Sample records for geoquimica isotopica sm-nd

  1. Crustal evolution of South American Platform based on Sm-Nd isotope geochemistry; Evolucao crustal da plataforma sul americana com base na geoquimica isotopica Sm-Nd

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    Sato, Kei


    Sm-Nd isotopic systematics is relevant to the topics of origin and evolution the of continental crust, where model ages refer to the time when crustal material was differentiated from the upper mantle. Alternative interpretations are due to a lack of adequate information on crustal processes and the variable composition of the mantle sources. The Sm-Nd methods are presented, and applied on rock materials from the South American Platform. The main conclusions indicate juvenile accretion with higher growth rates (peaks), around 3.7-3.5 Ga ({approx} 0.5% in volume), 3.1 - 2.9 Ga ({approx}16%), 2.7 - 2.6 ({approx} 9%), 2.2 - 1.9 (35%) and 1.3-1.0 (7%). The continental growth curve indicates that about 35 % of the crust was formed by 2.5 Ga, 88% by 1.8 Ga and 99% by 1.0 Ga, and the remaining {approx} 1 % was added in the Phanerozoic. Rapid crustal growth occurred between 2.2 and 1.9 Ga. The main period of continental crust formation occurred during the Paleoproterozoic, corresponding to 54 % in volume. Sm-Nd model ages, when compared with the crystallisation ages of granitoid rocks, furnish a rough estimate of juvenile vs. reworked material. Within the South American Platform about 45% of juvenile continental crust is still preserved within tectonic provinces of different ages. The remainder represents continental crust reworked in younger tectono-thermal events. In particular crustal reworking was predominating over juvenile accretion during Meso-Neoproterozoic. The Transbrasiliano Lineament is a megasuture, active in the Neoproterozoic, which separates a large northwestern mass, including the Amazonian and Sao Luis Cratons, from a southeastern mass, formed by a collage of cratonic fragments, of which the Sao Francisco and Rio de La Plata are the largest. The crustal evolutions of these two large continental masses are considered individually, and can be resumed following form: I - Old Archean rocks (>3.4 Ga) are found only within the south-eastern part (Gaviao Block

  2. Initial isotopic geochemistry ({delta} 18 O, {delta} D) of fluids from wells of the Los Humeros, Pue., geothermal field; Geoquimica isotopica ({delta} 18 O, {delta} D) inicial de fluidos de pozos del campo geotermico de Los Humeros, Pue.

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    Barragan Reyes, Rosa Maria; Arellano Gomez, Victor Manuel [Instituto de Investigaciones Electricas, Gerencia de Geotermia, Cuernavaca, Morelos (Mexico)]. E-mail:; Ramirez Montes, Miguel; Tovar Aguado, Rigoberto [Comision Federal de Electricidad, Gerencia de Proyectos Geotermoelectricos, Morelia, Michoacan (Mexico)


    de Los Humeros estan constituidos de una mezcla de aguas meteoricas de composicion isotopica muy ligera (paleofluidos) y aguas andesiticas. La relacion {delta} D vs {delta} 18 O para datos previos a la explotacion indica que los fluidos producidos estan constituidos por una mezcla de (al menos) dos fluidos de composicion isotopica diferente. En el extremo mas enriquecido de la relacion de mezcla se encontraron las composiciones isotopicas de los pozos H-23 y H-18 (localizados en el sur del campo), mientras que los fluidos mas ligeros se hallaron en el pozo H-16 original y posteriormente en el pozo H-16 reparado. Se encontro que la fase liquida de los pozos profundos se encuentra mas enriquecida en {delta} 18 O mientras que los pozos mas someros muestran valores mas ligeros, perfil que es indicativo de la ocurrencia de un proceso convectivo en el estado inicial. Con base en este perfil isotopico se establece que aunque la profundidad de las zonas productoras de los pozos H-1, H-12 y H-16 reparado son aproximadamente similares, su composicion isotopica es muy diferente. La composicion {delta} 18 O del pozo H-16 reparado parecia ser la de un vapor condensado, mientras que las de los pozos H-1 y H-12 se encontraron dentro del intervalo de valores de los pozos mas profundos (H-23). Esta caracteristica sugiere que los pozos H-1 y H-12 reciben fluidos muy profundos enriquecidos en {delta} 18 O. Estos resultados podrian ser de utilidad en el modelado conceptual del yacimiento.

  3. The Sm-Nd history of KREEP. [in lunar rocks (United States)

    Lugmair, G. W.; Carlson, R. W.


    Sm-Nd whole rock measurements on a variety of KREEP-rich samples from different landing sites are reported. Despite a variation of Nd and Sm concentrations of almost a factor of 3, the Sm-Nd ratios, as well as the Nd-143/Nd-144 values, show an extremely close grouping. No systematic differences between samples from different landing sites are resolved. These results are taken to be indicative of a moon-wide process having been responsible for the generation of the KREEP source reservoir, 4.36 plus or minus 0.06 AE ago, as estimated from model age calculation.

  4. Do supercontinents introvert or extrovert?: Sm-Nd isotope evidence (United States)

    Brendan Murphy, J.; Damian Nance, R.


    In recent years, two end-member models for the formation of supercontinents have emerged. In the classical Wilson cycle, oceanic crust generated during supercontinent breakup (the interior ocean) is consumed during subsequent amalgamation so that the supercontinent turns “inside in” (introversion). Alternatively, following supercontinent breakup, the exterior margins of the dispersing continental fragments collide during reassembly so that the supercontinent turns “outside in” (extroversion). These end-member models can be distinguished by comparing the Sm-Nd crust-formation ages of accreted mafic complexes (e.g., ophiolites) in the collisional orogens formed during supercontinent assembly with the breakup age of the previous supercontinent. For supercontinents generated by introversion, these crust-formation ages postdate rifting of the previous supercontinent. For supercontinents generated by extroversion, the oceanic lithosphere consumed during reassembly predates breakup of the previous supercontinent, so that crust-formation ages of accreted mafic complexes are older than the age of rifting. In the Paleozoic Appalachian-Caledonide-Variscan orogen, a key collisional orogen in the assembly of Pangea, crust-formation ages of accretionary mafic complexes postdate the formation of the Iapetus Ocean (i.e., are younger than ca. 0.6 Ga), suggesting supercontinent reassembly by introversion. By contrast, the Neoproterozoic East African and Brasiliano orogens, which formed during the amalgamation of Gondwana, are characterized by mafic complexes with crust-formation ages (ca. 0.75 1.2 Ga) that predate the ca. 750 Ma breakup of Rodinia. Hence, these complexes must have formed from lithosphere in the exterior ocean that surrounded Rodinia, implying that this ocean was consumed during the amalgamation of Gondwana. These data indicate that Pangea and Gondwana were formed by introversion and extroversion, respectively, implying that supercontinents can be assembled

  5. Sm-Nd age of the fazenda brasileiro gabbro, Bahia, Brazil: example of robust behavior of the Sm-Nd isotopic system under extreme hydrothermal alteration

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    Márcio M. Pimentel


    Full Text Available The Fazenda Brasileiro gold mineralization is hosted by a gabbroic sill, intrusive into metavolcanicmetasedimentary rocks of the Rio Itapicuru Greenstone Belt, São Francisco Craton. The 2.05 Ga old mineralization is associated with intense shearing and hydrothermal alteration, and the host gabbro is altered to a series of rocks rich in sericite, chlorite, actinolite, carbonate and quartz. Twelve whole-rock samples of the gold mineralization, representing varied degrees of alteration, from rocks with preserved igneous textures to the ore (quartz-carbonate-sulfide-chlorite, were studied by the Sm-Nd method. All analytical points resulted in an isochron (MSWD = 1.9 indicating the age of 2142 +/- 47 Ma (1s and Epsilon Nd (T of +1.2. Chlorite-sericite-carbonate rich hydrothermal rocks indicate the age of 2148 +/- 57 Ma and Epsilon Nd (T of +1.1. The positive Epsilon Nd (T suggest limited or no contamination with older continental crust, compatible with an oceanic setting for the tholeiites. Combined withREEdata, the Sm-Nd isotopic results reveal that the hydrothermal alteration, although intense, was unable to alter significantly the Sm/Nd ratios of the original igneous rocks and did not cause important scatter of the analytical points, providing a rare example of robust behavior of the isotopic system, even under intense hydrothermal alteration.A mineralização de ouro de Fazenda Brasileiro é hospedada por um sill gabróico intrusivo em rochas metavulcânicas/metassedimentares do Greenstone Belt do Rio Itapicuru, Craton do São Francisco. A mineralização, com idade de ca. 2.05 Ga, está associada com forte cizalhamento e alteração hidrotermal, e o gabro hospedeiro está alterado para rochas ricas em clorita, actinolita, carbonato e quartzo. Doze amostras de rocha total representando graus variados de alteração hidrotermal, desde rochas com texturas ígneas reliquiares até o minério (quartzo-carbonato-sulfeto-clorita, foram estudadas pelo

  6. SM-ND Age and REE Systematics of Larkman Nunatek 06319: Closed System Fractional Crystallization of a Shergottite Magma (United States)

    Shafer, J. T.; Brandon, A. D.; Lapen T. J.; Righter, M.; Peslier, A. H.


    Sm-Nd isotopic data were collected on mineral separates and bulk rock powders of LAR 06319, yielding an age of 180+/-13 Ma (2(sigma)). This age is concordant with the Lu-Hf age (197+/-29 Ma, [1]) determined in conjunction with these data and the Sm-Nd age (190+/-26 Ma) of Shih et al., 2009 [2]. The Sm-Nd data form at statistically significant isochron (Fig. 1) that is controlled largely by leachate-residue pairs (samples with the R suffix are residues after leaching in cold 2N HCl for 10 minutes).

  7. Geochemistry and geochronology U-Pb and Sm/Nd data of the orthogneiss from Pontalina region (GO), Brazil; Geoquimica e geocronologia U-Pb e Sm-Nd dos ortognaisses da regiao de Pontalina (GO), Brasil

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    Navarro, Guillermo Rafael Beltran, E-mail: [Universidade Estadual Paulista Julio de Mesquisa Filho (UNESP), Rio Claro, SP (Brazil). Inst. de Geociencias e Ciencias Exatas. Programa de Pos-Graduacao em Geologia Regional; Zanardo, Antenor, E-mail: [Universidade Estadual Paulista Julio de Mesquisa Filho (UNESP), Rio Claro, SP (Brazil). Dept. de Petrologia e Metalogenia; Conceicao, Fabiano Tomazini da, E-mail: [Universidade Estadual Paulista Julio de Mesquisa Filho (UNESP), Rio Claro, SP (Brazil). Dept. de Planejamento Territorial e Geoprocessamento; Montibeller, Cibele Carolina, E-mail: [Universidade Estadual Paulista Julio de Mesquisa Filho (UNESP), Rio Claro, SP (Brazil). Curso de Geologia


    Orthogneisses of tonalitic to granodioritic composition with calc-alkaline, metaluminous to peraluminous characteristics crop out at the region of Pontalina. The orthogneisses exhibit negative anomalies of Nb, Ta, P and Ti relative to rare earth elements (REE) and litophile elements, besides low contents of Nb, Ta, Y and Yb, similar to the rocks formed in subduction environments. U-Pb geochronological data show a neoproterozoic (681.5 {+-} 7.7 Ma) crystallization for the orthogneisses. The Nd isotope data yielded weakly negative to positive {epsilon}{sub Nd}(T) (+3.2 up to -0.1), with T{sub DM} model ages of {approx} 1.2 Ga. The combined geochemical and isotopic data suggest that the protolith of these orthogneisses are representative of neoproterozoic juvenile magmas, probably developed in an island arc system, generated during a ca.700 and 600 Ma event of crustal accretion in the western edge of the Sao Francisco Craton. (author)

  8. Rb-Sr And Sm-Nd Ages, and Petrogenesis of Depleted Shergottite Northwest Africa 5990 (United States)

    Shih, C. Y.; Nyquist, L. E.; Reese, Y.; Irving, A. J.


    Northwest Africa (NWA) 5990 is a very fresh Martian meteorite recently found on Hamada du Draa, Morocco and was classified as an olivine-bearing diabasic igneous rock related to depleted shergottites [1]. The study of [1] also showed that NWA 5990 resembles QUE 94201 in chemical, textural and isotopic aspects, except QUE 94201 contains no olivine. The depleted shergottites are characterized by REE patterns that are highly depleted in LREE, older Sm-Nd ages of 327-575 Ma and highly LREE-depleted sources with Nd= +35+48 [2-7]. Age-dating these samples by Sm-Nd and Rb-Sr methods is very challenging because they have been strongly shocked and contain very low abundances of light rare earth elements (Sm and Nd), Rb and Sr. In addition, terrestrial contaminants which are commonly present in desert meteorites will compromise the equilibrium of isotopic systems. Since NWA 5990 is a very fresh meteorite, it probably has not been subject to significant desert weathering and thus is a good sample for isotopic studies. In this report, we present Rb-Sr and Sm-Nd isotopic results for NWA 5990, discuss the correlation of the determined ages with those of other depleted shergottites, especially QUE 94201, and discuss the petrogenesis of depleted shergottites.

  9. Rb-Sr and Sm-Nd chronology and genealogy of mare basalts from the Sea of Tranquility (United States)

    Papanastassiou, D. A.; Depaolo, D. J.; Wasserburg, G. J.


    Rb-Sr and Sm-Nd ages of two Apollo 11 mare basalts, high-K basalt 10072 and low-K basalt 10062, are reported. Rb-Sr, Sm-Nd, and Ar-40-Ar-39 ages are in good agreement and indicate an extensive time interval for filling of the Sea of Tranquility, presumably by thin lava flows, in agreement with similar observations for the Ocean of Storms. Initial Sr and Nd isotopic compositions on Apollo 11 basalts reveal at least two parent sources producing basalts. The Sm-Nd isotopic data demonstrate that low-K and high-Ti basalts from Apollo 11 and 17 derived from distinct reservoirs, while low-Ti Apollo 15 mare basalt sources have Sm/Nd similar to the sources of Apollo 11 basalts. Groupings of mare basalt based on Ti content and on isotopic data do not coincide.

  10. Change of Sm-Nd isotope composition during weathering of till (United States)

    Öhlander, Björn; Ingri, Johan; Land, Magnus; Schöberg, Hans


    Weathering of till in northern Sweden results in the formation of well-developed spodosols. The till is dominated by 1.9-1.8 Ga granitic material. The REE are among the elements most strongly depleted during weathering, and the loss of REE from the E-horizon decreases as the atomic number increases. To study if weathering leads to a change of the Nd isotope composition, we have analysed the Nd isotopic composition of the various horizons including living plants and humus of two profiles of weathered till (typic haplocryods) in northern Sweden. As much as between 65.6 and 75.3% of the Sm and Nd in the fraction has been lost from the E-horizon, and between 32.5 and 54.7% from the B-horizon. Nd has been lost to a slightly greater extent than Sm. The two C-horizon samples have ɛ Nd(0) values of -22.1 and -23.2. Corresponding E-horizon values are -18.1 and -20.2. The B-horizon values are intermediate between the values of the E and C horizons. It is concluded that the weathering leads to a change in the Sm/Nd ratio resulting in a change of the Sm-Nd isotope composition. The plant and humus samples deviate even more from the unweathered till. For one station the results could be interpreted as if the Sm and Nd taken up by the plants had similar isotope characteristics as the amounts of these elements released by weathering in the E-horizon. For the other station it is probable that the Nd isotope composition of the organic samples is dominated by Nd released by till weathering which, however, is mixed with another Nd-source, possibly an airborne component. The explanation to the change of isotope compostion in the till is that a larger proportion of the Nd released by weathering is released from minerals with a lower Sm/Nd ratio than the bulk soil, compared with the amount released from minerals with a higher Sm/Nd ratio. Although the various REE-carrying minerals had the same initial Nd isotopic composition, 1.8-1.9 Ga of decay of 147Sm to 143Nd has resulted in a

  11. Sm-Nd Isotopic Studies of Two Nakhlites, NWA 5790 and Nakhla (United States)

    C.-Y. Shih; Nyquist, L. E.; Reese, Y.; Jambon, A.


    NWA 5790 is a Martian meteorite recently found in the Mauritania part of the Saharan desert and is classified as a nakhlite, containing a small amount of interstitial plagioclase. Unlike other Martian meteorites ( e.g., shergottites), nakhlites have been only moderately shocked and their original igneous textures are still well-preserved. In this report, we present Sm-Nd isotopic data for NWA 5790 and Nakhla, a rare "fall" nakhlite, correlate their ages with those of other nakhlites and discuss their petrogenesis.

  12. Promise and Pitfalls of Lu/Hf-Sm/Nd Garnet Geochronology (United States)

    King, R. L.; Vervoort, J. D.; Kohn, M. J.; Zirakparvar, N. A.; Hart, G. L.; Corrie, S. L.; Cheng, H.


    Our ability to routinely measure Lu-Hf and Sm-Nd isotopes in garnet allows broad new applications in geochronology, petrology, and tectonics. However, applications of these data can be limited by challenges in interpreting the petrologic record and preparing garnets for analysis. Here, we examine petrologic and chemical pitfalls encountered in garnet geochronology. Petrologic factors influencing trace element compositions in garnet include reactions that modify REE availability and partitioning (1,2), kinetically limited transfer of REEs to garnet (3), and bulk compositional heterogeneities (4). Interpreting the effects of these processes on Sm/Nd and Lu/Hf ages requires characterizing REE zonation prior to isotope analysis and age interpretation. Because garnet fractions are traditionally picked from crushed samples without regard to intracrystalline origins or chemistries, isochrons will represent mixtures derived to varying degrees from all periods of garnet growth. While measured zoning might generally indicate what garnet portion dominates the Lu/Hf or Sm/Nd budget, traditional mineral separation will rarely realize the chronologic potential afforded by high precision Hf and Nd isotope measurements. The potential use of alternative techniques, such as microsampling, necessitates selective digestion and/or leaching to eliminate inclusions within garnet. For Sm/Nd geochronology, H2SO4 leaching removes LREE-rich phosphates (e.g. apatite), but not silicates (e.g. epidote), precluding Sm-Nd dating of some rocks. For Lu/Hf geochronology, ubiquitous zircon microinclusions (c. 1 μm) can significantly disrupt age determinations. Microinclusions cannot be detected optically or separated physically, requiring selective chemical digestion. If complete digestion methods, such as bomb digestion, are used for garnet fractions, then "common Hf" from zircon will be contained in final solutions. These mixed analyses are of dubious utility and will fall into one of two

  13. Sm-Nd dating of Fig Tree clay minerals of the Barberton greenstone belt, South Africa (United States)

    Toulkeridis, T.; Goldstein, S. L.; Clauer, N.; Kroner, A.; Lowe, D. R.


    Sm-Nd isotopic data from carbonate-derived clay minerals of the 3.22-3.25 Ga Fig Tree Group, Barberton greenstone belt, South Africa, form a linear array corresponding to an age of 3102 +/- 64 Ma, making these minerals the oldest dated clays on Earth. The obtained age is 120-160 m.y. younger than the depositional age determined by zircon geochronology. Nd model ages for the clays range from approximately 3.39 to 3.44 Ga and almost cover the age variation of the Barberton greenstone belt rocks, consistent with independent evidence that the clay minerals are derived from material of the belt. The combined isotopic and mineralogical data provide evidence for a cryptic thermal overprint in the sediments of the belt. However, the highest temperature reached by the samples since the time of clay-mineral formation was <300 degrees C, lower than virtually any known early Archean supracrustal sequence.

  14. Rb-Sr and Sm-Nd Study of Asuka 881394: Evidence of "Late" Metamorphism (United States)

    Nyquist, L. E.; Shih, C.-Y.; Reese, Y.; Takeda, H.


    The Asuka 881394 achondrite contains fossil Al-26 and Mn-53 [1,2,3] and has a Pb-207/Pb-206 age of 4566.5 plus or minus 0.2 Ma [3], the oldest for an achondrite. Preliminary results showed initial Sm-146/Sm-144 = (7.4 plus or minus 1.2) x 10(exp -3), indicative of an ancient age, but Rb-87 - Sr-87 and Sm-147 - Nd-143 ages of 4370 plus or minus 60 and 4490 plus or minus 20 Ma, resp. [1], were younger than expected from the presence of short-lived nuclides. We revisit the Rb-Sr and Sm-Nd chronology of A881394 in an attempt to establish whether late metamorphism led to inconsistency in its apparent ages.

  15. Decoupled Rb-Sr and Sm-Nd isotopic evolution of the continental crust (United States)

    Goldstein, S. L.


    Evidence was presented that the Rb-Sr and Sm-Nd isotopic systems are decoupled in crust-mantle evolution. Rare earth element (including Sm and Nd) residue principally in silicates, and are resistant to mobilization by weathering and metamorphism. In contrast, Rb and Sr are easily fractionated by crustal processes and residue in carbonates as well as in silicates. As a result, continental Sr, but not Nd, can be recycled into the mantle by exchange of seawater with basalt at spreading ridges and by subduction of carbonates associated with ridge processes. These effects result in mean Rb-Sr ages of the continental crust and of the upper mantle that are too young. Crustal growth curves based largely on Rb-Sr data, such that of Hurley and Rand, are therefore incorrect.

  16. Garnet Sm-Nd and U-Pb systems: A case study of a granulite from the European Variscan belt

    Institute of Scientific and Technical Information of China (English)


    This study presents zircon and garnet ages of a mafic granulite from the high-grade Variscan basement of the Black Forest, Germany and discuss isotope closure temperature of garnet Sm-Nd and U-Pb systems. Zircon grains yield 207Pb/206Pb ages between ~340 and ~414 Ma by the U-Pb and evaporation methods. In contract, garnet dating gives Sm-Nd and Pb-Pb isochron ages of (398±3) Ma and (411±14) Ma, respectively, which are older than most of zircon ages. These data imply that most of zircons lost radiogenic Pb, probably due to metamictization or recrystallisation during the granulite-facies metamorphism (~800℃) at ~340 Ma. Garnet Sm-Nd and U-Pb systems preserve chronological information of pro-grade metamorphism, probably profiting from a fluid-absence metamorphic environment. These results demonstrate that garnet mineral can be a better candidate than zircon mineral to date high-grade metamorphism by the U-Pb and Sm-Nd methods in some cases.


    Institute of Scientific and Technical Information of China (English)

    XU De-ru; LIANG Xin-quan; CHEN Guang-hao; HUANG Zhi-long


    Sm-Nd isotopic compositions of eight lamprophyre samples, which come from the Gezhen gold-bearing shear zone on western Hainan Island, are measured. The Sm-Nd isochron age is 495.98±13.14 Ma, (143Nd/144Nd) 0=0.512094, εNd(t) ranges from +1.80 to +2.00 and TDM from 982 Ma to 1196 Ma (average: 1060 Ma). The authors point out that the whole-rock Sm-Nd isochron age (495.98 ± 13.14 Ma) really represents the petrogenetic age of lamprophyre and the time of magmatism during subsequent subduction.

  18. Age and origin of the Cortlandt Complex, New York: Implications from Sm-Nd data (United States)

    Domenick, M.A.; Basu, A.R.


    Sm-Nd systematics for nine whole-rock samples of hornblende norites, pyroxenites and a lamprophyre from various parts of the Cortlandt Complex were analyzed. Six of these samples from the central and eastern parts of the complex give an isochron age of 430??34 (2 ??) Ma with an e{open}Nd value of -2.9??0.5, and the other three samples from the western part, including the lamprophyre, define a similar age of 394??33 (2 ??) Ma but with a distinctly different e{open}Nd value of -1.4??0.4. The two different initial 143Nd/144Nd ratios corresponding to these e{open}-values are interpreted to reflect continental crustal contamination of the lamprophyric parental liquid prior to final emplacement and crystal fractionation to produce the different rock types of the complex. The intrusion age of 430 Ma for the complex clearly post-dates the major metamorphic event of the Taconic orogeny. The Nd-isotopic data also suggest a relationship between the Cortlandt Complex and a belt of lamprophyric dike rocks to the west, known as the Beemerville trend, which cuts across the metamorphic trends of the Taconic (Ratcliffe 1981). ?? 1982 Springer-Verlag.

  19. Rb-Sr and Sm-Nd Isotopic Studies of Lunar Green and Orange Glasses (United States)

    Shih, C.-Y.; Nyquist, L. E.; Reese, Y.


    Lunar volcanic glassy beads have been considered as quenched basaltic magmas derived directly from deep lunar mantle during fire-fountaining eruptions [1]. Since these sub-mm size glassy melt droplets were cooled in a hot gaseous medium during free flight [2], they have not been subject to mineral fractionations. Thus, they represent primary magmas and are the best samples for the investigation of the lunar mantle. Previously, we presented preliminary Rb- Sr and Sm-Nd isotopic results for green and orange glassy samples from green glass clod 15426,63 and orange soil 74220,44, respectively [3]. Using these isotopic data, initial Sr-87/Sr-86 and Nd ratios for these pristine mare glass sources can be calculated from their respective crystallization ages previously determined by other age-dating techniques. These isotopic data were used to evaluate the mineralogy of the mantle sources. In this report, we analyzed additional glassy samples in order to further characterize isotopic signatures of their source regions. Also, we'll postulate a relationship between these two major mare basalt source mineralogies in the context of lunar magma ocean dynamics.

  20. Super-chondritic Sm/Nd ratios in Mars, the Earth and the Moon. (United States)

    Caro, Guillaume; Bourdon, Bernard; Halliday, Alex N; Quitté, Ghylaine


    Small isotopic differences in the atomic abundance of neodymium-142 (142Nd) in silicate rocks represent the time-averaged effect of decay of formerly live samarium-146 (146Sm) and provide constraints on the timescales and mechanisms by which planetary mantles first differentiated. This chronology, however, assumes that the composition of the total planet is identical to that of primitive undifferentiated meteorites called chondrites. The difference in the 142Nd/144Nd ratio between chondrites and terrestrial samples may therefore indicate very early isolation (planetary isochron yielding an age of differentiation of 40 +/- 18 Myr for the martian mantle. This isochron does not pass through the chondritic reference value (100 x epsilon(142)Nd = -21 +/- 3; 147Sm/144Nd = 0.1966). The Earth, Moon and Mars all seem to have accreted in a portion of the inner Solar System with approximately 5 per cent higher Sm/Nd ratios than material accreted in the asteroid belt. Such chemical heterogeneities may have arisen from sorting of nebular solids or from impact erosion of crustal reservoirs in planetary precursors. The 143Nd composition of the primitive mantle so defined by 142Nd is strikingly similar to the putative endmember component 'FOZO' characterized by high 3He/4He ratios.

  1. Sm-Nd, Rb-Sr, and Mn-Cr Ages of Yamato 74013 (United States)

    Nyquist, L. E.; Shih, C.- Y.; Reese, Y.D.


    Yamato 74013 is one of 29 paired diogenites having granoblastic textures. The Ar-39 - Ar-40 age of Y-74097 is approximately 1100 Ma. Rb-Sr and Sm-Nd analyses of Y-74013, -74037, -74097, and -74136 suggested that multiple young metamorphic events disturbed their isotopic systems. Masuda et al. reported that REE abundances were heterogeneous even within the same sample (Y-74010) for sample sizes less than approximately 2 g. Both they and Nyquist et al. reported data for some samples showing significant LREE enrichment. In addition to its granoblastic texture, Y-74013 is characterized by large, isolated clots of chromite up to 5 mm in diameter. Takeda et al. suggested that these diogenites originally represented a single or very small number of coarse orthopyroxene crystals that were recrystallized by shock processes. They further suggested that initial crystallization may have occurred very early within the deep crust of the HED parent body. Here we report the chronology of Y-74013 as recorded in chronometers based on long-lived Rb-87 and Sm-147, intermediate- lived Sm-146, and short-lived Mn-53.

  2. Sm-Nd age dating of high- pressure granulites and amphi- bolite from Sanggan area, North China craton

    Institute of Scientific and Technical Information of China (English)


    The high pressure (HP) metamorphic age has been dated to HP rocks from the Sanggan area, North China craton. We have got garnet+whole rock isochron ages of (1 842±38) Ma for HP granulite, and (1 856 ± 26) Ma for HP amphibolite. The Sm-Nd whole rock isochron of HP granulites give out an age of (1 870±150) Ma with Nd deplet-ed mantle model age of (2 402-2 482) Ma. Considering the Nd isotope homogenization during the peak metamorphism of the HP granulite, Sm-Nd closure temperature and the retention of Nd isotopic memory in garnets partially broken down during decompression, all these isochron ages are thought to be HP metamorphic age. Furthermore, we pro-posed that the HP metamorphism took place at the end of Paleoproterozoic during the large-scale collision and assem-bly of the North China craton.

  3. Sm-Nd dating and Nd-Sr isotopic characteristics of the Shimian ophiolite suite, Sichuan Province

    Institute of Scientific and Technical Information of China (English)


    By measuring the Sm-Nd and Rb-Sr isotopic compositions of harzburgite and gabbro from Shimian ophiolite suite, we got the whole rock Sm-Nd isochron age of (938±30) Ma (2?), and the ??Nd of 7.6±0.8 (2?), which shows that the ophiolite was formed at the Early Neoproterozoic. The obvious change (0.70209-0.70708) of ISr values of the ophiolite is caused by the meteoric hydrothermal alteration. The high ? Nd values indicate that the primitive magma was derived from the intense depleted mantle reservoir. It is suggested that this area was in a back-arc basin environment during the Early Neoproterozic.

  4. Whole-rock Pb and Sm-Nd isotopic constraints on the growth of southeastern Laurentia during Grenvillian orogenesis (United States)

    Fisher, C.M.; Loewy, S.L.; Miller, C.F.; Berquist, P.; Van Schmus, W. R.; Hatcher, R.D.; Wooden, J.L.; Fullagar, P.D.


    The conventional view that the basement of the southern and central Appalachians represents juvenile Mesoproterozoic crust, the final stage of growth of Laurentia prior to Grenville collision, has recently been challenged. New whole-rock Pb and Sm-Nd isotopic data are presented from Meso protero zoic basement in the southern and central Appalachians and the Granite-Rhyolite province, as well as one new U-Pb zircon age from the Granite-Rhyolite province. These data, combined with existing data from Mesoproterozoic terranes throughout southeastern Laurentia, further substantiate recent suggestions that the southern and central Appalachian basement is exotic with respect to Laurentia. Sm-Nd isotopic compositions of most rocks from the southern and central Appalachian basement are consistent with progressive growth through reworking of the adjacent Granite-Rhyolite province. However, Pb isotopic data, including new analyses from important regions not sampled in previous studies, do not correspond with Pb isotopic compositions of any adjacent crust. The most distinct ages and isotopic compositions in the southern and central Appalachian basement come from the Roan Mountain area, eastern Tennessee-western North Carolina. The data set indicates U-Pb zircon ages up to 1.8 Ga for igneous rocks, inherited and detrital zircon ages >2.0 Ga, Sm-Nd depleted mantle model (TDM) ages >2.0 Ga, and the most elevated 207Pb/204Pb observed in southeastern Laurentia. The combined U-Pb geochronologic and Sm-Nd and Pb isotopic data preclude derivation of southern and central Appalachian basement from any nearby crustal material and demonstrate that Grenville age crust in southeastern Laurentia is exotic and probably was transferred during collision and assembly of Rodinia. These new data better define the boundary between the exotic southern and central Appalachian basement and adjacent Laurentian Granite-Rhyolite province. ?? 2010 Geological Society of America.

  5. Sm-Nd for Norite 78236 and Eucrite Y980318/433: Implications for Planetary and Solar System Processes (United States)

    Nyquist, L. E.; Shih, C-Y.; Reese, Y. D.


    Here, we compare Sm-147-Nd-143 and Sm-146-Nd-142 data for lunar norite 78236 to those for approximately 4.54-4.56 Ga old cumulate eucrite Yamato 980318/433 and show that the norite data are compatible with its derivation from an isotopic reservoir similar to that from whence the eucrite pair came. Thus, lunar-like Sm-Nd isotopic systematics are not unique to the Earth-Moon system.

  6. Sm-Nd and Rb-Sr Ages for Northwest Africa 2977, A Young Lunar Gabbro from the PKT (United States)

    Nyquist, L. E.; Shih, C.-Y.; Reese, Y. D.; Irving, A. J.


    Northwest Africa (NWA) 2977 is an olivine gabbro cumulate equivalent to one of the lithologies in lunar mare breccia NWA 773 [1,2,3]. The Ar-39-Ar-40 age is 2.77+/-0.04 Ga based on the last approx.57% of the gas release [4], similar to results for NWA 773 [5]. A Sm-Nd age (T) of 2.865+/-0.031 Ga and Epsilon(sub Nd) = -7.84+/-0.22 for the NWA 773 gabbro reported by [6] has been revised to T = 2.993+/-=0.032 Ga, Epsilon(sub Nd) -4.5+/-0.3 [7]. Sm-147-Nd-143 isochron for NWA 2977: Whole rock, pyroxene, olivine, plagioclase, whole rock leachate (approx.phosphate) and the combined leachates from the mineral separates yield a well defined Sm-Nd isochron for an age T = 3.10+/-0.05 Ga and Epsilon(sub Nd-CHUR) = -3.74+/-0.26 [8], or Epsilon(sub Nd-HEDR) = -4.61+/-0.26 [9]. Rb-87-Sr-87 isochron: NWA 2977 contains only a modest amount of Rb and/or Sr contamination. The Sr-isotopic composition of the contaminant closely resembles that of seawater. The whole rock residue after leaching combined with leach residues for plagioclase and pyroxene define an isochron age of 3.29+/-0.11 Ga for initial Sr-87/Sr-86 = 0.70287+/-18. The olivine residue, with lower Sr abundance of approx 1.5 ppm, is only slightly displaced from the isochron. The relatively small uncertainties of the Rb-Sr isochron parameters and near-concordancy with the Sm-Nd age indicate that both the Rb-Sr and the Sm-Nd ages are reliable.

  7. Sm-Nd and Ar-Ar Studies of DHO 908 and 489: Implications for Lunar Crustal History (United States)

    Nyquist, L. E.; Shih, C. Y.; Reese, Y. D.; Park, J.; Bogard, D. D.; Garrison, D. H.; Yamaguchi, A.


    It is widely assumed that ferroan anorthosites (FANs) formed as flotation cumulates on a global lunar magma ocean (LMO). A corollary is that all FANs are approximately contemporaneous and formed with the same initial Nd-143/Nd-144 ratio. Indeed, a whole rock isochron for selected FANs (and An93 anorthosite) yields an isochron age of 4.42 +/- 0.13 Ga and initial Nd-143/Nd-144, expressed in epsilon-units, of epsilon(sub Nd,CHUR) = 0.3+/-0.3 relative to the CHondritic Uniform Reservoir , or epsilon(sub Nd,HEDPB)=-0.6+/-0.3 relative to the HED Parent Body. These values are in good agreement with the age (T) = 4.47+/-0.07 Ga, and epsilon(sub Nd,HEDPB) =-0.6 +/- 0.5 for FAN 67075. We also have studied anorthositic clasts in the Dhofar 908 and 489 lunar highland meteorites containing clasts of magnesian anorthosites (MAN) with Mg# approximately 75. Because of their relatively high Mg#, magnesian anorthosites should have preceded most FANs in crystallization from the LMO if both are LMO products. Thus, it is important to determine whether the Nd-isotopic data of MAN and FAN are consistent with a co-magmatic origin. We previously reported Sm-Nd data for white clast Dho 908 WC. Mafic minerals in this clast were too small to be physically separated for an isochron. However, we estimated initial Nd-143/Nd-144 for the clast by combining its bulk ("whole rock") Sm-Nd data with an Ar-39-Ar-40 age of 4.42+/-.04 Ga. Here we report additional Sm-Nd data for bulk samples of Dho 908 and its pair Dho 489.

  8. REE composition in scheelite and scheelite Sm-Nd dating for the Xuebaoding W-Sn-Be deposit in Sichuan

    Institute of Scientific and Technical Information of China (English)

    LIU Yan; DENG Jun; LI ChaoFeng; SHI GuangHai; ZHENG AiLi


    The scheelite with large size and euhedral shape from Xuebaoding, Sichuan Province is an ideal mineral to study REE patterns and Sm-Nd dating of non-gold deposits. The scheelite has diameters of 1―10 cm and colors of pale beige to deep orange. Most of these scheelites occur in association with beryl, cassiterite and muscovite. The rare earth elements indicate that scheelite samples from Xuebaoding W-Sn-Be deposits contain high concentrations of rare earth elements with total ΣREE+Y contents in the range of 369―1725 μg·g(-)1 and nearly all of these scheelite samples are enriched in LREE and depleted in HREE and have negative Eu anomalies. The REE patterns of the scheelites are similar to those of A-type granite with obvious tetrad effect, similar to that of type II scheelites. Based on reported fluid inclusion studies, the mineralizing-fluid of the Xuebaoding W-Sn-Be deposit indicates low Na activity. The REE patterns of the scheelite are probably controlled by partition coefficient in hydrothermal fluid. In the 147Sm/144Nd-143Nd/144Nd diagram, the scheelites show a linear array corresponding to an isochron age of 182.0±9.2 Ma (MSWD = 0.52). The Sm-Nd age represents the formation age of the scheelite and can indicate that the W, Sn and Be mineralization at Xuebaoding took place in the Early Yanshanian. The Sm-Nd dating result is important for the study of the multi-metal resources in western Sichuan Province.

  9. The Role of Accessory Phases in the Sm-Nd Isotope Systematics of the Acasta Gneiss Complex (United States)

    Bauer, A.; Fisher, C. M.; Vervoort, J. D.; Bowring, S. A.


    The Acasta Gneiss Complex (AGC) of the Slave Craton in the Northwest Territories, Canada, contains some of Earth's oldest continental crust. It is characterized by a range of compositionally diverse gneisses with crystallization ages of 3.3 to > 4.0 Ga1-5. The AGC has undergone a multistage history of metamorphism and deformation. Given these post-crystallization processes, the extent of Nd isotope heterogeneity suggested by published4-7 whole rock Sm-Nd analyses of these rocks has been called into question. Criticisms include the likelihood of mixed lithologies at the hand-sample scale and the potential for open-system behavior of the Sm-Nd isotopic system in these rocks. We obtained whole rock compositional, Sm-Nd and Lu-Hf isotope data paired with Hf in zircon and Nd in titanite and apatite data to further evaluate the isotope record, and use U-Pb and Lu-Hf of zircon as a basis for identifying mixed or complex samples. Preferential preservation of Lu-Hf over Sm-Nd isotope systematics in multiply deformed, complex rocks may be controlled by the minerals that dominate the Hf and Nd budgets, with the majority of the Hf effectively sheltered in zircon and the Nd largely hosted in accessory phases such as apatite and titanite. This composite dataset enables us to evaluate the possibility that Hf and Nd isotopic systematics have been decoupled in these samples that have such critical bearing on our understanding of early crust-forming processes. [1]Bowring and Williams (1999). CoMP, 134(1), 3-16. [2]Iizuka, T. et al. (2006) Geology, 34(4), 245-248. [3]Iizuka et al (2007). Precambrian Res, 153(3), 179-208. [4]Bowring et al. 1989. Nature, 340: 222-225. [5]Mojzsis et al. (2014). GCA, 133, 68-96. [6]Bowring and Housh (1995) Science 269, 1535-1540. [7]Moorbath et al (1997) Chem. Geol. 135, 213-231.

  10. Lu-Hf and Sm-Nd geochronology of garnet gneisses in the central Appalachians, U.S.: Implications for the timing and duration of Grenville Orogeny (United States)

    Vervoort, Jeff; Ramsey, Molly; Mulcahy, Sean; Aleinikoff, John; Southworth, Scott


    The Grenville orogeny is one of the most significant geological events in Earth's history with remnants of this event prominent on virtually every continent. Constraining its timing and duration is important not only for understanding the tectonics of the Grenville itself, but also for understanding supercontinent cycles and other questions of Earth's evolution. In order to provide better constraints on the timing of Grenvillian metamorphism, we analyzed garnet-bearing Mesoproterozoic ortho and paragneisses, collected along a 150 km transect in the northern Blue Ridge Province, using combined Lu-Hf and Sm-Nd geochronology. The orthogneisses have U-Pb zircon crystallization ages of ~1140 and 1100 Ma. The paragneisses have maximum depositional ages ~1050 to 1020 Ma, based on the youngest detrital zircon populations. Zircon overgrowths and monazite ages suggest metamorphic events between ~1050 and 960 Ma. The Lu-Hf and Sm-Nd data for these samples both yield robust garnet ages with large spread of parent/daughter ratios, low age uncertainties, and low MSWD values. Lu-Hf ages define a narrow time span (1043±12 Ma to 1016±4 Ma; wtd. mean, 1024±7 Ma, 2σ). The Sm-Nd ages, determined on the same solutions as Lu-Hf, also define a narrow time range but are systematically younger (974±11 Ma to 932±5 Ma; wtd. mean, 957±10 Ma). The average difference between Lu-Hf and Sm-Nd ages is 67 Ma; the oldest Sm-Nd age is 40 Ma younger than the youngest Lu-Hf age. These large systematic differences in the ages are enigmatic. While Sm-Nd ages younger than Lu-Hf are not uncommon, these differences are typically small. There are, however, potential explanations for these differences. (1) Lu partitions strongly into garnet during growth resulting in high Lu/Hf ratios in the core and yielding ages weighted toward the beginning of growth (e.g., Skora, 2006); no similar partitioning exists in Sm/Nd and these ages reflect mean garnet growth. (2) Lu diffuses much faster than Hf at elevated

  11. The Sm-Nd isotopic method in the geochronology laboratory of the University of Brasília

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    S.M.C.L. GIOIA


    Full Text Available Nd isotopes represent one of the best tools to investigate the processes involved in the evolution of the continental crust and mantle. This is due mainly to the similar geochemical behaviour of Sm and Nd, both light rare earth elements, which inhibits their fractionation during most varied geological processes. In order to carry out crustal evolution studies in central Brazil, the Sm-Nd isotopic method was implanted at the Geochronology Laboratory of the University of Brasília. The Sm-Nd separation methodology is basically that described in Richard et al. (1976, with the addition of some improvements. In this study we describe in detail the methodology used in Brasília. Precision and accuracy were checked with the international standards such as JB-3, BCR-1, BHVO-1 and La Jolla, and the following results were found: JB-3 (Nd=15.74 ppm and Sm=4.28 ppm, BCR-1 (143Nd/144Nd=0.512647±8, Nd=28.73 ppm and Sm=6.66 ppm, BHVO-1 (Nd=24.83 ppm and Sm=6.2 ppm and La Jolla (143Nd/144Nd=0.511835±14.

  12. Sm-Nd and Rb-Sr Isotopic Studies of Meteorite Kalahari 009: An Old VLT Mare Basalt (United States)

    Shih, C.-Y.; Nyquist, L. E.; Reese, Y.; Bischoff, A.


    Lunar meteorite Kalahari 009 is a fragmental basaltic breccia contain ing various very-low-Ti (VLT) mare basalt clasts embedded in a fine-g rained matrix of similar composition. This meteorite and lunar meteorite Kalahari 008, an anorthositic breccia, were suggested to be paired mainly due to the presence of similar fayalitic olivines in fragment s found in both meteorites. Thus, Kalahari 009 probably represents a VLT basalt that came from a locality near a mare-highland boundary r egion of the Moon, as compared to the typical VLT mare basalt samples collected at Mare Crisium during the Luna-24 mission. The concordant Sm-Nd and Ar-Ar ages of such a VLT basalt (24170) suggest that the extrusion of VLT basalts at Mare Crisium occurred 3.30 +/- 0.05 Ga ag o. Previous age results for Kalahari 009 range from approximately 4.2 Ga by its Lu-Hf isochron age to 1.70?0.04 Ga of its Ar-Ar plateau ag e. However, recent in-situ U-Pb dating of phosphates in Kalahari 009 defined an old crystallization age of 4.35+/- 0.15 Ga. The authors su ggested that Kalahari 009 represents a cryptomaria basalt. In this r eport, we present Sm-Nd and Rb-Sr isotopic results for Kalahari 009, discuss the relationship of its age and isotopic characteristics to t hose of other L-24 VLT mare basalts and other probable cryptomaria ba salts represented by Apollo 14 aluminous mare basalts, and discuss it s petrogenesis.

  13. Conflicting Lu-Hf and Sm-Nd ages in the garnet gneisses of the Central Appalachians, Eastern U.S.: Implications for the timing and duration of Grenville Orogeny and a case for using coupled Lu-Hf and Sm-Nd geochronology (United States)

    Vervoort, J. D.; Ramsey, M.; Aleinikoff, J. N.; Southworth, S.


    The Grenville orogeny is one of the most significant geological events in Earth's history with remnants of this event prominent on virtually every continent. Constraining its timing and duration is important not only for understanding the tectonics of the Grenville itself, but also for understanding supercontinent cycles and other questions of Earth's evolution. In order to provide better constraints on the timing of Grenvillian metamorphism, we analyzed garnet-bearing Mesoproterozoic ortho- and paragneisses, collected along a 150 km transect in the northern Blue Ridge Province, using combined Lu-Hf and Sm-Nd geochronology. The orthogneisses have U-Pb zircon crystallization ages of ~1140 and 1100 Ma. The paragneisses have maximum depositional ages ~1050-1020 Ma, based on the youngest detrital zircon populations. Zircon overgrowths and monazite suggest metamorphic events between ~1050 and 960 Ma. The Lu-Hf and Sm-Nd data for these samples both yield robust garnet ages with large spread of parent/daughter ratios, low age uncertainties, and low MSWD values. Lu-Hf ages define a narrow time span (1043×12 Ma to 1016×4 Ma; wtd. mean, 1024×7 Ma, 2σ). The Sm-Nd ages, determined on the same solutions as Lu-Hf, also define a narrow time range but are systematically younger (974×11 Ma to 932×5 Ma; wtd. mean, 957×10 Ma). The average difference between Lu-Hf and Sm-Nd ages is 67 Ma; the oldest Sm-Nd age is 40 Ma younger than the youngest Lu-Hf age. These large systematic differences in the ages are enigmatic. While Sm-Nd ages younger than Lu-Hf are not uncommon, these differences are typically small; nothing of this magnitude has been previously reported. There are, however, potential explanations for these differences. (1) Lu partitions strongly into garnet during growth yielding ages weighted toward the beginning of growth (e.g., Skora, 2006); no similar partitioning exists in Sm-Nd and these ages reflect mean garnet growth. (2) Lu diffuses much faster than Hf at

  14. Simultaneous in situ determination of U-Pb and Sm-Nd isotopes in monazite by laser ablation ICP-MS (United States)

    Goudie, Dylan J.; Fisher, Christopher M.; Hanchar, John M.; Crowley, James L.; Ayers, John C.


    are presented for in situ simultaneous determination of U-Pb and Sm-Nd isotopes in monazite using the Laser Ablation Split-Stream (LASS) method. This method uses a laser ablation system coupled to a magnetic-sector inductively coupled plasma mass spectrometer (HR) (ICP-MS) for measuring U-Pb isotopes and a multicollector (MC) ICP-MS for measuring Sm-Nd isotopes. Ablated material is split using a Y-connector and transported simultaneously to both mass spectrometers. In addition to Sm and Nd isotopes, the MC-ICP-MS is configured to also acquire Ce, Nd, Sm, Eu, and Gd elemental abundances. This approach provides age, tracer isotope, and trace element data in the same ablation volume, reducing sampling problems associated with fine-scale zoning in accessory minerals and minimizing the material needed for ablation. Precision and accuracy of the U-Pb method (and the precision of the Sm-Nd method) is demonstrated with results from well-characterized monazite reference materials. The LASS results agree within uncertainty with the isotope dilution thermal ionization mass spectrometry (ID-TIMS) U-Pb dates. The accuracy of the Sm-Nd method is assessed by comparing the LA-MC-ICP-MS results with ID-TIMS determinations on a well-characterized, in-house monazite reference material. The LASS method is then applied to monazite from the Birch Creek Pluton in the White Mountains of California as a case study to illustrate the utility of this method for solving geologic problems. The U-Pb ages and Sm-Nd isotopic data from the LASS method support the conclusions drawn from previous results that monazite can record timing and information about the source region(s) of hydrothermal fluids.

  15. Erosion of Archean continents: The Sm-Nd and Lu-Hf isotopic record of Barberton sedimentary rocks (United States)

    Garçon, M.; Carlson, R. W.; Shirey, S. B.; Arndt, N. T.; Horan, M. F.; Mock, T. D.


    Knowing the composition, nature and amount of crust at the surface of the early Earth is crucial to understanding the early geodynamics of our planet. Yet our knowledge of the Hadean-Archean crust is far from complete, limited by the poor preservation of Archean terranes, and the fact that less attention has been paid to the sedimentary record that tracks erosion of these ancient remnants. To address this problem and get a more comprehensive view of what an Archean continent may have looked like, we investigated the trace element and Sm-Nd, Lu-Hf isotopic records of Archean metasedimentary rocks from South Africa. We focused our study on sandstone and mudstone from drill core in the Fig Tree Group (3.23-3.26 Ga) of the Barberton granite-greenstone belt, but also analyzed the 3.4 Ga Buck Reef cherts and still older (3.5-3.6 Ga) meta-igneous rocks from the Ancient Gneiss Complex, Swaziland. Based on principal component analysis of major and trace element data, the Fig Tree metasedimentary rocks can be classified into three groups: crustal detritus-rich sediments, Si-rich sediments and Ca-, Fe-rich sediments. The detritus-rich sediments have preserved the Sm-Nd and Lu-Hf isotopic signatures of their continental sources, and hence can be used to constrain the composition of crust eroded in the Barberton area in the Paleoarchean period. Based on Sm/Nd ratios, we estimate that this crust was more mafic than today, with an average SiO2 content of 60.5 ± 2 wt.%. This composition is further supported by isotopic mixing calculations suggesting that the sedimentary source area contained equal proportions of mafic-ultramafic and felsic rocks. This implies that the Archean crust exposed to weathering was more mafic than today but does not exclude a more felsic composition at depth. Neodymium and Hf crustal residence ages show that the eroded crust was, on average, ∼300-400 Ma older than the deposition age of the sediments, which highlights the importance of intracrustal

  16. Sm-Nd dating and REE Composition of scheelite for the Honghuaerji scheelite deposit, Inner Mongolia, Northeast China (United States)

    Guo, Zhijun; Li, Jinwen; Xu, Xinying; Song, Zeyou; Dong, Xuzhou; Tian, Jing; Yang, Yuncheng; She, Hongquan; Xiang, Anping; Kang, Yongjian


    Sm-Nd analyses of seven scheelite samples from scheelite-quartz veins in the Honghuaerji scheelite deposit produce a well-defined linear array on an isochron diagram with a mean square weighted deviation (MSWD) of 0.87 corresponding to an age of 178.4 ± 2.9 Ma with εNd(t) = + 1.50. This age is interpreted to represent the age of scheelite mineralization. The scheelite Sm-Nd age is in good agreement with U-Pb ages obtained from a mineralization-related granite (179.4 ~ 178.6 Ma), indicating that there is no apparent age gap between granite crystallization and ore formation. Rare earth element (REE) abundances in the scheelite were determined by in situ laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and the scheelite samples contain elevated REE concentrations with total ΣREE + Y contents in the range of 3339 to 6321 ppm. The chondrite-normalized REE distribution patterns of all scheelites are middle REE (MREE)-enriched, with strong negative Eu-anomalies (Eu/Eu* = 0.09 ~ 0.23). The REE characteristics of the Honghuaerji scheelite suggest that REE3 + substituted into the Ca site along with Na and Nb (dominated by Na), whereas Eu is predominantly present as Eu2 + in the scheelite and may have crystallized from relatively reduced fluids. All sulfur isotope data (δ34S) for sulfide separates range from + 2.0 to + 3.8‰, with an average of 3.2‰. Measured 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios vary from 18.243 to 18.451, 15.494 to 15.574, and 37.933 to 38.340, respectively. On the basis of common Sr-Nd-Pb-Hf isotopic characteristics between the scheelite and the host granite and the positive initial Nd isotope ratios (+ 1.46 - + 1.52), low 87Sr/86Sr ratios (0.704983-0.705297) in the scheelites, it is inferred that the hydrothermal fluids responsible for tungsten mineralization at Honghuaerji were of magmatic origin with a mantle-derived signature. Based on the regional geology, tectonic evolution, and geochemical evidence, the

  17. Sm-Nd isotopic compositions of Cambrian-Ordovician strata at the Jinggangshan area in Jiangxi Province:Tectonic implications

    Institute of Scientific and Technical Information of China (English)

    SHEN WeiZhou; LING HongFei; SHU LiangShu; ZHANG FangRong; XIANG Lei


    Whole-rock Sm-Nd Isotopes were investigated for Cambrian-Ordovician strata from the Jinggangshan area beTween the Yangtze Block and Cathysla Block in South China. These strata were deposited as a greatly thick unit of muddy-sandy laminas with intercalated carbonate and organic carbon-bearing layers. They have low ε(t) values of -13.9 to -7.9 and old Nd model ages of 1842 to 2375 Ma. In t-tdiagram, they are far away from the concordant line but fall within the evolution zone of the Proterozoic crust of South China. This indicates that the Cambrian-Ordovician strata are mainly composed of mat-ters eroded from ancient Paleoproterozoic crust that may mainly consist of continental-derived detrital sediments with high maturity in the Cathyaia Block. However, the Ordovician Jueshangou Formation and Dui'erehi Formation have ε(t) values of -10.5 and -7.9 at the higher end of the above range and Nd model ages of 1842 to 2059 Ma at the lower end of the above range. This suggests involvement of more detritus that were eroded from the relatively juvenile crust from Late Paleoproterozoic to the Early Neoproterozoic. All the Nd model ages for the Cambrian-Ordovlcian sedimentary rocks in the Cathysia Block and the southeastern margin of the Yangtze Block are older than 1800 Ma, suggesting that no material from the Early Paleozoic depleted mantle-derived magmas was involved in these regions.

  18. Dating Melt Rock 63545 By Rb-Sr and Sm-Nd: Age of Imbrium; Spa Dress Rehearsal (United States)

    Nyquist, L. E.; Shih, C. Y.; Reese, Y. D.


    Apollo 16 sample 63545 was initially described as one of a group of 19 generally rounded, fine-grained, crystalline rocks that were collected as rake samples [1]. This 16 g "rocklet" was collected at Station 13 on the ejecta blanket of North Ray Crater at the foot of Smoky Mountain [2]. Originally classified as a Very High Alumina (VHA) basalt on geochemical grounds [3], it was later argued to be an impact melt rock [4]. Here we report a Rb-Sr and Sm-Nd isotopic study that shows that some portions of the rock failed to reach isotopic equilibrium on last melting in agreement with the impact melt rock interpretation. Nevertheless, by omitting mineral fractions that are discordant with the majority of the data, we arrive at the time of last melting as 3.88 plus or minus 0.05 Ga ago. This age is in agreement with the Ar-39/Ar-40 plateau age of 3839 plus or minus 23 Ma [5], if the latter is adjusted for the 1.4-1.8% revision in the age of the hornblende monitor [6]. This investigation was undertaken in part as proof-of-concept for SPA-basin sample return.

  19. Sm-Nd isotope geochemistry and U/Pb geochronological data of the Campina Grande complex, Paraiba State, NE Brazil

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    Almeida, C.N. [Pernambuco Univ., Recife, PE (Brazil). Pos-Graduacao em Geociencias; Guimaraes, I.P.; Silva Filho, A.F. da [Pernambuco Univ., Recife, PE (Brazil). Dept. de Geologia; Beurlen, H. [Pernambuco Univ., Recife, PE (Brazil). Dept. de Engenharia de Minas


    The Campina Grande Complex (CCG) constitutes a 250 Km{sup 2} intrusion within the high grade gneiss-migmatitic terrain, in the contact zone between the Mesoproterozoic Pajeu-Paraiba Fold Belt and the Archean Caldas Brandao Massif of the Borborema Province, NE Brazil. The contact of the complex is made by the Guarabira Shear Zone (west) and the Campina Grande Shear Zone in the south. The CCG is composed of coarse grained porphyritic quartz-monzonites, quartz-monzodiorites and medium grained porphyritic granodiorites. Mafic enclaves are common and show composition ranging from diorites to quartz diorites. Field and petrographic features point out to magma mixing and mingling processes involved in the CCG evolution. Basalts of probably Cretaceous age occur as dykes cutting in the CCG. This work presents and discusses the Sm-Nd isotope geochemistry of the CCG and a gabro which occur very close to the south contact of the CCG. This also presents the U/Pb in zircon geochronological data for the CCG. (author) 4 refs., 2 figs.

  20. Rb-Sr and Sm-Nd isotope geochemistry and chronology of cherts from the Onverwacht Group (3.5 AE), South Africa (United States)

    Weis, D.; Wasserburg, G. J.


    An Rb-Sr and Sm-Nd isotopic analysis of Archean chert samples from the Onverwacht Group, South Africa is presented, showing the same characteristic Rb and Sr concentrations as Phanerozoic cherts, with a very large range of Rb-87/Sr-86 ratios. A good correlation line in the Rb-87 to Sr-87 evolution diagram, corresponding to an age of about 2119 My and an initial Sr-87/Sr-86 ratio of about 0.72246, is derived which may be interpreted as reflecting the age of rehomogenization of the Sr in the protolith and the recrystallization of these cherts due to circulating hydrothermal fluids during regional metamorphism about 1.4 AE after deposition of the Onverwacht Group. The Sm-Nd systematics reflect an ancient source age of about 3.5 AE.

  1. On the role of contamination and hybridism in formation of the composite Raumid pluton granites (Pamir Mnts.): Results of Sm-Nd Isotope Study (United States)

    Volkov, V. N.; Shatagin, K. N.; Kramchaninov, A. Yu.


    This work presents isotope Sm-Nd data obtained for bulk samples of granites of all 8 emplacement phases of the Raumid granite massif, which occurred 35 Ma ago at a hypabyssal depth during the orogenic stage of development of Southern Pamir fold system. The 147Sm/144Nd ratio in studied collection of granite samples ranges between 0.091 and 0.323; the ɛNd( T) value is-4.0. The Sm-Nd isotope study results suggest that all granite varieties distinguished in the Raumid massif are comagmatic formations and contamination and hybridization processes did not play any role in REE distribution in granites. At this, the source of parental magma did not change during granite generation. We assume that the only process, resulted in the trace element evolution in granites, was differentiation of three batches of magma sequentially uplifted from the source.

  2. Redetermination of the Sm-Nd Age and Initial (Epsilon)Nd of Lunar Troctolite 76535: Implications for Lunar Crustal Development (United States)

    Nyquist, Laurence E.; Shih, C.-Y.; Reese, Y. D.


    Lunar troctolite 76535 is an old lunar rock predating the era of the lunar cataclysmic bombardment, but its radiometrially determined ages have been discordant [1-3]. The most recent multi-chronometer study [4] gave preferred ages of 4226+/-35 Ma and 4236+/-15 Ma from a Pb-207/Pb-206 isochron and an U-Pb upper concordia intercept, resp. We derive an age of 4323+/-64 Ma from Sm-Nd data reported by [4] for the bulk rock and three mineral separates. They derived an age of approx.4.38 Ga from combined Rb-Sr data [3,4] by omitting data for olivine separates. Ar-39-Ar-40 ages of approx.4.2 Ga are summarized by [5]. New Sm-147-Nd-143 data presented here give an age of 4335+/-71 Ma in agreement with the Sm-Nd age from [4], whereas Sm-146-Nd-142 data give a model age T(sub LEW) = 4439+/-22 Ma. Further, initial (Epsilon)Nd-143 for 76535 conforms to the Nd-143 evolution expected in an urKREEP [6] reservoir, consistent with inheritance of urKREEP Sm-Nd systematics via assimilation. We show that urKREEP Sm-Nd systematics require the lunar initial (Epsilon)Nd-143 to exceed the Chondritic Uniform Reservoir (CHUR) value [7], but are consistent with evolution from initial (Epsilon)Nd-143 like that of the HED meteorite parent body as defined by a 4557+/-20 Ma internal isochron for the cumulate eucrites Y-980433 and Y- 980318 [8].

  3. Determining age of Pan African metamorphism using Sm-Nd garnet-whole rock geochronology and phase equilibria modeling in the Tasriwine ophiolite, Sirwa, Anti-Atlas Morocco (United States)

    Inglis, Jeremy D.; Hefferan, Kevin; Samson, Scott D.; Admou, Hassan; Saquaque, Ali


    Sm-Nd garnet-whole rock geochronology and phase equilibria modeling have been used to determine the age and conditions of regional metamorphism within the Tasriwine ophiolite complex, Sirwa, Morocco. Pressure and temperature estimates obtained using a NaCaKFMASHT phase diagram (pseudosection) and garnet core and rim compositions predict that garnet growth began at ∼0.72 GPa and ∼615 °C and ended at ∼0.8 GPa and ∼640 °C. A bulk garnet Sm-Nd age of 647.2 ± 1.7 Ma, calculated from a four point isochron that combines whole rock, garnet full dissolution and two successively more aggressive partial dissolutions, provides a precise date for garnet formation and regional metamorphism. The age is over 15 million years younger than a previous age estimate of regional metamorphism of 663 ± 13 Ma based upon a SHRIMP U-Pb date from rims on zircon from the Iriri migmatite. The new data provide further constraints on the age and nature of regional metamorphism in the Anti-Atlas mountains and emphasizes that garnet growth during regional metamorphism may not necessarily coincide with magmatism/anatexis which predominate the signature witnessed by previous U-Pb studies. The ability to couple PT estimates for garnet formation with high precision Sm-Nd geochronology highlights the utility of garnet studies for uncovering the detailed metamorphic history of the Anti-Atlas mountain belt.

  4. Neoarchean metamorphism recorded in high-precision Sm-Nd isotope systematics of garnets from the Jack Hills (Western Australia) (United States)

    Eccles, K. A.; Baxter, E. F.; Mojzsis, S. J.; Marschall, H.; Williams, M. L.; Jercinovic, M. J.


    Studies of metasedimentary rocks from the Jack Hills, which host Earth's oldest known detrital minerals, have focused on zircon and occasionally monazite or xenotime, but no attention has been directed toward one of the most common mineral markers of metamorphism: garnet. Garnet can provide a record of the post-depositional, prograde metamorphic history of Archean metasedimentary rocks. Additionally, the use of a newly developed detrital garnet dating technique [1,2] may reveal information about pre-depositional metamorphism that could address lingering questions about the nature and timing of Earth's earliest tectonometamorphic events. Here we investigate garnet from the Jack Hills metasedimentary rocks to test whether they record in situ metamorphism or are a detrital relict of even older metamorphic events. We identified garnet in two bulk quartz-pebble conglomerate samples collected from the 'discovery' outcrop at Eranondoo Hill in the Jack Hills of Western Australia. Electron microprobe analyses of polished grains and SEM measurements of unpolished grain surfaces are consistent, revealing garnet composition indicative of a single generation/population of predominantly almandine-spessartine solid solution (~10-35% mole fraction spessartine). Compositional maps of garnet grains reveal little zoning and no discontinuities, most consistent with a single growth event. Dating Jack Hills' garnet via the Sm-Nd system is possible due to continued development of small sample analysis techniques, including running NdO+ TIMS analyses with Ta2O5 activator [3] permitting nondestructive chemical prescreening technique (tabletop SEM) allows for grouping of multiple grains based on chemical similarity. Final Nd loads in the 450-750pg range routinely yield dates with precisions <×10Ma for two point isochrons between clean garnet (Sm/Nd ≥ 1.0) and their leached inclusion populations [2]. Four grouped garnet grain separates from one sample yield preliminary dates of 2703.6×6

  5. Elemental and Sm-Nd isotopic geochemistry on detrital sedimentary rocks in the Ganzi-Songpan block and Longmen Mountains

    Institute of Scientific and Technical Information of China (English)

    CHEN Yuelong; LIU Fei; ZHANG Hongfei; NIE Lanshi; JIANG Liting


    Systematic results of major and trace element geochemistry and Sm-Nd isotopic geochemistry on detrital sedimentary rocks of Precambrian to Triassic in the Ganzi-Songpan block and Longmen Mountains are presented. The rocks are classified into greywaekes or feldspar sandstones,grains of which are the mixtures of mafic rocks, felsic rocks,and quartz + calcite. Total rare earth elements (REE) contents of the rocks increase gradually and negative Eu anomalies become more obvious from Precambrian to Triassic, which may indicate intensifying crustal anatexis. Tectonic setting was stable during the Late Paleozoic, the refore there are obvious negative Ce anomalies. Nd model ages are between 1.6 Ga and 2.4 Ga, which are very similar to those of the Yangtze croton, South Qinling and North Qinling belts and quite different from those of the North China craton. There-fore, provenance of the sedimentary rocks in the Ganzi-Songpan block and Longmen Mountains was the Yangtze craton and/or the Qinling orogen, which evolved on the basis of the Yangtze craton. The correlation between provenances and tectonostratigraphic strata of the western Yangtze craton shows that the source materials should be primarily from Neoproterozoic. Secondary sources were Archean and Paleoproterozoic strata. Triassic clastic sedimentary rocks contain Late Paleozoic mantle-derived materials, represented by the Emeishan Permian flood basalts. Spatial distribution of initial Nd isotopic compositions indicates that denudating areas were in the east and the north and depositing areas of deep water were in the west and the south for the Ganzi-Songpan basin during Triassic.

  6. Ediacaran Palaeozoic tectonic evolution of the Ossa Morena and Central Iberian zones (SW Iberia) as revealed by Sm Nd isotope systematics (United States)

    López-Guijarro, Rafael; Armendáriz, Maider; Quesada, Cecilio; Fernández-Suárez, Javier; Murphy, J. Brendan; Pin, Christian; Bellido, Felix


    Sm-Nd isotopic analyses of Palaeozoic sedimentary and igneous rocks in the southwest Iberian Massif (western end of the European Variscan Belt) are presented in order to unravel its complex poly-orogenic evolution during the closure of the Rheic Ocean and the amalgamation of Pangea. The Gondwanan margin in southwest Iberia SW Iberia is subdivided into the Ossa Morena and Central Iberian zones, separated by the Badajoz-Córdoba Shear Zone which represents a cryptic suture zone between these terranes. The relationships between these terranes, and between units preserved within the suture zone (e.g. the Sierra Albarrana Group) during the Palaeozoic and Neoproterozoic are controversial. Sm-Nd isotopic studies of representative sedimentary sequences covering the entire pre-Variscan record of the Ossa Morena and Central Iberian zones show very similar characteristics from the uppermost Ediacaran onwards. These data indicate that their accretion to one another must have been completed by the Late Neoproterozoic-Ediacarin that time (an event assigned to Cadomian orogeny) and that they never separated substantially from each other since that time. The Sm-Nd isotopic composition of the Sierra Albarrana Group metasedimentary rocks is similar to that of the pre-Cadomian sequences of the Ossa Morena Zone (Serie Negra), suggesting derivation from a common source. The common provenance of the Palaeozoic sequences in the two zones is identical to that of the pre-Cadomian Serie Negra of the Ossa Morena Zone, which in accordance with the data presented herein and published U-Pb zircon data indicates a West African affinity.

  7. Sm-Nd and Rb-Sr Isotopic Systematics of a Heavily Shocked Martian Meteorite Tissint and Petrogenesis of Depleted Shergottites (United States)

    Shih, C.-Y.; Nyquist, L. E.; Park, J.; Agee, Carl B.


    Tissint is a very fresh Martian meteorite that fell near the town of Tissint in Morocco on July 18, 2011. It contains abundant olivine megacrysts (23%) in a fine-grained matrix of pyroxene (55%), maskelynitized plagioclase (15%), opaques (4%) and melt pockets (3%) and is petrographically similar to lithologies A and C of picritic shergottite EETA 79001 [1,2]. The presence of 2 types of shock-induced glasses and all 7 high-pressure mineral phases that were ever found in melt pockets of Martian meteorites suggests it underwent an intensive shock metamorphism of 25 GPa and 2000 C localized in melt pockets [2]. Mineral textures suggest that olivines, pyroxenes and plagioclases probably did not experience such hightemperature. Earlier determinations of its age yielded 596+/-23 Ma [3] and 616+/-67 Ma [4], respectively, for the Sm-Nd system and 583+/-86 Ma for the Lu-Hf system [4], in agreement with the 575+/-18 Ma age of the oldest olivine-phyric depleted shergottite Dho 019 [5]. However, the exposure ages of Tissint (1 Ma [1, 6, 7]) and Dho 019 (20 Ma [8]) are very different requiring two separate ejection events. These previously determined Sm-Nd and Lu-Hf ages are older than the Ar-Ar maskelynite plateau age of 524+/-15 Ma [9], reversing the pattern usually observed for Martian meteorites. In order to clarify these age issues and place models for Tissint's petrogenesis on a firm basis, we present new Rb-Sr and Sm- Nd isotopic results for Tissint, and discuss (a) the shock effects on them and the Ar-Ar chronometer, (b) correlation of the determined ages with those of other depleted shergottites, and (c) the petrogenesis of depleted shergottites. Since the meteorite is a recent fall, terrestrial contamination is expected to be minimal, but, the strong shock metamorphism might be expected to compromise the equilibrium of the isotopic systems.

  8. A combined Sm-Nd, Rb-Sr, and U-Pb isotopic study of Mg-suite norite 78238: Further evidence for early differentiation of the Moon

    Energy Technology Data Exchange (ETDEWEB)

    Edmunson, J; E.Borg, L; Nyquist, L E; Asmerom, Y


    Lunar Mg-suite norite 78238 was dated using the Sm-Nd, Rb-Sr, and U-Pb isotopic systems in order to constrain the age of lunar magma ocean solidification and the beginning of Mg-suite magmatism, as well as to provide a direct comparison between the three isotopic systems. The Sm-Nd isotopic system yields a crystallization age for 78238 of 4334 {+-} 37 Ma and an initial {var_epsilon}{sub Nd}{sup 143} value of -0.27 {+-} 0.74. The age-initial {var_epsilon}{sub Nd}{sup 143} (T-I) systematics of a variety of KREEP-rich samples, including 78238 and other Mg-suite rocks, KREEP basalts, and olivine cumulate NWA 773, suggest that lunar differentiation was completed by 4492 {+-} 61 Ma assuming a Chondritic Uniform Reservoir bulk composition for the Moon. The Rb-Sr isotopic systematics of 78238 were disturbed by post-crystallization processes. Nevertheless, selected data points yield two Rb-Sr isochrons. One is concordant with the Sm-Nd crystallization age, 4366 {+-} 53 Ma. The other is 4003 {+-} 95 Ma and is concordant with an Ar-Ar age for 78236. The {sup 207}Pb-{sup 206}Pb age of 4333 {+-} 59 Ma is concordant with the Sm-Nd age. The U-Pb isotopic systematics of 78238 yield linear arrays equivalent to younger ages than the Pb-Pb system, and may reflect fractionation of U and Pb during sample handling. Despite the disturbed nature of the U-Pb systems, a time-averaged {mu} ({sup 238}U/{sup 204}Pb) value of the source can be estimated at 27 {+-} 30 from the Pb-Pb isotopic systematics. Because KREEP-rich samples are likely to be derived from source regions with the highest U/Pb ratios, the relatively low {mu} value calculated for the 78238 source suggests the bulk Moon does not have an exceedingly high {mu} value.

  9. The usage of Sm/Nd isotopic signature of granites as a tool for defining sub-domains in the southern tectonic domain, Borborema province, NE, Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Silva Filho, A.F. da; Guimaraes, I.P.; Luna, E.B.A. [Pernambuco Univ., Recife, PE (Brazil). Dept. de Geologia; Van Schmus, W.R. [Kansas Univ., Lawrence, KS (United States). Dept. of Geology


    The geologic and geotectonic status of the PE-AL Massif (PAM), northeastern region of Brazil, has been debated over the past three decades by various authors and the complexity of the area could have been one among some reasons for such long debate, beside the lack of detailed geologic data. The work presents the characteristics of the various batholiths named as the Toritama -Arcoverde, Jaboatao-Garanhuns, Ipojuca-Atalaia, Maribondo-Correntes, Buique-Paulo Afonso, and Aguas Belas-Caninde batholiths. Finally, it shows the results of a Samarium/Neodymium (Sm/Nd) analysis of 55 samples that suggested the existence of two domains in the eastern PAM

  10. Emplacement age for the mafic-ultramafic plutons in the northern Dabie Mts. (Hubei): Zircon U-Pb, Sm-Nd and 40Ar/39Ar dating

    Institute of Scientific and Technical Information of China (English)


    The protoliths of mafic-ultramafic plutons in the northern Dabie Mts. (NDM) (Hubei) include pyroxenite and gabbro. The zircon U-Pb dating for a gabbro suggests that emplacement of mafic magma took place in the post-collisional setting at the age of 122.9(0.6 Ma. It is difficult to obtain a reliable Sm-Nd isochron age, due to disequilibrium of the Sm-Nd isotopic system. Two hornblende 40Ar/39Ar ages of 116.1(1.1 Ma and 106.6(0.8 Ma may record cooling of metamorphism in the mafic-ultramafic plutons in Hubei below 500(C. The hornblende 40Ar/39Ar ages for the mafic-ultramafic rocks in Hubei are evidently 15-25 Ma younger than those for the same rocks in Anhui, indicating that there is a diversity of the cooling rates for the mafic-ultramafic rocks in Hubei and Anhui. The difference in their cooling rates may be controlled by the north-dipping normal faults in the NDM. The intense metamorphism occurring in the mafic-ultramafic rocks in Hubei may result from the Yanshanian magmatic reheating and thermal fluid action induced by the Cretaceous migmatization. The geochemical similarity of these mafic-ultramafic rocks wherever in Hubei and Anhui may be attributed to the same tectonic setting via an identical genetic mechanism.

  11. Sm-Nd Ages of Two Meta-Anorthosite Complexes Around Holenarsipur: Constraints on the Antiquity of Archean Supracrustal Rocks of the Dharwar Craton

    Indian Academy of Sciences (India)

    Y J Bhaskar Rao; Anil Kumar; A B Vrevsky; R Srinivasan; G V Anantha Iyer


    Whole-rock Sm-Nd isochron ages are reported for two stratiform meta-anorthosite complexes emplaced into the Archean supracrustal-gneiss association in the amphibolite facies terrain around Holenarsipur, in the Dharwar carton, South India. While these metaperidotite-pyroxenite-gabbro-anorthosite complexes are petrologically and geochemically similar, they differ in the intensity of tectonic fabric developed during the late Archean (c.2.5Ga) deformation. They also differ in their whole-rock Sm-Nd isochron ages and initial Nd isotopic compositions: 3.285 ± 0.17 Ga, Nd = 0.82 ± 0.78 for the Honnavalli meta-anorthosite complex from a supracrustal enclave in the low-strain zone, and 2.495 ± 0.033 Ga, Nd = -2.2+-0.3 for the Dodkadnur meta-anorthosites from the high-strain southern arm of the Holenarsipur Supracrustal Belt (HSB). We interpret these results as indicating that the magmatic protoliths of both meta-anorthosite complexes were derived from a marginally depleted mantle at c.3.29 Ga but only the Dodkadnur rocks were isotopically reequilibrated on a cm-scake about 800 Ma later presumably due to the development of strong penetrative fabrics in them during Late Archean thermotectonic event around 2.5Ga. Our results set a younger age limit at c.3.29Ga for the supracrustal rocks of the HSB in the Dharwar craton.

  12. Provenance and sedimentary environments of the Proterozoic São Roque Group, SE-Brazil: Contributions from petrography, geochemistry and Sm-Nd isotopic systematics of metasedimentary rocks (United States)

    Henrique-Pinto, R.; Janasi, V. A.; Tassinari, C. C. G.; Carvalho, B. B.; Cioffi, C. R.; Stríkis, N. M.


    The Proterozoic metasedimentary sequences exposed in the São Roque Domain (Apiaí Terrane, Ribeira Belt, southeast Brazil) consist of metasandstones and meta-felspathic wackes with some volcanic layers of within-plate geochemical signature (Boturuna Formation), a passive margin turbidite sequence of metawackes and metamudstones (Piragibu Formation), and volcano-sedimentary sequences with MORB-like basalts (Serra do Itaberaba Group; Pirapora do Bom Jesus Formation). A combination of zircon provenance studies in metasandstones, whole-rock geochemistry and Sm-Nd isotopic systematics in metamudstones was used to understand the provenance and tectonic significance of these sequences, and their implications to the evolution of the Precambrian crust in the region. Whole-rock geochemistry of metamudstones, dominantly from the Piragibu Formation, points to largely granitic sources (as indicated for instance by LREE-rich moderately fractionated REE patterns and subtle negative Eu anomalies) with some mafic contribution (responding for higher contents of Fe2O3, MgO, V, and Cr) and were subject to moderate weathering (CIA - 51 to 85). Sm-Nd isotope data show three main peaks of Nd TDM ages at ca. 1.9, 2.1 and 2.4 Ga; the younger ages define an upper limit for the deposition of the unit, and reflect greater contributions from sources younger than the >2.1 Ga basement. The coincident age peaks of Nd TDM and U-Pb detrital zircons at 2.1-2.2 Ga and 2.4-2.5 Ga, combined with the possible presence of a small amount of zircons derived from mafic (gabbroid) sources with the same ages, as indicated by a parallel LA-ICPMS U-Pb dating study in metapsammites, are suggestive that these were major periods of crustal growth in the sources involving not only crust recycling but also some juvenile addition. A derivation from similar older Proterozoic sources deposited in a passive margin basin is consistent with the main sedimentary sequences in the São Roque Domain being broadly coeval and

  13. MKED1: A new titanite standard for in situ microanalysis of trace elements, Sm-Nd isotopes, and U-Pb geochronology (United States)

    Spandler, C.; Hammerli, J.; Hilbert-Wolf, H.; Sha, P.; Hu, Y.; Roberts, E.; Schmitz, M. D.


    Titanite has great potential as a petrogenetic indicator and mineral geochronometer as it can host high trace element concentrations and it occurs in a wide range of rock types. Here, we describe a potential new titanite standard for calibration of the chemical and isotopic composition of titanite of varying age and origin. Through comprehensive bulk analysis of mm-size crystal fragments and in-situ microanalysis, we show that the titanite, labeled MKED1, is largely free of inclusions and is homogenous at the level of analytical precision for major element, U-Pb isotope and Sm-Nd isotope composition. Some minor zoning in trace element composition is recognized using backscatter electron imaging, although the trace element concentrations of each of these zones are also very homogenous. MKED1 has high contents of REE, Th, U, and radiogenic Pb, but very low levels of common Pb. U-Pb isotope data (ID-TIMS and LA-ICP-MS) show MKED1 to be concordant with an age of ca. 1518 Ma. Cross calibration with other titanite standards demonstrates that MKED1 can be used as a primary standard for determining U-Pb ages of titanite ranging in age from Precambrian to Neogene. We also show that MKED1 is suitable as a Sm-Nd isotope standard due to its high REE concentrations and homogenous 147Sm/144Nd and 143Nd/144Nd content. We suggest MKED1 can be employed as a trace element, U-Pb isotope and Sm-Nd isotope standard for in situ or bulk analytical methods, including techniques that allow simultaneous collection of multiple elemental and/or isotopic data sets in situ. We present two case studies to demonstrate the potential of titanite analysis for resolving geological problems: The first examines the genesis of Cu-REE skarn mineralization from the Mt Isa Inlier, Australia, and the second study investigates the timing and origin of volcanism and sedimentation in the Western Branch of the East African Rift.

  14. Sm-Nd and Rb-Sr isotopic data on the sanukitoid intrusions of the Karelia, Baltic Shield (United States)

    Kovalenko, A. V.; Savatenkov, V. M.


    Sanukitoid intrusions from the Baltic Shield form post-tectonic differentiated intrusions 2.74-2.72 Ga old (Chekulaev, 1999, Lobach-Zhuchenko et al., 2000). They are represented by alkaline and calc-alkaline types which have high mg# (up to 0.6), strong LREE enrichment (Ce(N)=80-150, Yb(N)=4-7, Ce(N)/Yb(N)>20), high Sr, Ba (>1000 ppm), P2O5 (up to 1.5%) and Cr, Ni concentrations. Some intrusions contain rocks varying from ultramafite to quartz syenite. All sanukitoids are intruded by lamprophyre dykes having similar geochemical signatures. In this study we focus on the Karelian greenstone terrain within the Baltic Shield, in which sanukitoids are restricted to the younger western and central domains (2.7-2.9 Ga). Sanukitoids appear to be absent from the older Vodlozero domain (>3.0 Ga) in eastern Karelia (Lobach-Zhuchenko et al., 2000, Lobach-Zhuchenko et al., in press). About 70 Sm-Nd isotopic data on the sanukitoids of the Karelia were obtained. There is the regional distinction of the isotope composition of the rocks between the Central and West Karelian domains. The initial Epsilon Nd values and TDM range from +1.1 to +2.0 and 2.70-2.85 Ga accordingly in the youngest Central Karelian domain. The West Karelian intrusions yield an initial Epsilon Nd of -0.3- +0.7 and give the older TDM of about 2.82-2.92 Ga. It is to be noted that some intrusions of the Central Karelia domain, occurred closely to the ancient Vodlozero domain, also exhibit a similar range of initial Epsilon Nd and TDM to the intrusions of the West Karelia. There are narrow Nd isotopic compositional ranges within the individual intrusions. Rb-Sr isotopic system was studied in sanukitoids and lamprophyres of differentiated Panozero intrusion, Central Karelia. The initial 87Sr/86Sr isotope ratios range from 0.7000 to 0.7021 in these rocks indicating the derivation of these magmas from depleted mantle. Very low initial 87Sr/86Sr isotope ratios of the sanukitoids confirm the Nd isotopic characteristics

  15. Sm-Nd, K-Ar and petrologic study of some kimberlites from eastern United States and their implication for mantle evolution (United States)

    Basu, A.R.; Rubury, E.; Mehnert, H.; Tatsumoto, M.


    We provide new data on Sm-Nd systematics, K-Ar dating and the major element chemistry of kimberlites from the eastern United States (mostly from central New York State) and their constituent mineral phases of olivine, clinopyroxene, garnet, phlogopite and perovskite. In addition, we report Nd-isotopes in a few kimberlites from South Africa, Lesotho and from the eastern part of China. The major element compositions of the New York dike rocks and of their constituent minerals including a xenolith of eclogite are comparable with those from the Kimberley area in South Africa. The K-Ar age of emplacement of the New York dikes is further established to be 143 Ma. We have analyzed the Nd-isotopic composition of the following kimberlites and related rocks: Nine kimberlite pipes from South Africa and Lesotho, two from southern India; one from the U.S.S.R., fifteen kimberlite pipes and related dike rocks from eastern and central U.S. and two pipes from the Shandong Province of eastern China. The age of emplacement of these kimberlites ranges from 1300 million years to 90 million years. The initial Nd-isotopic compositions of these kimberlitic rocks expressed as e{open}NdIwith respect to a chondritic bulk-earth growth-curve show a range between 0 and +4, with the majority of the kimberlites being in the range 0 to +2. This range is not matched by any other suite of mantle-derived igneous rocks. This result strengthens our earlier conclusion that kimberlitic liquids are derived from a relatively primeval and unique mantle reservoir with a nearly chondritic Sm/Nd ratio. ?? 1984 Springer-Verlag.

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

    Institute of Scientific and Technical Information of China (English)

    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.

  17. Reconciliation of the excess 176Hf conundrum in meteorites: Recent disturbances of the Lu-Hf and Sm-Nd isotope systematics (United States)

    Bast, Rebecca; Scherer, Erik E.; Sprung, Peter; Mezger, Klaus; Fischer-Gödde, Mario; Taetz, Stephan; Böhnke, Mischa; Schmid-Beurmann, Hinrich; Münker, Carsten; Kleine, Thorsten; Srinivasan, Gopalan


    The long-lived 176Lu-176Hf and 147Sm-143Nd radioisotope systems are commonly used chronometers, but when applied to meteorites, they can reveal disturbances. Specifically, Lu-Hf isochrons commonly yield dates up to ∼300 Myr older than the solar system and varying initial 176Hf/177Hf values. We investigated this problem by attempting to construct mineral and whole rock isochrons for eucrites and angrites. Meteorites from different parent bodies exhibit similar disturbance features suggesting that a common process is responsible. Minerals scatter away from isochron regressions for both meteorite classes, with low-Hf phases such as plagioclase and olivine typically being most displaced above (or left of) reference isochrons. Relatively Hf-rich pyroxene is less disturbed but still to the point of steepening Lu-Hf errorchrons. Using our Lu-Hf and Sm-Nd data, we tested various Hf and Lu redistribution scenarios and found that decoupling of Lu/Hf from 176Hf/177Hf must postdate the accumulation of significant radiogenic 176Hf. Therefore early irradiation or diffusion cannot explain the excess 176Hf. Instead, disturbed meteorite isochrons are more likely caused by terrestrial weathering, contamination, or common laboratory procedures. The partial dissolution of phosphate minerals may predominantly remove rare earth elements including Lu, leaving relatively immobile and radiogenic Hf behind. Robust Lu-Hf (and improved Sm-Nd) meteorite geochronology will require the development of chemical or physical methods for removing unsupported radiogenic Hf and silicate-hosted terrestrial contaminants without disturbing parent-daughter ratios.

  18. U-Pb (SHRIMP) and Sm-Nd geochronology of basaltic green schists of the Aracuai orogen: implications for the age of the Macaubas group; Geocronologia U-Pb (SHRIMP) e Sm-Nd de xistos verdes basalticos do orogeno Aracuai: implicacoes para a idade do grupo Macaubas

    Energy Technology Data Exchange (ETDEWEB)

    Babinski, Marly [Universidade de Sao Paulo, SP (Brazil). Inst. de Geociencias. Centro de Pesquisas Geocronologicas]. E-mail:; Gradim, Rafael Jaude; Alkmim, Fernando Flecha de [Universidade Federal de Ouro Preto, MG (Brazil). Escola de Minas. Dept. de Geologia]. E-mails:;; Pedrosa-Soares, Antonio Carlos; Noce, Carlos Mauricio [Minas Gerais Univ., Belo Horizonte (Brazil). Inst. de Geociencias; Liu, Dunyi [Chinese Academy of Geological Sciences, Beijing (China). Beijing SHRIMP Lab.


    The age and stratigraphic position of the basaltic green schists of the Rio Preto valley, located in the western part of the Aracuai Belt (ca. 60 km north of Diamantina, Minas Gerais) were a matter of controversy in the geologic literature, because several authors correlated them to the Neo proterozoic Macaubas Group but others to the lower Espinhaco Supergroup (ca. 1.7 Ga). However, detailed studies demonstrate that these green schists represent an interplay of submarine basaltic volcanism, volcanoclastic sedimentation and fire fountaining, and that they belong to the Chapada Acaua Formation of the Macaubas Group (Gradim et al., 2005). Geochemical studies indicate that the green schist protoliths evolved in a continental intra plate environment. Zircon crystals were separated from a green schist sample and analyzed by the U-Pb SHRIMP method. A Sm-Nd whole-rock isotopic analysis was obtained from the same sample. The Sm- Nd model age of ca. 1.52 Ga suggests that the green schist protoliths are younger than the magmatism of the Espinhaco rift. Most analyzed zircon crystals show features of detrital grains. The older ages indicate zircon grains inherited from the Archean- Paleoproterozoic basement and from magmatic rocks of the Espinhaco rift. The younger U-Pb values constrain the maximum age of the green schist protoliths at ca. 1,16 Ga. (author)

  19. Combined Sm-Nd and Lu-Hf dating of garnets from the Putomayo foreland basin in south-central Colombia and implications (United States)

    Bloch, E. M.; Ibanez-mejia, M.; Ganguly, J.


