB)

    Arora, S K; Allawadhi, K L; Sood, B S [Punjabi Univ., Patiala (India). Nuclear Science Labs.

    1981-01-01

    L sub(III) subshell fluorescence yields in Pb, Th and U have been measured using photoionization for creating vacancies. The results have been compared with the available data and are found to agree with the recent measurements of Price made using K-L coincidence technique but higher than those of Stephenson made using fluorescent excitation of L sub(III) subshell.

  7. Mass spectrometric 230Th-234U-238U dating of the Devils Hole calcite vein

    International Nuclear Information System (INIS)

    Ludwig, K.R.; Simmons, K.R.; Szabo, B.J.; Riggs, A.C.; Winograd, I.J.; Landwehr, J.M.; Hoffman, R.J.

    1992-01-01

    The Devils Hole calcite vein contains a long-term climatic record, but requires accurate chronologic control for its interpretation. Mass-spectrometric U-series ages for samples from core DH-11 yielding 230 Th ages with precisions ranging from less than 1,000 years (2σ) for samples younger than ∼140 ka (thousands of years ago) to less than 50,000 years for the oldest samples (∼566 ka). The 234 U/ 238 U ages could be determined to a precision of ∼20,000 years for all ages. Calcite accumulated continuously from 566 ka until ∼60 ka at an average rate of 0.7 millimeter per 10 3 years. The precise agreement between replicate analyses and the concordance of the 230 Th/ 238 U and 234 U/ 238 U ages for the oldest samples indicate that the DH-11 samples were closed systems and validate the dating technique in general

  8. {sup 230}Th/U-dating of a late Holocene low uranium speleothem from Cuba

    Energy Technology Data Exchange (ETDEWEB)

    Fensterer, Claudia; Mangini, Augusta [Forschungsstelle Radiometrie, Heidelberg Academy of Sciences, Im Neuenheimer Feld 229, 69120 Heidelberg (Germany); Scholz, Denis; Hoffmann, Derik [School of Geographical Sciences, University of Bristol, University Road, BS8 1SS, Bristol (United Kingdom); Pajon, Jesus M, E-mail: Claudia.Fensterer@iup.uni-heidelberg.d [Department of Archaeology, Cuban Institute of Anthropology, Amargura No. 203, e/n Habana y Aguiar, Ciudad de La Habana, CP: 10 100 (Cuba)

    2010-03-15

    We present 22 U-series ages for a stalagmite from north-western Cuba based on multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) and thermal ionisation mass spectrometry (TIMS). Our results reveal that the stalagmite continuously grew within the last {approx}1400a. Low uranium content of the sample and thus, extremely low {sup 230}Th concentrations limit the precision and accuracy of {sup 230}Th/U-dating by TIMS. Samples measured by MC-ICPMS show a high variability of {sup 232}Th content along the growth axis with some sections significantly affected by initial {sup 230}Th from a detrital phase. An a-priori bulk earth ratio for ({sup 238}U/{sup 232}Th) cannot be used to accurately account for this initial {sup 230}Th. Using an age model based on the {sup 230}Th/U ages determined on samples with low or negligible {sup 232}Th concentration, we find that the ({sup 238}U/{sup 232}Th) activity ratio of the detrital phase is an order of magnitude larger than the bulk earth value, indicating the importance of an accurately determined correction factor.

  9. U-Pb ages related to uranium mineralization of Lagoa Real, Bahia - Brazil: tectonic implications

    Energy Technology Data Exchange (ETDEWEB)

    Chaves, Alexandre O.; Rios, Francisco J.; Oliveira, Lucilia A.R.; Alves, James V.; Fuzikawa, Kazuo; Neves, Jose M.C.; Chaves, Adriana M.D.V.; Prates, Sonia P. [Centro de Desenvolvimento da Tecnologia Nuclear (CDTN/CNEN-MG), Belo Horizonte, MG (Brazil)]. E-mail: aoc@cdtn.br; Tubrett, Michael [Memorial University of Newfoundland, NL (Canada). Inco Innovation Centre. MicroAnalysis Facility; Matos, Evando C. [Industrias Nucleares do Brasil S.A. (INB), Rio de Janeiro, RJ (Brazil)

    2007-07-01

    The uranium from Lagoa Real (Bahia/Brazil) is associated with syenitic magmatism (1904 {+-}44 Ma minimum age from upper intercept of zircon U-Pb discordia by LA-ICP-MS) belonging to a mafic/ felsic lithologic association linked to the final stages of 2.05-1.80 Ga Orosirian Orogeny, which acted in the Paramirim Block. These syenitic rocks are rich not only in albite, but also in U-rich titanite (source of uranium). In association with the development of the Orosirian ductile shear zones, the syenites were crystallized and deformed. The metamorphic reactions, which include intense recrystallization of magmatic minerals, led uraninite to precipitate (1868 {+-} 69 Ma; U-Pb by LA-ICP MS) under Redox control. A second population of uraninites was also generated by shear zones reactivation during 0.6-0.5 Ga Brasiliano Orogeny (605 {+-} 170 Ma; U-Pb by LA-ICP-MS). The geotectonic implications are: a) the importance of the Orosirian event in the Paramirim Block during paleoproterozoic Sao Francisco/Congo Craton edification and b) the influence of the Brasiliano event in the Paramirim Block during the West-Gondwana assembly processes, indicated by the 605 {+-} 170 Ma uraninite (second population) age and by the 483 {+-} 100 Ma lower intercept of the metamorphosed syenite U-Pb discordia. (author)

  10. Geochemical and Sm–Nd isotopic study of titanite from granitoid ...

    Indian Academy of Sciences (India)

    in granitic magmas that have equilibrated with titanite during fractional crystallization or partial melting ... Titanite; Kolar; Ramagiri; Dharwar craton; rare earth elements; Sm–Nd isotope dating. J. Earth Syst. Sci. 120, No. 2, April 2011, pp. 237–251 c Indian Academy of Sciences ... be altered by variations in temperature and/or.

  11. 230Th/234U dating of coral limestones and vertical uplift at Djibouti

    International Nuclear Information System (INIS)

    Faure, Hugues; Hoang, C.T.; Lalou, Claude

    1980-01-01

    Coral limestones sampled from marine terraces along the Afar coast have been dated by the 230 Th/ 234 U method. The ages confirm the stratigraphic unity of these formations and the existence of the paleo sea level dated 124 000 years ago in this region. These results permit to deduce the uplift rates of this littoral [fr

  12. Migration of 226 Ra, 228 Ra, 210 Pb, U and Th from phosphogypsum

    International Nuclear Information System (INIS)

    Silva, Nivaldo Carlos da; Cipriani, Moacir; Taddei, Maria Helena T.

    2002-01-01

    The physico-chemical availability of radioactive elements ( 210 Pb, 226 Ra, 228 Ra, Th and U) in Brazilian phosphogypsum was investigated in a large scale leaching experiment carried out in lysimeters, using phosphogypsum samples (approximately 1.2 tons) from two phosphoric acid industries. Lysimeters were built using cylindrical concrete containers with 0.9 m inner diameter and 2 m depth. The bottom of the lysimeter was filled with a 10 cm layer of gravel covered with geomembrane sheet. Under this layer a pipe was designed to drain the percolated water. Three lysimeters were filled with phosphogypsum from each industry and a mixture of both. As percolated water comes exclusively from the rain, sample was collected daily when available. Samples were then pooled weekly, carefully prepared and submitted to radiochemical analysis. Radiochemical characterization of phosphogypsum and percolated water was performed by radiochemical separation followed by gross alpha and beta counting ( 226 Ra, 228 Ra and 210 Pb) and UV-Vis spectrophotometry with Arsenazo III (U and Th). This experiment was carried out from 12/01/1999 to 01/22/2001, with a precipitation of 2,732 mm. It was observed that approximately 40% (534 L) of the rain fall percolated through the lysimeter 1. The analysis of 22 samples of percolated water from lysimeter 1 showed mean radionuclides activities of 70±30 mBqL -1 , 70±50 mBqL -1 , 100±60 mBqL -1 and 110±55 mBqL -1 for U, 226 Ra, 228 Ra and 210 Pb, respectively. Thorium activities were below detection limit. (author)

  13. U-Th/ESR combined dating of faunal remains from the Mousterian open site of Beauvais (France)

    International Nuclear Information System (INIS)

    Michel, V.; Masaoudi, H.; Falgueres, Ch.; Yokoyama, Y.; Locht, J.L.; Antoine, P.

    1999-01-01

    Faunal remains from the Beauvais open site 'La Justice' (Oise) are the subject of an U-Th dating (disequilibrium of the uranium chain) and an ESR dating (electronic spin resonance). This study was performed in order to identify the chronological situation of the Middle Paleolithic levels of this site located in the north of France, supposedly aged stage 4 after stratigraphic correlations. U-Th ages of bones and dentine are between 20 and 200 ka and are scattered; however, the combined ESR/U-Th ages of rhinoceros dental enamels are homogeneous and indicate that the archaeological levels were deposited between 60 to 40 ka. This period corresponds to the end of the oxygen isotopic stage 4 to the beginning of stage 3. (authors) stage 3. (authors)

  14. Application of the 227Th/230Th method to dating Pleistocene carbonates and comparison with other dating methods

    International Nuclear Information System (INIS)

    Gascoyne, M.

    1985-01-01

    The 227 Th/ 230 Th dating method is described in detail and its usefulness investigated by comparing ages of sixteen Pleistocene carbonates (mainly cave deposits) with those determined by the 231 Pa/ 235 U and 230 Th/ 234 U methods. The 227 Th/ 230 Th ages are found to be critically dependent on corrections for decay of 227 Th prior to alpha counting and ingrowth of daughter isotopes of 232 Th derived from clastic detritus. Of nineteen sets of ages determined for the sixteen samples, good agreement is found for only seven sets. Differences are attributed to low U content of some samples and the possibility of excess 227 Th in the calcite of samples younger than approx. 50 ky, possibly due to the coprecipitation of 231 Pa during formation. Calculated 'negative' 227 Th/ 230 Th ages may be a direct result of this process and the fact that unlike the other methods, the activity ratio is non-zero at zero age. Nevertheless, the 227 Th/ 230 Th is found to be a useful alternative dating technique for carbonates which are between approx. 50 and 300 ky, because no spiking is required. It also serves as a check for partial concordancy with ages dated by the other methods. (author)

  15. Using titanite petrochronology to monitor CO2-degassing episodes from the Himalayas

    Science.gov (United States)

    Rapa, Giulia; Groppo, Chiara; Rolfo, Franco; Petrelli, Maurizio; Mosca, Pietro

    2017-04-01

    Metamorphic degassing from active collisional orogens supplies a significant fraction of CO2 to the atmosphere, playing a fundamental role in the long-term (> 1 Ma) global carbon cycle (Gaillardet & Galy, 2008). The petro-chronologic study of the CO2-source rocks (e.g. calc-silicate rocks) in collisional settings is therefore fundamental to understand the nature, timing, duration and magnitude of the orogenic carbon cycle. So far, the incomplete knowledge of these systems hindered a reliable quantitative modelling of metamorphic CO2 fluxes. A detailed petrological modelling of a clinopyroxene + scapolite + K-feldspar + plagioclase + biotite + zoisite ± calcite calc-silicate rock from central Nepal Himalaya allowed us to identify and fully characterize - for the first time - different metamorphic reactions that led to the simultaneous growth of titanite and production of CO2. These reactions involve biotite (rather than rutile) as the Ti-bearing reactant counterpart of titanite. The results of petrological modelling combined with Zr-in-Ttn thermometry and U-Pb geochronology suggest that in the studied sample, most titanite grains grew during two nearly continuous episodes of titanite formation: a near-peak event at 730-740°C, 10 kbar, 25.5±1.5 Ma, and a peak event at 740-765°C, 10.5 kbar, 22±3 Ma. Both episodes of titanite growth are correlated to specific CO2-producing reactions, thus allowing to constrain the timing, duration and P-T conditions of the main CO2-producing events, as well as the amounts of CO2 produced. Assuming that fluids released at a depth of ca. 30 km are able to reach the Earth's surface 10 Ma after their production, it is therefore possible to speculate on the role exerted by the Himalayan orogenesis on the climate in the past. Gaillardet J. & Galy A. (2008): Himalaya-carbon sink or source? Science, 320, 1727-1728.

  16. Evaluation of potential of adsorption of U, Th, Pb, Zn and Ni by coconut fibers

    International Nuclear Information System (INIS)

    Monteiro, Raquel Almeida

    2009-01-01

    The residual biomass from agricultural activities has been evaluated as biosorbent for metals and organic composts from aqueous solutions, because of its adsorptive properties, low cost, abundance and to be a renewable resource. In this work, the efficiency of coir pith as biosorbent for the removal of U, Th, Pb, Zn e Ni ions from the aqueous solutions is presented. The coir pith is a by-product of the harvest of the coconut, a renewable natural source. The study was conducted by batch method. The influence of pH from 1 to 8, the dosage of the coir pith and the equilibrium time were studied. The adsorption of metal ions increased with the increase of pH and the dose. The Langmuir and Freundlich models were applied to describe the adsorption equilibrium isotherm. The kinetic process was studied using the pseudo-first order and pseudo-second order models. The Gibbs free energy was calculated. In the concentration range of 100 mg.L -1 - 500 mg.L -1 , the adsorption process was described better by the Langmuir equation for Pb 2+ and Zn 2+ ions and the Freundlich equation for UO 2 2 + , Th 4+ and Ni 2+ ions, and represented by the pseudo-second order model. The biosorption process for removal of metal ions from the solutions was considered spontaneous. The results were promising, showing perspectives of application of coir pith as biosorbent of U, Th, Pb, Zn and Ni ions in wastewater treatment processes. (author)

  17. Cooling rates and the depth of detachment faulting at oceanic core complexes: Evidence from zircon Pb/U and (U-Th)/He ages

    Science.gov (United States)

    Grimes, Craig B.; Cheadle, Michael J.; John, Barbara E.; Reiners, P.W.; Wooden, J.L.

    2011-01-01

    Oceanic detachment faulting represents a distinct mode of seafloor spreading at slow spreading mid-ocean ridges, but many questions persist about the thermal evolution and depth of faulting. We present new Pb/U and (U-Th)/He zircon ages and combine them with magnetic anomaly ages to define the cooling histories of gabbroic crust exposed by oceanic detachment faults at three sites along the Mid-Atlantic Ridge (Ocean Drilling Program (ODP) holes 1270D and 1275D near the 15??20???N Transform, and Atlantis Massif at 30??N). Closure temperatures for the Pb/U (???800??C-850??C) and (U-Th)/He (???210??C) isotopic systems in zircon bracket acquisition of magnetic remanence, collectively providing a temperature-time history during faulting. Results indicate cooling to ???200??C in 0.3-0.5 Myr after zircon crystallization, recording time-averaged cooling rates of ???1000??C- 2000??C/Myr. Assuming the footwalls were denuded along single continuous faults, differences in Pb/U and (U-Th)/He zircon ages together with independently determined slip rates allow the distance between the ???850??C and ???200??C isotherms along the fault plane to be estimated. Calculated distances are 8.4 ?? 4.2 km and 5.0 2.1 km from holes 1275D and 1270D and 8.4 ?? 1.4 km at Atlantis Massif. Estimating an initial subsurface fault dip of 50 and a depth of 1.5 km to the 200??C isotherm leads to the prediction that the ???850??C isotherm lies ???5-7 km below seafloor at the time of faulting. These depth estimates for active fault systems are consistent with depths of microseismicity observed beneath the hypothesized detachment fault at the TAG hydrothermal field and high-temperature fault rocks recovered from many oceanic detachment faults. Copyright 2011 by the American Geophysical Union.

  18. Determination of the concentration of 238U, 234U, 232Th, 228Th, 228Ra, 226Ra and 210Pb in the feces of workers from a mining company of niobium and their families

    International Nuclear Information System (INIS)

    Oliveira, Roges de; Lopes, Ricardo T.; Melo, Dunstana R.; Juliao, Ligia M.Q.C.

    2005-01-01

    The object of this study consists of an open mine from which Niobium ore (pyrochlore) is extracted and a metallurgy company, where Fe-Nb alloys are produced for export. For geological reasons, the main ore is associated to natural radionuclides U and Th, and its decay products. The concentration of 234 U, 238 U, 232 Th, 226 Ra and 228 Ra, 228 Th, including 210 Pb in fecal excretion of 12:0 am, 29 workers and 13 family members were determined. The technique employed for the determination of the elements was the sequential method of radiochemical separation, followed by alpha spectrometry and counting α and β in proportional detector. Statistically significant difference was observed in the concentration of 234 U and 238 U, in feces samples, among the group of mining workers and family members; as well as for 232 Th in the feces of workers of crushing and metallurgy groups when compared with the Family Group. No statistically significant difference was detected at a concentration of 226 Ra, 228 Ra and 210 Pb, in feces of any group of workers of the installation in relation to the family group

  19. Radiometric dating methods

    International Nuclear Information System (INIS)

    Bourdon, B.

    2003-01-01

    The general principle of isotope dating methods is based on the presence of radioactive isotopes in the geologic or archaeological object to be dated. The decay with time of these isotopes is used to determine the 'zero' time corresponding to the event to be dated. This paper recalls the general principle of isotope dating methods (bases, analytical methods, validation of results and uncertainties) and presents the methods based on natural radioactivity (Rb-Sr, Sm-Nd, U-Pb, Re-Os, K-Ar (Ar-Ar), U-Th-Ra- 210 Pb, U-Pa, 14 C, 36 Cl, 10 Be) and the methods based on artificial radioactivity with their applications. Finally, the methods based on irradiation damages (thermoluminescence, fission tracks, electron spin resonance) are briefly evoked. (J.S.)

  20. Study of in vivo generators Pb-212/Bi--212 and U-230/Th-226 for alpha radioimmunotherapy

    International Nuclear Information System (INIS)

    Le Du, A.

    2011-01-01

    Alpha-radioimmunotherapy is a promising cancer therapy that uses a-particles vectorized by monoclonal antibody to break down cancerous tumors. The notion of in vivo generator was introduced in 1989 by Leonard Mausner. The concept involves labeling of various molecular carriers (antibodies, peptides, etc) with intermediate half-life generator parents, which after accumulation in the desired tissue generate much shorter half-life daughter radionuclide. This thesis focuses on the study of two in vivo generators potentially interesting for alpha-radioimmunotherapy: Pb-212 / Bi-212 generator and U-230 / Th-226 generator. The first part of this work presents the Pb-212 / Bi-212 generator, two approaches allowing the vectorization. Chelation approach on a protein and an approach by encapsulation in liposomes have been proposed. This last approach appears to be the most interesting. In vitro stability studies have been performed on these labeling. The second part of this work presents the U-230 / Th-226 generator. Studies have first been made to achieve a theoretical model to describe the speciation of Th(IV) in human serum. The efficacy of DTPA as chelating agent for complexation of Th(IV) in human serum could thus be estimated. (author)

  1. LA-ICP-MS Pb-U Dating of Young Zircons from the Kos-Nisyros Volcanic Centre, SE Aegean Arc (Greece)

    Science.gov (United States)

    Guillong, M.; Von Quadt, A.; Peytcheva, I.; Bachmann, O.

    2014-12-01

    Zircon Pb-U dating has become a key technique for answering many important questions in geosciences. This paper describes a new LA-ICP-MS approach. We show, using previously dated samples of a large quaternary rhyolitic eruption in the Kos-Nisyros volcanic centre (the 161 ka Kos Plateau Tuff), that the precision of our LA-ICP-MS method is as good as via SHRIMP, while ID-TIMS measurements confirm the accuracy. Gradational age distribution over >140 ka of the Kos zircons and the near-absence of inherited cores indicate near-continuous crystallisation in a growing magma reservoir with little input from wall rocks. Previously undated silicic eruptions from Nisyros volcano (Lower Pumice, Nikia Flow, Upper Pumice), which are stratigraphically constrained to have happened after the Kos Plateau Tuff, are dated to be younger than respectively 124 ± 35 ka, 111 ± 42 ka and 70 ± 24 ka. Samples younger than 1 Ma were corrected for initial thorium disequilibrium using a new formula that also accounts for disequilibrium in 230Th decay. Guillong, M. et al., 2014, JAAS, 29, p. 963-967; doi: 10.1039/c4ja00009a.

  2. U and Th thin film neutron dosimetry for fission-track dating: application to the age standard Moldavite

    International Nuclear Information System (INIS)

    Iunes, P.J.; Bigazzi, G.; Hadler Neto, J.C.; Laurenzi, M.A.; Balestrieri, M.L.; Norelli, P.; Osorio Araya, A.M.; Guedes, S.; Tello S, C.A.; Paulo, S.R.; Moreira, P.A.F.P.; Palissari, R.; Curvo, E.A.C.

    2005-01-01

    Neutron dosimetry based on U and Th thin films was used for fission-track dating of the age standard Moldavite, the central European tektite, from the Middle Miocene deposit of Jankov (southern Bohemia, Czech Republic). Our fission-track age (13.98+/-0.58Ma) agrees with a recent 40 Ar/ 39 Ar age, 14.34+/-0.04Ma, based on several determinations on Moldavites from different sediments, including the Jankov deposit. This result indicates that the U and Th thin film neutron dosimetry represents a reliable alternative for an absolute approach in fission-track dating

  3. Preliminary U-Th Dating of Endogenic Gypsum From Lake Petén-Itzá, Guatemala

    Science.gov (United States)

    Gamble, V. C.; Gallup, C. D.; Hodell, D.; Anselmetti, F.; Brenner, M.; Ariztegui, D.

    2007-05-01

    Uranium-thorium dating of lake sediments can provide accurate ages beyond the range of radiocarbon dating. Many lakes have endogenic precipitation of calcium bearing minerals that allow for substitution by uranium within their crystal structures. The water chemistry of Lake Petén-Itzá, located in northern Guatemala, is dominated by calcium, sulfate and carbonate ions (Deevey et al. 1980; Curtis et al. 1998). Changes in regional climate due to suspected shifts in the ITCZ over the past 85,000 years resulted in both calcite and gypsum deposition, especially during drier periods (Hodell et al. 2006). Both precipitates incorporate uranium from the lake water and can be used for U-Th dating. U-Th dating is problematic in lake systems for several reasons: the potential for 1) diagenetic alteration or dissolution while the endogenic precipitates are settling and after deposition and 2) contamination by detrital thorium. Contamination is a primary issue because of the difficulty of separating the precipitates from the sediment. Despite these concerns, U-Th dating of lake sediments has the potential to be successful with careful selection of precipitates and thorough analysis of the precipitate, the lake system, and the diagenetic environment. Preliminary samples of Lake Petén-Itzá gypsum contain euhedral crystals, indicating a lack of post-depositional alteration. However, the samples have high background thorium levels, indicating the necessity of using the U-Th total sample dissolution isochron dating method (as described by Ku, 2000) to quantify authigenic thorium. Curtis J.H., Brenner M., Hodell D.A., Balser R.A., Islebe G.A., Hooghiemstra H. 1998. A multi-proxy study of Holocene environmental change in the Maya lowlands of Petén, Guatemala. Journal of Paleolimnology 19, 139-159. Deevey E.S., Brenner M., Flannery M.S., Yezdani G.H. 1980. Lakes Yaxha and Scanab, Petén, Guatemala: Limnology and hydrology. Arch. Hydrobiol. 57, 419-460. Hodell D.A., Anselmetti F

  4. A multi-radioisotope approach to dating sedimentation : applying Re-Os organic-rich shale and U-Pb authigenic xenotime dating to the Shannon and Pennine Basins

    OpenAIRE

    Stanislawska, Maja Anna

    2013-01-01

    Sedimentary rocks are the most abundant hthologies on the Earth, covering over 70% of the planet’s surface. Quantitative dating of sedimentary rocks (especially those devoid of fossils) is critical to understanding the past events and rates and duration of processes that shaped the Earth. Recent advances in geochronology of sedimentary rocks, such as Re-Os dating of organic-rich shales and U-Pb dating of authigenic xenotime, allow precise depositional and early diagenetic ages to be obtained,...

  5. Dating exhumed peridotite with spinel (U-Th)/He chronometry

    Science.gov (United States)

    Cooperdock, Emily H. G.; Stockli, Daniel F.

    2018-05-01

    The timing of cooling and exhumation of mantle peridotites in oceanic and continental settings has been challenging to determine using traditional geo- and thermochronometric techniques. Hence, the timing of the exhumation of mantle rocks to the Earth's surface at mid-ocean ridges, rifted and passive continental margins, and within continental volcanic and orogenic systems has remained largely elusive or only loosely constrained by relative age bracketing. Magmatic spinel [(Mg, Fe)(Al,Cr)2O4] is a ubiquitous primary mineral phase in mantle peridotites and is often the only primary mineral phase to survive surface weathering and serpentinization. This work explores spinel (U-Th)/He thermochronology as a novel tool to directly date the exhumation and cooling history of spinel-bearing mantle peridotite. Samples were chosen from a range of tectonic and petrologic settings, including a mid-ocean ridge abyssal peridotite (ODP Leg 209), an orogenic tectonic sliver of sub-continental mantle (Lherz massif, France), and a volcanic-rock hosted mantle xenolith (Green Knobs, NM). Spinel grains were selected based on grain size and morphology, screened for internal homogeneity using X-ray computed tomography, and air abraded to eliminate effects of alpha ejection/implantation. These case studies yield spinel He age results that are reproducible and generally in good agreement with independent age constraints. For ODP Leg 209, a spinel He age of 1.1 ± 0.3 Ma (2 SE) (n = 8) is consistent with independent U-Pb and magnetic anomaly ages for the exhumation of oceanic crust by detachment faulting along this segment of the slow-spreading ridge. Spinel from the Lherz massif yield He ages from 60-70 Ma (n = 3), which correspond well with independent thermochronometric constraints for cooling associated with Pyrenean collisional exhumation. Spinel from a mantle xenolith within a previously undated kimberlite diatreme at Green Knobs, New Mexico, generate a reproducible mean He age of 11

  6. U-Pb geochronology on zircon from the Aouli pluton, Haute Moulouya area, Morocco

    International Nuclear Information System (INIS)

    Oukemeni, D.; Krogh, T.E.

    1995-01-01

    The Aouli Pluton consists of four units: (1) granodiorite; (2) grey granite; (3) pink granite - these three units constituting a spatially continuous massif, and (4) muscovite granite, which is exposed in two small stocks somewhat removed from the other units. U-Pb ages obtained on zircon and titanite are 333 ± 2 Ma and 319 ± 1.5 Ma for the granodiorite and grey granite respectively. The 14 ma age difference between the granodiorite and the grey granite supports the multiple injection hypothesis which was the outcome of geochemical studies (Oukemeni and Bourne, 1993). These two rocks also contain an inherited component which has been dated at 1520 Ma in the granudiorite and at 1245 ma and 1804 Ma in the grey granite. The inherited components suggest the possible presence of Precambian crust below the Haute Moulouya. Since the intrusion is late-to post-tectonic (Oukemeni and Bourne, 1993), the age of the granodiorite (333 ± 2 Ma) indicates that the Hercynian deformation is pre-Visean in the Haute Moulouya area, and, by extension, throughout the eastern meseta region. (authors). 14 refs. 4 figs. 3 tabs

  7. The Wall-Rock Record of Incremental Emplacement in the Little Cottonwood-Alta Magmatic and Hydrothermal System, Wasatch Mountains, Utah, U.S.A.

    Science.gov (United States)

    Stearns, M.; Callis, S.; Beno, C.; Bowman, J. R.; Bartley, J. M.

    2017-12-01

    Contact aureoles record the cumulative effects on wall rocks of magma emplacement. Like the plutons they surround, contact aureoles have long been regarded to form geologically instantaneously. Protracted incremental emplacement of plutons must be reconciled with the wall-rock record of heat and mass transfer. Fundamental questions include how heat and material move from intrusions into their aureoles and how long that process takes. The Little Cottonwood stock is surrounded by a 2 km-wide contact aureole that contains prograde AFM mineral assemblages in the pelitic layers of the Proterozoic Big Cottonwood Formation. The Alta stock is surrounded by a well characterized 1 km-wide contact aureole containing both prograde AFM and CMS mineral assemblages in Ophir Shale and Mississippian dolostones, respectively. Understanding the petrogenesis of these aureoles requires the timing of magmatism and wall-rock metamorphism to be independently determined. Preliminary petrochronology (U/Th-Pb dates and trace element concentrations collected by LASS-ICP-MS) from the inner aureoles of both intrusions establishes a protracted history of monazite (re)crystallization from 35-25 Ma in the Little Cottonwood aureole and 35 Ma in the Alta aureole. Little Cottonwood aureole monazites are characterized by a positive age correlation with heavy rare earth elements (HREE) and a negative correlation with Eu/Eu*. Alta aureole monazites have a similar range of the HREE concentrations and Eu/Eu* variation. Zircon growth interpreted to record emplacement-level magmatic crystallization of the western Little Cottonwood stock ranges from 33-28 Ma near the contact. Multi-grain U-Pb zircon TIMS dates from the Alta stock range from 35-33 Ma and are interpreted to suggest the full range of emplacement-level magmatism in the Alta stock. Additionally, in situ U-Pb titanite dates from the Alta stock record intermittent high temperature hydrothermal activity in the stock margin from 35-24 Ma. These new

  8. The SHRIMP zircon U-Pb dating of felsic volcanic rocks and its geological significance from yutian group in southern jiangxi

    International Nuclear Information System (INIS)

    Ji Chunyu; Wu Jianhua

    2010-01-01

    Past researches have showed that the Rb-Sr isochron ages of felsic end member for r hyolite-basalt b imodal volcanic rocks of Yutian Group in the Changpu and Longnan Basin in Southern Jiangxi Province are 175 ∼ 148 Ma, not only does its amplitude change more significantly, but it does not match with the Rb-Sr isochron ages (179 ∼ 173 Ma) of basic end member. As a result, I choose a method of zircon U-Pb dating with a higher accuracy, to obtain the rhyolite in the bottom of bimodal volcanic rocks in the Changpu Basin and the dacite in the top of of bimodal volcanic rocks in the Longnan Basin, whose zircon SHIRMP U-Pb age are respectively (195.2 ± 2.8) Ma and (191 ± 1.7) Ma. What's more, they are both almost the same in the error limit. It shows that the bimodal volcanic rocks in these both two basins are the product of the same session of magma movement. Simultaneously, it explains they form in a flash during the eruption intervals. According to the the newest International Stratigraphic Chart (Gradsrein et al. , 2004), in terms of geological age, the bimodal volcanic rocks in Changpu Basin and Longnan Basin, belonging to the early Early Jurassic. The zircon SHIRMP U-Pb age are distinctly older than the whole-rock Rb-Sr isochron age, it is probably because of the deviation of the dating method for the wholerock Rb-Sr isochron age. The zircon SHIRMP U-Pb age of bimodal volcanic rocks are 191 ∼ 195 Ma in Southern Jiangxi Province, which indicates that there had been an extensional environment. And after the bimodal volcanic activity, The zircon SHIRMP U-Pb age of felsic volcanic rocks are 145 ∼ 130 Ma. Both of the ages shows a as long as 45 Ma quiet period between 190 Ma and 145 Ma. It is unreasonable possible to interpreted by the single pattern of pacific plate subducting to eurasian plate. (authors)

  9. Properties and recrystallization of radiation damaged pyrochlore and titanite

    Energy Technology Data Exchange (ETDEWEB)

    Zietlow, Peter

    2016-11-02

    Radiation damage in minerals is caused by the alpha-decay of incorporated radionuclides, such as U and Th and their decay products. The effect of thermal annealing (400-1400 K) on radiation-damaged pyrochlores has been investigated by Raman scattering, X-ray powder diffraction (XRD), and combined differential scanning calorimetry/thermogravimetry (DSC/TG) (Zietlow et al., in print). The analysis of three natural radiation-damaged pyrochlore samples from Miass/Russia (6.4 wt% Th, 23.1.10{sup 18} a-decay events per gram (dpg)), Zlatoust/Russia (6.3 wt% Th, 23.1.10{sup 18} dpg), Panda Hill/Tanzania (1.6 wt% Th, 1.6.10{sup 18} dpg), and Blue River/Canada (10.5 wt% U, 115.4.10{sup 18} dpg), are compared with a crystalline reference pyrochlore from Schelingen (Germany). The type of structural recovery depends on the initial degree of radiation damage (Panda Hill 28 %, Blue River 85 %, Zlatoust and Miass 100 % according to XRD), as the recrystallization temperature increases with increasing degree of amorphization. Raman spectra indicate reordering on the local scale during annealing-induced recrystallization. As Raman modes around 800 cm{sup -1} are sensitive to radiation damage (Vandenborre and Husson 1983, Moll et al. 2011), the degree of local order was deduced from the ratio of the integrated intensities of the sum of the Raman bands between 605 and 680 cm{sup -1} devided by the sum of the integrated intensities of the bands between 810 and 860 cm{sup -1}. The most radiation damaged pyrochlores (Miass and Zlatoust) show an abrupt recovery of both, its short- (Raman) and long-range order (X-ray) between 800 and 850 K. The volume decrease upon recrystallization in Zlatoust pyrochlore was large enough to crack the sample repeatedly. In contrast, the weakly damaged pyrochlore (Panda Hill) begins to recover at considerably lower temperatures (near 500 K), extending over a temperature range of ca. 300 K, up to 800 K (Raman). The pyrochlore from Blue River shows in its

  10. Th-Pb ion probe dating of zoned hydrothermal monazite and its implications for repeated shear zone activity: An example from the Central Alps, Switzerland

    Science.gov (United States)

    Bergemann, C.; Gnos, E.; Berger, A.; Whitehouse, M.; Mullis, J.; Wehrens, P.; Pettke, T.; Janots, E.

    2017-04-01

    Th-Pb age dating of zoned hydrothermal monazite from alpine-type fissures/clefts is a powerful tool for constraining polyphase deformation at temperatures below 350°C and presents an alternative to K/Ar and 40Ar/39Ar dating techniques for dating brittle tectonics. This study considers the relationship between cleft orientations in ductile shear zones and cleft mineral crystallization during subsequent brittle overprinting. In the Grimsel area, located in the Aar Massif of the Central Alps, horizontal clefts formed during a primary thrust dominated deformation, while younger and vertically oriented clefts developed during secondary strike-slip movements. The change is due to a switch in orientation between the principal stress axes σ2 and σ3. The transition is associated with monazite crystallization and chloritization of biotite at around 11.5 Ma. Quartz fluid inclusion data allow a link between deformation stages and temperatures to be established and indicate that primary monazite crystallization occurred in both cleft systems at 300-350°C. While cleft monazite crystallization ceases at 11 Ma in inactive shear zones, monazite growth, and/or dissolution-reprecipitation continues under brittle deformation conditions in vertical clefts during later deformation until 7 Ma. This younger shear zone activity occurs in association with dextral strike-slip movement of the Rhone-Simplon fault system. With the exception of varying Th/U values correlated with the degree of oxidation, there is only limited compositional variation in the studied cleft monazites.

  11. The first case study of 230Th/U and 14C dating of mid-valdai organic deposits

    Science.gov (United States)

    Maksimov, F. E.; Kuznetsov, V. Yu.; Zaretskaya, N. E.; Subetto, D. A.; Shebotinov, V. V.; Zherebtsov, I. E.; Levchenko, S. B.; Kuznetsov, D. D.; Larsen, E.; Lysö, A.; Jensen, M.

    2011-05-01

    From the viewpoint of precision and reliability of radioisotopic dating, deposits whose quantitative age can be determined through several methods of geochronometry are of special interest. The mutually conforming finite 14C and 230Th/U dates of buried Neopleistocene organic deposits, taken from the Tolokonka section by the North Dvina River (100 km downstream from the city of Kotlas), have been obtained for the first time in Russia. The stratigraphical reference of these results to those obtained via the optically induced luminescence for upper and lower bedding layers has been established. The presented geochronometric data have allowed us to consider the age of oxbow lake organic deposits completely reliable and refer the time of their formation to the Tyrbei warming within the MIS-3. The applicability of the new version of the 230Th/U method for dating of interglacial and interstadial deposits, for the purpose of solving the Middle and Late Neopleistocene chronostratigraphy issues, is confirmed.

  12. 230Th/234U dates of late Pleistocene corals from Kita- and Minami-Diato Island, Okinawa, Japan

    International Nuclear Information System (INIS)

    Omura, Akio; Iwata, Hideki; Ota, Yoko; Koba, Motoharu; Kawana, Toshio.

    1991-01-01

    Alpha spectrometric Th-230/U-234 dating was applied to 50 Pleistocene corals from Kita- and Minami-Daito Islands, both have been well known as the noteworthy representatives of raised atolls. The Th-230/U-234 dates ranged from 113±6 to 133±6 ka (123±1 ka on average) in the autochthonous corals from Kita-, and from 111±5 to 159±10 ka (123±1 ka on average) in those from Minami-Daito Island, intimating that the fringing reefs have been developed during the high sea level stand of the last interglacial maximum. These dates are correlative to the oxygen isotope stage 5e. The upper limit of occurrence of the dated autochthonous corals was 8.1 m in Kita- and 11 m in Minami-Daito Island. Besides, the somewhat younger dates corresponding to OIS-5a or 5c were obtained from some allochthonous corals in a detrital limestone unit in Kita-Daito Island. However, hermatypic corals were alive, forming small scale reefs in shallow sea around Kita-Daito Island. The former shoreline was proved by the presence of raised surf bench at some localities, where the dated autochthonous corals were collected. (K.I.)

  13. Isotopic composition of Pb and Th in interplinian volcanics from Somma-Vesuvius volcano, Italy

    International Nuclear Information System (INIS)

    Cortini, M.; De Vivo, B.; Somma, R.; Ayuso, R.A.; Holden, P.

    2004-01-01

    We present a detailed isotopic study of volcanic rocks emitted from Somma-Vesuvius volcano during three periods of interplinian activity: 'Protohistoric' (3550 y B.P. to 79 A.D.), 'Ancient Historic' (79 to 472 A.D.) and 'Medieval' (472 to 1631 A.D.). Pb isotopic compositions of two acid leached fractions and whole rock residues of 37 whole rock samples (determined by Somma et al., 2001) show that each of the three interplinian periods is distinguished by small, systematic, and unique uranogenic and thorogenic Pb isotopic trends. This key and novel feature is compatible with the notion that the Pb isotopic data reflect small-scale source heterogeneity operating over relatively short periods of time. From this representative group of samples, a selected set of nine whole rocks were analyzed for Th isotopes. 232 Th/ 238 U ratios in the source can be obtained independently from Pb and from Th isotopes. Those obtained from Pb isotopes represent source ratios, time-integrated over the whole age of the earth; they range from 3.9 to 4.1. 232 Th/ 238 U obtained from Th isotopes are those of the present source. They are lower, and cluster around 3.5; this difference probably indicates recent U enrichment of the present source. The behavior of Pb, as inferred by its isotopic ratios, is quite distinct from that of Sr and Nd isotopes: Pb isotope variations are not correlated to Sr or Nd isotope variations. The isotopic contrast is compatible with the idea that the isotopes were decoupled during magmatic production, evolution, and ascent through the crust. Thus, the Pb isotopes do not reflect the effects of the same processes as in the case of the Sr and Nd isotopes, or, as we also favor, they do not necessarily reflect the same source contributions into the magmas. Moreover, the Pb isotopic evolution of the interplinian rocks chiefly reflects mixing, driven by processes that are superimposed on, and independent of, other source contributions that determine the isotopic

  14. The isotopic dating of crystals

    International Nuclear Information System (INIS)

    Giuliani, G.; Cheilletz, A.

    1995-01-01

    The first part of this work deals with the answer to the question : why are the crystals dated ? Then, some isotopic dating methods are described : U-Th-Pb, K-Ar, 40 Ar/ 39 Ar, Rb-Sr, Sm-Nd, fission traces, carbon 14 methods. Examples concerning emeralds and diamonds are given. (O.L.). 12 refs., 2 figs

  15. CONCH: A Visual Basic program for interactive processing of ion-microprobe analytical data

    Science.gov (United States)

    Nelson, David R.

    2006-11-01

    A Visual Basic program for flexible, interactive processing of ion-microprobe data acquired for quantitative trace element, 26Al- 26Mg, 53Mn- 53Cr, 60Fe- 60Ni and U-Th-Pb geochronology applications is described. Default but editable run-tables enable software identification of secondary ion species analyzed and for characterization of the standard used. Counts obtained for each species may be displayed in plots against analysis time and edited interactively. Count outliers can be automatically identified via a set of editable count-rejection criteria and displayed for assessment. Standard analyses are distinguished from Unknowns by matching of the analysis label with a string specified in the Set-up dialog, and processed separately. A generalized routine writes background-corrected count rates, ratios and uncertainties, plus weighted means and uncertainties for Standards and Unknowns, to a spreadsheet that may be saved as a text-delimited file. Specialized routines process trace-element concentration, 26Al- 26Mg, 53Mn- 53Cr, 60Fe- 60Ni, and Th-U disequilibrium analysis types, and U-Th-Pb isotopic data obtained for zircon, titanite, perovskite, monazite, xenotime and baddeleyite. Correction to measured Pb-isotopic, Pb/U and Pb/Th ratios for the presence of common Pb may be made using measured 204Pb counts, or the 207Pb or 208Pb counts following subtraction from these of the radiogenic component. Common-Pb corrections may be made automatically, using a (user-specified) common-Pb isotopic composition appropriate for that on the sample surface, or for that incorporated within the mineral at the time of its crystallization, depending on whether the 204Pb count rate determined for the Unknown is substantially higher than the average 204Pb count rate for all session standards. Pb/U inter-element fractionation corrections are determined using an interactive log e-log e plot of common-Pb corrected 206Pb/ 238U ratios against any nominated fractionation-sensitive species pair

  16. Metamorphic evolution and U-Pb zircon SHRIMP geochronology of the Belizário ultramafic amphibolite, Encantadas Complex, southernmost Brazil

    Directory of Open Access Journals (Sweden)

    Hartmann Léo A.

    2003-01-01

    Full Text Available The integrated investigation of metamorphism and zircon U-Pb SHRIMP geochronology of the Belizário ultramafic amphibolite from southernmost Brazil leads to a better understanding of the processes involved in the generation of the Encantadas Complex. Magmatic evidence of the magnesian basalt or pyroxenite protolith is only preserved in cores of zircon crystals, which are dated at 2257 ± 12 Ma. Amphibolite facies metamorphism M1 formed voluminous hornblende in the investigated rock possibly at 1989 ± 21 Ma. This ultramafic rock was re-metamorphosed at 702±21 Ma during a greenschist facies eventM2; the assemblage actinolite + oligoclase + microcline + epidote + titanite + monazite formed by alteration of hornblende. The metamorphic events are probably related to the Encantadas Orogeny (2257±12 Ma and Camboriú Orogeny (~ 1989 Ma of the Trans-Amazonian Cycle, followed by an orogenic event (702±21 Ma of the Brasiliano Cycle. The intervening cratonic period (2000-700 Ma corresponds to the existence of the Supercontinent Atlantica, known regionally as the Rio de la Plata Craton.

  17. Rapid evolution of ritual architecture in central Polynesia indicated by precise 230Th/U coral dating.

    Science.gov (United States)

    Sharp, Warren D; Kahn, Jennifer G; Polito, Christina M; Kirch, Patrick V

    2010-07-27

    In Polynesia, the complex Society Islands chiefdoms constructed elaborate temples (marae), some of which reached monumental proportions and were associated with human sacrifice in the 'Oro cult. We investigated the development of temples on Mo'orea Island by 230Th/U dating of corals used as architectural elements (facing veneers, cut-and-dressed blocks, and offerings). The three largest coastal marae (associated with the highest-ranked chiefly lineages) and 19 marae in the inland 'Opunohu Valley containing coral architectural elements were dated. Fifteen corals from the coastal temples meet geochemical criteria for accurate 230Th/U dating, yield reproducible ages for each marae, and have a mean uncertainty of 9 y (2sigma). Of 41 corals from wetter inland sites, 12 show some diagenesis and may yield unreliable ages; however, the majority (32) of inland dates are considered accurate. We also obtained six 14C dates on charcoal from four marae. The dates indicate that temple architecture on Mo'orea Island developed rapidly over a period of approximately 140 y (ca. AD 1620-1760), with the largest coastal temples constructed immediately before initial European contact (AD 1767). The result of a seriation of architectural features corresponds closely with this chronology. Acropora coral veneers were superceded by cut-and-dressed Porites coral blocks on altar platforms, followed by development of multitier stepped altar platforms and use of pecked basalt stones associated with the late 'Oro cult. This example demonstrates that elaboration of ritual architecture in complex societies may be surprisingly rapid.

  18. U-Pb geochronologic constraints on Paleoproterozoic orogenesis in the northwestern Makkovik Province, Labrador, Canada

    International Nuclear Information System (INIS)

    Ketchum, J.W.F.; Dunning, G.R.; Dunning, G.R.

    1997-01-01

    A 45 km wide, shear-zone-bounded segment of the northwestern Makkovik Province, Labrador, is underlain by Archean gneisses derived from the adjacent Nain craton. This lithotectonic block (Kaipokok domain) was reworked at high metamorphic grade, overthrust by supracrustal sequences (Lower Aillik and Moran Lake groups), and intruded by granitoid plutons during the Paleoproterozoic. Initial amphibolite-facies reworking of the Kaipokok domain at 1896 ± 6 Ma is indicated by U-Pb ages of metamorphic zircon from a foliated Kikkertavak metadiabase dyke. This is one of the oldest Paleoproterozoic tectonic events dated thus far in northeast Laurentia and may be linked with ca. 1890 Ma plutonism documented elsewhere in the Kaipokok domain. Intrusion of granitoid plutons at 1882 -6 +10 , 1877 ± 5, and 1871 -3 +4 Ma in the Kaipokok Bay area postdates early thick- and thin-skinned thrusting (possibly east to northeast directed) that involved Lower Aillik Group strata. U-Pb titanite ages of 1866 - 1847 Ma in part record a metamorphic event that followed this plutonic-tectonic activity. These early events are temporally and kinematically difficult to reconcile with accretion of juvenile Makkovikian terranes in the southeast and may instead be related to early stages of the ca. 1.91 - 1.72 Ga Torngat orogeny along the western margin of the Nain craton. In contrast, high-grade metamorphism, dextral shearing, and northwestward thrusting between 1841 and 1784 Ma, including crystallization of an Iggiuk granitic vein at 1811 ± 8 Ma, are in accord with accretion of Makkovikian terranes in a dextral transpressional regime (Makkovikian orogeny sensu stricto). Coeval sinistral transpression in the Torngat orogen suggests that both orogenic belts accommodated relative northward tectonic escape of the Nain craton during this interval. (author)

  19. SHRIMP U-Pb zircon dating of Archean core complex formatio and pancratonic strike-slip deformation in the East Pilbara Granite-Greenstone Terrain

    NARCIS (Netherlands)

    Zegers, T.E.; Nelson, D.R.; Wijbrans, J.R.; White, S.H.

    2001-01-01

    Sensitive high-resolution ion microprobe (SHRIMP) U-Pb dating of zircons from granitic rocks in the East Pilbara Granite-Greenstone Terrain has provided time constraints for main tectonic events in the Shaw Granitoid Complex and has shown that deformation was intricately related to granitoid

  20. From opening to subduction of an oceanic domain constrained by LA-ICP-MS U-Pb zircon dating (Variscan belt, Southern Armorican Massif, France)

    Science.gov (United States)

    Paquette, J.-L.; Ballèvre, M.; Peucat, J.-J.; Cornen, G.

    2017-12-01

    In the Variscan belt of Western Europe, the lifetime and evolution of the oceanic domain is poorly constrained by sparse, outdated and unreliable multigrain ID-TIMS U-Pb zircon dating. In this article, we present a complete in situ LA-ICP-MS dataset of about 300 U-Pb zircon analyses obtained on most of the ophiolitic and eclogitic outcrops of Southern Brittany, comprising new dating of previously published zircon populations and newly discovered rock samples. In situ dating and cathodo-luminescence imaging of each zircon grain yields new absolute time-constraints on the evolution of the Galicia-Moldanubian Ocean. The new results confirm that the opening of this oceanic domain is well defined at about 490 Ma. In contrast, the generally-quoted 400-410 Ma-age for the high-pressure event related to the subduction of the oceanic crust is definitely not recorded in the zircons of the eclogites. In light of these new data, we propose that the obduction of oceanic rocks occurred at about 370-380 Ma while the high-pressure event is recorded at 355 Ma in only a few zircon grains of some eclogite samples. Additionally, this large scale dating project demonstrates that the zircons from eclogites do not systematically recrystallise during the high pressure event and consequently their U-Pb systems do not record that metamorphism systematically. These zircons rather preserve the isotopic memory of the magmatic crystallization of their igneous protolith. Another example of an eclogite sample from the French Massif Central illustrates the frequent mistake in the interpretation of the ages of the early hydrothermal alteration of zircons in the oceanic crust versus partial or complete recrystallization during eclogite facies metamorphism.

  1. Trace- and rare-earth element geochemistry and Pb-Pb dating of black shales and intercalated Ni-Mo-PGE-Au sulfide ores in Lower Cambrian strata, Yangtze Platform, South China

    Science.gov (United States)

    Jiang, Shao-Yong; Chen, Yong-Quan; Ling, Hong-Fei; Yang, Jing-Hong; Feng, Hong-Zhen; Ni, Pei

    2006-08-01

    The Lower Cambrian black shale sequence of the Niutitang Formation in the Yangtze Platform, South China, hosts an extreme metal-enriched sulfide ore bed that shows >10,000 times enrichment in Mo, Ni, Se, Re, Os, As, Hg, and Sb and >1,000 times enrichment in Ag, Au, Pt, and Pd, when compared to average upper continental crust. We report in this paper trace- and rare-earth-element concentrations and Pb-Pb isotope dating for the Ni-Mo-PGE-Au sulfide ores and their host black shales. Both the sulfide ores and their host black shales show similar trace-element distribution patterns with pronounced depletion in Th, Nb, Hf, Zr, and Ti, and extreme enrichment in U, Ni, Mo, and V compared to average upper crust. The high-field-strength elements, such as Zr, Hf, Nb, Ta, Sc, Th, rare-earth elements, Rb, and Ga, show significant inter-element correlations and may have been derived mainly from terrigenous sources. The redox sensitive elements, such as V, Ni, Mo, U, and Mn; base metals, such as Cu, Zn, and Pb; and Sr and Ba may have been derived from mixing of seawater and venting hydrothermal sources. The chondrite-normalized REE patterns, positive Eu and Y anomalies, and high Y/Ho ratios for the Ni-Mo-PGE-Au sulfide ores are also suggestive for their submarine hydrothermal-exhalative origin. A stepwise acid-leaching Pb-Pb isotope analytical technique has been employed for the Niutitang black shales and the Ni-Mo-PGE-Au sulfide ores, and two Pb-Pb isochron ages have been obtained for the black shales (531±24 Ma) and for the Ni-Mo-PGE-Au sulfide ores (521±54 Ma), respectively, which are identical and overlap within uncertainty, and are in good agreement with previously obtained ages for presumed age-equivalent strata.

  2. U-Th isotopic systematics at 13deg N east Pacific Ridge segment

    International Nuclear Information System (INIS)

    Ben Othman, D.; Allegre, C.J.

    1990-01-01

    Fresh basaltic glasses have been analyzed for U-Th disequilibrium systematics as part of an extensive study on the East Pacific Rise (EPR) at 12deg 45'N. These samples are well described in terms of major and trace elements as well as in Nd, Pb and Sr isotopes. Our results show significant heterogeneities in the mantle source at a small scale, and show heterogeneities at larger scales also when compared to other EPR data. U and Th concentration and isotopic data rule out fractional crystallization as a main process and support a mixing model in agreement with the marble cake model developed by Allegre and Turcotte and constrained by trace elements and Nd, Sr and Pb isotopes on the same samples by Prinzhofer et al. Based on the high ( 230 Th/ 232 Th) isotopic ratios on recent tholeiites especially the Th/U values inferred for their sources clearly show that the upper mantle Th/U has decreased with time. (orig.)

  3. U-Pb ages for two tonalitic gneisses, pegmatitic granites, and K-feldspar porphyries, Olkiluoto study site, Eurajoki, SW Finland

    International Nuclear Information System (INIS)

    Maenttaeri, I.; Lindberg, A.; Aaltonen, I.

    2007-08-01

    Secondary ion microprobe zircon U-Pb ages have been determined for two tonalitic gneisses, two pegmatitic granites, and two potassium feldspar porphyry samples from the Olkiluoto study site, Eurajoki, S-W Finland. Moreover, monazites from the Kfeldspar porphyries were dated using TIMS U-Pb method. The tonalitic gneiss A1879 TTG 1 reveals bimodal zircon population and for A1880 TTG it is homogeneous. The samples yield similar overlapping concordia ages of 1851 ± 5 Ma and 1856 ± 5 Ma, respectively. The pegmatitic granite samples A1881 PGR 1 and A1883 PGR 2 have mostly zircons resembling those of the TTG's. The supposed pegmatitic zircons with high U and low Th are strongly altered. The zircon U-Pb data of A1881 PGR 1 plot roughly in two separate lines on a concordia diagram. The apparently younger ∼1.79 Ga data are all from the high U and low Th/U zircons and therefore certainly set the minimum age for the A1881 PGR 1. It is suggested, that the ∼1.85 Ga data comprise analyses from inherited zircons as it include both lower and higher Th/U zircons and 1.85 Ga coevals with age of the tonalitic gneisses. Thus, the apparent age for the A1881 PGR 1 is ∼1.79 Ga. The U-Pb data of sample A1883 PGR 2 also divide into two groups. The higher Th/U, inherited zircons determine an age of 1852 ± 9 Ma which is the same as that of the TTG's. The low Th/U zircon data scatter and the age of 1.83 Ga for A1883 PGR 2 is only poorly determined. The both potassium feldspar porphyry samples A1882 KFP 1 and A1884 KFP 2 reveal heterogeneous zircon populations. The A1882 KFP 1 zircons showing magmatic zoning in BSE images conceivably determine a concordia age of 1842± 6 Ma for the rock. In addition to that a few ∼1.9 Ga inherited zircon and metamorphic low Th/U rims with ages between 1.88 Ga and 1.83 Ga were detected. The age for the youngest metamorphic zircon rims overlaps with that of the magmatic zircons. The zircons in the other KFP sample A1884 show a wide range of ages

  4. LA-ICP-MS U-Pb apatite dating of Lower Cretaceous rocks from teschenite-picrite association in the Silesian Unit (southern Poland

    Directory of Open Access Journals (Sweden)

    Szopa Krzysztof

    2014-08-01

    Full Text Available The main products of volcanic activity in the teschenite-picrite association (TPA are shallow, sub-volcanic intrusions, which predominate over extrusive volcanic rocks. They comprise a wide range of intrusive rocks which fall into two main groups: alkaline (teschenite, picrite, syenite, lamprophyre and subalkaline (dolerite. Previous 40Ar/39Ar and 40K/40Ar dating of these rocks in the Polish Outer Western Carpathians, performed on kaersutite, sub-silicic diopside, phlogopite/biotite as well as on whole rock samples has yielded Early Cretaceous ages. Fluorapatite crystals were dated by the U-Pb LA-ICP-MS method to obtain the age of selected magmatic rocks (teschenite, lamprophyre from the Cieszyn igneous province. Apatite-bearing samples from Boguszowice, Puńców and Lipowa yield U-Pb ages of 103± 20 Ma, 119.6 ± 3.2 Ma and 126.5 ± 8.8 Ma, respectively. The weighted average age for all three samples is 117.8 ± 7.3 Ma (MSWD = 2.7. The considerably smaller dispersion in the apatite ages compared to the published amphibole and biotite ages is probably caused by the U-Pb system in apatite being less susceptible to the effects of hydrothermal alternation than the 40Ar/39Ar or 40K/40Ar system in amphibole and/or biotite. Available data suggest that volcanic activity in the Silesian Basin took place from 128 to 103 Ma with the the main magmatic phase constrained to 128-120 Ma.

  5. The Sima de los Huesos hominids date to beyond U/Th equilibrium (>350 kyr) and perhaps to 400-500 kyr: New radiometric dates

    Science.gov (United States)

    Bischoff, J.L.; Shamp, D.D.; Aramburu, Arantza; Arsuaga, J.L.; Carbonell, E.; Bermudez de Castro, Jose Maria

    2003-01-01

    The Sima de los Huesos site of the Atapuerca complex near Burgos, Spain contains the skeletal remains of at least 28 individuals in a mud breccia underlying an accumulation of the Middle Pleistocene cave bear (U. deningeri). Earlier dating estimates of 200 to 320 kyr were based on U-series and ESR methods applied to bones, made inaccurate by unquantifiable uranium cycling. We report here on a new discovery within the Sima de los Huesos of human bones stratigraphically underlying an in situ speleothem. U-series analyses of the speleothem shows the lower part to be at isotopic U/Th equilibrium, translating to a firm lower limit of 350 kyr for the SH hominids. Finite dates on the upper part suggest a speleothem growth rate of c. 1 cm/32 kyr. This rate, along with paleontological constraints, place the likely age of the hominids in the interval of 400 to 600 kyr. ?? 2002 Elsevier Science Ltd. All rights reserved.

  6. Pb-Pb and U-Pb zircon ages of archean syntetocnic granites of the Carajas metallogenic province, northern Brazil

    International Nuclear Information System (INIS)

    Barros, Carlos Eduardo de Mesquita; Sardinha, Alex Souza; Barbosa, Jaime dos Passos de Oliveira; Krimski, Robert; Macambira, Moacir Jose Buenano

    2001-01-01

    The Carajas Metallogenic Province is located in the southeastern Amazonian Craton. It has been divided in two domains, the southernmost comprises the Rio Maria region and the northernmost corresponds to Caraj region (Souza et al. 1996). The former domain is made up of Archean greenstone sequences (2,97 Ga), TTG (2,9 Ga) and calc-alkaline granitoids (2,87 Ga) (Macambira and Lafon 1995, Leite et al. 1999, Althoff et al. 2000). The Carajas block is constituted of minor mafic granulites (3,00 Ga) and quartzofeldspathic gneisses (2,81 Ga), metavolcanosedimentary sequences (2,76 Ga) and granites (2,76 to 2,56 Ga) (Machado et al. 1991; Huhn et al. 1999, Pidgeon et al. 2000). Widespread anorogenic A-type granites are found in both areas (Docegeo 1988; Dall'Agnol et al. 1994). In the last two decades several authors (Lindenamyer et al. 1994, Barros and Barbey 1998, Huhn et al. 1999 and others) have emphasized the role of the Archean granite magmatism in the tectonicthermal evolution in the Carajas Province. In this paper we discuss the tectonic significance of the Pb- Pb and U-Pb ages obtained in some granitoids from the Carajas region. The Estrela Granite Complex and the granitoids located to the north of Parauapebas were dated by Pb- Pb evaporation zircon method (cf. Kober 1987). Data are presented considering 2σ ∼ . The Pb corrections have been done in the basis of the evolution model of Pb in double stage (cf. Stacey and Kramers 1975). U-Pb zircon method (cf. Krogh 1973, Stacey and Kramers 1975, Parrish 1987, Ludwuig 1999), recently put on routine in the Para-Iso laboratories, was employed to date the granite from the Serra do Rabo area. Analyses were carried on the Finnigan Mat 262 spectrometer (au)

  7. Improvement Of The U-Th Method For Dating Of Impure Calcite Having A Large Amount Of Clay And Very Low Uranium Content

    Directory of Open Access Journals (Sweden)

    Samer Farkh

    2015-01-01

    Full Text Available Abstract The U-Th method also called series method of uranium is improved by a new experimental protocol and successfully applied to the impure calcite with uranium concentration 005 dpmg which was previously difficult to be dated accurately. Our experiments performed on 15 calcite samples taken from France and Morocco have highlighted the importance of this methodological improvement by enabling i the elimination of 100 of clay residues ii the reduction of calcite quantity necessary to the chemical manipulation from 20g to 5g iii the analysis of calcite samples poor in uranium and on the other hand rich with clay and iiii the reduction of the lower limit of the U-Th method from 10 Kyrs to 6 Kyrs. The optimization of U-Th method in this work provided a better dating of the accurate age of calcite. Thus this technique is important for the chemical analysis of stalagmite floors of different caves in the region of the Near East.

  8. Provenance of the lower Miocene of the Gulf of Mexico from detrital zircon double dating

    Science.gov (United States)

    xu, J.

    2013-12-01

    The lower Miocene interval of the Gulf of Mexico (GOM) has recently gained increasing attention from oil and gas industry due to its hydrocarbon potential below the salt canopy. However, it has been less well studied than both the underlying Oligocene and overlying middle Miocene strata. The lower Miocene worldwide is a transitional period of tectonic, climatic, and oceanographic change. In particular, it is a period of major tectonic reorganization in the western interior of North America (Rocky Mountains), involving a shift from the Oligocene thermal phase, with abundant volcanic activity recorded in the thick Frio/Vicksburg succession of the GOM, to the Miocene Basin-Range extensional phase. Climatic conditions also changed from a relatively arid Oligocene to wetter Miocene, resulting in increased sediment yields from exhumed tectonic structures. Previous provenance studies used proportions of quartz, feldspar and lithic fragments and consideration of likely river courses through known paleogeomorphological elements. Only limited detrital zircon (DZ) U-Pb studies on Paleocene strata have been undertaken and there has been no previous U-Pb and (U-Th)/He double dating in the GOM. In this study we apply the latest analytical approaches, such as DZ U-Pb dating to gain robust source terranes ages and more fully elucidate the complex sediment provenance and dispersal history of GOM. We also employ DZ (U-Th)/He (ZHe) dating, combined with DZ U-Pb, to not only define sedimentary provenance but also the exhumation histories of detrital source regions. Samples of lower Miocene outcrop exposures in Texas and Louisiana have been collected to discriminate the varied tectonic and drainage system changes across the basin in lateral. In addition, samples from the Eocene, Oligocene and middle Miocene have been obtained to reveal vertical shift of source terranes contributions. Our initial age data show detrital zircons of lower Miocene sediments come from a wide range of source

  9. Speleogenesis of the Hermannshöhle cave system (Austria): Constraints from .sup. 230./sup.Th/U-dating and palaeomagnetic analysis

    Czech Academy of Sciences Publication Activity Database

    Plan, L.; Schober, A.; Scholz, D.; Spötl, C.; Pruner, Petr; Bosák, Pavel

    2015-01-01

    Roč. 44, č. 3 (2015), s. 315-326 ISSN 0392-6672 Institutional support: RVO:67985831 Keywords : 230 Th/U-dating * palaeomagnetics * paragenesis * speleogenesis * valley incision Subject RIV: DE - Earth Magnetism, Geodesy, Geography Impact factor: 1.559, year: 2015

  10. Determination of natural radionuclides, U, Th-232, Ra-226, Ra-228, Pb-210 and K-40 in sediments from CananÉIa-Iguape System, Brazil

    International Nuclear Information System (INIS)

    Jesus, Gleyka J.D.; Chiozzini, Vitor G.; Saueia, Cátia H.R.; Nisti, Marcelo B.; Braga, Elisabete S.; Fávaro, Deborah I.T.; Universidade de São Paulo

    2017-01-01

    The Cananéia-Iguape estuarine-lagoon complex, located in the south of São Paulo State, Brazil, is a protected area recognized by UNESCO as part of the Biosphere Reserve, due to its importance as a natural ecosystem. However, along the years, the mining activities in the region affected the river basin, to such an extent that contamination was observed for As, Cu, Pb and Zn. Since the mining activities can also enhance the levels of natural radioactivity in the sediments, this study aimed to determine the activity concentration of the natural radionuclides (K-40, U, Ra-226, Pb-210, Th-232 and Ra-228) in 34 bottom sediments samples collected in the Cananéia-Iguape system. The samples were measured by gamma spectrometry, using a HPGe for the determination of K-40, Ra-226, Pb-210 and Ra-228. The concentration of U and Th-232 was determined by instrumental neutron activation analysis. The activity concentration of K-40 varied from 119 ± 17 to 522 ± 74 Bq kg"-"1; U-238 varied from 0.31 ± 0.05 to 5.8 ± 0.3 mg kg"-"1; Ra-226 varied from 3.7 ± 0.3 to 43.3 ± 1.5 Bq kg"-"1; Pb-210 varied from 5.8 ± 2.6 to 118 ± 12 Bq kg"-"1; Th-232 varied from 0.67 ± 0.02 to 16.6 ± 0.4 mg kg"-"1 and Ra-228 varied from 3.5 ± 0.6 to 64.9 ± 2.4 Bq kg"-"1. These results were compared with literature values for the region, indicating that they are the background of the region and no contamination was observed from NORM (Naturally Occurring Radioactive Material) industries. (author)

  11. Determination of natural radionuclides, U, Th-232, Ra-226, Ra-228, Pb-210 and K-40 in sediments from CananÉIa-Iguape System, Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Jesus, Gleyka J.D.; Chiozzini, Vitor G.; Saueia, Cátia H.R.; Nisti, Marcelo B.; Braga, Elisabete S.; Fávaro, Deborah I.T., E-mail: gjdjesus@ipen.br, E-mail: chsaueia@ipen.br, E-mail: mbnisti@ipen.br, E-mail: defavaro@ipen.br, E-mail: vitor.chio@usp.br, E-mail: edsbraga@usp.br [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil); Universidade de São Paulo (USP), SP (Brazil). Instituto Oceanográfico

    2017-07-01

    The Cananéia-Iguape estuarine-lagoon complex, located in the south of São Paulo State, Brazil, is a protected area recognized by UNESCO as part of the Biosphere Reserve, due to its importance as a natural ecosystem. However, along the years, the mining activities in the region affected the river basin, to such an extent that contamination was observed for As, Cu, Pb and Zn. Since the mining activities can also enhance the levels of natural radioactivity in the sediments, this study aimed to determine the activity concentration of the natural radionuclides (K-40, U, Ra-226, Pb-210, Th-232 and Ra-228) in 34 bottom sediments samples collected in the Cananéia-Iguape system. The samples were measured by gamma spectrometry, using a HPGe for the determination of K-40, Ra-226, Pb-210 and Ra-228. The concentration of U and Th-232 was determined by instrumental neutron activation analysis. The activity concentration of K-40 varied from 119 ± 17 to 522 ± 74 Bq kg{sup -1}; U-238 varied from 0.31 ± 0.05 to 5.8 ± 0.3 mg kg{sup -1}; Ra-226 varied from 3.7 ± 0.3 to 43.3 ± 1.5 Bq kg{sup -1}; Pb-210 varied from 5.8 ± 2.6 to 118 ± 12 Bq kg{sup -1}; Th-232 varied from 0.67 ± 0.02 to 16.6 ± 0.4 mg kg{sup -1} and Ra-228 varied from 3.5 ± 0.6 to 64.9 ± 2.4 Bq kg{sup -1}. These results were compared with literature values for the region, indicating that they are the background of the region and no contamination was observed from NORM (Naturally Occurring Radioactive Material) industries. (author)

  12. Ion-probe U–Pb dating of authigenic and detrital opal from Neogene-Quaternary alluvium

    Science.gov (United States)

    Neymark, Leonid; Paces, James B.

    2013-01-01

    Knowing depositional ages of alluvial fans is essential for many tectonic, paleoclimatic, and geomorphic studies in arid environments. The use of U–Pb dating on secondary silica to establish the age of Neogene-Quaternary clastic sediments was tested on samples of authigenic and detrital opal and chalcedony from depths of ∼25 to 53 m in boreholes at Midway Valley, Nevada. Dating of authigenic opal present as rinds on rock clasts and in calcite/silica cements establishes minimum ages of alluvium deposition; dating of detrital opal or chalcedony derived from the source volcanic rocks gives the maximum age of sediment deposition.Materials analyzed included 12 samples of authigenic opal, one sample of fracture-coating opal from bedrock, one sample of detrital opal, and two samples of detrital chalcedony. Uranium–lead isotope data were obtained by both thermal ionization mass spectrometry and ion-microprobe. Uranium concentrations ranged from tens to hundreds of μg/g. Relatively large U/Pb allowed calculation of 206Pb/238U ages that ranged from 1.64±0.36 (2σ) to 6.16±0.50 Ma for authigenic opal and from 8.34±0.28 to 11.2±1.3 Ma for detrital opal/chalcedony. Three samples with the most radiogenic Pb isotope compositions also allowed calculation of 207Pb/235U ages, which were concordant with 206Pb/238U ages from the same samples.These results indicate that basin development at Midway Valley was initiated between about 8 and 6 Ma, and that the basin was filled at long-term average deposition rates of less than 1 cm/ka. Because alluvium in Midway Valley was derived from adjacent highlands at Yucca Mountain, the low rates of deposition determined in this study may imply a slow rate of erosion of Yucca Mountain. Volcanic strata underlying the basin are offset by a number of buried faults to a greater degree than the relatively smooth-sloping bedrock/alluvium contact. These geologic relations indicate that movement on most faults ceased prior to erosional

  13. Temporal evolution of natural radionuclides distributions 238U, 234Th, 226Ra, 228Ra, 210Pb and 210Po in the Bransfield strait, Antarctica peninsula

    International Nuclear Information System (INIS)

    Lapa, Flavia Valverde

    2013-01-01

    Research on the distribution of natural radionuclides in Antarctica is rare and thus, there is great interest in to know their occurrence and factors related to its mobilization, transference and accumulation in this extremely fragile environment. Natural radionuclides have been used intensively as tracers in the ocean, helping to better understand processes as sinking and particle resuspension, water masses mixture and oceanic circulation. 234 Th (t½ = 24.1 days) is a particle-reactive radionuclide produced continuously in seawater by the decay of its soluble precursor conservative with salinity 238 U (t½ = 4.5 10 9 years). Since 234 Th presents relatively short half-life, it is used to quantify processes that occur in temporal scale varying from days to weeks. The disequilibrium 234 Th/ 238 U in the surface ocean has been applied to estimate carbon fluxes exported via sinking material. The flux of particles biologically productive out of the euphotic zone in the Southern Ocean has special attention due to its importance in the control of CO 2 atmospheric concentrations. The radionuclides 210 Pb (t½ = 22.3 years) and 210 Po (t½ = 138 days) are also particle-reactive. The disequilibrium 210 Po/ 210 Pb has been used to estimate fluxes of particles exported in the ocean in the time scale of weeks. The long-lived Ra isotopes, 226 Ra (t½ = 1,600 years) and 228 Ra (t½ = 5.75 years) are soluble in seawater, presenting unique properties that make them excellent tracers of water masses. This research work had the aim to study the distributions of natural radionuclides 238 U, 234 Th, 22 '6Ra, 22 '8Ra, 210 Pb and 210 Po in the Bransfield Strait during 2 samplings carried out in the 2011 Austral Summer (OPERANTAR XXIX and XXX). (author)

  14. Precise U-Pb Zircon Dating of the Syenite Phase from the Ditrau Alkaline Igneous Complex

    Directory of Open Access Journals (Sweden)

    Pană Dinu

    2000-04-01

    Full Text Available The Ditrău igneous complex represents the largest alkaline intrusion in the Carpathian-Pannonian region consisting of a plethora of rock types formed by complicated magmatic and metasomatic processes. A detailed U-Pb zircon age study is currently underway and the results for the syenite intrusion phase is reported herein. The U-Pb zircon emplacement age of the syenite of 229.6 +1.7/-1.2 Ma documents the quasi-contemporaneous production and emplacement of the gabbro and syenite magmas. We suggest that the syenite and associated granite formed by crustal melting during the emplacement of the mantle derived gabbroic magma around 230 Ma. The thermal contact aureole produced by the Ditrău alkaline igneous complex constrains the main tectonism recorded by surrounding metamorphic lithotectonic assemblages to be pre-Ladinian.

  15. First results of U-Pb dating of metamorphic rocks of the Greater Antilles arc: age of the Mabujina complex (Cuba)

    International Nuclear Information System (INIS)

    Bibikova, E.V.; Somin, M.L.; Gracheva, T.V.; Makarov, V.A.; Mil'yan, G.; Shukolyukov, Yu.A.; AN SSSR, Moscow

    1988-01-01

    U-Pb-dating of zircons, entering the composition of metamorphic rocks of the Mabujina complex, was conducted in order to solve the problem concerming the place of metamorphic complexes in the structure and tectonic evolution of the Greater Antilles arc. The accuracy of uranium and lead determination was equal to ± 1%, the accuracy of lead isotopic ratio determination with the use of TSN-206A mass-spectrometer- ±0.15%. Isotope data showed, that all examined zircons crystallized about 100 mil. years ago

  16. Trace elements (Rb, Cs, Sr, Pb, Th, U) bioavailability potential and speciation in the Piracicaba river bottom sediments, Sao Paulo, Brazil

    International Nuclear Information System (INIS)

    Fernandes, Alexandre Martins; Mortatti, Jefferson; Oliveira, Helder de; Bibian, Joao Paulo Rambelli; Moraes, Graziela Meneghel de; Probst, Jean-Luc

    2007-01-01

    It was studied the bioavailability potential of Rb, Cs, Sr, Pb, Th and U and their chemical speciation in Piracicaba river bottom sediments. This river system crosses important agricultural and urban areas of Sao Paulo state, which groups about 3 million people and receives a large load of agricultural, industrial and domestic wastes. The procedure used to estimate trace elements bioavailability potential was related to a 7-step sequential chemical extraction. This scheme was designed to dissolved and separate sample chemical phases, which can be affected by changes in physical-chemical conditions; in the following order: water soluble, exchangeable, bound to carbonates or acid fraction, bound to Mn-oxides, bound to Fe-oxides and bound to organic matter. Trace element concentrations were determined by Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) after each extraction step. With the used extraction procedure, it was possible to identify the fraction where some trace elements could be found in order to evaluate their bioavailability potential. Rb and Cs were particularly involved with the organic fraction, while Sr revealed to be associated mainly to the exchangeable fraction (clay minerals). Pb, Th and U were mainly bound to the residual and Fe-oxide fractions. (author)

  17. Outline of Upper Precambrian and Lower Paleozoic evolution of the Iberian Peninsula according to U-Pb dating of zircons

    International Nuclear Information System (INIS)

    Lancelot, J.R.; Allegret, A.; Iglesias Ponce de Leon, M.

    1985-01-01

    In the northwestern part of the Iberian Peninsula, recent geological studies have defined the following stratigraphic sequence from bottom to top: basal orthogneiss of Miranda do Douro is overlain by a complex of schist and greywacke which have been assigned to the Cambrian or late Precambrian; these are followed by the Ollo de Sapo gneisses of volcanic-sedimentary origin which in turn are overlain by the fossiliferous layers of the lower Ordovician. The schist and greywacke complex and the lower part of the Ollo de Sapo Formation are transected by granitic dikes (Viana del Bollo orthogneiss). All these rocks were folded, faulted, metamorphosed, and intruded by granite plutons during Variscan times. The emplacement of the Miranda do Douro and Viana del Bollo orthogneisses have been respectively dated at 618+-9 Ma and 465+-10 Ma by the U-Pb method on zircons. These data yield lower and upper limits for the deposition of the Ollo de Sapo Formation and demonstrate the occurrence of a Precambrian basement (''Pan-African'' or ''Cadomian'' orogeny) in the Variscan belt in the northwestern part of the Iberian Peninsula. The emplacement of Viana del Bollo orthogneiss could be genetically related to the main phase of crustal thinning (470-520 Ma) characteristic of the Prevariscan evolution of western Europe. Typology and U-Pb data of the Ollo de Sapo zircons indicate the occurrence of inherited old Precambrian zircons and yield an age of 325+-3 Ma for the Variscan main thermal event in the area considered. Four possible evolutionary models for the U-Pb system of the Ollo de Sapo zircons are discussed. (orig.)

  18. High-Resolution Zircon U-Pb CA-TIMS Dating of the Carboniferous—Permian Successions, Paraná Basin, Brazil

    Science.gov (United States)

    Griffis, N. P.; Mundil, R.; Montanez, I. P.; Isbell, J.; Fedorchuk, N.; Lopes, R.; Vesely, F.; Iannuzzi, R.

    2015-12-01

    The late Paleozoic Ice Age (LPIA) is Earth's only record of a CO2-forced climatic transition from an icehouse to greenhouse state in a vegetated world. Despite a refined framework of Gondwanan ice distribution, questions remain about the timing, volume, and synchronicity of high-latitude continental ice and the subsequent deglaciation. These questions ultimately preclude our understanding of linkages between ice volume, sea level, and high- and low-latitude climate. Poor constraints on the timing and synchronicity of glacial and interglacial transitions reflect a lack of high-resolution radioisotopic dates from high-latitude, ice-proximal Carboniferous-Permian successions. The Rio Bonito Fm in Rio Grande do Sul State of southern Brazil hosts the oldest non-glaciogenic Carboniferous- Permian deposits of the Paraná Basin, thus recording the icehouse-to-greenhouse transition. Despite a widespread effort over the last two decades to constrain these deposits in time by means of U-Pb zircon geochronology, published data sets of the Candiota and Faxinal coals of the Rio Bonito Fm host discrepancies that may reflect post- eruptive open system behavior of zircon and analytical artifacts. These discrepancies have hindered the correlation of the Candiota and Faxinal sediments within the larger Gondwanan framework. Here we present the first U-Pb ages on closed system single zircons using CA-TIMS techniques on Permo-Carboniferous ash deposits of the Paraná Basin. Preliminary results indicate two major and distinct coal-forming periods that are separated by ca 10 Ma. Our results and conclusions are not in agreement with multi- crystal U-Pb TIMS and SIMS ages that suggest coeval deposition of the Candiota and Faxinal coals. CA-TIMS analyses applied to zircons from additional ash deposits are aimed at constructing a robust chronostratigraphic framework for the Carboniferous- Permian succession of the Paraná Basin, which will facilitate a better understanding of the timing and

  19. Status and application of α-spectrometric 230Th/234U dating of fossil corals in Ryukyus, Japan and the Philippines

    International Nuclear Information System (INIS)

    Inagaki, Miyuki; Omura, Akio; Sasaki, Keiichi

    2007-01-01

    High-precision α-spectrometric 230 Th/ 234 U dating was achieved by recent improvements of measurement system and chemical procedures and enabled critical evaluation of age reliability. We review the status and application of α-spectrometric 230 Th/ 234 U dating of Pleistocene and Holocene corals to reconstruct past sea level changes and tectonic movements in Ryukyus, southwestern Japan and the Philippines in the western rim of circum-Pacific island arcs. The highest terrace in Kikai Island was formed during MIS 5c not MIS 5e that previously reported. Coral reef sediments deposited not only during MIS 5e but also during glacial periods, e.g. MIS 6 and 2, have been found in the Ryukyus. Coral reef sediments formed during MIS 2 were found at ca. 120 m below present sea level off Irabu Island located at 25degN. In addition, it was clear that three terraces developed during MIS 5e, 5c and 5a at Pamilacan Island on the Philippines. (author)

  20. Daily ingestion of 232Th, 238U, 226Ra, 228Ra and 210Pb in vegetables by inhabitants of Rio de Janeiro City

    International Nuclear Information System (INIS)

    Santos, E.E.; Lauria, D.C.; Amaral, E.C.S.; Rochedo, E.R.

