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Sample records for rb-sr isotopic composition

  1. Rb/Sr isotopic and compositional retentivity of muscovite during deformation

    NASA Astrophysics Data System (ADS)

    Eberlei, T.; Habler, G.; Wegner, W.; Schuster, R.; Körner, W.; Thöni, M.; Abart, R.

    2015-06-01

    Permian metapegmatite muscovite from the Upper-Austroalpine Matsch Unit in Southern Tyrol (Italy) was investigated regarding its Rb/Sr and compositional retentivity during Cretaceous Upper-greenschist facies deformation. The data imply that microstructurally relic Permian magmatic muscovite largely maintained its major and trace element compositions during deformation, whereas the Rb/Sr geochronometer is strongly affected by a net loss of Sr. Lower Sr concentrations of muscovite correlate with higher 87Rb/86Sr and 87Sr/86Sr ratios. In most samples, the muscovite grain size- and magnetic-fractions with the lowest 87Rb/86Sr and 87Sr/86Sr ratios preserve a Permo-Triassic muscovite-whole rock Rb/Sr apparent age interpreted as to reflect formation during or cooling after pegmatite emplacement. Contrastingly, muscovite fractions with higher 87Rb/86Sr and 87Sr/86Sr ratios are arranged along a roughly linear array with a positive correlation of the 87Rb/86Sr and 87Sr/86Sr ratios in the 87Rb/86Sr vs 87Sr/86Sr space. They yield successively lower muscovite-whole rock Rb/Sr apparent ages. We explain the variations in the Rb/Sr isotopic character of microstructurally relic muscovite by a, presumably deformation-related, loss of Sr during the Cretaceous event. Contemporaneously, only very limited amounts of isotopically different Sr from the matrix reservoir might possibly have entered the muscovite. Consequently, the Rb/Sr of the relic muscovite is affected by a net loss of Sr. The results imply that at temperatures of < 500 °C, deformation is supposed to be the predominant factor in controlling the Rb/Sr geochronometer of relic muscovite, by significantly reducing the characteristic length scale for volume diffusion. However, variations of the major and trace element compositions within Permian relic muscovite are interpreted to rather reflect primary compositional instead of deformation-related variations.

  2. Rb, Sr and strontium isotopic composition, K/Ar age and large ion lithophile trace element abundances in rocks and glasses from the Wanapitei Lake impact structure

    NASA Technical Reports Server (NTRS)

    Winzer, S. R.; Lum, R. K. L.; Schuhmann, S.

    1976-01-01

    Shock metamorphosed rocks and shock-produced melt glasses from the Wanapitei Lake impact structure have been examined petrographically and by electron microprobe. Eleven clasts exhibiting varying degrees of shock metamorphism and eight impact-produced glasses have been analyzed for Rb, Sr and Sr isotopic composition. Five clasts and one glass have also been analyzed for large ion lithophile (LIL) trace element abundances including Li, Rb, Sr, and Ba and the REE's. The impact event forming the Wanapitei Lake structure occurred 37 m.y. ago based on K/Ar dating of glass and glassy whole-rock samples. Rb/Sr isotopic dating failed to provide a meaningful whole-rock or internal isochron. The isotopic composition of the glasses can be explained by impact-produced mixing and melting of metasediments.

  3. Stanniferrous granites of Vietnam: Rb-Sr and Ar-Ar isotope age, composition, sources, and geodynamic formation conditions

    NASA Astrophysics Data System (ADS)

    Anh, Phan Luu; Vladimirov, A. G.; Kruk, N. N.; Polyakov, G. V.; Ponomarchuk, V. A.; Hoa, Tran Trong; Phuong, Ngo Thi; Kuibida, M. L.; Annikova, I. Yu.; Pavlova, G. G.; Kiseleva, V. Yu.

    2010-06-01

    Stanniferrous granite-leucogranite massifs in Vietnam to which the bedrock and placer commercial deposits of cassiterite are associated (Timtuc etc.) are of late Cretaceous age (˜85 Ma by Rb-Sr and Ar-Ar isotope dating). These massifs are presented by stocks and fracture intrusions (to 100 km2 in area) of simple homodromic structure: biotite granites ⇒ two-mica and muscovite leucogranites ⇒ topaz-containing aplites ⇒ rare-metal pegmatites.

  4. Rb-Sr and Sm-Nd isotopic variations in dissected crustal xenoliths

    NASA Technical Reports Server (NTRS)

    Lee, Der-Chuen; Halliday, Alex N.; Hunter, Robert H.; Holden, Peter; Upton, Brian G. J.

    1993-01-01

    The effect of magma-xenolith interaction on the Rb-Sr and Sm-Nd isotopic systematics was investigated by studying the Rb-Sr and Sm-Nd variations in dissected crustal xenoliths sampled from different localities across Scotland. The Nd isotopic compositions were found to be virtually uniform across each xenolith, but significant variations were found in Rb, Sr, and REE concentrations, as well as in Rb/Sr and Sm/Nd ratios and Sr isotopic composition. Most of these variations appear to be inherited from the protolith, but, in one case, they have been modified by melt infiltration from the host magma. The results lend confidence to the interpretation of the isotopic and chemical compositions of xenoliths transported in basaltic magmas as reflecting their source regions, but they also highlight the potential problems of interpreting Sm-Nd model ages from metamorphic rocks.

  5. Zircon U-Pb and K-feldspar megacryst Rb-Sr isotopic ages and Sr-Hf isotopic composition of the Mesozoic Heyu pluton, eastern Qingling orogen, China

    NASA Astrophysics Data System (ADS)

    Zhu, Xi-Yan; Chen, Fukun; Liu, Bing-Xiang; Siebel, Wolfgang

    2013-01-01

    Mesozoic granitoids are ubiquitous in China and have attracted the interests of many geologists not only because of their mineralization potential but also because they carry information on source material, emplacement mechanisms and crustal architecture. Most of the plutons were created by multi-stage magma emplacement and offer particular challenge for unraveling the emplacement and cooling history. A multi-isotope approach combined with single grain dating analyses provides a means to understand magma geneses even in complex magmatic settings. This study presents Rb-Sr isotope data for K-feldspar megacrysts and U-Pb ages and Hf isotopic composition for zircons from the composite Heyu pluton exposed in eastern Qinling orogen, central China. Zircon U-Pb concordia ages of 150 and 140 Ma and single K-feldspar Rb-Sr isochron ages between 133 and 121 Ma were obtained from early and late magmatic stages, respectively, consistent with slow cooling or isotopic re-equilibration of the Rb-Sr K-feldspar system. The distinct K-feldspar morphology of early and late intrusive phases is controlled largely by the emplacement depth, likely to be associated with a gravity-driven sinking model. Corresponding zircon ɛHf(t) values are - 21.8 to - 18.0 and - 17.2 to - 10.3 for early and late intrusive phases, respectively, indicating different magma sources.

  6. Derivation of Apollo 14 High-Al Basalts at Discrete Times: Rb-Sr Isotopic Constraints

    NASA Technical Reports Server (NTRS)

    Hui. Hejiu; Neal, Clive, R.; Shih, Chi-Yu; Nyquist, Laurence E.

    2012-01-01

    Pristine Apollo 14 (A-14) high-Al basalts represent the oldest volcanic deposits returned from the Moon [1,2] and are relatively enriched in Al2O3 (>11 wt%) compared to other mare basalts (7-11 wt%). Literature Rb-Sr isotopic data suggest there are at least three different eruption episodes for the A-14 high-Al basalts spanning the age range approx.4.3 Ga to approx.3.95 Ga [1,3]. Therefore, the high-Al basalts may record lunar mantle evolution between the formation of lunar crust (approx.4.4 Ga) and the main basin-filling mare volcanism (<3.85 Ga) [4]. The high-Al basalts were originally classified into five compositional groups [5,6], and then regrouped into three with a possible fourth comprising 14072 based on the whole-rock incompatible trace element (ITE) ratios and Rb-Sr radiometric ages [7]. However, Rb-Sr ages of these basalts from different laboratories may not be consistent with each other because of the use of different 87Rb decay constants [8] and different isochron derivation methods over the last four decades. This study involved a literature search for Rb-Sr isotopic data previously reported for the high-Al basalts. With the re-calculated Rb-Sr radiometric ages, eruption episodes of A-14 high-Al basalts were determined, and their petrogenesis was investigated in light of the "new" Rb-Sr isotopic data and published trace element abundances of these basalts.

  7. The Estherville mesosiderite: U-Pb, Rb-Sr, and Sm-Nd isotopic study of a polymict breccia

    SciTech Connect

    Brouxel, M.; Tatsumoto, M. )

    1991-04-01

    A systematic U-Pb, Sm-Nd, and Rb-Sr isotopic study shows that the Estherville mesosiderite was formed between 4.56 and 4.43 Ga. Observed isotopic heterogeneity is in agreement with multiple generations of meteoritic impacts described in other mesosiderites. At least part of the Estherville silicate fraction was formed early in solar system history as indicated by the Pb-Pb (4555 {plus minus} 35 Ma), U-Pb (4560 {plus minus} 31 Ma), Rb-Sr (4542 {plus minus} 203 Ma), and Sm-Nd (4533 {plus minus} 94 Ma) ages. Mesosiderites therefore present not only petrological but also geochronological similarities with eucrites. The Pb isotopic composition of the metal phase plots on the same isochron as the silicates, indicating formation and subsequent mixing with silicates early in the history of the solar system. This is consistent with previous observations indicating that iron was reduced during the silicate-magmatic stage, most likely a consequence of mixing with metal. In addition to these more-ancient portions of the Estherville breccia, other parts were formed later as suggested by the Pb-Pb (4422 {plus minus} 50 Ma) and U-Pb (4437 {plus minus} 11 Ma) ages observed in a second group of leaches and residues. This age is similar to some cumulate eucrite ages and may represent the formation of a second mesosiderite component. The Sm-Nd and the Rb-Sr ages obtained on Estherville show large errors that may be a consequence of the mixing between the 4.56 and 4.43 Ga endmembers. Estherville, like most mesosiderites, was affected by a major heating event around 3.5-3.7 Ga as shown by the Ar-Ar ages. This heating event partially disturbed the Rb-Sr isotopic system (Rb-Sr metamorphic ages range between 3.81 and 4.08 Ga).

  8. The Estherville mesosiderite: UPb, RbSr, and SmNd isotopic study of a polymict breccia

    USGS Publications Warehouse

    Brouxel, M.; Tatsumoto, M.

    1991-01-01

    A systematic UPb, SmNd, and RbSr isotopic study shows that the Estherville mesosiderite was formed between 4.56 and 4.43 Ga. Observed isotopic heterogeneity is in agreement with multiple generations of meteoritic impacts described in other mesosiderites. At least part of the Estherville silicate fraction was formed early in solar system history as indicated by the Pb-Pb (4555 ?? 35 Ma), UPb (4560 ?? 31 Ma), RbSr (4542 ?? 203 Ma), and SmNd (4533 ?? 94 Ma) ages. Mesosiderites therefore present not only petrological but also geochronological similarities with eucrites. The Pb isotopic composition of the metal phase plots on the same isochron as the silicates, indicating formation and subsequent mixing with silicates early in the history of the solar system. This is consistent with previous observations indicating that iron was reduced during the silicate-magmatic stage, most likely a consequence of mixing with metal. In addition to these more-ancient portions of the Estherville breccia, other parts were formed later as suggested by the Pb-Pb (4422 ?? 50 Ma) and UPb (4437 ?? 11 Ma) ages observed in a second group of leaches and residues. This age is similar to some cumulate eucrite ages and may represent the formation of a second mesosiderite component. The SmNd and the RbSr ages obtained on Estherville show large errors that may be a consequence of the mixing between the 4.56 and 4.43 Ga endmembers. Estherville, like most mesosiderites, was affected by a major heating event around 3.5-3.7 Ga as shown by the Ar-Ar ages (Bogard et al., 1990). This heating event partially disturbed the RbSr isotopic system (RbSr metamorphic ages range between 3.81 and 4.08 Ga). ?? 1991.

  9. Sm-Nd and Rb-Sr isotopic systematics of ureilites

    NASA Technical Reports Server (NTRS)

    Goodrich, Cyrena Anne; Patchett, P. Jonathan; Drake, Michael J.; Lugmair, Guenter W.

    1991-01-01

    The present evaluation of Sm-Nd and Rb-Sr isotopic data for seven ureilites establishes their divisions into three groups on the bases of Sm-Nd isotopic systematics. The first group of ureilites is made up of whole-rock samples whose highly depleted assemblages indicate Sm-Nd model ages consistent with 4.55 Ga. The second group of whole-rock samples of Kenna, Novo Urei, and ALHA77257 are heterogeneous mixtures of an unidentified light REE-enriched component and a light REE-depleted olivine-pyroxene assemblage. In the third group, LEW85440 neither has a model Sm-Nd age of 4.55 Ga nor plots of the 3.74 Ga isochron of the Kenna group; it might have had an evolution similar to the Kenna group, but involving different times and/or isotopic compositions.

  10. Rb-Sr isotopic composition of granites in the Western Krušné hory/Erzgebirge pluton, Central Europe: record of variations in source lithologies, mafic magma input and postmagmatic hydrothermal events

    NASA Astrophysics Data System (ADS)

    Dolejš, David; Bendl, Jiří; Štemprok, Miroslav

    2016-03-01

    The late Variscan (327-318 Ma) Western Krušné hory/Erzgebirge pluton (Czech Republic and Germany) represents a multiply emplaced intrusive sequence ranging from low-F biotite monzogranites (with rare minor bodies of gabbrodiorites and granodiorites) to high-F topaz-zinnwaldite alkali-feldspar granites. This granite suite is characterized by progressively increasing concentrations of incompatible elements (Li, Rb, F), monotonous decrease in mafic components and compatible elements (FeOtot, MgO, TiO2, CaO, Sr) with increasing silica. Consequently, this leads to extreme variations in the Rb/Sr ratios (0.52 to 59), which impose highly variable 87Rb/86Sr and 87Sr/86Sr signatures. The low-F biotite monzogranites represent isotopically heterogeneous mixture with (87Sr/86Sr)323 = 0.707-0.709 between partial melts from the Saxothuringian metasediments and mantle-derived mafic precursors. The medium-F two-mica microgranites show variable (87Sr/86Sr)323 = 0.708-0.714, indicating involvement of multiple precursors and more mature crustal protoliths. The evolved high-F topaz-zinnwaldite alkali-feldspar granites were derived from a precursor with (87Sr/86Sr)320 = 0.707-0.708 at 324-317 Ma by differentiation, which produced the extreme Rb/Sr enrichment and variations. The Li/Rb ratios remain nearly constant (~0.5), thus insensitive to the degree of geochemical differentiation. In comparison to terrestrial variations, the high Li/Rb values indicate derivation of granitic magmas from predominantly sedimentary precursors, in accord with 7Li-6Li and 143Nd-144Nd isotope composition reported previously. The Rb-Sr element variations in each granite unit are sligthly different and indicate ascent and emplacement of separate magma batches, which do not form a single liquid line of descent. We consider the enrichment of granites in incompatible elements (Li, Rb, F) and compatible depletion of ferromagnesian components, CaO and Sr as a combined effect of multiple precursors, changes in

  11. Re-Os, Rb-Sr, and O isotopic systematics of the Archean Kolar schist belt, Karnataka, India

    NASA Technical Reports Server (NTRS)

    Walker, Richard J.; Shirey, Steven B.; Hanson, Gilbert N.; Rajamani, V.; Horan, Mary F.

    1989-01-01

    The Re-Os, Rb-Sr, and O isotopic compositions of mafic and ultramafic amphibolites, gold ores, and granitic gneisses of the circa 2700 Ma Kolar schist belt are reported which reveal at least two episodes of postmagmatic alteration that affected these systems. The Re-Os isotopic systematics of many of the belt rocks indicate that Os was introduced to the area via fluids that carried very radiogenic Os, probably from ancient crust. The Rb-Sr systematics of most of these rocks indicate that the alteration event probably occurred no later than the early Proterozoic. Samples of several komatiitic amphibolites have very Os-187-depleted compositions, indicating that open-system behavior also occurred at a much later time than the late Archean or early Proterozoic. The results suggest that the Re-Os system may have only limited utility for geochronologic applications in regions for which postcrystallization noble metal mineralization is evident.

  12. Petrogenesis of Apollo 14 high-Al basalts: Constraints of Rb-Sr isotope and trace element data

    NASA Astrophysics Data System (ADS)

    Hui, H.; Neal, C. R.; Oshrin, J. G.

    2011-12-01

    Apollo 14 high-Al basalts, the oldest volcanic deposits returned from the Moon, can provide geologic records of the Moon between the formation of lunar crust (~4.4 Ga) and the main basin-filling mare volcanism (< 3.85 Ga). Various models have been proposed for the petrogenesis of the Apollo 14 high-Al basalts [e.g., 1,2]. Whole-rock incompatible trace element ratios define at least 3 compositional groups, and Rb-Sr radiometric age data show that at least three eruption episodes for the Apollo 14 high-Al basalts, each derived from different source regions at discrete times [2,3]. However, the literature Rb-Sr ages were determined by different labs over four decades. Such data may not be comparable due to different 87Rb decay constants and isochron iteration methods used. We have mined literature Rb-Sr isotopic data of Apollo 14 high-Al basalts [3-9] and re-processed them with a consistent 87Rb decay constant [10] using Isoplot 3.70 [11]. Four eruption episodes of Apollo 14 high-Al basalts were confirmed: 4.24±0.10 Ga, 4.03±0.03 Ga, 3.97±0.07 Ga and 3.92±0.03 Ga. Both Rb-Sr isotopic compositions and incompatible trace element ratios of bulk samples show that parental melts of Apollo 14 high-Al basalts formed through mixing of KREEP and other melted mantle cumulate(s). Melt evolution of Apollo 14 high-Al basalts has been investigated by comparing the equilibrium melt compositions (calculated from plagioclase compositions using relevant partition coefficients) to the fractional crystallization (FC) and assimilation and fractional crystallization (AFC) models. Trace-element petrogenetic modeling of high-Al basalts shows that the equilibrium melt compositions do not fall on a single AFC or FC trajectory. This could be indicative of fluctuating degrees of assimilation (i.e., variable r-values) and/or variable assimilant compositions during petrogenesis. The compositional micro-heterogeneity in Apollo 14 high-Al basalts may partially result from the following volcanic

  13. Rb-Sr and Sm-Nd Isotopic Studies of Antarctic Nakhlite MIL 03346

    NASA Technical Reports Server (NTRS)

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

    2006-01-01

    Nakhlites are olivine-bearing clinopyroxenites with cumulate textures, and probably came from Mars [e.g., 1]. A total of seven nakhlites have been identified so far. Unlike other martian meteorites (e.g., shergottites), nakhlites have been only moderately shocked and their original igneous textures are still well-preserved. Also, these meteorites have similarly older crystallization ages of approx.1.3 Ga compared to shergottites with ages of approx.0.18-0.57 Ga [e.g., 2]. MIL 03346 is characterized by abundant (approx.20 vol %) glassy mesostasis, indicating that it cooled rapidly and probably formed near the top [3] or at the bottom [4] of the chilled margin of a thick intrusive body. The mesostasis quenched from the trapped intercumulus liquid may provide information on the parent magma compositions of the nakhlites. In this report, we present Rb-Sr and Sm-Nd isotopic data for MIL 03346, discuss correlation of its age with those of other nakhlites and the nature of their source regions in the Martian mantle.

  14. Rb-Sr isotopic systematics of alkali-rich fragments in the Yamato-74442 LL-chondritic breccia

    NASA Astrophysics Data System (ADS)

    Yokoyama, Tatsunori; Misawa, Keiji; Okano, Osamu; Shih, Chi-Yu; Nyquist, Laurence E.; Simon, Justin I.; Tappa, Michael J.; Yoneda, Shigekazu

    2013-03-01

    We have undertaken mineralogical, petrographical and Rb-Sr isotopic studies on alkali-rich igneous rock fragments in the Yamato (Y)-74442 LL-chondritic breccia. The fragments are a few mm in size and are composed mainly of porphyritic olivine and dendritic pyroxene set in alkali-rich groundmass glass. Minor phases include chromite, troilite and metallic nickel-iron. Bulk chemical compositions of the fragments are almost identical to the host chondrite except for a depletion of sodium and an enrichment of potassium. Isotopic analyses of nine fragments from Y-74442 yield a Rb-Sr age of 4429±54 Ma (2σ) for λ(87Rb)=0.01402 Ga-1 with an initial ratio of 87Sr/86Sr=0.7144±0.0094 (2σ). Assuming precursors of the fragments formed 4568 Ma with 87Sr/86Sr=0.69889 when the Solar System formed, a time-averaged Rb/Sr (weight) ratio of the source material for the fragments is calculated to be 2.58+0.91/-0.93. The extremely high Rb/Sr value of this source is difficult to interpret by any igneous fractionation or liquid immiscibility, but can be explained by mixing of a chondritic component with an alkali-rich component formed in the early solar nebula. In our preferred model, the alkali component with Rb/Sr≫30 would have condensed from the residual nebular gas after removal of refractory strontium and must have been isolated for a long time in a region where the temperature was sufficiently low to prevent reaction with other silicates/oxides. A mixture of the alkali component (early nebular condensates) and the ferromagnesian component could reflect flash heating induced by impact on an LL-chondritic parent body at least 4429 Ma ago, and further enrichments of rubidium and potassium relative to strontium could have occurred during this event. The resulting impact-melt rocks could have been fragmented by later impact event(s) and finally incorporated into the Y-74442 parent body. Thus, a remarkable signature of alkali enrichments both in the early solar nebula and later on

  15. Re-Os, Rb-Sr, and O isotopic systematics of the Archean Kolar schist belt, Karnataka, India

    USGS Publications Warehouse

    Walker, R.J.; Shirey, S.B.; Hanson, G.N.; Rajamani, V.; Horan, M.F.

    1989-01-01

    The Re-Os, Rb-Sr, and O isotopic compositions of mafic and ultramafic amphibolites, gold ores, and granitic gneisses of the circa 2700 Ma Kolar schist belt reveal at least two episodes of post-magmatic alteration that affected these systems. The Re-Os isotopic systematics of many of the rocks of the belt indicate that Os was introduced to the area via fluids that carried very radiogenic Os ( 187Os 186Os2.4Ga > 39). The source of the radiogenic Os was likely ancient crust. On an outcrop scale, this alteration is also characterized by relatively minor additions of excess 87Sr and ??18O values higher than magmatic. The Rb-Sr systematics of most of these rocks are consistent with closed-system behavior since a period between 2700 and 2400 Ma ago, indicating that the alteration event likely occurred no later than the early Proterozoic. In contrast to this late Archean or early Proterozoic alteration, samples of several komatiitic amphibolites have very 187Os-depleted compositions, indicating that open-system behavior also occurred at a much later time. This alteration may have been caused by surficial weathering or the interaction of the rocks with fluids bearing unradiogenic Os. Results suggest that the Re-Os system may have only limited utility for geochronologic applications in regions for which post-crystallization noble metal mineralization is evident (e.g., gold ores). In such regions, however, the system may have an important application in assessing the timing and the ultimate sources of noble metal additions. ?? 1989.

  16. Textural and Rb-Sr isotopic evidence for late Paleozoic mylonitization within the Honey Hill fault zone southeastern Connecticut

    SciTech Connect

    O'Hara, K.D.; Gromet, L.P.

    1983-09-01

    A petrographic and Rb-Sr isotopic study of rocks within and near the Honey Hill fault zone places important constraints on its history of movement. Rb-Sr apparent ages for micas and plagioclase from these rocks have been reset and range from Permian to Triassic, considerably younger than the minimum stratigraphic age (Ordovician) of the rocks studied or of Acadian (Devonian) regional metamorphism. Permian Rb-Sr ages of dynamically recrystallized muscovite date the development of mylonite fabric. An older age is precluded by the excellent preservation of unrecovered quartz, which indicates that these rocks did not experience temperatures high enough to anneal quartz or thermally reset Rb-Sr isotopic systems in muscovite since the time of mylonitization. Metamorphic mineral assemblages and mineral apparent ages in rocks north of the fault zone indicate recrystallization under similar upper greenschist-lower amphibolite grade conditions during Permian to Triassic time. Collectively these results indicate that the Honey Hill fault zone was active during the Late Paleozoic and that ductile deformation and metamorphism associated with the Alleghanian orogeny extend well into southern Connecticut. An Alleghanian age for mylonitization within the Honey Hill fault zone suggests it should be considered as a possible site for the major Late Paleozoic strike-slip displacements inferred from paleomagnetic studies for parts of coastal New England and maritime Canada.

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

    NASA Technical Reports Server (NTRS)

    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.

  18. Rb-Sr Isotopic Studies Of Antarctic Lherzolitic Shergottite Yamato 984028

    NASA Technical Reports Server (NTRS)

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

    2009-01-01

    Yamato 984028 is a Martian meteorite found in the Yamato Mountains of Antarctica. It is classified as a lherzolitic shergottite and petrographically resembles several other lherzolitic shergottites, i.e. ALHA 77005, LEW 88516, Y-793605 and Y-000027/47/97 [e.g. 2-5]. These meteorites have similarly young crystallization ages (152-185 Ma) as enriched basaltic shergottites (157-203 Ma), but have very different ejection ages (approximately 4 Ma vs. approximately 2.5 Ma), thus they came from different martian target crater areas. Lherzolitic shergottites have mg-values approximately 0.70 and represent the most mafic olivine-pyroxene cumulates. Their parental magmas were melts derived probably from the primitive Martian mantle. Here we present Rb-Sr isotopic data for Y-984028 and compare these data with those obtained from other lherzolitic and olivine-phyric basaltic shergottites to better understand the isotopic characteristics of their primitive mantle source regions. Corresponding Sm-Nd analyses for Y-984028 are in progress.

  19. Equilibrium-disequilibrium relations in the Monte Rosa Granite, Western Alps: Petrological, Rb-Sr and stable isotope data

    USGS Publications Warehouse

    Frey, M.; Hunziker, J.C.; O'Neil, J.R.; Schwander, H.W.