    Garnet-whole rock (Grt-WR) ages of metapelites determined by the Lu-Hf decay system are almost always older than those determined by the Sm-Nd system. Unambiguous interpretation of the observed age differences has been hindered by a lack of adequate information about grain size, diffusion data for Hf in garnet, and in many cases about peak metamorphic conditions and cooling rates, all of which affect the closure temperatures of these decay systems. As part of a broader study on basement rocks from the Andean Putomayo foreland basin in south-central Colombia, we have determined the Lu-Hf and Sm-Nd Grt-WR ages of these rocks using painstakingly handpicked garnets of ~50 μm radius, and obtained ages of 1070 × 5.6 and 1007 × 2.9 Ma, respectively. By modeling the retrograde Fe-Mg zoning in garnet adjacent to biotite according to an asymptotic cooling model (1/T = 1/To + ηt) with the diffusion data from [1], an initial cooling rate of ~2-5 °C/Ma is obtained independently of the geochronological data; peak P-T conditions of ~8 kb, 675 °C are imposed by garnet-orthopyroxene thermobarometry. Using the above data in conjunction with the Nd diffusion data from [2] and Hf diffusion data from our recent study, we obtain closure temperatures for the Lu-Hf and Sm-Nd decay systems in garnet of ~545-565 °C and 415-430 °C, respectively. Results from analytical solutions [3, 4] and a more flexible numerical method are found to be in good agreement with one another. The calculated difference of closure temperatures predicts a difference of ~105-40 Ma between the ages determined by the two decay systems, as compared to the observed age difference of 63 × 6 Ma. The predicted peak metamorphic age derived from the measured and calculated resetting ages of the two decay systems is between ~1030 and 1185 Ma, as compared to the Lu-Hf age of 1070 ×1.9 Ma; we are currently working to obtain U-Pb zircon ages to better constrain this peak metamorphic age. In calculating these results

  20. Genesis and evolution of a syn-orogenic basin in transpression: Insights from petrography, geochemistry and Sm Nd systematics in the Variscan Pedroches basin (Mississippian, SW Iberia) (United States)

    Armendáriz, Maider; López-Guijarro, Rafael; Quesada, Cecilio; Pin, Christian; Bellido, Félix


    The Pedroches basin is an outstanding syn-orogenic Variscan (Mississippian) depocenter, located in the vicinity of, and overstepping onto the Neoproterozoic (Cadomian) suture between the Ossa Morena and Central Iberian zones of the SW Iberian Massif. Its formation appears to be related to transtensional processes at a major releasing bend in the reactivated suture during sinistral escape of the Ossa Morena Zone from the zone of frontal Variscan collision between northern Gondwana and Laurussia. Subsequent basin inversion resulted in compartmentalization and internal deformation, and was probably related to transpression at a restraining bend along the reactivated suture (Badajoz-Córdoba shear zone). Basin fill consists of both igneous and metasedimentary rocks generally deposited in a shallow marine, storm-dominated platform environment. By using new petrographic, geochemical and Sm-Nd isotopic data, we attempt to characterize: 1) the sources and geological evolution of the Pedroches basin fill, and 2) the processes involved in basin development and sediment supply and dispersal. Sampling was carried out in both sedimentary and igneous rocks belonging to three major structural units within the central part of the basin: Guadiato unit, Guadalbarbo unit and South Pedroches Valley unit. The combined Nd isotopic and geochemical data from the Pedroches Mississippian metasedimentary rocks indicate an upper continental crust provenance and a high degree of sedimentary recycling of these materials throughout the basin; i.e., they are derived from old, recycled upper crust without any significant juvenile component despite the presence of interbedded basaltic rocks. The igneous rocks in turn correspond to submarine basalts and trachy-andesitic basalts plus some hybrid rocks including crust-derived components. Concerning the mafic rocks, major element compositions reveal a tholeiitic and transitional tholeiitic character for the Guadalbarbo unit rocks (MORB type) and an

  1. Rb-Sr and Sm-Nd study of granite-charnockite association in the Pudukkottai region and the link between metamorphism and magmatism in the Madurai Block (United States)

    Sekaran, M. Chandra; Bhutani, Rajneesh; Balakrishnan, S.


    Pudukkottai region in the northeastern part of the Madurai Block exposes the garnetiferous pink granite that intruded the biotite gneiss. Charnockite patches are associated with both the rock types. Rb-Sr biotite and Sm-Nd whole-rock isochron ages indicate a regional uplift and cooling at ˜550 Ma. The initial Nd isotope ratios (\\varepsilon _{ {Nd}}t=-20 to -22) and Nd depleted-mantle model ages (TDM = 2.25 to 2.79 Ga) indicate a common crustal source for the pink-granite and associated charnockite, while the biotite gneiss and the charnockite within it represent an older crustal source (\\varepsilon _{ {Nd}}t= -29 and TDM = > 3.2 Ga). The Rb-Sr whole-rock data and initial Sr-Nd isotope ratios also help demonstrate the partial but systematic equilibration of Sr isotope and Rb/Sr ratios during metamorphic mineral-reactions resulting in an `apparent whole-rock isochron'. The available geochronological results from the Madurai Block indicate four major periods of magmatism and metamorphism: Neoarchaean-Paleoproterozoic, Mesoproterozoic, mid-Neoproterozoic and late-Neoproterozoic. We suggest that the high-grade and ultrahigh-temperature metamorphism was preceded by magmatism which `prepared' the residual crust to sustain the high P- T conditions. There also appears to be cyclicity in the tectono-magmatic events and an evolutionary model for the Madurai Block should account for the cyclicity in the preserved records.

  2. Petrogenesis and U-Pb and Sm-Nd geochronology of the Taquaral granite: record of an orosirian continental magmatic arc in the region of Corumba - MS

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    Letícia Alexandre Redes

    Full Text Available The Taquaral Granite is located on southern Amazon Craton in the region of Corumbá, westernmost part of the Brazilian state of Mato Grosso do Sul (MS, near Brazil-Bolivia frontier. This intrusion of batholitic dimensions is partially covered by sedimentary rocks of the Urucum, Tamengo Bocaina and Pantanal formations and Alluvial Deposits. The rock types are classified as quartz-monzodiorites, granodiorites, quartz-monzonites, monzo and syenogranites. There are two groups of enclaves genetically and compositionally different: one corresponds to mafic xenoliths and the second is identified as felsic microgranular enclave. Two deformation phases are observed: one ductile (F1 and the other brittle (F2. Geochemical data indicate intermediate to acidic composition for these rocks and a medium to high-K, metaluminous to peraluminous calk-alkaline magmatism, suggesting also their emplacement into magmatic arc settings. SHRIMP zircon U-Pb geochronological data of these granites reveals a crystallization age of 1861 ± 5.3 Ma. Whole rock Sm-Nd analyses provided εNd(1,86 Ga values of -1.48 and -1.28 and TDM model ages of 2.32 and 2.25 Ga, likely indicating a Ryacian crustal source. Here we conclude that Taquaral Granite represents a magmatic episode generated at the end of the Orosirian, as a part of the Amoguija Magmatic Arc.

  3. Rb-Sr and Sm-Nd Studies of Olivine-Phyric Shergottites RBT 04262 and LAR 06319: Isotopic Evidence for Relationship to Enriched Basaltic Shergottites (United States)

    Nyquist, L.E.; Shih, C.-Y.; Reese, Y.


    RBT 04262 and LAR 06319 are two Martian meteorites recently discovered in Antarctica. Both contain abundant olivines, and were classified as olivine-phyric shergottites. A detailed petrographic study of RBT 04262 suggested it should be reclassified as a lherzolitic shergottite. However, the moderately LREE-depleted REE distribution pattern indicated that it is closely related to enriched basaltic shergottites like Shergotty, Zagami, Los Angeles, etc. In earlier studies of a similarly olivinephyric shergottite NWA 1068 which contains 21% modal olivine, it was shown that it probably was produced from an enriched basaltic shergottite magma by olivine accumulation . As for LAR 06319, recent petrographic studies suggested that it is different from either lherzolitic shergottites or the highly LREE-depleted olivine-phyric shergottites. We performed Rb-Sr and Sm-Nd isotopic analyses on RBT 04262 and LAR 06319 to determine their crystallization ages and Sr and Nd isotopic signatures, and to better understand the petrogenetic relationships between them and other basaltic, lherzolitic and depleted olivine-phyric shergottites.

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

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


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

  5. Sm-Nd and Initial Sr-87/Sr-86 Isotopic Systematics of Asuka 881394 and Cumulate Eucrites Yamato 980318/433 Compared (United States)

    Nyquist, L. E.; Shih, C-Y; Young, Y. D.; Takeda, H.


    The Asuka 881394 achondrite contains fossil Al-26 and Mn-53 and has a Pb-206/Pb-207 age of 4566.5 +/- 0.2 Ma, the oldest for an achondrite. Recent re-investigation of A881394 yielded revised initial Sm-146/Sm-144 = (9.1 +/- 1.4) x 10(exp -3), a Sm-147-Nd-143 age of 4525 +/- 58 Ma, a Rb-87-Sr-87 age of 4490 +/- 130 Ma, and initial Sr-87/Sr-86 = 0.698991 +/- 19, respectively. The relatively large uncertainties in the Sm-Nd and Rb-Sr ages are due to disturbances of the isotopic systematics of tridymite and other minor phases. A preliminary value for the Sm-147-Nd-143 age of the Yamato 980318 cumulate eucrite of 4560 +/- 150 Ma was refined in later work to 4567 +/- 24 Ma as reported orally at LPSC 35. Similarly, a preliminary value for Sm-146/Sm-144 = (7.7 +/- 1.2) x 10 (exp -3) was refined to (6.0 +/- 0.3) x 10(exp -3). For Yamato 980433, a Sm-147-Nd-143 age of 4542 +/-42 Ma and Sm-146/Sm-144 = (5.7 +/- 0.5) x 10(exp -3) has been reported. Because these two cumulate eucrites are paired, we consider them to represent one igneous rock and present their combined isotopic data here.

  6. Age and sedimentary provenance of the Canastra and Vazante groups in the regions of Guarda-Mor and Unai, Minas Gerais, Sm-Nd and U-Pb methods, Brazil; Idade e proveniencia sedimentar dos grupos Canastra e Vazante nas regioes de Guarda-Mor e Unai, Minas Gerais, metodos Sm-Nd e U-Pb

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    Marimon, Rodrigo Schwantes; Dantas, Elton Luiz; Matteini, Massimo, E-mail:, E-mail: [Universidade de Brasilia (UnB), DF (Brazil). Instituto de Geociencias


    Sm-Nd and U-Pb isotopic data on rocks of the Canastra and Vazante groups suggest derivation from predominantly Meso to Paleoproterozoic sources for these tectonic units of the Brasilia Range. T{sub DM} model ages between 1.76 and 2.85 Ga are consistent with continuous supply of sources with long crustal residence time and / or mix between old and younger sources. Detrital zirconia around 1.0 Ga may indicate the maximum deposition age of the Canastra Group, as well as suggests an important Mesoproterozoic source in the derivation of these sediments. The analyzed samples are in different scales of push, that put side by side the diverse formations of the Canastra and Vazante. So tectonics can explain the change of origin between each one.

  7. Precambrian tholeiitic-dacitic rock-suites and Cambrian ultramafic rocks in the Pennine nappe system of the Alps: Evidence from Sm-Nd isotopes and rare earth elements (United States)

    Stille, P.; Tatsumoto, M.


    Major element, trace element and Sm-Nd isotope analyses were made of polymetamorphic hornblendefelses, plagioclase amphibolites and banded amphibolites from the Berisal complex in the Simplon area (Italy, Switzerland) to determine their age, origin and genetic relationships. In light of major and rare earth element data, the hornblendefelses are inferred to have originally been pyroxene-rich cumulates, the plagioclase amphibolites and the dark layers of the banded amphibolites to have been tholeiitic basalts and the light layers dacites. The Sm-Nd isotope data yield isochron ages of 475??81 Ma for the hornblendefelses, 1,018??59 Ma for the plagioclase amphibolites and 1,071??43 Ma for the banded amphibolites. The 1 Ga magmatic event is the oldest one ever found in the crystalline basement of the Pennine nappes. The Sm -Nd isotope data support the consanguinity of the tholeiitic dark layers and the dacitic light layers of the banded amphibolites with the tholeiitic plagioclase amphibolites and the ultramafic hornblendefelses. The initial e{open}Nd values indicate that all three rock types originated from sources depleted in light rare earth elements. We suggest that plagioclase and banded amphibolites were a Proterozoic tholeiite-dacite sequence that was strongly deformed and flattened during subsequent folding. The hornblendefelses are thought to be Cambrian intrusions of pyroxene-rich material. ?? 1985 Springer-Verlag.

  8. Petrogenesis, U-Pb and Sm-Nd geochronology of the Furna Azul Migmatite: partial melting evidence during the San Ignacio Orogeny, Paragua Terrane, SW Amazon Craton

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    Nascimento, Newton Diego Couto do; Ruiz, Amarildo Salina; Pierosan, Ronaldo; Lima, Gabrielle Aparecida de; Matos, Joao Batista; Lafon, Jean-Michel; Moura, Candido Augusto Veloso, E-mail:, E-mail:, E-mail:, E-mail:, E-mail:, E-mail:, E-mail: [Universidade Federal do Para (GEOCIAM/UFPA), Belem, PA (Brazil). Instituto Nacional de Ciencia e Tecnologia de Geociencias da Amazonia


    The Furna Azul Migmatite is a ∼10 km{sup 2} complex located in Pontes e Lacerda city, Mato Grosso, Brazil. It belongs to Paragua Terrane, limit with Rio Alegre Terrane, southeast of San Ignacio Province, in Amazon Craton. It consists of transitional metatexites with amphibolite enclaves and dioritic injections. The rocks were divided in residuum rich and leucosome rich; both have three deformation phases marked by folded stromatic layers affected by spaced foliation and metamorphosed in amphibolite facies, represented by garnet, biotite, sillimanite, and by the clinopyroxene in the enclaves. The metamorphic retrograde to greenschist is marked by formation of chlorite, muscovite and prehnite. Residuum-rich metatexites show higher CaO and Na{sub 2}O contents, separating them from K{sub 2}O, Ba and Rb enriched transitional metatexites. U-Pb on zircon and Sm-Nd whole-rocks dating indicates that the residuum-rich metatexite crystallized at 1436 ± 11 Ma, with a T{sub DM} age of 1.90 Ga and ε{sub Nd(1.43)} of -0.54, whereas the dioritic injection crystallized at 1341,7 ± 17 Ma with a T{sub DM} age of 1.47 Ga and ε{sub Nd(1.34)} of 3.39. These results indicate that the Furna Azul Migmatite protolith was formed during the San Ignacio Orogeny and was reworked during the same orogeny, as basement for collisional to post-magmatic granites from Pensamiento Intrusive Suite. (author)

  9. Geochemistry and Sm-Nd isotopic composition of the Imiter Pan-African granitoids (Saghro massif, eastern Anti-Atlas, Morocco): Geotectonic implications (United States)

    Baidada, Bouchra; Cousens, Brian; Alansari, Abdelkhalek; Soulaimani, Abderrahmane; Barbey, Pierre; Ilmen, Said; Ikenne, Moha


    The Imiter inlier (eastern part of the Moroccan Anti-Atlas) is located on the northwestern border of the West African Craton (WAC) and exhibits a range of Pan-African granitoids. Three massifs that crosscut the Imiter Saghro Group were targeted in this work: the Igoudrane granodiorite, Bou Teglimt granodiorite and Bou Fliou granite. We present here additional geochemical analyses (major and trace elements) and Sm-Nd isotopic data, which define two distinct groups: (i) the Igoudrane massif (677 Ma) and (ii) the Bou Teglimt granodiorite (576 Ma) and the Bou Fliou granite (550 Ma). Geochemical data confirm the calc-alkaline signature of the studied granitoids. Both groups of granitoids are slightly peraluminous and show strong negative anomalies in Nb, Ta and Ti in multi-element plots normalized to the primitive mantle. The granitoids have low 143Nd/144Nd initial ratios (0.5116-0.5117), with TDM model ages ranging from 1.73 to 1.52Ga. The εNd(t) values are negative, decreasing from the Igoudrane samples (-1.1 to -3.1) to the Bou Teglimt granodiorite (-3.0 to -3.3) and Bou Fliou (-4.2 to -4.8). All these data suggest a mixed magmatic origin involving a juvenile mantle source and an old, at least Paleoproterozoic crust. Given Mesoproterozoic rocks are lacking or very scarce in the Anti-Atlas, these results confirm the existence of an old cratonic basement beneath the eastern Anti-Atlas, and therefore suggest that the northern border of the West African Craton must be placed further to the north, as suggested by previous work in this region.

  10. Rb-Sr, Sm-Nd, K-Ca, O, and H isotopic study of Cretaceous-Tertiary boundary sediments, Caravaca, Spain: Evidence for an oceanic impact site

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    DePaolo, D.J.; Kyte, F.T.; Marshall, B.D.; O' Neil, J.R.; Smit, J.


    Isotopic ratios and trace element abundances were measured on samples of IR-enriched clay at the Cretaceous-Tertiary boundary, and in carbonate and marl from 5 cm below and 3 cm above the boundary. Samples were leached with acetic acid to remove carbonate, and with hydrochloric acid. Leachates and residues were measured. The Sr, Nd, O and H isotopic compositions of the boundary clay residues are distinct from those of the stratigraphically neighboring materials. The data indicate that most of the clay material was derived from a terrestrial source with relatively low /sup 87/Sr//sup 86/Sr and high /sup 143/Nd//sup 144/Nd ratios. The delta/sup 18/O data suggest that the detritus has been modified by submarine weathering. K-Ca and Rb-Sr systematics, as well as O isotope ratios of K-feldspar spherules within the boundary clay, suggest that they are predominantly authigenic and may have formed after the time of deposition. However, Sm-Nd and Rb-Sr isotopic data indicate that the spherules contain relict material that provides information on the nature of the original detritus. The isotopic evidence for foreign terrestrial detritus in the boundary clay, the low rare earth element concentrations and high Ni concentration, support the hypothesis of a terminal Cretaceous asteroidal impact that produced a global layer of fallout. The data are most easily explained if the impact sites was on oceanic crust rather than continental crust, and if a substantial fraction of the fallout was derived from relatively deep within the lithosphere (> 3 km). This would probably require a single large impactor. 60 references.

  11. Contributions to the petrography, geochemistry and geochronology (U-Pb and Sm-Nd) of the Paleoproterozoic effusive rocks from Iricoume Group, Amazonian Craton, Brazil

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    Marques, Suelen Nonata de Souza; Nascimento, Rielva Solimairy Campelo do, E-mail:, E-mail: [Universidade Federal do Amazonas (UFAM), Manaus, AM (Brazil). Inst. de Geociencias; Souza, Valmir da Silva; Dantas, Elton Luiz, E-mail:, E-mail: [Universidade de Brasilia (UnB), DF (Brazil). Inst. de Geociencias; Valerio, Cristovao da Silva, E-mail: [Universidade Federal de Roraima (UFRR), Boa Vista, RR (Brazil). Inst. de Geociencias


    The southernmost region of the Guyana shield, Amazonian craton, hosts large record of Paleoproterozoic effusive rocks of the Iricoume Group. They present remarkably well-preserved igneous textures and structures. The SiO{sub 2} contents reveal a bimodal association marked by a compositional gap between acid (SiO{sub 2} > 67 wt%) and intermediate (SiO{sub 2} < 57.7 wt%) rocks. The acid effusive rocks are rhyolites to rhyodacites with high SiO{sub 2}, alkali, Rb, Zr, Nb + Ta, La + Ce and 104 Ga/Al content and low Fe{sub 2}O{sub 3tot}, TiO{sub 2}, CaO, Sr and Co content. They exhibit subalkaline, metaluminous-to-peraluminous compositions, and geochemically compatible to A-type magmatism emplaced in post-collisional to within-plate tectonic settings. The intermediate rocks are andesitic/basalt to andesite relatively high contents of TiO{sub 2}, Al{sub 2}O{sub 3}, Fe{sub 2}O{sub 3total}, MgO, CaO, Sr and Co; low SiO{sub 2}, K{sub 2}O, Rb, Zr, Nb + Ta, La + Ce. They have subalkaline and metaluminous geochemical composition and plot on within-plate basalt field. The acid rocks crystallized at 1882 ± 11 Ma in U-Pb analyses for LA-MC-ICPMS zircon data. The Sm-Nd isotopic data on all rocks reveal a Nd TDM model ages between 2.59 and 2.16 Ga and ε{sub Nd}(t) values between -5.78 and 0.03, indicate that the magmatic evolution was related to the reworking of older Paleoproterozoic at the Rhyacian-Siderian period, continental crust (Transamazonian crust-forming event) with some mixing with a limited amount mantle-derived magmas or with contamination by Archean crust. The petrographic, geochemical and geochronological data presented in this paper suggest a within-plate to post-collisional tectonic setting for the Iricoume volcanism, involving lower crust uplift and generation of basalt magma in an extensional regime. (author)

  12. Emplacement age for the mafic-ultramafic plutons in the northern Dabie Mts. (Hubei): Zircon U-Pb, Sm-Nd and 40Ar/39Ar dating

    Institute of Scientific and Technical Information of China (English)

    WANG; Jianghai


    [1]Zhang, Q., Ma, B. L., Liu, R. X. et al., A remnant of continental lithospheric mantle above a subduction zone: Geochemical constraints on ultramafic rocks from Raobazhai area in Anhui Province, Sci. in China, Ser. B, 1995, 38(12): 1522- 1529.[2]Zhai, M. G., Cong, B. L., Petro-tectonics of the Sulu-Dabie Shan metamorphic belt, Central and East China, Sci. in China, Ser. D, 1996, 39(3): 319-328.[3]Li, S. G., Hart, S. R., Zheng, S. G. et al., Timing of collision between the North and South China Blocks-- the Sm-Nd isotopic age evidence, Sci. in China, Ser. B, 1989, 32(11): 1393-1400.[4]Ni, Y. H., Li, S. G., Sm-Nd ages of the syn-collisional mafic-ultramafic intrusions in the Dabie Mountains, Chinese Sci. Bull., 1998, 43(2): 160-163.[5]Chen, D. G., Wu, Y. B., Xia, Q. K. et al., Sm-Nd ages for the Jiaoziyan gabbro pluton and the characteristics of Nd isotopes, Acta Geosci. Sinica, 1997, 18(Suppl.): 9-11.[6]Jahn, B. M., Wu, F. Y., Lo, C. H. et al., Crust-mantle interaction induced by deep subduction of the continental crust: geochemical and Sr-Nd isotopic evidence from post-collisional mafic-ultramafic intrusions of the northern Dabie complex, central China, Chem. Geol., 1999, 157: 119-146.[7]Li, S. G., Jagoutz, E., Zhang, Z. Q. et al., Structure of high-metamorphic belt in the Dabie mountains and its tectonic implications, Chinese Sci. Bull., 1995, 40(Suppl.): 138-140.[8]Zhang, R. Y., Liou, J. G., Tsai, C. H., Petrogenesis of a high-temperature metamorphic terrain: a new interpretation for the north Dabie Shan, central China, J. Metamorphic Geol., 1996, 14: 319-333.[9]Wang, J. H., The Early Evolution of the Dabie Complex, with Special Reference to the Genetic Mechanism of Migmatites, Wuhan: China University of Geosciences Press, 1991, 1-140.[10]Suo, S. T., Zhong, Z. Q., You, Z. D., Extensional deformation of post ultrahigh-pressure metamorphism and exhumation process of ultrahigh-pressure metamorphic rocks in the Dabie massif

  13. Contrasting geochemical and Sm-Nd isotopic compositions of Archean metasediments from the Kongling high-grade terrain of the Yangtze craton: Evidence for cratonic evolution and redistribution of REE during crustal anatexis (United States)

    Gao, Shan; Ling, Wenli; Qiu, Yumin; Lian, Zhou; Hartmann, Gerald; Simon, Klaus


    Twenty-three clastic metasediments from the Kongling high-grade terrain of the Yangtze craton, South China were analyzed for major, trace and rare earth elements and Sm-Nd isotopic ratios. Associated dioritic-tonalitic-trondhjemitic (DTT) and granitic gneisses as well as amphibolites were also analyzed in order to constrain provenance. The results show that the clastic metasediments can be classified into 3 distinct groups in terms of mineralogical, geochemical and Sm-Nd isotopic compositions. Group A is characterized by having no to slight negative Eu anomalies (Eu/Eu∗ = 0.82-1.07), being high in Cr (191-396 ppm) and Ni (68-137 ppm), and low in Th (3.3-7.8 ppm) and REE (ΣREE = 99-156 ppm). These characteristics are similar to those of metasediments from Archean greenstone belts. In addition, the Group A metasediments have the value of the Chemical Index of Alteration (CIW) close to felsic gneisses. Their Sm-Nd isotopic, REE and trace element compositions can be interpreted by mixtures of the DTT gneisses and amphibolites. Dating of detrital zircons from 2 Group A samples by SHRIMP reveals a major concordant age group of 2.87-3.0 Ga, which is identical to the age of the trondhjemitic gneiss. These results strongly suggest that Group A was principally the first-cycle erosion product of the local Kongling DTT gneiss and amphibolite. Moreover, the higher than amphibolite Cr content and slight Eu depletion exhibited by some samples from this group infer that ultramafic rocks like komatiite and granite of probably 3.0-3.3 Ga in age also played a role. Group B is characterized by the presence of graphite and shows a more evolved composition similar to post-Archean shales with a prominent negative Eu anomaly (Eu/Eu∗ = 0.48-0.77) and high CIW. On paired Cr/Th vs La/Co and Co/Th plots, Group B samples conform to a two-end member mixing line of the Kongling granitic gneiss and amphibolite. However, data on Nd model age and CIW suggest that the granite component should

  14. Low-Temperature Sintering and Microwave Dielectric Properties of Bi0.9Ln0.05Li0.05V0.9Mo0.1O4 (Ln = Sm, Nd and La) Ceramics (United States)

    Wang, Zixing; Yuan, Changlai; Yang, Tao; Feng, Qin; Liu, Fei; Chen, Jinman; Zhou, Changrong; Chen, Guohua


    Microwave dielectric ceramics of Bi0.9Ln0.05Li0.05V0.9Mo0.1O4 (Ln = Sm, Nd and La) with a low firing temperature were prepared via conventional solid-state reaction. The phases and microstructures of the ceramics were characterized by x-ray diffraction and scanning electron microscopy. The temperature coefficients of resonant frequency in the three compositions increased as sintering temperature increased. It is worth noting that a phase transition of the Bi0.9Ln0.05Li0.05V0.9Mo0.1O4 (Ln = Sm, Nd and La) ceramics from a monoclinic to a tetragonal scheelite structure was found with an increase in sintering temperature. The densification temperatures of all compositions were below 700°C. Excellent microwave dielectric properties were obtained for the Bi0.9Nd0.05Li0.05V0.9Mo0.1O4 ceramic sintered at 650°C, with a dielectric constant of ~72.2, a quality factor of ~6467 GHz and a temperature coefficient of resonant frequency of ~2.6 ppm/°C. The Bi0.9Ln0.05Li0.05V0.9Mo0.1O4 (Ln = Sm, Nd and La) ceramics are chemically compatible with both Ag and Cu powders at their sintering temperatures, and are thus a promising candidate for use in LTCC technology applications.

  15. Sm-Nd data for mafic-ultramafic intrusions in the Svecofennian (1.88 Ga Kotalahti Nickel Belt, Finland – implications for crustal contamination at the Archaean/Proterozoic boundary

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    Hannu V. Makkonen


    Full Text Available Sm-Nd data were determined for eight mafic-ultramafic intrusions from the Svecofennian (1.88 Ga Kotalahti Nickel Belt, Finland. The intrusions represent both mineralized and barren types and are located at varying distances from the Archaean/Proterozoic boundary.The samples for the 23 Sm-Nd isotope analyses were taken mostly from the ultramafic differentiates. Results show a range in initial εNd values at 1880 Ma from -2.4 to +2.0. No relationship can be found between the degree of Ni mineralization and initial εNd values, whilea correlation with the geological domain and country rocks is evident. The Majasaari and Törmälä intrusions, which have positive εNd values, were emplaced within the Svecofennian domain in proximity to 1.92 Ga tonalitic gneisses, which have previously yielded initialεNd values of ca. +3. In contrast, the Luusniemi intrusion, which has an εNd value of -2.4 is situated close to exposed Archaean crust. Excluding two analyses from the Rytky intrusion, all data from the Koirus N, Koirus S, Kotalahti, Rytky and Kylmälahti intrusions, withinerror limits, fall in the range -0.7 ± 0.3. The results support the concept of contamination by Archaean material in proximity to the currently exposed craton margin. The composition of the proposed parental magma for the intrusions is close to EMORB, with initialεNd values near +4.

  16. U-Pb SHRIMP and Sm-Nd geochronology of the Silvânia Volcanics and Jurubatuba Granite: juvenile Paleoproterozoic crust in the basement of the Neoproterozoic Brasília Belt, Goiás, central Brazil

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    Full Text Available U-Pb SHRIMP and Sm-Nd isotopic ages were determined for felsic metavolcanic rocks from the Silvânia Sequence and Jurubatuba Granite in the central part of the Brasília Belt. Zircon grains from a metavolcanic sample yielded 2115 ± 23 Ma and from the granite yielded 2089 ± 14 Ma, interpreted as crystallization ages of these rocks. Six metavolcanic samples of the Silvânia Sequence yielded a six-point whole-rock Sm-Nd isochron indicating a crystallization age of 2262 ± 110 Ma and positive epsilonNd(T = +3.0 interpreted as a juvenile magmatic event. Nd isotopic analyses on samples from the Jurubatuba Granite have Paleoproterozoic T DM model ages between 2.30 and 2.42 Ga and epsilonNd(T values vary between -0.22 and -0.58. The oldest T DM value refers to a sedimentary xenolith in the granite. These results suggest crystallization ages of Silvânia volcanics and Jurubatuba Granite are the first evidence of a ca. 2.14-2.08 juvenile magmatic event in the basement of the central part of the Brasília Belt that implies the presence of arc/suture hidden in reworked basement of the Brasília Belt.

  17. Sm/Nd isotopic data for the Santana do Ipanema high-K mega dykes as evidence for Brasiliano decompression melting at the Pernambuco-Alagoas (PE-AL) Massif, Borborema province

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    Silva Filho, A.F. da; Guimaraes, I.P.; Luna, E.B.A.; Valadares, D.S. [Pernambuco Univ., Recife, PE (Brazil). Dept. de Geologia


    This work deals with the Sm-Nd signatures of some mega dykes located close to the Northern limit of the batholith in the Santana do Ipanema plutonic complex (SIC), which comprises 6 intrusive suites. Their composition ranges from syenites to quartz syenites. They are mesocratic to leucocratic, usually equigranular but sometimes porphyritic. Their accessory mineralogy is comprised of sphene, opaque, amphibole, {+-} pyroxene, apatite, zircon, biotite, allanite and epidote. The main minerals are microcline, plagioclase and quartz. The SIC rocks are metaluminous and intermediate to acid, with Si O{sub 2} ranging from 55,6 wt% to 66.4 wt% and Ba ranging from 3889 ppm to 10253 pp,. The K{sub 2} O/Na{sub 2} O ratio ranges widely as well, from 0,59 to 2.07, making these rocks a quite heterogeneous suite. The diagram shows two patterns, one with troughs at Nb, Zr and Ti, while the other one shows troughs at Nb, Hf and Eu. The Zr data available show a wide range, from 133 ppm to 314 ppm, suggesting this suite was the result of different degrees of partial melting of a same enriched LIL protolith. Five isotope Sm-Nd data has been obtained for these rocks, yielding epsilon Nd (0.60 Ga) values which ranges from -9.3 to -3.6, and Tdm which ranges from 2.34 Ga to 1.26 Ga. The isotope data agree with the heterogeneous character showed by the trace elements 3 refs.

  18. Sm-Nd and U-Pb isotopic constraints for crustal evolution during Late Neoproterozic from rocks of the Schirmacher Oasis, East Antarctica: geodynamic development coeval with the East African Orogeny (United States)

    Ravikant, V.; Laux, J.H.; Pimentel, M.M.


    Recent post-750 Ma continental reconstructions constrain models for East African Orogeny formation and also the scattered remnants of ~640 Ma granulites, whose genesis is controversial. One such Neoproterozoic granulite belt is the Schirmacher Oasis in East Antarctica, isolated from the distinctly younger Pan-African orogen to the south in the central Droning Maud Land. To ascertain the duration of granulite-facies events in these remnants, garnet Sm-Nd and monazite and titanite U-Pb IDTIMS geochronology was carried out on a range of metamorphic rocks. Garnet formation ages from a websterite enclave and gabbro were 660±48 Ma and 587±9 Ma respectively, and those from Stype granites were 598±4 Ma and 577±4 Ma. Monazites from metapelite and metaquartzite yielded lower intercept UPb ages of 629±3 Ma and 639±5 Ma, respectively. U-Pb titanite age from calcsilicate gneiss was 580±5 Ma. These indicate peak metamorphism to have occurred between 640 and 630 Ma, followed by near isobaric cooling to ~580 Ma. Though an origin as an exotic terrane from the East African Orogen cannot be discounted, from the present data there is a greater likelihood that Mesoproterozoic microplate collision between Maud orogen and a northerly Lurio-Nampula block resulted in formation of these granulite belt(s).

  19. Petrogenesis, U-Pb and Sm-Nd geochronology of the Furna Azul Migmatite: partial melting evidence during the San Ignácio Orogeny, Paraguá Terrane, SW Amazon Craton

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    Newton Diego Couto do Nascimento

    Full Text Available ABSTRACT: The Furna Azul Migmatite is a ~10 km2 complex located in Pontes e Lacerda city, Mato Grosso, Brazil. It belongs to Paraguá Terrane, limit with Rio Alegre Terrane, southeast of San Ignacio Province, in Amazon Craton. It consists of transitional metatexites with amphibolite enclaves and dioritic injections. The rocks were divided in residuum rich and leucosome rich; both have three deformation phases marked by folded stromatic layers affected by spaced foliation and metamorphosed in amphibolite facies, represented by garnet, biotite, sillimanite, and by the clinopyroxene in the enclaves. The metamorphic retrograde to greenschist is marked by formation of chlorite, muscovite and prehnite. Residuum-rich metatexites show higher CaO and Na2O contents, separating them from K2O, Ba and Rb enriched transitional metatexites. U-Pb on zircon and Sm-Nd whole-rocks dating indicates that the residuum-rich metatexite crystallized at 1436 ± 11 Ma, with a TDM age of 1.90 Ga and εNd(1.43 of -0.54, whereas the dioritic injection crystallized at 1341,7 ± 17 Ma with a TDM age of 1.47 Ga and εNd(1.34 of 3.39. These results indicate that the Furna Azul Migmatite protolith was formed during the San Ignácio Orogeny and was reworked during the same orogeny, as basement for collisional to post-magmatic granites from Pensamiento Intrusive Suite.

  20. Paleoproterozoic source contributions to the São Roque Group sedimentation: LA-MC-ICPMS U-Pb dating and Sm-Nd systematics of clasts from metaconglomerates of the Boturuna Formation

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    Larry Michael Heaman


    Full Text Available The So Roque Group is characterized by volcano-sedimentary sequences, in which deposition probably started in the late Paleoproterozoic. U-Pb dating by LA-MC-ICPMS of zircons extracted from predominantly equigranular monzogranites clasts from Morro Doce and Morro do Polvilho regions, yield paleoproterozoic ages of 2199 8.5 Ma and 2247 13 Ma, respectively. These represent the ages for the main source of granite for the metaconglomerates from the Boturuna Formation (basal unit of So Roque Group. Its polycyclic history is reinforced by the presence of inherited Archean zircons (2694 29 Ma found within the clasts. Moreover, these clasts have also been affected by the Neoproterozoic overprinting event as indicated by their lower intercept Concordia ages. Sm-Nd isotope data for the main clast varieties from the Morro Doce metaconglomerates yield TDM ages of 2.6 to 2.7 Ga, demonstrating that these granites are the recycling products of an Archean crustal component. The metaconglomerate arkosean framework yields slightly lower ENd(t values than those for the clasts, indicating that a younger and/or more primitive source also contributed to the Boturuna Formation.

  1. Paleoproterozoic source contributions to the Sao Roque Group sedimentation: LA-MC-ICPMS U-Pb dating and Sm-Nd systematics of clasts from metaconglomerates of the Boturuna Formation

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    Henrique-Pinto, Renato; Janasi, Valdecir de Assis; Tassinari, Colombo Celso Gaeta [Universidade de Sao Paulo (USP), SP (Brazil). Inst. de Geociencias. Dept. de Mineralogia e Geotectonica; Simonetti, Antonio [University of Notre Dame, South Bend (United States). Dept. of Civil Engineering and Geological Sciences; Heaman, Larry Michael, E-mail:, E-mail:, E-mail:, E-mail:, E-mail: [University of Alberta, Edmonton (Canada). Dept. of Earth and Atmospheric Sciences


    The Sao Roque Group is characterized by volcano-sedimentary sequences, in which deposition probably started in the late Paleoproterozoic. U-Pb dating by LA-MC-ICPMS of zircons extracted from predominantly equigranular monzogranites clasts from Morro Doce and Morro do Polvilho regions, yield paleoproterozoic ages of 2199 {+-}8.5 Ma and 2247 {+-}13 Ma, respectively. These represent the ages for the main source of granite for the metaconglomerates from the Boturuna Formation (basal unit of Sao Roque Group). Its polycyclic history is reinforced by the presence of inherited Archean zircons (2694 {+-}29 Ma) found within the clasts. Moreover, these clasts have also been affected by the Neoproterozoic overprinting event as indicated by their lower intercept Concordia ages. Sm-Nd isotope data for the main clast varieties from the Morro Doce metaconglomerates yield T{sub DM} ages of 2.6 to 2.7 Ga, demonstrating that these granites are the recycling products of an Archean crustal component. The metaconglomerate arkosean framework yields slightly lower {epsilon}{sub Nd(t)} values than those for the clasts, indicating that a younger and/or more primitive source also contributed to the Boturuna Formation. (author)

  2. Behaviour of the Sm-Nd and Rb-Sr systems of the mafic-ultramafic layered sequence from Ribeirao dos Motas (Archaean), meridional craton Sao Francisco: evidences of mantle source enrichment and isotopic fractionation; Comportamento dos sistemas Sm-Nd e Rb-Sr da sequencia acamadada mafico-ultramafico Ribeirao dos Motas (Arqueano), craton Sao Francisco Meridional: evidencias de enriquecimento mantelico e fracionamento isotopico

    Energy Technology Data Exchange (ETDEWEB)

    Carneiro, Mauricio Antonio; Carvalho Junior, Irneu Mendes de; Oliveira, Arildo Henrique de [Ouro Preto Univ., (UFOP), MG (Brazil). Dept. de Geologia]. E-mail:; Teixeira, Wilson [Sao Paulo Univ., SP (Brazil). Inst. de Geociencias. Dept. de Mineralogia e Geotectonica; Pimentel, Marcio Martins [Brasilia Univ., DF (Brazil). Inst. de Geociencias. Lab. de Geocronologia


    The Ribeirao dos Motas layered sequence (SARM) crops out in the southern part of the Sao Francisco Craton, Brazil. This sequence comprises phaneritic meta ultramafic and metamafic rocks, which, although slightly deformed and metamorphosed, retain primary igneous layers. Porphyritic rocks with idiomorphic pyroxene crystals and heteradcumulate and adcumulate textures are also present. Eighteen isotopic analyses were performed in the SARM, comprising rocks with primary (relict) textures, as well as rocks in amphibolite facies and retro-metamorphosed to green-schist facies. Seven samples yield a Sm/Nd isochron age of 2.79 +- 0.30 Ga (MSWD=1.2 e epsilon {sub Ndt}=+0.48), constraining the accretion time of the SARM rocks. The positive epsilon {sub Ndt} value coupled with the Rb/Sr evidence is consistent with mantle source relatively enriched in Nd and Sr isotopes. Nevertheless, some SARM samples display isotopic fractionation and disturbance, which can be ascribed to the following processes or their combinations: a) mobilization of the incompatible elements due to regional high grade metamorphism; b) isotopic changes during upper amphibolite facies overprint; c) isotopic resetting by low-grade fluids associated to the Claudio Shear zone, which is located nearby the SARM. (author)

  3. Petrology, geochemistry and Sm-Nd analyses on the Balkan-Carpathian Ophiolite (BCO - Romania, Serbia, Bulgaria): Remnants of a Devonian back-arc basin in the easternmost part of the Variscan domain (United States)

    Plissart, Gaëlle; Monnier, Christophe; Diot, Hervé; Mărunţiu, Marcel; Berger, Julien; Triantafyllou, Antoine


    The pre-Alpine basement of the Southern Carpathians/Western Balkans contains four ophiolitic massifs dismembered by Alpine tectonics, which define the ;Balkan-Carpathian Ophiolite; (BCO) for which the tectonic setting and age of formation are still debated (Precambrian or Early Devonian). In this contribution, we demonstrate that, in light of a Pre-Alpine restoration, the four massifs belonged to a unique slice of very complete, obducted oceanic lithosphere and we re-evaluate its tectonic setting. Large chromitite volumes with Al-rich spinel compositions (Cr# = 0.39-0.48), as well as major and trace geochemical results on basalts (slightly enriched N-MORBs with low negative Nb anomaly associated with calk-alkaline BABBs), point to a formation in a back-arc basin. Mantle spinel composition (Cr# = 0.49-0.51) and melting modeling indicate mean melting extents of 8.5-11% favouring intermediate spreading rate. New Sm-Nd dating on lower gabbroic rocks give a whole rock isochron, interpreted as the age of formation of the BCO crust at 409 ± 38 Ma, thus confirming an Early Devonian oceanic crust. The previous ∼563 Ma U-Pb zircon age can be interpreted as casual inheritance indicating the proximity of an old continental lithosphere. Taking into account the lithological evidences and paleocontinental affinities of the two recognized terranes separated by the BC oceanic basin (Balkans and Sredna Gora) and by analogy with other Variscan ophiolites in Western/Central Europe, we suggest that the BC ophiolite belong to the ∼400 Ma ophiolites group obducted between West and East Galatia and belonging to the southern Variscan suture. However, the BC ophiolite is the only one of this group obducted to the north and not involved in the Lower Allochthon/ophiolite/Upper Allochthon thrust pile, likely explaining its exceptional preservation. Finally, we tentatively propose a new unifying tectonic model where different terrane drift rates and highly oblique displacements create two

  4. Formation, obduction and provenance of the Støren-Bymarka-Løkken ophiolite, Central Norwegian Caledonides; constraints from geochronology, geochemistry, Sm-Nd and Lu-Hf data (United States)

    Slagstad, T.; Pin, C.; Roberts, D.; Kirkland, C. L.; Grenne, T.; Dunning, G.; Sauer, S.; Andersen, T.


    Suprasubduction-zone ophiolites are a characteristic feature of the Palaeozoic Caledonian-Appalachian orogenic belt, and mark the onset of convergence and closure of one or more oceans separating the Baltican, Laurentian and Avalonian continents, ending with continent-continent collision in the Mid Palaeozoic. The Bymarka-Løkken ophiolite in the Central Norwegian Caledonides is a variably tectonised ophiolite fragment, locally with an incomplete, but nevertheless well-preserved ophiolite pseudostratigraphy. Previous work has concluded that the ophiolite formed in an Early Ordovician suprasubduction-zone environment, most likely in an oceanic arc/back-arc basin system, but little is know about the evolution of the ophiolitic crust. There has also been some debate as to the whether obduction of the ophiolite upon the subjacent Gula Complex was onto Laurentia, Baltica, or a microcontinent of Baltican affinity. Here we present new, high-precision TIMS and SHRIMP zircon analyses from felsic rocks in the ophiolite. Combined with geochemical and Sm-Nd whole-rock and Lu-Hf zircon analyses from the same rocks, these data allow us to elucidate the timing of various stages in the evolution of the ophiolite. Plagiogranite bodies range in age from 493 to 480 Ma and have relatively juvenile isotopic compositions. Geochemical data suggest subduction-zone influence and we interpret this stage to represent formation of the ophiolite in an oceanic back-arc setting. At 480 Ma, a large granitoid body with an unradiogenic isotopic composition and strong subduction-zone geochemical signature intruded the ophiolite. We interpret this stage to reflect convergence in the back-arc basin and formation or migration of an oceanic arc. The unradiogenic isotopic composition probably reflects subduction of back-arc basin crust with sediments derived from the nearby continent or microcontinent. At 480-470 Ma, a greenstone-dominated conglomerate and an overlying volcaniclastic sequence was

  5. Geochemical evidences of the boiling phenomena in Los Humeros geothermal field; Evidencias geoquimicas del fenomeno de ebullicion en el campo de Los Humeros

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    Munguia Bracamontes, Fernando; Lopez Mendiola, Juan Manuel [Instituto de Investigaciones Electricas, Cuernavaca (Mexico)


    The geochemical behavior of the fluids in the geothermal field Los Humeros suggests the existence of a reservoir of relatively low permeability, with hydrostatic pressure gradients and thermodynamic conditions of pressure-temperature close to the boiling point in stationary conditions, that is, non-disturbed. Nevertheless, the fluid geochemistry also indicates the presence of steam under stationary conditions, mainly in the fault, fracture, fissure, etc. zones. The steam diminishes progressively as the extraction time increases, being replaced by boiling fluid. [Espanol] El comportamiento geoquimico de los fluidos en el campo geotermico de Los Humeros sugiere la existencia de un yacimiento de relativa baja permeabilidad, con gradientes de presion hidrostatica y condiciones termodinamicas de presion-temperatura cercanas al punto de ebullicion a condiciones estables; es decir, no perturbadas. Sin embargo, la geoquimica de los fluidos tambien indica la existencia de vapor bajo condiciones estables, principalmente en las zonas de fallas, fracturas, fisuras, etc. El vapor disminuye progresivamente conforme aumenta el tiempo de extraccion, siendo reemplazado por fluido en ebullicion.

  6. Petrographic and geochemical characterization and isotope analysis of U-PB (SHRIMP) in tuffaceous siltstone, Salitre formation, Sao Francisco supergroup, BA, Brazil; Caracterizacao petrografica, geoquimica e analises isotopicas U-PB (SRIMP) em siltito tufaceo, formacao Salitre Supergrupo Sao Francisco, Bahia

    Energy Technology Data Exchange (ETDEWEB)

    Santana, Ana; Chemale Junior, Farid, E-mail: [Universidade de Brasilia (UnB), DF (Brazil); Sherer, Claiton Marlon dos Santos [Universidade Federal do Rio Grande do Sul (UFRS), Porto Alegre, RS (Brazil)


    The Salitre Formation consists of neoproterozoic carbonate sequence overlying the Sao Francisco Craton (SFC) in Bahia. Data on the origin of such training are scarce, mainly due to their nature, essentially carbonate. In this study, from the petrographic characterization and geochemical thin levels of terrigenous, it was identified the contribution of volcanic material. Isotopic analysis of U-Pb, SHRIMP, indicate the existence of young grain, aged 669 ± 14 Ma (Cryogenian) - probable volcanism associated with the building of neoproterozoic mobile belts surrounding the SFC - and inherited zircons with the main population in the Paleoproterozoic and corresponding to the source area of the crystalline basement. Detrital zircons with ages between Statherian and Tonian have also been reported and have the source area the metasedimentary rocks of the Espinhaco Supergroup. (author)

  7. Mineralogical, Geochemical and Isotopic Characterisation of the Travertine Formation Associated with the Alicun de las Torres Thermal System (Province of Granada): Palaeoclimatic and Palaeoenvironmental Implications.; Caracterizacion Mineralogica, Geoquimica e Isotopica de los Travertinos Asociados al Sistema Termal de Alicun de las Torres (Provincia de Granada): Implicaciones Paleoclimaticas y Paleoambientales

    Energy Technology Data Exchange (ETDEWEB)

    Prado, A. J.; Delgado, A.; Crespo, M. T.; Martin, A.; Perez del Villar, L.


    In the framework of a Singular Strategic Project entitled: Advanced Technologies of Carbon, Capture and Storage (CCS), supported by the MICINN (Spain) and the FEDER founds (EU), specifically in the Carbon Storage Task, a comprehensive study on the CO{sub 2} leakage as DIC (Dissolved Inorganic Carbon) in the Alicun de Las Torres (Prov. of Granada) natural analogue Thermal System was envisaged. This analogous system is characterised by the presence of a very important travertine formation. In order to explain the formation of these travertine mass a detailed mineralogical, petrographic, geochemical and isotopic, including stable and radioactive isotopes, characterisation has been carried out. Based on these data, paleoclimatic and palaeoenvironmental conditions under which this travertine formation was formed, during a period of approximately 230Ky, have also been deduced. (Author) 234 refs.

  8. Geochemistry and isotopic characterization of rain in the zones of Los Azufres, Michoacan and Los Humeros, Puebla and its relation with geothermal fluids; Caracterizacion geoquimica e isotopica de lluvia en las zonas de Los Azufres, Michoacan y Los Humeros, Puebla y su relacion con fluidos geotermicos

    Energy Technology Data Exchange (ETDEWEB)

    Verma, Mahendra P; Santoyo, Socrates; Aragon, Alfonso [Instituto de Investigaciones Electricas, Temixco, Morelos (Mexico); Fernandez, Ma. Elena [Comision Federal de Electricidad Morelia, Michoacan (Mexico); Tovar, Rigoberto [Comision Federal de Electricidad, Los Azufres (Mexico); Casimiro, Emigdio; Sandoval, Fernando [Comision Federal de Electricidad, Los Humeros, Puebla (Mexico); Johnson, Craig [USGS, Denver, Colorado, (United States); Gerardo-Abaya, Jane [IAEA, Viena (Austria)


    This work presents the preliminary results of chemical and isotopic monitoring of rainwater in Los Humeros and Los Azufres geothermal fields and their surrounding during 1995-1998. The rainwater samples were collected in seven and eight sites in Los Humeros and Los Azufres, respectively. The alkalinity values of rainwater were positive in all Los Humeros sites, which indicates that there is no acid rain in the region. There were some samples with negative alkalinity at two sites in case of Los Azufres, Vivero and Guadalajara, but the values were very small. This means that there is some acidity in the rain. In case of Los Humeros a good correlation was observed between alkalinity and the concentration of calcium, which indicates that the samples were probably affected by dust. The concentration of anions Cl, SO{sub 4} {sup 2} and NO{sub 3} was very low in the rainwater samples in both fields, but there is a clearly defined trend. The concentration of NO{sub 3} and SO{sub 4}{sup 2} at Los Azufres dicreased with advance in the rainy season. There is no NO{sub 3} in the rain at Los Humeros. The values of NO{sub 3} in the rain of Mexico City were higher than 10 ppm. This indicates that NO{sub 3} in rainwater is related with the industrial contamination. This evidence suggests that the clouds formed in the Gulf of Mexico bring rain to the Central part of Mexico. Los Humeros is located east of any big industrial site, therefore the rainwater has less anthropogenic SO{sub 4} {sup 2} and NO{sub 3}. Rainwater at Los Azufres contains contaminants from industrial sites located to the east. It can be concluded that there is no discernible influence of geothermal emissions on rainwater acidity. The concentration of Cl{sup -} was very low and constant for all the rainy seson. The origin of Cl{sup -} is considered as marine. A mixing model for Cl{sup -}/SO{sub 4} {sup 2-} versus {delta}{sup 3}4S suggests that there is 10-25% sulfate from sea spray in rainwater at Los Humeros, whereas there is less then 10% sea spray sulfate at Los Azufres. The {delta}{sup 3}4S values of H{sub 2}S of geothermal fluid are very similar to those of rainwater. A compilation of {delta}{sup 3}4S values for different sources of sulfur emissions indicates that it is practically impossible to define the origin of sulfur in rainwater, but the combined results of chemical and isotopic monitoring suggest that the geothermal emissions have no contribution to rainwater acidity. [Spanish] Se presentan los resultados preliminares obtenidos del estudio de monitoreo quimico e isotopico de las precipitaciones pluviales en los campos geotermicos de Los Humeros, Los Azufres y sus zonas de referencia durante el periodo de lluvia 1995-1998. Se recolectaron las muestras de lluvia en siete de los sitios de Los Humeros y ocho de Los Azufres. Los valores de la alcalinidad resultaron positivos para casi todas las muestras de lluvia en Los Humeros, lo que indica que en esta zona no existe acidez. Algunos valores de alcalinidad en los sitios Vivero y Guadalajara de Los Azufres fueron negativos, aunque muy pequenos, por lo que se concluye que existe poca acidez en la lluvia en Los Azufres. En el caso de Los Humeros se encontro buena correlacion entre la alcalinidad y la concentracion de calcio, lo que sugiere que las muestras puedan estar afectadas probablemente por el polvo de la zona. La concentracion de aniones, Cl{sup -}, SO{sub 4} y NO{sub 3} es baja en ambos campos y con una tendencia bien definida. La concentracion de NO{sub 3} y SO{sub 4} en las lluvias de Los Azufres disminuye con el avance de la temporada. En el caso de Los Humeros casi no existe NO{sub 3} y SO{sub 4} en las lluvias de Los Azufres disminuye con el avance de la temporada. En el caso de Los Humeros casi no existe NO{sub 3}. Como referencia cabe senalar que los valores de NO{sub 3} en las lluvias de la ciudad de Mexico son superiores a 10 ppm e indican una relacion con la contaminacion industrial. Esto sugiere que el campo de Los Humeros, aun cuando se encuentra al oriente de la Ciudad de Mexico, recibe precipitaciones de agua de lluvia proveniente del Golfo de Mexico que aun no esta afectada por la contaminacion industrial. Lo contrario sucede en el campo de Los Azufres, (con concentracion de NO{sub 3} de hasta 3ppm), el cual esta ubicado al occidente de la Ciudad de Mexico, lo cual explica la posible acidez en las muestras de lluvia. La concentracion de Cl{sup -} es muy baja y constante durante toda la temporada de lluvias en ambos campos. El origen del Cl{sup -} en las lluvias ha sido considerado de origen marino. El modelo de mezcla entre SO{sub 4}{sup 2}/ Cl y {delta}{sup 3}4S comprueba esta hipotesis. En el campo geotermico de Los Humeros se tienen valores de entre 10 y 25% de SO{sub 4}{sup 2} de origen marino, mientras que en Los Azufres los valores fueron menores del 10%. Los valores de {delta}{sup 3}4S del H{sub 2}S de fluidos geotermicos son muy similares a los de las lluvias.

  9. Elementary and isotopic geochemistry of vein goethite in laterite-gossanic crusts from the Igarape Bahia gold mine (Carajas, Brazil); Geoquimica elementar e isotopica de Goethita de veios em crostas laterito-gossanicas da mina de ouro do Igarape Bahia (Carajas, Brasil)

    Energy Technology Data Exchange (ETDEWEB)

    Costa, Marcondes Lima da [Para Univ., Belem, PA (Brazil). Centro de Geociencias; Raith, Angelika [Fisons Instrumental Elemental Analysis, Winsford Chesfire (United Kingdom); Schumann, Thomas; Poellmann, Herbert [Halle-Wittenberg Univ., Halle (Germany). Inst. Geologische Wissenschaften


    The lateritic crusts of the gold mine from the Igarape Bahia, in Carajas, situated at Para state, Brazil, present themselves frequently sectioned by the goethite sub-vertical veins. The veins have the following measures: until 10 cm of thickness and more than 6 m of length. This work aims to characterize the textural, mineralogical and chemical aspects of these veins, in order to understand its evolution, mainly the relation with the laterites and its geological importance, including the aspects referents to the mineral prospecting. (author) 4 figs., 6 refs.; e-mail: mlc at

  10. U/Pb (SHRIMP), {sup 207}Pb/{sup 206}Pb, Rb/Sr, Sm/Nd e K/Ar geochronology of granite-greenstone terrains of Gaviao Block: implications for the Proterozoic and Archean evolution of Sao Francisco Craton, Brazil; Geocronologia U/Pb (SHRIMP), {sup 207}Pb/{sup 206}Pb, Rb/Sr, Sm/Nd e K/Ar dos terrenos granito-greenstone do Bloco do Gaviao: implicacoes para a evolucao arqueana e proterozoica do craton do Sao Francisco, Brasil

    Energy Technology Data Exchange (ETDEWEB)

    Leal, Luiz Rogerio Bastos


    The Gaviao Block (GB) in the northern portion of the Sao Francisco Craton-Northeast of Brazil, constitutes one of the oldest Archean fragments of the South American Platform Archean crust. GB underwent several events of juvenile accretion and reworking of continental crust along its evolutionary history, notably between the Archean and the Paleoproterozoic. {sup 207}Pb/{sup 206}Pb isotopic analyses were carried out in two zircons populations from strongly migmatized TTG terranes found in the proximity of Brumado: the first population (7 crystals) is taken as representative of the crystallization period of the TTG terranes at 3300 {+-} 45 Ma; the second (2 crystals) represents the age of the first even of metamorphism/migmatization at 2910 {+-} 10 Ma. {sup 207} Pb/{sup 206} Pb analyses in zircons from an outcrop of non-migmatized TTG in the area yielded a 3202 {+-} 15 Ma age (4 crystals), interpreted to be the crystallization period of the gneiss protolith. Sm/Nd analyses on the TTG rocks of the Brumado region yielded T{sub DM} model ages varying between 3.26 and 3.36 Ga and {epsilon}{sub Nd}{sup (t)} between -3.5 and +0.7. These data suggest the occurrence of juvenile accretions to the continental crust during the Archean, with differential involvement of crustal materials. The geochemical data of rare earth elements corresponding to the TTG terranes revealed moderate LRRE contents (La{sub N}=83,5), low HREE contents (La{sub N}=2,5) and a fairly fractionated pattern (La/Yb){sub N}=34, besides lack of negative Eu anomaly, showing that these rocks have similar compositions to those TTG terranes of cratonic continents, as well as some Archean rocks from CSF (e.g. Sete Voltas, Boa Vista). Finally, the youngest ages present in GB rocks (ca. 1.2-0.45 Ga) represent the role played by tectono thermal events, which produced partial or total rejuvenation of the Rb/Sr and K/Ar isotopic systems during the Espinhaco and Brasiliano cycles. In particular, K/Ar ages illustrate the

  11. Lu-Hf and Sm-Nd garnet geochronology

    DEFF Research Database (Denmark)

    Smit, Matthijs Arjen; Scherer, Erik E.; Mezger, Klaus


    are similar among grains having radii larger than 1.3 mm (weighted mean: 2714±6 Ma2714±6 Ma; 2 s.d.) and up to 20 Myr younger for finer fractions. In contrast, Sm–Nd dates are equal to or younger than the 2641–2637 Ma age of peak metamorphism. The roles of concurrently digested inclusions and core–rim Lu......To investigate the systematics of the 176Lu–176Hf and 147Sm–143Nd garnet chronometers, we performed REE and isotope analyses on garnet crystals of different size (0.55–3.1 mm radius) from a single granulite specimen (Archean Pikwitonei Granulite Domain, Manitoba, Canada). The Lu–Hf dates....../Sm fractionation are quantitatively evaluated and excluded as causes for the observed age heterogeneity. Instead, the isotope dates are interpreted to reflect partial loss of radiogenic 176Hf and 143Nd, and are used to constrain the systematics of the garnet chronometers at high temperature. The data constrain...

  12. Geochemistry of the thermal springs from San Antonio El Bravo zone, Chihuahua, Mexico; Geoquimica de manantiales termales de la zona de San Antonio El Bravo, Chihuahua, Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Tello Hinojosa, Enrique [Gerencia de Proyectos Geotermoelectricos de la Comision Federal de Electricidad, Morelia (Mexico)


    Isotopic and chemical analysis o water produced by 14 springs in the San Antonio El Bravo, Chihuahua, Mexico geothermal area, were carried out in order to establish the geochemical characteristics of the groundwater and to know their interaction with deeper geothermal fluids. We made two samplings of water and gases in 1984 and 1995. The chemical composition of waters produced by the springs in of sodium-bicarbonate-chloride type. It was found, according to the Na:K:Mg relative content, that most hot springs are located in the partial equilibrium zone, whereas the lowest temperature hot springs shift toward the groundwaters domain. The temperature estimated from gas geothermometry was 129 degrees celsius. The isotopic composition at Ojo Caliente and Infiernito springs presents enrichment in {delta}{sup 18}O, product rock-water interaction at high temperature. The Agua Roque spring is located in the line of meteoric waters. Analysis of metals was carried out too, the concentration of gold element is 0.09 mg/l in Ojo Caliente and Infiernito springs, whereas silver, aluminum and iron elements were not detected. The water quality of the springs for agricultural use, is classified between C2-S1, C3-S1, C3- S2, C4-S3 and C4-S4 types, that suggests that only the water from Agua Roque can be used for irrigation. The arsenic element was not detected but the concentration of the boron element is high for irrigation use (2.39 ppm). [Espanol] Los analisis quimicos e isotopicos de agua de 14 manantiales de la zona de San Antonio El Bravo. Chihuahua, Mexico, fueron realizados con el fin de conocer las caracteristicas geoquimicas del acuifero somero y su interaccion con fluidos geotermicos. Se realizaron 2 muestreos tanto de agua como de gases en 1984 y 1995. En ambos muestreos se encontro que la composicion quimica del agua de todos los manantiales es del tipo bicarbonatado-clorurado-sodico. De acuerdo con el contenido relativo de Na:K:Mg el agua de los manantiales mas calientes

  13. Geochemistry of the thermal springs from Piedras de Lumbre Zone, Chihuahua, Mexico; Geoquimica de los manantiales termales de la zona de Piedras de Lumbre, Chihuahua, Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Tello Hinojosa, Enrique [Gerencia de Proyectos Geotermoelectricos de la Comision Federal de Electricidad, Morelia (Mexico)


    Chemical analysis of water produced by 12 hot springs in the geothermal areas of Recubichi and Piedras de Lumbre, Chihuahua, Mexico were carried out in order to establish the geochemical characteristic of the groundwater and to know their interaction with deeper geothermal fluids. We made two sampling of water and gases in 1984 and 1995. The chemical composition of waters produced by the springs is of sulfate alkaline type. It was found, according to the Na:K:Mg relative content that most hot springs are located in the partial equilibrium zone, whereas the lowest temperature hot springs shift toward the groundwaters domain. The temperature estimated from gas geothermometry was 187 degrees celsius. It was found that the He has a deep origin, whereas the N{sub 2} is of atmospheric origin. Methane was not detected, suggesting that equilibria between gases and the liquid phase was reached at temperatures over 150 degrees celsius. The chemical compositions for the springs at Recubichi and Piedras de Lumbre zones are similar, so, it suggests that they have the same origin. The water quality of the springs for agricultural use, is classified between C2-S2 and C2-S3 types, that suggest that this water can be used for irrigation. The arsenic element was not detected and the concentration for the boron element is lower that 0.175 ppm. [Espanol] Los analisis quimicos de agua de 12 manantiales y 4 fumarolas de las zonas de Recubichi y Piedras de Lumbre, Chihuahua, Mexico fueron estudiados con el fin de conocer las caracteristicas geoquimicas del acuifero somero y su interaccion con fluidos geotermicos. Se realizaron 2 muestreos tanto de agua como de gases en 1984 y 1995. En ambos muestreos se encontro que la composicioon quimica del agua de todos los manantiales es del tipo sulfatado-sodico. De acuerdo con el contenido relativo de Na:K:Mg el agua de los manantiales mas calientes (93 grados celsius), se ubica en la zona de equilibrio parcial, mientras que en los de menor

  14. Reservoir geochemistry; Geoquimica de reservatorios

    Energy Technology Data Exchange (ETDEWEB)

    Lopes, Joelma Pimentel; Rangel, Mario Duncan; Morais, Erica Tavares de [PETROBRAS, Rio de Janeiro, RJ (Brazil). Centro de Pesquisas (CENPES)], Emails:,,; Aguiar, Helen G.M. de [Fundacao GORCEIX, Ouro Preto, MG (Brazil)], E-mail:


    Reservoir Geochemistry has many important practical applications during petroleum exploration, appraisal and development of oil fields. The most important uses are related to providing or disproving connectivity between reservoirs of a particular well or horizon. During exploration, reservoir geochemistry can indicate the direction of oil filling, suggesting the most appropriate places for drilling new wells. During production, studies of variations in composition with time and determination of proportions of commingled production from multiple zones, may also be carried out. The chemical constituents of petroleum in natural reservoirs frequently show measurable compositional variations, laterally and vertically. Due to the physical and chemical nature of petroleum changes with increasing maturity (or contribution of a second source during the filling process), lateral and vertical compositional variations exist in petroleum columns as reservoir filling is complete. Compositional variation can also be introduced by biodegradation or water washing. Once the reservoir is filled, density driven mixing and molecular diffusion tend to eliminate inherited compositional variations in an attempt to establish mechanical and chemical equilibrium in the petroleum column (England, 1990). Based on organic geochemical analysis it is possible to define these compositional variations among reservoirs, and use these data for developing of petroleum fields and for reservoir appraisal. Reservoir geochemistry offers rapid and low cost evaluation tools to aid in understanding development and production problems. Moreover, the applied methodology is relatively simple and gives reliable results, and can be performed routinely in any good geochemical laboratory at a relatively low cost. (author)

  15. Isotopic characterization of metabasites and amphibolites of the Acungui and Setuva Groups at the southern portion of de Ribeira Belt; Caracterizacao isotopica de metabasitos e anfibolitos dos Grupos Acungui e Setuva na porcao sul da Faixa Ribeira

    Energy Technology Data Exchange (ETDEWEB)

    Oliveira, Marcos Aurelio Farias de; Daitx, Elias Carneiro [Universidade Estadual Paulista (UNESP), Rio Claro, SP (Brazil). Dept. de Petrologia e Metalogenia; Maniesi, Vanderlei [Universidade Federal de Rondonia (UNIR), Porto Velho (Brazil); Teixeira, Wilson [Sao Paulo Univ., SP (Brazil). Inst. de Geociencias. Centro de Pesquisas Geocronologicas


    Pb, Rb, Sr, Sm and Nd isotope analyses were carried out on amphibolitic rocks from Campo Largo (PR), Rio Branco do Sul (PR) and Adrianopolis (PR) and for the metabasite from Adrianopolis and Apiai (SP), all belonging to the Acungui and Setuva Groups, southern portion of the Ribeira Belt. These occurrences were chosen because each exhibits geochemical data indicative of a mantle source, having different signatures. Geochronologic determinations are available only for the Apiai metagabro with Neoproterozoic ages of 617 +- 4 Ma (U/Pb in zircon) and 839 +- 85 Ma (Rb/Sr, whole rock). Age determinations by Sm/Nd mineral isochron using whole rock, plagioclase and pyroxene yield values of 885 +- 53 Ma for the Apiai metagabro and 820 +- 84 Ma for the Adrianopolis metabasite. These results agree within error with the Rb/Sr isochron of 839 +- 85 Ma may possibly be interpreted as the time of extraction of the magma from the mantle, as suggested by positive epsilon{sub Nd(850)} values (+2,76) from an Adrianopolis sample. An epsilon{sub Nd} values versus 87 Sr/86 Sr diagram shows that each studied occurrence plots in a different position, following approximately the mantle array trend, the most primitive being the metabasite of Adrianopolis, near the MORB field, and the most enriched being the amphibolite from the same region, near the enriched mantle and or crustal contamination field. The distinct difference in isotopic signatures between the amphibolite and metabasite suggest derivation from different mantle sources, as supported by available geochemical data. Nevertheless, some of the samples show isotopic evidence of the action of metamorphism, crustal contamination and weathering. (author)

  16. Heavy metals in geochemical sediment fractions of the border region between Baja California, Mexico, and California, USA; Metales pesados en fracciones geoquimicas de sedimentos de la region fronteriza de Baja California, Mexico, y California, EUA

    Energy Technology Data Exchange (ETDEWEB)

    Villaescusa-Celaya, Julio A; Gutierrez-Galindo, Efrain A; Flores-Munoz, Gilberto [Instituto de Investigaciones Oceanologicas, Universidad Autonoma de Baja California, Ensenada, B.C., (Mexico)


    water in the coastal zone are being transported outside the region. [Spanish] En este estudio se evalua la concentracion de los metales pesados Cu, Zn, Ni, Cr, Pb, Cd, Ag, Mn y Fe en las diferentes fracciones geoquimicas del sedimento, como una medida para conocer el impacto de las descargas de agua residuales sobre los sedimentos costeros de la region. Para este proposito, durante un crucero oceanografico realizado en abril de 1992 (ECOBAC IV), se recolectaron 20 muestras de sedimento superficial en la plataforma costera de la region fronteriza de Baja California (Mexico) y California (EUA). Las muestras de sedimento se sometieron a un procedimiento de extraccion secuencial, disenado para obtener las fracciones geoquimicas operacionalmente definidas como: intercambiable (F1), carbonatos (F2), oxihidroxidos de Fe y Mn (F3), materia organica/sulfuros (F4) y residual o litogenica (F5). La especiacion operacional de los metales indica que las principales fases que acumulan metales en el sedimento son la matriz detrital o litogenica, los oxihidroxidos de Fe y Mn y la materia organica/sulfuros, en este orden. La distribucion espacial de los metales pesados en la fase reactiva (definida como la suma de F1-F4) presento, en general, una tendencia a aumentar en concentracion en sedimentos alejados de la costa. Los metales pesados en la fase reactiva aparentemente son controlados por la concentracion de hierro reactivo en los sedimentos, con excepcion del Pb, el Cd y la Ag. Esto sugiere que estos ultimos elementos son controlados por otros procesos, tales como el material particulado de origen biogenico. En contraste, la distribucion espacial de los metales pesados en la fase detrital presento un comportamiento inverso, esto es, las mayores concentraciones de metales se encuentran cercanas a la costa frente a la planta de tratamiento de aguas residuales de Punta Bandera, Baja California. Las concentraciones promedio de metales totales (suma de F1-F5) fueron de 7.6, 40, 21, 68

  17. Chemical and isotopic characteristics of rainwater at Los Humeros geothermal field, Puebla, Mexico and surrounding areas; Caracteristicas quimicas e isotopicas del agua de lluvia en el campo geotermico de Los Humeros, Puebla, Mexico y zonas aledanas

    Energy Technology Data Exchange (ETDEWEB)

    Tovar Aguado, Rigoberto; Cruz Grajales, Irma [Comision Federal de Electricidad, Los Humeros, Puebla (Mexico)


    A study of chemical and isotopic characteristics of rainwater at Los Humeros geothermal field was undertaken for the second consecutive year. Samples were collected in seven stations-two inside the field and five on the periphery. In 1996, a total of 99 samples were collected and 104 were collected in 1997. Of these, 19-18.26% of the total-had a negative alkalinity. The Atempan (No.5) and Campamento (No.1) stations showed the highest number of anomalous samples (31.25 and 27.8%, respectively). Anomalous samples in Perote station were not observed a result that we attribute to the predominant wind direction. The results for the Campamento station are attributed to the thermal inversion phenomena occurring when the samples with negative alkalinity were obtained. Concentrations of cations in some samples were relatively high, with the maximum concentration of calcium in the Los Humeros station (79.7 ppm) . Other significantly high values were found in the Texcal station (34.8 ppm) and Perote (33.8 ppm) due to the presence of dust particles scattered in the air and because of the lack of pavement where the sampling stations are located. Another factor affecting these figures could be the presence of block and lime factories in the neighborhood. Although measured concentrations may seem high, reports exist with similar concentrations in nongeothermal areas. Oxygen-18 and deuterium contents were determined for each stations, mixing anomalous samples. The results show that the most enriched samples correspond to the San Juan Xiutetelco, Puebla (No. 6) station and the minimum to the Perote Veracruz (No. 7) station. The concentration of SO{sub 4} has marine and industrial origins, with a contribution of the first source ranging between 10 and 25 percent. [Spanish] En el campo geotermico de Los Humeros, Puebla se realizo, por segundo ano consecutivo, la caracterizacion quimica e isotopica de agua de lluvia en muestras colectadas en siete estaciones, dos localizadas dentro

  18. Sm-Nd isotope dating of hydrothermal calcites from the Xikuangshan antimony deposit, Central Hunan

    Institute of Scientific and Technical Information of China (English)


    The research on Samarium-Neodymium isotope systematics of hydrothermal calcites from the Xikuangshan antimony deposit, Central Hunan, places precise timing constraints on the Sb mineralization in this area. It is revealed that the Xikuangshan deposit formed during the late Jurassic-early Cretaceous Period, the early- and late- stage mineralization took place at (155.5 ± 1.1) Ma and (124.1 ± 3.7) Ma, respectively. The accurate age determination of mineralization is very crucial for revealing the super-enrichment mechanism of the element Sb at the Xikuangshan mine, and lays some foundations for the further understandings of its ore genesis and mineralization mechanism.

  19. Sm-Nd-Pu timepieces in the Angra dos Reis meteorite (United States)

    Lugmair, G. W.; Marti, K.


    Isotope ratios and age estimations are presented for the ultramafic pyroxenite Angra dos Reis meteorite. A pyroxene-phosphate internal isochron age of 4.55 plus or minus 0.04 eons was obtained, in agreement with reported Pb-Pb ages. It is suggested that Sm-146 decay led to an increase in the ratio of Nd-142 to Nd-144 in pyroxene, which is greater than the ratio of the Nd isotopes in phosphates. The effect of Pu-244 on the fission xenon components in pyroxene and phosphate is examined. The ratios of Pu-244 to Nd, U-238, and Th-232 are compared for pyroxene and phosphate separates. The exposure age of the meteorite, as obtained by the Kr-81 to Kr-83 method, was found to be 55.5 plus or minus 1.2 million years.

  20. Effect of alcohol and formaldehyde on the ä13C and ä15N isotopic composition of Plagioscion squamosissimus and Hypophthalmus edentatus (Pisces, Osteichthyes = Efeito do alcool e formol sobre a composicao isotopica de ƒÂ13C e de ƒÂ15N em Plagioscion squamosissimus e Hypophthalmus edentatus (Pisces, Osteichthyes

    Directory of Open Access Journals (Sweden)

    Gislaine Iachstel Manetta


    Full Text Available The present study investigates the ƒÂ13C and ƒÂ15N isotopic composition in frozen samples (control, samples in alcohol and in formaldehyde of Plagioscion squamosissimus and Hypophthalmus edentatus. From each individual we extracted a strip of muscle from the region above the lateral line, in the dorsal fin base, that was divided into three equal parts, each one was submitted to one type of treatment: freeze . control group (-15oC, conservation in alcohol 70%and fixation in formaldehyde 4%. Samples were kept under those treatments for 30 days, washed and submerged in distilled water for 4 hours. Afterwards, they were dried up in air oven at 60oC for 48 hours and macerated until the obtaining of a fine powder. A significant difference was found in isotopic values of carbon and nitrogen, between the control and the samples in alcohol and formaldehyde, except for ƒÂ13C from the H. edentatus samples in formaldehyde. The carbon isotopic values of samples in alcohol were mostly enriched compared to control, whereas the samples in formaldehyde presented depleted values in relation to the control. The nitrogen isotopic values for both samples preserved in alcohol and formaldehyde were enriched when compared to the values of frozen samples, independently of used preservatives. Therefore, the isotopic correction should be accomplished according to the isotope and preservative employed for species of freshwater fish.O presente estudo investiga a composicao isotopica de ƒÂ13C e ƒÂ15N entre as amostras congeladas (controle, em alcool e em formol de Plagioscion squamosissimus e Hypophthalmus edentatus. De cada individuo foi extraida uma faixa de musculo localizada na regiao acima da linha lateral, na base da nadadeira dorsal, a qual foi subdividida em tres partes iguais, sendo cada uma delas submetida a um tipo de tratamento: congelamento - grupo control (-15oC, conservacao em alcool 70% e fixacao em formol 4%. As amostras foram mantidas nos

  1. Geochemistry and Nd-Sr isotopic signatures of the Pensamiento Granitoid Complex, Rondonian-San Ignacio Province, eastern precambrian shield of Bolivia: petrogenetic constraints for a mesoproterozoic magmatic arc setting;Geoquimica e assinaturas Nd-Sr do Complexo Granitoide Pensamiento, provincia Rondoniana-San Ignacio, pre-cambriano de Bolivia Oriental: caracterizacao petrogenetica de um arco magmatico no mesoproterozoico

    Energy Technology Data Exchange (ETDEWEB)

    Matos, Ramiro, E-mail: rmatoss@igc.usp.b [Universidad Mayor de San Andre (UMSA), La Paz (Bolivia, Plurinational State of). Inst. de Investigaciones Geologicas y del Medio Ambiente; Teixeira, Wilson; Bettencourt, Jorge Silva, E-mail: wteixeir@usp.b, E-mail: jsbetten@usp.b [Universidade de Sao Paulo (IGC/USP), SP (Brazil). Inst. de Geociencias. Dept. de Mineralogia e Geotectonica; Geraldes, Mauro Cesar, E-mail: geraldes@uerj.b [Universidade do Estado do Rio de Janeiro (FG/UERJ), RJ (Brazil). Faculdade de Geologia


    The Pensamiento Granitoid Complex (PGC), located in the northern part of the eastern Precambrian shield of Bolivia, is tectonically assigned to the Rondonian-San Ignacio Province (1.55 - 1.30 Ga) of the Amazonian Craton that is made up by Archean and Proterozoic provinces. The Proterozoic ones result from accretionary orogens that become successively younger south westwards, such as the Rondonian/San Ignacio (1.37 - 1.32 Ga) and the Sunsas orogenies (1.20 - 1.00 Ga). The PGC crops out mainly on the 'Paragua craton' bounded to the south by the Sunsas belt, and composed of granites and subvolcanic terms, and subordinately of syenites, granodiorites, tonalites, trondhjemites and diorites as orogenic representatives of the Rondonian/San Ignacio Orogeny, intrusive into the Lomas Maneches (ca. 1.68 Ga) and Chiquitania (ca. 1.7 Ga) complexes. Thirteen whole rock chemical analyses for major, trace and REE elements were performed for the La Junta, San Martin, Diamantina, Porvernir, San Cristobal, Piso Firme plutons of the PGC. The negative trends of MgO, Al{sub 2}O{sub 3} and CaO contents with increasing SiO{sub 2} suggest that fractional crystallization played an important role in the petrogenesis of the investigated rocks. The data also indicate a mainly peraluminous, sub-alkaline to high-K calc-alkaline composition, and fractionated LREE/HREE patterns are consistent with a magmatic arc character for these plutons. SHRIMP U-Pb zircon ages of the La Junta and San Martin syn- to late-kinematic plutons are 1347 {+-} 21 Ma and 1373 {+-} 20 Ma respectively, and the Sm-Nd T{sub DM} model ages are between 1.9 to 2.0 Ga, while {epsilon}{sub Nd(1330)} values range from +1.8 to -4.3, respectively. In addition, the late- to post-kinematic Diamantina pluton yields SHRIMP U-Pb zircon age of 1340 {+-} 20 Ma, and variable Sm-Nd T{sub DM} model ages (1.6 to 1.9 Ga) and {epsilon}{sub Nd(1330)} values (+0.4 to -1.2) that are comparable with previous results found for other coeval

  2. Controversial Pb-Pb and Sm-Nd isotope results in the early Archean Isua (West Greenland) oxide iron formation

    DEFF Research Database (Denmark)

    Frei, Robert; Rosing, Minik; Stecher, Ole


    as crystal overgrowths in the magnetite-rich bands. The timing of the hydrothermal event during which apatite was deposited within the BIF remains uncertain, but a TCHUR model age of 1.85 Ga from the apatite-dominated HCl leachate may point to a close genetic relationship with local Proterozoic metamorphism...

  3. Rb-Sr and Sm-Nd Ages of Zagami DML and SR Isotopic Heterogeneity in Zagami (United States)

    Nyquist, L.aurenceE.; Shih, C.-Y.; Reese, Y. D.


    Zagami contains lithologic heterogeneity suggesting that it did not form in a homogeneous, thick lava flow [1]. We have previously investigated the Sr and Nd isotopic systematics of Coarse-Grained (CG) and Fine-Grained (FG) lithologies described by [2]. Both appear to belong to Normal Zagami (NZ) [1,3], but their initial Sr-isotopic compositions differ [4,5]. Here we report new analyses of the Dark Mottled Lithology (DML, [3]) that show its age and initial Sr and Nd isotopic compositions to be identical within error limits with those of CG, but Sr initial isotopic compositions differ from those of FG.

  4. The geodynamic evolution of the eastern Sierras Pampeanas based on geochemical, Sm-Nd, Pb-Pb and SHRIMP data

    DEFF Research Database (Denmark)

    Drobe, M; Lopez de Luchi, M; Steenken, A;


    Whole-rock geochemical analyses using major and trace elements in combination with the Sm–Nd and Pb–Pb isotope systems, together with SHRIMP age dating on metasedimentary rocks from the Sierras de Chepes, the Sierras de Co´rdoba, the Sierra Norte and the San Luis Formation in the Sierra de San Luis...

  5. Behavior patterns of chemical and isotopic species (2006-2007) in the Los Azufres, Mich., geothermal field, as a response to reinjection; Patrones de comportamiento de especies quimicas e isotopicas (2006-2007) en el campo geotermico de Los Azufres, Mich., en respuesta a la reinyeccion

    Energy Technology Data Exchange (ETDEWEB)

    Barragan R, Rosa Maria; Arellano G, Victor Manuel; Martinez E, Ignacio; Aragon A, Alfonso [Instituto de Investigaciones Electricas, Cuernavaca, Morelos (Mexico)]. E-mail:; Reyes D, Lisette; Gonzalez, Rubi [Comision Federal de Electricidad, Gerencia de Proyectos Geotermoelectricos, Residencia de Los Azufres, Morelia, Michoacan (Mexico)


    quimicos e isotopicos ({delta}18 O y {delta}D) de fluidos de pozos del campo geotermico de Los Azufres, Mich., obtenidos en 2006 y 2007, para investigar los cambios ocurridos en sus patrones de comportamiento y su relacion con el proceso de reinyeccion de fluidos al yacimiento. El analisis de los datos comprendio las estimaciones de cloruros en las descargas totales, temperaturas de yacimiento, exceso de vapor en los fluidos de alimentacion, las concentraciones de CO{sub 2} en las descargas totales y en la fase liquida del yacimiento y las saturaciones de liquido en la formacion. Con los resultados se elaboraron mapas de isovalores de los parametros mencionados correspondientes a 2006 y 2007 para investigar su evolucion con respecto a los mapas obtenidos en 2005, asi como su relacion con las historias de reinyeccion. Se correlacionaron las composiciones isotopicas de los fluidos incluyendo los de reinyeccion para estimar efectos de mezcla de fluidos. Los resultados indican que las variables estudiadas responden a las tasas de reinyeccion en el campo. Las relaciones {delta}D vs {delta}18 O indican que un buen numero de pozos del campo producen diferentes proporciones de retornos de reinyeccion; en la zona norte los pozos AZ-65D, AZ-13, AZ-32, AZ-9A, AZ-9AD, AZ-28A, AZ-69D y AZ-44 producen una mayor proporcion mientras que los pozos AZ-5, AZ-28 y AZ-19 entre otros, producen una menor proporcion. En la zona sur los pozos AZ-2A, AZ-16AD, AZ-46 y AZ-33 producen relativamente altas proporciones de retornos de reinyeccion mientras que los pozos AZ-34, AZ-36 y AZ-37 producen menores proporciones. La distribucion de saturaciones de liquido hallada en 2007 muestra que las areas de maxima saturacion han disminuido con respecto a las distribuciones de este parametro en 2005 y 2006. En 2007 las saturaciones maximas de liquido se localizaron alrededor de los pozos AZ-22 y AZ-23 (zona sur) y AZ-28, AZ-32, AZ-45 y AZ-48 (zona norte), mientras que las saturaciones minimas se localizaron en

  6. De la geoquimica al paisaje: composicion elemental de los suelos

    NARCIS (Netherlands)

    Martinez-Cortizas, A.; Costa-Casais, M.; Kaal, J.; Ferro-Vazquez, C.; Pontevedra-Pombal, X.; Viveen, W.


    El objeto de este libro es el estudio del arte rupestre en la Edad de Bronce hasta la Edad del Hierro en Campo Lameiro (Pontevedra, Galicia), en el que se ha combinado la metodología arqueológica, histórica, etnográfica y paleoambitental, para completar el contexto arqueológico de los petroglifos añ

  7. De la geoquimica al paisaje: composicion elemental de los suelos

    NARCIS (Netherlands)

    Martinez-Cortizas, A.; Costa-Casais, M.; Kaal, J.; Ferro-Vazquez, C.; Pontevedra-Pombal, X.; Viveen, W.


    El objeto de este libro es el estudio del arte rupestre en la Edad de Bronce hasta la Edad del Hierro en Campo Lameiro (Pontevedra, Galicia), en el que se ha combinado la metodología arqueológica, histórica, etnográfica y paleoambitental, para completar el contexto arqueológico de los petroglifos

  8. Insights into the patterns and locations of erosion in the Himalaya — A combined fission-track and in situ Sm Nd isotopic study of detrital apatite (United States)

    Foster, G. L.; Carter, A.


    Understanding the role that climate, erosion and tectonics play in determining the mean relief, elevation and general form of a mountain range over time has become the focus of much recent research in the field of tectonic geomorphology. A crucial constraint in these studies is the long-term exhumation rate, which is increasingly being examined using detrital minerals from the sedimentary rock record that represent the eroded remnants of the orogen. A classic field area of such studies is the Himalayan orogen — the Earth's largest mountain range. We describe here a novel approach that uses the in situ analysis of Nd isotopes by laser ablation multicollector inductively coupled plasma mass spectrometry of fission-track dated apatite grains to unambiguously tie them to their source regions. We demonstrate the capability of this new approach on several modern and Holocene river sand samples from the Himalayan orogen and determine, because of the large isotopic differences in the constituent tectonostratigraphic units, both the location and magnitude of long-term erosion. In agreement with previous studies we are able to show that in the Central and Eastern Himalaya long-term denudation is focussed within the High Himalayan Crystalline Series (HHCS) at average rates of ˜ 2 mm/yr. Average long-term rates are similar in the Western Himalaya sampled by the Indus River and largely reflect erosional denudation of the Western Indian Himalaya and the Western Syntaxis (the Nanga Parbat Haramosh Massif and South Karakoram Metamorphic Complex). Notably, the Asian continent supplies significantly more apatites to the mouth of the Indus than they do to the Bengal delta. The ability to reconstruct the patterns of long-term erosion in the Himalaya using detrital apatites from a few samples collected from major transverse drainages provides confidence in the utility of this approach to examine the locations and magnitude of long-term erosion in the past.

  9. Petrography, geochemistry and Sm-Nd isotopes of the granites from eastern of the Tapajós Domain, Pará state

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    Flávio Robson Dias Semblano

    Full Text Available ABSTRACT: The Tapajós Domain, located in the southern portion of the Amazonian Craton, is a tectonic domain of the Tapajós-Parima Province, a Paleoproterozoic orogenic belt adjacent to a reworked Archean crust, the Central Amazonian Province. This domain has been interpreted as the product of an assemblage of successive magmatic arcs followed by post-orogenic A-type magmatism formed ca. 1880 Ma-old granites of the Maloquinha Intrusive Suite. The study presented here was carried out in four granitic bodies of this suite (Igarapé Tabuleiro, Dalpaiz, Mamoal and Serra Alta from the eastern part of the Tapajós Domain, as well as an I-type granite (Igarapé Salustiano related to the Parauari Intrusive Suite. The A-type granites are syenogranites and monzogranites, and alkali feldspar granites and quartz syenites occur subordinately. These rocks are ferroan, alkalic-calcic to alkalic and dominantly peraluminous, with negative anomalies of Ba, Sr, P and Ti and high rare earth elements (REE contents with pronounced negative Eu anomaly. This set of features is typical of A-type granites. The Igarapé Salustiano granite encompasses monzogranites and quartz monzonites, which are magnesian, calcic to calc-alkalic, high-K and mainly metaluminous, with high Ba and Sr contents and depleted pattern in high field strength elements (HFSE and heavy rare earth elements (HREE, characteristic of I-type granites. The source of magma of these A-type granites is similar to post-collisional granites, while the I-type granite keeps syn-collisional signature. Most of the studied granites have εNd (-3.85 to -0.76 and Nd TDM model ages (2.22 to 2.46 Ga compatible with the Paleoproterozoic crust of the Tapajós Domain. We conclude that the Archean crust source (εNd of -5.01 and Nd TDM of 2.6 Ga was local for these A-type granites.

  10. Paleoproterozoic magmatism across the Archean-Proterozoic boundary in central Fennoscandia: Geochronology, geochemistry and isotopic data (Sm-Nd, Lu-Hf, O) (United States)

    Lahtinen, Raimo; Huhma, Hannu; Lahaye, Yann; Lode, Stefanie; Heinonen, Suvi; Sayab, Mohammad; Whitehouse, Martin J.


