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Sample records for sm-nd isotope geochemistry

  1. Crustal evolution of South American Platform based on Sm-Nd isotope geochemistry

    International Nuclear Information System (INIS)

    Sato, Kei

    1998-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Sato, Kei

    1998-07-01

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

  3. Chemical methods for Sm-Nd separation and its application in isotopic geological dating

    International Nuclear Information System (INIS)

    Guo Qifeng.

    1990-01-01

    Three chemical methods for Sm-Nd separation are mainly desribed: low chromatography of butamone-ammonium thiocyanate for hight concentration Sm and Nd separation, P 240 column chromatography for medium concentration Sm-Nd separation, and pressure ion exchange for low concentration Sm-Nd. The first Sm-Nd synchrone obtained in China with Sm-Nd methods is introduced and Sm-Nd isotopic geological dating in Early Archaean rocks in eastern Hebei has been determined

  4. The Cambrian to Devonian odyssey of the Brabant Massif within Avalonia: A review with new zircon ages, geochemistry, Sm-Nd isotopes, stratigraphy and palaeogeography

    Science.gov (United States)

    Linnemann, Ulf; Herbosch, Alain; Liégeois, Jean-Paul; Pin, Christian; Gärtner, Andreas; Hofmann, Mandy

    2012-05-01

    This study provides an up-to-date and comprehensive review of the Early Palaeozoic evolution of the Brabant Massif belonging to the Anglo-Brabant Deformation Belt. Situated at the southeastern side of Avalonia microplate, it is the only well-known part of the northern passive margin of the Rheic Ocean. The Cambrian-Silurian sedimentary pile is > 13 km thick, with > 9 km for the Cambrian only. The unraveling of this continuous registration reflects the successive rifting and drifting of Avalonia from the Gondwana mainland, followed by soft-collisional processes with Baltica and finally the formation of Laurussia. Based on recently established detailed stratigraphy, sedimentology and basin development, on U-Pb LA-ICP-MS analyses of igneous and detrital zircon grains along with geochemical data including Sm-Nd isotopes, a new geodynamic and palaeogeographic evolution is proposed. Brabant Megasequence 1 (lower Cambrian to lowermost Ordovician, > 9 km thick) represents an embayment of the peri-Gondwanan rift from which the Rheic Ocean has evolved. Detrital zircon ages demonstrate that the Brabant is a typical peri-Gondwanan terrane with a major Pan-African (Neoproterozoic age) and a mixed West African and Amazonian source (Palaeoproterozoic, Archaean and some Mesoproterozoic age). The transition towards the Avalonia drifting is marked by an unconformity and a short volcanic episode. The northward drift of Avalonia towards Baltica is recorded by the Megasequence 2 (Middle to Upper Ordovician, 1.3 km thick). The source for Mesoproterozoic zircons vanished, as the result of the Rheic Ocean opening and the isolation from Amazonian sources. The transition to Megasequence 3 is marked by a drastic change in palaeobathymetry and an important (sub)volcanic episode during a tectonic instability period (460-430 Ma), reflecting the Avalonia-Baltica soft docking as also shown by the reappearance of Mesoproterozoic detrital zircons, typical of Baltica. Unradiogenic Nd isotope

  5. Polycyclic evolution of the Quadrilatero Ferrifero: an analysis based on the actual knowledge of the U-Pb geochronology and Sm-Nd isotopic geochemistry

    International Nuclear Information System (INIS)

    Carneiro, Mauricio Antonio; Noce, Carlos Mauricio; Teixeira, Wilson

    1995-01-01

    The tectonic evolution of the Quadrilatero Ferrifero region, based on geochronological U-Pb, Pb-Pb, Sm-Nd, Rb-Sr e K-Ar data, is characterized by several processes of crustal growth, which began in Middle Archean. The Lower Archean geological evolution of the Quadrilatero Ferrifero was finished by the Rio de Velhas tectono-thermal event around 2,78 Ga. After this, during the proterozoic era, three tectono-sedimentary cycles took place on this Lower Archean crustal fragment, whose products are represented by the meta sedimentary sequences of the Minas Supergroup, Itacolomi Group and Espinhaco Supergroup. The Transamazonico Event (ca. 2,0 Ga) ended the geological evolution of Minas Supergroup, but its geological records did not have the same size imprints throughout region. Many places, such as the Bonfim Metamorphic Complex, were not affected by this tectonic event. Later tectonic event. Later tectonic events (e.g. Brasiliano) had even more discrete geological occurred during the Proterozoic era, when many sedimentary basins developed (e.g. Espinhaco and Sao Francisco basins). (author)

  6. Do supercontinents introvert or extrovert?: Sm-Nd isotope evidence

    Science.gov (United States)

    Brendan Murphy, J.; Damian Nance, R.

    2003-10-01

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

  7. Sm-Nd isotope system of oldest granulites of Anabar Shield

    International Nuclear Information System (INIS)

    Spiridonov, V.G.; Sukhanov, M.K.; Karpenko, S.F.; Lyalikov, A.V.; AN SSSR, Moscow

    1991-01-01

    The first results of applying Sm-Nd method for dating the oldest basic and ultrabasic rocks of the Anabar Shield are presented. The content and isotopic composition of Sm and Nd were determined by the methods of mass-spectroscopy with isotopic dilution. The obtained values of metamorphic ages (3063 ± 80 million years) are in good agreement with U-Pb method data for zircon

  8. The neoproterozoic Goias magmatic arc, central Brazil: a review and new Sm-Nd isotopic data

    International Nuclear Information System (INIS)

    Pimentel, Marcio Martins; Fuck, Reinhardt Adolfo; Gioia, Simone Maria Costa Lima

    2000-01-01

    In this study we review the main characteristics and geochronological/isotopic data of metaigneous rocks of the juvenile Neoproterozoic Goias Magmatic Arc in central Brazil. Some new Sm-Nd isotopic data are also presented for both the southern (Arenopolis) and northern (Mara Rosa) sections of the arc. In the south, granitoids of the Choupana-Turvania area yielded a Sm-Nd whole-rock isochron age of 863± 97 Ma and e Nd (T) of +4.1 T D M model ages vary between 0.94 and 1.13 Ga. Metavolcanic rocks in the Pontalina region have a Sm-Nd whole rock isochron age of 762 ± 77 Ma and e Nd (T) of +2.9. T DM values are between 0.96 and 1.10 Ga. In the northern section of the Goias Arc, mylonitic gneisses of the Serra Azul ridge, an important N30E shear zone, were investigated and have a Sm-Nd isochron age of 3058 ± 120 Ma and initial e Nd value of ca.+ 2.1. This data suggests that the Serra Azul ridge might represent either a mylonitized fragment of the Archaen terranes exposed just to the south, or the sialic basement of the Araguaia Belt supracrustal, along the eastern margin of the Amazon Craton. The geochronological data available so far indicate a long history of arc formation and amalgamation on the western margin of the Sao Francisco-Congo continent during the Neoproterozoic. The history of convergence of continental masses is partially coeval with the fragmentation of Rodinia, indicating that the western margin (present geographic reference) of that continent occupied a peripheral setting in the Rodinia super continent. (author)

  9. The neoproterozoic Goias magmatic arc, central Brazil: a review and new Sm-Nd isotopic data

    Energy Technology Data Exchange (ETDEWEB)

    Pimentel, Marcio Martins; Fuck, Reinhardt Adolfo; Gioia, Simone Maria Costa Lima [Brasilia Univ., DF (Brazil). Inst. de Geociencias]. E-mail: marcio@unb.br

    2000-03-01

    In this study we review the main characteristics and geochronological/isotopic data of metaigneous rocks of the juvenile Neoproterozoic Goias Magmatic Arc in central Brazil. Some new Sm-Nd isotopic data are also presented for both the southern (Arenopolis) and northern (Mara Rosa) sections of the arc. In the south, granitoids of the Choupana-Turvania area yielded a Sm-Nd whole-rock isochron age of 863{+-} 97 Ma and e{sub Nd} (T) of +4.1 T{sub D}M model ages vary between 0.94 and 1.13 Ga. Metavolcanic rocks in the Pontalina region have a Sm-Nd whole rock isochron age of 762 {+-} 77 Ma and e{sub Nd} (T) of +2.9. T {sub DM} values are between 0.96 and 1.10 Ga. In the northern section of the Goias Arc, mylonitic gneisses of the Serra Azul ridge, an important N30E shear zone, were investigated and have a Sm-Nd isochron age of 3058 {+-} 120 Ma and initial e{sub Nd} value of ca.+ 2.1. This data suggests that the Serra Azul ridge might represent either a mylonitized fragment of the Archaen terranes exposed just to the south, or the sialic basement of the Araguaia Belt supracrustal, along the eastern margin of the Amazon Craton. The geochronological data available so far indicate a long history of arc formation and amalgamation on the western margin of the Sao Francisco-Congo continent during the Neoproterozoic. The history of convergence of continental masses is partially coeval with the fragmentation of Rodinia, indicating that the western margin (present geographic reference) of that continent occupied a peripheral setting in the Rodinia super continent. (author)

  10. A Sm-Nd isotopic study of atmospheric dusts and particulates from major river systems

    International Nuclear Information System (INIS)

    Goldstein, S.L.; Cambridge Univ.; O'Nions, R.K.; Hamilton, P.J.

    1984-01-01

    143 Nd/ 144 Nd ratios, and Sm and Nd abundances, are reported for particulates from major and minor rivers of the Earth, continental sediments, and aeolian dusts collected over the Atlantic, Pacific, and Indian Oceans. Overall, Sm/Nd ratios and Nd isotopic compositions in contemporary continental erosion products vary within the small ranges of 147 Sm/ 144 Nd=0.115 +- 0.01 and 143 Nd/ 144 Nd=0.51204 +- 0.0002 (epsilonsub(Nd)=-11.4 +- 4). The average period of residence in the continental crust is estimated to be 1.70 +- 0.35 Ga. These results combined with data from the literature have implications for the age, history, and composition of the sedimentary mass and the continental crust: (1) The average 'crustal residence age' of the whole sedimentary mass is about 1.9 Ga. (2) The range of Nd isotope compositions in the continent derived particulate input to the oceans is the same as Atlantic sediments and seawater, but lower than those of the Pacific, demonstrating the importance of Pacific volcanism to Pacific Nd chemistry. (3) The average ratio of Sm/Nd is about 0.19 in the upper continental crust, and has remained so since the early Archean. This precludes the likelihood of major mafic to felsic or felsic to mafic trends in the overall composition of the upper continental crust through Earth history. (4) Sediments appear to be formed primarily by erosion of continental crust having similar Sm/Nd ratios, rather than by mixing of mafic and felsic compositions. (5) The average ratio of 143 Nd/ 144 Nd approx.= 0.5117 (epsilonsub(Nd) approx.= -17) in the upper continental crust, assuming its mean age is about 2 Ga. (6) The uniformity of the Sm-Nd isotopic systematics in river and aeolian particulates primarily reflects efficient recycling of old sediment by sedimentary processes on a short time scale compared to the amount of time the material has resided in the crust. (orig.)

  11. Komatiites of the Onverwacht Group, S. Africa: REE geochemistry, Sm/Nd age and mantle evolution

    Science.gov (United States)

    Jahn, Bor-Ming; Gruau, G.; Glikson, A. Y.

    1982-08-01

    Komatiites of the Tjakastad Subgroup of the Onverwacht Group (S. Africa) were dated by the Sm/Nd method. A whole-rock isochron yields an age of 3.56±0.24 (2 σ) AE, with initial 143Nd/144Nd ratio of 0.50818±23 (2 σ), corresponding to ɛ Nd( T)= + 1.9±4.5. This age is interpreted as the time of initial Onverwacht volcanism. This result agrees with earlier Sm/Nd data of Hamilton et al. (1979) and is consistent with the Rb-Sr result of Jahn and Shih (1974). Komatiites may be divided into 3 groups based on the typology of heavy REE distributions (Jahn and Gruau 1981). According to this scheme, the Onverwacht komatiites of the present study belong to two groups: the predominant Group II rocks showing (Gd/Yb)N≃1.4, CaO/Al2O3 = 1.33, Al2O3/TiO2≃10.6; and the subordinate Group III rocks with (Gd/Yb)Nconnotation of the chemical parameters, such as CaO/Al2O3, (Gd/Yb)N or Al2O3/TiO2 ratio has not been firmly established. The characteristic “high” CaO/Al2O3 or (Gd/Yb)N ratios in many Onverwacht Group rocks can also be explained as a result of local short-term mantle heterogeneity.

  12. Rb-Sr and Sm-Nd Isotopic Studies of Lunar Green and Orange Glasses

    Science.gov (United States)

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

    2012-01-01

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

  13. Constraining Mantle Differentiation Processes with La-Ce and Sm-Nd Isotope Systematics

    Science.gov (United States)

    Willig, M.; Stracke, A.

    2016-12-01

    Cerium (Ce) and Neodymium (Nd) isotopic ratios in oceanic basalts reflect the time integrated La-Ce and Sm-Nd ratios, and hence the extent of light rare earth element element (LREE) depletion or enrichment of their mantle sources. New high precision Ce-Nd isotope data from several ocean islands define a tight array in ԑCe-ԑNd space with ԑNd = -8.2±0.4 ԑCe + 1.3±0.9 (S.D.), in good agreement with previous data [1, 2]. The slope of the ԑCe-ԑNd array and the overall isotopic range are sensitive indicators of the processes that govern the evolution of the mantle's LREE composition. A Monte Carlo approach is employed to simulate continuous mantle-crust differentiation by partial melting and recycling of crustal materials. Partial melting of mantle peridotites produces variably depleted mantle and oceanic crust, which evolve for different time periods, before the oceanic crust is recycled back into the mantle including small amounts of continental crust (GLOSS [3]). Subsequently, depleted mantle and recycled materials of variable age and composition melt, and the respective melts mix in different proportions. Mixing lines strongly curve towards depleted mantle, and tend to be offset from the data for increasingly older and more depleted mantle. Observed ԑCe-ԑNd in ridge [1] and ocean island basalts and the slope of the ԑCe-ԑNd array therefore define upper limits for the extent and age of LREE depletion preserved in mantle peridotites. Very old average mantle depletion ages (> ca. 1-2 Ga) for the bulk of the mantle are difficult to reconcile with the existing ԑCe-ԑNd data, consistent with the range of Nd-Hf-Os model ages in abyssal peridotites [4-6]. Moreover, unless small amounts of continental crust are included in the recycled material, it is difficult to reproduce the relatively shallow slope of the ԑCe-ԑNd array, consistent with constraints from the ԑNd - ԑHf mantle array [7]. [1] Makishima and Masuda, 1994 Chem. Geol. 118, 1-8. [2] Doucelance et al

  14. Sm-Nd isotope system of the Ukrainian shield (Korosten'sky massif) anorthosite-granite formation

    Energy Technology Data Exchange (ETDEWEB)

    Bogatikov, O A; Karpenko, S F; Sukhanov, M K; Spiridonov, V G

    1988-01-01

    The results of Sm-Nd isotope investigation of rocks of the Ukrainian shield anorthosite-granite association are described; this association, according to the geologic data, is the latest association in a seriesof self-contained anorthosited. The latters are connected with considerable masses of rapakiwi-granited. Isotope analysis is carried out by mass spectrometry. Isotope ratios /sup 147/Sm//sup 144/Nd and /sup 143/Nd//sup 144/Nd for five samples investigated are presented. Isotope data obtained are marked to be important information about the origin of rocks studied. Evident age difference of granite and basic components of the association is established, that idnores the possibility of the rock formation during crystallization differentiation. The basic value of the radiometric 1.89-1.74 milliared years age of the Ukrainian shield anorthosites lied in the fact that these data confirm once more the specific nature of the earth's crust evolution especially at early stages of its formation.

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

    International Nuclear Information System (INIS)

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

    1997-01-01

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

  16. Fluid inclusion, geochemical, Rb-Sr and Sm-Nd isotope studies on ...

    Indian Academy of Sciences (India)

    10

    geochemistry and geochronology of two such tungsten mineralized granite plutons at. 18 ... 55 et al. 1994, Torsvik et al. 2001a; Pandit et al. 2003; Ashwal et al. 2013). ..... fractionation of plagioclase feldspar (Chappell and White, 1974). Pearce ...

  17. Zircon U-Pb geochronology, Sm-Nd and Pb-Pb isotope systematics of Ediacaran post-collisional high-silica Acampamento Velho volcanism at the Tupanci area, NW of the Sul-Rio-Grandense Shield, Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Sommer, Carlos Augusto; Leitzke, Felipe Padilha; Lima, Evandro Fernandes de; Barreto, Carla Joana Santos; Matté, Vinicius; Philipp, Ruy Paulo; Conceição, Rommulo Vieira, E-mail: casommer@sinos.net, E-mail: eflgeologo@gmail.com, E-mail: ruy.philipp@ufrgs.br, E-mail: rommulo.conceicao@ufrgs.br [Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, RS (Brazil). Instituto de Geociências; Lafon, Jean Michel, E-mail: lafonjm@ufpa.br [Universidade Federal do Pará (UFPA), Belém, PA (Brazil). Laboratório de Geologia Isotópica; Basei, Miguel Ângelo Stipp, E-mail: baseimas@usp.br [Universidade de São Paulo (CPGeo/IGc/USP), São Paulo, SP (Brazil)

    2017-10-15

    We present new U-Pb zircon ages and Sm-Nd-Pb isotopic data for volcanic and hypabyssal acid rocks from the northernmost exposure of the Acampamento Velho Formation in the NW portion of the Sul-Rio-Grandense Shield, Brazil. The first volcanic episode, grouped in the high-Ti rhyolites from the Tupanci hill, shows age of 579 ± 5.6 Ma, which is in agreement with the post-collisional Acampamento Velho Formation volcanism in the Bom Jardim Group of the Camaquã Basin. A poorly constrained age of 558+/- 39Ma was obtained for rhyolites from the low-Ti group at the Picados Hill, which may indicate a younger acid volcanism, or a greater time span for the volcanism of the Acampamento Velho Formation in southernmost Brazil. Regarding magmatic sources, Sm/Nd isotopic data coupled to Pb isotopes and a review of trace element geochemistry indicate different amounts of Paleoproterozoic (Dom Feliciano, Pinheiro Machado Suite) to Neoproterozoic (Rio Vacacaí terrane) lower crust melting. Our data, coupled with literature data, contribute to a better understanding of the stratigraphic evolution for the Neoproterozoic post-collisional volcanic successions of the Camaquã Basin in the Sul-Rio-Grandense Shield. (author)

  18. New Sm-Nd isotopic data from the Southern Aracuai-Ribeira belt: Parabaiba Do Sul group and associated granitic intrusions

    International Nuclear Information System (INIS)

    Medeiros, Silvia Regina de; Wiedemann, Cristina Maria

    2001-01-01

    The Aracuai-Ribeira belt is a Neoproterozoic orogenic belt extending along the Brazilian Coast, bordering the eastern margin of the Sao Francisco craton (Pedrosa Soares et al., in press). In this work we start unveiling the magmatic source characteristics of the southern Espirito Santo segment of this belt through the use of new Sm-Nd data were obtained from exactly the same sample which Sollner et al. (1991), took their U-Pb and Rb-Sr measurements (the major isotopic informations available up to now) allowing thus a correlation with this previous geochronologic work, contributing for an improvement of the evolution model of the whole belt (au)

  19. First data on Sm-Nd isotope systematics of the Kholodnikansk greenstone belt metavolcanites, the Southern Aldan shield

    International Nuclear Information System (INIS)

    Lavrik, S.N.; Mishkin, M.A.; Moiseenko, V.G.; Zhuravlev, D.Z.

    2002-01-01

    The age of the Kholodnikansk greenstone metavolcanites, located in the south of the Southern Aldan shield, is determined through the method of the Sm-Nd dating with the purpose of studying its earth crust constituent segments formation. The obtained metavolcanites isochronous age, equal to 2.41±0.08 billion years testifies to the fact, that the processes of the early proterozoic activation (2.2-2.4 billion years ago) were manifested not only within the limits of the Central-Aldan complex but also in the south of the Aldan shield [ru

  20. An evaluation of a single-step extraction chromatography separation method for Sm-Nd isotope analysis of micro-samples of silicate rocks by high-sensitivity thermal ionization mass spectrometry

    International Nuclear Information System (INIS)

    Li Chaofeng; Li Xianhua; Li Qiuli; Guo Jinghui; Li Xianghui; Liu Tao

    2011-01-01

    Graphical abstract: Distribution curve of all eluting fractions for a BCR-2 (1-2-3.5-7 mg) on LN column using HCl and HF as eluting reagent. Highlights: → This analytical protocol affords a simple and rapid analysis for Sm and Nd isotope in minor rock samples. → The single-step separation method exhibits satisfactory separation effect for complex silicate samples. → Corrected 143 Nd/ 144 Nd data show excellent accuracy even if the 140 Ce 16 O + / 144 Nd 16 O + ratio reached to 0.03. - Abstract: A single-step separation scheme is presented for Sm-Nd radiogenic isotope system on very small samples (1-3 mg) of silicate rock. This method is based on Eichrom LN Spec chromatographic material and affords a straightforward separation of Sm-Nd from complex matrix with good purity and satisfactory blank levels, suitable for thermal ionization mass spectrometry (TIMS). This technique, characterized by high efficiency (single-step Sm-Nd separation) and high sensitivity (TIMS on NdO + ion beam), is able to process rapidly (3-4 h), with low procedure blanks ( 143 Nd/ 144 Nd ratios and Sm-Nd concentrations are presented for eleven international silicate rock reference materials, spanning a wide range of Sm-Nd contents and bulk compositions. The analytical results show a good agreement with recommended values within ±0.004% for the 143 Nd/ 144 Nd isotopic ratio and ±2% for Sm-Nd quantification at the 95% confidence level. It is noted that the uncertainty of this method is about 3 times larger than typical precision achievable with two-stage full separation followed by state-of-the-art conventional TIMS using Nd + ion beams which require much larger amounts of Nd. Hence, our single-step separation followed by NdO + ion beam technique is preferred to the analysis for microsamples.

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

    Science.gov (United States)

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

    2013-12-01

    Studies of metasedimentary rocks from the Jack Hills, which host Earth's oldest known detrital minerals, have focused on zircon and occasionally monazite or xenotime, but no attention has been directed toward one of the most common mineral markers of metamorphism: garnet. Garnet can provide a record of the post-depositional, prograde metamorphic history of Archean metasedimentary rocks. Additionally, the use of a newly developed detrital garnet dating technique [1,2] may reveal information about pre-depositional metamorphism that could address lingering questions about the nature and timing of Earth's earliest tectonometamorphic events. Here we investigate garnet from the Jack Hills metasedimentary rocks to test whether they record in situ metamorphism or are a detrital relict of even older metamorphic events. We identified garnet in two bulk quartz-pebble conglomerate samples collected from the 'discovery' outcrop at Eranondoo Hill in the Jack Hills of Western Australia. Electron microprobe analyses of polished grains and SEM measurements of unpolished grain surfaces are consistent, revealing garnet composition indicative of a single generation/population of predominantly almandine-spessartine solid solution (~10-35% mole fraction spessartine). Compositional maps of garnet grains reveal little zoning and no discontinuities, most consistent with a single growth event. Dating Jack Hills' garnet via the Sm-Nd system is possible due to continued development of small sample analysis techniques, including running NdO+ TIMS analyses with Ta2O5 activator [3] permitting Ma for two point isochrons between clean garnet (Sm/Nd ≥ 1.0) and their leached inclusion populations [2]. Four grouped garnet grain separates from one sample yield preliminary dates of 2703.6×6.0Ma, 2612.4×6.0Ma, 2605.0×5.5Ma, and 2567.3×8.3Ma, while the second sample yielded a date of 2579.6×4.6 Ma (2σ). Compositional and geochronologic data indicate likely in situ garnet growth during a late

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

    Energy Technology Data Exchange (ETDEWEB)

    Marques, Suelen Nonata de Souza; Nascimento, Rielva Solimairy Campelo do, E-mail: suelen-marques@hotmail.com, E-mail: rielva@ufam.edu.br [Universidade Federal do Amazonas (UFAM), Manaus, AM (Brazil). Inst. de Geociencias; Souza, Valmir da Silva; Dantas, Elton Luiz, E-mail: vsouza@unb.br, E-mail: elton@unb.br [Universidade de Brasilia (UnB), DF (Brazil). Inst. de Geociencias; Valerio, Cristovao da Silva, E-mail: cristovao@igeo.ufrr.br [Universidade Federal de Roraima (UFRR), Boa Vista, RR (Brazil). Inst. de Geociencias

    2014-07-01

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

  3. Geochemistry of silicon isotopes

    Energy Technology Data Exchange (ETDEWEB)

    Ding, Tiping; Li, Yanhe; Gao, Jianfei; Hu, Bin [Chinese Academy of Geological Science, Beijing (China). Inst. of Mineral Resources; Jiang, Shaoyong [China Univ. of Geosciences, Wuhan (China).

    2018-04-01

    Silicon is one of the most abundant elements in the Earth and silicon isotope geochemistry is important in identifying the silicon source for various geological bodies and in studying the behavior of silicon in different geological processes. This book starts with an introduction on the development of silicon isotope geochemistry. Various analytical methods are described and compared with each other in detail. The mechanisms of silicon isotope fractionation are discussed, and silicon isotope distributions in various extraterrestrial and terrestrial reservoirs are updated. Besides, the applications of silicon isotopes in several important fields are presented.

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

    Science.gov (United States)

    Stille, P.; Tatsumoto, M.

    1985-04-01

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

  5. SHELL ISOTOPE GEOCHEMISTRY

    African Journals Online (AJOL)

    ABSTRACT: The land snail Limicolaria kambeul chudeaui Germain was collected ... Key words/phrases: Ethiopia, isotope geochemistry, Lake Tilo, Limicolaria .... 1984), (c) 6'80 values of precipitation at Addis Ababa, with i 1 S.D. bars for the .... (breakfast cereal), deionised water and cuttlefish bone, the carbon and oxygen.

  6. Sm-Nd in marine carbonates and phosphates: implications for Nd isotopes in seawater and crustal ages

    International Nuclear Information System (INIS)

    Shaw, H.F.; Wasserburg, G.J.

    1985-01-01

    This study explores the possibility of establishing Nd isotopic variations in seawater over geologic time. Calcite, aragonite and apatite are examined as possible phases recording seawater values of epsilonsubNd. Modern, biogenic and inorganically precipitated calcite and aragonite from marine environments were found to have Nd concentrations of from 0.2 to 70 ppb, showing that primary marine CaCO 3 contains little REE and that Nd/Ca is not greatly enhanced relative to seawater during carbonate precipitation. Very young marine limestone and dolomite containing no continental detritus have approx. 200 ppb Nd. All the carbonates are LREE enriched. Modern and very young Atlantic and Pacific carbonates have epsilonsub(Nd) in the range of shallow Atlantic and Pacific seawater respectively, implying that they derive their REE from local seawater. The Nd in well preserved carbonate fossils is 4 ppb, much greater than in their modern counterparts but like the high values found for carbonates in other studies. Results are also reported for apatite. They suggest that sedimentary apatite can be used to determine epsilonsub(Nd)(T) in ancient seawater. The seawater values so inferred range between -1.7 and -8.9 over the last 700 my and lie in the range of modern seawater, showing no evidence for drastic changes. (U.K.)

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-11-01

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

  8. Investigating sediment size distributions and size-specific Sm-Nd isotopes as paleoceanographic proxy in the North Atlantic Ocean: reconstructing past deep-sea current speeds since Last Glacial Maximum

    OpenAIRE

    Li, Yuting

    2017-01-01

    To explore whether the dispersion of sediments in the North Atlantic can be related to modern and past Atlantic Meridional Overturning Circulation (AMOC) flow speed, particle size distributions (weight%, Sortable Silt mean grain size) and grain-size separated (0–4, 4–10, 10–20, 20–30, 30–40 and 40–63 µm) Sm-Nd isotopes and trace element concentrations are measured on 12 cores along the flow-path of Western Boundary Undercurrent and in the central North Atlantic since the Last glacial Maximum ...

  9. Calcium stable isotope geochemistry

    Energy Technology Data Exchange (ETDEWEB)

    Gausonne, Nikolaus [Muenster Univ. (Germany). Inst. fuer Mineralogie; Schmitt, Anne-Desiree [Strasbourg Univ. (France). LHyGeS/EOST; Heuser, Alexander [Bonn Univ. (Germany). Steinmann-Inst. fuer Geologie, Mineralogie und Palaeontologie; Wombacher, Frank [Koeln Univ. (Germany). Inst. fuer Geologie und Mineralogie; Dietzel, Martin [Technische Univ. Graz (Austria). Inst. fuer Angewandte Geowissenschaften; Tipper, Edward [Cambridge Univ. (United Kingdom). Dept. of Earth Sciences; Schiller, Martin [Copenhagen Univ. (Denmark). Natural History Museum of Denmark

    2016-08-01

    This book provides an overview of the fundamentals and reference values for Ca stable isotope research, as well as current analytical methodologies including detailed instructions for sample preparation and isotope analysis. As such, it introduces readers to the different fields of application, including low-temperature mineral precipitation and biomineralisation, Earth surface processes and global cycling, high-temperature processes and cosmochemistry, and lastly human studies and biomedical applications. The current state of the art in these major areas is discussed, and open questions and possible future directions are identified. In terms of its depth and coverage, the current work extends and complements the previous reviews of Ca stable isotope geochemistry, addressing the needs of graduate students and advanced researchers who want to familiarize themselves with Ca stable isotope research.

  10. Calcium stable isotope geochemistry

    International Nuclear Information System (INIS)

    Gausonne, Nikolaus; Schmitt, Anne-Desiree; Heuser, Alexander; Wombacher, Frank; Dietzel, Martin; Tipper, Edward; Schiller, Martin

    2016-01-01

    This book provides an overview of the fundamentals and reference values for Ca stable isotope research, as well as current analytical methodologies including detailed instructions for sample preparation and isotope analysis. As such, it introduces readers to the different fields of application, including low-temperature mineral precipitation and biomineralisation, Earth surface processes and global cycling, high-temperature processes and cosmochemistry, and lastly human studies and biomedical applications. The current state of the art in these major areas is discussed, and open questions and possible future directions are identified. In terms of its depth and coverage, the current work extends and complements the previous reviews of Ca stable isotope geochemistry, addressing the needs of graduate students and advanced researchers who want to familiarize themselves with Ca stable isotope research.

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

    International Nuclear Information System (INIS)

    Silva Filho, A.F. da; Guimaraes, I.P.; Luna, E.B.A.; Van Schmus, W.R.

    1997-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1997-12-31

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

  13. Application of specific extraction chromatographic methods to the Rb-Sr, Sm-Nd isotope study of geological samples: The Hombreiro-Santa Eulalia Granite (Lugo, NW Spain)

    OpenAIRE

    Santos Zalduegui, J. F.; Pin, C.; Aranguren, A.; Gil Ibarguchi, José Ignacio

    1996-01-01

    The analytical application to geological samples of three new chromatographic resins, TRU-Spec ®, Sr-Spec ® and LN-Spec ®) has been investigated. Seven samples of the Hombreiro massif (Lugo, NW Spain) have been studied, that yield a Rb-Sr age of 298 ±5 Ma (SrQ = 0.7086, MSWD = 7.64) for the magma crystallization. Sm-Nd data results for the same massif give eNd values dose to -2 at 300 Ma. This suggests that the origin of the magma might be related to the partial melting of immature sediments,...

  14. The history of a continent from U-Pb ages of zircons from Orinoco River sand and Sm-Nd isotopes in Orinoco basin river sediments

    Science.gov (United States)

    Goldstein, S.L.; Arndt, N.T.; Stallard, R.F.

    1997-01-01

    We report SHRIMP U-Pb ages of 49 zircons from a sand sample from the lower Orinoco River, Venezuela, and Nd model ages of the fine sediment load from the main river and tributaries. The U-Pb ages reflect individual magmatic or metamorphic events, the Sm-Nd model ages reflect average crustal-residence ages of the sediment sources. Together they allow delineation of the crust-formation history of the basement precursors of the sediments. The U-Pb ages range from 2.83 to 0.15 Ga, and most are concordant or nearly so. Discrete age groupings occur at ??? 2.8, ??? 2.1, and ??? 1.1 Ga. The oldest group contains only three samples but is isolated from its closest neighbors by a ??? 600 Ma age gap. Larger age groupings at ??? 2.1 and ??? 1.1 Ga make up about a third and a quarter of the total number of analyses, respectively. The remaining analyses scatter along concordia, and most are younger than 1.6 Ga. The ??? 2.8 and ??? 2.1 Ga ages correspond to periods of crust formation of the Imataca and Trans-Amazonian provinces of the Guyana Shield, respectively, and record intervals of short but intensive continental growth. These ages coincide with ??? 2.9 and ??? 2.1 Ga Nd model ages of sediments from tributaries draining the Archean and Proterozoic provinces of the Guyana Shield, respectively, indicating that the U-Pb ages record the geological history of the crystalline basement of the Orinoco basin. Zircons with ages corresponding to the major orogenies of the North Atlantic continents (the Superior at ??? 2.7 Ga and Hudsonian at 1.7-1.9 Ga) were not found in the Orinoco sample. The age distribution may indicate that South and North America were separated throughout their history. Nd model ages of sediments from the lower Orinoco River and Andean tributaries are ??? 1.9 Ga, broadly within the range displayed by major rivers and dusts. This age does not coincide with known thermal events in the region and reflects mixing of sources with different crust-formation ages. The

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

    Directory of Open Access Journals (Sweden)

    Mohammad Hassan Karimpour

    2013-10-01

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

  16. Reconciliation of the excess 176Hf conundrum in meteorites: Recent disturbances of the Lu-Hf and Sm-Nd isotope systematics

    Science.gov (United States)

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

    2017-09-01

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

  17. Provenance and depositional age of the neoproterozoic volcanometasedimentary sequence in the Santa Terezinha region, Goias based on U-Pb single zircon and Sm-Nd isotope data

    International Nuclear Information System (INIS)

    Dantas, Elton Luiz; Jost, Hardy; Fuck, Reinhardt A.; Pimentel, Marcio Martins; Brod, Jose Affonso

    2001-01-01

    Some of the volcano-sedimentary sequences of the Tocantins Province have been considered to be formed during the evolution of a Neoproterozoic intra oceanic island arc system (Pimentel et al., 2000). However, the interpretation of supra crustal rocks of some areas of the central portions of the Goias Massif, such as the region of Santa Terezinha de Goias, is still controversial. These rocks have been considered either as part of the Archean greenstone belts or as Paleoproterozoic sequences (Ribeiro Filho 1981, Souza and Le Neto 1981, Machado et al.1981, Ribeiro Filho and Lacerda Filho 1985, Biondi and Pidevin 1994, Arantes et al. 1991) rather than an extension of the Neoproterozoic Mara Rosa magmatic arc (Viana et al.1995, Pimentel et al. 1997). An area of about 800 km 2 near the town of Santa Terezinha de Goias was recently mapped on a 1:25.000 scale (Jost et al. 2001). Its northern part consists of Proterozoic supra crustal rocks in tectonic contact with Archean rocks in the south. We present new Sm-Nd and U-Pb zircon data for the supra crustal rocks that crop out in the northern part of the area and discuss their provenance and depositional age (au)

  18. Shrimp and conventional U-Pb age, Sm-Nd isotopic characteristics and tectonic significance of the K-rich Itapuranga suite in Goias, Central Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Pimentel, Marcio M.; Dantas, Elton L.; Fuck, Reinhardt A. [Brasilia Univ., DF (Brazil). Inst. de Geociencias. Lab. de Geocronologia]. E-mail: marcio@unb.br; mmp1103@terra.com.br; Armstrong, Richard A. [Australian National Univ., Canberra (Australia). Research School of Earth Sciences

    2003-03-15

    The Itapuranga alkali granite and Uruana quartz syenite are large K-rich E W-elongated intrusions, in the central part of the Neoproterozoic Brasilia Belt, central Brazil. They are associated with Pireneus lineaments, which cut the regional NNW-SSE structures of the southern part of the belt. SHRIMP and conventional U-Pb data for the Itapuranga and Uruana intrusions indicate crystallization ages of 624 {+-} 10 Ma and 618 {+-} Ma, respectively. Three zircon cores from the Itapuranga granite yielded U-Pb ages between 1.79 and 1.49 Ga. Sm-Nd T{sub DM} ages for both intrusions are 1.44 Ga and epsilon{sub Nd}(T) values are -5.1 and -5.7, suggesting the input of material derived from older (Paleo- to Mesoproterozoic) sialic crust in the origin of the parental magmas. Magma mixing structures indicate co-existence of mafic and felsic end-members. The felsic end-member of the intrusions is dominantly represented by crust-derived melts, formed in response to the invasion of Paleo/Mesoproterozoic sialic crust by alkali-rich mafic magmas at ca. 620 Ma. These intrusions are roughly contemporaneous with, or perhaps slightly younger than, the peak of regional metamorphism in the southern Brasilia Belt. Their emplacement along the Pireneus lineament suggest a syn-tectonic origin for them, most probably in transtensional settings along these faults. (author)

  19. Shrimp and conventional U-Pb age, Sm-Nd isotopic characteristics and tectonic significance of the K-rich Itapuranga suite in Goias, Central Brazil

    International Nuclear Information System (INIS)

    Pimentel, Marcio M.; Dantas, Elton L.; Fuck, Reinhardt A.; Armstrong, Richard A.

    2003-01-01

    The Itapuranga alkali granite and Uruana quartz syenite are large K-rich E W-elongated intrusions, in the central part of the Neoproterozoic Brasilia Belt, central Brazil. They are associated with Pireneus lineaments, which cut the regional NNW-SSE structures of the southern part of the belt. SHRIMP and conventional U-Pb data for the Itapuranga and Uruana intrusions indicate crystallization ages of 624 ± 10 Ma and 618 ± Ma, respectively. Three zircon cores from the Itapuranga granite yielded U-Pb ages between 1.79 and 1.49 Ga. Sm-Nd T DM ages for both intrusions are 1.44 Ga and epsilon Nd (T) values are -5.1 and -5.7, suggesting the input of material derived from older (Paleo- to Mesoproterozoic) sialic crust in the origin of the parental magmas. Magma mixing structures indicate co-existence of mafic and felsic end-members. The felsic end-member of the intrusions is dominantly represented by crust-derived melts, formed in response to the invasion of Paleo/Mesoproterozoic sialic crust by alkali-rich mafic magmas at ca. 620 Ma. These intrusions are roughly contemporaneous with, or perhaps slightly younger than, the peak of regional metamorphism in the southern Brasilia Belt. Their emplacement along the Pireneus lineament suggest a syn-tectonic origin for them, most probably in transtensional settings along these faults. (author)

  20. The Hadean upper mantle conundrum: evidence for source depletion and enrichment from Sm-Nd, Re-Os, and Pb isotopic compositions in 3.71 Gy boninite-like metabasalts from the Isua Supracrustal Belt, Greenland

    Science.gov (United States)

    Frei, Robert; Polat, Ali; Meibom, Anders

    2004-04-01

    Here we present Sm-Nd, Re-Os, and Pb isotopic data of carefully screened, least altered samples of boninite-like metabasalts from the Isua Supracrustal Belt (ISB, W Greenland)that characterize their mantle source at the time of their formation. The principal observations of this study are that by 3.7-3.8 Ga melt source regions existed in the upper mantle with complicated enrichment/depletion histories. Sm-Nd isotopic data define a correlation line with a slope corresponding to an age of 3.69 ± 0.18 Gy and an initial εNd value of +2.0 ± 4.7. This Sm-Nd age is consistent with indirect (but more precise) U-Pb geochronological estimates for their formation between 3.69-3.71 Ga. Relying on the maximum formation age of 3.71 Gy defined by the external age constraints, we calculate an average εNd [T = 3.71 Ga] value of +2.2 ± 0.9 (n = 18, 1σ) for these samples, which is indicative of a strongly depleted mantle source. This is consistent with the high Os concentrations, falling in the range between 1.9-3.4 ppb, which is similar to the estimated Os concentration for the primitive upper mantle. Re-Os isotopic data (excluding three outliers) yield an isochron defining an age of 3.76 ± 0.09 Gy (with an initial γOs value of 3.9 ± 1.2), within error consistent with the Sm-Nd age and the indirect U-Pb age estimates. An average initial γOs [T = 3.71 Ga] value of + 4.4 ± 1.2 (n = 8; 2σ) is indicative of enrichment of their source region during, or prior to, its melting. Thus, this study provides the first observation of an early Archean upper mantle domain with a distinctly radiogenic Os isotopic signature. This requires a mixing component characterized by time-integrated suprachondritic Re/Os evolution and a Os concentration high enough to strongly affect the Os budget of the mantle source; modern sediments, recycled basaltic crust, or the outer core do not constitute suitable candidates. At this point, the nature of the mantle or crustal component responsible for the

  1. Regional Sm-Nd isotopic study of the central part of the Brasilia belt, Goias: implications of the age and origin of the Anapolis-Itaucu granulitic complex and metasedimentary rocks of the Araxa Group, central region, Brazil

    International Nuclear Information System (INIS)

    Pimentel, Marcio Martins; Fuck, Reinhardt Adolfo; Fischel, Danielle Piuzanna

    1999-01-01

    In the central part of the Brasilia Belt, central Brazil, a high grade terrain, the Anapolis-Itaucu Complex, is exposed within the metasedimentary rocks of the Araxa Group. The Anapolis-Itaucu Complex in Goias represents a complex association of high-grade rocks including mafic-ultramafic bodies, charnockites, enderbites, as well as aluminous granulites of sedimentary origin, associated with marbles and quartzites, Narrow volcano-sedimentary belts formed mainly by amphibolites and micashists are also recognized within the complex. This high-grade terrain has been traditionally interpreted as part of the old (Archaean/Paleoproterozoic) sialic basement to the Neo- or mesoproterozoic sediments of the Araxa Group, Brasilia Belt. The granulites and metasediments of the Araxa Group are intruded by a large number of granite intrusions, many of which slow peraluminous character. Sm-Nd isotopic analyses for the garnet-and sillimanite-bearing aluminous granulites indicate T DM model ages between ca. 1.3 and 1.6 Ga. These values represent the upper limit for the age of the protoliths of the granulites, demonstrating that they are (at least in part) younger than suggested in previous models. The intrusive granites have a Sm-Nd isotopic pattern which is not much different from that observed for the felsic granulites, with T DM model ages ranging in the interval between ca. 1.37 and 1.85 Ga. The isotopic compositions of the granitic and granulitic rocks investigated are also similar to those determined for metasediments of the internal zone of the Brasilia Belt (Araxa Group) in central-southern Goias. These metasediments show Nd model ages between ca. 1.2 and 2.2 Ga. The preliminary isotopic data presented are consistent with a model in which the voluminous granitic magmatism identified in the Anapolis-Itaucu Complex and adjacent areas is Neoproterozoic in age, being the result of re-melting of the older sialic crust. The peraluminous nature of many of these granites

  2. Re-Os, Sm-Nd, U-Pb, and stepwise lead leaching isotope systematics in shear-zone hosted gold mineralization: genetic tracing and age constraints of crustal hydrothermal activity

    Science.gov (United States)

    Frei, R.; Nägler, Th. F.; Schönberg, R.; Kramers, J. D.

    1998-06-01

    A combined Re-Os, Sm-Nd, U-Pb, and stepwise Pb leaching (PbSL) isotope study of hydrothermal (Mo-W)-bearing minerals and base metal sulfides from two adjacent shear zone hosted gold deposits (RAN, Kimberley) in the Harare-Shamva greenstone belt (Zimbabwe) constrain the timing of the mineralizing events to two periods. During an initial Late Archean event (2.60 Ga) a first molybdenite-scheelite bearing paragenesis was deposited in both shear zone systems, followed by a local reactivation of the shear systems during an Early Proterozoic (1.96 Ga) tectono-thermal overprint, during which base metal sulfides and most of the gold was (re-)deposited. While PbSL has revealed an open-system behavior of the U-Pb systematics in molybdenite and wolframite from the RAN mine, initial Archean Re-Os ages are still preserved implying that this system in these minerals was more resistant to the overprint. A similar retentivity could be shown for the Sm-Nd system in scheelite and powellite associated with the above ore minerals. Re-Os isotopic data from the Proterozoic mineralization in the Kimberley mine point to a recent gain of Re, most pronouncedly affecting Fe-rich sulfides such as pyrrhotite. A significant Re-loss in powellitic scheelite (an alteration phase of molybdenite-bearing scheelite), coupled with a marked loss of U in W-Mo ore minerals, complements the observation of a major Re uptake in Fe-sulfides during oxidizing conditions in a weathering environment. Pyrrhotite under these conditions behaves as an efficient Re-sink. Lead isotope signatures from PbSL residues of molybdenite, powellite, and quartz indicate a continental crustal source and/or contamination for the mineralizing fluid by interaction of the fluids with older sedimentary material as represented by the direct host country rocks. Our investigation reveals the potential of the Re-Os isotopic system applied to crustal hydrothermal ore minerals for genetic tracing and dating purposes. The simplified chemical

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

    International Nuclear Information System (INIS)

    Guerrot, C.

    1989-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2004-10-15

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

  5. Growth of the continental crust: constraints from radiogenic isotope geochemistry

    International Nuclear Information System (INIS)

    Taylor, P.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

  6. Rb-Sr, Sm-Nd and Lu-Hf isotope systematics of the lunar Mg-suite: the age of the lunar crust and its relation to the time of Moon formation.

    Science.gov (United States)

    Carlson, Richard W; Borg, Lars E; Gaffney, Amy M; Boyet, Maud

    2014-09-13

    New Rb-Sr, (146,147)Sm-(142,143)Nd and Lu-Hf isotopic analyses of Mg-suite lunar crustal rocks 67667, 76335, 77215 and 78238, including an internal isochron for norite 77215, were undertaken to better define the time and duration of lunar crust formation and the history of the source materials of the Mg-suite. Isochron ages determined in this study for 77215 are: Rb-Sr=4450±270 Ma, (147)Sm-(143)Nd=4283±23 Ma and Lu-Hf=4421±68 Ma. The data define an initial (146)Sm/(144)Sm ratio of 0.00193±0.00092 corresponding to ages between 4348 and 4413 Ma depending on the half-life and initial abundance used for (146)Sm. The initial Nd and Hf isotopic compositions of all samples indicate a source region with slight enrichment in the incompatible elements in accord with previous suggestions that the Mg-suite crustal rocks contain a component of KREEP. The Sm/Nd-(142)Nd/(144)Nd correlation shown by both ferroan anorthosite and Mg-suite rocks is coincident with the trend defined by mare and KREEP basalts, the slope of which corresponds to ages between 4.35 and 4.45 Ga. These data, along with similar ages for various early Earth differentiation events, are in accord with the model of lunar formation via giant impact into Earth at ca 4.4 Ga. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

  7. U-Pb zircon geochronology and Sm-Nd-Pb isotopic constraint for precambrian plutonic rocks in the northeastern part of Ryeongnam massif, Korea

    International Nuclear Information System (INIS)

    Chang, Ho-Wan

    2003-01-01

    The Ryeongnam massif is composed of Precambrian gneisses, Paleozoic and Mesozoic sedimentary rocks and extensive Triassic-Jurassic plutonic rocks of felsic to mafic composition. In the northeast Ryeongnam massif, the oldest rocks belong to the Sobaegsan gneiss complex, which is composed of orthogneisses, paragneisses and mafic plutonic rocks. U-Pb zircon ages for the felsic and mafic intrusive bodies within the Sobaegsan gneiss complex are: the Icheon granite gneiss, 2357±43 and 2342±47 Ma; the Buncheon granite gneiss, 1963±5 Ma; the Pyeonghae granite gneiss, 1936±21 Ma; the Ogbang amphibolite, 1918±10 Ma; the Imwon leucogranite gneiss, 1826±20 Ma. The Hyeondong biotite schist, which is intruded by the Buncheon granite gneiss and the Ogbang amphibolite, yielded an age of 2271±44 Ma. The Nd-Sm-Pb isotopic data indicate that the felsic plutonic rocks are derived from an older Archean crust. The Nd T DM ages are Archean, and the εNd values are negative for the felsic rocks and positive for the amphibolite. Common Pb isotope compositions also indicate a crustal source for the felsic intrusives. The U-Pb ages of Precambrian rocks of the Ryeongnam massifs are similar to those in the Gyeonggi massif, and may have a similar crustal evolutionary history. The Precambrian rocks of South Korea could be related either to the North China block or to the South China block, as the isotope ages and patterns are not unique to either block. Similarly, a geologic correlation with Japan, although possible, is tenuous at present. (author)

  8. Rb-Sr and Sm-Nd chronology and genealogy of mare basalts from the Sea of Tranquility

    Science.gov (United States)

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

    1977-01-01

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

  9. Mixed Messages from Garnet Lu-Hf and Sm-Nd Geochronology

    Science.gov (United States)

    Vervoort, J. D.; Wang, D.; Johnson, T. A.

    2017-12-01

    Garnet geochronology provides important information on the timing and conditions of metamorphism. As a major indicator mineral formed during metamorphism, its direct dating can not only help establish the timing of metamorphism, provide the "t" for P-T-t paths, but also, if the dated garnet can be placed in a textural context, can provide information on the timing of deformational features. With advances in chemistry and mass spectrometry, garnet Lu-Hf and Sm-Nd geochronology has become an important geochronological tool and we can now reliably (if not routinely) date a wide variety of garnet compositions formed under diverse conditions. In the course of dating a variety of lithologies using both Lu-Hf and Sm-Nd isotope systems, however, some intriguing results have emerged. Although there are many examples where the Lu-Hf and Sm-Nd systems give the same date within uncertainty, there are also many cases where these systems yield significantly different dates, and the differences between these dates can be considerable—many 10's of Ma of and even 100's of Ma. For example, in garnet-bearing Mesoproterozoic gneisses from across the Blue Ridge Province in Virginia, both Lu-Hf and Sm-Nd analyses (determined on the same solutions) define narrow time spans, but with the Sm-Nd dates systematically younger (for orthogneisses Lu-Hf dates are 1032 to 1019 Ma whereas Sm-Nd dates are 965 to 949 Ma—a difference of 67 to 80 Ma). There are many other examples of systematically younger Sm-Nd garnet dates in both the literature and with our ongoing research. Potential explanations for these differences include: 1) strong partitioning of Lu into garnet during growth yielding ages weighted toward the beginning of growth; 2) faster Lu diffusion from high Lu regions after garnet formation, potentially leading to isochron rotation and anomalously old Lu-Hf dates; and 3) differences in closure temperatures of the two isotope systems. We will review several examples of divergent Lu

  10. SM-ND Age and REE Systematics of Larkman Nunatek 06319: Closed System Fractional Crystallization of a Shergottite Magma

    Science.gov (United States)

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

    2010-01-01

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

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

    Directory of Open Access Journals (Sweden)

    Somayeh Samiee

    2016-12-01

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

  12. Isotopic geochemistry at Wairakei

    International Nuclear Information System (INIS)

    Stewart, M.K.

    1985-12-01

    Deuterium measurements on geothermal water at Wairakei are consistent with the water being derived from rainfall which has percolated down from the surface. The oxygen-18 content, however, is enriched compared to average rainfall. This 18 O shift is due to isotopic exchange between water and rock at greater-than-explored depths. The magnitude of the shift implied that the mass ration (W/R) of water that has passed through the system (W) to the rock it has exchanged with (R) is about 1 assuming open (i.e. single-pass) conditions. (The ratio is about 2 if it has been a closed system, but this is thought to be less likely). The residence time of water underground cannot be determined from tritium and carbon-14 measurements at present, but arguments based on the argon isotope and deuterium contents suggest mean residence times of a few tens of thousand years. The water-rock ratio and large natural outflow of thermal water prior to exploitation are consistent with this. The 18 O content of the water has changed only slightly, and the D content not at all, during exploitation at Wairakei (measurements from 1963, 1974 and 1981). An initial tendency for the 18 O to increase because of steam loss (also shown more clearly by chloride), has been followed by decrease of 18 O (and chloride) because of dilution with infiltrating near-surface water in parts of the field

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

    Science.gov (United States)

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

    2017-08-01

    The origin of the incompatible trace element (ITE) characteristics of enriched shergottites has been critical for examining two contradicting scenarios to explain how these Martian meteorites form. The first scenario is that it reflects ITE enrichment in an early-formed mantle reservoir whereas the second scenario attributes it to assimilation of ancient Martian crust (∼4-4.5 Ga) by ITE-depleted magmas. Strongly differentiated shergottite magmas may yield added constraints for determining which scenario can best explain this signature in enriched shergottites. The meteorite Northwest Africa (NWA) 856 is a basaltic shergottite that, unlike many enriched shergottites, lacks olivine and has undergone extensive differentiation from more primitive parent magma. In similarity to other basaltic shergottites, NWA 856 is comprised primarily of compositionally zoned clinopyroxenes (45% pigeonite and 23% augite), maskelynite (23%) and accessory minerals such as ulvöspinel, merrillite, Cl-apatite, ilmenite, pyrrhotite, baddeleyite and silica polymorph. The CI-chondrite normalized rare earth element (REE) abundance patterns for its maskelynite, phosphates, and its whole rock are flat with corresponding light-REE depletions in clinopyroxenes. The 87Rb-87Sr and 147Sm-143Nd internal isochron ages are 162 ± 14 (all errors are ±2σ) Ma and 162.7 ± 5.5 Ma, respectively, with an initial εNdI = -6.6 ± 0.2. The Rb-Sr isotope systematics are affected by terrestrial alteration resulting in larger scatter and a less precise internal isochron age. The whole rock composition is used in MELTS simulations to model equilibrium and fractional crystallization sequences to compare with the crystallization sequence from textural observations and to the mineral compositions. These models constrain the depth of initial crystallization to a pressure range of 0.4-0.5 GPa (equivalent to 34-42 km) in anhydrous conditions at the Fayalite-Magnetite-Quartz buffer, and consistently reproduce the

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

    Science.gov (United States)

    Steshenko, Ekaterina; Bayanova, Tamara; Serov, Pavel

    2015-04-01

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

  15. Radiogenic isotope geochemistry of sedimentary and aquatic systems

    International Nuclear Information System (INIS)

    Stille, P.; Shields, G.

    1997-01-01

    The following topics are discussed: Basic principles of isotopic geochemistry; weathering; isotopic geochemistry of river water; isotopic geochemistry in the environment; isotopic composition of seawater past and present (Sr, Nd, Pb, Os, Ce); isotope geochemistry of detrital and authigenic clay minerals in marine sediemnts (Rb-Sr, K-Ar, O); the Sm-N isotope system in detrital and authigenic argillaceous sediments. (SR), provided they are of exceptional interest and focused on a single topic. (orig./SR)

  16. Radiogenic isotope geochemistry of sedimentary and aquatic systems

    Energy Technology Data Exchange (ETDEWEB)

    Stille, P.; Shields, G. [Centre National de la Recherche Scientifique (CNRS), 67 - Strasbourg (France). Centre de Sedimentologie et Geochimie de la Surface

    1997-12-31

    The following topics are discussed: Basic principles of isotopic geochemistry; weathering; isotopic geochemistry of river water; isotopic geochemistry in the environment; isotopic composition of seawater past and present (Sr, Nd, Pb, Os, Ce); isotope geochemistry of detrital and authigenic clay minerals in marine sediemnts (Rb-Sr, K-Ar, O); the Sm-N isotope system in detrital and authigenic argillaceous sediments. (SR), provided they are of exceptional interest and focused on a single topic. (orig./SR)

  17. Rb-Sr And Sm-Nd Ages, and Petrogenesis of Depleted Shergottite Northwest Africa 5990

    Science.gov (United States)

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

    2011-01-01

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

  18. On models in the geochemistry of isotopes

    International Nuclear Information System (INIS)

    Wetzel, K.

    1978-01-01

    Models are playing an increasing role in the deepening of our understanding of the laws of occurrence of stable and radioactive isotopes in nature. The properties of concrete global and regional models of the geochemistry of isotopes are derived from a general model characterizing the cycling of chemical elements and their isotopes in nature. The importance of global models as well as the relationships between global and regional models are considered. The introduction of a parameter describing the velocity of both mass and isotope transfer, taking into consideration the global resources, renders possible the linkage of global models with regional ones. (author)

  19. First data on Sm-Nd systematization of Khanka Massif metamorphic rocks, Primor'e

    International Nuclear Information System (INIS)

    Mishkin, M.A.; Khanchuk, A.I.; Zhuravlev, D.Z.; Lavrik, S.N.

    2000-01-01

    The age of the metamorphic rocks of the Khanka massif, Primor'e, is determined through the method of the Sm-Nd isotopic dating. The results of the isotopic studies on the amphibolites of the Nakhimov suite of the Khanka massif indicated that the rocks of this suite are not older than 1.7 billion years. The obtained age corresponds to the time of the amphibolite protolith formation, the source whereof is the moderately depleted mantle. The isotopic age of the amphibole and plagioclase mineral fractions constitutes 733 ± 25 mln years, which reflects the time of the Nakhimov suite rocks metamorphism [ru

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

    Directory of Open Access Journals (Sweden)

    Flávio Robson Dias Semblano

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

  1. Shrimp and conventional U-Pb age, Sm-Nd isotopic characteristics and tectonic significance of the K-rich Itapuranga suite in Goiás, Central Brazil

    Directory of Open Access Journals (Sweden)

    MÁRCIO M. PIMENTEL

    2003-03-01

    Full Text Available The Itapuranga alkali granite and Uruana quartz syenite are large K-rich EW-elongated intrusions, in the central part of the Neoproterozoic Brasília Belt, central Brazil. They are associated with Pireneus lineaments, which cut the regional NNW-SSE structures of the southern part of the belt. SHRIMP and conventional U-Pb data for the Itapuranga and Uruana intrusions indicate crystallization ages of 624 ± 10 Ma and 618 ± 4 Ma, respectively. Three zircon cores from the Itapuranga granite yielded U-Pb ages between 1.79 and 1.49 Ga. Sm-Nd T DM ages for both intrusions are 1.44 Ga and epsilonNd(T values are -5.1 and -5.7, suggesting the input of material derived from older (Paleo- to Mesoproterozoic sialic crust in the origin of the parental magmas. Magma mixing structures indicate co-existence of mafic and felsic end-members. The felsic end-member of the intrusions is dominantly represented by crust-derived melts, formed in response to the invasion of Paleo/Mesoproterozoic sialic crust by alkali-rich mafic magmas at ca. 620 Ma. These intrusions are roughly contemporaneous with, or perhaps slightly younger than, the peak of regional metamorphism in the southern Brasília Belt. Their emplacement along the Pireneus lineament suggest a syn-tectonic origin for them, most probably in transtensional settings along these faults.O alcali-granito de Itapuranga e o quartzo-sienito de Uruana são corpos alongados na direção E-W na porção central da Faixa Brasília. Eles são associados com o lineamento dos Pireneus, que cortam as estruturas regionais NNW da faixa. Dados U-Pb (SHRIMP e convencional para as intrusões de Itapuranga e Uruana indicaram idades de 624 ± 10 Ma e 618 ± 4 Ma, respectivamente. Núcleos de três cristais de zircão do granito Itapuranga têm idades entre 1.79 e 1.49 Ga. Idades modelo Sm-Nd são de 1.44 Ga e valores de épsilonNd(T são -5.1 e -5.7, indicando participação de crosta siálica mais antiga (Paleo- a Mesoproteroz

  2. Handbook of environmental isotope geochemistry

    Energy Technology Data Exchange (ETDEWEB)

    Baskaran, Mark (ed.) [Wayne State Univ., Detroit, MI (United States). Dept. Geology

    2011-07-01

    Applications of radioactive and stable isotopes have revolutionized our understanding of the Earth and near-earth surface processes. The utility of the isotopes are ever-increasing and our sole focus is to bring out the applications of these isotopes as tracers and chronometers to a wider audience so that they can be used as powerful tools to solve environmental problems. New developments in this field remain mostly in peer-reviewed journal articles and hence our goal is to synthesize these findings for easy reference for students, faculty, regulators in governmental and non-governmental agencies, and environmental companies. While this volume maintains its rigor in terms of its depth of knowledge and quantitative information, it contains the breadth needed for wide variety problems and applications in the environmental sciences. This volume presents all of the newer and older applications of isotopes pertaining to the environmental problems in one place that is readily accessible to readers. This book not only has the depth and rigor that is needed for academia, but it has the breadth and case studies to illustrate the utility of the isotopes in a wide variety of environments (atmosphere, oceans, lakes, rivers and streams, terrestrial environments, and sub-surface environments) and serves a large audience, from students and researchers, regulators in federal, state and local governments, and environmental companies. (orig.)

  3. Sm-Nd age of ultrabasite-basite massifs of east part of Baikal-Mujya ophiolite belt

    International Nuclear Information System (INIS)

    Izokh, A.Eh.; Gibsher, A.S.; Zhuravlev, D.Z.; Balykin, P.A.

    1998-01-01

    Two stratified ultrabasite-basite massifs of the Urals mountains were selected for isotope-geochemical studies. The intrusives, related to plutonic members of the island-arc associations, were used for dating. The Sm-Nd method indicated that one more belt, namely the Vend belt, is taking shape in the Baikal-Mujya tectonic collage alongside with the later Riphean (pre-Baikal) episubconduction belt of stratified intrusives [ru

  4. Pb-Pb age and Rb-Sr and Sm-Nd isotope signature of paleoproterozoic syenitic plutonism in the south of Salvador-Curaca mobile belt: Sao Felix Syenitic Massif, Bahia-Brazil

    International Nuclear Information System (INIS)

    Rosa, Maria de Lourdes da Silva; Conceicao, Herbet; Leal, Luiz Rogerio Bastos

    2001-01-01

    The Sao Felix Syenitic Massif (MSSF) has a tabular shape with about 32 km 2 that represents the south expression of the aligned syenitic plutonism, which occur in the middle part of Salvador-Curaca mobile belt (CMSC). Single zircon dating by stepwise Pb evaporation methodology yields an age of 2098 ± 1 Ma to SFSM. This data correlate the emplacement of the SFSM with the late stages of SCMB stabilization. This massif is isotopically characterized by negative epsilon neodymium values (-1.45 to -2.89) and low initial strontium ratio (0.701 to 0.704). SFSM isotopic signature is similar to the ones displayed by the others syenites from the belt and reflects an enriched source which should be related to a metasomatic enriched mantle. (author)

  5. Application of environmental isotope tracing technology to geothermal geochemistry

    International Nuclear Information System (INIS)

    Shang Yingnan

    2006-01-01

    This paper reviews the recent application and development of environmental isotope tracing technology to geothermal geochemistry in the following aspects: gas isotopes (He, C) tracing of warm springs; H, O isotope tracing on the origin and cause of geothermal water, environmental isotope dating of geothermal water, and the advantage of excess parameter of deuterium (d) in geothermal research. The author also suggests that isotope method should combine with other geological methods to expand its advantage. (authors)

  6. Dating of the Francevillian sedimentary series and mineralogic and isotopic (Sm, Nd, Rb, Sr, K, Ar, U, O and C) characterization of the gangue of the reactors 10 and 13. Preliminary report

    International Nuclear Information System (INIS)

    Gautier-Lafaye, F.; Stille, P.; Bros, R.; Taieb, R.

    1993-01-01

    This paper summarizes the various ages reported for the diagenetic events in the Francevillian sedimentary series (Precambrian era) and the fission reactors of Oklo. Obviously, differences exist between the ages obtained on the silicate minerals and the ages obtained on the Uranium ores and on the reactors. Clay minerals which crystallized during the fission reactions yield younger ages than the reactors themselves. Similarly, the diagenetic clays (1870 Ma) show younger ages than the Uranium ores (2000 Ma). This is in contrast to mineralogical and field evidence indicating that Uranium mineralization occurred during diagenesis of the Francevillian sediments. These antithetical results give rise to several questions. Does the age obtained on the diagenetic clays date a late thermal event or does the age of the Uranium mineralization reflect a multistage U-Pb history. This work tries to bring answers with the help of new isotopic analysis and studies mineralogy of the gangue of reactors and isotopic compositions in Uranium ores. 8 refs., 4 figs

  7. Rb-Sr and Sm-Nd isotopic compositions and Petrogenesis of ore-related intrusive rocks of gold-rich porphyry copper Maherabad prospect area (North of Hanich), east of Iran

    International Nuclear Information System (INIS)

    Malekzadeh Shafaroudi, A.; Karimpour, M. H.; Mazaheri, S. A.

    2010-01-01

    The Maherabad gold-rich porphyry copper prospect area is located in the eastern part of Lut block, east of Iran. This is the first porphyry Cu-Au prospecting area which is discovered in eastern Iran. Fifteen mineralization-related intrusive rocks range (Middle Eocene 39 Ma) in composition from diorite to monzonite have been distinguished. Monzonitic porphyries had major role in Cu-Au mineralization. The ore bearing porphyries are I-type, meta luminous, high-Kcalc-alkaline to shoshonite intrusive rocks which were formed in island arc setting. These rocks are characterized by average of SiO 2 > 59 wt %, Al 2 O 3 > 15 wt %, MgO 2 O> 3 wt %, Sr> 870 ppm, Y 55, moderate Light rare earth elements, relatively low heavy rare earth elements and enrichment LILE (Sr, Cs, Rb, K and Ba) relative to HFSE (Nb, Ta, Ti, Hf and Zr). They are chemically similar to some adakites, but their chemical signatures differ in some ways from normal adakites, including higher K 2 O contents and K 2 O/Na 2 O ratios and lower Mg, (La/Yb) N , (Ce/Yb) N and εNd in Maherabad rocks. Maherabad intrusive rocks are the first K-rich adakites that can be related with subduction zone. Partial melting of mantle hybridized by hydrous, silica-rich slab-derived melts or/and input of enriched mantle-derived ultra-potassic magmas during or prior to the formation and migration of adakitic melts could be explain their high K 2 O contents and K 2 O/Na 2r atios. Low Mg values and relatively low MgO, Cr and Ni contents imply limited interaction between adakite-like magma and mantle wedge peridotite. The initial 87 Sr/ 86 Sr and ( 143 Nd/ 144 Nd)i was recalculated to an age of 39 Ma (unpublished data). Initial 87 Sr/ 86 Sr ratios for hornblende monzonite porphyry are 0.7047-0.7048. The ( 143 Nd/ 144 Nd)i isotope composition are 0.512694-0.512713. Initial εNd isotope values 1.45-1.81. These values could be considered as representative of oceanic slab-derived magmas. Source modeling indicates that high-degree of

  8. Stable isotope geochemistry. 3. rev. and enl. ed.

    International Nuclear Information System (INIS)

    Hoefs, J.

    1987-01-01

    Stable Isotope Geochemistry is an authoritative book comprising theoretical and experimental principles; surveying important fractionation mechanisms affecting the most important elements; discussing the natural variations of geologically important reservoirs. This updated 3rd edition, with a completely rewritten and extended main part, contains two new chapters on stable isotope composition of mantle material and on changes of the ocean during the geological past. (orig.)

  9. The geochemistry of stable chlorine and bromine isotopes

    Energy Technology Data Exchange (ETDEWEB)

    Eggenkamp, Hans [Onderzock and Beleving, Bussum (Netherlands)

    2014-11-01

    First book solely dedicated to the geochemistry of chlorine and bromine isotopes. Detailed description of analytical techniques, including their advantages and disadvantages. Indication of research fields where measurement of these isotopes is especially useful. This book provides detailed information on the history, analysis and applications of chlorine and bromine isotope geochemistry. Chlorine and bromine are geochemically unique as they prefer to exist as single charged negative ions. For this reason isotope fractionation reflects mostly processes that are not related to changes in the redox state and this fractionation is generally modest. The book will describe the processes that are most easily detected using these isotopes. Also isotope variations, and processes that cause them, measured in oxidised species such as perchlorates and in organic molecules will be described in this book.

  10. Stable isotope geochemistry : definitions, terminology, measurement and some applications

    International Nuclear Information System (INIS)

    Faure, K.

    2005-01-01

    In 1936, Alfred Nier produced the first precise measurement of isotope abundance ratios and his design still remains the basis of stable isotope mass spectrometry. With this gift from the physicists for routine measurement of isotope ratios, earth scientists began to explore the natural variations of isotopes. Thus began a new era in geoscience research with the hydrological cycle and marine palaeoclimatic research being the first topics to be investigated. Stable isotope measurements have been applied to many fundamental problems in geochemistry, petrology and paleoclimatology, as well as related fields in archaeology, anthropology, physical chemistry, biology and forensic sciences. (author). 52 refs., 11 figs., 2 tabs

  11. Evaluation of the effects of alteration and leaching on Sm Nd and Lu Hf systematics in submarine mafic rocks

    Science.gov (United States)

    Thompson, Patricia M. E.; Kempton, Pamela D.; Kerr, Andrew C.

    2008-08-01

    Nd and Hf isotope systematics of oceanic basaltic rocks are often assumed to be largely immune to the effects of hydrothermal alteration. We have tested this assumption by comparing Nd and Hf isotope data for acid-leached Cretaceous oceanic basalts from Gorgona and DSDP Leg 15 with unleached data on the same rocks. Hf isotope values and Lu/Hf ratios are relatively unaffected by leaching, but 143Nd/ 144Nd values of leached samples are significantly higher than those of unleached fractions of the same sample in most cases. Furthermore, the Sm/Nd ratios of the majority of leached samples are 10-40% greater than those of unleached samples. X-ray diffraction studies indicate that selective removal of secondary minerals, such as smectite, during the acid leaching process is responsible for the fractionation of Sm/Nd ratios. These results have implications for interpretation of the Hf-Nd isotope systematics of ancient submarine rocks (older than ~ 50 Ma), as (1) the age-corrected 143Nd/ 144Nd ratio may not be representative of the primary magmatic signature and (2) the uncertainty of the age-corrected ɛNd value may exceed the assumed analytical precision.