    1976-01-01

    Nine samples from the Monte Rosa Granite have been investigated by microscopic, X-ray, wet chemical, electron microprobe, stable isotope and Rb-Sr and K-Ar methods. Two mineral assemblages have been distinguished by optical methods and dated as Permian and mid-Tertiary by means of Rb-Sr age determinations. The Permian assemblage comprises quartz, orthoclase, oligoclase, biotite, and muscovite whereas the Alpine assemblage comprises quartz, microcline, albite+epidote or oligoclase, biotite, and phengite. Disequilibrium between the Permian and Alpine mineral assemblages is documented by the following facts: (i) Two texturally distinguishable generations of white K-mica are 2 M muscovite (Si=3.1-3.2) and 2 M or 3 T phengite (Si=3.3-3.4). Five muscovites show Permian Rb-Sr ages and oxygen isotope fractionations indicating temperatures between 520 and 560 ?? C; however, K-Ar ages are mixed or rejuvenated. Phengite always shows mid-Tertiary Rb-Sr ages, (ii) Two biotite generations can be recognized, although textural evidence is often ambiguous. Three out of four texturally old biotites show mid-Tertiary Rb-Sr cooling ages while the oxygen isotopic fractionations point to Permian, mixed or Alpine temperatures, (iii) Comparison of radiogenic and stable isotope relations indicates that the radiogenic isotopes in the interlayer positions of the micas were mobilized during Alpine time without recrystallization, that is, without breaking Al-O or Si-O bonds. High Ti contents in young muscovites and biotites also indicate that the octahedral (and tetrahedral) sites remained undisturbed during rejuvenation. (iv) 'Isotopic reversals' in the order of O18 enrichment between K-feldspar and albite exist. Arguments for equilibrium during Permian time are meagre because of Alpine overprinting effects. Texturally old muscovites show high temperatures and Permian Rb-Sr ages in concordancy with Rb-Sr whole rock ages. For the tectonically least affected samples, excellent concordance

  20. Rb-Sr Isotopic Systematics of Alkali-Rich Fragments in the Yamato-74442 LL-Chondritic Breccia

    NASA Technical Reports Server (NTRS)

    Yokoyama, T.; Misawa, K.; Okano, O.; Shih, C.-Y.; Nyquist, L. E.; Simo, J. I.; Tappa, M. J.; Yoneda, S.

    2012-01-01

    Alkali-rich igneous fragments were identified in the brecciated LL-chondrites, Kr henberg (LL5)], Bhola (LL3-6) and Yamato (Y)-74442 (LL4), and show characteristic fractionation patterns of alkaline elements. The K-Rb-Cs-rich fragments in Kr henberg, Bhola, and Y-74442 are very similar in mineralogy and petrography (olivine + pyroxene + glass), suggesting that they could have come from related precursor materials. We have undertaken Rb-Sr isotopic studies on alkali-rich fragments in Y-74442 to precisely determine their crystallization ages and the isotopic signatures of their precursor material(s).

  1. Crystallization history of rhyolites at Long Valley, California, inferred from combined U-series and Rb-Sr isotope systematics

    NASA Astrophysics Data System (ADS)

    Heumann, Arnd; Davies, Gareth R.; Elliott, Tim

    2002-05-01

    In this study, we present 87Rb/ 86Sr and 230Th/ 238U isotope analyses of glasses and phenocrysts from postcaldera rhyolites erupted between 150 to 100 ka from the Long Valley magmatic system. Both isotope systems indicate complex magma evolution with preeruptive mineral crystallization and magma fractionation, followed by extended storage in a silicic magma reservoir. Glass analyses yield a Rb-Sr isochron of 257 ± 39 ka, which can be explained by a feldspar-fractionation event ˜150 ky before eruption. Individual feldspar-glass pairs confirm this age result. A mineral 230Th- 238U isochron in a low-silica rhyolite from the Deer Mountain Dome defines an age of 236 ± 1 ka, but the glass and whole rock do not lie on the isochron. U-Th fractionation of the rocks is controlled by the accessory minerals zircon and probably allanite, which crystallized at 250 ± 3 ka and 187 ± 9 ka, respectively. All major mineral phases contain accessory mineral phases; therefore, the mineral isochron represents a mixture of zircon and allanite populations. A precision of ±1 ka for the mixing array implies that the minor phases must have crystallized within this timescale. Longer periods of crystal growth would cause the mixing array to be less well defined. U-series data from other low- and high-silica rhyolites indicate younger accessory mineral crystallization events at ˜200 and 140 ka, probably related to the thermal evolution of the magma reservoir. These crystallization events are, however, only documented by the accessory minerals and had no further influence on bulk magma compositions. We interpret the indistinguishable age results from both isotope systems (˜250 ka) to record the fractionation of small magma batches by filter pressing from a much larger underlying magma volume, followed by physical isolation and extended storage at the top of the magma reservoir for up to 150 ky.

  2. Rb-Sr whole-rock and mineral ages, K-Ar, 40Ar/39Ar, and U-Pb mineral ages, and strontium, lead, neodymium, and oxygen isotopic compositions for granitic rocks from the Salinian Composite Terrane, California:

    USGS Publications Warehouse

    Kistler, R.W.; Champion, D.E.

    2001-01-01

    This report summarizes new and published age and isotopic data for whole-rocks and minerals from granitic rocks in the Salinian composite terrane, California. Rubidium-strontium whole-rock ages of plutons are in two groups, Early Cretaceous (122 to 100 Ma) and Late Cretaceous (95 to 82 Ma). Early Cretaceous plutons occur in all granitic rock exposures from Bodega Head in the north to those from the Santa Lucia and Gabilan Ranges in the central part of the terrane. Late Cretaceous plutons have been identified in the Point Reyes Peninsula, the Santa Lucia and the Gabilan Ranges, and in the La Panza Range in the southern part of the terrane. Ranges of initial values of isotopic compositions are 87Sr/86Sr, 0.7046-0.7147, δ18O, +8.5 to +12.5 per mil, 206Pb/204Pb, 18.901-19.860, 207Pb/204Pb, 15.618-15.814, 208Pb/204Pb, 38.569- 39.493, and εNd, +0.9 to -8.6. The initial 87Sr/86Sr=0.706 isopleth is identified in the northern Gabilan Range and in the Ben Lomond area of the Santa Cruz Mountains, in Montara Mountain, in Bodega Head, and to the west of the Farallon Islands on the Cordell Bank. This isotopic boundary is offset about 95 miles (160km) by right-lateral displacements along the San Gregorio-Hosgri and San Andreas fault systems.

  3. Rb-Sr and Sm-Nd isotopic study of the Glen Mountains layered complex: Initiation of rifting within the southern Oklahoma aulacogen

    NASA Astrophysics Data System (ADS)

    Lambert, David D.; Unruh, D. M.; Gilbert, M. Charles

    1988-01-01

    Rb-Sr and Sm-Nd isotopic data for rocks and minerals of the Glen Mountains layered complex (GMLC), a midcontinent mafic layered intrusion in the Wichita Mountains of southwestern Oklahoma, constrain the time of initiation of rifting within the southern Oklahoma aulacogen and provide information on the chemistry of the early Paleozoic mantle. Four whole-rock samples define a Rb-Sr isochron corresponding to a maximum crystallization age of 577 ±165 Ma and an initial Sr isotopic composition of 0.70359 ±2. These whole-rock analyses do not define a Sm-Nd isochron; rather, they display a significant range in initial Nd isotopic composition (ɛNd = 3.63-5.35). A three-point Sm-Nd mineral-whole-rock (internal) isochron for an anorthositic gabbro provides a crystallization age of 528 ±29 Ma. These data suggest that the GMLC was emplaced into the southern Oklahoma aulacogen during the initial phase of rifting along the southern margin of the North American craton in the early Paleozoic. This Sm-Nd internal isochron age is within analytical uncertainty of U-Pb zircon ages for granites and rhyolites from the Wichita Mountains; therefore, mafic and felsic magmatism may have been contemporaneous within the rift during the early stages of development. Hybrid rocks and composite dikes in the Wichita Mountains provide field evidence for contemporaneous mafic and felsic magmas. Initial Sr and Nd isotopic data suggest that magmas parental to the GMLC were derived from a depleted mantle source. However, Nd isotopic data for the GMLC plot distinctly below data for the depleted mantle source cited by DePaolo and thus suggest that the parental magmas of the GMLC were either contaminated by Proterozoic crust of the southern midcontinent or were derived from a heterogeneous mantle source region that had variable initial Nd isotopic compositions.

  4. Sm-Nd and Rb-Sr Isotopic Studies of Meteorite Kalahari 009: An Old VLT Mare Basalt

    NASA Technical Reports Server (NTRS)

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

    2008-01-01

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

  5. Rb-Sr Isotopic Systematics of Felsic Igneous Rocks, Wichita Mountains, Oklahoma

    NASA Astrophysics Data System (ADS)

    Min, K.; Gilbert, M. C.

    2001-12-01

    Recently determined Rb-Sr isotopic characteristics of twelve of the recognized felsic units of the Cambrian Southern Oklahoma Aulacogen, which crop out in the Wichita Mountains of the southwestern Oklahoma, give some clues to the petrogenesis of these felsic units. 1) Plots of 87Rb/86Sr vs. 87Sr/86Sr form subsets yielding dates of 516 Ma and 522 Ma, discrepancies of about 10 to 20 Ma from the U-Pb zircon age for the Mount Scott Granite of 534 Ma, probably attributable to a systematic loss of radiogenic 87Sr for these units. 2) The Mount Scott Granite and related units (n=7) including Medicine Park Granite and Saddle Mountain Granite give a probable pseudoisochron of 516\\pm4{}Ma and an initial 87Sr/86Sr of 0.7045\\pm4{}, indicating derivation from a primitive mantle source with little crustal contamination. 3) A well-regressed line of 522\\pm2{} Ma with an initial 87Sr/86Sr of 0.7059\\pm7{} is shown by the Long Mountain Granite (n=3), one of the finer-grained western granites, and the Fort Sill Section of the Carlton Rhyolite (n=2) in the eastern Wichitas, which indicates that both were possibly derived contemporaneously from a mixed crustal-mantle source. 4) The Lugert Granite of the western Wichitas has variable and relatively high 87Sr/86Sr initials at 516 Ma probably indicating heterogeneous crustal sources. Interpretation of these data can be made with the following scenario: The earliest known felsic unit is the Carlton Rhyolite, Fort Sill Section. This must have been generated mostly from crustal melting around large mafic plutons in the mid- to lower crust. Crustal melting around the mafic plutons continued to generate liquids rising to the emplacement position, e.g., Long Mountain Granite. Following this, the host magma for the Mount Scott set of units originated dominantly by fractional crystallization from the mafic plutons. Subsequently, additional mafic magma must have moved into the lower- to mid-crust, at some other stratigraphic level, melting a

  6. Rb-Sr and Sm-Nd isotopic study of the Glen Mountains layered complex: initiation of rifting within the southern Oklahoma aulacogen

    SciTech Connect

    Lambert, D.D.; Unruh, D.M.; Gilbert, M.C.

    1988-01-01

    Rb-Sr and Sm-Nd isotopic data for rocks and minerals of the Glen Mountains layered complex (GMLC), a midcontinent mafic layered intrusion in the Wichita Mountains of southwestern Oklahoma, constrain the time of initiation of rifting within the southern Oklahoma aulacogen and provide information on the chemistry of the early Paleozoic mantle. Four whole-rock samples define a Rb-Sr isochron corresponding to a maximum crystallization age of 577 +/- 165 Ma and an initial Sr isotopic composition of 0.70359 +/- 2. A three-point Sm-Nd mineral-whole-rock (internal) isochron for an anorthositic gabbro provides a crystallization age of 528 +/- 29 Ma. These data suggest that the GMLC was emplaced into the southern Oklahoma aulacogen during the initial phase of rifting along the southern margin of the North American craton in the early Paleozoic. This Sm-Nd internal isochron age is within analytical uncertainty of U-Pb zircon ages for granites and rhyolites from the Wichita Mountains; therefore, mafic and felsic magmatism may have been contemporaneous within the rift during the early stages of development. Hybrid rocks and composite dikes in the Wichita Mountains provide field evidence for contemporaneous mafic and felsic magmas. Initial Sr and Nd isotopic data suggest that magmas parental to the GMLC were derived from a depleted mantle source. However, Nd isotopic data for the GMLC plot distinctly below data for the depleted mantle source cited by DePaolo and thus suggest that the parental magmas of the GMLC were either contaminated by Proterozoic crust of the southern midcontinent or were derived from a heterogenous mantle source region that had variable initial Nd isotopic compositions.

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

    SciTech Connect

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

    2008-11-17

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

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

    USGS Publications Warehouse

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

    1983-01-01

    Isotopic ratios and trace element abundances were measured on samples of Ir-enriched clay at the Cretaceous-Tertiary boundary, and in carbonate and marl from 5 cm below and 3 cm above the boundary. Samples were leached with acetic acid to remove carbonate, and with hydrochloric acid. Leachates and residues were measured. The Sr, Nd, O and H isotopic compositions of the boundary clay residues are distinct from those of the stratigraphically neighboring materials. The data indicate that most of the clay material was derived from a terrestrial source with relatively low 87Sr/86Sr and high 143Nd/144Nd ratios. The ??18O data suggest that the detritus has been modified by submarine weathering. K-Ca and Rb-Sr systematics, as well as O isotope ratios of K-feldspar spherules within the boundary clay, suggest that they are predominantly authigenic and may have formed after the time of deposition. However, Sm-Nd and Rb-Sr isotopic data indicate that the spherules contain relict material that provides information on the nature of the original detritus. The isotopic evidence for foreign terrestrial detritus in the boundary clay, the low rare earth element concentrations and high Ni concentration, support the hypothesis of a terminal Cretaceous asteroidal impact that produced a global layer of fallout. The data are most easily explained if the impact site was on oceanic crust rather than continental crust, and if a substantial fraction of the fallout was derived from relatively deep within the lithosphere (>3 km). This would probably require a single large impactor. ?? 1983.

  9. The Estherville mesosiderite - U-Pb, Rb-Sr, and Sm-Nd isotopic study of a polymict breccia

    NASA Astrophysics Data System (ADS)

    Brouxel, M.; Tatsumoto, M.

    1991-04-01

    The U-Pb, Rb-Sr, and Sm-Nd isotopic systematics of the Estherville mesoderite were studied using analytical procedures and mass spectrometric techniques similar to those reported by Nakamura et al. (1976), Tatsumoto et al. (1987), and Premo et al. (1989) to analyze 21 separates of a 13-g Estherville clast, obtained either by handpicking or by using density and magnetic separation methods. The results on the Pb-Pb and U-Pb ages (about 4555 and about 4560 Ma, respectively) indicate that at least a part of the Estherville silicate fraction was formed early in the history of solar system. Younger Pb-Pb and U-Pb ages (about 4.43 Ga) were also obtained, confirming the heterogeneity of the Estherville mesoderite that is in agreement with the Wasson and Rubin (1985) suggestion of several generations of meteoritic impacts. The Sm-Nd and Rb-Sr ages were found to be close to 4.56 Ga.

  10. The Estherville mesosiderite - U-Pb, Rb-Sr, and Sm-Nd isotopic study of a polymict breccia

    NASA Technical Reports Server (NTRS)

    Brouxel, M.; Tatsumoto, M.

    1991-01-01

    The U-Pb, Rb-Sr, and Sm-Nd isotopic systematics of the Estherville mesoderite were studied using analytical procedures and mass spectrometric techniques similar to those reported by Nakamura et al. (1976), Tatsumoto et al. (1987), and Premo et al. (1989) to analyze 21 separates of a 13-g Estherville clast, obtained either by handpicking or by using density and magnetic separation methods. The results on the Pb-Pb and U-Pb ages (about 4555 and about 4560 Ma, respectively) indicate that at least a part of the Estherville silicate fraction was formed early in the history of solar system. Younger Pb-Pb and U-Pb ages (about 4.43 Ga) were also obtained, confirming the heterogeneity of the Estherville mesoderite that is in agreement with the Wasson and Rubin (1985) suggestion of several generations of meteoritic impacts. The Sm-Nd and Rb-Sr ages were found to be close to 4.56 Ga.

  11. The Chronology and Petrogenesis of the Mare Basalt Clast from Lunar Meteorite Dhofar 287: Rb-Sr and Sm- Nd Isotopic Studies

    NASA Technical Reports Server (NTRS)

    Shih, C.-Y.; Nyquist, L. E.; Reese, Y.; Wiesmann, H.; Nazarov, M. A.; Taylor, L. A.

    2002-01-01

    The Sm-Nd isochron for lunar mare basalt meteorite Dhofar 287A yields T = 3.46 +/- 0.03 Ga and Nd = 0.6 +/- 0.3. Its Rb-Sr isotopic system is severely altered. The basalt is unique, probably coming from an enriched mantle source. Additional information is contained in the original extended abstract.

  12. Three-System Isotopic of Lunar Norite 78238: Rb-Sr Results

    NASA Technical Reports Server (NTRS)

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

    2005-01-01

    The duration of lunar magma ocean (LMO) crystallization is poorly constrained (Fig. 1). Three techniques employed to determine the age of LMO solidification are 1) dating ferroan anorthosites (FANs), thought to be primary cumulates from the LMO, 2) calculating model ages for KREEP, the most incompatible element enriched material that remained after approx.99.5% of the LMO crystallized [1], and 3) constraining the age of the oldest KREEP-rich magnesium suite (Mg-suite) or alkali suite rock. Dating FANs is difficult because the samples are essentially monomineralic and contain low abundances of many elements used in isotopic dating. In addition, the young ages determined for some FANs may be related to impact metamorphism, potentially making FANs non-ideal for dating the age of LMO crystallization (e.g., [2]). Model ages for KREEP formation are dependent on the assumptions of the initial isotopic composition and parent/daughter ratio of the source. However, lunar rocks are susceptible to isotopic resetting and volatile element loss during shock, and are therefore unlikely to yield consistent model LMO crystallization ages (e.g., [3]). Rocks from the Mg-suite contain KREEP, indicating that they formed after LMO crystallization, and have old ages that indicate they formed almost immediately after the LMO crystallized (Fig. 1). Therefore, precisely dating the oldest Mg-suite rock is a promising way to constrain the age of LMO solidification.

  13. Origin and evolution of the Ilmeny-Vishnevogorsky carbonatites (Urals, Russia): insights from trace-element compositions, and Rb-Sr, Sm-Nd, U-Pb, Lu-Hf isotope data

    NASA Astrophysics Data System (ADS)

    Nedosekova, I. L.; Belousova, E. A.; Sharygin, V. V.; Belyatsky, B. V.; Bayanova, T. B.

    2013-02-01

    The carbonatites of the Ilmeny-Vishnevogorsky Alkaline Complex (IVAC) are specific in geological and geochemical aspects and differ by some characteristics from classic carbonatites of the zoned alkaline-ultramafic complexes. Geological, geochemical and isotopic data and comparison with relevant experimental systems show that the IVAC carbonatites are genetically related to miaskites, and seem to be formed as a result of separation of carbonatite liquid from a miaskitic magma. Appreciable role of a carbonate fluid is established at the later stages of carbonatite formation. The trace element contents in the IVAC carbonatites are similar to carbonatites of the ultramafic-alkaline complexes. The characteristic signatures of the IVAC carbonatites are a high Sr content, a slight depletion in Ba, Nb, Та, Ti, Zr, and Hf, and enrichment in HREE in comparison with carbonatites of ultramafic-alkaline complexes. This testifies a specific nature of the IVAC carbonatites related to the fractionation of a miaskitic magma and to further Late Paleozoic metamorphism. Isotope data suggest a mantle source for IVAC carbonatites and indicate that moderately depleted mantle and enriched EMI-type components participated in magma generation. The lower crust could have been involved in the generation of the IVAC magma.

  14. Rb-Sr and Sm-Nd Isotopic Studies of Martian Depleted Shergottes SaU 094/005

    NASA Technical Reports Server (NTRS)

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

    2007-01-01

    Sayh al Uhaymir (SaU) 094 and SaU 005 are olivine-phyric shergottites from the Oman desert and are considered as pairs. [e.g., 1]. They are very similar to the Libyan desert shergottite Dar al Gani (DaG) 476 in petrology, chemistry and ejection age [2-6]. This group of shergottites, also recognized as depleted shergottites [e.g. 7] has been strongly shocked and contains very low abundances of light rare earth elements (REE). In addition, terrestrial contaminants are commonly present in meteorites found in desert environments. Age-dating these samples is very challenging, but lower calcite contents in the SaU meteorites suggest that they have been subjected to less severe desert weathering than their DaG counterparts [3-4]. In this report, we present Rb-Sr and Sm-Nd isotopic results for SaU 094 and SaU 005, discuss the correlation of their ages with those of other similar shergottites, and discuss their petrogenesis.

  15. Rb Sr and K Ar systems of biotite in surface environments regulated by weathering processes with implications for isotopic dating and hydrological cycles of Sr isotopes

    NASA Astrophysics Data System (ADS)

    Jeong, Gi Young; Cheong, Chang-Sik; Kim, Jeongmin

    2006-09-01

    Biotite is widely used for Rb-Sr and K-Ar isotopic dating and influences Sr isotope geochemistry of hydrological regimes. The isotopic system of biotite behaves diversely in response to surface weathering; i.e. the complete preservation of original Rb-Sr and K-Ar isotopic ages or dramatic reduction. In this study, we have explored the relation between the behavior of isotopic systems and complex weathering processes of biotites in the weathering profiles distributed on the Mesozoic granitoids in South Korea. In the lower parts of the profiles, biotite in the early stages of weathering was transformed into either oxidized biotite or hydrobiotite, with a mass release of 87Sr and 40Ar forced by the rapid oxidation of ferrous iron. During the transformation to oxidized biotite, 87Sr and 40Ar were preferentially released relative to Rb and K, respectively, via solid-state diffusion through the biotite lattice, resulting in a drastic reduction of original isotopic age. The reduction of Rb-Sr age was greater than that of K-Ar age because K was preferentially released over Rb whereas 87Sr and 40Ar were released proportionally to each other. However, during the transformation of biotite to hydrobiotite (i.e., to regularly interstratified biotite-vermiculite), 87Sr, Rb, 40Ar, and K were completely retained in the alternating biotite interlayer, and thus the original isotopic age can be preserved. In the upper parts of the profiles, where iron oxidation was almost completed, 87Sr, Rb, 40Ar, and K were gradually and proportionally released, with no further significant change in isotopic age during the gradual transformation of the early-formed oxidized biotite into hydrobiotite and vermiculite or during their final decomposition to kaolinite. The ratios and amounts of isotopes released from weathered biotites are dependent upon the degree of iron oxidation and the pathways of mineralogical transformation. Regional and local variations in isotopic systems affected by particular

  16. Hf-W, Sm-Nd, and Rb-Sr isotopic evidence of late impact fractionation and mixing of silicates on iron meteorite parent bodies

    NASA Astrophysics Data System (ADS)

    Snyder, Gregory A.; Lee, Der-Chuen; Ruzicka, Alex M.; Prinz, Martin; Taylor, Lawrence A.; Halliday, Alex N.

    2001-03-01

    We report the first Sm-Nd and Rb-Sr isotopic analyses of silicate inclusions in four IIE iron meteorites: Miles, Weekeroo Station A and B, and Watson. We also report the Hf-W isotopic composition of a silicate inclusion from Watson and 182W/ 184W of the host FeNi metal in all four IIEs. The host metal in Watson has a negative ɛW value (-2.21±0.24), similar to or higher than other iron meteorites [1,35] and consistent with segregation of metal from silicate early in solar system history. However, the large silicate inclusion in the Watson IIE iron yielded a chondritic ɛW value (-0.50±0.55), thus indicating a lack of equilibration with the FeNi host within the practical lifetime of activity of the parent 182Hf (˜50 Ma). One of the silicate inclusions in Miles is roughly chondritic in major-element composition, has a present-day ɛNd of +10.3, relatively non-radiogenic 87Sr/ 86Sr (0.714177±13), and a TCHUR age of 4270 Ma. Two silicate inclusions from Weekeroo Station and one from Watson exhibit fractionated Sm/Nd and Rb/Sr ratios, and more radiogenic 87Sr/ 86Sr (0.731639±12 to 0.791852±11) and non-radiogenic ɛNd values (-5.9 to -13.4). The silicate inclusion in Watson has a TCHUR age of 3040 Ma, in agreement with previously determined 4He and 40Ar gas retention ages, indicative of a late thermal event. A later event is implied for the two silicate inclusions in Weekeroo Station, which yield indistinguishable TCHUR ages of 698 and 705 Ma. Silicate inclusions in IIE iron meteorites formed over a period of 3 billion yr by impacts, involving an H-chondrite parent body and an FeNi metal parent body. The LILE-enriched nature of some of these silicates suggests several stages of melting, mixing, and processing. However, there is little evidence to suggest that the silicates in the IIE irons were ever in equilibrium with the host FeNi metal.

  17. Sm-Nd and Rb-Sr isotope systematics of an Archean anorthosite and related rocks from the Superior Province of the Canadian Shield

    NASA Technical Reports Server (NTRS)

    Ashwal, L. D.; Wooden, J. L.; Phinney, W. C.; Morrison, D. A.

    1985-01-01

    Sm-Nd and Rb-Sr isotopic data for the Bad Vermilion Lake anorthosite in the Rainy Lake area of the Superior Province of northwesten Ontario show that direct ages of Archean anorthosites can be obtained with these isotopic systems despite the effects of low-grade metamorphism. There is sufficient spread in Sm/Nd between plagioclase megacrysts and coexisting mafic groundmass to allow the determination of reasonably precise internal Sm-Nd isochrons. Initial isotopic ratios of Nd and Sr add to the growing body of data indicating the Superior Province is underlain by depleted mantle.

  18. An extremely low U Pb source in the Moon: UThPb, SmNd, RbSr, and 40Ar 39Ar isotopic systematics and age of lunar meteorite Asuka 881757

    USGS Publications Warehouse

    Misawa, K.; Tatsumoto, M.; Dalrymple, G.B.; Yanai, K.