    The central Fennoscandia is characterized by the Archean-Proterozoic (AP) boundary and the Central Finland Granitoid Complex (CFGC), a roundish area of approximately 40,000 km2 surrounded by supracrustal belts. Deep seismic reflection profile FIRE 3A runs across these units, and we have re-interpreted the profile and crustal evolution along the profile using 1.92-1.85 Ga plutonic rocks as lithospheric probes. The surface part of the profile has been divided into five subareas: Archean continent (AC) in the east, AP, CFGC, boundary zone (BZ) and the Bothnian Belt (BB) in the west. There are 12 key samples from which zircons were studied for inclusions and analyzed (core-rim) by ion probe for U-Pb dating and oxygen isotopes, followed by analyzes for Lu-Hf by LA-MC-ICP-MS. The AC plutonic rocks (1.87-1.85 Ga) form a bimodal suite, where the proposed mantle source for the mafic rocks is 2.1-2.0 Ga metasomatized lower part of the Archean subcontinental lithospheric mantle (SCLM) and the source for the felsic melts is related plume-derived underplated mafic material in the lower crust. Variable degrees of contamination of the Archean lower crust have produced "subduction-like" Nb-Ta anomalies in spidergrams and negative εNd (T) values in the mafic-intermediate rocks. The felsic AC granitoids originate from a low degree melting of eclogitic or garnet-bearing amphibolites with titanite ± rutile partly prevailing in the residue (Nb-Ta fractionation) followed by variable degree of assimilation/melting of the Archean lower crust. The AP plutonic rocks (ca. 1.88 Ga) can be divided into I-type and A-type granitoids (AP/A), where the latter follow the sediment assimilation trend in ASI diagram, have high δ18O values (up to 8‰) in zircons and exhibit negative Ba anomalies (Rb-Ba-Th in spidergram), as found in sedimentary rocks. A mixing/assimilation of enriched mantle-derived melts with melts from already migmatized sedimentary rocks ± amphibolites is proposed. The CFGC is characterized by both I-type and A-type (CFGC/A) intermediate and felsic granitoids. The I-type granitoids are divided into two groups at ≥ 1885 Ma and ≤ 1882 Ma, where the latter overlap in age with the CFGC/A granitoids. Both I-type CFGC and CFGC/A granitoids are interpreted to have formed from mixing of Paleoproterozoic SCLM-derived melts with crustal melts from hydrous and dry intermediate-felsic igneous sources, respectively. The geochemistry, dominantly δ18O values below 6.5‰ in zircons and TDM (2.11-2.42 Ga) of the CFGC granitoids favor the occurrence of older crust (ca. 2.1-2.0 Ga) in their genesis. The BZ granitoids are similar in age but more juvenile with TDM ages between 1.94 Ga and 2.16 Ga. The 1.92 Ga granodiorite in the BB is correlated with juvenile gneissic tonalites and granodiorites found from the AP boundary. We suggest that the present high-velocity lower crust under the CFGC is composed of melt-extracted granulites (crustal source age ≥ 2.0 Ga) and mafic cumulates which both formed during 1.90-1.88 Ga arc magmatism. The ≤ 1.88 Ga stage represents the end of compression/transpression and is followed by 1.87-1.86 Ga buckling, forming the Bothnian Oroclines.

  11. Dating and source determination of volcanic rocks from Khunik area (South of Birjand, South Khorasan using Rb-Sr and Sm-Nd isotopes

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    Somayeh Samiee


    Full Text Available The Khunik area is located in the south of Birjand, Khorasan province, in the eastern margin of Lut block. Tertiary volcanic rocks have andesite to trachy-andesite composition. Dating analyzing by Rb-Sr method on plagioclase and hornblende as well as whole-rock isochron method was performed on pyroxene-hornblende andesite rock unit. On this basis the emplacement age is Upper Paleocene (58±11 Ma. These rocks have initial 87Sr/86Sr and εNd 0.7046-0.7049 and 2.16-3.12, respectively. According to isotopic data, volcanic rocks originated from depleted mantle and have the least crust contamination while it was fractionated. Geochemically, Khunik volcanic rocks have features typical of calk-alkaline to shoshonite and are metaluminous. Enrichment in LILEs and typical negative anomalies of Nb and Ti are evidences that the volcanic rocks formed in a subduction zone and active continental margin. Modeling suggests that these rocks were derived dominantly from 1–5% partial melting of a mainly spinel garnet lherzolite mantle source that is metasomatized by slab-derived fluid.

  12. Geology, mineralization, Rb-Sr & Sm-Nd geochemistry, and U–Pb zircon geochronology of Kalateh Ahani Cretaceous intrusive rocks, southeast Gonabad

    Directory of Open Access Journals (Sweden)

    Mohammad Hassan Karimpour


    Full Text Available Kalateh Ahani is located 27 km southeast of Gonabad within the Khorasan Razavi province. The area is part of Lut Block. Sub-volcanic monzonitic rocks intruded regional metamorphosed Shemshak Formation (Jurassic age. Magnetic susceptibility of less altered monzonitic rocks is 0.6%., As, Pb and Zn > 1%, Au up to 150 ppb and Sn = 133 ppm. The Sn content of vein in the northern part of Kalateh Ahani (Rud Gaz is > 1%. Based on mineralization, alteration and geochemistry, it seems that Sn mineralization is associated with the Cretaceous monzonitic rocks. Zircon U–Pb dating indicates that the age of the monzonitic rocks associated with mineralization is 109 Ma (Lower Cretaceous. Based on (87Sr/86Sri = 0.71089-0.710647 and (143Nd/144Ndi = 0.512113-0.51227 of the monzonitic rocks, the magma for these rocks were originated from the continental crust. This research has opened new window with respect to Sn-Cu mineralization and exploration within the Lut Block which is associated with Cretaceous granitoid rocks (reduced type, ilmenite series originated from the continental crust.

  13. Rb-Sr and Sm-Nd geochronology of the Cana Brava layered mafic-ultramafic intrusion, Brazil, and considerations regarding its tectonic evolution

    Energy Technology Data Exchange (ETDEWEB)

    Correia, Ciro Teixeira; Girardi, Vicente A.V.; Tassinari, Colombo C.G. [Sao Paulo Univ., SP (Brazil). Inst. de Geociencias; Jost, Hardy [Brasilia Univ., DF (Brazil). Dept. de Geociencias


    The Cana Brava complex is an anorogenic stratiform complex, whose layers dip from 30{sup 0} to 50{sup 0} NW. The massif is made up of five units composed of layers containing several associations of cumulus phases and variable amounts of inter-cumulus minerals. Transition between units are characterized by abrupt changes in the composition of these phases. From base to top, the sequence consists of amphibolites (PICB1), overlain by serpentinites (PICB2), metawebsterites (PICB3), and metagabbros (PICB4 and PICB5). This sequence was originally formed by microgabbros, peridotites, websterites, and gabbros. Isotopic data indicate that the parental magma of the Cana Brava complex evolved as follows: mantle derivation at about 2.5 Ga and subsequent retention at subcrustal levels; intrusion within the Palmeiropolis volcano-sedimentary sequence and igneous crystallization at about 2.0 Ga; (c) Metamorphism and ductile-ruptile deformation under compression at about 1.3 Ga; and (d) Further metamorphic reequilibration during the Brasiliano Cycle at about 0.77 Ga. (Author) 27 refs., 7 figs., 2 tabs.

  14. Evaluating crustal contributions to enriched shergottites from the petrology, trace elements, and Rb-Sr and Sm-Nd isotope systematics of Northwest Africa 856 (United States)

    Ferdous, J.; Brandon, A. D.; Peslier, A. H.; Pirotte, Z.


    The origin of the incompatible trace element (ITE) characteristics of enriched shergottites has been critical for examining two contradicting scenarios to explain how these Martian meteorites form. The first scenario is that it reflects ITE enrichment in an early-formed mantle reservoir whereas the second scenario attributes it to assimilation of ancient Martian crust (∼4-4.5 Ga) by ITE-depleted magmas. Strongly differentiated shergottite magmas may yield added constraints for determining which scenario can best explain this signature in enriched shergottites. The meteorite Northwest Africa (NWA) 856 is a basaltic shergottite that, unlike many enriched shergottites, lacks olivine and has undergone extensive differentiation from more primitive parent magma. In similarity to other basaltic shergottites, NWA 856 is comprised primarily of compositionally zoned clinopyroxenes (45% pigeonite and 23% augite), maskelynite (23%) and accessory minerals such as ulvöspinel, merrillite, Cl-apatite, ilmenite, pyrrhotite, baddeleyite and silica polymorph. The CI-chondrite normalized rare earth element (REE) abundance patterns for its maskelynite, phosphates, and its whole rock are flat with corresponding light-REE depletions in clinopyroxenes. The 87Rb-87Sr and 147Sm-143Nd internal isochron ages are 162 ± 14 (all errors are ±2σ) Ma and 162.7 ± 5.5 Ma, respectively, with an initial εNdI = -6.6 ± 0.2. The Rb-Sr isotope systematics are affected by terrestrial alteration resulting in larger scatter and a less precise internal isochron age. The whole rock composition is used in MELTS simulations to model equilibrium and fractional crystallization sequences to compare with the crystallization sequence from textural observations and to the mineral compositions. These models constrain the depth of initial crystallization to a pressure range of 0.4-0.5 GPa (equivalent to 34-42 km) in anhydrous conditions at the Fayalite-Magnetite-Quartz buffer, and consistently reproduce the observed mineralogy throughout the sequence with progressive crystallization. The Ti/Al ratios in the clinopyroxenes are consistent with initial crystallization occurring at these depths followed by polybaric crystallization as the parent magma ascended to the surface. The REE abundances in the clinopyroxenes and maskelynite are consistent with progressive crystallization in a closed system. The new results for NWA 856 are combined with other shergottite data and are compared to mixing and assimilation and fractional crystallization (AFC) models using depleted shergottite magmas and ancient Martian crust as end-members. The models indicate that the range of REE abundances and ratios, when taken in isolation, can be successfully explained for all shergottites by crustal contamination. However, no successful crustal contamination model can explain the restricted εNdI of -6.8 ± 0.2 over the wide range of Mg# (0.65-0.25), and corresponding trace element variations from enriched shergottites to depleted shergottites. The findings indicate that the origin of the long-term ITE-enriched signature in enriched shergottites and the geochemical variability seen in shergottites is not a result of crustal contamination but instead reflects ancient mantle heterogeneity.

  15. U Pb zircon (TIMS and SIMS) and Sm Nd whole-rock geochronology of the Gour Oumelalen granulitic basement, Hoggar massif, Tuareg shield, Algeria (United States)

    Peucat, Jean Jacques; Drareni, Amar; Latouche, Louis; Deloule, Etienne; Vidal, Philippe


    Two major granulitic units are recognized in the Gour Oumelalen area. One of the units is composed partially of Archean gneisses (Red Gneiss complex) with U-Pb zircon SIMS and TIMS ages of approximately 2.7 Ga. Although they were formed from 3.0- to 3.2-Ga-old precursors, as indicated by Nd model ages, we find no evidence of any older history (≈3.5 Ga) as suggested by previous Pb-Pb ages. The other formation (Gour Oumelalen supergroup) is a metasedimentary sequence at least partly of Paleoproterozoic age, as indicated by zircon dates of a metavolcanic rock at approximately 2.2 Ga. A later magmatic event is recorded at approximately 1.9 Ga in both units and related to coeval granulite-facies metamorphism that affected both units. Nd model ages at approximately 2.0 Ga suggest an accretion of juvenile crust formation at that time. The existence of T DM Nd model ages intermediate between 2.5 and 2.9 Ga could result from the mixing of 3.2 and 2.0-Ga-old material or may reflect separate events.

  16. Relaciones isotópicas Sm/Nd en rocas graníticas y miloníticas de Sierras Pampeanas del noroeste Argentino

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    Kawashita, K.


    Full Text Available The Velasco, Copacabana and Paimán Ranges in Sierras Pampeanas, are constituted mainly by paleozoic plutonic bodies of the Famatinian cycle (Huaco, Antinaco and Paimán and for mylonitic rocks (TIPA Shear Zone, originated as a consequence of dynamic events happening during the Upper Ordovician-Devonian. The last magmatic event of the area would probably have of devonian age (Granite San Blas. Model-ages of two stages were calculated based on 147Sm/144Nd relationships; the obtained values are closely grouped at around 1594 Ma. and the more plausible interpretation seems to be a reworking of an Early Proterozoic protolith.Las sierras de Velasco, Copacabana y Paimán, en el ambiente de Sierras Pampeanas, están constituidas principalmente por cuerpos plutónicos del Paleozoico inferior, relacionados con el ciclo Famatiniano (Granitos Huaco, Antinaco y Paimán y por rocas miloníticas (Faja Milonítica TiPA, originadas a partir de estos protolitos como consecuencia de eventos dinámicos acaecidos durante el Ordovícico superior-Devónico. El último evento magmático del área es de edad probablemente devónica (Granito San Blas. Se calcularon edades modelos de «dos estadios» en base a relaciones 147Sm/144Nd; los valores obtenidos se presentan estrechamente agrupadas en torno a 1594 Ma. y se interpretan a este basamento como un protolito del Proterozoico medio retrabajado.

  17. Rb-Sr, Sm-Nd, K-Ca, O, and H isotopic study of Cretaceous-Tertiary boundary sediments, Caravaca, Spain Evidence for an oceanic impact site

    Energy Technology Data Exchange (ETDEWEB)

    Depaolo, D.J.; Kyte, F.T.; Marshall, B.D.


    The results of isotopic and trace-element-abundance analyses of Ir-enriched Cretaceous-Tertiary-boundary clay sediments from Caravaca, Spain, and of adjacent carbonate and marl layers, are presented. Acetic-acid and HCl leachates and residues were analyzed by isotope dilution to determine K, Rb, Sr, Sm, and Nd concentrations and Sr-87/Sr-86 and Nd-143/Nd-144 ratios. The stable isotope ratios delta-D, delta-(C-13), and delta-(0-18) were also determined. The results are presented in tables and graphs and compared with published data on the Caravaca sediments and on samples from other locations. The boundary clay is found to be distinguished from the adjacent layers by its isotopic ratios and to be of mainly terrestrial, lithospheric (deeper than 3-km) origin. Although submarine-weathering effects are evident and difficult to quantify, the degree of variation in Ni, Ir, Sr, and REE concentrations is considered too large to be attributed to postdepositional processes alone. These findings are seen as evidence for the ocean impact of a large single asteroid producing a worldwide blanket of ejecta, a large injection of water vapor into the atmosphere, and perhaps a gigantic tsunami, at the end of the Cretaceous period.

  18. New constraints on the geochronology and Sm-Nd isotopic characteristics of Bas-Drâa mafic dykes, Anti-Atlas of Morocco (United States)

    El Bahat, Abdelhakim; Ikenne, Moha; Cousens, Brian; Söderlund, Ulf; Ernst, Richard; Klausen, Martin B.; Youbi, Nasrrddine


    The Precambrian inliers of the Anti-Atlas belt across the southern part of Morocco contain numerous mafic dyke and sill swarms, which are thought to represent the erosional remnants of Proterozoic Large Igneous Provinces (LIPs). As part of an extended research campaign to date and characterize these LIPs, two amphiboles from one dyke within the Bas-Drâa inlier (western Anti-Atlas) yielded consistent 40Ar-39Ar ages of 611 Ma ± 1.3; i.e., evidence of magmatic activity during the Ediacaran (635-542 Ma). Furthermore, Nd isotope ratios and model ages identifies four groups of dykes within the Bas-Drâa inlier, all of which were derived from a previously enriched mantle reservoir with very low 143Nd/144Nd ratios (0.51065-0.51170) and corresponding εNd(t) values (-16.44 to -2.45). Such low Nd-ratios arguably reflect either a contribution of crustal components, such as the Paleoproterozoïc schisto-granitic basement, or metasomatic modification of the sub-continental lithospheric mantle.

  19. Rb-Sr and Sm-Nd Isotope Systematics of Shergottite NWA 856: Crystallization Age and Implications for Alteration of Hot Desert SNC Meteorites (United States)

    Brandon, A. D.; Nyquist, L. E.; Shih, C.-Y.; Wiesmann, H.


    Nakhlite NWA 998 was discovered in Algeria in 2001, and is unique among the six known members of this group of Martian meteorites in containing significant modal orthopyroxene. Initial petrologic and isotopic data were reported by Irving et al. This 456 gram stone consists mainly of sub-calcic augite with subordinate olivine and minor orthopyroxene, titanomagnetite, pyrrhotite, chlorapatite, and intercumulus An(sub 35) plagioclase. We report here preliminary results of radiogenic isotopic analyses conducted on fragmental material from the main mass.

  20. Multi-elemental Gd, Eu, Sm, Nd isotope ratio measurements by liquid chromatography coupled to MC-ICPMS with variable Faraday cup configurations during elution. (United States)

    Guéguen, Florence; Nonell, Anthony; Isnard, Hélène; Vio, Laurent; Chartier, Frédéric


    The high-precision isotopic characterization of actinides and fission products in nuclear samples is fundamental for various applications such as the management of spent nuclear fuel or the validation of neutronic calculation codes. However multi-elemental isotope ratio measurements by mass spectrometric techniques are hampered by the presence of both spectral and non-spectral interferences as complex sample matrices are encountered in such topics, but also due to the lack of high precision mass spectrometers able to cover the entire mass spectrum. This work describes a new LC-MC-ICPMS approach allowing simultaneous high-precision and multi-elemental isotope ratio measurements of four fission products of interest for nuclear issues (Nd, Sm, Eu, Gd) within a single elution run. Variable motorized Faraday cup configurations were successively used during a specifically designed elution procedure in order to take into account the non-natural Nd, Sm, Eu, Gd isotopic compositions encountered in irradiated nuclear samples. This new method, involving the relevant isotopic reference standard injection timings for on-line mass bias corrections, was validated by the analysis of a simulated fission product fraction from a (235)U-irradiated target. Reproducibilities better than 2‰ (k=2), comparable to those obtained by off-line measurements and the classic sample-standard bracketing mass bias correction approach, were obtained for all isotope ratios, except those involving isotopes with a transient signal peak apex lower than 100mV, for which the reproducibilities were comprised between 2‰ and 6‰.

  1. Petrography and geochronology (U/Pb-Sm/Nd) the Passagem Granite, Pensamiento Granitoid Complex, Paragua Terrane, SW Amazon Craton, Mato Grosso, Brazil; Petrologia e geocronologia (U/Pb-Sm/Nd) do Granito Passagem, Complexo Granitoide Pensamiento, SW do Craton Amazonico (MT)

    Energy Technology Data Exchange (ETDEWEB)

    Jesus, Gisely Carmo de, E-mail: [Universidade Federal de Mato Grosso (ICET/UFMT), Cuiaba, MT (Brazil). Inst. de Ciencias Exatas e da Terra. Programa de Pos-Graduacao em Geociencias; Sousa, Maria Zelia Aguiar de, E-mail: [Universidade Federal de Mato Grosso(ICET/UFMT), Cuiaba, MT (Brazil). Inst. de Ciencias Exatas e da Terra. Dept. de Recursos Minerais; Ruiz, Amarildo Salina; Matos, Joao Batista de, E-mail:, E-mail: jmatos@cpd.ufmt.b [Universidade Federal de Mato Grosso (ICET/UFMT), Cuiaba, MT (Brazil). Inst. de Ciencias Exatas e da Terra. Dept. de Geologia Geral


    The Passagem granite includes stocks, plugs and dikes located in the Ricardo Franco hill - Vila Bela da Santissima Trindade region - state of Mato Grosso, central Brazil. The Passagem Granite is included in the Paragua terrane - SW Amazonian Craton. It consists of isotropic monzogranite, sienogranite and more rarely granodiorites with leucocratic dark gray to white color. These rocks range from hypidomorphic inequigranular to xenomorphic texture, fine to medium grained. Biotite is the only primary mafic present as essential phase and characterize an expanded slightly acid sequence formed by a sub-alkaline magmatism of high-potassium calc-alkaline, slightly peraluminous composition from arc magmatic tectonic environment during a post-collisional period. Mechanism of fractional crystallization of plagioclase, biotite, titanite, apatite and zircon associated with simultaneous crustal assimilation are suggested for the evolution of these rocks. The results support the hypothesis of a post-collisional magmatism in the Paragua terrane at 1284 +- 20 Ma corresponding to the crystallization age of the Passagem granite. This paper propose that Passagem Granite represents as an extension in Brazilian terrane of the Pensamiento Granitoid Complex. (author)

  2. Isotope techniques in hydrology and sedimentology; Tecnicas isotopicas em hidrologia e sedimentologia

    Energy Technology Data Exchange (ETDEWEB)

    Bomtempo, Virgilio Lopardi [Centro de Desenvolvimento da Tecnologia Nuclear (CDTN), Belo Horizonte, MG (Brazil). Coordenacao de Desenvolvimento Cientifico e Tecnologico. Supervisao de Tecnicas Nucleares


    Water is the foundation of all life on Earth. Although two thirds of the terrestrial surface are covered by water (estimated volume is 1.5 billion cubic meters), just 2% of this total are fresh water, most of it locked in glaciers, ice caps and in deep groundwater reservoirs. Only 2,000 cubic kilometers are estimated to be available for consumption. Water resources have become more and more scarce, and the utilization becomes increasingly costly, due to the impact caused by over-exploitation and by diversified fronts of pollution. Specialists have been working in the development and in the application of several techniques to face this problem and to produce sustainable solutions. Isotope techniques represent a group of widespread tools that have been used along many years, and have become outstanding in hydrological investigation. This paper introduces a comprehensive review of the isotope techniques, taking into account environmental isotopes (stable and radioactive), artificial tracers and the use of radioactive sealed sources. Potentialities and limitations, future perspectives, as well as risks and benefits are also discussed. (author) 6 refs., 1 tab.; e-mail: vlb at

  3. Lithium isotopic separation: preliminary studies; Separacao isotopica de litio: estudos preliminares

    Energy Technology Data Exchange (ETDEWEB)

    Macedo, Sandra Helena Goulart de


    In order to get the separation of natural isotopes of lithium by electrolytic amalgamation, an electrolytic cell with a confined mercury cathode was used to obtain data for the design of a separation stage. The initial work was followed by the design of a moving mercury cathode electrolytic cell and three experiments with six batches stages were performed for the determination of the elementary separation factor. The value obtained, 1.053, was ill agreement: with the specialized literature. It was verified in all experiments that the lithium - 6 isotope concentrated in the amalgam phase and that the lithium - 7 isotope concentrated in the aqueous phase. A stainless-steel cathode for the decomposition of the lithium amalgam and the selective desamalgamation were also studied. In view of the results obtained, a five stages continuous scheme was proposed. (author)

  4. La asociacion Monzonitica del Domo Anatectico del Tormes: geoquimica y petrogenesis

    Directory of Open Access Journals (Sweden)

    López Plaza, M.


    Full Text Available In certain peripheral zones of the Anatectic Tormes Dome there exists a group of rocks, which are from basic to acid as well as rich in alkali feldspar, apatite and allanite. Such an unusual mineralogy makes the rocks to be enriched in K20, P2O5, LREE and other elements of low ionic potential. Their geochemical signature is related to the volcanic shoshonites, to the vaugnerites of the French Central Massif as well as to the monzonitic series of Ballon, being, in turn, almost exceptional in the iberian variscan. The least evolved terms are rather fractionated, therefore, they are not primary melts. During the differentiation, the saturation of accessory phases such as apatite, allanite and zircon exerts an important effect in the evolution of the residual liquid giving rise to an inflection point in the Harker diagrams. From the good adjustments obtained in mass balance and Rayleigh fractionation modelling, we can infer that the process of fractional crystallization is the dominant one. In this respect, the porphyritic granitoids can be derived from a liquid of monzodioritic composition, being rocks genetically to the associated acid rocks. The corroded cores of plagioclase and the spatial relations suggest the existence of different pulses of magma from basic to acid coming from the same magmatic chamber.En dos bandas del Domo anatéctico del Tormes aparece un conjunto de rocas plutónicas desde básicas a ácidas ricas en feldespato potásico, apatito y allanita. Esta mineralogía tan particular hace que estén enriquecidas en K20, P205, LREE y otros elementos de bajo potencial iónico. Su quimismo es afín a las shoshonitas volcánicas, a las vaugneritas del Macizo Central francés y a las series monzoníticas de Ballon, siendo, a su vez, casi excepcional en el varisco ibérico. Los términos menos evolucionados están bastante fraccionados por lo que no se trata de fundidos primarios. Durante la diferenciación existen fases accesorias como apatito, allanita y circón cuya saturación ejerce un importante efecto en la evolución del líquido residual originando evoluciones quebradas en los diagramas de Harker. A partir de los buenos ajustes obtenidos con las modelizaciones por balance de masas y fraccionación Rayleigh se infiere que el proceso de cristalización fraccionada es el dominante. En este sentido, se pueden hacer derivar los granitoides porfídicos a partir de un líquido de composición monzodiorítica, por lo que no quedan desconectadas las rocas básicas de las ácidas asociadas. Los núcleos corroídos de plagioclasa y las relaciones espaciales parecen indicar que han existido distintos pulsos de magma desde básicos a ácidos procedentes de la misma cámara magmática.

  5. Overview of the geochemistry and Rb/Sr, Sm/Nd isotopes of Middle Jurassic and Tertiary granitoid intrusions: a new insight on tectono-magmatism and mineralization of this period in Iran

    Directory of Open Access Journals (Sweden)

    Mohammad Ali Jazi


    Full Text Available One of the most intensive occurrences of magmatism in Iran was in the middle Jurassic period. Among the granitoid intrusions in this period as discrete bodies or complexes can be pointed to Aligoodarz, Alvand, Astaneh, Boroujerd, Malayer, and Chah-Dozdan in the Sanandaj-Sirjan zone; Shir-kuh and Ayrakan in the Central Iran zone; Shah-kuh, Sorkh-kuh and Kalateh-Ahani in the Lut Block. These granitoids are mostly peraluminous and belong to high-K calc-alkaline series. CaO/Na2O ratios (0.12 to 8.37 mostly suggest a clay-free source for formation of the intrusive rocks magma. Chondrite-normalized Rare Earth Elements (REEs diagram do not display high enrichment of Light Rare Earth Elements (LREEs than Heavy Rare Earth Elements (HREEs and general pattern is relatively flat. In addition, diagram shows Eu negative anomaly, which can be attributed to indicate reducing conditions in formation of magma and/or magma derived from plagioclase depth as source. The lower continental crust-normalized spider diagram indicates enrichment in LILE (Rb, Cs, and K and LREE (La and Ce and depletion in Ba, Nb, Ta, Sr, and Ti. Initial 87Sr/86Sr ratios are 0.70609 to 0.71938 and initial εNd values are negative (from -6.51 to -1.1 indicating that magma derived from continental crust. Geochemical and isotopic evidence of the intrusive rocks shows continental crust origin (S-type granitoid and due to continental collision. Geological findings such as stop in sedimentation, regional metamorphism, ophiolite displacement, and continental collision-related mineralization confirm continental collision between Iranian and Arabian plates in the Middle Jurassic period.

  6. The history of crustal uplift and metamorphic evolution of Panzhihua-Xichang micro-palaeoland, SW China:Constraints on Sm-Nd, 40Ar/39Ar and FT ages of granulites

    Institute of Scientific and Technical Information of China (English)

    XU Shijin; LIU Wenzhong; WANG Rucheng; YU Hangbo; LI Daming; WAN Jinglin; FANG Zhong


    Panzhihua-Xichang (Panxi) micro-palaeoland is the oldest terrane on the western margin of the Yangtze Block. Some intermediate-basic granulites are considered to be the crystalline basement of lower crust in the terrane. Granulite-facies metamorphism of the granulites was developed in the period from 1186 Ma to 1128 Ma. The origin of granulites was related to the collision orogenic process occurring when the micro-palaeolands merged to form the Rodinia Supercontinent. Amphibolite-facies retrogressive metamorphism of granulites took place in the period from 877 Ma to 825 Ma. This period was consistent with the breakup time of the Rodinia Supercontinent. 40Ar/39Ar ages and fission track (FT) ages of granulites in the Panxi micro-palaeoland show that the vertical movement history of crustal rocks was a slow uplift process of the rigid terrane in the time from Neoproterozoic to Mesozoic. The subduction of India Plate towards Euroasia Plate resulted in the rapid uplift of the Qinghai-Tibetan Block in Cenozoic.Meanwhile, the Qinghai-Tibetan Block moved towards east. Consequently the Panxi terrane was uplifted rapidly. As a result of the collision orogeny between the Qinghai-Tibetan Block and the Panxi terrane, the granulite-facies crystalline basement in this region was exhumed and exposed to the surface.

  7. Cambrian ensialic rift-related magmatism in the Ossa-Morena Zone (Évora Aracena metamorphic belt, SW Iberian Massif): Sm Nd isotopes and SHRIMP zircon U Th Pb geochronology (United States)

    Chichorro, M.; Pereira, M. F.; Díaz-Azpiroz, M.; Williams, I. S.; Fernández, C.; Pin, C.; Silva, J. B.


    The Late Ediacaran (c. 560-550 Ma) Série Negra sediments of the Évora-Aracena metamorphic belt, Ossa-Morena Zone, SW Iberian Massif, preserve a record of the erosion of an Avalonian-Cadomian magmatic arc and subsequent related turbiditic sedimentation. Detrital zircon from the Série Negra is characterized by predominantly Ediacaran and Cryogenian ages, with few Paleoproterozoic and Archean cores, and a marked lack of Grenvillian ages. These features, when combined with the metasediments' enrichment in LREE (La/Yb = 14), negative Eu-anomalies, low 147Sm/ 144Nd values (0.121) and negative ɛNd 550 = - 5.5, indicate that the protolith Série Negra sediments were derived from a continental magmatic arc. A period of Late Cadomian (ca. 560-540 Ma) tectonism was followed by an extended episode of widespread bimodal magmatism related to Cambrian (ca. 540-500 Ma) rifting. This tectonic inversion is expressed in the geological record by a regional Early Cambrian unconformity. SHRIMP zircon U-Th-Pb ages from four felsic orthogneisses from the Évora Massif record Cambrian (527 ± 10 Ma, 522 ± 5 Ma, 517 ± 6 Ma and 505 ± 5 Ma) crystallization ages for their igneous protoliths. This confirms the existence of widespread Lower Paleozoic igneous activity in the Ossa-Morena Zone: (i) a Lower Cambrian (ca. 535-515 Ma) igneous-felsic dominated-sedimentary complex (with calc-alkaline signature and associated carbonate and siliciclastic deposition), and (ii) a Middle Cambrian-?Ordovician (ca. 515-490 Ma) igneous-bimodal-sedimentary complex (with calc-alkaline and tholeiitic signatures and associated dominant siliciclastic deposition, but also carbonate sediments). The Cambrian felsic magmatism was characterized by negative Eu-anomalies, (La/Lu) N = 0.8-11, 147Sm/ 144Nd = 0.1289-0.1447 and ɛNd 500 ranging from - 1.5 to - 0.8. A tendency towards peraluminous compositions suggests late fractionation, low degrees of partial melting, or the mixing of crustal and mantle-derived material in the magma source region. Some felsic rocks possibly represent the last residual melts of high-temperature, zircon-undersaturated mafic magmas later affected by crustal contamination, while others indicate partial melting of crustal metasediments variably contaminated by basaltic liquids. The transition from early felsic dominated to later more mafic magmatism suggests the gradual opening of the system to tholeiitic N-E-MORB products (Th N/Ta N < 1.0). The as yet undated (Cambrian-?Ordovician) E-MORB amphibolites have 147Sm/ 144Nd = 0.1478-0.1797 and ɛNd 500 values ranging from + 6.4 to + 7.3, while the N-MORB amphibolites have 147Sm/ 144Nd = 0.1818-0.1979 and ɛNd 500 values of + 5.8 and + 7.0, reaching a maximum of + 9.1. In contrast, other amphibolites have a negative Ta-anomaly (1.35 < Th N/Ta N < 2.41) reminiscent of lavas from "orogenic" settings or alternatively, typical of crustally-contaminated within-plate magmas. These "VAB-like" amphibolites have 147Sm/ 144Nd values ranging from 0.1639 to 0.1946 and ɛNd 500 values of + 3.5 to + 5.2, suggesting derivation by crustal assimilation processes. The sub-alkaline igneous precursors of the amphibolites were most likely generated in a rift setting by asthenospheric upwelling. These results strengthen the proposed geodynamic scenarios for the SW Iberian Massif by which Cadomian accretion gave rise to an ensialic rift that developed into a proto-oceanic basin and incipient spreading (opening of the Rheic Ocean?). A similar transition from a convergent to a divergent plate boundary during the Ediacaran to Cambrian-?Ordovician has also been reported in other segments of the northern Gondwana margin.

  8. Geochemistry, U-Pb geochronology, Sm-Nd and O isotopes of ca. 50 Ma long Ediacaran High-K Syn-Collisional Magmatism in the Pernambuco Alagoas Domain, Borborema Province, NE Brazil (United States)

    Francisco da Silva Filho, Adejardo; de Pinho Guimarães, Ignez; Santos, Lucilene; Armstrong, Richard; Van Schmus, William Randall


    The Pernambuco Alagoas (PEAL) domain shows the major occurrence of granitic batholiths of the Borborema Province, NE Brazil, with Archean to Neoproterozoic range of Nd TDM model ages, giving clues on the role of granites during the Brasiliano orogeny. SHRIMP U/Pb zircon geochronological data for seven granitic intrusions of the PEAL domain divide the studied granitoids into three groups: 1) early-to syn-collision granitoids with crystallization ages ca. 635 Ma (Serra do Catú pluton), 2) syn-collision granitoids with crystallization ages 610-618 Ma (Santana do Ipanema, Água Branca, Mata Grande and Correntes plutons) and 3) late-to post-collision granitoids with ages of ca. 590 Ma (Águas Belas, and Cachoeirinha plutons). The intrusions of group 1 and 2, except the Mata Grande and Correntes plutons, show Nd TDM model ages ranging from 1.2 to 1.5 Ga, while the granitoids from group 3, and Mata Grande Pluton and Correntes plutons have Nd TDM model ages ranging from 1.7 to 2.2 Ga. The studied granitoids with ages plutons, together with the available Nd isotopic data suggest that the Brasiliano orogeny strongly reworked older crust, of either Paleoproterozoic or Tonian ages. The studied granitoids are coeval with calc-alkaline granitoids of the Transversal Zone and Sergipano domains and rare high-K calc-alkaline granitoids from the Transversal Zone domain. Such large volumes of high-K granitoids with crystallization ages older than 600 Ma are not recorded in the Transversal Zone domains, suggesting that at least between 600 and 650 Ma, the granitic magmatism of these two areas were distinct. However, the studied granitoids (630-580 Ma) located in the north part of the PEAL domain, north of the Palmares shear zone are coeval with granitoids of similar geochemical compositions in the Transversal Zone domain. It suggests that the southeastern part of the Transversal Zone and the northern part of the PEAL domains belonged to the same crustal block during the Brasiliano/Pan-African orogeny.

  9. Geochemistry and Sm-Nd systematics of the 1.67 Ga Buanji Group of southwestern Tanzania: Paleo-weathering, provenance and paleo-tectonic setting implications

    Directory of Open Access Journals (Sweden)

    Charles H. Kasanzu


    The lower Buanji Formation yielded a depleted mantle Nd model age (TDM of ∼2100 Ma which indicates an Eburnean parentage. TDM ages of 2486–2155 Ma and 2535–2379 Ma obtained from middle and upper Buanji formations, respectively, suggest a progressive increase of sedimentary input from the Tanzania Craton up-stratigraphy. The Eburnean TDM ages of the lower Buanji rocks are attributed to their derivation through denudation of a decaying topographic high composed predominantly of rocks that were generated during the Palaeoproterozoic Ubendian orogenesis, possibly in the realm of Columbian Supercontinent assembly. Overlapping TDM ages between the middle and upper Buanji formations suggest multiple sources involving mixing of detritus from Archaean cratonic rocks and the Palaeoproterozoic Ubendian belt. However, the Archaean signal is relatively more pronounced in the upper Buanji Formation, suggesting sediments derivation from the craton, to the north of the basin. The middle Buanji Formation suggests more diverse protolith, given the relatively larger spread in the TDM ages. The Nb/Ta, Zr/Sm and Ce/Pb ratios coupled with the negative Nb and Ta anomalies, relative to primitive mantle, suggest that the tectonic setting of the source rocks for the Buanji sediments was a subduction zone akin to that generating modern Island Arc Basalts. Thus, we suggest that the Buanji's palaeogeography is consistent with an extensional continental backarc basin during the late Paleoproterozoic.

  10. Geocronologia U-Pb (SHRIMP) e Sm-Nd de xistos verdes basálticos do orógeno araçuaí: implicações para a idade do grupo macaúbas.


    Babinski,Marly; Soares, Antônio Carlos Pedrosa; Gradim, Rafael Jaude; Alkmim, Fernando Flecha de; Noce, Carlos Maurício; Liu, Dunyi


    No vale do Rio Preto, setor ocidental do Orógeno Araçuaí (ca. 60 km a NE de Diamantina), ocorrem xistos verdes de filiação basáltica, cuja idade e posição estratigráfica foram motivo de controvérsia, pois os autores dividiram-se naqueles que os atribuíram ao Grupo Macaúbas (Neoproterozóico) e naqueles que os correlacionaram ao Supergrupo Espinhaço inferior (ca. 1,7 Ga). Entretanto, estudos detalhados demonstram que os xistos verdes representam derrames basálticos submarinos, sedimentação vulc...

  11. SIMS U-Pb, Sm-Nd isotope and geochemical study of an arkosite-amphibolite suite, Peräpohja Schist Belt: evidence for ca. 1.98 Ga A-type felsic magmatism in northern Finland

    Directory of Open Access Journals (Sweden)

    Eero Hanski


    Full Text Available In the northern and north-eastern part of the Peräpohja Schist Belt, northern Finland, an extensive supracrustal rock unit has been identified which is composed of alternating amphibolitic and arkositic components. The amphibolites form layers whose thickness varies from one millimeter to some tens of meters, being most often a few tens of centimeters. They represent mafic tuff beds deposited concurrently with more abundant arkositic rocks. Most of the arkosites have a modal and major and trace element compositionsimilar to that of A2-type granites. For example, they exhibit high LREE/HREE, negative Eu anomalies, and flat HREE and are moderately enriched in Nb, Zr, and Y. The genesis of the arkosites is enigmatic as they show features supporting either a volcaniclastic or an epiclastic origin. In the latter case, they were derived via erosion of a source dominated by A2-type granitic rocks. Previous conventional ID-TIMS and new SIMS U-Pb dating of zircons from two arkosite samples and one mica schist sample, all three picked from the northern part of the schist belt, indicate that these rocks contain a single population of zircons with an age of ca. 1975 Ma suggesting that they are among the youngest supracrustal rocks in the schist belt. In contrast, one mica schist sample from the western part of the belt revealed only the presence of Archean zircons. The samples do not differ markedly in terms of their Nd isotopecomposition as they all have a moderately negative εNd(1900 Ma. Regardless of the genesis of the arkosites, their isotopic and geochemical data suggest a previously unknown occurrence of extensive A-type felsic magmatism at ca. 1.98 Ga, contemporaneously withsome continental flood basalts. However, concrete evidence for this felsic A-type magmatism in the form of ca. 1.98 Ga felsic plutonic rocks is virtually absent in the presently exposed Fennoscandian Shield.

  12. Reassessment and new chronological data (Ar/Ar, Rb/Sr and Sm/Nd) from the Pelotas batholith, Rio Grande do Sul state: petrogenesis implications and reactivation age of the shear zones; Reavaliacao e novos dados geocronologicos (Ar/Ar, Rb/Sr e Sm/Nd) do batolito Pelotas, no Rio Grande do Sul: implicacoes petrogeneticas e idade de reativacao das zonas de cisalhamento

    Energy Technology Data Exchange (ETDEWEB)

    Philipp, Ruy Paulo; Chemale Junior, Farid [Rio Grande do Sul Univ., Porto Alegre (Brazil). Inst. de Geociencias. Centro de Estudos em Petrologia e Geoquimica]. E-mail:; Machado, Romulo [Sao Paulo Univ., SP (Brazil). Inst. de Geociencias. Dept. de Mineralogia e Geotectonica


    SHRIMP and conventional U-Pb and Pb/Pb evaporation dating of zircon from the Pelotas batholith indicates one group of ages between 625 and 633 Ma for the Pinheiro Machado suite, and another group between 575 and 599 Ma for the Viamao, Encruzilhada do Sul and Dom Feliciano suites. Sr 87/Sr 86 isotopic ratios of 0.7060-0.7016, epsilon{sub Nd} values of -5 and -10, and Nd T{sub DM} model ages between 2200 and 1600 Ma suggest that the suites were mainly derived by melting of Paleoproterozoic crust formed during the Tranzamazonic Cycle. Basic magmatism and heterogeneous magma mixing in the Pinheiro Machado, Viamao, Encruzilhada do Sul and Dom Feliciano suite and the Piquiri alkaline magmatism, with Pb/Pb zircon evaporation ages between 610 and 615 Ma, suggest that a mantle component also contributed to the formation of the Pelotas batholith. 39 Ar/40 Ar determinations in micas from mylonitic rocks of high- and low-dip shear zones showed ages between 540 and 530 Ma, which show that important tectonic events occurred after the emplacement of the batholith. This event developed in a transpressive regime, was responsible for the reactivation of older shear zones, and was probably contemporaneous with the development of the Camaqua basin. (author)

  13. Structural studies of type N superconductive compounds: R{sub 2-x}Ce{sub x}CuO{sub 4{+-}{delta}} (R = Gd, Eu, Sm, Nd, Pr); influences of chemical treatments on physical properties; Etudes structurales des composes supraconducteurs de type N: R{sub 2-x}Ce{sub x}CuO{sub 4{+-}{delta}} (R = Gd, Eu, Sm, Nd, Pr); influences des traitements chimiques sur les proprietes physiques

    Energy Technology Data Exchange (ETDEWEB)

    Vigoureux, P.


    Different chemical treatments of R{sub 2-x}Ce{sub x}CuO{sub 4{+-}{delta}} compounds monocrystals (gadolinium, europium, samarium, neodymium and praseodymium cuprates) modify their physical properties especially their superconductive properties. The presented chemical treatments are: the substitution of the trivalent rare earth element R by an other trivalent lanthanide, its substitution by tetravalent cerium, and heat treatment under low oxygen pressure. After these chemical treatments, structural modifications are observed by neutrons and X-rays diffraction, and allow to precise their actions: size effect of the rare earth element on the deformation of the CuO{sub 2} planes, links between deformation and superconductivity and magnetic properties. (A.B.). 394 refs/.

  14. The isotopic analysis of boron by charged particle irradiation; Analise isotopica de boro utilizando feixes de particulas carregadas

    Energy Technology Data Exchange (ETDEWEB)

    Vinagre Junior, Ubirajara M.; Costa, Vilmar L. da; Suita, Julio C.; Teixeira, Danilo L.; Bernedo, Alfredo V.B.; Cabral, Tania S. [Instituto de Engenharia Nuclear (IEN), Rio de Janeiro, RJ (Brazil)


    An analytical isotopic method for boron analysis is discribed, based in the spectrometry of protons at 130{sup 0} C from scattering and/or reactions like {sup 10} B(p,p){sup 10} B and {sup 11} B(p,p){sup 11} B which were simultaneously measured. The basic parameters involved in such measurements, are discussed including cinematic, angular distribution, preparation of targets and its substracs. Particle spectra of targets with natural isotopic concentration and enriched in {sup 10} B are presented. The ratio [{sup 11} B(p{sub o})/{sup 10} B(p{sub o})] at 130{sup 0} C for targets of {sup nat} B in respect of the incident proton beam energy between 14 and 24 MeV are shown. The results of our enriched {sup 10} B are compared with results obtained in mass spectrometry. (author). 14 refs., 6 figs., 1 tab.

  15. Geochemical of clay formations : study of Spanish clay REFERENCE; Geoquimica de formaciones arcillosas: estudio de la Arcilla Espanola de REFERENCE

    Energy Technology Data Exchange (ETDEWEB)

    Turrero, M. J.; Pena, J.


    Clay rocks are investigated in different international research programs in order to assess its feasibility for the disposal of high level radioactive wastes. This is because different sepcific aspects: they have low hydraulic conductivity (10''-11-10''-15 m/s), a high sorption capacity, self-sealing capacity of facults and discontinuities and mechanical resistance. Several research programs on clay formations are aimed to study the chemistry of the groundwater and the water-rock reactions that control it: e. g. Boom Clay (Mol, Belgium), Oxford Clay /Harwell, United Kingdom), Toarcian Clay (Tournemire, France), Palfris formation (Wellenberg, Switzerland), Opalinus Clay (Bure, France). Based on these studies, consdierable progress in the development of techniques for hydrologic, geochemical and hydrogeochemical characterization of mudstones has been accomplished (e. g. Beaufais et al. 1994, De Windt el al. 1998. Thury and Bossart 1999, Sacchi and Michelot 2000) with important advances in the knowledge of geochemical process in these materials (e. g. Reeder et al. 1993, Baeyens and Brandbury 1994, Beaucaire et al. 2000, Pearson et al., 2003).Furtermore, geochemical modeling is commonly used to simulate the evolution of water chemistry and to understand quantitatively the processescontrolling the groundwater chemistry (e. g. Pearson et al. 1998, Tempel and Harrison 2000, Arcos et al., 2001). The work presented here is part of a research program funded by Enresa in the context of its R&D program. It is focused on the characterization of a clay formation (reference Argillaceous Formation, RAF) located within the Duero Basin (north-centralSpain). The characterisation of th ephysical properties,, fluid composition, mineralogy, water-rock reaction processes, geochemical modelling and sorption properties of the clays from the mentioned wells is the main purpose of this work. (Author)

  16. Gas geochemistry of Los Humeros geothermal field, Mexico; Geoquimica de gases del campo geotermico de Los Humeros, Puebla, Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Barragan R, Rosa Maria; Arellano G, Victor M; Nieva G, David; Portugal M, Enrique; Garcia G, Alfonso; Aragon A, Alfonso [Instituto de Investigaciones Electricas, Temixco, Morelos (Mexico); Torres A, Ignasio S [Centro de Investigacion en Energia, Temixco, Morelos (Mexico); Tovar A, Rigoberto [Comision Federal de Electricidad, Los Humeros, Puebla (Mexico)


    Gas data of Los Humeros geothermal field were analyzed. A new method, which is based on the Fischer-Tropch reactions and on the combined pyrite-magnetite mineral equilibrium, was used. Reservoir temperature and reservoir excess steam were estimated for the starting stage of the field by using early data taken from producing wells at controlled conditions. The same parameters were also obtained for the present stage by using 1997 gas data. Reservoir temperatures ranged from 275 and 337 Celsius degrees and positive values for reservoir excess steam fractions were obtained for the starting stage. For well H-1 no excess steam was found since this well was fed by the shallower liquid-dominated reservoir. Results for 1997 showed lower scattering compared to early data and the possible occurrence of a heating process in the shallower stratum which could due to exploitation. [Spanish] En este articulo se presenta un analisis de datos de la fase gaseosa producida por pozos productores del campo geotermico de Los Humeros mediante un metodo que considera el equilibrio de la reaccion de Fischer-Tropsh y el equilibrio de minerales pirita-hematia y pirita-magnetita. Este metodo provee la temperatura del yacimiento y el exceso de vapor presente en la descarga total de los pozos. Los resultados se discuten tanto para el estado inicial del yacimiento utilizando los primeros datos de produccion en los que el flujo del pozo estuvo controlado y los obtenidos en 1997 que representan el estado actual del yacimiento. En el estado inicial se estimaron temperaturas de yacimiento de entre 275 y 337 grados Celsius y excesos de vapor positivos, con excepcion del pozo H-1 que se alimenta del estrato somero dominado por liquido. Los resultados obtenidos para 1997 muestran una dispersion menor y la probable ocurrencia de un proceso de calentamiento del estrato somero propiciado por la explotacion.

  17. Gas geochemistry: a new technology to evaluate petroleum systems; Geoquimica de gases: uma nova tecnologia em avaliacao de sistemas petroliferos

    Energy Technology Data Exchange (ETDEWEB)

    Santos Neto, Eugenio Vaz dos [PETROBRAS, Rio de Janeiro, RJ (Brazil). Centro de Pesquisas. Gerencia de Geoquimica]. E-mail:


    In the last decade hydrocarbon gas geochemistry has significantly evolved especially regarding to the widespread use of GC-C-IRMS (Gas chromatography-combustion-ion ratio monitoring system) techniques that allowed accurate measurements of {delta}{sup 13} C in the C{sub 1}-C{sub 4} fraction. Also, due to the improvement of the sampling procedures, sample collection - relatively small amounts of gas samples at low pressure - has become easier, sample transportation has become safer - the risk of accidents has been reduced - and analysis has become faster. The 'state-of-the-art' of the use of gas geochemistry to study processes within petroleum systems is discussed in this paper. The discussion is mainly focused on the identification of the hydrocarbon gas origin (biogenesis versus thermo genesis, mixing) and hydrocarbon gas generation (primary versus secondary cracking), including the inference of the relative thermal evolution and possible secondary alterations caused by biodegradation, secondary migration and eventually leakage from petroleum accumulations. Brief comments were also made about the new technologies involving noble gases and their potential use as tracers of processes in petroleum systems. Additionally, the origin of non-hydrocarbon gases in petroleum accumulations is succinctly discussed, as well as their possible economic impacts. The use of gas geochemistry techniques has brought a significant improvement in the understanding of petroleum systems under exploration in Brazil and in other parts of the world. Besides, on-going research projects suggest that there is a great potential for technological advances, e.g., adding the hydrogen isotopic composition of hydrocarbons to the interpretations, and also integrating the available results to the isotopic variations of noble gases. (author)

  18. The Alto Paraguay Alkaline Province: petrographic, geochemical and geochronological characteristics; Provincia alcalina Alto Paraguai: caracteristicas petrograficas, geoquimicas e geocronologicas

    Energy Technology Data Exchange (ETDEWEB)

    Velazquez Fernandez, Victor


    The Alto Paraguay Province is located at the border of the State of Mato Grosso do Sul and Paraguay, between the coordinates 21 deg 10{sup `}to 23 deg 25{sup `}of Southern latitude and 57 deg 10{sup `} to 58 deg 00{sup `}, having the city of Porto Murtinho as the main reference point. The geotectonic domain of the area is governed by the precambric units of the Southern extreme of the Amazonic craton which developed a long and accentuated activity, giving rise to folds and important faults, that in several cases seem to have exerted an effective control of the magmatic manifestations. Radiometric data indicate that the emplacement of the syenitic bodies took place in the Permo-Triassic period, with a major incidence in the interval 260-240 Ma, representing thus, an important phase of alkaline magmatic affinity associated to the Parana Basin which is believed is to be unique, since the other known areas (Central, Amambay and Rio Apa Provinces, Paraguay, Velasco Province, Bolivia) are considerably younger (140-120 Ma). Syenitic rocks from the Alto Paraguay Province show wide variation in the ratio {sup 87} Sr/{sup 86} Sr (0.703361 - 0.707734). Excluding the Cerro Boggiani rocks (0.703837-0.707734), values for the nepheline syenites (0.703361-0.703672) general lower than those of the other syenites types. Alkaline syenites cover the interval 0.703510- 0.703872, while quartz syenites and syenogranites are 0.704562 and 0.707076, respectively. geologic evidence, in addition to petrographic, geochemical and isotopic (Sr) data, suggest that the syenitic rocks have been derived from an unique mantelic parental liquid, by fractional crystallization and assimilation processes, which are assumed to be occurred during the emplacement of the magma in the crust. (author) 124 refs., 52 figs., 7 tabs.

  19. 白云鄂博矿床白云石型矿石中独居石单颗粒U-Th-Pb-Sm-Nd定年%Single-grain U-Th-Pb-Sm-Nd dating of monazite from dolomite type ore of the Bayan Obo deposit

    Institute of Scientific and Technical Information of China (English)

    刘玉龙; 陈江峰; 李惠民; 钱卉; 肖国望; 张台荣


    使用交换树脂TRU Spec同时分离REE、U、Th、Pb及其他的元素,然后用阴离子交换树脂纯化Pb并用萃淋树脂分离纯化Sm和Nd,Sm、Nd、U和Pb的定量测定借助同位素稀释法,Th的定量测定则用ICP-MS分析,Nd和Pb同位素组成分析用质谱法(TIMS),从而实现独居石U-Th-Pb-Sm-Nd联合定年.用这种方法可以在同一样品上,同时得到U-Th-Pb和Sm-Nd同位素年龄记录.白云鄂博矿床白云石型稀土矿石中12个单颗粒独居石的U-Th-Pb-Sm-Nd同位素联合定年给出Sm-Nd等时线年龄为1008±320 Ma,其中8个独居石的Th-Pb等时线年龄为1231±200Ma,此二年龄在误差范围内相似.在同一组独居石样品上得到一致的Th-Pb与Sm-Nd的中元古年龄,表明白云鄂博在中元古代的稀土成矿作用是可能的.本文独居石的Th-Pb 和Sm-Nd年龄与以前报道的独居石加里东期Th-Pb年龄差别很大,此问题尚需进一步研究.

  20. The Sm-Nd isotopic ages of the Early Precambrian mafic-ultramafic volcanic rocks in Yiyang, Hunan%湖南益阳早前寒武纪镁铁质-超镁铁质火山岩的Sm-Nd同位素年龄

    Institute of Scientific and Technical Information of China (English)

    郭乐群; 唐晓珊; 彭和求


    益阳地区出露的似层状-层状镁铁质-超镁铁质火山岩的时代归属有不同的观点.研究认为其主要岩石类型为玄武质科马提岩和拉斑玄武岩.岩石地球化学和同位素年龄显示:玄武质科马提岩Sm-Nd全岩等时线年龄为(3 028±47)Ma,属中、新太古代洋中脊-岛弧火山岩;拉斑玄武岩年龄为(2 216±38)Ma,属古元古代.这一结果揭示了早前寒武纪在古扬子微板块(川中微板块)东南有多岛弧洋盆,湖南深部地壳有绿岩基底.

  1. {Ln(III)[mu(5)-kappa(2),kappa(1),kappa(1),kappa(1),kappa(1)-1,2-(CO2)(2)C6H4][isonicotine][H2O]}(2)Cu(I) x X (Ln = Eu, Sm, Nd; X = ClO4-, Cl-): a new pillared-layer approach to heterobimetallic 3d-4f 3d-network solids. (United States)

    Cheng, Jian-Wen; Zheng, Shou-Tian; Ma, En; Yang, Guo-Yu


    A new series of heterometallic lanthanide(III)-copper(I) coordination polymers Ln2(bdc)2(ina)2(H2O)2Cu x X (Hina = isonicotinic acid; H2bdc = 1,2-benzenedicarboxylic acid; Ln = Eu (1), Sm (2), Nd (3), X = ClO4-; Ln = Nd (4), X = Cl-) have been hydrothermally synthesized in the presence/absence of HClO4. Both compounds are isostructural and contained two distinct units of 2D Ln-bdc layers and linear [Cu(ina)2]-. The linear [Cu(ina)2]- complexes act as pillars and further link the Ln-bdc layers resulting in four heterometallic metal-organic frameworks, which represent the first pillared-layer 3d-4f framework with two distinct types of channels along the b and c axes. The compounds can be specified by the Schläfli symbol (47.63)(47.68) as a novel 3D (5,6)-connected net. Furthermore, the IR, TGA, PXRD, and UV-vis spectral and luminescent properties of 1-4 were also studied.

  2. Spectrometry and dosimetry of isotopic sources of neutrons by means of artificial neural networks; Espectrometria y dosimetria de fuentes isotopicas de neutrones mediante redes neuronales artificiales

    Energy Technology Data Exchange (ETDEWEB)

    Vega C, H. R.; Ortiz R, J. M.; Hernandez D, V. M; Martinez B, M. R. [Universidad Autonoma de Zacatecas, Unidad Academica de Estudios Nucleares, Calle Cipres No. 10, Fracc. La Penuela, 98068 Zacatecas (Mexico); Gallego, E.; Lorente, A. [Universidad Politecnica de Madrid, Departamento de Ingenieria Nuclear, C/Jose Gutierrez Abascal No. 2, 28006 Madrid (Spain); Barquero, R., E-mail: [Hospital del Rio Hortega, C/Dulzaina No. 2, 47012 Valladolid (Spain)


    The artificial neural networks technology has been applied to reconstruct the neutrons spectra of two isotopic sources: {sup 252}Cf, and {sup 241}Am-Be. Also, this technology has been applied to obtain the effective dose, E, and the personal dose equivalents, Hp(10) and environmental, H *(10). To obtain the spectra and the doses only were used the count rates produced in a Bonner Spheres spectrometer with a scintillator of {sup 6}LiI(Eu) of 0.4 {phi} x 0.4 cm{sup 2}. The equivalent environmental dose and the spectra of the sources were also obtained by means of the reconstruction code BUNKIUT. When comparing the results obtained by means of both procedures it was found that they are consistent. (Author)

  3. Isotopic Evolution of Wells in the Geothermal Field of Los Azufres, Michoacan, Mexico; Evolucion isotopica de fluidos de pozos del campo geotermico de Los Azufres, Michoacan, Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Barragan Reyes, Rosa Maria; Portugal Marin, Enrique; Arellano Gomez, Victor Manel; Aragon Aguilar, Alfonso [Instituto de Investigaciones Electricas (Mexico); Sandoval Medina, Fernando [Comision Federal de Electricidad (Mexico)


    Isotopic ({delta}{sup 1}8 O and {delta}D) data from production and reinjection web fluids from the Los Azufres geothermal field were interpreted in order to define reservoir evolution and the occurrence of physical processes as a result of exploitation. The study included data of 30 wells, which were sampled in September, 2000. General results indicate that different phenomena seem to occur in both zones of the field. In the southern zone there are two different trends of behavior: a mixture of fluids evidenced by the {delta}D versus {delta}{sup 1}8 O trend with a positive slope, was interpreted as the result of reservoir vapor separation at a temperature above 220 Celsius degrees, since for temperatures above 220 Celsius degrees deuterium behaves as a volatile component. No well-defined {delta}{sup D} vs {delta}{sup 1}8 O trend was found for the northern zone, but some points seem to fit the same negative slope trend found in the souther zone. The study of reservoir temperatures estimated by different approaches for particular wells through time, as well as temperature results obtained with a heat and flow well simulator, suggest that reservoir boiling occurs in localized areas in both zone of the field. This process is probably due to exploitation. [Spanish] Se interpretaron datos isotopicos ({delta}{sup 1}8 O y {delta}D) de fluidos de pozos productores y de reinyeccion del campo geotermico de Los Azufres, Michoacan, Mexico, para definir la evolucion del yacimiento y la ocurrencia de procesos fisicos como resultado de la explotacion. En el estudio se consideran datos de treinta pozos segun el muestreo realizado en septiembre de 2000. El estudio de la evolucion en el tiempo de las estimaciones de temperatura de yacimiento mediante diferentes tecnicas, asi como la temperatura obtenida de simulacion de pozos, sugiere que ocurre ebullicion en areas localizadas en ambas zonas del campo debido a la explotacion. Los resultados generales indican la existencia de diferentes fenomenos en ambas areas del campo. En la parte sur se definen dos tendencias de comportamiento isotopico: una con pendiente positiva que indica mezcla de fluidos y en cuyo extremo enriquecido isotopicamente se encuentra el fluido de reinyeccion; la otra tendencia con pendiente negativa resulta de un proceso de ascenso y condensacion parcial de vapor en el yacimiento a una temperatura mayor de 220 grados Centigrados, ya que por encima de esta temperatura el deuterio se comporta como una especie volatil. En contraste, para la seccion norte del campo no se encontro una tendencia bien definida, aunque algunos puntos parecen ajustarse a la relacion de pendientes negativa hallada para la zona sur.

  4. Hydrochemical and isotopic differentiation of the aquifers Missao Velha and Mauriti, Ceara State, Brazil; Diferenciacao hidroquimica e isotopica dos aquiferos Missao Velha e Mauriti, Ceara, Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Leite, Julio Cesar Bastos; Santiago, Marlucia Freitas; Mendes Filho, Josue; Frischkorn, Horst; Silva, Carla M.S. Vidal [Ceara Univ., Fortaleza, CE (Brazil)


    The Cariri region, in the South of Ceara State, comprises the most important sedimentary basin of the State. The exclusive source for domestic, agricultural and industrial use is underground water. The formations, from top to bottom, Rio da Batateira, Missao Velha, and Mauriti constitute the main aquifers in the Cariri Valley. Intensive tectonics resulted in complex hydrogeologic conditions which cause mixing of waters of different origin. Thus, one of our tasks is just to find specific characteristics that can differentiate the origins. We used chemical analyses (major ions, calcite saturation indexes, electric conductivity) and radiocarbon measurements for finding correlations between parameters that characterize waters from the different aquifers. (author) 3 refs., 1 tab.

  5. Caracterización hidrogeoquímica e isotopica de areas de recarga en el acuífero de San Salvador.


    Barrera de Calderon , Marcia Lizeth


    El agua subterránea y el ciclo hidrológico -- La composición del agua subterránea -- Unidades de la composición isotópica del agua -- Geología de la cuenca del rio Acelhuate -- Caracterización hidrogeoquímica e isotópica del agua subterránea en la microcuenca alta del rio Acelhuate.

  6. Impact of statistical uncertainty of the neutron spectrum in the isotopic evolution of fuel; Impacto de la incertidumbre estadistica del espectro neutronico en la evoluacion isotopica del combustible

    Energy Technology Data Exchange (ETDEWEB)

    Ortega, P.


    The results obtained and presented in this study for different calculation conditions (number of stories, number of steps burning, etc.) and their simultaneous impact on neutron spectrum and isotopic composition and a methodology is proposed to determine the minimum parameters for calculation given uncertainty in the results of isotopic composition with high burnup, both UO{sub 2} and MOX fuel.

  7. Isotopic characterization of uranium in soils of the Ipanema National Forest (FLONA-Ipanema); Caracterizacao isotopica de uranio em solos da Floresta Nacional de Ipanema (FLONA-Ipanema)

    Energy Technology Data Exchange (ETDEWEB)

    Silva, F.B.; Marques, F.H., E-mail:, E-mail: [Laboratorio de Pocos de Caldas (LAPOC/CNEN-MG), Pocos de Caldas, MG (Brazil); Enzweiler, J.; Ladeira, F.S.B., E-mail:, E-mail: [Universidade Estadual de Campinas (UNICAMP), Campinas, SP (Brazil). Instituto de Geociencias


    The National Forest of Ipanema (FLONA) is situated on a geological anomaly, known as 'Domo de Aracoiaba'. The soils of the area include Oxisols, Inceptsols and Alfisols. The amount of uranium and respective isotope activities in a soil depend on the parental rock and on the pedologic processes. The aim of this study was to investigate the activities for uranium isotopes ({sup 238}U, {sup 234}U, {sup 235}U) and the activity ratio (AR) {sup 234}U/ {sup 238}U or secular equilibrium for different soil types of the area collected at horizons A and B. The amount of uranium showed no significant differences for soils generated from alkaline intrusive rocks and sandstone, however, secular equilibrium was observed for Oxisol (RA = 1), while Inceptsol presented RA> 1 and the other soils, Alfisols, presented RA values <1. (author)

  8. Xe-135 and Sm-149 Isotopic Evolution Analysis Xesamo code; Analisis de la Evolucion Isotopica del Xe-135 y Sm-149. Programa Xesamo

    Energy Technology Data Exchange (ETDEWEB)

    Caro, R.; Gallego, J.; Martinez Fanegas, R.


    In this report the time evolution analysis of the nuclides concentration Xe-135 and Sm-149 as a function of the neutron flux is carried out. The neutron flux may be any function of time. It is analyzed as well the reactivity changes associated with the xenon and samarium concentration variations. (Author) 5 refs.

  9. Isotope stratigraphy of cenozoic carbonate sequences of Brazilian Northern coast; Estratigrafia isotopica de sequencias carbonaticas cenozoicas da Costa Norte do Brasil

    Energy Technology Data Exchange (ETDEWEB)

    Rodrigues, Rene; Takaki, Tikae [PETROBRAS, Rio de Janeiro, RJ (Brazil). Centro de Pesquisas


    Study of sedimentary rocks formation process on the Northern coast of Brazil, its stratigraphy characteristic, methodology of dating process to determine rocks age and correlation with carbonates sequences of Atlantic ocean (North and South) are presented. Results of analysed samples, isotopics studies, its dating, and comparative studies with samples analyzed in other sites are also discussed. 3 figs., 19 refs

  10. Petrografia y geoquimica de las rocas intrusivas aflorantes entre los municipios de Mistrato y Belen de Umbria (Departamento de Risaralda, Cordillera Occidental Colombiana)

    National Research Council Canada - National Science Library

    Vallejo Hincapie, Diego Felipe; Salazar Rios, Andres Felipe; Toro Toro, Luz Mary


    Las rocas Intrusivas objeto de estudio afloran en los municipios de Mistrato y Belen de Umbria, Departamento de Risaralda, sobre el flanco oriental de la Cordillera Occidental y al oeste del Sistema...

  11. The necessity of renovation of the fundamental concepts of geochemistry for the geothermal systems; La necesidad de renovacion de los conceptos fundamentales de geoquimica para los sistemas geotermicos

    Energy Technology Data Exchange (ETDEWEB)

    Mahendra Jaiswal, Pal Verma [Instituto de Investigaciones Electricas, Temixco, Morelos (Mexico)


    In this article the exhaustive experimentation of the compilation of the experimental data of quartz solubility is presented along with the saturation curve water - steam and in the zone of compressed liquid. On the base of these data a regression relation was derived, which is valid for the entire range of temperature from 0 to 374 Celsius degrees. This study was developed by Mahendra Pal Verma Jaiswal, researcher of the Instituto de Investigaciones Electricas (IIE) [Spanish] En este articulo se presenta el experimento exhaustivo de la recopilacion de los datos experimentales de la solubilidad de cuarzo a lo largo de la curva de saturacion agua - vapor y en la zona de liquido comprimido. Sobre la base de estos datos se derivo una relacion de regresion, la cual es valida para todo el rango de temperatura desde 0 a 374 grados Celsius. Este estudio fue desarrollado por Mahendra Pal Verma Jaiswal, investigador del Instituto de Investigaciones Electricas (IIE)

  12. Hydrocarbons origin and classification of the Sergipe-Alagoas Basin: geochemical characterization; Origem e classificacao dos hidrocarbonetos da Bacia Sergipe-Alagoas: caracterizacao geoquimica

    Energy Technology Data Exchange (ETDEWEB)

    Babinski, Nelson A.; Santos, Regina C.R. dos [PETROBRAS, Rio de Janeiro, RJ (Brazil). Centro de Pesquisas


    Researches made on Sergipe-Alagoas sedimentary basin, found some oil and gas accumulations. Geochemical characterization based on isotopics and chromatographic studies, and chemical analysis of these oils are discussed. These analysis permitted identification of three oils types with distinct characteristics. The correlation between these oils with the generator rocks, construction of a model to demonstrate the generation, transport and accumulation of oil on these basin, are also related. 12 figs., 5 refs

  13. Geochemistry of the waters of the Descoberto River hydrographic basin, Brasilia/DF - Brazil; Geoquimica das aguas da bacia hidrografica do Rio Descoberto, Brasilia/DF - Brasil

    Energy Technology Data Exchange (ETDEWEB)

    Carmo, Marcileia Silva do [Universidade Federal do Para, Belem, PA (Brazil). Centro de Geociencias]. E-mail:; Boaventura, Geraldo Resende [Universidade de Brasilia, DF (Brazil). Inst. de Geociencias; Oliveira, Edivan Costa [Centro Federal de Educacao Tecnologica do Para (CEFET-PA), Belem, PA (Brazil). Coordenacao de Quimica


    The objective of this paper is to investigate the physical and chemical quality of the water of the Descoberto River during the dry and rainy seasons by measuring pH, temperature, electric conductivity, total dissolved solids, turbidity, color, alkalinity and NO{sub 3}-, SO{sub 4}{sup 2-}, PO{sub 4}{sup 3-}, NH{sub 4}+, Cl{sup -} and HCO{sub 3}-, and the elements Sr, Mo, Cd, Y, Ti, Ca, V, Mg, Fe, Si, Ni, Zr, Cu, Al, Cr, Mn, Ba, Co, Zn, P, Na and K. The results showed high concentrations in both seasons, with dilution along the course of the river, minimizing for a while problems that compromise the quality of the water of this source. However, a progressive deterioration can occur due to an increase in the discharge of pollutants, resulting from population growth, agricultural activities and other factors. (author)

  14. Mineralogia y geoquimica de los sedimentos de algunas lagunas del N de la provincia de Málaga (S de España

    Directory of Open Access Journals (Sweden)

    Benavente, J.


    Full Text Available Similar compositional and genetic characteristics for the recently deposited sediments in some lakes and ponds of the north of the Málaga province have been observed. Nevertheless, it seems to exist some differences in their mineralogical and geochemical evolution as well as in the degree of alteration of the original sediment. The mineral alterations produced in these confined lacustrine basins, with pH higher than 8, are controlled by ionic exchange between water and sediment. According to the mineral alteration degree three stadiums of mineral evolution have been detected. In addition the mineralogical and geochemical evolution and the hydrochemical characteristic of the aqueous environment are related. The study has shown that some neoformation processes of Mgrich minerals also occur.Se han observado características composicionales y genéticas similares en los sedimentos más recientes de algunas lagunas del norte de la provincia de Málaga, si bien parecen existir diferencias en su evolución mineralógica y geoquímica y en el grado de alteración del sedimento original. Las alteraciones minerales producidas en estos medios lacustres confinados, con pH superior a 8, están controladas por los intercambios iónicos entre el agua y el sedimento. Según el grado de alteración mineral detectado se han observado tres estadios de evolución mineral para estos sedimentos. Igualmente, se observa una relación entre la evolución mineralógica y geoquímica y las características hidroquímicas del agua existente en el medio. El estudio ha mostrado indicios de neoformación de minerales ricos en Mg+2.

  15. Chemical, physical and isotopic characterization of U{sub 3}Si{sub 2}, for nuclear forensics purposes; Caracterizacao quimica, fisica e isotopica de U{sub 3}Si{sub 2} para fins forenses nucleares

    Energy Technology Data Exchange (ETDEWEB)

    Rosa, Daniele Scarpim


    In the early 1990's, the first illicit trafficking of nuclear and radioactive materials was observed mainly in Europe. A decade marked by numerous cases of seizures of these materials. As a result, these events have become the subject of criminal forensic investigations and develop from there, nuclear forensics. In Brazil there are no illicit trafficking official records of nuclear material, however, is widely known the extraction and illegal transportation of radioactive geological materials, and the materials pieces attachment used as shielding for radioactive sources. One of the main tools used in nuclear forensics is the nuclear materials databases establishment. These documents must contain the most information as possible about the physical, chemical and nuclear material seized, allowing the identification of their origin, manufacturing process or age. Thus, it sets characteristic composition standards of each material, called 'chemical signatures' (chemical finger print). In this work nuclear forensic protocol was adopted as well as the three stages of assessment suggested by International Atomic Energy Agency (IAEA) in identifying the origin of uranium silicide (U{sub 3}Si{sub 2}). Assays were performed in order to make physical, chemical and isotopic characterization of the studied materials and compared the data with those obtained for other uranium compounds (Uranium tetrafluoride, UF{sub 4}; uranium oxide, UO{sub 2} and U{sub 3}O{sub 8}; Yellow cake) by establishing a characteristic signature for each one. Through the assays the uranium compounds were classify by origin groups, as far as they are from different manufactured process and/ or origin. It was also possible to show the importance of a nuclear forensic database during an investigation of a nuclear forensic event. (author)

  16. Identification of the mechanisms and origin of salinization of groundwaters in coastal aquifers by means of isotopic techniques; Identificacion de los mecanismos y del orgien de la salinizacion del agua subterranea en acuiferos costeros mdiante tecnicas isotopicas

    Energy Technology Data Exchange (ETDEWEB)

    Araguas, L. J.; Quejido, A. J.


    To study the origin of salinity and the mechanisms operating in coastal aquifers, a set of tools is available to determine the essential aspects of the hydrogeological behaviour of the system. these tools are based on the integrated use of hydrochemical parameters (major constituents and trace elements) and isotopic parameters (oxygen, hydrogen, sulfur, carbon, strontium and boron). In addition to the active intrusion of seawater, salinization in coastal areas may be influenced by various human activities that accelerate the degradation of water quality, such as concentrated pumping, intensive farming techniques with return of irrigation water, or reuse of urban and industrial waste water. Characterization of the dominant processes and mechanisms is required for suitable management of the resource and implementation of corrective measures. (Author)

  17. Optimization of the isotopic analysis of UF{sub 6} by quadrupole mass spectrometry technique; Otimizacao da analise isotopica de UF{sub 6} utilizando-se a tecnica de espectrometria de massas por quadrupolo

    Energy Technology Data Exchange (ETDEWEB)

    Porto, Peterson


    In the present work a procedure for determination of the isotopic ratio {sup 238}U/{sup 235}U in UF{sub 6} samples was established using a quadrupole mass spectrometer with ionization by electron impact and ion detection by Faraday cup or electron multiplier. For this, the following items were optimized in the spectrometer: the parameters in the ion source that provided the most intense peak, with good shape, for the corresponding mass of the most abundant isotope; the resolution that reduced the non linear effects and the number of analytic cycles that reduced the uncertainty in the results. The measurement process was characterized with respect to the effects of mass discrimination, linearity and memory effect. The mass discrimination showed to be linearly dependent of the sample pressure in the batch volume, for the pressure ranges from 0.15 to 0.30 mbar and from 0.30 to 0.40 mbar. The spectrometer was shown linear in the measurement of isotopic ratios between 0.005 and 0.045. The memory factor for the ion source and for the introduction system were, respectively, 1.000 {+-} 0.001 and 1.003 {+-} 0.003; the first one can be ignored, the second one can be eliminated by washing the batch volume with the new sample. A methodology for routine analysis of UF{sub 6} samples and the determination of the uncertainties were set up in details as well. (author)

  18. Spanish Network for Isotopes in Precipitation: Isotope Spatial distribution and contribution to the knowledge of the hydrological cycle; La Red Espanola de Vigilancia de Isotopos en la Precipitacion (REVIP): distribucion isotopica espacial y aportacion al conocimiento del ciclo hidrologico

    Energy Technology Data Exchange (ETDEWEB)

    Diaz-Teijeiro, M. F.; Rodriguez-Arevalo, J.; Castano, S.


    The results of seven years of operation of the Spanish Network for Isotopes ({sup 2}H, {sup 1}8O y {sup 3}H) in Precipitation (REVIP) are shown. this Network is managed since 2000 by the Centro de Estudios de Tecnicas Aplicadas of the Centro de Estudios y Experimentacion de Obras Publicas (CEDEX) in collaboration with the Agencia Estatal de Meteorologia (AEMET). The results of REVIP are sent to the International Atomic Energy Agency (IAEA) in order to be integrated in the Global Network for Isotopes in Precipitation (GNIP). The spatial distribution of stable isotopes ({sup 1}8O h {sup 2}H) in precipitation in Spain follows a multiple regression model, based on two geographic factors: latitude and elevation, which is strongly correlated with temperature, an important factor controlling isotope fractionation. This information on {sup 1}8O and {sup 2}H is useful to trace surface and ground waters and, combined with the information, about the spatial and temporal distribution of the Tritium ({sup 3}H) concentration in precipitation, allows to date these waters in order to estimate flow directions and velocities, and to evaluate the residence time of water resources and aquifer vulnerability. (Author)

  19. Water isotopic characterization of hypersaline formation of a petroleum field Reconcavo basin, Brazil; Caracterizacao isotopica de aguas de formacao hipersalinas de um campo de petroleo da Bacia do Reconcavo, Brasil

    Energy Technology Data Exchange (ETDEWEB)

    Teles, Danilo Ribeiro de Sa; Azevedo, Antonio Expedito Gomes de, E-mail:, E-mail: [Universidade Federal da Bahia (UFBA), Salvador, BA (Brazil). Inst. de Fisica. Centro de Pesquisa em Geofisica e Geologia; Santos, Christian Pereira Lopes dos, E-mail: [Instituto Federal Baiano, Salvador, BA (Brazil)


    Formation water is the water present in reservoir rock pores, produced together with petroleum. Usually it is hyper saline with concentrations that can be higher than 250 g/l of dissolved solids. The concentration of the dissolved elements and the isotopic composition of the water and of some of the dissolved elements can be excellent tracers to study the dynamic of underground fluid flux, the mixing of distinct sources and the origin of salinization of these waters. This work reports the isotopic composition ({delta}{sup 2}H , {delta}{sup 18}O) and electrical conductivity (EC) of formation waters from 10 wells of a petroleum field of the Reconcavo Basin, looking for their evolution, interaction with the minerals and rocks and reservoir interconnection. The samples have electric conductivity ranging from 84 to 137 mS/cm, with conductivity increasing with depth of production zone. It is observed an enrichment of deuterium and oxygen-18 with the depth of production zone, probably due to water-rock interactions that were probably increased by higher temperatures of the deeper levels and longer residence times. The samples from the production zone between 1450 to 1520 m, drained by 7 of the 10 wells sampled, show a small range in isotopic composition and in electric conductivity, indicating homogeneity in this level of the reservoir. In the shallow level of 450 m the values of {delta}{sup 2}H , {delta}{sup 18}O and EC are lower, with isotopic composition similar to the oceanic water, possibly representing the original water that entered the reservoir during the sedimentation of the basin. (author)

  20. Uranium determination in sea water using the isotopic dilution technique and HR-ICPMS; Determinacao de uranio em agua do mar por meio da tecnica de diluicao isotopica e HR-ICPMS

    Energy Technology Data Exchange (ETDEWEB)

    Pereira, Marcio Henrique da Costa; Sarkis, Jorge Eduardo de Souza; Hortellani, Marcos Antonio, E-mail:, E-mail: jesarkis@ipen.b [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil); Nascimento, Marcos R.L. [Laboratorio de Pocos de Caldas (LAPOC/CNEN-MG), MG (Brazil)


    In this work, the uranium total and the isotopic composition in seawater were calculated using the isotopic dilution applied to the mass spectrometry. The used tracer was a {sup 233}U solution . Near 99 % of the present salts in the matrix were separated by evaporation up to the saturation point. The uranium present in aqueous phase was separated from the matrix through the ion exchange chromatography using the strong Dowex 1 x 8 200-400 mesh anionic resin in chloridric medium 12 M. The analyses were performed in a high resolution mass spectrometer with plasma inductively coupled source. The method validation was done using the seawater standard CASS-4 (Near shore Seawater Reference Material for Trace metals) produced by the NRC C. The procedure allowed to obtain the fractions exempt of salts, having as consequence a greater stability in the analytical signal, and a rise in the instrumental revenue for a great number of samples. The uranium found in the samples was present in levels considered naturals and were obtained with a precision near 2 %

  1. Phosphorus kinetics in ovine fed with different phosphorus sources, using the isotopic dilution technique; Cinetica do fosforo em ovinos suplementados com diferentes fontes fosfatadas, atraves da tecnica de diluicao isotopica

    Energy Technology Data Exchange (ETDEWEB)

    Vitti, D.M.S.S.; Abdalla, A.L. [Centro de Energia Nuclear na Agricultura (CENA), Piracicaba, SP (Brazil); Meirelles, C.F. [Sao Paulo Univ., Piracicaba, SP (Brazil). Escola Superior de Agricultura Luiz de Queiroz


    Phosphorus kinetics in fluids and tissues of sheep was studied. Sixteen castrated sheep were kept in metabolism cages, receiving a semipuried diet containing as phosphorus sources dicalcium phosphate (BIC), monoammonium phosphate (MAP), superphosphate (SPT) and Tapita phosphate (TAP) 200 {mu}Ci P-32 was intravenously injected in each sheep and blood and feces were collected for eight days. From the specific activities in feces and plasma the endogenous phosphorus and the absorption coefficient were calculated. plasma P-32 half-life was determined. Nine days after injection the animals were killed and liver, kidney and muscle and bone samples were collected. P-32 retention and specific activities in tissues were determined. Endogenous phosphorus and absorption coefficient values were 54.44 {+-} 15.31 mh/kg live weight and 0.60; 47.98 {+-} 12.44 and 0.56; 39.70 {+-} 7.29 and 0.49; 59.11 {+-} 17.12 and 0.58 respectively bor BIC, MAP, TAP and SPT. P-32 retention by tissues was 0.29 {+-} 0.09; 0.27 {+-} 0.06; 0.16 {+-} 0.04 and 0.08 {+-} 0.03 dose/g fresh matter, respectively for bone, liver, kidney and muscle. It was concluded that animals which received TAP showed differences in absorption, distribution and P-32 retention by fluids and tissues. Phosphorus availability was lower for this source. (author) 14 refs., 1 tab.

  2. Soil available nitrogen measurement by the electro-ultrafiltration and isotopic dilution technique; Medida do nitrogenio disponivel do solo pela tecnica da eletro-ultrafiltracao e diluicao isotopica ({sup 15} N)

    Energy Technology Data Exchange (ETDEWEB)

    Diez, J.A.; Polo, A. [Consejo Superior de Invetsigaciones Cientificas, Madrid (Spain). Centro de Ciencias Medioambientales


    The goal of this work was the evaluation of the available nitrogen of a soil by means of the electro-ultrafiltration (EUF) technique in comparison with the nitrogen taken up plants. The experiment was carried out in posts maintained in a greenhouse, using a yellow Latosol from the Central Amazon rain forest. It was fertilized with labelled K N O{sub 3} (10,616 at % {sup 15} N), using a dose of 254,5 mg N/pot Soil samples were submitted to an extraction by EUF for the quantification of the available nitrogen and after Brachiaria humidicola was cultivated for 60 days. The origin of the nitrogen (fertilizer or soil) was measured by the isotopic dilution technique in soil, EUF extracts and plants. The results showed that both technique values were in the same order of magnitude, with similar percentages of mobilized nitrogen in relation to the total nitrogen in the soil. In relation to the nitrogen derived from fertilizer, the EUF technique extracted 3,48 times more nitrogen than the plants. Nevertheless we have to take into account that the dose of fertilizer was excessive for a species with low capacity of nitrogen assimilation. (author) 10 refs., 4 tabs.

  3. Estimation of the activity and isotopic composition of the fuel elements of the reactor in decaying; Estimacion de la actividad y composicion isotopica de los elementos combustibles del reactor en decaimiento

    Energy Technology Data Exchange (ETDEWEB)

    Aguilar H, F. [ININ, 52045 Ocoyoacac, Estado de Mexico (Mexico)


    At the present time its are had 59 fuel elements, 3 control bars with follower and 2 instrumented irradiated fuels that its are decaying in the pool of the reactor. The burnt one that its have these fuels is not uniform, the quantity of U-235 that contain at the moment it varies between 33.5 g up to 35.2 and its have a decay of at least 12 years. The burnt of the fuels was obtained with the CREMAT code, this burnt was takes like base to estimate the current isotopic inventory and the activity of the same ones using the ORIGEN2 code. (Author)

  4. Determination of the {delta}{sup 13}C (per mille) isotopic rate of the Brazilian beer pilsen type; Determinacao da razao isotopica {delta}{sup 13}C (per mille) de cerveja clara tipo pilsen nacional

    Energy Technology Data Exchange (ETDEWEB)

    Rossete, Alexssandra L.R.M.; Bendassolli, Jose Albertino [Centro de Energia Nuclear na Agricultura (CENA), Piracicaba, SP (Brazil). Lab. de Isotopos Estaveis; Lopes, Fabio [Centro de Energia Nuclear na Agricultura (CENA), Piracicaba, SP (Brazil). Lab. de Ecologia Isotopica; Martinelli, Luiz Antonio [Universidade Estadual de Londrina, PR (Brazil). Dept. de Fisica. Lab. de Fisica Nuclear Aplicada


    Beer has been consumed in Brazil since the XIX century. However, at that time, this beverage was imported from England, and the first Brazilian breweries just appeared at the end of the XX century. Basically, beer is made from: malt of barley, Humulus lupulus, water and yeast. In this work, twenty brands of national beer (Pilsen type), and also two different cereals, barley, a C3 metabolism plant, corn, a C4 plant, were analysed to determine their isotope composition {delta}{sup 13} C (per mille) utilizing a mass spectrometer Delta Plus Finigam and Anca S.L. An aliquot of each sample was transferred using a capillary of glass to a tin capsule contends a small amount of sorbitol. The isotope compositions, {delta}{sup 13} C, of barley and corn samples determined were -27.2 and -11.5 per mille, respectively. These results were used to calculate the equation of mixture model. Considering the beer samples, the {delta}{sup 13} C ranged from -18.3 to -23.1 per mille; this result means that the percentage of C3 plant is from 43.3 to 73.9 per mille. In this manner, it is possible to concluded that all beer samples has malted cereals (C4 plant), as far as the low values of C3 plants were presented in these samples as shown through the equation of mixtures model. (author)

  5. Chemical and isotopic characterization of rainwater in Los Azufres, Michoacan, Mexico and its surroundings. Caracterizacion quimica e isotopica de las precipitaciones pluviales en el campo geotermico de Los Azufres, Michoacan, Mexico y en zonas de referencia

    Energy Technology Data Exchange (ETDEWEB)

    Verma, Mahendra Pal (Instituto de Investigaciones Electricas, Cuernavaca (Mexico)); Barrera Gonzalez, Victor; Sandoval Medina, Fernando; Tapia Salazar, Ruth; Casimiro Espinoza, Emigdio (Residencia de Los Azufres, Morelia (Mexico)); Fernandez Solorzano, Ma Elena (Departamento de Exploracion, Gerencia de Proyectos Geotermoelectricos de la Comision Federal de Electricidad, Morelia (Mexico)); Rye, Robert; Gent, Carol; Johnson, Craig (USGS, Denver, CO. (United States))


    The results obtained from the chemical and isotopic monitoring of rainwater in Los Azufres and its surroundings in the period May to September, 1995 are presented. Eight sampling sites were selected to collect rainwater: six in the Los Azufres and its surroundings and two in the offices of the Comision Federal de Electricidad (CFE) in Morelia and Guadalajara. The anions Cl-, SO[sub 4] [sup 2]- and NO[sub 3]- were analyzed in about 350 samples. The rainwater has very low content of carbonic species (i.e. total dissolved CO[sub 2]). Due to it, it is not possible to analyze alkalinity with traditional titration method. The Gran Titration method was implemented to determine alkalinity (or acidity) and carbonic speciation in the samples. The values of acidity (negative of alkalinity) are in the range of 10[sup -4] to 10[sup -6] eq/l and are positive only for the sites Vivero and Guadalajara. The space and time distribution of the chemical and isotopic species in the rainwater could provide the information about the source of acidity. The species S0[sub 4][sup 2]- and NO[sub 3]- contribute to the acidity. To study the isotopic composition of dissolved sulfate, a system is designed to collect 100 1 of rainwater. The dissolved sulfate ions were extracted in the form of barium sulfate to analyze sulfur-34 and oxygen-18. The values of (d34S are around -1.5% in Los Azufres and its surroundings and in the CFE office in Morelia whereas they are very different in the CFE office in Guadalajara (-0.3%). The same values of d34S in Los Azufres and Morelia indicates a regional source of sulfate and is not related to the Los Azufres geothermal system.

  6. Development of a simplified methodology for the isotopic determination of fuel spent in Light Water Reactors; Desarrollo de una metodologia simplificada para la determinacion isotopica del combustible gastado en reactores de agua ligera

    Energy Technology Data Exchange (ETDEWEB)

    Hernandez N, H.; Francois L, J.L. [FI-UNAM, 04510 Mexico D.F. (Mexico)]. e-mail:


    The present work presents a simplified methodology to quantify the isotopic content of the spent fuel of light water reactors; their application is it specific to the Laguna Verde Nucleo electric Central by means of a balance cycle of 18 months. The methodology is divided in two parts: the first one consists on the development of a model of a simplified cell, for the isotopic quantification of the irradiated fuel. With this model the burnt one is simulated 48,000 MWD/TU of the fuel in the core of the reactor, taking like base one fuel assemble type 10x10 and using a two-dimensional simulator for a fuel cell of a light water reactor (CPM-3). The second part of the methodology is based on the creation from an isotopic decay model through an algorithm in C++ (decay) to evaluate the amount, by decay of the radionuclides, after having been irradiated the fuel until the time in which the reprocessing is made. Finally the method used for the quantification of the kilograms of uranium and obtained plutonium of a normalized quantity (1000 kg) of fuel irradiated in a reactor is presented. These results will allow later on to make analysis of the final disposition of the irradiated fuel. (Author)

  7. Isotope Dilution - Thermal Ionisation Mass Spectrometric Analysis for Tin in a Fly Ash Material; Analisis de Estano en una Ceniza de Combustion mediante Espectrometria de Masas de Ionizacion Termica con Dilucion Isotopica

    Energy Technology Data Exchange (ETDEWEB)

    Hernandez, C.; Fernandez, M.; Quejido, A. L.


    Isotope dilution-thermal ionisation mass spectrometry (ID-TIMS) analysis has been applied to the determination of tin in a fly ash sample supplied by the EC Joint Research Centre (Ispra, Italy). The proposed procedure includes the silica gel/phosphoric acid technique for tin thermal ionisation activation and a strict heating protocol for isotope ratio measurements. Instrumental mass discrimination factor has been previously determined measuring a natural tin standard solution. Spike solutions has been prepared from 112Sn-enriched metal and quantified by reverse isotope dilution analysis. Two sample aliquots were spiked and tin was extracted with 4,5 M HCI during 25 min ultrasound exposure time. Due to the complex matrix of this fly ash material, a two-step purification stage using ion-exchange chromatography was required prior TIMS analysis. Obtained results for the two sample-spike blends (10,10 + - 0,55 y 10,50 + - 0,64 imolg-1) are comprarable, both value and uncertainty. Also a good reproducibility is observed between measurements. The proposed ID-TIMS procedure, as a primary method and due to the lack of fly ash reference material certified for tin content, can be used to validate more routine methodologies applied to tin determination in this kind of materials. (Author) 75 refs.

