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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 erupted

  2. Sr, Nd, Pb Isotope geochemistry and magma evolution of the potassic volcanic rocks, Wudalianchi, Northeast China

    USGS Publications Warehouse

    Junwen, W.; Guanghong, X.; Tatsumoto, M.; Basu, A.R.

    1989-01-01

    Wudalianchi volcanic rocks are the most typical Cenozoic potassic volcanic rocks in eastern China. Compositional comparisons between whole rocks and glasses of various occurrences indicate that the magma tends to become rich in silica and alkalis as a result of crystal differentiation in the course of evolution. They are unique in isotopic composition with more radiogenic Sr but less radiogenic Pb.87Sr /86 Sr is higher and143Nd/144Nd is lower than the undifferentiated global values. In comparison to continental potash volcanic rocks, Pb isotopes are apparently lower. These various threads of evidence indicate that the rocks were derived from a primary enriched mantle which had not been subjected to reworking and shows no sign of incorporation of crustal material. The correlation between Pb and Sr suggests the regional heterogeneity in the upper mantle in terms of chemical composition. ?? 1989 Institute of Geochemistry, Chinese Academy of Sciences.

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

  6. Peri-Amazonian provenance of the Proto-Pelagonian basement (Greece), from zircon U-Pb geochronology and Lu-Hf isotopic geochemistry

    NASA Astrophysics Data System (ADS)

    Zlatkin, Olga; Avigad, Dov; Gerdes, Axel

    2014-01-01

    The basement of the Pelagonian zone of the Hellenides, in the Eastern Mediterranean realm, has been shaped by mid-Neoproterozoic (700 Ma) and Variscan (300 Ma) igneous activities. In the present study, detrital zircon U-Pb geochronology and Lu-Hf isotope geochemistry of ca. 700 Ma-aged granites and of pre-700 Ma metasediments from the Pelagonian zone allow a genuine perspective into the provenance and origin of this terrane which hosts one of the oldest sedimentary sequences known in SE Europe. Pelagonian crustal vestiges comprising 700 Ma granitoids and their hosting metasediments are termed here "Proto-Pelagonian".

  7. 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

  8. Petrogenesis of the Late Triassic volcanic rocks in the Southern Yidun arc, SW China: Constraints from the geochronology, geochemistry, and Sr-Nd-Pb-Hf isotopes

    NASA Astrophysics Data System (ADS)

    Leng, Cheng-Biao; Huang, Qiu-Yue; Zhang, Xing-Chun; Wang, Shou-Xu; Zhong, Hong; Hu, Rui-Zhong; Bi, Xian-Wu; Zhu, Jing-Jing; Wang, Xin-Song

    2014-03-01

    Studies on zircon ages, petrology, major and trace element geochemistry, and Sr-Nd-Hf-Pb isotopic geochemistry of intermediate volcanic rocks from the Southern Yidun arc, Sanjiang-Tethyan Orogenic Belt, SW China have been undertaken in this paper. They are used to discuss the petrogenesis of these rocks and to constrain the tectonic setting and evolution of the Yidun arc. These intermediate volcanic rocks were erupted at ca. 220 Ma (U-Pb zircon ages). Trachyandesite is the dominant lithology among these volcanic rocks, and is mainly composed of hornblende and plagioclase, with minor clinopyroxene and biotite. A hornblende geobarometer suggests that the stagnation of magma in the lower crust, where plagioclase crystallization was suppressed while hornblende crystallized, giving rise to high Sr/Y ratios that are one of the distinguishing features of adakites, after the primary magma originated from the lithospheric mantle wedge. Steeply right-inclined Rare Earth Element (REE) pattern combined with high La/Yb ratios suggests adakitic affinity of these volcanic rocks, implying that slab-melt from the subducting oceanic crust is a necessary component in the primary magma. Besides, trace element geochemistry and isotopic geochemistry also indicate that partial melting of pelagic sediments in the subduction zone and noticeable contamination with the lower crust were involved in the evolution of parental magma of these volcanic rocks. Based on previous work on the Northern Yidun arc and this study, we propose that the subduction was initiated in the Northern Yidun arc and extended to the southern part and that the Northern Yidun arc is an island arc while the Southern Yidun arc represents a continental arc, probably caused by the existence of the Zhongza Massif, that was invoked to be derived from Yangtze Block, as a possible basement of the Southern Yidun arc.

  9. 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.

  10. Major element, REE, and Pb, Nd and Sr isotopic geochemistry of Cenozoic volcanic rocks of eastern China: implications for their origin from suboceanic-type mantle reservoirs

    USGS Publications Warehouse

    Basu, A.R.; Wang, Junwen; Huang, Wankang; Xie, Guanghong; Tatsumoto, M.

    1991-01-01

    Major- and rare-earth-element (REE) concentrations and UThPb, SmNd, and RbSr isotope systematics are reported for Cenozoic volcanic rocks from northeastern and eastern China. These volcanic rocks, characteristically lacking the calc-alkaline suite of orogenic belts, were emplaced in a rift system which formed in response to the subduction of the western Pacific plate beneath the eastern Asiatic continental margin. The rocks sampled range from basanite and alkali olivine basalt, through olivine tholeiite and quartz tholeiite, to potassic basalts, alkali trachytes, pantellerite, and limburgite. These rock suites represent the volcanic centers of Datong, Hanobar, Kuandian, Changbaishan and Wudalianchi in northeastern China, and Mingxi in the Fujian Province of eastern China. The major-element and REE geochemistry is characteristic of each volcanic suite broadly evolving through cogenetic magmatic processes. Some of the outstanding features of the isotopic correlation arrays are as follows: (1) NdSr shows an anticorrelation within the field of ocean island basalts, extending from the MORB end-member to an enriched, time-averaged high Rb Sr and Nd Sr end-member (EM1), (2) SrPb also shows an anticorrelation, similar to that of Hawaiian and walvis Ridge basalts, (3) NdPb shows a positive correlation, and (4) the 207Pb 204Pb vs 206Pb 204Pb plot shows linear arrays parallel to the general trend (NHRL) for MORB on both sides of the geochron, although in the 208Pb 204Pb vs 206Pb 204Pb plot the linear array is significantly displaced above the NHRL in a pattern similar to that of the oceanic island basalts that show the Dupal signatures. In all isotope correlation patterns, the data arrays define two different mantle components-a MORB-like component and an enriched mantle component. The isotopic data presented here clearly demonstrate the existence of Dupal compositions in the sources of the continental volcanic rocks of eastern China. We suggest that the subcontinental mantle

  11. 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

  12. 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

  13. 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.

  14. 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

  15. 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.

  16. 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

  17. Geochemistry and zircon U-Pb ages and Hf isotopic composition of Permian alkali granitoids of the Phan Si Pan zone in northwestern Vietnam

    NASA Astrophysics Data System (ADS)

    Hiếu, Phạm Trung; Chen, Fu-kun; Thủy, Nguyễn Thị Bích; Cu'ò'ng, Nguyễn Quốc; Li, Shuang-quing

    2013-09-01

    The late Permian granitoids exposed in the Phan Si Pan zone of northwestern Vietnam consist mainly of the Ye Yen Sun metaluminous granites and the Nam Xe-Tam Duong peralkaline granites. Laser ablation inductively coupled plasma mass spectrometry U-Pb zircon analysis reveals that both the granite suites were emplaced from 253 Ma to 251 Ma. They have a distinctive A-type geochemistry of high 10,000 × Ga/Al ratios of 3.0-5.7 and are also characterized by elevated contents of high field strength elements, A/CNK values of 0.85-1.58, negative Eu-anomalies. Magmatic zircons from the granitoids exhibit positive initial ɛHf values ranging from 6.4 to 15.9 and yield single-stage depleted mantle Hf model ages of 257-663 Ma. This Hf isotopic feature implies significant contribution of juvenile mantle material to the magmas of the spatially and temporally associated Ye Yen Sun metaluminous and Nam Xe-Tam Duong peralkaline granites.

  18. Geochemistry and S, Pb isotope of the Yangla copper deposit, western Yunnan, China: Implication for ore genesis

    NASA Astrophysics Data System (ADS)

    Yang, Xi-An; Liu, Jia-Jun; Cao, Ye; Han, Si-Yu; Gao, Bing-yu; Wang, Huan; Liu, Yue-Dong

    2012-07-01

    The Yangla copper deposit, situated in the middle section of Jinshajiang tectonic belt between Zhongza-Zhongdian block and Changdu-Simao block, is a representative and giant copper deposit that has been discovered in Jinshajiang-Lancangjiang-Nujiang region in recent years. There are coupled relationships between Yangla granodiorite and copper mineralization in the Yangla copper deposit. Five molybdenite samples yielded a well-constrained 187Re-187Os isochron age of 233.3 ± 3 Ma, the metallogenesis is therefore slightly younger than the crystallization age of the granodiorite. S, Pb isotopic compositions of the Yangla copper deposit indicate that the ore-forming materials were derived from the mixture of upper crust and mantle, also with the magmatic contributions. In the late Early Permian, the Jinshajiang Oceanic plate was subducted to the west, resulting in the formation of a series of gently dipping thrust faults in the Jinshajiang tectonic belt, meanwhile, accompanied magmatic activities. In the early Late Triassic, which was a time of transition from collision-related compression to extension in the Jinshajiang tectonic belt, the thrust faults were tensional; it would have been a favorable environment for forming ore fluids. The ascending magma provided a channel for the ore-forming fluid from the mantle wedge. After the magma arrived at the base of the early-stage Yangla granodiorite, the platy granodiorite at the base of the body would have shielded the late-stage magma from the fluid. The magma would have cooled slowly, and some of the ore-forming fluid in the magma would have entered the gently dipping thrust faults near the Yangla granodiorite, resulting in mineralization.

  19. Isotope Geochemistry Researches in China

    NASA Astrophysics Data System (ADS)

    Chen, James H.

    The publication of Isotope Geochemistry Researches in China represents a major milestone in such research in China. Every isotope geochemist will find at least one informative article in his or her own field of interest in this large and comprehensive volume.The book is divided into 27 chapters, written by 41 authors, and the scope, content, and quality of the chapters are variable. In general, each is a review or an overview of a topic in geochemistry. Some of the chapters are very short and provide only a very general overview. Others are long and provide a detailed and more comprehensive review of a specific subject. Most are translated into English and they are generally professionally done. The quality of the figures and tables varies, but most are clear and informative. An extensive, current bibliography (some in Chinese publications) is provided at the end of the book for each chapter, but there is no index.To help readers find the localities of the areas studied, a table is appended containing names in English and Chinese with latitude and longitude, but no map is included.

  20. 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.

  1. Provenance and paleogeography of the Late Cretaceous Mengyejing Formation, Simao Basin, southeastern Tibetan Plateau: Whole-rock geochemistry, U-Pb geochronology, and Hf isotopic constraints

    NASA Astrophysics Data System (ADS)

    Wang, Licheng; Liu, Chenglin; Gao, Xiang; Zhang, Hua

    2014-05-01

    The Late Cretaceous Mengyejing Formation, which contains the only pre-Quaternary potash salt deposit in the Simao Basin, southeastern Tibet, is thought to be genetically related to the Maha Sarakham Formation in the Khorat Basin. The provenance and paleogeography of these two basins have been under debate, although little diagnostic evidence has been previously published. A combined analysis of whole rock geochemistry, zircon U-Pb chronology, and Hf isotopic compositions was performed to characterize the provenance of the Mengyejing Formation. These formation's sandstones are characterized by moderate chemical index of alteration (CIA) values. These values, together with plots of the Th/U-Th ratios, suggest that certain samples have undergone moderate weathering and sedimentary recycling. The major and trace elements (La/Th-Hf, Th/Sc-Zr/Sc, Eu/Eu*-Th/Sc, TiO2-Fe2O3T + MgO, Al2O3/SiO2-Fe2O3T + MgO, K2O/Na2O-SiO2) indicate that the sedimentary sources were felsic rocks from an active continental margin or continental arc with a minor amount of recycled sediment from a passive continental margin. The Mengyejing Formation contains detrital zircons primarily with U-Pb ages of 2.45-2.57 Ga, 1.8-1.9 Ga, 740-880 Ma, 410-470 Ma, and 215-300 Ma. The results reveal that the pre-Devonian zircons are derived from the recycled sediments of the Yangtze block originating in the Qinling Orogenic Belt, and they share this provenance with the coeval sediments in the Khorat Basin. The magmatic rocks of the Ailaoshan and Lincang areas are responsible for supplying the Devonian to Triassic detrital zircons. These provenance data combined with published paleocurrent results suggest that the Simao Basin was situated on the western margin of the Khorat Basin during the Late Cretaceous. The basins were connected when marine incursion occurred. We propose that pre-Devonian materials from the southwestern Sichuan Basin first supplied detritus to the Simao Basin and subsequently to the Khorat

  2. 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.

  3. 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

  4. 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.

  5. 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.

  6. Geology, geochronology, geochemistry, and Pb-isotopic compositions of Proterozoic rocks, Poachie region, west-central Arizona; a study of the east boundary of Proterozoic Mojave crustal province

    USGS Publications Warehouse

    Bryant, Bruce; Wooden, J.L.; Nealey, L. David

    2001-01-01

    The Poachie region at the south edge of the Colorado Plateau transition zone in western Arizona is underlain by early and middle Proterozoic plutonic rocks locally separated by screens of amphibolite-facies early Proterozoic metamorphic rocks and is in the eastern part of the Mojave crustal province, as shown by 35 Pb-isotope analyses of rocks and feldspars. Previously published mapping, 10 U-Pb zircon ages, 55 rock analyses, and other studies in the larger region of the transition zone lead to interpretation of the history and origin of the Proterozoic crust.

  7. 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

  8. Zircon U-Pb ages, geochemistry, and Sr-Nd-Pb-Hf isotopes of the Nuri intrusive rocks in the Gangdese area, southern Tibet: Constraints on timing, petrogenesis, and tectonic transformation

    NASA Astrophysics Data System (ADS)

    Chen, Lei; Qin, Ke-Zhang; Li, Guang-Ming; Li, Jin-Xiang; Xiao, Bo; Zhao, Jun-Xing; Fan, Xin

    2015-01-01

    Abundant magmatic rocks of various ages are exposed in Gangdese, southern Tibet. These rocks play an important role in understanding the tectonic transformation from the subduction of Neo-Tethyan oceanic crust to the collision of the Indian and Asian continents. Based on zircon U-Pb ages, geochemistry, and Sr-Nd-Pb-Hf isotopic data of the Late Cretaceous to early Oligocene (~ 96-30 Ma) intrusive rocks in the Nuri Cu-W-Mo deposit, we discuss the Late Cretaceous to early Oligocene tectonic transformation of the region and the origin of Oligocene Cu-W-Mo mineralization in southern Gangdese. The Nuri intrusive rocks represent three magmatic episodes: 96-91, 56-52, and 33-30 Ma. The 96-91 and 56-52 Ma rocks have relatively low (87Sr/86Sr)i (0.7041 to 0.7060), and high εNd(t) (+ 3.1 to + 3.5) and εHf(t) values (+ 3.7 to + 15); the 33-30 Ma rocks have relatively high (87Sr/86Sr)i (0.7061 to 0.7063) and Pb isotopes, and low εNd(t) (- 3.8 to - 1.8) and εHf(t) values (+ 0.6 to + 10.1). The three stages of intrusive rocks have geochemical characteristics that are similar to those of coeval rocks in Gangdese. The 96-91 and 33-30 Ma rocks are adakitic, whereas the 56-52 Ma rocks have characteristics of arc calc-alkaline magmatic rocks. The 96-91 Ma rocks were produced by the partial melting of Neo-Tethyan basaltic oceanic crust and minor sediments, whereas the 56-52 Ma rocks were generated by the partial melting of juvenile crust and the 33-30 Ma rocks were formed by the melting of Indian plate lower crust contaminated with overlying mantle materials. On the basis of the regional tectonic and magmatic characteristics, we suggest that Neo-Tethyan oceanic slab subduction and slab roll-back occurred from ~ 100 to 65 Ma, collision between the Indian and Asian continents occurred at 65 to 40 Ma, Neo-Tethyan oceanic slab break-off took place at ~ 50 Ma, and the Indian continent subducted northwards beneath the Asian continent at ~ 30 Ma. From the Late Cretaceous (96-91 Ma) to

  9. Sr, Nd and Pb Isotope Geochemistry of Near-ridge Seamounts in Eastern Pacific: Implications for Upper Mantle Composition and EPR Magmatic Segmentation

    NASA Astrophysics Data System (ADS)

    Castillo, P. R.; White, W. M.; Batiza, R.

    2005-12-01

    Near-ridge seamount lavas tend to reflect the true composition of the upper mantle source of MORB because these are generated by relatively smaller degrees of melting of smaller volumes of the mantle compared to nearby axial lavas; they also by-pass the axial chamber mixing and fractionation processes that are responsible for the relatively more uniform chemical and isotopic composition of normal-MORB. New Sr, Nd and Pb isotope data combined with published data for lavas from near-ridge seamounts on either side of the EPR segment between the 11o45' OSC and Orozco Transform at 15o00' show latitudinal isotopic variation very similar to that shown by the rise axial lavas (Castillo et al., G3 1, 1999). Seamount and axial lavas at both ends of the rise segment have on average slightly higher and more limited range of 143Nd/144Nd, but slightly lower 206Pb/204Pb and 87Sr/86Sr ratios than lavas at the center of the segment. Some of the seamounts are located on ~8 Ma rise flank crust although most of the seamount lavas are fairly young (e.g., lavas from Seamount 6 on ~3 Ma crust are only 3 to 900 kyr - Graham et al., Nature 326, 1987). Thus near-ridge seamount isotope data provide the first documentation for a large-scale (~350 km long x ~720 km wide), systematic compositional variation of the upper mantle source of EPR MORB. Such a scale of variation is larger and longer than the size and <1 myr life span of the majority of non-transform offsets, which are supposed to be responsible for the along-axis compositional variations of EPR MORB according to the "bottoms up" model of magmatic segmentation.

  10. 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.

  11. 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

  12. 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

  13. Sr, Nd and Pb Isotope Geochemistry for the Volcanic Rocks From the Aono and Abu Volcanic Groups in the SW Japan arc

    NASA Astrophysics Data System (ADS)

    Shimoda, G.; Morishita, Y.; Nohda, S.

    2002-12-01

    Although, there is no deep seismic activity beneath the W. Honshu Island in the SW Japan arc, recent seismic studies have revealed the existence of an aseismic slab beneath the area. Thus, the volcanism in the W. Honshu Island is considered to be related to the subduction. Since the subducting Philippine Sea plate caused inter-arc spreading, the volcanism of the Aono and Abu volcanic groups in the W. Honshu Island are inferred to be produced at the high temperature condition. The Aono volcanic group is one of volcanic groups, which comprise the volcanic front on the SW Japan arc, while the Abu volcanic group is on rather backarc side of the Aono volcanic group. In order to evaluate the origin of the volcanic rocks from the Aono and Abu volcanic groups, Sr, Nd and Pb isotopic and trace element compositions were determined. Nb troughs on a spider diagram indicate that these rocks are related to subduction process. Furthermore, high Sr/Y ratios and low Y concentrations of these rocks indicate that these are adakitic magma, which suggests that the magmas were produced by altered oceanic crust melting. Isotopic compositions of these rocks are situated between those of the Shikoku basin basalt and mantle xenoliths from the SW Japan arc on 87Sr/86Sr vs. 143Nd/144Nd and Pb-Pb diagrams. These show that geochemical characteristics of these rocks were produced by the mixing of a depleted slab derived component with an enriched mantle component. A 1/Sr vs. 87Sr/86Sr diagram designates that the depleted and enriched components have high and low Sr concentrations, respectively. Considering phase assemblages during melting processes of mantle peridotite and subducting altered oceanic crust, lower and higher Sr concentrations reflect lherzolite and eclogite melting respectively. This is consistent with the isotopic composition. To test the altered oceanic crust melting as a possible mechanism for the production of Aono and Abu volcanic rocks, melting calculations were conducted

  14. 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

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

    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.

  16. 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.

  17. A-type granites from the Pan-African orogenic belt in south-western Chad constrained using geochemistry, Sr-Nd isotopes and U-Pb geochronology

    NASA Astrophysics Data System (ADS)

    Isseini, Moussa; André-Mayer, Anne-Sylvie; Vanderhaeghe, Olivier; Barbey, Pierre; Deloule, Etienne

    2012-11-01

    The Zabili granitic pluton (SW Chad) exposed in the Mayo Kebbi massif is dominated by a coarse-grained hornblende biotite granite grading into a fine-grained biotite granite along its southern margin. Petrologic (micrographic intergrowth of quartz and alkali feldspars, granophyric microstructures, the presence of fluorite and bastnaesite as accessory minerals) and geochemical data (high silica, alkalis and Fe/Mg, depletions in CaO, MgO, TiO2; high Ga, Nb, Zr, Ga/Al, REE, depletions in Ba, Sr, Eu and compatible elements) indicate that this pluton consists of A-type granites crystallized from hot (apatite and zircon saturation temperatures ranging from 744 °C to 923 °C), extremely differentiated magmas. U-Pb zircon geochronology indicates that the magmas crystallized at 567 ± 10 Ma and reveals the presence of older Neoproterozoic xenocrystic zircons at 668 ± 5 Ma in both facies. Within the fine-grained biotite granite, discordant zircons with U-Pb and Pb-Pb ages ranging from Neoproterozoic to Archaean are also reported. The 668 ± 5 Ma old zircons are considered to derive from country-rocks while discordant zircons, characterized by angular shapes, internal fractures and inherited cores, are likely to represent multi-sources detrital crystals that have recorded at least one metamorphic event. Old pre-Neoproterozoic zircons are reported for the first time for rocks of the Mayo Kebbi massif and they attest to the contribution of an old basement (likely to be the Eastern Nigeria basement and/or the Congo craton) involved in a collisional event with a juvenile Neoproterozoic crust prior to the emplacement of the Zabili granitic pluton. Initial ɛNd values calculated for the Zabili pluton range from + 2.6 to + 7.0, the highest value recorded by one sample from the coarse-grained hornblende-biotite granite being close to the one of the depleted mantle at 570 Ma (ɛNd = + 7.4). Combining geochronology, Nd isotopes composition and geochemical modeling, leads us to

  18. 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 °C, 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 the

  19. Petrogenesis of gold-mineralized magmatic rocks of the Taerbieke area, northwestern Tianshan (western China): Constraints from geochronology, geochemistry and Sr-Nd-Pb-Hf isotopic compositions

    NASA Astrophysics Data System (ADS)

    Tang, Gong-Jian; Wang, Qiang; Wyman, Derek A.; Sun, Min; Zhao, Zhen-Hua; Jiang, Zi-Qi

    2013-09-01

    Many Late Paleozoic Cu-Au-Mo deposits occur in the Central Asian Orogenic Belt (CAOB). However, their tectonic settings and associated geodynamic processes have been disputed. This study provides age, petrologic and geochemical data for andesites and granitic porphyries of the Taerbieke gold deposit from the Tulasu Basin, in the northwestern Tianshan Orogenic Belt (western China). LA-ICP-MS zircon U-Pb dating indicates that the granitic porphyries have an Early Carboniferous crystallization age (349 ± 2 Ma) that is broadly contemporaneous with the eruption age (347 ± 2 Ma) of the andesites. The andesites have a restricted range of SiO2 (58.94-63.85 wt.%) contents, but relatively high Al2O3 (15.39-16.65 wt.%) and MgO (2.51-6.59 wt.%) contents, coupled with high Mg# (57-69) values. Geochemically, they are comparable to Cenozoic sanukites in the Setouchi Volcanic Belt, SW Japan. Compared with the andesites, the granitic porphyries have relatively high SiO2 (72.68-75.32 wt.%) contents, but lower Al2O3 (12.94-13.84 wt.%) and MgO (0.10-0.33 wt.%) contents, coupled with lower Mg# (9-21) values. The andesites and granitic porphyries are enriched in both large ion lithophile and light rare earth elements, but depleted in high field strength elements, similar to those of typical arc magmatic rocks. They also have similar Nd-Hf-Pb isotope compositions: ɛNd(t) (+0.48 to +4.06 and -0.27 to +2.97) and zircons ɛHf(t) (+3.4 to +8.0 and -1.7 to +8.2) values and high (206Pb/204Pb)i (18.066-18.158 and 17.998-18.055). We suggest that the Taerbieke high-Mg andesitic magmas were generated by the interaction between mantle wedge peridotites and subducted oceanic sediment-derived melts with minor basaltic oceanic crust-derived melts, and that the magmas then fractionated to produce the more felsic members (i.e., the Taerbieke granitic porphyries) during late-stage evolution. Taking into account the Carboniferous magmatic record from the western Tianshan Orogenic Belt, we suggest that

  20. 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

  1. 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

  2. Late Triassic intrusive complex in the Jidong region, Jiamusi-Khanka Block, NE China: Geochemistry, zircon U-Pb ages, Lu-Hf isotopes, and implications for magma mingling and mixing

    NASA Astrophysics Data System (ADS)

    Yang, Hao; Ge, Wen-chun; Zhao, Guo-chun; Dong, Yu; Xu, Wen-liang; Ji, Zheng; Yu, Jie-jiang

    2015-05-01

    Whole-rock major and trace element geochemistry together with zircon U-Pb ages and Lu-Hf isotope compositions are reported for a Late Triassic intrusive complex in the Jidong region, Jiamusi-Khanka Block, NE China. Zircon U-Pb dating yields ages between 211 and 208 Ma for enclaves of microgranular diorite and quartz diorite, and between 211 and 209 Ma for the host granitoids. These ages correlate with a previously established intensive Late Triassic magmatic event along the eastern Asian margin. Field observations, together with petrographic features, geochemistry, and zircon Hf isotope data, preclude simple crystal fractionation or restite unmixing as a genetic link for the various rock types within the intrusive complex. The syenogranite suite has high SiO2 (75.5-76.3 wt.%) and low MgO (0.15-0.19 wt.%), and yields enriched LILE and LREE patterns. Most of the zircons in the syenogranites have two-stage model ages of 766 and 1461 Ma, together with positive εHf(t) values of + 0.6 to + 9.1. These results indicate that the granitoid magmas were generated by partial melting of Meso- to Neoproterozoic lower crust. The gabbro suite has a restricted range of SiO2 (46.1-51.9 wt.%) together with high Mg# values (49-70) and high concentrations of Ni, Co, and Cr. Zircons from two diorite samples have single-stage Hf model ages of 557-787 Ma and εHf(t) values of + 1.9 to + 8.3 that are consistent with the coeval gabbros previously studied in the Jidong region. These features, together with the observation that all the gabbros are enriched in LREE and LILE, suggest that the mafic magmas were derived from melting of depleted Neoproterozoic lithospheric mantle that had been metasomatized by slab-derived fluids. It is concluded that the dominant igneous suites within the Late Triassic intrusive complex formed by mingling/mixing of felsic and mafic magmas. The geochemical data, combined with regional geological investigations, indicate that the Late Triassic intrusive complex

  3. Geochemistry, PbPb single zircon ages and NdSr isotope composition of Precambrian rocks from southern and eastern Ethiopia: implications for crustal evolution in East Africa

    NASA Astrophysics Data System (ADS)

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

    1998-02-01

    Geochemical and isotope data for granitoid rocks from southern and eastern Ethiopia delineate the presumed margin of the Pan-African juvenile terrain of the Arabian-Nubian Shield against an older crustal segment of unknown origin extending from eastern Ethiopia to northern Somalia. Granitoids from southern Ethiopia have higher Na 2O and {Na20 }/{K2O} and lower Cr and Ni than granitoids with comparable SiO 2 values from eastern Ethiopia. In southern Ethiopia three periods of magmatism are identified on the basis on single zircon {207Pb}/{206Pb} evaporation ages, namely at ˜850, ˜750-700 and ˜650-550 Ma, and these correlate well with events documented from other parts of Ethiopia and the Arabian-Nubian Shield. The initial ɛNd(700 Ma) and ɛsr(700 Ma) values range from -1.2 to +3.2 and from -13.4 to + 3.7, respectively, which precludes any significant contribution from much older continental crust in the generation of these rocks. Neodymium mean crustal residence ages, based on a depleted mantle model, range from 0.96 to 1.26 Ga. These data support the interpretation that southern Ethiopia constitutes part of the Arabian-Nubian Shield. In contrast, granitoids from eastern Ethiopia show geochemical features of S-type granites. In eastern Ethiopia Pal aeo-Neoproterozoic zircon ages (781-2489 Ma) are found. Initial ɛNd(700 Ma) and ɛsr(700 Ma) values range from-4.3 to -18.3 and + 33.3 to + 99.8, respectively. Neodymium mean crustal residence ages range from 1.62 to 2.88 Ga. These data, in comparison to the western and southern parts of Ethiopia, are indicative of considerable reworking of pre-Pan-African crust. Variations in age, SrNd isotope ratios and chemistry of the granitoids on a regional scale also suggest the existence of two separate basement terrains between southern and eastern Ethiopia, which may be separated by a tectonic line now concealed by Phanerozoic rocks. This tectonic line may represent a major tectonic boundary between the juvenile Arabian

  4. 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

  5. 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.

  6. Zircon U-Pb geochronology, geochemistry, and Sr-Nd-Hf isotopes of granitoids in the Yulekenhalasu copper ore district, northern Junggar, China: Petrogenesis and tectonic implications

    NASA Astrophysics Data System (ADS)

    Yang, Fuquan; Chai, Fengmei; Zhang, Zhixin; Geng, Xinxia; Li, Qiang

    2014-03-01

    The Yulekenhalasu porphyry copper deposit is located in the Kalaxiange'er metallogenic belt in northern Junggar, China. We present the results from zircon U-Pb geochronology, and geochemical and Sr-Nd-Hf isotope analyses of the granitoids associated with the ore deposits with a view to constrain their petrogenesis and tectonic setting. The granitoids consist of quartz diorite, diorite porphyry, porphyritic monzonite, and quartz porphyry, emplaced at 382, 379, 375-374, and 348 Ma, respectively, which span Late Devonian to early Carboniferous ages. The ore-bearing intrusion is mainly diorite porphyry, with subordinate porphyritic monzonite. The Late Devonian intrusions are characterized by SiO2 contents of 54.5-64.79 wt.%, Na2O contents of 3.82-8.24 wt.%, enrichment in Na, light rare-earth elements (LREEs), and large ion lithophile elements. They also display relative depletion in Y, Ba, P, Nb, Ta, and Ti, and weak negative Eu anomalies (δEu = 0.6-0.87). The early Carboniferous quartz porphyry is characterized by high SiO2 content (72.26-73.35 wt.%), enrichment in LREEs, K, and Sr, and relative depletion in Y (10.82-12.52 ppm) and Yb (1.06-1.15 ppm). The Late Devonian and early Carboniferous granitoids are characterized by positive ɛNd(t) values (5.2-10.1, one sample at - 1.9), positive ɛHf(t) values (7.46-18.45), low (87Sr/86Sr)i values (0.70363-0.70476), and young crustal residence ages. These data indicate that the sources of the granitoids were mainly mantle-derived juvenile rocks. Geochemical and Nd-Sr-Hf isotopic data demonstrate that the Late Devonian granitoids formed in an oceanic island arc, and they were formed from different sources, among which the mineralized diorite porphyry might have originated from a mixed slab-derived and mantle wedge melt source. The early Carboniferous quartz porphyry was likely emplaced in a mature island arc environment, and was probably derived from juvenile crust.

  7. 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.