  12. Stable isotope geochemistry : definitions, terminology, measurement and some applications

    International Nuclear Information System (INIS)

    Faure, K.

    2004-01-01

    Stable isotope measurements have been applied to many fundamental problems in geochemistry, petrology, and paleoclimatology, as well as related fields in archaeology, anthropology, physical chemistry, biology and forensic sciences. These applications can be broadly classified into four main types: thermometry, tracers, reaction mechanisms and chemostratigraphy. 52 refs., 11 figs., 2 tabs

  13. REE, Sm-Nd and U-Pb zircon study of eclogites from the Alpine External Massifs (Western Alps): Evidence for crustal contamination

    International Nuclear Information System (INIS)

    Paquette, J.L.; Eidgenoessische Technische Hochschule, Zurich; Menot, R.P.; Peucat, J.J.

    1989-01-01

    A geochemical and geochronological study of the Alpine External Crystalline Massifs (AECM) of Aiguilles Rouges, Belledonne and Argentera was undertaken in order to constrain the geodynamic evolution of this segment of the Variscan foldbelt. Another aim of the study is to characterize the behaviour of isotopic markers, in particular the U-Pb zircon system, under high-grade metamorphic conditions. The whole-rock geochemistry of eclogites and amphibolites was investigated using major and trace element (including the REE) analytical techniques; isotopic studies were performed by application of the Sm-Nd whole-rock and U-Pb zircon methods. In terms of regional geological history, the early development of metamorphic and magmatic activity in the AECM is typical of the extensional tectonic regime observed throughout the Variscan foldbelt during the Cambro-Ordovician (i.e. basic magmatism dated at 475-450 Ma). The composition of the metabasic rocks is closely similar to tholeiites emplaced into thinned continental crust which are generally associated with the initial stages of oceanic rifting. The source regions for these metabasics are characterized by initial ε Nd values between +6 and +8, suggesting depleted mantle sources influenced by a weak crustal component and/or the existence of a metasomatised lithosphere. The multi-stage eclogite-facies metamorphism is dated at 425-395 Ma (i.e. Silurian). An application of the U-Pb method, associated with the artificial abrasion of zircon grains, has led to the recognition of a weak crustal contamination in the metabasic protoliths. This is implied by the Archaean and Lower Proterozoic upper intercepts on Concordia - devoid of geological significance - which reflect the presence of a pre-existing basement to the AECM. (orig./WL)

  14. Sm-Nd and Ar-Ar Studies of DHO 908 and 489: Implications for Lunar Crustal History

    Science.gov (United States)

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

    2011-01-01

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

  15. Strontium isotopic geochemistry of intrusive rocks, Puerto Rico, Greater Antilles

    International Nuclear Information System (INIS)

    Jones, L.M.; Kesler, S.E.

    1980-01-01

    The strontium isotope geochemistry is given for three Puerto Rican intrusive rocks: the granodioritic Morovis and San Lorenzo plutons and the Rio Blanco stock of quartz dioritic composition. The average calculated initial 87 Sr/ 86 Sr ratios are 0.70370, 0.70355 and 0.70408, respectively. In addition, the San Lorenzo data establish a whole-rock isochron of 71 +- 2 m.y., which agrees with the previously reported K-Ar age of 73 m.y. Similarity of most of the intrusive rocks in the Greater Antilles with respect to their strontium isotopic geochemistry regardless of their major element composition indicates that intrusive magmas with a wide range of composition can be derived from a single source material. The most likely source material, in view of the available isotopic data, is the mantle wedge overlying the subduction zone. (orig.)

  16. Sm-Nd study of Precambrian crustal development in the Prieska-Copperton region, Cape Province

    International Nuclear Information System (INIS)

    Cornell, D.H.; Hawkesworth, C.J.; Van Calsteren, P.; Scott, W.D.

    1986-01-01

    Samples representing the major lithological units between Copperton and Prieskapoort in the Cape Province have been analysed for Sm and Nd concentrations and Nd isotopic compositions. The ∼ 3000 Ma Marydale Group is shown to extend without major chronostratigraphic breaks from slightly metamorphosed basalt and arkose west of the Doornberg Fault at Prieskapoort to highly metamorphosed gneisses east of the Brakbos Fault at Copperton. Evidence is found of plutonic alkaline igneous activity, and possibly volcanism, which occurred during the ∼ 1 900 Ma Kheis tectogenesis. Early Proterozoic material apparently dominates the lower crustal region of the eastern Namaqua Province sampled by kimberlites. Sm-Nd data for the Copperton Formation of the Namaqua Province places an upper limit of ∼ 1 514 Ma and lower limit of ∼ 1 350 Ma on its origin. Omission of basaltic samples from the isochron regression yields the younger age, which is more easily reconciled with Pb isotope data. Volcanism is envisaged from a mantle source with a history of light rare-earth depletion relative to the chondritic earth model. By analogy with modern tectonic environments, the Copperton Formation probably formed in an active continental margin or island arc environment

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  18. Geochemistry of the stable isotopes of silicon

    Energy Technology Data Exchange (ETDEWEB)

    Douthitt, C B [California Inst. of Tech., Pasadena (USA). Div. of Geological and Planetary Sciences

    1982-08-01

    One hundred thirty two new measurements of the relative abundances of the stable isotopes of silicon in terrestrial materials are presented. The total variation of delta/sup 30/Si found is 6.2 parts per thousand, centered on the mean of terrestrial mafic and ultramafic igneous rocks, delta/sup 30/Si = -0.4 parts per thousand. Igneous rocks show limited variation; coexisting minerals exhibit small, systematic silicon isotopic fractionations that are roughly 1/3 the magnitude of concomitant oxygen isotopic fractionations at 1150/sup 0/C. In both igneous minerals and rocks, delta/sup 30/Si shows a positive correlation with silicon content, as does delta/sup 18/O. Opal from both sponge spicules and sinters is light, with delta/sup 30/Si = -2.3 and -1.4 parts per thousand respectively. Large delta/sup 30/Si values of both positive and negative sign are reported for the first time from clay minerals, opaline phytoliths, and authigenic quartz. All highly fractionated samples were precipitated from solution at low temperatures; however, aqueous silicon is not measurably fractionated relative to quartz at equilibrium. A kinetic isotope fractionation of approximately 3.5 parts per thousand is postulated to occur during the low temperature precipitation of opal and, possibly, poorly ordered phyllosilicates, with the silicate phase being enriched in /sup 28/Si. This fractionation, coupled with a Rayleigh precipitation model, is capable of explaining most non-magmatic delta/sup 30/Si variations.

  19. Isotopic geochemistry of Fernando de Noronha

    International Nuclear Information System (INIS)

    Gerlach, D.C.; Stormer, J.C. Jr.; Mueller, P.A.

    1987-01-01

    Volcanic and hybabyssal rocks ranging in age from 12 to 3 Ma from the Fernando de Noronha archipelago in the western equatorial Atlantic Ocean can generally be devided into two age-compositional groups that have variable and distinct isotopic compositions. Predominantly older alkali basalts and trachytes are generally characterized by more radiogenic Sr-isotopic ( 87 Sr/ 86 Sr=0.70457-0.70485) compositions and less radiogenic Nd-isotopic ( 143 Nd/ 144 Nd=0.51271-0.51281) and Pb-isotopic ( 206 Pb/ 204 Pb=19.132-19.282) compositions relative to the generally younger, more alkaline Si-undersaturated rocks which include nephelinites, ankaratrites, and melilitites ( 87 Sr/ 86 Sr=0.70365-0.70418, 143 Nd/ 144 Nd=0.51277-0.51290, 206 Pb/ 204 Pb=19.317-19.565). These variations suggest the influence of at least two separate components in the source(s) of both series. One component is characterized by high Rb/Sr and low μ, possibly derived from delaminated subcontinental lithosphere, whereas the other has high μ and low Rb/Sr similar to the source of St. Helena lavas. A third component is suggested by correlated compositions in the latest alkaline, Si-undersaturated lavas, and this component may be derived from depleted mantle. These isotopic variations in conjunction with the generally increasing degree of alkalinity with time are consistent with the temporal depletion of a low-μ, high Rb/Sr component and increasing contributions from a high-μ component in the source of the volcanic rocks of Fernando de Noronha. (orig.)

  20. Stable isotope geochemistry : definitions, terminology, measurement and some applications

    International Nuclear Information System (INIS)

    Faure, K.

    2009-01-01

    In 1936, Alfred Nier produced the first precise measurement of isotope abundance ratios and his design still remains the basis of stable isotope mass spectrometry. With this gift from the physicists for routine measurement of isotope ratios, earth scientists began to explore the natural variations of isotopes. Thus began a new era in geoscience research with the hydrological cycle and marine palaeolimatic research being the first topics to be investigated. Stable isotope measurements have been applied to many fundamental problems in geochemistry, petrology, and paleoclimatology, as well as related fields in archaeology, anthropology, physical chemistry, biology and forensic sciences. These applications can be broadly classified into four main types: 1. Thermometry: Formation temperatures of rock and mineral systems are determined on the basis of temperature-dependent fractionations of the isotopic ratios between two or more cogenetic phases. 2. Tracers: Reservoirs like the ocean, the mantle, meteroic waters and organic matter have distinct stable isotope signatures that can be used to trace the origin of rocks, fluids, contaminants etc. 3. Reaction mechanism: Distinctions can be made between diffusion and recrystallization, open and closed systems and bacterial and thermogenic processes. 4. Chemostratigraphy: Abrupt changes (excursions) in the stable isotope ratios of ocean sediments and certain terrestrial materials can be used as stratigraphic markers. (author). 56 refs., 11 figs., 2 tabs.

  1. Stable isotope geochemistry : definitions, terminology, measurement and some applications

    International Nuclear Information System (INIS)

    Faure, K.

    2014-01-01

    In 1936, Alfred Nier produced the first precise measurement of isotope abundance ratios and his design still remains the basis of stable isotope mass spectrometry. With this gift from the physicists for routine measurement of isotope ratios, earth scientists began to explore the natural variations of isotopes. Thus began a new era in geoscience research with the hydrological cycle and marine palaeoclimatic research being the first topics to be investigated. Stable isotope measurements have been applied to many fundamental problems in geochemistry, petrology, and paleoclimatology, as well as related fields in archaeology, anthropology, physical chemistry, biology and forensic sciences. These applications can be broadly classified into four main types: 1. Thermometry: Formation temperatures of rock and mineral systems are determined on the basis of temperature-dependent fractionations of the isotopic ratios between two or more cogenetic phases. 2. Tracers: Reservoirs like the ocean, the mantle, meteoric waters and organic matter have distinct stable isotope signatures that can be used to trace the origin of rocks, fluids, contaminants etc. 3. Reaction mechanism: Distinctions can be made between diffusion and recrystallization, open and closed systems and bacterial and thermogenic processes. 4. Chemostratigraphy: Abrupt changes (excursions) in the stable isotope ratios of ocean sediments and certain terrestrial materials can be used as stratigraphic markers. (author)

  2. Stable isotope geochemistry: definitions, terminology, measurement and some applications

    International Nuclear Information System (INIS)

    Faure, K.

    2015-01-01

    In 1936, Alfred Nier produced the first precise measurement of isotope abundance ratios and his design still remains the basis of stable isotope mass spectrometry. With this gift from the physicists for routine measurement of isotope ratios, earth scientists began to explore the natural variations of isotopes. Thus began a new era in geoscience research with the hydrological cycle and marine palaeoclimatic research being the first topics to be investigated. Stable isotope measurements have been applied to many fundamental problems in geochemistry, petrology, and paleoclimatology, as well as related fields in archaeology, anthropology, physical chemistry, biology and forensic sciences. These applications can be broadly classified into four main types: 1. Thermometry: Formation temperatures of rock and mineral systems are determined on the basis of temperature-dependent fractionations of the isotopic ratios between two or more cogenetic phases. 2. Tracers: Reservoirs like the ocean, the mantle, meteoric waters and organic matter have distinct stable isotope signatures that can be used to trace the origin of rocks, fluids, contaminants etc. 3. Reaction mechanism: Distinctions can be made between diffusion and recrystallization, open and closed systems and bacterial and thermogenic processes. 4. Chemostratigraphy: Abrupt changes (excursions) in the stable isotope ratios of ocean sediments and certain terrestrial materials can be used as stratigraphic markers. (author).

  3. Stable isotope geochemistry : definitions, terminology, measurement and some applications

    International Nuclear Information System (INIS)

    Faure, K.

    2012-01-01

    In 1936, Alfred Nier produced the first precise measurement of isotope abundance ratios and his design still remains the basis of stable isotope mass spectrometry. With this gift from the physicists for routine measurement of isotope ratios, earth scientists began to explore the natural variations of isotopes. Thus began a new era in geoscience research with the hydrological cycle and marine palaeoclimatic research being the first topics to be investigated. Stable isotope measurements have been applied to many fundamental problems in geochemistry, petrology, and paleoclimatology, as well as related fields in archaeology, anthropology, physical chemistry, biology and forensic sciences. These applications can be broadly classified into four main types: 1. Thermometry: Formation temperatures of rock and mineral systems are determined on the basis of temperature-dependent fractionations of the isotopic ratios between two or more cogenetic phases. 2. Tracers: Reservoirs like the ocean, the mantle, meteoric waters and organic matter have distinct stable isotope signatures that can be used to trace the origin of rocks, fluids, contaminants etc. 3. Reaction mechanism: Distinctions can be made between diffusion and recrystallization, open and closed systems and bacterial and thermogenic processes. 4. Chemostratigraphy: Abrupt changes (excursions) in the stable isotope ratios of ocean sediments and certain terrestrial materials can be used as stratigraphic markers. (author). 89 refs., 12 figs., 2 tabs.

  4. Stable isotope geochemistry : definitions, terminology, measurement and some applications

    International Nuclear Information System (INIS)

    Faure, K.

    2008-01-01

    In 1936, Alfred Nier produced the first precise measurement of isotope abundance ratios and his design still remains the basis of stable isotope mass spectrometry. With this gift from the physicists for routine measurement of isotope ratios, earth scientists began to explore the natural variations of isotopes. Thus began a new era in geoscience research with the hydrological cycle and marine palaeolimatic research being the first topics to be investigated. Stable isotope measurements have been applied to many fundamental problems in geochemistry, petrology, and paleoclimatology, as well as related fields in archaeology, anthropology, physical chemistry, biology and forensic sciences. These applications can be broadly classified into four main types: 1. Thermometry: Formation temperatures of rock and mineral systems are determined on the basis of temperature-dependent fractionations of the isotopic ratios between two or more cogenetic phases. 2. Tracers: Reservoirs like the ocean, the mantle, meteroic waters and organic matter have distinct stable isotope signatures that can be used to trace the origin of rocks, fluids, contaminants etc. 3. Reaction mechanism: Distinctions can be made between diffusion and recrystallization, open and closed systems and bacterial and thermogenic processes. 4. Chemostratigraphy: Abrupt changes (excursions) in the stable isotope ratios of ocean sediments and certain terrestrial materials can be used as stratigraphic markers. (author). 56 refs., 11 figs., 2 tabs

  5. Stable isotope geochemistry : definitions, terminology, measurement and some applications

    International Nuclear Information System (INIS)

    Faure, K.

    2009-01-01

    In 1936, Alfred Nier produced the first precise measurement of isotope abundance ratios and his design still remains the basis of stable isotope mass spectrometry. With this gift from the physicists for routine measurement of isotope ratios, earth scientists began to explore the natural variations of isotopes. Thus began a new era in geoscience research with the hydrological cycle and marine palaeolimatic research being the first topics to be investigated. Stable isotope measurements have been applied to many fundamental problems in geochemistry, petrology, and paleoclimatology, as well as related fields in archaeology, anthropology, physical chemistry, biology and forensic sciences. These applications can be broadly classified into four main types: 1. Thermometry: Formation temperatures of rock and mineral systems are determined on the basis of temperature-dependent fractionations of the isotopic ratios between two or more cogenetic phases. 2. Tracers: Reservoirs like the ocean, the mantle, meteroic waters and organic matter have distinct stable isotope signatures that can be used to trace the origin of rocks, fluids, contaminants etc. 3. Reaction mechanism: Distinctions can be made between diffusion and recrystallization, open and closed systems and bacterial and thermogenic processes. 4. Chemostratigraphy: Abrupt changes (excursions) in the stable isotope ratios of ocean sediments and certain terrestrial materials can be used as stratigraphic markers. (author). 56 refs., 11 figs., 2 tabs

  6. Stable isotope geochemistry : definitions, terminology, measurement and some applications

    International Nuclear Information System (INIS)

    Faure, K.

    2016-01-01

    In 1936, Alfred Nier produced the first precise measurement of isotope abundance ratios and his design still remains the basis of stable isotope mass spectrometry. With this gift from the physicists for routine measurement of isotope ratios, earth scientists began to explore the natural variations of isotopes. Thus began a new era in geoscience research with the hydrological cycle and marine palaeoclimatic research being the first topics to be investigated. Stable isotope measurements have been applied to many fundamental problems in geochemistry, petrology, and paleoclimatology, as well as related fields in archaeology, anthropology, physical chemistry, biology and forensic sciences. These applications can be broadly classified into four main types: 1. Thermometry: Formation temperatures of rock and mineral systems are determined on the basis of temperature-dependent fractionations of the isotopic ratios between two or more cogenetic phases. 2. Tracers: Reservoirs like the ocean, the mantle, meteoric waters and organic matter have distinct stable isotope signatures that can be used to trace the origin of rocks, fluids, contaminants etc. 3. Reaction mechanism: Distinctions can be made between diffusion and recrystallization, open and closed systems and bacterial and thermogenic processes. 4. Chemostratigraphy: Abrupt changes (excursions) in the stable isotope ratios of ocean sediments and certain terrestrial materials can be used as stratigraphic markers. (author).

  7. Stable isotope geochemistry : definitions, terminology, measurement and some applications

    International Nuclear Information System (INIS)

    Faure, K.

    2013-01-01

    In 1936, Alfred Nier produced the first precise measurement of isotope abundance ratios and his design still remains the basis of stable isotope mass spectrometry. With this gift from the physicists for routine measurement of isotope ratios, earth scientists began to explore the natural variations of isotopes. Thus began a new era in geoscience research with the hydrological cycle and marine palaeoclimatic research being the first topics to be investigated. Stable isotope measurements have been applied to many fundamental problems in geochemistry, petrology, and paleoclimatology, as well as related fields in archaeology, anthropology, physical chemistry, biology and forensic sciences. These applications can be broadly classified into four main types: 1. Thermometry: Formation temperatures of rock and mineral systems are determined on the basis of temperature-dependent fractionations of the isotopic ratios between two or more cogenetic phases. 2. Tracers: Reservoirs like the ocean, the mantle, meteoric waters and organic matter have distinct stable isotope signatures that can be used to trace the origin of rocks, fluids, contaminants etc. 3. Reaction mechanism: Distinctions can be made between diffusion and recrystallization, open and closed systems and bacterial and thermogenic processes. 4. Chemostratigraphy: Abrupt changes (excursions) in the stable isotope ratios of ocean sediments and certain terrestrial materials can be used as stratigraphic markers. (author). 91 refs., 12 figs., 2 tabs.

  8. STABLE ISOTOPE GEOCHEMISTRY OF MASSIVE ICE

    Directory of Open Access Journals (Sweden)

    Yurij K. Vasil’chuk

    2016-01-01

    Full Text Available The paper summarises stable-isotope research on massive ice in the Russian and North American Arctic, and includes the latest understanding of massive-ice formation. A new classification of massive-ice complexes is proposed, encompassing the range and variabilityof massive ice. It distinguishes two new categories of massive-ice complexes: homogeneousmassive-ice complexes have a similar structure, properties and genesis throughout, whereasheterogeneous massive-ice complexes vary spatially (in their structure and properties andgenetically within a locality and consist of two or more homogeneous massive-ice bodies.Analysis of pollen and spores in massive ice from Subarctic regions and from ice and snow cover of Arctic ice caps assists with interpretation of the origin of massive ice. Radiocarbon ages of massive ice and host sediments are considered together with isotope values of heavy oxygen and deuterium from massive ice plotted at a uniform scale in order to assist interpretation and correlation of the ice.

  9. Stable isotope geochemistry of deep sea cherts

    Energy Technology Data Exchange (ETDEWEB)

    Kolodny, Y; Epstein, S [California Inst. of Tech., Pasadena (USA). Div. of Geological Sciences

    1976-10-01

    Seventy four samples of DSDP (Deep Sea Drilling Project) recovered cherts of Jurassic to Miocene age from varying locations, and 27 samples of on-land exposed cherts were analyzed for the isotopic composition of their oxygen and hydrogen. These studies were accompanied by mineralogical analyses and some isotopic analyses of the coexisting carbonates. delta/sup 18/0 of chert ranges between 27 and 39 parts per thousand relative to SMOW, delta/sup 18/0 of porcellanite - between 30 and 42 parts per thousand. The consistent enrichment of opal-CT in porcellanites in /sup 18/0 with respect to coexisting microcrystalline quartz in chert is probably a reflection of a different temperature (depth) of diagenesis of the two phases. delta/sup 18/0 of deep sea cherts generally decrease with increasing age, indicating an overall cooling of the ocean bottom during the last 150 m.y. A comparison of this trend with that recorded by benthonic foraminifera (Douglas et al., Initial Reports of the Deep Sea Drilling Project; 32:509(1975)) indicates the possibility of delta/sup 18/0 in deep sea cherts not being frozen in until several tens of millions of years after deposition. Cherts of any Age show a spread of delta/sup 18/0 values, increasing diagenesis being reflected in a lowering of delta/sup 18/0. Drusy quartz has the lowest delta/sup 18/0 values. On land exposed cherts are consistently depleted in /sup 18/0 in comparison to their deep sea time equivalent cherts. Water extracted from deep sea cherts ranges between 0.5 and 1.4 wt%. deltaD of this water ranges between -78 and -95 parts per thousand and is not a function of delta/sup 18/0 of the cherts (or the temperature of their formation).

  10. Lu-Hf and Sm-Nd garnet geochronology

    DEFF Research Database (Denmark)

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

    2013-01-01

    To investigate the systematics of the 176Lu–176Hf and 147Sm–143Nd garnet chronometers, we performed REE and isotope analyses on garnet crystals of different size (0.55–3.1 mm radius) from a single granulite specimen (Archean Pikwitonei Granulite Domain, Manitoba, Canada). The Lu–Hf dates are simi...

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

    Science.gov (United States)

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

    2008-12-01

    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 ‰, but gradual small improvements in analytical capability now yield 0.05 to 0.1 ‰ 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 experimental tests and

  12. V Congress of Spanish Geochemistry

    International Nuclear Information System (INIS)

    1993-01-01

    This proceedings book present the lectures of V Spanish geochemistry Congress. The sessions were: 1.- Materials geochemistry and geologic process. 2.- Geochemistry prospection 3.- Environmental geochemistry 4.- Isotopic geochemistry 5.- Organic geochemistry 6.- Natural materials geochemistry for industry 7.- Hydrogeochemistry 8.- Mathematical models in geochemistry 9.- Analysis methods in geochemistry 10.-Training of geochemistry 11.-Cosmochemistry

  13. Isotope geochemistry of xenoliths from East Africa. Implications for development of mantle reservoirs and their interaction

    Energy Technology Data Exchange (ETDEWEB)

    Cohen, R S; O' Nions, R K [Cambridge Univ. (UK). Dept. of Earth Sciences; Dawson, J B [Sheffield Univ. (UK). Dept. of Geology

    1984-05-01

    Pd, Nd and Sr isotope analyses together with U, Pb, Sm, Nd, Rb and Sr concentrations have been obtained for separated phases of lherzolite and bulk rock mafic granulite xenoliths in Recent volcanics from Tanzania. A garnet lherzolite from the Lashaine vent has yielded the least radiogenic Pb (/sup 206/Pb//sup 204/PB=15.55) and Nd (/sup 143/Nd//sup 144/Nd=0.51127; epsilon/sup 0/sub(Nd)=-26.7) isotope compositions recorded so far for an ultramafic xenolith, and /sup 87/Sr//sup 86/Sr=0.83604. The Pb isotope compositions of the mafic granulites are variable 15.77isotope results suggest that the mantle part of the continental lithosphere beneath Tanzania has components that have undergone a complex history that includes major chemical fractionations ca. 2.0 Ga ago. A phlogopite-amphibole vein from the Pello Hill sample has Sr, Nd and Pb isotope compositions similar to those of mid-ocean ridge basalts, indicating both a young emplacement age for the vein material and a source which had an isotopic signature characteristic of depleted mantle. The Sr, Nd and Pb isotope systematics of ultramafic xenoliths do not conform with those of MORB, particularly in terms of their Pb-Sr, and Nd-Pb relationship. In this regard they are similar to some ocean islands and could be a viable source material for some ocean island basalts at least. The mantle part of the continental lithosphere is as likely to contain recycled components derived from the continental crust as are other regions of mantle. If the mantle part of continental lithosphere is invoked as a source for ocean islands, it does not negate the possibility that substantial recycled components are involved.

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

    Science.gov (United States)

    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

  15. Sm-Nd age of the Stillwater complex and the mantle evolution curve for neodymium

    International Nuclear Information System (INIS)

    DePaolo, D.J.; Wasserburg, G.J.

    1979-01-01

    An internal isochron determined for a gabbro from the Stillwater complex by the Sm-Nd method yields a precise age of 2701 +- 8 Myr and initial 143 Nd/ 144 Nd 0.508248 +- 12. The initial is close to the CHUR evolution curve but clearly displaced below it by epsilonsub(Nd) = 2.8 +- 0.2. A spectrum of total rocks in the Stillwater complex ranging from anorthosite to pyroxenite were found to lie on the same isochron to within experimental error indicating the same age and initial. These data demonstrate that some ancient mantle-derived rocks have initial 143 Nd/ 144 Nd which deviate substantially from the CHUR evolution curve at the time of their formation. This implies that there was early layering in the mantle with substantial REE fractionation (approximately 6 to 12% Nd/Sm enrichment) or that the Stillwater complex was highly contaminated with REE from much older continental crust during emplacement. The results show the necessity of high-precision ages and initial 143 Nd/ 144 Nd values in order to properly describe REE fractionation in the mantle. While the Sm-Nd age results show no indication of any irregularities, we have confirmed that the Rb-SR data for the Stillwater are highly disturbed. This comparison indicates that the Sm-Nd parent-daughter system may be much less susceptible to element redistribution during metamorphism, therefore permitting wide application of this technique to rocks of complex histories. (author)

  16. Dating Melt Rock 63545 By Rb-Sr and Sm-Nd: Age of Imbrium; Spa Dress Rehearsal

    Science.gov (United States)

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

    2011-01-01

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

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

    International Nuclear Information System (INIS)

    Pimentel, M.M.; Heaman, L.; Fuck, R.A.

    1992-01-01

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

  18. Sm-Nd dating of the Verkhneundytkansky massif of autonomous anorthosites (Aldanian Shield)

    International Nuclear Information System (INIS)

    Sukhanov, M.K.; Lennikov, A.M.; Zhuravlev, D.Z.

    1991-01-01

    Geochronological investigation of four typical rocks of the Verkhneundyransky anorthosite massif as well as rock-forming minerals of one of the samples is carried out by the method of Sm-Nd dating. Model ayes of the investigated rocks which were calculated with respect to the depleted mantle, constitute 2.22-2.35 bullion ylars which well agrees with the isochronous age. The experimental points fall well on the regression line which attests that the crystallization of the investigated massif proceeded rather fast and the latter could not assimilate the crustal matter to a considerable extent

  19. Rb-Sr and Nd-Sr isotope geochemistry and petrogenesis of the Misho Mountains mafic dikes (NW Iran

    Directory of Open Access Journals (Sweden)

    Maryam Ahankoub

    2017-02-01

    Full Text Available Introduction There are some theories about the Paleotethys event during the Paleozoic that have been proposed by geologists (Metcalfe, 2006. Some scientist offered some pieces of evidence about the northern margin of Gondwana (Zhu et al., 2010. The Paleotethys Ocean and Hercynian orogenic report first in Iran, have been Offered from the Morrow and Misho Mountain (Eftekharnejad, 1981. Misho Mountains is located between the north and south Misho faults and cause the formation of a positive flower structure (Moayyed and Hossainzade, 2011. There is theory about Misho southern fault as the best candidate of the Paleotethys suture zone (Moayyed and Hossainzade, 2011. Geochemistry and Sr –Nd isotopic data of the A2 granitic and Synite rocks of the East Misho, indicate that the magmatism post collision has occurred in the active continental margin by extensional zones of the following the closure of the Paleotethys (Ahankoub, 2012. Granite and syenite rocks have been cut by mafic dikes. Mafic dikes are often formed in extensional tectonic settings related to mantle plume or continental break –up (Zhu et al., 2009. In this paper, we use the geochemistry and Nd-Sr isotope data to determined petrogenesis, tectono-magmatic setting and age of Misho mafic dikes. Materials and methods After petrography study of 30 thin sections of mafic dike rocks, 8 samples were selected for whole-rock chemical analyses using ICP-MS and ICP-AES instruments by ACME Company in Vancouver, Canada. We prepared 6 sample For Sm-Nd and Rb-Sr analysis. Sr and Nd isotope ratios were measured with a thermal ionization mass spectrometer, VG Sector 54–30 at the Nagoya University. The isotope abundances of Rb, Sr, Nd, and Sm were measured by the ID method with a Finnigan MAT Thermoquad THQ thermal ionization quadrupole mass spectrometer at the Nagoya University. NBS987 and JNdi-1 were measured as natural Sr and Nd isotope ratio standards (Tanaka et al., 2000. Averages and 2σ errors

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2005-12-15

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

  1. Proceedings of 1. international symposium on applied isotope geochemistry (AIG-1)

    International Nuclear Information System (INIS)

    Aaberg, G.; Joergensen, E.B.

    1993-09-01

    The publication is a compilation of abstracts from the ''1. international symposium on applied isotope geochemistry (AIG-1)'' in Norway. The symposium was the first of its kind taking up different applications of most of the available isotopic systems and thus covered a wide range of topics from: 1) Water resources, hydrology, geomedicine and environmental problems, 2) Petroleum exploration and production, 3) Mineral exploration and 4) Analytical methods

  2. Rb-Sr and Sm-Nd isotopic relations and ages of the Brasiliano granitic magmatism of the eastern region of the Dom Feliciano belt in the Rio Grande do Sul State, South region Brazil: evidences of the reworking of a paleoproterozoic continental crust, South region, Brazil

    International Nuclear Information System (INIS)

    Frantz, Jose Carlos; Koester, Edinei; Teixeira, Roberto Santos; Botelho, Nilson Francisquini; Pimentel, Marcio Martins; Potrel, Alan

    1999-01-01

    The granitoids belonging to the brasiliano cycle from the eastern region at the Dom Feliciano Belt in the Rio Grande do Sul state have had Rb-Sr data that indicated bodies which were intruded between 800 and 585 Ma. The T DM ages are suggesting the participation of an older source in their generation. This source could be represented by a long period enriched mantle, much than would be expected during the evolution of the magmatic arcs, or could be represented by the interaction between an older continental crust and mantle during a continental collision regime. The tectonic evolution of this area., the existence of a long period of time between the granitic intrusions associated to the tangential regime and to the transpressive regime and to the transpressive regime ones, the isotopic relations between Sr and nd and the very low negative values of ε N dt are suggesting a strong participation of an older continental crust. This older continental crust, may be constituted by gneissic protoliths of paleoproterozoic ages and generated during the evolution of the Transamazonic Cycle, has participated in the formation of the sources of the granitic magmatism of this part of the belt. The variations of the T DM ages and of the Nd ratios in the calc-alkaline granitoids are suggesting different proportions of mixture between and older continental crust and mantle or different homogenization grades in the magmas sources. For the peraluminous granites, that have be resulted from continental crustal melt, there are indications of different sources to the different bodies. (author)

  3. Petrogenesis of Miocene alkaline volcanic suites from western Bohemia. Whole rock geochemistry and Sr-Nd-Pb isotopic signatures.

    Czech Academy of Sciences Publication Activity Database

    Ulrych, Jaromír; Krmíček, Lukáš; Tomek, Č.; Lloyd, F. E.; Ladenberger, A.; Ackerman, Lukáš; Balogh, K.

    2016-01-01

    Roč. 76, č. 1 (2016), s. 77-93 ISSN 0009-2819 Institutional support: RVO:67985831 Keywords : Bohemian Massif * Cenozoic alkaline volcanism * Geochemistry * K-Ar ages * Sr-Nd-Pb isotopes Subject RIV: DD - Geochemistry Impact factor: 1.380, year: 2016

  4. Clumped-isotope geochemistry of carbonates: A new tool for the reconstruction of temperature and oxygen isotope composition of seawater

    Energy Technology Data Exchange (ETDEWEB)

    Bernasconi, Stefano M., E-mail: Stefano.bernasconi@erdw.ethz.ch [Geological Institute, ETH Zuerich, Sonneggstrasse 5, 8092 Zuerich (Switzerland); Schmid, Thomas W.; Grauel, Anna-Lena [Geological Institute, ETH Zuerich, Sonneggstrasse 5, 8092 Zuerich (Switzerland); Mutterlose, Joerg [Institut fuer Geologie, Mineralogie und Geophysik, Ruhr Universitaet Bochum, Universitaetsstr. 150, 44801 Bochum (Germany)

    2011-06-15

    Highlights: > Clumped-isotope thermometry of carbonates is discussed. > Clumped isotopes of Belemnites show higher sea surface temperatures than commonly assumed for the lower Cretaceous. > The potential of clumped-isotope measurement on foraminifera is discussed. - Abstract: Clumped-isotope geochemistry deals with State of ordering of rare isotopes in molecules, in particular with their tendency to form bonds with other rare isotopes rather than with the most abundant ones. Among its possible applications, carbonate clumped-isotope thermometry is the one that has gained most attention because of the wide potential of applications in many disciplines of the earth sciences. In particular, it allows reconstructing the temperature of formation of carbonate minerals without knowledge of the isotopic composition of the water from which they were formed. In addition, the O isotope composition of the waters from which they were formed can be calculated using the {delta}{sup 18}O of the same carbonate sample. This feature offers new approaches in paleoclimatology for reconstructing past global geochemical cycles. In this contribution two applications of this method are presented. First the potential of a new analytical method of measurement of clumped isotopes on small samples of foraminifera, for high-resolution SST and seawater {delta}{sup 18}O reconstructions from marine sediments is shown. Furthermore the potential of clumped isotope analysis of belemnites, for reconstructing seawater {delta}{sup 18}O and temperatures in the Cretaceous is shown.

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

    Energy Technology Data Exchange (ETDEWEB)

    Marimon, Rodrigo Schwantes; Dantas, Elton Luiz; Matteini, Massimo, E-mail: rsmarimon@hotmail.com, E-mail: elton@unb.br [Universidade de Brasilia (UnB), DF (Brazil). Instituto de Geociencias

    2015-07-01

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

  6. The provenance and Sm/Nd Model ages of siliciclastic supracrustal rocks of the Faina and Santa Rita Greenstone belts, Goias, Brazil

    International Nuclear Information System (INIS)

    Resende, Marcelo Goncalves; Jost, Hardy; Lima, Bruno Eustaquio Moreira; Teixeira, Alexandre de Amorim

    1999-01-01

    The Faina and Santa Rita greenstone belts are two N 60 deg C W trending synclinoria separated by a N 30 deg C E strike-slip fault and rest allochtonous on the adjacent Uva and Caicara granite-gneiss complexes. The belts are made up of lower metakomatiites, followed by metabasalts and thick metasedimentary sequences deposited under contrasting paleogeographic settings. In Faina, the sequence consists of two complete shelf cycles, the first resting on basalts by an erosional unconformity. In Santa Rita, the basalts give gradually place to carbonaceous metashales, unconformably overlain by metarhythmites. Provenance based on trace element geochemistry, mineral chemistry of chloride and muscovite, source-are modeling and REE elements indicate that protoliths of the first shelf cycle of Faina and the carbonaceous metashales of Santa Rita formed under the influence of a source area dominated by mafic ultramafic rocks, whilst during the sedimentation of the second shelf cycle and the metarhythmites of Santa Rita the source-area was dominated by TTG granitoids. Sm-Nd model ages of the lower sedimentary packages vary between 3.0 and 2.8 Ga and the upper between 2.7 and 2.6 Ga. These intervals coincide, respectively, with the estimated age of the underlying, and with the Sm-Nd, Rb-Sr e U-Pb ages of the main granitoids and gneisses of the adjacent complexes. The same data indicate that, during the sedimentation of the first shelf cycle of Faina and the carbonaceous metashales of Santa Rita, both basins had independent source-areas, but shared the same source during the upper sections. Weathering nature and intensity of the source-area calculated by means of geochemical a data suggest that the dramatic change of provenance from the lower to the upper sections is due to the shift from tectonically stable to unstable regimes, interpreted as resulting from the emergence of the island arc whose roots are represented by the adjacent granite-gneiss complexes. (author)

  7. Sm-Nd whole-rock isotope system of the Eye-Dashwa Lakes pluton

    International Nuclear Information System (INIS)

    Futa, K.

    1990-01-01

    An unaltered drill-core sample of the Eye-Dashwa Lakes pluton (sample ATK-1 (990.97-996.78)) is light rare earth enriched, with a 147 Sm/ 144 Nd ratio of 0.08699 and a 143 Nd/ 144 Nd ratio of 0.510815. The depleted mantle model age of 2.68 Ga agrees with emplacement ages, indicating that parental magma or its protolith was derived directly from a depleted mantle and that the crustal residence time was short

  8. Fluid inclusion, geochemical, Rb-Sr and Sm-Nd isotope studies on ...

    Indian Academy of Sciences (India)

    10

    Degana granites is quiet high and ranges from 958 to 1907 ppm except B-24, Zr .... According to Pearson's hard soft acid base (HSAB) principle, tungsten which occurs ... could explain lower Sr abundances in the Balda and Degana granites, Rb ...... Oceanic ridge granites (ORG), within-plate granite (WPG), volcanic arc ...

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

    International Nuclear Information System (INIS)

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

    2001-01-01

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

  10. Stable isotope geochemistry of the Tongonan geothermal system, Leyte, Philippines

    International Nuclear Information System (INIS)

    Hulston, J.R.; Stewart, M.K.

    1982-01-01

    Stable isotope and geochemical data on samples from natural features, shallow wells and deep wells collected over a number of years from the Tongonan area of Leyte have been evaluated. The variations in the isotopic compositions of the thermal waters are used to describe natural processes occurring within the system. The effect of the ''excess enthalpy'' of the deep wells on the isotope data is formulated. Water from the deep Tongonan wells shows an oxygen-18 shift of 5 per mille, which is larger than at Wairakei and Broadlands, probably in part because of the high temperatures at Tongonan. Recent measurements indicate that the deuterium shift is very much smaller than previously thought. Isotopic measurements of methane in the gases suggests differing flows from the Eastern and Central Philippine faults

  11. Isotopic and noble gas geochemistry in geothermal research

    Energy Technology Data Exchange (ETDEWEB)

    Kennedy, B.M.; DePaolo, D.J. [Lawrence Berkeley National Lab., CA (United States)

    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.

  12. U-Pb SHRIMP and Sm-Nd geochronology of the Silvania Volcanics and Jurubatuba Granite: juvenile paleoproterozoic crust in the basement of the Neo proterozoic Brasilia Belt, Goias, central Brazil

    International Nuclear Information System (INIS)

    Fischel, Danielle P.; Pimentel, Marcio M.; Fuck, Reinhardt A.; Armstrong, Richard

    2001-01-01

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

  13. Re-appraisal of the Santa Rita Greenstone Belt stratigraphy, central Brazil, based on new U-Pb SHRIMP age and Sm-Nd data of felsic metavolcanic rocks

    International Nuclear Information System (INIS)

    Pimentel, Marcio Martins; Jost, Hardy; Fuck, Reinhardt Adolfo; Junges, Sergio Luiz; Armstrong, Richard; Resende, Marcelo Goncalves

    2000-01-01

    The Santa Rita greenstone belt represents one of the supracrustal belts of the Archaen terranes of Goias, central Brazil. The stratigraphic sequence of this greenstone belt comprises a lower of komatities and basalts and an upper metasedimentary unit made of carbonaceous schits, chert, iron formation and marble, unconformably overlain by clastic metasedimentary rocks. Felsic metavolcanics occur at the interface between the metabasalts and the upper metasedimentary pile. U-Pb SHRIMP age for zircons from the felsic metavolcanics reveal that it is not part of the Archaean sequence, but represents the product of mesoproterozoic (1580 ± 12 Ma) magmatic event. Sm-Nd isotopic data (initial e CHUR values between -10.5 and -14.9) and T DM values of 3.0 and 3.2 Ga, within the range of the surrounding TTG terranes, indicate that the original felsic magmas were produced by re-melting of Archaen crust. The data demonstrate that the Goias greenstone belt contains infolded and imbricated proterozoic rocks, as previously suggested by Sm-Nd isotopic analyses of some of the upper detrital metasedimentary rocks. (author)

  14. U-Pb SHRIMP and Sm-Nd geochronology of the Silvania Volcanics and Jurubatuba Granite: juvenile paleoproterozoic crust in the basement of the Neo proterozoic Brasilia Belt, Goias, central Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Fischel, Danielle P.; Pimentel, Marcio M.; Fuck, Reinhardt A. [Brasilia Univ., DF (Brazil). Inst. de Geociencias; Armstrong, Richard [Australian National Univ., Canberra (Australia). Research School of Earth Sciences

    2001-09-15

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

  15. Re-appraisal of the Santa Rita Greenstone Belt stratigraphy, central Brazil, based on new U-Pb SHRIMP age and Sm-Nd data of felsic metavolcanic rocks

    Energy Technology Data Exchange (ETDEWEB)

    Pimentel, Marcio Martins; Jost, Hardy; Fuck, Reinhardt Adolfo; Junges, Sergio Luiz [Brasilia Univ., DF (Brazil). Inst. de Geociencias]. E-mail: marcio@unb.br; Armstrong, Richard [Australian National Univ., Canberra, ACT (Australia). Research School of Earth Sciences; Resende, Marcelo Goncalves [Universidade Catolica de Brasilia, DF (Brazil). Curso de Graduacao em Engenharia Ambiental

    2000-03-01

    The Santa Rita greenstone belt represents one of the supracrustal belts of the Archaen terranes of Goias, central Brazil. The stratigraphic sequence of this greenstone belt comprises a lower of komatities and basalts and an upper metasedimentary unit made of carbonaceous schits, chert, iron formation and marble, unconformably overlain by clastic metasedimentary rocks. Felsic metavolcanics occur at the interface between the metabasalts and the upper metasedimentary pile. U-Pb SHRIMP age for zircons from the felsic metavolcanics reveal that it is not part of the Archaean sequence, but represents the product of mesoproterozoic (1580 {+-} 12 Ma) magmatic event. Sm-Nd isotopic data (initial e{sub CHUR} values between -10.5 and -14.9) and T{sub DM} values of 3.0 and 3.2 Ga, within the range of the surrounding TTG terranes, indicate that the original felsic magmas were produced by re-melting of Archaen crust. The data demonstrate that the Goias greenstone belt contains infolded and imbricated proterozoic rocks, as previously suggested by Sm-Nd isotopic analyses of some of the upper detrital metasedimentary rocks. (author)

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

    Directory of Open Access Journals (Sweden)

    FISCHEL DANIELLE P.

    2001-01-01

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

  17. The age and emplacement of obducted oceanic crust in the Urals from Sm-Nd and Rb-Sr systematics

    International Nuclear Information System (INIS)

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

    1985-01-01

    The Urals contain a 2000 km belt of mafic-ultramafic bodies. The Sm-Nd and Rb-Sr systematics of two of these bodies, the Kempersai Massif in the South Ural Mountains and the Voykar-Syninsky Ophiolite Complex in the Polar Ural Mountains have been examined. These data confirm the hypothesis that these bodies represent fragments of pre-collision oceanic crust and establish constraints on the nature and timing of events in the Uralian Orogeny. Two Kempersai gabbros define Sm-Nd internal isochrons of 397 +- 20 My and 396 +- 33 My with epsilonsub(Nd)(T) = +8.7 -+ 0.6 and +8.4 -+ 1.3, respectively. Whole rock samples of pillow basalt, diabase, gabbros, troctolite, and a metasediment give Sm-Nd values which lie on this isochron indicating that these rocks are genetically related and have an igneous crystallization age of 397 My. Whole rock samples of Voykar-Syninsky diabase, gabbros, and clinopyroxenite give Sm-Nd values which lie on or within proportional 1 epsilon-unit of this isochron indicating an age and epsilonsub(Nd)(T) virtually identical to those of Kempersai. epsilonsub(Nd)(T) for the Kempersai and Voykar-Syninsky mafic samples range from +7.3 to +9.0 with an average value of +8.4. This indicates that the Urals ophiolites are derived from an ancient depleted mantle source and are most plausibly pieces of the oceanic crust and lithosphere. The fact that a metasediment has the same epsilonsub(Nd)(397 My) as the other samples indicates derivation from an oceanic source with negligible continental input. epsilonsub(Nd)(T) for the massifs is proportional 1.5 epsilon-units lower than the average for modern MORBs. (orig./HSI)

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

    Energy Technology Data Exchange (ETDEWEB)

    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

  19. The geochemistry of the stable isotopes of silicon

    International Nuclear Information System (INIS)

    Douthitt, C.B.

    1982-01-01

    One hundred thirty two new measurements of the relative abundances of the stable isotopes of silicon in terrestrial materials are presented. The total variation of delta 30 Si found is 6.2 parts per thousand, centered on the mean of terrestrial mafic and ultramafic igneous rocks, delta 30 Si = -0.4 parts per thousand. Igneous rocks show limited variation; coexisting minerals exhibit small, systematic silicon isotopic fractionations that are roughly 1/3 the magnitude of concomitant oxygen isotopic fractionations at 1150 0 C. In both igneous minerals and rocks, delta 30 Si shows a positive correlation with silicon content, as does delta 18 O. Opal from both sponge spicules and sinters is light, with delta 30 Si = -2.3 and -1.4 parts per thousand respectively. Large delta 30 Si values of both positive and negative sign are reported for the first time from clay minerals, opaline phytoliths, and authigenic quartz. All highly fractionated samples were precipitated from solution at low temperatures; however, aqueous silicon is not measurably fractionated relative to quartz at equilibrium. A kinetic isotope fractionation of approximately 3.5 parts per thousand is postulated to occur during the low temperature precipitation of opal and, possibly, poorly ordered phyllosilicates, with the silicate phase being enriched in 28 Si. This fractionation, coupled with a Rayleigh precipitation model, is capable of explaining most non-magmatic delta 30 Si variations. (author)

  20. New Carbonate Standard Reference Materials for Boron Isotope Geochemistry

    Science.gov (United States)

    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

  1. Isotope geochemistry of water in Gulf Coast Salt Domes

    International Nuclear Information System (INIS)

    Knauth, L.P.; Kumar, M.B.; Martinez, J.D.

    1980-01-01

    Water found as active leaks and isolated pools in the Weeks Island, Jefferson Island, and Belle Isle salt mines of south Louisiana has delta 18 O values ranging from -4 to +11.5% 0 and deltaD values from -2.3 to -53% 0 . One sample from Weeks Island and one from Jefferson Island are isotopically similar to local surface waters and are clearly of meteoric origin. All other samples are too enriched in 18 O to be meteoric waters. In the Weeks Island mine the isotopic data define a linear array given by deltaD=3.0delta 18 O-40.1. Active leaks define the positive end of this array. Isolated pools are interpreted as inactive leaks with initial delta 18 O and deltaD values of +9.1 +- 0.5% 0 and -11% 0 +- 7% 0 , which have subsequently exchanged with water vapor in the mine air to produce the linear array of delta values. The water derived from active leaks in these three mines is too enriched in 18 O and too depleted in D to be connate ocean water or evaporite connate water trapped in the salt. Isotopic composition of water derived from the dehydration of gypsum is probably dissimilar to that of the active leaks. It is unlikely that the water has originated from the dehydration of gypsum. It is also unlikely that isotopic exchange with anhydrite is responsible for observed 18 O enrichments. Nonmeteroric water from the active leaks displays the type of 18 O enrichments characteristic of saline formation waters, where water exchanges isotopically with calcite and clay minerals. It is concluded that the nonmeteoric waters are formation waters which have become incorporated in the salt. From the observed 18 O enrichment it is calculated that formation waters were incorporated during diapiric rise of the salt at a depth of 3--4 km and have been trapped within the salt for 10--13 m.y. Large volumes of salt within salt domes are not naturally penetrated by meteoric groundwaters but can contain limited amounts of trapped formation water

  2. Isotope geochemistry of sulfur in forest soils and in new groundwater below forest soils

    International Nuclear Information System (INIS)

    Mayer, B.

    1993-04-01

    The isotope geochemistry of sulphur in aerobic forest soils and new groundwater below forest soils was investigated for the purpose of investigating the transport and transformation behaviour of sulfate in the water-unsaturated zone. The effects of hydrodynamic and biogeochemical processes on the development of seepage water sulfate isotopes between depositions and groundwater were investigated by means of laboratory experiments, profile studies, lysimeter experiments, and field studies in order to determine the sulphur conversion processes. Dissolved sulphur from precipitates, seepage water, creek water and groundwater, as well as sulphur extracted from soil samples, were precipitated in the form of BaSO 4 or AgS 2 , decomposed thermally into SO 2 or CO 2 , and the 34 S/ 32 S and 18 O/ 16 O isotope ratios were determined by mass spectrometry. (orig.) [de

  3. Barium isotope geochemistry of subduction-zone magmas

    Science.gov (United States)

    Yu, H.; Nan, X.; Huang, J.; Wörner, G.; Huang, F.

    2017-12-01

    Subduction zones are crucial tectonic setting to study material exchange between crust and mantle, mantle partial melting with fluid addition, and formation of ore-deposits1-3. The geochemical characteristics of arc lavas from subduction zones are different from magmas erupted at mid-ocean ridges4, because there are addition of fluids/melts from subducted AOC and its overlying sediments into their source regions in the sub-arc mantle4. Ba is highly incompatible during mantle melting5, and it is enriched in crust (456 ppm)6 relative to the mantle (7.0 ppm)7. The subducted sediments are also enriched in Ba (776 ppm of GLOSS)8. Moreover, because Ba is fluid soluble during subduction, it has been used to track contributions of subduction-related fluids to arc magmas9 or recycled sediments to the mantle10-11. To study the Ba isotope fractionation behavior during subduction process, we analyzed well-characterized, chemically-diverse arc lavas from Central American, Kamchatka, Central-Eastern Aleutian, and Southern Lesser Antilles. The δ137/134Ba of Central American arc lavas range from -0.13 to 0.24‰, and have larger variation than the arc samples from other locations. Except one sample from Central-Eastern Aleutian arc with obviously heavy δ137/134Ba values (0.27‰), all other samples from Kamchatka, Central-Eastern Aleutian, Southern Lesser Antilles arcs are within the range of OIB. The δ137/134Ba is not correlated with the distance to trench, partial melting degrees (Mg#), or subducting slab-derived components. The samples enriched with heavy Ba isotopes have low Ba contents, indicating that Ba isotopes can be fractionated at the beginning of dehydration process with small amount of Ba releasing to the mantle wedge. With the dehydration degree increasing, more Ba of the subducted slab can be added to the source of arc lavas, likely homogenizing the Ba isotope signatures. 1. Rudnick, R., 1995 Nature; 2. Tatsumi, Y. & Kogiso, T., 2003; 3. Sun, W., et al., 2015 Ore

  4. The provenance and Sm/Nd Model ages of siliciclastic supracrustal rocks of the Faina and Santa Rita Greenstone belts, Goias, Brazil; Proveniencia e idades modelo Sm/Nd das rochas siliciclasticas arqueanas dos greenstone belts de Faina e Santa Rita, Goias

    Energy Technology Data Exchange (ETDEWEB)

    Resende, Marcelo Goncalves [Universidade Catolica de Brasilia, DF (Brazil); Jost, Hardy [Brasilia Univ., DF (Brazil). Inst. de Geociencias; Lima, Bruno Eustaquio Moreira; Teixeira, Alexandre de Amorim

    1999-09-01

    The Faina and Santa Rita greenstone belts are two N 60 deg C W trending synclinoria separated by a N 30 deg C E strike-slip fault and rest allochtonous on the adjacent Uva and Caicara granite-gneiss complexes. The belts are made up of lower metakomatiites, followed by metabasalts and thick metasedimentary sequences deposited under contrasting paleogeographic settings. In Faina, the sequence consists of two complete shelf cycles, the first resting on basalts by an erosional unconformity. In Santa Rita, the basalts give gradually place to carbonaceous metashales, unconformably overlain by metarhythmites. Provenance based on trace element geochemistry, mineral chemistry of chloride and muscovite, source-are modeling and REE elements indicate that protoliths of the first shelf cycle of Faina and the carbonaceous metashales of Santa Rita formed under the influence of a source area dominated by mafic ultramafic rocks, whilst during the sedimentation of the second shelf cycle and the metarhythmites of Santa Rita the source-area was dominated by TTG granitoids. Sm-Nd model ages of the lower sedimentary packages vary between 3.0 and 2.8 Ga and the upper between 2.7 and 2.6 Ga. These intervals coincide, respectively, with the estimated age of the underlying, and with the Sm-Nd, Rb-Sr e U-Pb ages of the main granitoids and gneisses of the adjacent complexes. The same data indicate that, during the sedimentation of the first shelf cycle of Faina and the carbonaceous metashales of Santa Rita, both basins had independent source-areas, but shared the same source during the upper sections. Weathering nature and intensity of the source-area calculated by means of geochemical a data suggest that the dramatic change of provenance from the lower to the upper sections is due to the shift from tectonically stable to unstable regimes, interpreted as resulting from the emergence of the island arc whose roots are represented by the adjacent granite-gneiss complexes. (author)

  5. Primordial crustal growth in northern Nigeria: preliminary Rb-Sr and Sm-Nd constraints from Kaduna migmatite-gneiss complex

    International Nuclear Information System (INIS)

    Dada, S. S.; Briqueu, L.; Birck, J. L.

    1998-01-01

    The Kaduna Migmatite-Gneiss Complex in the central area of the Northern shield includes variably migmatised granitotrondhjemitic gneisses and amphibolite of hitherto unknown age. The amphibolite enclaves and dykes are metatholeiites with comparatively unfractionated rare-earth patterns. The two main rock units (TTG and amphibolite) exhibit complementary geochemical signatures in the normalised abundance patterns of relatively incompatible elements and suggest possible derivation of the gneisses from subduction related mafic material. Sm-Nd and Rb-Sr isotopic data document early Archaean crustal formation of new crust and its subsequent late Archaean differentiation. These preliminary results form an evidence for a more extended crustal history in the heart of the Pan-African domain (ca. 600 Ma.). They suggest the differentiation of juvenile crustal protolith from a chondritic reservoir about 3.5 Ga. for the gneiss-amphibolite bimodal suite. A tectonothermal event about 3.1-3.0 Ga led to the emplacement of an early gneiss as indicated from Rb-Sr and U-Ph zircon analyses. Subsequent differentiation and/or reworking around 2.8-2.7 Ga is coherent with the Liberian orogeny within the West African- Latino American subregion

  6. Archean crustal growth of the Imataca complex, Amazonian craton: Evidence from U-Pb-Sm-Nd and Rb-Sr geochronology

    International Nuclear Information System (INIS)

    Tassinari, C.C.G.; Teixeira, W; Nutman, A.P; Szabo, G.; Mondin, M.; Sato, K; Santos, A.P; Siso, C.S

    2001-01-01

    The Archean Imataca Complex (IC), NW Amazonian Craton, forms a ENE-trending, fault-bounded block adjacent to the Paleoproterozoic Maroni-Itacai as magmatic arc (2.2 2.0 Ga) (Tassinari and Macambira, 1999). The IC rocks are complexely deformed, exhibiting elongated and symmetrical domes and thrusts combined with isoclinal folds. Transcurrent faults are also important, like the Guri Fault System - a zone of multiple faulting, shearing and mylonitization along the southeastern edge of the IC. In a pre-Pangean reconstruction using paleomagnetic data from rocks of the African counterpart, the Guri System is contiguous to the Sassandra (Ivory coast) and Zednes (Mauritaine) faults, in agreement also with the comparable geologic evolution between the NW Amazonian and the West Africa cratons, during the Archean and Late-Paleoproterozoic. The IC mainly composed of medium- to high grade quartz-feldspathic paragneiss, exhibits extensive mortar, augen, flaser and mylonitic textures. Calc-alkaline gneiss and granitoid rocks of igneous protolith are also present in the IC, as well as dolomitic marbles, orthopyroxene and magnetite quartzites, and BIFs that include huge ore deposits of Algoma type. Moreover, migmatite injections and anatexis (devoid of metasedimentary components) are widespread in the western part of Complex, the largest migmatite mass centered in Cerro La Ceiba. This paper reports zircon U-Pb SHRIMP, Sm-Nd and Rb-Sr isotopic data of different IC rocks in order to investigate their age and geological evolution within the tectonic framework of the Amazonian Craton (au)

  7. Sm-Nd, Rb-Sr and K-Ar age constraints of the El Molle and Barroso plutons, western Sierra de San Luis, Argentina

    International Nuclear Information System (INIS)

    Sato, A.M.; Gonzalez, P.D; Petronilho, L.A; Llambias, E.J.; Varela, R; Basei, M.A.S

    2001-01-01

    Within the Early Paleozoic Famatinian orogeny of Southern Sierras Pampeanas (Sierra de San Luis and Sierra de Cordoba), the post-orogenic granitoids are characterized by circular intrusions. The published Rb-Sr and K-Ar ages from plutons in the Sierra de San Luis range between 408 and 320 Ma (see synthesis in Llambias et al., 1998). The El Molle and Barroso plutons (Sims et al., 1997; Gonzalez and Sato, 2000) are the two main exposures of a post-orogenic intrusive complex located in the western area of the Sierra de San Luis basement. They also exhibit an overall circular map view of almost 8 km in diameter, and are emplaced in a metamorphic complex developed through pre-Famatinian (Proterozoic? to Early Paleozoic) to Famatinian (Early Paleozoic) orogenies (Gonzalez and Llambias, 1998; von Gosen and Prozzi, 1998). We are carrying out isotopic datings of the El Molle and Barroso plutons in order to contribute to the understanding of the magmatic and metamorphic evolution of the final stages of the Famatinian orogenic cycle in the Sierra de San Luis. The first results of the Sm-Nd, Rb-Sr and K-Ar dates are here presented (au)

  8. Hydrogeochemistry and isotope geochemistry of Velenje Basin groundwater

    Directory of Open Access Journals (Sweden)

    Tjaša Kanduč

    2016-08-01

    Full Text Available The geochemical and isotopic composition of groundwater in the Velenje Basin, Slovenia, was investigated between the years 2014 to 2015 to identify the geochemical processes in the major aquifers (Pliocene and Triassic and the water–rock interactions. Thirty-eight samples of groundwater were taken from the aquifers, 19 in the mine and 19 from the surface. Groundwater in the Triassic aquifer is dominated by HCO3–, Ca2+ and Mg2+ with δ13C DIC values in the range from -19.3 to -2.8 ‰, indicating degradation of soil organic matter and dissolution of carbonate minerals. In contrast, groundwater in the Pliocene aquifers is enriched in Mg2+, Na+, Ca2+, K+, and Si, and has high alkalinity, with δ13CDIC values in the range of -14.4 to +4.6 ‰. Based on the δ13CDIC values in all the aquifers (Pliocene and Triassic, both processes inflence the dissolution of carbonate minerals and dissolution of organic matter and in the Pliocene aquifers, methanogenesis as well. Based on Principal Component Analysis (PCA, and on geochemical and isotopic data we conclude that the following types of groundwater in Velenje Basin are present: Triassic aquifers with higher pH and lower conductivity and chloride, Pliocene, Pliocene 1 and Pliocene 2 aquifers with lower pH and higher conductivity and chloride contents, and Pliocene 3 and Pliocene 2, 3 aquifers with the highest pH values and lowest conductivities and chloride contents. 87Sr/86Sr tracer was used for the fist time in Slovenia to determine geochemical processes (dissolution of silicate versus carbonate fraction in Velenje Basin groundwater of different aquifers dewatering Pliocene and Triassic strata. 87Sr/86Sr values range from 0.70820 to 0.71056 in groundwater of Pliocene aquifers and from 0.70808 to 0.70910 in groundwater of the Triassic aquifer. This indicates that dissolution of the carbonate fraction prevails in both aquifers, while in Pliocene aquifers, an additional silicate weathering prevails with

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

    Science.gov (United States)

    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

  10. Isotope hydrology and geochemistry of northern Chile groundwaters

    Directory of Open Access Journals (Sweden)

    1995-01-01

    Full Text Available HYDROLOGIE ISOTOPIQUE ET GEOCHIMIE DES EAUX SOUTERRAINES DU NORD CHILI. Cet article est un résumé des études de caractérisation d’aquifères situés dans la Pampa del Tamarugal et du Salar de Atacama au nord du Chili à l’aide d’isotopes. Les objectifs principaux de ces études étaient d’obtenir de l’information sur l’origine et le temps de résidence des eaux souterraines, la qualité des eaux, les taux d’évaporation des salars et la relation entre les inondations et la recharge des aquifères. Les principales conclusions de ces études sont les suivantes: a la majorité de l’eau souterraine est de bonne qualité à l’exception des zones situées près des salars b un système multi-aquifère a été identifié dans le bassin de la Pampa del Tamaragual en relation avec des zones de recharges situées à différentes altitudes et c une importante portion des eaux souterraines dans les aquifères de la Pampa devraient êtres considérées comme une ressource non renouvelable. HIDROLOGÍA ISOTÓPICA Y GEOQUÍMICA DE LAS AGUAS SUBTERRÁNEAS DEL NORTE DE CHILE. En este trabajo se presenta un resumen de estudios que se han realizado en el Norte de Chile, en acuíferos localizados en la Pampa del Tamarugal y en el Salar de Atacama. Los principales objetivos de esos estudios fueron obtener información sobre el origen y el tiempo de residencia del agua subterránea, calidad química del agua, tasas de evaporación desde los salares y evaluar la relación entre inundaciones y recarga a los acuíferos. Las principales conclusiones de estos estudios fueron las siguientes: a la mayoría del agua subterránea es de buena calidad, con la excepción de las áreas cercanas a los salares b se identificó en la cuenca de la Pampa del Tamarugal un sistema de multiacuífero relacionado a áreas de recargas localizadas en diferentes altitudes c una parte importante del agua subterránea en la Pampa del Tamarugal tiene que ser tratada como un recurso

  11. Application of the Rb-Sr, Pb-Pb and Sm-Nd systems on the Salobe 3A polymetallic deposit, Carajas Mineral Province, Para, Brazil; Aplicacao dos sistemas Rb-Sr, Pb-Pb e Sm-Nd do deposito polimetalico do Salobo 3A, Provincia Mineral de Carajas, Para

    Energy Technology Data Exchange (ETDEWEB)

    Mellito, Katia Maria

    1998-07-01

    The Salobo 3A polymetallic Cu (Au-Mo-Ag) deposit, located in the northern part of the Carajas Mineral Province, Para, consists of a metavolcano-sedimentary sequence represented by iron formation, amphibolite, schist and quartzite of the Igarape Salobo Group. This rock sequence rest uncomformably on the gneissic basement of the Xingu Complex. The copper mineralization hosted by iron formation consists of bornite-chalcocite and bornite-chalcopyrite disseminations associated with magnetite. The geochronological data determined through the application of the Rb-Sr, Sm-Nd and Pb-Pb methods, contribute to characterize the complex evolution of both the geological setting and the cupriferous mineralization of the Salobo deposit. The 3.11-2.92 Ga interval (T{sub DM}, Sm-Nd, whole rock) represents the age of the igneous protholith of the gneiss. The {epsilon}{sub Nd} values calculated for the time of the gneiss formation (2859 Ma) vary between +1.02 and -1.08, and indicate a short period between the mantle-crust differentiation epoch and the gneiss formation. Moreover, the {epsilon}{sub Nd} parameter suggest a mantle source with late crustal contamination. The application of the leaching technique allows a gradual extraction of Pb at each leaching step and it was applied to chalcocite and magnetite. The 2762 {+-} 180 Ma and 2776 {+-} 240 Ma ages determined on those minerals are interpreted to be close to the epoch of the formation of the copper mineralization with Uu and Th enrichment and of the iron formation deposition, respectively, in a conventional setting. The leaching technique was also applied to tourmaline from gneiss and quartzite, and the age near to 2400 Ma was attributed to its formation. The random variability of the Pb isotope compositions of the tourmaline together with its petrographic characteristics suggest the boron source is not associated with the metassedimentary rocks of the Igarape Salobo Group. The Sm-Nd mineral isochron attributed to schists

  12. Age and sedimentary provenance of the Canastra and Vazante groups in the regions of Guarda-Mor and Unai, Minas Gerais, Sm-Nd and U-Pb methods, Brazil

    International Nuclear Information System (INIS)

    Marimon, Rodrigo Schwantes; Dantas, Elton Luiz; Matteini, Massimo

    2015-01-01

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

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

    International Nuclear Information System (INIS)

    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 (δ 13 C) as a result of these reactions; and (5) using carbon-14 ( 14 C) data to calculate velocity

  14. Application of heavy stable isotopes in forensic isotope geochemistry: A review

    International Nuclear Information System (INIS)

    Aggarwal, Jugdeep; Habicht-Mauche, Judith; Juarez, Chelsey

    2008-01-01

    Light stable isotopes have been used for many years to characterize the source and transport of materials. More recently heavy isotope systems such as Sr, Nd and Pb have been added to this list in order to aid source identification. With the advent of multiple collector ICP-MS, the range of isotopic tools now available has increased considerably, however, until the isotope systematics of these new non-traditional isotope systems have become better understood, they will not be as useful in characterizing material source and transportation. Applications using heavy metal stable isotopes (mostly traditional heavy isotopes) have reached most avenues in science, including earth sciences, archaeology, anthropology, animal physiology, ecology and toxicology. This field will continue to grow as new applications are developed and techniques become simpler and quicker. This paper provides a review of how this field has grown and presents two new applications using Pb and Sr isotopes in glazes to determine the source of ore used in glazes, and using Sr isotopes to determine the origin of undocumented deceased Mexican border crossers

  15. Application of heavy stable isotopes in forensic isotope geochemistry: A review

    Energy Technology Data Exchange (ETDEWEB)

    Aggarwal, Jugdeep [W.M. Keck Isotope Laboratory, Department of Earth Sciences, University of California, Santa Cruz, CA 95064 (United States)], E-mail: jaggarwal@pmc.ucsc.edu; Habicht-Mauche, Judith; Juarez, Chelsey [Department of Anthropology, University of California, Santa Cruz, CA 95064 (United States)

    2008-09-15

    Light stable isotopes have been used for many years to characterize the source and transport of materials. More recently heavy isotope systems such as Sr, Nd and Pb have been added to this list in order to aid source identification. With the advent of multiple collector ICP-MS, the range of isotopic tools now available has increased considerably, however, until the isotope systematics of these new non-traditional isotope systems have become better understood, they will not be as useful in characterizing material source and transportation. Applications using heavy metal stable isotopes (mostly traditional heavy isotopes) have reached most avenues in science, including earth sciences, archaeology, anthropology, animal physiology, ecology and toxicology. This field will continue to grow as new applications are developed and techniques become simpler and quicker. This paper provides a review of how this field has grown and presents two new applications using Pb and Sr isotopes in glazes to determine the source of ore used in glazes, and using Sr isotopes to determine the origin of undocumented deceased Mexican border crossers.

  16. Geochemistry of Archaean supracrustal belts in SW Greenland

    DEFF Research Database (Denmark)

    Szilas, Kristoffer

    This PhD-thesis investigates the geological formation environment of c. 3200-3000 million-year-old volcanic rocks from SW Greenland, using whole-rock geochemical data in combination with U-Pb, Sm-Nd and Lu-Hf isotope data. The following three supracrustal areas were studied: (1) The Tartoq Group ...

  17. Genesis of hydrothermal alterations using stable isotope geochemistry in Takestan area (Tarom zone

    Directory of Open Access Journals (Sweden)

    Batool Taghipou

    2015-12-01

    Full Text Available Hydrothermal alteration processes are extensively took place on volcanic and pyroclstics of Takestan area. Existence of abundant, deep fracturing and subvolcanic intrusions are enhanced extend hydrothermal alteration zones. The following alteration zones are determined: propylitic, argillic, advanced argillic and sillicic. There are outcropped and widespread in different size and limit. Formation of siliceous sinter, silicified tuffs with preserved primary sedimentary layering including pure mineralized alunite patches are most outstanding. Quartz, sussoritic plagioclase, chlorite, sericite and alunite are main mineral constituents in the volcanics. On the basis of geochemical data volcanic rocks are rhyolite, dacite, andesite, andesitic-basalt and basalt in composition. Acid-sulfate zone is the type of alteration in Tarom area and alunite is an index mineral of this zone. Results of 18O, D and 34S stable isotope geochemistry on altered minerals (muscovite, kaolinite and alunite, revealed that alteration fluids are magmatic in origin.