  8. Geochemistry of natural radionuclide in soils surrounding a mining and plant uranium concentration;Geoquimica de radionuclindeos naturais em solos de areas circunvizinhas a uma unidade de mineracao e atividade de uranio

    Energy Technology Data Exchange (ETDEWEB)

    Cardoso, Gildevan Viana, E-mail: [Instituto Nacional de Colonizacao e Reforma Agraria (INCRA), Rio de Janeiro, RJ (Brazil); Amaral Sobrinho, Nelson Moura Brasil do; Mazur, Nelson, E-mail: nelmoura@ufrrj.b, E-mail: nelmazur@ufrrj.b [Universidade Federal Rural do Rio de Janeiro (UFRRJ), Seropedica, RJ (Brazil). Inst. de Agronomia. Dept. de Solos; Wasserman, Maria Angelica Vergara, E-mail: [Instituto de Radioprotecao e Dosimetria (IRD/CNEN-RJ), Rio de Janeiro, RJ (Brazil)


    The environmental impacts resulting from uranium exploration and processing are to a great extent identical to those caused by extractive mining activities in general. This study aimed to determine the geochemical partitioning of the natural radionuclides {sup 238}U, {sup 226}Ra and {sup 210}Pb in areas surrounding the Uranium Mining and Concentration Plant (URA) of the Brazilian Nuclear Industries S.A., in the uranium deposit region of Lagoa Real, in Caetite, southwestern Bahia state. Representative soil samples of the main regional soil classes were collected from the layer 0-20 cm, in five areas around the URA. The level of total activity and geochemical fractionation (F1 slightly acidic, F2 reducible, F3 oxidisable, F4 alkaline, and F5 residual) were determined for the five areas. The average total radioactivity levels were, in Bq kg{sup -1} soil: 50 for {sup 238}U, 51 for {sup 226}Ra, and 159 for {sup 210}Pb. During the potentially bioavailable phase (F1) 11 % were extracted for {sup 238}U, 13 % for {sup 226}Ra and 3 % for {sup 210}Pb. The bioavailability of {sup 238}U was higher in more acidic soils and the affinity for iron oxides was greater, unlike in the case of {sup 226}Ra, with the greatest bioavailability. {sup 210}Pb was predominantly associated with F5. The high percentage of {sup 238}U, {sup 226}Ra and {sup 210}Pb in the geochemical fraction F5 indicates that the concentrations observed in the five soils are predominantly associated to the parent material of these soils, rather than to an artificial contamination caused by the URA activity. (author)

  9. Geochemistry and Geochronology U-Pb SHRIMP of granites from Peixoto de Azevedo: Alta Floresta Gold Province; Geoquimica e geocronologia U-Pb (SHRIMP) de granitos da regiao de Peixoto de Azevedo: Provincia Aurifera Alta Floresta, MT

    Energy Technology Data Exchange (ETDEWEB)

    Silva, Fernanda Rodrigues da; Barros, Marcia Aparecida Sant' Ana; Pierosan, Ronaldo; Pinho, Francisco Edigio Cavalcante; Tavares, Carla; Rocha, Jhonattan, E-mail:, E-mail:, E-mail:, E-mail:, E-mail:, E-mail: [Universidade Federal de Mato Grosso (UFMT), Cuiaba, MT (Brazil). Inst. de Ciencias Exatas e da Terra; Rocha, Mara Luiza Barros Pita; Vasconcelos, Bruno Rodrigo; Dezula, Samantha Evelyn Max, E-mail:, E-mail:, E-mail: [Universidade de Brasilia (UNB), Brasilia, DF (Brazil). Programa de Pos-Graduacao em Geologia


    The analysis of petrographic, geochemical and geochronological data of granites in the Peixoto de Azevedo region, Mato Grosso, Brazil, in the eastern portion of the Alta Floresta Gold Province, led to the recognition of two granitic bodies bounded by regional major faults and shear zones. In the northwestern portion a body with featured as biotite granodiorite, coarse-grained, with porphyritic to inequigranular texture, metaluminous to peraluminous, high-K calc-alkaline and magnesium character. In the southeastern portion of the area, a biotite monzogranite coarse-grained, with equigranular to porphyritic texture, slightly peraluminous, high-K calc-alkaline and dominantly of ferrous character. U- Pb dating (SHRIMP) showed that the biotite monzogranite has an age of 1869 ± 10 Ma, similar to the Matupa Intrusive Suite, while the biotite granodiorite has an age of 1781 ± 10 Ma, that is the age expected to Peixoto Granite. Both units show patterns of rare earth elements with enrichment of light over heavy and negative Eu anomaly (La{sub N}/Yb{sub N} » 7.6 to 17.31 and ratios Eu/EU{sup ⁎} between 0.46 – 0.72 for biotite monzogranite and La{sub N}/Yb{sub N} » 7.13 to 29.09 with ratios Eu/Eu{sup ⁎} between 0.25 - 0.40 for the biotite granodiorite). Trace elements pattern for both present negative anomalies of Ba, P, Ti and Nb indicating an evolution from mineral fractionation and subduction related sources. In this paper, it is suggested that the monzogranite Matupa was developed in mature arc tectonic environment. For the Peixoto Granite, two hypotheses are suggested: (a) it was developed in younger magmatic arc environment associated with the Colider Magmatism or (b) it was generated in extensional tectonic environment during the Columbia Super continent break up. (author)

  10. Augen gneisses versus Augen gneisses from the Jaguaribeana Belt, northeastern region from Brazil: stratigraphy, geochemistry and U-Pb ages; Augen gnaisses versus Augen gnaisses da faixa Jaguaribeana, NE do Brasil: estratigrafia, geoquimica e idades U-Pb

    Energy Technology Data Exchange (ETDEWEB)

    Sa, Jaziel Martins; Silva, Elvis Roberto da [Rio Grande do Norte Univ., Natal, RN (Brazil). Dept. de Geologia; Bertrand, Jean Michel [Savoie Univ., 73 - Chambery (France). Lab. de Geodynamique; Leterrier, Jacques [Centre National de la Recherche Scientifique (CNRS), 54 - Nancy (France). Centre de Recherches Petrographiques et Geochimiques


    The Jaguaribeana Belt is located at Borborema Province, Ceara State, Brazil and this study aims to present Uranium-Lead (U-Pb) data and the augen gneisses petrographic and geochemical study of the Jaguaribe Belt, and to realize comparisons between these and the augen gneisses from the Oros Belt. It describes the geological characteristics of this region, the augen gneisses petrography and geochemical data and the U-Pb method results for a discussion about the augen gneisses from the Oros and Jaguaribe Belt 10 refs., 6 figs.

  11. Geochemical characteristics of water from the reservoir of the hydrothermal system of Las Tres Virgenes, Baja California Sur, Mexico; Caracteristicas geoquimicas de las aguas del reservorio del sistema hidrotermal actual de Las Tres Virgenes, Baja California Sur, Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Gonalez Partida, Eduardo [Universidad Nacional Autonoma de Mexico (Mexico); Tello Hinojosa, Enrique [Comision Federal de Electricidad (Mexico); Pal Verma, Mahendra [Instituto de Investigaciones Electricas (Mexico)


    The Las Tres Virgenes geothermal field is a liquid dominated system. The separated produced by the wells are sodium-chloride type, which is a characteristic of totally equilibrated geothermal brine. The temperature of water-rock interaction in the reservoir is 280 Celsius degrees. the chemical composition of gases corresponds to the one expected in a geothermal environment. The CO{sub 2} is the predominating gas and it is superior in 90% in weight to the total of existing gases. The gas contents is less than 1% in weight, in the case of the wells LV-1 and LV-3. It is also possible to conclude that the gases are in equilibrium with the liquid phase at a temperature of 280 Celsius degrees. With respect to water quality, it is saline, from high to very high and the contents of exchangeable sodium is also very high, resulting in waters not fit for agricultural usage. [Spanish] El yacimiento geotermico de Las Tres Virgenes, en Baja California Sur, Mexico, es un sistema de liquido dominante, en donde el agua separada producida por los pozos presenta un caracter clorurado-sodico caracteristico de una salmuera de origen geotermico totalmente equilibrada. El sistema agua-roca se encuentra en equilibrio a una temperatura de 280 grados centigrados , dicha temperatura son congruentes con las estimadas para las fases gaseosas y liquidas. La composicion quimica de los gases corresponde a la esperada en un ambiente geotermico. El CO{sub 2} es el predominante y es superior a 90% en peso del total de los gases presentes. El contenido de gas es menor de 1% en peso en el caso de los pozos LV-1 y LV-3. Tambien se puede concluir que los gases estan en equilibrio en las fases liquidas a una temperatura de 280 grados centigrados. Con respecto a la calidad del agua, presenta una salinidad de alta a muy alta y el contenido de sodio intercambiable tambien es muy alto, por lo que dichas aguas no son muy aptas para el cultivo.

  12. U/Pb geochronology and paleo and proterozoic orthogneisses geochemistry from the Taquaritinga region - Pernambuco State, Brazil; Geocronologia U/Pb e geoquimica de ortognaisses paleo e mesoproterozoicos da regiao de Taquaritinga, PE

    Energy Technology Data Exchange (ETDEWEB)

    Sa, Jaziel Martins [Rio Grande do Norte Univ., Natal, RN (Brazil). Dept. de Geologia; Bertrand, Jean Michel [Savoie Univ., 73 - Chambery (France). Lab. de Geodynamique; Leterrier, Jacques [Centre National de la Recherche Scientifique (CNRS), 54 - Nancy (France). Centre de Recherches Petrographiques et Geochimiques


    The Taquaritinga region is located at the Borborema Province Transversal Zone, northeastern part of Brazil, and not existing geochronological data in this region, this study intended to furnish some information for a geotectonics evolution knowledge. It presents the geological characteristics of this region, describes the various kinds of chemical analysis realized in the gneisses, involving major, minor and rare earth elements, and shows the geochronological data that suggests the orthogneisse age and the epoch of this geotectonic event 8 refs., 2 figs.

  13. Geochemical signature of columbite-tantalite and radiometric survey of radioactive pegmatites in the region of Parelhas, Rio Grande do Norte, Brazil; Assinatura geoquimica de columbita-tantalita e levantamento radiometrico de pegmatitos radioativos da regiao de Parelhas, RN, Brasil

    Energy Technology Data Exchange (ETDEWEB)

    Moura, Jorge Costa de


    This thesis is the result of geochemical, structural and radiometric investigations on radioactive pegmatites of the Borborema Pegmatitic Province in Northeast Brazil. The studied area, located in the surroundings of the city of Parelhas in the region of the Serra da Borborema, is well known for its thousands of pegmatitic bodies exploited in primitive mines called 'garimpos'. The main goal was to find an efficient, cheap and routine inspection procedure to identify the origin of commercialized radioactive columbite-tantalite (coltan) ore. The Brazilian Nuclear Energy Agency (CNEN) controls uranium commerce and nuclear activity in Brazil. Without an effective method to characterize coltan ores from different localities it is impossible to control the trade. The here presented new method was developed by correlating structural features of these pegmatites with the geochemical behavior of their coltan samples. It was found that the variation of the ratio U/Th versus Nb{sub 2}O{sub 5}/Ta{sub 2}O{sub 5} provides geochemical signatures (analytical fingerprints) for the source location of such ore. A test of the new method with coltan samples of commercial batches from the Brazilian states Amapa and Rondonia also generated distinct geochemical signatures. A radiometric survey (CPS) was carried out in several mines and pegmatites to study the environmental impact of gamma radiation. It included in situ measurements of pegmatite walls, host rocks, soil, and accumulated water and revealed that gamma emitters are hardly solubilized and environmental gamma radiation therefore generally is not enhanced to a dangerous level. (author)

  14. The geochemistry in the Manzanares river flood plain sediments as a way to assess environmental impact; La geoquimica en los sedimentos de la llanura de inundacion del Manzanares como medio para evaluar el impacto ambiental

    Energy Technology Data Exchange (ETDEWEB)

    Adanez, P.; Garcia Cortes, A.; Locutura, J.


    Flood plains are an important component of drainage systems, as they act like transport channels and stores or sinks for suspended sediment deposited during the floods. A geochemical study in flood plain sediments is a reliable method to reconstruct the evolution of anthropic contamination through time in a basin. As an application of this method, the flood plain of the Manzanares River (Madrid) has been examined, as an example of urban environment. Samples have been collected through the flood plain vertical profile at two different selected sites upstream and downstream the city of Madrid. The samples have been sieved at six sizes of grain in which trace elements have been analysed by ICP-MS and INAA. This study highlights an increase in the contents of contaminant elements in the profile sampled downstream as well as an enrichment of these elements as the sediment is younger. (Author) 19 refs.

  15. Geochemical characterization and comparative study of plagiogranites from the South portuguese and Ossa-Morena Zones (SW Iberian Massif, Spain); Caracterizacion geoquimica y estudio comparativo de plagiogranitos de las Zonas Surportuguesa y Ossa-Morena (SO del Macizo Iberico, Espana)

    Energy Technology Data Exchange (ETDEWEB)

    Bellido, F.; Diez-Montes, A.; Sanchez-Garcia, T.


    Plagiogranites and albitic rocks belonging to contrasted magmatic associations of different ages and geo dynamic environments outcrop in Ossa-Morena (OMZ) and Sur portuguese (SPZ) Zones. OMZ plagiogranites are related with Cambrian-Ordovician rifting and represent a part of the felsic members of a bimodal magmatic suite and show oceanic plagiogranites affinities. SPZ plagiogranites are related with a Carboniferous volcano-plutonic calc-alkaline suite related with Variscan Orogeny. Both plagiogranites show many similar petrological and geochemical characteristics but display some different immobile elements ratios as La/Nb, Th/Nb, Th/La that are unaltered by metamorphism, magmatic differentiation and alteration processes and prove differences in their sources. SPZ plagiogranites show a more compositional homogeneity than OMZ ones. This is interpreted as a proof of cogenetic origin for SPZ plagiogranites and heterogeneous origin for OMZ plagiogranites, derived from the mix of different sources (astenospheric, lithospheric and crustal). (Author) 23 refs.

  16. Petrographical and geochemical characterization and deformation conditions of the San Cristobal pluton, Sierra de Velasco, La Rioja, Argentina; Caracterizacion petrografica y geoquimica y condiciones de deformacion del pluton San Cristobal, Sierra de Velasco, La Rioja, Argentina

    Energy Technology Data Exchange (ETDEWEB)

    Bellos, L.I.; Toselli, A.J.; Rossi, J.N.; Grosse, P.; Rosa, J.D. de la; Castro, A.


    The San Cristobal pluton is a 35 km2 granitic body that outcrops at the southestern tip of the Sierra de Velasco, located west of La Rioja city, Argentina. It is formed by monzogranites and syenogranites, together with scarce granodiorites, with medium to fine-grained, equigranular to slightly porphyritic textures. Their mineral assemblage consists of quartz + microcline + plagioclase + biotite {+-} muscovite + zircon + apatite + magnetite. The granite contains dioritic to tonalitic mafic enclaves. The central and eastern parts of the granite have been deformed by the NNW-SSE trending South Mylonitic shear zone formed by mylonitic rocks. The metamorphic host-rock is represented by scarce greenschist facies xenoliths and hornfels with the high T/P assemblage K-feldspar - cordierite - biotite {+-} sillimanite. The granites are calc-alkaline, weak- to moderately peraluminous, and formed as part of a continental magmatic arc developed along the active margin of western Gondwana during the Early Paleozoic. The depth of emplacement of the San Cristobal pluton is estimated at {approx}12 km. (Author).

  17. Fluid geochemistry associated associated to rocks: preliminary tests om minerals of granite rocks potentially hostess of radioactive waste repository; Geoquimica de fluidos associados a rochas: testes preliminares em minerais de rochas granitoides potencialmente hospedeiras de repositorios de rejeitos radioativos

    Energy Technology Data Exchange (ETDEWEB)

    Amorim, Lucas E.D.; Rios, Francisco J.; Oliveira, Lucilia A.R. de; Alves, James V.; Fuzikawa, Kazuo; Garcia, Luiz; Ribeiro, Yuri, E-mail: LDAmorim@cdtn.b [Centro de Desenvolvimento da Tecnologia Nuclear (CDTN/CNEN-MG), Belo Horizonte, MG (Brazil); Matos, Evandro C. de [Industrias Nucleares do Brasil S.A. (INB), Caetite, BA (Brazil)


    Fluid inclusions (FI) are micro cavities present on crystals and imprison the mineralizer fluids, and are formed during or posterior to the mineral formation. Those kind of studies are very important for orientation of the engineer barrier projects for this purpose, in order to avoid that the solutions present in the mineral FI can affect the repository walls. This work proposes the development of FI micro compositional studies in the the hostess minerals viewing the contribution for a better understanding of the solution composition present in the metamorphosis granitoid rocks. So, micro thermometric, microchemical and characterization of the material confined in the FI, and the hostess minerals. Great part of the found FI are present in the quartz and plagioclase crystals. The obtained data on the mineral compositions and their inclusions will allow to formulate hypothesis on the process which could occurs at the repository walls, decurrens from of the corrosive character (or not) of the fluids present in the FI, and propose measurements to avoid them

  18. Correlazioni mediante l’analisi 87Sr/86Sr sugli strati calcareo marnosi del gruppo del Cilento e sue implicazioni


    Danna, Massimo


    In questo lavoro è stato condotto uno studio cronostratigrafico e di correlazione sui megastrati calcareo-marnosi (“fogliarine Auctt.”) delle formazioni del “Gruppo del Cilento” (sensu Nardi et alii, 2003) e della formazione di Albidona Auctt., e sui livelli calcareo-marnosi più o meno litoidi, di spessore variabile da centimetrico a metrico, intercalati a diverse altezze stratigrafiche nelle suddette formazioni, utilizzando il rapporto degli isotopi 87Sr/86Sr. La stratigrafia isotopica de...

  19. Determination of concentrations and isotopic ratio of uranium in groundwaters drawn from two deep wells drilled in granitic rocks belonging to Itu intrusive suite; Determinacao das concentracoes e razoes isotopicas de uranio em aguas subterraneas extraidas de pocos perfurados em rochas da suite intrusiva de Itu (SP)

    Energy Technology Data Exchange (ETDEWEB)

    Souza, Francisca de; Reyes, Erika; Marques, Leila Soares [Sao Paulo Univ., SP (Brazil). Inst. de Astronomia, Geofisica e Ciencias Atmosfericas. Dept. de Geofisica]. E-mail:;;


    This paper presents the first results obtained in the determination of dissolved uranium concentrations and ({sup 234}U/{sup 238}U) activity ratios of groundwaters drawn from two deep wells drilled in granitic rocks belonging to Itu Intrusive Suite, which is located at eastern Sao Paulo State. One of the wells, whose groundwaters have been analyzed, is located in Salto Town, while the other one is located in Itu Town. The groundwater sampling is monthly and begun on September, 2004, in order to investigate possible sazonal variations. The alpha spectrometry technique, associated with isotopic dilution method, has been used for these determinations. The data obtained up to now show that the groundwaters from Salto present uranium concentrations significantly lower ((0.098 {+-} 0.007) - (0.17 {+-} 0.01) ng/g) than those from Itu ((0.22 {+-} 0.02) - (0.31 {+-} 0.02) ng/g). The {sup 234}U and {sup 238}U isotopes of the investigated groundwaters from both wells are in radioactive disequilibrium, with ({sup 234}U/{sup 238}U) activity ratios systematically higher than unity. Although the groundwaters from Salto well are characterized by low {sup 234}U and {sup 238}U specific activities they present higher ({sup 234}U/{sup 238}U) activity ratios than those from Itu. The observed differences on the behavior of uranium concentrations and ({sup 234}U/{sup 238}U) activity ratios in the groundwaters from the two wells are very probably due to the large variety of granitic rocks from Itu Intrusive Suite, which are characterized by distinct uranium abundances. (author)

  20. Hydrogeological and Hydrogeochemical Modelling of the Alicun de las Torres Termal System (Province of Granada). Isotope Hydrochemistry and Gases in Groundwaters; Modelizacion Hidrogeologica e Hidrogeoquimica del Sistema Termal de Alicun de Las Torres (Provincia de Granada). Hidroquimica Isotopica y Gases en Aguas

    Energy Technology Data Exchange (ETDEWEB)

    Prado Perez, A. J.; Delgado, A.; Crespo, M. T.; Martin, A.; Vaselli, O.; Perez del Villar, L.


    In the framework of a Singular Strategic Project entitled: {sup A}dvanced Technologies of Carbon, Capture and Storage (CCS){sup ,} supported by the MICINN (Spain) and the FEDER founds (EU), specifically in the Carbon Storage Task, a comprehensive study on the CO{sub 2} leakage as DIC (Dissolved Inorganic Carbon) in the Alicun de Las Torres (Prov. of Granada) natural analogue thermal system was envisaged. This analogous system is characterised by the presence of a very important travertine formation, which can be considered as a permanent and stable sink for CO{sub 2}. In order to explain the formation of these travertine mass an hydrogeological and hydrogeochemical model of the area has been established by using the hydrochemical data, the stable and radioactive isotope characteristics, the dissolved inorganic carbon, as well as the chemical and isotopic composition of the free and dissolved gases of the above mentioned Thermal System. (Author) 11 refs.

  1. Sr and Nd isotopic signature of the high-K calc-alkaline magmatism of the central Ribeira belt: the Sao Pedro Granite in Lumiar, RJ; Assinatura isotopica de Sr e Nd do magmatismo calcio-alcalino de alto-K na Faixa Ribeira central: o exemplo do Granito Sao Pedro em Lumiar, RJ

    Energy Technology Data Exchange (ETDEWEB)

    Mendes, Julio Cezar; Medeiros, Silvia Regina de; Chaves, Eduardo Amorim, E-mail:, E-mail:, E-mail: [Departamento de Geologia, Universidade Federal do Rio de Janeiro, Rio de Janeiro (RJ) (Brazil)


    In the central-northern Ribeira belt there are many granitic to granodioritic bodies showing varied shape and size, characterizing a late- to post-collisional Ca-alkaline, cordilleran I-type province. The Sao Pedro Granite occurs in the mountain region of Rio de Janeiro State as small post-collisional bodies. It presents isotropic fabric, equigranular to seriate inequigranular texture, as well as local concentration of allanite, which gives discrete composition and texture variation to the rock. The granite has a high-K calcalkaline to alkali-calcic character and weakly peraluminous nature. Despite its short geochemical variation, high Ba, Zr and Th contents besides low concentrations of MgO and CaO are noticeable. High REE contents are associated with fractionated REE patterns showing strong negative Eu anomalies. A crustal origin for the granite can be assumed by its very negative and positive .Nd and .Sr values, respectively, as well as by 87Sr/86Sr initial ratios ranging from 0,718 to 0,740. TDM ages point to paleoproterozoic source, which agrees with geological time of intensive crust generation. (author)

  2. Hydrochemistry and isotopic composition (δ{sup 13}C, δ{sup 15}N) in six dunes lagoons in the National Park of Lencois Maranhenses, Maranhao, Brazil; Hidroquimica e composicao isotopica (δ13C, δ15N) em seis lagoas de dunas no Parque Nacional dos Lencois Maranhenses, Maranhao, Brasil

    Energy Technology Data Exchange (ETDEWEB)

    Ramos Junior, Jayme Teixeira; Suzuki, Marina Satika; Meirelles, Brunele de Araujo; Rangel, Thiago Pessanha; Oliveira, Braulio Cherene Vaz de, E-mail:, E-mail:, E-mail:, E-mail:, E-mail: [Universidade Estadual do Norte Fluminense (UENF), Campos dos Goytacazes, RJ (Brazil). Centro de Biociencias e Biotecnologia. Lab. de Ciencias Ambientais


    This study aims to evaluate the physicochemical parameters, nutrients and isotopic composition (δ{sup 13}C, δ{sup 15}N) of dissolved organic matter and MPS in six lakes located in the Maranhenses National Park, Maranhao State, under varying degrees of anthropic impact and distance from the sea. The physical and chemical parameters were measured in the field with portable devices; for total alkalinity, nutrients and photosynthetic pigments, samples were collected and analysed in the laboratory; the isotopic composition of carbon and nitrogen was determined from the particulate material retained on the filter and in the extract generated in the PPL filtration resin column. The limnological variables were assessed in both the dry and rainy seasons. The high rainfall caused a dilution effect for most of the elements studied in the rainy season. The elemental composition of the particulate fraction was 58% lower than the fraction dissolved. The carbon isotopic composition was lighter in the rainy season as a result of dilution and loading of allochthonous impoverished organic matter. (author)

  3. Determination of the isotopic ratio {sup 234} U/{sup 238} U and {sup 235} U/{sup 238} U in uranium commercial reagents by alpha spectroscopy; Determinacion de la relacion isotopica {sup 234} U/{sup 238} U y {sup 235} U/{sup 238} U en reactivos comerciales de uranio por espectrometria alfa

    Energy Technology Data Exchange (ETDEWEB)

    Iturbe G, J.L


    In this work the determination of the isotope ratio {sup 234} U/{sup 238} U and {sup 235} U/{sup 238} U obtained by means of the alpha spectroscopy technique in uranium reagents of commercial marks is presented. The analyzed uranium reagents were: UO{sub 2} (*) nuclear purity, UO{sub 3} (*) poly-science, metallic uranium, uranyl nitrate and uranyl acetate Merck, uranyl acetate and uranyl nitrate Baker, uranyl nitrate (*) of the Refinement and Conversion Department of the ININ, uranyl acetate (*) Medi-Lab Sigma of Mexico and uranyl nitrate Em Science. The obtained results show that the reagents that are suitable with asterisk (*) are in radioactive balance among the one {sup 234} U/{sup 238} U, since the obtained value went near to the unit. In the case of the isotope ratio {sup 235} U/{sup 238} U the near value was also obtained the one that marks the literature that is to say 0.04347, what indicates that these reagents contain the isotope of {sup 235} U in the percentage found in the nature of 0.71%. The other reagents are in radioactive imbalance among the {sup 234} U/{sup 238} U, the found values fluctuated between 0.4187 and 0.1677, and for the quotient of activities {sup 235} U/{sup 238} U its were of 0.0226, and the lowest of 0.01084. Also in these reagents it was at the {sup 236} U as impurity. The isotope of {sup 236} U is an isotope produced artificially, for what is supposed that the reagents that are in radioactive imbalance were synthesized starting from irradiated fuel. (Author)

  4. Antropización de un sistema acuífero multicapa mediterráneo (Campo de Cartagena, SE España). Aproximaciones hidrodinámicas, geoquimicas e isotópicas: Anthropization of a semiarid mediterranean multi-layer aquifer system (Campo de Cartagena, SE Spain). Hydrodynamic, geochemical and isotopic approaches.


    Baudron, Paul Jean Theo


    El Campo de Cartagena constituye un caso paradigmático en el que se pueden observar importantes modificaciones hidrológicas y ambientales relacionadas con el uso intensivo de aguas subterráneas para regadío en zonas semiáridas del Mediterráneo. En el último siglo, esta zona históricamente desértica se ha convertido en una de las áreas agrícolas más productivas del país. El desarrollo agrícola se ha basado en el uso de las aguas subterráneas, con la perforación de captaciones cada vez más prof...

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

    Energy Technology Data Exchange (ETDEWEB)

    Valladares, Claudia Sayao


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

  6. Petrological mineralogical and geochemical characterization of the granitoids and fracture fillings developed in Ratones Mines (Spain); Caracterizacion petrologica, mineralogica, geoquimica y evaluacion del comportamiento geoquimico de las REE en la fase solida (granitoides y rellenos fisurales) del sistema de interaccion agua-roca delentorno de la Mina Ratones

    Energy Technology Data Exchange (ETDEWEB)

    Buil Gutierrez, B. [Ciemat. Madrid (Spain)


    The petrological, mineralogical and geochemical characterisation of the granitoids and fracture fillings developed in the Ratones Mine (Caceres, Spain) has been done in order to understand rock-water interaction processes which control water geochemical parameters. Special interest has been devoted to the analysis and interpretation of REE patterns in the solid phase (granitoids and fracture fillings) because they constitute geochemical tracers in water-rock interaction process. Moreover, REE are considered as actinide analogues. In order to characterise the solid phase (granitoids and fracture fillings) several investigation scales (system, outcrop, whole rock, mineral and geochemical components) have been considered and different types of samples have been analysed. These factors control the methodological approach used in this investigation. The analytical methods we have used in this investigation are microscope, qualitative and semi-quantitative methods (XRD, SEM,EDAX) and quantitative methods (ICP-MS, XRF, EM, LAM-IC-MS). The bulk of the granitoids located around the Ratones Mine Belongs to the alkaline feldspar granite-sienogranite lihotype and they show a peraluminous and subalkaline pattern. From the mineralogical point of view, they are composed by quartz, K-feldspar (Or>90%), showing sericitation, moscovitization and turmolinization altherations, alkaline plagioclase (An-=-3%), usually altered to sericite, saussirite and less frequently affected by moscovitization processes, Fe-Al biotite, frequently affected by chloritization processes and sometimes replaced by muscovite, and finally muscovite (>2% celadonite and <4% paragonite) both of primary and secondary origin. The differences observed between the different lithotypes are related with the modal proportion of the principal minerals,with the presence or absence of certain accessory minerals ( turmaline, cordierite), with specific textural patterns, grain size and also with the richness in specific trace elements. (Author)

  7. The reuse of regenerated water for irrigation of a golf course: evolution geochemistry and probable affection to a volcanic aquifer (Canary Islands); La reutilizacion de aguas regeneradas para riego de un campo de golf: evolucion geoquimica y probable afeccion a un acuifero volconico (Islas Canarias)

    Energy Technology Data Exchange (ETDEWEB)

    Cabrera, M. C.; Palacios, M. P.; Estevez, E.; Cruz, T.; Hernandez-Moreno, J. M.; Fernandez-Vera, J. R.


    Irrigation reuse of treated urban wastewater presents unquestionable advantages, but recently some possible unfavourable effects that need to be studied in the long term have been detected. The Bandama golf course, located at the NE of Gran Canaria, has been selected to develop an integrated study of the affection on a medium-long term, due to it has been irrigated with reused water for more than 30 years. The characterization of irrigation water, soil, soil lixiviate and aquifer functioning has allowed to obtain preliminary conclusions pointing to the importance of the soil nature, the precipitation, the irrigation management and the hydrogeologic conditions in the soil and aquifer response, In the study area, this is complicated for the existence of about 250 m thick unsaturated zone conformed by volcanic materials where water must flow through fractures, making impossible to be sampled. (Author) 7 refs.

  8. Metallogenetic characterization of granitoid rocks through geochemical prospection: the Lagoa Real example related to uranium mineralization in Bahia state, Brazil; Caracterizacao metalogenetica de corpos gratinoides atraves de prospeccao geoquimica: o exemplo da suite intrusiva Lagoa Real relacionada a mineralizacoes de uranio no Estado da Bahia

    Energy Technology Data Exchange (ETDEWEB)

    Oliveira, J.E., E-mail: [Servico Geologico do Brasil (GEREMI/SUREG/SA/CPRM), Salvador, BA (Brazil)


    Within a broad metallogenetic evaluation program carried out by CPRM - Geological Survey of Brazil in covenant with the CBPM - Companhia Baiana de Pesquisa Mineral in the central part of the Sao Francisco Craton, the Lagoa Real granitoid rocks was one of the selected targets. The work included geochemical exploration supplemented by follow-in survey and integrated 1:200.000 scale geochemical cartography. The Lagoa Real granitoid was recognized with composition ranging from monzogranitic to alcaligranitic type. The geochemical surveying led to the definition of the metallogenetic specialization of the granitoid rock, with characteristic geochemical and mineralogic associations. These associations are related to uranium mineralization. The genetic model using stream sediment and pan concentrate data, show similarity with the metallogenetic model of zonal partitioning proposed by Routhier (1963), for plutonogenic lode deposits with potential for Sn, W, Nb, Be, REE, Au, and U. In this work emphasis is given to the importance of the integrated use of different prospective methods toward the evaluation of granitoid systems, particularly the combination of geochemical surveying methods with results for a better understanding of the geologic and metallogenetic settings. (author)

  9. Petrology and geochemistry of the Los Cuartos granite, Tafi del Valle, Tucuman, northwest of Argentina: its integration to the regional magmatic layout; Petrologia y geoquimica del granito Los Cuartos, Tafi del Valle, Tucuman, noroeste de Argentina: integracion al esquema magmatico regional

    Energy Technology Data Exchange (ETDEWEB)

    Lopez, J.P.; Bellos, L.I.


    Los Cuartos Granite crops out on the western flank of the Cumbres Calchaquies, east of Tafi del Valle, Tucuman Province, Argentina. It has a granitic to granodioritic composition, of two micas, being biotite dominant. The granite is medium grained and inequigranular, with rare K-feldspar megacrysts. It contains host-rock xenoliths with different degrees of assimilation. The granite intrusion produced contact metamorphism in the surrounding basement, with development of andalucite porphyroblasts and poikiloblastic biotite. The granite is calk-alkaline and peraluminous, and is K- and P-rich and Ca- and Napoor compared to other granitoids of the region. The pluton shows late-tectonic features with regard to the regional deformation. The granite possibly intruded during the Ordovician (Famatinian Cycle) and its emplacement was structurally controlled by the Tafi Megafracture. Los Cuartos Granite and other intrusive bodies of the region share similar petrographical, geochemical, structural and geochronological characteristics. (Author).

  10. Rb-Sr geochronology and geochemical characteristics of mafic dikes in the Nova Lacerda and Conquista D'Oeste region, Mato Grosso, SW Amazonian Craton; Geocronologia Rb-Sr e caracteristicas geoquimicas dos diques maficos da regiao de Nova Lacerda e Conquista D'Oeste (MT), porcao sudoeste do Craton Amazonico

    Energy Technology Data Exchange (ETDEWEB)

    Costa, Paulo Cesar Correa da; Matos, Joao Batista de [Universidade Federal de Mato Grosso (UFMT), Cuiaba, MT (Brazil). Dept. de Recursos Minerais; Grupo de Pesquisas em Evolucao Crustal e Metalogenia Guapore, Cuiaba, MT (Brazil)], e-mail:, e-mail:; Girardi, Vicente Antonio Vitorio [Universidade de Sao Paulo (USP), SP (Brazil). Inst. de Geociencias. Dept. de Mineralogia e Geotectonica], e-mail:; Ruiz, Amarildo Salina [Universidade Federal de Mato Grosso (UFMT), Cuiaba, MT (Brazil). Dept. de Geologia Geral; Grupo de Pesquisas em Evolucao Crustal e Metalogenia Guapore, Cuiaba, MT (Brazil)], e-mail:


    In the Nova Lacerda and Conquista D'Oeste regions, Mato Grosso State, SW part of the Amazonian Craton, mafic dikes trending NNW intrude the Nova Lacerda Granite (1462{+-}12 Ma), within the Jauru Domain, in the Rondonia-San Ignacio Province (1.55 - 1.3 Ga). The mafic swarm comprises diabases, metadiabases and amphibolites. Metadiabases originated from uralitization of diabases. These rocks have tholeiitic affinity and predominant basaltic composition. Some samples are andesi-basalts. The ages of diabases and metabasites are 1380 {+-} 32 Ma and 1330 {+-} 120 Ma respectively. Geochemical data indicate that the compositional variation of diabases and metadiadases is due to fractional crystallization of evolved tholeiitic magmas. The origin of the basaltic magmas is related to a heterogeneous mantle source. (author)

  11. A Mercury-like component of early Earth yields uranium in the core and high mantle (142)Nd. (United States)

    Wohlers, Anke; Wood, Bernard J


    Recent (142)Nd isotope data indicate that the silicate Earth (its crust plus the mantle) has a samarium to neodymium elemental ratio (Sm/Nd) that is greater than that of the supposed chondritic building blocks of the planet. This elevated Sm/Nd has been ascribed either to a 'hidden' reservoir in the Earth or to loss of an early-formed terrestrial crust by impact ablation. Since removal of crust by ablation would also remove the heat-producing elements--potassium, uranium and thorium--such removal would make it extremely difficult to balance terrestrial heat production with the observed heat flow. In the 'hidden' reservoir alternative, a complementary low-Sm/Nd layer is usually considered to reside unobserved in the silicate lower mantle. We have previously shown, however, that the core is a likely reservoir for some lithophile elements such as niobium. We therefore address the question of whether core formation could have fractionated Nd from Sm and also acted as a sink for heat-producing elements. We show here that addition of a reduced Mercury-like body (or, alternatively, an enstatite-chondrite-like body) rich in sulfur to the early Earth would generate a superchondritic Sm/Nd in the mantle and an (142)Nd/(144)Nd anomaly of approximately +14 parts per million relative to chondrite. In addition, the sulfur-rich core would partition uranium strongly and thorium slightly, supplying a substantial part of the 'missing' heat source for the geodynamo.

  12. National Geochronological Database (United States)

    U.S. Geological Survey, Department of the Interior — Radiometric ages of geological materials by K-Ar, Rb-Sr, Sm-Nd, fission track, and U-Th-Pb dating methods. A revision of DDS-14 correcting locations and providing...

  13. Structural anomalies associated with the electronic and spin transitions in LnCoO(3)

    NARCIS (Netherlands)

    Knizek, K; Jirak, Z; Hejtmanek, J; Veverka, M; Marysko, M; Maris, G; Palstra, TTM; Knížek, K.; Maryško, M.


    A powder X-ray diffraction study, combined with magnetic susceptibility and electric transport measurements, was performed on a series of LnCoO(3) perovskites (Ln = Y, Dy, Gd, Sm, Nd, Pr and La) over a temperature range 100-1000 K. A non-standard temperature dependence of the observed thermal expans

  14. Sm/Nd Evolution of Upper Mantle and Continental Crust:Constraints on Gowth Rates of the Continental Crust

    Institute of Scientific and Technical Information of China (English)



    A new approach to the investigation of the Sm/Nd evolution of the upper mantle directly from the data on lherzolite xenoliths is described in this paper.It is demonstrated that the model age TCHUR of an unmetasomatic iherzolite zenolith ca represent the mean depletion age of its mantle source, thus presenting a correlation trend between fSm/Nd and the mean depletion age of the upper mantle from the data on xenoliths.This correlation trend can also be derived from the data on river suspended loads as well as from granitoids.Based on the correlation trend mentioned above and mean depletion ages of the upper mantle at various geological times, an evolution curve for the mean fSm/Nd value of the upper mantle through geological time has been established.It is suggested that the upwilling of lower mantle material into the upper mantle and the recycling of continental crust material during the Archean were more active ,thus maintaining fairly constantfSm/Nd and εNd values during this time period. Similarly ,an evolution curve for the mean fSm/Nd value of the continental crust through geological time has also been established from the data of continental crust material.In the light of both evolution curves for the upper mantle and continental crust ,a growth curve for the continental crust has been worked out ,suggesting that :(1)about 30%(in volume )of the present crust was present as the continental crust at 3.8 Ga ago ;(2)the growth rate was much lower during the Archean ;and (3)the Proterozoic is another major period of time during which the continental crust wsa built up .

  15. Age of Anzishan granulites in the Mianxian-Lueyang suture zone of Qingling orogen: With a discussion of the timing offinal assembly of Yangtze and North China craton blocks

    Institute of Scientific and Technical Information of China (English)


    Many granulite blocks have been recently discovered in the Anzishan area, Mianxian County, Shaanxi Province, in the central segment of the Mianxian-Lueyang suture zone. Sm-Nd isochron and 40Ar/39Ar ages of mineral samples of granulites from this area are reported in the note. The granulite mineral samples give a Sm-Nd isochron age of t=(206 ( 55) Ma (2(), with INd = 0.51302(7(2() and MSWD = 1.6, and a biotite 40Ar/39Ar plateau age of (199.7(1.7) Ma (2(). The formation and uplift of the granulites were related to subduction of the Yangtze block beneath the South Qinling microcontinent and their collision and the final amalgamation of the Yangtze and Sino-Korean craton blocks in the Indosinian, and their age is consistent with or close to those of the Dabie ultrahigh-pressure and high-pressure metamorphic rocks, so have great tectonic significance.

  16. Geology of the Curimatau medium region (Paraiba State, Brazil) and the emplacement of the Dona Ines granite associated to the Brasiliano transcurrent shear zones; Geologia da Regiao do Medio Curimatau (PB) e o alojamento do granito de Dona Ines associado a zonas de cisalhamento transcorrentes brasilianas

    Energy Technology Data Exchange (ETDEWEB)

    Borges, Sergio Vieira Freire


    In an area of about 700 Km{sup 2} located in the northeast of Paraiba State and having as main point the town of Dona Ines, a geologic/structural mapping, a gravimetric survey and radiometric dating using the Rb/Sr method in whole rock and Sm.Nd model ages were undertaken in order to study and to understand the geology of this portion of terrain, the emplacement of the Dona Ines granitoids and its relationship with the enclosing rocks and the deformation acting at the time of the intrusion. The age of the pluton of Dona Ines was determined by the Rb/Sr whole rock method as 560 {+-} 20 Ma (end of Brasiliano Cycle in the region). Sm.Nd model ages in granitoids of Araras, Belem and Dona Ines have revealed paleoproterozoic ages for their crustal sources, as indicated by the negative {epsilon}{sub nd} of this rock 128 refs., 95 figs., 6 tabs., 7 maps

  17. Geochronology and Nd and Pb isotope characteristics of gabbro dikes in the Luobusha ophiolite, Tibet

    Institute of Scientific and Technical Information of China (English)


    We report a combined internal and whole-rock Sm-Nd isochron age, and Nd and Pb isotopic data for gabbro dikes of the Luobusha ophiolite in Tibet. The Sm-Nd isochron of data for two whole rocks and plagioclase and clinopyroxene separates from one of the rocks yields a Middle Jurassic age of (177±31) Ma (with an initial εNd(t) = +8),which provides a significant bound on the time of formation of the Luobusha ophiolite. The Nd and Pb isotopic characteristics of the dike indicate an Indian-Ocean-type isotopic affinity, and we conclude that the Luobusha ophiolite formed in an oceanic setting during the Middle Jurassic.``

  18. Crystallization Age and Source Signature of Chassigny (United States)

    Misawa, K.; Shih, C.-Y.; Reese, Y.; Nyquist, L. E.


    Chassigny is the Martian dunite composed of cumulate olivine (92%), chromite (1.4%), pyroxene (5%) and interstitial feldspar (1.7%). Although nakhlites (clinopyroxenite) are less intensely affected by shock metamorphism, Chassigny has been subjected to a peak shock pressure of about 35 GPa. The cosmic-ray exposure age of Chassigny (11.3 +/- 0.6 Ma) is comparable to those of nakhlites, suggesting launch pairing of these meteorites. Prior chemical and isotopic studies of Chassigny suggest that the meteorite crystallized approx. 1.3 Ga ago and is closely related to nakhlites. Nevertheless, compared to other Martian meteorites there are limited isotopic data for Chassigny. To examine the relationship of Chassigny to nakhlites, we have undertaken new Rb-Sr and Sm-Nd isotopic studies. Here we present the new Sm-Nd isotopic data for Chassigny and discuss the nature of its source materials.

  19. Petrology, chemistry, age and irradiation history of Luna 24 samples (United States)

    Wasserburg, G. J.; Papanastassiou, D. A.; Mcculloch, M. T.; Huneke, J. C.; Dymek, R. F.; Depaolo, D. J.; Chodos, A. A.; Albee, A. L.; Radicati Di Brozolo, F.


    The results of petrological, chemical, isotopic age determination and irradiation studies of sample 24170 from the 170 cm depth of the regolith core returned from Mare Crisium by Luna 24 are presented. The sample is found to be comprised of fragments from a single igneous rock, with mineralogical evidence indicating it to be a mare basalt. The crystallization age is determined by Sm-Nd and Ar(40)-Ar(39) ages to be 3.30 AE, establishing the presence of relatively young flows. All soil samples show low trace element compositions with minimum contamination by KREEPUTh-rich materials. Rb-Sr and Sm-Nd relations reflect the absence of significant fractionation at ages younger than 4.5 AE. One soil sample shows extremely large neutron capture effects, imposing a new lower limit to the neutron production rate in the regolith and requiring the addition of irradiated materials from depth.

  20. Ar-Ar and Rb-Sr Ages of the Tissint Olivine-phyric Martian Shergottite (United States)

    Park, J.; Herzog, G. F.; Nyquist, L. E.; Shih, C.-Y.; Turin, B.; Lindsay, F. N.; Delaney, J. S.; Swisher, C. C., III; Agee, C.


    The fifth martian meteorite fall, Tissint, is an olivine-phyric shergottite that contains olivine macrocrysts (approximately 1.5 mm) [1]. [2] reported the Sm-Nd age of Tissint as 596 plus or minus 23 Ma along with Rb-Sr data that defined no isochron. [3] reported Lu-Hf and Sm-Nd ages of 583 plus or minus 86 Ma and 616 plus or minus 67 Ma, respectively. The cosmic-ray exposure ages of Tissint are 1.10 plus or minus 0.15 Ma based on 10Be [4], and 1.0-1.1 Ma, based on 3He, 21Ne, and 38Ar [5,6].We report Ar-Ar ages and Rb-Sr data.

  1. Geochronology, geochemistry and tectonic implications of Xiongshan diabasic dike swarm, northern Fujian

    Institute of Scientific and Technical Information of China (English)

    任胜利; 李继亮; 周新华; 孙敏


    Sm/Nd isotopic age determination showed that Xiongshan dike swarm was at 585.7 Ma±30 Ma. The trace element geochemistry and Sr/Nd/Pb isotope geochemistry studies indicate that the dike swarm was products of back-arc basin spreading ridge and the magma originated from the depleted mantle region which was metasomatized by LTLE-rich liquids/melts derived from subduction slab.

  2. Re-Os isotopic system and formation age of subcontinental lithosphere mantle

    Institute of Scientific and Technical Information of China (English)


    The determination of the formation age of subcontinental Lithosphere Mantle (SCLM) is a widely concerned issue in mantle geochemistry. It is difficult to obtain the formation age of SCLM using lithophile isotopic systems such as Rb-Sr, Sm-Nd, U-Th-Pb, etc., but as siderophile elements, the Re-Os isotopic system provides a powerful tool for that work. Here a comprehensive review on the recent development in Re-Os dating for SCLM has been given.

  3. Methods of isotopic geochronology (United States)

    Gorokhov, I. M.; Levchenkov, O. A.

    Papers are presented on such topics as the age of the chemical elements; the age of meteorites, the moon, and the earth; isotopic ages of the most ancient terrestrial formations; and the Archean evolution of Enderby Land in the Antarctic as evidenced by isotopic dating. Consideration is also given to a uranium-lead geochronology technique for investigating Precambrian ore deposits, a Pb-Pb technique of zircon dating, and the potentials and limitations of Sm-Nd geochronology.

  4. The first dating results for gabbro of the dunite-clinopyroxenite-gabbro complex of the Chistop massif (North Urals) (United States)

    Petrova, G. A.; Ronkin, Yu. L.; Lvov, P. A.; Maslov, A. V.


    The first data on the Late Riphean age by U-Pb and Sm-Nd analysis (≥922 ± 14 and 686 ± 19 Ma, respectively) were obtained for rocks of the dunite-clinopyroxenite-gabbro complex of the Chistop massif in the Patinum-bearing Belt of the Urals. These data allow one to assume that the formation of the Ural paleoocean probably started immediately after the break-up of Rodinia.

  5. Age, temperature and pressure of metamorphism in the Tasriwine Ophiolite Complex, Sirwa, Morocco (United States)

    Samson, S. D.; Inglis, J.; Hefferan, K. P.; Admou, H.; Saquaque, A.


    Sm-Nd garnet-whole rock geochronology and phase equilbria modeling have been used to determine the age and conditions of regional metamorphism within the Tasriwine ophiolite complex,Sirwa, Morocco. Pressure and temperature estimates obtained using a NaCaKFMASHT phase diagram (pseudosection) and garnet core and rim compositions predict that garnet growth began at ~0.72GPa and ~615°C and ended at ~0.8GPa and ~640°C. A bulk garnet Sm-Nd age of 645.6 × 1.6 Ma, calculated from a four point isochron that combines whole rock, garnet full dissolution and two successively more aggressive partial dissolutions, provides a precise date for garnet formation and regional metamorphism. The age is nearly 20 million years younger than a previous age estimate of regional metamorphism of 663 × 14 Ma based upon a SHRIMP U-Pb date from rims on zircon from the Irri migmatite. The new data provide further constraints on the age and nature of regional metamorphism in the Anti-Atlas mountains and emphasizes that garnet growth during regional metamorphism may not necessarily coincide with magmatism/anatexis which predominate the signature witnessed by previous U-Pb studies. The ability to couple PT estimates for garnet formation with high precision Sm- Nd geochronology highlights the utility of garnet studies for uncovering the detailed metamorphic history of the Anti-Atlas mountain belt.

  6. Disturbed Sr and Nd Isotope Systematics in Zircons With Concordant SHRIMP U-Pb Ages (United States)

    Weaver, K. L.; Bennett, V. C.; Depaolo, D. J.; Mundil, R.


    Little is known about the Sr- and Nd-isotopic systematics of zircon. With slow diffusion rates and a high resistance to weathering, zircon should preserve accurate age information and initial Sr and Nd isotopic ratios. As a common accessory mineral, it could provide petrogenetic information for rocks that have been altered, weathered, or metamorphosed. We have investigated the Sm-Nd and Rb-Sr systematics of zircons from unmetamorphosed granitic rocks that have yielded concordant U-Pb SHRIMP (Sensitive High Resolution Ion Microprobe) ages and have depleted mantle signatures for Nd and Sr isotopes. Zircon populations from mantle-derived igneous rocks with ages of 0.1, 1.7, and 3.8 Ga were chosen for Sr and Nd isotopic analysis. Low concentrations (Sr, 4 to 8 ppm and Nd, 6 to 12 ppm) and small grain size necessitate the use of multigrain aliquots. Meaningful results can be obtained only if all of the zircons in the rock are a coherent population with homogeneous ages throughout and among grains. Zircon U-Pb ages were characterized using the SHRIMP RG, and trace element concentrations were measured by LA-ICPMS. The populations are homogeneous and the material ablated by the ion beam ( ˜~20 μ m spot size) shows little evidence of lead loss. Results on zircons of 100 Ma and 1700 Ma indicate that both the Rb-Sr and Sm-Nd systems have been severely disturbed. For the 1700 Ma granitic rocks from the Yavapai sequence of Arizona, zircon Sm-Nd apparent ages are ca. 1000 Ma! Leaching was used to remove contributions from adhering or included minerals, but leached residues that presumably most closely approximate the composition of the pure zircon (e.g. have high Sm/Nd) are no less disturbed than unleached samples. Despite the U-Pb SHRIMP ages indicating a closed system, the zircons have failed to preserve a reasonable age or initial isotopic composition for Sr and Nd, indicating that parts of the crystal might be severely affected by radiation damage resulting in disturbed

  7. Isotopic behaviour of fluids from the Los Humeros, Puebla (Mexico) geothermal field; Comportamiento isotopico de fluidos de pozos del campo geotermico de Los Humeros, Puebla, Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Barragan R, Rosa Maria; Portugal M, Enrique; Arellano G, Victor Manuel [Instituto de Investigaciones Electricas, Cuernavaca (Mexico); Tello L, Mirna del Rocio; Tello H, Enrique [gerencia de Proyectos Geotermoelectricos de la Comision Federal de Electricidad, Morelia (Mexico)


    Isotopic data from well fluids from the Los Humeros geothermal field were interpreted. Twenty wells were monitored during 1994-1996 in order to study the reservoir behavior as a result of exploitation. The isotopic composition of the total discharge and also that for the reservoir liquid phase were calculated considering the reservoir excess steam at reservoir temperature. This temperature was estimated to be between 280 degrees celsius and 325 degrees celsius through the CO{sub 2}/H{sub 2} geothermometer. The isotopic values for reservoir fluids were found in the ranges: between -8 and -1% for d{sup 18}O and -75 and -55% for dD. Isotopic patterns suggested the occurrence of a mixing process between reservoir and reinjection fluids since a linear trend (dD vs d{sup 18}O) with positive slope was found. The reservoir fluid for well H-7 (sampled June 1996) was found to be the isotopically lightest extreme of the relationship, while the reinjection fluid constituted the isotopically heaviest component. [Espanol] Con el fin de conocer la respuesta del yacimiento geotermico de Los Humeros a la extraccion y reinyeccion de fluidos, se llevo a cabo el monitoreo de especies isotopicas d{sup 18}O y dD en fluidos de 20 pozos del campo durante 1994-1996. Se calculo la composicion isotopica del fluido de la descarga total y de la fase liquida del yacimiento, corrigiendose los valores obtenidos para la descarga total considerando el parametro exceso de vapor a la temperatura estimada de yacimiento. La temperatura del yacimiento se estimo entre 280 grados celsius y 325 grados celsius mediante el geotermometro basado en la relacion CO{sub 2}/H{sub 2}. La composicion isotopica de los fluidos del yacimiento se encuentra en un amplio rango de valores: entre -8 y -1% para d{sup 18}O y entre -75 -55% para dD. Los resultados sugieren la ocurrencia de interferencia de fluidos de reinyeccion, ya que al correlacionar el contenido de deuterio contra el de oxigeno-18, los datos se alinean en

  8. Chronologic implications for slow cooling of troctolite 76535 and temporal relationships between the Mg-suite and the ferroan anorthosite suite (United States)

    Borg, Lars E.; Connelly, James N.; Cassata, William S.; Gaffney, Amy M.; Bizzarro, Martin


    Ages have been obtained using the 87Rb-87Sr, 147Sm-143Nd, and 146Sm-142Nd isotopic systems for one of the most slowly cooled lunar rocks, Apollo 17 Mg-suite troctolite 76535. The 147Sm-143Nd, 146Sm-142Nd, and Rb-Sr ages derived from plagioclase, olivine, and pyroxene mineral isochrons yield concordant ages of 4307 ± 11 Ma, 4299+29/-35 Ma, and 4279 ± 52 Ma, respectively. These ages are slightly younger than the age determined on ferroan anorthosite suite (FAS) rock 60025 and are therefore consistent with the traditional magma ocean model of lunar differentiation in which the Mg-suite is intruded into the anorthositic crust. However, the Sm-Nd ages record when the rock passed below the closing temperature of the Sm-Nd system in this rock at ∼825 °C, whereas the Rb-Sr age likely records the closure temperature of ∼650 °C. A cooling rate of 3.9 °C/Ma is determined using the ages reported here and in the literature and calculated closure temperatures for the Ar-Ar, Pb-Pb, Rb-Sr, and Sm-Nd systems. This cooling rate is in good agreement with cooling rates estimated from petrographic observations. Slow cooling can lower apparent Sm-Nd crystallization ages by up to ∼80 Ma in the slowest cooled rocks like 76535, and likely accounts for some of the variation of ages reported for lunar crustal rocks. Nevertheless, slow cooling cannot account for the overlap in FAS and Mg-suite rock ages. Instead, this overlap appears to reflect the concordance of Mg-suite and FAS magmatism in the lunar crust as indicated by ages calculated for the solidus temperature of 76535 and 60025 of 4384 ± 24 Ma and 4383 ± 17, respectively. Not only are the solidus ages of 76535 and 60025 nearly concordant, but the Sm-Nd isotopic systematics suggest they are derived from reservoirs that were minimally differentiated prior to ∼4.38 Ga. Although the Sr isotopic composition of 60025 indicates its source was minimally differentiated, the Sr isotopic composition of 76535 indicates it underwent

  9. LREE-rich Component in Ureilites: Further Evidence of Terrestrial Contamination (United States)

    Kita, N. T.; Misawa, K.; Tatsumoto, M.


    The origin of acid-leachable light (L) REE-rich components in ureilites is now a controversial issue between two groups who favor two different ideas: terrestrial contamination [1, 2] or metasomatism on the ureilite parent body [3, 4, 5]. Although Goodrich and her co-workers and we have obtained the same Sm-Nd trend from Kenna, Novo Urei, ALH 77257 [3, 5], and Goalpara [1, 2], Goodrich and others interpreted the trend as an isochron with an age of 3.79 Ga [5] whereas we interpreted the data as terrestrial contamination yielding a mixing line [2]. In this paper, we further discuss the Sm-Nd data of possible contaminants based on continental crustal data of from various parts of the world with various ages. Recently, Goodrich and Lugmair [5] pointed out that four different ureilites (Kenna, Novo Urei, Goalpara, ALH 77257) from the different recovery locations define a single Sm-Nd line, which can not be explained by terrestrial contamination because of the wide range of Nd compositions. However, by comparing recovery locations to their geological characters, it will be noted that all of these four ureilites were recovered from areas with Phanerozoic ages: Kenna which is Neogene, Novo Urei which is Paleogene to Jurassic, Goalpara which is Quaternary, and ALH 77257 which is Jurassic to Paleozoic. Phanerozoic sediments show similar Sm-Nd compositions all over the world [6] and plot very close to LREE-rich samples of Kenna. For this reason, it is not surprising that these four ureilites define a single contamination mixing trend. On the other hand, PCA 82506, which defines a "4.23 Ga isochron" using its acid-leachate and residue [4], was recovered from an area with Permian and Precambrian ages. Data from East Antarctica Precambrian rocks [7] plot along this "isochron", indicating that this ureilite was contaminated with terrestrial REE typical of old crustal material in Antarctica Similarly, the Rb-Sr systematics of ureilite are also explained as contamination by

  10. Chondrite barium, neodymium, and samarium isotopic heterogeneity and early Earth differentiation. (United States)

    Carlson, Richard W; Boyet, Maud; Horan, Mary


    Isotopic variability in barium, neodymium, and samarium in carbonaceous chondrites reflects the distinct stellar nucleosynthetic contributions to the early solar system. We used 148Nd/144Nd to correct for the observed s-process deficiency, which produced a chondrite 146Sm-142Nd isochron consistent with previous estimates of the initial solar system abundance of 146Sm and a 142Nd/144Nd at average chondrite Sm/Nd ratio that is lower than that measured in terrestrial rocks by 21 +/- 3 parts per million. This result strengthens the conclusion that the deficiency in 142Nd in chondrites relative to terrestrial rocks reflects 146Sm decayand earlyplanetary differentiation processes.

  11. Geochronology Intermediary Laboratory implantation at the Rio Grande do Norte Federal University: the dating of the Serrinha Granitoid (RN) and the correlate Brasiliana extensional deformation; Implantacao do Laboratorio Intermediario de Geocronologia na UFRN: a datacao do granitoide de Serrinha (RN) e da deformacao extensional brasiliana correlata

    Energy Technology Data Exchange (ETDEWEB)

    Macedo, Maria Helena F.; Sa, Emanuel F. Jardim de; Souza, Zorano S. [Pernambuco Univ., Recife, PE (Brazil). Nucleo de Pesquisa em Geodinamica e Geofisica; Mendes, Franklin S. [Pernambuco Univ., Recife, PE (Brazil). Curso de Quimica; Ramalho, Karlos A.C. [Pernambuco Univ., Recife, PE (Brazil). Curso de Geologia


    The article describes the activities developed by the Geochronology Intermediary Laboratory at the Federal University of the Rio Grande do Norte, a Brazilian university, where there were the preoccupation of establishing strategies for a geochronological development. It relates the Rubidium-Strontium (Rb/Sr) and Samarium-Neodymium (Sm/Nd) methods, describing the analysis realized in these methodologies. Afterward, it presents the geological and petrographic situation of the Granitoide de Serrinha, located at Rio Grande do Norte State, Brazil and its geochronological data 8 refs., 2 figs.

  12. Identification of biologically recycled continental materials in banded iron formations (United States)

    Li, W.; Beard, B. L.; Johnson, C.


    The controversy on the origin of banded iron formations (BIFs) has lasted for many decades. Studies prior to the 1970s suggested that Fe in BIFs was supplied from continental riverine inputs[1], but discovery of midocean ridge hydrothermal systems in the 1970s and identification of positive Eu anomaly in BIF samples led to an alternative model where hydrothermal vents provided Fe in BIFs[2]. Although the latter model has became widely accepted, it should be noted that interpretations of Fe sources for BIFs using the abundance and isotopic composition of rare earth elements (REEs) are based on an assumption that transport and deposition of REEs and Fe were coupled. We address the question of Fe sources and pathways for BIFs by combining stable Fe isotopes with radiogenic Nd isotopes as well as REE measurements to test proposals that Fe in BIFs was hydrothermally sourced. The samples investigated are from a type section of the Dales Gorge member of the 2.5 Ga Brockman Iron Formation, the world's most extensive Superior-type BIF that represents the climax of BIF deposition in the geologic record. Large variations were observed in both Fe and Nd isotope compositions of the BIF samples, and there is a positive correlation between the bulk rock ɛNd and δ56Fe values. In addition, there is a negative corelation between ɛNd and Sm/Nd ratios. In order to explain the observed correlations in those isotopic and elemental data, a two-component model, where mixing between a high ɛNd, low Sm/Nd hydrothermal endmember and a low ɛNd, low δ56Fe, but high Sm/Nd continental endmember occurred prior to deposition of the BIF, is required. The low-δ56Fe, high-Sm/Nd endmember is best explained by microbial dissimilatory iron reduction (DIR) in the coastal sediments, which fractionated Fe isotopes and REEs and released these components back to water column that were ultimately precipitated in BIFs. The range and distribution of ɛNdvalues in the BIF samples suggest that the amount

  13. Comparative High Field Magneto-transport Of Rare Earth Oxypnictides With Maximum Transition Temperatures

    Energy Technology Data Exchange (ETDEWEB)

    Balakirev, Fedor F [Los Alamos National Laboratory; Migliori, A [MPA-NHMFL; Riggs, S [NHMFL-FSU; Hunte, F [NHMFL-FSU; Gurevich, A [NHMFL-FSU; Larbalestier, D [NHMFL-FSU; Boebinger, G [NHMFL-FSU; Jaroszynski, J [NHMFL-FSU; Ren, Z [CHINA; Lu, W [CHINA; Yang, J [CHINA; Shen, X [CHINA; Dong, X [CHINA; Zhao, Z [CHINA; Jin, R [ORNL; Sefat, A [ORNL; Mcguire, M [ORNL; Sales, B [ORNL; Christen, D [ORNL; Mandrus, D [ORNL


    We compare magnetotransport of the three iron-arsenide-based compounds ReFeAsO (Re=La, Sm, Nd) in very high DC and pulsed magnetic fields up to 45 and 54 T, respectively. Each sample studied exhibits a superconducting transition temperature near the maximum reported to date for that particular compound. While high magnetic fields do not suppress the superconducting state appreciably, the resistivity, Hall coefficient, and critical magnetic fields, taken together, suggest that the phenomenology and superconducting parameters of the oxypnictide superconductors bridges the gap between MgB{sub 2} and YBCO.

  14. High-Field Magnetization of Light Rare-Earth Metals

    DEFF Research Database (Denmark)

    McEwen, K.A.; Cock, G.J.; Roeland, L.W.;


    The magnetization of single crystals of Eu, Sm, Nd, Pr, and Pr-Nd alloys has been measured in fields up to 37 T (370 kG). The results give new information on the magnetic properties of these metals. Of particular interest is a first-order transition from a nonmagnetic to a metamagnetic phase...... in double-hexagonal close-packed Pr, due to the crossing of crystal-field levels, when a field of about 32 T is applied in the hard direction at low temperatures....

  15. Thorium and uranium variations in Apollo 17 basalts, and K-U systematics (United States)

    Laul, J. C.; Fruchter, J. S.


    It is found that Apollo 11 low-K and in particular Apollo 17 mare basalts show a wide range of Th/U ratios unlike other rocks; such variations cannot be explained by near surface crystal fractionation. A two-stage fractional crystallization-partial melting model involving a clinopyroxene cumulate as the major phase can explain the variations in Th/U ratios. Due to the Sm-Nd systematics constraint, several source cumulates are invoked to explain the observed Th/U continuum.

  16. Optical properties of zirconia doped with yttria and some rare earth oxides (United States)

    Haberko, Jakub; Trenczek-Zając, Anita; Zientara, Dariusz; Adamczyk, Anna; Haberko, Krzysztof; Bućko, Mirosław M.


    Nanometric powders of cubic zirconia stabilized with yttria and rare element oxides (Sm, Nd, Gd) were prepared by crystallization under hydrothermal conditions. The powders were uniaxially compacted, repressed isostatically, pressure-less sintered in oxygen atmosphere and hot isostatically pressed under 300 MPa Ar atmosphere. Fully dense samples were polished from both sides. The optical properties were analyzed based on the spectral dependence of the transmittance (T) and reflectance (R). Spectroscopic measurements have shown that all materials fabricated in the present work are highly transparent, with total transmission above 90% towards the long-wavelength end of the near-IR range of the spectrum. Discussion of these results will be given.

  17. Calculation and Analysis of Mean Opacity of Gold Mixtures

    Institute of Scientific and Technical Information of China (English)

    YAN An-ying; JIANG Ming; CHENG Xin-lu; YANG Xiang-dong


    A screened hydrogenic model for l splitting (SHML) is used to calculate the Rosseland mean opacities of high-Z Au, Ta, Yb, Ho, Gd, Sm, Nd, Sn, Ag plasmas and mixtures of gold and these elements at high temperature (T=200-400eV) and dense (ρ=1g/cm3).From the calculated Rosseland mean opacities of the mixtures, Au-Nd seems to be a better choice than other mixtures.Simultaneously, the reason that the mean opacities of mixture of Au-Sn decrease slightly when T=400eV is analyzed.

  18. Nanopartículas semiconductoras: una alternativa para la degradación de contaminantes orgánicos presentes en agua residual y la generación de energía de manera sustentable




    En el presente trabajo se llevó a cabo la síntesis y caracterización de nanopartículas de óxidos semiconductores, tipo perovskita de las familias con fórmula general, NaMO3:A (M = Ta y Nb; A = La, Sm, Nd e Y). Estos óxidos se obtuvieron a 600 y 800°C. Además, se encontró que estos semiconductores presentan excelentes propiedades como fotocatalizadores en las reacciones de degradación de contaminantes orgánicos, tales como rodamina B (RB) y azul de metileno (AM), así...

  19. New age data and geothermobarometric estimates from the Apuseni Mountains (Romania); evidence for Cretaceous amphibolite-facies metamorphism (United States)

    Reiser, Martin; Schuster, Ralf; Spikings, Richard; Tropper, Peter; Fügenschuh, Bernhard


    New Ar-Ar ms, Rb-Sr bt and Sm-Nd grt age data in combination with microprobe analyses and structural data from the Apuseni Mountains provide new constraints for the tectonic evolution of the Tisza and Dacia Mega-Units during the Late Jurassic-Late Cretaceous time interval, which is of special importance for the present day arrangement of tectonic units in the Alpine-Carpathian-Dinaridic region. Late Jurassic obduction of Transylvanian Ophiolites (155 Ma) partially reset Ar-Ar ms ages at the top of the Biharia Nappe System in the Dacia Mega-Unit. New Sm-Nd grt ages and P-T estimates yielded amphibolite-facies conditions of 500°C and about 0.8 GPa during the Early Cretaceous (125 Ma Sm-Nd age) for the Dacia Mega-Unit and during late Early Cretaceous times (104 Ma Sm-Nd age) for the Tisza Mega-Unit. This implies that not only the Dacia Mega-Unit, but also the Tisza Mega-Unit experienced a strong regional metamorphic overprint accompanying Alpine deformation. New 95 Ma Ar-Ar ms and 81 Ma Rb-Sr bt ages from the Bihor Nappe (Tisza Mega-Unit), in combination with fission track ages constrain rapid cooling of more than 20°C/Ma after the thermal maximum. The amplitude of cooling corresponds to data from the Dacia Mega-Unit, which started cooling 20 Ma earlier, but at a rate of only about 12°C/Ma. Kinematic indicators and stretching lineations show NE-directed, in-sequence nappe stacking for the Tisza and Dacia Mega-Units during "Austrian Phase" deformation (125-100 Ma). Following the Austrian Phase, the Dacia Mega-Unit was thrust over the Tisza Mega-Unit during the Turonian Phase (93-89 Ma). Constrained through NW-directed kinematic indicators and 94-80 Ma Rb-Sr bt ages, this tectonic phase is responsible for a pervasive retrograde greenschist-facies overprint and the geometry of the present-day nappe stack in the Apuseni Mountains.

  20. Stability constants of La(III), Pr(III), Nd(III), Sm(III), Gd(III), Tb(III) and Dy(III) complexes with N-(2-hydroxyphenyl) p-toluene sulphonamide

    Energy Technology Data Exchange (ETDEWEB)

    Chopra, S.C.; Mathur, K.C. (Jodhpur Univ. (India). Dept. of Chemistry)


    The dissociation constants of the ligand and stability constants of La(III), Pr(III), Nd(III), Sm(III), Gd(III), Tb(III) and Dy(III) complexes with N-(2-hydroxyphenyl) p-toluene sulphonamide have been determined potentiometrically using Calvin-Bjerrum pH titration technique at 30 +- 1deg C and = 0.1 M (NaClO/sub 4/) in aqueous medium. The stability constants of these metal complexes are found to follow the order Dy > Tb > Gd > Sm > Nd > Pr > La.

  1. The Conductivity of Co-dopant Ceria Electrolyte

    Institute of Scientific and Technical Information of China (English)

    XIE Guang-yuan; CUI Kun; XIAO Jian-zhong; QIAN Xiao-liang


    A kind of novel ceria electrolyte was examined.Various trivalent oxides were added as co-dopants to Ce0.8Gd0.2O1.9,and their effects on the conductivity of ceria electrolyte were discussed.It has been found that the co-dopant of trivalent oxides of Sm,Nd,La and Y improves the ionic conductivity notably.Furthermore,the fine original powders,co-dopant and higher sintering temperature may hasten the sintering.

  2. Dating samples of lunar soil from the Mare Crisium by the Ar/39/-Ar/40/ technique (United States)

    Shanin, L. L.; Arakeliants, M. M.; Bogatikov, O. A.; Ivanenko, V. V.; Pupyrev, Iu. G.; Tarasov, L. S.; Frikh-Khar, D. I.


    Two samples (dolerite and gabbro fragments) from a depth of 184 cm in the Luna 24 core are dated using the Ar(39)-Ar(40) technique. The values obtained are found to be lower than all published isotopic ages for the Luna 24 samples. An analysis of possible dating errors of the lunar samples, together with the good agreement of the results from the Ar(39)-Ar(40) technique of geochronologic standards and anorthosite from the Korosten pluton with the results from Rb-Sr, U-Pb, and Sm-Nd methods, attests the reliability of the values.

  3. Samarium-neodymium evolution of meteorites

    Energy Technology Data Exchange (ETDEWEB)

    Prinzhofer, A.; Papanastassiou, D.A.; Wasserburg, G.J. (California Inst. of Tech., Pasadena (United States))


    The authors have obtained Sm-Nd data on two differentiated meteorites, Ibitira, a eucrite with distinct basaltic texture and with evidence of crystallization; and Morristown, a group 3A mesosiderite; as well as on Acapulco, an unclassified meteorite with chondritic chemical composition and a highly recrystallized texture. They have demonstrated the presence of in situ decay of short-lived {sup 146}Sm in these meteorites with initial abundance of {sup 146}Sm/{sup 144}Sm from 0.009 to 0.007 for the different meteorites. Precisely defined {sup 147}Sm-{sup 143}Nd internal isochrons were obtained yielding ages of 4.60 {+-} 0.03 AE for Acapulco, 4.47 {+-} 0.02 AE for Morristown, and 4.46 {+-} 0.02 AE for Ibitira. The corresponding initial {sup 143}Nd/{sup 144}Nd values obtained were 0.2 {+-} 0.9, 2.1 {+-} 0.7, and 1.6 {+-} 0.8 {var epsilon}u (epsilon units). Detailed consideration of the coupled {sup 147}Sm-{sup 143}Nd and {sup 146}Sm-{sup 142}Nd systematics and of the elevated initial {sup 143}Nd/{sup 144}Nd values indicates the presence of inconsistencies in the data for the two Sm-Nd parent-daughter pairs in spiteof the precise isochrons. The authors present a model which provides an interpretation of the paired Sm-Nd systematics in terms of an impulsive disturbance. The results indicate that three meteorites studied are relatively ancient objects, formed within the first 50 to 100 m.y. of the solar system, by planetary differentiation and impact processes, and were subjected to late metamorphism. The time of late metamorphism is substantially younger than 4.4 AE and possibly as recent as {approximately}3.9 AE. This metamorphism has resulted in partial, very limited reequilibration between plagioclase and phosphate, resulting in the observed shifts in initial {sup 143}Nd/{sup 144}Nd, Sm-Nd model ages, and the {sup 142}Nd/{sup 144}Nd abundances, but preserving the major temporal structures of early original formation and later disturbances.

  4. Paleoproterozoic Potassic Granitoids in the Sushui Complex from the Zhongtiao Mountains, Northern China:Geochronology, Geochemistry and Petrogenesis

    Institute of Scientific and Technical Information of China (English)

    TIAN Wei; LIU Shuwen; ZHANG Huafeng


    Paleoproterozoic potassic granitoids in the southern Sushui Complex from the Zhongtiao Mountains yielded SHRIMP zircon U-Pb ages of 1968-1944 Ma. Lithologically, the potassic granitoid series consists chiefly of monzodiorite, quartz monzonite and syenogranite. Their trace elements and Sm-Nd isotope characteristics indicate that they were derived from partial melting of Archean TTG rocks in an overthickened continental crust. Petrogenesis of this potassic granitoid series implies a collisional environment within the Trans-North China Orogen in the Paleoproterozoic, which supports a tectonic model of Eastern and Western Continental Blocks being amalgamated in the Paleoproterozoic.

  5. Découverte de coésite dans la ceinture métamorphique UHP d'âge Paléozoïque inférieur du Nord-Qaidam, Chine nord-occidentale (United States)

    Yang, Jingsui; Xu, Zhiqin; Song, Shuguang; Zhang, Jianxin; Wu, Cailai; Shi, Rendeng; Li, Haibing; Brunel, Maurice


    Coesite and graphite were discovered as inclusions in zircon separates from pelitic gneiss associated with a large eclogite body in the North Qaidam UHP terrane. This finding suggests UHP metamorphism at pressures below the diamond stability field. This supports previous indirect UHP evidences, such as polycrystalline quartz inclusions in eclogitic garnet, quartz lamellae in omphacite and P- T estimates for both eclogite and garnet peridotite. The U/Pb and Sm/Nd isotopic ages from the North Qaidam eclogite indicated that continental subduction occurred in Early Palaeozoic, most probably in relation with the collision between the Sino-Korean and Yangtze plates.

  6. Granulite fades Nd-isotopic homogenization in the Lewisian complex of northwest Scotland (United States)

    Whitehouse, M.J.


    A published Sm-Nd whole-rock isochron of 2,920 ?? 50 Myr, obtained from a wide range of lithologies in the Lewisian complex of north-west Scotland, was interpreted1 as the time of protolith formation. This date is ???260 Myr older than estimates for the timing of high-grade metamorphism in the complex at ??? 2,660 Myr2'3, and this period is considered to represent the duration of the Lewisian crustal accretion-differentiation superevent (CADS)4. Here we give new Sm-Nd data, obtained specifically from granulite facies tonalitic gneisses, that yield a date of 2,600 ??155 Myr. Although depleted-mantle model ages (tDM suggest >200 Myr of premetamorphic crustal residence, the regression date and its associated initial Nd-isotopic parameters demonstrate Nd-isotopic homogenization during the high-grade event, as well as the probability of general rare-earth-element (REE) mobility. Models for selective element depletion in the complex have previously assumed REE immobility since 2,920 Myr, but the data presented here suggest that a reappraisal of the depletion mechanism is required. ?? 1988 Nature Publishing Group.

  7. Polymetamorphism of the Variscan Basement of the Moldanubian Black Forest (Germany) Documented in Zircon and Garnet Minerals from Gneisses

    Institute of Scientific and Technical Information of China (English)



    High-grade metamorphic Variscan basement is exposed in the Moldanubian zone of the Black Forest (BF), being the internal zone of the European Variscan belt. Zircon grains from K-rich felsic orthogneisses and an anatectic paragneiss in the Moldanubian Black Forest demonstrate a multi-stage crystallization at ~ 600 Ma, ~ 480 Ma, ~ 400 - 380 Ma, and ~350 Ma. The last three stages of crystallization probably represent metamorphic overprint during pre-Variscan and Variscan metamorphism.Using stepwise leaching procedures, garnet minerals from felsic orthogneisses as well as paragneisses in the Moldanubian Black Forest yielded Early Carboniferous Sm-Nd ages (~ 330- 340 Ma), which are consistent with the well-constrained Variscan HT metamorphic event,and Early Palaeozoic ( ~480 Ma) to Devonian ( ~400 - 370 Ma) Pb-Pb ages. The coincidence of growth time for zircon and garnet minerals at Early Palaeozoic is interpreted as dating a metamorphic event. These garnet data demonstrate that the Moldanubian BF basement underwent at least two metamorphic events during the Early Palaeozoic and Early Carboniferous.During the Variscan HT metamorphism, the Sm-Nd system of garnet was disturbed, but not the U-Pb system, implying the peak metamorphic temperature was lower than ~800℃.

  8. Geochronology of the Dahongshan Group

    Institute of Scientific and Technical Information of China (English)

    胡霭琴; 朱炳泉; 等


    The Dahongshan Group is divided into five formations from the bottom to the top:the Laochanghe For-mation;the Manganghe Formation;the Hongshan Formation ,the Feiweihe Formation and the Potou For-mation.As can be seen form the U-Pb Concordia plot for zircon fractions collected from the metamorphic sodic lava of the Hongshan Formation,the upper intersect age with the Concordia is 1665.55-10.86+13.56Ma.Sm-Nd dating of four whole-rock samples and one hornblende from the Manganghe and Hongshan forma-tions yielded an isochron age of 1657±82Ma .This result is in good agreement with the zircon U-Pb age and thus can represent the formation age of the Dahongshan Group.The initial143Nd/144Nd ratio is esti-mated at 0.510646,with END(T)=+3.1±1.8.In addition the Dahongshan Group rocks are character-ized by low REE contents,with δEu>1.All this goes to show that the original rocks of the Dahongshan Group were derived from a depleted mantle.The calculated Sm-Nd model ages range from-1900 to -2000Ma,representing the time of crust/mantle differentiation in the area studied.From the above results,in conjunction with the time-scale scheme for China,the Dahongshan Group should be assigned to the Middle Proterozoic.

  9. Early Paleozoic (Pan African) thermal event of the Larsemann Hills and its neighbours, Prydz Bay, East Antarctica

    Institute of Scientific and Technical Information of China (English)

    赵越; 宋彪; 张宗清; 富云莲; 陈廷愚; 王彦斌; 任留东; 姚玉鹏; 李继亮; 刘小汉


    The early Paleozoic (Pan African) thermal event of the Larsemann Hills and its adjacent areas, East Antarctica is discussed based upon the isotope ages we obtained. An Sm-Nd internal isochron for a representative mafic granulite yields an age of 540 Ma±75 Ma. Another Sm-Nd internal isochron, which is made up of the assemblage of the peak metamorphism and its whole rock as well, gives an age of 497 Ma ± 7 Ma The isotopic chronological data of single zircon stepwise evaporation dating and 40Ar-39Ar analysis provide further evidence for the early Paleozoic event of high-grade metamorphism in the region. The data from the field geological investigation in the Larsemann Hills also show that there is not only strong regional partial melting but also low-pressure granulite-facies metamorphism accompanied by it in the region. The early Paleozoic (Pan African) thermal event of the region may be related to the final formation of the East Antarctica craton, even of Gondwanaland.

  10. Comparative behavior of Sr, Nd and Hf isotopic systems during fluid-related deformation at middle crust levels (United States)

    Luais, Béatrice; Le Carlier de Veslud, Christian; Géraud, Yves; Gauthier-Lafaye, François


    We have carried out a comparative Rb-Sr, Sm-Nd and Lu-Hf isotopic study of a progressively deformed hercynian leucogranite from the French Massif Central, belonging to the La Marche ductile shear zone, in order to investigate the respective perturbation of these geochronometers with fluid induced deformation. The one-meter wide outcrop presents a strongly deformed and mylonitized zone at the center, and an asymmetric deformation pattern with a higher deformation gradient on the northern side of the zone. Ten samples have been carefully collected every 10 cm North and South away from the strongest deformed mylonitic zone. They have been analyzed for a complete major, trace element data set, oxygen isotopes, Rb-Sr, Sm-Nd and Lu-Hf isotopic systematics. We show that most of major and trace elements except SiO 2, alkaline elements (K 2O, Rb), and some metal transition elements (Cu), are progressively depleted with increasing deformation. This depletion includes REE + Y, but also HFS elements (Ti, Hf, Zr, Nb) which are commonly considered as immobile elements during upper level processes. Variations in elemental ratios with deformation, e.g. decrease in LREE/MREE- HREE, Nd/Hf, Th/Sr, increase in Rb/Sr, U/Th and constant Sr/Nd, lead to propose the following order of element mobility: U ≫ Th > Sr = Nd ≫ Hf + HREE. We conclude in agreement with previous tectonic and metallogenic studies that trace element patterns across the shear zone result from circulation of oxidizing F-rich hydrothermal fluids associated with deformation. A temperature of the fluid of 470-480 °C can be deduced from the δ 18O equilibrium between quartz-muscovite pairs. Elemental fractionation induces perturbation of the Rb-Sr geochronometer. The well-defined 87Rb/ 86Sr- 87Sr/ 86Sr correlation gives an apparent age of 294 ± 19 Ma, slightly younger than the 323 ± 4 Ma age of leucogranites in this area. This apparent age is interpreted as dating event of intense deformation and fluid circulation

  11. Combined garnet and zircon geochronology and trace elements studies - constraints of the UHP-(U)HT evolution of Orlica-Śnieżnik Dome (NE Bohemian Massif). (United States)

    Walczak, Katarzyna; Anczkiewicz, Robert; Szczepański, Jacek; Rubatto, Daniela


    The Orlica-Śnieżnik Dome (OSD), located on the NE margin of the Bohemian Massif, is predominantly composed of amphibolite-facies orthogneiss that contain bodies of HP and UHP eclogites and granulites. Numerous geochronological studies have been undertaken to constrain the timing of the ultra-high grade metamorphic event. Despite this, the exact timing of UHP-(U)HT conditions remain dubious (e.g. Brueckner et al., 1991; Anczkiewicz et al., 2007; Bröcker et al., 2009 & 2010). We have utilized garnet and zircon geochronology to provide time constraints on the evolution of the UHT-(U)HP rocks of the OSD. We have combined the ages with trace element analyses in garnet and zircon to better understand the significance of the obtained ages in petrological context. Lu-Hf grt-wr dating of peritectic garnet from two felsic granulites constrained the time of its initial growth at 346.9 ± 1.2 and 348.3 ± 2.0 Ma, recording peak conditions of 2.7 GPa and 950°C (e.g. Ferrero et al., 2015). In situ U-Pb SHRIMP dating of zircon from the same granulite gave a younger age of 342.2 ± 3.4 Ma. HREE partitioning between garnet rim and metamorphic zircon indicate their growth in equilibrium, hence, the U-Pb zircon date constrains the terminal phase of garnet crystallization. Similar ages were obtained from two eclogite bodies from Międzygórze and Nowa Wieś localities; Lu-Hf (grt-cpx-wr) dating provided ages of 346.5 ± 2.4 and 348.1 ± 9.1 Ma for samples from Międzygórze and Nowa Wieś, respectively. The same age (within error) of 346.3 ± 5.2 Ma was reported by Bröcker et al. (2010) for zircon from the Międzygórze eclogite. Comparison of REE concentrations in garnet (this study) and in metamorphic zircon (reported in Bröcker et al., 2010) indicate that garnet and zircon crystallized in equilibrium. Furthermore, M-HREE patterns observed in both garnet and zircon strongly suggest their growth at eclogite facies conditions. Sm-Nd garnet ages obtained for both felsic and mafic

  12. Early differentiation of the silicate Earth : new constraints from isotopic investigation of rocks from the lunar highlands (United States)

    Boyet, M.; Carlson, R.; Borg, L.; Connelly, J.; Horan, M.


    The isotopic similarity in O, Mo, W, Si, and Fe between lunar and terrestrial samples suggests that the two planetary bodies were equilibrated in the energetic aftermath of the giant impact that gave birth to the Moon [1]. Coupled 142Nd-143Nd isotope systematics of lunar samples including both low-Ti and high-Ti mare basalts along with KREEP basalts have been used to constrain the age of crystallization of the lunar interior [2-5]. These studies show that the Sm-Nd system in the lunar mantle closed in the interval of 180-250 Ma after the beginning of solar system formation, depending on the model considered for lunar mantle differentiation (1 or 2 stage-model and initial lunar Sm/Nd ratio). Does this age represent the age of Moon formation? A prolonged lunar magma ocean (LMO) might be expected given the insulating effect of the thick plagioclase crust, so closure of the Sm-Nd system in the lunar mantle, particularly in a late stage LMO component like KREEP, might substantially post-date lunar formation. We have recently determined a new age of 4360±3 Ma for the ferroan anorthosite (FAN) 60025 using the 207Pb-206Pb, 147Sm-143Nd and 146Sm-142Nd isotope systems [6]. This study is the first in which a single sample of FAN yielded consistent ages from multiple isotope dating techniques, strongly suggesting that this age indicates the time at which the sample crystallized. In order to pursue the question of whether Moon formation occurred over 100 Ma after solar system formation, we have investigated a number of lunar rocks sampling the highland crust from both the FAN and the Mg-suite groups. Internal Sm-Nd isochron on the norite 77215 yields an age of 4296±20 Ma, in agreement with the young age determined on 60025. We will show that our new data obtained on the 146Sm-142Nd systematics of the lunar crust support the scenario of a relative young age for the Moon. Thus, these results offer a unique opportunity to better constrain the composition of the terrestrial

  13. The tungsten isotopic composition of Eoarchean rocks: Implications for early silicate differentiation and core-mantle interaction on Earth (United States)

    Iizuka, Tsuyoshi; Nakai, Shun'ichi; Sahoo, Yu Vin; Takamasa, Asako; Hirata, Takafumi; Maruyama, Shigenori


    We have measured 182W/ 184W for Eoarchean rocks from the Itsaq Gneiss Complex (3.8-3.7 Ga pillow meta-basalts, a meta-tonalite, and meta-sediments) and Acasta Gneiss Complex (4.0-3.6 Ga felsic orthogneisses) to assess possible W isotopic heterogeneity within the silicate Earth and to constrain W isotopic evolution of the mantle. The data reveal that 182W/ 184W values in the Eoarchean samples are uniform within the analytical error and indistinguishable from the modern accessible mantle signature, suggesting that the W isotopic composition of the upper mantle has not changed significantly since the Eoarchean era. The results imply either that chemical communication between the mantle and core has been insignificant in post-Hadean times, or that a lowermost mantle with a distinctive W isotope signature has been isolated from mantle convective cycling. Most terrestrial rock samples have a 0.2 ɛ142Nd/ 144Nd higher than the chondrite average. This requires either the presence of a hidden enriched reservoir formed within the first 30 Ma of the Solar System, or the bulk Earth having a ˜ 5% higher Sm/Nd than the chondrite average. We explored the relevance of the 182Hf- 182W isotope system to the 146Sm- 142Nd isotope system during early silicate differentiation events on Earth. In this context, we demonstrate that the lack of resolvable 182W excesses in the Itsaq rocks, despite 142Nd excesses compared to the modern accessible mantle, is more consistent with the view that the bulk Earth has a non-chondritic Sm/Nd. In the non-chondritic Sm/Nd Earth model, the 182W- 142Nd chronometry constrains the age of the source mantle depletion for the Itsaq samples to more than ˜ 40 Ma after the Solar System origin. Our results cannot confirm the previous report of 182W anomalies in the Eoarchean Itsaq meta-sediments, which were interpreted as reflecting an impact-derived meteoritic component.

