Sample records for ca 3700ma zircons

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

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


    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

  2. Role of CA-EDTA on the Synthesizing Process of Cerate-Zirconate Ceramics Electrolyte

    Sharizal Hasan; Nur Athirah Abdullah; Nafisah Osman


    The role of a combination between citric acid (CA) and ethylenediaminetetra acetic acid (EDTA) as chelating agents in preparation of BaCe0.54Zr0.36Y0.1O2.95 powder by a modified sol-gel method is reported. The precursor solutions were prepared from metal nitrate salts (M+), chelating agents (C), and ethylene glycol (EG) at molar ratio of M+ : C : EG = 3 : 2 : 3. Chemical and phase transformation of samples during thermal decomposition were analyzed by thermogravimetric analysis (TGA) and Four...

  3. Development of mixed conducting dense nickel/Ca-doped lanthanum zirconate cermet for gas separation application

    Highlights: ► Phase pure La1.95Ca0.05Zr2O7-δ (LCZ) material is prepared by combustion synthesis. ► LCZ and Ni-LCZ bulk samples are prepared with theoretical density close to 100%. ► Bulk electrical conductivity ∼400 S/cm is obtained for Ni–LCZ cermet at 750 °C. -- Abstract: La1.95Ca0.05Zr2O7-δ (LCZ) and Ni–LCZ cermet have been prepared by combustion synthesis and conventional solid state mixing methods respectively. Both the materials are sintered in air and controlled atmosphere (5% H2 in Ar). The density obtained for the material sintered at 1400 °C in controlled atmosphere is found to be more than 99.5%. This sintering temperature (1400 °C) is considered to be much lower compared to the conventional sintering temperature. The corresponding total conductivity for such Ni–LCZ cermet materials is ∼400 S/cm measured at 750 °C having 40 vol% of Ni and 60 vol% LCZ.

  4. Isomorphous miscibility in MEO4 (scheelite) - LnVO4 (zircon) systems, where M=Ca, Sr, Ba, Cd, Pb; E=Mo, W; Ln=Y and lanthanides

    Method of X-ray phase analysis was used to study phase relations in MEO4 (scheelite) - LnVO4 (zircon) systems, where M=Ca, Sr, Ba, Cd, Pb; E=Mo, W; Ln=Y, Ce, Nd, Eu. Formation of limited solid solutions M1-xVxO4 was established. Evaluation of isomorphous miscibility in scheelite-zircon systems according to the statements of energy theory of isomorphous miscibility was conducted

  5. Permian U-Pb (CA-TIMS) zircon ages from Australia and China: Constraining the time scale of environmental and biotic change

    Denyszyn, S. W.; Mundil, R.; Metcalfe, I.; He, B.


    In eastern Australia, the interconnected Bowen and Sydney Basins are filled with terrestrial sediments of late Paleozoic to early Mesozoic age. These sedimentary units record significant evolutionary events of eastern Gondwana during the time interval between two major mass extinctions (end Middle Permian and Permian-Triassic), and also provide lithological evidence for the Carboniferous-Permian Late Paleozoic Ice Age of southern Pangea, considered to be divisible into up to seven discrete glaciation events in Australia [e.g., 1]. These glaciations are currently assigned ages that indicate that the last of the glaciations predate the end Middle Permian mass extinction at ca. 260 Ma. However, the estimates for the time and durations are largely based on biostratigraphy and lithostratigraphy that, in the absence of robust and precise radioisotopic ages, are unacceptably fragile for providing an accurate high-resolution framework. Interbedded with the sediments are numerous tuff layers that contain zircon, many of which are associated with extensive coal measures in the Sydney and Bowen Basins. Published SHRIMP U-Pb zircon ages [2, 3] have been shown to be less precise and inaccurate when compared to ages applying the CA-TIMS method to the same horizons. Also within the late Middle Permian, the eruption of the Emeishan flood basalts in SW China has been proposed to have caused the end Middle Permian mass extinction [e.g., 4], though a causal link between these events demands a rigorous test that can only be provided by high-resolution geochronology. We present new U-Pb (CA-TIMS) zircon ages on tuff layers from the Sydney and Bowen Basins, with the purpose of generating a timescale for the Upper Permian of Australia to allow correlation with different parts of the world. Initial results, with permil precision, date a tuff layer within the uppermost Bandanna Fm. to ca. 252 Ma, a tuff within the Moranbah Coal Measures to ca. 256 Ma, and a tuff within the Ingelara Fm. to

  6. Stability and oxygen ionic conductivity of zircon-type Ce 1- xAxVO 4+ δ ( A=Ca, Sr)

    Tsipis, E. V.; Kharton, V. V.; Vyshatko, N. P.; Shaula, A. L.; Frade, J. R.


    Zircon-type Ce 1- xAxVO 4+ δ ( A=Ca, Sr; x=0-0.2) are stable in air up to approximately 1300 K, whilst further heating or reducing oxygen partial pressure leads to formation of A-site deficient zircon and CeO 2- δ phases. The stability boundaries of Ce 1- xAxVO 4+ δ are comparable to those of vanadium dioxide and calcium orthovanadate. At oxygen pressures lower than 10 -15 atm, perovskite-type CeVO 3- δ is formed. The oxygen ion transference numbers of Ce 1- xAxVO 4+ δ, determined by faradaic efficiency measurements in air, vary in the range from 2×10 -4 to 6×10 -3 at 973-1223 K, increasing with temperature. The oxygen ionic conductivity has activation energy of 87-112 kJ/mol and is essentially independent of A-site dopant content. Contrary to the ionic transport, p-type electronic conductivity and Seebeck coefficient of Ce 1- xAxVO 4+ δ are influenced by the divalent cation concentration. The average thermal expansion coefficients of Ce 1- xAxVO 4+ δ, calculated from high-temperature XRD and dilatometric data in air, are (4.7-6.1)×10 -6 K -1.

  7. Stability and oxygen ionic conductivity of zircon-type Ce1-xAxVO4+δ (A=Ca, Sr)

    Zircon-type Ce1-xAxVO4+δ (A=Ca, Sr; x=0-0.2) are stable in air up to approximately 1300 K, whilst further heating or reducing oxygen partial pressure leads to formation of A-site deficient zircon and CeO2-δ phases. The stability boundaries of Ce1-xAxVO4+δ are comparable to those of vanadium dioxide and calcium orthovanadate. At oxygen pressures lower than 10-15 atm, perovskite-type CeVO3-δ is formed. The oxygen ion transference numbers of Ce1-xAxVO4+δ, determined by faradaic efficiency measurements in air, vary in the range from 2x10-4 to 6x10-3 at 973-1223 K, increasing with temperature. The oxygen ionic conductivity has activation energy of 87-112 kJ/mol and is essentially independent of A-site dopant content. Contrary to the ionic transport, p-type electronic conductivity and Seebeck coefficient of Ce1-xAxVO4+δ are influenced by the divalent cation concentration. The average thermal expansion coefficients of Ce1-xAxVO4+δ, calculated from high-temperature XRD and dilatometric data in air, are (4.7-6.1)x10-6 K-1

  8. In situ zircon U-Pb and Hf-O isotopic results for ca. 73 Ma granite in Hainan Island: Implications for the termination of an Andean-type active continental margin in southeast China

    Jiang, Xiao-Yan; Li, Xian-Hua


    We report in the paper integrated analyses of in situ zircon U-Pb ages, Hf-O isotopes, whole-rock geochemistry and Sr-Nd isotopes for the Longlou granite in northern Hainan Island, southeast China. SIMS zircon U-Pb dating results yield a crystallization age of ˜73 Ma for the Longlou granite, which is the youngest granite recognized in southeast China. The granite rocks are characterized by high SiO2 and K2O, weakly peraluminous (A/CNK = 1.04-1.10), depletion in Sr, Ba and high field strength elements (HFSE) and enrichment in LREE and large ion lithophile elements (LILE). Chemical variations of the granite are dominated by fractional crystallization of feldspar, biotite, Ti-Fe oxides and apatite. Their whole-rock initial 87Sr/86Sr ratios (0.7073-0.7107) and ɛNd(t) (-4.6 to -6.6) and zircon ɛHf(t) (-5.0 to 0.8) values are broadly consistent with those of the Late Mesozoic granites in southeast China coast. Zircon δ18O values of 6.9-8.3‰ suggest insignificant involvement of supracrustal materials in the granites. These granites are likely generated by partial melting of medium- to high-K basaltic rocks in an active continental margin related to subduction of the Pacific plate. The ca. 73 Ma Longlou granite is broadly coeval with the Campanian (ca. 80-70 Ma) granitoid rocks in southwest Japan and South Korea, indicating that they might be formed along a common Andean-type active continental margin of east-southeast Asia. Tectonic transition from the Andean-type to the West Pacific-type continental margin of southeast China likely took place at ca.70 Ma, rather than ca. 90-85 Ma as previously thought.

  9. Zircon Recycling in Arc Intrusions

    Miller, J.; Barth, A.; Matzel, J.; Wooden, J.; Burgess, S.


    Recycling of zircon has been well established in arc intrusions and arc volcanoes, but a better understanding of where and how zircons are recycled can help illuminate how arc magma systems are constructed. To that end, we are conducting age, trace element (including Ti-in-zircon temperatures; TzrnTi) and isotopic studies of zircons from the Late Cretaceous (95-85 Ma) Tuolumne Intrusive Suite (TIS) in the Sierra Nevada Batholith (CA). Within the TIS zircons inherited from ancient basement sources and/or distinctly older host rocks are uncommon, but recycled zircon antecrysts from earlier periods of TIS-related magmatism are common and conspicuous in the inner and two most voluminous units of the TIS, the Half Dome and Cathedral Peak Granodiorites. All TIS units have low bulk Zr ([Zr]825°C), [Zr] in the TIS is a factor of 2 to 3 lower than saturation values. Low [Zr] in TIS rocks might be attributed to a very limited supply of zircon in the source, by disequilibrium melting and rapid melt extraction [1], by melting reactions involving formation of other phases that can incorporate appreciable Zr [2], or by removal of zircon at an earlier stage of magma evolution. Based on a preliminary compilation of literature data, low [Zr] is common to Late Cretaceous N.A. Cordilleran granodioritic/tonalitic intrusions (typically Tzrnsat [3]. A corollary is that slightly older zircon antecrysts that are common in the inner units of the TIS could be considered inherited if they are derived from remelting of slightly older intrusions. Remelting at such low temperatures in the arc would require a source of external water. Refs: [1] Sawyer, J.Pet 32:701-738; [2] Fraser et al, Geology 25:607-610; [3] Harrison et al, Geology 35:635- 638

  10. Zircon Saturation Re-Revisited

    Boehnke, P.; Trail, D.; Schmitt, A. K.; Watson, E. B.; Harrison, M.


    Zircon saturation in silicate melts has been utilized for magma thermometry and predicting the survival of zircon xenocrysts in crustal melts for nearly 30 years. The original calibration, which assumed only compositional (M = [2Ca+Na+K]/[AlxSi]) and temperature controls, was bolstered by subsequent experimental investigations and thermometry of volcanic rocks and glasses. These latter studies, while confirming the general predictions of the model, suggested that other environmental parameters (e.g., pressure, H 2O, halogens, [Fe], oxygen fugacity, etc.) might have second-order effects. Given the tremendous advances in micro-analytical capabilities over the intervening three decades, we have returned to this question with a view to obtaining a refined zircon solubility calibration as a function of P, T, [H2O] and FM (= [Na+K+2(Ca+Mg+Fe)]/[AlxSi]). Detailed SEM imaging of the original low-temperature crystallization experiments (1.2-2.1 kbar) revealed limitations of this approach and we chose instead to use a new experimental design in which shattered Mud Tank zircon is infiltrated by melts of selected composition and water contents. 10 kbar hydrothermal experiments (925o and 850oC) were run for sufficiently long durations (2 to 3 days) to ensure microscale diffusive equilibration of Zr released by zircon dissolution into the intercrystalline melt pools. Sectioned run products were analyzed by SIMS ion imaging of selected areas where glass is exposed in close proximity to or surrounded by Mud Tank zircon fragments. Ion imaging has the advantage of permitting high spatial resolution (3 μm) analysis of the glasses allowing assessment of Zr equilibration. Using synthetic glass standards, we found [Zr] in anhydrous glasses to be enhanced by ca. 20% relative to hydrous (at 6 wt.% H2O). Our new experiments and re-analysis of the earlier glasses broadly reproduce the original calibration, albeit with substantially enhanced (factor of five) precision compared to the

  11. Ceramic with zircon coating

    Wang, Hongyu (Inventor)


    An article comprises a silicon-containing substrate and a zircon coating. The article can comprise a silicon carbide/silicon (SiC/Si) substrate, a zircon (ZrSiO.sub.4) intermediate coating and an external environmental/thermal barrier coating.

  12. Alkaline Earth Metal Zirconate Perovskites MZrO3 (M=Ba(2+), Sr(2+), Ca(2+)) Derived from Molecular Precursors and Doped with Eu(3+) Ions.

    Drąg-Jarząbek, Anna; John, Łukasz; Petrus, Rafał; Kosińska-Klähn, Magdalena; Sobota, Piotr


    The effect of alkaline earth metal alkoxides on the protonation of zirconocene dichloride was investigated. This approach enabled the design of compounds with preset molecular structures for generating high-purity binary metal oxide perovskites MZrO3 (M=Ba(2+), Sr(2+), Ca(2+)). Single-source molecular precursors [Ba4 Zr2 (μ6 -O)(μ3 ,η(2)-OR)8 (OR)2(η(2) -HOR)2 (HOR)2 Cl4], [Sr4 Zr2 (μ6 -O)(μ3 ,η(2)-OR)8 (OR)2 (HOR)4 Cl4], [Ca4 Zr2 (μ6-O)(μ3 ,η(2)-OR)8 (OR)2 Cl4], and [Ca6 Zr2 (μ2 ,η(2)-OR)12 (μ-Cl)2 (η(2) -HOR)4 Cl6 ]⋅8 CH2 Cl2 were prepared via elimination of the cyclopentadienyl ring from Cp2 ZrCl2 as CpH in the presence of M(OR)2 and alcohol ROH (ROH=CH3OCH2 CH2OH) as a source of protons. The resulting complexes were characterized by elemental analysis, IR and NMR spectroscopy, and single-crystal X-ray diffraction. The compounds were then thermally decomposed to MCl2 /MZrO3 mixtures. Leaching of MCl2 from the raw powder with deionized water produced highly pure perovskite-like oxide particles of 40-80 nm in size. Luminescence studies on Eu(3+)-doped MZrO3 revealed that the perovskites are attractive host lattices for potential applications in display technology. PMID:26891039

  13. Chemical durability of zircon

    Trocellier, Patrick; Delmas, Robert


    Zircon (ZrSiO 4) exhibits a strong structural affinity for uranium and thorium together with a very high chemical durability. This makes it a potential crystalline host matrix to immobilize actinides issued from separation of nuclear wastes. Irradiation induces amorphization of the crystalline structure (the metamictization process) and thus may decrease the chemical durability of the material. Leaching tests have been conducted on natural zircons from Brazil and Madagascar at 96°C for a period of 1 month, using deionized water. Leachates have been analysed by inductively coupled plasma mass spectrometry (ICP-MS) and UV-visible spectrophotometry. Zircon solid surfaces have been investigated by coupling scanning electron microscopy and X-ray microanalysis (SEM-EDX) with nuclear microprobe analysis ( μPIXE, μRBS and μERDA). From the mass balance between leachates and hydrated surfaces, the probable mechanisms of zircon aqueous alteration are presented and discussed.

  14. Chemical durability of zircon

    Zircon (ZrSiO4) exhibits a strong structural affinity for uranium and thorium together with a very high chemical durability. This makes it a potential crystalline host matrix to immobilize actinides issued from separation of nuclear wastes. Irradiation induces amorphization of the crystalline structure (the metamictization process) and thus may decrease the chemical durability of the material. Leaching tests have been conducted on natural zircons from Brazil and Madagascar at 96 deg. C for a period of 1 month, using deionized water. Leachates have been analysed by inductively coupled plasma mass spectrometry (ICP-MS) and UV-visible spectrophotometry. Zircon solid surfaces have been investigated by coupling scanning electron microscopy and X-ray microanalysis (SEM-EDX) with nuclear microprobe analysis (μPIXE, μRBS and μERDA). From the mass balance between leachates and hydrated surfaces, the probable mechanisms of zircon aqueous alteration are presented and discussed

  15. A Further Investigation of the Exceptional Zircon Aggregate in Lunar Thin Section 73235,82

    Pidgeon, R. T.; Nemchin, a. A.; Meyer, C.


    Introduction: Smith et al. described an exceptional zircon assemblage in thin section 82 from lunar breccia 73235 which, in transmitted light, resembles a cluster of pomegranate seeds, situated in a clast dominated by bytownite (Fig.1). They reported that high-contrast back-scattered electron (BSE) images of the zircon assemblage clearly show an overgrowth around most of the crystals. Most significantly these authors reported that the age of the rims of ca 4.18Ga is 120 million years younger than age of the interiors, dated at ca 4.31Ga. Smith et al. concluded that ca 4.31 billion years ago a relatively large (500+micron) zircon crystallized within a clast of Ca rich plagioclase. The zircon was fractured into numerous smaller crystals and was subsequently overgrown by a second generation of zircon at approximately 4.18Ga.

  16. Trace element and oxygen isotope composition of Hawaiian hotspot zircon

    Vazquez, J. A.; Bindeman, I. N.; Shamberger, P. J.; Hammer, J. E.


    The trace element and isotopic compositions of zircon are increasingly used to delimit the provenance of detrital minerals in sedimentary rocks, as well as the dynamics and timescales of magmagenesis and metamorphism. Numerous studies document the characteristics of zircon hosted by continental and MORB-related rocks, but the characteristics of zircon generated in magmas from oceanic hotspots are relatively unknown. We present the trace element and O-isotope compositions of Hawaiian zircon from gabbroic and dioritic xenoliths sampled by Holocene basalts at Hualalai volcano. The plutonic zircon yield U-Pb and 238U-230Th ages of ca. 250 ka and 40 ka and grew from intrusions of highly fractionated alkalic magma lodged at >10 km depths (Shamberger & Hammer, 2006; Vazquez et al., 2007). Individual Hualalai zircon are euhedral to anhedral with inclusions of feldspars, pyroxenes, and trachytic glass. Zoning apparent in cathodoluminescence images is generally indistinct, but a significant minority of crystals has rims with relatively high luminescence. Ion microprobe analyses of individual zircon crystals reveal trace element zoning that generally correlates with luminescence. Up to 20-fold variation in HREE concentrations, with overall positive correlation between Eu/Eu* and Ti and inverse correlation between Hf and Ti, characterize Hualalai zircon. These relations are similar to those reported for zircon from some felsic suites related by cooling-induced fractionation. Luminescent rims have relatively low REE, Hf, and Y, but have Ti concentrations like their corresponding interiors. Ti-in-zircon thermometry yields temperatures between 800-1000°C after adjustments for sub-unity TiO2 and SiO2 activities using silicate-oxide equilibria. These temperatures are generally consistent with temperatures derived from two-feldspar and glass-pyroxene pairs included by single zircon crystals. Despite compositional differences, zircon interiors and luminescent rims yield 238U-230Th

  17. Zircon decomposition with dolomite in the presence of fluxes

    The process of direct preparation of zirconium dioxide from zircon using natural dolomite as well as effect on the process and quality of the prepared dioxide of the fluxes-calcium salts (CaCl2, CaF2) is investigated. Distribution of the zirconium, silicon and calcium oxides by the products of the reaction depending on ratio of the using reagents is studied

  18. Barium zirconate base ceramics

    The chemical corrosion at high temperatures is a serious problem in the refractory materials field, leading to degradation and bath contamination by elements of the refractory. The main objective of this work was to search for ceramics that could present higher resistance to chemical attack by aggressive molten oxides. The general behaviour of a ceramic material based on barium zirconate (Ba Zr O3) with the addition of different amounts of liquid phase former was investigated. The densification behaviour occurred during different heat treatments, as well as the microstructure development, as a function of the additives and their reactions with the main phase, were observed and are discussed. (author)

  19. Mineral chemistry of a zircon-bearing, composite, veined and metasomatised upper-mantle peridotite xenolith from kimberlite

    Dawson, J. B.; Hill, P. G.; Kinny, P. D.


    Zircon-bearing veins in a harzburgite xenolith from kimberlite have imposed Ca-metasomatism on the harzburgite wall rock, in addition to adding K, Fe, Ti and OH. The zircon, previously dated to have an age similar to that of the xenolith-hosting kimberlite, shows higher Y, Nb, Ba, REE, Th and U contents than other mantle-derived zircons. Peripheral alteration of the zircon to baddeleyite and zirconolite, and alteration of vein ilmenite to perovskite suggest reaction with an evolving carbonatitic kimberlite melt. The high Cr2O3 content (0.77 wt%) of the zirconolite extends the compositional range of terrestrial zirconolite.

  20. Preliminary U-Pb zircon ages of high-grade rocks in southern Kerala, India

    South Kerala in southwestern India offers interesting khondalite-charnockite assemblages suitable for detailed multidisciplinary case studies on granulite petrogenesis. Arrested charnockite formation is also characteristic of the terrain. Absolute ages of the khondalites are poorly constrained; limited U-Pb zircon data for various rock types of south Kerala khondalite belt have been obtained. Zircons from khondalite sensu-stricto and garnet-biotite gneiss of possible sedimentary origin give a concordia upper-intercept apparent age of ca. 2200 Ma, suggesting that the khondalites contain detrital material that is at least early Proterozoic in age; the data yield a lower intercept apparent age of ca. 400-600 Ma, but it is not clear if this represents new zircon growth and episodic Pb loss at that time (preferred) or is an artifact of normal diffusive loss of radiogenenic Pb. Zircons from retrograded granulitic gneisses have zircon upper-intercept apparent ages of ca. 1550 Ma, indicating either a younger protolith age or, more probably, greater radiogenic Pb loss during subsequent migmatite-grade metamorphism that caused retrogression of the granulite. Since all the zircon populations are complex, more detailed analyses will need to be pursued to resolve age relationships of these rocks with greater certainty. Monazite from a retrograded granulitic gneiss, yields a concordant age of ca. 520 Ma; this age is probably related to late Proterozoic-early Cambrian regional thermal event is south Kerala and is correlative with a similar event in Sri Lanka. (author). 25 refs., 4 figs., 1 tab

  1. Phonon dispersion relation in zircon

    The silicate mineral zircon is one of the major constituents of the earth's crust. The low thermal expansion, structural and chemical stability of zircon ZrSiO4 (space group I41/amd; Z=2) enable it as a host material for radioactive elements uranium and thorium in the earth's crust. Phonon spectrum is needed to understand the thermodynamic behaviour of this mineral. Lattice dynamical calculations of the phonon dispersion relation have been carried out and some acoustic phonons of zircon have also been measured

  2. Chemical characteristics of zircon from A-type granites and comparison to zircon of S-type granites

    Breiter, Karel; Lamarão, Claudio Nery; Borges, Régis Munhoz Krás; Dall'Agnol, Roberto


    The trace element content in zircons from A-type granites and rhyolites was investigated by using back-scattered electron images and electron microprobe analyses. The studied Proterozoic (Wiborg batholith, Finland and Pará, Amazonas and Goiás states, Brazil) and Variscan (Krušné Hory/Erzgebirge, Czech Republic and Germany) plutons cover a wide range of rocks, from large rapakivi-textured geochemically primitive plutons to small intrusions of F-, Li-, Sn-, Nb-, Ta-, and U-enriched rare-metal granites. While zircon is one of the first crystallized minerals in less fractionated metaluminous and peraluminous granites, it is a late-crystallized phase in peralkaline granites and in evolved granites that may crystallize during the whole process of magma solidification. The early crystals are included in mica, quartz, and feldspar; the late grains are included in fluorite or cryolite or are interstitial. The zircon in hornblende-biotite and biotite granites from the non-mineralized plutons is poor in minor and trace elements; the zircon in moderately fractionated granite varieties is slightly enriched in Hf, Th, U, Y, and HREEs; whereas the zircon in highly fractionated ore-bearing granites may be strongly enriched in Hf (up to 10 wt.% HfO2), Th (up to 10 wt.% ThO2), U (up to 10 wt.% UO2), Y (up to 12 wt.% Y2O3), Sc (up to 3 wt.% Sc2O3), Nb (up to 5 wt.% Nb2O5), Ta (up to 1 wt.% Ta2O5), W (up to 3 wt.% WO3), F (up to 2.5 wt.% F), P (up to 11 wt.% P2O5), and As (up to 1 wt.% As2O5). Metamictized zircons may also be enriched in Bi, Ca, Fe, and Al. The increase in the Hf content coupled with the decrease in the Zr/Hf value in zircon is one of the most reliable indicators of granitic magma evolution. In the zircon of A-type granites, the Zr/Hf value decreases from 41-67 (porphyritic granite) to 16-19 (equigranular granite) in the Kymi stock, Finland, and from 49-52 (biotite granite) to 18-36 (leucogranite) in the Pedra Branca pluton, Brazil. In the in situ strongly

  3. Composition of the zircon surface

    Composition of functional groups on zircon surface was studied by the methods of potentiometry, diffuse reflectance spectroscopy and analysis of adsorption of organic acids and based. It was ascertained that zircon surface properties are similar to silica ones to a greater extent than those of ZrO2. Composition of zircon surface at pH values ≤ pH0 (where pH0 - point of zero charge of zircon reached at pH 5.9) does not differ from composition of its volumetric phase (ZrO2:SiO2 = 1:1.4), however, at pH > pH0 increase in the share of ≡ ZrOH surface groups occurs

  4. In-situ trace element analyses and Pb-Pb dating of zircons in granulite from Huangtuling, Dabieshan by LAM-ICP-MS

    吴元保; 陈道公; 夏群科; 涂湘林; 程昊; 杨晓志


    It is revealed by CL images that there are multi-stage growth internal structures of zircons in the Huangtuling granulite, including the inherited zircons, protolith zircons, sector and planar zone zircons and retrograde zircons. In-situ trace element compositions and Pb-Pb ages have been analyzed by LAM-ICP-MS. The sector and the planar zone domains show typical trace element characteristics of granulite zircon (low Th, U, Th/U, total REEs, clear negative Eu anomalies, relatively depleted HREE and small differential degree between MREE and HREE, etc.), indicating that they formed during granulite-facies metamorphism. The protolith zircons have trace element characteristics of crustal zircon (high Th, U, Th/U, total REEs and enriched HREEs, etc.). 12 analyzed spots on granulite-facies domains give a weighted mean 207Pb/206Pb age of (2154±26) Ma (MSWD = 3.8), which is the best estimated age of granulite-facies metamorphism of this sample. The weighted mean 207Pb/206Pb age of 5 analyzed spots on protolith zircon domains is (2714 ± 22) Ma (MSWD = 1.4), which represents the protolith forming time. The discovery of ca. 3.4 Ga inherited zircon indicates that there are Palaeoarchean continental materials in this area. The interpretation of formation conditions and the ages of zircons can be constrained by simultaneous in-situ analysis of trace elements and ages.

  5. Detrital Zircon Geochronology of Cretaceous and Paleogene Strata Across the South-Central Alaskan Convergent Margin

    Bradley, Dwight; Haeussler, Peter; O'Sullivan, Paul; Friedman, Rich; Till, Alison; Bradley, Dan; Trop, Jeff


    Talkeetna Mountains (schist of Hatcher Pass) and, immediately to the south, the northernmost sedimentary sequence of the Matanuska forearc basin (Arkose Ridge Formation). Detrital zircons from the Paleogene Arkose Ridge Formation are as young as 61 and 70 Ma; the population is dominated by a single Late Cretaceous peak at 76 Ma; the oldest zircon is 181 Ma. Sedimentological evidence clearly shows that the conglomeratic Arkose Ridge Formation was derived from the Talkeetna Mountains; our detrital zircon data support this inference. Zircons dated at ca. 90 Ma in the Arkose Ridge sample suggest that buried or unmapped plutons of this age may exist in the Talkeetnas. This is a particularly interesting age as it corresponds to the age of the supergiant Pebble gold-molybdenum-copper porphyry prospect near Iliamna and suggests a new area of prospectivity for Pebble-type deposits. The schist of Hatcher Pass, which was previously assigned a Jurassic depositional age, yielded surprisingly young Late Cretaceous detrital zircons, the youngest at 75 Ma. The probability density curve has four Cretaceous peaks from 76 to 102 Ma, a pair of Late Jurassic peaks at 155 and 166 Ma, three Early Jurassic to Late Triassic peaks at 186, 197, and 213 Ma, minor Carboniferous peaks at 303 and 346 Ma, and a minor Paleoproterozoic peak at 1828 Ma. The schist of Hatcher Pass was largely derived from Mesozoic arc sources, most likely the Wrangellia composite terrane, with some contribution from one or more older, inboard sources, probably including the Yukon-Tanana terrane. We postulate that the schist of Hatcher Pass represents metamorphosed rocks of the Valdez Group that were subducted and then exhumed along the Chugach terrane's 'backstop' during Paleogene transtension. Western Alaska Range - Six detrital zircon samples were collected from a little studied belt of turbidites in Tyonek quadrangle on strike with the Kahiltna assemblage of the central Alaska Range. Many of the sandstones ar

  6. Determination of uranium in zircon

    Cuttitta, F.; Daniels, G.J.


    A routine fluorimetric procedure is described for the determination of trace amounts of uranium in zircon. It employs the direct extraction of uranyl nitrate with ethyl acetate using phosphate as a retainer for zirconium. Submicrogram amounts or uranium are separated in the presence of 100,000 times the amount of zirconium. The modified procedure has been worked out using synthetic mixtures of known composition and zircon. Results of analyses have an accuracy of 97-98% of the contained uranium and a standard deviation of less than 2.5%. ?? 1959.

  7. WA zircon undermines major theory

    Analysis of a tiny zircon crystal found in Western Australia suggests the Earth had oceans and continents just 50 million years after a giant impact was supposed to have melted the planet and formed the Moon. The 200-micron crystal comes from ancient rocks in the remote Jack Hills area. Radiometric dating puts its age at 4.404 billion years, more than 100 million years older than the next-oldest known fragment of the Earth. More surprisingly, the ratio of oxygen isotopes indicates the material that formed the zircon had reacted with liquid water - suggesting the Earth had oceans much earlier than anyone had expected. The conventional model is that the top 1000 kilometres of the Earth was molten rock at the time, says John Valley, a geologist at the University of Wisconsin in Madison. The Earth formed 4.55 billion years ago, but the impact of a Mars-sized body about 4.45 billion years ago was thought to have melted the planet again and splashed material into space which formed the Moon. The discovery presents 'real problems' for the lunar impact theory, according to Allan Treiman of the Lunar and Planetary Institute in Houston. On impact. 'an incredible amount of heat gets dumped into the Earth - all the heat of the impact, plus the heat of the object's core' he said. Cooling would take a long time. With only 50 million years between the supposed impact and the time the zircon formed, 'you're running out of time to create the Moon and have the Earth cool down enough to have oceans,' Treiman said. Although a magma ocean might lose heat quickly, cooling would slow once a solid crust covered the liquid. The ancient zircon suggests the Earth's surface was solid rock 4.4 billion years ago, and had even developed continents. Zircons normally form in granites or andesites and these rocks result from the melting of crustal rock and subsequent eruption on continents. The isotope concentration of 180 in the zircon indicates the rocks that melted had previously reacted with

  8. Topological Modeling of Metamict Zircon

    Hobbs, L. W.; Zhang, Y.; Yuan, X.


    Zircon (ZrSiO4) is the most studied metamict mineral and a leading model for candidate ceramic hosts designed to encapsulate highly radioactive nuclear waste and excess plutonium. It is also emblematic of compound oxide ceramics with a potential to phase separate in the amorphized state. Several groups have carried out ab initio or molecular dynamics (MD) simulations of melt-quenched or radiation-disordered zircon. A tendency for silica tetrahedra to polymerize, implying incipient phase separation, has been noted, but adequate descriptors of the amorphous state capable of distinguishing between different disordered arrangements have not been available. This contribution details critical modifications made to empirical potentials used in MD simulations and useful improvements in modeling efficiency that have facilitated constant pressure simulations of quenched and displacement cascade-amorphized zircon. The simulated end- states have been subjected to topological assessment algorithms for enumerating coordinations, bond lengths and bond angles; counting primitive rings and identifying structure-defining local primitive-ring clusters; and assessing degree of coordination-unit polymerization. The topologies of simulated melt, melt-quenched and cascade-amorphized disordered arrangements have been found to be different and distinguishable. A two-body Born-Mayer empirical potential with ZBL short-range repulsive term was fit to major structural, elastic, thermal and dielectric properties of crystalline zircon, but it was noted that the best crystalline fit, with non-stoichiometric partial ion charges, led to unrealistic coordinations in amorphized arrangements and uncontrolled expansions in constant pressure simulations because of silica polymerization. Therefore, stoichiometrically charge-balanced partial charges were instead chosen and optimized; the optimal choice of O-1.2, Si+2.4, Zr+2.4 led to realistic coordinations (Zr 7, Si 4) and well-behaved constant

  9. Surface morphology and reactivity of natural zircon

    Zircon is a mineral known to be highly resistant to weathering. It may also survive to several geological cycles including metamorphism and anatexis. However, in some environments (hydrothermal fluids, tropical soils), zircon may loose its resistance and use of zirconium as an immobile element in weathering mass balance studies has been questioned. In addition, loss of crystal structure due to the accumulation of radiation induced defects, i.e. metamictization, strongly modifies the bulk thermodynamic properties of zircon.As surface properties are known to control the silicate weathering rates and may be different from bulk properties, a detailed study of the surface of zircons from tropical soils and sediments has been undertaken in order to better understand the resistance of zircon to dissolution. Surface chemistry of zircons was probed by Rutherford backscattering analysis whereas their surface morphology was analyzed by Scanning Electron Microscopy and Tapping Mode Atomic Force Microscopy. First results show contrasted surface morphologies depending on the crystallographic nature of the observed face. Concerning the well crystallized zircon, these contrasts can be interpreted from theoretical surface structures. In the case of variably metamict zircon, the metamictization degree can be probed using Raman spectroscopy and is shown to partly control the surface morphology of zircons originating from weathering environments. In both cases, no strong chemical modification was found near the surface of zircon. (authors)

  10. Fission track dating of zircon: a multichronometer

    Scattering in Fission Track ages of zircons of a single rock is possible when they present morphological and geochemical variations, if the greatest care is not taken in the choice of the etching conditions and the counting of tracks. The Fission Track study of two heterogeneous populations of zircons from the Mont Blanc granite and from the Gran Paradiso gneisses allows to show that zircon may work as a multichronometer

  11. Metallic lead nanospheres discovered in ancient zircons.

    Kusiak, Monika A; Dunkley, Daniel J; Wirth, Richard; Whitehouse, Martin J; Wilde, Simon A; Marquardt, Katharina


    Zircon (ZrSiO4) is the most commonly used geochronometer, preserving age and geochemical information through a wide range of geological processes. However, zircon U-Pb geochronology can be affected by redistribution of radiogenic Pb, which is incompatible in the crystal structure. This phenomenon is particularly common in zircon that has experienced ultra-high temperature metamorphism, where ion imaging has revealed submicrometer domains that are sufficiently heterogeneously distributed to severely perturb ages, in some cases yielding apparent Hadean (>4 Ga) ages from younger zircons. Documenting the composition and mineralogy of these Pb-enriched domains is essential for understanding the processes of Pb redistribution in zircon and its effects on geochronology. Using high-resolution scanning transmission electron microscopy, we show that Pb-rich domains previously identified in zircons from East Antarctic granulites are 5-30 nm nanospheres of metallic Pb. They are randomly distributed with respect to zircon crystallinity, and their association with a Ti- and Al-rich silica melt suggests that they represent melt inclusions generated during ultra-high temperature metamorphism. Metallic Pb is exceedingly rare in nature and previously has not been reported in association with high-grade metamorphism. Formation of these metallic nanospheres within annealed zircon effectively halts the loss of radiogenic Pb from zircon. Both the redistribution and phase separation of radiogenic Pb in this manner can compromise the precision and accuracy of U-Pb ages obtained by high spatial resolution methods. PMID:25848043

  12. Radiation damage effects in zircon

    Trachenko, Kostya; Dove, Martin; Salje, Ekhard


    Zircon, ZrSiO_4, is important for geology and geochronology, and has been proposed as a host material to immobilize highly radioactive materials from dismantled weapons and nuclear waste from power stations [1]. In these applications zircon is exposed to alpha-irradiation. Computer simulations have started to be employed to simulate radiation damage in zircon [2], but the origin and microscopic mechanisms of the most important structural changes in zircon - unit cell expansion and large macroscopic swelling at higher doses, strong shear deformation of the crystalline lattice, and polymerization of SiOn units [3], remain unknown. Here, we perform the molecular dynamics simulation of highly energetic recoils in zircon. Basing on the simulation results, we propose the simple picture of the density change in the damaged region that consists of the depleted and densified matter. We find that the experimentally observed structural changes originate from the interaction of the damaged region with the surrounding crystalline lattice: the shear of the lattice around the damaged region causes shear deformation and expansion of the unit cells. The polymers of connected SiOn polyhedra are most commonly present in the densified shell at the periphery of the damaged region. [1] R C Ewing et al, J. Mater. Res. 10, 243 (1995); W J Weber et al, B E Burakov et al, in Scientific Basis for Nuclear Waste Management XIX, 25-32 and 33-40 (Plenum, New York, 1996); R C Ewing, et al in Crystalline Ceramics: Waste Forms for the Disposal of Weapons Plutonium, NATO Workshop Proceedings 65 (Academic Publishers, Dordrecht, The Netherlands, 1996). [2] B Park et al, Phys. Rev. B, 64, 174108 (1-16) (2001); J P Crocombette and D Ghaleb, J. Nucl. Mater., 295, 167 (2001); K Trachenko et al, J. Appl. Phys., 87, 7702 (2000); K Trachenko et al, J. Phys.: Cond. Matt., 13, 1947 (2001). [3] T Murakami et al, Am. Min., 76, 1510 (1991); H D Holland and D Gottfried, Acta Cryst. 8, 291 (1955).; W J Weber, J. Am

  13. Thermal Forensics of Zircons from the Mesoproterozoic Sudbury Impact Structure (ontario, Canada)

    Prado, D.; Mojzsis, S. J.