    2002-01-01

    The concentrations of the naturally occurring radionuclides 232 Th, 238 U, 210 Pb, 226 Ra and 228 Ra were determined in the vegetables (leafy vegetables, fruit, root, bean and rice) and derived products (sugar, coffee, manioc flour, wheat flour, corn flour and pasta) consumed most by the adult inhabitants of Rio de Janeiro City. A total of 88 samples from 26 different vegetables and derived products were analyzed. The highest contribution to radionuclide intake arises from bean, wheat flour, manioc flour, carrot, rice, tomato and potato consumption. The estimated daily intakes due to the consumption of vegetables and derived products are 1.9 mBq of 232 Th (0.47 μg), 2.0 mBq of 238 U (0.17 μg), 19 mBq of 226 Ra, 26 mBq of 210 Pb and 47 mBq of 228 Ra. The estimated annual effective dose due to the ingestion of vegetables and their derived products with the long-lived natural radionuclides is 14.5 μSv. Taking into account literature data for water and milk from Rio de Janeiro the dose value increases to 29 μSv, with vegetables and derived products responsible for 50% of the dose and water for 48%. 210 Pb (62%) and 228 Ra (24%) were found to be the main sources for internal irradiation

  1. Sm-Nd geochemistry and U-Pb geochronology of the Preissac and Lamotte leucogranites, Abitibi Subprovince

    International Nuclear Information System (INIS)

    Ducharme, Y.; Stevenson, R.K.; Machado, N.

    1997-01-01

    The Lacorne Block in the Southern Volcanic Zone of the Abitibi Subprovince is composed of interleaved metavolcanic and metasedimentary rocks that are intruded by syn- to posttectonic diorites, granodiorites, and granites. These rocks form the Lacorne, Lamotte, and Preissac plutons, which can be divided into an early suite of dioritic - granodioritic rocks and a later suite of S-type, Ieucocratic granites with an estimated age of 2640 Ma. This study presents Sm - Nd data and U - Pb monazite and titanite ages for the late leucocratic granites of the Preissac and Lamotte plutons. A biotite -muscovite monzogranitic phase of the Lamotte pluton is dated at 2647 ± 2 Ma, but similar phases of the Preissac pluton are dated at 2681 - 2660 Ma. These ages extend the period of leucogranitic plutonism for this area to 40 Ma and suggest that the age of collision of the Abitibi and the Pontiac subprovinces occurred before 2685 Ma. The ε Nd values for the leucogranites range from -1 to +3 and suggest an origin largely through melting of sediments having a juvenile isotopic signature (i.e.. a short crustal residence time). Possible sources of the leucogranites include metasedimentary rocks of the Pontiac Subprovince, the Lacorne Block, and the Southern Abitibi Volcanic Zone, but the ε Nd values of the granites are most consistent with melting of metasediments of the Southern Volcanic Zone. We suggest that sediments of the Southern Volcanic Zone formed an accretionary prism along the southern continental margin of the Abitibi before collision with the Pontiac Subprovince. This prism was subsequently trapped between the two colliding margins, subducted, and partially melted to produce the Lamotte, Preissac, and Lacorne leucogranites. (author)

  2. In situ detrital zircon (U-Th)/He thermochronology

    Science.gov (United States)

    Tripathy, A.; Monteleone, B. D.; van Soest, M. C.; Hodges, K.; Hourigan, J. K.

    2010-12-01

    Detrital studies of both sand and rock are relevant to many problems, ranging from the climate and tectonics feedback debate to the long-term record of orogenic evolution. When applying the conventional (U-Th)/He technique to such studies, two important issues arise. Often, only euhedral grains are permissible for analysis in order to make simple geometric corrections for α-recoil. In detrital samples, this is problematic because euhedral grains can be scarce due to mechanical abrasion during transport, and potentially introduce bias in favour of more proximally sourced grains. Second, inherent to detrital studies is the need to date many grains (>100) per sample to ensure a representative sampling of the sediment source region, thus making robust conventional detrital studies both expensive and time-consuming. UV laser microprobes can improve this by permitting careful targeting of the grain interior away from the α-ejection zone, rendering the α-recoil correction unnecessary, thus eliminating bias toward euhedral grains. In the Noble Gas, Geochemistry, and Geochronology Laboratory at ASU, apatite and zircon have been successfully dated using in situ methods. For this study, the conventional and in situ techniques are compared by dating zircons from a modern river sand that drains a small catchment in the Mesozoic-Cenozoic Ladakh Batholith in NW India. This sample has a simple provenance, which allows us to demonstrate the robustness of the in situ method. Moreover, different microbeam techniques will be explored to establish the most efficient approach to obtain accurate and precise U-Th concentrations using synrock, which is our powdered, homogenized, and reconstituted zircon-rock standard. Without this, such in situ U-Th data would be difficult to obtain. 117 zircons were dated using the conventional (U-Th)/He method, revealing dates ranging from 9.70±0.35 to 106.6±3.5 Ma (2σ) with the major mode at 26 Ma. For comparison, 44 grains were dated using the in

  3. U-Pb Dating of Calcite to Constrain Basinal Brine Flux Events: An Example from the Upper Midwest USA

    Science.gov (United States)

    Rasbury, T.; Luczaj, J.

    2017-12-01

    Calcite forms in a variety of settings and can be the product of surface to deep basinal fluids. As such, this mineral can uniquely record details of the fluids responsible for its formation. The forms of calcium carbonates and their stratigraphic relationships from the thin section to the regional scale give important insights on pulses of fluids. A fundamental question is the age of such fluid pulses. While calcite excludes uranium (U) from its crystal structure, some is incorporated and depending on the U/Pb ratio, this provides an opportunity for radiometric dating. Calcite crystals of various sizes and crystal habits are found in Paleozoic carbonate rocks throughout the region from the western Michigan basin to the upper Mississippi valley. These are typically associated with Mississippi Valley-type (MVT) mineralization, including galena, sphalerite, and iron sulfides, but typically post-date the main MVT event. We have analyzed a variety of these calcites and find multiple generations of calcite, separated by tens of millions of years. The initial Pb isotope ratios are similar to the isotope ratios of nearby galena, strongly suggesting a genetic relationship. Our oldest ages are 200 Ma, and we find ages ranging into the Cenozoic. Based on the Paleozoic-hosted galena Pb-isotope isoscapes from the region, the fluids may have been sourced from both the Michigan and Illinois basins. An important and unanswered question is what would cause significant fluid movement out of the basins substantially after Appalachian orogenesis. Noble gas data from brines in the Michigan Basin have a mantle component and have been suggested to be responsible for recognized elevated temperatures across the basin (Ma et al., 2009). Multiple thermal events during the Paleozoic and Mesozoic eras may have an internal heat source related to reactivation of faults of the Keweenawan Rift system below the Michigan Basin. Perhaps a mantle heat source from below episodically fluxes into the

  4. Use of radiometric (Cs-137, Pb-210), geomorphic, and stratigraphic techniques to date recent oxbow sediments in the Rio Puerco drainage Grants uranium region, New Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Popp, C.J.; Dehn, M. (New Mexico Inst. of Mining and Tech., Socorro (United States)); Hawley, J.W.; Love, D.W. (New Mexico Bureau of Mines and Mineral Resources, Socorro (United States))

    1988-06-01

    In the absence of historic geochemical baseline data for the Grants uranium region, environmental changes resulting from uranium mine-mill activities can be determined only by indirect methods. A methodology for determining the age of recent sediments in streams draining the region has been established based on combined geomorphic, stratigraphic, and radiometric dating techniques. Because clay-rich sediments retain possible radionuclides and heavy metals derived from mineralization and mined sources, sample sites which contain fine-grained deposits that both predate and postdate mine-mill activity were located in abandoned-channel segments (oxbows) of major streams draining the eastern Grants uranium region. Aerial photographs (and derivative maps) taken between 1935 and 1971 provided the historical and geomorphic documentation of approximate dates of oxbow formation and ages of alluvial fills in the abandoned-channel segments. Pits were dug at these oxbow sites to determine stratigraphy and composition of the deposits. Samples collected from pit walls and auger holes below the pits were subjected to radiometric analysis by gamma ray spectrometry for the artificial radionuclide Cs-137 and the natural radionuclide Pb-210 as well as other U-238 and Th-232 daughters. Because of the dynamic nature of the system, absolute dating with Cs-137 was not possible but samples could be dated as either pre- or post-1950. The 1950 date is important because it marked the beginning of the uranium exploitation in the region. The Pb-210 dating was not possible because background Pb-210 was very high relative to fallout Pb-210.

  5. Levels in 223Th populated by α decay of 227U

    Science.gov (United States)

    Kalaninová, Z.; Antalic, S.; Heßberger, F. P.; Ackermann, D.; Andel, B.; Kindler, B.; Laatiaoui, M.; Lommel, B.; Maurer, J.

    2015-07-01

    Levels in 223Th populated by the α decay of 227U were investigated using α -γ decay spectroscopy. The 227U isotope was produced in the fusion-evaporation reaction 22Ne +208Pb at the velocity filter separator for heavy-ion reaction products at Gesellschaft für Schwerionenforschung in Darmstadt (Germany). Several new excited levels and γ transitions were identified in 223Th . An improved α -decay scheme of 227U was suggested. The experimental α -decay energy spectrum of 227U was compared with the Monte Carlo simulation performed using the toolkit geant4.

  6. U-Pb dating of two granite types from Soultz (Rhine Graben, France); Datation U-Pb des deux facies du granite de Soultz (fosse rhenan, France)

    Energy Technology Data Exchange (ETDEWEB)

    Cocherie, A.; Guerrot, C.; Genter, A. [Bureau de Recherches Geologiques et Minieres (BRGM), 45 - Orleans (France); Fanning, C.M. [Research School of Earth Sciences, ANU, Canberra, (Australia)

    2004-07-01

    Deep boreholes drilled in the basement of the Rhine Graben at Soultz-sous-Forets have shown the presence of an ubiquitous monzogranite. Borehole GPK-2, with a total depth of 5090 m, also intersected a more leucocratic fine-grained two-mica granite, locally present below 4860 m depth and continuously found between 5047 and 5090 m. Thanks to trace elements and in particular to REE (rare-earth elements), it could be shown that the leucocratic rock is a differentiated expression of the potassic magma that was at the origin of the monzogranite pluton. This model agrees with Sr-Nd isotope data, even though a slight contribution from the pre-existing basement should be considered as well. Use of the U-Pb method on monzogranite from EPS-1 - after zircon dissolution - has yielded an emplacement age of 334.0 + 3.8/-3.5 Ma (2 {sigma}). Point dates obtained by SHRIMP II on the rare zircons from the fine-grained granite showed that it was emplaced in a basement with very heterogeneous ages, ranging from Early Proterozoic to Silurian. (author)

  7. U-Th-PbT Monazite Gechronology in the South Carpathian Basement: Variscan Syn-Metamorphic Tectonic Stacking and Long-Lasting Post-Peak Decompressional Overprints

    Science.gov (United States)

    Săbău, G.; Negulescu, E.

    2012-12-01

    Dating metamorphic events appears to be unsatisfactorily addressed by most of the widely-employed and otherwise accurate and productive isotopic techniques, because the phases and systems investigated do not directly relate to the metamorphic events themselves. An adequate answer to this challenge is instead provided by microprobe-assisted chemical U-Th-PbT monazite geochronology, by its spatial resolution, truly in situ character and the possibility to reference analyses against well-defined textural environments and features, as well as a qualitative timeframe derived therefrom. Though chemical U-Th-PbT monazite geochronology is increasingly applied to seek answers ranging form a general characterization to fine details of the thermotectonic evolution of magmatic and metamorphic rocks, there are so far, unlike in the case of isotopic geochronological methods, no clearly defined standard analytical and data processing protocols. Two main reasons for this have to be mentioned, namely that chemical U-Th-PbT chronology is actually a proxy for isotopic geochronology, and the quantification of the errors and their propagation cannot be directly assessed because apparent ages are related to the measured element concentrations by an implicit function, the law of radioactive decay. Current approaches rely on treating calculated individual age values as primary data, a priori grouping of analyses supposed (and subsequently tested) to be coeval, and their statistical processing in order to obtain age values. An alternative approach we applied in basement units of the South Carpathians consists in an explicit approximation of the age formula and associated errors propagated from element concentrations to age values, and individual treatment of each age datum. The separation of the age clusters from the overall age spectrum of each sample was operated by tracing the variations of the normalized age gradient on the age spectrum sorted by increasing age values, and fine

  8. U-Pb geochronology of zircons form lunar Breccia 73217 using a sensitive high mass-resolution ion microprobe

    International Nuclear Information System (INIS)

    Compston, W.; Williams, I.S.

    1984-01-01

    U-Pb age determinations on four lunar zircons from existing thin-sections of one highland breccia, 73217, using the recently constructed ion microprobe SHRIMP, are reported. The analytical reproducibility of SHRIMP is demonstrated, and procedures for measuring Pb/U, Th/U, and corecting for initial Pb are explained. Electron microprobe analyses for the zircons are also reported. The results show that the four zircons survived the lunar cataclysm without any identifiable effects on their U-Pb systematics. All four indicate a single age of 4356 +23 or -14 m.y. The zircons have experienced small variable amounts of Pb loss since crystallization, from almost zero up to about 10 percent. If this occurred during one later event, then age of the latter is between 1100 and 2300 m.y. 18 references

  9. Models dated by {sup 210}Pb; Modelos de fechado por {sup 210}Pb

    Energy Technology Data Exchange (ETDEWEB)

    Sanchez-Cabeza, Joan-Albert [Organismo Internacional de la Energia Atomica, Laboratorios del Medio Marino (Monaco); Ruiz-Fernandez, Ana Carolina [Universidad Nacional Autonoma de Mexico, Instituto de Ciencias del Mar y Limnologia (Mexico)

    2012-07-01

    The {sup 210}Pb{sub ex} present in sediments, regardless of their origin, decays following the law of radioactive decay. If the rate of sediment accumulation and flow of {sup 210}Pb are constant and there are no redistribution processes of {sup 210}Pb{sub ex} in the sediment, a profile of {sup 210}Pb{sub ex} should be perfectly exponential. Although some of these conditions are not met in all cases and observed profiles are rarely found perfect exponentials, models dated by {sup 210}Pb described in this chapter allow to obtain valid dated. Anyway, the models described should be seen as tools of interpretation and the dates obtained as estimates to be corroborated by alternative observations. It is recommended to the reader to go deeper into the topics discussed in this chapter reading references and bibliography at the end. Throughout, the closed system hypothesis must be met. For dating of sediments implies that the radionuclide used is integrated into the matrix tested unaffected by redistribution processes. No cases of mixed sediments or showing evidence of mobility by diagenesis are addressed in this chapter, although we believe that in some circumstances estimates of the accumulation rates are provided but not of the age of formation. Starting with the first published use of {sup 210}Pb as a tool dating ice cores, different authors develop model conditions adapted to the dating of sediments. In this chapter we describe the most widely used models, which are based on assumptions about the flow of {sup 210}Pb{sub ex} the sediment surface, the rate of accumulation and concentration of initial{sup 210}Pb{sub ex} in surface sediments. The models describing nomenclatures have been different and even contradictory. To facilitate reading of the chapter we propose a nomenclature based on the fundamental assumptions of each model (not in implementation) and have homogenised the nomenclature used. While the model most commonly used for dating sediments is the CF

  10. Study of two new methods of geochronometry: dating method of carbonaceous formations by U-series disequilibrium gamma spectrometry; ESR dating method of rich U-content fossil dental enamel

    International Nuclear Information System (INIS)

    Ma, Jean-Luc

    1984-01-01

    First, the U-series disequilibrium dating method was re-examined using non-destructive γ-spectrometry. A new low-background (≤ 10 ppb U- equivalent) Ge-HP γ-spectrometer has been used to date travertine with small U-content (∼ 0.1 ppm) and low (≤ 5%) Th/U , content, by comparison with old-limestone γ-spectra. Second, a new ESR dating method has been developed using fossil dental enamel which is rich in U-content (10 - 100 ppm). Both methods were applied to Arago Cave (Tautavel, France): - with an ionium-age of 120 ka (10%), the upper travertine seems to have been set up during the Riss-deglaciation period. - the high (∼ 50%) Th/U-content samples of the intermediate travertine are un-datable. - the ESR-age of EQUUS mosbachensis enamel is 400 ka (10%) for the G-soil of Arago. XXI H. erectus, and 600 ka (10%) for the Q-soil above (- 1 m) of the lower travertine of which Io-age is older than 350 ka. (author)

  11. Determination of Sediment Profile for 210Pb, Pb, U and Th from Sultan Abu Bakar Dam Due to Soil Erosion from Highland Agriculture Area, Cameron Highlands, Malaysia

    OpenAIRE

    Zaini Hamzah; Seh D. Riduan; Ahmad Saat

    2011-01-01

    Problem statement: Sultan Abu Bakar Dam in Cameron Highlands act as a catchments to accumulate all eroded soil carried by the run off flow through Bertam River, the main river that passes through the highland agriculture area. All suspended solid that carried out by the river contain various kind of hazard potential to the environment. U, Th and Pb are the potential hazard elements carried out by water and accumulate at the dam. Approach: Five sampling point were selected where five 30cm core...

  12. Application of the 226Ra-230Th-234U and 227Ac-231Pa-235U radiochronometers to uranium certified reference materials

    International Nuclear Information System (INIS)

    Rolison, J.M.; Treinen, K.C.; McHugh, K.C.; Gaffney, A.M.; Williams, R.W.

    2017-01-01

    Uranium certified reference materials (CRM) issued by New Brunswick Laboratory were subjected to dating using four independent uranium-series radiochronometers. In all cases, there was acceptable agreement between the model ages calculated using the 231 Pa- 235 U, 230 Th- 234 U, 227 Ac- 235 U or 226 Ra- 234 U radiochronometers and either the certified 230 Th- 234 U model date (CRM 125-A and CRM U630), or the known purification date (CRM U050 and CRM U100). The agreement between the four independent radiochronometers establishes these uranium certified reference materials as ideal informal standards for validating dating techniques utilized in nuclear forensic investigations in the absence of standards with certified model ages for multiple radiochronometers. (author)

  13. U-Th-Pb systematics of some granitoids from the northeastern Yilgarn Block, Western Australia and implications for uranium source rock potential

    Energy Technology Data Exchange (ETDEWEB)

    Stuckless, J S; Nkomo, I T [Geological Survey, Denver, CO (USA); Bunting, J A [Geological Survey of Western Australia, Perth

    1981-11-01

    The Mount Boreas-type granite and spatially associated syenitic granitoid of Western Australia yield Pb-Pb ages of 2370 +- 100 Ma and 2760 +- 210 Ma, respectively. Th-Pb ages, although less precise, are concordant with these ages, and therefore the apparent ages are interpreted to be the crystallisation ages for these two units. U-Pb ages are variable and for the most part anomalously old, which suggests a Cainozoic uranium loss. However, this loss is generally small (3..mu..g/g); therefore, neither granitoid in its fresh state provides a good source for nearby calcrete-hosted uranium deposits. The possibility remains that the Mount Boreas-type granite that has been completely weathered during the Tertiary could have been a source for the calcrete-type uranium deposits in W.A. Although the Mount Boreas-type granite is highly fractionated, it does not bear a strong geochemical imprint of a sedimentary precursor. This feature contrasts it with apparently fresh granitoids from other parts of the world that have lost large amounts of uranium (approx. 20..mu..g/g) and are associated with large roll-type and other low temperature-type uranium deposits.

  14. 210Pb-137Cs dating of glacial lake sediments

    International Nuclear Information System (INIS)

    Graham, I.J.; Ditchburn, R.G.; Barry, B.J.

    2004-01-01

    Sediments deposited in New Zealand lakes in the recent past provide excellent archives of local climate change via their trapped biodiversity, varve structure ad sedimentological composition. To unlock the archival information, accurate and fine-scale dating of the deposits is essential. A combination of 210 Pb and 137 Cs dating provides the most reliable and robust approach. Under favourable conditions, 210 Pb dating can provide a detailed chronology to c.120-140 y, and can be accurately calibrated by 137 Cs for the last 40 y or thereabouts. (author). 6 refs., 4 figs

  15. Paleozoic age of high-pressure metamorphic rocks of the Dakh salient, North-Western Caucasus: results of U-Pb-geochronological study

    International Nuclear Information System (INIS)

    Somin, M.L.; Levchenkov, O.A.; Kotov, A.B.; Makeev, A.F.; Komarov, A.N.; Ro, N.I.; Lavrishchev, V.A.; Lebedev, V.A.

    2007-01-01

    U-Pb geochronological studies of an ancient component of the Dakh salient, i.e. metaaplites, which are vein fine-grained rocks made up by albite, microcline, quartz and potash mica, were made. Besides, K-Ar dating of granodiorites breaking through metamorphic rocks was conducted. U-Pb dating of accessory zircons (353 mln. years) defines the lower age boundary of the Dakh salient rock metamorphism. Its upper boundary was identified by K-Ar dating (301 ± 10 mln. years) of hornfels blende of nonmetamophized granodiorites [ru

  16. Lifetime of an ocean island volcano feeder zone: constraints from U-Pb dating on coexisting zircon and baddeleyite, and 40/39Ar age determinations, Fuerteventura, Canary Islands

    Science.gov (United States)

    Allibon, James; Ovtcharova, Maria; Bussy, Francois; Cosca, Michael; Schaltegger, Urs; Bussien, Denise; Lewin, Eric

    2011-01-01

    High-precision isotope dilution - thermal ionization mass spectrometry (ID-TIMS) U-Pb zircon and baddeleyite ages from the PX1 vertically layered mafic intrusion Fuerteventura, Canary Islands, indicate initiation of magma crystallization at 22.10 ± 0.07 Ma. The magmatic activity lasted a minimum of 0.52 Ma. 40Ar/39Ar amphibole dating yielded ages from 21.9 ± 0.6 to 21.8 ± 0.3, identical within errors to the U-Pb ages, despite the expected 1% theoretical bias between 40Ar/39Ar and U-Pb dates. This overlap could result from (i) rapid cooling of the intrusion (i.e., less than the 0.3 to 0.6 Ma 40Ar/39Ar age uncertainties) from closure temperatures (Tc) of zircon (699-988 °C) to amphibole (500-600 °C); (ii) lead loss affecting the youngest zircons; or (iii) excess argon shifting the plateau ages towards older values. The combination of the 40Ar/39Ar and U/Pb datasets implies that the maximum amount of time PX1 intrusion took to cool below amphibole Tc is 0.8 Ma, suggesting PX1 lifetime of 520,000 to 800,000 Ma. Age disparities among coexisting baddeleyite and zircon (22.10 ± 0.07/0.08/0.15 Ma and 21.58 ± 0.15/0.16/0.31 Ma) in a gabbro sample from the pluton margin suggest complex genetic relationships between phases. Baddeleyite is found preserved in plagioclase cores and crystallized early from low silica activity magma. Zircon crystallized later in a higher silica activity environment and is found in secondary scapolite and is found close to calcite veins, in secondary scapolite that recrystallised from plagioclase. close to calcite veins. Oxygen isotope δ18O values of altered plagioclase are high (+7.7), indicating interaction with fluids derived from host-rock carbonatites. The coexistence of baddeleyite and zircon is ascribed to interaction of the PX1 gabbro with CO2-rich carbonatite-derived fluids released during contact metamorphism.

  17. Zircon U-Pb age and Hf-O isotopes of felsic rocks from the Atlantis Bank, Southwest Indian Ridge

    Science.gov (United States)

    Liu, C. Z.; Zhang, W. Q.

    2017-12-01

    Hole U1473A was drilled to 790 meters below seafloor on the Atlantis Bank, an oceanic core complex in the Southwest Indian Ridge, where the upper crust has been removed by detachment faulting. The recovered core consists dominantly of olivine gabbro, with subordinate gabbro, gabbro with varying Fe-Ti oxide concentrations. Felsic veins intermittently occur throughout the whole core section. Zircons separated from twenty-four felsic samples have been conducted for U-Pb dating and O isotope analyses on the Cameca 1280 and Lu-Hf isotopes by laser ablation coupled with a MC-ICPMS. The zircons have highly variable contents of U (12-2078 ppm) and Th (5-801 ppm), yielding Th/U ratios of 0.33-0.81. They are typical oceanic zircons as defined by the trace element discrimination plots of Grimes et al. (2015). The weighted mean 206Pb/238U ages of the analyzed zircons vary from 11.29 to 12.57 Ma. Age differences between felsic veins throughout the whole core are not resolved within analytical uncertainty of the SIMS measurements. All felsic samples have similar zircon Hf isotope compositions, with initial 176Hf/177Hf ratios of 0.283126-0.283197 and ɛHf values of 12.76-15.27. Zircons from all felsic samples but one have mantle-like δ18O values of 5.14-5.50‰. Zircons from one sample show partial resorption or total recrystallization; in comparison, they have lower δ18O values of 4.81±0.21‰. Such characteristics provide clear evidence for hydrothermal alteration after magmatic intrusion.

  18. High spatial resolution U-Pb geochronology and Pb isotope geochemistry of magnetite-apatite ore from the Pea Ridge iron oxide-apatite deposit, St. Francois Mountains, southeast Missouri, USA

    Science.gov (United States)

    Neymark, Leonid; Holm-Denoma, Christopher S.; Pietruszka, Aaron; Aleinikoff, John N.; Fanning, C. Mark; Pillers, Renee M.; Moscati, Richard J.

    2016-01-01

    The Pea Ridge iron oxide-apatite (IOA) deposit is one of the major rhyolite-hosted magnetite deposits of the St. Francois Mountains terrane, which is located within the Mesoproterozoic (1.5–1.3 Ga) Granite-Rhyolite province in the U.S. Midcontinent. Precise and accurate determination of the timing and duration of oreforming processes in this deposit is crucial for understanding its origin and placing it within a deposit-scale and regional geologic context. Apatite and monazite, well-established U-Pb mineral geochronometers, are abundant in the Pea Ridge orebody. However, the potential presence of multiple generations of dateable minerals, processes of dissolution-reprecipitation, and occurrence of micrometer-sized intergrowths and inclusions complicate measurements and interpretations of the geochronological results. Here, we employ a combination of several techniques, including ID-TIMS and high spatial resolution geochronology of apatite and monazite using LA-SC-ICPMS and SHRIMP, and Pb isotope geochemistry of pyrite and magnetite to obtain the first direct age constraints on the formation and alteration history of the Pea Ridge IOA deposit. The oldest apatite TIMS 207Pb*/206Pb* dates are 1471 ± 1 and 1468 ± 1 Ma, slightly younger than (but within error of) the ~1474 to ~1473 Ma U-Pb zircon ages of the host rhyolites. Dating of apatite and monazite inclusions within apatite provides evidence for at least one younger metasomatic event at ~1.44 Ga, and possibly multiple superimposed metasomatic events between 1.47 and 1.44 Ga. Lead isotop analyses of pyrite show extremely radiogenic 206Pb/204Pb ratios up to ~80 unsupported by in situ U decay. This excess radiogenic Pb in pyrite may have been derived from the spatially associated apatite as apatite recrystallized several tens of million years after its formation. The low initial 206Pb/204Pb ratio of ~16.5 and 207Pb/204Pb ratio of ~15.4 for individual magnetite grains indicate closed U-Pb system behavior in

  19. 230Th-238U radioactive disequilibria in tholeiites from the FAMOUS zone (Mid-Atlantic Ridge, 36050'N): Th and Sr isotopic geochemistry

    International Nuclear Information System (INIS)

    Condomines, M.; Morand, P.; Allegre, C.J.

    1981-01-01

    We analyzed, U, Th and 230 Th/ 232 Th activity ratios for a few tholeiites from the Mid-Atlantic Ridge FAMOUS zone at 36 0 50'N. The results show a fairly wider scatter for both Th/U and ( 230 Th/ 232 Th) ratios. Seawater contamination appears to be responsible for this scatter and, for the uranium, produces an increase in content yielding a ( 234 U/ 238 U) ratio greater than 1 and, for the Th, an increase of the ( 230 Th/ 232 Th) ratio which is a very sensitive indicator for contamination. Also, the latter often is selective: U, Th and Sr are not affected in the same manner. When discarding all data for contaminated samples, the FAMOUS zone appears to be very homogeneous with a Th/U ratio value of 3.05 and a ( 230 Th/ 232 Th) ratio value of 1.24. Comparison with other active volcanic areas reveals a negative correlation between ( 230 Th/ 232 Th) and 87 Sr/ 86 Sr ratios for present lavas which is indicative of a consistency in Th-U and Rb-Sr fractionation in the source regions of these magmas. The Th isotopic geochemistry can thus provide useful information for the study of present volcanism, information as valuable as that from Sr, Pb or Nd isotopes. (orig.)

  20. Noble Gases in Alpine Gold: U/Th-He Dating and Excesses of Radiogenic He and AR

    Science.gov (United States)

    Eugster, O.; Hofmann, B.; Krahenbuhl, U.; Neuenschwander, J.

    1992-07-01

    Gold precipitates in hydrothermal fluids along with other heavy elements, such as Ag and Pt. In order to explore the possibility of dating the formation of gold we determined the concentrations of U, Th, and their decay product ^4He, as well as the K and ^40Ar concentrations in vein-type gold and in placer gold samples. The gold-quartz veins at Brusson in the south-western alps were formed approximately 32 Ma ago during an episode of tectonic uplift (Diamond, 1990). Alpine material was deposited as sediment layers in the region of central Switzerland and placer gold is thus relatively abundant in the rivers of the Napf area. We washed placer gold from the river Grosse Fontanne in 1990 and 1991. Placer gold that had been collected from the river Kruempelgraben in 1933 and a sample of vein-type free gold grown on quartz rock from the Brusson area (Val d'Ayas) have been obtained from the Museum of Natural History in Bern. Table 1 gives the results. Most of the ^4He is released above 1050 degrees C, that is when gold melts, indicating that gold is extremely well retentive for He. From the ^4He concentration of (269 +- 20) x 10^-8 cm^3 STP/g, (0.4 +- 0.1) ppm U, and (0.9 +- 0.3) ppm Th for vein-type gold we calculate a U/Th-He age of (36 +- 8)Ma. This age agrees within errors with the proposed age of 32 Ma. The data given in Table 1 show that all placer gold samples contain excesses of radiogenic ^4He and ^40Ar relative to the concentrations expected from the U/Th and K decay, respectively, if we assume a formation age of 32 Ma. The quartz sample is depleted in ^4He but strongly enriched in radiogenic ^40Ar. The excess of ^40Ar(sub)rad is easier to explain than that of ^4He. Vein-type gold and placer gold contain quartz inclusions (Schmid, 1973). The high ^40Ar(sub)rad content of quartz (Table 1) indicates that the ^40Ar(sub)rad excess of gold originates from quartz inclusions. Excess ^4He in gold must be of radiogenic origin. Taking ^20Ne and ^36Ar as a measure for the

  1. Reassessment of the geologic evolution of selected precambrian terranes in Brazil, based on SHRIMP U-Pb data, part 2: mineiro and Aracuai orogens and Southern Sao Francisco craton; Reavaliacao da evolucao geologica em terrenos pre-cambrianos brasileiros com base em novos dados U-Pb SHRIMP, parte 2: orogeno Aracuai, cinturao mineiro e craton Sao Francisco Meridional

    Energy Technology Data Exchange (ETDEWEB)

    Silva, Luiz Carlos da; Pimentel, Marcio [Brasilia Univ., DF (Brazil). Inst. de Geociencias]. E-mail: luizcarlos@aneel.gov.br; Leite, Carlos Augusto; Vieira, Valter Salino; Silva, Marcio Antonio da; Paes, Vinicius Jose de Castro; Cardoso Filho, Joao Moraes [Companhia de Pesquisas de Recursos Minerais (CPRM), Belo Horizonte, MG (Brazil); Armstrong, Richard [Australian National Univ., Canberra (Australia). Research School of Earth Sciences; Noce, Carlos Mauricio; Pedrosa-Soares, Antonio Carlos [Minas Gerais Univ., Belo Horizonte (Brazil). Inst. de Geociencias. Centro de Pesquisa Manuel Teixeira da Costa; Carneiro, Mauricio Antonio [Ouro Preto Univ., MG (Brazil). Dept. de Geologia

    2002-12-15

    Aracuai Orogen, the Caparao charnockitic granulite, revealed magmatic crystallization age of ca. 2195 Ma. Zircons from an amphibolite of the Pocrane Complex, also a basement inlier within the Aracuai Orogen, yielded an age of ca. 1500 Ma. Both inliers furnished well-constrained neo proterozoic metamorphic overprint at ca. 590 Ma. The sub alkaline gneissic granite from the Salto da Divisa Suite yielded a magmatic crystallization age of ca. 870 Ma, close to U-Pb ages of the continental rift magmatism found in the African counterpart of the Aracuai Orogen. Four gneissic granites from the Aracuai Orogen (three of them previously interpreted as part of the Archean/Paleoproterozoic basement) were dated in the range of ca. 560-570 Ma, and were correlated to the {gamma}2{sub 2} syn-collisional magmatism. Borders of some zircon grains from the older (ca. 570 Ma) dated unit (Nanuque Granite) yielded ages around 500 Ma, similar to U-Pb ages obtained from titanite, monazite and zircon in other localities from the Aracuai Orogen. This youngest ages could be related to heating effects caused by melting of country rocks and ascent of magmas formed during the collapse of the orogen. (author)

  2. The magmatic evolution and genesis of the Quaternary basanite-trachyphonolite suite of Itasy (Madagascar) as inferred by geochemistry, Sr-Nd-Pb isotopes and trace element distribution in coexisting phases

    Science.gov (United States)

    Melluso, L.; Tucker, R. D.; Cucciniello, C.; le Roex, A. P.; Morra, V.; Zanetti, A.; Rakotoson, R. L.

    2018-06-01

    The Itasy is a Pleistocene-Holocene volcanic field in central Madagascar, located to the west of the Ankaratra volcanic complex. It comprises scoria cones and lava domes (>120), with associated pyroclastic fall and mafic lava flows, covering an area of ab. 400 km2. The last volcanic episodes probably dated ca. 6000-7100 y BP; warm springs and geysers are active. The juvenile samples comprise a peculiar, almost bimodal, rock suite ranging from potassic leucite-kaersutite-bearing basanites, tephrites and phonotephrites, to benmoreites and titanite-haüyne-bearing trachyphonolites (MgO from 9-10 wt% to 0.1 wt%). These rocks show continuous and overlapping variations in the bulk-rock and phase composition (olivine, clinopyroxene, amphibole, feldspar, leucite, haüyne, nepheline, oxides, apatite, titanite, glass and other accessories). The basanites have homogeneous isotopic composition (87Sr/86Sr = 0.70366-0.70378, 143Nd/144Nd = 0.51274-0.51277, 206Pb/204Pb = 18.7-18.9, 207Pb/204Pb = 15.53-15.56; 208Pb/204Pb = 38.89-39.01), and a marked enrichment in the most incompatible elements (LILE and HFSE reach 100-215 times primitive mantle). These features are consistent with low degrees of partial melting of a volatile-, LILE- and HFSE-rich, amphibole-bearing peridotitic mantle induced by uplift during an E-W-directed extensional regime, as is found in central Madagascar. The marked changes in the geochemical composition, and small variations of the Sr-Nd-Pb isotopes in the trachyphonolites (87Sr/86Sr = 0.70425-0.70446, 143Nd/144Nd = 0.51266-0.51269, 206Pb/204Pb = 18.18-18.39, 207Pb/204Pb = 15.49-15.51; 208Pb/204Pb = 38.38-39.57) with respect to basanites and tephrites point to a limited amount of crustal contamination by the relatively low-206Pb/204Pb, low-143Nd/144Nd, high-87Sr/86Sr Precambrian basement rocks (of Middle Archean to Late Proterozoic age), and highlight the geochemical effects of titanite and anorthoclase removal on the trace element fractionation trends, a

  3. A Procedure for the Sequential Determination of Radionuclides in Phosphogypsum Liquid Scintillation Counting and Alpha Spectrometry for 210Po, 210Pb, 226Ra, Th and U Radioisotopes

    International Nuclear Information System (INIS)

    2014-01-01

    Since 2004, the Environment Programme of the IAEA has included activities aimed at the development of a set of procedures for the determination of radionuclides in terrestrial environmental samples. Reliable, comparable and 'fit for purpose' results are essential requirements for any decision based on analytical measurements. For the analyst, tested and validated analytical procedures are extremely important tools for the production of such analytical data. For maximum utility, such procedures should be comprehensive, clearly formulated, and readily available to both the analyst and the customer for reference. In this publication, a combined procedure for the sequential determination of 210Po, 210Pb, 226Ra, Th and U radioisotopes in phosphogypsum is described. The method is based on the dissolution of small amounts of phosphogypsum by microwave digestion, followed by sequential separation of 210Po, 210Pb, Th and U radioisotopes by selective extraction chromatography using Sr, TEVA and UTEVA resins. Radium-226 is separated from interfering elements using Ba(Ra)SO4 co-precipitation. Lead-210 is determined by liquid scintillation counting. The alpha source of 210Po is prepared by autodeposition on a silver plate. The alpha sources of Th and U are prepared by electrodeposition on a stainless steel plate. A comprehensive methodology for the calculation of results, including the quantification of measurement uncertainty, was also developed. The procedure is introduced as a recommended procedure and validated in terms of trueness, repeatability and reproducibility in accordance with ISO guidelines

  4. First 226Ra- 210Pb dating of a young speleothem

    Science.gov (United States)

    Condomines, M.; Rihs, S.

    2006-10-01

    Whereas the method based on the decrease of excess 210Pb has already been used to date young (Age determination of recent cave deposits using excess 210Pb — A new technique, Geophys. Res. Lett. 20 (1993) 603-606.]), this paper presents the first dating of a speleothem through the 226Ra- 210Pb method. Dating of a young hydrothermal stalagmite from the Mt Cornadore cave (St Nectaire, French Massif Central) was made possible by the high 226Ra and negligible 210Pb contents of such carbonates, formed by precipitation from CO 2-rich thermal waters. ( 210Pb/ 226Ra) ratios regularly increase with depth along the axis of the 33 cm long stalagmite. The age-depth relationship can be interpreted by two main phases of growth, with high but variable axial growth rates of 5.3 mm/yr from 1909 to 1967, and 2.6 mm/yr from 1967 to 1989 (alternatively, the oldest phase can be subdivided in three episodes with growth rates varying from 2 to 7 mm/yr). Thin-section examination reveals the presence of numerous laminae, indicating infra-annual variations. We suggest that this fine layered structure might reflect short-term fluctuations in drip waters, possibly induced by near-surface mixing between thermal and ground waters, and ultimately linked to the pluviometry. A detailed examination of this laminated structure combined with 226Ra- 210Pb dating could thus provide a high-resolution record of local paleohydrological fluctuations.

  5. Temporal evolution of natural radionuclides distributions {sup 238}U, {sup 234}Th, {sup 226}Ra, {sup 228}Ra, {sup 210}Pb and {sup 210}Po in the Bransfield strait, Antarctica peninsula; Evolucao temporal das distribuicoes dos radionuclideos naturais {sup 238}U, {sup 234}Th, {sup 226}Ra, {sup 228}Ra, {sup 210}Pb and {sup 210}Po no estreito de Bransfiel, peninsula Antartica

    Energy Technology Data Exchange (ETDEWEB)

    Lapa, Flavia Valverde

    2013-07-01

    Research on the distribution of natural radionuclides in Antarctica is rare and thus, there is great interest in to know their occurrence and factors related to its mobilization, transference and accumulation in this extremely fragile environment. Natural radionuclides have been used intensively as tracers in the ocean, helping to better understand processes as sinking and particle resuspension, water masses mixture and oceanic circulation. {sup 234}Th (t½ = 24.1 days) is a particle-reactive radionuclide produced continuously in seawater by the decay of its soluble precursor conservative with salinity {sup 238}U (t½ = 4.5 10{sup 9} years). Since {sup 234}Th presents relatively short half-life, it is used to quantify processes that occur in temporal scale varying from days to weeks. The disequilibrium {sup 234}Th/{sup 238}U in the surface ocean has been applied to estimate carbon fluxes exported via sinking material. The flux of particles biologically productive out of the euphotic zone in the Southern Ocean has special attention due to its importance in the control of CO{sub 2} atmospheric concentrations. The radionuclides {sup 210}Pb (t½ = 22.3 years) and {sup 210}Po (t½ = 138 days) are also particle-reactive. The disequilibrium {sup 210}Po/{sup 210}Pb has been used to estimate fluxes of particles exported in the ocean in the time scale of weeks. The long-lived Ra isotopes, {sup 226}Ra (t½ = 1,600 years) and {sup 228}Ra (t½ = 5.75 years) are soluble in seawater, presenting unique properties that make them excellent tracers of water masses. This research work had the aim to study the distributions of natural radionuclides {sup 238}U, {sup 234}Th, {sup 22}'6Ra, {sup 22}'8Ra, {sup 210}Pb and {sup 210}Po in the Bransfield Strait during 2 samplings carried out in the 2011 Austral Summer (OPERANTAR XXIX and XXX). (author)

  6. Transfer of 238U, 230Th, 226Ra, and 210Pb from soils to tree and shrub species in a Mediterranean area

    International Nuclear Information System (INIS)

    Blanco Rodriguez, P.; Vera Tome, F.; Lozano, J.C.; Perez Fernandez, M.A.

    2010-01-01

    The soil-to-plant transfer factors of natural uranium isotopes ( 238 U and 234 U), 230 Th, 226 Ra, and 210 Pb were studied in a disused uranium mine located in the Extremadura region in the south-west of Spain. The plant samples included trees (Quercus ilex, Quercus suber, and Eucalyptus cameldulensis) and one shrub (Cytisus multiflorus). All of them are characteristic of Mediterranean environments. The activity concentrations in leaves and fruit were determined for the tree species at different stages of growth. For the shrub, the total above-ground fraction was considered in three seasons. For old leaves and fruit, the highest activity concentrations were found in Eucalyptus cameldulensis for all the radionuclides studied, except in the case of 230 Th that presented similar activity concentrations in all of the tree species studied. In every case, the transfer to fruit was less than the transfer to leaves. In the shrub, the results depended on the season of sampling, with the highest value obtained in spring and the lowest in autumn. Important correlations were obtained for 238 U and 226 Ra between the activity ratio in soils with that in leaves or fruit.

  7. U-Pb dating on zircons for the la Borie eclogite (Haut-Allier, France) and consequences for the pre-Variscan evolution of the Western Europe

    Energy Technology Data Exchange (ETDEWEB)

    Ducrot, J.; Lancelot, J.R. (Montpellier-2 Univ., 44 (France). Lab. de Geochimie-Isotopique); Marchand, J. (Nantes Univ., 34 (France). Lab. de Petrologie et Minerologie)

    1983-03-01

    A crystallization age of 432sub(-10)/sup +20/Ma has been determined for the 'La Borie' eclogite (Haut-Allier, France), by U-Pb dating on zircons. This age is yielded by the upper intercept with the Concordia curve. In agreement with recent dates obtained in the southern part of the Massif Central, in Brittany and in Vendee, these data indicate that the high-pressure/high-temperature-metamorphic phase representative of the pre-Variscan evolution of the western Europe, took place at the Silurian/Ordovician boundary. This high-pressure/high-temperature metamorphism could be significant of subduction processes more or less synchronous, preceeding the main continental collision responsible of the Variscan belt.

  8. U-Pb dating on zircons for the la Borie eclogite (Haut-Allier, France) and consequences for the pre-Variscan evolution of the Western Europe

    International Nuclear Information System (INIS)

    Ducrot, J.; Lancelot, J.R.; Marchand, J.

    1983-01-01

    A crystallization age of 432sub(-10) +20 Ma has been determined for the 'La Borie' eclogite (Haut-Allier, France), by U-Pb dating on zircons. This age is yielded by the upper intercept with the Concordia curve. In agreement with recent dates obtained in the southern part of the Massif Central, in Brittany and in Vendee, these data indicate that the high-pressure/high-temperature-metamorphic phase representative of the pre-Variscan evolution of the western Europe, took place at the Silurian/Ordovician boundary. This high-pressure/high-temperature metamorphism could be significant of subduction processes more or less synchronous, preceeding the main continental collision responsible of the Variscan belt. (s.s.). (orig.)

  9. The 210Pb technique for dating sediments, and some applications

    International Nuclear Information System (INIS)

    Eakins, J.D.

    1983-01-01

    The use of 210 Pb for dating sediment in time scale 100-150 years is described. Various methods of determination of 210 Pb concentration are reviewed and the problem of the initial 210 Pb concentration using two models for interpretation of data is discussed. (author)

  10. 230Th/234U dating of the quaternary spring travertines in the Arava Rift Valley of Israel and paleoclimatic implications

    International Nuclear Information System (INIS)

    Kronfeld, J.

    1988-07-01

    Springs and lake deposits (travertines) sampled along the western margins of the Arava segment of the Dead Sea Rift Valley, Israel, were studied as a potential source of palaeoclimatic information. The 230 Th/ 234 U disequilibrium method was used to determine the age of the investigated deposits. The radiometric dating was supplemented by detailed petrographic and chemical analyses of the collected samples. Detailed petrographic observations of the analysed travertine samples suggest their deposition under moderately-arid conditions, alternating with arid to extremely arid periods. This evidence is consistent with the preliminary conclusions drawn from palynological studies in the area. Dating by the 230 Th/ 234 U disequilibrium method indicates that most travertine ages correspond to oceanic 18 O stages 5 and 7. The good correspondence between apparent ages as deduced from the position of the travertines in vertical and lateral successions and the radiometric ages, lends credibility to the radiometric ages. The clustering of ages during the warm 18 O stages bears similarity to the temporal distribution of middle to late Pleistocene sapropelic horizons in the Eastern Mediterranean Basin which further leads to suspicion that during insolation maxima monsoonal cells originating in the Indian Ocean have shifted northwards reaching the latitude of the Arava and Negev Highlands. Refs and figs

  11. Time constraints on the tectonic evolution of the eastern Sierras Pampeanas (Central Argentina)

    DEFF Research Database (Denmark)

    Siegesmund, Siegfried; Steenken, A; Martino, R D

    2010-01-01

    The application of the SHRIMP U/Pb dating technique to zircon and monazite of different rock types of the Sierras de Córdoba provides an important insight into the metamorphic history of the basement domains. Additional constraints on the Pampean metamorphic episode were gained by Pb/Pb stepwise...... leaching (PbSL) experiments on two titanite and garnet separates. Results indicate that the metamorphic history recorded by Crd-free gneisses (M2) started in the latest Neoproterozoic/earliest Cambrian (553 and 543 Ma) followed by the M4 metamorphism at ~530 Ma that is documented in the diatexites. Zircon...

  12. U-Th-Pb zircon geochronology on igneous rocks in the Toija and Salittu Formations, Orijärvi area, southwestern Finland: constraints on the age of volcanism and metamorphism

    Directory of Open Access Journals (Sweden)

    Christopher L. Kirkland

    2008-01-01

    Full Text Available Zircons from a felsic volcanic rock in the Toija Formation and a synvolcanic gabbro intrusion in the Salittu Formation within the Orijärvi area were dated by U-Th-Pb SIMS in order to provide depositional constraints on these formations. Zircon crystals from the felsic rock preserve a two-stage crystallisation history with zoned core domains and homogeneous rim domains. Inner domains yield a 1878±4 Ma concordia age, interpreted to determine the crystallisation of this rock. Rims yield a 1815±3 Ma concordia age interpretedto determine the regional metamorphism. Small rounded zircon grains from the Salittu gabbro, located within the Jyly shear zone, yield a concordia age of 1792±5 Ma. We interpret the grain textures to suggest that they recrystallised from inherited zircon seeds during the heat and fluid flow into the shear zone. Although no direct ages for the Salittu Formation have been recovered, field relationships imply that it was deposited between 1878−1875 Ma.

  13. The 40Ar/39Ar and U/Pb dating of young rhyolites in the Kos-Nisyros volcanic complex, Eastern Aegean Arc, Greece: Age discordance due to excess 40Ar in biotite

    Science.gov (United States)

    Bachmann, O.; Schoene, B.; Schnyder, C.; Spikings, R.

    2010-08-01

    High-precision dating of Quaternary silicic magmas in the active Kos-Nisyros volcanic center (Aegean Arc, Greece) by both 40Ar/39Ar on biotite and U/Pb on zircon reveals a complex geochronological story. U/Pb ID-TIMS multi and single-grain zircon analyses from 3 different units (Agios Mammas and Zini domes, Kefalos Serie pyroclasts) range in age from 0.3 to 0.5 to 10-20 Ma. The youngest dates provide the maximum eruption age, while the oldest zircons indicate inheritance from local continental crust (Miocene and older). Step-heating 40Ar/39Ar experiments on 1-3 crystals of fresh biotite yielded highly disturbed Ar-release patterns with plateau ages typically older than most U/Pb ages. These old plateau ages are probably not a consequence of inheritance from xenocrystic biotites because Ar diffuses extremely fast at magmatic temperatures and ratios are reset within a few days. On the basis of (1) elevated and/or imprecise 40Ar/36Ar ratios, (2) shapes of the Ar release spectra, and (3) a high mantle 3He flux in the Kos-Nisyros area, we suggest that biotite crystals retained some mantle 40Ar that led to the observed, anomalously old ages. In contrast, sanidine crystals from the only sanidine-bearing unit in the Kos-Nisyros volcanic center (the caldera-forming Kos Plateau Tuff) do not appear to store any excess 40Ar relative to atmospheric composition. The eastern edge of the Aegean Arc is tectonically complex, undergoing rapid extension and located close to a major structural boundary. In such regions, which are characterized by high fluxes of mantle volatiles, 40Ar/39Ar geochronology on biotite can lead to erroneous results due to the presence of excess 40Ar and should be checked either against 40Ar/39Ar sanidine or U/Pb zircon ages.

  14. U-Pb dating, geochemistry, and tectonic implications of the Songpan-Ganzi block and the Longmen Shan, Chiba

    International Nuclear Information System (INIS)

    Chen, Y.L.; Li, D.P.; Zhou, J.

    2009-01-01

    The Songpan-Ganzi triangular tectonic block is surrounded by the East Kunlun-Qaidam block in the north, the Qiangtang block in the southwest, and the Longmen Shan in the southeast. The Longmen Shan is the eastern margin of the Tibetan Plateau in Central Asia. The tectonic affinity and relationship of these regions with the Yangtze and North China blocks have been rigorously debated. In this paper, we present our recent studies on the geochemistry of the Precambrian to Triassic classic sedimentary rocks from this area. Detrital zircons were extracted from the sedimentary rocks for U-Pb dating by SHRIMP and LA-ICP-MS. Nd depleted mantle model ages indicate that these provenances have an affinity to the Yangtze craton and Qinling Shan, in contrast to those of the North China craton. All strata, from Cambrian to late Triassic, contain detrital zircon U-Pb ages of 1400 to 600 Ma, with most falling between 900-720 Ma. The Songpan-Ganzi block was the most important part of the Northern Tethys in the Triassic period, in addition to being the largest flysch basin in the world. The Longmen Shan thrust belt comprises both the telescoped, unmetamorphosed, shallow water carbonate-dominated passive margin of the Yangtze craton and its crystalline basement. The western and northern margins of the Yangtze craton, as well as the Qinling Shan, were the sources of sediments in the Songpan-Ganzi block and the Longmen Shan. The oldest dated detrital zircons indicate that the Yangtze craton started forming during the period 2800-2200 Ma. Because the basement of the Yangtze craton experienced multi-episodic intracrustal processes, the oldest basement components account for only a small portion of the provenance components. The detrital zircon ages of 2200-1400 Ma indicate a major contribution of the Qinling Shan and/or the northwestern margin of the Yangtze craton to the clastic sediments in the Songpan-Ganzi block. The presence of detrital zircon of Neoproterozoic to Triassic ages

  15. Reassessment of the geologic evolution of selected precambrian terranes in Brazil, based on SHRIMP U-Pb data, part 2: mineiro and Aracuai orogens and Southern Sao Francisco craton

    International Nuclear Information System (INIS)

    Silva, Luiz Carlos da; Pimentel, Marcio; Armstrong, Richard; Noce, Carlos Mauricio; Pedrosa-Soares, Antonio Carlos; Carneiro, Mauricio Antonio

    2002-01-01

    Aracuai Orogen, the Caparao charnockitic granulite, revealed magmatic crystallization age of ca. 2195 Ma. Zircons from an amphibolite of the Pocrane Complex, also a basement inlier within the Aracuai Orogen, yielded an age of ca. 1500 Ma. Both inliers furnished well-constrained neo proterozoic metamorphic overprint at ca. 590 Ma. The sub alkaline gneissic granite from the Salto da Divisa Suite yielded a magmatic crystallization age of ca. 870 Ma, close to U-Pb ages of the continental rift magmatism found in the African counterpart of the Aracuai Orogen. Four gneissic granites from the Aracuai Orogen (three of them previously interpreted as part of the Archean/Paleoproterozoic basement) were dated in the range of ca. 560-570 Ma, and were correlated to the γ2 2 syn-collisional magmatism. Borders of some zircon grains from the older (ca. 570 Ma) dated unit (Nanuque Granite) yielded ages around 500 Ma, similar to U-Pb ages obtained from titanite, monazite and zircon in other localities from the Aracuai Orogen. This youngest ages could be related to heating effects caused by melting of country rocks and ascent of magmas formed during the collapse of the orogen. (author)

  16. The effect of melt composition on the partitioning of trace elements between titanite and silicate melt

    Science.gov (United States)

    Prowatke, S.; Klemme, S.

    2003-04-01

    The aim of this study is to systematically investigate the influence of melt composition on the partitioning of trace elements between titanite and different silicate melts. Titanite was chosen because of its important role as an accessory mineral, particularly with regard to intermediate to silicic alkaline and calc-alkaline magmas [e.g. 1] and of its relative constant mineral composition over a wide range of bulk compositions. Experiments at atmospheric pressure were performed at temperatures between 1150°C and 1050°C. Bulk compositions were chosen to represent a basaltic andesite (SH3 - 53% SiO2), a dacite (SH2 - 65 SiO2) and a rhyolite (SH1 - 71% SiO2). Furthermore, two additional experimental series were conducted to investigate the effect of Al-Na and the Na-K ratio of melts on partitioning. Starting materials consisted of glasses that were doped with 23 trace elements including some selected rare earth elements (La, Ce, Pr, Sm, Gd, Lu), high field strength elements (Zr, Hf, Nb, Ta) and large ion lithophile elements (Cs, Rb, Ba) and Th and U. The experimental run products were analysed for trace elements using secondary ion mass spectrometry at Heidelberg University. Preliminary results indicate a strong effect of melt composition on trace element partition coefficients. Partition coefficients for rare-earth elements uniformly show a convex-upward shape [2, 3], since titanite accommodates the middle rare-earth elements more readily than the light rare-earth elements or the heavy rare-earth elements. Partition coefficients for the rare-earth elements follow a parabolic trend when plotted against ionic radius. The shape of the parabola is very similar for all studied bulk compositions, the position of the parabola, however, is strongly dependent on bulk composition. For example, isothermal rare-earth element partition coefficients (such as La) are incompatible (D>1) in alkali-poor melt compositions. From our experimental data we present an model that combines

  17. U-Pb ages of uraniferous opals and implications for the history of beryllium, fluorine, and uranium mineralization at Spor Mountain, Utah

    Science.gov (United States)

    Ludwig, K. R.; Lindsey, D.A.; Zielinski, R.A.; Simmons, K.R.

    1980-01-01

    The U-Pb isotope systematics of uraniferous opals from Spor Mountain, Utah, were investigated to determine the suitability of such material for geochronologic purposes, and to estimate the timing of uranium and associated beryllium and fluorine mineralization. The results indicate that uraniferous opals can approximate a closed system for uranium and uranium daughters, so that dating samples as young as ???1 m.y. should be possible. In addition, the expected lack of initial 230Th and 231Pa in opals permits valuable information on the initial 234U/238U to be obtained on suitable samples of ???10 m.y. age. The oldest 207Pb/235U apparent age observed, 20.8 ?? 1 m.y., was that of the opal-fluorite core of a nodule from a beryllium deposit in the Spor Mountain Formation. This age is indistinguishable from that of fission-track and K-Ar ages from the host rhyolite, and links the mineralization to the first episode of alkali rhyolite magmatism and related hydrothermal activity at Spor Mountain. Successively younger ages of 13 m.y. and 8-9 m.y. on concentric outer zones of the same nodule indicate that opal formed either episodically or continuously for over 10 m.y. Several samples of both fracture-filling and massive-nodule opal associated with beryllium deposits gave 207Pb/235U apparent ages of 13-16 m.y., which may reflect a restricted period of mineralization or perhaps an averaging of 21- and <13-m.y. periods of opal growth. Several samples of fracture-filling opal in volcanic rocks as young as 6 m.y. gave 207Pb/235U ages of 3.4-4.8 m.y. These ages may reflect hot-spring activity after the last major eruption of alkali rhyolite. ?? 1980.

  18. Rates of carbonate soil evolution from carbon, U- and Th-series isotope studies: Example of the Astian sands (SE France)

    Science.gov (United States)

    Barbecot, Florent; Ghaleb, Bassam; Hillaire-Marcel, Claude

    2015-04-01

    In carbonate rich soils, C-isotopes (14C, 13C) and carbonate mass budget may inform on centennial to millennial time scale dissolution/precipitation processes and weathering rates, whereas disequilibria between in the U- and Th-decay series provide tools to document high- (228Ra-228Th-210Pb) to low- (234U, 230Th, 231Pa, 226Ra) geochemical processes rate, covering annual to ~ 1Ma time scales, governing both carbonate and silicate soil fractions. Because lithology constitutes a boundary condition, we intend to illustrate the behavior of such isotopes in soils developed over Astian sands formation (up to ~ 30% carbonate) from the Béziers area (SE France). A >20 m thick unsaturated zone was sampled firstly along a naturally exposed section, then in a cored sequence. Geochemical and mineralogical analyses, including stable isotopes and 14C-measurements, were complemented with 228U, 234U, 230Th, 226Ra, 210Pb and 228Th, 232Th measurements. Whereas the upper 7 m depict geochemical and isotopic features forced by dissolution/precipitation processes leading to variable radioactive disequilibria, but overall deficits in more soluble elements of the decay series, the lower part of the sequence shows strong excesses in 234U and 230Th over parent isotopes (i.e., 238U and 234U, respectively). These features might have been interpreted as the result of successive phases of U-loss and gains. However, 226Ra and 230Th are in near-equilibrium, thus leading to conclude at a more likely slow enrichment process in both 234Th(234U) and 230Th, which we link to dissolved U-decay during groundwater recharge events. In addition, 210Pb deficits (vs parent 226Ra) are observed down to 12 m along the natural outcropping section and below the top-soil 210Pb-excess in the cored sequence, due to gaseous 222Rn-diffusion over the cliff outcrop. Based on C-isotope and chemical analysis, reaction rates at 14C-time scale are distinct from those estimates at the short- or long-lived U-series isotopes

  19. Molybdenite Re-Os, zircon U-Pb dating and Lu-Hf isotopic analysis of the Xiaerchulu Au deposit, Inner Mongolia Province, China

    Science.gov (United States)

    Wang, Jia-xin; Nie, Feng-Jun; Zhang, Xue-ni; Jiang, Si-hong

    2016-09-01

    The Xiaerchulu Au deposit, located in the Southern Orogenic Belt (SOB) of Western Inner Mongolia (WIM), is hosted in an Early Permian (271-261 Ma) volcanic-plutonic sequence. Mineralization took place in silicified biotite granites or along the contact zone between the Neoproterozoic Baiyinbaolage Group and the biotite granite. In order to constrain the timing of the Xiaerchulu mineralization and discuss the petrogenesis of the hosting granites, molybdenite Re-Os, and zircon U-Pb and, Lu-Hf, and REE, geochemical, and Sr-Nd isotopic studies were completed in this study. We measured Re-Os isotopes of six molybdenite samples from the main ore body, which yielded a weighted average model age of 261.7 ± 1.5 Ma with a MSWD of 0.55, indicating that the time of mineralization was at ca. 262 Ma. High precision U-Pb dating for the studied granites yields Permian 206Pb/238U ages ranging from 271 to 269 Ma. These age data confirm that both the intrusion and related mineralization were initiated in Early Permian period. These granites are strongly peraluminous with A/CNK = 1.11-1.12, high SiO2-K2O contents, as well as containing biotite and muscovite, indicating a petrogenesis of typical S-type granites, the above consideration is also consistent with the result of discrimination diagrams. The Re contents of molybdenite, εNd(t), and zircon εHf(t), as well as the 176Hf/177Hf values of the granites, fall into the ranges from 1.153 to 2.740 μg/g, - 11.1 to - 9.3, - 8.8 to - 0.9, and 0.282358 to 0.282688, respectively. All of this evidence suggests that the metals were derived from a predominantly crustal source, the granites originated from crust in an extensional setting, and the rejuvenation of the continent may have play an important role during the ore-forming processes of the Early Permian epoch.

  20. 210Pb sediment dating in coastal transition zones: tropical saltmarshes.

    Science.gov (United States)

    Ruiz-Fernandez, A. C.; Sanchez-Cabeza, J. A.; Carnero-Bravo, V.; Perez-Bernal, L. H.

    2016-12-01

    Sea level rise (SLR) is one of the climate change effects expected to have the largest impact on coastal environments. SLR rates are not uniform around the planet and, therefore, local and regional data and trends are needed for proper adaptation plans. As long term monitoring stations of SLR are very scarce in most of the world, SLR trends obtained from 210Pb-dated sediment cores from tropical saltmarshes have become a practical alternative to obtain SLR trends within the past century, under the assumption that these ecosystems accrete at a similar rate to SLR. However, tropical saltmarshes are challenging environments for 210Pb dating: they are regularly dry, intermittently covered by seawater only during the highest tides, and sedimentary records often reflect the transition between terrestrial and marine environments (e.g. changes in grain size distribution, organic matter content and elemental composition) with all these factors contributing for atypical 210Pb depth profiles. In addition, 137Cs, the chronostratigraphic marker most commonly used to corroborate 210Pb dating, fails to be preserved in the sedimentary record in tropical areas, owing to its solubility in marine waters, if at all detectable. The present study describes the challenges and proposed solutions for 210Pb dating saltmarsh sediment cores from two saltmarsh areas (southern Gulf of California and Yucatan Peninsula) including the use of plutonium isotopes for corroboration purposes. Acknowledgements: projects CONACYT CB2010/153492 and PDCPN201301/214349; UNAM PAPIIT-IN203313 and the PRODEP network "Aquatic contamination: levels and effects" (year 3).

  1. U-Pb Ages of Secondary Silica at Yucca Mountain, Nevada: Implications for the Paleohydrology of the Unsaturated Zone

    International Nuclear Information System (INIS)

    L.A. Neymark; Y. Amelin; J.B. Paces; Z.E. Peterman

    2001-01-01

    U, Th, and Pb isotopes were analyzed in layers of opal and chalcedony from individual millimeter- to centimeter-thick calcite and silica coatings at Yucca Mountain, Nevada, USA, a site that is being evaluated for a potential high-level nuclear waste repository. These calcite and silica coatings on fractures and in lithophysal cavities in Miocene-age tuffs in the unsaturated zone (UZ) precipitated from descending water and record a long history of percolation through the UZ. Opal and chalcedony have high concentrations of U (10 to 780 ppm) and low concentrations of common Pb as indicated by large values of 206 Pb/ 204 Pb (up to 53,806), thus making them suitable for U-Pb age determinations. Interpretations of U-Pb isotopes in opal samples at Yucca Mountain are complicated by the incorporation of excess 234 U at the time of mineral formation, resulting in reverse discordance of U-Pb ages. However, the 207 Pb/ 235 U ages are much less affected by deviation from initial secular equilibrium and provide reliable ages of most silica deposits between 0.6 and 9.8 Ma. For chalcedony subsamples showing normal age discordance, these ages may represent minimum times of deposition. Typically, 207 Pb/ 235 U ages are consistent with the microstratigraphy in the mineral coating samples, such that the youngest ages are for subsamples from outer layers, intermediate ages are from inner layers, and oldest ages are from innermost layers. 234 U and 230 Th in most silica layers deeper in the coatings are in secular equilibrium with 238 U, which is consistent with their old age and closed system behavior during the past 0.5 m.y. U-Pb ages for subsamples of silica layers from different microstratigraphic positions in individual calcite and silica coating samples collected from lithophysal cavities in the welded part of the Topopah Spring Tuff yield slow long-term average depositional rates of 1 to 5 mm/m.y. These data imply that the deeper parts of the UZ at Yucca Mountain maintained long

  2. Age of the emerald mineralization from the Itabira-Nova Era District, Minas Gerais, Brazil, based on LA-ICP-MS geochronology of cogenetic titanite

    Directory of Open Access Journals (Sweden)

    Hanna Jordt-Evangelista

    Full Text Available ABSTRACT: In the Itabira-Nova Era Emerald District, southeast Brazil, gemological emerald is extracted from underground mines found in schist-type deposits at the contact zone of the Archean Metavolcanosedimentary Sequence of the Guanhães Complex and Paleoproterozoic anorogenic granites of the Borrachudos Suite. Schist-type deposits are commonly generated by reactions enhanced by deformation and heat during regional metamorphism. The age of the mineralization in the region has been a matter of debate for decades: Ages ranging from the Archean to the Neoproterozoic are mentioned in the literature. In the mineralized zone from the Piteiras mine fluorine-aluminum-bearing titanite is found in metamafic rocks. The fluorine content was probably derived from the Borrachudos granites and pegmatites like the beryllium for emerald, thus both minerals could have been generated during the same event. U-Pb titanite geochronology via laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS was performed on a thin section of a phlogopite-plagioclase-hornblende schist from the Piteiras mine. The determined age of 576 ± 7 Ma is also the probable age for emerald generation during the Brasiliano cycle, which was the only tectonometamorphic event postdating the intrusion of the granites. This event provided heat and fluids necessary for reactions between the Be- and the Cr-bearing rocks, thus enabling the formation of emeralds.

  3. 210Pb dating of Baltic Sea sediments

    International Nuclear Information System (INIS)

    Gellermann, R.

    1990-01-01

    The paper reports on the results of 210 Pb measurement in sediment cores from the Baltic Sea. The models used for the interpretation are derived and discussed. In general, the sedimentation parameters calculated with different models are consistent. However, parameters of cores independently taken on same partly show clearly differing values. The reasons of this observation have to be analysed by further studies. An essential problem considered in this paper is the dating of disturbed sediments. The use of such cores for the reconstruction of the input history of chemical indicators requires a deconvolution of data. The response function necessary for this procedure can be derived from 210 Pb measurements. The results of such a reconstruction considerably differ from those obtained by conventional dating models. The analysis of the measuring uncertainty of the indicator (e.g. lead) in the deconvolution procedure unveals the limits of the method and prevents it from overinterpretation. (orig.) [de

  4. Molybdenum mineralization at Alpeiner Scharte, Tyrol (Austria): results of in-situ U-Pb zircon and Re-Os molybdenite dating

    International Nuclear Information System (INIS)

    Langthaler, K.J.; Raith, J.G.; Cornell, D.H.; Stein, H.J.; Melcher, F.

    2004-01-01

    Vein-type Mo mineralization at Alpeiner Scharte occurs in the Penninic units of the western Tauern Window in the Eastern Alps. Three types of previously undated metagranitoids (central gneisses) are distinguished and preserve intrusive contacts with pre-Alpine metamorphosed supracrustal rocks. The granitic protoliths represent fractionated late to post-orogenic, calc-alkaline, I-type magmas with minor S-type components. The Mo veins are restricted to a biotite and alkali feldspar-rich gneiss variety and occur in E-W trending normally sub-vertical quartz veins with adjacent thin discontinuous garnet- and biotite-rich zones; the latter are interpreted as metamorphosed vein selvages. Prior to this work the age of the intrusive host rocks as well as the age of Mo mineralization were unknown. The pre-Alpine Mo deposit and its host rocks were affected by four Alpine deformation events (D 1 -D 4 ) and Young-Alpine regional metamorphism. The P-T conditions of this metamorphic event were ∼ 550 o C and ∼ 8 kbar and are in agreement with results of previous regional studies. Zircon grains from two orthogneiss samples were dated with the U-Pb method using ion probe techniques. Zircons from the metagranitic host rock of the Mo-veins yielded an emplacement age of 306.8 ± 3.8 Ma (2σ). A second sample from a more leucocratic gneiss lacking Mo-veins gave 305.0 ± 6.6 Ma (2 σ). Re-Os dating of molybdenite from the veins yielded an age of 306.8 ± 3.1 Ma in good agreement with the U-Pb zircon ages. This study confirms one of two alternative hypotheses discussed in the literature. lt supports the idea that vein-type Mo-mineralization in the western Tauern Window is genetically related to Late Carboniferous (Westphalian) granitoids that were emplaced during the late to post-orogenic stage of the Variscan orogeny. They do not constitute an Alpine metamorphic-hydrothermal deposit. This study further confirms the strength of the Re-Os molybdenite chronometer, in that it was

  5. U-Pb isotopic dating of zircon from damaogou granite stock of Guangshigou uranium deposit in Danfeng area and it's significance

    International Nuclear Information System (INIS)

    Zuo Wenqian; Sha Yazhou; Chen Bing; Luo Zhongcheng; Zhang Zhanshi

    2010-01-01

    Danfeng area is an important pegmatite-type uranium production area in China, Guangshigou deposit is one of the biggest and the most important uranium deposit in this areas, Damaogou granite stock has a very close relationship with Guangshigou uranium deposit. Therefore the accurate formation dating and its evolution history of this stock is crucial for understanding the mineralization of this district. LA-ICP-MS U-Pb dating of zircon has been applied and yield the formation age of 418.3 ± 8.8 Ma of Damaogou stock, which is corresponding to the uranium mineralization age in Guangshigou deposit. The age of 1980.5 ± 19.47 Ma revealed by residual zircon might infer that Damaogou stock was derived from Qinling group, while the age of 465 Ma for the inner core of zircon grain E might represent the formation age of Huichizi gneissoid monzonitic granite. There was 30 Ma time gap between the formation of Huichizi pluton and Damaogou stock. (authors)

  6. How 210Pb dating gives information about volcanic radionuclides

    International Nuclear Information System (INIS)

    Whitehead, N.E.

    1998-01-01

    In lake sediments from the Taupo Volcanic Zone, the 1886 Tarawera tephra is often observed. The tephra contains unsupported 210 Pb which corresponds to its stratigraphic age, and shows that the 210 Pb has been adsorbed in its passage through the air, but not from the volatiles in the volcano itself which would be expected to contain the radionuclide. It is shown that only a small portion of the available 210 Pb in normal air was scavenged by the tephra. Sedimentation rates derived using the tephra were similar to those from 210 Pb dating. Some lakes showed excess 210 Pb inventories, ascribed to lake-bed geothermal activity. Contrary to expectation of increased erosion following deposition of an ash layer, sedimentation rates were less

  7. Geochronological investigation of the Ingerdal granite gneiss and discordant pegmatites from the western gneiss region, Norway

    International Nuclear Information System (INIS)

    Tucker, R.D.; Krogh, T.E.

    1988-01-01

    A seven-point (three zircon and four titanite ) U-Pb discordia-line from the Ingdal granite gneiss defines upper- and lover-intercept ages of 1653 ±2 Ma and 396 ±5 Ma interpreted as the time of Ingdal granite emplacement, and the time of gneiss formation and partial Pb-loss from zircon and titanite during a regional metamorphic event, respectively. These isotopic data suggest that this part of the western gneiss region was heated and cooled very quickly at both the upper- and lower-intercept ages, and that it did not experience significant Sveconorwegian (appr. 1250-900 Ma) or Finnmarkian (appr. 530-480 Ma) isotopic disturbance. A six-point Rb-Sr whole-rock errorchron (MSWD=11) from the same body of the Ingdal granite gneiss defines a date of 1665 ±49 Ma interpreted as a less precise age of granite emplacement. Rb-Sr mineral dates from three strongly discordant, non-foliated granite pegmatites fall in the age range of 415-379 Ma. A Rb-Sr biotite date of 372 ±4 Ma from the Ingdal granite gneiss establishes a minimum age of isotopic disturbance in the region

  8. Time-scale calibration by U-Pb geochronology: Examples from the Triassic Period

    Science.gov (United States)

    Mundil, R.

    2009-05-01

    U-Pb zircon geochronology, pioneered by Tom Krogh, is a cornerstone for the calibration of the time scale. Before Krogh's innovations, U-Pb geochronology was essentially limited by laboratory blank Pb (typically hundreds of nanograms) inherent in the then existing zircon dissolution and purification methods. The introduction of high pressure HF dissolution combined with miniature ion exchange columns (1) reduced the blank by orders of magnitude and allowed mass-spectrometric analyses of minute amounts of material (picograms of Pb and U). Krogh also recognized the need for minimizing the effects of Pb loss, and the introduction of the air-abrasion technique was the method of choice for two decades (2), until the development of the combined annealing and chemical abrasion technique resulted in essentially closed system zircons (3). These are the prerequisite for obtaining precise (permil-level) and accurate radio-isotopic ages of individual zircons contained in primary volcanic ash deposits, which are primary targets for the calibration of the time scale if they occur within fossil bearing sediments. A prime example is the calibration of the Triassic time scale which improved significantly using these techniques. The ages for the base and the top of the Triassic are constrained by U-Pb ages to 252.3 (4) and 201.5 Ma (5), respectively. These dates also constrain the ages of major extinction events at the Permian-Triassic and Triassic-Jurassic boundaries, and are statistically indistinguishable from ages obtained for the Siberian Traps and volcanic products from the Central Atlantic Magmatic Province, respectively, suggesting a causal link. Ages for these continental volcanics, however, are mostly from the K-Ar (40Ar/39Ar) system which requires accounting and correcting for a systematic bias of ca 1 % between U-Pb and 40Ar/39Ar isotopic ages (the 40Ar/39Ar ages being younger) (6). Robust U-Pb age constraints also exist for the Induan- Olenekian boundary (251.2 Ma, (7

  9. The Carboniferous to Jurassic evolution of the pre-Alpine basement of Crete: Constraints from U-Pb and U-(Th)-Pb dating of orthogneiss, fission-track dating of zircon, structural and petrological data

    Czech Academy of Sciences Publication Activity Database

    Romano, S. S.; Brix, M. R.; Dörr, K.; Fiala, Jiří; Krenn, E.; Zulauf, G.

    2006-01-01

    Roč. 260, - (2006), s. 69-90 ISSN 0375-6440 Institutional research plan: CEZ:AV0Z30130516 Keywords : tectonic-evolution * Carboniferous * Jurassic * uranium-lead-dating * orthogneiss * fission-track-dating * zircon * structural-geology * petrology * metamorphism * high-temperature Subject RIV: DB - Geology ; Mineralogy

  10. Development of numerical models for Monte Carlo simulations of Th-Pb fuel assembly

    Directory of Open Access Journals (Sweden)

    Oettingen Mikołaj

    2017-01-01

    Full Text Available The thorium-uranium fuel cycle is a promising alternative against uranium-plutonium fuel cycle, but it demands many advanced research before starting its industrial application in commercial nuclear reactors. The paper presents the development of the thorium-lead (Th-Pb fuel assembly numerical models for the integral irradiation experiments. The Th-Pb assembly consists of a hexagonal array of ThO2 fuel rods and metallic Pb rods. The design of the assembly allows different combinations of rods for various types of irradiations and experimental measurements. The numerical model of the Th-Pb assembly was designed for the numerical simulations with the continuous energy Monte Carlo Burnup code (MCB implemented on the supercomputer Prometheus of the Academic Computer Centre Cyfronet AGH.