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

    Science.gov (United States)

    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 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.

  19. Mott state and quantum critical points in rare-earth oxypnictides RO1-xFxFeAS (R= La, Sm, Nd, Pr, Ce)

    NARCIS (Netherlands)

    Giovannetti, G.; Kumar, S.; van den Brink, J.

    2008-01-01

    We investigate the magnetic phase diagram of the newly discovered iron-based high temperature oxypnictide superconductors of the type RO1-xFxFeAs, with rare earths R=La, Sm, Nd, Pr and Ce by means of ab initio SGGA and SGGA+U density functional computations. We find undoped LaOFeAs to be a Mott

  20. New Sm/Nd and U/Pb geochronological constraints of the Archean to neoproterozoic evolution of the Amparo basement complex of the Central Ribeira Belt, Southeastern Brazil

    International Nuclear Information System (INIS)

    Fetter, A.H.; Hackspacher, P.C.; Ebbert, H.D; Dantas, E.L; Costa, A.C.D. da

    2001-01-01

    The Amparo Basement Complex is a distinctive collage of migmatitic tronjhemitetonalite- granodiorite (TTG) orthogneisses that represents the older basement exposures within the Central Ribeira Belt, a Late Neoproterozoic (ca. 600 Ma) collisional belt in southeastern Brazil. These basement gneisses are overlain by Mesoproterozoic to Neoproterozoic supracrustal sequences, and intruded by Neoproterozoic collisional granitoids. Pioneering Rb/Sr, Pb/Pb and K/Ar geochronological studies of the Amparo Complex, e.g. (Wernick et al., 1981; Wernick and Oliveira, 1986; Arthur, 1988; Tassinari, 1988; Campos Neto, 1991) provided some initial insights into the antiquity and geologic evolution of the complex, but little about the crustal evolution of the constituent gneisses. Furthermore, the susceptibility of these systems to partial isotopic resetting, left some doubt about the timing and true number of geologic events recorded by these polydeformed rocks. Recent Sm/Nd whole rock (Dantas et al., 2000) and new U/Pb single crystal zircon and monazite data obtained from the Amparo Complex, however, now furnish information on the crustal growth history of the basement and provide precise age constraints on the timing of events related to the geologic evolution of the complex. Based on these new data, it appears that the oldest rocks within the complex are polymigmatized tronjhemitic gneisses located near the town of Amparo. The oldest phase of this migmatite yields a U/Pb zircon age of 3,024 +/- 9 Ma. Sm/Nd data from this locale yields a Nd T(DM) model age of 3.28 Ga suggesting that the genesis of this crustal unit involved some input from yet older crust. Data from banded tonalitic gneisses collected ca. 50 km south of Amparo indicate that subsequent Archean crustal growth around the older core occurred around 2.77 Ga (U/Pb zircon age of 2,772 +/- 26 Ma. A Nd T(DM) model age of 3.02 Ga obtained from these tonalites also indicate enrichment from older crustal sources during their

  1. Late Guadalupian evolution of the Delaware Basin: insights from stable isotope and trace element geochemistry

    Science.gov (United States)

    Smith, B.; Kerans, C.

    2017-12-01

    Accurate characterization of mixed carbonate and evaporite deposits requires an understanding of basin-scale physical, chemical, and biological processes. In these settings, carbonate geochemistry often responds to changes in the prevailing conditions in the water column. It follows that the geochemical record presents a potential aid for interpretation of depositional systems provided that it is relatively free of diagenetic overprint. This is seldom the case in shallow-water settings as processes such as meteoric diagenesis and early dolomitization obscure or erase the original geochemical signal. Fine grained deep-water sediments are more likely to retain their original geochemical characteristics. If reliable shelf-to-basin correlations can be established, then basinal deposits provide critical data not only for the interpretation of deep water environments, but overall basin evolution as well. This study examines variations in trace element and stable isotope geochemistry from the Delaware Basin of West Texas and New Mexico. Interpretation of geochemical data within a pre-existing shelf-to-basin stratigraphic framework suggests a link between basin water chemistry and sea level changes during the entirety of the Guadalupian. This link is supported analogies to modern silled basins where changes in sea level and thus recharge across the sill can control nutrient input, circulation, and bottom water oxygenation. In light of these relationships, the filling of the Delaware Basin with basin-centered evaporites at the end of the Guadalupian likely represents the culmination of a more gradual, cyclic evolution towards basin restriction. Ongoing work will continue to focus on tying regional-scale changes in basin water chemistry to the combined geochemical and physical sedimentological records.

  2. Sr isotope geochemistry of East Alpine mineral deposits and mass spectrometric analyses of fluid inclusions

    International Nuclear Information System (INIS)

    Grum, W.

    1995-05-01

    Strontium isotope geochemistry and deformational history of selected carbonate-hosted deposits from different tectonic positions in the Eastern Alps were studied. In this context an equipment has been constructed to analyze the composition of volatile components of fluid inclusions (FI). Based on the results of Sr-isotopic investigations two groups of deposits are discriminated: Deposits formed by formation waters and/or metamorphogenic fluids: Tux (magnesite, scheelite), Otterzug (barite), Lassing (magnesite), Rabenwald (talc), Laussa and Mooseck (fluorite). The mineralizing fluids are derived from different sedimentary rock series and therefore 87 Sr/ 86 Sr-ratios vary between 0.707 and 0.719. Deposits situated along fault zones: Lassing (talc), Gasteiner Tal (Silberpfennig area; gold), Schlaining (stibnite) and Waldenstein (specularite). Sr isotope ratios of the mineralizing fluids from Lassing, Waldenstein and Schlaining ranges from 0.7112 to 0.7127 and are therefore thought to have scavenged the East Alpine crystalline. The mineralizing solutions of the Gasteiner Tal deposit may either have equilibrated with low radiogenic sedimentary or with (ultra-)basic rocks. A cracking chamber has been constructed in order to open FI by cracking for mass spectrometric analysis of volatile components. Gases are analysed using a quadrupole mass spectrometer. The desorption of gas from metal and sample surfaces during cracking can be neglected. The amount of gas released from the mineral lattices was studied. With that fast method ore bearing from barren host rocks have been distinguished by different composition of the FI at the Brixlegg barite mineralization (Eastern Alps). Within the Galway fluorite deposit (Ireland) different fluids were involved and mass spectrometric analysis were carried out to characterize these different fluids and to identify their origin. (author)

  3. Isotopic signature of Madeira basaltic magmatism

    International Nuclear Information System (INIS)

    Kogarko, L.N.; Karpenko, S.F.; Bibikova, E.V.; Mato, Zh.

    2000-01-01

    Chemical composition of the basalts of Madeira Island is studied. To assess the isotopic sources of magmatism the Pb-Sr, Sm-Nd, U-Th-Pb systems were investigated in a number of basalts. It is shown that the island's rocks are characterized by the mostly deplet sources in relation to Pb-Sr and Sm-Nd systems ( 87 Sr/ 86 Sr - 0.70282-0.70292, 143 Nd/ 144 Nd - 0.52303-0.51314). Isotopic composition of lead testifies that the magmatism reservoir is some enriched. It is concluded that the magmatism of Madeira Island is a new example of world ocean island's volcanism [ru

  4. The isotopic dating of crystals

    International Nuclear Information System (INIS)

    Giuliani, G.; Cheilletz, A.

    1995-01-01

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

  5. History of the Pasamonte achondrite: relative susceptibility of the Sm-Nd, Rb-Sr, and U-Pb systems to metamorphic events

    International Nuclear Information System (INIS)

    Unruh, D.M.; Tatsumoto, M.; Nakamura, N.

    1977-01-01

    The Rb-Sr, Sm-Nd, and U-Pb systematics of the eucrite Pasamonte have been studied in order to investigate the relative susceptibility of the different systems to post-crystallization events and to determine the age and history of the meteorite. The Rb-Sr and 238 U- 206 Pb data of mineral separates do not define an isochron but the Sm-Nd data define an internal isochron which corresponds to the formation age of 4.58+-0.12 b.y. (10 9 years). The 207 Pb- 206 Pb data of mineral separates define an apparent age of 4.53+-0.03 b.y., however it is concluded that this age, while in agreement with the Sm-Nd age, is not strictly valid since the U-Pb data indicate at least three stages of evolution. The U-Pb data indicate that the parent body of the meteorite experienced brecciation shortly after the formation of the parent body surface (approximately 4.2-4.45 b.y. ago) and a recent disturbance (collision) 6+-30 m.y. ago. The latter age is within the range of cosmic ray exposure ages for achondrites. (Auth.)

  6. Strontium isotope geochemistry of groundwater affected by human activities in Nandong underground river system, China

    Energy Technology Data Exchange (ETDEWEB)

    Jiang Yongjun, E-mail: jiangjyj@swu.edu.cn [School of Geographical Sciences, Southwest University, Chongqing 400715 (China)] [Institute of Karst Environment and Rock Desertification Rehabilitation, Chongqing 400715 (China)

    2011-03-15

    Research highlights: {yields} Spatio-temporal variations of Sr concentrations and Sr isotopic composition of groundwater were investigated in a karst underground river system. {yields} Agricultural fertilizers and sewage effluents significantly modified the natural Sr isotopic signature of karst groundwater. {yields} Sr in the carbonate aquifers was relatively non-radiogenic, with low Sr concentrations, while anthropogenic Sr correlated with agricultural fertilizers and sewage effluents was relatively radiogenic, with higher Sr concentrations. {yields} {sup 87}Sr/{sup 86}Sr ratios can provide key information for natural and anthropogenic sources in karst groundwater. - Abstract: The Nandong Underground River System (NURS) is located in a typical karst area dominated by agriculture in SE Yunnan Province, China. Groundwater plays an important role in the social and economical development in the area. The effects of human activities (agriculture and sewage effluents) on the Sr isotope geochemistry were investigated in the NURS. Seventy-two representative groundwater samples, which were collected from different aquifers (calcite and dolomite), under varying land-use types, both in summer and winter, showed significant spatial differences and slight seasonal variations in Sr concentrations and {sup 87}Sr/{sup 86}Sr ratios. Agricultural fertilizers and sewage effluents significantly modified the natural {sup 87}Sr/{sup 86}Sr ratios signature of groundwater that was otherwise dominated by water-rock interaction. Three major sources of Sr could be distinguished by {sup 87}Sr/{sup 86}Sr ratios and Sr concentrations in karst groundwater. Two sources of Sr are the Triassic calcite and dolomite aquifers, where waters have low Sr concentrations (0.1-0.2 mg/L) and low {sup 87}Sr/{sup 86}Sr ratios (0.7075-0.7080 and 0.7080-0.7100, respectively); the third source is anthropogenic Sr from agricultural fertilizers and sewage effluents with waters affected having radiogenic {sup 87

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

    DEFF Research Database (Denmark)

    Frei, Robert; Rosing, Minik; Stecher, Ole

    1999-01-01

    Pb stepwise leaching (PbSL) determinations on two magnetite-enriched fractions of a BIF sample from the northeastern part of the Isua supracrustal belt (West Greenland) yield an isochron of 3691 ± 22 Ma (MSWD = 0.4). In combination with previously published geochronological constraints for a mini...

  8. Data Reduction of Laser Ablation Split-Stream (LASS) Analyses Using Newly Developed Features Within Iolite: With Applications to Lu-Hf + U-Pb in Detrital Zircon and Sm-Nd +U-Pb in Igneous Monazite

    Science.gov (United States)

    Fisher, Christopher M.; Paton, Chad; Pearson, D. Graham; Sarkar, Chiranjeeb; Luo, Yan; Tersmette, Daniel B.; Chacko, Thomas

    2017-12-01

    A robust platform to view and integrate multiple data sets collected simultaneously is required to realize the utility and potential of the Laser Ablation Split-Stream (LASS) method. This capability, until now, has been unavailable and practitioners have had to laboriously process each data set separately, making it challenging to take full advantage of the benefits of LASS. We describe a new program for handling multiple mass spectrometric data sets collected simultaneously, designed specifically for the LASS technique, by which a laser aerosol is been split into two or more separate "streams" to be measured on separate mass spectrometers. New features within Iolite (https://iolite-software.com) enable the capability of loading, synchronizing, viewing, and reducing two or more data sets acquired simultaneously, as multiple DRSs (data reduction schemes) can be run concurrently. While this version of Iolite accommodates any combination of simultaneously collected mass spectrometer data, we demonstrate the utility using case studies where U-Pb and Lu-Hf isotope composition of zircon, and U-Pb and Sm-Nd isotope composition of monazite were analyzed simultaneously, in crystals showing complex isotopic zonation. These studies demonstrate the importance of being able to view and integrate simultaneously acquired data sets, especially for samples with complicated zoning and decoupled isotope systematics, in order to extract accurate and geologically meaningful isotopic and compositional data. This contribution provides instructions and examples for handling simultaneously collected laser ablation data. An instructional video is also provided. The updated Iolite software will help to fully develop the applications of both LASS and multi-instrument mass spectrometric measurement capabilities.

  9. Oxygen isotope geochemistry of Laurentide ice-sheet meltwater across Termination I

    Science.gov (United States)

    Vetter, Lael; Spero, Howard J.; Eggins, Stephen M.; Williams, Carlie; Flower, Benjamin P.

    2017-12-01

    We present a new method that quantifies the oxygen isotope geochemistry of Laurentide ice-sheet (LIS) meltwater across the last deglaciation, and reconstruct decadal-scale variations in the δ18O of LIS meltwater entering the Gulf of Mexico between ∼18 and 11 ka. We employ a technique that combines laser ablation ICP-MS (LA-ICP-MS) and oxygen isotope analyses on individual shells of the planktic foraminifer Orbulina universa to quantify the instantaneous δ18Owater value of Mississippi River outflow, which was dominated by meltwater from the LIS. For each individual O. universa shell, we measure Mg/Ca (a proxy for temperature) and Ba/Ca (a proxy for salinity) with LA-ICP-MS, and then analyze the same O. universa for δ18O using the remaining material from the shell. From these proxies, we obtain δ18Owater and salinity estimates for each individual foraminifer. Regressions through data obtained from discrete core intervals yield δ18Ow vs. salinity relationships with a y-intercept that corresponds to the δ18Owater composition of the freshwater end-member. Our data suggest that from 15.5 through 14.6 ka, estimated δ18Ow values of Mississippi River discharge from discrete core intervals range from -11‰ to -21‰ VSMOW, which is consistent with δ18O values from both regional precipitation and the low-elevation, southern margin of the LIS. During the Bølling and Allerød (14.0 through 13.3 ka), estimated δ18Ow values of Mississippi River discharge from discrete core intervals range from -22‰ to -38‰ VSMOW. These values suggest a dynamic melting history of different parts of the LIS, with potential contributions to Mississippi River outflow from both the low-elevation, southern margin of the LIS and high-elevation, high-latitude domes in the LIS interior that were transported to the ablation zone. Prior to ∼15.5 ka, the δ18Owater value of the Mississippi River was similar to that of regional precipitation or low-latitude LIS meltwater, but the Ba

  10. Geochemistry of the Congo and Amazon river systems. Boron isotopic geochemistry in corals. Continental erosion and ocean pH

    International Nuclear Information System (INIS)

    Gaillardet, J.

    1995-01-01

    Two main geological processes control the CO 2 concentration in the atmosphere at a geological time scale: CO 2 outgasing from the interior of the Earth and CO 2 consumption by continental weathering. In the thesis, we initiate two different directions that can be useful to constraint the past climate evolution models. The first one is the extensive study of the largest rivers of the world using the classical geochemical analyses (major and trace elements, Sr-Nd-Pb isotopes) and modelling approaches. The study case of this thesis are the Congo and Amazon Basin. In particular, the coupling between chemical and physical erosion is examined and related to the hydrologic and tectonic parameters. Relief, thus tectonics appear to best control CO 2 consumption by rock weathering. The second part of the work is devoted to the measurement of boron isotopic ratio in corals because it may be used as a proxy for paleo-ocean pH. It could thus bring important pieces of information on the global C cycle and climate evolution. The technical part is extensively described and the method applied to the corals from the last interglacial period. Our conclusion is that corals are likely to be influence by early diagenetic changes that modify the boron isotopic composition of corals. We thus propose a test to select the samples. (author)

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

    Energy Technology Data Exchange (ETDEWEB)

    Henrique-Pinto, Renato; Janasi, Valdecir de Assis; Tassinari, Colombo Celso Gaeta [Universidade de Sao Paulo (USP), SP (Brazil). Inst. de Geociencias. Dept. de Mineralogia e Geotectonica; Simonetti, Antonio [University of Notre Dame, South Bend (United States). Dept. of Civil Engineering and Geological Sciences; Heaman, Larry Michael, E-mail: renatohp@usp.br, E-mail: vajanasi@usp.br, E-mail: ccgtassi@usp.br, E-mail: antonio.simonetti.3@nd.edu, E-mail: larry.heaman@ualberta.ca [University of Alberta, Edmonton (Canada). Dept. of Earth and Atmospheric Sciences

    2012-12-15

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

  12. Study the mechanisms of recharge of the phreatic aquifers, south east egypt, using environmental isotopes and hydro geochemistry

    International Nuclear Information System (INIS)

    Hassan, T.M.; Awad, M.A.; Hamza, M.S.

    1994-01-01

    The recharge rate is the most critical factor to groundwater resources management especially in semi-arid and arid areas. This paper presents a study on the feasibility of a groundwater development plan for south east egypt area. Environmental stable isotopes (oxygen-18 and deuterium), and hydro geochemistry techniques were used to investigate the recharge sources of groundwater. The examined groundwater wells tap the quaternary, basement and Nubian sandstone aquifers. The isotopic compositions of these groundwater samples indicate that there is a mixing among three different sources of recharge, local precipitation, palaeo water and sea water intrusion along the coastal plain, from the hydrochemical point of view, the predominant water types reflect meteoric, as well as marine waters genesis. The changes in salinity depend upon the dissolution of terrestrial salts, distance from the catchment area and seepage from deep aquifers. 7 figs., 2 tabs

  13. Niobium-Thorium-Strontium-Rare Earth Element Mineralogy and Preliminary Sulphur Isotope Geochemistry of the Eaglet Property, East-Central British Columbia (NTS 093A/10W)

    Czech Academy of Sciences Publication Activity Database

    Hora, Z. D.; Langrová, Anna; Pivec, Edvín; Žák, Karel

    2010-01-01

    Roč. 2009, č. 1 (2010), s. 93-96 ISSN 0381-243X Institutional research plan: CEZ:AV0Z30130516 Keywords : fluorite * celestite * pyrochlore * thorite * titanbetafite * bastnaesite * sulphur isotopes * Eaglet deposit * MINFILE 093A46 Subject RIV: DD - Geochemistry http://www.empr.gov.bc.ca/Mining/Geoscience/PublicationsCatalogue/Fieldwork/Documents/2009/08_Hora_2009.pdf

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

    Science.gov (United States)

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

    2016-12-01

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

  15. U-Pb, Sm-Nd and Rb-Sr systematics of mid-ocean ridge basalt glasses

    Energy Technology Data Exchange (ETDEWEB)

    Cohen, R S; Evensen, N M; Hamilton, P J; O' Nions, R K [Columbia Univ., Palisades, NY (USA). Lamont-Doherty Geological Observatory

    1980-01-10

    The measurement of Pb, Nd and Sr isotopes in basalt glasses from mid-ocean ridges reveals correlations in isotope parameters which have important implications for the differentiation history of the mantle.

  16. Provenance and depositional age of metavolcano-sedimentary sequences of the Santa Terezinha de Goias, based on Sm-Nd and U-Pb zircon single grain

    International Nuclear Information System (INIS)

    Dantas, Ellton Luiz; Jost, Hardy; Fuck, Reinhardt A.; Brod, Jose Afonso; Pimentel, Marcio Martins; Meneses, Paulo Roberto

    2001-01-01

    Supracrustal rocks of the Santa Terezinha de Goias region, Central Brazil, presumably represent a southern extension of the Mara Rosa magmatic arc tectonically juxtaposed to Archean terrains and consist of a meta volcanic unit and a meta sedimentary unit. The aim of the paper is to present and discuss the first U-Pb and Sm-Nd data of rocks belonging to both units of that region. U-Pb data of zircons from a felsic meta volcanic rock inter layered with chlorite-rich schists (metandesites?) yield a concordant age of of 660 My, while the Sm-Nd model age of a variety of chlorite-schists indicate a juvenile age between 1.1 and 1.3 Ga. These data indicate that the meta volcanic rocks are Neo proterozoic in age and may be correlated with rocks of the Mara Rosa magmatic arc. On the other hand, the prevailing provenance of rocks belonging to the meta sedimentary unit indicate a Paleoproterozoic, or older, source. Thus, the deposition of both units are explained by means of the erosion of source-areas of variable age. (author)

  17. U-Pb SHRIMP and Sm-Nd geochronology of the Anapolis-Itaucu complex, Araxa group and associated granites: Neoproterozoic high grade metamorphism and magmatism in the Central part of the Brasilia Belt, Goias

    International Nuclear Information System (INIS)

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

    2001-01-01

    The Tocantins Province (Almeida et al. 1981) in central Brazil is a Neoproterozoic orogenic zone developed between the Amazon and Sao Francisco cratons and possibly a third continental block, known as Parapanema Block, hidden below the sedimentary rocks of the Parana Basin. The Tocantins Province comprises the eastward vergent Brasilia Belt, adjacent to the Sao Francisco Craton (Marini et al. 1984), and the westward vergent Paraguay and Araguaia belts, developed on the eastern margin of the Amazon Craton. According to Trompette (1997), the Brasilia and Araguaia belts had sedimentation starting at around 1.1-1.0 Ga and final closure at 0.6 Ga. In the northern part of the Brasilia Belt occur the Barro Alto, Canabrava and Niquelandia maficultramafic layered complexes. Inconclusive U-Pb isotopic data indicate ages between ca. 1600 and 2000 Ma for these intrusions that were affected by highgrade metamorphism ca. 740-790 Ma ago, during the Neoproterozoic (Ferreira Filho et al. 1994; Suita et al. 1994; Correia et al. 1997). In the southern part of the Brasilia Belt, in central Goias , is the Anapolis-Itaucu granulite complex. It consists of a large complex of high-grade rocks, volcano-sedimentary sequences and granites, exposed in between metasediments of the Araxa Group, the main constituent of the internal zone of the Neoproterozoic Brasilia Belt (Fuck et al. 1994). These granulites have traditionally been interpreted as the exposure of Archean sialic basement to the sediments of the Brasilia Belt (Danni et al. 1982, Marini et al. 1984; Lacerda Filho and Oliveira 1995). This work reports the results of a regional Sm- Nd isotopic investigation and U-Pb SHRIMP data in order to assess (i) the nature of the protoliths of the Araxa Group in this area; (ii) the nature and the high grade metamorphism of rocks from Anapolis-Itaucu Complex; (iii) the crystallization and metamorphism of aluminous granites (au)

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

    OpenAIRE

    Frédéric Moynier; Toshiyuki Fujii

    2017-01-01

    Stable Ca isotopes are fractionated between bones, urine and blood of animals and between soils, roots and leaves of plants by >1000?ppm for the 44Ca/40Ca ratio. These isotopic variations have important implications to understand Ca transport and fluxes in living organisms; however, the mechanisms of isotopic fractionation are unclear. Here we present ab initio calculations for the isotopic fractionation between various aqueous species of Ca and show that this fractionation can be up to 3000?...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1990-11-01

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

  20. Geochemistry, Nd-Pb Isotopes, and Pb-Pb Ages of the Mesoproterozoic Pea Ridge Iron Oxide-Apatite–Rare Earth Element Deposit, Southeast Missouri

    Science.gov (United States)

    Ayuso, Robert A.; Slack, John F.; Day, Warren C.; McCafferty, Anne E.

    2016-01-01

    Iron oxide-apatite and iron oxide-copper-gold deposits occur within ~1.48 to 1.47 Ga volcanic rocks of the St. Francois Mountains terrane near a regional boundary separating crustal blocks having contrasting depleted-mantle Sm-Nd model ages (TDM). Major and trace element analyses and Nd and Pb isotope data were obtained to characterize the Pea Ridge deposit, improve identification of exploration targets, and better understand the regional distribution of mineralization with respect to crustal blocks. The Pea Ridge deposit is spatially associated with felsic volcanic rocks and plutons. Mafic to intermediate-composition rocks are volumetrically minor. Data for major element variations are commonly scattered and strongly suggest element mobility. Ratios of relatively immobile elements indicate that the felsic rocks are evolved subalkaline dacite and rhyolite; the mafic rocks are basalt to basaltic andesite. Granites and rhyolites display geochemical features typical of rocks produced by subduction. Rare earth element (REE) variations for the rhyolites are diagnostic of rocks affected by hydrothermal alteration and associated REE mineralization. The magnetite-rich rocks and REE-rich breccias show similar REE and mantle-normalized trace element patterns.Nd isotope compositions (age corrected) show that: (1) host rhyolites have ɛNd from 3.44 to 4.25 and TDM from 1.51 to 1.59 Ga; (2) magnetite ore and specular hematite rocks display ɛNd from 3.04 to 4.21 and TDM from 1.6 to 1.51 Ga, and ɛNd from 2.23 to 2.81, respectively; (3) REE-rich breccias have ɛNd from 3.04 to 4.11 and TDM from 1.6 to 1.51 Ga; and (4) mafic to intermediate-composition rocks range in ɛNd from 2.35 to 3.66 and in TDM from 1.66 to 1.56. The ɛNd values of the magnetite and specular hematite samples show that the REE mineralization is magmatic; no evidence exists for major overprinting by younger, crustal meteoric fluids, or by externally derived Nd. Host rocks, breccias, and

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

    Science.gov (United States)

    Moynier, Frédéric; Fujii, Toshiyuki

    2017-03-01

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

  2. Geofluids Assessment of the Ayub and Shafa Hot Springs in Kopet-Dagh Zone (NE Iran: An Isotopic Geochemistry Approach

    Directory of Open Access Journals (Sweden)

    Hossein Mohammadzadeh

    2017-01-01

    Full Text Available Geothermal energy has a wide range of uses in our life. It is very important to characterize the temperature and the depth of geothermal reservoirs. The aim of this paper is the determination of type, origin source of water temperature, and depth of water circulation in the Ayub-Peighambar and Shafa (AP and SH hot springs, located in NE Iran, using hydrogeochemistry and environmental isotopes (2H and 18O. AP hot spring has elevated temperature (36–40°C and as such is very important for balneotherapy and geotourism industry purposes. The average values of δ18O and δ2H for this hot spring (−10‰ and −73‰, resp. are analogous to that of geothermal and meteoric waters. This indicates that the heat source cannot be related to volcanic activities (with average δ18O value of about 5‰ and it is most probably associated with geothermal gradient with deep circulation of groundwater through faults. Based on Na-K geothermometers coupled with isotopic (18O and 2H geochemistry the temperature of the AP geothermal reservoir was estimated to be in the range of 100–150°C with 3–5 and 4.2 kilometres’ depth, respectively. Chemically, the AP samples are CaSO4 facies with a chemically homogeneous source and steam heated waters type.

  3. Using isotope geochemistry to discuss the role of crust-mantle interaction in the formation of endogenetic mega-deposits

    International Nuclear Information System (INIS)

    Zhang Lisheng

    2005-01-01

    Isotope characteristics of some mega-deposits from literature and new results on twenty deposits (ten of them are mega-deposits) show that there exists traces of crust-mantle interaction. It has been established that the interaction all took place in the mantle under many situations. The theory of isotope geochemistry on the genesis of mega-deposits has been discussed. According to the theory, these deposits are a kind of special phenomena, but they have a common factor, i.e. mantle metasomatism produced by the crust-mantle interaction in the mantle no matter what the ore-forming elements diversity may be. The granites with great accumulation of uncompatible elements can be considered as the analogues of mega-deposits. According to the statistical results, it is possible that they formed at a period before about 2 Ga during which the recycling of the materials was accompanied with the obvious crust-mantle interaction and can produce the volatile components which are poor in the mantle. (authors)

  4. Sulfur and lead isotope geochemistry of the orogenic gold deposits in the eastern Kunlun area, Qinghai province

    International Nuclear Information System (INIS)

    Feng Chengyou; Zhang Dequan; Li Daxin; She Hongquan; Zhu Huaping

    2003-01-01

    Based on researches on the basic geological characteristics and sulfur and lead isotopic geochemistry of four typical gold deposits, it is considered that they have many similar geo-geochemical characteristics and are all related genetically to orogenic process. Therefore, they should belong to a type of orogenic gold deposits according to the newest classification of gold deposits provided by Kerrich et al. (2000). There is a big change in the average 34 S values of the sulfides selected from different deposits, varying from -3.7‰-4.4‰ and tower-shape distribution is apparent. The lead isotope in four gold deposits is characterized by high compositions and minor changes, with 206 Pb/ 204 Pb > 18.3380, 207 Pb/ 204 Pb > 15.5555, 208 Pb/ 204 Pb >38.1796 in ores and wall-rocks, it can be concluded that the ore-forming material consisting of sulfur and lead are mainly derived from wall-rocks. Intensive subduction and collision during late Paleozoic and early Mesozoic not only formed deep faults, large-scale shear belt, and low-order folds and faults but also induced fluidization and mineralization, and resulted in formation and zonal distribution of several large or medium gold deposits in this area. (authors)

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

    Science.gov (United States)

    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.

  6. Isotopic Geochemistry Applied on Mortars of the Katholikon of the Monastery of Timios Prodromos in the Prefecture of Serres, Greece

    Science.gov (United States)

    Dotsika, Elissavet; Iliadis, Efstathios; Kyropoulou, Daphne; Karalis, Petros

    2017-12-01

    The Monastery of Timios Prodromos is the most important Byzantine monument in the prefecture of Serres and one of the most important monastic foundations of Byzantine times in Northern Greece. It was founded in the late 13th century from Ioannikios and then renovated by his nephew, Joachim. The catholic dates back to the 14th century, and specifically between 1300-1333, under the rule of the second founder Joachim. Considering the pathology of Byzantine mural, for the most effective work on removal of over-paintings layer, fixing, restoration, recovery and maintenance of the painted surface and the substrate, it was decided the sampling from exact points of the mural painting representing the different phases, in order to determine their composition, the technology of construction materials, corrosion mechanisms and the proposal for restoration methodology. The methods to be used require very small quantities of material. The measurements are considered almost non-destructive and based on isotopic geochemistry. The techniques used are X-ray diffraction (XRD), scanning electron microscopy (SEM / EDXA) and isotopic analyzes (d18O and d13C) in a mass spectrometer (IRMS). The study of the samples was carried out by scanning electron microscopy with X-ray microanalyser and analysis of stable isotopes. The study shows that apart from the calcite present in all pigment samples, straw was used as a binder. There is also a mixing of dyes to produce the desired tint while in many cases there are different colour layers. The decay in the mural is extensive, especially in the lower layers of the wall, which have been severely affected by humidity and candle smoke. The creation of gypsum on the surface of the murals is intense and evident in most of the spectra taken

  7. Studies of geothermal background and isotopic geochemistry of thermal waters in Jiangxi Province

    International Nuclear Information System (INIS)

    Zhou Wenbin; Sun Zhanxue; Li Xueli; Shi Weijun

    1996-10-01

    The terrestrial heat flow measurement, isotope and geochemical techniques have been systematically applied to the geothermal systems in Jiangxi Province. Results show that the thermal waters in the study area all belong to the low-medium temperature convective geothermal system, which essentially differs from high temperature geothermal systems with deep magmatic heat sources. It has been proven that the isotope and geochemical techniques are very useful and effective in geothermal exploration. (13 refs., 14 tabs., 8 figs.)

  8. Geochemistry contribution of Pb isotopes on basalts origin study from Parana basin, Brazil

    International Nuclear Information System (INIS)

    Marques, L.S.; Dupre, B.; Allegre, C.J.

    1990-01-01

    This paper presents thirty new Pb-isotope and concentration data for low- and high-tiO sub(2) continental flood basalts of the Parana Basin. The results obtained from representative samples show significant differences with respect to type and location of these basic rocks. The low- and high-TiO sub(2) basalts from the northern region of the Parana Basin exhibit very similar Pb-isotope compositions. On the other hand, the low-TiO sub(2) basalts of central and southern areas, which exhibit low Sr initial isotope ratios (less than 0,7060), show very small variation in Pb isotope compositions which are highly enriched in radiogenic Pb in comparison with the analogues of northern region. The high-TiO sub(2) basic rocks analysed from northern and central regions have the same values for Pb isotope ratios, which are slightly more radiogenic compared with high-TiO sub(2) basalts from southern region. The data obtained, combined with other geochemical (major and trace elements, including rare earths) and isotope (Sr and Nd) results support the view that the basalts from northern and southern areas of the Parana Basin originated in lithospheric mantle reservoirs with different geochemical characteristics. (author)

  9. Sm-Nd isochrone of 2,1 Ga in ores of two samples from Santa Maria Chico Granulite Complex

    International Nuclear Information System (INIS)

    Hartmann, L.A.

    1987-01-01

    Sm and Nd isotopes were determined on garnet and plagioclasse from a metapelite and on garnet and clinopyroxene from a mafic gneiss. The age of this metamorphic event in the Santa Maria Chico Granulite Complex is 2.1 Ga. The age of generaion of the protoliths is 2.6 Ga, as determined on total rock samples. (author) [pt

  10. Variation of lithium isotope geochemistry during basalt weathering and secondary mineral transformations in Hawaii

    Science.gov (United States)

    Ryu, Jong-Sik; Vigier, Nathalie; Lee, Sin-Woo; Lee, Kwang-Sik; Chadwick, Oliver A.

    2014-11-01

    Lithium isotopes are a potential tracer of silicate weathering but the relationship between lithium isotope compositions and weathering state still need to be established with precision. Here, we report Li concentrations and Li isotope compositions of soils developed along a 4 million year humid-environment chronosequence in the Hawaiian Islands. Li concentrations are variable with depth and age, ranging from 0.24 to 21.3 ppm, and significant Li depletions (up to 92%) relative to parent basalts are systematically enhanced towards the surface. Our calculations show that the relative contribution from atmospheric deposits to the Li soil budget remains small, with a maximum contribution from dust Li of 20% at the oldest site. This is explained by the capacity of the weathering products to retain, within the profiles, the Li coming from basalt alteration, and allows us to explore more specifically the role of alteration processes on soil Li isotope signatures. The δ7Li values display a large range between -2.5‰ and +13.9‰. The youngest soils (0.3 ka) display the same δ7Li value as fresh basalt, regardless of depth, despite ∼30% Li loss by leaching, indicating that there is little Li isotope fractionation during the incipient stage of weathering. δ7Li values for the older soils (⩾20 ka) vary non-linearly as a function of time and can be explained by progressive mineral transformations starting with the synthesis of metastable short-range order (nano-crystalline) minerals and followed by their transformation into relatively inert secondary minerals. Results highlight significant Li isotope fractionation during secondary mineral formation and in particular during Li uptake by kaolinite. Finally, we suggest that the non-monotonous evolution of the regolith δ7Li value over the last 4 Ma is consistent with climatic variations, where congruent release of Li isotopes occurs during warmer periods.

  11. Strontium isotope geochemistry of groundwater in the central part of the Dakota (Great Plains) aquifer, USA

    International Nuclear Information System (INIS)

    Gosselin, David C.; Edwin Harvey, F.; Frost, Carol; Stotler, Randy; Allen Macfarlane, P.

    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

  12. Groundwater geochemistry of nile delta-desert interface 1.isotope hydrology

    International Nuclear Information System (INIS)

    Hussein, M.F.; Nada, A.A.; Awad, M.A.

    1995-01-01

    Sustenance and environmental protection of groundwater supply is of major concern in the integral environmental development in the arid to sub-arid regions in the Nile basin. Isotope data ( 18O , 2H and 3H ) of groundwater in the west of the Nile delta indicates the contribution of palaeo groundwater component (in the range 0.1 - 0.8 with means of 0.39 and 0.52 for tahrir and khatatbah, respectively) along with sub recent recharge from the delta aquifer and recent recharge from irrigation conveyance canals in desert. Isotope mixing model (developed as Two-input table using excel TM spreads heat on apple Macintosh TM) is proposed to explain the apparent discrepancies in groundwater isotopic composition of khatatbah and tahrir areas assuming the contribution of two isotopically different palaeo-oples with two isotopically similar maind delta groundwater poles. About 0.30% 1 8 O depletion per 10 Km downstream is detected and low northward groundwater recharge is suggested along 75 Km of the western strip of rosetta Nile. Higher sub-recent recharge from the main delta aquifer is believed to take place in khatatbah than tahrir whereas the last is believed to be replenished at present from the irrigation/ drainage network and irrigated fields with higher pollution risk for groundwater system in tahrir aquifer is exposed to northern marine intrusion. Lowering of the piezo metric level is to be expected in the newly exploited desertic areas under over pumping. 9 figs

  13. GEOCHEMISTRY AND ISOTOPE HYDROLOGY OF AN URBAN AQUIFER, SUBTROPICAL AFRICA, CENTRAL AFRICAN REPUBLIC

    International Nuclear Information System (INIS)

    HUSSEIN, M.F.; ISLAM, A.; GAMAL, S.; GAETAN, M.; DJEBEBE, C.

    2008-01-01

    Africa south of the Great Sahara has abundant water resources, however, its aquifers are seldom studied and/or inadequately managed. This study presents a geochemical and isotope hydrology study on the aquifer of Bangui city, the capital of the Central African Republic (RCA), on the northern borders of Congo with RCA.The obtained chemical data demonstrated the role of biogenic CO 2 gas, solid phases and cation exchange in the hydrochemistry of the studied groundwater. The conjunctive use of the major dissolved constituents and the isotope contents ( 18 O and 2 H) showed that the alteration of primary silicates and the dissolution of carbonates are the predominant processes that locally define the zones of dilute and relatively charged groundwater, respectively.The isotope data illustrated that evaporation is non-significantly contributing to the water loss from the aquifer, while transpiration (process that goes almost without isotopic fractionation) is prevailing in the water balance of the local drainage basin, with a significant fraction of the transpired vapour being recycled. An isotopic i nverse continental effect(eastward from Cameron to RCA) is explained through differences in air temperatures, amount and altitude of precipitation rather than by inverse movement of humid air masses westward in Central Africa

  14. The isotope geochemistry of hot springs gases and waters from Coromandel and Hauraki

    International Nuclear Information System (INIS)

    Lyon, G.L.; Giggenbach, W.F.

    1992-01-01

    Carbon, hydrogen and oxygen stable isotope analyses have been made on carbon dioxide,methane and water from warm and hot springs in the Coromandel Peninsula and Hauraki Plains. Most of the waters are isotopically unaltered meteoric waters. Methane δ 1 3C values vary widely, from -30%o to -72%o. Warm springs in swamps at Maketu and Kerepehi have microbial methane probably added to the water near the surface. Puriri, Okoroire and Miranda springs produce thermally derived methane, and the Hot Water Beach gas is similar to the Kaitoke gas in chemistry and isotopic composition but altered by shallow microbial oxidation. The Te Aroha gas, though, is not inconsistent with a geothermal origin and the boiling springs and oxygen-isotope altered water are further evidence for high temperatures. Other spring gases have mixtures of thermogenic and microbial methane and none are closely similar to major NZ geothermal CH 4 composition. CO 2 , which is usually present in lesser amounts than N 2 , has isotopic values which suggest a geothermal origin at Te Aroha and Maketu, but otherwise indicates a crustal origin. The dominance of N 2 implies that the fluid flows are tectonic fracture flow rather than geothermal. 3 He/ 4 He data gives further evidence of no major contribution from magmatic material except at Maketu, on the NW boundary of the TVZ. (author). 24 refs., 4 figs., 2 tabs

  15. Provenance and depositional age of metavolcano-sedimentary sequences of the Santa Terezinha de Goias, based on Sm-Nd and U-Pb zircon single grain; Proveniencia e idade deposicional de sequencias metavulcano-sedimentares da regiao de Santa Terezinha de Goias, baseada em dados isotopicos Sm-Nd e U-Pb em monocristal de zircao

    Energy Technology Data Exchange (ETDEWEB)

    Dantas, Ellton Luiz; Jost, Hardy; Fuck, Reinhardt A.; Brod, Jose Afonso; Pimentel, Marcio Martins; Meneses, Paulo Roberto [Brasilia Univ., DF (Brazil). Inst. de Geociencias]. E-mail: elton@unb.br

    2001-09-01

    Supracrustal rocks of the Santa Terezinha de Goias region, Central Brazil, presumably represent a southern extension of the Mara Rosa magmatic arc tectonically juxtaposed to Archean terrains and consist of a meta volcanic unit and a meta sedimentary unit. The aim of the paper is to present and discuss the first U-Pb and Sm-Nd data of rocks belonging to both units of that region. U-Pb data of zircons from a felsic meta volcanic rock inter layered with chlorite-rich schists (metandesites?) yield a concordant age of of 660 My, while the Sm-Nd model age of a variety of chlorite-schists indicate a juvenile age between 1.1 and 1.3 Ga. These data indicate that the meta volcanic rocks are Neo proterozoic in age and may be correlated with rocks of the Mara Rosa magmatic arc. On the other hand, the prevailing provenance of rocks belonging to the meta sedimentary unit indicate a Paleoproterozoic, or older, source. Thus, the deposition of both units are explained by means of the erosion of source-areas of variable age. (author)

  16. Variation of stable silicon isotopes. Analytical developments and applications in Precambrian geochemistry

    International Nuclear Information System (INIS)

    Abraham, Kathrin

    2010-01-01

    The work presented in this thesis predominantly deals with bulk-rock measurements of silicon stable isotopes on a Multi Collector-ICP-MS. Analyses were performed in cooperation with the Royal Museum for Central Africa, Belgium. The first section describes how the first analysis of δ 30 Si on a conventional Nu PlasmaTM Multi-Collector ICP-MS instrument can be enabled by the elimination of 14N16O interference overlying the 30Si peak. The determination of δ 30 Si was rendered possible owing to new instrumental upgrades that facilitate the application of a higher mass resolution. The careful characterisation of appropriate reference materials is indispensable for the assessment of the accuracy of a measurement. The determination of U.S. Geological Survey (USGS) reference materials represents the second objective of this section. The analysis of two Hawaiian standards (BHVO-1 and BHVO-2) demonstrates precise and accurate δ 30 Si determinations and provides cross-calibration data as a quality control for other laboratories. The second section focuses on coupled silicon-oxygen isotopic evidences for the origin of silicification in mafic volcanic rocks of the Barberton Greenstone Belt, South Africa. In contrast to the modern Earth, silicification of near-surface layers, including chert formation, were widespread processes on the Precambrian ocean floor, and demonstrate the ubiquity of extreme silica mobilization in the early Earth. This section outlines the investigation of silicon and oxygen isotopes on three different stratigraphic sections of variably silicified basalts and overlying bedded cherts from the 3.54 Ga, 3.45 Ga and 3.33 Ga Theespruit, Kromberg and Hooggenoeg Formations, respectively. Silicon isotopes, oxygen isotopes and the variable SiO 2 -contents demonstrate a positive correlation with silicification intensity in all three sections, with varying gradients of δ 30 Si vs. δ 18 O arrays for different sections. Seawater has been regarded as the most

  17. Variation of stable silicon isotopes. Analytical developments and applications in Precambrian geochemistry

    Energy Technology Data Exchange (ETDEWEB)

    Abraham, Kathrin

    2010-05-28

    The work presented in this thesis predominantly deals with bulk-rock measurements of silicon stable isotopes on a Multi Collector-ICP-MS. Analyses were performed in cooperation with the Royal Museum for Central Africa, Belgium. The first section describes how the first analysis of δ{sup 30}Si on a conventional Nu PlasmaTM Multi-Collector ICP-MS instrument can be enabled by the elimination of 14N16O interference overlying the 30Si peak. The determination of δ{sup 30}Si was rendered possible owing to new instrumental upgrades that facilitate the application of a higher mass resolution. The careful characterisation of appropriate reference materials is indispensable for the assessment of the accuracy of a measurement. The determination of U.S. Geological Survey (USGS) reference materials represents the second objective of this section. The analysis of two Hawaiian standards (BHVO-1 and BHVO-2) demonstrates precise and accurate δ{sup 30}Si determinations and provides cross-calibration data as a quality control for other laboratories. The second section focuses on coupled silicon-oxygen isotopic evidences for the origin of silicification in mafic volcanic rocks of the Barberton Greenstone Belt, South Africa. In contrast to the modern Earth, silicification of near-surface layers, including chert formation, were widespread processes on the Precambrian ocean floor, and demonstrate the ubiquity of extreme silica mobilization in the early Earth. This section outlines the investigation of silicon and oxygen isotopes on three different stratigraphic sections of variably silicified basalts and overlying bedded cherts from the 3.54 Ga, 3.45 Ga and 3.33 Ga Theespruit, Kromberg and Hooggenoeg Formations, respectively. Silicon isotopes, oxygen isotopes and the variable SiO{sub 2}-contents demonstrate a positive correlation with silicification intensity in all three sections, with varying gradients of δ{sup 30}Si vs. δ{sup 18}O arrays for different sections. Seawater has been

  18. Contributions of isotopic bio-geochemistry to the analysis of water - soil - root interactions

    International Nuclear Information System (INIS)

    Cayet, S.

    2001-07-01

    The aim of this work is to study the origin of the isotopic signal of the water produced by plants transpiration. It stresses more particularly on the water movements between the soil and the plant in a context of heterogenous water availability for the root system. The use of water isotopes ( 18 O and 2 H) should allow to precise the water extraction depth of the roots and the plant strategy in front of a hydric stress of edaphic origin. The first chapter presents the place of water in the soil-plant-atmosphere continuum, the different potential sources of water accessible to the plant, the principles of water absorption and the hydric transfer in the plant in relation with the variations of water absorption and of the evaporative conditions. The isotopic method is introduced with the natural variability of the isotopic composition of the atmospheric and soil waters. Finally, the reaction of the plant in front of a hydric stress is described. The second chapter presents a series of experiments carried out in the natural environment and shows the problems encountered during the determination of water origin in heterogenous hydric availability conditions. The third chapter describes the experiments performed in controlled environment. One series of experiments is performed in homogenous hydric availability condition. The aim is to analyze the isotopic signal emitted by the plant and its significance with respect to the feeding water. The second series of experiments is performed in heterogenous hydric availability conditions and in stable or variable climatic conditions. In the last chapter, the different experiments performed in natural environment are presented, first in optimum hydric availability conditions, and second in variable hydric conditions. These experiments allow to reconstruct the isotopic signal of the soil water which is recorded by the plant and to precise the preferential areas of water extraction by the roots, and the competitive behaviour of

  19. Sr and Nd isotope geochemistry of coexisting alkaline magma series, Cantal, Massif Central, France

    International Nuclear Information System (INIS)

    Downes, H.

    1984-01-01

    Sr and Nd isotope analyses are presented for Tertiary continental alkaline volcanics from Cantal, Massif Central, France. The volcanics belong to two main magma series, silica-saturated and silica-undersaturated (with rare nephelinites). Trace element and isotopic data indicate a common source for the basic parental magmas of both major series; the nephelinites in contrast must have been derived from a mantle source which is isotopically and chemically distinct from that which gave rise to the basalts and basanites. 87 Sr/ 86 Sr initial ratios range from 0.7034 to 0.7056 in the main magma series (excluding rhyolites) and 143 Nd/ 144 Nd ratios vary between 0.512927 and 0.512669; both are correlated with increasing SiO 2 in the lavas. The data can be explained by a model of crustal contamination linked with fractional crystallisation. This indicates that crustal magma chambers are the sites of differentiation since only rarely do evolved magmas not show a crustal isotopic signature and conversely basic magmas have primitive isotopic ratios unless they contain obviuos crustal-derived xenocrysts. Potential contaminants include lower crustal granulites or partial melts of upper crustal units. Equal amounts of contamination are required for both magma series, refuting hypotheses of selective contamination of the silica-saturated series. The isotopic characteristics of the apparently primary nephelinite lavas demonstrates widespread heterogeneity in the mantle beneath Cantal. Some rhyolites, previously thought to be extremely contaminated or to be crustally derived, are shown to have undergone post-emplacement hydrothermal alteration. (orig.)

  20. Chlorine isotopic geochemistry of salt lakes in the Qaidam Basin, China

    Digital Repository Service at National Institute of Oceanography (India)

    Liu, W.G.; Xiao, Y.K.; Wang, Q.Z.; Qi, H.P.; Wang, Y.H.; Zhou, Y.M.; Shirodkar, P.V.

    *Cl+ ion. Int. J. Mass Spectrom. Ion Process., 116: crysatallization of saline minerals in salt lake. J. Salt Lake 183-192. Sci., 2: 35-40 (in Chinese). Xiao, Y.K., Sun, D.P., Wang, Y.H., Qi, H.P. and Jin, L., 1992. Boron isotopic compositions of brine..., sediments, and source water in Da Qaidam Lake, Qinghai, China. Geochim. Cos- mochim. Acta, 56: 1.561-1568. Xiao, Y.K., Jin, L., Liu. W.G., Qi, H.P., Wang, W.H. and Sun, D.P., 1994a. The isotopic compositions of chlorine in Da Qaidam Lake. Chin. Sci...

  1. A Review of the Stable Isotope Bio-geochemistry of the Global Silicon Cycle and Its Associated Trace Elements

    Directory of Open Access Journals (Sweden)

    Jill N. Sutton

    2018-01-01

    Full Text Available Silicon (Si is the second most abundant element in the Earth's crust and is an important nutrient in the ocean. The global Si cycle plays a critical role in regulating primary productivity and carbon cycling on the continents and in the oceans. Development of the analytical tools used to study the sources, sinks, and fluxes of the global Si cycle (e.g., elemental and stable isotope ratio data for Ge, Si, Zn, etc. have recently led to major advances in our understanding of the mechanisms and processes that constrain the cycling of Si in the modern environment and in the past. Here, we provide background on the geochemical tools that are available for studying the Si cycle and highlight our current understanding of the marine, freshwater and terrestrial systems. We place emphasis on the geochemistry (e.g., Al/Si, Ge/Si, Zn/Si, δ13C, δ15N, δ18O, δ30Si of dissolved and biogenic Si, present case studies, such as the Silicic Acid Leakage Hypothesis, and discuss challenges associated with the development of these environmental proxies for the global Si cycle. We also discuss how each system within the global Si cycle might change over time (i.e., sources, sinks, and processes and the potential technical and conceptual limitations that need to be considered for future studies.

  2. Investigations on boron isotopic geochemistry of salt lakes in Qaidam basin, Qinghai

    Digital Repository Service at National Institute of Oceanography (India)

    Xiao, Y; Shirodkar, P.V.; Liu, W.G.; Wang, Y; Jin, L.

    of brine and are related to boron origin, the corrosion of salt and to certain chemical constituents. The distribution of boron isotopes in Quidam Basin showed a regional feature: salt lake brines in the west and northwest basin have the highest d11B values...

  3. Strontium isotope geochemistry of alluvial groundwater: a tracer for groundwater resources characterisation

    Directory of Open Access Journals (Sweden)

    P. Négrel

    2004-01-01

    Full Text Available This study presents strontium isotope and major ion data of shallow groundwater and river water from the Ile du Chambon catchment, located on the Allier river in the Massif Central (France. There are large variations in the major-element contents in the surface- and groundwater. Plotting of Na vs. Cl contents and Ca, Mg, NO3, K, SO4, HCO3, Sr concentrations reflect water–rock interaction (carbonate dissolution for Ca, Mg, HCO3 and Sr because the bedrock contains marly limestones, agricultural input (farming and fertilising and sewage effluents (for NO3, K, SO4, although some water samples are unpolluted. Sr contents and isotope ratios (87Sr/86Sr vary from 0.70892 to 0.71180 along the hydrological cycle in the groundwater agree with previous work on groundwater in alluvial aquifers in the Loire catchment. The data plot along three directions in a 87Sr/86Sr v. 1/Sr diagram as a result of mixing, involving at least three geochemical signatures–Allier river water, and two distinct signatures that might be related to different water-rock interactions in the catchment. Mixing proportions are calculated and discussed. The alluvial aquifer of the Ile du Chambon catchment is considered, within the Sr isotope systematic, in a larger scheme that includes several alluvial aquifers of the Loire Allier catchment. Keywords: : Loire river, major and trace elements, Sr isotopic ratio, alluvial aquifer, hydrology

  4. Isotope geochemistry of waters affected by mining activities in Sierra Minera and Portman Bay (SE, Spain)

    International Nuclear Information System (INIS)

    García-Lorenzo, Mari Luz; Martínez-Sánchez, María José; Pérez-Sirvent, Carmen; Agudo, Inés; Recio, Clemente

    2014-01-01

    Highlights: • Waters have a meteoric origin even in samples located near the shore. • Marine infiltration only takes place in the deepest layers. • Sulfate enrichment was caused by oxidative dissolution of pyrite by ferric iron. - Abstract: The objective of this work was to evaluate processes affecting waters from Portman Bay by way of stable isotopic analysis, particularly H and O stable isotopes from water and S and O from dissolved sulfates. In addition, surface waters from Sierra Minera were examined for the purpose of determining if these waters are affected by similar processes. The results obtained indicate that Portman Bay 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 Fe 3+ was predominant in the surface, and controlled by Acidithiobacillus ferrooxidans, while at depth, sulfate reduction occurred

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

    Science.gov (United States)

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

    2008-12-01

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

  6. U/Pb (SHRIMP), 207Pb/206Pb, Rb/Sr, Sm/Nd e K/Ar geochronology of granite-greenstone terrains of Gaviao Block: implications for the Proterozoic and Archean evolution of Sao Francisco Craton, Brazil

    International Nuclear Information System (INIS)

    Leal, Luiz Rogerio Bastos

    1998-01-01

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

  7. Groundwater geochemistry of nile delta-desert interface 1.isotope hydrology

    Energy Technology Data Exchange (ETDEWEB)

    Hussein, M F [Cairo University, Dept., of Soil and water, Giza, Gamma Street, (Egypt); Nada, A A; Awad, M A [Atomic Energy Authority, Nuclear Chemistry Dept., P.o. Box 13759, Cairo, (Egypt)

    1995-10-01

    Sustenance and environmental protection of groundwater supply is of major concern in the integral environmental development in the arid to sub-arid regions in the Nile basin. Isotope data ({sup 18O}, {sup 2H} and {sup 3H}) of groundwater in the west of the Nile delta indicates the contribution of palaeo groundwater component (in the range 0.1 - 0.8 with means of 0.39 and 0.52 for tahrir and khatatbah, respectively) along with sub recent recharge from the delta aquifer and recent recharge from irrigation conveyance canals in desert. Isotope mixing model (developed as Two-input table using excel{sup TM} spreads heat on apple Macintosh{sup TM)} is proposed to explain the apparent discrepancies in groundwater isotopic composition of khatatbah and tahrir areas assuming the contribution of two isotopically different palaeo-oples with two isotopically similar maind delta groundwater poles. About 0.30% {sup 1}8{sup O} depletion per 10 Km downstream is detected and low northward groundwater recharge is suggested along 75 Km of the western strip of rosetta Nile. Higher sub-recent recharge from the main delta aquifer is believed to take place in khatatbah than tahrir whereas the last is believed to be replenished at present from the irrigation/ drainage network and irrigated fields with higher pollution risk for groundwater system in tahrir aquifer is exposed to northern marine intrusion. Lowering of the piezo metric level is to be expected in the newly exploited desertic areas under over pumping. 9 figs.

  8. Isotope geochemistry of waters affected by acid mine drainage in old labour sites (SE, Spain).

    Science.gov (United States)

    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.

  9. Implications of Nb/U, Th/U and Sm/Nd in plume magmas for the relationship between continental and oceanic crust formation and the development of the depleted mantle

    Science.gov (United States)

    Campbell, Ian H.

    2002-05-01

    The Nb/U and Th/U of the primitive mantle are 34 and 4.04 respectively, which compare with 9.7 and 3.96 for the continental crust. Extraction of continental crust from the mantle therefore has a profound influence on its Nb/U but little influence on its Th/U. Conversely, extraction of midocean ridge-type basalts lowers the Th/U of the mantle residue but has little influence on its Nb/U. As a consequence, variations in Th/U and Nb/U with Sm/Nd can be used to evaluate the relative importance of continental and basaltic crust extraction in the formation of the depleted (Sm/Nd enriched) mantle reservoir. This study evaluates Nb/U, Th/U, and Sm/Nd variations in suites of komatiites, picrites, and their associated basalts, of various ages, to determine whether basalt and/or continental crust have been extracted from their source region. Emphasis is placed on komatiites and picrites because they formed at high degrees of partial melting and are expected to have Nb/U, Th/U, and Sm/Nd that are essentially the same as the mantle that melted to produce them. The results show that all of the studied suites, with the exception of the Barberton, have had both continental crust and basaltic crust extracted from their mantle source region. The high Sm/Nd of the Gorgona and Munro komatiites require the elevated ratios seen in these suites to be due primarily to extraction of basaltic crust from their source regions, whereas basaltic and continental crust extraction are of subequal importance in the source regions of the Yilgarn and Belingwe komatiites. The Sm/Nd of modern midocean ridge basalts lies above the crustal extraction curve on a plot of Sm/Nd against Nb/U, which requires the upper mantle to have had both basaltic and continental crust extracted from it. It is suggested that the extraction of the basaltic reservoir from the mantle occurs at midocean ridges and that the basaltic crust, together with its complementary depleted mantle residue, is subducted to the core

  10. Geochemistry and Nd-Sr isotopic signatures of the Pensamiento Granitoid Complex, Rondonian-San Ignacio Province, eastern precambrian shield of Bolivia: petrogenetic constraints for a mesoproterozoic magmatic arc setting

    International Nuclear Information System (INIS)

    Matos, Ramiro; Teixeira, Wilson; Bettencourt, Jorge Silva; Geraldes, Mauro Cesar

    2009-01-01

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

  11. Boron geochemistry from some typical Tibetan hydrothermal systems: Origin and isotopic fractionation

    International Nuclear Information System (INIS)

    Zhang, Wenjie; Tan, Hongbing; Zhang, Yanfei; Wei, Haizhen; Dong, Tao

    2015-01-01

    The Tibetan plateau is characterized by intense hydrothermal activity and abnormal enrichment of trace elements in geothermal waters. Hydrochemistry and B isotope samples from geothermal waters in Tibet were systematically measured to describe the fractionation mechanisms and provide constraints on potential B reservoirs. B concentrations range from 0.35 to 171.90 mg/L, and isotopic values vary between −16.57 ‰ and +0.52 ‰. Geothermal fields along the Indus-Yarlung Zangbo suture zone and N–S rifts are observed with high B concentrations and temperatures. The similar hydrochemical compositions of high-B geothermal waters with magmatic fluid and consistent modeling of B isotopic compositions with present δ"1"1B values imply that the B in high-B geothermal waters is mainly contributed by magmatic sources, probably through magma degassing. In contrast, geothermal fields in other regions of the Lhasa block have relatively low B concentrations and temperatures. After considering the small fractionation factor and representative indicators of Na/Ca, Cl/HCO_3, Na + K and Si, the conformity between modeling results and the isotopic compositions of host rocks suggests that the B in low-temperature geothermal fields is mainly sourced from host rocks. According to simulated results, the B in some shallow geothermal waters not only originated from mixing of cold groundwater with deep thermal waters, but it was also contributed by equilibration with marine sedimentary rocks with an estimated proportion of 10%. It was anticipated that this study would provide useful insight into the sources and fractionation of B as well as further understanding of the relationships between B-rich salt lakes and geothermal activities in the Tibetan plateau. - Highlights: • Chemical and boron isotopic data of geothermal waters in Tibetan plateau were introduced. • Unusual enrichment of boron in Tibetan geothermal waters is related to magmatic and host rocks. • Boron

  12. Isotope and minor element geochemistry of high arsenic groundwater from Hangjinhouqi, the Hetao Plain, Inner Mongolia

    International Nuclear Information System (INIS)

    Deng Yamin; Wang Yanxin; Ma Teng

    2009-01-01

    High As groundwater is widely distributed in the northwestern Hetao Plain, an arid region with slow groundwater flow. Arsenic concentration in groundwater ranges from 1 to 1000 μg/L. Most water samples have elevated salinities, with Cl and/or HCO 3 as the dominant anions and Na as the dominant cation. High concentrations of As in shallow aquifers are associated with strongly reducing conditions, as evidenced by high concentrations of dissolved organic C (DOC), NH 4 , dissolved sulfide, arsenite and dissolved CH 4 , and relatively low concentrations of NO 3 - and SO 4 2- . Results of the hydrochemical, and H and O isotope geochemical studies indicate that evapotranspiration is an important process controlling the enrichment of Na and Cl as well as trace elements such as As, B, F and Br in groundwater. In Na-HCO 3 -dominated groundwaters, As, B and F were enriched. Decades of irrigation using Yellow River water has resulted in elevation of the groundwater level, which has accelerated salt accumulation in shallow groundwater and surface soil. In addition, irrigation is responsible for the release of some components from aquifer materials and mixing with saline groundwaters, as indicated by minor element and isotope geochemical data. Used to trace groundwater flow paths, Sr isotope composition also indicates that bedrock weathering is one of the primary sources of As in groundwater in the study area.

  13. Carbon isotope geochemistry of the Cretaceous-Tertiary section of the Wasserfallgraben, Lattengebirge, southeast Germany

    International Nuclear Information System (INIS)

    Arneth, J.D.; Matzigkeit, U.; Boos, A.

    1985-01-01

    Carbonates and organic matter in sediments of the Cretaceous-Tertiary (C/T) section of the Wasserfallgraben, Lattengebirge (Bavaria) have been investigated. All parameters - the carbonate content (Csub(carb)), its isotopic composition (delta 13 Csub(carb),delta 18 Osub(carb)) as well as the organic carbon content (Csub(org)), its isotopic composition (delta 13 Csub(org)) and the H/C ratio of the sedimentary organic matter - display systematic variations across the C/T boundary which cannot be attributed to a single cause. The boundary zone as a whole is tectonically disturbed and shows significant features of detrital contaminations. Unidirectional shift in delta 13 Csub(carb) and delta 13 Csub(org) are observed when directly comparing Maastrichtian (latest Cretaceous) and Danian (earliest Tertiary) sediments. These synchronous isotope displacements towards more negative readings are interpreted to reflect the reduced photosynthetic activity as consequence of the mass extinction at the C/T boundary. The results may have some bearings on other C/T profiles investigated where measurements on the reduced carbon species are still lacking. (orig.)

  14. Geochemistry and isotope hydrology of groundwaters in the Stripa Granite: results and preliminary interpretation

    International Nuclear Information System (INIS)

    Fritz, P.; Barker, J.F.; Gale, J.E.

    1979-04-01

    The results of geochemical and isotopic analyses on water samples from the granite at Stripa, Sweden, are presented. Groundwater samples collected from shallow, private wells; surface boreholes; and boreholes drilled from the 330 m and 410 m mine levels were analyzed for their major ion chemistry, dissolved gases, and environmental isotope contents. The principal change in the chemical load with depth is typified by chloride concentration, which increases from less than 5 mg/liter to about 300 mg/liter. There is a parallel increase in pH, which changes from about 6.5 to over 9.75. It is important to notice that calcite saturation is maintained and that, because of rising pH, dissolved inorganic carbon is lost. The total carbonate content thus decreases from about 70 mg/liter to less than 7 mg/liter. The 18 O and deuterium analyses demonstrate that different fracture systems contain different water masses, whose age increases with depth. Groundwater age determinations with 14 C and isotopes of the uranium decay series strongly indicate that water ages exceed 25,000 years. The 13 C contents of the aqueous carbonate in these groundwaters indicate groundwater recharge through vegetated soil, presumably during an interglacial period. The 13 C and 18 O determinations show that most fracture calcites have formed in a wide variety of depositional environments, and not in the waters circulating today

  15. Ca Isotope Geochemistry in Marine Deep Sea Sediments of the Eastern Pacific

    Science.gov (United States)

    Wittke, A.; Gussone, N. C.; Derigs, D.; Schälling, M.; Teichert, B. M.

    2017-12-01

    Ca isotope ratio analysis (δ44/40Ca) is a powerful tool to investigate diagenetic reactions in marine sedimentary porewater systems, as it is sensitive to processes such as carbonate dissolution, precipitation, recrystallization, ion exchange and deep fluid sources, due to the isotopic difference between dissolved Ca and solid carbonate minerals (e.g. [1];[2]). We analyzed eight sediment cores of the (paleo-) Pacific equatorial age transect. Two sediment cores show decreasing Ca isotope profiles starting at the sediment/water interface with seawater-like values down to sediment-like values due to recrystallization and an increasing in the bottom part again to seawater-like values. The other studied cores show different degrees of flattening of this middle bulge. We interpret this pattern either as an effect of sediment composition and thickness, decreasing recrystallization rates and/or fluid flux or a combination of all of these factors at the respective sampling sites. Element concentration profiles and Sr-isotope variations on some of these sediment cores show a similar behavior, supporting our findings ([3]; [4]). Seawater influx at (inactive) seamounts is supposed to cause seawater-like values at the bottom of the sediment cores by fluids migrating through the oceanic basement (e.g. [5]). While [6] hypothesizes that two seamounts or bathymetric pits are connected, with a recharge and a discharge site [7] say that uptaken fluids could be released through the surrounding seafloor as well due to diffusive exchange with the underlying oceanic crust. Our Ca isotope results combined with a transport reaction model approach support the latter hypothesis. References: [1] Teichert B. M., Gussone N. and Torres M. E. (2009) [2] Ockert C., Gussone N., Kaufhold S. and Teichert B. (2013) [3] Pälike H., Lyle M., Nishi H., Raffi I., Gamage K. and Klaus A. (eds.) (2010) [4] Voigt J., Hathorne E. C., Frank M., Vollstaedt H. and Eisenhauer A. (2015) [5] Villinger H. W

  16. The clumped-isotope geochemistry of exhumed marbles from Naxos, Greece

    Science.gov (United States)

    Ryb, U.; Lloyd, M. K.; Stolper, D. A.; Eiler, J. M.

    2017-07-01

    Exhumation and accompanying retrograde metamorphism alter the compositions and textures of metamorphic rocks through deformation, mineral-mineral reactions, water-rock reactions, and diffusion-controlled intra- and inter-mineral atomic mobility. Here, we demonstrate that these processes are recorded in the clumped- and single-isotope (δ13 C and δ18 O) compositions of marbles, which can be used to constrain retrograde metamorphic histories. We collected 27 calcite and dolomite marbles along a transect from the rim to the center of the metamorphic core-complex of Naxos (Greece), and analyzed their carbonate single- and clumped-isotope compositions. The majority of Δ47 values of whole-rock samples are consistent with exhumation- controlled cooling of the metamorphic complex. However, the data also reveal that water-rock interaction, deformation driven recrystallization and thermal shock associated with hydrothermal alteration may considerably impact the overall distribution of Δ47 values. We analyzed specific carbonate fabrics influenced by deformation and fluid-rock reaction to study how these processes register in the carbonate clumped-isotope system. Δ47 values of domains drilled from a calcite marble show a bimodal distribution. Low Δ47 values correspond to an apparent temperature of 260 °C and are common in static fabrics; high Δ47 values correspond to an apparent temperature of 200 °C and are common in dynamically recrystallized fabrics. We suggest that the low Δ47 values reflect diffusion-controlled isotopic reordering during cooling, whereas high Δ47 values reflect isotopic reordering driven by dynamic recrystallization. We further studied the mechanism by which dynamic recrystallization may alter Δ47 values by controlled heating experiments. Results show no significant difference between laboratory reactions rates in the static and dynamic fabrics, consistent with a mineral-extrinsic mechanism, in which slip along crystal planes was associated

  17. Stratigraphy and stable isotope geochemistry of the carbonate sequence from the Paraguay belt

    International Nuclear Information System (INIS)

    Santos, Roberto Ventura.; Alvarenga, Carlos Jose Souza de; Dantas, Elton Luiz

    2001-01-01

    Two main Neoproterozoic carbonate sequences occur central Brazil both of which are stratiphicaly above glacial derived sediments. An older carbonate sequence occurs over the Sao Francisco Craton and in the surrounding folded belts (Rio Preto, Aracuai Ribeira and Brasilia). These carbonates overlie glacial diamictites that were related to the 'Sturtian' event dated between 0.7 and 0.9 Ga (Toulkeridis et al. 1999, Santos et al., 2000). A second carbonate sequence is described in the Paraguay Belt and postdated Vendian/Varegian glaciation sediments from the end of the Neoproterozoic. This glacial event has been reported in many studies concerning the Gondwana and the Laurentia supercontinent (Trompette, 1996; Condon and Prave, 2000; Myrow and Kaufman, 1999). In the Paraguay Belt the Vendian- Varangian glaciation rocks are characterized by a glaciomarine sequence, that occur at the border of the basin, and by glacial derived turbidites deposits, that occur in the deeper parts of the basin (Alvarenga and Trompette, 1992). Near the city of Corumba this glaciomarine sequence is overlaid by carbonate rocks containing Ediacaran-like fauna in which has been described Corumbella werneri and Cloudina Lucianoi (Hahn et al., 1982; Walde et al., 1982; Zaine and Fairchild, 1985; 1987). These carbonates have been interpreted as cap carbonates and the age of their fossils have been attributed to the Vendian Superior (590-545 MA) (Alvarenga and Trompette, 1992, Trompette 1996). Isotope stratigraphy studies have been widely used to study cap carbonate rocks that overlie Sturtian and Vendian- Varagian glaciogenic rocks. Stratigraphic correlation of these units is usually difficult because their lack fossils and there is no precise dating method that could be applied to these rocks. Hence, most studies concerning Neoproterozoic carbonates have concentrated on their stromatilites and microfossils content as well as on carbon isotope variations. In the present study, we present new carbon

  18. C–O Stable Isotopes Geochemistry of Tunisian Nonsulfide Zinc Deposits: A First Look

    Directory of Open Access Journals (Sweden)

    Hechmi Garnit

    2018-01-01

    Full Text Available A preliminary C–O stable isotopes geochemical characterization of several nonsulfide Zn-Pb Tunisian deposits has been carried out, in order to evidence the possible differences in their genesis. Nonsulfide ores were sampled from the following deposits: Ain Allegua, Jebel Ben Amara, Jebel Hallouf (Nappe Zone, Djebba, Bou Grine, Bou Jaber, Fedj el Adoum, Slata Fer (Diapir Zone, Jebel Ressas, Jebel Azreg, Mecella (North South Axis Zone, Jebel Trozza, Sekarna (Graben Zone. After mineralogical investigation of selected specimens, the C–O stable isotopic study was carried out on smithsonite, hydrozincite, cerussite and calcite. The data have shown that all the carbonate generations in the oxidized zones of Ain Allegua and Jebel Ben Amara (Nappe Zone, Bou Jaber, Bou Grine and Fedj el Adoum (Diapir Zone, Mecella and Jebel Azreg (North South Zone have a supergene origin, whereas the carbonates sampled at Sekarna (Graben Zone (and in limited part also at Bou Jaber precipitated from thermal waters at moderately high temperature. Most weathering processes that controlled the supergene alteration of the Zn-Pb sulfide deposits in Tunisia had probably started in the middle to late Miocene interval and at the beginning of the Pliocene, both periods corresponding to two distinct tectonic pulses that produced the exhumation of sulfide ores, but the alteration and formation of oxidized minerals could have also continued through the Quaternary. The isotopic characteristics associated with the weathering processes in the sampled localities were controlled by the different locations of the sulfide protores within the tectonic and climatic zones of Tunisia during the late Tertiary and Quaternary.