    The Sudbury Igneous Complex (SIC) forms the central part of the Mesoproterozoic (ca. 1.85 Ga) Sudbury impact structure and comprises three lithological units: norite (bottom), quartz gabbro, and granophyre (top). To determine the precise timing of the impact and the subsequent thermal behavior of the crust to this impact, an experimental approach was formulated to directly assess the associated impact energies by exploiting the crystallo-chemical response of zircon (Zr(SiO4)). The differential (slow) diffusional response of constituent elements (e.g. U, Th, Pb, REEs, Ti) in zircon at different temperatures and time-scales of the thermal pulse associated with impact makes this mineral an ideal recorder of the timing and condition of impact energies. Because titanium concentration in zircon is a function of temperature, we can also use this relationship a useful thermometer to probe time vs. temperature during the impact and its aftermath. Here, we report our studies of individual zircon grains extracted from SIC norite and granophyre drill core samples via standard heavy-mineral techniques (no zircons were found in the quartz gabbro unit). Grains were both hand-picked under an optical microscope and cast in epoxy, or entire heavy-mineral aliquots were cast without bias that arises from hand-picking. Electron imaging was used to identify individual zircons; many of the norite zircons displayed sets of planar deformation features (PDFs) attributable to shock wave deformation from impact, but none of the granophyre zircons displayed such structures. The largest and least altered grains from the sample aliquot we prepared were removed from their mounts and recast in epoxy with standard zircon AS-3 in anticipation of titanium thermometry and uranium-lead geochronology by high-resolution ion microprobe in depth-profile mode. Depth profiling reveals relationships between zircon growth time and the geochemical environment during crystallization and cooling after impact. We

  14. U-Pb age and Hf-O isotopes of detrital zircons from Hainan Island: Implications for Mesozoic subduction models

    Jiang, Xiao-Yan; Li, Xian-Hua; Collins, W. J.; Huang, Hui-Qing


    A compilation of magmatic ages from the Mesozoic South China Block suggests a number of "magmatic quiescence" periods at ca. 205-195 Ma, ca. 150-140 Ma and ca. 125-115 Ma, casting doubt on tectonic models that suggest ongoing Andean-type subduction along the South China continental margin. However, SIMS U-Pb analyses on two detrital zircon samples from the Cretaceous Lumuwan Formation on Hainan Island, southeast China, reveal three major age peaks at ca. 120 Ma, ca. 155 Ma and ca. 235 Ma. Zircons of these ages are mostly euhedral and show typical magmatic oscillatory zoning, suggesting short-distance transport from nearby magmatic sources. The extremely rare occurrence of ca. 120 Ma magmatic records onshore suggests that detrital zircons of this age population may be derived from a source proximal to Hainan Island but presently missing. Therefore, our data provide new evidence for ongoing magmatic activity in late Mesozoic South China. In situ Hf and O isotope analyses of the Mesozoic detrital zircons reveal large variations in both εHf(t) (- 21.2 to 10.5) and δ18O (4.4‰ to 13.6‰) values. A general negative correlation between them suggests the reworking of old supracrustal materials (average crustal residence age of ca. 2.0 Ga) by juvenile mantle-derived magmas. The progression of increasing εHf(t) and decreasing δ18O values of zircons from the Triassic to the Cretaceous suggests progressive crustal growth during the Mesozoic. The results are consistent with hybridization at an active continental margin. We briefly review tectonic models for the Indosinian orogeny and suggest that the petrologic evidence indicates that Mesozoic magmatism was part of the circum-Pacific accretionary orogens that formed along the continental margin of East Asia no later than ca. 250 Ma and continued at least to the late Cretaceous.

  15. Zircon-rutile-ilmenite froth flotation process

    This patent describes a method for separating a mixture of minerals comprising at least zircon, ilmenite and rutile. It comprises adding an acid solution to the mixture to acidify to a pH of between about 2.0 and 6.0; adding starch to the mixture to depress the ilmenite and the rutile; adding a source of fluoride ions to the mixture to provide a negative surface charge on the zircon surface to activate the zircon; adding an amine cationic collector to the mixture to float the activated zircon; subjecting the mixture containing the added acid solution, the fluoride ions, the starch and the cationic collector, to froth flotation; and withdrawing a float product comprising the zircon and a sink product comprising the ilmenite and rutile

  16. Radiation effects in zircon and apatite

    Zircon and apatite form as actinide host phases in several high-level waste forms and have been proposed as host phases for the immobilization of plutonium and other actinides. Self-radiation damage from α-decay of the incorporated Pu (or other actinides) can affect the durability and performance of these actinide-bearing phases. Natural zircons and apatites, with ages up to 4 billion years, provide abundant evidence for their long-term durability because of their wide spread use in geochronology and fission-track dating. Detailed studies of natural zircons and apatites, 238Pu-containing zircon, a 244Cm-containing silicate apatite, and ion-irradiated zircon, natural apatite, and synthetic silicate apatites provide a unique basis for the analysis of α-decay effects over broad time scales. Recent results of some of these studies are presented here

  17. Solidification of simulated actinides by natural zircon

    YANG Jian-Wen; LUO Shang-Geng


    Natural zircon was used as precursor material to produce a zircon waste form bearing 20wt% simulated actinides (Nd2O3 and UO2) through a solid state reaction by a typical synroc fabrication process. The fabricated zircon waste form has relatively good physical properties (density 5.09g/cm3, open porosity 4.0%, Vickers hardness 715kg/mm2). The XRD, SEM/EDS and TEM/EDS analyses indicate that there are zircon phases containing waste elements formed through the reaction. The chemical durability and radiation stability are determined by the MCC-1method and heavy ion irradiation; the results show that the zircon waste form is highly leach resistance and relatively stable under irradiation (amorphous dose 0.7dpa). From this study, the method of using a natural mineral to solidify radioactive waste has proven to be feasible.

  18. Zircon xenocryst resorption and magmatic regrowth at El Chichón Volcano, Chiapas, Mexico

    Pack, Brenda; Schmitt, Axel K.; Roberge, Julie; Tenorio, Felipe Garcia; Damiata, Brian N.


    El Chichón volcano is the only active volcano located within the Chiapanecan Volcanic Arc in southern Mexico, which lies between the Trans-Mexican Volcanic Belt and the Central American Volcanic Arc. Previous studies have shown that ~ 12 eruptions have occurred at El Chichón within the last 8000 years, forming a complex of lava domes with a central crater and surrounding pyroclastic deposits. Here, we report the discovery of zircon in Holocene El Chichón rocks, which were analyzed by high spatial resolution imaging (color cathodoluminescence CCL) and isotopic (secondary ionization mass spectrometry SIMS) methods to resolve core and rim crystallization ages. Pumice samples from five proximal pyroclastic flow and fall-out deposits were collected based on published stratigraphy. Two of the samples were further (re-)classified by new 14C dates. In addition, we sampled two lavas from the 1982 eruption and from remnants of the older Somma lava complex. Zircon crystals were dated using 230Th/238U disequilibrium (U-Th) and U-Pb geochronology. U-Th zircon ages fall between near eruption ages and ca. 84 ka, with overlapping ages in all samples. By contrast, zircon core U-Pb ages range between ca. 290 Ma and 1.9 Ga. These ages are consistent with xenocrystic origins and their heterogeneity indicates derivation from clastic country rocks. Strong age contrasts between inherited xenocrystic and young magmatic domains in individual zircon crystals are evidence for arrested assimilation of crustal rocks where initially zircon-undersaturated magmas cooled rapidly to form a crystal mush or subsolidus amalgamate as a crustally contaminated boundary layer. This layer contributed zircon crystals to eruptible magma during episodic recharge events followed by partial melt extraction, mixing and homogenization. Zircon overgrowths are significantly older than major minerals whose U-series ages and sharp zonation boundaries suggest crystallization only within a few ka before eruption

  19. Interaction of Bi, Pb(2223) precursors with metal zirconates

    The new technique of oxide barriers has significantly increased the transverse resistivity of the sheath material and reduced the ac losses in Ag/Bi, Pb(2223) multifilamentary tapes. In order to find a suitable oxide barrier material and to understand the effects of the barrier on the superconducting filament, we have studied the interaction of Pb-doped Bi(2223) with five different zirconates: BaZrO3, SrZrO3, CaZrO3, PbZrO3 and Sr0.5Ca0.5ZrO3, from different sources. The interaction is studied in three different ways: by directly adding the zirconate to the Bi, Pb(2223) powder, by studying the interactions in diffusion couples and by fabricating Bi, Pb(2223) tapes with these barrier materials and measuring their transport properties. Ultrafine commercial SrZrO3 powder has been found to be a very suitable and low-cost barrier material. (author)

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

    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.; Lin, Y. T.; Liu, Y.; Tang, G. Q.


    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.

  1. Records of magmatic change as preserved in zircon: examples from the Yellowstone Volcanic Field

    Rivera, T. A.


    Zircon crystals have been used as proxies for their host magmatic composition and as records of the evolution and differentiation of silicic magma systems through the use of integrated techniques such as cathodoluminescence imaging, LA-ICPMS trace element analysis, thermometry, and high-precision CA-IDTIMS U/Pb dating. This petrochronologic approach can aid in identifying crystal populations arising from discrete pulses of magmatism, reconstructing the growth histories of those populations, quantifying the chemical evolution of the host magma, and determining the timing and tempo of that chemical evolution. The Yellowstone Volcanic Field hosts both large and small volume silicic eruptions whose zircon records can provide insights to magmatic processes using a petrochronologic approach. Morphological and thermochemical trends preserved in zircon grains extracted from the three Yellowstone super-eruptions and a small volume precursory eruption indicate that magmatism in the volcanic field is punctuated, characterized by numerous pulses of melting, differentiation, and solidification occurring prior to eruption. U/Pb zircon dating constrains magma assembly to geologically short timescales, with populations of earlier solidified zircon incorporated into the nascent magma just prior to eruption. This requires punctuated intervals of high magmatic flux be superimposed on longer durations of a much lower background flux. Thus super-eruptions within the Yellowstone Volcanic Field result from rapid production and evolution of magma, and preceded by periods of smaller volume magma production that undergo similar differentiation processes over comparable timescales.

  2. Thorium-rich zircon from the Idar pegmatite, Sabarkantha district, Gujarat

    Cyrtolite variety of zircon rich in thorium occurs as pockets of radiating, multiple intergrowth crystals in a pegmatite emplaced in the Idar granite, Sabarkantha district, Gujarat. It has a lower specific gravity (3.86-4.4) and micro-hardness (676-835), compared to crystalline zircon (4.71 and 841-1468) respectively. The mineral analysed lower contents of SiO2 (23.89%) and ZrO2 + HfO2 (43.36%), compared to normal zircon, and high contents of ThO2 (5.06%), UO2 (0.74%), rare earth oxides (REO) (7.88%), FeO (4.44%), CaO (1.98%), MnO (1.26%), H2O (7.95%). Accumulated damage to the crystal structure caused by the presence of appreciable amount of radioelements (5.06% ThO2 ad 0.74% UO2) and also REO (7.88%) in the phase, aided in its metamictisation, hydration and alteration resulting in cyrtolite formation. On heating at 900degC the re-crystallised material yielded zircon x-ray pattern. The d spacings, intensities of the reflections obtained and increase in the size of unit cell determined for the specimen, compared to that of standard zircon, matches well with the observations made for similar metamict cyrtolites studied by others. (author)

  3. Zircon dating of oceanic crustal accretion.

    Lissenberg, C Johan; Rioux, Matthew; Shimizu, Nobumichi; Bowring, Samuel A; Mével, Catherine


    Most of Earth's present-day crust formed at mid-ocean ridges. High-precision uranium-lead dating of zircons in gabbros from the Vema Fracture Zone on the Mid-Atlantic Ridge reveals that the crust there grew in a highly regular pattern characterized by shallow melt delivery. Combined with results from previous dating studies, this finding suggests that two distinct modes of crustal accretion occur along slow-spreading ridges. Individual samples record a zircon date range of 90,000 to 235,000 years, which is interpreted to reflect the time scale of zircon crystallization in oceanic plutonic rocks. PMID:19179492

  4. Detrital zircons from the Ordovician rocks of the Pyrenees: Geochronological constraints and provenance

    Margalef, Aina; Castiñeiras, Pedro; Casas, Josep Maria; Navidad, Marina; Liesa, Montserrat; Linnemann, Ulf; Hofmann, Mandy; Gärtner, Andreas


    The first LA-ICP-MS U-Pb detrital zircon ages from quartzites located below (three samples) and above (one sample) the Upper Ordovician unconformity in the Central Pyrenees (the Rabassa Dome, Andorra) were investigated. The maximum depositional age for the Jújols Group, below the unconformity, based on the youngest detrital zircon population, is around 475 Ma (Early Ordovician), whereas for the Bar Quartzite Fm., above the unconformity, the presence of only two zircons of 442 and 443 Ma precludes obtaining a precise maximum sedimentation age. A time gap of ~ 20 million years for the Upper Ordovician unconformity in the Pyrenees can be proposed, similar to that of the Sardic unconformity in Sardinia. The similar age patterns obtained on both sides of the Upper Ordovician unconformity suggest that there was no change in the source area of these series, while the absence of a Middle Ordovician age population may be due to a lack of sedimentation at that time. The four study samples present very similar U-Pb age patterns: the main age populations correspond to Neoproterozoic (Ediacarian-Cryogenian, ca. 550-750 Ma); Grenvillian (Tonian-Stenian, ca. 850-1100 Ma); Paleoproterozoic (Orosirian, ca.1900-2100 Ma) and Neoarchean (ca. 2500-2650 Ma). The similarity with the Sardinian age distribution suggests that these two terranes could share the same source area and that they were paleogeographically close in Ordovician times in front of the Arabian-Nubian Shield.

  5. Metamictization of zircon: Raman spectroscopic study

    Raman spectroscopy of radiation-damaged natural zircon samples shows increased line broadening and shifts of phonon frequencies with increasing radiation dose. Stretching and bending frequencies of SiO4 tetrahedra soften dramatically with increasing radiation damage. The frequency shifts can be used to determine the degree of radiation damage. Broad spectral bands related to Si-O stretching vibrations between 900 and 1000 cm-1 were observed in metamict/amorphous zircon. The radiation-dose-independent spectral profiles and the coexistence of this broad background and relative sharp Raman modes in partially damaged samples indicate that these bands are correlated with amorphous domains in zircon. The spectral profiles of metamict zircon suggest that in comparison with silica, the SiO4 tetrahedra are less polymerized in metamict zircon. This study also shows that ZrO2 and SiO2 are not the principal products of metamictization in zircon. No indication of bulk chemical unmixing of zircon into ZrO2 and SiO2 was found in 26 samples with a large variation of radiation damage (maximum dose: 23.5x1018 α-events g-1). Only one sample showed clearly, in all measured sample areas, extra sharp lines at 146, 260, 312, 460 and 642 cm-1 characteristic of tetragonal ZrO2. The geological (and possibly artificial heating) history of this sample is not known. It is concluded that radiation damage without subsequent high temperature annealing does not cause unmixing of zircon into constituent oxides. (author)

  6. Thermoluminescence of zircon: a kinetic model

    Turkin, AA; Van Es, HJ; Vainshtein, DI; den Hartog, HW


    The mineral zircon, ZrSiO4, belongs to a class of promising materials for geochronometry by means of thermoluminescence (TL) dating. The development of a reliable and reproducible method for TL dating with zircon requires detailed knowledge of the processes taking place during exposure to ionizing radiation, long-term storage, annealing at moderate temperatures and heating at a constant rate (TL measurements). To understand these processes one needs a kinetic model of TL. This paper is devote...

  7. Mineral zircon: A novel thermoluminescence geochronometer

    Van Es, HJ; Vainshtein, DI; De Meijer, RJ; den Hartog, HW; Donoghue, JF; Rozendaal, A.


    Mineral zircon contains trace amounts (typically 10-1000 ppm) of the alpha-emitters uranium and thorium, which irradiate this mineral internally. This outstanding feature of zircon turns out to be extremely useful when this mineral is applied as a thermoluminescence (TL) dating medium, because the build-up of the age-dependent luminescence is dominated by the presence of well-defined internal radioactive sources and the contributions to the dose from external radiation sources are two orders ...

  8. Component geochronology in the polyphase ca. 3920 Ma Acasta Gneiss

    Mojzsis, Stephen J.; Cates, Nicole L.; Caro, Guillaume; Trail, Dustin; Abramov, Oleg; Guitreau, Martin; Blichert-Toft, Janne; Hopkins, Michelle D.; Bleeker, Wouter


    The oldest compiled U–Pb zircon ages for the Acasta Gneiss Complex in the Northwest Territories of Canada span about 4050–3850 Ma; yet older ca. 4200 Ma xenocrystic U–Pb zircon ages have also been reported for this terrane. The AGC expresses at least 25 km2 of outcrop exposure, but only a small subset of this has been documented in the detail required to investigate a complex history and resolve disputes over emplacement ages. To better understand this history, we combined new ion microprobe235,238U–207,206Pb zircon geochronology with whole-rock and zircon rare earth element compositions ([REE]zirc), Ti-in-zircon thermometry (Tixln) and 147Sm–143Nd geochronology for an individual subdivided ∼60 cm2 slab of Acasta banded gneiss comprising five separate lithologic components. Results were compared to other variably deformed granitoid-gneisses and plagioclase-hornblende rocks from elsewhere in the AGC. We show that different gneissic components carry distinct [Th/U]zirc vs. Tixln and [REE]zirc signatures correlative with different zircon U–Pb age populations and WR compositions, but not with 147Sm–143Nd isotope systematics. Modeled  [REE] from lattice-strain theory reconciles only the ca. 3920 Ma zircons with the oldest component that also preserves strong positive Eu∗ anomalies. Magmas which gave rise to the somewhat older (inherited) ca. 4020 Ma AGC zircon age population formed at ∼IW (iron–wüstite) to ca. 3920 Ma emplacement age for the AGC is contemporaneous with bombardment of the inner solar system. Analytical bombardment simulations show that crustal re-working from the impact epoch potentially affected the precursors to the Acasta gneisses.

  9. Component geochronology in the polyphase ca. 3920 Ma Acasta Gneiss

    Mojzsis, Stephen J.; Cates, Nicole L.; Caro, Guillaume; Trail, Dustin; Abramov, Oleg; Guitreau, Martin; Blichert-Toft, Janne; Hopkins, Michelle D.; Bleeker, Wouter


    The oldest compiled U-Pb zircon ages for the Acasta Gneiss Complex in the Northwest Territories of Canada span about 4050-3850 Ma; yet older ca. 4200 Ma xenocrystic U-Pb zircon ages have also been reported for this terrane. The AGC expresses at least 25 km2 of outcrop exposure, but only a small subset of this has been documented in the detail required to investigate a complex history and resolve disputes over emplacement ages. To better understand this history, we combined new ion microprobe 235,238U-207,206Pb zircon geochronology with whole-rock and zircon rare earth element compositions ([REE]zirc), Ti-in-zircon thermometry (Tixln) and 147Sm-143Nd geochronology for an individual subdivided ˜60 cm2 slab of Acasta banded gneiss comprising five separate lithologic components. Results were compared to other variably deformed granitoid-gneisses and plagioclase-hornblende rocks from elsewhere in the AGC. We show that different gneissic components carry distinct [Th/U]zirc vs. Tixln and [REE]zirc signatures correlative with different zircon U-Pb age populations and WR compositions, but not with 147Sm-143Nd isotope systematics. Modeled DWRzircon [REE] from lattice-strain theory reconciles only the ca. 3920 Ma zircons with the oldest component that also preserves strong positive Eu∗ anomalies. Magmas which gave rise to the somewhat older (inherited) ca. 4020 Ma AGC zircon age population formed at ˜IW (iron-wüstite) to ca. 3920 Ma emplacement age for the AGC is contemporaneous with bombardment of the inner solar system. Analytical bombardment simulations show that crustal re-working from the impact epoch potentially affected the precursors to the Acasta gneisses.

  10. Proterozoic-Cambrian detrital zircon and monazite ages from the Anakie lnlier, central Queensland: Grenville and Pacific-Gondwana signatures

    The Anakie Metamorphic Group is a complexly deformed, dominantly metasedimentary succession in central Queensland. Metamorphic cooling is constrained to ca 500 Ma by previously published K-Ar ages. Detrital-zircon SHRIMP U-Pb ages from three samples of greenschist facies quartz-rich psammites (Bathampton Metamorphics), west of Clermont, are predominantly in the age range 1300-1000Ma (65-75%). They show that a Grenville-aged orogenic belt must have existed in northeastern Australia, which is consistent with the discovery of a potential Grenville source farther north. The youngest detrital zircons in these samples are ca 580 Ma, indicating that deposition may have been as old as latest Neoproterozoic. Two samples have been analysed from amphibolite facies pelitic schist from the western part of the inlier (Wynyard Metamorphics). One sample contains detrital monazite with two age components of ca 580-570 Ma and ca 540 Ma. The other sample only has detrital zircons with the youngest component between 510Ma and 700Ma (Pacific-Gondwana component), which is consistent with a Middle Cambrian age for these rocks. These zircons were probably derived from igneous activity associated with rifting events along the Gondwanan passive margin. These constraints confirm correlation of the Anakie Metamorphic Group with latest Neoproterozoic - Cambrian units in the Adelaide Fold Belt of South Australia and the Wonominta Block of western New South Wales. Copyright (2001) Geological Society of Australia

  11. Jurassic zircons from the Southwest Indian Ridge.

    Cheng, Hao; Zhou, Huaiyang; Yang, Qunhui; Zhang, Lingmin; Ji, Fuwu; Dick, Henry


    The existence of ancient rocks in present mid-ocean ridges have long been observed but received less attention. Here we report the discovery of zircons with both reasonably young ages of about 5 Ma and abnormally old ages of approximate 180 Ma from two evolved gabbroic rocks that were dredged from the Southwest Indian Ridge (SWIR) in the Gallieni fracture zone. U-Pb and Lu-Hf isotope analyses of zircons were made using ion probe and conventional laser abrasion directly in petrographic thin sections. Young zircons and their host oxide gabbro have positive Hf isotope compositions (εHf = +15.7-+12.4), suggesting a highly depleted mantle beneath the SWIR. The spread εHf values (from-2.3 to-4.5) of abnormally old zircons, together with the unradiogenic Nd-Hf isotope of the host quartz diorite, appears to suggest an ancient juvenile magmatism along the rifting margin of the southern Gondwana prior to the opening of the Indian Ocean. A convincing explanation for the origin of the unusually old zircons is yet to surface, however, an update of the theory of plate tectonics would be expected with continuing discovery of ancient rocks in the mid-oceanic ridges and abyssal ocean basins. PMID:27185575

  12. Jurassic zircons from the Southwest Indian Ridge

    Cheng, Hao; Zhou, Huaiyang; Yang, Qunhui; Zhang, Lingmin; Ji, Fuwu; Dick, Henry


    The existence of ancient rocks in present mid-ocean ridges have long been observed but received less attention. Here we report the discovery of zircons with both reasonably young ages of about 5 Ma and abnormally old ages of approximate 180 Ma from two evolved gabbroic rocks that were dredged from the Southwest Indian Ridge (SWIR) in the Gallieni fracture zone. U–Pb and Lu–Hf isotope analyses of zircons were made using ion probe and conventional laser abrasion directly in petrographic thin sections. Young zircons and their host oxide gabbro have positive Hf isotope compositions (εHf = +15.7–+12.4), suggesting a highly depleted mantle beneath the SWIR. The spread εHf values (from‑2.3 to‑4.5) of abnormally old zircons, together with the unradiogenic Nd-Hf isotope of the host quartz diorite, appears to suggest an ancient juvenile magmatism along the rifting margin of the southern Gondwana prior to the opening of the Indian Ocean. A convincing explanation for the origin of the unusually old zircons is yet to surface, however, an update of the theory of plate tectonics would be expected with continuing discovery of ancient rocks in the mid-oceanic ridges and abyssal ocean basins.

  13. Radiation damage in zircon and monazite

    Monazite and zircon respond differently to ion irradiation and to thermal and irradiation-enhanced annealing. The damage process (i.e., elastic interactions leading to amorphization) in radioactive minerals (metamictization) is basically the same as for the ion-beam-irradiated samples with the exception of the dose rate which is much lower in the case of natural samples. The crystalline-to-metamict transition in natural samples with different degrees of damage, from almost fully crystalline to completely metamict, is compared to the sequence of microstructures observed for ion-beam-irradiated monazite and zircon. The damage accumulation process, representing the competing effects of radiation-induced structural disorder and subsequent annealing mechanisms (irradiation-enhanced and thermal) occurs at much higher temperatures for zircon than for monazite. The amorphization dose, expressed as displacements per atom, is considerably higher in the natural samples, and the atomic-scale process leading to metamictization appears to develop differently. Ion-beam-induced amorphization data were used to calculate the α-decay-event dose required for amorphization in terms of a critical radionuclide concentration, i.e., the concentration above which a sample of a given age will become metamict at a specific temperature. This equation was applied to estimate the reliability of U-Pb ages, to provide a qualitative estimate of the thermal history of high-U natural zircons, and to predict whether actinide-bearing zircon or monazite nuclear waste forms will become amorphous (metamict) over long timescales

  14. Intrinsic disorders and annealing metamict zircon as wave-guides

    The study of intrinsic disorders in zircon showed that at certain temperature during an annealing process, both Schottky and interstitial disorders would dominate the zircon structure. This time would be the best time to implant relative ions by diffusion, or directly to use an accelerator to implant these ions, then anneal the metamict zircon to tailor the characteristics of the zircon as wave-guides

  15. Detrital zircon U-Pb geochronology, Lu-Hf isotopes and REE geochemistry constrains on the provenance and tectonic setting of Indochina Block in the Paleozoic

    Wang, Ce; Liang, Xinquan; Foster, David A.; Fu, Jiangang; Jiang, Ying; Dong, Chaoge; Zhou, Yun; Wen, Shunv; Van Quynh, Phan


    In situ U-Pb geochronology, Lu-Hf isotopes and REE geochemical analyses of detrital zircons from Cambrian-Devonian sandstones in the Truong Son Belt, central Vietnam, are used to provide the information of provenance and tectonic evolution of the Indochina Block. The combined detrital zircon age spectra of all of the samples ranges from 3699 Ma to 443 Ma and shows with dominant age peaks at ca. 445 Ma and 964 Ma, along with a number of age populations at 618-532 Ma, 1160-1076 Ma, 1454 Ma, 1728 Ma and 2516 Ma. The zircon age populations are similar to those from time equivalent sedimentary sequences in continental blocks disintegrated from the East Gondwana during the Phanerozoic. The younger zircon grains with age peaks at ca. 445 Ma were apparently derived from middle Ordovician-Silurian igneous and metamorphic rocks in Indochina. Zircons with ages older than about 600 Ma were derived from other Gondwana terrains or recycled from the Precambrian basement of the Indochina Block. Similarities in the detrital zircon U-Pb ages suggest that Paleozoic strata in the Indochina, Yangtze, Cathaysia and Tethyan Himalayas has similar provenance. This is consistent with other geological constrains indicating that the Indochina Block was located close to Tethyan Himalaya, northern margin of the India, and northwestern Australia in Gondwana.

  16. Eocene Kashmar granitoids (NE Iran): Petrogenetic constraints from U-Pb zircon geochronology and isotope geochemistry

    Shafaii Moghadam, Hadi; Li, Xian-Hua; Ling, Xiao-Xiao; Santos, Jose F.; Stern, Robert J.; Li, Qiu-Li; Ghorbani, Ghasem


    Kashmar granitoids outcrop for ~ 100 km along the south flank of the Sabzevar ophiolite (NE Iran) and consist of granodiorite and monzogranite along with subordinate quartz monzonite, syenogranite and aplitic dikes. These granitoids intruded Early to Middle Eocene high-K volcanic rocks and can spatially be grouped into eastern and western granitoids. Five samples of granite have identical zircon U-Pb ages of ca. 40-41 Ma. The granitoids have quite high K2O (~ 1.3-5.3 wt.%) and Na2O (~ 1.1-4.6 wt.%) with SiO2 ranging between ~ 62 and 77 wt.%. They are metaluminous to peraluminous, calc-alkaline and I-type in composition. Their chondrite-normalized REE patterns are characterized by LREE enrichment and show slight negative Eu anomalies. Kashmar granitoids have low whole rock εNd (- 0.43 to - 2.3), zircon εHf values (- 1.9 to + 7.2), and somewhat elevated δ18O (+ 6.1 to + 8.7‰) in the range of I-type granites. The Kashmar granitoids show Early Neoproterozoic zircon second-stage Hf and bulk rock Nd model ages at ca. 500-1000 Ma (associated with ca. 640 Ma old inherited zircons). Bulk rock Nd-Sr isotopic modeling suggests that 10-20% assimilation of Cadomian lower crust by juvenile mantle melts and then fractional crystallization (AFC process) can explain the Sr-Nd isotopic compositions of Kashmar granitoids. Kashmar granitoids are products of crustal assimilation by mantle melts associated with extension above the subducting Neotethyan Ocean slab beneath SW Eurasia. Similar subduction-related extension was responsible for the flare-up of Eocene-Oligocene magmatism across Iran, associated with core complex formation in central Iran.

  17. Preparation of zircon nozzle for the Tundish

    Zircon sand of two different particle distribution with 2 percent of ground pyrophyllite were adopted to prepare the dense specimens of the stopper nozzle for the tundish. The molding pressure of 600kg/cm2 brought about the superior properties to those obtained at the pressure of 300kg/cm2, and as the firing temperatures were increased from 1,3500C to 1,6000C, better characteristics resulted. The addition of 2 percent MgCr2O2 to zircon pyrophyllite batch was more effective in corrosion-resistance to the blast furnace-slag. (author)

  18. Precise zircon U-Pb ages from the Marra Mamba iron formation and Wittenoom formation, Hamersley Group, Western Australia

    The Mt Bruce Supergroup of the Pilbara Craton of Western Australia was laid down in the Hamersley Basin, unconformably over a basement of granite-greenstone terrane, and consists of the Fortescue. Hamersley and Turee Creek Groups. The base of the -230 m-thick Marra Mamba Iron Formation, the lowest formation of the Hamersley Group. marks the onset of the major banded iron-formation deposition that characterizes the group. Ion microprobe U-Pb isotope analyses of zircons from a tuff band (NS3) within a high-grade iron orebody in the uppermost (Mt Newman) member show two distinct, and non-overlapping, age populations. Fifteen grains from the younger group of 16 have a pooled age of 2597±5 Ma (95% confidence), interpreted as the age of syndepositional volcanism: individual grains of the older group of 8, with ages between ca 2950 Ma and ca 2820 Ma, are interpreted as xenocrysts derived from basement rocks transected by the rising magma. The conformably overlying Wittenoom Formation, ∼300-600 m thick, consists largely of dolomitic rocks. Zircons from a submarine fallout tuff within the uppermost (Bee Gorge) member also have two non-overlapping zircon age populations. Most of the 23 zircons analysed belong to an older population with near-concordant ages between ca 2750 and ca 2650 Ma., but 12 analysed spots from 7 grains have a pooled age of 2561 ±8 Ma. This is interpreted to be the age of volcanism coeval with deposition. The older zircons were probably derived from tuffs of Fortescue Group age, entrained with the Crystal-rich Tuff ejectamenta during its explosive, probably phreatoplinian, eruption. Copyright (1998) Blackwell Science Asia

  19. Phase relations and conductivity of Sr-zirconates and La-zirconates

    Poulsen, F.W.; Vanderpuil, N.


    The formation of the strontium zirconates SrZrO3, Sr4Zr3O10, Sr3Zr2O7 and Sr2ZrO4, and of the lanthanum zirconates La2Zr2O7 and La2-xYZr2O7 at 1450-degrees-C was investigated by x-ray powder diffraction and DTA. Three different routes of synthesis were tested. In the Sr-zirconate system, single......-C. The conductivity of the Sr-zirconates increases with increasing Sr/Zr ratio. Samples with a nominal composition corresponding to Sr2ZrO4 have a conductivity of 7.5 x 10(-5) and 5.9 x 10(-4) S/cm at 750 and 1000-degrees-C, respectively. For all samples one observes low activation energies for ionic...

  20. Trace Element Zoning and Incipient Metamictization in a Lunar Zircon: Application of Three Microprobe Techniques

    Wopenka, Brigitte; Jollife, Bradley L.; Zinner, Ernst; Kremser, Daniel T.


    We have determined major (Si, Zr, Hf), minor (Al, Y, Fe, P), and trace element (Ca, Sc, Ti, Ba, REE, Th, U) concentrations and Raman spectra of a zoned, 200 microns zircon grain in lunar sample 14161,7069, a quartz monzodiorite breccia collected at the Apollo 14 site. Analyses were obtained on a thin section in situ with an ion microprobe, an electron microprobe, and a laser Raman microprobe. The zircon grain is optically zoned in birefringence, a reflection of variable (incomplete) metamictization resulting from zo- nation in U and Th concentrations. Variations in the concentrations of U and Th correlate strongly with those of other high-field-strength trace elements and with changes in Raman spectral parameters. Concentrations of U and Th range from 21 to 55 ppm and 6 to 31 ppm, respectively, and correlate with lower Raman peak intensities, wider Raman peaks, and shifted Si-O peak positions. Concentrations of heavy rare earth elements range over a factor of three to four and correlate with intensities of fluorescence peaks. Correlated variations in trace element concentrations reflect the original magmatic differentiation of the parental melt approx. 4 b.y. ago. Degradation of the zircon structure, as reflected by the observed Raman spectral parameters, has occurred in this sample over a range of alpha-decay event dose from approx. 5.2 x 10(exp 14) to 1.4 x 10(exp 15) decay events per milligram of zircon, as calculated from the U and Th concentrations. This dose is well below the approx. 10(exp 16) events per milligram cumulative dose that causes complete metamictization and indicates that laser Raman microprobe spectroscopy is an analytical technique that is very sensitive to the radiation-induced damage in zircon.

  1. Zircon ion microprobe dating of high-grade rocks in Sri Lanka

    Kroener, A.; Williams, I.S.; Compston, W.; Baur, N.; Vitanage, P.W.; Perera, L.R.K.


    The high-grade gneisses of Sri Lanka display spectacular in-situ granulitization phenomena similar to those observed in southern India and of current interest for evolutionary models of the lower continental crust. The absolute ages of these rocks are poorly constrained and so, using the SHRIMP ion microprobe, the authors have analyzed small spots on zircons from upper amphibolite to granulite grade quartzitic and pelitic metasediments. Detrital grains from a metaquartzite of the Highland Group preserve premetamorphic U-Pb ages of between 3.17 and 2.4 Ga and indicate derivation of the sediment from an unidentified Archean source terrain. The Pb-loss patterns of these zircons and the other samples suggest severe disturbance at ca 1100 Ma ago, which the authors attribute to high-grade regional metamorphism. Two pelitic gneisses contain detrital zircons with ages up to 2.04 Ga and also record an approx. = 1100 Ma event that is also apparent from metamorphic rims around old cores and new zircon growth. A granite intrusive into the Highland Group granulites records an emplacement age of 1000-1100 Ma as well as metamorphic disturbance some 550 Ma ago but also contains older, crustally derived xenocrysts. Zircons from a metaquartzite xenolith within the granitoid Vijayan Complex are not older than approx. 1100 Ma; therefore the Vijayan is neither Archean in age nor acted as basement to the Highland Group, as previously proposed. The authors suggest that the Vijayan Complex formed significantly later than the Highland Group and that the two units were brought into contact through post-1.1 Ga thrusting. Although the granulitization phenomena in India and Sri Lanka are similar, the granulite event in Sri Lanka is not Archean in age but took place in the late Proterozoic.

  2. Going back in time with zircon

    Uranium-lead age dating, with zircon as the agent is the most recent advance in exploring rocks and minerals to define their stratigraphic sequence. The authors believe it will have a tremendous effect on the accurate mapping of the earth's mineral resources, including those of Antartica; indeed, even of the moon

  3. Paleoproterozoic mojaveprovince in northwestern Mexico? Isotopic and U-Pb zircon geochronologic studies of precambrian and Cambrian crystalline and sedimentary rocks, Caborca, Sonora

    Lang, Farmer G.; Bowring, S.A.; Matzel, J.; Maldonado, G.E.; Fedo, C.; Wooden, J.


    Whole-rock Nd isotopic data and U-Pb zircon geochronology from Precambrian crystalline rocks in the Caborca area, northern Sonora, reveal that these rocks are most likely a segment of the Paleoproterozoic Mojave province. Supporting this conclusion are the observations that paragneiss from the ??? 1.75 Ga Bamori Complex has a 2.4 Ga Nd model age and contains detrital zircons ranging in age from Paleo- proterozoic (1.75 Ga) to Archean (3.2 Ga). Paragneisses with similar age and isotopic characteristics occur in the Mojave province in southern California. In addition, "A-type" granite exposed at the southern end of Cerro Rajon has ca 2.0 Ga Nd model age and a U-Pb zircon age of 1.71 Ga, which are similar to those of Paleoproterozoic granites in the Mojave province. Unlike the U.S. Mojave province, the Caborcan crust contains ca. 1.1 Ga granite (Aibo Granite), which our new Nd isotopic data suggest is largely the product of anatexis of the local Precambrian basement. Detrital zircons from Neoproterozoic to early Cambrian miogeoclinal arenites at Caborca show dominant populations ca. 1.7 Ga, ca. 1.4 Ga, and ca. 1.1 Ga, with subordinate Early Cambrian and Archean zircons. These zircons were likely derived predominately from North American crust to the east and northeast, and not from the underlying Caborcan basement. The general age and isotopic similarities between Mojave province basement and overlying miogeoclinal sedimentary rocks in Sonora and southern California is necessary, but not sufficient, proof of the hypothesis that Sonoran crust is allochthonous and was transported to its current position during the Mesozoic along the proposed Mojave-Sonora megashear. One viable alternative model is that the Caborcan Precambrian crust is an isolated, autochthonous segment of Mojave province crust that shares a similar, but not identical, Proterozoic geological history with Mojave province crust found in the southwest United States ?? 2005 Geological Society of America.