  11. U-Pb SHRIMP and Sm-Nd geochronology of the paleoproterozoic Silvania magmatic arc in the neoproproterozoic Brasilia Belt, Goias, Central Brazil

    International Nuclear Information System (INIS)

    Fischel, D.P.; Pimentel, M.M.; Fuck, R.A; Armstrong, R

    2001-01-01

    The Brasilia Belt is a large Neoproterozoic orogen formed along the western margin of the Sao Francisco/Congo Craton in central Brazil. It comprises: (i) a thick Meso-Neoproterozoic metasedimentary/sedimentary pile with eastward tectonic vergence; (ii) a large Neoproterozoic juvenile arc in the west (Goias Magmatic Arc); and (iii) a micro-continent (or exotic sialic terrain) formed by Archean rock units (the Crixas -Goias granitegreenstones) and associated Proterozoic formations (Almeida et al. 1981, Fuck et al. 1993,1994, Pimentel et al. 2000a, b). The sialic basement on which the Brasilia Belt sediments were deposited is poorly understood, despite being well exposed in some areas of Goias and Tocantins. Gneiss and volcano-sedimentary units form most of this basement. Early studies have suggested that these rock units are dominantly Archean ( Danni et al. 1982, Marini et al. 1984). However, recent Sm- Nd isotopic studies have indicated that most of them are Paleoproterozoic (Sato 1998, Pimentel et al. 1999a, 2000b). Granite gneiss to the south and east of the Barro Alto mafic-ultramafic layered complex has been dated at 2128+/- 15 Ma (Correia et al. 1997). Calc-alkaline granite gneiss from Almas-Dianopolis is dated at ca. 2.2-2.45 Ga old (U-Pb SHRIMP on zircon and titanite, Cruz et al. 2000). The latter is probably the western extension of Paleoproterozoic rocks which underlie the San Francisco Craton to the east of the northern part of the Brasilia Belt. In central Goias, a large part of the Brasilia Belt is underlain by high-grade metamorphic rocks known as the Anapolis-Itaucu Complex, together with surrounding greenschist to amphibolite facies Mesoto Neoproterozoic cover metasediments of the Araxa group. These rocks represent the main constituent of the internal zone of the Brasilia Belt (Fuck et al. 1994, Pimentel et al. 2000b). Between the Araxa Group, and the easternmost part of the Anapolis-Itaucu Complex a volcano-sedimentary association known as Silvania

  12. Precise Th/U-dating of small and heavily coated samples of deep sea corals

    Science.gov (United States)

    Lomitschka, Michael; Mangini, Augusto

    1999-07-01

    Marine carbonate skeletons like deep-sea corals are frequently coated with iron and manganese oxides/hydroxides which adsorb additional thorium and uranium out of the sea water. A new cleaning procedure has been developed to reduce this contamination. In this further cleaning step a solution of Na 2EDTA (Na 2H 2T B) and ascorbic acid is used which composition is optimised especially for samples of 20 mg of weight. It was first tested on aliquots of a reef-building coral which had been artificially contaminated with powdered ferromanganese nodule. Applied on heavily contaminated deep-sea corals (scleractinia), it reduced excess 230Th by another order of magnitude in addition to usual cleaning procedures. The measurement of at least three fractions of different contamination, together with an additional standard correction for contaminated carbonates results in Th/U-ages corrected for the authigenic component. A good agreement between Th/U- and 14C-ages can be achieved even for extremely coated corals.

  13. Petrogenesis and zircon U-Pb dating of skarnified pyroxene-bearing dioritic rocks in Bisheh area, south of Birjand, eastern Iran

    Directory of Open Access Journals (Sweden)

    Malihe Nakhaei

    2014-10-01

    -collector static mode measurements. Several measurements of SRM-987 during the study period yielded a mean of 87Sr/86Sr = 0.71032 ± 2 (error is the 2σ mean. Measured 87Sr/86Sr ratios were corrected to SRM-987 = 0.71028. Measured 143Nd/144Nd was normalized to 146Nd/144Nd = 0.7219. Analyses were conducted as dynamic mode, three-collector measurements. Several measurements of the La Jolla Nd standard during the study period yielded a mean of 143Nd/144Nd = 0.511838 ± 8 (error is the 2σ mean. Results In the Bisheh area that is located east of Lut block, pyroxene-bearing dioritic rocks are high-K calk-alkaline and meta-aluminous. Primitive mantle-normalized trace element spider diagrams display strong enrichment in LILE, such as Rb, Ba, and Cs, and depletion in some HFSE, e.g., Nb, P, Ti, Y and Yb. Chondrite-normalized REE diagrams show (La/YbN ratios ranging from 7.75 to 8.63 and small negative Eu anomalies. These features along with high Th/Yb and Ta/Yb ratios show that magmatism is related to continental margin subduction. Obvious depletion of Nb and Ti, relatively high values of Mg#, initial 87Sr/86Sr (0.70606 and 143Nd/144Nd (0.512424 ratios as well as εNd (-3.05 suggest that the magma originated from an enriched mantle with crustal contamination. High values of Rb, Th and K and low amount of P and Ti support the magma contamination in upper crust during magma evolution. Zircon U-Pb age dating for a porphyritic pyroxene diorite sample yield an age of 44.07±0.69 Ma indicating middle Eocene (Lutetian. Discussion The isotopic value for the Bisheh dioritic porphyry can be considered as indicative of lithospheric mantle melting. The trace element characteristics of these rocks can be used to characterize their mantle source. The MORB normalized trace element pattern (Pearce, 1983 of all samples shows a negative anomaly for Nb, Ti and Ta. The negative anomaly of these elements can be explained by the presence of a residual TNT phase (Ti-Nb-Ta, e.g., rutile, ilmenite and perovskite

  14. Mobility of Ra-226 and Heavy Metals (U, Th and Pb) from Pyritic Uranium Mine Tailings under Sub-aqueous Disposal Conditions - 59283

    International Nuclear Information System (INIS)

    Dave, Nand K.

    2012-01-01

    All uranium mines in the Elliot Lake uranium mining district of north-central Ontario, Canada, have been closed due to low ore grade and prevailing market conditions. A majority of the waste management facilities have been rehabilitated and decommissioned with in-situ shallow water covers to minimize sulphide oxidation, and hence acid generation and release of metal enriched effluents. Laboratory lysimeter studies were undertaken to evaluate the leaching characteristics and mobility of Ra-226 and other heavy metals (U, Th and Pb) from pyritic uranium mine tailings under sub-aqueous disposal conditions for assessing the long-term radiological stability of such waste repositories. The experiments were conducted using three types of un-oxidized tailings: fine, coarse and gypsum depleted mill total tailings. Shallow water covers of depth ∼ 0.3 m were established using natural lake water. The leaching characteristics of radium and other major and trace metals were determined by monitoring both surface and pore water qualities as a function of time. The results showed that Ra-226 was leached from surface of the submerged tailings and released to both surface water and shallow zone pore water during initial low sulphate ion concentration of the surface water cover in all three cases. The release of Ra-226 was further enhanced with the onset of weak acidic conditions in the surface water covers of both coarse and gypsum depleted mill total tailings. With additional acid generation and increasing sulphate and iron concentrations, the dissolved Ra-226 concentrations in the water covers of these tailings gradually decreased back to low levels. Pb was also leached and mobilized with the development of moderate acidic conditions at the surface of the submerged coarse and gypsum deplete tailings. No leaching of U and Th was observed. (authors)

  15. SHRIMP U-Pb zircon dating of Pedras Grandes Suite, southern Santa Catarina State, Brazil

    Directory of Open Access Journals (Sweden)

    Andréa R. Jelinek

    2005-03-01

    Full Text Available Two major magmatic pulses of the granitic Florianópolis Batholith in Santa Catarina State, southern Brazil, occurred between 613±5Ma and 595±5 Ma, during the Neoproterozoic Brasiliano Cycle. These ages were obtained by U-Pb isotopic determinations with the sensitive high mass-resolution ion microprobe on igneous zircons from Pedras Grandes Suite in Santa Catarina State. Euhedral zircons remained unaltered close to a fluorite vein deposited at 180?C or more. These ages suggest a northern limit for the Pedras Grandes Suite, explaining the spatial relationship between the fluorite veins and the source rock.Dois dos principais pulsos da atividade granítica no Batólito Florianópolis em Santa Catarina ocorreram entre 613 ±5 Ma e 595 ±5 Ma, durante o Neoproterozóico do Ciclo Brasiliano. Estas idades foram obtidas a partir dedeterminações isotópicas U-Pb em cristais de zircão da Suite Pedras Grandes por "Sensitive high-resolution íon microprobe" - SHRIMP II. Os cristais de zircão permaneceram inalterados mesmo mediante condições hidrotermais com temperaturas iguais e, até mesmo, superiores a 180ºC. Estas idades sugerem a delimitação norte do Maciço Pedras Grandes, explicando a relação espacial existente entre os filões de fluorita e a rocha fonte destas mineralizações.

  16. U and Th background contents in the Crimea rocks, Th/U ratio interpretation

    International Nuclear Information System (INIS)

    Gerasimov, Yu.G.; Voronova, M.A.; AN Ukrainskoj SSR, Kiev. Inst. Geologicheskikh Nauk)

    1981-01-01

    Radiogeochemical sampling of rocks in the Crimea is carried out. Analyses for U are made by luminescence method, while for Th by X-ray one. About 1000 samples, characterizing the whole stratigraphical cross section except Pz of crystalline rocks, have been analyzed. Low background values for U and Th are established; U content of 1.3-2.3 g/kg and Th content of 7.0-9.0 g/kg are predominant, that is lower than the clark of the earth crust. The distribution of radioelements in stepper and submontane Crimea is gradual, while in mountain part - the mosaic one. Results of Th/U ratios interpretation are presented [ru

  17. U-Pb age for some base-metal sulfide deposits in Ireland: genetic implications for Mississippi Valley-type mineralization

    International Nuclear Information System (INIS)

    Duane, M.J.; Welke, H.J.; Allsopp, H.L.

    1986-01-01

    Evidence is presented that links the timing of vein-type (Cu-Ag(U)) to stratiform Mississippi Valley-type (MVT, Pb-Zn) ore events in Ireland. The rare occurrence of pitchblende, coffinite(?), and brannerite mineralization, which is regarded as a precursor component to the sulfide mineralization in the Gortdrum deposit (Ireland), provides the first direct radiometric dating tool for these carbonate-hosted deposits. The U-Pb (340 +25/-20 Ma) and Pb-Pb (359 +/- 26 Ma) whole-rock ages constrain the uranium and base-metal mineralizing events to the Early Carboniferous. The data support a model according to which MVT and earlier uranium mineralization stages of some major ore bodies resulted from fracturing coincident with large basin-dewatering events. The Pb-Pb and concordia data are consistent with an Early Carboniferous age for the mineralization at Gortdrum and agree closely with a previously published Rb-Sr age of 359 +/- 22 Ma, obtained for Missouri glauconites. Furthermore, other comparative geologic data from Ireland and from North American MVT mineral provinces support a model of Pb-Zn-Cu(U) mobilization on a regional scale that implicates the later closing stages of the proto-Atlantic. 40 references, 3 figures, 1 table

  18. U-Pb detrital zircon geochronology from the basement of the Central Qilian Terrane: implications for tectonic evolution of northeastern Tibetan Plateau

    Science.gov (United States)

    Liu, Changfeng; Wu, Chen; Zhou, Zhiguang; Yan, Zhu; Jiang, Tian; Song, Zhijie; Liu, Wencan; Yang, Xin; Zhang, Hongyuan

    2018-03-01

    The Tuolai Group dominates the Central Qilian Terrane, and there are different opinions on the age and tectonic attribute of the Tuolai Group. Based on large-scale geologic mapping and zircon dating, the Tuolai Group is divided into four parts: metamorphic supracrustal rocks, Neoproterozoic acid intrusive rocks, early-middle Ordovician acid intrusive rocks and middle Ordovician basic intrusive rocks. The metamorphic supracrustal rocks are the redefined Tuolai complex-group and include gneiss and schist assemblage by faulting contact. Zircon U-Pb LA-MC-ICP-MS dating was conducted on these samples of gneiss and migmatite from the gneiss assemblage, quartzite, two-mica schist and slate from the schist assemblage. The five detrital samples possess similar age spectra; have detrital zircon U-Pb main peak ages of 1.7 Ga with youngest U-Pb ages of 1150 Ma. They are intruded by Neoproterozoic acid intrusive rocks. Therefore, the Tuolai Group belonging to late Mesoproterozoic and early Neoproterozoic. With this caveat in mind, we believe that U-Pb detrital zircon dating, together with the geologic constraints obtained from this study and early work in the neighboring regions. We suggest that the formation age of the entire crystalline basement rocks of metasedimentary sequence from the Central Qilian Terrane should be constrained between the Late Mesoproterozoic and the Late Neoproterozoic, but not the previous Paleoproterozoic. The basement of the Central Qilian Terrane contains the typical Grenville ages, which indicates the Centre Qilian Terrane have been experienced the Grenville orogeny event.

  19. Petrogenesis of the Yaochong granite and Mo deposit, Western Dabie orogen, eastern-central China: Constraints from zircon U-Pb and molybdenite Re-Os ages, whole-rock geochemistry and Sr-Nd-Pb-Hf isotopes

    Science.gov (United States)

    Chen, Wei; Xu, Zhaowen; Qiu, Wenhong; Li, Chao; Yu, Yang; Wang, Hao; Su, Yang

    2015-05-01

    The Dabie orogen is among the most famous continent-continent collisional orogenic belts in the world, and is characterized by intensive post-collisional extension, magmatism and Mo mineralization. However, the genetic links between the mineralization and the geodynamic evolution of the orogen remain unresolved. In this paper, the Yaochong Mo deposit and its associated granitic stocks were investigated to elucidate this issue. Our new zircon U-Pb ages yielded an Early Cretaceous age (133.3 ± 1.3 Ma) for the Yaochong granite, and our molybdenite Re-Os dating gave a similar age (135 ± 1 Ma) for the Mo deposit. The Yaochong stock is characterized by high silica and alkali but low Mg, Fe and Ca. It is enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs: Rb, K, Th and U), but strongly depleted in heavy REEs, and high field strength elements (HFSEs: Nb, Ta, Ti and Y). The Yaochong granite has initial 87Sr/86Sr ratios of 0.7087-0.7096, and Pb isotopic ratios of (206Pb/204Pb)i = 16.599-16.704, (207Pb/204Pb)i = 15.170-15.618 and (208Pb/204Pb)i = 36.376-38.248. The granite has εNd(t) of -18.0 to -16.3 and εHf(t) values of -26.5 to -20.0. All these data indicate that the Yaochong granite is a high-K calc-alkaline fractionated I-type granite, and may have originated from partial melting of the thickened Yangtze continental crust. The Mo ores also show low radiogenic Pb isotopes similar to the Yaochong stock. Medium Re content in molybdenite (21.8-74.8 ppm) also suggests that the ore-forming materials were derived from the thickened lower crust with possibly minor mixing with the mantle. Similar to the Eastern Dabie orogen, the thickened crust beneath the Western Dabie orogen may also have experienced tectonic collapse, which may have exerted fundamental geodynamic controls on the two-stage Mo mineralization in the region.

  20. Electron Backscatter Diffraction (EBSD) Analysis and U-Pb Geochronology of the Oldest Lunar Zircon: Constraining Early Lunar Differentiation and Dating Impact-Related Deformation

    Science.gov (United States)

    Timms, Nick; Nemchin, Alexander; Grange, Marion; Reddy, Steve; Pidgeon, Bob; Geisler, Thorsten; Meyer, Chuck

    2009-01-01

    The evolution of the early moon was dominated by two processes (i) crystallization of the Lunar Magma Ocean (LMO) and differentiation of potassium-rare earth element-phosphorous-rich residual magma reservoir referred to as KREEP, and (ii) an intense meteorite bombardment referred to as lunar cataclysm . The exact timing of these processes is disputed, and resolution relies on collection and interpretation of precise age data. This study examines the microstructure and geochronology of zircon from lunar impact breccias collected during the Apollo 17 mission. A large zircon clast within lunar breccia 72215,195 shows sector zoning in optical microscopy, cathodoluminescence (CL) imaging and Raman mapping, and indicates that it was a relict fragment of a much larger magmatic grain. Sensitive high resolution ion microprobe (SHRIMP) U-Pb analysis of the zircon shows that U and Th concentration correlate with sector zoning, with darkest CL domains corresponding with high-U and Th (approx.150 and approx.100 ppm respectively), and the brightest-CL sectors containing approx.30-50 ppm U and approx.10-20 ppm Th. This indicates that variations in optical CL and Raman properties correspond to differential accumulation of alpha-radiation damage in each sector. Electron backscatter diffraction (EBSD) mapping shows that the quality of electron backscatter patterns (band contrast) varies with sector zoning, with the poorest quality patterns obtained from high-U and Th, dark-CL zones. EBSD mapping also reveals a deformation microstructure that is cryptic in optical, CL and Raman imaging. Two orthogonal sets of straight discrete and gradational low-angle boundaries accommodate approx.12 misorientation across the grain. The deformation bands are parallel to the crystallographic {a}-planes of the zircon, have misorientation axes parallel to the c-axis, and are geometrically consistent with formation by dislocation creep associated with {010} slip. The deformation bands are unlike curved

  1. 238U-234U-230Th-232Th systematics and the precise measurement of time over the past 500,000 years

    International Nuclear Information System (INIS)

    Edwards, R.L.; Chen, J.H.; Wasserburg, G.J.

    1987-01-01

    We have developed techniques to measure the 230 Th abundance in corals by isotope dilution mass spectrometry. This, coupled with our previous development of mass spectrometric techniques for 234 U and 232 Th measurement, has allowed us to reduce significantly the analytical errors in 238 U- 234 U- 230 Th dating and greatly reduce the sample size. We show that 6x10 8 atoms of 230 Th can be measured to ±30per mille (2 σ) and 2x10 10 atoms of 230 Th to ±2per mille. The time over which useful age data on corals can be obtained ranges from a few years to ≅ 500 ky. The uncertainty in age, based on analytical errors, is ±5 y(2 σ) for a 180 year old coral (3 g), ±44 y at 8294 years and ±1.1 ky at 123.1 ky (250 mg of coral). We also report 232 Th concentrations in corals (0.083-1.57 pmol/g) that are more than two orders of magnitude lower than previous values. Ages with high analytical precision were determined for several corals that grew during high sea level stands ≅ 120 ky ago. These ages lie specifically within or slightly postdate the Milankovitch insolation high at 128 ky and support the idea that the dominant cause of Pleistocene climate change is Milankovitch forcing. (orig.)

  2. Cretaceous joints in southeastern Canada: dating calcite-filled fractures

    Science.gov (United States)

    Schneider, David; Spalding, Jennifer; Gautheron, Cécile; Sarda, Philippe; Davis, Donald; Petts, Duane

    2017-04-01

    To resolve the timing of brittle tectonism is a challenge since the classical chronometers required for analyses are not often in equilibrium with the surrounding material or simply absent. In this study, we propose to couple LA-ICP-MS U-Pb and (U-Th)/He dating with geochemical proxies in vein calcite to tackle this dilemma. We examined intracratonic Middle Ordovician limestone bedrock that overlies Mesoproterozoic crystalline basement, which are cut by NE-trending fault zones that have historic M4-5 earthquakes along their trace. E-W to NE-SW vertical joint sets, the relatively youngest stress recorded in the bedrock, possess 1-7 mm thick calcite veins that seal fractures or coat fracture surfaces. The veins possess intragranular calcite that are lined with fine-grained calcite along the vein margin and can exhibit µm- to mm-scale offset (e.g. displaced fossil fragments in host rock). Calcite d18O and d13C values are analogous to the bulk composition of Middle to Late Ordovician limestones, and suggest vein formation from a source dominated by connate fluids. The calcite contain trails of fluid inclusions commonly along fractures, and 3He/4He analyses indicate a primitive, deep fluid signature (R/Ra: 0.5-2.7). Trace element geochemistry of the calcite is highly variable, generally following the elevated HREE and lower LREE of continental crust trends but individual crystals from a single vein may vary by three orders of magnitude. LA-ICP-MS geochemical traverse across veins show elevated concentrations along (sub)grain boundaries and the vein-host rock contact. Despite abundant helium concentrations, (U-Th)/He dating was unsuccessful yielding highly dispersed dates likely from excess helium derived from the fluid inclusions. However, LA-ICP-MS U-Pb dating on calcite separated from the veins yielded model ages of 110.7 ± 6.8 Ma (MSWD: 0.53; n: 16) to 81.4 ± 8.3 Ma (MSWD: 2.6; n: 17). Since all veins are from the same ENE-trend, we regressed all the calcite dates

  3. Thermobarometry and electron-microprobe Th-U-Pb monazite dating in garnet metapelites from the Capelinha Formation, Aracuai Orogen, Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Queiroga, Glaucia Nascimento; Martins, Maximiliano de Souza; Castro, Marco Paulo de; Jordt-Evangelista, Hanna; Silva, Ana Lucia da, E-mail: glauciaqueiroga@yahoo.com.br, E-mail: maximilianomartins@yahoo.com.br, E-mail: marco_pcastro@yahoo.com, E-mail: hanna@degeo.ufop.br, E-mail: alucia.silva@hotmail.com [Universidade Federal de Ouro Preto (UFOP), Ouro Preto, MG (Brazil). Escola de Minas. Departamento de Geologia; Pedrosa-Soares, Antonio Carlos, E-mail: pedrosa@igc.ufmg.br [Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG (Brazil). Instituto de Geociencias. Departamento de Geologia; Schulz, Bernhard, E-mail: bernhard.schulz@mineral.tu-freiberg.de [TU Bergakademie - Institute of Mineralogy, Freiberg - Saxony (Germany)

    2016-01-15

    The Capelinha Formation (Macaubas Group) consists of a lower quartzitic unit with metamafic intercalations and an upper metapelitic sequence. It occurs in a complex tectono-metamorphic sector of the Aracuai orogen, where post-collisional collapse-related structures superimposed collisional structures. The garnet-bearing assemblages started crystallization in the collisional deformation stage that formed the main regional foliation around 570 Ma. Garnet porphyroblasts display a well developed growth zonation of Fe-Mg-Ca-Mn and show, from core to rim, increasing almandine and pyrope contents in contrast with decreasing grossular and spessartine contents. Mineral relations and microstructures provide criteria for local equilibria and a structurally controlled application of geothermobarometry based on cation exchange and net transfer reactions. The P-T values calculated from cores to rims of garnets, aligned along clockwise trends, resulted in increasing temperatures (from 500 deg C up to 620 deg C) under decompression conditions (from 8.0 kbar to 4.5 kbar). The Th-UPb dating of homogeneous monazites by electron microprobe revealed a recrystallization period at around 490 - 480 Ma. These ages can be related to the tectono-thermal event associated with the gravitational collapse, constraining the youngest time limit for metamorphic processes in the Aracuai orogen. (author)

  4. A comparison of lead pollution record in Sphagnum peat with known historical Pb emission rates in the British isles and the Czech Republic

    Energy Technology Data Exchange (ETDEWEB)

    Novak, M.; Erel, Y.; Zemanova, L.; Bottrell, S.H.; Adamova, M. [Czech Geological Survey, Prague (Czech Republic)

    2008-12-15

    Vertical Pb concentration gradients and isotope ratios (Pb-206/Pb-207, Pb-208/Pb-207) are reported for five Pb-210-dated Sphagnum peat profiles. The studied peat bogs are in the British Isles (Thorne Moors, England; Mull, Scotland; and Connemara, Eire) and central Europe (Ocean, northern Czech Republic: Rybarenska slat, southern Czech Republic). Both the U.K. and the Czech Republic experienced maximum Pb emissions from Ag-Pb smelting around 1880. Pb emissions from coal burning peaked in 1955 in the U.K, and in the 1980s in the Czech Republic. In both countries, use of alkyl-lead additives to gasoline resulted in large Pb emissions between 1950 and 2000. We hypothesized that peaks in Pb emissions from smelting, coal burning and gasoline burning, respectively, should be mirrored in the peat profiles. However, a more complicated pattern emerged. Maximum annual Pb accumulation rates occurred in 1870 at Ocean, 1940 at Thorne Moors, 1988 at Rybarenska slat, and 1990 at Mull and Connemara. Atmospheric Pb inputs decreased in the order Thorne Moors {ge} Ocean > Rybarenska slat > Mull > Connemara. The Ocean bog was unique in the central European region in that its maximum Pb pollution dated back to the 19th century and coincided with maximum Pb smelting at Freiberg and Pribram. In contrast, numerous previously studied sites showed no Pb accumulation maximum in the 19th century, but increasing pollution until the 1980s. It remains unclear why Ocean did not record the regional peak in Pb emissions caused by high coal and gasoline burning around 1980, while an array of nearby bogs studied previously did record the 1980 coal/gasoline peak, but no 1880 smelting peak. Mean Pb-206/Pb-207 ratios of potential pollution sources were 1.07 and 1.11 for gasoline, 1.17 and 1.17 for local ores, and 1.18 and 1.19 for coal in the U.K. and the Czech Republic, respectively.

  5. Dating recent sediments by 210 Pb: problems and solutions

    International Nuclear Information System (INIS)

    Appleby, P.G.

    1998-01-01

    Accurate dating by 210 Pb is of crucial importance to a wide range of programs studying environmental records stored in natural archives such as lake sediments or peat bog accumulations. There are two simple models, commonly referred to as the CRS and CIC models. Of these, the CRS (constant rate of 210 Pb supply) model is perhaps the most widely used. The main principles of this model are exemplified by cores from three Finnish lakes with annually laminated sediments, all of which contained layers recording dilution of the atmospheric 210 Pb flux by increased sedimentation. 210 Pb dates calculated using the CRS model were in good agreements with those determined by laminae counting. There are however circumstances where the CIC (constant initial concentration) model is appropriate, e.g. in a core from Devoke Water, where the CRS model was invalidated by an abrupt discontinuity in the sediment record. In a very real sense these models should in the first instance be regarded as tools whose purpose is to determine, as far as practicable, the processes that have generated the data contained in the sediment record. In each case the 210 Pb data must be individually assessed in light of any independent chrono-stratigraphic evidence such as that provided by 137 Cs or 241 Am. The object of this presentation is to highlight the conceptual framework that forms the basis of this assessment and to show how it can be used to solve problems that have arisen in a number of practical cases. These include the use of hybrid models where there has been a variable 2 10 Pb supply, corrections for inaccuracies in the calculation of radiometric inventories, and the impact of large variations in 226 Ra activity

  6. U-Th dating of broken speleothems from Cacahuamilpa cave, Mexico: Are they recording past seismic events?

    Science.gov (United States)

    Méjean, Pauline; Garduño-Monroy, Victor-Hugo; Pinti, Daniele L.; Ghaleb, Bassam; Bouvier, Laura; Gomez-Vasconcelos, Martha G.; Tremblay, Alain

    2015-01-01

    Cacahuamilpa cave is one of the largest karst systems in Central Mexico. The cave contains numerous massive speleothems broken and fallen following oriented directions, damaged during cataclysmic geological events. One fallen and two broken speleothems were sampled in the Cacahuamilpa cave for dating the rupture event using measured U-Th disequilibrium ages. A total of eight small carbonate cores were drilled perpendicular and longitudinal to the rupture surface. Results showed three groups of ages (weighted average): 0.95 ± 0.02 ka, 28.8 ± 0.2 ka and 88.0 ± 0.7 ka. This indicates that the construction of the Cacahuamilpa karst system, for which no absolute ages existed before this study, initiated at least since Late Pleistocene. The first two groups of ages might be related to two distinct episodes of intense seismic activity. Calculated minimum horizontal ground acceleration and frequency values of the seismic events needed to create the rupture of the stalagmites dated at 0.95 ± 0.02 ka and 28.8 ± 0.2 ka range between 1.3 and 2.0 m s-2 and between 13.4 and 20.8 Hz, respectively. These parameters are compatible with earthquakes of magnitude equal or higher than 7 M, with an epicentral distance between 50 and 100 km from the Cacahuamilpa cave. The stalagmite rupture dated at 88.0 ± 0.7 ka might result from the invasion of the cave by one of the older lahars deposits of the nearby volcano Nevado del Toluca, and successively fell by gravity instability.

  7. REIMEP-22 inter-laboratory comparison. ''U Age Dating - determination of the production date of a uranium certified test sample''

    Energy Technology Data Exchange (ETDEWEB)

    Venchiarutti, Celia; Richter, Stephan; Jakopic, Rozle; Aregbe, Yetunde [European Commission, Joint Research Centre (JRC), Geel (Belgium). Institute for Reference Materials and Measurements (IRMM); Varga, Zsolt; Mayer, Klaus [European Commission, Joint Research Centre (JRC), Karlsruhe (Germany). Institute for Transuranium Elements (ITU)

    2015-07-01

    The REIMEP-22 inter-laboratory comparison aimed at determining the production date of a uranium certified test sample (i.e. the last chemical separation date of the material). Participants in REIMEP-22 on ''U Age Dating - Determination of the production date of a uranium certified test sample'' received one low-enriched 20 mg uranium sample for mass spectrometry measurements and/or one 50 mg uranium sample for a-spectrometry measurements, with an undisclosed value for the production date. They were asked to report the isotope amount ratios n({sup 230}Th)/n({sup 234}U) for the 20 mg uranium sample and/or the activity ratios A({sup 230}Th)/A({sup 234}U) for the 50 mg uranium sample in addition to the calculated production date of the certified test samples with its uncertainty. Reporting of the {sup 231}Pa/{sup 235}U ratio and the respective calculated production date was optional. Eleven laboratories reported results in REIMEP-22. Two of them reported results for both the 20 mg and 50 mg uranium certified test samples. The measurement capability of the participants was assessed against the independent REIMEP-22 reference value by means of z- and zeta-scores in compliance with ISO 13528:2005. Furthermore a performance assessment criterion for acceptable uncertainty was applied to evaluate the participants' results. In general, the REIMEP-22 participants' results were satisfactory. This confirms the analytical capabilities of laboratories to determine accurately the age of uranium materials with low amount of ingrown thorium (young certified test sample). The Joint Research Centre of the European Commission (EC-JRC) organised REIMEP-22 in parallel to the preparation and certification of a uranium reference material certified for the production date (IRMM-1000a and IRMM-1000b).

  8. A review of the statistical principles of geochronometry. II. Additional concepts pertinent to radiogenic U-Pb studies

    International Nuclear Information System (INIS)

    Eglington, B.M.; Harmer, R.E.

    1993-01-01

    A summary is provided of statistical regression techniques as applied to radiogenic uranium-lead data. The model-dependent nature of U-Pb regression calculations, both for isochrons and errorchrons, is emphasized throughout. Near concordant U-Pb radiogenic data preserve better information about the original age of the samples than do more discordant data, yet most conventional regression techniques assign more importance to the discordant data than to those near concordia. The links between mathematical techniques for regression and conceptual models are highlighted and critically examined and methods illustrated to deal with the discordant data. Comparison of dates from different laboratories or researchers requires that the techniques applied be statistically valid and, in most cases, that the model-dependent assumptions be compatible. This is particularly important for U-Pb radiogenic data where the influence of model-dependent assumptions may have a greater influence than in the case of whole-rock techniques. A consistent approach is proposed for treating data at South African laboratories in order ro facilitate comparison of results. Recommendations are presented as regards the minimum requirements to be met when reporting radiogenic U-Pb isotope data so that future geochronologists may benefit. 35 refs., 2 tabs., 6 figs

  9. Dating hapuka otoliths using 210 Pb/226 Ra, with comments on dating orange roughy otoliths

    International Nuclear Information System (INIS)

    Whitehead, N.E.; Ditchburn, R.G.

    1996-01-01

    It is shown that Hapuka otoliths cannot be reliably dated using the 210 Pb/ 226 Ra method because contrary to previous assumptions, excess 210 Pb is incorporated into the outer layers of otoliths which have been taken from old fish, though the 226 Ra incorporation remains normal. This is shown to apply also to Orange Roughy otoliths. Ages based on calculations using previously published methods will be artificially old. (author). 13 refs., 2 tabs., 3 figs

  10. High-precision ID-TIMS zircon U-Pb geochronology using new 1013 Ohm resistors

    Science.gov (United States)

    Von Quadt, A.; Buret, Y.; Large, S.; Peytcheva, I.; Trinquier, A.; Wotzlaw, J. F.

    2015-12-01

    Faraday cups equipped with high gain amplifiers provide a means to measure small ion beams in static mode without the limited linear range of ion counting systems. We tested the application of newly available 1013 Ohm resistors to ID-TIMS zircon U-Pb geochronology using a range of natural and synthetic reference materials. The TritonPlus-RPQ at the Institute of Geochemistry and Petrology, ETH Zurich, is equipped with five new 1013 Ohm resistors and one MasCom secondary electron multiplier, allowing to measure the 202-204-205-206-207-208Pb masses in static mode. U is measured subsequently as U-oxide (265-267-270UO2) during a second step, also in static Faraday mode. The gain calibration of the 1013 Ohm resistors was performed using the procedure of Trinquier (2014), with 144Nd-146Nd being measured using 1011 Ohm resistor and 142-143-145-148-150Nd being measured using 1013 Ohm resitors (Trinquier, 2014; Koornneef et al., 2014). Standard deviations of the noise in all five new 1013 Ohm resistors are lower than 5.0 x 10-6 over a 6 month period, with no shift occurring over this time interval. This new detector set-up was tested by analyzing natural zircon standard materials and synthetic U/Pb solutions (www.earthime.org), ranging in age from ~2 Ma to ~600 Ma. All natural zircon standards were chemically abraded (Mattinson, 2005) and all samples were spiked with the ET2535 tracer solution. U-Pb dates obtained using the static measurement routine are compared to measurements employing dynamic peak jumping routines on the MasCom multiplier. This study illustrates the benefits and current limitations of using high gain amplifiers to measure small ion beams for zircon U-Pb geochronology compared to conventional dynamic ion counting techniques. Mattinson, J.M. (2005) Chemical Geology 220:47-66; Trinquier, A. (2014) Application Note 30281; Koornneef, J. et al (2014) Analytica Chimica Acta 819:49-55.

  11. New SHRIMP U-Pb zircon ages of the metapelitic granulites from NW of Madurai, Southern India

    International Nuclear Information System (INIS)

    Prakash, D.

    2010-01-01

    Zircon cathodoluminescent imaging and SHRIMP U-Pb dating were carried out for metapelitic rocks (sapphirine-hearing granulites and garnet-cordierite gneisses) from the NW of Madurai, Southern India. The cathodoluminescence images reveal the complex, inhomogeneous internal structure having irregular-shaped core and overgrowths. Zircon grains have obliterated oscillatory zoning. SHRIMP U-Pb chronological results yield ages of 550 ± 15 Ma and 530 ± 50 Ma as a time of metamorphic overprint, and the age of 2509 ± 12 Ma and 2509 ± 30 Ma corresponding to a timing of protolith formation for sapphirine-bearing granulites and garnet-cordierite gneisses respectively. Zircon ages reflect that continental crust in the NW of Madurai region resulted from the recycling of Archaean protolith of an igneous origin similar to the preserved crust in the southern part of Dharwar craton. The present SHRIMP U-Pb zircon ages are in close agreement with earlier published Nd isotopic data which suggest an extended precrustal history of their protoliths. The abraded zircon grains indicate multiple recycling and repeated metamorphism that has ultimately resulted in present day continental crust exposed in Madurai region. These SHRIMP U-Pb zircon ages from metapelitic UHT granulites are also significant to understanding the architecture of the SGT during the amalgamation of Gondwana in Neoproterozoic time. (author)

  12. Heterogeneity in the 238U/235U Ratios of Angrites.

    Science.gov (United States)

    Tissot, F.; Dauphas, N.; Grove, T. L.

    2016-12-01

    Angrites are differentiated meteorites of basaltic composition, of either volcanic or plutonic origin, that display minimal post-crystallization alteration, metamorphism, shock or impact brecciation. Because quenched angrites cooled very rapidly, all radiochronometric systems closed simultaneously in these samples. Quenched angrites are thus often used as anchors for cross-calibrating short-lived dating methods (e.g., 26Al-26Mg) and the absolute dating techniques (e.g, Pb-Pb). Due to the constancy of the 238U/235U ratio in natural samples, Pb-Pb ages have long been calculated using a "consensus" 238U/235U ratio, but the discovery of resolvable variations in the 238U/235U ratio of natural samples, means that the U isotopic composition of the material to date also has to be determined in order to obtain high-precision Pb-Pb ages. We set out (a) to measure at high-precision the 238U/235U ratio of a large array of angrites to correct their Pb-Pb ages, and (b) to identify whether all angrites have a similar U isotopic composition, and, if not, what were the processes responsible for this variability. Recently, Brennecka & Wadhwa (2012) suggested that the angrite-parent body had a homogeneous 238U/235U ratio. They reached this conclusion partly because they propagated the uncertainties of the U isotopic composition of the various U double spikes that they used onto the final 238U/235U ratio the sample. Because this error is systematic (i.e., it affects all samples similarly), differences in the δ238U values of samples corrected by the same double spike are better known than one would be led to believe if uncertainties on the spike composition are propagated. At the conference, we will present the results of the high-precision U isotope analyses for six angrite samples: NWA 4590, NWA 4801, NWA 6291, Angra dos Reis, D'Orbigny, and Sahara 99555. We will show that there is some heterogeneity in the δ238U values of the angrites and will discuss the possible processes by

  13. U-Pb Data On Apatites With Common Lead Correction : Exemples From The Scottish Caledonides

    Science.gov (United States)

    Jewison, E.; Deloule, E.; Villeneuve, J.; Bellahsen, N.; Labrousse, L.; Rosenberg, C.; Pik, R.; Chew, D.

    2017-12-01

    Apatite is a widely used mineral in low-temperature thermochronology (U-Th/He and AFT). The use of apatite in U-Pb geochronology has a great potential, given its closure temperature around 450°C, for orogen thermostructural evolution studies. However, since apatite can accumulate significant amount of initial Pb in its structure, its use can be hindered by the lack of 204 Pb estimations. To work around this, two options are commonly used : either use a ploting sytem that does not require corrected ratios, or use a proxy to estimate 204Pb and use it to correct the ratios. In this study we use a SIMS to mesure 204Pb in order to compare Tera-Wasserburg diagram and corrected ages to examine the cooling pattern in the northern Highlands of Scotland. The Highlands is an extensively studied caledonian collision wedge which results from the closure of the Iapétus Ocean during the Orodivician-Silurian. Two orogenic events are related to this closing, the grampian event (480-460Ma) and the scandian event (435-415 Ma) that culminated in the stacking of major ductile thrusts. The thermal history of thoses nappes are hence complex and the cooling pattern poorly constrained. Corrected apatite U-Pb ages provide new constrains on ductile wedge building and improve our understanding of mid to lower-crustal deformation and orogenic exhumation. Thoses corrected ages yield equivalent errors and mean ages from the classic method. Those data suggest a global cooling younger than previously thought and a sequence departing from a simple forward sequence. We thus present a refined thermal evolution and conceptualize a model of ductile wedge evolution.

  14. Mass-spectrometric mining of Hadean zircons by automated SHRIMP multi-collector and single-collector U/Pb zircon age dating: The first 100,000 grains

    Science.gov (United States)

    Holden, Peter; Lanc, Peter; Ireland, Trevor R.; Harrison, T. Mark; Foster, John J.; Bruce, Zane

    2009-09-01

    The identification and retrieval of a large population of ancient zircons (>4 Ga; Hadean) is of utmost priority if models of the early evolution of Earth are to be rigorously tested. We have developed a rapid and accurate U-Pb zircon age determination protocol utilizing a fully automated multi-collector ion microprobe, the ANU SHRIMP II, to screen and date these zircons. Unattended data acquisition relies on the calibration of a digitized sample map to the Sensitive High Resolution Ion MicroProbe (SHRIMP) sample-stage co-ordinate system. High precision positioning of individual grains can be produced through optical image processing of a specified mount location. The focal position of the mount can be optimized through a correlation between secondary-ion steering and the spot position on the target. For the Hadean zircon project, sample mounts are photographed and sample locations (normally grain centers) are determined off-line. The sample is loaded, reference points calibrated, and the target positions are then visited sequentially. In SHRIMP II multiple-collector mode, zircons are initially screened (ca. 5 s data acquisition) through their 204Pb corrected 207Pb/206Pb ratio; suitable candidates are then analyzed in a longer routine to obtain better measurement statistics, U/Pb, and concentration data. In SHRIMP I and SHRIMP RG, we have incorporated the automated analysis protocol to single-collector measurements. These routines have been used to analyze over 100,000 zircons from the Jack Hills quartzite. Of these, ca. 7%, have an age greater than 3.8 Ga, the oldest grain being 4372 +/- 6 Ma (2[sigma]), and this age is part of a group of analyses around 4350 Ma which we interpret as the age when continental crust first began to coalesce in this region. In multi-collector mode, the analytical time taken for a single mount with 400 zircons is approximately 6 h; whereas in single-collector mode, the analytical time is ca. 17 h. With this productivity, we can produce

  15. Inverted Apatite (U-Th)/He and Fission-track Dates from the Rae craton, Baffin Island, Canada and Implications for Apatite Radiation Damage-He Diffusivity Models

    Science.gov (United States)

    Ault, A. K.; Reiners, P. W.; Thomson, S. N.; Miller, G. H.

    2015-12-01

    Coupled apatite (U-Th)/He and fission-track (AFT) thermochronology data from the same sample can be used to decipher complex low temperature thermal histories and evaluate compatibility between these two methods. Existing apatite He damage-diffusivity models parameterize radiation damage annealing as fission-track annealing and yield inverted apatite He and AFT dates for samples with prolonged residence in the He partial retention zone. Apatite chemistry also impacts radiation damage and fission-track annealing, temperature sensitivity, and dates in both systems. We present inverted apatite He and AFT dates from the Rae craton, Baffin Island, Canada, that cannot be explained by apatite chemistry or existing damage-diffusivity and fission track models. Apatite He dates from 34 individual analyses from 6 samples range from 237 ± 44 Ma to 511 ± 25 Ma and collectively define a positive date-eU relationship. AFT dates from these same samples are 238 ± 15 Ma to 350 ± 20 Ma. These dates and associated track length data are inversely correlated and define the left segment of a boomerang diagram. Three of the six samples with 20-90 ppm eU apatite grains yield apatite He and AFT dates inverted by 300 million years. These samples have average apatite Cl chemistry of ≤0.02 wt.%, with no correlation between Cl content and Dpar. Thermal history simulations using geologic constraints, an apatite He radiation damage accumulation and annealing model, apatite He dates with the range of eU values, and AFT date and track length data, do not yield any viable time-temperature paths. Apatite He and AFT data modeled separately predict thermal histories with Paleozoic-Mesozoic peaks reheating temperatures differing by ≥15 °C. By modifying the parameter controlling damage annealing (Rmr0) from the canonical 0.83 to 0.5-0.6, forward models reproduce the apatite He date-eU correlation and AFT dates with a common thermal history. Results imply apatite radiation damage anneals at

  16. U-Pb ages of detrital zircon from Pegasus Group, Stewart Island

    International Nuclear Information System (INIS)

    Walker, N.; Tulloch, A.J.; Allibone, A.

    1998-01-01

    Stewart Island (New Zealand) is relatively unaffected by Cenozoic deformation related to the present-day plate boundary and has thus been a locale of investigations that focus on the relationship between Mesozoic continental margin magmatic rocks and the Western Province (WP) of NZ. Pegasus Group metasedimentary rocks represent the only candidate for WP equivalents on Stewart Island. We measured U-Pb and 207 Pb / 206 Pb ages of detrital zircons from the Pegasus Group in an effort to validate the correlation with the WP. On SI, Pegasus Group is exposed over a small area in the southern Tin Range where it forms amphibolite facies roof pendants and screens among plutons of mid Paleozoic to mid Cretaceous age. Mica schists predominate, with lesser amounts of psammite and metaquartzite and rare calcareous schist and amphibolite. Zircons were extracted from metaquarzite and 24 grains were chosen on the basis of morphology for geochronologic investigation. Sixteen single crystals were dated by U-Pb TIMS; 8 additional grains were studied by the total evaporation method described by Kober. Despite vigorous air abrasion prior to processing, the 16 grains measured by conventional U-Pb TIMS yielded slightly normally discordant ages that we interpret to reflect minor Pb-loss. The 8 grains studied by the total evaporation method yielded more than four analytically identical /sup 207 Pb / 206 Pb ages within each grain at progressively higher temperatures (1515-1580 degrees C) of evaporation. The results permit the following general conclusions: 1) the age range of 420-2700 Ma is grossly similar to that reported from the Greenland Group/Victoria Paragneiss (Ireland 1992) of the Buller Terrane, WP; 2) the zircon population is dominantly 530-680 Ma but a subsidiary population is 900-1100 Ma; 3) no zircons with ages that match the timing of the Ross Orogen (530-480 Ma) were identified; 4) two grains of 420 Ma and a 453 Ma are probably too young for the paleontogically

  17. Transfer of {sup 238}U, {sup 230}Th, {sup 226}Ra, and {sup 210}Pb from soils to tree and shrub species in a Mediterranean area

    Energy Technology Data Exchange (ETDEWEB)

    Blanco Rodriguez, P. [Natural Radioactivity Group, Facultad de Ciencias, Universidad de Extremadura, Avda. de Elvas s/n, 06071 Badajoz (Spain); Vera Tome, F. [Natural Radioactivity Group, Facultad de Ciencias, Universidad de Extremadura, Avda. de Elvas s/n, 06071 Badajoz (Spain)], E-mail: fvt@unex.es; Lozano, J.C. [Natural Radioactivity Group, Facultad de Ciencias, Universidad de Extremadura, Avda. de Elvas s/n, 06071 Badajoz (Spain); Laboratorio de Radiaciones Ionizantes, Facultad de Ciencias, Universidad de Salamanca, 37008 Salamanca (Spain); Perez Fernandez, M.A. [Natural Radioactivity Group, Facultad de Ciencias, Universidad de Extremadura, Avda. de Elvas s/n, 06071 Badajoz (Spain); Area de Ecologia, Universidad Pablo Olavide, Carretera de Utrera km. 1, 41013 Sevilla (Spain)

    2010-06-15

    The soil-to-plant transfer factors of natural uranium isotopes ({sup 238}U and {sup 234}U), {sup 230}Th, {sup 226}Ra, and {sup 210}Pb were studied in a disused uranium mine located in the Extremadura region in the south-west of Spain. The plant samples included trees (Quercus ilex, Quercus suber, and Eucalyptus cameldulensis) and one shrub (Cytisus multiflorus). All of them are characteristic of Mediterranean environments. The activity concentrations in leaves and fruit were determined for the tree species at different stages of growth. For the shrub, the total above-ground fraction was considered in three seasons. For old leaves and fruit, the highest activity concentrations were found in Eucalyptus cameldulensis for all the radionuclides studied, except in the case of {sup 230}Th that presented similar activity concentrations in all of the tree species studied. In every case, the transfer to fruit was less than the transfer to leaves. In the shrub, the results depended on the season of sampling, with the highest value obtained in spring and the lowest in autumn. Important correlations were obtained for {sup 238}U and {sup 226}Ra between the activity ratio in soils with that in leaves or fruit.

  18. U-Pb studies of the Appley Bridge meteorite

    International Nuclear Information System (INIS)

    Gale, N.H.; Arden, J.W.; Hutchinson, R.

    1979-01-01

    The U and Pb concentration in samples from the interior of the 10.9 kg stone BM 1920, 40 (British Museum), the isotopic composition of lead, a lead-lead diagram for whole meteorite samples of Appley Bridge, and a U-Pb concordia diagram for whole meteorite samples of Appley Bridge from different measurements are treated. (HK) 891 HK/HK 892 MB [de

  19. Possibility of wine dating using the natural Pb-210 radioactive isotope

    International Nuclear Information System (INIS)

    Hubert, Ph.; Pravikoff, M.S.; Gaye, J.

    2015-01-01

    To control the authenticity of an old wine without opening the bottle, we developed a few years ago a method based on the measurement of the 137 Cs activity. However, for recent vintages, the 137 Cs activity drops to far too low values (most of the time less than 10 mBq/L for a 10-year-old wine) for this method to perform correctly. In this paper we examine the possibility to date wines using the natural radio-element 210 Pb which has a 22-year period. This new method we propose implies the opening of the bottle and the follow-on destruction of the wine itself, which means that it can only be used for investigating non-expensive bottles or wine lots where there are multiple bottles of the same provenance. Uncertainties on the resulting 210 Pb radioactivity values are large, up to more than 50%, mainly due to local atmospheric variations, which prevents us to carry out precise dating. However it can be used to discriminate between an old wine (pre-1952) and a young wine (past-1990), an information that cannot be obtained with the other techniques based on other isotopes ( 137 Cs, 14 C or tritium). - Highlights: • We correlate the measured 210 Pb activity in wine to the vintage year. • A precise dating with 210 Pb is still difficult. • The method is complementary to the 137 Cs technique we previously developed

  20. Radiometric dating by alpha spectrometry on uranium series nuclides

    International Nuclear Information System (INIS)

    Wijk, A. van der.

    1987-01-01

    This thesis describes the analytical and technical procedures that are required for routine application of both the 230 Th/ 234 U disequilibrium dating method for peat and the 210 Pb dating method for lake sediments. Its principal aim is to test, refine and discuss the reliability and validity of these methods. On the other hand, the analytical procedures that were introduced open a wide range of other interesting fields of research that are not necessarily restricted to geological problems only. Chapter 5 reports an obviously not foreseen application: detection of alpha emitting nuclides released in the first weeks of May, 1986 during the accident with the nuclear power plant in Chernobyl, USSR. 128 refs.; 43 figs.; 15 tabs

  1. A comparison of lead pollution record in Sphagnum peat with known historical Pb emission rates in the British Isles and the Czech Republic

    Science.gov (United States)

    Novak, Martin; Erel, Yigal; Zemanova, Leona; Bottrell, Simon H.; Adamova, Marie

    Vertical Pb concentration gradients and isotope ratios ( 206Pb/ 207Pb, 208Pb/ 207Pb) are reported for five 210Pb-dated Sphagnum peat profiles. The studied peat bogs are in the British Isles (Thorne Moors, England; Mull, Scotland; and Connemara, Eire) and central Europe (Ocean, northern Czech Republic; Rybarenska slat, southern Czech Republic). Both the U.K. and the Czech Republic experienced maximum Pb emissions from Ag-Pb smelting around 1880. Pb emissions from coal burning peaked in 1955 in the U.K. and in the 1980s in the Czech Republic. In both countries, use of alkyl-lead additives to gasoline resulted in large Pb emissions between 1950 and 2000. We hypothesized that peaks in Pb emissions from smelting, coal burning and gasoline burning, respectively, should be mirrored in the peat profiles. However, a more complicated pattern emerged. Maximum annual Pb accumulation rates occurred in 1870 at Ocean, 1940 at Thorne Moors, 1988 at Rybarenska slat, and 1990 at Mull and Connemara. Atmospheric Pb inputs decreased in the order Thorne Moors ≥ Ocean > Rybarenska slat > Mull > Connemara. The Ocean bog was unique in the central European region in that its maximum Pb pollution dated back to the 19th century and coincided with maximum Pb smelting at Freiberg and Pribram. In contrast, numerous previously studied sites showed no Pb accumulation maximum in the 19th century, but increasing pollution until the 1980s. It remains unclear why Ocean did not record the regional peak in Pb emissions caused by high coal and gasoline burning around 1980, while an array of nearby bogs studied previously did record the 1980 coal/gasoline peak, but no 1880 smelting peak. Mean 206Pb/ 207Pb ratios of potential pollution sources were 1.07 and 1.11 for gasoline, 1.17 and 1.17 for local ores, and 1.18 and 1.19 for coal in the U.K. and the Czech Republic, respectively. The calculated percentages of gasoline-derived Pb in peat (≤55% for the British Isles and ≤63% for the Czech Republic

  2. Chemical Th-U-total Pb isochron ages of zircon and monazite from granitic rocks of the Negele area, southern Ethiopia

    International Nuclear Information System (INIS)

    Yihunie, Tadesse

    2003-01-01

    CHIME (Chemical Th-U-total Pb Isochron Method) age determinations were made on zircon and monazite grains from granitoid samples in the Negele area of southern Ethiopia. A 611±32 Ma zircon age was obtained from a syn-tectonic hornblende-biotite granite of the Alghe domain. A 453±29 Ma zircon age and a 459±16 Ma monazite age were also obtained from post-tectonic two-mica granites of the Alghe domain and the Kenticha domain, respectively. Since these ca. 450 Ma zircon and monazite ages coincide well, as significant post-tectonic granitic magmatism appears to have occurred in southern Ethiopia in early Paleozoid time. The new CHIME age results indicate at least two episodes of granitic magmatism in southern Ethiopia in the late Proterozoic to early Paleozoic, with a ca. 150 Ma interval between syn- and post-tectonic granitic emplacements, and have a important geochronological constraint on the evolution of the East African Orogen. (author)

  3. Phase transitions of titanite CaTiSiO5 from density functional perturbation theory

    Science.gov (United States)

    Malcherek, Thomas; Fischer, Michael

    2018-02-01

    Phonon dispersion of titanite CaTiSiO5 has been calculated using the variational density functional perturbation theory. The experimentally known out-of-center distortion of the Ti atom is confirmed. The distortion is associated with a Bu mode that is unstable for wave vectors normal to the octahedral chain direction of the C 2 /c aristotype structure. The layer of wave vectors with imaginary mode frequencies also comprises the Brillouin zone boundary point Y (0 ,1 ,0 ) , which is critical for the transition to the P 21/c ground-state structure. The phonon branch equivalent to the imaginary branch of the titanite aristotype is found to be stable in malayaite CaSnSiO5. The unstable phonon mode in titanite leads to the formation of transoriented short and long Ti-O1 bonds. The Ti as well as the connecting O1 atom exhibit strongly anomalous Born effective charges along the octahedral chain direction [001], indicative of the strong covalency in this direction. Accordingly and in contrast to malayaite, LO-TO splitting is very large in titanite. In the C 2 /c phase of titanite, the Ti-O1-Ti distortion chain is disordered with respect to neighboring distortion chains, as all chain configurations are equally unstable along the phonon branch. This result is in agreement with diffuse x-ray scattering in layers normal to the chain direction that is observed at temperatures close to the P 21/c to C 2 /c transition temperature and above. The resulting dynamic chains of correlated Ti displacements are expected to order in two dimensions to yield the P 21/c ground-state structure of titanite.

  4. Can 210Pb be used for dating of cryoconites?

    International Nuclear Information System (INIS)

    Lettner, Herbert; Wilflinger, Thomas; Hubmer, Alexander; Bossew, Peter; Slupetzky, Heinz

    2013-01-01

    Cryoconites ('cold dust', derived from Greek) are aeolian sediments accumulated on glacier-surface and subsequently altered by microbiological activity. As there is no other solid matrix than airborne material anthropogenic and artificial radionuclides are exceptionally enriched and the highest activities in environmental media are to be found in cryoconites. On alpine glaciers these sediments can be dated with artificial radionuclide and nuclide ratios like 134 Cs/ 137 Cs and 239+240 Pu/ 238 Pu, because the glaciers have been affected by global fallout and Chernobyl fallout as well. The dating methods are based on different isotopic ratios in either source. To allocate any fixed age might be problematic in a dynamic system like a glacier, where mixing of cryoconites occur quite frequently, albeit the mixing processes tend be limited in time. To overcome the shortcomings of the artificial nuclides due to labor intensive measurement and low activity concentrations of the Pu-isotopes or short half life of 134 Cs, we tried to use 210 Pb as a source of age information. 210 Pb is more or less deposited constantly over time, the activity concentrations are very high - up to 60 kBq/kg - and its half life of 22.3 years turned out to be sufficient to cover the observed sedimentation history of roughly 100 years for the cryoconite deposition. The measurement of 210 Pb and simple age allocation with absolute 210 Pb activities is thus proposed as a quick and cost-effective method for age allocation of cryoconites. (author)

  5. Origin and evolution of multi-stage felsic melts in eastern Gangdese belt: Constraints from U-Pb zircon dating and Hf isotopic composition

    Science.gov (United States)

    Guo, Liang; Zhang, Hong-Fei; Harris, Nigel; Pan, Fa-Bin; Xu, Wang-Chun

    2011-11-01

    This integrated study of whole rock geochemistry, zircon U-Pb dating and Hf isotope composition for seven felsic rocks from the Nyingchi Complex in eastern Himalayan syntaxis has revealed a complex magmatic history for the eastern Gangdese belt. This involves multiple melt sources and mechanisms that uniquely identify the tectonic evolution of this part of the Himalayan orogen. Our U-Pb zircon dating reveals five stages of magmatic or anatectic events: 165, 81, 61, 50 and 25 Ma. The Jurassic granitic gneiss (165 Ma) exhibits εHf(t) values of + 1.4 to + 3.5. The late Cretaceous granite (81 Ma) shows variable εHf(t) values from - 0.9 to + 6.2, indicating a binary mixing between juvenile and old crustal materials. The Paleocene granodioritic gneiss (61 Ma) has εHf(t) values of + 5.4 to + 8.0, suggesting that it originated from partial melting of a juvenile crustal material. The Eocene anatexis is recorded in the leucosome, which has Hf isotopic composition similar to that of the Jurassic granite, indicating that the leucosome could be derived from partial melting of the Jurassic granite. The late Oligocene biotite granite (25 Ma) shows adakitic geochemical characteristics, with Sr/Y = 49.3-56.6. The presence of a large number of inherited zircons and negative εHf(t) values suggest that it sourced from anatexis of crustal materials. In contrast to the Gangdese batholiths that are mainly derived from juvenile crustal source in central Tibet, the old crustal materials play an important role for the magma generation of the felsic rocks, suggesting the existence of a crustal basement in the eastern Gangdese belt. These correspond to specific magmatic evolution stages during the convergence between India and Asia. The middle Jurassic granitic gneiss resulted from the northward subduction of the Neo-Tethyan oceanic slab. The late Cretaceous magmatism is probably related to the ocean ridge subduction. The Paleocene-Eocene magmatism, metamorphism and anatexis are

  6. High-spatial resolution SIMS U-Pb zircon dating on Malay tin granites: New insights to crustal evolution of the Malaysian Peninsula

    Science.gov (United States)

    Ng, S.; Searle, M. P.; Whitehouse, M. J.; Chung, S.; Robb, L. J.; Ghani, A. A.; Sone, M.

    2012-12-01

    The Southeast Asian tin granite province has previously been recognized as comprising three distinct granitic belt (Cobbing et al., 1986): (1) Middle Permian - Late Triassic Eastern Province with mainly subduction-related I-type granites associated with Cu-Au deposits, (2) Late Permian - Early Jurassic Main Range Province with mainly S-type granites associated with Sn-W deposits, and (3) Late Triassic - Cretaceous Western Province with mixed I- and S-type granites associated with Sn-W deposits. These ages were obtained mainly using whole rock Rb-Sr and K-Ar geochronology in the 70s and 80s, methods that are no longer considered suitable for obtaining crystallization ages of granites due to unstable behaviour of these isotopes in hydrothermal systems. During 2011 we collected over 50 samples of granites across all three zones in Northern Malaysia for U-Pb dating using high-spatial resolution precision SIMS at the Swedish Museum of Natural History. The results reveal a westward younging trend across the Malay Peninsula. The Eastern Province hornblende- and biotite-granites in Eastern Malaysia formed by subduction-related processes have ages lying between 220-285 Ma. The Main Range Province dominantly S-type granites in west and central Malaysia have ages lying between 206-226 Ma. These include dominantly biotite granites with less common tourmaline+biotite leucocratic granites related to crustal thickening processes following collision of Sibumasu with Indochina and closing of the Palaeo-Tethyan Bentong-Raub suture zone. Some enigmatic young Cretaceous zircon rim ages (c. 81-80 Ma) may indicate a young hydrothermal - metasomatic origin for some tin mineralization from both the Eastern Province (Tioman Island) and the Western province (Phuket, Thailand) (Searle et al., 2012). Granites in Malaysia cannot be simply categorized as I-, S- or A-type as most of them failed to show distinctive minerals for classification and there is considerable overlap in geochemical

  7. Tracking the multiple-stage exhumation history and magmatic-hydrothermal events of the West Junggar region, NW China: Evidence from 40Ar/39Ar and (U-Th)/He thermochronology

    Science.gov (United States)

    Yin, Jiyuan; Chen, Wen; Xiao, Wenjiao; Long, Xiaoping; Tao, Ni; Liu, Li-Ping; Yuan, Chao; Sun, Min

    2018-06-01

    To decipher cooling events in the West Junggar region, biotite and K-feldspar 40Ar/39Ar, and zircon and apatite (U-Th)/He isotopic analyses of intrusive rocks were carried out. Previous U-Pb data showed that intrusive bodies in the Baogutu area were emplaced at 315-310 Ma. U-Pb and zircon (U-Th)/He dating results (313-241 Ma) suggest that a magmatic-hydrothermal event lasted for 72 Ma in the Baogutu area of the West Junggar region. Early-stage high temperature alteration (900-300 °C) lasted for 6-2 Ma and was followed by prolonged phyllic and argillic alteration lasting 67-63 Ma between 350 and 200 °C. Finally, slower cooling occurred between 200 and 70 °C, accompanied by post-mineralization uplift and erosion. In this study, three main episodes of relatively rapid cooling were distinguished in the West Junggar region, i.e. late Carboniferous-early Permian (307-277 Ma), middle Triassic (241-232 Ma) and early Cretaceous (145-120 Ma). The first rapid cooling during the late Carboniferous-early Permian was possibly associated with the release of magmatic heat. The middle Triassic and early Cretaceous cooling and exhumation are interpreted as a response to collision(s) between the Qiangtang and Kunlun-Qaidam or Lhasa blocks. The Cenozoic India-Eurasia collision, however, may have had little or no effect on modern tectonic reactivation of the West Junggar region.

  8. Combined dendrochronological and radiocarbon dating of six Russian icons from the 15th-17th centuries

    Science.gov (United States)

    Dolgikh, A. V.; Matskovsky, V. V.; Voronin, K. V.; Solomina, O. N.

    2017-06-01

    The results of dendrochronological and radiocarbon dating by means of accelerator mass spectrometry (AMS) of six medieval icons, originating from northern European Russia and painted on wooden panels made from Scots pine, dated to the 15th to 17th centuries are presented. The panels of each icon were studied using dendrochronology. Five to six AMS dates were obtained for four icons. Although five icons were dendro-dated successfully, one failed to be reliably cross-dated with the existing master tree-ring chronologies and it was dated by radiocarbon wiggle-matching. Dendrochronological dating and wiggle-matching of radiocarbon dates allowed us to determine the narrow chronological intervals of icon creation.

  9. Leaching studies of natural and synthetic titanite, a potential host for wastes from the reprocessing of Canadian nuclear fuel

    International Nuclear Information System (INIS)

    Hayward, P.J.; Doern, F.E.; Cecchetto, E.V.; Mitchell, S.L.

    1983-01-01

    Glass ceramics (i.e., glasses subjected to controlled crystallization) with synthetic titanite as the major crystalline phase are being considered as potential hosts for the radioactive wastes arising from possible future reprocessing of nuclear fuel in Canada. In order to assess the stability of titanite in the anticipated environment of a disposal vault sited 500-1000 m deep within a granitic pluton in the Canadian Shield, leaching experiments have been performed with natural and synthetic titanite, using a synthetic groundwater whose composition is based on findings from a recent borehole-survey. The results are in qualitative agreement with calculations of solution equilibria for titanite and its main alteration products, and indicate that titanite should be stable and suffer no net leaching under anticipated conditions in the vault

  10. Age of hydrothermal processes in the central iberian zone (Spain according TO U-Pb dating of cassiterite and apatite

    Directory of Open Access Journals (Sweden)

    Н. Г. Ризванова

    2017-06-01

    Full Text Available Results of isotope-geochemical studies by PbLS step-leaching method of cassiterite from greisens located in Logrosán granite massif (Central Iberian Zone, Spain and apatite from hydrothermal quartz-apatite vein on its exocontact indicate that in both cases a hydrothermal event is recorded in the interval of 114-126 Ma, which has been accompanied by lead supply. Within the limits of estimation error, the same age around 120 Ma corresponds to crystallization of hydrothermal apatite, formation of sticks and micro-inclusions in cassiterite from greisens and is suggested for Au-As-Sb-Pb ore mineralization, which calls for further confirmation. Xenogenous zircon from quartz-apatite vein does not react to this relatively low-temperature hydrothermal event either with building up new generations (sticks, areas of recrystallization or with rebalancing of U-Pb isotope system. The age of greisen formation has been confirmed to be around 305 Ma by PbLS method on final phases of cassiterite leaching. Earlier it was estimated with 40Ar/39Ar method on muscovite.

  11. U-Th-Pb systematics of precambrian rocks in the Laramie Mountains, Wyoming

    International Nuclear Information System (INIS)

    Nkomo, I.T.; Rosholt, J.N.; Dooley, J.R. Jr.

    1979-01-01

    Uranium, thorium and lead concentrations and the isotopic composition of whole-rock samples of granite from the Laramie Mountains, Wyoming, suggest intrusion of the granite no later than 2530 +- 80 m.y. ago. The uranium in surface samples is present in amounts that are insufficient to account for the observed lead isotopic composition. However, some core samples of heavily fractured rock show an extreme isotopic disequilibrium between 238 U and 206 Pb. Their uranium concentrations are generally far in excess (up to 60%) of average amounts required to support the measured lead-206. Radioactive disequilibrium measurements indicate that large amounts of uranium were gained by these fractured rocks during the last 150,000 years. Lead data on K-feldspar separated from the rocks analyzed suggest that lead has been assimilated by these minerals since time of crystallization. 8 figures, 6 tables

  12. U-Pb systematics in iron meteorites: uniformity of primordial lead

    International Nuclear Information System (INIS)

    Goepel, C.; Manhes, G.; Allegre, C.J.

    1985-01-01

    Pb isotopic compositions and U-Pb abundances were determined in the metal phase of six iron meteorites: Canyon Diablo IA, Toluca IA, Odessa IA, Youndegin IA, Deport IA and Mundrabilla An. Prior to complete dissolution, samples were subjected to a series of leachings and partial dissolutions. Isotopic compositions and abundances of the etched Pb indicate a contamination by terrestrial Pb which is attributable to previous cutting of the meteorite. Pb isotopic compositions measured in the decontaminated samples are identical within 0.2% and essentially confirm the primordial Pb value defined by Tatsumoto et al. (1973). These data invalidate more radiogenic Pb isotopic compositions published for iron meteorites, which are the result of terrestrial Pb contamination introduced mainly by analytical procedure. Our results support the idea of a solar nebula which was isotopically homogeneous for Pb 4.55 Ga ago. The new upper limit for U-abundance in iron meteorites, 0.001 ppb, is in agreement with its expected thermodynamic solubility in the metal phase. (author)

  13. Quantifying time in sedimentary successions by radio-isotopic dating of ash beds

    Science.gov (United States)

    Schaltegger, Urs

    2014-05-01

    global environmental and biotic disturbance (from ash bed analysis in biostratigraphically or cyclostratigraphically well constrained marine sections) with volcanic activity; examples are the Triassic-Jurassic boundary and the Central Atlantic Magmatic Province (Schoene et al. 2010), or the lower Toarcian oceanic anoxic event and the Karoo Province volcanism (Sell et al. in prep.). High-precision temporal correlations may also be obtained by combining high-precision U-Pb dating with biochronology in the Middle Triassic (Ovtcharova et al., in prep.), or by comparing U-Pb dates with astronomical timescales in the Upper Miocene (Wotzlaw et al., in prep.). References Guex, J., Schoene, B., Bartolini, A., Spangenberg, J., Schaltegger, U., O'Dogherty, L., et al. (2012). Geochronological constraints on post-extinction recovery of the ammonoids and carbon cycle perturbations during the Early Jurassic. Palaeogeography, Palaeoclimatology, Palaeoecology, 346-347(C), 1-11. Ovtcharova, M., Bucher, H., Schaltegger, U., Galfetti, T., Brayard, A., & Guex, J. (2006). New Early to Middle Triassic U-Pb ages from South China: Calibration with ammonoid biochronozones and implications for the timing of the Triassic biotic recovery. Earth and Planetary Science Letters, 243(3-4), 463-475. Ovtcharova, M., Goudemand, N., Galfetti, Th., Guodun, K., Hammer, O., Schaltegger, U., Bucher, H. Improving accuracy and precision of radio-isotopic and biochronological approaches in dating geological boundaries: The Early-Middle Triassic boundary case. In preparation. Schoene, B., Schaltegger, U., Brack, P., Latkoczy, C., Stracke, A., & Günther, D. (2012). Rates of magma differentiation and emplacement in a ballooning pluton recorded by U-Pb TIMS-TEA, Adamello batholith, Italy. Earth and Planetary Science Letters, 355-356, 162-173. Schoene, B., Latkoczy, C., Schaltegger, U., & Günther, D. (2010). A new method integrating high-precision U-Pb geochronology with zircon trace element analysis (U-Pb TIMS

  14. Reappraisal of Los Humeros Volcanic Complex by New U/Th Zircon and 40Ar/39Ar Dating: Implications for Greater Geothermal Potential

    Science.gov (United States)

    Carrasco-Núñez, G.; Bernal, J. P.; Dávila, P.; Jicha, B.; Giordano, G.; Hernández, J.

    2018-01-01

    Longevity and size of magmatic systems are fundamental factors for assessing the potential of a geothermal field. At Los Humeros volcanic complex (LHVC), the first caldera-forming event was reported at 460 ± 40 ka. New zircon U/Th and plagioclase 40Ar/39Ar dates of pre-, syn- and postcaldera volcanics allow a reappraisal of the evolution of the geothermally active LHVC. The age of the voluminous Xaltipan ignimbrite (115 km3 dense rock equivalent [DRE]) associated with the formation of the Los Humeros caldera is now constrained by two geochronometers (zircon U/Th and plagioclase 40Ar/39Ar dating) to 164 ± 4.2 ka, which postdates a long episode of precaldera volcanism (rhyolitic domes), the oldest age of which is 693.0 ± 1.9 ka (40Ar/39Ar). The inferred short residence time (around 5 ka) for the paroxysmal Xaltipan ignimbrite is indicative of rapid assembly of a large magma body and rejuvenation of the system due to recurrent recharge magmas, as it has been occurred in some other large magmatic systems. Younger ages than previously believed have been obtained also for the other voluminous explosive phases of the Faby fall tuff at ˜70 ka and the second caldera-forming Zaragoza ignimbrite with 15 km3 DRE, which erupted immediately after. Thus, the time interval that separates the two caldera-forming episodes at Los Humeros is only 94 kyr, which is a much shorter interval than suggested by previous K-Ar dates (410 kyr). This temporal proximity allows us to propose a caldera stage encompassing the Xaltipan and the Zaragoza ignimbrites, followed by emplacement at 44.8 ± 1.7 ka of rhyolitic magmas interpreted to represent a postcaldera, resurgent stage. Rhyolitic eruptions have also occurred during the Holocene (˜1,200 km3) and these new ages indicating much younger caldera-forming volcanism than previously believed are fundamental factors in the application of classical conductive models of heat resource, enhancing the heat production capacity and favor a higher

  15. Pb/Pb isochron ages and Pb isotope geochemistry of Bambui Group carbonate rocks from the southern portion of the Sao Francisco Basin

    International Nuclear Information System (INIS)

    Babinski, M.

    1993-01-01

    This study involves the establishment of chemical and analytical procedure for Pb/Pb dating of Neo proterozoic carbonate rocks and their application to obtaining isochron ages of Bambui Group rocks from the southern portion of the Sao Francisco Basin, Minas Gerais State. The Pb isotopic compositions and U and Pb concentrations determined on more than 90 samples (≅ 600 analyses) from Sete Lagoas do Jacare formations, Bambui Group, from different parts of the basin, showed four distinct types of Pb, here called types I, II, III and IV. Type I Pb was found in samples with low Pb concentrations and relatively high U concentrations. Type II Pb is present in samples with relatively high Pb concentrations and low U concentrations it is non-radiogenic crustal Pb. Type III Pb is also found in samples with high Pb concentrations and low U concentrations but it is radiogenic crustal Pb. Type IV Pb occurs in samples with U/Pb ratios lower than 1 and is intermediate in composition between Type III and Type I Pb. According to the data presented in this paper it is suggested that carbonate rocks from Sete Lagoas Formations were deposited before 686±69 Ma. Rocks from the Lagoa do Jacare Formation, contained only Type II Pb, which does not permit determination of a Pb/Pb age. During the interval from 690 to 500 Ma, the Pb isotope system of the carbonate rocks from the Sao Francisco Basin was disturbed, and in some areas it was totally reset. The imprecise U/Pb ages of 550-600 Ma obtained from some of the carbonate rocks reflect this disturbance. The ages determined in this study are in agreement with most of the published ages of the tectonism from the Brasiliano fold belts marginal to Sao Francisco Craton, showing that the isotopic systems of Sao Francisco Basin rocks were largely affected by brasiliano tectonism. (author)

  16. 230Th/234U age of a Mousterian site in France

    International Nuclear Information System (INIS)

    Schwarcz, H.P.; Blackwell, B.

    1983-01-01

    The 230 Th/ 234 U dating method has been used to determine the age of a travertine layer in the Pech 1 cave of Sarlat, South-West France. The reported age of 123 +- 15 kyr is consistent with deposition of this travertine during isotope state 5e, the warmest substage of the last inter-glacial. It is shown that this result is consistent with geological and paleontological estimates of the age of sediments filling the cave. (U.K.)

  17. Calorimetric investigation of (Pb0.45Bi0.55)-U system

    International Nuclear Information System (INIS)

    Agarwal, Renu; Samui, Pradeep; Mukerjee, S.K.; Ramakumar, K.L.

    2016-01-01

    Lead-bismuth eutectic (LBE) is being considered as a coolant of future high temperature reactors. As lead and bismuth are good spallation target material, they are planned to be used in accelerator driven reactor systems (ADS). Under the clad breach conditions these elements may come in direct contact with uranium of metallic fuel. In our labs, we had earlier investigated binary interactions of U-Pb and U-Bi. To assess interaction behaviour of 'U' with the eutectic melt, it was planned to measure enthalpy of mixing of LBE-U and compares it with the binary mixing. SEM-EDS studies of the product formed after mixing of LBE and 'U' were carried out to establish coexisting phases and their compositions. UPb 3 is Pb-rich compound of U-Pb and UBi 2 is Bi-rich compound of U-Bi. So addition of 'U' in (Pb 0.45 Bi 0.55 ) will result in formation of the more stable compound among UPb 3 and UBi 2

  18. Episodic Holocene eruption of the Salton Buttes rhyolites, California, from paleomagnetic, U-Th, and Ar/Ar dating

    Science.gov (United States)

    Wright, Heather M.; Vazquez, Jorge A.; Champion, Duane E.; Calvert, Andrew T.; Mangan, Margaret T.; Stelten, Mark E.; Cooper, Kari M.; Herzig, Charles; Schriener Jr., Alexander

    2015-01-01

    In the Salton Trough, CA, five rhyolite domes form the Salton Buttes: Mullet Island, Obsidian Butte, Rock Hill, North and South Red Hill, from oldest to youngest. Results presented here include 40Ar/39Ar anorthoclase ages, 238U-230Th zircon crystallization ages, and comparison of remanent paleomagnetic directions with the secular variation curve, which indicate that all domes are Holocene. 238U-230Th zircon crystallization ages are more precise than but within uncertainty of 40Ar/39Ar anorthoclase ages, suggesting that zircon crystallization proceeded until shortly before eruption in all cases except one. Remanent paleomagnetic directions require three eruption periods: (1) Mullet Island, (2) Obsidian Butte, and (3) Rock Hill, North Red Hill, and South Red Hill. Borehole cuttings logs document up to two shallow tephra layers. North and South Red Hills likely erupted within 100 years of each other, with a combined 238U-230Th zircon isochron age of: 2.83 ± 0.60 ka (2 sigma); paleomagnetic evidence suggests this age predates eruption by hundreds of years (1800 cal BP). Rock Hill erupted closely in time to these eruptions. The Obsidian Butte 238U-230Th isochron age (2.86 ± 0.96 ka) is nearly identical to the combined Red Hill age, but its Virtual Geomagnetic Pole position suggests a slightly older age. The age of aphyric Mullet Island dome is the least well constrained: zircon crystals are resorbed and the paleomagnetic direction is most distinct; possible Mullet Island ages include ca. 2300, 5900, 6900, and 7700 cal BP. Our results constrain the duration of Salton Buttes volcanism to between ca. 5900 and 500 years.

  19. Provenance analysis of the Late Triassic Yichuan Basin: constraints from zircon U-Pb geochronology

    Directory of Open Access Journals (Sweden)

    Meng Xianghong

    2018-03-01

    Full Text Available Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS U-Pb dating has been performed on detrital zircons from the Chunshuyao Formation sandstone of Yichuan Basin. The ages of 85 detrital zircon grains are divided into three groups: 252-290 Ma, 1740-2000 Ma, and 2400-2600 Ma. The lack of Early Paleozoic and Neoproterozoic U-Pb ages indicates that there is no input from the Qinling Orogen, because the Qinling Orogen is characterized by Paleozoic and Neoproterozoic material. In combination with previous research, we suggest that the source of the Chunshuyao Formation is most likely recycled from previous sedimentary rocks from the North China Craton. In the Late Triassic, the Funiu ancient land was uplifted which prevented source material from the Qinling Orogen. Owing to the Indosinian orogeny, the strata to the east of the North China Craton were uplifted and eroded. The Yichuan Basin received detrital material from the North China Craton.

  20. 75 FR 17742 - Filing Dates for the Georgia Special Election in the 9th Congressional District

    Science.gov (United States)

    2010-04-07

    ... 9th Congressional District AGENCY: Federal Election Commission. ACTION: Notice of filing dates for special election. SUMMARY: Georgia has scheduled a special general election on May 11, 2010, to fill the U... participate in the Georgia Special General and Special Runoff Elections shall file a 12-day Pre-General Report...