  19. Isotope geochemistry of drainage from an acid mine impaired watershed, Oakland, California

    International Nuclear Information System (INIS)

    Butler, Thomas W.

    2007-01-01

    Oxidation of sulfides at the Leona Heights Sulfur Mine has resulted in the liberation of acid, SO 4 and metals to Leona Creek. Previous research at the site has indicated Fe(II) oxidation at rates faster than would be predicted by abiotic oxidation alone, particularly in the segment of stream between the Adit and Leona Street sample stations. In order to assess the mechanisms responsible for sulfide oxidation, samples were collected for isotopic analysis of water and SO 4 , the results of which were used to develop a stoichiometric isotope-balance model. This exercise indicated that the percentage of water-derived oxygen in SO 4 increased spatially from between 56% and 64% at the Adit to between 71% and 72% at Leona Street, illustrating that increased sulfide oxidation via Fe(III) was occurring within, or as water flows over, the waste rock, relative to water emanating directly from the former mine. The incorporation of water-derived oxygen in SO 4 during pyrite oxidation is a process controlled by Fe oxidizing bacteria such as A. ferrooxidans at low pH. The role of bacteria was further supported by estimates of the rate constant for Fe oxidation between sampling stations, yielding values that were approximately 10 6 faster than abiotic Fe oxidation alone. Stable isotopic analysis of water further indicates a close correlation of adit spring water to the local meteoric water line, while 3 H data indicate a groundwater apparent age, or time of travel from its primary zone of recharge, of 34 S data, in conjunction with reported albitized feldspars within the Leona Rhyolite host rock, indicate a magmatic origin of ore sulfur, contrary to previous interpretations at the site

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

    Directory of Open Access Journals (Sweden)

    Letícia Alexandre Redes

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

  1. Angular non-critical phase-matching second-harmonic-generation characteristics of RECOB (RE = Tm, Y, Gd, Sm, Nd and La) crystals.

    Science.gov (United States)

    Liu, Yanqing; Wang, Zhengping; Yu, Fapeng; Qi, Hongwei; Yang, Xiuqin; Yu, Xiaoqiang; Zhao, Xian; Xu, Xinguang

    2017-05-15

    For the first time, the angular non-critical phase-matching (A-NCPM) second-harmonic-generation (SHG) characteristics of a family of monoclinic oxoborate crystals, RECa 4 O(BO 3 ) 3 (RECOB, RE = Tm, Y, Gd, Sm, Nd and La), were comprehensively investigated. For all of the realizable A-NCPM SHG styles, the feature parameters including PM wavelength, angular, wavelength and temperature acceptance bandwidths, have been derived from the theory and verified by the experiments. We discovered that the closer the ion radius between RE 3+ and Ca 2+ , the smaller the birefringence, and the better the A-NCPM SHG properties. As a result, for the Type-I SHG on Y-axis which has the largest effective nonlinear optical coefficient (d eff ) among the three realizable A-NCPM styles, NdCOB crystal presents the longest PM wavelength (927 nm), the largest angular acceptance bandwidth (Δθ⋅l 1/2 = 84.3 mrad·cm 1/2 , Δϕ⋅l 1/2 = 58.8 mrad·cm 1/2 ), and the broadest wavelength acceptance bandwidth (8.7 nm). This discovery will contribute to the design of new NCPM materials, at the same time the parameter formula will be helpful for the theoretical prediction of NCPM performance.

  2. First-principles calculation of structural and energetic properties for A2Ti2O7 (A = Lu, Er, Y, Gd, Sm, Nd, La)

    International Nuclear Information System (INIS)

    Zhang, Z.L.; Xiao, H.Y.; Zu, Xiaotao T.; Gao, Fei; Weber, William J.

    2009-01-01

    A first-principles method has been employed to investigate the structural and energetic properties for A2Ti2O7 (A = Lu, Er, Y, Gd, Sm, Nd, La), including the formation energies of the cation antisite-pair, the anion Frenkel pair that defines anion-disorder, and the coupled cation antisite-pair/anion-Frenkel. It is proposed that the interaction may have more significant influence on the radiation resistance behavior of titanate pyrochlores, although the interactions are relatively much stronger than the interactions. It is found that the defect formation energies are not simple functions of the A-site cation radii. The formation energy of the cation antisite-pair increases continuously as the A-site cation varies from Lu to Gd, and then decreases continuously with the variation of the A-site cation from Gd to La, in excellent agreement with the radiation-resistance trend of the titanate pyrochlores. The band gaps in these pyrochlores were also measured, and the band gap widths changed continuously with cation radius.

  3. Geochemistry of trace elements and Sr- Nd isotopes of foraminifera shell from the Okinawa Trough

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Trace elemental associations and Sr - Nd isotopic compositions are of important to recognition of biogenic material from mixed marine sediments. The foraminifera shell from the Okinawa Trough strongly enrichesSr, P, Mn andBa, enriches Li, U, Th, Sc, Co, Cu, Pb, Zn, Cr, Rb, Y, Sb and light rare earth elements, slightly enriches V, Ga, Zr, Nb, Cd and middle rare earth elements,is short of Mo, In, Sn, Cs, Hf, Ta, W, Ti, Bi and heavy rare earth elements. The mechanism of elemental enrichment in forminifera is the concentrations of trace elements in sea water and selective absorption of trace elements during foraminifera living, as well as the geochemical affinity between major elements and trace elements. The REE (rare earth elements) partition pattern of foraminifera shell of the Okinawa Trough shows enrichment of middle rare earth elements with slightly negative Ce anomaly,which are different from those of foraminifera of the Pacific Ocean. The Sr, Nd isotopic ratios of the Okinawa Trough foraminifera are 0.709 769 and 0.512 162, respectively, which are different not only from those of oceanic water, but also from those of river water of China's Mainland, the former is slightly higher than those of oceanic water, but much lower than those of river water; the latter is slightly lower than those of oceanic water, but higher than those of river water, demonstrating that the Okinawa Trough sea water has been influenced by river water of China's Mainland.

  4. Geochemistry and environmental isotope of groundwater from the upper Cretaceous aquifer of Orontes basin (Syria)

    International Nuclear Information System (INIS)

    Al-Charideh, A.

    2010-03-01

    Chemical and environmental isotopes have been used for studying the Upper Cretaceous aquifer systems in the Middle Orontes basin. The results indicate that the salinity of groundwater (0.2 to 2 g/l) reveals the dissolution of evaporate rocks is the main factor of high salinity especially in the Homes depression. The degree of salinity and its spaces distribution are basically related to the pattern of groundwater movement in the Upper cretaceous aquifer. The stable isotopes composition of groundwater in the Homes depression are more depleted by -2.5% and -17.0% for δ 18 O and δ 2 H respectively, than the groundwater from Hama elevation, suggested different origin and recharge time between this two groundwater groups. Estimates of their mean subsurface residence times have been constrained on the basis of 14 C D IC. The corrected ages of groundwater are recent and less to 10 thousand years in Hama uplift. However, the corrected age of groundwater in the Homs depression range between 10 to 25 thousand years indicate late Pleistocene recharge period. (author)

  5. An investigation of the stable isotopes, geochemistry and morphology of major streams in Dominica, Lesser Antilles: 2014 - 2017

    Science.gov (United States)

    Kopas, D. C.; Joseph, E. P.; Frey, H. M.

    2017-12-01

    The island of Dominica is a recently active (pH and temperature, were recorded and water samples taken and analyzed for alkalinity, major elements (cations and anions), trace elements and stable isotopes (carbon, deuterium, and oxygen). Variations in water chemistry and river morphology were compared to various parameters, including precipitation, landslide locations, and lithology for each of the catchments. Within the study period, on August 27th, 2015, a significant tropical storm, Erika, made landfall in Dominica, depositing more than 500 mm of rainfall in 10 hours. There was little infiltration of the rainwater (over 50-60% run-off), which resulted in significant landslides, flash floods and damage to infrastructure and loss of life. Despite the obvious morphologic changes to the streams and high discharge during the storm event, preliminary analysis has shown little change in major stream geochemistry following the passage of Tropical Storm Erika. The 10-month time gap between the storm and the post-storm field sampling in June 2016 may be a factor of why geochemical changes were not observed. One of the most significant variations of stream composition during the study period was annual shifts in δD between -1.3 to -5.8 ‰ and δ18O between -1.98 to -2.61 ‰. A possible factor influencing the δ18O of surface waters is seasonal variation in rainfall. The dominant control on precipitation δ18O values is the amount effect, whereby rainfall amount and δ18O are inversely correlated. This relationship is a proxy for changes in δ18O values of surface waters. The data also suggest that hydrothermal fluids are not a prominent contributor to Dominican rivers, despite the presence of active volcanism and numerous hydrothermal systems on the island. The exceptions are the White River, which drains the Valley of Desolation and Boiling Lake and the Lamothe River, which drains the Cold Soufrierre.

  6. A reconnaissance Rb-Sr, Sm-Nd, U-Pb, and K-Ar study of some host rocks and ore minerals in the West Shasta Cu- Zn district, California ( USA).

    Science.gov (United States)

    Kistler, R.W.; McKee, E.H.; Futa, K.; Peterman, Z.E.; Zartman, R.E.

    1985-01-01

    The Copley Greenstone, Balaklala Rhyolite, and Mule Mountain stock in the West Shasta Cu-Zn district, California, have Rb-Sr, Sm-Nd, U-Pb, and K-Ar systematics that indicate they are a cogenetic suite of ensimatic island-arc rocks about 400 Ma. Pervasive alteration and mineralization of these rocks, for the most part, was syngenetic and the major component of the mineralizing fluid was Devonian seawater. K-Ar ages of quarz-sericite concentrates from ore horizons and Rb-Sr systematics of a few rock and ore specimens record a later thermal and mineralizing event in the district of about 260 Ma. Contamination of some rocks with pelagic sediments is indicated by the Sm-Nd data. -Authors

  7. Possible influence of clay contamination on B isotope geochemistry of carbonaceous samples

    International Nuclear Information System (INIS)

    Deyhle, Annette; Kopf, Achim

    2004-01-01

    The authors report results from an experimental study on mixtures of pure endmembers of natural clay and carbonate. The scientific rationale is an evaluation as to what extent B contents and B isotopes of carbonate samples may be obscured as a result of contamination with clay, particularly since both authigenic carbonates and biogenic carbonates (e.g. microfossil tests) often contain some clay. Three aliquots of a series of samples (each containing 0, 20, 40, 60, 80, 100% clay) were analyzed. Set 1 was washed with distilled, de-ionized water; for set 2 the HCl soluble parts were dissolved in 2 M HCl after washing; set 3 was completely digested with 30M HF prior to a series of ion exchanges. Isotope data of the endmembers are 6.6 per mille (100% marble) and -4.6%o (100% clay), with the clay being the dominant B source (ca. 50 ppm compared with 11 B adsorbed =12.9-14.1%o±0.5%o), while no B was mobilized from the carbonate. The HCl-dissolvable B in washed samples of set 2 show slightly increasing B contents with higher clay contents, suggesting that dissolution of the marble as well as B mobilization from the clay account for this trend. δ 11 B isotopes tend towards more negative values when clay content increases, indicating that some structurally-bound B is lost from the sheets of linked (Si, Al)O 4 tetrahedra of the clay mineral. This result shows that not only B adsorption, but possibly diffusion or weathering of broken edges of clay minerals releases some structurally bound B of clay minerals. Set 3, where bulk samples were completely HF-digested, shows as expected a linear increase in B concentrations and decreasing δ 11 B ratios with increasing clay content. The overall results suggest that relatively small amounts of clay (e.g. as contamination in a microfossil test) have no significant impact on the B content and δ 11 B measured for the carbonate, but that care has to be taken if clay exceeds 10wt.% (e.g. carbonate concretions, chimneys, etc.)

  8. Isotopic and hydro geochemistry research in ground water from Provincia de Entre Rios (Republica Argentina)

    International Nuclear Information System (INIS)

    Tujchneider, Ofelia Clara; Carmen Paris, Marta del; Fili, Mario Felipe; D'Elia, Monica Patricia

    1994-01-01

    In order to study the groundwater dynamics of the Northwest of the Entre Rios Province (Republica Argentina), supported on the regional knowledge resulting from previous reports, a detailed investigation is developed. The most important aquifer of the region, conformed by sands of the Ituzaingo and Parana Formations (Mioceno-Plioceno) underlies Hernandarias Formation (Pleistoceno) thick clays cover. This confinement condition, and the complex hydrodynamic behaviour as a result of the heterogeneity of the hydrogeological sequence, impeded determine with clearness the existence of actual and direct connections with the exterior cycle. The application of classical geohydrochemical methodologies complemented with both isotopic and heavy metals measurements, and data geostatistical processing, allows to formulate hypothesis about groundwater origin and the incidence of the autochthonous recharge. (author)

  9. Stable isotope geochemistry and evidence for meteoric diagenesis in Kudankulam formation, Tamil Nadu

    International Nuclear Information System (INIS)

    Armstrong Altrin Sam, J.; Ramasamy, S.; Makhnach, A.

    2001-01-01

    The results obtained from stable isotope study of Neogene carbonates of Kudankulam, Tamil Nadu show negative values for δ 13c arbon, which range from -2.6% to -9.7% PDB. The δ 18O values range from -4.5% to -11.4% PDB. The depleted nature of the δ 18O and δ 13C values suggests the strong effect of meteoric diagenesis in the Kudankulam carbonates. Standard bivariate plots of δ 18O versus δ 13C for carbonate materials/rocks helped to identify their depositional and diagenetic environments. Petrographic study points out large-scale emplacement of ferroan sparry calcite cement into vugs and other leached cavities. (author)

  10. Isotopic and hydro geochemistry study of the granular aquifer from Comarca Lagunera, Mexico

    International Nuclear Information System (INIS)

    Gonzalez Hita, Luis; Sanchez Diaz, Luis Felipe

    1994-01-01

    The Comarca Lagunera is one of Mexico's biggest agricultural regions. Its water sources are the Nazas and Aguanaval Rivers and a quaternary granular aquifer. The over exploitation of the aquifer has led to deteriorated groundwater quality due to the presence of arsenic. This study aims to determine the origin and evolution of the arsenic and to update the system's hydrogeochemical information. The methodology used is based on an analysis of the physical framework and on the hydrogeochemical and isotope characterization of the groundwater. An interpretation of the results shows that the arsenic could have originated in two geological events: first, the magmatic processes that generated the region's intrusive and extrusive igneous rocks, and second, the sedimentation of alluvial-lacustrine materials bearing arsenic, which were transported by the Nazas and Aguanaval Rivers during the aquifer's formation. (author)

  11. The Itataia phosphate-uranium deposit (Ceará, Brazil) new petrographic, geochemistry and isotope studies

    Science.gov (United States)

    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

  12. Strontium isotope geochemistry of soil and playa deposits near Yucca Mountain, Nevada

    International Nuclear Information System (INIS)

    Marshall, B.D.; Mahan, S.A.

    1994-01-01

    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

  13. Compilation of gas geochemistry and isotopic analyses from The Geysers geothermal field: 1978-1991

    Science.gov (United States)

    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.

  14. Musa's granite and Rio Maria's granodiorite Rb/Sr isotopic ages and geochemistry

    International Nuclear Information System (INIS)

    Gastal, M.C.P.; Macambira, M.J.B.; Medeiros, H.; Dall'Agnol, R.

    1987-01-01

    The Musa Granite and the Rio Maria Granodiorite are located at the eastern margin of the Amazonian craton, in the Rio Maria region, where a typical granite-greenstone terrain is characterized. Rb-Sr dating of six samples from different facies of Rio Maria Granodiorite furnished an age of 2564 ± 68 Ma with initial 87 Sr/ 86 Sr radio (IR) of 0.70288 ± 0.00092 (whole rock isochron; 1 ο error; MSWD = 2.26). Thirteen samples from the three facies of Musa Granite (monzogranites, syenogranites and intermediate to felsic hypabyssal rocks) gave Rb-Sr whole rock isochron with an age of 1692 ± 11 Ma and IR of 0.70777 ± 0.00023 (1 ο error, MSWD = 1.89). A preliminary attempt to individualize geochronologically the three facies was done resulting different ages and IRs. There is a coincidence between these ages and the emplacement sequence of these facies of the pluton. The actual meaning of the Rio Maria Granodiorite Rb-Sr age is still uncertain. It could be related to the end of the magmatic crystallization of the batholith as well as to the metamorphic-mylonitic event that affect it. Considering that the Jamon and Musa Granites are petrologically similar that they occur in the same area, it is interesting to note that latter is apparently a little older than the former. The IRs obtained for the two plutons are also not coincident. The isotopic Rb-Sr available data show that the exposed rocks of the Rio Maria Granodiorite have not been able to generate magmas with the compositions of the monzongranitic and the hypabyssal facies of the Musa pluton. On the other hand, rocks isotopically similar to the Rio Maria Granodiorite would theorically be able to generate the Jamon and a magma with the characteristics of the syenogranitic facies of the Musa pluton. (author) [pt

  15. Geochronology, radiogenic isotope geochemistry, and petrogenesis of Sang bast Paleo-tethys monzogranite, Mashhad, Iran

    International Nuclear Information System (INIS)

    Karimpour, M. H.; Farmer, G.L.; Stern, C.R.

    2010-01-01

    The study area is located in northeastern Iran (south of Mashhad). Paleo-Tethys Ocean opened during Silurian time and subduction under Turan plate was started in Late Devonian. By Late Triassic (225 Ma) there was no Paleo-Tethys left on an Iranian transect, therefore Turan plate obducted over Iran Plate. Two stages of low grade regional metamorphism are exposed, that are related to Hercynian (Late Paleozoic) and Cimmerian (Jurassic) oro genies. The Paleo-Tethys remnants (meta-ophiolite and meta-flysch) were intruded by Sang bast monzogranite. Chemically, monzogranite is moderately peraluminous S-type granitoid. It has low values of magnetic susceptibility [(5 to 11) * 10 -5 SI] therefore it is classified as belonging to the ilmenite-series of reduced type granitoids. Monzogranite is characterized by strong light rare earth element enrichment and less low heavy rare earth element. All samples have very small negative Eu anomalies (Eu/Eu * = 0.62 to 0.88). Total rare earth element content of monzogranite is between 212-481 ppm. The result of U-Pb zircon age dating of monzogranite is 201.3 ± 3.6 Ma (Upper Triassic, Rhaetian time). The initial 87 Sr/ 86 Sr and 143 Nd/ 144 Nd ratios for monzogranite is (0.706776 and 0.512219) when recalculated to an age of 201 Ma, consistent with the new radiometric. The initial 87 Sr/ 86 Sr and 143 Nd/ 144 Nd ratios for slate is (0.720613 and 0.511601) respectively when recalculated to an age of 201 Ma, consistent with the new radiometric results. Initial εNd isotope values for monzogranite is -3.13 and the slate is -15.19. Based on radiogenic isotopic data and rare earth element monzogranite magma originated either from lower continental crust which was very different from slate or it is originated from mantle and contaminated in continental crust during ascending.

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

    Science.gov (United States)

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

    2008-01-01

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

  17. Organic geochemistry and stable isotope composition of New Zealand carbonate concretions and calcite fracture fills

    International Nuclear Information System (INIS)

    Pearson, M.J.; Nelson, C.S.

    2005-01-01

    Carbonate concretion bodies, representing a number of morphological types, and associated calcite fracture fills, mainly from New Zealand, have been studied both organically and inorganically. Extracted organic material is dominated by a complex polymeric dark brown highly polar fraction with a subordinate less polar and lighter coloured lipid fraction. The relative proportion of the two fractions is the principal control on the colour of fracture fill calcites. Concretions are classified mainly by reference to their carbonate stable carbon and oxygen isotope and cation composition. Typical subspherical calcitic septarian concretions, such as those in the Paleocene Moeraki and the Eocene Rotowaro Siltstones, contain carbon derived mainly by bacterial sulfate reduction in marine strata during early diagenesis. Other concretions, including a septarian calcitic type from the Northland Allochthon, have a later diagenetic origin. Siderite concretions, abundant in the nonmarine Waikato Coal Measures, are typically dominated by methanogenic carbon, whereas paramoudra-like structures from the Taranaki Miocene have the most extreme carbon isotope compositions, probably resulting from methane formation or oxidation in fluid escape conduits. Lipids from concretion bodies and most fracture fill calcites contain significant concentrations of fatty acids. Concretion bodies dominated by bimodally distributed n-fatty acids with strong even-over-odd preference, in which long chain n-acids are of terrestrial origin, have very low hydrocarbon biomarker maturities. Concretion bodies that lack long chain n-acids often have higher apparent biomarker maturity and prominent alpha-omega diacids. Such diacids are abundant in fracture fill calcites at Rotowaro, especially where calcite infills the septaria of a siderite concretion in the non-marine Waikato Coal Measures, and support the view that fluid transport resulted in carbonate entrapment of the fracture-hosted acids. Diacids also

  18. Sr isotope geochemistry of voluminous acidic pyroclastics erupted at 1-3 Ma in Northeast Japan

    International Nuclear Information System (INIS)

    Shirahase, Teruo; Tamanyu, Shiro; Togashi, Shigeko

    1989-01-01

    Sr isotope ratios are analyzed for voluminous acidic pyroclastics erupted at 1 - 3 Ma in five areas on the volcanic front of Northeast Japan. The initial values of 87 Sr/ 86 Sr ratios range from 0.7040 to 0.7055. There is no significant difference in ratios between 1 - 3 Ma acidic pyroclastics and 0 - 1 Ma andesitic volcanics in each area in spite of differences in age and in mean SiO 2 content. On the other hand, the ratios in both of 1 - 3 Ma and 0 - 1 Ma volcanics vary along arc in the same manner. The changes of Sr and Rb contents in each area are consistent with systematic changes by fractional crystallization. The low 87 Sr/ 86 Sr ratios and chemistry suggest that 1 - 3 Ma acidic pyroclastics of Northeast Japan formed by a high degree of fractional crystallization from basic magma which is common in genesis with young andesitic volcanism. The mechanisms of the formation of the basic magma and the character of mantle source in each area have not changed for the past 3 Ma. Degrees of fractional crystallization changed with changes of the tectonic condition of shallow magma chamber from a weak horizontal compression stress field to a strong one. (author)

  19. Strontium isotope geochemistry of soil and playa a deposits near Yucca Mountain, Nevada

    International Nuclear Information System (INIS)

    Marshall, B.D.; Mahan, S.A.

    1994-01-01

    The isotopic composition of strontium contained in the carbonate fractions of soils provides an excellent tracer which can be used to test models for their origin. This paper reports data on surface coatings and cements, eolian sediments, playas and alluvial fan soils which help to constrain a model for formation of the extensive calcretes and fault infilling in the Yucca Mountain region. The playas contain carbonate with a wide range of strontium compositions; further work will be required to fully understand their possible contributions to the pedogenic carbonate system. Soils from an alluvial fan to the west of Yucca Mountain show that only small amounts of strontium are derived from weathering of silicate detritus. However, calcretes from a fan draining a carbonate terrane have strontium compositions dominated locally by the limestone strontium component. Although much evidence points to an eolian source for at least some of the strontium in the pedogenic carbonates near Yucca Mountain, an additional component or past variation of strontium composition in the eolian source is required to model the pedogenic carbonate system

  20. Geochemistry of CI chondrites: Major and trace elements, and Cu and Zn Isotopes

    Science.gov (United States)

    Barrat, J. A.; Zanda, B.; Moynier, F.; Bollinger, C.; Liorzou, C.; Bayon, G.

    2012-04-01

    In order to check the heterogeneity of the CI chondrites and determine the average composition of this group of meteorites, we analyzed a series of six large chips (weighing between 0.6 and 1.2 g) of Orgueil prepared from five different stones. In addition, one sample from each of Ivuna and Alais was analyzed. Although the sizes of the chips used in this study were “large”, our results show evidence for minor chemical heterogeneity in Orgueil, particularly for alkali elements and U. After removal of one outlier sample, the spread of the results is considerably reduced. For most of the 46 elements analyzed in this study, the average composition calculated for Orgueil is in very good agreement with previous CI estimates. This average, obtained with a “large” mass of samples, is analytically homogeneous and is suitable for normalization purposes. Finally, the Cu and Zn isotopic ratios are homogeneously distributed within the CI parent body with a spread of less than 100 ppm per atomic mass unit (amu).

  1. Isotope geochemistry of hydrothermal alteration in East of Esfahan, Central Iran

    Science.gov (United States)

    Taghipour, Sedigheh; Taghipour, Batoul

    2010-05-01

    In the Cenozoic magmatic belt of Central Iran, the Eocene volcanics and pyroclastics from the East of Esfahan underwent extensive hydrothermal alteration. The Eocene volcanics composed mostly of andesite lava and tuffs have been altered. The survey area is laterally zoned from an inner quartz-sericite alteration zone to an outer propylitic zone. Quartz-sericite alteration is predominant (>95%), but smaller zones of alunite-jarosite and silicified zones are present and superimposed onto a quartz-sericite alteration. In the quartz-sericite zone all altered rocks are light grayish to whitish in color and porphyritic with aphanitic groundmass. Concentrations of alunite and jarosite veinlets and stockworks are dispersed irregularly in this zone. Alunite and jarosite occur also as coatings on fractured rocks. All types of alunite occurrences are brick-red, cream, white and buff in colors, while jarosite is brown to rusty in colors. To verify, chemical composition of alunite and jarosite were identified by X-ray diffraction in mineral assemblages. Major alteration zones show inclusions of propylite, quartz sericite, advanced argillic and silicified zones. These alunites are mainly porcelaneous and their compositions show a solid solution between alunite and jarosite. In alteration zones, the mineral assemblage is characterized by alunite-jarosite + quartz + sericite + alkali feldspars + chlorite ± turquoise ± barite ± iron oxides. There are numerous alunite and jarosite occurrences, mainly as veinlets, in parts of the advanced argillic zone. Alunite δ18O and δ D values range from -1.76 to 8.81‰ and from -52.86 to -129.26‰ respectively. Field observations, mineralogical evidence and results from light element stable isotope data (δ18O, δ D and δ34S); indicate that in this area alunitization is supergene in origin.

  2. Radiocarbon and stable-isotope geochemistry of organic and inorganic carbon in Lake Superior

    Science.gov (United States)

    Zigah, Prosper K.; Minor, Elizabeth C.; Werne, Josef P.

    2012-03-01

    We present a lake-wide investigation of Lake Superior carbon and organic matter biogeochemistry using radiocarbon, stable isotope, and carbon concentrations. Dissolved inorganic carbon (DIC) abundance in the lake was 121-122 Tg C, with offshore concentration andδ13C values being laterally homogenous and tightly coupled to the physical and thermal regime and biochemical processes. Offshore Δ14C of DIC (50-65‰) exhibited lateral homogeneity and was more 14C enriched than co-occurring atmospheric CO2 (˜38‰); nearshore Δ14C of DIC (36-38‰) was similar to atmospheric CO2. Dissolved organic carbon (DOC) abundance was 14.2-16.4 Tg C. DOC's concentration and δ13C were homogenous in June (mixed lake), but varied laterally during August (stratification) possibly due to spatial differences in lake productivity. Throughout sampling, DOC had modern radiocarbon values (14-58‰) indicating a semilabile nature with a turnover time of ≤60 years. Lake particulate organic carbon (POC, 0.9-1.3 Tg C) was consistently 13C depleted relative to DOC. The δ15N of epilimnetic particulate organic nitrogen shifted to more negative values during stratification possibly indicating greater use of nitrate (rather than ammonium) by phytoplankton in August. POC's radiocarbon was spatially heterogeneous (Δ14C range: 58‰ to -303‰), and generally 14C depleted relative to DOC and DIC. POC 14C depletion could not be accounted for by black carbon in the lake but, because of its spatial and temporal distribution, is attributed to sediment resuspension. The presence of old POC within the epilimnion of the open lake indicates possible benthic-pelagic coupling in the lake's organic carbon cycle; the ultimate fate of this old POC bears further investigation.

  3. Annual and seasonal distribution of intertidal foraminifera and stable carbon isotope geochemistry, Bandon Marsh, Oregon, USA

    Science.gov (United States)

    Milker, Yvonne; Horton, Benjamin; Vane, Christopher; Engelhart, Simon; Nelson, Alan R.; Witter, Robert C.; Khan, Nicole S.; Bridgeland, William

    2014-01-01

    We investigated the influence of inter-annual and seasonal differences on the distribution of live and dead foraminifera, and the inter-annual variability of stable carbon isotopes (d13C), total organic carbon (TOC) values and carbon to nitrogen (C/N) ratios in bulk sediments from intertidal environments of Bandon Marsh (Oregon, USA). Living and dead foraminiferal species from 10 stations were analyzed over two successive years in the summer (dry) and fall (wet) seasons. There were insignificant inter-annual and seasonal variations in the distribution of live and dead species. But there was a noticeable decrease in calcareous assemblages (Haynesina sp.) between live populations and dead assemblages, indicating that most of the calcareous tests were dissolved after burial; the agglutinated assemblages were comparable between constituents. The live populations and dead assemblages were dominated by Miliammina fusca in the tidal flat and low marsh, Jadammina macrescens, Trochammina inflata and M. fusca in the high marsh, and Trochamminita irregularis and Balticammina pseudomacrescens in the highest marsh to upland. Geochemical analyses (d13C, TOC and C/N of bulk sedimentary organic matter) show no significant influence of inter-annual variations but a significant correlation of d13C values (R = 20.820, p , 0.001), TOC values (R = 0.849, p , 0.001) and C/N ratios (R = 0.885, p , 0.001) to elevation with respect to the tidal frame. Our results suggest that foraminiferal assemblages and d13C and TOC values, as well as C/N ratios, in Bandon Marsh are useful in reconstructing paleosea-levels on the North American Pacific coast.

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

    Energy Technology Data Exchange (ETDEWEB)

    Nascimento, Newton Diego Couto do; Ruiz, Amarildo Salina; Pierosan, Ronaldo; Lima, Gabrielle Aparecida de; Matos, Joao Batista; Lafon, Jean-Michel; Moura, Candido Augusto Veloso, E-mail: newtongeologia@hotmail.com, E-mail: asruiz@gmail.com, E-mail: ronaldo.pierosan@yahoo.com.br, E-mail: gabilimagel@gmail.com, E-mail: lafonjm@ufpa.br, E-mail: prof.jmatos@gmail.com, E-mail: candido@ufpa.br [Universidade Federal do Para (GEOCIAM/UFPA), Belem, PA (Brazil). Instituto Nacional de Ciencia e Tecnologia de Geociencias da Amazonia

    2016-11-01

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

  5. Impacts of changes in groundwater recharge on the isotopic composition and geochemistry of seasonally ice-covered lakes: insights for sustainable management

    Science.gov (United States)

    Arnoux, Marie; Barbecot, Florent; Gibert-Brunet, Elisabeth; Gibson, John; Noret, Aurélie

    2017-11-01

    Lakes are under increasing pressure due to widespread anthropogenic impacts related to rapid development and population growth. Accordingly, many lakes are currently undergoing a systematic decline in water quality. Recent studies have highlighted that global warming and the subsequent changes in water use may further exacerbate eutrophication in lakes. Lake evolution depends strongly on hydrologic balance, and therefore on groundwater connectivity. Groundwater also influences the sensitivity of lacustrine ecosystems to climate and environmental changes, and governs their resilience. Improved characterization of groundwater exchange with lakes is needed today for lake preservation, lake restoration, and sustainable management of lake water quality into the future. In this context, the aim of the present paper is to determine if the future evolution of the climate, the population, and the recharge could modify the geochemistry of lakes (mainly isotopic signature and quality via phosphorous load) and if the isotopic monitoring of lakes could be an efficient tool to highlight the variability of the water budget and quality. Small groundwater-connected lakes were chosen to simulate changes in water balance and water quality expected under future climate change scenarios, namely representative concentration pathways (RCPs) 4.5 and 8.5. Contemporary baseline conditions, including isotope mass balance and geochemical characteristics, were determined through an intensive field-based research program prior to the simulations. Results highlight that future lake geochemistry and isotopic composition trends will depend on four main parameters: location (and therefore climate conditions), lake catchment size (which impacts the intensity of the flux change), lake volume (which impacts the range of variation), and lake G index (i.e., the percentage of groundwater that makes up total lake inflows), the latter being the dominant control on water balance conditions, as revealed by

  6. Impacts of changes in groundwater recharge on the isotopic composition and geochemistry of seasonally ice-covered lakes: insights for sustainable management

    Directory of Open Access Journals (Sweden)

    M. Arnoux

    2017-11-01

    Full Text Available Lakes are under increasing pressure due to widespread anthropogenic impacts related to rapid development and population growth. Accordingly, many lakes are currently undergoing a systematic decline in water quality. Recent studies have highlighted that global warming and the subsequent changes in water use may further exacerbate eutrophication in lakes. Lake evolution depends strongly on hydrologic balance, and therefore on groundwater connectivity. Groundwater also influences the sensitivity of lacustrine ecosystems to climate and environmental changes, and governs their resilience. Improved characterization of groundwater exchange with lakes is needed today for lake preservation, lake restoration, and sustainable management of lake water quality into the future. In this context, the aim of the present paper is to determine if the future evolution of the climate, the population, and the recharge could modify the geochemistry of lakes (mainly isotopic signature and quality via phosphorous load and if the isotopic monitoring of lakes could be an efficient tool to highlight the variability of the water budget and quality. Small groundwater-connected lakes were chosen to simulate changes in water balance and water quality expected under future climate change scenarios, namely representative concentration pathways (RCPs 4.5 and 8.5. Contemporary baseline conditions, including isotope mass balance and geochemical characteristics, were determined through an intensive field-based research program prior to the simulations. Results highlight that future lake geochemistry and isotopic composition trends will depend on four main parameters: location (and therefore climate conditions, lake catchment size (which impacts the intensity of the flux change, lake volume (which impacts the range of variation, and lake G index (i.e., the percentage of groundwater that makes up total lake inflows, the latter being the dominant control on water balance conditions, as

  7. Nd isotopes and crustal growth rate

    International Nuclear Information System (INIS)

    Albarede, F.

    1988-01-01

    Sm/Nd isotopic constraints on crustal growth is discussed. In order to constrain Sm/Nd fractionation between continental crust and depleted mantle, an extensive data base of isotopic measurements (assumed to be adequately representative of continental crust) was compiled. The results imply that the evolution of depleted mantles was roughly linear, with no major discontinuities over the course of geologic time. This is different from other determinations of depleting mantle evolution, which show nonlinear behavior. The Sm/Nd evolution lines for continental crust and depleted mantle intersect between 3.8 to 4.0 Ga, which may indicate that the onset of continental growth was later than 4.5 Ga. A mathematical model is described, the results of which imply that time integrated crustal additions from the mantle are about 1.8 to 2.5 cu km/a, whereas crustal subtractions by sediment recycling are about 0.6 to 1.5 cu km/a. This results in a net time integrated crustal growth rate of about 1 cu km/a, which is similar to present day rates determined, for example, by Reymer and Schubert

  8. Combined Lu-Hf and Sm-Nd geochronology of the Mariánské Lázně Complex: New constraints on the timing of eclogite- and granulite-facies metamorphism

    Science.gov (United States)

    Collett, Stephen; Štípská, Pavla; Schulmann, Karel; Peřestý, Vít; Soldner, Jeremie; Anczkiewicz, Robert; Lexa, Ondrej; Kylander-Clark, Andrew

    2018-04-01

    Lu-Hf and Sm-Nd garnet-whole rock geochronology combined with petrographic observations, minero-chemical variations, thermodynamic modelling and structural data was used to constrain the P-T-t-d evolution of eclogites from the Mariánské Lázně Complex (Bohemian Massif). Boudins of mostly isotropic eclogite with relict steep eclogite-facies fabric are affected by steep migmatitic foliation, which is followed on a regional scale by the development of almost pervasive, predominantly SE-dipping, extensional foliation. The structural succession shows continuous transition from eclogite to garnetiferous migmatitic amphibolite and to amphibolite migmatite. A least retrogressed sample of eclogite shows clusters of fine-grained inclusion-poor garnet, omphacite relicts surrounded by a fine-grained clinopyroxene-plagioclase symplectite with minor amphibole, biotite-plagioclase intergrowths after white mica, kyanite with plagioclase-spinel coronas and accessory rutile. Rare potassic white mica occurs as inclusions in omphacite. A more retrogressed eclogite, with no omphacite or kyanite relicts, contains inclusion-poor garnet surrounded by amphibole-plagioclase corona in a matrix dominated by plagioclase-amphibole symplectite with minor clinopyroxene. In places, the symplectite is overgrown by coarse-grained amphibole. Peak P-T conditions, inferred from combined conventional thermobarometry and phase-equilibria modelling and based on inclusions of white mica (up to 3.33 Si p.f.u.), matrix omphacite (Jd33-36) and garnet core (Alm33-38Prp38-42Grs22-25Sps1) compositions are 25 kbar at 650-750 °C. A HT overprint occurred at 14-18 kbar and >800 °C based on coexisting clinopyroxene (Jd18-24), plagioclase (An18-35), and amphibole (Na(B) modelling of garnet mantle compositions. Lu-Hf and Sm-Nd garnet geochronology has been applied to both samples, an older age (c. 390 Ma) obtained by the Lu-Hf method is interpreted as the timing of HP metamorphism, while c. 15 Ma younger ages were

  9. Archean evolution of Enderby Land (Antarctica) and isotope-geochronological evidences for its ancient history

    International Nuclear Information System (INIS)

    Krylov, D.P.; Belyatskij, B.V.

    1987-01-01

    Revew of published isotope-geochronological data on Ender by Land (Antarctica), which is the region of highly metamorphic formations predominant development which includes ancient rock relicts, is presented. Three tectonic-thermal events present the Archeau evolution in the region. Correlation of isotope-geochronological (U-Pb, Rb-Sr, Sm-Nd) data with micro textural processing allows to estimate tectonic-thermal events age: 3000-3100 about 2900 and about 2500 million years. Metamorphism of 3000-3100 million years age has essentially modified all the isotope systems, while model calculations for evolution of U-Pb, Rb-Sr, Sm-Nd systems have shown that rocks primary formation accurred 3500-3900 million years ago

  10. Isotope hydrology and baseflow geochemistry in natural and human-altered watersheds in the Inland Pacific Northwest, USA

    Science.gov (United States)

    Ricardo Sanchez-Murillo; Erin S. Brooks; William J. Elliot; Jan Boll

    2015-01-01

    This study presents a stable isotope hydrology and geochemical analysis in the inland Pacific Northwest (PNW) of the USA. Isotope ratios were used to estimate mean transit times (MTTs) in natural and human-altered watersheds using the FLOWPC program. Isotope ratios in precipitation resulted in a regional meteoric water line of ä2H = 7.42·ä18O + 0.88 (n = 316; r2 = 0.97...

  11. 230Th-238U radioactive disequilibria in tholeiites from the FAMOUS zone (Mid-Atlantic Ridge, 36050'N): Th and Sr isotopic geochemistry

    International Nuclear Information System (INIS)

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

    1981-01-01

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

  12. Geology and stable isotope geochemistry of Paleoarchean sulfur. Formation, preservation and geobiology of ancient pyrite and barite

    NARCIS (Netherlands)

    Roerdink, D.L.|info:eu-repo/dai/nl/318834340

    2013-01-01

    Sulfur isotopes in ancient sulfate and sulfide minerals provide a comprehensive record of microbial processes involved in the early sulfur cycle on Earth. However, the interpretation of these isotopic signatures requires information on the geological context of such samples, because abiotic

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

    Directory of Open Access Journals (Sweden)

    Alireza Almasi

    2015-04-01

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

  14. High-resolution C and O stable isotope geochemistry of the early Aptian OAE1a at Cau (Prebetic Zone, Spain): Preliminary results from sediment core.

    Science.gov (United States)

    Alejandro Ruiz-Ortiz, Pedro; Aguado, Roque; Castro, José Manuel; Gallego, David; de Gea, Ginés Alfonso; Jarvis, Ian; Molina, José Miguel; Nieto, Luis Miguel; Pancost, Richard; Quijano, María Luisa; Reolid, Matías; Rodriguez, Rafael; Skelton, Peter; Weisser, Helmut

    2017-04-01

    The occurrence of time intervals of enhanced deposition of organic matter (OM) during the Cretaceous, defined as Oceanic Anoxic Events (OAE), reflect abrupt changes in global carbon cycling. The Aptian OAE1a (120 Ma), represents an excellent example, recorded in all the main ocean basins, associated to massive burial of organic matter in marine sediments [1]. Much research has been done on the OAE1a from different sections in the world over the last decades, including the definition of the C-isotope stratigraphy of the event [2]. Notwithstanding, higher-resolution studies across the entire event will be crucial to shed light into the precise timing and rates of the different environmental and biotic changes that occurred. The Cau section is located in the easternmost part of the Prebetic Zone (Betic Cordillera), which represents the platform deposits of the Southern Iberian palaeomargin. The Lower Aptian of the Cau section is represented by a hemipelagic unit (Almadich Formation, ca. 200 m thick), deposited in a highly subsiding sector of a tilted block, located in the distal parts of the Prebetic Platform. Previous studies of the Lower Aptian of the Cau section have focused on the stratigraphy, bioevents, C-isotope stratigraphy, and organic and elemental geochemistry [3], [4], and in the reconstruction of pCO2 from organic geochemistry proxies [5]. All these studies reveal that the Cau section represents an excellent site to investigate the OAE 1a, based on its unusual high thickness and stratigraphic continuity, the quality and preservation of fossils and the geochemical signatures. Here we present the first results of a high-resolution carbonate C-isotope study based on the the analysis of three new research cores drilled at Cau in autumn 2015 [6]. These new data represent an important advance in the knowledge of the C-isotope record of the OAE 1a, presenting a more continuous record at a higher resolution than previous studies. This leads to the refining of the

  15. Geochronology (Rb-Sr, Sm-Nd and Pb-Pb) of the proterozoic granulitic and granitic rocks around Usilampatti, Madurai district, Tamil Nadu: implication on age of various lithounits

    International Nuclear Information System (INIS)

    Pandey, U.K.; Pandey, B.K.; Krishnamurthy, P.

    2005-01-01

    Rb-Sr, Sm-Nd and Pb-Pb systematics on mafic granulites, intermediate- charnockites, charnockites, calc-granulites, orthogneisses, leptynites, granites and two (2) mineral samples (microcline and muscovite) from pegmatite have been studied. Sm-Nd model ages (T DM ) for most of the rocks cluster around 2.1 Ga. Calc-granulites gave Rb-Sr whole rock isochron age of 1339 ± 110 Ma with initial 87 Sr/ 86 Sr ratio (I.R.) = 0.709. Mesoproterozoic age for the Metasedimentary Group of rocks (calc-granulites) has been inferred based on their 87 Sr/ 86 Sr ratio also. Granites and leptynites have yielded Rb-Sr whole rock isochron ages of 823± 38 Ma, with I.R. = 0.713 and 894± 82 Ma, with I.R. = 0.708 respectively which are younger than the calc-granulites. Microcline and muscovite from pegmatite gave Rb-Sr model ages as 532 and 491 Ma respectively. Granites, leptynites and calc-granulites are derived from the crustal source as indicated by their high initial 87 Sr/ 86 Sr ratios. Most probably the protolith of the granitic and granulitic rocks is of Palaeoproterozoic age in this part of the Madurai Block. The minimum age of granulite grade of metamorphism has been inferred at c. 850 Ma, indirectly on the basis of Rb-Sr ages of leptynites, which normally form during the evolution of granulite facies assemblages. Both granulite facies metamorphism and granitic magmatism probably took place during Neoproterozoic period correlatable to the early phase of Pan-African orogeny. Later decompression, causing mineral scale resetting of the Rb-Sr and Sm-Nd systematics, around 450-550 Ma, may correspond to the final exhumation, which brought the middle to lower crustal granulites to upper crustal levels, during the last phase of Pan-African activity. As per ages obtained on various lithounits in the present study the Metasedimentary Group of rocks (Mesoproterozoic) are younger than the Charnockite Group of rocks (Palaeoproterozoic) followed by the rocks belonging to the Migmatite Complex

  16. Geochronology (Rb-Sr, Sm-Nd and Pb-Pb) of the proterozoic granulitic and granitic rocks around Usilampatti, Madurai District, Tamil Nadu: implication on age of various lithounits

    International Nuclear Information System (INIS)

    Pandey, U.K.; Pandey, B.K.; Krishnamurthy, P.

    2005-01-01

    Rb-Sr, Sm-Nd and Pb-Pb systematics on mafic granulites, intermediate-charnockites, charnockites, calc- granulites, orthogneisses, leptynites, granites and two (2) mineral samples (microcline and muscovite) from pegmatite have been studied. Sm-Nd model ages (T DM ) for most of the rocks cluster around 2.1 Ga. Calc-granulites gave Rb-Sr whole rock isochron age of 1339± 110 Ma with initial 87 Sr/ 86 Sr ratio (IR)= 0.709. Mesoproterozoic age for the metasedimentary group of rocks (calc-granulites) has been inferred based on their 86 Sr/ 86 Sr ratio also. Granites and leptynites have yielded Rb-Sr whole rock isochron ages of 823 ± 38 Ma, with I.R. = 0.713 and 894± 82 Ma, with I.R.= 0.708 respectively which are younger than the calc-granulites. Microcline and muscovite from pegmatite gave Rb-Sr model ages as 532 and 491 Ma respectively. Granites, leptynites and calc-granulites are derived from the crustal source as indicated by their high initial 87 Sr/ 86 Sr ratios. Most probably the protolith of the granitic and granulitic rocks is of Palaeoproterozoic age in this part of the Madurai Block. The minimum age of granulite grade of metamorphism has been inferred at c. 850 Ma, indirectly on the basis of Rb-Sr ages of leptynites, which normally form during the evolution of granulite facies assemblages. Both granulite facies metamorphism and granitic magmatism probably took place during Neoproterozoic period correlatable to the early phase of Pan-African orogeny. Later decompression, causing mineral scale resetting of the Rb-Sr and Sm-Nd systematics, around 450-550 Ma, may correspond to the final exhumation, which brought the middle to lower crustal granulites to upper crustal levels, during the last phase of Pan-African activity. As per ages obtained on various lithounits in the present study the Metasedimentary Group of rocks (Mesoproterozoic) are younger than the Charnockite Group of rocks (Palaeoproterozoic) followed by the rocks belonging to the Migmatite Complex

  17. Isotopic chronometry of zoned garnets: Growth kinetics and metamorphic histories

    International Nuclear Information System (INIS)

    Vance, D.; O'Nions, R.K.

    1990-01-01

    Basic information on the chronological and pressure-temperature evolution of regional metamorphic terrains may in principle be derived from metamorphic garnets because of the similarly low diffusivities of Sm, Nd and major cations in this mineral. We report here Sm-Nd and Rb-Sr isotopic and major element data on prograde garnets from regionally metamorphosed pelites from Newfoundland. The garnets preserve a prograde major element zonation as well as a sympathetic variation in Sm/Nd ratio. Sm-Nd data for separated portions of the garnet from core to rim provide both upper limits on the time for garnet growth and demonstrate synchronous growth of different garnet grains on a hand specimen scale. The Rb-Sr data on the same garnet fractions are in general agreement with these results but in some cases cannot be interpreted in terms of growth. A minimum heating rate of 3 K Ma -1 is derived by combining the estimates for garnet growth time with the apparent temperature interval over which the garnet grew, deduced from the major element zonation. This value is similar to the minimum suggested by theoretical models for the thermal evolution of thickened continental crust. The growth rate is within the range of 1.3-19 mm Ma -1 , set respectively by the isotopic data and the likely upper limit for heating rate during regional metamorphism. These growth rates appear too slow to be controlled by surface reaction and suggest that other factors, such as transport, may be rate-limiting. In this case, the limits set of the effective diffusion coefficient for material transport to the growth site (=0.4-6.1x10 -17 m 2 s -1 ) suggest that grain boundary diffusion is probably the transport mechanism for supply of material to the growing garnet. (orig.)

  18. Investigation of Chemical and Physical Changes to Bioapatite During Fossilization Using Trace Element Geochemistry, Infrared Spectroscopy and Stable Isotopes

    Science.gov (United States)

    Suarez, C. A.; Kohn, M. J.

    2013-12-01

    Bioapatite in the form of vertebrate bone can be used for a wide variety of paleo-proxies, from determination of ancient diet to the isotopic composition of meteoric water. Bioapatite alteration during diagenesis is a constant barrier to the use of fossil bone as a paleo-proxy. To elucidate the physical and chemical alteration of bone apatite during fossilization, we analyzed an assortment of fossil bones of different ages for trace elements, using LA-ICP-MS, stable isotopes, and reflected IR spectroscopy. One set of fossil bones from the Pleistocene of Idaho show a diffusion recrystallization profile, however, rare earth element (REE) profiles indicate diffusion adsorption. This suggests that REE diffusion is controlled by changing (namely decreasing) boundary conditions (i.e. decreasing concentration of REE in surrounding pore fluids). Reflected IR analysis along this concentration profile reveal that areas high in U have lost type A carbonate from the crystal structure in addition to water and organics. Stable isotopic analysis of carbon and oxygen will determine what, if any, change in the isotopic composition of the carbonate component of apatite has occurred do to the diffusion and recrystallization process. Analysis of much older bone from the Cretaceous of China reveal shallow REE and U concentration profiles and very uniform reflected IR spectra with a significant loss of type A carbonate throughout the entire bone cortex. Analysis of stable isotopes through the bone cortex will be compared to the stable isotopes collected from the Pleistocene of Idaho.

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

    Energy Technology Data Exchange (ETDEWEB)

    Leal, Luiz Rogerio Bastos

    1998-07-01

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

  20. The radiogenic and stable Sr isotope geochemistry of basalt weathering in Iceland: Role of hydrothermal calcite and implications for long-term climate regulation

    Science.gov (United States)

    Andrews, M. Grace; Jacobson, Andrew D.

    2017-10-01

    Several studies have examined the geochemistry of Icelandic rivers to quantify the relationship between basalt weathering and long-term climate regulation. Recent research has suggested that the chemical weathering of hydrothermal and metamorphic calcite contributes significant quantities of HCO3- to the Icelandic riverine flux (Jacobson et al., 2015). Because the HCO3- derives from volcanic CO2 that was sequestered in mineral form prior to atmospheric injection, the strength of the basalt weathering feedback occurring in Iceland may be lower than previously realized. To test these hypotheses, we analyzed the radiogenic and stable Sr isotope composition (87Sr/86Sr and δ88/86Sr) of the same suite of water, rock, and mineral samples as examined in Jacobson et al. (2015), and we developed a simple model of the long-term C cycle that considers the transformation of volcanic CO2 to HCO3- during subsurface silicate weathering, which is a precursor to hydrothermal calcite formation. Interpretations based on 87Sr/86Sr and Ca/Sr ratios suggest that conservative, three-component mixing between basalt, calcite, and atmospheric deposition adequately explains river geochemistry. On average, the δ88/86Sr values of glacial and non-glacial rivers (0.414‰ and 0.388‰, respectively) are generally higher than those for basalt (0.276‰); however, calcite δ88/86Sr values (0.347‰) are also higher than those for basalt and span the range of riverine values. Thus, riverine δ88/86Sr values are also consistent three-component mixing between basalt, calcite, and atmospheric deposition. Isotopic fractionation is not required to explain riverine trends. Finally, model equations for the long-term C cycle demonstrate that subsurface silicate weathering reduces the magnitude of the volcanic CO2 degassing flux, which in turn causes the atmosphere to stabilize at lower pCO2 values compared to the case where no subsurface silicate weathering occurs. However, the proportion of the net

  1. On the source material of magmas - with special reference to Nd isotopic ratios of igneous rocks

    International Nuclear Information System (INIS)

    Shuto, Kenji

    1980-01-01

    In 1973, the Sm-Nd method was first used for the measurement of the absolute age of igneous rocks and meteorites. Subsequently in the following years, the research works by means of the Nd isotopic ratio in igneous rocks have been made strenuously in order to reveal the chemistry of the source materials of magma giving rise to the igneous rocks and further the evolution process of mantle and earth's crust. The fundamental items for the Sm-Nd method are explained. Then, the research results more important in the above connection are given. Finally, the ideas by the author concerning the source materials of magma are presented from the data available on the Nd isotopes in meteorites and igneous rocks. The following matters are described: the fundamentals of Sm-Nd method, the Nd content in seawater, the negative correlation between Nd and Sr isotopic ratios in igneous rocks, magma source materials and Nd isotopes, and considerations on magma source materials. (J.P.N.)

  2. U-Pb and Sm-Nd preliminary geochronologic data on the Yaounde series, Cameroon: re-interpretation of the granulitic rocks as the suture of a collision in the ''Centrafrican'' belt

    International Nuclear Information System (INIS)

    Schmus, W.R. Van; Penaye, J.; Toteu, S.F.; Nzenti, J.P.

    1993-01-01

    U-Pb on zircons and Sm-Nd on whole-rock analyses have been applied on the schists, micaschists and granulitic gneisses of the Yaounde series. The results fix the granulitic metamorphism in the Yaounde series at 620±10 Ma and the deposition of the series during the Upper Proterozoic. In addition, another remnant of Lower Proterozoic basement, previously recognized in northern Cameroon, has been identified at Kekem northwest of the Yaounde series. The Yaounde granulitic unit is re-interpreted as the suture of a Pan-African collision between a passive margin (Archean Congo craton and its Birrimian Nyong cover) to the south and an intensive granitized active margin (dismembered eburnian basement and Upper Proterozoic series) to the north. (author). 14 refs., 4 figs

  3. Isotope hydrology and baseflow geochemistry in natural and human-altered watersheds in the Inland Pacific Northwest, USA.

    Science.gov (United States)

    Sánchez-Murillo, Ricardo; Brooks, Erin S; Elliot, William J; Boll, Jan

    2015-01-01

    This study presents a stable isotope hydrology and geochemical analysis in the inland Pacific Northwest (PNW) of the USA. Isotope ratios were used to estimate mean transit times (MTTs) in natural and human-altered watersheds using the FLOWPC program. Isotope ratios in precipitation resulted in a regional meteoric water line of δ(2)H = 7.42·δ(18)O + 0.88 (n = 316; r(2) = 0.97). Isotope compositions exhibited a strong temperature-dependent seasonality. Despite this seasonal variation, the stream δ(18)O variation was small. A significant regression (τ = 0.11D(-1.09); r(2) = 0.83) between baseflow MTTs and the damping ratio was found. Baseflow MTTs ranged from 0.4 to 0.6 years (human-altered), 0.7 to 1.7 years (mining-altered), and 0.7 to 3.2 years (forested). Greater MTTs were represented by more homogenous aqueous chemistry whereas smaller MTTs resulted in more dynamic compositions. The isotope and geochemical data presented provide a baseline for future hydrological modelling in the inland PNW.

  4. Integration of inorganic and isotopic geochemistry with endocrine disruption activity assays to assess risks to water resources near unconventional oil and gas development in Garfield County, CO.

    Science.gov (United States)

    Harkness, J.; Kassotis, C.; Cornelius, J.; Nagel, S.; Vengosh, A.

    2016-12-01

    The rise of hydraulic fracturing in the United States has sparked a debate about the impact of oil and gas development on the quality of water resources. Wastewater associated with hydraulic fracturing includes injection fluid that is a mixture of sand, freshwater and synthetic organic chemicals, flowback water that is a mixture of injection fluid and formation brine, and produced water that is primarily brine. The fluids range in salinity and chemical composition that can have different environmental impacts. We analyzed the inorganic and isotope geochemistry of 58 surface and groundwater samples near and away from unconventional oil and gas operations (UOG), along with hormonal profiles via bioassays. Cl (0.12 to 198 mg/L), Na (1.2 to 518 mg/L) and Sr (1.4 to 2410 ug/L) were higher in both groundwater and surface water near UOG wells. Four surface waters and one groundwater had Br/Cl indicative of brine contamination (>1.5x10-3). Three of the SW samples also had 87Sr/86Sr ratios similar to values found in produced or flowback water (0.7118 and 0.7158, respectively) from the Williams-Fork formation and elevated compared to background ratios (0.71062 to 0.7115). Increased progestogenic activity was observed in groundwater near UOG operations and inncreased estrogenic, androgenic, progestogenic, anti-androgenic, anti-progestogenic, and anti-glucocorticoid activities in surface water near UOG operations. The association of increased EDCs with inorganic and isotopic indicators of UOG wastewater provides evidence for possible environmental and health impacts from drilling activity.

  5. New isotope data from the Koperberg Suite and some associated rocks, Okiep district, Namaqualand, South Africa

    International Nuclear Information System (INIS)

    Clifford, T.N.; Barton, E.S.; Retief, E.A.; Rex, D.C.

    1990-01-01

    The Koperberg Suite is an anorthosite-charnockite kindred and 1500 bodies of these rocks have been recognised in the Okiep district and 30 of them have been mined for copper since 1852. The suite is intrusive into country rocks. New isotope data presented includes U-Pb zircon and whole-rock Pb-Pb, Rb-Sr, Sm-Nd and Ar-Ar analyses. 10 refs

  6. Geochemistry and oxygen isotope composition of main-group pallasites and olivine-rich clasts in mesosiderites

    DEFF Research Database (Denmark)

    Greenwood, Richard C.; Barrat, Jean-Alix; Scott, Edward R. D.

    2015-01-01

    origin. Although the Dawn mission did not detect mesosiderite-like material on Vesta, evidence linking the mesosiderites and HEDs includes: (i) theirnearly identical oxygen isotope compositions; (ii) the presence in both of coarse-grained Mg-rich olivines; (iii) both have synchronous Lu-Hf and Mn-Cr ages...

  7. Characterization of the sedimentary organic matter preserved in Messel oil shale by bulk geochemistry and stable isotopes

    NARCIS (Netherlands)

    Bauersachs, T.; Schouten, S.; Schwark, L.

    2014-01-01

    We investigated a 150 m thick drill core section of Messel oil shale using bulk geochemical and stable isotope techniques in order to determine the organic matter sources and the environmental conditions that prevailed during the deposition of the lacustrine sequence. High Corg values (on average

  8. Combined iron and magnesium isotope geochemistry of pyroxenite xenoliths from Hannuoba, North China Craton: implications for mantle metasomatism

    Science.gov (United States)

    Zhao, Xin Miao; Cao, Hui Hui; Mi, Xue; Evans, Noreen J.; Qi, Yu Han; Huang, Fang; Zhang, Hong Fu

    2017-06-01

    We present high-precision iron and magnesium isotopic data for diverse mantle pyroxenite xenoliths collected from Hannuoba, North China Craton and provide the first combined iron and magnesium isotopic study of such rocks. Compositionally, these xenoliths range from Cr-diopside pyroxenites and Al-augite pyroxenites to garnet-bearing pyroxenites and are taken as physical evidence for different episodes of melt injection. Our results show that both Cr-diopside pyroxenites and Al-augite pyroxenites of cumulate origin display narrow ranges in iron and magnesium isotopic compositions (δ57Fe = -0.01 to 0.09 with an average of 0.03 ± 0.08 (2SD, n = 6); δ26Mg = - 0.28 to -0.25 with an average of -0.26 ± 0.03 (2SD, n = 3), respectively). These values are identical to those in the normal upper mantle and show equilibrium inter-mineral iron and magnesium isotope fractionation between coexisting mantle minerals. In contrast, the garnet-bearing pyroxenites, which are products of reactions between peridotites and silicate melts from an ancient subducted oceanic slab, exhibit larger iron isotopic variations, with δ57Fe ranging from 0.12 to 0.30. The δ57Fe values of minerals in these garnet-bearing pyroxenites also vary widely (-0.25 to 0.08 in olivines, -0.04 to 0.25 in orthopyroxenes, -0.07 to 0.31 in clinopyroxenes, 0.07 to 0.48 in spinels and 0.31-0.42 in garnets). In addition, the garnet-bearing pyroxenite shows light δ26Mg (-0.43) relative to the mantle. The δ26Mg of minerals in the garnet-bearing pyroxenite range from -0.35 for olivine and orthopyroxene, to -0.34 for clinopyroxene, 0.04 for spinel and -0.68 for garnet. These measured values stand in marked contrast to calculated equilibrium iron and magnesium isotope fractionation between coexisting mantle minerals at mantle temperatures derived from theory, indicating disequilibrium isotope fractionation. Notably, one phlogopite clinopyroxenite with an apparent later metasomatic overprint has the heaviest δ57Fe

  9. Isotope geochemistry of fluid inclusions in Permian halite with implications for the isotopic history of ocean water and the origin of saline formation waters

    International Nuclear Information System (INIS)

    Knauth, L.P.; Beeunas, M.A.

    1986-01-01

    deltaD and delta 18 O values have been determined for fluid inclusions in 45 samples of Permian halite. The inclusions are enriched in 18 O relative to the meteoric water line but are depleted in D relative to ocean water. Inclusions with the more positive delta-values coincide with the isotopic compositions expected for evaporating sea water which follows a hooked trajectory on a deltaD-delta 18 O diagram. Inclusions with more negative delta-values may represent more highly evaporated sea water but probably reflect synsedimentary or diagenetic mixing to those of a modern evaporite pan to indicate that Permian sea water was isotopically similar to modern sea water. Connate evaporite brines can have negative delta-values because of the probable hooked isotope trajectory of evaporating sea water and/or synsedimentary mixing of evaporite brines with meteoric waters. (author)

  10. Geochemistry, water balance, and stable isotopes of a “clean” pit lake at an abandoned tungsten mine, Montana, USA

    International Nuclear Information System (INIS)

    Gammons, Christopher H.; Pape, Barbara L.; Parker, Stephen R.; Poulson, Simon R.; Blank, Carrine E.

    2013-01-01

    Highlights: • An abandoned open pit mine is now a 30 m deep lake with excellent water quality. • Concentrations of sulfate, nutrients, and most trace metals are extremely low. • Based on water isotopes, the lake is 30% evaporated with a 2.5 yr residence time. • Stable isotopes of DIC and DO track in-lake bio-geochemical processes. • Phytoplankton are active at depths as great as 20 m. - Abstract: The Calvert Mine is a small tungsten-rich (scheelite) skarn deposit in a remote, mountainous region of southwest Montana, USA. The open-pit mine closed in the 1970s and subsequently flooded to form a pit lake that is roughly conical in shape, 30 m deep and 120 m in diameter, with no surface inlet or outlet. The lake is holomictic with a groundwater flow-through hydrology and an estimated residence time of 2.5–5 y. Water isotopes show that the lake is at an approximate steady state with respect to water balance and has experienced 30% evaporation. The lake has a near-neutral pH, exceptional clarity, and extremely low concentrations of nutrients, sulfate, and most metals, including tungsten. Manganese concentrations are slightly elevated and increase with depth towards the sediment–water interface. Despite seasonally anoxic conditions in the deep water, dissolved Fe concentrations are orders of magnitude lower than Mn, suggesting that insufficient organic carbon is present in the sediment of this oligotrophic lake to drive bacterial Fe reduction. Based on stable isotope fingerprinting, diffuse seepage that enters a nearby headwater stream at the base of a large waste-rock pile can be directly linked to the partially evaporated pit lake. However, this seepage has neutral pH and low metal concentrations, and poses no threats to the environment. Stable isotopes of dissolved inorganic carbon (DIC) and dissolved oxygen (DO) are used to track the relative importance of photosynthesis and respiration with depth. In summer, a zone of high productivity exists near the

  11. Using Stable Isotope Geochemistry to Determine Changing Paleohydrology and Diagenetic Alteration in the Late Cretaceous Kaiparowits Formation, UT USA

    Science.gov (United States)

    Yamamura, Daigo

    The Western Interior Basin of the North America preserves one of the best sedimentary and paleontological records of the Cretaceous in the world. The Upper Cretaceous Kaiparowits Formation is a rapidly deposited fluvial sequence and preserves one of the most complete terrestrial fossil record of the North America. Such a unique deposit provides an opportunity to investigate the interaction between the physical environment and ecology. In an effort to decipher such interaction, stable isotope composition of cements in sedimentary rocks, concretions and vertebrate fossils were analyzed. Despite the difference in facies and sedimentary architecture, the isotope composition does not change significantly at 110 m from the base of the formation. Among the well-preserved cement samples, stable isotope composition indicates a significant hydrologic change within the informal Middle unit; a 6.37‰ depletion in delta13C and 3.30‰ enrichment in delta 18O occurs at 300 m above the base of the formation. The isotope values indicate that the sandstone cements below 300 m were precipitated in a mixing zone between marine and terrestrial groundwater, whereas the cements in upper units were precipitated in a terrestrial groundwater. Despite the difference in physical appearance (i.e. color and shape), the isotopic compositions of cements in concretions are similar to well-cemented sandstone bodies in similar stratigraphic positions. Isotope compositions of the host rock are similar to that of mudrock and weathered sandstone, suggesting the origin of cementing fluids for the sandstone and concretions were the same indicating that: 1) the concretions were formed in shallow groundwater and not related to the groundwater migration, or 2) all cements in upper Kaiparowits Formation are precipitated or altered during later stage groundwater migration. Average delta18Oc from each taxon show the same trend as the delta18Op stratigraphic change, suggesting delta18Oc is still useful as a

  12. On the origin of cratonic `high-mu' isotopic signatures

    Science.gov (United States)

    Reimink, J. R.; Carlson, R.; Shirey, S. B.; Pearson, D. G.; Kamber, B. S.

    2017-12-01

    Some Archean cratons (i.e. Slave, Wyoming) contain Neoarchean granitoids with initial Pb isotopic compositions indicative of derivation from sources characterized by high time-integrated U/Pb ratios (high-mu [1]). Single-stage high-m precursor source reservoir separation from the depleted mantle occurred no later than 3.9 Ga [2]. However, multi-stage separation could have occurred in the Hadean, suggesting that recycling or reworking of Eoarchean/Hadean crust played a significant role in the generation of Neoarchean granitic crust in many cratons. The Sm-Nd system is similar to the U-Pb system in that it has a short-lived parent-daughter pair (146Sm-142Nd) that is sensitive to very early differentiation events, as well as a long-lived parent-daughter pair (147Sm-143Nd) that is sensitive to differentiation throughout all of Earth history. The 103 Ma half-life of 146Sm makes it sensitive only to Sm/Nd fractionation that occurred in the Hadean, providing a useful tracker for very early differentiation events. Indeed, evidence for Neoarchean remelting of ancient crust in another craton has come from analyses of the paired Sm-Nd isotope systems from the Hudson Bay terrane of the northeastern Superior Province. These results indicate that the source of 2.7 Ga Hudson Bay terrane granitoids was Hadean mafic crust, and not Eoarchean felsic crust [3]. Here, we present new data from Neoarchean granites located in the Slave and Wyoming cratons, along with modeling of the dual paired-isotope systems of U-Pb and Sm-Nd to achieve a tighter constraint on the composition of the precursors and the timing of their melting. Combining our newly collected 142Nd data with the high-m signature of these Neoarchean rocks, we evaluate precursor source separation ages along with the source Sm/Nd and U/Pb compositions. In the simplest end-member scenarios, use of the 142Nd system allows us to test whether the cratonic high-mu signature was created by melting of Hadean mafic crust or Eoarchean

  13. The Leadville Mine Drainage Tunnel Catastrophe: A Case Study of How Isotope Geochemistry Provided Forensic Evidence to Inform Policy Decisions

    Science.gov (United States)

    Williams, M. W.; Wireman, M.; Liu, F.; Gertson, J.