    1993-01-01

    We have undertaken UThPb, SmNd, RbSr, and 40Ar 39Ar isotopic studies on Asuka 881757, a coarse-grained basaltic lunar meteorite whose chemical composition is close to low-Ti and very low-Ti (VLT) mare basalts. The PbPb internal isochron obtained for acid leached residues of separated mineral fractions yields an age of 3940 ?? 28 Ma, which is similar to the U-Pb (3850 ?? 150 Ma) and Th-Pb (3820 ?? 290 Ma) internal isochron ages. The Sm-Nd data for the mineral separates yield an internal isochron age of 3871 ?? 57 Ma and an initial 143Nd 144Nd value of 0.50797 ?? 10. The Rb-Sr data yield an internal isochron age of 3840 ?? 32 Ma (??(87Rb) = 1.42 ?? 10-11 yr-1) and a low initial 87Sr 86Sr ratio of 0.69910 ?? 2. The 40Ar 39Ar age spectra for a glass fragment and a maskelynitized plagioclase are relatively flat and give a weighted mean plateau age of 3798 ?? 12 Ma. We interpret these ages to indicate that the basalt crystallized from a melt 3.87 Ga ago (the Sm-Nd age) and an impact event disturbed the Rb-Sr system and completely reset the K-Ar system at 3.80 Ga. The slightly higher Pb-Pb age compared to the Sm-Nd age could be due to the secondary Pb (from terrestrial and/or lunar surface Pb contamination) that remained in the residues after acid leaching. Alternatively, the following interpretation is also possible; the meteorite crystallized at 3.94 Ga (the Pb-Pb age) and the Sm-Nd, Rb-Sr, and K-Ar systems were disturbed by an impact event at 3.80 Ga. The crystallization age obtained here is older than those reported for low-Ti basalts (3.2-3.5 Ga) and for VLT basalts (3.4 Ga), but similar to ages of some mare basalts, indicating that the basalt may have formed from a magma related to a basin-forming event (Imbrium?). The age span for VLT basalts from different sampling sites suggest that they were erupted over a wide area during an interval of at least ~500 million years. The impact event that thermally reset the K-Ar system of Asuka 881757 must have been post

  19. Constraints on Martian Differentiation Processes from Rb-Sr and Sm-Nd Isotopic Analyses of the Basaltic Shergottite QUE 94201

    NASA Technical Reports Server (NTRS)

    Borg, Lars E.; Nyquist, Larry E.; Taylor, Larry A.; Wiesmann, Henry; Shih, Chi-Y.

    1997-01-01

    Isotopic analyses of mineral, leachate, and whole rock fractions from the Martian shergottite meteorite QUE 94201 yield Rb-Sr and Sm-Nd crystallization ages of 327 +/- 12 and 327 +/- 19 Ma, respectively. These ages are concordant, although the isochrons are defined by different fractions within the meteorite. Comparison of isotope dilution Sm and Nd data for the various QUE 94201 fractions with in situ ion microprobe data for QUE 94201 minerals from the literature demonstrate the presence of a leachable crustal component in the meteorite. This component is likely to have been added to QUE 94201 by secondary alteration processes on Mars, and can affect the isochrons by selectively altering the isotopic systematics of the leachates and some of the mineral fractions. The absence of crustal recycling processes on Mars may preserve the geochemical evidence for early differentiation and the decoupling of the Rb-Sr and Sm-Nd isotopic systems, underscoring one of the fundamental differences between geologic processes on Mars and the Earth.

  20. A 2.5 G.a. reworked sialic crust: Rb-Sr ages and isotopic geochemistry of late archaean volcanic and plutonic rocks from E. Finland

    NASA Astrophysics Data System (ADS)

    Martin, Hervé; Querré, Guirec

    1984-03-01

    In east-central Finland, Archaean terrains present three main lithologic units: a) gneissic basement, emplaced from 2.86 G.a. to 2.62 G.a., b) greenstone belt (2.65 G.a.) and c) calc-alkaline magmatism (2.50 G.a. to 2.40 G.a). Twenty three rocks of the calc-alkaline suite have been chosen for geochronologic and Rb-Sr isotopic studies. These rocks are subdivided into three groups: 1) acid volcanics from Luoma, 2) augen gneiss from Arola, and 3) post kinematik pink leucogranite from Arola. The 2.50±0.10 G.a. age of the Luoma volcanics indicates that they represent the upper part of a greenstone belt composed of a single sequence of volcanic rocks. The ages, initial 87Sr/86Sr (ISr) and major element compositions of the augen gneisses of Arola and Suomussalmi indicate that these rocks are the plutonic equivalents of the Luoma acid volcanics. The Arola pink leucogranite marks the terminal phase of Archaean magmatic activity (from 2.86 G.a. to 2.41 G.a.). This was followed by at least 0.40 G.a. of quiescence. The ISr and major element compositions suggest that the genesis of the calc-alkaline magmatic rocks involved crustal materials, but all their geochemical features cannot be explained without the participation of mafic greenstone belt materials. The first crustal components had low I and low K2O/ Na2O ratios while the younger ones (calc-alkaline magmas) had medium to high ISr and high K2O/Na2O ratios. Thus the petrogenetic processes have changed with time from ensimatic to ensialic, implying major reworking of preexisting crustal materials. This evolution leads to the accretion of the continental crust from the mantle.

  1. Rb-Sr and Sm-Nd isotopic and REE studies of igneous components in the bulk matrix domain of Martian breccia Northwest Africa 7034

    NASA Astrophysics Data System (ADS)

    Nyquist, Laurence E.; Shih, Chi-Yu; McCubbin, Francis M.; Santos, Alison R.; Shearer, Charles K.; Peng, Zhan X.; Burger, Paul V.; Agee, Carl B.

    2016-03-01

    The bulk matrix domain of the Martian breccia NWA 7034 was examined petrographically and isotopically to better understand the provenance and age of the source material that make up the breccia. Both 147Sm-143Nd and 146Sm-142Nd age results for mineral separates from the bulk matrix portion of breccia NWA 7034 suggest that various lithological components in the breccia probably formed contemporaneously ~4.44 Ga ago. This old age is in excellent agreement with the upper intersection ages (4.35-4.45 Ga) for U-Pb discordia and also concordia defined by zircon and baddeleyite grains in matrix and igneous-textured clasts. Consequently, we confirm an ancient age for the igneous components that make up the NWA 7034 breccia. Substantial disturbance in the Rb-Sr system was detected, and no age significance could be gleaned from our Rb-Sr data. The disturbance to the Rb-Sr system may be due to a thermal event recorded by bulk-rock K-Ar ages of 1.56 Ga and U-Pb ages of phosphates at about 1.35-1.5 Ga, which suggest partial resetting from an unknown thermal event(s), possibly accompanying breccia formation. The NWA 7034 bulk rock is LREE enriched and similar to KREEP-rich lunar rocks, which indicates that the earliest Martian crust was geochemically enriched. This enrichment supports the idea that the crust is one of the enriched geochemical reservoirs on Mars that have been detected in studies of other Martian meteorites.

  2. Sm-Nd and Rb-Sr isotopic systematics of the Pea Ridge Fe-P deposit and related rocks, southeast Missouri

    SciTech Connect

    Marikos, M.A.; Barton, M.D. . Dept. of Geosciences)

    1993-03-01

    Pea ridge is a discordant Middle Proterozoic Fe-P deposit hosted in rhyolite tuffs and flows of the 1.4--1.5 Ga St. Francois terrane. Host rocks and the deposit are cut by basalt and aplite/pegmatite dikes. The deposit overlies a blind pluton which is partially surrounded by a trachytic ring complex. In the deposit, which is mined for Fe, early Qtz+Amph+Mag+Ap rock is cut by Mag+Ap+Qtz rock. Subsequently, portions of the deposit and host rocks were brecciated, oxidized and silicified to produce a complex suite of rocks enriched in Hem+Qtz+Ksp+Mu. Late breccia pipes/dikes cut the complex and were mineralized with Bar+Ksp+Flu+Chl+Cc+REE-phosphates. Sm/Nd and Rb/Sr isotopic systematics have been studied to: (1) constrain source(s) of igneous rocks and deposit components, (2) refine ages of magmatism, mineralization, and later hydrothermal activity, (3) begin regional comparison of isotopic systematics in SE Missouri Fe deposits, and (4) complement ongoing Missouri DGLS/USGS studies. Fourteen combined Sm-Nd and Rb-Sr analyses were done on materials including two host rhyolites, two nearby trachytes, two gneiss samples representing plausible basement, two intramineral dikes, and six samples of mineralization.

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

    NASA Technical Reports Server (NTRS)

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

    2010-01-01

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

  4. Sm-Nd, Rb-Sr, and /sup 18/O//sup 16/O isotopic systematics in an oceanic crustal section: Evidence from the Samial ophiolite

    SciTech Connect

    McCulloch, M.T.; Gregory, R.T.; Wasserburg, G.J.; Taylor, H.P. Jr.

    1981-04-10

    The Sm-Nd, Rb-Sr, and /sup 18/O//sup 16/O isotopic systems have been used to distinguish between the effects of seafloor hydrothermal alteration and primary magmatic isotopic variations. The Sm-Nd isotopic system is essentially unaffected by seawater alteration, while the Rb-Sr and /sup 18/O//sup 16/O systems are sensitive to hydrothermal interactions with seawater. Sm-Nd mineral isochrons from the cumulate gabbros of the Samail ophiolite have an initial /sup 143/Nd//sup 144/Nd ratio of e/sub Nd/ = 7.8 +- 0.3, which clearly substantiates the oceanic affinity of this complex. The initial /sup 143/Nd//sup 144/Nd ratios for the harzburgite, plagiogranite, sheeted diabase dikes, and basalt units have a limited range in e/sub Nd/ of from 7.5 to 8.6, indicating that all the lithologies have distinctive oceanic affinities, although there is also some evidence for small isotopic heterogeneities in the magma reservoirs. The Sm-Nd mineral isochrons give crystallization ages of 128 +- 20 m.y. and 150 +- 40 m.y. from Ibra and 100 +- 20 m.y. from Wadi Fizh, which is approximately 300 km NW of Ibra. These crystallization ages are interpreted as the time of formation of the oceanic crust. The /sup 87/Sr//sup 86/Sr initial ratios on the same rocks have an extremely large range of from 0.7030 to 0.7065 and the d/sup 18/O values vary from 2.6 to 12.7. These large variations clearly demonstrate hydrothermal interaction of oceanic crust with seawater.

  5. 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

    PubMed Central

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

    2014-01-01

    New Rb-Sr, 146,147Sm-142,143Nd 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, 147Sm-143Nd=4283±23 Ma and Lu-Hf=4421±68 Ma. The data define an initial 146Sm/144Sm ratio of 0.00193±0.00092 corresponding to ages between 4348 and 4413 Ma depending on the half-life and initial abundance used for 146Sm. 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—142Nd/144Nd 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. PMID:25114305

  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.

    PubMed

    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. PMID:25114305

  7. U/Pb, Sm/Nd and Rb/Sr geochronological and isotopic study of northern Sierra Nevada ophiolitic assemblages, California

    NASA Astrophysics Data System (ADS)

    Saleeby, J. B.; Shaw, H. F.; Niemeyer, Sidney; Moores, E. M.; Edelman, S. H.

    1989-06-01

    Distinct ophiolitic assemblages occur as oceanic basement within three of the four regional tectonic belts of the northern Sierra Nevada. New U/Pb zircon, Sm/Nd and Rb/Sr data are presented for each assemblage, providing critical geochronological and isotopic constraints on the petrogenesis and tectonic evolution of the ophiolitic and associated ensimatic assemblages. Ophiolitic assemblages include from west to east the Smartville complex, Central belt and Feather River belt. The Smartville complex represents an island arc volcanic-plutonic sequence with a major late-stage sheeted dike swarm. The Sm/Nd systems from a wide compositional spectrum of rocks record a 178±21 Ma petrogenetic age and an ɛ Nd(T)=+9.2±0.6. Zircon U/Pb systems on an uppermost dacite yield a 164±2 Ma age, and on a number of plagiogranite screens and dikes from the sheeted complex 162±1 Ma ages. The Central and Feather River belts are structurally complex polygenetic assemblages. The U/Pb zircon and Sm/Nd systems record major ˜205 Ma and ˜315 Ma petrogenetic events respectively both involving depleted mantle derived magmas. Such magmatism probably occurred in marginal basin/transform systems developed within an older oceanic depleted mantle basement regime. Both Sm/Nd and U/Pb zircon systems show local components of Proterozoic sialic material. The sialic contaminants were probably introduced into the system as craton derived detritus. It is doubtful that any of the ophiolitic assemblages studied represent genetically related crust-upper mantle sequences generated during the development of new oceanic lithosphere. Integration of the geochronological data with geological relations reveals a pattern of petrogenesis and tectonics whereby progressively younger ensimatic terranes were added to the continental margin through time by plate convergence, and were ultimately welded into North American sial by a crosscutting batholithic belt. This accretionary pattern is reflected in both the

  8. A Rb-Sr and Sm-Nd Isotope Geochronology and Trace Element Study of Lunar Meteorite LaPaz Icefield 02205

    NASA Technical Reports Server (NTRS)

    Rankenburg, K.; Brandon, A. D.; Norman, M. D.

    2007-01-01

    Rubidium-strontium and samarium-neodymium isotopes of lunar meteorite LaPaz Icefield (LAP) 02205 are consistent with derivation of the parent magma from a source region similar to that which produced the Apollo 12 low-Ti olivine basalts followed by mixing of the magma with small amounts (1 to 2 wt%) of trace element-enriched material similar to lunar KREEP-rich sample SaU 169. The crystallization age of LAP 02205 is most precisely dated by an internal Rb-Sr isochron of 2991+/-14 Ma, with an initial Sr-87/Sr-88 at the time of crystallization of 0.699836+/-0.000010. Leachable REE-rich phosphate phases of LAP 02205 do not plot on a Sm-Nd mineral isochron, indicating contamination or open system behavior of the phosphates. Excluding anomalous phases from the calculation of a Sm-Nd isochron yields a crystallization age of 2992+/-85 (initial Epsilon Nd-143 = +2.9+/-0.8) that is within error of the Rb-Sr age, and in agreement with other independent age determinations for LAP 02205 from Ar-Ar and U-Pb methods. The calculated Sm-147/Nd-144 source ratios for LAP 02205, various Apollo 12 and 15 basalts, and samples with strong affinities to KREEP (SaU 169, NWA 773, 15386) are uncorrelated with their crystallization ages. This finding does not support the involvement of a common KREEP component as a heat source for lunar melting events that occurred after crystallization of the lunar magma ocean.

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

    NASA Technical Reports Server (NTRS)

    Depaolo, D. J.; Kyte, F. T.; Marshall, B. D.; Oneil, J. R.; Smit, J.

    1983-01-01

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

  10. Decoupling of the Lu-Hf, Sm-Nd, and Rb-Sr isotope systems in eclogites and a garnetite from the Sulu ultra-high pressure metamorphic terrane: Causes and implications

    NASA Astrophysics Data System (ADS)

    Liu, Yung-Hsin; Yang, Huai-Jen; Takazawa, Eiichi; Satish-Kumar, Madhusoodhan; You, Chen-Feng

    2015-10-01

    cores from the Yangtze craton, suggesting the dominance of protolith characteristics on the Lu-Hf isotope system. Being controlled by different processes, the Rb-Sr, Sm-Nd, and Lu-Hf isotope systems of the investigated samples are therefore decoupled. The εNd(220)-εHf(220) compositions of the samples deviate from the εNd(t)-εHf(t) trend of intraplate lavas to high εHf(220) at a given εNd(220) and are within the arc lava field. The protolith εNd(780)-εHf(780) compositions calculated from metamorphic initials using igneous Sm/Nd and Lu/Hf ratios show a similar distribution pattern, strengthening the arc affinity of the eclogites. These arc signatures together with the felsic-mafic bimodal geochemical features of the UHP rocks from the Sulu terrane are explained as the characteristics of protoliths generated by backarc rifting.

  11. Rb-Sr and oxygen isotopic study of alkalic rocks from the Trans-Pecos magmatic province, Texas: Implications for the petrogenesis and hydrothermal alteration of continental alkalic rocks

    SciTech Connect

    Lambert, D.D.; Malek, D.J.; Dahl, D.A. )

    1988-10-01

    Rb-Sr and O isotopic data for mid-Tertiary alkalic rocks from the Trans-Pecos magmatic province of west Texas demonstrate that hydrothermal alteration and fluid/rock (cation exchange) interactions have affected the isotope geochemistry of these rocks. Strontium and O isotopic data for late-stage minerals in an alkali basalt (hawaiite) still record two episodes of fluid/rock interactions. These data suggest that later meteoric fluids introduced Sr with a Cretaceous marine {sup 87}Sr/{sup 86}Sr ratio into minerals with significant cation exchange capacity. Dilute HCl leaching experiments demonstrate the removal of this labile or exchangeable Sr from the alkali basalt. Rb-Sr isotopic data for the leached alkali basalt and handpicked calcite record a crystallization age of 42 Ma, consistent with K-Ar data for an unaltered alkali basalt (hawaiite) dike from the same area (42.6 {plus minus} 1.3 Ma). Leaching experiments on one phonolite suggest the Sr isotopic variability in unleached phonolite and nepheline trachyte samples may be attributed to Sr in secondary calcite and zeolites, which have an upper Cretaceous marine {sup 87}Sr/{sup 86}Sr ratio. Rb-Sr isotopic data for leached phonolite and sanidine separate yield an age of 36.5 {plus minus} 0.8 Ma, within analytical uncertainty of a K-Ar biotite age (36.0 {plus minus} 1.1 Ma) of another phonolite. These leaching experiments demonstrate that the Rb-Sr isotopic systematics of hydrothermally-altered continental alkalic rocks may be significantly improved, providing more reliable geochronologic and isotopic tracer information necessary in constructing precise models of mantle sources.

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

    NASA Technical Reports Server (NTRS)

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

    2009-01-01

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

  13. Rb-Sr and Sm-Nd Isotopic Studies of Lunar Highland Meteorite Y86032 and Lunar Ferroan Anorthosites 60025 and 67075

    NASA Technical Reports Server (NTRS)

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

    2005-01-01

    Lunar meteorite Yamato (Y) 86032 is a feldspathic breccia containing anorthositic fragments similar to ferroan anorthosite (FAN) clasts commonly found in Apollo 16 highland rocks. Previous Ar-39-Ar-40 analyses of a grey anorthositic clast (,116 GC) in Y86032 revealed an old degassing age of 4.39 plus or minus 0.06 Ga, which is as old as crystallization ages of some FANs e.g. 60025, 67016 and 67215, as determined by the more robust Sm-Nd radiometric method. The calculated initial Nd value for the clast is -1.8 plus or minus 0.3 for the age. The old age and its negative initial Nd value indicate that Y86032 contains components of the primitive lunar crust related to the lunar magma ocean (LMO). We undertook further Rb-Sr and Sm-Nd isotopic investigation of three major lithologies in the meteorite as described in the mineralogical and petrological studies. Ar-39-Ar-40 analyses of these component lithologies are presented in this volume. Also, we analyzed two Apollo 16 FANs, 60025 and 67075, to compare their ages and isotopic signatures to Y86032. Y86032 probably came from a feldspathic highland terrane (FHT) on the northern farside highlands, a locality not sampled by the Apollo and Luna missions.

  14. Timing of the formation of the Changba-Lijiagou Pb-Zn ore deposit, Gansu Province, China: Evidence from Rb-Sr isotopic dating of sulfides

    NASA Astrophysics Data System (ADS)

    Hu, Qiaoqing; Wang, Yitian; Mao, Jingwen; Wei, Ran; Liu, Shengyou; Ye, Dejin; Yuan, Qunhu; Dou, Ping

    2015-05-01

    The giant Changba-Lijiagou Pb-Zn deposit is located in the north of the Xihe-Chengxian (abbreviated as "Xicheng") ore cluster in Gansu Province, China. The orebodies in the deposit are mainly hosted in the marble, dolomitic marble, and biotite-calcite-quartz schist of the Middle Devonian Anjiacha Formation. The genesis of the deposit has previously been argued to be of SEDEX type (sedimentary exhalative type) or of epigenetic hydrothermal type. This paper reports results of Rb-Sr isotopic dating on sphalerite and pyrite taken from the main orebody, which yield an isochron age of 222.3 ± 2.2 Ma for eight sphalerite samples, and 222.0 ± 3.0 Ma for the eight sphalerite samples combined with four pyrite samples, indicating that the deposit formed during the Late Triassic. The (87Sr/86Sri) value of the sphalerite is 0.71370 ± 0.00013, and that of the sphalerite and pyrite is 0.71371 ± 0.00014, which are identical within experimental error, suggesting that the ore metals are derived mainly from the continental crust. By integrating the present results with the regional geology, we propose that the Changba-Lijiagou Pb-Zn deposit is a product of regional hydrothermal mineralization processes, forced by tectono-magmatic activities, which took place in the Xicheng ore cluster during Triassic orogenic processes.

  15. Sm-Nd and Rb-Sr Isotopic Systematics of a Heavily Shocked Martian Meteorite Tissint and Petrogenesis of Depleted Shergottites

    NASA Technical Reports Server (NTRS)

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

    2014-01-01

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

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

    NASA Technical Reports Server (NTRS)

    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.

  17. Sm-Nd and Rb-Sr Ages for MIL 05035: Implications for Surface and Mantle Sources

    NASA Technical Reports Server (NTRS)

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

    2007-01-01

    The Sm-Nd and Rb-Sr ages and also the initial Nd and Sr isotopic compositions of MIL 05035 are the same as those of A-881757. Comparing the radiometric ages of these meteorites to lunar surface ages as modeled from crater size-frequency distributions as well as the TiO2 abundances and initial Sr-isotopic compositions of other basalts places their likely place of origin as within the Australe or Humboldtianum basins. If so, a fundamental west-east lunar asymmetry in compositional and isotopic parameters that likely is due to the PKT is implied.

  18. Some new aspects of dating eclogites in orogenic belts: Sm-Nd, Rb-Sr, and Pb-Pb isotopic results from the Austroalpine Saualpe and Koralpe type-locality (Carinthia/Styria, southeastern Austria)

    NASA Astrophysics Data System (ADS)

    Thöni, Martin; Jagoutz, Emil

    1992-01-01

    New Sm-Nd, Rb-Sr, and Pb-Pb isotope data on eclogites and metagabbros from the Austroalpine Koralpe and Saualpe basement nappes of the eastern Alps are presented. These rocks are encased in polymetamorphic gneisses and micaschists that yield tNdCHUR ages of between 1.04 and 1.81 Ga. ɛ0Nd values from seven eclogite whole rocks range between +7.0 and +10.8; 147Sm /144Nd is close to modern DM In a 208pb /206Pb diagram all samples plot very close to the MORB field. Most analyses of the major mineral components, garnet, clinopyroxene, zoisite/epidote, phengite, amphibole and rutile, show disequilibrium in all three isotopic systems. Internal Sm-Nd and Rb-Sr mineral isochron ages range between 53 and 151 Ma. A minimum age of around 100 Ma is estimated for the crystallization of the high-P paragenesis garnet + omphacite + zoisite + kyanite + amphibole + quartz + rutile ± phengite + accessories, on the basis of these results. Later thermal overprint, fluid activity, and retrogression during exhumation of the eclogites involved (re-)crystallization of amphibole and garnet, thus leading in part to geochronologically poorly interpretable isochrons, without strict time significance. The last (eo-Alpine) thermal climax, involving static (re-)crystallization of garnet, staurolite and kyanite within the eclogite host rocks, is defined by concordant Sm-Nd and Rb-Sr isochrons on garnet, white mica, and staurolite at around 90 ± 3 Ma. Biotite Rb-Sr ages from these rocks range between 57 and 92 Ma. Plagioclase, pyroxene, and whole rock, analyzed from a relic gabbro core that shows continuous transition into eclogite from the southern Koralpe, yielded a Sm-Nd isochron of 275 ± 18 Ma, and an initial 143Nd /144Nd ratio of 0.51271 ± 2 ( ɛtNd = + 8.4 ± 0.5). This age is interpreted to date primary magmatic crystallization, thus setting also an uppermost time limit for eclogite metamorphism in the study area. The same outcrop yields a Sm-Nd isochron age for garnet and whole rock

  19. Isotope systematics and shock-wave metamorphism: II. U-Pb and Rb-Sr in naturally shocked rocks; the Haughton Impact Structure, Canada

    SciTech Connect

    Schaerer, U. ); Deutsch, A. )

    1990-12-01

    Minerals and whole rocks from crystalline fragments collected in the allochthonous polymict breccia of the 23-Ma-old Haughton impact crater on Devon Island (Arctic Canada) were analyzed for U-Pb, K, and Rb-Sr in order to constrain degrees of shock-wave induced perturbations in these systems. The results show that shock-wave metamorphism at {ge}50 GPa with onset of total melting does not significantly affect the U-Pb chronometers in monazite and zircon. Monazite preserved its age of crystallization during high-grade metamorphism at 1928.2 (+2.1/{minus}2.0) Ma (2 {sigma}-errors) as dated by the upper intercept of 2-9% discordant monazites. The same analyses yield a lower intercept age of 277.5 (+35.1/{minus}35.0) Ma in the concordia diagram, demonstrating that discordancy is not a direct effect of shock-wave metamorphism but a product of time integrated Pb-diffusion prior to the impact event, which occurred 23 Ma ago. This constrains maximal shock-induced Pb-loss to less than 3% including possible alteration-related Pb diffusion from the shock damaged grains. In 1903.1 (+1.4/{minus}1.1) Ma old monazite from an unshocked reference gneiss, recent Pb-loss also reaches 3% corroborating the occurrence of weak alteration-related U/Pb fractionation. The data substantiate that U-Pb discordance patterns are not a reliable chronometer to data impact events.

  20. U-Th-Pb and Rb-Sr measurements on some Apollo 14 lunar samples.

    NASA Technical Reports Server (NTRS)

    Tatsumoto, M.; Hedge, C. E.; Doe, B. R.; Unruh, D. M.

    1972-01-01

    The concentrations of selected elements and elemental ratios in some Apollo 14 samples are presented in a table. Another table shows the isotopic composition of lead and strontium in some Apollo 14 samples. Graphs are provided with lead isotope ratio plots and a strontium evolution diagram. Rb-Sr ages are discussed together with isochron age methods of U-Th-Pb, a primary Pb-Pb isochron, a secondary Pb-Pb isochron, U-Pb concordia age relations, and U-Th-Pb concordia relations. Breccias and some soil samples as well as a basalt sample give evidence of significant enrichment of lead relative to uranium and thorium billions of years ago at the Fra Mauro site.