  14. Detrital zircon geochronology and Nd isotope geochemistry of an early Paleozoic succession in Korea: (United States)

    Lee, Yong Il; Choi, Taejin; Lim, Hyoun Soo; Orihashi, Yuji


    This study reports the results of an analysis of U-Pb ages of detrital zircons and Nd isotope compositions from the well-established lower Paleozoic platform succession developed on the Precambrian gneiss and metasedimentary rocks in South Korea. The three stratigraphic units in the basal part of the succession are the Jangsan, Myeonsan, and Myobong Formations. The unfossiliferous Jangsan (white­to­pink quartz sandstone) and Myeonsan (dark-gray ilmenite-rich sandstone/shale) Formations are in fault contact and are generally considered to be coeval (Early Cambrian). Both formations are also generally considered to be conformably overlain by the dark­ gray, fossiliferous, fine-grained Myobong Formation (late Early-early Middle Cambrian). We here report U-Pb ages of detrital zircons and Nd isotopic data from the Jangsan, Myeonsan, and Myobong Formations. The Jangsan and Myeonsan Formations provide Archean-Paleoproterozoic U-Pb ages, but the former is characterized by Archean Sm-Nd model ages and the latter by late Paleoproterozoic Sm-Nd model ages, which is indicative of a significant change in provenance. This suggests that the Jangsan Formation predates the Myeonsan Formation. The Myobong Formation provides dominantly Meso- to Neoproterozoic U-Pb ages and Sm-Nd model ages that are slightly younger than those of the Myeonsan Formation. Contrary to the conventional wisdom, the combined evidence of unconformable contact and marked changes in zircon U-Pb ages and Nd isotopic compositions suggests that the Myobong Formation overlies the Jangsan and Myeonsan Formations unconformably. Considering the metamorphic age of the immediately underlying Precambrian basement metasediments (0.8 to 0.9 Ga), this stratigraphic relationship strongly suggests that the Jangsan Formation may be Neoproterozoic in age and that the Myeonsan Formation may be latest Neoproterozoic to Early Cambrian and calls for reevaluation of Precambrian-Paleozoic history of the Korean Peninsula. The

  15. Timing and duration of garnet granulite metamorphism in magmatic arc crust, Fiordland, New Zealand (United States)

    Stowell, H.; Tulloch, A.; Zuluaga, C.; Koenig, A.


    Pembroke Granulite from Fiordland, New Zealand provides a window into the mid- to lower crust of magmatic arcs. Garnet Sm-Nd and zircon U-Pb ages constrain the timing and duration of high-P partial melting that produced trondhjemitic high Sr/Y magma. Trace element zoning in large, euhedral garnet is compatible with little post growth modification and supports the interpretation that garnet Sm-Nd ages of 126.1??2.0 and 122.6??2.0. Ma date crystal growth. Integration of the garnet ages with U-Pb zircon ages elucidates a history of intrusion(?) and a protracted period of high-temperature metamorphism and partial melting. The oldest zircon ages of 163 to 150. Ma reflect inheritance or intrusion and a cluster of zircon ages ca. 134. Ma date orthopyroxene-bearing mineral assemblages that may be magmatic or metamorphic in origin. Zircon and garnet ages from unmelted gneiss and garnet reaction zones record garnet granulite facies metamorphism at 128 to 126. Ma. Peritectic garnet and additional zircon ages from trondhjemite veins and garnet reaction zones indicate that garnet growth and partial melting lasted until ca. 123. Ma. Two single fraction garnet ages and young zircon ages suggest continued high-temperature re-equilibration until ca. 95. Ma. Phase diagram sections constrain orthopyroxene assemblages to growth. Results demonstrate the utility of integrated U-Pb zircon and Sm-Nd garnet ages, and phase diagram sections for understanding the nature, duration, and conditions of deep crustal metamorphism and melting. Geochronologic and thermobarometric data for garnet granulite indicate that thickening of arc crust, which caused high-pressure metamorphism in northern Fiordland, must have occurred prior to 126. Ma, that loading occurred at a rate of ca. 0.06. GPa/m.y., and that garnet granulite metamorphism lasted 3-7m.y. Locally-derived partial melts formed and crystallized in considerably less than 10 and perhaps as little as 3m.y. ?? 2010 Elsevier B.V.

  16. Calorimetria nucleare in collisioni tra ioni pesanti ad energie intermedie (United States)

    Spezzi, L.


    Nel presente lavoro di tesi ci si e' occupati di uno studio sistematico di misure di temperatura ed energia di eccitazione in sistemi nucleari formati in reazioni tra ioni pesanti ad energie intermedie. La temperatura a stata misurata tramite due diversi metodi: rapporto tra le rese di isotopi che differiscono di uno stesso numero di nucleoni ( d/t-3He/4He , 3He/4He -6Li/7Li) - temperatura isotopica -, e rapporto tra le popolazioni degli stati eccitati in frammenti instabili (5Li e 6Li) che decadono in particelle leggere in coincidenza - temperatura di emissione. Le misure in esame sono state effettuate presso i Laboratori Nazionali del Sud per i sistemi 93Nb+93Nb, 93Nb+116,124Sn, 116,120Sn+116,124Sn e 116Sn+93Nb ad energie comprese tra 17 e 40 A MeV. L'apparato di rivelazione era costituito da un odoscopio ad alta granularite (96 telescopi Si (50micron)-Si(300micron)-CsI(Tl) ) e basse soglie di rivelazione, utilizzato sia per identificare risonanze in frammenti eccitati che per misure di rese di isotopi di frammenti con 2<=Z<=6, e dal multirivelatore FIASCO che, grazie alla misura contemporanea di posizione e tempo di volo dei frammenti provenienti dal proiettile (PLF - Projectile Like Fragments) e dal bersaglio (TLF - Target Like Fragment), e' stato utilizzato per misurare direttamente l'energia di eccitazione del sistema in studio. Analisi precedenti, condotte nell'ambito di varie collaborazioni, hanno messo in evidenza la possible esistenza di una transizione di fase liquido-gas del primo ordine nella materia nucleare. In tale contesto, ci siamo occupati di una verifica della curva calorica nucleare, ovvero della correlazione esistente fra temperatura ed energia di eccitazione del sistema, indagando, nel contempo, sulla sua dipendenza dalla massa del sistema che si frammenta. Si e' effettuato, inoltre, un confronto fra i due diversi metodi di misura della temperatura (temperatura isotopica e di emissione): l'andamento plateau-like della curva calorica e' stato

  17. High-Pressure Synthesis of SmFeAsO{sub 1-x}F{sub x}(x=0.2) Single Crystals

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Hyun Sook; Park, Jae Hyun; Lee, Jae Yeap; Lee, Hu Jong [Dept. of Physics, Pohang University of Science and Technology, Pohang (Korea, Republic of); Kim, Ju Young; Cho, B. K. [Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju (Korea, Republic of); Jung, Chang Uk [Dept. of Physics, Hankuk University of Foreign Studies, Yongin (Korea, Republic of)


    Fluorine-doped SmFeAsO{sub 1-x}F{sub x} single crystals with the nominal value of x=0.2 were grown at 1350-1450 degrees C under the pressure of 3.3 GPa by using the self-flux method. Plate-shaped single crystals in the range of a few-150 {mu}m in their lateral size were obtained. The detailed crystal structure was analyzed by using the x-ray diffractometry. Superconducting transition temperature, determined by the resistive transition, of a single crystal was about 49 K with a narrow resistive transition width of {approx}K. A relatively sharp transition, a low residual resistivity, and a large residual resistivity ratio compared with those reported for REFeAsO{sub 1-x}F{sub x}(RE=Sm, Nd) single crystals indicate the high quality of our single crystals.

  18. Rare-Earth Calcium Oxyborate Piezoelectric Crystals ReCa4O(BO33: Growth and Piezoelectric Characterizations

    Directory of Open Access Journals (Sweden)

    Fapeng Yu


    Full Text Available Rare-earth calcium oxyborate crystals, ReCa4O(BO33 (ReCOB, Re = Er, Y, Gd, Sm, Nd, Pr, and La , are potential piezoelectric materials for ultrahigh temperature sensor applications, due to their high electrical resistivity at elevated temperature, high piezoelectric sensitivity and temperature stability. In this paper, different techniques for ReCOB single-crystal growth are introduced, including the Bridgman and Czochralski pulling methods. Crystal orientations and the relationships between the crystallographic and physical axes of the monoclinic ReCOB crystals are discussed. The procedures for dielectric, elastic, electromechanical and piezoelectric property characterization, taking advantage of the impedance method, are presented. In addition, the maximum piezoelectric coefficients for different piezoelectric vibration modes are explored, and the optimized crystal cuts free of piezoelectric cross-talk are obtained by rotation calculations.

  19. Geochemistry of Archaean supracrustal belts in SW Greenland

    DEFF Research Database (Denmark)

    Szilas, Kristoffer

    . (3) The Nunatak 1390 area contains ultramafic rocks with geochemical characteristics similar to high-Ti komatiites, but they show geochemical signs of a juvenile slab melt contribution. Their high MgO contents may thus reflect flux-melting of a refractory mantle source, as is the case for boninites......This PhD-thesis investigates the geological formation environment of c. 3200-3000 million-year-old volcanic rocks from SW Greenland, using whole-rock geochemical data in combination with U-Pb, Sm-Nd and Lu-Hf isotope data. The following three supracrustal areas were studied: (1) The Tartoq Group...... geochemical mixing trends between juvenile felsic and mafic end-members. This suggests that partial melting and magma mixing by mafic underplating and slab melt metasomatism of the mantle source region were important in forming rocks of andesitic composition, which is also observed in some modern island arcs...

  20. Geochronology and Nd isotope geochemistry of the Gameleira Cu-Au deposit, Serra dos Carajás, Brazil: 1.8-1.7 Ga hydrothermal alteration and mineralization (United States)

    Pimentel, Márcio M.; Lindenmayer, Zara G.; Laux, Jorge H.; Armstrong, Richard; de Araújo, Janice Caldas


    The Gameleira deposit is one of several important Cu-Au deposits associated with the late Archean (ca. 2.7 Ga) volcanic rocks of the Itacaiúnas supergroup in the Carajás mineral province, southeastern Pará. It comprises mainly biotite- and sulphide-rich veins and quartz-grunerite-biotite-gold hydrothermal veins that cut andesitic rocks. It is interpreted as representative of the Fe oxide Cu-Au class of deposit. Sm-Nd isotopic data indicate an age of 2719±80 Ma (MSWD=3.0) and ɛNd( T) of -1.4 for the host meta-andesites. Metavolcanic rocks and cogenetic gabbros give an age of 2757±81 Ma (1 σ) with ɛNd( T) of -0.8. This is considered the best estimate for the crystallization age of the Gameleira volcanic and subvolcanic rocks. Negative ɛNd( T) and Archean TDM model ages (mostly between 2.8 and 3.1 Ga) suggest some contamination with older crustal material. The andesitic/gabbroic rocks are cut by two generations of granite dykes. The older has striking petrographic and geochemical similarities to the ca. 1.87 Ga alkali-rich Pojuca granite, which is exposed a few kilometers to the northwest of the deposit. The younger is a leucogranite with a U-Pb SHRIMP age of 1583+9/-7 Ma. Neodymium isotopic analyses of the two generations of granites indicate a strong crustal affinity and possible derivation from reworking of the Archean crust. The quartz-grunerite-gold hydrothermal vein yields a Sm-Nd isochron (MSWD=.83) age of 1839±15 Ma (1 σ) with ɛNd( T) of -9.2. Pervasive potassic alteration, represented by the widespread formation of biotite in the country rocks, is dated by Ar-Ar at 1734±8 Ma, and a similar age of 1700±31 Ma (1 σ) is indicated by the Sm-Nd isochron for the biotite-sulphide veins. Similar to that for the quartz-grunerite vein, the ɛNd( T) value for the sulphide-rich veins is strongly negative (-8.2), thereby suggesting that the original fluids percolated through, leached, or were derived from igneous rocks with an Archaean Nd isotopic signature

  1. A Comparison of Anorthositic Lunar Lithologies: Variation on the FAN Theme (United States)

    Nyquist, L. E.; Shih, C-Y.; Yamaguchi, A.; Mittlefehldt, D. W.; Peng, Z. X.; Park, J.; Herzog, G. F.; Shirai, N.


    Certain anorthositic rocks that are rare in the returned lunar samples have been identified among lunar meteorites. The variety of anorthosites in the Apollo collection also is more varied than is widely recognized. James eta. identified three lithologies in a composite clast o ferroan anorthosite (FAN)-suite rocks in lunar breccia 64435. They further divided all FANs into four subgroups: anorthositic ferroan (AF), mafic magnesian (MM), mafic ferroan (MF), and anorthositic sodic (AS, absent in the 64435 clast). Here we report Sm-Nd isotopic studies of the lithologies present in the 64435 composite clast and compare the new data to our previous data for lunar anorthosites incuding lunar anorthositic meteorites. Mineralogy-petrography, in situ trace element studies, Sr-isotope studies, and Ar-Ar chronology are included, but only the Nd-isotopic studies are currently complete.

  2. Two billion years of magmatism recorded from a single Mars meteorite ejection site (United States)

    Lapen, Thomas J.; Righter, Minako; Andreasen, Rasmus; Irving, Anthony J.; Satkoski, Aaron M.; Beard, Brian L.; Nishiizumi, Kunihiko; Jull, A. J. Timothy; Caffee, Marc W.


    The timing and nature of igneous activity recorded at a single Mars ejection site can be determined from the isotope analyses of Martian meteorites. Northwest Africa (NWA) 7635 has an Sm-Nd crystallization age of 2.403 ± 0.140 billion years, and isotope data indicate that it is derived from an incompatible trace element–depleted mantle source similar to that which produced a geochemically distinct group of 327- to 574-million-year-old “depleted” shergottites. Cosmogenic nuclide data demonstrate that NWA 7635 was ejected from Mars 1.1 million years ago (Ma), as were at least 10 other depleted shergottites. The shared ejection age is consistent with a common ejection site for these meteorites. The spatial association of 327- to 2403-Ma depleted shergottites indicates >2 billion years of magmatism from a long-lived and geochemically distinct volcanic center near the ejection site. PMID:28164153

  3. Geochemistry and chronology of Se' ertengshan greenstone, Inner Mongolia

    Institute of Scientific and Technical Information of China (English)

    LIU Jianzhong; WANG Lili; ZHANG Fuqin; LI Chunlai; ZOU Yongliao; OUYANG Ziyuan; XU Lin


    This paper deals with the meta-mafic volcanic rocks of the Gongyiming iron deposit at Baotou, Inner Mongolia. The major and trace elements and REE data indicate that the meta-mafic volcanic rocks occurred in the environment similar to a modern continental rift. Sm-Nd and Rb-Sr isotopic studies indicated that the meta-basic rocks were formed during the Early Neoarchean from 2800 Ma to 2900 Ma and reworked during the Late Neoarchean (2500 Ma) by metamorphism. Because of the separation of the North China Craton from the Siberia Craton during the Middle Proterozoic ( 1600 Ma), the Rb-Sr systematics of the rocks has been changed. The Se' ertengshan greenstone seems to occur during the Middle Archean. A stable continental crust may have existed during the Paleoarchean.

  4. Source of ore-forming substances and theoretical problems of metallogeny relevant to the Bayan Obo Fe-REE ore deposits in Inner Mongolia,China

    Institute of Scientific and Technical Information of China (English)

    曹荣龙; 朱寿华; 王俊文


    The source of rare earth elements (REE) ore-forming substances is identified to be extremelydistinct from that of iron ores.The Bayan Obo Fe-REE ore deposits were generated by a composite processof both crustal and mantle source mineralization.The original iron bodies are of a sedimentary deposit fromsupergenesis,while the REE ores have been formed by mantle fluid metasomatism superimposed upon thepre-existing iron bodies.It is believed that the REE ore deposit would be controlled by intracontinental hotspot.The H8 dolomite in mine regions belongs to normal sedimentary carbonate rock,its C and O isotopiccomposition rules out the possibility comparable with magrnatic carbonatite.The Sm-Nd isochrons of separatedREE minerals have shown two REE peak mineralization periods:early-middle Proterozoic (1 700 Ma±480 Ma) andCaledonia (424-402 Ma).

  5. River Valley pluton, Ontario - A late-Archean/early-Proterozoic anorthositic intrusion in the Grenville Province (United States)

    Ashwal, Lewis D.; Wooden, Joseph L.


    This paper presents Nd, Sr, and Pb isotopic data indicating a late-Archean/early-Proterozoic age for the River Valley anorthositic pluton of the southwestern Grenville Province of Sudbury, Ontario. Pb-Pb isotopic data on 10 whole-rock samples ranging in composition from anorthosite to gabbro yield an age of 2560 + or - 155 Ma. The River Valley pluton is thus the oldest anorthositic intrusive yet recognized within the Grenville Province. The Sm-Nd isotopic system records an age of 2377 + or - 68 Ma. High Pb-208/Pb-204 of deformed samples relative to igneous-textured rocks implies Th introduction and/or U loss during metamorphism in the River Valley area. Rb-Sr data from igneous-textured and deformed samples and from mineral separates give an age of 2185 + or - 105 Ma, indicating substantial disturbance of the Rb-Sr isotopic system.

  6. Northwest Africa 8159: An approximately 2.3 Billion Year Old Martian Olivine-Bearing Augite Basalt (United States)

    Simon, J. I.; Peters, T. J.; Tappa, M. J.; Agee, C. B.


    Based on petrology, mineralogy, and bulk composition, the new NWA 8159 martian meteorite is distinct from all known samples from Mars. In particular, the augite compositional trends are unique, but most similar to those of nakhite intercumulus. Whether NWA 8159 represents a new lithology or is related to a known meteorite group remains to be determined. Sr and Nd isotopic analyses will allow comparison of source characteristics with SNC and other new ungrouped meteorites (e.g., NWA 7635). Here we report initial Rb-Sr and Sm-Nd isotopic results for NWA 8159 with the objective to determine its formation age and to potentially identify similarities and potential source affinities with other martian rocks.

  7. Systematic Structural Elucidation for the Protonated Form of Rare Earth Bis(porphyrinato) Double-Decker Complexes: Direct Structural Evidence of the Location of the Attached Proton. (United States)

    Yamashita, Ken-Ichi; Sakata, Naoya; Ogawa, Takuji


    Direct structural evidence of the presence and location of the attached proton in the protonated form of rare earth bis(porphyrinato) double-decker complexes is obtained from an X-ray diffraction study of single crystals for a series of protonated forms of bis(tetraphenylporphyrinato) complexes [M(III)(tpp)(tppH)] (M = Tb, Y, Sm, Nd, and La). When CHCl3 is used as a solvent for crystallization of the complexes, their nondisordered molecular structures are obtained and the attached proton is identified on one of the eight nitrogen atoms. Use of other solvents affords another type of crystal, in which the position of the proton is disordered and thus the molecular structure is averaged. La complex also affords the disordered average structure even when CHCl3 is used for crystallization. A variable-temperature diffraction study for the Tb complex reveals that the dynamics of the proton in the nondisordered crystal is restricted.

  8. Re-interpretation of zircon date in a carbonatite dyke at the Bayan Obo giant REE-Fe-Nb deposit,China

    Institute of Scientific and Technical Information of China (English)


    @@ Recent re-valuation of the dating of the carbonatite dykes associated with the REE-Fe-Nb giant deposit at Bayan Obo has revealed an anomaly with one of the dates. Inspection of the post-1990 literature for the carbonatite dykes and H8 dolomite rocks and ores of Bayan Obo provides age data in the range 1223 +65 Ma to 1656 Ma, as Table 1 shows. Since Sm and Nd are relatively immobile elements, most of the Sm-Nd dates are considered to be little changed by the subsequent mineralization processes. That the dates occur in two clusters, 1656 ~ 1500 Ma and 1312 ~ 1223 Ma might refer to two related periods of carbonatitic magmatic activity, but that is not relevant at this moment.

  9. 稀土元素同位素质谱分析样品的纸色层法制备

    Institute of Scientific and Technical Information of China (English)



    Reported in this paper is a method of analysis of REE isotopes in RE minerals by paper chromatography-mass spectrometry. The pre-treatment of ore samples was followed by paper chromatography to obtain individual pure rate-earth elements. REE isotopic: analysis was carried out on a TSN-206 mass spectrometer. In paper chromatography butanone-9 M NH4SCN·HNO3 ( 150:2:1.5, V/V) was used as developing agent. In the light of the areas and colors of color spots on the paper chromatograms of rare-earth elements the contents of various rare-earth elements and Sm/Nd ratios can be roughly estimated. This method has the advantages of simple equipment, easy operation and direct estimation, as has been confirmed by the results of mass spectrometric analysis of Nd isotopes in some RE minerals. The relative standard deviations involved in most determined values are within the range of 0.02%.

  10. In situ Nd isotopic measurement of natural geological materials by LA-MC-ICPMS

    Institute of Scientific and Technical Information of China (English)

    YANG YueHeng; SUN JinFeng; XIE LieWen; FAN HongRui; WU FuYuan


    Using newly determined Sm isotopic abundances for correcting the isobaric interference of 144Sm on 144Nd and the established mass bias relationship between Sm and Nd, a series of in situ Nd isotopic measurements were conducted for relatively high Nd concentrations of natural geological materials, including apatite, titanite, monazite and perovskite on a Neptune multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS), coupled to a 193 nm ArF excimer laser ablation system. The results show that Ce has no significant influence on the precision and accuracy of Nd isotopic analyses for LREE-enriched geological minerals and that our approach is efficient in obtaining reliable 143Nd/144Nd and 147Sm/144Nd ratios for those materials with Sm/Nd<1 (147Sm/144Nd<0.6). When combined with trace element and U-Pb isotope data, the in situ Nd isotopic data can provide important information on geological processes.

  11. Accurate measurement of neodymium isotopic composition using Neptune MC-ICP-MS

    Institute of Scientific and Technical Information of China (English)

    Yueheng YANG; Hongfu ZHANG; Liewen XIE; Fuyuan WU


    This paper reports the measurement of the Neodymium isotopic composition by Neptune Multiple Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICP-MS) over the last two years. Although there is concomitant Cerium in the chemical separation process, this has no significant influence on the Neodymium analysis. As for the sample containing small amounts of Samarium (Sm/Nd<0.04), direct calibration for isobaric interference and mass discrimina-tion by the exponential law can be obtained by assuming that Samarium mass discrimination is the same as that of Neodymium. Geological samples after traditional chemi-cal separation were measured by Neptune MC-ICP-MS and Thermal Ionization Mass Spectrometry (TIMS) respectively. The results show that Neptune MC-ICP-MS can measure Neodymium isotopic composition as precisely the TIMS does and is even more effective and less time-consuming than the TIMS Method.

  12. The Acasta Gneiss - a Hadean cratonic nucleus (United States)

    Sprung, P.; Scherer, E. E.; Maltese, A.; Bast, R.; Bleeker, W.; Mezger, K.


    The known terrestrial rock record lacks undisputed, chemically intact Hadean crust. Direct evidence from this eon has been restricted to zircon grains within younger rocks [1]. The Acasta Gneiss Complex (AGC; NT, CA) has yielded zircon with Hadean domains [e.g., 2,3], but the time at which AGC rocks became closed chemical systems is unclear [4,5]. Determining this `time of last disturbance' (tld) would provide a minimum protolith age, and is crucial for using radiogenic isotope compositions of bulk rocks to trace crust-mantle evolution. Recent studies mostly focused on the `low-strain' eastern AGC [e.g., 6, 7], which records an evolving, early-mid Archean cratonic nucleus [7]. We also studied the `high-strain' banded gneiss in the western AGC, which hosts >4 Ga zircon domains [2,3], too. Our focusing lay on adjoining, lithologically distinct bands [8] of two distinct chemical groups: A) Mafic, chondrite-normalized LaN/YbN ≦20, slightly HFSE- depleted, and B) TTG-like, LaN/YbN up to 145, markedly HFSE-depleted. Six adjacent bands yield a well-defined 4 Ga Sm-Nd isochron with a ɛNd4Ga of +2 and ɛHf4Ga values from +1 to +6. Within-band Sm-Nd and Lu-Hf systematics imply younger mineral re-equilibration [9]. We interpret the 4 Ga Sm-Nd isochron to date the physical juxtaposition of bands in the gneiss unit and to define tld among bands for elements less mobile and diffusive than Sm and Nd. Contrasting Sm-Nd results from the same unit [10] likely are due to sampling at too fine a scale. Digestion of metamict pre-tld zircon likely caused the scatter in Lu-Hf. Both decay systems hint at the existence of a possibly local, strongly depleted Hadean mantle domain. The TTG-like bands are 0.4 Gyr older than similar rocks in the `low-strain' eastern AGC [7]. The AGC was thus an evolved cratonic nucleus already at 4 Ga, possibly with a depleted lithospheric keel. [1] Cavosie et al. (2004) Prec. Res. 135, 251-279 [2] Bowring & Williams (1999) CMP 134, 3-16 [3] Iizuka et al

  13. Geologic and Isotopic Models for the Carpathian Crystalline Evolution

    Directory of Open Access Journals (Sweden)

    Ioan Coriolan Balintoni


    Full Text Available The majority of Carpathian metamorphics protoliths have TDM model Sm/Nd ages between 1.6 and 2.0 Ga. This suggests an important episode of continental crust formation after the 2.0 Ga. The Biharia lithogroup (Apuseni Mountains and the Tulghes lithogroup (East Carpathians furnished Zircon U/Pb ages from metagranitoids and acid metavolcanics, respective, around 500 Ma; this is a sign of existence of some Lower Proterozoic protoliths among Carpathian metamorphics. The bimodal intrusions which are piercing the volcano-sedimentary sequence of Paiuseni lithogroup in Highiş Massif (Apuseni Mountains have given Permian ages on Zircon U/Pb data. The Paiuseni lithogroup probably represents the fill of a rift basin of the same age. The Arieseni, Muntele Mare and Vinta granitoid intrusions from Apuseni Mountains, with U/Pb ages between Lower Devonian and Permian, indicates some contractional and extensional processes, in connection with Variscan Orogeny.

  14. Interpretation of Ferroan Anorthosite Ages and Implications for the Lunar Magma Ocean (United States)

    Neal, C. R.; Draper, D. S.


    Ferroan Anorthosites (FANs) are considered to have purportedly crystallized directly from the lunar magma ocean (LMO) as a flotation crust. LMO modeling suggests that such anorthosites started to form only after greater than 70 percent of the LMO had crystallized. Recent age dates for FANs have questioned this hypothesis as they span too large of an age range. This means a younger age for the Moon-forming giant impact or the LMO hypothesis is flawed. However, FANs are notoriously difficult to age-date using the isochron method. We have proposed a mechanism for testing the LMO hypothesis through using plagioclase trace element abundances to calculate equilibrium liquids and compare them with LMO crystallization models. We now examine the petrography of the samples that have Sm-Nd (Samarium-Neodymium) age dates (Rb-Sr (Rubidium-Strontium) isotopic systematics may have been disturbed) and propose a relative way to age date FANs.

  15. Uranium, thorium and REE partitioning into sulfide liquids: Implications for reduced S-rich bodies (United States)

    Wohlers, Anke; Wood, Bernard J.


    We have performed experiments at 1.5 GPa over the temperature range 1400-2100 °C to determine the partitioning of lithophile elements (U, Th, Eu, Sm, Nd, Zr, La, Ce, Yb) between sulfide liquid, low-S metals and silicate melt. The data demonstrate pronounced increases in partitioning of all the lithophile elements into sulfide at very low FeO contents (10 in some cases. Similarly DSm may be >2 under the same conditions of low silicate FeO. This strong partitioning behaviour is found only be important in S-rich metals, however because the observed effect of low FeO on partitioning is uniquely confined to metallic melts close to stoichiometric FeS in composition.

  16. Reconstruction of protoliths of metamorphic rocks and tectonic setting of Wolegen Group

    Institute of Scientific and Technical Information of China (English)


    Parametamorphic rocks from Arong County in southeastern Inner Mongolia-Daxinganling district are regarded as Proterozoic in age,belonging to the Wolegen Group and composed of volcanoclastic and sandstone in origin,and have been disputed in tectonic setting.Because of the stability in metamorphism,the rare earth dements indicate the features of their protoliths.The authors integrated the petrologic methods with the geochemical parameters which include ∑REE,∑LREE/∑HREE,δCe,δEu,La/Yb,Sm/Nd,Th/Sc and the standard values of chondrite.The results show that the protoliths of Wolengen Group may be a group of voleanoclastic and continental margin elastic rocks,and their tectonic setting is the continent island arc.

  17. Construction of mass-age curves for the continental crust: An empirical model and an example from the western US (United States)

    Depaolo, D. J.; Schubert, G. S.; Linn, Ann


    The methodology of determining crustal mass-age curves is discussed. Problems in doing this include determination of model ages and accounting for mixing of materials of different ages during crust forming processes. These difficulties can be overcome with some reasonable assumptions and estimates of rock volumes based on areal proportions. This technique was used to construct a reasonably well constrained mass-age curve for the southwestern U.S. based on isotopic measurements on over 100 samples. The results imply that the crust in this area grew episodically at 2.8, 1.8, and 0.1 Ga. It is estimated that it would take on the order of 10000 to 100000 individual Sm-Nd isotopic measurements to carry out a similar exercise for continental crust world wide.

  18. Isotope geochronology of Dapingzhang spilite-keratophyre formation in Yunnan Province and its geological significance

    Institute of Scientific and Technical Information of China (English)

    钟宏; 胡瑞忠; 叶造军; 涂光炽


    On the basis of the geological field investigations and isotope geochronological studies the Sm-Nd isochron age (513 Ma?0 Ma), Rb-Sr isochron age (511 Ma? Ma) and K-Ar age (312-317 Ma) of the Dapingzhang spilite-keratophyre formation in Yunnan Province are presented. From these geochronological data it is evidenced that this suite of volcanic rocks was formed in the Cambrian and the parent magma was derived from a depleted mantle, which was influenced by crustal contamination and/or seawater hydrothermal alteration. During the Late Carboniferous the volcanic rocks experienced relatively strong geological reworking. This study provides geochronological evidence for the occurrence of Cambrian volcanic rocks in the Sanjiang (three-river) area.

  19. Isotope geochronology of Dapingzhang spilite-keratophyre formation in Yunnan Province and its geological significance

    Institute of Scientific and Technical Information of China (English)


    On the basis of the geological field investigations and isotope geochronological studies the Sm-Nd isochron age (513 Ma±40 Ma),Rb-Sr isochron age (511 Ma±8 Ma) and K-Ar age (312-317 Ma) of the Dapingzhang spilite-keratophyre formation in Yunnan Province are presented.From these geochronological data it is evidenced that this suite of volcanic rocks was formed in the Cambrian and the parent magma was derived from a depleted mantle,which was influenced by crustal contamination and/or seawater hydrothermal alteration.During the Late Carboniferous the volcanic rocks experienced relatively strong geological reworking.This study provides geochronological evidence for the occurrence of Cambrian volcanic rocks in the Sanjiang (three-river) area.

  20. A nucleosynthetic origin for the Earth’s anomalous 142Nd composition (United States)

    Burkhardt, C.; Borg, L. E.; Brennecka, G. A.; Shollenberger, Q. R.; Dauphas, N.; Kleine, T.


    A long-standing paradigm assumes that the chemical and isotopic compositions of many elements in the bulk silicate Earth are the same as in chondrites. However, the accessible Earth has a greater 142Nd/144Nd ratio than do chondrites. Because 142Nd is the decay product of the now-extinct 146Sm (which has a half-life of 103 million years), this 142Nd difference seems to require a higher-than-chondritic Sm/Nd ratio for the accessible Earth. This must have been acquired during global silicate differentiation within the first 30 million years of Solar System formation and implies the formation of a complementary 142Nd-depleted reservoir that either is hidden in the deep Earth, or lost to space by impact erosion. Whether this complementary reservoir existed, and whether or not it has been lost from Earth, is a matter of debate, and has implications for determining the bulk composition of Earth, its heat content and structure, as well as for constraining the modes and timescales of its geodynamical evolution. Here we show that, compared with chondrites, Earth’s precursor bodies were enriched in neodymium that was produced by the slow neutron capture process (s-process) of nucleosynthesis. This s-process excess leads to higher 142Nd/144Nd ratios; after correction for this effect, the 142Nd/144Nd ratios of chondrites and the accessible Earth are indistinguishable within five parts per million. The 142Nd offset between the accessible silicate Earth and chondrites therefore reflects a higher proportion of s-process neodymium in the Earth, and not early differentiation processes. As such, our results obviate the need for hidden-reservoir or super-chondritic Earth models and imply a chondritic Sm/Nd ratio for the bulk Earth. Although chondrites formed at greater heliocentric distances and contain a different mix of presolar components than Earth, they nevertheless are suitable proxies for Earth’s bulk chemical composition.

  1. Nd-isotopes in selected mantle-derived rocks and minerals and their implications for mantle evolution (United States)

    Basu, A.R.; Tatsumoto, M.


    The Sm-Nd systematics in a variety of mantle-derived samples including kimberlites, alnoite, carbonatite, pyroxene and amphibole inclusions in alkali basalts and xenolithic eclogites, granulites and a pyroxene megacryst in kimberlites are reported. The additional data on kimberlites strengthen our earlier conclusion that kimberlites are derived from a relatively undifferentiated chondritic mantle source. This conclusion is based on the observation that the e{open}Nd values of most of the kimberlites are near zero. In contrast with the kimberlites, their garnet lherzolite inclusions show both time-averaged Nd enrichment and depletion with respect to Sm. Separated clinopyroxenes in eclogite xenoliths from the Roberts Victor kimberlite pipe show both positive and negative e{open}Nd values suggesting different genetic history. A whole rock lower crustal scapolite granulite xenolith from the Matsoku kimberlite pipe shows a negative e{open}Nd value of -4.2, possibly representative of the base of the crust in Lesotho. It appears that all inclusions, mafic and ultramafic, in kimberlites are unrelated to their kimberlite host. The above data and additional Sm-Nd data on xenoliths in alkali basalts, alpine peridotite and alnoite-carbonatites are used to construct a model for the upper 200 km of the earth's mantle - both oceanic and continental. The essential feature of this model is the increasing degree of fertility of the mantle with depth. The kimberlite's source at depths below 200 km in the subcontinental mantle is the most primitive in this model, and this primitive layer is also extended to the suboceanic mantle. However, it is clear from the Nd-isotopic data in the xenoliths of the continental kimberlites that above 200 km the continental mantle is distinctly different from their suboceanic counterpart. ?? 1980 Springer-Verlag.

  2. Evolution of Migmatitic Granulite Complexes: implications from Lapland Granulite Belt, Part II: isotopic dating

    Directory of Open Access Journals (Sweden)

    Pekka Tuisku


    Full Text Available The migmatitic metapelites of the Lapland granulite belt (LGB in the NE part of the Fennoscandian Shield represent an arc-related greywacke basin metamorphosed in the granulite facies. Detrital zircons from migmatitic metapelites are derived from 1.94 - 2.9 Ga old acid source rocks (U-Pb SIMS ages. The clustering of detrital zircon ages between 1.97 and 2.2 Ga is problematic, because abundant felsic crust of this age is absent in the shield. The metasediments are characterized by Sm-Nd model ages of ca. 2.3 Ga. A younger, 1905-1880 Ma population of homogeneous zircons was formed during regional metamorphism. The peak high-grade metamorphism took place at ~1900 Ma and the latest chronological record from subsequent decompression and cooling phase is from ca. 1870 Ma. The norite-enderbite series of the LGB represents arc-magmas, which were intruded into the metasediments at ~1920-1905 Ma ago according to zircon U-Pb ages and were probably an important heat source for metamorphism. Older, zoned zircon grains in a quartz norite vein, initial εNd values of 0 to +1 and the continuous spectrum of LILE enrichment in the enderbite-series probably reflect assimilation of metasediments by magmas. Monazite U-Pb ages of migmatitic metasediments in the range 1906-1910±3 Ma overlap the late stage of enderbite intrusion and growth of early metamorphic zircons. Garnet-whole rock Sm-Nd ages from leucosomes in the range 1880-1886±7 Ma are concurrent with the growth of the youngest metamorphic zircons and probably indicate the crystallization of leucosomes of the influence of a fluid liberated from them. Isotopic and petrologic data reveal that the evolution of Lapland Granulite belt from the erosion of source rocks to the generation of a sedimentary basin, its burial, metamorphism and exhumation took place within ca. 60 Ma.

  3. Age, provenance and tectonic setting of the high-grade Jequitinhonha Complex, Araçuaí Orogen, eastern Brazil

    Directory of Open Access Journals (Sweden)

    Tatiana Gonçalves Dias

    Full Text Available ABSTRACT: The Jequitinhonha Complex of the northeastern Araçuaí orogen is an extensive sedimentary unit metamorphosed in the amphibolite-granulite facies transition around 580-545 Ma. The unit consists of Al-rich (kinzigitic paragneisses with decametric intercalations of graphite gneisses and quartzites, and centimetric to metric lenses of calcsilicate rocks. A new detrital zircon U-Pb age spectrum is reported for a sample of quartzite, and whole-rock geochemical (major and trace elements, 9 samples and Sm-Nd isotope data (10 samples for Jequitinhonha Complex paragneiss. Together with published data these show that: (1 the geochemistry of paragneiss samples of the Jequitinhonha Complex are similar to those of passive margin sedimentary protoliths; (2 detrital zircon data yield U-Pb age populations between ca. 0.9 and 2.5 Ga; and (3 Sm-Nd TDM model ages range from 1.6 to 1.8 Ga and εNd(575 Ma around -7.5. The data reveal a mixture of Cryogenian to Mesoproterozoic rift-related igneous rocks with the Palaeoproterozoic-Archaean basement rocks of the São Francisco-Congo palaeocontinent as the main source areas, and also support the correlation between the Jequitinhonha Complex and the passive margin units of the upper Macaúbas Group, constituting the precursor basin of the orogen. Our results, with the absence of ophiolites in the Jequitinhonha Complex, reinforce the interpretation that the São Francisco-Congo palaeocontinent was not divided to the north of the focused region, suggesting an ensialic termination of a gulf during the Neoproterozoic.

  4. The 3.5 Ga Siurua trondhjemite gneiss in the Archaean Pudasjärvi Granulite Belt, northern Finland

    Directory of Open Access Journals (Sweden)

    Tapani Mutanen


    Full Text Available In the Archaean Pudasjärvi Complex the pyroxene-bearing rocks are considered to form a belt, the Pudasjärvi Granulite Belt (PGB. The major rock types of the PGB are metaigneous mafic and felsic granulites, and trondhjemite gneisses. Red alaskites, white leucogranites and trondhjemitic pegmatoids are locally abundant. Ion microprobe U-Pb analyses on zircons suggest a magmatic age of ca. 3.5 Ga for the trondhjemite gneiss in Siurua, considered the oldest rock so far identified in the Fennoscandian Shield. The old age is supported by the Sm-Nd depleted mantle model age of 3.5 Ga, and by conventional U-Pb zircon data, which have provided a minimum age of 3.32 Ga. The U-Pb sims-data on the Siurua gneiss are, however, heterogeneous and suggest several stages of zircon growth, mostly at 3.5–3.4 Ga. An inherited core in one crystal provided an age of 3.73Ga, whereas the youngest two analyses yield ages of 3.1 and 3.3 Ga. Metamorphic monazite formed in the Siurua gneiss ca. 2.66 Ga ago, roughly contemporaneously with the high-grade metamorphism recorded by zircon in a mafi c granulite. Magmatic zircons from a felsic high-grade rock provide ages of ca. 2.96 Ga, but no zircons coeval with the 2.65 Ga metamorphism were detected by ion-microprobe. As a whole the PGB seems to be a tectonic block-mosaic containing rocks with Sm-Nd crustal formation ages ranging from 3.5 to 2.8 Ga.

  5. Isotopic contrasts within the Internal Liguride ophiolite (N. Italy): the lack of a genetic mantle-crust link (United States)

    Rampone, Elisabetta; Hofmann, Albrecht W.; Raczek, Ingrid


    It is widely accepted that oceanic lithosphere is generated by partial melting of fertile mantle peridotites producing basaltic melts and residual peridotites. This theory implies a cogenetic relationship between peridotites and associated crustal rocks, but the actual existence of such a genetic link has been tested in very few places. In this paper, we use Sr and Nd isotopes to test the relationship between mafic and ultramafic mantle rocks from a MORB-type ophiolite in the Internal Liguride Units of the Northern Apennines. This ophiolite is a remnant of the oceanic lithosphere of the Jurassic Ligurian Tethys, and consists of depleted mantle peridotites intruded by a gabbroic complex and covered by pillow lavas and ophiolitic breccias. Whole rocks and mineral separates from the gabbroic rocks yield a Sm-Nd isochron with an age of 164±14 Ma. The whole rock data for pillow lavas are also consistent with this isochron, yielding an initial value of ɛ Nd (164)=8.6±0.3 (1σ). The mantle peridotites, by contrast, have ɛ Nd(164) values ranging from 11.9 to 14.8, indicating an extreme depletion unlike that seen in modern oceanic mafic and ultramafic rocks. These results demonstrate that some ophiolites consist of mantle and crustal sections that are not genetically linked by a simple melt-residue relationship, and consequently do not represent mature oceanic lithosphere. Similar evidence has previously been available only from the Xigaze and Trinity ophiolites. The Internal Liguride peridotites yield Sm-Nd model ages of about 270 Ma, assuming a normally depleted mantle source with ɛ Nd = 9, indicating a Permian time of `extra' depletion. The ophiolite thus consists of mantle peridotites which were depleted during Permian time, and were later intruded and covered by MORB-type magmas during Jurassic time. On a regional scale, this interpretation is consistent with widespread evidence that extensional processes leading to asthenospheric upwelling and magma production

  6. Early Cambrian granitoids of North Gondwana margin in the transition from a convergent setting to intra-continental rifting (Ossa-Morena Zone, SW Iberia) (United States)

    Sánchez-García, T.; Pereira, M. F.; Bellido, F.; Chichorro, M.; Silva, J. B.; Valverde-Vaquero, P.; Pin, Ch.; Solá, A. R.


    Two distinct Cambrian magmatic pulses are recognized in the Ossa-Morena Zone (SW Iberia): an early rift-(ER) and a main rift-related event. This Cambrian magmatism is related to intra-continental rifting of North Gondwana that is thought to have culminated in the opening of the Rheic Ocean in Lower Ordovician times. New data of whole-rock geochemistry (19 samples), Sm-Nd-Sr isotopes (4 samples) and ID-TIMS U-Pb zircon geochronology (1 sample) of the Early Cambrian ER plutonic rocks of the Ossa-Morena Zone are presented in this contribution. The ER granitoids (Barreiros, Barquete, Calera, Salvatierra de los Barros and Tablada granitoid Massifs) are mostly peraluminous granites. The Sm-Nd isotopic data show moderate negative ɛNdt values ranging from -3.5 to +0.1 and TDM ages greatly in excess of emplacement ages. Most ER granitoids are crustal melts. However, a subset of samples shows a transitional anorogenic alkaline tendency, together with more primitive isotopic signatures, documenting the participation of lower crust or mantle-derived sources and suggesting a local transient advanced stage of rifting. The Barreiros granitoid is intrusive into the Ediacaran basement of the Ossa-Morena Zone (Série Negra succession) and has yielded a crystallization age of 524.7 ± 0.8 Ma consistent with other ages of ER magmatic pulse. This age: (1) constrains the age of the metamorphism developed in the Ediacaran back-arc basins before the intrusion of granites and (2) defines the time of the transition from the Ediacaran convergent setting to the Lower Cambrian intra-continental rifting in North Gondwana.

  7. Feldspathic Meteorites MIL 090034 and 090070: Late Additions to the Lunar Crust (United States)

    Nyquist, L. E.; Shirai, N.; Yamaguchi, A.; Shih, C.-Y.; Park, J.; Ebihara, M.


    Our studies of the Miller Range lunar meteorites MIL 090034, 090036, and 090070 show them to be a diverse suite of rocks from the lunar highlands hereafter referred to as MIL 34, MIL 36, and MIL 70, resp. MIL34 and MIL70, the focus of this work, are crystalline melt breccias. Plagioclase compositions in both peak sharply around An96-97. Mg numbers of olivine vary from 58-65 with a few higher values. MIL36 is a regolith breccia. MIL 34 and MIL 70 have some of the highest Al2O3 abundances of lunar highland meteorites, indicating that they have among the largest modal abundances of plagioclase for lunar meteorites. They have lower Sc and Cr abundances than nearly all lunar highland meteorites except Dho 081, Dho 489 and Dho 733. MIL34 and MIL70 also have similar cosmic ray exposure (CRE) ages of approximately 1-2 Ma indicating they are launch paired. (MIL36 has a larger CRE age approximately greater than 70 Ma). Park et al. found a variation in Ar-Ar ages among subsamples of MIL 34 and MIL70, but preferred ages of 3500+/-110 Ma for the "Dark" phase of MIL 34 anorthite and 3520+/-30 Ma for the "Light" phase of MIL70. Bouvier et al. reported a Pb-Pb age of 3894+/-39 Ma for a feldspathic clast of MIL 34 and a similar age for a melt lithology. Here we reexamine the Rb-Sr and Sm-Nd isotopic data, which show complexities qualitatively consistent with those of the Ar-Ar and Pb-Pb data. The Sm-Nd data in particular suggest that the feldspathic compositions of MIL 34 and MIL 70 formed during initial lunar geochemical differentiation, and REE modeling suggests a relatively late-stage formation.

  8. Evolution of the Bhandara-Balaghat granulite belt along the southern margin of the Sausar Mobile Belt of central India

    Indian Academy of Sciences (India)

    H M Ramachandra; Abhinaba Roy


    The Bhandara-Balaghat granulite (BBG) belt occurs as a 190 km long, detached narrow, linear, NE-SW to ENE-WSW trending belt that is in tectonic contact on its northern margin with the Sausar Group of rocks and is bordered by the Sakoli fold belt in the south. The Bhandara part of the BBG belt is quite restricted, comprising a medium to coarse grained two-pyroxene granulite body that is of gabbroic composition and preserves relic igneous fabric. The main part of the belt in Arjuni-Balaghat section includes metasedimentary (quartzite, BIF, Al- and Mg-Al metapelites) and metaigneous (metaultramafic, amphibolite and two-pyroxene granulite) protoliths interbanded with charnockite and charnockitic gneiss. These rocks, occurring as small bands and enclaves within migmatitic and granitic gneisses, show polyphase deformation and metamorphism. Geochemically, basic compositions show tholeiitic trend without Fe-enrichment, non-komatitic nature, continental affinity and show evolved nature. Mineral parageneses and reaction textures in different rock compositions indicate early prograde, dehydration melt forming reactions followed by orthopyroxene stability with or without melt. Coronitic and symplectitic garnets have formed over earlier minerals indicating onset of retrograde IBC path. Evidences for high temperature ductile shearing are preserved at places. Retrogressive hydration events clearly post-date the above paths. The present study has shown that the BBG belt may form a part of the Bastar Craton and does not represent exhumed oceanic crust of the Bundelkhand Craton. It is further shown that rocks of the BBG belt have undergone an earlier high-grade granulite metamorphism at 2672 ± 54 Ma (Sm-Nd age) and a post-peak granulite metamorphism at 1416 ± 59 Ma (Sm-Nd age, 1380 ± 28 Ma Rb-Sr age). These events were followed by deposition of the Sausar supracrustals and Neoproterozoic Sausar orogeny between 973 ± 63 Ma and 800 ± 16 Ma (Rb-Sr ages).

  9. Nature of the Precambrian metamorphic blocks in the eastern segment of Central Tianshan:Constraint from geochronology and Nd isotopic geochemistry

    Institute of Scientific and Technical Information of China (English)

    LIU; Shuwen; GUO; Zhaojie; ZHANG; Zhicheng; LI; Qiugen; ZH


    Granitoid gneisses are widespread in Precambrian metamorphic blocks of eastern segment of the Central Tianshan Tectonic Zone, and they have intrusive contact relationships with their metamorphic sedimentary country rocks of Proterozoic Xingxingxia and Kawabulag groups. Zircon U-Pb ages from a granodioritic gneiss (IW11-1) and a parametamorphic schist (W05-9) are determined at the Weiya area. Euhedral prismatic zircons from the granodioritic gneiss (IW11-1) provide U-Pb isotopic discordia intercept ages of 1218±17 Ma and 426±26 Ma, respectively, and euhedral prismatic zircons from the parametamorphic schist (W05-9) display U-Pb isotopic discordia intercept ages of 1216±74 Ma and 290±15 Ma, respectively. A whole-rock Sm-Nd isotopic isochron is determined in augen granitoid gneiss samples at the Ganggou-Kumishi area and we obtain the isochron age of 1142±120 Ma, and its εNd(t) = -4.3. These geochronological data suggest that these Precambrian metamorphic basement blocks within eastern segment of the Central Tianshan Tectonic Zone can be produced during 1140-1220 Ma, and occur a nearly homochronous metamorphism. Integrated to these geochronological data, Nd depleted mantle model ages (TDM) and epsilon Nd(t) values of these granitoid gneiss samples indicate that they can derive from mixing in various scales both magmas from mantle and crust sources at a late Mesoproterozoic active continental margin tectonic environment. Similarity in geochronology, Sm-Nd isotopic geochemistry between Weiya-Xingxingxia, Pargangtag and Ganggou-Kumishi areas suggests that they could be a bigger uniform metamorphic basement block, which could be formed by the assembly of the supercontinent Rodinia and be separated by late geological processes.

  10. A Idade e Natureza da Fonte do Granito do Moinho, Faixa Ribeira, Sudeste do Estado de São Paulo

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    Colombo Celso Gaeta Tassinari


    Full Text Available Este trabalho apresenta novos dados geocronológicos U-Pb SHRIMP em zircões e Sm-Nd em rocha total do Granito doMoinho, que ocorre nas imediações da cidade de Nazaré Paulista, Estado de São Paulo. Este granito apresenta característicasin- a tardi-tectônica em relação à Orogenia Brasiliana e é intrusivo nas seqüências mesoproterozóicas do Grupo Serra doItaberaba, no segmento central da Faixa de Dobramentos Ribeira. Adicionalmente, foram reavaliados dados isotópicos de Pbobtidos em amostras de rocha total e feldspatos potássicos disponíveis na literatura. A idade U-Pb SHRIMP obtida emmonocristais de zircões ígneos do granito foi de 620 ± 11 Ma, sendo interpretada como a época de cristalização desta rocha.As idades modelo Sm-Nd obtidas situaram-se entre 2,0 e 1,9 Ga, mostrando que o magma foi produzido por fusão parcial derochas pré-existentes, derivadas do manto superior no Paleoproterozóico. As composições isotópicas de Pb das amostras doGranito do Moinho indicam, a exemplo dos isótopos de Nd, uma fonte também crustal e com participação de rochas doGrupo Serra do Itaberaba, de idade mesoproterozóica.

  11. A nucleosynthetic origin for the Earth's anomalous (142)Nd composition. (United States)

    Burkhardt, C; Borg, L E; Brennecka, G A; Shollenberger, Q R; Dauphas, N; Kleine, T


    A long-standing paradigm assumes that the chemical and isotopic compositions of many elements in the bulk silicate Earth are the same as in chondrites. However, the accessible Earth has a greater (142)Nd/(144)Nd ratio than do chondrites. Because (142)Nd is the decay product of the now-extinct (146)Sm (which has a half-life of 103 million years), this (142)Nd difference seems to require a higher-than-chondritic Sm/Nd ratio for the accessible Earth. This must have been acquired during global silicate differentiation within the first 30 million years of Solar System formation and implies the formation of a complementary (142)Nd-depleted reservoir that either is hidden in the deep Earth, or lost to space by impact erosion. Whether this complementary reservoir existed, and whether or not it has been lost from Earth, is a matter of debate, and has implications for determining the bulk composition of Earth, its heat content and structure, as well as for constraining the modes and timescales of its geodynamical evolution. Here we show that, compared with chondrites, Earth's precursor bodies were enriched in neodymium that was produced by the slow neutron capture process (s-process) of nucleosynthesis. This s-process excess leads to higher (142)Nd/(144)Nd ratios; after correction for this effect, the (142)Nd/(144)Nd ratios of chondrites and the accessible Earth are indistinguishable within five parts per million. The (142)Nd offset between the accessible silicate Earth and chondrites therefore reflects a higher proportion of s-process neodymium in the Earth, and not early differentiation processes. As such, our results obviate the need for hidden-reservoir or super-chondritic Earth models and imply a chondritic Sm/Nd ratio for the bulk Earth. Although chondrites formed at greater heliocentric distances and contain a different mix of presolar components than Earth, they nevertheless are suitable proxies for Earth's bulk chemical composition.

  12. Consequences for an Alternative Earth Composition: A Decade of Insight (United States)

    Jackson, M. G.; Jellinek, M.; Carlson, R. W.


    This year marks the 10th anniversary of the landmark discovery showing that modern terrestrial mantle-derived lavas have 142Nd/144Nd ratios ~18 ppm higher than ordinary chondrites. One interpretation of this discovery is that the accessible Earth has a Sm/Nd ratio that is 5-7% higher than chondrites, which resulted from an early (20-30 Ma after accretion), catastrophic extraction of geochemically-enriched crust from the Earth's mantle (Boyet and Carlson, Science, 2005). The location of this early-formed enriched reservoir is unknown (it is either hidden in the deep Earth or was lost to space by impact erosion), but is critical, as it hosts the equivalent of the modern continents' budget of the radioactive heat-producing elements: U, Th and K. If the early-enriched reservoir is no longer in the Earth, there are profound implications for the geochemical and thermal evolution of the planet. First, the bulk silicate Earth would have a present-day 143Nd/144Nd of ~0.5130, and all modern terrestrial mantle and crustal reservoirs were ultimately derived from a non-chondric mantle with superchondritic Sm/Nd. Second, this composition matches the most frequently-occurring 143Nd/144Nd ratio (0.5130, PREMA) in ocean island basalts, including lavas with primitive 3He/4He, and suggests that large portions of the mantle sampled by OIB remain little-modified with respect to 143Nd/144Nd. Third, the modern continents were extracted from a previously depleted mantle, meaning that the modern mantle is pervasively depleted in highly incompatible elements, and that the mantle's radiogenic heat production is 50% lower than in chondrite-based models. The new bulk silicate Earth composition therefore presents challenges for describing the thermal history of the planet, but may lead to a stable plate tectonic regime over time and could be more conducive to supporting a habitable world.

  13. Tracking the Depleted Mantle Signature in Melt Inclusions and Residual Glass of Basaltic Martian Shergottites using Secondary Ionization Mass Spectrometry (United States)

    Peters, Timothy J.; Simon, Justin I.; Jones, John H.; Usui, Tomohiro; Economos, Rita C.; Schmitt, Axel K.; McKeegan, Kevin D.


    Trace element abundances of depleted shergottite magmas recorded by olivine-hosted melt inclusions (MI) and interstitial mesostasis glass were measured using the Cameca ims-1270 ion microprobe. Two meteorites: Tissint, an olivine-­phyric basaltic shergottite which fell over Morocco July 18th 2001; and the Antarctic meteorite Yamato 980459 (Y98), an olivine-phyric basaltic shergottite with abundant glassy mesostasis have been studied. Chondrite-­normalized REE patterns for MI in Tissint and Y98 are characteristically LREE depleted and, within analytical uncertainty, parallel those of their respective whole rock composition; supporting each meteorite to represent a melt composition that has experienced closed-­system crystallization. REE profiles for mesostasis glass in Y98 lie about an order of magnitude higher than those from the MI; with REE profiles for Tissint MI falling in between. Y98 MI have the highest average Sm/Nd and Y/Ce ratios, reflecting their LREE depletion and further supporting Y98 as one of our best samples to probe the depleted shergotitte mantle. In general, Zr/Nb ratios overlap between Y98 and Tissint MI, Ce/Nb ratios overlap between Y98 MI and mesostasis glass, and Sm/Nd ratios overlap between Y98 mesostasis glass and Tissint MI. These features support similar sources for both, but with subtle geochemical differences that may reflect different melting conditions or fractionation paths during ascent from the mantle. Interestingly, the REE patterns for both Y98 bulk and MI analyses display a flattening of the LREE that suggests a crustal contribution to the Y98 parent melt. This observation has important implications for the origins of depleted and enriched shergottites.


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    Full Text Available Molti ricercatori in questi ultimi anni si sono interessati al problema
    della composizione delle meteoriti; dai risultati sperimentali si
    è cercato trarre elementi circa la genesi di questi materiali, questione
    ancora aperta, ed avere informazioni sui processi chimici e termodinamici
    cui le meteoriti furono soggette prima della loro caduta sulla
    Uno degli aspetti del problema è quello dell'abbondanza percentuale
    degli elementi chimici e della loro composizione isotopica nella
    materia meteorica dei diversi tipi : ciò perché esso è connesso con
    quello piii generale dell'origine e distribuzione degli elementi nel cosmo
    e nella terra, nonché con quello dell'età delle meteoriti (l .
    In un recente lavoro Urey e collaboratori (-, esaminando un gran
    numero di analisi chimiche effettuate su questi materiali, sono pervenuti
    alla formulazione di alcuni criteri di classificazione in base alla
    percentuale dei componenti più abbondanti ed alla presenza o meno
    di disomogeneità strutturali nella massa fondamentale. Fra gli elementi
    meno abbondanti presentano particolare interesse quelli delle due famiglie
    radioattive naturali Torio e Uranio; le loro concentrazioni sono
    state determinate per alcune meteoriti siliciche (stonv ineteorites e
    per qualcuna ferrica (iron meteorites

  15. Isotope-geochemical Nd-Sr evidence of Palaeoproterozoic plume magmatism in Fennoscandia and mantle-crust interaction on stages of layered intrusions formation (United States)

    Serov, Pavel; Bayanova, Tamara; Kunakkuzin, Evgeniy; Steshenko, Ekaterina


    Palaeoproterozoic Fennoscandian layered intrusions belong to the pyroxenite-gabbronorite-anorthosite formation and spread on a vast area within the Baltic Shield. Based on isotope U-Pb, Sm-Nd, Rb-Sr and Re-Os data the duration of this formation can be to 100-130 Ma (2.53-2.40 Ga) [Serov et. al., 2008; Bayanova et. al., 2009]. We have studied rocks of layered PGE-bearing Fedorovo-Pansky, Monchetundra, Burakovsky, Olanga group intrusions and Penikat intrusion. According to recent and new complex Nd-Sr-REE data magma source of the vast majority of these intrusions was a mantle reservoir with unusual characteristics: negative values of ɛNd (from 0 to -4) and ISr = 0.702-0.706, flat spectra of REE (value of (La/Yb)N ~ 1.0-5.8) with positive Eu-anomalies [Bayanova et. al., 2009; Bayanova et. al., 2014]. However, the distribution of REE for ore-bearing gabbronorite intrusions Penikat (Sm-Nd age is 2426 ± 38 Ma [Ekimova et. al., 2011]) has a negative Eu-anomalies. This may be due to the formation of plagioclase and its removal from the magma chamber. One of the aims of isotope geochemical investigations is to establish the contribution of mantle components in the formation of layered intrusions rocks and the degrees of contamination of the magma source by crustal material. To calculate the proportion of mantle component model binary mixture was used [Jahn et. al., 2000]. As the mantle components we used data for CHUR: ɛNd = 0, [Nd] = 1.324 [Palm, O'Neil, 2003] and for crustal components were used host-rocks Nd-data. The proportion of mantle component for the studied intrusions was 77-99%. Also, data were obtained for the Monchetundra dike complex and amphibolized gabbro, for which the proportion of mantle material was 20-40%. For these rocks a significant crustal contamination is most likely. This process resulted in low values of ɛNd, a direct relationship between ɛNd and Nd concentration, and significant differences between the U-Pb and Sm-Nd model ages. A

  16. Meteorites, Continents, Heat, and Non-Steady State Geodynamics (United States)

    White, W. M.; Morgan, J. P.


    Previous geochemical estimates of terrestrial radiogenic heat production were based on the assumption that refractory lithophile elements, such as the REE, U, and Th, are present in the Earth in chondritic relative proportions (the 'modified chondritic Earth' model, e.g., McDonough & Sun, Chem. Geol., 120: 223, 1995). However, 142Nd/144Nd ratios in modern terrestrial materials are 10 and 18 ppm higher than in enstatite and ordinary chondrites, respectively. One explanation is that the Sm/Nd ratio in the Earth, or at least the observable part of it, is 3 to 6% higher than chondritic, implying the Earth is non-chondritic, even for refractory lithophile elements. The most likely explanation is that a low Sm/Nd igneous protocrust formed as the Earth accreted and was lost through collisional erosion. A protocrust 3 to 6% enriched in Nd relative to Sm would have been even more strongly enriched in the more highly incompatible elements K, U, and Th. Calculations based on a model of protocrust formation and collisional erosion (O'Neill, & Palme, Phil. Trans. R. Soc. A366: 4205, 2008) that satisfy both Sm-Nd and Lu-Hf isotopic constraints imply U and Th concentrations in the bulk silicate Earth (BSE) that are 20 to 40% lower than in the 'modified chondritic Earth' model. Assuming a K/U = 13800 for the BSE, the K concentration is 10 to 30% lower than previously believed. This corresponds to a terrestrial heat production of 3.0 to 3.9 pW/kg or 11.9 to 15.8 TW. At the high end, these estimates are in excellent agreement with those of Lyubetskaya & Korenaga (JGR, 112: B03211, 2007), but are much lower than the 20 TW value derived from the 'modified chondritic Earth' model. Of this, some 5 to 10 TW of heat production is in the continental crust, leaving ≤10 TW of heat production in the mantle. For comparison, recent estimates of U, Th, and K in the depleted mantle imply heat production in the range of 0.7-1.0 pW/kg; if the depleted mantle occupies the entire mantle, this

  17. The Acasta Gneisses revisited: Evidence for an early depleted mantle (United States)

    Scherer, E. E.; Sprung, P.; Bleeker, W.; Mezger, K.


    The oldest known mineral samples crystallized on the Earth are the up to 4.4 Ga zircon grains from the Jack Hills, Australia [e.g., 1,2]. Zircon, which is datable by U-Pb, contains ca. 1 wt% Hf, and has very low Lu/Hf, is well suited to recording the initial 176Hf/177Hf of its parent magma. It has therefore been widely used to track Earth’s crust-mantle differentiation over time and to estimate the relative amounts of juvenile and recycled components that contributed to Archean and Hadean crust. [e.g., 3,4,5,6]. Zircon studies may be subject to sampling bias, however: Juvenile mafic magmas are likely to stem from depleted sources, but are less likely to crystallize zircon. Processes such as host-rock metamorphism, remelting, weathering of the host rock, and sedimentary transport of grains may have further biased the zircon population. Metamict grains or those with high aspect ratios are likely to be destroyed by these processes, potentially biasing the zircon Hf record toward enriched compositions such that the degree of mantle depletion remains poorly defined before 4 Ga. In addition, incorrect age assignments to Hf analyses result in spurious initial ɛHf values. Here, we attempt to overcome these issues by investigating the bulk rock Lu-Hf and Sm-Nd systematics of some of the oldest rocks on Earth, the Acasta Gneisses (Northwest Territories, Canada). Earlier studies showed that zircon grains in these gneisses tend to come from enriched sources [e.g, 3,7,8] and are thus of little use for directly tracking the degree of mantle depletion. Furthermore, the gneisses themselves have been multiply metamorphosed and are often affected by mixing: The banded gneisses in particular comprise several magmatic precursor rocks of different age that have been repeatedly folded into each other. This promted questions of whether zircon ages should be used in the calculation of bulk rock initial epsilon Nd, and whether linear trends on Sm-Nd isochron represented meaningful

  18. Rare earth element variations resulting from inversion of pigeonite and subsolidus reequilibration in lunar ferroan anorthosites (United States)

    James, O.B.; Floss, C.; McGee, J.J.


    depletion of the calculated liquids is a relic of formation of these phases from primary LREE-depleted minerals. Thus, if one attempts to calculate the compositions of equilibrium liquids from pyroxene compositions, it is important to establish that the pyroxenes are primary. In addition, our data suggest that experimental studies have underestimated solid-liquid Ds for REEs in pigeonite and that REE contents of liquids calculated using these Ds are overestimates. Our results have implications for Sm-Nd age studies. Our work shows that if pigeonite inversion and/or subsolidus reequilibration between augite and orthopyroxene occured significantly after crystallization, and if pyroxene separates isolated for Sm-Nd studies do not have the bulk composition of the primary pyroxenes, then the Sm-Nd isochron age and ??Nd will be in error. Copyright ?? 2002 Elsevier Science Ltd.

  19. Preliminary Sr-Nd isotope study of the Hadong-Sanchung anorthositic rocks in Korea: Implication for their origin and for the Precambrian tectonics%韩国Hadong-Sanchung地区斜长岩Sr-Nd同位素初步研究--成因和前寒武纪构造意义

    Institute of Scientific and Technical Information of China (English)



    斜长岩呈长条带出露于朝鲜半岛南部,侵入到年代约为2.0 Ga的Yeongnam前寒武纪基底岩石中,虽然岩石类型简单(斜长岩和辉长岩质斜长岩),但可以同世界已知块状类型斜长岩相对比.这些斜长岩具有几个重要的差别,例如呈层状构造,镁铁相成分是角闪石而不是辉石,并且不具斜方辉石巨晶.应用Rb-Sr和Sm-Nd同位素系统研究这些岩石的年龄和成因,测定出一种页理化辉长岩质斜长岩矿物的Sm-Nd等时线年龄为1 678±90 Ma,推断其为侵位年龄,因为中生代绿岩相变质期间这些岩石的Sm-Nd同位素体系呈封闭状态.这一年龄和过去曾报道的元古宙块状斜长岩的年龄范围(1.1~1.7 Ga)相吻合.认为斜长岩成因可以用所谓元古宙斜长岩事件来解释.斜长岩的岩浆活动对朝鲜半岛南部前寒武纪基底岩石的构造历史有重要意义.全岩εNd(t)值范围-1.6~-5.2,而87Sr/86Sr初始值变化于0.704~0.706之间,据此可解释地幔成因的斜长岩岩浆是在其结晶作用期间吸收了地壳物质的结果.然而不能排除是下地壳源的可能性.%The anorthositic rocks in southern part of Korean peninsula occur as a long belt, intruding the ca. 2.0 Ga old Precambrianbasement rocks of the Yeongnam massif. Although they have simple rock types (anorthosite and gabbroic anorthosite) comparable towell known massif-type anorthosites worldwide, they possess several important differences such as layered structure, amphibole ratherthan pyroxene as a mafic phase, and no orthopyroxene megacrysts. The age of intrusion was not available previously. We have appliedRb-Sr and Sm-Nd isotope systematics to investigate the age and origin of these rocks. One foliated gabbroic anorthosite defines a Sm-Nd mineral isochron age of 1678 ± 90 Ma. This age is tentatively interpreted as the emplacement age because of apparently closed-sys-tem behavior of Sm-Nd system in these rocks during greenschist

  20. Evolution of the South African mantle — A case study of garnet peridotites from the Finsch diamond mine (Kaapvaal craton); part 1: Inter-mineral trace element and isotopic equilibrium (United States)

    Lazarov, Marina; Brey, Gerhard P.; Weyer, Stefan


    A thorough assessment of inter-mineral equilibrium is essential for the understanding of trace element partitioning and also for the interpretation of isotopic data. Here we investigated high temperature (~ 1200 °C and 6 GPa) garnet peridotite xenoliths from the Kaapvaal craton (Finsch mine, South Africa), with exceptionally well equilibrated mineral major element compositions, for their trace element and isotopic inter-mineral equilibrium. Trace element compositions for all major mineral phases, i.e. olivine, orthopyroxene (opx), clinopyroxene (cpx) and garnet, were analysed by laser ablation inductively coupled plasma mass spectrometry (ICP-MS). Garnet, cpx and opx of selected samples were analysed for their Sm-Nd and Lu-Hf isotope compositions by multi collector ICP-MS. Most important mineral characteristics include: a) olivines from most samples are enriched in high-field-strength elements relative to other incompatible trace elements. Their lithium content correlates negatively with Mg#, indicating a depletion signature; b) all other minerals are depleted in heavy and middle rare earth elements (H- and M-REE) and enriched in light REE and large ion lithophile elements. This implies a complex history of depletion and metasomatic overprint for the Finsch cratonic mantle; c) orthopyroxene has similarly shaped trace element patterns as cpx, with one to two orders of magnitude lower abundances; and d) both, garnet and cpx, display variable, mostly positive ɛHf coupled with moderate variations in ɛNd. Trace element partitioning between garnet/cpx, cpx/opx and garnet/opx, displays only a weak pressure and temperature dependency. However, equilibrium partitioning of most trace elements between garnet and cpx shows a strong compositional dependency, i.e. on the Cr- (and Ca-) content of the garnets. Garnet-cpx partition coefficients follow a second grade polynomial correlation with Cr2O3 of garnet, whereby high chromium garnets (Cr2O3 > 6 wt.%) have generally higher

  1. Numerical modeling of Etla Valley aquifer, Oax., Mexico: Evolution and remediation scenarios

    Energy Technology Data Exchange (ETDEWEB)

    Flores-Marquez, E. L; Martinez-Serrano, R. G; Chavez, R. E; Crusillo, Y [Instituto de Geofisica, Universidad Nacional Autonoma de Mexico, Mexico D.F. (Mexico); Jimenez, G [Facultad de Ingenieria, Benemerita Universidad Autonoma de Puebla, Puebla (Mexico); Camops-Enriquez, O [Instituto de Geofisica, Universidad Nacional Autonoma de Mexico, Mexico D.F. (Mexico)


    Short-term evolution (for 2001, 2005 and 2015) for the shallow aquifer of Etla Valley, Oaxaca, southern Mexico, was simulated based in a 3D hydrological model elaborated from the available geological, geophysical, geochemical, and hydrologic parameters. The numerical simulations were based on Visual MODFLOW code. These simulations indicate that, if the actual extraction regime is maintained, the drawdown of the potentiometric surface will get worse to the SE of the study area (i. e. beneath Oaxaca city). The prevailing aquifer flow direction favors the ground water pollution by fertilizers and leakage from the sewage network (dumped to the Atoyac river). According to the numerical simulation, remediation of this situation is possible if the wells located in the neighborhood of Oaxaca City are relocated at the recharge zones (i. e. at the feet from Sierra de Juarez). This remediation scenario will allow a recovery of the drawdown of the potentiometric surface. [Spanish] Se presenta un modelo geohidrologico evolutivo 3D a corto plazo (para los anos 2001, 2005 y 2015) del acuifero somero del Valle de Etla, Oaxaca, sureste de Mexico, basado en los parametros disponibles de geologia, geofisica, geoquimica e hidrologia. Las simulaciones numericas fueron realizadas en Visual MODFLOW. Estas simulaciones indican que, si el actual regimen de extraccion es mantenido, el abatimiento de la superficie potenciometrica puede ser mayor en el SE del area de estudio (i. e. cerca de la ciudad de Oaxaca). La contaminacion por fertilizantes y por las fugas de drenaje es favorecida por la direccion de flujo imperante en el acuifero (vaciandose en el rio Atoyac). De acuerdo a las simulaciones numericas, existe una posible remediacion de este proceso, relocalizando los pozos situados en la ciudad de Oaxaca en las zonas de recarga (i. e. en las faldas de la Sierra de Juarez). Este escenario de remediacion permitiria una recuperacion en el nivel de la superficie potenciometrica.

  2. Geochemistry of Archean Mafic Amphibolites from the Amsaga Area, West African Craton, Mauritania: Occurrence of Archean oceanic plateau (United States)

    El Atrassi, Fatima; Debaille, Vinciane; Mattielli, Nadine; Berger, Julien


    While Archean terrains are mainly composed of a TTG (Tonalite-trondhjemite-granodiorite) suite, more mafic lithologies such as amphibolites are also a typical component of those ancient terrains. Although mafic rocks represent only ~10% of the Archean cratons, they may provide key evidence of the role and nature of basaltic magmatism in the formation of the Archean crust as well as the evolution of the Archean mantle. This study focuses on the Archean crust from the West African craton in Mauritania (Amsaga area). The Amsaga Archean crust mainly consists of TTG and thrust-imbricated slices of mafic volcanic rocks, which have been affected by polymetamorphic events from the amphibolite to granulite facies. We report the results of a combined petrologic, Sm-Nd isotopic, major element and rare earth element (REE) study of the Archean amphibolites in the West African craton. This study was conducted in order to characterize these rocks, to constrain the time of their formation and to evaluate their tectonic setting and their possible mantle source. Our petrological observations show that these amphibolites have fine to medium granoblastic and nematoblastic textures. They are dominated by amphibolite-facies mineral assemblages (mainly amphibole and plagioclase), but garnet and clinopyroxene occur in a few samples. These amphibolites have tholeiitic basalt composition. On a primitive mantle-normalized diagram, they display fairly flat patterns without negative anomalies for either Eu or Nb-Ta. We have shown using Sm-Nd whole rock isotopic data that these amphibolites formed at 3.3 ±0.075 Ga. They have positive ɛNdi values (+5.2 ± 1.6). These samples show isotopically juvenile features, which rule out the possibility of significant contamination of the protolith magmas by ancient continental crust. Based on these geochemical data we propose that the tholeiitic basalts were formed in an oceanic plateau tectonic setting from a mantle plume source and that they have a

  3. SIMS zircon ages and Nd isotope systematics of the 2.2 Ga mafic intrusions in northern and eastern Finland

    Directory of Open Access Journals (Sweden)

    Eero Hanski


    Full Text Available Using the SIMS, ID-TIMS and Sm-Nd isotopic methods and the electron microprobe, we have studied several differentiated mafic intrusions of the c. 2.2 Ga gabbro-wehrlite association (GWA from four Paleoproterozoic schist belts and the Archean Kuhmo Greenstone Belt. Back-scattered electron images and electron microprobe analyses revealed that zircon crystals vary from well-preserved to turbid and highly altered with individual grains often displaying irregular, hydrated, CaO-bearing domains. In the most pristine domains, suitable for establishing the crystallization ages, SIMS 207Pb/206Pb ages fall in the range of 2210–2220 Ma, which is consistent with the most concordant ID-TIMS UPb ages. One of the studied intrusions that had previously yielded a conventional U-Pb date of less than 2.0 Ga, could be shown by spot analysis to belong to the 2.2 Ga family. In contrast to the well-preserved zircon domains, altered domains exhibit a variable and often strong U-Pb discordance up to 70 % and have distinctly lower 207Pb/206Pb ages. Some zircon grains record isotopic resetting at the time of the Svecofennian orogeny(ca. 1.8–1.9 Ga, while the most discordant ones project in the concordia diagram to late Paleozoic lower intercept ages indicating a relative recent Pb loss. The mineral chemistry of zircon suggests that the leakage of radiogenic Pb can be ascribed to an opensystembehavior related to hydrothermal alteration via action of CaCl2-bearing fluids.Common albitization of plagioclase in the GWA intrusions has caused this mineral to behave as an open system with regard to the Sm-Nd isotopic systematics. Despite this uncertainty, our Nd isotopic data indicate that the magma that produced the GWA intrusions in various parts of northern and eastern Finland was isotopically homogeneousand had an initial εNd(2220 Ma value of c. +0.6 precluding significant upper crustal contamination upon emplacement and subsequent fractional crystallization.

  4. Petrogenesis and geochemistry of circa 2.5 Ga granitoids in the Zanhuang Massif: Implications for magmatic source and Neoarchean metamorphism of the North China Craton (United States)

    Wang, Junpeng; Kusky, Timothy; Wang, Lu; Polat, Ali; Wang, Songjie; Deng, Hao; Fu, Jianmin; Fu, Dong


    The tectonic framework of the North China Craton (NCC) during late Archean to early Paleoproterozoic (circa 2.5 Ga) is still lacking comprehensive understanding due to subsequent strong deformation and metamorphic overprinting events. Circa 2.5 Ga magmatic and metamorphic activities are widely spread throughout the NCC, which can be used as an efficient target to better understand the tectonic evolution at this period. In this study, based on a detailed field, structural, geochemical, geochronological and Sm-Nd isotopic study, we focus our work on the Haozhuang granitoids in the Zanhuang Massif located at the eastern margin of the Central Orogenic Belt of the NCC. The granitoids mainly include undeformed pegmatite and granodiorite. One pegmatite and two granodiorite samples yield zircon 207Pb/206Pb ages of 2513 ± 29 Ma, 2511 ± 36 Ma and 2528 ± 18 Ma, respectively. The granodiorites show metaluminous and shoshonitic to high-K calc-alkaline series characteristics with A-type granite affinity. The circa 2.5 Ga granodiorites have highly negative εNd(t) values (- 29.22 - 33.12) and TDM model ages between 2671 Ma and 3151 Ma. This work shows clearly, from whole-rock major and trace elements and Sm-Nd isotopic studies, that the Haozhuang granodiorites were derived from partial melting of old and thickened TTG crust rather than mantle sources, and formed in a subduction-related tectonic setting. With geochemical comparison studies to other similar-aged granitic rocks in the Zanhuang Massif, we suggest that these granitic rocks possibly have a certain correlation during the magma evolution. Coupled with our previous geochemical and isotopic studies on circa 2.5 Ga mafic dike swarms, we propose that the similar-aged granitic rocks and mafic dike swarms were produced by an east-dipping subduction polarity reversal event following an arc-continent collision between the Fuping/Wutai island arc and Eastern Block of the NCC above a west-dipping slab. The east

  5. Nd isotopic compositions of the Tethyan Himalayan Sequence in southeastern Tibet

    Institute of Scientific and Technical Information of China (English)


    The Himalayan orogen consists of three major lithologic units that are separated by two major north-dipping faults: the Lesser Himalayan Sequence (LHS) below the Main Central Thrust (MCT), the Greater Himalayan Crystalline Complex (GHC) above the MCT, and the Tethyan Himalayan Sequence (THS) juxtaposed by the South Tibet Detachment fault (STD) over the GHC. Due to widespread meta-morphism and intense deformation, differentiating the above three lithologic units is often difficult. This problem has been overcome by the use of Sm-Nd isotopic analysis. The previous studies suggested that the LHS can be clearly distinguished from the GHC and THS by their Nd isotope compositions. However, the lack of detailed and systematic Sm-Nd isotopic studies of the THS across the Himalaya in general has made differentiation of this unit from the nearby GHC impossible, as the two appear to share overlapping Nd compositions and model ages. To address this problem, we systematically sam-pled and analyzed Nd isotopes of the THS in southeastern Tibet directly north of Bhutan. Our study identifies two distinctive fields in a εNd -TDM plot. The first is defined by the εNd(210 Ma) values of -3.45 to -7.34 and TDM values of 1.15 to 1.29 Ga from a Late Triassic turbidite sequence, which are broadly similar to those obtained from the Lhasa block. The second field is derived from the Early Cretaceous meta-sedimentary rocks with εNd(130 Ma) values from -15.24 to -16.61 and TDM values from 1.63 to 2.00 Ga; these values are similar to those obtained from the Greater Himalayan Crystalline Complex in Bhutan directly south of our sampling traverse, which has εNd(130 Ma) values of -10.89 to -16.32 and Nd model ages (TDM) of 1.73 to 2.20 Ga. From the above observations, we suggest that the Late Triassic strata of the southeast Tibetan THS were derived from the Lhasa block in the north, while the Early Cretaceous strata of the THS were derived from a source similar to the High Himalayan Crystalline

  6. Sluggish Hadean geodynamics: Evidence from coupled 146,147Sm-142,143Nd systematics in Eoarchean supracrustal rocks of the Inukjuak domain (Québec) (United States)

    Caro, G.; Morino, P.; Mojzsis, S. J.; Cates, N. L.; Bleeker, W.


    The discovery of deficits in 142Nd/144Nd in mafic rocks of the Nuvvuagittuq supracrustal belt (NSB) has triggered a debate about the possible preservation of Hadean (pre-3.85 Ga) crustal remnants in the little-known but areally extensive Innuksuac complex (3.6-3.8 Ga, Inukjuak domain, Northeast Superior Province, Canada). Geochronological investigations in the NSB, however, are hampered by the poor preservation and highly disturbed isotopic record of various mafic (amphibolite) lithologies that host the 142Nd anomalies. Here we present 146Sm-142Nd and 147Sm-143Nd data for rocks of extrusive magmatic and sedimentary protoliths from the Ukaliq supracrustal belt, a newly discovered volcano-sedimentary enclave enclosed in granitoid gneisses of the Inukjuak domain. Our study also includes the first 146Sm-142Nd data for quartz-magnetite rocks (banded iron-formation; BIF) of the NSB and the Eoarchean Isua supracrustal belt (ISB) in southern West Greenland. We show that Ukaliq amphibolites carry variably negative 142Nd anomalies, ranging from 0 to -10 ppm, which are positively correlated with their Sm/Nd ratio. If considered as an isochron relationship, the 146Sm-142Nd array yields an apparent Hadean emplacement age of 4215-76+50 Ma. The negative 142Nd anomalies, however, appear to be mainly restricted to amphibolites with boninitic affinities, likely reflecting inheritance from an enriched mantle source. In contrast, tholeiitic and ultramafic lavas have normal μ142Nd regardless of their Sm/Nd ratio. Furthermore, BIF from Ukaliq and Nuvvuagittuq lack the negative 142Nd anomalies that should have been produced by in situ decay of 146Sm had these sediments been deposited prior to ca. 4.1 Ga. Instead, they exhibit μ142Nd identical to that measured in Isua BIF. Collectively, our results suggest that the 146Sm-142Nd array characterizing mafic lithologies of Ukaliq and Nuvvuagittuq is an inherited signature with doubtful chronological significance. We interpret the volcanic

  7. Highly evolved juvenile granites with tetrad REE patterns: the Woduhe and Baerzhe granites from the Great Xing'an Mountains in NE China (United States)

    Jahn, Bor-ming; Wu, Fuyuan; Capdevila, R.; Martineau, F.; Zhao, Zhenhua; Wang, Yixian


    In NE China, voluminous granitoids were emplaced in late Paleozoic and Mesozoic times. We report here Sr-Nd-O isotopic and elemental abundance data for two highly evolved granitic plutons, Woduhe and Baerzhe, from the Great Xing'an Mountains. They show a rather "juvenile" Sr-Nd isotopic signature and a spectacular tetrad effect in their REE distribution patterns as well as non-CHARAC (charge-and-radius-controlled) trace element behavior. The emplacement ages are constrained at 130±4 Ma for the Woduhe and 122±5 Ma for the Baerzhe granites by Rb-Sr and Sm-Nd isotope analyses. Both granites are also characterized by low but imprecise initial 87Sr/ 86Sr ratios of about 0.703. The Nd-Sr isotope data argue for their generation by melting of dominantly juvenile mantle component with subordinate recycled ancient crust. This is largely compatible with the general scenario for much of the Phanerozoic granitoids emplaced in the Central Asian Orogenic Belt. The parental magmas for both the Woduhe and Baerzhe granites have undergone extensive magmatic differentiation, during which intense interaction of the residual melts with aqueous hydrothermal fluids (probably rich in F and Cl) resulted in the non-CHARAC trace element behavior and the tetrad effect of REE distribution. Both the Woduhe and Baerzhe granites show the characteristic trace element patterns of rare-metal granites, but their absolute abundances differ by as much as two orders of magnitude. The oxygen isotope compositions of the two granites have been severely disturbed. Significant 18O depletion in feldspar, but not so much in quartz, suggests that the hydrothermal alteration took place in a temperature condition of 300-500 °C. This subsolidus hydrothermal alteration is decoupled from the late-stage magma-fluid interaction at higher temperatures. Despite the two distinct and intense events of "water-rock" interaction, the Rb-Sr and Sm-Nd geochronological systems seem to have maintained closed, hence, suggesting

  8. The reliability of ∼2.9 Ga old Witwatersrand banded iron formations (South Africa) as archives for Mesoarchean seawater: Evidence from REE and Nd isotope systematics (United States)

    Viehmann, Sebastian; Bau, Michael; Smith, Albertus J. B.; Beukes, Nicolas J.; Dantas, Elton L.; Bühn, Bernhard


    Pure marine chemical sediments, such as (Banded) Iron Formations, (B)IFs, are archives of geochemical proxies for the composition of Precambrian seawater and may provide information about the ancient hydrosphere-atmosphere system. We here present rare earths and yttrium (REY) and high precision Sm-Nd isotope data of ∼2.90 Ga old Superior-type BIFs from the Witwatersrand Supergroup, South Africa, and compare those with data for near-contemporaneous BIFs from the correlative Pongola Supergroup (Superior-type BIF) and from the Pietersburg Greenstone Belt (Algoma-type IF), respectively. All Witwatersrand samples studied display the typical general REY distribution of Archean seawater, but their REY anomalies are less pronounced and their immobile element concentrations are higher than those of other pure (B)IFs. These observations indicate the presence of significant amounts of detrital aluminosilicates in the Witwatersrand BIFs and question the reliability of the Contorted Bed and Water Tower BIFs (Parktown Formation, West Rand Group) as archives of Mesoarchean seawater. Significant post-depositional alteration of the REY budget and the Sm-Nd isotope system is not observed. The Nd isotopic compositions of the purest BIF samples, i.e. the most reliable archives for Witwatersrand seawater, show initial εNd values between -3.95 and -2.25. This range is more negative than what is observed in ambient shales, indicating a decoupling of suspended and dissolved loads in the "near-shore" Witwatersrand Basin seawater. However, εNd range overlaps with that of the correlative Pongola BIF (Alexander et al., 2008). The deeper-water Algoma-type Pietersburg BIF shows more positive (i.e. more mantle-like) εNd2.9Ga values, supporting the hypothesis that a significant amount of its REY inventory was derived from black smoker-style, high-temperature hydrothermal fluids that had altered seafloor basalts. In marked contrast, the dissolved REY budgets (including the Nd isotopic

  9. Timing of Precambrian melt depletion and Phanerozoic refertilization events in the lithospheric mantle of the Wyoming Craton and adjacent Central Plains Orogen (United States)

    Carlson, R.W.; Irving, A.J.; Schulze, D.J.; Hearn, B.C.


    Garnet peridotite xenoliths from the Sloan kimberlite (Colorado) are variably depleted in their major magmaphile (Ca, Al) element compositions with whole rock Re-depletion model ages generally consistent with this depletion occurring in the mid-Proterozoic. Unlike many lithospheric peridotites, the Sloan samples are also depleted in incompatible trace elements, as shown by the composition of separated garnet and clinopyroxene. Most of the Sloan peridotites have intermineral Sm-Nd and Lu-Hf isotope systematics consistent with this depletion occurring in the mid-Proterozoic, though the precise age of this event is poorly defined. Thus, when sampled by the Devonian Sloan kimberlite, the compositional characteristics of the lithospheric mantle in this area primarily reflected the initial melt extraction event that presumably is associated with crust formation in the Proterozoic-a relatively simple history that may also explain the cold geotherm measured for the Sloan xenoliths. The Williams and Homestead kimberlites erupted through the Wyoming Craton in the Eocene, near the end of the Laramide Orogeny, the major tectonomagmatic event responsible for the formation of the Rocky Mountains in the late Cretaceous-early Tertiary. Rhenium-depletion model ages for the Homestead peridotites are mostly Archean, consistent with their origin in the Archean lithospheric mantle of the Wyoming Craton. Both the Williams and Homestead peridotites, however, clearly show the consequences of metasomatism by incompatible-element-rich melts. Intermineral isotope systematics in both the Homestead and Williams peridotites are highly disturbed with the Sr and Nd isotopic compositions of the minerals being dominated by the metasomatic component. Some Homestead samples preserve an incompatible element depleted signature in their radiogenic Hf isotopic compositions. Sm-Nd tie lines for garnet and clinopyroxene separates from most Homestead samples provide Mesozoic or younger "ages" suggesting

  10. SHRIMP single zircon U-Pb dating of the Kongling high-grade metamorphic terrain: Evidence for >3.2 Ga old continental crust in the Yangtze craton

    Institute of Scientific and Technical Information of China (English)

    GAO; Shan; (


    [1]Liu, G. L., New progress in the geochronology of the Kongling terrain, Regional Geology of China, 1987, 1: 95.[2]Zheng, W. Z., Liu, G. L., Wang, X. W., Geochronology of the Archean Kongling terrain, Bull. Yichang Inst. Geol. Miner. Resour. (in Chinese), 1991, 16: 97-105.[3]Yuan, H. H., Zhang, Z. L., Liu, W. et al., Dating of zircons by evaporation method and its application, Mineral. Petrol. (in Chinese), 1991, 11: 72.-79[4]Ling, W. L., Gao, S., Zheng, H. F. et al., Sm-Nd isotopic dating of Kongling terrain, Chinese. Sci. Bull., 1998, 43(1): 86-89.[5]Gao, S., Ling, W. L., Qiu, Y. et al., Contrasting geochemical and Sm-Nd isotopic compositions of Archean metasediments from the Kongling high-grade terrain of the Yangtze craton: evidence for cratonic evolution and redistribution of REE during crustal anatexis, Geochim. Cosmochim. Acta, 1999, 63: 2071-2088.[6]Gao, S., Zhang, B. R., The discovery of Archean TTG gneisses in northern Yangtze craton and their implications, Earth Sci. (in Chinese, with English abstract), 1990, 15: 675-679.[7]Dong, S. B., Metamorphism and Its Relation to the Crustal Evolution in China (in Chinese), Beijing: Geological Publishing House, 1986. [8]Composton, W., Williams, I. S., Meyer, C., U-Pb geochronology of zircons from lunar breccia 73217 using sensitive high mass-resolution ion microprobe, J. Geophys. Res., 1984, 89(B): 252-534.[9]Williams, I. S., Composton, W., Black, L. P et al., Unsupported radiogenic Pb in zircon: a case of anomalously high Pb-Pb, U-Pb and Th-Pb ages, Contrib. Mineral. Petrol., 1984, 88: 322-327.[10] Nelson, D. R., Evolution of the Archean granite-greenstone terrains of the Eastern Goldfileds, Western Australia: SHRIMP U-Pb zircon constraints, Precambrian Res., 1997, 83: 57-81.[11] Ling, W. L., Geochronology and crustal growth of the Paleoproterozoic basements along the northern margin of the Yangzte craton, Earth Sci., 1996, 21(5): 491—493.