  1. 77 FR 56208 - Filing Dates for the Kentucky Special Election in the 4th Congressional District

    Science.gov (United States)

    2012-09-12

    ... 4th Congressional District AGENCY: Federal Election Commission. ACTION: Notice of filing dates for special election. SUMMARY: Kentucky has scheduled a general election on November 6, 2012, to fill the U.S... required to file reports in connection with the Special General Election on November 6, 2012, shall file a...

  2. Geochemie a zirkonové U-Pb stáří derflického granodioritu z dyjského masivu

    Czech Academy of Sciences Publication Activity Database

    Svojtka, Martin; Breiter, Karel; Ďurišová, Jana; Ackerman, Lukáš; Veselovský, F.; Šmerda, J.

    2017-01-01

    Roč. 50, č. 1 (2017), s. 17-24 ISSN 0514-8057 R&D Projects: GA ČR GA13-15390S Institutional support: RVO:67985831 Keywords : Bohemian Massif * Cadomian granitoids * Thaya (Dyje) Massif * zircon U-Pb dating Subject RIV: DB - Geology ; Mineralogy OBOR OECD: Geology

  3. Calymmian magmatism in the basement of the Jauru Terrain (Rondonian - San Ignacio Province), Amazon Craton: U-Pb and Sm-Nd geochemistry and geochronology

    Energy Technology Data Exchange (ETDEWEB)

    Fachetti, Frankie James Serrano; Costa, Ana Claudia Dantas da; Silva, Carlos Humberto da, E-mail: frankiefachetti@hotmail.com, E-mail: acdcosta@ufmt.br, E-mail: chsilva@ufmt.br [Universidade Federal de Mato Grosso (UFMT), Cuiaba, MT (Brazil). Instituto de Ciencias Exatas e da Terra

    2016-11-01

    The Taquarussu Orthogneiss and the Guadalupe Granodiorite, part of the Rondonian-San Ignacio Province basement, southwest of the Amazonian Craton, correspond to oriented bodies with a NW trend. The rocks show granodiorite composition with minor occurrences of coarse grained monzogranites consisting essentially of plagioclase, quartz, microcline, orthoclase and biotite. The accessory minerals are amphibole, titanite, garnet, apatite, epidote, zircon and opaque. The geochemical data indicate that the rocks are classified as granodiorites and monzogranites, with an intermediate to acid magmatism, sub-alkaline character, from the calc-alkaline to the high-K calc-alkaline series, with alumina ratios ranging from metaluminous to lightly peraluminous. The rocks were classified as generated in volcanic islands arc environment and the U-Pb data (SHRIMP zircon) show a concord age 1575 ± 6 Ma. The Sm-Nd model age (T{sub DM}) is 1.63 Ga with εNd (t = 1.57 Ga) ranging from -1.52 to +0.78. These data indicate that these rocks are probably a juvenile crust with a possible contamination of crustal rocks. (author)

  4. Determination of Pb-210 and U-238 in environment samples by direct measurement using low energy γ spectrometry

    International Nuclear Information System (INIS)

    Godoy, J.M. de; Mendonca, A.H.; Sachett, I.A.

    1985-01-01

    The determination of Pb-210 and U-238 by γ spectrometry in environmental samples was carried out using the 47 KeV (4%) line for Pb-210 and the 63 KeV (3,9%) line from Th-234 to U-238. An intrinsic Ge detector with 0,8 KeV resolution for the 60 KeV line of Am-41 was employed. The eficiency was determined by using the radionuclide water solution. The samples were measured in a cylindric geometry with 7 cm diameter and 3 cm hight with a mass ranging from 25 to 180g, depending on the density. The self absorption correction factor for each sample was determined by using an external source of Pb-210 and Am-241. The results showed good agreement with the radiochemical analysis values. The diferences were lower than 20%; the detection limit changed from sample to sample staying on the pCi/g range for the 200 minutes couting time. (Author) [pt

  5. IRMM-1000a and IRMM-1000b. Uranium reference materials certified for the production date based on the 230Th/234U radiochronometer. Part II. Certification

    International Nuclear Information System (INIS)

    Venchiarutti, C.; Richter, S.; Jakopic, R.; Aregbe, Y.; Varga, Z.; Nicholl, A.; Krajko, J.; Mayer, K.

    2016-01-01

    The IRMM-1000a and IRMM-1000b uranium reference materials, of 20 and 50 mg uranium, respectively, were produced by the European Commission Joint Research Centre's Institute for Reference Materials and Measurements (EC-JRC-IRMM) in collaboration with the Institute for Transuranium Elements (EC-JRC-ITU). They are novel uranium reference materials certified for the production date based on the 230 Th/ 234 U radiochronometer, i.e. the date of the last chemical separation of these two radionuclides. The certified reference value and its uncertainty, homogeneity and stability of the material were established in accordance with the ISO Guide 34:2009 and the 'Guide to the Expression of Uncertainty in Measurement'. (author)

  6. U-Pb, Re-Os and Ar-Ar dating of the Linghou polymetallic deposit, Southeastern China: Implications for metallogenesis of the Qingzhou-Hangzhou metallogenic belt

    Science.gov (United States)

    Tang, Yanwen; Xie, Yuling; Liu, Liang; Lan, Tingguan; Yang, Jianling; Sebastien, Meffre; Yin, Rongchao; Liang, Songsong; Zhou, Limin

    2017-04-01

    The Qingzhou-Hangzhou metallogenic belt (QHMB) in Southeastern China has gained increasingly attention in recent years. However, due to the lack of reliable ages on intrusions and associated deposits in this belt, the tectonic setting and metallogenesis of the QHMB have not been well understood. The Linghou polymetallic deposit in northwestern Zhejiang Province is one of the typical deposits of the QHMB. According to the field relationships, this deposit consists of the early Cu-Au-Ag and the late Pb-Zn-Cu mineralization stages. Molybdenite samples with a mineral assemblage of molybdenite-chalcopyrite-pyrite ± quartz are collected from the copper mining tunnel near the Cu-Au-Ag ore bodies. Six molybdenite samples give the Re-Os model ages varying from 160.3 to 164.1 Ma and yield a mean age of 162.2 ± 1.4 Ma for the Cu-Au-Ag mineralization. Hydrothermal muscovite gives a well-defined Ar-Ar isochron age of 160.2 ± 1.1 Ma for the Pb-Zn-Cu mineralization. Three phases of granodioritic porphyry have been distinguished in this deposit, and LA-ICP-MS zircon U-Pb dating shows that they have formed at 158.8 ± 2.4 Ma, 158.3 ± 1.9 Ma and 160.6 ± 2.1 Ma, comparable to the obtained ages of the Cu-Au-Ag and Pb-Zn-Cu mineralization. Therefore, these intrusive rocks have a close temporal and spatial relationship with the Cu-Au-Ag and Pb-Zn-Cu ore bodies. The presences of skarn minerals (e.g., garnet) and vein-type ores, together with the previous fluid inclusion and H-O-C-S-Pb isotopic data, clearly indicate that the Cu-Au-Ag and Pb-Zn-Cu mineralization are genetically related to these granodiorite porphyries. This conclusion excludes the possibility that this deposit is of ;SEDEX; type and formed in a sag basin of continental rifts setting as previously proposed. Instead, it is proposed that the Linghou polymetallic and other similar deposits in the QHMB, such as the 150-160 Ma Yongping porphyry-skarn Cu-Mo, Dongxiang porphyry? Cu, Shuikoushan/Kangjiawang skarn Pb

  7. Archean and proterozoic in the West-European Hercynian chain: isotopic geochemistry (Sr-Nd-Pb) and U-Pb geochronology on zircons

    International Nuclear Information System (INIS)

    Guerrot, C.

    1989-01-01

    The first part of this research thesis reports the study of isotopic (Sr-Nd-Pb) geochemistry and U-Pb geochronology on zircons in the immersed granulites of the Bay of Biscay: U-Pb geochronology on zircons, Nd isotopic geochemistry, Sr isotopic geochemistry, common Pb, Rb-Sr, Sm-Nd and rare earth data on minerals, comparison with other European granulites, comparison with West-Africa, study of Archean and proterozoic in the Hercynian chain. The second part reports the study of the U-Pb geochronology on zircon in the Cadomian, and the third part addresses the Sr-Nd isotopic geochemistry of some Cadomian granitoid, and the crust contamination in different regions [fr

  8. A Reassessment of U-Th and 14C Ages for Late-Glacial High-Frequency Hydrological Events at Searles Lake, California

    Science.gov (United States)

    Lin, J.C.; Broecker, W.S.; Hemming, S.R.; Hajdas, I.; Anderson, Robert F.; Smith, G.I.; Kelley, M.; Bonani, G.

    1998-01-01

    U-Th isochron ages of tufas formed on shorelines suggest that the last pluvial event in Lake Lahontan and Searles Lake was synchronous at about 16,500 cal yr B.P. (equivalent to a radiocarbon age of between 14,000 and 13,500 yr B.P.), whereas the timing of this pluvial event determined by radiocarbon dating is on the order of 1000 yr younger. The timing of seven distinct periods of near desiccation in Searles Lake during late-glacial time has been reinvestigated for U-Th age determination by mass spectrometry. U-Th dating of evaporite layers in the interbedded mud and salt unit called the Lower Salt in Searles Lake was hampered by the uncertainty in assessing the initial 230Th/232Th of the samples. The resulting ages, corrected by a conservative range of initial 230Th/ 232Th ratios, suggest close correlation of the abrupt changes recorded in Greenland ice cores (Dansgaard-Oeschger events) and wet-dry conditions in Searles Lake between 35,000 and 24,000 Cal yr B.P. ?? 1998 University of Washington.

  9. The Heart of China revisited: II Early Paleozoic (ultra)high-pressure and (ultra)high-temperature metamorphic Qinling orogenic collage

    Science.gov (United States)

    Bader, Thomas; Franz, Leander; Ratschbacher, Lothar; de Capitani, Christian; Webb, A. Alexander G.; Yang, Zhao; Pfänder, Jörg A.; Hofmann, Mandy; Linnemann, Ulf

    2013-07-01

    Orogens with multiple (ultra)high-pressure ((U)HP) and (ultra)high-temperature ((U)HT) metamorphic events provide a complex but telling record of oceanic and continental interaction. The Early Paleozoic history of the "Heart of China," the Qinling orogenic collage, offers snapshots of at least three (U)HP and two (U)HT metamorphic events. The preservation of remnants of both oceanic and continental domains together with a ≥110 Myr record of magmatism allows the reconstruction of the processes that resulted in this disparate metamorphism. Herein, we first illuminate the pressure-temperature-time (P-T-t) evolution of the Early Paleozoic (U)HP and (U)HT events by refining the petrographic descriptions and P-T estimates, assess published, and employ new U/Th-Pb zircon, monazite, and titanite, and 40Ar-39Ar phengite geochronology to date the magmatic and metamorphic events. Then we explore how the metamorphic and magmatic events are related tectonically and how they elucidate the affinities among the various complexes in the Qinling orogenic collage. We argue that a Meso-Neoproterozoic crustal fragment—the Qinling complex—localized subduction-accretion events that involved subduction, oceanic-arc formation, and back-arc spreading along its northern margin, and mtantle-wedge exhumation and spreading-ridge subduction along its southern margin.

  10. Lead 210 and moss-increment dating of two Finnish Sphagnum hummocks

    International Nuclear Information System (INIS)

    El-Daoushy, F.

    1982-01-01

    A comparison is presented of 210 Pb dating data with mass-increment dates of selected peat material from Finland. The measurements of 210 Pb were carried out by determining the granddaughter product 210 Po by means of the isotope dilution. The ages in 210 Pb yr were calculated using the constant initial concentration and the constant rate of supply models. (U.K.)

  11. Methodology of the carbonates dating by the uranium series unbalance by mass spectrometry

    International Nuclear Information System (INIS)

    Lima, Barbara Alcantara Ferreira

    2006-01-01

    There are many dating methods largely used according to the kind of material to be dated. Methods that rely on the time-dependency of geochemical disequilibrium between daughter and parent isotope, from the '2 38 U, 235 U and 232 Th natural decay system, whose final members are stable Pb isotopes, are the most useful in a broader variety of geological, hydrological and archaeological problems. The use of this method in cave deposits like speleothems and clastic sediments proved to be a powerful tool to study past climatic and environmental changes. Speleothems like stalagmites are frequently used in paleoenvironmental interpretations. This method may be applied to rocks and underground water dating, erosion studies, transport and sedimentation processes, interactions between rock-groundwater, among others. The present work focuses on the chemical preparation of the U-Th method including the chemical procedures to avoid laboratory contamination and the mass spectrometer precise calibration in order to get high reproducibility. The process has many steps: samples preparation; digestion and chromatographic separation using standards and samples already dated in other laboratories; determination of the isotopic ratios by mass spectrometers, and a case study based on a stalagmite from Joao Arruda cave, Bonito, Mato Grosso State, Brazil. The obtained data shows the reliability of the method works, mostly in relation to co precipitation of U and Th and to the chromatographic separation of these metals. It is also observed that the obtained dates are within the errors for each sample and are very similar to the dates obtained in other laboratories (validated to this methodology). Further improvements are necessary to achieve better results, mostly related to the reading method in the MC-ICP-MS. The case study in the JA-5 stalagmite shows that it stopped growing around 2,0 ky. This is a different result from that obtained on JA-3 stalagmite, from the same cave, but placed

  12. U-Pb isotope systematics in josephinites and associated rocks

    Energy Technology Data Exchange (ETDEWEB)

    Goepel, C.; Manhes, G.; Allegre, C.J. (Lab. Geochimie et Cosmochimie, I.P.G., 75 - Paris (France))

    1990-02-01

    Josephinite nodules, composed of metallic nickel iron alloy intergrown with andradite garnet, are found in the peridotitic section of an obducted ophiolite in SW Oregon. The origin of josephinite is widely debated: for example, previous investigation have proposed it as a byproduct of low temperature synserpentinization processes linked to the intrusion of dikes or and its derivation from primitive mantle, conceivably from as deep as the core mantle boundary. We report U-Pb data from josephinites, wyrdite (a rock associated with josephinite) consisting of rutile and ilmente intergrown with silicates, and their surrounding rocks (hornblende diorites and harzburgites). The measured Pb isotopic composition of all decontaminated, leached josephinite metal samples plots in the Pb-Pb diagram just above/in the MORB field, while the first leachates are characterized by higher {sup 207}Pb/{sup 204}Pb ratios. The isotopic Pb composition measured in the leachates of the wyrdite defines a line whose slope corresponds to an age of 159{plus minus}8 Myr. The harzburgites show a wide spread in Pb isotopic compositions; all samples lie above the MORB field and three samples plot to the left side of the 4.55 AE geochron. The hornblende diorite dikes, characterized by the highest U and Pb concentrations of all studied rocks, plot in the MORB field. None of these different rocks is characterized by a single or homogeneous Pb composition. All samples are affected by secondary alteration processes: the circulation of hydrothermal fluids disturbed the dikes and ultramafic rocks and serpentinization processes have affected harzburgites, josephinites, and wyrdites. Thus the Pb isotopic composition measured today represents a mixture of initial Pb, radiogenic Pb and inherited Pb in variable proportions. Concerning the origin of josephinite these results show a close relationship between josephinite, wyrdite, and the dikes. (orig./WB).

  13. U-Th dating reveals regional-scale decline of branching Acropora corals on the Great Barrier Reef over the past century

    Science.gov (United States)

    Clark, Tara R.; Roff, George; Zhao, Jian-xin; Feng, Yue-xing; Done, Terence J.; McCook, Laurence J.; Pandolfi, John M.

    2017-09-01

    Hard coral cover on the Great Barrier Reef (GBR) is on a trajectory of decline. However, little is known about past coral mortality before the advent of long-term monitoring (circa 1980s). Using paleoecological analysis and high-precision uranium-thorium (U-Th) dating, we reveal an extensive loss of branching Acropora corals and changes in coral community structure in the Palm Islands region of the central GBR over the past century. In 2008, dead coral assemblages were dominated by large, branching Acropora and living coral assemblages by genera typically found in turbid inshore environments. The timing of Acropora mortality was found to be occasionally synchronous among reefs and frequently linked to discrete disturbance events, occurring in the 1920s to 1960s and again in the 1980s to 1990s. Surveys conducted in 2014 revealed low Acropora cover (shifted baseline.

  14. U-Th-He dating of diamond-forming C-O-H fluids and mantle metasomatic events

    Science.gov (United States)

    Weiss, Y.; Class, C.; Goldstein, S. L.; Winckler, G.; Kiro, Y.

    2017-12-01

    Carbon- and water-rich (C-O-H) fluids play important roles in the global material circulation, deep Earth processes, and have major impacts on the sub-continental lithospheric mantle (SCLM). Yet the origin and composition of C-O-H fluids, and the timing of fluid-rock interaction, are poorly constrained. `Fibrous' diamonds encapsulate C-O-H mantle fluids as μm-scale high-density fluid (HDF) inclusions. They can be directly sampled, and offer unique opportunities to investigate metasomatic events involving C-O-H fluids and the SCLM through Earth history. Until now no technique has provided reliable age constraints on HDFs. We applied a new in-vacuum crushing technique to determine the He abundances and 3He/4He ratios of HDFs in diamonds from the Kaapvaal lithosphere, South Africa. Three diamonds with saline HDFs have 3He/4He=3-4Ra. In 4He/3He vs 238U/3He space they define an `isochron' age of 96±45Ma, representing the first radiometric age reported for HDFs, and thus for C-O-H mantle fluids. In addition, a diamond with silicic HDFs and two that carry carbonatitic HDFs have low 3He/4He=0.07-0.6Ra. Using the measured U, Th, 4He and 3He contents of these diamonds, and the equation for 4He production from U-Th decay, we calculate 3He/4He as a function of time. Metasomatic fluids are derived from MORB, SCLM or subducted components with R/Ra=3-10, and this is assumed as the HDFs initial composition. The silicic and carbonatitic HDFs signify two older metasomatic events at 350 and 850 Ma, respectively. Thus, our new data reveal 3 metasomatic episodes in the Kaapvaal SCLM during the last 1 Ga, each by a different metasomatic agent. These 3 episodes correspond to late-Mesozoic kimberlite eruptions at 85 Ma, and the regional Namaqua-Natal and Damara Orogenies at 1 Ga and 500 Ma. We propose that the radioactive U-Th-He system in HDF-bearing diamonds can be used as a tool to provide meaningful radiometric ages of deep C-O-H fluids, and the timing of SCLM metasomatic events.

  15. Extraction of Th and U from Swiss granites

    International Nuclear Information System (INIS)

    Bajo, C.

    1980-12-01

    The extraction, at the laboratory level, of U and Th from Swiss granites is discussed. The Mittagfluh, Bergell and Rotondo granites and the Giuv syenite offered a wide range of U and Th concentrations; 7.7 to 20.0 ppm U and 25.5 to 67.0 ppm Th. U and Th were determined in the leach solutions by the fission track method and by spectrophotometry, respectively. Samples containing less than 0.3 μg U and 4 μg Th, could be measured with an accuracy of 10% for U and 5% for Th. Leach tests were performed during which the following parameters were varied: granite-type, grain size, acid-type, acid concentration, temperature and time. There were very great leaching differences between the granites studied. Temperature was the most important parameter. Sharp differences in extraction occurred between 20 0 C, 50 0 C and 80 0 C. At 80 0 C, more than 85% U and Th were extracted. The extraction curve (percent extracted as a function of time) of aliquots sampled after 1, 2, 4, 8, 12 and 24 hours showed a plateau after 8 hours. The half life of the reaction was between one and two hours. As a general rule, Th was better extracted than U. (Auth.)

  16. Sedimentation rate and {sup 210}Pb sediment dating at Apipucos reservoir, Recife, Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Figueiredo, Marcela D.C. de; Silva, Danubia B. da; Cunha, Manuela S. da; Rodrigues, Kelia R.G.; Pedroza, Eryka H.; Melo, Roberto T. de; Oliveira, Aristides; Hazin, Clovis A.; Souza, Vivianne L.B. de, E-mail: rtmelo@cnen.gov.b, E-mail: chazin@cnen.gov.b, E-mail: vlsouza@cnen.gov.b [Centro Regional de Ciencias Nucleares (CRCN-NE/CNEN-PE), Recife, PE (Brazil)

    2011-07-01

    The Apipucos Reservoir is located in Recife, State of Pernambuco, and, several districts of the metropolitan area use this reservoir to dispose waste and sewage. Dating sediments uses {sup 210}Pb from the atmosphere which is formed as a result of {sup 222}Rn emanation from the soil. Atmospheric lead, carried by rain, is called non-supported {sup 21}'0Pb, to differentiate it from the one contained in the sediment, in balance with the {sup 226}Ra. The model chosen for dating sediments depends on certain conditions: in an environment where the amount of sediment influx can vary, the constant rate of supply model is adopted. On the other hand, in environments where the sedimentation rate is constant and the sediment can be considered to have a constant initial concentration of unsupported {sup 210}Pb and the (CIC) model is applied. A 70-cm long, 5-cm internal-diameter wide core was collected for sediment dating. Each core was sliced, into 5 or 10 cm intervals. Samples were dried at 105 deg C, and about 5 g dry material from each sample was dissolved with acids. The {sup 210}Pb and {sup 226}Ra contents were separated and determined by beta and alpha counting by using a gas-flow proportional counter. Sediment ages were calculated by the two models, and for the second and fourth sampling points, both models could be used. The results showed an increase in sedimentation rate over the last 50 - 60 years. We can conclude that the top sediment layer is dated from 30 years ago. We can also conclude that the CRS is the best applicable model to use in this area. (author)

  17. Interaction between U and Th on their uptake, distribution, and toxicity in V S. alfredii based on the phytoremediation of U and Th.

    Science.gov (United States)

    Huang, Zhenling; Tang, Siqun; Zhang, Lu; Ma, Lijian; Ding, Songdong; Du, Liang; Zhang, Dong; Jin, Yongdong; Wang, Ruibing; Huang, Chao; Xia, Chuanqin

    2017-01-01

    Variant Sedum alfredii Hance (V S. alfredii) could simultaneously take up U and Th from water with the highest concentrations recorded as 1.84 × 10 4 and 6.72 × 10 3  mg/kg in the roots, respectively. Th stimulated U uptake by V S. alfredii roots at Th 10 (10 μM of Th), however, the opposite was observed at Th 100 (100 μM of Th). A similar result was found in the effect of U on the uptake of Th by V S. alfredii. Subcellular fractionation studies of V S. alfredii indicated that U and Th were mainly stored in cell wall fraction, and much less was found in organelle and soluble fractions. Chemical form examination results showed that water-soluble U and Th were the predominant chemical forms in this plant. Addition of the other radionuclide in aqueous solutions altered the concentration and percentage of U or Th in cell wall fraction and in water-soluble form, resulting in the change of the uptake capacity of U or Th by V S. alfredii roots. Comparing with single U or Th treatment, the plant cells revealed more swollen chloroplasts and enhanced thickening in cell walls under the U 100  + Th 100 treatment, as observed by TEM. Those results collectively displayed that V S. alfredii may be utilized as a potential plant to simultaneously remove U and Th from aqueous solutions (rhizofiltration).

  18. New data for paleoprotherozoic PGE-bearing anorthosite of Kandalaksha massif (Baltic shield): U-Pb and Sm-Nd ages

    Science.gov (United States)

    Steshenko, Ekaterina; Bayanova, Tamara; Serov, Pavel

    2015-04-01

    The aims of this researches were to study the isotope U-Pb age of zircon and rutile and Sm-Nd (rock forming and sulphide minerals) on Kandalaksha anorthosite massif due to study of polimetamorphic history. In marginal zone firstly have been obtained the presence of sulphide mineralization with PGE (Chashchin, Petrov , 2013). Kandalaksha massif is located in the N-E part of Baltic shield and consists of three parts. Marginal zone (mesocratic metanorite) lies at the base of the massif. Main zone is composed of leucocratic metagabbro. The upper zone is alteration of mataanorthosite and leucocratic metagabbro. All rocks were subjected to granulate polymetamorphism. Two fractions of single grains from anorthosite of the massif gave precise U-Pb age, which is equal to 2450± 3 Ma. Leucocratic gabbro-norite were dated by U-Pb method, with age up to 2230 ± 10 Ma. This age reflects the time of granulite metamorphism according to data of (Mitrofanov, Nirovich, 2003). Two fractions of rutile have been analyzed by U-Pb method and reflect age of 1700 ± 10 Ma. It is known that the closure temperature of U-Pb system rutile is 400-450 ° C (Mezger et.al., 1989), thus cooling processes of massif rocks to these temperatures was about 1.7 Ga. These data reflect one of the stages of metamorphic alteration of the massif. Three stages of metamorphism are distinguished by Sm-Nd method. Isotope Sm-Nd dating on Cpx-WR line gives the age of 2311 Ma which suggested of high pressure granulite metamorphism. Moreover Cpx-Pl line reflect the age 1908 Ma of low pressure granulite metamorphism. Also two-points (Grt-Rt) Sm-Nd isochrone yield the age 1687 Ma of the last metamorphic alterations in Kandalaksha anorthosite massif. Model Sm-Nd age of the leucocratic gabbro-norite is 2796 Ma with positive ɛNd (+0.32). It means that the source of gabbro-norite was mantle reservoir. All investigations are devoted to memory of academician PAS F. MItrofanov which was a leader of scientific school for

  19. Characterization and zircon SHRIMP U-Pb geochronology of the subvolcanic rocks from Yarumalito Porphyry System, Marmato District, Colombia; Caracterizacao e geocronologia SHRIMP U-Pb em zircao das rochas subvulcanicas do sistema porfiro Yarumalito, Distrito de Marmato, Colombia

    Energy Technology Data Exchange (ETDEWEB)

    Henrichs, Isadora A.; Frantz, Jose Carlos; Marques, Juliana C.; Castoldi, Marco S., E-mail: isahenrichs@gmail.com, E-mail: jose.frantz@ufrgs.br, E-mail: juliana.marques@ufrgs.br [Universidade Federal do Rio Grande do Sul (UFRS), Porto Alegre, RS (Brazil). Instituto de Geociencias; Ordonez-Carmona, Oswaldo, E-mail: oswaldo.geologo@gmail.com [Universidad Nacional de Colombia, Medellin (Colombia). Facultad de Minas; Sato, Kei, E-mail: keisato@usp.br [Universidade de Sao Paulo (USP), Sao Paulo, SP (Brazil). Centro de Pesquisas Geocronologicas

    2014-09-15

    The mining District of Marmato, located in the Central Cordillera, is considered one of the oldest gold districts in Colombia and its exploration dates back to the Inca’s times, being exploited regularly for more than a thousand years. Inserted in this context lies the Yarumalito porphyry system (YPS), characterized to concentrate ore in structure related veins and stockworks. The YPS is related to the Miocene magmatism of the Combia Formation. In this paper, the subvolcanic rocks directly associated with the mineralized zones were described in order to obtain U-Pb ages in zircon to the intrusions. Selected samples from two fertile intrusions, one andesitic (more abundant in the area) and other dioritic (more restricted), were carefully described and dated by SHRIMP. The results points to a very restricted interval for the ages, with weighted average {sup 206}Pb/{sup 238}U varying from 7,00 ± 0,15 Ma for the andesitic porphyry and 6.95 ± 0.16 Ma for the dioritic porphyry. These results constrain the Yarumalito system to the final stages of the Combia magmatism and suggest a brief period for the crystallization of the mineralized subvolcanic rocks in the area and in the Marmato District. (author)

  20. U/Th dating by SHRIMP RG ion-microprobe mass spectrometry using single ion-exchange beads

    Science.gov (United States)

    Bischoff, J.L.; Wooden, J.; Murphy, F.; Williams, Ross W.

    2005-01-01

    We present a new analytical method for U-series isotopes using the SHRIMP RG (Sensitive High mass Resolution Ion MicroProbe) mass spectrometer that utilizes the preconcentration of the U-series isotopes from a sample onto a single ion-exchange bead. Ion-microprobe mass spectrometry is capable of producing Th ionization efficiencies in excess of 2%. Analytical precision is typically better than alpha spectroscopy, but not as good as thermal ionization mass spectroscopy (TIMS) and inductively coupled plasma multicollector mass spectrometry (ICP-MS). Like TIMS and ICP-MS the method allows analysis of small samples sizes, but also adds the advantage of rapidity of analysis. A major advantage of ion-microprobe analysis is that U and Th isotopes are analyzed in the same bead, simplifying the process of chemical separation. Analytical time on the instrument is ???60 min per sample, and a single instrument-loading can accommodate 15-20 samples to be analyzed in a 24-h day. An additional advantage is that the method allows multiple reanalyses of the same bead and that samples can be archived for reanalysis at a later time. Because the ion beam excavates a pit only a few ??m deep, the mount can later be repolished and reanalyzed numerous times. The method described of preconcentrating a low concentration sample onto a small conductive substrate to allow ion-microprobe mass spectrometry is potentially applicable to many other systems. Copyright ?? 2005 Elsevier Ltd.

  1. Regulation of ex vivo tyrosine hydroxylase (TH) activity is not altered by chronic lead (Pb) exposure

    International Nuclear Information System (INIS)

    Lasley, S.M.; Green, M.C.

    1991-01-01

    Previous studies have suggested that chronic Pb exposure results in impaired regulation of CNS dopamine (DA) synthesis in rats. The present study was designed to directly assess TH activity in exposed animals compared to controls, employing a pharmacological model that assesses the functional status of dopaminergic synthesis-modulating autoreceptors. At birth dams received 0.2% Pb acetate in drinking water. Offspring were weaned to and maintained on the same solution until termination at 60 or 120 days. Rats were given saline or a DA agonist (EMD 23448 or CGS 15855A) 45 min before sacrifice followed 15 min later by gamma-butyrolactone (GBL). Regional TH activity was measured by a modification of the tritium release method. DA content was determined by liquid chromatography. The ability of EMD 23448 to prevent the GBL-induced increase in DA content was significantly diminished in caudate-putamen (C-P) of exposed rats compared to controls, similar to previous observations. However, an analogous effect of Pb on TH activity in this drug model was not observed using CGS 15855A in rats either 60 or 120 days of age. These findings suggest that chronic Pb exposure has no effect on autoreceptor-mediated regulation of TH in DA neurons when TH activity is measured ex vivo

  2. Growth and Yield Stimulation of Winter Oilseed Rape (Brasssica Napus L. by Mg-Titanit Fertiliser

    Directory of Open Access Journals (Sweden)

    Kováčik Peter

    2014-12-01

    Full Text Available The effort to achieve higher yields at the required qualitative level has led to the intensive studying the problems of the rational usage of the titanium containing fertilisers by the agricultural research in the course the previous thirty years. Therefore, the objective of the experiment was to evaluate the impact of two doses of Mg-Titanit (0.2 l/ha and 0.4 l/ha on the formation of the aboveground and underground phytomass, also on the total chlorophyll in leaves, on the titanium and nitrogen content in the seeds and straw, on the quantity and quality of winter rape yield. The doses were applied two or three times on the leaves of winter rape (BBCH 50-52, BBCH 59, BBCH 66-67. The experiment was realized on the Haplic Chernozem (48°42´ N, 17°70´ E - Western Slovakia during two farming years (2009/2010 and 2010/2011. The results showed that all three applications of Mg-Titanit in both doses stimulated the formation of aboveground and underground phytomass of winter rape. The highest growth of phytomass was detected after the second application. The application of Mg-Titanit in the growth phases BBCH 50-52 and BBCH 59 increased the contents of both chlorophylls (a and b, where the growth of chlorophyll b content was more considerable than the growth of chlorophyll a content. The third spraying by Mg-Titanit decreased the content of the total chlorophyll. The application of Mg-Titanit had the positive impact on the yield of seeds, straw and fat content in the winter oilseed rape seeds.

  3. High-resolution tephrochronology of the Wilson Creek Formation (Mono Lake, California) and Laschamp event using 238U-230Th SIMS dating of accessory mineral rims

    Science.gov (United States)

    Vazquez, Jorge A.; Lidzbarski, Marsha I.

    2012-12-01

    Sediments of the Wilson Creek Formation surrounding Mono Lake preserve a high-resolution archive of glacial and pluvial responses along the eastern Sierra Nevada due to late Pleistocene climate change. An absolute chronology for the Wilson Creek stratigraphy is critical for correlating the paleoclimate record to other archives in the western U.S. and the North Atlantic region. However, multiple attempts to date the Wilson Creek stratigraphy using carbonates and tephras yield discordant results due to open-system effects and radiocarbon reservoir uncertainties as well as abundant xenocrysts. New ion microprobe 238U-230Th dating of the final increments of crystallization recorded by allanite and zircon autocrysts from juvenile pyroclasts yield ages that effectively date eruption of key tephra beds and delimit the timing of basal Wilson Creek sedimentation to the interval between 26.8±2.1 and 61.7±1.9 ka. Tephra (Ash 15) erupted during the geomagnetic excursion originally designated the Mono Lake excursion yields an age of 40.8±1.9 ka, indicating that the event is instead the Laschamp excursion. The new ages support a depositional chronology from magnetostratigraphy that indicates quasi-synchronous glacial and hydrologic responses in the Sierra Nevada and Mono Basin to regional climate change, with intervals of lake filling and glacial-snowpack melting that are in phase with peaks in spring insolation.

  4. High-resolution tephrochronology of the Wilson Creek Formation (Mono Lake, California) and Laschamp event using 238U-230Th SIMS dating of accessory mineral rims

    Science.gov (United States)

    Vazquez, Jorge A.; Lidzbarski, Marsha I.

    2012-01-01

    Sediments of the Wilson Creek Formation surrounding Mono Lake preserve a high-resolution archive of glacial and pluvial responses along the eastern Sierra Nevada due to late Pleistocene climate change. An absolute chronology for the Wilson Creek stratigraphy is critical for correlating the paleoclimate record to other archives in the western U.S. and the North Atlantic region. However, multiple attempts to date the Wilson Creek stratigraphy using carbonates and tephras yield discordant results due to open-system effects and radiocarbon reservoir uncertainties as well as abundant xenocrysts. New ion microprobe 238U-230Th dating of the final increments of crystallization recorded by allanite and zircon autocrysts from juvenile pyroclasts yield ages that effectively date eruption of key tephra beds and delimit the timing of basal Wilson Creek sedimentation to the interval between 26.8±2.1 and 61.7±1.9 ka. Tephra (Ash 15) erupted during the geomagnetic excursion originally designated the Mono Lake excursion yields an age of 40.8±1.9 ka, indicating that the event is instead the Laschamp excursion. The new ages support a depositional chronology from magnetostratigraphy that indicates quasi-synchronous glacial and hydrologic responses in the Sierra Nevada and Mono Basin to regional climate change, with intervals of lake filling and glacial-snowpack melting that are in phase with peaks in spring insolation.

  5. Uranium content and U-Th dating of fossil bones and dental tissues from Lazaret cave

    International Nuclear Information System (INIS)

    Michel, V.; Falgueres, Ch.; Yokoyama, Y.

    1997-01-01

    Fossil bone and dental tissues from Lazaret cave and modern ones are here the subject of a comparative microscopical study. Porous tissues such as dentine and bone have retained their Haversian and Tomes canals respectively. However, cracked areas with calcite were detected, indicating a water percolation within porous tissues and an alteration of tissue in places. In addition, compact fossil enamel is particularly well preserved. These results are essential for U-Tb and ESR dating application. Uranium contents, U-Tb ages of two fossil mandibular tissues, two tibias and of six burnt fossil bones are presented and discussed. (authors)

  6. 238U, 234U and 230Th in uranium miners' lungs

    International Nuclear Information System (INIS)

    Singh, M.P.; Wrenn, M.E.; Archer, V.E.; Saccomanno, G.

    1981-01-01

    Fourteen uranium miners' lungs from Colorado plateau were collected at autopsy and the concentrations of 238 U, 234 U and 230 Th were determined by radiochemical procedures utilizing solvent extraction - alpha spectrometric techniques. The uranium and thorium isotopes are in near equilibrium with average concentrations of 238 U, 234 U and 230 Th being 89.3, 95.2 and 91.1 pCi/kg respectively. The combined average radiation dose rate to lung from these three isotopes is about 24.2 mrad/year at death excluding the unmeasured contribution from the 226 Ra and daughters. The average concentration of 230 Th is about 65 times higher than the mean concentration of 230 Th in lungs of non-miners dying at comparable ages from the same region

  7. 210Pb, 230Th, and 10Be in Central Indian Basin seamount sediments: Signatures of degassing and hydrothermal alteration of recent origin

    Digital Repository Service at National Institute of Oceanography (India)

    Nath, B.N.; Borole, D.V.; Aldahan, A.; Patil, S; Mascarenhas-Pereira, M.B.L.; Possnert, G.; Ericsson, T.; Ramaswamy, V.; Gupta, S

    , 230 Th, and 10 Be in Central Indian Basin seamount sediments: Signatures of degassing and hydrothermal alteration of recent origin B. N. Nath, 1 D. V. Borole, 1 A. Aldahan, 2 S. K. Patil, 3 M. B. L. Mascarenhas-Pereira, 1 G. Possnert, 4 T. Ericsson, 2... V. Ramaswamy, 1 and S. M. Gupta 1 Received 4 March 2008; revised 17 March 2008; accepted 8 April 2008; published 14 May 2008. [1] Isotopic ( 210 Pb, 238 U- 230 Th, 10 Be), major and trace elements, and micromorphological and microchemical data, were...

  8. Apollo 12 breccia 12013: Impact-induced partial Pb loss in zircon and its implications for lunar geochronology

    Science.gov (United States)

    Thiessen, F.; Nemchin, A. A.; Snape, J. F.; Bellucci, J. J.; Whitehouse, M. J.

    2018-06-01

    Apollo 12 breccia 12013 is composed of two portions, one grey in colour, the other black. The grey portion of the breccia consists mainly of felsite thought to have formed during a single crystallisation event, while the black part is characterized by presence of lithic fragments of noritic rocks and individual plagioclase crystals. In this study, U-Pb analyses of Ca-phosphate and zircon grains were conducted in both portions of the breccia. The zircon grains within the grey portion yielded a large range of ages (4154 ± 7 to 4308 ± 6 Ma, 2σ) and show decreasing U and Th concentrations within the younger grains. Moreover, some grains exhibit recrystallisation features and potentially formation of neoblasts. The latter process requires high temperatures above 1600-1700 °C leading to the decomposition of the primary zircon grain and subsequent formation of new zircon occurring as neoblasts. As a result of the high temperatures, the U-Pb system of the remaining original zircon grains was most likely open for Pb diffusion causing partial resetting and the observed range of 207Pb/206Pb ages. The event that led to the Pb loss in zircon could potentially be dated by the U-Pb system in Ca-phosphates, which have a weighted average 207Pb/206Pb age across both lithologies of 3924 ± 3 Ma (95% conf.). This age is identical within error to the combined average 207Pb/206Pb age of 3926 ± 2 Ma that was previously obtained from Ca-phosphates within Apollo 14 breccias, zircon grains in Apollo 12 impact melt breccias, and the lunar meteorite SaU 169. This age was interpreted to date the Imbrium impact. The zircon grains located within the black portion of the breccia yielded a similar range of ages (4123 ± 13 to 4328 ± 14 Ma, 2σ) to those in the grey portion. Given the brecciated nature of this part of the sample, the interpretation of these ages as representing igneous crystallisation or resetting by impact events remains ambiguous since there is no direct link to their

  9. 238U, 234U and 232Th in seawater

    International Nuclear Information System (INIS)

    Chen, J.H.; Edwards, R.L.; Wasserburg, G.J.

    1986-01-01

    We have developed techniques to determine 238 U, 234 U and 232 Th concentrations in seawater by isotope dilution mass spectrometry. Using these techniques, we have measured 238 U, 234 U and 232 Th in vertical profiles of unfiltered, acidified seawater from the Atlantic and 238 U and 234 U in vertical profiles from the Pacific. Determinations of 234 U/ 238 U at depths ranging from 0 to 4900 m in the Atlantic (7 0 44'N, 40 0 43'W) and the Pacific (14 0 41'N, 160 0 01'W) Oceans are the same within experimental error (±5per mille, 2σ). The average of these 234 U/ 238 U measurements is 144±2per mille (2σ) higher than the equilibrium ratio of 5.472 x 10 -5 . U concentrations, normalized to 35per mille salinity, range from 3.162 to 3.281 ng/g, a range of 3.8%. The average concentration of the Pacific samples (31 0 4'N, 159 0 1'W) is ∝1% higher than that of the Atlantic (7 0 44'N, 40 0 43'W and 31 0 49'N, 64 0 6'W). 232 Th concentrations from an Atlantic profile range from 0.092 to 0.145 pg/g. The observed constancy of the 234 U/ 238 U ratio is consistent with the predicted range of 234 U/ 238 U using a simple two-box model and the residence time of deep water in the ocean determined from 14 C. The variation in salinity-normalized U concentrations suggests that U may be much more reactive in the marine environment than previously thought. (orig./WB)

  10. Sequential determination of U and Th isotopes, 226Ra, 228Ra, 210Pb, and 210Po in mushroom

    International Nuclear Information System (INIS)

    Rosa, Mychelle M.L.; Taddei, Maria Helena T.; Dias, Fabiana F.; Maihara, Vera A.

    2009-01-01

    For this study, mushroom samples were collected in Brazil at the Sao Paulo Metropolitan Region and at the Pocos de Caldas Plateau (PC; a region of elevated natural radioactivity, which houses the first Brazilian uranium mine). This paper discusses a sequential methodology to determine natural series radionuclides in mushrooms, such as uranium ( 238 U and 234 U) and thorium ( 232 Th, 230 Th, and 228 Th) isotopes, radium-226, radium-228, as well as lead-210 and polonium-210; using Alpha Spectrometry, Gamma Spectrometry, and Total Alpha and Beta Counting. The method involves total sample dissolution in a closed system in order to avoid loss of Polonium and employment of specific chromatographic resins for radionuclide purification. A subsequent interpretation of the results can provide information on pollutants present in mushrooms and infer possible contamination in the areas sampled as well as allow an association of measured concentrations to radioactive anomalies in the Plateau. (author)

  11. U-Pb geochronology of Martín García, Sola, and Dos Hermanas Islands (Argentina and Uruguay): Unveiling Rhyacian, Statherian, Ectasian, and Stenian of a forgotten area of the Río de la Plata Craton

    Science.gov (United States)

    Santos, João O. S.; Chernicoff, Carlos J.; Zappettini, Eduardo O.; McNaughton, Neal J.; Greau, Y.

    2017-12-01

    The Río de la Plata Craton is one of the three major cratons of South America. The craton is largely covered by sedimentary basins where its most exposed area is Buenos Aires-Piedra Alta Province (Chernicoff et al., 2014). This province includes the Martín García Island in the confluence of Uruguay River and the Río de la Plata estuary. Despite to be a reference area for the craton the Martín García Island lacks modern geological investigation. We present U-Pb SIMS (secondary ion mass spectrometer) geochronological data on zircon and titanite, as well as Hf isotope determinations on zircon, from rocks of Martín García Island (Argentina), Sola and Dos Hermanas Islands (Uruguay) and from Paso Severino Formation (Uruguay). We investigated: 1) Rhyacian intermediate-to acidic plutonic, arc-type rocks of the Florida Belt dated between 2090 Ma and 2115 Ma, derived from juvenile Neoarchean crust (TDMHf: 2.52 Ga; average εHf: +3.62); 2) Rhyacian metadacite (San José metamorphic belt) of 2127 Ma; 3) Statherian metagabbros of 1724-1734 Ma, with Transplatense inheritance; 4) Early Ectasian metagabbro of 1392 Ma, with Rhyacian inheritance; and 5) Stenian metagabbros of 1193 Ma (TDMHf: 2.00 Ga, εHf: 0.1). Most of the dated orthogneisses show Brasilian-age (from 778 to 550 Ma) Pb loss in the zircons, interpreted to be caused by shearing or uplifting during Neoproterozoic. The results show that the area is not exclusively Rhyacian in age but encompasses Statherian, Ectasian, and Stenian gabbros. The last two are interpreted as distal intrusions associated to the Sunsás Orogen. All post-Transplatense metagabbros have geochemical signature of island arc basalt derived from primitive mantle with enrichment of LILE and depletion of HFSE. These characteristics point to the recurrence of magma chambers intermittently active during the Rhyacian, Statherian, Ectasian, and Stenian, all with a similar source. The term "Transplatense" is used to replace "Trans-Amazonian" events

  12. Pb, U, Ti, Hf and Zr distributions in zircons determined by proton microprobe and fission track techniques

    International Nuclear Information System (INIS)

    Clark, G.J.; Gulson, B.L.; Cookson, J.A.

    1979-01-01

    A proton microprobe has been used to determine Pb, Tl, Hf and Zr distributions across four single zircon crystals separated from a 'rapakivi' granite. The Pb and Zr data are quantitative: Pb and Tl concentrations were below the measurable limits for determinations in situ by most other techniques. The distribution of U in the same crystals was determined by the fission track technique. Limits on precision of U allow only a qualitative correlation of U and Pb, whereas the Tl and Pb correlation is more exactly determined. Zircons with distinct cores and overgrowths exhibited uniform Zr and Hf concentrations across the crystals, whereas the high U rims and 'inclusions' (domains) also had high Tl and Pb contents. Since almost all the Pb in these zircons is derived by radioactive decay of U, the Tl substitution has paralleled that of U. The results indicate that the high U domains are 'hot spots' rather than a separate mineral phase. The strong positive correlation of U and Pb indicates that there is little U daughter product migration relative to U, within the crystal. However, for the zircon population investigated here, the data are equivocal on the question of whether U addition to zircon crystals is associated with new zircon growth or not. In either case, the heterogeneous U and Pb distributions complicate any interpretations of U-Pb isotopic analysis for such zircon populations. (author)

  13. Implantation of alpha spectrometry methodology for the determination of U and Th isotopes in igneous rocks: application to the study of radioactive desequilibrium in the Trindade Island, Brazil

    International Nuclear Information System (INIS)

    Santos, Rosana Nunes dos

    2001-01-01

    This work describes the implementation of experimental procedures for alpha spectrometry measurement of 238 U, 234 U and 230 Th activities in silicates. The best experimental conditions were defined using 233 U, 232 U and 229 Th radioactive tracers and simulating the usual conditions found in processing silicates. The chemical procedures consists of the following steps: radioactive tracer addition and sample dissolution by acid digestion, U and Th pre-concentration by co-precipitation, element separation and purification by ion exchange chromatography and electrodeposition in inox steel disks. In order to evaluate its effectiveness, the procedure was applied to the Brazilian geological standards BB-1 (basalt) and GB-1 (granite). The obtained chemical yields for uranium and thorium are of about 60% and 70%, respectively, for both matrices. The described methodology furnishes activity measurements with less than 4% relative precision and accuracies of about 1%, that are essential for petrogenetic applications. The 238 U and 232 Th series disequilibrium conditions were investigated by alpha spectrometry, together with neutron activation analysis and natural gamma-ray spectrometry. 234 U/ 238 U, 238 U/ 232 Th and 230 Th/ 232 Th activity ratios and the 234 Th, 214 Pb, 214 Bi, 235 U, 228 Ac, 212 Pb, 212 Bi and 208 Tl specific activities were obtained. These results were interpreted with the help of additional constraints given by the larger and smaller elements concentrations, measured by X-ray fluorescence. The 232 Th series is in secular radioactive equilibrium in all analysed samples. In the case of the 238 U series, the equilibrium condition was verified, as expected, in the oldest rocks from the Trindade Island (Trindade Complex and Desejado Sequence). On the other hand, the results show that, in the samples from the last three volcanic episodes in the island (Morro Vermelho Formation, Valado Formation and Vulcao do Paredao), the 230 Th and 238 U are not in

  14. Timing of porphyry (Cu-Mo) and base metal (Zn-Pb-Ag-Cu) mineralisation in a magmatic-hydrothermal system—Morococha district, Peru

    Science.gov (United States)

    Catchpole, Honza; Kouzmanov, Kalin; Bendezú, Aldo; Ovtcharova, Maria; Spikings, Richard; Stein, Holly; Fontboté, Lluís

    2015-12-01

    The Morococha district in central Peru is characterised by economically important Cordilleran polymetallic (Zn-Pb-Ag-Cu) vein and replacement bodies and the large Toromocho porphyry Cu-Mo deposit in its centre. U-Pb, Re-Os, and 40Ar/39Ar geochronology data for various porphyry-related hydrothermal mineralisation styles record a 3.5-Ma multi-stage history of magmatic-hydrothermal activity in the district. In the late Miocene, three individual magmatic-hydrothermal centres were active: the Codiciada, Toromocho, and Ticlio centres, each separated in time and space. The Codiciada centre is the oldest magmatic-hydrothermal system in the district and consists of a composite porphyry stock associated with anhydrous skarn and quartz-molybdenite veins. The hydrothermal events are recorded by a titanite U-Pb age at 9.3 ± 0.2 Ma and a molybdenite Re-Os age at 9.26 ± 0.03 Ma. These ages are indistinguishable from zircon U-Pb ages for porphyry intrusions of the composite stock and indicate a time span of 0.2 Ma for magmatic-hydrothermal activity. The small Ticlio magmatic-hydrothermal centre in the west of the district has a maximum duration of 0.3 Ma, ranging from porphyry emplacement to porphyry mineralisation at 8.04 ± 0.14 Ma (40Ar/39Ar muscovite cooling age). The Toromocho magmatic-hydrothermal centre has a minimum of five recorded porphyry intrusions that span a total of 1.3 Ma and is responsible for the formation of the giant Toromocho Cu-Mo deposit. At least two hydrothermal pulses are identified. Post-dating a first pulse of molybdenite mineralisation, wide-spread hydrous skarn covers an area of over 6 km2 and is recorded by five 40Ar/39Ar cooling ages at 7.2-6.8 Ma. These ages mark the end of the slowly cooling and long-lived Toromocho magmatic-hydrothermal centre soon after last magmatic activity at 7.26 ± 0.02 Ma. District-wide (50 km2) Cordilleran base metal vein and replacement bodies post-date the youngest recorded porphyry mineralisation event at Toromocho

  15. A brief review of 210Pb sediment dating models and uncertainties in a world of global change

    Science.gov (United States)

    Sanchez-Cabeza, J. A.; Ruiz-Fernandez, A. C.

    2016-12-01

    Irrespective of the model names used, assumptions and (usually forgotten) uncertainties, the fact is that 210Pb sediment dating is an increasingly relevant tool in our world of global change. 210Pb dating results are needed to assess historical trends of sea level rise, quantify blue carbon fluxes and reconstruct environmental records of biogeochemical proxies for diverse processes in the aquatic ecosystems (such as ocean acidification, hypoxia and pollution). Although in the past 210Pb profiles departing from "ideal" decay trends were usually discarded, all profiles have useful information. In this work we review the principles and assumptions of the most common 210Pb dating models, and propose a logical formulation and classification of the models. 210Pb dating models provide two kinds of results: chronologies (i.e. age models) and accumulation rates. In many cases, the use of sediment and/or mass accumulation rates (SAR and MAR) is needed to assess environmental fluxes or, simply, to describe changes, such as catchment erosion or saltmarsh accretion. Although uncertainty quadratic propagation is a well-known technique, it requires that all variables are fully independent and requires demanding mathematical expressions which might lead to wrong results. We present here a Monte Carlo method that makes calculation easier and, likely, error-free. Not unexpectedly, the most important uncertainty sources are measurement uncertainties, which impose limitations on common techniques such as gamma spectrometry. 210Pb chronology does not cover all anthropogenic impacts, such as those caused by ancient civilizations, so radiocarbon also plays an important role in this kind of work. We also conceptually revise the limitations of both techniques and encourage scientists to link both dating techniques with a symmetrically open mind. Acknowledgements: projects CONACYT PDCPN2013-01/214349 and CB2010/153492, UNAM PAPIIT-IN203313, PRODEP network "Aquatic contamination: levels and

  16. 238U, 234U and 230Th in uranium miners' lungs

    International Nuclear Information System (INIS)

    Singh, N.P.; Wrenn, M.E.; Bennett, D.B.; Archer, V.; Saccomanno, G.

    1982-01-01

    Fourteen uranium miners' lungs from the Colorado Plateau were collected at autopsy and the concentrations of 238 U, 234 U and 230 Th were determined by radiochemical procedures utilizing solvent extraction and alpha spectrometric techniques. The uranium and thorium isotopes are in near equilibrium with average concentrations of 238 U, 234 U and 230 Th being 89.3, 95.2, and 91.1 pCi/kg respectively. The combined average radiation dose rate to lung from these three isotopes is about 24.1 mrad/year at death excluding the unmeasured contribution from the 226 Ra and daughters. The average concentration of 230 Th is about 65 times higher than the mean concentration of 230 Th in lungs of non-miners from the same region dying at comparable ages

  17. Uranium-lead dating method at the Pará-Iso isotope geology laboratory, UFPA, Belém - Brazil

    Directory of Open Access Journals (Sweden)

    Robert S. Krymsky

    2007-03-01

    Full Text Available Analytical procedures for U-Pb isotope dilution analyses at the Pará-Iso isotope geology laboratory of the Federal University of Pará (UFPA are described in detail. The procedures are applied to zircon, titanite, rutile, apatite, columbite-tantalite and whole rock. Reagent preparation and chemical processing are done in clean-room conditions. Samples are dissolved using TeflonTM microcapsules in steel jacket TeflonTM Parr InstrumentTM bomb or TeflonTM screw cap containers. U and Pb are separated using anion exchange AG 1x8 resin columns. Typical blanks for mineral sample amounts of 0.01 to 1.0 mg are less than 1 pg U and 20-30 pg Pb. Isotope analysis of the U and Pb from the same filament are carried out using a Finnigan MAT 262 mass-spectrometer in static and dynamic modes. The current analytical level is demonstrated on analyses of international standard zircon 91500 with three different 235U-205Pb and 235U-208Pb isotope tracers and whole rock standards. Results of analyses of two zircon samples are also presented.Os procedimentos analíticos para análises U-Pb por diluição isotópica no Laboratório de Geologia Isotópica (Pará-Iso da Universidade Federal do Pará (UFPA são descritos detalhadamente. Esses procedimentos são aplicados para análises de zircão, titanita, rutilo, apatita, columbita-tantalita e rocha total. A purificação dos reagentes e os procedimentos químicos são feitos em salas limpas. As amostras são dissolvidas em microcápsulas de Teflon em bombas do tipo Parr InstrumentTM. U e Pb são separados em colunas com resina de troca iônica AG 1x8. Os brancos de procedimento para amostra típica(0,01-1 mg são menores que 1 pg de U e 20-30 pg de Pb. As análises isotópicas de Pb e de U são feitas em um único filamento de Re em um espectrômetro de massa Finnigan MAT 262 nos modos estático e dinâmico. O nível analítico atual é comprovado pelas análises do padrão internacional de zircão 91500, usando tr

  18. Critical evaluation and thermodynamic optimization of the U-Pb and U-Sb binary systems

    International Nuclear Information System (INIS)

    Wang, Jian; Jin, Liling; Chen, Chuchu; Rao, Weifeng; Wang, Cuiping; Liu, Xingjun

    2016-01-01

    A complete literature review, critical evaluation and thermodynamic optimization of the phase diagrams and thermodynamic properties of U-Pb and U-Sb binary systems are presented. The CALculation of PHAse Diagrams (CALPHAD) method was used for the thermodynamic optimization, the results of which can reproduce all available reliable experimental phase equilibria and thermodynamic data. The modified quasi-chemical model in the pair approximation (MQMPA) was used for modeling the liquid solution. The Gibbs energies of all terminal solid solutions and intermetallic compounds were described by the compound energy formalism (CEF) model. All reliable experimental data of the U-Pb and U-Sb systems have been reproduced. A self-consistent thermodynamic database has been constructed for these binary systems; this database can be used in liquid-metal fuel reactor (LMFR) research.

  19. Bayesian integration of radioisotope dating (210Pb, 137Cs, 241Am, 14C) and an 18-20th century mining history of Brotherswater, English Lake District

    Science.gov (United States)

    Schillereff, Daniel; Chiverrell, Richard; Macdonald, Neil; Hooke, Janet; Welsh, Katharine; Piliposyan, Gayane; Appleby, Peter

    2014-05-01

    Lake sediment records are often a useful tool for investigating landscape evolution as geomorphic changes in the catchment are reflected by altered sediment properties in the material transported through the watershed and deposited at the lake bed. Recent research at Brotherswater, an upland waterbody in the Lake District, northwest England, has focused on reconstructing historical floods from their sedimentary signatures and calculating long-term sediment and carbon budgets from fourteen sediment cores extracted from across the basin. Developing accurate chronological control is essential for these tasks. One sediment core (BW11-2; 3.5 m length) from the central basin has been dated using artificial radionuclide measurements (210Pb, 137Cs, 241Am) for the uppermost sediments and radiocarbon (14C) for lower sediments. The core appears to span the past 1500 years, however a number of problems have arisen. We present our explanations for these errors, the independent chronological techniques used to generate an accurate age-depth model for this core and methods for its transferral to the other 13 cores extracted from the basin. Two distinct 137Cs markers, corresponding to the 1986 Chernobyl disaster and 1960s weapons testing, confirm the 210Pb profile for sediment deposition since ~1950, but calculations prior to this appear erroneous, possibly due to a hiatus in the sediment record. We used high-resolution geochemical profiles (measured by XRF) to cross-correlate with a second 210Pb-dated chronology from a more distal location, which returned more sensible results. Unfortunately, the longer 14C sequence exhibits two age-reversals (radiocarbon dates that are too old). We believe the uppermost two dates are erroneous, due to a shift in inflow location as a flood prevention method ~1900 A.D., dated using information from historical maps. The lower age-reversal coincides with greater supply of terrigenous material to the lake (increased Zr, K, Ti concentrations

  20. Application of U-Th-Pb phosphate geochronology to young orogenic gold deposits: New age constraints on the formation of the Grass Valley gold district, Sierra Foothills province, California

    Science.gov (United States)

    Taylor, Ryan D.; Goldfarb, Richard J.; Monecke, Thomas; Fletcher, Ian R.; Cosca, Michael A.; Kelly, Nigel M.

    2015-01-01

    The Grass Valley orogenic gold district in the Sierra Nevada foothills province, central California, the largest historic gold producer of the North American Cordillera, comprises both steeply dipping east-west (E-W) veins located along lithologic contacts in accreted ca. 300 and 200 Ma oceanic rocks and shallowly dipping north-south (N-S) veins hosted by the Grass Valley granodiorite; the latter have yielded about 70 percent of the 13 million ounces of historic lode gold production in the district. The oceanic host rocks were accreted to the western margin of North America between 200 and 170 Ma, metamorphosed to greenschist and amphibolite facies, and uplifted between 175 and 160 Ma. Large-scale magmatism in the Sierra Nevada occurred between 170-140 Ma and 120-80 Ma, with the Grass Valley granodiorite being emplaced during the older episode of magmatism. Uranium-lead isotopic dating of hydrothermal xenotime yielded the first absolute age of 162±5 Ma for the economically more significant N-S veins. The vein-hosted xenotime, as well as associated monazite, are unequivocally of hydrothermal origin as indicated by textural and chemical characteristics, including grain shape, lack of truncated growth banding, lack of a Eu anomaly, and low U and Th concentrations. Furthermore, the crack-seal texture of the veins, with abundant wallrock slivers, suggests their formation as a result of episodic fluid flow possibly related to reoccurring seismic events, rather than a period of fluid exsolution from an evolving magma. The N-S veins are temporally distinct from a younger 153-151 Ma gold event that was previously reported for the E-W veins. Overlapping U-Pb zircon (159.9±2.2 Ma) and 40Ar/39Ar biotite and hornblende (159.7±0.6 to 161.9±1.4 Ma) ages and geothermobarometric calculations indicate that the Grass Valley granodiorite was emplaced at ca. 160 Ma at elevated temperatures (~800°C) within approximately 3 km of the paleosurface and rapidly cooled to the ambient

  1. Mineralogical and Geochemical Study of Titanite Associated With Copper Mineralization in the Hopper Property, Yukon Territory, Canada

    Science.gov (United States)

    Blumenthal, V. H.; Linnen, R. L.

    2009-05-01

    Copper mineralization in central Yukon is well known, but the metallogeny of the Ruby Range batholith, west of the copper belt, is poorly understood. The Hopper property, situated in the south western part of the Yukon in the Yukon-Tanana terrane, contains copper mineralization hosted by granodiorite and quartz feldspar porphyry of cal-alkaline affinity. These rock units, interpreted to be part of the Ruby Range batholith, intruded metasediments of the Ashihik Metamorphic Suite rocks. Mafic dykes cross cut the intrusion followed by aplite dykes. Small occurrences of skarn also occur in the area and some of these contain copper mineralization. The copper mineralization at the Hopper property appears to have a porphyry-type affinity. However, it is associated with a shear zone and propylitic alteration unlike other typical copper porphyry-type deposits. This raises the question whether or not the mineralization is orthomagmatic in origin, i.e., whether or not this is a true porphyry system. The main zone of mineralization is 1 kilometer long and 0.5 kilometer wide. It is characterized by disseminated chalcopyrite and pyrite, which also occur along fractures. Molybdenite mineralization was found to be associated with slickensides. Alteration minerals associated with the copper mineralization are chlorite, epidote-clinozoisite, carbonate and titanite. Chlorite and epidote-clinozoisite are concentrated in the mineralized zone, whereas an earlier potassic alteration shows a weaker spatial correlation with the mineralization. The association of the mineralization with propylitic alteration leads us to believe the mineralization is shear related, although a deeper porphyritic system may be present at depth. Two populations of titanite at the Hopper property are recognized based on their shape, size and association with other minerals. The first population, defined by a length of 100 micrometers to 1 centimeter, euhedral boundaries, and planar contacts with other magmatic

  2. Atmospheric dust contribution to budget of U-series nuclides in weathering profiles. The Mount Cameroon volcano

    Science.gov (United States)

    Pelt, E.; Chabaux, F. J.; Innocent, C.; Ghaleb, B.

    2009-12-01

    Analysis of U-series nuclides in weathering profiles is developed today for constraining time scale of soil and weathering profile formation (e.g., Chabaux et al., 2008). These studies require the understanding of U-series nuclides sources and fractionation in weathering systems. For most of these studies the impact of aeolian inputs on U-series nuclides in soils is usually neglected. Here, we propose to discuss such an assumption, i.e., to evaluate the impact of dust deposition on U-series nuclides in soils, by working on present and paleo-soils collected on the Mount Cameroon volcano. Recent Sr, Nd, Pb isotopic analyses performed on these samples have indeed documented significant inputs of Saharan dusts in these soils (Dia et al., 2006). We have therefore analyzed 238U-234U-230Th nuclides in the same samples. Comparison of U-Th isotopic data with Sr-Nd-Pb isotopic data indicates a significant impact of the dust input on the U and Th budget of the soils, around 10% for both U and Th. Using Sr-Nd-Pb isotopic data of Saharan dusts given by Dia et al. (2006) we estimate U-Th concentrations and U-Th isotope ratios of dusts compatible with U-Th data obtained on Saharan dusts collected in Barbados (Rydell H.S. and Prospero J.M., 1972). However, the variations of U/Th ratios along the weathering profiles cannot be explained by a simple mixing scenario between material from basalt and from the defined atmospheric dust pool. A secondary uranium migration associated with chemical weathering has affected the weathering profiles. Mass balance calculation suggests that U in soils from Mount Cameroon is affected at the same order of magnitude by both chemical migration and dust accretion. Nevertheless, the Mount Cameroon is a limit case were large dust inputs from continental crust of Sahara contaminate basaltic terrain from Mount Cameroon volcano. Therefore, this study suggests that in other contexts were dust inputs are lower, or the bedrocks more concentrated in U and Th

  3. Timing of the Permian-Triassic biotic crisis: implications from new zircon U/Pb age data (and their limitations)

    Science.gov (United States)

    Mundil, Roland; Metcalfe, Ian; Ludwig, Kenneth R.; Renne, Paul R.; Oberli, Felix; Nicoll, Robert S.

    2001-04-01

    data require a significant increase in the age of the Permian-Triassic boundary by more than 2 myr compared to the previous study, which shifts the age to a value older than 253 Ma. Second, neither our data nor those from previous work can confirm or negate the possibility of a very abrupt biotic crisis. Third, even large suites of very high-quality, single-zircon U-Pb analyses for these tuffs cannot, in most cases, yield objective, reliable, and robust dates with accuracies at the sub-myr level - though the temptation to perform arbitrary selection of subsets of the analyses for that purpose is almost irresistible. The last conclusion is not an indictment of zircon U/Pb dating in general (other rocks and other zircon populations can - and do - behave very differently), and further technical advances will likely improve our ability to prepare grains or sub-grains of adequately enhanced quality for analysis. Consequently, the results of the present study strongly suggest that for problems requiring time-scale accuracy, inferences from zircon U-Pb dating must be based on sufficiently large suites of single-crystal or crystal domain, high-precision analyses (<1% error) that are realistically interpreted.

  4. Geology, mineralization, U-Pb dating and Sr-Nd isotope geochemistry of intrusive bodies in northeast of Kashmar

    Directory of Open Access Journals (Sweden)

    Alireza Almasi

    2015-04-01

    Full Text Available Alireza Almasi1, Mohammad Hassan Karimpour1*, Khosrow Ebrahimi Nasrabadi1, Behnam Rahimi1, Urs KlÖtzli2 and Jose Francisco Santos3 Introduction The study area is located in central part of the Khaf- Kashmar-Bardeskan belt which is volcano-plutonic belt at the north of the Dorouneh fault in the north of Lut block. The north of the Lut block is affected by tectonic rotation and subduction processes which occur in the east of Iran (Tirrul et al., 1983. The magmatism of Lut block begins in Jurassic and continues in Tertiary (Aghanabati, 1995. Karimpour (Karimpour, 2006 pointed out the Khaf-Kashmar-Bardeskan belt has significant potential for IOCG type mineralization such as Kuh-e-Zar, Tannurjeh, and Sangan (Karimpour, 2006; Mazloumi, 2009. The data gathered on the I-type intrusive rocks include their field geology, petrography, U–Pb zircon dating and Sr–Nd isotope and also alteration and mineralization in the study area. Materials and methods - Preparation of 150 thin sections of rock samples for study of petrography and alteration of the intrusive rocks. - Magnetic susceptibility measuring of intrusive rocks. - U-Pb dating in zircon of I-type intrusive rocks by Laser-Ablation Multi Collector ICP-MS method. - Sr-Nd analysis on 5 samples of I-type intrusive rocks by Multi-Collector Thermal Ionization Mass Spectrometer (TIMS VG Sector 54 instrument. - Mineralography and paragenetic studies of ore-bearing quartz veins and geochemical analysis for 28 samples. - Production of the geology, alteration and mineralization maps by scale: 1:20000 in GIS. Results Oblique subduction in southern America initiated an arc-parallel fault and shear zones in the back of continental magmatic arc (Sillitoe, 2003. Because of this event, pull-apart basins were formed and high-K to shoshonitic calc-alkalineI- and A-type magmatism occur (Sillitoe, 2003. Most important deposits accompany with this magmatism are Au-Cu deposits types and Fe-Skarns (Sillitoe, 2003. We have

  5. Padrt'stock (Teplá–Barrandian unit, Bohemian Massif): Petrology, geochemistry, U-Pb zircon dating of granodiorite, and Re-Os age and origin of related molybdenite mineralization

    Czech Academy of Sciences Publication Activity Database

    Žák, Karel; Svojtka, Martin; Breiter, Karel; Ackerman, Lukáš; Zachariáš, J.; Pašava, J.; Veselovský, F.; Litochleb, J.; Ďurišová, Jana; Haluzová, Eva

    2014-01-01

    Roč. 59, č. 4 (2014), s. 351-366 ISSN 1802-6222 R&D Projects: GA ČR GA13-15390S Institutional support: RVO:67985831 Keywords : geochemistry * petrology * Re–Os molybdenite dating * Teplá–barrandian unit * U–Pb zircon dating * Variscan granitoids Subject RIV: DD - Geochemistry Impact factor: 1.405, year: 2014

  6. Analysis of photofission reactions of 235U, 238U, 232Th, 209Bi, natPb, 197Au, natPt, natW, 181Ta, and 27Al by photons of 69 MeV

    International Nuclear Information System (INIS)

    Paiva, Eduardo de

    1997-04-01

    Fission reactions induced in 235 U, 238 U, 232 Th, 209 Bi nat Pb, 197 Au, nat Pt, nat W, 181 Ta. and 27 Al nuclei by monochromatic photons of 69 MeV produced at the LADON facility of the Frascati National Laboratories (INFN-LNF, Frascati, Italy) have been analyzed on the basis of a simplified two-step model. In the first step of the reaction the incoming photon is considered to be absorbed by a neutron-proton pair ('quasi-deuteron') leading to excitation of the nucleus, followed, in the second step, by a mechanism of particle evaporation-fission competition for the excited residual nucleus. Estimates of nuclear fissility at 69 MeV show to be critically dependent on the parameter r (ratio of the level-density parameter at the fission saddle point to the level-density parameter of the residual nucleus after neutron evaporation), which can be determined in a semiempirical way from induced fission reaction data for various nuclei obtained at 60 - 80 MeV of excitation energy. Fissilities calculated by means of the simplified photofission reactions model are then compared with experimental data available in the literature. (author)

  7. On the Application of Macros to the Automation of different Dating Models Using ''210 Pb

    International Nuclear Information System (INIS)

    Gasco, C.; Anton, M. P.; Ampudia, J.

    2002-01-01

    Different Dating models based on 210 Pb measurements, used for verifying recent events are shown in this report as well as, models that describe different processes affecting the vertical distribution of radionuclides in lacustrine and marine sediments. Macro-Commands are programmes included in calculation work sheets that allow automatised operations to run. In this report macros are used to: a) obtain 210 Pb results from a data base created from different sampling campaigns b) apply different dating models automatically c) optimise the diffusion coefficient employed by models through standards deviation calculations among experimental values and those obtained by the model. (Author) 21 refs

  8. Thermodynamic assessment of the HTGR fuel system Th-U-C-O

    International Nuclear Information System (INIS)

    Ugajin, M.; Shiba, K.

    1978-01-01

    Carbon monoxide pressures and uranium segregation at 2000 K have been calculated for the three-phase equilibria [(ThU)O 2 + (ThU)C 2 + C] in the Th-U-C-O system. This study is concerned with the thermochemical behavior of (Th, U)O 2 particle fuel for the high-temperature gas-cooled reactor (HTGR). The following two points are considered: (1) Reduction of the in-particle CO pressure of (Th, U)O 2 kernels by doping (Th, U)C 2 to make it an oxygen getter. (2) Prediction of U segregation between (Th, U)O 2 and (Th, U)C 2 , doped in the kernel. (Auth.)

  9. Geochronology of Hydrothermal Processes Leading to the Formation of the Au–U Mineralization at the Rompas Prospect, Peräpohja Belt, Northern Finland: Application of Paired U–Pb Dating of Uraninite and Re–Os Dating of Molybdenite to the Identification of Multiple Hydrothermal Events in a Metamorphic Terrane

    Directory of Open Access Journals (Sweden)

    Ferenc Molnár

    2017-09-01

    Full Text Available The Peräpohja belt comprises a greenschist to amphibolite facies; multiply-folded supracrustal sequence of quartzites; mafic volcanics; carbonate rocks; black shales; mica schists and greywackes deposited from ca. 2.44 Ga to 1.92 Ga; during protracted rifting of the Archaean basement. Metamorphism and multiple folding of the basin fill occurred during the Svecofennian orogeny (1.92–1.80 Ga. The Rompas Au–U mineralization is hosted within deformed and metamorphosed calcsilicate veins in mafic volcanics. Textural evidence suggests that deposition and periods of uraninite re-mobilization were followed by localized hydrocarbon-bearing fluid flow which produced pyrobitumen crusts around grains of uraninite. Gold precipitated during the latest hydrothermal event at around 1.75 Ga. In situ U–Pb dating of uraninite by laser ablation inductively coupled mass spectroscopy (LA-ICP-MS, and Re–Os dating of molybdenite, indicate that primary hydrothermal uranium mineralization forms two age clusters; about 2.03–2.01 and 1.95–1.94 Ga. Resetting of the U–Pb system and precipitation of new generations of uraninite are associated with major deformation and metamorphic stages of the Svecofennian orogeny at 1.91–1.89 Ga, 1.85 Ga, and 1.80 Ga. Gold deposition was synchronous with the emplacement of the 1.75–1.78 Ga late/post-orogenic granitoids. The gold-producing hydrothermal event is also recorded by Re–Os dating of molybdenite from the gold-bearing Mg-metasomatized metasedimentary and metavolcanic units at the Palokas prospect; a few kilometres from Rompas. Results of this study confirm that some domains in the structure of uraninite may preserve the original crystallization age, despite an overprinting amphibolite facies metamorphic and other hydrothermal events. The study supports the utility of in situ U–Pb dating of uraninite and the ability of Re–Os dating to assist in sorting out different hydrothermal events in areas with complex

  10. U-Pb ages in zircon of some classic granites from the Borborema province

    International Nuclear Information System (INIS)

    Neves, Benjamin Bley de Brito; Basei, Miguel Angelo Stipp; Passarelli, Claudia Regina; Santos, Edilton Jose dos

    2003-01-01

    The Neoproterozoic evolution of the Borborema Province in the east-northeast part of the South American platform exhibits remarkable, much studied granitic plutonism. In 1967 F. F. Almeida and co-workers discriminated a series of granitic typologies as 'Conceicao type', 'Itaporanga type' etc, mostly based upon general geological features and petrographic grounds. This preliminary classification has somehow been maintained in all subsequent papers up to now, despite all the newly observed plutons and the newly generated tectonic, geochemical and isotopic data since then. Samples of these classical types of granites from their type-localities were analyzed geo chronologically using the U-Pb method in zircons in response to the felt needs of the geological community, because previous age-determinations involved less accurate methods. The new data have been added to all other preexisting U-Pb data (from other granitic bodies) obtained over the last decade, making it possible to recognize three main stages of granitic magmatism for the Borborema Province: 650-625 Ma, 580-570 Ma and 545-520 Ma. The last group of dates is closely association with the escape tectonics of the Brasiliano-Pan African collage, which preceded the assembly of the super continental landmass of Western Gondwana. (author)

  11. Colossal positive magnetoresistance in surface-passivated oxygen-deficient strontium titanite

    KAUST Repository

    David, Adrian; Tian, Yufeng; Yang, Ping; Gao, Xingyu; Lin, Weinan; Shah, Amish B.; Zuo, Jian-Min; Prellier, Wilfrid; Wu, Tao

    2015-01-01

    ,000% at a temperature of 2 K and a magnetic field of 9 T) discovered in degenerate semiconducting strontium titanite (SrTiO3) single crystals capped with ultrathin SrTiO3/LaAlO3 bilayers. The low-pressure high-temperature homoepitaxial growth of several unit

  12. 230Th-234U Model-Ages of Some Uranium Standard Reference Materials

    International Nuclear Information System (INIS)

    Williams, R.W.; Gaffney, A.M.; Kristo, M.J.; Hutcheon, I.D.

    2009-01-01

    The 'age' of a sample of uranium is an important aspect of a nuclear forensic investigation and of the attribution of the material to its source. To the extent that the sample obeys the standard rules of radiochronometry, then the production ages of even very recent material can be determined using the 230 Th- 234 U chronometer. These standard rules may be summarized as (a) the daughter/parent ratio at time=zero must be known, and (b) there has been no daughter/parent fractionation since production. For most samples of uranium, the 'ages' determined using this chronometer are semantically 'model-ages' because (a) some assumption of the initial 230 Th content in the sample is required and (b) closed-system behavior is assumed. The uranium standard reference materials originally prepared and distributed by the former US National Bureau of Standards and now distributed by New Brunswick Laboratory as certified reference materials (NBS SRM = NBL CRM) are good candidates for samples where both rules are met. The U isotopic standards have known purification and production dates, and closed-system behavior in the solid form (U 3 O 8 ) may be assumed with confidence. We present here 230 Th- 234 U model-ages for several of these standards, determined by isotope dilution mass spectrometry using a multicollector ICP-MS, and compare these ages with their known production history

  13. Mercury contamination history of an estuarine floodplain reconstructed from a 210Pb-dated sediment core (Berg River, South Africa)

    CSIR Research Space (South Africa)

    Kading, TJ

    2009-01-01

    Full Text Available in this 210Pb-dated sediment core at <50 ng g_1 HgT throughout the core, but with 1.3 ng g_1 methylmercury in surface sediments. The 210Pb dating of the core provides a first record of mercury deposition to the site and reveals the onset of enhanced mercury...

