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Sample records for pb isotope geochemistry

  1. Pb isotope geochemistry of Piton de la Fournaise historical lavas

    NASA Astrophysics Data System (ADS)

    Vlastélic, Ivan; Deniel, Catherine; Bosq, Chantal; Télouk, Philippe; Boivin, Pierre; Bachèlery, Patrick; Famin, Vincent; Staudacher, Thomas

    2009-07-01

    Variations of Pb isotopes in historical lavas (1927-2007) from Piton de la Fournaise are investigated based on new (116 samples) and published (127 samples) data. Lead isotopic signal exhibits smooth fluctuations (18.87 < 206Pb/ 204Pb < 18.94) on which superimpose unradiogenic spikes ( 206Pb/ 204Pb down to 18.70). Lead isotopes are decoupled from 87Sr/ 86Sr and 143Nd/ 144Nd, which display small and barely significant variations, respectively. No significant change of Pb isotope composition occurred during the longest (> 3 years) periods of inactivity of the volcano (1939-1942, 1966-1972, 1992-1998), supporting previous inferences that Pb isotopic variations occur mostly during and not between eruptions. Intermediate compositions (18.904 < 206Pb/ 204Pb < 18.917) bracket the longest periods of quiescence. In this respect, the highly frequent occurrence of an intermediate composition (18.90 < 206Pb/ 204Pb < 18.91), which clearly defines an isotopic baseline during the most recent densely sampled period (1975-2007), either suggests direct sampling of plume melts or sampling of a voluminous magma reservoir that buffers Pb isotopic composition. Deviations from this prevalent composition occurred during well-defined time periods, namely 1977-1986 (radiogenic signature), 1986-1990 and 1998-2005 (unradiogenic signatures). The three periods display a progressive isotopic drift ending by a rapid return (mostly during a single eruption) to the isotopic baseline. The isotopic gradients could reflect progressive emptying of small magma reservoirs or magma conduits, which are expected to be more sensitive to wall-rock interactions than the main magma chamber. These gradients provide a lower bound ranging from 0.1 to 0.17 km 3 for the size of the shallow magma storage system. The isotopic shifts (March 1986, January 1990 and February 2005) are interpreted as refilling the plumbing system with deep melts that have not interacted with crustal components. The volume of magma

  2. Geochemistry: how well can Pb isotopes date core formation?

    PubMed

    Kamber, Balz S; Kramers, Jan D

    2006-11-02

    Timescale and the physics of planetary core formation are essential constraints for models of Earth's accretion and early differentiation. Wood and Halliday use the apparent mismatch in core-formation dates determined from tungsten (W) and lead (Pb) chrono-meters to argue for a two-stage core formation, involving an early phase of metal segregation followed by a protracted episode of sulphide melt addition. However, we show here that crust-;mantle Pb isotope systematics do not require diachronous core formation. Our observations indicate that very early (< or = 35 Myr) core formation and planet accretion remain the most plausible scenario.

  3. REE and Sr, Nd, Pb isotopic geochemistry of Huangyishan basalt, Kuandian, Liaoning, Northeast China

    USGS Publications Warehouse

    Xie, G.-h.; Wang, J.-w.; Wei, K.-j.; Liu, C.-q.; Tatsumoto, M.; Basn, A.R.

    1990-01-01

    In the light of major element geochemistry, mineral chemistry and REE and isotopic data, the small but apparent isotopic differences between the Cenozoic volcanic rocks east and west of the Tancheng-Lujiang fault are believed to be caused by the mixing and metasomatism of crustal and mantle material in the mantle source region in response to Pacific plate subduction. The presence of phlogopite and pargasite in mantle xenoliths lends strong support to mantle metasomatism. ?? 1990.

  4. The Ellsworth terrane, coastal Maine: Geochronology, geochemistry, and Nd-Pb isotopic composition - Implications for the rifting of Ganderia

    USGS Publications Warehouse

    Schulz, K.J.; Stewart, D.B.; Tucker, R.D.; Pollock, J.C.; Ayuso, R.A.

    2008-01-01

    The Ellsworth terrane is one of a number of fault-bounded blocks that occur along the eastern margin of Ganderia, the western-most of the peri-Gondwanan domains in the northern Appalachians that were accreted to Laurentia in the Paleozoic. Geologic relations, detrital zircon ages, and basalt geochemistry suggest that the Ellsworth terrane is part of Ganderia and not an exotic terrane. In the Penobscot Bay area of coastal Maine, the Ellsworth terrane is dominantly composed of bimodal basalt-rhyolite volcanic sequences of the Ellsworth Schist and unconformably overlying Castine Volcanics. We use new U-Pb zircon geochronology, geochemistry, and Nd and Pb isotopes for these volcanic sequences to constrain the petrogenetic history and paleotectonic setting of the Ellsworth terrane and its relationship with Ganderia. U-Pb zircon geochronology for rhyolites indicates that both the Ellsworth Schist (508.6 ?? 0.8 Ma) and overlying Castine Volcanics (503.5 ?? 2.5 Ma) are Middle Cambrian in age. Two tholefitic basalt types are recognized. Type Tb-1 basalt, present as pillowed and massive lava flows and as sills in both units, has depleted La and Ce ([La/Nd]N = 0.53-0.87) values, flat heavy rare earth element (REE) values, and no positive Th or negative Ta anomalies on primitive mantle-normalized diagrams. In contrast, type Th-2 basalt, present only in the Castine Volcanics, has stightly enriched LREE ([La/Yb]N = 1.42-2.92) values and no Th or Th anomalies. Both basalt types have strongly positive ??Nd (500) values (Th-1 = +7.9-+8.6; Th-2 = +5.6-+7.0) and relatively enriched Pb isotopic compositions (206Ph/204Pb = 18.037-19.784; 207/204Pb = 15.531-15.660; 2088Pb/204Pb = 37.810-38.817). The basalts have compositions transitional between recent normal and enriched mid-ocean-ridge basalt, and they were probably derived by partial melting of compositionatly heterogeneous asthenosphenc mantle. Two types of rhyolite also are present. Type R-1 rhyolite, which mostly occurs as tuffs

  5. U-Pb geochronology, geochemistry, and H-O-S-Pb isotopic compositions of the Leqingla and Xin'gaguo skarn Pb-Zn polymetallic deposits, Tibet, China

    NASA Astrophysics Data System (ADS)

    Wang, Liqiang; Cheng, Wenbin; Tang, Juxing; Kang, Haoran; Zhang, Yan; Li, Zhuang

    2016-01-01

    The Leqingla and Xin'gaguo deposits are two representative skarn Pb-Zn polymetallic deposits of the Gangdese Pb-Zn polymetallic belt, Tibet, China. LA-ICP-MS zircon U-Pb dating of the mineralization-related biotite granites from both the Leqingla and Xin'gaguo deposits yielded weighted mean ages of 60.8 Ma and 56.5 Ma, respectively, which can be inferred as their mineralization ages. The Leqingla biotite granite is characterized by high Al2O3, total Fe, Na2O, and low K2O. In comparison, the Xin'gaguo biotite granite is characterized by relative higher K2O but lower Al2O3, total Fe, and Na2O. Geochemical and mineralogical characteristics indicate that the Leqingla and Xin'gaguo biotite granites are calc-alkaline I-type granite and High K calc-alkaline I-type granite, respectively. Both the Leqingla and Xin'gaguo biotite granites are enrichment in LREE and LILEs and depletion in HFSEs, and they were formed at the India-Asia collision stage. δ18O and δD values for the Leqingla and Xin'gaguo deposits are -8.8‰ to 5.3‰ and -140.4‰ to -90.1‰, -4.5‰ to 7.0‰ and -117.3‰ to -81.0‰, respectively, indicating magma fluids mixed with meteoric water in ore-forming fluids. δ34S values (-11.6‰ to -0.3‰) of ore sulfides from the Leqingla deposit show characteristics of biogenetic sulfur isotope compositions, suggesting sulfur for the Leqingla deposit were sourced from wall rocks of the Mengla and Luobadui Formation, which are rich in organic materials. δ34S values of ore sulfides from the Xin'gaguo deposits show bimodal distribution (-5.0‰ to -1.6‰ and 1.6-2.1‰), indicating sulfur in the Xin'gaguo deposit were derived from both wall rocks and magma. In the Leqingla deposit, most ore sulfides have the similar Pb isotopic compositions with that of the mineralization-related biotite granite, suggesting the biotite granite supplied most of the ore-forming metals. Pb isotopic compositions of ore sulfides and Hf isotopic compositions of biotite granite show

  6. Magmatic processes at Popocatepetl volcano, Mexico: petrology, geochemistry and Sr-Nd-Pb isotopes

    NASA Astrophysics Data System (ADS)

    Schaaf, P.; Stimac, J.; Siebe, C.; Mac¡as, J.

    2003-12-01

    crystallization, recycling, assimilation, and degassing in relatively evolved magma chambers. The 1996 and 1997 dome eruptions confirm that dacitic magma currently resides beneath Popo and is episodically recharged by more mafic magma, fostering eruption and excess degassing. Two-oxide thermometry and the presence of FeCu sulfide globules confirm that these magmas erupted at T = 930§C and fO2 = -10.2 log, below anhydrite stability. 87Sr/86Sr, e-Nd and 206Pb/204Pb ratios are between 0.70365 and 0.70463, +6.4 and +3.0, and 18.618 and 18.781, respectively. Andesitic to dacitic rocks of Popo formed by mafic recharge, fractionation, and mixing of dacitic to basaltic magmas in mature crustal chambers. Plagioclase accumulation and recycling related to protracted fractionation and assimilation of earlier emplaced magmas and their wallrocks was also important.

  7. Major, trace element and isotope geochemistry (Sr-Nd-Pb) of interplinian magmas from Mt. Somma-Vesuvius (Southern Italy)

    USGS Publications Warehouse

    Somma, R.; Ayuso, R.A.; de Vivo, B.; Rolandi, G.

    2001-01-01

    Major, trace element and isotopic (Sr, Nd, Pb) data are reported for representative samples of interplinian (Protohistoric, Ancient Historic and Medieval Formations) activity of Mt. Somma-Vesuvius volcano during the last 3500 years. Tephra and lavas exhibit significant major, trace element and isotopic variations. Integration of these data with those obtained by previous studies on the older Somma suites and on the latest activity, allows to better trace a complete petrological and geochemical evolution of the Mt. Somma-Vesuvius magmatism. Three main groups of rocks are recognized. A first group is older than 12.000 yrs, and includes effusive-explosive activity of Mt. Somma. The second group (8000-2700 yrs B.P.) includes the products emitted by the Ottaviano (8000 yrs. B.P.) and Avellino (3550 yrs B.P.) plinian eruptions and the interplinian activity associated with the Protohistoric Formation. Ancient Historic Formation (79-472 A.D.), Medieval Formation (472-1139 A.D.) and Recent interplinian activity (1631-1944 A.D.) belong to the third group of activity (79-1944 A.D.). The three groups of rocks display distinct positive trends of alkalis vs. silica, which become increasingly steeper with age. In the first group there is an increase in silica and alkalis with time, whereas an opposite tendency is observed in the two younger groups. Systematic variations are also evident among the incompatible (Pb, Zr, Hf, Ta, Th, U, Nb, Rb, Cs, Ba) and compatible elements (Sr, Co, Cr). REE document variable degrees of fractionation, with recent activity displaying higher La/Yb ratios than Medieval and Ancient Historic products with the same degree of evolution. N-MORB normalized multi-element diagrams for interplinian rocks show enrichment in Rb, Th, Nb, Zr and Sm (> *10 N-MORB). Sr isotope ratios are variable, with Protohistoric rocks displaying 87Sr/86Sr= 0.70711-0.70810, Ancient Historic 87Sr/86Sr=0.70665-0.70729, and Medieval 87Sr/86Sr=0.70685-0.70803. Neodymium isotopic

  8. Sr and Pb isotopic geochemistry of feldspars and implications for the growth of megacrysts in plutonic settings.

    NASA Astrophysics Data System (ADS)

    Munnikhuis, J.; Glazner, A. F.; Coleman, D. S.; Mills, R. D.

    2015-12-01

    Why megacrystic textures develop in silicic igneous rocks is still unknown. One hypothesis is that these crystals nucleate early in a magma chamber with a high liquid content. A supportive observation of this hypothesis is areas in plutons with high concentrations of megacrysts suggesting flow sorting. Another group of hypotheses suggest megacrystic textures form during protracted late-stage coarsening in a low-melt, interlocked matrix due to either thermal oscillations from incremental pluton emplacement, or Ostwald ripening. Isotopic analyses of large, euhedral K-feldspar megacrysts from the Cretaceous intrusive suites of the Sierra Nevada batholith (SNB) provide new insight into their origin. Megacrysts from the SNB reach the decimeter scale, are Or rich (85-90%), are perthitic, and host mineral inclusions of nearly all phases in the host rock. In-situ micro-drilling of transects, from core to rim, of the alkali feldspars provides material for Sr and Pb isotopic analyses by thermal ionization mass spectrometry (TIMS). Preliminary 87Sr/86Sr(i) isotopic data from samples from the Cathedral Peak Granodiorite, of the Tuolumne Intrusive Suite range from 0.706337 to 0.706452 (~1.6ɛSr) near the cores, whereas a sawtooth pattern with larger variability, 0.706179 to 0.706533 (~5ɛSr), occurs nears the rims. We interpret these preliminary data to indicate that the late portion of growth (i.e. crystal rim) was dominated by either cannibalism of small K-feldspar crystals with isotopic variability, or by addition of isotopically diverse late components to the magma. By comparing the Sr and Pb isotopic stratigraphy of megacrysts from a variety of rock matrices and different granitoids in the SNB isotopic trends can be evaluated to determine if crystals sizes are dependent on disequilibrium processes or grow at a steady state.

  9. Sources of granite magmatism in the Embu Terrane (Ribeira Belt, Brazil): Neoproterozoic crust recycling constrained by elemental and isotope (Sr-Nd-Pb) geochemistry

    NASA Astrophysics Data System (ADS)

    Alves, Adriana; Janasi, Valdecir de Assis; Campos Neto, Mario da Costa

    2016-07-01

    Whole rock elemental and Sr-Nd isotope geochemistry and in situ K-feldspar Pb isotope geochemistry were used to identify the sources involved in the genesis of Neoproterozoic granites from the Embu Terrane, Ribeira Belt, SE Brazil. Granite magmatism spanned over 200 Ma (810-580 Ma), and is dominated by crust-derived relatively low-T (850-750 °C, zircon saturation) biotite granites to biotite-muscovite granites. Two Cryogenian plutons show the least negative εNdt (-8 to -10) and highest mg# (30-40) of the whole set. Their compositions are strongly contrasted, implying distinct sources for the peraluminous (ASI ∼ 1.2) ∼660 Ma Serra do Quebra-Cangalha batholith (metasedimentary rocks from relatively young upper crust with high Rb/Sr and low Th/U) and the metaluminous (ASI = 0.96-1.00) ∼ 630 Ma Santa Catarina Granite. Although not typical, the geochemical signature of these granites may reflect a continental margin arc environment, and they could be products of a prolonged period of oceanic plate consumption started at ∼810 Ma. The predominant Ediacaran (595-580 Ma) plutons have a spread of compositions from biotite granites with SiO2 as low as ∼65% (e.g., Itapeti, Mauá, Sabaúna and Lagoinha granites) to fractionated muscovite granites (Mogi das Cruzes, Santa Branca and Guacuri granites; up to ∼75% SiO2). εNdT are characteristically negative (-12 to -18), with corresponding Nd TDM indicating sources with Paleoproterozoic mean crustal ages (2.0-2.5 Ga). The Guacuri and Santa Branca muscovite granites have the more negative εNdt, highest 87Sr/86Srt (0.714-0.717) and lowest 208Pb/206Pb and 207Pb/206Pb, consistent with an old metasedimentary source with low time-integrated Rb/Sr. However, a positive Nd-Sr isotope correlation is suggested by data from the other granites, and would be consistent with mixing between an older source predominant in the Mauá granite and a younger, high Rb/Sr source that is more abundant in the Lagoinha granite sample. The

  10. Geology, isotope geochemistry and geochronology of the Jinshachang carbonate-hosted Pb-Zn deposit, southwest China

    NASA Astrophysics Data System (ADS)

    Zhou, Jia-Xi; Bai, Jun-Hao; Huang, Zhi-Long; Zhu, Dan; Yan, Zai-Fei; Lv, Zhi-Cheng

    2015-02-01

    The Jinshachang Pb-Zn deposit, an exceptionally radiogenic Pb-enriched sulfide deposit, hosted by dolostone of the Upper Sinian (Neoproterozoic) Dengying Formation and the Lower Cambrian Meishucun Formation, is located in the western Yangtze Block, about 300 km northeast of Kunming city in southwest China. Ore bodies in this deposit are dominated by strata-bound type and steeply dipping vein type. Primary ores in these two types are composed of sphalerite, galena, fluorite, barite and quartz with massive, banded, veined and disseminated structures. Twenty-seven ore bodies in the Jinshachang deposit host 4.6 million tons of sulfide ores at average grades of 4.07 wt.% Pb and 5.03 wt.% Zn. Quartz separates from the sulfide ores have δDH2O values ranging from -137‰ to -86.2‰ with an average of -114‰ (n = 7), lower than those of magmatic, metamorphic and meteoric water, suggesting a contribution of organic water. δ34SCDT values of ninety-one sulfide separates range from +1.1‰ to +13.4‰ with an average of +5.7‰, lower than those of evaporites (δ34SCDT = +15‰ to +35‰) in the Cambrian to Triassic sedimentary strata in NE Yunnan province. δ34SCDT values of eight barite separates range from +32‰ to +35‰ (average +34‰), within the range of evaporites. These data suggest that S2- in the hydrothermal fluids derived from evaporites by thermo-chemical sulfate reduction (TSR), whereas SO42- directly originated from the evaporites. Six sulfide separates have highly radiogenic 206Pb/204Pb ratios ranging from 20.74 to 21.18 (average 20.92), 207Pb/204Pb ratios ranging from 15.85 to 15.89 (average 15.87), and 208Pb/204Pb ratios ranging from 40.89 to 41.42 (average 41.16). The Pb isotopes of the sulfides plot above the upper crust Pb average evolution curve and overlap the Cambrian sedimentary rocks, but are different from the Sinian dolostone. This indicates a crustal source of Pb most likely derived from the Cambrian sedimentary rocks. The initial 87Sr/86Sr

  11. Uranium-Lead Zircon Ages and Sr, Nd, and Pb Isotope Geochemistry of Selected Plutonic Rocks from Western Idaho

    USGS Publications Warehouse

    Unruh, Daniel M.; Lund, Karen; Kuntz, Mel A.; Snee, Lawrence W.

    2008-01-01

    Across the Salmon River suture in western Idaho, where allochthonous Permian to Cretaceous oceanic rocks are juxtaposed against Proterozoic North American rocks, a wide variety of plutonic rocks are exposed. Available data indicate much variation in composition, source, and structural state of these plutons. The plutonic rocks were long described as the western border zone of the Cretaceous Idaho batholith but limited pre-existing age data indicate more complicated origins. Because the affinity and age of the plutonic rocks cannot be reliably determined from field relations, TIMS U-Pb dating in conjunction with Sr, Nd, and Pb isotopic studies of selected plutons across the suture in western Idaho were undertaken. The data indicate three general groups of plutons including (1) those that intruded the island arc terranes during the Triassic and Jurassic, those that intruded near the western edge of oceanic rocks along the suture in the Early Cretaceous, and the plutons of the Idaho batholith that intruded Proterozoic North American rocks in the Late Cretaceous. Plutons that intruded Proterozoic North American rocks commonly include xenocrystic zircons and in several cases, ages could not be determined. The least radiogenic Sr and most radiogenic Nd are found among the Blue Mountains superterrane island arc samples. Suture-zone plutons have isotopic characteristics that span the range between Idaho batholith and island arc samples but mostly follow island arc signatures. Plutons of the Idaho batholith have the most radiogenic initial Pb and Sr ratios and the least radiogenic Nd of the samples analyzed.

  12. Petrology and Sr-Nd-Pb isotope geochemistry of Late Cretaceous continental rift ignimbrites, Kap Washington peninsula, North Greenland

    NASA Astrophysics Data System (ADS)

    Thorarinsson, Sigurjon B.; Holm, Paul M.; Duprat, Helene I.; Tegner, Christian

    2012-03-01

    The Late Cretaceous-Palaeocene (71-61 Ma) Kap Washington Group (KWG) volcanic sequence is exposed at the north coast of Greenland. The sequence is bimodal and was erupted in a continental rift setting during the opening of the Arctic Ocean. The succession exposed on the Kap Washington peninsula, which forms the bulk of the KWG sequence (> 5 km thick), has been sampled along four traverses with a combined stratigraphic thickness of ca. 1500 m. The sampled sequence is dominated by silicic ignimbrites (69-79 wt.% SiO2) showing geochemical features typical of ferroan, A-type granitoids. The ignimbrites range from sparsely phyric, mildly peraluminous compositions [ASI = Al2O3/(CaO + Na2O + K2O) = 1.05-1.20] to feldspar + quartz ± sodic amphibole ± Fe-Ti oxide phyric peralkaline compositions [PI = (Na2O + K2O)/Al2O3 = 1.00-1.40]. The peraluminous ignimbrites appear to overlie the peralkaline ignimbrites, although stratigraphy is complicated by faulting. Fiamme imbrication indicates that both types were erupted from a vent area located north of the Kap Washington peninsula. The peralkaline ignimbrites have Sr-Nd-Pb isotopic compositions which overlap with the compositions of KWG basalts, indicating a dominantly basaltic source. The more peralkaline compositions were generated by up to ca. 50% fractional crystallisation of alkali feldspar-quartz-dominated assemblages from mildly peralkaline parental magmas, themselves probably derived by fractionation of trachytic magmas. The peraluminous ignimbrites have slightly negative ɛNd(i) and more radiogenic 207Pb/204Pbi and 208Pb/204Pbi. Modelling indicates that they are not cogenetic with the peralkaline ignimbrites and they are inferred to have originated by partial melting of hybridised mafic crust. Petrographic evidence suggests that magma mixing was an important process and variations in Nd-Pb isotopes and trace element ratios indicate mixing between peralkaline and peraluminous magma batches.

  13. High-spatial-resolution isotope geochemistry of monazite (U-Pb & Sm-Nd) and zircon (U-Pb & Lu-Hf) in the Old Woman and North Piute Mountains, Mojave Desert, California

    NASA Astrophysics Data System (ADS)

    Phillips, Stacy E.; Hanchar, John M.; Miller, Calvin F.; Fisher, Christopher M.; Lancaster, Penny J.; Darling, James R.

    2014-05-01

    Recent improvements in analytical capabilities allow us to reveal details of magmatic processes at an increasingly finer spatial and temporal scale. In situ analyses of the isotopic and trace element composition of accessory minerals at the sub-grain scale have proven to be effective tools for solving a wide range of geological problems. This study presents new data on accessory minerals including monazite & zircon, examined by in situ LA-ICP-MS and Laser Ablation Split Stream (LASS) techniques, analyzing multiple isotopic systems (U-Pb + Sm-Nd, and U-Pb + Lu-Hf in monazite and zircon, respectively) in order to track geochemical changes over time through a magmatic system. The late Cretaceous granitoids of the Old Woman Mountains in the Mojave Desert, California, provide an excellent opportunity to apply these analytical techniques. The peraluminous granites of the Sweetwater Wash, Painted Rock, and North Piute plutons represent different depths of the magmatic system, and are well understood in terms of field relations and whole-rock geochemistry. A preliminary study on the Sweetwater Wash monazites (Fisher et al., in preparation) has revealed significant inter-grain isotopic heterogeneity in the ɛNd composition of the source region (~1700 Ma); however, the U-Pb ages show an isotopic resetting during emplacement at ~75 Ma. This decoupling of U-Pb and Sm-Nd isotopic systems is suggested by Fisher et al. to be due to recrystallisation and/or dissolution-reprecipitation of monazite. If grain boundary diffusion of Pb overrides the more kinetically limited volume diffusion, then the U-Pb systematics will be reset while Sm and Nd remain immobile in the monazite structure as essential structural components of the lattice. This new data will allow the further investigation of these preliminary results, providing new insights into the observed isotopic disequilibrium, with the LASS technique accurately linking the multiple isotopic systems. This will provide important

  14. Elemental and Sr-Nd-Pb isotope geochemistry of the Cenozoic basalts in Southeast China: Insights into their mantle sources and melting processes

    NASA Astrophysics Data System (ADS)

    Sun, Pu; Niu, Yaoling; Guo, Pengyuan; Ye, Lei; Liu, Jinju; Feng, Yuexing

    2017-02-01

    We analyzed whole-rock major and trace elements and Sr-Nd-Pb isotopes of the Cenozoic basalts in Southeast China to investigate their mantle source characteristics and melting process. These basalts are spatially associated with three extensional fault systems parallel to the coast line. After correction for the effect of olivine microlites on bulk-rock compositions and the effect of crystal fractionation, we obtained primitive melt compositions for these samples. These primitive melts show increasing SiO2, Al2O3 but decreasing FeO, MgO, TiO2, P2O5, CaO and CaO/Al2O3 from the interior to the coast. Such spatial variations of major element abundances and ratios are consistent with a combined effect of fertile source compositional variation and increasing extent and decreasing pressure of decompression melting from beneath the thick lithosphere in the interior to beneath the thin lithosphere in the coast. These basalts are characterized by incompatible element enrichment but varying extent of isotopic depletion. This element-isotope decoupling is most consistent with recent mantle source enrichment by means of low-degree melt metasomatism that elevated incompatible element abundances without yet having adequate time for isotopic ingrowth in the mantle source regions. Furthermore, Sr and Nd isotope ratios show significant correlations with Nb/Th, Nb/La, Sr/Sr* and Eu/Eu*, which substantiates the presence of recycled upper continental crustal material in the mantle sources of these basalts. Pb isotope ratios also exhibit spatial variation, increasing from the interior to the coastal area. The significant correlations of major element abundances with Pb isotope ratios indicate that the Pb isotope variations also result from varied extent and pressure of decompression melting. We conclude that the elevated Pb isotope ratios from the interior to coast are consistent with increasing extent of decompression melting of the incompatible element depleted mantle matrix, which

  15. U-Pb Dating, whole rock and Sr-Nd-Pb-O isotope geochemistry of collisional magmatism in the CACC: Çiçekdaǧ igneous complex (ÇIC)

    NASA Astrophysics Data System (ADS)

    Deniz, Kiymet; Kagan Kadioglu, Yusuf; Stuart, Finlay; Ellam, Rob; Boyce, Adrian; Condon, Daniel

    2015-04-01

    these intrusive rocks have experienced fractional crystallisation coupled with crustal assimilation. The calcalkaline and alkaline series show enrichment in LILE and LREE relative to HFSE and HREE. These rocks have moderate 208Pb/204Pb (38.87-39.16) and 207Pb/204Pb (15.62-15.71) and high 206Pb/204Pb (18.76-18.81). Both trace element and Pb isotope data indicate enriched mantle source (EM-II). Mafic alkaline rocks differed with their low 206Pb/204Pb (17.55-17.62). These rocks are derived from subduction modified lithospheric mantle. The geochemistry and Sr-Nd-O isotope data of ophiolitic rocks and late alkaline dykes are very similar. Both of them have flat REE pattern, high 87Sr/86Sr and 143Nd/144Nd, low δ18O values (1.9-4.0), moderate 208Pb/204Pb (38.81-38.97, 38.51-38.91) and 207Pb/204Pb (15.62-15.70, 15.54-15.69) and high 206Pb/204Pb (18.37-18.77, 18.39-18.73). All data indicate heterogeneous mantle source. Trace element ratio diagrams suggest depleted mantle source and subduction enrichment for late alkaline dykes. Dy versus Dy/Yb diagram and calculated partial melting curves suggest 20-25% degree of partial melting of amphibole-phlogopite bearing spinel lherzolitic mantle sources. Ba/Rb versus Rb/Sr diagram indicate the presence of amphibole in the mantle source of ophiolitic rocks and phlogopite for the late alkaline dykes. U-Pb dating of zircon yielded crystallization ages of 73.74±0.027-73.78±0.046 and 73.78±0.071 for calcalkaline series and alkaline series, respectively. Both series are coexistence and may have coevally been confined from same sources.

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

  17. Zircon-apatite U-Pb geochronology, zircon Hf isotope composition and geochemistry of granite batholith in the northern Mexico: Implications for Tectonomagmatic evolution of southern Cordillera.

    NASA Astrophysics Data System (ADS)

    Mahar, M. A.; Goodell, P.

    2015-12-01

    We present the zircon-apatite U-Pb ages and zircon Hf isotope composition of the granite batholith exposed at the western boundary of Chihuahua. Granidiorite samples were analyzed from both, north and south of the Rio El Fuerte and Sinforosa Lineament. Based on previous studies, the WWN-EES trending Sinforosa Lineament is proposed as the manifestation of a terrane boundary between Seri in the north and Tahue terrane in the south. Zircon U-Pb data indicate that the magmatism spans a time period of 36 Ma from 89 to 53 Ma to the north of the Sinforosa Lineament while granodiorites in the south of the Sinforosa Lineament are dated at 59 Ma. The U-Pb apatite ages are variable in the north of the Sinforosa Lineament and range from 86-51 Ma. These apatite dates are 1-28 Ma younger than the corresponding zircon U-Pb crystallization ages. This indicates variable cooling rates and moderate to shallow emplacement. In contrast, in the south of the Sinforosa Lineament, the U-Pb apatite ages (64-59 Ma) are indistinguishable from the zircon U-Pb age (59 Ma), indicating rapid cooling and shallow emplacement. Zircon morphology and U-Pb dating revealed the absence of inherited component in the zircon ages, as no inheritance of any age has been observed. Most of the northwestern Mexico is underlain by Precambrian-Paleozoic-Jurassic basement. However, in the study area, U-Pb dating does not support the involvement of the older basement in generating the granite magmas. The weighted mean initial ɛHf (t) isotope composition of granodiorites on both sides of the Sinforosa Lineament varies from +2 to +5. However, Hf isotope composition in the south of the Sinforosa Lineament is more heterogeneous and relatively evolved with weighted Mean ɛHf (t) = +1.45. The Hf isotope composition is consistent with the previously reported near bulk silicate Sr-Nd isotope values. We suggest that the magmatic rocks in this region are not derived from melting of a felsic older crust beneath the batholith

  18. Characteristics of lead geochemistry and the mobility of Pb isotopes in the system of pedogenic rock-pedosphere-irrigated riverwater-cereal-atmosphere from the Yangtze River delta region, China.

    PubMed

    Wang, Cheng; Wang, Jianhua; Yang, Zhongfang; Mao, Changping; Ji, Junfeng

    2013-11-01

    Knowledge of the characteristics of Pb and its isotopic transfer in different compartments is scant, especially for the mobility of Pb isotopes in the geochemical cycle. The present study characterizes differential Pb transport mechanism and the mobility of Pb isotopes in the pedogenic parent rock-pedosphere-irrigated riverwater-cereal-atmosphere system in the Yangtze River delta region, by determining Pb concentration and Pb isotopic ratios of pedogenic parent rocks, fluvial suspended particle matter, tillage soils, soil profiles, irrigated riverwater, fertilizer, Pb ore, cereal roots and grains. The results show that Pb isotopes in the geochemical cycle generally follow the equation of (208)Pb/(206)Pb=-1.157×(206)Pb/(207)Pb+3.46 (r(2)=0.941). However, Pb isotopes have different mobility in different environmental matrixes. Whereas in the pedosphere, the heavier Pb ((208)Pb) usually shows stronger mobility relative to the lighter Pb, and is more likely to transfer into soil exchangeable Pb fraction and carbonates phase. The lighter Pb shows stronger transfer ability from soil to cereal grain via root compared to the heavier Pb. However, the cereal grains have lower (206)Pb/(207)Pb and higher (208)Pb/(206)Pb ratios than root and tillage soil, similar to the airborne Pb and anthropogenic Pb, implying that a considerable amount of Pb in cereal grains comes from the atmosphere. The estimate model shows that 16.7-52.6% (average: 33.5%) of Pb in rice grain is the airborne Pb.

  19. Geochemistry, Sr-Nd-Pb isotopes and geochronology of amphibole- and mica-bearing lamprophyres in northwestern Iran: Implications for mantle wedge heterogeneity in a palaeo-subduction zone

    NASA Astrophysics Data System (ADS)

    Aghazadeh, Mehraj; Prelević, Dejan; Badrzadeh, Zahra; Braschi, Eleonora; van den Bogaard, Paul; Conticelli, Sandro

    2015-02-01

    Lamprophyres of different age showing distinctive mineralogy, geochemistry and isotopic ratios are exposed in northwestern Iran. They can be divided into Late Cretaceous sannaite, Late Oligocene-Early Miocene camptonite (amphibole-bearing) and Late Miocene minette (mica-bearing) and spessartite (amphibole-bearing) lamprophyres. Sannaites have high-Ti amphibole along with high-Ti and Al clinopyroxene, and they are characterised by homogeneous enrichment in incompatible trace elements with troughs at Pb. Spessartites have hornblende and low-Al and Ti clinopyroxene, and they are characterised by enriched incompatible trace element pattern with depletions of Nb, Ta, Pb, and Ti with respect to large ion lithophile elements. Minettes have high-Ti and Al brown mica and low-Al and Ti clinopyroxene, and similar to spessartite, are characterised by fractionation of high field strength elements with respect to large ion lithophile elements, with troughs at Nb, Ta, and Ti and a peak at Pb. Minettes show high initial 87Sr/86Sr values up to 0.70760 and low initial 143Nd/144Nd down to 0.512463 with a negative correlation, consistent with the trace element distribution related with an enriched mantle source modified after sediment recycling during subduction and continental collision. Cretaceous sannaites and Early Miocene spessartites show low initial 87Sr/86Sr approaching 0.70447 and high 143Nd/144Nd values up to 0.512667, which are consistent with a depleted within-plate mantle source. Minette and spessartite lamprophyres show high initial 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values, whereas sannaites have lower, but variable, initial 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values with respect to those of calc-alkaline lamprophyres. Minettes originated by partial melting of a metasomatised lithospheric mantle following siliciclastic sediment recycling by subduction. In contrast, sannaites were generated from the partial melting of a similar lithospheric mantle that was

  20. Mesozoic magmatism and timing of epigenetic Pb-Zn-Ag mineralization in the western Fortymile mining district, east-central Alaska: Zircon U-Pb geochronology, whole-rock geochemistry, and Pb isotopes

    USGS Publications Warehouse

    Dusel-Bacon, Cynthia; Aleinkoff, J.N.; Day, W.C.; Mortensen, J.K.

    2015-01-01

    Epigenetic Pb-Zn-Ag ± Cu prospects in the western Fortymile district are spatially associated with splays of the northeast-trending Kechumstuk sinistral-normal fault zone and with ca. 68-66 Ma felsic intrusions and dikes. The similarity between Pb isotope compositions of feldspars from the Late Cretaceous igneous bodies and sulfides from the epithermal prospects suggests a Late Cretaceous age for most of the mineralization. Fluid flow along the faults undoubtedly played a major role in mineralization. We interpret displacement on the northeast-trending faults to be a far-field effect of dextral translation along Late Cretaceous plate-scale boundaries and faults that were roughly parallel to the subsequently developed Denali and Tintina fault systems, which currently bound the region.

  1. Origin of the granites and related Sn and Pb-Zn polymetallic ore deposits in the Pengshan district, Jiangxi Province, South China: constraints from geochronology, geochemistry, mineral chemistry, and Sr-Nd-Hf-Pb-S isotopes

    NASA Astrophysics Data System (ADS)

    Xu, Bin; Jiang, Shao-Yong; Luo, Lan; Zhao, Kui-Dong; Ma, Liang

    2016-05-01

    The Pengshan Sn and Pb-Zn polymetallic deposits are located in the south margin of the Jiujiang-Ruichang (Jiurui) district of the Middle-Lower Yangtze River Metallogenic Belt in South China. Four large deposits include Huangjinwa, Zengjialong, Jianfengpo, and Zhangshiba, the former three are Sn-dominant deposits which occur as stratiform orebodies in the contact zones of the Pengshan granites and within the country rock strata, whereas Zhangshiba consists of stratiform Pb-Zn orebodies within the Precambrian metasedimentary strata. In this study, we present results on zircon U-Pb ages, major and trace elements, and mineral chemistry as well as Sr-Nd-Hf isotope data of the granites, Pb and S isotopes of both the Sn-dominant and Pb-Zn dominant deposits, and U-Pb dating of cassiterite from the Pengshan district. SHRIMP and LA-ICP-MS zircon U-Pb dating shows that the Pengshan granites were emplaced in the Early Cretaceous (129-128 Ma), which is in good agreement with the U-Pb dating (130-128 Ma) of cassiterite from the Jianfengpo Sn deposit. The Pengshan granites consist mainly of weakly peraluminous highly fractionated I-type affinity granitic rocks. Detailed elemental and isotopic data suggest that the granites formed by partial melting of Mesoproterozoic metamorphic basement materials with minor input of mantle-derived melts. The mineral chemistry of biotite demonstrates that the Pengshan granitic magma had a low oxygen fugacity, thereby precluding the tin dominantly partitioning into the rock-forming silicate minerals and favoring accumulation in the exsolved residual liquid during magma crystallization stages. Sulfur isotopes show a relatively heavy sulfur isotopic composition from 5.8 to 17.6 ‰, and no difference for sulfur isotopes between the Sn deposits (5.8-13.4 ‰, Huangjinwa, Zengjialong, Jianfengpo) and the Pb-Zn deposit (mostly 7.1-13.0 ‰, except for one 17.6 ‰, Zhangshiba). The sulfur isotope data of pyrite from the host sedimentary rocks show

  2. Origin of the granites and related Sn and Pb-Zn polymetallic ore deposits in the Pengshan district, Jiangxi Province, South China: constraints from geochronology, geochemistry, mineral chemistry, and Sr-Nd-Hf-Pb-S isotopes

    NASA Astrophysics Data System (ADS)

    Xu, Bin; Jiang, Shao-Yong; Luo, Lan; Zhao, Kui-Dong; Ma, Liang

    2017-03-01

    The Pengshan Sn and Pb-Zn polymetallic deposits are located in the south margin of the Jiujiang-Ruichang (Jiurui) district of the Middle-Lower Yangtze River Metallogenic Belt in South China. Four large deposits include Huangjinwa, Zengjialong, Jianfengpo, and Zhangshiba, the former three are Sn-dominant deposits which occur as stratiform orebodies in the contact zones of the Pengshan granites and within the country rock strata, whereas Zhangshiba consists of stratiform Pb-Zn orebodies within the Precambrian metasedimentary strata. In this study, we present results on zircon U-Pb ages, major and trace elements, and mineral chemistry as well as Sr-Nd-Hf isotope data of the granites, Pb and S isotopes of both the Sn-dominant and Pb-Zn dominant deposits, and U-Pb dating of cassiterite from the Pengshan district. SHRIMP and LA-ICP-MS zircon U-Pb dating shows that the Pengshan granites were emplaced in the Early Cretaceous (129-128 Ma), which is in good agreement with the U-Pb dating (130-128 Ma) of cassiterite from the Jianfengpo Sn deposit. The Pengshan granites consist mainly of weakly peraluminous highly fractionated I-type affinity granitic rocks. Detailed elemental and isotopic data suggest that the granites formed by partial melting of Mesoproterozoic metamorphic basement materials with minor input of mantle-derived melts. The mineral chemistry of biotite demonstrates that the Pengshan granitic magma had a low oxygen fugacity, thereby precluding the tin dominantly partitioning into the rock-forming silicate minerals and favoring accumulation in the exsolved residual liquid during magma crystallization stages. Sulfur isotopes show a relatively heavy sulfur isotopic composition from 5.8 to 17.6 ‰, and no difference for sulfur isotopes between the Sn deposits (5.8-13.4 ‰, Huangjinwa, Zengjialong, Jianfengpo) and the Pb-Zn deposit (mostly 7.1-13.0 ‰, except for one 17.6 ‰, Zhangshiba). The sulfur isotope data of pyrite from the host sedimentary rocks show

  3. Whole-Rock Geochemistry and Zircon U-Pb Isotopes of the Late Cretaceous Granitoids of the Eastern Taurus (turkey): Implications for Petrogenesis and Geodynamic Setting

    NASA Astrophysics Data System (ADS)

    Beyarslan, Melahat; Lin, Yu-Chin; Chung, Sun-Lin; Feyzi Bingol, Ahmet; Yildirim, Esra

    2015-04-01

    The granitoid plutons out crop largely in the Eastern Taurus, in Turkey. New data, including a combination of field relation, U-Pb zircon geochronology and rock geochemistry on the granitoids in the Eastern Taurus of the Tethyan orogen in Turkey, come from four plutons ( Pertek, Baskil, Göksun and Şifrin). Pertek, Baskil and Göksun plutons consist mainly of diorite, quartz-diorites, tonalite, granodiorites and granites of I-type, with minor monzonite, the Şifrin pluton consists of syenogranite, syenite, monzogranite, monzonite. U-Pb zircon geochronology of four samples of diorite and granite from Pertek and Baskil plutons indicate ages of 86±2 - 79 ± 1Ma. U-Pb zircon geochronology of four samples from the Şifrin granitoid yield ages 77±1-72±1 Ma. Considering these ages, emplacement of the plutons took place during Late Cretaceous (Santonian-Campanian), from 86 to 72 Ma. Although the SiO2 of rocks forming granitoids varies in wide range ( 46.792- 74.092 wt%), they show arc and syn-collision geochemical affinity, with enrichment of LILE (K, Rb, Sr and Ba) and depletion of HFSE (Nb, Ta and Ti) and P. Geochemical data indice that the diorite, tonalite and granodiorite are low-K tholeiite, monzodiorite, monzogranite, granite and K-granite are calc-alkaline and high-K calc-alkaline and monzonite, syenomonzonite and syenite of Şifrin pluton and some samples of the Pertek pluton are shoshonitic. The Eastern Taurus granitoids would be formed by partial melting of possible juvenile arc-derived rocks during subduction of the South Branch of the Neo-Tethyan oceanic crust and subsequent arc-continent collision.

  4. Mid-Neoproterozoic intraplate magmatism in the northern margin of the Southern Granulite Terrane, India: Constraints from geochemistry, zircon U-Pb geochronology and Lu-Hf isotopes

    NASA Astrophysics Data System (ADS)

    Deeju, T. R.; Santosh, M.; Yang, Qiong-Yan; Pradeepkumar, A. P.; Shaji, E.

    2016-11-01

    The northern margin of the Southern Granulite Terrane in India hosts a number of mafic, felsic and alkaline magmatic suites proximal to major shear/paleo-suture zones and mostly represents magmatism in rift-settings. Here we investigate a suite of gabbros and granite together with intermediate (dioritic) units generated through mixing and mingling of a bimodal magmatic suite. The massive gabbro exposures represent the cumulate fraction of a basic magma whereas the granitoids represent the product of crystallization in felsic magma chambers generated through crustal melting. Diorites and dioritic gabbros mostly occur as enclaves and lenses within host granitoids resembling mafic magmatic enclaves. Geochemistry of the felsic units shows volcanic arc granite and syn-collisional granite affinity. The gabbro samples show mixed E-MORB signature and the magma might have been generated in a rift setting. The trace and REE features of the rocks show variable features of subduction zone enrichment, crustal contamination and within plate enrichment, typical of intraplate magmatism involving the melting of source components derived from both depleted mantle sources and crustal components derived from older subduction events. The zircons in all the rock types show magmatic crystallization features and high Th/U values. Their U-Pb data are concordant with no major Pb loss. The gabbroic suite yields 206Pb/238U weighted mean ages in the range of 715 ± 4-832.5 ± 5 Ma marking a major phase of mid Neoproterozoic magmatism. The diorites crystallized during 206Pb/238U weighted mean age of 724 ± 6-830 ± 2 Ma. Zircons in the granite yield 206Pb/238U weighted mean age of 823 ± 4 Ma. The age data show broadly similar age ranges for the mafic, intermediate and felsic rocks and indicate a major phase of bi-modal magmatism during mid Neoproterozoic. The zircons studied show both positive and negative εHf(t) values for the gabbros (-6.4 to 12.4), and negative values for the diorites (-7

  5. The role of ridge subduction in determining the geochemistry and Nd–Sr–Pb isotopic evolution of the Kodiak batholith in southern Alaska

    USGS Publications Warehouse

    Ayuso, Robert A.; Haeussler, Peter J.; Bradley, Dwight C.; Farris, David W.; Foley, Nora K.; Wandless, Gregory A.

    2009-01-01

    The Paleocene Kodiak batholith, part of the Sanak–Baranof belt of Tertiary near-trench intrusive rocks, forms an elongate body (~ 150 km long) that transects Kodiak Island from SW to NE. The batholith consists of three zones (Southern, Central, and Northern) of kyanite-, muscovite-, and garnet-bearing biotite tonalite and granodiorite and less abundant granite that intruded an accretionary prism (Kodiak Formation, and Ghost Rocks Formation). Small and likely coeval bodies (Northern, Western, and Eastern satellite groups) of quartz gabbro, diorite, tonalite, granodiorite, and leucogranite flank the batholith. The batholith is calc-alkalic, has an aluminum saturation index of > 1.1, FeOt/(FeOt + MgO) ~ 0.65 (at SiO2 = 65 wt.%), and increases in SiO2 (~ 61 wt.%–73 wt.%) and decreases in TiO2 (~ 0.9 wt.%–0.3 wt.%) from SW to NE. As a group, the granitic rocks have light REE-enriched chondrite-normalized patterns with small or no negative Eu anomalies, primitive mantle-normalized negative anomalies for Nb and Ti, and positive anomalies for Pb. Small to large negative anomalies for Th are also distinctive. The quartz gabbros and diorites are generally characterized by generally flat to light REE chondrite-normalized patterns (no Eu anomalies), and mantle-normalized negative anomalies for Nb, Ti, and P. Pb isotopic compositions (206Pb/204Pb = 18.850–18.960; 207Pb/204Pb = 15.575–15.694; 208Pb/204Pb = 38.350–39.039) are intermediate between depleted mantle and average continental crust. The Southern zone and a portion of the Central zone are characterized by negative εNd values of − 3.7 to − 0.3 and TDM ages ranging from ~ 838 Ma to 1011 Ma. Other granitic rocks from the Central and Northern zones have higher εNd values of − 0.4 to + 4.7 and younger TDM ages of ~ 450 to 797 Ma. Granitic and mafic plutons from the Eastern satellites show a wide range of εNdvalues of − 2.7 to + 6.4, and TDM ages from 204 Ma to

  6. Zircon U-Pb dating, geochemistry and Sr-Nd-Pb-Hf isotopes of the Wajilitag alkali mafic dikes, and associated diorite and syenitic rocks: Implications for magmatic evolution of the Tarim large igneous province

    NASA Astrophysics Data System (ADS)

    Zou, Si-Yuan; Li, Zi-Long; Song, Biao; Ernst, Richard E.; Li, Yin-Qi; Ren, Zhong-Yuan; Yang, Shu-Feng; Chen, Han-Lin; Xu, Yi-Gang; Song, Xie-Yan

    2015-01-01

    The Early Permian Tarim large igneous province (Tarim LIP) consists mainly of basaltic lavas, mafic-ultramafic intrusions including dikes and, syenite bodies in the Tarim Basin, NW China. A major unit of the Tarim LIP, the Wajilitag intrusive complex, consists of olivine pyroxenite, clinopyroxenite and gabbro units (from bottom to top), diorite and syenite rocks occurred in the upper part of the complex and alkali mafic dikes intrude the clinopyroxenite phase. Here we report the zircon U-Pb age and Hf isotopes, geochemical characteristics and Sr-Nd-Pb isotopic data of the alkali mafic dikes, and diorite, aegirine-nepheline syenite and syenite porphyry units in the Wajilitag intrusive complex. Zircons from the diorite and alkali mafic rocks yield concordant crystallization ages of 275.2 ± 1.2 Ma and 281.4 ± 1.7 Ma, respectively. The diorite and syenitic rocks in Wajilitag area have a narrow range of SiO2 contents (51.9-57.3 wt.%), and are enriched in total alkalis (Na2O + K2O = 8.3-14.3 wt.%), among which the aegirine-nepheline syenite and syenite porphyry have the geochemical affinity of A-type granites. The alkali mafic rocks and syenitic rocks have high Al2O3 (19.4-21.1 wt.%), Zr, Hf, Ba contents, total rare earth element abundances and LREE/HREE ratios and low Mg# value, K, P and Ti contents. Diorites have lower Al2O3 contents, total REE abundances and LREE/HREE ratios and higher Mg# values than the alkali mafic rocks and syenitic rocks. The diorites and syenitic rocks have low initial 87Sr/86Sr ratios (0.7034-0.7046), and high εNd(t) values (0.1-4.1) and zircon εHf(t) values (- 0.9-4.4). All the diorites and syenitic rocks show the 206Pb/204Pb ratios ranging of 18.0-19.5, 207Pb/204Pb of 15.4-15.6 and 208Pb/204Pb of 38.0-39.9. Sr-Nd isotopic ratios indicate a FOZO-like mantle source for the diorite and syenitic rocks, similar to that of the mafic-ultramafic rocks in the Wajilitag complex. In contrast, zircon Hf isotopes of basalt and syenite elsewhere in the

  7. Tectono-magmatic evolution of the Chihuahua-Sinaloa border region in northern Mexico: Insights from zircon-apatite U-Pb geochronology, zircon Hf isotope composition and geochemistry of granodiorite intrusions

    NASA Astrophysics Data System (ADS)

    Mahar, Munazzam Ali; Goodell, Philip C.; Feinstein, Michael Nicholas

    2016-11-01

    We present the whole-rock geochemistry, LA-ICP-MS zircon-apatite U-Pb ages and zircon Hf isotope composition of the granodioritic plutons at the southwestern boundary of Chihuahua with the states of Sinaloa and Sonora. These granodiorites are exposed in the north and south of the Rio El Fuerte in southwest Chihuahua and northern Sinaloa. The magmatism spans over a time period of 37 Ma from 90 to 53 Ma. Zircons are exclusively magmatic with strong oscillatory zoning. No inheritance of any age has been observed. Our new U-Pb dating ( 250 analyses) does not support the involvement of older basement lithologies in the generation of the granitic magmas. The U-Pb apatite ages from granodiorites in southwest Chihuahua vary from 52 to 70 Ma. These apatite ages are 1 to 20 Ma younger than the corresponding zircon U-Pb crystallization ages, suggesting variable cooling rates from very fast to 15 °C/Ma ( 800 °C to 500 °C) and shallow to moderate emplacement depths. In contrast, U-Pb apatite ages from the Sinaloa batholith are restricted from 64 to 61 Ma and are indistinguishable from the zircon U-Pb ages range from 67 to 60 Ma within the error, indicating rapid cooling and very shallow emplacement. However, one sample from El Realito showed a larger difference of 20 Ma in zircon-apatite age pair: zircon 80 ± 0.8 Ma and apatite 60.6 ± 4 Ma, suggesting a slower cooling rate of 15 °C/Ma. The weighted mean initial εHf (t) isotope composition (2σ) of granodiorites varies from + 1.8 to + 5.2. The radiogenic Hf isotope composition coupled with previous Sr-Nd isotope data demonstrates a significant shift from multiple crustal sources in the Sonoran batholithic belt to the predominant contribution of the mantle-derived magmas in the southwest Chihuahua and northern Sinaloa. Based on U-Pb ages, the absence of inheritance, typical high Th/U ratio and radiogenic Hf isotope composition, we suggest that the Late Cretaceous-Paleogene magmatic rocks in this region are not derived from

  8. Carbon isotope geochemistry and geobiology

    NASA Technical Reports Server (NTRS)

    Desmarais, D.

    1985-01-01

    Carbon isotope fractionation values were used to understand the history of the biosphere. For example, plankton analyses confirmed that marine extinctions at the end of the Cretaceous period were indeed severe (see Hsu's article in Sundquist and Broeker, 1984). Variations in the isotopic compositions of carbonates and evaporitic sulfates during the Paleozoic reflect the relative abundances of euxinic (anoxic) marine environments and organic deposits from terrestrial flora. The carbon isotopic composition of Precambrian sediments suggest that the enzyme ribulose bisphosphate carboxylase has existed for perhaps 3.5 billion years.

  9. Geochronology, geochemistry and Sr-Nd-Pb isotopic constraints on the origin of the Qian’echong porphyry Mo deposit, Dabie orogen, east China

    NASA Astrophysics Data System (ADS)

    Gao, Yang; Mao, Jingwen; Ye, Huishou; Li, Faling; Li, Yongfeng; Luo, Zhengzhuan; Xiong, Bikang; Meng, Fang

    2014-05-01

    The giant Qian’echong porphyry molybdenum deposit is located in the Dabie orogen, east China. The molybdenum mineralization mainly occurs as molybdenite-bearing quartz veins hosted by the Devonian Nanwan Formation in the external contact zone of the Qian’echong stock. The Qian’echong stock comprises an earlier formed monzogranite and a later formed granite porphyry. Sensitive high-resolution ion microprobe (SHRIMP) zircon U-Pb dating constrains the timing of crystallization of the monzogranite and granite porphyry to 130 ± 2 and 129 ± 2 Ma, respectively. The Re-Os model ages of six molybdenite samples range from 127.9 ± 1.9 to 129.7 ± 1.9 Ma with an isochron age of 129.4 ± 1.5 Ma, which are all consistent within errors with the zircon U-Pb ages, indicating an Early Cretaceous magmatic and mineralization event. The Qian’echong granites have moderate negative Eu anomalies and are relatively enriched in light rare earth elements (REE), but depleted in heavy REE, Y, and high field strength elements (HFSE; e.g., Nb, Ta, and Ti). The Qian’echong granites are I-type rather than A- or S-type, and they have high (87Sr/86Sr)i (0.706771-0.710326) and low ɛNd(t) (-25.5 to -16.8). Two-stage Nd model ages (T2DM) vary between 2.29 and 2.99 Ga. Sr-Nd-Pb isotopic data suggest that the Qian’echong granites were not derived from the North China Craton (NCC), but rather were generated from the Yangtze Craton (YC) lower crust. Paleoproterozoic inherited zircon age and whole-rock chemical and Sr-Nd-Pb isotopic data suggest that the Qian’echong granites were derived mainly from partial melting of ultrahigh pressure eclogites, with incorporation of some Paleoproterozoic to Archean YC crustal materials at lower crustal levels. Delamination or foundering of eclogitic lower crust, which extensively occurred in the Dabie orogen during the Early Cretaceous, had not taken place beneath the Qian’echong deposit when it formed. The Qian’echong molybdenum deposit formed in

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  11. Isotope geochemistry in 1990s

    SciTech Connect

    Billo, S.M.

    1995-12-31

    The intense interest in radioactive minerals as a source of atomic energy, and their application in searching for ore deposits and also in gamma-ray and neutron logging oil wells, have opened new vistas in every science. Many minerals containing elements of high atomic weight are radioactive, and emit a radiation which affects a photographic plate and may be detected by means of a sensitive phosphorescent screen. Most of the elements as found in nature are a mixture of isotopes. isotopes are atoms of one element which have different masses. Uranium, thorium, potassium, and rubidium isotopes are also used to date minerals and rocks. Organic materials that have been in equilibrium with CO{sub 2}-photosynthetic cycle during the past 50,000 years are dated by carbon-14 method. The stable isotopes of H{sub 2}, C, N{sub 2}, O{sub 2}, and S are intimately associated with the atmosphere, hydrosphere, and lithosphere and are used in probing water resources.

  12. Paleoproterozoic crustal evolution in the East Sarmatian Orogen: Petrology, geochemistry, Sr-Nd isotopes and zircon U-Pb geochronology of andesites from the Voronezh massif, Western Russia

    NASA Astrophysics Data System (ADS)

    Terentiev, R. A.; Savko, K. A.; Santosh, M.

    2016-03-01

    Andesites and related plutonic rocks are major contributors to continental growth and provide insights into the interaction between the mantle and crust. Paleoproterozoic volcanic rocks are important components of the East Sarmatian Orogen (ESO) belonging to the East European Craton, although their petrogenesis and tectonic setting remain controversial. Here we present petrology, mineral chemistry, bulk chemistry, Sr-Nd isotopes, and zircon U-Pb geochronological data from andesites and related rocks in the Losevo and Vorontsovka blocks of the ESO. Clinopyroxene phenocrysts in the andesites are depleted in LREE, and enriched in HFSE (Th, Nb, Zr, Hf, Ti) and LILE (Ba, Sr). Based on the chemistry of pyroxenes and whole rocks, as well as Fe-Ti oxides, we estimate a temperature range of 1179 to 1262 °С, pressures of 11.3 to 13.0 kbar, H2O content of 1-5 wt.%, and oxygen fu gacity close to the MH buffer for the melts of the Kalach graben (KG) and the Baygora area (BA) andesites. Our zircon U-Pb geochronological data indicate new zircon growth during the middle Paleoproterozoic as displayed by weighted mean 207Pb/206Pb ages of 2047 ± 17 Ma and 2040 ± 16 Ma for andesite and dacite-porphyry of the BA, and 2050 ± 16 Ma from high-Mg basaltic andesite of the KG. The andesites and related rocks of the KG and BA are characterized by high magnesium contents (Mg # up to 0.68). All these volcanic rocks are depleted in LREE and HFSE, and display negative Nb and Ti anomalies relative to primitive mantle. The high-Mg bulk composition, and the presence of clinopyroxene phenocrysts suggests that the parent melts of the KG and BA suite were in equilibrium with the mantle rocks. The rocks show positive εNd(T) values and low initial 87Sr/86Sr, suggesting that the magmas were mostly derived from metasomatized mantle source. The geochemical differences between the two andesite types are attributed to: the predominance of fractional crystallization, and minor role of contamination in

  13. Zircon U-Pb age, Hf isotopic compositions and geochemistry of the Silurian Fengdingshan I-type granite Pluton and Taoyuan mafic-felsic Complex at the southeastern margin of the Yangtze Block

    NASA Astrophysics Data System (ADS)

    Zhong, Yufang; Ma, Changqian; Zhang, Chao; Wang, Shiming; She, Zhenbing; Liu, Lei; Xu, Haijin

    2013-09-01

    This work presents an integrated study of zircon U-Pb ages and Hf isotope along with whole-rock geochemistry on Silurian Fengdingshan I-type granites and Taoyuan mafic-felsic intrusive Complex located at the southeastern margin of the Yangtze Block, filling in a gap in understanding of Paleozoic I-type granites and mafic-intermediate igneous rocks in the eastern South China Craton (SCC). The Fengdingshan granite and Taoyuan hornblende gabbro are dated at 436 ± 5 Ma and 409 ± 2 Ma, respectively. The Fengdingshan granites display characteristics of calc-alkaline I-type granite with high initial 87Sr/86Sr ratios of 0.7093-0.7127, low ɛNd(t) values ranging from -5.6 to -5.4 and corresponding Nd model ages (T2DM) of 1.6 Ga. Their zircon grains have ɛHf(t) values ranging from -2.7 to 2.6 and model ages of 951-1164 Ma. The Taoyuan mafic rocks exhibit typical arc-like geochemistry, with enrichment in Rb, Th, U and Pb and depletion in Nb, Ta. They have initial 87Sr/86Sr ratios of 0.7053-0.7058, ɛNd(t) values of 0.2-1.6 and corresponding T2DM of 1.0-1.1 Ga. Their zircon grains have ɛHf(t) values ranging from 3.2 to 6.1 and model ages of 774-911 Ma. Diorite and granodiorite from the Taoyuan Complex have initial 87Sr/86Sr ratios of 0.7065-0.7117, ɛNd(t) values from -5.7 to -1.9 and Nd model ages of 1.3-1.6 Ga. The petrographic and geochemical characteristics indicate that the Fengdingshan granites probably formed by reworking of Neoproterozoic basalts with very little of juvenile mantle-derived magma. The Taoyuan Complex formed by magma mixing and mingling, in which the mafic member originated from a metasomatized lithospheric mantle. Both the Fengdingshan and Taoyuan Plutons formed in a post-orogenic collapse stage in an intracontinental tectonic regime. Besides the Paleozoic Fengdingshan granites and Taoyuan hornblende gabbro, other Neoproterozoic and Indosinian igneous rocks located along the southeastern and western margin of the Yangtze Block also exhibit decoupled

  14. Cryogenian alkaline magmatism in the Southern Granulite Terrane, India: Petrology, geochemistry, zircon U-Pb ages and Lu-Hf isotopes

    NASA Astrophysics Data System (ADS)

    Santosh, M.; Yang, Qiong-Yan; Ram Mohan, M.; Tsunogae, T.; Shaji, E.; Satyanarayanan, M.

    2014-11-01

    The Southern Granulite Terrane (SGT) in India preserves the records of the formation and recycling of continental crust from Mesoarchean through Paleoproterozoic to Neoproterozoic and Cambrian, involving multiple subduction-accretion-collision associated with major orogenic cycles. A chain of unmetamorphosed and undeformed alkaline magmatic intrusions occurs along the northern margin of the SGT aligned along paleo-suture zones. Here we investigate two representative plutons from this suite, the Angadimogar syenite (AM) and the Peralimala alkali granite (PM) through field, petrological, geochemical, zircon U-Pb and Lu-Hf studies. Magma mixing and mingling textures and mineral assemblages typical of alkaline rocks are displayed by these plutons. The whole-rock major and trace element data characterize their alkaline nature. In trace element discrimination diagrams, the AM rocks straddle between the VAG (volcanic-arc granites) and WPG (within plate granites) fields with most of the samples confined to the VAG field, whereas the PM rocks are essentially confined to the WPG field. The diversity in some of the geochemical features between the two plutons is interpreted to be the reflection of source heterogeneities. Most zircon grains from the AM and PM plutons display oscillatory zoning typical of magmatic crystallization although some grains, particularly those from the PM pluton, show core-rim structures with dark patchy zoned cores surrounded by irregular thin rims resulting from fluid alteration. The weighted mean 206Pb/238U ages of the magmatic zircons from three samples of the AM syenite are in the range of 781.8 ± 3.8 Ma to 798 ± 3.6 Ma and those from two samples of the PM alkali granite yield ages of 797.5 ± 3.7 Ma and 799 ± 6.2 Ma. A mafic magmatic enclave from the AM pluton shows weighted mean 206Pb/238U age of 795 ± 3.3 Ma. The AM and PM plutons also carry rare xeneocrystic zircons which define upper intercept concordia ages of 3293 ± 13 Ma and 2530

  15. U-Pb-Nd-Hf isotope geochemistry of the Mesoproterozoic A-type granites in Mannefallknausane, western Dronning Maud Land, Antarctica

    NASA Astrophysics Data System (ADS)

    Ramo, O. T.; Kurhila, M.; Luttinen, A. V.; Andersen, T.

    2009-12-01

    The bedrock of western Dronning Maud Land, Antarctica records several stages of anorogenic magmatism. The Grenvillean-age metamorphic basement gneisses of Heimefrontfjella and Mannefallknausane were intruded by mafic dikes (Bauer et al., 2003) and A-type granite plutons (Jacobs, 1991) at circa 1 Ga. A 590 Ma suite of mafic dikes manifests a subsequent episode of Proterozoic anorogenic magmatism (Bauer et al., 2003). Jurassic (180 Ma) continental flood basalts (CFBs), their intrusive equivalents, and associated alkaline mafic rocks represent the third and youngest episode of anorogenic magmatism (Luttinen et al., 1998; Romu and Luttinen, 2007). The crystalline bedrock in western Dronning Maud Land is composed of the Archean Grunehogna craton and the Mesoproterozoic Maud mobile belt. About 100 km south of Archean-Proterozoic transition, in the Proterozoic realm, nunataks of Mannefallknausane (74.5oS, 15oW) are dominated by Precambrian granitoid rocks and rare paragneisses. Three principal granites can be identified: a white, garnet-bearing K-feldspar-megacrystic biotite granite; a red biotite-hornblende±clinopyroxene granite with or without plagioclase-mantled K-feldspar-megacrysts (rapakivi texture); and a dark green porphyritic charnockite with orthopyroxene and hornblende. The presence of rapakivi texture, the mode of occurrence, and geochemical composition of the granites of Mannefallknausane imply A typology. For two varieties of the red granite (wiborgite and pyterlite), our new U-Pb data imply crystallization ages of 1073 ± 6 Ma and 1084 ± 8 Ma, respectively. These are compatible with a U-Pb zircon upper intercept age of 1073 ± 8 Ma of the charnockite (Arndt et al., 1991). The initial Nd isotope composition of these rocks is relatively radiogenic [epsilon-Nd (1075 Ma) value of the biotite granite -0.5; red granite +0.3, +0.5; charnockite +1.4], as is that of a country-rock gneiss from the surrounding bedrock (+1.0). Initial zircon epsilon-Hf values of the

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

  17. Anatexis of mafic and felsic lower crust: Geochemistry and Nd, Sr and Pb isotopes of late-orogenic granodiorites and leucogranites (Damara orogen, Namibia)

    NASA Astrophysics Data System (ADS)

    Osterhus, Lennart; Jung, Stefan

    2010-05-01

    The Damara orogen (Namibia) represents a well-exposed and deeply eroded orogenic mobile belt consisting of the north-south trending Kaoko belt and the northeast-southwest trending intracontinental Damara belt. The latter has been subdivided into a Northern, a Central and a Southern Zone based on stratigraphy, metamorphic grade, structure and geochronology. The late-orogenic granodioritic to leucogranitic Gawib pluton is a cross-cutting, pear-shaped post-tectonic stock within the southern Central Zone which is elsewhere dominated by basement rocks, high-grade metasedimentary rocks of the Tinkas Formation and syn-orogenic granites (Salem-type). The non-foliated granodiorites consist of plagioclase, quartz, microcline, hornblende and biotite whereas the leucogranites consist of microcline, quartz, plagioclase and biotite. Major element variation of the granodiorites show two distinct magma types were some samples have high TiO2, MgO and Fe2O3 and low Al2O3 and others have low TiO2, MgO and Fe2O3 and high Al2O3. Based on high REE, Nb, Zr and Y concentrations some granodiorites can be classified as A-type granitoids. Strontium concentrations are high in the granodiorites (up to 939 ppm) and decrease to < 200 ppm in the leucogranites. Rb/Sr ratios are low (1) in the leucogranites. Granodiorites have moderately radiogenic initial 87Sr/86Sr ratios (0.7088-0.7132), strongly negative initial ɛ Nd values (ca. -12) and comparatively unradiogenic Pb isotope data, the latter obtained on acid-leached feldspar separates. Leucogranites have more radiogenic initial 87Sr/86Sr ratios (0.7223-0.7336) and more negative initial ɛ Nd values (ca. -18). Pb isotopes tend to be less radiogenic than in the granodiorites. The mean crustal residence ages of the granodiorites, expressed as depleted mantle Nd model ages, are ca. 2.0 Ga but the leucogranites tend to have older Nd model ages (2.5 Ga). Therefore, a likely source for the granodiorites and leucogranites is a sequence of mafic to

  18. Trace element and Nd, Sr, Pb isotope geochemistry of Kilauea Volcano, Hawai'i, near-vent eruptive products: 1983-2001

    USGS Publications Warehouse

    Thornber, Carl R.; Budahn, James R.; Ridley, W. Ian; Unruh, Daniel M.

    2003-01-01

    This open-file report serves as a repository for geochemical data referred to in U.S. Geological Survey Professional Paper 1676 (Heliker, Swanson, and Takahashi, eds., 2003), which includes multidisciplinary research papers pertaining to the first twenty years of Puu Oo Kupaianaha eruption activity. Details of eruption characteristics and nomenclature are provided in the introductory chapter of that volume (Heliker and Mattox, 2003). Geochemical relations of this data are depicted and interpreted by Thornber (2003), Thornber and others (2003a) and Thornber (2001). This report supplements Thornber and others (2003b) in which whole-rock and glass major-element data on ~1000 near-vent lava samples collected during the 1983 to 2001 eruptive interval of Kilauea Volcano, Hawai'i, are presented. Herein, we present whole-rock trace element compositions of 85 representative samples collected from January 1983 to May 2001; glass trace-element compositions of 39 Pele’s Tear (tephra) samples collected from September 1995 to September 1996, and whole-rock Nd, Sr and Pb isotopic analyses of 10 representative samples collected from September 1983 to September 1993. Thornber and others (2003b) provide a specific record of sample characteristics, location, etc., for each of the samples reported here. Spreadsheets of both reports may be integrated and sorted based upon time of formation or sample numbers. General information pertaining to the selectivity and petrologic significance of this sample suite is presented by Thornber and others (2003b). As justified in that report, this select suite of time-constrained geochemical data is suitable for constructing petrologic models of pre-eruptive magmatic processes associated with prolonged rift zone eruption of Hawaiian shield volcanoes.

  19. Geochemistry and zircon U-Pb-Hf isotopes of the granitoids of Baolidao and Halatu plutons in Sonidzuoqi area, Inner Mongolia: Implications for petrogenesis and geodynamic setting

    NASA Astrophysics Data System (ADS)

    Hu, Chuansheng; Li, Wenbo; Xu, Cheng; Zhong, Richen; Zhu, Feng

    2015-01-01

    The Baolidao and Halatu plutons are located in the Northern Orogenic Belt (NOB) in Sonidzuoqi area of Inner Mongolia, which has an important significance for the tectonic evolution of Xing-Meng Orogenic Belt (XMOB). The two plutons have been intensively studied but the conclusions are still controversial. Combined with the previous study, this paper gives new geological data about the two correlative plutons for gaining a better understanding of their petrogenesis and the geodynamic setting. The Baolidao granitoids contain two different series, calc-alkaline series mainly formed in the Ordovician and high K calc-alkaline series mainly formed in the Carboniferous. The Halatu granites are formed in the Triassic and belong to high-K calc-alkaline series. This study got the zircon U-Pb ages of 316-322 Ma for the Baolidao granitoids and 233 ± 2 Ma for the Halatu syenogranites, respectively. In the tectonic discrimination diagrams, they mainly fall into the area of post-orogenic granites (POG). Hf isotopic analyses for the Baolidao granitoids (Sample BLD-1 and 3) shows εHf (t) = 3.0-14.0, with two-stage Hf model age (TDM2) of 436-1138 Ma. The Halatu syenogranite (Sample HLT-1) also shows a depleted εHf (t) = 3.8-8.2, with TDM2 of 741-1024 Ma, suggesting the major involvement of juvenile crustal components. The various εHf values of the Carboniferous Baolidao and Triassic Halatu granitoids indicates a hybrid magma source of juvenile material with old crustal component, and the εHf (t) values decrease from the Carboniferous to Triassic, suggesting the increasing proportion of old continental material during this period. Combined with the regional geology, the Carboniferous Baolidao granitoids are possibly not arc rocks, but originated from the post-collisional setting. The Triassic Halatu granites were formed in the subsequently extensional environment.

  20. The Isotope Geochemistry of Abyssal Peridotites and Related Rocks

    DTIC Science & Technology

    1993-06-01

    Oceanography/ Applied Ocean Science San d E n g in e e r in g ftoo I • •OFTI DOCTORAL DISSERTATION I The Isotope Geochemistry of Abyssal Peridotites and...Related Rocks "- . .. .. .. 1 , ".:i• . Jonathan E. Snow , ’ I .June 1993 I .o. I I I WHOI-93-36 I The Isotope Geochemistry of Abyssal Peridotites and...States Government. This thesis should be cited as: Jonathan E. Snow, 1993. The Isotope Geochemistry of Abyssal Peridotites and Related Rocks. Ph.D

  1. Subduction-related Late Carboniferous to Early Permian Magmatism in the Eastern Pontides, the Camlik and Casurluk plutons: Insights from geochemistry, whole-rock Sr-Nd and in situ zircon Lu-Hf isotopes, and U-Pb geochronology

    NASA Astrophysics Data System (ADS)

    Karsli, Orhan; Dokuz, Abdurrahman; Kandemir, Raif

    2016-12-01

    Late Carboniferous to early Permian granitoid rocks represent a volumetrically minor component of the Eastern Pontide lithosphere, but they preserve useful information about the region's tectonomagmatic history. The Casurluk and Camlik plutons primarily consist of gabbro, gabbroic diorite, diorite, monzogabbro, monzodiorite and monzonite, which intrude early to middle Carboniferous granitic basement rocks in the region. In this study, we use in situ zircon U-Pb ages and Lu-Hf isotopic values, whole-rock Sr-Nd isotopic values, and mineral chemistry and geochemistry of these plutons to determine petrogenesis and crustal evolution; we also discuss geodynamic implications. LA-ICP-MS zircon U-Pb dating of magmatic zircons from the rocks suggests that the plutons were emplaced during the late Carboniferous to early Permian (302 Ma). The metaluminous and I-type intrusive rocks belong to the high-K calc-alkaline series. In addition, they are relatively enriched in light rare earth elements (LREEs) and large-ion lithophile elements (LILEs); they are depleted in heavy rare earth elements (HREEs) and high field strength elements (HFSEs), such as Nb and Ti. All of the samples have homogeneous initial ISr values (0.70675 to 0.70792) and low εNd (t) values (- 5.1 to - 3.3). Zircons from the rocks of both plutons have uniform negative to slightly positive εHf (t) values (- 3.5 to 1.4) and old Hf two-stage model ages (1323 to 1548 Ma), implying that they have the same source, as well as suggesting the involvement of old enriched lithospheric mantle materials during their magma genesis. These results, combined with the εHf (t) values and two-stage model ages, demonstrate that the primary magmas were derived from partial melting of old lithospheric mantle material metasomatized by subduction-related fluids. Considering other regional geological data from the Sakarya Zone where these plutons formed, we conclude that late Carboniferous to early Permian magmatism in the area

  2. Lower Carboniferous post-orogenic granites in central-eastern Sierra de Velasco, Sierras Pampeanas, Argentina: U-Pb monazite geochronology, geochemistry and Sr-Nd isotopes

    NASA Astrophysics Data System (ADS)

    Grosse, Pablo; Söllner, Frank; Báez, Miguel A.; Toselli, Alejandro J.; Rossi, Juana N.; de La Rosa, Jesus D.

    2009-07-01

    The central-eastern part of the Sierra de Velasco (Sierras Pampeanas, NW Argentina) is formed by the large Huaco (40 × 30 km) and Sanagasta (25 × 15 km) granite massifs and the small La Chinchilla stock (2 × 2 km). The larger granites intrude into Ordovician metagranitoids and crosscut Devonian (?) mylonitic shear zones, whereas the small stock sharply intrudes into the Huaco granite. The two voluminous granites are biotitic-muscovitic and biotitic porphyritic syeno- to monzogranites. They contain small and rounded tonalitic and quartz-dioritic mafic microgranular enclaves. The small stock is an equigranular, zinnwaldite- and fluorite-bearing monzogranite. The studied granites are silica-rich (SiO2 >70%), potassium-rich (K2O >4%), ferroan, alkali-calcic to slightly calk-alkalic, and moderately to weakly peraluminous (A/CNK: 1.06-1.18 Huaco granite, 1.01-1.09 Sanagasta granite, 1.05-1.06 La Chinchilla stock). They have moderate to strong enrichments in several LIL (Li, Rb, Cs) and HFS (Nb, Ta, Y, Th, U) elements, and low Sr, Ba and Eu contents. U-Pb monazite age determinations indicate Lower Carboniferous crystallization ages: 350-358 Ma for the Huaco granite, 352.7 ± 1.4 Ma for the Sanagasta granite and 344.5 ± 1.4 Ma for the La Chinchilla stock. The larger granites have similar ɛNd values between -2.1 and -4.3, whereas the younger stock has higher ɛNd of -0.6 to -1.4, roughly comparable to the values obtained for the Carboniferous San Blas granite (-1.4 to -1.7), located in the north of the sierra. The Huaco and Sanagasta granites have a mainly crustal source, but with some participation of a more primitive, possibly mantle-derived, component. The main crustal component can be attributed to Ordovician peraluminous metagranitoids. The La Chinchilla stock derives from a more primitive source, suggesting an increase with time in the participation of the primitive component during magma genesis. The studied granites were generated during a post-orogenic period

  3. Zircon U-Pb age, Hf isotope and geochemistry of Carboniferous intrusions from the Langshan area, Inner Mongolia: Petrogenesis and tectonic implications

    NASA Astrophysics Data System (ADS)

    Liu, Min; Zhang, Da; Xiong, Guangqiang; Zhao, Hongtao; Di, Yongjun; Wang, Zhong; Zhou, Zhiguang

    2016-04-01

    Late Paleozoic was a critical period for the tectonic evolution of the northern margin of the Alxa-North China craton, but the evolutionary history is not well constrained. The Carboniferous intrusions in the Langshan area in the western part of the northern margin of the Alxa-North China craton are mainly composed of tonalite, quartz diorite, olivine gabbro and pyroxene peridotite. Zircon LA-ICP-MS U-Pb dating indicates that the Langshan Carboniferous intrusions were emplaced at ca. 338-324 Ma. The quartz diorites are characterized by high amounts of compatible trace elements (Cr, Ni and V) and high Mg# values, which may suggest a significant mantle source. The positive Pb and negative Nb-Ta-Ti anomalies, the variable εHf(t) (-6.9 to 2.0) values and the old Hf model ages (1218-1783 Ma) imply some involvement of ancient continental materials in its petrogenesis. The tonalite has relatively high Sr/Y ratios, low Mg#, Yb and Y contents, features of adakite-like rocks, negative εHf(t) values (-9.8 to -0.1) and older Hf model ages (1344-1953 Ma), which suggest significant involvement of ancient crust materials and mantle-derived basaltic component in its petrogenesis. The high Mg# values, high Cr and Ni contents, and low Zr and Hf contents of the mafic-ultramafic rocks show evidence of a mantle source, and the relatively low zircon εHf(t) values (-5.9 to 3.2) might point to an enriched mantle. The trace element characteristics indicate the influence of subducted sediments and slab-derived fluids. In the tectonic discrimination diagrams, all the rocks plot in subduction-related environment, such as volcanic arc and continental arc. Considering the regional geology, we suggest that the Carboniferous intrusions in the Langshan area were likely emplaced during the late stage of the southward subduction of the Paleo-Asian Ocean plate, which formed a continental arc along the northern margin of the Alxa-North China craton.

  4. Zircon U-Pb age, Lu-Hf isotope, mineral chemistry and geochemistry of Sundamalai peralkaline pluton from the Salem Block, southern India: Implications for Cryogenian adakite-like magmatism in an aborted-rift

    NASA Astrophysics Data System (ADS)

    Renjith, M. L.; Santosh, M.; Li, Tang; Satyanarayanan, M.; Korakoppa, M. M.; Tsunogae, T.; Subba Rao, D. V.; Kesav Krishna, A.; Nirmal Charan, S.