  11. Nd Isotope and U-Th-Pb Age Mapping of Single Monazite Grains by Laser Ablation Split Stream Analysis (United States)

    Fisher, C. M.; Hanchar, J. M.; Miller, C. F.; Phillips, S.; Vervoort, J. D.; Martin, W.


    Monazite is a common accessory mineral that occurs in medium to high grade metamorphic and Ca-poor felsic igneous rocks, and often controls the LREE budget (including Sm and Nd) of the host rock in which it crystallizes. Moreover, it contains appreciable U and Th, making it an ideal mineral for determining U-Th-Pb ages and Sm-Nd isotopic compositions, both of which are readily determined using in situ techniques with very high spatial resolution like LA-MC-ICPMS. Here, we present the results of laser ablation split stream analyses (LASS), which allows for simultaneous determination of the age and initial Nd isotopic composition in a single analysis. Analyses were done using a 20mm laser spot that allowed for detailed Nd isotope mapping of monazite grains (~30 analyses per ~250mm sized grain). Combined with LREE ratios (e.g., Sm/Nd, Ce/Gd, and Eu anomalies) these results yield important petrogenetic constraints on the evolution of peraluminous granites from the Old Woman-Piute batholith in southeastern California. Our findings also allow an improved understanding of the causes of isotope heterogeneity in granitic rocks. U-Th-Pb age mapping across the crystals reveals a single Cretaceous age for all grains with precision and accuracy typical of laser ablation analyses (~2%). In contrast, the concurrent Nd isotope mapping yields homogeneous initial Nd isotope compositions for some grains and large initial intra-grain variations of up to 8 epsilon units in others. The grains that yield homogeneous Nd isotope compositions have REE ratios suggesting that they crystallized in a fractionally crystallizing magma. Conversely, other grains, which also record fractional crystallization of both feldspar and LREE rich minerals, demonstrate a change in the Nd isotope composition of the magma during crystallization of monazite. Comparison of inter- and intra-grain Nd isotope compositions reveals further details on the potential mechanisms responsible for isotope heterogeneity

  12. Single crystal U-Pb zircon age and Sr-Nd isotopic composition of impactites from the Bosumtwi impact structure, Ghana: Comparison with country rocks and Ivory Coast tektites. (United States)

    Ferrière, Ludovic; Koeberl, Christian; Thöni, Martin; Liang, Chen


    The 1.07 Myr old Bosumtwi impact structure (Ghana), excavated in 2.1-2.2 Gyr old supracrustal rocks of the Birimian Supergroup, was drilled in 2004. Here, we present single crystal U-Pb zircon ages from a suevite and two meta-graywacke samples recovered from the central uplift (drill core LB-08A), which yield an upper Concordia intercept age of ca. 2145 ± 82 Ma, in very good agreement with previous geochronological data for the West African Craton rocks in Ghana. Whole rock Rb-Sr and Sm-Nd isotope data of six suevites (five from inside the crater and one from outside the northern crater rim), three meta-graywacke, and two phyllite samples from core LB-08A are also presented, providing further insights into the timing of the metamorphism and a possibly related isotopic redistribution of the Bosumtwi crater rocks. Our Rb-Sr and Sm-Nd data show also that the suevites are mixtures of meta-greywacke and phyllite (and possibly a very low amount of granite). A comparison of our new isotopic data with literature data for the Ivory Coast tektites allows to better constrain the parent material of the Ivory Coast tektites (i.e., distal impactites), which is thought to consist of a mixture of metasedimentary rocks (and possibly granite), but with a higher proportion of phyllite (and shale) than the suevites (i.e., proximal impactites). When plotted in a Rb/Sr isochron diagram, the sample data points (n = 29, including literature data) scatter along a regression line, whose slope corresponds to an age of 1846 ± 160 Ma, with an initial Sr isotope ratio of 0.703 ± 0.002. However, due to the extensive alteration of some of the investigated samples and the lithological diversity of the source material, this age, which is in close agreement with a possible "metamorphic age" of ∼ 1.8-1.9 Ga tentatively derived from our U-Pb dating of zircons, is difficult to consider as a reliable metamorphic age. It may perhaps reflect a common ancient source whose Rb-Sr isotope

  13. 40Ar- 39Ar dating of detrital muscovite in provenance investigations: a case study from the Adelaide Rift Complex, South Australia (United States)

    Haines, Peter W.; Turner, Simon P.; Kelley, Simon P.; Wartho, Jo-Anne; Sherlock, Sarah C.


    Detrital zircon ages are commonly used to investigate sediment provenance and supply routes. Here, we explore the advantages of employing multiple, complimentary techniques via a case study of the Neoproterozoic and Cambrian of the Adelaide Rift Complex, South Australia. Detrital muscovite Ar-Ar ages are presented from stratigraphic units, or equivalents, that have previously been the subject of U-Pb detrital zircon dating, and, in some cases, whole-rock Sm-Nd isotope studies. The zircon age ranges and whole-rock Sm-Nd isotope data suggest that early Neoproterozoic sediments from near the base of the Adelaide Rift Complex comprise a mixture of detritus derived from the adjacent Gawler Craton (Palaeoproterozoic to earliest Mesoproterozoic) and overlying Gairdner flood basalts. In contrast, detrital muscovites from this level have a broad scatter of Mesoproterozoic infrared (IR) laser total fusion Ar-Ar ages, while UV laser traverses indicate that the age spread reflects partial resetting by multiple heating events, rather than a mixture of sources. Younger Neoproterozoic sediments document replacement of the Gawler Craton by the more distant Musgrave and/or Albany-Fraser Orogens as the main provenance. The Cambrian Kanmantoo Group marks an abrupt change in depositional style and a new sediment source. The Kanmantoo Group have older Nd model ages than underlying strata, yet are dominated by near to deposition-aged (˜500-650 Ma) detrital zircons and muscovites, suggesting rapid cooling and exhumation of a tectonically active provenance region. Although this source remains uncertain, evidence points towards the distant Pan-African orogenic belts. Deposition in the Adelaide Rift Complex was terminated in the late Early Cambrian by the Delamerian Orogeny, and the results of previous detrital mineral dating studies from the Lachlan Fold Belt to the east are consistent with at least partial derivation of these sediments from reworked upper Adelaide Rift Complex (Kanmantoo

  14. The role of phosphates for the Lu-Hf chronology of meteorites (United States)

    Debaille, Vinciane; Van Orman, James; Yin, Qing-Zhu; Amelin, Yuri


    The 176Lu-176Hf isotopic system is widely used for dating and tracing cosmochemical and geological processes, but still suffers from two uncertainties. First, Lu-Hf isochrons for some early Solar System materials have excess slope of unknown origin that should not be expected for meteorites with ages precisely determined with other isotopic chronometers. This observation translates to an apparent Lu decay constant higher than the one calculated by comparing ages obtained with various dating methods on terrestrial samples. Second, unlike the well constrained Sm/Nd value (to within 2%) for the chondritic uniform reservoir (CHUR), the Lu/Hf ratios in chondrites vary up to 18% when considering all chondrites, adding uncertainty to the Lu/Hf CHUR value. In order to better understand the Lu-Hf systematics of chondrites, we analyzed mineral fractions from the Richardton H5 chondrite to construct an internal Lu-Hf isochron, and set up a numerical model to investigate the effect of preferential diffusion of Lu compared to Hf from phosphate, the phase with the highest Lu-Hf ratio in chondrites, to other minerals. The isochron yields an age of 4647 ± 210 million years (Myr) using the accepted 176Lu decay constant of 1.867 ± 0.008 ×10-11yr-1. Combining this study with the phosphate fractions measured in a previous study yields a slope of 0.08855 ± 0.00072, translating to a 176Lu decay constant of 1.862 ± 0.016 ×10-11yr-1 using the Pb-Pb age previously obtained, in agreement with the accepted value. The large variation of the Lu/Hf phosphates combined with observations in the present study identify phosphates as the key in perturbing Lu-Hf dating and generating the isochron slope discrepancy. This is critical as apatite has substantially higher diffusion rates of rare earth elements than most silicate minerals that comprise stony meteorites. Results of numerical modeling depending of temperature peak, size of the grains and duration of the metamorphic event, show that

  15. Nd-142/Nd-144 in bulk planetary reservoirs, the problem of incomplete mixing of interstellar components and significance of very high precision Nd-145/Nd-144 measurements (United States)

    Harper, C. L., Jr.; Jacobsen, S. B.


    Apart from the challenge of very high precision Nd-142/Nd-144 ratio measurement, accurate applications of the coupled Sm-(146,147)-Nd-(142,143) systematics in planetary differentiation studies require very precise knowledge of the present-day (post-Sm-146 decay) Nd-142/Nd-144 ratios of bulk planetary objects (BP). The coupled systematics yield model ages for the time of formation of Sm/Nd-fractionated reservoirs by differentiation of Sm/Nd-unfractionated bulk planetary reservoirs. Estimates of (Nd-142/Nd-144)(sub BP) and (Nd-143/Nd-144)(sub BP) therefore provide the critical baseline relative to which these model ages are referenced. In the Sm-147-Nd-143 systematics, Nd-143/Nd-144 variations are mostly large; therefore, small variations in initial Nd-143/Nd-144 ratios generally can be ignored. However, in the case of Sm-146-Nd-142, the range of Nd-142/Nd-144 divergence for differentiated planetary reservoirs is much smaller. Consequently Sm-(146,147)-Nd-(142,143) model ages are sensitive to small variations in bulk planetary Nd-142/Nd-144 (both present-day and initial). One major unanswered question is whether or not Nd shelf standards (CIT Nd beta/Ames metal, La Jolla, NASA-JSC/Ames metal) have Nd-142/Nd-144 identical to the bulk Earth or otherwise might record some degree of radiogenic evolution in an early-fractionated reservoir. Our discussions of earth Earth differentiation based on Nd-142/Nd-144 in Isua and Acasta samples have employed a working assumption: (Nd-142/Nd-144)(sub Nd beta) = (Nd-142/Nd-144)(sub Bulk Earth). This requires experimental justification and is apparently contradicted by chondrite Nd-142/Nd-144 measurements, which have been interpreted to indicate: (Nd-142/Nd-144)(sub JSC/Ames metal) = ((Nd-142/Nd-144)(sub CHUR) = 35 plus or minus 8 ppm). At present, interpretations of the early Earth and Moon hinge largely on this issue. Because Ba in bulk chondrite samples exhibit similar magnitude nuclear anomalies, attributable to incomplete mixing

  16. Emplacement Ages and Geochemical Characteristics of Grabbroic Intrusions and Prospecting Orientation of Related Deposit in Luodian, Guizhou Province

    Institute of Scientific and Technical Information of China (English)

    FANG Weixuan; HU Ruizhong; SU Wenchao; XIAO Jiafei


    Emplacement ages, geochemical characteristics and analysis of continental dynamics ongabbroic intrusions in Luodian County, Guizhou Province, have been discussed based on studies ofisotopic chronology (the whole-rock Sm-Nd and Rb-Sr isochron methods), major elements, traceelements and PGE. Intrusive activities of the gabbroic intrusions in the study area took place during theLate Yanshanian Orogenic Movement (the Cretaceous Period), as indicated by the Sm-Nd isochronages (t)=(99.6±4.5) (2σ) Ma and by the Rb-Sr isochron ages t=(97±1.6) (2o) Ma. The gabbroic intrusionsare attached to mafic rocks in cal-alkaline basaltic series. They occurred as dikes and might be formedunder an extensional background of the continent. Differentiation of their magmatic crystallizationresulted in obvious zonation of petrography. In the gabbroic intrusions of this study, large ion lithophileelements and LREE are enriched, and the chondrite-normalized REE distribution pattern is leftwardinclined without anomalies of δCe or δEu, and there are high concentrations of PGE and ratios of Pd/Ir(averaging 4.21). All of these imply that their source areas may be basaltic magma in the upper mantlewith high-level partial melting, derived from EMl-type enriched mantle. It is different from Emeishanbasalt, which may be related to the upper mantle at low-grade partial melting. Emplacementmechanism of the gabbroic intrusions in this study may suppose to be asthenosphere upheaving as anisolated hot wave in the presence of mantle fluid, resulting in basaltic magma intruded into thecontinental crust as a diapiric intrusion. Therefore, uplifting of faulting-block and extensionaldeformation could take place in the shallow part of the continental crust while vertical amassing andaccretion of magmatic materials in the deep part of the continental crust. These special processes couldsupposed to be a special background of continental dynamics for this large-scale epithermalmetaliogenic domain, such as Au

  17. Nd isotopic characteristics of post-Archean sediments from the Eastern Nanling Range: Evidence for crustal evolution

    Institute of Scientific and Technical Information of China (English)

    SHEN Weizhou; YU Jinhai; ZHAO Lei; CHEN Zelin; LIN Hengcai


    A systematic Sm-Nd isotopic study was carried out for sediments and metasediments of different ages from Mesoproterozoic to early Mesozoic era in southwestern Fujian, Eastern Nanling Range. The results show that Nd model age (tDM) and εNd(t) value of most sediments are closely similar to those of Paleoproterozoic Mayuan Group, indicating that they may mainly be the recycling product of Paleoproterozoic crustal materials. However, the Nd model age significantly decreases with a corresponding increase in the εNd(t) value at Neoproterozoic (ca. 0.8-0.7 Ga) and Late Paleozoic (ca. 0.25 Ga), respectively. This is manifested by prominent vales and apexes on the diagrams of tDM vs. tStr. (stratum age) and εNd(t) vs. tStr.. The decrease in tDM and the increase in εNd(t) are explained as a result of the significant incorporation of juvenile crustal materials that originated from depleted mantle due to strong lithospheric extension during both periods. It appears that tectonic magmatism in the Neoproterozoic and the Late Paleozoic is of prominent importance in affecting the geochemical nature of sediments in South China.

  18. Mass-spectrometric REE analysis in sulphide minerals

    Directory of Open Access Journals (Sweden)

    Irina R. Elizarova


    Full Text Available The standard samples of diorite, granite and anorthosite (National Centre for Petrographic and Geochemical Research (CRPG CNRS, Nancy, France were analyzed to measure rare-earth element (REE concentrations by the ICP MS method (quadrupole ELAN 9000 DRC-e without preliminary dilution and concentration procedures. The certified values of REE concentrations measured on ELEMENT-2 mass-spectrometer by ICP MS method in Nancy are also well reproduced on ELAN 9000. The mass-spectrometer analytical environment and modes of operation were adjusted to detect REE in sulphide minerals by the example of the pyrite from the PGE Penikat layered intrusion (Finland and chalcopyrite from the Talnakh deposit (Kazakhstan. The total REE content in the pyrite is ca. 3.5 ppm, that is enough to establish Sm-Nd age of pyrite. By the example of State Standard Sample 2463 (Apatite, Russia it is shown how to apply the mineral/chondrite spectra to evaluate the accuracy of the REE analytical results.

  19. Tinjauan Kemungkinan Sebaran Unsur Tanah Jarang (REE di Lingkungan Panas Bumi

    Directory of Open Access Journals (Sweden)

    Danny Zulkifli Herman


    Full Text Available areas occur mainly in an environment of volcanic/magmatic arc where magma chambers play a role as heat sources. The environment is situated within the convergent plate boundaries. A variety of igneous rocks is associated with this environment ranging from basalt (gabbro to rhyolite (granite but andesite is normally the most abundant igneous rock. The most obvious geothermal indications are exhibited by some surface manifestations comprising hot water seepage, fumaroles, hot spring, geyser, and hydrotermal alteration zones which are being evidences of an active hydrothermal system beneath the surface as a part of volcanism. Despite being a causal factor for alteration of country rocks, most hydrothermal fluids enable to change distribution pattern and content of rare earth elements (REE for instance Ce, Eu, La, Lu, Sm, Nd, and Y particularly during a reaction process. This may have a connection with development of element mobility rates, whilst the characteristics of REE pattern within hydrothermal fluid would have a high variable due to dependency of their original magma source. Considering the important role of hydrothermal fluid in REE mobility development, it is inspired to review the possible relationship of active hydrothermal system and potency of REE distribution pattern in areas of geothermal manifestation.  

  20. Ediacaran to Cambrian magmatic suites in the Rio Grande do Norte domain, extreme Northeastern Borborema Province (NE of Brazil): Current knowledge (United States)

    do Nascimento, Marcos Antonio Leite; Galindo, Antonio Carlos; de Medeiros, Vladimir Cruz


    The Ediacaran-Cambrian plutonic activity is one of the most important geological features of the Rio Grande do Norte Domain (Borborema Province, NE Brazil). It is represented by several batholiths, stocks and dykes. Based on the petrographic, geochemical and geochronological characteristic of different rocks, this plutonic activity can be grouped in six separate suites: shoshonitic (Shos), porphyritic high-K calc-alkaline (PHKCalcAlk), equigranular high K calc-alkaline (EHKCalcAlk), calc-alkaline (CalcAlk), alkaline (Alk) and charnockitic alkaline (ChAlk). Geochemically, the Shos, CalcAlk and Alk suites are differentiated from the others, while ChAlc can be distinguished from the others in some diagrams. The greatest difficulty lies in distinguishing between the chemically similar PHKCalcAlk and EHKCalcAlk. To this end, existing geochronological data as well as related petrographic and textural field aspects may be used to distinguish the two mentioned suites (PHKCalcAlk and EHKCalcAlk). Petrographically, the Shos suite has composition between gabbro/diorite and quartz monzonite. Monzogranites (with subordinate granodiorites and quartz monzonites) predominate in both PHKCalcAlk and EHKCalcAlk. Calc is composed of granodiorites to tonalites. Alc is formed by alkali feldspar granites (with subordinate alkali feldspar quartz syenites and syenogranites), whereas ChAlc has quartz mangerites and charnockites. The suites were emplaced between the Ediacaran (635-541 Ma) and Cambrian (541-485 Ma), predominantly in the Ediacaran, based on 34 U-Pb datings (zircon, titanite, monazite and columbite-tantalite), 17 Rb-Sr (whole rock) and 1 Sm-Nd (total rock and mineral) internal isochrons. The Shos suite has U-Pb ages varying from 599 ± 16 (Poço Verde pluton) to 579 ± 7 (Acari and São João do Sabugi plutons), slightly older than those of the PHKCalcAlk suite, which ranges between 591 ± 4 Ma (Totoró pluton) and 544 ± 7 Ma (São José de Espinharas pluton). The Calc

  1. Small scale heterogeneity of Phanerozoic lower crust: evidence from isotopic and geochemical systematics of mid-Cretaceous granulite gneisses, San Gabriel Mountains, southern California (United States)

    Barth, A.P.; Wooden, J.L.; May, D.J.


    An elongate belt of mid-Cretaceous, compositionally banded gneisses and granulites is exposed in Cucamonga terrane, in the southeastern foothills of the San Gabriel Mountains of southern California. Banded gneisses include mafic granulites of two geochemical types: type 1 rocks are similar to high Al arc basalts and andesites but have higher HFSE (high-field-strength-element) abundances and extremely variable LILE (largeion-lithophile-element) abundances, while type 2 rocks are relatively low in Al and similar to alkali rich MOR (midocean-ridge) or intraplate basalts. Intercalated with mafic granulites are paragneisses which include felsic granulites, aluminous gneisses, marble, and calc-silicate gneisses. Type 1 mafic granulites and calcic trondhjemitic pegmatites also oceur as cross-cutting, synmetamorphic dikes or small plutons. Small-scale heterogeneity of deep continental crust is indicated by the lithologic and isotopic diversity of intercalated ortho-and paragneisses exposed in Cucamonga terrane. Geochemical and isotopic data indicate that K, Rb, and U depletion and Sm/Nd fractionation were associated with biotite +/- muscovite dehydration reactions in type 1 mafic granulites and aluminous gneisses during high-grade metamorphism. Field relations and model initial isotopic ratios imply a wide range of protolith ages, ranging from Early Proterozoic to Phanerozoic. ?? 1992 Springer-Verlag.

  2. Variscan terrane of deep-crustal granulite facies in Yushugou area, southern Tianshan

    Institute of Scientific and Technical Information of China (English)

    王润三; 周鼎武; 王居里; 王焰; 刘养杰


    The Yushugou terrane of deep-crustal granulite facies in southern Tianshan consists of two parts, granulite and metaperidotite. The whole terrane is a metamorphism of (high-pressure) granulite facies, and typical mineral associations are: Gt-Cpx-Pl-Tit-Ilm (±Qz) (silica-saturated and oversaturated mafic rocks), Gt-Ky (pseudomorph)-Pl-Ru-Ilm±Qz (metapelitic rocks) and Spi-Opx-Cpx-Ol (meta-ultramafic rocks). The peak-stage P-T conditions are 795—964℃, 0.97—1.42 GPa, which are obtained with mineral chemistry, assemblage analyses and P-T estimation. The Sm-Nd isochron age of peak-stage metamorphic minerals is (315±3.62) Ma. All of these indicate that the terrane is a deep-crustal body, which subduets to the depth of 40—50 km in the middle late-Paleozoic, undergoing metamorphism of (high-pressure) granulite facies, and exhumed again to the surface by tectonic uplifting.

  3. Efficient visible and near-infrared photoluminescent attapulgite-based lanthanide one-dimensional nanomaterials assembled by ion-pairing interactions. (United States)

    Xu, Jun; Zhang, Ye; Chen, Hao; Liu, Weisheng; Tang, Yu


    Attapulgite, a one-dimensional fibrillar nanomaterial present in nature, with its extreme stability, is a promising material to act as a new carrier of luminescent lanthanide complexes for further applications. Herein, a series of lanthanide complexes Na[Ln(TTA)4] have been attached to attapulgite (Atta) via ion-pairing interactions, generating the first example of attapulgite-based visible and near-infrared (NIR) luminescent lanthanide one-dimensional nanomaterials, where TTA is 2-thenoyltrifluoroacetonate and Ln is Eu, Sm, Nd, Er or Yb. The hybrid materials were characterized by CHN elemental analysis, inductively coupled plasma-atomic emission spectroscopy (ICP), powder X-ray diffraction (PXRD), thermogravimetry (TG), transmission electron microscopy (TEM), and UV-vis absorption spectra. In order to investigate the photophysical behaviours of these materials, the visible and NIR luminescent spectra and the energy transfer process have been systematically investigated. Moreover, efforts have been made to produce Eu- and Sm-based plastic attapulgite materials by utilizing poly(methyl methacrylate) (PMMA) matrices, and the dispersibility of the lanthanide-doped hybrids in PMMA provides them with a high mechanical strength. The lanthanide-doped attapulgite appears to be an interesting material for photophysical applications. The results of this work would have potential significance for the design and assembly of luminescent lanthanide materials for light-emitting diodes (LED), sunlight-conversion films, optical amplifiers, solar concentrators, and lasers.

  4. Constraints to the timing of India-Eurasia collision; a re-evaluation of evidence from the Indus Basin sedimentary rocks of the Indus-Tsangpo Suture Zone, Ladakh, India (United States)

    Henderson, Alexandra L.; Najman, Yani; Parrish, Randall; Mark, Darren F.; Foster, Gavin L.


    Deposited within the Indus-Tsangpo suture zone, the Cenozoic Indus Basin sedimentary rocks have been interpreted to hold evidence that may constrain the timing of India-Eurasia collision, a conclusion challenged by data presented here. The Eurasian derived 50.8-51 Ma Chogdo Formation was previously considered to overlie Indian Plate marine sedimentary rocks in sedimentary contact, thus constraining the timing of collision as having occurred by this time. Using isotopic analysis (U-Pb dating on detrital zircons, Ar-Ar dating on detrital white mica, Sm-Nd analyses on detrital apatite), sandstone and conglomerate petrography, mudstone geochemistry, facies analysis and geological mapping to characterize and correlate the formations of the Indus Basin Sedimentary rocks, we review the nature of these contacts and the identification and correlation of the formations. Our results reveal that previously interpreted stratigraphic contacts identifying Chogdo Formation unconformably overlying Indian plate sedimentary rocks are incorrect. Rather, we suggest that the inaccuracy of previous interpretations is most likely a result of Formation misidentification and thus cannot be used to constrain the timing of India-Asia collision.

  5. Hafnium isotope results from mid-ocean ridges and Kerguelen. (United States)

    Patchett, P.J.


    176Hf/177Hf ratios are presented for oceanic volcanic rocks representing both extremes of the range of mantle Hf-Nd-Sr isotopic variation. Hf from critical mid-ocean ridge basalts shows that 176Hf/177Hf does indeed have a greater variability than 143Nd/144Nd and 87Sr/86Sr in the depleted mantle. This extra variation is essentially of a random nature, and can perhaps be understood in terms of known Rb/Sr-Sm/Nd-Lu/Hf fractionation relationships. At the other extreme of mantle isotopic compositions, 176Hf/177Hf ratios for igneous rocks from the Indian Ocean island of Kerguelen show a closely similar variation to published 143Nd/144Nd ratios for the same samples. Comparison of Hf-Nd-Sr isotopic relatonships for Tristan da Cunha, Kerguelen and Samoa reveals divergences in the mantle array for ocean-island magma sources, and perhaps suggests that these irregularities are largely the result of an extra component of 87Sr/86Sr variation.-G.R.

  6. Hafnium isotope variations in oceanic basalts (United States)

    Patchett, P. J.; Tatsumoto, M.


    Hafnium isotope ratios generated by the beta(-) decay of Lu-176 are investigated in volcanic rocks derived from the suboceanic mantle. Hf-176/Hf-177 and Lu/Hf ratios were determined to precisions of 0.01-0.04% and 0.5%, respectively, by routine, low-blank chemistry. The Hf-176/Hf-177 ratio is found to be positively correlated with the Nd-143/Nd-144 ratio and negatively correlated with the Sr-87/Sr-86 and Pb-206/Pb-204 ratios, and to increase southwards along the Iceland-Reykjanes ridge traverse. An approximate bulk earth Hf-176/Hf-177 ratio of 0.28295 is inferred from the bulk earth Nd-143/Nd-144 ratio, which requires a bulk earth Lu/Hf ratio of 0.25, similar to the Juvinas eucrite. Midocean ridge basalts are shown to account for 60% of the range of Hf isotope ratios, and it is suggested that Lu-Hf fractionation is decoupled from Sm-Nd and Rb-Sr fractionation in very trace-element-depleted source regions as a result of partial melting.

  7. Tinjauan Kemungkinan Sebaran Unsur Tanah Jarang (REE di Lingkungan Panas Bumi

    Directory of Open Access Journals (Sweden)

    Danny Zulkifli Herman


    Full Text Available areas occur mainly in an environment of volcanic/magmatic arc where magma chambers play a role as heat sources. The environment is situated within the convergent plate boundaries. A variety of igneous rocks is associated with this environment ranging from basalt (gabbro to rhyolite (granite but andesite is normally the most abundant igneous rock. The most obvious geothermal indications are exhibited by some surface manifestations comprising hot water seepage, fumaroles, hot spring, geyser, and hydrotermal alteration zones which are being evidences of an active hydrothermal system beneath the surface as a part of volcanism. Despite being a causal factor for alteration of country rocks, most hydrothermal fluids enable to change distribution pattern and content of rare earth elements (REE for instance Ce, Eu, La, Lu, Sm, Nd, and Y particularly during a reaction process. This may have a connection with development of element mobility rates, whilst the characteristics of REE pattern within hydrothermal fluid would have a high variable due to dependency of their original magma source. Considering the important role of hydrothermal fluid in REE mobility development, it is inspired to review the possible relationship of active hydrothermal system and potency of REE distribution pattern in areas of geothermal manifestation.  

  8. Geochemistry of the Peramora Mélange and Pulo do Lobo schist: geochemical investigation and tectonic interpretation of mafic mélange in the Pangean suture zone, Southern Iberia (United States)

    Dahn, Dustin R. L.; Braid, James A.; Murphy, J. Brendan; Quesada, Cecilio; Dupuis, Nicole; McFarlane, Christopher R. M.


    The Peramora Mélange is part of an accretionary complex between the South Portuguese Zone (a fragment of Laurussia) and the Ossa Morena Zone (para-autochthonous Gondwana) and is an expression of the Pangean suture zone in southwestern Iberia. The suture zone is characterized by fault-bounded units of metasedimentary rocks, mélanges, and mafic complexes. Detailed geologic mapping of the Peramora Mélange reveals a complex pattern of imbricated schists and mafic block-in-matrix mélanges. Geochemical signatures of the Pulo do Lobo schist (PDL) are consistent with derivation from both mafic and continental sources. The mafic block-in-matrix mélange displays normal mid-ocean ridge basalt (NMORB) geochemical signature, juvenile Sm-Nd isotopic compositions, and a range of zircon ages similar to those observed in the PDL, suggesting a sedimentary component. Taken together, these data suggest a complex tectonic history characterized by erosion of a NMORB source, mélange formation, and imbrication during underplating occurring during the final stages of continent-continent collision.

  9. The growth of the continental crust: Constraints from radiogenic isotope geochemistry (United States)

    Taylor, Paul N.


    Most models for evolution of continental crust are expressed in the form of a diagram illustrating the cumulative crustal mass (normalized relative to the present crustal mass) as a function of time. Thus, geochronological data inevitably play a major role in either constructing or testing crustal growth models. For all models, determining the start-time for effective crustal accretion is of vital importance. To this end, the continuing search for, and reliable characterization of, the most ancient crustal rock-units remains a worthy enterprise. Another important role for geochronology and radiogenic isotope geochemistry is to assess the status of major geological events as period either of new crust generation or of reworking of earlier formed continental crust. For age characterization of major geological provinces, using the critieria outined, the mass (or volume) of crust surviving to the present day should be determinable as a function of crust formation age. More recent developments, however, appear to set severe limitations on recycling of crust, at least by the process of sediment subduction. In modeling crustal growth without recycling, valuable constaints on growth rate variations through time can be provided if variations in the average age of the continental crust can be monitored through geological history. The question of the average age of the exposed continental crust was addressed by determining Sm-Nd crustal residence model ages (T-CR) for fine-grained sediment loads of many of the world's major rivers.

  10. Age determination and development of experimental methods for quaternary fault and formation

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Kwang Sik; Choi, M. S.; Kim, J. M. [Korea Basic Science Institute, Daejeon (Korea, Republic of)] (and others)


    Late cretaceous to early tertiary movement ages were constrained by Rb-Sr and K-Ar dating of fault rocks near the Uljin Nuclear Power Plants. These ages are well reproducible and consistent with geologic context. Tectonic evolution of the northeastern Yeongnam massif, the site of the Uljin Nuclear Power Plants, was investigated on the basis of Rb-Sr, Sm-Nd and Pb isotopic systematics and geochemistry of precambrian basement rocks including the Hosanri Formation, Buncheon granite gneiss, biotite granite gneiss, and Hongjesa granite. The optical ages from the Suryum fault outcrop represent the younger limit of sedimentation timing because they are simply based upon the present-day water content. The lower, Qt{sub 2} terrace at about 18m elevation is correlated with Marine Isotopic Stage (MIS) 5a, although its apparent optical age was consistently reported from 71 to 48 ka. Correlation of shoreline elevations indicates the correspondence of the Qt{sub 3a} terrace to MIS 5e, which is supported by stratigraphically concordant optical ages for aeolian sand dunes at the north of the Suryum site. This time scale yields an uplift rate of 0.266 m/ka, requiring the revision of conventional view that the Korean peninsula is tectonically very stable.

  11. The nature of Mesoarchaean seawater and continental weathering in 2.85 Ga banded iron formation, Slave craton, NW Canada (United States)

    Haugaard, Rasmus; Ootes, Luke; Creaser, Robert A.; Konhauser, Kurt O.


    Banded iron formations (BIF) have been extensively used as proxies to infer the chemical composition of ancient bulk seawater. However, their proximity to ancient crust suggests that they might also be used to reveal the composition of emergent continental landmass at the time of their deposition. Here we use the combination of geochemistry and Sm-Nd isotopes on a layer-by-layer basis to interpret the relative contributions of hydrothermal, hydrogenous and terrestrial input to one of the oldest documented Superior-type BIF in the world. The ∼2.85 Ga Central Slave Cover Group BIF is deposited within a rift basin related to a continental margin and is found associated with basement gneisses, as well as shoreline and shallow-shelf type facies, such as fuchsitic quartzite and pebble-to-cobble conglomerate, that confirm a near-shore depositional setting for the BIF. The BIF ranges from a pure chemical oxide (magnetite)-silicate (grunerite + actinolite) sediment with low Al2O3 (segment exhibiting negative εNd(t) values averaging -1.1 and another with positive εNd(t) values averaging +2.5. This suggests input of dissolved REY into the upper seawater from weathering of isotopically different crustal components in the source region. Collectively, we speculate that the low REY in the upper seawater and the overall low Ni content implies a highly weathered crustal surface that was unable to contribute a significant dissolved load to the shelf environment.

  12. Application of neodymium isotope ratio measurements for the origin assessment of uranium ore concentrates. (United States)

    Krajkó, Judit; Varga, Zsolt; Yalcintas, Ezgi; Wallenius, Maria; Mayer, Klaus


    A novel procedure has been developed for the measurement of (143)Nd/(144)Nd isotope ratio in various uranium-bearing materials, such as uranium ores and ore concentrates (UOC) in order to evaluate the usefulness and applicability of variations of (143)Nd/(144)Nd isotope ratio for provenance assessment in nuclear forensics. Neodymium was separated and pre-concentrated by extraction chromatography and then the isotope ratios were measured by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The method was validated by the measurement of standard reference materials (La Jolla, JB-2 and BCR-2) and the applicability of the procedure was demonstrated by the analysis of uranium samples of world-wide origin. The investigated samples show distinct (143)Nd/(144)Nd ratio depending on the ore type, deposit age and Sm/Nd ratio. Together with other characteristics of the material in question, the Nd isotope ratio is a promising signature for nuclear forensics and suggests being indicative of the source material, the uranium ore.

  13. Excess Ar-40 in the Zagami Shergottite: Does It Reveal Crystallization History? (United States)

    Bogard, Donald D.; Park, Jisun


    The Zagami basaltic shergottite has fine- and coarse-grained (FG & CG) areas, which may reflect partial crystallization in a deep, slowly cooled magma chamber to form Mg-rich pyroxene cores, followed by entrainment of these crystals into a magma that rose and crystallized near the surface. Late-stage melt pockets formed mesostasis and feldspar (maskelynite) having a range of compositions, but low water abundance. Higher I(sub Sr) in the FG portion may result from the second stage having incorporated old crustal rocks that failed to reach isotopic equilibrium. Zagami, like other shergottites, contains excess Ar-40(sub xs) beyond that expected from internal decay of K-40 during its Sm-Nd age of 177 Myr. We suggest that at least a portion of this Ar-40(sub xs) in Zagami and some other shergottites was inherited from the magma, much as is the case of MORBs on Earth. We made Ar-39-Ar-40 age determinations on feldspar and pyroxene separates from both the FG and CG portions of Zagami. If Zagami experienced an evolving fractional crystallization history, including possible crustal contamination of the magma, that might be indicated in differing amounts of Ar-40(sub xs) between mineral phases and between FG and CG portions.

  14. Structure, magnetization, and magnetostriction of Sm-R-Fe (R = Pr, Nd) thin films

    Institute of Scientific and Technical Information of China (English)

    WANG Bowen; CAO Shuying; WENG Ling; HUANG Wenmei; SUN Ying


    The structure, magnetization, and magnetostriction of Sm0.9Pr0.1Fex and Sm1-xNdxFe1.9 thin films have been investigated using X-ray diffraction, vibrating sample magnetometer, and optical cantilever method. It is found that the structure of Sm0.9Pr0.1Fex thin films consists of an Sm-Pr-Fe amorphous phase when x ≤ 2.69 and that of Sm1-xNdxFe1.9 thin films consists of an Sm-Nd-Fe amorphous phase. The in-plane magnetization of Sm0.9Pr0.1Fex thin films increases with increase in the Fe content, and low values of the in-plane coercivity occur in the range of 1.62 ≤ x ≤ 2.28. The magnetostriction value of Sm0.9Pr0.1Fex thin films increases with increasing the Fe content when x ≤ 1.94 and decreases when x > 1.94. The in-plane magnetostriction of Sm1-xNdxFe1.9 thin films under low magnetic fields has been improved by the substitution of Nd for Sm when x = 0.2.

  15. 印度与欧亚板块东部碰撞边界——腾冲火山岩的Nd-Sr同位素与微量元素研究

    Institute of Scientific and Technical Information of China (English)

    朱炳泉; 毛存孝


    The Tengchong volcanies in western Yunnan Province, China, are located in the eastern part of the collision margin between Indian and Eurasian Plates. Alternating extention and compression controlled the eruption, from late Tertiary to Holeeno, of at least 5 groups of volcanics consisting of a Major series of hlgh-Al basalts (3 groups), a high-K andesite-dacite group and a high-Mg basalt group. The Major series has a range of GNd from +0.7 to-6.7 and Sr87/Sr86 from 0.70595 to 0.70881, exhibiting good linear correlations between Zr/Ni and Zr as well as between Nd. and both Sm/Nd and 1/Nd and similar chondrite-normalized incompatible element patterns. This suggests an ecologitic source metasomatized with fluids derived from parts of thesubducted Indian plate.The high-K andesite-dacite group shows a more extreme isotopic composition of GNd=-12.3, Sr87/Sr66=0.71124. It is chemically comparable to the calc-alkaline lavas in Xizang and could be resulted from mixing between shallow mantle zones and lower crust. The high-Mg basalt group has Sr87/Sr86-0.708 and slightly negative GNd (-2). They are similar, in chemical composition and possibly also in source, to the intraplate basalts in east China. A partial melting model of isotopic tmequilibrium system has been proposed to explain the isotope and trace element correlations of Tengchong volcanics.

  16. Photon management properties of rare-earth (Nd,Yb,Sm)-doped CeO2 films prepared by pulsed laser deposition. (United States)

    Balestrieri, Matteo; Colis, Silviu; Gallart, Mathieu; Schmerber, Guy; Bazylewski, Paul; Chang, Gap Soo; Ziegler, Marc; Gilliot, Pierre; Slaoui, Abdelilah; Dinia, Aziz


    CeO2 is a promising material for applications in optoelectronics and photovoltaics due to its large band gap and values of the refractive index and lattice parameters, which are suitable for silicon-based devices. In this study, we show that trivalent Sm, Nd and Yb ions can be successfully inserted and optically activated in CeO2 films grown at a relatively low deposition temperature (400 °C), which is compatible with inorganic photovoltaics. CeO2 thin films can therefore be efficiently functionalized with photon-management properties by doping with trivalent rare earth (RE) ions. Structural and optical analyses provide details of the electronic level structure of the films and of their energy transfer mechanisms. In particular, we give evidence of the existence of an absorption band centered at 350 nm from which energy transfer to rare earth ions occurs. The transfer mechanisms can be completely explained only by considering the spontaneous migration of Ce(3+) ions in CeO2 at a short distance from the RE(3+) ions. The strong absorption cross section of the f-d transitions in Ce(3+) ions efficiently intercepts the UV photons of the solar spectrum and therefore strongly increases the potential of these layers as downshifters and downconverters.

  17. Early differentiation of the Earth and the Moon. (United States)

    Bourdon, Bernard; Touboul, Mathieu; Caro, Guillaume; Kleine, Thorsten


    We examine the implications of new 182W and 142Nd data for Mars and the Moon for the early evolution of the Earth. The similarity of 182W in the terrestrial and lunar mantles and their apparently differing Hf/W ratios indicate that the Moon-forming giant impact most probably took place more than 60Ma after the formation of calcium-aluminium-rich inclusions (4.568Gyr). This is not inconsistent with the apparent U-Pb age of the Earth. The new 142Nd data for Martian meteorites show that Mars probably has a super-chondritic Sm/Nd that could coincide with that of the Earth and the Moon. If this is interpreted by an early mantle differentiation event, this requires a buried enriched reservoir for the three objects. This is highly unlikely. For the Earth, we show, based on new mass-balance calculations for Nd isotopes, that the presence of a hidden reservoir is difficult to reconcile with the combined 142Nd-143Nd systematics of the Earth's mantle. We argue that a likely possibility is that the missing component was lost during or prior to accretion. Furthermore, the 142Nd data for the Moon that were used to argue for the solidification of the magma ocean at ca 200Myr are reinterpreted. Cumulate overturn, magma mixing and melting following lunar magma ocean crystallization at 50-100Myr could have yielded the 200Myr model age.

  18. Petrochemistry and geochemistry of HP metabasites from Haiyangsuo in Sulu UHP belt of eastern China

    Institute of Scientific and Technical Information of China (English)


    Abundant metabasites occur in highly deformed granitic and migmatitic gneisses as blocks and lenses of tens of meter size around the Haiyangsuo area, northeast part of Sulu UHP belt, eastern China. They comprise garnet-pyroxene granulites, eclogitized granulites and amphibolites. Their protolith compositions were mainly olivine tholeiite and quartz tholeiite, and show variation from Mg-rich to Fe-rich component as tholeiitic cumulates. Pearce's element ratio slopes suggested that protolith of these rocks were comagmatic, and generated from a primary magma by fractional crystallization of plagioclase, olivine and clinopyroxene. The crystallization differentiation has also been evidenced by trace elements, such as parallel REE patterns, Ni vs Ce variations, Sr increasing depletions, although the large ion lithophile elements (LILE) were modified to different extent during metamorphism. Trace element composition and Nd isotopes indicate a depleted mantle origin for these rocks. But they are not likely to be fragments of ophiolites or tholeiites connected with subduction, they formed probably at intra-continent environment. Sm-Nd whole rock isochron age of 2252±180Ma indicates approximately the formation age of igneous protolith of these rocks, almost 2000Ma earlier than the formation of the Dabie-Sulu UHP collision zone at about 240-220 Ma.

  19. U-Pb zircon SHRIMP data from the Cana Brava layered complex: new constraints for the mafic-ultramafic intrusions of Northern Goiás, Brazil (United States)

    Giovanardi, T.; Girardi, V. A. V.; Correia, C. T.; Sinigoi, S.; Tassinari, C. C. G.; Mazzucchelli, M.


    The Cana Brava Complex is the northernmost and least well known layered intrusion of a discontinuous belt of mafic-ultramafic massifs within the Brasilia Belt, which also comprises theNiquelândia and Barro Alto complexes. Available geochronological data from a range of techniques (K/Ar, Ar/Ar, Rb/Sr, Sm/Nd and U/Pb) provide a range of possible ages (time span from 3.9 Ga to 450 Ma), hence a precise and reliable age for the Cana Brava Complex is still lacking. Also, preliminary isotopic and geochemical data of the Cana Brava Complex suggest a significant crustal contamination, which could have affected bulk-rock Sr and Nd systematics resulting in meaningless age determinations. In this paper, we present new U-Pb SHRIMP zircon analyses from four samples of different units of the Cana Brava Complexwhich suggest that the intrusion occurred during the Neoproterozoic, between 800 and 780 Ma, i.e. at the same age ofNiquelândia. Discordant older 206Pb/238U ages are provided by inherited zircons, and match the age of the metamorphism of the embedding Palmeirópolis Sequence.

  20. East Scandinavian and Noril'sk plume mafic large igneous provinces of Pd-Pt ores: Geological and metallogenic comparison (United States)

    Mitrofanov, F. P.; Bayanova, T. B.; Korchagin, A. U.; Groshev, N. Yu.; Malitch, K. N.; Zhirov, D. V.; Mitrofanov, A. F.


    This paper compares the geological, geophysical, and isotopic geochemical data on the Paleoproterozoic East Scandinavian Pd-Pt province in the Baltic Shield and the Late Paleozoic Noril'sk Pd-Pt province in the Siberian Craton. Both provinces contain large magmatic PGE deposits: low-sulfide in the Baltic Shield and high-sulfide in the Siberian Craton. Multidisciplinary evidence shows that the East Scandinavian mafic large igneous province, which has a plume nature, is intracratonic and was not subjected to the crucial effect of subduction-related and other contamination processes, whereas the Noril'sk province is pericratonic with substantial crustal contamination of the intrusive processes. Low-sulfide Pd-Pt deposits dominate in the East Scandinavian province, while high-sulfide Ni-Cu-PGE deposits play the leading role in the Noril'sk province. The U-Pb, Sm-Nd, and Rb-Sr isotopic data indicate multistage and long-term (tens of millions of years) geological history of mafic large igneous provinces. The plume magmatism with specific geochemistry and metallogeny is probably related to lower mantle sources.

  1. The 1590-1520 Ma Cachoeirinha magmatic arc and its tectonic implications for the Mesoproterozoic SW Amazonian craton crustal evolution

    Directory of Open Access Journals (Sweden)

    Ruiz Amarildo S.


    Full Text Available Isotopic and chemical data of rocks from the Cachoeirinha suite provide new insights on the Proterozoic evolution of the Rio Negro/Juruena Province in SW Amazonian craton. Six U-Pb and Sm-Nd analyses in granitoid rocks of the Cachoeirinha suite yielded ages of 1587-1522 Ma and T DM model ages of 1.88-1.75 Ga (EpsilonNd values of -0.8 to +1.0. In addition, three post-tectonic plutonic rocks yielded U-Pb ages from 1485-1389 Ma (T DM of 1.77-1.74 Ga and EpsilonNd values from -1.3 to +1.7. Variations in major and trace elements of the Cachoeirinha suite rocks indicate fractional crystallization process and magmatic arc geologic setting. These results suggest the following interpretations: (1 The interval of 1590-1520 Ma represents an important magmatic activity in SW Amazonian craton. (2 T DM and arc-related chemical affinity supportthe hypothesis that the rocks are genetically associated with an east-dipping subduction zone under the older (1.79-1.74 Ga continental margin. (3 The 1590-1520 Ma age of intrusive rocks adjacent to an older crust represents similar geological framework along the southern margin of Baltica, corroborating the hypothesis of tectonic relationship at that time.

  2. The tectonic evolution of the Neoproterozoic Brasília Belt, central Brazil: a geochronological and isotopic approach

    Directory of Open Access Journals (Sweden)

    Márcio Martins Pimentel

    Full Text Available ABSTRACT: The Brasília Belt is one of the most complete Neoproterozoic orogens in western Gondwana. Rapid progress on the understanding of the tectonic evolution of the belt was achieved due to new U-Pb data, combined with Sm-Nd and Lu-Hf analyses. The evolution of the Brasília orogen happened over a long period of time (900 - 600 Ma involving subduction, magmatism and terrain accretion, as a result of the consumption of the Goiás oceanic lithosphere. Provenance studies, based on U-Pb zircon data, indicate that the sedimentary rock units record different tectonic settings and stages of the evolution of the orogen. The Paranoá and Canastra groups represent passive margin sequences derived from the erosion of the São Francisco Craton. The Araxá and Ibiá groups, however, have dominant Neoproterozoic detrital zircon populations, as young as 650 Ma, suggesting derivation from the Goiás Magmatic Arc. The Goiás Magmatic Arc represents a composite arc terrain, formed by the accretion of older (ca. 0.9 - 0.8 Ga intraoceanic island arc(s, followed by more evolved continental arcs. It extends for several thousand kilometers, from SW Goiás, through NE Brazil and into Africa. Metamorphism took place between 650 - 630 Ma reflecting final closure of the Goiás Ocean and continental collision.

  3. U-Pb (LA-ICP-MS of detrital zircon and whole rock Nd and geochemical constraints on the provenance, depositional age and tectonic setting of the metasedimentary Piriá Basin, northern Brazil: implications for the evolution of the Gurupi Belt

    Directory of Open Access Journals (Sweden)

    Elem Cristina dos Santos Lopes

    Full Text Available ABSTRACT: The Piriá Basin (Piriá Formation is a hemi-graben shaped basin that developed over Precambrian rocks of the Gurupi Belt. The lithological content comprises four interfingered lithofacies: (1 arkose and greywacke with pelite layers, (2 laminated siltstones and pelites, (3 arkose with hummocky stratification, and (4 oligomictic conglomerate. This sequence was formed in alluvial fans (conglomerate, and fluvial systems (arkose, greywacke, siltstones and pelites that were established and evolved during the migration of the subsidence. The sedimentary sequence underwent anquimetamorphism and very weak tectonic deformation. U-Pb analyses of detrital zircon set the maximum depositional age at 591 Ma and indicate several sediment sources, that range in age from the Neoproterozoic to the Archean. The main sources are from the Rhyacian, which is the main period of continental crust formation in the São Luís cratonic fragment and the basement of the Gurupi Belt. Neoproterozoic sources were important in the eastern segment of the basin. Ages from unknown sources in the region so far have also been recorded. Combined, the U-Pb zircon data, the whole-rock geochemical and Sm-Nd results, and the petrographic information revealed proximal felsic to intermediate provenance, in addition to recycled sedimentary sources. As a whole, our data suggest that the Piriá Formation was deposited in a post-orogenic basin related to the final stage of evolution of the Brasiliano cycle of orogenies, which built up the Gurupi Belt.

  4. Solid earth as a recycling systems and the lateral growth of Precambrian North America (United States)

    Veizer, Jan


    If plotted on mass vs time diagrams, geologic entities (for example, continental and oceanic crust, sediments, and mineral resources) display an exponential (power law) relationship, with entity per unit time increasing toward the present. This relationship is consistent with the concept of recycling and can be simulated mathematically. The approach is based on the plate tectonic theory and considers area-age or mass-age distributions of crystalline basement and sediments for major global tectonic realms. Each tectonic realm is characterized by a specific lifespan, which is an inverse function of its recycling rate. The estimated average half-area of half-mass ages are given. The corresponding parameters for continental crust are 690 Ma for K/Ar, and approximately 1200 Ma for Rb/St and U-Th/Pb dating pairs. Tectonic diversity preserved in the geologic record is therefore a function of time, with oceanic tectonic realms, because of their rapid recycling, underrepresented in the rocks older than approximately 300 Ma. The Sm/Nd isotopic systematic of sediments suggest that, for a near steady-state post-Archean sedimentary mass, recycling is approximately 90 + or - 5 percent cannibalistic. This yields an estimated upper limit on crust-mantle exchange via sediment subduction of approximately 1.1 + or - 0.5 x 10 g a(sup -1) considerably less than demanded by isotopic constraints. The discrepancy may indicate the existence of additional loci, such as orogenic belts, for significant crust-mantle interaction.

  5. National uses and needs for separated stable isotopes in physics, chemistry, and geoscience research (United States)

    Zisman, M. S.

    Present uses of separated stable isotopes in the fields of physics, chemistry, and the geosciences were surveyed to identify current supply problems and to determine future needs. Demand for separated isotopes remains strong, with 220 different nuclides having been used in the past three years. The largest needs, in terms of both quantity and variety of isotopes, are found in nuclear physics research. Current problems include a lack of availability of many nuclides, unsatisfactory enrichment of rare species, and prohibitively high costs for certain important isotopes. Demand for separated isotopes is expected to remain roughly at present levels, although a shift toward more requests for highly enriched rare isotopes is predicted. Use of neutron rich nuclides below A = 100 for producing exotic ion beams at various accelerators and use of transition metal nuclei for nuclear magnetic resonance spectroscopy are expected to expand. An increase in the need for calibration standards for techniques of radiological dating, such as Sm/Nd and Lu/Hf is predicted, but in relatively small quantities. Most members of the research community would be willing to pay considerably more than they do now to maintain adequate supplies of stable isotopes.

  6. Tracing Proterozoic arc mantle Hf isotope depletion of southern Fennoscandia through coupled zircon U-Pb and Lu-Hf isotopes (United States)

    Petersson, Andreas; Bjärnborg, Karolina; Scherstén, Anders; Gerdes, Axel; Næraa, Tomas


    Constraints on the composition of the depleted mantle Sm-Nd and Lu-Hf crust formation ages have a long history of scientific debate. When calculating mantle extraction ages, and constructing crustal growth models, a linear evolution of incompatible trace elements in a depleted mantle since > 4 Ga is routinely used. Mantle depletion however varies regionally and over time and subduction of sediments and oceanic crust renders a mantle-wedge variously enriched relative to a modelled depleted mantle. Here we show that primitive mantle-derived subduction related gabbroic intrusions from southern Fennoscandia have Hf isotope compositions that are enriched relative to a MORB-like linear depleted mantle evolution curve. Extrapolation of primitive Paleoproterozoic gabbro suites enables the construction of a regional mantle evolution curve, providing improved constraints on model ages, crustal residence times and the fraction of juvenile versus reworked continental crust. Convergent margins are assumed to be one of the main sites of continental crust growth, and using an overly depleted mantle source yield model ages that are too old, and hence cumulative crustal growth models show too much crust generation early in the Earth's history. The approach of using the Hf isotope composition of zircon from primitive subduction related gabbroic intrusions as a proxy for mantle Hf isotope composition, piloted in this study, can be applied to other convergent margins.

  7. Age and characteristics of the Loma del Aire unit (SW Iberia): Implications for the regional correlation of the Ossa-Morena Zone (United States)

    Sánchez-García, T.; Quesada, C.; Bellido, F.; Dunning, G. R.; Pin, Ch.; Moreno-Eiris, E.; Perejón, A.


    Finding of ca. 620 Ma old zircons in a volcanic rock of the Loma del Aire unit, one of many structural divisions in the Ossa Morena Zone, some years ago, attracted much attention to this unit, which would contain, if proven, the oldest rocks so far dated not only in Ossa Morena but also in the entire Iberian Massif. In this paper, new field, petrographic, whole-rock geochemical and Sm-Nd isotope data as well as new TIMS U-Pb zircon ages are presented, which collectively allow a much better characterization and dating as Cambrian of the rock sequence in the Loma del Aire unit; the previously found ca. 620 Ma old zircon population is now interpreted as xenocrysts incorporated in the Cambrian magma. Our data together with recently published provenance studies, bear important implications concerning the nature and evolution of the underlying lithospheric basement of the Ossa Morena Zone, which shares many characteristics with the Neoproterozoic peri-West-African craton arc systems currently exposed in the Precambrian inliers of the Moroccan Anti-Atlas, the North Armorican Zone of Brittany, Normandy and the Channel Islands (Cadomian Arc), and the Saxo-Thuringian and Teplá-Barrandian Zones of the Bohemian Massif. A correlation of the Ossa Morena zone with these arc systems in the Neoproterozoic and Early Paleozoic is thus proposed.

  8. Origin of bentonites and clastic sediments of the Paleocene Basilika Formation, Svalbard (United States)

    Elling, Felix; Spiegel, Cornelia; Estrada, Solveig; Davis, Donald; Reinhardt, Lutz; Henjes-Kunst, Friedhelm; Allroggen, Niklas; Dohrmann, Reiner; Piepjohn, Karsten; Lisker, Frank


    The Paleocene was a time of transition for the Arctic, with magmatic activity of the High Arctic Large Igneous Province giving way to magmatism of the North Atlantic Large Igneous Province in connection to plate tectonic changes in the Arctic and North Atlantic. In this study we investigate the Paleocene magmatic record and sediment pathways of the Basilika Formation exposed in the Central Tertiary Basin of Svalbard. By means of geochemistry, Sm-Nd isotopic signatures and zircon U-Pb geochronology we investigate the characteristics of several bentonite layers contained in the Basilika Formation, as well as the provenance of the intercalated clastic sediments. Our data show that the volcanic ash layers of the Basilika Formation, which were diagenetically altered to bentonites, originate from alkaline continental-rift magmatism such as the last, explosive stages of the High Arctic Large Igneous Province in North Greenland and the Canadian Arctic. The volcanic ash layers were deposited on Svalbard in a flat shelf environment with dominant sediment supply from the east. Dating of detrital zircons suggests that the detritus was derived from Siberian sources, primarily from the Verkhoyansk Fold-and-Thrust Belt, which would require transport over ~3000 km across the Arctic.

  9. Geochronological, stable isotopes and fluid inclusion constraints for a premetamorphic development of the intrusive-hosted Björkdal Au deposit, northern Sweden (United States)

    Billström, K.; Broman, C.; Jonsson, E.; Recio, C.; Boyce, A. J.; Torssander, P.


    The Björkdal gold deposit, bound to a quartz vein system which is mainly hosted by a quartz-monzodioritic intrusion, is situated at the easternmost part of the 1.9 Ga Skellefte base metal district in the Fennoscandian shield. Three fluid stages may be distinguished, referred to as a “barren” stage, a main gold stage, and a remobilization stage, respectively. From oxygen and hydrogen isotope evidence, it is argued that fluids of different origins (magmatic and surface waters) penetrated the ore zone at the inferred stages, but regional metamorphic fluids appear essentially only to have redistributed elements. Early quartz veining took place during a pre-metamorphic stage at ca. 1.88 Ga, as evidenced by unradiogenic galena data and an Sm-Nd scheelite errorchron of 1,915 ± 32 Ma (MSWD = 0.25). Temporarily, the main ore-forming stage was closely related to the first barren stage and took place during a major uplift event close to 1.88 Ga. Although other source rocks cannot be totally ruled out, available isotope data (O, S, Sr and Pb) are seemingly consistent with the view that these elements, and by inference other ore elements, were derived from the host intrusion.

  10. Sm—Nd and Zircon U—Pb Isotopic Constraints on the Age of Formation of the Precambrian Crust in Southeast China

    Institute of Scientific and Technical Information of China (English)

    李献华; 赵振华; 等


    Nd model ages(TDM) of the Pre-Mesozoic crustal rock samples from Southeast China range from 1.2 to 3.5Ga.Two age peaks of 1.4Ga and 1.8 Ga are observed in the histogram of TDM model ages.Available U-Pb zircon inheritance ages are concentrated around 1.2-1.4Ga,1.8Ga and 2.5Ga,respectively.The combined use of Sm-Nd and U-Pb zircon inheritance ages suggests that the formation of the Precambrian curst is of episodic character.The oldest crustal nucleus may have been formed during the Late Archean(2.5Ga or older?).A rapid production of the crust took place 1.8 Ga ago,consistent with the global crust formation event at 1.7-1.9Ga.Another important episode of the addition of juvenile crustal material from the mantle in Southeast China took place 1.2-1.4Ga ago,during which the pre-existing crust was strongly reworked and/or remelted.

  11. Multi-isotopic system geochronology of low temperature eclogite from Huangzhen, Southern Dabie Terrain

    Institute of Scientific and Technical Information of China (English)

    CHEN Daogong; E. Deloule; CHENG Hao; XIA Qunke; WU Yuanbao


    Zircon U-Pb thermal ionization mass-spectrometer (TIMS) and secondary ion mass-spectrometer (SIMS) dating, mica and amphibole 40Ar-39Ar dating and mineral Sm-Nd isotopic compositions of Huangzhen Iow temperature eclogite and country granitic gneiss are carried out. The zircon U-Pb weighted average SIMS age is (231.6±9.7) Ma for one eclogite.The mica 40Ar-39Ar isochron age is (232.6±2.1) Ma and the lowest plateau age is (221.7±2.4)Ma from same sample. U-Pb TIMS concordant ages from other eclogite zircons are from (221.3± 1.4) Ma to (222.5±2.3) Ma. U-Pb SIMS low intercept age from country granitic gneiss is (221±35) Ma. The retrograde amphibole 40Ar-39Ar isochron age is (205.9± 1.0) Ma. Except for mica,which may contain excess 40Ar, all the ages represent peak and retrograde metamorphism of low temperature eclogites. It is indicated that the Huangzhen low temperature eclogites differ from Xiongdian low temperature eclogites of north of the Northern Dabie Terrain in metamorphic ages.Huangzhen low temperature eclogites share one coherent HP-UHP terrain with high temperature eclogites from Southern Dabie Terrain and they may have differences in subduction depth and cooling rates during exhumation.

  12. Geochronology of the granitoid hosted Salamangone gold deposit, Lourenco district, Amapa State, Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Nogueira, Sonia Aparecida Abissi [Secretaria de Meio Ambiente, Sao Paulo, SP (Brazil). Instituto Geologico]. E-mail:; Bettencourt, Jorge Silva [Sao Paulo Univ., SP (Brazil). Inst. de Geociencias. Dept. de Mineralogia e Geotectonica]. E-mail:; Tassinari, Colombo Celso Gaeta [Sao Paulo Univ., SP (Brazil). Inst. de Geociencias. Centro de Pesquisas Geocronologicas]. E-mail:


    The Salamangone deposit occurs in the Lourenco Gold District, Amapa. It is associated to Paleoproterozoic Metamorphosed supracrustal rocks and a calc-alkaline complex. The deposit lies within a metaluminous weakly peraluminous, calc-alkaline tonalitic-granodioritic pluton. The Au-mineralization consists on an epigenetic quartz-vein system, enriched in Au and As and structurally controlled by a ductile-brittle shear zone. U-Pb zircon analysis of tonalite gave a crystallization age of 2.16 {+-} 0.13 Ga, whereas Sm-Nd T{sub DM} model ages of tonalite and granodiorite range from 2.24 to 2.34 Ga. e{sub Nd} (T) vary from 2.88 to 3.02. Additional whole rock Rb-Sr isochron ages on granitoids yielded values in the range of 2.17 to 2.28 Ga, with {sup 87} Sr/{sup 86} Sr initial ratio of 0.702. The isotopic data and geochemical signature of granitoids suggest that the Lourenco region, as well as the neighboring areas in French Guyana, represents a vast area largely floored by accreted juvenile arc terranes without evidence of Archean crust contamination, being related to the development of a calc-alkaline magmatic arc, which was produced within the Maroni-Itacaiunas Province, during a major Paleoproterozoic orogenic event. (author)

  13. 地质样品Nd同位素激光原位等离子体质谱(LA-MC-ICPMS)测定

    Institute of Scientific and Technical Information of China (English)

    杨岳衡; 孙金凤; 谢烈文; 范宏瑞; 吴福元



  14. The geochemical and temporal evolution of the continental lithosphere and its relationship to continental-scale faulting: The Karakoram Fault, eastern Karakoram, NW Himalayas (United States)

    Phillips, Richard J.; Searle, Michael P.; Parrish, Randall R.


    New laser ablation multicollector-inductively coupled plasma-mass spectrometry and isotope dilution-thermal ionization mass spectrometry U-Pb ages, coupled with Sm-Nd isotope and geochemical analysis, define the temporal and geochemical evolution of the continental lithosphere in the eastern Karakoram, India, NW Himalaya. Our analysis demonstrates that magmatism occurred between ~108 and 69 Ma and ~22 and 13 Ma. The new age data, coupled with geochemical examination of the granitoids, confirm a parallel evolution with the western Karakoram in Pakistan and supports a model of regional continental crustal thickening and related metamorphism. Middle to Late Cretaceous magmatism immediately adjacent to the Karakoram fault suggests that crustal melting and associated metamorphism are unrelated to shearing along the fault. Miocene leucogranite magmatism occurred almost exactly concomitant with the emplacement of the Baltoro batholith in Pakistan. These trans-Karakoram leucogranites also display similar geochemical evolution trends. Our new data clearly link the leucogranites along the fault to the regional Baltoro batholith and related metamorphic complexes to the west. This supports previous work suggesting that magmatism and metamorphism were not syn-kinematic with continental-scale faulting. The data demonstrate that the Karakoram fault could not have accommodated lateral offset in this region prior to ~16 Ma, limiting the long-term averaged slip rate to a maximum of ~10 mm/yr.

  15. Site occupancy of Sm in (Nd1-xSmx)5(Fe1-yTiy)17 (United States)

    Chu, Z.; Yelon, W. B.; Missell, F. P.; Murakami, R. K.


    The ferromagnetic compound Nd5Fe17 has a large average Fe moment (2.1 μB), a reasonably high Curie temperature (503 K), but basal plane spin orientation. Partial replacement of Nd by Sm leads to a uniaxial spin arrangement with substantial anisotropy field. Natural Sm has a large neutron absorption cross section (5650 b) which is usually thought to prevent neutron diffraction measurements unless Sm is replaced by a separated isotope with low absorption. However, the unique geometry of the MURR neutron powder diffractometer allows measurements on thin samples and data have been successfully collected on samples with up to about 50% Sm (Nd2.5Sm2.5Fe17). Samples prepared without Ti contain the 2:17 phase as well as the 5:17 phase, while those prepared with Ti have a very high concentration of the 5:17 phase which forms more readily (with minor amounts of TiFe2). The locations of Sm atoms in these compounds have been determined. These results may provide important information about the crystal fields at different sites in the 5:17 phase and suggest improved routes for synthesis of this potentially useful compound.

  16. Paleoproterozoic anorogenic granitoids of the Zheltav sialic massif (Southern Kazakhstan): Structural position and geochronology (United States)

    Tretyakov, A. A.; Degtyarev, K. E.; Sal'nikova, E. B.; Shatagin, K. N.; Kotov, A. B.; Ryazantsev, A. V.; Pilitsyna, A. V.; Yakovleva, S. Z.; Tolmacheva, E. V.; Plotkina, Yu. V.


    The basement of the Zheltav sialic massif (Southern Kazakhstan) is composed of different metamorphic rocks united into the Anrakhai Complex. In the southeastern part of the massif, these rocks form a large antiform with the core represented by amphibole and clinopyroxene gneissic granite varieties. By their chemical composition, dominant amphibole (hastingsite) gneissic granites correspond to subalkaline granites, while their petroand geochemical properties make them close to A-type granites. The U-Pb geochronological study of accessory zircons yielded an age of 1841 ± 6 Ma, which corresponds to the crystallization age of melts parental for protoliths of amphibole gneissic granites of the Zheltav Massif. Thus, the structural-geological and geochronological data make it possible to define the Paleoproterozoic (Staterian) stage of anorogenic magmatism in the Precambrian history of the Zheltav Massif. The combined Sm-Nd isotopic—geochronological data and age estimates obtained for detrital zircons indicate the significant role of the Paleoproterozoic tectono-magmatic stage in the formation of the Precambrian continental crust of sialic massifs in Kazakhstan and northern Tien Shan.

  17. Feldspar Variability in Northwest Africa 7034 (United States)

    Santos, A. R.; Lewis, J. A.; Agee, C. B.; Humayun, M.; McCubbin, F. M.; Shearer, C. K.


    The martian meteorite Northwest Africa 7034 (and pairings) is a breccia that provides important information about the rocks and processes of the martian crust (e.g., 1-3). Additional information can be gleaned from the components of the breccia. These components, specifically those designated as clasts, record the history of their parent rock (i.e., the rock that has been physically broken down to produce the clasts). In order to study these parent rocks, we must first determine which clasts within the breccia are de-rived from the same parent. Previous studies have be-gun this process (e.g., 4), but the search for genetic linkages between clasts has not integrated clasts with different grain sizes. We begin to take this approach here, incorporating igneous-textured clasts with both fine and coarse mineral grains. In NWA 7034, almost all materials (clasts and breccia matrix) are composed of the same mineral assemblages (feldspar, pyroxene, Fe-Ti oxides, apatite) with largely the same mineral compositions [1, 4-6]. Bulk breccia Sm-Nd systematics define a single isochron [7]. These observations are consistent with a majority of the components within NWA 7034 originating from the same geochemical source and crystallizing at roughly the same time.

  18. Visible-near-infrared luminescent lanthanide ternary complexes based on beta-diketonate using visible-light excitation. (United States)

    Sun, Lining; Qiu, Yannan; Liu, Tao; Feng, Jing; Deng, Wei; Shi, Liyi


    We used the synthesized dinaphthylmethane (Hdnm) ligand whose absorption extends to the visible-light wavelength, to prepare a family of ternary lanthanide complexes, named as [Ln(dnm)3 phen] (Ln = Sm, Nd, Yb, Er, Tm, Pr). The properties of these complexes were investigated by Fourier transform infrared (FT-IR) spectroscopy, diffuse reflectance (DR) spectroscopy, thermogravimetric analyses, and excitation and emission spectroscopy. Generally, excitation with visible light is much more advantageous than UV excitation. Importantly, upon excitation with visible light (401-460 nm), the complexes show characteristic visible (Sm(3+)) as well as near-infrared (Sm(3+), Nd(3+), Yb(3+), Er(3+), Tm(3+), Pr(3+)) luminescence of the corresponding lanthanide ions, attributed to the energy transfer from the ligands to the lanthanide ions, an antenna effect. Now, using these near-infrared luminescent lanthanide complexes, the luminescent spectral region from 800 to 1650 nm, can be covered completely, which is of particular interest for biomedical imaging applications, laser systems, and optical amplification applications.

  19. Chronology and geochemistry of metavolcanic rocks from Heigouxia Valley in the Mian-Lue tectonic zone, South Qinling——Evidence for a Paleozoic oceanic basin and its close time

    Institute of Scientific and Technical Information of China (English)

    李曙光; 孙卫东; 张国伟; 陈家义; 杨永成


    The metavolcanic rocks of greenschist fades developed at Heigouxia Valley in the Mian-Lue tectonic zone, South Qinling orogenic belt is a bimodal volcanic series. It is composed of K-poor, Na-rich tholeiite and dacite-rhyolite. The trace elements characteristics with flat REE pattern of these tholeiites are similar to those of MORB. The Sm-Nd whole rock isochron age of(242±21) Ma and Rb-Sr whole rock isochron age of (221±13) Ma of this metavolcanic series consistently indicate their rnetamorphic time. Their relatively high initial εNd value of +6.1 at the rnetamorphic age (242 Ma) suggest that the volcanic rocks were derived from a depleted MORB type mantle source. Their trace elements and Nd isotope compositions suggest an oceanic basin developed from a rift on the continental margin of the Yangtze Block during the late Paleozoic and closed in the Triassic, This is the first case clearly showing the existence of relict of late Paleozoic oceanic crust in Fast Qinling belt, which provides important ev

  20. Micro-analysis by U-Pb method using LAM-ICPMS and its applications for the evolution of sedimentary basins: the example from Brasilia Belt; Micro-analise pelo metodo U-Pb usando LAM-CIPMS e suas aplicacoes para a evolucao de bacias sedimentares: o exemplo da faixa Brasilia

    Energy Technology Data Exchange (ETDEWEB)

    Pimentel, Marcio Martins; Matteini, Massimo; Junges, Sergio Luiz; Giustina, Maria Emilia Schutesky Della; Dantas, Elton Luiz; Buhn, Bernhard, E-mail: [Universidade de Brasilia (UnB), DF (Brazil). Instituto de Geociencias; Rodrigues, Joseneusa Brilhante [Servico Geologico do Brasil (CPRM), Brasilia, DF (Brazil)


    The U-Pb geochronological method using LAM-MC-ICPMS represents an important tool to investigate the geological evolution of sedimentary basins, as well as its geochronology, through the determination of upper limits for the depositional ages of detrital sedimentary rocks. The method has been applied in the Geochronology Laboratory of the Universidade de Brasilia, and in this study, a brief review of the provenance data for the sediments of the Neoproterozoic Brasilia Belt is presented and their significance for the evolution of the orogen is discussed. The results indicate that the Paranoa and Canastra Groups represent passive margin sequences formed along the western margin of the Sao Francisco-Congo continent. The Vazante Group presents similar provenance patterns, although Sm-Nd isotopic results suggest that its upper portions had contributions from younger (Neoproterozoic) sources, possibly from the Neoproterozoic Goias Magmatic Arc. On the other hand, metasediments of the Araxa and Ibia groups contain an important proportion of material derived from Neoproterozoic sources, demonstrating that they represent syn-orogenic basins. The provenance pattern of the Bambui Group is marked by an important Neoproterozoic component, showing that it constitutes a sedimentary sequence which is younger than 600 Ma, representing a foreland basin to the Brasilia Belt. (author)

  1. Determination of the provenance of cocoa by soil protolith ages and assessment of anthropogenic lead contamination by pb/nd and lead isotope ratios. (United States)

    Manton, William I


    The Pb contents of chocolate and the products it flavors are among the highest of all commonly consumed substances. Others have shown that this Pb is acquired by cocoa beans after harvesting and is concentrated in their shells, portions of which are ground up with the cotyledons during processing. It is shown here that the shells also contain the lanthanides Nd and Sm, which they appear to take up more slowly than Pb when dried on bare soil. Consideration of Pb/Nd ratios, model Sm-Nd ages and the isotope ratios of Pb and Sr indicates that, in the absence of contamination, the relationship between Pb and Nd in shells is y = 13.1x(-0.383), where x is the Nd concentration in microg/kg and y is the Pb/Nd ratio. For cocoa powders, the relationship is y = 114x(-0.988). Samples that plot above these curves are probably contaminated. Model ages indicate where the cocoa of cocoa powders is grown, and these same considerations point to African samples being uncontaminated but samples from Asia containing 50% anthropogenic Pb of Australian origin. No measurable Pb contamination occurs during the transport of beans and the manufacture of chocolate.

  2. Lunar and Planetary Science XXXV: Terrestrial Planets: Building Blocks and Differentiation (United States)


    The session "Terrestrial Planets: Building Blocks and Differentiation: included the following topics:Magnesium Isotopes in the Earth, Moon, Mars, and Pallasite Parent Body: High-Precision Analysis of Olivine by Laser-Ablation Multi-Collector ICPMS; Meteoritic Constraints on Collision Rates in the Primordial Asteroid Belt and Its Origin; New Constraints on the Origin of the Highly Siderophile Elements in the Earth's Upper Mantle; Further Lu-Hf and Sm-Nd Isotopic Data on Planetary Materials and Consequences for Planetary Differentiation; A Deep Lunar Magma Ocean Based on Neodymium, Strontium and Hafnium Isotope Mass Balance Partial Resetting on Hf-W System by Giant Impacts; On the Problem of Metal-Silicate Equilibration During Planet Formation: Significance for Hf-W Chronometry ; Solid Metal-Liquid Metal Partitioning of Pt, Re, and Os: The Effect of Carbon; Siderophile Element Abundances in Fe-S-Ni-O Melts Segregated from Partially Molten Ordinary Chondrite Under Dynamic Conditions; Activity Coefficients of Silicon in Iron-Nickel Alloys: Experimental Determination and Relevance for Planetary Differentiation; Reinvestigation of the Ni and Co Metal-Silicate Partitioning; Metal/Silicate Paritioning of P, Ga, and W at High Pressures and Temperatures: Dependence on Silicate Melt Composition; and Closure of the Fe-S-Si Liquid Miscibility Gap at High Pressure and Its Implications for Planetary Core Formation.

  3. Characteristics of Magmatic Rocks and Tectonic Setting of Mazhuangshan Area,East Tianshan,China

    Institute of Scientific and Technical Information of China (English)

    陈世忠; 周济元; 等


    The Mazhuangshan area lies in northeast to Aqikekuduke,where are distributed in-termediate-acid rocks,which were formed in the Middle-Late Carboniferous epoch.The magmatic rocks are peraluminous and belong to calcareous series.All values of ACNK(1.03-2.12),ANK(1.67-2.93),SI(4.1-33),δ(0.71-4.82),La/∑REE(0.09-0.26) ∑LREE/∑HREE(1.76-11.01),(La/Sm)N(1.60-6.35),(Sm/Nd)N(0.33-0.58),(La/Yb)N(4.7-12.1),LaN/Lux(5.9-11.8),(Ce/Yb)N(3.14-6.64),δEu(0.38-1.06),RbN/SrN(41-120)and Sr(0.02-0.2)demonstrate they vary with D_I(45-90).S-B diagram also shows that the lithophile elements are abundant in acidic magmatic rocks,Moreover,it is concluded that the primitive magma originated from a subduction zone at the continental edge,and underwent fractional crystallization and contamination,then generated the magmatic rocks,The multi-cation index(R:3055-3993,R2:286-438) shows that the primitive magma originated from the mantle,All these conclusions are beneficial for exploring gold deposits in the area.

  4. Geochemistry and magnetostratigraphy of Deccan flows at Anjar, Kutch

    Indian Academy of Sciences (India)

    A D Shukla; N Bhandari; Sheela Kusumgar; P N Shukla; Z G Ghevariya; K Gopalan; V Balaram


    Chemical analysis of nine Deccan flow basalts at Anjar, Kutch, western India, indicates that all,except the uppermost flow F-9, are alkaline. In their major and trace element composition, the alkali basalts resemble Ocean island basalts (OIB). Similarities of many diagnostic trace element ratios (e.g. Sm/Nd, Ba/Nb,Y/Nb and Zr/Nb) are similar to those found in the Réunion Island basalts. The uppermost basalt is tholeiitic and chemically resembles the least contaminated Deccan basalt (Ambenali type). The Anjar basalts have iridium concentration ranging between 2 and 178 pg/g. Some of these values are higher by about an order of magnitude compared to the Ir concentration in other basalts of the Deccan. A synthesis of chemical, palaeomagnetic and geochronologic data enables us to construct a chemical and magnetic stratigraphy for these flows. The three flows below the iridium enriched intertrappean bed (IT III) show normal magnetic polarity whereas all except one of the upper basalts show reversed magnetic polarity. The sequence seems to have started in polarity zones 31N and probably continued up to 28R or 27R. The results presented here support the view that Deccan volcanism in Kutch occurred on a time span of a few million years.

  5. Dielectric and electromechanical properties of rare earth calcium oxyborate piezoelectric crystals at high temperatures. (United States)

    Yu, Fapeng; Zhang, Shujun; Zhao, Xian; Yuan, Duorong; Qin, Lifeng; Wang, Qing-Ming; Shrout, Thomas R


    The electrical resistivity, dielectric, and electromechanical properties of ReCa(4)O(BO(3))(3) (ReCOB; Re = Er, Y, Gd, Sm, Nd, Pr, and La) piezoelectric crystals were investigated as a function of temperature up to 1000 °C. Of the studied crystals, ErCOB and YCOB were found to possess extremely high resistivity (p): p > 3 × 10(7) ω.cm at 1000 °C. The property variation in ReCOB crystals is discussed with respect to their disordered structure. The highest electromechanical coupling factor κ(26) and piezoelectric coefficient d(26) at 1000°C, were achieved in PrCOB crystals, with values being on the order of 24.7% and 13.1 pC/N, respectively. The high thermal stability of the electromechanical properties, with variation less than 25%, together with the low dielectric loss (factor (>1500) at elevated temperatures of 1000 °C, make ErCOB, YCOB, and GdCOB crystals promising for ultrahigh temperature electromechanical applications.

  6. National uses and needs for separated stable isotopes in physics, chemistry, and geoscience research

    Energy Technology Data Exchange (ETDEWEB)

    Zisman, M.S.


    Present uses of separated stable isotopes in the fields of physics, chemistry, and the geosciences have been surveyed to identify current supply problems and to determine future needs. Demand for separated isotopes remains strong, with 220 different nuclides having been used in the past three years. The largest needs, in terms of both quantity and variety of isotopes, are found in nuclear physics research. Current problems include a lack of availability of many nuclides, unsatisfactory enrichment of rare species, and prohibitively high costs for certain important isotopes. It is expected that demands for separated isotopes will remain roughly at present levels, although there will be a shift toward more requests for highly enriched rare isotopes. Significantly greater use will be made of neutron-rich nuclides below A = 100 for producing exotic ion beams at various accelerators. Use of transition metal nuclei for nuclear magnetic resonance spectroscopy will expand. In addition, calibration standards will be required for the newer techniques of radiological dating, such as the Sm/Nd and Lu/Hf methods, but in relatively small quantities. Most members of the research community would be willing to pay considerably more than they do now to maintain adequate supplies of stable isotopes.

  7. Disturbance of isotope systematics in meteorites during shock and thermal metamorphism and implications for shergottite chronology

    Energy Technology Data Exchange (ETDEWEB)

    Gaffney, A M; Borg, L E; Asmerom, Y


    Shock and thermal metamorphism of meteorites from differentiated bodies such as the Moon and Mars have the potential to disturb chronometric information contained in these meteorites. In order to understand the impact-related mechanisms and extent of disturbance to isochrons, we undertook experiments to shock and heat samples of 10017, a 3.6 billion year old lunar basalt. One sub-sample was shocked to 55 GPa, a second subsample was heated to 1000 C for one week, and a third sub-sample was maintained as a control sample. Of the isotope systems analyzed, the Sm-Nd system was the least disturbed by shock or heat, followed by the Rb-Sr system. Ages represented by the {sup 238}U-{sup 206}Pb isotope system were degraded by shock and destroyed with heating. In no case did either shock or heating alone result in rotated or reset isochrons that represent a spurious age. In some cases the true crystallization age of the sample was preserved, and in other cases age information was degraded or destroyed. Although our results show that neither shock nor thermal metamorphism alone can account for the discordant ages represented by different isotope systems in martian meteorites, we postulate that shock metamorphism may render a meteorite more susceptible than unshocked material to subsequent disturbance during impact-related heating or aqueous alteration on Mars or Earth. The combination of these processes may result in the disparate chronometric information preserved in some meteorites.

  8. Zoning and sectoriality of the florencite and xenotime group minerals from quartz veins, the Subpolar Urals (United States)

    Repina, S. A.


    A detailed study of the florencite and xenotime assemblage from quartz veins of Au-REE occurrences in the Subpolar Urals allowed the REE fractionation and distribution of REE mixtures in the crystal structure to be characterized. In minerals of selective composition, isomorphic mixtures of LREE and HREE are divided into lanthanum Lasg (La-Pr) and samarium Smsg (Nd-Eu) subgroups in florencite and gadolinium Gdsg (Gd-Dy) and ytterbium Ybsg (Ho-Lu) subgroups in xenotime. Concentrations of elements from these subgroups are inversely proportional to each other. Each florencite or xenotime crystal is characterized by several mineral varieties: xenotime-(Y) and Gd-bearing xenotime-(Y), florencite-(Sm), -(Nd), and -(Ce); they are selectively distributed by growth zones and pyramids of the crystal with formation of direct and inverse zoning. In both cases, cores of the crystals are enriched in HREE. The correlation between REEs, Y, and such trace elements as As, S, Ca, Sr, U, and Sc is established. REE deportment is considered in minerals formed as products of primary crystallization and hydrothermal redeposition. The REE fractionation is interpreted in terms of quantum mechanics.

  9. Geothermal exploration results at the Ceboruco volcano, Nayarit State, Mexico; Resultados de la exploracion geotermica en el volcan Ceboruco en el estado de Nayarit, Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Venegas S, Saul [Gerencia de Proyectos Geotermoelectricos de la Comision Federal de Electricidad, Morelia (Mexico)


    Since the seventies, in Mexico, the thermal areas census and the geothermal exploration have been carried out by the Geothermal Division of Comision Federal de Electricidad (CFE), including geological, geophysical and geochemical studies and deep exploratory wells, most of them located in the Mexican Volcanic Belt (MVB). In recent years, the exploration has been intensified in the northwestern sector of this regional structure, called the Tepic-Chapala graben, also named by some authors as the Zacoalco-Tepic graben. Due to the large volumes of plio-quaternary volcanism between the tectonic limits of the Sierra Madre Occidental (SMO) and the Jalisco Block (JB), one of the greatest geothermal interest areas is located between the large volcanic apparatus of Ceboruco, Domes of San Pedro, and Tepetiltic, in the State of Nayarit, where CFE has drilled 3 deep exploratory wells. The obtained results, demonstrate that the tectonic limit between SMO and BJ physiographic provinces is much more complex than initially proposed and the hypothetical Quaternary continental rift type structure, could be of Miocene age, because in the three wells discordant lithologic contact was observed between the BJ and the MVB. Also the measured thermal gradient in the Ceboruco No. 1 well (112 degrees celsius to 2800 m), does not correspond the typical heat flow of this type of recent structures. [Espanol] La Gerencia de Proyectos Geotermoelectricos, dependiente de la Comision Federal de Electricidad (CFE), ha realizado desde 1970, el censo de focos termales en el pais. La prospeccion geotermica con base en estudios de geologia, geofisica, geoquimica y construccion tanto de pozos exploratorios profundos como de desarrollo, define a la estructura del Eje Neovolcanico Mexicano (ENM), como la provincia fisiografica con mayores posibilidades para el desarrollo de la energia geotermica. En el sector noroccidental de esta estructura regional, en los limites tectonicos de la Sierra Madre Occidental

  10. Deep water invasions in oil fields of the gulf of Mexico: a challenge for the application of environmental isotopes; Invasiones de aguas profundas en yacimientos petroleros del golfo de Mexico: un reto para la aplicacion de isotopos ambientales

    Energy Technology Data Exchange (ETDEWEB)

    Birkle, Peter [Instituto de Investigaciones Electricas, Cuernavaca, Morelos (Mexico)


    It was verified the use of environmental isotopes as a useful method to improve the efficiency of the present exploitation in oil fields of the Gulf of Mexico. In general, the stable isotopes like deuterium, 18 O, 13 C, 37 Cl, 87 Sr and 34 S, support in questions on the origin of waters, its quality, the geochemistry evolution, recharge processes, interaction water-rock, origin of the salinity and contamination processes, whereas the radioactive isotopes (Tritium, 14 C, 36 I and 129 I) provide information on the time of circulation, the origin and the age of underground waters. Since year 1998, the Gerencia de Geotermia of the Instituto de Investigaciones Electricas is making investigation projects in the oil fields of the Actives of Production Luna, Pol-Chuc, Chilpilla-Colomo (all of them in the state of Tabasco) and Cactus-Sitio Grande (Chiapas) in the South Region of PEMEX Exploration and Production (PEP). As primary target of these studies hidrogeological models were developed on the migration and circulation of the fluids in the oil fields with the purpose of limiting the water invasion in producing wells and to increase the crude oil production. [Spanish] Se comprobo el uso de los isotopos ambientales como un metodo util para mejorar la eficiencia de la explotacion actual en yacimientos petroleros del golfo de Mexico. En general, los isotopos estables como deuterio, 18 O, 13 C, 37 Cl, 87 Sr y 34 S, apoyan en cuestiones sobre el origen de las aguas, su calidad, la evolucion geoquimica, procesos de recarga, interaccion agua-roca, origen de la salinidad y procesos de contaminacion, mientras que los isotopos radiactivos (Tritio, 14 C, 36 l Y 129 I) proporcionan informacion sobre el tiempo de circulacion, el origen y la edad de las aguas subterraneas. Desde el ano 1998, la Gerencia de Geotermia del Instituto de Investigaciones Electricas esta realizando proyectos de investigacion en los campos petroleros de los activos de Produccion Luna, Pol-Chuc, Chilpilla

  11. Physiological traits for drought phenotyping in cotton = Traços fisiológicos para fenotipagem de algodoeiro sob seca

    Directory of Open Access Journals (Sweden)

    Giovani Greigh de Brito


    plantas dos cultivares em estudo atingissem -3,0 MPa, ponto no qual coletaram-se amostras foliares para analises fisiologicas. Apos, irrigou-se as plantas ate a obtencao de valor superior a 50% do potencial hidrico foliar (-1,50 MPa. Avaliaram-se a eficiencia fotoquimica maxima (Fv/Fm, o conteudo de clorofila via indice SPAD, o conteudo relativo de agua (CRA, o extravasamento de eletrolitos, a composicao isotopica do carbono (ƒÂ13C, o rendimento de algodao em caroco por planta e a qualidade da fibra. A disruptura de membrana via extravasamento de eletrolitos e a ƒÂ13C apresentaram-se como potenciais indicadores fisiologicos visando a selecao de genotipos de algodoeiro tolerantes ao deficit hidrico.

  12. Sr, Nd, and Pb isotopes of ultramafic xenoliths in volcanic rocks of Eastern China: enriched components EMI and EMII in subcontinental lithosphere (United States)

    Tatsumoto, M.; Basu, A.R.; Wankang, H.; Junwen, W.; Guanghong, X.


    The UThPb, SmNd, and RbSr isotopic systematics of mafic and ultramafic xenolithic rocks and associated megacrystic inclusions of aluminous augite and garnet, that occur in three alkalic volcanic suites: Kuandian in eastern Liaoning Province, Hanluoba in Hebei Province, and Minxi in western Fujian Province, China are described. In various isotopic data plots, the inclusion data invariably fall outside the isotopic ranges displayed by the host volcanic rocks, testifying to the true xenolithic nature of the inclusions. The major element partitioning data on Ca, Mg, Fe, and Al among the coexisting silicate minerals of the xenoliths establish their growth at ambient mantle temperatures of 1000-1100??C and possible depths of 70-80 km in the subcontinental lithosphere. Although the partitioning of these elements reflects equilibrium between coexisting minerals, equilibria of the Pb, Nd, and Sr isotopic systems among the minerals were not preserved. The disequilibria are most notable with respect to the 206Pb 204Pb ratios of the minerals. On a NdSr isotopic diagram, the inclusion data plot in a wider area than that for oceanic basalts from a distinctly more depleted component than MORB with higher 143Nd 144Nd and a much broader range of 87Sr 86Sr values, paralleling the theoretical trajectory of a sea-water altered lithosphere in NdSr space. The garnets consistently show lower ?? and ?? values than the pyroxenes and pyroxenites, whereas a phlogopite shows the highest ?? and ?? values among all the minerals and rocks studied. In a plot of ??207 and ??208, the host basalts for all three areas show lower ??207 and higher ??208 values than do the xenoliths, indicating derivation of basalts from Th-rich (relative to U) sources and xenoliths from U-rich sources. The xenolith data trends toward the enriched mantle components, EMI and EMII-like, characterized by high 87Sr 86Sr and ??207 values but with slightly higher 143Nd 144Nd. The EMI trend is shown more distinctly by the host

  13. Tectono-metamorphic evolution and timing of the melting processes in the Svecofennian Tonalite-Trondhjemite Migmatite Belt: An example from Luopioinen, Tampere area, southern Finland

    Directory of Open Access Journals (Sweden)

    Mouri, H.