  8. Paleocene and Early Eocene volcanic ash layers in the Schlieren Flysch, Switzerland: U-Pb dating and Hf-isotopes of zircons, pumice geochemistry and origin

    NASA Astrophysics Data System (ADS)

    Koch, Simone; Winkler, Wilfried; Von Quadt, Albrecht; Ulmer, Peter

    2015-11-01

    Thin mm to cm thick bentonite layers of Paleocene to Early Eocene age in the Tonsteinschichten of the Schlieren Flysch represent volcanic ash layers. Heavy mineral analysis of the layers indicates basic to acidic volcanic sources. U/Pb dating of single zircon crystals of a Paleocene layer (WW1948) by LA-ICP-MS points to an eruption at 59.87 ± 0.41 Ma, whereas ID-TIMS shows an eruption age of 60.96 ± 0.07 Ma. Taking into account the external precision of LA-ICP-MS analyses of 1-2% both ages are overlapping and indicate an apparent minimal durations of zircon crystallization of 350 ka. Hf-isotope analysis of the same zircon crystals reveals the hybrid character of the source magma. The geochemical composition of the pumice grains of all bentonite layers is strongly affected by alteration. Nevertheless, the original character of the volcanic source can be evaluated. The Paleocene ashes (Lower Tonsteinschichten, LT) show a more fractionated multi-element pattern than the ashes of Early Eocene (Upper Tonsteinschichten, UT). The LT ash series are of rhyodacite to dacite character whereas the UT ashes fall in the field of alkali basalts. Both ash series seem to originate from a within-plate volcanic setting according to their trace element concentrations. Geochemical and temporary counterparts can be found in ash layers from Anthering (Austria) and the Danish Basin. As proposed for those ashes, volcanism connected to the opening of the North Atlantic might be the source as well for the ashes in the Schlieren Flysch. By comparison of the composition of rocks from the British Paleogene Igneous Province BPIP and the Schlieren Flysch ashes many correlations can be drawn which supports the suggestion of a North Atlantic origin of the Alpine ashes.

  9. Geochemistry and detrital zircon U-Pb and Hf isotopes of the paragneiss suite from the Quanji massif, SE Tarim Craton: Implications for Paleoproterozoic tectonics in NW China

    NASA Astrophysics Data System (ADS)

    Zhang, Lu; Wang, Qinyan; Chen, Nengsong; Sun, Min; Santosh, M.; Ba, Jin

    2014-12-01

    The Delingha paragneiss suite in the Quanji massif, southeastern Tarim Craton, is composed of mica schist, paragneiss, leptynite and quartzite, similar to the 'khondalite suites' described from elsewhere in the world. The mica schist is rich in Al2O3 (up to ∼26 wt%) and contains graphite and diagnostic minerals including sillimanite and garnet, with metamorphism under amphibolite-facies to locally granulite-facies conditions as manifested by association with amphibolite and granulite. The detrital zircon U-Pb ages and geochemical data indicate that the protolith materials of the Delingha paragneiss suite were mainly sourced from 2.20 to 2.45 Ga granites, felsic volcanic rocks and TTG, and were deposited at 2.17-1.92 Ga. The detrital zircon Hf and whole-rock Nd isotopes document important crustal growth at ∼2.5-2.7 Ga. The detrital zircon age spectra, the whole rock Nd and zircon Hf model ages, the low-maturity of the protolith, and short-distance transportation suggest that the detritus were derived from the underlying Delingha Complex and the lower Dakendaban sub-Group. The timing of magmatic activities in the source region, the depositional age and metamorphic histories of the Delingha paragneiss suite are all comparable to those recorded in the khondalite belt along northern margin of the Ordos Block in the North China Craton. Our study shows that the 2.2-2.45 Ga magmatic rocks were generated in arc or active continental margin settings, suggesting a prolonged subduction and accretion history prior to final amalgamation (∼2.5-1.8 Ga) to form the unified North China Craton and the assembly of the Tarim Craton in NW China.

  10. 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.

  11. Petrogenesis and tectonic settings of volcanic rocks of the Ashele Cu-Zn deposit in southern Altay, Xinjiang, Northwest China: Insights from zircon U-Pb geochronology, geochemistry and Sr-Nd isotopes

    NASA Astrophysics Data System (ADS)

    Wu, Yufeng; Yang, Fuquan; Liu, Feng; Geng, Xinxia; Li, Qiang; Zheng, Jiahao

    2015-11-01

    The Early-Mid-Devonian Ashele Formation of the southern margin of the Chinese Altay hosts the Ashele Cu-Zn volcanogenic massive sulfide (VMS) deposit and consists of intercalated volcanic and sedimentary rocks that have experienced regional greenschist-facies metamorphism. We studied the petrography, zircon U-Pb geochronology, geochemistry, and Sr-Nd isotopes of dacites and basalts in order to understand the petrogenesis of these rocks and the regional tectonic evolution. Two dacites yielded LA-MC-ICP-MS zircon U-Pb ages of 402 ± 6 Ma and 403 ± 2 Ma. The dacites are calc-alkaline, and characterized by high Na2O/K2O ratios (3.6-9.3), and high Mg# values (47-63), enrichment in large ion lithophile elements (LILE) and light rare earth elements (LREE), depletion in Nb, Ta, Ti, and P, and relatively positive εNd(t) values (+3.6 to +7.5), collectively suggesting a sanukitic magma affinity. The variations in the major and trace elements of the dacites indicate that Fe-Ti oxide, plagioclase, and apatite were fractionated during their petrogenesis. The basalts are tholeiitic, and are characterized by high Mg# values (66-73), and negative Nb and Ta anomalies. The geochemical characteristics of the basalts are similar to those of N-MORB. Those characteristics together with the positive εNd(t) values (+6.8 to +9.2) of the basalts, indicate that the precursor magma was derived mainly from an N-MORB-type depleted asthenospheric mantle in an island arc setting. The geochemical similarities between the basalts and dacites indicate that they both originated from a similar depleted mantle source via partial melting under different magmatic conditions in each case, possibly related to ridge subduction.

  12. Provenance and tectonic setting of Proterozoic metasedimentary sequences of the São Roque Domain, Ribeira Fold Belt, Brazil: a combination of whole-rock geochemistry, Sm-Nd isotopic systematics and detrital zircon U-Pb geochronology

    NASA Astrophysics Data System (ADS)

    Henrique Pinto, Renato; Janasi, Valdecir de A.; Barnes, Sarah-Jane; Borges Carvalho, Bruna; Tassinari, Colombo C. G.; Basei, Miguel A. S.

    2014-05-01

    The Proterozoic São Roque Group (Ribeira Fold Belt, southeast Brazil) is a metasedimentary sequence deposited in a marine environment consisting of proximal metasandstones and meta-felspathic wackes with some volcanic layers (Boturuna Formation) and more distal metawackes and metamudstones (Piragibu Formation). A combination of zircon provenance studies in metasandstones (textural and trace-element analysis and U-Pb geochronology) and whole-rock major and trace-element geochemistry and Sm-Nd isotopic systematics in metamudstones was used to understand the provenance and tectonic significance of this sequence, and their implications to the evolution of the Precambrian crust in the region. Whole-rock geochemistry indicates that the sources are largely granitic (as indicated for instance by the LREE-rich moderately fractionated REE patterns and subtle negative Eu anomalies) with some mafic contribution (responsible for higher contents of Fe2O3, MgO, V, and Cr) and were subject to moderate weathering (CIA - 60 to 82). The trace element signatures in detrital zircons indicate that most of them are derived from plagioclase-rich felsic rocks, as indicated by strong positive Ce anomalies, high (Lu/Sm)N ratios, low U/Yb, and a concave-down shape of the intermediate REE in chondrite-normalized plots. A significant proportion of the zircon crystals show rounded cores with growth zoning truncated and overgrown by a thin rim that has dark color in cathodoluminescence images. These overgrowths are chemically distinct, being enriched in trace elements, especially the LREE, and were dated at 584±47 Ma, reflecting the regional Neoproterozoic metamorphism. Sm-Nd isotope data for Piragibu Formation metamudstones show four main groups of Nd TDM ages at ca. 1.9 Ga, 2.1 Ga, 2.4 Ga and 3.0 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 oldest Nd TDM age (3.0 Ga) is similar

  13. A list of references on lead isotope geochemistry through 1966

    USGS Publications Warehouse

    Doe, Bruce R.

    1968-01-01

    This bibliography was constructed to be as complete as possible for terminal papetrs containing new data relative to the geochmical applications of Common lead U-Th-Pb isotopic dating PbPb210, Pb212, Pb214 No effort was made for completeness of: Annual report, Yearbooks, etc. Review papers although many are included. Abstract and these are omitted.

  14. 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.

  15. The provenance of Archean clastic metasediments in the Narryer Gneiss Complex, western Australia: Trace element geochemistry, Nd isotopes, and U-Pb ages for detrital zircons

    SciTech Connect

    Maas, R. Curtin Univ., Perth ); McCulloch, M.T. )

    1991-07-01

    Clastic metasedimentary rocks of mid-Archean age from the Mt. Narryer and Jack Hills metasedimentary belts have REE patterns resembling those of mid- to late-Archean pelitic-quartzitic cratonic sequences elsewhere, and post-Archean continental rocks in general. Detrital zircons in the metasediments range in age from ca. 3,000 to 3,700 Ma. This indicates a provenance from mature cratonic sources controlled by K-rich granitic rocks. Additional minor sediment sources were identified as older, mainly chemical sedimentary sequences, ultramafic rocks, and felsic rocks characterized by low HREE contents, perhaps of tonalitic affinity. Differences between sedimentary REE patterns and those in the surrounding 3.73-3.0 Ga orthogneiss terrain, and between detrital zircon ages and the age distribution in the gneisses, suggest that the present association of the metasedimentary belts with the orthogneiss terrain is of tectonic origin. The occurrence of detrital zircons with U-Pb ages > 4 Ga in certain quartzites and conglomerates of the Jack Hills and Mt. Narryer metasedimentary sequences indicates a further, most likely granitic, source. {epsilon}{sub Nd}(T{sub Dep}) values in Jack Hills metasediments vary widely (+5 to {minus}12) but have a smaller range in the Mt. Narryer belt ({minus}5 to {minus}9). The lowest {epsilon}{sub Nd} values of both sequences are interpreted to reflect the presence of detritus derived from 4.1-4.2 Ga old LREE-enriched continental crust in proportions considerably larger ({ge} 10%) than estimated previously from the abundance of pre-4 Ga detrital zircons ({approx}3%). This would imply the former existence of significant volumes of pre-4 Ga continental crust in the provenance of the Mt. Narryer and Jack Hills metasediments.

  16. 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

  17. Zircon U-Pb age and Sr-Nd-Hf-O isotope geochemistry of the Paleocene-Eocene igneous rocks in western Gangdese: Evidence for the timing of Neo-Tethyan slab breakoff

    NASA Astrophysics Data System (ADS)

    Wang, Rui; Richards, Jeremy P.; Hou, Zeng-qian; An, Fang; Creaser, Robert A.

    2015-05-01

    Northward Neo-Tethyan oceanic lithosphere subduction beneath southern Tibet in the Mesozoic-Early Cenozoic produced continental arc magmas in the ~ 1600 km-long Gangdese belt. The most voluminous magmatism occurred in the Paleocene-Eocene, and is characterized by extensive I-type calc-alkaline to high-K calc-alkaline Linzizong volcanic rocks, and coeval plutons. These rocks have been extensively studied in the eastern Gangdese belt (east of ∼ 89°E), but few data exist from the western Gangdese belt. New data for eleven samples of these rocks, combined with existing data from the literature, show that they are similar to the eastern Gangdese belt rocks, with relative depletions in Nb, Ta, P, and Ti, and enrichments in Rb, Ba, Th, U, K, Pb, Zr, and Hf on a primitive mantle-normalized trace element diagrams, typical of continental arc-related igneous rocks. However, compared to the east, western Gangdese igneous rocks range to higher K2O contents (up to 6.1 wt.%), higher (87Sr/86Sr)i ratios (up to 0.7151), and lower εNdi values (down to - 8.1), suggesting that an evolved crustal source was involved in arc magmatism. The Gangdese arc magmatism lasted to ~ 80 Ma, and has a gap or quiescent period afterwards. Starting at ~ 69 Ma, the arc magmatism initiated and shifted southward from ~ 30.5°N to ~ 29.5°N in southern Tibet with an abrupt change of India-Asia convergence rate. The magmas through the whole Gangdese belt at ~ 69-53 Ma are characterized by intermediate εNdi values (- 0.6 to + 4.0), positive εHfi values (+ 3.8 to + 7.1), intermediate δ18O values (+ 5.0‰ to + 6.5‰), and low Th/Y and La/Yb ratios (< 20). These magmas were likely derived from the mantle with crustal contamination by MASH process in response to Neo-Tethyan slab rollback as proposed by previous studies. The Sr-Nd-Hf-O isotopic compositions of Linzizong volcanic rocks and coeval intrusions are relatively homogeneous during ~ 69-53 Ma, but show a wide range at ~ 53-50 Ma. Zircon

  18. 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.

  19. K-Ar ages and Pb, Sr isotopic characteristics of Cenozoic volcanic rocks in Shandong Province, China

    USGS Publications Warehouse

    Daogong, C.; Zicheng, P.; Lanphere, M.A.; Zartman, R.E.

    1985-01-01

    28 samples of Cenozoic volcanic rocks collected from Shandong Province have been dated by K-Ar method. They are mainly Neogene with an age range of 4-19 m. y. The basalts from Linqu and Yishui in west Shandong Province are Miocene and those from Penglai and Qixia in east Shandong Province are Miocene and Pliocene in age. The basalts from Wudi in north Shandong Province are Middle-Early Pleistocene in age. In each area the duration of volcanic eruption was estimated at about 2-3 m. y. Pb and Sr isotopic compositions and U, Th, Pb, Rb, Sr, and major elements in most of the samples were determined. The isotopic compositions are:206Pb/204Pb-16.92-18.48,207Pb/204Pb-15.30-15.59,208Pb/204Pb-37.83-38.54, and (87Sr/86Sr)i-0.70327-0.70632. There are some positive or negative linear correlations between206Pb/204Pb and207Pb/204Pb, Pb isotopes and Pb content, Pb isotopes and Sr isotopes, and Sr isotopes and other elements. The basaltic rocks from east and west Shandong Province have somewhat differences in isotopic composition and element content. The basalts probably are products of multi-stage evolution of the mantle. They have preserved the primary features of the source, although they were influenced, to some extent, by the contamination of crustal materials. ?? 1985 Institute of Geochemistry, Chinese Academy of Sciences.

  20. 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

  1. Pb Isotopes Track Asian Pollution in California

    NASA Astrophysics Data System (ADS)

    Ewing, S. A.; Christensen, J. N.; Brown, S. T.; Vancuren, R. A.; Cliff, S. S.; Depaolo, D. J.

    2008-12-01

    The transport of Asian pollution to North America has broad implications for global climate models and regional air quality regulation. In the western US, rising atmospheric Pb levels have been evident since the mid-1990s despite the phase-out of leaded gasoline. We use Pb isotopes to fingerprint the trans-Pacific component of atmospheric pollution in California. We measured Pb isotopes in airborne particles collected at two sites west (Mt. Tamalpais) and east (Chabot Observatory, Oakland Hills) of the San Francisco Bay Area, from winter 2007 through late spring 2008. We also analyzed archived springtime samples from inland sites throughout central California. Wintertime values of 206Pb/207Pb vs. 208Pb/207Pb at Chabot Observatory form a linear array that is consistent with published data for San Francisco Bay waters, whereas published values for Chinese cities and loess fall along a separate and distinct array for that region, consistent with our analysis of samples collected at Hefei, China in 2002. Between March and May 2008, the Tamalpais and Chabot samples diverge from the California regional array toward the Chinese array. About half of the central California samples also show a strong Asian influence. We quantify the divergence of values from the regional California array as Δ208Pb = (208Pb/207Pb)expected - (208Pb/207Pb) )observed, where (208Pb/207Pb)expected is derived from a linear fit to the wintertime samples at Chabot Observatory. These Δ208Pb values increase between winter and spring at both Mt. Tamapais and Chabot Observatory, and are higher at Mt. Tamalpais, despite lower Pb concentrations at that site. They indicate that up to 80% of the Pb in the Tamalpais samples, and up to 40% of the Pb in the Chabot Observatory samples, reflect trans-Pacific transport. The lower proportion in the Chabot samples -- where there is often more Pb -- indicates dilution by local urban sources. Our data provide conclusive evidence of Asian air pollution reaching

  2. 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.

  3. Petrology and Sr, Nd, and Pb isotope geochemistry of mid-ocean ridge basalt glasses from the 11°45'N to 15°00'N segment of the East Pacific Rise

    NASA Astrophysics Data System (ADS)

    Castillo, P. R.; Klein, E.; Bender, J.; Langmuir, C.; Shirey, S.; Batiza, R.; White, W.

    2000-11-01

    Basaltic glasses from the geophysically well-studied section of the East Pacific Rise (EPR) between 11°45'N to 15°00'N range from normal mid-ocean ridge basalts (MORB) to transitional MORB and their major element variations correlate with isotopic and trace element indices of enrichment. To first order, basalts enriched in Na8.0, incompatible elements, 87Sr/86Sr, and 206Pb/204Pb but low in Fe8.0 and 143Nd/144Nd are more prevalent along the shallow portions of the ridge axis. In detail, the samples can be divided into two chemical and geographical Groups: the southern bathymetric dome, extending from the 11°45'N overlapping spreading center to ~14°10'N, and the northern Group, extending from ~14°10'N to the Orozco transform. The boundary between these two Groups is apparent in a change in isotopic composition. Results indicate that there are three mantle source components that produce the compositional variability observed among samples from the 11°45'N to 15°00'N segment of the EPR: a depleted mantle component, a seamount-type enriched mantle component, and an Indian MORB-like mantle component. South of ~14°10'N, the geochemical variability is dominated by binary mixing between a depleted mantle component and an enriched component similar to near-ridge seamounts. North of ~14°10'N, the low 206Pb/204Pb, high 207Pb/204Pb Indian MORB-like component exerts a major influence on the geochemical variability of the axial lavas. Regional averages of major element composition (e.g., Na8.0 and Fe8.0) show relatively limited variability consistent with the restricted range in depth for this region and plot within the Pacific field of the previously defined global trends. Major element variations among individual samples, however, parallel the global array, and their correlation with indices of mantle enrichment supports the idea that the ``Pacific-type local trend'' results from small-scale heterogeneities in the mantle beneath the EPR. Our results also indicate that

  4. 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.

  5. 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.

  6. B, Sr and Pb isotope geochemistry of high-pressure Alpine metaperidotites monitors fluid-mediated element recycling during serpentinite dehydration in subduction mélange (Cima di Gagnone, Swiss Central Alps)

    NASA Astrophysics Data System (ADS)

    Cannaò, E.; Agostini, S.; Scambelluri, M.; Tonarini, S.; Godard, M.

    2015-08-01

    Tectonic mixing of slab- and mantle-derived materials at the interface between converging plates highly enhances fluid-mediated mass transfer from the slab to the overlying mantle. Subduction mélanges can provide information about the interaction among different slices accreted at plate interface domains, with implications on the tectonic and geochemical evolution of the plate-interface itself. At Cima di Gagnone, pelitic schists and gneiss enclose chlorite harzburgite and garnet peridotite lenses, like in subduction mélanges located in-between downgoing slabs and overlying mantle. These peridotites host MORB-type eclogite and metarodingite, and derive from dehydration of serpentinized mantle protoliths. Their enrichment in fluid-mobile B, As, Sb, U, Th is the result of an early-stage oceanic serpentinization, followed by interaction with host metasediments during subduction burial. Here we define the element exchange process in the Gagnone mélange by means of the B, Sr and Pb isotope analysis of its main lithologies (ultramafic, mafic rocks and paragneiss). The 87Sr/86Sr and 206Pb/204Pb ratios of ultramafic rocks (0.7090-0.7124 and 18.292-18.837, respectively) show enrichments in radiogenic Sr and Pb after exchange with the host paraschist (up to 0.7287 87Sr/86Sr; 18.751 206Pb/204Pb). The δ11B values of peridotites (down to -10‰) point to a combined effect of (1) 11B release to deserpentinization fluids (serpentinized protoliths likely had positive δ11B and lower radiogenic Sr, Pb), and of (2) exchange with fluids from the surrounding metasediments. The whole Gagnone rock-suite is finally overprinted by retrograde fluids that essentially bring to an increase in radiogenic Pb (about 19.0 206Pb/204Pb) and to values of 0.710 87Sr/86Sr and of -10‰ δ11B. The recognition of different stages of interaction between mantle rocks and sedimentary/crustal reservoirs allows us to define the geochemical effects related to the early coupling of such rocks along the

  7. Effects of Simple Leaching of Crushed and Powdered Materials on High-precision Pb Isotope Analyses

    NASA Astrophysics Data System (ADS)

    Todd, E.; Stracke, A.

    2013-12-01

    We present new results of simple 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 6N HCl in two steps, first hot and then in an ultrasonic bath, and washed with ultrapure H2O before conventional sample digestion and chromatographic purification of Pb. Pb isotope analyses were determined with Tl-doped MC-ICP-MS. Intra- and inter-session analytical reproducibility of repeated analyses of both synthetic Pb solutions and Pb from single digests of chemically processed natural samples were generally < 100 ppm (2 S.D.). The comparison of leached and unleached samples shows that leaching reliably removes variable amounts of different contaminants for different starting materials. For repeated digests of a single sample, the leached samples reproduce better than the unleached ones, showing that leaching effectively removes heterogeneously distributed extraneous Pb. However, the reproducibility of repeated digests of variably contaminated natural samples is up to an order of magnitude worse than the analytical reproducibility of ca. 100 ppm. More complex leaching methods (e.g., Nobre Silva et al., 2009) yield Pb isotope ratios within error of and with similar reproducibility to our method, showing that the simple leaching method is reliable. The remaining Pb isotope heterogeneity of natural samples, which typically exceeds 100 ppm, is thus attributed to inherent isotopic sample heterogeneity. Tl-doped MC-ICP-MS Pb ratio determination is therefore a sufficiently precise method for Pb isotope analyses in natural rocks. More precise Pb double- or triple-spike methods (e.g., Galer, 1999; Thirlwall, 2000), may exploit their full potential only in cases where natural isotopic sample heterogeneity is demonstrably negligible. References: Galer, S., 1999, Chem. Geol. 157, 255-274. Nobre Silva, et al. 2009, Geochemistry Geophysics Geosystems 10, Q08012

  8. Infrared spectroscopy and hydrogen isotope geochemistry of hydrous silicate glasses

    SciTech Connect

    Epstein, S.; Stolper, E.

    1992-01-01

    The focus of this project is the combined appication of infrared spectroscopy and stable isotope geochemistry to the study of hydrogen-bearing species dissolved in silicate melts and glasses. We are conducting laboratory experiments aimed at determining the fractionation of D and H between melt species (OH and H{sub 2}O) and hydrous vapor and the diffusivities of these species in glasses and melts. Knowledge of these parameters is critical to understanding the behavior of hydrogen isotopes during igneous processes and hydrothermal processes. These results also could be valuable in application of glass technology to development of nuclear waste disposal strategies.

  9. 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.

  10. 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. PMID:27303032

  11. 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

  12. 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.

  13. Beryllium isotope geochemistry in tropical river basins

    SciTech Connect

    Brown, E.T.; Edmond, J.M. ); Raisbeck, G.M.; Bourles, D.L.; Yiou, F. ); Measures, C.I. )

    1992-04-01

    The distributions of beryllium-9 and beryllium-10 in rivers within the Orinoco and Amazon basins have been examined to extend the understanding of their geochemical cycles and to develop their use both in geochronometry, and in studying erosional processes. Analyses of {sup 9}Be in dissolved and suspended material from rivers with a wide range of chemical compositions indicate that its geochemistry is primarily controlled by two major factors: (1) its abundance in the rocks of the watershed and (2) the extent of its adsorption onto particle surfaces. The relative importance of these parameters in individual rivers is determined by the extent of interaction with flood-plain sediments and the riverine pH. This understanding of {sup 9}Be geochemistry forms a basis for examination of the geochemical cycling of {sup 10}Be. In rivers which are dominated by interaction with sediments, the riverine concentration of dissolved {sup 10}Be is far lower than that in the incoming rainwater, indicating that a substantial proportion of it is retained within the soils of the basin or is adsorbed onto riverine particles. However, in acidic rivers in which the stable dissolved Be concentration is determined by the Be level in the rocks of the drainage basin, dissolved {sup 10}Be has essentially the same concentration as in precipitation. These observations imply that the soil column in such regions must be saturated with respect to {sup 10}Be, and that the ratio of the inventory to the flux does not represent an age, as may be the case in temperate latitudes, but rather a residence time.

  14. 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.

  15. 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.

  16. 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. PMID:25908819

  17. Whole-rock geochemistry and Sr-Nd-Pb isotope systematics of the Late Carboniferous volcanic rocks of the Awulale metallogenic belt in the western Tianshan Mountains (NW China): Petrogenesis and geodynamical implications

    NASA Astrophysics Data System (ADS)

    Ge, Songsheng; Zhai, Mingguo; Safonova, Inna; Li, Dapeng; Zhu, Xiyan; Zuo, Pengfei; Shan, Houxiang

    2015-07-01

    The Awulale metallogenic belt (AMB) of the western Tianshan (NW China) includes Late Carboniferous (ca. 320 Ma) ore-bearing volcanic rocks of the Dahalajunshan Formation. The petrogenesis and tectonic setting of these volcanic rocks are important for the understanding of the tectonic evolution and metallogeny of the western Tianshan. This paper presents new major and trace elements and Sr-Nd-Pb isotope data from the Dahalajunshan volcanic rocks, which are mainly calc-alkaline basaltic trachy-andesite and trachy-andesite with subordinate basalt, trachy-basalt and rhyolite. The variations of major and trace elements in the mafic and intermediate volcanic rocks indicate the fractionation of pyroxene and magnetite or hornblende, magnetite, apatite and plagioclase, respectively, during their petrogenesis. The Dahalajunshan volcanic rocks have similar primitive mantle-normalized diagrams and chondrite-normalized rare-earth element (REE) patterns suggesting their similar mantle source(s). They are characterized by enrichment in large ion lithophile elements (LILEs) and light REEs (LREEs), depletion in heavy REEs (LaN/YbN ≈ 2.80 to 9.59) and high field strength elements (HFSEs) and εNd(t) ranging from + 1.2 to + 6.0 at 86Sr/87Sr(t) = 0.7047-0.7063 and 206Pb/204Pbi = 17.49-18.19. Both the geochemical and isotopic data indicate that the volcanic rocks were probably derived by low-degree melting of sub-arc lithospheric mantle modified by fluids in a continental arc setting. Our obtained results, in conjunction with previous published data, allow us to suggest that the southward subduction of Junggar oceanic crust continued until the Late Carboniferous and was followed by a tectonic shift from continental arc to post-collisional extension environment.

  18. 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.

  19. Easter microplate evolution: Pb isotope evidence

    NASA Astrophysics Data System (ADS)

    Hanan, Barry B.; Schilling, Jean-Guy

    1989-06-01

    We report on 53 Pb isotope analyses of basalts from 48 dredge stations occupied along the spreading boundaries of the Easter microplate and adjacent East Pacific Rise (EPR). Also included in the study are seven analyses of basalts from Easter and Sala y Gomez islands. A major anomaly is observed on the East Rift, around 27°S, where this ridge is shallowest and closest to Easter and Sala y Gomez islands. Basalts from the West Rift are less radiogenic. The means for the two rift populations are distinct, but their ranges overlap significantly. On the average, there is a systematic westward decrease in radiogenic Pb content with distance from Sala y Gomez. The Pb isotope anomaly is confined to the boundaries of the Microplate and the total range exceeds that of the entire EPR, both in the most and the least end of radiogenic Pb content. Radiogenic Pb content covaries with (La/Sm)N ratios with the exception of a nepheline-normative picritic basalt glass outlier. The trends are curvilinear. There is no correlation between the Pb isotope ratios and the bulk composition of the lavas. In Pb versus Pb isotope diagrams, basalts from the East and West rifts form two tight linear trends of statistically indistinguishable slope. Basalts from Easter and Sala y Gomez islands lie on the upper end of these trends. A binary mixing process between a radiogenic source similar to that present beneath Sala y Gomez and the large ion lithophile element (LILE)-depleted mid-ocean ridge basalt (MORB) source is strongly suggested. There is no trace of the Dupal anomaly beneath the microplate nor beneath Easter or Sala y Gomez Islands. If the Dupal anomaly is indeed continuous and of semi global extent, it must lie deeper in the mantle than the depths at which basaltic melts take source beneath the microplate and these two islands. There is also no correlation between the apparent dispersion of Pb isotope ratios and the rate at which the various ridge segments of the microplate spread. Tests

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

    PubMed

    Wiederhold, Jan G

    2015-03-01

    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.

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

    PubMed

    Wiederhold, Jan G

    2015-03-01

    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. PMID:25640608

  2. 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

  3. The role of recycled oceanic crust in magmatism and metallogeny: Os-Sr-Nd isotopes, U-Pb geochronology and geochemistry of picritic dykes in the Panzhihua giant Fe-Ti oxide deposit, central Emeishan large igneous province, SW China

    NASA Astrophysics Data System (ADS)

    Hou, Tong; Zhang, Zhaochong; Encarnacion, John; Santosh, M.; Sun, Yali

    2013-04-01

    The picritic dykes occurring within fine-grained gabbro in the marginal zone and in the surrounding Proterozoic wall-rock marbles of the Panzhihua Fe-Ti oxide deposit closely correspond in bulk composition with the nearby Panzhihua intrusion. These dykes offer important constraints on the nature of the mantle source of the Panzhihua ore-bearing intrusion and its possible link to the Emeishan plume. U-Pb zircon dating of the picritic dyke yields a crystallization age of 261.4 ± 4.6 Ma, coeval with the timing of the main Panzhihua gabbroic intrusion and Late Permian Emeishan flood basalts. The Panzhihua picritic dykes contain 37.63-43.41 wt% SiO2, 1.15-1.56 wt% TiO2, 11.43-13.25 wt% TFe2O3, and 20.96-28.87 wt% MgO. Primitive-mantle-normalized patterns of the rocks are comparable to those of ocean island basalt. The rocks define a relatively small range of Os isotopic compositions and a low Os signature of -0.13 to +2.76 for γOs (261 Ma). In combination with their Sr-Nd-Os isotopic compositions, we interpret that these rocks were derived from the Emeishan plume sources as well as the interactions of plume melts with the overlying lithosphere which had been extensively affected by eclogite-derived melts from the deep-subducted oceanic slab. Partial melting induced by an upwelling mantle plume that involved an eclogite or pyroxenite component in the lithospheric mantle could have produced the parental Fe-rich magma. Our study suggests that plume-lithosphere interaction might have played a key role in generating many world-class Fe-Ti oxide deposits clustered in the Panxi area.

  4. 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

  5. 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

  6. 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

  7. Petrogenesis of syntectonic granites emplaced at the transition from thrusting to transcurrent tectonics in post-collisional setting: Whole-rock and Sr-Nd-Pb isotope geochemistry in the Neoproterozoic Quatro Ilhas and Mariscal Granites, Southern Brazil

    NASA Astrophysics Data System (ADS)

    Florisbal, Luana Moreira; Bitencourt, Maria de Fátima; Janasi, Valdecir de Assis; Nardi, Lauro Valentim Stoll; Heaman, Larry M.

    2012-11-01

    The Neoproterozoic post-collisional period in southern Brazil (650-580 Ma) is characterized by substantial volumes of magma emplaced along the active shear zones that compose the Southern Brazilian Shear Belt. The early-phase syntectonic magmatism (630-610 Ma) is represented by the porphyritic, high-K, metaluminous to peraluminous Quatro Ilhas Granitoids and the younger heterogranular, slightly peraluminous Mariscal Granite. Quatro Ilhas Granitoids include three main petrographic varieties (muscovite-biotite granodiorite — mbg; biotite monzogranite — bmz; and leucogranite — lcg) that, although sharing some significant geochemical characteristics, are not strictly comagmatic, as shown by chemical and Sr-Nd-Pb isotope data. The most primitive muscovite-biotite granodiorite was produced by contamination of more mafic melts (possibly with some mantle component) with peraluminous crustal melts; the biotite monzogranite, although more felsic, has higher Ca, MgO, TiO2 and Ba, and lower K2O, FeOt, Sr and Rb contents, possibly reflecting some mixing with coeval mafic magmas of tholeiitic affinity; the leucogranite may be derived from pure crustal melts. The Mariscal Granite is formed by two main granite types which occur intimately associated in the same pluton, one with higher K (5-6.5 wt.% K2O) high Rb and lower CaO, Na2O, Ba and Zr as compared to the other (3-5 wt.% of K2O). The two Mariscal Granite varieties have compositional correspondence with fine-grained granites (fgg) that occur as tabular bodies which intruded the Quatro Ilhas Granoitoids before they were fully crystallized, and are inferred to correspond to the Mariscal Granite feeders, an interpretation that is reinforced by similar U-Pb zircon crystallization ages. The initial evolution of the post-collisional magmatism, marked by the emplacement of the Quatro Ilhas Granitoids varieties, activated sources that produced mantle and crustal magmas whose emplacement was controlled both by flat-lying and

  8. 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 εHf(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 εHf(t) and εNd(t) indicate sources with long crustal residence for all studied granite plutons, the observed range is more radiogenic than the

  9. Helium isotope geochemistry of some volcanic rocks from Saint Helena

    NASA Astrophysics Data System (ADS)

    Graham, David W.; Humphris, Susan E.; Jenkins, William J.; Kurz, Mark D.