    2016-01-01

    The Sundamalai peralkaline pluton is one among the Cryogenian alkaline plutons occurring in the Dharmapuri Rift Zone (DRZ) of the Salem Block in the Southern Granulite Terrane (SGT) of India. Here we present zircon U-Pb age and Lu-Hf isotopic composition, mineral chemistry and geochemistry of the pluton to explore the petrogenesis and geodynamic implications. Systematic modal variation of orthoclase, Na-plagioclase, Ca-amphibole (ferro-edenite and hastingsite) and quartz developed quartz-monzonite and granite litho units in the Sundamalai pluton. Thermometry based on amphibole-plagioclase pair suggests that the pluton was emplaced and solidified at around 4.6 kbar pressure with crystallization of the major phases between 748 and 661 °C. Estimated saturation temperature of zircon (712-698 °C) is also well within this range. However, apatite saturation occurred at higher temperatures between 835 and 870 °C, in contrast with monazite saturation (718-613 °C) that continued up to the late stage of crystallization. Estimated oxygen fugacity values (log fO2: -14 to -17) indicate high oxidation state for the magma that stabilized titanite and magnetite. The magmatic zircons from Sundamalai pluton yielded a weighted mean 206Pb/238U age of 832.6 ± 3.2 Ma. Geochemically, the Sundamalai rocks are high-K to shoshonitic, persodic (Na2O/K2O ratio > 1), silica-saturated (SiO2:65-72 wt.%), and peralkaline in composition (aluminum saturation index, ASI < 1; Alkalinity index, AI < 0). The initial magma was mildly metaluminous which evolved to strongly peralkaline as result of fractional crystallization (plagioclase effect) controlled differentiation between quartz-monzonite and granite. Both rock types have high content of Na2O (5.1-6.3 wt.%), Ba (350-2589 ppm) and Sr (264-1036 ppm); low content of Y (8.7-17 ppm) and Yb (0.96-1.69 ppm); elevated ratios of La/Yb (11-46) and Sr/Y (46-69) and are depleted in Ti, with a positive Sr anomaly suggesting an adakite-like composition and

  5. Pb isotopic heterogeneity in basaltic phenocrysts

    SciTech Connect

    Bryce, Julia G.; DePaolo, Donald J.

    2002-06-01

    The Pb isotopic compositions of phenocrystic phases in young basaltic lavas have been investigated using the Getty-DePaolo method (Getty S. J. and DePaolo D. J. [1995] Quaternary geochronology by the U-Th-Pb method. Geochim. Cosmochim. Acta 59, 3267 3272), which allows for the resolution of small isotopic differences. Phenocryst, matrix, and whole rock analyses were made on samples from the 17 Myr-old Imnaha basalts of the Columbia River Group, a zero-age MORB from the Mid-Atlantic Ridge, and a ca. 260 kyr-old tholeiite from Mount Etna. Plagioclase feldspar phenocrysts have low-(U, Th)/Pb, and in each sample the plagioclase has significantly lower 206Pb/207Pb and 208Pb/207Pb values than whole rock, matrix, and magnetite-rich separates. The Pb isotopic contrast between plagioclase and matrix/whole rock is found in three samples with varying grain sizes (0.5 2 cm for the Imnaha basalt and MORB and <1 mm for the Etna sample) from different tectonic settings, suggesting that these results are not unique. The isotopic contrasts are only slightly smaller in magnitude than the variations exhibited by whole rock samples from the region. The Imnaha basalts also have Sr isotopic heterogeneity evident only in plagioclase phenocrysts, but the MORB and Etna lavas do not. The isotopic heterogeneities reflect magma mixing, and indicate that isotopically diverse magmas were mixed together just prior to eruption. The results reinforce indications from melt inclusion studies that magma source region isotopic heterogeneities have large amplitudes at short length scales, and that the isotopic variations imparted to the magmas are not entirely homogenized during segregation and transport processes.

  6. H, O, Sr, Nd, and Pb isotope geochemistry of the Latir volcanic field and cogenetic intrusions, New Mexico, and relations between evolution of a continental magmatic center and modifications of the lithosphere

    USGS Publications Warehouse

    Johnson, C.M.; Lipman, P.W.; Czamanske, G.K.

    1990-01-01

    Over 200 H, O, Sr, Nd, and Pb isotope analyses, in addition to geologic and petrologic constraints, document the magmatic evolution of the 28.5-19 Ma Latir volcanic field and associated intrusive rocks, which includes multiple stages of crustal assimilation, magma mixing, protracted crystallization, and open- and closed-system evolution in the upper crust. In contrast to data from younger volcanic centers in northern New Mexico, relatively low and restricted primary ??18O values (+6.4 to +7.4) rule out assimilation of supracrustal rocks enriched in 18O. Initial 87Sr/86Sr ratios (0.705 to 0.708), ??18O values (-2 to-7), and 206Pb/204Pb ratios (17.5 to 18.4) of metaluminous precaldera volcanic rocks and postcaldera plutonic rocks suggest that most Latir rocks were generated by fractional crystallization of substantial volumes of mantle-derived basaltic magma that had near-chondritic Nd isotope ratios, accompanied by assimilation of crustal material in two main stages: 1) assimilation of non-radiogenic lower crust, followed by 2) assimilation of middle and upper crust by inter-mediate-composition magmas that had been contaminated during the first stage. Magmatic evolution in the upper crust peaked with eruption of the peralkaline Amalia Tuff (???26 Ma), which evolved from metaluminous parental magmas. A third stage of late, roofward assimilation of Proterozoic rocks in the Amalia Tuff magma is indicated by trends in initial 87Sr/86Sr and 206Pb/204Pb ratios from 0.7057 to 0.7098 and 19.5 to 18.8, respectively, toward the top of the pre-eruptive magma chamber. Highly evolved postcaldera plutons are generally fine grained and are zoned in initial 87Sr/86Sr and 206Pb/204Pb ratios, varying from 0.705 to 0.709 and 17.8 to 18.6, respectively. In contrast, the coarser-grained Cabresto Lake (???25 Ma) and Rio Hondo (???21 Ma) plutons have relatively homogeneous initial 87Sr/86Sr and 206Pb/204Pb ratios of approximately 0.7053 and 17.94 and 17.55, respectively. ??18O values for

  7. Palaeoproterozoic continental arc magmatism, and Neoproterozoic metamorphism in the Aravalli-Delhi orogenic belt, NW India: New constraints from in situ zircon U-Pb-Hf isotope systematics, monazite dating and whole-rock geochemistry

    NASA Astrophysics Data System (ADS)

    Kaur, Parampreet; Zeh, Armin; Chaudhri, Naveen

    2017-04-01

    Presently, the extent, origin and petrogenesis of late Palaeoproterozoic (ca. 1.85 Ga) magmatism in the north-central Aravalli-Delhi orogenic belt, NW India and subsequent metamorphic overprints are poorly constrained. Results of new in situ zircon U-Pb-Hf isotope analyses in combination with whole-rock elemental and isotopic data provide the first hard evidence that granitoid magmatism occurred in a continental magmatic arc setting between 1.86 and 1.81 Ga. The Hf-Nd model ages of 3.0-2.6 Ga and inherited zircon grains of 3.3-2.5 Ga indicate abundant reworking of Archaean crust. Flat HREE patterns with negative Eu anomalies furthermore reveal that the granitoids were generated from garnet-free and plagioclase-rich sources at shallow depths. Significant isotope variation among granitoid samples (εHft = -3.7 to -9.0; εNdt = -4.8 to -7.9) indicate that the reworked Archaean crust was not completely homogenised during the Palaeoproterozoic. This is best reflected by zircon Hf-isotope variation of ca. 9.5 epsilon units within the oldest granitoid sample. Zircon grains from this sample define three discrete Hf-isotope groups at εHf1.86Ga = -8.9, -4.8 and -1.6. These are interpreted to result from mixing of zircon-saturated magmas derived from three distinct sources within the crust prior to solidification. A monazite U-Pb isochron age of 868 ± 4 Ma from one of the granitoid samples furthermore indicates that the Aravalli fold belt was affected by an important post-magmatic overprint, perhaps related to the widespread metasomatic, granulite metamorphic and/or magmatic events during the same time span.

  8. Reliability of stable Pb isotopes to identify Pb sources and verifying biological fractionation of Pb isotopes in goats and chickens.

    PubMed

    Nakata, Hokuto; Nakayama, Shouta M M; Yabe, John; Liazambi, Allan; Mizukawa, Hazuki; Darwish, Wageh Sobhy; Ikenaka, Yoshinori; Ishizuka, Mayumi

    2016-01-01

    Stable Pb isotope ratios (Pb-IRs) have been recognized as an efficient tool for identifying sources. This study carried out at Kabwe mining area, Zambia, to elucidate the presence or absence of Pb isotope fractionation in goat and chicken, to evaluate the reliability of identifying Pb pollution sources via analysis of Pb-IRs, and to assess whether a threshold for blood Pb levels (Pb-B) for biological fractionation was present. The variation of Pb-IRs in goat decreased with an increase in Pb-B and were fixed at certain values close to those of the dominant source of Pb exposure at Pb-B > 5 μg/dL. However, chickens did not show a clear relationship for Pb-IRs against Pb-B, or a fractionation threshold. Given these, the biological fractionation of Pb isotopes should not occur in chickens but in goats, and the threshold for triggering biological fractionation is at around 5 μg/dL of Pb-B in goats.

  9. Magnesium isotope geochemistry in arc volcanism.

    PubMed

    Teng, Fang-Zhen; Hu, Yan; Chauvel, Catherine

    2016-06-28

    Incorporation of subducted slab in arc volcanism plays an important role in producing the geochemical and isotopic variations in arc lavas. The mechanism and process by which the slab materials are incorporated, however, are still uncertain. Here, we report, to our knowledge, the first set of Mg isotopic data for a suite of arc lava samples from Martinique Island in the Lesser Antilles arc, which displays one of the most extreme geochemical and isotopic ranges, although the origin of this variability is still highly debated. We find the δ(26)Mg of the Martinique Island lavas varies from -0.25 to -0.10, in contrast to the narrow range that characterizes the mantle (-0.25 ± 0.04, 2 SD). These high δ(26)Mg values suggest the incorporation of isotopically heavy Mg from the subducted slab. The large contrast in MgO content between peridotite, basalt, and sediment makes direct mixing between sediment and peridotite, or assimilation by arc crust sediment, unlikely to be the main mechanism to modify Mg isotopes. Instead, the heavy Mg isotopic signature of the Martinique arc lavas requires that the overall composition of the mantle wedge is buffered and modified by the preferential addition of heavy Mg isotopes from fluids released from the altered subducted slab during fluid-mantle interaction. This, in turn, suggests transfer of a large amount of fluid-mobile elements from the subducting slab to the mantle wedge and makes Mg isotopes an excellent tracer of deep fluid migration.

  10. Magnesium isotope geochemistry in arc volcanism

    NASA Astrophysics Data System (ADS)

    Teng, Fang-Zhen; Hu, Yan; Chauvel, Catherine

    2016-06-01

    Incorporation of subducted slab in arc volcanism plays an important role in producing the geochemical and isotopic variations in arc lavas. The mechanism and process by which the slab materials are incorporated, however, are still uncertain. Here, we report, to our knowledge, the first set of Mg isotopic data for a suite of arc lava samples from Martinique Island in the Lesser Antilles arc, which displays one of the most extreme geochemical and isotopic ranges, although the origin of this variability is still highly debated. We find the δ26Mg of the Martinique Island lavas varies from -0.25 to -0.10, in contrast to the narrow range that characterizes the mantle (-0.25 ± 0.04, 2 SD). These high δ26Mg values suggest the incorporation of isotopically heavy Mg from the subducted slab. The large contrast in MgO content between peridotite, basalt, and sediment makes direct mixing between sediment and peridotite, or assimilation by arc crust sediment, unlikely to be the main mechanism to modify Mg isotopes. Instead, the heavy Mg isotopic signature of the Martinique arc lavas requires that the overall composition of the mantle wedge is buffered and modified by the preferential addition of heavy Mg isotopes from fluids released from the altered subducted slab during fluid-mantle interaction. This, in turn, suggests transfer of a large amount of fluid-mobile elements from the subducting slab to the mantle wedge and makes Mg isotopes an excellent tracer of deep fluid migration.

  11. Infrared Spectroscopy and Stable Isotope Geochemistry of Hydrous Silicate Glasses

    SciTech Connect

    Stolper, Edward

    2007-03-05

    The focus of this DOE-funded project has been the study of volatile components in magmas and the atmosphere. Over the twenty-one year period of this project, we have used experimental petrology and stable isotope geochemistry to study the behavior and properties of volatile components dissolved in silicate minerals and melts and glasses. More recently, we have also studied the concentration and isotopic composition of CO2 in the atmosphere, especially in relation to air quality issues in the Los Angeles basin.

  12. Magnesium isotope geochemistry in arc volcanism

    PubMed Central

    Teng, Fang-Zhen; Hu, Yan

    2016-01-01

    Incorporation of subducted slab in arc volcanism plays an important role in producing the geochemical and isotopic variations in arc lavas. The mechanism and process by which the slab materials are incorporated, however, are still uncertain. Here, we report, to our knowledge, the first set of Mg isotopic data for a suite of arc lava samples from Martinique Island in the Lesser Antilles arc, which displays one of the most extreme geochemical and isotopic ranges, although the origin of this variability is still highly debated. We find the δ26Mg of the Martinique Island lavas varies from −0.25 to −0.10, in contrast to the narrow range that characterizes the mantle (−0.25 ± 0.04, 2 SD). These high δ26Mg values suggest the incorporation of isotopically heavy Mg from the subducted slab. The large contrast in MgO content between peridotite, basalt, and sediment makes direct mixing between sediment and peridotite, or assimilation by arc crust sediment, unlikely to be the main mechanism to modify Mg isotopes. Instead, the heavy Mg isotopic signature of the Martinique arc lavas requires that the overall composition of the mantle wedge is buffered and modified by the preferential addition of heavy Mg isotopes from fluids released from the altered subducted slab during fluid−mantle interaction. This, in turn, suggests transfer of a large amount of fluid-mobile elements from the subducting slab to the mantle wedge and makes Mg isotopes an excellent tracer of deep fluid migration. PMID:27303032

  13. Isotope geochemistry of caliche developed on basalt

    NASA Astrophysics Data System (ADS)

    Knauth, L. Paul; Brilli, Mauro; Klonowski, Stan

    2003-01-01

    Enormous variations in oxygen and carbon isotopes occur in caliche developed on < 3 Ma basalts in 3 volcanic fields in Arizona, significantly extending the range of δ 18O and δ 13C observed in terrestrial caliche. Within each volcanic field, δ 18O is broadly co-variant with δ 13C and increases as δ 13C increases. The most 18O and 13C enriched samples are for subaerial calcite developed on pinnacles, knobs, and flow lobes that protrude above tephra and soil. The most 18O and 13C depleted samples are for pedogenic carbonate developed in soil atmospheres. The pedogenic caliche has δ 18O fixed by normal precipitation in local meteoric waters at ambient temperatures and has low δ 13C characteristic of microbial soil CO 2. Subaerial caliche has formed from 18O-rich evapoconcentrated meteoric waters that dried out on surfaces after local rains. The associated 13C enrichment is due either to removal of 12C by photosynthesizers in the evaporating drops or to kinetic isotope effects associated with evaporation. Caliche on basalt lava flows thus initially forms with the isotopic signature of evaporation and is subsequently over-layered during burial by calcite carrying the isotopic signature of the soil environment. The large change in carbon isotope composition in subsequent soil calcite defines an isotopic biosignature that should have developed in martian examples if Mars had a "warm, wet" early period and photosynthesizing microbes were present in the early soils. The approach can be similarly applied to terrestrial Precambrian paleocaliche in the search for the earliest record of life on land. Large variations reported for δ 18O of carbonate in Martian meteorite ALH84001 do not necessarily require high temperatures, playa lakes, or flood runoff if the carbonate is an example of altered martian caliche.

  14. Isotope geochemistry. Biological signatures in clumped isotopes of O₂.

    PubMed

    Yeung, Laurence Y; Ash, Jeanine L; Young, Edward D

    2015-04-24

    The abundances of molecules containing more than one rare isotope have been applied broadly to determine formation temperatures of natural materials. These applications of "clumped" isotopes rely on the assumption that isotope-exchange equilibrium is reached, or at least approached, during the formation of those materials. In a closed-system terrarium experiment, we demonstrate that biological oxygen (O2) cycling drives the clumped-isotope composition of O2 away from isotopic equilibrium. Our model of the system suggests that unique biological signatures are present in clumped isotopes of O2—and not formation temperatures. Photosynthetic O2 is depleted in (18)O(18)O and (17)O(18)O relative to a stochastic distribution of isotopes, unlike at equilibrium, where heavy-isotope pairs are enriched. Similar signatures may be widespread in nature, offering new tracers of biological and geochemical cycling.

  15. Oxygen and hydrogen isotope geochemistry of zeolites

    NASA Technical Reports Server (NTRS)

    Karlsson, Haraldur R.; Clayton, Robert N.

    1990-01-01

    Oxygen and hydrogen isotope ratios for natural samples of the zeolites analcime, chabazite, clinoptilolite, laumontite, mordenite, and natrolite have been obtained. The zeolite samples were classified into sedimentary, hydrothermal, and igneous groups. The ratios for each species of zeolite are reported. The results are used to discuss the origin of channel water, the role of zeolites in water-rock interaction, and the possibility that a calibrated zeolite could be used as a low-temperature geothermometer.

  16. Metal stable isotope signatures as tracers in environmental geochemistry.

    PubMed

    Wiederhold, Jan G

    2015-03-03

    The biogeochemical cycling of metals in natural systems is often accompanied by stable isotope fractionation which can now be measured due to recent analytical advances. In consequence, a new research field has emerged over the last two decades, complementing the traditional stable isotope systems (H, C, O, N, S) with many more elements across the periodic table (Li, B, Mg, Si, Cl, Ca, Ti, V, Cr, Fe, Ni, Cu, Zn, Ge, Se, Br, Sr, Mo, Ag, Cd, Sn, Sb, Te, Ba, W, Pt, Hg, Tl, U) which are being explored and potentially applicable as novel geochemical tracers. This review presents the application of metal stable isotopes as source and process tracers in environmental studies, in particular by using mixing and Rayleigh model approaches. The most important concepts of mass-dependent and mass-independent metal stable isotope fractionation are introduced, and the extent of natural isotopic variations for different elements is compared. A particular focus lies on a discussion of processes (redox transformations, complexation, sorption, precipitation, dissolution, evaporation, diffusion, biological cycling) which are able to induce metal stable isotope fractionation in environmental systems. Additionally, the usefulness and limitations of metal stable isotope signatures as tracers in environmental geochemistry are discussed and future perspectives presented.

  17. Small scale inhomogeneity in the mantle source of the Cape Verde hotspot is probably related to plume complexity: implications from Sr, Nd and high precision Pb isotopes and geochemistry

    NASA Astrophysics Data System (ADS)

    Holm, P. M.; Sørensen, R. V.

    2009-04-01

    The volcanic rocks of one of the major islands of the Cape Verde hotspot have been investigated in order to test mantle plume models. From the centre of the Cape Verde Rise an array of islands trend west, the northern HIMU-type Cape Verde Islands. Of these, São Nicolau (SN) is the easternmost and Santo Antão the westernmost. Sixty samples of primitive (MgO = 9-14 wt%) basanitic composition from SN that represent the four volcanic stages of the 9 - 0.1 Ma evolution of the island have been analysed for Sr, Nd and high precision Pb isotopic composition. Pb ranges to a less radiogenic composition than on SA [1] and has lower 8/4 than the rocks of the southern EM1-type Cape Verde islands. Most SN lavas have a young HIMU character with negative 7/4. The most radiogenic Pb at SN is less thorogenic than Pb at SA. Temporal variation is also evident: An intermediate age group of samples have particularly low La/Nb = 0.4 - 0.5 and the least LREE-enrichment for SN. The youngest group of rocks has the lowest Zr/Nb = 2.5 - 3.0 and the most unradiogenic Sr and radiogenic Nd in the archipelago. At least four of the mantle source components for the SN magmas are different from any found in the SA magmas. High precision Pb data allow identification of parallel trends for northern SN and the southern island Santiago, which therefore must have unrelated source components. For the northern Cape Verde islands source compositions vary from E to W as well as with time. This cannot be explained by stationary enriched lithosphere components. The derivation of melts from a complex plume source is modelled. [1] Holm P.M., Wilson J.R., Christensen B.P., Hansen S.L., Hein K.M., Mortensen A.K., Pedersen R., Plesner S., and Runge M.K. (2006) JPetrol 47, 145-189.

  18. 40Ar/39Ar Geochronology, Isotope Geochemistry (Sr, Nd, Pb), and petrology of alkaline lavas near Yampa, Colorado: migration of alkaline volcanism and evolution of the northern Rio Grande rift

    USGS Publications Warehouse

    Cosca, Michael A.; Thompson, Ren A.; Lee, John P.; Turner, Kenzie J.; Neymark, Leonid A.; Premo, Wayne R.

    2014-01-01

    Volcanic rocks near Yampa, Colorado (USA), represent one of several small late Miocene to Quaternary alkaline volcanic fields along the northeast margin of the Colorado Plateau. Basanite, trachybasalt, and basalt collected from six sites within the Yampa volcanic field were investigated to assess correlations with late Cenozoic extension and Rio Grande rifting. In this paper we report major and trace element rock and mineral compositions and Ar, Sr, Nd, and Pb isotope data for these volcanic rocks. High-precision 40Ar/39Ar geochronology indicates westward migration of volcanism within the Yampa volcanic field between 6 and 4.5 Ma, and the Sr, Nd, and Pb isotope values are consistent with a primary source in the Proterozoic subcontinental lithospheric mantle. Relict olivine phenocrysts have Mg- and Ni-rich cores, whereas unmelted clinopyroxene cores are Na and Si enriched with finely banded Ca-, Mg-, Al-, and Ti-enriched rims, thus tracing their crystallization history from a lithospheric mantle source region to one in contact with melt prior to eruption. A regional synthesis of Neogene and younger volcanism within the Rio Grande rift corridor, from northern New Mexico to southern Wyoming, supports a systematic overall southwest migration of alkaline volcanism. We interpret this Neogene to Quaternary migration of volcanism toward the northeast margin of the Colorado Plateau to record passage of melt through subvertical zones within the lithosphere weakened by late Cenozoic extension. If the locus of Quaternary alkaline magmatism defines the current location of the Rio Grande rift, it includes the Leucite Hills, Wyoming. We suggest that alkaline volcanism in the incipient northern Rio Grande rift, north of Leadville, Colorado, represents melting of the subcontinental lithospheric mantle in response to transient infiltration of asthenospheric mantle into deep, subvertical zones of dilational crustal weakness developed during late Cenozoic extension that have been

  19. Neoarchean-Early Paleoproterozoic and Early Neoproterozoic arc magmatism in the Lützow-Holm Complex, East Antarctica: Insights from petrology, geochemistry, zircon U-Pb geochronology and Lu-Hf isotopes

    NASA Astrophysics Data System (ADS)

    Tsunogae, Toshiaki; Yang, Qiong-Yan; Santosh, M.

    2016-10-01

    The Lützow-Holm Complex (LHC) of East Antarctica forms part of the Neoproterozoic-Cambrian high-grade metamorphic segment of the East African-Antarctic Orogen. Here we present new petrological, geochemical, and zircon U-Pb and Lu-Hf isotopic data for meta-igneous rocks including charnockite, felsic gneiss, metagabbro, and mafic granulite from the LHC and evaluate the Neoarchean to Early Paleoproterozoic (ca. 2.5 Ga) and Early Neoproterozoic (ca. 1.0 Ga) arc magmatic events. The trace element geochemical signatures reveal a volcanic arc affinity for the charnockites from Sudare Rocks and Vesleknausen and felsic gneiss from Rundvågshetta, suggesting that the protoliths of these rocks were derived from felsic arc magmas. In contrast, metagabbros from Skallevikshalsen and Austhovde, occurring as boudins in metasediments, show non-arc signatures (within-plate basalt or mid-oceanic ridge basalt). The upper intercept ages of magmatic zircons in charnockite plotted on concordia diagrams yielded 2508 ± 14 Ma (Sudare Rocks) and 2490 ± 18 Ma (Vesleknausen), clearly suggesting a Neoarchean to Early Paleoproterozoic arc magmatic event. A subsequent thermal event during Early Neoproterozoic traced by 206Pb/238U age of oscillatory-zoned core of zircon in mafic granulite from Langhovde (973 ± 10 Ma) is consistent with a similar Early Neoproterozoic magmatic event reported from the LHC, suggesting a second stage of arc magmatism. The timing of peak metamorphism has been inferred from 206Pb/238U mean ages of structureless zircons in metagabbros from Skallevikshalsen and Austhovde, mafic granulite from Langhovde, and felsic gneiss from Rundvågshetta in the range of 551 ± 5.4 to 584 ± 5.0 Ma. Zircon Lu-Hf data of Neoarchean charnockites from Sudare Rocks and Vesleknausen indicate that the protolith magma was sourced from Paleo- to Neoarchean juvenile components mixed with reworked ancient crustal materials. Protolith magmatic rock of the felsic gneiss from Rundvågshetta might

  20. Early Cretaceous arc volcanic suite in Cebu Island, Central Philippines and its implications on paleo-Pacific plate subduction: Constraints from geochemistry, zircon U-Pb geochronology and Lu-Hf isotopes

    NASA Astrophysics Data System (ADS)

    Deng, Jianghong; Yang, Xiaoyong; Zhang, Zhao-Feng; Santosh, M.

    2015-08-01

    The Philippine island arc system is a collage of amalgamated terranes of oceanic, continental and island arc affinities. Here we investigate a volcanic suite in Cebu Island of central Philippines, including basalt, diabase dike, basaltic pyroclastic rock and porphyritic andesite. LA-ICP-MS U-Pb geochronology of zircon grains from the porphyritic andesite and pyroclastic rock yielded ages of 126 ± 3 Ma and 119 ± 2 Ma, respectively, indicating an Early Cretaceous age. The age distribution of the detrital zircons from river sand in the area displays a peak at ca. 118 Ma, close to the age of the pyroclastic rock. The early Cretaceous volcanic rocks in the central Philippines were previously regarded as parts of ophiolite complexes by most investigators, whereas the Cebu volcanics are distinct from these, and display calc-alkaline affinity and island arc setting, characterized by high LREE/HREE ratios and low HFSE contents. These features are similar to the Early Cretaceous arc basalts in the Amami Plateau and east Halmahera in the northernmost and southernmost West Philippine Basin respectively. Zircon Hf isotopes of the pyroclastic rocks show depleted nature similar to those of the Amami Plateau basalts, implying the subducted Pacific-type MORB as probable source. Zircon Hf isotopes of the porphyritic andesite show slight enrichment relative to that of the pyroclastic rocks and MORB, indicating subducted sediments as a minor end-member in the source. The Hf isotopic compositions of the volcanic rocks are also reflected in the detrital zircons from the river sands. We propose that the volcanic rocks of Cebu Island were derived from partial melting of sub-arc mantle wedge which was metasomatized by dehydration of subducted oceanic crust together with minor pelagic sediments. Within the tectonic environment of Southeast Asia during Early Cretaceous, the volcanic rocks in Cebu Island can be correlated to the subduction of paleo-Pacific plate. The Early Cretaceous

  1. 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

    NASA Astrophysics Data System (ADS)

    Janasi, Valdecir de Assis; Andrade, Sandra; Vasconcellos, Antonio Carlos B. C.; Henrique-Pinto, Renato; Ulbrich, Horstpeter H. G. J.

    2016-07-01

    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

  2. U-Pb geochronology and geochemistry of the Morro-Islay volcanic complex, southern California

    NASA Astrophysics Data System (ADS)

    Beck, M. D.; Johnston, S. M.

    2011-12-01

    The Morro-Islay volcanic complex is an important reference point in southern California used to reconstruct the tectonic setting of the North American continental margin during the early evolution of the San Andreas Fault. The age and petrologic formation of the Morro-Islay volcanic complex directly affects the accuracy of these reconstructions, and therefore its geologic properties should be reexamined as new techniques become available. Here, we present new U-Pb geochronology and geochemistry results to place constraints on the timing of the Morro-Islay volcanic complex and add to the existing geochemical database. Samples for U-Pb analysis were collected from felsic units exposed at Cerro Cabrillo to the west and Islay Hill to the east, and processed in the mineral separation laboratory at Cal Poly San Luis Obispo to extract zircons. U-Pb isotopic ratios for individual zircon grains were then determined using laser ablation ICP mass spectrometry in the dual-ICP laboratory at the University of California, Santa Barbara. The age of Cerro Cabrillo was determined to be 26.7 +0.2/-0.1 Ma and the age of Islay Hill was determined to be 26.7 +0.1/-0.1 Ma. Geochemical samples, preferentially selected for the most mafic compositions identified in thin section, were collected from Morro Rock and Cerro Cabrillo, both near the western end of the complex. Despite point counts that suggested relatively high mafic content in the two samples, whole rock geochemistry from these samples yielded high silica concentrations with Morro Rock classified as a dacite and Cerro Cabrillo Classified as a rhyolite. Both samples contain significant trace element depletions in Nb, Ta, Sr, and Ti, with subtle negative Eu anomalies and flat HREE signatures. This new data significantly tightens the age range for the formation of the Morro-Islay volcanic complex and supports previous tectonic reconstructions of Southern California in the Oligocene. In addition, the new geochemical and

  3. Geochemistry, zircon U-Pb and Lu-Hf isotopes of an Early Cretaceous intrusive suite in northeastern Jiangxi Province, South China Block: Implications for petrogenesis, crust/mantle interactions and geodynamic processes

    NASA Astrophysics Data System (ADS)

    Deng, Zhengbin; Liu, Shuwen; Zhang, Lifei; Wang, Zongqi; Wang, Wei; Yang, Pengtao; Luo, Ping; Guo, Boran

    2014-07-01

    The Early Cretaceous Tieshan intrusive suite, in northeastern Jiangxi Province along the northern margin of the Eastern Cathaysia Block, is composed of diabase porphyrites, monzodiorites, syenite porphyries, quartz monzonites, monzogranites and granite porphyries. LA-ICPMS zircon U-Pb isotopic analyses reveal that this intrusive complex was emplaced between 142 Ma and 117 Ma. The ~ 135 Ma diabase porphyrites, monzodiorites, and syenite porphyries are characterized by low to moderate SiO2 and MgO contents, with high K2O and total alkaline contents. These rocks exhibit slightly to strongly fractionated REE patterns and upper crust-like multi-element patterns with depletions of Nb, Ta and Ti, and show strongly negative εHf (t) values of - 9.0 to - 11.8. All these patterns are identical to those of the Caiyuan syenites, Huangtuling gabbros in the east, and Lengshuikeng trachyandesites and quartz syenites in the west. These geochemical and zircon Lu-Hf isotopic features indicate that their magmatic precursors were generated by 0.2%-2% partial melting of a phlogopite-bearing enriched subcontinental lithospheric mantle source that was metasomatized by sediments. The ~ 117 Ma quartz monzonite has slightly higher εHf (t) values (- 5.6 to - 8.7) like those of the Honggong syenites, indicating an interaction between the asthenosphere and the lithosphere. The ~ 142-134 Ma granite porphyries and monzogranites are characterized by high SiO2 levels but low concentrations of refractory elements, and show enrichment of LREEs and LILEs, with variable negative anomalies of Nb, Ta, Ti, Sr, P and Ba in multi-element diagrams normalized by primitive mantle. The monzogranite exhibits strongly negative εHf (t) values of - 10.5 to - 13.3 and TDM2 (Hf) values of 1849-2023 Ma, and the granite porphyries display relatively wide εHf (t) values of - 7.2 to - 13.4 and TDM2 (Hf) values of 1645-2043 Ma, indicating that these monzogranites and granite porphyries are highly fractionated granites

  4. 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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

    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 <600 Ma are high-K, calc-alkaline, shoshonitic and those with ages <600 Ma are transitional high-K calc-alkaline to alkaline. The volcanic arc signatures associated with the Paleoproterozoic Nd TDM model ages are interpreted as inherited from the source rocks. The oldest ages and lower Nd TDM model ages are recorded from granitoids intruded in the southwest part of the PEAL domain, suggesting that these intrusions are associated with slab-tearing during convergence between the PEAL and the Sergipano domains. Zircon oxygen isotopic data in some of the studied 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

  5. Anthropogenic Pb input into Bohai Bay, China: Evidence from stable Pb isotopic compositions in sediments

    NASA Astrophysics Data System (ADS)

    Ning-jing, Hu; Peng, Huang; Hui, Zhang; Ai-mei, Zhu; Ji-hua, Liu; Jun, Zhang; Lian-hua, He

    2015-10-01

    To investigate the source of Pb within Bohai Bay, Pb concentrations and Pb isotopic compositions (204Pb, 206Pb, 207Pb, and 208Pb) of surface sediments in this area were determined. The Pb concentration in this bay varied widely from 6.9 to 39.2 μg/g (average: 21.8±7.8 μg/g), and the Pb isotopic compositions ranged from 0.8338 to 0.8864 (average: 2.0997±0.0180) for 208Pb/206Pb and from 2.0797 to 2.1531 (average: 0.8477±0.0135) for 207Pb/206Pb, presenting in three distinct clusters. The Pb isotopic ratios of sediments from the northeastern (NE zone) and northwestern (NW zone) coastal areas were significantly influenced by anthropogenic sources such as coal combustion and automobile emission. In sediments from the central and southern Bohai Bay (C-S zone); however, Pb mainly originated from the Yellow River catchment, as a result of lithogenic sediment (from rock weathering) accumulation. The Pb isotopic ratios further indicate that, apart from riverine inputs, the neighboring large-scale ports and aerosols significantly contributed to the anthropogenic Pb contained in these sediments. Pb contamination in the Haihe and Luanhe river mouths as well as in the regions near ports is also suggested from anthropogenic enrichment factors. As cities and ports continue to develop around Bohai Bay, a long-term extensive sewage monitoring program is highly recommended.

  6. Calculation of uncertainties of U-Pb isotope data

    USGS Publications Warehouse

    Ludwig, K. R.

    1980-01-01

    Equations are derived for the estimation of errors and error correlations for various types of U-Pb isotope data, taking into account ion-beam instabilities, run-to-run variability in mass-discrimination, uncertainties in Pb and U concentrations, and uncertainties in initial-Pb and blank-Pb amount and isotopic composition. Equations are also given for the calculation of concordia intercept errors. ?? 1980.

  7. Ca isotopic geochemistry of an Antarctic aquatic system

    NASA Astrophysics Data System (ADS)

    Lyons, W. Berry; Bullen, Thomas D.; Welch, Kathleen A.

    2017-01-01

    The McMurdo Dry Valleys, Antarctica, are a polar desert ecosystem. The hydrologic system of the dry valleys is linked to climate with ephemeral streams that flow from glacial melt during the austral summer. Past climate variations have strongly influenced the closed-basin, chemically stratified lakes on the valley floor. Results of previous work point to important roles for both in-stream processes (e.g., mineral weathering, precipitation and dissolution of salts) and in-lake processes (e.g., mixing with paleo-seawater and calcite precipitation) in determining the geochemistry of these lakes. These processes have a significant influence on calcium (Ca) biogeochemistry in this aquatic ecosystem, and thus variations in Ca stable isotope compositions of the waters can aid in validating the importance of these processes. We have analyzed the Ca stable isotope compositions of streams and lakes in the McMurdo Dry Valleys. The results validate the important roles of weathering of aluminosilicate minerals and/or CaCO3 in the hyporheic zone of the streams, and mixing of lake surface water with paleo-seawater and precipitation of Ca-salts during cryo-concentration events to form the deep lake waters. The lakes in the McMurdo Dry Valleys evolved following different geochemical pathways, evidenced by their unique, nonsystematic Ca isotope signatures.

  8. Isotopic and noble gas geochemistry in geothermal research

    SciTech Connect

    Kennedy, B.M.; DePaolo, D.J.

    1997-12-31

    The objective of this program is to provide, through isotopic analyses of fluids, fluid inclusions, and rocks and minerals coupled with improved methods for geochemical data analysis, needed information regarding sources of geothermal heat and fluids, the spatial distribution of fluid types, subsurface flow, water-rock reaction paths and rates, and the temporal evolution of geothermal systems. Isotopic studies of geothermal fluids have previously been limited to the light stable isotopes of H, C, and O. However, other isotopic systems such as the noble gases (He, Ne, Ar, Kr and Xe) and reactive elements (e.g. B, N, S, Sr and Pb) are complementary and may even be more important in some geothermal systems. The chemistry and isotopic composition of a fluid moving through the crust will change in space and time in response to varying chemical and physical parameters or by mixing with additional fluids. The chemically inert noble gases often see through these variations, making them excellent tracers for heat and fluid sources. Whereas, the isotopic compositions of reactive elements are useful tools in characterizing water-rock interaction and modeling the movement of fluids through a geothermal reservoir.

  9. Isotope geochemistry and fluid inclusion study of skarns from Vesuvius

    USGS Publications Warehouse

    Gilg, H.A.; Lima, A.; Somma, R.; Belkin, H.E.; de Vivo, B.; Ayuso, R.A.

    2001-01-01

    We present new mineral chemistry, fluid inclusion, stable carbon and oxygen, as well as Pb, Sr, and Nd isotope data of Ca-Mg-silicate-rich ejecta (skarns) and associated cognate and xenolithic nodules from the Mt. Somma-Vesuvius volcanic complex, Italy. The typically zoned skarn ejecta consist mainly of diopsidic and hedenbergitic, sometimes "fassaitic" clinopyroxene, Mg-rich and Ti-poor phlogopite, F-bearing vesuvianite, wollastonite, gehlenite, meionite, forsterite, clinohumite, anorthite and Mg-poor calcite with accessory apatite, spinell, magnetite, perovskite, baddeleyite, and various REE-, U-, Th-, Zr- and Ti-rich minerals. Four major types of fluid inclusions were observed in wollastonite, vesuvianite, gehlenite, clinopyroxene and calcite: a) primary silicate melt inclusions (THOM = 1000-1050??C), b) CO2 ?? H2S-rich fluid inclusions (THOM = 20-31.3??C into the vapor phase), c) multiphase aqueous brine inclusions (THOM = 720-820??C) with mainly sylvite and halite daughter minerals, and d) complex chloride-carbonate-sulfate-fluoride-silicate-bearing saline-melt inclusions (THOM = 870-890??C). The last inclusion type shows evidence for immiscibility between several fluids (silicate melt - aqueous chloride-rich liquid - carbonate/sulfate melt?) during heating and cooling below 870??C. There is no evidence for fluid circulation below 700??C and participation of externally derived meteoric fluids in skarn formation. Skarns have considerably variable 206Pb/204Pb (19.047-19.202), 207Pb/204Pb (15.655-15.670), and 208Pb/204Pb (38.915-39.069) and relatively low 143Nd/144Nd (0.51211-0.51244) ratios. The carbon and oxygen isotope compositions of skarn calcites (??13CV-PDB = -5.4 to -1.1???; ??18OV-SMOW = 11.7 to 16.4???) indicate formation from a 18O- and 13C-enriched fluid. The isotope composition of skarns and the presence of silicate melt inclusion-bearing wollastonite nodules suggests assimilation of carbonate wall rocks by the alkaline magma at moderate depths (< 5

  10. Anthropogenic Pb input into Bohai Bay, China: Evidence from stable Pb isotopic compositions in sediments

    NASA Astrophysics Data System (ADS)

    Hu, Ningjing; Huang, Peng

    2016-04-01

    Anthropogenic Pb input into Bohai Bay, China: Evidence from stable Pb isotopic compositions in sediments Hu Ning-jinga, Huang Pengb,, Liu Ji-huaa, a First Institute of Oceanography, State Oceanic Administration, Qingdao 266061, China b Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China To investigate the source of Pb within Bohai Bay, Pb concentrations and Pb isotopic compositions (204Pb, 206Pb, 207Pb, and 208Pb) of surface sediments in this area were determined. The Pb concentration in this bay varied widely from 6.9 to 39.2 μg/g (average: 21.8 ± 7.8 μg/g), and the Pb isotopic compositions ranged from 0.8338 to 0.8864 (average: 2.0997 ± 0.0180) for 208Pb/206Pb and from 2.0797 to 2.1531 (average: 0.8477 ± 0.0135) for 207Pb/206Pb, presenting in three distinct clusters. The Pb isotopic ratios of sediments from the northeastern (NE zone) and northwestern (NW zone) coastal areas were significantly influenced by anthropogenic sources such as coal combustion and automobile emission. In sediments from the central and southern Bohai Bay (C-S zone); however, Pb mainly originated from the Yellow River catchment, as a result of lithogenic sediment (from rock weathering) accumulation. The Pb isotopic ratios further indicate that, apart from riverine inputs, the neighboring large-scale ports and aerosols significantly contributed to the anthropogenic Pb contained in these sediments. Pb contamination in the Haihe and Luanhe river mouths as well as in the regions near ports is also suggested from anthropogenic enrichment factors. As cities and ports continue to develop around Bohai Bay, a long-term extensive sewage monitoring program is highly recommended.

  11. SPATIAL Short Courses Build Expertise and Community in Isotope Geochemistry

    NASA Astrophysics Data System (ADS)

    Riggs, E. M.; Bowen, G. J.

    2015-12-01

    The SPATIAL short course at the University of Utah is designed for graduate students and professionals in the earth and environmental sciences from around the globe. An integral part of the broader, NSF-funded Inter-university Training for Continental-scale Ecology (ITCE) project, the course is an intensive two-week field, classroom and laboratory experience with internationally-known researchers as instructors. The course focuses on stable isotope geochemistry coupled with spatial analysis techniques. Participants do not typically know each other or this research community well upon entering. One of the stated goals of the overall project is to build a community of practice around these techniques. This design is common in many professional fields, but is not often applied at the graduate level nor formally assessed in the earth sciences. Paired pre- and post-tests were administered before the start and after the close of the short courses over 3 years. The survey is a set of instruments adapted from social-cognitive psychology measuring changes in identity and community with other items to measure content knowledge outcomes. We see a subtle, consistent convergence of identities between large-scale isotope geochemistry and participants' research areas. Results also show that the course generates an increase in understanding about stable isotopes' use and application. The data show the SPATIAL course is very effective at bringing students together socially with each other and with faculty to create an environment that fosters community and scientific cooperation. Semi-structured pre-and post- interviews were conducted to understand the program elements that generated gains in learning and community. Participants were selected based on initial responses on the pre-survey to capture the range of initial conditions for the group. Qualitative analysis shows that the major factors for participants were 1) ready access to researchers in an informal setting during the

  12. Final report of the key comparison CCQM-K98: Pb isotope amount ratios in bronze

    NASA Astrophysics Data System (ADS)

    Vogl, Jochen; Yim, Yong-Hyeon; Lee, Kyoung-Seok; Goenaga-Infante, Heidi; Malinowskiy, Dmitriy; Ren, Tongxiang; Wang, Jun; Vocke, Robert D., Jr.; Murphy, Karen; Nonose, Naoko; Rienitz, Olaf; Noordmann, Janine; Näykki, Teemu; Sara-Aho, Timo; Ari, Betül; Cankur, Oktay

    2014-01-01

    Isotope amount ratios are proving useful in an ever increasing array of applications that range from studies unravelling transport processes, to pinpointing the provenance of specific samples as well as trace element quantification by using isotope dilution mass spectrometry (IDMS). These expanding applications encompass fields as diverse as archaeology, food chemistry, forensic science, geochemistry, medicine and metrology. However, to be effective tools, the isotope ratio data must be reliable and traceable to enable the comparability of measurement results. The importance of traceability and comparability in isotope ratio analysis has already been recognized by the Inorganic Analysis Working Group (IAWG) within the CCQM. While the requirements for isotope ratio accuracy and precision in the case of IDMS are generally quite modest, 'absolute' Pb isotope ratio measurements for geochemical applications as well as forensic provenance studies require Pb isotope ratio measurements of the highest quality. To support present and future CMCs on isotope ratio determinations, a key comparison was urgently needed and therefore initiated at the IAWG meeting in Paris in April 2011. The analytical task within such a comparison was decided to be the measurement of Pb isotope amount ratios in water and bronze. Measuring Pb isotope amount ratios in an aqueous Pb solution tested the ability of analysts to correct for any instrumental effects on the measured ratios, while the measurement of Pb isotope amount ratios in a metal matrix sample provided a real world test of the whole chemical and instrumental procedure. A suitable bronze material with a Pb mass fraction between 10 and 100 mg•kg-1 and a high purity solution of Pb with a mass fraction of approximately 100 mg•kg-1 was available at the pilot laboratory (BAM), both offering a natural-like Pb isotopic composition. The mandatory measurands, the isotope amount ratios n(206Pb)/n(204Pb), n(207Pb)/n(204Pb) and n(208Pb)/n(204Pb

  13. Nuclear Volume Effects in Equilibrium Stable Isotope Fractionations of Hg, Tl and Pb Isotope Systems

    NASA Astrophysics Data System (ADS)

    Yang, S.; Liu, Y.

    2014-12-01

    Many evidences showed that heavy isotope systems could be significantly fractionated as the consequence of the nuclear volume effect (NVE) or so-called nuclear field shift effect. Here we investigate NVEs of Hg, Tl and Pb isotope systems by using quantum chemistry computational methods with careful evaluation on quantum relativistic effects via the Dirac's formalism of full-electron wavefunction. Our results generally agree with previous studies but with noticeable differences in many cases. With the unique NVE driving force, equilibrium 202Hg/198Hg and 205Tl/203Tl isotopes can be fractionated up to 3.94‰ and 2.78‰ at 0℃, respectively, showing potentially large equilibrium isotope fractionations can be expected for future studies of these two isotope systems. Moreover, the NVE causes large mass-independent fractionations (MIF) for odd-mass isotopes (e.g., ∆199NVHg and ∆201NVHg) and small MIFs for even-mass isotopes (e.g., ∆200NVHg). For Pb isotope system, NVEs induce isotope fractionations up to 1.62‰ (207Pb/206Pb) and 4.06‰ (208Pb/206Pb) at 0℃. However, contributions from classical mass-dependent driving force are small, about 0.1-0.5‰ for 207Pb/206Pb and 0.2-0.9‰ for 208Pb/206Pb. We find that Pb4+-bearing species can be significantly enriched heavy isotopes than Pb2+-bearing species. Comparing to Pb0, Pb2+-bearing species even enrich lighter Pb isotopes. A very strange and interesting thing is that the beta value of Pb2+-bearing species can be smaller than the unity (1.000). Similar thing has been found on Tl+-bearing species. This is an impossible and unexplained situation if only based on classical mass-dependent isotope fractionation theory (e.g., Bigeleisen-Mayer equation). The consequence is that the different direction of beta values of Pb2+-bearing species will let the Pb isotope fractionation even larger when they fractionate with Pb4+-bearing species. Moreover, NVEs also cause mass-independent fractionation (MIF) of odd 207Pb

  14. The Pb isotopic compositions of lower crustal xenoliths and the evolution of lower crustal Pb

    NASA Astrophysics Data System (ADS)

    Rudnick, Roberta L.; Goldstein, Steven L.

    1990-05-01

    Pb isotopic compositions for three suites of well-characterized granulite facies xenoliths from a diversity of crustal settings (the Chudleigh and McBride volcanic provinces, Queensland, Australia and the Eifel volcanics, West Germany) are presented here. All three suites plot to the right of the 4.57 Ga geochron, similar to the published Pb results of other mafic granulite xenoliths. Correlations between Sr, Nd and Pb isotopes in the three suites measured here point to an origin by mixing of mantle-derived basaltic magmas with lower crust at the time of basaltic underplating (i.e., < 100 Ma for Chudleigh, ˜ 300 Ma for McBride, ˜ 450 Ma for Eifel). Because the Pb concentration of the continental crust is much greater than that of mantle-derived basaltic magmas, the Pb isotopic compositions of the magmas are shifted dramatically by the mixing, allowing delineation of the isotopic characteristics of the lower crust. In all three cases, this lower crust had radiogenic Pb and Sr isotopic compositions and unradiogenic Nd isotopic compositions, yielding Proterozoic Nd model ages. Such radiogenic lower crust contrasts markedly with the Pb isotopic characteristics of most Precambrian granulite facies terrains. Whereas the Nd isotopes reflect the average age of crust formation, the Pb isotopic characteristics of the lower crust appear to be a function of the tectonothermal age of the crust: unradiogenic Pb can only develop in regions which have remained stable for long time periods (e.g., cratons), whereas in areas where orogenies have occurred subsequent to crustal formation, the Pb isotopic composition of the lower crust is "rejuvenated" through mixing with radiogenic Pb from upper crust and mantle-derived magmas. Thus, after orogeny, the Pb isotopic composition of the lower crust resembles that of the upper crust. On the basis of this proposed orogenic age-Pb isotope correlation, we estimate the Pb isotopic composition of the lower crust using the data for granulite

  15. Pb isotopes in drinking water: a new strategy for detection of low Pb sources

    EPA Science Inventory

    Source detection of low concentrations of Pb in water, for instance less than 15 µg L-1, may require a new methodology as the tolerances of Pb in drinking water are further reduced. It appears that the isotope properties of Pb may aid discrimination among natural sources and anth...

  16. Geochemistry of beryllium isotopes: Applications in geochronometry. Doctoral thesis

    SciTech Connect

    Brown, E.T.

    1990-01-01

    The cosmogenic radioisotope beryllium-10 (half-life= 1.5 Myr) has been determined in suites of samples from tropical river systems and from areas of the oceans influenced by input from the continents, and also within the mineral lattices of quartz grains from Antarctic moraines. These data have been used to investigate the geochemistry of 10Be and apply that knowledge to development of geochronometric techniques. Beryllium-10 is primarily produced by neutron-induced spallation of 14N and 16O in the atmosphere; its flux to the Earth's surface at low latitude was examined through measurements in tropical rainfall. Distributions of 10Be and 9Be (the stable isotope) in dissolved and particulate phases in tropical rivers were used, in conjunction with major ion data, to delineate the geochemical cycle of Be in these river systems. The present work applies in situ cosmogenic production to the examination of the deposition history of moraines of varying ages in Antarctica. It also yields estimates of 10Be and 26Al production rates: 6.4(+5.9-1.5) at/g yr and 42(+20-6) at/g yr at sea level and high geomagnetic latitude.

  17. Tracing source and migration of Pb during waste incineration using stable Pb isotopes.

    PubMed

    Li, Yang; Zhang, Hua; Shao, Li-Ming; He, Pin-Jing

    2017-04-05

    Emission of Pb is a significant environmental concern during solid waste incineration. To target Pb emission control strategies effectively, the major sources of Pb in the waste incineration byproducts must be traced and quantified. However, identifying the migration of Pb in each waste component is difficult because of the heterogeneity of the waste. This study used a laboratory-scale incinerator to simulate the incineration of municipal solid waste (MSW). The Pb isotope ratios of the major waste components ((207)Pb/(206)Pb=0.8550-0.8627 and (208)Pb/(206)Pb=2.0957-2.1131) and their incineration byproducts were measured to trace sources and quantify the Pb contribution of each component to incineration byproducts. As the proportions of food waste (FW), newspaper (NP), and polyethylene bag (PE) in the artificial MSW changed, the contribution ratios of FW and PE to Pb in fly ash changed accordingly, ranging from 31.2% to 50.6% and from 35.0% to 41.8%, respectively. The replacement of PE by PVC significantly increased the partitioning and migration ratio of Pb. The use of Pb isotope ratios as a quantitative tool for tracing Pb from raw waste to incineration byproducts is a feasible means for improving Pb pollution control.

  18. Initial subduction of the Paleo-Pacific Oceanic plate in NE China: Constraints from whole-rock geochemistry and zircon U-Pb and Lu-Hf isotopes of the Khanka Lake granitoids

    NASA Astrophysics Data System (ADS)

    Liu, Kai; Zhang, Jinjiang; Wilde, Simon A.; Zhou, Jianbo; Wang, Meng; Ge, Maohui; Wang, Jiamin; Ling, Yiyun

    2017-03-01

    Northeast China is located in the eastern part of the Central Asian Orogenic Belt (CAOB) and was influenced by Paleo-Pacific subduction during the Mesozoic. Abundant granitoids from the late Paleozoic to early Mesozoic in NE China record this process, including the Khanka Lake granitoids, which resulted in extensive growth of continental crust in the area. However, the question of how and when the Paleo-Pacific tectonic system began to affect NE China is still highly controversial. The Khanka Lake granitoids can be subdivided into two main components based on their geochemical characteristics, namely granodiorite and syenogranite. The granodiorite has a U-Pb age of 249 Ma and is adakite-like (enriched in LREE and LILEs with high Mg#, Sr, La/Yb, Sr/Y and Na2O/K2O), with zircon εHf(t) values of - 0.65 to 1.61, produced by the magma mixing between melting of the lower continental crust and juvenile basaltic magma. The syenogranite has zircon U-Pb ages of 209 to 199 Ma and geochemical features of highly fractionated I-type granites, with high SiO2, total alkalis and low Mg (and Mg#), Fe, Cr and Ni, and positive zircon εHf(t) of 1.72 to 5.12, indicating an origin from remelting of juvenile crust. The granitoids were intruded by felsic veins between 195 and 184 Ma with positive zircon εHf(t) from 0.57 to 5.32. The εHf(t) values of the granitoids become more positive as the zircon U-Pb ages become younger, suggesting continuous melting of juvenile crust during subduction. It is concluded that the Khanka Lake granitoids record the early stage of subduction of the Paleo-Pacific Oceanic plate, which commenced at least ca. 250 Ma ago.

  19. Geochemistry: does U-Pb date Earth's core formation?

    PubMed

    Yin, Qing-zhu; Jacobsen, Stein B

    2006-11-02

    Constraining the timing of the formation of Earth's core, which defines the birth of our planet, is essential for understanding the early evolution of Earth-like planets. Wood and Halliday and Halliday discuss the apparent discrepancy between the U-Pb (60-80 Myr) and Hf-W clocks (30 Myr) in determining the timescale of Earth's accretion and core formation. We find that the information the authors present is at times contradictory (for example, compare Fig. 1 in ref. 1 with Fig. 1 in ref. 2) and confusing and could suggest that the U-Pb clock constrains core formation better than the Hf-W system. Here we point out the limitations of the U-Pb system and show that the U-Pb age cannot be used to argue for protracted accretion and/or core formation (>50 Myr) because this clock only records the processes that occurred during the last 1% of Earth's accretion and core formation in the Wood and Halliday mechanism.

  20. Pb isotopes in surficial pelagic sediments from the North Atlantic

    NASA Technical Reports Server (NTRS)

    Hamelin, B.; Grousset, F.; Sholkovitz, E. R.

    1990-01-01

    The concentration of Pb and its isotopic composition were measured in samples from the surface of sea-water sediments obtained from the northeastern Atlantic, the Sargasso Sea, and the U.S. continental shelf, with the purpose of investigating changes in Pb sources due to the anthropogenic perturbation that took place in modern times. It was found that the anthropogenic Pb input to marine sediments due to the increase of Pb contamination over the ocean during the last century could be identified in all these samples. However, samples from eastern and western Atlantic had very different Pb isotopic profiles, each reflecting the character of anthropogenic Pb emissions from the European and U.S. industries, respectively.

  1. Sr-Nd-Hf-Pb Isotope Ratios in Recent NE Lau Lavas

    NASA Astrophysics Data System (ADS)

    Todd, E.; Gill, J. B.; Freymuth, H.

    2009-12-01

    Sr-Nd-Hf-Pb isotope ratios in recently erupted NE Lau lavas are being measured and results will be presented. The recent W. Mata boninites lie slightly west of the northern termination of the Tongan volcanic front in an area where previously dredged boninites are enriched in LREE and HFSE. They are interpreted as containing an OIB-type mantle source component fluxed by slab-derived fluids (Falloon et al., 2007; Pearce et al., 2007). However, their Sr-Nd-Pb isotope ratios do not match any known component from the Samoan plume, pelagic sediment, or Louisville Ridge-derived volcaniclastic sediment. Their most distinctive isotopic characteristics are low 87Sr/86Sr and high 206Pb/204Pb relative to Nd-Hf isotope ratios. They are displaced toward HIMU-type basalts from the Cook-Austral islands (e.g., Tubuai) and have been interpreted as derived from diverse HIMU, EMI, and EMII mantle source components that are carried southward from beneath the Pacific Plate into the NE Lau Basin. Basalts from the NE Lau Spreading Center have more of a Indian-MORB source than do the boninites, and are similar to the <3 Ma OIB-type basalts from Fiji (Gill, 1984 and unpub.). If so, then some diverse enriched “plums” melt out of southward-advecting MORB-source “pudding” over as little as 100 km, whereas others persist for ~500 km to Fiji. Data for the recently erupted samples will test these interpretations, and will be compared to characteristics of the earliest (7.4 Ma) boninitic lavas in the region that have less of the OIB component. References: T. J. Falloon, L. Danyushevsky, A. J. Crawford, R. Maas, J. D. Woodhead, S. Eggins, S. Bloomer, D. J. Wright, S. K. Zlobin, and A. R. Stacey. Multiple mantle plume components involved in the petrogenesis of subduction-related lavas from the northern termination of the Tonga Arc and northern Lau Basin: Evidence from the geochemistry of arc and backarc submarine volcanics. Geochemistry, Geophysics, Geosystems, 8(Q09003):45, 2007. J. B. Gill

  2. Zircon U-Pb geochronology, and elemental and Sr-Nd-Hf-O isotopic geochemistry of post-collisional rhyolite in the Chiang Khong area, NW Thailand and implications for the melting of juvenile crust

    NASA Astrophysics Data System (ADS)

    Qian, Xin; Wang, Yuejun; Feng, Qinglai; Zi, Jian-Wei; Zhang, Yuzhi; Chonglakmani, Chongpan

    2016-06-01

    Volcanic rocks are widely exposed within the Chiang Khong-Lampang-Tak igneous zone in NW Thailand. A representative rhyolite sample from the Chiang Khong area yielded a zircon U-Pb age of 230.7 ± 1.1 Ma (n = 20, MSWD = 0.98). The Chiang Khong rhyolites are characterized by low TiO2 (0.29-0.62 wt%) and MgO (0.04-0.82 wt%) with A/CNK values of 0.95-1.06 (one outlier at 1.47), and can be classified as highly fractionated I-type rhyolites. They are enriched in LILEs and LREEs, and depleted in HFSEs. Two representative samples have 87Sr/86Sr (i) ratios of 0.70497 and 0.70527, and the ɛNd (t) values fall at +1.1 and +1.3, respectively. ɛHf (t) and δ18O in zircon are between +4.7 to +12.0 and 5.3 to 5.9 ‰, respectively. Our geochemical data suggest that the Chiang Khong rhyolites formed by partial melting of juvenile mafic lower crust in a post-collisional setting. Deep crustal anatexis was probably induced by upwelling asthenospheric mantle, shortly after slab detachment subsequent to closure of the Paleo-Tethys.

  3. Zircon U-Pb age and Sr-Nd-Hf isotope geochemistry of the Ganluogou dioritic complex in the northern Triassic Yidun arc belt, Eastern Tibetan Plateau: Implications for the closure of the Garzê-Litang Ocean

    NASA Astrophysics Data System (ADS)

    Wu, Tao; Xiao, Long; Wilde, Simon A.; Ma, Chang-Qian; Li, Zi-Long; Sun, Yi; Zhan, Qiong-Yao

    2016-04-01

    The Triassic Yidun arc belt (YAB) lies between the Jinshajiang suture zone to the west and the Garzê-Litang suture zone to the east, Eastern Tibetan Plateau. To study the YAB can not only help us to better understand the evolutionary history of the Garzê-Litang Ocean but can also provide some important information to constrain the evolution of the eastern Paleo-Tethys. In this paper, the geochronological and geochemical data of the Ganluogou dioritic complex were systematically investigated in order to decipher the geodynamic setting of the complex and to further determine the final closure time of the Garzê-Litang Ocean. The Ganluogou dioritic complex is located in the northern part of the YAB. It consists of ferrodiorite, diorite and a mixing zone between them and is the largest intermediate-mafic pluton in the YAB. The ferrodiorites were emplaced at 213 ± 2 Ma have low SiO2 and high Fe2O3* contents, whereas the diorites formed at 209 ± 2 Ma and have relatively higher SiO2, Na2O + K2O, Th, U, Zr, and Hf contents, but lower Al2O3, MgO, CaO, Co, and Sr contents than the ferrodiorites. Relative to the primitive mantle both the ferrodiorites and diorites are depleted in Nb and Ta. However, the ferrodiorites exhibit strong depletion in Zr and Hf, whereas the diorites contain relatively higher Th and U contents without negative Zr and Hf anomalies. Both rock-types have similar chondrite-normalized rare earth element patterns with (La/Yb)N ratios = 4.4 to 18.2, and show weak Eu anomalies, with Eu/Eu* of 0.47 to 1. They both show narrow ranges in Sr-Nd-Hf isotopic compositions. However, the ferrodiorites contain lower initial 87Sr/86Sr ratios (0.7052-0.7057) and relatively higher εNd(t) values (- 3.8 to - 2.4) than the diorites, which record values of 0.7062-0.7066 and - 5.5 to - 5.7, respectively. For the zircon Hf isotopic composition, the ferrodiorites also exhibit higher 176Hf/177Hf ratios (0.282738-0.282804) and more depleted εHf(t) values (3.4-5.6) than

  4. U-Pb isotopic systematics of ferroan anorthosite 60025

    NASA Technical Reports Server (NTRS)

    Premo, W. R.; Tatsumoto, M.

    1993-01-01

    Preliminary U-Pb isotopic data from separates of ferroan anorthosite 60025 confirm its antiquity at approximately 4.42 Ga. Three Pb-Pb isochron ages involving different sets of mineral separates vary by only 20 million years, but indicate derivation of the sets from isotopically distinct magma sources. If this anorthosite was a monomict cumulate product formed during the Moon's early primary differentiation stage, then residual liquids of crystallizing magmas were evolving isotopically, even at the cm-scale, over the duration of the crystallization period. Another explanation is that this sample is simply a polymict breccia and that the Pb isotopic results are a result of subsequent mechanical mixing of mineral assemblages from various cumulate piles formed coevally at approximately 4.42 Ga from isotopically distinct magma sources. In our ongoing search for early lunar Pb isotopic compositions, we have analyzed Apollo 16 anorthosites 67075 and 62337 and Apollo 17 high-Mg suite cumulates (troctolite 76535, norite 78235, and dunite 72415). The U-Pb isotopic systematics have been better behaved in the high-Mg suite rocks than in the anorthosites that have shown evidence of mineral assemblages of mixed parentage. Our aim in analyzing anorthosite 60025 was to avoid or minimize this problem as it had been considered essentially monomict, although recent work has shown that not only is 60025 polymict, but shows textual evidence of at least two episodes of deformation. Of five splits studied by James, Lindstrom and McGee, the four mineral splits appeared monomict, whereas the whole-rock split was considered polymict. Previous isotopic work indicate that this anorthosite was quite primitive, a claim that was apparently confirmed by the U-Pb isotopic age of 4.51 +/- .01 Ga on three plagioclase separates. However, a Sm-Nd internal isochron age of 4.44 +/- 0.02 Ga was determined using plagioclase, olivine, and mafic mineral separates, creating some doubt about the anorthosite

  5. Isotopic equilibration between dissolved and suspended particulate lead in the Atlantic Ocean - Evidence from Pb-210 and stable Pb isotopes

    NASA Technical Reports Server (NTRS)

    Sherrell, Robert M.; Boyle, Edward A.; Hamelin, Bruno

    1992-01-01

    Vertical profiles of, on one hand, the stable Pb isotopic composition, and on the other, the ratio of total Pb to Pb-210 in suspended particles, are noted to closely track contemporaneous depth variations in these ratios for dissolved Pb throughout the upper 2 km of the Sargasso Sea near Bermuda. A simple flux model suggests that the effect of deep ocean scavenging processes on the flux and isotopic composition of Pb sinking on large particles was minor throughout the preanthropogenic, and most of the anthropogenic era: but it has become more important as surface inputs decrease to preleaded gasoline levels, perhaps exceeding the contribution of surface-derived Pb flux in the next decade.

  6. Geochemistry and zircon U-Pb-Hf isotopes of Early Paleozoic arc-related volcanic rocks in Sonid Zuoqi, Inner Mongolia: Implications for the tectonic evolution of the southeastern Central Asian Orogenic Belt

    NASA Astrophysics Data System (ADS)

    Chen, Yan; Zhang, Zhicheng; Li, Ke; Yu, Haifei; Wu, Tairan

    2016-11-01

    An Early Paleozoic acid volcanic sequence has been recently detected southeast of Sonid Zuoqi in central Inner Mongolia to constrain the tectonic evolution of the Central Asian Orogenic Belt in this area. First, the volcanic rocks have zircon U-Pb ages of 439-445 Ma. They are characterized by (a) a high silica content, moderate alkali content and low iron content; (b) enrichment in light rare earth elements, depletion of heavy rare earth elements, and negative Eu anomalies; and (c) negative Nb, Ta, and Ti anomalies. Finally, the volcanic samples yield εHf(t) values of - 4.7 to + 9.2 with TDM2 ages of 835-1724 Ma. For petrogenesis, they were possibly arc derived, from predominant juvenile materials with subordinate ancient continental crust. Combined with previous studies, the Early Paleozoic Sonid Zuoqi arc magmatism can be divided into three stages: a primitive arc stage represented by 464-490 Ma low-K, calcic granitoids; a normal continental arc stage represented by 439-445 Ma medium-K, calcic to calcic-alkalic plutons and volcanic rocks and a syn-collisional stage represented by 423-424 Ma high-K granites. Furthermore, the timing and tectonic settings of the above magmatic rocks show similarities to those in Xilinhot and other areas of the northern Early to Mid-Paleozoic orogenic belt (NOB), although the rock assemblies and their proportions vary more or less in different areas. Accordingly, the NOB that formed on this arc was probably attributed to the northward subduction of the Paleo-Asian Ocean beginning at 500 Ma, which experienced this type of arc development and was terminated by a soft collision before the Late Devonian.

  7. Origin of the Ediacaran Porongos Group, Dom Feliciano Belt, southern Brazilian Shield, with emphasis on whole rock and detrital zircon geochemistry and U-Pb, Lu-Hf isotopes

    NASA Astrophysics Data System (ADS)

    Pertille, Juliana; Hartmann, Léo Afraneo; Philipp, Ruy Paulo; Petry, Thales Sebben; de Carvalho Lana, Cristiano

    2015-12-01

    The Porongos Group is the major component of a fold and thrust belt located in the central portion of the Dom Feliciano Belt in the Sul-Riograndense Shield, Brazil. In this paper, the variations in composition of sediments and the depositional time are presented. Major and trace elements indicate that Porongos Group is composed mostly of immature sediments derived from intermediate felsic sources with minor contribution from mature recycled sources. U-Pb SHRIMP ages for a chlorite schist (sample 300) exhibit a proeminent population of 570-800 Ma, subordinate population of 1800-2250 Ma and minor population of 1200 Ma, whereas for a schist (sample 198) the main population is 1050-1500 and minor populations are 2040-2300 and 580-800 Ma. The ɛHf values of Neoproterozoic grains indicate variable degrees of crustal reworking (ɛHf = -18 to -4) with three main TDM model ages (2.2, 1.8, 1.5 Ga). The Paleoproterozoic grains include a few Archean (3.2-2.5 Ga) TDM ages. The trace elements of all analyzed detrital zircon grains reflect continental crust origin. According to the data set, the sediments of the Porongos Group were derived from locally eroded granitic rocks of the Dom Feliciano Belt and from the uplifted Paleoproterozoic basement (La Plata Craton). Further analytical signal and total magnetic field maps delimit regionally the shape and extension of the Porongos fold and thrust belt and includes the Capané region. We conclude that the duration of Porongos Group basin filling probably lasted from 650 to 570 Ma in a foreland tectonic setting of the Dom Feliciano Belt.

  8. Dynamics of the Galapagos hotspot from helium isotope geochemistry

    SciTech Connect

    Kurz, M.D.; Geist, D.

    1999-12-01

    The authors have measured the isotopes of He, Sr, Nd and Pb in a number of lava flows from the Galapagos Archipelago; the main goal is to use magmatic helium as a tracer of plume influence in the western volcanoes. Because the Galapagos lava flows are so well preserved, it is also possible to measure surface exposure ages using in situ cosmic-ray-produced {sup 3}He. The exposure ages range from {lt}0.1 to 580 Ka, are consistent with other chronological constrains, and provide the first direct dating of these lava flows. The new age data demonstrate the utility of the technique in this important age range and show that the western Galapagos volcanoes have been erupting distance compositions simultaneously for the last {approximately}10 Ka. The magmatic {sup 3}He/{sup 4}He ratios range from 6.0 to 27 times atmospheric (R{sub a}), with the highest values found on the islands of Isabella (16.8 R{sub a} for Vulcan Sierra Negra) and Fernandina (23 to 27 R{sub a}). Values from Santa Cruz are close to typical mid-ocean ridge basalt values (MORB, of {approximately}9 R{sub 2}) and Pinta has a {sup 3}He/{sup 4}He ratio lower than MORB (6.9 R{sub a}). These data confirm that the plume is centered beneath Fernandina which is the most active volcano in the archipelago and is at the leading edge of plate motion. The data are consistent with previous isotopic studies, confirming extensive contributions from depleted asthenospheric or lithospheric mantle sources, especially to the central islands. The most striking aspect of the helium isotopic data is that the {sup 3}He/{sup 4}He ratios decrease systematically in all directions from Fernandina. This spatial variability is assumed to reflect the contribution of the purest plume component to Fernandina magmatism, and shows that helium is a sensitive indicator of plume influence. The highest {sup 3}He/{sup 4}He ratios are found in volcanoes with lowest Na{sub 2}O(8) and FeO(8), which may relate to source composition as well as degree

  9. Pb isotopes in surficial pelagic sediments from the North Atlantic

    SciTech Connect

    Hamelin, B.; Grousset, F. ); Sholkovitz, E.R. )

    1990-01-01

    The authors measured Pb isotopic composition and concentration in sediment samples close to the sea water interface in 6 box-cores from the NE Atlantic, 2 box-cores from the Sargasso Sea, and one from the US continental shelf. The anthropogenic Pb input to marine sediments due to the increase of Pb contamination over the ocean during the last century can be identified in all these cores. In the eastern part of the Atlantic, i.e., in regions under aeolian influence from Europe, Pb pollution can be recognized using its distinctive unradiogenic composition, clearly different from the upper-crustal values commonly found in pre-Holocene sediments. In contrast, Pb pollution in regions influenced by North American sources can be identified only in detailed concentration profiles because the American Pb pollution has an isotopic composition much closer to that of the natural detrital Pb input coming from weathering of the continental crust. Pb excess inventories are in good agreement with fluxes estimated from sediment-trap data and with the time record of Pb-contamination increase given by analyses in coral growth bands. Inventories of Pb contamination to the sediments of the Mud Patch (American shelf) are tenfold higher (84 {mu}g/cm{sup 2}) than those to Hatteras and Bermuda abyssal plains (4.3 and 2.8 {mu}g/cm{sup 2}).

  10. Pb Isotopes as Tracers of Weathering in Glacial Systems

    NASA Astrophysics Data System (ADS)

    Martin, E. E.; Deuerling, K. M.; Scribner, C. A.; Martin, J. B.; Clements, K.

    2013-12-01

    Incongruent chemical weathering of freshly exposed continental material produces weathering solutions with Sr and Pb isotopic values that are distinctly more radiogenic than the parent material. As soils age, weathering becomes more congruent and the isotopic ratio in the solution approaches the composition of parent material. In light of this response, rapid increases in seawater Pb isotopes in the North Atlantic over the last deglacial have been attributed to incongruent weathering of fine grained glacial sediment exposed as the ice sheet retreated. This theory has not been tested using modern glacial river systems due to concerns about contamination by anthropogenic Pb. In this study we analyzed Pb isotopes from: 1) leachates of moraine material, 2) bedload and river water samples along a proglacial river, and 3) sediment and water samples from closed basin lakes in deglaciated terrains, from the Kangerlussuaq region of western Greenland. As expected, 0.1N HCl leachates of moraine soils exhibit 206,207,208Pb/204Pb ratios that are more radiogenic than the bulk soil. Samples from a Little Ice Age moraine close to the Russell Glacier exhibit greater offsets between the leachate and bulk soil Pb isotopes than samples from Orkendalen moraines (6.8 ka), which also record a slightly greater offset than Umivit-Keglen moraines (7.3 ka). Proglacial Watson (Akuliarusuarsuup Kuua) River water samples collected closest to the Russell Glacier also record the most radiogenic Pb isotopes and the largest increase relative to bedload values. Bedload 206Pb/204Pb ratios along the 40 km length of the proglacial river are 14.7+/0.6. Values for all water samples are distinctly more radiogenic than bedload, with the highest value (18.02) closest to the glacier and a general decreasing trend to ~15.82 farthest from the glacier. For comparison to anthropogenic Pb isotopes, 206Pb/207Pb ratios are 1.00+/-.03 for bedload, with water values ranging from 1.18 to 1.06 in a decreasing trend

  11. Sr-Nd-Pb-Hf isotope systematics of the Hugo Dummett Cu-Au porphyry deposit (Oyu Tolgoi, Mongolia)

    NASA Astrophysics Data System (ADS)

    Dolgopolova, A.; Seltmann, R.; Armstrong, R.; Belousova, E.; Pankhurst, R. J.; Kavalieris, I.

    2013-04-01

    Major and trace element geochemistry including Sr-Nd-Pb-Hf isotopic data are presented for a representative sample suite of Late Devonian to Early Carboniferous plutonic and volcanic rocks from the Hugo Dummett deposit of the giant Oyu Tolgoi porphyry Cu-Au district in South Gobi, Mongolia. Sr and Nd isotopes (whole-rock) show restricted ranges of initial compositions, with positive ɛNdt mainly between + 3.4 and + 7.4 and (87Sr/86Sr)t predominantly between 0.7037 and 0.7045 reflecting magma generation from a relatively uniform juvenile lithophile-element depleted source. Previously dated zircons from the plutonic rocks exhibit a sample-averaged range of ɛHft values of + 11.6 to + 14.5. Depleted-mantle model ages of 420-830 (Nd) and 320-730 Ma (zircon Hf) limit the involvement of pre-Neoproterozoic crust in the petrogenesis of the intermediate to felsic calc-alkaline magmas to, at most, a minor role. Pb isotopes (whole-rock) show a narrow range of unradiogenic initial compositions: 206Pb/204Pb 17.40-17.94, 207Pb/204Pb 15.43-15.49 and 208Pb/204Pb 37.25-37.64, in agreement with Sr-Nd-Hf isotopes indicating the dominance of a mantle component. All four isotopic systems suggest that the magmas from which the large Oyu Tolgoi porphyry system was generated originated predominantly from juvenile material within the subduction-related setting of the Gurvansayhan terrane.

  12. Estimating distributions of endogenous and exogenous Pb in soils by using Pb isotopic ratios.

    PubMed

    Semlali, R M; van Oort, F; Denaix, L; Loubet, M

    2001-11-01

    Metal contamination of soils by diffuse atmospheric deposition is a worldwide phenomenon. The assessment of incorporation of exogenous metal contaminants in soils is of major environmental importance. Once entering in the soil's biogeochemical cycling, specific pedogenetic soil processes govern metal distribution patterns with depth. In this paper, we attempt to estimate the distribution of endogenous and exogenous Pb in two soils with contrasting pedogenesis, both representative of undisturbed ecosystems. Pb isotope analyses were performed using high-precision thermal ionization mass spectrometry. Endogenous and exogenous Pb concentrations and exogenous 206Pb/207Pb ratios of the samples were calculated using bulk Pb and Sc concentrations and bulk 206Pb/207Pb ratios. Endogenous Pb distribution was in agreementwith dominant soil characteristics, almost constant in the young Andosol and with a clear minimum and maximum in the eluvial and illuvial horizons of the Podzol. The distribution of exogenous Pb was closely related to that of organic C in both soils. Exogenous Pb was evidenced in significant amounts at depth. Using moderate dispersive particle-size fractionation allowed us to evidence the presence of exogenous Pb in functional soil compartments and to highlight preferential distributions of Pb, according to pedology.

  13. Underplating generated A- and I-type granitoids of the East Junggar from the lower and the upper oceanic crust with mixing of mafic magma: Insights from integrated zircon U-Pb ages, petrography, geochemistry and Nd-Sr-Hf isotopes

    NASA Astrophysics Data System (ADS)

    Liu, Wei; Liu, Xiu-Jin; Liu, Li-Juan

    2013-10-01

    Whole rock major and trace element, Nd-Sr and zircon Hf isotopic compositions and secondary-ion mass spectrometry zircon U-Pb ages of eleven granitoid intrusions and dioritic rocks from the East Junggar (NW China) were analyzed in this study. The East Junggar granitoids were emplaced during terminal Early to Late Carboniferous (325-301 Ma) following volcanic eruption of the Batamayi Formation. Zircons from the East Junggar granitoids yielded 210 concordant 206Pb/238U ages which are all younger than 334 Ma and exhibit ɛHf(t) values distinctly higher than Devonian arc volcanic-rocks. Seismic P-wave velocities of deep crust of the East Junggar proper resemble those of oceanic crust (OC). These characteristics suggest absence of volcanic rock and volcano-sedimentary rock of Devonian and Early Carboniferous from the source region. The East Junggar granitoids show ɛNd(t) and initial 87Sr/86Sr values substantially overlapping those of the Armantai ophiolite in the area. The Early Paleozoic OC with seamount-like composition as the Zhaheba-Armantai ophiolites remained in the lower crust and formed main source rock of the East Junggar granitoids. Based on petrography and geochemistry, the East Junggar granitoids are classified into peralkaline A-type in the northern subarea, I-type (I1 and I2 subgroups) mainly in the north and A-type in the south of the southern subarea. The perthitic or argillated core and oligoclasic rim with an argillated boundary of feldspar phenocrysts and inclusion of perthites or its overgrowth by matrix plagioclase, in the monzogranites (northern subarea), suggest mixing of peralkaline granitic magma with mafic magma. In the north of the southern subarea, the presence of magmatic microdioritic enclaves (MMEs) in the I1 subgroup granitoids, transfer of plagioclase phenocrysts and hornblendes between host granodiorite and the MME across the boundary and a prominent resorption surface in the plagioclase phenocrysts indicate mixing of crustal magma (I2

  14. Geochemistry

    ERIC Educational Resources Information Center

    Ailin-Pyzik, Iris B.; Sommer, Sheldon E.

    1977-01-01

    Enumerates some of the research findings in geochemistry during the last year, including X-ray analysis of the Mars surface, trace analysis of fresh and esterarine waters, and analysis of marine sedements. (MLH)

  15. Radioactive halos and ion microprobe measurement of Pb isotope ratios

    NASA Technical Reports Server (NTRS)

    Gentry, R. V.