  4. Mechanisms and timescales of generating eruptible rhyolitic magmas at Yellowstone caldera from zircon and sanidine geochronology and geochemistry

    Stelten, Mark; Cooper, Kari M.; Vazquez, Jorge A.; Calvert, Andrew T.; Glessner, Justin G


    We constrain the physical nature of the magma reservoir and the mechanisms of rhyolite generation at Yellowstone caldera via detailed characterization of zircon and sanidine crystals hosted in three rhyolites erupted during the (ca. 170 – 70 ka) Central Plateau Member eruptive episode – the most recent post-caldera magmatism at Yellowstone. We present 238U-230Th crystallization ages and trace-element compositions of the interiors and surfaces (i.e., unpolished rims) of individual zircon crystals from each rhyolite. We compare these zircon data to 238U- 230Th crystallization ages of bulk sanidine separates coupled with chemical and isotopic data from single sanidine crystals. Zircon age and trace-element data demonstrate that the magma reservoir that sourced the Central Plateau Member rhyolites was long-lived (150 – 250 kyr) and genetically related to the preceding episode of magmatism, which occurred ca. 256 ka. The interiors of most zircons in each rhyolite were inherited from unerupted material related to older stages of Central Plateau Member magmatism or the preceding late Upper Basin Member magmatism (i.e., are antecrysts). Conversely, most zircon surfaces crystallized near the time of eruption from their host liquids (i.e., are autocrystic). The repeated recycling of zircon interiors from older stages of magmatism demonstrates that sequentially erupted Central Plateau Member rhyolites are genetically related. Sanidine separates from each rhyolite yield 238U-230Th crystallization ages at or near the eruption age of their host magmas, coeval with the coexisting zircon surfaces, but are younger than the coexisting zircon interiors. Chemical and isotopic data from single sanidine crystals demonstrate that the sanidines in each rhyolite are in equilibrium with their host melts, which considered along with their near-eruption crystallization ages suggests that nearly all CPM sanidines are autocrystic. The paucity of antecrystic sanidine crystals relative to

  5. Age distribution of detrital zircons in the psammitic schist of the Sanbagawa Belt, southwest Japan

    We measured the 206Pb/238U age distribution of detrital zircons in five psammitic schist samples from the Sanbagawa Belt in east-central Shikoku and the western Kii Peninsula to constrain their depositional age. The age-distribution diagrams for the five psammitic schist samples all show that detrital zircons of 100 to 90 Ma are most abundant and the age of the youngest zircon in each sample is less than 80 Ma. Considering the age of the retrogressive metamorphism of these psammitic schists, ca. 80-60 Ma, the protoliths age of the psammitic schists is constrained to 75-70 Ma, correlative to the age of the sandstone of the Middle Shimanto Belt (Yanai, 1984). A similar age-distribution has already been reported for two psammitic schist samples from the Central Unit of the Sanbagawa Belt in the Kanto Mountains (Tsutsumi et al., 2009). Thus the Sanbagawa Belt is most widely occupied by metamorphic rocks originating from rocks of the Middle Shimanto Belt. We also measured the 206Pb/238U age distribution of detrital zircons in Turonian sandstone from the Northern Shimanto Belt in the central Kii Peninsula. The age-distribution diagram shows that detrital zircons of around 128 Ma are most abundant and the age of the youngest zircon in the sample is about 100 Ma. A similar age-distribution has already been reported from a psammitic schist sample from the Southern Unit of the Sanbagawa Belt in the Kanto Mountains, overlying the Central Unit (Tsutsumi et al., 2009). The protolith age is still younger than the metamorphic age of the eclogites in central Shikoku, ca. 120-110 Ma (Okamoto et al., 2004), which occupy the uppermost portion of the Sanbagawa Belt. Although some previous studies suggested that the Sanbagawa Belt consists of metamorphosed Late Jurassic to Early Cretaceous accretionary complex, the present study shows that the belt is largely occupied by metamorphosed Late Cretaceous rocks: the Shimanto Metamorphic Rocks of Aoki et al. (2007). As a result, the

  6. Comparing pre- and post-chemical abrasion ages for Miocene Peach Springs Tuff zircon from ID-TIMS and SIMS analyses

    Lidzbarski, M. I.; Mundil, R.; Miller, J. S.; Vazquez, J. A.


    The Miocene Peach Spring Tuff (PST) is a voluminous (>600 km3), zoned ignimbrite (trachyte to high-SiO2 rhyolite) that is exposed widely in eastern California, western Arizona, and southernmost Nevada, which was erupted from the Silver Creek caldera in the southwestern Black Mountains, AZ. PST serves as a regionally widespread marker unit and its eruption age has been determined to 18.8 to 18.9 Ma by 40Ar/39Ar methods, when corrected for systematic bias and normalized to the U-Pb system (Renne et al., 2010,). We performed ion-microprobe (SIMS) U-Pb dating of zircon from individual pumice clasts from PST to evaluate the growth history of zircon in the PST magma system. Sectioned, polished zircon from conventional epoxy mounts allows dating of internal growth domains (e.g. cores, interiors, and near-rim), whereas mounting unpolished zircon in indium and analyzing unpolished crystal faces provides a means to selectively sample the final increments of crystal growth (Reid and Coath, 2000). Combining U-Pb ages of unpolished zircon rims with near-rim interior analyses on sectioned grains yields a mean age of ca. 18.3 Ma, whereas ages of cores of sectioned crystals yield a mean of ca. 18.9 Ma. Several zircons have rim and/or core ages that are several hundred thousand years older or younger than these means (up to 1 m.y. total spread), although the uncertainties for individual SIMS ages are 2 to 5% (2 sigma uncertainty). Therefore, the distribution of ages is challenging to resolve. A modest number of the older grains are plausibly recycled antecrysts, but we suspect that the youngest zircons may have experienced Pb-loss. Failure to account for the possibility of inheritance and Pb-loss may lead to erroneous interpretations about crystallization in the PST system. In order to evaluate and mitigate the effects of Pb-loss, we employed the chemical abrasion (CA) technique of Mattinson (2005), which effectively eliminates domains in zircon that have suffered Pb-loss, and

  7. Detrital zircon evidence for progressive underthrusting in Franciscan metagraywackes, west-central California

    Snow, C.A.; Wakabayashi, J.; Ernst, W.G.; Wooden, J.L.


    We present new U/Pb ages for detrital zircons separated from six quartzose metagraywackes collected from different Franciscan Complex imbricate nappes around San Francisco Bay. All six rocks contain a broad spread of Late Jurassic-Cretaceous grains originating from the Klamath-Sierra Nevada volcanic-plutonic arc. Units young structurally downward, consistent with models of progressive underplating and offscraping within a subduction complex. The youngest specimen is from the structurally lowest San Bruno Mountain sheet; at 52 Ma, it evidently was deposited during the Eocene. None of the other metagraywackes yielded zircon ages younger than 83 Ma. Zircons from both El Cerrito units are dominated by ca. 100-160 Ma grains; the upper El Cerrito also contains several grains in the 1200-1800 Ma interval. These samples are nearly identical to 97 Ma metasedimentary rock from the Hunters Point shear zone. Zircon ages from this m??lange block exhibit a broad distribution, ranging from 97 to 200 Ma, with only a single pre-Mesozoic age. The Albany Hill specimen has a distribution of pre-Mesozoic grains from 1300 to 1800 Ma, generally similar to that of the upper El Cerrito sheet; however, it contains zircons as young as 83 Ma, suggesting that it is significantly younger than the upper El Cerrito unit. The Skaggs Spring Schist is the oldest studied unit; its youngest analyzed grains were ca. 144 Ma, and it is the only investigated specimen to display a significant Paleozoic detrital component. Sedimentation and subduction-accretion of this tract of the trench complex took place along the continental margin during Early to early-Late Cretaceous time, and perhaps into Eocene time. Franciscan and Great Valley deposition attests to erosion of an Andean arc that was active over the entire span from ca. 145 to 80 Ma, with an associated accretionary prism built by progressive underthrusting. We use these new data to demonstrate that the eastern Franciscan Complex in the northern and

  8. Radioactivity in Zircon from Jos, Central Nigeria

    Mining and processing of zircon along with other minerals, generally for export purposes, have been taking place in Jos, central Nigeria, for several decades. Over the years, there has been increasing concern about the radiological impact resulting from these activities. A previous assessment in the vicinity of processing areas reported an annual dose of 50 mSv which by far exceeds the 1 mSv dose limit for members of the public. In the study, the activity concentrations of 238U and 232Th in 28 samples of zircon from Jos were determined using neutron activation analysis. The results gave concentrations of 466 μg/g (5.75 Bq/g) for 238U and 7054 μg/g (28.62 Bq/g) for 232Th. These results complement the results of earlier assessments and may assist in the proper management of these activities and the choice and implementation of appropriate protective measures. (author)

  9. Investigation into dilution of zircon suspensions

    Investigated is the influence of a number of dilution additives in acid as well as in alkali media on the viscosity of utterly destructed structure of zircon suspensions. It is shown that practically all tested additives, except the extracts of fir (0.5 %) and quebracho (0.25-0.5 %), decrease more or less the ultimate stress of the shift and viscosity of utterly destructed structure. It is stated that the usage of complex additive on the basis of syntan-5, triethanolamine and oxalic acid ammonium, in certain ratios provide suspensions of fine-dispersed zircon after washing with polyacrylamide addition, sufficient yield and viscosity in alkali medium. The properties of castings of such suspensions correspond to ones of suspensions with acid media without polyacrilamide usage

  10. Studies on plasma dissociation of zircon

    Zircon (zirconium silicate) is a major source of zirconium metal. Extraction of zirconium involves chlorination step to convert zirconium silicate to ZrCl4 and SiCl4. SiCl4 is separated and zirconium tetrachloride is reduced with magnesium to yield zirconium metal. Instead of this direct chlorination of zircon, it can be converted to zirconia by thermal plasma dissociation followed by alkali leaching process to separate silica. The resulting zirconium oxide can be used for zirconium extraction. This would result in considerable savings of chlorine consumption and also would eliminate the SiCl4 separation step. The Laser and Plasma Technology Division has developed a 20 kW laboratory 1 scale plasma reactor, which consists of a DC plasma torch mounted on a water cooled reaction chamber, DC power source, water cooling and gas feed system and a powder feeder. The system has been used to study in-flight dissociation of zircon in the thermal plasma jet. Dissociation studies were carried out over 5-16 kW power range. The plasma processed product was characterized by x-ray diffraction technique, which showed that it consisted of zirconium dioxide and silica. The extent of dissociation was estimated by gravimetric method involving alkali leaching of silica. Results of the study indicate that the extent of dissociation strongly depends on input power and other parameters such as plasma gas flow rate. Complete dissociation could be achieved at an input power of 12 kW. The average temperature at the nozzle exit of the plasma torch has been calculated for various input power levels. Calculations on heat transfer to the particles and residence time required to effect dissociation of zircon particles injected in the plasma jet have been carried out for various input power levels and particle sizes ranging from 20-150 microns. Details of the experiments and results will be discussed in the paper. (author)

  11. A kinetic model of zircon thermoluminescence

    Turkin, A.A.; Es, H.J. van; Vainshtein, D.I.; Hartog, H.W. den


    A kinetic model of zircon thermoluminescence (TL) has been constructed to simulate the processes and stages relevant to thermoluminescent dating such as: filling of electron and hole traps during the excitation stage both for natural and laboratory irradiation; the time dependence of fading after laboratory irradiation; TL experiments both after laboratory and natural irradiation. The goal is to inspect qualitative behavior of the system and to unravel the processes and determine the paramete...

  12. Zirconium oxide obtainment from brazilian zircon concentrate

    This work presents the experimental results of studies about alkaline melting, acid leaching and sulfation steps for obtention of zirconium oxide and partially stabilized zirconia by yttrium and rare-earth coprecipitation in chlorine medium, starting from the brazilian zircon concentrate. Using statistical methods of factorial design and the Packett-Burman approach, the results are discussed and the optimal conditions of the production steps were determined. (author)

  13. Heavy-ion irradiation tracks in zircon

    Heavy-ion irradiation (14 MeV/u Pb ions) of zircon crystals gives rise to linear latent tracks of 80x10-10 m diameter and length 140 μm. Direct observation of the track core, by high-voltage high-resolution electron microscopy at atomic resolution, reveals a core having roughly circular cross-section, with some facetting of the core/matrix interface on [101] planes of zircon. The core diameter appears quite uniform. Conventional transmission electron microscopy (bright- and dark-field imaging) reveals an elastic strain field extending for a short distance into the zircon matrix. This appears to drop off more rapidly with distance, say 1/R2, than do dislocation strain fields (∼ 1/R). Analysis of the various contrast mechanisms yields the result that the core is essentially amorphous. The observations confirm directly earlier conclusions based on track etching and electrical conductivity measurements, that the irradiation damage is confirmed to a 50-100 Aangstroem core region of atomically-disordered material, with virtually no damage outside this region. Mechanisms for track production are discussed briefly, but it is concluded that the problem, which is now defined by this structural analysis, has not been fully-appreciated by condensed matter physicists. In particular a damage confinement mechanism is required, which is not intuitively obvious. Some tentative suggestions along this direction are proposed. 33 refs., 9 figs

  14. Thermoluminescence of zircon: a kinetic model

    Turkin, A A; Vainshtein, D I; Hartog, H W D


    The mineral zircon, ZrSiO sub 4 , belongs to a class of promising materials for geochronometry by means of thermoluminescence (TL) dating. The development of a reliable and reproducible method for TL dating with zircon requires detailed knowledge of the processes taking place during exposure to ionizing radiation, long-term storage, annealing at moderate temperatures and heating at a constant rate (TL measurements). To understand these processes one needs a kinetic model of TL. This paper is devoted to the construction of such a model. The goal is to study the qualitative behaviour of the system and to determine the parameters and processes controlling TL phenomena of zircon. The model considers the following processes: (i) Filling of electron and hole traps at the excitation stage as a function of the dose rate and the dose for both (low dose rate) natural and (high dose rate) laboratory irradiation. (ii) Time dependence of TL fading in samples irradiated under laboratory conditions. (iii) Short time anneali...

  15. Determinations of major, minor and trace elements including U and Th in heavy minerals assemblage-zircon using ICP-AES

    The current study is a new approach for the sample solution preparation in analyzing Zircon, Baddeylite and other zirconium minerals using phosphate flux. Sample is fused with the mixture of NaHPO4 and Na2HPO4 in the ratio 1:1 (flux). Modifications in the procedures have been done depending upon the elements to be analyzed. The sample is fused directly with phosphate salts and the stable solution obtained is analyzed for about 30 elements (Si, Zr, Hf, Si, Ti, Al, Fe, Mn, Ca, Mg, Ba, V, Sc, Th, U and REEs) by ICP-AES. Otherwise, the sample is treated first with HF to remove silica then fused with phosphate salts. This flux is used for the rapid decomposition and dissolution of silicate minerals for the first time. In nature zirconium mainly occurs as silicate (e.g. Zircon) and oxide (e.g. Baddeleyite). Zircon chemistry is relatively simple and usually ZrO2, HfO2 and SiO2 compose more than 99% of the total oxides. Previous investigations have documented the presence of as many as 50 elements in zircon. Zircon is very useful mineral for industrial use, geochemical and petro-genetic works as well as provenance studies, whereas Baddeleyite is commonly used in industrial purposes. Zircon is one of the most chemically stable compounds, so, very aggressive reaction conditions are require to breakdown the strong binding between zirconium and silicon parts in the compound. It normally requires the analysis of Zr, Hf, Si, Ti, Al, Fe, Mn, Ca, Mg, V, Ba, Sc, U, Th, and REEs. Several fusion methods are used to decompose zircon, like, KHSO4, NaF-KHF2, Na2O2, and LiBO2. In most cases fuming is a must, involving evolution of SO3 fumes in the atmosphere. All the above procedures are multistep, lengthy and tedious. Moreover, Silica has to be analyzed separately

  16. Role of zircon in tracing crustal growth and recycling

    Compston, W.; Williams, I. S.; Armstrong, R. A.; Claoue-Long, J. C.; Kinny, P. D.; Foster, J. J.; Kroener, A.; Pidgeon, R. T.; Myers, J. S.


    Single crystal ion probe ages of zircons is discussed, which allow much better time resolution compared to other geochronological methods, although the technique is not without problems. Rocks from two areas that contain composite zircon populations, including true magmatic zircons as well as a variety of xenocrystic types are described. It is often difficult to distinguish these; xenocrystic zircons, for example, cannot always be identified on the basis of morphology alone. Additional evidence is needed before making age interpretations. Evidence is also presented of zircon growth long after the original time of crystallization, in some cases apparently at temperatures less than 300 C. The spectacular discovery of 4.1 to 4.2 Ga detrital zircons in metaquartzites from the Mount Narryer area of Western Australia is described. Similar zircons with ages as old as 4276 Ma have been found in the nearby Jack Hills area. The source areas or parent lithologies of these zircons have not yet been determined, but the author expects that they may be unrecognized or buried antecedents of the K rich Narryer gneisses. U or Th concentrations of zircon cannot be used to discriminate between felsic and mafic source rocks.

  17. Oxygen isotopic composition and U-Pb discordance in zircon

    Booth, A.L.; Kolodny, Y.; Chamberlain, C.P.; McWilliams, M.; Schmitt, A.K.; Wooden, J.


    We have investigated U-Pb discordance and oxygen isotopic composition of zircon using high-spatial resolution ??18O measurement by ion microprobe. ??18O in both concordant and discordant zircon grains provides an indication of the relationship between fluid interaction and discordance. Our results suggest that three characteristics of zircon are interrelated: (1) U-Pb systematics and concomitant age discordance, (2) ??18O and the water-rock interactions implied therein, and (3) zircon texture, as revealed by cathodoluminescence and BSE imaging. A key observation is that U-Pb-disturbed zircons are often also variably depleted in 18O, but the relationship between discordance and ??18O is not systematic. ??18O values of discordant zircons are generally lighter but irregular in their distribution. Textural differences between zircon grains can be correlated with both U-Pb discordance and ??18O. Discordant grains exhibit either a recrystallized, fractured, or strongly zoned CL texture, and are characteristic of 18O depletion. We interpret this to be a result of metamictization, leading to destruction of the zircon lattice and an increased susceptibility to lead loss. Conversely, grains that are concordant have less-expressed zoning and a smoother CL texture and are enriched in 18O. From this it is apparent that various stages of water-rock interaction, as evidenced by systematic variations in ??18O, leave their imprint on both the texture and U-Pb systematics of zircon. Copyright ?? 2005 Elsevier Ltd.

  18. Determination of major, minor and trace elements in zircon, heavy mineral assemblage, using ICP-OES

    One of the biggest challenges in analyzing heavy minerals assemblage/refractory minerals is the complexity of the sample matrices. Zircon is one of the most stable chemical compounds due to the strong bond between zirconia and silica in its molecule. The current study is a new approach for the Sample Solution preparation in analyzing heavy minerals, Zircon, Baddeylite and other zircon containing minerals, using phosphate salts. A simple reagent which acts as a flux and also as a complexing agent is used for the rapid decomposition and dissolution of silicate minerals for the first time. Modifications in the procedures have been done depending upon the elements to be analyzed. The sample is fused directly with phosphate salts and the stable solution obtained is analyzed for about 30 elements (Si, Zr, Hf, Si, Ti, Al, Fe, Mn, Ca, Mg, Ba, V, Sc, Th, U and REEs) by ICP-OES. Otherwise the sample is treated first with HF to remove silica then fused with phosphate salts. In this case Si cannot be analyzed. Trueness and reproducibility were assessed by analyzing Certified Reference Material (CRM), synthetic mixtures and against the established standard procedures. The procedure has been applied successfully to heavy minerals received from beach sands of India. The proposed method is accurate and the precision is characterized by an RSD varying from 0.5 to 3.0% (n=5), from element to element. (author)

  19. [The characteristics of microstructure and chemical compositions of K-feldspar, sphene and zircon with zoning structure].

    Liu, Chun-Hua; Wu, Cai-Lai; Lei, Min; Qin, Hai-Peng; Li, Ming-Ze


    K-feldspar, sphene and zircon in quartz monzonite from Shahewan, south Qinling, showing strong zoning structure. Characteristics of microstructure and chemical compositions of K-feldspar, sphene and zircon with zoning structure were investigated using advanced instruments of electron probe micro analyses equipped with wavelength dispersive spectrometer (EPM-WDS), scanning electron microscopy with energy dispersive spectrometer (SEM-EDS) and laser ablation--inductively coupled plasma--mass spectrometry (LA-ICP-MS). Our study suggests that K+ could be substituted by small amounts of Na+, Ca2+, Ba2+, Fe2+ and Ce3+. Ca2+ in sphene could be replaced by V3+, Ce3+, Ba2+ and Ti4+ could be substituted by both Fe2+ and Al3+. Zircon contains trace elements like Fe, Th, U, Nb, Ta, Y, Hf, Yb and Pb. Concentration of Si, Al, K, Ca, Na, Mg and Ba in K-feldspar ranked from high to low, among which the contents of K and Na are negatively correlated, the lighter part of BSE images featuring K-feldspar is attributed to comparably higher Ba content, additionally, Si and K contents are elevated while Na content decreased rimward. Ca, Si, Ti, Ba, V, Ce, Al and Fe concentration listed downward, among which higher iron content corresponds to brighter portion of BSE images. Element concentration of zircon could be ranked from high to low as Zr, Si, Nd, Ce, Hf, U, Pb and Th, in which Hf and Zr exhibit negatively correlated. Zr concentration increased while Hf, U and Th concentration decreased from core to rim. PMID:24159884

  20. First SHRIMP U Pb zircon dating of granulites from the Kontum massif (Vietnam) and tectonothermal implications

    Nam, Tran Ngoc; Sano, Yuji; Terada, Kentaro; Toriumi, Mitsuhiro; Van Quynh, Phan; Dung, Le Tien


    The Kontum massif in Central Vietnam represents the largest continuous exposure of crystalline basement of the Indochina craton. The central Kontum massif is chiefly made of orthopyroxene granulites (enderbite, charnockite) and associated rocks of the Kannack complex. Mineral assemblages and geothermobarometric studies have shown that the Kannack complex has severely metamorphosed under granulite facies corresponding to P-T conditions of 800-850°C and 8±1 kbars. Twenty-three SHRIMP II U-Pb analyses of eighteen zircon grains separated from a granulite sample of the Kannack complex yield ca 254 Ma, and one analysis gives ca 1400 Ma concordant age for a zoned zircon core. This result shows that granulites of the Kannack complex in the Kontum massif have formed from a high-grade granulite facies tectonothermal event of Indosinian age (Triassic). The cooling history and subsequent exhumation of the Kannack complex during Indosinian times ranged from ˜850°C at ca 254 Ma to ˜300°C at 242 Ma, with an average cooling rate of ˜45°C/Ma.

  1. Uranium-lead ages of zircon megacrysts and zircon included in corundum from Peixe Alcaline complex (Brazil)

    The Peixe Alkaline Complex, Brazil, contains unusual mineral occurrences. Among them are zircon megacrysts (there are centimetric zircons) that have been subject of economic exploitation since the 1970's. But these crystals have not been studied in detail, in particular with respect to their isotope composition and U-Pb age. Pegmatites bearing corundum megacrysts also occur inside this complex. These corundum megacrysts also contain millimetric-sized zircon inclusions, which have never been studied before. The geochronological study of these zircons are important both for the understanding of the complex and the pegmatitic corundum, as well for an improved understanding of the regional geological evolution (au)

  2. Feasibility limits in using cerium as a surrogate for plutonium incorporation in zircon, zirconia and pyrochlore

    Cerium is a well-known surrogate element for Pu that is widely used in experiments on the synthesis and study of ceramic waste forms for actinide immobilization. Cathodoluminescence (CL) images and emission spectra from synthetic zircon, (Zr,...)SiO4, cubic zirconia, (Zr,Y,Gd,...)O2 and pyrochlore, Ca(HfGd,...)Ti2O7, individually doped with Ce and Pu were investigated. It was determined that some of the Ce, which was added as Ce4+ in the form of CeO2, was converted to the 3+ valence state during synthesis of zircon-based ceramics by sintering in air and in argon gas. However, Pu-doped zircon synthesized in air under the same conditions does not exhibit the CL emission of Pu3+. Analysis of CL spectra of cubic zirconia doped with Ce as well as Pu suggests that both ions are in the tetra-valent state in these synthetic materials. However, the CL peak of Ce-doped zirconia is almost identical to that of pure zirconia (2.6 eV). The CL peak for Pu-doped zirconia is shifted to 2.4 eV. No CL emission of Ce3+ or Pu3+ was observed in pyrochlore samples. The CL spectra for Ce-and Pu-doped pyrochlore samples were almost identical. We suggest that under oxidizing conditions Ce is good surrogate of Pu for experiments on the synthesis of pyrochlore-based and acceptable enough for zirconia-based ceramics. The use of Ce as Pu surrogate for zircon-based ceramics should be considered as limited. Copyright (2001) Material Research Society

  3. Is ''metamictization'' of zircon a phase transition?

    Metamictization is the transition from the crystalline to an aperiodic or amorphous state due to alpha-decay event damage from constituent radionuclides (238U, 235U, and 232Th) and their daughters. However, this transformation in minerals is part of a larger class of radiation-induced transformations to the amorphous state that has received considerable recent attention as a result of ion- and electron-beam experiments on metals, intermetallics, simple oxides, and complex ceramics and minerals. Diffuse X-ray scattering from single crystals of metamict zircon reveals residual crystallinity even at high fluences (up to 7.2 x 1018 α-decay events/g). The experimental evidence does not suggest that radiation-induced amorphization is a phase transition. The observations are in good agreement with a nonconvergent, heterogeneous model of amorphization in which damage production is a random process of cascade formation and overlap at increasing fluence. Instead of an amorphization transition, the existence of a percolation transition is postulated. At the level of radiation damage near the percolation point, the heterogeneous strain broadening of X-ray diffraction profiles is reduced whereas the particle-size broadening increases. Simultaneously, the macroscopic swelling of the zircon becomes larger than the maximum expansion of the unit-cell parameters. A suitable empirical parameter that characterizes this transition is the flux, Ds, at which the macroscopic expansion is identical to the maximum expansion of the crystallographic unit cell. In zircon, Ds = 3.5·1018 α-decay events/g

  4. Natural radioactivity and radon specific exhalation rate of zircon sands

    Righi, S.; Verita, S.; Bruzzi, L. [Bologna Univ., Centro Interdipartimentale di Ricerca per le Scienze Ambientali and Dipt. di Fisica, Ravenna (Italy); Albertazzi, A. [Italian Ceramic Center, Bologna (Italy)


    The study focuses on the radon emanation from zircon sands and their derivatives, which are widely used in many sectors of industry. In particular, the results obtained by experimental measurements on samples of zircon sands and zircon flours commonly used in Italian ceramic industries are reported. Zircon sands contain a significant concentration of natural radioactivity because Th and U may substitute zirconium in the zircon crystal lattice. The relevant routes of exposure of workers to T.E.N.O.R.M. from zircon materials are external radiation and internal exposure, either by inhalation of aerosols in dusty working conditions or by inhalation of radon in workplaces. The main objective of this investigation is to provide experimental data able to better calculate the internal exposure of workers due to radon inhalation. Zircon samples were surveyed for natural radioactivity, radon specific exhalation rate and emanation fraction. Measurements of radioactivity concentration were carried out using {gamma}-spectrometry. Methods used for determining radon consisted in determining the {sup 222}Rn activity accumulated in a vessel after a given accumulation build-up time. The average activity concentrations of {sup 238}U and {sup 232}Th in samples result about 2600 and 550 Bq kg-1, respectively; these concentrations are significantly higher than the world average noticed in soils, rocks and Earth crust. The {sup 222}Rn specific exhalation rates result very low probably due to the low porosity of the material and the consequent difficulty for radon to be released from the zircon crystal lattice. (author)

  5. Natural radioactivity and radon specific exhalation rate of zircon sands

    The study focuses on the radon emanation from zircon sands and their derivatives, which are widely used in many sectors of industry. In particular, the results obtained by experimental measurements on samples of zircon sands and zircon flours commonly used in Italian ceramic industries are reported. Zircon sands contain a significant concentration of natural radioactivity because Th and U may substitute zirconium in the zircon crystal lattice. The relevant routes of exposure of workers to T.E.N.O.R.M. from zircon materials are external radiation and internal exposure, either by inhalation of aerosols in dusty working conditions or by inhalation of radon in workplaces. The main objective of this investigation is to provide experimental data able to better calculate the internal exposure of workers due to radon inhalation. Zircon samples were surveyed for natural radioactivity, radon specific exhalation rate and emanation fraction. Measurements of radioactivity concentration were carried out using γ-spectrometry. Methods used for determining radon consisted in determining the 222Rn activity accumulated in a vessel after a given accumulation build-up time. The average activity concentrations of 238U and 232Th in samples result about 2600 and 550 Bq kg-1, respectively; these concentrations are significantly higher than the world average noticed in soils, rocks and Earth crust. The 222Rn specific exhalation rates result very low probably due to the low porosity of the material and the consequent difficulty for radon to be released from the zircon crystal lattice. (author)

  6. Extinct Plutonium Geochemistry of Ancient Hadean Zircons

    Turner, G.; Gilmour, J.; Crowther, S.; Busfield, A.; Mojzsis, S.; Harrison, M.


    The abundance of 244Pu in the early solar system has important implications for r-process nucleosynthesis and models of noble gas transport within the Earth's mantle. Our recent discovery(1) of xenon isotopes from the in-situ decay of 244Pu in ancient Jack Hills zircons promises to provide a new time-sensitive window on the first 500 Ma of Earth history. We have extended this initial work by the use of resonance ioniisation mass spectrometry to analyse xenon released by stepped heating from 17 individual zircons with Pb-Pb ages in the range 3.95 to 4.18 Ga. Our immediate objectives are to determine the causes of variations in the inferred Pu/U ratios and in the longer term to determine the initial Pu/U ratio of the Earth. The Pu/U ratios calculated for individual zircons may be expected to vary as a result of igneous fractionation and also from differential loss of Pu and U fission xenon in the last 4 Ga. We have studied the effects of xenon loss by irradiating the zircons with thermal neutrons to generate xenon from 235U neutron fission in order to determine U/Xe ratios and apparent ages. 131Xe/134Xe and 132Xe/134Xe ratios can be used to calculate the relative contributions from 244Pu and 238U spontaneous fission and 235U neutron fission. The measured Pu/U ratios (back calculated to 4.56 Ga on the basis of the individual Pb-Pb ages) range from zero to 0.012. The highest ratio in our initial study was 0.008 (note that the published ratio has been revised upwards on the basis of improved decay parameters for 238U spontaneous fission). Comparison of Pb-Pb and U-Xe ages indicate varying amounts of xenon loss, over 50% in some cases. While this accounts for some of the variability in the inferred Pu/U, igneous fractionation may also play a part, and we are currently attempting to investigate this by a comparison with REE abundances. Reference: (1) Turner et al. (2004) Science, 306, 89-91.

  7. Large swelling and percolation in irradiated zircon

    Trachenko, K; Salje, E K H


    We study the effect of large swelling in irradiated zircon. We perform molecular dynamics simulation of the overlap of two radiation events and find that the damage produced in the second event scatters away from the densified boundary of the damaged region implanted previously. This serves as the microscopic mechanism of the increase of volume occupied by the damage. The additive nature of this effect results in large swelling observed experimentally. We translate the damage accumulation into the percolation problem, and show that volume swelling is a percolation phenomenon, with the swelling curve increasing rapidly at the percolation threshold. (letter to the editor)

  8. Auto-regenerative thermoluminescence dating using zircon inclusions

    Fired ceramics containing zircon inclusions have been dated by allowing the zircons to regenerate their own thermoluminescence (TL) signal, hence auto-regenerative TL dating. The technique is conceptually straightforward. One first measures the TL accrued since the last heating of the material. The zircon grains are then stored for six months and the TL signal regenerated through self-irradiation is measured. Since the internal dose-rate for zircon is dominated by the internal component the age of the sample is simply given by the ratio of the natural to auto-regenerated signal times the laboratory storage period. The technique, however, requires the measurement of a very small auto-regenerated signal, which introduces a number of experimental and physical complications. The methods for overcoming these problems and successfully dating zircons by auto-regeneration are described. (Author)

  9. Luminescence dating of zircon using an imaging photon detector

    The luminescence dating of zircon can be difficult with conventional photomultipliers because of the combined background from dark current and black-body radiation. Previously the latter problem has been minimized by imaging the thermoluminescence (TL) to blank off regions of the disc which do not hold zircons. A better approach is to replace the photomultiplier with an imaging photon detector (IPD). Recent advances in technology have resulted in an instrument which approaches the performance characteristics of conventional photomultipliers. The great advantage for zircon dating is that the TL from individual grains can easily be integrated and the effects of both dark current and black-body radiation from all other regions neglected. The IPD has been used in the dating of several pottery and volcanic samples, as well as for procedural developments in the dating of zircon from sediment. The performance characteristics of the IPD are described, together with some examples of its application to zircon dating. (author)

  10. Detrital zircon geochronology by LA-ICP-MS of the Neoarchean Manjeri Formation in the Archean Zimbabwe craton- the disappearance of Eoarchean crust by 2.7 Ga?

    Sawada, Hikaru; Maruyama, Shigenori; Sakata, Shuhei; Hirata, Takafumi


    For the ca. 2.7 Ga (Neoarchean) clastic rocks in the Belingwe greenstone belt (Manjeri Formation), U-Pb age of detrital zircon grains were analyzed by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). The Manjeri Formation, composed of sandstone, quartzite, and limestone with stromatolites, was deposited in a shallow marine setting along the ancient passive continental margin of the Zimbabwe craton. Nearly 100 detrital zircon grains, for each from two sandstone samples in central Zimbabwe, were separated for U-Pb dating. Age spectra of detrital zircon grains of two analyzed sandstones of the Manjeri Formation show more or less the same multiple age clusters: i.e., ca. 2.9 Ga, ca. 3.15 Ga, ca. 3.3 Ga, and ca. 3.5 Ga. These age spectra reflect nature of the provenance of proto-Zimbabwe, which was considerably different from that of the modern Zimbabwe craton. The age clusters of ca. 2.9 Ga, ca. 3.3 Ga, and ca. 3.5 Ga are correlated with those of extant basement rocks of the present Zimbabwe craton, whereas the ca. 3.15 Ga cluster has no corresponding unit within the craton, except for detrital zircons from the 2.65 Ga Shamvaian Group in a neighboring area of the Zimbabwe craton. The extremely old (3.85 Ga; Eoarchean) detrital zircon grains, previously reported from the ca. 2.9 Ga and ca. 3.4 Ga sandstones elsewhere in the craton, were not detected at all in the present two analyzed samples. As no Eoarchean (>3.8 Ga) basement rocks remain in the Zimbabwe craton at present either, the present study confirmed that the Eoarchean crustal rocks once occurred in the proto-Zimbabwe craton but they had been removed secondarily from the provenance of Neoarchean and younger basins prior to 2.7 Ga. Possible geologic processes for such disappearance of older crusts may include the physiological separation by continental rifting, subduction erosion, and/or other crustal recycling processes.

  11. Zirconia (NC) zircon as a potential standard

    Covey, A. K.; Braun, S. A.; Gualda, G. A.; Bream, B. R.; Fisher, C.; Wooden, J. L.; Schmitz, M. D.


    As microanalysis continues to advance and become more widespread there is a greater need for abundant and suitable age standards. Megacrystic zircons from the inactive Freeman Mine near Zirconia, NC were collected from weathered mine dump piles. Zirconia zircon crystals are large (> 1 mm) relative to typical zircons (up to 100s μm) and easily obtained; attributes that make them attractive as a potential standard. We present here preliminary data and assess the suitability of Zirconia zircons as a U-Pb geochronology, Hf-isotope and trace-element standard. Grains are variably fluorescent (Callahan et al, Southeastern Geol., 2007), and we used shortwave fluorescence to separate grains with high, medium, low/no fluorescence from one another. Images were taken of the grains before mounting and post-polishing to understand the fluorescence characterization of the surface to the core. After preparing the grains, we found that the fluorescence was not homogenous and did not provide a good means of separating out grains. In order to investigate the differences in fluorescence, we collected cathodoluminescence (CL) and backscatter electron (BSE) images and energy dispersive spectroscopy (EDS) maps using a Tescan Vega 3 LMU equipped with an Oxford X-max 50 mm2 solid-state EDS detector at Vanderbilt University. This allowed division of the grains into two types: (a) grains with finely oscillatory zoned rims, which are variably crosscut by dull-CL irregular zones, sometimes showing hourglass zoning; and (b) grains with cores showing more irregular, patchy zoning with and without thin oscillatory rims. EDS maps show no major element zoning in the zircon grains, but reveal a variety of inclusions, particularly of quartz and thorite. Preliminary U-Pb ages were obtained using a Perkin Elmer Elan DRCII ICP-MS coupled with a New Wave/Mechantek 213 nm Nd:YAG laser ablation system at Vanderbilt University. A total of ~150 individual ages on oscillatory-zoned (Type a) crystals yield a

  12. Selection of Raw Materials for the Reactive Sinterling of Zircon Porous Ceramics

    SHENYi; ZHANGWenli; 等


    The effect of three kinds of zircon raw materials on the sinterability and properties of porous zircon ceramics have been investigated.The results have shown that all the tested fired compacts are of high porosity,However,the sintering process are different for different raw materials.The preferable selected raw materials for porous zircon ceramics were commercials zircon and quartz.

  13. The complex systematics of zircons in migmatitic gneisses: An example from an Archean migmatite along the Patos Shear Zone, Borborema Province, NE Brazil

    The Northem Tectonic Domain Borborema Province, in Northeast of Brazil records a complex history of tectonic activity ranging from 3.4 Ga to 0.6 Ga (Brito Neves, 1995 and Dantas, 1996). U-Pb systematics of zircons from a migmatitic gneiss just north of the Patos Shear Zone provide an excellent example of the difficulties encountered using conventional single-grain U/Pb zircon geochronology in polydeformed gneiss terranes. Our conventional single grain zircon analyses of a migmatite yielded Archean ages between ca. 3.3 at 2.8 a, as well as some highly discordant Paleoproterozoic ages. Subsequent cathodoluminescence images of these zircon grains showed complex internal structures that possibly record up to 4 separate stages of zircon growth. With such internal complexity, is impossible resolve primary crystallization ages as well as the ages of subsequent overgrowth events using conventional single grain analyses. Such resolution will require analyses of the individual grain domains using the SHRIMP method (au)

  14. Carbonitridation of mechanically activated mixtures of zircon and carbon

    Setoudeh, N., E-mail: [Materials Engineering Department, Yasouj University, Yasouj (Iran, Islamic Republic of); Welham, N.J., E-mail: [West Australian School of Mines, Curtin University, PO Box U1977, Perth, Western Australia (Australia)


    Highlights: • Formation temperature of ZrN and ZrC decreased to 1400 °C in the five hours milled sample. • Either ZrC or ZrN were observed in the heating of 6:1 C:Zircon samples under argon/nitrogen atmospheres. • Amount of tetragonal zirconia increased in nitrogen atmosphere. • Percentage of tetragonal zirconia increased at higher C:Zircon ratios. -- Abstract: Two different stoichiometries of zircon (ZrSiO{sub 4}) and activated carbon (C:zircon molar ratios of 3:1 and 6:1) were milled together at for 5 h and subjected to thermo-gravimetric analysis (TGA). TGA runs were performed under argon and nitrogen atmospheres. The main mass loss reaction started at around 1200 °C in all samples, but the mass loss was greater in the 6:1 C:zircon ratio samples in nitrogen. X-ray diffraction (XRD) of the residues showed the decomposition of zircon was nearly complete. Traces of ZrN along with monoclinic and tetragonal forms of zirconia were observed in the nitrogen atmosphere, however only zirconia was present after heating in argon. Heating the 6:1 C:zircon molar ratio sample for 1 h at 1400 °C in argon resulted in the formation of ZrC and SiC, in nitrogen ZrN was formed.