    1992-05-01

    3He/ 4He ratios have been measured for olivine and clinopyroxene phenocrysts in 7-15 m.y. old basaltic lavas from the island of St. Helena. Magmatic helium was effectively resolved from post-eruptive radiogenic helium by employing various extraction techniques, including in vacuo crushing, and stepwise heating or fusion of the powders following crushing. The inherited 3He/ 4He ratio at St. Helena is 4.3-5.9 R A. Helium isotope disequilibrium is present within the phenocrysts, with lower 3He/ 4He upon heating and fusion of the powders following crushing, due to radiogenic ingrowth or to α-particle implantation from the surrounding (U + Th)-rich lavas. A single crushing analysis for clinopyroxene in a basalt from Tubuaii gave 3He/ 4He= 7.1 R A. 3He/ 4He ratios at St. Helena and Tubuaii (HIMU hotspots characterized by radiogenic Pb isotope signatures) are similar to 3He/ 4He ratios previously measured at Tristan da Cunha and Gough Island (EM hotspots characterized by low 206Pb/ 204Pb ). Overall, the He sbnd Sr sbnd Pb isotope systematics at these islands are consistent with a mantle origin as contiguous, heterogeneous materials, such as recycled crust and/or lithosphere. 3He/ 4He ratios at HIMU hotspots are similar to mantle xenoliths which display nearly the entire range of Pb isotope compositions found at ocean islands, and are only slightly less than values found in mid-ocean ridge basalts (7-9 R A). This suggests that the recycled materials were injected into the mantle within the last 10 9 yrs.

  10. 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

  11. 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

  12. 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

  13. 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.

  14. Extending the calibration of marine barite Pb isotope records

    NASA Astrophysics Data System (ADS)

    Erhardt, A. M.; Paytan, A.

    2010-12-01

    Lead isotopes in marine barite have been emerging as a new proxy for intermediate water conditions. Marine barite forms at intermediate water depths and incorporates Pb into its matrix at ~2ppm. The isotopic composition of this Pb is retained as the barite settles in the water column, allowing us to reconstruct the Pb isotopic ratios of intermediate water. Lead and its isotopes are introduced into the ocean primarily through the weathering of continental rock. These rocks may have distinct isotopic signatures, depending on the age of the eroded material and weathering style. Lead has a short residence time in the ocean. As a result of these characteristics, different water masses have distinct lead isotope signatures that depend on the Pb sources (riverine and atmospheric) to the water mass at the point of origin. Since anthropogenic pollution has irrevocably altered Pb concentrations and isotope ratios, calibration of Pb proxies relies on data collected from other sources. Currently, ferromanganese nodules have been utilized for seawater Pb reconstructions. As nodules form at the seafloor, for intermediate water depth these records are limited to isolated seamounts in the open ocean. As a result, the calibration of intermediate water column Pb isotopes requires the characterization of signatures using barite form a whole spectrum of regions. This study reports Pb isotopes in barite from a broad range of locations and extends the current core top data from the equatorial Pacific.

  15. Provenancing anthropogenic Pb within the fluvial environment: developments and challenges in the use of Pb isotopes.

    PubMed

    Bird, Graham

    2011-05-01

    The potentially deleterious presence of ore-derived Pb within riverine environments has been a long-term impact of industrial and anthropogenic activity in general. The surface drainage network has been widely established as a key transport mechanism and storage environment for anthropogenically-derived Pb and other potentially harmful trace metals. Lead isotopes ((204)Pb, (206)Pb, (207)Pb, (208)Pb) have been utilized as a geochemical tracer of Pb origin in a variety of environmental media, notably in atmospheric aerosols. However, given the relative complexity of dispersal processes within riverine environments, the use of Pb isotopes as geochemical tracers has been relatively limited and it is only relatively recently that a growing body of research has applied Pb isotopes to provenancing fluvially-dispersed Pb. This paper seeks to synthesize the developments in the use of Pb isotopes within riverine environments. In doing so it outlines the Pb-isotope fingerprinting technique and associated analytical developments, and assesses the application of Pb isotopes in establishing the origin and dispersal mechanisms of anthropogenically- and geogenically-derived Pb at a range of temporal and spatial scales. Of particular importance are the approaches quantifying source inputs using Pb isotopic signatures and the challenges faced, and options available in quantifying source inputs at the catchment scale; where Pb may be sourced from a variety (n=>2) of sources. The Pb isotopic signature of contemporary riverine Pb loads is shown to reflect a spatially complex influence of mineralization chemistry, anthropogenic activity as well as the hydro-morphological controls exerted upon Pb release, dispersal and storage. In relation to this, the long-term environmental legacy, and its influence upon Pb fingerprinting studies, of tetra-ethyl Pb, sourced from the combustion of leaded-petrol is also discussed. Finally, this paper places the use of Pb isotopes in the context of

  16. Calcium Isotope Geochemistry: Research Horizons and Nanoscale Fractionation Processes

    SciTech Connect

    Yang, W; Simon, J I; DePaolo, D J; Watkins, J M; Richter, F M; Fantle, M S; Ryerson, F J; Ewing, S A; Turchyn, A V; Owens, T L

    2008-10-28

    Interest in studies of calcium isotope variations in nature continues to increase. Investigations span human biology, plants and soils, oceanography and paleoclimate, early solar system processes, aqueous geochemistry, and silicate liquid structure. Variations in the 44Ca/40Ca ratio are generally small, about 5 {per_thousand}, but gradual small improvements in analytical capability now yield 0.05 to 0.1 {per_thousand} resolution. The field is still plagued by a lack of universal standards for isotope ratios and data representation, but these are secondary issues. Traditional isotopic systems have been based in equilibrium thermodynamics, which can explain the magnitude and sign of observed mass-dependent fractionation behavior. For Ca isotopes this is not the case. There is still no reliable way to estimate the equilibrium free energy associated with isotopic exchange between most phases of interest. Experiments are difficult to interpret because it is almost impossible to precipitate minerals from aqueous solution at equilibrium at low temperature. Some studies suggest that, for example, there is no equilibrium isotopic fractionation between calcite and dissolved aqueous Ca. There is good evidence that most Ca isotopic fractionation is caused by kinetic effects. The details of the controlling processes are still missing, and without this mechanistic understanding it is difficult to fully understand the implications of natural isotopic variations. Recent work on dissolved Ca, calcite, and sulfates in both laboratory and natural settings is shedding light on where the fractionation may arise. There is emerging evidence for mass dependent fractionation associated with aqueous diffusion, but probably the primary source of the effects is in the details of precipitation of minerals from solution. This makes the fractionation potentially dependent on a number of factors, including solution composition and mineral growth rate. The next challenge is to develop appropriate

  17. Zircon U-Pb ages, geochemistry, and Nd-Hf isotopes of the TTG gneisses from the Jiaobei terrane: Implications for Neoarchean crustal evolution in the North China Craton

    NASA Astrophysics Data System (ADS)

    Shan, Houxiang; Zhai, Mingguo; Wang, Fang; Zhou, Yanyan; Santosh, M.; Zhu, Xiyan; Zhang, Huafeng; Wang, Wei

    2015-02-01

    The Precambrian basement in the Jiaobei terrane is largely composed of Tonalite-Trondhjemite-Granodiorite (TTG) suite of rocks and offers important insights into the crustal evolution history of the North China Craton (NCC). The LA-ICP-MS zircon U-Pb age data presented in this study show that the magmatic protoliths of the TTG gneisses formed during 2508-2547 Ma and recorded the Paleoproterozoic metamorphism (∼1905 Ma). The rocks are enriched in LILE (Rb, Ba and Sr) and depleted in HFSE (Nb, Ta, Zr and Hf). They are characterized by high Sr contents (406-2906 ppm), Sr/Y ratios (31.3-355) and subchondritic Nb/Ta ratios (18.5-68.9). The TTGs show relatively high ΣREE contents (72.0-266 ppm) with strongly enriched LREE ((La/Yb)N = 11.5-121) and positive or negligible negative Eu anomalies (Eu/Eu∗ = 0.84-1.89). These geochemical features suggest that the magma source might have been rutile-bearing amphibole eclogite. Their high Mg# numbers (42-56) and high Cr (153-285 ppm) and Ni contents (22.2-74.5 ppm) indicate interaction with the mantle wedge during magma ascent. The whole rock εNd (t) values (+2.6 to +3.8) and most of the magmatic zircon εHf (t) values (+1.3 to +7.6) suggest juvenile to evolved isotopic signatures. All these lines of evidence suggest that the TTG rocks in this study formed through partial melting of subducted oceanic slab in a continental arc environment. The drill holes in the Jiaobei terrane are dominated by ∼2.5 Ga TTG gneisses, suggesting that the TTG magma at ∼2.5 Ga is more widely distributed deep underground than that of ∼2.7-2.9 Ga, at least within the approachable depth range of our research. Some zircon grains from Jiaobei TTGs give high εHf (t) values plotting above the curve of 0.75 ∗ εHf of DM, and their TCDM ages are very close to the time of the zircon crystallization. However, the majority of the εHf (t) values fall below the curve of 0.75 ∗ εHf of DM and their TCDM ages are concentrated between ∼2.7-2.9 Ga

  18. 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.

  19. 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

  20. 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.

  1. 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

  2. Lead (Pb) fluxes and Pb isotopic compositions from Masaya Volcano, Nicaragua

    NASA Astrophysics Data System (ADS)

    Vallelonga, P.; Mather, T. A.

    We report Pb concentrations and isotopic compositions measured in plume aerosol and Pele's hair (lava) samples collected from Masaya volcano, Nicaragua, to provide the first data pertaining to Pb emissions from the Central American volcanic arc. Lead isotopic compositions, determined by Thermal Ionisation Mass Spectrometry, in the Pele's hair samples were found to be 206Pb/ 207Pb˜1.196, 208Pb/ 207Pb˜2.46 and 206Pb/ 204Pb˜18.6. Mean Pb fluxes from Masaya were calculated to be 1.0 ton Pb yr -1 with a mean plume Pb/S (gas) ratio of 1.3×10 -5. Also, it was found that the majority of Pb emitted was present in the fine aerosol (<2.5 μm diameter) fraction but that the percentage of Pb in the fine aerosol fraction decreased from 96% in the dry daytime plume to 61% in the condensed night-time plume. The contribution from the filter blank was usually a substantial fraction of the total amount of Pb measured, requiring the data to be corrected for blank contributions using Pb isotopic systematics.

  3. 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

  4. Archean Pb Isotope Evolution: Implications for the Early Earth.

    NASA Astrophysics Data System (ADS)

    Vervoort, J. D.; Thorpe, R.; Albarede, F.; Blichert-Toft, J.

    2008-12-01

    The U-Pb isotope system provides us with a powerful tool for understanding the chemical evolution of the Earth. Pb isotopes in Archean rocks, however, have not been widely utilized because U mobility makes initial Pb isotope ratios from old silicate rocks difficult, if not impossible, to determine. Galenas in syngenetic volcanogenic massive sulfide (VMS) deposits, however, provide snapshots of initial Pb ratios because their Pb isotopic composition is time invariant at their formation (U/Pb=0). The Pb isotopic record from galenas from rocks of all age have been utilized for over 70 years to answer a wide range of scientific problems beginning with Al Nier's pioneering work analyzing Pb isotopes in the 1930's but are no longer widely used by the isotopic community because they have been produced by older TIMS techniques. We have begun a re-examination of Archean Pb by an extensive analysis of over 100 galena samples from Archean VMS deposits throughout the Superior and Slave Provinces in Canada as well as from other VMS deposits in Finland, South Africa and Western Australia. The goal of this work is to provide modern, high precision measurements and update an old, but venerable, Pb isotopic data set. We feel these data provide important constraints on not only the Pb isotopic evolution of the Earth, but planetary differentiation and recycling processes operating in the first 2 b.y. of Earth's history. Our analytical techniques include dissolving the Pb sulfide minerals, purifying them with ion chromatography, and analyzing them using MC-ICPMS at both Washington State University (Neptune) and Ecole Normale Superieure in Lyon, France (Nu). All Pb solutions are doped with Tl in order to correct for mass fractionation. In this abstract we report preliminary galena Pb isotope data from 6 VMS deposits in the Abitibi greenstone belt: Chibougamu, Matagami, Noranda, Normetal, Timmins, and Val d"Or. These deposits are all approximately 2.7 Ga in age but in detail vary from 2

  5. 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...

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

    PubMed

    Yin, Qing-zhu; Jacobsen, Stein B

    2006-11-01

    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.

  7. 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.

  8. Which minerals control the Nd-Hf-Sr-Pb isotopic compositions of river sediments?

    NASA Astrophysics Data System (ADS)

    Garcon, M.; Chauvel, C.; France-Lanord, C.; Limonta, M.; Garzanti, E.

    2013-12-01

    River sediments naturally sample and average large areas of eroded continental crust. They are ideal targets not only for provenance studies based on isotopic compositions, but also to establish average continental crust isotopic values. However, in large fluvial systems, mineral sorting processes significantly modify the mineralogy, and thus the geochemistry of the transported sediments. We still do not know, in any quantitative way, to what extent mineral sorting affects and fractionates the isotopic compositions of river sediments. Here, we focus on this issue and try to decipher the role of each mineral species in the bulk isotopic compositions of bedloads and suspended loads sampled at the outflow of the Ganga River that drains the Himalayan mountain range. We analyzed Nd, Hf, Sr and Pb isotopic compositions as well as trace element contents of a large number of pure mineral fractions (K-feldspar, plagioclase, muscovite, biotite, magnetite, zircon, titanite, apatite, monazite/allanite, amphibole, epidote, garnet, carbonate and clay) separated from bedload sediments. We combine these data with mineral proportions typical of the Ganga sediments to perform Monte-carlo simulations that quantify the contribution of individual mineral species to the Nd, Hf, Sr and Pb isotopic budgets of bedloads and suspended loads. We show that the isotopic systematic of river sediments is entirely buffered by very few minerals. Despite their extremely low proportions in sediments, zircon and monazite/allanite control Hf and Nd isotopes, respectively. Feldspars, epidote and carbonate buffer the Sr isotopic budget while clay, feldspars and heavy minerals dominate Pb isotopes. We also demonstrate that the observed difference in Hf, Sr and Pb isotopic compositions between bedloads and suspended loads reflects their different mineral proportions. Our findings highlight the need to be very careful about the choice of isotopic compositions measured on sediments when used as source

  9. 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.

  10. 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.

  11. 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

  12. The Pb isotopic evolution of the Martian mantle constrained by initial Pb in Martian meteorites

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    The Pb isotopic compositions of maskelynite and pyroxene grains were measured in ALH84001 and three enriched shergottites (Zagami, Roberts Massif 04262, and Larkman Nunatuk 12011) by secondary ion mass spectrometry. A maskelynite-pyroxene isochron for ALH84001 defines a crystallization age of 4089 ± 73 Ma (2σ). The initial Pb isotopic composition of each meteorite was measured in multiple maskelynite grains. ALH84001 has the least radiogenic initial Pb isotopic composition of any Martian meteorite measured to date (i.e., 206Pb/204Pb = 10.07 ± 0.17, 2σ). Assuming an age of reservoir formation for ALH84001 and the enriched shergottites of 4513 Ma, a two-stage Pb isotopic model has been constructed. This model links ALH84001 and the enriched shergottites by their similar μ value (238U/204Pb) of 4.1-4.6 from 4.51 Ga to 4.1 Ga and 0.17 Ga, respectively. The model employed here is dependent on a chondritic μ value (~1.2) from 4567 to 4513 Ma, which implies that core segregation had little to no effect on the μ value(s) of the Martian mantle. The proposed Pb isotopic model here can be used to calculate ages that are in agreement with Rb-Sr, Lu-Hf, and Sm-Nd ages previously determined in the meteorites and confirm the young (~170 Ma) ages of the enriched shergottites and ancient, >4 Ga, age of ALH84001.

  13. Geochemistry.

    ERIC Educational Resources Information Center

    Fyfe, William S.

    1979-01-01

    Techniques in geochemistry continue to improve in sensitivity and scope. The exciting areas of geochemistry still include the classical fields of the origin of the elements and objects in space, but environmental crisis problems are important as well. (Author/BB)

  14. 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.

  15. 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.

  16. 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.

  17. Pb Nd isotopic constraints on sedimentary input into the Lesser Antilles arc system

    NASA Astrophysics Data System (ADS)

    Carpentier, Marion; Chauvel, Catherine; Mattielli, Nadine

    2008-07-01

    The Lesser Antilles arc is a particularly interesting island arc because it is presently very active, it is located perpendicular to the South American continent and its chemical and isotopic compositions display a strong north-south gradient. While the presence in the south of a thick pile of sedimentary material coming from the old South American continent has long been suspected to explain the geochemical gradient, previous studies failed to demonstrate unambiguously a direct link between the arc lava compositions and the subducted sediment compositions. Here, we present new Nd, Sm, Th, U and Pb concentrations and Nd-Pb isotopic data for over 60 sediments from three sites located in the fore arc region of the Lesser Antilles arc. New data for DSDP Site 543 drill core located east of Dominica Island complement the data published by White et al. [White, W.M., Dupré, B. and Vidal, P., 1985. Isotope and trace element geochemistry of sediments from the Barbados Ridge-Demerara Plain region, Atlantic Ocean. Geochimica et Cosmochimica Acta, 49: 1875-1886.] and confirm their relatively uniform isotopic compositions (i.e., 206Pb/ 204Pb between 19.13 and 19.53). In contrast, data obtained on DSDP Site 144 located further south, on the edge of the South American Rise and on sediments from Barbados Island are much more variable ( 206Pb/ 204Pb ranges from 18.81 to 27.69). The very radiogenic Pb isotopic compositions are found in a 60 m thick black shale unit, which has no age equivalent in the Site 543 drill core. We interpret the peculiar composition of the southern sediments as being due to two factors, (a) the proximity of the South American craton, which contributes coarse grain old detrital material that does not travel far from the continental shelf, and (b) the presence of older sediments including the thick black shale unit formed during Oceanic Anoxic events 2 and 3. The north-south isotopic change known along the Lesser Antilles arc can be explained by the observed

  18. 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

  19. 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}).

  20. 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

  1. Pb isotopic evidence for early Archaean crust in South Greenland

    NASA Technical Reports Server (NTRS)

    Taylor, P. N.; Kalsbeek, F.

    1986-01-01

    The results of an isotopic remote sensing study focussed on delineating the extent of Early Archean crust north and south of the Nuuk area and in south Greenland is presented. Contamination of the Late Archean Nuk gneisses and equivalents by unradiogenic Pb uniquely characteristic of Amitsoq gneiss was detected as far south as Sermilik about 70 km south of Nuuk and only as far north as the mouth of Godthabsfjord. This study was extended to the southern part of the Archean craton and the adjoining Early Proterozoic Ketilidian orogenic belt where the Pb isotopes suggest several episodes of reworking of older uranium depleted continental crust. The technique of using the Pb isotope character of younger felsic rocks, in this case Late Archean and Early Proterozoic gneisses and granites to sense the age and isotopic character of older components, is a particularly powerful tool for reconstructing the evolutionary growth and development of continental crust.

  2. Reconstruction of historical atmospheric Pb using Dutch urban lake sediments: a Pb isotope study.

    PubMed

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

    2014-06-15

    Lake sediments provide a record of atmospheric Pb deposition and changes in Pb isotope composition. To our knowledge, such an approach has not previously been performed in The Netherlands or linked to national air monitoring data. Results are presented for Pb content and isotope composition of (137)Cs dated lake sediments from 2 Dutch urban lakes. Between 1942 and 2002A.D. anthropogenic atmospheric Pb deposition rates in the two lakes varied from 12±2 to 69±16μgcm(-2)year(-1). The rise and fall of leaded gasoline is clearly reflected in the reconstructed atmospheric Pb deposition rates. After the ban on leaded gasoline, late 1970s/early 1980s, atmospheric Pb deposition rates decreased rapidly in the two urban lakes and the relative contributions of other anthropogenic Pb sources - incinerator ash (industrial Pb) and coal/galena - increased sharply. Atmospheric Pb deposition rates inferred from the lake record a clear relationship with nearby measured annual mean air Pb concentrations. Based on this relationship it was estimated that air Pb concentrations between 1942 and 2002A.D. varied between 5 and 293ng/m(3).

  3. Petrogenesis of Malaysian tin granites: geochemistry, fractional crystallization, U-Pb zircon geochronology and tectonic setting

    NASA Astrophysics Data System (ADS)

    Wai-Pan Ng, Samuel; Searle, Mike; Whitehouse, Martin; Chung, Sun-Lin; Ghani, Azman; Robb, Laurence; Sone, Masatoshi; Oliver, Grahame; Gardiner, Nick; Roselee, Mohammad

    2014-05-01

    The Malaysian tin granites forming the backbone of the Thai-Malay Peninsula has been long recognized with two distinct granitic provinces:- 1. Early Permian to Late Triassic Eastern Province with mainly "I-type" (Hbl)-Bt granites with associated Cu-Au deposits, with subordinate Bt granites hosting limited Sn-W deposits, and 2. Late Triassic Main Range Province with mainly "S-type" Bt granites with associated Sn-W deposits, and subordinate (Hbl)-Bt granites. New geochemical data show that Chappell and White's (1974) I-S granite classification adopted in the existing model does not adequately distinguish the granites from one another as previously implied. Trace element geochemistry and Sr-Nd isotopic compositions show that the Malaysian tin granites in both provinces have transitional I-S characteristics. In addition, they inherited within-plate signature from Cambro-Ordovician Gondwana-related source rocks. Previous ages were obtained by whole rock Rb-Sr and biotite K-Ar geochronology in the 70s and 80s, dating methods that may not accurately represent the crystallization age of granites. We re-sampled the entire Malaysian Peninsula and 40 samples were collected for high-precision U-Pb SIMS dating on extracted zircon grains in order to better constrain the magmatic and tectonic evolution of Southeast Asia. The crystallization ages of the Eastern Province granitoids have been constrained ranging from 220 to 290 Ma, while the Main Range (Western) Province granitoids have ages ranging from 200 to 230 Ma. A progressive westward younging trend is apparent across the Eastern Province, but becomes less obvious in the Main Range Province. Our model suggests two east dipping subduction zones. We suggest that subduction roll-back along the Bentong-Raub suture might account for the westward younging trend, in the Eastern province. A second Late Triassic east-dipping subduction zone beneath western Malaysia is proposed in order to explain the "I-type" components to the Main

  4. 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)

  5. 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.

  6. Evolution of Eastern Arctic crust revealed from zircon U-Pb, O and Hf isotopic records.

    NASA Astrophysics Data System (ADS)

    Gottlieb, E. S.; Akinin, V. V.; Miller, E. L.

    2015-12-01

    Zircon U-Pb ages, in conjunction with O and Hf isotope geochemistry, obtained from Proterozoic to Cretaceous supracrustal metamorphic to magmatic rocks (total 30 samples) collected from Cretaceous granite-gneiss dome and magmatic arc complexes located along Arctic cost of Chukotka, Neoproterozoic basement exposures on Wrangel Island, and crustal xenoliths-bearing Neogene alkali basalts on Zhokhova Island (De Long archipelago, Russian Arctic) provide new insights about evolution of crust in Arctic Alaska-Chukotka block. The oldest magmatic zircons yield U-Pb ages ranging from 710 to 570 Ma have depleted mantle-like Hf and O isotopic signatures (d18O range predominantly from +5.3 to +6.2 ‰, whereas ɛHf(i) ranges from +8 to +13), suggesting the juvenile crust formation during Cryogenian-Ediacaran, roughly correlated with Rodinia breakup. Zircons from Devonian (390-360 Ma) to Cretaceous (105-88 Ma) arc granites and rhyolites have increasingly heavier O isotopic composition (up to +6.5 to +9.0 ‰), and less radiogenic ɛHf(i) (as low as to -2.5 to -10), suggesting significant anatexis of the eastern Arctic crust associated with Devonian and Cretaceous age pluton forming events.

  7. 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.

  8. The Beiminghe skarn iron deposit, eastern China: Geochronology, isotope geochemistry and implications for the destruction of the North China Craton

    NASA Astrophysics Data System (ADS)

    Shen, Jun-Feng; Santosh, M.; Li, Sheng-Rong; Zhang, Hua-Feng; Yin, Na; Dong, Guo-Cheng; Wang, Yan-Juan; Ma, Guang-Gang; Yu, Hong-Jun

    2013-01-01

    The Beiminghe (BMH) iron ore in the southern part of the Taihang Mountain (TM), Hebei province, is one of the largest skarn iron deposits in China. Here we report phlogopite 40Ar-39Ar and zircon U-Pb age data, as well as sulfur, lead, and He-Ar isotope geochemistry of pyrite from the ores and skarnitized rocks in the deposit in an attempt to constrain the timing and mechanism of formation of the mineralization. The phlogopite 40Ar-39Ar and LA-ICP-MS zircon U-Pb data show markedly consistent ages constraining the timing of ore formation as 136-137 Ma. The presence of several inherited zircons with late Archean or Paleoproterozoic ages indicates the participation of the basement rocks during the ore-forming process. The δ34S values of pyrite from the ores range from 12.2 to 16.5‰, with 206Pb/204Pb = 17.84-18.79, 207Pb/204Pb = 15.46-15.62, and 208Pb/204Pb = 37.93-39.75, suggesting that continental crust is the major contributor. This is further confirmed by the He-Ar isotope data (3He/4He = 0.0648-0.1886 Ra, mean 0.1237Ra; 40Ar/36Ar = 311.7-22909.4; and 40Ar*/4He = 0.036-0.421). The Mesozoic magmatism and metallogeny in the BMH correlate well with the peak event of lithospheric thinning and destruction of the North China Craton during this process, the early Precambrian lower crustal rocks in the region were re-melted through underplating of mantle magmas, leading to the formation of the Beiminghe monzodioritic pluton. Minor mantle input occurred during the evolution of the monzodiorite magma, which scavenged the ore-forming materials from the lower crust. Interaction of the magmas and fluids with the surrounding rocks resulted in the formation of the Beiminghe skarn iron deposits. The magmatism and metallogeny in the Taihang Mountain are signatures of the extensive craton destruction and lithospheric thinning in the eastern part of the North China Craton during Mesozoic, probably associated with Pacific slab subduction.

  9. 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.

  10. 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. PMID:27586918

  11. 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.

  12. 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...

  13. 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. PMID:19665172

  14. U-Pb geochronology and geochemistry of Zahedan and Shah Kuh plutons, southeast Iran: Implication for closure of the South Sistan suture zone

    NASA Astrophysics Data System (ADS)

    Mohammadi, Ali; Burg, Jean-Pierre; Bouilhol, Pierre; Ruh, Jonas

    2016-04-01

    We present U-Pb zircon crystallization ages combined with major and trace element analyses, Sr-Nd isotopes and zircon in-situ Hf isotope analyses of intermediate to granitic intrusions along the southern segment of the N-S trending Sistan suture zone in eastern Iran. The Zahedan and Shah-Kuh Eocene plutons consist in a series of granite-granodiorite-rhyolite with U-Pb zircon ages of 40.5-44.3 Ma and ca. 28.9-30.9 Ma. Isotope geochemistry and modeling suggest that 40.5-44.3 Ma plutons represent melts derived from the turbidites of the surrounding accretionary wedge. Melting of the wedge was induced by the intrusion of mantle magmas, with subsequent interaction between mantle- and turbiditic melts being responsible for the wide range of compositions. Most of the 28.9-30.9 Ma magmas were generated from mantle melting, with assimilation of the surrounding turbidites. The rare setting of within-wedge intrusions is attributed to mantle upwelling reaching wedge sediments at the inception of delamination processes, which signal the end of subduction-related deformational and thermal events in the Sistan suture zone.

  15. A list of references on lead isotope geochemistry, 1967-1969 (with an addendum to the list through 1966)

    USGS Publications Warehouse

    Doe, Bruce R.

    1971-01-01

    This bibliography was constructed to be as complete as possible for terminal papers containing new data relative to the geochemical applications of: Common lead U-The-Pb isotopic dating PbPb210, Pb212, Pb214 No effort was made for completeness of: Annual reports, Yearbooks, etc. Review papers although many are included. Abstracts and theses are omitted.

  16. 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...

  17. 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.

  18. 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.

  19. 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.

  20. Infrared spectroscopy and hydrogen isotope geochemistry of hydrous silicate glasses. Progress report

    SciTech Connect

    Epstein, S.; Stolper, E.

    1992-03-01

    The focus of this project is the combined appication of infrared spectroscopy and stable isotope geochemistry to the study of hydrogen-bearing species dissolved in silicate melts and glasses. We are conducting laboratory experiments aimed at determining the fractionation of D and H between melt species (OH and H{sub 2}O) and hydrous vapor and the diffusivities of these species in glasses and melts. Knowledge of these parameters is critical to understanding the behavior of hydrogen isotopes during igneous processes and hydrothermal processes. These results also could be valuable in application of glass technology to development of nuclear waste disposal strategies.

  1. 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

  2. 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

  3. 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

  4. 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

  5. Sulfur Isotope Geochemistry of the Lost City Hydrothermal Vent Fluids

    NASA Astrophysics Data System (ADS)

    Frueh-Green, G. L.; Bernasconi, S. M.; Butterfield, D. A.; Kelley, D. S.

    2004-12-01

    At the Lost City Hydrothermal Vent Field (Mid-Atlantic Ridge, 30° N), reactions between seawater and ultramafic rocks produce high alkaline (pH 9 to 11) fluids that are venting at temperatures of 40 to 90° C and result in the formation of up to 60m tall carbonate-brucite structures. The fluids are enriched in hydrogen, methane and other hydrocarbons, and support dense microbial communities. We present sulfur isotope data of dissolved sulfate and coexisting sulfide in the fluids venting at Lost City, which together with C-isotope data provide constraints on the links between chemical and biological processes associated with serpentinization. The sulfur isotope composition of sulfate increases from seawater values of +21‰ (VCDT) in fluids with sulfate concentrations of 28 mM to values of up to +30‰ in the low sulfate-, high pH end-member hydrothermal fluids. Sulfide concentrations range between 50 and 2780 micromolar. Sulfur isotope compositions of the sulfides lie in a narrow range of +34 to +37‰ (VCDT) and show no clear correlation with concentrations. The isotopic compositions of dissolved inorganic carbon vary between -0.5‰ (VPDB) in the high sulfate samples and -18‰ in the low sulfate samples. This covariance indicates active sulfate reduction in the vent structures and/or in the shallow serpentinite subsurface. Sulfate reduction likely contributes to the variability of carbon isotope compositions observed in both the dissolved inorganic carbon and the carbonate minerals forming the structures. These data, together with C- and O-isotope data of the vent structures, provide evidence that methane oxidation coupled with sulfate reduction during mixing of the more pristine, hydrogen and methane-rich hydrothermal end-member fluids with seawater is an important process in hydrothermal carbonate precipitation at Lost City. Our results are consistent with previous microbiological and organic geochemical studies, which indicate a close association of methane

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

    USGS Publications Warehouse

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

    2005-01-01

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

  7. 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

  8. 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.