    1974-01-01

    This investigation was to obtain, if possible, the Pb isotope ratios of both lunar and meteoritic troilite grains by utilizing ion microprobe techniques. Such direct in situ measurement of Pb isotope ratios would eliminate contamination problems inherent in wet chemistry separation procedures, and conceivably determine whether lunar troilite grains were of meteoritic origin. For comparison purposes two samples of meteoritic troilite were selected (one from Canyon Diablo) for analysis along with two very small lunar troilite grains (approximately 50-100 microns). It was concluded that the ion microprobe as presently operating, does not permit the in situ measurement of Pb isotope ratios in lunar or meteoritic troilite. On the basis of these experiments no conclusions could be drawn as to the origin of the lunar troilite grains.

  16. Excitation energies of superdeformed states in the Pb isotopes

    SciTech Connect

    Wilson, A. N.; Byrne, A. P.; Dracoulis, G. D.; Davidson, P. M.; Lane, G. J.; Huebel, H.; Rossbach, D.; Schonwasser, G.; Korichi, A.; Hannachi, F.; Lopez-Martens, A.; Clark, R. M.; Fallon, P.; Macchiavelli, A. O.; Ward, D.

    2006-04-26

    Measurements of the excitation energies of superdeformed states via the observation of single-step linking transitions have now been made in three even-A Pb nuclei, with a quasicontinuum analysis providing a limit in a fourth, odd-A case. These results allow us to take the first steps towards establishing systematic trends in excitation energies and binding energies in the second minimum in Pb isotopes.

  17. Assessment of pollution aerosols sources above the Straits of Dover using lead isotope geochemistry.

    PubMed

    Deboudt, K; Flament, P; Weis, D; Mennessier, J P; Maquinghen, P

    1999-09-15

    We assess the capability of lead isotopes to study the transport of pollution aerosols above the Straits of Dover by collecting atmospheric aerosols above the Eastern Channel and the Southern Bight of the North Sea. During the same period, we characterized the lead isotopic signature of the main industrial sources on the French coast near the Straits of Dover. Urban and automobile-derived aerosols were also collected. Due to the phasing out of lead in gasoline, the urban isotopic composition (206Pb/207Pb = 1.158 +/- 0.003) has become more radiogenic, although it is highly variable. On a regional scale, major industrial emissions have a well-defined isotopic composition (1.13 < 206Pb/207Pb < 1.22), more radiogenic than the petrol-lead signature (1.06 < 206Pb/207Pb < 1.12). These results together with those measured near the main coastal highway show that the automobile source has become a minor component of particulate lead in air. On a local scale, Dunkerque, the most urbanized and industrialized area along the Straits of Dover, may transiently control elevated lead concentrations. Except for the occurrence of local and regional range transport episodes, lead concentrations in the Straits of Dover can be related to remote or semi-remote pollution source emissions. Combining air mass retrospective trajectories and related lead abundances and isotopic compositions, it can be shown that lead aerosols originating from eastern Europe have an isotopic signature (1.145 < 206Pb/207Pb < 1.169) different from the isotopic composition of west-European lead aerosols (1.111 < 206Pb/207Pb < 1.142). The influence of remote North American sources is suggested, with caution, due to uncertainties in meteorological calculations.

  18. Pb - Isotopes and Pulses of the Deccan Plume

    NASA Astrophysics Data System (ADS)

    Basu, A. R.; Yannopoulos, A. S.

    2015-12-01

    Mantle plumes are generally implicated for flood basalt generation in both continental and oceanic environments by impact of large plume heads beneath or within the lithosphere. The Deccan and Siberian flood basalt eruptions, synchronous with the Cretaceous-Paleogene and end-Permian extinctions, respectively, continue to fascinate geoscientists in search for the "kill-mechanisms" by impacts, volcanisms or both. Recently, Richards et al. (2015) proposed that bulk of the Deccan eruption was triggered by the Chicxulub impact. We showed (Basu et al., 1993) that early (68.5 Ma) and late (65 Ma) alkalic pulses of the Deccan were before and after the impact event at 66 Ma. Here, we focus on an extensive volcano-stratigraphic study of Pb isotopic systematics of 69 basaltic samples from 3 subgroups and 12 formations of the Deccan, each sampled from bottom to top along the stratigraphic section, covering the 3km thick 12 Deccan formations. Pb is sensitive to crustal contamination of mantle plume-derived magmas as both the upper and lower mantle are low in Pb (0.02 - 0.15 ppm) compared to ~ 4 ppm in continental crust. The lower Deccan formations of Kalsubai and Lonavala have initial 206Pb/204Pb with a widely varying range (16.543 - 22.823) indicating continental crustal contamination. In contrast, the upper formations of the Wai subgroup show a narrow range of 16.883 to 18.956, reflecting the plume signature. In addition, the 206Pb/204Pb and 207Pb/204Pb data of the Kalsubai subgroup lavas give an isochron age of 2603±140 Ma (single-stage, µ = 8). The Wai subgroup shows a narrow and restricted Pb isotopic range plotting closer to the Geochron. We interpret these data to infer that the basement rocks of the Deccan, the Archean Indian craton, were assimilated by the upwelling melt, ultimately clearing the conduit passages for the lavas sourced from direct melting of the plume head.

  19. Accurate electron affinity of Pb and isotope shifts of binding energies of Pb-

    NASA Astrophysics Data System (ADS)

    Chen, Xiaolin; Ning, Chuangang

    2016-08-01

    Lead (Pb) was the last element of the group IVA whose electron affinity had a low accuracy around 10 meV before the present work. This was due to the generic threshold photodetachment measurement that cannot extent well below 0.5 eV due to the light source limitation. In the present work, the electron affinity of Pb was determined to be 2877.33(13) cm-1 or 0.356 743(16) eV for the isotope m = 208. The accuracy was improved by a factor of 500 with respect to the previous laser photodetachment electron spectroscopy. Moreover, remarkable isotope shifts of the binding energy of Pb- 6p3 4S3/2 - Pb 6p2 3P2 were observed for m = 206, 207, and 208.

  20. Accurate electron affinity of Pb and isotope shifts of binding energies of Pb(.).

    PubMed

    Chen, Xiaolin; Ning, Chuangang

    2016-08-28

    Lead (Pb) was the last element of the group IVA whose electron affinity had a low accuracy around 10 meV before the present work. This was due to the generic threshold photodetachment measurement that cannot extent well below 0.5 eV due to the light source limitation. In the present work, the electron affinity of Pb was determined to be 2877.33(13) cm(-1) or 0.356 743(16) eV for the isotope m = 208. The accuracy was improved by a factor of 500 with respect to the previous laser photodetachment electron spectroscopy. Moreover, remarkable isotope shifts of the binding energy of Pb(-) 6p(3) (4)S3/2 - Pb 6p(2) (3)P2 were observed for m = 206, 207, and 208.

  1. ISOTOPIC EVALUATION OF PB OCCURRENCES IN THE RIVERINE ECOSYSTEMS OF THE KANKAKEE WATERSHED, ILLINOIS-INDIANA.

    EPA Science Inventory

    Environmental background levels of Pb were measured in ponds, river waters, sediments, suspended sediments, rocks, and air particulates within the Kankakee watershed during the period of 1995 to 1999. Stable isotopic Pb distinguised airborne Pb and its incorporation into riverin...

  2. USE OF STABLE ISOTOPES IN ENVIRONMENTAL AND FORENSIC GEOCHEMISTRY STUDIES

    EPA Science Inventory

    Stable carbon and hydrogen isotopes have been used for many decades in the petroleum industry, but the development of combined gas chromatography-isotope ratio mass spectrometry (GCIRMS) has led to a virtual explosion in application of this technique not only in petroleum explora...

  3. The Marine Geochemistry of Iron and Iron Isotopes

    DTIC Science & Technology

    2004-09-01

    oxides in seawater, ɘ.1 nmol/kg at pH 8.2, 25 °C, and I atm (KUMA et al., 1996; MILLERO, 1998). This observation is attributed to organic Fe...greatly on the material used in experiments (e.g., atmospherically weathered aerosols versus soil or loess) and the leaching conditions chosen ( pH 1...If there is fractionation of Fe isotopes by phytoplankton during uptake (preferentially taking up the lighter Fe isotopes) and isotopically light Fe

  4. A study of REE and Pb, Sr and Nd isotopes in garnet-lherzolite xenoliths from Mingxi, Fujian Province

    USGS Publications Warehouse

    Wankang, H.; Junwen, W.; Basu, A.R.; Tatsumoto, M.

    1993-01-01

    The REE and Pb, Sr, Nd isotopes in three xenoliths from limburgite and scoria-breccias, including spinel-lherzolite, spinel-garnet-lherzolite and phlogopite-gamet-lherzolite, were analysed. The REE contents of the xenoliths are 1.3 to 3.3 times those of the chondrites with their REE patterns characterized by weak LREE depletion. The143Nd/144Nd values of whole rocks and minerals range from 0.51306 to 0.51345 with ??Nd=+ 8.2- +15.8,206Pb/204 Pb < 18.673, and207Pb/204Pb < 15.574. All this goes to show that the upper mantle in Mingxi at the depth of 67-82 km is a depleted mantle of MORB type, with87Sr/86 Sr ratios 0.70237-0.70390. In Nd-Sr diagram the data points of whole rocks are all out of the mantle array, implying that the xenoliths from Mingxi have more radiogenic Sr isotopes than those of the mantle array. ?? 1993 Institute of Geochemistry, Chinese Academy of Sciences.

  5. A Pb isotopic resolution to the Martian meteorite age paradox

    NASA Astrophysics Data System (ADS)

    Bellucci, J. J.; Nemchin, A. A.; Whitehouse, M. J.; Snape, J. F.; Kielman, R. B.; Bland, P. A.; Benedix, G. K.

    2016-01-01

    Determining the chronology and quantifying various geochemical reservoirs on planetary bodies is fundamental to understanding planetary accretion, differentiation, and global mass transfer. The Pb isotope compositions of individual minerals in the Martian meteorite Chassigny have been measured by Secondary Ion Mass Spectrometry (SIMS). These measurements indicate that Chassigny has mixed with a Martian reservoir that evolved with a long-term 238U/204Pb (μ) value ∼ two times higher than those inferred from studies of all other Martian meteorites except 4.428 Ga clasts in NWA7533. Any significant mixing between this and an unradiogenic reservoir produces ambiguous trends in Pb isotope variation diagrams. The trend defined by our new Chassigny data can be used to calculate a crystallization age for Chassigny of 4.526 ± 0.027 Ga (2σ) that is clearly in error as it conflicts with all other isotope systems, which yield a widely accepted age of 1.39 Ga. Similar, trends have also been observed in the Shergottites and have been used to calculate a >4 Ga age or, alternatively, attributed to terrestrial contamination. Our new Chassigny data, however, argue that the radiogenic component is Martian, mixing occurred on the surface of Mars, and is therefore likely present in virtually every Martian meteorite. The presence of this radiogenic reservoir on Mars resolves the paradox between Pb isotope data and all other radiogenic isotope systems in Martian meteorites. Importantly, Chassigny and the Shergottites are likely derived from the northern hemisphere of Mars, while NWA 7533 originated from the Southern hemisphere, implying that the U-rich reservoir, which most likely represents some form of crust, must be widespread. The significant age difference between SNC meteorites and NWA 7533 is also consistent with an absence of tectonic recycling throughout Martian history.

  6. Clumped isotope geochemistry of mid-Cretaceous (Barremian-Aptian) rudist shells: paleoclimatic and paleoenvironmental implications

    NASA Astrophysics Data System (ADS)

    Huck, S.; Steuber, T.; Bernasconi, S.; Weissert, H.

    2012-04-01

    The Cretaceous period is generally considered to have been a time of climate warmth, but there is an ongoing dispute about the existence of Cretaceous cool episodes - including the short-termed installation of polar ice caps. The Late Barremian-Early Aptian represents a Cretaceous key interval in terms of paleoclimate and paleoceanography, as it provides evidence for (i) a cooler climate (Pucéat et al., 2003) and (ii) a considerable seasonality of sea surface temperatures (SSTs) at low latitudes (Steuber et al., 2005). The timing and significance of these cool episodes, however, are not well constrained. Recently published TEX86 data, in contrast to oxygen isotope paleotemperature estimates, now are in support of a climate scenario with equable hot (~30° C) tropical SSTs from the Early Cretaceous onwards. The aim of this project is to reconstruct the evolution of Barremian-Aptian sea-surface temperatures (SSTs) in the tropical Tethyan realm by use of a combined geochemical approach including oxygen isotope analysis and carbonate clumped-isotope thermometry. Paleotemperature proxies are based on the isotope geochemistry of low-Mg calcite of pristine rudist bivalve shells (Toucasia, Requienia) collected from different carbonate platform settings, including the Provence platform in SE France and the Adriatic Carbonate platform in Croatia. Carbonate clumped-isotope geochemistry deals with the state of ordering of rare isotopes in molecules, in particular with their tendency to form bonds with other rare isotopes (13C-18O) rather than with the most abundant ones. Carbonate clumped-isotope thermometry has been shown to allow for reconstructing (i) the temperature of carbonate mineral formation and calculating (ii) the isotopic composition of the water from which carbonate minerals were formed (by using the δ18O of the analysed carbonate sample). Our approach seeks to provide insights into possible biases in temperature estimates of different paleothermometers

  7. Temporal trends of pollution Pb and other metals in east-central Baffin Island inferred from lake sediment geochemistry.

    PubMed

    Michelutti, Neal; Simonetti, Antonio; Briner, Jason P; Funder, Svend; Creaser, Robert A; Wolfe, Alexander P

    2009-10-15

    Concentrations and stable isotope ratios of lead (Pb) from lake sediments were used to quantify temporal patterns of anthropogenic Pb pollution in the Clyde River region of Baffin Island, Arctic Canada. Surface sediments from eight lakes on eastern Baffin Island and one from northern-most Greenland, spanning a gradient of 20 degrees latitude, showed great variability with respect to Pb concentration and stable isotopic Pb ratios, with little apparent latitudinal trend. To constrain the temporal evolution of regional Pb pollution, a well-dated core from one of the sites, Lake CF8 on east-central Baffin Island, was analyzed geochemically at high stratigraphic resolution. A pronounced decrease in the (206)Pb/(207)Pb ratio occurs in sediments deposited between 1923 and the mid-1970s, likely reflecting alkyl-Pb additives derived from the combustion of fossil fuels at a global scale. A two-component mixing model indicates that 17-26% of the Pb in the labile fraction of sediments deposited in Lake CF8 between 2001 and 2005 is from anthropogenic input. A Pb-Pb co-isotopic plot ((206)Pb/(207)Pb vs.(208)Pb/(206)Pb ratios) of the Lake CF8 time series data indicates multiple possible sources of industrial Pb pollution. Despite widespread reductions in industrial Pb emissions since the 1970s, there is no evidence for attendant reductions of pollution Pb at Lake CF8. Enhanced scavenging from increased primary production as well as changing precipitation rates as climate warms may represent important factors that modulate Pb deposition to Lake CF8, and Arctic lakes elsewhere.

  8. Geological, rare earth elemental and isotopic constraints on the origin of the Banbanqiao Zn-Pb deposit, southwest China

    NASA Astrophysics Data System (ADS)

    Li, Bo; Zhou, Jia-Xi; Huang, Zhi-Long; Yan, Zai-Fei; Bao, Guang-Ping; Sun, Hai-Rui

    2015-11-01

    elemental and isotopic data suggest that the REE, C and S in the ore-forming fluids of the Banbanqiao deposit were mainly originated from the carbonate host rocks, while the Pb and O were primarily derived from radiogenic Pb- and 18O-depleted sources, which are most likely to be the underlying Proterozoic basement rocks. Studies on the geology, rare earth elements and isotope geochemistry indicate that the Banbanqiao deposit is a carbonate-hosted, stratiform, anticline-controlled, epigenetic and high grade Zn-Pb deposit formed by elemental compositions of mixed origin, and is a typical SYG-type deposit in the western Yangtze Block, southwest China.

  9. Invited review article: Recent developments in isotope-ratio mass spectrometry for geochemistry and cosmochemistry.

    PubMed

    Ireland, Trevor R

    2013-01-01

    Mass spectrometry is fundamental to measurements of isotope ratios for applications in isotope geochemistry, geochronology, and cosmochemistry. Magnetic-sector mass spectrometers are most common because these provide the best precision in isotope ratio measurements. Where the highest precision is desired, chemical separation followed by mass spectrometric analysis is carried out with gas (noble gas and stable isotope mass spectrometry), liquid (inductively coupled plasma mass spectrometry), or solid (thermal ionization mass spectrometry) samples. Developments in in situ analysis, including ion microprobes and laser ablation inductively coupled plasma mass spectrometry, have opened up issues concerning homogeneity according to domain size, and allow ever smaller amounts of material to be analyzed. While mass spectrometry is built solidly on developments in the 20th century, there are new technologies that will push the limits in terms of precision, accuracy, and sample efficiency. Developments of new instruments based on time-of-flight mass spectrometers could open up the ultimate levels of sensitivity per sample atom.

  10. High-precision measurements of seawater Pb isotope compositions by double spike thermal ionization mass spectrometry.

    PubMed

    Paul, Maxence; Bridgestock, Luke; Rehkämper, Mark; van DeFlierdt, Tina; Weiss, Dominik

    2015-03-10

    A new method for the determination of seawater Pb isotope compositions and concentrations was developed, which combines and optimizes previously published protocols for the separation and isotopic analysis of this element. For isotopic analysis, the procedure involves initial separation of Pb from 1 to 2L of seawater by co-precipitation with Mg hydroxide and further purification by a two stage anion exchange procedure. The Pb isotope measurements are subsequently carried out by thermal ionization mass spectrometry using a (207)Pb-(204)Pb double spike for correction of instrumental mass fractionation. These methods are associated with a total procedural Pb blank of 28±21 pg (1sd) and typical Pb recoveries of 40-60%. The Pb concentrations are determined by isotope dilution (ID) on 50 mL of seawater, using a simplified version of above methods. Analyses of multiple aliquots of six seawater samples yield a reproducibility of about ±1 to ±10% (1sd) for Pb concentrations of between 7 and 50 pmol/kg, where precision was primarily limited by the uncertainty of the blank correction (12±4 pg; 1sd). For the Pb isotope analyses, typical reproducibilities (±2sd) of 700-1500 ppm and 1000-2000 ppm were achieved for (207)Pb/(206)Pb, (208)Pb/(206)Pb and (206)Pb/(204)Pb, (207)Pb/(204)Pb, (208)Pb/(204)Pb, respectively. These results are superior to literature data that were obtained using plasma source mass spectrometry and they are at least a factor of five more precise for ratios involving the minor (204)Pb isotope. Both Pb concentration and isotope data, furthermore, show good agreement with published results for two seawater intercomparison samples of the GEOTRACES program. Finally, the new methods were applied to a seawater depth profile from the eastern South Atlantic. Both Pb contents and isotope compositions display a smooth evolution with depth, and no obvious outliers. Compared to previous Pb isotope data for seawater, the (206)Pb/(204)Pb ratios are well correlated

  11. Avian digestive tract simulation to study the effect of grit geochemistry and food on Pb shot bioaccessibility.

    PubMed

    Martinez-Haro, Monica; Taggart, Mark A; Green, Andy J; Mateo, Rafael

    2009-12-15

    Lead shot dissolution was investigated in a dynamic in vitro simulated avian gizzard-intestine system. The method allows simulated digestive fluid to pass (at intervals) from a gizzardlike environment to an intestine-based one, and then considers the dissolution of Pb shot (0-3 pellets) in the presence of differing grit geochemistries (siliceous and calcareous) and variable amounts of food (0-4 g of partially milled wheat seed). Dissolved Pb levels in simulated gizzards were consistently higher in the presence of siliceous, than with calcareous, grit. This was also seen in simulated intestines, except when less food was used (0-1 g), when Pb levels in solution were higher in calcareous systems. The Pb concentrations in gizzard and intestine solutions increased directly with the number of Pb shot used. In all treatments Pb levels in intestine liquids were lower than in gizzard liquids. Calcareous grit simulations maintained 2.5-34 times more Ca in solution than those that used siliceous grit. Dietary supplementation with calcareous grit may reduce Pb bioaccessibility of ingested Pb shot in birds by reducing gizzard acidity, by enhancing Pb precipitation (as Pb-carbonate), and by promoting higher dissolved Ca levels in the intestine, which may then compete with Pb for intestinal absorption.

  12. Oxygen isotope geochemistry of The Geysers reservoir rocks, California

    SciTech Connect

    Gunderson, Richard P.; Moore, Joseph N.

    1994-01-20

    Whole-rock oxygen isotopic compositions of Late Mesozoic graywacke, the dominant host rock at The Geysers, record evidence of a large liquid-dominated hydrothermal system that extended beyond the limits of the present steam reservoir. The graywackes show vertical and lateral isotopic variations that resulted from gradients in temperature, permeability, and fluid composition during this early liquid-dominated system. All of these effects are interpreted to have resulted from the emplacement of the granitic "felsite" intrusion 1-2 million years ago. The {delta}{sup 18}O values of the graywacke are strongly zoned around a northwest-southeast trending low located near the center of and similar in shape to the present steam system. Vertical isotopic gradients show a close relationship to the felsite intrusion. The {delta}{sup 18}O values of the graywacke decrease from approximately 15 per mil near the surface to 4-7 per mil 300 to 600 m above the intrusive contact. The {delta}{sup 18}O values then increase downward to 8-10 per mil at the felsite contact, thereafter remaining nearly constant within the intrusion itself. The large downward decrease in {delta}{sup 18}O values are interpreted to be controlled by variations in temperature during the intrusive event, ranging from 150{degree}C near the surface to about 425{degree}C near the intrusive contact. The upswing in {delta}{sup 18}O values near the intrusive contact appears to have been caused by lower rock permeability and/or heavier fluid isotopic composition there. Lateral variations in the isotopic distributions suggests that the effects of temperature were further modified by variations in rock permeability and/or fluid-isotopic composition. Time-integrated water:rock ratios are thought to have been highest within the central isotopic low where the greatest isotopic depletions are observed. We suggest that this region of the field was an area of high permeability within the main upflow zone of the liquid

  13. Dynamic variability of dissolved Pb and Pb isotope composition from the U.S. North Atlantic GEOTRACES transect

    NASA Astrophysics Data System (ADS)

    Noble, Abigail E.; Echegoyen-Sanz, Yolanda; Boyle, Edward A.; Ohnemus, Daniel C.; Lam, Phoebe J.; Kayser, Rick; Reuer, Matt; Wu, Jingfeng; Smethie, William

    2015-06-01

    This study presents dissolved Pb concentration and isotopic composition distributions from GEOTRACES GA03, the U.S. North Atlantic Transect. Pb in the ocean is primarily derived from anthropogenic sources and Pb fluxes into the North Atlantic Ocean have been steadily decreasing following the phase-out of alkyl leaded gasoline usage in North America and Europe between 1975 and 1995. A compilation of dissolved Pb profiles from three stations occupied repeatedly during the last three decades reveals a dramatic decrease in concentrations within the surface layers and the thermocline maxima, although elevated concentrations greater than 60 pmol/kg are still observed in the center of the North Atlantic gyre where ventilation timescales are longer than at the western boundary. The evolution of stable Pb isotopes at these stations shows a shift from dominantly North American-like composition in surface waters in the early 1980s towards a more European-like composition in later years. The most recent shallow signatures at the Bermuda Atlantic Time Series station (BATS) show an even more recent trend returning to higher 206Pb/207Pb ratios after the completed phase-out of leaded gasoline in Europe, presumably because recently deposited Pb is more strongly influenced by industrial and incineration Pb than by residual alkyl leaded gasoline utilization. In surface waters, trends toward a more prominent European influence are also found in the middle of the basin and toward the European coast, coincident with higher concentrations of surface dissolved Pb. Scavenging of anthropogenic Pb is observed within the TAG hydrothermal plume, and it is unclear if there is any significant contribution to deep water by basaltic Pb leached by hydrothermal fluids. In the upper water column, many stations along the transect show Pb concentration maxima at ~100 m depth, coincident with a low 206Pb/207Pb isotopic signature that is typical of European emission sources. Although Pb ores from the

  14. Long-Term Performance of Pb Isotopic Analysis by TIMS with 202Pb-205Pb Double Spike

    NASA Astrophysics Data System (ADS)

    Amelin, Y.; Connelly, J. N.

    2008-05-01

    The 202Pb-205Pb-233U-235U spike (Pb DS), prepared at the Geological Survey of Canada in 2005 [1], and the 202Pb-205Pb-235U spike, prepared at the Department of Geosciences, University of Oslo [2], have been used for more than two years. Both spikes are routinely used for TIMS analysis of Pb with internal fractionation correction for U-Pb dating of various rocks and minerals, including dating perovskite [2] and meteorites and their components [1, 4-7]. A few hundred standard and sample Pb DS analyses were acquired with these two spikes using Triton TI mass spectrometers at the Geological Survey of Canada, US Geological Survey and the Australian National University, a Finnigan-MAT 261 mass spectrometer at The University of Texas at Austin and a Finnigan-MAT 262 mass spectrometer at the University of Oslo. All analyses were performed using high efficiency silicic acid emitter [8] and a static multicollector mode if the samples were sufficiently large to produce an ion beam greater than ca. 2-5×10-14 A on 206Pb and 207Pb. These data allow us to evaluate long - term performance of the Pb DS procedure for sub-nanogram samples of Pb. The performance of this procedure is evaluated on the basis of the long-term reproducibility of analyses of isotopic standards, and from improving quality of linear fits in Pb-Pb isochron diagrams (and, hence, improved precision of ages) compared to the same data reduced using external normalization. The data for 0.3 ng loads of SRM-981, analyzed with the batches of samples in 2006 and 2007 at the GSC, yield the mean 204Pb/206Pb of 0.05904±0.00013 (0.226% 2σ), #207Pb/206Pb of 0.91483±0.00018 (0.020% 2σ)), and 208Pb/206Pb of 2.16771±0.00054 (0.025% 2σ)). These values and errors are similar to those reported in [1] for the loads of the same size, and to the values obtained for similar loads at the USGS and at ANU over shorter periods of time. The precision and reproducibility of sample analysis and standard analyses is similar, and

  15. New Carbonate Standard Reference Materials for Boron Isotope Geochemistry

    NASA Astrophysics Data System (ADS)

    Stewart, J.; Christopher, S. J.; Day, R. D.

    2015-12-01

    The isotopic composition of boron (δ11B) in marine carbonates is well established as a proxy for past ocean pH. Yet, before palaeoceanographic interpretation can be made, rigorous assessment of analytical uncertainty of δ11B data is required; particularly in light of recent interlaboratory comparison studies that reported significant measurement disagreement between laboratories [1]. Well characterised boron standard reference materials (SRMs) in a carbonate matrix are needed to assess the accuracy and precision of carbonate δ11B measurements throughout the entire procedural chemistry; from sample cleaning, to ionic separation of boron from the carbonate matrix, and final δ11B measurement by multi-collector inductively coupled plasma mass spectrometry. To date only two carbonate reference materials exist that have been value-assigned by the boron isotope measurement community [2]; JCp-1 (porites coral) and JCt-1 (Giant Clam) [3]. The National Institute of Standards and Technology (NIST) will supplement these existing standards with new solution based inorganic carbonate boron SRMs that replicate typical foraminiferal and coral B/Ca ratios and δ11B values. These new SRMs will not only ensure quality control of full procedural chemistry between laboratories, but have the added benefits of being both in abundant supply and free from any restrictions associated with shipment of biogenic samples derived from protected species. Here we present in-house δ11B measurements of these new boron carbonate SRM solutions. These preliminary data will feed into an interlaboratory comparison study to establish certified values for these new NIST SRMs. 1. Foster, G.L., et al., Chemical Geology, 2013. 358(0): p. 1-14. 2. Gutjahr, M., et al., Boron Isotope Intercomparison Project (BIIP): Development of a new carbonate standard for stable isotopic analyses. Geophysical Research Abstracts, EGU General Assembly 2014, 2014. 16(EGU2014-5028-1). 3. Inoue, M., et al., Geostandards and

  16. Iron isotope geochemistry in the Antarctic cryptoendolithic microbial ecosystem

    NASA Astrophysics Data System (ADS)

    Sun, H.

    2002-05-01

    The stable isotope composition of iron is a potentially powerful tracer of biogeochemical cycles because iron is ubiquitous, it is required by all organisms, and it is resistant to alterations during diagenesis. Here we report evidence of biological iron isotope fractionation in the weathering process of sandstone in McMurdo Dry Valleys, Antarctica, caused by the cryptoendolithic lichen-dominated microbial community that live below the rock surface. The fungi secrete oxalic acid, which under the sunlight reduces and dissolves the iron in the colonized zone. The mobilized iron diffuses to the rock surface and the rock interior below the organisms where it is re-oxidized. This leaching process is shown to prefer lighter isotopes of iron, leaving the colonized layer enriched in del 56Fe by as much 0.8 per mil. Had endolithic microorganisms occurred on Mars as commonly believed, they might have left similar iron biosignatures, well preserved in rocks because of the absence of subsequent aqueous activities.

  17. Mg isotopes geochemistry in the Han River basin, Korea

    NASA Astrophysics Data System (ADS)

    Ryu, J.; Lee, S.; Lee, K.; Shin, H.

    2012-12-01

    The Han River basin is the largest river system in South Korea, consisting of two major branches: the North Han River (NHR) and South Han River (SHR). Distinct differences in the lithology between the NHR and SHR (silicates vs. carbonates) allow us to constrain the behavior of Mg isotopes during chemical weathering. We collected water samples as well as rock samples in summer 2011. The lithological difference between the NHR and SHR is reflected in major ions and dissolved Sr isotope compositions; lower major ion concentrations and high 87Sr/86Sr ratios in the NHR but higher major ion concentrations and low 87Sr/86Sr ratios in the SHR. Dissolved Mg in the NHR yielded heavier Mg isotope compositions, ranging from -1.14 to -0.67‰ of δ26MgDSM3 with an average of -0.85‰ (n=6), than that in the SHR, ranging from -1.34 to -0.74‰ of δ26MgDSM3 with an average of -1.15‰ (n=6). The river waters draining only carbonates have much lower δ26MgDSM3 values (-1.34 to -1.27‰, n=3), similar to other rivers draining carbonates. This implies that biological fractionation such as plant uptake would be limited because a geographical environment in the Han River basin is almost same. Mineral saturation indices indicate that the river waters are undersaturated with respect to primary and secondary minerals such as smectite but waters draining the carbonates are oversaturated with respect to calcite and dolomite. Hence, the lower δ26MgDSM3 values in the NHR relative to source rocks could be mainly attributed to the fractionation during silicate mineral dissolution. Contrary to the NHR, δ26MgDSM3 values in the SHR indistinguishable from those of the carbonates imply that carbonates dissolution/precipitation would not fractionate Mg isotopes. This study indicates that Mg isotopes could be used to constrain riverine Mg sources.

  18. Sulfur isotope and porewater geochemistry of Florida escarpment seep sediments

    USGS Publications Warehouse

    Chanton, J.P.; Martens, C.S.; Paull, C.K.; Coston, J.A.

    1993-01-01

    Distributions of porewater constituents, SO4=, NH4+, Cl-, ???CO2, and H2S, solid phase iron, and sulfur concentrations, and the sulfur isotopic composition of dissolved and solid phases were investigated in sediments from abyssal seeps at the base of the Florida escarpment. Despite the apparent similarity of seep sediment porewater chemistry to that of typical marine sediments undergoing early diagenesis, relationships between chemical distributions and isotopic measurements revealed that the distribution of pore fluid constituents was dominated by processes occurring within the platform rather than by in situ microbial processes. Ammonium and sulfate concentrations were linearly correlated with chloride concentrations, indicating that variations in porewater chemistry were controlled by the admixture of seawater and a sulfate depleted brine with a chlorinity of 27.5 ?? 1.9%. and 2.2 ?? 1.3 mM ammonium concentration. At sites dominated by seepage, dissolved sulfate isotopic composition remained near seawater values despite depletion in porewater concentrations. Porewater ???CO2 concentrations were found to be elevated relative to seawater, but not to the extent predicted from the observed sulfate depletion. Sediment solid phase sulfur was predominantly pyrite, at concentrations as high as 20% S by weight. In contrast to typical marine deposits, pyrite concentrations were not related to the quantity of sedimentary organic matter. Pyrite ??34S values ranged from -29%. to + 21%. (CDT). However, only positive ??34S values were observed at sites associated with high pyrite concentrations. Isotopically heavy pyrite was observed at sites with porewater sulfate of seawater-like isotopic composition. Isotopically light pyrite was associated with sites where porewater sulfate exhibited ??34S values greater than those in seawater, indicating the activity of in situ microbial sulfate reduction. Thus, dual sulfide sources are suggested to explain the range in sediment pyrite

  19. Discrimination of the Cigarettes Geographical Origin by DRC-ICP-MS Measurements of Pb Isotope Compositions

    NASA Astrophysics Data System (ADS)

    Guo, W.; Hu, S.; Jin, L.

    2014-12-01

    Trace Pb are taken up with the same isotopic ratios as is present in the source soil, and the isotopic composition of Pb could used to reflect these sources and provide powerful indicators of the geographic origin of agriculture products derived from vegetative matter. We developed a simple and high throughput method, which based on DRC-ICP-MS for determination of Pb isotope ratios for discriminating the geographic origin of cigarettes. After acid digestion procedure, the cigarette digested solutions were directly analyzed by ICP-QMS with a DRC pressurized by the non-reactive gas Ne. In the DRC, Ne molecules collision with Pb ions and improves Pb isotope ratios precision 3-fold, which may be due to the collisional dampling smoothes out the ion beam fluctuations. Under the optimum DRC rejection parameter Q (RPq = 0.45), the main matrix components (K, Na, Ca, Mg, Al, Fe etc.) originating from cigarettes were filtered out. Mass discrimination of 208Pb/206Pb ratio in Ne DRC mode increased 0.3% compared to the standard mode, the mass bias due to the in-cell Ne gas collision can be accurately corrected by NIST 981 Pb isotope standard. This method was verified by a tobacco reference material CTV-OTL-2. Results of 208Pb/206Pb and 207Pb/206Pb were 2.0848 ± 0.0028 (2δ) and 0.8452 ± 0.0011 (2δ) for CTA-VTL-2, which were agreed with the literature values (208Pb/206Pb = 2.0884 ± 0.0090 and 207Pb/206Pb = 0.8442 ± 0.0032). The precision of Pb isotope ratios (208Pb/206Pb and 207Pb/206Pb) for the cigarette samples are ranged from 0.01 to 0.08% (N = 5). It has sufficient precision to discriminate 91 different brand cigarettes originated from four different geographic regions (Shown in Fig).

  20. Biogeochemistry of a mesotrophic lake and it's carbon isotope geochemistry

    NASA Astrophysics Data System (ADS)

    Cheng, S.; Ehresman, W.; Sadurski, S. E.

    2010-12-01

    Crystal Lake, located in west-central Ohio, is the main lake of a series of 4 interconnected lakes. The location and orientation indicate that they are most likely moulin-induced glacial lakes. Crystal Lake is about 5 hectares (12.5 acres). The maximum depth and mean depth are about 11.9 meters and 3.8 meters, respectively. As a result of this high depth-to-surface area ratio, it creates a strong thermal stratification during warm season. The lake was classified as eutrophic lake. However, the water quality has improved in the past decades. The chlorophyll in the epillimnion and upper metalimlion is about 4 μg/l and the Secchi disk depth is about 3.0 meters (10 feet). It is therefore reclassified as mesotrophic lake. Dissolved oxygen maximum (15.6 ppm) and pH peak (8.6) existed at 4.1 meter on August 16, 2010. At around 7.3 meter, where redox potential reading shows a sudden change from oxidizing to reducing , a ~half meter layer of dense purple sulfur bacteria coincides with turbidity, chlorophyll, and sulfate maxima. The chemical depth profiles are a result of thermal stratification, oxygenic photosynthesis by algae, non-oxygenic photosynthesis by purple sulfur bacteria, and respiration in the hypolimnion. Precipitation of calcium carbonate in the epilimnion and metalimnion is coupled by it’s dissolution in the hypolimnion. The purpose of the current project is to present extensive background study to form the framework for quantifying the carbon isotope evolution with multiple reaction pathways. Carbon isotope composition of dissolved inorganic carbon is being analyzed. Wigley-Plummer-Pearson mass transfer model will be used for the quantification of carbon isotope reaction pathways.

  1. Lithium isotope geochemistry and origin of Canadian shield brines.

    PubMed

    Bottomley, D J; Chan, L H; Katz, A; Starinsky, A; Clark, I D

    2003-01-01

    Hypersaline calcium/chloride shield brines are ubiquitous in Canada and areas of northern Europe. The major questions relating to these fluids are the origin of the solutes and the concentration mechanism that led to their extreme salinity. Many chemical and isotopic tracers are used to solve these questions. For example, lithium isotope systematics have been used recently to support a marine origin for the Yellowknife shield brine (Northwest Territories). While having important chemical similarities to the Yellowknife brine, shield brines from the Sudbury/Elliot Lake (Ontario) and Thompson/Snow Lake (Manitoba) regions, which are the focus of this study, exhibit contrasting lithium behavior. Brine from the Sudbury Victor mine has lithium concentrations that closely follow the sea water lithium-bromine concentration trajectory, as well as delta6Li values of approximately -28/1000. This indicates that the lithium in this brine is predominantly marine in origin with a relatively minor component of crustal lithium leached from the host rocks. In contrast, the Thompson/Snow Lake brine has anomalously low lithium concentrations, indicating that it has largely been removed from solution by alteration minerals. Furthermore, brine and nonbrine mine waters at the Thompson mine have large delta6Li variations of approximately 30/1000, which primarily reflects mixing between deep brine with delta6Li of -35 +/- 2/1000 and near surface mine water that has derived higher delta6Li values through interactions with their host rocks. The contrary behavior of lithium in these two brines shows that, in systems where it has behaved conservatively, lithium isotopes can distinguish brines derived from marine sources.

  2. U-Pb ages, geochemistry, C-O-Nd-Sr-Hf isotopes and petrogenesis of the Catalão II carbonatitic complex (Alto Paranaíba Igneous Province, Brazil): implications for regional-scale heterogeneities in the Brazilian carbonatite associations

    NASA Astrophysics Data System (ADS)

    Guarino, Vincenza; Wu, Fu-Yuan; Melluso, Leone; de Barros Gomes, Celso; Tassinari, Colombo Celso Gaeta; Ruberti, Excelso; Brilli, Mauro

    2016-09-01

    The Catalão II carbonatitic complex is part of the Alto Paranaíba Igneous Province (APIP), central Brazil, close to the Catalão I complex. Drill-hole sampling and detailed mineralogical and geochemical study point out the existence of ultramafic lamprophyres (phlogopite-picrites), calciocarbonatites, ferrocarbonatites, magnetitites, apatitites, phlogopitites and fenites, most of them of cumulitic origin. U-Pb data have constrained the age of Catalão I carbonatitic complex between 78 ± 1 and 81 ± 4 Ma. The initial strontium, neodymium and hafnium isotopic data of Catalão II (87Sr/86Sri = 0.70503-0.70599; ɛNdi = -6.8 to -4.7; 176Hf/177Hf = 0.28248-0.28249; ɛHfi = -10.33 to -10.8) are similar to the isotopic composition of the Catalão I complex and fall within the field of APIP kimberlites, kamafugites and phlogopite-picrites, indicating the provenance from an old lithospheric mantle source. Carbon isotopic data for Catalão II carbonatites (δ13C = -6.35 to -5.68 ‰) confirm the mantle origin of the carbon for these rocks. The origin of Catalão II cumulitic rocks is thought to be caused by differential settling of the heavy phases (magnetite, apatite, pyrochlore and sulphides) in a magma chamber repeatedly filled by carbonatitic/ferrocarbonatitic liquids (s.l.). The Sr-Nd isotopic composition of the Catalão II rocks matches those of APIP rocks and is markedly different from the isotopic features of alkaline-carbonatitic complexes in the southernmost Brazil. The differences are also observed in the lithologies and the magmatic affinity of the igneous rocks found in the two areas, thus demonstrating the existence of regional-scale heterogeneity in the mantle sources underneath the Brazilian platform.

  3. Pb isotopes as tracers of mining-related Pb in lichens, seaweed and mussels near a former Pb-Zn mine in West Greenland.

    PubMed

    Søndergaard, Jens; Asmund, Gert; Johansen, Poul; Elberling, Bo

    2010-05-01

    Identification of mining-related contaminants is important in order to assess the spreading of contaminants from mining as well as for site remediation purposes. This study focuses on lead (Pb) contamination in biota near the abandoned 'Black Angel Mine' in West Greenland in the period 1988-2008. Stable Pb isotope ratios and total Pb concentrations were determined in lichens, seaweed and mussels as well as in marine sediments. The results show that natural background Pb ((207)Pb/(206)Pb: 0.704-0.767) and Pb originating from the mine ore ((207)Pb/(206)Pb: 0.955) have distinct isotopic fingerprints. Total Pb in lichens, seaweed, and mussels was measured at values up to 633, 19 and 1536 mg kg(-1) dry weight, respectively, and is shown to be a mixture of natural Pb and ore-Pb. This enables quantification of mining-related Pb and shows that application of Pb isotope data is a valuable tool for monitoring mining pollution.

  4. Biogeochemistry and isotope geochemistry of a landfill leachate plume.

    PubMed

    van Breukelen, Boris M; Röling, Wilfred F M; Groen, Jacobus; Griffioen, Jasper; van Verseveld, Henk W

    2003-09-01

    The biogeochemical processes were identified which improved the leachate composition in the flow direction of a landfill leachate plume (Banisveld, The Netherlands). Groundwater observation wells were placed at specific locations after delineating the leachate plume using geophysical tests to map subsurface conductivity. Redox processes were determined using the distribution of solid and soluble redox species, hydrogen concentrations, concentration of dissolved gases (N(2), Ar, and CH(4)), and stable isotopes (delta15N-NO(3), delta34S-SO(4), delta13C-CH(4), delta2H-CH(4), and delta13C of dissolved organic and inorganic carbon (DOC and DIC, respectively)). The combined application of these techniques improved the redox interpretation considerably. Dissolved organic carbon (DOC) decreased downstream in association with increasing delta13C-DOC values confirming the occurrence of degradation. Degradation of DOC was coupled to iron reduction inside the plume, while denitrification could be an important redox process at the top fringe of the plume. Stable carbon and hydrogen isotope signatures of methane indicated that methane was formed inside the landfill and not in the plume. Total gas pressure exceeded hydrostatic pressure in the plume, and methane seems subject to degassing. Quantitative proof for DOC degradation under iron-reducing conditions could only be obtained if the geochemical processes cation exchange and precipitation of carbonate minerals (siderite and calcite) were considered and incorporated in an inverse geochemical model of the plume. Simulation of delta13C-DIC confirmed that precipitation of carbonate minerals happened.

  5. Isotope ratios in Geochemistry - highest sensitivity and scan speed

    NASA Astrophysics Data System (ADS)

    Chemnitzer, Rene; Hamester, Meike

    2013-04-01

    The applications for trace elemental analysis are steadily increasing: beside the classical fields such as environmental and semiconductor analysis more and more interest for trace elemental analysis in food, geochemical analysis and material characterization can be observed, not to forget hot topics such as analysis of isotope ratios and nanoparticles. At the same time the requirements for lower detection limits, sample throughput, matrix robustness, and easy to use instruments are increasing. An important performance characteristic for ICP-MS is the sensitivity. The Bruker aurora Elite achieves a sensitivity of 1.5 GHz/ppm, which directly translates to smaller spot sizes when doing laser ablation in geochemical analyses, and with that avoiding counting statistical limitations in the single digit µm spot size range. In combination with shortest integration times of 0.1ms it comes close to an almost simultaneous measurement with a single-collector ICP-MS. At the same time, other important parameters such as low oxide ratios and abundance sensitivity are maintained, at the typical low levels of a quadrupole ICP-MS. The presentation will describe the layout of an ICP-MS designed for highest sensitivity and show by means of application examples like laser ablation ICP-MS and liquid analysis the performance for isotope ratio analyses.

  6. Integrated modelling of enhanced in situ biodenitrification in a fractured aquifer: biogeochemistry and isotope geochemistry

    NASA Astrophysics Data System (ADS)

    Rodríguez-Escales, Paula; Folch, Albert; van Breukelen, Boris M.; Vidal-Gavilan, Georgina; Soler, Albert

    2014-05-01

    Enhanced in-situ biodenitrification is a feasible technology to recovery groundwater polluted by nitrates and achieves drinking water standards. Under optimum conditions, nitrate is reduced by autochthonous bacteria trough different reactions until arrive to harmless dinitrogen gas. Isotopic fractionation monitoring in field applications allows knowing the exact degree and the real scope of this technology. Using the Rayleigh equation the change in the isotope ratio of the nitrate molecule (δ15N-NO3-, δ18O-NO3-) is related to the fraction of molecules remaining as a result of biodenitrification. However, Rayleigh application at field scale is sometimes limited due to other processes involved during groundwater flow such as dispersion or adsorption and geological media heterogeneities that interferes in concentration values. Then, include isotope fractionation processes in reactive transport models is a useful tool to interpret and predict data from in-situ biodenitrification. We developed a reactive transport model of enhanced in situ application at field scale in a fractured aquifer that considers biogeochemical processes as well as isotope fractionation to enable better monitoring and management of this technology. Processes considered were: microbiological- exogenous and endogenous nitrate and sulfate respiration coupled with microbial growth and decay, geochemical reactions (precipitation of calcite) and isotopic fractionation (δ15N-NO3-; δ18O- NO3- and carbon isotope network). The 2-D simulations at field scale were developed using PHAST code. Modeling of nitrate isotope geochemistry has allowed determining the extent of biodenitrification in model domain. We have quantified which is the importance in decreasing of nitrate concentrations due to biodegradation (percentage of biodegradation, 'B%') and due to dilution process (percentage of dilution, 'D%'). On the other hand, the stable carbon isotope geochemistry has been modeled. We have considered the

  7. Isotope Geochemistry Survey in Ierissos Gulf Basin, North Greece

    NASA Astrophysics Data System (ADS)

    Chantzi, Paraskevi; Dotsika, Elissavet; Raco, Brunella

    2016-10-01

    Major element chemistry of water samples in Ierissos gulf basin is dominated by Ca2+, Mg2+ and HCO3 - ions. Water rock interaction is an important mechanism in the mineralization of waters. A link between Skouries and Gomati samples (Mg-HCO3) was detected reflecting the well documented M. Panagia-Gomati fault. In Neochori and M. Panagia samples were identified fluids with different origin. Regarding surface waters, extended bicarbonates action of meteoric waters and reductive conditions, probably control As concentration in surface water. Generally, surface waters in Kokkinolakas basin exceed the WHO limits for As, Sb, Cr, Ni, Cd, Pb, Mn, Fe in great rates as natural immobilization mechanisms are suspended.

  8. Pb isotopic composition of Paleozoic sediments derived from the Appalachian orogen

    SciTech Connect

    Krogstad, E.J. . Dept. of Geology)

    1993-03-01

    Differences in [sup 207]Pb/[sup 204]Pb at restricted ranges of [sup 206]Pb/[sup 204]Pb are robust indicators of differences in the earliest history of crust or mantle reservoirs, surviving later changes in U/Pb that may be due to melting, metamorphism, or sedimentary reworking. Ayuso and Bevier (1991) have used the [sup 207]Pb/[sup 204]Pb differences between Late Paleozoic granites in the N. Appalachians to trace their sources in either Laurentian (Grenville) lithosphere, or docked (Avalonian) lithosphere. If the Pb isotopic composition of Avalonian lithosphere is unique to that source among all lithospheric reservoirs in the Appalachian orogeny, the sediments shed off the orogen should record the first appearance of rocks with this extraneous Pb isotopic composition as they become accreted. The high [sup 207]Pb/[sup 204]Pb at similar [sup 206]Pb/[sup 204]Pb that may be indicative of all outboard terranes occurs in sedimentary rocks younger than middle Ordovician in New York and Maine, and younger than Ordovician in Virginia. Older sediments (Hadrynian, Cambrian), as well as autochthonous basement and paraautochonous basement slices, have lower [sup 207]Pb/[sup 204]Pb at similar [sup 206]Pb/[sup 204]Pb. The low [sup 207]Pb/[sup 204]Pb at similar [sup 206]Pb/[sup 204]Pb shown by these rocks may be a locally diagnostic signature of Late Proterozoic Laurentian lithosphere. The high [sup 207]Pb/[sup 204]Pb at similar [sup 206]Pb/[sup 204]Pb may be a locally diagnostic signature of Late Proterozoic accreted terranes. Rocks with accreted terrane Pb isotopic composition became dominant in the provenance of sediments along the strike of the Appalachian orogen by middle Ordovician time.

  9. Oxygen isotope geochemistry of mafic magmas at Mt. Vesuvius

    NASA Astrophysics Data System (ADS)

    Dallai, Luigi; Raffaello, Cioni; Chiara, Boschi; Claudia, D'oriano

    2010-05-01

    Pumice and scoria from different eruptive layers of Mt. Vesuvius volcanic products contain mafic minerals consisting of High-Fo olivine and Diopsidic Pyroxene. These phases were crystallized in unerupted trachibasaltic to tephritic magmas, and were brought to surface by large phonolitic/tephri-phonolitic (e.g. Avellino and Pompei) and/or of tephritic and phono-tephritic (Pollena) eruptions. A large set of these mm-sized crystals was accurately separated from selected juvenile material and measured for their chemical compositions (EPMA, Laser Ablation ICP-MS) and 18O/16O ratios (conventional laser fluorination) to constrain the nature and evolution of the primary magmas at Mt. Vesuvius. Uncontaminated mantle δ18O values are hardly recovered in Italian Quaternary magmas, mostly due to the widespread occurrence of crustal contamination of the primary melts during their ascent to the surface (e.g. Alban Hills, Ernici Mts., and Aeolian Islands). At Mt. Vesuvius, measured olivine and clinopyroxene share quite homogeneous chemical compositions (Olivine Fo 85-90 ; Diopside En 45-48, respectively), and represent phases crystallized in near primary mafic magmas. Trace element composition constrains the near primary nature of the phases. Published data on volatile content of melt inclusions hosted in these crystals reveal the coexistence of dissolved water and carbon dioxide, and a minimum trapping pressure around 200-300 MPa, suggesting that crystal growth occurred in a reservoir at about 8-10 km depth. Recently, experimental data have suggested massive carbonate assimilation (up to about 20%) to derive potassic alkali magmas from trachybasaltic melts. Accordingly, the δ18O variability and the trace element content of the studied minerals suggest possible contamination of primary melts by an O-isotope enriched, REE-poor contaminant like the limestone of Vesuvius basement. Low, nearly primitive δ18O values are observed for olivine from Pompeii eruption, although still

  10. Metal(loid) distribution and Pb isotopic signatures in the urban environment of Athens, Greece.

    PubMed

    Kelepertzis, Efstratios; Komárek, Michael; Argyraki, Ariadne; Šillerová, Hana

    2016-06-01

    Lead concentrations and isotopic compositions of contaminated urban soils and house dusts from Athens, Greece, have been determined to identify possible sources of Pb contamination and examine relationships between these two environmental media. Different soil particle sizes (<2000 μm, <200 μm, <100 μm, <70 μm, <32 μm) and chemical fractions (total, EDTA-extractable and acetic acid-extractable (HAc)) were analyzed for their Pb content and isotopic composition. Metal(loid)s (Pb, Zn, Cu, As, Ni, Cr, Mn, Fe) are significantly enriched in the finest fraction. The Pb isotopic compositions were similar for the different soil particle size fractions and different chemical extractions. The HAc extraction proved to be a useful procedure for tracing anthropogenic Pb in urban soil. The range of (206)Pb/(207)Pb ratios (1.140-1.180) in Athens soil suggests that the Pb content represents an accumulated mixture of Pb deposited from past vehicular emissions and local natural sources. The contribution of anthropogenic Pb to total soil Pb ranged from 36% to 95%. The Pb isotopic composition of vacuum house dusts ((206)Pb/(207)Pb = 1.1.38-1.167) from Athens residents is mostly comparable to that of urban soil suggesting that exterior soil particles are transferred into homes. As a result, anthropogenic Pb in house dust from Athens urban environment principally originated from soil particles containing Pb from automobile emissions (former use of leaded gasoline).

  11. Threshold photoneutron cross sections for {sup 208,207,206}Pb isotopes

    SciTech Connect

    Kondo, T.; Utsunomiya, H.; Akimune, H.; Yamagata, T.; Iwamoto, C.; Kamata, M.; Itoh, O.; Toyokawa, H.; Lui, Y.-W.

    2010-06-01

    Photoneutron cross sections for three Pb isotopes ({sup 206}Pb, {sup 207}Pb, {sup 208}Pb) near neutron threshold were measured with the laser inverse-Compton scattering gamma rays at the National Institute of Advanced Industrial Science and Technology. The cross section data are presented.

  12. Petrogenesis and origin of modern Ethiopian rift basalts: Constraints from isotope and trace element geochemistry

    NASA Astrophysics Data System (ADS)

    Ayalew, D.; Jung, S.; Romer, R. L.; Kersten, F.; Pfänder, J. A.; Garbe-Schönberg, D.

    2016-08-01

    The source of continental rift-related basalts and their relation to rifting processes is a continuous matter of debate. We present major and trace element and Sr, Nd, Hf and Pb isotope data for axial rift basalts from eight volcanic centres (Ayelu, Hertali, Dofan, Fantale, Kone, Bosetti and Gedemsa, from NE to SW) in Afar and Main Ethiopian Rift (MER) to assess their source regions and their genetic relationships. These lavas have geochemical characteristics, i.e., a peak at Ba, Nb and troughs at K and Rb in primitive mantle-normalised multielement diagrams, which are consistent with predominant melting of an amphibole-bearing lithospheric mantle. However, the isotopic compositions for these lavas are heterogeneous (87Sr/86Sr = 0.70354-0.70431, 143Nd/144Nd = 0.51280-0.51294, 176Hf/177Hf = 0.28301-0.28315, 206Pb/204Pb = 18.48-19.31, 207Pb/204Pb = 15.53-15.62, 208Pb/204Pb = 38.61-39.06) and require various mantle reservoirs with distinctive isotopic signatures. The range of isotopic compositions requires the involvement of three distinct source components from the asthenospheric and veined lithospheric mantle. Progressive rifting leads to lithosperic thinning and upwelling of hot asthenospheric mantle, which induces melting of the veined lithospheric mantle. The trace element characteristics of the lavas are dominated by the vein material, which has a higher trace element content than the surrounding mantle. The isotopic composition of the vein material, however, is not very different from the ambient mantle, giving rise of apparent uncoupling of trace element and isotope constraints for the melt source. The uprising basaltic liquids in part inherit a lithospheric trace element signature, while their isotopic compositions are mostly unaffected due to short residence times within the lithosphere in context with progressive rifting and lithospheric thinning. Thus, the geochemical and isotope data are consistent with a multi-component source prevailing beneath the Afar

  13. Mineralogy and stable isotope geochemistry of hydrothermally altered oceanic rocks

    USGS Publications Warehouse

    Stakes, D.S.; O'Neil, J.R.

    1982-01-01

    Mineralogical and isotopic variations observed in altered glassy and crystalline rocks from the East Pacific Rise and the Mid-Atlantic Ridge provide information about the temperatures of alteration and seawater/rock ratios for various hydrothermal regimes within the oceanic crust. A systematic increase in alteration temperature is evident for the glassy rocks in the sequence: (1) nontronite and celadonite vesicle fillings (35??C), (2) saponite-rich pillow breccias (130-170??C), (3) calcite-rich greenstone breccias and epidote-rich greenstone (200-350??C). These results include the highest temperatures thus far reported for saponite formation. The "seawater-dominated" hydrothermal alteration process that formed the saponite-rich pillow breccias is characterized by high water/rock ratios (>50:1), low to moderate temperatures, a seawater origin of most of the carbon in vein calcites (??13 C ??? 0) and the predominance of Fe-rich saponite and calcite as secondary phases. Greenstones (chlorite-quartz-epidote) and greenstone breccias (chlorite-quartz-albite-calcite) are altered in a "rock-dominated" system with lower water/rock ratios (50:1 to < 1:1), higher temperatures, and vein calcites with carbon that is principally of magmatic origin (??13 C ??? -4). The crystalline rocks (diabase, gabrro, and metagabbro) are affected to varying degrees by pervasive high-temperature seawater interactions that commence soon after solidification, producing varying proportions of fine-grained secondary minerals including talc, smectite, chlorite, vermiculite, actinolite, and sodic plagioclase. Hydrothermal solutions, derived from alteration of the crystalline rocks, are of the appropriate temperature and isotopic composition to alter the overlying glassy rocks to the observed mineralogies as well as being the source of metal-rich deposits associated with the oceanic spreading centers. ?? 1982.

  14. Geochemistry

    ERIC Educational Resources Information Center

    Brett, Robin; Hanshaw, Bruce B.

    1978-01-01

    The past year has seen the development of certain fields of geochemical research including Nd-Sm isotope studies of meteorites and ancient terrestrial rocks; the use of the consortium approach of assembling a multidisciplined team to tackle a problem; and the handling and analysis of small quantities of materials. (Author/MA)

  15. Monitoring Lead (Pb) Pollution and Identifying Pb Pollution Sources in Japan Using Stable Pb Isotope Analysis with Kidneys of Wild Rats

    PubMed Central

    Nakata, Hokuto; Nakayama, Shouta M. M.; Oroszlany, Balazs; Ikenaka, Yoshinori; Mizukawa, Hazuki; Tanaka, Kazuyuki; Harunari, Tsunehito; Tanikawa, Tsutomu; Darwish, Wageh Sobhy; Yohannes, Yared B.; Saengtienchai, Aksorn; Ishizuka, Mayumi

    2017-01-01

    Although Japan has been considered to have little lead (Pb) pollution in modern times, the actual pollution situation is unclear. The present study aims to investigate the extent of Pb pollution and to identify the pollution sources in Japan using stable Pb isotope analysis with kidneys of wild rats. Wild brown (Rattus norvegicus, n = 43) and black (R. rattus, n = 98) rats were trapped from various sites in Japan. Mean Pb concentrations in the kidneys of rats from Okinawa (15.58 mg/kg, dry weight), Aichi (10.83), Niigata (10.62), Fukuoka (8.09), Ibaraki (5.06), Kyoto (4.58), Osaka (4.57), Kanagawa (3.42), and Tokyo (3.40) were above the threshold (2.50) for histological kidney changes. Similarly, compared with the previous report, it was regarded that even structural and functional kidney damage as well as neurotoxicity have spread among rats in Japan. Additionally, the possibility of human exposure to a high level of Pb was assumed. In regard to stable Pb isotope analysis, distinctive values of stable Pb isotope ratios (Pb-IRs) were detected in some kidney samples with Pb levels above 5.0 mg/kg. This result indicated that composite factors are involved in Pb pollution. However, the identification of a concrete pollution source has not been accomplished due to limited differences among previously reported values of Pb isotope composition in circulating Pb products. Namely, the current study established the limit of Pb isotope analysis for source identification. Further detailed research about monitoring Pb pollution in Japan and the demonstration of a novel method to identify Pb sources are needed. PMID:28075384

  16. Monitoring Lead (Pb) Pollution and Identifying Pb Pollution Sources in Japan Using Stable Pb Isotope Analysis with Kidneys of Wild Rats.

    PubMed

    Nakata, Hokuto; Nakayama, Shouta M M; Oroszlany, Balazs; Ikenaka, Yoshinori; Mizukawa, Hazuki; Tanaka, Kazuyuki; Harunari, Tsunehito; Tanikawa, Tsutomu; Darwish, Wageh Sobhy; Yohannes, Yared B; Saengtienchai, Aksorn; Ishizuka, Mayumi

    2017-01-10

    Although Japan has been considered to have little lead (Pb) pollution in modern times, the actual pollution situation is unclear. The present study aims to investigate the extent of Pb pollution and to identify the pollution sources in Japan using stable Pb isotope analysis with kidneys of wild rats. Wild brown (Rattus norvegicus, n = 43) and black (R. rattus, n = 98) rats were trapped from various sites in Japan. Mean Pb concentrations in the kidneys of rats from Okinawa (15.58 mg/kg, dry weight), Aichi (10.83), Niigata (10.62), Fukuoka (8.09), Ibaraki (5.06), Kyoto (4.58), Osaka (4.57), Kanagawa (3.42), and Tokyo (3.40) were above the threshold (2.50) for histological kidney changes. Similarly, compared with the previous report, it was regarded that even structural and functional kidney damage as well as neurotoxicity have spread among rats in Japan. Additionally, the possibility of human exposure to a high level of Pb was assumed. In regard to stable Pb isotope analysis, distinctive values of stable Pb isotope ratios (Pb-IRs) were detected in some kidney samples with Pb levels above 5.0 mg/kg. This result indicated that composite factors are involved in Pb pollution. However, the identification of a concrete pollution source has not been accomplished due to limited differences among previously reported values of Pb isotope composition in circulating Pb products. Namely, the current study established the limit of Pb isotope analysis for source identification. Further detailed research about monitoring Pb pollution in Japan and the demonstration of a novel method to identify Pb sources are needed.

  17. Pb, Sr, and Nd isotopes in basalts and sulfides from the Juan de Fuca Ridge

    NASA Technical Reports Server (NTRS)

    Hegner, E.; Tatsumoto, M.

    1987-01-01

    Isotopic Pb, Sr, and Nd data were collected by the Alvin submersible from seven basalt glasses in the southern Juan de Fuca Ridge (JFR), giving similar ratios for Pb-206/Pb-204 of about 18.45, for Pb-207/Pb-204 of about 15.47, for Pb-208/Pb-204 of about 37.81, for Sr-87/Sr-86 of about 0.70249, and for Nd-143/Nd-144 of about 0.51315. Data suggest that the basalts are all cogenetic, and that four of the samples are also comagmatic. It is concluded that isotopic data for the JFR and seamount basalts provide additional support for the mantle blob cluster model (Allegre et al., 1984), suggesting the involvement of multiple components in the genesis of ridge basalts, and including an unusual end-member that has nonradiogenic Sr and variable Pb-206/Pb-204 isotopic compositions.

  18. Thermal Water's Isotope Geochemistry Study of Evros Area, NE Greece

    NASA Astrophysics Data System (ADS)

    Elissavet, Dotsika; Paraskevi, Chantzi

    2016-10-01

    Thermal waters from Evros area were collected and subjected to chemical and isotopic analysis in order to understand all the physicochemical mechanisms (mixing, dilution, precipitating) that contribute to the shallow and deep geothermal water tables and determine the origin of these fluids as well as their mineralization. Physicochemical characteristics EC, T°C, pH was determined at the field. The ionic concentrations of samples indicate solutions with high salinity. Two chemical water types were arisen: Na-SO4 concerning low temperatures and shallow aquifers and Na- Cl concerning high temperatures and deeper geothermal circulation. The ratio Br/Cl definitely considered marine origin indicator is the same as the sea confirming the involvement of the seawater in the geothermal system. The marine component and water-rock interaction process under high temperatures seem to contribute to the mineralization of thermal waters. Moreover, water-rock interaction process is also responsible for the alternation of δ18O values. Geothermometers concluded to a middle enthalpy geothermal field.

  19. Pb Concentration and Stable PB Isotopes in Dated-Core Sediments in the Ulleung Basin, East/japan Sea

    NASA Astrophysics Data System (ADS)

    Woo, J.; Choi, M.; Kim, D.

    2008-12-01

    This study investigated temporal and spatial variation of Pb and stable Pb isotopes accumulated in Ulleung Basin core sediments (12) using MC ICP/MS in order to identify the sources of anthropogenic Pb in the East/Japan Sea. Leached (1M HCl) Pb concentration and isotope ratios (207Pb/206Pb and 208Pb/206Pb) ware constant at around 20 mg/kg and 0.845 and 2.092 from 1700 to 1930 year, respectively and increased steadily up to 40 mg/kg and 0.873 to 2.129 at the beginning of 2000s, increased up to twice in concentration and as much as 3.31% and 1.64%. On the other hand, residual Pb concentrations were nearly constant for past 400 yrs. From the vertical profiles of Pb concentration and two end-members mixing model, anthropogenic Pb concentration and isotope ratios were estimated. The transport pathways of anthropogenic Pb could be estimated from 1) the comparison between the inventories of excess 210Pb in each sediment column and the input fluxes from the atmosphere and seawater column, 2) between the accumulation rate of anthropogenic Pb and mass accumulation rate of sediments. From the detailed evaluation for the pathways and isotope ratios of anthropogenic Pb, we proposed probable source of anthropogenic Pb. Pb emission by coal burning from the China and Korea initiated the accumulation of anthropogenic Pb in the sediments of East/Japan Sea from 1930s. The accumulation of Pb increased by the addition of anti-nocking agents from both countries untill beginning of 1990s, but from the middle of 1990s to the present, the phase-out of gasoline additives and the rapid increase of coal burning from China maintained the atmospheric Pb levels in the Ulleung basin nearly similar to before. However the local sources (e.g. ocean dumping) within this basin might take an important role in the rapid increase of anthropogenic Pb accumulation in slope areas from the middle of 1990s.

  20. A century long sedimentary record of anthropogenic lead (Pb), Pb isotopes and other trace metals in Singapore.

    PubMed

    Chen, Mengli; Boyle, Edward A; Switzer, Adam D; Gouramanis, Chris

    2016-06-01

    Reconstructing the history of metal deposition in Singapore lake sediments contributes to understanding the anthropogenic and natural metal deposition in the data-sparse Southeast Asia. To this end, we present a sedimentary record of Pb, Pb isotopes and eleven other metals (Ag, As, Ba, Cd, Co, Cr, Cu, Ni, Tl, U and Zn) from a well-dated sediment core collected near the depocenter of MacRitchie Reservoir in central Singapore. Before the 1900s, the sedimentary Pb concentration was less than 2 mg/kg for both soil and sediment, with a corresponding (206)Pb/(207)Pb of ∼1.20. The Pb concentration increased to 55 mg/kg in the 1990s, and correspondingly the (206)Pb/(207)Pb decreased to less than 1.14. The (206)Pb/(207)Pb in the core top sediment is concordant with the (206)Pb/(207)Pb signal of aerosols in Singapore and other Southeast Asian cities, suggesting that Pb in the reservoir sediment was mainly from atmospheric deposition. Using the Pb concentration in the topmost layer of sediment, the estimated atmospheric Pb flux in Singapore today is ∼1.6 × 10(-2) g/m(2) yr. The concentrations of eleven other metals preserved in the sediment were also determined. A principal component analysis showed that most of the metals exhibit an increasing trend towards 1990s with a local concentration peak in the mid-20(th) century.

  1. Tree rings as Pb pollution archives? A comparison of 206Pb/207Pb isotope ratios in pine and other environmental media.

    PubMed

    Bindler, Richard; Renberg, Ingemar; Klaminder, Jonatan; Emteryd, Ove

    2004-02-05

    Tree rings, if validated as an environmental archive for pollution, would provide a convenient, geographically widespread archive for studying the temporal and spatial distribution of atmospheric pollutants. We collected tree-ring records from Scots pine (Pinus sylvestris L.), ranging in age from 100 to 300 years and from one spruce (Picea abies), from sites in southern and northern Sweden and analyzed their stable lead isotopic composition (206Pb/207Pb). These results are compared to the Pb isotopic composition in soil profiles from each of the sites and temporal changes in the 206Pb/207Pb ratio in peat and lake sediment deposits in Sweden. The mineral soils at each site are characterized by high 206Pb/207Pb ratios (> 1.35), while the ratios in the mor layer are low (1.14-1.16) and characterized by atmospheric lead pollution. The 206Pb/207Pb ratios of the tree rings, typically approximately 1.18-1.20, indicate a significant (10-30%) contribution of Pb derived from the underlying mineral soil. While peat and lake sediment records show that the 206Pb/207Pb ratio of atmospheric deposition has varied over time, with a pronounced trough between approximately 1930 and 1990, the tree rings show no similar trend. Further comparison of published Pb isotope data from other tree-ring records with time series from peat bogs and herbarium samples also shows poor agreement, and indicates that tree rings always contain a mixture of pollution Pb and Pb from the underlying mineral soil. The majority of Pb in the wood is derived from atmospheric pollution either directly, through aerial interception, or indirectly, through uptake from the large pool of accumulated pollution Pb in the soil. Since the Pb isotope ratios of the wood indicate that some natural Pb is taken up into the tree, then it must also be concluded that some fraction of the pollution Pb in the wood is likewise taken up from the forest soil. Based on the Pb isotope analyses, we can only conclude that dendrochemical

  2. Trace Metals, Rare Earths, Carbon and Pb Isotopes as Proxies of Environmental Catastrophe at the Permian - Triassic Boundary in Spiti Himalayas, India

    NASA Astrophysics Data System (ADS)

    Ghosh, N.; Basu, A. R.; Garzione, C. N.; Ghatak, A.; Bhargava, O. N.; Shukla, U. K.; Ahluwalia, A. D.

    2015-12-01

    Himalayan sediments from Spiti Valley, India preserve geochemical signatures of the Permian - Triassic (P-Tr) mass extinction in the Neo-Tethys Ocean. We integrate new sedimentological and fossil record with high-resolution geochemical-isotopic data from Spiti that reveals an ecological catastrophe of global proportions. Trace elements of U, Th, Nb, Ta, Zr, Hf, the rare earths (REE) and carbon, oxygen and lead isotopes measured across the P-Tr boundary in Spiti are used as proxies for evaluating abrupt changes in this continental shelf environment. δ13Corg excursions of 2.4‰ and 3.1‰ in Atargu and Guling P-Tr sections in Spiti Valley are associated with an abrupt fall of biological productivity while δ13Ccarb and δ18Ocarb record of these sediments shows effects of diagenesis. Here, the P-Tr boundary is compositionally distinct from the underlying Late Permian gray shales, as a partly gypsiferous ferruginous layer that allows additional geochemical-isotopic investigation of sedimentary sources. Conspicuous Ce - Eu anomalies in the light REE-enriched Late Permian shales reflect the source composition of the adjacent Panjal Trap basalts of Kashmir. An abrupt change of this source to continental crust is revealed by Nb - Ta and Zr - Hf anomalies at the P-Tr ferruginous layer and continuing through the overlying Early Triassic carbonate rocks. Pb concentration and isotope ratios of 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb identify changes in the sedimentary element flux, distinguishing the Late Permian shales from the distinct siliciclastic continental crustal signature in the Early Triassic carbonates. These geochemical-isotopic constraints on the sedimentary geochemistry of one of the most critical transitions in geological record establish the utility of multi-proxy datasets for paleoenvironmental reconstructions.

  3. The Pb isotopic record of historical to modern human lead exposure.

    PubMed

    Kamenov, George D; Gulson, Brian L

    2014-08-15

    Human teeth and bones incorporate trace amounts of lead (Pb) from the local environment during growth and remodeling. Anthropogenic activities have caused changes in the natural Pb isotopic background since historical times and this is reflected in the Pb isotopes of historical European teeth. Lead mining and use increased exponentially during the last century and the isotopic compositions of modern human teeth reflect the modern anthropogenic Pb. USA teeth show the most radiogenic Pb and Australian teeth show the least radiogenic Pb, a result of different Pb ores used in the two regions. During the last century the Australian Pb was exported to Europe, Asia, South America, and Africa, resulting in swamping of the local environmental Pb signal by the imported Pb. As a result, the modern human teeth in Europe show a significant drop to lower isotopic values compared with historical times. Similarly, modern human teeth in other regions of the world show similar Pb isotopic ratios to modern European teeth reflecting the Pb imports. The specific pattern of human Pb exposure allows us to use the Pb isotopic signal recorded in the skeleton as a geo-referencing tool. As historical European teeth show a distinct Pb signal, we can identify early European skeletal remains in the New World and likely elsewhere. In modern forensic investigations we can discriminate to some extent Eastern Europeans from Western and Northern Europeans. Australians can be identified to some extent in any region in the world, although there is some overlap with Western European individuals. Lead isotopes can be used to easily identify foreigners in the USA, as modern USA teeth are distinct from any other region of the world. By analogy, USA individuals can be identified virtually in any other region of the world.

  4. Pb, Sr, Nd and Hf isotopic evidence of multiple sources for Oahu, Hawaii basalts

    NASA Technical Reports Server (NTRS)

    Stille, P.; Unruh, D. M.; Tatsumoto, M.

    1983-01-01

    Pb, Sr, Nd and Hf isotopic compositions of Oahu volcanics indicate that the three principal volcanic series on Oahu Koolau, Honolulu and Waianae - were derived from isotopically distinct sources. Honolulu and Waianae basalts plot on the Nd-Pb-Sr 'mantle plane' whereas Koolau data plot distinctly below the plane.

  5. The Use of Lead Isotope and Rare Earth Element Geochemistry for Forensic Geographic Provenancing

    NASA Astrophysics Data System (ADS)

    Carey, A.; Darrah, T.; Harrold, Z.; Prutsman-Pfeiffer, J.; Poreda, R.

    2008-12-01

    Lead isotope and rare earth element composition of modern human bones are analyzed to explore their utility for geographical provenancing. DNA analysis is the standard for identification of individuals. DNA analysis requires a DNA match for comparison. Thus, DNA analysis is of limited use in cases involving unknown remains. Trace elements are incorporated into bones and teeth during biomineralization, recording the characteristics of an individual's geochemical environment. Teeth form during adolescence, recording the geochemical environment of an individual's youth. Bones remodel throughout an individual's lifetime. Bones consist of two types of bone tissue (cortical and trabecular) that remodel at different rates, recording the geochemical environment at the time of biomineralization. Cortical bone tissue, forming the outer surface of bones, is dense, hard tissue that remodels in 25-30 yrs. Conversely, trabecular bone tissue, the inner cavity of bones, is low density, porous and remodels in 2-5 years. Thus, analyzing teeth and both bone tissues allows for the development of a geographical time line capable of tracking immigration patterns through time instead of only an individual's youth. Geochemical isotopic techniques (Sr, O, C, N) have been used for geographical provenancing in physical anthropology. The isotopic values of Sr, C, O, N are predominantly a function of soil compositions in areas where food is grown or water is consumed. Application of these provenancing techniques has become difficult as an individual's diet may reflect the isotopic composition of foods obtained at the local grocer as opposed to local soil compositions. Thus, we explore the use of REEs and Pb isotopes for geographical provenancing. Pb and REEs are likely more reliable indicators of modern geographical location as their composition are high in bio-available sources such as local soils, atmospheric aerosols, and dust as opposed to Sr, C, O, N that are controlled by food and

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

    USGS Publications Warehouse

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

    2004-01-01

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

  7. Evidence of a connection between the Atlantic and Mediterranean during the Messinian Salinity Crisis from Pb and Nd isotopes

    NASA Astrophysics Data System (ADS)

    Modestou, Sevasti; Gutjahr, Marcus; Fietzke, Jan; Rodés, Ángel; Frank, Martin; Bolhão Muiños, Susana; Ellam, Rob; Flecker, Rachel

    2014-05-01

    Prior to the opening of the Gibraltar Strait at 5.33 Ma, the Betic (southern Spain) and Rifian (northern Morocco) marine palaeocorridors linked the Mediterranean to the Atlantic. Although the central regions of these corridors have been heavily eroded due to uplift, evidence published to date indicates that both closed before the onset of the Messinian Salinity Crisis (MSC; 5.97 to 5.33 Ma [1, 2]). However, pre-MSC corridor closure presents a paradox, as the volume of halite deposited within the Mediterranean basin requires several times the volume of seawater contained in the basin itself. In this regard, radiogenic isotopes such as Sr, Pb, and Nd can provide key information about the timing of exchange through the Betic and Rifian palaeogateways. Due to the resolvable isotopic difference in Nd isotope signatures of outgoing Mediterranean and incoming Atlantic water masses, demonstrated both for the present day as well as the past environment, this isotope system can be used to identify exchange between these two water bodies. Although less well constrained to date, the Pb isotope system can be used in a similar manner due to its short residence time in seawater and interbasin variability. A high resolution Pb isotope record extracted using laser ablation from ferromanganese crust 3514-6 (recovered from the Lion Seamount, NE Atlantic, water depth 690-940 m) indicates a relatively constant Pb isotope signature before, during and after the MSC period. The previously published [3] Nd isotope record of crust 3514-6 corroborates that the crust was deposited in a current distinct from NE Atlantic Deep water or Antarctic Intermediate Water, the principal currents in the region of the Lion Seamount. The combined Pb and Nd isotope evolution suggests that Mediterranean Outflow Water (MOW) was continuously advected into the NE Atlantic during and after the MSC. Furthermore, preliminary Nd isotope records from Late Miocene sediments collected in the Sorbas Basin, Spain

  8. Lead (Pb) isotopic fingerprinting and its applications in lead pollution studies in China: a review.

    PubMed

    Cheng, Hefa; Hu, Yuanan

    2010-05-01

    As the most widely scattered toxic metal in the world, the sources of lead (Pb) observed in contamination investigation are often difficult to identify. This review presents an overview of the principles, analysis, and applications of Pb isotopic fingerprinting in tracing the origins and transport pathways of Pb in the environment. It also summarizes the history and current status of lead pollution in China, and illustrates the power of Pb isotopic fingerprinting with examples of its recent applications in investigating the effectiveness of leaded gasoline phase-out on atmospheric lead pollution, and the sources of Pb found in various environmental media (plants, sediments, and aquatic organisms) in China. The limitations of Pb isotopic fingerprinting technique are discussed and a perspective on its development is also presented. Further methodological developments and more widespread instrument availability are expected to make isotopic fingerprinting one of the key tools in lead pollution investigation.

  9. Combined Sr, Nd, Pb and Hf isotopic constraints on the origin of Shatsky Rise (NW Pacific)

    NASA Astrophysics Data System (ADS)

    Geldmacher, J.; Heydolph, K.; Murphy, D. T.; Romanova, I.; Mahoney, J. J.; Hoernle, K.