  1. NWA 7034 Martian Breccia: Disturbed Rb-Sr Systematics, Preliminary Is Approximately 4.4 Ga Sm-Nd Age

    NASA Technical Reports Server (NTRS)

    Nyquist, L. E.; Shih, C.-Y.; Peng, Zhan Xiong; Agee, C

    2013-01-01

    Agee et al. [1] reported a Rb-Sr age of 2.089 [plus or minus] 0.081 Ga for the unique Martian meteoritic breccia NWA 7034 making it the oldest Martian basalt, dating to the early Am-azonian epoch [2] of Martian geologic history. We have attempt-ed to confirm this exciting result. Our new Rb-Sr analyses show the Rb-Sr isotopic system to be disturbed, but preliminary Sm-Nd data suggest an even older age of approximately 4.4 Ga for at least some brec-cia components.

  2. Rb-Sr and Sm-Nd Isotope Systematics of Shergottite NWA 856: Crystallization Age and Implications for Alteration of Hot Desert SNC Meteorites

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

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

  3. Age and provenance of the target materials for tektites and possible impactites as inferred from Sm-Nd and Rb-Sr systematics

    NASA Technical Reports Server (NTRS)

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

    1982-01-01

    Chemical, trace element, and isotopic compositions of tektites are consistent with production by melting of sediments derived from the old terrestrial continental crust. Each tektite group is characterized by a uniform Nd model age, interpreted as the time of formation of the crustal segment which weathered to form the parent sediment for the tektites. Sr model ages are variable within each group, reflecting Rb-Sr fractionation, and, in the favorable limit of very high Rb/Sr ratios, approach the time of sedimentation of the parent material which melted to form the tektites. Unlike tektites, which are dense homogeneous objects, sanidine spherules are porous, fine grained inhomogeneous objects. The leaching experiment employed by the present study shows that the sanidine spherules could have been formed by an oceanic impact involving basaltic crust and overlying sediments or seawater.

  4. Timing of Early Proterozoic collisional and extensional events in the granulite-gneiss-charnockite-granite complex, Lake Baikal, USSR: A U-Pb, Rb-Sr, and Sm-Nd isotopic study

    SciTech Connect

    Aftalion, M. ); Bibikova, E.V. ); Bowes, D.R. ); Hopwood, A.M. ); Perchuk, L.L. )

    1991-11-01

    In the Sharyzhalgay Complex of the Lake Baikal region in eastern Siberia Early Proterozoic collisional and extensional events were separated by ca. 100 m.yr. The earlier collisional event, associated with the development of granulites and gneisses as the result of high-grade dynamothermal metamorphism, took place close to 1965 {plus minus} 4 Ma. A {sup 207}Pb/{sup 204}Pb vs. {sup 206}Pb/{sup 204}Pb isochron for zircon from five size fractions and a six point Rb-Sr whole-rock errorchron give generally corresponding ages of 1956 {plus minus} 8 and 1963 {plus minus} 163 Ma, respectively. The later extensional event, associated with charnockitization due to the uprise of fluids and heat in a regime corresponding to the middle to upper crustal levels of a Basin and Range-type province, was initiated in the 1880-1860 Ma period. The event was continued with magmatic emplacement of granitic masses into the deep levels of caldera-like structures, possibly during the upper time range of lower concordia intercept ages of 1817 +30/{minus}32 and 1797 +40/{minus}44 Ma for two distinctly different zircon populations in a pyroxene-bearing granodiorite interpreted as an evolved (and contaminated) product of the mantle-derived magma that was the source of CO{sub 2} involved in the charnockitization. Upper intercept ages of 2784 +48/{minus}45 and 2775 +61/{minus}55 Ma indicate late Archean crust at depth as the source region of the incorporated zircon. T{sub DM} ages from Sm-Nd isotopic data show that the protolith of the lithologically layered supracrustal assemblage, subsequently polyphase deformed and polymetamorphosed in Early Proterozoic times, was also formed in Early Proterozoic (not Archean) times.

  5. Rb-Sr ages of the Archean rocks from the Vermilion district, northeastern Minnesota

    NASA Technical Reports Server (NTRS)

    Jahn, B.-M.; Murthy, V. R.

    1975-01-01

    The Vermilion district in Northeastern Minnesota is a classic example of a lower Precambrian greenstone-granite terrane in the Superior Province of the Canadian Shield. The present study presents new Rb-Sr isotopic data for the Ely Greenstone, the Newton Lake Formation, granitic pebbles that occur within the Ely Greenstone, a graywacke composite of the Knife Lake Group, and some Algoman granites whose data are complementary to those of Peterman et al. (1972). The isochron ages obtained are statistically indistinguishable and therefore cannot be used to resolve the timing of specific geologic events. Volcanic extrusion, granitic intrusion, and metamorphism are shown to be less contemporaneous events which probably took place within a time span of less than 50 m.y. A major conclusion is that a granitic basement probably did not underlie the Ely Greenstone.

  6. Rb-Sr age of troctolite 76535

    NASA Technical Reports Server (NTRS)

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

    1976-01-01

    Rb-Sr systematics is studied for the lunar troctolite 76535 in phases covering a wide range of Rb and Sr concentrations. A line is obtained corresponding to an age of 4.61 plus or minus 0.07 AE and an initial Sr-87/Sr-86 of 0.69900 plus or minus 0.00003. The Rb-Sr age of 4.55 plus or minus 0.10 AE for the dunite (72417) and that of the troctolite are in approximate agreement and permit an interpretation that these rocks formed during a single major lunar differentiation which presumbly produced an anorthositic-gabbroic lunar crust and layered upper mantle.

  7. In-situ Rb-Sr geochronology

    NASA Astrophysics Data System (ADS)

    Anderson, F. S.; Nowicki, K.; Whitaker, T.

    This paper reports on the first rubidium-strontium (Rb-Sr) radiometric dates using a Laser Desorption Resonance Ionization Mass Spectrometry (LDRIMS) instrument capable of being miniaturized for flight to another planet. The LDRIMS instrument produces dates in under 24 hours, requires minimal sample preparation, and avoids the interference and mass resolution issues associated with other geochronology measurements. We have begun testing the bench-top prototype on the Boulder Creek Granite (BCG), from Colorado, comprised primarily of a gneissic quartz monzonite and granodiorite; whole rock Rb-Sr TIMS measurements result in dates of 1700± 40 Ma [1]. Data reduction of the LDRIMS Rb-Sr measurements on calibrated repeat runs result in a date for the BCG of 1.727± 0.087 Ga (n=288, MSWD=1). Most geochronology applications are willing to accept an MSWD up to ~2.7; at MSWD=2, the precision improves to ± 0.062 Ga. This technology is moving from lab prototype to field deployable instrument, and provides an opportunity to directly address the science goals of Mars Sample Return (MSR) within the bounds posed by current scientific, fiscal, and political pressures on the Mars program. Additionally, LDRIMS could potentially be flown to the Moon under the Discovery or New Frontiers program. We posit that in-situ geochronology missions to Mars to triage and validate samples for Mars Sample Return (MSR) are technically feasible in the 2018-2022 time frame.

  8. K-Ca and Rb-Sr Dating of Lunar Granite 14321 Revisited

    NASA Technical Reports Server (NTRS)

    Simon, Justin I.; Shih, C.-Y.; Nyquist, L. E.

    2011-01-01

    K-Ca and Rb-Sr age determinations were made for a bulk feldspar-rich portion of an Apollo rock fragment of the pristine lunar granite clast (14321,1062), an acid-leached split of the sample, and the leachate. K-Ca and Rb-Sr data were also obtained for a whole rock sample of Apollo ferroan anorthosite (FAN, 15415). The recent detection [1] of widespread intermediate composition plagioclase indicates that the generation of a diversity of evolved lunar magmas maybe more common and therefore more important to our understanding of crust formation than previously believed. Our new data strengthen the K-Ca and Rb-Sr internal isochrons of the well-studied Apollo sample 14321 [2], which along with a renewed effort to study evolved lunar magmas will provide an improved understanding of the petrogenetic history of evolved rocks on the Moon.

  9. Early Permian stage of formation of gold-ore deposits of northeastern Transbaikalia: Isotope-geochronological (Rb-Sr and 39Ar-40Ar) data for the Uryakh ore field

    NASA Astrophysics Data System (ADS)

    Chugaev, A. V.; Nosova, A. A.; Abramov, S. S.; Chernyshev, I. V.; Bortnikov, N. S.; Larionova, Yu. O.; Goltsman, Yu. V.; Moralev, G. V.; Volfson, A. A.

    2015-08-01

    This work presents the first results of geochronological study of metasomatic rocks accompanying gold-bearing quartz veins of the Uryakh ore field (UOF). Based on the Rb-Sr and 39Ar-40Ar geochronological data, it is shown that hydrothermal metasomatic processes in the ore field occurred about 280 Ma ago (Early Permian) and they are correlated with the terminal phases of formation of the Angara-Vitim batholith.

  10. Rb-Sr studies of CI and CM chondrites

    NASA Technical Reports Server (NTRS)

    Mittlefehldt, D. W.; Wetherill, G. W.

    1979-01-01

    Rb-Sr whole rock analyses have been performed on 2 CI and 3 CM chondrites. Four of these stones (Ivuna, Orgueil, Cold Bokkeveld and Erakot) were previously studied in this laboratory and were shown to be discordant from a 4.6 Gyr isochron. The fifth, Murchison, was not previously studied. The new data support the discordance of the first four stones, and indicate that Murchison is also discordant. Studies of Sr isotope ratios in unspiked Orgueil show that the discordance is not due to inhomogeneities in the Sr-84/Sr-86 ratio caused by incomplete mixing of nucleosynthesis products. In order to gauge the effects of weathering, two leaching experiments were performed on fresh, interior samples of Murchison; one for a period of 1.5 hr and the other for 117 hr. The results indicate that the relative solubility of nonradiogenic Sr is approximately twice that of Rb and radiogenic Sr is more soluble than the nonradiogenic Sr.

  11. Resetting of RbSr ages of volcanic rocks by low-grade burial metamorphism

    USGS Publications Warehouse

    Asmeroma, Y.; Damon, P.; Shafiqullah, M.; Dickinson, W.R.; Zartman, R.E.

    1991-01-01

    We report a nine-point RbSr whole-rock isochron age of 70??3 Ma (MSWD 3.97) for Mid-Jurassic volcanic rocks. The same rocks have also been dated by the UThPb method on zircon, giving a crystallization age of 166 ?? 11 Ma, over twice as old as the RbSr age. The data demonstrate that whole-rock RbSr ages of volcanic rocks, even lava flows with SiO2 content as low as 57 wt.%, are susceptible to complete resetting. The rocks range in composition from rhyodacite tuffs to andesite lavas. The complete breakdown of all major minerals that contain Rb and Sr resulted in an alteration mineral assemblage consisting of phengite, albite, secondary quartz, and minor amounts of chlorite and epidote. Phengite is the K-bearing product of the breakdown of biotite and K-feldspar. Pressure during low-grade metamorphism of the volcanic rocks, estimated from phengite composition to have been in the range of 4 to 6 kbar, points to thrust-related burial as the main cause of resetting. Consequently, such reset isochrons may date large-scale events such as regional thrusting and metamorphism. The coherent resetting of the RbSr isochron suggests large-scale pervasive fluid movement during thrust-related burial metamorphism. ?? 1991.

  12. Rb-Sr age of the Shergotty achondrite and implications for metamorphic resetting of isochron ages

    NASA Technical Reports Server (NTRS)

    Nyquist, L. E.; Bogard, D. D.; Wooden, J.; Bansal, B.; Wiesmann, H.; Mckay, G.

    1979-01-01

    The age of the Shergotty achondrite is determined by Rb-Sr isotope analysis and the metamorphic resetting of isochron ages, which is presumed to have occurred during a shock event in the history of the meteorite, is discussed. The isochron best fitting the Rb-Sr evolution diagram is found to correspond to an age of 165 million years, with an initial Sr-87/Sr-86 value of 0.72260. Different apparent ages obtained by the K-Ar and Sm-Nd methods are interpreted in terms of a model which quantifies the degree of resetting of internal isochron ages by low temperature solid state diffusion. On the basis of these considerations, it is concluded that Shergotty crystallized from a melt 650 million years ago, was shock heated to 300 to 400 C after its parent body was involved in a collision 165 million years ago, and was first exposed to cosmic rays two million years ago.

  13. Comparative geochronology in the reversely zoned plutons of the Bottle Lake Complex, Maine: U-Pb on zircons and Rb-Sr on whole rocks

    USGS Publications Warehouse

    Ayuso, R.A.; Arth, Joseph G.; Sinha, A.K.; Carlson, J.; Wones, D.R.

    1984-01-01

    The Bottle Lake Complex is a composite granitic batholith emplaced into Cambrian to Lower Devonian metasedimentary rocks. Both plutons (Whitney Cove and Passadumkeag River) are very coarse grained hornblende and biotite-bearing granites showing petrographic and geochemical reverse zonation. Two linear whole rock Rb/Sr isochrons on xenolith-free Whitney Cove and Passadumkeag River samples indicate ages of 379??5 m.y. and 381??4 m.y., respectively, in close agreement with published K-Ar ages for biotite from Whitney Cove of 377 m.y. and 379 m.y., and for hornblende 40Ar/39Ar determinations from Passadumkeag River which indicate an age of 378??4 m.y. The initial Sr isotopic ratio for Whitney Cove is 0.70553 and for Passadumkeag River is 0.70414. A whole-rock isochron on a suite of xenoliths from the Passadumkeag River granite indicates a whole rock Rb-Sr age of 496??14 m.y., with an initial Sr isotopic ratio of 0.70262. Two types of zircon exhibiting wide petrographic diversity are evident in variable proportions throughout the batholith. One of these types is preferentially found in a mafic xenolith and it is widely dispersed in the host granites forming discrete grains and probably as inclusions in the other type of zircon. U-Pb analyses of zircons give concordia intercept ages of 399??8 m.y. for Whitney Cove, 388??6 m.y. for Passadumkeag River, 415 m.y. for a mafic xenolith in Passadumkeag River, and 396??32 for combined Whitney Cove and Passadumkeag River granite. The zircons show a spread of up to 20 m.y. in the 207Pb/206Pb ages. Omitting the finest zircon fraction in the Passadumkeag River results in a concordia intercept age of 381??3 m.y., in better agreement with the whole-rock Rb-Sr and mineral K-Ar ages. For the Whitney Cove pluton, exclusion of the finest fraction does not bring the zircon age into agreement with the Rb-Sr data. Age estimates by the whole rock Rb-Sr, mineral K-Ar and Ar-Ar methods suggest that the crystallization age of the plutons is

  14. Sm-Nd and Rb-Sr Ages for Northwest Africa 2977, A Young Lunar Gabbro from the PKT

    NASA Technical Reports Server (NTRS)

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

    2009-01-01

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

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

    NASA Technical Reports Server (NTRS)

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

    The Sm-Nd and Rb-Sr isotopic characteristics of two mafic-ultramafic bodies, the Kemperai Massif in the South Ural Mountains and the Voykar-syninsky Massif in the Polar Ural mountains are examined. The data are found to be consistent with the hypothesis that these bodies represent fragments of old oceanic crust. Whole rock samples of pillow basalt, troctolite, gabbros, diabase, and a metasediment give Sm-Nd values which lie on this isochron indicating that the rock units are genetically related and formed 397 My ago. Basic and ultrabasic rocks from Kempersai and Voykar-Syninsky have an initial isotopic composition at time T, epsilon Nd(397 My), of +8.4, indicating derivation for an ancient depleted mantle source. The Sr isotopic data and the correlation with epsilon Nd indicate extensive alteration by seawater which is particularly strong on ultrabasic rocks. The results show that the segments of oceanic crust formed at least 80 My before the collision that produced the Urals.

  17. Evidence for a late thermal event of unequilibrated enstatite chondrites: a Rb-Sr study of Qingzhen and Yamato 6901 (EH3) and Khairpur (EL6)

    USGS Publications Warehouse

    Torigoye, N.; Shima, M.

    1993-01-01

    The Rb-Sr whole rock and internal systematics of two EH3 chondrites, Qingzhen and Yamato 6901, and of one EL6 chondrite, Khairpur, were determined. The internal Rb-Sr systematics of the EH3 chondrites are highly disturbed. Fractions corresponding to sulfide phases show excess 87Sr, while other fractions corresponding to silicate phases produce a linear trend on a Rb-Sr evolution diagram. If these linear relations are interpreted as isochrons, the ages of the silicate phases are 2.12?? 0.23 Ga and 2.05 ??0.33 Ga with the initial Sr isotopic ratios of 0.7112 ?? 0.0018 and 0.7089 ?? 0.0032, for Qingzhen and Yamato 6901, respectively. The Rb-Sr results are interpeted as indicative of a late thermal event about 2Ga ago on the parent bodies of these EH3 chondrites. These ages agree well with previously published K-Ar ages. An older isochron age of 4.481 ?? 0.036 Ga with a low initial Sr isotopic ratio of 0.69866 ?? 0.00038 was obtained for the data from silicate fractions of Khairpur, indicating early petrological equilibrium on the parent body of EL6 chondrites. -from Authors

  18. Concordant Rb-Sr and Sm-Nd Ages for NWA 1460: A 340 Ma Old Basaltic Shergottite Related to Lherzolitic Shergottites

    NASA Technical Reports Server (NTRS)

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

    2006-01-01

    Preliminary Rb-Sr and Sm-Nd ages reported by [1] for the NWA 1460 basaltic shergottite are refined to 336+/-14 Ma and 345+/-21 Ma, respectively. These concordant ages are interpreted as dating a lava flow on the Martian surface. The initial Sr and Nd isotopic compositions of NWA 1460 suggest it is an earlier melting product of a Martian mantle source region similar to those of the lherzolitic shergottites and basaltic shergottite EETA79001, lithology B. We also examine the suggestion that generally "young" ages for other Martian meteorites should be reinterpreted in light of Pb-207/Pb-206 - Pb-204/Pb-206 isotopic systematics [2]. Published U-Pb isotopic data for nakhlites are consistent with ages of approx.1.36 Ga. The UPb isotopic systematics of some Martian shergottites and lherzolites that have been suggested to be approx.4 Ga old [2] are complex. We nevertheless suggest the data are consistent with crystallization ages of approx.173 Ma when variations in the composition of in situ initial Pb as well as extraneous Pb components are considered.

  19. Rb-Sr isochron age of the Manicouagan melt sheet, Quebec, Canada

    NASA Technical Reports Server (NTRS)

    Jahn, B.; Floran, R. J.; Simonds, C. H.

    1978-01-01

    Rb-Sr isotopic data for mineral separates from a rock of the Manicouagan impact melt sheet define an isochron of age T = 214 + or - 5 (2 sigma) m.y. which agrees with the K-Ar age of 210 + or - 8 (2 sigma) calculated by Wolfe (1971). The initial Sr-87/Sr-86 ratio I is found to be 0.70991 + or - 0.00007 (2 sigma); four whole rock samples yield age-corrected I values ranging from 0.70965 to 0.71006. These high I values support the hypothesis that the melt sheet was derived by total melting of Grenville basement rocks during the impact event 214 m.y. ago.

  20. Rb-Sr study of a lunar dunite and evidence for early lunar differentiates

    NASA Technical Reports Server (NTRS)

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

    1975-01-01

    An Rb-Sr study of Boulder 3 from Station 2 sampled during the Apollo 17 mission is reported. The investigated boulder is a metaclastic rock, inferred to have come from the South Massif, and contains a variety of lithic clasts. Since the rock type may be critical in understanding lunar differentiation processes, an extensive investigation was carried out of the dunite clast and other clasts as well as of the fine-grained matrix. The investigation had the purpose to define the age of crystallization of the dunite and to determine the extent to which later metamorphism of the host rock may have effected the isotopic systematics of this clast. The isochron determined yielded an age of 4.55 plus or minus 0.10 AE for the dunite. This result demonstrates that differentiation began close to the time of formation of the moon and that relics of this process are preserved.

  1. Structure-related geochemical (REE) and isotopic (K-Ar, Rb-Sr, {delta}{sup 18}O) characteristics of clay minerals from Rotliegend sandstone reservoirs (Permian, northern Germany)

    SciTech Connect

    Zwingmann, H.; Clauer, N.; Gaupp, R.

    1999-09-01

    Euhedral illite cementing the gas-bearing sandstone reservoirs of the Rotliegend in the Niedersaechsische rift system (northern Germany) was studied along a horst-to-graben cross-section to examine its chemical and isotopic characteristics. The data show that differentiated illite particles grew during a tectono-thermal event marked by distinct episodic hydrothermal activities along fault drains and in the poral space of sandstones at 210 Ma and at 195 to 190 Ma in horst positions, at 185 to 175 Ma in the nearby graben, and at 170 to 165 Ma in both the horst and graben. Varied REE distribution patterns and initial {sup 87}Sr/{sup 86}Sr ratios (from 0.7124 to 0.7142) relative to illite-particle size outline a high chemical variability of the fluids during illite growth. The {delta}{sup 18}O values of illite range from +20.0 to +12.4% and those of chlorite from +12.0 to +6.9%. The changing {delta}{sup 18}O values of the minerals most likely relate to varied {delta}{sup 18}O values of the fluids, or to different water/rock ratios during crystallization. Differences among the REE and {sup 87}Sr/{sup 86}Sr tracers and the {delta}{sup 18}O values of different generations of illite also suggest a changing fluid chemistry relative to time. significant positive Eu anomalies and negative Ce anomalies in the REE distributions of illite suggest feldspar alteration by the migrating fluids in oxidizing environments.

  2. Rb-Sr and Sm-Nd study of granite-charnockite association in the Pudukkottai region and the link between metamorphism and magmatism in the Madurai Block

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  3. Rb-Sr and Sm-Nd study of granite-charnockite association in the Pudukkottai region and the link between metamorphism and magmatism in the Madurai Block

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  4. Pre-4.0 billion year weathering on Mars constrained by Rb-Sr geochronology on meteorite ALH84001

    NASA Astrophysics Data System (ADS)

    Beard, Brian L.; Ludois, James M.; Lapen, Thomas J.; Johnson, Clark M.

    2013-01-01

    The timing and nature of aqueous alteration of meteorite ALH84001 has important implications for the history of water on early Mars, the evolution of the Martian atmosphere, and the potential for early Mars habitability. Rubidium-Sr isotope analyses of mineral separates from igneous-textured and carbonate-rich aliquots of Martian meteorite ALH84001 constrain the age of alteration and the source of fluids. The carbonate-rich aliquot defines a precise Rb-Sr isochron between maskelynite, orthopyroxene, and chromite of 3952±22 Ma, and this is interpreted to represent a shock resetting event that was broadly coeval with carbonate precipitation. Carbonate, bulk rock, and multi-mineral separates all have high 87Sr/86Sr ratios that can only have been produced by alteration via a fluid derived through interaction with high Rb/Sr phyllosilicates that were produced prior to 3950 Ma. These data confirm that the source of Sr in the fluids was previously altered crustal rock, consistent with fluids that underwent low-temperature water-rock interaction (Eiler et al., 2002; Halvey et al., 2011). These results therefore provide evidence for wet, clay-rich conditions on the surface of Mars prior to ˜4.2 Ga.

  5. Sm-Nd, Rb-Sr, and Mn-Cr Ages of Yamato 74013

    NASA Technical Reports Server (NTRS)

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

    2009-01-01

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

  6. Rb-Sr and Sm-Nd Study of the D'Orbigny Angrite

    NASA Technical Reports Server (NTRS)

    Tonui, E. K.; Ngo, H.H.; Papanastassiou, D. A.

    2003-01-01

    D'Orbigny, is a relatively a new angrite find. Angrites are achondrites that show unique mineralogy and typically ancient crystallization ages. D Orbigny has been described extensively by. We have initiated a study of D Orbigny. A Pb-Pb model age of 4559 Ga has been reported. The presence of Pu-244 fission Xe in D Orbigny has also been reported. We present Sm-Nd and Rb-Sr results and a Mn-53-Cr-53 study is in progress. We had expected to find a relatively well-behaved Sm-Nd system, and distinct evidence for the Sm-146-Nd-142 system. Emphasis in this study was placed on the precise measurement of initial Sr-87/Sr-86, since primitive initial Sr-87/Sr-86 may be characteristic of the angrite parent body. Sr isotope measurements were obtained in the recently completed laboratories at JPL, using the ThermoFinnigan Triton mass spectrometer. Due to lower amounts of Nd and Sm, Sm-Nd data were obtained on the Lunatic I spectrometer at Caltech, due to established high ionization techniques, on this instrument using light rare earth oxide ions.

  7. Rb-Sr geochronology of the region between the Antarctic Peninsula and the Transantarctic Mountains: Haag nunataks and Mesozoic granitoids

    NASA Astrophysics Data System (ADS)

    Millar, I. L.; Pankhurst, R. J.

    Seventy-two new Rb-Sr whole-rock analyses are reported for Haag Nunataks, Mount Woollard, the Whitmore Mountains, the Pirrit and Nash hills, and Pagano Nunatak. For Haag Nunataks, three isochrons for gneisses and later aplogranite and microgranite sheets establish the age of crustal formation as 1000-1100 Ma. No other basement rocks of this age are known from the Antarctic Peninsula or Ellsworth Land. Results from the migmatite-pegmatite complex at Mount Woollard are inconclusive but do not suggest that this represents Precambrian crystalline basement. Provisional results for the Whitmore Mountains granites are compatible with crystallization of all components within error of a 182±5 Ma isochron for fine-grained microgranite, but variation in initial 87Sr/86Sr from 0.707 for porphyritic granites to 0.722 for the microgranite rule out simple crystal fractionation models which require a common parental magma. The granites of the Ellsworth-Thiel mountains ridge are well dated as Middle Jurassic by the new data: Pirrit Hills 173±3 Ma, Nash Hills 175±8 Ma, and Pagano Nunatak 175±8 Ma. Initial 87Sr/86Sr ratios of 0.707, 0.712, and 0.716, respectively, confirm that these are intracratonic S-type granites with a large crustal component involved in magma generation. The dolerite of Lewis Nunatak is shown by its Rb, Sr, and 87Sr/86Sr composition to be a member of the Jurassic Ferrar Supergroup.

  8. Predicting the Isotopic Composition of Subduction-Filtered Subducted Oceanic Crust and Sediment

    NASA Astrophysics Data System (ADS)

    White, W. M.