  15. Carbonitridation of mechanically activated mixtures of zircon and carbon

    Highlights: • Formation temperature of ZrN and ZrC decreased to 1400 °C in the five hours milled sample. • Either ZrC or ZrN were observed in the heating of 6:1 C:Zircon samples under argon/nitrogen atmospheres. • Amount of tetragonal zirconia increased in nitrogen atmosphere. • Percentage of tetragonal zirconia increased at higher C:Zircon ratios. -- Abstract: Two different stoichiometries of zircon (ZrSiO4) and activated carbon (C:zircon molar ratios of 3:1 and 6:1) were milled together at for 5 h and subjected to thermo-gravimetric analysis (TGA). TGA runs were performed under argon and nitrogen atmospheres. The main mass loss reaction started at around 1200 °C in all samples, but the mass loss was greater in the 6:1 C:zircon ratio samples in nitrogen. X-ray diffraction (XRD) of the residues showed the decomposition of zircon was nearly complete. Traces of ZrN along with monoclinic and tetragonal forms of zirconia were observed in the nitrogen atmosphere, however only zirconia was present after heating in argon. Heating the 6:1 C:zircon molar ratio sample for 1 h at 1400 °C in argon resulted in the formation of ZrC and SiC, in nitrogen ZrN was formed

  16. Detrital zircon U-Pb reconnaissance of the Franciscan subduction complex in northwestern California

    Dimitru, Trevor; Ernst, W. Gary; Hourigan, Jeremy K.; McLaughlin, Robert J.


    In northwestern California, the Franciscan subduction complex has been subdivided into seven major tectonostratigraphic units. We report U-Pb ages of ≈2400 detrital zircon grains from 26 sandstone samples from 5 of these units. Here, we tabulate each unit's interpreted predominant sediment source areas and depositional age range, ordered from the oldest to the youngest unit. (1) Yolla Bolly terrane: nearby Sierra Nevada batholith (SNB); ca. 118 to 98 Ma. Rare fossils had indicated that this unit was mostly 151-137 Ma, but it is mostly much younger. (2) Central Belt: SND; ca. 103 too 53 Ma (but poorly constrained), again mostly younger than previously thought. (3) Yager terrane: distant Idaho batholith (IB); ca. 52 to 50 Ma. Much of the Yager's detritus was shed during major core complex extension and erosion in Idaho that started 53 Ma. An eocene Princeton River-Princeton submarine canyon system transported this detritus to the Great Valley forearc basin and thence to the Franciscan trench. (4) Coastal terrane: mostly IB, ±SNB, ±nearby Cascade arc, ±Nevada Cenozoic ignimbrite belt; 52 to <32 Ma. (5) King Range terrane: dominated by IB and SNB zircons; parts 16-14 Ma based on microfossils. Overall, some Franciscan units are younger than previously thought, making them more compatible with models for the growth of subduction complexes by positive accretion. From ca. 118 to 70 Ma, Franciscan sediments were sourced mainly from the nearby Sierra Nevada region and were isolated from southwestern US and Mexican sources. From 53 to 49 Ma, the Franciscan was sourced from both Idaho and the Sierra Nevada. By 37-32 Ma, input from Idaho had ceased. The influx from Idaho probably reflects major tectonism in Idaho, Oregon, and Washington, plus development of a through-going Princeton River to California, rather than radical changes in the subduction system at the Franciscan trench itself.

  17. Moessbauer study of the structure of Fe - zircon system

    Iron-doped silicate (zircon), prepared by a ceramic method with the addition of LiF as mineralizer, was analyzed by X-ray powder diffraction (XRD) and 57Fe Moessbauer spectroscopy to obtain information on the solid solution formation. The results of X-ray diffraction and Moessbauer spectroscopy have shown that only a small fraction of iron, about 1.5 mol%, is incorporated in the zircon structure as paramagnetic Fe3+ species while the remaining Fe3+ cations form magnetic α-Fe2O3 particles which are trapped within the zircon matrix. (author)

  18. A Raman spectroscopic study of zircons on micro-scale and Its significance in explaining the origin of zircons

    Bao, Xuezhao; Lu, Songnian


    The magmatic and metamorphic zircons were investigated with Raman spectrum microprobe analysis. We found notable differences between these two kinds of zircons exhibited by the variation trend of Raman peak intensity from core to rim of a crystal. In magmatic zircons, the intensity and the ratio H/W of Raman spectrum peaks gradually decrease from core to rim of a crystal, which is produced by an increase in metamictization degree and suggests an increase in U and Th concentrations from core to rim. In metamorphic zircons, there are two kinds of crystals according to their Raman spectra: the first group of zircons exhibits a variation trend opposite to those of magmatic zircons, tending to increase in the Raman peak intensity and H/W value from core to rim of a crystal, which is produced by a decrease in metamictization degree and indicates a decrease of U and Th concentrations from core to rim of a crystal. The second group of zircons exhibits no change in Raman peak intensity and H/W value through a crystal....

  19. Evolution of the African continental crust as recorded by U-Pb, Lu-Hf and O isotopes in detrital zircons from modern rivers

    Iizuka, Tsuyoshi; Campbell, Ian H.; Allen, Charlotte M.; Gill, James B.; Maruyama, Shigenori; Makoka, Frédéric


    To better understand the evolutionary history of the African continental crust, a combined U-Pb, Lu-Hf and O isotopic study has been carried out by in situ analyses of approximately 450 detrital zircon grains from the Niger, Nile, Congo, Zambezi and Orange Rivers. The U-Pb isotopic data show age peaks at ca. 2.7, 2.1-1.8, 1.2-1.0, ca. 0.8, 0.7-0.5 and ca. 0.3 Ga. These peaks, with the exception of the one at ca. 0.8 Ga, correspond with the assembly of supercontinents. Furthermore, the detrital zircons that crystallized during these periods of supercontinent assembly have dominantly non-mantle-like O and Hf isotopic signatures, in contrast to the ca. 0.8 Ga detrital zircons which have juvenile characteristics. These data can be interpreted as showing that continental collisions during supercontinent assembly resulted in supermountain building accompanied by remelting of older continental crust, which in turn led to significant erosion of young igneous rocks with non-mantle-like isotopic signatures. Alternatively, the data may indicate that the major mode of crustal development changed during the supercontinent cycle: the generation of juvenile crust in extensional settings was dominant during supercontinent fragmentation, whereas the stabilization of the generated crust via crustal accretion and reworking was important during supercontinent assembly. The Lu-Hf and O isotope systematics indicate that terreigneous sediments could attain elevated 18O/16O via prolonged sediment-sediment recycling over long crustal residence time, and also that reworking of carbonate and chert which generally have elevated 18O/16O and low Hf contents is minor in granitoid magmatism. The highest 18O/16O in detrital zircon abruptly increased at ca. 2.1 Ga and became nearly constant thereafter. This indicates that reworking of mature sediments increased abruptly at that time, probably as a result of a transition in the dynamics of either granitoid crust formation or sedimentary evolution

  20. Characterization of zirconized silica supports for HPLC

    The preparation and characterization of zirconized silica has been investigated. The material was prepared via the reaction of silica with zirconium tetrabutoxide, optimized by a central composite design and response surface methodology. The new material was characterized by nitrogen adsorption-desorption investigations (BET/BJH) showing specific surface areas adequate for use as a chromatographic support. DRUVS, FTIR, XPS, XAS, XRF and SEM methods also were used to characterize the new material. It was shown that silica networks were not significantly modified with the introduction of zirconium. Surface analyses show that there is appreciable element enrichment at the surface, while significant changes in binding energies of Zr 3d, Si 2p, and O 1s have been detected. The above observations indicate that Si-O-Zr bonds were formed, with zirconium grafted onto the silica surface, yielding a support suitable for HPLC

  1. Zircon Archean of the Transuralian megazone

    Krasnobaev, A. A.; Puchkov, V. N.; Puzhakov, B. A.; Busharina, S. V.; Sergeeva, N. D.


    The Il'inka metamorphic complex (IC) is located in the Transuralian megazone at the latitude of the Chelyabinsk granite pluton, east of the Chelyabinsk graben. The petrological, mineralogical, and age data on the IC indicate the presence of Archean complexes during its formation. Taking into account the importance of the age data on IC, zircons were additionally analyzed using a SHRIMP. For the Transuralian megazone, the analytical data allowed us for the first time to establish the presence of the Neoarchean (2715 ± 15 Ma) substance and two stages of metamorphism of gneisses. The early stage was in the Paleoproterozoic (1970-2130 Ma). The metamorphism of 648 ± 18 Ma ends the evolution of IC.

  2. Thermal expansion in lead zirconate titanate


    The volume anomalies with temperature variations in tin-modified lead zirconate titanate ceramics are investigated. Experimental results show that the volume changes are related to the phase transitions induced with temperature. The magnitude and orientation of crystal volume changes are dependent on the particular phase transition. When antiferroelectrics is transformed to ferroelectrics or paraelectrics the volume expands. Oppositely when ferroelectrics is transformed to antiferroelectrics or paraelectrics the volume contracts. In the transition of antiferroelectric orthorhombic structure to tetragonal structure or ferroelectric low-temperature rhombohedral structure to high-tem- perature rhombohedral structure, there are also revealed apparent anomalies in the curves of thermal expansion. Among them, the volume strain caused by the transition between antiferroelectrics and ferroelectrics is the biggest in magnitude, and the linear expansion dL/L0 and the expansion coefficient (dL/L0)/dT can reach 2.810?3 and 7.5 × 10?4 K?1 respectively.

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

    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)

  4. Thermal behaviour of amorphous zircon prepared by ball milling

    Results are presented on the recrystallisation behaviour of the mineral zircon (ZrSiO4) which has been amorphised by ball milling. X-ray diffraction and thermal analysis techniques were used to investigate the structural evolution after mechanical treatment. Phase transformations detected by the differential thermal analysis technique included transient formation of tetragonal or pseudo cubic ZrO2, followed by recrystallisation of zircon at reduced temperatures of around 1000 C. The behaviour of the milled samples was compared to literature data concerning amorphous zircon prepared by other techniques, including natural and ion beam radiation damage and sol-gel processing. The ball milled zircon was found to have similar thermal behaviour, but had a structural recovery temperature 180-600 C lower than that found for other amorphous samples. (orig.)

  5. Contribution to the study of xenotime and zircon flotation

    Flotation and electrokinetics behaviour have studied with xenotime (YPO4) and zircon (Zr Si O4) from a mixture of grains with 90% xenotime and 10% zircon, produced in cassiterite concentration process. Micro flotation and zeta potential have been also studied, by using oleic acid P.A. and DP1-6256 as collectors, and sodium metasillicate and Procol DA911 as modifier agents

  6. Petrogenesis of Late Permian sodic metagranitoids in southeastern Korea: SHRIMP zircon geochronology and elemental and Nd-Hf isotope geochemistry

    Cheong, Chang-sik; Kim, Namhoon; Kim, Jeongmin; Yi, Keewook; Jeong, Youn-Joong; Park, Chan-Soo; Li, Huai-kun; Cho, Moonsup


    One of the striking tectonomagmatic features recently found in southeastern Korea is the occurrence of ca. 250 Ma high-silica adakite. Sodic metagranitoids mainly consisting of tonalitic-trondhjemitic-granodioritic gneisses occur in the Andong-Cheongsong area adjacent to the Yeongdeok adakite site. To investigate temporal and petrogenetic relationships of these orthogneisses with the adakite, we conducted SHRIMP zircon U-Pb dating as well as elemental and Nd-Hf isotopic analyses. Zircon core ages of the orthogneisses (ca. 262-251 Ma) confirm the widespread occurrence of arc-related Late Permian magmatism in southeastern Korea. The Late Triassic (ca. 230 Ma) zircon overgrowths reflect a thermal overprint probably related to the initiation of another subduction system. The analyzed orthogneisses have major element compositions comparable to the Phanerozoic adakites and Archean TTG suite, such as high SiO2 (58.7-65.5 wt.%) and Al2O3 (17.1-19.1 wt.%) contents and Na2O/K2O ratios (1.83-4.95). However, their moderate Sr/Y (35-43) and La/Yb (14-53) ratios and negative Eu anomalies (Eu/Eu* = 0.75-0.95) are incompatible with the key features reported from the Yeongdeok adakite. Moreover, initial whole-rock εNd (-7.9 to -3.3) and zircon εHf (-0.3 ± 2.4) values of the orthogneisses negate a direct derivation from the subducted slab. Our elemental and Nd-Hf isotopic data collectively suggest that the protoliths of the tonalitic-trondhjemitic-granodioritic gneisses were generated by partial melting of mafic lower crust at depths shallower than the garnet stability field. Our Nd and Hf model ages of the gneisses, together with those previously reported from the Mesozoic granitoids indicate a selective involvement of young source materials along the margin of the Yeongnam massif. The Hf isotopic compositions of zircons from a trondhjemitic gneiss attest to the involvement of primitive melts during their crystallization. The ridge subduction and consequent development of a slab

  7. Preparation of Zircon Whisker Using Carbon Black as Reducing Agent

    WANG San-Hai, JIANG Wei-Hui, FENG Guo, LIU Jian-Min, MIAO Li-Feng, WANG Hong-Da


    Full Text Available Zircon whisker was synthesized at 700°C via non-hydrolytic Sol-Gel method using anhydrous zirconium tetrachloride (ZrCl4 as zirconium source, tetraethylorthosilicate (TEOS as silicon source, lithium fluoride (LiF as mineralizer, ethanol as solvent and carbon black as reducing agent. Thermogravimetric analysis and differential thermal analysis (TG-DTA, X-ray diffraction analysis (XRD and transmission electron microscope (TEM were employed to characterize the influences of adding ways and amount of carbon black on the synthesis and morphology of zircon whisker. The results show that the carbon black added in form of suspension is favorable to the one-dimension growth of zircon. When 6wt% carbon black is added, optimized zircon whiskers are achieved along the growth direction of [001], which diameter and aspect ratio are in the range of 30­90 nm and 6­15, respectively. Because of carbon black reacting with oxygen to form carbon dioxide and monoxide, the adding way and amount of carbon black efficiently regulate the oxygen partial pressure in the reaction system. Reducing oxygen partial pressure can form more SiF4 gas, which is the basis of one-dimensional direction growth of zircon. However, excessively low oxygen partial pressure is against the ZrSiO4 formation. Therefore, appropriate oxygen partial pressure can promote the growth of zircon whisker.

  8. Phonon dispersion relation in zircon: an inelastic neutron scattering study

    Full text: The silicate mineral zircon ZrSiO4 (space group I41/amd ; Z=2) is a host mineral for radioactive elements uranium and thorium in the earth's crust. Zircon undergoes a zircon to scheelite type phase transition at high pressure and temperature. Phonon spectrum is needed to develop a reliable interatomic potential model for the calculation of thermodynamic properties of zircon at high temperature and pressure. We earlier reported the low energy part (5-32 MeV) of the phonon dispersion curves along (100) and (001) directions from a natural single crystal of zircon (volume 4 cc) using triple axis spectrometer at Dhruva. The measurements at high energies requires good energy resolution and intensity. Continuing our work on zircon we have measured the phonon dispersion relation up to 50 MeV from the same single crystal at ISIS, UK using PRISMA spectrometer which is a multi analyser crystal spectrometer employing the time of flight technique. The low energy part of the phonon spectrum measured at Trombay is in good agreement with that measured at ISIS, UK. An independent lattice dynamical model is used for the calculations of one phonon inelastic structure factors for the selection of Bragg points for the inelastic measurements. The measurements are in good agreement with our lattice dynamical calculations

  9. Ion irradiation effects in natural garnets: Comparison with zircon

    The behavior of garnet (A3B2(XO4)3; Ia3d; Z=8) under ion-beam irradiation was investigated in order to compare its radiation susceptibility to another orthosilicate: zircon, ZrSiO4. Five natural end-member compositions were examined by in situ transmission electron microscopy during irradiation with 1.0 MeV Kr2+ over the temperature range of 50-1070 K. The critical amorphization temperature, above which amorphization does not occur, was 1030 K for andradite, but could not be determined for the other garnet composition because the Tc was higher than the highest temperature of the experiment. Based on topologic criterion, the degree of structural freedom in garnet is ∼-2.25 and for zircon ∼-1.5. Based on topology the critical amorphization dose for garnet should be higher than that of zircon; however, the average amorphization dose of garnet (0.20 dpa) is lower than that of zircon (0.37 dpa) at room temperature. This may be the result of the assumed value for the displacement energies, Ed, used in the calculation of dpa. Garnet did not decompose, while zircon decomposes to SiO2+ZrO2 during the ion irradiation at high temperature. This behavior may be related to the phase relations of garnet which melts congruently and zircon which decomposes to ZrO2+SiO2

  10. Creation of a continent recorded in zircon zoning

    Moser, D.E.; Bowman, J.R.; Wooden, J.; Valley, J.W.; Mazdab, F.; Kita, N.


    We have discovered a robust microcrystalline record of the early genesis of North American lithosphere preserved in the U-Pb age and oxygen isotope zoning of zircons from a lower crustal paragneiss in the Neoarchean Superior province. Detrital igneous zircon cores with ??18O values of 5.1???-7.1??? record creation of primitive to increasingly evolved crust from 2.85 ?? 0.02 Ga to 2.67 ?? 0.02 Ga. Sharp chemical unconformity between cores and higher ??18O (8.4???-10.4???) metamorphic overgrowths as old as 2.66 ?? 0.01 Ga dictates a rapid sequence of arc unroofing, burial of detrital zircons in hydrosphere-altered sediment, and transport to lower crust late in upper plate assembly. The period to 2.58 ?? 0.01 Ga included ???80 m.y. of high-temperature (???700-650 ??C), nearly continuous overgrowth events reflecting stages in maturation of the subjacent mantle root. Huronian continental rifting is recorded by the youngest zircon tip growth at 2512 ?? 8 Ma (??? 600 ??C) signaling magma intraplating and the onset of rigid plate behavior. This >150 m.y. microscopic isotope record in single crystals demonstrates the sluggish volume diffusion of U, Pb, and O in zircon throughout protracted regional metamorphism, and the consequent advances now possible in reconstructing planetary dynamics with zircon zoning. ?? 2008 The Geological Society of America.

  11. Early Mesozoic paleogeography and tectonic evolution of the western United States: Insights from detrital zircon U-Pb geochronology, Blue Mountains Province, northeastern Oregon

    LaMaskin, T.A.; Vervoort, J.D.; Dorsey, R.J.; Wright, J.E.


    This study assesses early Mesozoic provenance linkages and paleogeographic-tectonic models for the western United States based on new petrographic and detrital zircon data from Triassic and Jurassic sandstones of the "Izee" and Olds Ferry terranes of the Blue Mountains Province, northeastern Oregon. Triassic sediments were likely derived from the Baker terrane offshore accretionary subduction complex and are dominated by Late Archean (ca. 2.7-2.5 Ga), Late Paleoproterozoic (ca. 2.2-1.6 Ga), and Paleozoic (ca. 380-255 Ma) detrital zircon grains. These detrital ages suggest that portions of the Baker terrane have a genetic affinity with other Cordilleran accretionary subduction complexes of the western United States, including those in the Northern Sierra and Eastern Klamath terranes. The abundance of Precambrian grains in detritus derived from an offshore complex highlights the importance of sediment reworking. Jurassic sediments are dominated by Mesozoic detrital ages (ca. 230-160 Ma), contain significant amounts of Paleozoic (ca. 290, 380-350, 480-415 Ma), Neoproterozoic (ca. 675-575 Ma), and Mesoproterozoic grains (ca. 1.4-1.0 Ga), and have lesser quantities of Late Paleoproterozoic grains (ca. 2.1-1.7 Ga). Detrital zircon ages in Jurassic sediments closely resemble well-documented age distributions in transcontinental sands of Ouachita-Appalachian provenance that were transported across the southwestern United States and modified by input from cratonal, miogeoclinal, and Cordilleran-arc sources during Triassic and Jurassic time. Jurassic sediments likely were derived from the Cordilleran arc and an orogenic highland in Nevada that yielded recycled sand from uplifted Triassic backarc basin deposits. Our data suggest that numerous Jurassic Cordilleran basins formed close to the Cordilleran margin and support a model for moderate post-Jurassic translation (~400 km) of the Blue Mountains Province. ?? 2011 Geological Society of America.

  12. Zircon crytallization and recycling in the magma chamber of the rhyolitic Kos Plateau Tuff (Aegean arc)

    Bachman, O.; Charlier, B.L.A.; Lowenstern, J. B.


    In contrast to most large-volume silicic magmas in continental arcs, which are thought to evolve as open systems with significant assimilation of preexisting crust, the Kos Plateau Miff magma formed dominantly by crystal fractionation of mafic parents. Deposits from this ??? 60 km3 pyroclastic eruption (the largest known in the Aegean arc) lack xenocrystic zircons [secondary ion mass spectrometry (SIMS) U-Pb ages on zircon cores never older than 500 ka] and display Sr-Nd whole-rock isotopic ratios within the range of European mantle in an area with exposed Paleozoic and Tertiary continental crust; this evidence implies a nearly closed-system chemical differentiation. Consequently, the age range provided by zircon SIMS U-Th-Pb dating is a reliable indicator of the duration of assembly and longevity of the silicic magma body above its solidus. The age distribution from 160 ka (age of eruption by sanidine 40Ar/39Ar dating; Smith et al., 1996) to ca. 500 ka combined with textural characteristics (high crystal content, corrosion of most anhydrous phenocrysts, but stability of hydrous phases) suggest (1) a protracted residence in the crust as a crystal mush and (2) rejuvenation (reduced crystallization and even partial resorption of minerals) prior to eruption probably induced by new influx of heat (and volatiles). This extended evolution chemically isolated from the surrounding crust is a likely consequence of the regional geodynamics because the thinned Aegean microplate acts as a refractory container for magmas in the dying Aegean subduction zone (continent-continent subduction). ?? 2007 Geological Society of America.

  13. Zircon crystallization and recycling in the magma chamber of the rhyolitic Kos Plateau Tuff (Aegean arc)

    Bachman, O.; Charlier, B.L.A.; Lowenstern, J. B.


    In contrast to most large-volume silicic magmas in continental arcs, which are thought to evolve as open systems with significant assimilation of preexisting crust, the Kos Plateau Tuff magma formed dominantly by crystal fractionation of mafic parents. Deposits from this ~60 km3 pyroclastic eruption (the largest known in the Aegean arc) lack xenocrystic zircons [secondary ion mass spectrometry (SIMS) U-Pb ages on zircon cores never older than 500 ka] and display Sr-Nd whole-rock isotopic ratios within the range of European mantle in an area with exposed Paleozoic and Tertiary continental crust; this evidence implies a nearly closed-system chemical differentiation. Consequently, the age range provided by zircon SIMS U-Th-Pb dating is a reliable indicator of the duration of assembly and longevity of the silicic magma body above its solidus. The age distribution from 160 ka (age of eruption by sanidine 40Ar/39Ar dating; Smith et al., 1996) to ca. 500 ka combined with textural characteristics (high crystal content, corrosion of most anhydrous phenocrysts, but stability of hydrous phases) suggest (1) a protracted residence in the crust as a crystal mush and (2) rejuvenation (reduced crystallization and even partial resorption of minerals) prior to eruption probably induced by new influx of heat (and volatiles). This extended evolution chemically isolated from the surrounding crust is a likely consequence of the regional geodynamics because the thinned Aegean microplate acts as a refractory container for magmas in the dying Aegean subduction zone (continent-continent subduction).

  14. Zircon U-Pb ages and geochemical characteristics of granitoids in Nagqu area, Tibet

    Sun, Sai-Jun; Sun, Wei-Dong; Zhang, Li-Peng; Zhang, Rong-Qing; Li, Cong-Ying; Zhang, Hong; Hu, Yong-Bin; Zhang, Zhao-Rong


    This paper reports zircon LA-ICP-MS U-Pb ages and Hf-O isotopic ratios, and whole-rock major and trace element data of Early Cretaceous felsic intrusive rocks from Nagqu area, the northern Lhasa subterrane, southern Tibet. LA-ICP-MS zircon U-Pb dating of biotite granites and biotite monzogranites in the area yields magmatic crystallization ages of ca. 112 Ma, which suggests that they were emplaced in the late Early Cretaceous. Both rocks show high-K calc-alkaline to shoshonitic composition and slightly-moderately peraluminous signature. They are enriched in the alkalis, Rb, Th, K, U and light rare earth elements, depleted in Nb, Ta, Ti and P, and characterized by high Al2O3 contents (12-16 wt.%), high Rb/Sr ratios (1.3-33) and low Mg# values (15-39). Their magmatic zircons have negative εHf(t) values (from - 25.9 to 0.5) and high positive δ18O values (from 7.9‰ to 11.5‰). All the above characteristics indicate that Nagqu biotite monzogranites and biotite granites were likely derived from hybrid melts of sediments from the continent crust with minor mantle-derived input, then experienced varied degrees of fractional crystallization. The Nagqu intrusion is a component of the late Early Cretaceous magmatic flare-up event that occurred during ~ 120-100 Ma in the northern and partly central Lhasa subterranes. This magmatic flare-up is marked with a great compositional diversity (basalt, rhyolite, adakitic rocks, dioritic enclave, biotite monzogranite and granite) that might be caused by the slab breakoff of the southward subducting Bangong-Nujiang oceanic lithosphere, or more likely by slab window opening, which may have significantly contributed to juvenile crustal growth of the northern Lhasa subterrane.

  15. The Minerageny of Two Groups of Zircons from Plagioclase- Amphibolite of Mayuan Group in Northern Fujian

    Bao, Xuezhao


    Zircon can crystallize in a wide range of physical and chemical conditions. At the same time, it has very high stability and durability. Therefore zircon can grow and survive in a variety of geological processes. In addition, the diffusivity of chemical compositions in its crystal is very low. Consequently, we can trace back the evolution history of the planetary materials containing zircon by zircon U-Th-Pb geochronology and geochemistry studies. However, this depends on our ability to decipher its genesis, namely magmatic or metamorphic origins. In this paper, magmatic and metamorphic zircons were found from plagioclase-amphibolite samples. Their geneses have been determined by zircon morphology, chemical composition zonations and geological field setting combined with their zircon U-Th-Pb ages. We have found obvious differences in micro-scale Raman spectra between these magmatic and metamorphic zircons. The magmatic zircons exhibit a high sloping background in their Raman spectra, but the metamorphic zirco...

  16. Detrital zircon geochronology of some neoproterozoic to triassic rocks in interior alaska

    Bradley, D.C.; McClelland, W.C.; Wooden, J.L.; Till, A.B.; Roeske, S.M.; Miller, M.L.; Karl, S.M.; Abbott, J.G.


    We report 777 U-Pb SHRIMP detrital zircon ages from thirteen sandstones and metasandstones in interior Alaska. About sixty grains per sample were analyzed; typically, half to three-fourths of these were concordant within ?? 10%. Farewell terrane. Two quartzites were collected from Ruby quadrangle and a third from Taylor Mountains quadrangle. All three are interpreted to represent a low stratigraphic level in the Nixon Fork platform succession; the samples from Ruby quadrangle are probably late Neoproterozoic, and the sample from Taylor Mountains quadrangle is probably Cambrian in age. The youngest detrital zircon in any of the three is 851 Ma. The two Ruby quadrangle samples area almost identical: one has a major age cluster at 1980-2087 and minor age clusters at 944-974 and 1366-1383 Ma; the other has a major age cluster at 1993-2095 Ma and minor age clusters at 912-946 and 1366-1395 Ma. The Taylor Mountains sample shows one dominant peak at 1914-2057 Ma. Notably absent are zircons in the range 1800-1900 Ma, which are typical of North American sources. The detrital zircon populations are consistent with paleontological evidence for a peri- Siberian position of the Farewell terrane during the early Paleozoic. Mystic subterrane of the Farewell terrane. Three graywackes from flysch of the Mystic subterrane, Talkeetna quadrangle, were sampled with the expectation that all three were Pennsylvanian. Asample from Pingston Creek is Triassic (as revealed by an interbedded ash dated at ca. 223 Ma) and is dominated by age clusters of 341-359 and 1804-1866 Ma, both consistent with a sediment source in the Yukon-Tanana terrane. Minor age clusters at 848-869 and 1992-2018 Ma could have been sourced in the older part of the Farewell terrane. Still other minor age clusters at 432-461, 620-657, 1509-1536, and 1627-1653 Ma are not readily linked to sources that are now nearby. Asample from Surprise Glacier is mid-Mississippian or younger. Adominant age cluster at 1855-1883 and a

  17. Geochronology and geochemistry of zircon from the northern Western Gneiss Region: Insights into the Caledonian tectonic history of western Norway

    Gordon, Stacia M.; Whitney, Donna L.; Teyssier, Christian; Fossen, Haakon; Kylander-Clark, Andrew


    The Western Gneiss Region (WGR) of Norway is divided by the Møre-Trøndelag shear zone (MTSZ) into a southern region that contains domains of Caledonian ultrahigh-pressure (UHP) metamorphic rocks (> 2.5 GPa) and a northern area of similar Caledonian-aged rocks that record a maximum pressure reported thus far of ~1.5 GPa. Although both regions contain similar lithologies (primarily migmatitic quartzofeldspathic gneiss containing mafic lenses) and structural relationship of basement rocks to infolded nappes, this difference in maximum pressure implies a difference in tectonic history (continental subduction south of the shear zone, none to the north) and raises questions about the role of the MTSZ in the metamorphic history (including exhumation) of the WGR. Previous geochronology results indicated a difference in timing of peak metamorphism (older in north, younger in south). In order to better understand the tectonic history of the northern WGR and the MTSZ, and in particular the late- to post-Caledonian tectonic history, U-Pb zircon geochronology and trace-element abundances were obtained using the split-stream, laser-ablation ICPMS technique from metabasaltic lenses and migmatitic quartzofeldspathic host rocks from the structurally lowest exposed region of the northern WGR (Roan Peninsula basement), as well as leucosomes from an intercalated portion of the Seve Nappe Complex and a pegmatite in the MTSZ. Zircon from Roan gneiss and metabasite yield metamorphic ages of ca. 410-406 Ma, and zircon from a variety of migmatite samples (foliation-parallel leucosome to dikes) indicate melt crystallization at ca. 410 to 405 Ma. The Seve Nappe leucosomes yield only early Caledonian dates that cluster at ca. 437 Ma and ca. 465 Ma, suggesting that the allochthons in this region did not experience (or record) the same Scandian tectonic history as the basement rocks. Zircon from a weakly deformed pegmatite dike within the MTSZ crystallized at ca. 404 Ma, indicating that this

  18. New SHRIMP zircon results from Broken Hill: towards robust stratigraphic and event timing

    Full text: Zircon U-Pb SHRIMP geochronology is a powerful means of elucidating geological ages, providing that it is integrated with unequivocal field constraints, and providing that the fundamental assumptions which are behind any isotopic dating methods are geologically validated. In an attempt to better quantify the timing of Broken Hill's complex history and to reduce some current uncertainties, we report initial results from a new U-Pb SHRIMP investigation. This program was planned within the background of our own disparate stratigraphic and structural approaches to Broken Hill geology, and with objectives to (a) benchmark our new age results with those of previous workers as well as our own previous work in the Broken Hill Group, (b) evaluate and test the evidence for reported Archaean basement terrain, (c) date stratigraphic units in the upper parts of the Willyama Supergroup, (d) better constrain the timing of deformational events. Our U-Pb SHRIMP work on zircons from layered paragneisses in the Redan Geophysical Zone near Farmcote was catalysed by Nutman and Ehlers' (1998a) preferred interpretation that these 'strondhjemitic' gneisses represent an original ∼2650 Ma protolith. Our work finds zircon provenance age signatures typical of almost all ca. 1700 Ma metasediments, whether in the Broken Hill Block or other Australian Palaeoproterozoic settings. This therefore suggests that the rocks are not Archaean basement, but are part of a Thackaringa Group package possibly deposited about 1705-1710 Ma ago. New SHRIMP work on the Alma Gneiss provides a magmatic age of 1704±3 Ma, and a minimum stratigraphic age for host Thackaringa Group. This result is within error of our ages for other granitoids (1703±3 Ma, 1704±3 Ma) in the same stratigraphic position near Farmcote. As the Thackaringa Group is no more than 1000-1500 metres thick and includes 1710-1700 Ma detrital zircons, pan of the Alma Gneiss intrusion may well have been shallowly intruded, and akin to

  19. Brittle-ductile deformation effects on zircon crystal-chemistry and U-Pb ages: an example from the Finero Mafic Complex (Ivrea-Verbano Zone, western Alps)

    Langone, Antonio; José Alberto, Padrón-Navarta; Zanetti, Alberto; Mazzucchelli, Maurizio; Tiepolo, Massimo; Giovanardi, Tommaso; Bonazzi, Mattia


    A detailed structural, geochemical and geochronological survey was performed on zircon grains from a leucocratic dioritic dyke discordantly intruded within meta-diorites/gabbros forming the External Gabbro unit of the Finero Mafic Complex. This latter is nowadays exposed as part of a near complete crustal section spanning from mantle rocks to upper crustal metasediments (Val Cannobina, Ivrea-Verbano Zone, Italy). The leucocratic dyke consists mainly of plagioclase (An18‑24Ab79‑82Or0.3‑0.7) with subordinate amounts of biotite, spinel, zircon and corundum. Both the leucocratic dyke and the surrounding meta-diorites show evidence of ductile deformation occurred under amphibolite-facies conditions. Zircon grains (up to 2 mm in length) occur mainly as euhedral grains surrounded by fine grained plagioclase-dominated matrix and pressure shadows, typically filled by oxides. Fractures and cracks within zircon are common and can be associated with grain displacement or they can be filled by secondary minerals (oxides and chlorite). Cathodoluminescence (CL) images show that zircon grains have internal features typical of magmatic growth, but with local disturbances. However EBSD maps on two selected zircon grains revealed a profuse mosaic texture resulting in an internal misorientation of ca. 10o. The majority of the domains of the mosaic texture are related to parting and fractures, but some domains show no clear relation with brittle features. Rotation angles related to the mosaic texture are not crystallographically controlled. In addition, one of the analysed zircons shows clear evidence of plastic deformation at one of its corners due to indentation. Plastic deformation results in gradual misorientations of up to 12o, which are crystallographically controlled. Trace elements and U-Pb analyses were carried out by LA-ICP-MS directly on petrographic thin sections and designed to cover the entire exposed surface of selected grains. Such investigations revealed a strong

  20. Bias in Crustal Growth Models Based on age and Isotopic Composition of Detrital Zircon: The Role of Zircon Fertility

    Samson, S. D.


    Early models of continental crustal growth based on the ages of crystallization of granitoids were abandoned once it was understood that many silicic magmas form by remelting pre-existing crustal materials. Subsequent crustal evolution models focused on the age and whole-rock isotopic composition of granitoids or on the isotopic composition of fine-grained clastic sedimentary rocks; rare studies examined both igneous and sedimentary rock compositions. Recently there has been a resurgence of emphasizing major crustal growth events by compiling the ages of detrital zircon. This has led to interesting speculations, such as some supercontinent forming events represent the world's largest orogenies and periods of crustal growth, that there may have been significant hiatuses of crustal production in geologic time, and that there was episodicity in magma generation that is asynchronous with apparent growth peaks based on isotopic compositions of sedimentary rocks. Some workers have emphasized that the apparent trends observed in detrital zircon ages could be a function of selective preservation rather than a strict indication of the timing of major magmatic episodes. Others have noted that relying on ages of detrital crystals is equivalent to basing growth models on granitoid ages and does not discriminate between juvenile magmas and melts formed by complete crustal recycling. More sophisticated approaches involve dating detrital zircon crystals followed by determining their hafnium isotopic composition thereby assessing if the zircon crystallized from a juvenile or recycled magma. While this latter approach holds promise for constraining episodes of juvenile crustal construction it is based on the assumption that the abundance of detrital zircon of a certain age directly reflects the volume of magma generated at that time. In other words, the assumption is implicitly made that the 'zircon fertility' of most magmas is uniform. The assumption of uniform fertility is

  1. Calcium zirconate: preparation, properties and application to the solid oxide galvanic cells

    Stoichiometric, and doped with a small amount of CaO, calcium zirconate dense samples were prepared. X-ray analysis revealed that the solid solution was formed in the concentration range up to x=0.06 in the {xCaO+(1-x)CaZrO3} mixture. The activity of CaO in the solid solution was determined by the emf method at the temperatures 1073 and 1273 K. The electrical conductivity was measured using both dc four-probe and ac impedance spectroscopy methods. The maximum conductivity values were observed for the sample with x=0.06. This sample was used for further investigation. The oxygen-ion transference number, estimated by the emf method, appeared to be close to unity. The partial electronic (electron and electron hole) conductivities, deduced from current-potential curves following the polarisation method, were found to be very small with respect to total electrical conductivity. Then, the sample was tested as an electrolyte in solid oxide galvanic cells. In this way, the values of the standard free enthalpy of formation of cobalt and nickel silicates at the temperatures 1073 and 1273 K were determined and compared with those obtained by other authors

  2. Crystallization process of zircon and fergusonite during hydrothermal alteration in Nechalacho REE deposit, Thor Lake, Canada

    Hoshino, M.; Watanabe, Y.; Murakami, H.; Kon, Y.; Tsunematsu, M.


    The core samples of two drill holes, which penetrate sub-horizontal mineralized horizons at Nechalacho REE deposit in the Proterozoic Thor Lake syenite, Canada, were studied in order to clarify magmatic and hydrothermal processes that enriched HFSE (e.g. Zr, Nb, Y and REE). Zircon is the most common REE minerals in Nechalacho REE deposit. The zircon is divided into five types as follows: Type-1 zircon occurs as single grain in phlogopite and the chondrite-normalized REE pattern is characterized by a steeply-rising slope from the LREE to the HREE with a positive Ce-anomaly and negative Eu-anomaly. This chemical characteristic is similar to that of igneous zircon. Type-2 zircon consists of HREE-rich magmatic porous core and LREE-Nb-F-rich hydrothermal rim. This type zircon is mostly included in phlogopite and fluorite, and occasionally in microcline. Type-3 zircon is characterized by euhedral to anhedral crystal, occurring in a complex intergrowth with REE fluorocarbonates. Type-3 zircons have high contents of REE, Nb and fluorine. Type-4 zircon consists of porous-core and -rim zones, but their chemical compositions are similar to each other. This type zircon is a subhedral crystal rimmed by fergusonite. Type-5 zircon is characterized by smaller, porous and subhedral to anhedral crystals. The interstices between small zircons are filled by fergusonite. Type-4 and -5 zircons show low REE and Nb contents. Occurrences of these five types of zircon are different according to the depth and degree of the alteration by hydrothermal solutions rich in F- and CO3 of the two drill holes, which permit a model for evolution of the zircon crystallization in Nechalacho REE deposit as follows: (1) type-1 (single magmatic zircon) is formed in miaskitic syenite. (2) LREE-Nb-F-rich hydrothermal zircon formed around HREE-rich magmatic zircon (type-2 zircon); (3) type-3 zircon crystallized thorough F and CO3-rich hydrothermal alteration of type-2 zircon which formed the complex

  3. Fabrication of zircon for disposition of weapons plutonium

    This is the final report of a one-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). In an effort to address the problems of long term storage and nuclear waste minimization, zircon has been proposed as a host medium for plutonium and other actinides recovered from dismantled nuclear weapons. The objective of this work is to investigate the feasibility of large scale fabrication of Pu-bearing zircon. Since PuO2 is thermodynamically less stable than ZrO2, it is expected that the process parameters determined for synthesizing ZrSiO4 (zircon) would be applicable to those for PuSiO4 (Pu-zircon). Furthermore, since the foremost concern in plutonium processing is the potential for contamination release, this work emphasizes the development of process parameters, using zircon first, to anticipate potential material problems in the containment system for reaction mixtures during processing. Stoichiometric mixtures of ZrO2 and SiO2, in hundred-gram batches, have been subjected to hot isostatic pressing (HIP) at temperatures near 1,500 C and pressures approximately 10,000 psi. The product materials have been analyzed by x-ray powder diffraction, and are found to consist of zircon after approximately two hours of reaction time. From this work, it is clear that the fabrication of large quantities of Pu-zircon is feasible. The most notable result of this work is evidence for the existence of container problems. This result, in turn, suggests potential solutions to these problems. Experiments with the quartz inner container, the glass sealant, a sacrificial metal barrier, and a metal outer container are being investigated to mitigate these potential hazards

  4. Evidence for multi-cycle sedimentation and provenance constraints from detrital zircon U-Pb ages: Triassic strata of the Lusitanian basin (western Iberia)

    Pereira, M. F.; Gama, C.; Chichorro, M.; Silva, J. B.; Gutiérrez-Alonso, G.; Hofmann, M.; Linnemann, U.; Gärtner, A.