    2012-12-01

    The submarine Shatsky Rise plateau in the northwest Pacific Ocean (ca. 1500 km east of Japan) formed during the Late Jurassic to Early Cretaceous. Based on magnetic reversals combined with bathymetric data, the three main volcanic edifices Tamu, Ori and Shirshov massifs are proposed to have successively formed by massive volcanism along a southwest-northeast moving, rapidly spreading triple junction. To investigate a proposed interaction of a possible mantle plume head with the spreading system, Shatsky Rise was drilled during IODP Expedition 324 in 2009 (Expedition 324 Scientists, 2010). Based on major and trace element compositions, the origin of the vast majority of the recovered rocks can be explained by derivation from a normal mid-ocean ridge basalt (MORB)-like source, although a distinct depletion in heavy rare earth elements implies that melting started at greater depth (Sano et al. in press). A small fraction of samples (all from Ori massif), however, exhibit higher ratios of highly over moderately incompatible trace element ratios indicating an enriched (plume?) source. We present compiled Sr, Nd, Pb and Hf isotope ratios from all three volcanic edifices of Shatsky Rise and will discuss them in the light of the new trace element study. Most isotope data overlap with Pacific MORB composition although regional variations can be seen. Whereas lavas from three drill sites on the oldest edifice, Tamu massif, yield fairly uniform compositions, a wider spread is found for lavas erupted on the younger edifices, Ori and Shirshov, suggesting that the source has become more heterogeneous with time (also consistent with the trace element data). This variation could reflect a decreasing degree of melting (and therefore less homogenization of inherent plume heterogeneities) or less effective stirring and mixing during the interaction of the spreading center with a waning plume head. Interestingly, lavas from the Ori and Shirshov massifs have generally lower 143Nd/144Nd

  10. Anorogenic nature of magmatism in the Northern Baikal volcanic belt: Evidence from geochemical, geochronological (U-Pb), and isotopic (Pb, Nd) data

    USGS Publications Warehouse

    Neymark, L.A.; Larin, A.M.; Nemchin, A.A.; Ovchinnikova, G.V.; Rytsk, E. Yu

    1998-01-01

    The Northern Baikal volcanic belt has an age of 1.82-1.87 Ga and extends along the boundary between the Siberian Platform and the Baikal foldbelt. The volcanic belt is composed of volcanics of the Akitkan Group and granitic rocks of the Irel and Primorsk complexes. The geochemistry of the rocks points to the intraplate anorogenic nature of the belt. U-Pb zircon dating of the Chuya granitoids revealed that they are older (2020-2060 Ma) than the Northern Baikal volcanic belt and, thus, cannot be regarded as its component. Data on the Pb isotopic system of feldspars from the granitoids confirm the contemporaneity of all volcanic rocks of the belt except the volcanics of the upper portion of the Akitkan Group (Chaya Formation). Our data suggest its possibly younger (???1.3 Ga) age. The isotopic Nd and Pb compositions of the acid volcanic rocks provide evidence of the heterogeneity of their crustal protoliths. The volcanics of the Malaya Kosa Formation have ??Nd(T) = -6.1, ??2 = 9.36, and were most probably produced with the participation of the U-depleted lower continental crust of Archean age. Other rocks of the complex show ??Nd(T) from -0.1 to -2.4, ??2 = 9.78, and could have been formed by the recycling of the juvenile crust. The depletion of the Malaya Kosa volcanics in most LILEs and HFSEs compared with other acid igneous rocks of the belt possibly reflects compositional differences between the Late Archean and Early Proterozoic crustal sources. The basaltic rocks of the Malaya Kosa Formation (??Nd varies from -4.6 to -5.4) were produced by either the melting of the enriched lithospheric mantle or the contamination of derivatives of the depleted mantle by Early Archean lower crustal rocks, which are not exposed within the area. Copyright ?? 1998 by MAEe Cyrillic signK Hay??a/Interperiodica Publishing.

  11. Heavy metals pollution and pb isotopic signatures in surface sediments collected from Bohai Bay, North China.

    PubMed

    Gao, Bo; Lu, Jin; Hao, Hong; Yin, Shuhua; Yu, Xiao; Wang, Qiwen; Sun, Ke

    2014-01-01

    To investigate the characteristics and potential sources of heavy metals pollution, surface sediments collected from Bohai Bay, North China, were analyzed for the selected metals (Cd, Cr, Cu, Ni, Pb, and Zn). The Geoaccumulation Index was used to assess the level of heavy metal pollution. Pb isotopic compositions in sediments were also measured to effectively identify the potential Pb sources. The results showed that the average concentrations of Cd, Cr, Cu, Ni, Pb, and Zn were 0.15, 79.73, 28.70, 36.56, 25.63, and 72.83 mg/kg, respectively. The mean concentrations of the studied metals were slightly higher than the background values. However, the heavy metals concentrations in surface sediments in Bohai Bay were below the other important bays or estuaries in China. The assessment by Geoaccumulation Index indicated that Cr, Zn, and Cd were classified as "the unpolluted" level, while Ni, Cu, and Pb were ranked as "unpolluted to moderately polluted" level. The order of pollution level of heavy metals was: Pb > Ni > Cu > Cr > Zn > Cd. The Pb isotopic ratios in surface sediments varied from 1.159 to 1.185 for (206)Pb/(207)Pb and from 2.456 to 2.482 for (208)Pb/(207)Pb. Compared with Pb isotopic radios in other sources, Pb contaminations in the surface sediments of Bohai Bay may be controlled by the mix process of coal combustion, aerosol particles deposition, and natural sources.

  12. Strontium isotope geochemistry of groundwaters and streams affected by agriculture, Locust Grove, MD

    USGS Publications Warehouse

    Böhlke, J.K.; Horan, M.

    2000-01-01

    The effects of agriculture on the isotope geochemistry of Sr were investigated in two small watersheds in the Atlantic coastal plain of Maryland. Stratified shallow oxic groundwaters in both watersheds contained a retrievable record of increasing recharge rates of chemicals including NO3/-, Cl, Mg, Ca and Sr that were correlated with increasing fertilizer use between about 1940 and 1990. The component of Sr associated with recent agricultural recharge was relatively radiogenic (87Sr/86Sr = 0.715) and it was overwhelming with respect to Sr acquired naturally by water-rock interactions in the oxidized, non-calcareous portion of the saturated zone. Agricultural groundwaters that penetrated relatively unoxidized calcareous glauconitic sediments at depth acquired an additional component of Sr from dissolution of early tertiary marine CaCO3 (87Sr/86Sr=0.708) while undergoing O2 reduction and denitrification. Ground-water discharge contained mixtures of waters of various ages and redox states. Two streams draining the area are considered to have higher 87Sr/86Sr ratios and NO3/- concentrations than they would in the absence of agriculture; however, the streams have consistently different 87Sr/86Sr ratios and NO3/- concentrations because the average depth to calcareous reducing (denitrifying) sediments in the local groundwater flow system was different in the two watersheds. The results of this study indicate that agriculture can alter significantly the isotope geochemistry of Sr in aquifers and streams and that the effects could vary depending on the types, sources and amounts of fertilizers added, the history of fertilizer use and groundwater residence times. (C) 2000 Elsevier Science Ltd.

  13. Isotope exchange between natural and anthropogenic Pb in the coastal waters of Singapore: exchange experiment, Kd model, and implications for the interpretation of coastal 210Pb data

    NASA Astrophysics Data System (ADS)

    Boyle, E. A.; Chen, M.; Zurbrick, C.; Carrasco, G. G.

    2015-12-01

    Observations from annually-banded corals and seawater samples show that marine lead (Pb) in the coastal waters of Singapore has an isotopic composition that does not match that of the anthropogenic aerosols in this region, unlike what is seen in most parts of the open ocean. The 206Pb/207Pb composition of Singaporean marine Pb is 1.18-1.20 whereas the local aerosols are 1.14-1.16. In order to explore this discrepancy further, we collected a large volume water from the Johor River estuary (flowing from Malaysia to the northern border of Singapore), added a distinct isotope spike (NBS981, 206Pb/207Pb =1.093) to an unfiltered sample, and followed the dissolved isotope composition of the mixture during the following two months. The initial dissolved Pb concentration was 18.3 pmol/kg with 206Pb/207Pb of 1.200. "Total dissolvable" Pb released after acidification of the in the unfiltered sample was 373 pmol/kg with 206Pb/207Pb of 1.199, indicating that there is a large particulate Pb reservoir with an isotopic composition comparable to regional crustal natural Pb. The isotope spike should have brought the dissolved 206Pb/207Pb to 1.162, but less than a day after isotope spiking, the dissolved Pb had risen to 1.181 and continued a slow increase to 1.197 over the next two months. This experiment demonstrates that Johor estuary particulate matter contains a large reservoir of exchangeable Pb that will modify the isotopic composition of deposited aeolian aerosol anthropogenic Pb. We have modeled the evolution of Pb and Pb isotopes in this experiment with a single Kd -type model that assumes that there are two or three different Pb reservoirs with different exchange time constants. This observation has implications for isotope equilibrium between high Pb/210Pb continental particles and low Pb/210Pb ocean waters - what is merely isotope equilibration may appear to be 210Pb scavenging.

  14. Large-scale tectonic cycles in Europe revealed by distinct Pb isotope provinces

    NASA Astrophysics Data System (ADS)

    Blichert-Toft, Janne; Delile, Hugo; Lee, Cin-Ty; Stos-Gale, Zofia; Billström, Kjell; Andersen, Tom; Hannu, Huhma; Albarède, Francis

    2016-10-01

    Lead isotopic systematics of U-poor minerals, such as sulfides and feldspars, can provide unique insights into the origin and evolution of continents because these minerals "freeze in" the Pb isotopic composition of the crust during major tectonothermal events, allowing the history of a continent to be told through Pb isotopes. Lead model ages constrain the timing of crust formation while time-integrated U/Pb, Th/Pb, and Th/U ratios shed light onto key geochemical processes associated with continent formation. Using ˜6800 Pb isotope measurements of primarily lead ores and minor K-feldspar, we mapped out the Pb isotope systematics across Europe and the Mediterranean. Lead model ages define spatially distinct age provinces, consistent with major tectonic events ranging from the Paleozoic to the Proterozoic and latest Archean. However, the regions defined by time-integrated U/Pb and Th/Pb ratios cut across the boundaries of age provinces, with high U/Pb systematics characterizing most of southern Europe. Magmatic influx, followed by segregation of dense sulfide-rich mafic cumulates, resulted in foundering of U- and Th-poor lower crust, thereby changing the bulk composition of the continental crust and leading to distinct time-integrated U-Th/Pb provinces. We show that the tectonic assembly of small crustal fragments leaves the crust largely undifferentiated, whereas the formation of supercontinents results in fundamental changes in the composition of the crust, identifiable in time and space by means of Pb isotope systematics. Observations based on Pb isotopes open up a new perspective on possible relationships between crustal thickness and geodynamic processes, in particular the role of crustal foundering into the mantle and the mechanisms responsible for the existence of cratons.

  15. Elucidating the magmatic history of the Austurhorn silicic intrusive complex (southeast Iceland) using zircon elemental and isotopic geochemistry and geochronology

    NASA Astrophysics Data System (ADS)

    Padilla, A. J.; Miller, C. F.; Carley, T. L.; Economos, R. C.; Schmitt, A. K.; Coble, M. A.; Wooden, J. L.; Fisher, C. M.; Vervoort, J. D.; Hanchar, J. M.

    2016-09-01

    The Austurhorn intrusive complex (AIC) in southeast Iceland comprises large bodies of granophyre and gabbro, and a mafic-silicic composite zone (MSCZ) that exemplifies magmatic interactions common in Icelandic silicic systems. Despite being one of Iceland's best-studied intrusions, few studies have included detailed analyses of zircon, a mineral widely recognized as a valuable tracer of the history and evolution of its parental magma(s). In this study, we employ high spatial resolution zircon elemental and isotopic geochemistry and U-Pb geochronology as tools for elucidating the complex construction and magmatic evolution of Austurhorn's MSCZ. The trace element compositions of AIC zircon crystals form a broad but coherent array that partly overlaps with the geochemical signature for zircons from Icelandic silicic volcanic rocks. Typical of Icelandic zircons, Hf concentrations are relatively low (<10,000 ppm) and Ti concentrations range from 5 to 40 ppm (Ti-in-zircon model temperatures = 761-981 °C). Zircon δ18O values vary from +2.2 to +4.8 ‰, consistent with magmatic zircons from other Icelandic silicic rocks, and preserve evidence for recycling of hydrothermally altered crust as a significant contribution to the generation of silicic magmas within the AIC. Zircon ɛ Hf values generally range from +11 to +15. This range overlaps with that of Icelandic basalts from off-rift settings as well as the least depleted rift basalts, suggesting that the AIC developed within a transitional rift environment. In situ zircon U-Pb ages yield a weighted mean of 6.52 ± 0.03 Ma for the entire complex, but span a range of ~320 kyr, from 6.35 ± 0.08 to 6.67 ± 0.06 Ma (2 σ SE). Gabbros and the most silicic units make up the older part of this range, while granophyres and intermediate units make up the younger part of the complex, consistent with field relationships. We interpret the ~320 kyr range in zircon ages to represent the approximate timescale of magmatic construction

  16. The isotope systematics of a juvenile intraplate volcano: Pb, Nd, and Sr isotope ratios of basalts from Loihi Seamount, Hawaii

    USGS Publications Warehouse

    Staudigel, H.; Zindler, A.; Hart, S.R.; Leslie, T.; Chen, C.-Y.; Clague, D.

    1984-01-01

    Sr, Nd, and Pb isotope ratios for a representative suite of 15 basanites, alkali basalts, transitional basalts and tholeiites from Loihi Seamount, Hawaii, display unusually large variations for a single volcano, but lie within known ranges for Hawaiian basalts. Nd isotope ratios in alkali basalts show the largest relative variation (0.51291-0.51305), and include the nearly constant tholeiite value ( ??? 0.51297). Pb isotope ratios show similarly large ranges for tholeiites and alkali basalts and continue Tatsumoto's [31] "Loa" trend towards higher 206Pb 204Pb ratios, resulting in a substantial overlap with the "Kea" trend. 206Pb 204Pb ratios for Loihi and other volcanoes along the Loa and Kea trends [31] are observed to correlate with the age of the underlying lithosphere suggesting lithosphere involvement in the formation of Hawaiian tholeiites. Loihi lavas display no correlation of Nd, Sr, or Pb isotope ratios with major element compositions or eruptive age, in contrast with observations of some other Hawaiian volcanoes [38]. Isotope data for Loihi, as well as average values for Hawaiian volcanoes, are not adequately explained by previously proposed two-end-member models; new models for the origin and the development of Hawaiian volcanoes must include mixing of at least three geochemically distinct source regions and allow for the involvement of heterogeneous oceanic lithosphere. ?? 1984.

  17. The 1998-2001 submarine lava balloon eruption at the Serreta ridge (Azores archipelago): Constraints from volcanic facies architecture, isotope geochemistry and magnetic data

    NASA Astrophysics Data System (ADS)

    Madureira, Pedro; Rosa, Carlos; Marques, Ana Filipa; Silva, Pedro; Moreira, Manuel; Hamelin, Cédric; Relvas, Jorge; Lourenço, Nuno; Conceição, Patrícia; Pinto de Abreu, Manuel; Barriga, Fernando J. A. S.

    2017-01-01

    The most recent submarine eruption observed offshore the Azores archipelago occurred between 1998 and 2001 along the submarine Serreta ridge (SSR), 4-5 nautical miles WNW of Terceira Island. This submarine eruption delivered abundant basaltic lava balloons floating at the sea surface and significantly changed the bathymetry around the eruption area. Our work combines bathymetry, volcanic facies cartography, petrography, rock magnetism and geochemistry in order to (1) track the possible vent source at seabed, (2) better constrain the Azores magma source(s) sampled through the Serreta submarine volcanic event, and (3) interpret the data within the small-scale mantle source heterogeneity framework that has been demonstrated for the Azores archipelago. Lava balloons sampled at sea surface display a radiogenic signature, which is also correlated with relatively primitive (low) 4He/3He isotopic ratios. Conversely, SSR lavas are characterized by significantly lower radiogenic 87Sr/86Sr, 206Pb/204Pb and 208Pb/204Pb ratios than the lava balloons and the onshore lavas from the Terceira Island. SSR lavas are primitive, but incompatible trace-enriched. Apparent decoupling between the enriched incompatible trace element abundances and depleted radiogenic isotope ratios is best explained by binary mixing of a depleted MORB source and a HIMU­type component into magma batches that evolved by similar shallower processes in their travel to the surface. The collected data suggest that the freshest samples collected in the SSR may correspond to volcanic products of an unnoticed and more recent eruption than the 1998-2001 episode.

  18. Hf-Nd Isotopic and Trace-Element Geochemistry of Global Subducting Sediments

    NASA Astrophysics Data System (ADS)

    Vervoort, J. D.; Plank, T.; Patchett, P. J.

    2001-12-01

    Ferromanganese nodules, crusts, and associated metalliferous clays have long been known to have anomalously high Lu/Hf ratios and highly radiogenic Hf relative to Nd (Patchett et al., 1984; White et al., 1986). These oceanic sediments are some of the few terrestrial materials where Hf and Nd isotopes deviate from the crust-mantle array. This distinctive isotopic signature, therefore, has the potential to trace the fate of oceanic sediments through the subduction zone and into the mantle. It has recently been suggested, for example, that pelagic sediments can be detected in some Hawaiian basalts (Blichert-Toft et al., 1999) and in volcanic rocks from the Luzon arc (Marini et al., 2000) based on their Hf-Nd isotopic compositions. The weak link in this approach, however, is that we do not know, in any quantitative way, how widespread this anomalous signature is in oceanic sediments, what compositions are responsible for this signature, or how volumetrically important these compositions are in terms of the total sediment flux into subduction zones and the mantle. Most marine sediments analyzed thus far have been collected on or near the ocean floor and constitute an incomplete and unrepresentative inventory of the sediment column bound for the subduction zone. There is some reason to suspect that much of the sediment flux is not particularly anomalous, either in terms of Lu/Hf ratios or Hf and Nd isotopic compositions. The most dominant sediment types entering many subduction zones (terrigenous and other continentally derived sediments), have normal Lu/Hf ratios and Hf-Nd isotopic compositions that are indistinguishable from the crust-mantle array. An examination is needed of the Hf-Nd isotopic composition of oceanic sediments, the major and trace-element geochemistry of global sediment flux, how such compositions may relate to Hf-Nd isotopic behavior, and potential Lu/Hf and Nd/Hf fractionation in subduction zones. In addition, the origin of the high Lu/Hf and

  19. A "Tail" Of Two Mines: Determining The Sources Of Lead In Mine Waters Using Pb Isotopes

    NASA Astrophysics Data System (ADS)

    Cousens, B. L.; Allen, D. M.; Lepitre, M. E.; Mortensen, J. K.; Gabites, J. E.; Nugent, M.; Fortin, D.

    2004-12-01

    Acid mine drainage can be a significant environmental problem in regions where mine tailings are exposed to surface water and shallow groundwater flow. Whereas high metal concentrations in surface waters and groundwaters indicate that metals are being mobilized, these data do not uniquely identify the source of the contamination. The isotopic composition of Pb in mine waters is a superb tracer of Pb sources, because the isotopic composition of ore Pb is usually significantly different from that of host rocks, other surficial deposits, and aerosols. We have investigated metal mobility at two abandoned Pb-Zn mines in different geological settings: the sediment-hosted Sullivan Mine in southeastern British Columbia, and the New Calumet Mine of western Quebec that is hosted in metamorphic rocks of the Grenville Province. Ores from both mines have homogeneous Pb isotopic compositions that are much less radiogenic than surrounding host rocks. At Sullivan, the Pb isotopic compositions of water samples define a mixing line between Sullivan ore and at least one other more radiogenic end-member. Water samples with high Pb concentrations (0.002 to 0.3 mg/L) generally are acidic and have Pb isotope ratios equal to Sullivan ore, whereas waters with low Pb contents have near-neutral pH and have variably more radiogenic Pb isotope ratios. Thus not all the waters collected in the study area originate from Sullivan ore or mining operations, as previously thought. The dominant source of ore Pb in mine waters are the waste rock dumps. Based on their isotopic compositions, host shales or aerosols from the local Pb smelter are potential sources of non-Sullivan ore Pb; local glacial tills are an unlikely source due to their heterogeneous Pb isotopic composition. Similarly, at the New Calumet mine, water samples collected in direct contact with either ore at the surface or tailings have high Pb concentrations (up to 0.02 mg/L) and Pb isotope ratios equal to New Calumet Pb-Zn ore. However

  20. Coupling meteorology, metal concentrations, and Pb isotopes for source attribution in archived precipitation samples.

    PubMed

    Graney, Joseph R; Landis, Matthew S

    2013-03-15

    A technique that couples lead (Pb) isotopes and multi-element concentrations with meteorological analysis was used to assess source contributions to precipitation samples at the Bondville, Illinois USA National Trends Network (NTN) site. Precipitation samples collected over a 16month period (July 1994-October 1995) at Bondville were parsed into six unique meteorological flow regimes using a minimum variance clustering technique on back trajectory endpoints. Pb isotope ratios and multi-element concentrations were measured using high resolution inductively coupled plasma-sector field mass spectrometry (ICP-SFMS) on the archived precipitation samples. Bondville is located in central Illinois, ~250km downwind from smelters in southeast Missouri. The Mississippi Valley Type ore deposits in Missouri provided a unique multi-element and Pb isotope fingerprint for smelter emissions which could be contrasted to industrial emissions from the Chicago and Indianapolis urban areas (~125km north and east, of Bondville respectively) and regional emissions from electric utility facilities. Differences in Pb isotopes and element concentrations in precipitation corresponded to flow regime. Industrial sources from urban areas, and thorogenic Pb from coal use, could be differentiated from smelter emissions from Missouri by coupling Pb isotopes with variations in element ratios and relative mass factors. Using a three endmember mixing model based on Pb isotope ratio differences, industrial processes in urban airsheds contributed 56±19%, smelters in southeast Missouri 26±13%, and coal combustion 18±7%, of the Pb in precipitation collected in Bondville in the mid-1990s.

  1. Pb isotopic study on soils from Domizio-Flegreo Littoral area, Napoli, Italy

    NASA Astrophysics Data System (ADS)

    Grezzi, G.; Ayuso, R. A.; Lima, A.; Albanese, S.; de Vivo, B.

    2009-04-01

    The Domizio - Flegreo Littoral area, together with the Agro Aversano area, are part of a Site of National Interest for pollution assessment. This area is located along the north coastal zone of the Campania region (Italy) and has an extension of about 855 Km2. We analyzed soils for heavy metal content in order to study and discriminate the impact of natural and anthropogenic sources. We collected 292 soil surface samples (5-15 cm depth) and produced maps showing the distribution of heavy metals in the soils. On the basis of the geographic distribution of heavy metals, 9 soil profiles were also collected for detailed examination (1 meter from surface). From each soil profile, we collected 10 soil samples (1/10 cm) in the urban and suburban areas of the littoral area. Also, we collected 8 groundwater samples likely associated with the soils. Pb isotope compositions of these soils and waters help to constrain the impact of anthropogenic and natural components on the soil profiles. Possible anthropogenic end-members include pesticides used in the area. Lead isotope compositions of soils known to contain anomalously high values of heavy metals were measured in order to determine the sources of the Pb and, by inference, sources of other metals that are likely to share similar geochemical behaviour in the surface environment (e.g., As). Acid-leach compositions of the soils represent Pb that is adsorbed to mineral surfaces, whereas residue compositions may reflect bedrock. Labile Pb (acid-leach fractions) from the soils shows a range in compositions of 207Pb/206Pb = 0.8275 to 0.8486, and 208Pb/206Pb = 2.0488 to 2.0873. The isotope values vary and decrease with depth. The Pb isotope ratios obtained on groundwater samples range from about 207Pb/206Pb = 0.8516 to 0.8636, 208Pb/206Pb = 2.0706 to 2.1064. The Pb isotope ratios in the soil profiles and groundwater are generally consistent with multiple sources that include anthropogenic Pb. Surface soil samples from Giugliano

  2. Zircon U-Pb-Hf isotopes, bulk-rock geochemistry and petrogenesis of Middle to Late Triassic I-type granitoids in the Xing'an Block, northeast China: Implications for early Mesozoic tectonic evolution of the central Great Xing'an Range

    NASA Astrophysics Data System (ADS)

    Yang, Hao; Ge, Wen-chun; Yu, Qian; Ji, Zheng; Liu, Xi-wen; Zhang, Yan-long; Tian, De-xin

    2016-04-01

    We report zircon U-Pb age data, Hf isotopes, and bulk-rock geochemical data for the Middle to Late Triassic granitoids in the Taerqi-Chabaqi-Kutihe region within the Xing'an Block of the central Great Xing'an Range, northeast China. Euhedral to subhedral zircon grains were extracted from the nine representative granitoids. These zircons exhibit oscillatory zoning typical of a magmatic origin. The zircon U-Pb determinations on the monzogranite, syenogranite and quartz diorite samples yielded ages between 244 Ma and 206 Ma, which essentially suggests that the magmatism in the Xing'an Block occurred during the Middle to Late Triassic period. Geochemically, these granitoids have SiO2 = 62.97-76.31 wt%, A/CNK = 1.03-1.51, and K2O/Na2O = 0.40-2.39, we infer that they belong to high-K calc-alkaline series and are peraluminous I-type granites in nature. The major and trace element systematics indicate that these granitoids have different origins. Among them, the 244 Ma syenogranite of Taerqi and the 230-206 Ma monzogranite and syenogranite of Kutihe were probably generated from partial melting of pre-existing juvenile arc-type rocks in a relatively shallow crustal level. The 210 Ma quartz diorite of Chabaqi likely originated from the hybridization between a depleted mantle component and the juvenile subducted oceanic crustal materials that were buried to depths of the middle to lower continental crust. The 212 Ma monzogranite and syenogranite of Kutihe were probably generated from the partial melting of miscellaneous lower crustal materials at high pressure conditions. By combining these new data with regional geological data, we conclude that the early Mesozoic evolution of the central Great Xing'an Range was governed by two superimposed tectonic regimes, i.e., (1) post-orogenic extension due to slab break-off after the closure of the Paleo-Asian oceanic basin along the Hegenshan-Heihe suture belt, and (2) back-arc extension associated with the southward subduction of

  3. Pb isotopes in anorthositic breccias 67075 and 62237 - A search for primitive lunar lead

    NASA Technical Reports Server (NTRS)

    Premo, W. R.; Tatsumoto, M.; Wang, J.-W.

    1989-01-01

    The lunar Pb isotopic evolution is explored based on an investigation of the U-Th-Pb systematics of the primitive Apollo 16 anorthositic breccias 76075 and 62237. The isotope data for acid-leached residues from 67075 lie within or on a triangle formed by plagioclase, opaques, and a pyroxen-olivine mixture, and the isotope data for 62237 lie within or on a triangle formed by plagioclase, olivine, and pyroxene. The results suggest that the moon had high first-stage values for the Pb evolution equations from the onset.

  4. Oxygen isotope activities and concentrations in aqueous salt solutions at elevated temperatures: Consequences for isotope geochemistry

    USGS Publications Warehouse

    Truesdell, A.H.

    1974-01-01

    Studies of the effect of dissolved salts on the oxygen isotope activity ratio of water have been extended to 275??C. Dehydrated salts were added to water of known isotope composition and the solutions were equilibrated with CO2 which was sampled for analysis. For comparison similar studies were made using pure water. Results on water nearly coincide with earlier calculations. Salt effects diminish with increasing temperature only for solutions of MgCl2 and LiCl. Other salt solutions show complex behavior due to the temperature-dependent formation of ion pairs of changing character. Equilibrium fractionations (103 ln ??) between 1 molal solutions and pure water at 25, 100, and 275??C are: NaCl 0.0, -1.5, +1.0; KCl 0.0, -1.0, +2.0; LiCl -1.0, -0.6, -0.5; CaCl2 -0.4, -1.8, +0.8; MgCl2 -1.1, -0.7, -0.3; MgSO4 -1.1, +0.1, -; NaF (0.8 m) 0.0, -1.5, -0.3; and NH4Cl (0.55 m) 0.0, -1.2, -1.3. These effects are significant in the isotope study of hot saline fluids responsible for ore deposition and of fluids found in certain geothermal systems. Minor modification of published isotope geothermometers may be required. ?? 1974.

  5. Monazite RW-1: a homogenous natural reference material for SIMS U-Pb and Th-Pb isotopic analysis

    NASA Astrophysics Data System (ADS)

    Ling, Xiao-Xiao; Huyskens, Magdalena H.; Li, Qiu-Li; Yin, Qin-Zhu; Werner, Ronald; Liu, Yu; Tang, Guo-Qiang; Yang, Ya-Nan; Li, Xian-Hua

    2016-10-01

    Well-characterized matrix-matched natural mineral references of known age are an important prerequisite for SIMS (secondary ion mass spectrometry) U-Th-Pb dating. We have characterized RW-1, a 44 g yellowish-brown single monazite specimen from a Norwegian pegmatite as an excellent hi-Th reference material for secondary ion mass spectrometric U-Th-Pb dating. A total of 206 secondary ion mass spectrometric analyses over six analytical sessions were performed on different monazite fragments of RW-1. The analyses resulted in 207Pb-based common lead corrected 206Pb/238U ages and Th-Pb ages with overall 2 % (2 SD = standard deviation) variations, indicating the good U-Th-Pb system homogeneity. The homogeneity of Th content of 11.8 ± 1.0 wt% (2 SD) and Th/U of 42 ± 3 (2 SD) make this crystal also a good compositional reference material. We used the combined ID-TIMS(Pb)/ID-MC-ICP-MS(U) technique (i.e. isotope dilution thermal ionization mass spectrometry for Pb, and isotope dilution multi-collector inductively-coupled plasma mass spectrometry for U) to determine U-Pb ages of the monazite samples studied. The mean 207Pb/235U age of 904.15 ± 0.26 Ma (95 % confidence level) is recommended as the best estimate crystallization age for RW-1 monazite. Considering that the most commonly distributed U-Pb monazite reference materials have rather low ThO2, we suggest that this RW-1 monazite with its ThO2 of 13.5 wt% is a suitable reference material providing investigators more confidence when dating high-Th monazite unknowns.

  6. Pb isotopes in sulfides from mid-ocean ridge hydrothermal sites

    SciTech Connect

    LeHuray, A.P.; Church, S.E.; Koski, R.A.; Bouse, R.M.

    1988-04-01

    The authors report Pb isotope ratios of sulfides deposited at seven recently active mid-ocean ridge (MOR) hydrothermal vents. Sulfides from three sediment-starved sites on the Juan de Fuca Ridge contain Pb with isotope ratios identical to their local basaltic sources. Lead in two deposits from the sediment-covered Escanaba Trough, Gorda Ridge, is derived from the sediments and does not appear to contain any basaltic component. There is a range of isotope ratios in a Guaymas Basin deposit, consistent with a mixture of sediment and MOR basalt Pb. Lead in a Galapagos deposit differs slightly from known Galapagos basalt Pb isotope values. The faithful record of Pb isotope signatures of local sources in MOR sulfides indicates that isotope ratios from ancient analogues ca be used as accurate reflections of ancient oceanic crustal values in ophiolite-hosted deposits and continental crustal averages in sediment-hosted deposits. The preservation of primary ophiolitic or continental crustal Pb isotope signatures in ancient MOR sulfides provides a powerful tool for investigation of crustal evolution and for fingerprinting ancient terranes.

  7. Geochemistry of primordial Pb, Bi, and Zn in Apollo 15 samples

    NASA Technical Reports Server (NTRS)

    Allen, R. O., Jr.; Jovanovic, S.; Reed, G. W., Jr.

    1973-01-01

    Primordial Pb as Pb-204 is present in Apollo 15 samples in concentrations ranging from less than 0.2 ppb in basalts to 6 ppb in soils. An acid soluble, pH-5-6, readily volatile component of this Pb is present, possibly as PbBr2; the remainder is correlated with the metal content of the sample. Leachable Bi and Pb-204 are correlated; residual Bi is probably present in a phosphate, possibly apatite. Zn is also highly leachable; residual Zn and Pb-204 are correlated.

  8. Large Pb Isotopic Variations in Pre-shield Stage Kilauea Magmas

    NASA Astrophysics Data System (ADS)

    Shimizu, N.; Sisson, T. W.; Layne, G. D.

    2001-12-01

    Volcaniclastic sediments found from a scarp below the mid-slope bench at water depths between 3,000 and 5,000m offshore south of Kilauea, Hawaii, contain abundant glass shards that represent submarine eruptions from an ancestral Kilauea volcano (Lipman et al., 2000; Sisson et al., 2001). Their major element compositions range from tholeiites/transitional basalts to alkali basalts to basanites and nephelinites. Pb isotopic compositions of the glasses were determined using a Cameca IMS 1270 ion microprobe at Woods Hole Oceanographic Institution. Replicate analyses of basalt glass stnadards show that 208Pb/206Pb and 207Pb/206Pb ratios could be determined in basalt glasses with external precisions better than 0.15% (1σ ) in a spot of 30 μ m across. Results show that: (1) a range of Pb isotopic compositions observed in the glasses are much greater than the entire spectrum of the Hawaiian volcanics. 208Pb/206Pb ratios vary from 2.099 to 2.004 and 207Pb/206Pb from 0.864 to 0.805. (2) There appear to be three distinct compositions, with each being represented by diverse magmatic compositions. There appears to be no significant mixing between them, and they form a linear array in a 208/206 vs 207/206 space, encompassing the entire Hawaiian Pb isotopic composition array. The least radiogenic composition (208Pb/206Pb=2.099, 207Pb/206Pb=0.864) in on an extension of the Honolulu Volcanics array, whereas the most radiogenic composition (208Pb/206Pb=2.004, 207Pb/206Pb=0.805) is far more radiogenic than any known Hawaiian magmas. The intermediate composition (208Pb/206Pb=2.041, 207Pb/206Pb=0.827) is close to the "Kea" endmember composition proposed by Eiler et al. (1998). The ancestral Kilauea nephelinites are derived from two distinct sources with radiogenic compositions and are quite distinct from all other Hawaiian post-erosional nephelinites. It is evident that diverse sources were tapped during the pre-shield stage Kilauea magmatism, and that melts erupted without mixing

  9. Basalt Pb isotope analysis and the prehistoric settlement of Polynesia.

    PubMed

    Weisler, M I; Woodhead, J D

    1995-03-14

    The prehistoric settlement of the Pacific Ocean has intrigued scholars and stimulated anthropological debate for the past two centuries. Colonized over a few millennia during the mid to late Holocene, the islands of the Pacific--displaying a wide diversity of geological and biotic variability--provided the stage for endless "natural experiments" in human adaptation. Crucial to understanding the evolution and transformation of island societies is documenting the relative degree of interisland contacts after island colonization. In the western Pacific, ideal materials for archaeologically documenting interisland contact--obsidian, pottery, and shell ornaments--are absent or of limited geographic distribution in Polynesia. Consequently, archaeologists have relied increasingly on fine-grained basalt artifacts as a means for documenting colonization routes and subsequent interisland contacts. Routinely used x-ray fluorescence characterization of oceanic island basalt has some problems for discriminating source rocks and artifacts in provenance studies. The variation in trace and major element abundances is largely controlled by near-surface magma-chamber processes and is broadly similar between most oceanic islands. We demonstrate that Pb isotope analysis accurately discriminates rock source and is an excellent technique for charting the scale, frequency, and temporal span of imported fine-grained basalt artifacts found throughout Polynesia. The technique adds another tool for addressing evolutionary models of interaction, isolation, and cultural divergence in the eastern Pacific.

  10. Coupling Meteorology, Metal Concentrations, and Pb Isotopes for Source Attribution in Archived Precipitation Samples

    EPA Science Inventory

    A technique that couples lead (Pb) isotopes and multi-element concentrations with meteorological analysis was used to assess source contributions to precipitation samples at the Bondville, Illinois USA National Trends Network (NTN) site. Precipitation samples collected over a 16 ...

  11. European isotopic signatures for lead in atmospheric aerosols: a source apportionment based upon 206Pb/207Pb ratios.

    PubMed

    Flament, Pascal; Bertho, Marie-Laure; Deboudt, Karine; Véron, Alain; Puskaric, Emile

    2002-09-16

    To investigate the capability of the lead isotope signature technique to support a source apportionment study at a Continental scale, atmospheric particulate matter was collected at Cap Gris-Nez (Eastern Channel, northern France), over one year (1995-1996). Four days retrospective trajectories of air masses were available during each sampling experiment. Twenty-eight samples, for which the origin of aerosols was unambiguously determined, were selected for isotopic measurements. Considering the Enrichment Factors, EF(Crust) of lead and its size distribution, we show that lead is mostly from anthropogenic origin and mainly associated with [0.4 < diameter < 0.9 microm] particles. The extent to which various Continental sources influence the lead abundance in aerosols is exhibited by considering both the lead concentration and the origin of air masses. Lead concentration is higher by a factor of approximately seven, when air masses are derived from Continental Europe, by comparison with marine air masses. Taking into account these concentrations and the vertical movements of air masses, we compare the different isotopic compositions using a statistical non-parametric test (Kolmogorov-Smirnov). We produce evidence that, for most of the cases, air masses originating from Continental Europe exhibit a more radiogenic composition (1.134 < 206Pb/207Pb < 1.172) than air masses coming from the United Kingdom (1.106 < 206Pb/207Pb < 1.124). Generally, lead isotopic compositions in aerosols are clearly distinct from the gasoline signatures in European countries, strongly suggesting that automotive lead is no longer the major component of this metal in the air. Gasoline and industrial isotopic signatures could explain the origin of lead in our aerosol samples. A source apportionment based upon 206Pb/207Pb ratios, suggests that the difference between British (206Pb/207Pb = 1.122 +/- 0.038) and Continental (206Pb/207Pb = 1.155 +/- 0.022) signatures may be largely explained by

  12. The combined application of organic sulphur and isotope geochemistry to assess multiple sources of palaeobiochemicals with identical carbon skeletons

    NASA Technical Reports Server (NTRS)

    Kohnen, M. E.; Schouten, S.; Sinninghe Damste, J. S.; de Leeuw, J. W.; Merrit, D.; Hayes, J. M.

    1992-01-01

    Five immature sediments from a Messinian evaporitic basin, representing one evaporitic cycle, were studied using molecular organic sulphur and isotope geochemistry. It is shown that a specific carbon skeleton which is present in different "modes of occurrence" ("free" hydrocarbon, alkylthiophene, alkylthiolane, alkyldithiane, alkylthiane, and sulphur-bound in macromolecules) may have different biosynthetic precursors which are possibly derived from different biota. It is demonstrated that the mode of occurrence and the carbon isotopic composition of a sedimentary lipid can be used to "reconstruct" its biochemical precursor. This novel approach of recognition of the suite of palaeobiochemicals present during the time of deposition allows for identification of the biological sources with an unprecedented specificity.

  13. Mass-dependent and -independent fractionation of isotopes in Ni and Pb chelate complex formation reactions

    NASA Astrophysics Data System (ADS)

    Nomura, Masao; Kudo, Takashi; Adachi, Atsuhiko; Aida, Masao; Fujii, Yasuhiko

    2013-11-01

    Mass independent fractionation (MIF) has been a very interesting topic in the field of inorganic isotope chemistry, in particular, geo- and cosmo- chemistry. In the present work, we studied the isotope fractionation of Ni(II) and Pb(II) ions in complex formation with chelating reagent EDTA. To obtain clear results on the mass dependence of the isotope fractionation, we have conducted long-distance ion exchange chromatography of Ni(II) and Pb(II), using chelate complex reagent EDTA. The results apparently show that the isotope fractionation in Ni complex formation system is governed by the mass dependent rule. On the other hand the isotope fractionation in the Pb complex system is governed by the mass independent rule or the nuclear volume effect.

  14. Mass-dependent and -independent fractionation of isotopes in Ni and Pb chelate complex formation reactions

    SciTech Connect

    Nomura, Masao; Kudo, Takashi; Adachi, Atsuhiko; Aida, Masao; Fujii, Yasuhiko

    2013-11-13

    Mass independent fractionation (MIF) has been a very interesting topic in the field of inorganic isotope chemistry, in particular, geo- and cosmo- chemistry. In the present work, we studied the isotope fractionation of Ni(II) and Pb(II) ions in complex formation with chelating reagent EDTA. To obtain clear results on the mass dependence of the isotope fractionation, we have conducted long-distance ion exchange chromatography of Ni(II) and Pb(II), using chelate complex reagent EDTA. The results apparently show that the isotope fractionation in Ni complex formation system is governed by the mass dependent rule. On the other hand the isotope fractionation in the Pb complex system is governed by the mass independent rule or the nuclear volume effect.

  15. Direct Pb Isotopic Analysis of a Nuclear Fallout Debris Particle from the Trinity Nuclear Test.

    PubMed

    Bellucci, Jeremy J; Snape, Joshua F; Whitehouse, Martin J; Nemchin, Alexander A

    2017-02-07

    The Pb isotope composition of a nuclear fallout debris particle has been directly measured in post-detonation materials produced during the Trinity nuclear test by a secondary ion mass spectrometry (SIMS) scanning ion image technique (SII). This technique permits the visual assessment of the spatial distribution of Pb and can be used to obtain full Pb isotope compositions in user-defined regions in a 70 μm × 70 μm analytical window. In conjunction with backscattered electron (BSE) and energy-dispersive spectroscopy (EDS) mapping of the same particle, the Pb measured in this fallout particle cannot be from a major phase in the precursor arkosic sand. Similarly, the Pb isotope composition of the particle is resolvable from the surrounding glass at the 2σ uncertainty level (where σ represents the standard deviation). The Pb isotope composition measured in the particle here is in excellent agreement with that inferred from measurements of green and red trinitite, suggesting that these types of particles are responsible for the Pb isotope compositions measured in both trinitite glasses.

  16. Pb, Sr, and Nd isotopes in basalts and sulfides from the Juan de Fuca Ridge

    SciTech Connect

    Hegner, E.; Tatsumoto, M.

    1987-10-10

    Pb, Sr, Nd isotopes of seven basalt glasses collected by the submersible Alvin from the southern Juan de Fuca Ridge (SJFR) are almost identical (/sup 206/Pb//sup 204/Pbapprox.18.45, /sup 207/Pb//sup 204/Pbapprox.15.47, /sup 208/Pb//sup 204/Pbapprox.37.81, /sup 87/Sr//sup 86/Srapprox.0.70249, /sup 143/Nd//sup 144/Ndapprox.0.51315). Whereas all basalts appear cogenetic, four of the samples have uniform abundances of U, Th, Rb, Nd, Sm, Pb, and Sr, indicating that they are also comagmatic. Two basalt glasses dredged previously at the SJFR have similar isotopic compositions but higher concentrations of U, Th, and Pb. The /sup 206/Pb//sup 204/Pb ratios are intermediate between generally less radiogenic ridge basalts from south of the Juan de Fuca Ridge (JFR) and often more radiogenic basalts from the northern JFR and NE Pacific seamounts. Sr and Nd isotopic compositions closely resemble data of other ridge basalts from the northernmost East Pacific Rise and are intermediate between isotopically more diverse seamount basalts produced nearby.

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    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

  18. Tracing of industrial aerosol sources in an urban environment using Pb, Sr, and Nd isotopes.

    PubMed

    Geagea, Majdi Lahd; Stille, Peter; Gauthier-Lafaye, François; Millet, Maurice

    2008-02-01

    A comprehensive Pb-Sr-Nd isotope tracer study of atmospheric trace metal pollution has been performed in the urban environment of Strasbourg-Kehl. Filter dust of the principal pollutant sources (waste incinerators, thermal power plant and steel plant) and soot of car and ship exhausts have been analyzed. In addition tree barks (as biomonitors) and PM10 have been analyzed to trace and determine the distribution of the pollution in the environment. The industrial sources have highly variable epsilonNd values (-9.7 and -12.5 for incinerators and -17.5 for steel plant). Much higher epsilonNd values have been found for soot of car exhausts (-6 and -6.9). These high values make the Nd isotope system a powerful tool for the discrimination of traffic emissions but especially for the identification of diesel derived particles in the urban environment. The 206Pb/207Pb isotope ratios of gasoline are low (1.089) compared to diesel soot (1.159). The 26Pb/207Pb ratios of 1.151-1.152 for the steel plant and 1.152 for the solid waste incinerator are close to the Pb isotope ratio of diesel. The 87Sr/ 8Sr isotope ratios of the principal industrial sources vary significantly: 0.7095 for the domestic solid waste incinerator, 0.709 for the steel plant, and 0.7087 for car exhaust soot. PM10 aerosols collected in the urban center of Strasbourg show the influence of the pollutant sources at 3-7 km distance from the center. Most of the aerosols Pb isotopic compositions suggest Pb admixtures from at least three sources: a natural background and in function of the wind direction the domestic waste incinerator (S-wind) or the steel plant and the chemical waste incinerator (NE-wind). The traffic contribution can only be estimated with help of Nd isotopes. Therefore the clear identification of different pollutant sources in the urban environment is only possible by combining the three different isotope systems and is based on the fact that significant differences exist between the Pb, Sr, and

  19. Pb isotope variations in olivine-hosted melt inclusions from South Tyrrhenian volcanoes

    NASA Astrophysics Data System (ADS)

    Rose-Koga, E. F.; Koga, K. T.; Schiano, P.; Shimizu, N.; Whitehouse, M.; Clocchiatti, R.

    2009-12-01

    Melt inclusions in primitive olivine crystals isolate the instantaneous composition of primitive magmas. Recent studies have reported a very large range of isotope ratios among olivine-hosted melt inclusions from some single volcanoes even though the erupted lavas from these volcanoes are isotopically homogeneous. This implies that magmas with different isotopic compositions exist in the volcanic plumbing system before melt aggregation, reflecting a range of source compositions. Volcanoes in the South Italy region (Stromboli, Vulcano islands, Mount Etna including Aci Castello, the oldest Etnean volcanics, as well as present-day Etnean basalts, Marsili seamount and Ustica Island) shows a wide spectrum of magma-types where predominantly calc-alkaline magmatism is found in the Aeolian Islands and a magmatism of Na-alkaline nature dominates the nearby Eastern Sicily volcanoes (Mount Etna) and Ustica Island. The complex geodynamic evolution of this region is the probable cause of this diverse magma composition produced from the Pliocene to recent times. We analyzed 12 olivine-hosted melt inclusions from those six volcanoes for Pb isotopes by a multicollection SIMS 1280 (NMNH Stockholm, Sweden) and volatiles by a monocollection SIMS 1280 (WHOI, USA). The repeated 207Pb/206Pb measurements of the GOR132 glass standard (20 ppm Pb) yielded a 0.15% relative variation (1 sigma of the distribution). For the modern Etna (2002 lava), the 207Pb/206Pb isotope variations of the melt inclusions overlap and extend that of the whole rocks (from 0.788±0.002 to 0.820±0.002 (MI) relative to 0.7863 to 0.8037 (WR)). The melt inclusions from Aci Costello display more clustered and intermediate 207Pb/206Pb values between 0.801±0.003 and 0.811±0.005. The Pb isotope variations of the melt inclusions from the other volcanoes displays value similar to that of their whole rock data, up to 207Pb/206Pb of 0.828 for Marsili melt inclusions. There are no obvious correlations between Pb isotopes

  20. Isotopic signatures for natural versus anthropogenic Pb in high-altitude Mt. Everest ice cores during the past 800 years.

    PubMed

    Lee, Khanghyun; Hur, Soon Do; Hou, Shugui; Burn-Nunes, Laurie J; Hong, Sungmin; Barbante, Carlo; Boutron, Claude F; Rosman, Kevin J R

    2011-12-15

    A long-term record, extending back 800 years (1205 to 2002 AD), of the Pb isotopic composition ((206)Pb/(207)Pb and (208)Pb/(207)Pb) as well as Pb concentrations from high altitude Mt. Everest ice cores has the potential to identify sources and source regions affecting natural and anthropogenic Pb deposition in central Asia. The results show that the regional natural background Pb isotope signature (~1.20 for (206)Pb/(207)Pb and ~2.50 for (208)Pb/(207)Pb) in the central Himalayas was dominated by mineral dust over the last ~750 years from 1205 to 1960s, mostly originating from local sources with occasional contributions of long-range transported dust probably from Sahara desert and northwestern India. Since the 1970s, the Pb isotope ratios are characterized by a continuous decline toward less radiogenic ratios with the least mean ratios of 1.178 for (206)Pb/(207)Pb and 2.471 for (208)Pb/(207)Pb in the period 1990-1996. The depression of the (206)Pb/(207)Pb and (208)Pb/(207)Pb values during the corresponding periods is most likely due to an increasing influence of less radiogenic Pb of anthropogenic origin mainly from leaded gasoline used in South Asia (India as well as possibly Bangladesh and Nepal). From 1997 to 2002, isotopic composition tends to show a shift to slightly more radiogenic signature. This is likely attributed to reducing Pb emissions from leaded gasoline in source regions, coinciding with the nationwide reduction of Pb in gasoline and subsequent phase-out of leaded gasoline in South Asia since 1997. An interesting feature is the relatively high levels of Pb concentrations and enrichment factors (EF) between 1997 and 2002. Although the reason for this feature remains uncertain, it would be probably linked with an increasing influence of anthropogenic Pb emitted from other sources such as fossil fuel combustion and non-ferrous metal production.

  1. The lead (Pb) isotope signature, behaviour and fate of traffic-related lead pollution in roadside soils in The Netherlands.

    PubMed

    Walraven, N; van Os, B J H; Klaver, G Th; Middelburg, J J; Davies, G R

    2014-02-15

    In this study the origin, behaviour and fate of anthropogenic Pb in sandy roadside soils were assessed by measuring soil characteristics, Pb isotope composition and content. In 1991 and 2003 samples were taken at different depth intervals at approximately 8 and 75 m from two highways in The Netherlands. The Pb isotope composition of the litter layer ((206)Pb/(207)Pb=1.12-1.14) differs from the deeper soil samples ((206)Pb/(207)Pb=1.20-1.21). Based on a mixing model it is concluded that the samples contain two Pb sources: natural Pb and anthropogenic Pb, the latter mainly derived from gasoline. (206)Pb/(207)Pb ratios demonstrate that the roadside soils were polluted to a depth of ~15 cm. Within this depth interval, anthropogenic Pb content is associated with organic matter. Although Pb pollution only reached a depth of ~15 cm, this does not mean that the topsoils retain all anthropogenic Pb. Due to the low pH and negligible binding capacity of soils at depths >15 cm, anthropogenic Pb migrated towards groundwater after reaching depths of >15 cm. The Pb isotope composition of the groundwater ((206)Pb/(207)Pb=1.135-1.185) establishes that groundwater is polluted with anthropogenic Pb. The contribution of anthropogenic Pb to the groundwater varies between ~30 and 100%. Based on the difference in soil Pb content and Pb isotope compositions over a period of 12 years, downward Pb migration is calculated to vary from 72 ± 95 to 324 ± 279 mg m(-2)y(-1). Assuming that the downward Pb flux is constant over time, it is calculated that 35-90% of the atmospherically delivered Pb has migrated to the groundwater.

  2. Geochemistry of the Ediacaran-Early Cambrian transition in Central Iberia: Tectonic setting and isotopic sources

    NASA Astrophysics Data System (ADS)

    Fuenlabrada, José Manuel; Pieren, Agustín P.; Díez Fernández, Rubén; Sánchez Martínez, Sonia; Arenas, Ricardo

    2016-06-01

    A complete Ediacaran-Early Cambrian stratigraphic transition can be observed in the southern part of the Central Iberian Zone (Iberian Massif). Two different stratigraphic units, underlying Ordovician series, display geochemical and Sm-Nd isotopic features in agreement with an evolving geodynamic setting. Pusa Shales (Early Cambrian) rest unconformably on greywackes of the Lower Alcudian Formation (Late Ediacaran). Both sequences present minor compositional variations for major and trace element contents and similar REE patterns, close to those of PAAS (Post Archean Australian Shale). Trace element contents and element ratios suggest mixed sources, with intermediate to felsic igneous contributions for both units. Tectonic setting discrimination diagrams for the Ediacaran greywackes indicate that these turbiditic series were deposited in a sedimentary basin associated with a mature active margin (volcanic arc). However, the compositions of the Cambrian shales fit better with a more stable context, a back-arc or retro-arc setting. εNd(T) and TDM ages are compatible with dominance of a similar cratonic source for both sequences, probably the West Africa Craton. εNd565 values for the Ediacaran greywackes (- 3.0 to - 1.4) along with TDM ages (1256-1334 Ma) imply a significant contribution of juvenile material, probably derived from the erosion of the volcanic arc. However, εNd530 values in the Cambrian shales (- 5.2 to - 4.0) together with older TDM ages (1444-1657 Ma), suggest a higher contribution of cratonic isotopic sources, probably derived from erosion of the adjacent mainland. Coeval with the progressive cessation of arc volcanism along the peri-Gondwanan realm during the Cambrian, there was a period of more tectonic stability and increasing arrival of sediments from cratonic areas. The geochemistry of the Ediacaran-Cambrian transition in Central Iberia documents a tectonic switch in the periphery of Gondwana, from an active margin to a more stable context

  3. Reactive transport modelling of biogeochemical processes and carbon isotope geochemistry inside a landfill leachate plume

    NASA Astrophysics Data System (ADS)

    van Breukelen, Boris M.; Griffioen, Jasper; Röling, Wilfred F. M.; van Verseveld, Henk W.

    2004-06-01

    The biogeochemical processes governing leachate attenuation inside a landfill leachate plume (Banisveld, the Netherlands) were revealed and quantified using the 1D reactive transport model PHREEQC-2. Biodegradation of dissolved organic carbon (DOC) was simulated assuming first-order oxidation of two DOC fractions with different reactivity, and was coupled to reductive dissolution of iron oxide. The following secondary geochemical processes were required in the model to match observations: kinetic precipitation of calcite and siderite, cation exchange, proton buffering and degassing. Rate constants for DOC oxidation and carbonate mineral precipitation were determined, and other model parameters were optimized using the nonlinear optimization program PEST by means of matching hydrochemical observations closely (pH, DIC, DOC, Na, K, Ca, Mg, NH 4, Fe(II), SO 4, Cl, CH 4, saturation index of calcite and siderite). The modelling demonstrated the relevance and impact of various secondary geochemical processes on leachate plume evolution. Concomitant precipitation of siderite masked the act of iron reduction. Cation exchange resulted in release of Fe(II) from the pristine anaerobic aquifer to the leachate. Degassing, triggered by elevated CO 2 pressures caused by carbonate precipitation and proton buffering at the front of the plume, explained the observed downstream decrease in methane concentration. Simulation of the carbon isotope geochemistry independently supported the proposed reaction network.

  4. The growth of the continental crust: Constraints from radiogenic isotope geochemistry

    NASA Technical Reports Server (NTRS)

    Taylor, Paul N.

    1988-01-01

    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.

  5. A routine high-precision method for Lu-Hf isotope geochemistry and chronology

    USGS Publications Warehouse

    Patchett, P.J.; Tatsumoto, M.

    1981-01-01

    A method for chemical separation of Lu and Hf from rock, meteorite and mineral samples is described, together with a much improved mass spectrometric running technique for Hf. This allows (i) geo- and cosmochronology using the176Lu???176Hf+??- decay scheme, and (ii) geochemical studies of planetary processes in the earth and moon. Chemical yields for the three-stage ion-exchange column procedure average 90% for Hf. Chemical blanks are <0.2 ng for Lu and Hf. From 1 ??g of Hf, a total ion current of 0.5??10-11 Ampere can be maintained for 3-5 h, yielding 0.01-0.03% precision on the ratio176Hf/177Hf. Normalisation to179Hf/177Hf=0.7325 is used. Extensive results for the Johnson Matthey Hf standard JMC 475 are presented, and this sample is urged as an international mass spectrometric standard; suitable aliquots, prepared from a single batch of JMC 475, are available from Denver. Lu-Hf analyses of the standard rocks BCR-1 and JB-1 are given. The potential of the Lu-Hf method in isotope geochemistry is assessed. ?? 1980 Springer-Verlag.

  6. Reactive transport modelling of biogeochemical processes and carbon isotope geochemistry inside a landfill leachate plume.

    PubMed

    van Breukelen, Boris M; Griffioen, Jasper; Röling, Wilfred F M; van Verseveld, Henk W

    2004-06-01

    The biogeochemical processes governing leachate attenuation inside a landfill leachate plume (Banisveld, the Netherlands) were revealed and quantified using the 1D reactive transport model PHREEQC-2. Biodegradation of dissolved organic carbon (DOC) was simulated assuming first-order oxidation of two DOC fractions with different reactivity, and was coupled to reductive dissolution of iron oxide. The following secondary geochemical processes were required in the model to match observations: kinetic precipitation of calcite and siderite, cation exchange, proton buffering and degassing. Rate constants for DOC oxidation and carbonate mineral precipitation were determined, and other model parameters were optimized using the nonlinear optimization program PEST by means of matching hydrochemical observations closely (pH, DIC, DOC, Na, K, Ca, Mg, NH4, Fe(II), SO4, Cl, CH4, saturation index of calcite and siderite). The modelling demonstrated the relevance and impact of various secondary geochemical processes on leachate plume evolution. Concomitant precipitation of siderite masked the act of iron reduction. Cation exchange resulted in release of Fe(II) from the pristine anaerobic aquifer to the leachate. Degassing, triggered by elevated CO2 pressures caused by carbonate precipitation and proton buffering at the front of the plume, explained the observed downstream decrease in methane concentration. Simulation of the carbon isotope geochemistry independently supported the proposed reaction network.

  7. Coexistence of galenas with different Pb isotopic composition in Los Pedroches batholith area (Spain)

    NASA Astrophysics Data System (ADS)

    García de Madinabeitia, S.; Santos Zalduegui, J. F.; Larrea, F. J.; Carracedo, M.; Gil Ibarguchi, J. I.

    2003-04-01

    The Los Pedroches batholith region (S Spain) includes three separated mining districts: Linares, La Carolina and Los Pedroches. The Pb isotopic composition of thirty-three galenas from this sector has been measured. On the basis of the Pb data two types of mineralization are established. A first type including: (i) the Linares and La Carolina districts where ore-bearing filons cut Hercynian granites or their hostrocks (SE of the batholith), and (ii) the so-called "peribatholithic" ore bodies represented by scarce mines in the host-rock of the batholith; all of them exhibit homogeneous Pb isotopic compositions of: 206Pb/204Pb = 18.236, 207Pb/204Pb = 15.615, 208Pb/204Pb = 38.347 and a model age of ca. 324 Ma. The second type is represented by a huge N120^oE hydrotermal vein (the El Zumajo vein) intrusive in granitoid bodies of the batholith; the Pb isotopic composition of the vein is: 206Pb/204Pb = 18.457, 207Pb/204Pb = 15.636, 208Pb/204Pb = 38.611 and a model age of ca. 201 Ma. Analysed K-feldspars from batholithic granodiorite and granites have Pb isotopic compositions similar to those reported previously from Hercynian granites of the area (1) and to the galenas of Linares, La Carolina and "peribatholithic" ores. The whole dataset reveals a Pb evolution curve with μ_2 = 9.8 and ω_2 = 38.3, close to the model curve for the "orogen" (2). This suggests for Linares, La Carolina and the "peribatholithic" mineralizations a Pb source related to that of the granites. The pre-Tremadoc metasedimentary rocks of the area, with Pb isotopic composition (3) very close to that of feldspars and galenas studied is proposed as a possible source of Pb for both the granites and associated mineralizations, although the Pb isotopic composition of El Zumajo calls for a different origin. The observed difference in Pb isotopic ratios of the studied galenas points to, at least, two ore-forming events: (i) one relating older mineralizations and granitoid intrusives, in agreement with

  8. Pb isotope constaints on the extent of crustal recycling into a steady state mantle

    NASA Technical Reports Server (NTRS)

    Galer, S. J. G.; Goldstein, S. L.; Onions, R. K.

    1988-01-01

    Isotopic and geochemical evidence was discussed against recycling of continental crust into the mantle. Element ratios such as Sm/Nd, Th/Sc, and U/Pb in sedimentary masses have remained relatively constant throughout Earth history, and this can only be reconciled with steady state recycling models if new crustal materials added from the mantle have had similar ratios. Such recycling models would also require shorter processing times for U, Th, and Pb through the mantle than are geodynamically reasonable. Models favoring subduction of pelagic sediments as the only recycling mechanism fail to account for the Pb isotopic signature of the mantle. Recycling of bulk crust with Pb isotopic compositions similar to those expected for primitive mantle would be permissable with available data, but there appear to be no plausible tectonic mechanisms to carry this out.

  9. Tracing lead pollution sources in abandoned mine areas using stable Pb isotope ratios.

    PubMed

    Yoo, Eun-Jin; Lee, Jung-A; Park, Jae-Seon; Lee, Khanghyun; Lee, Won-Seok; Han, Jin-Seok; Choi, Jong-Woo

    2014-02-01

    This study focused on Pb isotope ratios of sediments in areas around an abandoned mine to determine if the ratios can be used as a source tracer. For pretreatment, sediment samples were dissolved with mixed acids, and a multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS, Nu plasma II) was used to investigate the Pb isotopic composition of the samples. The measured isotope ratios were then corrected for instrumental mass fractionation by measuring the (203)Tl/(205)Tl ratio. Repeated measurements with the NIST SRM 981 reference material showed that the precision of all ratios was below 104 ppm (±2σ) for 50 ng/g. The isotope ratios ((207)Pb/(206)Pb) found were 0.85073 ± 0.0004~0.85373 ± 0.0003 for the main stream, while they were 0.83736 ± 0.0010 for the tributary and 0.84393 ± 0.0002 for the confluence. A binary mixing equation for isotope ratios showed that the contributions of mine lead to neighboring areas were up to 60%. Therefore, Pb isotope ratios can be a good source tracer for areas around abandoned mines.

  10. Lead (Pb) Isotope Baselines for Studies of Ancient Human Migration and Trade in the Maya Region

    PubMed Central

    Kamenov, George D.; Gilli, Adrian; Hodell, David A.; Emery, Kitty F.; Brenner, Mark; Krigbaum, John

    2016-01-01

    We examined the potential use of lead (Pb) isotopes to source archaeological materials from the Maya region of Mesoamerica. The main objectives were to determine if: 1) geologic terrains throughout the Maya area exhibit distinct lead isotope ratios (206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb), and 2) a combination of lead and strontium ratios can enhance sourcing procedures in the Mesoamerica region. We analyzed 60 rock samples for lead isotope ratios and a representative subset of samples for lead, uranium, and thorium concentrations across the Maya region, including the Northern Lowlands of the Mexican Yucatan Peninsula, the Southern Lowlands of Guatemala and Belize, the Volcanic Highlands, the Belizean Maya Mountains, and the Metamorphic Province/Motagua Valley. Although there is some overlap within certain sub-regions, particularly the geologically diverse Metamorphic Province, lead isotopes can be used to distinguish between the Northern Lowlands, the Southern Lowlands, and the Volcanic Highlands. The distinct lead isotope ratios in the sub-regions are related to the geology of the Maya area, exhibiting a general trend in the lowlands of geologically younger rocks in the north to older rocks in the south, and Cenozoic volcanic rocks in the southern highlands. Combined with other sourcing techniques such as strontium (87Sr/86Sr) and oxygen (δ18O), a regional baseline for lead isotope ratios can contribute to the development of lead isoscapes in the Maya area, and may help to distinguish among geographic sub-regions at a finer scale than has been previously possible. These isotope baselines will provide archaeologists with an additional tool to track the origin and movement of ancient humans and artifacts across this important region. PMID:27806065

  11. Lead (Pb) Isotope Baselines for Studies of Ancient Human Migration and Trade in the Maya Region.

    PubMed

    Sharpe, Ashley E; Kamenov, George D; Gilli, Adrian; Hodell, David A; Emery, Kitty F; Brenner, Mark; Krigbaum, John

    2016-01-01

    We examined the potential use of lead (Pb) isotopes to source archaeological materials from the Maya region of Mesoamerica. The main objectives were to determine if: 1) geologic terrains throughout the Maya area exhibit distinct lead isotope ratios (206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb), and 2) a combination of lead and strontium ratios can enhance sourcing procedures in the Mesoamerica region. We analyzed 60 rock samples for lead isotope ratios and a representative subset of samples for lead, uranium, and thorium concentrations across the Maya region, including the Northern Lowlands of the Mexican Yucatan Peninsula, the Southern Lowlands of Guatemala and Belize, the Volcanic Highlands, the Belizean Maya Mountains, and the Metamorphic Province/Motagua Valley. Although there is some overlap within certain sub-regions, particularly the geologically diverse Metamorphic Province, lead isotopes can be used to distinguish between the Northern Lowlands, the Southern Lowlands, and the Volcanic Highlands. The distinct lead isotope ratios in the sub-regions are related to the geology of the Maya area, exhibiting a general trend in the lowlands of geologically younger rocks in the north to older rocks in the south, and Cenozoic volcanic rocks in the southern highlands. Combined with other sourcing techniques such as strontium (87Sr/86Sr) and oxygen (δ18O), a regional baseline for lead isotope ratios can contribute to the development of lead isoscapes in the Maya area, and may help to distinguish among geographic sub-regions at a finer scale than has been previously possible. These isotope baselines will provide archaeologists with an additional tool to track the origin and movement of ancient humans and artifacts across this important region.

  12. Metallic elements and isotope of Pb in wet precipitation in urban area, South America

    NASA Astrophysics Data System (ADS)

    Migliavacca, Daniela Montanari; Teixeira, Elba Calesso; Gervasoni, Fernanda; Conceição, Rommulo Vieira; Raya Rodriguez, Maria Teresa

    2012-04-01

    The atmosphere of urban areas has been the subject of many studies to show the atmospheric pollution in large urban centers. By quantifying wet precipitation through the analysis of metallic elements (ICP/AES) and Pb isotopes, the wet precipitation of the Metropolitan Area of the Porto Alegre (MAPA), Brazil, was characterized. The samples were collected between July 2005 and December 2007. Zn, Fe and Mn showed the highest concentration in studied sites. Sapucaia do Sul showed the highest average for Zn, due to influence by the steel plant located near the sampling site. The contribution of anthropogenic emissions from vehicular activity and steel plants in wet precipitation and suspended particulate matter in the MAPA was identified by the isotopic signatures of 208Pb/207Pb and 206Pb/207Pb. Moreover the analyses of the metallic elements allowed also to identify the contribution of other anthropic sources, such as steel plants and oil refinery.

  13. A Water Geochemistry Study of Indian Wells Valley, Inyo and Kern Counties, California. Supplement. Isotope Geochemistry and Appendix H.

    DTIC Science & Technology

    1990-09-01

    0.01 0.0C Lead ( Pb ) () 0.01 0.w Mercury (Hg) () 0.0002 0.0D2 Selenium (Se) () 0.005 0.01 Silver (Aq) () 0.01 0.0s T- e-’e.", te "-es5 h r" ay - H-9...10________i_ Lead ( Pb ) 1051 _ 3 0O Manganese (Mn) 1055 < f i 3 iC) Mercur ( O) 71900 I-e- . / Selenium (Se) _ 1147f Silver(Ag) 1077 Zinc (Zn) 092i / ,0...ug/L Lead ( Pb ) 1051_ I I 1 I 1 0 50 ug/L+ Manganese (Mn) 1055 < ŗ 1 0 2 ug/L Mercury 1Hg) 71900 1 I I 10 ug/L -Selenium (Se) 1147 f I I 1 5- 50 ug/L

  14. Genesis of the Bangbule Pb-Zn-Cu polymetallic deposit in Tibet, western China: Evidence from zircon U-Pb geochronology and S-Pb isotopes

    NASA Astrophysics Data System (ADS)

    Kan, Tian; Zheng, Youye; Gao, Shunbao

    2016-04-01

    The Banbule Pb-Zn-Cu skarn deposit is located in the Longger-Gongbujiangda volcanic magma arc in the Gangdese-Nyainqentanglha Plate. It is the only lead-zinc polymetallic deposit discovered in the westernmost Nyainqentanglha metallogenic belt. The measured and indicated resources include 0.9 Mt of Pb+Zn (4.77% Pb and 4.74% Zn, respectively), 6499 t of Cu, and 178 t of Ag (18.75g/t Ag). The orebodies mainly occur as lenses, veins and irregular shapes in the contact zone between the quartz-porphyry and limestone of the Upper Permian Xiala Formation, or in the boundaries between limestone and sandstone. Pb-Zn-Cu mineralization in the Banbule deposit is closely associated with skarns. The ore minerals are dominated by galena, sphalerite, chalcopyrite, bornite, and magnetite, with subordinate pyrite, malachite, and azurite. The gangue minerals are mainly garnet, actinolite, diopside, quartz, and calcite. The ore-related quartz-porphyry displays LA-ICP-MS zircon U-Pb age of 77.31±0.74 Ma. The δ34S values of sulfides define a narrow range of -0.8 to 4.7‰ indicating a magmatic source for the ore-forming materials. Lead isotopic systematics yield 206Pb/204Pb of 18.698 to 18.752, 207Pb/204Pb of 15.696 to 15.760, and 208Pb/204Pb of 39.097 to 39.320. The data points are constrained around the growth curves of upper crust and orogenic belt according to the tectonic discrimination diagrams. The calculated Δβ - Δγ values plot within the magmatic field according to the discrimination diagram of Zhu et al. (1995). The S-Pb isotopic data suggest that Bangbule is a typical skarn deposit, and the Pb-Zn-Cu mineralization is genetically related to the quartz-porphyry in the mining district. The discovery of the Bangbule deposit indicates that there is metallogenic potential in the westernmost Nyainqentanglha belt, which is of great importance for the exploration work in this area.

  15. Geochemistry, geochronology and isotope geology of Nakfa intrusive rocks, northern Eritrea: products of a tectonically thickened Neoproterozoic arc crust

    NASA Astrophysics Data System (ADS)

    Teklay, M.; Kröner, A.; Mezger, K.

    2001-08-01

    The north-south-trending Neoproterozoic volcano-sedimentary plutonic associations in northern Eritrea are part of the Nubian Shield. The Nakfa intrusive rocks range in composition from gabbro to syeno-diorite to granite and alkaline syenite and intrude supracrustal rocks of volcanic and sedimentary origin. All granitoid rocks are metaluminous or slightly peraluminous and have typical I-type chemical signatures. The calc-alkaline intrusive rocks and the alkaline syenites have geochemical characteristics (e.g. low Nb values) typical of arc intrusives and plot as volcanic arc granites on various discriminant diagrams. Single zircon evaporation Pb-Pb ages and conventional multigrain U-Pb ages on zircons and titanites yielded emplacement ages of ˜620-640 Ma. These are comparable to those of adjacent juvenile terranes in the Nubian Shield. No pre-Pan-African rocks have so far been found in northern Eritrea. Isotopic data show a limited range, with initial ɛ Nd values ranging from 3.5 to 5.6 and initial Sr ratios from 0.7018 to 0.7037. The high positive initial ɛ Nd values and low initial Sr ratios indicate that the granitoid rocks were derived from a mantle and/or juvenile crustal source with no, or only insignificant, contribution from an older continental component. This is further supported by the absence of inherited zircons and the lack of rocks of continental affinity. Leached K-feldspars from Nakfa intrusive rocks have Pb isotope ratios ( 206Pb/ 204Pb = 17.60-17.88, 207Pb/ 204Pb = 15.49-15.53 and 208Pb/ 204Pb = 37.12-37.37) similar to those for 'oceanic leads' from Saudi Arabia, which are interpreted as manifesting a mantle source. Hence, the Pb isotope ratios, in agreement with the Sr and Nd isotopic data, indicate an insignificant involvement of older crustal components in the generation of Pan-African crust in northern Eritrea. The ages and isotopic characteristics of the Nakfa intrusive rocks are comparable to those of adjacent juvenile terranes in the

  16. Isotopic generator for /sup 212/Pb and /sup 212/Bi

    SciTech Connect

    Zucchini, G.L.; Friedman, A.M.

    1982-01-01

    A large potential exists for the use of short lived alpha emitting isotopes for therapeutic purposes. Most prior research has been performed with isotopes such as /sup 211/At which require a cyclotron for production. It obviously would be more convenient to use a long lived isotopic generator system. For this reason, we have undertaken a study of the properties of several such generators, one of which, /sup 228/Th, is described here.

  17. Isotopic (Pb, Sr, Nd, C, O) evidence for plume-related sampling of an ancient, depleted mantle reservoir

    NASA Astrophysics Data System (ADS)

    Chen, Wei; Simonetti, Antonio

    2015-02-01

    The exact mantle source for carbonatite melts remains highly controversial. Despite their predominant occurrence within continental (lithospheric) domains, the radiogenic isotope data from young (< 200 Ma) carbonatite complexes worldwide overlap the fields defined by present-day oceanic island basalts (OIBs). This feature suggests an intimate petrogenetic relationship with asthenospheric mantle. New Pb, Sr, C, and O isotopic data are reported here for constituent minerals from the Oka carbonatite complex, which is associated with the Cretaceous Monteregian Igneous Province (MIP), northeastern North America. The Pb isotope data define linear arrays in Pb-Pb isotope diagrams, with the corresponding Sr isotope ratios being highly variable (0.70314-0.70343); both these features are consistent with open system behavior involving at least three distinct mantle reservoirs. Compared to the isotope composition of known mantle sources for OIBs and carbonatite occurrences worldwide, the least radiogenic 207Pb/204Pb (14.96 ± 0.07) and 208Pb/204Pb (37.29 ± 0.15) isotopic compositions relative to their corresponding 206Pb/204Pb ratios (18.86 ± 0.08) reported here are distinct, and indicate the involvement of an ancient depleted mantle (ADM) source. The extremely unradiogenic Pb isotope compositions necessitate U/Pb fractionation early in Earth's history (prior to 4.0 Ga ago) and growth via a multi-stage Pb evolution model. The combined stable (C and O) and radiogenic isotopic compositions effectively rule out crustal/lithosphere contamination during the petrogenetic history of the Oka complex. Instead, the isotopic variations reported here most likely result from the mixing of discrete, small volume partial melts derived from a heterogeneous plume source characterized by a mixed HIMU-EM1-ADM signature.

  18. Reconstruction of historical lead contamination and sources in Lake Hailing, Eastern China: a Pb isotope study.

    PubMed

    Zhang, Rui; Guan, Minglei; Shu, Yujie; Shen, Liya; Chen, Xixi; Zhang, Fan; Li, Tiegang; Jiang, Tingchen

    2016-05-01

    The history records of lead and its stable isotopic ratios were determined in a sediment core to receive anthropogenic impacts on the Lake Hailing in eastern China. The sediment core was dated based on (210)Pb, (137)Cs, and (239+240)Pu. The historical changes of Pb/Al and Pb isotope ratios showed increasing trend upward throughout the core, suggesting changes in energy usage and correlating closely with the experience of a rapid economic and industrial development of the catchment, Linyi City, in eastern China. Based on the mixing end member model of Pb isotope ratios, coal combustion emission dominated anthropogenic Pb sources in the half part of the century contributing 13 to 43 % of total Pb in sediment. Moreover, contributions of chemical and organic fertilizer were 1-13 and 5-14 %, respectively. In contrast, the contribution of leaded gasoline was low than 8 %. The results indicated that historical records of Pb contamination predominantly sourced from coal combustion and chemical and organic fertilizer in the catchment. In addition, an increase of coal combustion source and fertilizers was found throughout the sediment core, whereas the contribution of leaded gasoline had declined after 2000s, which is attributed to the phaseout of leaded gasoline in China.

  19. Lead fluxes and 206Pb/207Pb isotope ratios in rime and snow collected at remote mountain-top locations (Czech Republic, Central Europe): Patterns and sources

    NASA Astrophysics Data System (ADS)

    Cimova, Nikoleta; Novak, Martin; Chrastny, Vladislav; Curik, Jan; Veselovsky, Frantisek; Blaha, Vladimir; Prechova, Eva; Pasava, Jan; Houskova, Marie; Bohdalkova, Leona; Stepanova, Marketa; Mikova, Jitka; Krachler, Michael; Komarek, Arnost

    2016-10-01

    During three winter seasons (2009-2011), Pb concentrations were measured in precipitation at 10 high-elevation sites in the Czech Republic, close to the borders with Austria, Germany, Poland, and Slovakia. Soluble and insoluble Pb forms were quantified in snow (vertical deposition), and rime (horizontal deposition). The objective was to compare Pb input fluxes into ecosystems via vertical and horizontal deposition, and to identify the residual Pb pollution sources in an era of rapidly decreasing industrial pollution. Lead soluble in diluted HNO3 made up 96% of total Pb deposition, with the remaining 4% Pb bound mainly in silicates. Three times higher concentrations of soluble Pb in rime than in snow, and 2.5 times higher concentrations of insoluble Pb in rime than in snow were associated with slightly different Pb isotope ratios. On average, the 206Pb/207Pb ratios in rime were higher than those in snow. Higher mean 206Pb/207Pb ratios of insoluble Pb (1.175) than in soluble Pb (1.165) may indicate an increasing role of geogenic Pb in recent atmospheric deposition. A distinct reversal to more radiogenic 206Pb/207Pb ratios in snow and rime in 2010, compared to literature data from rain-fed Sphagnum peatlands (1800-2000 A.D.), documented a recent decrease in anthropogenic Pb in the atmosphere of Central Europe. Since the early 1980s, Pb concentrations in snow decreased 18 times in the rural south of the Czech Republic, but only twice in the industrial north of the Czech Republic. Isotope signatures indicated that Pb in today's atmospheric deposition is mainly derived from Mesozoic ores mined/processed in Poland and coal combustion in the Czech Republic and Poland.

  20. Diamond growth history from in situ measurement of Pb and S isotopic compositions of sulfide inclusions

    NASA Astrophysics Data System (ADS)

    Rudnick, Roberta L.; Eldridge, C. Stewart; Bulanova, Galina P.