    2008-12-01

    A state of emergency was declared in February 2008 because of fears that a blocked drainage tunnel in the Leadville mining district of Colorado could cause a catastrophic flood. An estimated 1 billion gallons of metals-laden water poses an eminent threat to the city of Leadville and the headwaters of the Arkansas river. Within days of the declaration of a state of emergency, Governor Ritter and Senator Salazer of Colorado, along with a host of other local and statewide politicians, visited the site and emphasized the need to develop a fast yet safe mitigation plan. Here we provide information from a case study that illustrates how a suite of isotopic and hydrologic tools enables identification of critical, site-specific variables essential in developing a science plan to guide targeted remediation of the Leadville drainage tunnel. The isotopic tools, including both stable and radiogenic isotopes, provided clear and compelling evidence of water sources and flowpaths in an area that has undergone extensive perturbations, including the drilling of more than 2,000 mine shafts. This forensic evidence was the key information in developing a plan to plug the drainage tunnel several hundred feet underground, divert a major source of polluted water from reaching the collapsed tunnel and piping it to an existing treatment plant, and guidance on where to place pumps in additional mine shafts, and the drilling of new wells to pump water in case the plugging of the tunnel caused water to pool up and raise the water table to dangerous heights. This particular case of forensic hydrology using isotopic tools not only provides the scientific basis for an operational plan to defuse a life- and property-threatening situation, it also provides the basis for decommissioning an existing water treatment plant, which will result in savings of over 1 million annually in operational costs. Decommissioning the existing water treatment plant will pay for the tunnel mitigation within several

  14. New Rb-Sr isotopic ages and geochemistry of granitic gneisses from southern Bastar: implications for crustal evolution

    International Nuclear Information System (INIS)

    Sarkar, G.; Gupta, S.N.; Bishui, P.K.

    1994-01-01

    Deformed gneisses from the southern Bastar craton yield Rb-Sr whole-rock ages of 2560 Ma and 2659 Ma with initial Sr ratios ranging between 0.70899 and 0.70726 respectively. The isotopic data are found to be scattered even at the outcrop scale which possibly indicate large-scale reworking of the gneisses during the period. The high initial Sr ratios that associate with scattering of the isotopic data reflect reworking of older gneisses. Geochemically, these gneisses are considered to be derived from an amphibolitic or basaltic protolith. The 2095 Ma (initial Sr ratio of 0.74312) old leucocratic granite intrusive into these gneisses represent early Proterozoic magmatic activity. Based on the available isotopic and geochemical data, it is suggested that the Bastar craton represents a polyphase, multicomponent terrain developed by repeated magmatism at a much earlier, probably during mid-Archaean, time and was extensively reworked during the time span between end-Archaean and early Proterozoic period. This reworking may be synchronous with coalescing of smaller crustal components possibly during the end-Archaean time. (author). 21 refs., 5 figs., 2 tabs

  15. Applications of isotope geochemistry to the reconstruction of Yucca Mountain, Nevada, paleohydrology -- Status of investigations: June 1996

    International Nuclear Information System (INIS)

    Whelan, J.F.; Moscati, R.J.; Allerton, S.B.M.; Marshall, B.D.

    1998-01-01

    Tunneling of the Exploratory Studies Facility has offered the opportunity to sample and examine occurrences of secondary mineralization found in the unsaturated-zone tuffs of Yucca Mountain, nevada. Petrographic and paragenetic analyses, calcite and silica-phase stable isotopic analyses, and preliminary strontium tracer isotope and radiocarbon age analyses of these samples indicate that (1) an early stage of secondary mineralization consisting largely of chalcedony and quartz, but possibly with or slightly preceded by calcite, probably formed at warmer than ambient temperatures; (2) later secondary mineralization consisting of calcite and opal appears completely consistent with formation from percolation of surface infiltration whose solute load and carbon isotopic compositions reflect passage through the overlying soils; (3) based on textural studies, all unsaturated-zone secondary mineral occurrences exposed within the Exploratory Studies Facility tunnel, with the exception of the vapor-phase assemblages that formed at high temperatures during cooling of the tuffs, probably formed in unsaturated settings; and (4) calcite radiocarbon ages, based on preliminary results, have not been compromised by post-depositional exchange with carbon-bearing water and gases in the unsaturated zone

  16. Mineralogy, Geochemistry and Stable Isotope Investigation of Gürkuyu Sb Mineralization (Gediz-Kütahya-NW Turkey

    Directory of Open Access Journals (Sweden)

    Yeşim ÖZEN

    2016-11-01

    Full Text Available Abstract. The Gürkuyu Sb mineralization is located in the western part of Anatolian tectonic belt, in southern part of İzmir-Ankara zone and in northern part of Menderes Massif. The mineralization located at west of the Koca hill in east of Gürkuyu village of Gediz (Kütahya-Turkey has been characterized through the detailed examinations involving sulfur and oxygen isotope. Serpentinites of Dağardı melange and crystallized limestones of Budağan limestone were hydrothermally altered by hydrothermal solutions, come from fissures and fractures due to tectonic movement during the thrust of melange and occurred silicified zone. Gürkuyu Sb mineralization suggest that occurred in this silicified zone. In Gürkuyu mineralization, primary ore minerals are antimonite and pyrite, secondary ore minerals are senarmontite, valentinite, orpiment and realgar. Quartz and calcite are the most common gangue minerals. In Gürkuyu Sb mineralization, δ34S values of stibnite are ranged from 1.0 ‰ to 1.3 ‰. δ18O values of quartz are ranged is 15.8 ‰ in Gürkuyu mineralization. Sulfur and oxygen isotope values are similar to the values for magmatic rocks and to the values for fluids of magmatic origin.Keywords: Stable isotope, Gürkuyu, Sb mineralization, Gediz, Kütahya, NW Turkey.

  17. Elemental hydrochemistry and hydro geochemistry of the uranium isotopes in Alter do Chao formation, Manaus (Amazon - Brazil)

    International Nuclear Information System (INIS)

    Silva, Marcio Luiz da; Bonotto, Daniel Marcos

    2006-01-01

    The water exploitation at Manaus city, Amazonas State, Brazil, takes place from Negro River and tubular wells, being performed by a private company. This paper evaluates the hydrochemistry and geochemical behavior of uranium isotopes ( 238 U and 234 U) in groundwaters from Manaus city, with the aim to characterize the contaminants or pollutants that possibly are affecting the quality of the underground hydrological resources, as well as to evaluate the potential use of the natural U-isotopes as hydrological tracers in the aquifer studied. The U-isotopes analysis allowed to determine 234 U/ 238 U activity ratios of 1.2-4.4, and dissolved uranium concentration of 0.003-1.1 μg.L -1 (ppb). These results and those concerning the others parameters indicated that the waters are appropriate for human consumption, permitting to classify the hydrological system as acid-reducing, and to say that the waters leach minerals in strata containing low U content.(author)

  18. Assessment of the origin and geothermal potential of the thermal waters by hydro-isotope geochemistry: Eskisehir province, Turkey.

    Science.gov (United States)

    Yuce, Galip; Italiano, Francesco; Yasin, Didem; Taskiran, Lutfi; Gulbay, Ahmet Hilmi

    2017-05-01

    The thermal fluids vented over Eskisehir province have been investigated for their origin and to estimate the geothermal potential of the area. Thermal waters as well as bubbling and dissolved gases were collected and analysed for their chemical and isotopic features. Their isotopic composition varies in the range from -11.5 to -7.7 ‰ for δ 18 O, -84 and -57 ‰ for δ 2 H, and 0-7.2 TU for tritium. The gases (bubbling and dissolved) are mostly N 2 -dominated with a significant amount of CO 2 . The helium isotopic ratios are in the range of 0.2-0.66 R/Rac, indicate remarkable mantle-He contribution ranging between 2 and 10 % in the whole study area. Considering the estimated geothermal gradient about three times higher than the normal gradient, and the reservoir temperatures estimated to be between 50 and 100 °C using quartz and chalcedony geothermometers, a circulation model was built where possible mixing with shallow waters cool down the uprising geothermal fluids.

  19. Applications of isotope geochemistry to the reconstruction of Yucca Mountain, Nevada, paleohydrology -- Status of investigations: June 1996

    Energy Technology Data Exchange (ETDEWEB)

    Whelan, J.F.; Moscati, R.J.; Allerton, S.B.M.; Marshall, B.D.

    1998-11-01

    Tunneling of the Exploratory Studies Facility has offered the opportunity to sample and examine occurrences of secondary mineralization found in the unsaturated-zone tuffs of Yucca Mountain, nevada. Petrographic and paragenetic analyses, calcite and silica-phase stable isotopic analyses, and preliminary strontium tracer isotope and radiocarbon age analyses of these samples indicate that (1) an early stage of secondary mineralization consisting largely of chalcedony and quartz, but possibly with or slightly preceded by calcite, probably formed at warmer than ambient temperatures; (2) later secondary mineralization consisting of calcite and opal appears completely consistent with formation from percolation of surface infiltration whose solute load and carbon isotopic compositions reflect passage through the overlying soils; (3) based on textural studies, all unsaturated-zone secondary mineral occurrences exposed within the Exploratory Studies Facility tunnel, with the exception of the vapor-phase assemblages that formed at high temperatures during cooling of the tuffs, probably formed in unsaturated settings; and (4) calcite radiocarbon ages, based on preliminary results, have not been compromised by post-depositional exchange with carbon-bearing water and gases in the unsaturated zone.

  20. Zircon U-Pb chronology, geochemistry and Sr-Nd-Pb isotopic compositions of the Volcanic Rocks in the Elashan area, NW China: petrogenesis and tectonic implications

    Science.gov (United States)

    Zhou, H.; Wei, J.; Shi, W.; Li, P.; Chen, M.; Zhao, X.

    2017-12-01

    Elashan area is located in the intersection of the East Kunlun Orogenic Belt (EKOB) and the West Qinling Orogenic (WQOB). We present petrology, zircon U-Pb ages, whole-rock geochemistry and Sr-Nd-Pb isotopic compositions from the andesite and felsic volcanic rocks (rhyolite and rhyolitic tuffs) in Elashan group volcanic rock. The LA-ICP-MS zircon U-Pb age data indicate that the volcanic rocks are emplaced at 250 247 Ma. The volcanic rocks have high -K and aluminum - peraluminous characteristics, A/CNK = 1.07 1.82, δ ranges from 1.56 2.95, the main body is calc-alkaline rock. They are enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs) and depleted in some high field strength elements (HFSEs, e.g., Nb, Ta, P and Ti), while having a flat heavy REE (HREEs) pattern. The ∑REE values of 178.68 to 298.11 ppm, average 230.50 ppm. The LREE/HREE values of 4.39 to 11.78 ppm, average 6.77 ppm. REE fractionation is obvious, REE distribution curve was right smooth, and have slightly negative Eu anomalies (Eu/Eu*=0.44-0.80, average 0.60), which as similar to the island arc volcanic rocks. The volcanic rocks have initial 87Sr/86Sr ratios of 0.71028-0.71232, ɛNd(t) values of -6.7 to -7.6, with T2DM-Nd ranging from 1561 to 1640 Ma. Pb isotopic composition (206 Pb / 204 Pb)t = 18.055 18.330, (207 Pb / 204 Pb)t = 15.586 15.618, (208 Pb / 204 Pb)t = 37.677 38.332. Geochemical and Sr-Nd-Pb isotopes indicates that Elashan group volcanic magma derived mainly from the lower crust. Elashan group volcanic rocks is the productive East Kunlun block and West Qinling block collision, which makes the thicken crust caused partial melting in the study area. The source rocks is probably from metamorphic sandstone of Bayankala. But with Y-Nb and Rb-(Y+Nb), R1-R2 and Rb/10-Hf-Ta*3 diagrams showing that intermediate-acid rocks mainly formed in volcanic arc-collision environment, probably the collision event is short , therefore rocks retain the original island

  1. Hydrochemistry, mineralogy and sulfur isotope geochemistry of acid mine drainage at the Mt. Morgan mine environment, Queensland, Australia

    International Nuclear Information System (INIS)

    Edraki, M.; Golding, S.D.; Baublys, K.A.; Lawrence, M.G.

    2005-01-01

    Mineralogical, hydrochemical and S isotope data were used to constrain hydrogeochemical processes that produce acid mine drainage from sulfidic waste at the historic Mount Morgan Au-Cu mine, and the factors controlling the concentration of SO 4 and environmentally hazardous metals in the nearby Dee River in Queensland, Australia. Some highly contaminated acid waters, with metal contents up to hundreds of orders of magnitude greater than the Australia-New Zealand environmental standards, by-pass the water management system at the site and drain into the adjacent Dee River. Mine drainage precipitates at Mt. Morgan were classified into 4 major groups and were identified as hydrous sulfates and hydroxides of Fe and Al with various contents of other metals. These minerals contain adsorbed or mineralogically bound metals that are released into the water system after rainfall events. Sulfate in open pit water and collection sumps generally has a narrow range of S isotope compositions (δ 34 S = 1.8-3.7%o) that is comparable to the orebody sulfides and makes S isotopes useful for tracing SO 4 back to its source. The higher δ 34 S values for No. 2 Mill Diesel sump may be attributed to a difference in the source. Dissolved SO 4 in the river above the mine influence and 20 km downstream show distinctive heavier isotope compositions (δ 34 S = 5.4-6.8%o). The Dee River downstream of the mine is enriched in 34 S (δ 34 S = 2.8-5.4%o) compared with mine drainage possibly as a result of bacterial SO 4 reduction in the weir pools, and in the water bodies within the river channel. The SO 4 and metals attenuate downstream by a combination of dilution with the receiving waters, SO 4 reduction, and the precipitation of Fe and Al sulfates and hydroxides. It is suggested here that in subtropical Queensland, with distinct wet and dry seasons, temporary reducing environments in the river play an important role in S isotope systematics

  2. Amino acid stable isotope applications to deep-sea corals: A molecular geochemistry approach to reconstructing past ocean conditions

    Science.gov (United States)

    McMahon, K.; McCarthy, M. D.; Guilderson, T. P.; Sherwood, O.; Williams, B.; Larsen, T.; Glynn, D. S.

    2017-12-01

    Future climate change is predicted to alter ocean productivity, food web dynamics, biogeochemical cycling, and the efficacy of the biological pump. Proteinaceous deep-sea corals act as "living sediment traps," providing long-term, high-resolution records of exported surface ocean production and a window into past changes in ocean condition as a historical context for potential future changes. Here, we present recent work developing the application of compound-specific stable isotope analysis of individual amino acids to proteinaceous deep-sea corals to reconstruct past changes in phytoplankton community composition and biogeochemical cycling. We present new calibrations for molecular isotope comparisons between metabolically active coral polyp tissue and bioarchival proteinaceous skeleton. We then applied these techniques to deep-sea corals from the North Pacific Subtropical Gyre (NPSG) to reconstruct centennial to millennial time scale changes in phytoplankton community composition and biogeochemical cycling as a function of regional climate change. This work suggests that the NPSG has undergone multiple major phytoplankton regime shifts over the last millennium between prokaryotic and eukaryotic phytoplankton communities and associated sources of nitrogen fueling production. The most recent regime, which started around the end of the Little Ice Age and the onset of the Industrial era, is unprecedented in the last 1000 years and resulted in a 30-50% increase in diazotrophic cyanobacteria contribution to export production and an associated 17-27% increase in N2-fixation in the NPSG over last century. By offering the first direct phylogenetic context for long-term shifts in isotopic records of exported particulate organic matter, our data represent a major step forward in understanding the evolution of marine plankton community dynamics, food web architecture, biogeochemical cycling, and the climate feedback loops through the biological pump.

  3. The Serchio River catchment, northern Tuscany: Geochemistry of stream waters and sediments, and isotopic composition of dissolved sulfate

    International Nuclear Information System (INIS)

    Cortecci, Gianni; Dinelli, Enrico; Boschetti, Tiziano; Arbizzani, Paola; Pompilio, Loredana; Mussi, Mario

    2008-01-01

    The Serchio River and its tributaries in northern Tuscany were investigated for the chemical and isotopic compositions of waters and bed sediments. Bedrocks are mostly limestone/dolomite and siliciclastics, thermal spring systems are present in the catchment, and the main industrial activity is represented by paper-mills. Main results obtained are: (1) major ions in solution appear to be basically controlled by precipitation and lithology, as well as subordinately by direct inputs of thermal springs, (2) human influence on metals in the waters along the main Serchio and Lima rivers is indicated at a number of sites by increases in concentration compared to the chemical composition of upstream tributaries, (3) S and O isotope compositions delineate two main sources for aqueous SO 4 2- , that is dissolution of Triassic evaporite (directly or via thermal springs) and oxidation of sulfide dispersed in siliciclastic rocks. Anthropogenic contributions are probable, but they cannot be quantitatively assessed. Only SO 4 2- in the notoriously polluted Ozzeri tributary is suspected to be largely anthropogenic, and (4) the chemical composition of bed sediments is mainly influenced by lithology, apart from a number of technogenic elements in the upper part of the Serchio River and in some tributaries. Contamination possibly occurs at other sites, but geochemical indications are weak

  4. Alunite in the Pascua-Lama high-sulfidation deposit: Constraints on alteration and ore deposition using stable isotope geochemistry

    Science.gov (United States)

    Deyell, C.L.; Leonardson, R.; Rye, R.O.; Thompson, J.F.H.; Bissig, T.; Cooke, D.R.

    2005-01-01

    The Pascua-Lama high-sulfidation system, located in the El Indio-Pascua belt of Chile and Argentina, contains over 16 million ounces (Moz) Au and 585 Moz Ag. The deposit is hosted primarily in granite rocks of Triassic age with mineralization occurring in several discrete Miocene-age phreatomagmatic breccias and related fracture networks. The largest of these areas is Brecha Central, which is dominated by a mineralizing assemblage of alunite-pyrite-enargite and precious metals. Several stages of hydrothermal alteration related to mineralization are recognized, including all types of alunite-bearing advanced argillic assemblages (magmatic-hydrothermal, steam-heated, magmatic steam, and supergene). The occurrence of alunite throughout the paragenesis of this epithermal system is unusual and detailed radiometric, mineralogical, and stable isotope studies provide constraints on the timing and nature of alteration and mineralization of the alunite-pyiite-enargite assemblage in the deposit. Early (preore) alteration occurred prior to ca. 9 Ma and consists of intense silicic and advanced argillic assemblages with peripheral argillic and widespread propylitic zones. Alunite of this stage occurs as fine intergrowths of alunite-quartz ?? kaolinite, dickite, and pyrophyllite that selectively replaced feldspars in the host rock. Stable isotope systematics suggest a magmatic-hydrothermal origin with a dominantly magmatic fluid source. Alunite is coeval with the main stage of Au-Ag-Cu mineralization (alunite-pyrite-enargite assemblage ore), which has been dated at approximately 8.8 Ma. Ore-stage alunite has an isotopic signature similar to preore alunite, and ?? 34Salun-py data indicate depositional temperatures of 245?? to 305??C. The ??D and ?? 18O data exclude significant involvement of meteoric water during mineralization and indicate that the assemblage formed from H2S-dominated magmatic fluids. Thick steam-heated alteration zones are preserved at the highest elevations in

  5. Gas and Isotope Geochemistry of 81 Steam Samples from Wells in The Geysers Geothermal Field, Sonoma and Lake Counties, California

    Science.gov (United States)

    Lowenstern, Jacob B.; Janik, Cathy J.; Fahlquist, Lynne; Johnson, Linda S.

    1999-01-01

    The Geysers geothermal field in northern California, with about 2000-MW electrical capacity, is the largest geothermal field in the world. Despite its importance as a resource and as an example of a vapor-dominated reservoir, very few complete geochemical analyses of the steam have been published (Allen and Day, 1927; Truesdell and others, 1987). This report presents data from 90 steam, gas, and condensate samples from wells in The Geysers geothermal field in northern California. Samples were collected between 1978 and 1991. Well attributes include sampling date, well name, location, total depth, and the wellhead temperature and pressure at which the sample was collected. Geochemical characteristics include the steam/gas ratio, composition of noncondensable gas (relative proportions of CO2, H2S, He, H2, O2, Ar, N2, CH4, and NH3), and isotopic values for deltaD and delta18O of H2O, delta13C of CO2, and delta34S of H2S. The compilation includes 81 analyses from 74 different production wells, 9 isotopic analyses of steam condensate pumped into injection wells, and 5 complete geochemical analyses on gases from surface fumaroles and bubbling pools. Most samples were collected as saturated steam and plot along the liquid-water/steam boiling curve. Steam-togas ratios are highest in the southeastern part of the geothermal field and lowest in the northwest, consistent with other studies. Wells in the Northwest Geysers are also enriched in N2/Ar, CO2 and CH4, deltaD, and delta18O. Well discharges from the Southeast Geysers are high in steam/gas and have isotopic compositions and N2/Ar ratios consistent with recharge by local meteoric waters. Samples from the Central Geysers show characteristics found in both the Southeast and Northwest Geysers. Gas and steam characteristics of well discharges from the Northwest Geysers are consistent with input of components from a high-temperature reservoir containing carbonrich gases derived from the host Franciscan rocks. Throughout the

  6. Iodine budget in surface waters from Atacama: Natural and anthropogenic iodine sources revealed by halogen geochemistry and iodine-129 isotopes

    International Nuclear Information System (INIS)

    Álvarez, Fernanda; Reich, Martin; Snyder, Glen; Pérez-Fodich, Alida; Muramatsu, Yasuyuki; Daniele, Linda; Fehn, Udo

    2016-01-01

    Iodine enrichment in the Atacama Desert of northern Chile is widespread and varies significantly between reservoirs, including nitrate-rich “caliche” soils, supergene Cu deposits and marine sedimentary rocks. Recent studies have suggested that groundwater has played a key role in the remobilization, transport and deposition of iodine in Atacama over scales of millions-of-years. However, and considering that natural waters are also anomalously enriched in iodine in the region, the relative source contributions of iodine in the waters and its extent of mixing remain unconstrained. In this study we provide new halogen data and isotopic ratios of iodine ("1"2"9I/I) in shallow seawater, rivers, salt lakes, cold and thermal spring water, rainwater and groundwater that help to constrain the relative influence of meteoric, marine and crustal sources in the Atacama waters. Iodine concentrations in surface and ground waters range between 0.35 μM and 26 μM in the Tarapacá region and between 0.25 μM and 48 μM in the Antofagasta region, and show strong enrichment when compared with seawater concentrations (I = ∼0.4 μM). In contrast, no bromine enrichment is detected (1.3–45.7 μM for Tarapacá and 1.7–87.4 μM for Antofagasta) relative to seawater (Br = ∼600 μM). These data, coupled to the high I/Cl and low Br/Cl ratios are indicative of an organic-rich sedimentary source (related with an “initial” fluid) that interacted with meteoric water to produce a mixed fluid, and preclude an exclusively seawater origin for iodine in Atacama natural waters. Iodine isotopic ratios ("1"2"9I/I) are consistent with halogen chemistry and confirm that most of the iodine present in natural waters derives from a deep initial fluid source (i.e., groundwater which has interacted with Jurassic marine basement), with variable influence of at least one atmospheric or meteoric source. Samples with the lowest isotopic ratios ("1"2"9I/I from ∼215 to ∼1000 × 10"

  7. Petrogenesis of Mesozoic granites in the Xitian, South China: Evidence from whole-rock geochemistry and zircon isotopes

    Science.gov (United States)

    Liu, Q.; Sun, J.; He, M.; Hou, Q.; Niu, R.

    2017-12-01

    Mesozoic granitoids are widespread in southeastern China, which accompanied with lots of world-famous polymetallic deposits. The mineralization is believed to be related to the Mesozoic granitic magmatism. However, the petrogenesis of these granites and their relation to the mineralization are still debated. As a typical granitic pluton, Xitian granites from the eastern Hunan Province are formed during this period and associated with tungsten-tin deposit. Whole-rock geochemical, SIMS zircon geochronology and oxygen isotopes, as well as LA-ICPMS zircon Lu-Hf isotopic analyses, were carried out on a suite of rocks from Xitian granitic pluton to constrain their magmatic sources and petrogenesis. Xitian granitic pluton is mainly composed of biotite adamellite, biotite granite, fine-grained granite. SIMS and LA-ICPMS U-Pb dating of zircons indicate that there are two episodes of these rocks, i.e., Late Triassic granites (227-233Ma) and Late Jurassic granites (150-154Ma). The Xitian granites are silica-rich, potassic and weakly peraluminous. Petrographic and geochemical features show that they are highly fractionated I-type granites. The combined elemental and isotopic results indicated that the Late Triassic granite in Xitian area experienced a process of crystal fractionation of crustal-derived magmas coupled with strong assimilation of the surrounding rocks. The occurrence of Jurassic granitoids in Xitian area is attributed to ascending of mantle-derived magmas, which provide heat for partial melting of crustal materials. The Late Jurassic granite may be derived from juvenile crust or partial melting of ancient crustal rocks, whereas high degrees of crystal fractionation further enriched tungsten-tin in the evolved granitic rocks. This work was financially supported by the Research Cooperation between Institute and University of Chinese Academy of Sciences grant (Y552012Y00), Public Welfare Project of the Ministry of land and Resources of China (201211024

  8. Isotope geochemistry of brasiliano age, coarsely porphyritic, K-calc-alkalic granitoids and associated K-diorites, northeast Brazil

    International Nuclear Information System (INIS)

    Sial, A.N.; Mariano, G.; Ferreira, V.P.

    1989-01-01

    Several porphyritic, K-calc-alkalic were syntectonically intruded in NE Brazil during the Brasiliano orogeny. They show bi-(qz) diorite and coarsely porphyritic granodiorite to qz monzonite ('Itaporanga-type') in commingling zones on a scale of cm to m irrespective of whether plutons are at the margins of the NE-trending Cachoeirinha-Salgueiro Fold Belt (CSF) or intruded metasediments of the Serido Fold Belt (SFB). The bi(qz) diorites are found in magmatic or stromatic structures and narrow dikes wich intruded the felsic facies. SiO 2 in the porphyritic facies ranges from 61 to 72% with K 2 O usually > Na 2 O. K-diorities exhibit SiO 2 from 50 to 58%, MgO from 2 to 10% and K 2 O from 2 to 5%. Both facies are usually Ba and Sr-enriched, with similar, highly fractionated REE patterns, lacking free of Eu anomaly. Quartz 180 values are considered homogeneous on the scale of these intrusions in the CSF, (8 to 10 per milSMOW). Bi-(qz) diorites exhibit slightly higher 180 (9.5 to 10.5 per milSMOW). In the SFB both facies are lower than 180. The oxygen isotope data for the porphyritic facies are compatible with I-type source with some metasedimentary component of variable proportion. As bi(qz) diorites were formed pre- to post-porphyritic facies intrusion, their high LREE, K and 180 reflect their source rather than the interaction with the potassic felsic magma. Preliminarly sulfur isotope values suggest that porphyritic facies of granitoids in the SBF are lower in 34S than those in the CSF. Rb and Sr isotopes reflect source heterogeneity, complicated by mixing relations. Ages span from 510 to 630 Ma suggesting that the Itaporanga-type association was formed during uplift and cooling of the Pan-African I and onset of the Pan-African II orogenies, recognized in West Africa. (author) [pt

  9. Isotope geochemistry of recent magmatism in the Aegean arc: Sr, Nd, Hf, and O isotopic ratios in the lavas of Milos and Santorini-geodynamic implications

    Science.gov (United States)

    Briqueu, L.; Javoy, M.; Lancelot, J.R.; Tatsumoto, M.

    1986-01-01

    In this comparative study of variations in the isotopic compositions (Sr, Nd, O and Hf) of the calc-alkaline magmas of the largest two volcanoes, Milos and Santorini, of the Aegean arc (eastern Mediterranean) we demonstrate the complexity of the processes governing the evolution of the magmas on the scale both of the arc and of each volcano. On Santorini, the crustal contamination processes have been limited, effecting the magma gradually during its differentiation. The most differentiated lavas (rhyodacite and pumice) are also the most contaminated. On Milos, by contrast, these processes are very extensive. They are expressed in the 143Nd/144Nd vs. 87Sr/86Sr diagram as a continuous mixing curve between a mantle and a crustal end member pole defined by schists and metavolcanic rocks outcropping on these volcanoes. In contrast with Santorini, the least differentiated lavas on Milos are the most contaminated. These isotopic singularities can be correlated with the geodynamic evolution of the Aegean subduction zone, consisting of alternating tectonic phases of distension and compression. The genesis of rhyolitic magmas can be linked to the two phases of distension, and the contamination of the calc-alkaline mantle-derived magmas with the intermediate compressive phase. The isotopic characteristics of uncontaminated calc-alkaline primitive magmas of Milos and Santorini are directly comparable to those of magmas generated in subduction zones for which a contribution of subducted sediments to partial melts from the mantle is suggested, such as in the Aleutian, Sunda, and lesser Antilles island arcs. However, in spite of the importance of the sediment pile in the eastern Mediterranen oceanic crust (6-10 km), the contribution of the subducted terrigenous materials remains of limited amplitude. ?? 1986.

  10. French days on stable isotopes

    International Nuclear Information System (INIS)

    2000-01-01

    These first French days on stable isotopes took place in parallel with the 1. French days of environmental chemistry. Both conferences had common plenary sessions. The conference covers all aspects of the use of stable isotopes in the following domains: medicine, biology, environment, tracer techniques, agronomy, food industry, geology, petroleum geochemistry, cosmo-geochemistry, archaeology, bio-geochemistry, hydrology, climatology, nuclear and particle physics, astrophysics, isotope separations etc.. Abstracts available on CD-Rom only. (J.S.)

  11. Strontium isotopic and trace element geochemistry of the saddle mountains and Grande Ronde Basalts of the Columbia River Basalt Group

    International Nuclear Information System (INIS)

    Nelson, D.O.

    1980-01-01

    The Columbia River Basalt (CRB) group displays significant variations in major and trace element and Sr isotopic compositions. These compositions reflect complex and variable origins for the CRB magmas. Among the most varied is the Saddle Mountains Basalt (SMB) in which Sr ratios vary from 0.7078 to 0.7147 +- 0.002. The higher ratios reflect contamination through consistent correlations with major element compositions. Modeling suggests contamination by assimilation of 4.4 to 9.4 wt % of radiogenic crustal rocks. High delta 18 O values (up to +7.68 per mil) support the model. Age and field relations suggest that the contamination flowrocks are not the result of progressive contamination of a single magma, but rather reflect the contamination of independent magmas during this ascent

  12. Geochronology, geochemistry and Hf–Sr–Nd isotopes of the ore-bearing syenite from the Shapinggou porphyry Mo deposit, East Qinling-Dabie orogenic belt

    Directory of Open Access Journals (Sweden)

    Tao He

    2016-12-01

    Full Text Available The Shapinggou Mo deposit is located in the western Dabie mountains, the eastern part of the Qinling-Dabie molybdenum orogenic belt. Shapinggou Mo deposit is a concealed deposit with the ore body mainly hosted by explosive breccia of Gaijing and the granite porphyry as well as the syenite of Shapinggou. Geochemistry study show that the SiO2 contents of Shapinggou syenite range from 61.74 to 69.93%, and the A/CNK from 0.95 to 1.06, classified as metaluminous to weak peraluminous, belonging to alkalic to shoshonitic series. The Mo deposits in Qinling Mo belt formed in two main periods, i.e., the first period occurred in to the Early Cretaceous (145–130 Ma, the second period in the late Early Cretaceous (130–110 Ma. Most of the Mo deposits in Dabie region formed in the second period. The results of zircon U–Pb show that the age of the Shapinggou syenite is 111.3 ± 1.2 Ma, which belongs to the second period. Proterozoic-Archean inherited zircons suggest that it may include some more ancient crustal material like Kongling group. The ɛHf(t values of Shapinggou syenite range from −15.6 to −8.0, TDM2(Hf from 1.7 to 2.16 Ga, respectively. The ɛNd(t values of the Shapinggou syenite range from −12.29 to −11.76, TDM2(Nd from 1.85 to 1.89 Ga, the 87Sr/86Sr from 0.709 to 0.710, respectively. Results of zircon Hf isotope and whole rock Sr–Nd isotope of Shapinggou syenite indicate that the Mo ore-forming materials were mainly generated from old Yangtze craton, e.g., gneiss from Dabie orogeny, mixed with some juvenal mantle materials. The geodynamics of the Shapinggou Mo deposit corresponded to an extension period in Eastern China, which caused by large scale lithospheric thinning. The delamination caused asthenosphere upwelling and crust-mantle interaction, which provided the ore-forming material and heat.

  13. Geochemistry of Late Mesozoic mafic dykes in western Fujian Province of China:Sr-Nd isotope and trace element constraints

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The Bancun diabase dyke and the Bali hornblende gabbro dyke in western Fuiian Province were emplaced in the Early and Late Cretaceous periods,respectively;the former is designated to calc-alkaline series and the latter to K-high-calc-alkaline rock series.Both the dykes are characterized by such geochemical characteristics as high Al and Na2O>K2O.As for the Bancun dyke,A12O3=16.32%-17.54%and K2O/Na2O=0.65-0.77;as for the Bali dyke,A12O3=16.89%-17.81%and K2O,Na2O=O.93-O.99.Both the Bancun and Bali mafic dykes are relatively endched in LILE and LREE,but depleted in HSFE, displaying the geochemical characteristics of continental marginal arc,with high initial Sr isotopic ratios and low εNd values,The (87Sr/86Sr)i ratios of the Bancun diabase dyke are within the range of 0.708556-0.70903 and their εNd(t)values vary between-6.8 and-6.3;those of the Bali hornblende dyke are within the range of 0.708556-0.710746 and their εNd(t) values are -4.7--4.7,showing the characteristics of enriched mantle EM Ⅱ.The isotope and trace element data showed that the mafic dykes have not experienced obvious crustal contamination,and metasomatism caused by subduction fluids is the main factor leading to LILE and UREE enrichments.The enriched mantle is the source region for the mafic dykes,and mixing of subduction fluid metasomatized enriched mantle and EM Ⅱ-type mantle constituted the mantle source region of both the Bancun and Bali mafic dykes.Upwelling of the asthenosphere mantle provided sufficient heat energy for the generation of magmas.In accordance with the discrimination diagram of their tectonic settings as well as their trace element geochemical characteristics,it is considered that the dykes both at Bancun and Bali possess the characteristics of continental marginal arc,revealing the tectonic environment of formation of the mafic dykes,the continental dynamic background as an intraplate tensional belt in which the mafic dykes were emplaced.Meanwhile,it is also indicated

  14. Compound-specific isotope analysis of light elements using gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) and its application to geochemistry

    International Nuclear Information System (INIS)

    Naraoka, Hiroshi; Yamada, Keita; Matsumoto, Kohei; Ishiwatari, Ryoshi

    1997-01-01

    Compound-specific isotope analysis has been developed recently using gas chromatography/combustion/mass spectrometry (GC/C/IRMS). This paper summarizes principles and progress of GC/C/IRMS, and reviews recent some important works using this new method. GC/C/IRMS is a novel tool for (1) biomarker analysis in sediments and living matter, (2) paleoenvironment analysis including reconstruction of ancient biogeochemical processes, (3) geochemical cycle study of organic compounds in a terrestrial-marine system, (4) evaluation of maturity and diagenesis of organic matter including petroleum formation, (5) ecological analysis, (6) evaluation of anthropologenic pollution in environment, (7) detection of extraterrestrial organic compounds and the formation mechanism study, (8) tracer studies in environment. (author)

  15. Sr, Nd isotope geochemistry of volcanic rock series and its geological significance in the middle Okinawa Trough

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    There exists extensive basic-acidic volcanic rock series in the middle section of the Okinawa Trough. Different types of these volcanic rocks have their own average strontium ratios of 0.704 749, 0.705 062, 0.708 771, 0.704 840 and 0.720 301 with average 143Nd/144Nd ratios of 0.512 820, 0.512 673, 0.512 413, 0.512 729 and 0.512 034. These ratios of Sr and Nd isotopes all fall on a theoretic hyperbolic curve of mixing between two end-members of MORB and rhyolitic magma. So we infer that these different kinds of volcanic rocks in the middle Okinawa Trough are the erupted product in different stages of formation and evolution of the trough crust. MORB magma, which had suffered assimilation, mixed with the early-formed crust-derived rhyolitic partial melt mass at different ratios; then, these mixed magma erupted and formed volcanic rock types of the trough. This study indicates that the Okinawa Trough is coming into a stage of submarine spreading from the stage of continental rift.

  16. Sr, Nd isotope geochemistry of volcanic rock series and its geological significance in the middle Okinawa Trough

    Institute of Scientific and Technical Information of China (English)

    孟宪伟; 陈志华; 杜德文; 吴金龙

    2000-01-01

    There exists extensive basic-acidic volcanic rock series in the middle section of the Okinawa Trough. Different types of these volcanic rocks have their own average strontium ratios of 0.704749, 0.705062, 0.708771, 0.704840 and 0.720301 with average 143Nd/144Nd ratios of 0.512 820, 0.512 673, 0.512 413, 0.512 729 and 0.512 034. These ratios of Sr and Nd isotopes all fall on a theoretic hyperbolic curve of mixing between two end-members of MORE and rhyolitic magma. So we infer that these different kinds of volcanic rocks in the middle Okinawa Trough are the erupted product in different stages of formation and evolution of the trough crust. MORE magma, which had suffered assimilation, mixed with the early-formed crust-derived rhyolitic partial melt mass at different ratios; then, these mixed magma erupted and formed volcanic rock types of the trough. This study indicates that the Okinawa Trough is coming into a stage of submarine spreading from the stage of continental rift.

  17. Composition, oxygen isotope geochemistry, and origin of smectite in the metalliferous sediments of the Bauer Deep, southeast Pacific

    Energy Technology Data Exchange (ETDEWEB)

    Cole, T G [Imperial Coll. of Science and Technology, London (UK). Geology Dept.

    1985-01-01

    The sediments of the Bauer Deep, an open ocean basin situated on the northwest Nazca Plate in the southeast Pacific, constitute a regional metalliferous deposit dominated by authigenic smectite. Two 2-metre long cores from the Bauer Deep were examined to investigate the nature and origin of the smectite. Infra-red and Mossbauer spectroscopy, and wet chemical analysis (LiBO/sub 2/ fusion) of isolated smectite, indicate the mineral is a Mg-rich, Al-rich nontronite. Oxygen isotopic compositions for isolated smectite are uniform and translate to a non-hydrothermal temperature of formation of about 3 deg C. SEM observations show an abundance of well-preserved biogenic opal in surface and near surface sediment but postburial dissolution and transformation of this phase to smectite is evident at depth. Smectite formation is the result of interaction between iron oxyhydroxide, ponded in the Bauer Deep following a hydrothermal origin at the adjacent East Pacific Rise, and biogenic opal. A reaction mechanism is proposed. Regional factors control smectite formation. In particular, formation is inhibited in areas of CaCO/sub 3/ accumulation (topographic elevations) but favoured in areas of oxyhydroxide and opal ponding (topographic depressions.)

  18. Composition, oxygen isotope geochemistry, and origin of smectite in the metalliferous sediments of the Bauer Deep, southeast Pacific

    International Nuclear Information System (INIS)

    Cole, T.G.

    1985-01-01

    The sediments of the Bauer Deep, an open ocean basin situated on the northwest Nazca Plate in the southeast Pacific, constitute a regional metalliferous deposit dominated by authigenic smectite. Two 2-metre long cores from the Bauer Deep were examined to investigate the nature and origin of the smectite. Infra-red and Mossbauer spectroscopy, and wet chemical analysis (LiBO 2 fusion) of isolated smectite, indicate the mineral is a Mg-rich, Al-rich nontronite. Oxygen isotopic compositions for isolated smectite are uniform and translate to a non-hydrothermal temperature of formation of about 3 deg C. SEM observations show an abundance of well-preserved biogenic opal in surface and near surface sediment but postburial dissolution and transformation of this phase to smectite is evident at depth. Smectite formation is the result of interaction between iron oxyhydroxide, ponded in the Bauer Deep following a hydrothermal origin at the adjacent East Pacific Rise, and biogenic opal. A reaction mechanism is proposed. Regional factors control smectite formation. In particular, formation is inhibited in areas of CaCO 3 accumulation (topographic elevations) but favoured in areas of oxyhydroxide and opal ponding (topographic depressions.) (author)

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

    Science.gov (United States)

    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. Oxygen isotope geochemistry of the lassen volcanic center, California: Resolving crustal and mantle contributions to continental Arc magmatism

    Science.gov (United States)

    Feeley, T.C.; Clynne, M.A.; Winer, G.S.; Grice, W.C.

    2008-01-01

    This study reports oxygen isotope ratios determined by laser fluorination of mineral separates (mainly plagioclase) from basaltic andesitic to rhyolitic composition volcanic rocks erupted from the Lassen Volcanic Center (LVC), northern California. Plagioclase separates from nearly all rocks have ??18O values (6.1-8.4%) higher than expected for production of the magmas by partial melting of little evolved basaltic lavas erupted in the arc front and back-arc regions of the southernmost Cascades during the late Cenozoic. Most LVC magmas must therefore contain high 18O crustal material. In this regard, the ??18O values of the volcanic rocks show strong spatial patterns, particularly for young rhyodacitic rocks that best represent unmodified partial melts of the continental crust. Rhyodacitic magmas erupted from vents located within 3.5 km of the inferred center of the LVC have consistently lower ??18 O values (average 6.3% ?? 0.1%) at given SiO2 contents relative to rocks erupted from distal vents (>7.0 km; average 7.1% ?? 0.1%). Further, magmas erupted from vents situated at transitional distances have intermediate values and span a larger range (average 6.8% ?? 0.2%). Basaltic andesitic to andesitic composition rocks show similar spatial variations, although as a group the ??18O values of these rocks are more variable and extend to higher values than the rhyodacitic rocks. These features are interpreted to reflect assimilation of heterogeneous lower continental crust by mafic magmas, followed by mixing or mingling with silicic magmas formed by partial melting of initially high 18O continental crust (??? 9.0%) increasingly hybridized by lower ??18O (???6.0%) mantle-derived basaltic magmas toward the center of the system. Mixing calculations using estimated endmember source ??18O values imply that LVC magmas contain on a molar oxygen basis approximately 42 to 4% isotopically heavy continental crust, with proportions declining in a broadly regular fashion toward the

  1. Mineralization, geochemistry, fluid inclusion and sulfur stable isotope studies in the carbonate hosted Baqoroq Cu-Zn-As deposit (NE Anarak

    Directory of Open Access Journals (Sweden)

    Mohammad Ali Jazi

    2015-10-01

    bacterial sulfate reduction or by nonbacterial sulfate reduction through a reaction with organic materialin the sedimentary rocks (thermochemical sulfate reduction. However, the narrow range of δ34S and positive values indicates that they were not produced by bacterial sulfate reduction.Partial thermochemical reduction of sulfates has apparently produced light sulfurvalues (~ 21‰ lighter and it has been effective inthe deposition of ore minerals. Organic matter occurs as graphite in the Baqoroq formation in proximity of Baqoroq deposit (Cherepovsky et al., 1982. Discussion Epigenetic, stratabound and discordant Cu-Zn-As mineralization in the Baqoroq deposit occurs as open space filling of upper Cretaceous rocks. Host rock is partially dolomitized by ascending warm, saline fluids. Seawater sulfates were the source of the sulfidesulfur and the sulfate in the barite. The reduced sulfur was generated by partial thermochemical reduction and it was effective inthe deposition ofthe ore minerals. Based onthe evidence of carbonate host rocks, the absence of igneous activity, the open space filling texture, mineralogy, dolomite alteration, ore geochemistry (As and Sb high content and absence of Bi, microthermometric data of ore bearing fluid and sulfur isotope values, the Baqoroq deposit is very similar to the carbonate hosted copper deposits in Africa and in particular the Tsumeb deposit in Namibia. The Baqoroqdepositmay have been produced bymetamorphicfluids during orogenyrelated to theclosureof the Neo-Tethys ocean. References Cherepovsky, N., Plyaskin, V., Zhitinev, N., Kokorin, Y., Susov, M., Melnikov, B. and Aistov, L., 1982. Report on detailed geological prospecting in Anarak area (Central Iran Nakhlak locality. Geological Survey of Iran and Technoexport Company, Tehran. Report 14, 196 pp. Jazi, M.A., Karimpour, M.H., Malekzadeh, A. and Rahimi, B., 2015. Stratigraphic, lithological and structural controls in placement of Nakhlak deposit (northeast of Esfahan. Advanced

  2. Sr and Nd isotope geochemistry and tectonics during subduction and rifting in Sierra Santa Ursula, Sonora, Northwestern Mexico

    International Nuclear Information System (INIS)

    Mora-Klepeis, G.

    2000-01-01

    The western margin of North America was affected by a convergent plate boundary from the Cretaceous through the Early Tertiary. Volcanic rocks produced by subduction-related arc magmatism in northwestern Mexico are concentrated in two northwest-trending belts subparallel to the continental margin. One of these is the Sierra Madre Occidental, where mid-Tertiary magmatism consisted mostly of calc-alkaline rhyolitic ignimbrite and minor andesite produced between ∼ 46 and 28 Ma (McDowell et al., 1990). The second (younger) northwest-trending belt is located along the eastern margin of the Baja California Peninsula and in the Gulf of California region of mainland Mexico. This belt is composed mostly of andesite, but includes some basalt and dacite whose ages range from about 24 to 11 Ma (Hausback, 1984). A transition to rifting began after a mid-Tertiary cessation of subduction, eventually creating the Gulf of California extensional province. Four markedly different magma types comprising mainly tholeiitic and alkalic rocks and minor calc-alkaline and peralkaline rocks were erupted throughout the last 13 Ma and record the history of rifting of the Gulf of California (Sawlan, 1991). The aim of the present paper is to distinguish the nature of the 24-8.5 Ma magmatism emplaced on the eastern side of the Gulf of California in the state of Sonora, by the use of stratigraphic, geochemical and isotopic data. Preliminary Sr and Nd results show that three groups of magmas are present in the area suggesting a heterogeneous source. This can be interpreted as the result of magmas being erupted at different stages of subduction and rifting during the tectonic evolution of this part on North America

  3. Alteration mineralogy, mineral chemistry and stable isotope geochemistry of the Eocene pillow lavas from the Trabzon area, NE Turkey

    Science.gov (United States)

    Abdioğlu Yazar, Emel

    2018-02-01

    The Eocene subaqueous volcanic units in NE Turkey developed as pillow, closely packed pillow, isolated pillow, pillow breccia, hyaloclastite breccia and rare peperitic facies with red micritic limestones. They are locally set on volcaniclastic sandstone and claystone alternations and gradually pass to tuffs and volcanic breccias. The pillow lava samples generally exhibit intersertal, intergranular, microlitic porphyritic, variolitic, vesicular and glomeroporphyritic and glassy textures with clinopyroxene (Wo47-52En40-45Fs6-8), plagioclase (An10 to An96), olivine (Fo79-87) and Fe-Ti oxides (Usp0-0.27). Saponite, interlayered chlorite/saponite, rare beidellite and calcite were determined after olivine, rarely after plagioclase as well as in the glassy groundmass. Illite was restricted to plagioclase and the glassy groundmass. Na-Ca zeolites, chlorites/saponites, beidellite, dolomite and calcite occur as void infillings and in the glassy groundmass. Mineralogical, lithochemical and isotopic interpretations as well as thermometric calculations reveal a low-temperature seawater alteration in a semi-closed environment for the alteration of primary minerals and volcanic glass in addition to sealed vesicles and open systems for crosscutting veins. Due to the short exposure time intervals of seawater to rocks, the total chemistry of the rocks is not fully changed and most of the elements seem to be immobile, remaining in the system as a result of precipitation in voids and cracks. Thermometric estimations indicate that, the temperature of heated seawater is approximately 160 °C at the highest point especially in the vesicles, and decreases to approximately 85 °C due to circulation, resulting in alterations of the primary phases and volcanic glass.

  4. Study of the geochemistry of the cosmogenic isotope 10Be and the stable isotope 9Be in oceanic environment. Application to marine sediment dating

    International Nuclear Information System (INIS)

    Bourles, D.

    1988-01-01

    The radioisotope 10 Be is formed by spallation reactions in the atmosphere. It is transferred to the oceans in soluble form by precipitation and dry deposition. The stable isotope 9 Be comes from erosion of soils and rocks in the Earth's crust. It is transported by wind and rivers and introduced to the oceans probably in both soluble and insoluble form. 9 Be was measured by atomic absorption spectrometry and 10 Be by A.M.S. The distribution of 10 Be and 9 Be between each phase extracted and the 10 Be/ 9 Be ratios associated were studied in recent marine sediments from Atlantic, Pacific, Indian oceans and Mediterranean sea. The results show that for beryllium the two essential constituent phases of marine sediments are: - the authigenic phase incorporates the soluble beryllium and the detritic phase. The 10 Be/ 9 Be ratio associated with the authigenic fraction varies with location. This suggests that the residence time of beryllium in the soluble phase is lower or comparable to the mixing time of the oceans. The evolution with time of the authigenic 10 Be/ 9 Be ratio is discussed [fr

  5. Geochemistry of redox-sensitive elements and sulfur isotopes in the high arsenic groundwater system of Datong Basin, China

    International Nuclear Information System (INIS)

    Xie Xianjun; Ellis, Andre; Wang Yanxin; Xie Zuoming; Duan Mengyu; Su Chunli

    2009-01-01

    High arsenic groundwater in the Quaternary aquifers of Datong Basin, northern China contain As up to 1820 μg/L and the high concentration plume is located in the slow flowing central parts of the basin. In this study we used hydrochemical data and sulfur isotope ratios of sulfate to better understand the conditions that are likely to control arsenic mobilization. Groundwater and spring samples were collected along two flow paths from the west and east margins of the basin and a third set along the basin flow path. Arsenic concentrations range from 68 to 670 μg/L in the basin and from 3.1 to 44 μg/L in the western and eastern margins. The margins have relatively oxidized waters with low contents of arsenic, relatively high proportions of As(V) among As species, and high contents of sulfate and uranium. By contrast, the central parts of the basin are reducing with high contents of arsenic in groundwater, commonly with high proportions of As(III) among As species, and low contents of sulfate and uranium. No statistical correlations were observed between arsenic and Eh, sulfate, Fe, Mn, Mo and U. While the mobility of sulfate, uranium and molybdenum is possibly controlled by the change in redox conditions as the groundwater flows towards central parts of the basin, the reducing conditions alone cannot account for the occurrence of high arsenic groundwater in the basin but it does explain the characteristics of arsenic speciation. With one exception, all the groundwaters with As(III) as the major As species have low Eh and those with As(V) have high Eh. Reductive dissolution of Fe-oxyhydroxides or reduction of As(V) are consistent with the observations, however no increase in dissolved Fe concentration was noted. Furthermore, water from the well with the highest arsenic was relatively oxidizing and contained mostly As(V). From previous work Fe-oxyhydroxides are speculated to exist as coatings rather than primary minerals. The wide range of δ 34 S [SO4] values (from

  6. Geochemistry of redox-sensitive elements and sulfur isotopes in the high arsenic groundwater system of Datong Basin, China

    Energy Technology Data Exchange (ETDEWEB)

    Xie Xianjun [MOE Key Laboratory of Biogeology and Environmental Geology and School of Environmental Studies, China University of Geosciences, Wuhan 430074 (China); Ellis, Andre [Department of Geological Sciences, University of Texas at El Paso, TX 79968-0555 (United States); Wang Yanxin, E-mail: yx.wang@cug.edu.cn [MOE Key Laboratory of Biogeology and Environmental Geology and School of Environmental Studies, China University of Geosciences, Wuhan 430074 (China); Xie Zuoming; Duan Mengyu; Su Chunli [MOE Key Laboratory of Biogeology and Environmental Geology and School of Environmental Studies, China University of Geosciences, Wuhan 430074 (China)

    2009-06-01

    High arsenic groundwater in the Quaternary aquifers of Datong Basin, northern China contain As up to 1820 {mu}g/L and the high concentration plume is located in the slow flowing central parts of the basin. In this study we used hydrochemical data and sulfur isotope ratios of sulfate to better understand the conditions that are likely to control arsenic mobilization. Groundwater and spring samples were collected along two flow paths from the west and east margins of the basin and a third set along the basin flow path. Arsenic concentrations range from 68 to 670 {mu}g/L in the basin and from 3.1 to 44 {mu}g/L in the western and eastern margins. The margins have relatively oxidized waters with low contents of arsenic, relatively high proportions of As(V) among As species, and high contents of sulfate and uranium. By contrast, the central parts of the basin are reducing with high contents of arsenic in groundwater, commonly with high proportions of As(III) among As species, and low contents of sulfate and uranium. No statistical correlations were observed between arsenic and Eh, sulfate, Fe, Mn, Mo and U. While the mobility of sulfate, uranium and molybdenum is possibly controlled by the change in redox conditions as the groundwater flows towards central parts of the basin, the reducing conditions alone cannot account for the occurrence of high arsenic groundwater in the basin but it does explain the characteristics of arsenic speciation. With one exception, all the groundwaters with As(III) as the major As species have low Eh and those with As(V) have high Eh. Reductive dissolution of Fe-oxyhydroxides or reduction of As(V) are consistent with the observations, however no increase in dissolved Fe concentration was noted. Furthermore, water from the well with the highest arsenic was relatively oxidizing and contained mostly As(V). From previous work Fe-oxyhydroxides are speculated to exist as coatings rather than primary minerals. The wide range of {delta}{sup 34}S

  7. Petrology and oxygen isotope geochemistry of the Pucon ignimbrite - Southern Andean volcanic zone, Chile: Implications for genesis of mafic ignimbrites

    International Nuclear Information System (INIS)

    McCurry, Michael; Schmidt, Keegan

    2001-01-01

    eruptions were originally dissolved within in the pre-PI magma. They document an important repeating pattern between chemically evolved compositions and explosive eruptions at Volcan Villarrica that is particularly prominent in the cases of the two largest ignimbrite-forming eruptions. They infer that the precursor magma chamber became compositionally stratified through time, with the most evolved, volatile rich magma accumulating towards the top of the chambers, and culminating in voluminous mafic ignimbrite eruptions. In this study we characterize petrologic, geochemical and oxygen isotope characteristics of magmatic pyroclasts from the Pucon Ignimbrite, and one accidental granitoid lithic, extending on the previous work by Clavero (1996) and Lopez-Escobar and Moreno (1995). We critically evaluate previous models, and combine ours and previous data to constrain and develop an alternate petrogenetic model of magmatic evolution of the pre-PI magma chamber, focusing on possible sources of volatiles derived from country rocks and from processes operating within the original magma chamber. We also document the occurrence of a previously unidentified, dacitic, magmatic enclave component of the ignimbrite (au)

  8. Os, Nd and Sr isotope and trace element geochemistry of the Muli picrites: Insights into the mantle source of the Emeishan Large Igneous Province

    Science.gov (United States)

    Li, Jie; Xu, Ji-Feng; Suzuki, Katsuhiko; He, Bin; Xu, Yi-Gang; Ren, Zhong-Yuan

    2010-09-01

    A suite of picrites and basalts from the Muli area, in the northwestern part of the Emeishan continental flood basalt province, provides new and valuable information on the geochemistry of the Emeishan Large Igneous Province (LIP) and its source. The Muli picrites can be classified as type-1 or type-2. The former shows ocean-island basalt-like trace element characteristics, with γ Os (260 Ma) values and ɛ Nd (260 Ma) values ranging from + 7.5 to + 11.5 and from + 6.0 to + 7.8, respectively. This is the first time that picrites with highly radiogenic Os and high Os contents (up to 3.3 ppb) have been recognized in the Emeishan LIP. These characteristics probably reflect a relatively enriched component in the Emeishan LIP source. The type-2 picrites are characterized by non-radiogenic γ Os (260 Ma) values ranging from - 4.2 to - 0.3, and they may be further subdivided into type-2A and type-2B picrites. Type-2A picrites contain moderate amounts of the light rare earth elements (LREEs), have low Ce N/Yb N values (1.1-2.0), and a relatively high initial ɛ Nd (+ 5.0 to + 6.6). In terms of Os and Nd isotopes, the Muli type-2A picrites are similar to the Song Da komatiites of Vietnam and the Gorgona Island picrites, revealing the existence of a depleted mantle component in the Emeishan LIP source. In contrast with the type-2A picrites, type-2B lavas exhibit a negative Nb anomaly and relatively lower initial ɛ Nd and γ Os values (Nb/La > 1.8; ɛ Nd (260 Ma) = - 5.5 to + 6.4; γ Os (260 Ma) = - 4.2 to - 1.9), suggesting that the type-2B lavas have a depleted mantle source, similar to type-2A, but that the type-2B lavas are also influenced by various degrees of mixing of depleted plume-derived melt, sub-continental lithospheric mantle, and/or continental crust. Given that the basalts in the Muli area show similar geochemical features to those of the type-2B picrites, their origins are inferred to be similar.

  9. The chemical conditions of the late Archean Hamersley basin inferred from whole rock and pyrite geochemistry with Δ33S and δ34S isotope analyses

    Science.gov (United States)

    Gregory, Daniel D.; Large, Ross R.; Halpin, Jacqueline A.; Steadman, Jeffery A.; Hickman, Arthur H.; Ireland, Trevor R.; Holden, Peter

    2015-01-01

    The well-preserved late Archean sedimentary rocks of the Fortescue and Hamersley Basins in Western Australia offer fascinating insights into early earth ocean chemistry prior to the Great Oxidation Event (GOE). In this study, we use a combination of whole rock geochemistry, LA-ICPMS trace element analysis of sedimentary pyrite and pyrrhotite and SHRIMP-SI sulfur isotope analyses to elucidate the chemical changes in these sedimentary rocks. These proxies are used to examine chemical conditions of the ocean during the late Archean. Two to three periods of oxygen enrichment prior to the deposition of banded iron formations (BIF) can be identified. One minor stage of general increase in whole rock enrichment factors and trace element content of pyrite is observed up stratigraphy in the Jeerinah Formation, Fortescue Basin and a more substantial stage is present in the Paraburdoo and Bee Gorge Members of the Wittenoom Formation, Hamersley Basin. Some of the trace element enrichments indicate organic matter burial flux (Ni, Cr, Zn, Co and Cu) which suggests an increase in biological productivity. If the increased biological activity reflects an increase in cyanobacteria activity then an associated increase in oxygen is likely to have occurred during the deposition of the Bee Gorge Member. An increase in atmospheric oxygen would result in continental weathering of sulfide and other minerals, increasing the trace element content of the water column via erosion and avoiding excessive depletion of trace elements due to drawdown in seawater. Since some of these trace elements may also be limiting nutrients (such as Mo and Se) for the cyanobacteria, the degree of biological productivity may have further increased due to the increasing amount of trace elements introduced by oxygenation in a positive feedback loop. These periods of increased productivity and oxygen rise stopped prior to the onset of BIF deposition in the Hamersley Basin. This may be due to the ocean reaching an

  10. Uranium project. Geochemistry prospection

    International Nuclear Information System (INIS)

    Lambert, J.

    1983-01-01

    Geochemistry studies the distribution of the chemicals elements in the terrestrial crust and its ways to migrate. The terminology used in this report is the following one: 1) Principles of the prospection geochemistry 2) Stages of the prospection geochemistry 3)utility of the prospection geochemistry 4) geochemistry of uranium 5) procedures used within the framework of uranium project 6) Average available 7) Selection of the zones of prospection geochemistry 8) Stages of the prospection, Sample preparation and analisis 9) Presentation of the results

  11. Using Nd-Sr isotopes and rare earth elements to study sediment provenance of the modern radial sand ridges in the southwestern Yellow Sea

    International Nuclear Information System (INIS)

    Rao, Wenbo; Mao, Changping; Wang, Yigang; Huang, Huiming; Ji, Junfeng

    2017-01-01

    The radial sand ridges (RSRs) in the southwestern Yellow Sea off the Jiangsu Coast, East China have been intensively studied at least since 1975. Despite decades of studies, the provenance of the RSR sediments remains uncertain. In this study, the Nd-Sr isotopic and REE geochemical compositions of residual sediments (i.e., the acid-insoluble fractions) were investigated to determine the provenance of the RSR sediments. The Nd isotopic composition, PAAS-normalized REE patterns and characteristic parameters (e.g., Sm/Nd, (La/Sm)_N, (Gd/Yb)_N) were merely associated with source rocks but not with particle sorting while the Sr isotopic composition and REE contents of residual sediments were affected by particle sorting in addition to source rocks. The onshore RSR sediments originated mainly from mixing of the fine-grained sediments from various parts of the offshore RSR in terms of REE geochemical and isotopic analyses. Isotopic and REE geochemical comparison further reveals that the RSRs off the Jiangsu Coast were fed chiefly by the dispersal of surface sediments from the Yangtze River Mouth. Surface sediments from the Yangtze River Mouth were directly dispersed to the RSRs along the Jiangsu Coast and significantly affected the seaward part of the offshore RSR and the old Yellow River Delta area by a northward branch of the Changjiang Diluted Freshwater Plume. Only minor quantities of surface sediments from the modern Yellow River Mouth were introduced into the RSRs by the Jiangsu Coastal Current and mainly contaminated the landward part of the offshore RSR area. Our findings highlighted the potential of the Nd isotopes with REE geochemistry to trace the provenance of coastal sediments. - Highlights: • Nd isotopic and REE geochemical compositions of coastal and estuary sediments are mainly associated with source rocks. • Onshore RSR sediments originate from mixing of fine-grained sediments from various parts of the offshore RSR. • The RSRs off the Jiangsu Coast

  12. Geochemistry and Nd-isotope systematics of chemical and terrigenous sediments from the Dun Mountain Ophiolite, New Zealand

    International Nuclear Information System (INIS)

    Sivell, W.J.

    2002-01-01

    . Metalliferous contributions to red and green TA in the overlying terrigenous sedimentary sequence also link these facies to early DMOB back-arc eruptives. The red and green TA pass upwards into ungraded Atomodesmid-bearing grey TA, implying turbidite deposition in a shallowing marine environment. The (mainly andesitic) TA show systematic trends of decreasing Eu/Eu* and ε Nd (T) with increasing Ε-REE, La/Y, Th/Sc, and SiO 2 . Th abundances and Th/Sc ratios (up to 1.6) in the TA are akin to those of calc-alkaline magmas in continental arcs, and are significantly greater than island-arc or ophiolitic volcanics. A narrow range of positive ε Nd (T) values (+0.5 to +2.0) for the TA suggests a young differentiated continental arc source, less dissected than the quartzofeldspathic plutonic provenance for the Torlesse (ε Nd (T) N /Yb N = 2.5-2.8) in the sandstones resemble island-arc tholeiites (IAT). The breccias have low Eu/Eu* (c. 0.72), Ce N /Yb N = 1.6, Th/Sc (0.1-0.2), and Tb N /Yb N c. 1.0, features transitional between the sandstones and DMOB plagiogranites. Importantly, the sandstones and breccias show high positive initial Nd ratios (ε Nd (T) = +5 to +8) akin to values for Brook Street IAT (ε Nd (T) = +9). This implies juvenile (mantle-derived) source rocks for both the mafic and felsic younger terrigenous sediments, compatible with crustal residence (mean provenance) ages less than for the TA. Little continental input is permitted by Nd-isotopic data for these rocks. Whereas the early DMOB pillow basalt - chemical sediment - TA assemblage was emplaced in a back-arc setting, with influx of detritus in part from an active continental margin (possibly within the New England Orogen), the younger DMOB terrigenous sediment association shows a close kinship with bimodal DMOB magmatism related to infant arc volcanic centres in an extensional forearc regime. Turbidite sands and mass-flow deposits were shed into proximal fault-bound basins isolated from continental clastic

  13. The hydro- and multi-isotope geochemistry of iron-rich ground waters emerging at the southern Baltic Sea coast line

    Science.gov (United States)

    Lipka, Marko; Wu, Zijun; Escher, Peter; Struck, Ulrich; Dellwig, Olaf; Schafmeister, Maria; Böttcher*, Michael E.

    2013-04-01

    Iron-rich groundwater springs emerging at the shore zone of the southern Baltic Sea (BS; Site Meschendorf) were examined on a seasonal base for a period of about two years. Besides major, minor, and trace elements, stable isotopes of water (H-2, O-18), dissolved inorganic carbon (DIC; C-13), and sulfate (S-34) were analyzed. The stream bed sediment was extracted for the geochemistry of the newly formed precipitates and further characterized via SEM-EDAX. Subsequently, the hydrogeochemical results were subjected to a thermodynamic analysis via the PHREEQC speciation model. The springs emerge from small pits (about 60 cm diameter; up to 15cm depth). Surrounding sediments are sandy with gravels found at depth and corresponding high permeabilities. The positions of different springs on the shore zone were stable during the investigation period while the shape of the pits and the stream beds may vary due to wind- and wave-driven forces. Selected measurements of spring yield discharges close to 10 L/min. The H-2 and O-18 contents of the spring waters indicate the ground water to originate from relatively young mixed meteoric waters. The hydrochemistry of the springs was similar and showed some variability in between which indicates that the genetic processes for the ground water before reaching the surface may slightly differ. The springs are characterized by dissolved Ca, Mg, Na, DIC and sulfate, mainly reflecting the interaction with soils and bedrocks in the recharge area that is dominated by marly till. The oxygen-free ground water is rich in Fe, P, and DIC. Iron and dissolved sulfate originate from the oxidation of pyrite, as further confirmed by the 34-S signature of sulfate. The carbon isotope signature of DIC indicates a mixture of biogenic CO2 from the soil zone with some water-rock interaction with carbonate minerals. The streams flow towards the BS and, in contact with the atmosphere, outgas carbon dioxide and takes up oxygen. Upon CO2-degassing, C-12 is

  14. An overview on geochemistry of Proterozoic massif-type ...

    Indian Academy of Sciences (India)

    A critical study of 311 published WR chemical analyses, isotopic and mineral chemistry of ... Keywords. Massif anorthosite complexes; overview; geochemistry; high-Al gabbro. J. Earth ...... (123–2920 ppm) unlike the experimental results of.

  15. Isotopic and chemical evidence for three accretionary magmatic arcs ( 1.79 - 1.42 Ga) in the SW Amazon Craton, Mato Grosso State, Brazil

    International Nuclear Information System (INIS)

    Geraldes, Mauro Cesar; Teixeira, Wilson; Schmus, William Randall van

    2000-01-01

    Twenty-one U/Pb ages of granitoids in the SW Amazon craton define three crustal accretionary events during the Paleo-and Mesoproterozoic that represent significant portions of the Rio Negro-Juruena Province and the Rondonian/San Ignacio province. Two events refer to the Rio Negro-Juruena province: The Alto Jauru greenstone belt comprises acid volcanics and tonalite to granite gneisses with U/Pb ages from 1790 to 1750 Ma. Sm/Nd isotopic data (e N -d (t) from +2.6 to +2.2 and T DM from 2.0 to 1.80 Ga) indicate a volcanic arc with juvenile signatures for these units. The second event (Cachoeirinha arc) comprises granites to tonalites with U/Pb ages from 1580 to 1530 Ma. Sm/Nd results. (author)

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2009-07-01

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

  17. Anatomy of a cluster IDP. Part 2: Noble gas abundances, trace element geochemistry, isotopic abundances, and trace organic chemistry of several fragments from L2008#5

    Science.gov (United States)

    Thomas, K. L.; Clemett, S. J.; Flynn, G. J.; Keller, L. P.; Mckay, David S.; Messenger, S.; Nier, A. O.; Schlutter, D. J.; Sutton, S. R.; Walker, R. M.

    1994-01-01

    The topics discussed include the following: noble gas content and release temperatures; trace element abundances; heating summary of cluster fragments; isotopic measurements; and trace organic chemistry.

  18. Marine geochemistry ocean circulation, carbon cycle and climate change

    CERN Document Server

    Roy-Barman, Matthieu

    2016-01-01

    Marine geochemistry uses chemical elements and their isotopes to study how the ocean works. It brings quantitative answers to questions such as: What is the deep ocean mixing rate? How much atmospheric CO2 is pumped by the ocean? How fast are pollutants removed from the ocean? How do ecosystems react to the anthropogenic pressure? The book provides a simple introduction to the concepts (environmental chemistry, isotopes), the methods (field approach, remote sensing, modeling) and the applications (ocean circulation, carbon cycle, climate change) of marine geochemistry with a particular emphasis on isotopic tracers. Marine geochemistry is not an isolated discipline: numerous openings on physical oceanography, marine biology, climatology, geology, pollutions and ecology are proposed and provide a global vision of the ocean. It includes new topics based on ongoing research programs such as GEOTRACES, Global Carbon Project, Tara Ocean. It provides a complete outline for a course in marine geochemistry. To favor a...

  19. Age and origin of anorthosites, charnockites, and granulites in the Central Virginia Blue Ridge: Nd and Sr isotopic evidence

    Science.gov (United States)

    Pettingill, H.S.; Sinha, A.K.; Tatsumoto, M.