    Laser ablation ICP-MS U-Pb analyses were conducted on detrital zircons of Triassic sandstone and conglomerate from the Lusitanian basin in order to: i) document the age spectra of detrital zircon; ii) compare U-Pb detrital zircon ages with previous published data obtained from Upper Carboniferous, Ordovician, Cambrian and Ediacaran sedimentary rocks of the pre-Mesozoic basement of western Iberia; iii) discuss potential sources; and iv) test the hypothesis of sedimentary recycling. U-Pb dating of zircons established a maximum depositional age for this deposit as Permian (ca. 296 Ma), which is about sixty million years older compared to the fossil content recognized in previous studies (Upper Triassic). The distribution of detrital zircon ages obtained points to common source areas: the Ossa-Morena and Central Iberian zones that outcrop in and close to the Porto-Tomar fault zone. The high degree of immaturity and evidence of little transport of the Triassic sediment suggests that granite may constitute primary crystalline sources. The Carboniferous age of ca. 330 Ma for the best estimate of crystallization for a granite pebble in a Triassic conglomerate and the Permian-Carboniferous ages (age spectra found in Triassic strata are also the result of recycling from the Upper Carboniferous Buçaco basin, which probably acted as an intermediate sediment repository. U-Pb data in this study suggest that the detritus from the Triassic sandstone and conglomerate of the Lusitanian basin is derived from local source areas with features typical of Gondwana, with no sediment from external sources from Laurussia or southwestern Iberia.

  5. Detrital zircon U-Pb ages of the Proterozoic metaclastic-sedimentary rocks in Hainan Province of South China: New constraints on the depositional time, source area, and tectonic setting of the Shilu Fe-Co-Cu ore district

    Wang, Zhilin; Xu, Deru; Hu, Guocheng; Yu, Liangliang; Wu, Chuanjun; Zhang, Zhaochong; Cai, Jianxin; Shan, Qiang; Hou, Maozhou; Chen, Huayong


    The Shilu Fe-Co-Cu ore district, located at Hainan Province of South China, is well known for high-grade hematite-rich Fe ores and also two Precambrian host successions, i.e. the Shilu Group and the overlying Shihuiding Formation. This district has been interpreted as a banded iron formation (BIF) deposit-type, but its depositional time, source area and depositional setting have been in debate due to poor geochronological work. Detrital zircon U-Pb dating aided by cathodoluminescence imaging has been carried out on both the Shilu Group and Shihuiding Formation. Most of the zircon grains from both the successions are subrounded to rounded in morphology and have age spectra between 2000 Ma and 900 Ma with two predominant peaks at ca. 1460-1340 Ma and 1070 Ma, and three subordinate peaks at ca. 1740-1660 Ma, 1220 Ma and 970 Ma. The similar age distribution suggests the same depositional system for both successions. Linked to the geological and paleontological signatures, the Shihuiding Formation is better re-interpreted as the top, i.e. Seventh member of the Shilu Group, rather than a distinct Formation. The youngest statistical zircon age peaks for both successions, i.e. ca. 1070-970 Ma may define the maximum depositional time of the Shilu Group and interbedded BIFs. At least two erosional sources are required for deposition of the studied detrital zircons, with one proximal to provide the least abraded zircons and the other distal or recycled to offer the largely abraded zircons. The predominance of rounded or subrounded zircons over angular zircons probably implies a relatively stable tectonic setting during deposition. Given the Precambrian tectonics of Hainan Island, a retro-arc foreland basin is proposed for the deposition of the Shilu Group and interbedded BIFs. In comparison with those from the South China and other typical Grenvillian orogens, the detrital zircon age populations reveal that Hainan Island had crystalline basement similar to neither the Yangtze

  6. Petrography and detrital zircon study of late Carboniferous sequences in the southwestern North China Craton: Implications for the regional tectonic evolution and bauxite genesis

    Cai, Shuhui; Wang, Qingfei; Liu, Xuefei; Feng, Yuewen; Zhang, Ying


    The North China Craton (NCC) has been flanked by the North Qilian and North Qinling arc-accretionary belts to the south and southwest since ∼400 Ma. The part of the NCC to the east of the Alax terrane (E-NCC) experienced a long sedimentary hiatus and tectonic quiescence between the Middle Ordovician and the late Carboniferous. The northern margin of the E-NCC was reactivated and uplifted with contemporaneous volcanism during the late Carboniferous, an event that partly induced the transformation of the E-NCC from an erosional platform to a continental sedimentary basin. However, the factors controlling this transformation are still not fully understood. A series of sedimentary rocks overlying Ordovician carbonates in the southwestern E-NCC contains a lower iron-oxide layer and an upper phyllosilicate layer. Detrital zircons from different parts of the profile, from the base to the top of the two layers, have similar U-Pb ages. These zircons have a minimum age of ca. 300 Ma and a prominent peak at ca. 450 Ma, with subordinate peaks at ca. 1000 and 2500 Ma. The near-identical minimum age for the two layers suggests they were semi-simultaneously deposited in the late Carboniferous after the long hiatus in sedimentation. Detrital zircons with ages of ∼450 Ma have initial Hf isotopic compositions that vary from large negative to elevated positive. These data, together with the trace element compositions of these zircons, indicate that these minerals formed in a continental arc environment. Samples from the upper sedimentary layer contain mica group minerals that are weakly buckled and fractured, and have weathered to form clay minerals, including chlorite and illite. This suggests that the protolith of this sedimentary layer was dominated by mica schist or mica-bearing granitoid that most likely located near the adjoined part between the North Qilian and North Qinling arc-accretionary belts. Detrital zircons with the youngest ages (ca. 300 Ma) were considered to

  7. Evidence of proterozoic crust under the coastal Cordillera of Central Chile: Grenville age xenocrystic zircons in cretaceous volcanic rocks

    In the central Andes, Proterozoic basement rocks outcrop in isolated areas from beneath a Mesozoic and Cenozoic cover in southern Peru, northernmost Chile, Bolivia, and in northwestern Argentina. Their role in Andean magmatism and metallogenesis is well documented. In the southern Central Andes, Proterozoic rocks are so far known to outcrop in Argentina, east of the continental divide. In the course of U-Pb dating of the bimodal volcanic and sub-volcanic host rocks for Mesozoic manto-type copper deposits, we have encountered xenocrystic zircon with Proterozoic and Paleozoic ages. In the Punta del Cobre Cu-Fe (Au) District (27o30' S / 70o15' W) 22 km south of Copiapo xenocrystic zircon in the Lower Cretaceous host dacite yields ca. 1 Ga ages. In the El Soldado Cu District, (32o38' S /71o04' W), 120 km northwest of Santiago, scarce and strongly resorbed zircon crystals in the Lower Cretaceous host rhyodacite yield ages of 0.5 to 1.3 Ga. The early Cretaceous bimodal volcanic and subvolcanic rocks, which consists of primitive calc-alkaline basalts and rhyodacites, display geochemical evidence of crustal contamination. Our results suggest that, during their formation and ascent, the felsic magmas picked up zircons in the Proterozoic and Paleozoic crystalline basement of the Coastal Cordillera. The presence of Proterozoic (Grenville age) basement underlying localities as close as 30 km from the Pacific coast has implications for the extent and age of the Chilenia Terrane and gives further credence to correlation models that juxtapose eastern North America (Laurentia) and southwestern South America (Gondwana) during the Late Proterozoic (au)

  8. Provenance shift in Cambrian mid-Baltica: detrital zircon chronology of Ediacaran–Cambrian sandstones in Estonia

    Yukio Isozaki


    Full Text Available In order to clarify the tectono-sedimentary history of Paleozoic Baltica, age spectra of detrital zircon grains from the Ediacaran (Kotlin Regional Stage and Lower Cambrian sandstones (lowermost Lontova and Lükati formations in western Estonia in central Baltica were analyzed by LA-ICPMS. The abundant occurrence of Archean to Mesoproterozoic (2800–1000 Ma zircon grains was confirmed in all samples. The new data provided the following information on the provenance of siliciclastic material as well as a major change in the sedimentary regime of the Paleo-Baltic basin during the Early Cambrian: (1 the Ediacaran–Lower Cambrian Paleo-Baltic basin received abundant terrigenous clastics from the core of Baltica underlain by the Archean–Mesoproterozoic crystalline crust, (2 the exposed surface area of the 1600 Ma Rapakivi granites apparently was more extensive during the Ediacaran–Early Cambrian than at present, (3 a major re-organization of the basin geometry occurred in the middle Early Cambrian (ca 530–515 Ma in central Baltica, inducing a change in the sediment supply system, (4 in contrast to the total absence of Neoproterozoic detrital zircon grains before the middle Early Cambrian, their sudden appearance at this time, together with consistent occurrence at least until the mid-Devonian, suggests a significant uplift event located in southeast Baltica and/or in a more easterly land domain (e.g., in Sarmatia, (5 possible sources for the Neoproterozoic zircon grains include the peripheral mobile belts with pan-African signatures around Baltica, e.g., the so-called Gondwanan fragments along the Tornquist margin to the southwest and the Timanian belt along the northeastern margin.

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

    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 207Pb/206Pb 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

  10. 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

    Zulauf, G.; Dörr, W.; Krahl, J.; Lahaye, Y.; Chatzaras, V.; Xypolias, P.


    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

  11. Dielectric and piezoelectric properties of neodymium oxide doped lead zirconate titanate ceramics

    Janardan Singh; N C Soni; S L Srivastava


    The dielectric and electromechanical properties of lead zirconate titanate [Pb(Zr, Ti)O3] ceramic added with neodymium oxide have been systematically studied employing the vector impedance spectroscopic (VIS) technique. The specimens were prepared using the mixed oxide route by adding different mol% of Nd2O3 (0.1 to 7 mol%) in [Pb(Zr, Ti)O3] near morphotropic phase boundary. Piezoelectric equivalent circuit parameters , , $C_a$ in series and $C_b$ in parallel have been determined by simulating /Z/ and plots. Electromechanical coupling coefficients and strain constants for the radial modes show a peak at about 3 mol%, the dielectric constant peaks at about 1 mol% and voltage constants peak at about 0.75 mol% of Nd2O3.

  12. Pb-Pb zircon ages of Archaean metasediments and gneisses from the Dharwar craton, southern India: Implications for the antiquity of the eastern Dharwar craton

    Maibam, B.; Goswami, J. N.; Srinivasan, R.


    207Pb-206Pb ages of zircons in samples of metasediments as well as ortho- and para-gneisses from both the western and the eastern parts of the Dharwar craton have been determined using an ion microprobe. Detrital zircons in metasedimentary rocks from both yielded ages ranging from 3.2 to 3.5 Ga. Zircons from orthogneisses from the two parts also yielded similar ages. Imprints of younger events have been discerned in the ages of overgrowths on older zircon cores in samples collected throughout the craton. Our data show that the evolution of the southwestern part of eastern Dharwar craton involved a significant amount of older crust (>3.0 Ga). This would suggest that crust formation in both the western and eastern parts of the Dharwar craton took place over similar time interval starting in the Mesoarchaean at ca. 3.5 Ga and continuing until 2.5 Ga. Our data coupled with geological features and geodynamic setting of the Dharwar craton tend to suggest that the eastern Dharwar craton and the western Dharwar craton formed part of a single terrane.

  13. Pb–Pb zircon ages of Archaean metasediments and gneisses from the Dharwar craton, southern India: Implications for the antiquity of the eastern Dharwar craton

    B Maibam; J N Goswami; R Srinivasan


    207Pb–206Pb ages of zircons in samples of metasediments as well as ortho- and para-gneisses from both the western and the eastern parts of the Dharwar craton have been determined using an ion microprobe. Detrital zircons in metasedimentary rocks from both yielded ages ranging from 3.2 to 3.5 Ga. Zircons from orthogneisses from the two parts also yielded similar ages. Imprints of younger events have been discerned in the ages of overgrowths on older zircon cores in samples collected throughout the craton. Our data show that the evolution of the southwestern part of eastern Dharwar craton involved a significant amount of older crust (< 3.0 Ga). This would suggest that crust formation in both the western and eastern parts of the Dharwar craton took place over similar time interval starting in the Mesoarchaean at ca. 3.5 Ga and continuing until 2.5 Ga. Our data coupled with geological features and geodynamic setting of the Dharwar craton tend to suggest that the eastern Dharwar craton and the western Dharwar craton formed part of a single terrane.

  14. Protocol for TL dating with zircon: Computer simulation of temperature and dose rate effects

    Turkin, AA; Va Es, HJ; Vainshtein, DI; den Hartog, HW


    Natural zircon is irradiated internally by U and Th impurities. After exposure to ionizing irradiation zircon exhibits thermoluminescence (TL), which can be used to calculate the irradiation dose and the sample age. A kinetic model for TL of zircon developed earlier is used to model the processes relevant for dating. The response of zircon to irradiation at different dose rates is simulated for different temperatures. Several scenarios for the dating procedure are considered, including labora...

  15. Incorporation of network in synthesis of zircon-imprinted polymer and its effect on zircon ion extraction

    Aladin, S.; Amran, M. B.; Buchari, B.; Arcana, I. M.


    The material polymer functionalized on SPE have been developed by ion- imprinted polymer. The ion-polymer with zircon ion as imprint ions were synthesized via bulk polymerization methods by forming binary complex Zr-Xylenol orange in 2-methoxy ethanol and copolymerizing in the presence of styrene as a monomer functional, divinyl benzene as a monomer cross-linker, and peroxide as an initiator. The zircon-imprinted polymer produced the porous polymer. It was indicated that zircon ion imprints were released under conditioning. The polymer particles both prior to and after leaching have been characterized by IR, SEM-EDS, TEM, and pore size. Incorporation of network polymer using divinyl benzene as the cross-linker were performances tested on zircon ion extraction, and the optimum of the mole ratio of styrene/DVB was observed about 1. The decrease of percent extraction of zircon ion when the mole ration of styrene/divinyl benzene polymers were covered, and it was evidenced by the decrease in total pore volume.

  16. Investigation of Trace Elements in Zircon by Nuclear Techniques

    Sixteen samples of Zircon from 4 locations, i.e., Nong Bawn, Namyun, Phrae and Cambodia, were studied by x-ray fluorescence and neutron activation analysis techniques. The result shows that the major elements are Zr and Si while Hf is the minor element. By neutron activation analysis, the trace elements found in every sample were Al. Sc, Y, La, Dy, Yb, Au, Th and U. For samples from Phrae, Tb and Er were also found and the concentration of Al, Dy, Th and U were higher than any other area. It is also found that the color of Zircon samples that contain Tb and Er became darker after irradiation and the present of Al, Sc, , La, Dy, Yb, Au, Th and U might cause the Zircon opaque

  17. Thermoluminescent dating using zircon grains from archaeological ceramics

    A new thermoluminescence dating technique is described which uses zircon grains separated from ceramics. Because the zircons are orders of magnitude more radioactive than typical ceramics or soil, no burial information is needed. Nearly all of the natural dose is from internal alpha particles so effects of ground water and supralinearity are negligible. In a test programme on potsherds of known age, ages for individual homogeneous (unzoned) grains were within 20% of the archaeologic ages; the mean ages of 2 to 5 grains from a potsherd lay within 7% of the archaeologic age on average. The main limitations are that zoned zircon grains must be avoided (which makes the procedure somewhat laborious) and a sample at least 1 g in size is required. (author)

  18. High-pressure crystal chemistry of zircon, monazite, scheelite and related minerals

    Full text: Many crystal structures of ABO4 compounds consists AO8 bisdisphenoids and BO4 tetrahedra. They include important mineral structures, e.g. zircon (ZrSiO4), anhydrite (CaSO4), silver perchlorate (AgClO4), and scheelite (CaWO4). These oxides, because of their compositional diversity and structural simplicity, played a key role in developing comparative crystal chemistry. In addition, zircon-type oxides exist in Nature being important minerals in the Earth mantle. Due to their incorporation of rare-earth (RE) elements they control the RE distribution in igneous rocks. Thus, the knowledge of their high-pressure (HP) structural behavior is relevant for mineral physics and chemistry (also for petrology). On the other hand, last decade RE phosphates and vanadates gained attention due to their optical and luminescent properties. Furthermore, given the crystal-chemical similarity between RE and actinides, phosphates were investigated for their use as solid-state repository for radioactive waste. The study of the HP mechanical and structural properties of ABO4 oxides is relevant for all these subjects. In this presentation different HP pressure studies performed in zircon-, monazite-, and scheelite-type oxides and related minerals (e.g. wolframite, barite, and anhydrite) are reviewed. The studies include XRD, EXAFS, and Raman experiments using a diamond-anvil cell up to 50 GPa as well as ab initio calculations. The combination of the experiments and calculations reveals the existence of complex HP phase-diagrams. In particular, the occurrence of pressure-induced phase transitions is discussed in detail. The differential bond compressibility of different polyhedra is also commented and related to the anisotropic compressibility of the structures. Results for tungstates, molybdates, vanadates, phosphates, chromates, arsenates, silicates, and germanates are shown. Finally, a systematic for the HP structural sequence of the studied oxides is present and discussed (e

  19. Zircon-scale insights into the history of a Supervolcano, Bishop Tuff, Long Valley, California, with implications for the Ti-in-zircon geothermometer

    Reid, M.R.; Vazquez, J.A.; Schmitt, A.K.


    Zircon has the outstanding capacity to record chronological, thermal, and chemical information, including the storage history of zoned silicic magma reservoirs like the one responsible for the Bishop Tuff of eastern California, USA. Our novel ion microprobe approach reveals that Bishop zircon rims with diverse chemical characteristics surround intermediate domains with broadly similar compositions. The highest Y, REE, U, and Th concentrations tend to accompany the largest excesses in Y + REE3+:P beyond what can be explained by xenotime substitution in zircon. Apparent Ti-in-zircon temperatures of <720??C for zircon rims are distinctly lower than most of the range in eruption temperatures, as estimated from FeTi-oxide equilibria and zircon solubility at quench. While permissive of crystallization of zircon at near-solidus conditions, the low Ti-in-zircon temperatures are probably better explained by sources of inaccuracy in the temperature estimates. After apparently nucleating from different melts, zircons from across the Bishop Tuff compositional spectrum may have evolved to broadly similar chemical and thermal conditions and therefore it is possible that there was no significant thermal gradient in the magma reservoir at some stage in its evolution. There is also no compelling evidence for punctuated heat ?? chemical influxes during the intermediate stages of zircon growth. Judging by the zircon record, the main volume of the erupted magma evolved normally by secular cooling but the latest erupted portion is characterized by a reversal in chemistry that appears to indicate perfusion of the magma reservoir by-or zircon entrainment in-a less evolved melt from the one in which the zircons had previously resided. ?? 2010 Springer-Verlag.

  20. Dating of zircons by the fission track method

    This work describes the methodology to date zircons by the Fission Track Method. A brief discussion is made of the physical principles of the method, physical properties of zircons and the geochemical properties of uranium. When starting with a hand sample, a mineral separation is required; to do this the following steps are needed: crushing and sieving of the sample, washing and drying, magnetic separation, heavy liquid separation (Bromoform 2.89 g/cm3, Diyodomethane = 3.31 g/cm3), and manual separation on a stereoscopic microscope. Once the zircon concentrate is obtained, these are mounted on a FEP teflon mount, then polished and etched on an eutectic mix of 10 g. of KOH + 7.2 g. of NaOH, heated to 210 Centigrade degrees. Afterwards the mounts are prepared for irradiation, sterilizing and putting on top of them an external detector (a thin sheet of muscovite poor in uranium content). The package is then wrapped in plastic and sent to the reactor together with standard zircons of known age (Fish Canyon Tuff: Naeser, 1981), mounted in the same way, plus standard glasses of known uranium content. The package was irradiated in a site known as SIRCA (Rotatory Capsules Irradiation System). Then the package is left to decay for several days, and then the external detectors are etched in a 48% concentrated hydrofluoric acid for 5 minutes. Once the samples are processed through the mentioned steps, spontaneous tracks appear in the zircons and induced tracks appear in the external detectors. On counting the tracks one obtains ρs (spontaneous track density) and ρ1 (induced track density). These two parameters together with another one called '#zeta #' (obtained from the standard zircons and glasses), are used to obtain the age of the sample. Zircons from Cerro de Mercado, Durango were dated and the age obtained was 30 ±5 Ma. This date is in agreement with similar results obtained by Fleisher and Naeser (1975) for zircons of the same locality and dated by the same

  1. Plutonium stabilization in zircon: Effects of self-radiation

    Weber, W. J.; Hess, N. J.; Williford, R. E.; Heinisch, H. L.; Begg, B. D.; Conradson, S. D.; Ewing, R. C.


    Zircon (ZrSiO4) is the most thoroughly studied of all candidate ceramic phases for the stabilization of plutonium. Self-radiation damage from α-decay of the 239Pu, which releases a 5.16 MeV α-particle and a 0.086 MeV 235U recoil nucleus, can significantly affect the structure and properties of zircon. Recent computer simulations using energy minimization techniques indicate that the lowest energy configuration occurs for a defect cluster composed of two near-neighbor Pu3+ substitutions on Zr4+ sites and a neighboring charge-compensating oxygen vacancy.

  2. Zircon U-Pb, O, and Hf isotopic constraints on Mesozoic magmatism in the Cyclades, Aegean Sea, Greece

    Fu, Bin; Bröcker, Michael; Ireland, Trevor; Holden, Peter; Kinsley, Leslie P. J.


    Compared to the well-documented Cenozoic magmatic and metamorphic rocks of the Cyclades, Aegean Sea, Greece, the geodynamic context of older meta-igneous rocks occurring in the marble-schist sequences and mélanges of the Cycladic Blueschist Unit is as yet not fully understood. Here, we report O-Hf isotopic compositions of zircons ranging in age from ca. 320 Ma to ca. 80 Ma from metamorphic rocks exposed on the islands of Andros, Ios, Sifnos, and Syros with special emphasis on Triassic source rocks. Ion microprobe (SHRIMP II) single spot oxygen isotope analysis of pre-Cretaceous zircons from various felsic gneisses and meta-gabbros representing both the marble-schist sequences and the mélanges of the study area yielded a large range in δ18O values, varying from 2.7 ‰ to 10.1 ‰ VSMOW, with one outlier at -0.4 %. Initial ɛHf values (-12.5 to +15.7) suggest diverse sources for melts formed between Late Carboniferous to Late Cretaceous time that record derivation from mantle and reworked older continental crust. In particular, variable δ18O and ɛHf( t) values for Triassic igneous zircons suggest that magmatism of this age is more likely rift- than subduction-related. The significant crustal component in 160 Ma meta-gabbros from Andros implies that some Jurassic gabbroic rocks of the Hellenides are not part of SSZ-type (supra-subduction zone) ophiolites that are common elsewhere along the margin of the Pelagonian zone.

  3. Synthesis of submicron CaZrO{sub 3} in combustion reactions

    Khaliullin, Sh. M., E-mail:; Zhuravlev, V. D.; Bamburov, V. G.; Ermakova, L. V. [Russian Academy of Sciences, Institute of Solid State Chemistry, Ural Branch (Russian Federation)


    Submicron CaZrO{sub 3} powder is obtained in combustion reactions (solution combustion synthesis—SCS) with glycine. It is found that SCS reduces the sintering temperature of CaZrO{sub 3} powders. The dielectric properties of calcium zirconate ceramics are studied by the electrochemical impedance method. It is shown that a ceramics of powders obtained by the SCS method has high dielectric characteristics.

  4. Developing Zircon as a Probe of Planetary Impact History

    Wielicki, Matthew


    The identification of Meteor Crater in Arizona as an extraterrestrial impact by Eugene Shoemaker provided the first evidence of this geologic phenomenon and opened the door to a new field of research that has eventually lead to the identification of over ~150 terrestrial impact structures. Subsequently impacts have been evoked in the formation of the moon, delivery of volatiles and bio-precursors to early Earth, creation of habitats for the earliest life and, in more recent times, major mass extinction events. However, understanding the impact flux to the Earth-Moon system has been complicated by the constant weathering and erosion at Earth's surface and the complex nature of impactite samples such that only a hand full of terrestrial craters have been accurately and precisely dated. Currently 40Ar/39Ar step-heating analysis of impactite samples is commonly used to infer impact ages but can be problematic due to the presence of relic clasts, incomplete 40Ar outgassing or excess 40Ar, and recoil and shock effects. The work presented here attempts to develop zircon geochronology to probe planetary impact histories as an alternative to current methods and provides another tool by which to constrain the bolide flux to the Earth-Moon system. Zircon has become the premier geo-chronometer in earth science and geochemical investigation of Hadean zircon from Western Australia has challenged the long-standing, popular conception that the near-surface Hadean Earth was an uninhabitable and hellish world; Zircons may preserve environmental information regarding their formation and thus provide a rare window into conditions on early Earth. Isotopic and petrologic analyses of these ancient grains have been interpreted to suggest that early Earth was more habitable than previously envisioned, with water oceans, continental crust, and possibly even plate tectonics. The Hadean is also suspected to be a time of major planetary bombardment however identifying impact signatures within

  5. Petrography and zircon U-Pb isotopic study of the Bayanwulashan Complex: Constrains on the Paleoproterozoic evolution of the Alxa Block, westernmost North China Craton

    Wu, Sujuan; Hu, Jianmin; Ren, Minghua; Gong, Wangbin; Liu, Yang; Yan, Jiyuan


    The Bayanwulashan Metamorphic Complex (BMC) exposes along the eastern margin of the Alxa Block, the westernmost part of the North China Craton (NCC). BMC is principally composed of metamorphic rocks with amphibole plagiogneiss, biotite plagioclase gneiss and granitic gneiss. Our research has been focused on the petrography and zircon U-Pb geochronology of the BMC to better understand the evolution of the Alxa Block and its relationship with the NCC. Evidences from field geology, petrography, and mineral chemistry indicate that two distinct metamorphic assemblages, the amphibolite and greenschist facies, had overprinted the preexisting granitic gneiss and suggest that the BMC experienced retrograde metamorphic episodes. The LA-ICP-MS zircon U-Pb ages reveal that the primary magmatic activities of BMC were at ca. 2.30-2.24 Ga and the two metamorphic events were at ca. 1.95-1.91 Ga and ca. 1.88-1.85 Ga respectively. These ages indicate that BMC initially intruded during Paleoproterozoic, not as previously suggested at Archean period. The Early Paleoproterozoic metamorphic records and the magmatic thermochronological data in BMC exhibit different evolution paths between the Alxa Block and the NCC. The Alxa Block was most likely an independent Early Paleoproterozoic terrain. Following different amalgamation processes, The Alxa Block combined with Western Block at ca. 1.95 Ga and then united with NCC at ca. 1.85 Ga.

  6. Energetic study of the defect structure of zircon as a host form for nuclear waste

    A set of potential parameters for modeling zircon structure by atomistic simulation techniques was obtained. A reasonable structure model of zircon was established by fitting important properties of zircon. Based on the equilibrium configuration, the formation energies of the basic point defects and the intrinsic disorders in zircon were calculated. The calculated heats of solution of substituting Pu for Zr in different ratios showed that there was an immiscible gap at the composition ratio (Pu 75 mol %-Zr 25 mol %), which means that the amount of substituting Pu for Zr should be confined in 50 mol % when using zircon to immobilize Pu

  7. Kinetics of Pb and U losses from metamict zircon under different P-T-X conditions

    Peculiarities of the kinetics of Pb and U migration from zircon under elevated P, T - parameters depending on the solution chemical composition. 206Pb and 238U contents in zircon were measured in experiments in the case of zircon-solution interaction. It is shown that Pb migration from metamict zircon is controlled by transportation of its atoms in the solution. Low activation energy of Pb in the mineral explains the observed large losses of radiogenic Pb under hypergene conditions. Recrystallization process in the temperature range of 400-600 deg C hampers the migration of Pb atoms. U migration from zircon to the solution is accompanied by its entry into new compounds

  8. Hf isotope compositions and chronology of magmatic zircons from Tarim continental flood basalts: implications for magmatic evolution of the Early Permian Tarim Large Igneous Province in NW China

    Li, Y.; Li, Z.; Yu, X.; Langmuir, C. H.; Yang, S.; Chen, H.


    The Early Permian Tarim Large Igneous Province (TLIP) in the Tarim cratonic block of northwestern China has been largely regarded to be genetically linked with a mantle plume. Recently, some euhedral zircon crystals with magmatic growth zoning have been obtained from the Tarim continental flood basalts (TCFB) for detailed U-Pb chronological and genetic study. The zircons have the concordant 206Pb/238U ages of 297~283 Ma, coinciding with the previously reported whole-rock 40K/39Ar and 40Ar/39Ar ages (292~283 Ma) of their host basalts. In-situ LA-MC-ICPMS Lu-Hf isotopic analyses of Early Permian zircons from the Keping area of the TCFB reveal that the zircons from two basalt sub-groups (Groups 1a, 1b) have a narrow range of 176Hf/177Hf ratios between 0.282422 and 0.282568. Their corresponding ɛHf(t) (t = 290 Ma) values (-6.8~-1.4) are generally lower than their host basalts (-2.3~2.1), and distinctively different from the intrusive rocks (3.0~7.1) and their zircons (4.9~8.8) from the TLIP and the Precambrian crustal rocks (extrusion of basalts and been captured as xenocrysts by the rapidly erupted basaltic lavas. Almost the same ɛHf(t) values between the corroded and uncorroded zircons suggest that the zircons have preserved the initial Hf isotopic compositions from their original source region. Moreover, the very close but relatively higher ɛHf(t) values from the zircons than the inferred sub-continental lithospheric mantle (SCLM) beneath Tarim in the Early Permian [ɛHf(t) = -8.7~-5.2; t = 290 Ma] indicate that the zircons were probably originated from the SCLM with minor addition of depleted mantle magmas during the mantle source partial melting. Both the zircons and their host basalts have almost the same formation ages (~290 Ma) and Hf TDM model ages (ca. 1300~1000 Ma), suggesting that they may have a similar mantle source region. The relatively higher ɛHf(t) values of the basalts than zircons further indicate that more depleted mantle components have been

  9. Late Neoproterozoic magmatism in South Qinling, Central China: Geochemistry, zircon U-Pb-Lu-Hf isotopes and tectonic implications

    Wang, Ruirui; Xu, Zhiqin; Santosh, M.; Yao, Yuan; Gao, Li'e.; Liu, Chunhua


    The Neoproterozoic tectonic evolution of the northern margin of the Yangtze Block in South China remains debated. In this study, we present results from LA-ICP-MS zircon U-Pb geochronology on a suite of intermediate-felsic rocks in South Qinling, Central China which show a mean age of ca. 630 Ma. The zircon εHf(t) values of these rocks mostly range from + 0.44 to + 14.78. Geochemically, the granites and syenite show high total alkali contents, with enrichment in LREE, LILE (Rb, Ba, and K), and HFSE (Th, U, Nb, Ta, Zr, and Hf), and depletion in Sr, P, and Ti, similar to the features of A-type granites. The meta-diorite shows high Na2O, with depletion in Eu, Ti, and LILE (Sr, Rb, Ba, and K), and enrichment in HFSE (Th, U, Nb, Ta, Zr, and Hf). The geochemical features are consistent with formation of the intermediate-felsic suite through fractionation from underplated basaltic magma that originated from sub-continental lithospheric mantle metasomatized by asthenosphere-derived oceanic-island-basalt-like (OIB-like) melts, coupled with minor crustal contamination. We correlate the ca. 630 Ma magmatism with a back-arc rift setting that probably developed in relation to slab tearing during continued slab rollback.

  10. Zircon U-Pb ages and geochemistry of igneous and metamorphic rocks in the northern Prince Charles Mountains, Antarctica

    High-grade metamorphic and felsic igneous rocks from the northern Prince Charles Mountains, East Antarctica, have been characterised geochemically and dated from SHRIMP zircon geochronological data. Around 980 Ma ago, voluminous magmas representing a combination of mantle-derived and intracrustal melts, including orthopyroxene- quartz monzonite ('charnockite') on Loewe Massif and granitic and syenitic intrusions on Mount Collins, were emplaced during a regional high-grade tectonothermal event. Garnet leucogneiss sheets on Mount McCanhy, the products of local partial melting, were also emplaced at about this time. The geology of Fisher Massif is exceptional in that a ca 1280-Ma metavolcanic sequence and coeval granodiorite have been metamorphosed only up to the lower amphibolite facies, and intruded by a ca 1020-Ma biotite granite. None of the analysed samples shows, in its isotopic systematics, the effects of 500-Ma events, prominent elsewhere in East Antarctica. Rare inherited components, 1850-1900 Ma old, were found in some samples. A paragneiss on Mount Meredith yielded 2500-2800-Ma and 1800-2100-Ma detrital zircon populations. (authors)

  11. Magma mixing and the generation of isotopically juvenile silicic magma at Yellowstone caldera inferred from coupling 238U–230Th ages with trace elements and Hf and O isotopes in zircon and Pb isotopes in sanidine

    Stelten, Mark E.; Cooper, Kari M.; Vazquez, Jorge A.; Reid, Mary R.; Barfod, Gry H.; Wimpenny, Josh; Yin, Qing-Zhu


    The nature of compositional heterogeneity within large silicic magma bodies has important implications for how silicic reservoirs are assembled and evolve through time. We examine compositional heterogeneity in the youngest (~170 to 70 ka) post-caldera volcanism at Yellowstone caldera, the Central Plateau Member (CPM) rhyolites, as a case study. We compare 238U–230Th age, trace-element, and Hf isotopic data from zircons, and major-element, Ba, and Pb isotopic data from sanidines hosted in two CPM rhyolites (Hayden Valley and Solfatara Plateau flows) and one extracaldera rhyolite (Gibbon River flow), all of which erupted near the caldera margin ca. 100 ka. The Hayden Valley flow hosts two zircon populations and one sanidine population that are consistent with residence in the CPM reservoir. The Gibbon River flow hosts one zircon population that is compositionally distinct from Hayden Valley flow zircons. The Solfatara Plateau flow contains multiple sanidine populations and all three zircon populations found in the Hayden Valley and Gibbon River flows, demonstrating that the Solfatara Plateau flow formed by mixing extracaldera magma with the margin of the CPM reservoir. This process highlights the dynamic nature of magmatic interactions at the margins of large silicic reservoirs. More generally, Hf isotopic data from the CPM zircons provide the first direct evidence for isotopically juvenile magmas contributing mass to the youngest post-caldera magmatic system and demonstrate that the sources contributing magma to the CPM reservoir were heterogeneous in 176Hf/177Hf at ca. 100 ka. Thus, the limited compositional variability of CPM glasses reflects homogenization occurring within the CPM reservoir, not a homogeneous source.

  12. Rare earth elements in synthetic zircon. 1. synthesis, and rare earth element and phosphorus doping.

    Hanchar, J. M.; Finch, R. J.; Hoskin, W. O.; Watson, E. B.; Cherniak, D. J.; Mariano, A. N.; Chemical Engineering; George Washington Univ.; Univ. of Canterbury; Australian National Univ.; Rensselaer Polytechnic Inst.


    Sedimentary mineral assemblages commonly contain detrital zircon crystals as part of the heavy-mineral fraction. Age spectra determined by U-Pb isotopic analysis of single zircon crystals within a sample may directly image the age composition--but not the chemical composition--of the source region. Rare earth element (REE) abundances have been measured for zircons from a range of common crustal igneous rock types from different tectonic environments, as well as kimberlite, carbonatite, and high-grade metamorphic rocks, to assess the potential of using zircon REE characteristics to infer the rock types present in sediment source regions. Except for zircon with probable mantle affinities, zircon REE abundances and normalized patterns show little intersample and intrasample variation. To evaluate the actual variation in detrital zircon REE composition in a true sediment of known mixed provenance, zircons from a sandstone sample from the Statfjord Formation (North Sea) were analyzed. Despite a provenance including high-grade metasediment and granitoids and a range in zircon age of 2.82 b.y., the zircon REEs exhibit a narrow abundance range with no systematic differences in pattern shape. These evidences show zircon REE patterns and abundances are generally not useful as indicators of provenance.

  13. Mineralogical and microtextural characterization of ''gel-zircon'' from the Manibay uranium mine, Kazakhstan

    Gel-zircon, an unusual Zr-silicate phase from the Manibay uranium mine, northern Kazakhstan, was studied using X-ray diffraction (XRD), electron microprobe energy dispersive X-ray spectroscopy (EDS) and high resolution transmission electron microscopy (HRTEM). XRD results indicate that gel-zircon is mostly amorphous and occurs with numerous impurity phases. Microprobe EDS results indicate a UO2 content up to 9.14 wt.% HRTEM images revealed that the microtexture of gel-zircon consists of nanocrystallites of zircon, 2--10 nm in size, in a dominantly amorphous matrix. Despite the U-Pb age of 420 ± 25 my and the lack of significant crystallinity, the gel-zircon is an apparently chemically durable phase. Leaching of uranium ores which contain gel-zircon as the major U-bearing phase is impossible using existing uranium plant technologies. The alpha-decay dose, 2.64 displacements per atom (dpa), corresponding to the age of gel-zircon is much higher than that (0.5 dpa) required to cause metamictization of crystalline zircon. However, the morphology of gel-zircon which occurs as veins up to 5 mm thick and tens of mm long does not indicate initial crystallinity. Initially crystalline natural zircons often preserve their crystal morphology after metamictization. This amorphous phase is analogous to the highly damaged state characteristic of zircon proposed as a waste form for the disposition of excess weapons plutonium

  14. Extrusion and properties of lead zirconate titanate piezoelectric ceramics

    Cai, S.; Millar, C.E.; Pedersen, L.;


    The purpose of this work was to develop a procedure for fabricating electroceramic actuators with good piezoelectric properties. The preparation of lead zirconate titanate (PZT) piezoelectric ceramic rods and tubes by extrusion processing is described. The microstructure of extrudates...... was investigated in comparision with different processing conditions. Finally, the measuremental results of density, dielectric and piezoelectric properties are reported and analyzed....