  14. SHRIMP U-Pb dating of detrital zircons in metamorphic rocks from northern Kyushu, western Japan

    International Nuclear Information System (INIS)

    Tsutsumi, Yukiyasu; Yokoyama, Kazumi; Terada, Kentaro; Sano, Yuji

    2003-01-01

    Radiometric ages of detrital zircons in psammitic schists from the Nagasaki, Kurume, Konoha and Kiyama areas, northern Kyushu, were obtained from 238 U/ 206 Pb ratio and isotopic compositions of Pb using a Sensitive High Resolution Ion Microprobe (SHRIMP II). Zircons from the Nagasaki, Kurume and Konoha areas show bimodal age distribution with peaks at ca. 1900 Ma and 250 Ma. It is suggested from this study that the older zircons were derived from Proterozoic landmass and the Korean Peninsula. Zircons from the Kiyama metamorphic rock show a different pattern with ages concentrated at 380-590 Ma. Such zircons are rare in rock samples from the Nagasaki, Kurume and Konoha areas, indicating that Kiyama rocks and a different origin than those from the other three areas. The youngest zircons from the Kiyama, Nagasaki, Kurume and Konoha areas show ages of 382±23 Ma, 238±13 Ma, 249±13 Ma, and 175±4 Ma, respectively, These data mark the upper age limit of their deposition. Since a continuous igneous activity occurred during the period from 300 to 170 Ma in Far East Asia, and the metamorphic age has been close to the zircon age of each area, these youngest ages for the Nagasaki, Kurume and Konoha areas are considered nearly contemporary to the depositional ages. An evaluation of the nature of metamorphism and available ages suggest the possibility that the Nagasaki metamorphic rocks as well as the schist from the Kurume area belong to the Suo zone of the Sangun belt, whereas the metamorphic rocks in the Konoha area may belong to the Ryoke belt or Suo zone of the Sangun belt. (author)

  15. Zircon U-Pb geochronology and Sr-Nd-Pb-Hf isotopic constraints on the timing and origin of Mesozoic granitoids hosting the Mo deposits in northern Xilamulun district, NE China

    Science.gov (United States)

    Shu, Qihai; Lai, Yong; Zhou, Yitao; Xu, Jiajia; Wu, Huaying

    2015-12-01

    Located in the east section of the Central Asian orogen in northeastern China, the Xilamulun district comprises several newly discovered molybdenum deposits, primarily of porphyry type and Mesozoic ages. This district is divided by the Xilamulun fault into the southern and the northern parts. In this paper, we present new zircon U-Pb dating, trace elements and Hf isotope, and/or whole rock Sr-Nd-Pb isotopic results for the host granitoids from three Mo deposits (Yangchang, Haisugou and Shabutai) in northern Xilamulun. Our aim is to constrain the age and petrogenesis of these intrusions and their implications for Mo mineralization. Zircon U-Pb LA-ICP-MS dating shows that the monzogranites from the Shabutai and Yangchang deposits formed at 138.4 ± 1.5 and 137.4 ± 2.1 Ma, respectively, which is identical to the molybdenite Re-Os ages and coeval well with the other Mo deposits in this region, thereby indicating an Early Cretaceous magmatism and Mo mineralization event. Zircon Ce/Nd ratios from the mineralized intrusions are significantly higher than the barren granites, implying that the mineralization-related magmas are characterized by higher oxygen fugacity. These mineralized intrusions share similar zircon in-situ Hf and whole rock Sr-Nd isotopic compositions, with slightly negative to positive εHf(t) ranging from - 0.8 to + 10.0, restricted εNd(t) values from - 3.7 to + 1.6 but a little variable (87Sr/86Sr)i ratios between 0.7021 and 0.7074, indicative of formation from primary magmas generated from a dominantly juvenile lower crust source derived from depleted mantle, despite diverse consequent processes (e.g., magma mixing, fractional crystallization and crustal contamination) during their evolution. The Pb isotopes (whole rock) also show a narrow range of initial compositions, with (206Pb/204Pb)i = 18.03-18.88, (207Pb/204Pb)i = 15.48-15.58 and (208Pb/204Pb)i = 37.72-38.28, in agreement with Sr-Nd-Hf isotopes reflecting the dominance of a mantle component

  16. Production of 231Pa and 232U by irradiation of 230Th/232Th mixtures

    International Nuclear Information System (INIS)

    Kluge, E.; Lieser, K.H.

    1981-01-01

    The production of 231 Pa and of 232 U by irradiating a 230 Th/ 232 Th mixture (containing 12 mol per cent 230 Th) in form of ThO 2 at a thermal neutron flux of 6.9 x 10 13 cm -2 s -1 for 4 months was investigated. Pa, U and Th were separated and the chemical yields were determined. 2.6% of the 230 Th were transformed into 231 Pa and 0.13% into 232 U. These values are higher than those calculated for a thermal flux, but lower than those calculated for a flux ratio epithermal to thermal = 0.03. 231 Pa and 232 U were isolated in form of a protactinium solution and of U 3 O 8 with 94.9 and 89.1% chemical yields, respectively. Foreign activities were not detected. Thorium was recuperated and isolated as ThO 2 , with a chemical yield of 93.6%. (orig.)

  17. Preparations of high density (Th,U)O2 pellets

    International Nuclear Information System (INIS)

    Akabori, Mitsuo; Ikawa, Katsuichi

    1986-07-01

    Preparations of high density and homogeneous (Th,U)O 2 pellets by a powder metallurgy method were examined. (Th,U)O 2 powders were prepared by calcining coprecipitates of ammonium uranate and thorium hydroxide derived from nitrates and mixed sols, and by calcining mixed oxalates precipitated from nitrates. (Th,U)O 2 pellets were characterized with respect to sinterability, lattice parameter, microstructure, homogeneity and stoichiometry. Sintering atmospheres had a significant effect upon all the properties of the derived pellets. The sinterability of (Th,U)O 2 was most favourable in oxidizing and reducing atmospheres for ThO 2 -rich and UO 2 -rich compositions, respectively, and can be enhanced by presence of water vapour in sintering atmospheres. In addition, highly homogeneous (Th,U)O 2 pellets with 99 % in theoretical density were derived from the sol powders. (author)

  18. Biological effect on removal of Th-234, Po-210 and Pb-210 from surface water in Funka Bay, Japan

    Energy Technology Data Exchange (ETDEWEB)

    Tanaka, N; Takeda, Y; Tsunogai, S [Hokkaido Univ., Hakodate (Japan). Dept. of Chemistry

    1983-10-01

    Vertical and temporal variations in the radioactivities of Th-234, Pb-210 and Po-210 were measured at a station in Funka Bay from April 1979 to February 1980. The inventory of Th-234 showed a minimum in early spring, when a spring bloom of phytoplankton was observed, then a steady increase to a maximum value in late summer, just before open sea water invaded the bay and a secondary phytoplankton bloom started. The inventories of Pb-210 and Po-210 also showed minima in early spring. These results suggest that the removal of these nuclides from sea water is accelerated by biological activity. The concentration of Th-234 decreased with depth, but those of Po-210 and Pb-210 were higher in the bottom water in August 1979 when the bay water was strongly stratified. This may be due to the supply of Pb-210 and Po-210 from the bottom. However, if the supply of these nuclides is expected in sediment particles, the concentrations of these nuclides in suspended matter were not sufficient to explain their increments in the bottom water. Residence times of Th, Pb and Po were estimated.

  19. U-Pb isotopic evidence pertaining to the age and genesis of uranium mineralisation in Karoo sediments

    International Nuclear Information System (INIS)

    Allsopp, H.L.; Welke, H.J.; Armstrong, R.A.; Clough, W.; Evans, I.B.

    1984-01-01

    Preliminary investigations have been carried out, using the uranium-lead isotopic method, on the uranium mineralisation that occurs within the Karoo sediments. Two occurences were studied, namely the lower Beaufort sediments (Adelaide Subgroup) in the Beaufort West area and the Molteno Formation sediments in the Ficksburg area. The objective were to determine the age of the mineralisation and to study the mode of formation of the ores. The pattern of U-Pb apparent ages for all the Karoo samples is 207 Pb/ 206 Pb age >> 207 Pb* 235 U age > 206 Pb* 238 U age

  20. SHRIMP zircon U-Pb age and its significances of volcanic rocks from banshi basin in south jiangxi province

    International Nuclear Information System (INIS)

    Wang Baofeng; Wu Jianhua

    2011-01-01

    SHRIMP zircon U-Pb dating is applied to geochronological study for tuff of original Jilongzhang formation and rhyolite of original Banshi formation in Banshi basin, located in the Sannan (Longnan, Dingnan, Quannan) -Xunwu volcanic rocks belts in the south of Jiangxi. The result shows that zircon SHRIMP U-Pb age of the tuff is (142.5 ± 1.3) Ma and the age of the rhyolite is (131.4 ± 1.3) Ma. According to the latest international stratigraphic chart, the boundary between Jurassic and Cretaceous is (145.4 ± 4.0) Ma. So original Jilongzhang Formation and original Banshi Formation in Banshi basin were formed during early Early Cretaceous. The volcanic series in Banshi basin belongs to only one volcanic cycle. The features of the rock associations consistent with Wuyi group on the Xiajiang-Guangfeng volcanic rocks belts in the north of Jiangxi, so original Jilongzhang formation falls under E'huling formation and original Banshi formation falls under Shixi formation. (authors)

  1. Zircon U-Pb and molybdenite Re-Os geochronology and Sr-Nd-Pb-Hf isotopic constraints on the genesis of the Xuejiping porphyry copper deposit in Zhongdian, Northwest Yunnan, China

    Science.gov (United States)

    Leng, Cheng-Biao; Zhang, Xing-Chun; Hu, Rui-Zhong; Wang, Shou-Xu; Zhong, Hong; Wang, Wai-Quan; Bi, Xian-Wu

    2012-10-01

    The Xuejiping porphyry copper deposit is located in northwestern Yunnan Province, China. Tectonically, it lies in the southern part of the Triassic Yidun island arc. The copper mineralization is mainly hosted in quartz-dioritic and quartz-monzonitic porphyries which intruded into clastic-volcanic rocks of the Late Triassic Tumugou Formation. There are several alteration zones including potassic, strong silicific and phyllic, argillic, and propylitic alteration zones from inner to outer of the mineralized porphyry bodies. The ages of ore-bearing quartz-monzonitic porphyry and its host andesite are obtained by using the zircon SIMS U-Pb dating method, with results of 218.3 ± 1.6 Ma (MSWD = 0.31, N = 15) and 218.5 ± 1.6 Ma (MSWD = 0.91, N = 16), respectively. Meanwhile, the molybdenite Re-Os dating yields a Re-Os isochronal age of 221.4 ± 2.3 Ma (MSWD = 0.54, N = 5) and a weighted mean age of 219.9 ± 0.7 Ma (MSWD = 0.88). They are quite in accordance with the zircon U-Pb ages within errors. Furthermore, all of them are contemporary with the timing of the Garzê-Litang oceanic crust subduction in the Yidun arc. Therefore, the Xuejiping deposit could be formed in a continental margin setting. There are negative ɛNd(t) values ranging from -3.8 to -2.1 and relatively high initial 87Sr/86Sr ratios from 0.7051 to 0.7059 for the Xuejiping porphyries and host andesites. The (206Pb/204Pb)t, (207Pb/204Pb)t and (208Pb/204Pb)t values of the Xuejiping porphyries and host andesites vary from 17.899 to 18.654, from 15.529 to 15.626, and from 37.864 to 38.52, respectively, indicative of high radiogenic Pb isotopic features. In situ Hf isotopic analyses on zircons by using LA-MC-ICP-MS exhibit that there are quite uniform and slightly positive ɛHf(t) values ranging from -0.2 to +3.2 (mostly between 0 and +2), corresponding to relatively young single-stage Hf model ages from 735 Ma to 871 Ma. These isotopic features suggest that the primary magmas of the Xuejiping porphyries and

  2. Metamorphic P-T path and zircon U-Pb dating of HP mafic granulites in the Yushugou granulite-peridotite complex, Chinese South Tianshan, NW China

    Science.gov (United States)

    Zhang, Lu; Zhang, Lifei; Xia, Bin; Lü, Zeng

    2018-03-01

    Co-existing granulite and peridotite may represent relics of the paleo-suture zone and provides an optimal opportunity for better understanding of orogeny between two blocks. In this study, we carried out petrological and U-Pb zircon dating investigation on the HP mafic granulites associated with peridotite complex at Yushugou in Chinese South Tianshan. The studied samples include garnet-bearing high-pressure mafic granulites which can be subdivided into two types: Type I orthopyroxene-free and Type II orthopyroxene-bearing granulites and amphibolite. Type I granulite (Y21-2) has a mineral assemblage of garnet (33 vol.%), clinopyroxene (32 vol.%) and plagioclase (30 vol.%); and Type II granulite (Y18-8) has a mineral assemblage of garnet (22 vol.%), clinopyroxene (10 vol.%), orthopyroxene (14 vol.%), plagioclase (45 vol.%) and quartz. Garnet in both granulites exhibits core-rim structure characterized by increasing grossular and decreasing pyrope from core to rim. Petrographic observations and phase equilibrium modeling using THERMOCALC in the NCFMASHTO system for the mafic granulites (Y21-2 and Y18-8) show three stages of metamorphism: Stage I (granulite facies) was recognized by the large porphyroblastic garnet core, with P-T conditions of 9.8-10.4 Kbar and 860-900 °C (Y21-2) and 9.9-10.6 Kbar and 875-890 °C (Y18-8), respectively; Stage II (HP granulite facies) has peak P-T conditions of 12.1 Kbar at 755 °C (Y21-2) and 13.8 Kbar at 815 °C (Y18-8) using mineral assemblages combining with garnet rim compositions with maximum grossular and minimum pyrope contents; Stage III (amphibolite facies) was characterized by the development of calcic amphibole in granulites with temperature of 446-563 °C. Therefore, an anticlockwise P-T path characterized by simultaneous temperature-decreasing and pressure-increasing was inferred for the Yushugou HP mafic granulite. Studies of zircon morphology and inclusions, combined with zircon U-Pb dating and REE geochemistry

  3. 230Th-238U disequilibria in historical lavas from Iceland

    International Nuclear Information System (INIS)

    Condomines, M.; Morand, P.; Alleegre, C.J.; Sigvaldason, G.

    1981-01-01

    The 230 Th- 238 U disequilibrium studies on historical lavas from Iceland show a relative homogeneity for Th/U ratios and also a variation for ( 230 Th/ 232 Th) activity ratios at the scale of the island. The ( 230 Th/ 238 U) disequilibrium ratio is always greater than 1 which indicates that partial melting produces magmas with Th/U ratios greater than those of the mantle source. Furthermore, there seems to be a correlation between the variations of ( 230 Th/ 232 Th) (and delta 18 O) ratios and the geographical location of the samples along the active zones of Iceland. We develop and discuss several models in order to explain these variations. (orig.)

  4. Thermal and exhumation history of Sakhalin Island (Russia) constrained by apatite U-Pb and fission track thermochronology

    Science.gov (United States)

    Glorie, Stijn; Alexandrov, Igor; Nixon, Angus; Jepson, Gilby; Gillespie, Jack; Jahn, Bor-Ming

    2017-08-01

    Sakhalin Island represents a key locality to study the tectonic evolution of the western Pacific. The island is located at the Amur-Okhotsk plate margin and records a complex thermotectonic history. Apatite double dating (U-Pb and fission track) and thermal history modelling were applied to three late Eocene granitoid massifs within central and southern Sakhalin: the Aniva, Okhotsk and Langeri complexes. Apatite U-Pb results yield consistent late Eocene (∼40-37 Ma) ages, suggesting rapid post-magmatic cooling. Apatite fission track results reveal bimodal age distributions with late Eocene - early Oligocene (∼38-33 Ma) and early Miocene (∼20-17 Ma) age populations that can be correlated with variations in Uranium and Chlorine concentrations. Thermal history modelling translates the AFT age bimodality into two-phase cooling histories. The timing of the early cooling phase (∼38-33 Ma) corresponds with the apatite U-Pb ages, indicating rapid cooling to at least ∼100 °C during the late Oligocene. The second cooling phase at ∼20-17 Ma cooled the samples to near-surface temperatures. Both cooling phases correspond with regional unconformities and subsequent accelerations in sedimentation rate, suggesting that cooling was a response to rapid exhumation. In addition, our data suggests that the studied terranes record differential exhumation with respect to the structural architecture. The Miocene exhumation pulse is coeval with the timing of transpressional fault displacement and the subsequent opening of the Kuril Basin.

  5. Pb isotope constaints on the extent of crustal recycling into a steady state mantle

    International Nuclear Information System (INIS)

    Galer, S.J.G.; Goldstein, S.L.; Onions, R.K.

    1988-01-01

    Isotopic and geochemical evidence was discussed against recycling of continental crust into the mantle. Element ratios such as Sm/Nd, Th/Sc, and U/Pb in sedimentary masses have remained relatively constant throughout Earth history, and this can only be reconciled with steady state recycling models if new crustal materials added from the mantle have had similar ratios. Such recycling models would also require shorter processing times for U, Th, and Pb through the mantle than are geodynamically reasonable. Models favoring subduction of pelagic sediments as the only recycling mechanism fail to account for the Pb isotopic signature of the mantle. Recycling of bulk crust with Pb isotopic compositions similar to those expected for primitive mantle would be permissable with available data, but there appear to be no plausible tectonic mechanisms to carry this out

  6. Timing of sediment-hosted Cu-Ag mineralization in the Trans-Hudson orogen at Janice Lake, Wollaston Domain, Saskatchewan, Canada

    Science.gov (United States)

    Perelló, José; Valencia, Víctor A.; Cornejo, Paula; Clifford, John; Wilson, Alan J.; Collins, Greg

    2018-04-01

    The Janice Lake Cu-Ag mineralization in the Wollaston Domain of northern Saskatchewan is hosted by a metasedimentary sequence in the upper part of the Wollaston Supergroup of the Trans-Hudson orogen. The Wollaston Supergroup was deposited between 2070 and 1865 Ma in a foreland basin setting constructed over Archean basement of the Hearne craton. The Trans-Hudson orogen underwent final collision and peak metamorphism at 1810 Ma, during consolidation of Laurentia and its amalgamation with the Columbia supercontinent. Titanite is a common constituent of the post-peak metamorphic assemblages of Trans-Hudson lithotectonic units and accompanied disseminated sediment-hosted Cu sulfide mineralization at Janice Lake. Titanite crystals, intergrown with chalcocite over a strike-length of 2 km of Cu-bearing stratigraphy, were dated by the ID-TIMS and LA-ICP-MS U-Pb methods, returning an age range from 1780 to 1760 Ma and a weighted average age of 1775 ± 10 Ma. The titanite ages effectively date the associated chalcocite-dominated sediment-hosted Cu-Ag mineralization and its formation during initial post-orogenic uplift and cooling, 30 myr after peak metamorphism. The age-range and tectonic setting of the Janice Lake mineralization confirms that sediment-hosted Cu mineralization was an integral part of the metallogenic endowment of Columbia and that its emplacement coincided with the continental-scale Trans-Hudson orogeny rather than with diagenesis and extensional basin development 100 myr earlier.

  7. A study of U-Pb isotopic evolutionary system in Chanziping uranium deposit

    International Nuclear Information System (INIS)

    Xu Weichang; Huang Shijie; Xia Yuliang.

    1988-01-01

    Chanziping uranium deposit occurred in the black siliceous slate of Lower cambrian. The uranium mineralization was controlled by both interstratified fault belt and the ore-bearing beds. Based on the study of the U-Pb isotopic system of the various rocks, ores and minerals in the ore-bearing beds, the authors find out the obvious disequilibrium of U-Pb isotopic composition in most rock samples which indicates the loss of uranium form the ore-bearing beds and surrounding granite. Its counting loss ranges from 30 to 80%. The age of rich ores of the U-Pb concordance diagram and the U-Pb three stage model are t 1 = 523 ± 19M. Y. , t 2 = 22 ± 2 M.Y.. The isochronal ages for pitchblend are 75 ± 4 M.Y., 43 ± 7 M.Y., and for rock is 416 M.y.. These data shows that the uranium in ore-bearing beds was mainly derived from the ore-bearing beds itself and partly from the surrounding granite. The ore deposit can be considered to be of stratabound uranium deposit of sedimentation and late transformation type

  8. Pan-African U-Pb zircon age from apatite-magnetite veins of eastern ghats granulite belt, India

    International Nuclear Information System (INIS)

    Kovach, V.P.; Salnikova, E.B.; Kotov, A.B.; Yakovleva, S.Z.; Rao, A.T.

    1997-01-01

    206 Pb/ 238 U ages of zircon correspond to 502±3 Ma and 207 Pb/ 206 Pb ages are equal to 508±14 Ma. U-Pb isotopic study of the Kasipatnam zircon has led to the recognition of pan-African thermal event in the eastern ghats granulite belt, India. (author)

  9. Determination of sedimentation rates in Izmir Bay by 210Pb dating technique

    International Nuclear Information System (INIS)

    Ichedef, M.; Yener, G.; Ugur, A.; Oezden, B.; Goenuelalan, F.; Akoezcan, S.; Bueyuekisik, B.; Koeksal, E. Y.

    2006-01-01

    Environmental 2 10Pb (natural) dating technique was applied to determine sedimentation rates in Izmir Bay, near the heavily industrialized Turkish Coastal zone of the Aegean Sea. Core samples from different 20 stations in the inner bay were collected with core sampler and sedimentation rates were estimated from the vertical distribution of excess 2 10Pb. Core samples were stored for a period of 2-3 half-lives (9-14 months) of 2 10Po (t 1 /2=138 d) before analysis to allow build-up of 2 10Po from 2 10Pb. Po was collected on cupper disks by electrochemical deposition. Then, 2 10Pb activities were determined undirectly from 2 10Po activities. Measurement of 2 10Po were made through its 5.30 MeV alpha particle emission, using 2 09Po as the internal tracer. Measurements were made by PIPS (Passivated Implanted Planar Silicon) detector. The sedimentation rates for core samples analysed so far were calculated to vary from 0.198 cm y - 1 to 0.489 cm y - 1. The highest unsupported 2 10Pb concentrations (104 Bq kg - 1) were measured in the 8.station where the Ilica, Bayrakli and Bornova streams empty, and nearest to the harbour

  10. 230Th-234U Model-Ages of Some Uranium Standard Reference Materials

    Energy Technology Data Exchange (ETDEWEB)

    Williams, R W; Gaffney, A M; Kristo, M J; Hutcheon, I D

    2009-05-28

    The 'age' of a sample of uranium is an important aspect of a nuclear forensic investigation and of the attribution of the material to its source. To the extent that the sample obeys the standard rules of radiochronometry, then the production ages of even very recent material can be determined using the {sup 230}Th-{sup 234}U chronometer. These standard rules may be summarized as (a) the daughter/parent ratio at time=zero must be known, and (b) there has been no daughter/parent fractionation since production. For most samples of uranium, the 'ages' determined using this chronometer are semantically 'model-ages' because (a) some assumption of the initial {sup 230}Th content in the sample is required and (b) closed-system behavior is assumed. The uranium standard reference materials originally prepared and distributed by the former US National Bureau of Standards and now distributed by New Brunswick Laboratory as certified reference materials (NBS SRM = NBL CRM) are good candidates for samples where both rules are met. The U isotopic standards have known purification and production dates, and closed-system behavior in the solid form (U{sub 3}O{sub 8}) may be assumed with confidence. We present here {sup 230}Th-{sup 234}U model-ages for several of these standards, determined by isotope dilution mass spectrometry using a multicollector ICP-MS, and compare these ages with their known production history.

  11. Datation U_Pb : âge de mise en place du magmatisme bimodal des Jebilet centrales (chaîne Varisque, Maroc). Implications géodynamiquesU_Pb dating: emplacement age of the bimodal magmatism of central Jebilet (Variscan Belt, Morocco). Geodynamic implications

    Science.gov (United States)

    Essaifi, Abderrahim; Potrel, Alain; Capdevila, Ramon; Lagarde, Jean-Louis

    2003-01-01

    The bimodal magmatism of central Jebilet is dated to 330.5 +0.68-0.83 Ma by UPb dating on zircons. This age, similar to that of the syntectonic Jebilet cordierite-bearing granitoids, corresponds to the age of the local major tectonometamorphic event. The syntectonic plutonism of the Jebilet massif, composed of tholeiitic, alkaline, and peraluminous calc-alkaline series, is variegated. Magmas emplacement was favoured by the local extension induced by the motion along the western boundary of the Carboniferous basins of the Moroccan Meseta. The Jebilet massif exemplifies the activation of various magmas sources during an episode of continental convergence and crustal wrenching.

  12. 234U/230Th ratio as an indicator of redox state, and U, Th and Ra behavior in briney aquifers

    International Nuclear Information System (INIS)

    Laul, J.C.; Smith, M.R.; Hubbard, N.

    1985-06-01

    The 234 U/ 230 Th ratio serves as an in-situ indicator of the redox state in groundwater aquifers. The higher this ratio, the more U there is in the +6 state and thus a lesser reducing environment. Radium is retarded in the shallow aquifer and its sorption is dependent on the CaSO 4 content and redox state. Relative to Ra, U and Th are highly sorbed. The total retardation factor for Th is approx.1400 and mean sorption time for 228 Th is approx.10 days in the shallow zone. The desorption rate of Ra is significantly slower in the shallow than in the deep aquifer. There is no effect of colloids in brines. 6 refs., 5 figs., 2 tabs

  13. U enrichment and Th/U fractionation in Archean boninites: Implications for paleo-ocean oxygenation and U cycling at juvenile subduction zones

    Science.gov (United States)

    Manikyamba, C.; Said, Nuru; Santosh, M.; Saha, Abhishek; Ganguly, Sohini; Subramanyam, K. S. V.

    2018-05-01

    Phanerozoic boninites record enrichments of U over Th, giving Th/U: 0.5-1.6, relative to intraoceanic island arc tholeiites (IAT) where Th/U averages 2.6. Uranium enrichment is attributed to incorporation of shallow, oxidized fluids, U-rich but Th-poor, from the slab into the melt column of boninites which form in near-trench to forearc settings of suprasubduction zone ophiolites. Well preserved Archean komatiite-tholeiite, plume-derived, oceanic volcanic sequences have primary magmatic Th/U ratios of 4.4-3.6, and Archean convergent margin IAT volcanic sequences, having REE and HFSE compositions similar to Phanerozoic IAT equivalents, preserve primary Th/U of 4-3.6. The best preserved Archean boninites of the 3.0 Ga Olondo and 2.7 Ga Gadwal greenstone belts, hosted in convergent margin ophiolite sequences, also show relative enrichments of U over Th, with low average Th/U ∼3 relative to coeval IAT, and Phanerozoic counterparts which are devoid of crustal contamination and therefore erupted in an intraoceanic setting, with minimal contemporaneous submarine hydrothermal alteration. Later enrichment of U is unlikely as Th-U-Nb-LREE patterns are coherent in these boninites whereas secondary effects induce dispersion of Th/U ratios. The variation in Th/U ratios from Archean to Phanerozoic boninites of greenstone belts to ophiolitic sequences reflect on genesis of boninitic lavas at different tectono-thermal regimes. Consequently, if the explanation for U enrichment in Phanerozoic boninites also applies to Archean examples, the implication is that U was soluble in oxygenated Archean marine water up to 600 Ma before the proposed great oxygenation event (GOE) at ∼2.4 Ga. This interpretation is consistent with large Ce anomalies in some hydrothermally altered Archean volcanic sequences aged 3.0-2.7 Ga.

  14. Assessment of natural radionuclides concentration from 238U and 232Th series in Virginia and Burley varieties of Nicotiana tabacum L

    International Nuclear Information System (INIS)

    Silva, Carolina Fernanda da

    2015-01-01

    Brazil is the largest exporter and second largest producer of tobacco worldwide, according to the crop production of 2013/2014. The tobacco plant (Nicotiana tabacum L.) is used to manufacture all derivatives and the chemical composition of the resulting tobacco products varies with the type of tobacco leaves, how they are grown, the region where they are cultivated, the characteristics of preparation (compression, filter and paper) and the temperature variations resulting from the incomplete combustion of tobacco. Tobacco products are extensively used throughout the world, and the most consumed are cigarettes, cigars and narghile. The damaging effects that these products cause to human health are discussed globally, and many surveys are performed with the aim of relating the use of these products with various illnesses. There is a lack of information about the radiological characterization of the tobacco plant both in international and Brazilian literature. The objective of this study was to determine the concentration of radionuclides 238 U, 234 U, 230 Th, 22 '6Ra, 210 Pb and 210 Po, members from the 238 U decay series, and the radionuclides 232 Th and 228 Ra members of the 232 Th decay series in the varieties Burley and Virginia, which are the most cultivated in Brazil. Plants from these varieties were cultivated in pots with organic substrate and fertilizer and also acquired from the producers and analyzed by alpha spectrometry for U and Th isotopes and 210 Po determination, and gross alpha and beta counting, 228 Ra, 226 Ra and 210 Pb determination. The whole plant, from both places, was analyzed; root, stem, leaves, as well as the organic substrate, the fertilizers, and the soil. The results for U and Th isotopes presented values below the detection limits of the methods to the leaves and stems of all plants analyzed, with measurable results only in roots, soil, and substrate. The radionuclides 226 Ra, 228 Ra, 210 Pb, and 210 Po, were determined in most

  15. 230Th/238U and 226Ra/230Th fractionation in young basaltic glasses from the East Pacific Rise

    International Nuclear Information System (INIS)

    Reinitz, I.; Turekian, K.K.

    1989-01-01

    Mid-ocean ridge basalt (MORB) glasses treated to remove manganese and iron oxyhydroxide coatings containing U and Th decay chain nuclides sequestered from the ambient aqueous environment show little fractionation of ( 230 Th) from ( 238 U), but extensive enrichment of ( 226 Ra) over ( 230 Th). Chronometry based on ( 230 Th)-( 238 U) disequilibrium yields a mean age of 151,000 ± 55,000 (2σ) years ago for Th-U fractionation, from a source region with Th/U (atom ratio) = 1.58 ± 0.43 (2σ). ( 226 Ra) excesses over ( 230 Th) indicate an enrichment event more recent than the fractionation of Th from U. ( 226 Ra/ 230 Th) correlates well with K/U, providing a rough means of estimating the age since eruption of MORB glasses. (orig.)

  16. Gamma Spectrometric Determination of U, Th, K and Some Geochemical Applications

    International Nuclear Information System (INIS)

    Dodona, A.; Tashko, A.

    2001-01-01

    The application of 'in situ' gamma-spectrometric method (''infinite'' environment), made possible the simultanious determination of U, Th and K. 4 channel gamma-spectrometric analyser with NaI(TI) scintilation counter crystal detector (103 cm 3 φ=50x50mm) was used to determin U, Th(more than 1-2 ppm) and K (more than 1%) in laboratory conditions. The detector was inserted into a lead camera and calibrated for measurement geometry with vessel of ''Marineli'' type of a 17o cm 3 volume. The study of main factors, which influence in the gamma spectrometric measurements, (the technical, physical, geometrical and time parameters) has been carried out. International standards of U, Th, K and internal monitoring standard samples are used for the calibration. External analytical control has been realized by other radiometric and chemical methods. The detection limits ( 1 ppm Th, 2ppm U and 1% K) and the relative errors (17-20% for 1-10 ppm U, Th and 10-15% for more than 10 ppm U, Th and more than 1% K) guarantee a quantitative analysis that may be used successfully in the geochemical studies. Some geochemical applications, based on the content of Th, U and Th/U ratio in rocks samples that we have we have analyzed with this method, are shown in this paper. U, Th and their ratio are used as trace elements to indicate the differences between the acidic magmatic rocks of Albania (Th/U ratio=2-6 and>10). The bimodal character of Th/U scattering in ignimbrides and monzonites (Korabi zone) shows that in addition to the ''normal'' rocks, there are also some ones enriched with Th, So, the differential analysis of Th, U, and K may be used as geochemical exploration criteria for the radioactive and non-radioactive mineralization, such as REE (Rare Earth Elements), phospghorites, bauxites, placers etc. (authors)

  17. Two mineralization events in the Baiyinnuoer Zn-Pb deposit in Inner Mongolia, China: Evidence from field observations, S-Pb isotopic compositions and U-Pb zircon ages

    Science.gov (United States)

    Jiang, Si-Hong; Chen, Chun-Liang; Bagas, Leon; Liu, Yuan; Han, Ning; Kang, Huan; Wang, Ze-Hai

    2017-08-01

    The Xing-Mong Orogenic Belt (XMOB) is located in the eastern part of the Central Asian Orogenic Belt (CAOB) and has experienced multiple tectonic events. The Baiyinnuoer Pb-Zn deposit may be a rare case that documents two periods of mineralization in the tectonically complex XMOB. There are two types of Pb-Zn mineralization in the deposit: (1) skarn-type ore, hosted by the skarn in the contact zone between marble and granodiorite and within the marble and (2) vein-type ore, hosted by crystal tuff and feldspar porphyry. This study revealed that the host rocks, mineral assemblages, mineralization occurrences, S-Pb isotopes, and ages between the two types of ore are notably different. Zircon U-Pb dating indicates that the granodiorite was emplaced in the Early Triassic (244 ± 1 to 242 ± 1 Ma), the crystal tuff was deposited in the Early Cretaceous (140 ± 1 to 136 ± 1 Ma), and the feldspar porphyry was intruded in the Early Cretaceous (138 ± 2 to 136 ± 2 Ma). The first skarn mineralization occurred at ∼240 Ma and the second vein-type Pb-Zn mineralization took place between 136 and 129 Ma. Thus the Triassic orebodies were overprinted by Early Cretaceous mineralization. The sphalerite and galena from the skarn mineralization have higher δ34S values (-4.7 to +0.3‰) than the sphalerite, galena and aresenopyrite from the vein-type mineralization (-7.5 to -4.2‰), indicating different sulfur sources or ore-forming processes for the two types of mineralization. The Pb isotopic compositions of the two types of ore are very similar, suggesting similar lead sources. Geochemistry and Nd-Pb-Hf isotopic systematics of the igneous rocks in the region show that the Triassic granodiorite was generated from hybridization of mafic and felsic magmas due to strong crust-mantle interaction under the collisional setting that resulted following the closure of the Paleo-Asian Ocean and the collision of North China and Siberian cratons at the end of the Permian; while the

  18. U-Pb geochronology documents out-of-sequence emplacement of ultramafic layers in the Bushveld Igneous Complex of South Africa.

    Science.gov (United States)

    Mungall, James E; Kamo, Sandra L; McQuade, Stewart

    2016-11-14

    Layered intrusions represent part of the plumbing systems that deliver vast quantities of magma through the Earth's crust during the formation of large igneous provinces, which disrupt global ecosystems and host most of the Earth's endowment of Pt, Ni and Cr deposits. The Rustenburg Layered Suite of the enormous Bushveld Igneous Complex of South Africa has been presumed to have formed by deposition of crystals at the floor of a subterranean sea of magma several km deep and hundreds of km wide called a magma chamber. Here we show, using U-Pb isotopic dating of zircon and baddeleyite, that individual chromitite layers of the Rustenburg Layered Suite formed within a stack of discrete sheet-like intrusions emplaced and solidified as separate bodies beneath older layers. Our U-Pb ages and modelling necessitate reassessment of the genesis of layered intrusions and their ore deposits, and challenge even the venerable concept of the magma chamber itself.

  19. REE, Sm-Nd and U-Pb zircon study of eclogites from the Alpine External Massifs (Western Alps): Evidence for crustal contamination

    International Nuclear Information System (INIS)

    Paquette, J.L.; Eidgenoessische Technische Hochschule, Zurich; Menot, R.P.; Peucat, J.J.

    1989-01-01

    A geochemical and geochronological study of the Alpine External Crystalline Massifs (AECM) of Aiguilles Rouges, Belledonne and Argentera was undertaken in order to constrain the geodynamic evolution of this segment of the Variscan foldbelt. Another aim of the study is to characterize the behaviour of isotopic markers, in particular the U-Pb zircon system, under high-grade metamorphic conditions. The whole-rock geochemistry of eclogites and amphibolites was investigated using major and trace element (including the REE) analytical techniques; isotopic studies were performed by application of the Sm-Nd whole-rock and U-Pb zircon methods. In terms of regional geological history, the early development of metamorphic and magmatic activity in the AECM is typical of the extensional tectonic regime observed throughout the Variscan foldbelt during the Cambro-Ordovician (i.e. basic magmatism dated at 475-450 Ma). The composition of the metabasic rocks is closely similar to tholeiites emplaced into thinned continental crust which are generally associated with the initial stages of oceanic rifting. The source regions for these metabasics are characterized by initial ε Nd values between +6 and +8, suggesting depleted mantle sources influenced by a weak crustal component and/or the existence of a metasomatised lithosphere. The multi-stage eclogite-facies metamorphism is dated at 425-395 Ma (i.e. Silurian). An application of the U-Pb method, associated with the artificial abrasion of zircon grains, has led to the recognition of a weak crustal contamination in the metabasic protoliths. This is implied by the Archaean and Lower Proterozoic upper intercepts on Concordia - devoid of geological significance - which reflect the presence of a pre-existing basement to the AECM. (orig./WL)

  20. Teneur en uranium et datation U-Th des tissus osseux et dentaires fossiles de la grotte du Lazaret

    Science.gov (United States)

    Michel, Véronique; Falguères, Christophe; Yokoyama, Yuji

    1997-09-01

    Fossil bone and dental tissues from Lazaret cave and modern ones are here the subject of a comparative microscopical study. Porous tissues such as dentine and bone have retained their Haversian and Tomes canals respectively. However, cracked areas with calcite were detected, indicating a water percolation within porous tissues and an alteration of tissue in places. In addition, compact fossil enamel is particularly well preserved. These results are essential for U-Th and ESR dating application. Uranium contents, U-Th ages of two fossil mandibular tissues, two tibias and of six burnt fossil bones are presented and discussed.

  1. Radiocrystallographic study of titanites from Xerem, Rio de Janeiro

    International Nuclear Information System (INIS)

    Baptista, A.; Baptista, N.R.

    1987-01-01

    The conclusions of the radiocrystallographic studies in titanite crystals - CaTi[SiO 4 ] (0,0H,F) from two rocks with different petrogenesis, from Xerem, Rio de Janeiro State are described. The rocks was granite and nepheline-gneiss and the Spetrochemical analysis showed different compositions to crystals from each one of the rocks. This different composition was eough to development of comparative study using optical determination and petrographic analysis. (C.D.G.) [pt

  2. Assessment of natural radionuclides concentration from {sup 238}U and {sup 232}Th series in Virginia and Burley varieties of Nicotiana tabacum L; Avaliacao da concentracao dos radionuclideos naturais das series do {sup 238}U e {sup 232}Th nas variedades Burley e Virginia da Nicotiana tabacum L.

    Energy Technology Data Exchange (ETDEWEB)

    Silva, Carolina Fernanda da

    2015-07-01

    Brazil is the largest exporter and second largest producer of tobacco worldwide, according to the crop production of 2013/2014. The tobacco plant (Nicotiana tabacum L.) is used to manufacture all derivatives and the chemical composition of the resulting tobacco products varies with the type of tobacco leaves, how they are grown, the region where they are cultivated, the characteristics of preparation (compression, filter and paper) and the temperature variations resulting from the incomplete combustion of tobacco. Tobacco products are extensively used throughout the world, and the most consumed are cigarettes, cigars and narghile. The damaging effects that these products cause to human health are discussed globally, and many surveys are performed with the aim of relating the use of these products with various illnesses. There is a lack of information about the radiological characterization of the tobacco plant both in international and Brazilian literature. The objective of this study was to determine the concentration of radionuclides {sup 238}U, {sup 234}U, {sup 230}Th, {sup 22}'6Ra, {sup 210}Pb and {sup 210}Po, members from the {sup 238}U decay series, and the radionuclides {sup 232}Th and {sup 228}Ra members of the {sup 232}Th decay series in the varieties Burley and Virginia, which are the most cultivated in Brazil. Plants from these varieties were cultivated in pots with organic substrate and fertilizer and also acquired from the producers and analyzed by alpha spectrometry for U and Th isotopes and {sup 210}Po determination, and gross alpha and beta counting, {sup 228}Ra, {sup 226}Ra and {sup 210}Pb determination. The whole plant, from both places, was analyzed; root, stem, leaves, as well as the organic substrate, the fertilizers, and the soil. The results for U and Th isotopes presented values below the detection limits of the methods to the leaves and stems of all plants analyzed, with measurable results only in roots, soil, and substrate. The

  3. Volcano-climate interactions during the PETM and U-Pb dating from the Fur Formation, Denmark

    Science.gov (United States)

    Jones, Morgan; Augland, Lars; Svensen, Henrik; Tegner, Christian; Planke, Sverre; Willumsen, Pi

    2016-04-01

    The Palaeocene-Eocene Thermal Maximum (PETM) at ~56 Ma is one of the most extreme global warming events in Earth's history. Vast quantities of CO2 and CH4 were released to the atmosphere, causing a rapid (within 20,000 years) 5-6 °C warming that persisted for ~170,000 years. The PETM occurred during an abnormally warm period in Earth history, and was followed by other hyperthermal events later in the Eocene. The PETM also coincided with the second and major pulse of magmatism from the North Atlantic Igneous Province (NAIP) during the break-up of Laurentia and Eurasia at 54-56 Ma. Evidence of explosive volcanism is prevalent at Fur, an island in northern Denmark, where over 180 distinct >1 cm thick ash horizons are preserved in a shallow marine succession (numbered from #-39 to #+140). These ash layers are believed to have originated from volcanic centres in east Greenland and western UK, which indicates that that they were formed during very large volcanic eruptions. Here we present the results of two key sections of the Fur Formation: a beach section at Stolleklint that includes sediment deposited syn-PETM, and a quarry section at Jenshøj that encompasses post-PETM sediments. A detailed chemostratigraphic log of δ13C (TOC) and δ15N values through the section suggests that there may be part of sequence missing, either through glaciotectonism or a depositional hiatus. The δ13C values around ash #-33 are typical of the PETM negative carbon isotope excursion (-31 to -32 ‰), yet are back to background values of ~-26 ‰ just four metres up section. The quarry section around ash #+19 displays further variations in δ13C values, suggesting a coincidence with one of the later Eocene hyperthermal events. High precision U-Pb dating of magmatic zircons from ash layer #+19 conforms to a post-PETM depositional age, giving a mean deposition rate of approximately ~5 cm kyr-1. The correlation between the largest ash layers (#-33 and #+19) and the largest perturbations to

  4. Weight perceptions, misperceptions, and dating violence victimization among U.S. adolescents.

    Science.gov (United States)

    Farhat, Tilda; Haynie, Denise; Summersett-Ringgold, Faith; Brooks-Russell, Ashley; Iannotti, Ronald J

    2015-05-01

    Dating violence is a major public health issue among youth. Overweight/obese adolescents experience peer victimization and discrimination and may be at increased risk of dating violence victimization. Furthermore, given the stigma associated with overweight/obesity, perceptions and misperceptions of overweight may be more important than actual weight status for dating violence victimization. This study examines the association of three weight indices (weight status, perceived weight, and weight perception accuracy) with psychological and physical dating violence victimization. The 2010 baseline survey of the 7-year NEXT Generation Health Study used a three-stage stratified clustered sampling design to select a nationally representative sample of U.S. 10th-grade students (n = 1,983). Participants who have had a boyfriend/girlfriend reported dating violence victimization and perceived weight. Weight status was computed from measured height/weight. Weight perception accuracy (accurate/underestimate/overestimate) was calculated by comparing weight status and perceived weight. Gender-stratified regressions examined the association of weight indices and dating violence victimization. Racial/ethnic differences were also examined. The association of weight indices with dating violence victimization significantly differed by gender. Overall, among boys, no associations were observed. Among girls, weight status was not associated with dating violence victimization, nor with number of dating violence victimization acts; however, perceived weight and weight perception accuracy were significantly associated with dating violence victimization, type of victimization, and number of victimization acts. Post hoc analyses revealed significant racial/ethnic differences. White girls who perceive themselves (accurately or not) to be overweight, and Hispanic girls who are overweight, may be at increased risk of dating violence victimization. These findings suggest a targeted approach to

  5. Early cretaceous zircon SHRIMP U-Pb age of the trachyte and its significances of the Gan-Hang belt

    International Nuclear Information System (INIS)

    Liu Feiyu; Wu Jianhua; Liu Shuai

    2009-01-01

    The Shixi basin was located at Gan-Hang tectonic volcanic uranium deposit of rock-magma belt which belong to a part of the Mesozoic volcanic rocks in the northeastern of China. The appearance of the trachyte in Shixi basin have the majoy elements characteristic of the shoshonite series volcanic rocks. To determine the geological age of trachyte have very important significance on the geodynamics research and the study on the cause of uranium mineralization. The zircons of the trachyte have clear ring and high Th/U ratio which belong to the typical magmatic zircons. The zircon SHRIMP U-Pb dating resules show that 14points' age range is very smaller is 132-144 Ma and the weighted average age is (137.00±0.94)Ma which represents the diagenetic age of volcanic rocks. Accronding to the latest International Stratigraphic Chart the boundary of Jurassic and Cretaceous is (145.4±4.0)Ma. So the trachyte of Shixi Group belong to early Cretaceous. The large-scale acidic volcanic activity occurred in the Early Cretaceous in Southeastern China, and the Volcanic uranium deposit of Gan-Hang tectonic belt relate to Alkali metasomatism Uranium mineralization also occurred in the Early Cretaceous (120-130 Ma). The determined of trachyte in Shixi Group in the Early Cretaceous show that the acidic volcanic activity have connection with magma activity and the early Uranium mineralization consistent with the Alkali magma activity. (authors)

  6. Geology and U-Pb geochronology of the Banabuiu granite, Northeastern Ceara, Brazil; Geologia y geocronologia U-Pb del granito de Banabuiu, Noreste de Ceara, Brasil

    Energy Technology Data Exchange (ETDEWEB)

    Lima, M. N.; Nogueira Neto, J. A.; Azevedo, M. R.; Valle Aguado,

    2010-07-01

    The Banabuiu massif crops out in the Central Ceara Domain (DCC) of the Borborema Province (NE Brasil), as an N-S elongate granite intrusion, concordant with the regional structures. It was emplaced into basement rocks of Paleoproterozoic age, extensively transformed into gneisses and migmatites during the Brasilian orogeny ({approx}600 Ma). Using U-Pb zircon dating, the crystallization age of the Banabuiu syn-kinematic two-mica granite was estimated at 578.6 {+-} 6.5 Ma. The granite is strongly peraluminous (A/CNK 1,098 - 1,134) and shows a typical S-type geochemical signature. The {epsilon}Nd{sub 5}80 values are strongly negative ({epsilon}Nd{sub 5}80 = -19 a - 23) and partially overlap with those of the Paleoproterozoic gneissmigmatite complex ({epsilon}Nd{sub 5}80 = -12 to -26), suggesting that the parental magmas of the Banabuiu granite could have been produced by partial melting of similar crustal materials. (Author) 21 refs.

  7. The behavior of particle-reactive tracers in a high turbidity environment: 234Th and 210Pb on the Amazon continental shelf

    International Nuclear Information System (INIS)

    Smoak, J.M.; DeMaster, D.J.; Pope, R.H.; Kuehl, S.A.; McKee, B.A.

    1996-01-01

    Excess 234 Th and 210 Pb seabed inventories were measured in cores collected from the Amazon continental shelf to examine particle scavenging and seabed dynamics. Typical excess 210 Pb inventories range from 100 to 300 dpm cm -2 , and the total excess 210 Pb inventory for the Amazon shelf was determined to be 2.7 x 10 17 dpm. The 210 Pb measurements indicate that particle-reactive species are scavenged not only form the Amazon River but also from the lateral advection of offshore water. In order to sustain the 210 Pb inventories, the volume of water supplied by the lateral advection from offshore must be approximately five to ten times the water discharge of the Amazon River. This lateral advection supplies about 67% of the total excess 210 Pb to the Amazon continental shelf with relatively small contributions from riverine input (31%), atmospheric fallout (2.3%), and in-situ production (0.1%). The 234 Th inventories were measured on four cruises, which occurred during periods of differing river discharge, wind stress, and flow rates of the North Brazil Current. The 234 Th excess seabed inventories show large spatial and seasonal variability, with a range from 0 to 22 dpm cm -2 . This approach indicates that for most of the shelf, the inventories of the shorter-term tracer ( 234 Th) are less than predicted by the inventories of the longer-term tracer ( 210 Pb). There are two explanations for this trend. The first is that a larger portion of the 234 Th inventory occurs in the fluid muds or the water column relative to 210 Pb. The second is that the supply of offshore water, scavenging efficiency, and/or deposition have been lower over the two year study period relative to the last one hundred years. 38 refs., 7 figs

  8. Anthropogenic contributions to atmospheric Hg, Pb and As accumulation recorded by peat cores from southern Greenland and Denmark dated using the 14C "bomb pulse curve"

    Science.gov (United States)

    Shotyk, W.; Goodsite, M. E.; Roos-Barraclough, F.; Frei, R.; Heinemeier, J.; Asmund, G.; Lohse, C.; Hansen, T. S.

    2003-11-01

    = 1.1481 ± 0.0002 in the leached fraction and 1.1505 ± 0.0002 in the residual fraction) which is too radiogenic to be explained in terms of gasoline lead alone, but compares well with values for U.K. coals. In contrast, the lowest values for 206Pb/ 207Pb in the DK profile (1.1370 ± 0.0003 in the leached fraction and 1.1408 ± 0.0003 in the residual fraction) are found in the sample dating from AD 1979: this shows that the maximum contribution of leaded gasoline occurred approximately 25 yr after the zenith in total anthropogenic Pb deposition.

  9. Magmatic tempo of Earth's youngest exposed plutons as revealed by detrital zircon U-Pb geochronology.

    Science.gov (United States)

    Ito, Hisatoshi; Spencer, Christopher J; Danišík, Martin; Hoiland, Carl W

    2017-09-29

    Plutons are formed by protracted crystallization of magma bodies several kilometers deep within the crust. The temporal frequency (i.e. episodicity or 'tempo') of pluton formation is often poorly constrained as timescales of pluton formation are largely variable and may be difficult to resolve by traditional dating methods. The Hida Mountain Range of central Japan hosts the youngest exposed plutons on Earth and provides a unique opportunity to assess the temporal and spatial characteristics of pluton emplacement at high temporal resolution. Here we apply U-Pb geochronology to zircon from the Quaternary Kurobegawa Granite and Takidani Granodiorite in the Hida Mountain Range, and from modern river sediments whose fluvial catchments include these plutons in order to reconstruct their formation. The U-Pb data demonstrate that the Kurobegawa pluton experienced two magmatic pulses at ~2.3 Ma and ~0.9 Ma; whereas, to the south, the Takidani pluton experienced only one magmatic pulse at ~1.6 Ma. These data imply that each of these magmatic systems were both spatially and temporally distinct. The apparent ~0.7 Myr age gap between each of the three magmatic pulses potentially constrains the recharge duration of a single pluton within a larger arc plutonic complex.

  10. Nové U-Pb datování zirkonů z bohutínského pně v příbramské rudní oblasti

    Czech Academy of Sciences Publication Activity Database

    Žák, Karel; Svojtka, Martin; Breiter, Karel; Ďurišová, Jana; Veselovský, F.; Pašava, J.

    2015-01-01

    Roč. 2014, č. 1 (2015), s. 43-49 ISSN 0514-8057 R&D Projects: GA ČR GA13-15390S Institutional support: RVO:67985831 Keywords : Bohemian Massif * Central Bohemian Pluton * Bohutím Stock * zircon U-Pb dating Subject RIV: DB - Geology ; Mineralogy

  11. M sub shell X-ray emission cross section measurements for Pt, Au, Hg, Pb, Th and U at 8 and 10 keV synchrotron photons

    International Nuclear Information System (INIS)

    Kaur, Gurpreet; Gupta, Sheenu; Tiwari, M.K.; Mittal, Raj

    2014-01-01

    Highlights: • First time M sub shell fluorescence cross section measurements at 8 and 10 keV photons. • Comparison with theoretical evaluations from different model data for parameters. • Explained the large deviations from the trend of parameters with atomic number Z. • A specific pattern of cross sections with Z is predicted in the region, 78 ⩽ Z ⩽ 92. • Confirmation of prediction requires more experiment in these Z and energy region. -- Abstract: M sub shell X-ray emission cross sections of Pt, Au, Hg, Pb, Th and U at 8 and 10 keV photon energies have been determined with linearly polarized photon beam from Indus-2 synchrotron source. The measured cross sections have been reported for the first time and were used to check the available theoretical Dirac–Hartree–Slater (DHS) and Dirac–Fock (DF) values reported in literature and also the presently derived Non Relativistic Hartree–Slater (NRHS), DF and DHS values for M ξ , M δ , M α , M β , M γ , M m1 and M m2 group of X-rays

  12. U-Th-Ra disequilibria at the Masaya (Nicaragua); Desequilibres U-Th-Ra au Masaya (Nicaragua)

    Energy Technology Data Exchange (ETDEWEB)

    Sigmarsson, O; Condomines, M [Centre de Recherches Volcanologiques, CNRS URA-10, 63 - Clermont Ferrand (France)

    1997-12-31

    {sup 238}U-{sup 230}Th-{sup 226}Ra radioactive disequilibria were measured in several basalt samples of the post-caldera flows of the Masaya volcano (Nicaragua). {sup 230}Th/{sup 232}Th ratios are from the highest known in the world (about 2.53) with {sup 230}Th/{sup 238}U ratios close to 1. These exceptionally high isotopic thorium ratios from the Masaya and other neighboring volcanoes (Conception, Cerro Negro, Momotombo) are followed by very high {sup 10}Be/{sup 9}Be ratios (60 10{sup -11} for the 1722 flow). These geochemical characteristics with {delta}{sup 18}O of typical mantle origin (5.55) suggest an influence of the subducted sediments fluids in the magma source. The age of the metasomatism ranges from 10 to 0.3 Ma. Initial {sup 226}Ra/{sup 230}Th ratios measured in four historical flows vary from 1.3 to 1.4 and are anti-correlated with the Th content. These variations are probably linked to the fractionated crystallisation of plagioclase minerals. The initial {sup 226}Ra/Ba ratio remains constant and suggests the existence of a huge stationary magmatic reservoir. This hypothesis is also confirmed by the disproportion between the SO{sub 2} quantity emitted by the volcano and by the degassing of lavas on the ground. The {sup 226}Ra excess observed in the Masaya lavas can be the result of a second stage of metasomatism which occurred less than 8000 years B.P. during partial fusion. Abstract only. (J.S.).

  13. U-Th-Ra disequilibria at the Masaya (Nicaragua); Desequilibres U-Th-Ra au Masaya (Nicaragua)

    Energy Technology Data Exchange (ETDEWEB)

    Sigmarsson, O.; Condomines, M. [Centre de Recherches Volcanologiques, CNRS URA-10, 63 - Clermont Ferrand (France)

    1996-12-31

    {sup 238}U-{sup 230}Th-{sup 226}Ra radioactive disequilibria were measured in several basalt samples of the post-caldera flows of the Masaya volcano (Nicaragua). {sup 230}Th/{sup 232}Th ratios are from the highest known in the world (about 2.53) with {sup 230}Th/{sup 238}U ratios close to 1. These exceptionally high isotopic thorium ratios from the Masaya and other neighboring volcanoes (Conception, Cerro Negro, Momotombo) are followed by very high {sup 10}Be/{sup 9}Be ratios (60 10{sup -11} for the 1722 flow). These geochemical characteristics with {delta}{sup 18}O of typical mantle origin (5.55) suggest an influence of the subducted sediments fluids in the magma source. The age of the metasomatism ranges from 10 to 0.3 Ma. Initial {sup 226}Ra/{sup 230}Th ratios measured in four historical flows vary from 1.3 to 1.4 and are anti-correlated with the Th content. These variations are probably linked to the fractionated crystallisation of plagioclase minerals. The initial {sup 226}Ra/Ba ratio remains constant and suggests the existence of a huge stationary magmatic reservoir. This hypothesis is also confirmed by the disproportion between the SO{sub 2} quantity emitted by the volcano and by the degassing of lavas on the ground. The {sup 226}Ra excess observed in the Masaya lavas can be the result of a second stage of metasomatism which occurred less than 8000 years B.P. during partial fusion. Abstract only. (J.S.).

  14. Dissolution behaviour of 238U, 234U and 230Th deposited on filters from personal dosemeters

    International Nuclear Information System (INIS)

    Beckova, V.; Malatova, I.

    2008-01-01

    Kinetics of dissolution of 238 U, 234 U and 230 Th dust deposited on filters from personal alpha dosemeters was studied by means of a 26-d in vitro dissolution test with a serum ultra-filtrate simulant. Dosemeters had been used by miners at the uranium mine 'Dolni Rozinka' at Rozna, Czech Republic. The sampling flow-rate as declared by the producer is 4 l h -1 and the sampling period is typically 1 month. Studied filters contained 125 ± 6 mBq 238 U in equilibrium with 234 U and 230 Th; no 232 Th series nuclides were found. Half-time of rapid dissolution of 1.4 d for 238 U and 234 U and slow dissolution half-times of 173 and 116 d were found for 238 U and 234 U, respectively. No detectable dissolution of 230 Th was found. (authors)

  15. U-Pb geochronology by La-CIP-MS and petrography of Sao Carlos massif - stanniferous province of Rondonia

    International Nuclear Information System (INIS)

    Debowski, Beatriz P.; Geraldes, Mauro Cesar; Nogueira, Camila; Almeida, Bruna Saar de

    2015-01-01

    U-Pb dating by ICP-MS-LA were performed in four samples of the Massif Sao Carlos massif, representative of the younger Granites of Rondonia belonging to the stanniferous province of the same State. Dated samples are granites of pink in colour and coarse-grained to porphyry with main mineralogy consisting of feldspar pertitic to mesopertitic, quartz, plagioclase in lower proportion, biotite and amphibole in some cases. Ages obtained were 986 ± 14 Ma, 974 ± 10 Ma, ± 8 Ma 992.7 and 996 ± 8 Ma and represent the age of crystallization of the Massif. Such ages are concordant with others reported on the bibliography ratifying the inclusion of the massif in the younger Granites of Rondonia, which are directly associated with the most significant mineralization of cassiterite in the State

  16. Application of the 210Pb-dating technique to evaluate environmental changes resulting from recent human activities

    International Nuclear Information System (INIS)

    Jenkinson, A.V.; Chisari, R.; Farrar, Y.J.; Heijnis, H.; McOrist, G.D.; Hallegraeff, G.; Hughes, M.; Napoli, M.; James, J.M.; McMinn, A.; Thomson, P.; Smith, J.D.; Tinker, R.A.

    1997-01-01

    The 210 Pb-dating technique has shown particular promise for the study of recent environmental change by enabling the establishment of chronologies for contemporary environmental processes. In this paper two case studies are discussed. Case Study (1) looks at trace element and heavy metal levels in the estuaries of the Georges River and the Hacking River which are partly located in suburban Sydney and Case Study (2) looks at blooms of the toxic dinoflagellate Gymnodinium catenatum which were first observed in Tasmanian waters, principally the Huon and Derwent Rivers in 1980. In both cases the 210 Pb dating technique has been used to establish the sequence of sediment deposition in order to associate an age to the sediment layer which contains the entity under investigation

  17. Tectonic implications of U-Pb (zircon) Geochronology of Chor Granitoids of the Lesser Himalaya, Himachal Pradesh, NW Himalaya

    Science.gov (United States)

    Singh, P.; Bhakuni, S. S.

    2017-12-01

    Granitoids of various ages ranging from Proterozoic to Tertiary occur throughout the Himalayan fold-thrust belt. The occurrence of the Neoproterozoic granitoids are very less in the Himalayan orogen. One of the best example of Neoproterozoic granitoids is Chor granitoids, which are the intrusive granite bodies in the Paleoproterozoic of the Lesser Himalayan Crystallines of the Jutogh Group. In the central part these granites are non-foliated homogeneous that are porphyritic and peraluminous in nature (Singh et al., 2002; Bhargava et al., 2014, 2016), whereas in the peripheral part these are foliated showing south directed shear sense of movement. In this work we present the U-Pb (zircon) geochronology of two different granites samples of the Chor granitoids of Himachal Pradesh, NW Himalaya. The Jutogh Group of rocks is thrust over the Lesser Himalayan Sequence along the Jutogh Thrust or MCT. The geochronology of the Chor Granitoids and Lesser Himalayan Crystallines and their relationship with each other, including with the Indian shield are sparsely obscure. U-Pb zircon geochrnological age populations from these granitoids yield ages between 780 and 980 Ma. One sample gives the prominent age spectra for 206Pb/238U with weighted mean age of 908.3 ± 6.7 Ma (2σ) MSWD = 2.4 (n = 18). Similarly another sample gives the age of crystallization with weight mean age of 917 ± 17 Ma (2σ) MSWD = 3 (n = 11) and Th/U ratios of both samples are >0.1, indicating their magmatic origin. As a result of ductile shearing of granites along the MCT during the Cenozoic Himalayan Orogeny, the age has reduced to 780 Ma. The Neoproterozoic age of Chor granite matches with the Neoproterozoic detrital zircon age (800 to 1000 Ma by Parrish and Hodges 1996, Decelles et al., 2000) of the HHC. On the basis of U-Pb (zircon) geochronological ages, it is revealed that the source of zircons of the Chor granite and HHC rocks was the northern margin of the Pan-African orogen. The Chor granitoids was

  18. Isotopic (U-Pb, Nd) and geochemical constraints on the origins of the Aileu and Gondwana sequences of Timor

    Science.gov (United States)

    Boger, S. D.; Spelbrink, L. G.; Lee, R. I.; Sandiford, M.; Maas, R.; Woodhead, J. D.

    2017-02-01

    Detrital zircon U-Pb age data collected from the argillitic sedimentary rocks of the Timorese Aileu Complex and Gondwana Sequence indicate that both units were derived from a common source containing 200-600 Ma, 900-1250 Ma and 1450-1900 Ma zircon. The modally most significant age population within this range of ages dates to c. 260 Ma. The observed spectrum of ages can be traced to the eastern active margin of Pangaea and its immediate foreland, which today is best exposed along the northeast coast of Australia. Compared to the relative homogeneity of the detrital zircon age data, geochemical and Nd isotopic data show that the mudstones of the Aileu Complex are on average more siliceous, have higher K2O/Na2O, Rb/Sr, Th/Sc and yield notably older Nd TDM model ages when compared to those from the Gondwana Sequence. These data are interpreted to suggest that, although both sequences share a common east Pangaea provenance, they were eroded from different sections of this active margin and deposited in spatially separated basins. The present proximity of these units is a result of their tectonic juxtaposition during the Pliocene to Recent collision between the northern edge of the Indo-Australia plate and the Banda Arc.

  19. Elevated uptake of Th and U by netted chain fern (Woodwardia areolata)

    International Nuclear Information System (INIS)

    Knox, A.S.; Kaplan, D.I.; Hinton, T.G.

    2008-01-01

    We assessed the ability of netted chain fern (Woodwardia areolata) to uptake U and Th from wetland soils on the U.S. Department of Energy's Savannah River Site in South Carolina. Netted chain fern had the highest Th and U concentrations of all plants collected from the wetland. Ferns grown in contaminated soil (329 mg x kg -1 Th, 44 mg x kg -1 U) in a greenhouse contained 6.4 mg x kg -1 Th and 5.3 mg x kg -1 U compared with 0.13 mg x kg -1 Th and 0.035 mg x kg -1 U in Bermuda grass (Cynodon dactylon). Netted chain fern has potential for the phytoremediation of soils contaminated with Th and U. (author)

  20. Zircon U-Pb dating of early Palaeozoic monzonitic intrusives from the Goonumbla area, New South Wales

    International Nuclear Information System (INIS)

    Butera, K.M.; Williams, I.S.; Blevin, P.L.; Simpson, C.J.

    2001-01-01

    Zircon U-Pb ages measured on four small intrusions into the succession of Ordovician volcanic rocks that hosts North Parkes Cu-Au mine northwest of Parkes. New South Wales. place limits on the age of the volcanic sequence. The basal Nelungaloo Volcanics are constrained by a cross-cutting monzodiorite to be ≥484.3 ± 2.9Ma (Early Ordovician). Similarly. the overlying basal Goonumbla Volcanics are constrained by another cross-cutting monzodiorite to be ≥450.8 ± 4.2Ma (Middle Ordovician). A later generation of monzonites intruded into the middle and upper Goonumbla Volcanics yield ages of 439.1 ± 4.5 and 438.9 ± 4.7 Ma (Siluro-Ordovician). These various ages are consistent with the ages of fossiliferous sediments within the volcanic sequence. and indicate that both the intrusive and volcanic rocks span an appreciable period of time-neither are the product of a single magmatic episode. Intrusion of the youngest monzonites and mineralisation was virtually contemporaneous. Copyright (2001) Geological Society of Australia

  1. Dissolution behaviour of 238U, 234U and 230Th deposited on filters from personal dosemeters.

    Science.gov (United States)

    Becková, Vera; Malátová, Irena

    2008-01-01

    Kinetics of dissolution of (238)U, (234)U and (230)Th dust deposited on filters from personal alpha dosemeters was studied by means of a 26-d in vitro dissolution test with a serum ultrafiltrate simulant. Dosemeters had been used by miners at the uranium mine 'Dolní Rozínka' at Rozná, Czech Republic. The sampling flow-rate as declared by the producer is 4 l h(-1) and the sampling period is typically 1 month. Studied filters contained 125 +/- 6 mBq (238)U in equilibrium with (234)U and (230)Th; no (232)Th series nuclides were found. Half-time of rapid dissolution of 1.4 d for (238)U and (234)U and slow dissolution half-times of 173 and 116 d were found for (238)U and (234)U, respectively. No detectable dissolution of (230)Th was found.

  2. Geochemistry of stream sediments, water and U-Th radiation anomaly around Neyshabour Fyrouzeh mine and its environmental impact on people living nearby villages

    International Nuclear Information System (INIS)

    Karimpour, M. H.; Malekzadeh Shafaroudi, A.

    2013-01-01

    Fyrouzeh mine is located about 55 km northwest of Neyshabour in the Province of Khorasan Razavi. The exposed rocks are mainly volcanic and intrusive with intermediate composition and all of them are altered. This mine is the first type of IOCG recognized in Iran with Cu-Au-LREE-U. Besides Cu-Au-U, this area shows As, Mo, Zn and Th anomalies. Geochemical evaluation of stream sediment with regard to environmental concern revealed high Cu anomalies. Rocks show high uranium anomalies (up to 35 ppm) higher than the standard values (1 ppm). Airborne radiometric maps show high U and Th anomalies in a broad area. Ag, Hg and Mn show anomalies within the stream sediments. Cu, Pb, Zn, Ag, Ni, Mn, Sb, Hg, and U content of both drinking and agricultural water are fortunately within the range of standard, only two samples have higher As content (more than 10 ppb). High level of U-Th radiation and contamination of stream sediment with respect to Cu, Hg, Ag, Mn and agricultural water to As are important environmental issues and people health therefore they need to be study.

  3. Assessing the applicability of Pb-210 dating technique in selected mangrove areas in the Philippines

    International Nuclear Information System (INIS)

    Sta Maria, E.J.; Lim, A.B.U.; Ebreo, C.M.H.; Ramirez, J.D.; Castro, K.M.I.; Garcia, M.C.C.; Navarette, I.A.; Salmo, S.G. III

    2015-01-01

    The Pb-210 dating technique has been widely used in many areas as a tool for historical reconstruction of pollution, eutrophication and the many impacts of man on the environment. In the Philippines, the technique has been used in bays (Manila Bay, Sorsogon Bay), in a sound, in a lagoon, in a lake and in a dam. To assess the technique’s applicability in a different environmental setting, sediment cores were collected from mangrove areas in Subic and Pangasinan for Pb-210 analysis. Initial Pb-210 results from these two mangrove areas reveals that Pb-210 is a promising tool for such a new setting. Using the Pb-210 profiles of the sediment cores indicated that Pangasinan mangrove area has a much lower sedimentation rate compared to the Subic mangrove area. The difference in the sediment rates of the two areas could be due to the existing topographic, geographic, hydrodynamic and environment conditions of the area. The age-control information provided by the Pb-210 data could be correlated with other existing data (Chemical and elemental data) for retrospective assessment of the study areas. (author)

  4. Neutron inelastic-scattering cross sections of 232Th, 233U, 235U, 238U, 239Pu and 240Pu

    International Nuclear Information System (INIS)

    Smith, A.B.; Guenther, P.T.

    1982-01-01

    Differential-neutron-emission cross sections of 232 Th, 233 U, 235 U, 238 U, 239 Pu and 240 Pu are measured between approx. = 1.0 and 3.5 MeV with the angle and magnitude detail needed to provide angle-integrated emission cross sections to approx. 232 Th, 233 U, 235 U and 238 U inelastic-scattering values, poor agreement is observed for 240 Pu, and a serious discrepancy exists in the case of 239 Pu

  5. Geochemistry, U-Pb SHRIMP zircon dating and Hf isotopes of the Gondwanan magmatism in NW Argentina: petrogenesis and geodynamic implications

    International Nuclear Information System (INIS)

    Poma, Stella; Zappettini, Eduardo O; Quenardelle, Sonia; Santos, Joao O; Koukharsky, Magdalena; Belousova, Elena; McNaughton, Neil

    2014-01-01

    We have carried out zircon U-Pb SHRIMP dating and Hf isotope determinations as well as geochemical analyses on three plutonic units of Gondwanan magmatism that crop out in NW Argentina. Two episodes of different age and genesis have been identified. The older one includes gabbros and diorites (Rio Grande Unit) of 267±3 Ma and granitoids (belonging to the Llullaillaco Unit) of 263±1 Ma (late Permian, Guadalupian); the parent magmas were generated in an intraplate environment and derived from an enriched mantle but were subsequently contaminated by crustal components. The younger rocks are granodiorites with arc signature (Chuculaqui Unit) and an age of 247±2 Ma (middle Triassic-Anisian). Hf isotope signature of the units indicates mantle sources as well as crustal components. Hf model ages obtained are consistent with the presence of crustal Mesoproterozoic (mainly Ectasian to Calymnian (T DM(c) =1.24 to 1.44 Ga-negative ε Hf m) and juvenile Cryogenian sources (T DM =0.65 to 0.79 Ga-positiveε Hf(T) , supporting the idea of a continuous, mostly Mesoproterozoic, basement under the Central Andes, as an extension of the Arequipa-Antofalla massif. The tectonic setting and age of the Gondwanan magmatism in NW Argentina allow to differentiate: a. Permian intra-plate magmatism developed under similar conditions to the upper section of the Choiyoi magmatism exposed in the Frontal Cordillera and San Rafael Block, Argentina; b. Triassic magmatism belonging to a poorly known subduction-related magmatic arc segment of mostly NS trend with evidence of porphyry type mineralization in Chile, allowing to extend this metallotect into Argentina

  6. SHRIMP-RG U-Pb isotopic systematics of zircon from the Angel Lake orthogneiss, East Humboldt Range, Nevada: Is this really archean crust?

    Science.gov (United States)

    Premo, Wayne R.; Castineiras, Pedro; Wooden, Joseph L.

    2008-01-01

    New SHRIMP-RG (sensitive high-resolution ion microprobe-reverse geometry) data confirm the existence of Archean components within zircon grains of a sample from the orthogneiss of Angel Lake, Nevada, United States, previously interpreted as a nappe of Archean crust. However, the combined evidence strongly suggests that this orthogneiss is a highly deformed, Late Cretaceous monzogranite derived from melting of a sedimentary source dominated by Archean detritus. Zircon grains from the same sample used previously for isotope dilution-thermal ionization mass spectrometry (ID-TIMS) isotopic work were analyzed using the SHRIMP-RG to better define the age and origin of the orthogneiss. Prior to analysis, imaging revealed a morphological variability and intragrain, polyphase nature of the zircon population. The SHRIMP-RG yielded 207Pb/206Pb ages between ca. 2430 and 2580 Ma (a best-fit mean 207Pb/206Pb age of 2531 ± 19 Ma; 95% confidence) from mostly rounded to subrounded zircons and zircon components (cores). In addition, several analyses from rounded to subrounded cores or grains yielded discordant 207Pb/206Pb ages between ca. 1460 and ca. 2170 Ma, consistent with known regional magmatic events. All cores of Proterozoic to latest Archean age were encased within clear, typically low Th/U (206Pb/238U ages between 72 and 91 Ma, consistent with magmatic ages from Lamoille Canyon to the south. An age of ca. 90 Ma is suggested, the younger 206Pb/238U ages resulting from Pb loss. The Cretaceous and Precambrian zircon components also have distinct trace element characteristics, indicating that these age groups are not related to the same igneous source. These results support recent geophysical interpretations and negate the contention that the Archean-Proterozoic boundary extends into the central Great Basin area. They further suggest that the world-class gold deposits along the Carlin Trend are not underlain by Archean cratonal crust, but rather by the Proterozoic Mojave

  7. Distribution of U and Th decay series and rare earth elements in sediments of Santos Basin. Correlation with industrial activities

    International Nuclear Information System (INIS)

    Silva, P.S.C.; Mazzilli, B.P.; Favaro, D.I.T.

    2005-01-01

    Santos Basin, located in Southwest Brazil, is considered the most important industrial region of the country. Among the industrial activities present, phosphate fertilizer plants are responsible for the production of 69 million tons of phosphogypsum waste, which is stockpiled in the surrounding environment. This waste concentrates radionuclides of the natural series as well as rare earth elements originally present in the phosphate rock used as raw material. Environmental impact of such activities in the sediments of the estuarine system by measuring the concentration of U, Th and rare earth elements and activity concentration of radionuclides 226 Ra, 228 Ra, 228 Th and 210 Pb. (author)

  8. Coupled 230Th/234U-ESR analyses for corals: A new method to assess sealevel change

    International Nuclear Information System (INIS)

    Blackwell, Bonnie A.B.; Teng, Steve J.T.; Lundberg, Joyce A.; Blickstein, Joel I.B.; Skinner, Anne R.

    2007-01-01

    Although coupled 230 Th/ 234 U-ESR analyses have become routine for dating teeth, they have never been used for corals. While the ESR age depends on, and requires assumptions about, the time-averaged cosmic dose rate, D-bar cos (t), 230 Th/ 234 U dates do not. Since D-bar cos (t) received by corals depends on the attenuation by any intervening material, D-bar cos (t) response reflects changing water depths and sediment cover. By coupling the two methods, one can determine the age and a unique D-bar cos,coupled (t) simultaneously. From a coral's water depth and sedimentary history as predicted by a given sealevel curve, one can predict D-bar cos,sealevel (t). If D-bar cos,coupled (t) agrees well with D-bar cos,sealevel (t), this provides independent validation for the curve used to build D-bar cos,sealevel (t). For six corals dated at 7-128 ka from Florida Platform reef crests, the sealevel curve by Waelbroeck et al. [2002. Sea-level and deep water temperature changes derived from benthonic foraminifera isotopic records. Quat. Sci. Rev. 21, 295-305] predicted their D-bar cos,coupled (t) values as well as, or better than, the SPECMAP sealevel curve. Where a whole reef can be sampled over a transect, a precise test for sealevel curves could be developed

  9. Measurement of distribution coefficients of U series radionuclides on soils under shallow land environment (2). pH dependence of distribution coefficients

    International Nuclear Information System (INIS)

    Sakamoto, Yoshiaki; Takebe, Shinichi; Ogawa, Hiromichi; Inagawa, Satoshi; Sasaki, Tomozou

    2001-01-01

    In order to study sorption behavior of U series radionuclides (Pb, Ra, Th, Ac, Pa and U) under aerated zone environment (loam-rain water system) and aquifer environment (sand-groundwater system) for safety assessment of U bearing waste, pH dependence of distribution coefficients of each element has been obtained. The pH dependence of distribution coefficients of Pb, Ra, Th, Ac and U was analyzed by model calculation based on aqueous speciation of each element and soil surface charge characteristics, which is composed of a cation exchange capacity and surface hydroxyl groups. From the model calculation, the sorption behavior of Pb, Ra, Th, Ac and U could be described by a combination of cation exchange reaction and surface-complexation model. (author)

  10. Evolution of Th and U whole-rock contents in the Ilimaussaq intrusion

    International Nuclear Information System (INIS)

    Bailey, J.C.; Rose-Hansen, J.; Loevborg, L.; Soerensen, H.

    1981-01-01

    A great variety of investigations have been made on the distribution of Th and U in the Ilimaussaq alkaline, South Greenland. The major emphasis has been placed on economic assessment of the Kvanefjeld uranium deposit but attention has also been given to the Th and U contents of rocks and minerals outside the deposit. In the present study, we present Th and U values largely obtained by laboratory gamma-ray spectrometric (GRS) analysis of a large collection of representative samples taken from all rock types of the intrusion. The results are discussed in relation to current knowledge and ideas on the petrologic evolution of the Ilimaussaq intrusion. The behaviour of Th and U in igneous systems is moderately well known. During closed-system fractional crystallization, Th and U are generally excluded from the cumulus phases and attain higher levels in successive residual magmas. In most cumulate sequences, they are held in the trapped liquid (mesostasis). In both magmas and cumulates, the Th/U ratio remains virtually unchanged from the ratio of the parent magma. Only a few examples are known where significant amounts of Th-, U-rich cumulus phases (e.g. perovskite, eudialyte) crystallise and disturb the Th/U ratio. At many loctions, fractional crystallization occurred under open-system conditions and Th and U were redistributed by mobile fluids. These are frequently concentrated in roof zones or added to the surrounding country rocks. Elsewhere, post-magmatic Th-U metasomatism may be so intense that few of the primary, magmatic features are preserved. Previous invetigators of Th and U at Ilimaussaq have found evidence for closed- and open-system conditions at different stages of the evolution, and also for post-magmatic metasomatism. (author)

  11. The sediment budget of an urban coastal lagoon (Jamaica Bay, NY) determined using 234Th and 210Pb

    Science.gov (United States)

    Renfro, Alisha A.; Cochran, J. Kirk; Hirschberg, David J.; Bokuniewicz, Henry J.; Goodbred, Steven L.