  9. Study of Pb sources by Pb isotope ratios in the airborne PM(10) of Zaragoza, Spain.

    PubMed

    Teresa de la Cruz, María; Laborda, Francisco; Callén, María Soledad; López, José Manuel; Mastral, Ana María

    2009-11-01

    Lead is a toxic trace element which produces harmful effects on human health, even at low concentrations, and it can be useful as ambient pollution tracer because the relative abundance of its four stable isotopes (204, 206, 207 and 208) depends on the emission source. This study was focused on the lead concentrations and isotope ratios in the PM10 of Zaragoza, in order to determine the main Pb pollution sources and to check whether the influence of the prohibition of leaded fuel was worthwhile. Two sampling campaigns from 2001 until 2004, the first one in which leaded gasoline was still effective and the second one with the phase-out, were carried out by using a high-volume air sampler able to trap the particulate matter equal to or less than 10 microm (PM10) on Teflon-coated fibre glass filters. Firstly, the Pb concentrations for the two sampling campaigns were analysed by inductively-coupled plasma optical emission spectrometry (ICP-OES). No statistically significant decrease in the Pb average concentration was obtained from the first to the second sampling. Enrichment factors showed that anthropogenic sources were prevalent during both samplings, in particular during 2001-2002. Afterwards, only those samples with higher concentrations than the limit of quantification of Pb were analysed to determine the lead isotopic composition by inductively-coupled plasma quadrupole mass spectrometry (ICP-QMS). To apply this analytical technique successfully, it was necessary to optimize the parameters affecting the measurement accuracy and precision. Differences were found regarding the lead isotope ratios for both periods finding that anthropogenic sources related to industrial processes were reflected on both campaigns. The gasoline contribution for the first campaign was 23% whereas for the second sampling this contribution was negligible, corroborating the success of the lead policies on the quality of the environment.

  10. 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).

  11. 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)

  12. 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.

  13. 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

  14. Mafic dykes intrusive into Pre-Cambrian rocks of the São Luís cratonic fragment and Gurupi Belt (Parnaíba Province), north-northeastern Brazil: Geochemistry, Sr-Nd-Pb-O isotopes, 40Ar/39Ar geochronology, and relationships to CAMP magmatism

    NASA Astrophysics Data System (ADS)

    Klein, Evandro L.; Angélica, Rômulo S.; Harris, Chris; Jourdan, Fred; Babinski, Marly

    2013-07-01

    Dykes of diabase and microgabbro intruded into Pre-Cambrian rocks of the São Luís cratonic fragment and Gurupi Belt, which are tectonic and erosive windows of the Parnaíba Basin in north-northeastern Brazil. Ar-Ar ages were determined, and major, trace element, and Nd-Sr-Pb-O isotopic compositions of these dykes were measured to provide insights into their age, and into the nature of their mantle sources and petrogenetic processes. The data have also been used to compare the chemical and isotopic signatures of the dykes with those of the Central Atlantic Magmatic Province (CAMP). Four chemical groups of mafic dykes have been identified. These comprise two subtypes of high-Ti rocks (i) HTi-1 (TiO2 < 2.3 wt.%; SiO2 > 47 wt.%), (ii) HTi-2 (TiO2 > 2.7 wt.%; SiO2 > 47 wt.%), in addition to (iii) evolved high-Ti (TiO2 > 4 wt.%; SiO2 of ~ 46 wt.%) and (iv) low-Si (TiO2 > 2.2 wt.%; SiO2 < 45 wt.%) rocks. 40Ar/39Ar geochronology of plagioclase returned ages of 201 ± 4 Ma and 193 ± 10 Ma for the HTi-2 subtype, and of 201 ± 2 Ma and 207 ± 9 Ma for the evolved high-Ti group. The HTi-1 and low-Si groups presented highly disturbed age spectra, and did not allow the definition of their emplacement ages. The Argon data indicate an age > 200 Ma for the low-Si group and are dubious with respect to the age of theHTi-1 subtype, if coeval with (i.e., ~ 200 Ma), or older than, the HTi-2 and evolved high-Ti types. All groups present δ18O values of pyroxene that are compatible with uncontaminated mantle-derived magmas. The HTi-1 subtype (average 143Nd/144Nd200 = 0.512644; 87Sr/86Sr200 = 0.7035; 206Pb/204Pb of 17.86) shows the less enriched and less fractionated (more primitive) trace element distribution of all groups. The HTi-2 subtype shows enriched trace element pattern and depleted Nd-Sr signature (143Nd/144Nd200 = 0.512610; 87Sr/86Sr200 = 0.7037) and average 206Pb/204Pb ratios of 17.23. The evolved high-Ti chemical group shows average ratios of 143Nd/144Nd200 = 0.512558, 87Sr

  15. 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. PMID:14649868

  16. 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.

  17. Pb-Pb Isotopic and X-ray Tomographic Constraints on the Origin of Chondrules

    NASA Astrophysics Data System (ADS)

    Charles, Christopher R. J.

    207Pb*/206Pb* chronometry was used to obtain the ages of Ca,Al-rich inclusions (CAIs) and chondrules found in ancient meteorites. Assuming a 238U/235U=137.88, Pb/Pb ages of chondrules in NWA801 (a CR2 meteorite) are 4564.6+/-1.0 Ma, chondrules in Mokoia (a CV3 chondrite) are 4564.2+/-1.1Ma, and CAIs in Mokoia are 4567.9+/-5.4 Ma. The Pb/Pb age of NWA801 chondrules is concordant with 26Al/ 26Mg ages of CR chondrules. However if a 238U/ 235U<137.88 is used, the age for NWA801 chondrules becomes younger by ˜1Ma and discordant with26Al/26Mg ages of CR chondrules. This suggests either a discrepancy with the U compositions or the initial Mg isotopic compositions of NWA801 chondrules. The shapes of NWA801 chondrules, and blebs of FeNi metal in the meteorite matrix, were further studied by 3D X-ray micro-computed tomography (CT). Most chondrules (92%) were 'armoured' with one discontinuous layer of FeNi metal. Two layers of FeNi metal (one on the exterior and one concentric through the interior separated by silicate) were rare <8%. Chondrules and matrix blebs occur as oblates, prolate, spheres and triaxial spheroids. It is proposed that the shapes were made free-floating in the nebula likely by ash-melting precursors into molten droplets that were vibrating as harmonic oscillators that 'froze-in' their shapes during cooling. Parent-body metamorphism and shock are not likely processes affecting the matrix-bleb and chondrule shapes. Chondrules with≥2 FeNi metal layers were likely formed by mergers and not by successive deposition and annealing of metal in multiple ash-melting events. Attempts to obtain 207Pb*/206Pb* ages from chondrules and CAIs by thermal extraction (TE)-TIMS were unsuccessful. However LA-ICP-MS was shown to be useful for rapidly determining Pb isotopic trends in meteorites and unknown objects. In particular, it was shown that 137La (T1/2=60ky) should be detectable in recently fallen meteorites using LaF-4 to suppress the 137Ba isobar during tandem

  18. 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

  19. 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

  20. 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.

  1. [Heavy metal contamination and Pb isotopic composition in natural soils around a Pb/Zn mining and smelting area].

    PubMed

    Sun, Rui; Shu, Fan; Hao, Wei; Li, Li; Sun, Wei-Ling

    2011-04-01

    The heavy metal (Pb, Zn, Cr, Cu, Cd, and Hg) concentrations in the A horizon and C horizon soils, collected around the Pb/Zn mining and smelting area of Shuikoushan in Hunan, China, were investigated, and the Pb isotopic compositions were also determined to identify the potential origin of Pb in the A horizon soil. Compared with C horizon soils, the A horizon soils exhibit elevated heavy metal concentrations, especially in the vicinity of the mining and smelting area. This reveals that the surface soil was contaminated to some degree. The contents of Pb, Zn, Cr, Cu, Cd, and Hg in soils are up to 3966.88, 2086.25, 135.31, 185.63, 56.15, and 16.434 mg/kg, respectively. The potential risks caused by different metals are in the order of Cd > Hg > Pb > Cu > Zn = Cr. Much higher potential ecological risk was observed for the central area (Shuikoushan Pb/Zn mining and smelting area) than for the surrounding area. About 34%, 33%, 11%, and 22% of the sampling sites demonstrate low, moderate, considerable, and very high potential ecological risk in the central area, while about 68%, 16%, 10%, and 6% of the sampling sites show low, moderate, considerable, and very high potential ecological risk in the surrounding area, respectively. Compared with the Pb isotopic compositions in the C horizon soils (206Pb/207Pb 1.168-1.246, 208 Pb/206 Pb 2.014-2.130), the Pb in the A horizon soils has lower 206 Pb/207Pb ratios (1.166-1.226) and higher 208Pb/206Pb ratios (2.043-2. 135). The Pb in the A horizon soils predominantly derives from two-component mixing resources. One is the parent materials of C horizon, and the other is the atmospheric deposition of the smelting flue gas dust.

  2. Helium isotope geochemistry of mid-ocean ridge basalts from the South Atlantic

    NASA Astrophysics Data System (ADS)

    Graham, David W.; Jenkins, William J.; Schilling, Jean-Guy; Thompson, Geoffrey; Kurz, Mark D.; Humphris, Susan E.

    1992-05-01

    We report new helium isotope results for 49 basalt glass samples from the Mid-Atlantic Ridge between 1°N and 47°S. 3He/ 4He in South Atlantic mid-ocean ridge basalts (MORB) varies between 6.5 and 9.0 R A (R A is the atmospheric ratio of 1.39 × 10 -6), encompassing the range of previously reported values for MORB erupted away from high 3He/ 4He hotspots such as Iceland. He, Sr and Pb isotopes show systematic relationships along the ridge axis. The ridge axis is segmented with respect to geochemical variations, and local spike-like anomalies in 3He/ 4He , Pb and Sr isotopes, and trace element ratios such as (La/Sm) N are prevalent at the latitudes of the islands of St. Helena, Tristan da Cunha and Gough to the east of the ridge. The isotope systematics are consistent with injection beneath the ridge of mantle "blobs" enriched in radiogenic He, Pb and Sr, derived from off-axis hotspot sources. The variability in 3He/ 4He along the ridge can be used to refine the hotspot source-migrating-ridge sink model. MORB from the 2-7°S segment are systematically the least radiogenic samples found along the mid-ocean ridge system to date. Here the depleted mantle source is characterized by 87Sr/ 86Sr of ˜ 0.7022, Pb isotopes close to the geochron and with 206Pb/ 204Pb of ˜ 17.7, and 3He/ 4He of 8.6-8.9 R A. The "background contamination" of the subridge mantle, by radiogenic helium derived from off-ridge hotspots, displays a maximum between ˜ 20 and 24°S. The He sbnd Pb and He sbnd Sr isotope relations along the ridge indicate that the 3He/ 4He ratios are lower for the hotspot sources of St. Helena, Tristan da Cunha and Gough than for the MORB source, consistent with direct measurements of 3He/ 4He ratios in the island lavas. Details of the He sbnd Sr sbnd Pb isotope systematics between 12 and 22°S are consistent with early, widespread dispersion of the St. Helena plume into the asthenosphere, probably during flattening of the plume head beneath the thick lithosphere

  3. 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.

  4. 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.

  5. 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. PMID:26967352

  6. Is the Low-Temperature Isotope Geochemistry of Mg Driven by Biology?

    NASA Astrophysics Data System (ADS)

    Galy, A.; Tipper, E. T.; Carder, E. A.; Dessert, C.

    2008-12-01

    In the last decade, the development of a new field of isotope geochemistry sometime referred as non traditional stable isotope geochemistry together with a renewed interest for the origin of life has raised one of the key question in biogeochemistry: how can we fingerprint life beyond the conventional use of C-based molecules? A general idea has been to recognise that biomediated chemical reactions are rarely at thermodynamic equilibrium and strongly affected by kinetics with an associated isotopic fractionation much greater than the isotopic fractionation characteristic of the equilibrium reaction. This approach led to the false idea that stable isotope of heavy elements (mass greater than 40) can only be fractionated by biological reaction and divalent cations and among them Magnesium (Mg) are no exception. Differences in the relative abundances of Mg three stable isotopes, 24Mg (78.99%), 25Mg (10.00%), and 26Mg (11.01%), could be expected because of the large relative mass differences between 26Mg and 24Mg. However, Mg-bonds are dominantly ionic (a weak bond) and while kinetic processes affect all type of physico-chemical reactions, the scale of the isotopic effect of thermodynamic equilibrium is strongly related to the strength of chemical bonds. This view is supported by the lack of Mg isotopic fractionation during magmatic differentiation (Teng et al., doi:10.1016/j.epsl.2007.06.004) and the very small isotopic differences (less than 0.1‰ in δ26Mg) among igneous rock, when their analysis are immune of analytical artefact (Tipper et al., ). Therefore, the range of almost 5‰ for aqueous solution and associated precipitated material (e.g. Young and Galy, Tipper et al., doi:10.1016/j.epsl.2006.07.037) could be interpreted as widespread kinetic isotopic fractionation by Mg mobilisation at the surface of the Earth. Indeed, large isotopic fractionations are generated by biomineralisations and the largest is associated with the precipitation of low-Mg calcite by

  7. Integration of TEM/Hrtem onservations and C-isotope geochemistry to characterize organic matter in early Archaean rocks

    NASA Astrophysics Data System (ADS)

    Glikson, M.; Golding, S.; Duck, L.; Webb, R.

    2009-04-01

    TEM was applied to observe and characterize carbonaceous materials (CM) extracted from black cherts in the 'white smoker type' deposit of the ca.3.5Ga (model Pb/Pb ages =3.49-3.51Ga) Dresser ormation, and the overlying black argillites of the 3.46Ga Salgash Subgroup, in the Pilbara of Western Australia. These were characterized by Transmission Electron Microscopy (TEM) coupled with electron dispersive spectral analysis (EDS), High Resolution TEM (HRTEM) to determine molecular ordering, and C-isotope geochemistry. Observations using TEM and HRTEM enabled morphological and fine structure distinctions between the various populations of CM both in the Dresser and Salgash samples. These formed the basis for their interpretations. Organic petrology using reflected light microscopy was applied to whole rock samples to observe mineral-organic relationship and structure relative to host rock texture. These supported insitu, syn-depositional mode for the Dresser Formation CM. Reflectance % (Ro) of CM determined on polished whole rock samples and polished resin-embedded CM concentrates enabled the reconstruction of its thermal history. These yielded several Ro populations in the Dresser Formation samples: probable microbial cells preserved in fluid inclusions within quartz crystals, severely thermally degraded CM possibly originally belonging to microbial cells, CM coating mineral grains and reworked CM particles. On the other hand, the Salgash suite of samples from the Apex Basalt Formation yielded consistent very high Ro values corresponding to graphite stage organic metamorphism. the weak optical anisotropy of the graphite points to a defferent mode of formation than regional metamorphism. Two main graphite forms have been identified, namely a platy and tubular. The tubular form when observed in HRTEM showed nano-tubes and fullerenes. Dresser Formation samples are isotopically light in the range of -32.1 to -38.2per mil supporting a biological source. Although in TEM four

  8. 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.

  9. 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.

  10. Estimation of groundwater velocities from Yucca Flat to the Amargosa Desert using geochemistry and environmental isotopes

    SciTech Connect

    Hershey, R.L.; Acheampong, S.Y.

    1997-06-01

    Geochemical and isotopic data from groundwater sampling locations can be used to estimate groundwater flow velocities for independent comparison to velocities calculated by other methods. The objective of this study was to calculate groundwater flow velocities using geochemistry and environmental isotopes from the southern end of Yucca Flat to the Amargosa Desert, considering mixing of different groundwater inputs from sources each and southeast of the Nevada Test Site (NTS). The approach used to accomplish the objective of this study consisted of five steps: (1) reviewing and selecting locations where carbon isotopic groundwater analyses, reliable ionic analysis, and well completion information are available; (2) calculating chemical speciation with the computer code WATEQ4F (Ball and Nordstrom, 1991) to determine the saturation state of mineral phases for each ground water location; (3) grouping wells into reasonable flowpaths and mixing scenarios from different groundwater sources; (4) using the computer code NETPATH (Plummer et al., 1991) to simulate mixing and the possible chemical reactions along the flowpath, and to calculate the changes in carbon-13/carbon-12 isotopic ratios ({delta}{sup 13}C) as a result of these reactions; and (5) using carbon-14 ({sup 14}C) data to calculate velocity.

  11. Chemical and isotopical characterisation of atmospheric pollution from urban and rural environments of the Rhine Valley (PCBs, trace elements and Sr-, Nd- and Pb- isotope determinations)

    NASA Astrophysics Data System (ADS)

    Guéguen, F.; Stille, P.; Millet, M.; Dietze, V.; Gieré, R.

    2010-05-01

    from traffic and the principal industrial activities. UCC normalized trace element distribution patterns of aerosols and tree bark are very similar. 206Pb/207Pb and 208Pb/207Pb isotope ratios of today's PM vary within a small range and are very similar to those of steel plant, waste incinerator and thermal power plant emissions. Older aerosols (collected 1995, before leaded petrol was phased out), have significantly lower Pb isotope ratios pointing to the impact of leaded gasoline at that time. Tree bark monitoring covers a 10-y history of Pb emissions. Combining Pb isotope ratios with 87Sr/86Sr and 143Nd/144Nd allows for a much better discrimination between the different anthropogenic emissions and might be suitable for source apportionments. PCBs concentrations of tree bark or PAS samples are generally correlated with trace element contents determined on the same material. PAS/tree bark PCBs ratio allows distinguishing between current or past contamination. 1Lahd Geagea, M., Stille, P., Gauthier-Lafaye, F., Perrone, Th., Aubert, D. 2008. Baseline determination of the atmospheric Pb, Sr and Nd isotopic compositions in the Rhine valley, Vosges mountains (France) and the Central Swiss Alps. Applied Geochemistry, 23, 1703-1714.

  12. 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

  13. 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.

  14. 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.

  15. 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

  16. Lead isotopes as a tracer of Pb origin in the sediments from Beijiang River, South China.

    PubMed

    Gao, Bo; Liang, Xirong; Zhou, Huaidong; Tu, Xianglin

    2012-01-01

    Concentrations and enrichment of heavy metals were determined in sediments collected from Beijiang River, South China. The Pb isotopic compositions in these sediment samples were also employed to effectively identify metal pollution sources. According to the measured Pb concentrations, the total Pb concentrations in sediments varied from 62.1 to 1,152.5 μg/g, with an average concentration of 249.6 μg/g. The assessment by Geoaccumulation Index indicates that Pb is at the 'strongly contaminated' level, indicating that the Pb pollution was mainly due to anthropogenic inputs. The observed isotopic ratios varied from 1.174 to 1.204 for ²⁰⁶Pb/²⁰⁷Pb, 2.452 to 2.478 for ²⁰⁸Pb/²⁰⁷Pb, 18.404 to 18.937 for ²⁰⁶Pb/²⁰⁴Pb, 15.631 to 15.790 for ²⁰⁷Pb/²⁰⁴Pb, 38.455 to 39.121 for ²⁰⁸Pb/²⁰⁴Pb. The majority of these ratios are lower than those reported for natural geological sources, especially for sediments collected from a smelter. Significant correlation between Pb concentration and isotopic ratios suggested possible binary mixing of Pb. Combined with Pb concentration and enrichment levels, our results show that Pb pollution in the sediments of Beijiang River was mainly derived from anthropogenic sources. The mining activities and metal smelting processing was the main source of Pb pollution in this region.

  17. 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

  18. 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

  19. Metrology and traceability of U-Pb isotope dilution geochronology (EARTHTIME Tracer Calibration Part I)

    NASA Astrophysics Data System (ADS)

    Condon, D. J.; Schoene, B.; McLean, N. M.; Bowring, S. A.; Parrish, R. R.

    2015-09-01

    Mixed 235U-233U-205Pb(-202Pb) tracers for U-Pb isotope-dilution isotope ratio mass spectrometry have been prepared under the auspices of the EARTHTIME Initiative. The methods and results for the preparation and calibration of the U/Pb ratio and isotopic abundances are given, and the various sources of uncertainty are discussed and quantified. The accuracy of the EARTHTIME U-Pb tracer isotopic composition can be traced back to SI units via a series of assay and isotopic composition reference materials combined with the experiments described herein. The parameters used in calculating U/Pb ratios (and inferentially U-Pb dates) have correlated uncertainties that result in a total uncertainty contribution to 206Pb/238U dates of ± < 0.03% (95% confidence). For suitable terrestrial materials such as zircon, when other sources of uncertainty have been minimised (e.g., open-system behaviour, 238U/235U variation, intermediate daughter product disequilibrium, common Pb, etc.) the U-Pb tracer calibration uncertainty is a limiting factor in the accuracy of U-Pb geochronology - but less so than the uncertainty in the 238U and 235U decay constants (±0.11 and 0.14% 2σ). The calibration approach of the mixed EARTHTIME 235U-233U-205Pb(-202Pb) tracers, in addition to updated values for reference materials (e.g., mixed gravimetric reference solutions), and parameters (e.g., Pb reference material assay), can be applied to other laboratory-specific U-Pb tracers and will facilitate the generation of accurate and directly inter-comparable U-Pb data.

  20. 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.

  1. 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.

  2. Lead isotope and Pb-Pb model age determinations of ores from Central Europe and their metallogenetic interpretation

    NASA Astrophysics Data System (ADS)

    Bielicki, K.-H.; Tischendorf, G.

    1991-02-01

    The paper presents lead isotope data from 211 samples from Phanerozoic lead-bearing ore occurrences in Central Europe, particularly from the Southern part of the former German Democratic Republic. The data are interpreted in terms of Amov's dynamic model of continuous lead isotope evolution. The relationships between thoro-genic and urano-genic model ages and the source of lead in different regional units are discussed. We observed differences in lead isotope evolution in the Hercynian internides and externides. Within the Moldanubian and Saxothuringian zones we distinguish five main lead-bearing ore associations: (1) Cambrian, stratiform base metal (Hermsdorf-Waldsassen; 206Pb/ 204Pb=17.50 17.70), (2) Devonian, vein type Sb-bearing, metamorphogene (neumühle-Hartmannsdorf; 17.80 18.00), (3) Upper Carboniferous-Permian, polymetallic, including tin, vein type (Kutna hora-Freiberg-Altenberg; 18.00 18.20), (4) Triassic (-Jurassic), Pb-Ba, vein type (Střibro-Halsbrücke; 18.20 18.60), (5) Cenozoic, polymetallic, vein type, riftogene (Roztoky-Banska Štiavnica; 18.80 19.10). Pb isotope characteristics from ores of the Montagne Noire and the Brioude-Massiac district correspond to this subdivision. Ore associations from the Rheno-Hercynian zone display higher 207Pb/204Pb ratios which can be explained by more evolved and less metamorphosed source rocks. Mineralizations of the eastern Harz (Straßberg-Neudorf) belong to the Permian association, those from the western Harz (Clausthal-Bad Grund) to the Triassic-Jurassic. Because of Pb isotope agreement the stratabound Rammelsberg and the vein bound Ramsbeck-I mineralization are presumed to be isogenetic. Pb isotope identity of distinct mineralizations in the basement zone (Halsbrücke-Bad Grund) and in the Triassic sediments (Gorny Slask-Mechernich-Bleiglanzbänke) suggests a strong genetic coherence. Pb isotope conformity between the Upper Carboniferous-Permian-Triassic ore associations and Hercynian postkinematic

  3. U-Pb geochronology and geochemistry of Eocene and Oligocene plutons in southeast Iran: Implication for closure of the South Sistan Suture Zone

    NASA Astrophysics Data System (ADS)

    Burg, Jean-Pierre; Mohammadi, Ali; Ruh, Jonas; Bouilhol, Pierre

    2016-04-01

    The N-S trending Sistan Suture Zone in eastern Iran is a splay of the Tethys sutures. It represents an oceanic embayment that separated the Central Iran from the Afghan continental blocks. Structural, tectonic and petrological/geochemical evidence define eastward subduction beneath the Afghan continental block of the Sistan inlet of the Mesozoic Tethys Ocean. Mapping of the area allowed reaching and sampling intermediate to granitic intrusions stretched along the southern segment of this collisional suture zone. U-Pb zircon crystallization ages combined with major and trace element analyses, dated the series of granite-granodiorite-rhyolite at ca 40.5-44.3 Ma and ca 28.9-30.9 Ma. Isotopic geochemistry, including Sr-Nd isotopes and Hf isotope analyses, and petrological modelling suggest that the 40.5-44.3 Ma plutons crystallized from melts largely derived from the turbidites of the host accretionary wedge. Melting of the deep wedge was induced by the intrusion of mantle magmas interacting with the crustal turbiditic melts, which is responsible for the wide range of compositions. Most of the 28.9-30.9 Ma magmas were generated from mantle melting, with assimilation of the surrounding turbidites. The rare setting of within-wedge intrusions is attributed to mantle upwelling reaching wedge sediments at the inception of delamination processes, which sign the end of subduction-related deformational and thermal events in the Sistan Suture Zone. Numerical modelling of subduction - magma production - intrusion and melting of wedge sediments further constrains this collisional to post-collisional scenario.

  4. Pb isotopic constraints on the formation of the Dikulushi Cu-Pb-Zn-Ag mineralisation, Kundelungu Plateau (Democratic Republic of Congo)

    NASA Astrophysics Data System (ADS)

    Haest, Maarten; Schneider, Jens; Cloquet, Christophe; Latruwe, Kris; Vanhaecke, Frank; Muchez, Philippe

    2010-04-01

    Base metal-Ag mineralisation at Dikulushi and in other deposits on the Kundelungu Plateau (Democratic Republic of Congo) developed during two episodes. Subeconomic Cu-Pb-Zn-Fe polysulphide ores were generated during the Lufilian Orogeny (c. 520 Ma ago) in a set of E-W- and NE-SW-oriented faults. Their lead has a relatively unradiogenic and internally inhomogeneous isotopic composition (206Pb/204Pb = 18.07-18.49), most likely generated by mixing of Pb from isotopically heterogeneous clastic sources. These sulphides were remobilised and enriched after the Lufilian Orogeny, along reactivated and newly formed NE-SW-oriented faults into a chalcocite-dominated Cu-Ag mineralisation of high economic interest. The chalcocite samples contain only trace amounts of lead and show mostly radiogenic Pb isotope signatures that fall along a linear trend in the 207Pb/204Pb vs. 206Pb/204Pb diagram (206Pb/204Pb = 18.66-23.65; 207Pb/204Pb = 15.72-16.02). These anomalous characteristics reflect a two-stage evolution involving admixture of both radiogenic lead and uranium during a young fluid event possibly c. 100 Ma ago. The Pb isotope systematics of local host rocks to mineralisation also indicate some comparable young disturbance of their U-Th-Pb systems, related to the same event. They could have provided Pb with sufficiently radiogenic compositions that was added to less radiogenic Pb remobilised from precursor Cu-Pb-Zn-Fe polysulphides, whereas the U most likely originated from external sources. Local metal sources are also suggested by the 208Pb/204Pb-206Pb/204Pb systematics of combined ore and rock lead, which indicate a pronounced and diversified lithological control of the immediate host rocks on the chalcocite-dominated Cu-Ag ores. The Pb isotope systematics of polysulphide mineralisation on the Kundelungu Plateau clearly record a diachronous evolution.

  5. 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

  6. 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.

  7. 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

  8. Assessment of dissolved Pb concentration and isotopic composition in surface waters of the modern global ocean

    NASA Astrophysics Data System (ADS)

    Pinedo-Gonzalez, P.; West, A. J.; Sanudo-Wilhelmy, S. A.

    2015-12-01

    Lead (Pb) produced by human activities, mainly from leaded gasoline combustion and high-temperature industries, dominates Pb in our present-day oceans. Previous studies have shown that surface ocean Pb concentrations and isotope ratios have varied in time and space, reflecting the changes in the amount of inputs and sources of anthropogenic Pb. However, data on surface ocean Pb is quite limited, especially for some basins like the Indian Ocean. In the present study, Pb concentrations and stable isotopes (208, 207, and 206) have been analyzed in surface water samples (3m depth) collected during the Malaspina Circumnavigation Expedition, 2010. Our results are compared with data from the literature to i) evaluate the changing status of metal contamination in surface waters of the global ocean over the last 30 years, and ii) propose potential sources of modern Pb to the oceans. Our results show that Pb concentrations in surface waters of the North Atlantic Ocean have decreased ~ 40% since 1975, attributable to the phase-out of leaded gasoline in North America. This result is corroborated by stable Pb isotope measurements. Furthermore, the isotopic gradient observed in surface waters of the studied transects in the north tropical and subtropical Atlantic Ocean can be attributed to simple mixing of European and African aerosols and Saharan Holocene loess. Results from an understudied transect in the Southern Indian Ocean give an indication of the source region of Pb delivered to this region. Although comparison with literature data is limited, mixing of Australian ores and African and Australian coals could potentially explain the measured Pb isotope composition. This study provides an opportunity to build on the work of previous oceanographic campaigns, enabling us to assess the impact of anthropogenic Pb inputs to the ocean and the relative importance of various Pb sources, providing new insights into the transport and fate of Pb in the oceans.

  9. Correlations between Pb isotopes and volatile elements in melt inclusions from Sao Miguel, Azores

    NASA Astrophysics Data System (ADS)

    Moreira, M. A.; Rose-Koga, E. F.; Koga, K. T.; Vlastelic, I.; Shimizu, N.; Whitehouse, M.

    2009-12-01

    Sao Miguel is the biggest eastern-most island of the Azores archipelago in the northern Atlantic and is known to have a very peculiar isotopic systematics including Sr, Nd and Pb. We studied 4 lavas of Sao Miguel, one is from the 1563 historical lava flow Queimado peak eruption, one is from Picos Volcanic zone and the two others are Pliocene ankaramites from the Nordest. The olivine phenocrysts of these samples have been documented for helium isotopes and show very radiogenic 3He/4He ratios (<6Ra). We analyzed 9 primitive olivine-hosted melt inclusions for both Pb isotopes and volatile element concentrations (H2O, CO2, F, S, and Cl). The Pb isotope ratios were measured 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). All the melt inclusions have 207Pb/206Pb (0.782 to 0.797) and 208Pb/206Pb (1.969 to 2.041) lower than MORB value (DMM: 0.857, 2.053), i.e., more radiogenic compositions. We found positive linear correlations between 207Pb/206Pb and CO2, F, S, and Cl. The correlations further improve when Pb isotope ratios are plotted against F/P2O5, and Cl/K2O. The Sao Miguel source is characterized by a mixing between a low 207Pb/206Pb and low 208Pb/206Pb in the Nordest coming from a long time residence of high (U+Th)/Pb recycled material, and a component with higher ratios, more similar to other islands from the central group. The low 3He/4He ratio measured on Nordest samples also suggests a high (U+Th)/3He in its source, which may be due to degassing presumably during an early stage of the recycling. The low 207Pb/206Pb with low volatiles samples could also be explain this early degassing. Samples with the highest 207Pb/206Pb are richer in volatile suggesting the presence of a volatile rich lithology beneath the Azores central group, which was also proposed by

  10. 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

  11. 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.

  12. 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.

  13. Using stable and radioactive isotopes to trace atmospherically deposited Pb in montane forest soils.

    PubMed

    Kaste, James M; Friedland, Andrew J; Stürup, Stefan

    2003-08-15

    Atmospheric deposition of lead (Pb) throughout the 1900s resulted in elevated amounts of this toxic metal even in remote forest soils of the northeastern United States. Soils can act as a net sink for metals and thus minimize groundwater and surface water contamination. Recent studies utilizing forest floor temporal data and models of total Pb in precipitation, surface soils, and streams have estimated the time scale of Pb release from soils. However, due to the limited availability and spatial variability of forest floor survey data, other methods for quantifying anthropogenic Pb movement are needed. This study uses the isotopic composition (206Pb/207Pb) of soil Pb and measurements of 210Pb and 226Ra to directly trace the transit of atmospherically deposited Pb in the soil profile. We also report on the recovery of an enriched 207Pb dose applied in 1984 to the surface of a soil plot in the coniferous forest at Camels Hump in Vermont. The isotopic composition of soil Pb in low elevation deciduous forests suggests that approximately 65% of the original atmospheric Pb load has migrated from the forest floor to the upper 10 cm of the mineral soil. Higher elevation sites with coniferous vegetation have thicker forest floors, which have prevented significant amounts of Pb from entering the mineral soil. After 17 years, the soil organic horizon in the coniferous zone prevented any penetration of the applied Pb into the mineral soil. Using 210Pb budgets in different soil compartments, we determine forest floor response times for atmospherically delivered Pb to be approximately 60 years in the low elevation deciduous forest zone and 150 years for the high elevation spruce-fir forest zone at Camels Hump. According to its distribution in the soil profile, we conclude that a dispersed release of anthropogenic Pb to groundwater and surface water is possible this century. Our results also offer independent confirmation of Pb deposition models previously generated for the region.