  15. Isotope age of zircons of metamorphic formations of Tien Shan

    Results of U-Pb and Pb-Pb determinations of age of zircons of metamorphic layers of Tien Shan, subjected to obvious and concealed contact action of intrusions tearing them are presented. It is shown that construction of discordance in these cases presents intrusion age as the true one

  16. Fission-track dating of zircon by laser ablation ICPMS

    Svojtka, Martin; Košler, J.

    Elsevier. Roč. 66, 15A (2002), s. A756. ISSN 0016-7037. [Goldschmidt Conference. 18.08.2002-23.08.2002, Davos] Institutional research plan: CEZ:AV0Z3013912 Keywords : fission-track * zircon * ICPMS-LA Subject RIV: DB - Geology ; Mineralogy

  17. Raman study of radiation-damaged zircon under hydrostatic compression

    Nasdala, Lutz; Miletich, Ronald; Ruschel, Katja; Váczi, Tamás


    Pressure-induced changes of Raman band parameters of four natural, gem-quality zircon samples with different degrees of self-irradiation damage, and synthetic ZrSiO4 without radiation damage, have been studied under hydrostatic compression in a diamond anvil cell up to ~10 GPa. Radiation-damaged zircon shows similar up-shifts of internal SiO4 stretching modes at elevated pressures as non-damaged ZrSiO4. Only minor changes of band-widths were observed in all cases. This makes it possible to estimate the degree of radiation damage from the width of the ν3(SiO4) band of zircon inclusions in situ, almost independent from potential “fossilized pressures” or compressive strain acting on the inclusions. An application is the non-destructive analysis of gemstones such as corundum or spinel: broadened Raman bands are a reliable indicator of self-irradiation damage in zircon inclusions, whose presence allows one to exclude artificial color enhancement by high-temperature treatment of the specimen.

  18. Evaluating the paleomagnetic potential of single zircon crystals using the Bishop Tuff

    Fu, Roger R; Lima, Eduardo A; Kehayias, Pauli; Araujo, Jefferson F D F; Glenn, David R; Gelb, Jeff; Einsle, Joshua F; Bauer, Ann M; Harrison, Richard J; Ali, Guleed A H; Walsworth, Ronald L


    Zircon crystals offer a unique combination of suitability for high-precision radiometric dating and high resistance to alteration. Paleomagnetic experiments on ancient zircons may potentially constrain the earliest geodynamo, which holds broad implications for the early Earth interior and atmosphere. However, the ability of zircons to record accurately the geomagnetic field has not been fully demonstrated. Here we conduct thermal and room temperature alternating field (AF) paleointensity experiments on 767.1 thousand year old (ka) zircons from the Bishop Tuff, California. The rapid emplacement of these zircons in a well-characterized magnetic field provides a high-fidelity test of the zircons intrinsic paleomagnetic recording accuracy. Successful dual heating experiments on nine zircons measured using a superconducting quantum interference device (SQUID) microscope yield a mean paleointensity of 46.2 +/- 18.8 microtesla (1sigma), which agrees closely with high-precision results from Bishop Tuff whole rock (43...

  19. Thermomagmatic evolution of Mesoproterozoic crust in the Blue Ridge of SW Virginia and NW North Carolina: Evidence from U-Pb geochronology and zircon geothermometry

    Tollo, Richard P.; Aleinikoff, John N.; Wooden, Joseph L.; Mazdab, Frank K.; Southworth, Scott; Fanning, Mark C.


    New geologic mapping, petrology, and U-Pb geochronology indicate that Mesoproterozoic crust near Mount Rogers consists of felsic to mafic meta-igneous rocks emplaced over 260 m.y. The oldest rocks are compositionally diverse and migmatitic, whereas younger granitoids are porphyritic to porphyroclastic. Cathodoluminescence imaging indicates that zircon from four representative units preserves textural evidence of multiple episodes of growth, including domains of igneous, metamorphic, and inherited origin. Sensitive high-resolution ion microprobe (SHRIMP) trace-element analyses indicate that metamorphic zircon is characterized by lower Th/U, higher Yb/Gd, and lower overall rare earth element (REE) concentrations than igneous zircon. SHRIMP U-Pb isotopic analyses of zircon define three episodes of magmatism: 1327 ± 7 Ma, 1180–1155 Ma, and 1061 ± 5 Ma. Crustal recycling is recorded by inherited igneous cores of 1.33–1.29 Ga age in 1161 ± 7 Ma meta-monzogranite. Overlapping ages of igneous and metamorphic crystallization indicate that plutons of ca. 1170 and 1060 Ma age were emplaced during episodes of regional heating. Local development of hornblende + plagioclase + quartz ± clinopyroxene indicates that prograde metamorphism at 1170–1145 Ma and 1060–1020 Ma reached upper-amphibolite-facies conditions, with temperatures estimated using Ti-in-zircon geothermometry at ~740 ± 40 °C during both episodes. The chemical composition of 1327 ± 7 Ma orthogranofels from migmatite preserves the first evidence of arc-generated rocks in the Blue Ridge, indicating a subduction-related environment that may have been comparable to similar-age systems in inliers of the Northern Appalachians and the Composite Arc belt of Canada. Granitic magmatism at 1180–1155 Ma and ca. 1060 Ma near Mount Rogers was contemporaneous with anorthosite-mangerite-charnockite-granite (AMCG) plutonism in the Northern Appalachian inliers and Canadian Grenville Province. Metamorphism at ca. 1160

  20. U-Pb SHRIMP zircon dating of high-grade rocks from the Upper Allochthonous Terrane of Bragança and Morais Massifs (NE Portugal); geodynamic consequences

    Mateus, A.; Munhá, J.; Ribeiro, A.; Tassinari, C. C. G.; Sato, K.; Pereira, E.; Santos, J. F.


    Bragança and Morais Massifs are part of the mega-klippen ensemble of NW Iberia, comprising a tectonic pile of four allochthonous units stacked above the Central-Iberian Zone autochthon. On top of this pile, the Upper Allochthonous Terrane (UAT) includes different high-grade metamorphic series whose age and geodynamic meaning are controversial. Mafic granulites provided U-Pb zircon ages at 399 ± 7 Ma, dating the Variscan emplacement of UAT. In contrast, U-Pb zircon ages of ky- and hb-eclogites, felsic/intermediate HP/HT-granulites and orthogneisses (ca. 500-480 Ma) are identical to those of gabbros (488 ± 10 Ma) and Grt-pyroxenites (495 ± 8 Ma) belonging to a mafic/ultramafic igneous suite that records upper mantle melting and mafic magma crustal underplating at these times. Gabbros intrude the high-grade units of UAT and did not underwent the HP metamorphic event experienced by eclogites and granulites. These features and the zircon dates resemblance among different lithologies, suggest that extensive age resetting of older events may have been correlative with the igneous suite emplacement/crystallisation. Accordingly, reconciliation of structural, petrological and geochronological evidence implies that the development and early deformation of UAT high-grade rocks should be ascribed to an orogenic cycle prior to ≈ 500 Ma. Undisputable dating of this cycle is impossible, but the sporadic vestiges of Cadomian ages cannot be disregarded. The ca. 500-480 Ma time-window harmonises well with the Lower Palaeozoic continental rifting that trace the Variscan Wilson Cycle onset and the Rheic Ocean opening. Subsequent preservation of the high heat-flow regime, possibly related to the Palaeotethys back-arc basin development (ca. 450-420 Ma), would explain the 461 ± 10 Ma age yielded by some zircon domains in felsic granulites, conceivably reflecting zircon dissolution/recrystallisation till Ordovician times, long before the Variscan paroxysm (ca. 400-390 Ma). This

  1. Tectonic implications of new single zircon Pb-Pb evaporation data in the Lossogonoi and Longido ruby-districts, Mozambican metamorphic Belt of north-eastern Tanzania

    Le Goff, Elisabeth; Deschamps, Yves; Guerrot, Catherine


    Three single zircon Pb-Pb evaporation dating studies were performed on felsic orthogneisses and migmatites from the Longido and Lossogonoi ruby districts, Mozambique Belt of north-eastern Tanzania, in order to better constrain the geological setting of gemstone mineralizations. Igneous emplacement ages of protoliths ranging between 2636 and 2448 Ma document for the first time the presence of a Neoarchean to Lower Paleoproterozoic (Siderian) basement reworked in the Late Neoproterozoic Mozambique Belt of north-eastern Tanzania. This ancient crust of unknown dimension is well documented farther south, but also in south-eastern Kenya. A shearing event under high-grade amphibolite facies conditions, postdating the Pan-African metamorphic peak at 640 Ma and following nappes emplacement is demonstrated at ca. 610 Ma from metamorphic zircons of Lossogonoi district. In Lossogonoi district, ruby crystallizes during this last stage of deformation.

  2. Middle Archaean age of Sargur group by single grain zircon dating and geochemical evidence for the clastic origin of metaquartzite from J.C. Pura greenstone belt, Karnataka

    Euhedral zircons from J.C. Pura metaquartzite were dated by single grain evaporation technique which yielded a Pb-Pb age of 3230 ± 5Ma. This date representing the maximum age of the Sargur metaquartzite is fully in accord with previous Sm-Nd model ages and SHRIMP U-Pb zircon ages (ca 3200 Ma) of Sargur rocks from nearby areas. The Sargur group is pervasively intruded by gneisses and granites around 3000 Ma. Still older gneisses seen in the neighbourhood such as the Gorur gneiss of 3300 Ma age may constitute a possible basement to the Sargur supracrustals and represent widespread early Archaean granitic crust of the Dharwar craton. (author). 45 refs., 6 tabs., 4 figs

  3. Chemical characteristics of zircon from A-type granites and comparison to zircon of S-type granites

    Breiter, Karel; Lamarão, C. N.; Krás Borges, R. M.; Dall'Agnol, R.

    1192/195, April (2014), s. 208-225. ISSN 0024-4937 Institutional support: RVO:67985831 Keywords : zircon * A-type granites * S-type granites * Wiborg batholith * Brazil * Krušné hory/Erzgebirge Subject RIV: DD - Geochemistry Impact factor: 4.482, year: 2014

  4. Latest Carboniferous closure of the Junggar Ocean constrained by geochemical and zircon U-Pb-Hf isotopic data of granitic gneisses from the Central Tianshan block, NW China

    Zhang, Xiaoran; Zhao, Guochun; Eizenhöfer, Paul R.; Sun, Min; Han, Yigui; Hou, Wenzhu; Liu, Dongxing; Wang, Bo; Liu, Qian; Xu, Bing


    Once situated between the Central Tianshan and Junggar terranes during Paleozoic time, the Junggar Ocean was a major southern branch of the Paleo-Asian Ocean. Thus, when and how it was closed are essential in understanding the final assembly of the Central Asian Orogenic Belt. However, the exact closure time of the Junggar Ocean remains unresolved due to the lack of reliable timing of collision-related regional metamorphism. This paper reports whole-rock geochemical and zircon U-Pb and Lu-Hf isotopic data for granitic gneisses from the northern margin of the Central Tianshan block, which can provide crucial constraints on the final closure of the Junggar Ocean. Mineral assemblages and geochemical suggest that the protoliths of the Central Tianshan gneisses are weakly peraluminous high-K calc-alkaline I-type granites, possessing typical subduction-related features such as strong enrichment in LREE and LILE and depletion in HFSE. Negative Eu anomalies (δEu = 0.46-0.81) and highly variable zircon Hf isotope compositions indicate various amounts of residual plagioclase in the source and crustal contamination during magma formation. LA-ICPMS U-Pb dating on magmatic-type zircons (72%), characterized by euhedral to subhedral shapes, concentric oscillatory zoning, high Th/U ratios (0.30-2.05) and large ranges of εHf(t) values (- 3.4 to + 8.7; up to 6 epsilon units in each sample), yields consistent weighted mean 206Pb/238U ages of ca. 325-320 Ma, interpreted as the crystallization ages of the granitic protoliths. Geochemical signatures and dominantly positive zircon εHf(t) values reveal that the protoliths were emplaced in a continental arc setting, pinpointing the development of a late Early to early Late Carboniferous continental arc system on the northern margin of the Central Tianshan block, probably related to the southward subduction of the Junggar oceanic plate. Meanwhile, younger ages at ca. 303-301 Ma were obtained on recrystallized zircon-rims and unzoned

  5. Age of meta-rhyolite of Marata sequence, Araxa Group, Goias: geochronology study by U-Pb in zircon, Rb-Sr and Sm-Nd methods

    U-Pb isotopic analyses in eight zircon fractions separated from a meta-rhyolite sample of the Marata sequence (Araxa Group, Goias) are presented. Two morphologically distinct zircon populations were identified: stubby prismatic crystals (width:length of 1:2 to 1:3) in which core-overgrowth relationships are observed; long prismatic crystals (needles) with width:length ratios of ca. 1:10. Analyses performed on group zircons indicated the presence of a ca. 2.0 Ga. old inherited component. Analyses of group zircons plot very close to the concordia and yield an upper intercepts age of 794 ± 10 Ma for the crystallization of the volcanic protolith. The study was complemented with whole-rock isotopic analyses by the Rb-Sr and Sm-Nd methods. Rb-Sr isochron obtained with samples from two different outcrops gave data of 829 ± 82 Ma (initial 87 Sr/86 Sr of 0.7057 ± 0.0157) and 691 ± 30 Ma (initial 87 Sr/86 Sr of 0.7337 ± 0.0034). The latter reflects a later Sr-isotopic re-homogenization episode, possibly associated with the intense deformation and metamorphism suffered by these rocks. Sm-Nd isotopic analyses on three samples reveal ENd (T) (T =794 Ma) values in the range of -6.1 to -9.5 which indicate the presence of older (early Proterozoic) crustal Nd. This is consistent with the inheritance pattern shown in the U-Pb isotopic results. (author)

  6. Component geochronology of the ca. 3920 Ma Acasta Gneiss

    Cates, Nicole L.; Mojzsis, Stephen J.; Caro, Guillaume; Hopkins, Michelle D.; Abramov, Oleg; Trail, Dustin; Bleeker, Wouter; Guitreau, Martin; Blichert-Toft, Janne


    Compiled U-Pb zircon ages of the oldest parts of the Acasta Gneiss Complex (AGC) in the Northwest Territories (Canada) span about 4050-3850 Ma (Stern and Bleeker, 1998); yet older 4200 Ma xenocrystic U-Pb zircon ages have also been reported for this terrane (Iizuka et al., 2006). The AGC has at least 50 km2 of outcrop exposure, but only a small subset has been documented in the detail required to investigate a complex history. To better understand this history, ion microprobe zircon geochronology was combined with whole-rock and zircon rare earth element compositions (+Y; [REE+Y]zirc) and Ti-in-zircon thermometry (Tixln) from a sub-divided ~60 cm2 slab of Acasta banded gneiss, and compared to other nearby variably deformed AGC granitoid gneiss samples. Micro-sampling by this method reveals components with distinctive [Th/U]zirc vs. Tixln and [REE+Y]zirc that are correlative with separate 235,238U-207,206Pb zircon age populations and whole-rock compositions, but not with 147Sm-143Nd isotope systematics. Lattice-strain theory used to model [REE+Y] reconciles U-Pb zircon geochronology for the individual components, which also preserve strong positive Eu* anomalies. Modeling shows that the magmas that gave rise to the oldest domains formed at contemporary oxygen fugacities. The AGC preserves a legacy older than about 4000 Ma, but this derives from incomplete assimilation of older crust. Magmatic emplacement at ca. 3920 Ma is contemporaneous with the Late Heavy Bombardment (LHB) of the Moon. Later superimposed Eoarchean events (3850-3720 Ma) are reminiscent of formation times for the Itsaq Gneiss Complex in West Greenland (Nutman et al., 1996), Nuvvuagittuq Supracrustal Belt in northern Québec (Cates et al. 2013), and Manfred Complex in Western Australia (Kinny et al., 1990). Equilibration of Sm-Nd occurred at the scale of individual components over the course of one or more of these events.

  7. Finite lattice distortion patterns in plastically deformed zircon grains

    E. Kovaleva


    Full Text Available This study examines finite deformation patterns of zircon grains from high-temperature natural shear zones. Various zircon-bearing rocks were collected in the Western Tauern Window, Eastern Alps, where they were deformed under amphibolite facies conditions, and in the Ivrea-Verbano Zone (IVZ, Southern Alps, where deformation is related with granulite-facies metamorphism. Among the sampled rocks are: granitic orthogneisses, meta-lamprophyres and paragneisses, all of which are highly deformed. The investigated zircon grains ranging from 10 to 50 microns were studied in situ using a combination of scanning electron microscope (SEM techniques, including secondary electron (SE, backscattered electron (BSE, forward scattered electron (FSE, cathodoluminescence (CL imaging, and crystallographic orientation mapping by electron backscatter diffraction analysis (EBSD, as well as micro-Raman spectroscopy. Energy-dispersive X-ray spectrometry (EDS was applied to host phases. Microstructural analysis of crystal-plastically deformed zircon grains was based on high-resolution EBSD maps. Three general types of finite lattice distortion patterns were detected: Type (I is defined by gradual bending of the zircon lattice with orientation changes of about 0.6° to 1.4° per μm without subgrain boundary formation. Type (II represents local gradual bending of the crystal lattice coupled with the formation of subgrain boundaries that have concentric semicircular shapes in 2-D sections. Cumulative grain-internal orientation variations range from 7° to 40° within single grains. Type (III is characterized by formation of subgrains separated by a well-defined subgrain boundary network, where subgrain boundaries show a characteristic angular closed contour in 2-D sections. The cumulative orientation variation within a single grain ranges from 3° to 10°. Types (I and (II predominate in granulite facies rocks, whereas type (III is restricted to the amphibolite facies

  8. Zircon dating of Neoproterozoic and Cambrian ophiolites in West Mongolia and implications for the timing of orogenic processes in the central part of the Central Asian Orogenic Belt

    Jian, Ping; Kröner, Alfred; Jahn, Bor-ming; Windley, Brian F.; Shi, Yuruo; Zhang, Wei; Zhang, Fuqin; Miao, Laicheng; Tomurhuu, Dondov; Liu, Dunyi


    We present new isotopic and trace element data to review the geochronological/geochemical/geological evolution of the central part of the Central Asian Orogenic Belt (CAOB), and find a fundamental geological problem in West Mongolia, which has traditionally been subdivided into northwestern early Paleozoic (formerly Caledonian) and southerly late Paleozoic (formerly Hercynian) belts by the Main Mongolian Lineament (MML). We resolve this problem with SHRIMP zircon dating of ophiolites and re-evaluation of much published literature. In Northwest Mongolia the Dariv-Khantaishir ophiolite marks the boundary between the Lake arc in the west and the Dzabkhan-Baydrag microcontinent in the east. Zircons from a microgabbro and four plagiogranites yielded weighted mean 206Pb/238U ages of 568 ± 5 Ma, 567 ± 4 Ma, 560 ± 8 Ma (Dariv), 573 ± 8 Ma and 566 ± 7 Ma (Khantaishir) that we interpret as reflecting the time of ophiolite formation (ca. 573-560 Ma). Metamorphic zircons from an amphibolite on a thrust boundary between the Khantaishir ophiolite and the Dzabkhan-Baydrag microcontinent formed at 514 ± 8 Ma, which we interpret as the time of overthrusting. In South Mongolia the Gobi Altai ophiolite and the Trans-Altai Gurvan Sayhan-Zoolen forearc with an ophiolite basement were investigated. Zircons of a layered gabbro (lower ophiolite crust) and a leucogabbro (mid-upper crust) of the Gobi Altai ophiolite yielded crystallization ages of 523 ± 5 Ma and 518 ± 6 Ma. The age data constrain the formation time of ophiolite within ca. 523-518 Ma. Zircons from four samples of the Gurvan Sayhan-Zoolen forearc, with similar hybrid adakite-boninite affinities, yielded 519 ± 4 Ma for an anorthosite, ≥ 512 ± 4 Ma for a hornblendite and 520 ± 5 and 511 ± 5 Ma for two diorites. The ophiolite basement has an upper age limit of 494 ± 6 Ma, determined by dating a tonalite dike cutting the Zoolen ophiolite. Integrating available zircon ages as well as geochemical and geological data

  9. Metasedimentary melting in the formation of charnockite: Petrological and zircon U-Pb-Hf-O isotope evidence from the Darongshan S-type granitic complex in southern China

    Jiao, Shu-Juan; Li, Xian-Hua; Huang, Hui-Qing; Deng, Xi-Guang


    Charnockites are Opx-bearing igneous rocks commonly found in high-grade metamorphic terranes. Despite being volumetrically minor, they show a wide range in both bulk geochemistry and intensive parameters. They form a characteristic component of the AMCG (anorthosite-mangerite-charnockite-granite) suite, but their association with typical S-type granites is less well-known. The Darongshan S-type granitic complex (DSGC) in Guangxi Province, southern China, contains granites varying in mafic silicate mineral assemblages from Bt + Crd (Darongshan suite) to Opx + Grt + Bt + Crd (Jiuzhou suite) and Opx + Crd ± Bt (Taima suite), corresponding to a geochemical transition from magnesian calc-alkalic to ferroan calc-alkalic. However, its genesis, even the accurate age of intrusion, remains highly contentious despite intensive research. In order to understand the genesis of charnockite and its genetic relationship with S-type granite; here, we first determined zircon U-Pb ages of each suite using a SIMS on the basis of a detailed petrological study. Zircon U-Pb ages show that all suites of the complex were emplaced contemporaneously at ca. 249 Ma. Monazite apparent U-Pb ages are indistinguishable from zircon U-Pb ages within analytical error. Further in situ zircon Hf-O isotope analyses reveal that the granitic complex was dominantly derived from reduced melting metasedimentary rocks (δ18Ozircon = ca. 11‰; εHf(t)zircon = ca. - 10; Δlog FMQ ≤ 0; Mn in apatite oxybarometer) with rare material input from the mantle. The variation in δ18O (7.8‰-12.9‰) is more likely a result of hybridization, whereas that in εHf(t) (- 31.9 to - 1.8) is a result of both hybridization and disequilibrium melting. The variation in mineralogy and geochemistry may be interpreted as a result of entrainment of peritectic garnets from biotite-dehydration melting. Nevertheless, heat input from mantle through basaltic intrusion/underplating is considered to play a major role in high

  10. The anatectic effect on the zircon Hf isotope composition of migmatites and associated granites

    Chen, Yi-Xiang; Gao, Peng; Zheng, Yong-Fei


    Zircon Hf isotope composition is widely used to trace the growth and evolution of continental crust. However, it is controversial whether the Hf isotope composition of magmatic zircons can faithfully reflect that of their sources, especially for S-type granites. In order to provide an insight into this issue, we have revisited the published Lu-Hf isotope data of zircons from well-studied migmatites and associated granites in the Sulu orogen and the Cathaysian terrane, respectively. The results show greatly elevated 176Hf/177Hf ratios (by more than 10ε units) for newly grown zircon domains compared to the relict zircon domains. This indicates considerable contributions from non-zircon Hf to anatectic melts during crustal anatexis and subsequent magmatism. Furthermore, this more radiogenic Hf isotope signature was not erased during magmatic processes such as crystal fractionation during melt ascent and emplacement. The budget of Hf isotopes in source rocks with respect to mineral Lu/Hf ratios suggests the involvement of Hf-bearing major minerals in anatectic reactions by dissolving Hf-bearing major minerals into the anatectic melts. The significant Hf isotope variations in some anatectic and magmatic zircon domains from the migmatites and granites suggest not only the source heterogeneity but also the variable non-zircon Hf contributions. As such, the Hf isotope compositions of anatectic and magmatic zircons are substantially dictated by the mass balance between the non-zircon Hf from anatectic reactions and the zircon-Hf from the dissolution of protolith zircons into the anatectic melts. They are primarily controlled by P-T conditions and mechanism of crustal anatexis, and the magmatic processes during melt evolution. The present study highlights the important contribution of non-zircon Hf to the anatectic and magmatic zircon domains. In this regard, the greatly elevated 176Hf/177Hf ratios for newly grown zircon domains in the migmatites and granites cannot reflect

  11. The Ordovician-Silurian tectonic evolution of the northeastern margin of the Tarim block, NW China: Constraints from detrital zircon geochronological records

    Dong, Shunli; Li, Zhong; Jiang, Lei


    The northeastern margin of the Tarim block is a key tectonic-unit for understanding the evolution processes and geodynamic mechanisms of basin-range coupling between the Paleo-Asian tectonic realm to the north and the Tarim block to the south during the Paleozoic period. Four Upper Ordovician-Silurian sandstone samples were collected from the Tabei and Quruqtagh areas for measuring the detrital zircon U-Pb dating and Hf isotopic compositions, with an aim to decipher the provenances and elucidate the tectonic implications. The results show that all the sandstone samples yield evident detrital zircon U-Pb age groups of ca. 1100-720 Ma and ca. 2100-1700 Ma, demonstrating that the Tarim block was once a part of the Rodinia and Columbia supercontinents during the Neoproterozoic and the Paleoproterozoic, respectively. Remarkably, the Upper Ordovician sandstone sample from the Tabei area yields a higher proportion in age group of ca. 1100-900 Ma than that of ca. 860-720 Ma, whilst the Lower Silurian sample yields the opposite result. The former and the latter age groups aforementioned are consistent with the age patterns of the tectono-thermal events in the Central Tianshan microcontinent and the Tarim block, respectively. Combined with valuable igneous rock information, it is indicative that the Central Tianshan microcontinent drifted away from the proto Tarim block (with attachment of the Central Tianshan microcontinent) most likely at the Early Silurian. The Upper Silurian sandstone in the South Quruqtagh area yield massive detrital zircon U-Pb ages with a peak age of ca. 450 Ma, combining the Late Ordovician magmatic rocks reported from the Central Tianshan and northeastern Tarim margin, which suggests that there was a broad magmatic arc along the northeastern proto Tarim margin during the Late Ordovician. The opening of the South Tianshan Ocean began in the Early Silurian and continued in the Late Silurian, leaving a remanent magmatic arc along northeastern Tarim

  12. Application of mineral binders during briquetting of zircon concentrate

    The paper studies a possibility to use mineral binders for briqueting zircon-blaring concentrates subject to chloride treatment in shaft furnaces. The effect of chloride treatment time and carbon content in the brickets on concentrates component break-down is investigated. Efficiency of mineral binder (bentonite and sodium silicate) application is confirmed: power consumption and treatment time decrease 8-10 times, a high level of concentrate break-down is achieved

  13. Feasibility of infrared analysis of iron in zircon

    A feasibility study has concluded that quantitative infrared analysis can be employed to determine the concentration of iron in zircon. The spectral transmission curves have shown that the iron absorption band is located at 1.15 microns. These curves also revealed a second absorption band at 1.49 microns. The source of this second peak is not known; but it exhibits some features which suggest its dependance on natural α-recoil damage. 23 references, 14 figures, 2 tables

  14. Comment on''Large Swelling and Percolation in Irradiated Zircon''

    A recent model for the large radiation-induced swelling behavior in irradiated zircon (ZrSiO4) is partially based on results of molecular dynamics simulations of the partial overlap of two collision cascades that predict a densified boundary of polymerized silica and the scattering of the second cascade away from the densified boundary (Trachenko K, Dove M T and Salje E K H 2003 J. Phys.: Condens. Matter 15 L1). These MD simulations are based on an atomic interaction potential for zircon (Trachenko K, Dove MT and Salje EKH 2001 J. Phys.: Condens. Matter 13 1947) for which, according to our analysis, only reproduces some of the crystallographic properties at equilibrium and do not adequately describe the scattering physics for zircon, and on simulation methodologies for which the standard procedures for boundary conditions of energetic events are ill-defined. In fact, the interatomic potential model used by Tranchenko et al yields a significantly more rigid structure, with very high Frenkel defect formation energies and extremely low entropy and specific heat capacity. The synergy of all these unphysical properties for zircon, naturally leads to highly localized collision cascades. Consequently, the reported results of the cascade simulations, which are events far from equilibrium, may be artifacts of both the potential model and simulation methodologies employed. Thus, the structural changes predicted by the simulations must be viewed cautiously, and these simulations results cannot be taken as confirmation of a new scattering physics process that is the basis for the proposed swelling model. In this comment, the deficiencies in the atomic interaction potential and methodologies employed by these authors are critically reviewed, and the validity of the cascade overlap simulations and proposed physics is discussed

  15. Plasma Sprayed Zircon Deposits Modified by Laser Treatment

    Kolman, Blahoslav Jan; Neufuss, Karel; Jančárek, A.; Dubský, Jiří; Chráska, Pavel

    Tallinn, 2003 - (Ugaste, U.), s. 69-78 ISBN 9985-58-276-4. ISSN 1736-0633. [Dense Plasma Interaction with Materials.. Tallinn (EE), 09.10.2003-11.10.2003] R&D Projects: GA ČR GA106/01/0094 Institutional research plan: CEZ:AV0Z2043910 Keywords : plasma, spraying, zircon Subject RIV: JK - Corrosion ; Surface Treatment of Materials

  16. Study of natural zircon-xenotime assemblages for estimation of the actinide waste forms stability

    In order to estimate compositions and structural stability of YPO4-ZrSiO4-USiO4-ThSiO4 solid solution, natural specimens of (U, Th)-enriched zircon-xenotime assemblages were studied. The samples were picked from granitic pegmatites of North Karelia of about 1,850 Ma age. TEM data show that amorphization of the zircon structure is not complete. Xenotime has typical crystal structure. ASEM and EPMA results indicate that zircon and xenotime are micro-heterogeneous in there compositions. Numerous micro-inclusions (3+ vs. Zr4+ and P5+ vs. Si4+). Data on high amounts of rare earth elements and phosphorus in natural zircons are result from REE-phosphate inclusions in analyzed zircons. Content of U in the zircon allowed the estimation of the solubility of coffinite end member to be no less than 5 mol.% USiO4

  17. Perfect zircon for rock dating no fairy tale

    The scheme used to date rocks is based on the radioactive decay of uranium. Minute traces of uranium locked inside the zircon crystals have been decaying over aeons, producing lead. Scientists know that the decay occurs at a fixed rate and how quickly it happens. By measuring the relative amounts of uranium and lead encased in the crystals, scientists can determine how old the rock is. But sometimes lead is lost from zircon crystals via processes such as weathering (if the rocks were exposed on the surface) or deformation and metamorphism (if the rocks had crystallised deep in the earth and been subjected to high temperatures and pressure). Hence the special nature of the Temora rocks- a 417 million years old zirconium-containing rock which have been partially exposed in recent times in a remote paddock in NSW, Australia. SHRIMP dating was used for initial tests on the Temora rocks. Then, in December last year, the sample was sent to the world-recognised authority, Canada's Royal Ontario Museum, for independent analysis and dating via chemical decomposition. The museum confirmed the near perfect quality of the zircon and its age

  18. Diffuse x-ray scattering from weakly metamict zircon

    Diffuse x-ray (Cu K1α) scattering from α-decay radiation-damaged natural zircon has been investigated at room temperature. Huang scattering around Bragg reflections was observed in samples with radiation doses between 0.06 and 2x1018 α-decay events g-1, but none in a highly crystalline natural zircon sample (18 α-decay events g-1). Huang scattering (∼q-2) dominates for small wavevectors, while Stokes-Wilson scattering (∼q-4) is observed at larger values of q from the Bragg reflection. The displacement field produced by α-decay radiation damage is shown to correspond to transverse shear waves. The unit-cell expansion observed in zircon is thus interpreted as originating as a consequence of the shear waves propagating in the crystal, rather than from simply longitudinal expansion waves. A cluster size between 70 and 140 A, depending on the degree of damage, characterizes the defect accumulation. (author)

  19. Radiological safety assessment in zircon sand handling plant

    In addition to the application of the zircon in nuclear field, there are other non-nuclear applications of zirconium where different grades of zircon sands are micronised to manufacture zirconium silicate to be used in ceramic tiles, sanitary wares etc. The zircon sand is either obtained locally or imported from two agencies abroad. The production of different grades of silicate involves specific physical and chemical processes and the quality of product changes with chemical compositions used, density of slurry and the particle size. A radiological protection survey was conducted at the plant where zirconium silicate (ZIRCOSIL) is being produced on commercial scale. Air monitoring carried out at this plant has shown radiation levels within the permissible limits. However the exposures rates, at the places where raw and finished products were stored, were found in the range of 0.35 - 1.96μ Sv/h. The final product has the specific concentration of 3.53 ± 0.03 kBq/Kg of 238U and 0.67± 0.008 kBq/kg of 232Th. (author)

  20. Extrapolation of zircon fission-track annealing models

    One of the purposes of this study is to give further constraints on the temperature range of the zircon partial annealing zone over a geological time scale using data from borehole zircon samples, which have experienced stable temperatures for ∼1 Ma. In this way, the extrapolation problem is explicitly addressed by fitting the zircon annealing models with geological timescale data. Several empirical model formulations have been proposed to perform these calibrations and have been compared in this work. The basic form proposed for annealing models is the Arrhenius-type model. There are other annealing models, that are based on the same general formulation. These empirical model equations have been preferred due to the great number of phenomena from track formation to chemical etching that are not well understood. However, there are two other models, which try to establish a direct correlation between their parameters and the related phenomena. To compare the response of the different annealing models, thermal indexes, such as closure temperature, total annealing temperature and the partial annealing zone, have been calculated and compared with field evidence. After comparing the different models, it was concluded that the fanning curvilinear models yield the best agreement between predicted index temperatures and field evidence. - Highlights: ► Geological data were used along with lab data for improving model extrapolation. ► Index temperatures were simulated for testing model extrapolation. ► Curvilinear Arrhenius models produced better geological temperature predictions

  1. The metamictization of zircon: Radiation dose-dependent structural characteristics

    A suite of gem zircon samples from Sri Lanka has been studied using infrared (IR) spectroscopy, X-ray diffraction, and chemical analysis. The degree of metamictization of the zircon, as indicated by unit-cell parameters, increases systematically with U-Th content up to the point of total metamictization. The appearance of IR spectra also varies as a function of metamictization. The appearance of IR spectra also varies as a function of metamictization; bands related to Si-O bonds and disappearance of bands related to Zr-O bonds indicates that the structure of metamict zircon consists of distorted and disoriented isolated silica tetrahedra with few if any undisplaced Zr cations. All spectroscopic indicators of crystalline order show that total metamictization is reached at an accumulated radiation dosage of ∼ 4.5 x 1015 alpha decay events per mg. Hydrous components enter the structure only after total metamictization, but the amounts are not correlated with U-Th content. In all cases OH was the only hydrous species detected

  2. Deciphering igneous and metamorphic events in high-grade rocks of the Wilmington complex, Delaware: Morphology, cathodoluminescence and backscattered electron zoning, and SHRIMP U-Pb geochronology of zircon and monazite

    Aleinikoff, J.N.; Schenck, W.S.; Plank, M.O.; Srogi, L.A.; Fanning, C.M.; Kamo, S.L.; Bosbyshell, H.


    High-grade rocks of the Wilmington Complex, northern Delaware and adjacent Maryland and Pennsylvania, contain morphologically complex zircons that formed through both igneous and metamorphic processes during the development of an island-arc complex and suturing of the arc to Laurentia. The arc complex has been divided into several members, the protoliths of which include both intrusive and extrusive rocks. Metasedimentary rocks are interlayered with the complex and are believed to be the infrastructure upon which the arc was built. In the Wilmingto n Complex rocks, both igneous and metamorphic zircons occur as elongate and equant forms. Chemical zoning, shown by cathodoluminescence (CL), includes both concentric, oscillatory patterns, indicative of igneous origin, and patchwork and sector patterns, suggestive of metamorphic growth. Metamorphic monazites are chemically homogeneous, or show oscillatory or spotted chemical zoning in backscattered electron images. U-Pb geochronology by sensitive high resolution ion microprobe (SHRIMP) was used to date complexly zoned zircon and monazite. All but one member of the Wilmington Complex crystallized in the Ordovician between ca. 475 and 485 Ma; these rocks were intruded by a suite of gabbro-to-granite plutonic rocks at 434 ?? Ma. Detrital zircons in metavolcanic and metasedimentary units were derived predominantly from 0.9 to 1.4 Ga (Grenvillian) basement, presumably of Laurentian origin. Amphibolite to granulite facies metamorphism of the Wilmington Complex, recorded by ages of metamorphic zircon (428 ?? 4 and 432 ?? 6 Ma) and monazite (429 ?? 2 and 426 ?? 3 Ma), occurred contemporaneously with emplacement of the younger plutonic rocks. On the basis of varying CL zoning patterns and external morphologies, metamorphic zircons formed by different processes (presumably controlled by rock chemistry) at slightly different times and temperatures during prograde metamorphism. In addition, at least three other thermal episodes are

  3. Study on roasting process of zircon-silica sol ceramic mould

    Zhang Yeming; Zeng Ming; Hu Li


    Dry stock of silica sol ceramic mould was prepared by using of colloidal moulding technique with an optimized vacuum drying process. Effect of roasting process on the shrinkage rate and compressive strength of zircon-silica sol ceramic mould, and the relationship between the roasting temperature and microstructure of zircon-silica sol ceramic mould were studied. The optimum roasting temperature of zircon-silica sol ceramic mould gained by the experiments is 900℃ and the holding time is 2 h. T...

  4. The significance of zircon characteristic and its uranium concentration in evaluation of uranium metallogenetic prospect

    Zircon characteristic and its relation to uranium metallogenetic process have been studied on the basis of physics properties and chemical compositions. It is indicated that the colour of zircon crystal is related to uranium concentration; on the basis of method of zircon population type of Pupin J.P., the sectional plan of zircon population type has been designed, from which result that zircon population type of uranium-producing rock body is distributed mainly in second section, secondly in fourth section; U in zircon presents synchronous increase trend with Th, Hf and Ta; the uranium concentration in zircon from uranium-producing geologic body increases obviously and its rate of increase is more than that of the uranium concentration in rock; the period, in which uranium concentration in zircon is increased, is often related to better uranium-producing condition in that period of this area. 1785 data of the average uranium concentration in zircon have been counted and clear regularity has been obtained, namely the average uranium concentrations in zircon in rich uranium-producing area, rock, geologic body and metallogenetic zone are all higher than that in poor or no uranium-producing area, rock, geologic body and metallogenetic zone. This shows that the average uranium concentration in zircon within the region in fact reflects the primary uranium-bearing background in region and restricts directly follow-up possibility of uranium mineralization. On the basis of this, the uranium source conditions of known uranium metallogenetic zones and prospective provinces have been discussed, and the average uranium concentrations in zircon from magmatic rocks for 81 districts have been contrasted and graded, and some districts in which exploration will be worth doing further are put forward

  5. A Zircon U-Pb Study of the Evolution of Lunar KREEP

    Meyer, Charles; Nemchin, A.; Pidgeon, R.; Whitehouse, M.; Vaughan, J.