    Full Text Available The Svecofennian Orogen is in southern Finland characterized by two major migmatite belts. These are the so-called Granite Migmatite Belt, in which Kfs-rich leucosomes predominate, and the Tonalite-Trondhjemite Migmatite Belt, which is characterized by Kfs-poor leucosomes and borders the former belt in the north. The present paper deals with selected migmatitic rocks from the latter belt. It is aimed to study the temporal and structural relationships of the different leucosome generations, and to establish the pressure-temperature-time paths of this belt. The Tonalite-Trondhjemite Migmatite Belt consists mainly of migmatitic rocks with various types of synorogenic granitoids and minor mafic and ultramafic crocks. The mesosome of the migmatites consist of garnet-sillimanite-biotite-plagioclase-cordierite-quartz assemblages with rare K-feldspar and late andalusite. The oldest leucosomes are dominated by plagioclase and quartz, and the content of K-feldspar increases in later leucosomes. Microtextural analysis in conjunction with THERMOCALC calculations and geothermometry shows that these rocks were metamorphosed at peak conditions of 700-750°C at 4-5 kbar and aH20 = 0.4-0.7. The formation of cordierite coronas around garnet and the late crystallization of andalusite suggest that the final stage of the P-T history was characterized by decompression and cooling within the andalusite stability field, estimated at 500-650°C and 3-4 kbar. Detailed isotopic dating of mesosome and leucosomes of the migmatites was undertaken by conventional U-Pb analyses on monazite and zircon, Sm-Nd analyses on garnet, and ion probe dating on zircon. The monazites are nearly concordant with an average age of 1878.5±1.5 Ma, and garnet-whole rock analyses show that the concordant leucosomes and the mesosome are coeval within error margins having ages of 1893±40 and 1871±14 Ma, respectively. However, garnet in the discordant vein leucosome provides an age of 1843±11

  14. Predicting the Isotopic Composition of Subduction-Filtered Subducted Oceanic Crust and Sediment (United States)

    White, W. M.


    The chemical and isotopic character of mantle plumes, which produce oceanic island volcanoes, are widely thought to reflect the presence of recycled oceanic crust and sediment. Isotopic systematics suggest the “cycle time” for this process is 1 Ga or longer, but it should be possible to use a simple mass balance approach to discern how the presently operating subduction zone filter affects the ratios of radioactive parent to radiogenic daughter isotopes. Simple uniformitarian assumptions can then be used to predict the present isotopic composition of anciently subducted lithosphere. Our underlying assumption in deciphering the subduction zone filter is that the flux of an element into the deep mantle is simply equal to the flux of element into the subduction zone less the flux of that element into subduction zone magmas. The former is readily calculated from published data. The latter can be calculated by estimating parental magma compositions, arc accretion rates, and the assumption that arc magma compositions differ from MORB only because of material derived from subducting crust and sediment. Using this approach for 8 intra-oceanic subduction zones, we find 73% of Th and Pb, 79% of U, 80% of Rb and Sr, 93% of Nd and 98% of Sm survive the subduction zone filter. The subduction zone filter systematically increases Sm/Nd ratios in all subduction zones, but the effect is small, with a weighted mean increase of 1.5%. The effect of subduction is to decrease the Sm/Nd of the mantle, but only slightly. The effect of subduction is to increase the Rb/Sr of the mantle, but the subduction zone filter does not have a systematic effect on Rb/Sr ratios: it significantly increases in Rb/Sr in 3 subduction zones and significantly decreases it in one; the weighted mean shows no significant change. The effect of the subduction zone filter on U/Pb is also not systematic. U/Pb ratios in the mantle fluxes are bimodal, with values equal to or lower than the bulk Earth value in 4

  15. Tectonics of Precambrian basement of the Tarim craton

    Institute of Scientific and Technical Information of China (English)

    GUO; Zhaojie; (


    [1]Jia Chengzao, Tectonic Characteristics and Petroleum, Tarim Basin, China (in Chinese), Beijing: Petroleum Industry Press, 1997, 29?/FONT>92.[2]Huang, T. K., Ren, J. S., Jiang, C. F. et al., The Geologic Evolution of China (in Chinese), Beijing: Geological Publishing House, 1980.[3]Che, Z. C., Liu, L., Liu, H. F. et al., Discovery and occurrence of high-pressure meta-pelitic rocks from Altun Mountain areas, Xinjiang Uygur Autonomous Region, Chinese Science Bulletin, 1995, 40(23): 1988.[4]An Yin, Nie Shangyou, A phanerozoic palinspastic reconstruction of China and its neighboring regions, in The Tectonic Evolution of Asia (eds. An Yin, Harrison, T. M.), London: Cambridge University Press, 1996, 442-485.[5]Sobel, E. R., Arnaud, N., A possible middle Paleozoic suture in the Altyn Tagh, NW China, Tectonics, 1999, 18(1): 67.[6]Xu, Z. Q., Yang, J. S., Zhang, J. X. et al., A comparison between the tectonic units on the two sides of the Altun sinistral strike-slip fault and the mechanism of lithospheric shearing, Acta Geologica Sinica (in Chinese with English abstract), 1999, 73(3): 193.[7]Guo, Z., J., Zhang, Z. C., Wang, J. J., Sm-Nd isochron age of ophiolite along northern margin of Altun Tagh Mountain and its significance, Chinese Science Bulletin, 1999, 44(5): 456.[8]Liu, L., Che, Z. C., Wang, Y. et al., The evidence of Sm-Nd isochron age for the early Paleozoic ophiolite in Mangya area, Altun Mountains, Chinese Science Bulletin, 1998, 43(15): 754.[9]Xinjiang Bureau of Geology and Mineral Resources, Regional Geology of Xinjiang Uygur Autonomous Region (in Chinese with English abstract), Beijing: Geological Publishing House, 1993, 555-557.[10]Gansu Bureau of Geology and Mineral Resources, Regional Geology of Gansu Province (in Chinese with English abstract), Beijing: Geological Publishing House, 1989.[11]Hu, A. Q., Rogers, G., Discovery of 3.3 Ga Archean rocks in North Tarim Block of Xinjiang, Western China, Chinese Science

  16. Geochemistry and Nd-Sr Isotopic Signatures of the Pensamiento Granitoid Complex, Rondonian-San Ignacio Province, Eastern Precambrian Shield of Bolivia: Petrogenetic Constraints for a Mesoproterozoic Magmatic Arc Setting

    Directory of Open Access Journals (Sweden)

    Ramiro Matos


    Full Text Available The Pensamiento Granitoid Complex (PGC, located in the northern part of the eastern Precambrian shield of Bolivia, istectonically assigned to the Rondonian-San Ignacio Province (1.55 - 1.30 Ga of the Amazonian Craton that is made up byArchean and Proterozoic provinces. The Proterozoic ones result from accretionary orogens that become successively youngersouthwestwards, such as the Rondonian/San Ignacio (1.37 - 1.32 Ga and the Sunsás orogenies (1.20 - 1.00 Ga. The PGCcrops out mainly on the “Paragua craton” bounded to the south by the Sunsás belt, and composed of granites and subvolcanicterms, and subordinately of syenites, granodiorites, tonalites, trondhjemites and diorites as orogenic representatives of theRondonian/San Ignacio Orogeny, intrusive into the Lomas Maneches (ca. 1.68 Ga and Chiquitania (ca. 1.7 Ga complexes.Thirteen whole rock chemical analyses for major, trace and REE elements were performed for the La Junta, San Martín, Diamantina,Porvernir, San Cristobal, Piso Firme plutons of the PGC. The negative trends of MgO, Al2O3 and CaO contents withincreasing SiO2 suggest that fractional crystallization played an important role in the petrogenesis of the investigated rocks.The data also indicate a mainly peraluminous, sub-alkaline to high-K calc-alkaline composition, and fractionated LREE/HREE patterns are consistent with a magmatic arc character for these plutons. SHRIMP U-Pb zircon ages of the La Junta andSan Martín syn- to late-kinematic plutons are 1347 ± 21 Ma and 1373 ± 20 Ma respectively, and the Sm-Nd TDM model agesare between 1.9 to 2.0 Ga, while εNd(1330 values range from +1.8 to -4.3, respectively. In addition, the late- to post-kinematicDiamantina pluton yields SHRIMP U-Pb zircon age of 1340 ± 20 Ma, and variable Sm-Nd TDM model ages (1.6 to 1.9 Ga andεNd(1330 values (+0.4 to -1.2 that are comparable with previous results found for other coeval plutons. The Porvenir, San Cristobaland Piso Firme plutons show ε

  17. Thermochronology of the Cornubian batholith in southwest England: Implications for pluton emplacement and protracted hydrothermal mineralization (United States)

    Chesley, J.T.; Halliday, A.N.; Snee, L.W.; Mezger, K.; Shepherd, T.J.; Scrivener, R.C.


    The metalliferous ore deposits of southwest England are associated with biotite-muscovite granites that intruded upper Paleozoic sediments and volcanic rocks at the end of the Hercynian Orogeny. The hydrothermal mineralization can be subdivided into four stages: 1. (1) exoskarns 2. (2) high-temperature tin and tungsten oxide-bearing sheeted greisen bordered veins and Sn-bearing tourmaline veins and breccias 3. (3) polymetallic quartz-tourmaline-chlorite-sulfide-fluorite-bearing fissure veins, which represent the main episode of economic mineralization 4. (4) late-stage, low-temperature polymetallic fluorite veins. U-Pb dating of monazite and xenotime and 40Ar 39Ar dating of muscovite were used to determine emplacement ages and cooling times for individual plutons within the Cornubian batholith, as well as separate intrusive phases within the plutons. In addition, 40Ar 39Ar ages from hornblende and secondary muscovite and Sm-Nd isochron ages from fluorite were employed to determine the relationship between pluton emplacement and different stages of mineralization. The U-Pb ages indicate that granite magmatism was protracted from ~300 Ma down to ~275 Ma with no evidence of a major hiatus. There is no systematic relation between the age of a pluton and its location within the batholith. The U-Pb ages for separate granite phases within a single pluton are resolvable and indicate that magma emplacement within individual plutons occurred over periods of as much as 4.5 myrs. Felsic porphyry dike emplacement was coeval with plutonism, but continued to ~270 Ma. The geochronologic data suggest that the Cornubian batholith originated from repeated melting events over 30 myrs and was formed by a series of small coalescing granitic bodies. Cooling rates of the main plutons are unrelated to emplacement age, but decrease from the southwest to the northeast from ~210??C myr-1 to ~60??C myr-1 with a mean of 100??C myr-1. These slow cooling rates appear to reflect the addition of

  18. Petrology, geochemistry, and age of low-Ti mare-basalt meteorite Northeast Africa 003-A: A possible member of the Apollo 15 mare basaltic suite (United States)

    Haloda, Jakub; Týcová, Patricie; Korotev, Randy L.; Fernandes, Vera A.; Burgess, Ray; Thöni, Martin; Jelenc, Monika; Jakeš, Petr; Gabzdyl, Pavel; Košler, Jan


    C/h) suggest that the parent melt of NEA 003-A crystallized in the lower part of a lava flow containing cumulate olivine (˜10%) and was probably derived from more primitive picritic magma by fractional crystallization processes. Sm-Nd dating yields an age of 3.09 ± 0.06 Ga which corresponds to the period of lower Eratosthenian lunar volcanic activity, and the near-chondritic ɛNd value of -0.4 ± 0.3 indicates that the meteorite could be derived from a slightly enriched mantle source similar to the Apollo 15 green glasses. Ar-Ar step release results are inconsistent with Sm-Nd ages suggesting that NEA 003-A was exposed to one or more impact events. The most extensive event took place at 1.8 Ga and the shock intensity was likely between 28 and 45 GPa. The absence of solar Ar suggests that NEA 003-A has not been directly exposed at the lunar surface but the cosmic ray exposure age of 209 ± 6 Ma suggests that NEA 003-A resided in the upper regolith for part of its history.

  19. Nd isotopic compositions of the Tethyan Himalayan Sequence in southeastern Tibet

    Institute of Scientific and Technical Information of China (English)

    DAI JinGen; YIN An; LIU WenCan; WANG ChengShan


    The Himalayan orogen consists of three major lithologic units that are separated by two major north-dipping faults: the Lesser Himalayan Sequence (LHS) below the Main Central Thrust (MCT), the Greater Himalayan Crystalline Complex (GHC) above the MCT, and the Tethyan Himalayan Sequence (THS) juxtaposed by the South Tibet Detachment fault (STD) over the GHC.Due to widespread meta-morphism and intense deformation, differentiating the above three lithologic units is often difficult.This problem has been overcome by the use of Sm-Nd isotopic analysis.The previous studies suggested that the LHS can be clearly distinguished from the GHC and THS by their Nd isotope compositions.However, the lack of detailed and systematic Sm-Nd isotopic studies of the THS across the Himalaya in general has made differentiation of this unit from the nearby GHC impossible, as the two appear to share overlapping Nd compositions and model ages.To address this problem, we systematically sampled and analyzed Nd isotopes of the THS in southeastern Tibet directly north of Bhutan.Our study identifies two distinctive fields in a εNd-TDM plot.The first is defined by the εNd(210 Ma) values of -3.45 to -7.34 and TDM values of 1.15 to 1.29 Ga from a Late Triassic turbidite sequence, which are broadly similar to those obtained from the Lhasa block.The second field is derived from the Early Cretaceous meta-sedimentary rocks with εNd(130 Ma) values from -15.24 to -16.61 and TDM values from 1.63 to 2.00 Ga; these values are similar to those obtained from the Greater Himalayan Crystalline Complex in Bhutan directly south of our sampling traverse, which has εNd(130 Ma) values of -10.89 to -16.32 and Nd model ages (TDM) of 1.73 to 2.20 Ga.From the above observations, we suggest that the Late Triassic strata of the southeast Tibetan THS were derived from the Lhasa block in the north, while the Early Cretaceous strata of the THS were derived from a source similar to the High Himalayan Crystalline Complex or

  20. Lithophile and siderophile element systematics of Earth's mantle at the Archean-Proterozoic boundary: Evidence from 2.4 Ga komatiites (United States)

    Puchtel, I. S.; Touboul, M.; Blichert-Toft, J.; Walker, R. J.; Brandon, A. D.; Nicklas, R. W.; Kulikov, V. S.; Samsonov, A. V.


    New Os isotope and highly siderophile element (HSE) abundance data, in combination with lithophile trace element and Sm-Nd, Lu-Hf, and Hf-W isotope data, are reported for komatiitic basalts from the Vetreny Belt and tonalites from the adjacent Vodla Block in the Fennoscandian Shield. Komatiitic basalts define a Re-Os isochron with an age of 2407 ± 6 Ma and an initial γ187Os = +1.7 ± 0.2 (2 SE). The Pt-Os data for chromite separates yield an average initial ε186Os = +0.03 ± 0.02 (2 SE). The 147Sm-143Nd and 176Lu-176Hf data for the komatiitic basalts give isochron ages and initial ratios of, respectively, 2403 ± 32 Ma and ε143Nd = -0.90 ± 0.09, and 2451 ± 79 Ma and ε176Hf = +0.4 ± 0.2 (2 SE). Bulk tonalites are characterized by average initial γ187Os, ε143Nd, and ε176Hf values of +304 ± 64, +1.8 ± 0.6, and +2.5 ± 1.6 (2 SE), respectively, when calculated for the ∼3.21 Ga age of the rocks. The komatiitic basalts and tonalites have μ142Nd values of, respectively, +0.5 ± 2.8 and -0.4 ± 5.2 (2 SD). By contrast, both the komatiitic basalts and tonalites exhibit positive 182W anomalies of +7.1 ± 4.5 and +12.6 ± 4.5 ppm (2 SD), respectively. The komatiitic basalts were derived from a komatiitic parental magma with ∼27 wt.% MgO; it was modified by both assimilation of the tonalites and fractional crystallization en route to the surface. Lithophile trace element data constrain the degree of crustal contamination to be 4.0 ± 0.4%. Highly siderophile element abundance data indicate that crustal contamination must have had a negligible effect on the Os isotopic composition of the komatiitic parental magma. By contrast, the Nd, Hf, and W isotope systematics of the komatiitic parental magma were strongly modified as a result of assimilation of the tonalites. The positive initial ε143Nd and ε176Hf values of the tonalites indicate that they formed via melting of a precursor with time-integrated suprachondritic Sm/Nd and Lu/Hf. This precursor was most

  1. SHRIMP Zircon U-Pb Chronology and Geochemistry of the Henglingguan and Beiyu Granitoids in the Zhongtiao Mountains, Shanxi Province

    Institute of Scientific and Technical Information of China (English)

    YU Shengqiang; LIU Shuwen; TIAN Wei; LI Qiugen; FENG Yonggang


    Henglingguan and Beiyu metamorphic granitoids, distributed in the northwest of the Zhongtiaoshan Precambrian complex, comprise trondhjemites and calc-alkaline monzogranites,displaying intrusive contacts with the Archean Zhaizi TTG gneisses. And the Beiyu metamorphic granitoids consist mainly of trondhjemites, distributed at the core of the Hujiayu anticline fold. New SHRIMP zircon U-Pb dating data show that the weighted mean 207Pb/206Pb ages are 2435.9 Ma and 2477 Ma for the Henglingguan metamorphic calc-alkaline monzogranites and Beiyu metamorphic trondhjemites, respectively, and reveal ~2600 Ma inherited core in magmatic zircons. Whole-rock geochemical data indicate that all the Henglingguan and Beiyu metamorphic trondhjemites and calcalkaline monzogranites belong to the metaluminous medium- and high-potassium calc-alkaline series.These rocks are characterized by relatively high total alkali contents (Na2O+K2O, up to 9.08%),depleted Nb, Ta, P and Ti, and right-declined REE patterns with moderate to high LREEs/HREEs fractionation (the mean ratio of (La/Yb)n = 25). The Henglingguan and Beiyu metamorphic trondhjemites display negative Rb, Th and K anomalies in the multi-element spider diagrams normalized by primitive mantle. Sm-Nd isotopic data reveal that these granitoids have initial εNd(t)=-1.2 to +2.4 and Nd depleted mantle model ages of TMD = 2622 Ma-2939 Ma. All these geochemical features indicate that these granitoids were formed in an continent-marginal arc, and the trondhjemites mainly originated from partial melting of juvenile basaltic materials and, howbeit, the Henglingguan metamorphic calc-alkaline monzogranites derived from recycling of materials in the ancient crust under a continent-marginal arc. The granitic magma underwent contamination and fractional crystallization during their formation.

  2. Geochronology and sources of late Neoproterozoic to Cambrian granites of the Saldania Belt (United States)

    Chemale, F.; Scheepers, R.; Gresse, P. G.; van Schmus, W. R.


    The Saldania Belt (SB), located in the southernmost part of South Africa, contains S-, I-, and A-type granites. Whole-rock Sm-Nd data for the Saldania granites indicate the presence of a juvenile as well as inherited crustal signature. The earlier S-type granites have ɛNd( t) values from -4.2 to -3.28 (for t = 550 Ma). In contrast, the intermediate I-type and youngest A-type and highly fractionated I-type granites display ɛNd values ranging from -1.44 to -3.68 (for t = 540 Ma) and from +3.66 to +5.1(for t = 530 Ma), respectively. The U-Pb single zircon data of A-type granites exposed in the Western Branch of the SB yielded dates from 524 ± 8 to 510 ± 4 Ma, whereas an S-type granite, situated in the Southern Branch of the SB and represented by the syn- to late-tectonic Rooiklip Granite, yielded an age of 527 ± 8 Ma. The volcano-sedimentary rocks intruded by these granites display Nd model ages from Ga to 1.67 Ga and ɛNd( t) values from -6.58 to +3.34 (for t = 560 Ma) with isotope signature similar to those of the granites. The S- and I-type granitic magmatism is mostly a product of melting of an earlier crust (Mesoproterozoic to Paleoproterozoic) with different degree of juvenile contribution. The obtained isotope data and field relationship support the hypothesis that the lithological units of the SB were affected by the late Neoproterozoic to Early Cambrian tectonism, related to compressive deformational processes at the southern margin of the Kalahari Plate and probably correlated with the Sierra La Ventana Belt basement.

  3. Geology, petrology, U-Pb (SHRIMP) geochronology of the Morrinhos granite - Paragua terrane, SW Amazonian craton: implications for the magmatic evolution of the San Ignacio orogeny

    Energy Technology Data Exchange (ETDEWEB)

    Franca, Ohana; Ruiz, Amarildo Salina; Sousa, Maria Zelia Aguiar de, E-mail:, E-mail:, E-mail: [Universidade Federal de Mato Grosso (UFMT), Cuiaba, MT (Brazil). Instituto de Ciencias Exatas e da Terra. Dept. de Geologia Geral; Batata, Maria Elisa Froes, E-mail: [Universidade Federal de Mato Grosso (UFMT), Cuiaba, MT (Brazil). Grupo de Pesquisa em Evolucao Crustal e Tectonica; Lafon, Jean-Michel [Universidade Federal do Para (GEOCIAM/UFPA), Belem, PR (Brazil). Inst. Nacional de Cencia e Tecnologia de Geociencias da Amazonia


    Morrinhos granite is a batholith body that is slightly elongated in the NNW direction and approximately 1,140 km{sup 2} long; it is located in the municipality of Vila Bela da Santissima Trindade of the state of Mato Grosso, Brazil, in the Paragua Terrane, Rondonian-San Ignacio Province, in the SW portion of the Amazonian Craton. This intrusion displays a compositional variation from tonalite to monzogranite, has a medium to coarse inequigranular texture and is locally porphyritic; biotite is the predominant mafic in one of the facies, and hornblende is predominant in the other, with both metamorphosed into the green schist facies. The studied rocks characterize an intermediate to acidic sequence that was formed by a subalkaline magmatism; the series is alkali-calcic to metaluminous to slightly peraluminous, and the rocks evolved through fractioned crystallization mechanisms. The structural data show two deformation phases represented by penetrative foliation (S{sub 1}) and open folds (D{sub 2}), and both phases were most likely related to the San Ignacio Orogeny. The geochronological (U-Pb SHRIMP) and isotopic (Sm-Nd) investigations of these rocks indicated a crystallization age of 1350±12Ma, T{sub DM} of approximately 1.77 Ga and εNd{sub (1.35}) with a negative value of -2.57, suggesting that their generation was related to a partial melting process of a Paleoproterozoic (Statherian) continental crust. The results herein indicate that the Morrinhos granite was generated in a continental magmatic arc in a late- to post-orogenic stage of the San Ignacio Orogeny, and it can be recognized as belonging to the Pensamiento Intrusive Suite. (author)

  4. Late formation and prolonged differentiation of the Moon inferred from W isotopes in lunar metals. (United States)

    Touboul, M; Kleine, T; Bourdon, B; Palme, H; Wieler, R


    The Moon is thought to have formed from debris ejected by a giant impact with the early 'proto'-Earth and, as a result of the high energies involved, the Moon would have melted to form a magma ocean. The timescales for formation and solidification of the Moon can be quantified by using 182Hf-182W and 146Sm-142Nd chronometry, but these methods have yielded contradicting results. In earlier studies, 182W anomalies in lunar rocks were attributed to decay of 182Hf within the lunar mantle and were used to infer that the Moon solidified within the first approximately 60 million years of the Solar System. However, the dominant 182W component in most lunar rocks reflects cosmogenic production mainly by neutron capture of 181Ta during cosmic-ray exposure of the lunar surface, compromising a reliable interpretation in terms of 182Hf-182W chronometry. Here we present tungsten isotope data for lunar metals that do not contain any measurable Ta-derived 182W. All metals have identical 182W/184W ratios, indicating that the lunar magma ocean did not crystallize within the first approximately 60 Myr of the Solar System, which is no longer inconsistent with Sm-Nd chronometry. Our new data reveal that the lunar and terrestrial mantles have identical 182W/184W. This, in conjunction with 147Sm-143Nd ages for the oldest lunar rocks, constrains the age of the Moon and Earth to Myr after formation of the Solar System. The identical 182W/184W ratios of the lunar and terrestrial mantles require either that the Moon is derived mainly from terrestrial material or that tungsten isotopes in the Moon and Earth's mantle equilibrated in the aftermath of the giant impact, as has been proposed to account for identical oxygen isotope compositions of the Earth and Moon.

  5. Lunar basalt chronology, mantle differentiation and implications for determining the age of the Moon (United States)

    Snape, Joshua F.; Nemchin, Alexander A.; Bellucci, Jeremy J.; Whitehouse, Martin J.; Tartèse, Romain; Barnes, Jessica J.; Anand, Mahesh; Crawford, Ian A.; Joy, Katherine H.


    Despite more than 40 years of studying Apollo samples, the age and early evolution of the Moon remain contentious. Following the formation of the Moon in the aftermath of a giant impact, the resulting Lunar Magma Ocean (LMO) is predicted to have generated major geochemically distinct silicate reservoirs, including the sources of lunar basalts. Samples of these basalts, therefore, provide a unique opportunity to characterize these reservoirs. However, the precise timing and extent of geochemical fractionation is poorly constrained, not least due to the difficulty in determining accurate ages and initial Pb isotopic compositions of lunar basalts. Application of an in situ ion microprobe approach to Pb isotope analysis has allowed us to obtain precise crystallization ages from six lunar basalts, typically with an uncertainty of about ± 10 Ma, as well as constrain their initial Pb-isotopic compositions. This has enabled construction of a two-stage model for the Pb-isotopic evolution of lunar silicate reservoirs, which necessitates the prolonged existence of high-μ reservoirs in order to explain the very radiogenic compositions of the samples. Further, once firm constraints on U and Pb partitioning behaviour are established, this model has the potential to help distinguish between conflicting estimates for the age of the Moon. Nonetheless, we are able to constrain the timing of a lunar mantle reservoir differentiation event at 4376 ± 18 Ma, which is consistent with that derived from the Sm-Nd and Lu-Hf isotopic systems, and is interpreted as an average estimate of the time at which the high-μ urKREEP reservoir was established and the Ferroan Anorthosite (FAN) suite was formed.

  6. Structural, petrological and geochronological analysis of the lithotypes from the Pien region (Parana State, Brazil) and adjacences; Analise estrutural, petrologica e geocronologica dos litotipos da Regiao de Pien (PR) e adjacencias

    Energy Technology Data Exchange (ETDEWEB)

    Harara, Ossama Mohamed


    The Pien area presents the major geotectonic domains separated by the Pien Shear Zone (PSZ). The northern one is the Rio Pien Granite-Mylonitic Suite composed by calc-alkaline granitoids of Neoproterozoic age. The southern domain is represented by the Amphibolite-Granulite where high grade metamorphism took place at the end of paleoproterozoic time. Considering the identified lithotypes, their geochemical affinity (particularly the Ti, Cr, Ni and REE content) and the geological context observed in the area, a geotectonical model of active continental margin related to subduction SSZ (Supra-Subduction Zone) is proposed. K-Ar on plagioclase from gabbronorites gave Neoproterozoic ages although Sm-Nd whole rock isochron yielded Paleoproterozoic ages. Based in geochemical data, it is proposed that the biotite gneiss and biotite-amphibole-gneiss which occur near the PSZ have a shoshonitic to high-K calc-alkaline features which are characteristic of active continental margins. K-Ar on biotite extracted from these rocks, gave Neoproterozoic ages. The available radiometric data for the Rio Pien mylonitic granitoids show that between 650-595 Ma the generation, deformation and cooling below the isotherm of 250 deg C occurred. On the other hand, the geochronological data for the Agudos do Sul Massif are in the 590-570 Ma interval showing its younger generation. The Sr{sup 87} / Sr{sup 86} initial ratios for both granitoids suggest more involvement of the continental crust in the origins of Agudos do Sul granitic Massif. The analyses of the entire set of the available data for the Pien area allows the suggestion of a geotectonic scenery related to the evolution of an active continental margin during the collages associated to the Brasiliano Cycle 201 refs., 130 figs., 6 tabs., 2 maps

  7. Geology and geochronology of Cardoso Island, in the southeastern coast of Sao Paulo State; Geologia e geocronologia da Ilha de Cardoso, sudeste do Estado de Sao Paulo

    Energy Technology Data Exchange (ETDEWEB)

    Weber, Werner


    This aim of work is the geological and geochronological study of rocks cropping out on Cardoso Island, on the southeastern coast of Sao Paulo States, close to be boundary with Parana State. The Island with an area of about 151 km{sup 2} is a protected area administered by the Forest Institute of Environment Secretariat of the State of Sao Paulo. It is mountanious, with a peak at 814 m, and is covered by dense Mata Atlantica vegetation. The terrains which compose the island are mainly an igneous complex with light grey leucocratic, inequigranular, medium - to coarse-grained syenites. The predominant Tres Irmaos Syenite (STI), composed of pyroxene, hornblende, and perthitic to mesoperthitic microcline, has a magmatic flow structures, and is cut by the Cambriu alkali-feldspar Granites (GC), which is pinkish grey, leucocratic and medium-grained. Geochemical analysis of STI and GC demonstrate their meta luminous alkaline nature and late-orogenic to an orogenic character. The geochronological results suggest that the bodies were formed between 620 and 570 My according to the U-Pb method in zircons, with cooling between 597 and 531 My (K-Ar in amphiboles). Whole rock Sm-Nd analysis yield T{sub DM} ages in the Meso and Paleoproterozoic (1.200 - 2.200 My). belt of low grade meta sedimentary rocks occurs in the northern part of the island. Quartz schist, quartz-mica schist and mica-quartz schist, often containing andaluzite and cordierite, predominate. The geochemical and geochronological data suggest that the sources of the metasediments were andesites of continental arc whose protolities separated from the mantle during the Paleoproterozoic, between 1.800 and 2.200 My. These metasediments probably continue on the continent in the Taquari region and extend southwards in narrow strips between the granitoids of the Paranagua Domain. Although quaternary deposits are expressive, they were not studied in details since they were not the objectives of this study. (author)

  8. Geochemistry and tectonostratigraphy of the basal allochthonous units of SW Iberia (Évora Massif, Portugal): Keys to the reconstruction of pre-Pangean paleogeography in southern Europe (United States)

    Fernández, Rubén Díez; Fuenlabrada, José Manuel; Chichorro, Martim; Pereira, M. Francisco; Sánchez-Martínez, Sonia; Silva, José B.; Arenas, Ricardo


    The basal allochthonous units of NW and SW Iberia are members of an intra-Gondwana suture zone that spreads across the Iberian Massif and was formed during the collision of Gondwana and Laurussia in the late Paleozoic. This suture zone is made of allochthonous terranes and is currently preserved as a tectonically dismembered ensemble. A multi-proxy analysis is applied to the basal allochthonous units of Iberia to test their affinity and potential usage for tracing a suture zone. A comparison of the lithostratigraphy, tectonometamorphic evolution, geochronology, and geochemical characteristics of the Ediacaran series of these units reveals striking affinities. They derive from rather similar immature sedimentary successions, deposited along the same continental margin, and in relation to a Cadomian magmatic arc. Sm-Nd systematics indicates that the isotopic sources are among the oldest of the Iberian Massif (ca. 2.15-1.5 Ga), suggesting a very strong contribution from the West African Craton. These Ediacaran series were affected by high-P and low- to medium-T metamorphism (blueschist to eclogite facies) during the Late Devonian (ca. 370 Ma). They occur below allochthonous ophiolitic sequences, and on top of autochthonous or parautochthonous domains lacking of high-P and low- to medium-T Devonian metamorphism, i.e., tectonically sandwiched between lithosphere-scale thrusts. The combination of all these characteristics makes these particular Ediacaran series different from the rest of the terranes of the Iberian Massif. Such singularity could be useful for tracing more occurrences of the same suture zone along the Variscan orogen, particularly in cases where its preservation and recognition may be cryptic. It also contributes to improve the paleogeographic reconstruction of the margin of Gondwana during the Ediacaran.

  9. Serpentinization Changes Nd, but not Hf Isotopes of Abyssal Peridotites (United States)

    Bizimis, M.; Frisby, C. P.; Mallick, S.


    Serpentinization of the oceanic lithosphere is a known sink for fluid mobile elements (B, Cl, Li, Sr, etc.), while high field strength elements (HFSE: e.g., Hf, Zr, Ti, Nb) are thought to be unaffected by it. In contrast, the fate of REE during serpentinization is equivocal. Correlations between REE and HFSE concentrations in abyssal peridotites suggest control by magmatic processes (Niu, 2004, J. Pet), while some LREE enrichments in serpentinized peridotites compared to their clinopyroxene (cpx) and Nd, Sr isotope data (Delacour et al., 2008, Chem. Geol.) imply seawater-derived REE addition to the mantle protolith (Paulick et al., 2006, Chem. Geol). To further constrain peridotite-seawater interaction during serpentinization we compare bulk rock and cpx Hf and Nd isotope data in partially (up to ~70%) serpentinized abyssal peridotites (9-16°E South West Indian Ridge). We also present a new method that improves yields in Hf, Nd and Pb separations from depleted (90% of Hf, Zr, Ti are retained in the residue. LA-ICPMS data shows that serpentine after olivine typically has higher LREE/HREE ratios than cpx, pronounced negative Ce anomalies, high U, Sr concentrations and low HFSE, unlike the coexisting cpx. These data are consistent with some seawater-derived LREE addition to peridotite during serpentinization, localized in the serpentine and other secondary phases, while cpx retains the magmatic value. This process will lower the Sm/Nd relative to Lu/Hf ratio in the peridotite and can lead to decoupled radiogenic Hf and unradiogenic Nd isotopes upon recycling and aging. Our data further testifies to the fidelity of Hf isotopes in tracing mantle processes, even in serpentinized rocks.

  10. An eastern Mediterranean analogue for the Late Palaeozoic evolution of the Pangaean suture zone in SW Iberia (United States)

    Brendan Murphy, J.; Braid, James A.; Quesada, Cecilio; Dahn, Dustin; Gladney, Evan; Dupuis, Nicolle


    It has long been recognized that the Late Paleozoic evolution of SW Iberia preserves a record of collision and suturing between Laurussia (South Portuguese Zone) and Gondwana (Ossa Morena Zone), which is one of the key events in the development of the Variscan orogen and the amalgamation of Pangea. The suture zone (Pulo do Lobo Zone) is classically considered to be an accretionary complex and is characterized by an assemblage of greenschist facies, polydeformed and imbricated meta-sedimentary rocks, mélanges, and mafic complexes. However recent work has shown some of the metasedimentary rocks and mélange were likely derived from neither the upper or lower plates. Mafic complexes in the mélange have NMORB compositions, highly depleted Sm-Nd isotopic signatures and geochronological data imply that their protoliths probably formed between ca. 350 and 340 Ma. Geochronological data also imply that components of the mafic mélange contain a paucity of ancient continental detritus. The Pulo do Lobo Zone was also intruded by ca. 360-310 Ma composite plutons and related dykes ranging from gabbro to granite in composition. The oldest phases of these intrusions are syn- to late-tectonic with respect to the deformation. Taken together these recent observations suggest that much of the tectonic evolution of the Pulo do Lobo suture zone post-dates the onset of collisional tectonics elsewhere in the Variscan orogen, and is broadly analogous to the complex Cenozoic tectonic evolution of the eastern Mediterranean oceanic tracts relative to the ongoing collision between the African, Eurasian and Arabian plates.

  11. How Depleted is the MORB mantle? (United States)

    Hofmann, A. W.; Hart, S. R.


    Knowledge of the degree of mantle depletion of highly incompatible elements is critically important for assessing Earth's internal heat production and Urey number. Current views of the degree of MORB source depletion are dominated by Salters and Stracke (2004), and Workman and Hart (2005). The first is based on an assessment of average MORB compositions, whereas the second considers trace element data of oceanic peridotites. Both require an independent determination of one absolute concentration, Lu (Salters & Stracke), or Nd (Workman & Hart). Both use parent-daughter ratios Lu/Hf, Sm/Nd, and Rb/Sr calculated from MORB isotopes combined with continental-crust extraction models, as well as "canonical" trace element ratios, to boot-strap the full range of trace element abundances. We show that the single most important factor in determining the ultimate degree of incompatible element depletion in the MORB source lies in the assumptions about the timing of continent extraction, exemplified by continuous extraction versus simple two-stage models. Continued crust extraction generates additional, recent mantle depletion, without affecting the isotopic composition of the residual mantle significantly. Previous emphasis on chemical compositions of MORB and/or peridotites has tended to obscure this. We will explore the effect of different continent extraction models on the degree of U, Th, and K depletion in the MORB source. Given the uncertainties of the two most popular models, the uncertainties of U and Th in DMM are at least ±50%, and this impacts the constraints on the terrestrial Urey ratio. Salters, F.J.M. and Stracke, A., 2004, Geochem. Geophys. Geosyst. 5, Q05004. Workman, R.K. and Hart, S.R., 2005, EPSL 231, 53-72.

  12. Geology, petrology, U-Pb (shrimp geochronology of the Morrinhos granite -Paraguá terrane, SW Amazonian craton: implications for the magmatic evolution of the San Ignácio orogeny

    Directory of Open Access Journals (Sweden)

    Ohana França

    Full Text Available Morrinhos granite is a batholith body that is slightly elongated in the NNW direction and approximately 1,140 km2 long; it is located in the municipality of Vila Bela da Santíssima Trindade of the state of Mato Grosso, Brazil, in the Paraguá Terrane, Rondonian-San Ignácio Province, in the SW portion of the Amazonian Craton. This intrusion displays a compositional variation from tonalite to monzogranite, has a medium to coarse inequigranular texture and is locally porphyritic; biotite is the predominant mafic in one of the facies, and hornblende is predominant in the other, with both metamorphosed into the greenschist facies. The studied rocks characterize an intermediate to acidic sequence that was formed by a subalkaline magmatism; the series is alkali-calcic to metaluminous to slightly peraluminous, and the rocks evolved through fractioned crystallization mechanisms. The structural data show two deformation phases represented by penetrative foliation (S1 and open folds (D2, and both phases were most likely related to the San Ignácio Orogeny. The geochronological (U-Pb SHRIMP and isotopic (Sm-Nd investigations of these rocks indicated a crystallization age of 1350 ± 12 Ma, TDMof approximately 1.77 Ga and εNd(1.35with a negative value of -2.57, suggesting that their generation was related to a partial melting process of a Paleoproterozoic (Statherian continental crust. The results herein indicate that the Morrinhos granite was generated in a continental magmatic arc in a late- to post-orogenic stage of the San Ignácio Orogeny, and it can be recognized as belonging to the Pensamiento Intrusive Suite.

  13. P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan (United States)

    Tan, Zhou; Agard, Philippe; Gao, Jun; John, Timm; Li, JiLei; Jiang, Tuo; Bayet, Léa; Wang, XinShui; Zhang, Xi


    The Chinese Southwestern Tianshan high- to ultra-high pressure low temperature (HP-UHP/LT) metamorphic belt exhibits well-preserved mafic layers, tectonic blocks/slices and boudins of different sizes and lithology embedded within dominant meta-volcanosedimentary rocks. Despite a wealth of previous studies on UHP relicts, P-T path estimates and age constraints for metamorphism, controversies still exist on P-T-t assessments and regional exhumation patterns (i.e., tectonic mélange versus internally coherent ;sub-belt; model). This study focuses on a group of coesite-bearing eclogite samples from a thick ( 5 m) layered metabasalt outcrop in order to unravel its detailed tectono-metamorphic evolution through space and time (both prograde, peak and exhumation). Using SIMS zircon U-Pb and oxygen isotope analyses, TIMS Sm-Nd multi-point isochron dating, in situ laser-ICP-MS trace-element analyses, classical thermobarometry and thermodynamic modeling, we link the multistage zircon growth to garnet growth and reconstruct a detailed P-T-time-isotopic evolution history for this UHP tectonic slice: from UHP peak burial 2.95 ± 0.2 GPa, 510 ± 20 °C around 318.0 ± 2.3 Ma to HP peak metamorphism 2.45 ± 0.2 GPa, 540 ± 20 °C at 316.8 ± 0.8 Ma, then, with eclogite-facies deformation 2.0 ± 0.15 GPa, 525 ± 25 °C at 312 ± 2.5 Ma, exhumed to near surface within ca. 303 to ca. 280 Ma. Our P-T-time-isotopic results combined with the compilation of regional radiometric data and P-T estimates notably point to the existence of a short-lived period of rock detachment and exhumation (< 10 Ma, i.e. at ca. 315 ± 5 Ma) with respect to subduction duration.

  14. Cambro-Ordovician magmatism in the Araçuaí Belt (SE Brazil): Snapshots from a post-collisional event (United States)

    De Campos, Cristina P.; de Medeiros, Silvia R.; Mendes, Julio C.; Pedrosa-Soares, Antonio C.; Dussin, Ivo; Ludka, Isabel P.; Dantas, Elton L.


    The focus of the present work is the rebound of the magmatism at the late stages of orogenic collapse in the Araçuaí Belt, in Brazil. At the end of the orogen bimodal inversely zoned plutons were emplaced along a tectonic corridor following the Atlantic coast of Brazil. This event culminates around 500 Ma. We review geology, petrography, geochemistry and geochronology of these plutonic structures in the region of Espírito Santo. New geochemical modeling of trace element data together with new whole rock Sm-Nd and Rb-Sr isotopic data depict a gradual process of mantle contamination during different stages of the orogen. In the post-orogenic stage contamination reaches extreme values. Basic rocks reach εNd(0.5Ga) values below -10. Gabbros to peridotites are more enriched in Ba, Zr, LREE and Sr than the surrounding metasediments. Four new U-Pb data sets from determinations in zircon and monazite crystals, (central northern part of the belt) confirm peak magma production around 500 ± 15 Ma, ranging up to 525 ± 3 Ma in one of the structures. Based on the pictured data, we discuss the significance of this magmatism and present a possible model: a process of gradational delamination of the subcontinental lithospheric mantle and adjacent deep continental crust through underplating. As a consequence, an already enriched mantle was dramatically further contaminated. At the end of this event the intrusion of alkaline melts, with less negative εNd (-5) and further enrichment in incompatible elements, point towards a new input of deeper juvenile mantle magma. Our data suggest the possible onset of a hotspot due to the destabilization of the asthenospheric mantle after orogenic collapse.

  15. Provenance and sedimentary analysis of the basal portion of the Bambuí Group at Arcos (MG

    Directory of Open Access Journals (Sweden)

    Matheus Kuchenbecker


    Full Text Available The origin and evolution of Bambuí Basin has been a matter of debate, in much intensified by the recent exploratory efforts carried out by public and private companies looking for natural gas. In the southeastern portion of the basin there are rare opportunities to access the contact between the sedimentary rocks and its basement, whose characteristics are crucial to understanding the processes of basin installation and the early sedimentation. The analysis of drill cores allowed us to describe the lowermost Bambuí Group in Arcos (MG region, including its basement. The sampled section displays as basement an archean granodiorite (ca. 2.8 – 2.9 Ga, fractured at the time of sedimentation. The Bambuí Group basal unit is dm-thick, massive lodgment tillite. Grains of zircon separated from the tillite matrix were dated and show a main age peak at ca. 2.8 Ga, indicating provenance from the own basement. On the tillite rests an impure limestone that passes gradually to a muddy unit, in a retrogradational filling trend. Terrigenous fragments in the impure limestone suggests that the basement has continued to be a source of sediments in the bottom of the section. The pelitic rocks that occurs to the top has a litochemical signature compatible with acidic source rocks, and shows Sm-Nd model ages of 1.7 Ga. These data suggests that rocks from the Brasília Belt have acted as a source for the pelitic rocks, supporting the interpretation of a foreland set for the basin.

  16. Geochemistry and Re-Os geochronology of the organic-rich sedimentary rocks in the Jingtieshan Fe-Cu deposit, North Qilian Mountains, NW China (United States)

    Yang, Xiuqing; Zhang, Zuoheng; Li, Chao; Duan, Shigang; Jiang, Zongsheng


    The Jingtieshan Group in the North Qilian Mountains, NW China, is dominantly composed of banded iron formations (BIFs), copper deposits and organic-rich sedimentary rocks (ORS, carbonaceous phyllite). X-ray diffraction analysis of the ORS shows the mineral assemblage to be quartz + clay minerals. The total organic carbon contents show a range of 0.44-1.72%. Here we present the results of the geochemistry and Re-Os geochronology of the ORS from the Jingtieshan Group. The high values of Chemical Index of Alteration (CIA), Chemical Index of Weathering (CIW), Plagioclase Index of Alteration (PIA), and Th/U ratio, indicate intense weathering. The Al2O3/TiO2, Zr/Sc, Th/Sc, La/Th ratios, high rare earth elements abundances, light rare earth elements enrichment (normalized to chondrite), and distinctly negative Eu anomalies, suggest that the Jingtieshan Group ORS were derived mainly from felsic volcanic units. The new Re-Os isochron age of 1308 ± 100 Ma (2σ, n = 6, MSWD = 23) broadly overlap with the previous published ages determined using Sm-Nd and U-Pb isotope systems. The new age represents the depositional age of the Jingtieshan Group, as well that of BIF in the Jingtieshan area. Furthermore, the initial 187Os/188Os ratios (0.44 ± 0.07) indicate that the Os in the seawater was dominantly derived from hydrothermal fluids (∼75%). The Ce anomaly (Ce/Ce∗ = 0.95-1.00) and V/(V + Ni) ratios (0.71-0.86), as well as the lack of enrichment in redox-sensitive trace elements such as U, V, Zn, Pb, Cu, Ni, Cr, Co and Mn, together with the presence of overlying BIF, suggest that the Jingtieshan area represents a ferruginous deep-water succession. This, and intense submarine hydrothermal activities contributed to the deposition of the Jingtieshan BIF.

  17. Thermochronology and geochemistry of the Pan-African basement below the Sab'atayn Basin, Yemen (United States)

    Veeningen, Resi; Rice, A. Hugh N.; Schneider, David A.; Grasemann, Bernhard


    Three important lithologies occur in two drill wells from the Pan-African basement underlying the Mesozoic Sab'atayn Basin, in a previously undocumented area of the Pan-African, 83 and 90 km NE of known exposures in Yemen. Cores from well 1 include amphibolite, with basaltic to andesitic compositions, affected by crustal contamination during emplacement into a thickened crust. Deeper in the well, an unfoliated dark red monzogranite has a U-Pb zircon age of 628.8 ± 3.1 Ma and a Rb-Sr biotite cooling age of 591.6 ± 5.8 Ma (∼300 °C). Regional constraints suggest emplacement in a transitional tectonic setting with compressional terrane amalgamation followed by extensional collapse. Sm-Nd isotope analysis yields a TDM model age of 1.24 Ga with negative εNd values, suggesting the monzogranite is part of the Al Bayda island arc terrane. Cores from well 2 contains a weakly deformed, massive (unbedded) medium grey meta-arkose exhibiting essentially no geochemical signature of weathering and with an almost pure dacitic composition. This rock may have been directly derived from an (extrusive) granitoid that was emplaced prior to, or during terrane amalgamation. A (U-Th-Sm)/He zircon age of 156 ± 14 Ma constrains the time of basement cooling to ∼180 °C, synchronous with basin formation. These lithologies provide new insights in the development of the Pan-African basement of Yemen, extending our knowledge of the nearby surface geology to the subsurface.

  18. Lead Isotopes in Olivine-Phyric Shergottite Tissint: Implications for the Geochemical Evolution of the Shergottite Source Mantle (United States)

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


    Geochemically-depleted shergottites are basaltic rocks derived from a martian mantle source reservoir. Geochemical evolution of the martian mantle has been investigated mainly based on the Rb-Sr, Sm-Nd, and Lu-Hf isotope systematics of the shergottites [1]. Although potentially informative, U-Th- Pb isotope systematics have been limited because of difficulties in interpreting the analyses of depleted meteorite samples that are more susceptible to the effects of near-surface processes and terrestrial contamination. This study conducts a 5-step sequential acid leaching experiment of the first witnessed fall of the geochemically-depleted olivinephyric shergottite Tissint to minimize the effect of low temperature distrubence. Trace element analyses of the Tissint acid residue (mostly pyroxene) indicate that Pb isotope compositions of the residue do not contain either a martian surface or terrestrial component, but represent the Tissint magma source [2]. The residue has relatively unradiogenic initial Pb isotopic compositions (e.g., 206Pb/204Pb = 10.8136) that fall within the Pb isotope space of other geochemically-depleted shergottites. An initial µ-value (238U/204Pb = 1.5) of Tissint at the time of crystallization (472 Ma [3]) is similar to a time-integrated mu- value (1.72 at 472 Ma) of the Tissint source mantle calculated based on the two-stage mantle evolution model [1]. On the other hand, the other geochemically-depleted shergottites (e.g., QUE 94201 [4]) have initial µ-values of their parental magmas distinctly lower than those of their modeled source mantle. These results suggest that only Tissint potentially reflects the geochemical signature of the shergottite mantle source that originated from cumulates of the martian magma ocean

  19. Lead in Martian Meteorites-- Observations and Inconsistencies: I. Chassigny (United States)

    Jones, J. H.; Simon, J. I.; Usui, T.


    The history of Pb isotope analyses of the martian meteorites (SNC) and their interpretations is laden with difficulties. Two different analytical groups have interpreted their ancient (= 4 Ga) shergottite Pb ages as primary [1-5]. A Nakhla age of approximately 4.3 Ga has been interpreted to be primary as well [2]. This is in stark contrast to the young (= 1.4 Ga) crystallization ages defined by the Rb-Sr, Sm-Nd, Lu-Hf, and KAr systems [6]. Possibly, a better interpretation for the ancient Pb ages is that they reflect the formation times of the various SNC source regions [7]. A difficulty in dealing with Pb is that terrestrial contamination is ubiquitous, unlike the other chronometer systems noted above. This issue is complicated by the fact that radioactive decay causes localized mineral damage. So washing and leaching to remove Pb contamination tends to remove in situ radiogenic Pb. This issue is further compounded because U and Th are often concentrated in phosphates and other minor phases, so the leaching process tends to remove these, especially phosphates. Another difficulty is that it is not clear whether the observed Pb isotopic variation in leachates, residues, and ion-microprobe analyses is due to terrestrial or to indigenous martian Pb contamination [e.g., 8]. A third difficulty is that the shergottites on the one hand, and the nakhlites and chassignites on the other, appear to have come from separate source regions with different chemical compositions [e.g., 7]. Thus, it is expected that their Pb isotopic characteristics would be different. And even if all these meteorite types came from the same source region, their igneous ages differ considerably. The nakhlites and chassignites are 1.4 Ga and the shergottites are = 600 Ma [e.g., 6]. This age difference alone should assure that the two distinct SNC groups have differing Pb isotopic signatures.

  20. Late Neoproterozoic to Carboniferous genesis of A-type magmas in Avalonia of northern Nova Scotia: repeated partial melting of anhydrous lower crust in contrasting tectonic environments (United States)

    Murphy, J. Brendan; Shellnutt, J. Gregory; Collins, William J.


    Avalonian rocks in northern mainland Nova Scotia are characterized by voluminous 640-600 Ma calc-alkalic to tholeiitic mafic to felsic magmas produced in a volcanic arc. However, after the cessation of arc activity, repeated episodes of felsic magmatism between ca. 580 Ma and 350 Ma are dominated by A-type geochemical characteristics. Sm-Nd isotopic data, combined with zircon saturation temperature estimates, indicate that these magmas were formed by high temperature (800-1050 °C) melting of the same anhydrous crustal source. Regional tectonic considerations indicate that A-type felsic magmatism was produced (1) at 580 Ma in a San Andreas-type strike slip setting, (2) at 495 Ma as Avalonia rifted off Gondwana, (3) at 465 and 455 in an ensialic island arc environment and (4) at 360-350 Ma during post-collisional, intra-continental strike-slip activity as Avalonia was translated dextrally along the Laurentian margin. These results attest to the importance of crustal source, rather than tectonic setting, in the generation of these A-type magmas and are an example of how additional insights are provided by comparing the geochemical and isotopic characteristics of igneous suites of different ages within the same terrane. They also suggest that the shallow crustal rocks in northern mainland Nova Scotia were not significantly detached from their lower crustal source between ca. 620 Ma and 350 Ma, a time interval that includes the separation of Avalonia from Gondwana, its drift and accretion to Laurentia as well as post-accretionary strike-slip displacement.

  1. Multi-mineral geochronology: insights into crustal behaviour during exhumation of an orogenic root (United States)

    LaFlamme, Crystal; McFarlane, Christopher R. M.; Fisher, Christopher M.; Kirkland, Christopher L.


    Under rare conditions, reworked cratons and their margins preserve the orogenic roots of ancient mountain-building events. However, based on the preservation of high-temperature ( 800 °C), middle and lower crustal metamorphic assemblages, present day exposure of these terrains is not simply a result of protracted denudation, but also must reflect a multifaceted exhumational history. In situ analysis within thin section preserves the textural setting of target minerals that can be used as thermochronometers such as U-Pb of zircon, monazite, titanite and apatite, and Sm-Nd of apatite. In situ analyses of these chronometers has the potential to provide critical timing constraints on exhumation processes related to decompression, melting and cooling across large metamorphic terrains. The Repulse Bay block of the Rae craton preserves a large composite amphibolite-granulite area (50,000 km2) of Archean orthogneiss, migmatite, and slivers of Proterozoic metasediments that underwent high-grade metamorphism, partial melting, ductile flow and finally exhumation during the Paleoproterozoic Trans-Hudson Orogeny. The granulite domain preserves dry granitoid assemblages, whereas the amphibolite domain is dominated by hydrated migmatites and orthogneiss. Metasediments occur in both domains and preserve mineral assemblages that are consistent with having undergone tectonometamorphic conditions of 9 kbar/800 °C during burial. U-Pb thermochronometers document identical cooling histories of the granulite and amphibolite domains through the U-Pb closure temperatures of titanite ( 650 °C) and apatite ( 450 °C). This suggests that melt-loss from the underlying granulite domain and melt-gain to the amphibolite domain prior to cooling through 650 °C are a controlling factor of the metamorphic assemblages across the composite granulite-amphibolite terrains such as the Repulse Bay block, rather than significant differences in burial history, cooling history, and/or reorganization of

  2. Isotopic Ages of the Carbonatitic Volcanic Rocks in the Kunyang Rift Zone in Central Yunnan,China

    Institute of Scientific and Technical Information of China (English)

    ZHANG Yongbei; WANG Guilan; NIE Jianfeng; ZHAO Chongshun; XU Chengyan; QIU Jiaxiang; Wang Hao


    The Mesoproterozoic Kunyang rift, which is located on the western margin of the Yangtze platform and the southern section of the Kangdian axis, is a rare massive Precambrian iron-copper polymetallic mineralization zone in China. The Mesoproterozoic Wulu (Wuding(Lufeng) basin in the middle of the rift is an elliptic basin controlled by a ring fracture system. Moreover, volcanic activities in the basin display zonation of an outer ring, a middle ring and an inner ring with carbonatitic volcanic rocks and sub-volcanic dykes discovered in the outer and middle rings. The Sm-Nd isochron ages have been determined for the outer-ring carbonatitic lavas (1685 Ma) and basaltic porphyrite of the radiating dyke swarm (1645 Ma) and the Rb-Sr isochron ages for the out-ring carbonatitic lavas (893 Ma) and the middle-ring dykes (1048 Ma). In combination of the U-Pb concordant ages of zircon (1743 Ma) in trachy-andesite of the corresponding period and stratum (1569 Ma) of the Etouchang Formation, as well as the Rb-Sr isochron age (1024 Ma) and K-Ar age (1186 Ma) of the dykes in the middle ring, the age of carbonatites in the basin is preliminarily determined. It is ensured that all of these carbonatites were formed in the Mesoproterozoic period, whereby two stages could be identified as follows: in the first stage, carbonatitic volcanic groups, such as lavas, pyroclastic rocks and volcaniclastic sedimentary rocks, were formed in the outer ring; in the second stage, carbonatitic breccias and dykes appeared in the middle ring. The metamorphic age of the carbonatitic lavas in the outer ring was determined to be concurrent with the end of the first stage of the Neoproterozoic period, corresponding to the Jinning movement in central Yunnan.

  3. The Caldas Novas dome, central Brazil: structural evolution and implications for the evolution of the Neoproterozoic Brası´lia belt (United States)

    D'el-Rey Silva, Luiz José Homem; Wolf Klein, Percy Boris; Walde, Detlef Hans-Gert


    The Caldas Novas dome (Goiaás state, central Brazil) lies in the southern segment of the Neoproterozoic Brası´lia belt (center of the Tocantins Province) between the Goiás magmatic arc and the margin of the ancient São Francisco plate. The core of the dome comprises rocks of the Meso-Neoproterozoic Paranoá group (passive margin psamitic-pelitic sediments and subgreenschist facies) covered by a nappe of the Neoproterozoic Araxá group (backarc basin pelitic-psamitic sediments and volcanics of greenschist facies, bitotite zone). Hot underground waters that emerge along fractures in the Paranoá quartzite and wells in the Araxá schist have made the Caldas Novas dome an international tourist attraction. A recent detailed structural analysis demonstrates that the dome area was affected by a D 1-D 3 Brasiliano cycle progressive deformation in the ˜750-600 Ma interval (published U-Pb and Sm-Nd data). During event D 1, a pervasive layer-parallel foliation developed coeval the regional metamorphism. Event D 2 (intense F 2 isoclinal folding) was responsible for the emplacement of the nappe. D 1 and D 2 record a regime of simple shear (top-to-SE relative regional movement) due to a WNW-ESE subhorizontal compression ( σ1). Event D 3 records a WSW-ENE compression, during which the dome rose as a large-scale F 3 fold, possibly associated with a duplex structure at depth. During the dome's uplift, the layers slid back and down in all directions, giving way to gravity-slide folds and an extensional crenulation cleavage. A set of brittle fractures and quartz veins constitutes the record of a late-stage D 4 event important for understanding the thermal water reservoir.

  4. Geochemical characteristics of pyrite in Duolanasayi gold deposit, Xinjiang

    Institute of Scientific and Technical Information of China (English)

    CHEN Guodong; XIAO Huiliang; WANG Henian; ZHOU Jiyuan


    The Duolanasayi gold deposit, 60 km NW of Habahe County, Xinjiang Uygur Autonomous Region, is a mid-large-scale gold deposit controlled by brittle-ductile shearing, and superimposed by albitite veins and late-stage magma hydrothermal solutions. There are four types of pyrite, which are contained in the light metamorphosed rocks (limestone, siltstone), altered-mineralized rocks (chlorite-schist, altered albite-granite, mineralized phyllite), quartz veins and carbonatite veinlets. The pyrite is the most common ore mineral. The Au-barren pyrite is present mainly in a simple form and gold-bearing pyrite is present mainly in a composite form. From the top downwards, the pyrite varies in crystal form from {100} and {210}+{100} to {210}+{100}+{111} to {100}+{111}. Geochemical studies indicate that the molecular contents of pyrite range from Fe1.057S2 to Fe0.941S2. Gold positively correlates with Mn, Sr, Zn, Te, Pb, Ba and Ag. There are four groups of trace elements: Fe-Cu-Sr-Ag, Au-Te-Co, As-Pb-Zn and Mn-V-Ti-Ba-Ni-Cr in pyrite. The REE characteristics show that the total amount of REE (ΣREE) ranges from 32.35×10 -6 to 132.18×10 -6; LREE/HREE, 4.466-9.142; (La/Yb)N, 3.719-11.133; (Eu/Sm)N, 0.553-1.656; (Sm/Nd)N, 0.602-0.717; La/Yb, 6.26-18.75; δEu, 0.628-2.309; δCe, 0.308-0.816. Sulfur isotopic compositions (δ 34S=-2.46‰--7.02‰) suggest that the sulfur associated with gold mineralization was derived from the upper mantle or lower crust.

  5. Zircon LA-ICP-MS U-Pb dating and Sr-Nd isotope study of the Guposhan granite complex, Guangxi, China

    Institute of Scientific and Technical Information of China (English)

    GU Shengyan; HUA Renmin; QI Huawen


    Zircon U-Pb dating by the LA-ICP-MS method was applied to determining the ages of different units of the Guposhan granite complex, among which the East Guposhan unit is 160.8±1.6 Ma, the West Guposhan unit is 165.0±1.9 Ma, and the Lisong unit is 163.0±1.3 Ma in age. Much similarity in ages of the three units has thus proved that the whole Guposhan granite complex was formed in the same period of time. They were the products of large-scale granitic magmatism through crust-remelting in the first stage of the Middle Yanshanian in South China. However, the three units have differences both in petrology and in geochemistry. Besides the differences in major, trace and rare-earth elements, they are distinct in their Rb-Sr and Sm-Nd isotopic compositions. The East Guposhan unit and Lisong unit and its enclaves have a similar (87Sr/86Sr)i value of 0.7064 with an average of εNd(t)=-3.03, indicating that more mantle material was evolved in the magma derivation; whereas the West Guposhan unit has a higher (87Sr/86Sr)i value of 0.7173 but a lower εNd(t) value of -5.00, and is characterized by strong negative Eu anomalies and higher Rb/Sr ratios, suggesting that its source materials were composed of relatively old crust components and new mantle-derived components. In addition, an inherited zircon grain in the East Guposhan unit (GP-1) yielded a 206Pb/238U age of 806.4 Ma, which is similar to the ages of the Jiulin cordierite granite in northern Jiangxi and of the Yinqiao migmatic granite in Guangxi in the HZH granite zone. All this may provide new evidence for Late Proterozoic magmatism in the HZH granite zone.

  6. A metasomatic mechanism for the formation of Earth's earliest evolved crust (United States)

    Baker, Don R.; Sofonio, Kassandra


    Following giant impacts the early Hadean Earth was shrouded in a steam atmosphere for durations on the order of 1 Ma. In order to investigate the potential of this atmosphere to fractionate major elements between various silicate reservoirs and influence a planet's geochemical evolution, we performed experiments simulating the interaction of a post-giant-impact steam atmosphere with a bulk silicate Earth (BSE) composition. Our experiments indicate that the composition of the solute in a water-rich atmosphere at 10 MPa and ∼727 °C is remarkably similar to that of Earth's modern continental crust and would constitute up to 10% of the solution mass. This solute composition is similar to solute compositions previously measured at higher pressures, but distinct from those of near-solidus peridotite melts. Mass balance calculations based upon the hypothesis that Earth's initial water concentration was similar to that in CI carbonaceous chondrites, and that degassing and metasomatism produced the BSE, indicate that metasomatism could produce from 10 to 300% of the mass of the modern crust. If instead the amount of metasomatism is estimated by the difference between the water concentration in the BSE and in the depleted upper mantle, then a mass of up to approximately 4% of the current crust could be produced by metasomatism. Using results of earlier research we find that the solute is expected to have a smaller Sm/Nd ratio than the residual BSE, and if the solute was formed early in Earth's history its Nd isotopic signatures would be highly enriched. Although we cannot be certain that the metasomatic process created a significant fraction of Earth's crust in the early Hadean, our research indicates that it has the potential to form crustal nuclei and possibly was responsible for the production of incompatible-element enriched reservoirs in the early Earth, as seen in the isotopic signatures of Archean rocks.

  7. Synthesis and photocatalytic property of layered perovskite tantalates, RbLnTa{sub 2}O{sub 7} (Ln = La, Pr, Nd, and Sm)

    Energy Technology Data Exchange (ETDEWEB)

    Machida, Masato; Yabunaka, Junichi; Kijima, Tsuyoshi


    The first example of an active layered tantalate photocatalyst containing partly filled lanthanide 4f shell is reported. A single phase of layered perovskite tantalates, RbLnTa{sub 2}O{sub 7}, could be obtained with Ln = La, Pr, Nd, and Sm; the ionic radii of these trivalent cations are required to be larger than 0.126 nm for constructing a perovskite slab. Under UV irradiation from a high-pressure Hg lamp, these layered tantalates demonstrated the photocatalytic activity for water splitting into stoichiometric H{sub 2}/O{sub 2} mixtures even without loading metal catalysts. The rates of H{sub 2} and O{sub 2} evolutions were found to be strongly dependent on the lanthanoids, increasing in the sequence of La {approx} Pr << Sm < Nd. The maximum rate of H{sub 2} evolution observed over RbNdTa{sub 2}O{sub 7} reached 47.0 {micro}mol/h. The absorption spectrum of RbNdTa{sub 2}O{sub 7} consists of the internal 4f transitions in the visible region and a broad band overlapping the band-gap transition in the UV region. The latter band indicates that a possible excitation process including the partly filled 4f shell plays a key role in photocatalytic reactions. Loading 0.5 wt % Ni onto RbNdTa{sub 2}O{sub 7} by simple impregnation significantly improved H{sub 2} evolution (117.2 {micro}mol/h).

  8. Primitive Solar System materials and Earth share a common initial 142Nd abundance (United States)

    Bouvier, A.; Boyet, M.


    The early evolution of planetesimals and planets can be constrained using variations in the abundance of neodymium-142 (142Nd), which arise from the initial distribution of 142Nd within the protoplanetary disk and the radioactive decay of the short-lived samarium-146 isotope (146Sm). The apparent offset in 142Nd abundance found previously between chondritic meteorites and Earth has been interpreted either as a possible consequence of nucleosynthetic variations within the protoplanetary disk or as a function of the differentiation of Earth very early in its history. Here we report high-precision Sm and Nd stable and radiogenic isotopic compositions of four calcium-aluminium-rich refractory inclusions (CAIs) from three CV-type carbonaceous chondrites, and of three whole-rock samples of unequilibrated enstatite chondrites. The CAIs, which are the first solids formed by condensation from the nebular gas, provide the best constraints for the isotopic evolution of the early Solar System. Using the mineral isochron method for individual CAIs, we find that CAIs without isotopic anomalies in Nd compared to the terrestrial composition share a 146Sm/144Sm-142Nd/144Nd isotopic evolution with Earth. The average 142Nd/144Nd composition for pristine enstatite chondrites that we calculate coincides with that of the accessible silicate layers of Earth. This relationship between CAIs, enstatite chondrites and Earth can only be a result of Earth having inherited the same initial abundance of 142Nd and chondritic proportions of Sm and Nd. Consequently, 142Nd isotopic heterogeneities found in other CAIs and among chondrite groups may arise from extrasolar grains that were present in the disk and incorporated in different proportions into these planetary objects. Our finding supports a chondritic Sm/Nd ratio for the bulk silicate Earth and, as a consequence, chondritic abundances for other refractory elements. It also removes the need for a hidden reservoir or for collisional erosion

  9. Lanthanide–lanthanide and lanthanide–defect interactions in co-doped ceria revealed by luminescence spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Avram, Daniel; Gheorghe, Cristina [National Institute for Laser, Plasma and Radiation Physics, P.O. Box MG-36, RO 76900 Bucharest-Magurele (Romania); Rotaru, Codruta; Cojocaru, Bogdan; Florea, Mihaela; Parvulescu, Vasile [University of Bucharest, Department of Chemical Technology and Catalysis, 4–12 Regina Elisabeta Bvd., Bucharest (Romania); Tiseanu, Carmen, E-mail: [National Institute for Laser, Plasma and Radiation Physics, P.O. Box MG-36, RO 76900 Bucharest-Magurele (Romania)


    Highlights: • (Sm, Nd) and (Sm, Eu) co-doped CeO{sub 2} are investigated by luminescence spectroscopy. • Local structure at Sm sites is not changed by Nd or Eu co-dopant. • Sm is not involved in non-radiative energy transfer to Nd or Eu co-dopant. • The excitation mode of perturbed Eu centre is modified by Sm co-dopant. - Abstract: Here, we present a first study on the local structure properties, lanthanide–lanthanide and lanthanide–defect interactions in lanthanide (Sm{sup 3+}/Nd{sup 3+} and Sm{sup 3+}/Eu{sup 3+}) co-doped CeO{sub 2} nanoparticles by use of luminescence spectroscopy. By comparing the emission/excitation spectra and decays measured with the single doped and co-doped ceria, it is established that the local structure at Sm{sup 3+} sites is not affected by the presence of the Nd{sup 3+} or Eu{sup 3+} co-dopant irrespective of concentration. The results suggest that the excess of oxygen vacancies generated by the co-dopant is not associated with Sm{sup 3+}, being more probably associated with the Nd{sup 3+}/Eu{sup 3+} or/and Ce{sup 4+} cations. It is also observed that Sm{sup 3+} is not involved in significant non-radiative energy transfer to Nd{sup 3+} or Eu{sup 3+} while the relative strong shortening of Nd{sup 3+} luminescence decay with concentration is most probably related to cross-relaxation in Nd{sup 3+}–Nd{sup 3+} pairs.

  10. Late Archaean mantle metasomatism below eastern Indian craton: Evidence from trace elements, REE geochemistry and Sr-Nd-O isotope systematics of ultramafic dykes

    Indian Academy of Sciences (India)

    Abhijit Roy; A Sarkar; S Jeyakumar; S K Aggrawal; M Ebihara; H Satoh


    Trace, rare earth elements (REE), Rb-Sr, Sm-Nd and O isotope studies have been carried out on ultramafic (harzburgite and lherzolite) dykes belonging to the newer dolerite dyke swarms of eastern Indian craton. The dyke swarms were earlier considered to be the youngest mafic magmatic activity in this region having ages not older than middle to late Proterozoic. The study indicates that the ultramafic members of these swarms are in fact of late Archaean age (Rb-Sr isochron age 2613 ± 177 Ma, Sri ∼0.702 ± 0.004) which attests that out of all the cratonic blocks of India, eastern Indian craton experienced earliest stabilization event. Primitive mantle normalized trace element plots of these dykes display enrichment in large ion lithophile elements (LILE), pronounced Ba, Nb and Sr depletions but very high concentrations of Cr and Ni. Chondrite normalised REE plots exhibit light REE (LREE) enrichment with nearly flat heavy REE (HREE; ( HREE)N ∼ 2-3 times chondrite, (Gd/Yb)N∼1). The Nd(t) values vary from +1.23 to −3.27 whereas 18O values vary from +3.16‰ to +5.29‰ (average +3.97‰ ± 0.75‰) which is lighter than the average mantle value. Isotopic, trace and REE data together indicate that during 2.6 Ga the nearly primitive mantle below the eastern Indian Craton was metasomatised by the fluid (±silicate melt) coming out from the subducting early crust resulting in LILE and LREE enriched, Nb depleted, variable Nd, low Sri(0.702) and low 18O bearing EMI type mantle. Magmatic blobs of this metasomatised mantle were subsequently emplaced in deeper levels of the granitic crust which possibly originated due to the same thermal pulse.

  11. Elemental geochemistry and Nd isotopic characteristics of the metasedimentary rocks from the metamorphic belt in central Jiangxi: Provenance and tectonically environmental constraints

    Institute of Scientific and Technical Information of China (English)

    HU Gongren; LIU Congqiang; ZHANG Bangtong; TANG Hongfeng; YU Ruilian


    The metamorphic belt in central Jiangxi, located in the compound terrain within the Cathaysia, Yangtze Block and Caledonian fold zone of South China, is composed dominantly of meta-argillo-arenaceous rocks, with minor amphibolite. These rocks underwent amphibolite-facies metamorphism. The meta-argillo-arenaceous rocks show large variations in major element composition, but have similar REE patterns and trace element composition, incompatible element and LIE enrichments [ high Th/Sc (0.57-3.59) , La/Sc ( 1.46 - 12.4), La/Yb (5.84 - 19.0) ] and variable Th/U ratios, with ∑REE = 129-296μg/g, δEu =0.51 -0.86, and (La/Yb)N = 3.95 -12.9. The Nd isotopic model ages tDM of these rocks vary from 1597 to 2124 Ma. Their 143 Nd/144 Nd values are low [εNd (0) = - 11.4 to -- 15.8]. Some conclusions have been drawn as follows: (1) The metamorphic rocks in central Jiangxi Province are likely formed in a tectonic environment at the passive continental margin of the Cathaysia massif. (2) The metamorphosed argillo-arenaceous rocks are composed dominantly of upper crustal-source rocks (Al- and Krich granitic or/and sedimentary rocks of Early Proterozoic), which experienced good sorting, slow deposition and more intense chemical weathering. (3) According to the whole-rock Sm-Nd isochron ages (1113±49 to 1199 ± 26 Ma) of plagioclase-amphibole (schist) and Nd isotopic model age tDM ( 1597 - 2124Ma) of meta-argillo-arenaceous rocks, the metamorphic belt in central Jiangxi Province was formed during the Middle Proterozoic ( 1100 - 1600 Ma).

  12. Pb-, Sr- and Nd-Isotopic systematics and chemical characteristics of cenozoic basalts, Eastern China (United States)

    Peng, Z.C.; Zartman, R.E.; Futa, K.; Chen, D.G.


    Forty-eight Paleogene, Neogene and Quaternary basaltic rocks from northeastern and east-central China have been analyzed for major-element composition, selected trace-element contents, and Pb, Sr and Nd isotopic systematics. The study area lies entirely within the marginal Pacific tectonic domain. Proceeding east to west from the continental margin to the interior, the basalts reveal an isotopic transition in mantle source material and/or degree of crustal interaction. In the east, many of the rocks are found to merge both chemically and isotopically with those previously reported from the Japanese and Taiwan island-arc terrains. In the west, clear evidence exists for component(s) of Late Archean continental lithosphere to be present in some samples. A major crustal structure, the Tan-Lu fault, marks the approximate boundary between continental margin and interior isotopic behaviors. Although the isotopic signature of the western basalts has characteristics of lower-crustal contamination, a subcrustal lithosphere, i.e. an attached mantle keel, is probably more likely to be the major contributor of their continental "flavor". The transition from continental margin to interior is very pronounced for Pb isotopes, although Sr and Nd isotopes also combine to yield correlated patterns that deviate strikingly from the mid-ocean ridge basalt (MORB) and oceanic-island trends. The most distinctive chemical attribute of this continental lithosphere component is its diminished U Pb as reflected in the Pb isotopic composition when compared to sources of MORB, oceanic-island and island-arc volcanic rocks. Somewhat diminished Sm Nd and elevated Rb Sr, especially in comparison to the depleted asthenospheric mantle, are also apparent from the Nd- and Sr-isotopic ratios. ?? 1986.

  13. Petrology and Geochronology of High-Grade Metamorphic Rocks from Cedros Island, Baja California, Mexico (United States)

    Gonzales, D.; Leech, M. L.


    High-grade metamorphic rocks exposed on Cedros Island, Baja California, Mexico, record the Mesozoic subduction history of western North America. Blocks of amphibolite, blueschist, and eclogite crop out in a serpentinite-matrix mélange on the southeast and southwestern parts of Cedros Island. Amphibolite blocks contain Amp + Ep + Ab + Chl ± Ms ± Grt ± Ttn ± Qz; blueschist blocks have the assemblage Na-Amp + Ms + Lw + Qz ± Ttn ± Grt ± Jd ± Chl; and eclogite blocks are comprised primarily of Omp + Grt with retrograde Na-Amp + Ms + Lw. Blueschists from Cedros have been dated using 40Ar/39Ar step-heating of white mica and sodic amphiboles that yield ages from 103 ± 4 Ma to 94.9 ± 1.1 Ma, respectively, that represent cooling during exhumation. Apatite fission-track dating gives ages from 32 ± 4 Ma to 22 ± 3 Ma that record exhumation through the upper crust. Related Mesozoic subduction zone rocks of the Franciscan Complex crop out in a serpentinite-matrix mélange along coastal northern California. The Franciscan rocks are older, yielding 40Ar/39Ar step-heating ages of hornblende from amphibolite ranging from 159 to 156 Ma and represent an older part of the subduction history of the oceanic Farallon plate along western North America. I will determine the prograde and peak metamorphic P-T conditions for these high-grade rocks using petrography, mineral chemistries, and isochemical phase diagram modeling with Perple_X to generate complete P-T paths. I will then supplement these data with Sm-Nd and Lu-Hf geochronology for these high-grade Cedros rocks to evaluate their subduction/exhumation history, and develop a tectonic model for these southernmost Franciscan-type rocks. Ultimately, I will compare my results to Franciscan rocks in northern California to better understand the Mesozoic subduction margin of western North America.

  14. Initiation of modern-style plate tectonics recorded in Mesoarchean marine chemical sediments (United States)

    Satkoski, Aaron M.; Fralick, Philip; Beard, Brian L.; Johnson, Clark M.


    The chemistry of the oceans in part reflects a balance between inputs from the continents and mantle. Traditionally, it has been thought that Archean ocean chemistry was dominated by mantle sources, but recent work has suggested that continental weathering during the Archean provided a much higher flux to the oceans than previously recognized. Here, we present new Rb-Sr and Sm-Nd isotope compositions on carbonate (dolomite and limestone) from the 2.94 Ga Red Lake and 2.80 Ga Steep Rock groups in the Superior Province, Canada to assess the potential impact continental weathering had on ocean chemistry during the Mesoarchean, a time when initiation of modern-style plate tectonics has been proposed to have occurred. The low Rb contents of all carbonate samples suggest that clastic contamination does not affect the Sr isotope compositions. Using O and Sr isotope modeling, we identified unaltered samples and estimate a 87Sr/86Sr ratio of 0.70173 for seawater at 2.94 Ga and 0.70182 at 2.80 Ga. Strontium isotope compositions from both Red Lake and Steep Rock indicate that seawater was significantly more radiogenic than contemporaneous mantle, and suggests that weathering of evolved continental crust was an important input to seawater. Continental weathering likely affected seawater chemistry through uplift of continental lithosphere during the initiation of modern-style plate tectonics at 3.2 Ga, a model that is contrary to those that suggest the Archean continents were small in extent and largely submerged. Initiation of modern-style plate tectonics and associated continental weathering had an important effect on the biosphere, including increased nutrient delivery, as well as creation of ecological niches that allowed development of the first biologically produced shallow marine redox gradients.

  15. Mineralogical, geochemical, fluid inclusion and isotope study of Hohentauern/Sunk sparry magnesite deposit (Eastern Alps/Austria): implications for a metasomatic genetic model (United States)

    Azim Zadeh, Amir M.; Ebner, Fritz; Jiang, Shao-Yong


    The magnesite deposit of Hohentauern/Sunk, hosted in Viseán carbonate rocks, is one of the best-exposed examples of "Veitsch type" sparry magnesite deposits, which are located in the Veitsch nappe of the Austroalpine Greywacke zone (Eastern Alps/Austria). The sparry magnesite is stratiform and stratabound within the Viseán Steilbachgraben Formation and displays distinct metasomatic features and textures. The sparry magnesite of the Hohentauern/Sunk deposit is characterized by pinolites, rosettes and banded (zebra) textures. Due to microinclusions of dolomite and redolomitzation, the CaO/MgO of magnesite is elevated. Concentrations of selected major and trace elements (Fe-Mn, Sr-Ba, Cr-Ni) in sparry magnesite indicate formation in a marine/evaporitic environment and by Mg2+-metasomatism. The REE patterns of magnesite are characterized by low LREE/HREE, depletion of LREE and a negative Ce anomaly. The δ18O (9.59 to 12.32 ‰ SMOW) and δ13C (-2.23 to -0.02 ‰ PDB) values of magnesite overlap with those published for magnesite formed by metasomatic replacement of dolomite. Fluid inclusions in the sparry magnesite indicate a high salinity (22.4 mass% NaCl equivalent) of the Mg-rich fluid; it is of marine/evaporitic origin. All geological, petrographical and geochemical features support a diagenetic dolomitization of the carbonate host rocks followed by magnesite formation via metasomatic replacement and redolomitization. Sm-Nd geochronology indicates a Late Carboniferous to Early Permian age for magnesite formation triggered by intraformational circulation of fluids derived from buried Carboniferous evaporites.

  16. Lithogeochemistry and geochronology of the subalkaline felsic plutonism that marks the end of the Paleoproterozoic orogeny in the Salvador-Esplanada belt, São Francisco craton (Salvador, state of Bahia, Brazil

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    Jailma Santos de Souza-Oliveira

    Full Text Available Studies conducted over the last decade concerning the rocks that underlie the municipality of Salvador have shown a complex geological history with a great diversity of medium- to high-grade metamorphic lithotypes, deformed in several phases and frequently cut by tabular mafic dykes and irregular granitic bodies. The latter, which were the subject of this study, frequently outcrop along the coastline of Salvador and are classified petrographically as monzo-syenogranites. They are classified as subalkaline and peraluminous according to their geochemical data, and stand out for being enriched in light rare earth elements and having a strong negative Europium (Eu anomaly. These rocks are produced from anatectic melts or through the interaction of mantle-derived magmas with crustal materials. The negative values of εNd(t (-6.08 corroborate with the crustal character and in the diagrams of tectonic ambience, they are plotted in the field of post-tectonic granites. The Sm-Nd model age (TDM around 2.9 Ga indicates a neoarchean source for these lithotypes, whereas their U-Pb zircon age (LA-ICPMS of 2,064 ± 36 Ma is similar to the U-Pb (SHRIMP and Pb-Pb (evaporation ages for late-tectonic granites of the Itabuna-Curaçá-Salvador belt. Considering the results of recent studies in the area of Salvador, the monzo-syenogranites can be interpreted as late-tectonic intrusions, since they are affected by dextral shear zones correlated with the last stage of deformation registered in the granulites of Salvador.

  17. Archaean and Palaeoproterozoic gneisses reworked during a Neoproterozoic (Pan-African) high-grade event in the Mozambique belt of East Africa: Structural relationships and zircon ages from the Kidatu area, central Tanzania (United States)

    Vogt, M.; Kröner, A.; Poller, U.; Sommer, H.; Muhongo, S.; Wingate, M. T. D.


    This study presents new zircon ages and Sm-Nd whole-rock isotopic compositions for high-grade gneisses from the Udzungwa Mountain area in the central part of the Mozambique belt, Tanzania. The study area comprises a succession of layered granulite-facies para- and orthogneisses, mostly retrograded to amphibolite-facies. The original intrusive contacts became obscured or severely modified during non-coaxial ductile deformation, and extensive shearing occurred during retrogression. Structures reflecting the early deformational history were mostly obscured when the rocks were transported into the lower crust as documented by severe flattening. Only the fragmented gneisses in the eastern part of the area testify to a brittle regime. Structures in narrow low strain zones that predate the currently observed layering are preserved in rootless isoclinal folds and boudins. Magmatic and detrital zircons from tonalitic to felsic orthogneisses and a metapelite sample were dated using the U-Pb and Pb-Pb evaporation methods and SHRIMP II. Cathodoluminiscence images reveal ubiquitous xenocrystic cores, rimmed by clear, unzoned overgrowth due to high-grade metamorphism. Discordant U-Pb data therefore reflect core-rim relationships, and it was not always possible to obtain precise crystallisation ages. The analyses reveal Neoarchaean, Palaeoproterozoic and Neoproterozoic protolith ages. Nd isotopic systematics yielded strongly negative ɛNd( t) -values and Neoarchaean to Palaeoproterozoic model ages, even for gneisses emplaced in the Neoproterozoic. The trace element distribution suggests upper crustal derivation of the gneisses. Therefore, our study provides evidence that recycling of older crust played a major role during the evolution of the Kidatu area. Neoarchaean rocks are interpreted to represent fragments of the Tanzania craton. Our results, together with those of earlier workers, lead to the conclusion that the central part of the Mozambique belt mainly consists of ancient

  18. Crustal contamination versus an enriched mantle source for intracontinental mafic rocks: Insights from early Paleozoic mafic rocks of the South China Block (United States)

    Xu, Wenjing; Xu, Xisheng; Zeng, Gang


    Several recent studies have documented that the silicic rocks (SiO2 > 65 wt.%) comprising Silicic Large Igneous Provinces are derived from partial melting of the crust facilitated by underplating/intraplating of ;hidden; large igneous province-scale basaltic magmas. The early Paleozoic intracontinental magmatic rocks in the South China Block (SCB) are dominantly granitoids, which cover a combined area of 22,000 km2. In contrast, exposures of mafic rocks total only 45 km2. These mafic rocks have extremely heterogeneous isotopic signatures that range from depleted to enriched (whole rock initial 87Sr/86Sr = 0.7041-0.7102; εNd(t) = - 8.4 to + 1.8; weighted mean zircon εHf(t) = - 7.4 to + 5.2), show low Ce/Pb and Nb/U ratios (0.59-13.1 and 3.5-20.9, respectively), and variable Th/La ratios (0.11-0.51). The high-MgO mafic rocks (MgO > 10 wt.%) tend to have lower εNd(t) values (- 4) and Sm/Nd ratios (> 0.255). The differences in geochemistry between the high-MgO and low-MgO mafic rocks indicate greater modification of the compositions of high-MgO mafic magmas by crustal material. In addition, generally good negative correlations between εNd(t) and initial 87Sr/86Sr ratios, MgO, and K2O, along with the presence of inherited zircons in some plutons, indicate that the geochemical and isotopic compositions of the mafic rocks reflect significant crustal contamination, rather than an enriched mantle source. The results show that high-MgO mafic rocks with fertile isotopic compositions may be indicative of crustal contamination in addition to an enriched mantle source, and it is more likely that the lithospheric mantle beneath the SCB during the early Paleozoic was moderately depleted than enriched by ancient subduction processes.

  19. Primary uranium sources for sedimentary-hosted uranium deposits in NE China: insight from basement igneous rocks of the Erlian Basin (United States)

    Bonnetti, Christophe; Cuney, Michel; Bourlange, Sylvain; Deloule, Etienne; Poujol, Marc; Liu, Xiaodong; Peng, Yunbiao; Yang, Jianxing


    Carboniferous-Permian, Triassic and Jurassic igneous basement rocks around the Erlian Basin in northeast China have been investigated through detailed mineralogical, whole-rock geochemistry, geochronological data and Sm-Nd isotope studies. Carboniferous-Permian biotite granites and volcanic rocks belong to a calc-alkaline association and were emplaced during the Late Carboniferous-Early Permian (313 ± 1-286 ± 2 Ma). These rocks are characterised by positive ɛNd(t) (3.3-5.3) and fairly young T DM model ages (485-726 Ma), suggesting a dominant derivation from partial melting of earlier emplaced juvenile source rocks. Triassic biotite granites belong to a high-K calc-alkaline association and were emplaced during the Middle Triassic (243 ± 3-233 ± 2 Ma). Their negative ɛNd(t) (-2 to -0.1) and higher T DM model ages (703-893 Ma) suggest a contribution from Precambrian crust during the magma generation processes, leading to a strong enrichment in K and incompatible elements such as Th and U. Highly fractionated magmas crystallised in U-rich biotite (up to 21 ppm U) and two-mica granites. In biotite granite, the major U-bearing minerals are uranothorite and allanite. They are strongly metamict and the major part of their uranium (90 %) has been released from the mineral structure and was available for leaching. Mass balance calculations show that the Triassic biotite granites may have, at least, liberated ˜14,000 t U/km3 and thus correspond to a major primary uranium source for the U deposits hosted in the Erlian Basin.

  20. Fragments of ancient lunar crust: Ferroan noritic anorthosites from the descartes region of the Moon (United States)

    Norman, M. D.; Alibert, C.; Mcculloch, M. T.


    Noritic anorthosite clasts from breccia 67016 have bulk compositions similar to that of the upper crust of the Moon and petrogenetic affinities with pristine ferroan anorthosites. Rb-Sr and Sm-Nd isotopic compositions of mineral separates from one of these clasts suggest very old (greater than or = 4.4 Ga) ages, but interpretation of these data is complicated by the multi-stage history of the clasts which involved magmatic crystallization, brecciation, subsolidus recrystallization, and sulfide metasomatism. These clasts record some of the earliest events on the Moon, including early crust formation, accretionary bombardment, and degassing of the lunar interior. Modal analyses of these clasts show they are now composed of about 70 percent plagioclase, 28 percent pyroxene, 2 percent troilite, and minor amounts of ilmenite and chromite. No metallic iron, phosphates, or other trace phases were observed. Olivine is very rare, occurring only as relicts within secondary troilite+pyroxene intergrowths which may reflect reaction of olivine with sulfurous vapors. PIXE proton microprobe analyses of the sulfides show that the metasomatism was accompanied by enrichments of Cu, Zn, Ni, Se, and Sb. The clasts have been only mildly shocked since the observed texture was established. Major and minor element mineral compositions are very homogeneous and strikingly similar to those of pristine ferroan anorthosites. Pyroxene compositions indicate equilibration temperatures of 850-900 C. Except for the sulfide and chalcophile element metasomatism, these clasts appear to be essentially monomict and probably represent a noritic member of the ferroan anorthosite suite. Their low Ni contents and Ni/Co ratios are consistent with the interpretation of these clasts as igneous rocks which have escaped mixing with meteoritic material.