    2016-10-01

    The sediment budget of Jamaica Bay (New York, USA) has been determined using the natural particle-reactive radionuclides 234Th and 210Pb. Inventories of excess thorium-234 (234Thxs, half-life = 24.1 d) were measured in bottom sediments of the Bay during four cruises from September 2004 to July 2006. The mean bay-wide inventory for the four sampling periods ranged from 3.5 to 5.0 dpm cm-2, four to six times that expected from 234Th production in the overlying water column. The presence of dissolved 234Th and a high specific activity of 234Thxs on particles at the bay inlet (∼30 dpm g-1) indicated that both dissolved and particulate 234Th could be imported into the bay from the ocean. Based on these observations, a mass balance of 234Th yields an annual input of ∼39 ± 14 × 1010 g sediment into the bay. Mass accumulation rates determined from profiles of excess 210Pb (half-life = 22.3 y) in sediment cores require annual sediment import of 7.4 ± 4.5 × 1010 g. Both radionuclides indicate that there is considerable marine-derived sediment import to Jamaica Bay, consistent with earlier work using 210Pb. Such sediment input may be important in sustaining longer-term accretion rates of salt marshes in the bay.

  12. Leaching behavior of U, Mn, Sr, and Pb from different particle-size fractions of uranium mill tailings.

    Science.gov (United States)

    Liu, Bo; Peng, Tongjiang; Sun, Hongjuan

    2017-06-01

    Pollution by the release of heavy metals from tailings constitutes a potential threat to the environment. To characterize the processes governing the release of Mn, Sr, Pb, and U from the uranium mill tailings, a dynamic leaching test was applied for different size of uranium mill tailings samples. Inductively coupled plasma atomic emission spectroscopy (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS) were performed to determine the content of Mn, Sr, Pb, and U in the leachates. The release of mobile Mn, Sr, Pb, and U fraction was slow, being faster in the initial stage and then attained a near steady-state condition. The experimental results demonstrate that the release of Mn, Sr, Pb, and U from uranium mill tailings with different size fractions is controlled by a variety of mechanisms. Surface wash-off is the release mechanism for Mn. The main release mechanism of Sr and Pb is the dissolution in the initial leaching stage. For U, a mixed process of wash-off and diffusion is the controlling mechanism.

  13. Segmentation and rejuvenation of the Greater Himalayan sequence in western Nepal revealed by in situ U-Th/Pb monazite petrochronology

    Science.gov (United States)

    Braden, Zoe; Godin, Laurent; Cottle, John M.

    2017-07-01

    In the western Nepal Himalaya, a major mountain building shear zone, the Main Central thrust, is exposed in multiple locations along its southward transport direction. The hanging wall of the Main Central thrust was sampled in both hinterland and foreland exposures, in the upper Karnali valley and around Jumla, respectively. In situ U-Th/Pb monazite petrochronology coupled with microstructural and petrographic observations reveals distinctly different timing of deformation, despite the geographic proximity and apparent structural continuity between the two regions. The Y content, the Gd to Yb ratio and the Eu anomaly in monazite constrain the timing of metamorphic reactions. Rocks in the upper Karnali valley record deformation associated with metamorphism at 18 Ma, melt crystallization starting at ca. 14 Ma and lasting until at least 11-10 Ma. In contrast, the Jumla region records a more protracted series of events with metamorphism initiating as early as 47 Ma and lasting until 18 Ma, punctuated by at least two periods of melt crystallization. In both areas, the age of melt crystallization decreases down section through the hanging wall towards the Main Central thrust. Ductile deformation in the Jumla region ceased around ca. 18 Ma, while rocks at similar structural positions in the hinterland in upper Karnali valley were still being actively deformed and melting at ca. 11 Ma. The southern, foreland-most, hanging-wall rocks (Jumla region) were consequently exhumed above the ductile-brittle transition while the northern hinterland-most hanging-wall rocks (upper Karnali valley) were still undergoing ductile deformation and partial melting.

  14. New U-Pb zircon ages and the duration and division of Devonian time

    Science.gov (United States)

    Tucker, R.D.; Bradley, D.C.; Ver Straeten, C.A.; Harris, A.G.; Ebert, J.R.; McCutcheon, S.R.

    1998-01-01

    Newly determined U-Pb zircon ages of volcanic ashes closely tied to biostratigraphic zones are used to revise the Devonian time-scale. They are: 1) 417.6 ?? 1.0 Ma for an ash within the conodont zone of Icriodus woschmidti/I. w. hesperius Lochkovian); 2) 408.3 ?? 1.9 Ma for an ash of early Emsian age correlated with the conodont zones of Po. dehiscens--Lower Po. inversus; 3) 391.4 ?? 1.8 Ma for an ash within the Po. c. costatus Zone and probably within the upper half of the zone (Eifelian); and 4) 381.1 ?? 1.3 Ma for an ash within the range of the Frasnian conodont Palmatolepis punctata (Pa. punctata Zone to Upper Pa. hassi Zone). U-Pb zircon ages for two rhyolites bracketing a palyniferous bed of the pusillites-lepidophyta spore zone, are dated at 363.8 ?? 2.2 Ma and 363 ?? 2.2 Ma and 363.4 ?? 1.8 Ma, respectively, suggesting an age of ~363 Ma for a level within the late Famennian Pa. g. expansa Zone. These data, together with other published zircon ages, suggest that the base and top of the Devonian lie close to 418 Ma and 362 Ma, respectively, thus lengthening the period of ~20% over current estimates. We suggest that the duration of the Middle Devonian (Eifelian and Givitian) is rather brief, perhaps no longer than 11.5 Myr (394 Ma-382.5 Ma), and that the Emsian and Famennian are the longest stages in the period with estimated durations of ~15.5 Myr and 14.5 Myr, respectively.

  15. Age of Saurashtra miliolites by U-Th decay series methods: possible implications to their origin

    International Nuclear Information System (INIS)

    Hussain, N.; Bhandari, N.; Ramanathan, K.R.; Somayajulu, B.L.K.

    1980-01-01

    The miliolite deposits of Saurashtra have been dated by 234 U, 230 Th, 231 Pa and 14 C methods. Concordant ages of approximately 10 5 years using the U decay series isotopes are obtained which agree with the ages of the coral reefs of Okha-Dwaraka coast suggesting a contemporaneous origin for both. The lower 14 C ages (<= 40,000 years) may be due to a recent influx of seawater or ground water. Quartz and clay minerals together constitute only <= 10% by weight, as such the aeolin characteristics of quartz grains may not be relevant to the origin of the miliolites. (auth.)

  16. U-Pb (SHRIMP II) Age of zircons from ash tuffs of the upper vendian Chernyi Kamen formation (Sylvitsa group, Middle Urals)

    International Nuclear Information System (INIS)

    Ronkin, Yu.L.; Grazhdankin, D.V.; Maslov, A.V.; Mizens, G.A.; Matukov, D.I.; Krupenin, M.T.; Petrov, G.A.; Lepikhina, O.P.; Kornilova, A.Yu.

    2006-01-01

    To make more precise the model of correlation of the Middle Urals western slope upper vendian layers with the White Sea remote layers one carried out the SHRIMP-II procedure base U-Pb-dating of the volcanogenic zircons from the ash tuffs and of the volcanogenic zircon enclosing argillites of the Middle Urals Chernyi Kamen formation. The obtained age value of the studied zircons equal to 557+-13 million years is in line with the geological data [ru

  17. Uranium Age Determination by Measuring the 230Th / 234U Ratio

    International Nuclear Information System (INIS)

    LAMONT, STEPHEN P.

    2004-01-01

    A radiochemical isotope dilution mass spectrometry method has been developed to determine the age of uranium materials. The amount of 230Th activity, the first progeny of 234U, that had grown into a small uranium metal sample was used to determine the elapsed time since the material was last radiochemically purified. To preserve the sample, only a small amount of oxidized uranium was removed from the surface of the sample and dissolved. Aliquots of the dissolved sample were spiked with 233U tracer and radiochemically purified by anion-exchange chromatography. The 234U isotopic concentration was then determined by thermal ionization mass spectrometry. Additional aliquots of the sample were spiked with 229Th tracer, and the thorium was purified using two sequential anion-exchange chromatography separations. The isotopic concentrations of 230Th and 232Th were determined by TIMS. The lack of any 232Th confirmed the assumption that all thorium was removed from the uranium sample at the time of purification. The 230Th and 234U mass concentrations were converted to activities and the 230Th/234U ratio for the sample was calculated. The experimental 230Th/234U ratio showed the uranium in this sample was radiochemically purified in about 1945. Isotope dilution thermal ionization mass spectrometry has sufficient sensitivity to determine the age of 100 samples of uranium. This method could certainly be employed as a nuclear forensic method to determine the age of small quantities of uranium metal or salts. Accurate determination of the ultra-trace 230Th radiochemically separated from the uranium is possible due to the use of 229Th as an isotope dilution tracer. The precision in the experimental age of the uranium could be improved by making additional replicate measurements of the 230Th/234U isotopic ratio or using a larger initial sample

  18. A Uranium-Lead Chronology of Speleothem Deposition in the Canadian Arctic

    Science.gov (United States)

    Gambino, C.; Shakun, J. D.; McGee, D.; Ramezani, J.; Khadivi, S.; Wong, C. I.

    2017-12-01

    The Artic is one of the fastest warming regions on the planet. Currently much of the Arctic is covered by permafrost, which contains approximately 1,700 gigatons of organic carbon. Permafrost thaw could release a substantial amount of this carbon as greenhouse gases into the atmosphere through microbial decomposition, potentially dramatically amplifying anthropogenic warming. However, the risk of permafrost thaw is uncertain, with models exhibiting a wide range of possibilities. Assessing the stability of permafrost during past interglacial periods enables evaluation of the sensitivity of permafrost to warming. Cave mineral deposits (speleothems) in areas currently covered with permafrost can act as a proxy for past permafrost thaw, as liquid water is one criteria of speleothem growth and thus implies thawed ground conditions. Previous uranium-thorium (U-Th) dating of speleothems (n=67) from a wide range of latitudes and permafrost zones across the southern Canadian Rockies, Northwest Territories, and the northern Yukon suggest deposition during Marine Isotope Stage (MIS) 11 and 13. The majority of U-Th dates of these speleothems, however, exceed the U-Th dating limit of 600 ka. In this study, we apply uranium-lead (U-Pb) geochronology to several of these speleothems to extend the records of speleothem growth further back in time. Initial results include a U-Pb age of 428 ± 14 ka that replicates a previous U-Th age of 416.8 ± 7.9 ka, and U-Pb ages on two other speleothems of 870 ± 100 ka and 1502 ± 30 ka. The results of currently in progress U-Pb analyses and a comparison of results with paleo-temperature and ice volume reconstructions will also be presented.

  19. Combined U-Th/He and 40Ar/39Ar geochronology of post-shield lavas from the Mauna Kea and Kohala volcanoes, Hawaii

    Energy Technology Data Exchange (ETDEWEB)

    Aciego, S.M.; Jourdan, F.; DePaolo, D.J.; Kennedy, B.M.; Renne, P.R.; Sims, K.W.W.

    2009-10-01

    Late Quaternary, post-shield lavas from the Mauna Kea and Kohala volcanoes on the Big Island of Hawaii have been dated using the {sup 40}Ar/{sup 39}Ar and U-Th/He methods. The objective of the study is to compare the recently demonstrated U-Th/He age method, which uses basaltic olivine phenocrysts, with {sup 40}Ar/{sup 39}Ar ages measured on groundmass from the same samples. As a corollary, the age data also increase the precision of the chronology of volcanism on the Big Island. For the U-Th/He ages, U, Th and He concentrations and isotopes were measured to account for U-series disequilibrium and initial He. Single analyses U-Th/He ages for Hamakua lavas from Mauna Kea are 87 {+-} 40 ka to 119 {+-} 23 ka (2{sigma} uncertainties), which are in general equal to or younger than {sup 40}Ar/{sup 39}Ar ages. Basalt from the Polulu sequence on Kohala gives a U-Th/He age of 354 {+-} 54 ka and a {sup 40}Ar/{sup 39}Ar age of 450 {+-} 40 ka. All of the U-Th/He ages, and all but one spurious {sup 40}Ar/{sup 39}Ar ages conform to the previously proposed stratigraphy and published {sup 14}C and K-Ar ages. The ages also compare favorably to U-Th whole rock-olivine ages calculated from {sup 238}U - {sup 230}Th disequilibria. The U-Th/He and {sup 40}Ar/{sup 39}Ar results agree best where there is a relatively large amount of radiogenic {sup 40}Ar (>10%), and where the {sup 40}Ar/{sup 36}Ar intercept calculated from the Ar isochron diagram is close to the atmospheric value. In two cases, it is not clear why U-Th/He and {sup 40}Ar/{sup 39}Ar ages do not agree within uncertainty. U-Th/He and {sup 40}Ar/{sup 39}Ar results diverge the most on a low-K transitional tholeiitic basalt with abundant olivine. For the most alkalic basalts with negligible olivine phenocrysts, U-Th/He ages were unattainable while {sup 40}Ar/{sup 39}Ar results provide good precision even on ages as low as 19 {+-} 4 ka. Hence, the strengths and weaknesses of the U-Th/He and {sup 40}Ar/{sup 39}Ar methods are

  20. U-TH-REE mobility and diffusion in granitic environments during alteration of accessory minerals and U-ores

    International Nuclear Information System (INIS)

    Cathelineau, M.; Vergneaud, M.

    1989-01-01

    U, Th and REE concentrations and distributions have been studied in granitic rocks, using a multidisciplinary approach involving micromapping of cracks in oriented samples, together with mineralogical and geochemical studies of the different U-Th-REE bearing phases. The behavior of U, Th and Nd, considered as chemical analogue elements of the radiotoxic nuclides, was investigated either in the vicinity of microsites (accessory mineral enviornment) or along plurimetric sections around U-ore bodies. The different granite minerals, especially the accessory minerals (uraninite, monazite, thorite, apatite, xeonotime), as well as U-ores, present different initial concentrations of U, Th and REE. Limitations to the analogy between these U-Th-REE concentrations and the radwastes is discussed as a function of their mineralogical features, chemical compostion, size and solubilities. These primary concentrations present different behavior when subjected to hydrothermal alteration, such as propylitization, phyllite type alteration, or clay alteration. Results show that in reduced media, in the temperature range 80-2000 0 C, the rate of mobilization of U, Th, REE is relatively moderate. However, fluids enriched in flourides, phosphates or carbonates may significantly solubilize and transport U and REE under specific conditions. In addition, the degree of opening of the microcracks and faults, as well as the oxidation-reduction processes, are critical parameters for the efficiency of the granitic geological barrier

  1. Determination of Pb-210 and actinides by extraction chromatography and anion exchange chromatography

    International Nuclear Information System (INIS)

    Kalmykov, St.N.; Sapozhnikov, Yu.A.

    1997-01-01

    This work is devoted to the determination of Pb-210 and actinides (Pu-238, Pu-239, Am-241, U-235, U-238, Th-232) by means of highly selective chromatographic resins and anion exchangers. The special interest was paid to the analysis of large quantities of samples with high concentration of competitive ions like ocean sediments, bone ash and others.The commercially available TRU-Spec chromatographic resins was used for separation of actinides from the matrix. Then U, Th, Am, and Pu were separated from other using anion exchange chromatography with AG-1X4 anionite in Cl - form, electro-deposed and α-counted.Pb-21- and Bi-210 were determined by liquid scintillation counting. The developed procedure is rather express, effective and could be adopted for the determination of radionuclides like Ba-133, Ra, Np-239

  2. Timing of metamorphism and exhumation in the Nordøyane ultra-high-pressure domain, Western Gneiss Region, Norway: New constraints from complementary CA-ID-TIMS and LA-MC-ICP-MS geochronology

    Science.gov (United States)

    Butler, J. P.; Jamieson, R. A.; Dunning, G. R.; Pecha, M. E.; Robinson, P.; Steenkamp, H. M.

    2018-06-01

    We present the results of a combined CA-ID-TIMS and LA-MC-ICP-MS U-Pb geochronology study of zircon and associated rutile and titanite from the Nordøyane ultra-high-pressure (UHP) domain in the Western Gneiss Region (WGR) of Norway. The dated samples include 4 eclogite bodies, 2 host-rock migmatites, and 2 cross-cutting pegmatites and leucosomes, all from the island of Harøya. Zircon from a coesite eclogite yielded an age of ca. 413 Ma, interpreted as the time of UHP metamorphism in this sample. Zircon data from the other eclogite bodies yielded metamorphic ages of ca. 413 Ma, 407 Ma, and 406 Ma; zircon trace-element data associated with 413 Ma and 407 Ma ages are consistent with eclogite-facies crystallization. In all of the eclogites, U-Pb dates from zircon cores, interpreted as the times of protolith crystallization, range from ca. 1680-1586 Ma, consistent with Gothian ages from orthogneisses in Nordøyane and elsewhere in the WGR. A zircon core age of ca. 943 Ma from one sample agrees with Sveconorwegian ages of felsic gneisses and pegmatites in the western part of the area. Migmatites hosting the eclogite bodies yielded zircon core ages of ca. 1657-1591 Ma and rim ages of ca. 395-392 Ma, interpreted as the times of Gothian protolith formation and Scandian partial melt crystallization, respectively. Pegmatite in an eclogite boudin neck yielded a crystallization age of ca. 388 Ma, interpreted as the time of melt crystallization. Rutile and titanite from 3 samples (an eclogite and two migmatites) yielded concordant ID-TIMS ages of 378-376 Ma. The results are similar to existing U-Pb data from other Nordøyane eclogites (415-405 Ma). In combination with previous pressure-temperature data from the coesite eclogite, these ages indicate that peak metamorphic conditions of 3 GPa/760 °C were reached ca. 413 Ma, followed by decompression to 1 GPa/810 °C by ca. 397 Ma and cooling below ca. 600 °C by ca. 375 Ma. The results are compatible with protracted UHP

  3. Preliminary results of U/Pb geochronology in Meridional Espinhaco Mountain

    International Nuclear Information System (INIS)

    Machado, N.; Schrank, A.; Abreu, F.R. de; Knauer, L.G.; Abreu, P.A.A.

    1989-01-01

    Some samples of the constituent unities from Meridional Espinhaco Mountain for geochronology determining by U/Pb method are presented. The analytical techniques described by Krogh and the Davis linear regression program are used for treating these samples. (author)

  4. The fission cross sections of 230Th, 232Th, 233U, 234U, 236U, 238U, 237Np, 239Pu and 242Pu relative 235U at 14.74 MeV neutron energy

    International Nuclear Information System (INIS)

    Meadows, J.W.

    1986-12-01

    The measurement of the fission cross section ratios of nine isotopes relative to 235 U at an average neutron energy of 14.74 MeV is described with particular attention to the determination of corrections and to sources of error. The results are compared to ENDF/B-V and to other measurements of the past decade. The ratio of the neutron induced fission cross section for these isotopes to the fission cross section for 235 U are: 230 Th - 0.290 +- 1.9%; 232 Th - 0.191 +- 1.9%; 233 U - 1.132 +- 0.7%; 234 U - 0.998 +- 1.0%; 236 U - 0.791 +- 1.1%; 238 U - 0.587 +- 1.1%; 237 Np - 1.060 +- 1.4%; 239 Pu - 1.152 +- 1.1%; 242 Pu - 0.967 +- 1.0%. 40 refs., 11 tabs., 9 figs

  5. U-Pb thermochronology of rutile from Alpine Corsica: constraints on the thermal evolution of the European margin during Jurassic continental breakup

    Science.gov (United States)

    Ewing, T. A.; Beltrando, M.; Müntener, O.

    2017-12-01

    U-Pb thermochronology of rutile can provide valuable temporal constraints on the exhumation history of the lower crust, given its moderate closure temperature and the occurrence of rutile in appropriate lithologies. We present an example from Alpine Corsica, in which we investigate the thermal evolution of the distal European margin during Jurassic continental rifting that culminated in the opening of the Alpine Tethys ocean. The Belli Piani unit of the Santa Lucia nappe (Corsica) experienced minimal Alpine overprint and bears a striking resemblance to the renowned Ivrea Zone lower crustal section (Italy). At its base, a 2-4 km thick gabbroic complex contains slivers of granulite facies metapelites that represent Permian lower crust. Zr-in-rutile temperatures and U-Pb ages were determined for rutile from three metapelitic slivers from throughout the Mafic Complex. High Zr-in-rutile temperatures of 850-950 °C corroborate textural evidence for rutile formation during Permian granulite facies metamorphism. Lower Zr-in-rutile temperatures of 750-800 °C in a few grains are partly associated with elongate strings of rutile within quartz ribbons, which record recrystallisation of some rutile during high-temperature shearing. Zr thermometry documents that both crystallisation and re-crystallisation of rutile occurred above the closure temperature of Pb in rutile, such that the U-Pb system can be expected to record cooling ages uncomplicated by re-crystallisation. Our new high-precision single-spot LA-ICPMS U-Pb dates are highly consistent between and within samples. The three samples gave ages from 160 ± 1 Ma to 161 ± 2 Ma, with no other age populations detected. The new data indicate that the Santa Lucia lower crust last cooled through 550-650 °C at 160 Ma, coeval with the first formation of oceanic crust in the Tethys. The new data are compared to previous depth profiling rutile U-Pb data for the Belli Piani unit1, and exploited to cast light on the tectonothermal

  6. Geochemistry and zircon U-Pb geochronology of the Pulang complex, Yunnan province, China

    International Nuclear Information System (INIS)

    Pang, Zhenshan; Du, Yangsong; Cao, Yi; Gao, Fuping; Wang, Gongwen; Dong, Qian

    2014-01-01

    The Pulang complex is located tectonically at the southern margin of the Yidun-Zhongdian island arc belt in Yunnan province, China, and is closely related to formation of the Pulang copper deposit, which is the largest copper deposit in Asia. The Pulang complex can be divided into three intrusion stages based on contact relationships and petrological characteristics: (1) a first stage of quartz dioritic porphyry; (2) a second stage of quartz monzonitic porphyry; and (3) a third stage of granodioritic porphyry. The crystallization ages of these intrusion stages were determined by single-zircon U-Pb dating, yielding ages of 221.0 ± 1.0, 211.8 ± 0.5, and 206.3 ± 0.7 Ma for the first, second, and third stages, respectively. These dates, integrated with previous geochronological data and field investigations, indicate that the second-stage quartz monzonitic porphyry has a close spatial and temporal relationship with the large Pulang porphyry copper deposit. These age data, geochemical and Sr-Nd isotopic results suggest that the Pulang complex formed in the Indo-Chinese epoch (257∼ 205 Ma) by multiphase intrusion of a mixture of mantle- and crust-derived magmas. (author)

  7. Pb-Pb zircon ages of the Porto Nacional high-grade metamorphic terrain, northern portion of the Goias Massif, central Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Gorayeb, Paulo Sergio de Sousa; Moura, Candido Augusto Veloso [Para Univ., Belem, PA (Brazil). Centro de Geociencias]. E-mail: gorayebp@ufpa.br; c_moura@ufpa.br; Barros, Gisele Ribeiro de [Para Univ., Belem, PA (Brazil). Programa Institucional de Bolsas de Iniciacao Cientifica (PIBIC)]. E-mail: agbarros@amazon.com.br

    2000-03-01

    Single zircon Pb-evaporation ages were determined for a mafic granulite, two enderbites and a kinzigite of the Porto Nacional High-Grade Metamorphic Terrain (PNHGT) in the Goias massif. Zircons from mafic granulites and one of the enderbites of yielded average {sup 207} Pb/{sup 206} Pb ages of 2125{+-}3 Ma and 2153{+-}1 Ma, respectively, being interpreted as minimum ages of the igneous protoliths. The other enderbite, whose zircons presented round terminations, yielded an average {sup 207} Pb/{sup 206} Pb age of 2097 {+-} 2 Ma. Zircons from the kinzigite, displaying cores and rims overgrowth, presented {sup 207} Pb/{sup 206} Pb ages ranging between 2027 and 2115 Ma. However, a very homogeneous zircon crystal without overgrowth yielded age of 2100 {+-} 2 Ma, with a distinctive low Th/U value (0.02). This zircon is interpreted as a metamorphic crystal and its age probably sets the age of the granulite facies metamorphism, indicating that the PNHGT is a result of the Transamazonian thermotectonic event. (author)

  8. Development of sequential analytical method for the determination of U-238, U-234, Th-232, Th-230, Th-228, Ra-226 and Ra-228 and its application in mineral waters

    International Nuclear Information System (INIS)

    Costa Lauria, D. da.

    1986-01-01

    A sequential analytical method for the determination of U-238, U-234, Th-232, Th-230, Th-228, Ra-226 and Ra-228 in environmental samples and applied to the analysis of mineral waters is studied. Thorium isotopes are coprecipitated with lanthanium fluoride before counting in alpha spectrometer, the uranium isotopes are determined by alpha spectrometry following extraction with TOPO onto a polymenic membrane. Radium-226 is determined with the radom emanation technique. (M.J.C.) [pt

  9. 210Pb and 137Cs dating of sediments from Zigetang Lake, Tibetan Plateau

    International Nuclear Information System (INIS)

    Yao, S.C.; Li, S.J.; Zhang, H.C.

    2008-01-01

    Zigetang Lake located in the central Tibetan Plateau was selected for the purpose of understanding of recent sedimentation rates. Based on 137 Cs dating marker, the sediment rate was 0.077 cm x yr -1 . The sedimentation rate was calculated to be 0.071 cm x yr -1 and 0.029 g x cm -2 x yr -1 on the basis of 210 Pb CIC model. 210 Pb CRS model was also used for understanding of recent sedimentation change. The sediment accumulation rates for the CRS model ranged from 0.022 to 0.038 g x cm -2 x yr -1 with an irregular high value of 0.12 g x cm -2 x yr -1 around 1932 at Zigetang Lake core in the past eighty years. (author)

  10. Isotope age of the rare metal pegmatite formation in the Kolmozero-Voron'ya greenstone belt (Kola region of the Fennoscandian shield): U-Pb (TIMS) microlite and tourmaline dating

    Science.gov (United States)

    Kudryashov, Nikolay; Lyalina, Ludmila; Mokrushin, Artem; Zozulya, Dmitry; Groshev, Nikolay; Steshenko, Ekaterina; Kunakkuzin, Evgeniy

    2016-04-01

    surface contamination being placed the ultrasonic bath with the 7N HNO3 solution. The discordia constructed for seven measured microlite weights is characterized by upper intercepts with concordia at 2454±8 Ma, which probably reflects the time of rare metal pegmatite crystallization, coeval with the age of tourmaline granites. Taking into consideration the obtained U--Pb age of microlite, it may be assumed that the tourmaline granites dated back to 2520±70 Ma served as the most probable parental rocks for rare metal pegmatites of the Vasin-Myl'k deposit. The work is supported by RFBR No 16-05-00367, No 16-05-00427 and project No 0231-2015-0005

  11. Geology, petrology and U-Pb geochronology of Serra da Rajada Granitic Pluton: implications about ediacaran magmatic evolution in NE portion of the Rio Piranhas-Serido Domain (NE of Borborema Province); Geologia, petrologia e geocronologia U-Pb do Pluton Granitico Serra da Rajada: implicacoes sobre a evolucao magmatica ediacarana na porcao do Dominio Rio Piranhas-Serido (NE da Provincia Borborema)

    Energy Technology Data Exchange (ETDEWEB)

    Costa, Alan Pereira da; Dantas, Alexandre Ranier, E-mail: alan.costa@cprm.gov.br, E-mail: alexandre.dantas@cprm.gov.br [Servico Geologico do Brasil (CPRM), Natal, RN (Brazil). Nucleo de Apoio de Natal/Superintendencia Regional de Recife; Nascimento, Marcos Antonio Leite do; Galindo, Antonio Carlos, E-mail: marcos@geologia.ufrn.br, E-mail: galindo@geologia.ufrn.br [Universidade Federal do Rio Grande do Norte (UFRN), Natal, RN (Brazil). Departamento de Geologia

    2015-12-15

    The Ediacaran plutonic activity, related to the Brazilian/Pan-African orogeny, is one of the most important geological features in the Borborema Province, formed by batholiths, stocks and dikes. The Serra da Rajada Granitic Pluton (SRGP), located in the central portion of the Rio Piranhas-Serido Domain, is an example of these bodies. This site is the target of cartographic, petrographic, lithochemical and geochronological studies. Its rocks are described as monzogranites consisting of K-feldspar, plagioclase (oligoclase-An{sub 23-24%}), quartz and biotite (main mafic), having as accessory minerals opaque, titanite, allanite, apatite and zircon. Chlorite, white mica and carbonate are alteration minerals. Lithochemical data from 15 samples show quite evolved rocks (SiO{sub 2} , 69% to 75%), rich in alkalis (Na{sub 2}O + K{sub 2}O ≥ 8.0%), depleted in MgO (≤ 0.45%), CaO (≤ 1.42%) and TiO{sub 2} (≤ 0.36%), and displaying moderate levels of Fe{sub 2}O{sub 3} t (2.16 to 3.53%). These rocks present a transitional nature between metaluminous and peraluminous (predominance of the latter) and have subalkaline/monzonitic affinity (high-K Calc-alkaline). Harker diagrams represent negative correlations in Fe{sub 2}O{sub 3}t, MgO and CaO, indicating fractionation of mafic and plagioclase. The REE spectrum show enrichment of light in relation to heavy REE (LaN/YbN = 23.70 to 10.13), with negative anomaly in Eu (Eu/ Eu* = 0.70 to 10.13) suggesting fractionation or accumulation in the feldspars source (plagioclase). Data integration allows correlating the SRGP rocks with those described as Equigranular high-K Calc-alkaline Suite. The U-Pb geochronology and Sm-Nd isotope dating indicate that the biotite monzogranite have a crystallization age of 557 ± 13 Ma and TDM model age of 2.36 Ga, respectively, and ε{sub Nd} value of - 20.10 for the crystallization age, allowing to infer a crustal source for the magma generated in the Paleoproterozoic age. (author)

  12. Matrix-Matched Iron-Oxide Laser Ablation ICP-MS U–Pb Geochronology Using Mixed Solution Standards

    Directory of Open Access Journals (Sweden)

    Liam Courtney-Davies

    2016-08-01

    Full Text Available U–Pb dating of the common iron-oxide hematite (α-Fe2O3, using laser-ablation inductively-coupled-plasma mass-spectrometry (LA-ICP-MS, provides unparalleled insight into the timing and processes of mineral deposit formation. Until now, the full potential of this method has been negatively impacted by the lack of suitable matrix-matched standards. To achieve matrix-matching, we report an approach in which a U–Pb solution and ablated material from 99.99% synthetic hematite are simultaneously mixed in a nebulizer chamber and introduced to the ICP-MS. The standard solution contains fixed U- and Pb-isotope ratios, calibrated independently, and aspiration of the isotopically homogeneous solution negates the need for a matrix-matched, isotopically homogenous natural iron-oxide standard. An additional advantage of using the solution is that the individual U–Pb concentrations and isotope ratios can be adjusted to approximate that in the unknown, making the method efficient for dating hematite containing low (~10 ppm to high (>1 wt % U concentrations. The above-mentioned advantage to this solution method results in reliable datasets, with arguably-better accuracy in measuring U–Pb ratios than using GJ-1 Zircon as the primary standard, which cannot be employed for such low U concentrations. Statistical overlaps between 207Pb/206Pb weighted average ages (using GJ-1 Zircon and U–Pb upper intercept ages (using the U–Pb mixed solution method of two samples from iron-oxide copper-gold (IOCG deposits in South Australia demonstrate that, although fractionation associated with a non-matrix matched standard does occur when using GJ-1 Zircon as the primary standard, it does not impact the 207Pb/206Pb or upper intercept age. Thus, GJ-1 Zircon can be considered reliable for dating hematite using LA-ICP-MS. Downhole fractionation of 206Pb/238U is observed to occur in spot analyses of hematite. The use of rasters in future studies will hopefully minimize

  13. Application of the {sup 210}Pb-dating technique to evaluate environmental changes resulting from recent human activities

    Energy Technology Data Exchange (ETDEWEB)

    Jenkinson, A.V.; Chisari, R.; Farrar, Y.J.; Heijnis, H.; McOrist, G.D. [Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW (Australia); Hallegraeff, G. [University of Tasmania, Tasmania, (Australia). Department of Plant Science; Hughes, M.; Napoli, M. [University of Sydney, Sydney, NSW (Australia). Department of Geology and Geophysics; James, J.M. [University of Sydney, NSW, (Australia). School of Chemistry; McMinn, A.; Thomson, P. [University of Tasmania, Tasmania, (Australia). Institute of Antartic and Southern Ocean Studies; Smith, J.D.; Tinker, R.A. [University of Melbourne, Parkville, VIC (Australia). School of Chemistry, Marine Chemistry Laboratory

    1997-10-01

    The {sup 210}Pb-dating technique has shown particular promise for the study of recent environmental change by enabling the establishment of chronologies for contemporary environmental processes. In this paper two case studies are discussed. Case Study (1) looks at trace element and heavy metal levels in the estuaries of the Georges River and the Hacking River which are partly located in suburban Sydney and Case Study (2) looks at blooms of the toxic dinoflagellate Gymnodinium catenatum which were first observed in Tasmanian waters, principally the Huon and Derwent Rivers in 1980. In both cases the {sup 210}Pb dating technique has been used to establish the sequence of sediment deposition in order to associate an age to the sediment layer which contains the entity under investigation 7 refs., 5 figs.

  14. Age of Saurashtra miliolites by U-Th decay series methods: possible implications to their origin

    Energy Technology Data Exchange (ETDEWEB)

    Hussain, N; Bhandari, N; Ramanathan, K R; Somayajulu, B L.K. [Physical Research Lab., Ahmedabad (India)

    1980-03-01

    The miliolite deposits of Saurashtra have been dated by /sup 234/U, /sup 230/Th, /sup 231/Pa and /sup 14/C methods. Concordant ages of approximately 10/sup 5/ years using the U decay series isotopes are obtained which agree with the ages of the coral reefs of Okha-Dwaraka coast suggesting a contemporaneous origin for both. The lower /sup 14/C ages (<= 40,000 years) may be due to a recent influx of seawater or ground water. Quartz and clay minerals together constitute only <= 10% by weight, as such the aeolin characteristics of quartz grains may not be relevant to the origin of the miliolites.

  15. Using U-Th-Pb petrochronology to determine rates of ductile thrusting: Time windows into the Main Central Thrust, Sikkim Himalaya

    Science.gov (United States)

    Mottram, Catherine M.; Parrish, Randall R.; Regis, Daniele; Warren, Clare J.; Argles, Tom W.; Harris, Nigel B. W.; Roberts, Nick M. W.

    2015-07-01

    Quantitative constraints on the rates of tectonic processes underpin our understanding of the mechanisms that form mountains. In the Sikkim Himalaya, late structural doming has revealed time-transgressive evidence of metamorphism and thrusting that permit calculation of the minimum rate of movement on a major ductile fault zone, the Main Central Thrust (MCT), by a novel methodology. U-Th-Pb monazite ages, compositions, and metamorphic pressure-temperature determinations from rocks directly beneath the MCT reveal that samples from 50 km along the transport direction of the thrust experienced similar prograde, peak, and retrograde metamorphic conditions at different times. In the southern, frontal edge of the thrust zone, the rocks were buried to conditions of 550°C and 0.8 GPa between 21 and 18 Ma along the prograde path. Peak metamorphic conditions of 650°C and 0.8-1.0 GPa were subsequently reached as this footwall material was underplated to the hanging wall at 17-14 Ma. This same process occurred at analogous metamorphic conditions between 18-16 Ma and 14.5-13 Ma in the midsection of the thrust zone and between 13 Ma and 12 Ma in the northern, rear edge of the thrust zone. Northward younging muscovite 40Ar/39Ar ages are consistently 4 Ma younger than the youngest monazite ages for equivalent samples. By combining the geochronological data with the >50 km minimum distance separating samples along the transport axis, a minimum average thrusting rate of 10 ± 3 mm yr-1 can be calculated. This provides a minimum constraint on the amount of Miocene India-Asia convergence that was accommodated along the MCT.

  16. Genesis of the Bangbule Pb-Zn-Cu polymetallic deposit in Tibet, western China: Evidence from zircon U-Pb geochronology and S-Pb isotopes

    Science.gov (United States)

    Kan, Tian; Zheng, Youye; Gao, Shunbao

    2016-04-01

    The Banbule Pb-Zn-Cu skarn deposit is located in the Longger-Gongbujiangda volcanic magma arc in the Gangdese-Nyainqentanglha Plate. It is the only lead-zinc polymetallic deposit discovered in the westernmost Nyainqentanglha metallogenic belt. The measured and indicated resources include 0.9 Mt of Pb+Zn (4.77% Pb and 4.74% Zn, respectively), 6499 t of Cu, and 178 t of Ag (18.75g/t Ag). The orebodies mainly occur as lenses, veins and irregular shapes in the contact zone between the quartz-porphyry and limestone of the Upper Permian Xiala Formation, or in the boundaries between limestone and sandstone. Pb-Zn-Cu mineralization in the Banbule deposit is closely associated with skarns. The ore minerals are dominated by galena, sphalerite, chalcopyrite, bornite, and magnetite, with subordinate pyrite, malachite, and azurite. The gangue minerals are mainly garnet, actinolite, diopside, quartz, and calcite. The ore-related quartz-porphyry displays LA-ICP-MS zircon U-Pb age of 77.31±0.74 Ma. The δ34S values of sulfides define a narrow range of -0.8 to 4.7‰ indicating a magmatic source for the ore-forming materials. Lead isotopic systematics yield 206Pb/204Pb of 18.698 to 18.752, 207Pb/204Pb of 15.696 to 15.760, and 208Pb/204Pb of 39.097 to 39.320. The data points are constrained around the growth curves of upper crust and orogenic belt according to the tectonic discrimination diagrams. The calculated Δβ - Δγ values plot within the magmatic field according to the discrimination diagram of Zhu et al. (1995). The S-Pb isotopic data suggest that Bangbule is a typical skarn deposit, and the Pb-Zn-Cu mineralization is genetically related to the quartz-porphyry in the mining district. The discovery of the Bangbule deposit indicates that there is metallogenic potential in the westernmost Nyainqentanglha belt, which is of great importance for the exploration work in this area.

  17. Paleoproterozoic source contributions to the Sao Roque Group sedimentation: LA-MC-ICPMS U-Pb dating and Sm-Nd systematics of clasts from metaconglomerates of the Boturuna Formation

    Energy Technology Data Exchange (ETDEWEB)

    Henrique-Pinto, Renato; Janasi, Valdecir de Assis; Tassinari, Colombo Celso Gaeta [Universidade de Sao Paulo (USP), SP (Brazil). Inst. de Geociencias. Dept. de Mineralogia e Geotectonica; Simonetti, Antonio [University of Notre Dame, South Bend (United States). Dept. of Civil Engineering and Geological Sciences; Heaman, Larry Michael, E-mail: renatohp@usp.br, E-mail: vajanasi@usp.br, E-mail: ccgtassi@usp.br, E-mail: antonio.simonetti.3@nd.edu, E-mail: larry.heaman@ualberta.ca [University of Alberta, Edmonton (Canada). Dept. of Earth and Atmospheric Sciences

    2012-12-15

    The Sao Roque Group is characterized by volcano-sedimentary sequences, in which deposition probably started in the late Paleoproterozoic. U-Pb dating by LA-MC-ICPMS of zircons extracted from predominantly equigranular monzogranites clasts from Morro Doce and Morro do Polvilho regions, yield paleoproterozoic ages of 2199 {+-}8.5 Ma and 2247 {+-}13 Ma, respectively. These represent the ages for the main source of granite for the metaconglomerates from the Boturuna Formation (basal unit of Sao Roque Group). Its polycyclic history is reinforced by the presence of inherited Archean zircons (2694 {+-}29 Ma) found within the clasts. Moreover, these clasts have also been affected by the Neoproterozoic overprinting event as indicated by their lower intercept Concordia ages. Sm-Nd isotope data for the main clast varieties from the Morro Doce metaconglomerates yield T{sub DM} ages of 2.6 to 2.7 Ga, demonstrating that these granites are the recycling products of an Archean crustal component. The metaconglomerate arkosean framework yields slightly lower {epsilon}{sub Nd(t)} values than those for the clasts, indicating that a younger and/or more primitive source also contributed to the Boturuna Formation. (author)

  18. Environmental geochemistry of 238U, 232Th, 40K and some heavy metals in River Nile sediments

    International Nuclear Information System (INIS)

    Siddeeg, S. M. B.

    2007-06-01

    Environmental geochemistry is concerned with the abundance, distribution, and mobility of chemical elements in surface materials at the surface of earth crust. This study aimed at better understanding of geochemical behavior of 238 U, 23 '2Th and 40 K in river sediments and some heavy elements with emphasis on Mg, Ca, Mn, Fe, Ni, Cu, Zn and Pb. The analysis was conducted for a total of 33 bulk sediment samples from White Nile, Blue Nile and River Nile within Khartoum, the samples were fractionated into seven grain sizes each (2000-1000, 1000-500, 500-250, 250-200, 200-125, 125-100 and > 100 μm), using high resolution gamma spectrometer for radionuclides measurements, whereas Particle Induced X-ray Emission (PIXE) was used for heavy metals analysis. On the average, the activity concentration of 238 U, 232 Th and 40 K were 17.90±5.23, 16.38±5.34 and 379.82±107.76 Bq -1 Kg in White Nile, 19.56±5.04, 17.72±4.69, and 494.36±105.79 Bq -1 Kg in Blue Nile and 19.27±2.88, 17.48±2.78, 359.50±83.15 Bq -1 Kg in the River Nile sediments. Results revealed inverse relationship between activity concentration and grain size in White and Blue Nile, while the trend is not clear in the River Nile. In general, the variation of the measured values within single grain size was smaller in White Nile compare to Blue and River Nile sediments, and it was observed that the data are highly scattered in grain size (200-125μm). The ratio between 238 U/ 232 Th is grater than unity in the three rivers indicating that there is relative enrichment of 238 U in the surface sediments. The activity concentration of the fallout radionuclide 137 Cs is one order of magnitude lower in the White Nile sediments (0.89±0.96) Bq -1 Kg compared to values in the Blue Nile sediments (3.60±1.55) Bq -1 Kg. Comparison of the values obtained for natural radionuclides and the fallout radionuclide ( 137 Cs in the three sites with the global data reflect low and /or insignificant difference. For heavy metal

  19. Evolution of Th and U whole-rock contents in the Ilimaussaq intrusion

    International Nuclear Information System (INIS)

    Bailey, J.C.; Rose-Hansen, J.; Soerensen, H.

    1981-01-01

    Thorium and uranium values of a large collction of representative samples taken from all rock types of the Ilimaussaq alkaline intrusion, South Greenland, are presented. The values are largely obtained by laboratory gamma-ray spectrometric (GRS) analysis. The results are discussed in relation to current knowledge and ideas on the petrologic evolution of the Ilimaussaq intrusion. It is concluded that (1) Rocks from the Ilimaussaq alkaline intrusion evolve to extremely high Th and U contents; (2) The evolution is characterised by appearance of low-Th/U cumulates due to the appearance of low-Th/U eudialyte as a liquidus phase; (3) Fractionation of the observed cumulus assemblages fails to explain all features of the Th-U evolution; (4) Losses of mobile fluids, rich in Th/U, occur in the final stages. (BP)

  20. New zircon U-Pb LA-ICP-MS ages and Hf isotope data from the Central Pontides (Turkey): Geological and geodynamic constraints

    Science.gov (United States)

    Çimen, Okay; Göncüoğlu, M. Cemal; Simonetti, Antonio; Sayit, Kaan

    2018-05-01

    The Central Pontides in northern Anatolia is located on the accretionary complex formed by the closure of Neotethyan Intra-Pontide Ocean between the southern Eurasian margin (Istanbul-Zonguldak Terrane) and the Cimmerian Sakarya Composite Terrane. Among other components of the oceanic lithosphere, it comprises not yet well-dated felsic igneous rocks formed in arc-basin as well as continent margin settings. In-situ U-Pb age results for zircons from the arc-basin system (öangaldağ Metamorphic Complex) and the continental arc (Devrekani Metadiorite and Granitoid) yield ages of 176 ± 6 Ma, 163 ± 9 Ma and 165 ± 3 Ma, respectively. Corresponding in-situ average (initial) 176Hf/177Hf initial ratios are 0.28261 ± 0.00003, 0.28267 ± 0.00002 and 0.28290 ± 0.00004 for these units and indicative of a subduction-modified mantle source. The new U-Pb ages and Hf isotope data from these oceanic and continental arc units together with regional geological constraints support the presence of a multiple subduction system within the Intra-Pontide Ocean during the Middle Jurassic.

  1. Age of origin of the polymetamorphosed Copperton Formation, Namaqua-Natal Province, determined by single grain zircon Pb-Pb dating

    International Nuclear Information System (INIS)

    Cornell, D.H.; Griffin, G.; Kroener, A.; Humphreys, H.

    1990-01-01

    The Copperton Formation of the Areachap Group in the Northern Cape Province is a strongly metamorphosed, predominantly metavolcanic unit which contains several massive sulphide deposits. Previous work on this unit has established a complex metamorphic history, the four main phases of which are fairly well dated by a combination of methods; however, the age of origin is still poorly constrained. Zircons extracted from the Smouspan Gneiss Member of the Copperton formation are euhedral and show a crystal habit which indicates an igneous and probably volcanic origin, with no discernable metamorphic component. Whole-grain thermal evaporation on four such zircon grains yielded a precise set of 207 Pb/ 206 Pb data which establishes a 1 285 ± 14 Ma age for the origin of the Smouspan Gneiss and Copperton Formation. Indications of a ∼1 600 Ma age from other parts of the Areachap Group should be treated with caution until more reliable data are obtained. 9 figs., 2 tabs., 29 refs

  2. Detrital zircon typology and U/Pb geochronology for the Miocene Ladrilleros-Juanchaco sedimentary sequence, Equatorial Pacific (Colombia): New constraints on provenance and paleogeography in northwestern South America

    Energy Technology Data Exchange (ETDEWEB)

    Osorio-Granada, E.; RESTREPO-MORENO, S.A.; MUÑOZ-VALENCIA, J.A.; TREJOS-TAMAYO, R.A.; PARDO-TRUJILLO, A.; BARBOSA-ESPITIA, A.A.

    2017-11-01

    Typology and internal texture analyses were performed on detrital zircons obtained from the Miocene sandstones of the Ladrilleros-Juanchaco sedimentary sequence (Colombia, Equatorial Pacific). This analysis was complemented with zircon U/Pb dating to identify typology-age associations as indicators of sediment provenance. Our results show that zircons with S and P dominant typologies have internal structures/zoning indicative of igneous, and potentially also metamorphic, origins. Morphometric results suggest limited transport from source areas. Both typology and U/Pb data point to the western Cordillera as the principal source of detrital materials for this sedimentary sequence. A paleogeographic reconstruction shows that, during the Late Miocene, significant portions of the western Cordillera were uplifted and actively eroding, thereby forming a fluvio-topographic barrier that prevented sediments from the central Cordillera reaching the Pacific basins. Exhumed Miocene plutons located along the axis of the western Cordillera may also have played a role as geomorphologically active massifs. This study demonstrates that typologic analysis on detrital zircon grains is a useful tool for establishing provenance and paleogeography in complex litho-tectonic areas where overlapping U/Pb signatures can lead to contradictory results.

  3. U4+ spectroscopic properties in Dsub(2d) with ThCl4, UCl4 and ThSiO4

    International Nuclear Information System (INIS)

    Khan Malek, C.

    1985-01-01

    This thesis is concerned with the study of the electronic structure of the tetravalent actinide ions in solid state. The technique used was high resolution optical spectroscopy. We deal with the U 4+ ion (sf 2 ) in the monocrystals ThCl 4 , UCl 4 , and ThSiO 4 where the U 4+ ion is substituded for the Th 4+ ion by doping. Visible and infrared optical spectra were recorded between 300 and 4.2K. With these three compounds, it is possible to compare the influence of different environments of Dsub(2d) symmetry: real symmetry for U 4+ in UCl 4 and ThSiO 4 ; approximate symmetry in ThCl 4 , whose structure is incommensurate and modulated at low temperature. The fitting of the data was carried out by diagonalizing the hamiltonian which describes the interactions of the U 4+ ion in a crystal field with its environment. This fitting procedure led to a coherent set of spectroscopic parameters. The fluorescence of U 4+ was observed in ThCl 4 and ThSiO 4 and the effect of the incommensurate structure of ThCl 4 on the optical spectra was studied. The symmetry of the U 4+ sites was identified by site selective excitation experiments and a relationship between the incommensurate structure and the lifetime of U 4+ energy levels was found. In conclusion, the U 4+ energy levels in a relatively low crystal field were determined for compounds that have a similar coordination polyhedron about the actinide ion. The values for these energy levels were then compared to those of lanthanide and 3d elements [fr

  4. Constraints on the timing of multiple thermal events and re-equilibration recorded by high-U zircon and xenotime: Case study of pegmatite from Piława Górna (Góry Sowie Block, SW Poland)

    Science.gov (United States)

    Budzyń, Bartosz; Sláma, Jiří; Kozub-Budzyń, Gabriela A.; Konečný, Patrik; Holický, Ivan; Rzepa, Grzegorz; Jastrzębski, Mirosław

    2018-06-01

    The application of zircon and xenotime geochronometers requires knowledge of their potential and limitations related to possible disturbance of the age record. The alteration of the intergrown zircon and xenotime in pegmatite from the Góry Sowie Block (SW Poland) was studied using the electron microprobe analysis, X-ray WDS compositional mapping, micro-Raman analysis, and LA-ICP-MS U-Pb dating of zircon and xenotime, as well as the U-Th-total Pb dating of uraninite. These microanalytical techniques were applied to understand the formation mechanisms of the secondary textures related to post-magmatic processes in the zircon and xenotime intergrowth, and to constrain their timing. Textural and compositional features combined with U-Pb data indicate that the pegmatite-related crystallization of the zircon and xenotime intergrowth occurred ca. 2.09 Ga (2086 ± 35 Ma for zircon and 2093 ± 52 Ma for xenotime), followed by the re-equilibration of zircon and xenotime ca. 370 Ma (373 ± 18 Ma and 368 ± 6 Ma, respectively) during the formation of the younger pegmatite. The zircon and xenotime were most likely derived from Precambrian basement rocks and emplaced in the pegmatite as a restite. The zircon preserved textures related to diffusion-reaction processes that affected its high-U core (up to ca. 9.6 wt% UO2), which underwent further metamictization and amorphization due to self-radiation damage. The zircon rim and xenotime were affected by coupled dissolution-reprecipitation processes that resulted in patchy zoning, age disturbance and sponge-like textures. Xenotime was also partially replaced by fluorapatite or hingganite-(Y) and Y-enriched allanite-(Ce). The termination of the low-temperature alteration was constrained by the U-Th-total Pb age of the uraninite inclusions that crystallized in zircon at 281 ± 2 Ma, which is consistent with the age of 278 ± 15 Ma obtained from the youngest cluster of U-Pb ages in the re-equilibrated high-U zircon domains. This study

  5. Th/U-233 multi-recycle in PWRs

    International Nuclear Information System (INIS)

    Yun, D.; Kim, T.K.; Taiwo, T.A.

    2010-01-01

    The use of thorium in current or advanced light water reactors (LWRs) has been of interest in recent years. These interests have been associated with the need to increase nuclear fuel resources and the perceived non-proliferation advantages of the utilization of thorium in the fuel cycle. Various options have been considered for the use of thorium in the LWR fuel cycle including: (1) its use in a once-through fuel cycle to replace non-fissile uranium or to extend fuel burnup due to its attractive fertile material conversion, (2) its use for fissile plutonium burning in limited recycle cores, and (3) its advantage in limiting the transuranic elements to be disposed off in a repository (if only Th/U-233 fuel is used). The possibility for thorium utilization in multirecycle system has also been considered by various researchers, primarily because of the potential for near breeders with Th/U-233 in the thermal energy range. The objective of this project is to evaluate the potential of the Th/U-233 fuel multirecycle in current LWRs, with focus this year on pressurized water reactors (PWRs). In this work, approaches for ensuring a sustainable multirecycle without the need for external source of makeup fissile material have been investigated. The intent is to achieve a design that allows existing PWRs to be used with minimal modifications. In all cases including homogeneous and heterogeneous assembly designs, the assembly pitch is kept consistent with that of the current PWRs (21.5 cm used). Because of design difficulties associated with using the same geometry and dimensions as a PWR core, the potential modifications (other than assembly pitch) that would be needed for PWRs to ensure a sustainable multirecycle system have been investigated and characterized. Additionally, the implications of the use of thorium on the LWR fuel cycle are discussed. In Section 2, background information on studies evaluating the use of thorium in the fuel cycle is provided, but focusing on

  6. Th/U-233 multi-recycle in PWRs.

    Energy Technology Data Exchange (ETDEWEB)

    Yun, D.; Kim, T. K.; Taiwo, T. A.; Nuclear Engineering Division

    2010-09-07

    The use of thorium in current or advanced light water reactors (LWRs) has been of interest in recent years. These interests have been associated with the need to increase nuclear fuel resources and the perceived non-proliferation advantages of the utilization of thorium in the fuel cycle. Various options have been considered for the use of thorium in the LWR fuel cycle including: (1) its use in a once-through fuel cycle to replace non-fissile uranium or to extend fuel burnup due to its attractive fertile material conversion, (2) its use for fissile plutonium burning in limited recycle cores, and (3) its advantage in limiting the transuranic elements to be disposed off in a repository (if only Th/U-233 fuel is used). The possibility for thorium utilization in multirecycle system has also been considered by various researchers, primarily because of the potential for near breeders with Th/U-233 in the thermal energy range. The objective of this project is to evaluate the potential of the Th/U-233 fuel multirecycle in current LWRs, with focus this year on pressurized water reactors (PWRs). In this work, approaches for ensuring a sustainable multirecycle without the need for external source of makeup fissile material have been investigated. The intent is to achieve a design that allows existing PWRs to be used with minimal modifications. In all cases including homogeneous and heterogeneous assembly designs, the assembly pitch is kept consistent with that of the current PWRs (21.5 cm used). Because of design difficulties associated with using the same geometry and dimensions as a PWR core, the potential modifications (other than assembly pitch) that would be needed for PWRs to ensure a sustainable multirecycle system have been investigated and characterized. Additionally, the implications of the use of thorium on the LWR fuel cycle are discussed. In Section 2, background information on studies evaluating the use of thorium in the fuel cycle is provided, but focusing on

  7. A precise 232Th-208Pb chronology of fine-grained monazite: Age of the Bayan Obo REE-Fe-Nb ore deposit, China

    Science.gov (United States)

    Wang, Jingyuan; Tatsumoto, M.; Li, X.; Premo, W.R.; Chao, E.C.T.

    1994-01-01

    We have obtained precise Th-Pb internal isochron ages on monazite and bastnaesite for the world's largest known rare earth elements (REE)-Fe-Nb ore deposit, the Bayan Obo of Inner Mongolia, China. The monazite samples, collected from the carbonate-hosted ore zone, contain extremely small amounts of uranium (less than 10 ppm) but up to 0.7% ThO2. Previous estimates of the age of mineralization ranged from 1.8 to 0.255 Ga. Magnetic fractions of monazite and bastnaesite samples (<60-??m size) showed large ranges in 232Th 204Pb values (900-400,000) and provided precise Th-Pb internal isochron ages for paragenetic monazite mineralization ranging from 555 to 398 Ma within a few percent error (0.8% for two samples). These results are the first indication that REE mineralization within the giant Bayan Obo ore deposit occurred over a long period of time. The initial lead isotopic compositions (low 206Pb 204Pb and high 208Pb 204Pb) and large negative ??{lunate}Nd values for Bayan Obo ore minerals indicate that the main source(s) for the ores was the lower crust which was depleted in uranium, but enriched in thorium and light rare earth elements for a long period of time. Zircon from a quartz monzonite, located 50 km south of the ore complex and thought to be related to Caledonian subduction, gave an age of 451 Ma, within the range of monazite ages. Textural relations together with the mineral ages favor an epigenetic rather than a syngenetic origin for the orebodies. REE mineralization started around 555 Ma (disseminated monazite in the West, the Main, and south of the East Orebody), but the main mineralization (banded ores) was related to the Caledonian subduction event ca. 474-400 Ma. ?? 1994.

  8. The 3.5 Ga granulites of the Bug polymetamorphic complex, Ukraine (U-Pb SHRIMP-II zircon data)

    Science.gov (United States)

    Lobach-Zhuchenko, Svetlana; Kaulina, Tatiana; Baltybaev, Shauket; Yurchenko, Anastasija; Balagansky, Victor; Skublov, Sergei; Sukach, Vitaliji

    2014-05-01

    The Bug polymetamorphic complex composes the south-west of the Ukrainian Shield. It experienced multistage deformation and metamorphism of 3.6 to 1.95 Ga. The age of protolith of the gneiss enderbite is up to 3.7-3.6 Ga (Claesson et al., 2006: Lobach-Zhuchenko et al., 2010, 2013; Bibikova et al, 2013). The 3.5 old granulitic zircon (sample UR132) was found in a light grey massive medium grained with weak foliation granulite from the Odessa quarry located at the right riverside of the Bug (N 48° 13' 55.2''; E 29° 59' 75''). The rock is mafic in composition (SiO2 = 51.50 wt%, #mg=0.43, (La/Yb)n =7.5), and shows enrichment in Sr (333 ppm), Zr (244 ppm), and Nb (12 ppm) compared to MORB. This contains antiperthitic plagioclase (An30-35), hypersthene (En0.46 Fs0.53 Wo0.01 ), diopside (En0.33 Fs0.20Wo0.47), quartz, ilmenite, magnetite, apatite, and zircon. Three types of zircon are recognized. (1) Large (~300 μm) isometric and oval grains displaying bright colour and sector zoning in CL. Some crystals have fir-tree texture. Isometric shape together with fir-tree zoning is typical for zircons growing under conditions of granulite- facies metamorphism (Hoskin and Schaltegger, 2003). These zircons are low in U and Th, have high Th/U ratios (0.61-1.1), and display decreasing of element contents from the centre to margin (ppm): U - 68 to 44, Th - 58 to 19, total REE - 723 to 406, Y - 1049 to 553, and Li - 1.23 to 0.91 at the constant (Lu/La)n ratios (4200-4600). Zircon's crystallization temperature calculated from the Ti content is 705 °C and is consistent with those calculated on the base of the mineral composition. (2) Small sized (60-100 μm) zircons. Most of these occur within plagioclase and truncate antiperthite lamellae. They show euhedral zoned cores and bright rims in CL. (3) Zircons principally distinguished from those of groups 1 and 2. These are dark in CL, some grains are severely structurally damaged and contain numerous inclusions (Qzt, Pl, Kfsp, rare Opx

  9. Availability of U-238 and Th-232 present in phosphogypsum used in agriculture: precision and accuracy of the methodology

    International Nuclear Information System (INIS)

    Malheiro, Luciano H.; Saueia, Catia H.R.; Mazzilli, Barbara P.

    2013-01-01

    Phosphogypsum (PG) can be classified as Technologically Enhanced Naturally Occurring Radioactive Material (TENORM), and it is obtained as a residue of the phosphate fertilizer industry. PG presents in its composition radionuclides of the natural U and Th series: mainly Ra-226, Ra-228, Th-232, Pb-210 and Po-210. The Brazilian producers stock the PG in dry stacks, posing risks to the surrounding environment. A possible solution to this problem is to reuse PG in agriculture; however, it is necessary to ensure that the radionuclides present in the PG will not be available to the agricultural products. This study is part of a research project sponsored by Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP - 2010-10587-0) entitled 'Availability of metals and radionuclides in tropical soils amended with phosphogypsum', and its objective is to evaluate the reliability of an optimal methodology to determine U-238 and Th-232 in samples of soils amended with PG through percolation with water. The methodology comprises a sequential radiochemical separation of the radionuclides present in the leachate. The UTEVA resin was used for the purification and separation of U-238 and Th-232, and the final activity concentrations were determined by alpha spectrometry. The precision and accuracy of the methodology were checked by measuring standard reference material. The results obtained for the relative error and relative standard deviation varied respectively from 2.34 % to 5.92 % and 6.10 % to 6.21 % for uranium, and from 0.42 % to 3.13 % and 9.68 % to 10.97 % for thorium. (author)

  10. Distribution of U and Th in Growth Zones of Manganese Nodules

    DEFF Research Database (Denmark)

    Kunzendorf, Helmar; Friedrich, G. H. W.

    1976-01-01

    Growth zones and individual sublayers from one manganese nodule and three manganese crusts from an area south of Hawaii were analysed for U and Th by the delayed-neutron counting technique. The concentrations of uranium and thorium in the manganese nodule are highest in the outermost zone on top...... to the sediment which has low concentrations of Fe, relative to the zone last exposed to sea water, has also low U contents (2.7 ppm). Th concentrations are higher in the outermost zone on top of the nodule (40 to a maximum of 130 ppm) than in the zone last exposed to the sediment (about 20 ppm Th). Manganese...... crusts contain up to 9 ppm U in the outermost zones last exposed to the sea water. They also have higher concentrations of Th (up to 64 ppm) relative to the inner zones of the crust growing on altered andesitic rock, which contains about 8 ppm U and about 26 ppm Th as an average....

  11. Separation of Th(IV) and U(VI) by extraction chromatography

    International Nuclear Information System (INIS)

    Nadkarni, M.N.; Mayankutty, P.C.; Pillai, N.S.

    1984-01-01

    Application of extraction chromatography to the analytical separation of Th(IV) and U(VI) has been investigated. The stationary phase was a macroporous resin Amberlite XE-270 impregnated with undiluted tri-n-butylphosphate (TBP) and the mobile phase was either 5.0M HNO 3 or 6M HCl. Separation of traces of Th(IV) from large quantities of U(VI) was achieved on a laboratory column by elution of the absorbed Th(IV) with 6M HCl. (author)

  12. Rates of sediment reworking at the HEBBLE site based on measurements of Th-234, Cs-137 and Pb-210

    International Nuclear Information System (INIS)

    DeMaster, D.J.; McKee, B.A.; Nittrouer, C.A.; Brewster, D.C.; Biscaye, P.E.

    1985-01-01

    Th-234, Cs-137 and Pb-210 measurements have been made on ten cores from the HEBBLE site on the Nova Scotian continental rise. Th-234 mixing coefficients from HEBBLE sediments show substantial lateral variability with values ranging from 1 to 33 cm 2 yr -1 . These mixing coefficients are one to two orders of magnitude greater than values from typical continental-rise and abyssal sediments because of high densities of benthic macrofauna. Th-234 data from HEBBLE cores indicate that particles at the sediment-water interface are mixed to depths of 1-5 cm on a 100-day time scale. Cs-137 and Pb-210 data indicate that on time scales of 30-100 yrs surface sediments are reworked to depths ranging from 1 to 12 cm. Based on Th-234 profiles from two HEBBLE cores collected less than 200 m apart during consecutive years, no temporal variability in mixing rate could be resolved. (Auth.)

  13. U–Pb, Rb–Sr, and U-series isotope geochemistry of rocks and fracture minerals from the Chalk River Laboratories site, Grenville Province, Ontario, Canada

    International Nuclear Information System (INIS)

    Neymark, L.A.; Peterman, Z.E.; Moscati, R.J.; Thivierge, R.H.

    2013-01-01

    Highlights: • AECL evaluates Chalk River Laboratories site as potential nuclear waste repository. • Isotope-geochemical data for rocks and fracture minerals at CRL site are reported. • Zircons from gneiss and granite yielded U–Pb ages of 1472 ± 14 and 1045 ± 6 Ma. • WR Rb–Sr and Pb–Pb systems do not show substantial large-scale isotopic mobility. • U-series and REE data do not support oxidizing conditions at depth in the past 1 Ma. - Abstract: As part of the Geologic Waste Management Facility feasibility study, Atomic Energy of Canada Ltd. (AECL) is evaluating the suitability of the Chalk River Laboratories (CRL) site in Ontario, situated in crystalline rock of the southwestern Grenville Province, for the possible development of an underground repository for low- and intermediate-level nuclear waste. This paper presents petrographic and trace element analyses, U–Pb zircon dating results, and Rb–Sr, U–Pb and U-series isotopic analyses of gneissic drill core samples from the deep CRG-series characterization boreholes at the CRL site. The main rock types intersected in the boreholes include hornblende–biotite (±pyroxene) gneisses of granitic to granodioritic composition, leucocratic granitic gneisses with sparse mafic minerals, and garnet-bearing gneisses with variable amounts of biotite and/or hornblende. The trace element data for whole-rock samples plot in the fields of within-plate, syn-collision, and volcanic arc-type granites in discrimination diagrams used for the tectonic interpretation of granitic rocks. Zircons separated from biotite gneiss and metagranite samples yielded SHRIMP-RG U–Pb ages of 1472 ± 14 (2σ) and 1045 ± 6 Ma, respectively, in very good agreement with widespread Early Mesoproterozoic plutonic ages and Ottawan orogeny ages in the Central Gneiss Belt. The Rb–Sr, U–Pb, and Pb–Pb whole-rock errorchron apparent ages of most of the CRL gneiss samples are consistent with zircon U–Pb age and do not indicate

  14. 40Ar/39Ar dating and zircon chronochemistry for the Izu-Bonin rear arc, IODP site U1437

    Science.gov (United States)

    Schmitt, A. K.; Konrad, K.; Andrews, G. D.; Horie, K.; Brown, S. R.; Koppers, A. A. P.; Busby, C.; Tamura, Y.

    2016-12-01

    The scientific objective of IODP Expedition 350 drilling at Site U1437 (31°47.390'N, 139°01.580'E) was to reveal the "missing half of the subduction factory": the rear arc of a long-lived intraoceanic subduction zone. Site U1437 lies in a 50 km long and 20 km wide volcano-bounded basin, 90 km west of the Izu arc front, and is the only IODP site drilled in the rear arc. The Izu rear arc is dominated by Miocene basaltic to dacitic seamount chains, which strike at a high angle to the arc front. Radiometric dating targeted a single igneous unit (1390 mbsf), and fine to coarse volcaniclastic units for which we present zircon and 40Ar/39Ar (hornblende, plagioclase, and groundmass) age determinations. All zircons analyzed as grain separates were screened for contamination from drill-mud (Andrews et al., 2016) by analyzing trace elements and, where material was available, O and Hf isotope compositions. Igneous Unit 1 is a rhyolite sheet and yielded concordant in-situ and crystal separate U-Pb zircon ages (13.7±0.3 Ma; MSWD = 1.3; n = 40 spots), whereas the 40Ar/39Ar hornblende plateau age (12.9±0.3; MSWD = 1.1; n = 9 steps) is slightly younger, possibly reflecting pre-eruptive zircon crystallization, or alteration of hornblende. U-Pb zircon and 40Ar/39Ar plateau ages from samples above igneous Unit 1 are concordant with biostratigraphic and paleomagnetic ages (available to 1300 mbsf), but plagioclase and groundmass samples below 1300 m become younger with depth, hinting at post-depositional alteration. A single zircon from 1600 mbsf yielded a U-Pb age of 15.4±1.8 Ma; its trace element composition resembles other igneous zircons from U1437, and is tentatively interpreted as a Middle Miocene age for the lowermost lithostratigraphic unit VII. Oxygen and Hf isotopic values of igneous zircon indicate mantle origins, with some influence of assimilation of hydrothermally altered oceanic crust evident in sub-mantle oxygen isotopic compositions. Lessons from site U1437 are

  15. Dating of Barra Bonita (Rio Tiete - Sao Paulo State, Brazil) reservoir sediments with 210 Pb: historical distribution of heavy metals

    International Nuclear Information System (INIS)

    Cazotti, Raul I.; Silverio, Patricia F.; Mozeto, Antonio A.; Nascimento, Marcos R.L. do

    2002-01-01

    This work presents data on 210 Pb dating and heavy metal contamination of sediment cores collected from the Barra Bonita reservoir, one of the hydroelectric reservoir built in the Tiete River, SE Brazil about 40 years ago. Age calculations were done through the CRS (constant rate of supply) and CIC (constant initial concentration) models. It is well known that dating of lake sediment which are ≥ 100 years old poses no problem as atmospheric 210 Pb activity decreases to almost zero with sediment depth. In this work we present considerations and suggestions towards the applicability of these two models for reservoir dating as a study-case and for lakes in general with ages ≤ 100 years. The results show a good agreement between the CRS and CIC models. In addition, it was also evaluated the historical contamination of heavy metals (total and acid-extractable fraction). Cr, Cu, Ni, Pb and Zn showed an increase in concentration from the bottom to the top part of the cores. This would probably reflect an increase in land use of the Barra Bonita reservoir watershed for the last 40 years. (author)

  16. Determination of the sedimentation rates in the Sepetiba bay northeastern area by using dating with the excesses 210 Pb radioisotope

    International Nuclear Information System (INIS)

    Forte, Cristiane Maria Sampaio

    1996-01-01

    210 Pb dating, using two modes of data analysis, CIC and CRS, was used to determine sedimentation in the North East part of Sepetiba Bay. 210 Pb was leached from samples using dilute HBr and subsequently separated onto anionic exchange columns, followed by re-extraction and precipitation as Pb CrO 4 . The original method was modified by the introduction of a pre-digestion step whose purpose was to liberate the lead bound as sulphide. The sedimentation rates found o.68 - 0.98 cm.y -1 were moderate, compared to other authors estimates. Dating using the CRS model showed a maximum rate of sedimentation in the period between 1954 and 1977, when the riverine input was probably at its greatest. The CRS model appears to be more applicable to the data, since it works over longer periods and allows for variations in sedimentation rate. (author)

  17. 238U-230Th radioactive disequilibria in the volcanic products from Izu arc volcanoes, Japan

    International Nuclear Information System (INIS)

    Kurihara, Yuichi; Takahashi, Masaomi; Sato, Jun

    2007-01-01

    The timescale of magmatic processes of Izu arc volcanoes, Japan, was estimated by the 238 U- 230 Th disequilibria in the volcanic products from the volcanoes. The majority of the 230 Th/ 238 U activity ratios of the products were less than unity, being enriched in 238 U relative to 230 Th. The ( 230 Th/ 232 Th)-( 238 U/ 232 Th)diagram for younger Fuji and Izu-Oshima volcanoes formed a whole rock isochrons, and the ages were 1x10 4 and 2x10 4 years, respectively. The ( 230 Th/ 232 Th) - ( 238 U/ 232 Th) data set for younger Fuji volcano formed a cluster on the diagram, while those of Izu-Oshima formed another cluster apparently apart from each other, suggesting that the concentration of U and Th may possibly be un-uniform in the mantle beneath Izu arc. (author)

  18. 238U-234U-230Th chronometry of Fe-Mn crusts: Growth processes and recovery of thorium isotopic ratios of seawater

    International Nuclear Information System (INIS)

    Chabaux, F.; Cohen, A.S.; O'Nions, R.K.; Hein, J.R.

    1995-01-01

    Comparison of ( 234 U) excess /( 238 U) and ( 230 Th)/( 232 Th) activity ratios in oceanic Fe-Mn deposits provides a method for assessing the closed-system behaviour of 238 U- 234 U- 230 Th, as well as variations in the initial uranium and thorium isotopic ratios of the precipitated metal oxides. This approach is illustrated using a Fe-Mn crust from Lotab seamount (Marshall Islands, west equatorial Pacific). Here we report uranium and thorium isotopic compositions in five subsamples from the surface of one large 5 cm diameter botyroid of this crust, and from two depth profiles of the outermost rim of the same botyroid. The decrease of ( 234 U) excess /( 238 U) and ( 230 Th/ 232 Th) activity ratio with depth in the two profiles gives mean growth rates, for the last 150 ka, of 7.8 ± 2 mm/Ma and 6.6 ± 1 mm/Ma, respectively. All data points (surface and core samples) but one, define a linear correlation in the Ln ( 230 Th/ 232 Th) - Ln [( 234 U) excess ( 238 U)] diagram. This correlation indicates that for all points the U-Th system remained closed after the Fe-Mn layer precipitated, and that the different samples possessed the same initial Uranium and thorium isotope ratios. Furthermore, these results show that the preserved surface of this Fe-Mn crust may not be the present-day growth surface, and that the thorium and uranium isotopic ratios of seawater in west equatorial Pacific have not changed during the past 150 ka. The initial thorium activity ratio is estimated from the correlation obtained between Ln( 230 Th/ 232 Th) and Ln [( 234 U) excess /( 238 U)

  19. Isotopegeochemical investigations and dating on minerals and fossils from sedimentary rocks: 1. Glauconites from Jura, Molasse and Helveticum (K-Ar, Rb-Sr), 2. 87Sr/86Sr-Isotope stratigraphy on marine and limnetic micro- and macro-fossils, 3. Primary minerals from tertiary bentonites and tuffs (U-Pb, K-Ar)

    International Nuclear Information System (INIS)

    Fischer, H.

    1988-01-01

    Glauconite investigations: the main problem in dating glauconites lies in the identification of authigenic minerals which have not been influenced by post-sedimentary processes. The age determination on glauconites from the three different tectonic units: the Jura mountains, the molasse basin and the Helvetic nappes, yield inconsistent results. Up to 35% too young K-Ar ''ages'' of glauconites from limestones from the Helvetic nappes can be traced to partial Ar loss caused by sediment-lithification and tectonic events. Sr-isotope stratigraphy: multiple analyses of recent samples from the Mediterranean Sea and from the North Atlantic show that the 87 Sr/ 86 Sr isotope ratios correspond well. In a stratigraphic ideal section from the Upper marine molasse a resolution of 206 Pb/ 238 U method zircons from the Fish Canyon Tuff were measured and yielded ages of 28.49±0.10, 24.46±0.11 and 28.46±0.13 Ma. These values correspond well with the published mean value of zircon and apatite fission track age of 28.4±0.7 Ma. Thus, the U-Pb method for dating young volcanic minerals seems to be suitable. However, the published mean value (''solid state age'') of Naeser et al. (1981) is higher than the published (''gas age'') mean value of 27.2±0.7 Ma based on biotite, sanidine, hornblende and plagioclase. (author) figs., tabs., refs

  20. Zircon and allanite U-Pb ID-TIMS ages of vaugnerites from the Calzadilla pluton, Salamanca (Spain): dating mantle-derived magmatism and post-magmatic subsolidus overprint

    International Nuclear Information System (INIS)

    López-Moro, F.J.; Romer, R. L.; López-Plaza, M.; González Sánchez, M.

    2017-01-01

    Basic to intermediate high-K, high-Mg mantle-derived rocks occur throughout the Iberian Massif and are particularly important in the Tormes Dome, where vaugnerites form several stocks and small plutons. One of the largest and geochemically most variable among these plutons is the Calzadilla pluton in the Tormes Dome that crystallized at 318 ± 1.4Ma (Bashkirian; U-Pb TIMS zircon). This age reveals that the vaugnerite pluton was emplaced during the transition from late D2 extensional deformation to early D3 contractional deformation (319 to 317Ma). Large-scale extension in the area resulted, on one hand, in extensive anatexis in the crust due to quasiisothermal decompression and mica-dehydration melting and, on the other hand, in the upwelling of the mantle, which induced partial melting of the enriched domains in the lithospheric mantle. The driving reason why crustal and mantle melts were coeval is extension. The U-Pb ID-TIMS age of allanite is not related to the emplacement nor cooling of the Calzadilla vaugnerite, but it seems to be related to a younger subsolidus overprint ca. 275Ma that, in the scale of the Central Iberian Zone, corresponds to a period of hydrothermal alteration, including episyenite formation and tungsten mineralization.

  1. Zircon and allanite U-Pb ID-TIMS ages of vaugnerites from the Calzadilla pluton, Salamanca (Spain): dating mantle-derived magmatism and post-magmatic subsolidus overprint

    Energy Technology Data Exchange (ETDEWEB)

    López-Moro, F.J.; Romer, R. L.; López-Plaza, M.; González Sánchez, M.

    2017-07-01

    Basic to intermediate high-K, high-Mg mantle-derived rocks occur throughout the Iberian Massif and are particularly important in the Tormes Dome, where vaugnerites form several stocks and small plutons. One of the largest and geochemically most variable among these plutons is the Calzadilla pluton in the Tormes Dome that crystallized at 318 ± 1.4Ma (Bashkirian; U-Pb TIMS zircon). This age reveals that the vaugnerite pluton was emplaced during the transition from late D2 extensional deformation to early D3 contractional deformation (319 to 317Ma). Large-scale extension in the area resulted, on one hand, in extensive anatexis in the crust due to quasiisothermal decompression and mica-dehydration melting and, on the other hand, in the upwelling of the mantle, which induced partial melting of the enriched domains in the lithospheric mantle. The driving reason why crustal and mantle melts were coeval is extension. The U-Pb ID-TIMS age of allanite is not related to the emplacement nor cooling of the Calzadilla vaugnerite, but it seems to be related to a younger subsolidus overprint ca. 275Ma that, in the scale of the Central Iberian Zone, corresponds to a period of hydrothermal alteration, including episyenite formation and tungsten mineralization.