    1984-01-01

    Rb-Sr isotopic data for anorthosites, charnockites, ferrodioritic to quartz monzonitic plutons, and high-grade gneisses of the Blue Ridge of central Virginia show evidence of post-emplacement metamorphism, but in some cases retain Grenville ages. The Pedlar River Charnockite Suite yields an isochron age of 1021 +/-36 Ma, (initial 87Sr/86Sr ratio of 0.7047 +/-6), which agrees with published U-Pb zircon ages. Five samples of that unit which contain Paleozoic mylonitic fabrics define a regression line of 683 Ma, interpreted as a mixing line with no age significance. Samples of the Roseland Anorthosite Complex show excessive scatter on a Rb-Sr evolution diagram probably due to Paleozoic (475 m.y.) metamorphism. Data from the ferrodioritic to quartz monzonitic plutons of the area yield an age of 1009 +/-26 Ma (inital ratio=0.7058 +/-4), which is in the range of the U-Pb zircon ages of 1000-1100 Ma. The Stage Road Layered Gneiss yields an age of 1147 +/-34 Ma (initial ratio of 0.7047 +/- 5). Sm-Nd data for the Pedlar River Charnockite Suite reflect a pre-Grenville age of 1489 +/-118 Ma (e{open}Nd=+6.7 +/-1.2). Data for the Roseland Anorthosite Complex and the ferrodioritic to quartz monzonitic plutons yield Grenville isochron ages of 1045 +/44 Ma (e{open}Nd=+1.0 +/-0.3) and 1027 +/-101 Ma (e{open}Nd=+1.4 +/-1.0), respectively. Two Roseland Anorthosite samples plot far above the isochron, demonstrating the effects of post-emplacement disturbance of Sm-Nd systematics, while mylonitized Pedlar River Charnockite Suite samples show no evidence of Sm-Nd redistribution. The disparity of the Sm-Nd age and other isotopic ages for the Pedlar River Charnockite Suite probably reflects a Sm-Nd "source" age, suggesting the presence of an older crust within this portion of the ca. 1 Ga old basement. ?? 1984 Springer-Verlag.

  20. Application of organic-geochemistry, coal-petrology and isotope-geochemistry to facies-analysis and hydrocarbon exploration in the NE-Paris Basin (Trias-Lias Luxemburg)

    International Nuclear Information System (INIS)

    Flekken, P.M.

    1978-01-01

    Triassic and Liassic sediments of NE-Paris Basin (Luxemburg) were investigated by organic-geochemical, coal petrographical and isotope-geochemical methods. The objective was to characterize the stratigraphic stages and to investigate the facies relations between them with a view to possible hydrocarbon exploration. The sediments contain an average of 3.1% organic carbon, 413 ug/g extractable organic matter (bitumen) and 0.65% insoluble, isolatable organic particles which constitute part of the kerogen. The non-isolatable kerogen is 2.4% of the whole rock. (orig./BR) [de

  1. Radiogenic age and isotopic studies: report 9. Current research 1995-F

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1997-12-31

    `Radiogenic Age and Isotopic Studies` is an annual collection of research presentations containing U-Pb, Sm-Nd, Rb-Sr, and {sup 40}Ar-{sup 39}Ar data generated by the Geochronology Laboratory under the auspices of the Continental Geoscience Division, Geological Survey of Canada. Report 9 contains 5 papers from regions across Canada, followed by a compilation of {sup 40}Ar-{sup 39}Ar and K-Ar ages. Authors herein present data, relate results to field settings, and make brief interpretations. Readers are thus reminded that much of the research encompassed represents `work-in-progress` and that more extensive publications may follow at a later date.

  2. Radiogenic age and isotopic studies: report 9. Current research 1995-F

    International Nuclear Information System (INIS)

    1996-01-01

    'Radiogenic Age and Isotopic Studies' is an annual collection of research presentations containing U-Pb, Sm-Nd, Rb-Sr, and 40 Ar- 39 Ar data generated by the Geochronology Laboratory under the auspices of the Continental Geoscience Division, Geological Survey of Canada. Report 9 contains 5 papers from regions across Canada, followed by a compilation of 40 Ar- 39 Ar and K-Ar ages. Authors herein present data, relate results to field settings, and make brief interpretations. Readers are thus reminded that much of the research encompassed represents 'work-in-progress' and that more extensive publications may follow at a later date

  3. Changing styles of crustal growth in Southern Africa: constraints from geochemical and Sr-Nd isotope studies in Archaean to Pan African terrains

    International Nuclear Information System (INIS)

    McDermott, F.; Hawkesworth, C.J.; Harris, N.B.W.

    1988-01-01

    Nd isotopic data was presented for southern Africa in support of episodic crustal growth. Over 50 percent of the continental crust there had formed before 2.5 Ga, and less than 10 percent was produced after about 1.0 Ga. The data imply a mean crustal age of about 2.4 Ga for southern Africa, and a higher rate of crustal growth than that derived from Australian shale data, particularly during the Proterozoic. Isotopic data from Damara metasediments imply that there is no need to invoke decoupling of the Rb-Sr and Sm-Nd systems in the continental crust

  4. Changing styles of crustal growth in Southern Africa: Constraints from geochemical and Sr-Nd isotope studies in Archaean to Pan African terrains

    Science.gov (United States)

    Mcdermott, F.; Hawkesworth, C. J.; Harris, N. B. W.

    1988-01-01

    Nd isotopic data was presented for southern Africa in support of episodic crustal growth. Over 50 percent of the continental crust there had formed before 2.5 Ga, and less than 10 percent was produced after about 1.0 Ga. The data imply a mean crustal age of about 2.4 Ga for southern Africa, and a higher rate of crustal growth than that derived from Australian shale data, particularly during the Proterozoic. Isotopic data from Damara metasediments imply that there is no need to invoke decoupling of the Rb-Sr and Sm-Nd systems in the continental crust.

  5. Geochemistry and petrogenesis of Mesoproterozoic A-type granitoids from the Danish island of Bornholm, southern Fennoscandia

    DEFF Research Database (Denmark)

    Johansson, Åke; Waight, Tod Earle; Andersen, Tom

    2016-01-01

    Granitoids and gneisses from the Danish island of Bornholm have been investigated using whole rock geochemistry, Sr and Nd isotope geochemistry and Hf isotopes in zircon. Recent U–Pb dating shows that the rocks were formed during a short time interval at 1.45 to 1.46 Ga, penecontemporaneous...

  6. Strontium geochemistry and carbon and oxygen isotopic compositions of Lower Proterozoic dolomite and calcite marbles from the Marmorilik Formation, West Greenland

    International Nuclear Information System (INIS)

    Garde, A.A.

    1979-01-01

    The Marmorilik Formation, Rinkian mobile belt, West Greenland, is a large, Lower Proterozoic carbonate-rock sequence, deformed and metamorphosed under greenschist to amphibolite facies conditions. The pre-deformation thickness of the sequence is at least 2000 m, with about 1400 m of dolomite marble and 350 m of calcite marble. Strontium contents of forty-two dolomite and calcite marbles range from 30 to 100 ppm and 300 to 800 ppm, respectively, whereas samples with calcite of secondary origin have strontium contents between 80 ppm and 200 ppm. Carbon and oxygen isotope ratios were determined for forty calcite and dolomite marbles as -0.2+-1.0 per 1000 delta 13 C and -9.9+-1.5 per 1000 delta 18 O (vs. PDB) and are compatible with the isotopic compositions of unmetamorphosed carbonates of similar age. Calcite from eight calciumsilicate rocks, breccias and calcite veins is significantly more negative in delta 13 C and delta 18 O. Five 13 C analyses of graphite in marble range from -9.6 to -14 per 1000. Possible post-depositional changes in the strontium content and carbon and oxygen isotope compositions are discussed. It is concluded that (a) the calcite marbles are not dedolomites and are therefore of primary origin, (b) the delta 13 C and delta 18 O values of the marbles are primary or diagenetic (i.e., pre-metamorphic), and (c) the isotopic composition of the graphite is compatible with, though not necessarily evidence for, a biogenic origin. (Auth.)

  7. Mantle heterogeneity in northeastern Africa: evidence from Nd isotopic compositions and hygromagmaphile element geochemistry of basaltic rocks from the Gulf of Tadjoura and southern Red Sea regions

    International Nuclear Information System (INIS)

    Barrat, J.A.; Jahn, B.M.; Auvray, B.; Hamdi, H.; Joron, J.L.

    1990-01-01

    Basaltic rocks from the Gulf of Tadjoura and southern Red Sea regions have been analysed for their Nd isotopic compositions and major and trace element concentrations. The wide variation in isotopic and geochemical compositions of the basaltic rocks is best explained by the mixing phenomenon involving a variety of mantle source components. To test the mixing hypothesis, a combined use of Nd isotopes and hygromagmaphile elemental ratios is proven very powerful. Three reservoirs have been identified as minimum components in their petrogenesis: (1) DMM (depleted MORB mantle), a mantle source depleted in light rare earth elements (LREE), which is the principal component of the N-MORB type basalts of this region; (2) REC (Ramad enriched component), equivalent to the hot-spot type of source detected in the south of Red Sea; (3) TEC (Tadjoura enriched component), a rather unique component located in the region of Tadjoura Gulf; it is characterised by a relative depletion in Rb, K, Th and U in a primitive mantle- or chondrite-normalised incompatible element pattern; this component could have been produced by mantle metasomatism of an originally depleted mantle. Mixing in various proportions of the above components is considered to be the principal mechanism for the formation of basalts with such diverse isotopic and trace element compositions. (orig.)

  8. Geochemistry of rare earths and oxygen isotopes in granitic rocks from Monte das Gameleiras and Dona Ines, Rio Grande do Norte-Paraiba border, Brazil

    International Nuclear Information System (INIS)

    Sial, A.N.

    1984-01-01

    The study of oxygen isotopes and rare earth elements in granitic plutons of Monte das Gameleiras and Dona Ines, Rio Grande do Norte-Paraiba border, in Brazil, to define the nature of source rock of progenitor magmas, is presented. (M.C.K.) [pt

  9. Radiogenic age and isotopic studies

    International Nuclear Information System (INIS)

    Parrish, R.R.

    1990-01-01

    This is one of an annual collection of reports presenting data from the Geochronology Section of the Continental Geoscience Division of the Geological Survey of Canada (GSC). The main purpose of this collection is to make geochronological and other radiogenic isotope data produced by the section available promptly to the geological community. Reports make full presentation of the data, relate these to field settings and make comparatively short interpretations. Other geochronological and isotope data produced in the laboratory but published in outside journals or separate GSC publications are summarized at the end of this report. Reports in this issue cover methods for Rb-Sr and Sm-Nd isotopic analyses; 40 Ar- 39 Ar ages for the New Quebec Crater and for basaltic rocks; U-Pb ages for a differentiated mafic sill in the Ogilvie Mountains, plutonic rocks in the Contwoyto-Nose Lakes are, zircons from the Anton Complex, the Clinton-Colden gabbro-anorthosite intrusion, the Himag plutonic suite, the Campbell granite, the Central Gneiss Belt, Silurian granites, a metarhyolite, plagiogranite and gabbro, and the Wage shear zone; Rb-Sr ages for granitic rocks; K-Ar and Rb-Sr geochronology of granites; a compilation of K-Ar ages; ages of archean and proterozoic mylonites and pre-Misi granitoid domes; and reconnaissance geochronology of Baffin Island

  10. Hydrochemistry and isotope geochemistry as management tools for groundwater resources in multilayer aquifers: A study case from the Po plain (Lomellina, South-Western Lombardy, Italy)

    Energy Technology Data Exchange (ETDEWEB)

    Pilla, G; Sacchi, E; Ciancetti, G; Braga, G [Dipartimento di Scienze della Terra, Universita di Pavia, Pavia (Italy); Zuppi, G M [Dipartimento di Scienze Ambientali, Universita Ca' Foscari di Venezia, Venice (Italy)

    2003-07-01

    Full text: The Po plain, located in Northern Italy, hosts a multi-layer alluvial aquifer of Quaternary age constituted by sands interbedded with clays. The plain supports most of the agricultural and industrial activities of Northern Italy, which are associated with groundwater pollution in the shallower portions of the aquifer. The increasing demand of water for industrial and domestic use has led to the exploitation of deeper layers of the aquifer, without a rational management of the resource. Only in the last decade, the government agencies have started a global evaluation of the quality standards of pumped groundwater, urged by the increasing need for clean water for domestic use. The task is particularly difficult because of missing or approximate well logs and the presence of multi-filter wells tapping in different aquifers. In this case the chemical and isotopic characterisation of groundwaters is the only reliable tool to reconstruct the geometry, the interconnections and the characteristics of the aquifers. This study, promoted by the local agency for groundwater management and protection (Amministrazione Provinciale di Pavia, settore tutela e valorizzazione ambientale - U.O.C. Acqua) focused on a limited portion of the Po plain, the Lomellina region, of approximately 900 km{sup 2}. The region is bound to the South by the Po river, to the East and West by the Sesia and the Ticino rivers respectively, and to the North by the administrative boundary. The study aimed at the hydrogeological, hydrochemical and isotopic characterisation of the aquifers, allowing to serve as basis for the correct management of the groundwater resource. A preliminary reconstruction of the hydrogeological asset of the Lomellina plain was performed through the analysis of the stratigraphic data from 102 municipal wells. On this basis, a shallow phreatic aquifer, reaching depths of about 50-60 m from the surface, and two groups of aquifers containing confined groundwater, were

  11. Slab-derived components in the subcontinental lithospheric mantle beneath Chilean Patagonia: Geochemistry and Sr-Nd-Pb isotopes of mantle xenoliths and host basalt

    Science.gov (United States)

    Jalowitzki, Tiago; Gervasoni, Fernanda; Conceição, Rommulo V.; Orihashi, Yuji; Bertotto, Gustavo W.; Sumino, Hirochika; Schilling, Manuel E.; Nagao, Keisuke; Morata, Diego; Sylvester, Paul

    2017-11-01

    In subduction zones, ultramafic xenoliths hosted in alkaline basalts can yield significant information about the role of potential slab-derived components in the subcontinental lithospheric mantle (SCLM). Chemical and isotopic heterogeneities in such xenoliths are usually interpreted to reflect melt extraction followed by metasomatic re-enrichment. Here we report new whole-rock major, trace element and isotopic (Sr-Nd-Pb) data for a Proterozoic suite of 17 anhydrous spinel-lherzolites and Eocene (new K-Ar data) host alkaline basalt found near Coyhaique ( 46°S), Aysén Region, Chile. These Patagonian nodules are located in a current back-arc position, 100 km east of the present day volcanic arc and 320 km from the Chile Trench. The mantle xenoliths consist of coarse- to medium-grained spinel-lherzolites with trace element compositions characteristic of a subduction zone setting, such as pronounced negative Nb, Ta and Ti anomalies coupled with significant enrichment of LILEs (e.g., U) and chalcophile elements (W, Pb and Sn). Most of them are characterized by flat to depleted light-rare earth element (LREE) patterns (Ce/YbN = 0.6-1.1) coupled with less radiogenic Sr-Pb (87Sr/86Sr = 0.702422-0.703479; 206Pb/204Pb = 18.212-18.539) and more radiogenic Nd isotopic compositions (143Nd/144Nd = 0.512994-0.513242), similar to the depleted mantle component (DMM or PREMA). In contrast, samples with slight LREE enrichment (Ce/YbN = 1.3-1.8) show more radiogenic Sr-Pb (87Sr/86Sr = 0.703791-0.704239; 206Pb/204Pb = 18.572-18.703) and less radiogenic Nd isotopic compositions (143Nd/144Nd = 0.512859-0.512934), similar to the EM-2 reservoir. These new geochemical and isotope data suggest that the Coyhaique spinel-lherzolites are derived from a heterogeneous SCLM resulting from mixing between a depleted mantle component and up to 10% of slab-derived components. The enriched component added to the SCLM represents variable extents of melts of both subducted Chile Trench sediments and

  12. Problems of applied geochemistry

    Energy Technology Data Exchange (ETDEWEB)

    Ovchinnikov, L N

    1983-01-01

    The concept of applied geochemistry was introduced for the first time by A. Ye. Fersman. He linked the branched and complicated questions of geochemistry with specific problems of developing the mineral and raw material base of our country. Geochemical prospecting and geochemistry of mineral raw materials are the most important sections of applied geochemistry. This now allows us the right to view applied geochemistry as a sector of science which applies geochemical methodology, set of geochemical methods of analysis, synthesis, geological interpretation of data based on laws governing theoretical geochemistry to the solution of different tasks of geology, petrology, tectonics, stratigraphy, science of minerals and other geological sciences, and also the technology of mineral raw materials, interrelationships of man and nature (ecogeochemistry, technogeochemistry, agrogeochemistry). The main problem of applied geochemistry, geochemistry of ore fields is the prehistory of ore formation. This is especially important for metallogenic and forecasting constructions, for an understanding of the reasons for the development of fields and the detection of laws governing their distribution, their genetic links with the general geological processes and the products of these processes.

  13. Petrography and stable isotope geochemistry of Oligocene-Miocene continental carbonates in south Texas: Implications for paleoclimate and paleoenvironment near sea-level

    Science.gov (United States)

    Godfrey, Conan; Fan, Majie; Jesmok, Greg; Upadhyay, Deepshikha; Tripati, Aradhna

    2018-05-01

    Cenozoic sedimentary rocks in the southern Texas Gulf Coastal Plains contain abundant continental carbonates that are useful for reconstructing terrestrial paleoclimate and paleoenvironment in a region near sea-level. Our field observations and thin section characterizations of the Oligocene and Miocene continental carbonates in south Texas identified three types of pedogenic carbonates, including rhizoliths, carbonate nodules, and platy horizons, and two types of groundwater carbonates, including carbonate-cemented beds and carbonate concretions, with distinctive macromorphologic and micromorphologic features. Based on preservations of authigenic microfabrics and variations of carbon and oxygen isotopic compositions, we suggest these carbonates experienced minimal diagenesis, and their stable isotopic compositions reflect paleoclimate and paleoenvironment in south Texas. Our Oligocene and Miocene carbonate clumped isotope temperatures (T(Δ47)) are 23-28 °C, slightly less than or comparable to the range of modern mean annual and mean warm season air temperature (21-27 °C) in the study area. These T(Δ47) values do not show any dependency on carbonate-type, or trends through time suggesting that groundwater carbonates were formed at shallow depths. These data could indicate that air temperature in south Texas was relatively stable since the early Oligocene. The reconstructed paleo-surface water δ18O values are similar to modern surface water which could indicate that meteoric water δ18O values also remained stable since the early Oligocene. Mean pedogenic carbonate δ13C values increased - 4.6‰ during the late Miocene, most likely reflecting an expansion of C4 grassland in south Texas. This study provides the first mid- and late Cenozoic continental records of paleoclimate and paleoecology in a low-latitude, near sea-level region.

  14. Ecophysiology of the hydrothermal vent snail Ifremeria nautilei and barnacle Eochionelasmus ohtai manusensis, Manus Basin, Papua New Guinea: Insights from shell mineralogy and stable isotope geochemistry

    Science.gov (United States)

    Bojar, Ana-Voica; Lécuyer, Christophe; Bojar, Hans-Peter; Fourel, François; Vasile, Ştefan

    2018-03-01

    Deep-sea vent communities live on a limited area characterized by sharp physico-chemical (temperature, salinity, pH) gradients. Around the vent, the fauna is distributed accordingly, showing characteristic niche partitioning for different groups of animals. In this study we investigate shell microstructure, minor elements and stable isotope compositions of two groups of organisms such as a snail, Ifremeria nautilei, and a crustacean, Eochionelasmus ohtai manusensis. Both organisms occupy distinct niches within the same hydrothermal vent field of the Manus Basin, Western Pacific. Powder XRD and electron microbeam analysis of a polished cross-section indicate that the shells are composed of microcrystalline calcite, with distinct Na, Mg, Sr, and S element contents. For both specimens 20-30 μm large weddellite crystals were found. The δ18O profiles were obtained perpendicular to the growth increments of I. nautilei and E. o. manusensis calcitic shells. Those profiles reveal isotopic variations of 0.5 and 0.6‰, respectively for both intra- and inter-shell measurements. For E. o. manusensis, the Mg content suggests continuous shell growth during the year, both δ18O and Mg data supporting cyclical variation of temperature at vent site. The calculated temperatures at sites with I. nautilei and E. o. manusensis range from 17° to 21.5°C and from 2.1° to 7.2°C, respectively, showing a similar variability of 5-6 °C. The δ13C values of the Ifremeria calcitic shell range from 3‰ to 4.6‰ (V-PDB), the isotopic composition being 13C-enriched relative to the surrounding inorganic pool. The δ13C values of the chitine layer covering the shell range from - 33 to - 31.1‰. The δ13C values of Eochionelasmus vary between 0‰ and 1‰, reflecting the surrounding inorganic DIC pool.

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

    International Nuclear Information System (INIS)

    Babinski, M.

    1993-01-01

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

  16. Geochemistry, water dynamics and metals: Major, trace elements, Pb and Sr isotope constraints on their origins and movements in a small anthropized catchment over a flood

    International Nuclear Information System (INIS)

    Luck, J.M.; Othman, D.B.

    1997-01-01

    Major, trace elements and Sr-Pb isotope data on the dissolved and particulate phases are reported for water samples taken regularly over the September flood of a Mediterranean river (S France). This river drains runoff from a small, carbonate, karstified watershed with Miocene and Jurassic lithologies, and characterized by agricultural, urban and road network activities. The objective is to combine all the data into a dynamic model for constraining the origin(s) and movements of waters and of their loads. Furthermore, for metals, it becomes then feasible to know their fate and bioavailability downstream

  17. Gas composition and isotopic geochemistry of cuttings, core, and gas hydrate from the JAPEX/JNOC/GSC Mallik 2L-38 gas hydrate research well

    Science.gov (United States)

    Lorenson, T.D.

    1999-01-01

    Molecular and isotopic composition of gases from the JAPEX/JNOC/GSC Mallik 2L-38 gas hydrate research well demonstrate that the in situ gases can be divided into three zones composed of mixtures of microbial and thermogenic gases. Sediments penetrated by the well are thermally immature; thus the sediments are probably not a source of thermogenic gas. Thermogenic gas likely migrated from depths below 5000 m. Higher concentrations of gas within and beneath the gas hydrate zone suggest that gas hydrate is a partial barrier to gas migration. Gas hydrate accumulations occur wholly within zone 3, below the base of permafrost. The gas in gas hydrate resembles, in part, the thermogenic gas in surrounding sediments and gas desorbed from lignite. Gas hydrate composition implies that the primary gas hydrate form is Structure I. However, Structure II stabilizing gases are more concentrated and isotopically partitioned in gas hydrate relative to the sediment hosting the gas hydrate, implying that Structure II gas hydrate may be present in small quantities.

  18. Pre-Hercynian hydrothermalism in South Iberia: lead isotope geochemistry constraints; Hydrothermalisme ante-hercynien en Sud-Iberie: apport de la geochimie isotopique du plomb

    Energy Technology Data Exchange (ETDEWEB)

    Marcoux, E.; Onezime, J. [Orleans Univ., Institut des Sciences de la Terre d' Orleans, 45 (France); Pascual, E. [Universite d' Huelva, Dept. de Geologia y MIneria, Huelva (Spain)

    2002-04-01

    Lead isotope study has been performed on massive sulphide deposits of Ossa-Morena and Aracena Belt (South Iberia). Results suggest the existence of at least two ancient hydrothermal events. The first one, Upper Brioverian in age ({approx}600-570 Ma), gave birth to Maria-Luisa and Puebla de la Reina massive sulphide deposits; it thus confirms the existence of a Cadomian orogen in South Iberia. Isotopic compositions indicate a local contribution of mantle-derived material (Maria Luisa mine), confirming the presence of ancient oceanic crust in Aracena Belt. This mineralizing event seems to extend till the Armorican Massif. The second episode, Eo-Hercynian in age ({approx}400-350 Ma) has allowed genesis of massive sulphide deposits of la Nava Paredon and Aguas Blancas, and could be coeval with the emplacement of South-Iberian massive sulphide ore deposits in the neighbouring South-Portuguese Zone. A more continental crustal source for later ore deposits could explain the much more important metal accumulation in this zone. (authors)

  19. Isotopic and trace element geochemistry of the Seligdar magnesiocarbonatites (South Yakutia, Russia): Insights regarding the mantle evolution beneath the Aldan-Stanovoy shield

    Science.gov (United States)

    Doroshkevich, Anna G.; Prokopyev, Ilya R.; Izokh, Andrey E.; Klemd, Reiner; Ponomarchuk, Anton V.; Nikolaeva, Irina V.; Vladykin, Nikolay V.

    2018-04-01

    The Paleoproterozoic Seligdar magnesiocarbonatite intrusion of the Aldan-Stanovoy shield in Russia underwent extensive postmagmatic hydrothermal alteration and metamorphic events. This study comprises new isotopic (Sr, Nd, C and O) data, whole-rock major and trace element compositions and trace element characteristics of the major minerals to gain a better understanding of the source and the formation process of the carbonatites. The Seligdar carbonatites have high concentrations of P2O5 (up to 18 wt%) and low concentrations of Na, K, Sr and Ba. The chondrite-normalized REE patterns of these carbonatites display significant enrichments of LREE relative to HREE with an average La/Ybcn ratio of 95. Hydrothermal and metamorphic overprints changed the trace element characteristics of the carbonatites and their minerals. These alteration processes were responsible for Sr loss and the shifting of the Sr isotopic compositions towards more radiogenic values. The altered carbonatites are further characterized by distinct 18O- and 13C-enrichments compared to the primary igneous carbonatites. The alteration most likely resulted from both the percolation of crustal-derived hydrothermal fluids and subsequent metamorphic processes accompanied by interaction with limestone-derived CO2. The narrow range of negative εNd(T) values indicates that the Seligdar carbonatites are dominated by a homogenous enriched mantle source component that was separated from the depleted mantle during the Archean.

  20. Barren Miocene granitoids in the Central Andean metallogenic belt, Chile: Geochemistry and Nd-Hf and U-Pb isotope systematics

    International Nuclear Information System (INIS)

    Deckart, Katja; Godoy, Estanislao; Bertens, Alfredo; Jerez, Daniela; Saeed, Ayesha

    2010-01-01

    Four Middle-to-Late Miocene barren plutonic complexes that occur between the giant porphyry copper deposits of the central Chilean Andes were selected for U-Pb LA-ICPMS geochronology and Hf-isotope systematics on single zircon grains. Major and trace elements and Sr-Nd-Hf isotope whole rock geochemical studies were undertaken to compare with slightly younger or coeval barren and fertile intrusive rocks between 32 o and 34 o S. The studied granitoids yield resolvable crystallization ages of 11.3±0.1 Ma (Cerro Meson Alto massif), 10.3±0.2 Ma (La Gloria pluton), 14.9±0.2 Ma/14.9±0.1 Ma (Yerba Loca stock) and 11.2±0.1 Ma/14.7±0.1 Ma (San Francisco Batholith). Major and trace elements discard an adakitic signature as suggested for coeval porphyric intrusions at 32 o S, slightly younger mineralized porphyries at Rio Blanco-Los Bronces deposit and other Cenozoic adakites. Volcanic host rocks are less fractionated than the intrusive rock units. The same observation can be made for the unmineralized northern plutons compared to the southern ones. Initial Sr-Nd isotope data show insignificant variation (0.703761-0.704118 and 0.512758- 0.512882), plotting in the mantle array. Trace element enrichment can be explained by addition of subducted-slab fluids and/or terrigenous sediments to the mantle wedge prior to and/or slight crustal input during magma ascent. Zircon grains separated from these barren intrusives share a similar initial εHf-data variation for the younger age group (10-12 Ma; 7.04-9.54) and show a more scattered range for the older one (14-15 Ma; 8.50-15.34); both sets plot between the DM and CHUR evolution lines. There is evidence that magma evolution was slightly distinct through time from older to younger barren magmatism, compared to a few fertile porphyritic rocks from Rio Blanco-Los Bronces porphyry copper deposit. It is suggested that chronological inconsistencies within these complexes might be related to differential shortening across the NE

  1. POTENTIALLY TOXIC ELEMENT CYCLES AND CHARACTERIZATION OF MULTIPLE SOURCES IN THE IRRIGATION DITCHES FROM THE RAVENNA COASTAL PLAIN THROUGH TRACE ELEMENTS AND ISOTOPE GEOCHEMISTRY

    Directory of Open Access Journals (Sweden)

    Livia Vittori Antisari

    2010-04-01

    Full Text Available While monitoring the physico-chemical characteristics, trace elements and O-H-Sr-B isotopic data were obtained in superficial waters from a number of irrigations canals and ditches in the Ravenna coastal plain, in order to highlight the cycling of potentially toxic elements and the different sources of the solutes. Surveys were conducted during March and July 2008, and considered as representative of the waters in winter and summer, respectively. In summer, the water mass balance in the network is mostly controlled by the ingression of freshwaters from the Canale Emiliano Romagnolo (CER. The O-H isotopic data indicated that, in winter, waters are primarily recharged from Apennine catchments and undergo evaporation to different extents.The boron isotopic signature indicates the important role played by the marine component. A major seawater contribution was evidenced in canals close to the coastline; however, the process controlling the origin of dissolved boron is not solely related to direct mixing with sea water but comprises an additional source probably related to water-soil exchanges and boron of marine origin leaching, owing to the prolonged exposure of alluvial sediments to sea water. An additional boron contribution from the agricultural practice was is also evidenced. Calculation based on the conservative behaviour of chloride ions indicated that in canals and ditches not directly connected with the sea up to the 80% of the Sr budget did not originate from seawater, indicating a source from Al-silicate minerals and supporting the hypothesis of significant soil-water interactions and chemical exchanges.The positive correlation between pH and dissolved oxygen in winter waters is likely to reflect CO2 consumption during algal photosynthesis, favouring the in-situ generation of colloidal particles due to the oxidative precipitation of ferric iron oxy-hydroxides and probably small carbonate particles able to adsorb trace metals on their

  2. Geochemistry, U-Pb SHRIMP zircon dating and Hf isotopes of the Gondwanan magmatism in NW Argentina: petrogenesis and geodynamic implications

    International Nuclear Information System (INIS)

    Poma, Stella; Zappettini, Eduardo O; Quenardelle, Sonia; Santos, Joao O; Koukharsky, Magdalena; Belousova, Elena; McNaughton, Neil

    2014-01-01

    We have carried out zircon U-Pb SHRIMP dating and Hf isotope determinations as well as geochemical analyses on three plutonic units of Gondwanan magmatism that crop out in NW Argentina. Two episodes of different age and genesis have been identified. The older one includes gabbros and diorites (Rio Grande Unit) of 267±3 Ma and granitoids (belonging to the Llullaillaco Unit) of 263±1 Ma (late Permian, Guadalupian); the parent magmas were generated in an intraplate environment and derived from an enriched mantle but were subsequently contaminated by crustal components. The younger rocks are granodiorites with arc signature (Chuculaqui Unit) and an age of 247±2 Ma (middle Triassic-Anisian). Hf isotope signature of the units indicates mantle sources as well as crustal components. Hf model ages obtained are consistent with the presence of crustal Mesoproterozoic (mainly Ectasian to Calymnian (T DM(c) =1.24 to 1.44 Ga-negative ε Hf m) and juvenile Cryogenian sources (T DM =0.65 to 0.79 Ga-positiveε Hf(T) , supporting the idea of a continuous, mostly Mesoproterozoic, basement under the Central Andes, as an extension of the Arequipa-Antofalla massif. The tectonic setting and age of the Gondwanan magmatism in NW Argentina allow to differentiate: a. Permian intra-plate magmatism developed under similar conditions to the upper section of the Choiyoi magmatism exposed in the Frontal Cordillera and San Rafael Block, Argentina; b. Triassic magmatism belonging to a poorly known subduction-related magmatic arc segment of mostly NS trend with evidence of porphyry type mineralization in Chile, allowing to extend this metallotect into Argentina

  3. Nd, Sr-isotopic provenance and trace element geochemistry of Amazonian foreland basin fluvial sands, Bolivia and Peru: Implications for ensialic Andean orogeny

    International Nuclear Information System (INIS)

    Basu, A.R.; Sharma, M.; DeCelles, P.G.

    1990-01-01

    Nd and Sr isotopes and the trace element contents, including the rare earths, were determined for fluvial sands of lithic arenite composition from the Madre de Dios foreland basin of Bolivia and Peru. On standard petrologic ternary diagrams, the sands fall in the recycled orogen provenance field and thus are similar to typical ancient foreland basin composition. The average rare earth elemental pattern of the sands is identical to the upper continental crustal average, as estimated from post-Archean composite shales of different continents. Ratio of Th/U, Co/Th, La/Sc and Th/Sc of the fluvial sands are intermediate between an average magmatic arc and an upper crustal average compositions. The dispersion of some trace elemental patterns in the sands can be attributed to fractionation of dense minerals, including zircon, during the sedimentation process. The variations of Nd isotopes in conjunction with the petrographic parameters of lithic metamorphic (Lm) and volcanic (Lv) fragments allow a two-fold classification of the sands. These two sand types can be interpreted in terms of mixing among three different provenances: one volcanic rock-suit with less negative ε Nd (O) parameter than the other volcanic suite, and a third metasedimentary source with ε Nd (O) value of around -12, which is considered to be similar to the average western Brazilian shield composition. Thus the overall compositions of the sands has been modeled as mechanical mixtures of two components, an Andean magmatic arc and the Brazilian shield-derived metasediments. The model is strongly supported by a plot of ε Nd (O) versus ε Sr (O) of the sands. In this plot, the Type 1 and 2 sands define two coherent hyperbolic trends contiguous with two different portions of the Andean magmatic trend. (orig./WB)

  4. Trace element and Sr-Nd-Pb isotope geochemistry of Rungwe Volcanic Province, Tanzania: Implications for a superplume source for East Africa Rift magmatism

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    Paterno R Castillo

    2014-09-01

    Full Text Available The recently discovered high, plume-like 3He/4He ratios at Rungwe Volcanic Province (RVP in southern Tanzania, similar to those at the Main Ethiopian Rift in Ethiopia, strongly suggest that magmatism associated with continental rifting along the entire East African Rift System (EARS has a deep mantle contribution (Hilton et al., 2011. New trace element and Sr-Nd-Pb isotopic data for high 3He/4He lavas and tephras from RVP can be explained by binary mixing relationships involving Early Proterozoic (+/- Archaean lithospheric mantle, present beneath the southern EARS, and a volatile-rich carbonatitic plume with a limited range of compositions and best represented by recent Nyiragongo lavas from the Virunga Volcanic Province also in the Western Rift. Other lavas from the Western Rift and from the southern Kenya Rift can also be explained through mixing between the same endmember components. In contrast, lavas from the northern Kenya and Main Ethiopian rifts can be explained through variable mixing between the same mantle plume material and the Middle to Late Proterozoic lithospheric mantle, present beneath the northern EARS. Thus, we propose that the bulk of EARS magmatism is sourced from mixing among three endmember sources: Early Proterozoic (+/- Archaean lithospheric mantle, Middle to Late Proterozoic lithospheric mantle and a volatile-rich carbonatitic plume with a limited range of compositions. We propose further that the African Superplume, a large, seismically anomalous feature originating in the lower mantle beneath southern Africa, influences magmatism throughout eastern Africa with magmatism at RVP and Main Ethiopian Rift representing two different heads of a single mantle plume source. This is consistent with a single mantle plume origin of the coupled He-Ne isotopic signatures of mantle-derived xenoliths and/or lavas from all segments of the EARS (Halldorsson et al., 2014.

  5. Isotope geochemistry and fluxes of carbon and organic matter in tropical small mountainous river systems and adjacent coastal waters of the Caribbean

    Science.gov (United States)

    Moyer, Ryan; Bauer, James; Grottoli, Andrea

    2012-01-01

    Recent studies have shown that small mountainous rivers (SMRs) may act as sources of aged and/or refractory carbon (C) to the coastal ocean, which may increase organic C burial at sea and subsidize coastal food webs and heterotrophy. However, the characteristics and spatial and temporal variability of C and organic matter (OM) exported from tropical SMR systems remain poorly constrained. To address this, the abundance and isotopic character (δ13C and Δ14C) of the three major C pools were measured in two Puerto Rico SMRs with catchments dominated by different land uses (agricultural vs. non-agricultural recovering forest). The abundance and character of C pools in associated estuaries and adjacent coastal waters were also examined. Riverine dissolved and particulate organic C (DOC and POC, respectively) concentrations were highly variable with respect to land use and sampling month, while dissolved inorganic C (DIC) was significantly higher at all times in the agricultural catchment. In both systems, riverine DOC and POC ranged from modern to highly aged (2,340 years before present), while DIC was always modern. The agricultural river and irrigation canals contained very old DOC (1,184 and 2,340 years before present, respectively), which is consistent with findings in temperate SMRs and indicates that these tropical SMRs provide a source of aged DOC to the ocean. During months of high river discharge, OM in estuarine and coastal waters had C isotope signatures reflective of direct terrestrial input, indicating that relatively unaltered OM is transported to the coastal ocean at these times. This is also consistent with findings in temperate SMRs and indicates that C transported to the coastal ocean by SMRs may differ from that of larger rivers because it is exported from smaller catchments that have steeper terrains and fewer land-use types.

  6. The 8th ICGG International Conference on Gas Geochemistry Preface: Fluids and tectonics

    Directory of Open Access Journals (Sweden)

    F. Italiano

    2007-06-01

    Full Text Available The 8th International Conference on Gas Geochemistry provided the opportunity for scientists from different countries to meet each other, exchange ideas on the state of the art in gas geochemistry, and discuss advance in fluid geochemistry. The 8th ICGG meeting focused on three main geologic environments currently interacting with the human life: volcanoes, earthquakes and hydrocarbons. Ninety-four presentations gave participants chance to cover a variety of important research topics on gas geochemistry in geosciences including: gas migration in terrestrial and marine environments, Earth degassing and its relation to seismicity, volcanic eruptions, rare gases and application of isotope techniques, measurement and analytical techniques.

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

    Science.gov (United States)

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

    2016-01-01

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

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

    International Nuclear Information System (INIS)

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

    1988-01-01

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

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

    Science.gov (United States)

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

    2014-11-01

    22 Ma correlating with the ages of the basement rocks from these areas. The initial 176Hf/177Hf isotope ratios of the zircon grains from the AM syenite fall in the range between 0.281771 and 0.282284, with moderately negative εHf(t) values between - 5.9 and 0.1. Similarly, the initial 176Hf/177Hf isotope ratios for the zircon grains of PM ultrapotassic granite range between 0.281197 and 0.281970, albeit with more negative εHf(t) values in the range between - 22.7 and - 0.3 (average εHf (t) value - 18.8). The Lu-Hf data suggest the involvement of variable extent of older crust with distinct crustal residence times, either in the form of assimilation during magma emplacement, or crustal recycling during magma genesis. Based on the geochemical and isotopic systematics, a possible petrogenetic model would be asthenospheric upwelling in an extensional setting, melting of enriched lithosphere, and interaction of the magmas with lower crustal domains with subduction-related components of various ages. The disposition of these alkali plutons along two paleo sutures that weld the Meso-Neoarchean crustal blocks in the northern periphery of SGT suggests that the zones of emplacement might represent an aborted rift. The paleo-sutures probably served as a weak zone along which extension occurred broadly coeval with the Cryogenian subduction further south.

  10. U–Pb, Rb–Sr, and U-series isotope geochemistry of rocks and fracture minerals from the Chalk River Laboratories site, Grenville Province, Ontario, Canada

    International Nuclear Information System (INIS)

    Neymark, L.A.; Peterman, Z.E.; Moscati, R.J.; Thivierge, R.H.

    2013-01-01

    Highlights: • AECL evaluates Chalk River Laboratories site as potential nuclear waste repository. • Isotope-geochemical data for rocks and fracture minerals at CRL site are reported. • Zircons from gneiss and granite yielded U–Pb ages of 1472 ± 14 and 1045 ± 6 Ma. • WR Rb–Sr and Pb–Pb systems do not show substantial large-scale isotopic mobility. • U-series and REE data do not support oxidizing conditions at depth in the past 1 Ma. - Abstract: As part of the Geologic Waste Management Facility feasibility study, Atomic Energy of Canada Ltd. (AECL) is evaluating the suitability of the Chalk River Laboratories (CRL) site in Ontario, situated in crystalline rock of the southwestern Grenville Province, for the possible development of an underground repository for low- and intermediate-level nuclear waste. This paper presents petrographic and trace element analyses, U–Pb zircon dating results, and Rb–Sr, U–Pb and U-series isotopic analyses of gneissic drill core samples from the deep CRG-series characterization boreholes at the CRL site. The main rock types intersected in the boreholes include hornblende–biotite (±pyroxene) gneisses of granitic to granodioritic composition, leucocratic granitic gneisses with sparse mafic minerals, and garnet-bearing gneisses with variable amounts of biotite and/or hornblende. The trace element data for whole-rock samples plot in the fields of within-plate, syn-collision, and volcanic arc-type granites in discrimination diagrams used for the tectonic interpretation of granitic rocks. Zircons separated from biotite gneiss and metagranite samples yielded SHRIMP-RG U–Pb ages of 1472 ± 14 (2σ) and 1045 ± 6 Ma, respectively, in very good agreement with widespread Early Mesoproterozoic plutonic ages and Ottawan orogeny ages in the Central Gneiss Belt. The Rb–Sr, U–Pb, and Pb–Pb whole-rock errorchron apparent ages of most of the CRL gneiss samples are consistent with zircon U–Pb age and do not indicate

  11. Stable Isotope Geochemistry of Extremely Well-Preserved 2.45-Billion-Year-Old Hydrothermal Systems in the Vetreny Belt, Baltic Shield: Insights into Paleohydrosphere

    Science.gov (United States)

    Zakharov, D. O.; Bindeman, I. N.

    2015-12-01

    The early Paleoproterozoic was an eventful period in the Earth's history. The first portions of free oxygen emerged in the atmosphere, Snowball Earth glaciations happened several times and the first supercontinent broke up due to extensive rifting. These events should have affected the stable isotopic composition of the hydrosphere. In this study, we use rocks that were altered in underwater hydrothermal systems to investigate the stable isotopic composition of the hydrosphere 2.39-2.45 billion years ago (hereinafter, Ga). Extremely low-δ18O (down to -27.5‰ SMOW) rocks from 2.39 Ga metamorphosed subglacial hydrothermal systems of the Belomorian belt, Baltic Shield formed at near-equatorial latitudes suggesting a Snowball (or Slushball) Earth glaciation. These results motivated us to look at temporally and geographically close hydrothermal systems from the unmetamorhposed 2.45 Ga Vetreny Belt rift. The length of the rift is 250 km and it is composed of high-Mg basalts, mafic-ultramafic intrusions and sedimentary successions. We examined several localities of high-Mg basalt flows that include astonishingly fresh pillow lavas, often with preserved volcanic glass, eruptive breccias, and hydrothermal alteration zones. Collected samples serve a great textural evidence of water-rock interaction that occurred in situ while basalts were cooling. The preliminary results from coexisting quartz and epidote (T, D18O=311°C), and from coexisting calcite and quartz (T, D18O=190°C) yield values of δ18O of involved water between -1.6 and -0.9 ‰. The values of δ13C in calcites vary between -4.0 and -2.3 ‰. It is likely that hydrothermal fluids operated in the Vetreny Belt rift were derived from seawater that is no different from modern oceanic water in terms of δ18O. Apparently, the rift was a Paleoproterozoic analog of the modern Red Sea, filled with oceanic water. The result is important because the Vetreny Belt rift predates the onset of Snowball Earth glaciation at 2

  12. Micromorphology and stable-isotope geochemistry of historical pedogenic siderite formed in PAH-contaminated alluvial clay soils, Tennessee, U.S.A

    Science.gov (United States)

    Driese, S.G.; Ludvigson, Greg A.; Roberts, J.A.; Fowle, D.A.; Gonzalez, Luis A.; Smith, J.J.; Vulava, V.M.; McKay, L.D.

    2010-01-01

    Alluvial clay soil samples from six boreholes advanced to depths of 400-450 cm (top of limestone bedrock) from the Chattanooga Coke Plant (CCP) site were examined micromorphologically and geochemically in order to determine if pedogenic siderite (FeCO3) was present and whether siderite occurrence was related to organic contaminant distribution. Samples from shallow depths were generally more heavily contaminated with polycyclic aromatic hydrocarbons (PAHs) than those at greater depth. The upper 1 m in most boreholes consisted of mixtures of anthropogenically remolded clay soil fill containing coal clinker, cinder grains, and limestone gravel; most layers of coarse fill were impregnated with creosote and coal tar. Most undisturbed soil (below 1 m depth) consisted of highly structured clays exhibiting fine subangular blocky ped structures, as well as redox-related features. Pedogenic siderite was abundant in the upper 2 m of most cores and in demonstrably historical (< 100 years old) soil matrices. Two morphologies were identified: (1) sphaerosiderite crystal spherulites ranging from 10 to 200 um in diameter, and (2) coccoid siderite comprising grape-like "clusters" of crystals 5-20 ??n in diameter. The siderite, formed in both macropores and within fine-grained clay matrices, indicates development of localized anaerobic, low-Eh conditions, possibly due to microbial degradation of organic contaminants. Stable-isotope compositions of the siderite have ??13C values spanning over 25%o (+7 to - 18%o VPDB) indicating fractionation of DIC by multiple microbial metabolic pathways, but with relatively constant ??18O values from (-4.8 ?? 0.66%o VPDB) defining a meteoric sphaerosiderite line (MSL). Calculated isotope equilibrium water ??18O values from pedogenic siderites at the CCP site are from 1 to 5 per mil lighter than the groundwater ??18O values that we estimate for the site. If confirmed by field studies in progress, this observation might call for a reevaluation of

  13. Investigating the hydrological significance of stalagmite geochemistry (Mg, Sr) using Sr isotope and particulate element records across the Late Glacial-to-Holocene transition

    Science.gov (United States)

    Belli, R.; Borsato, A.; Frisia, S.; Drysdale, R.; Maas, R.; Greig, A.

    2017-02-01

    The trace element and Sr isotope records in two coeval stalagmites characterized by different growth rates and flow regimes at Savi cave (Grotta Savi, NE Italy) reveal different sources and incorporation mechanisms for Mg and Sr. Mg is sourced primarily from dissolved cave host rock while particulate Mg derived from soil plays a subordinate role. The presence of particulate-borne Mg is inferred from the co-variation of Mg and particle-associated elements (Th, Al and Mn) which are preferentially concentrated in open columnar calcite layers. Variation in Mg concentrations corrected for particle-influenced components, the Mgc parameter, is controlled by water-rock interaction, with higher and lower Mgc during dry and wet phases, respectively. This is thought to reflect incongruent dissolution of Mg-rich phases. Correction of Sr concentrations for contributions from airborne exogenic Sr, based on 87Sr/86Sr ratios, yields the bedrock-only contribution (Src). Src variation in stalagmite calcite is influenced by speleothem growth rate and by variation of the calcite-water Sr partitioning in wet and dry phases, and only to a minor extent by incongruent dissolution of Mg-rich phases. Concentration profiles for Mgc and Srcg (corrected for growth rate effects) show inverse correlations and are inferred to show hydrological significance which is captured in a hydrological index, HI. We suggest HI provides robust information on water-rock interaction related to hydrological changes and can be utilized in both wet and semi-arid environments, provided the corrections for soil Mg and exogenic Sr can be applied with confidence. Application of the HI index allows correction of Grotta Savi oxygen isotope data, to yield a δ18Oc time series that shows when changes in moisture sources and atmospheric reorganization, or changes in moisture amount, were significant. This is especially evident during the Younger Dryas (YD). The Savi record supports the concept of a two-phase YD, marked by

  14. Noble Gas geochemistry of the newly discovered hydrothermal fields in the Gulf of California: preliminary He-isotope ratios from the Alarcon Rise and Pescadero basin vent sites

    Science.gov (United States)

    Spelz, R. M.; Lupton, J. E.; Evans, L. J.; Zierenberg, R. A.; Clague, D. A.; Neumann, F.; Paduan, J. B.

    2015-12-01

    Numerous submarine deep-sea hydrothermal vents related to volcanic activity of the East Pacific Rise (EPR) are situated along the Pacific margins of Mexico. Until recently, active hydrothermal venting was unknown between the Guaymas Basin and 21°N on the EPR. MBARI's recent oceanographic surveys have added 7 new active vent sites. In this study, we aimed to sample the high-temperature hydrothermal fluids emanating from two distinct vent sites, named Meyibo and Auka, located in the Alarcon Rise and Pescadero Basin, respectively. Mantle-derived He have long been identified in hydrothermal fluid releases. The presence of He in aqueous fluids with 3He/4He ratios greater than in-situ production values (~0.05 RA, where RA = air He or 1.4 x 10-6) indicates the presence of mantle-derived melts. Preliminary analyses of He-isotope ratios derived from the newly discovered Meyibo and Auka hydrothermal fields show high 3He/4He ratios (~8RA), typical of MORB's. Auka vent field, characterized by chimneys composed of light carbonate minerals and oil-like hydrocarbons, and temperatures between 250-290oC, show average values of ~7.87RA. In contrast, the black-smokers at the Meyibo field, composed of dark sulfide minerals and temperatures over 350oC, yielded a higher He ratio of ~8.24RA. Recently, it has become clear that regional maximum mantle He values correlate with the velocity structure in the mantle, therefore, He has the potential to map regions of the underlying mantle that are undergoing partial melting. Seismic records could then be compared with the geochemical He ratio signal and supply information regarding tectonics and other processes involved in the generation of these gases. The data presented here will be completing a totally new inventory of He results from hydrothermal vents in the EPR and fault-termination basins distributed along the P-NA plate boundary in the Gulf of California. The results will be further coupled with the analysis of other geochemical

  15. Devonian alkaline magmatism in the northern North China Craton: Geochemistry, SHRIMP zircon U-Pb geochronology and Sr-Nd-Hf isotopes

    Directory of Open Access Journals (Sweden)

    Dingling Huang

    2017-01-01

    Full Text Available The Wulanhada pluton is among the rare suite of Devonian alkaline plutons occurring along the northern margin of the North China Craton (NCC. The intrusion is mainly composed of quartz-monzonite. Here we report zircon SHRIMP U-Pb data from this intrusion which shows emplacement age of ca. 381.5 Ma. The rock is metaluminous with high (Na2O + K2O values ranging from 8.46 to 9.66 wt.%. The REE patterns of the rocks do not show any Eu anomaly whereas the primitive-mantle-normalized spider diagram shows strong positive Sr and Ba anomalies. The Wulanhada rocks exhibit high initial values of (87Sr/86Srt = 0.70762–0.70809, low ɛNd(t = −12.76 to −12.15 values and negative values of ɛHf(t = −23.49 to −17.02 with small variations in (176Hf/177Hft (0.281873–0.282049. These geochemical features and quantitative isotopic modeling results suggest that the rocks might have been formed through the partial melting of Neoarchean basic rocks in the lower crust of the NCC. The Wulanhada rocks, together with the Devonian alkaline rocks and mafic-ultramafic complex from neighboring regions, constitute a post-collisional magmatic belt along the northern NCC.

  16. Using biochemical and isotope geochemistry to understand the environmental and public health implications of lead pollution in the lower Guadiana River, Iberia: A freshwater bivalve study

    Energy Technology Data Exchange (ETDEWEB)

    Company, R. [CIMA, Faculty of Marine and Environmental Sciences, University of Algarve, Campus de Gambelas, 8005-139 Faro (Portugal)], E-mail: rcompany@ualg.pt; Serafim, A.; Lopes, B.; Cravo, A. [CIMA, Faculty of Marine and Environmental Sciences, University of Algarve, Campus de Gambelas, 8005-139 Faro (Portugal); Shepherd, T.J.; Pearson, G. [Department of Earth Sciences, Durham University, Science Labs., Durham DH1 3LE (United Kingdom); Bebianno, M.J. [CIMA, Faculty of Marine and Environmental Sciences, University of Algarve, Campus de Gambelas, 8005-139 Faro (Portugal)], E-mail: mbebian@ualg.pt

    2008-11-01

    Lead is a natural component of aquatic ecosystems with no known biological role and is highly toxic. Its toxicity stems from its ability to mimic biologically important metals and to produce membrane damage through lipid peroxidation (LPO). Most lead poisoning symptoms are thought to occur by interfering with an essential enzyme, {delta}-aminolevulinic acid dehydratase (ALAD), the activity of which is markedly inhibited by lead. The purpose of this work was to study the levels and effects of lead pollution (responses of ALAD and oxidative stress biomarker LPO) in the freshwater bivalve Corbicula fluminea along the lower Guadiana River (Portugal and Spain); a major river system impacted by historic mining pollution and more recent anthropogenic inputs. The results show that the enzymatic activity of ALAD is negatively correlated with the total Pb concentration of the whole tissue suggesting that ALAD has considerable potential as a biomarker of lead exposure in C. fluminea. To identify the sources of lead to which bivalves have been exposed, high precision {sup 206}Pb/{sup 204}Pb, {sup 207}Pb/{sup 204}Pb, {sup 208}Pb/{sup 204}/Pb ratios for C. fluminea confirm that historical mining activities in the Iberian Pyrite Belt are the dominant source of lead pollution in the lower Guadiana River. The isotope patterns however exhibit marked seasonal and geographic variation in response to rainfall and river water management. Locally, other anthropogenic sources of lead have been detected in C. fluminea close to population centres, thus adding to its versatility as a freshwater bio-indicator. Overall, the study highlights the value of natural ecosystems as monitors of water quality and their importance for public health assessment and surveillance.

  17. Hydro geochemistry and isotopic approach of coastal aquifer systems of Cap Bon : The case of tablecloths and the eastern coast of El Haourai - Tunisia

    International Nuclear Information System (INIS)

    Ben Hammouda, Fethi

    2008-01-01

    As many other semi-arid regions, the Cap Bon peninsula (N.E. Tunisia) shows a parallel increase in overexploitation and mineralization of groundwater resources. In the eastern coast and El Haouaria aquifers, the groundwater quality is threatened. Surveys including level measurements, water sampling, chemical analysis (ions Na+, Cl., Ca2+, Mg2+, Br.) and sotopes (18O, 2H, 3H, 13C, 14C) were performed in 2001, 2002 and 2003. Several analysis types were conducted and results are compared with the hydrodynamic information for identifying the main processes involved in the mineralization increase. Particularly, the isotopes were permitting the understanding of the hydrogeological of the concerned aquifers and the localization of the recharge zones. Because the regional situation along the seashore, the seawater intrusion in the unconfined Plio-quaternary aquifer, resulting from the groundwater overexploitation, and obvious explanation for the rising salinity is identified but is not the only cause of the qualitative degradation: the irrigation development that induces the soil leaching and the fertilizers transfer to groundwater over the whole aquifer extent is another major reason of the mineralization increase. Piezometric and salinity maps of the Plio-quaternary aquifer were established. The continuous increase in pumping has created several depressions in the water table, up to 12 m below msl and induced a deterioration of the water quality. The temporal changes in water-table level and salinity are often similar which suggests a strong link between them. Several geochemical approaches were performed to identify the importance of the marine intrusion in the increase in mineralization. The salinity of the groundwater appears to originate from dissolution of minerals in the aquifer system

  18. Constraints from geochemistry and oxygen isotopes for the hydrothermal origin of orthoamphibole mafic gneiss in the New Jersey Highlands, north-central Appalachians, USA

    Science.gov (United States)

    Volkert, Richard A.; Peck, William H.

    2017-12-01

    Rare exposures of orthoamphibole mafic (Oam) gneiss of Mesoproterozoic age in the north-central Appalachians are confined to the northwestern New Jersey Highlands where they form thin lens-shaped bodies composed of gedrite and sparse anthophyllite, oligoclase (An13-An20), biotite, magnetite, and local fluorapatite, rutile, and ilmenite. The gneiss is penetratively foliated and has sharp, conformable contacts against enclosing supracrustal paragneiss and marble. Orthoamphibole mafic gneiss is characterized by low SiO2 (48 ± 2.5 wt%), CaO (1.9 ± 1.3 wt%), and high Al2O3 (18 ± 1.2 wt%), Fe2O3 (10.5 ± 1.6 wt%), and MgO (12 ± 2.3 wt%). Trace element abundances overlap those of unaltered amphibolites in the study area and, coupled with δ18O values of 9.45 ± 0.6‰ (VSMOW) from gedrite separates, support an origin from a basalt protolith. The geochemical and isotopic data are consistent with the formation of Oam gneiss through sea floor hydrothermal alteration of basalt at low temperature of 150-200 °C. Mass-balance calculations indicate gains during alteration mainly in MgO and Al2O3 and losses in CaO, Sr, and light rare earth elements. Our results are compatible with the pre-metamorphic alteration of the basalt protoliths through chloritization and plagioclase dissolution that produced a Mg-rich and Ca-poor rock. Subsequent metamorphism of this chlorite-rich rock to the current mineral assemblage of Oam gneiss took place at ca. 1045 Ma, during the Ottawan phase of the Grenvillian Orogeny. The close spatial association in the study area of Oam gneiss bodies and sulfide occurrences suggests an affinity to the style of mineralization associated with volcanogenic massive sulfide (VMS)-type deposits.

  19. Using biochemical and isotope geochemistry to understand the environmental and public health implications of lead pollution in the lower Guadiana River, Iberia: a freshwater bivalve study.

    Science.gov (United States)

    Company, R; Serafim, A; Lopes, B; Cravo, A; Shepherd, T J; Pearson, G; Bebianno, M J

    2008-11-01

    Lead is a natural component of aquatic ecosystems with no known biological role and is highly toxic. Its toxicity stems from its ability to mimic biologically important metals and to produce membrane damage through lipid peroxidation (LPO). Most lead poisoning symptoms are thought to occur by interfering with an essential enzyme, delta-aminolevulinic acid dehydratase (ALAD), the activity of which is markedly inhibited by lead. The purpose of this work was to study the levels and effects of lead pollution (responses of ALAD and oxidative stress biomarker LPO) in the freshwater bivalve Corbicula fluminea along the lower Guadiana River (Portugal and Spain); a major river system impacted by historic mining pollution and more recent anthropogenic inputs. The results show that the enzymatic activity of ALAD is negatively correlated with the total Pb concentration of the whole tissue suggesting that ALAD has considerable potential as a biomarker of lead exposure in C. fluminea. To identify the sources of lead to which bivalves have been exposed, high precision (206)Pb/(204)Pb, (207)Pb/(204)Pb, (208)Pb/(204)/Pb ratios for C. fluminea confirm that historical mining activities in the Iberian Pyrite Belt are the dominant source of lead pollution in the lower Guadiana River. The isotope patterns however exhibit marked seasonal and geographic variation in response to rainfall and river water management. Locally, other anthropogenic sources of lead have been detected in C. fluminea close to population centres, thus adding to its versatility as a freshwater bio-indicator. Overall, the study highlights the value of natural ecosystems as monitors of water quality and their importance for public health assessment and surveillance.

  20. Using biochemical and isotope geochemistry to understand the environmental and public health implications of lead pollution in the lower Guadiana River, Iberia: A freshwater bivalve study

    International Nuclear Information System (INIS)

    Company, R.; Serafim, A.; Lopes, B.; Cravo, A.; Shepherd, T.J.; Pearson, G.; Bebianno, M.J.

    2008-01-01

    Lead is a natural component of aquatic ecosystems with no known biological role and is highly toxic. Its toxicity stems from its ability to mimic biologically important metals and to produce membrane damage through lipid peroxidation (LPO). Most lead poisoning symptoms are thought to occur by interfering with an essential enzyme, δ-aminolevulinic acid dehydratase (ALAD), the activity of which is markedly inhibited by lead. The purpose of this work was to study the levels and effects of lead pollution (responses of ALAD and oxidative stress biomarker LPO) in the freshwater bivalve Corbicula fluminea along the lower Guadiana River (Portugal and Spain); a major river system impacted by historic mining pollution and more recent anthropogenic inputs. The results show that the enzymatic activity of ALAD is negatively correlated with the total Pb concentration of the whole tissue suggesting that ALAD has considerable potential as a biomarker of lead exposure in C. fluminea. To identify the sources of lead to which bivalves have been exposed, high precision 206 Pb/ 204 Pb, 207 Pb/ 204 Pb, 208 Pb/ 204 /Pb ratios for C. fluminea confirm that historical mining activities in the Iberian Pyrite Belt are the dominant source of lead pollution in the lower Guadiana River. The isotope patterns however exhibit marked seasonal and geographic variation in response to rainfall and river water management. Locally, other anthropogenic sources of lead have been detected in C. fluminea close to population centres, thus adding to its versatility as a freshwater bio-indicator. Overall, the study highlights the value of natural ecosystems as monitors of water quality and their importance for public health assessment and surveillance

  1. Geochemistry and Petrogenesis of Biabanak–Bafq Mafic Mgmatism ...

    Indian Academy of Sciences (India)

    59

    13185-1494. Email: m_poshtkoohi@yahoo.com; Mobile No: +98 912 209 39 73 ...... petrologie et tectonique du precambrien et de sa couverture, Ph.D. thesis, universite ..... Applications of the 190Pt–186OS isotope system to geochemistry and.

  2. Contrasting isotopic mantle sources for proterozoic lamproites and kimberlites from the Cuddapah basin and eastern Dharwar craton: implication for proterozoic mantle heterogeneity beneath southern India

    International Nuclear Information System (INIS)

    Chalapathi Rao, N.V.; Gibson, S.A.; Pyle, D.M.; Dickin, A.P.

    1998-01-01

    Kimberlites intruding the Precambrian basement towards the western margin of the Cuddapah basin near Anantapur (1090 Ma) and Mahbubnagar (1360 Ma) in Andhra Pradesh have initial 87 Sr/ 86 Sr between 0.70205 to 0.70734 and σNd between +0.5 to +4.68. Mesoproterozoic lamproites (1380 Ma) from the Cuddapah basin (Chelima and Zangamarajupalle) and its NE margin (Ramannapeta) have initial 87 Sr/ 86 Sr between 0.70520 and 0.7390 and εNd from -6.43 to -8.29. Combined Sr- and Nd- isotopic ratios suggest that lamproites were derived from enriched sources which have time-averaged higher Rb/Sr and lower Sm/Nd ratios than the Bulk Earth whereas kimberlites were derived from depleted source with lower Rb/Sr and higher Sm/Nd ratios. Calculated T DM model ages suggest that the lamproite source enrichment (∼2 Ga) preceded that of kimberlites (∼1.37 Ga). Our work demonstrates the existence of isotopically contrasting upper mantle sources for southern Indian kimberlites and lamproites and provides evidence for a lateral, isotopically heterogeneous mantle beneath the Cuddapah basin and eastern Dharwar craton. The significance of our results in the context of diamond exploration is also highlighted. (author)

  3. 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

    Science.gov (United States)

    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 Sc(2-3 ppm), positive Sr anomaly and predominantly negative zircon εHf(t) values (-10.8 to -9.3 with an average of -10.2) and initial 176Hf/177Hf ratios (0.281947-0.282022) confirm a Paleoproterozoic crustal source. Based on the field and geochemical evidences, we propose that a previously metasomatized mafic lower-crustal source enriched in alkalis has undergone CO2-present partial melting as a result of asthenospheric upwelling beneath an aborted rifting along the DRZ generating the magma that crystallized the Sundamalai rocks

  4. Isotopes in day to day life

    Science.gov (United States)

    1984-06-01

    Developments are reported in the use of isotopic labeling and isotope irradiation in agriculture, medical science, hydrology, geochemistry, geophysics, environment pollution detection, and industries. Radioisotope instruments are described as well as techniques for gamma radiography, neutron radiography, and autoradiography. Isotope dating in geology and archaeology is covered. Basic scientific research topics in various areas are listed.

  5. DOE workshop: Sedimentary systems, aqueous and organic geochemistry

    International Nuclear Information System (INIS)

    1993-07-01

    A DOE workshop on sedimentary systems, aqueous and organic geochemistry was held July 15-16, 1993 at Lawrence Berkeley Laboratory. Papers were organized into several sections: Fundamental Properties, containing papers on the thermodynamics of brines, minerals and aqueous electrolyte solutions; Geochemical Transport, covering 3-D imaging of drill core samples, hydrothermal geochemistry, chemical interactions in hydrocarbon reservoirs, fluid flow model application, among others; Rock-Water Interactions, with presentations on stable isotope systematics of fluid/rock interaction, fluid flow and petotectonic evolution, grain boundary transport, sulfur incorporation, tracers in geologic reservoirs, geothermal controls on oil-reservoir evolution, and mineral hydrolysis kinetics; Organic Geochemistry covered new methods for constraining time of hydrocarbon migration, kinetic models of petroleum formation, mudstones in burial diagenesis, compound-specific carbon isotope analysis of petroleums, stability of natural gas, sulfur in sedimentary organic matter, organic geochemistry of deep ocean sediments, direct speciation of metal by optical spectroscopies; and lastly, Sedimentary Systems, covering sequence stratigraphy, seismic reflectors and diagenetic changes in carbonates, geochemistry and origin of regional dolomites, and evidence of large comet or asteroid impacts at extinction boundaries

  6. DOE workshop: Sedimentary systems, aqueous and organic geochemistry

    Energy Technology Data Exchange (ETDEWEB)

    1993-07-01

    A DOE workshop on sedimentary systems, aqueous and organic geochemistry was held July 15-16, 1993 at Lawrence Berkeley Laboratory. Papers were organized into several sections: Fundamental Properties, containing papers on the thermodynamics of brines, minerals and aqueous electrolyte solutions; Geochemical Transport, covering 3-D imaging of drill core samples, hydrothermal geochemistry, chemical interactions in hydrocarbon reservoirs, fluid flow model application, among others; Rock-Water Interactions, with presentations on stable isotope systematics of fluid/rock interaction, fluid flow and petotectonic evolution, grain boundary transport, sulfur incorporation, tracers in geologic reservoirs, geothermal controls on oil-reservoir evolution, and mineral hydrolysis kinetics; Organic Geochemistry covered new methods for constraining time of hydrocarbon migration, kinetic models of petroleum formation, mudstones in burial diagenesis, compound-specific carbon isotope analysis of petroleums, stability of natural gas, sulfur in sedimentary organic matter, organic geochemistry of deep ocean sediments, direct speciation of metal by optical spectroscopies; and lastly, Sedimentary Systems, covering sequence stratigraphy, seismic reflectors and diagenetic changes in carbonates, geochemistry and origin of regional dolomites, and evidence of large comet or asteroid impacts at extinction boundaries.

  7. Isotopes in everyday life

    International Nuclear Information System (INIS)

    Seligman, H.; Gillen, V.A.

    1990-12-01

    Isotopes represent a tool which can do certain jobs better, easier, quicker, more simply and cheaper than competitive methods. Some measurements could not be done at all without the use of isotopes as there are no alternative methods available. A short review of these tools of science in their different fields is given: food and agriculture, human health applications, industry, hydrology, geology, geochemistry, geophysics and dating, environment, basic scientific research

  8. Effects of interaction between ultramafic tectonite and mafic magma on Nd-Pb-Sr isotopic systems in the Neoproterozoic Chaya Massif, Baikal-Muya ophiolite belt

    Science.gov (United States)

    Amelin, Yuri V.; Ritsk, Eugeni Yu.; Neymark, Leonid A.

    1997-04-01

    Sm-Nd, Rb-Sr and U-Pb isotopic systems have been studied in minerals and whole rocks of harzburgites and mafic cumulates from the Chaya Massif, Baikal-Muya ophiolite belt, eastern Siberia, in order to determine the relationship between mantle ultramafic and crustal mafic sections. Geological relations in the Chaya Massif indicate that the mafic magmas were emplaced into, and interacted with older solid peridotite. Hand picked, acid-leached, primary rock-forming and accessory minerals (olivine, orthopyroxene, clinopyroxene and plagioclase) from the two harzburgite samples show coherent behavior and yield 147Sm/ 144Nd- 143Nd/ 144Nd and 238U/ 204Pb- 206Pb/ 204Pb mineral isochrons, corresponding to ages of 640 ± 58 Ma (95% confidence level) and 620 ± 71 Ma, respectively. These values are indistinguishable from the crystallization age of the Chaya mafic units of 627 ± 25 Ma (a weighted average of internal isochron Sm-Nd ages of four mafic cumulates). The Rb-Sr and Sm-Nd isotopic systems in the harzburgite whole-rock samples were disturbed by hydrothermal alteration. These alteration-related isotopic shifts mimic the trend of variations in primary isotopic compositions in the mafic sequence, thus emphasizing that isotopic data for ultramafic rocks should be interpreted with great caution. On the basis of initial Sr and Nd values, ultramafic and mafic rocks of the Chaya Massif can be divided into two groups: (1) harzburgites and the lower mafic unit gabbronorites withɛ Nd = +6.6 to +7.1 andɛ Sr = -11 to -16; and (2) websterite of the lower unit and gabbronorites of the upper mafic unit:ɛ Nd = +4.6 to +6.1 andɛ Sr = -8 to -9. Initial Pb isotopic ratios are identical in all rocks studied, with mean values of 206Pb/ 204Pb= 16.994 ± 0.023 and 207Pb/ 204Pb= 15.363 ± 0.015. The similarity of ages and initial isotopic ratios within the first group indicates that the isotopic systems in the pre-existing depleted peridotite were reset by extensive interaction with

  9. A new digestion and chemical separation technique for rapid and highly reproducible determination of Lu/Hf and Hf isotope ratios in geological materials by mc-ICP-MS

    DEFF Research Database (Denmark)

    Bizzarro, Martin; Baker, J.A.; Ulfbeck, D.

    2003-01-01

    for isotopic analysis of the Sm-Nd system and/or the other HFSE (Ti, Zr). Total procedural blanks for this technique are 5 g) samples. We present data from replicate digestions of international rock reference materials which....... The relative simplicity of this technique, coupled with the ease of digestion (and samplespike equilibration) of large difficult-to-dissolve samples, and the speed (2 days) with which samples can be digested and processed through the chemical separation scheme makes it an attractive new method for preparing...