  1. Characterization of archaeological pieces from San Miguel Ixtapan, Estado de Mexico with nuclear and conventional techniques; Caracterizacion de piezas arqueologicas provenientes de San Miguel Ixtapan, Estado de Mexico con tecnicas nucleares y convencionales

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    Almazan T, M.G


    In this work was used the technique of Neutron Activation Analysis to characterize obsidian samples and of archaeological ceramic coming from the archaeological site of San Miguel Ixtapan, Estado de Mexico; and samples of clay of three banks bordering to the site. The characterization of the ceramic, was complemented with the analysis of pastes (cooked clay) and pigments, with the techniques of X ray diffraction (XRD) and Scanning Electron Microscopy (SEM). With the technique of NAA was determined the concentration of 13 elements (Eu,Ce,Lu, Yb, U, Th, Sb, Cs, Sc, Rb, Fe, Co and La) in 44 obsidian samples, in some of them were also determined Na, K and Mn. The analysis of the data, with different techniques of multivariable analysis, indicated that the obsidian comes from three locations that are: Sierra de las Navajas in the Estado de Hidalgo, Zinaparo and Zinapecuaro, both located in the Estado de Michoacan. On the other hand, in the ceramic samples and local clay 19 elements were measured (Sm, Nd, Ce, Lu, Eu, Yb, U, Th, Tb, Cr, Hf, As, Sb, Cs, Sc, Rb, Fe, Co and La). The statistical analysis of the data revealed differences in the elementary composition of the samples, being three main groups that in accordance with the archaeological classification they correspond to the ceramic types: local, foreign and regional. By means of the determination of the elementary composition of the local clays was possible to identify the local ceramic. These results are confirmed with those of the study of XRD, in the one which were observed differences in the mineralogical composition among these three groups. (Author)

  2. Vestiges of a continental margin ophiolite type in the Novo Oriente region, Borborema Province, NE Brazil (United States)

    Pitombeira, João Paulo Araújo; Amaral, Wagner da Silva; Uchôa Filho, Evilarde Carvalho; Fuck, Reinhardt Adolfo; Dantas, Elton Luiz; Parente, Clóvis Vaz; da Costa, Felipe Grandjean; Veríssimo, César Ulisses Vieira


    The Novo Oriente Group is a restricted well-preserved metasedimentary sequence, composed of two tectonic-stratigraphic sequences in the southwestern portion of the Ceará Central Domain, NE Brazil. The Bonsucesso Formation comprises mainly quartzite and metamafic rocks and the Caraúbas Formation is dominantly metapelitic, with chemical sedimentary contribution, metamafic and metaultramafic rocks. New integrated field, geochemical data and Sm-Nd isotopes of the metaultramafic and metamafic rocks of the two formations have been investigated in order to determine their tectonic setting. The metaultramafic rocks are dominantly composed of deformed and undeformed serpentinites, chloritites, actinolitites, talc-chlorite schists, serpentine-talc schists, talc-rich siliceous rocks and subordinated listwänites. Geochemical data indicate that the serpentinites correspond to rocks resulting from the alteration of dunites depleted in HREE, similar to the pattern presented by subduction-zone serpentinites generated from exhumed sub-continental peridotites and hydrated during ocean-continent transition (OCT) rifting. The metamafic rocks, represented by metagabbros, hornblende metagabbros and metabasalts, consist of basic rocks of basaltic and tholeiitic affinity with signatures between E- and N-MORB and variable contamination by crustal components similar to the rocks formed from the interaction between mantle plumes and heavily thinned continental crust. Isotopic analysis indicates crustal assimilation with negative ɛNd and Paleoproterozoic TDM ages. The data suggest that metaultramafic and metamafic rocks correspond, respectively, to continental sub-lithospheric mantle exhumed in an area of ocean-continent transition (OCT), and mafic magmatism associated with the development of a magma-poor passive margin generated by the break-up of the Rodinia Supercontinent, which was later dismembered by the Brasiliano/Pan-African Orogeny collisional phase and preserved as a Continental

  3. Conventional U-Pb dating versus SHRIMP of the Santa Barbara Granite Massif, Rondonia, Brazil (United States)

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


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

  4. Primitive Solar System materials and Earth share a common initial (142)Nd abundance. (United States)

    Bouvier, A; Boyet, M


    The early evolution of planetesimals and planets can be constrained using variations in the abundance of neodymium-142 ((142)Nd), which arise from the initial distribution of (142)Nd within the protoplanetary disk and the radioactive decay of the short-lived samarium-146 isotope ((146)Sm). The apparent offset in (142)Nd abundance found previously between chondritic meteorites and Earth has been interpreted either as a possible consequence of nucleosynthetic variations within the protoplanetary disk or as a function of the differentiation of Earth very early in its history. Here we report high-precision Sm and Nd stable and radiogenic isotopic compositions of four calcium-aluminium-rich refractory inclusions (CAIs) from three CV-type carbonaceous chondrites, and of three whole-rock samples of unequilibrated enstatite chondrites. The CAIs, which are the first solids formed by condensation from the nebular gas, provide the best constraints for the isotopic evolution of the early Solar System. Using the mineral isochron method for individual CAIs, we find that CAIs without isotopic anomalies in Nd compared to the terrestrial composition share a (146)Sm/(144)Sm-(142)Nd/(144)Nd isotopic evolution with Earth. The average (142)Nd/(144)Nd composition for pristine enstatite chondrites that we calculate coincides with that of the accessible silicate layers of Earth. This relationship between CAIs, enstatite chondrites and Earth can only be a result of Earth having inherited the same initial abundance of (142)Nd and chondritic proportions of Sm and Nd. Consequently, (142)Nd isotopic heterogeneities found in other CAIs and among chondrite groups may arise from extrasolar grains that were present in the disk and incorporated in different proportions into these planetary objects. Our finding supports a chondritic Sm/Nd ratio for the bulk silicate Earth and, as a consequence, chondritic abundances for other refractory elements. It also removes the need for a hidden reservoir or

  5. Ar-Ar Analysis of Chelyabinsk: Evidence for a Recent Impact (United States)

    Beard, S. P.; Kring, D. A.; Isachsen, C. E.; Lapen, T. J.; Zolensky, M. E.; Swindle, T. D.


    The Chelyabinsk meteorite is an LL5 ordinary chondrite that fell as a spectacular fireball on February 15th, 2013, over the Ural region in Russia. The meteoroid exploded at an altitude of 25-30 km, producing shockwaves that broke windowpanes in Chelyabinsk and surrounding areas, injuring some 1500 people. Analyses of the samples show that the meteorite underwent moderate shock metamorphism (stage S4; 25-35 GPa) [1]. Most of the samples have a fusion crust ranging from 0.1-1mm thick, and roughly a third of the samples were composed of a dark fine-grained impact melt with chondrule fragments which were targeted for chronometry. A Pb-Pb age obtained by [2] of a shock-darkened and potentially melted sample of Chelyabinsk is reported as 4538.3 +/- 2.1 Ma, while a U-Pb study [3] gave an upper concordia intercept of 4454 +/- 67 Ma and a lower intercept of 585 +/- 390. Galimov et al. 2013 [1] suggest the Sm-Nd system records a recent impact event [290 Ma] that may represent separation from the parent body, while the Rb-Sr isotopic system is disturbed and does not give any definitive isochron. In order to better understand its history, we have performed 40Ar-39Ar analysis on multiple splits of two Chelyabinsk samples; clast- rich MB020f,2 and melt-rich MB020f,5. The term "clast-rich" lithology is meant to indicate a mechanical mixture of highly shock-darkened and less shocked components, both with some shock melt veining.

  6. Process optimization and kinetics for leaching of rare earth metals from the spent Ni-metal hydride batteries. (United States)

    Meshram, Pratima; Pandey, B D; Mankhand, T R


    Nickel-metal hydride batteries (Ni-MH) contain not only the base metals, but valuable rare earth metals (REMs) viz. La, Sm, Nd, Pr and Ce as well. In view of the importance of resource recycling and assured supply of the contained metals in such wastes, the present study has focussed on the leaching of the rare earth metals from the spent Ni-MH batteries. The conditions for the leaching of REMs from the spent batteries were optimized as: 2M H2SO4, 348K temperature and 120min of time at a pulp density (PD) of 100g/L. Under this condition, the leaching of 98.1% Nd, 98.4% Sm, 95.5% Pr and 89.4% Ce was achieved. Besides the rare earth metals, more than 90% of base metals (Ni, Co, Mn and Zn) were also leached out in this condition. Kinetic data for the dissolution of all the rare earth metals showed the best fit to the chemical control shrinking core model. The leaching of metals followed the mechanism involving the chemical reaction proceeding on the surface of particles by the lixiviant, which was corroborated by the XRD phase analysis and SEM-EDS studies. The activation energy of 7.6, 6.3, 11.3 and 13.5kJ/mol was acquired for the leaching of neodymium, samarium, praseodymium and cerium, respectively in the temperature range 305-348K. From the leach liquor, the mixed rare earth metals were precipitated at pH∼1.8 and the precipitated REMs was analyzed by XRD and SEM studies to determine the phases and the morphological features.

  7. Multiple sulfur isotope and mineralogical constraints on the genesis of Ni-Cu-PGE magmatic sulfide mineralization of the Monchegorsk Igneous Complex, Kola Peninsula, Russia (United States)

    Bekker, A.; Grokhovskaya, T. L.; Hiebert, R.; Sharkov, E. V.; Bui, T. H.; Stadnek, K. R.; Chashchin, V. V.; Wing, B. A.


    We present the results of a pilot investigation of multiple sulfur isotopes for the Ni-Cu-PGE sulfide mineralization of the ˜2.5 Ga Monchegorsk Igneous Complex (MIC). Base Metal Sulfide (BMS) compositions, Platinum Group Element (PGE) distributions, and Platinum Group Mineral (PGM) assemblages were also studied for different types of Ni-Cu-PGE mineralization. The uniformly low S content of the country rocks for the MIC as well as variable Sm-Nd isotope systematics and low-sulfide, PGE-rich mineralization of the MIC suggest that S saturation was reached via assimilation of silicates rather than assimilation of sulfur-rich lithologies. R-factor modeling suggests that the mixing ratio for silicate-to-sulfide melt was very high, well above 15,000 for the majority of our mineralized samples, as might be expected for the low-sulfide, PGE-rich mineralization of the MIC. Small, negative Δ33S values (from -0.23 to -0.04 ‰) for sulfides in strongly metamorphosed MIC-host rocks indicate that their sulfur underwent mass-independent sulfur isotope fractionation (MIF) in the oxygen-poor Archean atmosphere before it was incorporated into the protoliths of the host paragneisses and homogenized during metamorphism. Ore minerals from the MIC have similar Δ33S values (from -0.21 to -0.06 ‰) consistent with country rock assimilation contributing to sulfide saturation, but, also importantly, our dataset suggests that Δ33S values decrease from the center to the margin of the MIC as well as from early to late magmatic phases, potentially indicating that both local assimilation of host rocks and S homogenization in the central part of the large intrusion took place.

  8. Primary uranium sources for sedimentary-hosted uranium deposits in NE China: insight from basement igneous rocks of the Erlian Basin (United States)

    Bonnetti, Christophe; Cuney, Michel; Bourlange, Sylvain; Deloule, Etienne; Poujol, Marc; Liu, Xiaodong; Peng, Yunbiao; Yang, Jianxing


    Carboniferous-Permian, Triassic and Jurassic igneous basement rocks around the Erlian Basin in northeast China have been investigated through detailed mineralogical, whole-rock geochemistry, geochronological data and Sm-Nd isotope studies. Carboniferous-Permian biotite granites and volcanic rocks belong to a calc-alkaline association and were emplaced during the Late Carboniferous-Early Permian (313 ± 1-286 ± 2 Ma). These rocks are characterised by positive ɛNd( t) (3.3-5.3) and fairly young T DM model ages (485-726 Ma), suggesting a dominant derivation from partial melting of earlier emplaced juvenile source rocks. Triassic biotite granites belong to a high-K calc-alkaline association and were emplaced during the Middle Triassic (243 ± 3-233 ± 2 Ma). Their negative ɛNd( t) (-2 to -0.1) and higher T DM model ages (703-893 Ma) suggest a contribution from Precambrian crust during the magma generation processes, leading to a strong enrichment in K and incompatible elements such as Th and U. Highly fractionated magmas crystallised in U-rich biotite (up to 21 ppm U) and two-mica granites. In biotite granite, the major U-bearing minerals are uranothorite and allanite. They are strongly metamict and the major part of their uranium (90 %) has been released from the mineral structure and was available for leaching. Mass balance calculations show that the Triassic biotite granites may have, at least, liberated ˜14,000 t U/km3 and thus correspond to a major primary uranium source for the U deposits hosted in the Erlian Basin.

  9. Geohydrology model of the geothermal reservoirs at Los Humeros, Puebla, Mexico; Modelo hidrogeologico de los yacimientos geotermicos de los Humeros, Puebla, Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Cedillo Rodriguez, Fidel [Comision Federal de Electricidad, Perote, Veracruz (Mexico)


    the regional lateral water recharge. On the other hand, the circular faults of the collapsed calderas of Los Humeros and Los Petreros form impermeable barriers to lateral water flow. Geothermal reservoir recharge only occurs inside the collapsed Los Humeros caldera. [Spanish] Los estudios de petrologia de agua y gases, e ingenieria de yacimientos de los pozos geotermicos, indican la existencia de dos yacimientos geotermicos. Las correlaciones petrograficas estructurales y el estado de las tuberias de produccion de los pozos geotermicos reparados, desviados y no invertidos, confirma la presencia de dos yacimientos, uno superior no agresivo con pH neutro y fluido bicarbonatado-sodico alojado en andesitas de augita; el otro, inferior, de alta temperatura y pH acido, contenido en andesitas de hornblenda y basaltos con fluidos clorurados-sodicos, ambos separados por un horizonte de tobas vitreas. Las grandes elevaciones de los niveles potenciometricos de los pozos geotermicos impide inferir la direccion de flujo de los fluidos geotermicos profundos. Los resultados litologicos y piezometricos de los pozos geothermohidrologicos perforados dentro de la caldera de Los Humeros, tambien muestra la existencia de dos acuiferos superficiales, uno relativamente frio y otro caliente. Debido a las grandes distancias entre estos pozos, y al medio geologico en que se encuentran, tampoco en ellos es posible inferir la direccion de flujo. Los estudios regionales de hidrogeologia, geofisica, hidrogeoquimica y geologico- estructurales, permiten afirmar que los acuiferos (frio y caliente) no tienen comunicacion hidraulica, ni relacion geoquimica o geologica con los pozos, norias y manantiales de los alrededores de la region de Los Humeros. Por consiguiente, la recarga de los acuiferos frio y caliente ocurre dentro de la cuenca cerrada de la caldera de Los Humeros, delimitada por el parte aguas orografico. Estos acuiferos recargan a los yacimientos geotermicos a traves de fallas y fracturas

  10. Feasibility studies for the location of the exploratory borehole EN-1 at Los Negritos, Michoacan, Mexico; Antecedentes para la localizacion del pozo exploratorio EN-1 en Los Negritos, Michoacan, Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Bigurra Pimentel, Emilio; Casarrubias Unzueta, Zenon [Gerencia de Proyectos Geotermoelectricos de la Comision Federal de Electricidad, Morelia (Mexico)


    Los Negritos geothermal zone, is located in the northwestern portion of Michoacan state, 10 Km to the eastern of the Sahuayo town, 250 Km to the NW of Morelia city, and 140 Km to the southeast of Guadalajara, Jalisco state, in Mexico. The aim of this work, is to analyse the geological, geophysical and geochemical characteristics underground, and its relation with hot springs on the surface, in the drilling site of the exploratory well EN-1. Around the drilling site, there are volcanic rocks and lacustrine sediments of Upper Miocene and Upper Pliocene age. The older rocks are compound by Miocene andesites. Over this formation three are lacustrine sediments with Medium Miocene age, basaltic flows of Lower Pleistocene age and cinder cones emplaced during the Medium Pleistocene age; over this formation was deposited the last volcanic issue formed by vitric andesites of recent age. The recent rocks were affected by structural systems NE-SW (Los Negritos fault) and NW-SE. Geophysical studies confirm the location of deep structures NE-SW and NW-SE. The drilling area has a low resistivity anomaly of 8 Ohm.m. Geochemical results show sodic-chloride waters, while the geothermometers show temperatures from 150 to 200 degrees celsius. Drilling the well EN-1 we hope to confirm the geological sequence and the geophysical results, and to measure the temperatures and pressures existing at 2000 m depth. [Espanol] La zona geotermica de Los Negritos, se encuentra en la porcion noroccidental del estado de Michoacan, 10 km al oriente de la poblacion de Sahuayo, Michoacan, y 140 Km al SE de la ciudad de Guadalajara, Jalisco, Mexico. El objetivo de este trabajo es resumir las caracteristicas geologicas, geofisicas y geoquimicas del subsuelo y su relacion con las manifestaciones hidrotermales, en el sitio de la perforacion exploratoria EN-1. En los alrededores del sito de perforacion afloran rocas volcanicas y sedimentos lacustres, que comprenden edades desde el Mioceno Superior al

  11. Chemical changes in well fluids from the Los Humeros geothermal field: Evidences for deep recharge; Cambios quimicos en fluidos de pozos del campo geotermico de Los Humeros: Evidencia de recarga profunda

    Energy Technology Data Exchange (ETDEWEB)

    Barragan Reyes, Rosa Maria; Arellano Gomez, Victor Manuel [Instituto de Investigaciones Electricas, Gerencia de Geotermia, Cuernavaca, Morelos (Mexico)]. E-mail:; Flores Armenta, Magaly [Comision Federal de Electricidad, Gerencia de Proyectos Geotermoelectricos, Morelia, Michoacan (Mexico); Tovar Aguado, Rigoberto [Comision Federal de Electricidad (Mexico)


    Fluid (water and steam) chemical changes over time were studied in 20 wells in the Los Humeros, Mexico, geothermal field for the purpose of correlating such changes with physical processes occurring in the reservoir due to exploitation. Most wells (except well H-1) produce high-enthalpy fluids with almost no liquid, making gas geochemistry important in this field. Liquid-phase studies include fluid classification, determination of water-rock equilibrium state, and reservoir-temperature estimates. Changes in gas composition through time were studied using the Fischer-Tropsch (FT) reaction and the combined balance pyrite-hematite-magnetite (HSH2) as the buffer controlling H{sub 2}S fluid concentration. Data for most wells from 1987-1995 and 2000-2005 indicate the presence of deeper-fluid recharge, with maximum temperatures occurring in 1994-95 and 2005. The estimated temperature in well H-1 in 1994 was 305 degrees Celsius and the estimated temperature in well H-7 was 338 degrees Celsius in 1995. Temperature estimations from 2005 data were 222 degrees Celsius in well H-1D and 350 degrees Celsius in well H-7. These results are considered caused by the entrance of deeper fluids due to the increase of secondary permeability, which in turn is related to the seismicity increase in the zone. At the same time, re-injection returns in the steam phase were identified in well discharges during 1995-2000 by means of the FT-HSH2 diagram. [Spanish] Se realizo un estudio de los cambios quimicos ocurridos en fluidos (liquido y vapor) de veinte pozos del campo geotermico de Los Humeros, Pue., Mexico, con objeto de investigar la ocurrencia de procesos del yacimiento relacionados con la explotacion. La mayoria de los pozos (excepto el pozo H-1) se caracterizan por producir descargas de alta entalpia con escasa produccion de liquido, por lo que en este campo la geoquimica de gases juega un papel importante. El estudio de la fase liquida incluyo la clasificacion de los fluidos, la

  12. Isotopic Behaviour of fluids from the Los Azufres, Michoacan, (Mexico) Geothermal Wells; Comportamiento isotopico de fluidos de pozos del campo geotermico de Los Azufres, Michoacan, Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Barragan R, Rosa Maria; Arellano G, Victor Manuel; Portugal M, Enrique [Instituto de Investigaciones Electricas, Cuernavaca (Mexico); Tello L, Mirna del Rocio; Tello H, Enrique [Gerencia de Proyectos Geotermoelectricos de la Comision Federal de Electricidad, Morelia (Mexico)


    Isotopics data (oxygen-18 and deuterium) from production and reinjection well fluids from the Los Azufres geothermal field were interpreted in order to define the reservoir evolution and the occurrence of physical processes as a consequence of exploitation. The study included data for 25 wells for 1994-1996. Chemical and production data were also studied in order to explain the isotopic characteristics of the fluids. General results indicated that different phenomena seem to occur for both field zones. In the southern zone (Tejamaniles), a mixture of fluids was evidenced by the deuterium vs oxygen-18 tendency which provides a positive slope. The isotopically enriched fluid is constituted by the reinjection fluid. In the northern zone, (Maritaro) there was no evidence that the reinjection fluid is appearing in well discharges. For this zone the dominant process seems to be the reservoir vapour separation at a temperature above 220 degrees Celsius. This was suggested by the deuterium vs oxygen-18 tendency for which a negative slope was found. This trend is characteristics of a vapour separation process since for temperatures above 220 degrees Celsius deuterium behaves as a volatile component. The study of the reservoir temperatures estimated by different approaches for particular wells through time and the results obtained with a heat and fluid flow well simulator, suggest that reservoir boiling occurs in localized areas for both zones of the field. This process is probably due to exploitation. [Espanol] En este trabajo se presenta una interpretacion de datos de composicion isotopica (oxigeno-18 y deuterio) de fluidos de pozos productores y de reinyeccion del campo geotermico de Los Azufres. Estos datos se obtuvieron entre 1994 y 1996 con el proposito de definir la evolucion del yacimiento e identificar los procesos dominantes surgidos como consecuencia de la explotacion del campo. El estudio comprendio un numero de 25 pozos productores y de reinyeccion. La

  13. Re-Os and Lu-Hf isotopic constraints on the formation and age of mantle pyroxenites from the Bohemian Massif (United States)

    Ackerman, Lukáš; Bizimis, Michael; Haluzová, Eva; Sláma, Jiří; Svojtka, Martin; Hirajima, Takao; Erban, Vojtěch


    We report on the Lu-Hf and Re-Os isotope systematics of a well-characterized suite of spinel and garnet pyroxenites from the Gföhl Unit of the Bohemian Massif (Czech Republic, Austria). Lu-Hf mineral isochrons of three pyroxenites yield undistinguishable values in the range of 336-338 Ma. Similarly, the slope of Re-Os regression for most samples yields an age of 327 ± 31 Ma. These values overlap previously reported Sm-Nd ages on pyroxenites, eclogites and associated peridotites from the Gföhl Unit, suggesting contemporaneous evolution of all these HT-HP rocks. The whole-rock Hf isotopic compositions are highly variable with initial εHf values ranging from - 6.4 to + 66. Most samples show a negative correlation between bulk rock Sm/Hf and εHf and, when taking into account other characteristics (e.g., high 87Sr/86Sr), this may be explained by the presence of recycled oceanic sediments in the source of the pyroxenite parental melts. A pyroxenite from Horní Kounice has decoupled Hf-Nd systematics with highly radiogenic initial εHf of + 66 for a given εNd of + 7.8. This decoupling is consistent with the presence of a melt derived from a depleted mantle component with high Lu/Hf. Finally, one sample from Bečváry plots close to the MORB field in Hf-Nd isotope space consistent with its previously proposed origin as metamorphosed oceanic gabbro. Some of the websterites and thin-layered pyroxenites have variable, but high Os concentrations paralleled by low initial γOs. This reflects the interaction of the parental pyroxenitic melts with a depleted peridotite wall rock. In turn, the radiogenic Os isotope compositions observed in most pyroxenite samples is best explained by mixing between unradiogenic Os derived from peridotites and a low-Os sedimentary precursor with highly radiogenic 187Os/188Os. Steep increase of 187Os/188Os at nearly uniform 187Re/188Os found in a few pyroxenites may be connected with the absence of primary sulfides, but the presence of minor

  14. Direct Comparison of Detrital Garnet, Monazite, and Zircon Ages from a Southern Appalachian Tributary System for the French Broad River, North Carolina, USA (United States)

    Maneiro, K. A.; Baxter, E. F.; Samson, S. D.; Marschall, H.


    Nineteen detrital garnet ages from a tributary draining into the French Broad River of North Carolina represent the first full-scale deployment of a new detrital garnet geochronometer. Under the new geochronometer, inclusions within the garnet serve as a proxy for the original source rock and eliminate required assumption of a single source for detritus. Additionally, method development has advanced techniques for small sample Nd and Sm analysis by thermal ionization mass spectrometry (TIMS), allowing for Sm-Nd analysis of single detrital garnet grains for the first time. This is also the first dataset allowing direct comparison of detrital garnet, monazite, and zircon. The three proximate tributaries sampled drain a limited source lithology, and prior studies provide detrital monazite and zircon ages (e.g. Hietpas et al., 2010, Geology; Moecher et al., 2011, Geosphere). The weighted average age for tributary detrital monazite is 460.9 ± 2.5 Ma (95% confidence). Zircon cores failed to record Paleozoic metamorphism, while zircon rims gave a weighted average age of 443.5 ± 8.7 Ma (95% confidence). The tributary system is garnet-bearing, with garnet grains exceeding the current minimum volume required for single grain analysis (≥ 0.4 mm max. diameter). Previously reported initial ages from the garnet grains (Maneiro-Eccles, 2015, Goldschmidt) have been updated to include blank correction accounting for extremely small Nd loads; clean garnet analyses contain 17-445 pg Nd and repeat blanks indicate contribution of 4.31 ± 0.59 pg Nd. The resulting weighted average age for garnet is 438.8 ± 8.1 Ma (95% confidence). The weighted average ages for zircon rims and garnet overlap within error, while the monazite age is older (22.1 ± 8.5 Myr older than garnet, 17.4 ± 9.1 Myr older than zircon). Age variance between minerals could be attributed to monazite sampling bias, limited sample size, and either influence by a secondary tectonic event (e.g. the Cherokee Orogeny

  15. Petrogenesis of 3.15 Ga old Banasandra komatiites from the Dharwar craton, India: Implications for early mantle heterogeneity

    Directory of Open Access Journals (Sweden)

    J.M. Maya


    Full Text Available Spinifex-textured, magnesian (MgO >25 wt.% komatiites from Mesoarchean Banasandra greenstone belt of the Sargur Group in the Dharwar craton, India were analysed for major and trace elements and 147,146Sm-143,142Nd systematics to constrain age, petrogenesis and to understand the evolution of Archean mantle. Major and trace element ratios such as CaO/Al2O3, Al2O3/TiO2, Gd/Yb, La/Nb and Nb/Y suggest aluminium undepleted to enriched compositional range for these komatiites. The depth of melting is estimated to be varying from 120 to 240 km and trace-element modelling indicates that the mantle source would have undergone multiple episodes of melting prior to the generation of magmas parental to these komatiites. Ten samples of these komatiites together with the published results of four samples from the same belt yield 147Sm-143Nd isochron age of ca. 3.14 Ga with an initial ɛNd(t value of +3.5. High precision measurements of 142Nd/144Nd ratios were carried out for six komatiite samples along with standards AMES and La Jolla. All results are within uncertainties of the terrestrial samples. The absence of 142Nd/144Nd anomaly indicates that the source of these komatiites formed after the extinction of 146Sm, i.e. 4.3 Ga ago. In order to evolve to the high ɛNd(t value of +3.5 by 3.14 Ga the time-integrated ratio of 147Sm/144Nd should be 0.2178 at the minimum. This is higher than the ratios estimated, so far, for mantle during that time. These results indicate at least two events of mantle differentiation starting with the chondritic composition of the mantle. The first event occurred very early at ∼4.53 Ga to create a global early depleted reservoir with superchondritic Sm/Nd ratio. The source of Isua greenstone rocks with positive 142Nd anomaly was depleted during a second differentiation within the life time of 146Sm, i.e. prior to 4.46 Ga. The source mantle of the Banasandra komatiite was a result of a differentiation event that occurred

  16. Major element, REE, and Pb, Nd and Sr isotopic geochemistry of Cenozoic volcanic rocks of eastern China: implications for their origin from suboceanic-type mantle reservoirs (United States)

    Basu, A.R.; Wang, Junwen; Huang, Wankang; Xie, Guanghong; Tatsumoto, M.


    Major- and rare-earth-element (REE) concentrations and UThPb, SmNd, and RbSr isotope systematics are reported for Cenozoic volcanic rocks from northeastern and eastern China. These volcanic rocks, characteristically lacking the calc-alkaline suite of orogenic belts, were emplaced in a rift system which formed in response to the subduction of the western Pacific plate beneath the eastern Asiatic continental margin. The rocks sampled range from basanite and alkali olivine basalt, through olivine tholeiite and quartz tholeiite, to potassic basalts, alkali trachytes, pantellerite, and limburgite. These rock suites represent the volcanic centers of Datong, Hanobar, Kuandian, Changbaishan and Wudalianchi in northeastern China, and Mingxi in the Fujian Province of eastern China. The major-element and REE geochemistry is characteristic of each volcanic suite broadly evolving through cogenetic magmatic processes. Some of the outstanding features of the isotopic correlation arrays are as follows: (1) NdSr shows an anticorrelation within the field of ocean island basalts, extending from the MORB end-member to an enriched, time-averaged high Rb Sr and Nd Sr end-member (EM1), (2) SrPb also shows an anticorrelation, similar to that of Hawaiian and walvis Ridge basalts, (3) NdPb shows a positive correlation, and (4) the 207Pb 204Pb vs 206Pb 204Pb plot shows linear arrays parallel to the general trend (NHRL) for MORB on both sides of the geochron, although in the 208Pb 204Pb vs 206Pb 204Pb plot the linear array is significantly displaced above the NHRL in a pattern similar to that of the oceanic island basalts that show the Dupal signatures. In all isotope correlation patterns, the data arrays define two different mantle components-a MORB-like component and an enriched mantle component. The isotopic data presented here clearly demonstrate the existence of Dupal compositions in the sources of the continental volcanic rocks of eastern China. We suggest that the subcontinental mantle

  17. Constraints on formation and evolution of the lunar crust from feldspathic granulitic breccias NWA 3163 and 4881 (United States)

    McLeod, Claire L.; Brandon, Alan D.; Fernandes, Vera A.; Peslier, Anne H.; Fritz, Jörg; Lapen, Thomas; Shafer, John T.; Butcher, Alan R.; Irving, Anthony J.


    Lunar granulitic meteorites provide new constraints on the composition and evolution of the lunar crust as they are potentially derived from outside the Apollo and Luna landing sites. Northwest Africa (NWA) 3163, the focus of this study, and its paired stones NWA 4881 and NWA 4483, are shocked granulitic noritic anorthosites. They are petrographically and compositionally distinct from the Apollo granulites and noritic anorthosites. Northwest Africa 3163 is REE-depleted by an order of magnitude compared to Apollo granulites and is one of the most trace element depleted lunar samples studied to date. New in-situ mineral compositional data and Rb-Sr, Ar-Ar isotopic systematics are used to evaluate the petrogenetic history of NWA 3163 (and its paired stones) within the context of early lunar evolution and the bulk composition of the lunar highlands crust. The NWA 3163 protolith was the likely product of reworked lunar crust with a previous history of heavy REE depletion. The bulk feldspathic and pyroxene-rich fragments have 87Sr/86Sr that are indistinguishable and average 0.699282 ± 0.000007 (2σ). A calculated source model Sr TRD age of 4.340 ± 0.057 Ga is consistent with (1) the recently determined young FAS (Ferroan Anorthosite) age of 4.360 ± 0.003 Ga for FAS 60025, (2) 142Nd model ages for the closure of the Sm-Nd system for the mantle source reservoirs of the Apollo mare basalts (4.355-4.314 Ga) and (3) a prominent age peak in the Apollo lunar zircon record (c. 4.345 Ga). These ages are ∼100 Myr younger than predicted timescales for complete LMO crystallization (∼10 Myrs after Moon formation, Elkins-Tanton et al., 2011). This supports a later, major event during lunar evolution associated with crustal reworking due to magma ocean cumulate overturn, serial magmatism, or a large impact event leading to localized or global crustal melting and/or exhumation. The Ar-Ar isotopic systematics on aliquots of paired stone NWA 4881 are consistent with an impact event

  18. Geochemistry and petrogenesis of high-K "sanukitoids" from the Bulai pluton, Central Limpopo Belt, South Africa: Implications for geodynamic changes at the Archaean-Proterozoic boundary (United States)

    Laurent, Oscar; Martin, Hervé; Doucelance, Régis; Moyen, Jean-François; Paquette, Jean-Louis


    The Neoarchaean Bulai pluton is a magmatic complex intrusive in the Central Zone of the Limpopo Belt (Limpopo Province, South Africa). It is made up of large volumes of porphyritic granodiorites with subordinate enclaves and dykes of monzodioritic, enderbitic and granitic compositions. New U-Pb LA-ICP-MS dating on zircon yield pluton-emplacement ages ranging between 2.58 and 2.61 Ga. The whole pluton underwent a high-grade thermal overprint at ~ 2.0 Ga, which did not affect the whole-rock compositions for most of the major and trace-elements, as suggested by a Sm-Nd isochron built up with 16 samples and yielding an age consistent with U-Pb dating. The whole-rock major- and trace-element compositions evidence that the Bulai pluton belongs to a high-K, calc-alkaline to shoshonitic suite, as well as unequivocal affinities with "high-Ti" sanukitoids. Monzodioritic enclaves and enderbites have both "juvenile" affinities and a strongly enriched signature in terms of incompatible trace elements (LREE, HFSE and LILE), pointing to an enriched mantle source. Based on trace-element compositions, we propose the metasomatic agent at their origin to be a melt deriving from terrigenous sediments. We therefore suggest a two-step petrogenetic model for the Bulai pluton: (1) a liquid produced by melting of subducted terrigenous sediments is consumed by reactions with mantle peridotite, producing a metasomatic assemblage; (2) low-degree melting of this metasomatized mantle gives rise to Bulai mafic magmas. Such a model is supported by geochemical modelling and is consistent with previous studies concluding that sanukitoids result from interactions between slab melts and the overlying mantle wedge. Before 2.5 Ga, melting of hydrous subducted metabasalts produced large volumes of TTG (Tonalite-Trondhjemite-Granodiorite) forming most of the volume of Archaean continental crust. By constrast, our geochemical study failed in demonstrating any significant role played by melting of

  19. Petrology, Geochemistry and Nd-Sr-Pb Isotopic Properties of Volcanic Rocks in Daheishan Island, Penglai, Shandong Province

    Institute of Scientific and Technical Information of China (English)

    Fu Yongtao; Li Anchun


    The major elements, trace elements, K-Ar age and Sr-Nd-Pb isotopic systems of the Cenozoic volcanic rocks in Daheishan Island and Cishan, Penglai, Shandong Province are measured. The volcanic rocks ( olivine-nephelinite and nepheline-basanite ) in Daheishan Island erupted periodically in an interval of 0.32 Ma, from 8.72 Ma, 8.39 Ma, 8.08 Ma to 7.73 Ma. The volcanic rocks are all rich in light REEs. They are similar to the OIB-type alkali basalt in the trace elements normalized model by primordial mantle: rich in high field elements such as Nb and Ta, and imcompatible elements such as Cs, Rb, Ba, Th, U. The volcanic rocks show a depletion of K and Rb elements. It is suggested by the trace elements that the olivine-nephelinite in Daheishan Island is originated from deep resources under the continental mantle. ε Nd (0) values of the volcanic rocks in Daheishan Island and Cisban are 5.31 ~ 8.51 and 7.33 respectively, suggesting that the volcanic rocks are from the depleted mantle resources, which have higher Sm/Nd ratios than the CHUR. 143Nd /144Nd ratios of Daheishan Island olivine-nephelinite and Cishan alkali basalts are 0.512 910 ~ 0.513 074 and 0.513 014 respectively. The 87Sr /86Sr of Daheishan Island volcanic rocks are lower than that of Cishan, 0.703 427 ~ 0.703 482 and 0.703 895 respectively. The Daheishan Island olivinenephelinite has the Pb isotopic values as follows: 206Pb /204pb = 18.028 9 ~ 17.972 8, 207Pb /204pb= 15.435 8 ~ 15.402 2 and 208Pb /204Pb = 38.087 6 ~ 37.997 5, lower than those of Cishan basanite. The Cishan basanite has 206Pb /204pb = 18.240 1, 207Pb /204Pb = 15.564 5 and 208Pb /204pb = 38.535. The authors suggest that the olivine-nephelinite in Daheishan Island is similar to the E-type MORB or Hawaii OIB, and the alkali basalts in Cishan similar to the Kerguelen OIB. The dominant mantle components of DM+PREMA and perhaps DM ( Dupal type ) are the dominant mantle components for volcanic rocks in Daheishan Island and Cishan. The

  20. Idades SHRIMP U-Pb do Complexo Sertânia: Implicações Sobre a Evolução Tectônica da Zona Transversal, Província Borborema

    Directory of Open Access Journals (Sweden)

    Benjamim Bley de Brito Neves


    Full Text Available O Complexo Sertânia é uma seqüência metassedimentar com pequena contribuição metavulcânica, de facies anfibolitoalto, que ocorre no Terreno Alto Moxotó, Zona Transversal da Província Borborema. Vários levantamentos geológicos têmincluído esta unidade num complexo gnáissico-migmatítico indiviso, questionando, por decorrência, a subdivisão de terrenosproposta para esse domínio litotectônico. O presente trabalho apresenta as primeiras idades geocronológicas U-Pb SHRIMPem zircão e dados isotópicos Sm-Nd desta unidade. Os dados de campo e microscópicos revelaram a presença de uma fraçãovulcanoclástica de composição andesítica e dacítica ao lado da dominante componente clástica dessas supracrustais. Por outrolado, as imagens de catodoluminescência dos zircões mostraram cristais bem formados ou pouco arredondados, sugerindotratar-se de sedimentos pouco transportados. As idades calculadas são médias ponderadas com 95% de confidência, baseadasem agrupamentos de zircões de mesma geração. Foram obtidas idades em torno de 2,0 Ga, que representam a idade primáriade cristalização dos zircões, localmente com sobrecrescimento brasiliano. As rochas metaplutônicas do suposto embasamentosituam-se no mesmo intervalo de tempo, indicando uma contemporaneidade com a sedimentação das supracrustais. Os dadosisotópicos de Nd (idade modelo TDM e eNd(t confirmam a presença de fontes arqueanas e paleoproterozóicas. Esses dadosdemonstram o contraste entre as supracrustais do Terreno Alto Moxotó com as de outros terrenos da Zona Transversal, deidade meso a neoproterozóicas, o que impede sua correlação e implica numa individualização desse terreno como umcompartimento tectônico independente dos demais.

  1. Evolução do Segmento Norte do Orógeno Itabuna-Salvador-Curaçá: Cronologia da Acresção de Arcos, Colisão Continental e Escape de Terrenos

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    Elson Paiva Oliveira


    Full Text Available Datações de alta precisão em zircões (U-Pb e Pb-Pb e dados Sm-Nd e Pb-Pb em rocha-total são utilizados parareconstituir a evolução tectônica do Segmento Norte do Orógeno Itabuna-Salvador-Curaçá, nordeste do Cráton São Francisco.Acresções de crosta oceânica e/ou arcos insulares ocorreram há cerca de 3,3 Ga (Greenstone Belt Mundo Novo e entre 2,2 -2,12 Ga (Greenstone Belt do Rio Itapicuru e Seqüência Rio Capim. Margens continentais ativas, tipo andina, podem ter-seformado entre 3,08 - 2,98 Ga (migmatitos e TTG de Retirolândia-Santa Luz e granulitos do vale do Rio Jacurici e 2,69 - 2,63Ga (Complexo Caraíba. Entretanto, a colisão continental que construiu a estruturação atual do orógeno deve ter acontecidopor volta de 2109 Ma, como inferido da intrusão sintectônica do Tonalito Itareru, no limite entre o Greenstone Belt do RioItapicuru e gnaisses bandados do embasamento, no Bloco Serrinha. A continuação da colisão provocou escapes laterais deblocos (Bloco Uauá e intrusão de corpos graníticos alongados (Sienito Itiúba, domo de Ambrósio, quartzo-monzonito Capelado Alto Alegre ao longo do orógeno, entre aproximadamente 2084 Ma e 2039 Ma. A mudança de tectônica de convergênciade massas continentais para deslocamento de blocos ao longo do orógeno pode ter resultado de colisão oblíqua ou de tectônicade endentação.

  2. Genesis and formation conditions of deposits in the unique Strel'tsovka Molybdenum-Uranium ore field: New mineralogical, geochemical, and physicochemical evidence (United States)

    Aleshin, A. P.; Velichkin, V. I.; Krylova, T. L.


    The ambiguity of genetic interpretations of uranium ore formation at Mo-U deposits of the Strel’tsovka ore field led us to perform additional geochemical, mineralogical, and thermobarogeochemical studies. As a result, it has been established that closely related U and F were progressively gained in the Late Mesozoic volcanic rocks from the older basic volcanics (170 Ma) to the younger silicic igneous rocks (140 Ma). The Early Cretaceous postmagmatic hydrothermal epoch (140-125 Ma) is subdivided into preore, uranium ore, and first and second postore stages. The primary brannerite-pitchblende ore was formed in association with fluorite. At the first postore stage, this assemblage was replaced by a U-Si metagel, which was previously identified as coffinite. The metagel shows a wide compositional variation; its fine structure has been studied. The preore metasomatic alteration and related veined mineralization were formed under the effect of sodium (bicarbonate)-chloride solution at a temperature of 250-200°C. The uranium ore formation began with albitization and hematitization of rocks affected by supercritical fluid at 530-500°C; brannerite and pitchblende precipitated at 350-300°C. The chondrite-normalized REE patterns of pitchblende hosted in trachybasalt, trachydacite, and granite demonstrate a pronounced Sm-Nd discontinuity and a statistically significant tetrad effect of W type. These attributes were not established in REE patterns of rhyolites derived from the upper crustal magma chamber. This circumstance and a chronological gap of 5 Ma between silicic volcanism and ore formation do not allow us to suggest that uranium was derived from this magma chamber. According to the proposed model, the evolved silicic Li-F magma was a source of uranium. U4+, together with REE, was fractionated into the fluid phase as complex fluoride compounds. The uranium mineralization was deposited at a temperature barrier. It is suggested that hydromica alteration and the

  3. Evolution of a Neoproterozoic suture in the Iberian Massif, Central Portugal: New U-Pb ages of igneous and metamorphic events at the contact between the Ossa Morena Zone and Central Iberian Zone (United States)

    Henriques, S. B. A.; Neiva, A. M. R.; Ribeiro, M. L.; Dunning, G. R.; Tajčmanová, L.


    A Neoproterozoic suture is exposed at the contact between the Ossa Morena Zone and the Central Iberian Zone, in the Iberian Massif (Central Portugal), the westernmost segment of the European Variscides. Although, the Cadomian magmatic and tectonometamorphic events have been previously documented, their timing is still poorly constrained, particularly in the inner zones of the suture. We used geochronological (ID-TIMS U-Pb) data to establish the sequence of events, isotopic (Rb-Sr, Sm-Nd) data to characterize the magmatic sources and thermodynamic modelling to determine the maximum P-T conditions attained during the Cadomian metamorphism. The first event, in the future Ossa Morena Zone, is the onset of island arc magmatism represented mainly by tholeiites with a MORB signature. Their igneous crystallization age is unknown, but they are older than ca. 539 Ma. This magmatic activity was accompanied by deposition of fine-grained sediments in a Neoproterozoic basin. The second event is the evolution of the Cadomian magmatic arc in different stages. The earliest magmatic stage occurs at ca. 692 Ma, which is the oldest igneous age known in the Ossa Morena Zone. It is followed by the generation of subalkaline and peraluminous protoliths at ca. 569 Ma, with the isotopic signature of old crustal sources. The final phase of the arc magmatism (ca. 548-544 Ma) involved mainly partial melting of continental crust. The range of the main magmatic activity must have been between ca. 569 Ma and ca. 544 Ma as mentioned for other areas in the Ossa Morena Zone. A major metamorphic event, recorded in metamorphic monazite, zircon and titanite at ca. 540 Ma, attained upper amphibolite facies conditions close to the transition to granulite facies (7-8 kbar and 640-660 °C). It represents the continental arc accretion of the Ossa Morena Zone with the Iberian Autochthon passive margin (future Central Iberian Zone). The Early Ordovician rocks (ca. 483-477 Ma) were generated from depleted and

  4. Decoupling of whole-rock Nd-Hf and zircon Hf-O isotopic compositions of a 284 Ma mafic-ultramafic intrusion in the Beishan Terrane, NW China (United States)

    Su, Ben-Xun; Qin, Ke-Zhang; Lu, Ying-Huai; Sun, He; Sakyi, Patrick Asamoah


    Abundant Permian mafic-ultramafic intrusions in the Beishan Terrane, NW China, are parts of the Tarim large igneous province. Among these intrusions, Luodong intrusion is composed of dunite, wehrlite and gabbro. These rocks have whole-rock Sr-Nd-Hf and zircon Hf-O isotope compositions that display significant decoupling. The decoupling of these generally well-correlated systems demonstrates contrasting evolving trends. Systematic compositional and mineralogical controls on decoupling have been investigated. Wehrlites and gabbros show MORB-like trace element patterns with negligible crustal contamination. They have high initial 143Nd/144Nd [ɛNd(t) = +6.6 to +11.2] and 176Hf/177Hf [ɛHf(t) = +12.2 to +16.9] and low initial 87Sr/86Sr [(87Sr/86Sr)i = 0.702949-0.704098] ratios and plot within the MORB field, indicating that their parental magmas were derived from a depleted mantle source. The enrichment features are present in the zircon crystals separated from the gabbro. These homogeneously unzoned zircon crystals have high U concentrations, low Th/U ratios and a U-Pb age of 284.0 ± 2.3 Ma. They are therefore interpreted as having formed rapidly in a highly fractionated/evolved magma. Their ɛHf(t) and δ18O values range from -9.3 to -6.7 and +10.25 ‰ to +11.42 ‰, respectively. The decoupling is linked with crustal contamination by ancient crust (probably Proterozoic schist in the Beishan Terrane) that occurred during zircon crystallization. However, the contamination signature in the whole-rock composition was soon overprinted by magma mixing process. The inference is evidenced by zoning textures preserved in plagioclase, clinopyroxene, spinel and particularly olivine, and the presence of coeval diabase dykes cutting through the intrusion. The isotope decoupling observed in this mantle-plume-related mafic-ultramafic intrusion supports the idea that Nd-Hf decoupling and Lu/Hf and Sm/Nd parent/daughter variations exist only on a small hand-size scale in a

  5. Geochemistry of Monazite within Carbonatite Related REE Deposits

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    Wei Chen


    Full Text Available Approximately >50% of global rare earth element (REE resources are hosted by carbonatite related deposits, of which monazite is one of the most important REE minerals. Monazite dominates more than 30 carbonatite-related REE deposits around the world, including currently exploited mineralization at Bayan Obo and Mount Weld. These deposits are widely distributed across all continents, except Antarctica. Though rare, monazite occurs as the primary mineral in carbonatite, and mostly presents as a secondary mineral that has a strong association with apatite. It can partially or completely replace thin or thick overgrowth apatite, depending on the availability of REE. Other mineral phases that usually crystallize together with monazite include barite, fluorite, xenotime, sulfide, and quartz in a carbonate matrix (e.g., dolomite, calcite. This review of monazite geochemistry within carbonatite-related REE deposits aims to provide information regarding the use of monazite as a geochemical indicator to track the formation history of the REE deposits and also supply additional information for the beneficiation of monazite. The chemical compositions of monazite are highly variable, and Ce-monazite is the dominant solid solution in carbonatite related deposits. Most monazite displays steep fractionation from La to Lu, absent of either Eu or Ce anomalies in the chondrite normalized REE plot. The other significant components are huttonite and cheratite. Some rare sulfur-bearing monazite is also identified with an SO3 content up to 4 wt %. A 147Sm/144Nd ratio with an average ~0.071 for monazite within carbonatite-related ores is similar to that of their host rocks (~0.065, and is the lowest among all types of REE deposits. Sm/Nd variation of monazite from a single complex reflects the differentiation stage of magma, which decreases from early to late. Based on the differences of Nd and Sr abundances, Nd isotopic composition for monazite can be used to track

  6. Variaciones texturales y movilidad geoquímica asociadas a milonitización: la zona de cizalla del granitoide El Tigre, Sierra de Pie de Palo, Sierras Pampeanas Occidentales, San Juan

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    Brígida Castro De Machuca


    Full Text Available Una faja de cizalla dúctil con foliación milonítica de dirección NEE y buzamiento al sudeste, afecta a un granitoide mesoproterozoico (Granitoide El Tigre: 31º31'30''S-68º15'12''O que forma parte del basamento cristalino de la Sierra de Pie de Palo, Sierras Pampeanas Occidentales. El análisis cinemático de la faja indica una componente principal de desplazamiento de rumbo con sentido de movimiento dextral. En el granitoide no deformado (protolito se preservan asociaciones minerales y texturas relícticas, ígneas y metamórficas, que son obliteradas por la deformación. La milonitización operó en un sistema abierto provocando la movilización (ganancia o pérdida de casi todos los elementos mayores y traza, incluyendo las tierras raras e isótopos de Rb/Sr y Sm/Nd. Los cambios químicos fueron controlados mayormente por transporte sintectónico de fluidos y por transformaciones mineralógicas producidas durante la milonitización (disminución del contenido de granate, biotita y minerales accesorios y neoformación de mica blanca en la matriz de las milonitas. Las variaciones isotópicas entre el protolito y las milonitas también serían resultado de la intervención de fluidos durante la deformación, con interacción variable entre fluido y rocas de caja. Los cambios texturales, mineralógicos y químicos experimentados por el granitoide durante la milonitización, permiten reconstruir su evolución tectono-metamórfica y las condiciones metamórficas imperantes. Las asociaciones minerales y microestructuras de deformación de las milonitas sugieren para la faja de cizalla del granitoide El Tigre condiciones propias de la facies de esquistos verdes, con temperaturas inferiores a los 400 °C. Este evento deformante tuvo lugar a los 473 ± 10 Ma durante la orogenia Famatiniana.

  7. Geochemical constraints on komatiite volcanism from Sargur Group Nagamangala greenstone belt, western Dharwar craton, southern India: Implications for Mesoarchean mantle evolution and continental growth

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    Full Text Available We present field, petrographic, major and trace element data for komatiites and komatiite basalts from Sargur Group Nagamangala greenstone belt, western Dharwar craton. Field evidences such as crude pillow structure indicate their eruption in a marine environment whilst spinifex texture reveals their komatiite nature. Petrographic data suggest that the primary mineralogy has been completely altered during post-magmatic processes associated with metamorphism corresponding to greenschist to lower amphibolite facies conditions. The studied komatiites contain serpentine, talc, tremolite, actinolite and chlorite whilst tremolite, actinolite with minor plagioclase in komatiitic basalts. Based on the published Sm-Nd whole rock isochron ages of adjoining Banasandra komatiites (northern extension of Nagamangala belt and further northwest in Nuggihalli belt and Kalyadi belt we speculate ca. 3.2–3.15 Ga for komatiite eruption in Nagamangala belt. Trace element characteristics particularly HFSE and REE patterns suggest that most of the primary geochemical characteristics are preserved with minor influence of post-magmatic alteration and/or contamination. About 1/3 of studied komatiites show Al-depletion whilst remaining komatiites and komatiite basalts are Al-undepleted. Several samples despite high MgO, (Gd/YbN ratios show low CaO/Al2O3 ratios. Such anomalous values could be related to removal of CaO from komatiites during fluid-driven hydrothermal alteration, thus lowering CaO/Al2O3 ratios. The elemental characteristics of Al-depleted komatiites such as higher (Gd/YbN (>1.0, CaO/Al2O3 (>1.0, Al2O3/TiO2 (18 together with higher HREE, Y, Zr suggest their derivation from shallower upper mantle without garnet involvement in residue. The observed chemical characteristics (CaO/Al2O3, Al2O3/TiO2, MgO, Ni, Cr, Nb, Zr, Y, Hf, and REE indicate derivation of the komatiite and komatiite basalt magmas from heterogeneous mantle (depleted to primitive mantle at

  8. The process of glauconitization: chemical and isotopic evidence (United States)

    Stille, Peter; Clauer, Norbert


    Sequential leaching experiments were made on Recent glauconies and clay fractions of the associated mud from off-shore Africa near the estuary of the Congo River. Analyses of major/rare earth elements (REE) and Nd isotopic compositions on the resulting leachate and residue pairs allow identification of at least three important and isotopically distinct components which contributed to the glauconitization process: (1) a detrital component with relatively high 87Sr/86Sr and relatively low 143Nd/144Nd isotopic ratios; (2) a phosphate phase rich in REE and Sr with sea water Sr and Nd isotopic characteristics; (3) a component rich in organic matter and Ca with a sea water Sr isotopic signature, a relatively low Nd isotopic composition and elevated Sm/Nd ratios. This latter component probably represents the suspended organic and carbonate-rich river load. The detrital and the river components were mixed up in the muddy off-shore sediment, ingested by worms, and integrated into faecal pellets. The resulting material has Sr and Nd isotopic signatures intermediate between those of the detrital and river components, and represents the precursor of the glaucony minerals. During the subsequent dissolution-crystallization process, the glauconitic pellets remain isotopically closed to any external supply, but expulsion of Sr and Nd with increasing degree of maturation is observed without any effect on the Sr and Nd isotopic compositions. At a higher maturation stage (K2O>4.5%), the Sr and Nd isotopic compositions tend to decrease and increase, respectively, approximating the isotopic composition values of the phosphate-rich phase. Because the Sr and Nd concentrations decrease, the evolution of the glauconies toward lower Sr and higher Nd isotopic compositions can only be explained by expulsion of Sr and Nd of the detrital component with high Sr and low Nd isotopic signatures. Dissolution of the chemically unstable, wormdigested clay material from mud may be responsible for the

  9. Major element composition of an Early Enriched Reservoir: constraints from 142Nd/144Nd isotope systematics in the early Earth and high-pressure melting experiments of a primitive peridotite (United States)

    Kondo, Nozomi; Yoshino, Takashi; Matsukage, Kyoko N.; Kogiso, Tetsu


    The Accessible Silicate Earth (ASE) has a higher 142Nd/144Nd ratio than most chondrites. Thus, if the Earth is assumed to have formed from these chondrites, a complement low-142Nd/144Nd reservoir is needed. Such a low-142Nd/144Nd reservoir is believed to have been derived from a melt in the early Earth and is called the Early Enriched Reservoir (EER). Although the major element composition of the EER is crucial for estimating its chemical and physical properties (e.g., density) and is also essential for understanding the origin and fate of the EER, which are both major factors that determine the present composition of the Earth, it has not yet been robustly established. In order to determine the major element composition of the EER, we estimated the age and pressure-temperature conditions to form the EER that would best explain its Nd isotopic characteristics, based on Sm-Nd partitioning and its dependence on pressure, temperature, and melting phase relations. Our estimate indicates that the EER formed within 33.5 Myr of Solar System formation and at near-solidus temperatures and shallow upper-mantle pressures. We then performed high-pressure melting experiments on primitive peridotite to determine the major element composition of the EER at estimated temperature at 7 GPa and calculated the density of the EER. The result of our experiments indicates that the near-solidus melt is iron-rich komatiite. The estimated density of the near-solidus melt is lower than that of the primitive peridotite, suggesting that the EER melt would have ascended in the mantle to form an early crust. Given that high mantle potential temperatures are assumed to have existed in the Hadean, it follows that the EER melt was generated at high pressure and, therefore, its composition would have been picritic to komatiitic. As the formation age of the EER estimated in our study precedes the last giant, lunar-forming impact, the picritic to komatiitic crust (EER) would most likely have been

  10. Timing and sources of granite magmatism in the Ribeira Belt, SE Brazil: Insights from zircon in situ U-Pb dating and Hf isotope geochemistry in granites from the São Roque Domain (United States)

    Janasi, Valdecir de Assis; Andrade, Sandra; Vasconcellos, Antonio Carlos B. C.; Henrique-Pinto, Renato; Ulbrich, Horstpeter H. G. J.


    Eight new in situ U-Pb zircon age determinations by SHRIMP and LA-MC-ICPMS reveal that the main granitic magmatism in the São Roque Domain, which is largely dominated by metaluminous high-K calc-alkaline monzogranites with subordinate peraluminous leucogranites, occurred between 604 ± 3 and 590 ± 4 Ma. This small temporal range is ca. 20-30 Ma younger than previously admitted based on U-Pb TIMS dates from literature, some of which obtained in the same occurrences now dated. The observed discrepancy seems related to the presence of small Paleoproterozoic inherited cores in part of the zircon populations used for TIMS multigrain dating, which could also respond for the unusually high (up to 10 Ma) uncertainty associated with most of these dates. The younger age range now identified for the São Roque granite magmatism has important implications for the evolution of the Ribeira Fold Belt. Whilst previously admitted ages ca. 620-630 Ma substantiated correlations with the widespread and intensely foliated high-K calc-alkaline granitoid rocks of the neighbor Socorro-Guaxupé Nappe (potentially associated with an accretionary continental margin), the ˜600-590 Ma interval seems more consistent with a late deformation tectonic setting. Strongly negative ɛHf(t) characterize the magmatic zircons from the São Roque Domain granites. An eastward increase from -22 in the São Roque Granite to -11 in the Cantareira Granite and neighboring stocks suggests an across-domain shift in granite sources. Such eastward younging of sources, also indicated by Sm-Nd isotope data from granites and supracrustal sequences in neighboring domains, is suggestive that some of the first-order limits and discontinuities in this belt are not defined by the strike-slip fault systems traditionally taken to separate distinct domains. Although the negative ɛHf(t) and ɛNd(t) indicate sources with long crustal residence for all studied granite plutons, the observed range is more radiogenic than the

  11. Oceanic plateau model for continental crustal growth in the Archaean: A case study from the Kostomuksha greenstone belt, NW Baltic Shield (United States)

    Samsonov, A. V.; Shchipansky, A. A.; Jochum, K. P.; Mezger, K.; Hofmann, A. W.; Puchtel, I. S.


    Field studies combined with chemical and isotope data indicate that the Kostomuksha greenstone belt in the NW Baltic Shield consists of two lithotectonic terranes, one mafic igneous and the other sedimentary, separated by a major shear zone. The former contains submarine komatiite-basalt lavas and volcaniclastic lithologies, and the latter is composed of shelf-type rocks and BIF. Komatiitic and basaltic samples yield Sm-Nd and Pb-Pb isochron ages of 2843+/-39 and 2813+/-78 Ma, respectively. Their trace-element compositions resemble those of recent Pacific oceanic flood basalts with primitive-mantle normalized Nb/Th of 1.5-2.1 and Nb/La of 1.0-1.5. This is in sharp contrast with island arc and most continental magmas, which are characterized by Nb/(Th,La)N≪1. Calculated initial Nd-isotope compositions (ɛNd(T)=+2.8 to +3.4) plot close to an evolution line previously inferred for major orogens (``MOMO''), which is also consistent with the compositions of recent oceanic plateaux. The high liquidus temperatures of the komatiite magmas (1550°C) and their Al-depleted nature require an unusually hot (1770°C) mantle source for the lavas (>200°C hotter than the ambient mantle at 2.8 Ga), and are consistent with their formation in a deep mantle plume in equilibrium with residual garnet. This plume had the thermal potential to produce oceanic crust with an average thickness of ~30 km underlain by a permanently buoyant refractory lithospheric mantle keel. Nb/U ratios in the komatiites and basalts calculated on the basis of Th-U-Pb relationships range from 35 to 47 and are thus similar to those observed in modern MORB and OIB. This implies that some magma source regions of the Kostomuksha lavas have undergone a degree of continental material extraction comparable with those found in the modern mantle. The mafic terrane is interpreted as a remnant of the upper crustal part of an Archaean oceanic plateau. When the newly formed plateau reached the active continental margin

  12. MOMO - Revisited in light of 142Nd (United States)

    Stein, M.


    million years), which evolves after major overturn events during crust formation. It may be that the MOMO slope slightly declines through time due to mixing between the two reservoirs. Nevertheless, the implications of having early mantle with non-chondritic Sm/Nd ratios for issues like the abundance of U, Th, K, the Ar reservoir and the Urey ratio are similar for both models. The Cenozoic manifestation of the enriched (MOMO) mantle is the PREMA basalts (with ɛNd~ +5 and 87Sr/86Sr ~ 0.7035). The PREMA composition and D-MORB essentially form the “historical” mantle array proposed by DePaolo &Wasserburg (1976).

  13. Metasomatic control of water contents in the Kaapvaal cratonic mantle (United States)

    Peslier, A. H.; Woodland, A. B.; Bell, D. R.; Lazarov, M.; Lapen, T. J.


    suggest that the metasomatic events responsible for setting the water contents may date from the Archean at Kimberley and from the Proterozoic at Jagersfontein. Combined water with Lu-Hf and Sm-Nd isotopic data at Finsch (Lazarov et al., in press-a) and with Ar-Ar phlogopite ages at Liqhobong (Hopp et al., 2008) indicates that water addition by metasomatic melts occurred in the Proterozoic. Water contents of mantle minerals in Kaapvaal xenoliths measured here have been preserved since that time and can consequently be used in modelling viscosity and longevity of cratonic roots since at least the mid-Proterozoic.

  14. Geochemistry, Petrology, and Provenance of Magnetite-Rich Ortaklar Cu Deposit Hosting Basalts from Koçali Complex, Gaziantep, Turkey (United States)

    Yun, E.; Lee, I.; Kang, J.; Dönmez, C.; Yildirim, N.


    Magnetite-rich Cyprus type VMS deposit has been recently discovered from the Ortaklar-Gaziantep region within Koçali complex, SE Turkey. Magnetite rich sulfide ore bodies are in close contact with underlying footwall spilitic basalts. These basalts are part of Koçali mélange, which represents an accreted oceanic complex during closing of southern Neotethys. These extrusives are low-K, low alkali tholeiites with Ca rich, partially sericitized plagioclase subophitically enclosed by augite with disseminated Fe-Ti oxides and pyrite. Mineral crystallization sequence of plagioclase followed by augite and opaque is typical of MORB. Major and trace element analyses for least altered basalts based on LOI (1.5~3.6 wt%), Ce/Ce* (0.9~1.1) exhibit limited range of element abundances. Low Mg# (59~60) suggests that basalts were derived from moderately evolved magma with fractional crystallization. HFSE (Th, Nb, Hf, Zr) were used for tectonic discrimination and basalts were plotted within MORB end spectrum, near MORB-IAT boundary. N-MORB normalized La to Lu ranges from 0.4 to 0.9 times N-MORB with LREE depletion [(La/Sm)N = 0.58~0.67] and flat HREE [(Tb/Lu)N = 0.95~1.05]. Chondrite normalized REE patterns resemble those of N-MORB but characterized by severe LREE depletion [(La/Sm)CN = 0.35~0.45]. LREE depletion coupled with high Sm/Nd (0.36~0.43), high CaO/Na2O (5.0~6.2) and low Nb/Yb (0.23~0.39) suggest depleted N-MORB composition derived from the refractory mantle source. Analyzed basalts are similar to those found from other rift (Costa Rica Rift Hole 504b) and intra-transform fault (Siqueiros transform). Magnetite emplacement occurring close to the ore-host boundary and lack of pyrrhotite from hosting basalts imply an involvement of oxidized hydrothermal fluids. Basalts probably have formed by late stage, partial melting of the refractory mantle at low pressure, shallow depth, and H2O rich environment. Possible source of mantle heterogeneity can be identified by isotope

  15. On the issue of the Precambrian basement of the Arctic shelf (United States)

    Vernikovsky, Valery A.; Korago, Evgeny A.; Proskurnin, Vasily F.; Sobolev, Nikolay N.


    Many researchers of the geological structures of the Russian Arctic concluded that the basements of the terranes composing the Arctic shelf and continental slopes have a Precambrian age. It is assumed that these terranes are actually fragments of the ancient Arctida paleocontinent [Zonenshain, Natapov, 1987] that broke up as a result of rifting and its separate plates and terranes either were overlain by continental margins sediments or included in the fold belts in the periphery of the ocean. In the western part of the Russian Arctic, a Grenvillian and Mesoproterozoic basement was demonstrated for Svalbard, Novaya Zemlya and Taimyr Peninsula, and at least a Neoproterozoic basement was established for structures in the basement of Severnaya Zemlya archipelago. In the eastern part of the Russian Arctic, such proofs were almost nonexistent. In recent years, new information was obtained concerning the continental nature and Precambrian age of the basement crust of the New Siberian Islands and De Long archipelagos as well as probably the Mendeleev Ridge. For the New Siberian Islands and De Long archipelagos, a whole series of geochronological evidence was obtained in addition to geological data (horizontally bedding Early Paleozoic passive continental margin sediments (Cambrian, Ordovician) at Bennett Island). In magmatic and tuffaceous-sedimentary rocks of Henrietta and Zhokhov islands we discovered zircons that had formed from magmatic crystallization in the Late Neoproterozoic. New U-Pb data for zircons from rocks of these islands do not contradict isotopic dating obtained earlier by other methods - Ar/Ar and Sm/Nd in different laboratories. Considering different closure temperatures for isotopic systems, these new results complement each other. On the islands of the eastern sector of the Russian Arctic, a Neoproterozoic complex of rocks is most certainly established in the basement of the mesozoides of Vrangel Island. Here were discovered metamorphosed volcanics

  16. Study on Mineralization Age of Xiaoban Gold Deposit, Fujian Province

    Institute of Scientific and Technical Information of China (English)


    The Xiaoban gold deposit is a large-size deposit recently found in middle area of Fujian Province. It belongs to magmatic hydrothermal type occurred in Mayuan Group metamorphic rocks of Middle Proterozoic and is controlled by low angle fault (detachment) structures. The contents of Au in Mayuan Group metamorphic rocks, Caledonian-Indosinian deformed granite and early Yanshanian granite are higher with Au enrichment coefficient of 2.06-5.68, 5.11 and 6.67 than those in other geological bodies. And the higher enrichment coefficients (>2) of Ag, S, Sn and Te are similar to those of gold ore. Meanwhile, the distribution of Au in Mayuan Group metamorphic rocks and early Yanshanian granite with a low D-value (0.58 and 0.67) is favorable to gold mineralization. REE characteristics of gold ore, ratios of (LREE/HREE), (La/Sm)n, (Yb/Lu)n, (La/Tb)n and (Sm/Nd)n are similar to Mayuan Group metamorphic rocks, only non or little normal Eu abnormal of ore is dissimilar to metamorphic rocks. The δ(34S) of the gold ore, with a high homogenization, is (-4.7×10-3)-(-2.7×10-3). The study of inclusion indicates 180-249 ℃ of mineralization temperature, 3.69 %-11.81 % of salinities and 0.869-0.991 g/cm3 of densities of mineralization fluid. Based on hydrogen and oxygen isotope (δ(18O)=11.0×10-3-11.7×10-3, δ(D)=(-48×10-3)-(-62×10-3)) and initial w(87Sr)/w(86Sr) =0.715,combining to the analysis of geological history, regional metamorphism and magamtic activity, the authors confirm that the source for the ore fluid was mainly from magmatic, partly from metamorphic water, and with a little influence of meteoric water. Isotopic dating made on Rb-Sr isochron age of 182 Ma, by using alteration minerals of gold-ores from the deposit, indicates that the mineralization occurs in early Yanshanian epoch. This is close to the age of 187 Ma of the Anchun magmatite with a similar alteration and gold mineralization to the Xiaoban gold deposit. The age of early Yanshanian epoch of the Xiaoban

  17. Duration of a large Mafic intrusion and heat transfer in the lower crust: A SHRIMP U-Pb zircon Study in the Ivrea-Verbano Zone (Western Alps, Italy) (United States)

    Peressini, G.; Quick, J.E.; Sinigoi, S.; Hofmann, A.W.; Fanning, M.


    The Ivrea-Verbano Zone in the western Italian Alps contains one of the world's classic examples of ponding of mantle-derived, mafic magma in the deep crust. Within it, a voluminous, composite mafic pluton, the Mafic Complex, intruded lower-crustal, high-grade paragneiss of the Kinzigite Formation during Permian-Carboniferous time, and is now exposed in cross-section as a result of Alpine uplift. The age of the intrusion is still debated because the results of geochronological studies in the last three decades on different rock types and with various dating techniques range from 250 to about 300 Ma. Sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon age determinations on 12 samples from several locations within the Mafic Complex were performed to better constrain the age of the igneous event. The results indicate a long history of magma emplacement and cooling, which reconciles the spread in previously published ages. The main intrusive phase took place at 288 ?? 4 Ma, causing a perturbation of the deep-crustal geotherm, which relaxed to the Sm-Nd closure temperature in garnet-free mafic rocks after about 15-20 Myr of sub-solidus cooling at c. 270 Ma. These results suggest that large, deep crustal plutons, such as those identified geophysically at depths of 10-20 km within extended continental crust (e.g. Yellowstone, Rio Grande Rift, Basin and Range) may have formed rapidly but induced a prolonged thermal perturbation. In addition, the data indicate that a significant thermal event affected the country rock of the Mafic Complex at about 310 Ma. The occurrence of an upper amphibolite- to granulite-facies thermal event in the Kinzigite Formation prior to the main intrusive phase of the Mafic Complex has been postulated by several workers, and is corroborated by other geochronological investigations. However, it remains uncertain whether this event (1) was part of a prolonged perturbation of the deep-crustal geotherm, which started long before the onset of

  18. IODP Expedition 345: Characterizing Hydrothermal Alteration of Fast-Spreading EPR Lower Crust using O, Sr and Nd isotopics (United States)

    Marks, N.; Gillis, K. M.; Lindvall, R. E.; Schorzman, K.


    The Integrated Ocean Drilling Program (IODP) Expedition 345 sampled lower crustal primitive gabbroic rocks that formed at the fast-spreading East Pacific Rise (EPR) and are exposed at the Hess Deep Rift. The metamorphic mineral assemblages in the rocks recovered at Site U1415 record the cooling of primitive gabbroic lithologies from magmatic (>1000°C) to zeolite facies conditions (exposure onto the seafloor. The dominant alteration assemblage is characterized by lower grade greenschist (talc, serpentine, or clay minerals, and is commonly accompanied by prehnite microveins in plagioclase. The intensity of alteration varies with igneous lithology, in particular, the modal abundance of olivine, as well as proximity to zones of brittle fracturing and cataclasis. We have attempted to characterize the nature and extent of isotopic exchange associated alteration and cooling and present a record of variations in O, Sr, and Nd isotopic compositions in altered rocks from the lower plutonic crust at Hess Deep. The Rb-Sr and 18O/16O systems exhibit sensitivity to hydrothermal interactions with seawater; whereas the Sm-Nd system appears essentially undisturbed by the minimal alteration experienced by the rocks drilled at Site U1415. The 87Sr/86Sr isotopic compositions of olivine gabbros (Mg# 0.81-0.89) range from 0.702536-0.703950 (±0.000008). Higher 87Sr/86Sr ratios are strongly correlated with percentage of hydrous minerals, and are higher in samples with a greater modal abundance of olivine. These rocks have somewhat higher 87Sr/86Sr ratios than upper plutonic rocks from the Northern Escarpment at Hess Deep (Kirchner and Gillis, 2012), although their percentage of hydrous phases is apparently similar. The d18O in these rocks ranges from 0.23‰ to 4.65‰ (±0.67); troctolites have systematically lower d18O than the gabbro and gabbronorites. Preliminary Nd isotopic data appears to be consistent with previous measurements from the Site 894 gabbros, implying derivation from

  19. The belt of metagabbros of La Pampa: Lower Paleozoic back-arc magmatism in south-central Argentina (United States)

    Chernicoff, Carlos J.; Zappettini, Eduardo O.; Villar, Luisa M.; Chemale, Farid, Jr.; Hernández, Laura


    Combined geological, geochronological, geochemical and geophysical studies have led to identification of a large (˜300 km long, ˜5 km wide) N-S trending belt of metagabbros in the province of La Pampa, south-central Argentina. This belt, though only poorly exposed in the localities of Valle Daza and Sierra de Lonco Vaca, stands out in the geophysical data (aeromagnetics and gravity). Modeling of the aeromagnetic data permits estimation of the geometry of the belt of metagabbros and surrounding rocks. The main rock type exposed is metagabbros with relict magmatic nucleii where layering is preserved. A counterclockwise P-T evolution affected these rocks, i.e., during the Middle Ordovician the protolith reached an initial granulite facies of metamorphism (M1), evolving to amphibolite facies (M2). During the Upper Devonian, a retrograde, greenschist facies metamorphism (M3) partially affected the metagabbros. The whole-rock Sm-Nd data suggest a juvenile source from a depleted mantle, with model ages ranging from 552 to 574 Ma, and positive Epsilon values of 6.51-6.82. A crystallization age of 480 Ma is based on geological considerations, i.e. geochronological data of the host rocks as well as comparisons with the Las Aguilas mafic-ultramafic belt of Sierra de San Luis (central Argentina). The geochemical studies indicate an enriched MORB and back-arc signature. The La Pampa metagabbros are interpreted to be originated as a result of the extension that took place in a back-arc setting coevally with the Famatinian magmatic arc (very poorly exposed in the western part of the study area). The extensional event was 'aborted' by the collision of the Cuyania terrane with Pampia-Gondwana in the Middle Ordovician, causing deformation and metamorphism throughout the arc-back-arc region. The similarities between the La Pampa metagabbros and the mafic-ultramafic Las Aguilas belt of the Sierra de San Luis are very conspicuous, for example, the age (Lower Paleozoic), geochemical

  20. Phase equilibria modelling and zircon dating for Precambrian metapelites from Xinghuadukou Group in Lvlin Forest of Erguna Massif, NE China (United States)

    Xu, Jiulei; Zheng, Changqing; Tajcmanova, Lucie; Zhong, Xin; Xu, Xuechun; Han, Xiaomeng; Wang, Zhaoyuan


    Xinghuadukou Group, the basement metamorphic complex of Erguna Massif in NE China, is considered to be Mesoproterozoic with Sm-Nd age of 1157±32 Ma. However, the new zircon data from these metamorphic supracrustal rocks in Lvlin Forest show that they formed in Neoproterozoic with the age of 800 Ma. Old zircon age with 2.5 Ga, 2.0 Ga and 1.8 Ga, indicate that the Erguna Massif had an affinity to both Columbia and Rodinia continents. Furthermore, we also present 500 Ma metamorphic age in micashists and 500 Ma age of adjacent granitoids that might have thermally influenced its surrounding. No detailed studies have been undertaken on the metamorphic evolution of the Xinghuadukou Complex. The typical paragneissic mineral assemblage of garnet sillimanite mica schist is Grt+Sil+Bt+Mus+Qtz±Kfs. (Zhou et al., 2011) proposed that the Xinghuadukou Complex appears to have undergone similar granulite facies metamorphic conditions based on the similarity of mineral assemblages to the Mashan Complex in the Jiamusi Massif, NE China. However, the new phase equilibria modelling result shows that these rocks are high amphibolite facies product with 650℃. We can easily find K-feldspar formed by partial melting due to the consuming of muscovite. Also the remaining muscovite is directly connected with a fluid channel in thin sections which indicate that the remaining muscovite formed from retrograde with the existence of fluid. The zoned garnet has low MgO and high CaO content in rims and high MgO and low CaO content in core. It seems that this garnet has high pressure and low temperature (HP-LT) in rims and low pressure and high temperature (LP-HT) in core which would point to an anti-clockwise metamorphic evolution. Zhou, J.B., Wilde, S.A., Zhang, X.Z., Zhao, G.C., Liu, F.L., Qiao, D.W., Ren, S.M. and Liu, J.H., 2011b. A> 1300km late Pan-African metamorphic belt in NE China: new evidence from the Xing'an block and its tectonic implications. Tectonophysics, 509(3): 280-292.

  1. A self-activated silicate phosphor of Na{sub 5}YZrSi{sub 6}O{sub 18}

    Energy Technology Data Exchange (ETDEWEB)

    Guan, Ying; Qin, Lin; Huang, Yanlin [College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123 (China); Qin, Chuanxiang, E-mail: [College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123 (China); Wei, Donglei [Department of Physics and Center for Marine-Integrated Biomedical Technology, Pukyong National University, Busan 608-737 (Korea, Republic of); Seo, Hyo Jin, E-mail: [Department of Physics and Center for Marine-Integrated Biomedical Technology, Pukyong National University, Busan 608-737 (Korea, Republic of)


    Graphical abstract: Self-activated Na{sub 5}YZrSi{sub 6}O{sub 18} shows a bright green luminescence. It presents obvious LLP afterglow with duration time >3 h after the removal of excitation. The substitution of Y{sup 3+} by rare earth ions except Yb{sup 3+} cannot prolong the afterglow. It is proposed that the disorder in the lattices can result in different trap centers attributing to the long last phosphorescence. - Highlights: • Na{sub 5}YZrSi{sub 6}O{sub 18} was firstly developed to be a new bluish green-emitting silicate. • Na{sub 5}YZrSi{sub 6}O{sub 18} presents unusual properties: efficient excitation and longer emission wavelength. • Na{sub 5}YZrSi{sub 6}O{sub 18} shows long-lasting phosphorescence with duration time above 3 h. - Abstract: A new self-activated silicate phosphor of Na{sub 5}YZrSi{sub 6}O{sub 18} was prepared by a solid-state reaction method. The phase formation was confirmed by X-ray powder diffraction measurement. The photoluminescence excitation and emission spectra, X-ray-excited luminescence, decay curves, quantum efficiencies and the color coordinates were investigated. It can be efficiently excited by UV light and X-ray and presents unusual green emission (centered at 475 nm) from Zr{sup 4+} to O{sup 2−} charge transfer transition. Meanwhile, the phosphor shows long-lasting phosphorescence with duration time above 3 h after the removal of excitation. The afterglow curves and thermo-luminescence were measured for pure and rare earth ions (RE = Yb, Er, Ho, Dy, Tb, Sm, Nd) doped Na{sub 5}YZrSi{sub 6}O{sub 18}. The possible defects and the mechanism of long-lasting phosphorescence were suggested on the base of the strong disorder of the multiply cation sites in the lattices.

  2. Early Earth differentiation processes investigated through the short-lived 146Sm-142Nd and 182Hf-182W isotope systems (United States)

    Rizo Garza, H. L.; Walker, R. J.; Carlson, R.; Touboul, M.; Horan, M. F.; Puchtel, I. S.; Boyet, M.; Rosing, M. T.


    The earliest history of Earth is difficult to capture due to the scarcity and high degrees of alteration of ancient terrains. Nevertheless, short-lived isotope systems can provide important constraints on early geological processes. The 182Hf-182W (t1/2 = 8.9 Ma) and 146Sm-142Nd (t1/2=103 Ma) systems are variably sensitive to differentiation processes that occurred during the first 50 Ma and 500 Ma of Earth's history, respectively. Eoarchean mantle-derived rocks from the Isua supracrustal belt (southwest Greenland) show well-resolved anomalies in both 182W (+5 to +21 ppm) and 142Nd (-10 to +15 ppm) compared to terrestrial standards. While there is evidence that W was mobilized in the crust accessed by the Isua suite, W and Nd isotopic anomalies are interpreted to primarily reflect Hadean processes that affected the mantle precursors of these rocks. Variations in 142Nd do not correlate with those of 182W, however, suggesting different mechanisms for the origin and retention of the isotopic anomalies present in these two systems. The 142Nd data, combined with 143Nd data for the long-lived 147Sm-143Nd system, are interpreted to reflect silicate crystal-liquid fractionation 4.3 Ga ago. Variations of 182W in the Isua lavas mantle source could also have been produced as a result of Hf/W fractionation caused by silicate differentiation during the lifetime of 182Hf, but these processes would have to somehow be decoupled from the processes that affected Sm/Nd. Alternatively, 182W variability could be the result of combined early Hf/W fractionations caused by metal-silicate segregation within discrete mantle domains and late accretion processes. Variations in 182W and 142Nd observed in the Isua supracrustal rocks are similar to those observed in the ancient rocks from Nuvvuagittuq Greenstone Belt, the Acasta Gneiss Complex, and the Saglek Block, suggesting that similar processes affected diverse early Earth rocks.

  3. Early Differentiation Processes Recorded By 142Nd and 182W in Eoarchean Rocks from Isua (United States)

    Rizo Garza, H. L.; Walker, R. J.; Carlson, R. W.; Touboul, M.; Horan, M. F.; Puchtel, I. S.; Boyet, M.; Rosing, M. T.


    The earliest phases of Earth's evolution can be investigated using the short-lived 182Hf-182W and 146Sm-142Nd isotopic systems. Tungsten is siderophile while Hf is lithophile, so metal-silicate segregation greatly fractionates the Hf/W ratio of both planetary mantles and cores. Both daughter nuclides, W and Nd, are more incompatible than the parent nuclides Hf and Sm, so modification to Hf/W and Sm/Nd ratios in the silicate Earth can also be caused by crystal-liquid fractionation. However, because of the short half-lives of 182Hf and 146Sm (8.9 Ma and 103 Ma, respectively), variations in 182W and 142Nd can only be produced, respectively, during the first ~ 50 Ma and ~ 500 Ma of Earth's history. We will present data from Eoarchean mantle-derived samples from the Isua supracrustal belt. The mantle source(s) of these rocks was characterized by 182W and 142Nd excesses, relative to terrestrial standards and modern rocks, of up to 15 ppm and 13 ppm, respectively. The 182W/184W and 142Nd/144Nd ratios in the Isua rocks are not correlated, suggesting that, because of the different time scales for 142Nd and 182W growth, two or more events are required to account for the isotopic enrichments. The enrichments in 182W can be explained by Hf/W fractionation after a mean core formation age of ~30 Ma followed by mantle differentiation between 45-67 Ma. The 142Nd excesses, coupled with 147Sm-143Nd systematics, suggest that the mantle source of these rocks differentiated ~100 Ma after Solar system formation. Samples from the Isua Supracrustal belt, with ages between 3.8 Ga and 3.3 Ga, show gradual diminution of 142Nd anomalies until they are no longer resolved by ~ 3.3 Ga. By contrast, there is no diminishment of the 182W variability with time in the Isua suite. Tungsten concentrations of the samples studied range between 0.1 ppm and 3 ppm. The high W concentrations in some of these samples likely reflect the mobility of W in hydrous fluids and the modification of the original W of

  4. Guandishan Granitoids of the Paleoproterozoic Lüliang Metamorphic Complex in the Trans-North China Orogen:SHRIMP Zircon Ages,Petrogenesis and Tectonic Implications

    Institute of Scientific and Technical Information of China (English)

    LIU Shuwen; LI Qiugen; LIU Chaohui; LU Yongjun; ZHANG Fan


    The Paleoproterozoic Liiliang Metamorphic Complex(PLMC)is situated in the middle segment of the western margin of the Trans-North China Orogen(TNCO),North China Craton(NCC). As the most important Iithological assemblages in the southern part of the PLMC,Guandishan granitoids consist of early gneissic tonalities,granodiorites and gneissic monzogranites,and younger gneissic to massive monzogranites.Petrochemical features reveal that the early gneissic tonalities and granodiorites belong to the medium-K calc-alkaline series;the early gneissic monzogranites are transitional from high-K caic-alkaline to the shoshonite series;the younger gneissic to massive monzogranites belong to the high-k calc-alkaline series,and all rocks are characterized by right-declined REE patterns and negative Nb,Ta,Sr,P,and Ti anomalies in the primitive mantle normalized spidergrams.SHRIMP zircon U-Pb isotopic dating reveal that the early gneissic tonalities and granodiorites formed at ~2.17 Ga,the early gneissic monzogranites at ~2.06 Ga,and the younger gneissic to massive monzogranites at ~1.84 Ga.Sm-Nd isotopic data show that the early gneissic tonalities and granodiorites have εNd(t) values of +0.48 to -3.19 with Nd-depleted mantle model ages (TDM)of 2.76-2.47 Ga,and early gneissic monzogranites have εNd(t) values of -0.53 to -2.51 with TDM of 2.61-2.43 Ga,and the younger gneissic monzogranites have εNd(t) values of -6.41 to -2.78 with a TDM of 2.69-2.52 Ga.These geochemical and isotopic data indicate that the early gneissic tonalities,granodiorites,and monzogranites were derived from the partial melting of metamorphosed basaltic and pelitic rocks,respectively,in a continental arc setting.The younger gneissic to massive monzogranites were derived by partial melting of metamorphosed greywackes within the continental crust.Combined with previously regional data,we suggest that the PaleOproterOzOic granitoid magmatism in the Guandishan granitoids of the PLMC may provide the best

  5. The coupled 182W-142Nd record of early terrestrial mantle differentiation (United States)

    Puchtel, Igor S.; Blichert-Toft, Janne; Touboul, Mathieu; Horan, Mary F.; Walker, Richard J.


    New Sm-Nd, Lu-Hf, Hf-W, and Re-Os isotope data, in combination with highly siderophile element (HSE, including Re, Os, Ir, Ru, Pt, and Pd) and W abundances, are reported for the 3.55 Ga Schapenburg komatiites, South Africa. The Schapenburg komatiites define a Re-Os isochron with an age of 3550 ± 87 Ma and initial γ187Os = +3.7 ± 0.2 (2SD). The absolute HSE abundances in the mantle source of the Schapenburg komatiite system are estimated to be only 29 ± 5% of those in the present-day bulk silicate Earth (BSE). The komatiites were derived from mantle enriched in the decay products of the long-lived 147Sm and 176Lu nuclides (initial ɛ143Nd = +2.4 ± 0.1, ɛ176Hf = +5.7 ± 0.3, 2SD). By contrast, the komatiites are depleted, relative to the modern mantle, in 142Nd and 182W (μ182W = -8.4 ± 4.5, μ142Nd = -4.9 ± 2.8, 2SD). These results constitute the first observation in terrestrial rocks of coupled depletions in 142Nd and 182W. Such isotopic depletions require derivation of the komatiites from a mantle domain that formed within the first ˜30 Ma of Solar System history and was initially geochemically enriched in highly incompatible trace elements as a result of crystal-liquid fractionation in an early magma ocean. This mantle domain further must have experienced subsequent melt depletion, after 182Hf had gone extinct, to account for the observed initial excesses in 143Nd and 176Hf. The survival of early-formed 182W and 142Nd anomalies in the mantle until at least 3.55 Ga indicates that the products of early planetary differentiation survived both later planetary accretion and convective mantle mixing during the Hadean. This work moreover renders unlikely that variable late accretion, by itself, can account for all of the observed W isotope variations in Archean rocks.

  6. Geochemical characteristics and origin of the Lebowa Granite Suite, Bushveld Complex (United States)

    Hill, M.; Barker, F.; Hunter, D.; Knight, R.


    The ??? 2052-Ma Lebowa Granite Suite (LGS) represents the culminating phase of an Early Proterozoic magmatic cycle in the Central Transvaal area of the Kaapvaal Province. Following extrusion of at least 200,000 km3 of intermediate to acid volcanics (Rooiberg Felsite), mafic and ultramafic magmas intruded at 2065 Ma to form the Rustenburg Layered Suite (RLS). The LGS includes the Nebo, Makhutso, Bobbejaankop, Lease, and Klipkloof granites. The Nebo Granite intruded the Rooiberg Felsite as sheets up to 4 km thick above the RLS. Smaller stocks of the other granites crosscut the Nebo. We determined major- and trace-element compositions and oxygen, Rb-Sr, and Sm-Nd isotope ratios for samples of: Nebo Granite; Rooiberg Felsite; granophyre and granophyric granite; Makhutso, Bobbejaankop, and Lease granites; and feldspar porphyry from areas throughout the exposed area of the LGS (Dennilton, Verena Balmoral, Enkeldoorn, Sekhukhune Plateau, Zaaiplaats-Potgeitersrus, and Western Transvaal). Coherent floor-to-roof geochemical trends exist in some areas, although it is not possible to model them convincingly. Regional variations in geochemistry exist and likely are related to source variations in the estimated 200,000 km3 of the Nebo Granite sheets. ??18O for the LGS range from +5.9??? to +9.5???; if these are approximate primary magmatic values, pelitic sediments cannot have been an important source for the LGS. The Rb-Sr isotope system has been altered, a finding consistent with previous studies. A mineral isochron for Nebo Granite near Dennilton yields a York regression age of 1995 ?? 99 Ma, with initial 143Nd/144Nd = 0.50978??8 and ???CHUR=-5.12. Samples from the Sekhukhune Plateau have higher 143Nd/144Nd ratios than do Dennilton-area samples, suggesting that the former originated from older or less LREE-enriched sources. We suggest that intrusion of mafic to ultramafic magmas at depth in the continental crust triggered melting of Archean quartzofeldspathic crystalline