    1993-01-01

    In a continuing effort to understand crust-mantle dynamics, we have determined the S and Pb isotopic compositions of mantle sulfides encapsulated within diamonds from under the Siberian craton and compared these results to those of previously investigated African counterparts. Because diamond inclusions are isolated from exchange with surrounding mantle, they may preserve the history of diamond growth and act as direct tracers of the origins of mantle materials. Study of these inclusions may thus offer the best chance of recognizing global-scale interaction between Earth's crust and mantle. Although δ34S values of the Siberian sulfides do not deviate significantly from the mantle value of 0‰ ± 3‰, Pb isotopic compositions are highly variable. Pb isotopic compositions of sulfides from peridotitic suite diamonds generally plot near the terrestrial Pb growth curve, with model ages ranging between 0 and 2 Ga, whereas sulfides from eclogitic suite diamonds have radiogenic compositions, plotting beyond the growth curve. These results, which are similar to those for sulfides in African diamonds, suggest that the sulfides from eclogitic suite diamonds were derived from a source with an unusually high U/Pb ratio and may indicate a common process (such as subduction of crystal materials into the mantle) operating beneath Africa and Siberia. The absence of extremely radiogenic Pb in sulfides from eclogite xenoliths suggests that the radiogenic material from which eclogitic suite diamonds grew was a transient feature of the mantle, associated with diamond growth. The ultimate origin of this high U/Pb signature, however, remains enigmatic. Large variations in Pb isotopic composition of sulfides from different zones in a single peridotitic suite diamond document (1) crystallization of the diamond's core near 2.0 Ga, (2) growth of its outer zone in an environment with a high U/Pb ratio similar to the growth environment of eclogitic suite diamonds, and (3) growth of the

  1. Trace metal and carbon isotopic variations in cave dripwater and stalagmite geochemistry from northern Borneo

    NASA Astrophysics Data System (ADS)

    Partin, Judson W.; Cobb, Kim M.; Adkins, Jess F.; Tuen, Andrew A.; Clark, Brian

    2013-09-01

    We investigate stalagmite trace metal ratios and carbon isotopic composition (δ13C) as potential paleoclimate proxies by comparing cave dripwaters, stalagmites, and bedrock composition from Gunung Mulu and Gunung Buda National Parks in northern Borneo, a tropical rainforest karst site. Three year long, biweekly time series of dripwater Mg/Ca, Sr/Ca, and δ13C from several drips at our site are not correlated with rainfall variability, indicative of a relatively weak relationship between hydroclimate and dripwater geochemistry at our site. However, combining all of the dripwater geochemical data gathered over four field trips to our site (N > 300 samples), we find that drips with highly variable Mg[Sr]/Ca have relatively invariable δ18O values close to the mean. We hypothesize that increased residence times translate into reduced variance in dripwater δ18O through mixing in the epikarst as well as increased Mg[Sr]/Ca values through increased calcite precipitation in the epikarst. Mg/Ca, Sr/Ca, and δ13C time series from three overlapping stalagmites that grew over the last 27 kyrs are characterized by strong centennial-scale variations, and bear little resemblance to previously published, well-reproduced δ18O time series from the same stalagmites. The only shared signal among the three stalagmites' geochemical time series is a relative decrease of 1‰ in δ13C from the Last Glacial Maximum to the Holocene, consistent with a transition from savannah (C4) to rainforest (C3) conditions documented in nearby records. Taken together, our study indicates that stalagmite Mg[Sr]/Ca ratios are poor indicators of hydroclimate conditions at our site, while stalagmite δ13C exhibits some reproducible signals on glacial-interglacial timescales.

  2. Inorganic geochemistry data from Lake El'gygytgyn sediments: marine isotope stages 6-11

    NASA Astrophysics Data System (ADS)

    Minyuk, P. S.; Borkhodoev, V. Y.; Wennrich, V.

    2014-03-01

    Geochemical analyses were performed on sediments recovered by deep drilling at Lake El'gygytgyn in central Chukotka, northeastern Russia (67°30' N; 172°05' E). Major and rare element concentrations were determined using X-ray fluorescence spectroscopy (XRF) on the < 250 μm fraction from 617 samples dated to ca. 440 and 125 ka, which approximates marine isotope stages (MIS) 11 to 6. The inorganic geochemistry indicates significant variations in elemental composition between glaciations and interglaciations. Interglacial sediments are characterized by high contents of SiO2, Na2O, CaO, K2O, and Sr and are depleted in Al2O3, Fe2O3, TiO2, and MgO. An extreme SiO2 enrichment during MIS 11.3 and 9.3 was caused by an enhanced flux of biogenic silica (BSi). The geochemical structure of MIS 11 shows similar characteristics as seen in MIS 11 records from Lake Baikal (southeastern Siberia) and Antarctic ice cores, thereby arguing for the influence of global forcings on these records. High sediment content of TiO2, Fe2O3, MgO, Al2O3, LOI, Ni, Cr, and Zr typifies glacial stages, with the most marked increases during MIS 7.4 and 6.6. Reducing conditions during glacial times are indicated by peaks in the Fe2O3 content and coinciding low Fe2O3/MnO ratios. This conclusion also is supported by P2O5 and MnO enrichment, indicating an increased abundance of authigenic, fine-grained vivianite. Elemental ratios (CIA, CIW, PIA, and Rb/Sr) indicate that glacial sediments are depleted in mobile elements, like Na, Ca, K and Sr. This depletion was caused by changes in the sedimentation regime and thus reflects environmental changes.

  3. Magnesian anorthosites from the western highlands of the Moon: Isotope geochemistry and petrogenesis

    NASA Technical Reports Server (NTRS)

    Snyder, Gregory A.; Taylor, Lawrence A.; Halliday, Alex N.

    1993-01-01

    Breccias from the Apollo 14 landing site have provided a wealth of information on the genesis of the lunar highlands. Various pristine rock-types have been discovered in relative abundance including rare ferroan anorthosites and alkali-suite and magnesian-suite rocks. Mineral-chemical and radiogenic isotopic data are reported here for a newly discovered Mg-suite anorthosite from Apollo 14, sample 14303,347. Meyer et al. reported U-Pb zircon analyses of Mg-suite highlands rocks from the western limb of the Moon. We have compiled these ages and generated a weighted average age of 4211 = 6 Ma; some 200 Ma younger than ferroan anorthosites. Utilizing this age for Mg-anorthosite 14303,347, our data results in an initial epsilon(sub Nd) value of -1.0 and initial Sr-87/Sr-86 of 0.69915. Based on trace-element, isotopic, and mineral-chemical data, the western highlands Mg-suite is interpreted to be crustal precipitates of a picritic magma, which assimilated KREEPy trapped liquid from upper-mantle cumulates during its transport to the crust.

  4. Pb-, Sr- and Nd-Isotopic systematics and chemical characteristics of cenozoic basalts, Eastern China

    USGS Publications Warehouse

    Peng, Z.C.; Zartman, R.E.; Futa, K.; Chen, D.G.

    1986-01-01

    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.

  5. Petrogenesis of Challis volcanics from central and southwestern Idaho - Trace element and Pb isotopic evidence

    NASA Technical Reports Server (NTRS)

    Norman, Marc D.; Mertzman, Stanley A.

    1991-01-01

    An analysis of the lava flows and ash-flow tuffs in Idaho is conducted to determine the composition of the volcanics in terms of major and trace elements and Pb isotopic substances. Al2O3 is found to be low, MgO content is high, and the concentration of K2O is higher or equal to that of Na2O with respect to the lavas of mafic to intermediate composition. Trace elements and element ratios are compatible with the crustal component, and the Pb isotopic compositions suggest a lack of assimilation during crystallization. The evidence does not support the notion of a magma system related to subduction, and the data regarding Pb isotopes and trace elements point to a connection with the lithosphere. A model is proposed for the Challis volcanics in which they resulted from completely melting within the lithosphere and then extending during the late Mesozoic and early Cenozoic compression.

  6. Pb isotopes in Ascension Island rocks: oceanic origin for the gabbroic to granitic plutonic xenoliths

    NASA Astrophysics Data System (ADS)

    Weis, D.

    1983-02-01

    The Pb isotopic compositions and U and Pb concentrations of the lava series (alkali basalt to comendite) and of their plutonic xenoliths (gabbro to alkaline granite) of Ascension Island are reported. The data are used to evaluate the source of the xenoliths which formed two differentiation suites: the acidic and intermediate xenoliths together with most of the lavas on the one hand, and the gabbroic xenoliths and a basaltic tuff on the other hand. The Pb isotopic compositions imply a mantle origin for the source magmas of the xenoliths and confirm the possibility of generating granitic rocks in an oceanic environment by fractional crystallization of a mantle-derived magma whose geochemical and isotopic characteristics are comparable to the source magmas of oceanic island basalts.

  7. Total and partial photoneutron cross sections for Pb isotopes

    NASA Astrophysics Data System (ADS)

    Kondo, T.; Utsunomiya, H.; Goriely, S.; Daoutidis, I.; Iwamoto, C.; Akimune, H.; Okamoto, A.; Yamagata, T.; Kamata, M.; Itoh, O.; Toyokawa, H.; Lui, Y.-W.; Harada, H.; Kitatani, F.; Hilaire, S.; Koning, A. J.

    2012-07-01

    Using quasimonochromatic laser-Compton scattering γ rays, total photoneutron cross sections were measured for 206,207,208Pb near neutron threshold with a high-efficiency 4π neutron detector. Partial E1 and M1 photoneutron cross sections along with total cross sections were determined for 207,208Pb at four energies near threshold by measuring anisotropies in photoneutron emission with linearly polarized γ rays. The E1 strength dominates over the M1 strength in the neutron channel where E1 photoneutron cross sections show extra strength of the pygmy dipole resonance in 207,208Pb near the neutron threshold corresponding to 0.32%-0.42% of the Thomas-Reiche-Kuhn sum rule. Several μN2 units of B(M1)↑ strength were observed in 207,208Pb just above neutron threshold, which correspond to an M1 cross section less than 10% of the total photoneutron cross section.

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

    NASA Technical Reports Server (NTRS)

    Chen, J. H.

    1987-01-01

    Concentrations and isotopic compositions of U, Th, and Pb in three hydrothermal fluids from the Juan de Fuca Ridge were determined from samples obtained by the Alvin submersible. The samples were enriched in Pb and Th relative to deep-sea water, and were deficient in U. No clear relationship with Mg was found, suggesting nonideal mixing between the hot hydrothermal fluids and the cold ambient seawater. Values for U-234/U-238 have a seawater signature, and show a U-234 enrichment relative to the equilibrium value. The Pb isotopic composition has a uniform midocean ridge basalt signature, and it is suggested that Pb in these fluids may represent the best average value of the local oceanic crust.

  9. U-Pb isotope systematics and age of uranium mineralization, Midnite mine, Washington.

    USGS Publications Warehouse

    Ludwig, K. R.; Nash, J.T.; Naeser, C.W.

    1981-01-01

    Uranium ores at the Midnite mine, near Spokane, Washington, occur in phyllites and calcsilicates of the Proterozoic Togo Formation, near the margins of an anomalously uraniferous, porphyritic quartz monzonite of Late Cretaceous age. The present geometry of the ore zones is tabular, with the thickest zones above depressions in the pluton-country rock contact. Analyses of high-grade ores from the mine define a 207 Pb/ 204 Pb- 235 U/ 204 Pb isochron indicating an age of mineralization of 51.0 + or - 0.5 m.y. This age coincides with a time of regional volcanic activity (Sanpoil Volcanics), shallow intrusive activity, erosion, and faulting. U-Th-Pb isotopic ages of zircons from the porphyritic quartz monzonite in the mine indicate an age of about 75 m.y., hence the present orebodies were formed about 24 m.y. after its intrusion. The 51-m.y. time of mineralization probably represents a period of mobilization and redeposition of uranium by supergene ground waters, perhaps aided by mild heating and ground preparation and preserved by a capping of newly accumulated, impermeable volcanic rocks. It seems most likely that the initial concentration of uranium occurred about 75 m.y. ago, probably from relatively mild hydrothermal fluids in the contact-metamorphic aureole of the U-rich porphyritic quartz monzonite.Pitchblende, coffinitc, pyrite, marcasite, and hisingerite are the most common minerals in the uranium-bearing veinlets, with minor sphalerite and chalcopyrite. Coffinitc with associated marcasite is paragenetically later than pitchblende, though textural and isotopic evidence suggests no large difference in the times of pitchblende and colfinite formation.The U-Pb isotope systematics of total ores and of pitchblende-coffinite and pyrite-marcasite separates show that whereas open system behavior for U and Pb is essentially negligible for large (200-500 g) ore samples, Pb migration has occurred on a scale of 1 to 10 mm (out of pitchblende and coffinite and into pyrite

  10. Evaluating Young Volcanism at Baitoushan Volcano: Insights From Single Mineral Crystal Sr and Pb Isotope Analyses

    NASA Astrophysics Data System (ADS)

    Rodgers, S. L.; Ramos, F. C.; Gill, J. B.

    2008-12-01

    Baitoushan volcano, located along the North-Korea/China border, generated one of the largest caldera- forming rhyolitic eruptions in the northern hemisphere in the last 2000 years. In addition to a large ~1000AD comendite eruption, a pantellerite eruption occurred at ~0AD which left a small pumice deposit. We have evaluated the isotopic signatures of single mineral crystals and pumice fragments from this pantellerite to evaluate the sources, petrogenetic history, timing, and residence of highly alkaline rhyolitic magma at Baitoushan. Single mineral isotope characteristics of this pantellerite are complex. Rb/Sr analyses of whole pumice fragments suggest a pantellerite residence age of ~348ky, similar to residence ages determined for Long Valley Caldera and Valles Caldera. Individual potassium feldspar and clinopyroxene crystals have similarly variable and overlapping 87Sr/86Sr signatures that are different than those of host pumice fragments but similar to crystals erupted in the ~1000AD comendite. These same crystals define a linear trend in 207Pb/204Pb vs 206Pb/204Pb that suggests mixing between host pumice and a second currently unidentified endmember. Results, however, unequivocally demonstrate mixing and undermine any residence age associated with Rb/Sr isotope systematics of pumice fragments. Overall Sr and Pb isotope systematics reflect variable signatures as compared to all other recent eruptive products at Baitoushan and suggest highly variable processes involved in melt production and that select minerals may be shared between different eruptions spanning a 2000 to 4000 year time period.

  11. Some Pb and Sr isotopic measurements on eclogites from the Roberts Victor Mine, South Africa.

    NASA Technical Reports Server (NTRS)

    Manton, W. I.; Tatsumoto, M.

    1971-01-01

    Five nodules of eclogite, one nodule of garnet peridotite, and one sample of kimberlite from the Roberts Victor Mine in the Orange Free State were analyzed for concentrations of U, Th, Pb, Rb, and Sr, and also isotopic compositions of Pb and Sr. Results are presented and analyzed. They indicate that the Roberts Victor eclogites have been contaminated by lead from the host rock of kimberlite. This finding suggests that stepwise extraction of lead may be a means of obtaining the isotopic composition of the primary lead in kimberlitic eclogites.

  12. Isotope and trace element geochemistry of sediments from the Barbados Ridge-Demerara Plain region, Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    White, William M.; Dupré, Bernard; Vidal, Philippe

    1985-09-01

    Twenty-four piston core sediment samples and 13 sediments and 3 basalts from DSDP Leg 78 Site 543 were analyzed for Sr, Nd and Pb isotopic compositions. The results show sediment with highly radiogenic Pb 206Pb /204Pb up to 19.8) and rather radiogenic Sr and unradiogenic Nd has been deposited in the region since the Cretaceous. The source of this sediment is probably the Archean Guiana Highland, which is drained by the Orinoco River. Pb and Sr isotopic compositions and sediment thickness decrease and 143Nd /144Nd increases northward due to a decrease in turbiditic component. This decrease is partly due to the damming action of basement ridges. Rare earth concentrations in the sediments are somewhat low, due to the abundance of detrital and biogenic components in the sediment and rapid sedimentation rates. Both positive and negative Ce anomalies occur in the surface sediments, but only positive Ce anomalies occur in the Site 543 sediments. It is unlikely that sediment subducted to the source region of Lesser Antilles arc magmas could be the cause of negative Ce anomalies in those magmas. Isotopic compositions of Site 543 basalts show some effect of contamination by seawater-basalt reaction products and sediments. Beyond this, however, they are typical of "normal" depleted MORB.

  13. Isotope geochemistry of early Kilauea magmas from the submarine Hilina bench: The nature of the Hilina mantle component

    USGS Publications Warehouse

    Kimura, Jun-Ichi; Sisson, Thomas W.; Nakano, Natsuko; Coombs, Michelle L.; Lipman, Peter W.

    2006-01-01

    Submarine lavas recovered from the Hilina bench region, offshore Kilauea, Hawaii Island provide information on ancient Kilauea volcano and the geochemical components of the Hawaiian hotspot. Alkalic lavas, including nephelinite, basanite, hawaiite, and alkali basalt, dominate the earliest stage of Kilauea magmatism. Transitional basalt pillow lavas are an intermediate phase, preceding development of the voluminous tholeiitic subaerial shield and submarine Puna Ridge. Most alkalic through transitional lavas are quite uniform in Sr–Nd–Pb isotopes, supporting the interpretation that variable extent partial melting of a relatively homogeneous source was responsible for much of the geochemical diversity of early Kilauea magmas (Sisson et al., 2002). These samples are among the highest 206Pb/204Pb known from Hawaii and may represent melts from a distinct geochemical and isotopic end-member involved in the generation of most Hawaiian tholeiites. This end-member is similar to the postulated literature Kea component, but we propose that it should be renamed Hilina, to avoid confusion with the geographically defined Kea-trend volcanoes. Isotopic compositions of some shield-stage Kilauea tholeiites overlap the Hilina end-member but most deviate far into the interior of the isotopic field defined by magmas from other Hawaiian volcanoes, reflecting the introduction of melt contributions from both “Koolau” (high 87Sr/86Sr, low 206Pb/204Pb) and depleted (low 87Sr/86Sr, intermediate 206Pb/204Pb) source materials. This shift in isotopic character from nearly uniform, end-member, and alkalic, to diverse and tholeiitic corresponds with the major increase in Kilauea's magmatic productivity. Two popular geodynamic models can account for these relations: (1) The upwelling mantle source could be concentrically zoned in both chemical/isotopic composition, and in speed/extent of upwelling, with Hilina (and Loihi) components situated in the weakly ascending margins and the

  14. Pb enamel biomarker: Deposition of pre- and postnatal Pb isotope injection in reconstructed time points along rat enamel transect

    SciTech Connect

    Rinderknecht, A.L.; Kleinman, M.T.; Ericson, J.E. . E-mail: jeericso@uci.edu

    2005-10-01

    Exposure to lead (Pb) as well as other heavy metals in the environment is still a matter of public health concern. The development of the enamel biomarker for heavy metal exposure assessment is designed to improve studies of dose-effect relationships to developmental anomalies, particularly embryonic dysfunctions, and to provide a time-specific recount of past exposures. The work presented in this paper demonstrates maternal transfer across the placental barrier of the enriched isotope {sup 206}Pb tracer to the enamel of the rat pup. Likewise, injections of {sup 204}Pb-enriched tracer in the neonate rat resulted in deposition of the tracer in the enamel histology as measured by secondary ion microprobe spectrometry. Through enamel, we were able to observe biological removal and assimilation of prenatal and postnatal tracers, respectively. This research demonstrates that enamel can be used as a biomarker of exposure to Pb and may illustrate the toxicokinetics of incorporating Pb into fetal and neonatal steady-state system processes. The biomarker technique, when completely developed, may be applied to cross-sectional and longitudinal epidemiological research.

  15. Infrared spectroscopy and hydrogen isotope geochemistry of hydrous silicate glasses. Progress report, June 1, 1996--May 31, 1999

    SciTech Connect

    Epstein, S.; Stolper, E.

    1998-06-01

    This DOE-funded project (DE-FG03-ER13445, 6/1/96-5/31/99) emphasizes study of the behavior of volatiles in magmatic systems. The project is explicitly focused on the combined application of IR spectroscopy, experimental petrology, and stable isotope geochemistry to understanding the behavior and properties of the volatile components dissolved in silicate melts and glasses, although in recent years, our emphasis has broadened to include non-volatile aspects of stable isotope geochemistry. Results obtained during the current grant and previous grant periods confirm that when applied to study of well-chosen synthetic and natural systems, the combination of these approaches and techniques can yield insights of general petrological and volcanological value and of practical value to DOE. In particular, the results of our DOE-funded work has led to a deeper understanding of the physical chemistry of silicate melts as well as specific constraints on the thermal and chemical evolution of high-level magmatic systems of the sort being evaluated as potential geothermal and magmathermal energy sources. Moreover, our work has also contributed to understanding the behavior of H-, C-, and O-bearing species in amorphous and crystalline silicates, including the kinetics of their interactions; we believe these results will contribute to efforts to use silicates in the development of nuclear waste disposal strategies.

  16. Pb isotope composition in lichens and aerosols from eastern Sicily: Insights into the regional impact of volcanoes on the environment

    SciTech Connect

    Monna, F. ); Aiuppa, A.; Varrica, D. ); Dongarra, G. CNR, Palermo . Istituto Geochimica dei Fluidi)

    1999-08-01

    A total of 25 lichen thalli of Parmelia conspersa (Ehrh), collected at Vulcano island and at Mt. Etna, during a one-year biogeochemical survey, were analyzed for Pb, br, Al, Sc,[sup 206]Pb/[sup 207]Pb, and [sup 208]Pb/[sup 206]Pb ratios. Lead isotope ratios were also measured on aerosol samples from urban areas and industrial sites of Sicily. The observed [sup 206]Pb/[sup 207]Pb range for urban and industrial aerosols matches the anthropogenic signature. Lichens instead, are closer to the compositional field of [sup 206]Pb rich geogenic sources. This natural input is more evident at Vulcano island than at Mt. Etna, where the anthropogenic activities are considerably more effective. On the basis of lead isotope data, Pb/Br ratios and calculated lead enrichment factors, a natural lead pollution from volcanoes is suggested. Volcanic lead contribution ranges from 10 to 30% at Mt. Etna to 10--80% at Vulcano island.

  17. Pb-isotopic evidence for an early, enriched crust on Mars

    NASA Astrophysics Data System (ADS)

    Bellucci, J. J.; Nemchin, A. A.; Whitehouse, M. J.; Humayun, M.; Hewins, R.; Zanda, B.

    2015-01-01

    Martian meteorite NWA 7533 is a regolith breccia that compositionally resembles the Martian surface measured by orbiters and landers. NWA 7533 contains monzonitic clasts that have zircon with U-Pb ages of 4.428 Ga. The Pb isotopic compositions of plagioclase and alkali feldspars, as well as U-Pb isotopic compositions of chlorapatite in the monzonitic clasts of NWA 7533 have been measured by Secondary Ion Mass Spectrometry (SIMS). The U-Pb isotopic compositions measured from the chlorapatite in NWA 7533 yield an age of 1.357 ± 81 Ga (2σ). The least radiogenic Pb isotopic compositions measured in plagioclase and K-feldspar lie within error of the 4.428 Ga Geochron. These data indicate that the monzonitic clasts in NWA 7533 are a product of a differentiation history that includes residence in a reservoir that formed prior to 4.428 Ga with a μ-value (238U/204Pb) of at least 13.4 ± 1.7 (2 σ) and a κ-value (232Th/238U) of ∼4.3. This μ-value is more than three times higher than any other documented Martian reservoir. These results indicate either the Martian mantle is significantly more heterogeneous than previously thought (μ-value of 1-14 vs. 1-5) and/or the monzonitic clasts formed by the melting of Martian crust with a μ-value of at least 13.4. Therefore, NWA 7533 may contain the first isotopic evidence for an enriched, differentiated crust on Mars.

  18. Geochemistry and U-Pb zircon geochronology of the pegmatites in Ede area, southwestern Nigeria: A newly discovered oldest Pan African rock in southwestern Nigeria

    NASA Astrophysics Data System (ADS)

    Adetunji, A.; Olarewaju, V. O.; Ocan, O. O.; Ganev, V. Y.; Macheva, L.

    2016-03-01

    Field and petrographic studies, whole rock geochemistry and in-situ LA-ICP-MS geochemical and isotopic U-Pb measurements on zircons have been performed on granitic pegmatites of Ede area, southwestern Nigeria with a view to characterize them, determining their mineralization potentials, petrogenetic attributes and emplacement age. The pegmatites are hosted by migmatite gneiss complex, biotite-muscovite schist and associated quartzite. The textural and mineralogical characteristics of these pegmatites indicate the occurrence of two main varieties, namely, muscovite pegmatite and garnet pegmatite. Of less importance are inclusions and pods of graphic granite, quartz-microcline aplitic and pegmatitic bodies. At the present level of erosion, the parent igneous rocks of the pegmatites are not exposed. The two dominant pegmatite varieties show slightly different chemical peculiarities but similar peraluminous character. The average K/Rb ratios of 165 and 163, respectively, for muscovite and garnet pegmatites combined with other trace element compositions are indicative of affinity to muscovite class of pegmatite which are generally not promising for rare elements mineralization. However, the unusually high concentration of bismuth in the zircons indicates Bi mineralization in the area which can either be in the pegmatites or host rocks. The Nb/Ta ratios for both muscovite and garnet pegmatites range from 0.7 to 15.2 and 1.0 to 14.8, respectively. These Nb/Ta ratios and Eu anomalies are statistically similar for both pegmatites. These probably indicate the pegmatites crystallized from a common source but separated into crystallization paths that produced different pegmatite varieties through liquid-liquid immiscibity mechanism. In-situ measurements of REE, P, Y, Nb, Hf, Ta, Bi, Th and U of individual zircon grains show the existence of two chemically and texturally different domains which are indicative of alteration that may be due to interface-coupled dissolution

  19. Geochemistry, zircon U-Pb dating and Hf isotopies composition of Paleozoic granitoids in Jinchuan, NW China: Constraints on their petrogenesis, source characteristics and tectonic implication

    NASA Astrophysics Data System (ADS)

    Zeng, Renyu; Lai, Jianqing; Mao, Xiancheng; Li, Bin; Ju, Peijiao; Tao, Shilong

    2016-05-01

    Granitoids are widely distributed in Jinchuan at the southwestern margin of the North China plate, which is also an important area of mineral deposits. The research subject of this article are two Paleozoic granitoids, a cataclastic syenogranite and a granodiorite porphyry. This study presents whole rock geochemistry and zircon U-Pb-Hf isotope data for the two granitoids to determine their petrogenesis, source characteristics and tectonic significance. The cataclastic syenogranite is characterized by metaluminous composition with high potassium, and LaN/YbN from 39 to 48. The composition with strong negative Eu anomalies and Zircon saturation temperatures (TZr) from 947 to 1072 °C classify this intrusion as an A-type granite. The granodiorite porphyry is metaluminous with high sodium, sub-alkaline, LaN/YbN ratios from 27 to 32. These I-type intrusions have no Eu anomalies and TZr ranges from 818 to 845 °C. Both the cataclastic syenogranite and granodiorite porphyry show enrichment of LREE and LILE and depletion of HREE and HFSE, except Hf and Zr. Using single zircon LA-ICP-MS U-Pb dating, the emplacement age of the cataclastic syenogranite and granodiorite porphyry are determined at 433.4 ± 3.7 Ma and 361.7 ± 4.6 Ma, respectively. Zircons from the cataclastic syenogranits have uniform negative εHf(t) values (-11 ± 0.5 to -9 ± 0.5), implying the involvement of an old Palaeoproterozoic crustal source in magma genesis. The zircons from the granodiorite porphyry have εHf(t) values that range from -8 ± 1.0 to +10 ± 0.6, suggesting heterogeneous source materials involving both juvenile and ancient crust reworked crustal components. Based on the geological significance of granites at the southwestern margin of the North China plate, the closure of the North Qilian Ocean occurred at ∼444 Ma. Geochemical features suggest that the cataclastic syenogranite and granodiorite porphyry formed in an intraplate extensional and compressional setting, respectively. Hence

  20. Radiogenic Isotopes As Paleoceanographic Tracers in Deep-Sea Corals: Advances in TIMS Measurements of Pb Isotopes and Application to Southern Ocean Corals

    NASA Astrophysics Data System (ADS)

    Wilson, D. J.; van de Flierdt, T.; Bridgestock, L. J.; Paul, M.; Rehkamper, M.; Robinson, L. F.; Adkins, J. F.

    2014-12-01

    Deep-sea corals have emerged as a valuable archive of deep ocean paleoceanographic change, with uranium-series dating providing absolute ages and the potential for centennial resolution. In combination with measurements of radiocarbon, neodymium isotopes and clumped isotopes, this archive has recently been exploited to reconstruct changes in ventilation, water mass sourcing and temperature in relation to millennial climate change. Lead (Pb) isotopes in both corals and seawater have also been used to track anthropogenic inputs through space and time and to trace transport pathways within the oceans. Better understanding of the oceanic Pb cycle is emerging from the GEOTRACES programme. However, while Pb isotopes have been widely used in environmental studies, their full potential as a (pre-anthropogenic) paleoceanographic tracer remains to be exploited. In deep-sea corals, challenges exist from low Pb concentrations in aragonite in comparison to secondary coatings, the potential for contamination, and the efficient elemental separation required for measurement by thermal ionisation mass spectrometry (TIMS). Here we discuss progress in measuring Pb isotopes in coral aragonite using a 207Pb-204Pb double spike on a ThermoFinnigan Triton TIMS. For a 2 ng NIST-981 Pb standard, the long term reproducibility (using 1011 Ω resistors) is ~1000 ppm (2 s.d.) on 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios. We now show that using a new 1012 Ω resistor to measure the small 204Pb beam improves the internal precision on these ratios from ~500 ppm (2 s.e.) to ~250 ppm (2 s.e.) and we envisage a potential improvement in the long term reproducibility as a consequence. We further assess the internal precision and external reproducibility of our method using a BCR-2 rock standard and an in-house coral standard. Preliminary evidence on the application of this method to natural samples is derived from cleaning experiments and replication tests on deep-sea corals from the Southern

  1. Minor-element and Sr-isotope geochemistry of tertiary stocks, Colorado mineral belt

    USGS Publications Warehouse

    Simmons, E.C.; Hedge, C.E.

    1978-01-01

    Rocks of the northeast portion of the Colorado mineral belt form two petrographically, chemically and geographically distinct rock suites: (1) a silica oversaturated granodiorite suite; and (2) a silica saturated, high alkali monzonite suite. Rocks of the granodiorite suite generally have Sr contents less than 1000 ppm, subparallel REE patterns and initial 87Sr/ 86Sr ratios greater than 0.707. Rocks of the monzonite suite are restricted to the northeast part of the mineral belt, where few rocks of the granodiorite suite occur, and generally have Sr contents greater than 1000 ppm, highly variable REE patterns and 87Sr/86Sr initial ratios less than 0.706. Despite forming simple, smooth trends on major element variation diagrams, trace element data for rocks of the granodiorite suite indicate that they were not derived from a single magma. These rocks were derived from magmas having similar REE patterns, but variable Rb and Sr contents, and Rb/Sr ratios. The preferred explanation for these rocks is that they were derived by partial melting of a mixed source, which yielded pyroxene granulite or pyroxenite residues. The monzonite suite is chemically and petrographically more complex than the granodiorite suite. It is subdivided here into alkalic and mafic monzonites, and quartz syenites, based on the textural relations of their ferromagnesian phases and quartz. The geochemistry of these three rock types require derivation from separate and chemically distinct magma types. The preferred explanation for the alkalic monzonites is derivation from a heterogeneous mafic source, leaving a residue dominated by garnet and clinopyroxene. Early crystallization of sphene from these magmas was responsible for the severe depletion of the REE observed in the residual magmas. The lower Sr content and higher Rb/Sr ratios of the mafic monzonites requires a plagioclase-bearing source. The Sr-isotope systematics of the majority of these rocks are interpreted to be largely primary, and not

  2. Lead isotopes and trace metal ratios of aerosols as tracers of Pb pollution sources in Kanpur, India

    NASA Astrophysics Data System (ADS)

    Sen, Indra; Bizimis, Michael; Tripathi, Sachchida; Paul, Debajyoti; Tyagi, Swati; Sengupta, Deep

    2015-04-01

    The anthropogenic flux of Pb in the Earth's surface is almost an order of magnitude higher than its corresponding natural flux [1]. Identifying the sources and pathways of anthropogenic Pb in environment is important because Pb toxicity is known to have adverse effects on human health. Pb pollution sources for America, Europe, and China are well documented. However, sources of atmospheric Pb are unknown in India, particularly after leaded gasoline was phased out in 2000. India has a developing economy with a rapidly emerging automobile and high temperature industry, and anthropogenic Pb emission is expected to rise in the next decade. In this study, we report on the Pb- isotope compositions and trace metal ratios of airborne particulates collected in Kanpur, an industrial city in northern India. The Pb concentration in the airborne particulate matter varies between 14-216 ng/m3, while the other heavy metals vary by factor of 10 or less, e.g. Cd=0.3-3 ng/m3, As=0.4-3.5 ng/m3, Zn=36-161 ng/m3, and Cu=3-22 ng/m3. The 206Pb/207Pb, 208Pb/206Pb, and 208Pb/207Pb vary between 1.112 - 1.129, 2.123-2.141, and 2.409-2.424 respectively, and are highly correlated with each other (R2>0.9). Pb isotopes and trace metal data reveals that coal combustion is the major source of anthropogenic Pb in the atmosphere, with limited contribution from mining and smelting processes. We further conclude that combination of Pb isotope ratios and V/Pb ratios are powerful tracers for Pb source apportionment studies, which is otherwise difficult to differentiate based only on Pb systematics [1] Sen and Peucker-Ehrenbrink (2012), Environ. Sci. Technol.(46), 8601-8609

  3. Effects of simple acid leaching of crushed and powdered geological materials on high-precision Pb isotope analyses

    NASA Astrophysics Data System (ADS)

    Todd, Erin; Stracke, Andreas; Scherer, Erik E.

    2015-07-01

    We present new results of simple acid leaching experiments on the Pb isotope composition of USGS standard reference material powders and on ocean island basalt whole rock splits and powders. Rock samples were leached with cold 6 N HCl in an ultrasonic bath, then on a hot plate, and washed with ultrapure H2O before sample digestion in HF-HNO3 and chromatographic purification of Pb. Lead isotope analyses were measured by Tl-doped MC-ICPMS. Intrasession and intersession analytical reproducibilities of repeated analyses of both synthetic Pb solutions and Pb from single digests of chemically processed natural samples were generally better than 100 ppm (2 SD). The comparison of leached and unleached samples shows that leaching consistently removes variable amounts of contaminants that differ in Pb isotopic composition for different starting materials. For repeated digests of a single sample, analyses of leached samples reproduce better than those of unleached ones, confirming that leaching effectively removes most of the heterogeneously distributed extraneous Pb. Nevertheless, the external reproducibility of leached samples is still up to an order of magnitude worse than that of Pb solution standards (˜100 ppm). More complex leaching methods employed by earlier studies yield Pb isotope ratios within error of those produced by our method and at similar levels of reproducibility, demonstrating that our simple leaching method is as effective as more complex leaching techniques. Therefore, any Pb isotope heterogeneity among multiple leached digests of samples in excess of the external reproducibility is attributed to inherent isotopic heterogeneity of the sample. The external precision of ˜100 ppm (2 SD) achieved for Pb isotope ratio determination by Tl-doped MC-ICPMS is thus sufficient for most rocks. The full advantage of the most precise Pb isotope analytical methods is only realized in cases where the natural isotopic heterogeneity among samples in a studied suite is

  4. Geochronology, geochemistry and Sr-Nd-Hf isotopes of mafic dikes in the Huicheng Basin: Constraints on intracontinental extension of the Qinling orogen

    NASA Astrophysics Data System (ADS)

    Li, Wei; Dong, Yunpeng; Guo, Anlin; Liu, Xiaoming; Wang, Yuejun; Liu, Wenhang; Yang, Yuanzhen

    2015-05-01

    The diabase dikes intruded the Lower Cretaceous sandstone in the Huicheng Basin are key to understanding the Mesozoic tectonic evolution of the Qinling orogen. LA-ICP-MS zircon U-Pb dating yields a crystallization age of 107 ± 1 Ma for them. The dikes have low contents of SiO2 (42.46-50.16 wt.%), MgO (3.47-5.59 wt.%) with low Mg# of 49-59, and TiO2 (1.35-1.63 wt.%), high TFe2O3 (8.15-9.36 wt.%), Al2O3 (14.75-17.23 wt.%) and K2O (0.87-3.61 wt.%). Their Ni and Cr contents are in range of 16.8-111 and 45.7-315 ppm, respectively. They are significantly enriched in light rare earth elements and large ion lithophile elements (e.g., Cs, Pb and Ba), and depleted in Rb, K, P, and Ti. The dikes show relatively high whole-rock initial 87Sr/86Sr ratios (0.7071-0.7079) and negative εNd (t) values (-1.5 to -4.8) with single-stage Nd model ages of 941-1186 Ma. In addition, they have low zircon εHf (t) values (-8.6 to +3.5) with single-stage Hf model ages of 674-1117 Ma. Both elemental and isotopic geochemistry suggests that the magma of these dikes has undergone significant crystallization fractionation of olivine and pyroxene but weak crustal contamination during magma evolution. They were derived from partial melting of an enriched lithospheric mantle source. Together with regional geological data, these results suggest that the Qinling orogen experienced an intracontinental extension during the late Early Cretaceous.

  5. Trace element and isotopic geochemistry of Cretaceous magmatism in NE Asia: Spatial zonation, temporal evolution, and tectonic controls

    NASA Astrophysics Data System (ADS)

    Tikhomirov, Petr L.; Kalinina, Elena A.; Moriguti, Takuya; Makishima, Akio; Kobayashi, Katsura; Nakamura, Eizo

    2016-11-01

    Results of a comprehensive geochemical study (major and trace elements, and isotopes of Sr, Nd, Pb, Hf) of Cretaceous volcanic rocks from the Chukotka area in northeastern Russia are presented. Synthesis of available geological and geochronological data suggests diachronous onset of activity of the Okhotsk-Chukotka volcanic belt (OCVB), the largest magmatic province in the region. The OCVB consists of ca. 106 km3 of volcanic rocks. At 106-105 Ma, subduction-related magmatism initiated in the southern and central segments of the OCVB. In the Central and Northern Chukotka areas, where the northern OCVB is exposed, onset of arc magmatism occurred ca. 10 m.y. after extension-related magmatism of the Chaun igneous province at 109-104 Ma. Mafic rocks from the OCVB yield (87Sr/86Sr)80 Ma of 0.7033 to 0.7047, εNd80 Ma of 0.0 to 7.10, εHf80 Ma of 4.12 to 12.88, (206Pb/204Pb)80 Ma of 18.11 to 18.42, and (208Pb/204Pb)80 Ma of 37.96 to 38.21. Volcanic rocks from the Chaun province, as well as OCVB rocks from Northern Chukotka, originate from a relatively enriched source and have (87Sr/86Sr)80 Ma of 0.7088 to 0.7100, εNd80 Ma of - 5.81 to - 3.42, εHf80 Ma of - 3.40 to - 0.25, (206Pb/204Pb)80 Ma of 18.69 to 18.90, and (208Pb/204Pb)80 Ma of 38.65 to 38.86. No definitive across-arc elemental or isotopic zonation of the OCVB has been revealed, probably because of wide-scale crustal melting and subsequent contamination of mantle-derived melts. However, there is a clear along-arc isotopic zonation. In our interpretation, this results from heterogeneity of the subcontinental lithospheric mantle, which likely was a major contributor to the magma source. The similar isotopic signatures of silicic (dominantly crust-derived) and mafic (mantle-derived) volcanic rocks in each OCVB segment imply that remelting of juvenile mafic underplated material was the main process responsible for the crust-derived magma generation. These data from the major Cretaceous magmatic provinces of northeast

  6. Multiple sulfur isotope geochemistry of Dharwar Supergroup, Southern India: Late Archean record of changing atmospheric chemistry

    NASA Astrophysics Data System (ADS)

    Mishima, Kaoru; Yamazaki, Rie; Satish-Kumar, Madhusoodhan; Ueno, Yuichiro; Hokada, Tomokazu; Toyoshima, Tsuyoshi

    2017-04-01

    Earth's tectonic and climatic systems may have changed fundamentally before the Great Oxidation Event (GOE) at about 2.3 Ga. Sulfur Mass Independent Fractionation (S-MIF) has demonstrated that Earth's atmosphere was virtually oxygen-free before the GOE. During 3.0 to 2.4 Ga, the change in Δ33S and Δ36S signals may reflect the perturbation of atmospheric chemistry, though the mechanisms of the change are uncertain. Here, we reported multiple sulfur isotopic studies of Archean volcano-sedimentary sequences of the Dharwar Supergroup, distributed in the Chitradurga Schist Belt (CSB), Southern India. New field mapping and zircon U-Pb dating allows us to reconstruct detailed lithostratigraphy of the Dharwar Supergroup. The lower unit consists of post-3.0 Ga conglomerate, stromatolitic carbonate, siliciclastics with diamictite, chert/BIF and pillowed basalt in ascending order, all of which are older than the 2676 Ma dacite dyke that had intruded into the lower unit. The upper unit unconformably overlies the pillow basalts at the top of the lower unit, and consists of conglomerate/sandstone with ∼2600 Ma detrital zircons, komatiitic basalt, BIF and siliciclastic sequence with mafic volcanics. Sulfur isotope analysis of extracted sulfides shows MIF signals (Δ33S > + 1 ‰) with clear Δ33S- Δ36S correlations. The lower group of the Dharwar Supergroup shows a Δ36S / Δ33S slope of -1.48, the middle group shows -1.16 and -1.07, and the upper group shows -0.94. Reassessment of all the Archean S-MIF records from sedimentary rocks indicates that the Δ36S / Δ33S slope systematically changed during the Archean period. The observed trend in the Indian section is similar to those of its Pilbara-Kaapvaal equivalents, thus it could reflect a global atmospheric signature. Moreover, the isotopic trend seems to correlate with mid-Archean glaciation. Thus, the Δ36S / Δ33S slope could be a useful tracer for atmospheric chemistry and its link with climate change before the GOE.

  7. Hf Isotope Geochemistry of USGS Reference Materials and Various Labware: Insight into Potential Contaminant Sources

    NASA Astrophysics Data System (ADS)

    Weis, D.; Nobre Silva, I.; Kieffer, B.; Barling, J.; Pretorius, W.; Maerschalk, C.

    2005-12-01

    We have undertaken a high-precision geochemical and isotopic study of USGS reference materials by HR-ICP-MS, TIMS and MC-ICP-MS, including basalt (BCR-1,2; BHVO-1,2), andesite (AGV-1,2), rhyolite (RGM-1), syenite (STM-1,2), granodiorite (GSP-2), and granite (G-2,3). Only a few 176Hf/177Hf results are published on these materials and with the increased use of MC-ICP-MS it is critical to build a solid reference database. Standard hotplate dissolution was used, except for granitoid compositions where it involved a high-pressure bomb procedure. The reproducibility of 176Hf/177Hf is better than 100 ppm for granitoid compositions (G-2: 0.282523±8; G-3: 0.282505±20; GSP-2: 0.282059±27) and better than 65 ppm for basaltic/andesitic compositions in glassware and better than 30 ppm in teflon (BCR-2: 0.282872±9; BHVO-2: 0.283103±6). Overall, our results agree with the rare published data (BCR-1&2, BHVO-1 and RGM-1). Slight differences appear depending on the chemical procedure used to separate Hf and the type of labware used. There are systematic shifts in 176Hf/177Hf for basaltic compositions towards lower values (by 100-150 ppm) when non-teflon material is used. As a result, we then carried out a systematic trace element and isotopic study of various labware, including borosilicate glass and quartz columns and frits. Maximum concentrations (in ppm) of these materials (in the order listed above) are: Hf=16-0.3-22, Nd=0.8-0.1-23, Sr=8-0.08-16, Pb=1.4-0.5-14. The frit material appears the most variable in elemental concentration and isotopic composition, which might reflect various accumulations resulting from column chemistry. 176Hf/177Hf is 0.282198±4 in borosilicate glass and even lower in some of the frit material (<0.28195). Only a small amount of such unradiogenic material can account for the shifts observed in basaltic rocks. Our systematic study shows that careful analyses of rock reference materials with different compositional matrices are necessary, in

  8. Some Pb and Sr isotopic measurements on eclogites from the Roberts Victor mine, South Africa

    USGS Publications Warehouse

    Manton, W.I.; Tatsumoto, M.

    1971-01-01

    Five nodules of eclogite, one nodule of garnet peridotite and one sample of kimberlite from the Roberts Victor mine were analyzed for concentrations of U, Th, Pb, Rb and Sr and isotopic compositions of Pb and Sr. In the eclogites, U content ranges from 0.09 to 0.26 ppm, Th from 0.35 to 1.1 ppm, Pb from 0.79 to 5.5 ppm, Rb from 2.1 to 28 ppm and Sr from 133 to 346 ppm; 206Pb/204Pb ratios range from 14.8 to 18.5, 207Pb/204Pb from 14.9 to 15.7, 208Pb/204Pb from 35.2 to 38.5. The garnet peridotite contains 0.22 ppm U, 0.97 ppm Th, 1.05 ppm Pb, 6.9 ppm Rb and 108 ppm Sr and the kimberlite contains 2.5 ppm U, 30 ppm Th, 37 ppm Pb, 113 ppm Rb and 2040 ppm Sr. The lead in the eclogites has two components, a lead pyroextractable at 1100-1200?? and a non-pyroextractable residual lead. In three of the eclogites, which are to some extent altered, a proportion of the pyroextractable lead may be contaminating lead from the kimberlite, but an altered kyanite eclogite does not appear to be contaminated by this same kimberlite. The pyroextractable lead from a less altered eclogite contains a much larger proportion of 206Pb. Compositions calculated for the residual leads vary greatly. In many of the pyroextraction runs the primary eclogitic phases disappeared and the new phases plagioclase, clinopyroxene and a magnetic iron compound were formed. Why part of the lead should have been retained by these new phases is not understood. ?? 1971.

  9. Journal of Environmental Radioactivity special issue: international topical conference on Po and radioactive Pb isotopes.

    PubMed

    Holm, Elis; Garcia-Tenorio, Rafael

    2011-05-01

    An international conference on polonium (Po) and radioactive isotopes was held in Seville Spain, 26-28 October 2009 at the Centro Nacional de Aceleradores. It was attended by 138 participants from 38 different countries. The sessions covered all aspects on Po and lead (Pb) such as radiochemistry, terrestrial and marine radioecology, kinetics, sedimentation rates, atmospheric tracers, NORM industries and dose assessment.

  10. The use of Pb, Sr, and Hg isotopes in Great Lakes precipitation as a tool for pollution source attribution.

    PubMed

    Sherman, Laura S; Blum, Joel D; Dvonch, J Timothy; Gratz, Lynne E; Landis, Matthew S

    2015-01-01

    The anthropogenic emission and subsequent deposition of heavy metals including mercury (Hg) and lead (Pb) present human health and environmental concerns. Although it is known that local and regional sources of these metals contribute to deposition in the Great Lakes region, it is difficult to trace emissions from point sources to impacted sites. Recent studies suggest that metal isotope ratios may be useful for distinguishing between and tracing source emissions. We measured Pb, strontium (Sr), and Hg isotope ratios in daily precipitation samples that were collected at seven sites across the Great Lakes region between 2003 and 2007. Lead isotope ratios ((207)Pb/(206)Pb=0.8062 to 0.8554) suggest that Pb deposition was influenced by coal combustion and processing of Mississippi Valley-Type Pb ore deposits. Regional differences in Sr isotope ratios ((87)Sr/(86)Sr=0.70859 to 0.71155) are likely related to coal fly ash and soil dust. Mercury isotope ratios (δ(202)Hg=-1.13 to 0.13‰) also varied among the sites, likely due to regional differences in coal isotopic composition, and fractionation occurring within industrial facilities and in the atmosphere. These data represent the first combined characterization of Pb, Sr, and Hg isotope ratios in precipitation collected across the Great Lakes region. We demonstrate the utility of multiple metal isotope ratios in parallel with traditional trace element multivariate statistical modeling to enable more complete pollution source attribution.

  11. Isotope geochemistry reveals ontogeny of dispersal and exchange between main-river and tributary habitats in smallmouth bass Micropterus dolomieu.

    PubMed

    Humston, R; Doss, S S; Wass, C; Hollenbeck, C; Thorrold, S R; Smith, S; Bataille, C P

    2017-02-01

    Radiogenic strontium isotope ratios ((87) Sr:(86) Sr) in otoliths were compared with isotope ratios predicted from models and observed in water sampling to reconstruct the movement histories of smallmouth bass Micropterus dolomieu between main-river and adjacent tributary habitats. A mechanistic model incorporating isotope geochemistry, weathering processes and basin accumulation reasonably predicted observed river (87) Sr:(86) Sr across the study area and provided the foundations for experimental design and inferring fish provenance. Exchange between rivers occurred frequently, with nearly half (48%) of the 209 individuals displaying changes in otolith (87) Sr:(86) Sr reflecting movement between isotopically distinct rivers. The majority of between-river movements occurred in the first year and often within the first few months of life. Although more individuals were observed moving from the main river into tributaries, this pattern did not necessarily reflect asymmetry in exchange. Several individuals made multiple movements between rivers over their lifetimes; no patterns were found, however, that suggest seasonal or migratory movement. The main-river sport fishery is strongly supported by recruitment from tributary spawning, as 26% of stock size individuals in the main river were spawned in tributaries. The prevailing pattern of early juvenile dispersal documented in this study has not been observed previously for this species and suggests that the process of establishing seasonal home-range areas occurs up to 2 years earlier than originally hypothesized. Extensive exchange between rivers would have substantial implications for management of M. dolomieu populations in river-tributary networks.

  12. Large-scale shell-model calculations on the spectroscopy of N <126 Pb isotopes

    NASA Astrophysics Data System (ADS)

    Qi, Chong; Jia, L. Y.; Fu, G. J.

    2016-07-01

    Large-scale shell-model calculations are carried out in the model space including neutron-hole orbitals 2 p1 /2 ,1 f5 /2 ,2 p3 /2 ,0 i13 /2 ,1 f7 /2 , and 0 h9 /2 to study the structure and electromagnetic properties of neutron-deficient Pb isotopes. An optimized effective interaction is used. Good agreement between full shell-model calculations and experimental data is obtained for the spherical states in isotopes Pb-206194. The lighter isotopes are calculated with an importance-truncation approach constructed based on the monopole Hamiltonian. The full shell-model results also agree well with our generalized seniority and nucleon-pair-approximation truncation calculations. The deviations between theory and experiment concerning the excitation energies and electromagnetic properties of low-lying 0+ and 2+ excited states and isomeric states may provide a constraint on our understanding of nuclear deformation and intruder configuration in this region.

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

    NASA Technical Reports Server (NTRS)

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

    2014-01-01

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

  14. Elemental geochemistry and strontium-isotope stratigraphy of Cenomanian to Santonian neritic carbonates in the Zagros Basin, Iran

    NASA Astrophysics Data System (ADS)

    Navidtalab, Amin; Rahimpour-Bonab, Hossain; Huck, Stefan; Heimhofer, Ulrich

    2016-12-01

    A Neo-Tethyan upper Cenomanian-Santonian neritic carbonate ramp succession (Sarvak and Ilam formations), drilled in the Zagros Basin in southwest Iran, was investigated via detailed sedimentology, microfacies analysis, elemental geochemistry and Sr-isotope stratigraphy (SIS). The succession contains two exposure surfaces, which are known as the CT-ES and mT-ES (Cenomanian-Turonian and middle Turonian, respectively), and associated prominent negative carbon-isotope excursions that represent important regional stratigraphic marker horizons. Precise knowledge about the onset of platform exposure and the duration of the exposure-related hiatus, however, is currently lacking due to a rather low-resolved shallow-water biostratigraphic framework and a bulk carbonate carbon-isotope pattern that clearly differs from global Late Cretaceous reference curves. Therefore, the existing bio-chemostratigraphic framework was complemented by bulk carbonate strontium-isotope stratigraphy (SIS). As bulk carbonate material is in particular prone to diagenetic alteration, a careful selection of least altered samples has been carried out by means of elemental geochemistry and petrography. In contrast to what could be expected, the meteoric alteration of limestones beneath both exposure surfaces is not clearly expressed by increasing iron and manganese and coeval decreasing strontium contents. On the contrary, the impact of meteoric diagenesis is well illustrated via pronounced increases in Rb concentrations and concomitant prominent positive shifts to radiogenic strontium-isotope values, an observation that clearly reflects the decay of continentally derived 87Rb into 87Sr. Rubidium corrected strontium-isotope values place the CT-ES around the Cenomanian-Turonian boundary and point to an exposure duration of less than 0.4 Myr. This rather short-term CT-ES related hiatus is supported by petrographic evidence, which indicates a youth karstification stage of strata beneath the CT

  15. 210Pb chronology and trace metal geochemistry in the intertidal sediment of Qinjiang River estuary, China

    NASA Astrophysics Data System (ADS)

    Xia, Peng; Meng, Xianwei; Feng, Aiping; Yin, Ping; Wang, Xiangqin; Zhang, Jun

    2012-06-01

    Historical records of metal inputs were studied by using a sediment core collected from a sand-rich mudflat in the Qinjiang River estuary, China. 210Pb chronology was used to reconstruct the fluxes of Hg, Cu, Pb, Zn, Cd, Cr and As to the core site during the last 86 years. Based on the constant initial concentration model, the sedimentation rates are 1.18 cm year-1 in the top 30 cm sandy layer and 0.92 cm year-1 in the muddy bottom layer. To compensate for grain-size and mineralogy effects on metal concentrations, aluminum was used as the normalizing element. The enrichment factors ( EF) indicate that the natural inputs had prevailed up to the early 1980s. After this period, the intensity of human activities has resulted in continual increasing trend of metals towards the surface. Recent sediment samples from the Qinjiang River estuary are found moderately enriched by Cd ( EF>1.5) and slightly enriched by other metals ( EF<1.5). Considering that the drainage area of the Qinjiang River is mostly agricultural land, the increased Cd may be due to the usage of fertilizers and pesticides in agricultural activities and the combustion of fossil fuels.

  16. Field isotopic study of lead fate and compartmentalization in earthworm-soil-metal particle systems for highly polluted soil near Pb recycling factory.

    PubMed

    Goix, Sylvaine; Mombo, Stéphane; Schreck, Eva; Pierart, Antoine; Lévêque, Thibaut; Deola, Frédéric; Dumat, Camille

    2015-11-01

    Earthworms are important organisms in soil macrofauna and play a key role in soil functionality, and consequently in terrestrial ecotoxicological risk assessments. Because they are frequently observed in soils strongly polluted by metals, the influence of earthworm bioturbation on Pb fate could therefore be studied through the use of Pb isotopes. Total Pb concentrations and isotopic composition ((206)Pb, (207)Pb and (208)Pb) were then measured in earthworms, casts and bulk soils sampled at different distance from a lead recycling factory. Results showed decreasing Pb concentrations with the distance from the factory whatever the considered matrix (bulk soils, earthworm bodies or cast samples) with higher concentrations in bulk soils than in cast samples. The bivariate plot (208)Pb/(206)Pb ratios versus (206)Pb/(207)Pb ratios showed that all samples can be considered as a linear mixing between metallic process particulate matter (PM) and geochemical Pb background. Calculated anthropogenic fraction of Pb varied between approximately 84% and 100%. Based on Pb isotopic signatures, the comparison between casts, earthworms and bulk soils allowed to conclude that earthworms preferentially ingest the anthropogenic lead fraction associated with coarse soil organic matter. Actually, soil organic matter was better correlated with Pb isotopic ratios than with Pb content in soils. The proposed hypothesis is therefore a decrease of soil organic matter turnover due to Pb pollution with consequences on Pb distribution in soils and earthworm exposure. Finally, Pb isotopes analysis constitutes an efficient tool to study the influence of earthworm bioturbation on Pb cycle in polluted soils.

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

    SciTech Connect

    Chen, J.H.

    1987-10-10

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

  18. Plume-Lithosphere Interaction beneath the Snake River Plain, Idaho: Constraints from Pb, Sr, Nd, and Hf Isotopes

    NASA Astrophysics Data System (ADS)

    Jean, M. M.; Hanan, B. B.; Shervais, J. W.

    2011-12-01

    The Yellowstone-Snake River Plain (YSRP) volcanic province links 17 million years of volcanic activity that extends from the Owyhee Plateau in western Idaho/eastern Oregon to its current terminus underlying the Yellowstone Plateau. This investigation presents new Strontium, Neodymium, Lead, and Hafnium isotopic compositions of 25 basalts that represent four distinct areas of the YSRP (i.e., eastern province, central province, western province, Owyhee Plateau), which transect the ancient cratonic boundary of North America. The purpose of this study is to test and refine models for plume-lithosphere interaction and determines the mantle origin for YSRP basalts. New results shows: (1) low-K tholeiites from the eastern, central, and western SRP have ɛNd (-2 to -5.5), 87Sr/86Sr (0.7060-0.7071) and similar Pb-isotopes [206Pb/204Pb (17.8-18.6), 207Pb/204Pb (15.5-15.66), 208Pb/204Pb (38.4-39.1)]; (2) central SRP tholeiites are enriched in 208Pb/204Pb (~38.5-38.9), relative to eastern SRP basalts and define a 208Pb/204Pb trend, intermediate between the eastern SRP and Craters of the Moon lavas; (3) western SRP high-K basalts are depleted in ɛNd (> -1) and 87Sr/86Sr (0.7050-0.7057), relative to low-K tholeiites, and plot closer to "bulk silicate earth," but are enriched in 206Pb/204Pb (18.66-18.71), and have 207Pb/204Pb (15.62-15.65) and 208Pb/204Pb (39.1-39.2) isotope ratios similar to high-K basalts of Smith Prairie (Boise River Group 2); (4) Silver City basalt (>16.6 Ma) overlaps in Pb-isotope space with Imnaha basalt compositions (Columbia River Basalt Group); (5) new 177Hf/176Hf isotopic data lie above and parallel to the Mantle array in Nd and Hf isotope space and define a linear trend between Leucite Hills lavas and OIB basalts (i.e., Steens and Hawaii); (6) these basalts follow a systematic geographic pattern: eastern and central plain low-K tholeiites have low ɛNd (-3 to -5) and intermediate 206Pb/204Pb (~17.7-18.5), while western plain low-K tholeiites are

  19. Growth rate of a deep-sea coral using sup 210 Pb and other isotopes

    SciTech Connect

    Druffel, E.R.M.; King, L.I.; Belastock, R.A.; Buesseler, K.O. )

    1990-05-01

    A deep-sea coral was studied to determine its growth rate and to reconstruct time histories of isotope distributions in the deep ocean. The specimen was collected at a depth of 600 m off Little Bahama Banks using the Deep Submergence Vehicle (DSV) Alvin. The growth rate of the calcitic coral trunk was determined using excess {sup 210}Pb measured in concentric bands. Excess {sup 210}Pb was found in the outer half of the coral's radius, and a growth rate of 0.11 {plus minus} 0.02 mm/a is calculated. Assuming a constant growth rate during formation of the entire trunk, an age of 180 {plus minus} 40 a is estimated for the coral. The decrease observed in radiocarbon activities measured on the same bands (Griffin and Druffel, 1989) concurred with the growth rate estimated from excess {sup 210}Pb activity. {sup 239,240}Pu activities measured by mass spectrometry were also detected in the outer two bands of the coral, as expected from the {sup 210}Pb chronology. Stable oxygen and carbon isotopes measured in samples collected by a variety of techniques are positively correlated. This is evidence of a variable kinetic isotope effect most likely caused by variations in the skeletal growth rate. Long-lived corals such as this specimen have the potential for serving as integrators of seawater chemistry in the deep-sea over several century timescales.

  20. Helium- and lead-isotope geochemistry of oceanic volcanic rocks from the East Pacific and South Atlantic. Doctoral thesis

    SciTech Connect

    Graham, D.W.

    1987-01-01

    Glassy basalts erupted at young Pacific seamounts and along the mid-ocean ridge in the South Atlantic, and volcanic rocks from the island of St. Helena were studied for He and Pb isotopes. (U+TH)/He ages of seamount alkali basalts were determined from the isotope disequilibrium of (3)He/(4)He between He trapped in vesicles and that dissolved in the glass phase. The method allows alkalic lavas to be dated in the age range of 103 to 106 years. Tholclites at the EPR seamounts have He, Pb, Sr and Nd isotope compositions indistinguishable from MORB, while associated alkali basalts show more radiogenic signatures. The low (3)He/(4)He in the vesicles of alkali basalts (1.2-2.6 RA), their low helium concentrations, and systematic variations with extent of differentiation suggest that magmatic processes influence (3)He/(4)He in these alkalic lavas. Pb-Sr-Nd isotopes at Shimada seamount (17 deg N, 117 deg W) indicate the presence of enriched mantle beneath the East Pacific which resembles that beneath Samoa. Low (3)He/(4)He (4-5 RA) appears to be an inherent characteristic of the component. Much of the South Atlantic ridge axis displays (3)He/(4)He lower than normal MORB, and is apparently contaminated by off-axis hotspots. He-Pb systematics along the ridge suggest that (3)He/(4)He at St. Helena is less than MORB, consistent with values measured by in vacuo crushing of olivine and pyroxene in St. Helena rocks (approx. 5.8 RA).

  1. Do ages of authigenic K-feldspar date the formation of Mississippi valley-type Pb-Zn deposits, central and southeastern United States?: Pb isotopic evidence

    USGS Publications Warehouse

    Aleinikoff, J.N.; Walter, M.; Kunk, M.J.; Hearn, P.P.

    1993-01-01

    Pb concentrations and isotopic compositions have been determined for authigenic overgrowths and detrital cores of K-feldspar from Cambrian sedimentary rocks in Texas, Tennessee, and Pennsylvania (group 1) and southeastern Missouri (group 2). Overgrowths and cores were separated by abrasion and analyzed separately. The disparity in Pb isotopic ratios of group 1 overgrowths and Pb in nearby Mississippi Valley-type deposits implies that the regional authigenic K-feldspar event was not synchronous with ore deposition in the southeastern United States. In contrast, Pb isotopic ratios from group 2 authigenic K-feldspar are similar to ratios in ores of southeastern Missouri, suggesting a genetic relation in late Paleozoic time. -from Authors

  2. Li-Zn-Pb multi isotopic characterization of the Loire River Basin, France

    NASA Astrophysics Data System (ADS)

    Millot, R.; Desaulty, A.; Widory, D.; Bourrain, X.

    2013-12-01

    The Loire River in France is approximately 1010 km long and drains an area of 117 800 km2. Upstream, the Loire River flows following a south to north direction from the Massif Central down to the city of Orléans, 650 km from its source. The Loire River is one of the main European riverine inputs to the Atlantic Ocean. Over time, its basin has been exposed to numerous sources of anthropogenic metal pollutions, such as metal mining, industry, agriculture and domestic inputs. The Loire River basin is thus an excellent study site to develop new isotope systematics for tracking anthropogenic sources of metal pollutions (Zn and Pb) and also to investigate Li isotope tracing that can provide key information on the nature of weathering processes at the Loire River Basin scale. Preliminary data show that Li-Zn-Pb concentrations and isotopic compositions span a wide range in river waters of the Loire River main stream and the main tributaries. There is a clear contrast between the headwaters upstream and rivers located downstream in the lowlands. In addition, one of the major tributaries within the Massif Central (the Allier River) is clearly influenced by inputs resulting from mineralizations and thermomineral waters. The results showed that, on their own, each of these isotope systematics reveals important information about the geogenic or anthropogenic origin Li-Zn-Pb. Considered together, they are however providing a more integrated understanding of the overall budgets of these elements at the scale of the Loire River Basin.

  3. Evaluating the provenance of Permian-Triassic and Palaeocene-Eocene ash beds by high precision U-Pb and Lu-Hf isotopic analyses of zircons: linking local sedimentary records to global events

    NASA Astrophysics Data System (ADS)

    Eivind Augland, Lars; Jones, Morgan; Planke, Sverre; Svensen, Henrik; Tegner, Christian

    2016-04-01

    Zircons are a powerful tool in geochronology and isotope geochemistry, as their affinity for U and Hf in the crystal structure and the low initial Pb and Lu allow for precise and accurate dating by U-Pb ID-TIMS and precise and accurate determination of initial Hf isotopic composition by solution MC-ICP-MS analysis. The U-Pb analyses provide accurate chronostratigraphic controls on the sedimentary successions and absolute age frames for the biotic evolution across geological boundaries. Moreover, the analyses of Lu-Hf by solution MC-ICP-MS after Hf-purification column chemistry provide a powerful and robust fingerprinting tool to test the provenance of individual ash beds. Here we focus on ash beds from Permian-Triassic and Palaeocene successions in Svalbard and from the Palaeocene-Eocene Thermal Maximum (PETM) in Fur, Denmark. Used in combination with whole rock geochemistry from the ash layers and the available geochemical and isotopic data from potential source volcanoes, these data are used to evaluate the provenance of the Permian-Triassic and Palaeocene ashes preserved in Svalbard and PETM ashes in Denmark. If explosive eruptions from volcanic centres such as the Siberian Traps and the North Atlantic Igneous Province (NAIP) can be traced to distal basins as ash layers, they provide robust tests of hypotheses of global synchronicity of environmental changes and biotic crises. In addition, the potential correlation of ash layers with source volcanoes will aid in constraining the extent of explosive volcanism in the respective volcanic centres. The new integrated data sets will also contribute to establish new reference sections for the study of these boundary events when combined with stable isotope data and biostratigraphy.

  4. Nd, Pb, Sr, and O isotopic characterization of Saudi Arabian Shield terranes

    USGS Publications Warehouse

    Stoeser, D.B.; Frost, C.D.

    2006-01-01

    New Nd, Sr and O isotopic data for granitoid rocks of the Saudi Arabian Shield are presented together with published Nd, Pb, Sr and O isotopic data and all available geologic and geochronologic information to re-evaluate the terranes defined for the Saudi Arabian part of the Arabian-Nubian Shield. Three groups of terranes are identified: 1) the western arc terranes, 2) the eastern arc terranes, and 3) the Khida terrane. The Khida terrane is the only terrane composed of pre-Neoproterozoic continental crust. The western arc terranes are of oceanic arc affinity, and have the least radiogenic Pb and Sr and most radiogenic Nd isotopic compositions and some of the lowest ??18O values of any rocks of the Saudi Arabian Shield. Although some previous studies have characterized the eastern arc terranes as of continental affinity, this study shows that they too are composed of Neoproterozoic oceanic arcs, although their sources have slightly elevated 208Pb/204Pb, Nd, Sri, and ??18O values compared to the western arc terranes. These data suggest that either the isotopic composition of the mantle source for the western arc terranes is more depleted than that of the eastern arc terranes or the eastern arc terranes have been mixed with a small amount of cratonic source material, or both. We further elaborate on the Hulayfah-Ad Dafinah fault zone as a major boundary within the Saudi Arabian portion of the East African Orogen. With further study, its northern extension may be shown to pass through what has been defined as the Hail terrane, and its southern extension appears to lie under cover east of the Tathlith-Malahah terrane and extend into Yemen. It may represent the collision zone between East and West Gondwana, and at the very least it is an important suture between groups of arc terranes of contrasting isotopic composition caught between two converging continents.

  5. Isotopic and trace element geochemistry of alkalic-mafic-ultramafic-carbonatitic complexes and flood basalts in NE India: Origin in a heterogeneous Kerguelen plume

    NASA Astrophysics Data System (ADS)

    Ghatak, Arundhuti; Basu, Asish R.

    2013-08-01

    , nephelinites, sovites, melteigite in the first group and syenites and ijolites in the second. The Nd-Sr-Pb-isotopic and trace element geochemistry of the first group of carbonatitic-ultrabasic rocks are consistent with similar data of the RBST lavas of the present and previous studies, and are modeled as derived from a relatively primitive carbonated garnet peridotite source in the KP. In contrast, the syenites and ijolites of the second group show a wide range of Nd-Sr-Pb isotopic compositions, modeled by low-degree melts of an ancient recycled carbonated eclogite also in the KP. The KP thus reflects heterogeneities in the lower mantle-derived plume with carbonated components yielding ultrabasic melts at greater depths with low-degree melting, followed by rise of the plume at shallower depths causing tholeiitic flood basalt volcanism. Collectively, these data imply a zone of influence of the plate-motion-reconstructed KP head for ˜1000 km around the Bengal Basin, as represented by the widely scattered and diverse rock types of the RBST.

  6. {alpha} transitions to coexisting 0{sup +} states in Pb and Po isotopes

    SciTech Connect

    Xu Chang; Ren Zhongzhou

    2007-04-15

    The {alpha}-transitions ({delta}l=0) to ground and first excited 0{sup +} states in neutron deficient Pb and Po isotopes are systematically analyzed by the density-dependent cluster model. The magnitude of nuclear deformation of the coexisting 0{sub 1}{sup +} and 0{sub 2}{sup +} states is extracted directly from the experimental {alpha}-decay energies and half-lives. The phenomenon of shape coexistence around the Z=82 shell closure is clearly demonstrated in our present analysis. The obtained deformation values from Rn {yields} Po {yields} Pb decay chains are generally consistent with both the available experimental and theoretical studies.

  7. A Teaching Exercise to Introduce Stable Isotope Fractionation of Metals into Geochemistry Courses

    ERIC Educational Resources Information Center

    Weiss, Dominik J.; Harris, Caroline; Maher, Kate; Bullen, Thomas

    2013-01-01

    Variations in the isotopic composition of elements have been widely used to study earth's climate, biosphere, and interior, and more recently to track the fate of contaminants. Within the broad range of elements that exhibit measureable isotopic variations, metal stable isotopes are increasingly applied across the biological, geological,…

  8. Modeling crust-mantle evolution using radiogenic Sr, Nd, and Pb isotope systematics

    NASA Astrophysics Data System (ADS)

    Kumari, Seema; Paul, Debajyoti

    2015-04-01

    The present-day elemental and isotopic composition of Earth's terrestrial reservoirs can be used as geochemical constraints to study evolution of the crust-mantle system. A flexible open system evolutionary model of the Earth, comprising continental crust (CC), upper depleted mantle (UM) -source of mid-ocean ridge basalts (MORB), and lower mantle (LM) reservoir with a D" layer -source of ocean island basalts (OIB), and incorporating key radioactive isotope systematics (Rb-Sr, Sm-Nd, and U-Th-Pb), is solved numerically at 1 Ma time step for 4.55 Ga, the age of the Earth. The best possible solution is the one that produces the present-day concentrations as well as isotopic ratios in terrestrial reservoirs, compiled from published data. Different crustal growth scenarios (exponential, episodic, early and late growth), proposed in earlier studies, and its effect on the evolution of isotope systematics of terrestrial reservoirs is studied. Model simulations strongly favor a layered mantle structure satisfying majority of the isotopic constraints. In the successful model, which is similar to that proposed by Kellogg et al. (1999), the present-day UM comprises of 60% of mantle mass and extends to a depth 1600 km, whereas the LM becomes non-primitive and more enriched than the bulk silicate Earth, mainly due to addition of recycled crustal material. Modeling suggest that isotopic evolution of reservoirs is affected by the mode of crustal growth. Only two scenarios satisfied majority of the Rb-Sr and Sm-Nd isotopic constraints but failed to reproduce the present-day Pb-isotope systematics; exponential growth of crust (mean age, tc=2.3 Ga) and delayed and episodic growth (no growth for initial 900 Ma, tc=2.05 Ga) proposed by Patchett and Arndt (1986). However, assuming a slightly young Earth (4.45 Ga) better satisfies the Pb-isotope systematics. Although, the delayed crustal growth model satisfied Sr-Nd isotopic constraints, presence of early Hadean crust (4.03 and 4.4 Ga

  9. Pb-concentrations and Pb-isotope ratios in soils collected along an east-west transect across the United States

    USGS Publications Warehouse

    Reimann, Clemens; Smith, David B.; Woodruff, Laurel G.; Flem, Belinda

    2011-01-01

    Analytical results for Pb-concentrations and isotopic ratios from ca. 150 samples of soil A horizon and ca. 145 samples of soil C horizon collected along a 4000-km east–west transect across the USA are presented. Lead concentrations along the transect show: (1) generally higher values in the soil A-horizon than the C-horizon (median 21 vs. 16.5 mg/kg), (2) an increase in the median value of the soil A-horizon for central to eastern USA (Missouri to Maryland) when compared to the western USA (California to Kansas) (median 26 vs. 20 mg/kg) and (3) a higher A/C ratio for the central to eastern USA (1.35 vs. 1.14). Lead isotopes show a distinct trend across the USA, with the highest 206Pb/207Pb ratios occurring in the centre (Missouri, median A-horizon: 1.245; C-horizon: 1.251) and the lowest at both coasts (e.g., California, median A-horizon: 1.195; C-horizon: 1.216). The soil C-horizon samples show generally higher 206Pb/207Pb ratios than the A-horizon (median C-horizon: 1.224; A-horizon: 1.219). The 206Pb/207Pb-isotope ratios in the soil A horizon show a correlation with the total feldspar content for the same 2500-km portion of the transect from east-central Colorado to the Atlantic coast that shows steadily increasing precipitation. No such correlation exists in the soil C horizon. The data demonstrate the importance of climate and weathering on both Pb-concentration and 206Pb/207Pb-isotope ratios in soil samples and natural shifts thereof in the soil profile during soil-forming processes.

  10. Stable (206Pb, 207Pb, 208Pb) and radioactive (210Pb) lead isotopes in 1 year of growth of Sphagnum moss from four ombrotrophic bogs in southern Germany: Geochemical significance and environmental implications

    NASA Astrophysics Data System (ADS)

    Shotyk, William; Kempter, Heike; Krachler, Michael; Zaccone, Claudio

    2015-08-01

    The surfaces of Sphagnum carpets were marked with plastic mesh and 1 year later the production of plant matter was harvested in four ombrotrophic bogs from two regions of southern Germany: Upper Bavaria (Oberbayern, OB) and the Northern Black Forest (Nordschwarzwald, NBF). Radioactive, 210Pb was determined in solid samples using ultralow background gamma spectrometry while total Pb concentrations and stable isotopes (206Pb, 207Pb, 208Pb) were determined in acid digests using ICP-SMS. Up to 12 samples (40 × 40 cm) were collected per site, and 6-10 sites investigated per bog. The greatest variations within a given sampling site were in the range 212-532 Bq kg-1 for 210Pb activity, whereas 206Pb/207Pb and 208Pb/206Pb varied less than 1%. The median values of all parameters for the sites (6-10 per bog) were not significantly different. The median activities of 210Pb (Bq kg-1) in the mosses collected from the bogs in NBF (HO = 372 ± 56, n = 55; WI = 342 ± 58, n = 93) were slightly less from those in OB (GS = 394 ± 50, n = 55; KL = 425 ± 58, n = 24). However, the mosses in the NBF bogs exhibited much greater productivity (187-202 g m-2 a-1) compared to those of OB (71-91 g m-2 a-1), and this has a profound impact on the accumulation rates of 210Pb (Bq m-2 a-1), with the bogs in the NBF yielding fluxes (HO = 73 ± 30; WI = 65 ± 20) which are twice those of OB (GS = 29 ± 11; KL = 40 ± 13). Using the air concentrations of 210Pb measured at Schauinsland (SIL) in the southern Black Forest and average annual precipitation, the atmospheric fluxes of 210Pb at SIL (340 Bq m-2 a-1) exceeds the corresponding values obtained from the mosses by a factor of five, providing the first quantitative estimate of the net retention efficiency of 210Pb by Sphagnum. When the 210Pb activities of all moss samples are combined (n = 227), a significant decrease with increasing plant production rate is observed; in contrast, total Pb concentrations show the opposite trend. The contrasting

  11. Fingerprinting fluid sources in Troodos ophiolite complex orbicular glasses using high spatial resolution isotope and trace element geochemistry

    NASA Astrophysics Data System (ADS)

    Fonseca, Raúl O. C.; Kirchenbaur, Maria; Ballhaus, Chris; Münker, Carsten; Zirner, Aurelia; Gerdes, Axel; Heuser, Alexander; Botcharnikov, Roman; Lenting, Christoph

    2017-03-01

    The Troodos igneous complex (Cyprus) is a ca. 90 Ma old, well preserved supra-subduction zone ophiolite. Troodos is unique in that it shows evidence of fluid-saturation throughout the complex, from its base (i.e. podiform chromitites) to its uppermost units - the upper pillow lavas (UPL). However, it is unclear what the source of dissolved water in UPL tholeiites is, with possibilities including shallow seawater infiltration, assimilation of altered Troodos oceanic crust, recycled serpentinized oceanic crust, or subducted pelagic sediments. In order to identify and characterize these components we have carried out a detailed high-resolution study on tholeiitic lavas on orbicular structures and glasses from the UPL in Troodos. Basaltic orbicules were measured for their Sr-Nd-Hf-Pb isotope compositions, and in situ for their B isotopes using LA-MC-ICP-MS. UPL orbicules display a very narrow range in ɛ Nd and ɛ Hf (+7 to +8 and +13 to +15, respectively) indicating melting of a depleted mantle source. Lead isotopes, specifically 207Pb/204Pb vs. 206Pb/204Pb, form a mixing array with pelagic sediments. Furthermore, high-resolution characterization of individual orbicules revealed that UPL tholeiites display strong variability in 87Sr/86Sr (0.7039-0.7060) at the outcrop scale. Samples display δ11 B between -8.2 (± 0.5)‰ and +5.9 (± 1.1)‰ with an average B content of ca. 5 μg/g. Contrary to expectation, altered orbicules and their associated hyaloclastite matrixes display lower δ11 B (down to -10‰) and higher B contents (max. 200 μg/g) when compared to fresh glass. Furthermore, the orbicules studied here show little or no evidence of interaction with seawater, which is supported by their trace element contents and isotope compositions. When all isotope systems are taken into account, UPL lavas reflect melting of a depleted mantle source that was overprinted by hydrous sediment melts, and potentially, fluid-like subduction components that in part originate

  12. Tracing Provenance of Antarctic Glacio-marine Sediment Through Radiogenic Isotopes, Ar/Ar Hornblende Ages, and Bulk Geochemistry

    NASA Astrophysics Data System (ADS)

    Brachfeld, S.; van de Flierdt, T.; Hemming, S.; Goldstein, S. L.; Roy, M.; Gorring, M.; Williams, T.

    2007-05-01

    We are applying a suite of sediment provenance tracing techniques to Antarctic marine diamict samples. The composition of sediments derived from the glacial erosion of Antarctica provides an important framework for evaluating iceberg contributions to the ocean over time. We targeted glacial diamict samples where available, or sandy mud otherwise. This strategy ensures sampling and homogenization over large areas, avoids possible biasing in limited and heterogeneous outcrops, and avoids the competing influences of sediment redistribution by ocean currents. When completed, this ongoing study will provide an integrated characterization of the lithologic clast composition, bulk sediment geochemistry, iron oxide mineralogy and geochemistry, Ar/Ar ages of hornblende grains, and radiogenic isotope signatures of a circum-Antarctic sample set. This approach will allow the identification of the geographic regions from which Antarctic sediment was supplied to the Southern Ocean, and thus constrain ice sheet dynamics and behavior of surface currents. Ice proximal samples from West Antarctica, East Antarctica and the Antarctic Peninsula were collected from fjords, bays, and inner shelf basins. Subsamples were taken from piston cores, kasten cores, and surface grabs collected over the past 40 years by the U.S. Antarctic Program. Here we present preliminary results from the Wilkes Land margin, Marie Byrd Land, and the western Antarctic Peninsula, which constitute an Archean craton, Paleozoic to Cenozoic sequences, and a mixed though relatively younger bedrock geology, respectively. The Nd isotope composition of the < 63- micron fraction generally conforms to the results from a survey of circum-Antarctic distal samples (Roy et al., Chemical Geology, submitted). However, the George V Coast samples (143 E longitude) yielded eNd values of approximately -24, the lowest values yet found in our survey, implying very old Nd crustal residence ages. The hornblende grains from these East

  13. Pb isotope signatures in the North Atlantic: initial results from the U.S. GEOTRACES North Atlantic Transect

    NASA Astrophysics Data System (ADS)

    Noble, A.; Echegoyen-Sanz, Y.; Boyle, E. A.