    2010-12-01

    The chemical and isotopic character of mantle plumes, which produce oceanic island volcanoes, are widely thought to reflect the presence of recycled oceanic crust and sediment. Isotopic systematics suggest the “cycle time” for this process is 1 Ga or longer, but it should be possible to use a simple mass balance approach to discern how the presently operating subduction zone filter affects the ratios of radioactive parent to radiogenic daughter isotopes. Simple uniformitarian assumptions can then be used to predict the present isotopic composition of anciently subducted lithosphere. Our underlying assumption in deciphering the subduction zone filter is that the flux of an element into the deep mantle is simply equal to the flux of element into the subduction zone less the flux of that element into subduction zone magmas. The former is readily calculated from published data. The latter can be calculated by estimating parental magma compositions, arc accretion rates, and the assumption that arc magma compositions differ from MORB only because of material derived from subducting crust and sediment. Using this approach for 8 intra-oceanic subduction zones, we find 73% of Th and Pb, 79% of U, 80% of Rb and Sr, 93% of Nd and 98% of Sm survive the subduction zone filter. The subduction zone filter systematically increases Sm/Nd ratios in all subduction zones, but the effect is small, with a weighted mean increase of 1.5%. The effect of subduction is to decrease the Sm/Nd of the mantle, but only slightly. The effect of subduction is to increase the Rb/Sr of the mantle, but the subduction zone filter does not have a systematic effect on Rb/Sr ratios: it significantly increases in Rb/Sr in 3 subduction zones and significantly decreases it in one; the weighted mean shows no significant change. The effect of the subduction zone filter on U/Pb is also not systematic. U/Pb ratios in the mantle fluxes are bimodal, with values equal to or lower than the bulk Earth value in 4

  9. Spatial and temporal variations of Rb/Sr ratios of the bulk surface sediments in Lake Qinghai

    PubMed Central

    2010-01-01

    The Rb/Sr ratios of lake sediments have been suggested as indicators of weathering intensity by increasing work. However, the geochemistry of Rb/Sr ratios of lake sediments is variable between different lakes. In this study, we investigated the spatial and temporal patterns of Rb/Sr ratios, as well as those of other major elements in surface sediments of Lake Qinghai. We find that the spatial pattern of Rb/Sr ratios of the bulk sediments correlates well with that of the mass accumulation rate, and those of the terrigenous fractions, e.g., SiO2, Ti, and Fe. The temporal variations of Rb/Sr ratios also synchronize with those of SiO2, Ti, and Fe of each individual core. These suggest that Rb/Sr ratios of the surface sediments are closely related to terrigenous input from the catchment. Two out of eight cores show similar trends between Rb/Sr ratios and precipitation indices on decadal scales; however, the other cores do not show such relationship. The result of this study suggests that physical weathering and chemical weathering in Lake Qinghai catchment have opposite influence on Rb/Sr ratios of the bulk sediments, and they compete in dominating the Rb/Sr ratios of lake sediments on different spatial and temporal scales. Therefore, it is necessary to study the geochemistry of Rb/Sr ratio of lake sediments (especially that on short term timescales) particularly before it is used as an indicator of weathering intensity of the catchment. PMID:20615264

  10. Rb-Sr age of lunar igneous rocks 62295 and 14310

    NASA Technical Reports Server (NTRS)

    Mark, R. K.; Lee-Hu, C.-N.; Wetherill, G. W.

    1974-01-01

    Measurements of Rb-Sr ages of crystallization performed on igneous lunar highland rocks 62295 and 14310 are reported. Lunar sample 62295 is a mesostasis-rich spinel-troctolite very-high-alumina basalt exhibiting a variable igneous structure. Sample 14310 is a feldspathic KREEP-rich basalt. The determined ages probably date the cooling of shock melts.

  11. An In-Situ Rb-Sr Dating & Organics Characterization Instrument For A MER+ Sized Rover

    NASA Astrophysics Data System (ADS)

    Anderson, F.; Whitaker, T.; Nowicki, K.; Zacny, K.; Pierce, J.

    2012-12-01

    We posit that a Mars in-situ geochronology mission that will triage and validate samples for Mars Sample Return (MSR) is technically feasible in the 2018-2022 time frame and addresses the competing scientific, political, and fiscal requirements for flight in this decade.The mission must be responsive to the astrobiological and chronological science goals of the MEPAG, Decadal Survey (DS), and E2E-iSAG, and avoid the MSR appearance of long term political commitment and cost. These requirements can best be accomplished by a rover with a coring drill. JPL has reassessed the MER landing system performance, and determined that the system is capable of significantly higher landed mass (~40-60 kg plus reserve), allowing more sophisticated instruments to be carried. The instrument package is comprised of a time of flight (TOF) mass spectrometer combined with a laser desorption resonance ionization source to sensitively measure isobar free Rb-Sr isotopes for geochronology and organics characterization. The desorption laser is also used with a μRaman/LIBS for mineral characterization, which in combination with the TOF, will additionally provide measurements of K-Ar isotopes for a second form of radiometric dating. The laser desorption resonance ionization mass spectrometry (LDRIMS) technique avoids the interference and mass resolution issues associated with geochronology measurements, and has miniaturization potential. A sample is placed in the TOF mass spectrometer and surface atoms, molecules, and ions are desorbed with a 213 nm laser. Ions are suppressed by an electric field and the plume of expanding particles is present for many μs, during which it is first illuminated with laser light tuned to ionize only Sr, and then 1-3 μs later, for Rb. We have partially miniaturized the instrument, including Sr lasers, ablation laser, and mass spectrometer, and will soon to start using the instrument for field measurements. Our current prototype can measure the isotope ratio of

  12. Atomic Weights and Isotopic Compositions

    National Institute of Standards and Technology Data Gateway

    SRD 144 Atomic Weights and Isotopic Compositions (Web, free access)   The atomic weights are available for elements 1 through 111, and isotopic compositions or abundances are given when appropriate.

  13. Ar-Ar and Rb-Sr Ages of the Tissint Olivine-phyric Martian Shergottite

    NASA Technical Reports Server (NTRS)

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

    2013-01-01

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

  14. Assessment of sewage treatment plant effluents impact on river water quality using dissolved Rb/Sr ratio

    SciTech Connect

    Nirel, P.M.; Revaclier, R. )

    1999-06-15

    The authors present a new approach to elucidate and manage the impact of sewage effluents on river water quality using the dissolved Rb/Sr ratio. Rubidium is present in larger quantities than strontium in biological matrices (such as feces and urine), so that the ratio of these two elements represents an effective tracer. This is especially true in regions where the natural Rb/Sr ratio is low (calcareous regions). For a given water quality, the Rb/Sr ratio will remain constant, regardless of the river flow. Since both elements are easy to measure, this ratio has already been successfully used for pollution assessment in Geneva. The Rb/Sr ratio can also be used to model, for a given watershed, the capacity to withstand the effect of sewage effluent and to recover its natural quality.

  15. Tectonically reset Rb-Sr system during Late Ordovician terrane assembly in lapetus, western Ireland

    SciTech Connect

    Kennan, P.S.; Murphy, F.C.

    1987-12-01

    The uncertainty of a ca. 460 Ma age of mylonitization of acid igneous rocks in the western Irish Caledonides required reevaluation of the published Rb-Sr whole-rock data. The authors found that the data support an alternative ca. 426 +/- 10 Ma age of mylonitic resetting. This time of deformation relates to the assembly of suspect terranes during Late Ordovician closure of the Iapetus ocean.

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

    NASA Technical Reports Server (NTRS)

    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. Effects of weathering on the RbSr and KAr ages of biotite from the Morton Gneiss, Minnesota

    USGS Publications Warehouse

    Goldich, S.S.; Gast, P.W.

    1966-01-01

    Weathering has drastically reduced the RbSr and, to a lesser extent, the KAr age of biotite from the Morton Gneiss of southwestern Minnesota. The ages are approximately 75% and 25% lower than the corresponding ages for biotite from the fresh gneiss. The effects of even incipient weathering cannot be neglected in RbSr dating of biotite and, by analogy, of feldspar and whole-rock samples. ?? 1966.

  18. Roter Kamm Impact Crater, Namibia: Age Constraints from K-Ar, Rb-Sr, Fission Track, 10Be-26Al Studies

    NASA Astrophysics Data System (ADS)

    Koeberl, C.; Klein, J.; Matsuda, J.; Nagao, K.; Reimold, W. U.; Storzer, D.

    1992-07-01

    INTRODUCTION. The Roter Kamm impact crater is located in the Namib Desert in Namibia. The impact occurred in Precambrian granitic-granodioritic orthogneisses of the 1200-900-Ma-old Namaqualand Metamorphic Complex. The granites are invaded by quartz veins and quartz-feldspar-pegmatites. Gariep metasediments probably overlaid the Namaqualand complex at the time of the impact (Reimold and Miller, 1989). Previous estimates for the crater age are not well constrained: regional geology suggests an age of 5-10 Ma, while the only available ^40Ar-^39Ar age (Hartung et al., 1991) is 3.7 Ma. Fission tracks measured in apatites from granites found on or near the crater rim were not completely reset by the impact and suggest an uplift event around 20 Ma ago (Storzer et al., 1990). We are using several approaches to bracket the age of the crater: we have measured melt breccia and pseudotachylite K-Ar ages, and apatite fission track ages in several rim granites. We are comparing Rb-Sr isotope data for rim granites with known ages of regional resetting events (Allsopp et al., 1979). Finally, we are using ^10Be-^26Al measured by accelerator mass spectrometry to determine surface exposure ages for quartz excavated during the impact event. RESULTS AND DISCUSSION. The target rock composition and stratigraphy at Roter Kamm is relatively complicated. Melt breccias formed from pegmatites, gneisses, or schists, while pseudotachylites probably formed from gneissic basement or quartz-feldspar-pegmatites (Reimold and Miller, 1989). Whole rock Rb-Sr data for several granites yield 1498 Ma, and mineral separates from sample URK-M indicate an "age" of 466 Ma; these ages are similar to those of country rocks from the general area of the northwestern Cape/southern Namibia (Allsopp et al., 1979) which indicate two widespread regional resetting events at ca. 700 Ma (related to the Pan-African orogenic deformation), and ca. 500 Ma, related to a subsequent metamorphic event. For K-Ar ages, we

  19. Sm-Nd in marine carbonates and phosphates - Implications for Nd isotopes in seawater and crustal ages

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

    The possibility of establishing a record of variations in the isotopic composition of Nd in seawater over geologic time is explored. To construct such a record, a phase must be identified which incorporated Nd with the same isotopic composition as seawater at the time of its formation, preserves that composition, and which is relatively common in sediments. To evaluate the suitability of carbonates and phosphates, the Rb, Sr, Sm, and Nd concentrations and the Nd and Sr isotopic composition of a variety of modern and ancient marine calcite, aragonite, and apatite samples have been measured and the results are presented and discussed.

  20. Sm-Nd, Rb-Sr and U-Th-Pb systematics of granulite facies rocks from Fyfe Hills, Enderby Land, Antarctica

    NASA Astrophysics Data System (ADS)

    Depaolo, D. J.; Manton, W. I.; Grew, E. S.; Halpern, Martin

    1982-08-01

    New Sm-Nd isotopic measurements made on granulite-facies metamorphic rocks from East Antarctica provide firm evidence that crust of ~3,500-Myr age exists in the Fyfe Hills. Zircon U-Pb data provide further documentation for a granulite-facies event 2,500 Myr ago, during which Rb, U, Sm and Nd were highly mobile. The U-Pb and Rb-Sr isotopic systems were seriously disrupted and in most samples give meaningless model ages. In contrast, Sm-Nd model ages were offset only slightly. A large time interval of 1,000 Myr between the times of crust formation and granulite-facies metamorphism has not previously been reported for Archaean rocks, and suggests that 2,500 Myr ago the Fyfe Hills may have been located in an Andean- or Himalayan-type continental margin where crust already 1,000-Myr old was involved in an orogenic event.

  1. Resetting of Neoarchaean hornblendes from the Murmansk Terrane (Kola Peninsula, Russia) revealed by a combined 40Ar/39Ar and Rb-Sr analysis

    NASA Astrophysics Data System (ADS)

    de Jong, K.; Timmerman, M. J.; Cliff, R. A.; Wijbrans, J. R.; Daly, J. S.; Balagansky, V. V.

    2003-04-01

    We present isotope data from amphiboles from the 2.6--2.8 Ga Murmansk Terrane in the northern foreland of the 1.9 Ga Lapland-Kola Orogen of northern Fennoscandia. Most amphiboles are zoned with tschermakitic cores that progressively change to actinolite in 5--10 μm wide areas in rims, defect zones or adjacent to biotite. Biotite chiefly occurs along cleavages, fractures and grain boundaries of amphibole, showing that its hydration and fluid ingress are confined to lattice imperfections. Furnace step heating of hornblende separate MT-11 gave spectra with increasing apparent ages and Ca/K ratios (a proxy for 37ArCa/39Ar_K). Hornblende is intergrown with biotite that also occurs in the matrix. Yet, laser step heating of single hornblende grain MT-11 yielded flat spectra with Neoarchaean apparent ages and constant Ca/K ratios. This suggests that the hornblende grain that was drilled from a thin section and which was not affected by biotite growth retained its Neoarchaean age. In contrast, the hornblende separate with intergrown biotite from this sample has a partially reset Neoarchaean isotope system. Hornblende MT-27 has Neoarchaean apparent ages and lacks low Ca/K ratios in both single grain and mineral separate spectra; it is not affected by biotite growth and this mineral is also absent from the matrix. Age spectra of other hornblende separates have increasing apparent ages to 2.56--2.65 Ga during final 39Ar release; their Ca/K ratio spectra similarly increase. Low Ca/K ratios for gas release below 950^oC imply degassing of included biotite. Apparent ages of the first heating increments may be as young as 1.8 Ga, comparable to the K-Ar and 40Ar/39Ar ages of the youngest biotites. Hornblende-plagioclase pairs from aliquots used for 40Ar/39Ar furnace step heating yielded sharply discordant Rb-Sr ages. MT-11 yielded an 1881 ± 23 Ma Rb-Sr age that compares well with the K-Ar and 40Ar/39Ar ages of biotite in the sample. In contrast, hornblende of sample MT-27 has a

  2. Effect of sea water interaction on strontium isotope composition of deep-sea basalts

    USGS Publications Warehouse

    Julius, Dasch E.; Hedge, C.E.; Dymond, J.

    1973-01-01

    Analyses of rim-to-interior samples of fresh tholeiitic pillow basalts, deuterically altered holocrystalline basalts, and older, weathered tholeiitic basalts from the deep sea indicate that 87Sr 86Sr ratios of the older basalts are raised by low temperature interaction with strontium dissolved in sea water. 87Sr 86Sr correlates positively with H2O in these basalts; however, there is little detectable modification of the strontium isotope composition in rocks with H2O contents less than 1%. The isotope changes appear to be a function of relatively long-term, low-temperature weathering, rather than high-temperature or deuteric alteration. Strontium abundance and isotopic data for these rocks suggest that strontium content is only slightly modified by interaction with sea water, and it is a relatively insensitive indicator of marine alteration. Average Rb-Sr parameters for samples of apparently unaltered basalt are: Rb = 1.11 ppm; Sr = 132 ppm; 87Sr 86Sr = 0.70247. ?? 1973.

  3. Using trace element content and lead isotopic composition to assess sources of PM in Tijuana, Mexico

    NASA Astrophysics Data System (ADS)

    Salcedo, D.; Castro, T.; Bernal, J. P.; Almanza-Veloz, V.; Zavala, M.; González-Castillo, E.; Saavedra, M. I.; Perez-Arvízu, O.; Díaz-Trujillo, G. C.; Molina, L. T.

    2016-05-01

    PM2.5 samples were collected at two urban sites (Parque Morelos (PQM) and CECyTE (CEC)) in Tijuana during the Cal-Mex campaign from May 24 to June 5, 2010. Concentration of trace elements (Mg, Al, Ti, V, Mn, Fe, Co, Ni, Zn, Cu, Ga, As, Se, Rb, Sr, Mo, Cd, Sn, Sb, Ba, La, Ce, and Pb), and Pb isotopic composition were determined in order to study the sources of PM impacting each site. Other chemical analysis (gravimetric, elemental and organic carbon (EC/OC), and polycyclic aromatic hydrocarbons (PAHs)), were also performed. Finally, back-trajectories were calculated to facilitate the interpretation of the chemical data. Trace elements results show that CEC is a receptor site affected by mixed regional sources: sea salt, mineral, urban, and industrial. On the other hand, PQM seems to be impacted mainly by local sources. In particular, Pb at CEC is of anthropogenic, as well as crustal origin. This conclusion is supported by the lead isotopic composition, whose values are consistent with a combination of lead extracted from US mines, and lead from bedrocks in the Mexican Sierras. Some of the time variability observed can be explained using the back-trajectories.

  4. Rubidium-strontium isotope characteristics of lunar soils.

    NASA Technical Reports Server (NTRS)

    Cliff, R. A.; Lee-Hu, C.; Wetherill, G. W.

    1972-01-01

    Evaluation of K, Rb, and Sr concentrations and Sr isotopic composition for hand-picked fractions from the 175- to 1000-micron Apollo 12 fines samples 12032 and 12070 and for two less than 1-mm bulk fines samples, 14163,160 and 14259,21, from Apollo 14 which have model Rb-Sr ages close to 4.6 b.y. The Apollo 14 data indicate the presence of a radiogenic component of 4.6 b.y. model age like the Apollo 12 fines, confirming a very early geochemical differentiation of the moon. Progressively greater enrichment in K and Rb relative to the bulk fines is shown by microbreccia from both samples, ropy brown glass from 12032, and light-grey lithic fragments from 12032. Model Rb-Sr ages, based on a basaltic achondrite initial ratio, are generally close to 4.6 b.y. The microbreccias and ropy brown glass have model ages that are younger but indistinguishable from 4.6 b.y. within analytical error. Light grey lithic fragments from 12032 have a model age of 5.1 b.y. and must have had a multistage Rb/Sr evolution. The data are broadly compatible with two-component mixing models of the Apollo 12 fines. On the basis of modal composition, the microbreccia is considered the major nonbasaltic constituent.

  5. The geochemistry and isotopic composition of the mafic and intermediate igneous components of the Cape Granite Suite, South Africa

    NASA Astrophysics Data System (ADS)

    Jordaan, L. J.; Scheepers, R.; Barton, E. S.

    1995-07-01

    A number of small outcrops of igneous rocks, gabbroic to granodioritic in composition, occur scattered throughout the western Cape in South Africa. These outcrops, which are mostly intrusive into the Malmesbury metasedimentary sequence, define a small number of medium-sized plutons. A characteristic feature of the larger plutons is their composite nature. Each pluton consists of multiple intrusive phases; a few show extensive hydrothermal alteration. Plutons from Yzerfontein and Mud River, which occur in the Tygerberg terrane, are high-K calcalkaline (K-trans-alkaline) while all plutons from Malmesbury, which occurs in the Swartland terrane, are tholeiitic. The high-K suite correspond to other I-type Cape granites, whereas the tholeiitic Malmesbury plutons may be a precursor of A-type Cape granites in both the Tygerberg and Swartland terranes. Monzonite from the Yzerfontein pluton yielded a UPb age of 519±7 Ma on zircon mineral separates. Rb-Sr isotope data did not yield reliable ages, possibly due to alteration, but yielded distinct initial isotope ratios for the high-K calc-alkaline and the tholeiitic plutons. The δ34S isotope ratios of pyrite range from 1 to 2.7% for Yzerfontein and from 3.6 to 4.6% for Mud River, suggesting a magmatic source for the pyrite. PbPb data on whole rock and pyrite samples imply crustal input into all the original magmas.

  6. The significance of Rb-Sr glauconite ages, Bonneterre Formation, Missouri; Late Devonian-Early Mississippian brine migration in the midcontinent

    SciTech Connect

    Stein, H.J. ); Kish, S.A. )

    1991-05-01

    Rb-Sr mean model ages of 370 {plus minus} 10 Ma for glauconites from the Cambrian lower Bonneterre Formation in southern and central Missouri are in excellent agreement with a Rb-Sr isochron age of 359 {plus minus} 22 Ma for glauconites from the Magmont mine (Viburnum Trend) in the southeast Missouri lead district. The lower Bonneterre and Magmont mines ages probably reflect isotopic resetting, most likely associated with dolomitization and/or Mississippi Valley-type ore formation in the southeast Missouri lead district. The temporal relation between widespread dolomitization and ore formation in Missouri is unclear, but mounting evidence for two Devonian disturbances permits the following interpretation: (1) a Devonian timing (380-400 Ma) for widespread dolomitization, and (2) a Late Devonian-Early Mississippian timing (360-370 Ma) for ore formation in southeast Missouri. Late Devonian-Early Mississippian fluids associated with the earliest stages of collisional tectonics and metamorphism to the south and southeast may have been important in the formation of southeast Missouri ore deposits. These tectonically driven waters may themselves have been the Mississippi Valley-type ore fluids, entering Missouri by way of the Black Warrior basin and Reelfoot rift and/or the Arkoma basin. Alternatively, the movement of orogenic fluids hundreds of kilometers distant may have initiated and distally influenced the migration of more locally derived Mississippi Valley-type ore fluids. Broad regions of Missouri and adjacent areas experienced heating and crustal flexing in the Late Devonian, and consequently, preservation of elevated temperatures in Mississippi Valley-type fluids as they move great lateral distances may not be necessary for ore formation in southeast Missouri.

  7. Rb-Sr and Sm-Nd whole rock analyses of basalts of the Grao Para Group, Serra dos Carajas, Brazil

    SciTech Connect

    Olszewski, W.J. Jr.; Gibbs, A.K.; Wirth, K.R.

    1985-01-01

    The Grao Para Group at Serra dos Carajas in the Guapore Shield of Brazil is a 6 km thick sequence of bimodal metavolcanic rock with interbedded iron formations. Rhyolites are a minor part of the low grade meta-volcanic section, with the bulk consisting of subalkaline basalt, basaltic andesite, and shoshonite. Rb-Sr whole rock analyses of 7 basalts yield an age of 2687 +/- 54 Ma. This agrees well with an age of 2758 +/- 39 Ma from zircon U-Pb analyses of the interbedded rhyolites. Except for the allocthonous Imataca Complex of Venezuela, these dates for the Grao Para Group are the first well-constrained Archean ages from the Amazonian Craton. An even older age for the basement to the Grao Para Group is also implied. Sm-Nd whole-rock analyses of four of these basalts did not yield an isochron because of the limited range of /sup 147/Sm//sup 144/Nd values, but element of/sub Nd/ values relative to CHUR were calculated using the Rb-Sr age. The typical LREE-enrichment, lack of Ce depletion or spilitic alteration of alkalies, and the high Sr initial ratios, may indicate that these isotopic patterns were derived by incorporation of some older continental crust in the mafic melts. These data together with an element of/sub Sr/ of +63.6 might indicate significant seawater exchange with volcanic rocks derived from mantle with chondritic REE patterns. This demonstrates the presence of significant continental crust in the Archean and seawater-volcanic rock interaction in a rifting environment similar to modern analogs.

  8. Magnesium isotopic composition of achondrites

    NASA Astrophysics Data System (ADS)

    Sedaghatpour, Fatemeh; Teng, Fang-Zhen

    2016-02-01

    Magnesium isotopic compositions of 22 well-characterized differentiated meteorites including 7 types of achondrites and pallasite meteorites were measured to estimate the average Mg isotopic composition of their parent bodies and evaluate Mg isotopic heterogeneity of the solar system. The δ26Mg values are -0.236‰ and -0.190‰ for acapulcoite-lodranite and angrite meteorites, respectively and vary from -0.267‰ to -0.222‰ in the winonaite-IAB-iron silicate group, -0.369‰ to -0.292‰ in aubrites, -0.269‰ to -0.158‰ in HEDs, -0.299‰ to -0.209‰ in ureilites, -0.307‰ to -0.237‰ in mesosiderites, and -0.303‰ to -0.238‰ in pallasites. Magnesium isotopic compositions of most achondrites and pallasite meteorites analyzed here are similar and reveal no significant isotopic fractionation. However, Mg isotopic compositions of D‧Orbigny (angrite) and some HEDs are slightly heavier than chondrites and the other achondrites studied here. The slightly heavier Mg isotopic compositions of angrites and some HEDs most likely resulted from either impact-induced evaporation or higher abundance of clinopyroxene with the Mg isotopic composition slightly heavier than olivine and orthopyroxene. The average Mg isotopic composition of achondrites (δ26Mg = -0.246 ± 0.082‰, 2SD, n = 22) estimated here is indistinguishable from those of the Earth (δ26Mg = -0.25 ± 0.07‰; 2SD, n = 139), chondrites (δ26Mg = -0.28 ± 0.06‰; 2SD, n = 38), and the Moon (δ26Mg = -0.26 ± 0.16‰; 2SD, n = 47) reported from the same laboratory. The chondritic Mg isotopic composition of achondrites, the Moon, and the Earth further reflects homogeneity of Mg isotopes in the solar system and the lack of Mg isotope fractionation during the planetary accretion process and impact events.

  9. Rb-Sr and Sm-Nd Study of Asuka 881394: Evidence of "Late" Metamorphism

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

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

  10. Origins of massif-type anorthosites and related rocks-isotopic evidence from the southern Nain Anorthosite Complex, Labrador

    SciTech Connect

    Simmons, E.C.; Synder, G.A.; Kalamarides, R.I.; Wiebe, R.A.

    1985-01-01

    Leuconoritic rocks approaching magma compositions occur extensively throughout the southern Nain Anorthosite Complex, as fine-grained dikes and chill margins and even as coarser-grained samples from the intrusions themselves. These rocks are silica-saturated, with high A1203 (>19.5 WT%), low atomic Mg/Mg+Fe (<0.5), and have high total REE abundances with only small positive Eu anomalies. Sr-isotope data for these samples indicate a surprisingly large range of initial ratios at T=1.3 Ga: 0.7052-0.710; the Rb/Sr ratios for these samples are almost constant (approx. 0.03), resulting in a vertical array on a Rb/Sr isochron plot. Nd-isotope data for three of the samples, which cover the range of Sr-initial ratios yield element of values between -9.0 and -11.0; delta 180 values for two samples are 6.4 and 7.4. The low Mg/Mg+Fe ratios of these magmas indicate that they are not primary, mantle-derived melts; either these magmas resulted from extensive amounts of fractional crystallization of mantle-derived magmas, or they formed by partial melting of mafic/ultramafic material in the lower crust. The O-isotope data and large amounts of unsupported radiogenic Sr preclude the involvement of upper crustal materials in the generation of these magmas. The data are consistent with the involvement, either as a component in the source region, or as a contaminant, of material which had a low Sm/Nd and high Rb/Sr for a significant period of geologic time prior to partial melting, but a low Rb/Sr ratio at the time of partial melting.