  10. Stable-isotope geochemistry of the Pierina high-sulfidation Au-Ag deposit, Peru: Influence of hydrodynamics on SO42--H2S sulfur isotopic exchange in magmatic-steam and steam-heated environments

    Science.gov (United States)

    Fifarek, R.H.; Rye, R.O.

    2005-01-01

    The Pierina high-sulfidation Au-Ag deposit formed 14.5 my ago in rhyolite ash flow tuffs that overlie porphyritic andesite and dacite lavas and are adjacent to a crosscutting and interfingering dacite flow dome complex. The distribution of alteration zones indicates that fluid flow in the lavas was largely confined to structures but was dispersed laterally in the tuffs because of a high primary and alteration-induced permeability. The lithologically controlled hydrodynamics created unusual fluid, temperature, and pH conditions that led to complete SO42--H2S isotopic equilibration during the formation of some magmatic-steam and steam-heated alunite, a phenomenon not previously recognized in similar deposits. Isotopic data for early magmatic hydrothermal and main-stage alunite (??34S=8.5??? to 31.7???; ??18 OSO4=4.9??? to 16.5???; ??18 OOH=2.2??? to 14.4???; ??D=-97??? to -39???), sulfides (??34 S=-3.0??? to 4.3???), sulfur (??34S=-1.0??? to 1.1???), and clay minerals (??18O=4.3??? to 12.5???; ??D=-126??? to -81???) are typical of high-sulfidation epithermal deposits. The data imply the following genetic elements for Pierina alteration-mineralization: (1) fluid and vapor exsolution from an I-type magma, (2) wallrock buffering and cooling of slowing rising vapors to generate a reduced (H2S/SO4???6) highly acidic condensate that mixed with meteoric water but retained a magmatic ??34S???S signature of ???1???, (3) SO2 disproportionation to HSO4- and H2S between 320 and 180 ??C, and (4) progressive neutralization of laterally migrating acid fluids to form a vuggy quartz???alunite-quartz??clay???intermediate argillic???propylitic alteration zoning. Magmatic-steam alunite has higher ??34S (8.5??? to 23.2???) and generally lower ??18OSO4 (1.0 to 11.5???), ??18OOH (-3.4 to 5.9???), and ??D (-93 to -77???) values than predicted on the basis of data from similar occurrences. These data and supporting fluid-inclusion gas chemistry imply that the rate of vapor ascent for this

  11. Geochemistry and ore prospecting

    International Nuclear Information System (INIS)

    Le Caignec, R.

    1954-01-01

    Applied geochemistry is a new technique which helps the geologist in detecting ore deposits. Some deposits, even when they are covered with rather thick surface structures, form around these zones where the infinitesimal content of some elements of soils or waters is notably different. These 'anomalies' may be contemporaneous to the deposit-structure (primary dispersion) or may have occurred later (secondary dispersion). Various factors rule these anomalies: ore-stability, soil homogeneity, water conditions, topography, vegetation, etc... Applied geochemistry is in fact the study of analysis techniques of metal traces in soils as well as the geological interpretation of observed anomalies. This report gives practical data on sampling methods, yields, costs and also on special problems of uranium geochemistry. (author) [fr

  12. Proceedings of the 3. International symposium environmental geochemistry in tropical countries. Book of abstracts

    International Nuclear Information System (INIS)

    1999-01-01

    Theoretical and experimental papers are presented in these proceedings covering the following subjects: uranium mining and milling, geochemistry, land and water pollution, mineral wastes, iodine isotopes, gas chromatography, separation processes, environmental quality, qualitative and quantitative chemical analysis, rare earths, uranium isotopes, ground water, radionuclide migration, and sedimentary basins

  13. Juvenile helium in ancient rocks: II. U-He,K-Ar, Sm-Nd, and Rb-Sr systematics in the Monche Pluton. 3He/4He ratios frozen in uranium-free ultramafic rocks

    International Nuclear Information System (INIS)

    Tolstikhin, I.N.; Dokuchaeva, V.S.; Kamensky, I.L.; Amelin, Yu.V.

    1992-01-01

    The important geodynamic parameter, the 3 He/ 4 He ratio in rocks and fluids of the continental crust, is generally decreasing from the mantle values (≅ 10 -5 ) to the radiogenic ratio (≅ 10 -8 ) on the time scale of about 1 Ga or less. However, the ratios, observed in some ancient rocks and minerals, are much higher than the radiogenic value due to a preferential retention of trapped He, when compared with radiogenic helium and/or a low U/ 3 He ratio in a sample. The distribution of He, Ar, Nd, and Sr isotopes, K, Rb, Sm, and U in ultrabasic rocks, in rock-forming minerals, in ores from the 2.49 Ga Monche Pluton, and in basic rocks of the Main Range (the Kola Peninsula) enables one to distinguish sources of the rocks and trapped fluids and outline some peculiarities of petrogenetic and fluid processes. The initial values of var-epsilon Nd (T) = -0.9 ± 0.5 , 87 Sr/ 86 Sr(T) = 0.7021 ± 0.0002, for the 2.49 Ga Monche Pluton are rather similar to these for other layered intrusions of the Baltic Shield. They differ considerably from the model values for the depleted 2.5 Ga old mantle. The observed and rather different sources of 3 He and 4 He as well as the considerable constancy of their ratio in different minerals, separated from both the ultramafic rocks and gabbros, implies: (1) an intensive process of mixing between mantle and crustal components: a melt convection in the chamber may have occurred; (2) the two types of rocks could originate by crystallization differentiation of one and the same melt. Practically all 3 He and 4 He are concentrated in secondary amphiboles; hence the fluid which stimulated the metamorphic process was probably released from the ultramafite-bearing melt

  14. Geochemistry and mineralogy

    Energy Technology Data Exchange (ETDEWEB)

    Plecas, I.; Dimovic, S.; Orta, M.M.; Alba, M.D.; Alvero, R.; Becerro, A.I.; Castro, M.A.; Chain, P.; Escudero, A.; Naranjo, M.; Pavon, E.; Trillo, J.M.; Vejsada, J.; Vokal, A.; Zadvernyuk, H.P.; Fedorenko, Y.G.; Zlobenko, B.P.; Koromyslichenko, T.I.; Battaglia, S.; Cervelli, M.; Millot, R.; Girard, J.P.; Missana, T.; Garcia-Gutierrez, M.; Alonso, U.; Muurinen, A.; Carlsson, T.; Chain, P.; Alba, M.D.; Becerro, A.I.; Castro, M.A.; Escudero, A.; Gonzalez-Carrascosa, T.; Hurtado, S.; Pavon, E.; Villa, M.; Bourg, I.C.; Sposito, G.; Bourg, A.C.M.; Marques Fernandes, M.; Rabung, Th.; Dahn, R.; Baeyens, B.; Bradbury, M.H.; Breynaert, E.; Maes, A.; Bruggeman, C.; Maes, I.A.; Vancluysen, J.; Credoz, A.; Bildstein, O.; Jullien, M.; Raynal, J.; Petronin, J.C.; Trotignon, L.; Pokrovsky, O.; Jacquier, P.; Beaucaire, C.; Vuillaume, A.L.; Wittebroodt, Ch.; Ly, J.; Page, J.; Savoye, S.; Pitsch, H.; Jacques, D.; Wang, L.; Galunin, E.; Chain, P.; Alba, M.D.; Vidal, M.; Grandia, F.; Domenech, C.; Arcos, D.; Duro, L.; Bruno, J.; Andre, L.; Pauwels, H.; Azaroual, M.; Albrecht, A.; Romero, M.A.; Aerts, S.; Boven, P.; Van Geet, M.; Boever, P. de; Alonso, U.; Albarran, N.; Missana, T.; Garcia-Gutierrez, M.; Truche, L.; Berger, G.; Guillaume, D.; Jacquot, E.; Tournassat, Ch.; Lerouge, C.; Brendle, J.; Greneche, J.M.; Touzelet, St.; Blanc, Ph.; Gaucher, E.C.; Thoenen, T.; Klinkenberg, M.; Kaufhold, S.; Dohrmann, R.; Siegesmund, S.; Liu, D.J.; Bruggeman, C.; Maes, N.; Weber, T.; Trotignon, L.; Pozo, C.; Bildstein, O.; Combarieu, G. de; Frugier, P.; Menut, D

    2007-07-01

    This session gathers 52 articles (posters) dealing with: the influence of natural sorbents immobilization of spent ion exchange resins in cement; the chemical stability of rare-earth silicate; the mineralogical heterogeneity of Rokle bentonite and radionuclide adsorption: A case study for cesium; the rheological and sorption properties of clay-polymer composites; the clay mineral interactions with leachate solutions in landfills; the lithium isotope fractionation during adsorption onto mineral surfaces; the sorption of Sr{sup 2+} onto mixed smectite / illite clays; Eh and pH in the pore water of compacted bentonite; the chemical interaction of {sup 152}Eu with the clay barrier; the modeling of the acid-base surface chemistry of Montmorillonite; a time resolved laser fluorescence and X-ray absorption spectroscopy study of lanthanide/actinide sorption on clay minerals: influence of carbonate complexation; the structure elucidation and occurrence of Tc(IV) pyrogallol complexes; the geochemistry of Se(0) under boom clay conditions; an experimental and modelling study of pure secondary silicate minerals reactivity in geological CO{sub 2} sequestration conditions; an experimental evaluation of a retention model for major groundwater elements on the Tournemire argillite; modelling the long term interaction of cementitious pore water with Boom clay; the sorption-desorption of radionuclides and analogues in clays suitable for barriers; the modelling of the Redox evolution in the tunnel backfill of a high level nuclear waste repository; the reactivity of nitrates in the different storage compartments of type-b wastes; an investigation into the biodiversity of sulphate reducing bacteria in Boom clay; the colloid generation mechanisms from compacted bentonite under different geochemical conditions; the experimental reduction of aqueous sulphate by hydrogen in the context of the Callovo-Oxfordian argillite; cation exchanged Fe(II) and Sr as compared to other divalent cations

  15. Zircon Lu-Hf isotope systematics and U-Pb geochronology, whole-rock Sr-Nd isotopes and geochemistry of the early Jurassic Gokcedere pluton, Sakarya Zone-NE Turkey: a magmatic response to roll-back of the Paleo-Tethyan oceanic lithosphere

    Science.gov (United States)

    Karsli, Orhan; Dokuz, Abdurrahman; Kandemir, Raif

    2017-05-01

    The early Mesozoic was a critical era for the geodynamic evolution of the Sakarya Zone as transition from accretion to collision events in the region. However, its complex evolutionary history is still debated. To address this issue, we present new in situ zircon U-Pb ages and Lu-Hf isotope data, whole-rock Sr-Nd isotopes, and mineral chemistry and geochemistry data of plutonic rocks to better understand the magmatic processes. The Gokcedere pluton is mainly composed of gabbro and gabbroic diorite. LA-ICP-MS zircon U-Pb dating reveals that the pluton was emplaced in the early Jurassic (177 Ma). These gabbros and gabbroic diorites are characterized by relatively low SiO2 content of 47.09 to 57.15 wt% and high Mg# values varying from 46 to 75. The samples belong to the calc-alkaline series and exhibit a metaluminous I-type character. Moreover, they are slightly enriched in large ion lithophile elements (Rb, Ba, Th and K) and light rare earth elements and depleted in high field strength elements (Nb and Ti). Gabbroic rocks of the pluton have a depleted Sr-Nd isotopic composition, including low initial 87Sr/86Sr ranging from 0.705124 to 0.705599, relatively high ɛ Nd ( t) values varying from 0.1 to 3.5 and single-stage Nd model ages ( T DM1 = 0.65-0.95 Ga). In situ zircon analyses show that the rocks have variable and positive ɛ Hf ( t) values (4.6 to 13.5) and single-stage Hf model ages ( T DM1 = 0.30 to 0.65 Ga). Both the geochemical signature and Sr-Nd-Hf isotopic composition of the gabbroic rocks reveal that the magma of the studied rocks was formed by the partial melting of a depleted mantle wedge metasomatized by slab-derived fluids. The influence of slab fluids is mirrored by their trace-element characteristics. Trace-element modeling suggests that the primary magma was generated by a low and variable degree of partial melting ( 5-15%) of a depleted and young lithospheric mantle wedge consisting of phlogopite- and spinel-bearing lherzolite. Heat to melt the

  16. Proceedings of the 3. Brazilian Congress on Geochemistry; 1. Congress on Geochemistry from Portuguese Language Countries - Abstracts

    International Nuclear Information System (INIS)

    1991-01-01

    This congress presents topics about geochemistry, including litho-geochemistry, environmental geochemistry, hydro-geochemistry and surface geochemistry. Works on geochronology and nuclear methods in rocks and minerals are also described. (C.G.C.)

  17. Sediment Sources, Depositional Environment, and Diagenetic Alteration of the Marcellus Shale, Appalachian Basin, USA: Nd, Sr, Li and U Isotopic Constraints

    Science.gov (United States)

    Phan, T. T.; Capo, R. C.; Gardiner, J. B.; Stewart, B. W.

    2017-12-01

    The organic-rich Middle Devonian Marcellus Shale in the Appalachian Basin, eastern USA, is a major target of natural gas exploration. Constraints on local and regional sediment sources, depositional environments, and post-depositional processes are essential for understanding the evolution of the basin. In this study, multiple proxies, including trace metals, rare earth elements (REE), the Sm-Nd and Rb-Sr isotope systems, and U and Li isotopes were applied to bulk rocks and authigenic fractions of the Marcellus Shale and adjacent limestone/sandstone units from two locations separated by 400 km. The range of ɛNd values (-7.8 to -6.4 at 390 Ma) is consistent with a clastic sedimentary component derived from a well-mixed source of fluvial and eolian material of the Grenville orogenic belt. The Sm-Nd isotope system and bulk REE distributions appear to have been minimally affected by post-depositional processes, while the Rb-Sr isotope system shows evidence of limited post-depositional redistribution. While REE are primarily associated with silicate minerals (80-95%), REE patterns of sequentially extracted fractions reflect post-depositional alteration at the intergranular scale. Although the chemical index of alteration (CIA = 54 to 60) suggests the sediment source was not heavily weathered, Li isotope data are consistent with progressively increasing weathering of the source region during Marcellus Shale deposition. δ238U values in bulk shale and reduced phases (oxidizable fraction) are higher than those of modern seawater and upper crust. The isotopically heavy U accumulated in these authigenic phases can be explained by the precipitation of insoluble U in anoxic/euxinic bottom water. Unlike carbonate cement within the shale, the similarity between δ238U values and REE patterns of the limestone units and those of modern seawater indicates that the limestone formed under open ocean (oxic) conditions.

  18. Final results on the Jurassic-Cretaceous boundary in the Gresten Klippenbelt (Austria): Macro-, micro-, nannofossils, isotopes, geochemistry, susceptibility, gamma-log and palaeomagnetic data as environmental proxies of the early Penninic Ocean history

    Science.gov (United States)

    Lukeneder, A.; Halásová, E.; Kroh, A.; Mayrhofer, S.; Pruner, P.; Reháková, D.; Schnabl, P.; Sprovieri, M.

    2009-04-01

    -6 SI and the intensity of the natural remanent magnetization (NRM) varies between 31 and 615×10-6 A/m. The samples display a two- to three-component remanence. The average sampling density for the whole section was around two samples per 1 m of true thickness of limestone strata in these preliminary results. The next step of investigation will be to precisely determine the boundaries of magnetozones M19 and M20 including narrow reverse subzones with the high resolution sampling density for the whole section. Stable isotope data (C, O, Sr). High-resolution reconstruction of the carbon cycle, by isotope stratigraphy, is the key for drawing conclusions on the palaeooceanography of the Nutzhof area. The approach using oxygen isotope analysis, by constraining diagenesis impacts, will yield a picture of the Lower Cretaceous palaeoclimatology here. The investigations on istopes will be rigorously linked and networked with measurements and results of cyclostratigraphy and lithostratigraphy. C-istopes are extremely important calibration tools between ammonoids and magnetostratigraphy (Henning et al. 1999). Cyclostratigraphy is crucial in comparing the lithologic appearance of different units and the carbon isotope records. A detailed cyclostratigraphic reconstruction of the record will be carried out by comparing (1) the results obtained by time series analysis of the collected faunal and isotope proxy records with (2) the reconstructed lithologic cycle patterns of the studied sedimentary sections. A first-order floating cyclostratigraphy will be refined using a tentative calibration of the record to the available numerical solutions of the insolation curve. This approach should provide an absolute age for the different stratigraphic events recognised throughout the record. Gamma-log and Geochemistry. We conducted geochemical analyses of the carbonate, sulphur and organic carbon content in the limestones and marls of the different lithological units. The gamma log measures the

  19. The genetics of geochemistry

    OpenAIRE

    Croal, Laura R.; Gralnick, Jeffrey A.; Malasarn, Davin; Newman, Dianne K.

    2004-01-01

    Bacteria are remarkable in their metabolic diversity due to their ability to harvest energy from myriad oxidation and reduction reactions. In some cases, their metabolisms involve redox transformations of metal(loid)s, which lead to the precipitation, transformation, or dissolution of minerals. Microorganism/mineral interactions not only affect the geochemistry of modern environments, but may also have contributed to shaping the near-surface environment of the early Earth. For example, bacter...

  20. National uses and needs for separated stable isotopes in physics, chemistry, and geoscience research

    International Nuclear Information System (INIS)

    Zisman, M.S.

    1982-01-01

    Present uses of separated stable isotopes in the fields of physics, chemistry, and the geosciences have been surveyed to identify current supply problems and to determine future needs. Demand for separated isotopes remains strong, with 220 different nuclides having been used in the past three years. The largest needs, in terms of both quantity and variety of isotopes, are found in nuclear physics research. Current problems include a lack of availability of many nuclides, unsatisfactory enrichment of rare species, and prohibitively high costs for certain important isotopes. It is expected that demands for separated isotopes will remain roughly at present levels, although there will be a shift toward more requests for highly enriched rare isotopes. Significantly greater use will be made of neutron-rich nuclides below A = 100 for producing exotic ion beams at various accelerators. Use of transition metal nuclei for nuclear magnetic resonance spectroscopy will expand. In addition, calibration standards will be required for the newer techniques of radiological dating, such as the Sm/Nd and Lu/Hf methods, but in relatively small quantities. Most members of the research community would be willing to pay considerably more than they do now to maintain adequate supplies of stable isotopes

  1. National uses and needs for separated stable isotopes in physics, chemistry, and geoscience research

    Energy Technology Data Exchange (ETDEWEB)

    Zisman, M.S.

    1982-01-01

    Present uses of separated stable isotopes in the fields of physics, chemistry, and the geosciences have been surveyed to identify current supply problems and to determine future needs. Demand for separated isotopes remains strong, with 220 different nuclides having been used in the past three years. The largest needs, in terms of both quantity and variety of isotopes, are found in nuclear physics research. Current problems include a lack of availability of many nuclides, unsatisfactory enrichment of rare species, and prohibitively high costs for certain important isotopes. It is expected that demands for separated isotopes will remain roughly at present levels, although there will be a shift toward more requests for highly enriched rare isotopes. Significantly greater use will be made of neutron-rich nuclides below A = 100 for producing exotic ion beams at various accelerators. Use of transition metal nuclei for nuclear magnetic resonance spectroscopy will expand. In addition, calibration standards will be required for the newer techniques of radiological dating, such as the Sm/Nd and Lu/Hf methods, but in relatively small quantities. Most members of the research community would be willing to pay considerably more than they do now to maintain adequate supplies of stable isotopes.

  2. Geochemistry of impact glasses and target rocks from the Zhamanshin impact structure, Kazakhstan: Implications for mixing of target and impactor matter

    Czech Academy of Sciences Publication Activity Database

    Jonášová, Šárka; Ackerman, Lukáš; Žák, Karel; Skála, Roman; Ďurišová, Jana; Deutsch, A.; Magna, T.

    2016-01-01

    Roč. 190, 1 October (2016), s. 239-264 ISSN 0016-7037 R&D Projects: GA ČR GA13-22351S Institutional support: RVO:67985831 Keywords : impact glass * irghizites * geochemistry * meteoritic component * siderophile elements * osmium isotopes * Zhamanshin Subject RIV: DD - Geochemistry Impact factor: 4.609, year: 2016

  3. Study of the geochemistry of the cosmogenic isotope {sup 10}Be and the stable isotope {sup 9}Be in oceanic environment. Application to marine sediment dating; Etude de la geochimie de l`isotope cosmogenique {sup 10}Be et de son isotope stable {sup 9}Be en milieu oceanique. Application a la datation des sediments marins

    Energy Technology Data Exchange (ETDEWEB)

    Bourles, D

    1988-01-01

    The radioisotope {sup 10}Be is formed by spallation reactions in the atmosphere. It is transferred to the oceans in soluble form by precipitation and dry deposition. The stable isotope {sup 9}Be comes from erosion of soils and rocks in the Earth`s crust. It is transported by wind and rivers and introduced to the oceans probably in both soluble and insoluble form. {sup 9}Be was measured by atomic absorption spectrometry and {sup 10}Be by A.M.S. The distribution of {sup 10}Be and {sup 9}Be between each phase extracted and the {sup 10}Be/{sup 9}Be ratios associated were studied in recent marine sediments from Atlantic, Pacific, Indian oceans and Mediterranean sea. The results show that for beryllium the two essential constituent phases of marine sediments are: - the authigenic phase incorporates the soluble beryllium and the detritic phase. The {sup 10}Be/{sup 9}Be ratio associated with the authigenic fraction varies with location. This suggests that the residence time of beryllium in the soluble phase is lower or comparable to the mixing time of the oceans. The evolution with time of the authigenic {sup 10}Be/{sup 9}Be ratio is discussed.

  4. PETROCHEMISTRY, Pb ISOTOPE SYSTEMATICS, AND ...

    African Journals Online (AJOL)

    The petrology, geochemistry, geotectonic setting and common Pb isotope model ages for the granite gneisses in Ilesha schist belt have been studied and presented in this paper. These gneisses, apart from the normal rock-forming silicates, contain apatite, monazite, ilmenite and zircon in trace amounts. The occurrence of ...

  5. Constraints on the nature of the projectile using siderophile elements and triple-oxygen isotopes: Zhamanshin impact structure, Kazakhstan

    Czech Academy of Sciences Publication Activity Database

    Jonášová, Šárka; Ackerman, Lukáš; Žák, Karel; Skála, Roman; Magna, T.; Pack, A.; Deutsch, A.

    2016-01-01

    Roč. 51, SI, Supplement 1 (2016), A358-A358 ISSN 1086-9379. [Annual Meeting of the Meteoritical Society /79./. 07.08.2016-12.08.2016, Berlin] Institutional support: RVO:67985831 Keywords : impact glass * irghizites * geochemistry * meteoritic component * siderophile elements * osmium isotopes * triple-oxygen Isotopes * Zhamanshin Subject RIV: DD - Geochemistry

  6. Highly siderophile element geochemistry of peridotites and pyroxenites from Horní Bory, Bohemian Massif: Implications for HSE behaviour in subduction-related upper mantle

    Czech Academy of Sciences Publication Activity Database

    Ackerman, Lukáš; Pitcher, L.; Strnad, L.; Puchtel, I. S.; Jelínek, E.; Walker, R. J.; Rohovec, Jan

    2013-01-01

    Roč. 100, č. 1 (2013), s. 158-175 ISSN 0016-7037 R&D Projects: GA AV ČR KJB300130902 Institutional research plan: CEZ:AV0Z30130516 Institutional support: RVO:67985831 Keywords : alloy * high pressure * high temperature * igneous geochemistry * isotopic composition * mass balance * nappe * osmium isotope * peridotite * petrography * platinum group element * precipitation (chemistry) * pyroxenite * siderophile element * subduction * sulfide * upper mantle Subject RIV: DD - Geochemistry Impact factor: 4.250, year: 2013

  7. Lectures in isotope geology

    International Nuclear Information System (INIS)

    Jaeger, E.; Hunziker, J.C.

    1979-01-01

    Designed for a introductory course in geochronology and the geochemistry of stable isotopes, this text has been written by recognized experts in the field. Emphasis is on the interpretation and on applications, and examples of these are offered along with each technique. Extraterrestrial applications have been avoided and the treatment of pure experimentation has been kept at a minimum. This text will be appreciated by geologists who want to learn more about methods used in isotope geology, how they can be applied, and how to gauge their usefulness. (orig.) [de

  8. Geochemistry of natural technetium and plutonium

    International Nuclear Information System (INIS)

    Curtis, D.B.; Cappis, J.H.; Perrin, R.E.; Rokop, D.J.

    1987-01-01

    Technetium and plutonium in unprocessed nuclear reactor wastes are major concerns with regard to their containment in the geologic environment. Both nuclides have long half-lives; therefore, they will exist long after engineered barriers can be considered reliable. Consequently, strategies for the containment of these two elements depend on their retention in the geologic barrier until they have decayed to innocuous levels. Because these are the rarest elements in nature, there have been few direct observations of their geochemical behavior; predictions concerning their fate in the repository are based on properties that can be observed in the laboratory. The authors are attempting to complement the laboratory work by studying the geochemistry of natural plutonium and technetium. Ratios of anthropogenic to naturally occurring isotopes are discussed

  9. Further Sr and Nd isotopic results from peridotites of the Ronda Ultramafic Complex

    International Nuclear Information System (INIS)

    Reisberg, L.; Zindler, A.

    1989-01-01

    Clinopyroxenes derived from peridotites of the spinel and garnet facies of the Ronda Ultramafic Complex yield Sr and Nd isotopic ratios which extend the range of compositions found in the massif to values as depleted as 0.70205 for Sr and 0.51363 for Nd. Large-amplitude, short-wavelength isotopic variations are found to be uniquitous throughout the massif. In the garnet facies, some of these variations are shown to be produced by the tectonic disaggregation of mafic layers in an isotopically depleted peridotite matrix. Ages obtained from garnet-clinopyroxene Sm-Nd isochrons (about 22 m.y.) agree with previous determinations of the time of crustal emplacement. In the plagioclase facies, where the Sr and Nd isotopic compositions have been very strongly affected by recent cryptic metasomatism, detailed study of one sample reveals that intermineral Nd isotopic equilibrium exists between clinopyroxene, orthopyroxene, and plagioclase. This indicates that the metasomatism occurred at high temperatures, and thus probably within the mantle. A rough correlation between 143 Nd/ 144 Nd and 147 Sm/ 144 N, with an apparent 'age' of 1.3 b.y. and an initial ε Nd (0) value of +6.0, is observed among clinopyroxenes derived from river sediments from throughout the massif. This age is interpreted as the time that the massif left the convecting mantle and became incorporated into the sub-continental lithosphere. (orig.)

  10. Age of underground waters: isotopes contribution

    International Nuclear Information System (INIS)

    Chery, L.; Olive, Ph.

    2006-01-01

    Does water has an age? The age of underground waters can be the duration of their underground travel between their infiltration inside the ground and their captation at a spring or a drilled well. The isotopic geochemistry comes to the support of classical geochemistry to estimate these residence times. Radio-isotopes, like tritium for young waters or carbon 14 for old waters, are used as chronometers to interpret the recharge ways, the flow mechanisms and the residence times of underground waters. Their use is presented in this article with some theoretical recalls and some examples of application. (J.S.)

  11. Thermochronology and geochemistry of the Pan-African basement below the Sab'atayn Basin, Yemen

    Science.gov (United States)

    Veeningen, Resi; Rice, A. Hugh N.; Schneider, David A.; Grasemann, Bernhard

    2015-02-01

    Three important lithologies occur in two drill wells from the Pan-African basement underlying the Mesozoic Sab'atayn Basin, in a previously undocumented area of the Pan-African, 83 and 90 km NE of known exposures in Yemen. Cores from well 1 include amphibolite, with basaltic to andesitic compositions, affected by crustal contamination during emplacement into a thickened crust. Deeper in the well, an unfoliated dark red monzogranite has a U-Pb zircon age of 628.8 ± 3.1 Ma and a Rb-Sr biotite cooling age of 591.6 ± 5.8 Ma (∼300 °C). Regional constraints suggest emplacement in a transitional tectonic setting with compressional terrane amalgamation followed by extensional collapse. Sm-Nd isotope analysis yields a TDM model age of 1.24 Ga with negative εNd values, suggesting the monzogranite is part of the Al Bayda island arc terrane. Cores from well 2 contains a weakly deformed, massive (unbedded) medium grey meta-arkose exhibiting essentially no geochemical signature of weathering and with an almost pure dacitic composition. This rock may have been directly derived from an (extrusive) granitoid that was emplaced prior to, or during terrane amalgamation. A (U-Th-Sm)/He zircon age of 156 ± 14 Ma constrains the time of basement cooling to ∼180 °C, synchronous with basin formation. These lithologies provide new insights in the development of the Pan-African basement of Yemen, extending our knowledge of the nearby surface geology to the subsurface.

  12. Radiogenic Isotopes in Weathering and Hydrology

    Science.gov (United States)

    Blum, J. D.; Erel, Y.

    2003-12-01

    as on the observation that radiogenic isotopes are sometimes preferentially released compared to nonradiogenic isotopes of the same element during acid leaching of rocks ( Hart and Tilton, 1966; Silver et al., 1984; Erel et al., 1991). A major finding of these investigations was that weathering often results in anomalously young Rb-Sr isochron ages, and discordant Pb-Pb ages. Rubidium is generally retained relative to strontium in whole-rock samples, and in some cases radiogenic strontium and lead are lost preferentially to common strontium and lead from weathered minerals.The most widely utilized of these isotopic systems is Rb-Sr, followed by U-Pb. The K-Ar system is not directly applicable to most studies of rock-water interaction, because argon is a noble gas, and upon release during mineral weathering mixes with atmospheric argon, limiting its usefulness as a tracer in most weathering applications. Argon and other noble gas isotopes have, however, found important applications in hydrology (see Chapter 5.15). Three other isotopic systems commonly used in geochronology and petrology include Sm-Nd, Lu-Hf, and Re-Os. These parent and daughter elements are in very low abundance and concentrated in trace mineral phases. Sm-Nd, Lu-Hf, and Re-Os have been used in a few weathering studies but have not been utilized extensively in investigations of weathering and hydrology.The decay of 87Rb to 87Sr has a half-life of 48.8 Gyr, and this radioactive decay results in natural variability in the 87Sr/86Sr ratio in rubidium-bearing minerals (e.g., Blum, 1995). The trace elements rubidium and strontium are geochemically similar to the major elements potassium and calcium, respectively. Therefore, minerals with high K/Ca ratios develop high 87Sr/86Sr ratios over geologic timescales. Once released into the hydrosphere, strontium retains its isotopic composition without significant fractionation by geochemical or biological processes, and is therefore a good tracer for sources and

  13. Geochemistry of the mantle beneath the Rodriguez Triple Junction and the South-East Indian Ridge

    International Nuclear Information System (INIS)

    Michard, A.; Montigny, R.; Schlich, R.

    1986-01-01

    Rare earth element abundances and SR, Nd, Pb isotope compositions have been measured on zero-age dredge samples from the Rodriguez Triple Junction (RTJ) and the South-East Indian Ridge (SEIR). Along the SEIR, the geochemical ''halo'' of the St. Paul hot spot has a half-width of about 400 km and the data may be fairly well accounted for by a binary mixing between an Indian MORB-type component ( 87 Sr/ 86 Sr=0.7028, 143 Nd/ 144 Nd=0.51304, 206 Pb/ 204 Pb=17.8) and the plume type St. Paul component (0.7036, 0.5129 and 18.7 respectively). The alignment of the lead isotope data is particularly good with age of 1.95+-0.13 Ga and Th/U source value of 3.94. One sample dredged on the ridge 60 km southeast of St. Paul bears a definite Kertguelen isotopic signature. The RTJ has distinctive geochemical properties which contrast with those of the adjacent ridge segments. Low 206 Pb/ 204 Pb ratios which plots to the left of the geochron, rather high 208 Pb/ 204 Pb and 87 Sr/ 86 Sr ratios (17.4, 37.4, and 0.7031 respectively) a striking isotopic homogeneity, and variable LRE/HREE fractionation with (LA/S)sub(N) 0.3-0.8 make this triple junction an anomalous site. The geochemical properties of the Indian Ocean basalts have been examined using a three-component mantle model involving (a) a normal MORB-type source though to represent the depleted upper mantle matrix, (b) an OIB-type source of uncertain parentage (recycled oceanic crust), and (c) a component with low μ, Low Sm/Nd, high Rb/Sr (time-averaged value) which is tentatively assigned to ancient hydrothermal and abyssal sediments recycled in the mantle. The high 208 Pb/ 204 Pb and 87 Sr/ 86 Sr ratios typical of the Dupal anomaly are likely due to the widespread distribution of this latter component in the basalt source from this area, including that for MORBs. (orig.)

  14. Geochemistry of the mantle beneath the Rodriguez Triple Junction and the South-East Indian Ridge

    Science.gov (United States)

    Michard, A.; Montigny, R.; Schlich, R.

    1986-05-01

    Rare earth element abundances and Sr, Nd. Pb isotope compositions have been measured on zero-age dredge samples from the Rodriguez Triple Junction (RTJ) and the South-East Indian Ridge (SEIR), Along the SEIR. the geochemical "halo" of the St. Paul hot spot has a half-width of about 400 km and the data may be fairly well accounted for by a binary mixing between an Indian MORB-type component ( 87Sr/ 86Sr = 0.7028. 143Nd/ 144Nd = 0.51304. 206Pb/ 204Pb = 17.8) and the plume-type St. Paul component (0.7036, 0.5129, and 18.7 respectively). The alignment of the lead isotope data is particularly good with an apparent age of 1.95 ± 0.13 Ga and Th/U source value of 3.94. One sample dredged on the ridge 60 km southeast of St. Paul bears a definite Kerguelen isotopic signature. The RTJ has distinctive geochemical properties which contrast with those of the adjacent ridge segments. Low 206Pb/ 204Pb ratios which plots to the left of the geochron, rather high 208Pb/ 204Pb and 87Sr/ 87Sr ratios (17.4. 37.4, and 0.7031 respectively), a striking isotopic homogeneity, and variable LREE/HREE fractionation with (La/Sm) N, = 0.3-0.8 make this triple junction an anomalous site. The geochemical properties of the Indian Ocean basats have been examined using a three-component mantle model involving (a) a normal MORB-type source though to represent the depleted upper mantle matrix, (b) an OIB-type source of uncertain parentage (recycled oceanic crust?), and (c) a component with low μ. low Sm/Nd. high Rb/Sr (time-averaged value) which is tentatively assigned to ancient hydrothermal and abyssal sediments recycled in the mantle. The high 208Pb/ 204Pb and 87Sr/ 86Sr ratios typical of the Dupal anomaly are likely due to the widespread distribution of this latter component in the basalt source from this area. including that for MORBs.

  15. Geochemistry, age and strontium isotope composition of late tertiary and quaternary basalts and andesites in western Nevada and their relation to geothermal potential. Final report, October 1, 1982-December 31, 1983

    Energy Technology Data Exchange (ETDEWEB)

    Fultz, L.A.; Bell, E.J.; Trexler, D.T.

    1984-01-01

    This research was undertaken to characterize the late Cenozoic volcanic rocks associated with active geothermal systems in west-central Nevada. Petrographic and microprobe, geochemical and isotopic analysis and age dating techniques were used to characterize these young volcanic rocks. These data were combined with the limited data previously reported in the literature on these same volcanic areas to interpret their petrogenesis. The overall characterization resulted from integrating the petrogenesis with a structural-tectonic model of the region. Potassium-argon isotopic ages ranging up to 14 million years were determined for eight localities within the Reno 1 x 2/sup 0/ study region. These ages are consistent with the morphology of the volcanic landforms, the active geothermal systems associated with them, and with other isotopic ages reported in the literature for these and similar rocks within the study region. Petrographic analysis of hand specimens and thin-sections indicated mineralogic assemblages of the respective rock types and specific mineral textures and phenocryst compositions and characteristics. These identifications were further substantiated by microprobe analysis of selected phenocrysts and groundmass phases. Classification of the respective rock types was also based on chemical composition and normative calculations using the program PETCAL. Basaltic andesites are identified and described for Steamboat Hills, Table Mountain, Silver Springs, Churchill Butte, Cleaver Peak, Desert Peak and Carson City sites.

  16. A review of volatile compounds in tektites, and carbon content and isotopic composition of moldavite glass

    Czech Academy of Sciences Publication Activity Database

    Žák, Karel; Skála, Roman; Řanda, Zdeněk; Mizera, Jiří

    2012-01-01

    Roč. 47, č. 6 (2012), s. 1010-1028 ISSN 1086-9379 R&D Projects: GA ČR GA205/09/0991 Institutional research plan: CEZ:AV0Z30130516; CEZ:AV0Z10480505 Keywords : moldavites * geochemistry * ries * carbon stable isotopes * moldavites (Germany) Subject RIV: DD - Geochemistry Impact factor: 2.800, year: 2012

  17. SRP baseline hydrogeologic investigation: Aquifer characterization. Groundwater geochemistry of the Savannah River Site and vicinity

    Energy Technology Data Exchange (ETDEWEB)

    Strom, R.N.; Kaback, D.S.

    1992-03-31

    An investigation of the mineralogy and chemistry of the principal hydrogeologic units and the geochemistry of the water in the principal aquifers at Savannah River Site (SRS) was undertaken as part of the Baseline Hydrogeologic Investigation. This investigation was conducted to provide background data for future site studies and reports and to provide a site-wide interpretation of the geology and geochemistry of the Coastal Plain Hydrostratigraphic province. Ground water samples were analyzed for major cations and anions, minor and trace elements, gross alpha and beta, tritium, stable isotopes of hydrogen, oxygen, and carbon, and carbon-14. Sediments from the well borings were analyzed for mineralogy and major and minor elements.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2010-01-15

    Isotopic data ({delta} 18 O, {delta} D) from fluids from production wells at the Los Humeros, Pue., geothermal field were analyzed to investigate the possible origin of these fluids and the dominant processes of the reservoir at its initial state. According to pre-exploitation data, it is suggested the Los Humeros reservoir fluids are made of a mixture of meteoric water of very light isotopic composition (paleo-fluids) and andesitic water. The relationship {delta} D vs {delta} 18 O from pre-exploitation data indicates the produced fluids are composed of a mixture of (at least) two fluids with distinct isotopic compositions. At the more enriched end of the mixing relationship are the isotopic compositions of the wells H-23 and H-18 (located in the southern area of the field), while the lighter fluids were found in well H-16 (originally) and then in well H-16 (repaired). It was found that the liquid phases of deep wells are more enriched in {delta} 18 O while the shallow wells present lower values, suggesting a convection process at the initial state. Based on this isotopic profile, it is considered that even the production depths of the wells H-1, H-12 and H-16 (repaired) are just about the same, but their respective isotopic compositions are quite different. The {delta} 18 O value for well H-16 (repaired) seems to be that of condensate steam, while the corresponding values for wells H-1 and H-12 fall within the value interval of the deep wells (H-23). This suggests wells H-1 and H-12 are collecting very deep fluids enriched in {delta} 18 O. These results could be useful in creating a conceptual model of the reservoir. [Spanish] Se analizaron datos isotopicos ({delta}18 O, {delta}D) de los fluidos de pozos productores del campo geotermico de Los Humeros, Pue., para investigar el posible origen de los fluidos asi como los procesos dominantes del yacimiento en su estado inicial. De acuerdo con datos previos a la explotacion, se plantea que los fluidos del yacimiento

  19. Methane clumped isotopes: Progress and potential for a new isotopic tracer

    Energy Technology Data Exchange (ETDEWEB)

    Douglas, Peter M. J.; Stolper, Daniel A.; Eiler, John M.; Sessions, Alex L.; Lawson, Michael; Shuai, Yanhua; Bishop, Andrew; Podlaha, Olaf G.; Ferreira, Alexandre A.; Santos Neto, Eugenio V.; Niemann, Martin; Steen, Arne S.; Huang, Ling; Chimiak, Laura; Valentine, David L.; Fiebig, Jens; Luhmann, Andrew J.; Seyfried, William E.; Etiope, Giuseppe; Schoell, Martin; Inskeep, William P.; Moran, James J.; Kitchen, Nami

    2017-11-01

    The isotopic composition of methane is of longstanding geochemical interest, with important implications for understanding hydrocarbon systems, atmospheric greenhouse gas concentrations, the global carbon cycle, and life in extreme environments. Recent analytical developments focusing on multiply substituted isotopologues (‘clumped isotopes’) are opening a potentially valuable new window into methane geochemistry. When methane forms in internal isotopic equilibrium, clumped isotopes can provide a direct record of formation temperature, making this property particularly valuable for identifying different methane origins. However, it has also become clear that in certain settings methane clumped isotope measurements record kinetic rather than equilibrium isotope effects. Here we present a substantially expanded dataset of methane clumped isotope analyses, and provide a synthesis of the current interpretive framework for this parameter. We review different processes affecting methane clumped isotope compositions, describe the relationships between conventional isotope and clumped isotope data, and summarize the types of information that this measurement can provide in different Earth and planetary environments.

  20. Nd-isotopes in selected mantle-derived rocks and minerals and their implications for mantle evolution

    Science.gov (United States)

    Basu, A.R.; Tatsumoto, M.

    1980-01-01

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

  1. Isotope characteristics of the sulphide-bearing sequence of the areachap group in the Boksputs area, North-West Cape

    International Nuclear Information System (INIS)

    Cilliers, F.H.

    1987-06-01

    The Boksputs stratiform sulphide deposit is situated in the eastern marginal zone of the Namaqua Province, South Africa, within the Boksputs Formation (previously termed Jannelsepan Formation). Pyrite, chalcopyrite and sphalerite are the most abundant minerals in the disseminated and thinly banded ore. The sulphide mineralization and host rocks have been deformed by at least four phases of folding followed by shearing and faulting. Major and trace element abundances (including REE), U-Pb and Sm-Nd isotope systematics indicate that changes owing to metamorphism are essentially isochemical in the amphibolite, which was derived from a mantle source. U-Pb isotope analysis were carried out on 24 amphibolite, 6 gneiss, 6 quartz-monzodiorite and 7 pyrite samples while Sm-Nd isotope analyses were performed on 6 amphibolite samples. A Pb-Pb isochron age of 1665 ± 140 Ma for the amphibolite samples indicates that the metavolcanic succession was extruded or emplaced before the Namaqua tectogenesis. The 1271 ± 53 Ma isochron age obtained for the gneiss samples is thus interpreted as a reset age, reflecting the Namaqualand metamorphic episode. It is proposed that the Boksputs mineralization like the Prieska Cu-Zn ore body, Areachap ore and Kielder sulphides, formed approximately 1500 to 1600 Ma ago as a syngenetic exhalative deposit, in a tectonic environment dominated by mantle derived tholeiitic volcanism with contemporaneous sedimentation. It is suggested that the hydrothermal fluid responsible for mineralization originated from a primary source, which must have been homogeneous, with respect to lead isotopic composition, over a large distance. The diversity of the volcano-sedimentary successions below the different ore bodies and overall similarity in Pb isotopic character, negates the possibility that the metals were leached from these rocks and a source related to a deep seated magma of mantle origin is proposed. It is concluded that Pb isotope systematics can be used

  2. Fundamental studies in isotope chemistry. Progress report, 1 August 1981-1 August 1982

    International Nuclear Information System (INIS)

    Bigeleisen, J.

    1982-01-01

    This research program is concerned with isotope chemistry and its applications. A summary of isotope separation activities during the past 5 years is included. Isotope effects are used as probes for chemical reactions, geochemistry, meteorology, and molecular biology, and this report also summarizes progress made in this area

  3. petrography, compositional characteristics and stable isotope ...

    African Journals Online (AJOL)

    PROF EKWUEME

    Subsurface samples of the predominantly carbonate Ewekoro Formation, obtained from Ibese core hole within the Dahomey basin were used in this study. Investigations entail petrographic, elemental composition as well as stable isotopes (carbon and oxygen) geochemistry in order to deduce the different microfacies and ...

  4. Organic geochemistry of Czech amber

    Czech Academy of Sciences Publication Activity Database

    Havelcová, Martina; Sýkorová, Ivana; Mach, K.; Dvořák, Z.

    2015-01-01

    Roč. 11, č. 1 (2015), s. 146 ISSN 1336-7242. [Zjazd chemikov /67./. 07.09.2015-11.09.2015, Horný Smokovec] R&D Projects: GA ČR(CZ) GA13-18482S Institutional research plan: CEZ:AV0Z30460519 Keywords : fossil resin * amber * resinite Subject RIV: DD - Geochemistry

  5. Molecular environmental geochemistry

    Science.gov (United States)

    O'Day, Peggy A.

    1999-05-01

    The chemistry, mobility, and bioavailability of contaminant species in the natural environment are controlled by reactions that occur in and among solid, aqueous, and gas phases. These reactions are varied and complex, involving changes in chemical form and mass transfer among inorganic, organic, and biochemical species. The field of molecular environmental geochemistry seeks to apply spectroscopic and microscopic probes to the mechanistic understanding of environmentally relevant chemical processes, particularly those involving contaminants and Earth materials. In general, empirical geochemical models have been shown to lack uniqueness and adequate predictive capability, even in relatively simple systems. Molecular geochemical tools, when coupled with macroscopic measurements, can provide the level of chemical detail required for the credible extrapolation of contaminant reactivity and bioavailability over ranges of temperature, pressure, and composition. This review focuses on recent advances in the understanding of molecular chemistry and reaction mechanisms at mineral surfaces and mineral-fluid interfaces spurred by the application of new spectroscopies and microscopies. These methods, such as synchrotron X-ray absorption and scattering techniques, vibrational and resonance spectroscopies, and scanning probe microscopies, provide direct chemical information that can elucidate molecular mechanisms, including element speciation, ligand coordination and oxidation state, structural arrangement and crystallinity on different scales, and physical morphology and topography of surfaces. Nonvacuum techniques that allow examination of reactions in situ (i.e., with water or fluids present) and in real time provide direct links between molecular structure and reactivity and measurements of kinetic rates or thermodynamic properties. Applications of these diverse probes to laboratory model systems have provided fundamental insight into inorganic and organic reactions at

  6. The origin of an oceanic plateau: Isotope geochemistry (Sr, Nd, Pb and Hf) of volcanic rocks from IODP Site U1347 and ODP Site 1213 (Hf data) on the Shatsky Rise (Northwest Pacific)

    Science.gov (United States)

    Heydolph, K.; Geldmacher, J.; Hoernle, K.

    2011-12-01

    K.HEYDOLPH1*, J.GELDMACHER2, 1 ,K.HOERNLE1 1IFM-GEOMAR, Wischhofstr. 1-3. D-24148 Kiel, Germany, (*correspondence: kheydolph@ifm-geomar.de) 2 Integrated Ocean Drilling Program, Texas A&M University, 1000 Discovery Drive, College Station, Texas 77845-9547 (geldmacher@iodp.tamu.edu) The submarine Shatsky Rise plateau, a unique large igneous province (LIP) in the northwest Pacific Ocean ca. 1500 km east of Japan, is the only large intraoceanic plateau, which formed during the Late Jurassic to Early Cretaceous at a time period with numerous reversals of the Earth's magnetic field. These magnetic reversals combined with bathymetric data allow a detailed reconstruction of the tectonic history. Accordingly the three main volcanic edifices Tamu, Ori and Shirshov massifs formed by massive volcanism during a short time span along a southwest - northeast trending, rapidly spreading triple junction. Therefore, the magnetic and bathymetric data suggest that the Shatsky Rise formed through the interaction of a mantle plume head with a ridge [1, 2]. We present new Sr, Nd and Pb (double spike) and for the first time Hf isotope data from volcanic rocks of relatively fresh basaltic lava flows from recent IODP Exp. 324 Site U1347 and ODP Leg 198 Site 1213 (Hf data) both located on Tamu massif the southernmost (oldest) volcanic edifice of Shtasky Rise. Initial 176Hf/177Hf and 143Nd/144Nd isotopic compositions are fairly uniform throughout the entire holes ranging between 0.283076 to 0.283100 and 0.512903 to 0.512981 respectively, showing neither distinct MORB nor intraplate (plume) affinity. Relatively unradiogenic 87Sr/86Sr data ranging from 0.70276 to 0.70296 mostly overlaps with Pacific MORB like values. In a Nd vs Hf isotope plot they form a tight cluster at the edge of the Pacific MORB field below the present-day Hf-Nd mantle array. Although initial Pb double spike 206Pb/204Pb and 208Pb/204Pb isotopic compositions for Site U1347 range from 18.13 to 18.46 and 37.71 to 37

  7. Cold seeps in Monterey Bay, California: Geochemistry of pore waters and relationship to benthic foraminiferal calcite

    Energy Technology Data Exchange (ETDEWEB)

    Gieskes, Joris, E-mail: jgieskes@ucsd.edu [Scripps Institution of Oceanography, IOD-0208, 9500 Gilman Drive, La Jolla, CA 92093-0208 (United States); Rathburn, Anthony E. [Scripps Institution of Oceanography, IOD-0208, 9500 Gilman Drive, La Jolla, CA 92093-0208 (United States)] [Indiana State University, Department of Earth and Environmental Systems, Terre Haute, IN 47809 (United States); Martin, Jonathan B. [University of Florida, Department of Geological Sciences, Gainesville, FL 32611-2120 (United States); Perez, M. Elena [Indiana State University, Department of Earth and Environmental Systems, Terre Haute, IN 47809 (United States)] [The Natural History Museum, Department of Palaeontology, Cromwell Road, London SW7 5BD (United Kingdom); Mahn, Chris [Scripps Institution of Oceanography, IOD-0208, 9500 Gilman Drive, La Jolla, CA 92093-0208 (United States); Bernhard, Joan M. [Woods Hole Oceanographic Institution, Geology and Geophysics Department, MS52, Woods Hole, MA 02543 (United States); Day, Shelley [University of Florida, Department of Geological Sciences, Gainesville, FL 32611-2120 (United States)

    2011-05-15

    Highlights: > We describe the geochemistry of pore waters in the Clam Flats area of Monterey Bay. > The geochemical data are compared with the {delta}{sup 13}C chemistry of benthic foraminifera. > Living foraminifera indicate little effects of pore water low {delta}{sup 13}C (DIC) in the clam bed. > This phenomenon and its implications are discussed in detail. > Implications with regards to paleo-methane seepage are discussed. - Abstract: An extensive geochemical and biogeochemical examination of CH{sub 4} seeps in the Clam Flats area of Monterey Bay provides insight into the character of relationships between seep geochemistry and benthic foraminiferal geochemistry. The area is characterized by sulfide-rich fluids. Sulfide increases are associated with large increases in alkalinity, as well as small decreases in dissolved Ca and Mg. In addition, only small increases in NH{sub 4} are observed, but values of {delta}{sup 13}C of dissolved inorganic C are as low as -60 per mille at shallow depths (<3 cm). These observations indicate that all these processes are related to the bacterial oxidation of CH{sub 4}, which is transported upward by slow seepage of pore fluids. The geochemistry of the pore fluids should be relevant to the geochemistry of the carbonate tests of living and dead foraminifera. However, a profound disequilibrium of approximately an order of magnitude occurs between the {delta}{sup 13}C values of stained (cytoplasm-containing) foraminiferal carbonate and the C isotope values of ambient pore water dissolved inorganic C. Reasons are unclear for this isotopic disequilibrium, but have important implications for interpretations of foraminiferal carbonate as a paleoenvironmental proxy. Much fine scale work is needed to fully understand the relationships between the biogeochemistry of benthic foraminifera and the geochemistry of the pore waters where they live.

  8. Cold seeps in Monterey Bay, California: Geochemistry of pore waters and relationship to benthic foraminiferal calcite

    International Nuclear Information System (INIS)

    Gieskes, Joris; Rathburn, Anthony E.; Martin, Jonathan B.; Perez, M. Elena; Mahn, Chris; Bernhard, Joan M.; Day, Shelley

    2011-01-01

    Highlights: → We describe the geochemistry of pore waters in the Clam Flats area of Monterey Bay. → The geochemical data are compared with the δ 13 C chemistry of benthic foraminifera. → Living foraminifera indicate little effects of pore water low δ 13 C (DIC) in the clam bed. → This phenomenon and its implications are discussed in detail. → Implications with regards to paleo-methane seepage are discussed. - Abstract: An extensive geochemical and biogeochemical examination of CH 4 seeps in the Clam Flats area of Monterey Bay provides insight into the character of relationships between seep geochemistry and benthic foraminiferal geochemistry. The area is characterized by sulfide-rich fluids. Sulfide increases are associated with large increases in alkalinity, as well as small decreases in dissolved Ca and Mg. In addition, only small increases in NH 4 are observed, but values of δ 13 C of dissolved inorganic C are as low as -60 per mille at shallow depths ( 4 , which is transported upward by slow seepage of pore fluids. The geochemistry of the pore fluids should be relevant to the geochemistry of the carbonate tests of living and dead foraminifera. However, a profound disequilibrium of approximately an order of magnitude occurs between the δ 13 C values of stained (cytoplasm-containing) foraminiferal carbonate and the C isotope values of ambient pore water dissolved inorganic C. Reasons are unclear for this isotopic disequilibrium, but have important implications for interpretations of foraminiferal carbonate as a paleoenvironmental proxy. Much fine scale work is needed to fully understand the relationships between the biogeochemistry of benthic foraminifera and the geochemistry of the pore waters where they live.

  9. Petrogenesis and geodynamic implications of Ediacaran highly fractionated A-type granitoids in the north Arabian-Nubian Shield (Egypt): Constraints from whole-rock geochemistry and Sr-Nd isotopes

    Science.gov (United States)

    Sami, Mabrouk; Ntaflos, Theodoros; Farahat, Esam S.; Mohamed, Haroun A.; Hauzenberger, Christoph; Ahmed, Awaad F.

    2018-04-01

    Mineral chemistry, whole-rock geochemical and Sr-Nd isotopic data are reported for the Abu-Diab granitoids in the northern Arabian-Nubian Shield (ANS) of Egypt, to investigate their petrogenesis and geodynamic significance. Gabal Abu-Diab constitute a multiphase pluton, consisting largely of two-mica granites (TMGs) enclosing microgranular enclaves and intruded by garnet bearing muscovite granites (GMGs) and muscovite granites (MGs). The granitoids are weakly peraluminous (A/CNK = 1.01-1.12) and show high SiO2 (>72.9 wt%) and alkali (K2O + Na2O = 8.60-9.13) contents. The geochemical features show that they are post-collisional and highly fractionated A-type granitoids. Compared to their host TMGs, the microgranular enclaves are strongly peraluminous (A/CNK = 1.18-1.24) with lower SiO2 and higher abundances of trace elements. The TMGs are depleted in Ba, Nb, P and Ti and are enriched in LREEs relative to HREEs with weakly negative Eu anomalies (Eu/Eu* = 0.45-0.64). In contrast, the GMGs and MGs are extremely depleted in Ba, Sr and Ti and have tetrad-type REE patterns (TE1-3 = 1.1-1.3) with strongly pronounced negative Eu anomalies (Eu/Eu* = 0.03-0.26), similar to rare metals bearing granites. The Ediacaran (585 ± 24 Ma) TMGs, are characterized by restricted and relatively low initial 87Sr/86Sr ratios (0.70337-0.70382) that suggests their derivation from a depleted mantle source, with little contamination from the older continental crust. In contrast, the GMGs and MGs have extremely high 87Rb/86Sr and 87Sr/86Sr ratios that reflect the disturbance of the Rb-Sr isotopic system and may give an indication for magmatic-fluid interaction. However, all the granitoids display positive εNd(t) (4.41-6.57) and depleted mantle model ages TDM2 between 777 and 956 Ma, which indicate their derivation from a Neoproterozoic juvenile magma sources and preclude the occurrence of pre-Neoproterozoic crustal rocks in the ANS. The microgranular enclaves represent globules of hot mafic

  10. Geochronology, geochemistry, and Sr-Nd-Pb-Hf isotopes of the Zhunsujihua granitoid intrusions associated with the molybdenum deposit, northern Inner Mongolia, China: implications for petrogenesis and tectonic setting

    Science.gov (United States)

    Zhang, Xiaojun; Lentz, David R.; Yao, Chunliang; Liu, Rui; Yang, Zhen; Mei, Yanxiong; Fan, Xianwang; Huang, Fei; Qin, Ying; Zhang, Kun; Zhang, Zhenfei

    2018-03-01

    The Zhunsujihua porphyry molybdenum deposit, located in northern Inner Mongolia of China that belongs to Central-Asian Orogenic Belt (CAOB), is the only Mo deposit formed in the late Carboniferous in this area so far. Its mineralization is mainly restricted to the Zhunsujihua granitoid intrusions, which are composed of the main granodiorite (GD) and crosscutting, virtually coeval minor syn-ore leucogranite (LG) and diorite porphyry (DP) dykes. LA-ICP-MS zircon U-Pb dating yields crystallization ages of 300.0 ± 2.0, 299.3 ± 2.0, and 299.0 ± 2.6 Ma for the GD, LG, and DP, respectively. The major and trace element lithogeochemical data show that the GD and LG are metaluminous to weakly peraluminous, high-K calc-alkaline series with I-type granite characteristics, strongly oxidized, with low concentrations of Ba, Nb, Sr, P, and Ti and elevated K and Rb contents, indicating typical arc magmatic features. The LG is a product derived by extensive fractional crystallization of a parental magma similar to the GD as evident from the lower Eu/Eu*, Nb/Ta, Zr/Hf, and T Zr. The moderately altered DP exhibits high concentrations of K, Rb, Cs, LREE, Y, and low Sr/Y, with a positive ɛ Nd (300 Ma), which indicates a mantle or juvenile source associated with an arc setting. The Sr-Nd-Hf isotope data show low I Sr (0.70406-0.70461) and moderate ɛ Nd (300 Ma) (-0.9 to 1.5) for the GD and LG, and relatively high ɛ Hf (300 Ma) values (-3.6 to +11.2) for the GD, suggesting the magma mainly originated from the juvenile lower crust that was derived from depleted mantle, with a minor component of ancient continental crust. Lead isotope data have characteristics of a lower crust source with minor contamination by upper crustal material. Combined with previous research, the Zhunsujihua granitoid intrusions developed in an intracontinental volcanic arc (Uliastai) associated with northward subduction of the Paleo-Asian Ocean plate during late Carboniferous to early Permian; this suggests

  11. Elemental and Sr-Nd isotopic geochemistry of Cretaceous to Early Paleogene granites and volcanic rocks in the Sikhote-Alin Orogenic Belt (Russian Far East): implications for the regional tectonic evolution

    Science.gov (United States)

    Zhao, Pan; Jahn, Bor-ming; Xu, Bei

    2017-09-01

    The Sikhote-Alin Orogenic Belt in Russian Far East is an important Late Mesozoic to Early Cenozoic accretionary orogen related to the subduction of the Paleo-Pacific Plate. This belt was generated by successive accretion of terranes made of accretionary prisms, turbidite basins and island arcs to the continental margin of northeastern Asia (represented by the Bureya-Jiamusi-Khanka Block) from Jurassic to Late Cretaceous. In order to study the tectonic and crustal evolution of this orogenic belt, we carried out zircon U-Pb dating, and whole-rock elemental and Sr-Nd isotopic analyses on granites and volcanic rocks from the Primorye region of southern Sikhote-Alin. Zircon dating revealed three episodes of granitoid emplacement: Permian, Early Cretaceous and Late Cretaceous to Early Paleogene. Felsic volcanic rocks (mainly rhyolite, dacite and ignimbrite) that overlay all tectonostratigraphic terranes were erupted during 80-57 Ma, postdating the accretionary process in the Sikhote-Alin belt. The Cretaceous-Paleogene magmatism represents the most intense tectonothermal event in the Sikhote-Alin belt. Whole-rock major and trace elemental data show arc-like affinity for granitoids and volcanic rocks, indicating that they were likely generated in a supra-subduction setting. Their initial 87Sr/86Sr ratios range from 0.7048 to 0.7114, and εNd(t) values vary from +1.7 to -3.8 (mostly < 0). Thus, the elemental and Sr-Nd isotopic data suggest that the felsic magmas were generated by partial melting of source rocks comprising mantle-derived juvenile component and recycled crustal component. In addition to the occurrence in the Sikhote-Alin orogenic belt, Cretaceous to Early Paleogene magmatic rocks are also widespread in NE China, southern Korean peninsula, Japanese islands and other areas of Russian Far East, particularly along the coastal regions of the Okhotsk and Bering Seas. These rocks constitute an extended magmatic belt along the continental margin of NE Asia. The

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

    Science.gov (United States)

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

    2015-05-01

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

  13. Calcium Isotope Analysis by Mass Spectrometry

    Science.gov (United States)

    Boulyga, S.; Richter, S.

    2010-12-01

    The variations in the isotopic composition of calcium caused by fractionation in heterogeneous systems and by nuclear reactions can provide insight into numerous biological, geological, and cosmic processes, and therefore isotopic analysis finds a wide spectrum of applications in cosmo- and geochemistry, paleoclimatic, nutritional, and biomedical studies. The measurement of calcium isotopic abundances in natural samples has challenged the analysts for more than three decades. Practically all Ca isotopes suffer from significant isobaric interferences, whereas low-abundant isotopes can be particularly affected by neighboring major isotopes. The extent of natural variations of stable isotopes appears to be relatively limited, and highly precise techniques are required to resolve isotopic effects. Isotope fractionation during sample preparation and measurements and instrumental mass bias can significantly exceed small isotope abundance variations in samples, which have to be investigated. Not surprisingly, a TIMS procedure developed by Russell et al. (Russell et al., 1978. Geochim Cosmochim Acta 42: 1075-1090) for Ca isotope measurements was considered as revolutionary for isotopic measurements in general, and that approach is used nowadays (with small modifications) for practically all isotopic systems and with different mass spectrometric techniques. Nevertheless, despite several decades of calcium research and corresponding development of mass spectrometers, the available precision and accuracy is still not always sufficient to achieve the challenging goals. This presentation discusses figures of merits of presently used analytical methods and instrumentation, and attempts to critically assess their limitations. Additionally, the availability of Ca isotope reference materials will be discussed.

  14. Organic geochemistry and environmental instrumentation programs

    International Nuclear Information System (INIS)

    Anon.

    1988-01-01

    The areas of research of the Organic Geochemistry Group include (1) computer-assisted gas chromatrographic, qualitative, and quantitative analyses of coal-derived complex mixtures; (2) chemodynamic measurements in complex organic mixtures to study the transport and transformation processes of chemicals in the environment; (3) bioassay-directed characterization of mutagenic polycyclic aromatic hydrocarbons in coal-derived materials; (4) chemical and toxicological evaluation of condensates from mild coal gasification processes; (5) development of rapid (high-pressure liquid chromatography) characterization techniques for primary aromatic amines in coal-derived liquids; (6) study of flame ionization detector response factors and chemical structure in gas chromatography; (7) development of a simple, portable device for preconcentrating airborne aromatic amines to be analyzed by portable liquid chromatography; (8) initial uptake and release studies of perchloroethylene and trichloroethylene in pine needles; (9) application of stable carbon isotope techniques in tracing environmental pollutants; (10) development of control technology for hydrazine fuels by neutralization with hypochlorite II. The Environmental Instrumentation group is engaged in research to develop and build prototype field-portable devices and instruments for the detection, identification, and quantification of volatile hazardous gases in a variety of environmental and workplace settings

  15. U-Pb, Nd isotope and REE geochemistry in eclogites from the Cabo Ortegal Complex, Galicia, Spain: an example of REE immobility conserving MORB-like patterns during high-grade metamorphism

    International Nuclear Information System (INIS)

    Bernard-Griffiths, J.; Peucat, J.-J.; Cornichet, J.; Iglesias Ponce de Leon, M.; Gil Ibarguchi, J.I.

    1985-01-01

    REE abundances and Nd isotopic compositions were determined on representative samples of eclogite from the Cabo Ortegal Complex of northern Spain. Zircons were also separated from a whole-rock eclogite and analysed by the U-Pb radiometric method. Results indicate that eclogite facies metamorphism occurred between 480 and 420 Ma ago, but no precise constraint can be placed on the protolith age. The REE patterns observed suggest that there has been no significant alteration of the protolith whole-rock systems and that high-grade metamorphism has had little effect on the more mobile LREE. The eclogite protoliths were probably derived from ancient mantle sources with geochemical characteristics very similar to present-day MORB sources. This implies that LREE-depleted (N-type) tholeiites have been erupted at constructive plate margins since at least the early Palaeozoic and possibly long before. The Cabo Ortegal eclogites are allochthonous. They have been thrust up on to the continent and thus they can be compared to other eclogites which also show MORB-like characteristics (e.g., 90% of the eclogites of Vendee area of western France). (orig.)

  16. Alteration of organic matter during infaunal polychaete gut passage and links to sediment organic geochemistry. Part I: Amino acids

    NARCIS (Netherlands)

    Woulds, C.; Middelburg, J.J.; Cowie, G.L.

    2012-01-01

    Of the factors which control the quantity and composition of organic matter (OM) buried in marine sediments, the links between infaunal ingestion and gut passage and sediment geochemistry have received relatively little attention. This study aimed to use feeding experiments and novel isotope tracing

  17. Global water cycle: geochemistry and environment

    National Research Council Canada - National Science Library

    Berner, Elizabeth Kay; Berner, Robert A

    1987-01-01

    .... The book provides an integrated approach to global geochemistry and environmental problems and introduces the reader to some fundamental concepts of geology, oceanography, meteorology, environmental...

  18. NRC nuclear waste geochemistry 1983

    International Nuclear Information System (INIS)

    Alexander, D.H.; Birchard, G.F.

    1984-05-01

    The purpose of the meeting was to present results from NRC-sponsored research and to identify regulatory research issues which need to be addressed prior to licensing a high-level waste repository. Important summaries of technical issues and recommendations are included with each paper. The issue reflect areas of technical uncertainty addressed by the NRC Research program in geochemistry. The objectives of the NRC Research Program in geochemistry are to provide a technical basis for waste management rulemaking, to provide the NRC Waste Management Licensing Office with information that can be used to support sound licensing decisions, and to identify investigations that need to be conducted by DOE to support a license application. Individual papers were processed for inclusion in the Energy Data Base

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

    Science.gov (United States)

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

    2018-06-01

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

  20. Late Jurassic-Early Cretaceous episodic development of the Bangong Meso-Tethyan subduction: Evidence from elemental and Sr-Nd isotopic geochemistry of arc magmatic rocks, Gaize region, central Tibet, China

    Science.gov (United States)

    Zhang, Yu-Xiu; Li, Zhi-Wu; Yang, Wen-Guang; Zhu, Li-Dong; Jin, Xin; Zhou, Xiao-Yao; Tao, Gang; Zhang, Kai-Jun

    2017-03-01

    The Bangong Meso-Tethys plays a critical role in the development of the Tethyan realm and the initial elevation of the Tibetan Plateau. However, its precise subduction polarity, and history still remain unclear. In this study, we synthesize a report for the Late Jurassic-Early Cretaceous two-phase magmatic rocks in the Gaize region at the southern margin of the Qiangtang block located in central Tibet. These rocks formed during the Late Jurassic-earliest Cretaceous (161-142 Ma) and Early Cretaceous (128-106 Ma), peaking at 146 Ma and 118 Ma, respectively. The presence of inherited zircons indicates that an Archean component exists in sediments in the shallow Qiangtang crust, and has a complex tectonomagmatic history. Geochemical and Sr-Nd isotopic data show that the two-phase magmatic rocks exhibit characteristics of arc magmatism, which are rich in large-ion incompatible elements (LIIEs), but are strongly depleted in high field strength elements (HFSEs). The Late Jurassic-earliest Cretaceous magmatic rocks mixed and mingled among mantle-derived mafic magmas, subduction-related sediments, or crustally-derived felsic melts and fluids, formed by a northward and steep subduction of the Bangong Meso-Tethys ocean crust. The magmatic gap at 142-128 Ma marks a flat subduction of the Meso-Tethys. The Early Cretaceous magmatism experienced a magma MASH (melting, assimilation, storage, and homogenization) process among mantle-derived mafic magmas, or crustally-derived felsic melts and fluids, as a result of the Meso-Tethys oceanic slab roll-back, which triggered simultaneous back-arc rifting along the southern Qiangtang block margin.

  1. Geochemistry, geochronology and Nd isotopes of the Gogó da Onça Granite: A new Paleoproterozoic A-type granite of Carajás Province, Brazil

    Science.gov (United States)

    Teixeira, Mayara Fraeda Barbosa; Dall'Agnol, Roberto; Santos, João Orestes Schneider; de Sousa, Luan Alexandre Martins; Lafon, Jean-Michel

    2017-12-01

    The Gogó da Onça Granite (GOG) comprise a stock located in the Carajás Province in the southeastern part of Amazonian Craton near its border with the Araguaia Belt. Three facies were identified in the pluton: biotite-amphibole granodiorite, biotite-amphibole monzogranite and amphibole-biotite syenogranite. The GGO crosscut discordantly the Archean country rocks and are not foliated. All Gogó da Onça Granite varieties are metaluminous, ferroan A2-subtype granites with reduced character. The major and trace element behavior suggests that its different facies are related by fractional crystallization. Zircon and titanite U-Pb SHRIMP ages show that the pluton crystallized at ∼1880-1870 Ma and is related to the remarkable Paleoproterozoic magmatic event identified in the Carajás Province. Whole-rock Nd isotope data (TDM ages 2.78 to 2.81, εNd values of -9.07 to -9.48) indicate that the GOG magmas derived from an Archaean source compatible with that of some other Paleoproterozoic suites from Carajás Province. The GOG show significant contrasts with the Jamon and Velho Guilherme Paleoproterozoic suites from Carajás Province and the inclusion of the Gogó da Onça granite in any of these suites is not justified. The GOG is more akin to the Serra dos Carajás Suite and to the Seringa and São João granites of Carajás and to the Mesoproterozoic Sherman granite of USA and the Paleoproterozoic Suomenniemi Batholith of Finland. This study puts in evidence the relevance of precise geochronological data and estimation of magma oxidation state in the characterization and correlation of A-type granites.