  14. 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.

  15. 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.

  16. Pb contamination and isotopic composition of urban soils in Hong Kong.

    PubMed

    Wong, Coby Sze Chung; Li, Xiang Dong

    2004-02-01

    In the urban environment, intense human activities can lead to degradation of environmental quality and have potential long-term effects on human health. In the present study, Pb contamination of urban soil cores in Hong Kong was investigated using a combination of the 'total' concentration, chemical partitioning and isotopic composition of Pb in the soils. The analytical results showed that urban soil cores in close vicinity to high traffic volumes (> 40000 vehicles per day) were usually contaminated with Pb, suggesting atmospheric deposition of Pb as a consequence of vehicular emissions arising from the combustion of leaded gasoline in the past. Increasing Pb concentrations were generally associated with decreasing 206Pb/207Pb ratios of the contaminated soil cores, offering strong evidence of accumulation of Pb derived from anthropogenic sources. In selected contaminated soil cores, the 206Pb/207Pb ratios tended to increase in the order: carbonate < exchangeable < Fe-Mn oxide < organic < residual fractions. The distribution of the 206Pb/207Pb ratios in the five operationally defined chemical fractions showed that the 206Pb/207Pb ratios generally increased with increasing stability, demonstrating preferential association of anthropogenic Pb with the carbonate, exchangeable, Fe-Mn oxide and organic fractions in the soils.

  17. 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. PMID:7892194

  18. 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.

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

    PubMed Central

    Weisler, M I; Woodhead, J D

    1995-01-01

    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. PMID:7892194

  20. 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 ...

  1. Detrital zircon geochronology and Nd isotope geochemistry of an early Paleozoic succession in Korea:

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  2. The Fluid History of Jadeitites Near the Motagua Fault, Guatemala, as Revealed by Stable Isotope and Elemental Geochemistry

    NASA Astrophysics Data System (ADS)

    Niespolo, E. M.; Holk, G. J.; Neff, H.

    2014-12-01

    Stable isotopes and elemental geochemistry reveal a complex fluid history for jadeitites exposed both north and south of the Motagua Fault Zone (MFZ) in Guatemala. A companion study (Niespolo et al., 2014) utilized these data to source Mesoamerican jadeitite artifacts, as this region is the only source for such materials. Materials studied include jadeitites that range from 71% to 95% jadeite with minor albite and white mica. Jadeitites north of the MFZ have δ18OJadeite = +9.2±0.6‰ (n=6), δ18OAlbite = +9.4±0.3 (n=2), δ18OWhiteMica = +9.8±0.3 (n=3), and δDWhiteMica = -52± 4‰ (n=3). Jadeite δ18O values are 2-5‰ higher than those reported by Johnson and Harlow (1999), suggesting a diverse fluid history north of the MFZ. Water in apparent equilibrium at 400°C with north MFZ jadeitite has δ18O = +8.5‰ and δD = -25‰. Jadeites from Carrizal Grande south of the MFZ have δ18OJadeite = +6.8±0.6‰ (n=7), δ18OWhiteMica = +9.0±1.2 (n=6), and δDWhiteMica = -42±2‰ (n=5), with δ18OH2O = +6.4‰ and δDH2O = -15‰. In contrast, jadeitites from La Cieba south of the MFZ have δ18OJadeite = +7.5±1.4‰ (n=5), δ18OAlbite = +9.0, δ18OWhiteMica = +9.7±0.1 (n=2), and δDWhiteMica = -42±0‰ (n=2), with δ18OH2O = +7.2‰ and δDH2O = -14‰. Calculated fluids are consistent with those associated with the alteration of serpentinite in a subduction zone setting (e.g., Harlow and Sorenson, 2005). White mica, albite and jadeite are out of 18O/16O equilibrium. This suggests post-jadeite isotopic exchange, possibly during exhumation. North MFZ jadeites are enriched in Rb, Ba, Sc, Pb and Nd, and depleted in Sr, Ti, V, and Cr relative to chondrites. Carrizal Grande jadeites are depleted in Sr, Zr, V, and Cr, and enriched in REE and Rb.

  3. Progress integrating ID-TIMS U-Pb geochronology with accessory mineral geochemistry: towards better accuracy and higher precision time

    NASA Astrophysics Data System (ADS)

    Schoene, B.; Samperton, K. M.; Crowley, J. L.; Cottle, J. M.

    2012-12-01

    It is increasingly common that hand samples of plutonic and volcanic rocks contain zircon with dates that span between zero and >100 ka. This recognition comes from the increased application of U-series geochronology on young volcanic rocks and the increased precision to better than 0.1% on single zircons by the U-Pb ID-TIMS method. It has thus become more difficult to interpret such complicated datasets in terms of ashbed eruption or magma emplacement, which are critical constraints for geochronologic applications ranging from biotic evolution and the stratigraphic record to magmatic and metamorphic processes in orogenic belts. It is important, therefore, to develop methods that aid in interpreting which minerals, if any, date the targeted process. One promising tactic is to better integrate accessory mineral geochemistry with high-precision ID-TIMS U-Pb geochronology. These dual constraints can 1) identify cogenetic populations of minerals, and 2) record magmatic or metamorphic fluid evolution through time. Goal (1) has been widely sought with in situ geochronology and geochemical analysis but is limited by low-precision dates. Recent work has attempted to bridge this gap by retrieving the typically discarded elution from ion exchange chemistry that precedes ID-TIMS U-Pb geochronology and analyzing it by ICP-MS (U-Pb TIMS-TEA). The result integrates geochemistry and high-precision geochronology from the exact same volume of material. The limitation of this method is the relatively coarse spatial resolution compared to in situ techniques, and thus averages potentially complicated trace element profiles through single minerals or mineral fragments. In continued work, we test the effect of this on zircon by beginning with CL imaging to reveal internal zonation and growth histories. This is followed by in situ LA-ICPMS trace element transects of imaged grains to reveal internal geochemical zonation. The same grains are then removed from grain-mount, fragmented, and

  4. 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.

  5. 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.

  6. Laser Ablation Analyses of Pb Isotopes in Ancient Feldspars: Application to a Polymetamorphic Terrane, West Greenland

    NASA Astrophysics Data System (ADS)

    Krogstad, E. J.; Baker, J. A.; Waight, T. E.

    2001-12-01

    Laser ablation was used to sample the Pb isotopic compositions of various feldspars, as well as isotopic standards. The ablated material was analyzed by MC-ICP-MS. The resulting accuracy and external precision are comparable to conventional (i.e., not double or triple-spiked) feldspar Pb isotope analyses done by TIMS. However, the data can be acquired with no chemical separation and require only a few minutes per sample. A pilot study was made of the feldspars from a polymetamorphic terrane in West Greenland, in which Late Archean gneisses were deformed and metamorphosed during the Early Proterozoic. In this terrane, isotopic contrasts have long been sought to delineate any suture between discrete Archean continental blocks that might mark the site of ocean closure. Previous whole rock Nd and Pb isotopic studies had yielded equivocal results on the presence of such an isotopic discontinuity. The laser ablation feldspar data presented here, combined with existing whole rock Pb data, point to real differences in the sources of gneisses from various parts of the orogen. This indicates that the laser ablation method of sampling feldspar Pb holds real potential for future reconnaissance studies of old continental crust in a manner similar to that of zircon U-Pb geochronology studies.

  7. 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.

  8. 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. PMID:24342096

  9. 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.

  10. 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

  11. 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

  12. Pb-Nd Isotopes Indicate the Origin of Island Arc Terranes in the Early Paleozoic Pacific.

    PubMed

    Münker

    2000-03-01

    The Takaka Terrane in New Zealand is one of the best exposed arc fragments of the early Paleozoic Australian-Antarctic convergent margin and constitutes one of the most outboard terranes of this margin in paleogeographic reconstructions. Pb-Nd isotope compositions of clinopyroxenes from the Cambrian Devil River Volcanics of the Takaka Terrane enable identification of the location of the terrane in the Paleo-Pacific Ocean. The Devil River Volcanics, a suite of primitive arc and back-arc rocks, are interbedded with the partly continent-derived Haupiri Group sediments. Extremely radiogenic Pb and unradiogenic Nd compositions in the arc rocks cannot be explained by assimilation of the Haupiri Group sediments or a continental basement of such a composition. Pb isotope compositions of the Takaka Terrane sediments are much less radiogenic and overlap with crustal compositions of the Lachlan Fold Belt in Australia, suggesting that both units are derived from one source, the Australian-Antarctic Pacific margin. Pb-Nd isotope compositions in the Devil River Volcanics reflect contamination of their mantle sources by subducted sediments derived from Archean provinces in either Antarctica or Laurentia. Both provinces show characteristically high 207Pb/204Pb500 and were located at the Pacific rim in the Cambrian. Mixing between mantle and Proterozoic continental material from present western South America or eastern Laurentia cannot explain the high 207Pb/204Pb500 in the New Zealand rocks. As in New Zealand, extreme spreads in Pb-Nd isotope compositions in other Cambrian volcano-sedimentary sequences in southeast Australia and Tasmania can be explained by the same model, suggesting that all these fragments originated along the Australian-Antarctic Gondwana margin. Pb isotope compositions of arc rocks, therefore, provide a new tool for terrane analysis in the early Paleozoic Pacific ocean.

  13. Isotope shifts in the spectrum of Pb I

    NASA Astrophysics Data System (ADS)

    Wasowicz, T. J.; Kwela, J.

    2008-02-01

    Isotope shifts in twelve atomic lines of Pb I: 401.9 nm (6p6d 3F3→6p2 1D2), 405.8 nm (6p7s 3P1→6p2 3P2), 416.9 nm (6p6d 3F2→6p2 1D2), 434.0 nm (6p7d 3D1→6p2 1S0), 500.6 nm (6p7s 1P1→6p2 1S0), 520.3 nm (6p8s 3P1→6p2 1S0), 589.6 nm (6p8p 3D1→6p7s 3P0), 600.2 nm (6p8p 3D2→6p7s 3P1), 601.2 nm (6p8p 3D1→6p7s 3P1), 605.9 nm (6p8p 3P0→6p7s 3P1), 611.0 nm (6p8p 3P1→6p7s 3P0) and 723.1 nm (6p7s 3P1→6p2 1D2) have been measured. As a light source the discharge tube was used. The high resolution spectral apparatus consisted of a silver coated Fabry-Perot etalon and a grating spectrograph combined with a CCD camera used as a detector. In the analysis of the spectra a computer simulation technique was used. Our studies enabled us to separate the mass and the field effects and to determine values of changes of the mean square nuclear charge radii.

  14. Production and in vivo imaging of (203)Pb as a surrogate isotope for in vivo (212)Pb internal absorbed dose studies.

    PubMed

    Máthé, Domokos; Szigeti, Krisztián; Hegedűs, Nikolett; Horváth, Ildikó; Veres, Dániel S; Kovács, Béla; Szűcs, Zoltán

    2016-08-01

    (212)Pb is a clinically relevant therapeutic alpha emitter isotope. A surrogate, (203)Pb, if prepared with sufficiently high specific activity could be used to estimate (212)Pb in vivo absorbed doses. An improved production procedure of (203)Pb with a simple, new separation method and high specific radioactivity for imaging is reported. We determined the in-vivo biodistribution of (203)Pb in mice by SPECT/CT. This highlights application possibilities of (203)Pb for further in vivo and clinical uses (radiolabeled (212)Pb-peptide co-injection, dosimetry calculation).

  15. 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.

  16. 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.

  17. 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. PMID:15134877

  18. 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

  19. Constraints on slab inputs and mantle source compositions in the northern Cascade arc (Garibaldi belt) from Sr-Nd-Pb-Hf isotopes and trace elements in primitive basalts

    NASA Astrophysics Data System (ADS)

    Mullen, E. K.; Carpentier, M.; Weis, D.

    2011-12-01

    */206Pb* and ɛHf values decrease markedly to the north and are inversely correlated with TiO2. At a given ɛNd, Glacier Peak and Chilliwack samples have distinctly higher 208Pb*/206Pb* and ɛHf than other GVB samples, subdividing the GVB into two parallel isotopic trends. We conclude that GVB basalt geochemistry cannot be explained solely by reductions in slab age and sediment input; rather, slab contributions are superimposed on a mantle wedge with inherent arc-parallel compositional variability that is unrelated to the subduction regime. Trace element model calculations, phase equilibria, and Ba-Nb-La/Yb-Yb systematics indicate that the mantle sources of northern GVB basalts are more enriched in trace elements and Na than those in the south, reflecting different source compositions. This study demonstrates the importance of obtaining high precision isotopic data on arc basalts, as mantle source heterogeneities in arcs may not be revealed by trace element abundances alone. [1] Green (2006) Lithos 87, 23-49 [2] Green and Harry (1999) Earth Planet. Sci. Lett. 171, 367-381 [3] Green and Sinha (2005) Jour. Volc. Geoth. Res. 140, 107-132 [4] Mullen (2011) PhD dissert.

  20. 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.

  1. 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.

  2. Using Pb isotopes in surface media to distinguish anthropogenic sources from undercover uranium sources

    NASA Astrophysics Data System (ADS)

    Kyser, Kurt; Lahusen, Larry; Drever, Garth; Dunn, Colin; Leduc, Evelyne; Chipley, Don

    2015-09-01

    The response in elemental concentrations and Pb isotopes in various surface media from the Cigar West unconformity-type uranium deposit located at a depth of 450 m were measured to ascertain if element migration from the deposit can be detected at the surface. The media included clay-size fractions separated from the A2, B and C soil horizons, and tree cores and twigs from black spruce (Picea mariana) and jack pine (Pinus banksiana) trees. Lead isotopes were used to trace any effect on the surface media from the deposit at depth because the 207Pb/206Pb ratios in the ore are < 0.1, whereas the background values in the basin are > 0.7 and modern anthropogenic Pb from aerosols are near 0.9. The tree cores record their lowest and therefore most radiogenic 207Pb/206Pb ratios of < 0.7 near the surface projection of the deposit and associated structures, particularly in tree rings that predate any exploration and drilling activity in the area. The median 207Pb/206Pb ratios increase in the order C, B soil horizon clays, tree cores, A2 soil clays and twigs because of the increasing contribution of common Pb with high ratios from anthropogenic sources that affect the shallowest media the most. Although this anthropogenic Pb as well as that from the background dominates the composition of all media at the surface and the contribution from the deposit at depth is diminished toward the surface, ore-related Pb is still present as a few percent of the composition of pathfinder elements and Pb isotopes.

  3. Evidencing the Impact of Coastal Contaminated Sediments on Mussels Through Pb Stable Isotopes Composition.

    PubMed

    Dang, Duc Huy; Schäfer, Jörg; Brach-Papa, Christophe; Lenoble, Véronique; Durrieu, Gaël; Dutruch, Lionel; Chiffoleau, Jean-Francois; Gonzalez, Jean-Louis; Blanc, Gérard; Mullot, Jean-Ulrich; Mounier, Stéphane; Garnier, Cédric

    2015-10-01

    Heavily contaminated sediments are a serious concern for ecosystem quality, especially in coastal areas, where vulnerability is high due to intense anthropogenic pressure. Surface sediments (54 stations), 50 cm interface cores (five specific stations), river particles, coal and bulk Pb plate from past French Navy activities, seawater and mussels were collected in Toulon Bay (NW Mediterranean Sea). Lead content and Pb stable isotope composition have evidenced the direct impact of sediment pollution stock on both the water column quality and the living organisms, through the specific Pb isotopic signature in these considered compartments. The history of pollution events including past and present contaminant dispersion in Toulon Bay were also demonstrated by historical records of Pb content and Pb isotope ratios in sediment profiles. The sediment resuspension events, as simulated by batch experiments, could be a major factor contributing to the high Pb mobility in the considered ecosystem. A survey of Pb concentrations in surface seawater at 40 stations has revealed poor seawater quality, affecting both the dissolved fraction and suspended particles and points to marina/harbors as additional diffuse sources of dissolved Pb.

  4. 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.

  5. 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.

  6. 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.

  7. RECONSTRUCTING LAURENTIDE ICE SHEET MELTWATER GEOCHEMISTRY USING COMBINED STABLE ISOTOPE AND LASER ABLATION TRACE ELEMENT ANALYSES

    NASA Astrophysics Data System (ADS)

    Vetter, L.; Spero, H. J.; Eggins, S. M.; Flower, B. P.; Williams, C. C.

    2009-12-01

    Little is known about the oxygen isotope evolution of Northern hemisphere ice sheets during past glacial cycles, with the exception of results from models and calculations based on whole ocean δ18O change. Reconstructing changes in the δ18Owater of the global ocean assumes a homogeneous δ18O value for contributions from Northern hemisphere ice sheets with a mass balance contribution from the Southern hemisphere. Because oceanic δ18Ow forms a crucial baseline for deconvolving the combined signal of temperature and hydrologic changes recorded in foraminiferal calcite, constraints on the contributions of melting ice sheets form a fundamental component of reconstructions of global ocean δ18Ow changes on glacial timescales. Here we present a novel geochemical technique to compute the oxygen isotopic composition of Laurentide Ice Sheet (LIS) meltwater flowing into the Gulf of Mexico during periods of rapid ice sheet melting. The technique combines data from different types of geochemical analyses on individual shells of the planktonic foraminifera Orbulina universa to compute meltwater geochemistry, using laser ablation ICP-MS to measure Mg/Ca (a temperature proxy) and Ba/Ca (a salinity proxy) and isotope ratio mass spectrometry to measure δ18O (a temperature and δ18Owater proxy) on remaining shell material. O. universa has a very large temperature and salinity tolerance (9-30°C; 23-45 psu) and broad depth habitat (0-80 m), so an assemblage of individual shells from a single core interval records a range of water conditions. We have selected deglacial meltwater intervals from core MD02-2550 (26.95°N, 91.35°W, 2245 m water depth), collected from the anoxic Orca Basin in the Gulf of Mexico, for a proof of concept demonstration. From each interval, we combine measurements of Mg/Ca, Ba/Ca, and δ18O on 30-100 individual O. universa. The δ18O from each shell reflects the combined influence of temperature and δ18Owater, where this latter value is a function of

  8. 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.

  9. Elucidating the construction of the Austurhorn Intrusion, SE 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.; Fisher, C. M.; Hanchar, J. M.; Bindeman, I. N.; Wooden, J. L.; Sigmarsson, O.

    2013-12-01

    The Austurhorn Intrusive Complex (AIC) in SE Iceland comprises large bodies of granophyre, gabbro, and a mafic-felsic composite zone (MFCZ) that exemplifies mafic-felsic interactions common in Icelandic silicic systems. However, despite being one of Iceland's best-studied intrusions (Blake 1966; Furman et al 1992a,b; Thorarinsson & Tegner 2009), 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 in-situ zircon elemental and isotopic (hafnium and oxygen) geochemistry, as well as U-Pb geochronology, as tools for elucidating the complex construction and magmatic evolution of Austurhorn's MFCZ. The elemental compositions of AIC zircons form a broad but coherent array partly overlapping with the zircon geochemical signature for Icelandic silicic volcanic rocks (Carley et al 2011). With some exceptions (see below), Hf concentrations are low (less than 10,000 ppm), typical of Icelandic zircon, and Ti concentrations range from 6 to 25 ppm (Ti-in-zircon temps. 730-870°C). Their δ18O values are generally well-constrained at +2.5 to +4 ‰, consistent with other Icelandic magmatic zircon (Bindeman et al 2012) and preserving evidence for partial melting of hydrothermally-altered crust as the source of silicic magmas within the Austurhorn system. Epsilon-Hf values cluster tightly at +13×1 ɛ-units, suggesting a single source for the different units of the MFCZ. The notable exceptions to the trends described above are zircons from a high-silica granophyre displaying CL-dark zones and convoluted zoning. These fall well outside the AIC geochemical arrays, primarily distinguished by high Hf (up to 24,000 ppm) and lower Ti (down to 2 ppm), far higher Hf and lower Ti than any other analyzed Icelandic zircon, and extremely low δ18O values (down to -6 ‰). We interpret these to reflect multiple episodes of partial melting and melt extraction of the

  10. 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.

  11. Age of Alpine Corsica ophiolites revisited: Insights from in situ zircon U-Pb age and O-Hf isotopes

    NASA Astrophysics Data System (ADS)

    Li, Xian-Hua; Faure, Michel; Rossi, Philippe; Lin, Wei; Lahondère, Didier

    2015-04-01

    Knowledge of the age and timing of ophiolite sequences is essential for understanding the mechanisms of plate tectonics. The ophiolites in the Schistes Lustrés and the Upper nappes of Alpine Corsica represent remnants of the Liguria-Piemonte ocean basin that formed as a branch of the Central Atlantic basin during the opening of the Mesozoic Western Alpine Tethys. Despite numerous isotopic and paleontological studies, the age and timing of the ophiolites in the Schistes Lustrés nappe are still controversial. This study presents integrated in situ analyses of zircon U-Pb age and O-Hf isotopic data for ophiolitic gabbros and plagiogranites from three localities in the Schistes Lustrés nappe of Eastern Corsica. Our new results demonstrate that these rocks crystallized synchronously at ~ 159 Ma, approximately 10 m.y. younger than the ophiolites in the Balagne Upper nappe. Zircons from the gabbros and plagiogranites are characterized by highly positive εHf(t) (+ 15.0 to + 15.9) and mantle-like δ18O (5.2-5.4‰) values. Thus, these ophiolitic rocks were cogenetic, and crystallized from magmas produced by partial melting of a depleted, N-MORB type mantle. By contrast, in the Balagne Upper nappe, the ~ 169 Ma ophiolites contain numerous xenocrystic zircons inherited from a continental crust. Our current knowledge of isotopic geochronology and geochemistry supports a paleogeographic reconstruction, in which the earliest ophiolites in the Balagne nappe were emplaced close to a continental margin at ~ 169 Ma, while the N-MORB type ophiolites in the Schistes Lustrés nappe were likely formed approximately 10 m.y. later in the central part of the Liguria-Piemonte oceanic basin. The relative location of the Schistes Lustrés and Balagne Upper nappes with respect to continental margins is discussed.

  12. 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.

  13. Deciphering The Sources Of Cenozoic Volcanism In Central Mongolia Using Trace Element And Isotope Geochemistry

    NASA Astrophysics Data System (ADS)

    Hunt, A. C.; Parkinson, I. J.; Harris, N.; Rogers, N. W.; Barry, T.; Yondon, M.

    2009-12-01

    One of the largest regions of Cenozoic intra-plate volcanism stretches across central Asia from the Baikal Rift in Siberia, through central Mongolia to China. In Mongolia this is expressed as numerous small-volume alkali-basaltic cones and lavas, erupted since ca. 30 Ma. Currently, accepted models of melt generation for intraplate magmatism, such as mantle plumes, lithospheric extension and convective removal of the lithosphere, are difficult to reconcile with some aspects of volcanism and tectonics in this region. A suite of basalts erupted across an area of Cenozoic uplift in central Mongolia, known as the Hangai Dome, has been analysed for trace elements and Sr-Nd-Pb isotopes. New Pb isotope data were collected by double spike MC-ICP-MS at the Open University and have a long-term 2σ reproducibility better than 175 ppm for NBS 981. These data suggest progressive mixing between two distinct source regions in the genesis of the Hangai basalts. Older basalts, previously dated at 5.91 ± 0.02 Ma (Barry et al., 2003), are derived from a component with an asthenospheric signature similar to depleted Indian MORB. Younger basalts are increasingly mixed with a component with lower Pb and Sr ratios and an enriched trace element signature, which is similar in composition to some lamproites erupted in the western USA (Mirnejad and Bell, 2006). This represents a transition from asthenospheric to lithospheric melting through time. Furthermore, studies on mantle xenoliths from across the Hangai Dome indicate an elevated geotherm under the centre of the dome and significantly cooler conditions at its margins, interpreted to be the result of mantle upwellling (Harris et al., in review). Further numerical modelling will assess the relative contributions from lithospheric and asthenospheric sources in the genesis of these basalts, and contribute to understanding this enigmatic volcanic region. Barry, T. L., Saunders, A. D., Kempton, P. D., Windley, B.F., Pringle, M.S., Dorjnamjaa

  14. 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.

  15. 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.

  16. 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.

  17. REE characteristics and Pb, Sr and Nd isotopic compositions of steel plant emissions.

    PubMed

    Geagea, M Lahd; Stille, P; Millet, M; Perrone, Th

    2007-02-01

    A comprehensive Pb-Sr-Nd isotope and REE tracer study of atmospheric trace metal pollution by a steel plant situated to the north of the urban communities of Strasbourg (France) and Kehl (Germany) has been performed using tree barks as biomonitors. The 206Pb/207Pb and 208Pb/207Pb isotopic ratios of the steel plant's filter dust are similar to values found in dust of waste incinerators. The 87Sr/86Sr ratio is similar to present-day ratios of Phanerozoic or Precambrian granitic rocks. The 143Nd/144Nd isotopic composition is very low and corresponds to an (Nd) value of -17.5. Such a low value is characteristic of old Precambrian granitic rocks and banded iron formations. Thus, this low (Nd) value might point to the origin of the iron necessary for the steel production. The fact, that this isotopic composition does not occur in crustal rocks of Western Central Europe makes the Nd isotope ratio a powerful tool to trace steel plants atmospheric emissions. The rare earth element (REE) distribution pattern of the steel plant's filter dust shows very specific fractionations like La and Nd enrichments which are traceable in tree barks over a distance of 4 km. The Pb, Sr and Nd isotope ratios not only enable the steel plant's emissions to be traced in a north-easterly direction, along the principal wind pathway but also enables the interference of this emission at 4 km NE from the steel plant with another atmospheric component originating from the Strasbourg Rhine harbour to be identified.

  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. 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

  1. 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.

  2. 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.

  3. The fate of atmospherically derived Pb in Central European catchments: insights from spatial and temporal pollution gradients and Pb isotope ratios.

    PubMed

    Bohdalkova, Leona; Novak, Martin; Stepanova, Marketa; Fottova, Daniela; Chrastny, Vladislav; Mikova, Jitka; Kubena, Ales A

    2014-04-15

    Soils in polluted regions are generally regarded as a delayed, long-lasting source for Pb contamination of aquatic systems. Lead deposited on topsoil is slowly transported downward with particulate and colloidal organic matter, driven by infiltrating precipitation. Then, Pb is tightly retained in mineral soil. Lead export from catchments is extremely low and decoupled from the atmospheric input. We tested this hypothesis in 11 small catchments, differing in pollution levels. Input/ouput Pb fluxes were monitored for 14-15 years in an era of decreasing industrial Pb emission rates. Between 1996/1997 and 2010, Pb deposition fluxes decreased significantly, on average by 80%. At the beginning of the monitoring, Pb export constituted 2 to 58% of Pb input. At the end of the monitoring, Pb export constituted 2 to 95% of Pb input. Highly polluted sites in the northeast exported significantly more Pb than less polluted sites further south. The (206)Pb/(207)Pb isotope ratios of runoff (1.16) were identical to those of topsoil and present-day deposition, and different from mineral soil and bedrock. Lead isotope systematics and between-site flux comparisons indicated that a portion of the incoming Pb had a relatively short residence time in the catchments, on the order of decades.

  4. 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.

  5. Hyperfine structure and isotope shifts in 733.2 nm mixed forbidden line of Pb I

    NASA Astrophysics Data System (ADS)

    Wąsowicz, T. J.; Drozdowski, R.; Kwela, J.

    2007-05-01

    Studies of the hyperfine structure and isotope shifts in 733.2 nm mixed (M1+E2) multipole line of Pb I are presented. As a light source the electrodeless discharge tube was used. The high resolution spectral apparatus consisted of a silver coated Fabry-Perot etalon and a grating spectrograph combined with a CCD camera used as a detector. In the analysis of the spectra a computer simulation technique was used. The experiments with the isotope 207Pb yielded the hyperfine structure splitting constant A for the 3P1 and 1D2 levels of the 6s26p2 ground configuration. In the experiment with natural lead the isotope shifts between four stable isotopes (204, 206, 207, 208) were measured.

  6. The characteristic of Pb isotopic compositions in different chemical fractions in sediments from Three Gorges Reservoir, China.

    PubMed

    Han, Lanfang; Gao, Bo; Wei, Xin; Gao, Li; Xu, Dongyu; Sun, Ke

    2015-11-01

    To explore the distribution and sources of Pb within the Three Gorges Reservoir (TGR), Pb concentrations and isotope ratios were measured in sediment cores collected from one mainstream and three tributaries. The results showed that sediments contained an average of 43.54 mg kg(-1) of Pb, roughly 1.6 times higher than the geochemical background concentration. Mainstream sediments showed higher average Pb concentrations but slightly less (206)Pb/(207)Pb and more radiogenic (207)Pb/(208)Pb ratios than all tributaries. Most Pb occurred in reducible phases, with much less in exchangeable and oxidizable fractions; thus, Fe-Mn oxides may be the major sink of anthropogenic Pb. Bi-plots of (206)Pb/(207)Pb versus Pb content, and of (206)Pb/(207)Pb versus (207)Pb/(208)Pb, indicated that coal combustion was the predominant anthropogenic Pb source for exchangeable, reducible, and oxidizable fractions, while residual Pb mainly occurred naturally. The average percentage of coal consumption contribution was 61.1% for the Pb contamination in sediments in the lower reaches in the TGR region.

  7. 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

  8. Shapes and Collectivity in Neutron Deficient Even-Mass 188-198Pb Isotopes

    NASA Astrophysics Data System (ADS)

    Pakarinen, J.; Grahn, T.; Algora, A.; Bree, N.; Cocolios, T. E.; Diriken, J.; Fernier, P.; Gaffney, L. P.; Hadyńska-Klȩk, K.; Herzáň, A.; Iwanicki, J.; Jakobsson, U.; Jenkins, D.; Kesteloot, N.; Konki, J.; Lannoo, B.; Papadakis, P.; Peura, P.; Rahkila, P.; Rainovski, G.; Rapisarda, E.; Sambi, S.; Scheck, M.; Seidlitz, M.; Stora, T.; Van Duppen, P.; Warr, N.; Wenander, F.; Vermeulen, M. J.; Voulot, D.; Wrzosek-Lipska, K.; Zielińska, M.

    The neutron deficient 188-198Pb isotopes have been studied in a Coulomb excitation measurement employing the Miniball spectrometer and radioactive beams from REX-ISOLDE, CERN. These isotopes are of particular importance as they lie in a transitional region, where the intruding structures, associated with different deformed shapes, come down in energy close to the spherical ground state. For detailed analysis of the Coulomb excitation data, the understanding of the beam composition is essential.

  9. 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.

  10. 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.

  11. Geochemistry of the Patricia Zn-Pb-Ag Deposit (paguanta, NE Chile)

    NASA Astrophysics Data System (ADS)

    Chinchilla Benavides, D.; Merinero Palomares, R.; Piña García, R.; Ortega Menor, L.; Lunar Hernández, R.