  11. Structure and optical properties of a noncentrosymmetric borate RbSr{sub 4}(BO{sub 3}){sub 3}

    SciTech Connect

    Xia, M.J.; Li, R.K.

    2013-01-15

    A new noncentrosymmetric borate, RbSr{sub 4}(BO{sub 3}){sub 3} (abbreviated as RSBO), has been grown from Rb{sub 2}O--B{sub 2}O{sub 3}--RbF flux and its crystal structure was determined by single crystal x-ray diffraction. It crystallizes in space group Ama2 with cell parameters of a=11.128(10) A, b=12.155(15) A, c=6.952(7) A, Z=4. The basic structural units are isolated planar BO{sub 3} groups. Second harmonic generation (SHG) test of the title compound by the Kurtz-Perry method shows that RSBO can be phase matchable with an effective SHG coefficient about two-thirds as large as that of KH{sub 2}PO{sub 4} (KDP). Finally, based on the anionic group approximation, the optical properties of the title compound are compared with those of the structure-related apatite-like compounds with the formula 'A{sub 5}(TO{sub n}){sub 3}X'. - Graphical abstract: RbSr{sub 4}(BO{sub 3}){sub 3} and some other borate NLO compounds, namely Ca{sub 5}(BO{sub 3}){sub 3}F RCa{sub 4}(BO{sub 3}){sub 3}O (R=Y or Gd) and Na{sub 3}La{sub 2}(BO{sub 3}){sub 3} can be viewed as the derivatives of apatite. They have similar formula composed of five cations and three anion groups (we call them 5/3 structures). The detailed SHG coefficients and optical properties of the apatite-like NLO crystals were compared and summarized. Highlights: Black-Right-Pointing-Pointer A new noncentrosymmetric borate RbSr{sub 4}(BO{sub 3}){sub 3} was grown from flux. Black-Right-Pointing-Pointer The RbSr{sub 4}(BO{sub 3}){sub 3} can be viewed as a derivative of the apatite-like structure. Black-Right-Pointing-Pointer The structure and its relationship to the optical properties of RbSr{sub 4}(BO{sub 3}){sub 3} are compared with other NLO crystals with apatite-like structures. Black-Right-Pointing-Pointer The basic structural units are the planar BO{sub 3} groups in the structure. Black-Right-Pointing-Pointer Second harmonic generation (SHG) test shows that RbSr{sub 4}(BO{sub 3}){sub 3} can be phase matchable with an

  12. New Rb-Sr mineral ages temporally link plume events with accretion at the margin of Gondwana

    USGS Publications Warehouse

    Flowerdew, M.J.; Daly, J.S.; Riley, T.R.

    2007-01-01

    Five of six Rb-Sr muscovite mineral isochron ages from the Scotia Metamorphic Complex of the South Orkney Islands, West Antarctica, average 190 ± 4 Ma. The muscovite ages are interpreted to date foliation-formation and thus also accretion and subduction at the Gondwana margin. Coincident picrite and ferropicrite magmatism, indicative of melts from deep-seated depleted mantle, permits a causative link between accretion and the arrival of the Karoo – Ferrar – Chon Aike mantle plume in the Early Jurassic. Three biotite Rb-Sr mineral isochron ages are consistently younger and average 176 ± 5 Ma. The biotite ages may record post-metamorphic cooling or more likely retrogressive metamorphic effects during uplift.

  13. Sm-nd and rb-sr chronology of continental crust formation.

    PubMed

    McCulloch, M T; Wasserburg, G J

    1978-06-01

    Samarium-neodymium and rubidium-strontium isotopic systematics together with plausible assumptions regarding the geochemical evlution of continental crust material, have been used to ascertain the times at which segments of continental crust were formed. Analyses of composites from the Canadian Shield representing portions of the Superior, Slave, and Churchill structural provinces indicate that these provinces were all formed within the period 2.5 to 2.7 aeons. It has been possible to determine the mean age of sediment provenances, as studies of sedimentary rocks suggest that the samarium-neodymium isotopic system is not substantially disturbed during sedimentation or diagenesis. PMID:17740673

  14. Holocene moisture change revealed by the Rb/Sr ratio of aeolian deposits in the southeastern Mu Us Desert, China

    NASA Astrophysics Data System (ADS)

    Liu, Bing; Jin, Heling; Sun, Liangying; Sun, Zhong; Niu, Qinghe; Xie, Shengbo; Li, Guanhua

    2014-06-01

    Systematic analysis of the Rb and Sr contents and Rb/Sr ratios in different lithological units of the palaeosol-aeolian sequence in the southeastern Mu Us Desert revealed that the Rb/Sr ratio is an accurate proxy for past East Asian summer monsoonal strength and moisture change. A lower Sr content and a higher Rb/Sr ratio, chemical index of alteration (CIA), and clay and organic matter (OM) content in the palaeosol are coincident with stronger Asian summer monsoons and increased precipitation, whereas a higher Sr content and a lower Rb/Sr ratio, CIA, and clay and OM content correspond to a dry climate with weaker summer monsoonal strength. Based on these results, the history of Holocene moisture changes was reconstructed as follows: the moisture was lower before 7.5 ka and approached an optimal climate between 7.5 ka and 4.6 ka, afterwards, the climate tended to be dry. Additionally, six millennial-scale dry events were recorded at the times of ∼7.5 ka, 7.0-6.8 ka, 6.6-5.7 ka, 4.6-4.1 ka, 3.7-3.5 ka, and 3.3-2.5 ka, which were very accordant with cold phases evidenced by ice cores and deep-sea deposits in the low and high latitudes of the Northern Hemisphere. These were also coincident with weaker Asian summer monsoonal intervals revealed by stalagmites within the dating uncertainties, probably implying a prominent synchronism of Holocene millennial-scale climate changes in the Mu Us Desert and global climate changes.

  15. Chronology of lunar granite 12033,576: Resetting of Rb-Sr and K-Ca isochrons

    NASA Technical Reports Server (NTRS)

    Shih, C.-Y.; Wiesmann, H.; Garrison, D. H.; Nyquist, L. E.; Bogard, D. D.

    1993-01-01

    Lunar granite 12033,576 is a subsample of the 'large' (approximately 1 g) felsite 12033,507 which was identified from a collection of 4-10 mm particles from the 12033 soil sampled from the north rim of Head Crater in the eastern part of Oceanus Procellarum. Discordant ages of approximately 3.6, approximately 0.8, approximately 3.9, and approximately 2.2 Ga for this lunar granite were obtained, respectively, by the K-Ca, Ar-39/Ar-40, and U-Pb zircon methods in previous studies and by the Rb-Sr method is this study. Assuming the granite crystallized approximately 3.9 Ga ago (zircon age) and was shocked by meteoritic impacts at 0.8 Ga ago (Ar-39-Ar-40 age), the intermediate apparent ages by the Rb-Sr and K-Ca methods can be interpreted as reset by diffusion of the parent and daughter nuclides. The Rb-Sr age is less resistant to resetting than the K-Ca age, but more resistant that the Ar-39/Ar-40 age.

  16. Structural, elastic, electronic, magnetic and optical properties of RbSrX(C, SI, Ge) half-Heusler compounds

    NASA Astrophysics Data System (ADS)

    Ahmad, Mukhtar; Naeemullah; Murtaza, G.; Khenata, R.; Bin Omran, S.; Bouhemadou, A.

    2015-03-01

    In this study we present investigations pertaining to structural, elastic, electronic, magnetic and optical properties of RbSrC, RbSrSi and RbSrGe half-Heusler compounds. To carry out this study, full potential (FP) linearized augmented plane wave (LAPW), a scheme of calculations developed within the framework of density functional theory (DFT), is employed. To incorporate the exchange correlation (XC) energy and corresponding potential into the total energy calculations, generalized gradient approximation (GGA) parameterized by Wu-Cohen is taken into account. Analysis of band structures and densities of states (DOS) profiles illustrate the conducting nature in spin down state and the semiconducting nature in spin-up state. The bonding nature discussed via electron charge density plot reveals strong ionic bonding character of these compounds. At ambient conditions, calculations for elastic constants (Cij) and their related elastic moduli are also performed which point to their brittle character. The compounds are found to be ferromagnetic with 1 μB. The magnetic moment decreases from its integer value at high pressures for these compounds.

  17. Microfossils and Rb-Sr age of glauconite in the key section of the Upper Proterozoic of the northeastern part of the Russian plate (Keltmen-1 borehole)

    NASA Astrophysics Data System (ADS)

    Golubkova, E. Yu.; Zaitseva, T. S.; Kuznetsov, A. B.; Dovzhikova, E. G.; Maslov, A. V.

    2015-06-01

    Complex paleontological and isotope-geochronological study of clastic sediments of the Vychegda Depression (Mezen syneclise) has been carried out on samples retrieved from the Keltmen-1 borehole drilled in the junction zone of the Russian and Timan-Pechera plates. The stratigraphic structure of the clastic unit in the depth interval 1874-2910 m has been perfected. At the base of the unit, the new Okos Formation has been described: glauconite from it was dated by Rb-Sr to 807 ± 8 Ma. The obtained microphytologic characteristic of the upper part of the section is in agreement with lithological and geochemical data, allowing recognition of two Upper Vendian Formations: Ust-Pinega and Mezen. The stratigraphic hiatus between the Upper Riphean and Vendian deposits in the Keltmen-1 borehole reaches 200-250 M.y. For the first time Ediacaran acanthomorph microfossils of the genera Appendisphaera and Tanarium have been found in the high horizons of the Upper Vendian, proving their wider stratigraphic distribution.

  18. Rb-Sr age of the Civet Cat clast, 72255, 41. [radioactive age determination for lunar rocks

    NASA Technical Reports Server (NTRS)

    Compston, W.; Gray, C. M.

    1974-01-01

    Plagioclase rich clasts, orthopyroxene rich matrix, purified pyroxene, and plagioclase from the Civet Cat clast define a Rb-Sr isochron age of 4.18 + or - 0.04 x 10 to the 9th power yr and an initial Sr-87/Sr-86 ratio of 0.69922 + or - 0.00005. The fit of all data to the line is within error except for plagioclase 3, and blank corrections are essentially negligible. The decay constant used is 1.39 x 10 to the minus 11th power yr.

  19. Grosnaja ABCs: Magnesium isotope compositions

    NASA Technical Reports Server (NTRS)

    Goswami, J. N.; Srinivasan, G.; Ulyanov, A. A.

    1993-01-01

    Three CAI's from the Grosnaja CV3 chondrite were analyzed for their magnesium isotopic compositions by the ion microprobe. The selected CAI's represent three distinct types: GR4(compact Type A), GR7(Type B) and GR2(Type C). Petrographic studies indicate that all three Grosnaja inclusions were subjected to secondary alterations. The Type A CAI GR4 is primarily composed of melilite with spinel and pyroxene occurring as minor phases. The rim of the inclusion does not exhibit distinct layered structure and secondary alteration products (garnet, Fe-rich olivine and Na-rich plagioclase) are present in some localized areas near the rim region. The average major element compositions of different mineral phases in GR4 are given. Preliminary REE data suggest a depletion of HREE relative to LREE by about a factor of 3 without any clear indication of interelement fractionation. The CAI GR7 has textural and minerological characteristics similar to Type B inclusions. The REE data show a pattern that is similar to Group 6 with enrichment in Eu and Yb. In addition, a depletion of HREE compared to LREE is also evident in this object. Melilite composition shows a broad range of akermanite content (Ak(sub 15-55)). Detailed petrographic study is in progress. GR2 is a anorthite-rich Type C inclusion with large plagioclase laths intergrown with Ti-rich pyroxene. The average plagioclase composition is close to pure anorthite (An99).

  20. The significance of Rb-Sr glauconite ages, Bonneterre Formation, Missouri: Late Devonian-Early Mississippian brine migration in the midcontinent

    SciTech Connect

    Stein, H.J.; Kish, S.A. )

    1992-09-01

    In his comment on the paper by Stein and Kish (1991), Seidemann suggests that Rb-Sr glauconite dates from Missouri (and particularly those from the Magmont Mine in the Viburnum Trend) do not provide useful age information due to the 'mixing' of common strontium with radiogenic strontium in glauconites. In this reply the original authors address the points brought up by Seidemann and again provide some quantitative limits on the degree to which the addition of common strontium can affect calculated ages of minerals with high Rb/Sr ratios.

  1. Isotopic composition of gases from mud volcanoes

    SciTech Connect

    Valysaev, B.M.; Erokhin, V.E.; Grinchenko, Y.I.; Prokhorov, V.S.; Titkov, G.A.

    1985-09-01

    A study has been made of the isotopic composition of the carbon in methane and carbon dioxide, as well as hydrogen in the methane, in the gases of mud volcanoes, for all main mud volcano areas in the USSR. The isotopic composition of carbon and hydrogen in methane shows that the gases resemble those of oil and gas deposits, while carbon dioxide of these volcanoes has a heavier isotopic composition with a greater presence of ''ultraheavy'' carbon dioxide. By the chemical and isotopic composition of gases, Azerbaidzhan and South Sakhalin types of mud volcano gases have been identified, as well as Bulganak subtypes and Akhtala and Kobystan varieties. Correlations are seen between the isotopic composition of gases and the geological build of mud volcano areas.

  2. Isotopic analysis of basaltic fragments from lunar breccia 14321 - Chronology and petrogenesis of pre-Imbrium mare volcanism

    NASA Technical Reports Server (NTRS)

    Dasch, E. J.; Shih, C.-Y.; Bansal, B. M.; Wiesmann, H.; Nyquist, L. E.

    1987-01-01

    Internal (mineral) Rb-Sr isochrons were determined for six Apollo 14 mare basalts of lunar breccia 14321. The ages of these fragments, which represent the time of crystallization of the respective mafic lavas, range from about 4.05 to 4.24, and, possibly, to 4.33 Ga and are among the oldest dates reported for mare basalts. For three of the fragments, internal Sm-Nd isochron data were collected and initial Nd isotopic composition was determined. The results are discussed with reference to the original source of these different basaltic fragments.

  3. Isotopic compositions of the elements, 2001

    USGS Publications Warehouse

    Böhlke, J.K.; De Laeter, J. R.; De Bievre, P.; Hidaka, H.; Peiser, H.S.; Rosman, K.J.R.; Taylor, P.D.P.

    2005-01-01

    The Commission on Atomic Weights and Isotopic Abundances of the International Union of Pure and Applied Chemistry completed its last review of the isotopic compositions of the elements as determined by isotope-ratio mass spectrometry in 2001. That review involved a critical evaluation of the published literature, element by element, and forms the basis of the table of the isotopic compositions of the elements (TICE) presented here. For each element, TICE includes evaluated data from the "best measurement" of the isotope abundances in a single sample, along with a set of representative isotope abundances and uncertainties that accommodate known variations in normal terrestrial materials. The representative isotope abundances and uncertainties generally are consistent with the standard atomic weight of the element A r(E) and its uncertainty U[Ar(E)] recommended by CAWIA in 2001. ?? 2005 American Institute of Physics.

  4. Utilisation of Rb/Sr as proxy for mass wasting events in peat records from the Romanian Carpathians

    NASA Astrophysics Data System (ADS)

    Longman, Jack; Ersek, Vasile; Veres, Daniel; Salzmann, Ulrich

    2016-04-01

    Mass wasting events, including landslides, avalanches and flooding related to heavy rains can have a major impact on the local environment. Due to their association to extreme precipitation and glacial retreat, their occurrence is likely to increase as the climate changes in the future. As such, understanding their causation, and predicting their future impact is of paramount importance. To make such predictions, understanding of the relationship between the climate and the mass-wasting event is key. For this to happen, we must use historical records of mass wasting and climate to tie the two together. As a result, a reliable, quick and easy method for determining these events in the sedimentological record must be developed. The Rb/Sr ratio has been suggested as one indicator of mass wasting events, particularly based on lake sediment research in glaciated terrain. Our work was initially developed upon the behaviour of the two elements during weathering, considering that Rb commonly substitutes for K in mineral lattices and Sr commonly for Ca, due to similar ionic radii. Minerals containing K are much more resistant than Ca-bearing ones, and so there is enrichment in weathering products of Ca, and therefore Sr. As a result, Sr should be enriched in weathered material, resulting in a lowering of the Rb/Sr ratio. This assumption has been proven as reliable in similar research involving aeolian deposits and lake sediments. Here we present the first Holocene record based on this proxy from a peat archive from a raised mountain bog in the Romanian Carpathians, nested at the foot of an avalanche-prone glacial cirque. Our geochemical assessments are based on complete digestion of samples, and analysis via ICP-OES, rather than based only on core scanning. Initial results look promising, with the peat core below the active layer (acrotelm) and above the minerogenically-influenced zone producing strong correlation to the estimates of the minerogenic input over the bog based

  5. Geochemistry and Rb-sr geochronology of associated proterozoic peralkaline and subalkaline anorogenic granites from Labrador

    NASA Astrophysics Data System (ADS)

    Collerson, Kenneth D.

    1982-12-01

    Anorogenic granites of middle to late Proterozoic age in the Davis Inlet — Flowers Bay area of Labrador are subdivided on the basis of petrology and geochemistry into three coeval suites. Two of these are high-temperature anhydrous hypersolvus granites: a peralkaline aegirine-sodic-calcic to sodic amphibole-bearing suite and a non-alkaline fayalite-pyroxene-bearing suite. The third is a group of non-alkaline subsolvus hornblende-biotite-bearing granites. Associated with the hypersolvus peralkaline suite is a group of genetically related syenites and quartz syenites. The granites cut ca. 3,000 Ma old Archaean gneisses as well as Elsonian layered basic intrusions of the Nain Complex. One of these, a crudely layered mass which ranges in composition from gabbro to diorite and monzonite, appears to be related to the syenites. The peralkaline granites and some of the syenites are extremely enriched in the high field-strength elements such as Y, Zr, Nd, as well as Rb, Ga and Zn, and have low abundances of Ba, Sr and most of the transition elements. In contrast, the non-alkaline hypersolvus and subsolvus granites do not show the same degree of enrichment. Concentration of the highly charged cations in the peralkaline suite is believed to be the result of halogen-rich fluid activity during fractionation of the magma. The sodic evolution trend in the peralkaline suite is reflected mineralogically by the development of aegirine and aegirine-hedenbergite solid solutions, and by a spectacular amphibole compositional range from katophorite through winchite, richterite, riebeckite to arfvedsonite and ferro eckermannite. Accessory phases which are ubiquitous in these rocks include aenigmatite, astrophyllite, fluorite, monazite and zircon. The non-alkaline hypersolvus granites typically contain iron-rich phases such as fayalite, eulite, ferrosilite-hedenbergite, and annite rich biotite. In the subsolvus granites, amphiboles range in composition from edenite through common

  6. Rb-Sr ages of igneous rocks from the Apollo 14 mission and the age of the Fra Mauro formation.

    NASA Technical Reports Server (NTRS)

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

    1971-01-01

    Internal Rb-Sr isochrons were determined on four basaltic rocks and on a basaltic clast from a breccia from the Fra Mauro landing site. An internal isochron was determined for rock 12004 and yielded a value in agreement with previous results for basaltic rocks from the Apollo 12 site. The crystallization ages for Apollo 14 basalts are only 0.2 to 0.3 AE older than were found for mare basalts from the Sea of Tranquility. Assuming these leucocratic igneous rocks to be representative of the Fra Mauro site, it follows that there were major igneous processes active in these regions, and presumably throughout the highlands, at times only slightly preceding the periods at which the maria were last flooded.

  7. Single Variable and Multivariate Analysis of Remote Laser-Induced Breakdown Spectra for Prediction of Rb, Sr, Cr, Ba, and V in Igneous Rocks

    SciTech Connect

    Clegg, Samuel M; Wiens, Roger C.; Speicher, Elly A; Dyar, Melinda D; Carmosino, Marco L

    2010-12-23

    Laser-induced breakdown spectroscopy (LIBS) will be employed by the ChemCam instrument on the Mars Science Laboratory rover Curiosity to obtain UV, VIS, and VNIR atomic emission spectra of surface rocks and soils. LIBS quantitative analysis is complicated by chemical matrix effects related to abundances of neutral and ionized species in the resultant plasma, collisional interactions within plasma, laser-to-sample coupling efficiency, and self-absorption. Atmospheric composition and pressure also influence the intensity of LIBS plasma. These chemical matrix effects influence the ratio of intensity or area of a given emission line to the abundance of the element producing that line. To compensate for these complications, multivariate techniques, specifically partial least-squares regression (PLS), have been utilized to predict major element compositions (>1 wt.% oxide) of rocks, PLS methods regress one or multiple response variables (elemental concentrations) against multiple explanatory variables (intensity at each pixel of the spectrometers). Because PLS utilizes all available explanatory variable and eliminates multicollinearity, it generally performs better than univariate methods for prediction of major elements. However, peaks arising from emissions from trace elements may be masked by peaks of higher intensities from major elements. Thus in PLS regression, wherein a correlation coefficient is determined for each elemental concentration at each spectrometer pixel, trace elements may show high correlation with more intense lines resulting from optical emissions of other elements. This could result in error in predictions of trace element concentrations. Here, results of simple linear regression (SLR) and multivariate PLS-2 regression for determination of trace Rb, Sr, Cr, Ba, and V in igneous rock samples are compared. This study focuses on comparisons using only line intensities rather than peak areas to highlight differences between SLR and PLS.

  8. Determination of initial Sr-isotope compositions of dolostones from the Burlington-Keokuk Formations (Mississippian) of Iowa, Illinois, and Missouri

    SciTech Connect

    Banner, J.L.; Hanson, G.N.; Meyers, W.J.

    1986-05-01

    Sr-isotope compositions, and Rb and Sr concentrations were measured on fine-grained, nearly pure dolostones, each consisting predominantly of one cathodoluminescent generation of dolomite. The results differ significantly, depending on the dissolution method used. For example, one sample gives replicate /sup 87/Sr//sup 86/Sr analyses by leaching with 1.25N HCl of 0.71032 and 0.71062. Adding HF to the leaching process gave a value of 0.71216, whereas complete dissolution with concentrated HF, HNO/sub 3/, and HCl yields a value of 0.71219. Using the time of dolomitization with Rb (12.4 ppm) and Sr (59.7 ppm) concentrations for the completely dissolved sample gives an initial /sup 87/Sr//sup 86/Sr ratio of 0.70943. Similar results for other samples indicate that most Rb and radiogenic Sr are associated with minor clay fractions (predominantly glauconite) in the samples, and that HCl leaches Rb and Sr from clays to a variable extent. Morphologic relationships between dolomite, calcite, and nonpelloidal glauconite suggest that some clay formed episodically during various stages of nonmarine diagenesis. Sr-isotopic exchange may have occurred between carbonate and clay during major influxes of diagenetic fluids. To obtain initial /sup 87/Sr//sup 86/Sr ratios on samples that are completely dissolved, the following corrections are needed: isotopic equilibration between carbonate and clay, closure of the Rb-Sr system after diagenesis, and constraints on the timing of diagenesis. Such initial /sup 87/Sr//sup 86/Sr ratios give the isotopic composition of the carbonate phase at the time of its crystallization, whereas leaching with weak acid is not always carbonate selective and can produce ambiguous results.

  9. Strontium Isotopic Composition of Paleozoic Carbonate Rocks in the Nevada Test Site Vicinity, Clark, Lincoln, and Nye Counties, Nevada, and Inyo County, California

    USGS Publications Warehouse

    Paces, James B.; Peterman, Zell E.; Futo, Kiyoto; Oliver, Thomas A.; Marshall, Brian D.

    2007-01-01

    Ground water moving through permeable Paleozoic carbonate rocks represents the most likely pathway for migration of radioactive contaminants from nuclear weapons testing at the Nevada Test Site, Nye County, Nevada. The strontium isotopic composition (87Sr/86Sr) of ground water offers a useful means of testing hydrochemical models of regional flow involving advection and reaction. However, reaction models require knowledge of 87Sr/86Sr data for carbonate rock in the Nevada Test Site vicinity, which is scarce. To fill this data gap, samples of core or cuttings were selected from 22 boreholes at depth intervals from which water samples had been obtained previously around the Nevada Test Site at Yucca Flat, Frenchman Flat, Rainier Mesa, and Mercury Valley. Dilute acid leachates of these samples were analyzed for a suite of major- and trace-element concentrations (MgO, CaO, SiO2, Al2O3, MnO, Rb, Sr, Th, and U) as well as for 87Sr/86Sr. Also presented are unpublished analyses of 114 Paleozoic carbonate samples from outcrops, road cuts, or underground sites in the Funeral Mountains, Bare Mountain, Striped Hills, Specter Range, Spring Mountains, and ranges east of the Nevada Test Site measured in the early 1990's. These data originally were collected to evaluate the potential for economic mineral deposition at the potential high-level radioactive waste repository site at Yucca Mountain and adjacent areas (Peterman and others, 1994). Samples were analyzed for a suite of trace elements (Rb, Sr, Zr, Ba, La, and Ce) in bulk-rock powders, and 87Sr/86Sr in partial digestions of carbonate rock using dilute acid or total digestions of silicate-rich rocks. Pre-Tertiary core samples from two boreholes in the central or western part of the Nevada Test Site also were analyzed. Data are presented in tables and summarized in graphs; however, no attempt is made to interpret results with respect to ground-water flow paths in this report. Present-day 87Sr/86Sr values are compared to values

  10. Strontium Isotopic Composition of Paleozoic Carbonate Rocks in the Nevada Test Site Vicinity, Clark, Lincoln, and Nye Counties, Nevada and Inyo County, California.

    SciTech Connect

    James B. Paces; Zell E. Peterman; Kiyoto Futa; Thomas A. Oliver; and Brian D. Marshall.