    2012-12-01

    This study presents Pb isotope data from the US GEOTRACES North Atlantic Transect (US-GT-NAT) sampled during two cruises that took place during Fall 2010 and 2011. Almost all of the Pb in the modern ocean is derived from anthropogenic sources, and the North Atlantic has received major Pb inputs from the United States and Europe due to emissions from leaded gasoline and high temperature industrial processes. During the past three decades, Pb fluxes to the North Atlantic have decreased following the phasing out of leaded gasoline in the United States and Europe. Following the concentrations and isotope ratios of Pb in this basin over time reveals the temporal evolution of Pb in this highly-affected basin. The Pb isotope signatures reflect the relative importance of changing inputs from the United States and Europe as leaded gasoline was phased out faster in the United States relative to Europe. In the western North Atlantic, a shallow (~100-200m) low Pb-206/Pb-207 ratio feature was observed near the Subtropical Underwater salinity peak at many stations across the transect, coincident with shallow subsurface maxima in Pb concentration. This water mass originates from high-salinity surface water near 25°N (Defant), which is in the belt of European-Pb-gas-contaminated African aerosols, which we confirmed by Pb-206/Pb-207 ~ 1.17 from upper ocean samples from US-GT-NAT station 18 (23.24degN,38.04degW). At the Mid-Atlantic Ridge station, Pb scavenging onto iron oxides and sulfide was observed by a decrease in Pb concentrations within the TAG hydrothermal plume, although the isotopic signature within the plume was slightly (~3 permil) lower than the surrounding waters possibly indicating a small contribution of hydrothermal Pb or preferential uptake of the lighter isotope. In the Mediteranean Outflow plume near Lisbon, Pb-206/Pb-207 (~1.178) is also strongly influenced by European Pb. Further results from the section will be presented as more data will be available by the

  14. Isotope Geochemistry of Calcite Coatings and the Thermal History of the Unsaturated Zone at Yucca Mountain, Nevada

    SciTech Connect

    B.D. Marshall; J.F. Whelan

    2000-07-27

    Calcite and opal coatings found on fracture footwalls and lithophysal cavity bottoms in the volcanic section at Yucca Mountain (exposed in a tunnel) contain a record of gradual chemical and isotopic changes that have occurred in the unsaturated zone. The thin (less than 6 cm) coatings are composed primarily of calcite, opal, chalcedony, and quartz. Fluid inclusions in calcite that homogenize at greater than ambient temperatures provide impetus for geochronologic studies in order to determine the thermal history. In the welded Topopah Spring Tuff (12.7 Ma), U-Pb ages of opal and chalcedony layers provide evidence of a long history of deposition throughout the past 10 m.y. However, these ages can constrain the ages of associated calcite layers only in samples with an easily interpretable microstratigraphy. Strontium isotope ratios in calcite increase with microstratigraphic position from the base up to the outermost surface of the coatings. The strontium incorporated in these coatings records the systematic change in pore-water isotopic composition due to water-rock interaction primarily in the overlying nonwelded tuffs. A one-dimensional advection-reaction model simulates strontium isotope ratios measured in pore water extracted from core in three vertical boreholes adjacent to the tunnel. By calculating the strontium isotope compositions of the rocks at various past times, the model predicts a history of the strontium isotope ratios in the water that matches the record in the calcite and therefore provides approximate ages. Oxygen isotope ratios measured in calcite gradually increase with decreasing model strontium age. Assuming that the oxygen isotope ratio of the percolating water was relatively constant, this trend indicates a gradual cooling of the rocks over millions of years, in agreement with thermal modeling of magma beneath the 12-Ma Timber Mountain caldera just north of Yucca Mountain. This model predicts that temperatures significantly exceeding current

  15. Petrogenesis of synorogenic diorite-granodiorite-granite complexes in the Damara Belt, Namibia: Constraints from U-Pb zircon ages and Sr-Nd-Pb isotopes

    NASA Astrophysics Data System (ADS)

    Jung, S.; Kröner, A.; Hauff, F.; Masberg, P.

    2015-01-01

    The synorogenic Palmental complex (central Damara Belt, Nambia) consists of ca. 545 Ma old quartz diorites and rare granodiorites and ca. 520 Ma-old leucogranites, representing one of the earliest and most primitive phase of crustal plutonism predating the main high-T regional metamorphism. Most quartz diorites and one granodiorite evolved through multistage, polybaric evolutionary processes involving fractionation from a lithospheric mantle-derived melt, followed by fractional crystallization of mainly hornblende, plagioclase and apatite which is shown by decreasing MgO, FeO, CaO, TiO2 and P2O5 with increasing SiO2. Assimilation of felsic basement gneisses was also important during formation of these granitoids. Although their chemical characteristics (high LILE, low HFSE) resemble those of quartz diorites and granodiorites with calc-alkaline affinity, they differ in their enriched Sr (initial 87Sr/86Sr: 0.7061-0.7098) and Nd (initial εNd: -2.7 to -9.9) isotopic composition. Neodymium depleted mantle mean crustal residence ages range from 1.3 to 1.9 Ga for the quartz diorites including the granodiorite. These model ages correlate with major and trace element abundances, further substantiating that AFC processes modified the initial isotopic systematics. Lead (206Pb/204Pb: 17.43-17.68, 207Pb/204Pb: 15.61-15.66, 208Pb/204Pb: 38.19-38.49) isotopic composition are unradiogenic relative to other Damaran intrusive rocks but plot above the Stacey and Kramers (1975) reference line, indicating that the source underwent an ancient (pre Pan-African) increase in U/Pb and Th/U, followed by more recent U-depletion. Some variation in 206Pb/204Pb at high 207Pb/204Pb further indicates involvement of ancient crustal material, most likely through AFC processes. A cross-cutting leucogranite dyke has also evolved isotopic compositions (initial 87Sr/86Sr: 0.7326; initial εNd: -15.6; 206Pb/204Pb: 17.42, 207Pb/204Pb: 15.62, 208Pb/204Pb: 38.16) but in view of the apparent younger age of

  16. Cu-Zn-Pb multi isotopic characterization of a small watershed (Loire river basin, France)

    NASA Astrophysics Data System (ADS)

    Desaulty, A. M.; Millot, R.; Perret, S.; Bourrain, X.

    2015-12-01

    Combating metal pollution in surface water is a major environmental, public health and economic issue. Knowledge of the behavior of metals, such as copper (Cu), zinc (Zn) and lead (Pb) in sediments and dissolved load, is a key factor to improve the management of rivers. Recent advances in mass spectrometry related to the development of MC-ICPMS allow to analyze the isotopic composition of these elements, and previous studies show the effectiveness of isotopic analyses to determine the anthropogenic sources of pollution in environment. The goal of this study is to use the Cu-Zn-Pb multi-isotopic signature to track the pollutions in surface water, and to understand the complex processes causing the metals mobilization and transport in environment. More particularly we investigate the mechanisms of distribution between the dissolved load and particulate load, known to play an important role in the transport of metals through river systems. As case study, we chose a small watershed, poorly urbanized in the Loire river basin. Its spring is in a pristine area, while it is only impacted some kilometers further by the releases rich in metals coming from a hospital water treatment plant. First a sampling of these liquid effluents as well as dissolved load and sediment from upstream to downstream was realized and their concentrations and isotopic data were determined. Then to simulate a lot of potential natural and anthropogenic modifications of environmental conditions, we made sequential extraction protocol using various reagents on the sediments. Isotopic analyzes were performed also on the various extracting solutions. Isotopic ratios were measured using a Neptune MC-ICPMS at the BRGM, after a protocol of purification for Zn and Cu. The results showed that, these isotopic systematics reveal important informations about the mechanists of mobilization and transport of metals through river systems. However experiments performed under laboratory conditions will be necessary

  17. Evolution of Nd and Pb isotopes in Central Pacific seawater from ferromanganese crusts

    USGS Publications Warehouse

    Ling, H.F.; Burton, K.W.; O'Nions, R. K.; Kamber, B.S.; Von Blanckenburg, F.; Gibb, A.J.; Hein, J.R.

    1997-01-01

    Hydrogenetic ferromanganese crusts incorporate elements from ambient seawater during their growth on seamounts. By analysing Nd, Pb and Be isotope profiles within crusts it is possible to reconstruct seawater tracer histories. Depth profiles of 10Be/9Be ratios in three Pacific ferromanganese crusts have been used to obtain growth rates which are between 1.4 and 3.8 mm/Ma. Nd and Pb isotopes provide intact records of isotopic variations in Pacific seawater over the last 20 Ma or more. There were only small changes in Pb isotope composition in the last 20 Ma. This indicates a constant Pb composition for the erosional sources and suggests further that erosional Nd inputs may have been uniform too. ??ND values vary considerably with time and most probably reflect changes in ocean circulation. The ??ND values of the crusts not only vary as a function of age but also as a function of water depth. From 25 to 0 Ma, crust VA13/2 from 4.8 km water depth has a similar pattern of ??ND variation to the two shallower crusts from 1.8 and 2.3 km, but about 1.0 to 1.5 units more negative. This suggests that ??ND stratification in Pacific seawater, as demonstrated for the present day, has been maintained for at least 20 Ma. Each crust shows a decrease in ??ND from 3-5 Ma to the present, which is interpreted in terms of an increase in the NADW component present in the Pacific. From 10 to 3-5 Ma ago the crusts show an increase in ??ND. This suggests a decreasing role for a deep water source with ??ND less than circum-Pacific sources. In this regard the Panamanian gateway restriction from ???10 Ma with final closure at 3-5 Ma may have played an important role in reducing access of Atlantic-derived Nd to the Pacific.

  18. Trace element and isotope geochemistry of Cretaceous-Tertiary boundary sediments: identification of extra-terrestrial and volcanic components

    NASA Technical Reports Server (NTRS)

    Margolis, S. V.; Doehne, E. F.

    1988-01-01

    Trace element and stable isotope analyses were performed on a series of sediment samples crossing the Cretaceous-Tertiary (K-T) boundary from critical sections at Aumaya and Sopelano, Spain. The aim is to possibly distinguish extraterrestrial vs. volcanic or authigenic concentration of platinum group and other elements in K-T boundary transitional sediments. These sediments also have been shown to contain evidence for step-wise extinction of several groups of marine invertebrates, associated with negative oxygen and carbon isotope excursions occurring during the last million years of the Cretaceous. These isotope excursions have been interpreted to indicate major changes in ocean thermal regime, circulation, and ecosystems that may be related to multiple events during latest Cretaceous time. Results to date on the petrographic and geochemical analyses of the Late Cretaceous and Early Paleocene sediments indicate that diagenesis has obviously affected the trace element geochemistry and stable isotope compositions at Zumaya. Mineralogical and geochemical analysis of K-T boundary sediments at Zumaya suggest that a substantial fraction of anomalous trace elements in the boundary marl are present in specific mineral phases. Platinum and nickel grains perhaps represent the first direct evidence of siderophile-rich minerals at the boundary. The presence of spinels and Ni-rich particles as inclusions in aluminosilicate spherules from Zumaya suggests an original, non-diagenetic origin for the spherules. Similar spherules from southern Spain (Caravaca), show a strong marine authigenic overprint. This research represents a new approach in trying to directly identify the sedimentary mineral components that are responsible for the trace element concentrations associated with the K-T boundary.

  19. Time-series analysis of ion and isotope geochemistry of selected springs of the Nevada Test Site, Nye County, Nevada

    SciTech Connect

    Lyles, B.F.; Edkins, J.; Jacobson, R.L.; Hess, J.W.

    1990-11-01

    The temporal variations of ion and isotope geochemistry were observed at six selected springs on the Nevada Test Site, Nye County, Nevada and included: Cane, Whiterock, Captain Jack, Topopah, Tippipah, and Oak Springs. The sites were monitored from 1980 to 1982 and the following parameters were measured: temperature, pH, electrical conductance, discharge, cations (Ca{sup 2+}, Mg{sup 2+}. Na{sup +}, K{sup +}), anions Cl{sup {minus}}, SO{sub 4}{sup 2{minus}}. HCO{sub 3}{sup {minus}}, silica, stable isotopes ({delta}{sup 18}O, {delta}D, {delta}{sup 13}C), and radioactive isotopes ({sup 3}H, {sup 14}C). A more detailed study was continued from 1982 to 1988 at Cane and Whiterock Springs. Field microloggers were installed at these sites in 1985 to measure the high frequency response of temperature, electrical conductance, and discharge to local precipitation. Stage fluctuations near the discharge point dissolve minerals/salts as groundwater inundates the mineralized zone immediately above the equilibrium water table. This phenomena was most noticeable at Whiterock Spring and lagged the discharge response by several hours. Stable isotope analysis of precipitation and groundwater suggests a 1.5 to 2 month travel time for meteoric water to migrate from the recharge area to the discharge point. Groundwater age determinations suggest a mean age of approximately 30 years at Whiterock Spring and possibly older at Cane Spring. However, the short travel time and geochemical integrity of recharge pulses suggest that the waters are poorly mixed along the flow paths. 25 refs., 25 figs., 24 tabs.

  20. Characteristics of Heavy Metals and Pb Isotopic Composition in Sediments Collected from the Tributaries in Three Gorges Reservoir, China

    PubMed Central

    Gao, Bo; Zhou, Huaidong; Huang, Yong; Wang, Yuchun; Gao, Jijun; Liu, Xiaobo

    2014-01-01

    The concentrations, distribution, accumulation, and potential ecological risk of heavy metals (Cr, Cu, Zn, Ni, As, Pb, Cd, and Hg) in sediments from the Three Gorges Reservoir (TGR) tributaries were determined and studied. Pb isotopic compositions in sediments were also measured to effectively identify the potential Pb sources. The results showed that the average concentrations of heavy metals in sediment of TGR tributaries were higher than the local background values of soils and sediments in China. The assessment by Geoaccumulation Index indicated that Cu, Ni, and Hg were at the “slightly polluted” level and Cd was ranked as the “moderately polluted” level in tributary sediments of TGR. The assessment by Potential Ecological Risk Index showed that Hg and Cd were the predominant elements in tributary sediments in TGR. The Pb isotopic ratios in sediments varied from 1.171 to 1.202 for 206Pb/207Pb and from 2.459 to 2.482 for 208Pb/207Pb in TGR. All Pb isotopic ratios in sediments were similar to those from coal combustion, lead ores (the mining activities and smelting process), and cement material, indicating that these anthropogenic inputs may be the main sources for Pb pollution in sediments of TGR tributaries. PMID:24624045

  1. Isotopic composition of Pb in ore deposits of the Betic Cordillera, Spain; origin and relationship to other European deposits

    USGS Publications Warehouse

    Arribas , Antonio; Tosdal, Richard M.

    1994-01-01

    The Betic Cordillera in southern Spain is a complex Alpine fold belt that resulted from the Cretaceous through Cenozoic collision of Africa with Europe. The region is illustrative of one of the characteristics of the Alpine-Mediterranean orogen: the occurrence over a limited area of mineral deposits with a wide variety of host rocks, mineralization ages, and styles. The metamorphic basement in the Betic zone is characterized by a nappe structure of superimposed tectonostratigraphic units and consists of lower Paleozoic to Lower Triassic clastic metasedimentary rocks. This is overlain by Middle to Upper Triassic platform carbonate rocks with abundant strata-bound F-Pb-Zn-(Ba) deposits (e.g., Sierra de Gador, Sierra Alhamilla). Cretaceous to Paleogene subduction-related compression in southeastern Spain was followed by Miocene postcollisional extension and resulted in the formation of the Almeria-Cartagena volcanic belt and widespread hydrothermal activity and associated polymetallic mineralization. Typical Miocene hydrothermal deposits include volcanic-hosted Au (e.g., Rodalquilar) and Ag-rich base metal (e.g., Cabo de Gata, Mazarron) deposits as well as complex polymetallic veins, mantos, and irregular replacement bodies which are hosted by Paleozoic and Mesozoic metamorphic rocks and Neogene sedimentary and volcanic rocks (e.g., Cartagena, Sierra Almagrera, Sierra del Aguilon, Loma de Bas).Lead isotope compositions were measured on sulfide samples from nine ore districts and from representative fresh samples of volcanic and basement rock types of the region. The results have been used to evaluate ore-forming processes in southeastern Spain with emphasis on the sources of metals. During a Late Triassic mineralizing event, Pb was leached from Paleozoic clastic metasedimentary rocks and incorporated in galena in strata-bound F-Pb-Zn-(Ba) deposits ( 206 Pb/ 204 Pb = 18.332 + or - 12, 207Pb/ 204 Pb = 15.672 + or - 12, 208 Pb/ 204 Pb = 38.523 + or - 46). The second

  2. Sources and Evolution of Anthropogenic Lead in Northwestern Pacific Seawater: High Resolution Coral Pb Isotope Record

    NASA Astrophysics Data System (ADS)

    Wang, B.; You, C.; Nohda, S.

    2008-12-01

    Lattice-bound Lead in scleractinian coral skeletons provides a potential tracer to investigate the historical anthropogenic disturbance in the surface ocean. In this study, a Porites coral core collected from an islet offshore southeastern Taiwan was used to reconstruct decadal lead variation in surface seawater at northwestern Pacific. Seasonal Pb/Ca peaks are in accordance with rainfall episodes, while the long-term trend shows high lead input before 1970s. This can be attributed to extensively use of alkyl-lead in the region. Moreover, temporal variations of lead isotope display a significant change of lead sources in mid-20 th, coinciding with the Australian Pb imported period. These isotopic signatures also indicate contribution from China/Japan pollutant through atmospheric circulation during 1962-1998. This preliminary study infers that Pb in surface seawater is dominantly transported by ocean current and aeolian deposition from adjacent urban area, while Pb concentration may not reflect entirely the source flux due to potential loss during transportation.

  3. Pb Isotopes as an Indicator of the Asian Contribution to Particulate Air Pollution in Urban California

    SciTech Connect

    Ewing, Stephanie A.; Christensen, John N.; Brown, Shaun T.; Vancuren, Richard A.; Cliff, Steven S.; DePaolo, Donald J.

    2010-10-25

    During the last two decades, expanding industrial activity in east Asia has led to increased production of airborne pollutants that can be transported to North America. Previous efforts to detect this trans-Pacific pollution have relied upon remote sensing and remote sample locations. We tested whether Pb isotope ratios in airborne particles can be used to directly evaluate the Asian contribution to airborne particles of anthropogenic origin in western North America, using a time series of samples from a pair of sites upwind and downwind of the San Francisco Bay Area. Our results for airborne Pb at these sites indicate a median value of 29 Asian origin, based on mixing relations between distinct regional sample groups. This trans-Pacific Pb is present in small quantities but serves as a tracer for airborne particles within the growing Asian industrial plume. We then applied this analysis to archived samples from urban sites in central California. Taken together, our results suggest that the analysis of Pb isotopes can reveal the distribution of airborne particles affected by Asian industrial pollution at urban sites in northern California. Under suitable circumstances, this analysis can improve understanding of the global transport of pollution, independent of transport models.

  4. Pb isotopes as an indicator of the Asian contribution to particulate air pollution in urban California.

    PubMed

    Ewing, Stephanie A; Christensen, John N; Brown, Shaun T; Vancuren, Richard A; Cliff, Steven S; Depaolo, Donald J

    2010-12-01

    During the last two decades, expanding industrial activity in east Asia has led to increased production of airborne pollutants that can be transported to North America. Previous efforts to detect this trans-Pacific pollution have relied upon remote sensing and remote sample locations. We tested whether Pb isotope ratios in airborne particles can be used to directly evaluate the Asian contribution to airborne particles of anthropogenic origin in western North America, using a time series of samples from a pair of sites upwind and downwind of the San Francisco Bay Area. Our results for airborne Pb at these sites indicate a median value of 29% Asian origin, based on mixing relations between distinct regional sample groups. This trans-Pacific Pb is present in small quantities but serves as a tracer for airborne particles within the growing Asian industrial plume. We then applied this analysis to archived samples from urban sites in central California. Taken together, our results suggest that the analysis of Pb isotopes can reveal the distribution of airborne particles affected by Asian industrial pollution at urban sites in northern California. Under suitable circumstances, this analysis can improve understanding of the global transport of pollution, independent of transport models.

  5. Resolving arc processes through detrital zircon U-Pb geochronology and geochemistry: a case study from the southern California Mesozoic convergent margin

    NASA Astrophysics Data System (ADS)

    Johnston, S. M.; Kylander-Clark, A. R.

    2015-12-01

    Detrital zircon geochronology has been widely exploited to establish temporal characteristics in sedimentary source terranes. Detrital zircon geochemistry, however, has been largely overlooked given results from continentally derived igneous zircon that show subtle intersample variation in trace-element concentrations, and which make correlation between detrital zircon and their host terrane difficult. Nevertheless, recent studies suggest systematically variable geochemistry in McCoy Mountain detrital zircons derived from the southern California Mesozoic arc, and our preliminary data from the Peninsular Ranges batholith indicates strong correlations between whole-rock and zircon geochemistry. Here, we present coupled U-Pb geochronology and geochemistry measured by laser ablation split stream ICPMS on detrital zircons from Nacimiento block forearc sediments in Central California to characterize temporal and geochemical trends in the adjacent Mesozoic arc terrane. 1098 grains of Mesozoic age analyzed from 22 samples in the Nacimiento block define three periods of high magmatic flux in the Permian (270-250 Ma), Jurassic (170-140 Ma), and late Cretaceous (115-90 Ma). Zircon from the Permian arc is the least abundant of the three magmatic pulses, although they consistently display elevated Yb/Gd and U/Yb. Jurassic zircons display consistently low U/Yb, variably elevated Yb/Gd, abruptly higher Th/U and LREE from 155-145, and abruptly lower REE concentrations from 145-140 Ma. Zircon from the Cretaceous arc displays gradually increasing U/Yb, Th/U and LREE, with abruptly decreasing Yb/Gd at 95 Ma. The geochemical trends observed in the Nacimiento block detrital zircons of Cretaceous age are strikingly similar to temporal changes in geochemistry known from Cretaceous arc rocks of the Mojave and Peninsular Ranges, and strongly suggest a southern California provenance for Nacimiento block sediments. Furthermore, the similarity of geochemical trends between Cretaceous detrital

  6. Calcium isotope fractionation between aqueous compounds relevant to low-temperature geochemistry, biology and medicine

    PubMed Central

    Moynier, Frédéric; Fujii, Toshiyuki

    2017-01-01

    Stable Ca isotopes are fractionated between bones, urine and blood of animals and between soils, roots and leaves of plants by >1000 ppm for the 44Ca/40Ca ratio. These isotopic variations have important implications to understand Ca transport and fluxes in living organisms; however, the mechanisms of isotopic fractionation are unclear. Here we present ab initio calculations for the isotopic fractionation between various aqueous species of Ca and show that this fractionation can be up to 3000 ppm. We show that the Ca isotopic fractionation between soil solutions and plant roots can be explained by the difference of isotopic fractionation between the different first shell hydration degree of Ca2+ and that the isotopic fractionation between roots and leaves is controlled by the precipitation of Ca-oxalates. The isotopic fractionation between blood and urine is due to the complexation of heavy Ca with citrate and oxalates in urine. Calculations are presented for additional Ca species that may be useful to interpret future Ca isotopic measurements. PMID:28276502

  7. Calcium isotope fractionation between aqueous compounds relevant to low-temperature geochemistry, biology and medicine.

    PubMed

    Moynier, Frédéric; Fujii, Toshiyuki

    2017-03-09

    Stable Ca isotopes are fractionated between bones, urine and blood of animals and between soils, roots and leaves of plants by >1000 ppm for the (44)Ca/(40)Ca ratio. These isotopic variations have important implications to understand Ca transport and fluxes in living organisms; however, the mechanisms of isotopic fractionation are unclear. Here we present ab initio calculations for the isotopic fractionation between various aqueous species of Ca and show that this fractionation can be up to 3000 ppm. We show that the Ca isotopic fractionation between soil solutions and plant roots can be explained by the difference of isotopic fractionation between the different first shell hydration degree of Ca(2+) and that the isotopic fractionation between roots and leaves is controlled by the precipitation of Ca-oxalates. The isotopic fractionation between blood and urine is due to the complexation of heavy Ca with citrate and oxalates in urine. Calculations are presented for additional Ca species that may be useful to interpret future Ca isotopic measurements.

  8. Calcium isotope fractionation between aqueous compounds relevant to low-temperature geochemistry, biology and medicine

    NASA Astrophysics Data System (ADS)

    Moynier, Frédéric; Fujii, Toshiyuki

    2017-03-01

    Stable Ca isotopes are fractionated between bones, urine and blood of animals and between soils, roots and leaves of plants by >1000 ppm for the 44Ca/40Ca ratio. These isotopic variations have important implications to understand Ca transport and fluxes in living organisms; however, the mechanisms of isotopic fractionation are unclear. Here we present ab initio calculations for the isotopic fractionation between various aqueous species of Ca and show that this fractionation can be up to 3000 ppm. We show that the Ca isotopic fractionation between soil solutions and plant roots can be explained by the difference of isotopic fractionation between the different first shell hydration degree of Ca2+ and that the isotopic fractionation between roots and leaves is controlled by the precipitation of Ca-oxalates. The isotopic fractionation between blood and urine is due to the complexation of heavy Ca with citrate and oxalates in urine. Calculations are presented for additional Ca species that may be useful to interpret future Ca isotopic measurements.

  9. β-decay properties of neutron-deficient Pt, Hg, and Pb isotopes

    SciTech Connect

    Sarriguren, P.; Boillos, J. M.; Moreno, O.; Moya de Guerra, E.

    2015-10-15

    Neutron-deficient isotopes in the lead region are well established examples of the shape coexistence phenomenon in nuclei. In this work, bulk and decay properties, including deformation energy curves, charge mean square radii, Gamow-Teller (GT) strength distributions, and β-decay half-lives, are studied in neutron-deficient Pt, Hg, and Pb isotopes. The nuclear structure involved is described microscopically from deformed quasiparticle random-phase approximation calculations with residual interactions in both particle-hole and particle-particle channels, performed on top of a self-consistent deformed quasiparticle Skyrme Hartree-Fock basis. The sensitivity to deformation of the GT strength distributions in those isotopes is proposed as an additional complementary signature of the nuclear shape. The β-decay half-lives resulting from the GT strength distributions are compared to experiment to demonstrate the ability of the method.

  10. Ion Microprobe U-Pb Dating and Sr Isotope Measurement of Conodont

    NASA Astrophysics Data System (ADS)

    Sano, Y.; Ishida, A.; Kagoshima, T.; Takahata, N.

    2014-12-01

    We have developed a method of in situ ion microprobe U-Pb dating and Sr isotope measurement of biogenic apatite using NanoSIMS. This was applied to a protoconodont, an early Cambrian phosphate microfossil [1]. On a single fragment of a fossil derived from a sedimentary layer in the Meishucunian Yuhucun Formation, southern China [2], 23 spots provide a 238U/206Pb isochron age of 547 ± 43 Ma (2sigma), which is consistent with the depositional age, 536.5 ± 2.5 Ma estimated using zircon U-Pb dating of interbedded tuffs [3]. However, five spots on a small region in the same protoconodont yield an isochron age of 417 ± 74 Ma (2sigma), apparently younger than the formation age. The younger age might be attributable to a later hydrothermal event, perhaps associated with Caledonian orogenic activity recorded in younger zircon with an age of 420-440 Ma [4]. We measured Sr isotopic ratios of the protoconodont by NanoSIMS. In the older domain, 19 spots give the ratio of 0.71032 ± 0.00023 (2sigma), although seven spots on the younger region provide the ratio of 0.70862 ± 0.00045; which is significantly less radiogenic than the older domain. We also measured U-Pb age and Sr isotopes of a Carboniferous conodont derived from the Kinderhookian stage from the Illinois Basin region in North America. 20 spots yield a 238U/206Pb isochron age of 291 ± 56 Ma (2sigma), which is markedly younger than the depositional age of the fossil of 350-363 Ma. On the other hand, 9 spots give a Sr isotopic ratio of 0.70784 ± 0.00030, less radiogenic than the older domain of protoconodont. These data together with other isotopes such as Cl may provide a constraint on the model for chemical evolution of seawater. [1] Sano et al. (2014) J. Asian Earth Sci. 92, 10-17. [2] Condon et al. (2005) Science 308, 95-98. [3] Sawaki et al. (2008) Gondwana Res. 14, 148-158. [4] Guo et al. (2009) Geochem. J. 43, 101-122.

  11. Heavy metal input to agricultural soils from irrigation with treated wastewater: Insight from Pb isotopes

    NASA Astrophysics Data System (ADS)

    Kloppmann, Wolfram; Cary, Lise; Psarras, Georgios; Surdyk, Nicolas; Chartzoulakis, Kostas; Pettenati, Marie; Maton, Laure

    2010-05-01

    A major objective of the EU FP6 project SAFIR was to overcome certain drawbacks of wastewater reuse through the development of a new irrigation technology combining small-scale modular water treatment plants on farm level and improved irrigation hardware, in the aim to lower the risks related to low quality water and to increase water use efficiency. This innovative technology was tested in several hydro-climatic contexts (Crete, Italy, Serbia, China) on experimental irrigated tomato and potato fields. Here we present the heavy metal variations in soil after medium-term (3 irrigation seasons from 2006-2008) use of treated municipal wastewater with a special focus on lead and lead isotope signatures. The experimental site is located in Chania, Crete. A matrix of plots were irrigated, combining different water qualities (secondary, primary treated wastewater, tap water, partially spiked with heavy metals, going through newly developed tertiary treatment systems) with different irrigation strategies (surface and subsurface drip irrigation combined with full irrigation and partial root drying). In order to assess small scale heavy metal distribution around a drip emitter, Pb isotope tracing was used, combined with selective extraction. The sampling for Pb isotope fingerprinting was performed after the 3rd season of ww-irrigation on a lateral profile from a drip irrigator (half distance between drip lines, i.e. 50cm) and three depth intervals (0-10, 10-20, 20-40 cm). These samples were lixiviated through a 3 step selective extraction procedure giving rise to the bio-accessible, mobile and residual fraction: CaCl2/NaNO3 (bio-accessible fraction), DPTA (mobile fraction), total acid attack (residual fraction). Those samples were analysed for trace elements (including heavy metals) and major inorganic compounds by ICP-MS. The extracted fractions were then analysed by Thermal Ionisation Mass Spectrometry (TIMS) for their lead isotope fingerprints (204Pb, 206Pb, 207Pb, 208Pb

  12. Pyrogenic inputs of anthropogenic Pb and Hg to sediments of the Hood Canal, Washington, in the 20th century: source evidence from stable Pb isotopes and PAH signatures.

    PubMed

    Louchouarn, Patrick; Kuo, Li-Jung; Brandenberger, Jill M; Marcantonio, Franco; Garland, Charity; Gill, Gary A; Cullinan, Valerie

    2012-06-05

    Combustion-derived PAHs and stable Pb isotopic signatures ((206)Pb/(207)Pb) in sedimentary records assisted in reconstructing the sources of atmospheric inputs of anthropogenic Pb and Hg to the Hood Canal, Washington. The sediment-focusing corrected peak fluxes of total Pb and Hg (1960-70s) demonstrate that the watershed of Hood Canal has received greater atmospheric inputs of these metals than its mostly rural land use would predict. The tight relationships between the Pb, Hg, and organic markers in the cores indicate that these metals are derived from industrial combustion emissions. Multiple lines of evidence point to the Asarco smelter, located in the Main Basin of Puget Sound, as the major emission source of these metals to the watershed of the Hood Canal. The evidence includes (1) similar PAH isomer ratios in sediment cores from the two basins, (2) the correlations between Pb, Hg, and Cu in sediments and previously studied environmental samples including particulate matter emitted from the Asarco smelter's main stack at the peak of production, and (3) Pb isotope ratios. The natural rate of recovery in Hood Canal since the 1970s, back to preindustrial metal concentrations, was linear and contrasts with recovery rates reported for the Main Basin which slowed post late 1980s.

  13. Character of the pre-Mesozoic basement along the edge of the western US craton: Pb isotopic evidence from Mesozoic plutonism

    SciTech Connect

    Wooden, J.L.; Kistler, R.W.; Robinson, A.; Tosdal, R.M. ); Wright, J.E. . Dept. of Geology and Geophysics)

    1993-04-01

    The pre-Mesozoic cratonic crust of the western US was a composite of provinces composed mostly of Archean and Early Proterozoic rocks that had been truncated by Late Proterozoic rifting and had some new Paleozoic crust added along the western edge. Mesozoic and younger geologic events greatly obscured this pre-Mesozoic basement along the craton edge. However, the Pb isotopic signatures of Mesozoic plutons provide significant clues to the character of the crust in which they formed or were emplaced because of a strong contrast in Pb concentration between low-Pb, mantle-derived melts and Pb-rich crust. Thus, magmas whether derived from the crust or the mantle with subsequent crustal interaction, will likely have Pb isotopic compositions that reflect those of the crust. In the western US the Pb isotopic compositions of Mesozoic plutonic rocks have strong regional characteristics. Within the Early Proterozoic Mojave crustal province, Mesozoic plutonic rocks have a large range of 206Pb/204Pb ratios that plot above the crustal average, relatively high 207Pb/204Pb ratios that suggest an Archean contribution, and Pb and Sr isotopic compositions that are not correlated and that do not distinguish age groups. At the southern and western edge of this province where some 1.1 Ga rocks are exposed, 208Pb/204Pb ratios lie along the average crust model curve. These data suggest that any individual pluton provides a composite Pb isotopic composition for a discrete vertical section of the crust. Pb isotopic compositions of plutons in the Sierra Nevada and Great Basin are very different from those described above with 206Pb/204Pb ratios starting at 18.6, well-correlated Pb isotopic trends starting below the crustal model but extending to values that require input from the very radiogenic Wyoming province Archean crust, and good correlations between Pb and (1) Sr isotopic compositions and (2) W-E geographic position.

  14. Determining provenance of marine metal pollution in French bivalves using Cd, Zn and Pb isotopes

    NASA Astrophysics Data System (ADS)

    Shiel, Alyssa E.; Weis, Dominique; Cossa, Daniel; Orians, Kristin J.

    2013-11-01

    Cadmium, Zn and Pb isotopic compositions (MC-ICP-MS) and elemental concentrations (HR-ICP-MS) have been used to distinguish between natural and anthropogenic sources of these metals in bivalves collected from the coastlines of France (English Channel, Atlantic and Mediterranean coasts). The Cd isotopic signatures (δ114Cd = -1.08‰ to -0.52‰) exhibited by bivalves from the coastlines of France, excluding those from NE France, are within the range of those exhibited by bivalves from the USA East coast (δ114Cd = -1.20‰ to -0.54‰). This indicates the high prevalence of industry, as well as the low natural contributions of Cd from North Atlantic waters in both regions. Thus, the significance of anthropogenic Cd sources is similar. These significant anthropogenic contributions are identified for bivalves with a large range in tissue Cd concentrations. Importantly, French bivalves from the Gironde estuary and Marennes-Oléron basin (regions of historic and modern importance for oyster farming, respectively) exhibited the highest Cd levels of the study. Their Cd isotopic signatures indicate historical smelting emissions remain the primary Cd source despite the cessation of local smelting activities in 1986 and subsequent remedial efforts. No significant variability is observed in the δ66Zn values of the French bivalves (∼0.53‰), with the exception of the much heavier compositions exhibited by oysters from the polluted Gironde estuary (1.19-1.27‰). Lead isotopes do not fractionate during processing like Cd and Zn. They can, therefore, be used to identify emissions from industrial processes and the consumption of unleaded gasoline and diesel fuel as metal sources to French bivalves. Cadmium and Zn isotopes are successfully used here as tracers of anthropogenic processing emissions and are combined with Pb isotope "fingerprinting" techniques to identify metal sources.

  15. Copper isotope fractionation between aqueous compounds relevant to low temperature geochemistry and biology

    NASA Astrophysics Data System (ADS)

    Fujii, Toshiyuki; Moynier, Frédéric; Abe, Minori; Nemoto, Keisuke; Albarède, Francis

    2013-06-01

    Isotope fractionation between the common Cu species present in solution (Cu+, Cu2+, hydroxide, chloride, sulfide, carbonate, oxalate, and ascorbate) has been investigated using both ab initio methods and experimental solvent extraction techniques. In order to establish unambiguously the existence of equilibrium isotope fractionation (as opposed to kinetic isotope fractionation), we first performed laboratory-scale liquid-liquid distribution experiments. Upon exchange between HCl medium and a macrocyclic complex, the 65Cu/63Cu ratio fractionated by -1.06‰ to -0.39‰. The acidity dependence of the fractionation was appropriately explained by ligand exchange reactions between hydrated H2O and Cl- via intramolecular vibrations. The magnitude of the Cu isotope fractionation among important Cu ligands was also estimated by ab initio methods. The magnitude of the nuclear field shift effect to the Cu isotope fractionation represents only ˜3% of the mass-dependent fractionation. The theoretical estimation was expanded to chlorides, hydroxides, sulfides, sulfates, and carbonates under different conditions of pH. Copper isotope fractionation of up to 2‰ is expected for different forms of Cu present in seawater and for different sediments (carbonates, hydroxides, and sulfides). We found that Cu in dissolved carbonates and sulfates is isotopically much heavier (+0.6‰) than free Cu. Isotope fractionation of Cu in hydroxide is minimal. The relevance of these new results to the understanding of metabolic processes was also discussed. Copper is an essential element used by a large number of proteins for electron transfer. Further theoretical estimates of δ65Cu in hydrated Cu(I) and Cu(II) ions, Cu(II) ascorbates, and Cu(II) oxalate predict Cu isotope fractionation during the breakdown of ascorbate into oxalate and account for the isotopically heavy Cu found in animal kidneys.

  16. Whole-rock Pb and Sm-Nd isotopic constraints on the growth of southeastern Laurentia during Grenvillian orogenesis

    USGS Publications Warehouse

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

    2010-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  18. Mantle and crustal sources of Archean anorthosite: a combined in situ isotopic study of Pb-Pb in plagioclase and Lu-Hf in zircon

    NASA Astrophysics Data System (ADS)

    Souders, A. Kate; Sylvester, Paul J.; Myers, John S.

    2013-01-01

    Isotopic analyses of ancient mantle-derived magmatic rocks are used to trace the geochemical evolution of the Earth's mantle, but it is often difficult to determine their primary, initial isotope ratios due to the detrimental effects of metamorphism and secondary alteration. We present in situ analyses by LA-MC-ICPMS for the Pb isotopic compositions of igneous plagioclase (An75-89) megacrysts and the Hf isotopic compositions of BSE-imaged domains of zircon grains from two mantle-derived anorthosite complexes from south West Greenland, Fiskenæsset and Nunataarsuk, which represent two of the best-preserved Archean anorthosites in the world. In situ LA-ICPMS U-Pb geochronology of the zircon grains suggests that the minimum crystallization age of the Fiskenæsset complex is 2,936 ± 13 Ma (2σ, MSWD = 1.5) and the Nunataarsuk complex is 2,914 ± 6.9 Ma (2σ, MSWD = 2.0). Initial Hf isotopic compositions of zircon grains from both anorthosite complexes fall between depleted mantle and a less radiogenic crustal source with a total range up to 5 ɛHf units. In terms of Pb isotopic compositions of plagioclase, both anorthosite complexes share a depleted mantle end member yet their Pb isotopic compositions diverge in opposite directions from this point: Fiskenæsset toward a high-μ, more radiogenic Pb, crustal composition and Nunataarsuk toward low-μ, less radiogenic Pb, crustal composition. By using Hf isotopes in zircon in conjunction with Pb isotopes in plagioclase, we are able to constrain both the timing of mantle extraction of the crustal end member and its composition. At Fiskenæsset, the depleted mantle melt interacted with an Eoarchean (~3,700 Ma) mafic crust with a maximum 176Lu/177Hf ~0.028. At Nunataarsuk, the depleted mantle melt interacted with a Hadean (~4,200 Ma) mafic crust with a maximum 176Lu/177Hf ~0.0315. Evidence from both anorthosite complexes provides support for the long-term survival of ancient mafic crusts that, although unidentified at the

  19. Provenance of sedimentary kaolin deposits in Egypt: Evidences from the Pb, Sr and Nd isotopes

    NASA Astrophysics Data System (ADS)

    Baioumy, Hassan

    2014-12-01

    This work reports, for the first time, the Pb, Sr and Nd isotopes of the clay fractions (<2 μm) from sedimentary kaolin deposits in Egypt of different ages (Carboniferous and lower Cretaceous), localities (Sinai, Red Sea and Aswan), lithologies (flint and plastic) and clay minerals composition (pure kaolinite and mixture of kaolinite, illite and chlorite) to determine their source area compositions and examine the effect of provenance on their isotopic compositions. Measured (present day) and age-corrected Pb isotopes data (100 and 300 My for the Cretaceous and Carboniferous deposits, respectively) are more or less homogeneous in all deposits regardless of their ages, localities, and compositions. This, therefore, suggests that the Pb isotopes cannot be used as a tracer for source area compositions of these kaolin deposits. On the other hand, the studied kaolin deposits show variations in their measured and age-corrected Sr and Nd isotopes regarding to their ages and compositions. The Carboniferous illite-rich kaolin deposits in the Khaboba and Hasbar areas, Sinai have higher measured and age-corrected 87Sr/86Sr ratios (average of 0.715742 and 0.711156 for measured and age-corrected, respectively) compared to the non-illitic Carboniferous deposit at Abu Natash area (average of 0.70772 and 0.70769 for measured and age-corrected, respectively) and the lower Cretaceous deposits in all areas (average of 0.70827 and 0.70821 for measured and age-corrected, respectively). The Carboniferous kaolin deposits in the Khaboba and Hasbar areas also have lower 143Nd/144Nd ratios (average of 0.51206 and 0.51180 for measured and age-corrected, respectively) compared to the Carboniferous Abu Natash deposit (average of 0.51253 and 0.51231 for measured and age-corrected, respectively) as well as the lower Cretaceous deposits in all areas (average of 0.51248 and 0.51239 for measured and age-corrected, respectively). Initial εNd values are negative in the Carboniferous kaolin deposits

  20. Cenozoic marine geochemistry of thallium deduced from isotopic studies of ferromanganese crusts and pelagic sediments

    USGS Publications Warehouse

    Rehkamper, M.; Frank, M.; Hein, J.R.; Halliday, A.

    2004-01-01

    Cenozoic records of Tl isotope compositions recorded by ferromanganese (Fe-Mn) crusts have been obtained. Such records are of interest because recent growth surfaces of Fe-Mn crusts display a nearly constant Tl isotope fractionation relative to seawater. The time-series data are complemented by results for bulk samples and leachates of various marine sediments. Oxic pelagic sediments and anoxic marine deposits can be distinguished by their Tl isotope compositions. Both pelagic clays and biogenic oozes are typically characterized by ??205Tl greater than +2.5, whereas anoxic sediments have ??205Tl of less than -1.5 (??205Tl is the deviation of the 205Tl/203Tl isotope ratio of a sample from NIST SRM 997 Tl in parts per 104). Leaching experiments indicate that the high ??205Tl values of oxic sediments probably reflect authigenic Fe-Mn oxyhydroxides. Time-resolved Tl isotope compositions were obtained from six Fe-Mn crusts from the Atlantic, Indian, and Pacific oceans and a number of observations indicate that these records were not biased by diagenetic alteration. Over the last 25 Myr, the data do not show isotopic variations that significantly exceed the range of Tl isotope compositions observed for surface layers of Fe-Mn crusts distributed globally (??205 Tl=+12.8??1.2). This indicates that variations in deep-ocean temperature were not recorded by Tl isotopes. The results most likely reflect a constant Tl isotope composition for seawater. The growth layers of three Fe-Mn crusts that are older than 25 Ma show a systematic increase of ??205Tl with decreasing age, from about +6 at 60-50 Ma to about +12 at 25 Ma. These trends are thought to be due to variations in the Tl isotope composition of seawater, which requires that the oceans of the early Cenozoic either had smaller output fluxes or received larger input fluxes of Tl with low ??205Tl. Larger inputs of isotopically light Tl may have been supplied by benthic fluxes from reducing sediments, rivers, and/or volcanic

  1. Contamination and isotopic composition of Pb and Sr in offshore surface sediments from Jiulong River, Southeast China.

    PubMed

    Lin, Chengqi; Yu, Ruilian; Hu, Gongren; Yang, Qiuli; Wang, Xiaoming

    2016-11-01

    Concentrations and isotopic compositions of Pb and Sr in the surface sediment samples from Jiulong River, Southeast China, were determined to trace the sources of Pb and Sr. The average concentrations of Pb and Sr were 110.9 mg/kg and 69.2 mg/kg, approximately 3.2 and 2.0 times of the local soil background values, respectively. Average 62.9% of total Pb and 36.8% of total Sr in the investigated surface sediment samples were extracted by 0.5 mol/L HNO3. Pb and Sr presented slight contamination, and Pb showed low ecological risk for most of surface sediment samples in Jiulong River according to geo-accumulation index (Igeo) and potential ecological risk index (RI). The results of Pb isotopic compositions in sediment samples and potential sources showed that the Pb accumulated in the surface sediments of Jiulong River was mainly from parent material, coal combustion and Fujian Pb-Zn deposit, with the contribution rates of 34.4%, 34.0%, and 31.6%, respectively. The results of Pb isotopic compositions in 0.5 mol/L HNO3-extraction suggested that dilute HNO3-extraction was more sensitive in identifying anthropogenic Pb sources than total digestion. The results of Sr isotopic compositions showed that Sr accumulated in the surface sediments of Jiulong River estuary mainly derived from external source and natural source (parent material) with the contribution rates of 48.1% and 51.9%, respectively.

  2. Sr-Nd-Pb isotope systematics of mantle xenoliths from Somerset Island kimberlites: Evidence for lithosphere stratification beneath Arctic Canada

    NASA Astrophysics Data System (ADS)

    Schmidberger, S. S.; Simonetti, A.; Francis, D.

    2001-11-01

    Sr, Nd, and Pb isotopic compositions were determined for a suite of Archean garnet peridotite and garnet pyroxenite xenoliths and their host Nikos kimberlite (100 Ma) from Somerset Island to constrain the isotopic character of the mantle root beneath the northern Canadian craton. The Nikos peridotites are enriched in highly incompatible trace elements (La/Sm N = 4-6), and show 143Nd/ 144Nd (t) (0.51249-0.51276) and a large range in 87Sr/ 86Sr (t) (0.7047-0.7085) and Pb ( 206Pb/ 204Pb (t) = 17.18 to 19.03) isotope ratios that are distinct from those estimated for "depleted mantle" compositions at the time of kimberlite emplacement. The Nd isotopic compositions of the peridotites overlap those of the Nikos kimberlite, suggesting that the xenoliths were contaminated with kimberlite or a kimberlite-related accessory phase (i.e., apatite). The highly variable Sr and Pb isotopic compositions of the peridotites, however, indicate that kimberlite contribution was restricted to very small amounts (˜1 wt % or less). The high-temperature peridotites (>1100°C) that sample the deep Somerset lithosphere trend toward more radiogenic 87Sr/ 86Sr (t) (0.7085) and unradiogenic 206Pb/ 204Pb (t) (17.18) isotopic ratios than those of the low-temperature peridotites (<1100°C). This is in agreement with Sr isotopic compositions of clinopyroxene from the low-temperature peridotites ( 87Sr/ 86Sr (t) = 0.7038-0.7046) that are significantly less radiogenic than those of clinopyroxene from the high-temperature peridotites ( 87Sr/ 86Sr (t) = 0.7052-0.7091). The depth correlation of Sr isotopes for clinopyroxene and Sr and Pb isotopic compositions for the Nikos whole-rocks indicate that the deep Somerset lithosphere (>160 km) is isotopically distinct from the shallow lithospheric mantle. The isotopic stratification with depth suggests that the lower lithosphere is probably younger and may have been added to the existing Archean shallow mantle in a Phanerozoic magmatic event. The radiogenic Sr

  3. Origin of the Red Dog Zn-Pb-Ag deposits, Brooks Range, Alaska: Evidence from regional Pb and Sr isotope sources

    USGS Publications Warehouse

    Ayuso, R.A.; Kelley, K.D.; Leach, D.L.; Young, L.E.; Slack, J.F.; Wandless, G.; Lyon, A.M.; Dillingham, J.L.

    2004-01-01

    Pb and Sr isotope data were obtained on the shale-hosted Zn-Pb-Ag Red Dog deposits (Qanaiyaq, Main, Aqqaluk, and Paalaaq), other shale-hosted deposits near Red Dog, and Zn-Pb-Ag sulfide and barite deposits in the western and central Brooks Range. The Red Dog deposits and other shale-hosted Zn-Pb-Ag deposits near Red Dog are hosted in the Mississippian Kuna Formation, which is underlain by a sequence of marine-deltaic clastic rocks of the Upper Devonian to Lower Mississippian Endicott Group. Ag-Pb-Zn vein-breccias are found in the Endicott Group. Galena formed during the main mineralization stages in the Red Dog deposits and from the Anarraaq and Wulik deposits have overlapping Pb isotope compositions in the range 206Pb/204Pb = 18.364 to 18.428, 207Pb/204Pb = 15.553 to 15.621, and 208Pb/204Pb = 38.083 to 38.323. Galena and sphalerite formed during the main ore-forming stages in the Red Dog deposits define a narrow field on standard uranogenic and thorogenic Pb isotope diagrams. Lead in sulfides of the Red Dog district is less radiogenic (238U/204Pb: ?? = 9.51-9.77) than is indicated by the average crustal lead evolution model (?? = 9.74), a difference consistent with a long history of evolution at low ratios of ?? before the Carboniferous. The homogeneous regional isotopic reservoir of Pb may indicate large-scale transport and leaching of minerals with various ?? ratios and Th/Pb ratios. Younger and genetically unrelated fluids did not significantly disturb the isotopic compositions of galena and sphalerite after the main mineralization event in the Red Dog district. Some pyrite shows evidence of minor Pb remobilization. The overall lead isotope homogeneity in the shale-hosted massive sulfide deposits is consistent with three types of control: a homogeneous regional source, mixing of lead during leaching of a thick sedimentary section and fluid transport, or mixing at the site of deposition. Isotopic variability of the hydrothermal fluids, as represented by galena

  4. Boron isotope geochemistry during diagenesis. Part II. Applications to organic-rich sediments

    NASA Astrophysics Data System (ADS)

    Williams, Lynda B.; Hervig, Richard L.; Hutcheon, Ian

    2001-06-01

    The measured clay-water isotope fractionation for boron was applied to natural organic-rich sediments undergoing illitization. Two field areas were chosen that show illitization occurring over a range of temperatures (80-500°C). Samples representing diagenetic temperatures of illitization (80-200°C) are from the Gulf of Mexico sedimentary basin at 4 to 6-km depth in the Eocene Wilcox Fm and Jurassic Norphlet Fm. The higher temperatures of illitization (200-500°C) occur in a contact metamorphic aureole of the Cretaceous Pierre shale near Walsenburg, Colorado. Here the kinetics of the illitization reaction are more rapid than in a slowly subsiding sedimentary basin, but the chemical and mineralogical variations are minimized as complete illitization occurs over a small lateral distance in a single bentonite layer. These studies indicate that B-isotopes provide a more sensitive indicator of fluid variations in sedimentary basins than O-isotopes, and that B-isotope analyses of authigenic illite can be a valuable geochemical tracer of fluid/rock interactions. Boron isotope ratios in authigenic illite (pore filling) and muscovite (stylolites) from reservoir sandstones in the Gulf of Mexico are distinct from adjacent illitic mudstones, whereas the oxygen isotopic ratios show little variation. Fluids in equilibrium with the mudstones cannot precipitate the authigenic clays with higher δ 11B values measured in the hydrocarbon reservoirs. This suggests that the reservoir fluids were not in communication with the adjacent mudstone pore fluids but were introduced from another source area, perhaps carrying a B-isotopic label derived from the hydrocarbon source region. Authigenic illite formed in the Pierre shale meta-bentonite shows large isotopic fractionations of boron (20‰) during illitization at high temperatures. Incorporation of 500 ppm B in illite formed at 500°C shows that illite is a host for B even at metamorphic temperatures. By using the experimentally

  5. Pb-isotopic systematics of lunar highland rocks (>3.9 Ga): Constraints on early lunar evolution

    USGS Publications Warehouse

    Premo, W.R.; Tatsumoto, M.; Misawa, K.; Nakamuka, N.; Kita, N.I.

    1999-01-01

    The present lead (Pb)-isotopic database of over 200 analyses from nearly 90 samples of non-mare basalt, lunar highland rocks (>3.9 Ga) delineate at least three isotopically distinct signatures that in some combination can be interpreted to characterize the systematics of the entire database. Two are fairly new sets of lunar data and are typical of Pb data from other solar-system objects, describing nearly linear arrays slightly above the 'geochron' values, with 207Pb/206Pb values 500). Although the age and origin of this exotic Pb is not well constrained, it is interpreted to be related to the entrapment of incompatible-element-rich (U, Th) melts within the lunar upper mantle and crust between 4.36 and 4.46 Ga (urKREEP residuum?). The latest discovered Pb signature is found only in lunar meteorites and is characterized by relatively low source ?? values between 10 and 50 at 3.9 Ga. The fact that most lunar crustal rocks (>3.9 Ga) exhibit high 207Pb/206Pb values requires that they were derived from, mixed with, or contaminated by Pb produced from early-formed, high-?? sources. The ubiquity of these U-Pb characteristics in the sample collection is probably an artifact of Apollo and Luna sampling sites, all located on the near side of the Moon, which was deeply excavated during the basin-forming event(s). However, the newest Pb-isotopic data support the idea that the Moon originally had a ?? value of ~8 to 35, slightly elevated from Earth values, and that progressive U-Pb fractionations occurred within the Moon during later stages of differentiation between 4.36 and 4.46 Ga.

  6. Microbial sulfur metabolism evidenced from pore fluid isotope geochemistry at Site U1385

    NASA Astrophysics Data System (ADS)

    Turchyn, Alexandra V.; Antler, Gilad; Byrne, David; Miller, Madeline; Hodell, David A.

    2016-06-01

    At Site U1385, drilled during IODP Expedition 339 off the coast of Portugal on the continental slope, high-resolution sulfate concentration measurements in the pore fluids display non-steady-state behavior. At this site there is a zone of sulfate reduction in the uppermost seven meters of sediment, followed by a 38-meter interval where sulfate concentrations do not change, and finally sulfate concentrations are depleted to zero between 45 and 55 meters below seafloor. Below the sulfate minimum zone, there is abundant methane, suggesting that the lower sulfate consumption zone is coupled to anaerobic methane oxidation. We analyze pore water samples from IODP Site U1385 for sulfur and oxygen isotope ratios of dissolved sulfate, as well as the sulfur isotope composition of sedimentary pyrite. The sulfur isotopes in pore fluid sulfate display similar non-steady-state behavior similar to that of the sulfate concentrations, increasing over the uppermost zone of sulfate reduction and again over the lower zone of sulfate-driven anaerobic methane oxidation. The oxygen isotopes in sulfate increase to the 'apparent equilibrium' value in the uppermost zone of sulfate reduction and do not change further. Our calculations support the idea that sulfite to sulfide reduction is the limiting step in microbial sulfate reduction, and that the isotope fractionation expressed in the residual pore water sulfate pool is inversely proportional to the net sulfate reduction rate. The sulfur isotope composition of pyrite acquires one value in the uppermost sediments, which may be overprinted by a second value in the deeper sediments, possibly due to iron release during anaerobic methane oxidation or iron diffusion from a higher zone of bacterial iron reduction. Our results have implications for modeling the sulfur isotope composition of the pyrite burial flux in the global biogeochemical sulfur cycle.

  7. Pb and O isotopic constraints on the source of granitic rocks from Cape Breton Island, Nova Scotia, Canada

    USGS Publications Warehouse

    Ayuso, R.A.; Barr, S.M.; Longstaffe, F.J.

    1996-01-01

    Pb isotopic compositions of leached feldspars from twenty-three plutons in Cape Breton Island can be divided into two groups: anorthosite, syenite, and granite in the Blair River Complex, which have the least radiogenic compositions on the Island, and granitic rocks from terranes (Aspy, Bras d'Or, and Mira) to the south. Pb isotopic data for the Blair River Complex (206Pb/204Pb = 17.399-18.107; 207Pb/204Pb = 15.505-15.560; 208Pb/204Pb = 36.689-37.733) are consistent with an old source region ultimately derived from the mantle and contaminated by sialic crust. Oxygen isotopic compositions of syenite in the Blair River Complex (??18O = +8.0 to +8.5 permil) are slightly higher than anorthosite (+7.0 to +8.3 permil); a Silurian granite in the Blair River Complex has ??18O = +7.5 permil. Cambrian to Devonian plutons in the Aspy, Bras d'Or, and Mira terranes are more radiogenic (206Pb/204Pb = 18.192-18.981; 207Pb/204Pb = 15.574-15.712; 208Pb/ 204Pb =37.815-38.936) than the Blair River Complex and were generated from source regions having a predominant crustal Pb signature (high ??). The ??18O values of granites and granodiorites in the Aspy terrane (+7.5 to +9.2 permil; avg = +8.6 permil) and Bras d'Or (+3.7 to +11.3 permil; avg = +9.4 permil) are also consistent with involvement of sialic crust. Many Late Proterozoic granites from the Mira terrane have anomalously low ??18O values (+0.2 to +5.9 permil), perhaps produced from protoliths that had undergone hydrothermal alteration prior to melting. Paleozoic granitic rocks from the Aspy, Bras d'Or, and Mira terranes cannot be uniquely distinguished on the basis of their Pb and O isotopic compositions. The granitic rocks could have been generated during terrane amalgamation from combinations of unradiogenic (Grenville-like) and more radiogenic (Avalon-like) sources.

  8. Siderophile and chalcophile element abundances in oceanic basalts, Pb isotope evolution and growth of the earth's core

    NASA Technical Reports Server (NTRS)

    Newsom, H. E.; White, W. M.; Jochum, K. P.; Hofmann, A. W.

    1986-01-01

    The hypothesis that the mantle Pb isotope ratios reflect continued extraction of Pb into the earth's core over geologic time is evaluated by studying the depeletion of chalcophile and siderophile elements in the mantle. Oceanic basalt samples are analyzed in order to determine the Pb, Sr, and Nd isotropic compositions and the abundances of siderophile and chalcophile elements and incompatible lithophile elements. The data reveal that there is no systematic variation of siderophile or chalcophile element abundances relative to abundances of lithophile elements and the Pb/Ce ratio of the mantle is constant. It is suggested that the crust formation involves nonmagmatic and magmatic processes.

  9. Isotope geochemistry and the study of habitability and life on other planets (Invited)

    NASA Astrophysics Data System (ADS)

    Eiler, J.

    2010-12-01

    The question of life on other planets might be solved by a remarkable discovery — a martian coquina, or perhaps a tentacle print on a distant landscape. But, until this happens, evidence for life and, more generally, habitability will use indirect geochemical arguments such as isotope thermometers and biomarkers (molecular, isotopic, and elemental fingerprints of biology)., Understanding this evidence will also demand a quantitative planetary history based on isotopic dating. Laboratory study of samples derived from Mars or other solar-system bodies will be a focus of geochemical investigations aimed at such assessments. Examples of how this will be done can be found in studies of the Precambrian geologic record and Martian meteorites. Debates regarding environmental conditions and biogenicity of minerals and organic matter are common in the study of such materials. These controversies derive from simple but refractory problems with the geochemical principles we employ: Indicators of metabolism can be mimicked by abiologic reactions; paleo-environmental proxies generally require an understanding of related geochemical cycles (e.g., the isotopic budget of water); and, though many organic molecules are unambiguous biomarkers, diagenesis can transform them into compounds that resemble products of abiogenic organic synthesis. If planetary sample return is to produce definitive geochemical constraints on habitability and biology, we will require either luck or a new class of geochemical tools that explicitly address these problems. The spatial distribution of rare isotopes within molecular structures, including ‘clumping’ and position-specific isotope effects, offer new geochemical tools that could provide such solutions. For example, even a simple molecule like acetic acid (C2H4O2) has more than 200 distinct isotopic configurations when spatial distribution of isotopes is considered, and the proportions of these could reflect formation temperature, the nature of

  10. Pb isotopes in sediments of Lake Constance, Central Europe constrain the heavy metal pathways and the pollution history of the catchment, the lake and the regional atmosphere

    SciTech Connect

    Kober, B.; Wessels, M.; Bollhoefer, A.; Mangini

    1999-05-01

    Pb isotope ratios and Pb concentrations of well-dated sediments of Lake Constance, Central Europe have been analyzed using thermal ion mass spectrometry. Sequential extraction studies indicated isotope homogeneity of the leachable Pb components within the investigated layers. Since the middle of the 19th century a significant anthropogenic Pb component appeared in the lake sediments, and rapidly approaches concentration levels similar to that of the geogenic Pb background (20 ppm) at the beginning of the 20th century. Anthropogenic Pb was predominantly transferred to the lake sediments via the atmosphere. Pb sources were coal combustion, industrial ore processing and leaded gasoline. The flux of a fluvial Pb component to the lake sediments, additive to atmospheric Pb deposition, peaked in about 1960. This flux is attributed to (re)mobilization of Pb from polluted parts of the lake catchment, and indicates the change of catchment soils from a pollution sink to a heavy metal source. The strong reduction of anthropogenic Pb in the uppermost lake sediments since the 1960s has been caused by advances of environmental protection. The lake sediments record the changing fluxes and the isotope composition of the deposited aeolian Pb pollution. During the 20th century aeolian Pb fluxes to the lake sediments were in the range of 1--4 {micro}g/cm{sup 2}/a. During peak emission periods of gasoline Pb to the atmosphere (1960--1990) the aerosol Pb isotope composition was rather constant ({sup 206}Pb/{sup 207}Pb: 1.12--1.13) and probably a mixture of Canadian and Australian with Russian and Central European Pb types. Aeolian Pb isotope and Pb flux trends in the lake sediments as a whole agree well with the trends found in Alpine glaciers (Doering et al., 1997a,b) and in ombrotrophic peat bogs of Switzerland (Shotyk et al., 1996). However, different industrial Pb components were deposited in the archives of aeolian pollution during the early 20th century.

  11. Ca isotope stratigraphy across the Cenomanian-Turonian OAE 2: Links between volcanism, seawater geochemistry, and the carbonate fractionation factor

    NASA Astrophysics Data System (ADS)

    Du Vivier, Alice D. C.; Jacobson, Andrew D.; Lehn, Gregory O.; Selby, David; Hurtgen, Matthew T.; Sageman, Bradley B.

    2015-04-01

    2CO3- during CO2 uptake. Recent studies utilizing a variety of isotope proxies, e.g., Nd, Os, and Pb, implicate eruption of the Caribbean Large Igneous Province as a likely source of increased CO2. Moreover, integration of C, Ca, and Os isotope data reveals new information about the timing of events during the onset of OAE 2.

  12. Sulfur isotope geochemistry of ore and gangue minerals from the Silesian-Cracow Mississippi Valley-type ore district, Poland

    USGS Publications Warehouse

    Leach, D.L.; Vets, J.G.; Gent, C.A.

    1996-01-01

    Studies of the sulfur isotopic composition of ore and gangue minerals from the Silesian-Cracow Zn-Pb district were conducted to gain insights into processes that controlled the location and distribution of the ore deposits. Results of this study show that minerals from the Silesian-Cracow ore district have the largest range of sulfur isotope compositions in sulfides observed from any Mississippi Valley-type ore district in the world. The ??34S values for sulfide minerals range from +38 to -32 per mil for the entire paragenetic sequence but individual stages exhibit smaller ranges. There is a well developed correlation between the sulfur isotope composition and paragenetic stage of ore deposition. The first important ore stage contains mostly positive ??34S values, around 5 per mil. The second stage of ore formation are lower, with a median value of around -5 to -15 per mil, and with some values as low as -32 per mil. Late stage barite contains isotopically heavy sulfur around +32 per mil. The range in sulfur isotope compositions can be explained by contributions of sulfur from a variety of source rocks together with sulfur isotope fractionations produced by the reaction paths for sulfate reduction. Much of the variation in sulfur isotope compositions can be explained by bacterial reduction of sedimentary sulfate and disequilibrium reactions by intermediate-valency sulfur species, especially in the late-stage pyrite and sphalerite. Organic reduction of sulfate and thermal release of sulfur from coals in the Upper Silesian Coal Basin may have been important contributors to sulfur in the ore minerals. The sulfur isotopic data, ore mineral textures, and fluid inclusion data, are consistent with the hypothesis that fluid mixing was the dominant ore forming mechanism. The rather distinct lowering of ?? 34S values in sulfides from stage 2 to stage 3 is believed to reflect some fundamental change in the source of reduced sulfur and/or hydrology of the ore

  13. STABLE ISOTOPE GEOCHEMISTRY OF THERMAL FLUIDS FROM LASSEN VOLCANIC NATIONAL PARK, CALIFORNIA.

    USGS Publications Warehouse

    Janik, Cathy J.; Nehring, Nancy L.; Truesdell, Alfred H.

    1983-01-01

    In the Lassen vapor-dominated geothermal system, surface manifestations of thermal fluids at high elevations (1800-2500 m) include superheated and drowned fumaroles, steam-heated acid-sulfate hot springs, and low-chloride bicarbonate springs. Neutral high-chloride hot water discharges at lower elevations. Deuterium and oxygen-18 data establish genetic connections between these fluids and with local meteoric waters. Steam from the highest temperature fumarole at Bumpass Hell and water from the highest chloride hot spring have isotopic compositions corresponding to vapor-liquid equilibrium at 235 degree C. Carbon and sulfur isotope data suggest that the CO//2 and H//2S in the system did not entirely originate from magmatic sources, but probably include contributions from thermal metamorphism of marine sedimentary rocks. Observations suggest that carbon and sulfur isotope variations are useful indicators of gas reactions and flow paths in geothermal systems. Refs.

  14. The stable isotope geochemistry of volcanic lakes, with examples from Indonesia

    NASA Astrophysics Data System (ADS)

    Varekamp, J. C.; Kreulen, R.

    2000-04-01

    Stable isotope compositions ( δD, δ18O and δ34S) of volcanic lake waters, gas condensates and spring waters from Indonesia, Italy, Japan, and Russia were measured. The spring fluids and gas samples plot in a broad array between meteoric waters and local high-temperature volcanic gas compositions. The δD and δ18O data from volcanic lakes in East Indonesia plot in a concave band ranging from local meteoric waters to evaporated fluids to waters heavier than local high-temperature volcanic gases. We investigated isotopic fractionation processes in volcanic lakes at elevated temperatures with simultaneous mixing of meteoric waters and volcanic gases. An elevated lake water temperature gives enhanced kinetic isotope fractionation and changes in equilibrium fractionation factors, providing relatively flat isotope evolution curves in δ18O- δD diagrams. A numerical simulation model is used to derive the timescales of isotopic evolution of crater lakes as a function of atmospheric parameters, lake water temperature and fluxes of meteoric water, volcanic gas input, evaporation, and seepage losses. The same model is used to derive the flux magnitude of the Keli Mutu lakes in Indonesia. The calculated volcanic gas fluxes are of the same order as those derived from energy budget models or direct gas flux measurements in open craters (several 100 m 3 volcanic water/day) and indicate a water residence time of 1-2 decades. The δ34S data from the Keli Mutu lakes show a much wider range than those from gases and springs, which is probably related to the precipitation of sulfur in these acid brine lakes. The isotopic mass balance and S/Cl values suggest that about half of the sulfur input in the hottest Keli Mutu lake is converted into native sulfur.

  15. Applications of UThPb isotope systematics to the problems of radioactive waste disposal

    USGS Publications Warehouse

    Stuckless, J.S.

    1986-01-01

    Concentrations of U, Th and Pb, and the isotopic composition of Pb for whole-rock samples of granitoids show: (1) that open-system behavior is nearly universal in the surface and near-surface environment; and (2) that elemental mobility is possible to depths of several hundred meters. Several identified or at least postulated factors that control U and/or Pb mobility include: (1) the mineralogical sites for U and its daughter products; (2) access of groundwater to these sites; (3) the volume of circulating water; and (4) the chemistry of the groundwater. Studies of granitic samples from peralkaline complexes in the Arabian Shield have shown that most samples lost less than 20% of their U during recent exposure to the near-surface environment. Most of the U in these samples appears to be firmly bound in zircons. In contrast, most surface and shallow drill-core samples of the granite of Lankin Dome (Granite Mountains, Wyoming) have lost ??? 70% of their U. Most of the U in these samples is weakly bound in biotite and epidote-family minerals. The granite recovered during the Illinois Deep Drill Hole Project (Stephenson County, Illinois) is mineralogically similar to the granite of Lankin Dome, but this granite lost radiogenic Pb rather than U, probably as a result of exposure to groundwater that had a markedly different chemistry from that in the Granite Mountains. Studies of the Sherman Granite (Wyoming) and the Go??temar Granite (southeastern Sweden) have shown that U and/or Pb mobility is greatest in and near fractured rock. The greater mobility is interpreted to be the result of both a larger water/rock ratio in the fractured rock and exposure to water over an increased surface area (and consequently a greater number of uranium sites). Several types of geochemical and mineralogic data can be used to identify rock-water interaction in granites; however, if rock samples have favorable radiogenic to common Pb ratios, both the amount and approximate timing of U or Pb

  16. Sr, Nd, Pb and Os Isotopic Compositions of Lavas From the Mount Baker Volcanic Field, Cascade Arc

    NASA Astrophysics Data System (ADS)

    Mullen, E. K.; McCallum, I.; Brandon, A. D.

    2008-12-01

    We present the results of a trace element and Sr, Nd, Pb and Os isotopic study of the Mt. Baker volcanic field (MBVF), part of the northern segment of the Cascade magmatic arc known as the Garibaldi Belt. To date, only 4 Sr isotopic ratios (all from the Sulphur Creek flow) have been published. The Mount Baker volcanic field extends to 3.72 Ma and a case can be made for continuous magmatic activity in this region extending from 34 Ma to present. Our goal is to use isotope ratios to characterize the mantle source regions that underlie the Garibaldi Belt, to document the chemical inputs of slab fluid/melt, sediment, and lower crust, and to assess temporal and spatial variations in these factors. We measured 29 Sr and Nd isotopic ratios, 8 Pb isotopic ratios, and 9 Os isotopic ratios, representing the full age range and compositional diversity (calc- alkaline basalt through rhyolite) of the MBVF, including all known MBVF basalts. A 22.86-Ma gabbronorite from the adjacent Chilliwack batholith was analyzed as an analog for the modern mafic lower crust. All Mt. Baker lavas are calc-alkaline with the arc-characteristic signatures of HFSE depletion and LILE enrichment. MBVF 87Sr/86Sr values (0.703932 to 0.703057) and ɛNd (+4.71 to +7.79) are well correlated and lie within the mantle array. Mt. Baker Sr and Nd data are indistinguishable from other Garibaldi belt lavas (Green & Harry 1999, Green & Sinha 2005), and also overlap data from the neighboring Chilliwack batholith (Tepper 1996; Tepper et al. 1993). In contrast, central and southern Cascade arc lavas with similar Sr ratios have corresponding ɛNd values that are lower by ~2 epsilon units. The Garibaldi Belt and Chilliwack magmas are tapping a mantle source distinct from that of the rest of the Cascade arc. 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of MBVF basalts plot close to the NHRL, in a linear trend between Juan de Fuca MORB and Pacific sediment, indicating a sediment contribution to the MBVF magmas. With

  17. Isotopic Ag–Cu–Pb record of silver circulation through 16th–18th century Spain

    PubMed Central

    Desaulty, Anne-Marie; Telouk, Philippe; Albalat, Emmanuelle; Albarède, Francis

    2011-01-01

    Estimating global fluxes of precious metals is key to understanding early monetary systems. This work adds silver (Ag) to the metals (Pb and Cu) used so far to trace the provenance of coinage through variations in isotopic abundances. Silver, copper, and lead isotopes were measured in 91 coins from the East Mediterranean Antiquity and Roman world, medieval western Europe, 16th–18th century Spain, Mexico, and the Andes and show a great potential for provenance studies. Pre-1492 European silver can be distinguished from Mexican and Andean metal. European silver dominated Spanish coinage until Philip III, but had, 80 y later after the reign of Philip V, been flushed from the monetary mass and replaced by Mexican silver. PMID:21606351

  18. Strong Relationship between Hf-Nd-Pb Isotopes in Atlantic Sediments and the Lesser Antilles arc Composition

    NASA Astrophysics Data System (ADS)

    Carpentier, M.; Chauvel, C.; Mattielli, N.

    2006-12-01

    Geochemical variability of lavas from the Lesser Antilles arc is well established and is characterized by a chemical zoning from north to south along the arc. Lavas from the northern part of the arc have usually less radiogenic and less variable Sr and Pb isotopic compositions than those from the south. Possible explanations include a larger contribution from sediments in the source of the southern islands, and/or a north-south change in the chemical composition of the sediments that are subducted beneath the Lesser Antilles arc We conducted a geochemical study (Nd, Hf and Pb isotopic compositions) of Atlantic sediments coming from two different sites drilled during DSDP Leg 78 (site 543, 15.7N) and DSDP Leg 14 (site 144, 9.5N). At site 543, the sedimentary pile has epsilon Nd values between -14.6 and -11 and epsilon Hf between -10.6 and -1. 206Pb/204Pb ratios vary between 19.1 and 19.5. The sediment pile has an overall strong continental signature suggesting that their source is primarily detrital. This is in agreement with the interpretation of White et al. (1985) who suggested that the dominant source was the Archean Guiana Highland drained by the Orinoco River. Further south, at site 144, the succession consists of chalk ooze, marl and clays, and organic-rich black shales. Samples have epsilon Nd between -18.4 and -10 and epsilon Hf between -20.4 and -5.4 and the Pb isotopic compositions are extremely variable. Chalk ooze, marl and clay have 206Pb/204Pb ratios between 18.8 and 20.0, while the black shales have extremely radiogenic compositions with 206Pb/204Pb between 21.6 and 27.7. These compositions reflect the radioactive decay of authigenic uranium concentrated in organic- rich layers characterized by elevated 238U/204Pb ratios (100 up to 600). The isotopic compositions of sediments from both sites are largely influenced by continental input with Nd and Hf isotopes plotting in the continental domain of the "terrestrial array", but the southern site has more

  19. Identification of contamination in a lake sediment core using Hg and Pb isotopic compositions, Lake Ballinger, Washington, USA

    USGS Publications Warehouse

    Gray, John E.; Pribil, Michael J.; Van Metre, Peter C.; Borrok, David M.; Thapalia, Anita

    2013-01-01

    Concentrations and isotopic compositions of Hg and Pb were measured in a sediment core collected from Lake Ballinger, near Seattle, Washington, USA. Lake Ballinger has been affected by input of metal contaminants emitted from the Tacoma smelter, which operated from 1887 to 1986 and was located about 53 km south of the lake. Concentrations and loadings of Hg and Pb in Lake Ballinger increased by as much as three orders of magnitude during the period of smelting as compared to the pre-smelting period. Concentrations and loadings of Hg and Pb then decreased by about 55% and 75%, respectively, after smelting ended. Isotopic compositions of Hg changed considerably during the period of smelting (δ202Hg = −2.29‰ to −0.38‰, mean −1.23‰, n = 9) compared to the pre-smelting period (δ202Hg = −2.91‰ to −2.50‰, mean −2.75‰, n = 4). Variations were also observed in 206Pb/207Pb and 208Pb/207Pb isotopic compositions during these periods. Data for Δ199Hg and Δ201Hg indicate mass independent fractionation (MIF) of Hg isotopes in Lake Ballinger sediment during the smelting and post-smelting period and suggest MIF in the ore smelted, during the smelting process, or chemical modification at some point in the past. Negative values for Δ199Hg and Δ201Hg for the pre-smelting period are similar to those previously reported for soil, peat, and lichen, likely suggesting some component of atmospheric Hg. Variations in the concentrations and isotopic compositions of Hg and Pb were useful in tracing contaminant sources and the understanding of the depositional history of sedimentation in Lake Ballinger.

  20. Linking in-situ Hf isotopes in zircon with in-situ Pb isotopes in plagioclase: a microanalytical approach to characterize Archean anorthosite petrogenesis

    NASA Astrophysics Data System (ADS)

    Souders, K.; Sylvester, P.; Myers, J.

    2011-12-01

    Multiple isotope systems are often used to distinguish petrogenetic processes and determine the age and source of magmatic systems. Advances in laser ablation multi-collector ICPMS instrumentation have allowed Earth scientists to determine accurate and precise isotope ratios of minerals in-situ. Most studies have focused on measuring isotopes that are abundant within a mineral (e.g. Hf in zircon) but the integration of multiple ion counters into the collector configuration of MC-ICPMS instruments has provided the ability to measure isotope ratios of minor elements (e.g. Pb in plagioclase) in-situ. These abilities allow for an alternative approach to igneous petrogenesis. Instead of isotopic analysis of bulk samples, in-situ methods can be utilized to target specific domains preserved in individual minerals. Analysis of co-magmatic minerals in igneous rocks using multiple isotopic systems can be linked to solve a range of petrologic problems. As an example, we present in-situ analyses by LA-MC-ICPMS for Pb isotope compositions of preserved igneous plagioclase megacrysts and Hf isotope compositions of zircon grains from the 2936 Ma Fiskenæsset and 2914 Ma Nunataarsuk anorthosite complexes, southwestern Greenland, two of the best-preserved Archean anorthosites in the world. For both Fiskenæsset and Nunataarsuk, the initial Pb isotope compositions of plagioclase megacrysts and the initial ɛHf compositions of zircon grains extend beyond analytical uncertainty suggesting multiple sources contributed to the parent magma for both anorthosite complexes. Initial ɛHf of zircon grains from both anorthosite complexes fall between depleted mantle and a less radiogenic crustal source with a total range up to 5 ɛHf units. Plagioclase Pb isotope compositions from both anorthosite complexes share a depleted mantle end member yet diverge from this point: Fiskenæsset toward a high-μ, more radiogenic Pb crustal composition and Nunataarsuk toward a low-μ, less radiogenic Pb

  1. Evolution of the Mazatzal province and the timing of the Mazatzal orogeny: Insights from U-Pb geochronology and geochemistry of igneous and metasedimentary rocks in southern New Mexico

    USGS Publications Warehouse

    Amato, J.M.; Boullion, A.O.; Serna, A.M.; Sanders, A.E.; Farmer, G.L.; Gehrels, G.E.; Wooden, J.L.