    2013-12-01

    The Patricia Zn-Pb-Ag ore deposit is located within the Paguanta mining project, situated at the northern end of the Andean Oligocene Porphyry Copper Belt of Chile. The sulfide mineralization occurs as W-E oriented veins hosted in volcanic rocks, mainly andesite (pyroclastic, ash and lavas), of Upper Cretaceous to Middle Tertiary age. The ore mineralogy (obtained by EMPA analyses) comprises in order of abundance, pyrite, sphalerite (5.5 - 10.89 wt % Fe, 9.8-19 % molar FeS and 0.52 wt % Cd), galena, arsenopyrite, chalcopyrite and Ag-bearing sulfosalts. The veins show a zoned and banded internal structure with pyrite at the edges and sphalerite in the center. The Ag occurs mostly as Ag-Cu-Sb sulfosalts, in order of abundance: series freibergite - argentotennantite -polybasite and stephanite. Other minor Ag phases such as argentite, pyrargirite and diaphorite were also identified. These Ag phases are typically associated with the base-metal sulfides. Freibergite occurs filling voids within sphalerite, chalcopyrite and at the contact between sphalerite and galena. Polybasite, stephanite, pyrargirite and argentite are mostly in close association with freibergite. In the case of diaphorite, it commonly occurs filling voids between galena crystals or as inclusions within galena. Some minor Ag-bearing sulfosalts are also identified between pyrite crystals. The alteration minerals are dominated by chlorite, illite and kaolinite. The gangue minerals consist of quartz and carbonates identified by XRD as kutnahorite. We obtained linear correlation statistically significant only for Ag, As Au, Cd, Cu, Pb, Sb and Zn and therefore we generated an enhanced scatter plot matrix of these elements. Bulk rock analyses (ICP/MS and XRF) of drill cores show that Ag is strongly and positively correlated with Pb and As, moderately with Cd, Sb, Au and Zn and weakly with Cu, while Au is moderately and positively correlated with Ag, As, Cd, Sb and Zn and weakly with Cu and Pb. These results

  12. Stable isotope geochemistry of clay minerals from fossil and active hydrothermal systems, southwestern Hokkaido, Japan

    SciTech Connect

    Marumo, Katsumi; Longstaffe, F.J.; Matsubaya, Osamu

    1995-06-01

    Miocene submarine to Quaternary terrestrial volcanism in southwestern Hokkaido, Japan, is associated with hydrothermal clay alteration and mineralization, including Kuroko-type deposits at Kagenosawa (14.2 Ma, Cu > Zn, Pb > Au) and Minamishiraoi (12.5 Ma, Ba > Zn, Pb, Cu), vein-style at Noboribetsu ({le} 1.8 Ma). The {delta}D and {delta}{sup 18}O values of mica (sericite), mica-smectite, chlorite, chlorite-smectite, nacrite, dickite, kaolinite, and smectite were used to deduce the type(s) of hydrothermal fluid at each locality. Calculated compositions for Minamishiraoi and Kagenosawa fluids suggest that seawater was dominant, but some mixing with magmatic water is also indicated, particularly for the polymetallic Kagenosawa deposit. Hydrothermal fluids at Date, Chitose, and the Noboribetsu geothermal area were dominated by meteoric water. The {delta}D and {delta}{sup 18}O values of modern hot-spring waters at Noboribetsu closely parallel fluid compositions calculated for the clay alteration at Date, Chitose, and Noboribetsu. In vacuo TG patterns of other smectitic clays suggested gradual loss of hydroxyl-groups beginning near 200{degrees}C, rather than the more typical distinct separation between interlayer water at <200{degrees}C and hydroxyl-groups at >400{degrees}C. This behaviour constrains the maximum temperature that can be used for in vacuo preheating. Furthermore, shifts to lower {delta}D values (by as much as 19{per_thousand}) were obtained when this smectite was dispersed in low-D water for three weeks, perhaps indicating isotopic exchange. However, with appropriate care, {delta}D values obtained by conventional procedures (including preheating to {le}200{degrees}C) normally reproduced natural compositions of the smectitic clays with acceptable accuracy and precision.

  13. Monitoring of Pb Contamination in Loire Estuary: Trends, Distribution and Isotopic composition

    NASA Astrophysics Data System (ADS)

    Brach-Papa, Christophe; Chiffoleau, Jean-François; Knoery, Joel; Chouvelon, Tiphaine; Auger, Dominique; Bretaudeau, Jane; Crochet, Sylvette; Rozuel, Emmanuelle; Thomas, Batien; Vasileva, Emilia; Oriani, Anna Maria

    2014-05-01

    The Loire River is one of the largest river systems in Western Europe and constitutes a major continental input to marine environment in the Bay of Biscay. Its catchment area flows through agricultural, industrial areas and through a more and more urbanized estuary. Even if Loire River is not considered as a highly polluted system, some studies identified a Pb contamination of its estuary due to industrial inputs and combustion of leaded gasoline up to the mid 90's. A retrospective study, based on the analysis (Pb contents and isotopic composition) of Mytilus edulis samples collected by the French mussel watch program (RNO/ROCCH) has highlighted this contamination and its trend between 1985-2005 (Couture et al., 2010). This poster will first complete the work initiated by Couture et al. Pb contents and isotopic signatures in mussel samples collected by RNO/ROCCH over the last 10 years will be presented and discussed. Results will be compared to measurements performed on various environmental samples (sediment, biota…) collected in the frame of the environmental monitoring project RS2E started in 2012 by the "Observatoire des Sciences de l'Univers Nantes-Atlantique" (OSUNA). This new data will contribute to a better characterisation of Pb contents and distribution along the Loire Estuary. Moreover, some key samples will be submitted to HR-ICP-MS for Pb isotopic analysis. Discrimination of anthropic Pb sources requires both precise and accurate isotope ratio determination and also high versatility due to the complex matrix, which is typical for marine and estuarine samples. These measurements will contribute to a more accurate definition and characterisation of main actual anthropic Pb sources (urban, agricultural, industrial or atmospheric deposition). Couture R.- M., Chiffoleau J.-F., Auger D., Claisse D., Gobeil C. and Cossa D. (2010) Seasonal and decadal variation in lead sources to eastern north Atlantic mussels. Environ. Sci. Technol. 44, 1211-1216.

  14. Source identification of heavy metal contamination using metal association and Pb isotopes in Ulsan Bay sediments, East Sea, Korea.

    PubMed

    Chae, Jung Sun; Choi, Man Sik; Song, Yun Ho; Um, In Kwon; Kim, Jae Gon

    2014-11-15

    To determine the characteristics of metal pollution sources in Ulsan Bay, East Sea, 39 surface and nine core sediments were collected within the bay and offshore area, and analyzed for metals and stable lead (Pb) isotopes. Most surface sediments (>95% from 48 sites) had high copper (Cu), zinc (Zn), cadmium (Cd), and Pb concentrations that were as much as 1.3 times higher than background values. The primary source of metal contamination came from activities related to nonferrous metal refineries near Onsan Harbor, and the next largest source was from shipbuilding companies located at the mouth of the Taehwa River. Three different anthropogenic sources and background sediments could be identified as end-members using Pb isotopes. Isotopic ratios for the anthropogenic Pb revealed that the sources were imported ores from Australia, Peru, and the United States. In addition, Pb isotopes of anthropogenic Pb discharged from Ulsan Bay toward offshore could be determined.

  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. 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

  17. 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

  18. Trace elements and Pb isotopes in soils and sediments impacted by uranium mining.

    PubMed

    Cuvier, A; Pourcelot, L; Probst, A; Prunier, J; Le Roux, G

    2016-10-01

    The purpose of this study is to evaluate the contamination in As, Ba, Co, Cu, Mn, Ni, Sr, V, Zn and REE, in a high uranium activity (up to 21,000Bq∙kg(-1)) area, downstream of a former uranium mine. Different geochemical proxies like enrichment factor and fractions from a sequential extraction procedure are used to evaluate the level of contamination, the mobility and the availability of the potential contaminants. Pb isotope ratios are determined in the total samples and in the sequential leachates to identify the sources of the contaminants and to determine the mobility of radiogenic Pb in the context of uranium mining. In spite of the large uranium contamination measured in the soils and the sediments (EF≫40), trace element contamination is low to moderate (2Pb enrichment is highlighted, the Pb isotopic signature of the contaminated soils is strongly radiogenic. Measurements performed on the sequential leachates reveal inputs of radiogenic Pb in the most mobile fractions of the contaminated soil. Inputs of low-mobile radiogenic Pb from mining activities may also contribute to the Pb signature recorded in the residual phase of the contaminated samples. We demonstrate that Pb isotopes are efficient tools to trace the origin and the mobility of the contaminants in environments affected by uranium mining.

  19. Influence of temporal variations in water chemistry on the Pb isotopic composition of rainbow trout (Oncorhynchus mykiss).

    PubMed

    Miller, Jerry R; Anderson, Jamie B; Lechler, Paul J; Kondrad, Shannon L; Galbreath, Peter F; Salter, Emory B

    2005-11-01

    Field and laboratory investigations were undertaken to determine (1) the relations between discharge, Pb concentration, and the Pb isotopic composition of the dissolved load in Richland Creek, western North Carolina, and (2) the potential influence of varying Pb water chemistry on the Pb isotopic abundances in liver and bone tissues of rainbow trout (Oncorhynchus mykiss). Stream waters were characterized by relatively low Pb concentrations during periods of base flow exceeding 10 days in length. Moreover, greater than 65% of the Pb was derived from orchard soils located upstream of the monitoring site which are contaminated by lead arsenate. During small to moderate floods, the dissolved load exhibited Pb concentrations more than twice as high as those measured during base flow, but the contribution of Pb from lead arsenate was relatively low and varied directly with discharge. In contrast to smaller events, Pb from lead arsenate in an 8- to 10-year (overbank) event in May 2003 was minimal during peak flow conditions, suggesting that discharge-source relations are dependent on flood magnitude. The hydrologic and geochemical data demonstrate that aquatic biota in Richland Creek are subjected to short-term variations in Pb concentrations and Pb isotopic abundances within the dissolved load ranging from a few hours to few a weeks. Laboratory studies demonstrated that when rainbow trout were exposed to elevated Pb concentrations with a distinct isotopic fingerprint, the bone and liver rapidly acquire isotopic ratios similar to that of the water. Following exposure, bone retains Pb from the contaminant source for a period of months, while the liver excreted approximately 50% of the accumulated Pb within a few days and nearly all of the Pb within a few weeks. Differences in the rates of excretion resulted in contrasting isotopic ratios between the tissues. It seems plausible, then, that previously observed differences between the isotopic composition of bone and liver in

  20. 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.

  1. 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

  2. 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

  3. 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

  4. The effects of core formation on the Pb- and Tl- isotopic composition of the silicate Earth

    NASA Astrophysics Data System (ADS)

    Wood, Bernard J.; Nielsen, Sune G.; Rehkämper, Mark; Halliday, Alex N.

    2008-05-01

    We have performed metal-silicate partitioning experiments at 2 GPa and 1650-2180 °C to investigate the behaviour of Pb and Tl during terrestrial core formation. The aim was to test the hypothesis that metal core formation followed by late sulphide addition to the core resulted in the concentrations and isotopic compositions of Pb and Tl in the silicate Earth. We investigated DPbmet/sil and DTLmet/sil as functions of the sulphur content of the metal and measured the equilibrium Tl isotope fractionation between the coexisting phases. Lead is moderately siderophile under the likely conditions (initially reducing [Wade, J., Wood, B.J., Core formation and the oxidation state of the Earth, Earth Planet. Sci. Lett. 236(2005) 78-95.]) of core segregation on Earth so that the μ( 238U/ 204Pb) of the bulk silicate Earth should have increased by a factor of 6.5 ( DPb ˜ 13) as the core separated. In the case of Tl, core segregation should have reduced the Tl concentration of the BSE by about 50%. Neither the Pb nor Tl isotopic compositions of the bulk silicate Earth can, however, be completely explained by S-free iron core formation. Thallium isotopes were found not to be significantly fractionated by metal or sulphide separation from silicate. Addition of sulphur to the metal greatly increases metal-silicate partition coefficients for both Pb and Tl. DPbmet/sil increases by a factor of 15 and DTLmet/sil by a factor of 45 as S increases from 0 to 35% in the metal phase. This means that extraction of sulphide from a molten mantle would result in DPbsulph/sil of ˜ 40 and DTLsulph/sil of ˜ 60. We used the latter results to calculate the effects of late sulphide extraction on the Pb and Tl isotopic compositions of the silicate Earth. For a bulk Earth with μ of 0.7 addition of 1.6% sulphide to the core 100-140 Myr after the beginning of the solar system is sufficient to displace the Pb-isotopic composition of the silicate Earth into the region indicated by estimates in the

  5. 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.

  6. Geochemistry and isotope geochemistry of the Monfalcone thermal waters (northern Italy): inference on the deep geothermal reservoir

    NASA Astrophysics Data System (ADS)

    Petrini, R.; Italiano, F.; Ponton, M.; Slejko, F. F.; Aviani, U.; Zini, L.

    2013-09-01

    Geochemical investigations were carried out to define the origin of the low- to moderate-temperature thermal waters feeding the Monfalcone springs in northern Italy. Chemical data indicate that waters approach the composition of seawater. Mixing processes with cold low-salinity waters are highlighted. The δ18O and δD values are in the range -5.0 to -6.4 ‰, and -33 to -40 ‰, respectively, suggesting the dilution of the saline reservoir by karst-type freshwaters. A surplus of Ca2+ and Sr2+ ions with respect to a conservative mixing is ascribed to diagenetic reactions of the thermal waters with Cretaceous carbonates at depth. The measured Sr isotopic composition (87Sr/86Sr ratio) ranges between 0.70803 and 0.70814; after correction for the surplus Sr, a 87Sr/86Sr ratio indicating Miocene paleo-seawater is obtained. The dissolved gases indicate long-lasting gas-water interactions with a deep-originated gas phase of crustal origin, dominated by CO2 and marked by a water TDIC isotopic composition in the range -5.9 to-8.8 and helium signature with 0.08 < R/Ra < 0.27, which is a typical range for the crust. A possible scenario for the Monfalcone thermal reservoir consists of Miocene marine paleowaters which infiltrated through the karstic voids formed within the prevalently Cretaceous carbonates during the upper Eocene emersion of the platform, and which were entrapped by the progressive burial by terrigenous sediments.

  7. Identification of recycled continental material in the mantle from Sr, Nd and Pb isotope investigations

    NASA Astrophysics Data System (ADS)

    Cohen, R. S.; O'Nions, R. K.

    1982-11-01

    Pb, Nd and Sr isotope compositions of oceanic basalts have been used to identify recycled components of continent derivation in the mantle. The isotopic compositions of Sr, Nd and Pb, together with U, Pb, Sm, Nd, Rb, and Sr abundances have been determined for back-arc basalt glasses from the Scotia Sea and Parece Vela and West Philippine Basins, in addition to basalts from South Sandwich Islands, Ascension, St. Helena and Tristan da Cunha. Comparisons made between the isotopic compositions of South Sandwich Islands basalts and Atlantic MORB glasses permit the identification of recycled components of continent derivation in the source of the island arc basalts. Recycled Sr of continent derivation is also recognisable in back-arc basalt glasses from the Scotia Sea and Parece Vela and West Philippine Basins. However, contemporary reinjection of material with the isotopic structures similar to those identified as a component of island arc and back-arc regions cannot be the sole or dominant influence on the fine structure observed in MORB glasses from the Atlantic Ocean, nor the isotopic compositions of Tristan da Cunha, St. Helena and Ascension basalts. Recycled materials are likely to have been responsible for the generation of these heterogeneities only if they have been stored in the mantle for periods of time exceeding 10 9 years.

  8. Direct determination of lead isotopes (206Pb, 207Pb, 208Pb) in arctic ice samples at picogram per gram levels using inductively coupled plasma-sector field MS coupled with a high-efficiency sample introduction system.

    PubMed

    Krachler, Michael; Zheng, James; Fisher, David; Shotyk, William

    2004-09-15

    Adopting strict cleanroom procedures, ice samples from the Canadian High Arctic have been analyzed for Pb concentrations and Pb isotopes (206Pb, 207Pb, 208Pb) using ICP-SMS. The detection limit for Pb (0.06 pg g(-1)) was approximately 2 orders of magnitude lower than the lowest concentration of Pb in the ice samples (range, 4.3-1660 pg g(-1); median, 45 pg g(-1)). Acidification of ice samples with high-purity HNO3 for stabilization purposes contributed only 0.004 pg of Pb g(-1), which is an insignificant source of Pb. Using a new sample introduction system consisting of a heated (140 degrees C) minicyclonic spray chamber and a Peltier cooled condenser (2 degrees C) and by replacing the conventional sample cone with a high-performance cone, signal intensities for Pb were increased by approximately 1 order of magnitude. Thus, it was possible not only to measure Pb isotope ratios directly using ICP-SMS but also to achieve reasonable precision (approximately 0.2%) at low picogram per gram concentrations of total Pb. This precision is comparable to that achievable by thermal ionization mass spectrometry at such low Pb concentrations, but the ICP-SMS requires much less sample volume (approximately 2 mL), needs no sample pretreatment, and therefore is considerably faster and less expensive than the conventional approach. Even though absolute Pb concentrations in two ice samples dating from 1974 and 1852 were very similar (9 and 6 pg g(-1)) their fundamentally different isotopic signature (206Pb/207Pb: 1.169 +/- 0.002 vs 1.147 +/- 0.003) clearly indicates different sources of Pb. The analytical procedures described here, therefore, offer great promise for fingerprinting the predominant sources of atmospheric Pb in polar snow and ice.

  9. 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.

  10. 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.

  11. Tracing Cd, Zn and Pb pollution sources in bivalves using isotopes

    NASA Astrophysics Data System (ADS)

    Shiel, A. E.; Weis, D. A.; Orians, K. J.

    2010-12-01

    In a multi-tracer study, Cd, Zn and Pb isotopes (MC-ICP-MS) and elemental concentrations (HR-ICP-MS) are evaluated as tools to distinguish between natural and anthropogenic sources of these metals in bivalves from western Canada (British Columbia), the eastern USA, Hawaii and France. High Cd concentrations found in BC oysters have elicited economic and health concerns. The source of these high Cd levels is unknown but thought to be largely natural. High Cd levels in BC oysters are largely attributed to the natural upwelling of Cd-rich intermediate waters in the North Pacific as the δ114/110Cd (-0.69 to -0.09‰) and δ66/64Zn (0.28 to 0.36‰) values of BC oysters fall within the range reported for North Pacific seawater. Different contributions from anthropogenic sources account for the variability of Cd isotopic compositions of BC oysters; the lightest of these oysters are from the BC mainland. These oysters also have Pb isotopic compositions that reflect primarily anthropogenic sources (e.g., leaded and unleaded automotive gasoline and smelting of Pb ores, potentially historical). On the contrary, USA East Coast bivalves exhibit relatively light Cd isotopic compositions (δ114/110Cd = -1.20 to -0.54‰; lighter than reported for North Atlantic seawater) due to the high prevalence of industry on this coast. The Pb isotopic compositions of these bivalves indicate contributions from the combustion of coal. The large variability of environmental health among coastal areas in France is reflected in the broad range of Cd isotopic compositions exhibited by French bivalves (δ114/110Cd = -1.08 to -0.20‰). Oysters and mussels from the Marennes-Oléron basin and Gironde estuary have the lightest Cd isotopic compositions of the French oysters consistent with significant historical Cd emissions from the now-closed proximal Zn smelter. In these bivalves, significant declines in the Cd levels between 1984/7 and 2004/5 are not accompanied by a significant shift in the Cd

  12. Geochronology and isotope geochemistry of the Baogutu porphyry copper deposit in the West Junggar region, Xinjiang, China

    NASA Astrophysics Data System (ADS)

    Shen, Ping; Shen, Yuanchao; Pan, Hongdi; Li, Xian-hua; Dong, Lianhui; Wang, Jingbin; Zhu, Heping; Dai, Huawu; Guan, Weina

    2012-04-01

    The Baogutu copper deposit, a newly-discovered middle-sized porphyry copper deposit, is located in the West Junggar region of Xinjiang, NW China. Baogutu is associated with a Late Carboniferous intrusive complex that was emplaced into Lower Carboniferous volcano-sedimentary strata. The intrusive complex comprises main-stage diorites and minor late-stage diorite porphyries. Their intrusive activity occurred in 313.0 ± 2.2 Ma to 312.3 ± 2.2 Ma based on U-Pb zircon SIMS analyses. Molybdenite separated from ore-bearing quartz veins yields Re-Os model ages from 309.4 ± 4.4 Ma to 314.1 ± 4.5 Ma with a weighted mean age of 312.4 ± 1.8 Ma. Biotites, separated from fresh diorite and hydrothermal breccias in main-stage diorites, yield 40Ar/39Ar plateau ages of 308.26 ± 1.88 and 305.69 ± 1.76 Ma, respectively. These dates obtained from three independent dating techniques constrain the ore-forming age of the Baogutu deposit. Stable isotopes (H, O, S) and radiogenic isotope (Pb) have been used to discriminate the sources of the ore-forming fluid at Baogutu. The δ18O (1.14-1.74‰) and δD (-74‰ to -98‰) data indicate that the water of the ore-forming fluids was derived from magmatic water. The δ34S values (-0.24‰ to +0.4‰) show that the sulfur isotope composition of the ore fluids is characterized by magma sulfur. Lead isotope compositions (206Pb/204Pb = 17.92-18.89, 207Pb/204Pb = 15.45-15.62, 208Pb/204Pb = 37.68-38.36) indicate that the lead of the ore fluids is derived from the mantle. These data confirm the occurrence of a Cu-Au-Mo mineralizing event at Late Carboniferous in the Baogutu region and the ore-forming fluids are mainly derived from the mantle. The event is inferred to be associated with Late Carboniferous Junggar oceanic crust subduction.

  13. 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.

  14. 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. PMID:26025429

  15. 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

  16. 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

  17. 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.

  18. Thallium isotopes in Iceland and Azores lavas — Implications for the role of altered crust and mantle geochemistry

    NASA Astrophysics Data System (ADS)

    Nielsen, Sune G.; Rehkämper, Mark; Brandon, Alan D.; Norman, Marc D.; Turner, Simon; O'Reilly, Suzanne Y.

    2007-12-01

    Mantle plumes are commonly perceived to have both a chemical and dynamic link with the subduction of ocean crust into the mantle. In principle, this should lead to the observation of chemical and isotopic signatures that are characteristic of ocean crust and marine sediments in ocean island basalts. This study investigates the thallium (Tl) isotope systematics of lavas from Iceland and the Azores archipelago, in order to determine if their compositions were affected by admixing of ferromanganese sediments or upper ocean crust altered at low temperature. Such materials are known to display strongly fractionated Tl isotope signatures relative to the ambient upper mantle. Two samples from the island of Terceira in the Azores archipelago have Tl isotope compositions significantly different from normal mantle, and this suggests the presence of Fe-Mn sediments. Combined Pb and Tl isotope modelling indicates that the Tl anomalies are not a feature of the Azores plume but produced by assimilation of modern Fe-Mn sediments during magma ascent through the ocean crust. Excluding these two anomalous lavas from Terceira, the Iceland and Azores samples have identical Tl isotope compositions, with an overall mean of ɛ205Tl = - 1.5 ± 1.4 (2SD, n = 30) that is indistinguishable from the previously estimated upper mantle average ( ɛ205Tl = - 2.0 ± 0.5). The near-constant Tl isotope compositions of the Iceland and Azores lavas may indicate that the respective mantle plume sources contain virtually no Fe-Mn sediments or altered upper ocean crust. Alternatively, it is possible that the lack of Tl isotope variation reflects quantitative removal of fractionated Tl from the slab during subduction and dehydration. A less straightforward explanation is that past marine environments produced sediments and altered marine basalts with nearly unfractionated Tl isotope compositions. All three scenarios have important implications and future Tl isotope studies will be able to identify the

  19. 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

  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. 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.

  2. New Horizons in Global Trace Metal Oceanography: the Global Distribution of Pb, Pb Isotope, Fe, and Fe Colloids

    NASA Astrophysics Data System (ADS)

    Boyle, E. A.; Reuer, M. K.

    2001-12-01

    During the most recent epoch of inorganic and isotopic exploration of the global ocean (GEOSECS), trace element oceanography was in its infancy: GEOSECS obtained a global database for Ba, but apart from the analysis of Cd, Cu, Ni, and Mn in some samples from the project, the ocean was left largely unexplored for its trace element secrets. In subsequent decades, trace metal capabilities have advanced enormously, yet no global scale efforts to understand trace metals in the ocean have been mounted. The field has been the purview of small single investigator and limited process-oriented project science. This paucity of global scale trace metal investigation has occurred despite global scale oceanographic surveys (WOCE) and despite increasing recognition of the role of elements such as iron in regulating the global oceanic metabolism. It has also occurred despite increasingly sophisticated analytical and sampling technology progress, where many trace elements can be analyzed shipboard or on very small samples (10 ml or less) with sampling methods that collect large numbers of samples in an economical fashion. We argue that the time is ripe for new global-scale surveys of the trace metal composition of the ocean. It is scandalous that we are forced to model the oceanic behavior of an essential element such as iron lacking an even rudimentary description of its global distribution. The addition of a single profile in the Antarctic or near Hawaii can set the whole field on its head. As examples, we will present data on the distribution of Pb, Pb isotopes ratios, Fe, and Fe colloid distributions obtained in the past few years by plasma mass spectrometry. The utility of Pb as a measure of anthropogenic influence on ocean chemistry and as a tracer of ocean ventilation will be demonstrated, and the prospect for a global Fe database illuminated.

  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. REE, trace elements, Sr, Pb, C, and O isotopes in a zoned skarn ore deposit

    SciTech Connect

    Langmuir, C.; LeHuray, A.; Fairbanks, R.; Meinert, L.

    1985-01-01

    The Groundhog skarn in the Central Mining District, New Mexico, is zoned along its >2km length adjacent to a dike swarm which trends NE toward the Santa Rita porphyry Cu deposit. Isotopes and trace elements in whole rocks and mineral separates from skarn and adjacent carbonate allow the study of the source of the metals and the systematics of trace element behavior in a skarn system. (1) /sup 87/Sr//sup 86/Sr ratios are uniform (.7083 +/- 1) in the carbonate host, but they range up to .714 in hydrothermal calcite and pyx from the skarn, values distinct from both Santa Rita (.706) and carbonate. (2) delta/sup 18/O (SMOW) in carbonate ranges from (+6.3 -+ 23) and is correlated positively with delta/sup 13/C (-5.6-+2.4) and negatively with /sup 87/Sr//sup 86/Sr. Several trace elements also correlate with delta/sup 18/O. (3) Pb isotopes in galenas lie on the regression line for southwestern New Mexico Proterozoic crust. PbS from the skarn closest to Santa Rita has isotope ratios identical to PbS from the Santa Rita pit. (4) Most of the REE are not in gar or pyx. REE abundances are <1X chondrites after HC1 leaches, but in unleached samples can be >20X chondrites. All pyx separates have deep negative Ce and very deep Eu anomalies. Sr isotopes show that neither Santa Rita magma nor carbonate is the sole source of Sr. Pb isotopes are consistent with a Santa Rita source. The Ce anomaly suggests a seawater source for the REE. The data show that many of the metals in the skarn are not derived from the Santa Rita porphyry, and suggest that different elements may be derived from different source rocks.

  5. 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.

  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. 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.

  8. Accurate and precise Pb isotope ratio measurements in environmental samples by MC-ICP-MS

    NASA Astrophysics Data System (ADS)

    Weiss, Dominik J.; Kober, Bernd; Dolgopolova, Alla; Gallagher, Kerry; Spiro, Baruch; Le Roux, Gaël; Mason, Thomas F. D.; Kylander, Malin; Coles, Barry J.

    2004-04-01

    Analytical protocols for accurate and precise Pb isotope ratio determinations in peat, lichen, vegetable, chimney dust, and ore-bearing granites using MC-ICP-MS and their application to environmental studies are presented. Acid dissolution of various matrix types was achieved using high temperature/high pressure microwave and hot plate digestion procedures. The digests were passed through a column packed with EiChrom Sr-resin employing only hydrochloric acid and one column passage. This simplified column chemistry allowed high sample throughput. Typically, internal precisions for approximately 30 ng Pb were below 100 ppm (+/-2[sigma]) on all Pb ratios in all matrices. Thallium was employed to correct for mass discrimination effects and the achieved accuracy was below 80 ppm for all ratios. This involved an optimization procedure for the 205Tl/203Tl ratio using least square fits relative to certified NIST-SRM 981 Pb values. The long-term reproducibility (+/-2[sigma]) for the NIST-SRM 981 Pb standard over a 5-month period (35 measurements) was better than 350 ppm for all ratios. Selected ore-bearing granites were measured with TIMS and MC-ICP-MS and showed good correlation (e.g., r=0.999 for 206Pb/207Pb ratios, slope=0.996, n=13). Mass bias and signal intensities of Tl spiked into natural (after matrix separation) and in synthetic samples did not differ significantly, indicating that any residual components of the complex peat and lichen matrix did not influence mass bias correction. Environmental samples with very different matrices were analyzed during two different studies: (i) lichens, vegetables, and chimney dust around a Cu smelter in the Urals, and (ii) peat samples from an ombrotrophic bog in the Faroe Islands. The presented procedure for sample preparation, mass spectrometry, and data processing tools resulted in accurate and precise Pb isotope data that allowed the reliable differentiation and identification of Pb sources with variations as small as 0

  9. 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

  10. Boron occurrence in halite and boron isotope geochemistry of halite in the Qarhan Salt Lake, western China

    NASA Astrophysics Data System (ADS)

    Fan, QiShun; Ma, YunQi; Cheng, HuaiDe; Wei, HaiCheng; Yuan, Qin; Qin, ZhanJie; Shan, FaShou

    2015-06-01

    Previous studies have investigated boron (B) isotope composition of salt lake brines in the Qaidam Basin, western China. However, the research on B isotope geochemistry of halite from a sediment core in a typical sedimentary basin has been very limited. In this study, a 102-m-long drill core (ISL1A) was recovered from Qarhan Salt Lake in eastern Qaidam Basin. Forty-three halite samples from upper 44.0 m in ISL1A were collected and analyzed for chemical compositions (K+, Na+, Ca2 +, Mg2 +, Cl-, SO42 -, Sr2 + and B3 +) and B isotopes in order to investigate their relationships, and B isotope fractionation between halite and brines in the Qarhan Salt Lake. The results show that: (1) more B3 + and Mg2 + values in halite are low concentrations and more concentrated, and low B3 + concentrations have a strong correlation with low Mg2 + in halite, which imply that they might be the same source; (2) low Mg2 + values in halite from ISL1A have a similar trend with mMg2 + (molarity) of fluid inclusion brines from two sediment cores (east to ISL1A about 50 km) in the study area, suggesting that low B3 + and Mg2 + concentrations should derive from fluid inclusions in halite based on X-ray diffraction results in ISL1A that no borate and small amount of magnesium salts were deposited; (3) δ11B values of halite in ISL1A range from - 0.35 to + 5.84‰, which are in the range of those of river water and brines (- 1.0 to + 9.6‰), and almost overlapped with those of brines (+ 2.9 to + 7.5‰) in the Qarhan Salt Lake. These results suggest that no or minor B isotope fractionation between halite and brine occurred.

  11. Source and distribution of lead in the surface sediments from the South China Sea as derived from Pb isotopes.

    PubMed

    Zhu, Laimin; Guo, Laodong; Gao, Ziyou; Yin, Guan; Lee, Ben; Wang, Fei; Xu, Jiang

    2010-11-01

    Rapid economic development in East Asian countries has inevitably resulted in environmental degradation in the surrounding seas, and concern for the environment and its protection against pollutants is increasing. Identification of sources of contaminants and evaluation of current environmental status are essential to environmental pollution management, but relatively little has been done in the South China Sea (SCS). In order to investigate the abundance, distribution, and sources of Pb within the SCS, stable Pb isotopes and their ratios were employed to assess the contamination status and to differentiate between natural and anthropogenic origins of Pb in the surface sediments. The total Pb concentrations in sediments varied from 4.18 to 58.7 mg kg(-1), with an average concentration of 23.6 ± 8.9 mg kg(-1). The observed Pb isotope ratios varied from 18.039 to 19.211 for (206)Pb/(204)Pb, 15.228 to 16.080 for (207)Pb/(204)Pb, 37.786 to 39.951 for (208)Pb/(204)Pb, 1.176 to 1.235 for (206)Pb/(207)Pb, and 2.468 to 2.521 for (208)Pb/(207)Pb. The majority of these ratios are similar to those reported for natural detrital materials. Combined with Pb enrichment factor values, our results show that Pb found within most of the SCS sediments was mainly derived from natural sources, and that there was not significant Pb pollution from anthropogenic sources before 1998. Further studies are needed to reconstruct deposition history and for trend analysis.