  2. Nd isotopes, U-Pb single grain and SHRIMP zircon ages from basement rocks of the Tocantin Province

    International Nuclear Information System (INIS)

    Fuck, R.A.; Dantas, E.L.; Pimentel, M.M.; Junges, S.L.; Moraes, R

    2001-01-01

    Large areas of the northern part of the Brasilia Belt, Tocantins Province, central Brazil, are underlain by basement granite-gneiss terrain and associated volcano-sedimentary sequences, as well as felsic and mafic-ultramafic intrusions. The basement rocks are covered by the late Paleoproterozoic-Mesoproterozoic rift-related Arai and Natividade groups and intruded by 1.77 to 1.58 Ga an orogenic granites of the Goias Tin Province (Pimentel and Botelho, 2001). To the southwest they are un conformably overlain by the low-grade late Proterozoic Paranoa Group, whereas to the east they are in faulted contact with the Neoproterozoic Bambui Group at the western edge of the Sao Francisco Craton. To the north they are covered by Phanerozoic sediments of the Parnaiba and Sanfranciscana basins. Despite their large extension, granite-gneiss and associated supracrustals of SE Tocantins and NE Goias are still poorly known. Previous regional Rb-Sr and K-Ar isotopic studies indicated dominant early Proterozoic ages and late Proterozoic cooling ages (Hasui, et al. 1980, Fernandes et al. 1982). More detailed studies in the Almas-Dianopolis area (Costa, 1984) came up with similar results, although the region was interpreted as underlain by Archean granite-greenstone terrain, following previous suggestions by Costa et al. (1976). Recent work recognized the presence of two suites of deformed granitoids (Cruz and Kuyumjian, 1996, 1998). The oldest suite intruded the supracrustals and comprises hornblende-bearing tonalite gneiss, with minor trondhjemite, granodiorite, and quartz diorite. The younger suite comprises oval shaped biotite-bearing tonalite, trondhjemite, and granodiorite intrusions. Both suites display low-K calc-alkaline affinity, the younger being more Al-rich. Both are interpreted as TTG suites and were dated at 2,2 Ga using U-Pb SHRIMP (Cruz et al 2000). In the Porto Nacional area, Gorayeb et al. (2000) determined single zircon Pb-evaporation ages of 2.15 Ga in granulites

  3. Zircon U-Pb ages and geochemistry of migmatites and granites in the Foping dome: Evidence for Late Triassic crustal evolution in South Qinling, China

    Science.gov (United States)

    Zhang, He; Li, Shuang-Qing; Fang, Bo-Wen; He, Jian-Feng; Xue, Ying-Yu; Siebel, Wolfgang; Chen, Fukun

    2018-01-01

    Migmatites provide a record of melt formation and crustal rheology. In this study we present zircon U-Pb ages and geochemical composition of migmatites from the Foping dome and granites from the Wulong pluton. U-Pb results from migmatite zircons indicate two episodes of partial melting. Rim domains from a leucosome in the Longcaoping area yield an age of ca. 209 Ma. Migmatites collected from the Foping dome yield U-Pb zircon ages of 2910 to 190 Ma, suggesting the involvement of meta-sedimentary source components. Rim domains of the zircons with low Th/U ratios (pluton can be subdivided into high Sr/Y and low Sr/Y granites. U-Pb zircon ages vary from 219 to 214 Ma for the high Sr/Y granites and from 214 to 192 Ma for the low Sr/Y granites. High Sr/Y granites have higher Na2O and Sr contents than the low Sr/Y granites. They also lack negative Eu anomalies and are depleted in HREE compared to the low Sr/Y granites. Initial 87Sr/86Sr ratios and εNd values of all the samples roughly overlap with those of Neoproterozoic basement rocks exposed in South Qinling. Including previous studies, we propose that the high and low Sr/Y granites formed by melting of thickened and normal crust, respectively. Close temporal-spatial relationship of the high and low Sr/Y granites with the two-stage migmatization events implies variation of crustal thickness and thermal overprints of the orogenic crust in post-collisional collapse. Following the collision of South Qinling and the Yangtze block prior to 219 Ma, partial melting of the deep crust occurred. The melts migrated upwards to form the high Sr/Y granites. This process occurred rapidly and caused collapse of the thickened crust and carried heat upwards, leading to further partial melting within the shallower crust and formation of the low Sr/Y granites.

  4. Use of the ion microprobe in geological dating

    International Nuclear Information System (INIS)

    Compston, W.; Williams, I.S.; Black, L.P.

    1983-01-01

    SHRIMP, the Sensitive High Resolution Ion Microprobe with computerised control and data acquisition system, has recently been commissioned. It is used within the Research School of Earth Sciences, Australian National University, for the isotopic analysis of geological samples. Principles of operation and geological applications are outlined. One example described is the application to Pb-U dating of zircon

  5. Breaking through the uncertainty ceiling in LA-ICP-MS U-Pb geochronology

    Science.gov (United States)

    Horstwood, M.

    2016-12-01

    Sources of systematic uncertainty associated with session-to-session bias are the dominant contributor to the 2% (2s) uncertainty ceiling that currently limits the accuracy of LA-ICP-MS U-Pb geochronology. Sources include differential downhole fractionation (LIEF), `matrix effects' and ablation volume differences, which result in irreproducibility of the same reference material across sessions. Current mitigation methods include correcting for LIEF mathematically, using matrix-matched reference materials, annealing material to reduce or eliminate radiation damage effects and tuning for robust plasma conditions. Reducing the depth and volume of ablation can also mitigate these problems and should contribute to the reduction of the uncertainty ceiling. Reducing analysed volume leads to increased detection efficiency, reduced matrix-effects, eliminates LIEF, obviates ablation rate differences and reduces the likelihood of intercepting complex growth zones with depth, thereby apparently improving material homogeneity. High detection efficiencies (% level) and low sampling volumes (20um box, 1-2um deep) can now be achieved using MC-ICP-MS such that low volume ablations should be considered part of the toolbox of methods targeted at improving the reproducibility of LA-ICP-MS U-Pb geochronology. In combination with other strategies these improvements should be feasible on any ICP platform. However, reducing the volume of analysis reduces detected counts and requires a change of analytical approach in order to mitigate this. Appropriate strategies may include the use of high efficiency cell and torch technologies and the optimisation of acquisition protocols and data handling techniques such as condensing signal peaks, using log ratios and total signal integration. The tools required to break the 2% (2s) uncertainty ceiling in LA-ICP-MS U-Pb geochronology are likely now known but require a coherent strategy and change of approach to combine their implementation and realise

  6. Structure and luminescence of α and β ThBr4: optical properties of U4+ in α ThBr4

    International Nuclear Information System (INIS)

    Simoni, E.

    1988-05-01

    The aim of this work is to understand the comparative structural and intrinsic luminescence properties of the pure matrices α and β - ThBr 4 , and to study the electronic structure by optical spectroscopy of the U 4+ ion in the α-ThBr 4 matrix. 1)Under U.V. excitation, βThBr 4 is intensively fluorescent in the blue-purple and α-ThBr 4 is fluorescent in the red. The main results concerning β-ThBr 4 are the following: -the optical absorption in the U.V. is under the form of a sudden absorption front and for a same temperature, its threshold energy has the same value as the threshold energy of the excitation function and of the photocurrent peak; -the intensity and the life time of the emission decrease when the temperature increases from 300 K until 400 K ( extinction temperature). All the obtained results have been explained either with the molecular orbitals levels of the ThBr 8 4- cluster or with the valence and conduction bands of the pure matrix. 2)The absorption and emission spectra of U 4+ in α-ThBr 4 (in which U 4+ has a point symmetry S 4 ) obtained between 300 K and 4.2 K have allowed to index 30 levels. The calculation of the spectroscopic parameters F k , ξ and B k q has been carried out in symmetry D 2d and S 4 . The comparison of these parameters with those calculated for U 4+ in β-ThBr 4 and β-ThCl 4 show that the global force of the crystalline field is practically the same in the three matrices, but that the structure transformation β→α occurs more on the values of these B k q than on the change of the ligands Br - →Cl - . On the other hand, it has been possible with the α-ThBr 4 matrix, or the β-ThBr 4 and the β-ThCl 4 , to observe the fluorescence spectra of the U 4+ ion (particularly weak phonons energies). (O.M.)

  7. Influence of the cosmic-ray induced fission tracks on the fission track of extraterrestric minerals via the 238U spontaneous fission

    International Nuclear Information System (INIS)

    Damm, G.; Thiel, K.

    1977-01-01

    The age determined by counting fission tracks of lunar and meteorite materials is obviously falsified by additional fission track parts not to be accounted for by the spontaneous fission of uranium 238. For this p and n induced fissions of U, Th and other hreavy elements through the cosmic radiation come into consideration. In order to determine the possible part of such interference factors, a simulation experiment at the proton synchrocycloton (CERN, Geneva) has been carried out and independently of this, the production rates for the p and n induced U, Th, Bi, Pb and Au in the surface-near regolith layers of the moon were calculated. It could be seen that the irradiation age as well as the spacial distribution of the heavy metals in the samples to be dated must be considered. (RB) [de

  8. Coupled {sup 230}Th/{sup 234}U-ESR analyses for corals: A new method to assess sealevel change

    Energy Technology Data Exchange (ETDEWEB)

    Blackwell, Bonnie A.B. [Department of Chemistry, Williams College, Williamstown, MA 01267 (United States); RFK Science Research Institute, Glenwood Landing, NY 11547 (United States)], E-mail: bonnie.a.b.blackwell@williams.edu; Teng, Steve J.T. [RFK Science Research Institute, Glenwood Landing, NY 11547 (United States)], E-mail: mteng1584@gmail.com; Lundberg, Joyce A. [Department of Geography and Environmental Studies, Carleton University, Ottawa, ON, Canada K1S 5B6 (Canada)], E-mail: joyce_lundberg@carleton.ca; Blickstein, Joel I.B. [Department of Chemistry, Williams College, Williamstown, MA 01267 (United States); RFK Science Research Institute, Glenwood Landing, NY 11547 (United States); Skinner, Anne R. [Department of Chemistry, Williams College, Williamstown, MA 01267 (United States); RFK Science Research Institute, Glenwood Landing, NY 11547 (United States)], E-mail: anne.r.skinner@williams.edu

    2007-07-15

    Although coupled {sup 230}Th/{sup 234}U-ESR analyses have become routine for dating teeth, they have never been used for corals. While the ESR age depends on, and requires assumptions about, the time-averaged cosmic dose rate, D-bar{sub cos}(t), {sup 230}Th/{sup 234}U dates do not. Since D-bar{sub cos}(t) received by corals depends on the attenuation by any intervening material, D-bar{sub cos}(t) response reflects changing water depths and sediment cover. By coupling the two methods, one can determine the age and a unique D-bar{sub cos,coupled}(t) simultaneously. From a coral's water depth and sedimentary history as predicted by a given sealevel curve, one can predict D-bar{sub cos,sealevel}(t). If D-bar{sub cos,coupled}(t) agrees well with D-bar{sub cos,sealevel}(t), this provides independent validation for the curve used to build D-bar{sub cos,sealevel}(t). For six corals dated at 7-128 ka from Florida Platform reef crests, the sealevel curve by Waelbroeck et al. [2002. Sea-level and deep water temperature changes derived from benthonic foraminifera isotopic records. Quat. Sci. Rev. 21, 295-305] predicted their D-bar{sub cos,coupled}(t) values as well as, or better than, the SPECMAP sealevel curve. Where a whole reef can be sampled over a transect, a precise test for sealevel curves could be developed.

  9. Isotopic chemical weathering behaviour of Pb derived from a high-Alpine Holocene lake-sediment record

    Science.gov (United States)

    Gutjahr, Marcus; Süfke, Finn; Gilli, Adrian; Anselmetti, Flavio; Glur, Lukas; Eisenhauer, Anton

    2017-04-01

    Several studies assessing the chemical weathering systematics of Pb isotopes provided evidence for the incongruent release of Pb from source rocks during early stages of chemical weathering, resulting in runoff compositions more radiogenic (higher) than the bulk source-rock composition [e.g. 1]. Deep NW Atlantic seawater Pb isotope records covering the last glacial-interglacial transition further support these findings. Clear excursions towards highly radiogenic Pb isotopic input in the deep NW Atlantic seen during the early Holocene, hence after the large-scale retreat of the Laurentide Ice Sheet in North America, are interpreted to be controlled by preferential release of radiogenic Pb from U- and Th-rich mineral phases during early stages of chemical weathering that are less resistant to chemical dissolution than other rock-forming mineral phases [2-4]. To date, however, no terrestrial Pb isotope record exists that could corroborate the evidence from deep marine sites for efficient late deglacial weathering and washout of radiogenic Pb. We present a high-resolution adsorbed Pb isotope record from a sediment core retrieved from Alpine Lake Grimsel (1908 m.a.s.l.) in Switzerland, consisting of 117 Pb compositions over the past 10 kyr. This high-Alpine study area is ideally located for incipient and prolonged chemical weathering studies. The method used to extract the adsorbed lake Pb isotope signal is identical to previous marine approaches targeting the authigenic Fe-Mn oxyhydroxides fraction within the lake sediments [5, 6]. The Pb isotope compositions are further accompanied by various elemental ratios derived from the same samples that equally trace climatic boundary conditions in the Grimsel Lake area. The Pb isotopic composition recorded in Lake Grimsel is remarkably constant throughout the majority of the Holocene until ˜2.5 ka BP, despite variable sediment composition and -age, and isotopically relatively close to the signature of the granitic source rock

  10. Mianningite, (□,Pb,Ce,Na) (U"4"+,Mn,U"6"+) Fe"3"+_2(Ti,Fe"3"+)_1_8O_3_8, a new member of the crichtonite group from Maoniuping REE deposit, Mianning county, southwest Sichuan, China

    International Nuclear Information System (INIS)

    Ge, Xiangkun; Fan, Guang; Chen, Zhangru; Ai, Yujie; Li, Guowu

    2017-01-01

    Mianningite (IMA 2014-072), ideally (□,Pb,Ce,Na)(U"4"+,Mn,U"6"+) Fe"3"+_2(Ti,Fe"3"+)_1_8O_3_8, is a new member of the crichtonite group from the Maoniuping REE deposit, Mianning county, Sichuan province, China. It was found in fractures of lamprophyre veins and in the contact between lamprophyre and a later quartz-alkali feldspar syenite dyke with REE mineralization, and is named after its type locality. Associated minerals are microcline, albite, quartz, iron-rich phlogopite, augite, muscovite, calcite, baryte, fluorite, epidote, pyrite, magnetite, hematite, galena, hydroxylapatite, titanite, ilmenite, rutile, garnet-group minerals, zircon, allanite-(Ce), monazite-(Ce), bastnaesite-(Ce), parisite-(Ce), maoniupingite-(Ce), thorite, pyrochlore-group minerals and chlorite. Mianningite occurs as opaque subhedral to euhedral tabular crystals, up to 1-2 mm in size, black in color and streak, and with a submetallic luster. Mianningite is brittle, with a conchoidal fracture. Its average micro-indentation hardness is 83.8 kg/mm"2 (load 0.2 kg), which is equivalent to ∝6 on the Mohs hardness scale. Its measured and calculated densities are 4.62 (8) g/cm"3 and 4.77 g/cm"3, respectively. Under reflected light, mianningite is grayish white, with no internal reflections. It appears isotropic and exhibits neither bireflectance nor pleochroism. The empirical formula, calculated on the basis of 38 O atoms per formula unit (apfu), is [□_0_._3_2_2(Pb_0_._2_1_5Ba_0_._0_3_7Sr_0_._0_3_6Ca_0_._0_1_0)_Σ_0_._2_9_8(Ce_0_._1_2_8La_0_._0_7_7Nd_0_._0_1_2)_Σ_0_._2_1_7 (Na_0_._1_2_7K_0_._0_3_6)_Σ_0_._1_6_3]_Σ_0_1_._0_0_0(U"4"+_0_._4_4_7Mn_0_0_._2_9_3U"6 "+_0_._1_1_2Y_0_._0_9_1Zr_0_._0_2_3Th_0_._0_1_1)_Σ_0_._9_7_7(Fe"3"+_1_._2_2_4Fe"2"+_0_._2_4_3Mg_0_._0_2_3P_0_._0_0_8Si_0_._0_0_6 □_0_._4_9_6)_Σ_2_._0_0_0(Ti_1_2_._4_6_4Fe"3"+_5_._2_9_2V"5"+_0_._1_1_8Nb_0_._0_8_3Al_0_._0_2_6Cr"3"+_0_._0_1_7)_Σ_1_8_._0_0_0O_3_8. Mianningite is trigonal, belongs to the space group R anti 3, and has

  11. Uranium-lead dating of hydrothermal zircon and monazite from the Sin Quyen Fe-Cu-REE-Au-(U) deposit, northwestern Vietnam

    Science.gov (United States)

    Li, Xiao-Chun; Zhou, Mei-Fu; Chen, Wei Terry; Zhao, Xin-Fu; Tran, MyDung

    2018-03-01

    The Sin Quyen deposit in northwestern Vietnam contains economic concentrations of Cu, Au and LREE, and sub-economic concentration of U. In this deposit, massive and banded replacement ores are hosted in Neoproterozoic metapelite. The paragenetic sequence includes sodic alteration (stage I), calcic-potassic alteration and associated Fe-REE-(U) mineralization (stage II), Cu-Au mineralization (stage III), and sulfide-(quartz-carbonate) veins (stage IV). The Sin Quyen deposit experienced an extensive post-ore metamorphic overprint, which makes it difficult to precisely determine the mineralization age. In this study, zircon and monazite U-Pb geochronometers and the Rb-Sr isochron method are used to constrain the timing of mineralization. Zircon grains in the ore are closely intergrown or texturally associated with hydrothermal minerals of stage II (e.g., garnet, allanite, and hedenbergite). They may contain primary fluid inclusions and display irregular zoning in cathodoluminescence (CL) images. Zircon grains are rich in U (688 to 2902 ppm) and poor in Th (0.2 to 2.9 ppm). Their δ18OV-SMOW values range from 11.9 to 14.0‰, higher than those of typical magmatic zircon. These textural and compositional features imply that zircon precipitated from 18O- and U-rich hydrothermal fluids, coeval with the minerals of stage II. Monazite occurs in close association with stage II magnetite and allanite and has low contents of Th (<2700 ppm), indicative of a hydrothermal origin. Hydrothermal zircon and monazite have indistinguishable U-Pb ages of 841 ± 12 and 836 ± 18 Ma, respectively, representing the timing of Fe-REE mineralization. There is no direct isotopic constraint on the timing of the Cu-Au mineralization, but geological observations suggest that the Cu-Au and Fe-REE ores most likely formed within a single evolved hydrothermal process. In the plot of 87Rb/86Sr vs. 87Sr/86Sr, the composition of bulk-ore and biotite separates from ore lie along a reference line for 30 Ma

  12. The oceanic chemistry of the U- and Th-series nuclides

    International Nuclear Information System (INIS)

    Cochran, J.K.

    1982-01-01

    The subject is discussed under the headings: input and removal of U- and Th-series nuclides in the oceans; uranium (input to the oceans; in the coastal ocean; in the open ocean; in sediment pore water; removal from the oceans; sources and sinks of 234 U in the oceans); thorium (scavenging in the deep sea; 230 Th and 231 Pa balance; removal from the coastal and surface ocean); Ra-226 and Ra-228; radon (in surface waters; near bottom 222 Rn as a tracer for vertical mixing); lead-210; polonium-210. (U.K.)

  13. High-precision U-Pb geochronologic constraints on the Late Cretaceous terrestrial cyclostratigraphy and geomagnetic polarity from the Songliao Basin, Northeast China

    Science.gov (United States)

    Wang, Tiantian; Ramezani, Jahandar; Wang, Chengshan; Wu, Huaichun; He, Huaiyu; Bowring, Samuel A.

    2016-07-01

    The Cretaceous continental sedimentary records are essential to our understanding of how the terrestrial geologic and ecologic systems responded to past climate fluctuations under greenhouse conditions and our ability to forecast climate change in the future. The Songliao Basin of Northeast China preserves a near-complete, predominantly lacustrine, Cretaceous succession, with sedimentary cyclicity that has been tied to Milankocitch forcing of the climate. Over 900 meters of drill-core recovered from the Upper Cretaceous (Turonian to Campanian) of the Songliao Basin has provided a unique opportunity for detailed analyses of its depositional and paleoenvironmental records through integrated and high-resolution cyclostratigraphic, magnetostratigraphic and geochronologic investigations. Here we report high-precision U-Pb zircon dates (CA-ID-TIMS method) from four interbedded bentonites from the drill-core that offer substantial improvements in accuracy, and a ten-fold enhancement in precision, compared to the previous U-Pb SIMS geochronology, and allow a critical evaluation of the Songliao astrochronological time scale. The results indicate appreciable deviations of the astrochronologic model from the absolute radioisotope geochronology, which more likely reflect cyclostratigraphic tuning inaccuracies and omitted cycles due to depositional hiatuses, rather than suspected limitations of astronomical models applied to distant geologic time. Age interpolation based on our new high-resolution geochronologic framework and the calibrated cyclostratigraphy places the end of the Cretaceous Normal Superchon (C34n-C33r chron boundary) in the Songliao Basin at 83.07 ± 0.15 Ma. This date also serves as a new and improved estimate for the global Santonian-Campanian stage boundary.

  14. U-Th series nuclides in the Gulf of Mexico

    International Nuclear Information System (INIS)

    Scott, M.R.

    1981-01-01

    A study of U and Th series nuclides is being conducted on sediments from the Gulf of Mexico. Uranium concentrations as a function of depth have been determined, as well as changes in the 234 U/ 238 U activity ratio. The geochemical behavior of uranium in shelf sediments is discussed

  15. U-Pb (LA-ICPMS) zircon ages and Nd isotopes for granitoids of the Tamboril-Santa Quiteria Complex, Ceara Central Domain: implication for neoproterozoic syncollisional magmatism in north Borborema Province, Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Costa, Felipe Grandjean da; Araujo, Carlos Eduardo Ganade de; Vasconcelos, Antonio Maurilio, E-mail: felipe.costa@cprm.gov.br, E-mail: caegeo@gmail.com, E-mail: maurilio.vasconcelos@cprm.gov.br [Servico Geologico do Brasil (CPRM), Fortaleza, CE (Brazil); Amaral, Wagner da Silva, E-mail: wamaral@ufc.br [Universidade Federal do Ceara (UFC), Fortaleza, CE (Brazil). Departamento de Geologia; Rodrigues, Joseneusa Brilhante, E-mail: joseneusa.rodrigues@cprm.gov.br [Servico Geologico do Brasil (CPRM), Brasilia, DF (Brazil)

    2013-06-15

    The Tamboril-Santa Quiteria Complex (TSQC) is one of the largest Neoproterozoic plutonic manifestations in the north Borborema Province (NE Brazil). It represents an anatectic/igneous association characterized by a number of magmatic pulses that occurred in the 650-610 Ma interval. In this paper, we present U-Pb (LA-MC-ICP-MS) zircon ages and Nd isotopes for quartz monzonite and quartz diorites of the southern part of TSQC. The quartz monzonite belong to a hybrid granitoid association, including monzonite, syenites and quartz syenites, all with abundant mafic magmatic enclaves. A quartz monzonite sample yielded a U-Pb zircon age of 634 {+-} 10 Ma and a TDM age of 2.69 Ga. The quartz diorites are much more homogeneous in composition and yielded a U-Pb zircon age of 618 {+-} 23 Ma and a TDM age of 2.19 Ga. The presence of coeval mantle-derived magmatism and diatexites (crustal anatexis) post-dating high-pressure metamorphism (ca. 650 Ma), and together with high-temperature metamorphism (ca. 630-610 Ma), suggests that this large magmatic manifestation evolved in a collisional setting, probably related to slab break off during the Western Gondwana amalgamation. (author)

  16. Mianningite, (□,Pb,Ce,Na) (U{sup 4+},Mn,U{sup 6+}) Fe{sup 3+}{sub 2}(Ti,Fe{sup 3+}){sub 18}O{sub 38}, a new member of the crichtonite group from Maoniuping REE deposit, Mianning county, southwest Sichuan, China

    Energy Technology Data Exchange (ETDEWEB)

    Ge, Xiangkun; Fan, Guang; Chen, Zhangru; Ai, Yujie [Beijing Research Institute of Uranium Geology, Beijing (China); Li, Guowu [China Univ. of Geosciences, Beijing (China). Lab. of Crystal Structure; Shen, Ganfu [Chengdu Institute of Geology and Mineral Resources, Chengdu (China)

    2017-05-15

    Mianningite (IMA 2014-072), ideally (□,Pb,Ce,Na)(U{sup 4+},Mn,U{sup 6+}) Fe{sup 3+}{sub 2}(Ti,Fe{sup 3+}){sub 18}O{sub 38}, is a new member of the crichtonite group from the Maoniuping REE deposit, Mianning county, Sichuan province, China. It was found in fractures of lamprophyre veins and in the contact between lamprophyre and a later quartz-alkali feldspar syenite dyke with REE mineralization, and is named after its type locality. Associated minerals are microcline, albite, quartz, iron-rich phlogopite, augite, muscovite, calcite, baryte, fluorite, epidote, pyrite, magnetite, hematite, galena, hydroxylapatite, titanite, ilmenite, rutile, garnet-group minerals, zircon, allanite-(Ce), monazite-(Ce), bastnaesite-(Ce), parisite-(Ce), maoniupingite-(Ce), thorite, pyrochlore-group minerals and chlorite. Mianningite occurs as opaque subhedral to euhedral tabular crystals, up to 1-2 mm in size, black in color and streak, and with a submetallic luster. Mianningite is brittle, with a conchoidal fracture. Its average micro-indentation hardness is 83.8 kg/mm{sup 2} (load 0.2 kg), which is equivalent to ∝6 on the Mohs hardness scale. Its measured and calculated densities are 4.62 (8) g/cm{sup 3} and 4.77 g/cm{sup 3}, respectively. Under reflected light, mianningite is grayish white, with no internal reflections. It appears isotropic and exhibits neither bireflectance nor pleochroism. The empirical formula, calculated on the basis of 38 O atoms per formula unit (apfu), is [□{sub 0.322}(Pb{sub 0.215}Ba{sub 0.037}Sr{sub 0.036}Ca{sub 0.010}){sub Σ0.298}(Ce{sub 0.128}La{sub 0.077}Nd{sub 0.012}){sub Σ0.217} (Na{sub 0.127}K{sub 0.036}){sub Σ0.163}]{sub Σ01.000}(U{sup 4+}{sub 0.447}Mn{sub 00.293}U{sup 6} {sup +}{sub 0.112}Y{sub 0.091}Zr{sub 0.023}Th{sub 0.011}){sub Σ0.977}(Fe{sup 3+}{sub 1.224}Fe{sup 2+}{sub 0.243}Mg{sub 0.023}P{sub 0.008}Si{sub 0.006} □{sub 0.496}){sub Σ2.000}(Ti{sub 12.464}Fe{sup 3+}{sub 5.292}V{sup 5+}{sub 0.118}Nb{sub 0.083}Al{sub 0.026}Cr{sup 3

  17. The use of 210Pb and 137Cs in environmental studies

    International Nuclear Information System (INIS)

    Heijnis, H.

    1999-01-01

    The use of natural radioactivity in environmental studies has proven a very powerful tool to determine the dynamics of both natural and antrophogenic processes in our environment. The use of 14 C in archaeology and past climate studies has led to many scientific discoveries (the shroud of Turin and Utze t he ice-man from Austria are two examples). The use of the 238 U-decay series is of at least equal value to studies in archaeology and of past climates. Some of the Isotopes studied supplement 14 C (which is limited to 40,000 years) data and allow dating of samples formed up to 500,000 years ago (see McCullough, this book of abstracts, pages 19-23), others can be utilised to date very young sediments, which can't be dated by 14 C.The so-called 210 Pb dating method has been used over the past 3 decades to date recent sediment. The method uses the disequilibrium in the 238 U decay chain, caused by the escape of the intermediate daughter 222 Rn, a noble gas, from the earth's crust. In the atmosphere the 222 Rn decays via short-lived daughter isotopes to 210 Pb. This 210 Pb with a very convenient half-life of 22,3 years decays to stable 206 Pb. By measuring the surface activity of a sediment core and subsequent samples at regular intervals, a chronology for the sediment core can be established (relative to the surface). In addition to 210 Pb dating one could analyse the samples for l37 Cs to establish an independent chronology based on a pulse of radioactive Caesium. The pulse of 137 Cs originates from the atmospheric atomic-bomb test of the early sixties. The maximum of Caesium activity found in a core should correspond to the height of the tests (approximately 1963 in the Northern hemisphere). A combination of the two dating methods often leads to more reliable results in the chronology. Another use of 137 Cs is to test if the sediment has been subject to bio-turbation or other mixing. In the case of disturbance the proper pulse of Caesium would be smeared out and

  18. The U-Pb System in Schorlomite from Calcite-Amphobole-Pyroxene Pegmatite of the Afrikanda Complex (Kola Peninsula)

    Science.gov (United States)

    Salnikova, E. B.; Stifeeva, M. V.; Chakhmouradian, A. R.; Glebovitsky, V. A.; Reguir, E. P.

    2018-02-01

    The geochronological U-Pb study of shorlomite from igneous rocks of the alkali-ultramafic Afrikanda massif (Kola Peninsula) was performed. The results demonstrate the reliability of calcium garnet as a mineral for the U-Pb geochronology of a wide range of igneous rocks, i.e., carbonatite, syenite, foidolite, foidite, melilitolite, melilitite, lamprophyres, micaceous kimberlites, etc., and associated rare earth and trace elements (REE, Nb, Zr) mineralization.

  19. Zircon Geochronology (U-Pb, Petrography, Geochemistry and Radioisotopes of Bornaward Metarhyolites (Central Taknar Zone-Northwest of Bardaskan

    Directory of Open Access Journals (Sweden)

    Reza Monazzami Bagherzadeh

    2016-07-01

    Full Text Available Introduction The Bornaward area is located in the Northeastern Iran (in the Khorasan Razavi province 28 km northwest of the city of Bardaskan at 57˚ 46΄ to 57˚ 52΄ N latitude and 35˚ 21΄ to 35˚ 24΄E longitude. The Taknar structural zone, situated in the North central Iranian micro continent, is part of the Lut block (Forster, 1978. The Taknar zone is an allochthonous block bounded by the Darouneh and Taknar major faults. Much of this zone consists of metarhyolite-rhyodacite volcanic rocks, and rhyolitic tuff with interlayers of sandstone and dolomite (Taknar Formation. Analytical Results ICP-MS analysis of REE and minor elements of samples of the Bornaward metarhyolites was carried out at the ACME Laboratory in Vancouver, Canada. U-Pb dating of the metarhyolites was performed on isolated zircons in Crohn's Laser Lab, in Arizona (Gehrels et al., 2008. Measurement of Rb, Sr, Sm and Nd isotopes and (143Nd/144Ndi and (87Sr/86Sri ratios took place in the radioisotope laboratory of the University of Aveiro in Portugal. Petrography The volcanic rocks are porphyritic, commonly containing phenocrysts of orthoclase and rarely sanidine, quartz and intermediate plagioclase in a groundmass of fine-grained quartz and feldspar. An alteration has produced oriented needles of sericite and clay minerals, clusters of fine-grained green biotite and clots of epidote and chlorite. Geochemistry The compositions of the volcanic rocks are calc alkaline and high K- calc alkaline. The obtained Shand index (Al2O3/( CaO+Na2O+K2O is above 1.1, in the peraluminous S-type granite field (Chappell and White, 2001. Plotted on the TAS diagram (Middlemost, 1994, all the metarhyolite-rhyodacite samples are located in the sub-alkaline field and the majority fall into the rhyolite group. The metarhyolite-rhyodacites show enrichment of LREE with a moderately ascending pattern ((La/YbN=2.51-10.11 and La=46.45-145.48. Europium shows a negative anomaly (Eu/Eu*=0.23-0.71. U-Pb

  20. The Ellsworth terrane, coastal Maine: Geochronology, geochemistry, and Nd-Pb isotopic composition - Implications for the rifting of Ganderia

    Science.gov (United States)

    Schulz, K.J.; Stewart, D.B.; Tucker, R.D.; Pollock, J.C.; Ayuso, R.A.

    2008-01-01

    The Ellsworth terrane is one of a number of fault-bounded blocks that occur along the eastern margin of Ganderia, the western-most of the peri-Gondwanan domains in the northern Appalachians that were accreted to Laurentia in the Paleozoic. Geologic relations, detrital zircon ages, and basalt geochemistry suggest that the Ellsworth terrane is part of Ganderia and not an exotic terrane. In the Penobscot Bay area of coastal Maine, the Ellsworth terrane is dominantly composed of bimodal basalt-rhyolite volcanic sequences of the Ellsworth Schist and unconformably overlying Castine Volcanics. We use new U-Pb zircon geochronology, geochemistry, and Nd and Pb isotopes for these volcanic sequences to constrain the petrogenetic history and paleotectonic setting of the Ellsworth terrane and its relationship with Ganderia. U-Pb zircon geochronology for rhyolites indicates that both the Ellsworth Schist (508.6 ?? 0.8 Ma) and overlying Castine Volcanics (503.5 ?? 2.5 Ma) are Middle Cambrian in age. Two tholefitic basalt types are recognized. Type Tb-1 basalt, present as pillowed and massive lava flows and as sills in both units, has depleted La and Ce ([La/Nd]N = 0.53-0.87) values, flat heavy rare earth element (REE) values, and no positive Th or negative Ta anomalies on primitive mantle-normalized diagrams. In contrast, type Th-2 basalt, present only in the Castine Volcanics, has stightly enriched LREE ([La/Yb]N = 1.42-2.92) values and no Th or Th anomalies. Both basalt types have strongly positive ??Nd (500) values (Th-1 = +7.9-+8.6; Th-2 = +5.6-+7.0) and relatively enriched Pb isotopic compositions (206Ph/204Pb = 18.037-19.784; 207/204Pb = 15.531-15.660; 2088Pb/204Pb = 37.810-38.817). The basalts have compositions transitional between recent normal and enriched mid-ocean-ridge basalt, and they were probably derived by partial melting of compositionatly heterogeneous asthenosphenc mantle. Two types of rhyolite also are present. Type R-1 rhyolite, which mostly occurs as tuffs

  1. Data base structure and Management for Automatic Calculation of 210Pb Dating Methods Applying Different Models

    International Nuclear Information System (INIS)

    Gasco, C.; Anton, M. P.; Ampudia, J.

    2003-01-01

    The introduction of macros in try calculation sheets allows the automatic application of various dating models using unsupported ''210 Pb data from a data base. The calculation books the contain the models have been modified to permit the implementation of these macros. The Marine and Aquatic Radioecology group of CIEMAT (MARG) will be involved in new European Projects, thus new models have been developed. This report contains a detailed description of: a) the new implement macros b) the design of a dating Menu in the calculation sheet and c) organization and structure of the data base. (Author) 4 refs

  2. History of the Pasamonte achondrite: relative susceptibility of the Sm-Nd, Rb-Sr, and U-Pb systems to metamorphic events

    International Nuclear Information System (INIS)

    Unruh, D.M.; Tatsumoto, M.; Nakamura, N.

    1977-01-01

    The Rb-Sr, Sm-Nd, and U-Pb systematics of the eucrite Pasamonte have been studied in order to investigate the relative susceptibility of the different systems to post-crystallization events and to determine the age and history of the meteorite. The Rb-Sr and 238 U- 206 Pb data of mineral separates do not define an isochron but the Sm-Nd data define an internal isochron which corresponds to the formation age of 4.58+-0.12 b.y. (10 9 years). The 207 Pb- 206 Pb data of mineral separates define an apparent age of 4.53+-0.03 b.y., however it is concluded that this age, while in agreement with the Sm-Nd age, is not strictly valid since the U-Pb data indicate at least three stages of evolution. The U-Pb data indicate that the parent body of the meteorite experienced brecciation shortly after the formation of the parent body surface (approximately 4.2-4.45 b.y. ago) and a recent disturbance (collision) 6+-30 m.y. ago. The latter age is within the range of cosmic ray exposure ages for achondrites. (Auth.)

  3. Apatite fission track and (U-Th)/He dating of teschenite intrusions gives time constraints on accretionary processes and development of planation surfaces in the Outer Western Carpathians

    Energy Technology Data Exchange (ETDEWEB)

    Danisik, Martin; Frisch, Wolfgang [Tuebingen Univ. (Germany). Inst. of Geosciences; Panek, Tomas [Ostrava Univ. (Czech Republic). Dept. of Physical Geography and Geoecology; Matysek, Dalibor [Technical Univ. of Ostrava (Czech Republic). Dept. of Geological Engineering; Dunkl, Istvan [Geoscience Center Goettingen (Germany). Sedimentology and Environmental Geology

    2008-09-15

    The age of planation surfaces in the Podbeskydska pahorkatina Upland in the Outer Western Carpathians (OWC, Czech Republic) is constrained by low-temperature thermochronological dating methods for the first time. Our apatite fission track and apatite (U-Th)/He data measured on teschenite intrusions show that planation surfaces in the study area formed in post-Pannonian time (>7.1 Ma) and are therefore younger than traditionally believed. This contradicts the classical concepts, which stipulate that a large regional planation surface of Pannonian age (the so-called ''midmountain level'') developed in the whole Western Carpathians. Geodynamic implications of our data are the following: (i) the investigated Tesin and Godula nappes of the OWC were buried and thermally overprinted in the accretionary wedge in different ways, and consequently experienced different cooling histories. This indicates a dynamic basin setting with an active accretionary process in a subduction zone; (ii) accretionary processes in the OWC were active already during Late Eocene times. (orig.)

  4. Short-lived U and Th isotope distribution in a tropical laterite derived from granite (Pitinga river basin, Amazonia, Brazil): Application to assessment of weathering rate

    Science.gov (United States)

    Mathieu, D.; Bernat, M.; Nahon, D.

    1995-12-01

    We have analyzed samples of a 15 m thick profile weathered from the Madeira granite, located in the Pitinga basin river, north of Manaus, in the state of Amazonia, Brazil. This profile consists essentially of a yellow-red saprolite covered by a soil. U and Th concentrations are particularly high in the granite (20 and 80 μg/g respectively). Normalized element to Th concentrations indicate that Th is most resistant to chemical weathering, except to some extent in the top soil. Higher concentrations in the saprolite compared to the granite comprise a relative enrichment, resulting from a loss of mass. The saprolites are initially generated by a descending weathering front which alters the granite to a yellow-red saprolite, a second front, close to the top, turns the saprolite into a soil. Weathering has led to leaching of U. The 234U/ 238U and 230Th/ 238U isotopic ratios are in radioactive disequilibrium. Numerous nodules are present and apparently started to form at the base of the saprolite. These nodules achieve more developed form during their relative ascent until they are reached by the descending top front where they undergo dissolution. The Th and Pb are concentrated in the nodules close to the top front. The U, being more mobile, is strongly leached by the first front, and most of the remainder, freed by the second, engages in a descending flux which supplies the underlying saprolite. Using the data an attempt is made to model the isotopic distribution in the profile. We conclude that the first front has descended at a rate of 5 cm/1000 yt, and that the time needed to create the saprolite must have been around 300,000 yr.

  5. Investigation of tritium and 233U breeding in a fission-fusion hybrid reactor fuelling with ThO2

    International Nuclear Information System (INIS)

    Yildiz, K.; Sahin, S.; Sahin, H. M.; Acir, A.; Yalcin, S.; Altinok, T.; Bayrak, M.; Alkan, M.; Durukan, O.

    2007-01-01

    In the world, thorium reserves are three times more than natural Uranium reserves. It is planned in the near future that nuclear reactors will use thorium as a fuel. Thorium is not a fissile isotope because it doesn't make fission with thermal neutrons so it could be converted to 2 33U isotope which has very high quality fission cross-section with thermal neutrons. 2 33U isotope can be used in present LWRs as an enrichment fuel. In the fusion reactors, tritium is the most important fossil fuel. Because tritium is not natural isotope, it has to be produced in the reactor. The purpose of this work is to investigate the tritium and 2 33U breeding in a fission-fusion hybrid reactor fuelling with ThO 2 for Δt=10 days during a reactor operation period in five years. The neutronic analysis is performed on an experimental hybrid blanket geometry. In the center of the hybrid blanket, there is a line neutron source in a cylindrical cavity, which simulates the fusion plasma chamber where high energy neutrons (14.1 MeV) are produced. The conventional fusion reaction delivers the external neutron source for blankets following, 2 D + 3 T →? 4 He (3.5 MeV) + n (14.1 MeV). (1) The fuel zone made up of natural-ThO 2 fuel and it is cooled with different coolants. In this work, five different moderator materials, which are Li 2 BeF 4 , LiF-NaF-BeF 2 , Li 2 0Sn 8 0, natural Lithium and Li 1 7Pb 8 3, are used as coolants. The radial reflector, called tritium breeding zones, is made of different Lithium compounds and graphite in sandwich structure. In the work, eight different Lithium compounds were used as tritium breeders in the tritium breeding zones, which are Li 3 N, Li 2 O, Li 2 O 2 , Li 2 TiO 3 , Li 4 SiO 3 , Li 2 ZrO 3 , LiBr and LiH. Neutron transport calculations are conducted in spherical geometry with the help of SCALE4.4A SYSTEM by solving the Boltzmann transport equation with code CSAS and XSDRNPM, under consideration of unresolved and resolved resonances, in S 8 -P 3

  6. Compositional characterization of sintered (U,Th)O2 pellets by EDXRF using fused bead specimens

    International Nuclear Information System (INIS)

    Sanjay Kumar, S.; Dhara, Sangita; Misra, N.L.; Aggarwal, S.K.

    2015-01-01

    Fused bead specimens were used for analyzing sintered (U,Th)O 2 pellets by Energy Dispersive X-Ray Fluorescence (EDXRF) spectrometry. The bead specimens of calibration mixtures U 3 O 8 and ThO 2 were made by fusing them in Lithium Tetraborate/Metaborate fusion mixtures using a fusion bead machine. The EDXRF spectra of these beads were used for making calibration plot for U% determination in (U+Th) amounts. Using these calibration plots and EDXRF spectra of bead of sintered (U,Th)O 2 pellets, U% in these pellets was successfully determined. (author)

  7. Transfer of 210Po, 210Pb and 238U from some medicinal plants to their essential oils

    International Nuclear Information System (INIS)

    Al-Masri, M.S.; Amin, Y.; Ibrahim, S.; Nassri, M.

    2015-01-01

    Essential oils were extracted from 35 medicinal plants used by Syrians, organic compounds were determined in these oils and concentrations of 210 Po 210 Pb and 238 U were determined in the original plants and in the essential oils. The results showed that the highest activity concentrations of 210 Po and 210 Pb were found in leaves with large surfaces and in Sage were as high as 73.5 Bq kg −1 and 73.2 Bq kg −1 , respectively. The activity concentration of 238 U was as high as 4.26 Bq kg −1 in Aloe. On the other hand, activity concentrations of 210 Po ranged between 0.2 and 71.1 Bq kg −1 in extracted essential oils for Rosemary and False yellowhead, respectively. The activity concentration of 210 Pb reached 63.7 Bq kg −1 in Aloe oil. The activity concentrations of 238 U were very low in all extracted oils; the highest value was 0.31 Bq kg −1 in peel of Orange oil. The transfer of 210 Po and 210 Pb from plant to its oil was the highest for Eugenia; 7.1% and 5.5% for 210 Po and 210 Pb, respectively. A linear relationship was found between the transfer factor of radionuclides from plant to its essential oil and the chemical content of this oil. - Highlights: • Natural radionuclides 210 Po, 210 Pb and 238 U were determined in 35 medicinal plants and their essential oils. • The highest activity concentration of 210 Po and 210 Pb were 73.5 Bq kg −1 and 73.2 Bq kg −1 in Sage, respectively. • The transfer of 210 Po and 210 Pb from Eugenia plant to its oil was the highest amongst other plants. • The data obtained in this study can be considered the first reported data for medicinal plants and their oils in Syria

  8. Natural age dispersion arising from the analysis of broken crystals. Part I: Theoretical basis and implications for the apatite (U-Th)/He thermochronometer

    Science.gov (United States)

    Brown, Roderick W.; Beucher, Romain; Roper, Steven; Persano, Cristina; Stuart, Fin; Fitzgerald, Paul

    2013-12-01

    aim to maximise the natural dispersion of grain ages, not minimise it, and should aim to analyse circa 20-30 grains from each sample. The key observations and conclusions drawn here are directly applicable to other thermochronometers, such as the apatite, rutile and titanite U-Pb systems, where the diffusion domain is approximated by the physical grain size.

  9. Zircon U-Pb geochronology and geochemistry of granites in the Zhuguangshan complex, South China: Implications for uranium mineralization

    Science.gov (United States)

    Zhang, Long; Chen, Zhenyu; Li, Xiaofeng; Li, Shengrong; Santosh, M.; Huang, Guolong

    2018-05-01

    The Zhuguangshan complex, composed of Caledonian, Indosinian, and Yanshanian granites, and Cretaceous mafic dykes, is one of the most important granite-hosted uranium producers in South China. Here we present LA-ICP-MS zircon U-Pb and hornblende 40Ar/39Ar geochronology and whole-rock and biotite geochemistry for the granites in this complex to evaluate the magmatism and its constraints on uranium mineralization. Samples collected from the Fuxi, Youdong, Longhuashan, Chikeng, Qiling, and Sanjiangkou intrusions yield zircon weighted 206Pb/238U ages of 426.7 ± 5.4 Ma, 226.4 ± 3.5 Ma, 225.0 ± 2.7 Ma, 152.2 ± 3.0 Ma, 153.9 ± 2.1 Ma, and 155.2 ± 2.1 Ma, respectively. A new Ar-Ar dating of the hornblende of the diabase from the Changjiang uranium ore field yields a plateau age of 145.1 ± 1.5 Ma. These results coupled with published geochronological data indicate that six major magmatic events occurred in the study area at 420-435 Ma, 225-240 Ma, 150-165 Ma, 140 Ma, 105 Ma, and 90 Ma. Both U-bearing and barren granites occur in this complex, and they display differences in whole-rock and biotite geochemistry. The barren granites show higher Al2O3, CaO, TFMM, Rb, Zr, Ba, SI, Mg#, (La/Yb)N, and Eu/Eu*, but lower SiO2, ALK, Rb, DI, Rb/Sr, and TiO2/MgO than those of the U-bearing granites. Biotites in the U-bearing granites are close to the Fe-rich siderophyllite-annite end member with Fe/(Fe + Mg) ratios higher than 0.66, whereas those in the barren granites are relatively close to the Mg-rich eastonite-phlogopite end member with Fe/(Fe + Mg) ratios uranium ore potential of the granites in the Zhuguangshan complex. The geochemical variations of U-bearing and barren granites can serve as a potential detector for granite-hosted uranium deposits.

  10. High precision time calibration of the Permo-Triassic boundary mass extinction by U-Pb geochronology

    Science.gov (United States)

    Baresel, Björn; Bucher, Hugo; Brosse, Morgane; Schaltegger, Urs

    2014-05-01

    U-Pb dating using Chemical Abrasion, Isotope Dilution Thermal Ionization Mass Spectrometry (CA-ID-TIMS) is the analytical method of choice for geochronologists, who are seeking highest temporal resolution and a high degree of accuracy for single grains of zircon. The use of double-isotope tracer solutions, cross-calibrated and assessed in different EARTHTIME labs, coinciding with the reassessment of the uranium decay constants and further improvements in ion counting technology led to unprecedented precision better than 0.1% for single grain, and 0.05% for population ages, respectively. These analytical innovations now allow calibrating magmatic and biological timescales at resolution adequate for both groups of processes. To construct a revised and high resolution calibrated time scale for the Permian-Triassic boundary (PTB) we use (i) high-precision U-Pb zircon age determinations of a unique succession of volcanic ash beds interbedded with shallow to deep water fossiliferous sediments in the Nanpanjiang Basin (South China) combined with (ii) accurate quantitative biochronology based on ammonoids and conodonts and (iii) carbon isotope excursions across the PTB. Using these alignments allows (i) positioning the PTB in different depositional environments and (ii) solving age/stratigraphic contradictions generated by the index, water depth-controlled conodont Hindeodus parvus, whose diachronous first occurrences are arbitrarily used for placing the base of the Triassic. This new age framework provides the basis for a combined calibration of chemostratigraphic records with high-resolution biochronozones of the Late Permian and Early Triassic. Besides the general improvement of the radio-isotopic calibration of the PTB at the ±100 ka level, this will also lead to a better understanding of cause and effect relations involved in this mass extinction.

  11. U-Pb zircon and monazite geochronology of the Hercynian two-mica granite composite pluton of Cabeceiras de Basto (Northern Portugal); Geochronologie U-Pb sur zircon et monazite du massif composite de granite a deux micas hercynien de Cabeceiras de Basto (Nord-Portugal)

    Energy Technology Data Exchange (ETDEWEB)

    Almeida, A.; Noronha, F. [Universidade do Porto (Portugal). Centro de Geologia; Leterrier, J. [Centre de Recherches Petrographiques et Geochimiques, 54 - Vandoeuvre-les-Nancy (France); Bertrand, J.M. [Universite de Savoie, 73 - Le-Bourget-du-Lac (France). Laboratoire de geodynamique des Chaines alpines

    1998-06-01

    The zircon and monazite U-Pb minimum age of the Hercynian peraluminous two-mica composite granite pluton of Cabeceiras de Basto (Northern Portugal) is 311 {+-} 1 Ma (2 {sigma}). This age, well constrained by a concordant monazite of 311{+-}4 Ma (2{sigma}), is in good agreement with the age suggested for the syn-kinematic, syn-D3, Iberian granites of the Hercynian orogeny (315-305; Pinto et al., 1987). The ({sup 87}Sr/{sup 86}Sr){sub i} and {xi}{sub Nd} isotopic ratios, calculated for 311 Ma, suggest that the three granite units which constitute the massif may derive from an heterogeneous crustal source dated (upper intercept of the discordance) around 1200 Ma. (authors) 21 refs.

  12. Use of excess 210Pb and 228Th to estimate rates of sediment accumulation and bioturbation in Port Phillip Bay, Australia

    International Nuclear Information System (INIS)

    Hancock, G.J.; Hunter, J.R.

    1999-01-01

    Rates of sediment accumulation, sediment mixing and depositional particle fluxes were estimated by use of excess 210 Pb and 228 Th. In central Port Phillip Bay, there was a rapidly mixed surface layer and two layers of different mixing rates at 2-20 cm and 2145 cm depths. When the sediment profiles of excess 210 Pb and 228 Th were combined and diffusive mixing was assumed, the sediment accumulation rate in the 2-20 cm layer was constrained to be -1 . The mixing coefficient in the 2-20 cm layer was 5.0 ± 0.1 cm 2 year -1 . Hence, mixing rather than sedimentation governs the distribution of 210 Pb and 228 Th in the surficial 20 cm. Below 20 cm, the different mixing regime may be due to the dominance of deposit-feeders at these depths. Evidence for bioturbation to a depth of 50 cm was obtained from profiles of excess 210 Pb and 228 Ra deficiency. The mean residence time of particles in the central bay water column was 10 ± 2 days (a normalized depositional particle flux of 0.16 ± 0.02 g cm -2 year -1 ). This flux is three times the upper estimate of the sediment accumulation rate, indicating that most of the suspended particulate matter in the water column is resuspended bottom sediment. Copyright (1997) CSIRO Publishing

  13. Direct dating of Tantavel man by non-destructive gamma-ray spectrometry of fossil human skull Arago XXI

    International Nuclear Information System (INIS)

    Yokoyama, Yuji; Nguyen, Huu-Van

    1981-01-01

    A new method to date prehistoric samples is proposed. Non-destructive gamma-ray spectrometry with semi-conductor detector was used in the direct determination of the activities of 238 U, 234 U, 231 Pa, 230 Th and 228 Th. An age of (400sub(-96)sup(+infinite))x10 3 years was obtained from the 230 Th/ 238 U ratio of 0.975+-0.030 [fr

  14. Determination of U, Th and K in bricks by gamma-ray spectrometry, X-ray fluorescence analysis and neutron activation analysis

    Science.gov (United States)

    Bártová, H.; Kučera, J.; Musílek, L.; Trojek, T.; Gregorová, E.

    2017-11-01

    Knowledge of the content of natural radionuclides in bricks can be important in some cases in dosimetry and application of ionizing radiation. Dosimetry of naturally occurring radionuclides in matter (NORM) in general is one of them, the other one, related to radiation protection, is radon exposure evaluation, and finally, it is needed for the thermoluminescence (TL) dating method. The internal dose rate inside bricks is caused mostly by contributions of the natural radionuclides 238U, 232Th, radionuclides of their decay chains, and 40K. The decay chain of 235U is usually much less important. The concentrations of 238U, 232Th and 40K were measured by various methods, namely by gamma-ray spectrometry, X-ray fluorescence analysis (XRF), and neutron activation analysis (NAA) which was used as a reference method. These methods were compared from the point of view of accuracy, limit of detection (LOD), amount of sample needed and sample handling, time demands, and instrument availability.

  15. Direct Measurement of Initial 230TH/ 232TH Ratios in Central Texas Speleothems for More Accurate Age Determination

    Science.gov (United States)

    Wortham, B. E.; Banner, J. L.; James, E.; Loewy, S. L.

    2013-12-01

    Speleothems, calcite deposits in caves, preserve a record of climate in their growth rate, isotope ratios and trace element concentrations. These variables must be tied to precise ages to produce pre-instrumental records of climate. The 238U-234U- 230Th disequilibrium method of dating can yield precise ages if the amount of 230Th from the decay of radiogenic 238U can be constrained. 230Th in a speleothem calcite growth layer has two potential sources - 1) decay of radioactive 238U since the time of growth of the calcite layer; and 2) initial detrital 230Th, incorporated along with detrital 232Th, into the calcite layer at the time it grew. Although the calcite lattice does not typically incorporate Th, samples can contain impurities with relatively high Th contents. Initial 230Th/232Th is commonly estimated by assuming a source with bulk-Earth U/Th values in a state of secular equilibrium in the 238U-decay chain. The uncertainty in this 230Th/232Th estimate is also assumed, typically at +/-100%. Both assumptions contribute to uncertainty in ages determined for young speleothems. If the amount of initial detrital 230Th can be better quantified for samples or sites, then U-series ages will have smaller uncertainties and more precisely define the time series of climate proxies. This study determined the initial 230Th/232Th of modern calcite to provide more precise dates for central Texas speleothems. Calcite was grown on glass-plate substrates placed under active drips in central Texas caves. The 230Th/232Th of this modern calcite was determined using thermal ionization mass spectrometry. Results show that: 1) initial 230Th/232Th ratios can be accurately determined in these young samples and 2) measuring 230Th/232Th reduces the uncertainties in previously-determined ages on stalagmites from under the same drips. For example, measured initial 230Th/232Th in calcite collected on substrates from different locations in the cave at Westcave Preserve are 15.3 × 0.67 ppm

  16. Void reactivity feedback analysis for U-based and Th-based LWR incineration cycles

    Energy Technology Data Exchange (ETDEWEB)

    Lindley, B.A.; Parks, G.T. [Cambridge University Engineering Department, Trumpington Street, Cambridge, CB2 1PZ (United Kingdom); Franceschini, F. [Westinghouse Electric Company LLC, Cranberry Township, PA (United States)

    2013-07-01

    In reduced-moderation LWRs, an external supply of transuranic (TRU) can be incinerated by mixing it with a fertile isotope ({sup 238}U or {sup 232}Th) and recycling all the actinides after each cycle. Performance is limited by coolant reactivity feedback - the moderator density coefficient (MDC) must be kept negative. The MDC is worse when more TRU is loaded, but TRU feed is also needed to maintain criticality. To assess the performance of this fuel cycle in different neutron spectra, three LWRs are considered: 'reference' PWRs and reduced-moderation PWRs and BWRs. The MDC of the equilibrium cycle is analysed by reactivity decomposition with perturbed coolant density by isotope and neutron energy. The results show that using {sup 232}Th as a fertile isotope yields superior performance to {sup 238}U. This is due essentially to the high resonance η of U bred from Th (U3), which increases the fissility of the U3-TRU isotope vector in the Th-fueled system relative to the U-fueled system, and also improves the MDC in a sufficiently hard spectrum. Spatial separation of TRU and U3 in the Th-fueled system renders further improvement by hardening the neutron spectrum in the TRU and softening it in the U3. This improves the TRU η and increases the negative MDC contribution from reduced thermal fission in U3. (authors)

  17. Resonance Region Covariance Analysis Method and New Covariance Data for Th-232, U-233, U-235, U-238, and Pu-239

    International Nuclear Information System (INIS)

    Leal, Luiz C.; Arbanas, Goran; Derrien, Herve; Wiarda, Dorothea

    2008-01-01

    Resonance-parameter covariance matrix (RPCM) evaluations in the resolved resonance region were done for 232Th, 233U, 235U, 238U, and 239Pu using the computer code SAMMY. The retroactive approach of the code SAMMY was used to generate the RPCMs for 233U, 235U. RPCMs for 232Th, 238U and 239Pu were generated together with the resonance parameter evaluations. The RPCMs were then converted in the ENDF format using the FILE32 representation. Alternatively, for computer storage reasons, the FILE32 was converted in the FILE33 cross section covariance matrix (CSCM). Both representations were processed using the computer code PUFF-IV. This paper describes the procedures used to generate the RPCM with SAMMY.

  18. U-Th ages obtained by mass spectrometry in corals from Barbados: sea level during the past 130,000 years

    Energy Technology Data Exchange (ETDEWEB)

    Bard, Edouard; Hamelin, Bruno; Fairbanks, R.G. (Columbia Univ., Palisades, NY (USA). Lamont-Doherty Geological Observatory)

    1990-08-02

    The study of the sea level record during the last glacial cycle has primarily proceeded indirectly by means of oxygen isotope measurements on foraminifera from deep-sea sediments. The direct approach of dating sea level indicators stagnated during the past decade, mainly because the samples required to complete our knowledge of the past glaciations are below the present-day sea level. Using the {sup 14}C ages of Acropora palmata samples collected by drilling offshore the island of Barbados, we report the first detailed chronology for the last deglaciation. This radio-carbon chronology is limited to the past 30 kyr because of the short half-life of {sup 14}C (5,730 yr); we must therefore rely on other dating methods to obtain information for the whole last glacial cycle. During the past four years {sup 230}Th-{sup 234}U dating of corals by thermal-ionization mass spectrometry has been shown to be significantly more precise and accurate than the classical {alpha}-counting method. We have used this technique to measure U-Th ages in coral samples from the Barbados collection and from subaerially exposed outcrops. Here we present results bearing on the sea level record for the past 130,000 years; we conclude that the last deglaciation started 3,000 years earlier than previously thought and confirm that there were two surges in melt water at about 11 kyr and 14 kyr BP (before present). (author).

  19. U-Th ages obtained by mass spectrometry in corals from Barbados: sea level during the past 130,000 years

    International Nuclear Information System (INIS)

    Bard, Edouard; Hamelin, Bruno; Fairbanks, R.G.

    1990-01-01

    The study of the sea level record during the last glacial cycle has primarily proceeded indirectly by means of oxygen isotope measurements on foraminifera from deep-sea sediments. The direct approach of dating sea level indicators stagnated during the past decade, mainly because the samples required to complete our knowledge of the past glaciations are below the present-day sea level. Using the 14 C ages of Acropora palmata samples collected by drilling offshore the island of Barbados, we report the first detailed chronology for the last deglaciation. This radio-carbon chronology is limited to the past 30 kyr because of the short half-life of 14 C (5,730 yr); we must therefore rely on other dating methods to obtain information for the whole last glacial cycle. During the past four years 230 Th- 234 U dating of corals by thermal-ionization mass spectrometry has been shown to be significantly more precise and accurate than the classical α-counting method. We have used this technique to measure U-Th ages in coral samples from the Barbados collection and from subaerially exposed outcrops. Here we present results bearing on the sea level record for the past 130,000 years; we conclude that the last deglaciation started 3,000 years earlier than previously thought and confirm that there were two surges in melt water at about 11 kyr and 14 kyr BP (before present). (author)

  20. Ground water contamination with (238)U, (234)U, (235)U, (226)Ra and (210)Pb from past uranium mining: cove wash, Arizona.

    Science.gov (United States)

    Dias da Cunha, Kenya Moore; Henderson, Helenes; Thomson, Bruce M; Hecht, Adam A

    2014-06-01

    The objectives of the study are to present a critical review of the (238)U, (234)U, (235)U, (226)Ra and (210)Pb levels in water samples from the EPA studies (U.S. EPA in Abandoned uranium mines and the Navajo Nation: Red Valley chapter screening assessment report. Region 9 Superfund Program, San Francisco, 2004, Abandoned uranium mines and the Navajo Nation: Northern aum region screening assessment report. Region 9 Superfund Program, San Francisco, 2006, Health and environmental impacts of uranium contamination, 5-year plan. Region 9 Superfund Program, San Franciso, 2008) and the dose assessment for the population due to ingestion of water containing (238)U and (234)U. The water quality data were taken from Sect. "Data analysis" of the published report, titled Abandoned Uranium Mines Project Arizona, New Mexico, Utah-Navajo Lands 1994-2000, Project Atlas. Total uranium concentration was above the maximum concentration level for drinking water (7.410-1 Bq/L) in 19 % of the water samples, while (238)U and (234)U concentrations were above in 14 and 17 % of the water samples, respectively. (226)Ra and (210)Pb concentrations in water samples were in the range of 3.7 × 10(-1) to 5.55 × 102 Bq/L and 1.11 to 4.33 × 102 Bq/L, respectively. For only two samples, the (226)Ra concentrations exceeded the MCL for total Ra for drinking water (0.185 Bq/L). However, the (210)Pb/(226)Ra ratios varied from 0.11 to 47.00, and ratios above 1.00 were observed in 71 % of the samples. Secular equilibrium of the natural uranium series was not observed in the data record for most of the water samples. Moreover, the (235)U/(total)U mass ratios ranged from 0.06 to 5.9 %, and the natural mass ratio of (235)U to (total)U (0.72 %) was observed in only 16 % of the water samples, ratios above or below the natural ratio could not be explained based on data reported by U.S. EPA. In addition, statistical evaluations showed no correlations among the distribution of the radionuclide concentrations

  1. Measurements of 234U, 238U and 230Th in excreta of uranium-mill crushermen

    International Nuclear Information System (INIS)

    Fisher, D.R.; Jackson, P.O.; Brodacynski, G.G.; Scherpelz, R.I.

    1982-07-01

    Uranium and thorium levels in excreta of uranium mill crushermen who are routinely exposed to airborne uranium ore dust were measured. The purpose was to determine whether 230 Th was preferentially retained over either 234 U or 238 U in the body. Urine and fecal samples were obtained from fourteen active crushermen with long histories of exposure to uranium ore dust, plus four retired crushermen and three control individuals for comparison. Radiochemical procedures were used to separate out the uranium and thorium fractions, which were then electroplated on stainless steel discs and assayed by alpha spectrometry. Significantly greater activity levels of 234 U and 238 U were measured in both urine and fecal samples obtained from uranium mill crushermen, indicating that uranium in the inhaled ore dust was cleared from the body with a shorter biological half-time than the daughter product 230 Th. The measurements also indicated that uranium and thorium separate in vivo and have distinctly different metabolic pathways and transfer rates in the body. The appropriateness of current ICRP retention and clearance parameters for 230 Th in ore dust is questioned

  2. Comparative study of α and β-ThBr4: structure and luminescence. Spectroscopy of U4+ in α-ThBr4

    International Nuclear Information System (INIS)

    Simoni, E.

    1988-05-01

    UV absorption of β-ThBr 4 : presents a plain absorption front and for the same temperature the threshold energy has the same value than the threshold energy of excitation function and photocurrent peak. Emission intensity and lifetime decrease when temperature increases from 300 K to 400K (extinction temperature). Results are interpreted either by molecular orbital levels of the ThBr 8 4- cluster or either by conduction and valence bands of the matrix above. Absorption and emission spectra of U 4+ in α-ThBr 4 (where U 4+ has a S 4 symmetry) between 300 K and 4.2 K allow indexation of 30 levels. Spectroscopic parameters are calculated in D 2d and S 4 symmetry. Comparison of these parameters with those of U 4+ in β-ThBr 4 and β-ThCl 4 shows that crystal field force is practically the same in the three matrices but the structure transformation from β to α has more influence on B q k than ligand change from Br - to Cl - . Owing to very low phonon energy, fluorescence spectra of U 4+ is easy to observe in α-ThBr 4 as it is in β-ThBr 4 and ThCl 4 [fr

  3. Fission track dating of kimberlitic zircons

    International Nuclear Information System (INIS)

    Haggerty, S.E.

    1983-01-01

    The only reliable method for dating kimberlites at present is the lengthy and specialized hydrothermal procedure that extracts 206 Pb and 238 U from low-uranium zircons. This paper describes a second successful method by fission track dating of large single-crystal zircons, 1.0-1.5 cm in dimension. The use of large crystals overcomes the limitations imposed in conventional fission track analysis which utilizes crushed fragments. Low track densities, optical track dispersion, and the random orientation of polished surfaces in the etch and irradiation cycle are effectively overcome. Fission track ages of zircons from five African kimberlites are reported, from the Kimberley Pool (90.0 +- 6.5 m.y.), Orapa (87.4 +- 5.7 and 92.4 +- 6.1 m.y.), Nzega (51.1 +- 3.8 m.y.), Koffiefontein (90.9 +- 8.2 m.y.), and Val do Queve (133.4 +- 11.5 m.y.). In addition we report the first radiometric ages (707.9 +- 59.6 and 705.5 +- 61.0 m.y.) of crustal zircons from kimberlites in northwest Liberia. The fission track ages agree well with earlier age estimates. Most of the zircons examined in this study are zoned with respect to uranium but linear correlations are established (by regression analysis) between zones of variable uranium content, and within zones of constant uranium content (by analysis of variance). Concordance between the fission track method and the U/Pb technique is established and we concluded that track fading from thermal annealing has not taken place. Kimberlitic zircons dated in this study, therefore, record the time of eruption. (orig.)

  4. REIMEP-22 inter-laboratory comparison: "U Age Dating - Determination of the production date of a uranium certified test sample"

    OpenAIRE

    VENCHIARUTTI CELIA; VARGA ZSOLT; RICHTER Stephan; JAKOPIC Rozle; MAYER Klaus; AREGBE Yetunde

    2015-01-01

    The REIMEP-22 inter-laboratory comparison aimed at determining the production date of a uranium certified test sample (i.e. the last chemical separation date of the material). Participants in REIMEP-22 on "U Age Dating - Determination of the production date of a uranium certified test sample" received one low-enriched 20 mg uranium sample for mass spectrometry measurements and/or one 50 mg uranium sample for D-spectrometry measurements, with an undisclosed value for the production date. They ...

  5. Crystallographic Study of U-Th bearing minerals in Tranomaro, Anosy Region-Madagascar

    International Nuclear Information System (INIS)

    Sahoa, F.E.; Rabesiranana, N.; Raoelina Andriambololona; Geckeis, H.; Marquardt, C.; Finck, K.

    2011-01-01

    As an alternative to conventional fossil fuel, there is a renewed interest in the nuclear fuel to support increasing energy demand. New studies are then undertaken to characterize Madagascar U-Th bearing minerals. This is the case for the urano-thorianite bearing pyroxenites in the south East of Madagascar. In this region, several quarries were abandoned, after being mined by the French Atomic Energy Commission (C.E.A) in the fifties and sixties and are now explored by new mining companies. For this purpose, seven U-Th bearing mineral samples from old abandoned uranium quarries in Tranomaro, Amboasary Sud, Madagascar, have been collected. To determine the mineral microstructure, they were investigated for qualitative and quantitative identification of crystalline compounds using X-ray powder diffraction analytical method (XRD). Results showed that the U and Th compounds, as minor elements, are present in various crystalline structures. This is important to understand their environmental behaviours, in terms of crystallographic dispersion of U-Th minerals and their impacts on human health.

  6. Human lead exposure in a late 19th century mental asylum population

    Energy Technology Data Exchange (ETDEWEB)

    Bower, Nathan W. [Department of Chemistry, Colorado College, Colorado Springs, CO 80903-3294 (United States)]. E-mail: nbower@coloradocollege.edu; McCants, Sarah A. [Department of Chemistry, Colorado College, Colorado Springs, CO 80903-3294 (United States); Custodio, Joseph M. [Department of Chemistry, Colorado College, Colorado Springs, CO 80903-3294 (United States); Ketterer, Michael E. [Departments of Chemistry and Biochemistry, Northern Arizona University, Flagstaff, AZ 86011-5698 (United States); Getty, Stephen R. [Biological Sciences Curriculum Study, Colorado Springs, CO 80918 (United States); Hoffman, J. Michael [Department of Anthropology, Colorado College, Colorado Springs, CO 8090-3294 (United States)

    2007-01-01

    Lead isotope ratios and lead (Pb) levels were analyzed in 33 individuals from a forgotten cemetery at the Colorado Mental Health Institute at Pueblo, Colorado dating to 1879-1899. Isotopic ratios from healing bone fractures, cortical bone, and tooth dentine provide information about sources of Pb exposures over a range of time that illuminates individual's life histories and migration patterns. Historical records and Pb production data from the 19th century were used to create a database for interpreting Pb exposures for these African, Hispanic and European Americans. The analysis of these individuals suggests that Pb exposure noticeably impacted the mental health of 5-10% of the asylum patients in this frontier population, a high number by standards today, and that differences exist in the three ancestral groups' exposure histories.

  7. Human lead exposure in a late 19th century mental asylum population

    International Nuclear Information System (INIS)

    Bower, Nathan W.; McCants, Sarah A.; Custodio, Joseph M.; Ketterer, Michael E.; Getty, Stephen R.; Hoffman, J. Michael

    2007-01-01

    Lead isotope ratios and lead (Pb) levels were analyzed in 33 individuals from a forgotten cemetery at the Colorado Mental Health Institute at Pueblo, Colorado dating to 1879-1899. Isotopic ratios from healing bone fractures, cortical bone, and tooth dentine provide information about sources of Pb exposures over a range of time that illuminates individual's life histories and migration patterns. Historical records and Pb production data from the 19th century were used to create a database for interpreting Pb exposures for these African, Hispanic and European Americans. The analysis of these individuals suggests that Pb exposure noticeably impacted the mental health of 5-10% of the asylum patients in this frontier population, a high number by standards today, and that differences exist in the three ancestral groups' exposure histories

  8. Example dated with {sup 210}Pb; Ejemplo de fechado con {sup 210}Pb

    Energy Technology Data Exchange (ETDEWEB)

    Ruiz-Fernandez, Ana Carolina [Universidad Nacional Autonoma de Mexico, Instituto de Ciencias del Mar y Limnologia (Mexico); Sanchez-Cabeza, Joan-Albert [Organismo Internacional de la Energia Atomica, Laboratorios del Medio Marino (Monaco)

    2012-07-01

    In this chapter we describe in detail, using an example, the procedure to date a core with the technique of {sup 210}Pb using the models described in Chapter 7. Described below, one by one, the spreadsheets containing the information and calculations necessary to complete a profile geochronology of {sup 210}Pb core adapted from Gulf of Tehuantepec, Mexico. In this case, the old model obtained from the CA model could not be validated with {sup 137}Cs because the peak age of {sup 137}Cs is too old (1985 {+-} 3 years). Moreover, there was an investment of age between sections 2-3 and 3-4 cm because the activity of the lower section is higher than at the top, most likely due to a change in sediment accumulation. The average value of MAR (obtained with the CFCS model: 0.222 {+-} 0.016 g cm{sup -2} yr{sup -1}) is in good agreement with the range obtained with the model MAR CF (0.03 {+-} 0.02 to 0.30 {+-} 0.01 g cm{sup -2} yr{sup -1}). The chronology obtained with the CF model is well validated with the peak of {sup 137}Cs (section 6-7 cm: 1960-1972). SAR profiles and MAR show a progressive increase from the late nineteenth century, due to economic development and population growth in the Gulf of Tehuantepec. This growth, which has altered the coastal marine circulation and sedimentation regimes, had its greatest impact during the past two decades, after the establishment of three major industrial complexes in the region. [Spanish] En este capitulo describimos con detalle, utilizando un ejemplo, el procedimiento para fechar un core con la tecnica de {sup 210}Pb utilizando los modelos descritos en el Capitulo 7. A continuacion describimos, una a una, las hojas de calculo que contienen la informacion y los calculos necesarios para realizar la geocronologia de un perfil de {sup 210}Pb adaptado de un core del Golfo de Tehuantepec, Mexico. En este caso, el modelo de edad obtenido a partir del model CA no pudo ser validado con {sup 137}Cs porque la edad del pico de {sup 137}Cs

  9. Biogeochemical alteration effects on U/Th geochronology of Pleistocene corals, Penguin Bank, Molokai, Hawai`i

    Science.gov (United States)

    Herries, K.; Rubin, K. H.; Hellebrand, E.

    2017-12-01

    Meltwater Pulse 1a (MWP-1a) is a large, relatively fast sea level rise event that occurred during the last deglaciation. Critical questions remain about the exact timing of MWP-1a and can be answered using high precision geochronology. Coral reefs are able to yield ideal records of sea level and ocean changes during and after deposition. Glacial far-field fossilized coral reefs, such as the well-preserved Penguin Bank reef near Molokai, Hawai'i, provide understandings to past sea level events that are relatively unaffected by local deglacial sea level effects. Using uranium-thorium dating of pristine corals, we are able date sea level events to an error of ±25-50 years. However, most Penguin Bank coral samples have been biogeochemically disturbed by other mesophotic organisms either during their lifetime or after their death. In these samples, the main disturbances observed in hand specimen are (1) overgrowth by coralline algae, (2) bioerosion from boring organisms, (3) living organisms, like sponges, inside coral skeletons, and (4) discoloration due to detrital materials. These disturbances are capable of disrupting the concentration of U in the coral and/or δ 234U measured. Seawater alteration-sensitive ratios, such as Sr/Ca and Mg/Ca, act as a proxy for potential diagenetic effects on U distribution in the corals. U and Th isotopic data acquired on both pristine and altered parts of the corals are being used to determine the impacts of alteration in the measured ages. With these new data, it may be possible to derive a more accurate timing of MWP-1a and provide a more general method of determining the suitability of coral specimens for dating of the last deglaciation and past climate change.

  10. Measurements of distribution coefficient for Sn, Pb and Th on sand stone and tuff in saline type groundwater

    International Nuclear Information System (INIS)

    Nakazawa, Toshiyuki; Okada, Kenichi; Muroi, Masayuki; Shibata, Masahiro; Sasamoto, Hiroshi

    2004-02-01

    Japan Nuclear Cycle Development Institute (JNC) has developed the sorption database for bentonite and rocks in order to assess the retardation capacities of important radioactive elements in natural and engineered barriers in the H12 report. However, there are not enough distribution coefficient data for radioactive elements in saline type groundwater in the database. Sn (tin), Pb (lead) and Th(thorium) are important radioactive elements for performance assessment of high level radioactive waste disposal, thus we carried out the batch sorption experiments for these radioactive elements on sand stone and tuff. The experiments for each radioactive element were performed on the following conditions; Sn: Kd measurements using the solutions (distilled water or artificial sea water) reacted with sand stone. Pb: Kd measurements using solution (artificial sea water) reacted with sand stone or tuff. Th: Kd measurements using solution (artificial sea water) reacted with sand stone as a function of carbonate concentration. The results of experiment are summarized below; In the case of Sn, Kd were 0.4-1 m 3 /kg in distilled water type and approximately 1 m 3 /kg in artificial sea water type. And also, Kd was 0.3 m 3 /kg in artificial sea water adjusted Ph 12. In artificial sea water type, it was suggested that Kd decreased with pH. In the case of Pb, Kd were approximately 2 m 3 /kg on sand stone and 4-10 m 3 /kg on tuff in artificial sea water type. Kd on tuff was a little larger than that on sand stone. There were no distinctly differences depending on solid-liquid separation methods. In the case of Th, Kd was approximately 1-8 m 3 /kg in artificial sea water type. On the other hand, sorption of Th on sand stone was not observed (i.e., Kd = 0 m 3 /kg) in high carbonate solution. It was estimated that low Kd in high carbonate solution might be caused by speciation of because Th could form the anions in the solution such as hydroxo-carbonate complexes and carbonate complexes

  11. Dating method by fission tracks: some Brazilian examples

    International Nuclear Information System (INIS)

    Fonseca, Ariadne do Carmo

    1996-01-01

    The Fission Track method (TF) complements the dating of a interval of tectonic events occurred in low temperatures not detected by another radiometric methods. In the South part of Craton of Sao Francisco the dating of apatites of archaean rocks produced ages TF between 900 and 500 Ma, reflecting the progressive acting of the Brazilian margin mobile belts in the archaean craton areas. Apatite of some igneous and metamorphic rocks of the Braziliana age, in the Faixa Ribeira segment, between the Rio de Janeiro and Salvador cities, produced TF ages between 140 and 80 Ma. The basaltic and alkaline volcanism related to the Atlantic Ocean opening dated from this interval. The TF dating in apatites of the continental margin rocks allowed to date the event. In the Cabo Frio region (Southeastern part of Rio de Janeiro State), titanite and apatite of the Transamazonic orthognaisses produced TF dates between 190 and 80 to 40 Ma. The age around 190 Ma date previously the rift formation precursor of the South Atlantic Ocean opening, while the ages between 80 and 40 Ma were related to the alkaline rocks intrusion. The examples mentioned demonstrate the event diversity which may be dated by the Fission Tracks method, mainly in the craton area and margin belts study

  12. U-Pb zircon geochronology, Sr-Nd isotope geochemistry, and petrogenesis of oxidant granitoids at Keybarkuh, southwest of Khaf

    Directory of Open Access Journals (Sweden)

    Ehsan Salati

    2012-10-01

    Full Text Available Keybarkuh area is located 70 km southwest of Khaf, Khorasan Razavi province. The study area is situated in northeastern Lut block. The rock units in the area are Paleozoic metamorphic rocks and Cretaceous to Tertiary subvolcanic intrusions intruded as dike, stock and batholith; their composition varies from granite to diorite. Based on magnetic susceptibility, the intrusive rocks are divided into oxidant and reduced series. In this study, the oxidant intrusions are discussed. These intrusions are mostly high-K to shoshonitic and also meta-aluminous type. Their magma formed in subduction magmatic arc and they belong to I-type granitoid series. Enrichment of Large Ion Lithophile Elements (LILE such as Rb, Cs, K, Ba, and Th relative to High Field Stength Elements (HFSE such as Nb, Zr, and Ti supported the idea. Enrichment of Light Rare Earth Elements (LREE and depletion of Heavy Rare Earth Elements (HREE are also typical of subduction magmatism. Negative anomalies of Eu/Eu* can be attributed to the presence of residual plagioclase in a mantle source and contamination of magma by reduced continental crust. The amount of Nb > 11 ppm, lower ratio of Zr/Nb 0.706, initial 143Nd/144Nd (> 0.512 and εNd (< -3.5 indicate that magma contaminated by reduced continental crust. Hornblende biotite granodiorite porphyry dated using U-Pb zircon geochronology at 43.44 Ma (Middle Eocene. Based on calculated TDM, magma derived from ancient slab with 820 Ma age in the Keybarkuh area, was affected by the highest continental crust contamination during its ascent.