    2008-01-01

    New U-Pb zircon ages, geochemistry, and Nd isotopic data are presented from three localities in the Paleoproterozoic Mazatzal province of southern New Mexico, United States. These data help in understanding the source regions and tectonic setting of magmatism from 1680 to 1620 Ma, the timing of the Mazatzal orogeny, the nature of postorogenic maginatism, Proterozoic plate tectonics, and provide a link between Mazatzal subblocks in Arizona and northern New Mexico. The data indicate a period from 1680 to 1650 Ma in which juvenile felsic granitoids were formed, and a later event between 1646 and 1633 Ma, when these rocks were deformed together with sedimentary rocks. No evidence of pre-1680 Ma rocks or inherited zircons was observed. The igneous rocks have ENd(t) from -1.2 to +4.3 with most between +2 and +4, suggesting a mantle source or derivation from similar-aged crust. Nd isotope and trace element concentrations are consistent with models for typical are magmatism. Detrital zircon ages from metasedimentary rocks indicate that sedimentation occurred until at least 1646 Ma. Both local and Yavapai province sources contributed to the detritus. All of the samples older than ca. 1650 Ma are deformed, whereas undeformed porphyroblasts were found in the contact aureole of a previously dated 1633 Ma gabbro. Regionally, the Mlazatzal orogeny occurred mainly between 1654 and 1643 Ma, during final accretion of a series of island arcs and intervening basins that may have amalgamated offshore. Rhyolite magmatism in the southern Mazatzal province was coeval with gabbro intrusions at 1633 Ma and this bimodal magmatism may have been related to extensional processes following arc accretion. ?? 2007 Geological Society of America.

  2. Chlorine isotope geochemistry of Icelandic thermal fluids: Implications for geothermal system behavior at divergent plate boundaries

    NASA Astrophysics Data System (ADS)

    Stefánsson, Andri; Barnes, Jaime D.

    2016-09-01

    The chlorine isotope composition of thermal fluids from Iceland were measured in order to evaluate the source of chlorine and possible chlorine isotope fractionation in geothermal systems at divergent plate boundaries. The geothermal systems studied have a wide range of reservoir temperatures from 40 to 437 °C and in-situ pH of 6.15 to 7.15. Chlorine concentrations range from 5.2 to 171 ppm and δ37 Cl values are -0.3 to + 2.1 ‰ (n = 38). The δ37 Cl values of the thermal fluids are interpreted to reflect the source of the chlorine in the fluids. Geothermal processes such as secondary mineral formation, aqueous and vapor speciation and boiling were found to have minimal effects on the δ37 Cl values. However, further work is needed on incorporation of Cl into secondary minerals and its effect on Cl isotope fractionation. Results of isotope geochemical modeling demonstrate that the range of δ37 Cl values documented in the natural thermal fluids can be explained by leaching of the basaltic rocks by meteoric source water under geothermal conditions. Magmatic gas partitioning may also contribute to the source of Cl in some cases. The range of δ37 Cl values of the fluids result mainly from the large range of δ37 Cl values observed for Icelandic basalts, which range from -0.6 to + 1.2 ‰.

  3. Application of Hydrogen Isotope Geochemistry to Volcanology: Recent Perspective on Eruption Dynamics

    SciTech Connect

    Nakamura, M.; Kasai, Y.; Sato, N.; Yoshimura, S.

    2008-02-25

    Degassing of magma is central to understand the dynamics of volcanic eruption. Hydrogen isotopic composition of volcanic rocks reflects degassing processes. The natural obsidian samples in some eruptions typically show a gently and then rapidly decreasing {delta}D trends with decreasing water content; this led to the two-stage degassing model, with closed-system volatile exsolution (batch fractionation of hydrogen isotope) during the explosive phase followed by open-system degassing (Rayleigh fractionation) to produce the low {delta}D value of the dome and flow lavas. However, the relationship between pattern of degassing (and fractionation) and mode of eruption is controversial. Based on the CO{sub 2}/H{sub 2}O ratio of the obsidians, Rust et al. suggested that the analyzed samples with relatively constant {delta}D value and high water content were buffered (re-equilibrated) with vapor of relatively constant isotopic composition, assuming that silicic magma along conduit wall is fragmented and highly permeable. However, the timing and mechanism of the shift to open system degassing (Rayleigh fractionation) has not been clarified. To further constrain the eruption dynamics, experimental study on the hydrogen isotope fractionation during degassing would be helpful, although common noble metals used as sample capsules, including Au, are permeable to hydrogen at magmatic temperature, and even to water molecule in the prolonged run, probably due to the change of grain boundary properties such as thermal grooving.

  4. Chronology and isotopic geochemistry of apollo 14 basalts and Skaergard Gabbro, Eastern Greenland

    NASA Technical Reports Server (NTRS)

    Dasch, E. J.

    1986-01-01

    Work completed on Apollo 14 basalts has been published. The two dates obtained from these rocks comprised the oldest and two of the three oldest ages (4.1 and 4.3 billion years) known for lunar maria basalts; thus their ages are important in understanding the moon's earliest history. Owing to the antiquity of these rocks, two more fragments have been dated as part of a second ASEE/NASA SFF program. The new ages are 3.95 and 4.12 billion years, thus further establishing and amplifying the earlier results. This work, although perhaps more interesting for its chronologic information, was begun as a test of chemical and petrographic models. Fragments of Apollo basalt were placed into five categories, based on petrologic and chemical, especially rare-earth element, composition. Isotopic studies were begun in an attempt to determine if the five groups of basalts were related by age or initial isotopic composition (isotopic composition of lava at time of extrusion). Although a few of the representatives of the five groups have the same age and/or initial strontium-isotopic composition, within the analtytical uncertainties, most apparently are unrelated. Petrologic implications of these data will be published in an appropriate journal.

  5. Sulfur, carbon, hydrogen, and oxygen isotope geochemistry of the Idaho cobalt belt

    USGS Publications Warehouse

    Johnson, Craig A.; Bookstrom, Arthur A.; Slack, John F.

    2012-01-01

    Cobalt-copper ± gold deposits of the Idaho cobalt belt, including the deposits of the Blackbird district, have been analyzed for their sulfur, carbon, hydrogen, and oxygen isotope compositions to improve the understanding of ore formation. Previous genetic hypotheses have ranged widely, linking the ores to the sedimentary or diagenetic history of the host Mesoproterozoic sedimentary rocks, to Mesoproterozoic or Cretaceous magmatism, or to metamorphic shearing. The δ34S values are nearly uniform throughout the Blackbird dis- trict, with a mean value for cobaltite (CoAsS, the main cobalt mineral) of 8.0 ± 0.4‰ (n = 19). The data suggest that (1) sulfur was derived at least partly from sedimentary sources, (2) redox reactions involving sulfur were probably unimportant for ore deposition, and (3) the sulfur was probably transported to sites of ore for- mation as H2S. Hydrogen and oxygen isotope compositions of the ore-forming fluid, which are calculated from analyses of biotite-rich wall rocks and tourmaline, do not uniquely identify the source of the fluid; plausible sources include formation waters, metamorphic waters, and mixtures of magmatic and isotopically heavy meteoric waters. The calculated compositions are a poor match for the modified seawaters that form vol- canogenic massive sulfide (VMS) deposits. Carbon and oxygen isotope compositions of siderite, a mineral that is widespread, although sparse, at Blackbird, suggest formation from mixtures of sedimentary organic carbon and magmatic-metamorphic carbon. The isotopic compositions of calcite in alkaline dike rocks of uncertain age are consistent with a magmatic origin. Several lines of evidence suggest that siderite postdated the emplacement of cobalt and copper, so its significance for the ore-forming event is uncertain. From the stable isotope perspective, the mineral deposits of the Idaho cobalt belt contrast with typical VMS and sedimentary exhalative deposits. They show characteristics of deposit

  6. Isotope geochemistry of waters affected by acid mine drainage in old labour sites (SE, Spain).

    NASA Astrophysics Data System (ADS)

    Pérez-Sirvent, Carmen; Martinez-Sanchez, Maria Jose; Garcia-Lorenzo, Maria Luz; Agudo, Ines; Hernandez-Cordoba, Manuel; Recio, Clemente

    2015-04-01

    The ore deposits of this zone have iron, lead and zinc as the main metal components. Iron is present in oxides, hydroxides, sulfides, sulfates, carbonates, and silicates; lead and zinc occur in sulfides (galena and sphalerite, respectively), carbonates, sulfates, and lead or zinc-bearing (manganese, iron) oxides. Mining started with the Romans and activity peaked in the second half of the 19th century and throughout the 20th century until the 1980's. From 1940 to 1957, mineral concentration was made by froth flotation and, prior to this, by gravimetric techniques. The mining wastes, or tailings, with a very fine particle size were deposited inland (tailings dams) and, since 1957, huge releases were made in directly the sea coast. The objective of this work was to evaluate processes affecting waters from abandoned mine sites by way of stable isotopic analysis, particularly H and O stable isotopes from water and S and O from dissolved sulfates. Several common chemical and physical processes, such as evaporation, water-rock interaction and mixing could alter water isotopic composition. Evaporation, which causes an enrichment in δD and δ18O in the residual water, is an important process in semiarid areas. The results obtained indicate that, for sites near the coast, waters are meteoric, and marine infiltration only takes place in the deepest layers near the shore or if water remains stagnated in sediments with low permeability. The main source of sulfate was the oxidation of sulfides, resulting in the liberation of acid, sulfate and metals. In order to assess the mechanism responsible for sulfide oxidation, the stoichiometric isotope balance model and the general isotope balance model were tested, suggesting that the oxidation via Fe3+ was predominant in the surface, and controlled by A. ferrooxidans, while at depth, sulfate reduction occurred.

  7. Strontium isotope geochemistry of groundwater in the central part of the Dakota (Great Plains) aquifer, USA

    USGS Publications Warehouse

    Gosselin, D.C.; Harvey, F.E.; Frost, C.; Stotler, R.; Macfarlane, P.A.

    2004-01-01

    The Dakota aquifer of the central and eastern Great Plains of the United States is an important source of water for municipal supplies, irrigation and industrial use. Although the regional flow system can be characterized generally as east to northeasterly from the Rocky Mountains towards the Missouri River, locally the flow systems are hydrologically complex. This study uses Sr isotopic data from groundwater and leached aquifer samples to document the complex subsystems within the Dakota aquifer in Nebraska and Kansas. The interaction of groundwater with the geologic material through which it flows has created spatial patterns in the isotopic measurements that are related to: long-term water-rock interaction, during which varying degrees of isotopic equilibrium between water and rock has been achieved; and the alteration of NaCl fluids by water-rock interaction. Specifically, Sr isotopic data distinguish brines from Kansas and western Nebraska from those in eastern Nebraska: the former are interpreted to reflect interaction with Permian rocks, whereas the latter record interaction with Pennsylvanian rocks. The Sr isotopic composition of groundwater from other parts of Nebraska and Kansas are a function of the dynamic interaction between groundwater and unlithified sediments (e.g., glacial till and loess), followed by interaction with oxidized and unoxidized sediments within the Dakota Formation. This study illustrates the power of combining Sr chemistry with more conventional geochemical data to obtain a more complete understanding of groundwater flow systems within regional aquifer systems where extensive monitoring networks do not exist. ?? 2003 Elsevier Ltd. All rights reserved.

  8. Oxygen-isotope geochemistry of quaternary rhyolite from the Mineral Mountains, Utah, USA

    SciTech Connect

    Bowman, J.R.; Evans, S.H. Jr.; Nash, W.P.

    1982-03-01

    Oxygen isotope analyses were made of phenocryst and glass separates from four Quaternary rhyolite flows and domes in the Mineral Mountains, southwest Utah. With the exception of biotite in all samples and alkali feldspar in the rhyolite domes, all minerals appear to be in close oxygen isotope exchange equilibrium. The geothermometry equations proposed by Bottinga and Javoy (1973) and Javoy (1977) for quartz, alkali feldspar and magnetite produce the best agreement with temperature results fom two-feldspar and iron-titanium oxide geothermometry for these rhyolites. If the rhyolites were generated by partial melting in the crust, their whole-rock (glass) delta/sup 18/O values (6.3 to 6.9 permil) are consistent with generation from I-type (Chappell and White, 1974, O'Neil and Chappell, 1977; O'Neil et. al., 1977) sources.

  9. Comprehensive Pb-Sr-Nd-Hf isotopic, trace element, and mineralogical characterization of mafic to ultramafic rock reference materials

    NASA Astrophysics Data System (ADS)

    Fourny, Anaïs.; Weis, Dominique; Scoates, James S.

    2016-03-01

    Controlling the accuracy and precision of geochemical analyses requires the use of characterized reference materials with matrices similar to those of the unknown samples being analyzed. We report a comprehensive Pb-Sr-Nd-Hf isotopic and trace element concentration data set, combined with quantitative phase analysis by XRD Rietveld refinement, for a wide range of mafic to ultramafic rock reference materials analyzed at the Pacific Centre for Isotopic and Geochemical Research, University of British Columbia. The samples include a pyroxenite (NIM-P), five basalts (BHVO-2, BIR-1a, JB-3, BE-N, GSR-3), a diabase (W-2), a dolerite (DNC-1), a norite (NIM-N), and an anorthosite (AN-G); results from a leucogabbro (Stillwater) are also reported. Individual isotopic ratios determined by MC-ICP-MS and TIMS, and multielement analyses by HR-ICP-MS are reported with 4-12 complete analytical duplicates for each sample. The basaltic reference materials have coherent Sr and Nd isotopic ratios with external precision below 50 ppm (2SD) and below 100 ppm for Hf isotopes (except BIR-1a). For Pb isotopic reproducibility, several of the basalts (JB-3, BHVO-2) require acid leaching prior to dissolution. The plutonic reference materials also have coherent Sr and Nd isotopic ratios (<50 ppm), however, obtaining good reproducibility for Pb and Hf isotopic ratios is more challenging for NIM-P, NIM-N, and AN-G due to a variety of factors, including postcrystallization Pb mobility and the presence of accessory zircon. Collectively, these results form a comprehensive new database that can be used by the geochemical community for evaluating the radiogenic isotope and trace element compositions of volcanic and plutonic mafic-ultramafic rocks.

  10. Implications of formation water movement based on isotopic data and elemental geochemistry, southwestern Ontario

    SciTech Connect

    Frape, S.K.; Dollar, P.; Fritz, P.; Travail, R.A.; McNutt, R.H.; MacQueen, R.W.

    1986-08-01

    Formation waters in Paleozoic sediments analyzed for /sup 2/H, /sup 18/O, /sup 87/Sr//sup 86/Sr, tritium, and major/minor contents show the following. (1) The stable isotope contents are typical for formation brines, but have /sup 18/O and /sup 2/H values that group according to formation age, with waters in Cambrian strata being most depleted; and the most concentrated brines do not compare well to known Michigan basin brines. Many waters are Ca-Na-Cl brines similar to typical Canadian shield brines, although the origin of the various chemical species may be masked by intense rock-water interaction. (2) The /sup 87/Sr//sup 86/Sr values for Cambrian brines range from 0.7095 to 0.7102. In one detailed study, the brine and calcite cement had the same value (0.7095), which is slightly higher than Cambrian seawater (0.7091-0.7092), and indicates that the cement precipitated from the brine during diagenesis. The reservoir rock has a /sup 87/Sr//sup 86/Sr value of 0.7330, indicating little or no water/rock exchange. Sr isotopic values for Ordovician brines range from 0.7095 to 0.7103, which is higher than Ordovician seawater (0.7085). In contrast, the Silurian Salina Formation brines and Silurian seawater values are the same (0.7085-0.7087). Despite an active tectonic history, causing considerable faulting and movement within Paleozoic and Precambrian rock strata, the isotopic results for the Cambrian indicate isotopic equilibrium between brine and cement; therefore, these formation waters have not moved since the calcite formed.

  11. Uranium-thorium isotope geochemistry of saline ground waters from central Missouri

    SciTech Connect

    Banner, J.L.; Chen, J.H.; Wasserburg, G.J.

    1989-03-01

    The isotopic and elemental distributions of uranium and thorium were examined in a suite of saline ground waters from central Missouri using mass spectrometric techniques. The waters were sampled from natural springs and artesian wells in Mississippian and Ordovician aquifers and have a wide range in salinity (5 to 26 /per thousand/), deltaD (/minus/108 to /minus/45 /per thousand/), and delta/sup 18/O (/minus/14.7 to /minus/6.5 /per thousand/) values. The suite of samples has a large range in /sup 238/U (50 to 200 x 10/sup /minus/12/g/g) and /sup 232/Th (0.3 to 9.1 x 10/sup /minus/12/g/g) concentrations and extremely high /sup 234/U//sup 238/U activity ratios ranging from 2.15 to 16.0. These isotopic compositions represent pronounced uranium-series disequilibrium compared with the value of modern seawater (1.15) or the equilibrium value (1.00). For such /sup 234/U-enriched waters, /sup 234/U//sup 238/U isotope ratios can be determined with a precision of /+-/ 10 /per thousand/ (2sigma) on 10 mL of sample and less than /+-/5 /per thousand/ on 100 mL. In contrast to the large /sup 234/U enrichments, /sup 230/Th//sup 238/U activity ratios in the ground waters are significantly lower than the equilibrium value. The more saline samples have markedly higher /sup 234/U//sup 238/U activity ratios and lower deltaD and delta/sup 18/O values. Unfiltered and filtered (< 0.1 ..mu..m) aliquots of a saline sample have the same isotopic composition and concentration of uranium, indicating uranium essentially occurs entirely as a dissolved species. The filtered/unfiltered concentration ratio for thorium in this sample is 0.29, demonstrating the predominant association of thorium with particulates.

  12. Ca Isotope Evidence for Changes in the Carbonate Geochemistry of Seawater Across OAE 2

    NASA Astrophysics Data System (ADS)

    Lehn, G. O.; Jacobson, A. D.; Du Vivier, A.; Selby, D. S.; Hurtgen, M.; Sageman, B. B.

    2014-12-01

    We used a new high-precision MC-TIMS method to generate Ca isotope records (δ44/40Ca; 2SD = ± 0.04‰) for three sections spanning OAE 2: central Colorado, USA (Portland #1 core), southeastern France (Pont d'Issole), and Eastbourne, England (Eastbourne Chalk). The Eastbourne Chalk δ44/40Ca values are higher than previously reported but define a similar trend, where δ44/40Ca values increase prior to OAE 2 and then decrease at the onset. The Portland core and the Pont d'Issole section display comparable δ44/40Ca values, which increase by ~0.10 - 0.15‰ immediately at the onset of OAE 2 and then decrease to near-initial values across the event. According to a numerical model of the marine Ca cycle, reasonable changes to the riverine and hydrothermal input fluxes cannot explain the rate and magnitude of the positive isotope excursion. A decrease in the magnitude of the carbonate fractionation factor provides the best explanation for the data. Because a decrease in the fractionation factor corresponds to an increase in the Ca/CO3 ratio of seawater, we tentatively attribute the positive Ca isotope excursion to transient ocean acidification, i.e., a reduction in the concentration of CO3 during CO2 uptake. Other studies implicate eruption of the Caribbean Large Igneous Province as the most likely source of CO2.

  13. Isotope Geochemistry of Possible Terrestrial Analogue for Martian Meteorite ALH84001

    NASA Technical Reports Server (NTRS)

    Mojzsis, Stephen J.

    2000-01-01

    We have studied the microdomain oxygen and carbon isotopic compositions by SIMS of complex carbonate rosettes from spinel therzolite xenoliths, hosted by nepheline basanite, from the island of Spitsbergen (Norway). The Quaternary volcanic rocks containing the xenoliths erupted into a high Arctic environment and through relatively thick continental crust containing carbonate rocks. We have attempted to constrain the sources of the carbonates in these rocks by combined O-18/O-16 and C-13/C-12 ratio measurements in 25 micron diameter spots of the carbonate and compare them to previous work based primarily on trace-element distributions. The origin of these carbonates can be interpreted in terms of either contamination by carbonate country rock during ascent of the xenoliths in the host basalt, or more probably by hydrothermal processes after emplacement. The isotopic composition of these carbonates from a combined delta.18O(sub SMOW) and delta.13C(sub PDB) standpoint precludes a primary origin of these minerals from the mantle. Here a description is given of the analysis procedure, standardization of the carbonates, major element compositions of the carbonates measured by electron microprobe, and their correlated C and O isotope compositions as measured by ion microprobe. Since these carbonate rosettes may represent a terrestrial analogue to the carbonate "globules" found in the martian meteorite ALH84001 interpretations for the origin of the features found in the Spitsbergen may be of interest in constraining the origin of these carbonate minerals on Mars.

  14. Stable isotope geochemistry of acid mine drainage: Experimental oxidation of pyrite

    USGS Publications Warehouse

    Taylor, B.E.; Wheeler, M.C.; Nordstrom, D.K.

    1984-01-01

    Sulfate and water from experiments in which pyrite was oxidized at a pH of 2.0 were analyzed for sulfur and oxygen stable isotopes. Experiments were conducted under both aerobic and anaerobic sterile conditions, as well as under aerobic conditions in the presence of Thiobacillus ferrooxidans, to elucidate the pathways of oxidation. Oxygen isotope fractionation between SO2-4 and H2O varied from +4.0 %. (anaerobic, sterile) to + 18.0 %. (aerobic, with T. ferrooxidans.). The oxygen isotope composition of dissolved oxygen utilized in both chemical and microbially-mediated oxidation was also determined (+11.4 %., by T. ferrooxidans; +18.4 %., chemical). Contributions of water-derived oxygen and dissolved oxygen to the sulfate produced in the oxidation of pyrite could thus be estimated. Water-derived oxygen constituted from 23 to ~ 100 percent of the oxygen in the sulfate produced in the experiments, and this closely approximates the range of contribution in natural acid mine drainage. Oxidation of sulfides in anaerobic, water-saturated environments occurs primarily by chemical oxidation pathways, whereas oxidation of sulfides in well-aerated, unsaturated zone environments occurs dominantly by microbially mediated pathways. ?? 1984.

  15. Isotopic evolution of atmospheric Pb from metallurgical processing in Flin Flon, Manitoba: Retrospective analysis using peat cores from bogs.

    PubMed

    Shotyk, W; Rausch, N; Outridge, P M; Krachler, M

    2016-11-01

    Atmospheric Pb deposition was reconstructed using peat cores from bogs in the vicinity of Flin Flon, Manitoba, Canada, home to a zinc refinery and copper smelter. The Sask Lake (SL4-1) core was collected 85 km NW of Flin Flon and Kotyk Lake (KOL) 30 km NE. The distribution of Sr and U show that both profiles are predominantly minerotrophic (ie groundwater-fed), but the Pb concentration profile shows that Pb was received exclusively from the atmosphere. Graphs of (208)Pb/(206)Pb against (206)Pb/(207)Pb document atmospheric Pb contamination dating from the early to mid-1800's, well before the start of metallurgical processing (in 1930) and attributable to long-range atmospheric transport from other regions of North America. Industrial activities at Flin Flon clearly affected the concentrations, enrichment factor (calculated using Sc), and accumulation rates of Pb, but it is the similarity in isotopic composition, and contrast with crustal values ((206)Pb/(207)Pb ca. 1.20 to 1.22) which makes the connection to the Flin Flon ores. The KOL samples dating from 1925-1976 CE have a (206)Pb/(207)Pb of 1.032 ± 0.002 (n = 11) which approach the values for the Flin Flon ores ((206)Pb/(207)Pb = 1.008). But even at SL4-1, the peat samples dating from 1925-1976 CE have a (206)Pb/(207)Pb of 1.061 ± 0.022 (n = 18) which is well below the corresponding ratio of Canadian leaded gasoline ((206)Pb/(207)Pb = ca. 1.15). The SL4-1 site too, therefore, was clearly impacted by Pb from mining and metallurgy, despite the distance (88 km) from Flin Flon and being predominantly upwind. These two bogs not only provide the chronology of atmospheric Pb deposition for the past decades, but suggest that the extent of contamination may have been underestimated by previous studies.

  16. An ultra-clean technique for accurately analysing Pb isotopes and heavy metals at high spatial resolution in ice cores with sub-pg g(-1) Pb concentrations.

    PubMed

    Burn, Laurie J; Rosman, Kevin J R; Candelone, Jean-Pierre; Vallelonga, Paul; Burton, Graeme R; Smith, Andrew M; Morgan, Vin I; Barbante, Carlo; Hong, Sungmin; Boutron, Claude F

    2009-02-23

    Measurements of Pb isotope ratios in ice containing sub-pg g(-1) concentrations are easily compromised by contamination, particularly where limited sample is available. Improved techniques are essential if Antarctic ice cores are to be analysed with sufficient spatial resolution to reveal seasonal variations due to climate. This was achieved here by using stainless steel chisels and saws and strict protocols in an ultra-clean cold room to decontaminate and section ice cores. Artificial ice cores, prepared from high purity water were used to develop and refine the procedures and quantify blanks. Ba and In, two other important elements present at pg g(-1) and fg g(-1) concentrations in Polar ice, were also measured. The final blank amounted to 0.2+/-0.2 pg of Pb with (206)Pb/(207)Pb and (208)Pb/(207)Pb ratios of 1.16+/-0.12 and 2.35+/-0.16, respectively, 1.5+/-0.4 pg of Ba and 0.6+/-2.0 fg of In, most of which probably originates from abrasion of the steel saws by the ice. The procedure was demonstrated on a Holocene Antarctic ice core section and was shown to contribute blanks of only approximately 5%, approximately 14% and approximately 0.8% to monthly resolved samples with respective Pb, Ba and In concentrations of 0.12 pg g(-1), 0.3 pg g(-1) and 2.3 fg g(-1). Uncertainties in the Pb isotopic ratio measurements were degraded by only approximately 0.2%.

  17. Volcanism in the Sumisu Rift, I. Major element, volatile, and stable isotope geochemistry

    USGS Publications Warehouse

    Hochstaedter, A.G.; Gill, J.B.; Kusakabe, M.; Newman, S.; Pringle, M.; Taylor, B.; Fryer, P.

    1990-01-01

    A bimodal volcanic suite with KAr ages of 0.05-1.40 Ma was collected from the Sumisu Rift using alvin. These rocks are contemporaneous with island arc tholeiite lavas of the Izu-Ogasawara arc 20 km to the east, and provide a present day example of volcanism associated with arc rifting and back-arc basin initiation. Major element geochemistry of the basalts is most similar to that of basalts found in other, more mature back-arc basins, which indicates that back-arc basins need not begin their magmatic evolution with lavas bearing strong arc signatures. Volatile concentrations distinguish Sumisu Rift basalts from island arc basalts and MORB. H2O contents, which are at least four times greater than in MORB, suppress plagioclase crystallization. This suppression results in a more mafic fractionating assemblage, which prevents Al2O3 depletion and delays the initiation of Fe2O3(tot) and TiO2 enrichment. However, unlike arc basalts, Fe3+ ??Fe ratios are only slightly higher than in MORB and are insufficient to cause magnetite saturation early enough to suppress Fe2O3(tot) and TiO2 enrichment. Thus, major element trends are more similar to those of MORB than arcs. H2O, CO2 and S are undersaturated relative to pure phase solubility curves, indicating exsolution of an H2O-rich mixed gas phase. High H2O S, high ??D, and low (MORB-like) ??34S ratios are considered primary and distinctive of the back-arc basin setting. ?? 1990.

  18. Unraveling the sources of ground level ozone in the Intermountain Western United States using Pb isotopes.

    PubMed

    Christensen, John N; Weiss-Penzias, Peter; Fine, Rebekka; McDade, Charles E; Trzepla, Krystyna; Brown, Shaun T; Gustin, Mae Sexauer

    2015-10-15

    Ozone as an atmospheric pollutant is largely produced by anthropogenic precursors and can significantly impact human and ecosystem health, and climate. The U.S. Environmental Protection Agency has recently proposed lowering the ozone standard from 75 ppbv (MDA8 = Maximum Daily 8-Hour Average) to between 65 and 70 ppbv. This will result in remote areas of the Intermountain West that includes many U.S. National Parks being out of compliance, despite a lack of significant local sources. We used Pb isotope fingerprinting and back-trajectory analysis to distinguish sources of imported ozone to Great Basin National Park in eastern Nevada. During discrete Chinese Pb events (> 1.1 ng/m(3) & > 80% Asian Pb) trans-Pacific transported ozone was 5 ± 5.5 ppbv above 19 year averages for those dates. In contrast, concentrations during regional transport from the Los Angeles and Las Vegas areas were 15 ± 2 ppbv above the long-term averages, and those characterized by high-altitude transport 3 days prior to sampling were 19 ± 4ppbv above. However, over the study period the contribution of trans-Pacific transported ozone increased at a rate of 0.8 ± 0.3 ppbv/year, suggesting that Asian inputs will exceed regional and high altitude sources by 2015-2020. All of these sources will impact regulatory compliance with a new ozone standard, given increasing global background.

  19. U-Pb Dating of Carbonates: A Complement to Clumped Isotope Analyses

    NASA Astrophysics Data System (ADS)

    Rasbury, T.; Suarez, M. B.

    2014-12-01

    Carbonates are ubiquitous in nature, forming in a variety of settings at the surface and through burial. The field and petrographic relationships of carbonate phases can often be linked to the depositional setting and burial path(s) that the sedimentary pile has experienced. Clumped isotopes are taking on an important role of testing the temperature of formation of the carbonates, and combined with other approaches such as fluid inclusion analyses offers tremendous potential for testing basin evolution models. However, while the relative ages of carbonates are often fairly easily elucidated, the absolute ages of the events recorded in carbonates are not. U-Pb dating of carbonates offers the best potential for constraining the ages. However, not all fluids have favorable U/Ca ratios. U-Pb dated groundwater carbonates from the Late Triassic New Haven Arkose give an age of 211 +/- 2 Ma, consistent with the known age of deposition. Late bright luminescent calcite from the same formation gives an age of 81+/-11 Ma, constraining the age (both primary and secondary) of carbonate formation. Clumped isotope analyses of primary carbonate phases show somewhat elevated temperatures between 50-60o C, some 30 degrees hotter than other estimates for this Triassic equatorial setting, and are more likely the result of re-ordering of 13C-18O bonds at depth. Apparently the primary calcite, appears to have preserved its depositional U-Pb systematics, however bond re-ordering or recrystallization of these carbonates appear to reflect values closer to thermal equilibrium with the last phase of carbonate formation (bright luminescent calcite, 81 ± 11 Ma). Further work on these samples will target these younger calcites to determine if this later calcite phase records similar temperatures.

  20. Tracing the metasomatic and magmatic evolution of continental mantle roots with Sr, Nd, Hf and and Pb isotopes: A case study of Middle Atlas (Morocco) peridotite xenoliths

    NASA Astrophysics Data System (ADS)

    Wittig, Nadine; Pearson, D. Graham; Duggen, Svend; Baker, Joel A.; Hoernle, Kaj

    2010-02-01

    We studied clinopyroxenes from spinel-facies peridotite xenoliths sampled by the Quaternary intra-plate volcanism of the Middle Atlas (Morocco) and present new trace element and Sr-Nd-Hf isotope data. However, we focus in particular on Pb isotope data and 238U/ 204Pb and 232Th/ 204Pb ratios of these clinopyroxenes. This data allows us to investigate: (a) the timing of metasomatic events, (b) the prevalence and persistence of elevated 238U/ 204Pb, 232Th/ 238U and 232Th/ 204Pb in continental mantle roots and (c) the 238U/ 204Pb and 232Th/ 204Pb composition of putative basaltic melts generated from such metasomatised sub-continental lithospheric mantle (SCLM). Incompatible trace element concentrations in these clinopyroxenes are elevated, marked by high-field strength element depletion and fractionated elemental ratios (e.g., U/Nb, Zr/Hf) most consistent with enrichment due to carbonatitic liquids. Sr, Nd and Hf isotopes have an affinity to HIMU. U, Th and Pb abundances in the clinopyroxenes generally exceed estimates of primitive mantle clinopyroxene. Pb isotope compositions of these clinopyroxenes are radiogenic and vary between 206Pb/ 204Pb = 19.93-20.25, 207Pb/ 204Pb = 15.63-15.66 and 208Pb/ 204Pb = 39.72-40.23. These Pb isotope systematics result in generally negative Δ7/4 but positive Δ8/4; setting these samples distinctly apart from typical HIMU. These Pb isotope compositions are also distinct from the associated host volcanic rocks. 238U/ 204Pb and 232Th/ 204Pb of these clinopyroxenes, which range from 26 to 81 and 136 to 399, respectively, are elevated and more extreme than estimates of MORB- and HIMU-source mantle. The Pb isotope evolution of the clinopyroxenes suggests that the metasomatic enrichment is younger than 200 Ma, which discounts the volcanic activity due to the opening of the Atlantic and the onset of the collision of the African and Eurasian plates as processes generating the lithophile element and isotope composition of this continental

  1. The Estherville mesosiderite: U-Pb, Rb-Sr, and Sm-Nd isotopic study of a polymict breccia

    SciTech Connect

    Brouxel, M.; Tatsumoto, M. )

    1991-04-01

    A systematic U-Pb, Sm-Nd, and Rb-Sr isotopic study shows that the Estherville mesosiderite was formed between 4.56 and 4.43 Ga. Observed isotopic heterogeneity is in agreement with multiple generations of meteoritic impacts described in other mesosiderites. At least part of the Estherville silicate fraction was formed early in solar system history as indicated by the Pb-Pb (4555 {plus minus} 35 Ma), U-Pb (4560 {plus minus} 31 Ma), Rb-Sr (4542 {plus minus} 203 Ma), and Sm-Nd (4533 {plus minus} 94 Ma) ages. Mesosiderites therefore present not only petrological but also geochronological similarities with eucrites. The Pb isotopic composition of the metal phase plots on the same isochron as the silicates, indicating formation and subsequent mixing with silicates early in the history of the solar system. This is consistent with previous observations indicating that iron was reduced during the silicate-magmatic stage, most likely a consequence of mixing with metal. In addition to these more-ancient portions of the Estherville breccia, other parts were formed later as suggested by the Pb-Pb (4422 {plus minus} 50 Ma) and U-Pb (4437 {plus minus} 11 Ma) ages observed in a second group of leaches and residues. This age is similar to some cumulate eucrite ages and may represent the formation of a second mesosiderite component. The Sm-Nd and the Rb-Sr ages obtained on Estherville show large errors that may be a consequence of the mixing between the 4.56 and 4.43 Ga endmembers. Estherville, like most mesosiderites, was affected by a major heating event around 3.5-3.7 Ga as shown by the Ar-Ar ages. This heating event partially disturbed the Rb-Sr isotopic system (Rb-Sr metamorphic ages range between 3.81 and 4.08 Ga).

  2. Mesoproterozoic island arc magmatism along the south-eastern margin of the Indian Plate: Evidence from geochemistry and zircon U-Pb ages of mafic plutonic complexes

    NASA Astrophysics Data System (ADS)

    Subramanyam, K. S. V.; Santosh, M.; Yang, Qiong-Yan; Zhang, Ze-ming; Balaram, V.; Reddy, U. V. B.

    2016-11-01

    The Prakasam Igneous Province within the Nellore Schist Belt (NSB) preserves important imprints of mafic magmatism along the south-eastern margin of the Indian plate. Here we report petrology, geochemistry and zircon U-Pb age data from three gabbro plutons namely Purimetla, Kanigiri and P C Palle which intruded into the high grade rocks of the region. LA-ICP-MS U-Pb data on zircons from the three plutons reveal prominent late Mesoproterozoic ages of 1334 ± 15 Ma, 1338 ± 27 Ma and 1251.2 ± 9.4 Ma. The cumulative 207Pb/206Pb mean age of 1315 ± 11 Ma is interpreted to represent the timing of mafic magmatism in the Prakasam Igneous Province. These rocks show adcumulus to mesocumulus and poikilitic textures indicating fractional crystallization of plagioclase and clinopyroxenes in the Purimetla pluton whereas the Kanigiri and P C Palle intrusions possess hornblende and biotite suggesting the role of water during partial melting. The rocks show LREE enrichment (∑LREE/∑HREE = 2.2-15.0), marked Eu-anomalies (Eu/Eu∗ = 0.8-2.2) and fractionated patterns (LaN/YbN = 3-79). Primitive mantle normalised trace element spider diagrams indicate subduction modified arc signatures with LILE enrichment and depletion of Nb, Ti and Zr relative to Th and La. Tectonic discrimination diagrams show arc magmatic affinities for the three gabbro plutons consistent with subduction zone setting. We propose a tectonic model involving intra oceanic island arc accretion during late Mesoproterozoic along the eastern margin of the Indian continent.

  3. The plumbotectonic model for Pb isotopic systematics among major terrestrial reservoirs-A case for bi-directional transport

    USGS Publications Warehouse

    Zartman, R.E.; Haines, S.M.

    1988-01-01

    Version IV of plumbotectonics expands and refines the original model of Doe and Zartman (1979) and Zartman and Doe (1981) for explaining Pb (Sr, and Nd) isotopic systematics among major terrestrial reservoirs. A case for bi-directional transport among reservoirs is based on the observed isotopic compositions for different tectonic settings, and finds a rationale in the kinetics of plate tectonics. Chemical fractionation and radioactive decay create isotopic differences during periods of isolation of one reservoir from another, whereas dynamic processes allowing mixing between reservoirs tend to reduce these differences. Observed isotopic characteristics reflect a balance between these opposing tendencies and provide constraints on the extent and timing of fractionation and mixing processes. Plumbotectonics does not require interaction with a lower mantle or core reservoir over most of the Earth's lifetime, and, in fact, achieves a material balance consistent with no such exchange of material. Important evidence of the amount and timing of crustal recycling, and of the residence times of mantle heterogeneities lies in the coupled 207Pb 204Pb-206 Pb 204Pb systematics. We believe that examination of the published data base fully supports our contention of significant bi-directional transport of material among terrestrial reservoirs. Plumbotectonics allows us to explore many aspects of reservoir interaction, and to identify parameters that provide meaningful constraints on mantle-crust differentiation. We put forth a compromise fit to many of the model variables in version IV, which can serve as a reference for future work. ?? 1988.

  4. The origin of Cenozoic continental basalts in east-central China: Constrained by linking Pb isotopes to other geochemical variables

    NASA Astrophysics Data System (ADS)

    Xu, Zheng; Zheng, Yong-Fei; Zhao, Zi-Fu

    2017-01-01

    Cenozoic continental basalts in east-central China are characterized by OIB-like trace element patterns with more depleted to less enriched Sr-Nd isotope compositions. Such geochemical signatures are attributable to variable contributions to their mantle sources from crustal components in the oceanic subduction zone. A combined study of basalt Pb isotope variations with other geochemical variables indicates that four mantle and crustal components were involved in the basalt petrogenesis. Model calculations verify the geochemical transfer from the subducted crustal components to the mantle sources. The depleted MORB mantle component is indicated by the depleted Sr-Nd isotope compositions of basalts. Relatively high 206Pb/204Pb and low Δ8/4 ratios are ascribed to contributions from the igneous oceanic crust with high U/Pb and low Th/U ratios, low 206Pb/204Pb and high Δ8/4 ratios are ascribed to the lower continental crust, and high 206Pb/204Pb and high Δ8/4 ratios are linked to the seafloor sediment. This generates different compositions of mantle sources for these OIB-like continental basalts. The basalts with the most depleted Sr-Nd isotope compositions show Pb isotope compositions distinct from Pacific MORB but similar to Indian MORB, suggesting the occurrence of Indian type asthenospheric mantle beneath the continental lithosphere of eastern China. The depleted MORB mantle would be metasomatized by the three crustal components at the slab-mantle interface in oceanic subduction channel, generating the mantle sources that are enriched in melt-mobile incompatible trace elements and their pertinent radiogenic isotopes. Nevertheless, the crustal components were not directly incorporated in the forms of crustal rocks into the mantle sources, but underwent partial melting to produce the felsic melts that predominate the composition of those trace elements and their pertinent radiogenic isotopes in the basalts. As such, the depleted MORB mantle component was

  5. Os, Sr, Nd, and Pb isotope systematics of southern African peridotite xenoliths - Implications for the chemical evolution of subcontinental mantle

    NASA Technical Reports Server (NTRS)

    Walker, R. J.; Carlson, R. W.; Shirey, S. B.; Boyd, F. R.

    1989-01-01

    Isotope analyses of Os, Sr, Nd, and Pb elements were caried out on twelve peridotite xenoliths from the Jagersfontein, Letseng-la-terae, Thaba Patsoa, Mothae, and Premier kimberlites of southern Africa, to investigate the timing and the nature of melt extraction from the continental lithosphere and its relation to the continent formation and stabilization. The distinct Os and Pb isotopic characteristics found in these samples suggested that both the low- and the high-temperature peridotites reside in an ancient stable lithospheric 'keel' to the craton that has been isolated from chemical exchange with the sublithospheric mantle for time periods in excess of 2 Ga.

  6. Potential uses of stable isotope ratios of Sr, Nd, and Pb in geological materials for environmental studies.

    PubMed

    Nakano, Takanori

    2016-01-01

    The ratios of stable isotopes of certain elements in rocks and minerals have strong regional characteristics that are reflected in atmospheric components, in water, and in the living organisms that form Earth's surface environment as well as in agricultural and fishery products. Geologically derived stable isotope ratios can be used as a tracer for the source of many kinds of substances, with current geochemical techniques allowing the precise determination of numerous stable isotope ratios in both natural and manmade objects. This review presents examples of the use of stable isotopes as tracers within diverse dynamic ecosystems, focusing on Sr isotopes but also including examples of Nd and Pb isotopic analysis, and reviewing the potential of this technique for a wide range of environmental research, including determining the geographic origin of food and archeological materials.

  7. Potential uses of stable isotope ratios of Sr, Nd, and Pb in geological materials for environmental studies

    PubMed Central

    NAKANO, Takanori

    2016-01-01

    The ratios of stable isotopes of certain elements in rocks and minerals have strong regional characteristics that are reflected in atmospheric components, in water, and in the living organisms that form Earth’s surface environment as well as in agricultural and fishery products. Geologically derived stable isotope ratios can be used as a tracer for the source of many kinds of substances, with current geochemical techniques allowing the precise determination of numerous stable isotope ratios in both natural and manmade objects. This review presents examples of the use of stable isotopes as tracers within diverse dynamic ecosystems, focusing on Sr isotopes but also including examples of Nd and Pb isotopic analysis, and reviewing the potential of this technique for a wide range of environmental research, including determining the geographic origin of food and archeological materials. PMID:27302069

  8. Isotope and elemental geochemistry of Cretaceous fossiliferous concretions (Santana Formation, Brazil)

    NASA Astrophysics Data System (ADS)

    Heimhofer, Ulrich; Meister, Patrick; Bernasconi, Stefano M.; Ariztegui, Daniel; Martill, David M.; Schwark, Lorenz

    2014-05-01

    Exceptional three-dimensional fossil preservation (incl. phosphatization of soft-tissues) within organic carbon-rich mudstones is often associated with the formation of a protective carbonate shell surrounding the fossil specimen. Examples for this type of preservation are the Early Cretaceous fishes, turtles and pterosaurs from the Brazilian Santana Formation. Numerous studies proposed different conceptual models for concretion formation. Having new state-of-the-art geochemical tools at hand we revisited these models for the Santana Formation as an exemplary case. Differential compaction clearly indicates early precipitation of micritic calcite surrounding a central cavity containing the still decomposing fossil. The presence of pyrite forming a circular rim around the fossil and carbonate with negative carbon isotope compositions suggest intense sulphate reduction whereby the production of ammonium from the decay of proteins led to an increased alkalinity, which induced early carbonate precipitation. By means of micro-XRF scanning we found that pyrite is absent from the interior part of the concretions and that total iron content is very low, which indicate absence of sulphate reduction at the center of the concretions and possibly local onset of methanogenesis. We postulate that the central cavity may even have been filled with methane gas that evolved from the decaying animal. Methane diffusing outward was anaerobically oxidized in the surrounding sulphate reduction zone. Carbonate clumped isotopes revealed that micritic calcite formed early, but that these early precipitates are overprinted by two different late diagenetic cements precipitated at elevated temperatures. The occurrence of an outermost "cone-in-cone" calcite rim can be associated with burial showing temperatures of up to 60°C. Strontium-isotope ratios of matrix calcite and cement phases show radiogenic values (0.710416 to 0.712465), which are significantly higher than typical marine Cretaceous

  9. Ten years of elemental atmospheric metal fallout and Pb isotopic composition monitoring using lichens in northeastern France

    NASA Astrophysics Data System (ADS)

    Cloquet, Christophe; Estrade, Nicolas; Carignan, Jean

    2015-09-01

    We report on the chemical and Pb isotopic compositions of epiphytic lichens collected from small tree branches in the urban area of the city of Metz (NE France). Lichens were collected in five different years between 2001 and 2009. The data are first compared year to year in order to document any temporal change and trend in metal atmospheric fallout. The area studied was then subdivided into different zones on the basis of land use (urban, suburban, rural and industrial) in order to determine potential spatial gradients. The median concentrations and enrichment factors (EF, normalized to Al) of Pb and other metals (Cu, Zn, Cd, Ni, Cr, Hg, Fe) in lichens from the urban, suburban, and rural zones show no systematic variation between 2001 and 2008. However, the metal EFs show spatial variation and are generally highest in the urban area and lowest in the rural area. Lichens within the industrial zone (collected in 2009), which is dominated by steel industries, are richest in Al, Fe, Cr, Pb, and Zn. Although the Al concentration is high in these lichens, the EFs for the cited metals are several times higher than those measured in lichens from the other three zones. No significant differences were noted for Hg, Cd, Cu and or Ni. Pb isotopic compositions measured in lichens may be highly variable from year to year and from zone to zone. The variation is primarily interpreted to result from mixing between: (i) Pb added to gasoline (and recycled through re-emission of road dust in the atmosphere); (ii) regional industrial Pb from long-range transportation and/or mixed with urban Pb; and (iii) local industrial Pb. The median isotopic compositions of individual zones are distinct, suggesting variable mixing of these three sources. The annual variations show that 2001 was most affected by gasoline Pb, whereas 2003 and 2006 were more affected by the local steel industry.

  10. Zircon U-Pb ages, geochemical and Sr-Nd-Pb-Hf isotopic constraints on petrogenesis of the Tarom-Olya pluton, Alborz magmatic belt, NW Iran

    NASA Astrophysics Data System (ADS)

    Nabatian, Ghasem; Jiang, Shao-Yong; Honarmand, Maryam; Neubauer, Franz

    2016-02-01

    A petrological, geochemical and Sr-Nd-Pb isotopic study was carried out on the Tarom-Olya pluton, Iran, in the central part of the Alpine-Himalayan orogenic belt. The pluton is composed of diorite, monzonite, quartz-monzonite and monzogranite, which form part of the Western Alborz magmatic belt. LA-ICP-MS analyses of zircons yield ages from 35.7 ± 0.8 Ma to 37.7 ± 0.5 Ma, interpreted as the ages of crystallization of magmas. Rocks from the pluton have SiO2 contents ranging from 57.0 to 69.9 wt.%, high K2O + Na2O (5.5 to 10.3 wt.%) and K2O/Na2O ratio of 0.9 to 2.0. Geochemical discrimination criteria show I-type and shoshonitic features for the studied rocks. All investigated rocks are enriched in light rare earth elements (LREEs), large ion lithophile elements (LILEs), depleted in high-field strength elements (HFSEs), and show weak or insignificant Eu anomalies (Eu/Eu* = 0.57-1.02) in chondrite-normalized trace element patterns. The Tarom-Olya pluton samples also show depletions in Nb, Ta and Ti typical of subduction-related arc magmatic signatures. The samples have relatively low ISr (0.7047-0.7051) and positive εNd(36 Ma) (+ 0.39 to + 2.10) values. The Pb isotopic ratios show a (206Pb/204Pb)i ratio of 18.49-18.67, (207Pb/204Pb)i ratio of 15.58-15.61 and (208Pb/204Pb)i ratio of 38.33-38.77. The εHf(t) values of the Tarom-Olya pluton zircons vary from - 5.9 to + 8.4, with a peak at + 2 to + 4. The depleted mantle Hf model ages for the Tarom-Olya samples are close to 600 Ma. These isotope evidences indicate contribution of juvenile sources in petrogenesis of the Tarom-Olya pluton. Geochemical and isotopic data suggest that the parental magma of the Tarom-Olya pluton was mainly derived from a sub-continental lithospheric mantle source, which was metasomatized by fluids and melts from the subducted Neotethyan slab with a minor crustal contribution. Subsequent hot asthenospheric upwelling and lithospheric extension caused decompression melting in the final stage of

  11. Feldspar palaeo-isochrons from early Archaean TTGs: Pb-isotope evidence for a high U/Pb terrestrial Hadean crust

    NASA Astrophysics Data System (ADS)

    Kamber, B. S.; Whitehouse, M. J.; Moorbath, S.; Collerson, K. D.

    2001-12-01

    Feldspar lead-isotope data for 22 early Archaean (3.80-3.82 Ga) tonalitic gneisses from an area south of the Isua greenstone belt (IGB),West Greenland, define a steep linear trend in common Pb-isotope space with an apparent age of 4480+/-77 Ma. Feldspars from interleaved amphibolites yield a similar array corresponding to a date of 4455+/-540 Ma. These regression lines are palaeo-isochrons that formed during feldspar-whole rock Pb-isotope homogenisation a long time (1.8 Ga) after rock formation but confirm the extreme antiquity (3.81 Ga) of the gneissic protoliths [1; this study]. Unlike their whole-rock counterparts, feldspar palaeo-isochrons are immune to rotational effects caused by the vagaries of U/Pb fractionation. Hence, comparison of their intercept with mantle Pb-isotope evolution models yields meaningful information regarding the source history of the magmatic precursors. The locus of intersection between the palaeo-isochrons and terrestrial mantle Pb-isotope evolution lines shows that the gneissic precursors of these 3.81 Ga gneisses were derived from a source with a substantially higher time-integrated U/Pb ratio than the mantle. Similar requirements for a high U/Pb source have been found for IGB BIF [2], IGB carbonate [3], and particularly IGB galenas [4]. Significantly, a single high U/Pb source that separated from the MORB-source mantle at ca. 4.3 Ga with a 238U/204Pb of ca. 10.5 provides a good fit to all these observations. In contrast to many previous models based on Nd and Hf-isotope evidence we propose that this reservoir was not a mantle source but the Hadean basaltic crust which, in the absence of an operating subduction process, encased the early Earth. Differentiation of the early high U/Pb basaltic crust could have occurred in response to gravitational sinking of cold mantle material or meteorite impact, and produced zircon-bearing magmatic rocks. The subchondritic Hf-isotope ratios of ca. 3.8 Ga zircons support this model [5] provided that

  12. U-Pb zircon age, geochemical and Lu-Hf isotopic constraints of the Southern Gangma Co basalts in the Central Qiangtang, northern Tibet

    NASA Astrophysics Data System (ADS)

    Wang, Ming; Li, Cai; Xie, Chao Ming; Xu, Jian Xin; Li, Xing Kui

    2015-08-01

    A recent study suggests that the central Qiangtang is a key locality to investigate the evolution of the opening and closure of the Paleo-Tethys Ocean. Basalts are commonly associated with supercontinent fragmentation, and they have the potential to indicate the tectonic environment into which they were erupted. In this study, laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb zircon dating, whole-rock geochemistry, and zircon Hf isotope analysis were used to study newly discovered basalts in the southern Gangma Co area of central Qiangtang. Dating of magmatic zircons from three basalt samples indicates that the basalts erupted in the Late Devonian to early Carboniferous (early Tournaisian) at 360-350 Ma. The basalts are geochemically similar to within-plate basalts and formed from a depleted mantle source. We suggest that the basalts may have been a product of the breakup of the northern margin of Gondwana in the Late Devonian to early Carboniferous (360-350 Ma), which may be linked to the initial rifting and opening of the Paleo-Tethys Ocean in the Qiangtang area.

  13. Preliminary Gas and Isotope Geochemistry in the Rehai Geothermal Field, P.R. China

    SciTech Connect

    P., Zhao; Z., Liao

    1995-01-01

    Based on gas and sulphur isotopic composition, two types of steam in Rehai geothermal field are identified. One is with higher CO{sub 2} and H{sub 2}S concentration, the {delta}{sup 34}S of H{sub 2}S is in the range 2.49{per_thousand} to -1.04{per_thousand} (vs CDT), from which the H{sub 2}S-temperature is over than 250 C. The other is with lower CO{sub 2} and H{sub 2}S concentration, the {delta}{sup 34}S of H{sub 2}S is in the range -4.0{per_thousand} to -8.36{per_thousand}, from which the H{sub 2}S- and H{sub 2}-temperatures are 180 C-210 C, in good agreement with quartz temperature. The thermal water in the Rehai field is of local meteoric origin. Maximum {delta}{sup 18}O-value shift is less than 2.0{per_thousand} (vs SMOW). Mixing is widespread and could be identified on isotope and solute chemistry.

  14. The boron isotope geochemistry of the neogene borate deposits of western Turkey

    NASA Astrophysics Data System (ADS)

    Palmer, M. R.; Helvaci, C.

    1997-08-01

    We have analyzed the boron isotope composition of 80 borate minerals (major minerals: borax, colemanite, and ulexite; minor minerals: veatchite-A, tunellite, kernite, terrugite, probertite, meyer-hofferite, inderite, inyoite, hydroboracite, howlite, and pandermite) from the main deposits (Kirka, Bigadiç, and Emet) and two smaller deposits (Kestelek and Sultançayir) in the western Turkish borate deposits. Forty-three samples were also analysed for their Sr isotope composition. The data span a wide range in δ11B values from -1.6%o to -25.3%o. The δ 11B values of the main borate minerals are largely controlled by their mineralogy and the pH of the brines from which they precipitated. An inverse correlation between the average δ 11B and 87Sr/86Sr ratios of colemanite in the different deposits suggests there is some variation in the sources of boron and Sr to the deposits. Emet has the highest contribution from aluminosilicates and Kirka the highest contribution from Eocene carbonates, with Bigadiç occupying an intermediate position. The δ11B values of the minor borate minerals distinguish between those which are primary precipitates from the original brines (or formed from primary borates without boron loss from the system) and those which formed from alteration of preexisting borate minerals with substantial loss of boron from the system.

  15. Organic Geochemistry of the Hamersley Province: Relationships Among Organic Carbon Isotopes, Molecular Fossils, and Lithology

    NASA Technical Reports Server (NTRS)

    Eigenbrode, Jennifer L.

    2012-01-01

    Molecular fossils are particularly valuable ancient biosignatures that can provide key insight about microbial sources and ecology in early Earth studies. In particular, hopanes carrying 2-methyl or 3-methyl substituents are proposed to be derived from cyanobacteria and oxygen-respiring methanotrophs, respectively, based on both their modem occurrences and their Proterozoic and Phanerozoic sedimentary distributions. Steranes are likely from ancestral eukaryotes. The distribution of methylhopanes, steranes, and other biomarkers in 2.72-2.56 billion-year-old rocks from the Hamersley Province, Western Australia show relationships to lithology, facies, and isotopes of macromolecular carbon, and other biomarkers. These observations support biomarker syngenicity and thermal maturity. Moreover, ecological signatures are revealed, including a surprising relationship between isotopic values for bulk macromolecular carbon and the biomarker for methanotrophs. The record suggests that cyanobacteria were likely key organisms of shallow-water microbial ecosystems providing molecular oxygen, fixed carbon, and possibly fixed nitrogen, and methanotrophs were not alone in recycling methane and other C-13-depleted substrates.

  16. Modeling lead input and output in soils using lead isotopic geochemistry.

    PubMed

    Semlali, R M; Dessogne, J B; Monna, F; Bolte, J; Azimi, S; Navarro, N; Denaix, L; Loubet, M; Chateau, C; van Oort, F

    2004-03-01

    The aim of this study is to model downward migration of lead from the plow layer of an experimental site located in Versailles (about 15 km southwest of Paris, France). Since 1928, samples have been collected annually from the topsoil of three control plots maintained in bare fallow. Thirty samples from 10 different years were analyzed for their lead and scandium contents and lead isotopic compositions. The fluxes are simple because of the well-controlled experimental conditions in Versailles: only one output flux, described as a first-order differential function of the anthropogenic lead pool, was taken into account; the inputs were exclusively ascribed to atmospheric deposition. The combination of concentration and isotopic data allows the rate of migration from the plowed topsoil to the underlying horizon and, to a lesser extent, the atmospheric fluxes to be assessed. Both results are in good agreement with the sparse data available. Indeed, the post-depositional migration of lead appears negligible at the human time scale: less than 0.1% of the potentially mobile lead pool migrates downward, out of the first 25 cm of the soil, each year. Assuming future lead inputs equal to 0, at least 700 yr would be required to halve the amount of accumulated lead pollution. Such a low migration rate is compatible with the persistence of a major anthropogenic lead pool deposited before 1928. Knowledge of pollution history seems therefore to be of primary importance.

  17. Isotope geochemistry of thermal and nonthermal waters in the Valles caldera, Jemez Mountains, northern New Mexico

    SciTech Connect

    Vuataz, F.D.; Goff, F.

    1986-02-10

    Over 100 stable isotope and 45 tritium analyses from thermal and nonthermal waters of the Jemez Mountains region, New Mexico, have been used to define the hydrodynamics of the Valles caldera (Baca) geothermal system and related geothermal fluids of the region. Evaluation of 36 cold meteoric waters yields an equation for the Jemez Mountains meteoric water line of deltaD = 8delta/sup 18/O+12, while further evaluation of nine cold meteoric waters yields an equation relating recharge elevation to deuterium content of E(meters) = -44.9 (deltaD)-1154. Based on the deuterium content of five Baca well waters (223/sup 0/--294/sup 0/C), the average recharge elevation of the Valles geothermal system ranges from 2530 to 2890 m. This range of elevations falls between the elevations of the lowest point of the caldera floor (2400 m) and the summit of the resurgent dome inside the caldera (3430 m). Thus stable isotopes indicate that the caldera depression probably serves as a recharge basin for the deep geothermal system. Although cold spring waters of the Jemez Mountains region consist of meteoric water, tritium analyses show that most of them contain water between 20 and 75 years old.

  18. High Resolution, Pb Isotope Variability Within Historic Eruptions of the Cumbre Vieja Volcano, La Palma, Canary Islands

    NASA Astrophysics Data System (ADS)

    Locke, J. A.; Peterson, B. T.; Nelson, B. K.

    2005-12-01

    The range of time-scales over which ocean island basalt (OIB) magmatism taps different mantle heterogeneities is a fundamental dynamic of mantle plumes. The variability of long-lived radiogenic isotopes in OIB magmas erupted on time scales less than 100 years has been addressed primarily for Hawaiian magmas (e.g., Pietruszka et al., 2001). Similar data are relatively sparse for hot spots with low buoyancy fluxes. The Canary Islands have low eruption rates and have been historically active. The Cumbre Vieja volcano in southern La Palma, Canary Islands, has six, well-mapped, historic eruptions spanning the entire southern rift zone. We have investigated Pb isotope compositional variations expressed in magmas erupted in a series of events spanning 500 years (the 1480, 1585, 1677, 1712, 1949, and 1971 eruptions), and sampled in detail two of these events (the 1677 and 1712 eruptions) to document isotopic variability at the month to year time-scale as well as the 100-year time scale. Previous Pb isotope investigations of Cumbre Vieja did not reveal systematic variations (e.g., Marcantonio et al., 1995 and Ovchinnikova et al., 1995). With denser sampling (40 samples) and higher precision MC-ICP-MS analyses, we observe that radiogenic Pb isotope compositions over the 500 year eruptive history decrease systematically with time (206Pb/204Pb =19.669 -- 19.611, 207Pb/ 204Pb = 15.618 -- 15.602, 208Pb/204Pb = 39.530 -- 39.430). Detailed Pb isotope analyses of the 1677 and 1712 eruptions indicate isotopically homogeneous magmas within a single eruptive episode. However, samples from both the 1677 and 1712 eruptions display mineralogic evidence for magma mixing: 1677 samples include isotopically distinct gabbroic xenoliths, and both magmas have reversely- zoned clinopyroxene phenocrysts with corroded cores of Na-rich salite, and zoned overgrowths of Al-rich salite. With time, an increasing proportion of partial melt from a less radiogenic end-member within a heterogeneous plume

  19. Quantifying the signature of the industrial revolution from Pb and Cd isotopes in the Susquehanna Shale Hills Critical Zone Observatory

    NASA Astrophysics Data System (ADS)

    Ma, L.; Herndon, E.; Jin, L.; Sanchez, D.; Brantley, S. L.

    2013-12-01

    Anthropogenic forcings have dominated metal cycling in many environments. During the period of the industrial revolution, mining and smelting of ores and combustion of fossil fuels released non-negligible amounts of potentially toxic metals such as Pb, Cd, Mn, and Zn into the environment. The extent and fate of these metal depositions in soils during that period however, have not been adequately evaluated. Here, we combine Pb isotopes with Cd isotopes to trace the sources of metal pollutants in a small temperate watershed (Shale Hills) in Pennsylvania. Previous work has shown that Mn additions to soils in central PA was caused by early iron production, as well as coal burning and steel making upwind. Comparison of the Pb and Cd concentrations in the bedrock and soils from this watershed show that Pb and Cd in soils at Shale Hills are best characterized by addition profiles, consistent with atmospheric additions. Three soil profiles at Shale Hills on the same hillslope have very similar anthropogenic Pb inventories. Pb isotope results further reveal that the extensive use of local coals during iron production in early 19th century in Pennsylvania is most likely the anthropogenic Pb source for the surface soils at Shale Hills. Pb concentrations and isotope ratios were used to calculate mass balance and diffusive transport models in soil profiles. The model results further reveal that during the 1850s to 1920s, coal burning in local iron blasting furnaces significantly increased the Pb deposition rates to 8-14 μg cm-2 yr-1, even more than modern Pb deposition rates derived from the use of leaded gasoline in the 1940s to 1980s. Furthermore, Cd has a low boiling point (~760 °C) and easily evaporates and condenses. The evaporation and condensation processes could generate systematic mass-dependent isotope fractionation between Cd in coal burning products and the naturally occurring Cd in the sulfide minerals of coals. This fractionation indicates that Cd isotopes can

  20. Atmospheric Pb deposition since the Industrial Revolution recorded by five Swiss peat profiles: Enrichment factors, fluxes, isotopic composition, and sources

    SciTech Connect

    Weiss, D.; Shotyk, W.; Kramers, J.D.; Appleby, P.G.; Cheburkin, A.K.

    1999-05-01

    Atmospheric Pb deposition since the Industrial Revolution was studied in western, central, and southern Switzerland using five rural peat bogs. Similar temporal patterns were found in western and central Switzerland, with two distinct periods of Pb enrichment relative to the natural background: between 1880 and 1920 with enrichments ranging from 40 to 80 times, and between 1960 and 1980 with enrichments ranging from 80 to 100 times. The fluxes also were generally elevated in those time periods: in western Switzerland between 1.16 and 1.55 {micro}g cm{sup {minus}2} y{sup {minus}1} during the second period. Between the Industrial Revolution and 1985, nonradiogenic Pb became increasingly important in all five cores because of the replacement of coal by oil after ca. 1920, the use of Australian Pb in industry, and the extensive combustion of leaded gasoline after 1950. The introduction of unleaded gasoline in 1985 had a pronounced effect on the Pb deposition in all five cores. Enrichments dropped sharply, and the isotopic ratios reverted back toward natural values. The cores from western and central Switzerland showed very similar isotopic trends throughout the time period studied, implying that these sites were influenced contemporaneously by similar pollution sources and atmospheric pathways. Southern Switzerland revealed a different record with respect to the Pb pollution: it was dominated by a single massive Pb enrichment dated between 1930 and 1950.

  1. Deep drilling at the Siljan Ring impact structure: oxygen-isotope geochemistry of granite

    USGS Publications Warehouse

    Komor, S.C.; Valley, J.W.

    1990-01-01

    The Siljan Ring is a 362-Ma-old impact structure formed in 1700-Ma-old I-type granites. A 6.8-km-deep borehole provides a vertical profile through granites and isolated horizontal diabase sills. Fluid-inclusion thermometry, and oxygen-isotope compositions of vein quartz, granite, diabase, impact melt, and pseudotachylite, reveal a complex history of fluid activity in the Siljan Ring, much of which can be related to the meteorite impact. In granites from the deep borehole, ??18O values of matrix quartz increase with depth from near 8.0 at the surface to 9.5??? at 5760 m depth. In contrast, feldspar ??18O values decrease with depth from near 10 at the surface to 7.1??? at 5760 m, forming a pattern opposite to the one defined by quartz isotopic compositions. Values of ??18O for surface granites outside the impact structure are distinct from those in near-surface samples from the deep borehole. In the deep borehole, feldspar coloration varies from brick-red at the surface to white at 5760 m, and the abundances of crack-healing calcite and other secondary minerals decrease over the same interval. Superimposed on the overall decrease in alteration intensity with depth are localized fracture zones at 4662, 5415, and 6044 m depth that contain altered granites, and which provided pathways for deep penetration of surface water. The antithetic variation of quartz and feldspar ??18O values, which can be correlated with mineralogical evidence of alteration, provides evidence for interaction between rocks and impact-heated fluids (100-300?? C) in the upper 2 km of the pluton. Penetration of water to depths below 2 km was restricted by a general decrease in impact-fracturing with depth, and by a 60-m-thick diabase sill at 1500 m depth that may have been an aquitard. At depths below 4 km in the pluton, where water/rock ratios were low, oxygen isotopic compositions preserve evidence for limited high-temperature (>500?? C) exchange between alkali feldspar and fluids. The high

  2. Isotope Geochemistry and Chronology of Offshore Ground Water Beneath Indian River Bay, Delaware

    USGS Publications Warehouse

    Böhlke, John Karl; Krantz, David E.

    2003-01-01

    Results of geophysical surveys in Indian River Bay, Delaware, indicate a complex pattern of salinity variation in subestuarine ground water. Fresh ground-water plumes up to about 20 meters thick extending hundreds of meters offshore are interspersed with saline ground water, with varying degrees of mixing along the salinity boundaries. It is possible that these features represent pathways for nutrient transport and interaction with estuarine surface water, but the geophysical data do not indicate rates of movement or nutrient sources and reactions. In the current study, samples of subestuarine ground water from temporary wells with short screens placed 3 to 22 meters below the sediment-water interface were analyzed chemically and isotopically to determine the origins, ages, transport pathways, and nutrient contents of the fresh and saline components. Apparent ground-water ages determined from chlorofluorocarbons (CFCs), sulfur hexafluoride (SF6), tritium (3H), and helium isotopes (3He and 4He) commonly were discordant, but nevertheless indicate that both fresh and saline ground waters ranged from a few years to at least 50 years in age. Tritium-helium (3H-3He) ages, tentatively judged to be most reliable, indicate that stratified offshore freshwater plumes originating in distant recharge areas on land were bounded by relatively young saline water that was recharged locally from the overlying estuary. Undenitrified and partially denitrified nitrate of agricultural or mixed origin was transported laterally beneath the estuary in oxic and suboxic fresh ground water. Ammonium produced by anaerobic degradation of organic matter in estuarine sediments was transported downward in suboxic saline ground water around the freshwater plumes. Many of the chemical and isotopic characteristics of the subestuarine ground waters are consistent with conservative mixing of the fresh (terrestrial) and saline (estuarine) endmember water types. These data indicate that freshwater plumes

  3. Pb isotope variations among Bandelier Tuff feldspars: No evidence for a long-lived silicic magma chamber

    NASA Astrophysics Data System (ADS)

    Wolff, J. A.; Ramos, F. C.

    2003-06-01

    We report, for the first time, high-precision Pb isotope data from a high-silica rhyolite. Prior work on Sr isotopes in the 1.6 Ma Otowi Member of the Bandelier Tuff (Valles caldera, New Mexico) established that large 87Sr/86Sr variations exist among Otowi glasses and sanidine phenocrysts. While the glasses display unequivocal evidence for wall-rock contamination of the Otowi magma following sanidine growth, a positive correlation between 87Sr/86Sri and 87Rb/86Sr among the feldspars could be interpreted as either a mixing line or an in situ magmatic isochron dating a differentiation event ˜270 k.y. prior to eruption. The 206Pb/204Pb and 87Sr/86Sr ranges for Otowi sanidines are 17.790 ± 0.002 to 17.831 ± 0.002 and 0.7074 0.7052, respectively. This Pb isotope range cannot be produced by radiogenic ingrowth at the U/Pb ratios of the host magma on any geologically reasonable time scale, and hence is unequivocal evidence for open-system behavior of the Otowi magma prior to and/or concurrent with feldspar growth. Open-system behavior is predicted to control Sr isotope variations due to much higher concentrations of Sr, relative to Pb, in the country rock than in the magma. These observations therefore undermine any age significance of the Rb-Sr isotope variations. In the absence of supporting data, Rb-Sr relations alone do not impart any information about residence times of high-silica rhyolite magmas with subchondritic concentrations of Sr.

  4. Compilation of gas geochemistry and isotopic analyses from The Geysers geothermal field: 1978-1991

    USGS Publications Warehouse

    Lowenstern, Jacob B.; Janik, Cathy; Fahlquist, Lynne; Johnson, Linda S.

    1999-01-01

    We present 45 chemical and isotopic analyses from well discharges at The Geysers geothermal field and summarize the most notable geochemical trends. H2 and H2S concentrations are highest in the Southeast Geysers, where steam samples have δD and δ18O values that reflect replenishment by meteoric water. In the Northwest Geysers, samples are enriched in gas/steam, CO2, CH4, and N2/Ar relative to the rest of the field, and contain steam that is elevated in δD and δ18O, most likely due to substantial contributions from Franciscan-derived fluids. The δ13C of CO2, trends in CH4 vs. N2, and abundance of NH3 indicate that the bulk of the non-condensable gases are derived from thermal breakdown of organic materials in Franciscan meta-sediments.

  5. Methods for the separation of rhenium, osmium and molybdenum applicable to isotope geochemistry

    USGS Publications Warehouse

    Morgan, J.W.; Golightly, D.W.; Dorrzapf, A.F.

    1991-01-01

    Effective methods are described for the chemical separation of rhenium, osmium and molybdenum. The methods are based on distillation and anion-exchange chromatography, and have been the basis for rhenium-osmium isotope studies of ore deposits and meteorites. Successful anion-exchange separation of osmium requires both recognition and careful control of the osmium species in solution; thus, distillation of osmium tetroxide from a mixture of sulfuric acid and hydrogen peroxide is preferred to anion-exchange. Distribution coefficients measured for perrhenate in sulfuric acid media are sufficiently high (Kd > 500) for rhenium to be directly loaded onto an ion-exchange column from a distillation residue and subsequently eluted with nitric acid. Polymerization of molybdenum species during elution is prevented by use of a solution that is 1M in hydrochloric acid and 1M in sodium chloride. ?? 1991.

  6. Palynology and organic/isotope geochemistry of the Mae Moh Basin, Northern Thailand

    SciTech Connect

    Minh, L.V.; Abrajano, T.; Burden, E.; Winsor, L. ); Ratanasthien, B. )

    1994-07-01

    The Mae Moh basin is one of several Tertiary intermontane basins in northern Thailand, whose evolution has been linked to the collision of the Indian plate with the Eurasian plate since the early Eocene. As in most of these basins, lacustrine/swamp sedimentation in the Mae Moh basin can be broadly divided into an Oligocene to Miocene synrift sequence and a Miocene to Quarternary postrift sequence. The dominance of swamp flora recognized from spore and pollen assemblages (e.g., Polypodiidites usmensis, Verrucatosporites, Cyrtostachys), as well as the abundance of macrophytes and woody debris, indicate overwhelming hot and humid swamp conditions, with lake development restricted to relatively small areas. The distribution of alkanes and their compound-specific carbon isotope compositions are used to further show climatic variations affecting the lake/swamp ecology during the deposition of the synrift sequence.

  7. The Itataia phosphate-uranium deposit (Ceará, Brazil) new petrographic, geochemistry and isotope studies

    NASA Astrophysics Data System (ADS)

    Veríssimo, César Ulisses Vieira; Santos, Roberto Ventura; Parente, Clóvis Vaz; Oliveira, Claudinei Gouveia de; Cavalcanti, José Adilson Dias; Nogueira Neto, José de Araújo

    2016-10-01

    The Itataia phosphate-uranium deposit is located in Santa Quitéria, in central Ceará State, northeastern Brazil. Mineralization has occurred in different stages and involves quartz leaching (episyenitization), brecciation and microcrystalline phase formation of concretionary apatite. The last constitutes the main mineral of Itatiaia uranium ore, namely collophane. Collophanite ore occurs in massive bodies, lenses, breccia zones, veins or episyenite in marble layers, calc-silicate rocks and gneisses of the Itataia Group. There are two accepted theories on the origin of the earliest mineralization phase of Itataia ore: syngenetic (primary) - where the ore is derived from a continental source and then deposited in marine and coastal environments; and epigenetic (secondary) - whereby the fluids are of magmatic, metamorphic and meteoric origin. The characterization of pre- or post-deformational mineralization is controversial, since the features of the ore are interpreted as deformation. This investigation conducted isotopic studies and chemical analyses of minerals in marbles and calc-silicate rocks of the Alcantil and Barrigas Formations (Itataia Group), as well as petrographic and structural studies. Analysis of the thin sections shows at least three phosphate mineral phases associated with uranium mineralizaton: (1) A prismatic fluorapatite phase associated with chess-board albite, arfvedsonite and ferro-eckermannite; (2) a second fluorapatite phase with fibrous radial or colloform habits that replaces calcium carbonate in marble, especially along fractures, with minerals such as quartz, chlorite and zeolite also identified in calc-silicate rocks; and (3) an younger phosphate phase of botryoidal apatite (fluorapatite and hydroxyapatite) related with clay minerals and probably others calcium and aluminum phosphates. Detailed isotopic analysis carried out perpendicularly to the mineralized levels and veins in the marble revealed significant variation in isotopic

  8. Major, trace element and stable isotope geochemistry of synorogenic breccia bodies, Ellsworth Mountains, Antarctica

    USGS Publications Warehouse

    Craddock, J.P.; McGillion, M.S.; Webers, G.F.

    2007-01-01

    Cambrian carbonates in the Heritage Range of the Ellsworth Mountains, West Antarctica host a series of carbonate-rich breccia bodies that formed contemporaneously with the Permian Gondwanide orogen. The breccia bodies had a three-stage genesis, with the older breccias containing Cambrian limestone (and marble) clasts supported by calcite, whereas the younger breccias are nearly clast-free and composed entirely of matrix calcite. Breccia clasts, calcite matrix and detrital matrix samples were analyzed using x-ray fluorescence (major and trace elements), x-ray diffraction, and stable isotopes (C, O) and suggest that the breccias formed as part of a closed geochemical system, at considerable depth, within the Cambrian limestone host as the Ellsworth Mountains deformed into a fold-and-thrust belt along the margin of Gondwana

  9. The geochemistry of uranium and thorium isotopes in the Western Desert of Egypt

    SciTech Connect

    Dabous, A.A.

    1994-11-01

    The concentrations of {sup 238}U, {sup 234}U, {sup 232}Th, and {sup 228}Th have been measured in the groundwaters of the Bahariya and Farafra oases of the Western Desert of Egypt. These waters are characterized by normal amounts of U, but unusually high concentrations of Th. The pattern of variation of the parent isotopes, {sup 238}U and {sup 232}Th, as well as the daughter isotopes, {sup 234}U, {sup 230}Th, and {sup 228}Th, is systematic within and between the two oases. From the unusually consistent distribution of the {sup 234}U/{sup 238}U activity ratios one can conclude that the samples from both oases are representative of a two-component mixing system. One component, characterized by low U content and a high {sup 234}U/{sup 238}U activity ratio, is typical of deep artesian systems and probably represents flowthrough water derived from the Nubian highlands to the south. The second component is characterized by a greater U concentration and a low activity ratio. This signature is hypothesized as being derived by leaching of downward infiltrating water during pluvial times. The source of the U may be the uraniferous phosphate strata that overly the sandstone aquifer in both oasis areas. Higher Th values are associated with the artesian flow component of the mixing system and suggests that Th-bearing minerals may be abundant in the Nubian sandstone aquifer. The distribution of {sup 230}Th and {sup 228}Th in the water samples supports this interpretation.

  10. Radium isotope geochemistry of thermal waters, Yellowstone National Park, Wyoming, USA

    NASA Astrophysics Data System (ADS)

    Sturchio, N. C.; Bohlke, J. K.; Markun, F. J.

    1993-03-01

    Radium isotope activities ( 226Ra, 228Ra, and 224Ra), chemical compositions, and sulfur isotope ratios in sulfate were determined for water samples from thermal areas in Yellowstone National Park, Wyoming. Activities of 226Ra in these waters range from <0.2 to 37.9 dpm/kg. Activity ratios of 228Ra /226Ra range from 0.26 to 14.2, and those of 224Ra /228Ra range from 0.73 to 3.1. Radium concentrations are inversely correlated with aquifer equilibration temperatures (estimated from dissolved silica concentrations), while[ Ra/Ba] aq and 228Ra /226Ra activity ratios depend upon U/Ba and Th/U ratios in aquifer rocks. Major controls on Ra concentration in Yellowstone thermal waters are inferred to be (1) barite saturation (at Morris Geyser Basin, Mammoth Hot Springs, and other northern areas) and (2) zeolitewater ion exchange (at Upper Geyser Basin). The data are consistent with a model in which (1) radium and barium are supplied to water by bulk dissolution of aquifer rock, and (2) chemical equilibration of water with rock is rapid relative to the 1602 year half-life of 226Ra. The 228Ra /226Ra activity ratios of the waters may in some cases reflect surface enrichments of 232Th and/or may indicate that α-recoil input of 228Ra is rapid relative to water-rock chemical equilibration. Activity ratios of 224Ra /228Ra indicate a nearly ubiquitous 224Ra excess that generally increases with decreasing pH. Near-surface (≤100 m) thermal water flow velocities at Mammoth Hot Springs are estimated from 224Ra /228Ra variation to be ≥ 1 m h -1.