  12. 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

  13. 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,…

  14. Nuclear shape dependence of Gamow-Teller distributions in neutron-deficient Pb isotopes

    SciTech Connect

    Sarriguren, P.; Moreno, O.; Alvarez-Rodriguez, R.; Moya de Guerra, E.

    2005-11-01

    We study Gamow-Teller strength distributions in the neutron-deficient even isotopes {sup 184-194}Pb in a search for signatures of deformation. The microscopic formalism used is based on a deformed quasiparticle random-phase approximation (QRPA) approach, which involves a self-consistent quasiparticle deformed Skyrme Hartree-Fock (HF) basis and residual spin-isospin forces in both the particle-hole and particle-particle channels. By analyzing the sensitivity of the Gamow-Teller strength distributions to the various ingredients in the formalism, we conclude that the {beta} decay of these isotopes could be a useful tool to look for fingerprints of nuclear deformation.

  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. 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

  17. Correlated Nd, Sr and Pb isotope variation in Walvis Ridge basalts and implications for the evolution of their mantle source

    NASA Astrophysics Data System (ADS)

    Richardson, S. H.; Erlank, A. J.; Duncan, A. R.; Reid, D. L.

    1982-07-01

    Basement intersected in DSDP holes 525A, 528 and 527 on the Walvis Ridge consists of submarine basalt flows and pillows with minor intercalated sediments. These holes are situated on the crest and mid and lower northwest flank of a NNW-SSE-trending ridge block which would have closely paralleled the paleo mid-ocean ridge [13, 14]. The basalts were erupted approximately 70 m.y. ago, an age equivalent to that of immediately adjacent oceanic crust in the Angola Basin and consistent with formation at the paleo mid-ocean ridge [14]. The basalt types vary from aphyric quartz tholeiites on the ridge crest to highly plagioclase phyric olivine tholeiites on the ridge flank. These show systematic differences in incompatible trace element and isotopic composition. Many element and isotope ratio pairs form systematic trends with the ridge crest basalts at one end and the highly phyric ridge flank basalts at the other. The low 143Nd/ 144Nd (0.51238), 206Pb/ 204Pb (17.54), 208Pb/ 204Pb (15.47), 208Pb/ 204Pb (38.14) and high 87Sr/ 86Sr (0.70512) ratios of the ridge crest basalts suggest derivation from an old Nd/Sm-, Rb/Sr- and Pb/U-enriched mantle source. This isotopic signature is similar to that of alkaline basalts on Tristan de Cunha but offset to significantly lower Nd and Pb isotopic ratios. The isotopic ratio trends may be extrapolated beyond the ridge flank basalts with higher 143Nd/ 144Nd (0.51270), 206Pb/ 204Pb (18.32), 207Pb/ 204Pb (15.52), 208Pb/ 204Pb (38.77) and lower 87Sr/ 86Sr (0.70417) ratios in the direction of increasingly Nd/Sm-, Rb/Sr- and Pb/U-depleted source compositions. These isotopic correlations are equally consistent with mixing od depleted and enriched end member melts or partial melting of an inhomogenous, variably enriched mantle source. However, observe Zr sbnd Ba sbnd Nb sbnd Y interelement relationships are inconsistent with any simple two-component model of magma mixing, as might result from the rise of a lower mantle plume through the upper

  18. Disturbed Sr and Nd Isotope Systematics in Zircons With Concordant SHRIMP U-Pb Ages

    NASA Astrophysics Data System (ADS)

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

    2004-12-01

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

  19. 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.

  20. Pb isotopic composition, colour, and microstructure of monazites from a polymetamorphic rock in Antarctica

    NASA Astrophysics Data System (ADS)

    Black, Lance P.; Fitzgerald, John D.; Harley, Simon L.

    1984-02-01

    A moderate- to high-grade regionally metamorphosed paragneiss from Antarctica contains monazites of several different colours — brown, yellow and grey. Each colour type has a distinctive U-Pb isotopic composition which appears to result from different proportions of radiogenic Pb loss. Isotopic differences are neither related to La, Nd, Ce, P, Ca, Ti (and/or Ba), nor to U or Th content. All colour types have similar structures at the submicron scale, as determined by both conventional and high-resolution transmission electron microscopy (TEM). These show that the grains are essenttially non-metamict but are composed of 100 Å crystalline domains misoriented from each other by no more than 2× 10-3 radians, and separated by narrow confused boundary regions where misorientation is probably accommodated by imperfect atomic arrangements. These regions of mismatch form potential zones of high permeability/diffusivity which are believed to be fundamental to the isotopic and colour differences between grains. Colour type is apparently related to the capacity of different minerals to shield included monazite grains from fluids circulating in the rock system. The well aligned monazite U — Pb analyses produce concordia intercepts of 2429{-16/+17}Ma and 1087±29 Ma. Both ages are comparable to those of major geological events in this part of Antarctica. They are interpreted in terms of isotopic resetting through Pb loss, and original monazite crystallisation is thought to have occurred somewhat earlier, possibly at the time this terrain first underwent granulite-facies metamorphism, about 3070 Ma ago.

  1. Characteristics of heavy metals and Pb isotopic composition in sediments collected from the tributaries in three Gorges Reservoir, China.

    PubMed

    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 (206)Pb/(207)Pb and from 2.459 to 2.482 for (208)Pb/(207)Pb 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.

  2. 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

  3. Paleoproterozoic felsic magmatism of the Karelian Craton: petrogeochemistry, isotope geochemistry, and genesis

    NASA Astrophysics Data System (ADS)

    Bogina, M. M.; Zlobin, V. L.

    2012-04-01

    Intense rift magmatism at the Karelian craton at the Archean-Proterozoic boundary (2.5-2.4 Ga) was mainly represented by mafic rocks, which compose mafic-ultramafic layered intrusions and basaltic lava fields. Felsic rocks of this age are of limited abundance, but provide insight into the nature of magmatism in an extensional regime associated with incipient rifting. These felsic rocks are represented by metavolcanic rocks of dacitic to rhyolitic composition, which are spatially related with mafic volcanics, their plutonic analogues, as well as fields of "remobilized granites" among the Late Archean granitoids. Their U-Pb ages vary from 2434+8 Ma and 2361 + 15 Ma, with the younger ages of the latters. The Paleoproterozoic felsic voclanics and granitoids are ascribed to the calc-alkaline to subalkaline series with total alkalis from 4.1 to 7.3 wt % and the K predominance over Na. Their distinctive feature is elevated TiO2 content (up to 1.19 wt%), which is not typical of siliceous rocks and expressed in the presence of numerous rutile needles in quartz. Practically all rocks have high Fe mole fraction. In terms of alumina saturation index (ASI), the volcanics show wide variations from metaluminous to highly peraluminous rocks (from 0.9 to 1.6), whereas granites are metaluminous rocks (ASI = 0.9-1.0). The studied rocks show fractionated REE patterns with wide LREE variations ((La/Yb)N=2.09-17.08; (La/Sm)N=1.65-4.4) at weak HREE variations (Gd/Yb)N=0.66-2.09), which is typical of the rocks formed in an intracontinental setting. In the petrotectonic diagram, the granitoids fall in the field of A-type anorogenic granites, which is consistent with rifting setting of their formation. In terms of Y-Nb-Ga relations, they correspond to the rocks derived by crustal melting. Sm-Nd isotopic studies revealed that the volcanics are characterized by negative eNd from -3.6 to -2.4, while the granites have more radiogenic composition from -1.7 to -2.0. The model ages vary from 2770

  4. 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

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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

    2012-06-01

    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.

  11. 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

    2012-06-01

    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. PMID:22541021

  12. Sr-Pb isotopic studies of primitive and near-primitive basaltic magmas, Garibaldi volcanic belt, northern Cascadia subduction system

    NASA Astrophysics Data System (ADS)

    Green, N. L.; Sinha, A. K.

    2003-12-01

    The northern Cascadia subduction system is intimately associated with aseismic subduction of extremely young and presumably `hot' oceanic lithosphere beneath northwestern Washington and southwestern British Columbia. Sr and Pb isotopic analyses are presented for primitive and near-primitive (>6.0 wt. % MgO) basalts from a southeast-northwest transect along the Garibaldi volcanic belt (GVB), which overlies subducted oceanic lithosphere that decreases in age from ca. 22 m.y. below Glacier Peak at its southern end to about 13 m.y. beneath the northernmost eruptive centers in the Mosaic (Meager Mountain) and Salal Glacier-Bridge River areas. The basaltic rocks have initial 87Sr/86Sr ratios of 0.70317-0.70426, with minimum observed values in individual lava suites decreasing northward. Values of Pb isotopic ratios for GVB basaltic suites range from 18.22 to 18.97 for 206Pb/204Pb, from 15.51 to 15.59 for 207Pb/204Pb, and from 37.73 to 38.49 for 208Pb/204Pb. Sr isotopic compositions, unsupported by lava Rb contents, show positive correlations with Cs/Rb, La/Nb, Ba/La, Ba/Nb, Ba/Ta, B/La, B/Zr, Sr/Nd, and primitive mantle normalized Sr/P; and negative correlations with high field strength elements (HFSE: Nb, and Ta), FeO and other transition metals (Co and Zn), Ce/Pb,Cr/Ni, Sm/Yb, Ta/Yb, Hf/Yb, K/Ba, K/Sr, and La/Yb. Moderate to strong correlations between 87Sr/86Sr and ratios involving fluid-mobile and less-fluid-mobile elements are compatible with decreased slab input northward along the volcanic front as the subducted plate becomes hotter. The Pb isotopic compositions exhibit only limited variations when examined against position along the volcanic arc, but show uniform to extremely weak positive correlations of 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb with 87Sr/86Sr, Ba/La, Sr/Nd, Ba/Nb, Zr/Nb, Mg-Number and SiO2; and similarly weak negative correlation of Ce/Pb with 206Pb/204Pb and 207Pb/204Pb. The isotopic data suggest that GVB basaltic magmas have experienced with

  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. 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

  15. 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.

  16. 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.

  17. 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.

  18. 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

  19. 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.

  20. Summary and re-evaluation of the high-temperature isotope geochemistry of methane

    NASA Astrophysics Data System (ADS)

    Sackett, William M.; Conkright, M. E.

    1997-05-01

    Thirty years of research are brought together into one coherent summary of carbon and hydrogen isotope effects during the thermocatalytic production of methane from model compounds, petroleum, source rocks, and coals. The approach used by the authors and co-workers has been to pyrolyze model and natural compounds and to study the isotopic fractionations associated with molecular structure, temperature, and catalysis. The results from these experiments are summarized. A practical application of these pyrolysis experiments was the development of the pyrolysis-carbon isotope method (PCM) for determining kerogen maturity. This maturity indexing procedure is based on the isotopic difference between the total methane produced by exhaustive pyrolysis and the parent organic carbon and the mole ratio of methane to parent carbon. Data are also summarized for the thermal destruction of methane and carbon isotope exchange between methane and amorphous carbon and carbon dioxide. The latter results are important when determining the source of methane in hydrothermal fluids.

  1. 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.

  2. 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

  3. Controls on ostracod valve geochemistry: Part 2. Carbon and oxygen isotope compositions

    NASA Astrophysics Data System (ADS)

    Decrouy, Laurent; Vennemann, Torsten Walter; Ariztegui, Daniel

    2011-11-01

    The stable carbon and oxygen isotope compositions of fossil ostracods are powerful tools to estimate past environmental and climatic conditions. The basis for such interpretations is that the calcite of the valves reflects the isotopic composition of water and its temperature of formation. However, calcite of ostracods is known not to form in isotopic equilibrium with water and different species may have different offsets from inorganic precipitates of calcite formed under the same conditions. To estimate the fractionation during ostracod valve calcification, the oxygen and carbon isotope compositions of 15 species living in Lake Geneva were related to their autoecology and the environmental parameters measured during their growth. The results indicate that: (1) Oxygen isotope fractionation is similar for all species of Candoninae with an enrichment in 18O of more than 3‰ relative to equilibrium values for inorganic calcite. Oxygen isotope fractionation for Cytheroidea is less discriminative relative to the heavy oxygen, with enrichments in 18O for these species of 1.7 to 2.3‰. Oxygen isotope fractionations for Cyprididae are in-between those of Candoninae and Cytheroidea. The difference in oxygen isotope fractionation between ostracods and inorganic calcite has been interpreted as resulting from a vital effect. (2) Comparison with previous work suggests that oxygen isotope fractionation may depend on the total and relative ion content of water. (3) Carbon isotope compositions of ostracod valves are generally in equilibrium with DIC. The specimens' δ 13C values are mainly controlled by seasonal variations in δ 13C DIC of bottom water or variation thereof in sediment pore water. (4) Incomplete valve calcification has an effect on carbon and oxygen isotope compositions of ostracod valves. Preferential incorporation of CO32- at the beginning of valve calcification may explain this effect. (5) Results presented here as well as results from synthetic carbonate

  4. 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

  5. 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

  6. Lead isotope study of Zn-Pb ore deposits associated with the Basque-Cantabrian basin and Paleozoic basement, Northern Spain

    NASA Astrophysics Data System (ADS)

    Velasco, F.; Pesquera, A.; Herrero, J. M.

    1996-01-01

    A total of forty-three galena samples from syngenetic and epigenetic Pb-Zn mineralizations emplaced in the Lower Cretaceous Basque-Cantabrian basin and Paleozoic basement of the Cinco Villas massif in the western Pyrenees, have been analyzed for Pb-isotopic composition. Galena from sedex mineralizations hosted in Carboniferous clastic rocks in the Cinco Villas massif display an homogeneous lead isotopic signature (206Pb/2044Pb ≈ 18.43, 207Pb/204Pb ≈ 15.66, 208Pb/ 204Pb ≈ 38.69) suggesting a single lead reservoir. These values are slightly more radiogenic than lead from other European Hercynian deposits, possibly reflecting the influence of a more evolved upper crustal source. Underlying Paleozoic sediments are proposed as lead source for the Cinco Villas massif ores. Analyses from twenty-six galena samples from the four strata-bound ore districts hosted in Mesozoic rocks reveal the existence of two populations regarding their lead isotopic composition. Galena from the western Santander districts (e.g., Reocin) is characterized by more radiogenic isotope values (206Pb/204Pb ≈ 18.74, 207Pb/204Pb ≈ 15.67, 208Pb/ 204Pb ≈ 38.73) than those from the central and eastern districts (Troya-Legorreta, Central and Western Vizcaya, 206Pb/204Pb ≈ 18.59, 207Pb/204Pb ≈ 15.66, 208Pb/ 204Pb ≈ 38.73). In all districts, the most likely source for these mineralizations was the thick sequence of Lower Cretaceous clastic sediments. The existence of two separate lead isotopic populations could be the result of regional difference in the composition of the basement rocks and the clastic sediments derived of it or different evolution histories. In both sub-basins, isotopic ratios indicate an increase in crustal influence as the age of the ores decreases.

  7. 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.

  8. Sr, C, and O isotope geochemistry of Ordovician brachiopods: a major isotopic event around the Middle-Late Ordovician transition

    NASA Astrophysics Data System (ADS)

    Shields, Graham A.; Carden, Giles A. F.; Veizer, Jαn; Meidla, Tõnu; Rong, Jia-Yu; Li, Rong-Yu

    2003-06-01

    Here we present Sr, C, and O isotope curves for Ordovician marine calcite based on analyses of 206 calcitic brachiopods from 10 localities worldwide. These are the first Ordovician-wide isotope curves that can be placed within the newly emerging global biostratigraphic framework. A total of 182 brachiopods were selected for C and O isotope analysis, and 122 were selected for Sr isotope analysis. Seawater 87Sr/ 86Sr decreased from 0.7090 to 0.7078 during the Ordovician, with a major, quite rapid fall around the Middle-Late Ordovician transition, most probably caused by a combination of low continental erosion rates and increased submarine hydrothermal exchange rates. Mean δ 18O values increase from -10‰ to -3‰ through the Ordovician with an additional short-lived increase of 2 to 3‰ during the latest Ordovician due to glaciation. Although diagenetic alteration may have lowered δ 18O in some samples, particularly those from the Lower Ordovician, maximum δ 18O values, which are less likely to be altered, increase by more than 3‰ through the Ordovician in both our data and literature data. We consider that this long-term rise in calcite δ 18O records the effect of decreasing tropical seawater temperatures across the Middle-Late Ordovician transition superimposed on seawater δ 18O that was steadily increasing from ≤-3‰ standard mean ocean water (SMOW). By contrast, δ 13C variation seems to have been relatively modest during most of the Ordovician with the exception of the globally documented, but short-lived, latest Ordovician δ 13C excursion up to +7‰. Nevertheless, an underlying trend in mean δ 13C can be discerned, changing from moderately negative values in the Early Ordovician to moderately positive values by the latest Ordovician. These new isotopic data confirm a major reorganization of ocean chemistry and the surface environment around 465 to 455 Ma. The juxtaposition of the greatest recorded swings in Phanerozoic seawater 87Sr/ 86Sr and

  9. Stable isotope geochemistry of pore waters from the New Jersey shelf - No evidence for Pleistocene melt water

    NASA Astrophysics Data System (ADS)

    van Geldern, Robert; Hayashi, Takeshi; Böttcher, Michael E.; Mottl, Michael J.; Barth, Johannes A. C.; Stadler, Susanne

    2013-04-01

    Ocean Drilling Program, Volume 313, Tokyo, available at: http://publications.iodp.org/proceedings/313/313toc.htm. van Geldern, R., Hayashi, T., Böttcher, M. E., Mottl, M. J., Barth, J. A. C., and Stadler, S., 2013, Stable isotope geochemistry of pore waters and marine sediments from the New Jersey shelf: Methane formation and fluid origin: Geosphere, v. 9, no. 1, p. in press.

  10. 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.

  11. A review of applications of U-Th-Pb isotope systematics to investigations of uranium source rocks.

    USGS Publications Warehouse

    Stuckless, J.S.

    1987-01-01

    U, Th and Pb concentrations and the isotopic composition of Pb can be used to evaluate crystalline rocks as a source for U in sedimentary deposits. Under favourable geologic circumstances, the technique can yield information on both the timing and the amount of U released to the sedimentary environment. The technique is best suited to the study of Archean rocks that have high U/Pb, a known common Pb composition, and a simple two-stage history. Less ideal rock units can also be evaluated, but conclusions reached for rocks of Phanerozoic age or younger will generally be qualitative at best.-Author

  12. 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.

  13. 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.

  14. 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.

  15. Zircon U-Pb ages and O-Nd isotopic composition of basement rocks in the North Qinling Terrain, central China: evidence for provenance and evolution

    NASA Astrophysics Data System (ADS)

    Liu, Bing-Xiang; Qi, Yue; Wang, Wei; Siebel, Wolfgang; Zhu, Xi-Yan; Nie, Hu; He, Jian-Feng; Chen, Fukun

    2013-11-01

    The Qinling Group was previously interpreted as the oldest Precambrian basement unit of the North Qinling Terrain, recording its formation and early crustal evolution. The Qinling Group consists predominantly of gneisses, amphibolites, and marbles, which underwent multi-phase deformation and metamorphism. In order to better constrain the provenance and tectonic setting of this group and the evolution of the North Qinling orogenic belt, in situ U-Pb dating and oxygen isotopic analysis of zircons in combination with whole-rock geochemistry and Sr-Nd isotope analysis was performed on the two dominant rock types, amphibolite and felsic gneiss. Felsic gneisses exhibit enrichment of LREEs and LILEs (Rb, Ba, Th, K, Pb), negative Eu anomalies and depletion of HFSEs (Nb, Ta, P, Ti). The rocks have slightly elevated δ18O values (6.5-9.3 ‰) and initial ɛ Nd values of -4.6 corresponding to two-stage Nd model age of 1.99 Ga. Amphibolites are also enriched in LILEs and LREEs and depleted in Nb and Ta and have homogeneous δ18O values (5.0-6.0 ‰), but higher initial ɛ Nd values (2.8-3.3) and younger two-stage Nd model ages (1.29-1.24 Ga) compared to the gneisses. The zircon age record indicates that the gneisses and amphibolites were formed in a ~960 Ma volcanic arc environment rather than in a rift setting as previously suggested. A major metamorphic event took place during the Early Paleozoic. Based on the age spectrum of detrital zircons, the Qinling Group is interpreted as an autonomous geological unit, which was mainly derived mostly from 1,000 to 900 Ma old granitoid rocks. The North Qinling Terrain can be regarded as a remnant of the Grenville orogenic belt with an early Neoproterozoic evolution different from that of the North and South China blocks.

  16. 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.

  17. 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

  18. The boron isotope geochemistry of the Kirka borate deposit, western Turkey

    NASA Astrophysics Data System (ADS)

    Palmer, M. R.; Helvaci, C.

    1995-09-01

    We have measured the boron isotope composition of seventeen samples of borate minerals (colemanite, ulexite, and borax) and the 87Sr/ 86Sr ratio in thirteen borate samples from the Kirka borate deposit in western Anatolia, Turkey. These Neogene deposits were formed by evaporation of playa lakes fed by geothermal springs. The δ 11B values range from -14.9% o in colemanite to -1.6% o in borax. To a first approximation the relative differences in the δ 11B values of the borate minerals are consistent with their basic boron atomic configuration, but the magnitude of the boron isotope fractionation between the three minerals precludes their simultaneous precipitation from a brine with the same boron isotope composition and pH. Rather the data are consistent with precipitation of colemanite from a brine with lower pH than that required for ulexite precipitation, which in turn requires a lower pH than is needed for borax precipitation. The boron isotope data also suggest that the borate minerals did not maintain boron isotopic equilibrium with the brine after they precipitated. Rayleigh fractionation models indicate that during borax precipitation the δ 11B value of the brine was slightly heavier than during precipitation of ulexite and colemanite.

  19. 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

  20. 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

  1. 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.

  2. 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

  3. Geochemistry Meets Anthropology: the use of Sr Isotopes as Tracers for Ancient Human Migration.

    NASA Astrophysics Data System (ADS)

    Solis, G.; Schaaf, P.; Hernandez, T.; Horn, P.; Manzanilla, L.

    2005-12-01

    Sr isotopes have increasingly become an important tool in archeology and anthropology in determining provenance of humans. By comparing isotopic signatures of human teeth and bone with the soil environment, Sr isotope ratios have been used as tracers identifying living areas. Sr isotope ratios in tooth enamel reflect the source of diet during youth, whereas ratios in dentine and bones come from the food growing in local geologies around the time of death. However, since analytical procedures vary from lab to lab we present here our new technique and how it affects results. We studied 11 teeth and 12 bone samples from the archeological site of Teotihuacan, central Mexico, as well as soil and water from the locality. Mechanical sample preparation of all teeth involved isolation of the enamel layer with the aid of an orthodontical micro-tool. For some enamel samples up to three fractions (two leachates and residue) were obtained for measurement. Thoroughly cleaned bone material underwent no leaching. As an example, 87Sr/86Sr results from a sample with ratios of 0.70477 for bone (which is identical to highland soil), 0.70530 for first leachate, 0.70590 for second leachate, and 0.70668 (mean accuracy +/- 0.00004) for enamel, clearly show enamel contamination by mobile Sr probably from soil. We thus find that repeated cleaning and particularly repeated leaching procedures, including isotopic measurement of the leachates, are critical to differentiate primary from secondary Sr isotope ratios as product of interaction of soil, sediments and water from the substrate where burials took place.

  4. 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

  5. The Inter-Tropical Convergence Zone: A causal mechanism for Pb isotope cyclicity in Tropical Atlantic sediment cores

    NASA Astrophysics Data System (ADS)

    Abouchami, W.; Zabel, M.

    2003-04-01

    Lead isotopic compositions of bulk sediment cores from the Tropical Atlantic can be used to infer variations in the provenance of terrigenous input to the Tropical Atlantic during Pleistocene climate cycles. Pb isotope data were obtained using the triple spike method (Galer, 1999) on bulk sediments cores and cover the last six Marine Isotope Stages. The 200-ka high precision (2σ ˜100 ppm) Pb isotope records of the Ceará Rise (Western Atlantic, core GeoB1523-1, 3^o49'N, 41^o37'W, 3292 m) and Sierra Leone Rise (Eastern Atlantic, core GeoB2910-1, 4^o50'N, 21^o03'W, 2703 m) cores show a clear glacial-interglacial cyclicity, reflected by alternating unradiogenic Pb and radiogenic Pb. Changes in the relative proportions of the glacial (unradiogenic) and interglacial (radiogenic) Pb source(s) can be explained by changes in the erosional regime (chemical vs. physical) as a function of prevailing climate, combined with different mechanisms of Pb transport to the oceans (predominantly eolian in the Eastern Atlantic vs. riverine in the Western Atlantic). We interpret these regional changes as reflecting shifts in the mean latitude of the Inter-Tropical Convergence Zone that affects the hydrological cycle over South America and the wind systems over Africa. Our results strongly favor an increase in winter wind transport (rather than glacial hyper aridity) as the cause of enhanced glacial terrigenous fluxes observed in the Tropical Atlantic (Ruddiman, 1997). The two Atlantic Pb isotopic records exhibit strong correlations with Pleistocene sea level fluctuations, providing evidence for global teleconnection between tropical records and high latitude climate. Galer, S.J.G. (1999). Optimal double and triple spiking for high precision lead isotopic measurements. Chem. Geol. 154, 255-274. Ruddiman, W. F. (1997). Tropical Atlantic terrigenous fluxes since 25,000 yrs B.P., Mar. Geol., 136, 189-207.

  6. 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.

  7. Isotopic composition and concentration of Pb in suspended particulate matter of the Irish Sea reveals distribution and sources.

    PubMed

    Charlesworth, M E; Chenery, S; Mellor, A; Service, M

    2006-01-01

    The isotopic composition and concentration of Pb was measured in suspended particulate matter of the Irish Sea. Aerosol, surficial and pre-industrial sediment was also analysed to provide information on sources terms. Concentrations of Pb in suspended sediments were lower than previously reported which presumably reflects the international effort to reduce Pb inputs to the environment. Lead concentrations were highest in Liverpool Bay and lowest in the western Irish Sea. A significant negative relationship between Pb and salinity suggests that present inputs and the resuspension of relict lead associated with particles in areas significantly affected by freshwater discharges are the predominant sources of Pb to the Irish Sea. The isotopic composition of Pb in the stratified region of the western Irish Sea demonstrates that atmospheric sources are also significant to this region, which is consistent with current knowledge on the hydrography. Pb isotopic ratios show that water entering the Irish Sea through St George's Channel is significantly influenced by anthropogenic inputs prior to additional contamination by direct inputs to the Irish Sea. PMID:16194553

  8. [Study on heavy metal contaminations and the sources of Pb pollution in Jinghai Bay using the stable isotope technique].

    PubMed

    Xu, Lin-Bo; Gao, Qin-Feng; Dong, Shuang-Lin; Liu, Jia; Fu, Xiu-Juan

    2013-02-01

    The concentrations of typical heavy metals including Cu, Hg, Pb, Zn, Mn, Cd, Cr and As in the surface sediment and suspended particulate matter (SPM) in Jinghai Bay, Rongcheng city were tested. The degree of heavy metal pollution in the surface sediment was assessed according to the national standard of marine sediment quality. The potential ecological risk (PER) of heavy metals to marine ecosystem in Jinghai Bay was assessed using PER coefficient and risk index. The results showed that the levels of heavy metals and PER in the surface sediments were low enough to meet the requirement of the first class of the sediment quality standards except the levels of Cu and Zn in the sampling site S2 and Cd in S3, S4, S5 and S6 which met the requirements of the second class of the sediment quality standards. The PER coefficients of heavy metals increased following the sequence of Zn < Cr < Pb < Cu < As Pb, Zn, Mn, Hg and As in surface sediment. Stable isotope technique was used to trace the dominant sources of Pb contamination in surface sediments and SPM. The results showed that the ratios of 208Ph/204Pb, 207Pb/204Pb, 206Pb/204Pb and 206pb/207pb in surface sediment were more closely related to that of SPM. The ratio of 206pb/207Pb for both surface sediment and SPM was the lowest at the sampling site S2 and negatively correlated to the Pb concentration. The comparisons of Pb stable isotope ratio between the isotope ratios of natural and anthropogenic source showed that the Pb contamination was mainly derived from the human activities such as industrial discharges and leaded gasoline.

  9. Application of Hydrogen Isotope Geochemistry to Volcanology: Recent Perspective on Eruption Dynamics

    NASA Astrophysics Data System (ADS)

    Nakamura, M.; Kasai, Y.; Sato, N.; Yoshimura, S.

    2008-02-01

    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 δD 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 δD value of the dome and flow lavas[1,2]. However, the relationship between pattern of degassing (and fractionation) and mode of eruption is controversial[3]. Based on the CO2/H2O ratio of the obsidians, Rust et al.[4] suggested that the analyzed samples with relatively constant δD 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.

  10. Selenium isotope geochemistry: A new approach to characterizing the environmental chemistry of selenium. Final report

    SciTech Connect

    Volpe, A.M.; Esser, B.K.

    1997-02-05

    High levels of selenium in the environment will be a prominent water quality issue in the western United States for many years. Selenium accumulation is linked to increased rates of death and deformity in migratory birds, blind staggers in livestock, and selenosis in humans. In California, agricultural drain waters and oil refinery effluent contribute to high selenium content in the San Joaquin Valley and the San Francisco Bay. The importance of these industries to California`s economy precludes simple abatement, while the complexity of selenium cycling precludes simple remediation. The purpose of this project is to measure variations in the isotopic composition of selenium in water and soil samples caused by natural processes and to show, for the first time, the value of isotopic measurements in characterizing selenium pollution. The research seeks to identify sources of selenium pollution, determine processes in the selenium cycle, and support selenium remediation studies. The project required the successful integration of three components: (1) appropriate sampling a field setting showing Se enrichment and possibly isotopic fractionation, (2) analytical chemical methods for isolating and purifying the various species of Se in waters and sediment, and (3) mass spectroscopic instrumentation for high precision isotope abundance measurements.

  11. 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.

  12. 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.

  13. 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 ‰.

  14. The geochemistry of seawater neodymium isotopes in the TAG hydrothermal plume at the Mid Atlantic Ridge

    NASA Astrophysics Data System (ADS)

    Stichel, T.; Pahnke, K.; Goldstein, S. L.; Hartman, A. E.; Scher, H.

    2012-12-01

    Neodymium (Nd) isotopes are useful tracers for ocean circulation and trace metal cycling. However, there are many unknowns regarding the input mechanisms and removal processes, which need to be understood in order to utilize this tracer optimally. For example, there is only one published study of Nd isotopes in ocean ridge hydrothermal vent fluids and nearby seawater [1]. Rare earth elements (REE) patterns hydrothermal particles in earlier studies indicate a net removal of these elements [2]. However, the degree that this process impacts the dissolved REE budget, and whether there is isotopic exchange between the Nd in particulates and in seawater, is still largely unconstrained. We present new results on the distribution of Nd isotopes and Nd concentrations ([Nd]) from the Trans-Atlantic Geotraverse (TAG) hydrothermal vent field located at 26.14°N, 44.83°W and 3800 m water depth. The plume was detected by elevated particle density between 400 m and 600 m above the seafloor. The dominant water mass around TAG is North Atlantic Deep Water (NADW). First results show that Nd isotopes and [Nd] at about 200 m below the plume do not significantly deviate from overlying NADW. The Nd isotope composition of seawater here is ɛNd = -12.3 (±0.8). This value is identical to the lower NADW in this part of the Atlantic, and to the ɛNd value measured above the plume at 2100 m water depth with ɛNd = -12.2 (±0.3). We observe a higher [Nd] of 21.7 pmol/kg below the plume at 3600 m compared to 17.1 pmol/kg above the plume at 2100 m. At other open Atlantic sites, [Nd] are between 21 and 22 pmol/kg at this depth and thus reflecting typical values. We therefore conclude that the pronounced hydrothermal activity at the TAG field does not significantly influence Nd isotope ratios nor Nd concentrations in seawater directly over- and underlying the plume. More detailed analyses from within the actual plume will be carried out and presented to further address processes involved here

  15. 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

  16. Geochemistry of brachiopods: Oxygen and carbon isotopic records of Paleozoic oceans

    NASA Astrophysics Data System (ADS)

    Veizer, Ján; Fritz, Peter; Jones, Brian

    1986-08-01

    Combined trace element and isotope studies of 319 brachiopods, covering the Ordovician to Permian time span, show that δ 13C and δ 18O in well preserved specimens varied during the Paleozoic. The overall δ 13C secular trend is in accord with the previously published observations, but its details are obscured by vital isotopic fractionation effects at generic level. Nonetheless, the results suggest that the negative correlation between marine δ 13C carbonate and δ 34S sulphate deteriorates at time scales of ⩽ 10 6 years, due to the long residence time, and thus slow response, of SO 42- in the ocean. For oxygen isotopes, all Devonian and older specimens have δ 18O of ⩽ -4%, while the well preserved Permian samples have near-present day δ 18O of about -1% (PDB). This isotopic dichotomy is probably not due to post-depositional phenomena, salinity, or biogenic fractionation effects. This leaves open the perennial arguments for a change in 18O /16O of sea water versus warmer ancient oceans. The present data are difficult to explain solely by the temperature alternative. The coincidence of the proposed shift in δ 18O with the large Late Paleozoic changes in marine 87Sr /86Sr , 13C /12C , 34S /32S , and "sea level stands" argues for a tectonic cause and for a change in 18O /16O of sea water, although such explanation is difficult to reconcile with global balance considerations and with isotopic patterns observed in alteration products of ancient basalts and ophiolites. Whatever the precise cause, or combination of causes, the implications for tectonism and/or paleoclimatology are of first order significance.