  2. Petrology and geochemistry of the marbles and calcosilicated rocks from Ipira, Bahia - Brazil

    International Nuclear Information System (INIS)

    Oliveira, M.A.F.T. de.

    1976-01-01

    This work explains a study of marbles and diopsitites from Serra das Panelas, Ipira, Bahia, Brazil. Petrographic analysis, chemistry some elements, trace elements and rare earths, isotopic analysis of Strontium, carbon and oxigen, and geochronological determinations were done. The ages founded correspond to Transamazonic Orogenetic cicle, with Archean age, confirmed by the 18 O values found, which give to marble, ages about 2.500 my. The mineralogy and the texture give to marble an invulgar aspect, making a confusion with carbonate. The petrochemical data and the geochemistry of 13 C and 18 O isotopes showed that the marble and diopsitites was formed from the old marine carbonates. The geochemistry of rare earth suggests a strong correlation with carbonitic and alkaline rocks. An hybrid origem to this rocks is proposed. (C.D.G.) [pt

  3. Geochemical and multi-isotopic (87Sr/86Sr, 143Nd/144Nd, 238U/235U) perspectives of sediment sources, depositional conditions, and diagenesis of the Marcellus Shale, Appalachian Basin, USA

    Science.gov (United States)

    Phan, Thai T.; Gardiner, James B.; Capo, Rosemary C.; Stewart, Brian W.

    2018-02-01

    We investigate sediment sources, depositional conditions and diagenetic processes affecting the Middle Devonian Marcellus Shale in the Appalachian Basin, eastern USA, a major target of natural gas exploration. Multiple proxies, including trace metal contents, rare earth elements (REE), the Sm-Nd and Rb-Sr isotope systems, and U isotopes were applied to whole rock digestions and sequentially extracted fractions of the Marcellus shale and adjacent units from two locations in the Appalachian Basin. The narrow range of εNd values (from -7.8 to -6.4 at 390 Ma) is consistent with derivation of the clastic sedimentary component of the Marcellus Shale from a well-mixed source of fluvial and eolian material of the Grenville orogenic belt, and indicate minimal post-depositional alteration of the Sm-Nd system. While silicate minerals host >80% of the REE in the shale, data from sequentially extracted fractions reflect post-depositional modifications at the mineralogical scale, which is not observed in whole rock REE patterns. Limestone units thought to have formed under open ocean (oxic) conditions have δ238U values and REE patterns consistent with modern seawater. The δ238U values in whole rock shale and authigenic phases are greater than those of modern seawater and the upper crust. The δ238U values of reduced phases (the oxidizable fraction consisting of organics and sulfide minerals) are ∼0.6‰ greater than that of modern seawater. Bulk shale and carbonate cement extracted from the shale have similar δ238U values, and are greater than δ238U values of adjacent limestone units. We suggest these trends are due to the accumulation of chemically and, more likely, biologically reduced U from anoxic to euxinic bottom water as well as the influence of diagenetic reactions between pore fluids and surrounding sediment and organic matter during diagenesis and catagenesis.

  4. Origin of the subduction-related Carboniferous intrusions associated with the Yandong porphyry Cu deposit in eastern Tianshan, NW China: constraints from geology, geochronology, geochemistry, and Sr-Nd-Pb-Hf-O isotopes

    Science.gov (United States)

    Wang, Yin-Hong; Xue, Chun-Ji; Liu, Jia-Jun; Zhang, Fang-Fang

    2018-06-01

    The Yandong porphyry Cu deposit is located at the south margin of the Dananhu-Tousuquan arc belt in eastern Tianshan, northwest China. The Cu ores comprise mainly disseminations and vein zones in the potassic and phyllic alteration zones, and are predominantly hosted in diorite porphyry, tonalite, and quartz porphyry, which intruded into Carboniferous Qi'eshan Group volcanic rocks. The U-Pb ages indicate that four intrusions were emplaced between 338.6 ± 2.9 and 326.1 ± 2.6 Ma. Five molybdenite samples yield Re-Os model ages of 333.8-329.5 Ma with a weighted average age of 331.8 ± 2.1 Ma. Fourteen pyrite samples have 206Pb/204Pb of 17.776-18.959, 207Pb/204Pb of 15.410-15.534, and 208Pb/204Pb of 37.323-38.127, similar to the age-corrected data of the Yandong tonalite. The tonalite shows adakite-like characteristics (e.g., high Sr/Y ratios and low Y contents), and has positive ɛNd(t) and ɛHf(t) values, and low zircon O isotopes (3.7-4.6 ‰), suggesting that the melt was derived from partial melting of a subducted oceanic slab followed by mantle peridotite interaction. The diorite porphyry exhibits high Mg# and low Sr/Y values, slightly negative Eu anomalies, and positive ɛHf(t) values, indicating a lithospheric mantle source. The quartz porphyry, with stronger negative Eu anomalies, less evolved ɛHf(t) values, and low δ18O values (4.7-5.5 ‰), was probably derived from mantle melts that experienced mixing with lower crustal materials (melts or assimilation). The new data suggest that the Yandong intrusions formed in an arc setting. As the tonalite is genetically linked to the Cu mineralization, subduction-related slab melts must have played a key role in the formation of the Yandong deposit.

  5. Origin of the subduction-related Carboniferous intrusions associated with the Yandong porphyry Cu deposit in eastern Tianshan, NW China: constraints from geology, geochronology, geochemistry, and Sr-Nd-Pb-Hf-O isotopes

    Science.gov (United States)

    Wang, Yin-Hong; Xue, Chun-Ji; Liu, Jia-Jun; Zhang, Fang-Fang

    2017-10-01

    The Yandong porphyry Cu deposit is located at the south margin of the Dananhu-Tousuquan arc belt in eastern Tianshan, northwest China. The Cu ores comprise mainly disseminations and vein zones in the potassic and phyllic alteration zones, and are predominantly hosted in diorite porphyry, tonalite, and quartz porphyry, which intruded into Carboniferous Qi'eshan Group volcanic rocks. The U-Pb ages indicate that four intrusions were emplaced between 338.6 ± 2.9 and 326.1 ± 2.6 Ma. Five molybdenite samples yield Re-Os model ages of 333.8-329.5 Ma with a weighted average age of 331.8 ± 2.1 Ma. Fourteen pyrite samples have 206Pb/204Pb of 17.776-18.959, 207Pb/204Pb of 15.410-15.534, and 208Pb/204Pb of 37.323-38.127, similar to the age-corrected data of the Yandong tonalite. The tonalite shows adakite-like characteristics (e.g., high Sr/Y ratios and low Y contents), and has positive ɛNd(t) and ɛHf(t) values, and low zircon O isotopes (3.7-4.6 ‰), suggesting that the melt was derived from partial melting of a subducted oceanic slab followed by mantle peridotite interaction. The diorite porphyry exhibits high Mg# and low Sr/Y values, slightly negative Eu anomalies, and positive ɛHf(t) values, indicating a lithospheric mantle source. The quartz porphyry, with stronger negative Eu anomalies, less evolved ɛHf(t) values, and low δ18O values (4.7-5.5 ‰), was probably derived from mantle melts that experienced mixing with lower crustal materials (melts or assimilation). The new data suggest that the Yandong intrusions formed in an arc setting. As the tonalite is genetically linked to the Cu mineralization, subduction-related slab melts must have played a key role in the formation of the Yandong deposit.

  6. Advances in geochemistry during the last four decades: A personal perspective

    International Nuclear Information System (INIS)

    Galimov, Eric M.

    2009-01-01

    This is the author's speech at the meeting in Cologne (2007) to celebrate the 40th anniversary of the International Association of Geochemistry and Cosmochemistry, which the author served as the President in 2000 to 2004. The paper narrates the author's personal involvement in important scientific programs during the last 4 decades, including implementation of isotope techniques, oil-and-gas research, diamond research, deep-sea drilling, space research, molecular biology and the origin of life.

  7. Geochemistry and petrology of pyroxenite xenoliths from Cenozoic alkaline basalts, Bohemian Massif

    Czech Academy of Sciences Publication Activity Database

    Ackerman, Lukáš; Špaček, Petr; Medaris Jr., G.; Hegner, E.; Svojtka, Martin; Ulrych, Jaromír

    2012-01-01

    Roč. 57, č. 4 (2012), s. 199-219 ISSN 1802-6222 R&D Projects: GA ČR(CZ) GA205/09/1170 Institutional research plan: CEZ:AV0Z30130516; CEZ:AV0Z30120515 Institutional support: RVO:67985831 ; RVO:67985530 Keywords : pyroxenite * xenolith * Cenozoic * basalt * Sr-Nd isotopes * geothermobarometry Subject RIV: DD - Geochemistry Impact factor: 0.804, year: 2012

  8. Geochemistry of groundwater in the Beaver and Camas Creek drainage basins, eastern Idaho

    Science.gov (United States)

    Rattray, Gordon W.; Ginsbach, Michael L.

    2014-01-01

    The U.S. Geological Survey (USGS), in cooperation with the U.S. Department of Energy, is studying the fate and transport of waste solutes in the eastern Snake River Plain (ESRP) aquifer at the Idaho National Laboratory (INL) in eastern Idaho. This effort requires an understanding of the natural and anthropogenic geochemistry of groundwater at the INL and of the important physical and chemical processes controlling the geochemistry. In this study, the USGS applied geochemical modeling to investigate the geochemistry of groundwater in the Beaver and Camas Creek drainage basins, which provide groundwater recharge to the ESRP aquifer underlying the northeastern part of the INL. Data used in this study include petrology and mineralogy from 2 sediment and 3 rock samples, and water-quality analyses from 4 surface-water and 18 groundwater samples. The mineralogy of the sediment and rock samples was analyzed with X-ray diffraction, and the mineralogy and petrology of the rock samples were examined in thin sections. The water samples were analyzed for field parameters, major ions, silica, nutrients, dissolved organic carbon, trace elements, tritium, and the stable isotope ratios of hydrogen, oxygen, carbon, sulfur, and nitrogen. Groundwater geochemistry was influenced by reactions with rocks of the geologic terranes—carbonate rocks, rhyolite, basalt, evaporite deposits, and sediment comprised of all of these rocks. Agricultural practices near and south of Dubois and application of road anti-icing liquids on U.S. Interstate Highway 15 were likely sources of nitrate, chloride, calcium, and magnesium to groundwater. Groundwater geochemistry was successfully modeled in the alluvial aquifer in Camas Meadows and the ESRP fractured basalt aquifer using the geochemical modeling code PHREEQC. The primary geochemical processes appear to be precipitation or dissolution of calcite and dissolution of silicate minerals. Dissolution of evaporite minerals, associated with Pleistocene Lake

  9. A critical review of inductively coupled plasma-mass spectrometry for geoanalysis, geochemistry and hydrology, Part 1. Analytical performance

    Science.gov (United States)

    Brenner, I.B.; Taylor, Howard E.

    1992-01-01

    Present-day inductively coupled plasma-mass spectrometry (ICP-MS) instrumentation is described briefly. Emphasis is placed on performance characteristics for geoanalysis, geochemistry, and hydrology. Applications where ICP-MS would be indispensable are indicated. Determination of geochemically diagnostic trace elements (such as the rare earth elements [REE], U and Th), of isotope ratios for fingerprinting, tracer and other geo-isotope applications, and benchmark isotope dilution determinations are considered to be typical priority applications for ICP-MS. It is concluded that ICP-MS furnishes unique geoanalytical and environmental data that are not readily provided by conventional spectroscopic (emission and absorption) techniques.

  10. The centenary of the discovery of isotopes

    International Nuclear Information System (INIS)

    Soulie, Edgar

    2013-01-01

    This article recalls works performed by different scientists (Marckwald and Keetman, Stromholm and Svedberg, Soddy, Thompson, Aston) which resulted in the observation and identification of the existence of isotopes. The author also recalls various works related to mechanisms of production of isotopes, the discovery of uranium fission and the principle of chain reaction. The author notably evokes French scientists involved in the development of mass spectroscopy and in the research and applications on isotopes within the CEA after the Second World War. A bibliography of article and books published by one of them, Etienne Roth, is provided. References deal with nuclear applications of chemical engineering (heavy water and its production, chemical processes in fission reactors, tritium extraction and enrichment), isotopic fractioning and physical-chemical processes, mass spectrometry and isotopic analysis, isotopic geochemistry (on 07;Earth, search for deuterium in moon rocks and their consequences), first dating and the Oklo phenomenon, radioactive dating, water and climate (isotopic hydrology, isotopes and hailstone formation, the atmosphere), and miscellaneous scientific fields (nuclear measurements and radioactivity, isotopic abundances and atomic weight, isotopic separation and use of steady isotopes)

  11. Uranium districts defined by reconnaissance geochemistry in South Greenland

    International Nuclear Information System (INIS)

    Armour-Brown, A.; Steenfelt, A.; Kunzendorf, H.

    1983-01-01

    A reconnaissance exploration survey over 14 000 km 2 of Precambrian terrain in South Greenland using stream-sediment and stream-water samples delineated a central uranium district of 2000 km 2 with enhanced uranium levels and smaller anomalous zones in the south of the field area. Limited follow-up work located 8 pitchblende occurrences in this extensive district. The pitchblende is in veins which contain quartz, calcite, iron oxide, fluorite and minor sulphides. The isotopic (U-Pb) age of the pitchblende, which ranges from 1180-1090 Ma, corresponds to the late stages of Gardar alkaline igneous activity. It is concluded, therefore, that the reconnaissance geochemistry reflects a district-wide hydrothermal event related to the late volatile differentiates derived from the highly fractionated alkaline magma. A combination of primary and secondary features have complemented each other in enhancing the geochemical reconnaissance data and emphasized its importance but has not materially altered the interpretation. (Auth.)

  12. Application of stable isotopes in ecological research : it's all elemental

    International Nuclear Information System (INIS)

    Rogers, K.M.

    2005-01-01

    Stable isotopes have been used traditionally in the physical sciences, primarily in geochemistry, sedimentology, and oceanography. Increasingly, however, stable isotopes are also being used in the biological sciences. Application of stable isotopes in ecological studies can provide new and innovative ways of examining a host of topics of fundamental importance to biologists. These topics include, among others, feeding ecology and food webs, nutrient flow and assimilation, habitat use, migration patterns, and distribution and discrimination of species subpopulations. Furthermore, ecological research with isotopes can be applied at many levels (i.e. tissue and organ, whole animal, population, community, and ecosystem). (author). 38 refs., 2 figs

  13. Geochemical and Os–Hf–Nd–Sr Isotopic Characterization of North Patagonian Mantle Xenoliths: Implications for Extensive Melt Extraction and Percolation Processes

    Czech Academy of Sciences Publication Activity Database

    Mundl, A.; Ntaflos, T.; Ackerman, Lukáš; Bizimis, M.; Bjerg, E. A.; Wegner, W.; Hauzenberger, Ch. A.

    2016-01-01

    Roč. 57, č. 4 (2016), s. 685-715 ISSN 0022-3530 Institutional support: RVO:67985831 Keywords : metasomatism * Patagonia * radiogenic isotopes * Re–Os * SCLM Subject RIV: DD - Geochemistry Impact factor: 3.280, year: 2016

  14. A New Method for Low-Temperature Decomposition of Chromites and Dichromium Trioxide using Bromic Acid Evaluated by Chromium Isotope Measurements

    Czech Academy of Sciences Publication Activity Database

    Chrastný, V.; Rohovec, Jan; Čadková, E.; Pašava, J.; Farkaš, J.; Novák, M.

    2014-01-01

    Roč. 38, č. 1 (2014), s. 103-110 ISSN 1639-4488 Institutional support: RVO:67985831 Keywords : chromites * dichromium trioxide * decomposition * chromium isotopes * bromic acid Subject RIV: DD - Geochemistry Impact factor: 3.792, year: 2013

  15. Geochronology and Hf–Fe isotopic geochemistry of the Phanerozoic ...

    Indian Academy of Sciences (India)

    As the first magmatic phase, the ∼395 Ma intrusions were mainly derived from ..... Fe-mineralized pyroxenite. 0.03. 0.01. GST-3. Fe-mineralized pyroxenite. 0.17 ..... Damiao area record old Hf model ages of ∼1.5 Ga. ... for his help in the field.

  16. Geochemistry of carbon stable isotopes in the sea

    International Nuclear Information System (INIS)

    Duplessy, Jean-Claude

    1972-01-01

    This paper describes geochemical process which affect the distribution in the sea of the 13 C/ 12 C ratio of total inorganic dissolved CO 2 ; synthesis of the biomass and respiratory phenomena; oxidation of organic matter; dissolution of carbonates; run off waters; exchange of CO 2 between sea and atmosphere. Some applications to the paleoclimatology are presented. (author) [fr

  17. The Marine Geochemistry of Iron and Iron Isotopes

    Science.gov (United States)

    2004-09-01

    Analytical Chemistry 76(2), 322-327. Barbeau K. and Moffett J. W. (1998) Dissolution of iron oxides by phagotropic protists : using a novel method to...oxides by phagotropic protists : using a novel method to quantify reaction rates. Environmental Science and Technology 32, 2969-2975. Barbeau K. and

  18. Reconsideration of methane isotope signature as a criterion for the genesis of natural gas: influence of migration on isotopic signatures

    International Nuclear Information System (INIS)

    Pernaton, E.; Prinzhofer, A.; Schneider, F.

    1996-01-01

    Experiments were performed in the purpose of studying the isotopic consequences of the diffusional transport of hydrocarbon gases through sediment rocks. Linked to a numerical model, these gas diffusion experiments through as shale porous plug allowed us to correlate porosity and diffusivity of the migration medium. Significant isotopic fractionations (carbon and hydrogen) of methane, and ethane at a lesser degree were observed. This is in contradiction with the actual dogma of isotope geochemistry of natural gases which claims that no fractionation occurs during gas migration. The genetic characterization of natural gases by using the isotopic signature of methane appears as an ambiguous method. (author)

  19. Springwater geochemistry at Honey Creek State Natural Area, central Texas: Implications for surface water and groundwater interaction in a karst aquifer

    Science.gov (United States)

    Musgrove, M.; Stern, L. A.; Banner, J. L.

    2010-06-01

    SummaryA two and a half year study of two adjacent watersheds at the Honey Creek State Natural Area (HCSNA) in central Texas was undertaken to evaluate spatial and temporal variations in springwater geochemistry, geochemical evolution processes, and potential effects of brush control on karst watershed hydrology. The watersheds are geologically and geomorphologically similar, and each has springs discharging into Honey Creek, a tributary to the Guadalupe River. Springwater geochemistry is considered in a regional context of aquifer components including soil water, cave dripwater, springwater, and phreatic groundwater. Isotopic and trace element variability allows us to identify both vadose and phreatic groundwater contributions to surface water in Honey Creek. Spatial and temporal geochemical data for six springs reveal systematic differences between the two watersheds. Springwater Sr isotope values lie between values for the limestone bedrock and soils at HCSNA, reflecting a balance between these two primary sources of Sr. Sr isotope values for springs within each watershed are consistent with differences between soil compositions. At some of the springs, consistent temporal variability in springwater geochemistry (Sr isotopes, Mg/Ca, and Sr/Ca values) appears to reflect changes in climatic and hydrologic parameters (rainfall/recharge) that affect watershed processes. Springwater geochemistry was unaffected by brush removal at the scale of the HCSNA study. Results of this study build on previous regional studies to provide insight into watershed hydrology and regional hydrologic processes, including connections between surface water, vadose groundwater, and phreatic groundwater.

  20. Stable isotopes in mid-ocean ridge hydrothermal systems: Interactions between fluids, minerals, and organisms

    Science.gov (United States)

    Shanks, W. C., III; Böhlke, J. K.; Seal, R. R., II

    Studies of abundance variations of light stable isotopes in nature have had a tremendous impact on all aspects of geochemistry since the development, in 1947, of a gas source isotope ratio mass spectrometer capable of measuring small variations in stable isotope ratios [Nier, 1947] Stable isotope geochemistry is now a mature field, as witnessed by the proliferation of commercially available mass spectrometers installed at virtually every major academic, government, and private-sector research geochemistry laboratory. A recent search of a literature database revealed over 3,000 articles that utilized stable isotope geochemistry over the last 20 years. Nonetheless, many exciting new technical developments are leading to exciting new discoveries and applications. In particular, micro analytical techniques involving new generations of laser- and ion-microprobes are revolutionizing the types of analyses that can be done on spot sizes as small as a few tens of micrometers [Shanks and Criss, 1989]. New generations of conventional gas source and thermal ionization mass spectrometers, with high levels of automation and increased sensitivity and precision, are allowing analyses of large numbers of samples, like those needed for stable isotope stratigraphy in marine sediments, and are enabling the development and application of new isotopic systems.

  1. Applied Geochemistry Special Issue on Environmental geochemistry of modern mining

    Science.gov (United States)

    Seal, Robert R.; Nordstrom, D. Kirk

    2015-01-01

    Environmental geochemistry is an integral part of the mine-life cycle, particularly for modern mining. The critical importance of environmental geochemistry begins with pre-mining baseline characterization and the assessment of environmental risks related to mining, continues through active mining especially in water and waste management practices, and culminates in mine closure. The enhanced significance of environmental geochemistry to modern mining has arisen from an increased knowledge of the impacts that historical and active mining can have on the environment, and from new regulations meant to guard against these impacts. New regulations are commonly motivated by advances in the scientific understanding of the environmental impacts of past mining. The impacts can be physical, chemical, and biological in nature. The physical challenges typically fall within the purview of engineers, whereas the chemical and biological challenges typically require a multidisciplinary array of expertise including geologists, geochemists, hydrologists, microbiologists, and biologists. The modern mine-permitting process throughout most of the world now requires that potential risks be assessed prior to the start of mining. The strategies for this risk assessment include a thorough characterization of pre-mining baseline conditions and the identification of risks specifically related to the manner in which the ore will be mined and processed, how water and waste products will be managed, and what the final configuration of the post-mining landscape will be.In the Fall 2010, the Society of Economic Geologists held a short course in conjunction with the annual meeting of the Geological Society of America in Denver, Colorado (USA) to examine the environmental geochemistry of modern mining. The intent was to focus on issues that are pertinent to current and future mines, as opposed to abandoned mines, which have been the focus of numerous previous short courses. The geochemical

  2. Lead Isotopes in Olivine-Phyric Shergottite Tissint: Implications for the Geochemical Evolution of the Shergottite Source Mantle

    Science.gov (United States)

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

    2015-01-01

    Geochemically-depleted shergottites are basaltic rocks derived from a martian mantle source reservoir. Geochemical evolution of the martian mantle has been investigated mainly based on the Rb-Sr, Sm-Nd, and Lu-Hf isotope systematics of the shergottites [1]. Although potentially informative, U-Th- Pb isotope systematics have been limited because of difficulties in interpreting the analyses of depleted meteorite samples that are more susceptible to the effects of near-surface processes and terrestrial contamination. This study conducts a 5-step sequential acid leaching experiment of the first witnessed fall of the geochemically-depleted olivinephyric shergottite Tissint to minimize the effect of low temperature distrubence. Trace element analyses of the Tissint acid residue (mostly pyroxene) indicate that Pb isotope compositions of the residue do not contain either a martian surface or terrestrial component, but represent the Tissint magma source [2]. The residue has relatively unradiogenic initial Pb isotopic compositions (e.g., 206Pb/204Pb = 10.8136) that fall within the Pb isotope space of other geochemically-depleted shergottites. An initial µ-value (238U/204Pb = 1.5) of Tissint at the time of crystallization (472 Ma [3]) is similar to a time-integrated mu- value (1.72 at 472 Ma) of the Tissint source mantle calculated based on the two-stage mantle evolution model [1]. On the other hand, the other geochemically-depleted shergottites (e.g., QUE 94201 [4]) have initial µ-values of their parental magmas distinctly lower than those of their modeled source mantle. These results suggest that only Tissint potentially reflects the geochemical signature of the shergottite mantle source that originated from cumulates of the martian magma ocean

  3. Geomicrobiology; inseparable from low temperature geochemistry & mineralogy

    Science.gov (United States)

    Southam, G.

    2009-05-01

    Bacteria play an important role in catalyzing a wide array of biogeochemical processes that affect the dissolution of minerals, the aqueous geochemistry of their surroundings and secondary mineral formation. Processes occurring at the bacteria-mineral interface can occur on the scale of nanoenvironments and will normally extend to microenvironments or even, to macroscopic features where extensive growth of bacteria is supported. The action of bacteria in these systems can produce a wide range of biomarkers that can be preserved over geologic time periods. Possible biomarkers include dissolution features in mineral substrates, fossil structures of individual cells to complex cell-cell associations, and chemical (isotopic and organic) signatures. In any system, we need to focus at the scale of the bacteria themselves to appreciate the actual chemistry of their surroundings and the kinds of reactions that they can catalyse. For example, photosynthetic microbial mats in an Atlin, BC wetland create ideal conditions for biologically induced precipitation of magnesium carbonates, specifically dypingite Mg5(CO3)4(OH)25H2O, which we were unable to reproduce abiotically. The preservation of biosignatures over geologic time presents obvious challenges, and the effect of diagenesis on fossils and their mineralogical assemblages deserves attention, especially with respect to the preservation and analysis of materials on (or from) Mars. For this, we need to rely on our Earth analogue sites as a way to triage the wide range of samples that are available for collection and analysis. The preservation of organic materials and cells in salts is particularly interesting. Conversely, the hematite nodules on Mars may not be good samples to target in the search for a Martian biosphere. The possibility of finding an extant biosphere increases with depth; however, evidence from Earth's deep subsurface demonstrates that it does not contain an abundant biosphere. Bacteria thrive in

  4. Depletion, cryptic metasomatism, and modal metasomatism of central European lithospheric mantle: evidence from elemental and Li isotope compositions of spinel peridotite xenoliths, Kozákov volcano, Czech Republic

    Czech Academy of Sciences Publication Activity Database

    Medaris Jr., L. G.; Ackerman, Lukáš; Jelínek, E.; Magna, T.

    2015-01-01

    Roč. 104, č. 8 (2015), s. 1925-1956 ISSN 1437-3254 Institutional support: RVO:67985831 Keywords : Central European lithospheric mantle * geochemistry * geothermometry * Li isotopes * spinel peridotite xenoliths Subject RIV: DD - Geochemistry Impact factor: 2.133, year: 2015

  5. Barren Miocene granitoids in the Central Andean metallogenic belt, Chile: Geochemistry and Nd-Hf and U-Pb isotope systematics Granitoides estériles del Mioceno en la franja metalogénica de los Andes Centrales, Chile: geoquímica e isotopía de Nd-Hf y U-Pb

    Directory of Open Access Journals (Sweden)

    Katja Deckart

    2010-01-01

    Full Text Available Four Middle-to-Late Miocene barren plutonic complexes that occur between the giant porphyry copper deposits of the central Chilean Andes were selected for U-Pb LA-ICPMS geochronology and Hf-isotope systematics on single zircon grains. Major and trace elements and Sr-Nd-Hf isotope whole rock geochemical studies were under-taken to compare with slightly younger or coeval barren and fertile intrusive rocks between 32° and 34°S. The studied granitoids yield resolvable crystallization ages of 11.3±0.1 Ma (Cerro Mesón Alto massif, 10.3±0.2 Ma (La Gloria pluton, 14.9±0.2 Ma/14.9±0.1 Ma (Yerba Loca stock and 11.2±0.1 Ma/14.7±0.1 Ma (San Francisco Batholith. Major and trace elements discard an adakitic signature as suggested for coeval porphyric intrusions at 32°S, slightly younger mineralized porphyries at Río Blanco-Los Bronces deposit and other Cenozoic adakites. Volcanic host rocks are less fractionated than the intrusive rock units. The same observation can be made for the unmineralized northern plutons compared to the southern ones. Initial Sr-Nd isotope data show insignificant variation (0.703761-0.704118 and 0.512758-0.512882, plotting in the mantle array. Trace element enrichment can be explained by addition of subducted-slab fluids and/or terrigenous sediments to the mantle wedge prior to and/or slight crustal input during magma ascent. Zircon grains separated from these barren intrusives share a similar initial εHf i-data variation for the younger age group (10-12 Ma; 7.04-9.54 and show a more scattered range for the older one (14-15 Ma; 8.50-15.34; both sets plot between the DM and CLTUR evolution lines. There is evidence that magma evolution was slightly distinct through time from older to younger barren magmatism, compared to a few fertile porphyritic rocks from Río Blanco-Los Bronces porphyry copper deposit. It is suggested that chronological inconsistencies within these complexes might be related to differential shortening

  6. Uranium geochemistry of Orca Basin

    International Nuclear Information System (INIS)

    Weber, F.F. Jr.; Sackett, W.M.

    1981-01-01

    Orca Basin, an anoxic, brine-filled depression at a depth of 2200 m in the Northwestern Gulf of Mexico continental slope, has been studied with respect to its uranium geochemistry. Uranium concentration profiles for four cores from within the basin were determined by delayed-neutron counting. Uranium concentrations ranged from 2.1 to 4.1 ppm on a salt-free and carbonate-corrected basis. The highest uranium concentrations were associated with the lowest percentage and delta 13 C organic carbon values. For comparison, cores from the brine-filled Suakin and Atlantis II Deeps, both in the Red Sea, were also analyzed. Uranium concentrations ranged from 1.2 to 2.6 ppm in the Suakin Deep and from 8.0 to 11.0 ppm in the Atlantis II Deep. No significant correlation was found between uranium concentrations and organic carbon concentrations and delta 13 C values for these cores. Although anoxic conditions are necessary for significant uranium uptake by non-carbonate marine sediments, other factors such as dilution by rapidly depositing materials and uranium supply via mixing and diffusion across density gradients may be as important in determining uranium concentrations in hypersaline basin sediments. (author)

  7. Geochemistry of radioactive waste disposal

    International Nuclear Information System (INIS)

    Bird, G.W.

    1979-01-01

    Safe, permanent disposal of radioactive wastes requires isolation of a number of elements including Se, Tc, I, Sr, Cs, Pd, u, Np, Pu and Cm from the environment for a long period of time. The aquatic chemistry of these elements ranges from simple anionic (I - ,IO 3 - ) and cationic (Cs + ,Sr ++ ) forms to multivalent hydrolyzed complexes which can be anionic or cationic (Pu(OH) 2 + ,Pu(OH) 3 + , PuO 2 (CO 3 )(OH) - ,PuO 2 Cl - ,etc.) depending on the chemical environment. The parameters which can affect repository safety are rate of access and composition of grounwater, stability of the waste container, stability of the waste form, rock-water-waste interactons, and dilution and dispersion as the waste moves away from the repository site. Our overall research program on radioactive waste disposal includes corrosion studies of containment systems hydrothermal stability of various waste forms, and geochemical behaviour of various nuclides including solubilities, redox equilibria, hydrolysis, colloid fomation and transport ion exchange equilibria and adsorption on mineral surfaces and irreversible precipitation reactions. This paper discusses the geochemistry of I, Se, Tc, Cs, Sr and the actinide elements and potential mechanisms by which the mobility could be retarded if necessary

  8. Geochemistry of Natural Redox Fronts

    International Nuclear Information System (INIS)

    Hofmann, B.A.

    1999-05-01

    U, V, Cu, Ni, Au and Ag. The mineralogy of redox fronts is extremely complex, with redox fronts formed at elevated temperature showing more complex assemblages than lower temperature redox fronts. The redox behaviour of individual elements is discussed based on results from natural redox fronts and, to a more limited extent, on experimental evidence. Other aspects of redox fronts such as organic geochemistry, mineral phases, microbial activity, radiolysis and geochemical self-organisation are briefly reviewed. A short overview of active and fossil redox fronts in Northern Switzerland and Southwest Germany is given. The review also includes information on commercially available analytical methods suitable for redox front geochemistry. The general conclusion of this report is that there is widespread evidence that the elements U, Se, Pd and many others are systematically and efficiently immobilised at variable types of redox fronts. Co-precipitation is widely observed for the rare earth elements and perhaps for Th. While these general observations conform to the known geochemical properties of these elements, unexplained differences exist between the behaviour of some elements in different types of redox fronts, e.g. the strongly contrasting behaviour of the otherwise geochemically similar elements Ni and Co in the fossil meteorite Brunflo. Th is another element for which evidence of unusual geochemical behaviour exists at certain localities. A strong influence of local parameters that may be hard to identify appears to be one of the main obstacles in the interpretation of data from natural systems. The systematic overview of natural and human-induced redox fronts in this report allows types of redox fronts suitable for natural analogue studies to be identified. Particularly promising in this respect are weathering phenomena in homogeneous dumps of ore processing products (type IVb) and redox fronts formed by injection of seawater into deep oil reservoirs. (author)

  9. Au-bearing magnetite mineralizaion in Kashmar (alteration, mineralization, geochemistry, geochemistry and fluid inclusions;

    Directory of Open Access Journals (Sweden)

    Alireza Almasi

    2017-02-01

    Full Text Available Introduction The study area is located in the central part of the Khaf- Kashmar- Bardaskan volcano-plotunic belt (briefly KKBB. Several IOCG deposits such as Tanourjeh Au-bearing magnetite deposit and Kuh-e-Zar Specularite-rich Au deposit have been explored in KKBB. Geology, alteration, mineralization, geochemistry and fluid inclusion results in Kashmar suggest the IOCG type Au-bearing magnetite mineralization. These IOCG deposits at KKBB form at an active continental arc related to SSZ-type Sabzevar oceanic subduction. Materials and methods Use of Landsat 7+, IRS and Aster satellites. Petrography and alteration Studies in 150 thin sections of volcanic and intrusive rocks. Sampling of ore-bearing quartz vein and mineralography. Preparation of 28 geochemistry samples by the chip composite method of ore-bearing quartz vein and analyzing them in the ACME laboratory by Aqua Regia 1DX1. Fluid inclusions studies of 14 samples of quartz and barite related to the ore minerals of ore-bearing quartz vein by THM600 stage of Linkam company. Results Magmatic events in Kashmar occur at Paleocene-Eocene and include: (1 old mafic - intermediate volcano-plutonic series; (2 felsic volcanic and granitoids; and (3 parallel swarm dykes which are youngest (Almasi et al., 2016. Geochemically, Kashmar rocks are metaluminous to highly peraluminous and Tholeitic to calc-alkaline and shoshonitic in composition (Almasi et al., 2016. The field characteristics, together with isotope and geochemical analyses show that all rock types are essentially co-magmatic and post-collisional I-type (Almasi et al., 2016. Alteration of Kashmar is described in two ways: (1 intense ellipsoidal-linear Argillic-Sillicification and low sericitic with Silica caps and with medium widespread and propylitic alterations in triple regions, next to Dorouneh fault; and (2 Medium Hematite-Carbonate-Chlorite-Silicification alterations in Kamarmard heights. In parts of near the Doruneh fault, sometimes

  10. Isotopic signature of Pan-African rejuvenation in the Kerala Khondalite belt, southern India: implications for east Gondwana reassembly

    International Nuclear Information System (INIS)

    Unnikrishnan Warrier, C.

    1997-01-01

    Sm-Nd isotope systematics on mineral separates from sillimanite-and cordierite-bearing metapelite (khondalite), and garnet-and biotite-bearing gneiss (leptynite) from the Kerala Khondalite Belt (KKB), southern India, yielded mineral isochron ages (wr-feld-bio-gar) of 537±27 Ma (MSWD=0.9) and 534±26 Ma (MSWD=1.23) respectively. Rb-Sr systematics in the same samples gave wr-feld-bio mineral isochron ages of 437±9 Ma (MSWD=0.67) and 467±9 Ma (MSWD=0.76). These results provide the first mineral isochron ages for the regional metasedimentaries in the KKB. The ε (Nd T) values at 550 Ma for khondalite and leptynite are -22.7 and -21.8 respectively. These results demonstrate a complete rejuvenation of the crust during Pan-African times. Coeval alkaline plutons emplaced along fault-lineaments in this area suggest an extensional tectonic regime. Geochronologic correlations with the Lutzow-Holm bay complexes in east Antarctica, and the highland and southwestern complex of Sri Lanka show that a similar Pan-African tectono-thermal event manifested in all the east Gondwana crustal fragments. (author)

  11. Insights from stable S and O isotopes into biogeochemical processes and genesis of Lower Cambrian barite–pyrite concretions of South China

    Digital Repository Service at National Institute of Oceanography (India)

    Goldberg, T.; Mazumdar, A.; Strauss, H.; Shields, G.

    water trace metal chemistry of laminated sediments from the Gulf of California, Mexico. Marine Chemistry 14, 89-106. Canfield, D.E., 2001. Biogeochemistry of sulphur isotopes. In: Valley, J.W. & Cole, D.R. (Eds.), Stable Isotope Geochemistry. Reviews.... Age curves of sulphur and oxygen isotopes in marine sulphate and their mutual interpretation. Chemical Geology 28, 199-206. Coleman, M.L. & Raiswell, R., 1981. Carbon, oxygen and sulphur isotope variations in concretions from the Upper Lias of N...

  12. Proceedings of the national symposium on current trends in geochemistry, exploration and environment: abstract book

    International Nuclear Information System (INIS)

    2015-01-01

    The topics covered in this symposium are solid earth geochemistry and geochemical modeling, precambrian geology, geochemistry and petrogenesis, geochemistry, peterogenisis, sedimentology, chemostratigraphy and paleoclimate, atomic minerals, ferrous/non ferrous minerals, REE minerals, PGE and base metals, oil, hydrocarbons, industrial minerals and gem stones, hydrogeochemistry, environmental geochemistry, biogeochemistry and medical geology and analytical geochemistry and method development. Papers relevant to INIS are indexed separately

  13. Geochemistry Review Panel report on the SRP geochemistry program and draft geochemistry summary program plan (May, 1986) and discussion of panel recommendations

    International Nuclear Information System (INIS)

    1986-12-01

    The Geochemistry Review Panel (GRP) was established by the Salt Repository Project Office (SRPO) to help evaluate geochemistry-related issues in the US Department of Energy's nuclear waste repository program. The May 1986 meeting of the GRP reviewed the Salt Repository Program (SRP) geochemistry program developed by the Office of Nuclear Waste Isolation (ONWI). This program is described in the Draft Geochemistry Plan of April 9, 1986. This report documents the GRP's comments and recommendations on this subject and the ONWI responses to the specific points raised by the GRP

  14. Historical foundations of chemical geology and geochemistry

    NARCIS (Netherlands)

    Manten, A.A.

    1966-01-01

    Roughly, the name chemical geology has been used for as long as chemistry has been applied in geology; the name geochemistry was introduced by Schönbein, in 1838. Whereas initially the names were often regarded as synonymous, in our century there is a tendency to make a distinction between the two

  15. Geochemistry of sulphur in petroleum systems

    NARCIS (Netherlands)

    Sinninghe Damsté, J.S.; Orr, W.L.

    1990-01-01

    A renaissance in the 1980s concerning geochemistry of sulfur in fossil fuels makes an update of the subject timely. Papers developed from the 1989 ACS Symposium in Dallas provide a cross-section of recent research and progress in our understanding of the abundance and nature of organically bound

  16. Urban environmental geochemistry of trace metals

    International Nuclear Information System (INIS)

    Wong, Coby S.C.; Li Xiangdong; Thornton, Iain

    2006-01-01

    As the world's urban population continues to grow, it becomes increasingly imperative to understand the dynamic interactions between human activities and the urban environment. The development of urban environmental geochemistry has yielded a significant volume of scientific information about geochemical phenomena found uniquely in the urban environment, such as the distribution, dispersion, and geochemical characteristics of some toxic and potentially toxic trace metals. The aim of this paper is to provide an overview of the development of urban environmental geochemistry as a field of scientific study and highlight major transitions during the course of its development from its establishment to the major scientific interests in the field today. An extensive literature review is also conducted of trace metal contamination of the urban terrestrial environment, in particular of urban soils, in which the uniqueness of the urban environment and its influences on trace metal contamination are elaborated. Potential areas of future development in urban environmental geochemistry are identified and discussed. - Urban environmental geochemistry as a scientific discipline provides valuable information on trace metal contamination of the urban environment and its associated health effects

  17. Isotopes in the earth sciences

    Energy Technology Data Exchange (ETDEWEB)

    Bowen, Robert

    1988-01-01

    This book examines significant aspects of isotope applications in geology and geochemistry commencing with basic matters, such as atomic structure, stable nuclides and their fractionation, as well as the various decay modes of unstable nuclides. Modern mass spectrometry techniques including electrostatic tandem accelerators are followed by a review of radioisotope dating technology. The relatively new method using the rare earth elements samarium and neodymium are covered. Other geochronometers, applicable to both rocks and minerals not dateable otherwise, are included. A review is given of isotopes in the atmosphere, hydrosphere and lithosphere of the Earth. Those of oxygen and hydrogen together with the cosmogenic radionuclides tritium and radiocarbon are discussed in relation to the biosphere. The role of isotopes of carbon, nitrogen and sulphur is described and extended to fossil fuels and rocks as well as meteorites. Related themes such as Phanerozoic oceans, oceanic palaeothermometry, snow and ice stratigraphy and geothermal waters are covered. The field of isotopic palaeoecology is discussed. Radioactive wastes, their accumulation, dangers and disposal are investigated with especial reference to their environmental impacts.

  18. Isotopic clusters

    International Nuclear Information System (INIS)

    Geraedts, J.M.P.

    1983-01-01

    Spectra of isotopically mixed clusters (dimers of SF 6 ) are calculated as well as transition frequencies. The result leads to speculations about the suitability of the laser-cluster fragmentation process for isotope separation. (Auth.)

  19. Stable isotopes

    International Nuclear Information System (INIS)

    Evans, D.K.

    1986-01-01

    Seventy-five percent of the world's stable isotope supply comes from one producer, Oak Ridge Nuclear Laboratory (ORNL) in the US. Canadian concern is that foreign needs will be met only after domestic needs, thus creating a shortage of stable isotopes in Canada. This article describes the present situation in Canada (availability and cost) of stable isotopes, the isotope enrichment techniques, and related research programs at Chalk River Nuclear Laboratories (CRNL)

  20. Isotope separation

    International Nuclear Information System (INIS)

    Eerkens, J.W.

    1979-01-01

    A method of isotope separation is described which involves the use of a laser photon beam to selectively induce energy level transitions of an isotope molecule containing the isotope to be separated. The use of the technique for 235 U enrichment is demonstrated. (UK)

  1. A novel methodology to investigate isotopic biosignatures

    Science.gov (United States)

    Horner, T. J.; Lee, R. B. Y.; Henderson, G. M.; Rickaby, R. E. M.

    2012-04-01

    . coli (e.g. membranes, cytosol, etc.), including the catalytic metal atoms within CdCA. These experiments allow isotopic exchange reactions to be observed in biological systems at an unparalleled resolution, demonstrating that isotopic fractionation can occur, in vivo, on length scales as small as a few Å. We will explore future applications of this technique using the marine geochemistry of Cd as a case study. This experimental approach has great promise for studying the individual isotopic biosignatures of other biochemical reactions, in particular those which may have been active during early Earth History.

  2. Uranium project. Geochemistry prospection[Study of Uranium geochemical prospection in Uruguay]; Proyecto Uranio. Prospeccion geoquimica

    Energy Technology Data Exchange (ETDEWEB)

    Lambert, J

    1983-07-01

    Geochemistry studies the distribution of the chemicals elements in the terrestrial crust and its ways to migrate. The terminology used in this report is the following one: 1) Principles of the prospection geochemistry 2) Stages of the prospection geochemistry 3)utility of the prospection geochemistry 4) geochemistry of uranium 5) procedures used within the framework of uranium project 6) Average available 7) Selection of the zones of prospection geochemistry 8) Stages of the prospection, Sample preparation and analisis 9) Presentation of the results.

  3. Application of Stable Isotope Signatures in Food Traceability

    International Nuclear Information System (INIS)

    Nazaratul Ashifa Abdullah Salim; Roslanzairi Mostapha; Zainon Othman; Nor Afiqah Harun; Mohd Suhaimi Hamzah; Shamsiah Abdul Rahman; Md Suhaimi Elias; Salmah Moosa

    2015-01-01

    Stable isotope analysis has widely been used to trace the origin of organic materials in various fields, such as geochemistry, biochemistry, archaeology and petroleum. In past a decade, it has also become an important tool for food traceability study. The globalization of food markets and the relative ease with which food commodities are transported through and between countries and continents, means that consumers are increasingly concerned about the origin of the foods they eat. The natural abundance isotope variation such as carbon, nitrogen, hydrogen and oxygen are use as geographic tracers or marker to determine the geographic origin of fruits, crop, vegetables and food products from animal. The isotopic compositions of plant materials reflect various factors such as isotopic compositions of source materials and their assimilation processes as well as growth environments. This paper will discuss on stable carbon and nitrogen isotopic compositions in rice, advantages, limitations and potential of other analysis applications that can be incorporated in food traceability system. (author)

  4. Stable isotope deltas: Tiny, yet robust signatures in nature

    Science.gov (United States)

    Brand, Willi A.; Coplen, Tyler B.

    2012-01-01

    Although most of them are relatively small, stable isotope deltas of naturally occurring substances are robust and enable workers in anthropology, atmospheric sciences, biology, chemistry, environmental sciences, food and drug authentication, forensic science, geochemistry, geology, oceanography, and paleoclimatology to study a variety of topics. Two fundamental processes explain the stable isotope deltas measured in most terrestrial systems: isotopic fractionation and isotope mixing. Isotopic fractionation is the result of equilibrium or kinetic physicochemical processes that fractionate isotopes because of small differences in physical or chemical properties of molecular species having different isotopes. It is shown that the mixing of radioactive and stable isotope end members can be modelled to provide information on many natural processes, including 14C abundances in the modern atmosphere and the stable hydrogen and oxygen isotopic compositions of the oceans during glacial and interglacial times. The calculation of mixing fractions using isotope balance equations with isotope deltas can be substantially in error when substances with high concentrations of heavy isotopes (e.g. 13C, 2H, and 18O ) are mixed. In such cases, calculations using mole fractions are preferred as they produce accurate mixing fractions. Isotope deltas are dimensionless quantities. In the International System of Units (SI), these quantities have the unit 1 and the usual list of prefixes is not applicable. To overcome traditional limitations with expressing orders of magnitude differences in isotope deltas, we propose the term urey (symbol Ur), after Harold C. Urey, for the unit 1. In such a manner, an isotope delta value expressed traditionally as−25 per mil can be written as−25 mUr (or−2.5 cUr or−0.25 dUr; the use of any SI prefix is possible). Likewise, very small isotopic differences often expressed in per meg ‘units’ are easily included (e.g. either+0.015 ‰ or+15 per meg

  5. Dynamical geochemistry of the mantle

    Directory of Open Access Journals (Sweden)

    G. F. Davies

    2011-09-01

    Full Text Available The reconciliation of mantle chemistry with the structure of the mantle inferred from geophysics and dynamical modelling has been a long-standing problem. This paper reviews three main aspects. First, extensions and refinements of dynamical modelling and theory of mantle processing over the past decade. Second, a recent reconsideration of the implications of mantle heterogeneity for melting, melt migration, mantle differentiation and mantle segregation. Third, a recent proposed shift in the primitive chemical baseline of the mantle inferred from observations of non-chondritic 142Nd in the Earth. It seems most issues can now be resolved, except the level of heating required to maintain the mantle's thermal evolution.

    A reconciliation of refractory trace elements and their isotopes with the dynamical mantle, proposed and given preliminary quantification by Hofmann, White and Christensen, has been strengthened by work over the past decade. The apparent age of lead isotopes and the broad refractory-element differences among and between ocean island basalts (OIBs and mid-ocean ridge basalts (MORBs can now be quantitatively accounted for with some assurance.

    The association of the least radiogenic helium with relatively depleted sources and their location in the mantle have been enigmatic. The least radiogenic helium samples have recently been recognised as matching the proposed non-chondritic primitive mantle. It has also been proposed recently that noble gases reside in a so-called hybrid pyroxenite assemblage that is the result of melt from fusible pods reacting with surrounding refractory peridotite and refreezing. Hybrid pyroxenite that is off-axis may not remelt and erupt at MORs, so its volatile constituents would recirculate within the mantle. Hybrid pyroxenite is likely to be denser than average mantle, and thus some would tend to settle in the D" zone at the base of the mantle, along with some old subducted

  6. Isotopic evolution of Mauna Loa volcano

    International Nuclear Information System (INIS)

    Kurz, M.D.; Kammer, D.P.

    1991-01-01

    In an effort to understand the temporal helium isotopic variations in Mauna Loa volcano, we have measured helium, strontium and lead isotopes in a suite of Mauna Loa lavas that span most of the subaerial eruptive history of the volcano. The lavas range in age from historical flows to Ninole basalt which are thought to be several hundred thousand years old. Most of the samples younger than 30 ka in age (Kau Basalt) are radiocarbon-dated flows, while the samples older than 30 ka are stratigraphically controlled (Kahuku and Ninole Basalt). The data reveal a striking change in the geochemistry of the lavas approximately 10 ka before present. The lavas older than 10 ka are characterized by high 3 He/ 4 He (≅ 16-20 times atmospheric), higher 206 Pb/ 204 Pb (≅ 18.2), and lower 87 Sr/ 86 Sr(≅ 0.70365) ratios than the younger Kau samples (having He, Pb and Sr ratios of approximately 8.5 x atmospheric, 18.1 and 0.70390, respectively). The historical lavas are distinct in having intermediate Sr and Pb isotopic compositions with 3 He/ 4 He ratios similar to the other young Kau basalt (≅ 8.5 x atmospheric). The isotopic variations are on a shorter time scale (100 to 10,000 years) than has previously been observed for Hawaiian volcanoes, and demonstrate the importance of geochronology and stratigraphy to geochemical studies. The data show consistency between all three isotope systems, which suggests that the variations are not related to magma chamber degassing processes, and that helium is not decoupled from the other isotopes. However, the complex temporal evolution suggests that three distinct mantle sources are required to explain the isotopic data. Most of the Mauna Loa isotopic variations could be explained by mixing between a plume type source, similar to Loihi, and an asthenospheric source with helium isotopic composition close to MORB and elevated Sr isotopic values. (orig./WL)

  7. High field magnetization process of (Sm, Nd)2Fe17Ny compounds

    International Nuclear Information System (INIS)

    Yu, M.J.; Tang, N.; Liu, Y.L.; Tegus, O.; Lu, Y.; Kuang, J.P.; Yang, F.M.; Li, X.; Zhou, G.F.; Boer, F.R. de

    1992-01-01

    The crystal structure and high-field magnetization process of (Sm 1-x Nd x ) 2 Fe 17 N y compounds (x = 0.0, 0.1, ..., 1.0, 2 1-x Nd x ) 2 Fe 17 N y compounds were found to crystallize in the rhombohedral Th 2 Zn 17 structure. As x increases, the Curie temperature decreases. The anisotropy fields and easy magnetization direction were investigated from 1.5 K to room temperature by means of high-field magnetization measurements and AC-susceptibility measurements, combined with X-ray diffraction on random and magnetically aligned powder samples. The anisotropy field decreases with increasing x and approaches a minimum value at about x = 0.6, then increases again. A tentative spin phase diagram for the (Sm 1-x Nd x ) 2 Fe 17 N y series is presented. At room temperature, the easy magnetization direction remains along the c-axis up to x = 0.6. (orig.)

  8. Geochemistry of subduction zone serpentinites: A review

    OpenAIRE

    DESCHAMPS, Fabien; GODARD, Marguerite; GUILLOT, Stéphane; HATTORI, Kéiko

    2013-01-01

    Over the last decades, numerous studies have emphasized the role of serpentinites in the subduction zone geodynamics. Their presence and role in subduction environments are recognized through geophysical, geochemical and field observations of modern and ancient subduction zones and large amounts of geochemical database of serpentinites have been created. Here, we present a review of the geochemistry of serpentinites, based on the compilation of ~ 900 geochemical data of abyssal, mantle wedge ...

  9. Development of the near field geochemistry model

    International Nuclear Information System (INIS)

    Arcos, D.; Bruno, J.; Duro, L.; Grive, M.

    2000-01-01

    This report discusses in a quantitative manner the evolution of the near field geochemistry as a result of the interactions between two different introducing granitic groundwaters and the FEBEX bentonite as a buffer material. The two granitic groundwaters considered are: SR-5 water, sampled in a borehole at 500 m depth in Mina Ratones, and a mean composition of different granitic groundwaters from the iberian Massif. The steel canister has also been introduced by considering the iron corrosion in anoxic conditions. (Author)

  10. Source characteristics and tectonic setting of mafic-ultramafic intrusions in North Xinjiang, NW China: Insights from the petrology and geochemistry of the Lubei mafic-ultramafic intrusion

    Science.gov (United States)

    Chen, Bao-Yun; Yu, Jin-Jie; Liu, Shuai-Jie

    2018-05-01

    The newly discovered Lubei sulfide-bearing mafic-ultramafic intrusion forms the western extension of the Huangshan-Jin'erquan mafic-ultramafic intrusion belt in East Tianshan, NW China. The Lubei intrusion comprises hornblende peridotite, lherzolite, and harzburgite in its southern portion, gabbro in its middle portion, and hornblende gabbro in its northern portion. Intrusive relationships indicate that three magma pulses were involved in the formation of the intrusion, and that they were likely evolved from a common primitive magma. Estimated compositions of the Lubei primitive magma are similar to those of island arc calc-alkaline basalt except for the low Na2O and CaO contents of the Lubei primitive magma. This paper reports on the mineral compositions, whole-rock major and trace element contents, and Rb-Sr and Sm-Nd isotopic compositions of the Lubei intrusion, and a zircon LA-MC-ICP-MS U-Pb age for hornblende gabbro. The Lubei intrusion is characterized by enrichment in large-ion lithophile elements, depletion in high-field-strength elements, and marked negative Nb and Ta anomalies, with enrichment in chondrite-normalized light rare earth elements. It exhibits low (87Sr/86Sr)i ratios of 0.70333-0.70636 and low (143Nd/144Nd)i ratios of 0.51214-0.51260, with positive εNd values of +4.01 to +6.33. LA-ICP-MS U-Pb zircon ages yielded a weighted-mean age of 287.9 ± 1.6 Ma for the Lubei intrusion. Contemporaneous mafic-ultramafic intrusions in different tectonic domains in North Xinjiang show similar geological and geochemical signatures to the Lubei intrusion, suggesting a source region of metasomatized mantle previously modified by hydrous fluids from the slab subducted beneath the North Xinjiang region in the early Permian. Metasomatism of the mantle was dominated by hydrous fluids and was related to subduction of the Paleo-Asian oceanic lithosphere during the Paleozoic. Sr-Nd-Pb isotopic compositions suggest that the mantle source was a mixture of depleted mid

  11. Silicon isotope study of thermal springs in Jiaodong Region,Shandong Province

    Institute of Scientific and Technical Information of China (English)

    徐跃通; 李红梅; 冯海霞; 周晨; 吴元芳; 张邦花

    2001-01-01

    Based on δ30Si and δ32Si isotope geochemistry, the origin and evolutionary mechanism of thermal springs in Jiaodong region are studied. The mean value of δ30Si of dissolved silica of thermal spring water in Jiaodong is 0.1‰. Thermal spring water ages using δ32Si dating method range from 387a to 965a.

  12. Isotopic Tracing of Thallium Contamination in Soils Affected by Emissions from Coal-Fired Power Plants

    Czech Academy of Sciences Publication Activity Database

    Vaněk, A.; Grösslová, Z.; Mihaljevič, M.; Trubač, J.; Ettler, V.; Teper, L.; Cabala, J.; Rohovec, Jan; Zádorová, T.; Penížek, V.; Pavlů, L.; Holubík, O.; Němeček, K.; Houška, J.; Drábek, O.; Ash, C.

    2016-01-01

    Roč. 50, č. 18 (2016), s. 9864-9871 ISSN 0013-936X Institutional support: RVO:67985831 Keywords : environmental implications * isotope * fractionation * combustion * utility * health * oxides * silver * lead Subject RIV: DD - Geochemistry Impact factor: 6.198, year: 2016

  13. Long-term summer temperature variations in the Pyrenees from detrended stable carbon isotopes

    Czech Academy of Sciences Publication Activity Database

    Esper, J.; Konter, O.; Krusic, P. J.; Saurer, M.; Holzkaemper, S.; Büntgen, Ulf

    2015-01-01

    Roč. 42, č. 1 (2015), s. 53-59 ISSN 1897-1695 Institutional support: RVO:67179843 Keywords : tree-rings * climate sensitivity * past millennium * delta-o-18 * delta-c-13 * cellulose * wood * uncertainties * chronologies * variability * Climate change * paleoclimatology * stable isotope geochemistry * tree-rings * Europe Subject RIV: DG - Athmosphere Sciences, Meteorology Impact factor: 2.038, year: 2015

  14. Isotope and Nuclear Chemistry Division annual report, FY 1990, October 1, 1989--September 30, 1990

    International Nuclear Information System (INIS)

    Heiken, J.; Minahan, M.

    1991-06-01

    This report describes some of the major research and development programs of the Isotope and Nuclear Chemistry Division during FY 1990. The report includes articles on weapons chemistry, environmental chemistry, actinide and transition metal chemistry, geochemistry, nuclear structure and reactions, biochemistry and nuclear medicine, materials chemistry, and INC Division facilities and laboratories

  15. Isotope enrichment

    International Nuclear Information System (INIS)

    Garbuny, M.

    1979-01-01

    The invention discloses a method for deriving, from a starting material including an element having a plurality of isotopes, derived material enriched in one isotope of the element. The starting material is deposited on a substrate at less than a critical submonatomic surface density, typically less than 10 16 atoms per square centimeter. The deposit is then selectively irradiated by a laser (maser or electronic oscillator) beam with monochromatic coherent radiation resonant with the one isotope causing the material including the one istope to escape from the substrate. The escaping enriched material is then collected. Where the element has two isotopes, one of which is to be collected, the deposit may be irradiated with radiation resonant with the other isotope and the residual material enriched in the one isotope may be evaporated from the substrate and collected

  16. Sr isotopes at Copahue Volcanic Center, Neuquen, Argentina: Preliminary report

    International Nuclear Information System (INIS)

    Linares, E.; Ostera, H.A.; Cagnoni, M.C

    2001-01-01

    The Copahue Volcanic Center is located in the Cordillera Principal, at 38 L.S., in the Argentina- Chilean border. Detailed geological, geochronological and structural studies were carried out during the last decade (Pesce, 1989; Delpino y Bermudez, 1993; Linares et al., 1995, 1999; Folguera y Ramos, 2000; among others). We present Sr isotopes data on the main units of the Volcanic Center, coupled with a major element geochemistry, to constrain the evolution of the volcanic center (au)

  17. Stable isotopes

    International Nuclear Information System (INIS)

    Brazier, J.L.; Guinamant, J.L.

    1995-01-01

    According to the progress which has been realised in the technology of separating and measuring isotopes, the stable isotopes are used as preferable 'labelling elements' for big number of applications. The isotopic composition of natural products shows significant variations as a result of different reasons like the climate, the seasons, or their geographic origins. So, it was proved that the same product has a different isotopic composition of alimentary and agriculture products. It is also important in detecting the pharmacological and medical chemicals. This review article deals with the technology, like chromatography and spectrophotometry, adapted to this aim, and some important applications. 17 refs. 6 figs

  18. Isotope separation

    International Nuclear Information System (INIS)

    Bartlett, R.J.; Morrey, J.R.

    1978-01-01

    A method and apparatus is described for separating gas molecules containing one isotope of an element from gas molecules containing other isotopes of the same element in which all of the molecules of the gas are at the same electronic state in their ground state. Gas molecules in a gas stream containing one of the isotopes are selectively excited to a different electronic state while leaving the other gas molecules in their original ground state. Gas molecules containing one of the isotopes are then deflected from the other gas molecules in the stream and thus physically separated

  19. Genesis of Neoproterozoic granitoid magmatism in the Eastern Aracuai Fold Belt, eastern Brazil: field, geochemical and Sr-Nd isotopic evidence

    International Nuclear Information System (INIS)

    Celino, Joil Jose; Botelho, Nilson Francisquini; Pimentel, Marcio Martins

    2000-01-01

    The Neoproterozoic granitoid magmatism of the Aracuai Fold Belt (AFB) is an important element for the discussion of the evolution of this belt and its relationships with the African counterpart, the West Congo Belt. In the eastern part of the AFB, four different granitoid suites were recognized. The Nanuque Suite (NQS) comprises syn-tectonic peraluminous cordierite-bearing monzogranites. The Sao Paulinho Suite (SPS) consists of Th-rich peraluminous two mica or biotite-only granitoids. Calc-alkalic granitoids with magmatic epidote were grouped into the Itagimirim Suite (ITS) and post-tectonic charnockitic rocks were grouped into the Salomao Suite (SLS). Sm-Nd mineral isochron and Rb- isochron yielded ages of yielded ages of respectively 761 Ma and 714 Ma for the Nanuque and Sao Paulino suites. The general Sr-Nd isotopic characteristics of the granitoid suites and some country rocks indicate that the parental magmas were mostly the product of melting of the Paraiba do Sul metasediments. The chronological and genetic evolution the Neoproterozoic plutonism can be envisaged in a model of est-dipping subduction zone, followed by a continental collision between the Brasiliano/Pan-African (Brazil) and Congo (Africa cratons and final episodes of uplift and collapse. (author)

  20. Calibrating NIST SRM 683 as A New International Reference Standard for Zn Isotopes

    Science.gov (United States)

    Yang, Y.; Zhang, X.; Yu, H.; Huang, F.

    2017-12-01

    Zinc isotopes have been widely applied in the cosmochemical, geochemical, and environmental studies (Moynier et al. 2017). Obtaining precise Zn isotopic data for inter-laboratory comparison is a prerequisite to these applications. Currently, the JMC3-0749L is the primary reference standard for Zn isotopes (Albarède 2004), but it is not commercially available now. Thus, it is necessary to calibrate a new international primary reference standard for Zn isotopic analysis. Chen et al. (2016) showed that NIST SRM 683 (a pure Zn metal nugget of 140 grams) has a δ66ZnJMC of 0.12‰, which is falling within the range of natural Zn isotopic compositions, and it may a good candidate for the next generation of international reference standard (Chen et al. 2016). In order to further examine whether NIST SRM 683 has a homogeneous Zn isotopic composition, we measured more NIST SRM 683 by double-spike methods using MC-ICPMS (Conway et al. 2013). The metal nuggets of NIST SRM 683 were intensively sampled by micro-drilling. Zinc isotope analyses for two nuggets show that they have δ66Zn of 0.14 ± 0.02‰ (2SD, N = 32) and 0.13 ± 0.02‰ (2SD, N = 33), respectively. These values are similar to those of two Zn metal nuggets (0.11 ± 0.02‰ vs. 0.12 ± 0.02‰) reported previously by Chen et al. (2016). We fully dissolved one nugget, producing pure Zn solution with identical Zn isotopic composition with the drilling samples. All results strongly support that NIST SRM 683 is homogeneous in Zn isotopic compositions which could be an ideal candidate for the next reference for Zn isotopes. Tests on more metal nuggets will be performed in a few months for further confirming the Zn isotope compositions and homogeneity. Reference: Albarède et al., 2004. 'The stable isotope geochemistry of copper and zinc', Reviews in Mineralogy and Geochemistry, 55: 409-27. Chen et al., 2016. 'Zinc Isotopic Compositions of NIST SRM 683 and Whole-Rock Reference Materials', Geostandards and

  1. Formation and Evolution of the Continental Lithospheric Mantle: Perspectives From Radiogenic Isotopes of Silicate and Sulfide Inclusions in Macrodiamonds

    Science.gov (United States)

    Shirey, S. B.; Richardson, S. H.

    2007-12-01

    Silicate and sulfide inclusions that occur in diamonds comprise the oldest (>3 Ga), deepest (>140 km) samples of mantle-derived minerals available for study. Their relevance to the evolution of the continental lithosphere is clear because terrestrial macrodiamonds are confined to regions of the Earth with continental lithospheric mantle keels. The goals of analytical work on inclusions in diamond are to obtain paragenesis constraints, radiogenic ages, and initial isotopic compositions. The purpose is to place diamond formation episodes into the broader framework of the geological processes that create and modify the continental lithosphere and to relate the source of the C and N in diamond-forming fluids to understanding the Earth's C and N cycles in the Archean. Although sulfide and silicate inclusions rarely occur in the same diamond, they both can be grouped according to their geochemical similarity with the chief rock types that comprise the mantle keel: peridotite and eclogite. Silicate inclusions are classified as harzburgitic (depleted; olivine > Fo91, garnet Cr2O3 > 3 wt% and CaO from 0 to 5 wt%), lherzolitic (fertile), or eclogitic (basaltic; garnet Cr2O3 14 wt%; Os > 2 ppm) versus eclogitic (Ni bearing kimberlites, and the generosity of mining companies because of the extreme rarity of inclusions in suites of mostly gem-quality diamonds. Most isotopic work has been on the Kaapvaal-Zimbabwe craton with lesser work on the Slave, Siberian, and Australian cratons. Sm-Nd ages on silicate suites and Re-Os ages on sulfide suites confirm diamond formation from the Mesoarchean though the Neoproterozoic. Most important are the systematics across cratons in the context of crustal geology that lead to generalities about craton evolution. Inclusion suites date mantle keels as Mesoarchean and clearly point to subduction as the major process to form the earliest continental nuclei and to amalgamate the cratons in their present form. This is evident from the elevated

  2. Magnesium isotopic composition of the mantle

    Science.gov (United States)

    Teng, F.; Li, W.; Ke, S.; Marty, B.; Huang, S.; Dauphas, N.; Wu, F.; Helz, R. L.

    2009-12-01

    Studies of Mg isotopic composition of the Earth not only are important for understanding its geochemistry but also can shed light on the accretion history of the Earth as well as the evolution of the Earth-Moon system. However, to date, the Mg isotopic composition of the Earth is still poorly constrained and highly debated. There is uncertainty in the magnitude of Mg isotope fractionation at mantle temperatures and whether the Earth has a chondritic Mg isotopic composition or not. To constrain further the Mg isotopic composition of the mantle and investigate the behavior of Mg isotopes during igneous differentiation, we report >200 high-precision (δ26Mg French Polynesian volcanoes (Society island and Cook Austral chain); 3) olivine grains from Hawaiian volcanoes (Kilauea, Koolau and Loihi) and 4) peridotite xenoliths from Australia, China, France, Tanzania and USA. Global oceanic basalts and peridotite xenoliths have a limited (<0.2 ‰) variation in Mg isotopic composition, with an average δ26Mg = -0.25 relative to DSM3. Olivines from Hawaiian lavas have δ26Mg ranging from -0.43 to +0.03, with most having compositions identical to basalts and peridotites. Therefore, the mantle’s δ26Mg value is estimated to be ~ -0.25 ± 0.1 (2SD), different from that reported by Wiechert and Halliday (2007; δ26Mg = ~ 0) but similar to more recent studies (δ26Mg = -0.27 to -0.33) (Teng et al. 2007; Handler et al. 2009; Yang et al., 2009). Moreover, we suggest the Earth, as represented by the mantle, has a Mg isotopic composition similar to chondrites (δ26Mg = ~-0.33). The need for a model such as that of Wiechert and Halliday (2007) that involves sorting of chondrules and calcium-aluminum-rich inclusions in the proto planetary disc is thus not required to explain the Mg isotopic composition of the Earth.

  3. Water geochemistry to estimate reservoir temperature of Stabio springs, Switzerland

    Science.gov (United States)

    Pera, Sebastian; Soma, Linda

    2017-04-01

    Elettrica Ticinese References Balderer, W., Leuenberger, F., Frei, C., Surbeck, H., & Synal, H. A. (2007). Origin of the Thermal Waters of Stabio (Switzerland) and Sirmione (Italy) based on Isotope and Chemical Investigations. In Symposium on advances in isotope hydrology and its role in sustainable water resources management; Vienna (Austria); 21-25 May 2007 (Vol. 39, pp. 631-641). IAEA. Bernoulli, D. (1964). Zur Geologie des Monte Generoso. Ein Beitrag zur Kenntnis der südalpinen Sedimente. Beiträge zur Geologischen Karte der Schweiz Karte Schweiz. N.F. 118. Greber, E., Leu, W., Schumacher, M. E., & Wyss, R. (1997). Hydrocarbon provinces in the Swiss Southern Alps-a gas geochemistry and basin modelling study Fsl. Marine and Petroleum Geology, 14(1), 3-25 IAEA. (1984). Isotopes Hydrology 1983. In Proc. Vienna Symposium 1984. Vienna: IAEA

  4. Organic geochemistry of fossil resins from the Czech Republic

    Czech Academy of Sciences Publication Activity Database

    Havelcová, Martina; Sýkorová, Ivana; Mach, K.; Dvořák, Z.

    2014-01-01

    Roč. 10, August (2014), s. 303-312 ISSN 1878-5220. [Geochemistry of the Earth's Surface (GES) Meeting /10./. Paris, 18.08.2014-23.08.2014] R&D Projects: GA ČR(CZ) GA13-18482S Institutional support: RVO:67985891 Keywords : fossil resin * amber * resinite * TMAH-Py-GC/MS Subject RIV: DD - Geochemistry