    2007-08-07

    Ground water moving through permeable Paleozoic carbonate rocks represents the most likely pathway for migration of radioactive contaminants from nuclear weapons testing at the Nevada Test Site, Nye County, Nevada. The strontium isotopic composition (87Sr/86Sr) of ground water offers a useful means of testing hydrochemical models of regional flow involving advection and reaction. However, reaction models require knowledge of 87Sr/86Sr data for carbonate rock in the Nevada Test Site vicinity, which is scarce. To fill this data gap, samples of core or cuttings were selected from 22 boreholes at depth intervals from which water samples had been obtained previously around the Nevada Test Site at Yucca Flat, Frenchman Flat, Rainier Mesa, and Mercury Valley. Dilute acid leachates of these samples were analyzed for a suite of major- and trace-element concentrations (MgO, CaO, SiO2, Al2O3, MnO, Rb, Sr, Th, and U) as well as for 87Sr/86Sr. Also presented are unpublished analyses of 114 Paleozoic carbonate samples from outcrops, road cuts, or underground sites in the Funeral Mountains, Bare Mountain, Striped Hills, Specter Range, Spring Mountains, and ranges east of the Nevada Test Site measured in the early 1990's. These data originally were collected to evaluate the potential for economic mineral deposition at the potential high-level radioactive waste repository site at Yucca Mountain and adjacent areas (Peterman and others, 1994). Samples were analyzed for a suite of trace elements (Rb, Sr, Zr, Ba, La, and Ce) in bulk-rock powders, and 87Sr/86Sr in partial digestions of carbonate rock using dilute acid or total digestions of silicate-rich rocks. Pre-Tertiary core samples from two boreholes in the central or western part of the Nevada Test Site also were analyzed. Data are presented in tables and summarized in graphs; however, no attempt is made to interpret results with respect to ground-water flow paths in this report. Present-day 87Sr/86Sr values are compared to values

  11. Chemical and Sr-isotopic characteristics of the Luna 24 samples

    NASA Technical Reports Server (NTRS)

    Nyquist, L. E.; Mckay, G.; Wiesmann, H.; Bansal, B.; Wooden, J.

    1978-01-01

    The chemical and Sr isotopic characteristics of Luna 24 bulk soil samples are determined and interpreted within the framework of lunar mare basalt evolution. Major and trace element compositions lead to the suggestion of candidate rock types consisting of a basalt/gabbro with very low TiO2 and MgO content (52%), a very low TiO2 basalt with 10% MgO (23%), olivine vitrophyre (20%), low K Fra Mauro basalt (4%) and anorthositic gabbro (1%). The proposed compositions are supported by the agreement of mixing models based on the proposed compositions with observed soil compositions. Sr ratios for plagioclase samples imply a lower Sr-87/Sr-86 value for low Mg soils than for other mare basalts and higher Rb/Sr and a more evolved Sr ratio in high Mg basalts. Rb, Sr and rare earth element compositions for low Mg basalts fit a model of partial remelting of cumulates containing small amounts of plagioclase.

  12. Magnesium isotopic composition of the mantle

    NASA Astrophysics Data System (ADS)

    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 < 0.1‰, 2SD) analyses of Mg isotopes on 1) global mid-ocean ridge basalts covering major ridge segments of the world and spanning a broad range in latitudes, chemical and radiogenic isotopic compositions; 2) ocean island basalts from Hawaiian (Koolau, Kilauea and Loihi) and 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

  13. Isotopic Compositions of Evaporative Fluxes

    NASA Astrophysics Data System (ADS)

    Feng, X.; Lauder, A. M.; Kopec, B. G.; Dade, W. B.; Virginia, R. A.; Posmentier, E. S.

    2013-12-01

    The isotopic fluxes of evaporation from a water surface are typically computed using a one-dimensional model, originally conceptualized by Craig and Gordon (1965) and further developed and adapted to different natural settings (such as transpiration, open surface evaporation, etc.) by various investigators. These models have two distinguishing characteristics. First, there exists a laminar layer where molecular diffusion away from the water-air interface causes kinetic isotopic fractionation. The magnitude of this fractionation is controlled by the diffusion/transport coefficient of each vapor isotopologue in air and their concentration gradients, the latter being controlled by relative humidity, isotopic ratios of ambient air, and turbulent conditions (such as wind and surface roughness). Second, the horizontal variations are ignored. In particular, the effect of horizontal advection on isotopic variations in the ambient air is not considered. The research reported here addresses the effects of relinquishing the simplifying assumptions in both of these areas. We developed a model, in which the simplification of a purely laminar layer is dropped. Instead, we express the vertical transport coefficient as the sum of the molecular diffusivity, that differs for each water isotopologue, and the turbulent diffusivity that increases linearly with height but does not vary among water isotopologues. With this model, the kinetic isotopic effect reduces with height in the vicinity of the water surface, and the net isotopic fractionation through the boundary layer can be integrated. The advantage of this conceptualization is that the magnitude of kinetic isotopic fractionation can be assessed directly with changing environmental conditions, such as humidity and wind speed, rather than approximated by discontinuous empirical functions of the environmental conditions, as in the conventional models mentioned above. To address the effect of lateral heterogeneity, we expanded the

  14. Unusual mercury isotopic compositions in aqueous environment

    NASA Astrophysics Data System (ADS)

    Chen, J.; Hintelmann, H.; Zheng, W.; Feng, X.; Cai, H.; Wang, Z.; Yuan, S.

    2014-12-01

    Preliminary studies have demonstrated both mass-dependent fractionation (MDF) and mass-independent fractionation (MIF) of Hg isotopes in natural samples. Laboratory experiments showed that photochemical reduction of inorganic mercury (iHg) and methylmercury (MMHg) and liquid-vapour evaporation could produce MIF of odd Hg isotopes. This was thought to cause the MIF actually observed in aquatic organisms. Although isotopic measurements of Hg in aqueous environment would give direct evidence, little data was reported for surface water samples. Recent work reported, unexpectedly, positive MIF of odd Hg isotopes in both precipitation and ambient air, in contrast with the prediction of laboratory experiments and measurements of Hg accumulated in lichens . Intriguingly, MIF of even-mass Hg isotope (200Hg) was also recently determined in the atmosphere. In contrast with the now mainstream observation of odd Hg isotope anomaly that has several theoretical explanations, the hitherto mysterious even Hg isotope anomalies were neither reported in laboratory experiments, nor predicted by isotope fractionation mechanisms, highlighting the importance of further study on Hg isotopes in variable systems. Our measurements of lichens and lake water samples from different countries show for the first time significant Δ200Hg in surface terrestrial reservoirs, realizing a direct connection of even Hg isotope anomaly in the terrestrial reservoirs to the atmospheric deposition, and fulfilling the gap of Δ200Hg between the atmosphere and the terrestrial receptors. The specific odd Hg isotope compositions determined in lake waters also support the atmosphere contribution, and may be directly linked to the high Δ199Hg values largely determined and manifested on the top of aqueous food web. Our data show that the watershed Hg input is another contributing source, rather than the in-lake processes, to explain the lacustrine Hg isotope anomalies. Interestingly, lake sediments are isotopically

  15. Carbon isotopic composition of Amazon shelf sediments

    SciTech Connect

    Showers, W.J.; Angle, D.G.; Nittrouer, C.A.; Demaster, D.J.

    1985-02-01

    The distribution of carbon isotopes in Amazon shelf sediment is controlled by the same processes that are forming the modern subaqueous delta. The terrestrial (-27 to -25 per thousand) isotopic carbon signal observed in surficial sediments near the river mouth extends over 400 km northwest along the shelf. Terrestrial carbon is associated with areas of rapid sediment accumulation (topset and foreset regions). A sharp boundary between terrestrial (-27 to -25 per thousand) and marine (-23 to -22 per thousand) isotopic carbon values in surficial sediments is associated with a change in depositional conditions (foreset to bottomset regions) and a decrease in sediment accumulation rate. POC water-column isotopic values (-27 per thousand) near the river mouth are similar to the underlying surficial-sediment TOC isotopic values, but POC water-column samples collected 20 km off the river mouth have marine carbon isotopic values (-22 to -19 per thousand) and differ from the underlying surficial-sediment TOC isotopic values. These water column observations are related to variations in turbidity and productivity. Down-core isotopic variation is only observed in cores taken in areas of lower sediment accumulation rates. These observations indicate that the organic carbon in Amazon shelf sediment is dominantly terrestrial in composition, and the location of deposition of this carbon is controlled by modern processes of sediment accumulation. The modern Amazon shelf is similar to large clinoform shale deposits of the Cretaceous in North America. Thus, the stratigraphic setting may help predict the isotopic variations of carbon in ancient deposits.

  16. Nucleosynthesis and the Isotopic Composition of Stardust

    NASA Technical Reports Server (NTRS)

    Tielens, Alexander G. M.

    1997-01-01

    Various components have been isolated from carbonaceous meteorites with an isotopically anomalous elemental composition. Several of these are generally thought to represent stardust containing a nucleosynthetic record of their birthsites. This paper discusses the expected isotopic composition of stardust based upon astronomical observations and theoretical studies of their birthsites: red giants and supergiants, planetary nebulae, C-rich Wolf-Rayet stars, novae and supernovae. Analyzing the stardust budget, it is concluded that about 15% of the elements will be locked up in stardust components in the interstellar medium. This stardust will be isotopically heterogenous on an individual grain basis by factors ranging from 2 to several orders of magnitude. Since comets may have preserved a relatively unprocessed record of the stardust entering the solar nebula, isotopic studies of returned comet samples may provide valuable information on the nucleosynthetic processes taking place in the interiors of stars and the elemental evolution of the Milky Way.

  17. Stable isotope composition of Earth's large lakes

    NASA Astrophysics Data System (ADS)

    Jasechko, S.; Gibson, J. J.; YI, Y.; Birks, S. J.; Sharp, Z. D.

    2011-12-01

    Lakes cover about three percent of Earth's continental area. Large lakes can significantly influence lake shore and regional climates by increasing specific humidity during evaporation and by moderating air temperatures. Stable isotopes of oxygen and hydrogen can be used to quantify lake evaporation, providing a supplementary and often cost-advantageous alternative to conventional hydrologic approaches that require over lake monitoring. Further, stable isotopes in lake sediments are an established tool in paleolimnology; however, interpreting changes to a lake's past isotope composition requires a comprehensive understanding of contemporary controls. Here, δ18O and δ2H values of water in modern lakes exceeding roughly five hundred square kilometres are compiled (n > 35). Voluminous and seasonally mixed lakes - such as the North American Great Lakes - have the most homogenous stable isotope compositions, while perennially-stratified and shallow lakes show greater variability. A rudimentary stable isotope mass balance is used to assess evaporation fluxes from large lakes on Earth. The approach taken simultaneously constrains evaporation outputs for both oxygen and hydrogen stable isotopes by accounting for lake effects on the overlying atmosphere. Model development highlights important considerations such as isotopic stratification (Tanganyika), disequilibrium isotopic mass balances (Baikal), and non-steady hydrologic balances. Further, the isotope composition of Earth's continental surface water reservoir is calculated. This value - weighted to volume - is δ18O = -7.5±1.7 per mille relative to standard mean ocean water. The compiled data may be a useful tracer of continental evaporate in global atmospheric water cycle studies and could be coupled to climate models capable of incorporating oxygen-18 and deuterium tracers to improve or validate calculations of lake effects on regional water cycling.

  18. Effect of thermal maturation on the K-Ar, Rb-Sr and REE systematics of an organic-rich New Albany Shale as determined by hydrous pyrolysis

    USGS Publications Warehouse

    Clauer, Norbert; Chaudhuri, Sambhudas; Lewan, M.D.; Toulkeridis, T.

    2006-01-01

    Hydrous-pyrolysis experiments were conducted on an organic-rich Devonian-Mississippian shale, which was also leached by dilute HCl before and after pyrolysis, to identify and quantify the induced chemical and isotopic changes in the rock. The experiments significantly affect the organic-mineral organization, which plays an important role in natural interactions during diagenetic hydrocarbon maturation in source rocks. They produce 10.5% of volatiles and the amount of HCl leachables almost doubles from about 6% to 11%. The Rb-Sr and K-Ar data are significantly modified, but not just by removal of radiogenic 40Ar and 87Sr, as described in many studies of natural samples at similar thermal and hydrous conditions. The determining reactions relate to alteration of the organic matter marked by a significant change in the heavy REEs in the HCl leachate after pyrolysis, underlining the potential effects of acidic fluids in natural environments. Pyrolysis induces also release from organics of some Sr with a very low 87Sr/86Sr ratio, as well as part of U. Both seem to have been volatilised during the experiment, whereas other metals such as Pb, Th and part of U appear to have been transferred from soluble phases into stable (silicate?) components. Increase of the K2O and radiogenic 40Ar contents of the silicate minerals after pyrolysis is explained by removal of other elements that could only be volatilised, as the system remains strictly closed during the experiment. The observed increase in radiogenic 40Ar implies that it was not preferentially released as a volatile gas phase when escaping the altered mineral phases. It had to be re-incorporated into newly-formed soluble phases, which is opposite to the general knowledge about the behavior of Ar in supergene natural environments. Because of the strictly closed-system conditions, hydrous-pyrolysis experiments allow to better identify and even quantify the geochemical aspects of organic-inorganic interactions, such as

  19. Petrogenesis of lunar rocks: Rb-Sr constraints and lack of H2O

    NASA Technical Reports Server (NTRS)

    Albee, A. L.; Gancarz, A. J.

    1974-01-01

    Rb and Sr isotopic data and other chemical data indicate major lunar differentiation at about 4.6 AE and very limited subsequent differentiation. The constraints of limited differentiation post 4.6 AE and the apparent lack of H2O on the moon, when applied to the derivation and petrogenesis of lunar samples, suggest the following: (1) soil samples, breccias, metaclastic rocks, and feldspathic basalts represent mixtures of repeatedly-modified clastic material, which was ultimately derived from materials formed during the about 4.6 AE differentiation; and (2) mare basalts crystallized from melts which formed by partial melting and, which developed without equilibration between the melt and crystalline residuum.

  20. Lead and strontium isotopes in rocks of the Absaroka volcanic field, Wyoming

    USGS Publications Warehouse

    Peterman, Z.E.; Doe, B.R.; Prostka, H.J.

    1970-01-01

    The Absaroka volcanic field is comprised of predominant andesitic volcaniclastic rocks and less abundant potassium-rich mafic lavas (shoshonites and absarokites). Strontium and lead isotopic variations preclude a simple derivation from an isotopically uniform source: Sr87/Sr86, 0.7042 to 0.7090; Pb206/Pb204, 16.31 to 17.30; Pb208/Pb204, 36.82 to 37.64. We postulate that these rocks were derived from a lower crust or upper mantle which underwent a preferential loss of uranium relative to lead approximately 2800??200 m.y. ago. Variations in lead and strontium isotopic compositions are thought to reflect small inhomogeneities in U/Pb and Rb/Sr ratios in the source. ?? 1970 Springer-Verlag.

  1. Isotopic Compositions of Uranium Reference Materials

    NASA Astrophysics Data System (ADS)

    Jacobsen, B.; Borg, L. E.; Williams, R. W.; Brennecka, G.; Hutcheon, I. D.

    2009-12-01

    Uranium isotopic compositions of a variety of U standard materials were measured at Lawrence Livermore National Laboratory and are reported here. Both thermal ionization mass spectrometry (TIMS) and multi-collector inductively couple plasma mass spectrometry (MC-ICPMS) were used to determine ratios of the naturally occurring isotopes of U. Establishing an internally coherent set of isotopic values for a range of U standards is essential for inter-laboratory comparison of small differences in 238U/235U, as well as the minor isotopes of U. Differences of ~1.3‰ are now being observed in 238U/235U in natural samples, and may play an important role in understanding U geochemistry where tracing the origin of U is aided by U isotopic compositions. The 238U/235U ratios were measured with a TRITON TIMS using a mixed 233U-236U isotopic tracer to correct for instrument fractionation. This tracer was extremely pure and resulted in only very minor corrections on the measured 238U/235U ratios of ~0.03. The values obtained for 238U/235U are: IRMM184 = 137.698 ± 0.020 (n=15), SRM950a = 137.870 ± 0.018 (n=8), and CRM112a = 137.866 ± 0.030 (n=16). Uncertainties represent 2 s.d. of the population. Our measured value for IRMM184 is in near-perfect agreement with the certified value of 137.697 ± 0.042. However, the U isotopic compositions of SRM950a and CRM112a are not certified. Minor isotopes of U were determined with a Nu Plasma HR MC-ICPMS and mass bias was corrected by sample/standard bracketing to IRMM184, using its certified 238U/235U ratio. Thus, the isotopic compositions determined using both instruments are compatible. The values obtained for 234U/235U are: SRM950a = (7.437 ± 0.043)x10-3 (n=18), and CRM112a = (7.281 ± 0.050)x10-3 (n=16), both of which are in good agreement with published values. The value for 236U/235U in SRM950a was determined to be (8.48 ± 2.63)x10-6, whereas 236U was not detected in CRM112a. We are currently obtaining the U isotopic composition of

  2. Ab initio study of the RbSr electronic structure: Potential energy curves, transition dipole moments, and permanent electric dipole moments

    SciTech Connect

    Pototschnig, Johann V. Krois, Günter; Lackner, Florian; Ernst, Wolfgang E.

    2014-12-21

    Excited states and the ground state of the diatomic molecule RbSr were calculated by post Hartree-Fock molecular orbital theory up to 22 000 cm{sup −1}. We applied a multireference configuration interaction calculation based on multiconfigurational self-consistent field wave functions. Both methods made use of effective core potentials and core polarization potentials. Potential energy curves, transition dipole moments, and permanent electric dipole moments were determined for RbSr and could be compared with other recent calculations. We found a good agreement with experimental spectra, which have been obtained recently by helium nanodroplet isolation spectroscopy. For the lowest two asymptotes (Rb (5s {sup 2}S) + Sr (5s4d {sup 3}P°) and Rb (5p {sup 2}P°) + Sr (5s{sup 2} {sup 1}S)), which exhibit a significant spin-orbit coupling, we included relativistic effects by two approaches, one applying the Breit-Pauli Hamiltonian to the multireference configuration interaction wave functions, the other combining a spin-orbit Hamiltonian and multireference configuration interaction potential energy curves. Using the results for the relativistic potential energy curves that correspond to the Rb (5s {sup 2}S) + Sr (5s4d {sup 3}P°) asymptote, we have simulated dispersed fluorescence spectra as they were recently measured in our lab. The comparison with experimental data allows to benchmark both methods and demonstrate that spin-orbit coupling has to be included for the lowest states of RbSr.

  3. Fluid/rock Interaction History of a Faulted Rhyolite-Granite Contact Determined by Sr- Pb-Isotopes, Th/U-Disequilibria and Elemental Distributions (Eastern Rhine Graben Shoulder, SW-Germany)

    NASA Astrophysics Data System (ADS)

    Marbach, T.; Mangini, A.; Kober, B.; Schleicher, A.; Warr, L. N.

    2003-04-01

    Major and trace element analyses allow to obtain information concerning the chemical changes induced by alteration. Differences are partly petrographic because the profile crosses the granite-rhyolite contact, but they are also due to different alteration levels induced by fluid circulation along the fault system which has drained the alteration processes. The granite-rhyolite contact constitutes the primary structure. Only the most incompatible elements (Si, Al, Zr, Hf) retain their original signatures and reflect a mixing between typical granite and rhyolite lithologies across the altered zones (cataclasite). The more mobile elements show a different composition within the altered zones (cataclasite) notably a high leaching of cations. The geochemical tracers also suggest at least one strong hydrothermal event with reducing conditions in the altered zones. The isotopic analyses delivered qualitative and temporal information. The use of several isotopic systems, Rb/Sr-, U/Pb-isotopes and Th/U disequilibria, reveals a complex history of polyphase fluid/rock interaction following the Permian volcanic extrusion, showing notable disturbances during the late Jurassic hydrothermal activities, the Tertiary rifting of the Rhine Graben and more recent Quaternary alteration. The granite zone of the sampling profile has underwent an event which set up a new Rb-Sr isotopic composition and reset the Rb/Sr system which originatly corresponded to the Carboniferous intrusion ages. The Rb-Sr data of the granite samples produce a whole rock isochron of 152 ± 5,7 Ma (2σ error) in good agreement with the well-known late Jurassic hydrothermal event (135--160 Ma). The rocks evolution lines for Pb support a Tertiary hydrothermal event (54 Ma ± 16; 1σ error), potentially connected with the development of the Rhine Graben. The profile samples have undergone uranium and thorium redistribution processes which have occurred within the last ˜10^6 years. The samples of the altered zones

  4. Spinel peridotite xenoliths from the Tariat Depression, Mongolia. II: Geochemistry and Nd and Sr isotopic composition and their implications for the evolution of the subcontinental lithosphere

    NASA Astrophysics Data System (ADS)

    Stosch, H.-G.; Lugmair, G. W.; Kovalenko, V. I.

    1986-12-01

    A suite of spinel peridotite xenoliths from the Shavaryn-Tsaram volcano, Tariat Depression (central Mongolia) represents (for major elements) fertile to moderately depleted subcontinental lithosphere. Part of the variation of moderately incompatible trace elements is ascribed to small-scale mineralogical heterogeneities caused by processes like metamorphic differentiation accompanying partial melting or by mechanical segregation. Several bulk lherzolites show a high relative enrichment of the LREE over HREE which can be traced to a grain boundary phase genetically linked to, but not directly representing, the host basanitoid. In Nd and Sr isotopic composition the anhydrous peridotites cover the field of oceanic basalts (143Nd/144Nd = 0.5128-0.5133, 87Sr/86Sr = 0.7020-0.7039). In contrast, a phlogopite peridotite has a high 87Sr/86Sr and also a less radiogenic 143Nd/144Nd. The majority of "dry" lherzolites have Nd and Sr "bulk earth" model ages around 2 Ga. They may be interpreted as dating a small-degree (< ~5%) melting event which would not have severely affected the major element chemistry of the xenoliths. The ~2 Ga model ages may indicate a genetic relation between the lithospheric mantle and the stabilization of the continental crust in Mongolia at that time. Alternatively, if the peridotites are unrelated to the overlying crust, they may be pieces of a young asthenospheric diapir. Coexisting ortho-and clinopyroxenes are in Nd isotopic equilibrium for Iherzolites having equilibrated at temperatures around 950°C at mantle pressures. Disequilibrium melting models of mantle rocks are not supported by our data because for medium to coarse-grained mantle spinel peridotite the Rb-Sr and Sm-Nd isotopic systems close with respect to diffusional exchange at temperatures around 900°C, as indicated by recently published diffusion experiment results and supported by our data.

  5. Petrogenesis of lunar rocks: Rb-Sr constraints and lack of H2O

    NASA Technical Reports Server (NTRS)

    Albee, A. L.; Gancarz, A. J.

    1977-01-01

    Rb and Sr isotopic data and other chemical data indicate major lunar differentiation at about 4.6 AE (AE = 10 to the 9th power years) and very limited subsequent differentiation. The constraints of limited differentiation after 4.6 AE and the apparent lack of H2O on the moon, when applied to the derivation and petrogenesis of lunar samples, suggest the following: (1) soil samples, breccias, metaclastic rocks, and feldspathic basalts represent mixtures of repeatedly modified clastic material, which was utimately derived from materials formed during the 4.6 AE differentiation; and (2) mare basalts crystallized from melts which formed by partial melting, and which developed without equilibrium between the melt and crystalline residuum.

  6. Hard processing vs. episodic underplating of a terrain: isotopic signatures of mantle and crustal magmatic sources from the sub-continental lithosphere

    NASA Astrophysics Data System (ADS)

    Rasskazov, S.; Chuvashova, I.

    2012-04-01

    Hypothesese on origin of sub-continental lithosphere are tested, in this presentation, by isotopic data on magmatic liquids from crustal and mantle sources that might be genetically related or unrelated to each other. A common origin of the components reflects a radical recycling of a terrain resulted in separation of crustal and mantle constituents, characterized by a common inherited isochron of melt portions in U-Pb, Rb-Sr, and other isotope systems. A different origin assumes episodic underplating of growing sub-continental lithosphere that is reflected in contrast compositions of crustal and mantle sources, each of which yields melt potions with specific inherited isochrons. The lithospheric terrain of the former type produced 1) Late Tertiary volcanic rocks in the Shandong Peninsula, China with the inherited Pb-Pb isochron corresponding to the age of the eastern block of the North China craton (~2.57 Ga) (data of Zartman et al. [1991]), 2) Late Tertiary volcanic rocks in the Rungwe Province, Tanzania with the inherited Rb-Sr isochron corresponding to the end of the Pan-African orogeny (~0.46 Ga), and 3) Neoproterozoic (~0.9 Ga) dikes in the Gargan block of Eastern Siberia, Russia with the inherited Pb-Pb isochron corresponding to the age of the block basement (~2.7 Ga). The lithospheric terrain of the latter type yielded Cretaceous-Paleogene volcanic rocks in the Tien Shan, Kyrgyzstan and adjacent China with the inherited crustal and the newly formed mantle Rb-Sr isochrons of ~340 and ~50 Ma, respectively.

  7. Carbon isotope composition of Antarctic plants

    NASA Astrophysics Data System (ADS)

    Galimov, E. M.

    2000-05-01

    Carbon isotope compositions of Antarctic land plants are first reported. The most interesting feature is the isotope specificity of the species. For example Usnea antarctica from different locations shows relatively narrow range of the δ 13C-values from -22.44 to -21.29‰ (7 samples), Drepanocladus sp. from -24.86 to -23.49‰ (8 samples), and Andreaea depressincrvis from -23.87 to -23.23‰ (3 samples) etc. Usually, in inhabited lands and parts of the world with rich flora and developed soil, isotopic specificity of species is masked by variations of carbon isotope composition of CO 2. In Antarctic conditions influence of local sources of CO 2 on the isotope composition of CO 2 is appeared to be minimal. Therefore the δ 13C-variations inherent to individual plant physiology and biochemistry can be distinguished on the background of the stable level of the atmospheric CO 2 δ 13C-value. The latter is best to reflect the global state of the carbon cycle.