    SIMS U-Pb analyses show that zircons from breccias from Apollo 14 and Apollo 17 have essentially identical age distributions in the range 4350 to 4200 Ma but, whereas Apollo 14 zircons additionally show ages from 4200 to 3900 Ma, the Apollo 17 samples have no zircons with ages <4200 Ma. The zircon results also show an uneven distribution with distinct peaks of magmatic activity. In explaining these observations we propose that periodic episodes of KREEP magmatism were generated from a primary reservoir of KREEP magma, which contracted over time towards the centre of Procellarum KREEP terrane.

  6. Metamorphic zircon from Xindian eclogite, Dabie Terrain: U-Pb age and oxygen isotope composition


    Detailed CL image, U-Pb age and oxygen isotope composition in situ analyses for two metamorphic zircons from ultra-high pressure Xindian eclogite, Southern Dabie Terrain were carried out. There are two kinds of zircon in eclogite. The major subpopulation is podgy and isometric, and interpreted as protolith magmatic zircon with partial recrystallization. Its formation age is 811±22 Ma.The less abundant one is euhedral prismatic with core-rim structure and the rim being metamorphic overgrowth and formed at 221 -217 Ma. Zircon CL image strength is mainly controlled by U and Th contents. The magmatic zircon has its Th/U ratio around 1.3 and decreasing with recrystallization,whereas metamorphic zircon has Th/U ratio of lower than 0.1. Magmatic and metamorphic zircon domains all show very low oxygen isotopic compositions with average δ8O values of 1.8‰ and 2.8‰,respectively. The low δ18O values in protolith zircon indicated meteoric water involvement in their magma source region. It may correlate with snowball earth event during Neoproterozoic. It also indicates that protolith zircon could survive its oxygen isotope signature during Dabie eclogite facies UHP metamorphism.

  7. Peculiarities of accessory zircon from the carter seamount tuffs (Sierra Leone Rise in the East Atlantic)

    Petrova, V. V.; Skolotnev, S. G.; Chistyakova, N. I.


    In volcanic tuffs, dredged during Cruise 23 of the R/V Akademik Nikolaj Strakhov, accessory zircon was found; except for the mineral-forming components, there were ˜2% of ThO2 and 0.75% of Ce2O3 in zircon. During rapid uplift of magmatic masses to the ocean bottom surface, admixture elements isolated into specific minerals. As a result, destruction structures were formed in the rim parts of primary zircon crystals, and the new-formed association of zircon + thorite + cerite + thoriante + baddeleyite appeared.

  8. Paragneiss zircon geochronology and trace element geochemistry, North Qaidam HP/UHP terrane, western China

    Mattinson, C.G.; Wooden, J.L.; Zhang, J.X.; Bird, D.K.


    In the southeastern part of the North Qaidam terrane, near Dulan, paragneiss hosts minor peridotite and UHP eclogite. Zircon geochronology and trace element geochemistry of three paragneiss samples (located within a ???3 km transect) indicates that eclogite-facies metamorphism resulted in variable degrees of zircon growth and recrystallization in the three samples. Inherited zircon core age groups at 1.8 and 2.5 Ga suggest that the protoliths of these rocks may have received sediments from the Yangtze or North China cratons. Mineral inclusions, depletion in HREE, and absence of negative Eu anomalies indicate that zircon U-Pb ages of 431 ?? 5 Ma and 426 ?? 4 Ma reflect eclogite-facies zircon growth in two of the samples. Ti-in-zircon thermometry results are tightly grouped at ???660 and ???600 ??C, respectively. Inclusions of metamorphic minerals, scarcity of inherited cores, and lack of isotopic or trace element inheritance demonstrate that significant new metamorphic zircon growth must have occurred. In contrast, zircon in the third sample is dominated by inherited grains, and rims show isotopic and trace element inheritance, suggesting solid-state recrystallization of detrital zircon with only minor new growth. ?? 2009 Elsevier Ltd.

  9. Recrystallization of zircon and its effect on U-Pb dating

    Zircon is the most preferred mineral for U-Pb geochronology to obtain high precision mineral growth ages of crystalline rocks. In this work, a suite of discordant zircons from a leucosome of a garnet biotite gneiss from the Kerala Khondalite Belt, India were investigated by a combination of back-scattered electron imaging and SHRIMP analyses to ponder over the pattern of Pb-loss in recrystallized zircon. Previous attempts for U-Pb zircon dating of this rock type in the area have all resulted highly discordant ages

  10. Nuclear microprobe (PIXE) analyses of zircons as indicators of granite type

    Petrochemical investigation of the Cape Granite Suite illustrated that three major granitoid types exist namely S-, I-and A-types. Studies of zircon typologies of these granites confirmed that the three major types and their subtypes could be distinguished with relative ease. Using the typological classification as a base, zircons from the three granite groups were analysed by proton microprobe. The proton microprobe was utilized to enable the detection of elements normally present in low quantities in zircon. The results clearly illustrated that PIXE analyses may readily be used to discriminate zircons from S-, I- and A-type granites using the elements Th, Y and Yb

  11. Age of the Lava Creek supereruption and magma chamber assembly at Yellowstone based on 40Ar/39Ar and U-Pb dating of sanidine and zircon crystals

    Vazquez, J. A.; Matthews, N. E.; Calvert, A. T.


    The last supereruption from the Yellowstone Plateau formed Yellowstone caldera and ejected the >1000 km3 of rhyolite that composes the Lava Creek Tuff (LCT). Tephra from the eruption blanketed much of the western United States, and is a key Quaternary chronostratigraphic marker, in particular for dating deposition of mid-Pleistocene glacial and pluvial deposits in western North America. We performed 40Ar/39Ar dating of single sanidines to delimit eruption age, and ion microprobe U-Pb and trace-element analyses of crystal faces on single zircons to characterize magmatic evolution and date near-eruption crystallization, as well as analyses of crystal interiors to date the interval of zircon crystallization. Sanidines from the two LCT members A and B yield an 40Ar/39Ar isochron date of 631 ± 4 ka (2σ). Crystal faces on zircons from both members yield a weighted mean 206Pb/238U date of 627 ± 6 ka (2σ) and have trace element concentrations that vary with eruptive stratigraphy. Zircon interiors yield a weighted mean 206Pb/238U date of 660 ± 6 ka, and reveal reverse and/or oscillatory zoning of trace element concentrations, with many crystals containing high-U concentrations and dark cathodoluminescence (CL) cores. These crystals with high-U cores are possibly sourced from 'defrosting' of melt-impregnated margins of the growing subvolcanic reservoir. LCT sanidines mirror the variation of zircon composition within the eruptive stratigraphy, with crystals from upper LCT-A and basal LCT-B having bright-CL rims with high Ba concentrations, suggesting late crystallization after addition of less evolved silicic magma. The occurrence of distal LCT in stratigraphic sequences marking the Marine Isotope Stage 16-15 transition supports the apparent eruption age of ca. 631 ka. These results reveal that Lava Creek zircons record episodic heating, renewed crystallization, and an overall up-temperature evolution for Yellowstone's subvolcanic reservoir in the 103-104 year interval

  12. Southernmost Andes and South Georgia Island, North Scotia Ridge: Zircon U-Pb and muscovite {40Ar }/{39Ar } age constraints on tectonic evolution of Southwestern Gondwanaland

    Mukasa, Samuel B.; Dalziel, Ian W. D.


    Zircon U-Pb and muscovite {40Ar }/{39Ar } isotopic ages have been determined on rocks from the southernmost Andes and South Georgia Island, North Scotia Ridge, to provide absolute time constraints on the kinematic evolution of southwestern Gondwanaland, until now known mainly from stratigraphic relations. The U-Pb systematics of four zircon fractions from one sample show that proto-marginal basin magmatism in the northern Scotia arc, creating the peraluminous Darwin granite suite and submarine rhyolite sequences of the Tobifera Formation, had begun by the Middle Jurassic (164.1 ± 1.7 Ma). Seven zircon fractions from two other Darwin granites are discordant with non-linear patterns, suggesting a complex history of inheritances and Pb loss. Reference lines drawn through these points on concordia diagrams give upper intercept ages of ca. 1500 Ma, interpreted as a minimum age for the inherited zircon component. This component is believed to have been derived from sedimentary rocks in the Gondwanaland margin accretionary wedge that forms the basement of the region, or else directly from the cratonic "back stop" of that wedge. Ophiolitic remnants of the Rocas Verdes marginal basin preserved in the Larsen Harbour complex on South Georgia yield the first clear evidence that Gondwanaland fragmentation had resulted in the formation of oceanic crust in the Weddell Sea region by the Late Jurassic (150 ± 1 Ma). The geographic pattern in the observed age range of 8 to 13 million years in these ophiolitic materials, while not definitive, is in keeping with propagation of the marginal basin floor northwestward from South Georgia Island to the Sarmiento Complex in southern Chile. Rocks of the Beagle granite suite, emplaced post-tectonically within the uplifted marginal basin floor, have complex zircon U-Pb systematics with gross discordances dominated by inheritances in some samples and Pb loss in others. Of eleven samples processed, only two had sufficient amounts of zircon for

  13. Exploring for early bombardments on Earth from pre-3.85 Fa thermal effects recorded in Hadean zircons - a status report

    Mojzsis, S. J.; Abramov, O.; Harrison, T. M.; Kring, D. A.; Levison, H. F.; Trail, D.; Watson, E. B.


    We report on our progress with high-resolution ion microprobe U-Th-Pb depth profiles and Ti+REEs spot analysis which show that subsequent to their crystallization in melts under typical crustal conditions on Earth, some Hadean (pre-3.85 Ga) zircons record common age domains with unusual chemical and isotopic characteristics consistent with a high-temperature (possibly impact) origin. We have found evidence for later overprints caused by intense thermal alteration between 3.94-3.97 Ga in six of eight studied grains but no evidence for older events. These findings alert us to two fundamental things we did not know before about the probiotic potential of the Earth in the earliest solar system: (i) that the bombardment epoch did not result in complete 'Doomsday' scale destruction of the Earth's crust since the Moon-forming event at ca. 4.5 Ga; and (ii) age constraints on both sides of the ther-mally altered 3.94-3.97 Ga zircon domains are very good and so far our data show that no detectable thermal events are recorded by the zircons before ~3.97 Ga up to about 4.3 Ga. This observation is consistent with the output of new classes of dynamical models that successfully re-create the decay of impactor populations in the early solar system as recorded on the Moon and in meteorites.

  14. Evaluation of fission-track and U-Pb double dating method for identical zircon grains. Using homogeneous zircon grains in Kawamoto Granodiorite in Shimane prefecture, Japan

    Using the double-dating approach, we have conducted fission-track (FT) and U-Pb age dating on the same zircon grain to evaluate the reliability of the resulting age data. The zircon grains (OD-3) used for the investigation were collected from the Mihara Body of the Kawamoto Granodiorite, Shimane Prefecture, Japan. The zircon crystals yielded a FT age of 33 Ma, with a spontaneous FT density of 106-107 cm2. The U-Pb age data were obtained using inductively coupled plasma-mass spectrometry (ICP-MS) combined with a frequency quintupled Nd-YAG (λ=213 nm) laser ablation (LA) sample introduction system. The U-Pb age determinations on the zircon samples were performed after chemical leaching using 47% HF for 20 hrs at room temperature, or after FT etching using a KOH-NaOH eutectic solution for 20 hrs at 225degC. The resulting U-Pb age of 33 Ma was concordant with the FT age data, suggesting that there was no significant loss of Pb during etching or chemical preparation, thus indicating the feasibility of FT and U-Pb double dating of single zircon grains. The results indicate that the zircon grains (OD-3) from the Kawamoto Granodiorite (Mihara Body) can become a new working standard for precise U-Pb age determinations of young zircons. (author)

  15. Morphology versus U-Pb systematics in zircon: A high-resolution isotopic study of a zircon population from a Variscan dike in the Central Alps

    U/Pb isotopic measurements on individual zircon crystals combined with morphological analyses permit the identification of three distinct components within the zircon population of the Saedelhorn diorite, a Variscan dike from the western Gotthard (Central Alps, Switzerland): (i) 94% of the grains in the zircon population are elongate crystals with pronounced skeletal morphology indicative of rapid growth from a supercooled melt. (ii) 5% of the population consist of turbid, mostly subhedral zircons frequently showing D-type morphology and elevated uranium contents compared to the skeletal variety. Single-crystal and multi-grain U-Pb isotopic data of group (i) and (ii) zircons define an intrusion age of 293 + 5/ -4 m.y. for the dike. (iii) Rare, transparent zircon crystals (< 1% of the zircons population) yield apparent U-Pb ages in the range of 370-490 m.y. and display morphological and isotopic characteristics closely resembling those of a Caledonian orthogneiss intruded by the dike. This implies presence of assimilated wall-rock components in the macroscopically homogeneous dike sample. (orig./WB)

  16. Low energy 40Ca + 40Ca collisions

    This paper deals with the classical microscopic study of 40Ca + 40Ca collisions. Fusion cross-sections (σsub(CF)) for various incident energies, energy variations with time, shape deformation and the life time of resonance scattering (T) have been studied. Comparison of 40Ca + 40Ca results with those of 16O + 16O have also been made. (author)

  17. From a long-lived upper-crustal magma chamber to rapid porphyry copper emplacement: Reading the geochemistry of zircon crystals at Bajo de la Alumbrera (NW Argentina)

    Buret, Yannick; von Quadt, Albrecht; Heinrich, Christoph; Selby, David; Wälle, Markus; Peytcheva, Irena


    The formation of world class porphyry copper deposits reflect magmatic processes that take place in a deeper and much larger underlying magmatic system, which provides the source of porphyry magmas, as well as metal and sulphur-charged mineralising fluids. Reading the geochemical record of this large magmatic source region, as well as constraining the time-scales for creating a much smaller porphyry copper deposit, are critical in order to fully understand and quantify the processes that lead to metal concentration within these valuable mineral deposits. This study focuses on the Bajo de la Alumbrera porphyry copper deposit in Northwest Argentina. The deposit is centred on a dacitic porphyry intrusive stock that was mineralised by several pulses of porphyry magma emplacement and hydrothermal fluid injections. To constrain the duration of ore formation, we dated zircons from four porphyry intrusions, including pre-, syn- and post-mineralisation porphyries based on intersection relations between successive intrusion and vein generations, using high precision CA-ID-TIMS. Based on the youngest assemblages of zircon grains, which overlap within analytical error, all four intrusions were emplaced within 29 ka, which places an upper limit on the total duration of hydrothermal mineralisation. Re/Os dating of hydrothermal molybdenite fully overlaps with this high-precision age bracket. However, all four porphyries contain zircon antecrysts which record protracted zircon crystallisation during the ∼200 ka preceding the emplacement of the porphyries. Zircon trace element variations, Ti-in-zircon temperatures, and Hf isotopic compositions indicate that the four porphyry magmas record a common geochemical and thermal history, and that the four intrusions were derived from the same upper-crustal magma chamber. Trace element zoning within single zircon crystals confirms a fractional crystallisation trend dominated by titanite and apatite crystallisation. However, zircon

  18. Sm-Nd and zircon SHRIMP U-Pb dating of Huilanshan mafic granulite in the Dabie Mountains and its zircon trace element geochemistry

    HOU; Zhenhui; LI; Shuguang; CHEN; Nengsong; LI; Qiuli; LIU


    The mafic granulites from Huilanshan are outcropped on the center of the Luotian dome in the northern Dabie Mountains. The Sm-Nd isochron defined by granulite-facies metamorphic minerals (garnet + clinopyroxene + hypersthene) yields an age of 136(±)18 Ma indicating the early Cretaceous granulite-facies metamorphism. The cathodoluminescence (CL) images of zircons from the granulite show clearly core-mantle-rim structures. The zircon cores are characterized by typical oscillatory zoning and highly HREE enriched patterns, which suggests their magma origin. Some zircon cores among them with little Pb loss give SHRIMP U-Pb ages ranging from 753 to 780 Ma, which suggests that the protolith of Huilanshan granulite is Neoproterozoic mafic rocks. The zircon mantles usually cut across the oscillatory zone of the zircon cores have 3―10 times lower REE, Th, U, Y, Nb and Ta contents than the igneous zircon cores but have high common Pb contents. These characteristics suggest that they were formed by hydrothermal alteration of the igneous zircons. The part of zircon mantles with little Pb loss give a similar SHRIMP U-Pb age (716―780 Ma) to the igneous zircon cores, which implies that the hydrothermal events occurred closely to the magmatic emplacement. In view of the strong early Cretaceous magmatism in the Luotian dome, consequently, the Huilanshan mafic granulite was formed by heating of the Neoproterozoic mafic rocks in mid-low crust, which caused the granulite-facies metamorphism underneath the Dabie Mountains. The similarity between the granulite metamorphic age (136±18 Ma) defined by Sm-Nd isochron and K-Ar age of 123―127 Ma given by amphible from the gneiss in Luotian dome suggests a rapid uplifting of the Luotian dome, which may result in further exhumation of the ultrahigh pressure metamorphic rocks in the Dabie Mountains.

  19. The origin of high δ18O zircons: marbles, megacrysts, and metamorphism

    Cavosie, Aaron J.; Valley, John W.; Kita, Noriko T.; Spicuzza, Michael J.; Ushikubo, Takayuki; Wilde, Simon A.


    The oxygen isotope ratios (δ18O) of most igneous zircons range from 5 to 8‰, with 99% of published values from 1345 rocks below 10‰. Metamorphic zircons from quartzite, metapelite, metabasite, and eclogite record δ18O values from 5 to 17‰, with 99% below 15‰. However, zircons with anomalously high δ18O, up to 23‰, have been reported in detrital suites; source rocks for these unusual zircons have not been identified. We report data for zircons from Sri Lanka and Myanmar that constrain a metamorphic petrogenesis for anomalously high δ18O in zircon. A suite of 28 large detrital zircon megacrysts from Mogok (Myanmar) analyzed by laser fluorination yields δ18O from 9.4 to 25.5‰. The U-Pb standard, CZ3, a large detrital zircon megacryst from Sri Lanka, yields δ18O = 15.4 ± 0.1‰ (2 SE) by ion microprobe. A euhedral unzoned zircon in a thin section of Sri Lanka granulite facies calcite marble yields δ18O = 19.4‰ by ion microprobe and confirms a metamorphic petrogenesis of zircon in marble. Small oxygen isotope fractionations between zircon and most minerals require a high δ18O source for the high δ18O zircons. Predicted equilibrium values of Δ18O(calcite-zircon) = 2-3‰ from 800 to 600°C show that metamorphic zircon crystallizing in a high δ18O marble will have high δ18O. The high δ18O zircons (>15‰) from both Sri Lanka and Mogok overlap the values of primary marine carbonates, and marbles are known detrital gemstone sources in both localities. The high δ18O zircons are thus metamorphic; the 15-25‰ zircon values are consistent with a marble origin in a rock-dominated system (i.e., low fluid(external)/rock); the lower δ18O zircon values (9-15‰) are consistent with an origin in an external fluid-dominated system, such as skarn derived from marble, although many non-metasomatized marbles also fall in this range of δ18O. High δ18O (>15‰) and the absence of zoning can thus be used as a tracer to identify a marble source for high δ18O

  20. Effect of Pb loss on the ages of reference zircons QGNG and SL13, and of volcanic zircons from the Early Devonian Merrions and Turondale Formations, New South Wales

    Recent papers (Black et al. 1997; Jagodzinski and Black 1999) reported that SL13-referenced SHRIMP zircon ages are ca 1.3% younger than QGNG-referenced ages. It is shown here that these authors overestimated their analytical errors and as a consequence failed to register the presence of large and variable fractions of Pb loss within both QGNG (median 40% of spots) and SL13 (25%). If only the oldest 206Pb/238U age groups within each of the same 16 analytical sessions are selected for comparison, the 206Pb/238U ages of QGNG relative to SL13 agree with the Concordia intersection age by isotope dilution to within 0.4% (standard deviation). This observation eliminates the possibility of systematic bias. Jagodzinski and Black (1999) also overlooked Pb loss in their ages for the Early Devonian Turondale and Merrions Formations, which are corrected here for time-scale use. Copyright (2001) Geological Society of Australia

  1. Reconstructing deep crustal dynamics in a large, hot orogen: Application of integrated zircon petrochronology and petrological modeling to the Canadian Grenville Province

    Marsh, Jeffrey; Culshaw, Nicholas


    The timing and conditions of high pressure (HP) metamorphism, crustal anatexis, and shear zone formation are of primary importance in understanding lithosphere-scale dynamics of collisional orogens. Within the western Grenville Province, Ontario, Canada, a number of structural and metamorphic relationships are preserved that represent specific orogenic stages or processes. Lower allochthonous domains contain variably retrogressed mafic complexes that typically retain vestages of earlier HP metamorphic assemblages (e.g. garnet porphyroblasts, kyanite, and rutile) within a matrix dominated by incomplete decompression reactions (e.g. pseudomorphous diopside + sodic plagioclase intergrowths after omphacite and concentric coronas of aluminous minerals surrounding kyanite). Zircon from these samples yield U-Pb ages between 1085-1097 Ma, and exhibit REE characteristics consistent with crystallization in an eclogite-facies (garnet-rich, plagioclase-poor) mineral assemblage. REE partitioning between zircon and garnet suggests zircon growth coincided with the latter stages of garnet growth. Titanium concentrations in zircon constrain crystallization temperatures between ~678-736 °C, whereas Zr concentration in rutile yield crystallization temperatures of ~705-740 °C (for rutile inclusions in garnet) and 742-764 °C (for rutile in the matrix). Intersection of zircon and rutile crystallization temperature with the calculated stability field for the HP assemblage (Grt+Cpx+Ky+Rt+Zrn±Hbl) yields minimum pressures of ~15 kbar. Thus, HP metamorphism apparently occurred at ca. 1090 Ma across the orogen, at minimum depths of ~53 km and T ~700±50 °C, yielding a geothermal gradient of pegmatite-rich, amphibolite-facies shear zones by ca. 1100 Ma. Thus, petrochronological data constrain a sequence of nappe emplacement, HP metamorphism, and migmatization evolving over ~15-20 Myrs, apparently marking a transition in the deep crustal dynamics from a predominantly thickening phase to a

  2. (U-Th)/He Ages of Detrital Zircons From Paleozoic Strata of the Severnaya Zemlya Archipelago (Russian High Arctic): implication for testing the different tectonic models

    Ershova, Victoria; Anfinson, Owen; Prokopiev, Andrei; Khudoley, Andrei; Stockli, Daniel; Faleide, Jan Inge; Gaina, Carmen; Malyshev, Nikolay


    The Severnaya Zemlya archipelago comprises four main islands (Pioneer, October Revolution, Komsomolets and Bol'shevik), along with numerous other small islands, islets and island groups. It contains rocks varying in age from Late Cambrian to Permian and is a key area for understanding the tectonic evolution of the North Kara and Laptev Sea basins. Various models have been proposed for the Paleozoic history of the Kara Terrane: 1) Kara terrane inferred as a part of a larger continent block called Arctida (Zonenshain et al, 1990). 2) Lorenz et al. (2008a, 2008b) described the Kara terrane as a marginal part of Baltica. 3) The Kara Terrane existed as a separate terrane or microcontinent during the Paleozoic (Bogdanov et al., 1998; Gramberg & Ushakov, 2000; Metelkin et al., 2000, 2005) Here we present (U-Th)/He ages of detrital zircons collected from Ordovician - Devonian strata of Pioneer and October Revolution islands) along with Sedov Islands. All detrital zircon (U-Th)/He ages are older than age of host rocks indicating the samples were not buried deep enough (less than ~6-8 km) to reset the (U-Th)/He isotopic system. Thus, (U-Th)/He ages indicate the exhumational history of the clastic source region. The (U-Th)/He detrital zircon ages from Ordovician- Silurian strata, with a peak age of ca. 465 Ma, suggest the primary source region was located within the Caledonian Orogen, which is unknown in the modern vicinity of Severnaya Zemlya. The abundance of Caledonian (U-Th)/He zircon ages in the studied samples suggests a continuation of Caledonides northeastward across Barents shelf as previously inferred from pre-Permo-Carboniferous rifting restoration and illustrated by geophysical data. In contrast to older clastic rocks, (U-Th)/He detrital zircon ages from the Devonian deposits show a mixture of Ellesmerian and Caledonian ages with age peaks at ca. 365 Ma and 465 Ma and the youngest grains nearing the depositional age of the strata. The ages suggest the clastic

  3. Late Paleozoic magmatic record of Middle Gobi area, South Mongolia and its implications for tectonic evolution: Evidences from zircon U-Pb dating and geochemistry

    Zhu, Mingshuai; Miao, Laicheng; Baatar, Munkhtsengel; Zhang, Fochin; Anaad, Chimedtseren; Yang, Shunhu; Li, Xingbo


    Late Paleozoic subduction-accretion complexes occur widely in Middle Gobi area and provide a good opportunity for unraveling the Paleozoic tectonic evolution of South Mongolia. The magmatic rocks in the Tsavchir hudug district mainly consist of rhyolites and volcaniclastic rocks. The rhyolites show enrichment in LREE and LILE and negative Nb, Ta and Ti anomalies, indicating genesis in the subduction zone. A rhyolite sample from the Tsavchir hudug region yielded a SHRIMP 206Pb/238U zircon age of 315 ± 4 Ma (MSWD = 0.79, n = 15). The andesite overlying the Namdain hundy Early Paleozoic ophiolite shows adakite geochemical features, and the two andesite samples yielded SHRIMP 206Pb/238U zircon ages of 325 ± 3 Ma (MSWD = 1.6, n = 14) and 319 ± 4 Ma (MSWD = 0.56, n = 13), respectively, suggesting that the Carboniferous island arc formed on the basis of Early Paleozoic accretionary complex. The granodiorite sample that intrudes the Early Paleozoic accretion complex with adakite geochemical features yielded a SHRIMP 206Pb/238U zircon age of 333 ± 4 Ma (MSWD = 1.6, n = 16), representing the Late Paleozoic island arc intrusive. The SHRIMP U-Pb analyses for the tuff sandstones that occur associated with Early Paleozic oceanic inliers in Middle Gobi area suggest detrital zircons mainly stem from the Devonian-Carboniferous arc. The age data obtained from the ophiolite (528-509 Ma) and tuff sandstone indicate the accretion in Middle Gobi area lasted from Early Paleozoic to Late Paleozoic for at least ca. 200 Ma, suggesting the ocean of the accretionary complex was the major Paleo-Asain ocean basin. The subduction related magmatic belt in Middle Gobi area includes both Early Paleozoic and Late Paleozoic island arc activities, which is consistent with the accretion duration time obtained from accretionary complex and also attests the argument of major Paleo-Asain ocean basin.

  4. Phosphorus-controlled trace element distribution in zircon revealed by NanoSIMS

    Yang, Wei; Lin, Yangting; Hao, Jialong; Zhang, Jianchao; Hu, Sen; Ni, Huaiwei


    To better understand the origin of oscillatory zoning in zircons, distributions of REEs (represented by Ce, Sm, Dy and Lu), Y, Ti, Li and P in the igneous zircons (QH) from a felsic syenite in the Qinghu alkaline complex and metamorphic zircons (DMP06-14) from a banded granulite xenolith from Hannuoba basalts have been investigated with NanoSIMS. The NanoSIMS analyses reveal well correlation between the trace element distributions and the cathodoluminescence dark-bright zonings of zircons. The QH zircons with oscillatory zonings display large trace element variations within single grains by a factor up to 13.5, with Y and P ranging from 574 and 227 ppm in the bright zones to 7754 and 2464 ppm in the dark zones, respectively. By contrast, the DMP06-14 zircons without oscillatory zonings show much smaller trace element variations by a factor of 1.4, with Y ranging from 477 to 636 ppm and P from 331 to 467 ppm. Such large trace element variations in oscillatory zonings cannot be produced by compositional fluctuation in the magma chambers. The correlations between P and Y, REEs (Ce, Sm, Dy and Lu) ( R 2 > 0.97) indicate xenotime substitution in zircons. The oscillatory distribution of P in zircon could be formed by the fluctuation of P in the melt adjacent to the mineral-melt boundary, either because P diffuses slower than Zr in the melt or due to surfacial interaction of melt with crystals. Such a zoned distribution of P in turn controls the substitution types of phosphates in zircon, developing oscillatory distributions of Y and REEs. Our results indicate that apparent partition coefficients of Y and REEs between zircon and melt are controlled by P contents, which may result in the large discrepancy in zircon partitioning data.

  5. Mechanisms of radon loss from zircon: Microstructural controls on emanation and diffusion

    Eakin, Marty; Brownlee, S. J.; Baskaran, M.; Barbero, L.


    Understanding how radon escapes from minerals is important for many fields in Earth science, yet few studies have focused on the mechanisms for radon escape. We measured radon emanation rate and radon loss upon heating for crushed aliquots of three large zircon crystals from three localities: Mud Tank (Australia), Bancroft (Canada), and Malawi (Africa). Our study, in conjunction with published data, shows that the room temperature radon emanation coefficient (REC) varies over 5 orders of magnitude in zircon. For low U zircon, Mud Tank, there are variations in REC that appear to be related to annealing at different temperatures, possibly due to annealing of fission tracks, however, all REC values for Mud Tank zircon are within error of one another. Bancroft and Malawi zircons have higher U content and do not show any systematic relationship of REC to annealing temperature. Results from Mud Tank zircon suggest that partial annealing of fission tracks decreases REC, but when all fission tracks are annealed REC reaches a maximum. REC in zircons with high U content, Bancroft and Malawi, is slightly higher than in zircon with lower U, although results are within error. Results of measurements of radon loss upon heating suggest that radon diffusion is slow, ∼30% of the radon is lost during heating at 975 °C for 48 h. Samples heated a second time yield less fractional radon loss, ∼10%, suggesting that diffusion parameters are changed during heating at temperatures ⩾975 °C, which is likely the result of annealing of radiation damage. Diffusion parameters calculated from the fractional loss experiments reflect diffusion in highly radiation damaged or metamict zircons. Our results indicate that internal microstructures in zircon, such as fission tracks and alpha-radiation damage, influence radon escape for diffusion and recoil mechanisms, and hence if these effects can be further characterized, measurements of 222Rn escape have the potential to be useful for probing

  6. Detrital and volcanic zircon U-Pb ages from southern Mendoza (Argentina): An insight on the source regions in the northern part of the Neuquén Basin

    Naipauer, Maximiliano; Tapia, Felipe; Mescua, José; Farías, Marcelo; Pimentel, Marcio M.; Ramos, Victor A.


    The infill of the Neuquén Basin recorded the Meso-Cenozoic geological and tectonic evolution of the southern Central Andes being an excellent site to investigate how the pattern of detrital zircon ages varies trough time. In this work we analyze the U-Pb (LA-MC-ICP-MS) zircon ages from sedimentary and volcanic rocks related to synrift and retroarc stages of the northern part of the Neuquén Basin. These data define the crystallization age of the synrift volcanism at 223 ± 2 Ma (Cerro Negro Andesite) and the maximum depositional age of the original synrift sediments at ca. 204 Ma (El Freno Formation). Two different pulses of rifting could be recognized according to the absolute ages, the oldest developed during the Norian and the younger during the Rhaetian-Sinemurian. The source regions of the El Freno Formation show that the Choiyoi magmatic province was the main source rock of sediment supply. An important amount of detrital zircons with Triassic ages was identified and interpreted as a source area related to the synrift magmatism. The maximum depositional age calculated for the Tordillo Formation in the Atuel-La Valenciana depocenter is at ca. 149 Ma; as well as in other places of the Neuquén Basin, the U-Pb ages calculated in the Late Jurassic Tordillo Formation do not agree with the absolute age of the Kimmeridgian-Tithonian boundary (ca. 152 Ma). The main source region of sediment in the Tordillo Formation was the Andean magmatic arc. Basement regions were also present with age peaks at the Carboniferous, Neoproterozoic, and Mesoproterozoic; these regions were probably located to the east in the San Rafael Block. The pattern of zircon ages summarized for the Late Jurassic Tordillo and Lagunillas formations were interpreted as a record of the magmatic activity during the Triassic and Jurassic in the southern Central Andes. A waning of the magmatism is inferred to have happened during the Triassic. The evident lack of ages observed around ca. 200 Ma suggests

  7. Study and make sulfur dioxide treatment equipment for degradation process of fine silicate zircon ore by sulfuric acid

    The against absorbent method was researched by research group to solve the above issue. This method was carried out by adsorbent lime-milk agent on the buffer of porous material with diameter D=9 cm and height H=1.2 m. The main parameters were gained: absorbent effect reached 98% with lime-milk concentration of 14% in water, against air flow speed of 0.7 m/s and lime-milk output of 0.45 liter/minute. Base on the above main researched parameter, the SO2 treatment equipment system by sulfuric acid was worked out with the scale of 0.5 ton/batch/day; absorbent tower diameter D=0.47 m, buffer height H=3.5 m and expenditure of 33.2 kg CaO/ton of zircon silicate. (author)

  8. New assemly model of Jiangnan Orogen: insight from detrital zircon geochronology of pre-Cretaceous strata, South China

    Su, J.; Dong, S.


    The Jiangnan Orogen separates the Yangtze and Cathaysian Blocks in South China and provokes a longstanding debate on the amalgamation history between the two Blocks. The assembly of the two Blocks is termed Sibao orogeny marked by undeformed Late Neoproterozoic strata (Banxi Group) overlying on the deformed Early Neoproterozoic strata (Lengjiaxi Group) in China. Detrital zircons can provide critical links in recognizing the source history of a deposit, sedimentary dispersal systems and tectonic reconstructions. Therefore, fifteen sandstone samples taken from pre-Cretaceous strata of Yangtze Block are analyzed to constrain the evolution of the South China Block (SCB), especially the assembly between Yangtze and Cathaysia Blocks. The results show that the detrital zircons from the Neoproterozoic Lengjiaxi Group (ca. 830 Ma) near the boundary of large detachment fault of Hengshan have similar age populations with that in the other sites of the Jiangnan Orogen, different from that of the Kunyang and Dahongshan Groups (>960 Ma) in the southwestern margin of the Yangtze Block. The detrital zircons from Paleozoic samples have similar age populations with that in the Cathaysia Block. We infer that they originate from the Cathaysia Block, together with paleogeography, paleocurrent and former research. The detrital zircons of middle-late Jurassic sandstones in southwestern and central Yangtze yield dominant populations at 2.0-1.7 Ga and subordinate Groups of 2.6-2.4Ga, 0.7-0.8Ga and 0.6-0.4Ga. The provenance of late Triassic strata may be derived from southern Yangtze and North China Block due to the collisions among the Indosina, South China and North China Blocks, whereas the Jurassic sediments may be partly derived from uplift erosion of Jiangnan Orogen due to intra-continental orogeny induced by pacific subduction towards Eurasia Plate. The tectothermal event occurred at ca. 1.1-0.8 Ga has long been attributed to the assembly or breakup of Yangtze and Cathaysia Blocks

  9. Textures and geochemistry of zircons in ODP holes 735B and 1105A, Atlantis Bank, SWIR

    John, B. E.; Cheadle, M. J.; Rioux, M. E.; Wooden, J. L.; Baines, G.


    Zircon is a common accessory mineral in ocean crust, and an important chronometer for studying the timing and duration of crustal accretion. Here, we present a comprehensive textural/geochemical study of zircon in 25 samples from the length of ODP Hole 735B (1508m) and adjacent Hole 1105A (158m) at Atlantis Bank, South West Indian Ridge (SWIR). Two zircon-bearing rock suites include i) a dioritic suite comprising amphibole granodiorite, quartz diorite and diorite dikes/veins, and ii) a suite of oxide gabbro segregations/veins. Combined TIMS U/Pb dating (Rioux et al, this meeting) and SIMS REE and other trace element (TE) chemical analyses of these zircons provide constraints on the growth and thermal history of ocean crust, and melt evolution. Zircons from both drill holes vary in morphology, but are typically pristine, colorless euhedral to anhedral grains from ~50-1000 μm in the long dimension. Over 90% show weak sector zoning, and ~50% show oscillatory zoning in CL. Additional textures include: 1. resorbed rims in two dioritic veins; 2. high U rims in two additional dioritic veins; 3. internal resorption/recrystallization boundaries in one diorite dike and one oxide gabbro; 4. a sub-population of high U grains hosting mottled/spongy interiors, possibly indicative of disequilibrium/reaction, in one diorite dike; and 5. mineral/melt inclusions in zircons in most of the dioritic veins, and in ~50% of oxide gabbros. SIMS analyses of 390 zircons (>750 spot analyses) confirm that the zircons have TE concentrations (including U/Yb vs Hf) typical of those from ocean crust. U ranges from 800 ppm in zircons from the dioritic veins (mean 123 ppm), and 5 to >500 ppm in zircons from the oxide gabbros (mean 59 ppm). All analyzed zircons have steep positive REE slopes with distinct positive Ce and negative Eu anomalies (Ce/Ce* and Eu/Eu*), similar to other oceanic zircons. Zircons from dioritic veins are REE-enriched (ΣREE = 216-15670; mean 3000 ppm) and have significant

  10. New U-Pb zircon geochronology of the Choma-Kalomo Block (Zambia) and the Dete-Kamativi Inlier (Zimbabwe), with implications for the extent of the Zimbabwe Craton.

    Glynn, Sarah; Wiedenbeck, Michael; Master, Sharad; Frei, Dirk


    The Choma-Kalomo Block is a north-east trending, Mesoproterozoic terrane located in southern Zambia. It is composed of as yet undated gneissic basement with a high-grade metamorphosed supracrustal metasedimentary sequence, which is intruded by hornblende granites and gneisses of the Choma-Kalomo Batholith, that is dated between ca. 1.37 and 1.18 Ga. Our new zircon U-Pb age data on metasedimentary rocks of the Choma-Kalomo Block identifies samples of different ages, with slightly different provenances. The oldest metasedimentary rock is a muscovite-biotite schist, which has only Palaeoproterozoic detrital zircons, the two age clusters around 2.03-2.02 Ga and 1.8-1.9 Ga, correspond to the ages of granitic intrusion, and metamorphism, in the Magondi Mobile Belt on the western side of the Archaean Zimbabwe Craton. The second sample is a garnetiferous paragneiss, which contains both Palaeoproterozoic (2.04 Ga), and Mesoproterozoic zircons, ca. 1.36 Ga, derived from the granites of the Choma-Kalomo Batholith. The third sample is a biotite-muscovite schist, in which the detrital zircon ages fall into four separate clusters: ca. 3.39 Ga, ca. 2.7-2.6 Ga, ca. 2.1-1.7 Ga (with a peak at ca. 1.18 Ga), and 1.55 - 1.28 Ga. The Archaean zircons in this sample are derived from the Zimbabwe Craton, while the Palaeoproterozoic samples come from the Magondi belt, and the youngest zircons come from both phases of the Choma-Kalomo Batholith. A possible connection between the Choma-Kalomo Block and the Dete-Kamativi Inlier - some 150 km to the south-east in western Zimbabwe - has been proposed on the basis of similarities in the nature of their Sn-Ta-muscovite pegmatite mineralisation. The Dete-Kamativi Inlier, which is part of the Magondi Mobile Belt, is a window into Palaeoproterozoic north-east trending belts of deformed and metamorphosed supracrustal rocks. By dating localities which we suspect form the basement to the surrounding younger sediments, along with selected pegmatites

  11. Discordance of the U Pb system in detrital zircons: Implication for provenance studies of sedimentary rocks

    Nemchin, Alexander A.; Cawood, Peter A.