  17. 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.

  18. 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.

  19. Sources of metals in the Porgera gold deposit, Papua New Guinea: Evidence from alteration, isotope, and noble metal geochemistry

    NASA Astrophysics Data System (ADS)

    Richards, Jeremy P.; McCulloch, Malcolm T.; Chappell, Bruce W.; Kerrich, Robert

    1991-02-01

    The Porgera gold deposit is spatially and temporally associated with the Late Miocene, mafic, alkalic, epizonal Porgera Intrusive Complex (PIC), located in the highlands of Papua New Guinea (PNG). The highlands region marks the site of a Tertiary age continent-island-arc collision zone, located on the northeastern edge of the Australasian craton. The PIC was emplaced within continental crust near the Lagaip Fault Zone, which represents an Oligocene suture between the craton and volcano-sedimentary rocks of the Sepik terrane. Magmatism at Porgera probably occurred in response to the Late Miocene elimination of an oceanic microplate, and subsequent Early Pliocene collision between the craton margin and an arc system located on the Bismarck Sea plate. Gold mineralization occurred within 1 Ma of the time of magmatism. Metasomatism accompanying early disseminated Au mineralization in igneous host rocks resulted in additions of K, Rb, Mn, S, and CO 2, and depletions of Fe, Mg, Ca, Na, Ba, and Sr; rare-earth and high-field-strength elements remained largely immobile. Pervasive development of illite-K-feldspar-quartz-carbonate alteration assemblages suggests alteration by mildly acidic, 200 to 350°C fluids, at high water/ rock ratios. Strontium and lead isotopic compositions of minerals from early base-metal sulphide veins associated with K-metasomatism, and later quartz-roscoelite veins carrying abundant free gold and tellurides, are remarkably uniform (e.g., 87Sr /86Sr = 0.70745 ± 0.00044 [n = 10] , 207Pb /204Pb = 15.603 ± 0.004 [n = 15] ). These compositions fall between those of unaltered igneous and sedimentary host rocks, and specifically sedimentary rocks from the Jurassic Om Formation which underlies the deposit (igneous rocks: 87Sr /86Sr ≈ 0.7035 , 207Pb /204Pb ≈ 15.560 ; Om Formation: 87Sr /86Sr |t~ 0.7153 , 207Pb /204Pb ≈ 15.636 ). It is therefore suggested that the hydrothermal fluids acquired their Sr and Pb isotopic signatures by interaction with, or

  20. 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.

  1. 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.

  2. Sulfate contamination in groundwater near an abandoned mine: hydrogeochemical modeling, microbiology, and isotope geochemistry

    SciTech Connect

    Toran, L.E.

    1986-01-01

    Sulfide oxidation in a carbonate environment produces a groundwater problem similar to acid mine drainage, except the contaminant is sulfate. An example of this little-studied phenomenon occurred around the zinc-lead mines near Shullsburg, Wisconsin. Sulfate concentrations as high as 40 mmol/l (16 times the safe drinking water level) were found after the mines closed in 1979 and 11 wells were abandoned. The 1983 groundwater flow pattern showed groundwater flowing toward the mines to fill the cone of depression created by dewatering of the mines, thus localizing contamination. A three-dimensional groundwater flow model was constructed which predicts groundwater will begin flowing away from the mines between 1989 and 1994. However, sulfate levels should remain low in areas distant from the mines because of dilution of sulfate. Geochemical modeling of chemical reactions and isotope effects using the USGS computer program PHREEQE showed the importance of dolomite, calcite, CO/sub 2/, and iron hydroxides in controlling the water chemistry. Microbiological sampling and sulfur isotopes indicated that Thiobacillus bacteria that thrive under neutral pH conditions may be involved in the oxidation process. Acidophilic bacteria such as T. ferrooxidans were also found. The role of biological factors in oxidation was further investigated by oxidizing a variety of sulfide minerals in the presence of carbonate buffer. The oxygen isotope ratios from both inoculated and sterile experiments indicated a large portion of sulfate oxygen comes from water rather than atmospheric oxygen. The possibility of multiple reaction pathways makes it difficult to use oxygen isotopes to distinguish mechanisms of oxidation.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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. PMID:25934382

  9. 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.

  10. 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).

  11. 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.

  12. Chlorine isotope geochemistry of hydrothermally altered oceanic crust: Mineralogical controls and experimental constraints

    NASA Astrophysics Data System (ADS)

    Cisneros, M.; Barnes, J.; Jenkins, D. M.; Gardner, J. E.

    2012-12-01

    Chlorine stable isotopes (37Cl and 35Cl) can provide an important fingerprint for geochemical recycling of subducted oceanic lithosphere and fluid-rock interaction due to chlorine's high solubility in aqueous phases. To implement Cl isotopes as a tracer of volatile element recycling, we must constrain the δ37Cl value of potential Cl reservoirs and determine fractionation factors between Cl-bearing phases. δ37Cl and Cl concentrations of hydrothermally altered oceanic crust (AOC) samples from seven IODP/ODP/DSDP drill sites have been measured on bulk rock samples (n = 50). For ease of comparing results, samples are categorized into three lithologies: 1) extrusive lavas, 2) sheeted dikes, and 3) gabbros. Extrusive lava Cl concentrations vary from <0.01 wt% to 0.03 wt% (avg = 95 ppm Cl; n= 20) and δ37Cl values range from -1.4 to +1.0‰ (avg = 0.0 ± 0.6‰). Chlorine concentrations of the sheeted dikes range from < 0.01 wt% to 0.05 wt% (avg = 163 ppm Cl; n = 11) and δ37Cl values of dikes range from - 0.4 to + 1.4‰ (avg = 0.1 ± 0.3‰). Bulk chlorine concentrations of the gabbros range from < 0.01 wt% to 0.09 wt% (avg = 244 ppm Cl; n = 19). δ37Cl values of gabbros range from - 0.6 to + 1.8‰ (avg = 0.6 ± 0.6‰). Three general conclusions can be derived from these AOC bulk rock results: 1) δ37Cl values and Cl concentrations increase with increasing total amphibole content. 2) Based on re-calculations of mass balance equations using updated AOC Cl concentrations (~3 times higher than previous estimates, this study), the total amount of Cl recycled into the mantle is higher than previously estimated. 3) [Cl] and δ37Cl values can provide a crude estimate of metamorphic grade in AOC samples. Amphibole-water Cl isotope fractionation experiments are necessary for quantifying the magnitude of Cl fractionation and to aid in interpreting the range of natural Cl isotope variation. Determination of equilibrium fractionation factors between hydrous minerals and co

  13. 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

  14. 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.

  15. 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.

  16. 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

  17. 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.

  18. Exotic crustal components at the northern margin of the Bohemian Massif-Implications from Usbnd Thsbnd Pb and Hf isotopes of zircon from the Saxonian Granulite Massif

    NASA Astrophysics Data System (ADS)

    Sagawe, Anja; Gärtner, Andreas; Linnemann, Ulf; Hofmann, Mandy; Gerdes, Axel

    2016-06-01

    The Saxonian Granulite Massif is located at the northern margin of the Saxo-Thuringian Zone of the peri-Gondwana Bohemian Massif. Eight felsic and mafic granulites were studied with respect to their geochemistry and Usbnd Pb zircon geochronology. The felsic granulites are interpreted to be derived from continental crust of possible granitoid composition. An origin from depleted mantle sources with IAT to MORB composition can be assumed for the mafic granulites. The peak of metamorphism is thought to be timed at about 340 Ma, while several earlier metamorphic events are supposed to have occurred at about 355-360, 370-375, 405, and 450 Ma. They reveal a complex and polyphased geologic evolution of the Saxonian Granulite Massif. Protolith emplacement likely took place at c. 450 and 494 Ma. Hf isotopic data suggest Mesoproterozoic crustal ages at least for parts of the massif. As these crustal ages are exotic for the Bohemian Massif, their origin has to be searched elsewhere. Potential source areas could be Amazonia and Baltica, of which the latter is the one preferred. Furthermore, a composite architecture with at least two components-the felsic granulites with Mesoproterozoic crustal model ages, and the mafic granulites of potential island arc origin-is hypothesised. Their amalgamation to the recent appearance of the Saxonian Granulite Massif is likely bracketed between 375 and 340 Ma.

  19. 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

  20. 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. PMID:27302069

  1. The Cipoeiro gold deposit, Gurupi Belt, Brazil: Geology, chlorite geochemistry, and stable isotope study

    NASA Astrophysics Data System (ADS)

    Klein, Evandro L.; Harris, Chris; Giret, André; Moura, Candido A. V.

    2007-02-01

    The Cipoeiro gold deposit, located in the Gurupi Belt, northern Brazil, is hosted by tonalites of 2148 Ma. The deposit is controlled by splays related to the major strike-slip Tentugal shear zone, and at the deposit scale, the mineralization is confined to ductile-brittle shear zones. Mineralization style comprises thick quartz veins and narrow and discontinuous quartz-carbonate veinlets associated with disseminations in altered host rocks. The postmetamorphic hydrothermal paragenesis is composed of quartz, calcite, chlorite, white mica (phengite), pyrite, and minor albite. Electron microprobe analysis of chlorites reveals a relatively uniform chemical composition at depths of more than 100 m. The chlorites are characterized by (Fe + Mg) ratios between 0.37 and 0.47 and Al IV ranging between 2.22 and 2.59 a.p.f.u. and are classified as Fe-chlinochlore. Temperatures calculated by applying the Al IV contents of chlorites yield a relatively narrow interval of 305 ± 15°C. Stable isotope (O, H, C, S) compositions have been determined in silicate, carbonate, and sulfide minerals. The δ18O and δD values of the mineralizing fluid range from +2.4 to +5.7 and from -43‰ to -20‰, respectively, and are interpreted as having a metamorphic origin. The δ13C values of fluid CO 2 are in the range -10.7‰ to -3.9‰, whereas the fluid δ34S is around 0‰. Carbon and sulfur compositions are not diagnostic of their sources, compatible as they are with mantle, magmatic, or average crustal reservoirs. The hydrothermal paragenesis, chlorite-pyrite coexistence, temperature of ore formation, and sulfur isotope evidence indicate relatively reduced fO 2 conditions for the mineralizing fluid. Geologic, chemical, and isotopic characteristics of the Cipoeiro deposit are compatible with the class of orogenic gold deposits.

  2. 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

  3. Geochronology, geochemistry, and Sr-Nd-Hf isotopes of the early Paleozoic igneous rocks in the Duobaoshan area, NE China, and their geological significance

    NASA Astrophysics Data System (ADS)

    Wu, Guang; Chen, Yuchuan; Sun, Fengyue; Liu, Jun; Wang, Guorui; Xu, Bei

    2015-01-01

    The Duobaoshan area of northwestern Heilongjiang Province is the most important copper resource concentration region in NE China. To date, the Duobaoshan superlarge Cu-Mo deposit and the Tongshan large Cu-Mo deposit have been discovered in the Duobaoshan area. Both the deposits are hosted by granodiorites and volcanic rocks. Zircon LA-ICP-MS U-Pb dating indicates that these granodiorites emplaced approximately 479 Ma ago and that those volcanic rocks erupted between 447 and 450 Ma. The early Ordovicain granodiorites belong to the high-K to medium-K calc-alkaline series and are characterized by high Al2O3 and Sr contents, low Yb and Y contents, and relatively low Mg# values and Na2O/K2O ratios, with positive Eu or slight negative Eu anomalies (averaging 1.18). All of these geochemical characters are similar to those of the adakites generated by partial melting of a thickened lower crust in the world. Moreover, the granodiorites have low initial 87Sr/86Sr ratios (varying from 0.703474 to 0.704436), very high zircon εHf(t) and whole-rock εNd(t) values (varying from 13.0 to 16.8 and 5.27 to 5.46, respectively), and young zircon Hf and whole-rock Nd single-stage and two-stage model ages. Taking these geochemical characteristics and Sr-Nd-Hf isotope compositions together, we suggest that the early Ordovician granodiorites in the Duobaoshan area occurred in a post-collision environment and were formed by partial melting of a juvenile thickened lower crust dominated by depleted mantle-derived material. These late Ordovician volcanic rocks, which are composed of basalt, basaltic andesite, and andesite, belong to the tholeiitic or calc-alkaline series. They are generally enriched in large ion lithophile elements (LILEs) and depleted in high field strength elements (HFSEs; e.g., Nb, Ta, Zr, Hf, P, and Ti), consistent with the geochemistry of igneous rocks from island arcs or active continental margins. Compared with the early Ordovician granodiorites, these volcanic rocks

  4. Use of New 1013 Ohm Current Amplifiers in U and Pb Isotope Ratio Analysis by TIMS

    NASA Astrophysics Data System (ADS)

    Bouman, C.; Trinquier, A.; Lloyd, N. S.; Schwieters, J. B.

    2014-12-01

    Faraday cups can potentially be improved by a factor of 10 too. This presentation will focus on the analysis of small Pb and U using TIMS, for geochronology and nuclear forensics. In our setup, all U and Pb isotopes are measured simultaneously on Faraday cups, except 204Pb which is collected on the SEM since the 204Pb is the least abundant and required for common lead correction.

  5. Ion microprobe U-Pb dating and strontium isotope analysis of biogenic apatite

    NASA Astrophysics Data System (ADS)

    Sano, Y.; Toyoshima, K.; Takahata, N.; Shirai, K.

    2012-12-01

    Conodonts are micro-fossils chemically composed of apatite which occurred in the body of one animal. They are guide fossils to show formation ages of sedimentary sequences with the highest resolution [1] and good samples to verify the dating method. We developed the ion microprobe U-Pb dating of apatite [2] and applied the method to a Carboniferous conodont [3] by using a SHRIMP II installed at Department of Earth and Planetary Sciences, Hiroshima University. Recently we have developed the NanoSIMS U-Pb dating method and successfully measured the formation ages of monazite [4] and zircon [5] at Atmosphere and Ocean Research Institute, University of Tokyo. In this work we carried out the NanoSIMS U-Pb dating of biogenic apatite such as conodont. Since the spot size of NanoSIMS is smaller than SHRIMP II, it is easier to have multi-spots on the single fragment of biogenic apatite. Based on the isochron method of U-Pb system, we have calculated the formation ages. They are consistent with those in literature. In order to study the chemical evolution of ocean during the past 600 Million years, strontium isotopes (87Sr/86Sr) of fossil marine carbonate such as coral skeletons and foraminifera tests were measured and compiled [6]. However they are not robust when the age is older than 500Ma, partly due to post-depositional histories. Apatite is more stable and more resistant to the alteration than carbonate [7]. Recently we have developed the method of NanoSIMS strontium isotopic analysis of a fish otolith, which composed of aragonite [8]. In this work we carried out the strontium isotopic analysis of biogenic apatite. The advantage of the ion microprobe technique over the TIMS (thermal ionization mass spectrometer) and MC-ICP-MS (multi-collector inductively coupled argon plasma mass spectrometer) method is preservation of the important textural context and to provide an opportunity for other simultaneous analytical work with high spatial resolution. This is the case for

  6. 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

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. Geochemistry and Stable Isotopes of Tacana Volcano-Hydrothermal System, Mexico-Guatemala

    NASA Astrophysics Data System (ADS)

    Rouwet, D. /; Inguaggiato, S.; Taran, Y. /; Varley, N. /

    2003-12-01

    Tacana volcano (4100 m.s.n.m.), situated on the border between Chiapas (Mexico) and Guatemala is considered an active volcano. In May 1986, after a minor phreatic explosion, a fumarole field was formed at an altitude between 3200 and 3600 m.a.s.l. Around the volcano, at altitudes between 1500 and 2000 m.a.s.l., exist several thermal springs, with temperatures up to 63 degrees C. Incomplete chemical composition of the Agua Caliente thermal waters in the period 1986-1993 were presented by Medina (1986), De la Cruz-Reyna et al. (1989) and Armienta and De la Cruz-Reyna (1995), a chemical analysis of fumarole gases were published by Martini et al. (1986). This study presents the first series of isotope data of water and gases: hydrogen, oxygen, carbon and helium. Data on gas and water chemistry of several thermal spring waters and gases are presented in more detail than ever. Hydrogen and oxygen isotopes of Tacana thermal spring waters show that meteoric water is the main contribution for the thermal waters. Cation geothermometry of the spring waters confirm these meteoric contribution, as all waters are immature in a dynamic system of water-rock interaction with a constant infiltration of fresh meteoric waters (precipitation of 6000 mm per year). The relatively high bicarbonate (up to 1100 ppm) and sulphate (up to 1200 ppm) concentrations in the thermal waters suggest an important degassing up to 2500 m below the volcano summit, which indicates the presence of a extended and complex volcano-hydrothermal system. Helium isotopes of free and dissolved gases confirm the existence of a magmatic contribution, so as for fumarole gases (6.6 R/Ra) as for gases sampled at the thermal springs (5.7-6.2 R/Ra for free gases and between 0.50 and 5.55 R/Ra for dissolved gases). These values are typical for gases liberated at volcanoes in clasic volcanic arcs. The lower values for the dissolved He is probably due to an interaction with the granitic basement, which can be found at

  12. 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

  13. Fluid inclusions and isotopic characteristics of the Jiawula Pb-Zn-Ag deposit, Inner Mongolia, China

    NASA Astrophysics Data System (ADS)

    Li, Tiegang; Wu, Guang; Liu, Jun; Hu, Yanqing; Zhang, Yunfu; Luo, Dafeng; Mao, Zhihao

    2015-05-01

    , 207Pb/204Pb, and 208Pb/204Pb values of the ore minerals are in the ranges of 18.319-18.377, 15.499-15.596, and 38.094-38.314, respectively. Initial 87Sr/86Sr ratios of sulfides range from 0.712381 to 0.712770. The data for the S, Pb, and Sr isotopic systems indicate that the ore-forming metals and sulfur came from Mesozoic magma. The Jiawula deposit is a low-sulfidation epithermal Pb-Zn-Ag deposit, and fluid boiling is the dominant mechanism for the deposition of ore-forming materials.

  14. U-Pb isotopic systematics of shock-loaded and annealed baddeleyite: Implications for crystallization ages of Martian meteorite shergottites

    NASA Astrophysics Data System (ADS)

    Niihara, Takafumi; Kaiden, Hiroshi; Misawa, Keiji; Sekine, Toshimori; Mikouchi, Takashi

    2012-08-01

    Shock-recovery and annealing experiments on basalt-baddeleyite mixtures were undertaken to evaluate shock effects on U-Pb isotopic systematics of baddeleyite. Shock pressures up to 57 GPa caused fracturing of constituent phases, mosaicism of olivine, maskelynitization of plagioclase, and melting, but the phase transition from monoclinic baddeleyite structure to high-pressure/temperature polymorphs of ZrO2 was not confirmed. The U-Pb isotopic systems of the shock-loaded baddeleyite did not show a large-scale isotopic disturbance. The samples shock-recovered from 47 GPa were then employed for annealing experiments at 1000 or 1300 °C, indicating that the basalt-baddeleyite mixture was almost totally melted except olivine and baddeleyite. Fine-grained euhedral zircon crystallized from the melt was observed around the relict baddeleyite in the sample annealed at 1300 °C for 1 h. The U-Pb isotopic systems of baddeleyite showed isotopic disturbances: many data points for the samples annealed at 1000 °C plotted above the concordia. Both radiogenic lead loss/uranium gain and radiogenic lead gain/uranium loss were observed in the baddeleyite annealed at 1300 °C. Complete radiogenic lead loss due to shock metamorphism and subsequent annealing was not observed in the shock-loaded/annealed baddeleyites studied here. These results confirm that the U-Pb isotopic systematics of baddeleyite are durable for shock metamorphism. Since shergottites still preserve Fe-Mg and/or Ca zonings in major constituent phases (i.e. pyroxene and olivine), the shock effects observed in Martian baddeleyites seem to be less intense compared to that under the present experimental conditions. An implication is that the U-Pb systems of baddeleyite in shergottites will provide crystallization ages of Martian magmatic rocks.

  15. 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

  16. Nitrogen isotope geochemistry of organic matter and minerals during diagenesis and hydrocarbon migration

    NASA Astrophysics Data System (ADS)

    Williams, Lynda B.; Ferrell, Ray E., Jr.; Hutcheon, Ian; Bakel, Allen J.; Walsh, Maud M.; Krouse, H. Roy

    1995-02-01

    The magnitude of isotopic variations between organic and inorganic nitrogen was examined in samples from three stacked hydrocarbon reservoirs in the Fordoche Field (Louisiana Gulf Coast Basin, USA). Measurements were made of δ 15N in kerogen, bitumen, oil, formation water, and fixed-NH 4 extracted from mudstones, nonproductive sandstones, and productive sandstones. Nitrogen isotope fractionation occurs because 14N is released preferentially to 15N from organic molecules during thermal maturation. Released 14N goes into solution, or may be adsorbed by minerals, leaving crude oil enriched in 15N. Diagenetic clay minerals (e.g., illite) commonly form in the temperature range of hydrocarbon generation, and NH 4+ may be fixed in clay interlayers with an isotopic ratio similar to that of the migrating fluids. Results indicate that the influence of organic matter on mineral δ 15N depends on the timing of authigenic mineral formation relative to fluid migration. The average δ 15N of kerogen (3.2 ± 0.3‰) and fixed-NH 4 from mudstones (3.0 ± 1.4) is similar, while bitumen increases from +3.5 to +5.1‰ with depth. In deep reservoir sandstones (>100°C), the δ 15N of crude oil averages +5.2 ± 0.4‰, similar to the δ 15N of bitumen in the proposed source rocks. Formation waters are 14N-enriched with an average δ 15N of -2.2 ± 2.6‰. Fixed-NH 4 δ 15N values lie between that of the oil and water. The average δ 15N of fixed-NH 4 is 3.0 ± 1.2‰ in productive sandstones, and 0.2 ± 2.4‰ innonproductive sandstones. In the shallower reservoir sandstones (<90°C) fixed-NH 4 is apparently not influenced by the presently associated fluids. Productive and nonproductive sandstones have distinctly low average δ 15N values (-1.2 ± 0.8‰), yet crude oil (+11.1 ± 0.3‰) and water (+3.8 ± 0.1‰) have been 15N-enriched by ˜6‰ relative to the deeper reservoirs. This suggests that the present fluids migrated into the reservoir after authigenic illite had formed

  17. 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

  18. Sulphur isotope geochemistry of pyrite from the Upper Cretaceous Marshybank Formation, Western Interior Basin

    NASA Astrophysics Data System (ADS)

    McKay, J. L.; Longstaffe, F. J.

    2003-04-01

    Variations in the texture and sulphur isotopic composition of pyrite in the Upper Cretaceous Marshybank Formation are linked to depositional environment. Abundant, framboidal (and lesser euhedral) pyrite precipitated in offshore marine rocks. Moderate quantities of pyrite also crystallized in brackish, coastal plain rocks. However, in contrast to marine pyrite, coastal plain pyrite is dominantly euhedral in texture, reflecting direct precipitation from a porewater with a relatively low dissolved sulphide concentration. In the marine rocks, pyrite δ34S values range from -35.7‰ to +27.4‰ (avg. -4.8‰ Canyon Diablo Troilite, CDT). Pyrite within carbonate concretions hosted in these marine rocks has a similar isotopic composition (-49.8‰ to +10.6‰ CDT). However, isotopic values are often highly variable within individual concretions as a result of the heterogeneous nature of sulphate reduction and pyrite formation within marine sediments. Pyrite in coastal plain rocks is characterized by relatively high δ34S values (-4.2‰ to +35.5‰, avg. +13.2‰ CDT), while the overlying sideritized conglomerates have the lowest δ34S values reported for Cretaceous rocks from the Western Interior Basin of North America (-49.8‰ to -41.7‰ CDT). Very low δ34S values, which are only observed in the marine rocks, are indicative of microbial sulphate reduction and pyrite formation in a sulphate-replete (i.e., open) system. Higher δ34S values (up to +18‰), which were obtained for both the marine and coastal plain rocks, are indicative of progressive pyrite crystallization in a sulphate-limited (i.e., closed) system. Such conditions are expected in marine sediments as burial occurs, and in brackish (i.e., low sulphate) sediments. Pyrite with very high δ34S values (>+18‰) is common in the coastal plain rocks. These high values are the result of influx of 34S-enriched, residual sulphide derived from overlying marine units. A minor amount of 34S-enriched pyrite is also

  19. Boron, Sr, O, and H isotope geochemistry of groundwaters from Mt. Etna (Sicily) -- Hydrologic implications

    SciTech Connect

    Pennisi, M.; Leeman, W.P.; Tonarini, S.; Pennisi, A.; Nabelek, P.

    2000-03-01

    Combined B, O, H, and Sr isotopic studies of groundwaters from Mt. Etna provide new constraints on their origin and the consequences of fluid-rock interaction within this hydrologic system. Variations in {delta}{sup 18}O ({minus}9.7 to {minus}7.2%) and {delta}D ({minus}62 to {minus}23%) mainly lie along the regional meteoric water line and suggest that most waters originated as local precipitation. However, small shifts in {delta}{sup 18}O, and variable {sup 87}Sr/{sup 86}Sr (0.70355 to 0.70879) and {delta}{sup 11}B ({minus}5.2 to 25.8%) indicate that subsequent interactions occurred between the fluids and local rocks. High B/Cl ratios in all samples seemingly preclude direct involvement of seawater in the hydrologic system despite the proximity to the coast and, in some samples, elevated {sup 87}Sr/{sup 86}Sr and {delta}{sup 11}B. Two general end-member water types are recognized on the basis of their chemistry. These apparently are produced by interactions of local meteoric waters with the dominant reservoir rocks--either basaltic lavas of Etna or the underlying sediments, respectively; high {delta}{sup 11}B in the sediment-hosted end-member points to a significant marine carbonate contribution. Subsequent mixing between these or similar end-members produced a range of intermediate composition groundwaters. Certain anomalous water compositions require the presence locally of a distinct component with high B and moderate {delta}{sup 11}B (ca. 10%) but relatively low {sup 87}/Sr/{sup 86}Sr; an anthropogenic source for this component is plausible. One unusual sample has B and Sr isotopic compositions similar to the other volcanic rock-hosted waters, but anomalously high Cl content that likely reflects local magmatic outgassing near this sampling locality. In general, this study indicates that groundwater B and Sr isotopic compositions are rock-dominated; these data provide useful constraints on the origin and evolution of groundwaters.

  20. Isotope geochemistry of Quaternary deposits from the arid lands in northern China

    NASA Astrophysics Data System (ADS)

    Liu, Cong-Qiang; Masuda, Akimasa; Okada, Akihiko; Yabuki, Sadayo; Fan, Zi-Li

    1994-10-01

    Quaternary deposits of various types (lacustrine, desert sand, river, loess and loess-like deposits) from the southwestern Tarim Basin, North Tianshan, northwest China and the central Loess Plateau exhibit an epsilonNd(0) range from -5 to -12.8 and a Sm-147/Nd-144 range from 0.110 to 0.140. Their Nd-depleted mantle model ages are between 1.50 and 1.92 Ga, with a mean value of 1.7 Ga. Th/Sc ratios vary over a wide range from 0.1 to 2. Comparison of these geochemical signatures with those of the old Australian shales and modern Pacific Ocean dust suggests a continuous input of mantle-derived material into the crust over geological time. The deposits from the North Tianshan show clearly different chemical and isotopic features, with significantly higher Sm/Nd, high Nd-143/Nd-144, low Sr-87/Sr-86, and low La/Lu and Th/Sc ratios relative to those in the deposits from the other areas. This indicates a geological control on the local source, which has an overall young age and an erichment of basic components. The epsilonCe(0) values of two loess samples from the central Loess Plateau are +1.8 and 3.9, corresponding to depleted mantle model ages of 2.2 and 3.4 Ga. Like the Rb-Sr system, the evolution of the La-Ce isotopic system in the crust may be to some extent decoupled from the Sm-Nd system, due to La/Ce fractionation by sedimentary processes. We conclude that the loess can have originated from desert processes, since the difference in the chemistry of the desert sand and loess may result from mineral sorting during desert processes and aeolian transportation. The loess deposits on the central Loess Plateau chemically and isotopically resemble the desert loess deposits in the southwestern Tarim Basin but do not resemble those of the North Tianshan.

  1. 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

  2. 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 infillings 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 a fan draining a carbonate terrane have 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.

  3. 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

  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. 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.

  6. Chlorine and hydrogen isotope geochemistry of obsidian glasses: behavior during volcanic degassing at Mono Craters, CA

    NASA Astrophysics Data System (ADS)

    Prather, T.; Cisneros, M.; Befus, K.; Barnes, J.; Gardner, J. E.

    2012-12-01

    Volatile element concentrations (Cl, H2O, and CO2) and stable isotope compositions (δD and δ37Cl) of volcanic glasses (obsidians) (n = 30) have been determined toquantifythe behavior of chlorine stable isotopes (35Cl and 37Cl) during volcanic degassing. Pyroclastic obsidian samples werefrom tuff layers representing a single eruptive sequence that occurred around 1350 A.D. in the Mono Craters volcanic field, California. The Cl, H2O, and CO2 concentrations recorded by these eruptive obsidians track the chemical evolution of the magmatic system. The H2O and CO2 concentrations of the samples range from 0.37 to 2.08 wt% and 1 to 31ppm, respectively. H2Oand CO2 concentrations are strongly correlated and reflect the degassing trend of the eruptive sequence. Chlorine concentrations of obsidians range from 609 to 833 ppm and do not display a strong correlation with either H2O or CO2 concentrations. Obsidians were selected from two tuff layers: 1) a lower layer containing average H2O and CO2 concentrations of 1.5 ± 0.5 wt% and 22 ± 11ppm, respectively, and 2) an upper layer containing slightly lower average H2O and CO2 concentrations of 0.9 ± 0.5 wt% and 6 ± 5 ppm, respectively. Chlorine concentrations are essentially identical between the two layers, averaging 742 ± 58 ppm in the lower layer and 702 ± 75 ppm in the upper layer. Measured δD values of the obsidians vary between -63 to -74‰ (1σ = ±2‰) and display D/H ratios that decrease with lower total water content following a distillation trend dominated by open system degassing. δ37Cl values were measured on select samples from each of the two tuff layers. The samples from the lower layer have δ37Cl values between -1.8 to -2.0‰ (n = 3), whereas the samples from the upper layer have δ37Cl values between -1.3 and -1.4‰ (n = 3) (1σ = ±0.2‰). Despite the similar Cl concentrations between the two layers, the samples with lower δ37Cl values have higher Cl concentrations (763 ± 61 ppm Cl) than samples

  7. 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.

  8. 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.

  9. 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 proc