  13. Radioisotope dilution analyses of geological samples using 236U and 229Th

    International Nuclear Information System (INIS)

    Rosholt, J.N.

    1984-01-01

    The use of 236 U and 229 Th in alpha spectrometric measurements has some advantages over the use of other tracers and measurement techniques in isotope dilution analyses of most geological samples. The advantages are: 1) these isotopes do not occur in terrestrial rocks, 2) they have negligible decay losses because of their long half lives, 3) they cause minimal recoil contamination to surface-barrier detectors, 4) they allow for simultaneous determination of the concentration and isotopic composition of uranium and thorium in a variety of sample types, and 5) they allow for simple and constant corrections for spectral interferences, 0.5% of the 238 U activity is subtracted for the contribution of 235 U in the 236 U peak and 1% of the 229 Th activity is subtracted from the 230 Th activity. Disadvantages in using 236 U and 229 Th are: 1) individual separates of uranium and thorium must be prepared as very thin sources for alpha spectrometry, 2) good resolution in the spectrometer system is required for thorium isotopic measurements where measurement times may extend to 300 h, and 3) separate calibrations of the 236 U and 229 Th spike solution with both uranium and thorium standards are required. The use of these tracers in applications of uranium-series disequilibrium studies has simplified the measurements required for the determination of the isotopic composition of uranium and thorium because of the minimal corrections needed for alpha spectral interferences. (orig.)

  14. Radioisotope dilution analyses of geological samples using 236U and 229Th

    Science.gov (United States)

    Rosholt, J.N.

    1984-01-01

    The use of 236U and 229Th in alpha spectrometric measurements has some advantages over the use of other tracers and measurement techniques in isotope dilution analyses of most geological samples. The advantages are: (1) these isotopes do not occur in terrestrial rocks, (2) they have negligible decay losses because of their long half lives, (3) they cause minimal recoil contamination to surface-barrier detectors, (4) they allow for simultaneous determination of the concentration and isotopic composition of uranium and thorium in a variety of sample types, and (5) they allow for simple and constant corrections for spectral inferences, 0.5% of the 238U activity is subtracted for the contribution of 235U in the 236U peak and 1% of the 229Th activity is subtracted from the 230Th activity. Disadvantages in using 236U and 229Th are: (1) individual separates of uranium and thorium must be prepared as very thin sources for alpha spectrometry, (2) good resolution in the spectrometer system is required for thorium isotopic measurements where measurement times may extend to 300 h, and (3) separate calibrations of the 236U and 229Th spike solution with both uranium and thorium standards are required. The use of these tracers in applications of uranium-series disequilibrium studies has simplified the measurements required for the determination of the isotopic composition of uranium and thorium because of the minimal corrections needed for alpha spectral interferences. ?? 1984.

  15. U-Pb dating of silicic lavas, sills and syneruptive resedimented volcaniclastic deposits of the Lower Devonian Crudine Group, Hill End Trough, New South Wales

    International Nuclear Information System (INIS)

    Jagodzinski, E.A.; Black, L.P.

    1999-01-01

    The Hill End Trough of central-western New South Wales was an elongate deep marine basin that existed in the Lachlan Fold Belt from the early Late Silurian to late Early Devonian. It is represented by a regionally extensive. unfossiliferous sequence of interbedded turbidites and hemipelagites of substantially silicic Volcanic derivation, which passes laterally into contemporaneous shallow-water sedimentary rocks. The Turondale and Merrions Formations of the Lower Devonian Crudine Group are two prominent volcanogenic formations in the predominantly sedimentary trough sequence. They contain a range of primary and resedimented volcanic facies suitable for U-Pb dating. These include widespread subaqueous silicic lavas and/or lava cryptodomes. and thick sequences of crystal-rich volcaniclastic sandstone emplaced by a succession of muss-flows that were generated by interaction between contemporaneous subaerial pyroclastic flows and the sea. Ion microprobe dating of the two volcanogenic formations by means of the commonly used SL 13 zircon standard yields ages ranging between 411.3 ± 5.1 and 404.8 ± 4.8 Ma. Normalising the data against a different zircon standard (QGNG) yields preferred slightly older mean ages that range between 413.4 ± 6.6 and 407.1 ± 6.9 Ma. These ages broadly approximate the Early Devonian age that has been historically associated with the Crudine Group. However, the biostratigraphically inferred late Lochkovian - early Emsian (mid-Early Devonian) age for the Merrions Formation is inconsistent with the current Australian Phunerozoic Timescale, which assigns an age of 410 Ma to the Silurian-Devonian boundary, and ages of 404.5 Ma and 395.5 Ma to the base and top of the Pragian, respectively. There is, however, good agreement if the new ages are compared with the most recently published revision of the Devonian time-scale. This suggests that the Early Devonian stage boundaries of the Australian Phanerozoic Timescale need to be revised downward. The

  16. Th, Pa and U isotopes in an echinoderm, Encope grandis. An application to dating of some fossil samples from Southern Baja California

    Energy Technology Data Exchange (ETDEWEB)

    Omura, A [Kanazawa Univ. (Japan). Faculty of Science; Ku, T

    1979-03-01

    The application of /sup 230/Th and /sup 231/Pa growth methods to the hard tissues of living things, which are effective for the radiometric age measurement for latter Quaternary period, has been limited to certain corals, therefore it has been scarcely utilized in other areas than coral reefs. Reef coral fossils (Porites) were obtained from terrace deposits of Magdalena Island in Southern Baja California, and the methods were applied to them. At the time, the isotope compositions of Th, Pa and U in the shells of echinoderm Encope Grandis and of the living samples were examined. The estimated ages were in agreement with those of coral. It suggests that the reliable /sup 230/Th and /sup 231/Pa ages of sea-urchin fossils were presented for the first time and that the method is applicable to such fossils only if the conditions can be met. The results are highly significant, since the method may be used in other areas than coral reefs. (J.P.N.).

  17. Uranium/thorium dating of late Pleistocene peat deposits in N.W. Europe.

    NARCIS (Netherlands)

    Heijnis, Hendrik

    1992-01-01

    Dating of peat by means of uranium series disequilibrium (230-Th/234-U, also known as UTD) with special emphasis on dating the early Weichselian interstadial and last interglacial peats in north western Europe, is the subject of this study. ... Zie: Introduction

  18. Mercury anomalies as a proxy for large igneous province volicanism and effects on the carbon cycle in a U-Pb age-constrained section spanning the end-Triassic mass extinction, Levanto, Peru

    Science.gov (United States)

    Yager, J. A.; West, A. J.; Bergquist, B. A.; Thibodeau, A. M.; Corsetti, F. A.; Berelson, W.; Rosas, S.; Bottjer, D. J.

    2017-12-01

    Understanding the causes of the end-Triassic extinction and their potential relationship to Central Atlantic Magmatic Province (CAMP) volcanism necessitates careful correlation of carbon cycle records (largely from marine sections) and volcanism (largely from terrestrial successions) in a robust chronological framework. Here, we report stable carbon isotopes and mercury concentrations and isotopes from the Levanto section in Northern Peru as a putative proxy for CAMP (a large igneous province) in a marine section. Levanto represents deposition well below storm wave base and is lithologically homogenous before, during, and after the end-Triassic extinction interval, making it ideal for detailed chemostratigraphy. Furthermore, abundant intercalated ash beds allow us to correlate mercury concentrations in the marine record directly with CAMP basalt ages, providing a test of the correspondence of mercury anomalies with the eruption of CAMP volcanics. Age dating and C isotope analyses provide an opportunity to explore orbital tuning of the carbon isotope record and ground truth it with existing U-Pb ages from the section, a feature not available in any other marine sections examined to date. The abundance of U-Pb dated ashes in the Levanto section allows us to correlate orbital tuning with other basins, which lack absolute age control, providing a better understanding for the C cycle changes associated with the Triassic-Jurassic boundary.

  19. Oxidative stress modulates the cytokine response of differentiated Th17 and Th1 cells.

    Science.gov (United States)

    Abimannan, Thiruvaimozhi; Peroumal, Doureradjou; Parida, Jyoti R; Barik, Prakash K; Padhan, Prasanta; Devadas, Satish

    2016-10-01

    Reactive oxygen species (ROS) signaling is critical in T helper (Th) cell differentiation; however its role in differentiated Th cell functions is unclear. In this study, we investigated the role of oxidative stress on the effector functions of in vitro differentiated mouse Th17 and Th1 cells or CD4 + T cells from patients with Rheumatoid Arthritis using pro-oxidants plumbagin (PB) and hydrogen peroxide. We found that in mouse Th cells, non-toxic concentration of pro-oxidants inhibited reactivation induced expression of IL-17A in Th17 and IFN-γ in Th1 cells by reducing the expression of their respective TFs, RORγt and T-bet. Interestingly, in both the subsets, PB increased the expression of IL-4 by enhancing reactivation induced ERK1/2 phosphorylation. We further investigated the cytokine modulatory effect of PB on CD4 + T cells isolated from PBMCs of patients with Rheumatoid Arthritis, a well-known Th17 and or Th1 mediated disease. In human CD4 + T cells from Rheumatoid Arthritis patients, PB reduced the frequencies of IL-17A + (Th17), IFN - γ + (Th1) and IL-17A + /IFN - γ + (Th17/1) cells and also inhibited the production of pro-inflammatory cytokines TNF-α and IL-6. N-Acetyl Cysteine (NAC) an antioxidant completely reversed PB mediated cytokine modulatory effects in both mouse and human cells indicating a direct role for ROS. Together our data suggest that oxidative microenvironment can alter cytokine response of terminally differentiated cells and thus altering intracellular ROS could be a potential way to target Th17 and Th1 cells in autoimmune disorders. Copyright © 2016. Published by Elsevier Inc.

  20. Ca. 890 Ma magmatism in the northwest Yangtze block, South China: SIMS U-Pb dating, in-situ Hf-O isotopes, and tectonic implications

    Science.gov (United States)

    Zhou, Jiu-Long; Li, Xian-Hua; Tang, Guo-Qiang; Gao, Bing-Yu; Bao, Zhi-An; Ling, Xiao-Xiao; Wu, Li-Guang; Lu, Kai; Zhu, Yu-Sheng; Liao, Xin

    2018-01-01

    Early Neoproterozoic tectonics of the Yangtze block remains poorly understood because very limited igneous records are available from the time interval of ∼1000-870 Ma. In this paper, our new SIMS U-Pb dating results demonstrate that the Liushudian mafic intrusion and Pinghe alkaline complex in the northwest Yangtze block were emplaced at 888 ± 6 Ma and 891 ± 7 Ma, respectively, representing the products of a ∼890 Ma igneous event. Gabbros from the Liushudian intrusion have rather depleted zircon ɛHf(t) (mean = 10.4) and normal mantle-like zircon δ18O (mean = 5.97‰). Their parental magma was thus probably derived from asthenospheric mantle. Geochemically, these mafic rocks have an affinity to continental flood tholeiitic basalts rather than ocean island basalts, as previously thought. In contrast, an ijolite sample from the Pinghe complex has less depleted zircon ɛHf(t) (mean = 5.7) and anomalously high zircon and apatite δ18O (mean = 13.76‰ and 13.80‰, respectively). Such a characteristic δ18O signal, among the highest yet known for igneous zircons, could be either inherited from a magma source in metasomatized lithospheric mantle or acquired by assimilation of high-δ18O supracrustal materials (e.g., limestone, chert) during magma evolution. An intra-plate extensional environment is suggested for the ∼890 Ma igneous event in the northwest Yangtze block, although it is as yet unclear whether this igneous event is related to a mantle plume or not. It could be concluded that magmatism on the western periphery of the Yangtze block was not shut down between ∼1000 and ∼870 Ma, and the ∼890 Ma intra-plate igneous event may mark either the onset of Neoproterozoic continental rifting or the ending of Late Mesoproterozoic to Early Neoproterozoic lithospheric extension.

  1. The Pan-African Kekem gabbro-norite (West-Cameroon), U-Pb zircon age, geochemistry and Sr-Nd isotopes: Geodynamical implication for the evolution of the Central African fold belt

    Science.gov (United States)

    Kwékam, Maurice; Affaton, Pascal; Bruguier, Olivier; Liégeois, Jean-Paul; Hartmann, Gerald; Njonfang, Emmanuel

    2013-08-01

    The Kekem shoshonitic gabbro-norite association is part of the high-K calc-alkaline (HKCA) post-collisional magmatism, a major feature of the Pan-African Belt in Cameroon. LA-ICP-MS U-Pb zircon analyses provide an age of 576 ± 4 Ma for the Kekem complex. This age is interpreted as dating the emplacement of the massif during the waning stage of the Pan-African orogeny. The latter is related to dextral movements along the Central Cameroon Shear Zone (CCSZ). The REE patterns display enriched LREE (LaN/YbN = 14.2-23.5) while HREE present a nearly flat profile (DyN/YbN = 1.3-1.7), and the La/Sm and Sm/Yb ratios led to propose that the Kekem gabbro-norites have been derived from the partial melting of a garnet-spinel lherzolite mantle source. The negative Nb-Ta and Ti anomalies and the positive Pb anomalies indicate that this mantle source was modified by contribution of a subduction-related material. The low Ce/Pb (2.6-10.4) and Th/Yb ratios associated to high Ba/La ratios, indicate that source enrichment could be related to slab derived fluids. As a whole, the Kekem geochemical features suggest that primary gabbro-noritic magmas derived from a subduction-modified mantle source (metasomatised lithospheric mantle). Moderately high 86Sr/87Sr initial ratios (0.7068-0.7082), low ɛNd (-5 to -9) and old Nd TDM model ages (1.6-1.8 Ga) are interpreted to result from contamination of Neoproterozoic mantle by the Paleoproterozoic crust. The ca. 576 Ma movements along the CCSZ are related to a Neoproterozoic metacratonization of the northern margin of the Congo craton during the Pan-African orogeny. This metacratonization led to vertical planar lithospheric delamination along lithospheric transcurrent faults, asthenospheric uprise and partial melting of the Paleoproterozoic lithospheric mantle.

  2. Astronomical dating in the 19th century

    Science.gov (United States)

    Hilgen, Frederik J.

    2010-01-01

    Today astronomical tuning is widely accepted as numerical dating method after having revolutionised the age calibration of the geological archive and time scale over the last decades. However, its origin is not well known and tracing its roots is important especially from a science historic perspective. Astronomical tuning developed in consequence of the astronomical theory of the ice ages and was repeatedly used in the second half of the 19th century before the invention of radio-isotopic dating. Building upon earlier ideas of Joseph Adhémar, James Croll started to formulate his astronomical theory of the ice ages in 1864 according to which precession controlled ice ages occur alternatingly on both hemispheres at times of maximum eccentricity of the Earth's orbit. The publication of these ideas compelled Charles Lyell to revise his Principles of Geology and add Croll's theory, thus providing an alternative to his own geographical cause of the ice ages. Both Croll and Lyell initially tuned the last glacial epoch to the prominent eccentricity maximum 850,000 yr ago. This age was used as starting point by Lyell to calculate an age of 240 million years for the beginning of the Cambrium. But Croll soon revised the tuning to a much younger less prominent eccentricity maximum between 240,000 and 80,000 yr ago. In addition he tuned older glacial deposits of late Miocene and Eocene ages to eccentricity maxima around 800,000 and 2,800,000 yr ago. Archibald and James Geikie were the first to recognize interglacials during the last glacial epoch, as predicted by Croll's theory, and attempted to tune them to precession. Soon after Frank Taylor linked a series of 15 end-moraines left behind by the retreating ice sheet to precession to arrive at a possible age of 300,000 yr for the maximum glaciation. In a classic paper, Axel Blytt (1876) explained the scattered distribution of plant groups in Norway to precession induced alternating rainy and dry periods as recorded by the

  3. Preparation of UO{sub 2}, ThO{sub 2} and (Th,U)O{sub 2} pellets from photochemically-prepared nano-powders

    Energy Technology Data Exchange (ETDEWEB)

    Pavelková, Tereza [Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Břehová 7, 115 19 Praha 1 (Czech Republic); Čuba, Václav, E-mail: vaclav.cuba@fjfi.cvut.cz [Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Břehová 7, 115 19 Praha 1 (Czech Republic); Visser-Týnová, Eva de [Nuclear Research and Consultancy Group (NRG), Research & Innovation, Westerduinweg 3, 1755 LE Petten (Netherlands); Ekberg, Christian [Nuclear Chemistry/Industrial Materials Recycling, Chalmers University of Technology, SE-412 96 Göteborg (Sweden); Persson, Ingmar [Department of Chemistry and Biotechnology, Swedish University of Agricultural Sciences, P.O. Box 7015, SE-750 07 Uppsala (Sweden)

    2016-02-15

    Photochemically-induced preparation of nano-powders of crystalline uranium and/or thorium oxides and their subsequent pelletizing has been investigated. The preparative method was based on the photochemically induced formation of amorphous solid precursors in aqueous solution containing uranyl and/or thorium nitrate and ammonium formate. The EXAFS analyses of the precursors shown that photon irradiation of thorium containing solutions yields a compound with little long-range order but likely “ThO{sub 2} like” and the irradiation of uranium containing solutions yields the mixture of U(IV) and U(VI) compounds. The U-containing precursors were carbon free, thus allowing direct heat treatment in reducing atmosphere without pre-treatment in the air. Subsequent heat treatment of amorphous solid precursors at 300–550 °C yielded nano-crystalline UO{sub 2}, ThO{sub 2} or solid (Th,U)O{sub 2} solutions with high purity, well-developed crystals with linear crystallite size <15 nm. The prepared nano-powders of crystalline oxides were pelletized without any binder (pressure 500 MPa), the green pellets were subsequently sintered at 1300 °C under an Ar:H{sub 2} (20:1) mixture (UO{sub 2} and (Th,U)O{sub 2} pellets) or at 1600 °C in ambient air (ThO{sub 2} pellets). The theoretical density of the sintered pellets varied from 91 to 97%. - Highlights: • Photochemically prepared UO{sub 2}/ThO{sub 2} nano-powders were pelletized. • The nano-powders of crystalline oxides were pelletized without any binder. • Pellets were sintered at 1300 °C (UO{sub 2} and (Th,U)O{sub 2}) or 1600 °C (ThO{sub 2} pellets). • The theoretical density of the sintered pellets varies from 91 to 97%.

  4. Age intercalibration of 40Ar/39Ar sanidine and chemically distinct U/Pb zircon populations from the Alder Creek Rhyolite Quaternary geochronology standard

    DEFF Research Database (Denmark)

    Rivera, Tiffany; Storey, Michael; Schmitz, M. D.

    2013-01-01

    , and have less pronounced positive Ce and negative Eu anomalies, lower incompatible trace element contents, higher TiZR temperatures that range up to 840 °C, and significantly younger dates. The youngest Group A dates yield a weighted mean of 1.1978 ± 0.0046 Ma (2σ, including systematic uncertainties...... with the astronomical age estimate for the Cobb Mountain subchron determined by correlating the oxygen isotope record of the giant piston core MD972143 to the La93(1,1) orbital solution. On the basis of independent radio-isotopic and orbital forcing results, we propose the refined age of 1.1850 ± 0.0016 Ma (2σ external......We report results from a 40Ar/39Ar sanidine and CA-TIMS 238U/206Pb zircon dating study of eruption and crystal residence timescales of the Alder Creek Rhyolite (ACR), California, extruded during the Cobb Mountain normal-polarity subchron (C1r.2n). A 40Ar/39Ar ACR sanidine date of 1.1850 ± 0.0016 Ma...

  5. U-Pb age of granitoid rock from the quarry Dubna Skala - Mala Fatra Mts

    International Nuclear Information System (INIS)

    Cambel, B.; Shcherbak, N.P.; Bartnitsky, E.N.; Stepanyuk, L.M.

    1990-01-01

    The age of tonalite rock from the quarry Dubna Skala in the Mala Fatra mountains was determined by the U-Pb method. The measurements were carried out at the Institute of Geochemistry and Physics of Minerals in Kiev, USSR. The value measured, 353 m.y., is in a rather good agreement with the data obtained by the Rb-Sr method in core mountain ranges of the Western Carpathians. Nevertheless, in comparison with the Rb-Sr isochronal data from similar rocks and from the same regions, U-Pb geochronologic analyses largely give lower ages. So far, no unique explanation of this fact can be offered; apparently, the geochemical properties of the elements concerned play a major role in this. (author). 1 fig., 1 tab., 30 refs

  6. Complexation of Eu(III), Th(IV) and U(VI) by humic substances

    International Nuclear Information System (INIS)

    Moulin, V.; Reiller, P.; Dautel, C.; Plancque, G.; Laszak, I.; Moulin, C.

    1999-01-01

    Complexation of actinides by humic substances has been studied by different techniques depending on the actinide and its oxidation state. For trivalent actinide (using a rare earth element, Eu as an analogue of trivalent actinide), Time-Resolved Laser-Induced Fluorescence (TRLIF) has been retained as a method for direction speciation at low level. By varying pH and physicochemical conditions (absence of carbonate ions) and at fixed ionic strength, it is possible together to identify spectrally and temporally, all the hydroxo and carbonato complexes. This approach has also been retained for U(VI) as a model of hexavalent actinide, for which hydroxo complexes have been characterized by TRLIF (the simple carbonato complexes are not fluorescent). In the case of U(VI), titrations hy humic acids of U(VI) solutions at various pH have allowed to characterize organic complexes formed with U(VI): single complexes (UO 2 HA) and mixed complexes (UO 2 (OH) 3 HA). The impact on U(VI) speciation has then been identified. In the case of Th(IV) as a model of tetravalent actinides, a competitive method has been used to obtain data on the Th-HA system by studying the ternary system silica colloid/HA/Th at constant pH (Schubert method). Apparent interaction constants have been calculated depending on Th hydrolysis constants used. A study of the system Th/HA/silica has a function of pH and for different HA concentrations has shown the strong complexing character of humic acids towards Th in the pH range 4-9. (orig.)

  7. Spatial variability of initial 230Th/ 232Th in modern Porites from the inshore region of the Great Barrier Reef

    Science.gov (United States)

    Clark, Tara R.; Zhao, Jian-xin; Feng, Yue-xing; Done, Terry J.; Jupiter, Stacy; Lough, Janice; Pandolfi, John M.

    2012-02-01

    The main limiting factor in obtaining precise and accurate uranium-series (U-series) ages of corals that lived during the last few hundred years is the ability to constrain and correct for initial thorium-230 ( 230Th 0), which is proportionally much higher in younger samples. This is becoming particularly important in palaeoecological research where accurate chronologies, based on the 230Th chronometer, are required to pinpoint changes in coral community structure and the timing of mortality events in recent time (e.g. since European settlement of northern Australia in the 1850s). In this study, thermal ionisation mass spectrometry (TIMS) U-series dating of 43 samples of known ages collected from living Porites spp. from the far northern, central and southern inshore regions of the Great Barrier Reef (GBR) was performed to spatially constrain initial 230Th/ 232Th ( 230Th/ 232Th 0) variability. In these living Porites corals, the majority of 230Th/ 232Th 0 values fell within error of the conservative bulk Earth 230Th/ 232Th atomic value of 4.3 ± 4.3 × 10 -6 (2 σ) generally assumed for 230Th 0 corrections where the primary source is terrestrially derived. However, the results of this study demonstrate that the accuracy of 230Th ages can be further improved by using locally determined 230Th/ 232Th 0 values for correction, supporting the conclusion made by Shen et al. (2008) for the Western Pacific. Despite samples being taken from regions adjacent to contrasting levels of land modification, no significant differences were found in 230Th/ 232Th 0 between regions exposed to varying levels of sediment during river runoff events. Overall, 39 of the total 43 230Th/ 232Th 0 atomic values measured in samples from inshore reefs across the entire region show a normal distribution ranging from 3.5 ± 1.1 to 8.1 ± 1.1 × 10 -6, with a weighted mean of 5.76 ± 0.34 × 10 -6 (2 σ, MSWD = 8.1). Considering the scatter of the data, the weighted mean value with a more

  8. U-Pb age constraints for the La Tuna Granite and Montevideo Formation (Paleoproterozoic, Uruguay): Unravelling the structure of the Río de la Plata Craton

    Science.gov (United States)

    Pamoukaghlián, Karina; Gaucher, Claudio; Frei, Robert; Poiré, Daniel G.; Chemale, Farid; Frei, Dirk; Will, Thomas M.

    2017-11-01

    The Río de la Plata Craton is a continental block that crops out in Uruguay, eastern Argentina, southernmost Brazil and Paraguay. It comprises in Uruguay the Piedra Alta, Tandilia and Nico Pérez terranes, separated by the Colonia and the Sarandí del Yí megashears. The La Tuna Granite, which intrudes the Araminda metasandstones in the Tandilia Terrane, was considered Cambrian in age and the intruded sandstones were assigned to the Neoproterozoic Piedras de Afilar Formation. We show that the granite is Paleoproterozoic in age and that the host metasandstones do not belong to the Piedras de Afilar Formation, but to the Paleoproterozoic Montevideo Formation. U-Pb LA ICP-MS of zircon ages for the La Tuna Granite yielded a concordant crystallization age of 2156 ± 26 Ma. Furthermore a metamorphic event at 2010 ± 9 Ma is revealed by Pb stepwise leaching dating of monazites. U-Pb detrital zircon ages of the host Araminda metasandstone yield an upper intercept discordia age of 2152 ± 29 Ma, which marks the intrusion of the La Tuna pluton, and which is in accordance with the zircon U-Pb LA ICP MS constraints. A concordant U-Pb detrital zircon age of 2465 ± 40 Ma provides a maximum depositional age constraint for the metapsammites. Comparing quartz arenites of the Ediacaran Piedras de Afilar Formation with the Araminda metaquartzites, we conclude that they are very similar regarding petrology but they differ in age and metamorphic overprint. Detrital zircons in quartz arenites of the Piedras de Afilar Formation show youngest ages of 1.0 Ga. On the other hand, detrital zircons recovered from the Araminda metasandstones and the age of the intruding granite allow interpreting a depositional age between 2465 and 2150 Ma. Nd model ages show crustal residence times in average more than 200 myr older for the Tandilia Terrane both in Uruguay and Argentina, with a significant Neoarchean component, which is lacking in the Piedra Alta Terrane. Whereas the Piedra Alta Terrane was

  9. Thorium utilization in a small long-life HTR. Part I: Th/U MOX fuel blocks

    Energy Technology Data Exchange (ETDEWEB)

    Ding, Ming, E-mail: dingm2005@gmail.com [Delft University of Technology, Reactor Institute Delft, Mekelweg 15, 2629 JB, Delft (Netherlands); Harbin Engineering University, Nantong Street 145, 150001 Harbin (China); Kloosterman, Jan Leen, E-mail: j.l.kloosterman@tudelft.nl [Delft University of Technology, Reactor Institute Delft, Mekelweg 15, 2629 JB, Delft (Netherlands)

    2014-02-15

    Highlights: • We propose thorium MOX (TMOX) fuel blocks for a small block-type HTR. • The TMOX fuel blocks with low-enriched uranium are recommended. • More thorium decreases the reactivity swing of the TMOX fuel blocks. • Thorium reduces the negative temperature coefficient of the TMOX fuel blocks. • Thorium increases the conversion ratio of the TMOX fuel blocks. - Abstract: The U-Battery is a small, long-life and transportable high temperature gas-cooled reactor (HTR). The neutronic features of a typical fuel block with uranium and thorium have been investigated for a application of the U-Battery, by parametrically analyzing the composition and geometric parameters. The type of fuel block is defined as Th/U MOX fuel block because uranium and thorium are assumed to be mixed in each fuel kernel as a form of (Th,U)O{sub 2}. If the initially loaded mass of U-235 is mostly consumed in the early period of the lifetime of Th/U MOX fuel block, low-enriched uranium (LEU) as ignited fuel will not largely reduce the neutronic performance of the Th/U MOX fuel block, compared with high-enriched uranium. The radii of fuel kernels and fuel compacts and packing fraction of TRISO particles determine the atomic ratio of the carbon to heavy metal. When the ratio is smaller than 400, the difference among them due to double heterogeneous effects can be neglected for the Th/U MOX fuel block. In the range between 200 and 400, the reactivity swing of the Th/U MOX fuel block during 10 years is sufficiently small. The magnitude of the negative reactivity temperature coefficients of the Th/U MOX fuel block decreases by 20–45%, which is positive to reduce temperature defect of the Th/U MOX fuel block. The conversion ratio (CR) of the fuel increases from 0.48 (typical CR of the LEU-fueled U-Battery) to 0.78. The larger conversion ratio of the Th/U MOX fuel block reduces the reactivity swing during 10 years for the U-Battery.

  10. U-Series disequilibria, magma petrogenesis and flux rates along the depleted Tonga-Kermadec Island Arc

    International Nuclear Information System (INIS)

    Turner, S.; Hawkesworth, C.; Rogers, N.; Bartlett, J.; Smith, I.; Worthington, T.; Smith, I.; Worthington, T.

    1997-01-01

    The fluid contribution to the lava source has been calculated as -1 ppm Rb, 10 ppm Ba, 0.02 ppm U, 600 ppm K 0.2 ppm Pb and 30 ppm Sr. It has 87 Sr/ 86 Sr = 0.7035 and 206 Pb/ 204 Pb = 18.5 and thus is inferred to be derived from dehydration of the subducting altered oceanic crust. U-Th isotope disequilibria reflect the time since fluid release from the subducting slab and a pseudo-isochron through the lowest ( 230 Th/ 232 Th) lavas constrains this to be ∼ 50 000 yr. Significantly, U-Th isotope data record similar timescales in the Lesser Antilles (∼40 000 yr, Turner et al., 1996) and in the Marianas (30 000 yr, Elliott et al., 1996) which provides encouragement that these data reflect some general aspect of the flux rates beneath island arcs. Large 226 Ra excesses have also been reported from Tonga-Kermadec (( 226 Ra/ 230 Th) = 1.5-3.0, Gill and Williams, 1990). Since 226 Ra will return to secular equilibrium with 230 Th (( 226 Ra/ 230 Th) = 1) within 7500 yr of Ra/Th fractionation the 238 U/ 230 Th and 226 Ra/ 230 Th disequilibria are clearly decoupled (see also Turner et al., 1996). This is an unexpected result and clearly the 226 Ra/ 230 Th disequilibria must have developed after the process responsible for the major U/Th fractionation. It is suggested that Th-Ra isotope disequilibria record the time since partial melting and thus indicate rapid channelled magma ascent. Olivine gabbro xenoliths from Raoul are interpreted as cumulates to their host lavas with which they form zero age U-Th isochrons indicating that minimal time was spent in magma chambers. The subduction signature is not observed in lavas from the back arc island of Niuafo'ou and thus does not penetrate as far 200 km beyond the arc front volcanoes. These were derived from partial melting of fertile peridotite at 130-160 km depth with melt rates around 2 x 10 -4 kg m -3 yr -1 , possibly due to volatiles released from the breakdown of phengite and lawsonite in the underlying slab at 200 km

  11. Separation of uranium in bone rest for their dating

    International Nuclear Information System (INIS)

    Garcia R, G.; Ordonez R, E.; Tenorio, D.; Cordoba, L.

    2001-01-01

    The uranium (U) and thorium (Th) recovery, as fundamental part of the 'uranium serie' technique is an alternative method for dating of bone rests in Mexico. That so is how it has been possible its application for dating geological material and in this research it has been determined the age of some mammoth samples from the basin of Mexico valley. (Author)

  12. U-Pb zircon and biostratigraphic data of high-pressure/low-temperature metamorphic rocks of the Talea Ori: tracking the Paleotethys suture in central Crete, Greece

    Science.gov (United States)

    Zulauf, G.; Dörr, W.; Krahl, J.; Lahaye, Y.; Chatzaras, V.; Xypolias, P.

    2016-10-01

    Inherited deformation microfabrics of detrital quartz grains and U-Pb (Laser ablation (LA)-ICPMS and ID TIMS) ages of detrital zircons separated from the Phyllite-Quartzite Unit s.l. of the Talea Ori, central Crete, suggest strikingly different source rocks. Albite gneiss of the lower Rogdia Beds includes Cambrian and Neoproterozoic rounded zircons with main U-Pb age peaks at 628 and 988 Ma. These and minor Paleoproterozoic and Archean peaks, together with the lack of Variscan-aged and Mesoproterozoic zircons, are similar to the age spectra obtained from the Phyllite-Quartzite Unit s.str. of the Peloponnesus and eastern Crete and from the Taurides. All of these zircons should be derived from the northeastern passive margin of Gondwana (Cimmeria). Metatuffites of the uppermost Rogdia Beds and metasandstone of Bali beach, on the other hand, include euhedral detrital zircons displaying a Variscan U-Pb age spectra at ca. 300 Ma with concordia ages at 291 ± 3, 300 ± 1 Ma (Rogdia) and 286 ± 3, 300 ± 3, 313 ± 2 Ma (Bali). Both types of metasediments and their zircons are similar to those of the pre-Alpine basement and overlying Tyros Beds of eastern Crete, revealing a provenance at the southern active margin of Laurasia. Thus, in central Crete the Paleotethys suture should be situated inside the Rogdia Beds. Magmatic zircons separated from a rhyolite boulder of the lower Achlada Beds yielded a concordant U-Pb zircon age at 242 ± 2 Ma placing a maximum age for the deposition of the (meta)conglomerate from which the boulder was collected. This age is compatible with an Olenekian-early Anisian age of the underlying Vasilikon marble suggested by new findings of the foraminifera Meandrospira aff. pusilla. Both the Achlada Beds and the Vasilikon marble can be attributed to the lower Tyros Beds of eastern Crete. The Alpine deformation led to a pervasive mylonitic foliation, which is affecting most of the studied rocks. This foliation results from D2 top

  13. U/Pb zircon dating and Sr and Nd isotope characteristics of Permian volcanism in the Western Pyrenees: the Ossau and Anayet Massif. Datation U/Pb sur zircon et geochimie isotopique Sr et Nd du volcanisme permien des Pyrenees Occidentales (Ossau et Anayet)

    Energy Technology Data Exchange (ETDEWEB)

    Briqueu, L [Montpellier-2 Univ., 34 (France); Innocent, C [Aix-Marseille-3 Univ., 13 - Marseille (France)

    1993-03-01

    Several zircon populations have been extracted from a peraluminous rhyolite and from a dacite which are the rock types characteristic of the first two volcanic phases of the Pic du Midi d'Ossau (Eastern Pyrenees). Using a Concordia Diagram, their U/Pb isotopic study confirms that volcanism started in the Autunian age (272 to 278 My). These two volcanic cycles display initial Sr and Nd isotopic signatures which are comparable, and show a strong crustal imprint. Volcanism subsequently evolves towards an increasingly alkaline composition and the corresponding isotopic characteristics are compatible with a depleted asthenospheric mantle source.

  14. K X-rays and nuclear reaction times in the deep inelastic reactions U+U and U+Pb at 7.5 MeV/amu

    International Nuclear Information System (INIS)

    Stoller, C.

    1985-01-01

    The K-shell ionisation probability of the heavy reaction products emerging from binary deep inelastic collisions of U + U and U + Pb at 7.5 MeV/amu has been measured as a function of the total kinetic energy loss - Q. After subtraction of the ionisation probability due to internal conversion of γ-rays, a strongly Q-dependent Psub(K) is found, in agreement with theoretical predictions relating the change in ionisation probability to the nuclear sticking time. The deduced nuclear reaction times are in qualitative agreement with predictions from nuclear models of deep inelastic reactions. (orig.)

  15. 238U decay series nuclides in the northeastern Arabian Sea: scavenging rates and cycling processes

    International Nuclear Information System (INIS)

    Sarin, M.M.; Krishnaswami, S.; Ramesh, R.; Somayajulu, B.L.K.

    1994-01-01

    The extent of radioactive disequilibrium between 234 Th- 238 U, 210 Po- 210 Pb and 210 Pb- 226 Ra has been measured in four vertical profiles from the northeastern Arabian Sea, a region characterized by oxygen deficient and denitrification layers at intermediate depths. The most common feature of the data is that the dissolved concentrations of the daughter nuclides are considerably less than those of their parents, exceptions being the near equilibrium or excess concentrations of 210 Po (relative to 210 Pb) at ∼ 100 m and that of 210 Pb relative to 226 Ra in surface waters. These results suggest that scavenging of dissolved 234 Th, 210 Po and 210 Pb occurs throughout the water column in the northeastern Arabian Sea. (Author)

  16. U, TH and lanthanides in street soils of Sao Paulo city, Brazil

    International Nuclear Information System (INIS)

    Ticianelli, R.B.; Ribeiro, A.P.; Figueiredo, A.M.G.; Zanh, G.S.

    2013-01-01

    The study of lanthanide distribution in urban environments has become of interest over the last years, due to the increased industrial use of these elements. Sao Paulo is the 6th largest metropolitan region of the world, with about 20 million inhabitants in its metropolitan area, more than 9 million motor vehicles and intense industrial activity. There is little information on U, Th, and lanthanide contents in urban soils, and there are as of yet no reference values for these elements in soils of Sao Paulo city. The present study aimed to determine U, Th and lanthanide concentrations in soils adjacent to avenues of highly dense traffic downtown in Sao Paulo city, to assess their possible sources and potential environmental impacts. The analytical technique employed was Instrumental Neutron Activation Analysis (INAA). Th and U levels ranged from 4.0 to 37.0 mg kg -1 and from 1.6 to 18.7 mg kg -1 , respectively. These values are higher than literature values for U and Th in Brazilian superficial soils. The results obtained for the lanthanides indicate enrichment in La and Ce. However, a possible anthropogenic source should be investigated since high background values of these elements may be associated to the natural geological composition of the soils. (author)

  17. Structure and chemical durability of barium borosilicate glass–ceramics containing zirconolite and titanite crystalline phases

    International Nuclear Information System (INIS)

    Li, Huidong; Wu, Lang; Xu, Dong; Wang, Xin; Teng, Yuancheng; Li, Yuxiang

    2015-01-01

    In order to increase the solubility of actinides in the glass matrix, the effects of CaO, TiO 2 , and ZrSiO 4 addition (abbreviated as CTZ, in the mole ratio of 2:2:1) on crystalline phases, microstructure, and chemical durability of barium borosilicate glass–ceramics were investigated. The results show that the samples possess both zirconolite-2M and titanite phase when the CTZ content is greater than or equal to 45 wt.%. For the glass–ceramics with 45 wt.% CTZ (CTZ-45), only zirconolite-2M phase is observed after annealing at 680–740 °C for 2 h. The CTZ-45 possess zirconolite-2M and titanite phases after annealing at 700 °C first, and then annealing at 900–1050 °C for 2 h. Furthermore, the zirconolite-2M and titanite grains show a strip and brick shape, respectively. The CTZ-45 annealing at 950 °C shows the lower normalized leaching rates of B, Na and Nd when compared to that of CTZ-0 and CTZ-55. - Highlights: • CaO, TiO 2 , ZrSiO 4 (CTZ) as nucleating agents were added to barium borosilicate glass. • The samples with 45–55 wt% CTZ possess CaZrTi 2 O 7 -2M and CaTiSiO 5 crystalline phases. • CTZ-45 (45wt% CTZ) possesses only CaZrTi 2 O 7 -2M phase after annealing at 680–740 °C. • CTZ-45 possesses CaZrTi 2 O 7 -2M and CaTiSiO 5 phases after annealing at 900–1050 °C. • CTZ-45 annealing at 950 °C shows the lower leaching rates of B, Na and Nd than CTZ-0 and CTZ-55.

  18. Fallout isotope chronology of the near-surface sediment record of Lake Bolătău.

    Science.gov (United States)

    Bihari, Árpád; Karlik, Máté; Mîndrescu, Marcel; Szalai, Zoltán; Grădinaru, Ionela; Kern, Zoltán

    2018-01-01

    Fallout isotope ( 210 Pb ex, 137 Cs and 241 Am) based dating has been carried out on the near-surface sediment core collected from Lake Bolătău-Feredeu (Bukovina, Romania). The motivation was to improve the chronology of this recent section in connection with significant fluctuations observed in sediment accumulation rates, particle size distribution and primordial radioisotope (i.e. 40 K and 232 Th) composition. Previously only an extrapolation of a broad-range OxCal age-depth model, which was based on 8 AMS radiocarbon dates from the deeper part of a parallel sediment sequence and tentatively validated for the upper part using the double peaks of the 137 Cs activity concentration distribution, was available for the studied section (1-24 cm). Parallel to the previous 137 Cs measurement, 210 Pb and 226 Ra (for a more detailed, 210 Pb ex -based chronology), 241 Am (for an additional time-marker), as well as 40 K and 232 Th concentrations have also been determined by gamma-spectrometry. In case of the 210 Pb ex -based chronology, due to a large deviation from a pure exponential distribution, the Constant Flux (CF) model has been used for the calculation of sediment ages and accumulation rates. Although the broad-range OxCal and the CF model were broadly similar down to 22 cm, the 210 Pb ex -based ages are clearly superior in terms of uncertainty in the uppermost 12 cm, while the broad-range model has smaller uncertainty below 20 cm (>150 years). The CF model gave an average mass accumulation rate of (0.08 ± 0.03) g cm -2 yr -1 for sections 0-11 cm, and (0.03 ± 0.01) g cm -2 yr -1 for sections 12-22 cm, respectively. Significant changes have been observed in the depth distribution of both the particle size distribution and the elemental/isotopic composition of the sediment record, most likely related to the variation observable in the intensity and volume of precipitation in the catchment. The obtained high-resolution records of Lake Bolătău, including

  19. Hematite (U-Th)/He thermochronometry constrains intraplate strike-slip faulting on the Kuh-e-Faghan Fault, central Iran

    Science.gov (United States)

    Calzolari, Gabriele; Rossetti, Federico; Ault, Alexis K.; Lucci, Federico; Olivetti, Valerio; Nozaem, Reza

    2018-03-01

    The Kuh-e-Faghan strike-slip fault system (KFF), located to the northern edge of the Lut Block in central Iran, developed through a Neogene-Quaternary pulsed history of eastward fault propagation and fault-related exhumation. This system is a consequence of the residual stresses transmitted from the Arabia-Eurasia convergent plate boundary. Here we integrate structural and textural analysis with new and previously published apatite fission-track (AFT) and apatite (U-Th)/He (apatite He) results, chlorite thermomentry, and hematite (U-Th)/He data from hematite-coated brittle fault surfaces to constrain the timing of tectonic activity and refine patterns of late Miocene-Pliocene burial and exhumation associated with the propagation of the KFF. Twenty-nine hematite (U-Th)/He (hematite He) dates from three striated hematite coated slip surfaces from the KFF fault core and damage zone yield individual dates from 12-2 Ma. Petrographic analysis and chlorite thermometry of a polyphase, fossil fluid system in the KFF fault core document that fluid circulation and mineralization transitioned from a closed system characterized by pressure solution and calcite growth to an open system characterized by hot hydrothermal (T = 239 ± 10 °C) fluids and hematite formation. Hematite microtextures and grain size analysis reveal primary and secondary syntectonic hematite fabrics, no evidence of hematite comminution and similar hematite He closure temperatures ( 60-85 °C) in each sample. Integration of these results with thermal history modeling of AFT and apatite He data shows that KFF activity in the late Miocene is characterized by an early stage of fault nucleation, fluid circulation, hematite mineralization, and eastward propagation not associated with vertical movement that lasted from 12 to 7 Ma. Hematite He, AFT, and apatite He data track a second phase of fault system activity involving fault-related exhumation initiating at 7 Ma and continuing until present time. Our new data

  20. Glaciation control of melting rates in the mantle: U-Th systematics of young basalts from Southern Siberia and Central Mongolia

    Science.gov (United States)

    Rasskazov, S.; Chebykin, E.

    2012-04-01

    Eastern Sayans, Siberia and Hangay, Central Mongolia are mountainous uplifts effected by Quaternary volcanism, but only the former area was covered by glaciers that were as thick as 500 m. Glaciation time intervals were marked by moraines and sub-glacial hyaloclastite-bearing volcanic edifices, whereas interglacial ones were exhibited by sub-aerial "valley" flows and cinder cones. To estimate temporal variations of maximum rates of melting and mantle upwelling in the glacial and glacial-free areas, we measured radionuclides of the U-Th system for 74 samples of the Middle-Late Pleistocene through Holocene basalts by ICP-MS technique (Chebykin et al. Russian Geol. Geophys. 2004. 45: 539-556) using mass-spectrometer Agilent 7500ce. The obtained U-Th isochron ages for the Pleistocene volcanic units in the age interval of the last 400 Kyr are mostly consistent with results of K-Ar dating. The measured (230Th/238U) ratios for the Holocene basalts from both areas are within the same range of 1.08-1.16 (parentheses denote units of activity), whereas the 50 Kyr lavas yield, respectively, the higher and lower initial (230Th0/238U) ratios (1.18-1.46 and 1.05-1.13). This discrepancy demonstrates contrast maximum rates of melting in conventional garnet peridotite sources. We suggest that this dynamical feature was provided by the abrupt Late Pleistocene deglaciation that caused the mantle decompression expressed by the earlier increasing melting beneath Eastern Sayans than beneath Hangay. In the last 400 Kyr, magmatic liquids from both Eastern Sayans and Hangay showed the overall temporal decreasing (230Th0/238U) (i.e. relative increasing rates of melting and upwelling of the mantle) with the systematically lower isotopic ratios (i.e. increased mantle activity) in the former area than in the latter. The 400 Kyr phonotephrites in Hangay showed elevated concentrations of Th (6-8 ppm) and Th/U (3.7-3.9). The high (230Th0/238U) (4.3-6.0) reflected slow fractional melting

  1. CL-imaging and ion microprobe dating of single zircons from a high-grade rock from the Central Zone, Limpopo Belt, South Africa: Evidence for a single metamorphic event at ˜2.0 Ga

    Science.gov (United States)

    Mouri, H.; Brandl, G.; Whitehouse, M.; de Waal, S.; Guiraud, M.

    2008-02-01

    The combination of ion microprobe dating and cathodoluminescence (CL) imaging of zircons from a high-grade rock from the Central Zone of the Limpopo Belt were used to constrain the age of metamorphic events in the area. Zircon grains extracted from an orthopyroxene-gedrite-bearing granulite were prepared for single crystal CL-imaging and ion microprobe dating. The grains display complex zoning when using SEM-based CL-imaging. A common feature in most grains is the presence of a distinct core with a broken oscillatory zoned structure, which clearly appears to be the remnant of an original grain of igneous origin. This core is overgrown by an unzoned thin rim measuring about 10-30 μm in diameter, which is considered as new zircon growth during a single metamorphic event. Selected domains of the zircon grains were analysed for U, Pb and Th isotopic composition using a CAMECA IMS 1270 ion microprobe (Nordsim facility). Most of the grains define a near-concordant cluster with some evidence of Pb loss. The most concordant ages of the cores yielded a weighted mean 207Pb/ 206Pb age of 2689 ± 15 (2 σ) Ma, interpreted as the age of the protolith of an igneous origin. The unzoned overgrowths of the zircon grains yielded a considerably younger weighted mean 207Pb/ 206Pb age of ˜2006.5 ± 8.0 Ma (2 σ), and these data are interpreted to reflect closely the age of the ubiquitous high-grade metamorphic event in the Central Zone. This study shows clearly, based on both the internal structure of the zircons and the data obtained by ion microprobe dating, that only a single metamorphic event is recorded by the studied 2.69 Ga old rocks, and we found no evidence of an earlier metamorphic event at ˜2.5 Ga as postulated earlier by some workers.

  2. U/Th-isotopes as natural analogues for the mobility of actinides in granitic rocks

    International Nuclear Information System (INIS)

    Mengel, K.; Gerdes, A.

    2001-01-01

    The short-lived decay products of 238 U ( 234 U and 230 Th) can be used as natural analogues for actinides in a hard rock repository. Their mobility in the past may serve as a key for understanding actinide migration in the future. For generally old calcites of the HRL Aespoethe age of disturbance of 238 U/ 234 U and 234 U/ 230 Th activity ratios ranges from 30 000 to 436 000 years at degrees of disturbance ranging from 0.5 to 6.7. The results obtained imply that during the past 440 000 years U was mobile throughout the tunnel sections of the HRL Aespoeinvestigated here. For the FL Grimsel, the disequilibrium states of the 234 U/ 238 U and 230 Th/ 234 U activity ratios in fracture minerals (calcites silicates) also imply that the reactions causing isotopic disturbances have occurred within the past 500 000 years. The U/Th-isotope data of both the samples from the HRL Aespoeand the FL Grimsel have in common the mobilization of U in secondary fracture minerals by migrating solutions within the past 500 000 years. As for the question of a final disposal of radioactive waste in granite host rocks, the transport of U - and thus of similarly behaving actinides - in migrating underground solutions can therefore not be ruled out, if suitable hydraulic systems are considered. (orig.)

  3. 230Th/234U activity ratio in the products from Izu-Bonin island-arc volcanoes

    International Nuclear Information System (INIS)

    Kurihara, Y.; Takahashi, M.; Sato, J.

    2006-01-01

    Magma genesis at subduction zone is generally inferred to be induced by the partial melting of the mantle wedge by the addition of fluid derived from the subducting slab. Uranium-series disequilibria in the volcanic products are a useful tracer to understand various magma processes. Young island-arc volcanic rocks showed the characteristic feature of excess 234 U over 230 Th. Observation was carried out on the radioactive disequilibrium between 234 U and 230 Th in the volcanic products from Asama volcano and Izu-Mariana island-arc volcanoes. Thorium and Uranium in the volcanic rock samples were separated by anion-exchange resin and purified by TEVA·Spec. and UTEVA·Spec. resins, respectively. Purified Th and U were electrodeposited onto a stainless steel planchet for α-ray counting. U-234 and 230 Th in volcanic rock samples were determined by isotope dilution method coupled with α-ray spectrometry. 230 Th/ 234 U activity ratio in the volcanic products from Asama volcano and Izu-Bonin island-arc volcanoes were in radioactive disequilibrium, enriched in 234 U relative to 230 Th, which is often observed for volcanic products from young island-arc volcanic products. (author)

  4. Age of the granitic magmatism and the W-Mo mineralization in skarns of the Seridó belt (NE Brazil) based on zircon U-Pb (SHRIMP) and molybdenite Re-Os dating

    Science.gov (United States)

    Hollanda, Maria Helena B. M. de; Souza Neto, João A.; Archanjo, Carlos J.; Stein, Holly; Maia, Ana C. S.

    2017-11-01

    Over five hundred W-Mo skarns have been reported in the Neoproterozoic Seridó belt in the northeastern Brazil. The origin of these mineralizations has been attributed to metasomatic reactions occuring after the infiltration of hydrothermal fluids that are mostly derived from the plutonic magmatic activity that ranged between approximately 600 and 525 Ma. Here we date molybdenite using N-TIMS on Re-Os analysis of three major scheelite deposits (Brejuí, Bonfim and Bodó) hosted in the skarn horizons of the metasedimentary sequence. Molybdenite is an integral part of the mineralizations that include scheelite in skarns and, in the Bonfim deposit, gold concentrate in late brittle faults. The Re-Os ages are 554 ± 2 Ma (Brejuí), 524 ± 2 Ma (Bonfim) and 510 ± 2 Ma (Bodó). The age of the Brejuí molybdenite, however, appears to be anomalous based on the local geology of the deposit, which is located next to the contact of a batholith dated ca. 575 Ma. In turn, the Bonfim molybdenite yields similar ages in replicated samples with variable high Re contents. New U-Pb SHRIMP ages of four biotite (leuco)granite plutons vary from 577 ± 5 Ma to 526 ± 8 Ma, which overlap with molybdenite crystallization. These results indicate a close connection between the W-Mo mineralizations and the plutonic activity that intruded the belt after the peak HT/LP metamorphism. The latest pulses of felsic magmatism, which were contemporaneous with the emplacement of Be-Ta-Nb-Li pegmatites, therefore constitute a potential guide in the Seridó belt for prospective W-Mo deposits.

  5. Pb migration in the OKLO uranium deposit

    International Nuclear Information System (INIS)

    Gancarz, A.J.; Curtis, D.B.

    1979-01-01

    U-Pb and Pb isotopic data are presented which indicate that Pb is lost from host uraninite by diffusion, and that not only in situ uranogenic Pb but also the initial Pb is lost by diffusion. The conglomerate underlying the U deposit contains excess Pb and is both a transport zone and the repository for the Pb. 2 figures

  6. (U-Th)/He thermochronometry reveals Pleistocene punctuated deformation and synkinematic hematite mineralization in the Mecca Hills, southernmost San Andreas Fault zone

    Science.gov (United States)

    Moser, Amy C.; Evans, James P.; Ault, Alexis K.; Janecke, Susanne U.; Bradbury, Kelly K.

    2017-10-01

    The timing, tempo, and processes of punctuated deformation in strike-slip fault systems are challenging to resolve in the rock record. Faults in the Mecca Hills, adjacent to the southernmost San Andreas Fault, California, accommodate active deformation and exhumation in the Plio-Pleistocene sedimentary rocks and underlying crystalline basement. We document the spatiotemporal patterns of San Andreas Fault-related deformation as recorded in crystalline basement rocks of the Mecca Hills using fault microstructural observations, geochemical data, and hematite (n = 24) and apatite (n = 44) (U-Th)/He (hematite He, apatite He) thermochronometry data. Reproducible mean hematite He dates from minor hematite-coated fault surfaces in the Painted Canyon Fault damage zone range from ∼0.7-0.4 Ma and are younger than ∼1.2 Ma apatite He dates from adjacent crystalline basement host rock. These data reveal concomitant Pleistocene pulses of fault slip, fluid flow, and synkinematic hematite mineralization. Hematite textures, crystal morphology, and hematite He data patterns imply some damage zone deformation occurred via cyclic crack-seal and creep processes. Apatite He data from crystalline basement define distinct date-eU patterns and indicate cooling across discrete fault blocks in the Mecca Hills. Uniform ∼1.2 Ma apatite He dates regardless of eU are located exclusively between the Painted Canyon and Platform faults. Outside of this fault block, samples yield individual apatite He dates from ∼30-1 Ma that define a positive apatite He date-eU correlation. These patterns reveal focused exhumation away from the main trace of the San Andreas Fault at ∼1.2 Ma. Low-temperature thermochronometry of fault-related rocks provides an unprecedented window into the 105-106-yr record of San Andreas Fault-related deformation in the Mecca Hills and documents hematite deformation mechanisms that may be operative in other strike-slip faults world-wide.

  7. Upper Mississippi Pb as a mid-1800s chronostratigraphic marker in sediments from seasonally anoxic lakes in Eastern Canada

    Science.gov (United States)

    Gobeil, Charles; Tessier, André; Couture, Raoul-Marie

    2013-07-01

    Sediment cores from eight headwater lakes located in Southern Québec, Eastern Canada, were analyzed for Pb, stable Pb isotopes, and the radioelements 210Pb, 137Cs, 241Am and 226Ra. The depth profiles of stable Pb isotope ratios show, for the post-19th century period, the influence of several isotopically distinct anthropogenic lead sources, mainly including emissions from two Canadian smelters and from leaded gasoline combustion in Canada and in the United States. A most interesting feature of the profiles, however, is the presence of sharp stable Pb isotope ratio peaks near the depth horizon, where excess 210Pb becomes undetectable. Using a binary mixing model and assuming that natural Pb concentrations and isotopic compositions from the catchment are given by the pre-industrial sediments at the bottom of the cores, we find that a significant part of the anthropogenic Pb supplied to the sediments at this horizon originated from smelting activities in the Upper Mississippi Valley. We assess that the Pb isotope ratio peaks, also observed in the laminated sediments of the Pettaquamscutt Estuary, Rhode Island, USA, are an accurate chronostratigraphic marker for the validation of mid-19th century 210Pb-derived dates. Given that the study lakes are located up to 2000 km from the Mississippi Valley, we conclude that this isotopic Pb signal provides a widely distributed time-marker that is key to validate 210Pb chronologies in environmental archives from Eastern North America.

  8. The fission cross sections of /sup 230/Th, /sup 232/Th, /sup 233/U, /sup 234/U, /sup 236/U, /sup 238/U, /sup 237/Np, /sup 239/Pu and /sup 242/Pu relative /sup 235/U at 14. 74 MeV neutron energy

    Energy Technology Data Exchange (ETDEWEB)

    Meadows, J.W.

    1986-12-01

    The measurement of the fission cross section ratios of nine isotopes relative to /sup 235/U at an average neutron energy of 14.74 MeV is described with particular attention to the determination of corrections and to sources of error. The results are compared to ENDF/B-V and to other measurements of the past decade. The ratio of the neutron induced fission cross section for these isotopes to the fission cross section for /sup 235/U are: /sup 230/Th - 0.290 +- 1.9%; /sup 232/Th - 0.191 +- 1.9%; /sup 233/U - 1.132 +- 0.7%; /sup 234/U - 0.998 +- 1.0%; /sup 236/U - 0.791 +- 1.1%; /sup 238/U - 0.587 +- 1.1%; /sup 237/Np - 1.060 +- 1.4%; /sup 239/Pu - 1.152 +- 1.1%; /sup 242/Pu - 0.967 +- 1.0%. 40 refs., 11 tabs., 9 figs.

  9. Relict zircon U-Pb age and O isotope evidence for reworking of Neoproterozoic crustal rocks in the origin of Triassic S-type granites in South China

    Science.gov (United States)

    Gao, Peng; Zheng, Yong-Fei; Chen, Yi-Xiang; Zhao, Zi-Fu; Xia, Xiao-Ping

    2018-02-01

    Granites derived from partial melting of sedimentary rocks are generally characterized by high δ18O values and abundant relict zircons. Such relict zircons are valuable in tracing the source rocks of granites and the history of crustal anatexis. Here we report in-situ U-Pb ages, O isotopes and trace elements in zircons from Triassic granites in the Zhuguangshan and Jiuzhou regions, which are located in the Nanling Range and the Darongshan area, respectively, in South China. Zircon U-Pb dating yields magma crystallization ages of 236 ± 2 Ma for the Zhuguangshan granites and 246 ± 2 Ma to 252 ± 3 Ma for the Jiuzhou granites. The Triassic syn-magmatic zircons are characterized by high δ18O values of 10.1-11.9‰ in Zhuguangshan and 8.5-13.5‰ in Jiuzhou. The relict zircons show a wide range of U-Pb ages from 315 to 2185 Ma in Zhuguangshan and from 304 to 3121 Ma in Jiuzhou. Nevertheless, a dominant age peak of 700-1000 Ma is prominent in both occurrences, demonstrating that their source rocks were dominated by detrital sediments weathered from Neoproterozoic magmatic rocks. Taking previous results for regional granites together, Neoproterozoic relict zircons show δ18O values in a small range from 5 to 8‰ for the Nanling granites but a large range from 5 to 11‰ for the Darongshan granites. In addition, relict zircons of Paleozoic U-Pb age occur in the two granitic plutons. They exhibit consistently high δ18O values similar to the Triassic syn-magmatic zircons in the host granites. These Paleozoic relict zircons are interpreted as the peritectic product during transient melting of the metasedimentary rocks in response to the intracontinental orogenesis in South China. Therefore, the relict zircons of Neoproterozoic age are directly inherited from the source rocks of S-type granites, and those of Paleozoic age record the transient melting of metasedimentary rocks before intensive melting for granitic magmatism in the Triassic.

  10. U-Th age evidence from carbonate veins for episodic crustal deformation of Central Anatolian Volcanic Province

    Science.gov (United States)

    Karabacak, Volkan; Uysal, I. Tonguç; Ünal-İmer, Ezgi; Mutlu, Halim; Zhao, Jian-xin

    2017-12-01

    Central Anatolia represents one of the most outstanding examples of intraplate deformation related to both continental collision and back-arc extension generating non-uniformly distributed stress fields. In this study, we provide direct field evidence of various stress directions and investigate carbonate-filled fracture systems in the Central Anatolian Volcanic Province using U/Th geochronology and isotope geochemistry for evaluating the episodes of latest volcanic activity under regional stress. Field data reveal two independent fracture systems in the region. Successive fracture development has been controlled by two different volcanic eruption centers (Hasandağ Composite Volcano and Acıgöl Caldera). Trace element, and stable (C and O) and radiogenic (Sr) isotope compositions of carbonate veins indicate different fluid migration pathways for two different fracture systems. The U/Th age data for carbonate veins of two independent fracture systems indicate that the crustal deformation intensified during 7 episodic periods in the last 150 ka. The NNE-trending first fracture system was formed as a result of strain cycles in a period from 149 ± 2.5, through 91 ± 1.5 to 83 ± 2.5 ka BP. Subsequent deformation events represented by the ENE-trending second fracture zone have been triggered during the period of 53 ± 3.5, 44 ± 0.6 and 34 ± 1 ka BP before the first fracture zone resumed the activity at about 4.7 ± 0.15 ka BP. Although further studies are needed to evaluate statistical significance of age correlations, the periods of carbonate precipitation inferred from U-Th age distributions in this study are comparable with the previous dating results of surrounding volcanic eruption events.

  11. Radiological impact due to natural radionuclides (U and Th-isotopes) in soils from Salamanca, Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Mandujano G, C. D.; Sosa, M. [Universidad de Guanajuato, Division de Ciencias e Ingenierias, Loma del Bosque 103, Col. Lomas del Campestre, 37150 Leon, Guanajuato (Mexico); Mantero, J.; Manjon, G.; Garcia T, R. [Universidad de Sevilla, Grupo en Fisica Nuclear Aplicada, Av. Reina Mercedes No. 2, 41012 Sevilla (Spain); Costilla, R., E-mail: cmandujano@fisica.ugto.mx [Universidad de Guanajuato, Division de Ciencias de la Vida, Departamento de Ciencias Ambientales, Ex-Hacienda El Copal Km 9 Irapuato-Silao, 36500 Irapuato, Guanajuato (Mexico)

    2015-10-15

    Full text: Activity concentrations of U ({sup 238}U, {sup 234}U) and Th ({sup 232}Th, {sup 230}Th) radionuclides in samples of superficial urban soils surrounding an industrial complex in Salamanca, Mexico have been determined. Levels of naturally occurring radionuclides (Norm) in the environment may be affected due to the presence of different industrial activities in this zone, representing a potential radiological risk for the population which should be evaluated. Alpha-particle Spectrometry with Pips detectors has been used for the radiometric characterization. A well established radiochemical procedure was used for the isolation of the radionuclides of interest. Alkali fusion for sample digestion, liquid-liquid extraction with Tbp (tri-butyl-phosphate) for U and Th isolation and electrodeposition in stainless steel dishes for measurement conditioning has been used. The results cover the ranges of 10-42, 12-60, 12-52 and 11-51 Bq·kg{sup -1} for {sup 238}U, {sup 234}U, {sup 230}Th, and {sup 232}Th respectively, being not observed any clear anthropogenic increments in relation with the values normally found in unaffected soils. Although there is disequilibrium between U isotopes and {sup 230}Th in some soil samples, it can be attributed to natural processes. The radiological impact of the industrial activities in the surrounding soils can be then evaluated as very low. Hence, from the Radiological Protection point of view, the soils studied do not represent a radiological risk for the health of the population. (Author)

  12. Intercomparison of radionuclide measurements in marine sediment sample IAEA-368

    International Nuclear Information System (INIS)

    Ballestra, S.; Lopez, J.J.; Gastaud, J.; Parsi, P.; Vas, D.; Noshkin, V.

    1991-08-01

    The results of an intercomparison exercise on a Pacific Ocean sediment sample, IAEA-368, designed for the determination of artificial and natural radionuclides levels, are reported. The data from 89 laboratories representing 37 countries have been evaluated. The following are the recommended values, with confidence intervals, for 60 Co, 155 Eu, 210 7Pb, 226 Ra, 238 U, 238 Pu and 239+240 Pu (Reference date: 1 January 1990). Information values for 40 K, 90 Sr, 137 Cs, 228 Th, 230 Th, 232 Th, 234 U, 235 U and 241 Am are also reported. (author)

  13. Zircon U-Pb dating of Maherabad porphyry copper-gold prospect area: evidence for a late Eocene porphyry-related metallogenic epoch in east of Iran

    Directory of Open Access Journals (Sweden)

    Azadeh Malekzadeh Shafaroudi

    2011-04-01

    Full Text Available Eastern Iran has great potential for porphyry copper deposits, as a result of its past subduction zone tectonic setting that lead to extensive alkaline to calc-alkaline magmatic activity in Tertiary time. Maherabad is the first porphyry Cu-Au prospecting area which is discovered in eastern Iran. This is related to a succession o f monzonitic to dioritic porphyries stocks that were emplaced within volcanic rocks. Monzonitic porphyries have basic role in mineralization. Hydrothermal alteration zones are well developed including potassic, sericitic-potassic, quartz-sericite-carbonate-pyrite, quartz-carbonate-pyrite, silicified-propylitic, propylitic, carbonate and silicified zones. Mineralization occurs as Disseminated, stockwork and hydrothermal breccia. Based on early stage of exploration, Cu is between 179- 6830 ppm (ave. 3200 ppm and Au is up to 1000 ppb (ave. 570 ppb. This prospect is gold- rich porphyry copper deposit. Laser-ablation U-Pb dating of two samples from ore-related intrusive rocks indicate that these two monzonitic porphyries crystallized at 39.0 ± 0.8 Ma to 38.2 ± 0.8 Ma, within a short time span of less than ca. 1 Ma during the middle Eocene. This provides the first precise ages for metallogenic episode of porphyry-type mineralization. Also, the initial 87Sr/86Sr and (143Nd/144Ndi was recalculated to an age of 39 Ma. Initial 87Sr/86Sr ratios for monzonitic rocks are 0.7047-0.7048. The (143Nd/144Ndi isotope composition are 0.512694-0.512713. Initial ε Nd isotope values 1.45-1.81. Based on isotopic data the magma had originated beyond the continental crust. The study will be used for tectonic-magmatic setting and evolution of eastern Iran. Keywords: Lut block, Middle Eocene, Zircon, Geochronology, Laser ablation ICP-MS,

  14. Radionuclides (40K, 232Th and 238U) and Heavy Metals (Cr, Ni, Cu, Zn, As and Pb) Distribution Assessment at Renggam Landfill, Simpang Renggam, Johor, Malaysia

    Science.gov (United States)

    Zaidi, E.; FahrulRazi, MJ; Azhar, ATS; Hazreek, ZAM; Shakila, A.; Norshuhaila, MS; Omeje, M.

    2017-08-01

    The assessment of radioactivity levels and the distribution of heavy metals in soil samples at CEP Farm landfill, Renggam in Johor State was to determine the activity concentrations of naturally occurring radionuclides and heavy metal concentrations of this landfill. The background radiation was monitored to estimate the exposure level. The activity concentrations of radionuclides in soil samples were determined using HPGe gamma ray spectroscopy whereas the heavy metal concentration was measured using X-RF analysis. The mean exposure rate at the landfill site was 36.2±2.4 μR hr-1 and the annual effective dose rate at the landfill site was 3.19 ± 0.22 mSv yr-1. However, residential area has lower mean exposure dose rate of about 16.33±0.72 μR hr-1 and has an annual effective dose rate of 1.43±0.06 mSv yr-1 compared to landfill sites. The mean activity concentration of 40K, 238U and 232Th at landfill site were 239.95±15.89 Bq kg-1, 20.90±2.49 Bq kg-1 and 40.61±4.59 Bq kg-1, respectively. For heavy metal compositions, Cr, Ni and Cu have mean concentration of 232±10 ppm, 23±2 ppm, and 46±19 ppm, respectively. Whereas, Zn has concentration of 64±9 ppm and concentration of 12±1 ppm and 71±2 ppm was estimated for As and Pb respectively. The higher activity concentration of 40K down the slope through leaching process whereas the higher activity level of 238U content at the landfill site may be attributed to the soil disruption to local equilibrium.

  15. Element enrichment and U-series isotopic characteristics of the hydrothermal sulfides at Jade site in the Okinawa Trough

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    The geochemical and U-series isotopic characteristics of hydrothermal sulfide samples from the Jade site (127°04.5′E, 27°15′N, water depth 1300-1450 m) at Jade site in the Okinawa Trough were analyzed. In the hydrothermal sulfide samples bearing sulfate (samples HOK1 and HOK2), the LREEs are relatively enriched. All the hydrothermal sulfide samples except HOK1 belong to Zn-rich hydrothermal sulfide. In comparison with Zn-rich hydrothermal sulfides from other fields, the contents of Zn, Pb, Ag, Cd, Au and Hg are higher, the contents of Fe, Al, Cr, Co, Ni, Sr, Te, Cs, Ti and U lower, and the 210Pb radioactivity ratios and 210Pb/Pb ratios very low. In the hydrothermal sulfide mainly composed of sphalerite, the correlations between rare elements Hf and U, and Hf and Mn as well as that between dispersive elements Ga and Zn, are strongly positive; also the contents of Au and Ag are related to Fe-sulfide, because the low temperature promotes enrichment of Au and Ag. Meanwhile, the positive correlations between Fe and Bi and between Zn and Cd are not affected by the change of mineral assemblage. Based on the 210Pb/Pb ratios of hydrothermal sulfide samples (3.99×10-5-5.42×10?5), their U isotopic composition (238U content 1.15-2.53 ppm, 238U activity 1.07-1.87 dpm/g, 234U activity 1.15-2.09 dpm/g and 234U/238U ratio 1.07-1.14) and their 232Th and 230Th contents are at base level, and the chronological age of hydrothermal sulfide at Jade site in the Okinawa Trough is between 200 and 2000 yr.

  16. HPLC method for determination of Th, U and Pu in irradiated (Th,Pu)O{sub 2} using mandelic acid as an eluent

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Pranaw; Paul, Sumana; Jaison, Perumpillil George; Telmore, Vijay Madhukar; Alamelu, Devanathan; Aggarwal, Suresh Kumar [Bhabha Atomic Research Centre, Mumbai (India). Fuel Chemistry Div.

    2014-07-01

    Studies for chromatographic separation of Th, U(VI) and Pu(IV) were carried out using mandelic acid as an eluent. The different chromatographic conditions like concentration of mandelic acid, pH of the mobile phase, presence of MeOH and effect of ion interaction reagent (IIR) were studied. The method was optimized for the separation of Th, U(VI) and Pu(IV). At pH<3.5 of mobile phase, Pu(IV) was more retained compared to U(VI) whereas at pH>3.5, reverse trend was observed. The optimized parameters were employed for the separation and determination of Th, U(VI) and Pu(IV) in a dissolved solution of irradiated (Th,Pu)O{sub 2}. Sample treatment was optimized to minimize loss of Pu and Th during chromatographic determination. Studies were carried out using two IIRs to understand the anomalous chromatographic behavior of Pu(IV). Retention behavior of different oxidation states of Pu viz. Pu(III), Pu(IV) and Pu(VI) was also studied in mandelic acid.

  17. Superconductivity in the U(Th)-Y-Ba-Cu-O systems

    International Nuclear Information System (INIS)

    Qin Qizong; He Adi; Jia Weijie; Ma Lidun; Cheng Huansheng; Hua Zhongyi

    1989-01-01

    High T c superconductivity has been observed both resistively and magnetically in the new U(Th)-Y-Ba-Cu-O systems. The zero resistance temperature of the three samples with nominal composition of U 0.1 Y 1.1 Ba 0.8 Cu O 4-z , U 0.15 Y 1.05 Ba 0.8 Cu 4-z and Th 0.3 Y 0.8 Ba 0.8 Cu 4-z is 87K, 79K and 74K, respectively. The result of ac magnetic susceptibility measurement implies that the superconducting state is realized in the U-doped samples below 90K. The stoichimetry of the U-Y-Ba-Cu O superconductors has the aid of Rutherford backscattering and nuclear reaction 16 O(d, p) 17 O. The analytical results show that the 'real composition' of somples may be different from that of the nomial composition. The X ray diffraction analysis of the U-Y-Ba-Cu-O system shows that none of the peaks can be fitted to the uranium oxides and the other raw materiale structure, and its pattern may be attributed to new multiple phases with structure different from the known singlephase superconducting oxides

  18. Structural observations and U-Pb mineral ages from igneous rocks at the Archaean-Palaeoproterozoic boundary in the Salahmi Schist Belt, central Finland: constraints on tectonic evolution

    Directory of Open Access Journals (Sweden)

    Pietikäinen, K.

    1999-06-01

    Full Text Available The study area in Vieremä, central Finland, contains part of Archaean-Palaeoproterozoic boundary. In the east, the area comprises Archaean gneiss and the Salahmi Schist Belt. The rocks of the schist belt are turbiditic metagreywackes, with well-preserved depositional structures, occurring as Proterozoic wedge-shaped blocks, and staurolite schists, the latter representing higher-strained and metamorphosed equivalents of the metagreywackes. In the west of the area there is an Archaean gneiss block, containing strongly elongated structures, and deformed Svecofennian supracrustal rocks, which are cut by deformed granitoids. These are juxtaposed with the schist belt. The boundaries of these tectonometamorphic blocks are narrow, highly strained mylonites and thrust zones. The metamorphic grade of the supracrustal rocks increases from east to west, the increase being stepwise across the mylonitic block boundaries. The rocks are more deformed from east to west with younger structures overprinting. In the staurolite schists of the Salahmi Schist Belt, the most prominent structure is a lineation (L2 that overprints the bedding and axial plane foliation. In Sorronmäki quarry, at the western boundary of the schist belt, this Palaeoproterozoic lineation dominates all the structures in tonalite gneiss, which gives a U-Pb age of 2731±6 Ma. Southeast of the quarry, at the same boundary, the Salahmi schists have been overturned towards the northeast, suggesting that the Archaean gneiss at Sorronmäki has been thrust towards the northeast over these rocks. In the western part of the study area, the Leppikangas granodiorite that intrudes the Svecofennian supracrustal rocks gives a U-Pb age of 1891+6 Ma. In the granodiorite, a strong lineation formed by the intersection of two foliations, which maybe L2 is associated with thrusting towards the northeast. The monazite age of the Archaean Sorronmäki gneiss is 1817+3 Ma, and the titanite age of the Svecofennian

  19. Consultants' Meeting on Review Benchmarking of Nuclear Data for the Th/U Fuel Cycle. Summary Report

    International Nuclear Information System (INIS)

    Capote Noy, R.

    2011-02-01

    A summary is given of the Consultants' Meeting (CM) on Review and Benchmarking of Nuclear Data for the Th/U Fuel Cycle. An IAEA Coordinated Research Project (CRP) on 'Nuclear Data for Th/U Fuel Cycle' was concluded in 2005. The CRP activities resulted in new evaluated nuclear data files for 232 Th, 231 , 233 Pa (later adopted for the ENDF/B-VII.0 library) and improvements to existing evaluations for 232 , 233 , 234 , 236 U. Available nuclear data evaluations for 230 - 232 Th, 231,233 Pa and 232 , 233 , 234 U were reviewed including ROSFOND2010, CENDL-3.1, JENDL-4, JEFF-3.1.1, MINSKACT, and ENDF/B-VII.0 libraries. Benchmark results of available evaluations for 232 Th and 233 U were also discussed. (author)

  20. U-Pb zircon geochronology and Sm-Nd-Pb isotopic constraint for precambrian plutonic rocks in the northeastern part of Ryeongnam massif, Korea

    International Nuclear Information System (INIS)

    Chang, Ho-Wan

    2003-01-01

    The Ryeongnam massif is composed of Precambrian gneisses, Paleozoic and Mesozoic sedimentary rocks and extensive Triassic-Jurassic plutonic rocks of felsic to mafic composition. In the northeast Ryeongnam massif, the oldest rocks belong to the Sobaegsan gneiss complex, which is composed of orthogneisses, paragneisses and mafic plutonic rocks. U-Pb zircon ages for the felsic and mafic intrusive bodies within the Sobaegsan gneiss complex are: the Icheon granite gneiss, 2357±43 and 2342±47 Ma; the Buncheon granite gneiss, 1963±5 Ma; the Pyeonghae granite gneiss, 1936±21 Ma; the Ogbang amphibolite, 1918±10 Ma; the Imwon leucogranite gneiss, 1826±20 Ma. The Hyeondong biotite schist, which is intruded by the Buncheon granite gneiss and the Ogbang amphibolite, yielded an age of 2271±44 Ma. The Nd-Sm-Pb isotopic data indicate that the felsic plutonic rocks are derived from an older Archean crust. The Nd T DM ages are Archean, and the εNd values are negative for the felsic rocks and positive for the amphibolite. Common Pb isotope compositions also indicate a crustal source for the felsic intrusives. The U-Pb ages of Precambrian rocks of the Ryeongnam massifs are similar to those in the Gyeonggi massif, and may have a similar crustal evolutionary history. The Precambrian rocks of South Korea could be related either to the North China block or to the South China block, as the isotope ages and patterns are not unique to either block. Similarly, a geologic correlation with Japan, although possible, is tenuous at present. (author)