    Provenance studies involving U / Pb analysis of detrital zircons have become increasingly popular through the application of microanalytical techniques. Adopted one-dimensional methods for the presentation of detrital zircon data, such as probability density distribution plots, generally require various degrees of filtering of discordant analyses. However, a uniform approach for filtering does not exist, making comparison of data from different samples and sedimentary units, as well as different studies of detrital populations, extremely difficult. The problem is further complicated by the need to switch from 207Pb / 206Pb based ages to 206Pb / 238U ages when zircon populations within a sample show a range of ages from Archean to Proterozoic or even Phanerozoic. Ion probe analysis of multiple spots within a single zircon crystal and calculation of an internal isochron can potentially eliminate problems associated with discordance, but this is a time consuming approach. Comparison of internal isochron ages for zircons generated by multiple ion probe intra-grain zircon analyses from a sample of psammite within the Dalradian Supergroup of Scotland with a data set from the same sample based on single grain ion probe analysis using various filtering methods suggests good agreement between the two approaches particularly when filtering is based on the probability of concordance. However, when precise information is required, such as the age of the youngest zircon grains so as to accurately constrain the maximum depositional age of the strata, then multiple analyses of individual zircon grains may be required.

  12. Prediction of thermodynamic property of Pu-zircon and Pu-pyrochlore

    Xu, Hulfang; Wang, Yifeng


    Due to its high durability, zircon is often present as a heavy mineral in natural environments and is the oldest mineral that has been dated on the earth. There are four zircon structure phases of M4+SiO4 occurring in nature: zircon (ZrSiO4), hafnon (HfSiO4), thorite (ThSiO4), and coffinite (USiO4). These phases may form solid solution. Recent interest in zircon minerals stems from the study of highly durable radioactive waste forms. Crystalline phases of M4+SiO4 with zircon structure have been proposed as a durable ceramic waste form for immobilizing actinides such as Pu, Np, and U. To predict the behavior of zircon-based waste forms in a geologic repository environment as well as to optimize the fabrication of those waste forms, the thermodynamic and kinetic properties for zircon mineral phases have to be determined. In this paper, we use a linear free energy relationship to predict the Gibbs free energies of formation of Pu-bearing phases (Xu et al., 1999). The calculated results show that the PuSiO4 phase with zircon structure is unstable with respect to oxides of PuO2 and quartz. However, the PuSiO4 phase will be stable with respect to oxides of PuO2 and silica glass at low temperature.

  13. Strontium zirconate as silicon and aluminum scavenger in yttria stabilized zirconia

    Andersen, Thomas; Hansen, Karin Vels; Chorkendorff, Ib;


    Here we report on strontium zirconate as a getter for silicon dioxide and aluminum oxide in yttria stabilized zirconia (YSZ) single crystals for cleaning purposes. YSZ single crystals were covered with strontium zirconate powder and heat treated at 1450°C in water vapor. After treatment the YSZ...

  14. Extreme lithium isotopic fractionation in three zircon standards (Plešovice, Qinghu and Temora).

    Gao, Yu-Ya; Li, Xian-Hua; Griffin, William L; Tang, Yan-Jie; Pearson, Norman J; Liu, Yu; Chu, Mei-Fei; Li, Qiu-Li; Tang, Guo-Qiang; O'Reilly, Suzanne Y


    To understand the behavior of Li in zircon, we have analyzed the abundance and isotopic composition of Li in three zircon standards (Plešovice, Qinghu and Temora) widely used for microbeam analysis of U-Pb ages and O-Hf isotopes. We have mapped Li concentration ([Li]) on large grains, using a Cameca 1280HR Secondary Ion Mass Spectrometer (SIMS). All zircons have a rim 5-20 μm wide in which [Li] is 5 to 20 times higher than in the core. Up to ~20‰ isotopic fractionation is observed on a small scale in the rims of a single zircon grain. The measured δ(7)Li values range from -14.3 to 3.7‰ for Plešovice, -22.8 to 1.4‰ for Qinghu and -4.7 to 16.1‰ for Temora zircon. The [Li] and δ(7)Li are highly variable at the rims, but relatively homogenous in the cores of the grains. From zircon rim to core, [Li] decreases rapidly, while δ(7)Li increases, suggesting that the large isotopic variation of Li in zircons could be caused by diffusion. Our data demonstrate that homogeneous δ(7)Li in the cores of zircon can retain the original isotopic signatures of the magmas, while the bulk analysis of Li isotopes in mineral separates and in bulk-rock samples may produce misleading data. PMID:26594042

  15. Hydrothermal processing method of producing zirconia from Malaysia zircon

    Zircon is the major source for zirconium and it is available in Malaysia as an associated mineral from the tin mining industry. Zirconium chemicals especially zirconia has found wide applications especially as advanced materials and in high technology industries. Production of high purity zirconia normally requires the used of very high temperature. Hydrothermal process provides an alternative to this aspect by incorporating low temperature technique. In this paper characteristics studies were performed on product obtained from this method to ascertain its crystalline phases, purity and also particle size. Study was also done to determine the effect of temperature on these characteristics. (Author)

  16. Characterization and microstructure of porous lead zirconate titanate ceramics

    B Praveenkumar; H H Kumar; D K Kharat


    Porous lead zirconate titanate (PZT) ceramics are widely used because of their low acoustic impedance, high figure of merit and high hydrostatic sensitivity. In the present work, porous PZT ceramics were fabricated by incorporating polyethylene oxide (PEO) as pore-forming agent. Both PZT powder and PEO were mixed with a binder at different ratios and compaction was carried out. The samples were slowly heated to remove the pore-forming agent and binder without cracks, followed by controlled sintering and electrode forming. Samples were poled using corona poling technique. The ferroelectric properties and microstructure of the prepared ceramics were characterized. The correlation of porosity with microstructure and ferroelectric properties were discussed.

  17. Cosmogenic and nucleogenic ^3He in apatite, titanite, and zircon

    Farley, K. A.; Libarkin, J.; Mukhopadhyay, S; Amidon, W.


    Cosmogenic ^3He was measured in apatite, titanite, and zircon and cosmogenic ^(21)Ne in quartz at 13 depth intervals in a 2.7-m long drill core in a Miocene ignimbrite from the Altiplano of Bolivia. All three ^3He depth profiles as well as the ^(21)Ne profile attenuate exponentially with depth, indicating that both of these isotopes are cosmogenic in origin with no significant contribution from other sources. The attenuation lengthscale for ^3He production of Λ = 180 ± 11 g/cm^2 is consistent...

  18. Microstructural and analytical analysis of plasma dissociated zircon

    The investigation of the microstructure and distribution of impurities was carried out on plasma dissociated zircon (PDZ). The morphology of the PDZ and crystalline nature of the zirconia was determined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) while energy dispersive X-ray spectrometry (EDS) provided compositional information. The SEM and TEM results indicate that the morphology and crystalline nature of the zirconia varies as a result of the existence of a thermal gradient. The EDS results show that the majority of the impurities segregates to the silica phase of the PDZ.

  19. Teaching material for radiation education using zircon sand

    In this paper, we introduced safe and inexpensive student experiment using zircon and containing a uranium series, as well as a similar experiment using several chemicals and foods containing potasium 40. In practice, our experiments were confirmed to be available in classes of Chemistry and/or Earth Science. It should be noted here that they are also expected to be useful in many places other than senior high school because they do not need any dangerous chemicals or special techniques, and can make younger students more interested in radioactivity in their environment. (J.P.N.)

  20. Lead zirconate titanate cantilever for noncontact atomic force microscopy

    Miyahara, Y.; Fujii, T.; Watanabe, S.; Tonoli, A.; Carabelli, S.; Yamada, H.; Bleuler, H.


    Noncontact atomic force microscopy with frequency modulation detection is a promising technique for surface observation with true atomic resolution. The piezoelectric material itself can be an actuator and sensor of the oscillating probe simultaneously, without the need for additional electro-mechanical transducers or other measurement systems. A vertical resolution of 0.01 nm rms has been achieved using a microfabricated cantilever with lead zirconate titanate thin film in noncontact mode frequency modulation detection. The cantilever also has a sharpened pyramidal stylus with a radius of about 10 nm for noncontact atomic force microscopy.

  1. Colloidal stability of aqueous suspensions of barium zirconate

    Boschini, Frédéric; Rulmont, André; Cloots, Rudi; Moreno, R.


    In this article, the colloidal behaviour of aqueous suspensions of barium zirconate is investigated. The variation of zeta-potential as a consequence of changing the pH and the concentration of an anionic polyelectrolyte is studied, the isoelectric point occurring at pH 5.3. The IEP shifts down on calcining the powder and also when anionic polyelectrolytes are added. Rheological studies have been made on suspensions prepared to a solids loading of 27 vol.% (72 wt.%). Optimum dispersing condit...

  2. Vertical zonality of fractionated granite plutons reflected in zircon chemistry

    Breiter, Karel

    s. l : Universidad d Salamanca ; Escuela politécnica superior de Avila ; Universidad de Granada, 2011 - (Molina, J.; Scarrow, J.; Bea, F.; Montero, P.). s. 25-25 ISBN 978-84-694-5253-0. [Hutton Symposium on Granites and Related Rocks /7./. 04.07.2011-09.07.2011, Avila] Institutional research plan: CEZ:AV0Z30130516 Keywords : zircon * granite geochemistry * granite zonality * Cínovec * Beauvoir Subject RIV: DB - Geology ; Mineralogy,_posters,_Lithos_Special_Issue_files/abstracts_book_Hutton_ISBN.pdf

  3. Microwave-assisted hydrothermal synthesis of lead zirconate fine powders

    Apinpus Rujiwatra


    Full Text Available A rapid synthesis of lead zirconate fine powders by microwave-assisted hydrothermal technique is reported. The influences of type of lead precursor, concentration of potassium hydroxide mineraliser, applied microwave power and irradiation time are described. The synthesised powders were characterised by powder X-ray diffraction, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopic microanalysis and light scattering technique. The merits of the microwave application in reducing reaction time and improving particle mono-dispersion and size uniformity as well as the drawbacks, viz. low purity of the desired phase and increasing demand of mineraliser, are discussed in relation to conventional heating method.

  4. Trace elements in zircon from rocks of the Katugin rare-metal deposit

    Levashova, E. V.; Skublov, S. G.; Marin, Yu. B.; Lupashko, T. N.; Ilchenko, E. A.


    The Katugin deposit of economic Ta, Nb, Zr, U, REE, Y, and cryolite (Na3AlF6) ores is located in the Kalar district of the Chita region and classified as unique in Nb, Ta, and Y reserves hosted in rare-metal alkali granite. The distribution of trace elements (including REE) in zircon was studied for ore-bearing arfvedsonite-aegirine, biotite-riebeckite rocks, and zones of late recrystallization with nodular zircon clusters. The outer rims and marginal zones of zircon grains are depleted in almost all trace elements except for hafnium as compared with cores and central zones. Compositional features of zircon cores indicate their magmatic origin and do not prove metasomatic nature of the deposit. The similar REE patterns of zircon rims and cores, as well as other attributes assume postmagmatic or metamorphic origin of the rims.

  5. Phase quantification of mullite-zirconia and zircon commercial powders using PAC and XRD techniques

    Rendtorff, Nicolas M.; Conconi, Maria S.; Aglietti, Esteban F. [Centro de Tecnologia de Recursos Minerales y Ceramica (CETMIC: CONICET-CIC) (Argentina); Chain, Cecilia Y.; Pasquevich, Alberto F. [Universidad Nacional de La Plata, Departamento de Fisica, IFLP, Facultad de Ciencias Exactas (Argentina); Rivas, Patricia C. [CONICET (Argentina); Martinez, Jorge A., E-mail:; Caracoche, Maria C. [Universidad Nacional de La Plata, Departamento de Fisica, IFLP, Facultad de Ciencias Exactas (Argentina)


    The short range technique of the Perturbed Angular Correlation (PAC) and x-ray diffraction (Rietveld) methods have been employed to determine the phase content in commercial mullite-zirconia and zircon raw materials that are ordinarily used to produce ceramic materials. The PAC technique, which probes zirconium-containing compounds at nanoscopic level, showed that zircon contains crystalline ZrSiO{sub 4} and an important amount of a structurally distorted zircon, which is also observed accompanying monoclinic zirconia in mullite-zirconia. This particular zircon phase was not detected by the long range x-ray diffraction-Rietveld technique. After an annealing treatment, important changes in crystalline contents of the powders allow confirming, by the x-ray diffraction-Rietveld method, the preexistence of this particular zircon phase. This fact must be taken into account when preparing multicomposites based on the present raw materials.

  6. Partition coefficients of Hf, Zr, and REE between zircon, apatite, and liquid

    Fujimaki, H.


    Concentration ratios of Hf, Zr, and REE between zircon, apatite, and liquid were determined for three igneous compositions: two andesites and a diorite. The concentration ratios of these elements between zircon and corresponding liquid can approximate the partition coefficient. Although the concentration ratios between apatite and andesite groundmass can be considered as partition coefficients, those for the apatite in the diorite may deviate from the partition coefficients. The HREE partition coefficients between zircon and liquid are very large (100 for Er to 500 for Lu), and the Hf partition coefficient is even larger. The REE partition coefficients between apatite and liquid are convex upward, and large (D=10-100), whereas the Hf and Zr partition coefficients are less than 1. The large differences between partition coefficients of Lu and Hf for zircon-liquid and for apatite-liquid are confirmed. These partition coefficients are useful for petrogenetic models involving zircon and apatite. ?? 1986 Springer-Verlag.

  7. Phase quantification of mullite–zirconia and zircon commercial powders using PAC and XRD techniques

    The short range technique of the Perturbed Angular Correlation (PAC) and x-ray diffraction (Rietveld) methods have been employed to determine the phase content in commercial mullite–zirconia and zircon raw materials that are ordinarily used to produce ceramic materials. The PAC technique, which probes zirconium-containing compounds at nanoscopic level, showed that zircon contains crystalline ZrSiO4 and an important amount of a structurally distorted zircon, which is also observed accompanying monoclinic zirconia in mullite–zirconia. This particular zircon phase was not detected by the long range x-ray diffraction–Rietveld technique. After an annealing treatment, important changes in crystalline contents of the powders allow confirming, by the x-ray diffraction–Rietveld method, the preexistence of this particular zircon phase. This fact must be taken into account when preparing multicomposites based on the present raw materials.

  8. Single-zircon dating by stepwise Pb-evaporation constrains the Archean history of detrital zircons from the Jack Hills, Western Australia

    Pb isotope analyses have been carried out on 42 zircon grains from a Western Australian metaconglomerate using stepwise Pb-evaporation directly in the ion source of a thermal ionization mass spectrometer. The metaconglomerate is from the Archean Jack Hills Metasedimentary Belt, and is known from ion microprobe (''SHRIMP'') analyses to contain a complex zircon population with ages between 4.2 Ga and 3.1 Ga. The same complex pattern of ages is found by the Pb evaporation studies. Five grains yielded minimum crystallization ages from 4.17 Ga to 4.07 Ga. The main population appears significantly younger, having been generated at about 3.55-3.3 Ga. The agreement between the two analytical approaches confirms the SHRIMP results and demonstrates the value of the stepwise-evaporation technique in determining the age patterns of mixing zircon populations. In many of the evaporative Pb isotope records the 207/206 ratios remained constant for all evaporation steps, which we interpret as evaporation from concordant zircon phases. However, for the majority of zircons 207/206 ratios increased with increasing evaporation temperature, and usually approached constant values during evaporation at the highest temperatures. This can be attributed to mixing of different radiogenic Pb components from either crystalline zircon phases of different ages or from domains of isotopically disturbed metamict zircon. Present results confirm > 4 Ga zircon ages in the metaconglomerate from the Hack Hills and substantiate formation of crust at a very early stage in the evolution of the earth. Results also confirm a major crust-forming event 3.55-3.3 Ga ago. (orig.)

  9. Kwangsian and Indosinian reworking of the eastern South China Block: Constraints on zircon U-Pb geochronology and metamorphism of amphibolites and granulites

    Wang, Yuejun; Wu, Chunming; Zhang, Aimei; Fan, Weiming; Zhang, Yanhua; Zhang, Yuzhi; Peng, Touping; Yin, Changqin


    To constrain temporal-spatial patterns of the Kwangsian and Indosinian orogenic events and the Phanerozoic tectonic evolution of the eastern South China Block, this paper documents the zircon U-Pb geochronology of the high-grade metamorphic rocks for key outcrops in the eastern SCB and the P-T path for the Indosinian metamorphic amphibolites. Our data show that the representative amphibolites from the originally-defined Badou, Mayuan, Chencai, Zhoutan and Yunkai Groups and associated granulites yielded zircon U-Pb metamorphic ages of 428-468 Ma. The weighted mean ages of 221-246 Ma are also given by the metamorphic zircons from amphibolites and granulites in the Yunkai, Shiwandashan, northern Wuyi and southern Hunan regions. The two age groups are followed by the 40Ar/39Ar plateau ages of 406-438 Ma and 195-217 Ma for synkinematic minerals from major shear zones in the eastern South China Block, respectively. The age-spans of 406-468 Ma and 195-246 Ma roughly coincide with the formation time of the Kwangsian (396-462 Ma) and Indosinian (202-248 Ma) granites of the eastern South China Block, respectively. The strongly compressive deformation, metamorphism and granitic magmatism are roughly contemporaneous for the Kwangsian and Indosinian tectonothermal events in the eastern South China Block. They occurred over a similar spatial extent, only reaching westward to the Jiangnan-Xuefeng Domains across the Jiangshan-Shaoxing Fault. The amphibolites from Zhouyuan (SW Zhejiang Province) of the Cathaysia Block, which have the Indosinian zircon U-Pb metamorphic ages of 243-246 Ma, underwent three episodes of metamorphism (M1-M3) and yielded a near-isothermal decompression clockwise P-T path. In combination with other geological data, it is proposed that the ages of ca. 430 Ma and ca.230 Ma might be interpreted as the transformational time from the prograde- to retro-metamorphism for the Kwangsian and Indosinian events, respectively. The Kwangsian and Indosinian orogenic

  10. Resolving the age of Wilson Creek Formation tephras and the Mono Lake excursion using high-resolution SIMS dating of allanite and zircon rims

    Vazquez, J. A.; Lidzbarski, M. I.


    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 interbedded rhyolitic tephras yield discordant 14C and 40Ar/39Ar results due to open-system effects, carbon reservoir uncertainties, as well as abundant xenocrysts entrained during eruption. Ion microprobe (SIMS) 238U-230Th dating of the final increments of crystallization recorded by allanite and zircon autocrysts from juvenile pyroclasts yields ages that effectively date eruption of key tephra beds and resolve age uncertainties about the Wilson Creek stratigraphy. To date the final several micrometers of crystal growth, individual allanite and zircon crystals were embedded in soft indium to allow sampling of unpolished rims. Isochron ages derived from rims on coexisting allanite and zircon (± glass) from hand-selected pumiceous pyroclasts delimit the timing of Wilson Creek sedimentation between Ashes 7 and 19 (numbering of Lajoie, 1968) to the interval between ca. 27 to ca. 62 ka. The interiors of individual allanite and zircon crystals sectioned in standard SIMS mounts yield model 238U-230Th ages that are mostly Mono Craters volcanism and/or intrusions. Tephra (Ash 15) erupted during the geomagnetic excursion originally designated the Mono Lake excursion yields a rim isochron age of ca. 41 ka indicating that the recorded event is instead the Laschamp excursion. The results are consistent with a depositional chronology from correlation of relative paleointensity (Zimmerman et al., 2006) that indicates quasi-synchronous glacial and hydrologic responses in the Sierra Nevada and Mono Basin to climate change

  11. DFT and two-dimensional correlation analysis methods for evaluating the Pu3+–Pu4+ electronic transition of plutonium-doped zircon

    Highlights: • Effect of Pu f-shell electron on the electronic property of zircon is calculated via DFT and 2D-CA techniques. • Reasons of Pu f-shell electron influencing on electronic properties are systematically discussed. • Phase transitions are found at two point 2.8 mol% and 7.5 mol%. - Abstract: Understanding how plutonium (Pu) doping affects the crystalline zircon structure is very important for risk management. However, so far, there have been only a very limited number of reports of the quantitative simulation of the effects of the Pu charge and concentration on the phase transition. In this study, we used density functional theory (DFT), virtual crystal approximation (VCA), and two-dimensional correlation analysis (2D-CA) techniques to calculate the origins of the structural and electronic transitions of Zr1−cPucSiO4 over a wide range of Pu doping concentrations (c = 0–10 mol%). The calculations indicated that the low-angular-momentum Pu-fxy-shell electron excites an inner-shell O-2s2 orbital to create an oxygen defect (VO-s) below c = 2.8 mol%. This oxygen defect then captures a low-angular-momentum Zr-5p65s2 electron to form an sp hybrid orbital, which exhibits a stable phase structure. When c > 2.8 mol%, each accumulated VO-p defect captures a high-angular-momentum Zr-4dz electron and two Si-pz electrons to create delocalized Si4+ → Si2+ charge disproportionation. Therefore, we suggest that the optimal amount of Pu cannot exceed 7.5 mol% because of the formation of a mixture of ZrO8 polyhedral and SiO4 tetrahedral phases with the orientation (10-1). This study offers new perspective on the development of highly stable zircon-based solid solution materials

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

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


    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.

  13. Zircons reveal magma fluxes in the Earth's crust.

    Caricchi, Luca; Simpson, Guy; Schaltegger, Urs


    Magma fluxes regulate the planetary thermal budget, the growth of continents and the frequency and magnitude of volcanic eruptions, and play a part in the genesis and size of magmatic ore deposits. However, because a large fraction of the magma produced on the Earth does not erupt at the surface, determinations of magma fluxes are rare and this compromises our ability to establish a link between global heat transfer and large-scale geological processes. Here we show that age distributions of zircons, a mineral often present in crustal magmatic rocks, in combination with thermal modelling, provide an accurate means of retrieving magma fluxes. The characteristics of zircon age populations vary significantly and systematically as a function of the flux and total volume of magma accumulated in the Earth's crust. Our approach produces results that are consistent with independent determinations of magma fluxes and volumes of magmatic systems. Analysis of existing age population data sets using our method suggests that porphyry-type deposits, plutons and large eruptions each require magma input over different timescales at different characteristic average fluxes. We anticipate that more extensive and complete magma flux data sets will serve to clarify the control that the global heat flux exerts on the frequency of geological events such as volcanic eruptions, and to determine the main factors controlling the distribution of resources on our planet. PMID:25056063

  14. Significance of zircon trace element geochemistry, the Shihu gold deposit,western Hebei Province, North China

    CAO Ye; LI Shengrong; ZHANG Huafeng; LIU Xiaobin; LI Zhenzhen; AO Chong; YAO Meijuan


    The Shihu gold deposit is characterized by gold-bearing quartz-polymetallic sulfides and quartz veins. Both Mapeng granitoids batholith and intermediate-basic dikes intruded the metamorphic basement rocks, and are spatially associated with gold mineralization. Trace element abundances in zircons from the Shihu gold deposit, determined by laser-ablation microprobe ICPMS analysis, are sensitive to source rock type and crystallization environment. Concentrations of 21 trace elements were determined for zircons from granitoid rocks, diorites,quartz diorite porphyrites and gold-bearing quartz veins revealed some elemental characteristics and chondrite-normalized trace element patterns from different samples. There were no distinctive differences in REE concentrations of zircons from plutonic rocks and quartz veins, indicating that they probably had the same origin. Relatively flat chondrite-normalized REE patterns with (Yb/Sm)N ratios less than 60 characterized zircons from quartz diorite porphyrites and quartz veins. The highest Nb/Ta ratios were found in zircons from quartz diorite porphyrites, whereas the lowest ratios were found in quartz vein zircons. The Nb/Ta ratios were broadly correlated with HREE+Y contents, and had weak positive correlations with the depth of the Eu negative anomalies. High values U up to 0.4% and Th up to 0.1%, as well as positive correlations with REE+Y characterized zircons from quartz vein. The lowest Th/U ratios of zircons present in quartz veins reflected the relatively high concentration of U in hydrothermal fluid, and high Pb concentrations only typified quartz vein grains relatively enriched in U and Th.Zircons from quartz diorite porphyrites showed the most pronounced Ce anomalies, whereas weak Ce anomalies were typical of zircons from quartz veins, in which Eu/Eu* of zircons had a broadly negative correlation with Ce/Ce*. Trace element geochemistry of zircons from mineralized quartz veins and plutonic rocks confirmed that the

  15. Oxidation of zirconium diboride-silicon carbide ceramics under an oxygen partial pressure of 200 Pa: Formation of zircon

    The formation and evolution of zircon during oxidation of ZrB2-20 vol.% SiC ceramics under a low oxygen partial pressure of 200 Pa is studied. The formation mechanism of zircon is proposed according to experimental results and thermodynamic consideration. And the main reason to the formation of zircon can be attributed to the active oxidation of SiC. Two steps can be divided for the formation and evolution of zircon: (1) nucleation from silica glass; and (2) crystal growth into prism like particles. Furthermore, the emergence of zircon significantly improves the oxidation resistance performance.

  16. 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

    Costa, Felipe Grandjean da; Araujo, Carlos Eduardo Ganade de; Vasconcelos, Antonio Maurilio, E-mail:, E-mail:, E-mail: [Servico Geologico do Brasil (CPRM), Fortaleza, CE (Brazil); Amaral, Wagner da Silva, E-mail: [Universidade Federal do Ceara (UFC), Fortaleza, CE (Brazil). Departamento de Geologia; Rodrigues, Joseneusa Brilhante, E-mail: [Servico Geologico do Brasil (CPRM), Brasilia, DF (Brazil)


    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)

  17. U-Pb (LA-ICPMS zircon ages and Nd isotopes for granitoids of the Tamboril-Santa Quitéria Complex, Ceará Central Domain: implication for neoproterozoic syncollisional magmatism in north Borborema Province

    Felipe Grandjean da Costa


    Full Text Available The Tamboril-Santa Quitéria Complex (TSQC is one of the largest Neoproterozoic plutonic manifestations in the northBorborema Province (NE Brazil. It represents an anatectic/igneous association characterized by a number of magmaticpulses that occurred in the 650-610 Ma interval. In this paper, we present U-Pb (LA-MC-ICP-MS zircon ages and Ndisotopes for quartz monzonites and quartz diorites of the southern part of TSQC. The quartz monzonites belong to a hybridgranitoid association, including monzonites, 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 aremuch more homogeneous in composition and yielded a U-Pb zircon age of 618 ± 23 Ma and a TDM age of 2.19 Ga. Thepresence 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 manifestationevolved in a collisional setting, probably related to slab breakoff during the Western Gondwana amalgamation.

  18. 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

    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)

  19. Two Trends of Composition Variation of Zircons and Their Significance in Origin Discrimination

    Bao, Xuezhao


    Zircon can crystallize in a wide range of physical and chemical conditions. At the same time, it has very high stability and durability. Therefore zircon can grow and survive in a variety of geological processes. In addition, the diffusivity of chemical compositions in its crystal is very low. Consequently, we can trace back the evolution history of the planetary materials containing zircon by zircon U-Th-Pb geochronology and geochemistry studies. However, this depends on our ability to decipher its genesis,namely magmatic or metamorphic origins. In this paper, we have found that there are obvious differences between magmatic and metamorphic zircons in their chemical composition zonations. The magmatic zircons exhibit composition zonation of increasing HfO2, and (UO2 + ThO2) content and decreasing ZrO2/HfO2 ratio and ZrO2 content from inner to outer parts within each growth zone or from core to rim of a crysta1. The metamorphic zircons exhibit compositional variation trend opposite to that of magmatic (igneou...

  20. Surface characteristics and bioactivity of a novel natural HA/zircon nanocomposite coated on dental implants.

    Karamian, Ebrahim; Khandan, Amirsalar; Motamedi, Mahmood Reza Kalantar; Mirmohammadi, Hesam


    The surface characteristics of implant which influence the speed and strength of osseointegration include surface chemistry, crystal structure and crystallinity, roughness, strain hardening, and presence of impurities. The aim of this study was to evaluate the bioactivity and roughness of a novel natural hydroxyapatite/zircon (NHA/zircon) nanobiocomposite, coated on 316L stainless steel (SS) soaked in simulated body fluid (SBF). NHA/zircon nanobiocomposite was fabricated with 0 wt.%, 5 wt.%, 10 wt.%, and 15 wt.% of zircon in NHA using ball mill for 20 minutes. The composite mixture was coated on 316L SS using plasma spray method. The results are estimated using the scanning electron microscopy (SEM) observation to evaluate surface morphology, X-ray diffraction (XRD) to analyze phase composition, and transmission electron microscopy (TEM) technique to evaluate the shape and size of prepared NHA. Surfaces roughness tester was performed to characterize the coated nanocomposite samples. The maximum average R a (14.54 μm) was found in the NHA 10 wt.% of zircon coating. In addition, crystallinity (X c ) was measured by XRD data, which indicated the minimum value (X c = 41.1%) for the sample containing 10 wt.% of zircon. Maximum bioactivity occurred in the sample containing 10 wt.% of zircon, which was due to two reasons: first, the maximum roughness and, second, the minimum crystallinity of nanobiocomposite coating. PMID:24822204

  1. Zircon synthesis via sintering of milled SiO2 and ZrO2

    The formation of zircon (ZrSiO4) via sintering of milled SiO2 and ZrO2 powders was studied, and the effects of slurry vs dry milling, sintering time, and particle size on zircon yield were examined. It was found that very high zircon yields could be obtained via slurry milling, cold pressing, and sintering of the oxide precursors. The controlling factor in determining zircon yield was found to be the particle size of the SiO2 and ZrO2 powders. Zircon yield as a function of sintering time was examined, and found to be similar to previous studies in which sol-gel precursors seeded with zircon were used. SEM studies reveal a homogeneous product with particle sizes on the order of 1--5 microm. It was found that complete reaction to zircon can be achieved from a once-through milling, pressing, and sintering process of SiO2-ZrO2 powders

  2. Growth of the Tuolumne Batholith: Zircon Crystallization Temperature, Age and Trace Element Data

    Matzel, J.; Miller, J.; Mundil, R.; Wooden, J.; Mazdab, F.; Burgess, S.; Paterson, S.; Memeti, V.


    Deciphering the intrusive record of magma systems is essential to understanding the links between surface volcanism and the long-term storage and evolution of magma reservoirs. Here we use age and geochemical data from zircon crystals to track mixing between different parts of the Tuolumne Batholith (Sierra Nevada, California). U-Pb zircon TIMS analyses from all locations examined in the batholith exhibit appreciable dispersion of single crystal or crystal fragment ages (several 105 yrs to 1x106 yrs) and, in addition, display distinctly older ages that likely represent zircon crystals entrained from older parts of the Tuolumne magmatic system. Since techniques aimed at eliminating Pb loss (and thus age scatter) have been employed prior to analysis, we interpret the age dispersion to reflect real variation in the timing of zircon crystallization. Two samples that show a high degree of age dispersion (> 1 Myr) were selected for trace element analysis and Ti- in zircon geothermometry by SHRIMP-RG. Crystallization temperatures ranged from 780-640°C and averaged 695°C (aTiO2 0.75 based on presence of titanite). No clear correlation exists between crystal age and temperature, and in most cases, the temperatures from crystal centers are within uncertainty of the temperatures at the rims. Trace element ratios vary systematically with temperature (e.g. decreasing Th/U ratio with decreasing T) and are attributed to fractionation, although neither sample represents strongly fractionated melt. Low total Zr indicates that the magmas were initially undersaturated in zircon when emplaced, which is also consistent with late zircon crystallization. Combined evidence from TIMS age analyses, geothermometry and trace element data suggests that entrainment of zircon from older parts of the magmatic system occurred late in the history of the batholith, and recycling of zircon crystals during successive magmatic injections is compatible with progressive growth of a large, long

  3. New insights into Arctic paleogeography and tectonics from U-Pb detrital zircon geochronology

    Miller, E.L.; Toro, J.; Gehrels, G.; Amato, J.M.; Prokopiev, A.; Tuchkova, M.I.; Akinin, V.V.; Dumitru, T.A.; Moore, T.E.; Cecile, M.P.


    To test existing models for the formation of the Amerasian Basin, detrital zircon suites from 12 samples of Triassic sandstone from the circum-Arctic region were dated by laser ablation-inductively coupled plasma-mass spectrometry (ICP-MS). The northern Verkhoyansk (NE Russia) has Permo-Carboniferous (265-320 Ma) and Cambro-Silurian (410-505 Ma) zircon populations derived via river systems from the active Baikal Mountain region along the southern Siberian craton. Chukotka, Wrangel Island (Russia), and the Lisburne Hills (western Alaska) also have Permo-Carboniferous (280-330 Ma) and late Precambrian-Silurian (420-580 Ma) zircons in addition to Permo-Triassic (235-265 Ma), Devonian (340-390 Ma), and late Precambrian (1000-1300 Ma) zircons. These ages suggest at least partial derivation from the Taimyr, Siberian Trap, and/ or east Urals regions of Arctic Russia. The northerly derived Ivishak Formation (Sadlerochit Mountains, Alaska) and Pat Bay Formation (Sverdrup Basin, Canada) are dominated by Cambrian-latest Precambrian (500-600 Ma) and 445-490 Ma zircons. Permo-Carboniferous and Permo-Triassic zircons are absent. The Bjorne Formation (Sverdrup Basin), derived from the south, differs from other samples studied with mostly 1130-1240 Ma and older Precambrian zircons in addition to 430-470 Ma zircons. The most popular tectonic model for the origin of the Amerasian Basin involves counterclockwise rotation of the Arctic Alaska-Chukotka microplate away from the Canadian Arctic margin. The detrital zircon data suggest that the Chukotka part of the microplate originated closer to the Taimyr and Verkhoyansk, east of the Polar Urals of Russia, and not from the Canadian Arctic. Copyright 2006 by the American Geophysical Union.

  4. Extreme lithium isotopic fractionation in three zircon standards (Plešovice, Qinghu and Temora)

    Yu-Ya Gao; Xian-Hua Li; Griffin, William L.; Yan-Jie Tang; Norman J. Pearson; Yu Liu; Mei-Fei Chu; Qiu-Li Li; Guo-Qiang Tang; O’Reilly, Suzanne Y.


    To understand the behavior of Li in zircon, we have analyzed the abundance and isotopic composition of Li in three zircon standards (Plešovice, Qinghu and Temora) widely used for microbeam analysis of U-Pb ages and O-Hf isotopes. We have mapped Li concentration ([Li]) on large grains, using a Cameca 1280HR Secondary Ion Mass Spectrometer (SIMS). All zircons have a rim 5–20 μm wide in which [Li] is 5 to 20 times higher than in the core. Up to ~20‰ isotopic fractionation is observed on a small ...

  5. Natural radionuclides in zircon and related radiological impacts in mineral separation plants

    The activity concentration of uranium and thorium present in zircon obtained from mineral sand industries are presented. External gamma radiation levels and inhalation of airborne dust are found to be the significant routes of radiation exposure to occupational workers. The annual average dose attributed to zircon processing is estimated to be 2.3 mSv in the plants under study. This paper presents the results of external gamma measurements, estimation of airborne radioactivity in zircon process locations and radon and thoron in the occupational environment of two mineral separation plants in India. Analyses of the solid wastes and liquid effluent generated and resultant environmental impacts are indicated. (authors)

  6. Annealing of natural metamict zircons: II high degree of radiation damage

    Colombo, M


    In situ time-dependent high-temperature X-ray powder diffraction was used to study the amorphous to crystalline transition in natural zircons which are characterized by a high degree of radiation damage. It was possible to distinguish two stages of the annealing process: (i) the recovery of the heavily disturbed but still crystalline domains and (ii) the recrystallization of the amorphous regions. The first stage is very fast under the chosen experimental conditions and, at least apparently, is not thermally activated. The second stage is a diffusion-controlled process, whose products (zircon or zircon and zirconia phases) are strongly correlated to the annealing temperature.

  7. A precise UPb zircon age for the Archaean Pongola Supergroup volcanics in Swaziland

    Hegner, E.; Kroner, A.; Hunt, P.


    UPb dating of single abraded zircon grains from a Pongola Supergroup rhyodacite sample collected in southern Swaziland yields a crystallization age of 2985??1 Ma. This date is significantly older than our previously reported UPb age determined on highly discordant and unabraded zircons from the same sample. The new zircon age indicates that the formation of the Pongola volcanics occurred not much later than the emplacement of the youngest granitoids thought to be broadly coeval with the Dominion Group (Robb et al., 1991), and before deposition of the Lower West Rand Group (Barton et al., 1989). ?? 1994.

  8. Effect of α-damage on fission-track annealing in zircon

    Kasuya, Masao; Naeser, Charles W.


    The thermal stability of confined fission-track lengths in four zircon samples having different spontaneous track densities (i.e., different amounts of ??-damage) has been studied by one-hour isochronal annealing experiments. The thermal stability of spontaneous track lengths is independent of initial spontaneous track density. The thermal stability of induced track lengths in pre-annealed zircon, however, is significantly higher than that of spontaneous track lengths. The results indicate that the presence of ??-damage lowers the thermal stability of fission-tracks in zircon.

  9. Cation antisite disorder in uranium-doped gadolinium zirconate pyrochlores

    The incorporation of uranium into gadolinium zirconate (Gd2Zr2O7) is investigated by synchrotron X-ray powder diffraction and X-ray absorption near-edge structure (XANES) spectroscopy. The results suggest that the uranium cation is largely located on the pyrochlore B-site instead of the targeted A-site. Cation disorder in Gd2Zr2O7 and U-doped Gd2Zr2O7 is investigated by positron annihilation lifetime spectroscopy (PALS) which demonstrates the absence of cation vacancies in these systems. This work provides direct evidence for cation antisite (A- and B-site mixing) disorder in U-doped and off-stoichiometric Gd2Zr2O7 pyrochlore

  10. Ferroelastic domain switching fatigue in lead zirconate titanate ceramics

    The influence of the frequency and amplitude of cyclic mechanical loading on soft, tetragonal lead zirconate titanate (PZT) ceramics was investigated via neutron diffraction. Intensity change in the {2 0 0} reflections provided quantitative measurements of domain switching behavior, domain texture and the strain resulting from domain switching. The results are explained using a viscoelasticity model. It was found that the magnitude of applied stress affects the level of strain accumulated, while its frequency affects the time taken for the strain to reach saturation. Furthermore, markedly different behaviors are exhibited by poled and unpoled samples. For samples loaded under identical conditions, the frequency effect is more pronounced in unpoled samples and the accumulated ferroelastic strain is greater in poled samples