  11. New Results on the Palaeobiology of Bears on the Swabian Alb (Chronology, Isotopic Geochemistry and Palaeogenetics)

    NASA Astrophysics Data System (ADS)

    Muenzel, Susanne

    2010-05-01

    Paleogenetic investigations at three geographically close caves in the Ach Valley near Blaubeuren have revealed two different cave bear haplogroups. These two haplogroups correspond to Ursus spelaeus (haplogroup 1) and Ursus ingressus (haplogroup 4) (Rabeder & Hofreiter 2004, Die Höhle 55, 58-77). This genetic variability was first attested for Geißenklösterle and Sirgenstein cave, but the new genetic data attest them also for Hohle Fels. In all three caves Ursus ingressus replaced Ursus spelaeus around 28 000 B.P. The carbon and nitrogen isotopes of the two genetic types do not vary significantly, meaning that there is no dietary difference between them and Ursus spelaeus were in dietary competition with Ursus ingressus in the Ach valley. The radiocarbon dates suggested a sudden replacement (Hofreiter et al. 2007, Current Biology 17(4): R1-R3), which must have been accompanied by local extinction of the older cave bear, according to the dietary competition with the younger bear. The possible reasons for this replacement are not clear yet. Climatic changes are unlikely, since the faunal composition remains the same and the environmental data do not differ significantly. But we cannot exclude human impact on the cave bear population, since a cave bear vertebra with an embedded fragment of a flint projectile was recovered in the Gravettian layer AH IIcf dated to 27 830+150-140 B.P. and gives indisputable proof of the hunting of cave bears. Numerous cut marks proof an ongoing exploitation of this species. In this context, new radiocarbon dates and isotopic results on cave bears and coeval brown bears will help us to refine the possible scenarios of this complex evolutionary and ecological process. These results will be used to test hypotheses of competitive exclusion between the different bear species. This study will exemplify how combining evidence from different approaches can provide invaluable clues about palaeobiology of late Pleistocene large mammals such as

  12. Calcite genesis in the Upper Freeport coal bed as indicated by stable isotope geochemistry

    SciTech Connect

    Dulong, F.T.; Spiker, E.C.; Cecil, C.B.; Stanton, R.W.

    1985-01-01

    The grinding and sizing in float-sink testing of the Upper Freeport coal bed physically separates calcite of different origins. The different origins are distinguished by different isotopic compositions. The isotopic compositions of calcite indicates at least two, possibly three, stages of calcite formation in the Upper Freeport coal bed. Calcite samples obtained from cleat, and isolated from 8x100 mesh-1.8 specific gravity sink fraction and -100 mesh size fraction, are enriched in /sup 13/C. The dispersion in /sup 18/O values for all three sample types, as measured by the standard deviation, is 2.7 per mil relative to SMOW, which may indicate similar temperature of formation. In contrast, calcite from the 1.275 specific gravity float fraction is depleted in /sup 13/C (mean = -4.6 per mil), indicative of CO/sub 2/ generated from the oxidation of organic matter. The standard deviation of /sup 18/O values for these samples is 9.2 per mil, probably indicating variation in the temperature of formation. Limestone samples associated with the Upper Freeport coal bed are slightly depleted in /sup 13/C (mean = -3.1 per mil). Genesis of calcite in the coal apparently resulted from biotic, as well as, thermogenic processes. A second stage of calcite formation, resulting from fermentation and methanogenesis is in cleat, and in the 8x100 mesh-1.8 specific gravity sink and -100 mesh size fractions. Part of the calcite in the 1.275 specific gravity float fraction may have formed from thermally generated CO/sub 2/ released during coalification.

  13. Boron isotope geochemistry of the oceanic crust from DSDP/ODP Hole 504B

    SciTech Connect

    Ishikawa, Tsuyoshi; Nakamura, Eizo )

    1992-04-01

    Boron contents and boron isotopic compositions were determined for the uppermost 1.3 km section of typical 6.2 Ma oceanic crust from DSDP/ODP Hole 504B, Costa Rica Rift, Galapagos Spreading Center. Both the boron content and the {delta}{sup 11}B value in the oceanic crust are controlled by two types of alteration: (1) low-temperature alteration (0 to 60C; Zones 1 and 2) and (2) high-temperature hydrothermal alteration (200 to 400C; Zones 3 and 4). Basalts subjected to the low-temperature alteration are characterized by their relatively high boron contents (0.69 to 19.3 ppm) and high {delta}{sup 11}B values (+2.2 to +10.6{per thousand}), indicating uptake of boron into secondary phases in equilibrium with seawater or evolved seawater. Hydrothermally altered basalts contain less abundant boron (0.17 to 0.52 ppm) and relatively constant {delta}{sup 11}B values ({minus}0.1 to +1.0{per thousand}). Although basalts from the upper part of these hydrothermal zones (< 1,300 mbsf) show equilibrated boron content and {delta}{sup 11}B value with aqueous fluid, effective leaching of boron from basalt is predominant in the lower part (> 1,300 mbsf). Original boron content and {delta}{sup 11}B value of the Hole 504B MORB were 0.35 ppm and +0.2{per thousand}, respectively. The present data provide fundamental information in understanding of the distribution of boron and boron isotopes in the oceanic crust.

  14. Radium isotope geochemistry of thermal waters, Yellowstone National Park, Wyoming, USA

    SciTech Connect

    Sturchio, N.C.; Bohlke, J.K.; Markun, F.J. )

    1993-03-01

    Radium isotope activities ([sup 226]Ra, [sup 228]Ra, and [sup 224]Ra), chemical compositions, and sulfur isotope ratios in sulfate were determined for water samples from thermal areas in Yellowstone National Park, Wyoming. Activities of [sup 226]Ra in these waters range from <0.2 to 37.9 dpm/kg. Activity ratios of [sup 228]Ra/[sup 226]Ra range from 0.26 to 14.2, and those of [sup 224]Ra/[sup 228]Ra range from 0.73 to 3.1. Radium concentrations are inversely correlated with aquifer equilibration temperatures (estimated from dissolved silica concentrations), while [Ra/Ba][sub aq] and [sup 228]Ra/[sup 226]Ra activity ratios depend upon U/Ba and Th/U ratios in aquifer rocks. Major controls on Ra concentration in Yellowstone thermal waters are inferred to be (1) barite saturation (at Norris Geyser Basin, Mammoth Hot Springs, and other northern areas) and (2) zeolite-water ion exchange (at Upper Geyser Basin). The data are consistent with a model in which (1) radium and barium are supplied to water by bulk dissolution of aquifer rock, and (2) chemical equilibration of water with rock is rapid relative to the 1602 year half-life of [sup 226]Ra. The [sup 228]Ra/[sup 226]Ra activity ratios of the waters may in some cases reflect surface enrichments of [sup 232]Th and/or may indicate that [alpha]-recoil input of [sup 228]Ra is rapid relative to water-rock chemical equilibration. Activity ratios of [sup 224]Ra/[sup 228]Ra indicate a nearly ubiquitous [sup 224]Ra excess that generally increases with decreasing pH. Near-surface ([le]100 m) thermal water flow velocities at Mammoth Hot Springs are estimated from [sup 224]Ra/[sup 228]Ra variation to be [ge]1 m h[sup [minus]1]. 73 refs., 4 figs., 4 tabs.

  15. Mesoproterozoic arc magmatism in SE India: Petrology, zircon U-Pb geochronology and Hf isotopes of the Bopudi felsic suite from Eastern Ghats Belt

    NASA Astrophysics Data System (ADS)

    Dharma Rao, C. V.; Santosh, M.; Zhang, Zeming; Tsunogae, Toshiaki

    2013-10-01

    The southern segment of the Eastern Ghats Mobile Belt (EGMB) in India was an active convergent margin during Mesoproterozoic, prior to the final collision in Neoproterozoic during the assembly of the Rodinia supercontinent. Here we present mineralogical, whole-rock geochemical, zircon U-Pb and Hf isotopic data from a granitoid suite in the Bopudi region in the EGGB. The granitoid complex comprises quartz monzodiorite with small stocks of rapakivi granites. The monzodiorite, locally porphyritic, contains K-feldspar megacrysts, plagioclase, quartz, biotite and ortho-amphibole. The presence of mantled ovoid megacrysts of alkali feldspar embaying early-formed quartz, and the presence of two generations of the phenocrystic phases in the rapakivi granites indicate features typical of rapakivi granites. The K-feldspar phenocrysts in the rapakivi granite are mantled by medium-grained aggregates of microcline (Ab7 Or93), which is compositionally equivalent to the rim of Kfs phenocryst and Pl (An23-24 Ab75). The geochemistry of both the granitoids shows arc-like features for REE and trace elements. LA-ICP-MS zircon analyses reveal 207Pb/206Pb ages of 1582 (MSWD = 1.4) for the rapakivi granite 1605 ± 3 Ma (MSWD = 3.9) for the monzodiorite. The zircons from all the granitoid samples show high REE contents, prominent HREE enrichment and a conspicuous negative Eu anomaly, suggesting a common melt source. The zircons from the monzodiorite have a limited variation in initial 176Hf/177Hf ratios of 0.28171-0.28188, with ɛHf(t) values of -2.2 to +2.8. Correspondingly, their two-stage Hf isotope model ages (TDM2) ranging from 2.15 to 2.47 Ga probably suggest a mixed source for the magma involving melting of the Paleoproterozoic basement and injection of subduction-related juvenile magmas. The prominent Mesoproterozoic ages of these granitoids suggest subduction-related arc magmatism in a convergent margin setting associated with the amalgamation of the Columbia-derived fragments

  16. Variations in Pb concentrations and Pb-isotope ratios in soils collected along an east-west transect across the United States

    NASA Astrophysics Data System (ADS)

    Smith, David; Woodruff, Laurel; Reimann, Clemens; Flem, Belinda

    2014-05-01

    Soil A-horizon and C-horizon samples were collected along a 4000 km long transect cutting the USA from the west to the east coast. For purposes of site selection, the transect was divided into approximately 40-km segments. For each segment, a 1-km2 target area was selected at random. Soil A- and C-horizon samples were collected at a site within each target area that was most representative of the surrounding landscape. The samples were air-dried at ambient temperature, disaggregated, and sieved through a 2-mm stainless steel screen. The <2-mm material was crushed to <150 µm in a ceramic mill prior to chemical analysis. Lead was analyzed in all the A- and C-horizon samples by inductively coupled plasma-mass spectrometry following a 4-acid digestion. The complete dataset can be found in Smith et al., 2005. Pb-isotope ratio measurements were carried out on 159 soil A-horizon and 137 soil C-horizon samples on an inductively coupled sector field plasma mass spectrometer (SF-ICP-MS; ELEMENT 1, Finnigan MAT) in the laboratory of the Geological Survey of Norway (NGU), following a 7 N HNO3 digestion. Lead concentrations along the transect show (1) generally higher values in the soil A-horizon than the C-horizon (median 21 vs. 16.5 mg/kg), (2) an increase in the median value of the soil A-horizon for the central to eastern U.S. (Missouri to Maryland) when compared to the western U.S. (California to Kansas) (median 26 vs. 20 mg/kg) and (3) a higher A/C ratio for the central to eastern US (1.35 vs. 1.14). Lead isotopes show a distinct trend across the U.S., with the highest 206Pb/207Pb ratios occurring in the centre (Missouri, median A-horizon: 1.245; C-horizon: 1.251) and the lowest at both coasts (e.g. California, median A-horizon: 1.195; C-horizon:1.216). The soil C-horizon samples show generally higher 206Pb/207Pb ratios than the A-horizon (median C-horizon: 1.224; A-horizon: 1.219). The 206Pb/207Pb isotope ratios in the soil A horizon show a correlation with the total

  17. Ten years of elemental atmospheric metal fallout and Pb isotopic composition monitoring using lichens in north-eastern France

    NASA Astrophysics Data System (ADS)

    Cloquet, Christophe; Estrade, Nicolas

    2016-04-01

    We report on the chemical and Pb isotopic compositions of epiphytic lichens collected from small tree branches in the urban area of the city of Metz (NE France). Lichens were collected in five different years between 2001 and 2009. The data are first compared year to year in order to document any temporal changes and trends in metal atmospheric fallout. The area studied was then subdivided into different zones on the basis of land-use (urban, suburban, rural and industrial) in order to determine potential spatial gradients. The median concentrations and enrichment factors (EF, normalized to Al) of Pb and other metals (Cu, Zn, Cd, Ni, Cr, Hg, Fe) in lichens from the urban, suburban, and rural zones show no systematic variation between 2001 and 2008. However, the metal EFs show spatial variation and are generally highest in the urban area and lowest in the rural area. Lichens within the industrial zone (collected in 2009), which is dominated by steel industries, are richest in Al, Fe, Cr, Pb, and Zn. Although the Al concentration is high in these lichens, the EFs for the cited metals are several times higher than those measured in lichens from the other three zones. No significant differences were noted for Hg, Cd, Cu and or Ni. Lead isotopic compositions measured in lichens may be highly variable from year to year and from zone to zone. The variation is primarily interpreted to result from mixing between: (i) Pb added to gasoline (and recycled through re-emission of road dust in the atmosphere); (ii) regional industrial Pb from long-range transportation and/or mixed with urban Pb; and (iii) local industrial Pb. The median isotopic compositions of individual zones are distinct, suggesting variable mixing of these three sources. The annual variations show that 2001 was most affected by gasoline Pb, whereas 2003 and 2006 were more affected by the local steel industry.

  18. U-Pb ages and Sr, Pb and Nd isotope data for gneisses near the Kolar Schist Belt: Evidence for the juxtaposition of discrete Archean terranes

    NASA Technical Reports Server (NTRS)

    Krogstad, E. J.; Hanson, G. N.; Rajamani, V.

    1988-01-01

    Uranium-lead ages and Sr, Pb, and Nd isotopic data for gneisses near the Kolar Schist Belt and their interpretation as evidence for the juxtaposition of discrete Archean terranes were presented. The granodioritic Kambha gneiss east of the schist belt has a zircon age of 2532 + or - 3 Ma and mantle-like initial Sr, Pb, and Nd isotopic ratios. Therefore these gneisses are thought to represent new crust added to the craton in the latest Archean. By contrast, more mafic Dod gneisses and leucocratic Dosa gneisses west of the schist belt (2632 + or - 7 and 2610 + or - 10 Ma) show evidence for contamination of their magmatic precursors (LREE-enriched mantle-derived for the Dod gneisses) by older (greater than 3.2 Ga) continental crust. Fragments of this older crust may be present as granitic and tonalitic inclusions in the 2.6-Ga gneisses and in shear zones. The antiquity of these fragments is supported by their Nd, Sr, and Pb isotopic compositions and by 2.8 to greater than 3.2 Ga zircon cores.

  19. {beta}-decay in neutron-deficient Hg, Pb, and Po isotopes

    SciTech Connect

    Moreno, O.; Sarriguren, P.; Alvarez-Rodriguez, R.; Guerra, E. Moya de

    2006-05-15

    The effect of nuclear deformation on the energy distributions of the Gamow-Teller strength is studied in neutron-deficient Hg, Pb, and Po even isotopes. The theoretical framework is based on a self-consistent deformed Skyrme Hartree-Fock mean field with pairing correlations between like nucleons in BCS approximation and residual spin-isospin interactions treated in the proton-neutron quasiparticle random-phase approximation. After a systematic study of the Gamow-Teller strength distributions in the low-excitation-energy region, relevant for {beta}{sup +} decay, we have identified the best candidates to look for deformation signatures in their {beta}{sup +}-decay patterns. {beta}{sup +} half-lives and total Gamow-Teller strengths B(GT{sup {+-}}) are analyzed as well.

  20. Tracing diatom utilisation, and its fate, in Lake Baikal, Siberia: the application of silicon isotope geochemistry

    NASA Astrophysics Data System (ADS)

    Panizzo, V. N.; Swann, G. E. A.; Mackay, A. W.; Roberts, S.; Vologina, E.; Sturm, M.; Horstwood, M. S.

    2014-12-01

    The global biogeochemical cycling of silicon (Si) is intrinsically linked to the fate of CO2 in the earth's atmosphere. To date, most research has focused on the oceanic cycling of Si over glacial/interglacial timescales although, the importance of continental Si cycling (via abiotic and biotic processes) is now being addressed. Especially as the significant potential for Si sequestration in continental lake systems has been recently highlighted [1]. We present the first large-scale silicon isotope (δ30SiDSi) profiles of Lake Baikal's water column, where a comparison between both pre- and post-diatom growing season δ30SiDSi signatures are made. Samples were collected along a water profile (surface to 180 m) at numerous sites across Lake Baikal, with deep-water endmembers at 400 m and c. 1,500 m. All isotopic analyses were conducted on a Neptune + Multi-Collector ICP-MS at NIGL, UK, using wet plasma mode with Mg doping of samples and standard-sample-standard bracketing. Analytical reproducibility is 0.12‰ (2σ) and blanks are <1% of signal intensity. DSi concentrations of March water surface samples (South Basin only) range between c. 0.74 and 1.23 ppm while those collected in August are all <0.70 ppm, following seasonal biological utilisation. In turn Chlorophyll a values from South Basin profiles in August are greater (between c. 1.46 to 3.18 mg l-1) than March surface values (<0.70 mg l-1). Indeed, March δ30SiDSi surface values range between c. +2.16 and +2.45‰ while summer surface values range between c. +2.20 and +2.84‰, reflecting residual pool depletion after summer biological utilisation. δ30SiDSi values are >1‰ more enriched than dominant lake water inflows again reflecting diatom Si uptake. Annual open sediment traps deployed down Lake Baikal's water column yield δ30Sidiatom signatures of +1.25‰, which suggests that down-column diatom dissolution is minimal. Applying the diatom fractionation factor of -1.1‰[2] and adopting a closed system

  1. The origin of the Maozu carbonate-hosted Pb-Zn deposit, southwest China: Constrained by C-O-S-Pb isotopic compositions and Sm-Nd isotopic age

    NASA Astrophysics Data System (ADS)

    Zhou, Jiaxi; Huang, Zhilong; Yan, Zaifei

    2013-09-01

    The Maozu Pb-Zn deposit, located on the western margin of the Yangtze Block, southwest China, is a typical carbonate-hosted deposit in the Sichuan-Yunnan-Guizhou Pb-Zn metallogenic province with Pb + Zn reserves of about 2.0 million tonnes grading 4.15 wt.% Pb and 7.25 wt.% Zn. Its ore bodies are hosted in Sinian (635-541 Ma) Dengying Formation dolostone and show stratiform, vein and irregular textures. Ores are composed of sphalerite, galena, pyrite, calcite, dolomite, quartz and fluorite with massive, banded, disseminated and veined structures. The C-O-Sm-Nd isotopic compositions of hydrothermal calcites and S-Pb isotopic compositions of sulfides were analyzed to constrain the origin of the Maozu deposit. δ13CPDB and δ18OSMOW values of hydrothermal calcites range from -3.7‰ to -2.0‰ and +13.8‰ to +17.5‰, respectively, and plot near the marine carbonate rocks field in a plot of δ13CPDB vs. δ18OSMOW, with a negative correlation. It suggests that CO2 in the hydrothermal fluids was mainly originated from marine carbonate rocks, with limited influence from sedimentary organic matter. δ34SCDT values of sulfides range from +9.9‰ to +19.2‰, similar to that of Cambrian to Triassic seawater sulfate (+15‰ to +35‰) and evaporate (+15‰ to +30‰) in the Cambrian to Triassic sedimentary strata. It suggests that reduced sulfur was derived from evaporate in sedimentary strata by thermo chemical sulfate reduction. Sulfides have low radiogenic Pb isotope compositions (206Pb/204Pb = 18.129-18.375, 207Pb/204Pb = 15.640-15.686 and 208Pb/204Pb = 38.220-38.577) that plot in the field between upper crust and the orogenic belt evolution curve in the plot of 207Pb/204Pb vs. 206Pb/204Pb, and similar to that of age corrected Proterozoic basement rocks (Dongchuan and Kunyang Groups). This indicates that ore-forming metals were mainly derived from basement rocks. Hydrothermal calcite yields a Sm-Nd isotopic age of 196 ± 13 Ma, possibly reflecting the timing of Pb

  2. An alternative model for within plate basalts generation suggested by their major elements, trace elements and Pb-Sr-Nd isotope compositions

    NASA Astrophysics Data System (ADS)

    Mashima, H.

    2003-12-01

    Based on geochemistry, the recent favor model for within-plate basalts (WPB) is plumes with eclogite originally formed by inversion of basaltic oceanic crust into eclogite in subduction zones (e.g. Hauri, 1996). Melting experiments of basalt/peridotie hybrids (Kogiso and Takahashi, 1998), however, have demonstrated that the hybrid source model could not explain major element features of WPB, such as FeO* enrichment and Al2O3 depletion compared with MORB. Melting experiments of peridotites and basalt/peridotite hybrids indicate that the sources of WPB are peridotites abnormally enriched in FeO*. Such Fe-rich sources could not be formed by extraction of basalt melt from typical peridotite or mixing of basalt and typical peridotite. A potential candidate for the abnormally Fe-rich source is Archean peridotitic komatiite (APK) which is enriched in FeO* compared with typical peridotite. Attractive features of the recycled APK melting model are as follows: 1) It explains why within-plate basalts are FeO*-rich and Al2O3-poor relative to MORB because of large proportion of cpx in APK. 2) Moderate partial melting of APK forms LREE-enriched partial melts because of selective fusion of cpx. 3) It explains near bulk earth Nd isotope compositions because of relatively flat REE patterns of APK. 4) Archean age of APK is consistent with Pb isotope ofWPB suggesting their sources have Archean age. 5) Compositional spectrum of Archean komatiite suites ranging from peridotitic komatiite to basalts explains that of WPB from silica-under saturated basalt to silica-oversaturated andesite.

  3. Petrogenesis of Sveconorwegian magmatism in southwest Norway; constraints from zircon U-Pb-Hf-O and whole-rock geochemistry

    NASA Astrophysics Data System (ADS)

    Roberts, Nick M. W.; Slagstad, Trond; Parrish, Randall R.; Norry, Michael J.; Marker, Mogens; Horstwood, Matthew S. A.; Røhr, Torkil

    2013-04-01

    The Sveconorwegian orogen is traditionally interpreted as a Himalayan-scale continental collision, and the eastward continuation of the Grenville Province of Laurentia; however, it has recently been proposed that it represents an accretionary orogen without full-scale continental collision (Slagstad et al., in press). We suggest that magmatism is one of the key constraints to differentiate between different types of orogens; thus, detailed investigation of the timing and petrogenesis of the magmatic record is a requirement for better understanding of the Sveconorwegian orogen as a whole. Here, we present new U-Pb geochronology, zircon Hf-O isotope, and whole-rock geochemical data to constrain the petrogenesis of the early -Sveconorwegian Sirdal Magmatic Belt (SMB). The SMB is a batholithic-scale complex of intrusions that intrudes into most of the Rogaland-Hardangervidda Block in southwest Norway. Current age constraints put emplacement between ~1050 to 1020 Ma. New ages from the Suldal region indicate that the onset of SMB magmatism can be put back to 1070 Ma, which is some 30-50 Myrs prior to high-grade metamorphism. Average initial ɛHf signatures range from ~0 to 4; these overlap with later post-Sveconorwegian granites and with early-/pre-Sveconorwegian ferroan (A-type) granites. Average δ18O signatures range from ~5.7 to 8.7, except for one anomalous granite at ~11.6. The Hf-O signatures are compatible with a mixed mantle-crustal source. Crustal sources may include ~1500 Ma Telemarkian or ~1200 Ma juvenile crust. Hf-O bulk-mixing modelling using a 1500 Ma crustal source indicates >50 % mantle input. Although much further mapping and geochronological work is required, granitic magmatism appears to have persisted throughout much of the ~1100 to 900 Ma period that spans the Sveconorwegian orogen. This magmatism is consistently ferroan (i.e. dry); however, the SMB marks a clear transition to magnesian (i.e. wet) magmatism, with a return to ferroan magmatism at

  4. Excitation Energies of Superdeformed States in {sup 196}Pb: Towards a Systematic Study of the Second Well in Pb Isotopes

    SciTech Connect

    Wilson, A.N.; Singh, A.K.; Huebel, H.; Rossbach, D.; Schonwasser, G.; Davidson, P.M.; Dracoulis, G.D.; Lane, G.J.; Goergen, A.; Buforn, N.; Redon, N.

    2005-10-28

    The excitation energy of the lowest-energy superdeformed band in {sup 196}Pb is established using the techniques of time-correlated {gamma}-ray spectroscopy. Together with previous measurements on {sup 192}Pb and {sup 194}Pb, this result allows superdeformed excitation energies, binding energies, and two-proton and two-neutron separation energies to be studied systematically, providing stringent tests for current nuclear models. The results are examined for evidence of a 'superdeformed shell gap'.

  5. Excitation energies of superdeformed States in 196Pb: towards a systematic study of the second well in Pb isotopes.

    PubMed

    Wilson, A N; Singh, A K; Hübel, H; Davidson, P M; Görgen, A; Rossbach, D; Korichi, A; Astier, A; Azaiez, F; Bazzacco, D; Bourgeois, C; Buforn, N; Byrne, A P; Dracoulis, G D; Hannachi, F; Hauschild, K; Korten, W; Kröll, T; Lane, G J; Lopez-Martens, A; Redon, N; Reiter, P; Rossi-Alvarez, C; Schonwasser, G; Stezowski, O; Thirolf, P G

    2005-10-28

    The excitation energy of the lowest-energy superdeformed band in 196Pb is established using the techniques of time-correlated gamma-ray spectroscopy. Together with previous measurements on 192Pb and 194Pb, this result allows superdeformed excitation energies, binding energies, and two-proton and two-neutron separation energies to be studied systematically, providing stringent tests for current nuclear models. The results are examined for evidence of a "superdeformed shell gap."

  6. The changing nature of the 206Pb/207Pb isotopic ratio of lead in rainwater, atmospheric particulates, pine needles and leaded petrol in Scotland, 1982-1998.

    PubMed

    Farmer, J G; Eades, L J; Graham, M C; Bacon, J R

    2000-02-01

    The inductively coupled plasma-mass spectrometry (ICP-MS)-determined 206Pb/207Pb ratio of 145 samples of rainwater collected at 25 locations around Scotland during December 1997 and January 1998 and at three longterm monitoring stations in the northeast, central belt and southeast of the country from November 1997 to December 1998 averaged 1.144+/-0.017 (1 s). This represents a significant increase from the mean value of 1.120+/-0.016 recorded for the long-term sites in 1989 1991, only partly attributable to a concomitant increase in the 206Pb/207Pb ratio of leaded petrol from 1.075+/-0.013 to 1.088+/-0.007. The rainwater 206Pb/207Pb data for the late 1990s also contrast markedly with the lower 206Pb/207Pb ratios found for pine needle and atmospheric particulate samples from Scotland (e.g. Glasgow: 1.085+/-0.012 in 1985-1986, 1.099+/-0.007 in 1991-1992), England and Western Europe in this study for the period 1982-1992 when emissions of lead to the atmosphere from petrol-engined vehicles in the UK were approximately 2-9 times higher. The observed change in the lead isotopic signature of rainwater predominantly reflects the impact of measures, such as the introduction and growing uptake of unleaded petrol, to reduce car exhaust emissions of lead to the atmosphere in the UK. Based on the rainwater data, source apportionment calculations suggest a general decline in the contribution of leaded petrol to atmospheric lead in Scotland from 53-61% in 1989-1991 to 32-45% in 1997-1998, with a corresponding decline in the urban environment from 84-86% to 48-58%.

  7. Strontium isotope geochemistry of soil and playa deposits near Yucca Mountain, Nevada

    SciTech Connect

    Marshall, B.D.; Mahan, S.A.

    1994-12-31

    The isotopic composition of strontium contained in the carbonate fractions of soils provides an excellent tracer which can be used to test models for their origin. This paper reports data on surface coatings and cements, eolian sediments, playas and alluvial fan soils which help to constrain a model for formation of the extensive calcretes and fault infilling in the Yucca Mountain region. The playas contain carbonate with a wide range of strontium compositions; further work will be required to fully understand their possible contributions to the pedogenic carbonate system. Soils from an alluvial fan to the west of Yucca Mountain show that only small amounts of strontium are derived from weathering of silicate detritus. However, calcretes from a fan draining a carbonate terrane have strontium compositions dominated locally by the limestone strontium component. Although much evidence points to an eolian source for at least some of the strontium in the pedogenic carbonates near Yucca Mountain, an additional component or past variation of strontium composition in the eolian source is required to model the pedogenic carbonate system.

  8. Carbon isotope geochemistry of hydrocarbons in the Cerro Prieto geothermal field, Baja California Norte, Mexico

    USGS Publications Warehouse

    Des Marais, D.J.; Stallard, M.L.; Nehring, N.L.; Truesdell, A.H.

    1988-01-01

    Hydrocarbon abundances and stable-isotopic compositions were measured in wells M5, M26, M35 and M102, which represent a range of depths (1270-2000 m) and temperatures (275-330??C) in the field. In order to simulate the production of the geothermal hydrocarbons, gases were collected from the pyrolysis of lignite in the laboratory. This lignite was obtained from a well which sampled rock strata which are identical to those occurring in the field, but which have experienced much lower subsurface temperatures. In both the well and the laboratory observations, high-temperature environments favored higher relative concentrations of methane, ethane and benzene and generally higher ??13C-values in the individual hydrocarbons. The best correlation between the laboratory and well data is obtained when laboratory-produced gases from experiments conducted at lower (400??C) and higher (600??C) temperatures are mixed. This improved correlation suggests that the wells are sampling hydrocarbons produced from a spectrum of depths and temperatures in the sediments. ?? 1988.

  9. Carbon isotope geochemistry of hydrocarbons in the Cerro Prieto geothermal field, Baja California Norte, Mexico

    NASA Technical Reports Server (NTRS)

    Des Marais, D. J.; Stallard, M. L.; Nehring, N. L.; Truesdell, A. H.

    1988-01-01

    Hydrocarbon abundances and stable-isotopic compositions were measured in wells M5, M26, M35 and M102, which represent a range of depths (1270-2000 m) and temperatures (275-330 degrees C) in the field. In order to simulate the production of the geothermal hydrocarbons, gases were collected from the pyrolysis of lignite in the laboratory. This lignite was obtained from a well which sampled rock strata which are identical to those occurring in the field, but which have experienced much lower subsurface temperatures. In both the well and the laboratory observations, high-temperature environments favored higher relative concentrations of methane, ethane and benzene and generally higher delta 13C-values in the individual hydrocarbons. The best correlation between the laboratory and well data is obtained when laboratory-produced gases from experiments conducted at lower (400 degrees C) and higher (600 degrees C) temperatures are mixed. This improved correlation suggests that the wells are sampling hydrocarbons produced from a spectrum of depths and temperatures in the sediments.

  10. Oxygen isotope geochemistry of the silicic volcanic rocks of the Etendeka-Parana province: Source constraints

    SciTech Connect

    Harris, C.; Milner, S.C.; Armstrong, R.A. ); Whittingham, A.M. )

    1990-11-01

    Oxygen isotope ratios of pyroxene phenocrysts in the silicic volcanic rocks from the Cretaceous Etendeka-Parana flood basalt province (Namibia, South America) are believed to reflect the {delta}{sup 18}O values of the original magmas. The authors recognize a high {delta}{sup 18}O value type ({delta}{sup 18}O pyroxene {approximately} +10{per thousand}) found in the south of both regions, and a low {delta}{sup 18}O value type ({delta}{sup 18}O pyroxene {approximately} +6.5{per thousand}) found in the north. Other differences between thee two rhyolite types include higher concentrations of incompatible elements and lower initial {sup 87}Sr/{sup 86}Sr ratios in the low {delta}{sup 18}O value type. The authors suggest that the regional distribution of rhyolite types reflects differences in source composition, which can best be explained if the sources are lower crustal, Late Proterozoic mobile belt material (high {delta}{sup 18}O) and Archean lower crust (low {delta}{sup 18}O).

  11. Isotope geochemistry and modelling of the multi-aquifer system in the eastern part of Lithuania

    NASA Astrophysics Data System (ADS)

    Mokrik, Robert; Juodkazis, Vytautas; Štuopis, Anicetas; Mažeika, Jonas

    2014-06-01

    A steady-state groundwater flow model of three Quaternary intertill aquifers in the eastern part of Lithuania has been compiled. The distinction of separate modelled layers is based on hydraulic and isotope-hydrochemistry data criteria. 3H data were used to estimate the corrected groundwater age and were coupled with a groundwater-flow-dynamics model of the Quaternary aquifer system along a cross-section flow pathway from the Baltic Upland recharge area in eastern Lithuania towards the discharge area in the lowlands near the city of Kaunas in central Lithuania. The bicarbonate content in groundwater (214-462 mg/l) increases downgradient towards the lowland area. The other major constituents and total dissolved solids (TDS) have a trend analogous to the bicarbonate. The 14C activity of dissolved inorganic carbon (DIC) in the groundwater ranges from 41.4 to 85.7 pMC. With aquifer-system depth, active precipitation of aqueous solution takes place by dissolving minerals of calcite and dolomite and leakage of "old" groundwater from lower aquifers; the process is also traced by lower 14C and 3H activities and by more positive δ18O values in lowland areas.

  12. Dating the Indo-Asia collision in NW Himalaya: constraints from Sr-Nd isotopes and detrital zircon (U-Pb) and Hf isotopes of Paleogene-Neogene rocks in the Katawaz basin, NW Pakistan

    NASA Astrophysics Data System (ADS)

    Zhuang, Guangsheng; Najman, Yani; Millar, Ian; Chauvel, Catherine; Guillot, Stephane; Carter, Andrew

    2015-04-01

    The time of collision between the Indian and Asian plates is key for understanding the convergence history and the impact on climatic systems and marine geochemistry. Despite much active research, the fundamental questions still remain elusive regarding when and where the Indian plate collided with the Asian plate. Especially in the west Himalaya, the questions become more complex due to disputes on the amalgamation history of interoceanic Kohistan-Ladakh arcs (KLA) with Karakoram of the Asian plate and the Indian plate. Here, we present a result of multiple-isotopic geochemistry and geochronology study in the Katawaz Basin in NW Pakistan, a remnant oceanic basin on the western Indian plate which was the repository for the sediments eroded from the west Himalaya ( Qayyum et al., 1996, 1997a, 1997b, 2001; Carter et al., 2010), to evaluate the time and character of collision in this region. In this study, we analyzed 22 bulk mudstone samples for Sr-Nd isotopes and 11 medium-grained sandstones for detrital zircon (U-Pb) geochronology and Hf isotopes. We constructed the Cenozoic chronology in the Katawaz Basin based on our newly collected detrital zircon U-Pb ages and fission track ages. We present the first record of Katawaz chronology that constrained the Khojak Formation to be < 40 Ma to < 22 Ma. The result is consistent with the previous nanofossil study that constrained the upper part of underlying Nisai Formation to be the Middle to Late Eocene. Our current study revealed that the Katawaz sedimentary sequence ranges in age from Eocene to the earliest Miocene. The samples from the Nisai Formation show the 87Sr/86Sr - ɛNd values overlapping those of the end member of the Karakoram of Asian origin, revealing the arrival of Asian detritus on the Indian plate prior to 50 Ma. There are two parallel lines of evidence supporting this conclusion: (1) young zircon grains (< 120 Ma), characterizing the KLA and Karakoram, persistently exist throughout the whole sedimentary

  13. A Coast Mountains provenance for the Valdez and Orca groups, southern Alaska, based on Nd, Sr, and Pb isotopic evidence

    USGS Publications Warehouse

    Farmer, G.L.; Ayuso, R.; Plafker, G.

    1993-01-01

    Nd, Sr, and Pb isotopic data were obtained for fourteen fine- to coarse-grained samples of accreted flysch of the Late Cretaceous and early Tertiary Valdez and Orca Groups in southern Alaska to determine the flysch provenance. Argillites and greywackes from the Orca Group, as well as compositionally similar but higher metamorphic grade rocks from the Valdez Group, show a restricted range of correlated ??{lunate}Nd ( -0.6 to -3.8) and 87Sr 86Sr (0.7060-0.7080) at the time of sediment deposition ( ??? 50 Ma). Pb isotopic compositions also vary over a narrow range ( 206Pb 204Pb = 19.138-19.395, 207Pb 204Pb = 15.593-15.703, 208Pb 204Pb = 38.677-39.209), and in the Orca Group the samples generally become more radiogenic with decreasing ??{lunate}Nd and increasing 87Sr 86Sr. All samples have similar trace element compositions characterized by moderate light rare earth element enrichments, and low ratios of high field strength elements to large ion lithophile elements. Based on petrographic, geochemical, and isotopic data the sedimentary rocks are interpreted to have been derived largely from a Phanerozoic continental margin arc complex characterized by igneous rocks with ??{lunate}Nd values between 0 and -5. The latter conclusion is supported by the ??{lunate}Nd values of a tonalite clast and a rhyodacite clast in the Orca Group (??{lunate}Nd = -4.9 and -0.9, respectively). However, trondjemitic clasts in the Orca Group have significantly lower ??{lunate}Nd ( ??? -10) and require a derivation of a portion of the flysch from Precambrian crustal sources. The Nd, Sr, and Pb isotopic compositions of both the Valdez and Orca Groups overlap the values determined for intrusive igneous rocks exposed within the northern portion of the Late Cretaceous to early Tertiary Coast Mountains Plutonic Complex in western British Columbia and equivalent rocks in southeastern Alaska. The isotopic data support previous conclusions based on geologic studies which suggest that the flysch was

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

    PubMed

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

    2015-04-01

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

  15. Textures, trace elements, and Pb isotopes of sulfides from the Haopinggou vein deposit, southern North China Craton: implications for discrete Au and Ag-Pb-Zn mineralization

    NASA Astrophysics Data System (ADS)

    Li, Zhan-Ke; Li, Jian-Wei; Cooke, David R.; Danyushevsky, Leonid; Zhang, Lejun; O'Brien, Hugh; Lahaye, Yann; Zhang, Wen; Xu, Hai-Jun

    2016-12-01

    The Haopinggou deposit in the Xiong'ershan district, southern margin of the North China Craton, comprises numerous Au and Ag-Pb-Zn veins hosted in metamorphic rocks of the Late Archean to early Paleoproterozoic Taihua Group. Two stages of mineralization have been recognized: Stage 1 pyrite-quartz veins and Stage 2 Pb-Zn-sulfide veins. Some pyrite-quartz veins are surrounded or cut by Pb-Zn-sulfide veins, others occur as independent veins. Six generations of pyrite have been identified at Haopinggou: Py1 to Py3 in Stage 1 and Py4 to Py6 in Stage 2. Pyrites from Stage 1 are enriched in Au, As, Co, Ni, and Bi, whereas Stage 2 pyrites contain higher Ag, Pb, Zn, Sn, and Sb. Invisible Au mostly occurs as lattice-bound gold in Py2 (up to 92 ppm Au) and Py3 (up to 127 ppm Au) and has a close relationship with As. Native Au grains are also present in Py3 and likely resulted from mobilization and reprecipitation of the invisible Au previously locked in the precursor pyrite. This view is supported by extensive plastic deformation in Stage 1 pyrite as revealed by electron backscatter diffraction analysis. In Stage 2, Ag is mostly present as lattice-bound silver closely associated with Sb in galena (up to 798 ppm Ag). A variety of silver minerals are also present as inclusions within galena or as interstitial grains. These silver minerals were likely formed via Ag-Cu exchange reaction between tetrahedrite and galena or represent exsolution from galena due to a temperature decrease. Pb isotopic compositions differ remarkably between Stage 1 and Stage 2 sulfides, indicating different sources of lead. Pb in Stage 2 Pb-Zn-sulfide veins is consistent with the Haopinggou porphyry close to the veins. The field, textural, compositional, and lead isotopic data led us to conclude that the early gold-bearing pyrite-quartz veins and late silver-bearing Pb-Zn-sulfide veins likely formed from distinct fluid systems related to discrete mineralization events. Our study suggests that Au and Ag-Pb

  16. Applications of the 190Pt-186Os isotope system to geochemistry and cosmochemistry

    USGS Publications Warehouse

    Walker, R.J.; Morgan, J.W.; Beary, E.S.; Smoliar, M.I.; Czamanske, G.K.; Horan, M.F.

    1997-01-01

    Platinum is fractionated from osmium primarily as a consequence of processes involving sulfide and metal crystallization. Consequently, the 190Pt-186Os isotope system (190Pt ??? 186Os + ??) shows promise for dating some types of magmatic sulfide ores and evolved iron meteorites. The first 190Pt-186Os isochrons are presented here for ores from the ca. 251 Ma Noril'sk, Siberia plume, and for group IIAB magmatic iron meteorites. Given the known age of the Noril'sk system, a decay constant for 190Pt is determined to be 1.542 ?? 10-12a-1, with ??1% uncertainty. The isochron generated for the IIAB irons is consistent with this decay constant and the known age of the group. The 186Os/188Os ratios of presumably young, mantle-derived osmiridiums and also the carbonaceous chondrite Allende were measured to high-precision to constrain the composition of the modern upper mantle. These compositions overlap, indicating that the upper mantle is chondritic within the level of resolution now available. Our best estimate for this 186Os/188Os ratio is 0.119834 ?? 2 (2??M). The 190Pt/186Os ratios determined for six enstatite chondrites average 0.001659 ?? 75, which is very similar to published values for carbonaceous chondrites. Using this ratio and the presumed composition of the modern upper mantle and chondrites, a solar system initial 186Os/188Os ratio of 0.119820 is calculated. In comparison to the modern upper mantle composition, the 186Os/188Os ratio of the Noril'sk plume was approximately 0.012% enriched in 186Os. Possible reasons for this heterogeneity include the recycling of Pt-rich crust into the mantle source of the plume and derivation of the osmium from the outer core. Derivation of the osmium from the outer core is our favored model. Copyright ?? 1997 Elsevier Science Ltd.

  17. Annual and seasonal distribution of intertidal foraminifera and stable carbon isotope geochemistry, Bandon Marsh, Oregon, USA

    USGS Publications Warehouse

    Milker, Yvonne; Horton, Benjamin; Vane, Christopher; Engelhart, Simon; Nelson, Alan R.; Witter, Robert C.; Khan, Nicole S.; Bridgeland, William

    2014-01-01

    We investigated the influence of inter-annual and seasonal differences on the distribution of live and dead foraminifera, and the inter-annual variability of stable carbon isotopes (d13C), total organic carbon (TOC) values and carbon to nitrogen (C/N) ratios in bulk sediments from intertidal environments of Bandon Marsh (Oregon, USA). Living and dead foraminiferal species from 10 stations were analyzed over two successive years in the summer (dry) and fall (wet) seasons. There were insignificant inter-annual and seasonal variations in the distribution of live and dead species. But there was a noticeable decrease in calcareous assemblages (Haynesina sp.) between live populations and dead assemblages, indicating that most of the calcareous tests were dissolved after burial; the agglutinated assemblages were comparable between constituents. The live populations and dead assemblages were dominated by Miliammina fusca in the tidal flat and low marsh, Jadammina macrescens, Trochammina inflata and M. fusca in the high marsh, and Trochamminita irregularis and Balticammina pseudomacrescens in the highest marsh to upland. Geochemical analyses (d13C, TOC and C/N of bulk sedimentary organic matter) show no significant influence of inter-annual variations but a significant correlation of d13C values (R = 20.820, p , 0.001), TOC values (R = 0.849, p , 0.001) and C/N ratios (R = 0.885, p , 0.001) to elevation with respect to the tidal frame. Our results suggest that foraminiferal assemblages and d13C and TOC values, as well as C/N ratios, in Bandon Marsh are useful in reconstructing paleosea-levels on the North American Pacific coast.

  18. Isotope geochemistry of hydrothermal alteration in East of Esfahan, Central Iran

    NASA Astrophysics Data System (ADS)

    Taghipour, Sedigheh; Taghipour, Batoul

    2010-05-01

    In the Cenozoic magmatic belt of Central Iran, the Eocene volcanics and pyroclastics from the East of Esfahan underwent extensive hydrothermal alteration. The Eocene volcanics composed mostly of andesite lava and tuffs have been altered. The survey area is laterally zoned from an inner quartz-sericite alteration zone to an outer propylitic zone. Quartz-sericite alteration is predominant (>95%), but smaller zones of alunite-jarosite and silicified zones are present and superimposed onto a quartz-sericite alteration. In the quartz-sericite zone all altered rocks are light grayish to whitish in color and porphyritic with aphanitic groundmass. Concentrations of alunite and jarosite veinlets and stockworks are dispersed irregularly in this zone. Alunite and jarosite occur also as coatings on fractured rocks. All types of alunite occurrences are brick-red, cream, white and buff in colors, while jarosite is brown to rusty in colors. To verify, chemical composition of alunite and jarosite were identified by X-ray diffraction in mineral assemblages. Major alteration zones show inclusions of propylite, quartz sericite, advanced argillic and silicified zones. These alunites are mainly porcelaneous and their compositions show a solid solution between alunite and jarosite. In alteration zones, the mineral assemblage is characterized by alunite-jarosite + quartz + sericite + alkali feldspars + chlorite ± turquoise ± barite ± iron oxides. There are numerous alunite and jarosite occurrences, mainly as veinlets, in parts of the advanced argillic zone. Alunite δ18O and δ D values range from -1.76 to 8.81‰ and from -52.86 to -129.26‰ respectively. Field observations, mineralogical evidence and results from light element stable isotope data (δ18O, δ D and δ34S); indicate that in this area alunitization is supergene in origin.

  19. Paleoenvironment and the oxygen isotope geochemistry of ironstone of the Upper Ordovician Neda Formation, Wisconsin, USA

    SciTech Connect

    Yapp, C.J. )

    1993-05-01

    Geological evidence suggests that the goethite-dominated, oolitic ironstone of the Upper Ordovician Neda Formation in the north central United States was subaerially weathered in the Late Ordovician. The oxygen isotope ratios of the goethites in the [open quotes]hard[close quotes] and [open quotes]soft[close quotes] ores of this deposit are rather uniform with a [delta][sup 18]O value of about [minus]1.0[per thousand]. This [delta][sup 18]O value indicates the presence of meteoric water at the time of goethite formation and supports the idea that the goethites in hard and soft ores were formed in the same chemical weathering environment 440 million years ago. The [delta][sup 18]O value of accessory phosphate in some soft ore goethite-rich ooids was measured and combined with the goethite [delta][sup 18]O value to calculate a temperature of formation of about 23[degrees]C. The corresponding [delta][sup 18]O value of the ancient water was calculated to have been [minus]7.3[per thousand]. The relatively [open quotes]cool[close quotes] temperature calculated for the low-altitude, tropical site occupied by the Neda ironstone in the Late Ordovician is consistent with published evidence from fossil marine invertebrates for global cooling at that time. The [delta][sup 18]O value of [minus]7.3[per thousand] for the ancient tropical precipitation could indicate intense rainfall of a seasonal (perhaps monsoonal) character. 27 refs., 7 figs., 3 tabs.

  20. Tracing of ca 800 yr old mining activity in peat bog using Pb elemental concentrations and isotope compositions.

    NASA Astrophysics Data System (ADS)

    Baron, S.; Carignan, J.; Ploquin, A.

    2003-04-01

    Sixty sites of slags have been documented on the Mont-Lozère in southern France. The petrographic analysis shows that slags are metallurgical wastes (800 to 850 yr BP) which certainly result from smelting activity for lead and silver extraction (Ploquin et al., 2001). The aims of this study are: 1) to trace the source of Pb ores which supplied the smelting sites, by using the Pb isotopic composition of several surrounding Pb deposits, 2) to evaluate the actual pollution caused by these slags, by using elemental and isotopic compositions of soils, water and vegetation, and 3) to document the pollution history of the region, by using elemental and isotopic compositions of peat bog cores collected in the neighbourhood of the historical smelting sites. The lead isotopic composition of galena collected in most surrounding ores is very similar to that of different slag samples. On the other hand, the high precision of the results allowed us to select the mineralised areas which were probably the ore sources. The Pb isotopic composition of slags is even more homogeneous: 208/206 Pb: 2.092±0.002; 206/207 Pb: 1.179±0.001; 208/204 Pb: 38.663±0.025; 207/204 Pb: 15.665±0.006; 206/204 Pb: 18.476±0.023, and will allow source tracing in the environment. The "Narses Mortes" peat bog, around which two smelting sites have been reported, is strongly minerotrophic and contains 8 to 60% ash. A 1.40 m core have been retrieved and divided into 58 individual samples. Minerotrophic peat bog records both atmospheric deposition, soils leaching and the grounwater influence. The measured metal concentrations are normalised to Al contents of peat bog samples and the metal/Al ratios are compared to that of the Mont-Lozère granite: relative excess in metal concentrations are found in peat bog samples. An increasing excess of most metals (Pb, Zn, Cd...) was measured for surface samples, from 55 cm depth to the top of the core (23 cm depth). This profil might be attributed to atmospheric

  1. Tracking the provenance of Greenland-sourced, Holocene aged, individual sand-sized ice-rafted debris using the Pb-isotope compositions of feldspars and 40Ar/39Ar ages of hornblendes

    NASA Astrophysics Data System (ADS)

    White, Lee F.; Bailey, Ian; Foster, Gavin L.; Allen, Georgina; Kelley, Simon P.; Andrews, John T.; Hogan, Kelly; Dowdeswell, Julian A.; Storey, Craig D.

    2016-01-01

    The provenance of sand-sized ice-rafted debris (IRD) sourced from Greenland is currently difficult to determine. Such knowledge, if it could be ascertained with a high degree of certainty, could be applied to the Greenland-proximal marine records to improve both our understanding of modern-day spatial patterns of iceberg rafting and the past history of the Greenland Ice Sheet (GIS). Recent studies have highlighted the utility of the Pb-isotope composition of individual sand-sized feldspars and the 40Ar/39Ar ages of individual sand-sized hornblendes in this regard. However, before any such provenance toolkit can be applied to the palaeo-record, it is necessary first to determine whether this approach can be used to track the sources of known recent Greenland-proximal IRD deposition. To this end we present new records of the Pb-isotope composition and the 40Ar/39Ar ages of individual sand-sized grains of feldspars and hornblendes, respectively, from modern Greenland glacifluvial and fjord sands and Holocene to modern Greenland-proximal marine sediments. These new data demonstrate that sand-sized feldspars and hornblendes glacially eroded by the GIS exhibit distinct intra- and inter-tectonic terrane differences in their Pb-isotope compositions and ages and that these differences are clearly expressed in the geochemistry and geochronology of sand-sized IRD deposited in marine sediments around Greenland. Although overlap exists between some Greenland-proximal IRD 'source fields' defined by these data, our approach has the potential to both better understand spatial patterns of Greenland-derived IRD in the modern day as well as during past episodes of iceberg calving.

  2. Neutron-Rich Isotopes from 208Pb at 86 MeV/u

    NASA Astrophysics Data System (ADS)

    Tarasov, O. B.; Portillo, M.; Amthor, A. M.; Baumann, T.; Bazin, D.; Folden, C.; Ginter, T.; Hausmann, M.; Morrissey, D. J.; Pereira, J.; Sherrill, B. M.; Thoennessen, M.; Nociforo, C.

    2008-10-01

    An experiment to measure production yields from a beam of ^208Pb (86 MeV/u) on Be and Ni-targets has recently been performed. The A1900 fragment-separator [1] was used to analyze products from projectile fragmentation and abrasion-fission [2]. Isotopic identification of nuclides having A˜200 has been achieved, demonstrating that adequate A,Z,Q resolution at this energy region is possible when using silicon detectors. The verification of PID is done via detection of multiple charge state distributions of the primary beam, as well as γ-decay of known isomers with half-lives in the microsecond range. The results demonstrate that experiments with heavy nuclei are possible at the NSCL using beams of A>200. Production cross-sections have been extracted from the data that can help improve the accuracy of production models such as Abrasion-Ablation and Abrasion-Fission used in the LISE++ code [3]. The data reveal the existence of previously unreported isomeric transitions and further analysis is ongoing that may also lead to the observation of new isotopes. References: [1] D.J.Morrissey et al., Nucl. Instrum. Meth. B204 (2003) 90--96. [2] O.B. Tarasov, Tech. Rep. MSUCL1300, NSCL, Michigan St.Univ., 2005. [3] O.B. Tarasov, D. Bazin, Nucl. Phys. A 746 (2004) 411; www.nscl.msu.edu/lise .

  3. Sr-Nd-Pb isotope data for ultramafic xenoliths from Hierro, Canary Islands: Melt infiltration processes in the upper mantle

    NASA Astrophysics Data System (ADS)

    Whitehouse, M. J.; Neumann, E.-R.

    1995-03-01

    We present here Sr, Nd, and Pb-isotopic data from harzburgite (group I) and dunite-pyroxenite (group II) suite mantle xenoliths from the island of Hierro, one of the youngest and westernmost of the Canary Islands. A progressive leaching technique has been developed and applied to the whole-rock powder samples in order to identify and remove as far as possible any recent additions (host basalt and/or sea-water). Isotopic analyses of the leached residues show significant systematic differences between these two suites. Dunite-pyroxenite suite xenoliths (olivine pyroxenites, dunites and wehrlites) exhibit a relatively small range of isotopic compositions (87Sr/86Sr from 0.70292 to 0.70315; 143Nd/144Nd from 0.51295 to 0.51302; 206Pb/204Pb from 19.18 to 19.40) compared to the harzburgite suite (87Sr/86Sr from 0.70295 to 0.70320; 143Nd/144Nd from 0.51285 to 0.51296; 206Pb/204Pb from 18.85 to 19.41). In all isotope correlation diagrams the leached dunite-pyroxenite suite xenoliths plot between the Hierro basalt field and a hypothetical depleted mantle suggesting that these xenoliths may have been strongly infiltrated by Hierro-type basalt. Progressive leaching of this suite of samples showed removal of a component with more enriched Sr (higher 87Sr/86Sr relative to depleted mantle) and Nd (lower 143Nd/144Nd) isotopic compositions that is probably host basalt glass. The leached harzburgite suite xenoliths extend to more enriched Sr and Nd isotopic compositions than Hierro-type basalt but always have more depleted Pb. This relationship can best be explained if this suite has been subject to infiltration by earlier magmas of the Canary Island suite (in particular, those from Gran Canaria show appropriate compositional ranges), although additional infiltration by Hierro basalt cannot be ruled out. The leaching experiments for this suite mostly show removal of a radiogenic Sr component only (? seawater) which supports the interpretation of early infiltration and subsequent

  4. Pb isotopic investigation of aircraft-sampled emissions from the Horne smelter (Rouyn, Québec): Implications for atmospheric pollution in northeastern North America

    NASA Astrophysics Data System (ADS)

    Simonetti, Antonio; Gariépy, Clément; Banic, Catharine M.; Tanabe, Richard; Wong, Henry K.

    2004-08-01

    This study reports metal abundances and Pb isotope ratios of emissions from the Horne copper smelter, and ambient (ground level) atmosphere at Rouyn, Québec retrieved during 2-week field studies in the winter and summer seasons of 2000. Plume aerosols were sampled during horizontal and vertical passes using a DHC-6 Twin Otter aircraft, which typically tracked the plume up to 30 km from the stack. Samples of the 'background' atmospheric conditions were taken simultaneously from a ground site meteorological station located 2.5 km in the predominant upwind direction from the stack. Overall, metal concentrations (ng/m 3 of As, Cd, Cu, Pb, Se, Zn) for the in-plume samples are elevated by one or more orders of magnitude over those measured in the ground site samples. The Pb isotope compositions for the in-plume samples are extremely variable ( 206Pb/ 207Pb range from ˜1.120 to ˜1.170) but define well-constrained linear arrays in conventional Pb-Pb isotope plots. Correlations between metal concentrations (e.g. As/Pb, Cu/Pb, Zn/Pb) and the Pb isotope data are indicative of binary mixing between two anthropogenic end members; most probably imported industrial Pb found in recycled materials, and nonradiogenic Pb derived from Archean sulfide ore deposits. Pb isotope data from the winter ground site ('background') samples indicate that the ground level atmosphere at Rouyn contains a mixture of Pb emitted from the Horne smelter and long-range anthropogenic Pb transported from Eurasian pollution sources. Compared to the Pb isotope composition of epiphytic lichens, snowpack, and precipitations collected in 1990 to 1999 from adjacent geographic regions, the Pb isotope results obtained here suggest that aerosols emitted from the Horne smelter are dispersed into northeastern North America. However, future studies dealing with point source apportionment for this region of the globe will be rendered difficult due to the processing at the Horne smelter of recycled material

  5. Comparative geochemistry of four ferromanganese crusts from the Pacific Ocean and significance for the use of Ni isotopes as paleoceanographic tracers

    NASA Astrophysics Data System (ADS)

    Gueguen, Bleuenn; Rouxel, Olivier; Rouget, Marie-Laure; Bollinger, Claire; Ponzevera, Emmanuel; Germain, Yoan; Fouquet, Yves

    2016-09-01

    Ferromanganese (Fe-Mn) crusts are potential archive of the Ni isotope composition of seawater through time. In this study we aim at (1) understanding Ni isotope fractionation mechanisms and metal enrichment processes in Fe-Mn deposits, (2) addressing global vs. local control of Ni isotope composition of these deposits. Two Fe-Mn crusts from the North Pacific Ocean (Apuupuu Seamount, Hawaii) and two Fe-Mn crusts from the South Pacific Ocean (near Rurutu Island, Austral archipelago of French Polynesia) were characterized for their elemental geochemistry and Ni isotope composition. Geochemical analyses were performed at millimeter intervals in order to provide time-resolved record of Ni isotopes. Chronology and growth rates were determined using cosmogenic 10Be isotope abundances. The results show that, despite different growth rates, textures and geochemical patterns, Fe-Mn crusts from both North and South Pacific Oceans have fairly homogenous Ni isotope compositions over the last ∼17 Ma, yielding average δ60/58Ni values of 1.79 ± 0.21‰ (2sd, n = 31) and 1.73 ± 0.21‰ (2sd, n = 21) respectively. In one crust sample, however, layers directly in contact with the altered substrate show anomalously light δ60/58Ni values down to 0.25 ± 0.05‰ (2se) together with rejuvenated 10Be/9Be ratios correlating with elevated Ni/Mn ratios. Such patterns are best explained by protracted fluid-rock interactions leading to alteration of Mn-phases after crust formation. Isotopically light Ni would be the result of Ni isotope fractionation during adsorption rather than the contribution of external Ni sources (e.g. hydrothermal sources) having light Ni isotope compositions. The combination of our results with previously published data on Fe-Mn crusts indicates that the average Ni isotope composition in deep waters has not changed through the Cenozoic (∼70 Ma). We propose that Ni isotope variations in Fe-Mn crusts may not only record variations of Ni sources to the oceans, but

  6. Metal extent in blood of livestock from Dandora dumping site, Kenya: Source identification of Pb exposure by stable isotope analysis.

    PubMed

    Nakata, Hokuto; Nakayama, Shouta M M; Ikenaka, Yoshinori; Mizukawa, Hazuki; Ishii, Chihiro; Yohannes, Yared B; Konnai, Satoru; Darwish, Wageh Sobhy; Ishizuka, Mayumi

    2015-10-01

    Nairobi city in Kenya produces 2000 tons/day of garbage, and most of it is dumped onto the Dandora dumping site, home to a quarter-million residents. This study was conducted (1) to assess the contamination levels of nine metals and a metalloid (arsenic) in the blood of pigs, goats, sheep and cattle from Dandora, and (2) to identify a possible source of lead (Pb) pollution. Cadmium (Cd, 0.17-4.35 μg/kg, dry-wt) and Pb (90-2710 μg/kg) levels in blood were generally high, suggesting human exposure to Cd through livestock consumption and Pb poisoning among pigs (2600 μg/kg) and cattle (354 μg/kg). Results of Pb isotope ratios indicated that the major exposure route might differ among species. Our results also suggested a possibility that the residents in Dandora have been exposed to the metals through livestock consumption.

  7. Geology of Precambrian rocks and isotope geochemistry of shear zones in the Big Narrows area, northern Front Range, Colorado

    USGS Publications Warehouse

    Abbott, Jeffrey T.

    1970-01-01

    Rocks within the Big Narrows and Poudre Park quadrangles located in the northern Front Range of Colorado are Precambrian metasedimentary and metaigneous schists and gneisses and plutonic igneous rocks. These are locally mantled by extensive late Tertiary and Quaternary fluvial gravels. The southern boundary of the Log Cabin batholith lies within the area studied. A detailed chronology of polyphase deformation, metamorphism and plutonism has been established. Early isoclinal folding (F1) was followed by a major period of plastic deformation (F2), sillimanite-microcline grade regional metamorphism, migmatization and synkinematic Boulder Creek granodiorite plutonism (1.7 b.y.). Macroscopic doubly plunging antiformal and synformal structures were developed. P-T conditions at the peak of metamorphism were probably about 670?C and 4.5 Kb. Water pressures may locally have differed from load pressures. The 1.4 b.y. Silver Plume granite plutonism was post kinematic and on the basis of petrographic and field criteria can be divided into three facies. Emplacement was by forcible injection and assimilation. Microscopic and mesoscopic folds which postdate the formation of the characteristic mineral phases during the 1.7 b.y. metamorphism are correlated with the emplacement of the Silver Plume Log Cabin batholith. Extensive retrograde metamorphism was associated with this event. A major period of mylonitization postdates Silver Plume plutonism and produced large E-W and NE trending shear zones. A detailed study of the Rb/Sr isotope geochemistry of the layered mylonites demonstrated that the mylonitization and associated re- crystallization homogenized the Rb87/Sr 86 ratios. Whole-rock dating techniques applied to the layered mylonites indicate a probable age of 1.2 b.y. Petrographic studies suggest that the mylonitization-recrystallization process produced hornfels facies assemblages in the adjacent metasediments. Minor Laramide faulting, mineralization and igneous activity

  8. Pb, Nd, and Sr isotopic evidence for a multicomponent source for rocks of Cook-Austral Islands and heterogeneities of mantle plumes

    USGS Publications Warehouse

    Nakamura, Y.; Tatsumoto, M.

    1988-01-01

    Sr, Nd, and Pb isotopic compositions were measured in alkaline volcanic rocks (alkali basalt, ankaramite, nephelinite, phonolite, and trachyte) from the South Cook Islands (Aitutaki, Mauke, Rarotonga, Atiu, and Mangaia) and the Austral Islands (Rimatara and Rurutu). The results show that the Cook-Austral rocks have an extremely wide range in isotopic compositions of Pb: 206Pb 204Pb from 18.25 to 21.76, 207pb 204pb from 15.48 to 15.83, and sol208pb 204Pb from 38.37 to 40.62, whereas isotopic compositions of Sr and Nd are less variable. Isotopically, Mangaia, Rimatara, and Rurutu form one group (Mangaia group), which shows extremely radiogenic Pb isotopic compositions but near-MORB (mid-oceanic ridge basalts) values for Sr and Nd isotopic ratios. In contrast, samples from Aitutaki, Rarotonga, Mauke, and Atiu (Aitutaki group) have high 207Pb 204Pb and 208Pb 204Pb and moderately high 87Sr 86Sr (Dupal anomaly). The Aitutaki group could have been derived from heterogeneous mantle plumes, which rose from the enriched deep mantle (the almost primitive lower mantle or recycled continental and oceanic slabs). On the other hand, the Mangaia component could have been derived from the depleted upper mantle which may have been metasomatized with a CO2-rich fluid, as indicated by the near-MORB values of Sr and Nd isotopes. Although Pb isotopic data of the two groups cannot be distinguished from each other statistically, the end components of the Pb-Pb system do not match with those of the Nd-Sr system. Thus, the data must be explained by a multi-, at least three, component mixing model: the mantle plumes (Dupal component and a recycled oceanic slab), metasomatized upper mantle, and lithosphere. The K-Ar ages and isotopic characteristics of the Cook-Austral rocks indicate that if one mantle plume rises from the deep mantle in this region, it has separated into at least two segments on the way to the surface. ?? 1988.

  9. Pb, Nd, and Sr isotopic evidence for a multicomponent source for rocks of Cook-Austral Islands and heterogeneities of mantle plumes

    SciTech Connect

    Nakamura, Yoichi; Tatsumoto, Mitsunobu )

    1988-12-01

    Sr, Nd, and Pb isotopic compositions were measured in alkane volcanic rocks from the South Cook Islands and the Austral Islands. The results show that the Cook-Austral rocks have an extremely wide range in isotopic compositions of Pb: {sup 206}Pb/{sup 204}Pb from 18.25 to 21.76, {sup 207}Pb/{sup 204}Pb from 15.48 to 15.83, and {sup 208}Pb/{sup 204}Pb from 38.37 to 40.62, whereas isotopic compositions of Sr and Nd are less variable. Isotopically, Mangaia, Rimatara, and Rurutu form one group, which shows extremely ratiogenic Pb isotopic compositions but near-MORB (mid-ocean ridge basalts) values for Sr and Nd isotopic ratios. In contrast, samples from Aitutaki, Rarotonga, Mauke, and Atiu (Aitutaki group) have high {sup 207}Pb/{sup 204}Pb and {sup 208}Pb/{sup 204}Pb and moderately high {sup 87}Sr/{sup 86}Sr (Dupal anomaly). The Aitutaki group could have been derived from heterogeneous mantle plumes, which rose from the enriched deep mantle (the almost primitive lower mantle or recycled continental and oceanic slabs). On the other hand, the Mangaia component could have been derived from the depleted upper mantle which may have been metasomatized with a Co{sub 2}-rich fluid, as indicated by the near-MORB values of Sr and Nd isotopes. Although Pb isotopic data of the two groups cannot be distinguished from each other statistically, the end components of the Pb-Pb system do not match with those of the Nd-Sr system. Thus, the data must be explained by a multi-, at least three, component mixing model: the mantle plumes, metasomatized upper mantle, and lithosphere. The K-Ar ages and isotopic characteristics of the Cook-Austral rocks indicate that if one mantle plume rises from the deep mantle in this region, it has separated into at least two segments on the way to the surface.

  10. Labile pools of Pb in vegetable-growing soils investigated by an isotope dilution method and its influence on soil pH.

    PubMed

    Xie, Hong; Huang, Zhi-Yong; Cao, Ying-Lan; Cai, Chao; Zeng, Xiang-Cheng; Li, Jian

    2012-08-01

    Pollution of Pb in the surface of agricultural soils is of increasing concern due to its serious impact on the plant growth and the human health through the food chain. However, the mobility, activity and bioavailability of Pb rely mainly on its various chemical species in soils. In the present study, E and L values, the labile pools of isotopically exchangeable Pb, were estimated using the method of isotope dilution in three vegetable-growing soils. The experiments involved adding a stable enriched isotope ((206)Pb > 96%) to a soil suspension and to soils in which plants are subsequently grown, the labile pools of Pb were then estimated by measuring the isotopic composition of Pb in soil solutions and in the plant tissues, respectively. In addition, the correlation of E values and soil pH was investigated at the ranges of pH 4.5-7.0. The amount of labile Pb in soils was also estimated using different single chemical extractants and a modified BCR approach. The results showed that after spiking the enriched isotopes of (206)Pb (>96%) for 24 hours an equilibration of isotopic exchanges in soil suspensions was achieved, and the isotope ratios of (208)Pb/(206)Pb measured at that time was used for calculating the E(24 h) values. The labile pools of Pb by %E(24 h) values, ranging from 53.2% to 61.7% with an average 57%, were found to be significantly higher (p < 0.05) than the values estimated with L values, single chemical extractants and the Σ(BCR) values obtained with the BCR approach, respectively. A strong negative correlation (R(2) = 0.984) between E(24 h) values and soil pH was found in the tested soil sample. The results indicate that the %E(24 h) value can more rapidly and easily predict the labile pools of Pb in soils compared with L values, but it might be readily overestimated because of the artificial soil acidity derived from the spiked isotopic tracer and the excess of spiked enriched isotopes. The results also suggest that the amounts of Pb extracted

  11. High-Precision Th-Pb Dating by Isotope-Dilution TIMS+MC-ICPMS - Preliminary Results

    NASA Astrophysics Data System (ADS)

    Ickert, R. B.; Mundil, R.; Sharp, W. D.

    2014-12-01

    Relative to the U-Pb decay series, the Th-Pb decay series has received relatively little attention for geochronology although it offers promising applications in both high-resolution geochronology as well as thermochronology. The limitations are partly because Th measurements by thermal ionization have proven notoriously difficult, and for many geochronological applications, the additional information provided by Th-Pb has not been worth the effort required. However, the current generation of MC-ICPMS instruments provides nearly two orders of magnitude better sensitivity of Th than TIMS, eliminating this barrier to measurement and opening up this chronometer for new use. We have developed a method to measure relative abundances of Th, U and Pb by isotope dilution for high-precision geochronology. This method leverages the strengths of two instruments, the high sensitivity and stable mass fractionation of MC-ICPMS instruments for Th and U, and the low background, lack of isobaric interference, and signal stability of TIMS instruments for Pb. To make these measurements, we have calibrated a new synthetic isotope tracer that comprises a mixture of 229Th-233U-236U-202Pb-205Pb. The analytical strategy developed for accessory minerals is a hybrid of techniques previously developed for U-Pb ID-TIMS and U/230Th ID-MC-ICPMS, with a two-column HCl-HNO3 anion exchange procedure (one to separate U and Pb from matrix+Th, and the other to separate Th from matrix), followed by a recombination of the U and Th fractions for MC-ICPMS analysis while the Pb fraction is measured by TIMS. Th-Pb measurements are complementary to, and potentially as precise as the U-Pb gold standard, and the method will find application in certain geological problems, including (1) precisely determining the relative decay rates of 232Th and 238U, (2) dating materials that are young enough to be substantially affected by 230Th or 231Pa disequilibria, and (3) dating small quantities of high-Th minerals like

  12. The Estherville mesosiderite - U-Pb, Rb-Sr, and Sm-Nd isotopic study of a polymict breccia

    NASA Astrophysics Data System (ADS)

    Brouxel, M.; Tatsumoto, M.

    1991-04-01

    The U-Pb, Rb-Sr, and Sm-Nd isotopic systematics of the Estherville mesoderite were studied using analytical procedures and mass spectrometric techniques similar to those reported by Nakamura et al. (1976), Tatsumoto et al. (1987), and Premo et al. (1989) to analyze 21 separates of a 13-g Estherville clast, obtained either by handpicking or by using density and magnetic separation methods. The results on the Pb-Pb and U-Pb ages (about 4555 and about 4560 Ma, respectively) indicate that at least a part of the Estherville silicate fraction was formed early in the history of solar system. Younger Pb-Pb and U-Pb ages (about 4.43 Ga) were also obtained, confirming the heterogeneity of the Estherville mesoderite that is in agreement with the Wasson and Rubin (1985) suggestion of several generations of meteoritic impacts. The Sm-Nd and Rb-Sr ages were found to be close to 4.56 Ga.

  13. The Estherville mesosiderite - U-Pb, Rb-Sr, and Sm-Nd isotopic study of a polymict breccia

    NASA Technical Reports Server (NTRS)

    Brouxel, M.; Tatsumoto, M.

    1991-01-01

    The U-Pb, Rb-Sr, and Sm-Nd isotopic systematics of the Estherville mesoderite were studied using analytical procedures and mass spectrometric techniques similar to those reported by Nakamura et al. (1976), Tatsumoto et al. (1987), and Premo et al. (1989) to analyze 21 separates of a 13-g Estherville clast, obtained either by handpicking or by using density and magnetic separation methods. The results on the Pb-Pb and U-Pb ages (about 4555 and about 4560 Ma, respectively) indicate that at least a part of the Estherville silicate fraction was formed early in the history of solar system. Younger Pb-Pb and U-Pb ages (about 4.43 Ga) were also obtained, confirming the heterogeneity of the Estherville mesoderite that is in agreement with the Wasson and Rubin (1985) suggestion of several generations of meteoritic impacts. The Sm-Nd and Rb-Sr ages were found to be close to 4.56 Ga.

  14. Dating prograde fluid pulses during subduction by in situ U-Pb and oxygen isotope analysis

    NASA Astrophysics Data System (ADS)

    Gauthiez-Putallaz, Laure; Rubatto, Daniela; Hermann, Jörg

    2016-02-01

    The Dora-Maira whiteschists derive from metasomatically altered granites that experienced ultrahigh-pressure metamorphism at ~750 °C and 40 kbar during the Alpine orogeny. In order to investigate the P-T-time-fluid evolution of the whiteschists, we obtained U-Pb ages from zircon and monazite and combined those with trace element composition and oxygen isotopes of the accessory minerals and coexisting garnet. Zircon cores are the only remnants of the granitic protolith and still preserve a Permian age, magmatic trace element compositions and δ18O of ~10 ‰. Thermodynamic modelling of Si-rich and Si-poor whiteschist compositions shows that there are two main fluid pulses during prograde subduction between 20 and 40 kbar. In Si-poor samples, the breakdown of chlorite to garnet + fluid occurs at ~22 kbar. A first zircon rim directly overgrowing the cores has inclusions of prograde phlogopite and HREE-enriched patterns indicating zircon growth at the onset of garnet formation. A second main fluid pulse is documented close to peak metamorphic conditions in both Si-rich and Si-poor whiteschist when talc + kyanite react to garnet + coesite + fluid. A second metamorphic overgrowth on zircon with HREE depletion was observed in the Si-poor whiteschists, whereas a single metamorphic overgrowth capturing phengite and talc inclusions was observed in the Si-rich whiteschists. Garnet rims, zircon rims and monazite are in chemical and isotopic equilibrium for oxygen, demonstrating that they all formed at peak metamorphism at 35 Ma as constrained by the age of monazite (34.7 ± 0.4 Ma) and zircon rims (35.1 ± 0.8 Ma). The prograde zircon rim in Si-poor whiteschists has an age that is within error indistinguishable from the age of peak metamorphic conditions, consistent with a minimum rate of subduction of 2 cm/year for the Dora-Maira unit. Oxygen isotope values for zircon rims, monazite and garnet are equal within error at 6.4 ± 0.4 ‰, which is in line with closed

  15. Pb-Zn-Cd-Hg multi isotopic characterization of the Loire River Basin, France

    NASA Astrophysics Data System (ADS)

    Millot, R.; Widory, D.; Innocent, C.; Guerrot, C.; Bourrain, X.; Johnson, T. M.

    2012-12-01

    The contribution of human activities such as industries, agriculture and domestic inputs, becomes more and more significant in the chemical composition (major ions and pollutants such as metals) of the dissolved load of rivers. Furthermore, this influence can also be evidenced in the suspended solid matter known to play an important role in the transport of heavy metals through river systems. Human factors act as a supplementary key process. Therefore the mass-balance for the budget of catchments and river basins include anthropogenic disturbances. The Loire River in central France is approximately 1010 km long and drains an area of 117,800 km2. Initially, the Loire upstream flows in a south to north direction originating in the Massif Central, and continues up to the city of Orléans, 650 km from the source. In the upper basin, the bedrock is old plutonic rock overlain by much younger volcanic rocks. The Loire River then follows a general east to west direction to the Atlantic Ocean. The intermediate basin includes three major tributaries flowing into the Loire River from the left bank: the Cher, the Indre and the Vienne rivers; the main stream flows westward and its valley stretches toward the Atlantic Ocean. Here, the Loire River drains the sedimentary series of the Paris Basin, mainly carbonate deposits. The lower Loire basin drains pre-Mesozoic basement of the Armorican Massif and its overlying Mesozoic to Cenozoic sedimentary deposits. The Loire River is one of the main European riverine inputs to the Atlantic ocean. Here we are reporting concentration and isotope data for heavy metals Zn-Cd-Pb-Hg in river waters and suspended sediments from the Loire River Basin. In addition, we also report concentration and isotope data for these metals for the different industrial sources within the Loire Basin, as well as data for biota samples such as mussels and oysters from the Bay of Biscay and North Brittany. These organisms are known to be natural accumulators of

  16. Apatite U-Pb thermochronolgy applied to complex geological settings - insights from geo/thermochronology and geochemistry

    NASA Astrophysics Data System (ADS)

    Paul, Andre; Spikings, Richard; Ulyanov, Alexey; Chew, David

    2016-04-01

    Application of high temperature (>350oC) thermochronology is limited to the U-Pb system of accessory minerals, such as apatite, under the assumption that radiogenic lead is lost to thermally activated volume diffusion into an infinite reservoir. Cochrane et al. (2015) have demonstrated a working example from the northern Andes of South America. Predictions from volume diffusion theory were compared with measured single grain U-Pb date correlated to shortest diffusion radius and in-situ profiles measured by LA-ICP-MS. Results from both techniques were found to be in agreement with predictions from thermally activated, volume diffusion. However, outliers from the ID-TIMS data suggested some complexity, as grains were found to be too young relative to their diffusion radius. Interaction of multiple processes can be responsible for the alteration of apatite U-Pb dates such as: (1) metamorphic (over)growth, (2) fluid aided alteration/recrystallization and (3) metamictization and fracturing of the grain. Further, predictions from volume diffusion rely on the input parameters: (a) diffusivity, (b) activation energy and (c) shortest diffusion radius. Diffusivity and activation energy are potentially influenced by the chemical composition and subsequent changes in crystal structure. Currently there is one value for diffusion parameter and activation energy established for (Durango) apatite (Cherniak et al., 1991). Correlation between diffusivity/activation energy and composition has not been established. We investigate if correlations exist between diffusivity/activation energy and composition by obtaining single grain apatite U-Pb date and chemical compostion and correlating these to their diffusion radius. We test the consistency of apatite closure temperature, by comparing the apatite U-Pb dates with lower temperature thermochronometers such as white mica and K-feldspar Ar/Ar and by petrographic observations. We test if chemical information can be a proxy to identify

  17. Pb and Sr isotopic constraints on lithospheric magma sources during Mesozoic continental margin arc initiation, southern California

    SciTech Connect

    Barth, A.P. . Dept. of Geology); Tosdal, R.M.; Wooden, J.L. )

    1993-04-01

    Initiation of the Mesozoic Cordilleran arc in the southwestern US is marked by plutonism from about 241--213 Ma, exposed in the Granite Mountains in the southwestern Mojave Desert, through the Transverse Ranges to the Colorado River trough in southeastern California and southwestern Arizona. Plutons range in composition from diorite to granite, but quartz monzonite and monzodiorite predominate. Plutons intruded 1,700 to 1,100 Ma rocks of the Mojave crustal province [as defined isotopically by Wooden and Miller (1990) and Bennett and DePaolo (1987)], and episomal plutons locally intruded its deformed cratonal/miogeoclinal cover. Plutons emplaced during arc initiation overlap isotopically with local Proterozoic basement rocks, but typically have less radiogenic [sup 207]Pb/[sup 204]Pb, [sup 208]Pb/[sup 204]Pb and [sup 87]Sr/[sup 86]Sr than adjacent, more voluminous Middle-Late Jurassic and Late Cretaceous arc plutons. Among early arc plutons, an inter-suite trend toward more radiogenic Pb and [sup 87]Sr/[sup 86]Sr at similar silica contents reflects regional basement isotopic variability. Generally high Sr contents, low Rb/Sr and limited REE data suggest this inter-suite variations records heterogeneity in eclogite/garnet amphibolite facies mafic lithospheric magma sources, corresponding to mafic lower crust and/or upper mantle formed during 1,700 Ma orogenesis or rift-related magmatism at 1,100 Ma. Intra-suite trends toward less radiogenic Pb at constant or more radiogenic Sr reflect involvement of a U and Th depleted, silicic intracrustal contaminant. Distinctive magma sources and limited crustal interaction during emplacement probably reflects the relatively cool thermal structure of the nascent Cordilleran continental margin arc.

  18. Sr-Nd-Hf-Pb isotopic constraints on the origin of silicic lavas in the northern Cascade Arc