  8. Hydrogen isotope composition of magmatic water

    SciTech Connect

    Taylor, B.E. )

    1992-01-01

    Isotopic tracing of H[sub 2]O degassing in both small and very large rhyolitic magmas in continental tectonic settings (USA and New Zealand), and isotopic studies of high-temperature fumaroles (USA, Japan, and elsewhere) indicate that the hydrogen isotope compositions of magmatic waters vary primarily with the composition of source material and tectonic setting. Water from felsic magmas in volcanic arc settings has a mean [delta]D value off [minus]25 [+-] 5 permil, whereas water from volcanic and plutonic magmas in continental settings has a slightly lower mean [delta]D of [minus]40 [+-] 10 permil. These differences reflect the variation in composition of source materials: hydrated oceanic crust and marine sediments for the arc volcanoes, and largely metamorphic crust for magmas in continental settings. The isotopic record in certain ore deposits associated with felsic magmas (e.g., W skarns, Sn-W veins) and geothermal systems records the influx at critical times of magmatic water with a [delta]D value of [minus]35 to [minus]45 permil. This is best documented where isotopic contrast between magmatic and meteoric waters is large. The [delta]D of MORB H[sub 2]O presumably lies between the mean [delta]D for MORB glass ([minus]75 permil), the [delta]D of H[sub 2]O in equilibrium with this glass ([delta]D ca. [minus]35; assuming closed-system degassing).

  9. Seasonal and provenance controls on Nd Sr isotopic compositions of Amazon rivers suspended sediments and implications for Nd and Sr fluxes exported to the Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Viers, Jérôme; Roddaz, Martin; Filizola, Naziano; Guyot, Jean-Loup; Sondag, Francis; Brunet, Pierre; Zouiten, Cyril; Boucayrand, Carole; Martin, François; Boaventura, Géraldo Resende

    2008-10-01

    This study reports daily water discharge and suspended sediment load concentrations and Sm-Nd and Rb-Sr isotopic systematics and major and trace elements concentrations of twelve monthly sampled suspended load sediments of the Solimões and Madeira rivers, the two major Andean tributaries of the Amazon, during the year 2004. As observed in other long-term monitoring studies of Amazon Rivers, the maximum of suspended sediment load occurs before or during the rising water period (i.e. during the rainy season). In 2004, the Solimões River exported ˜ 289 × 10 6 tonnes of suspended sediments and the Madeira River 294 × 10 6 tonnes which correspond to erosion rates of 129 and 214 T/km 2/yr for the Solimoes and Madeira rivers basins, respectively. Both the Solimoes and Madeira suspended sediments are enriched in LREE over HREE and exhibit similar MREE enrichment; the difference being that the Madeira sediments are more fractionated than the Solimoes ones. When plotted in Al 2O 3-CaO + Na 2O-K 2O diagram, the suspended sediments of the Solimoes and Madeira rivers exhibit two different weathering trends which suggests that these sediments evolved along two different trends starting from felsic rocks with different chemical compositions. The Nd isotopic compositions (ɛNd) of the Solimoes sediments (- 8.9 to 9.9) are slightly more radiogenic than the corresponding values of the Madeira sediments (- 10.8 to - 12.1). The 87Sr/ 86Sr isotopic compositions of the Madeira sediments (0.728 to 0.740) are significantly more radiogenic than those of the Solimoes (0.713 to 0.717). Together with other major elements and REE evidences, these isotopic compositions suggest that the Solimoes sediments are more influenced by Andean volcanic arc detritus than the Madeira sediments that might be due to input of young basaltic products owing to strong volcanic activity in Ecuador. Mineralogical compositions as well as Nd isotopic compositions do not vary seasonally. Based on our data set

  10. Calcium isotopic composition of mantle peridotites

    NASA Astrophysics Data System (ADS)

    Huang, F.; Kang, J.; Zhang, Z.

    2015-12-01

    Ca isotopes are useful to decipher mantle evolution and the genetic relationship between the Earth and chondrites. It has been observed that Ca isotopes can be fractionated at high temperature [1-2]. However, Ca isotopic composition of the mantle peridotites and fractionation mechanism are still poorly constrained. Here, we report Ca isotope composition of 12 co-existing pyroxene pairs in 10 lherzolites, 1 harzburgite, and 1 wehrlite xenoliths collected from Hainan Island (South Eastern China). Ca isotope data were measured on a Triton-TIMS using the double spike method at the Guangzhou Institute of Geochemistry, CAS. The long-term external error is 0.12‰ (2SD) based on repeated analyses of NIST SRM 915a and geostandards. δ44Ca of clinopyroxenes except that from the wehrlite ranges from 0.85‰ to 1.14‰, while opx yields a wide range from 0.98‰ up to 2.16‰. Co-existing pyroxene pairs show large ∆44Caopx-cpx (defined as δ44Caopx-δ44Cacpx) ranging from 0 to 1.23‰, reflecting equilibrium fractionation controlled by variable Ca contents in the opx. Notably, clinopyroxene of wehrlite shows extremely high δ44Ca (3.22‰). δ44Ca of the bulk lherzolites and harzburgites range from 0.86‰ to 1.14‰. This can be explained by extracting melts with slightly light Ca isotopic compositions. Finally, the high δ44Ca of the wehrlite (3.22‰) may reflect metasomatism by melt which has preferentially lost light Ca isotopes due to chemical diffusion during upwelling through the melt channel. [1] Amini et al (2009) GGR 33; [2] Huang et al (2010) EPSL 292.

  11. The Chlorine Isotope Composition of Martian Meteorites

    NASA Astrophysics Data System (ADS)

    Sharp, Z. D.; Shearer, C. K.; Agee, C.; Burger, P. V.; McKeegan, K. D.

    2014-11-01

    The Cl isotope composition of martian meteorites range from -3.8 to +8.6 per mil. Ol-phyric shergottites are lightest; crustally contaminated samples are heaviest, basaltic shergottites are in-between. The system is explained as two component mixing.

  12. Carbonate abundances and isotopic compositions in chondrites

    NASA Astrophysics Data System (ADS)

    Alexander, C. M. O'd.; Bowden, R.; Fogel, M. L.; Howard, K. T.

    2015-04-01

    We report the bulk C abundances, and C and O isotopic compositions of carbonates in 64 CM chondrites, 14 CR chondrites, 2 CI chondrites, LEW 85332 (C2), Kaba (CV3), and Semarkona (LL3.0). For the unheated CMs, the total ranges of carbonate isotopic compositions are δ13C ≈ 25-75‰ and δ18O ≈ 15-35‰, and bulk carbonate C contents range from 0.03 to 0.60 wt%. There is no simple correlation between carbonate abundance and isotopic composition, or between either of these parameters and the extent of alteration. Unless accretion was very heterogeneous, the uncorrelated variations in extent of alteration and carbonate abundance suggests that there was a period of open system behavior in the CM parent body, probably prior to or at the start of aqueous alteration. Most of the ranges in CM carbonate isotopic compositions can be explained by their formation at different temperatures (0-130 °C) from a single fluid in which the carbonate O isotopes were controlled by equilibrium with water (δ18O ≈ 5‰) and the C isotopes were controlled by equilibrium with CO and/or CH4 (δ13C ≈ -33‰ or -20‰ for CO- or CH4-dominated systems, respectively). However, carbonate formation would have to have been inefficient, otherwise carbonate compositions would have resembled those of the starting fluid. A quite similar fluid composition (δ18O ≈ -5.5‰, and δ13C ≈ -31‰ or -17‰ for CO- or CH4-dominated systems, respectively) can explain the carbonate compositions of the CIs, although the formation temperatures would have been lower (~10-40 °C) and the relative abundances of calcite and dolomite may play a more important role in determining bulk carbonate compositions than in the CMs. The CR carbonates exhibit a similar range of O isotopes, but an almost bimodal distribution of C isotopes between more (δ13C ≈ 65-80‰) and less altered samples (δ13C ≈ 30-40‰). This bimodality can still be explained by precipitation from fluids with the same isotopic

  13. Isotopic composition of Silurian seawater

    SciTech Connect

    Knauth, L.P.; Kealy, S.; Larimer, S.

    1985-01-01

    Direct isotopic analyses of 21 samples of the Silurian hydrosphere preserved as fluid inclusions in Silurian halite deposits in the Michigan Basin Salina Group yield delta/sup 18/O, deltaD ranging from 0.2 to +5.9 and -26 to -73, respectively. delta/sup 18/O has the same range as observed for modern halite facies evaporite waters and is a few per thousand higher than 100 analyses of fluid inclusions in Permian halite. deltaD is about 20 to 30 per thousand lower than modern and Permian examples. The trajectory of evaporating seawater on a deltaD-delta/sup 18/O diagram initially has a positive slope of 3-6, but hooks strongly downward to negative values, the shape of the hook depending upon humidity. Halite begins to precipitate at delta values similar to those observed for the most /sup 18/O rich fluid inclusions. Subsequent evaporation yields progressively more negative delta values as observed for the fluid inclusions. The fluid inclusion data can be readily explained in terms of evaporating seawater and are consistent with the degree of evaporation deduced from measured bromide profiles. These data are strongly inconsistent with arguments that Silurian seawater was 5.5 per thousand depleted in /sup 18/O. delta/sup 18/O for evaporite waters is systematically related to that of seawater, and does not show a -5.5 per thousand shift in the Silurian, even allowing for variables which affect the isotope evaporation trajectory. The lower deltaD may indicate a component of gypsum dehydration waters or may suggest a D-depleted Silurian hydrosphere.

  14. Nd, O and Sr isotopic constraints on the origin of Precambrian rocks, southern Black Hills, South Dakota

    SciTech Connect

    Walker, R.J.; Hanson, G.N.; Papike, J.J.; O'Neil, J.R.

    1986-12-01

    The Nd, O and Sr isotopic characteristics of Precambrian metasedimentary, metavolcanic and granitic rocks from the Black Hills of South Dakota are examined. Two late-Archean granites (2.5-2.6 Ga) have T/sub DM/ ages of 3.05 and 3.30 Ga, suggesting that at least one of the granites was derived through the melting of significantly older crust. Early-Proterozoic metasedimentary rocks have T/sub DM/ ages that range from 2.32 to 2.45 Ga. These model ages, in conjunction with probable stratigraphic ages ranging from 1.9 to 2.2 Ga, indicate that mantle-derived material was added to the continental crust of this region during the early-Proterozoic. Previous studies of the Harney Peak Granite complex have reported U-Pb and Rb-Sr ages of about 1.71 Ga, and most granite samples examined in this study have Sr isotopic compositions consistent with that age. Two granite samples taken from the same sill, however, give two-point Rb-Sr and Sm-Nd ages of 2.08 +/- 0.08 and 2.20 +/- 0.20 Ga, respectively. In addition, whole-rock and apatite samples of the spatially associated Tin Mountain pegmatite give a Sm-Nd isochron age of 2000 +/- 100 Ma.

  15. U-Th-Pb isotope chronology of sulfide ores and rocks in the early Proterozoic metavolcanic belt of northern Wisconsin.

    USGS Publications Warehouse

    Afifi, A.; Doe, B.R.; Sims, P.K.; Delevaux, M.H.

    1984-01-01

    Lead from galena of massive sulphide deposits in the metavolcanic belt of northern Wisconsin was probably derived from 3700 m.y. old source material 1800-1900 m.y. ago. Approximately 3500 m.y. old rocks occur within 100-300 km to the north and west. The U-Th-Pb systems of the metavolcanic and granitic rocks in the belt were reset about 1600 m.y. ago during retrogressive metamorphism. The ages from lead isotope data are in accord with Rb/Sr whole-rock, Rb/Sr and K/Ar mineral, and U-Th-Pb zircon dating. A concordia plot of whole-rock lead data shows that many of the rocks lost lead 200-400 m.y. ago during uplift and erosion. Meta-volcanic rocks near Crandon, Wisconsin, had lead isotope compositions 20 m.y. ago that match those in the Pb-Zn ores in Palaeozoic rocks of the upper Mississippi valley. Possibly the volcanic rocks were a source of lead for the Pb-Zn ores. Similar ores might therefore occur between the northern Wisconsin metavolcanic belt and the upper Mississippi valley.-G.J.N.

  16. A strontium and neodymium isotopic study of Apollo 17 high-Ti mare basalts - Resolution of ages, evolution of magmas, and origins of source heterogeneities

    NASA Technical Reports Server (NTRS)

    Paces, James B.; Neal, Clive R.; Taylor, Lawrence A.; Nakai, Shun'ichi; Halliday, Alex N.

    1991-01-01

    The geochronological and compositional differences between previously identified magma types (A, B1, B2, and C) were investigated using high-precision Rb-Sr and Sm-Nd isotopic data for a set of Apollo 17 high-Ti mare basalt samples chosen to span the range of each of the magma types. These data, combined with previously reported geochemical ages, suggest that Apollo 17 volcanism was initially dominated by an eruption of Type B basalts. Data obtained from new whole-rock Sr and Nd isotopic analyses exhibited distinct differences in initial Sr and Nd isotopic compositions between Types A, B1, B2, and C basalts and were found to be consistent with existing petrogenetic models.

  17. The Cu isotopic composition of iron meteorites

    NASA Astrophysics Data System (ADS)

    Bishop, Matthew Cole; Moynier, Frederic; Weinstein, Charlotte; Fraboulet, Jean-Gabriel; Wang, Kun; Foriel, Julien

    2012-02-01

    High-precision Cu isotopic compositions have been measured for the metal phase of 29 iron meteorites from various groups and for four terrestrial standards. The data are reported as the δ65Cu permil deviation of the 65Cu/63Cu ratio relative to the NIST SRM 976 standard. Terrestrial mantle rocks have a very narrow range of variations and scatter around zero. In contrast, iron meteorites show δ65Cu approximately 2.3‰ variations. Different groups of iron meteorites have distinct δ65Cu values. Nonmagmatic IAB-IIICD iron meteorites have similar δ65Cu (0.03 ± 0.08 and 0.12 ± 0.10, respectively), close to terrestrial values (approximately 0). The other group of nonmagmatic irons, IIE, is isotopically distinct (-0.69 ± 0.15). IVB is the iron meteorite group with the strongest elemental depletion in Cu and samples in this group are enriched in the lighter isotope (δ65Cu down to -2.26‰). Evaporation should have produced an enrichment in 65Cu over 63Cu (δ65Cu >0) and can therefore be ruled out as a mechanism for volatile loss in IVB meteorites. In silicate-bearing iron meteorites, Δ17O correlates with δ65Cu. This correlation between nonmass-dependent and mass-dependent parameters suggests that the Cu isotopic composition of iron meteorites has not been modified by planetary differentiation to a large extent. Therefore, Cu isotopic ratios can be used to confirm genetic links. Cu isotopes thus confirm genetic relationships between groups of iron meteorites (e.g., IAB and IIICD; IIIE and IIIAB); and between iron meteorites and chondrites (e.g., IIE and H chondrites). Several genetic connections between iron meteorites groups are confirmed by Cu isotopes, (e.g., IAB and IIICD; IIIE and IIIAB); and between iron meteorites and chondrites (e.g., IIE and H chondrites).

  18. Isotopic composition of precipitation in Greece

    NASA Astrophysics Data System (ADS)

    Argiriou, Athanassios A.; Lykoudis, Spyros

    2006-08-01

    SummaryThe contribution of stable isotopes in meteorological, climatological and hydrological research is well known. Until this date and despite the fact that several hydrological studies of water sources in Greece have been published, no systematic isotopic study of precipitation has been performed in the country. This paper presents all the available isotopic data collected since 1960 in several Hellenic measurement stations. This data is divided in two periods: the first covers data that was collected in the past, in the frame of a preliminary survey of the isotope composition of precipitation in the Eastern Mediterranean Sea and specific hydrological studies; the second is the result of a three-year coordinated research project of the International Atomic Energy Agency, in which the authors participated, aiming at the systematic study of stable isotopes ( 2H and 18O) and 3H in precipitation around the Mediterranean basin. No statistically significant behavior between the two periods of data was found. The isotopic content of precipitation presents characteristics intermediate of those of the Eastern and Western Mediterranean. The tritium concentration in precipitation declines as expected towards the pre-bomb levels, however there is an indication that tritium concentrations are higher in Northern Greece.

  19. Pb-Sr-O-C isotope compositions of metacarbonate rocks of the Derbina Formation (East Sayan): Chemostratigraphic and geochronological significance

    NASA Astrophysics Data System (ADS)

    Gorokhov, I. M.; Kuznetsov, A. B.; Ovchinnikova, G. V.; Nozhkin, A. D.; Azimov, P. Ya.; Kaurova, O. K.

    2016-01-01

    The Pb-Sr-O-C isotope compositions of calcite marbles of the Derbina Formation, exposed in the northwestern part of the Derbina block of the East Sayan, were studied. Rocks of the Derbina Formation were metamorphosed under high-temperature amphibolite facies conditions. The carbonate constituent of marbles contains (ppm) 15-130 Mn, 130-160 Fe, 0.008-0.039 Rb, 645-2190 Sr, 0.565-0.894 U, and 0.288-1.42 Pb. These concentrations are similar to those in modern carbonate sediments. The values of δ13C in marbles of the Derbina Formation range from-0.6 to +1.4‰ PDB; the values of δ18O range from 21.5 to 28.6‰ SMOW. The 87Sr/86Sr ratio values in the two least altered rocks, which meet geochemical criteria of the Rb-Sr system preservation in high-grade carbonate rocks, are 0.70804 and 0.70829. The protolith ages of marbles determined using Sr and C chemostratigraphy lie within the interval of 560-530 Ma, which is regarded as the period of carbonate sedimentation. The slope of the straight line on the 206Pb/204Pb-207Pb/204Pb diagram ( n = 9, MSWD = 19) constructed on the basis of the data points of bulk carbonate constituents of all samples studied and those representing leachate steps of one of them in 0.5N HBr yields Late Vendian age (556 ± 31 (2σ) Ma. Taking into account the data on Sr and C isotope systematics of Derbina marbles, this age is regarded as the age of early diagenesis of carbonate sediments close to the age of sedimentation. Thus, metacarbonate rocks of the Derbina Formation preserved the pre-metamorphic chemostratigraphic and isotope-geochronological information. The age obtained testifies that formation of the carbonate cover of the Derbina block occurred in the Late Vendian. At the end of the Cambrian, carbonate deposits were metamorphosed during the Early Caledonian tectonic event in the southeastern part of the Central Asian Fold Belt.

  20. Tungsten Stable Isotope Compositions of Ferromanganese Crusts

    NASA Astrophysics Data System (ADS)

    Abraham, K.; Barling, J.; Hein, J. R.; Schauble, E. A.; Halliday, A. N.

    2014-12-01

    We report the first accurate and precise data for mass-dependent fractionation of tungsten (W) stable isotopes, using a double spike technique and MC-ICPMS. Results are expressed relative to the NIST 3136 W isotope standard as per mil deviations in 186W/184W (δ186W). Although heavy element mass-dependent fractionations are expected to be small, Tl and U both display significant low temperature isotopic fractionations. Theoretical calculations indicate that W nuclear volume isotopic effects should be smaller than mass-dependent fractionations at low temperatures. Hydrogenetic ferromanganese (Fe-Mn) crusts precipitate directly from seawater and have been used as paleoceanographic recorders of temporal changes in seawater chemistry. Crusts are strongly enriched in W and other metals, and are a promising medium for exploring W isotopic variability. Tungsten has a relatively long residence time in seawater of ~61,000 years, mainly as the tungstate ion (WO42-). Water depth profiles show conservative behaviour. During adsorption on Fe-Mn crusts, W species form inner-sphere complexes in the hexavalent (W6+) state. The major host phase is thought to be Mn oxides and the lighter W isotope is expected to be absorbed preferentially. Surface scrapings of 13 globally distributed hydrogenetic Fe-Mn crusts display δ186W from -0.08 to -0.22‰ (±0.03‰, 2sd). A trend toward lighter W isotope composition exists with increasing water depth (~1500 to ~5200m) and W concentration. One hydrothermal Mn-oxide sample is anomalously light and Mn nodules are both heavy and light relative to Fe-Mn crusts. Tungsten speciation depends on concentration, pH, and time in solution and is not well understood because of the extremely slow kinetics of the reactions. In addition, speciation of aqueous and/or adsorbed species might be sensitive to pressure, showing similar thermodynamic stability but different effective volumes. Thus, W stable isotopes might be used as a water-depth barometer in

  1. Isotopic Composition of Oxygen in Lunar Zircons

    NASA Technical Reports Server (NTRS)

    Nemchin, A. A.; Whitehouse, M. J.; Pidgeon, R. T.; Meyer, C.

    2005-01-01

    The recent discovery of heavy oxygen in zircons from the Jack Hills conglomerates Wilde et al. and Mojzsis et al. was interpreted as an indication of presence of liquid water on the surface of Early Earth. The distribution of ages of Jack Hills zircons and lunar zircons appears to be very similar and therefore analysis of oxygen in the lunar grains may provide a reference frame for further study of the early history of the Earth as well as give additional information regarding processes that operated on the Moon. In the present study we have analysed the oxygen isotopic composition of zircon grains from three lunar samples using the Swedish Museum of Natural History CAMECA 1270 ion microprobe. The samples were selected as likely tests for variations in lunar oxygen isotopic composition. Additional information is included in the original extended abstract.

  2. ISOTOPIC COMPOSITIONS OF URANIUM REFERENCE MATERIALS

    SciTech Connect

    Jacobsen, B; Borg, L; Williams, R; Brennecka, G; Hutcheon, I

    2009-09-03

    Uranium isotopic compositions of a variety of U standard materials were measured at Lawrence Livermore National Laboratory and are reported here. Both thermal ionization mass spectrometry (TIMS) and multi-collector inductively couple plasma mass spectrometry (MC-ICPMS) were used to determine ratios of the naturally occurring isotopes of U. Establishing an internally coherent set of isotopic values for a range of U standards is essential for inter-laboratory comparison of small differences in {sup 238}U/{sup 235}U, as well as the minor isotopes of U. Differences of {approx} 1.3{per_thousand} are now being observed in {sup 238}U/{sup 235}U in natural samples, and may play an important role in understanding U geochemistry where tracing the origin of U is aided by U isotopic compositions. The {sup 238}U/{sup 235}U ratios were measured with a TRITON TIMS using a mixed {sup 233}U-{sup 236}U isotopic tracer to correct for instrument fractionation. this tracer was extremely pure and resulted in only very minor corrections on the measured {sup 238}U/{sup 235}U ratios of {approx} 0.03. The values obtained for {sup 238}U/{sup 235}U are: IRMM184 = 137.698 {+-} 0.020 (n = 15), SRM950a = 137.870 {+-} 0.018 (n = 8), and CRM112a = 137.866 {+-} 0.030 (n = 16). Uncertainties represent 2 s.d. of the population. The measured value for IRMM184 is in near-perfect agreement with the certified value of 137.697 {+-} 0.042. However, the U isotopic compositions of SRM950a and CRM112a are not certified. Minor isotopes of U were determined with a Nu Plasma HR MC-ICPMS and mass bias was corrected by sample/standard bracketing to IRMM184, using its certified {sup 238}U/{sup 235}U ratio. Thus, the isotopic compositions determined using both instruments are compatible. The values obtained for {sup 234}U/{sup 235}U are: SRM950a = (7.437 {+-} 0.043) x 10{sup -3} (n = 18), and CRM112a = (7.281 {+-} 0.050) x 10{sup -3} (n = 16), both of which are in good agreement with published values. The value for

  3. Rb-Sr-analyses of apollo 16 melt rocks and a new age estimate for the imbrium basin: lunar basin chronology and the early heavy bombardment of the moon

    SciTech Connect

    Deutsch, A.; Stoeffler, D.

    1987-07-01

    Rb-Sr-model ages on 7 impact glass-bombs and internal Rb-Sr isochrons for two crystalline impact melt rocks from the Apollo 16 collection have been determined. The post-Cayley glass-bombs with model ages between 4.75 +- 0.45 AE and 3.97 +- 0.08 AE can be classified according to their calculated single stage (/sup 87/Rb/sup 86/Sr)/sub I/-ratios: 67728, 67946, and 67627.8 point to a KREEP-free precursor terrain - the Descartes highlands; whereas 63566, 67567, 67627.10 and 67629 are derived from the more heterogeneous Cayley plains. The very feldspar-rich impact melt rock 65795, which is compositionally similar to the group of feldspathic microporphyritic melt breccias (FM-suite), yields a crystallization age of 3.81 +- 0.04 AE (2sigma; lambda/sup 87/Rb = 1.42/sup -11/ yr/sup -1/) and I/sub Sr/ of .69929 +- 3. The authors suggest that the Imbrium basin and the related Fra Mauro and Cayley formations were formed 3.77 +- 0.02 AE ago and could be even as young as 3.75 AE. As a consequence, they adopt 3.92 +- 0.03 AE, 3.87 +- 0.03 AE, and 3.84 +- 0.04 AE as ages for the Nectaris, Serenitatis, and Crisium basins, respectively, in agreement with the relative crater densities measured on the ejecta blankets of these basins. The proposed age sequence leads to an average formation interval for the observed 12-13 Nectarian basins of 7 to 14 m.y. leaving approx. 30 pre-Nectarian basins of unknown age. These facts suggest that there is no late terminal lunar cataclysm in the sense of a culmination of the lunar impact rate at approx. 3.8 AE ago. Rather, the observations are compatible with a steeply and steadily decreasing flux of impactors in the sense of an early heavy bombardment which started at the time of the moon's accretion and terminated around 3.75 AE ago.

  4. Reconstruction of crustal blocks of California on the basis of initial strontium isotopic compositions of Mesozoic granitic rocks

    USGS Publications Warehouse

    Kistler, Ronald Wayne; Peterman, Zell E.

    1978-01-01

    Initial 87Sr/ 86 Sr was determined for samples of Mesozoic granitic rocks in the vicinity of the Garlock fault zone in California. These data along with similar data from the Sierra Nevada and along the San Andreas fault system permit a reconstruction of basement rocks offset by the Cenozoic lateral faulting along both the San Andreas and Garlock fault systems. The location of the line of initial 87Sr/ 86 Sr = 0.7060 can be related to the edge of the Precambrian continental crust in the western United States. Our model explains the present configuration of the edge of Precambrian continental crust as the result of two stages of rifting that occurred about 1,250 to 800 m.y. ago, during Belt sedimentation, and about 600 to 350 m.y. ago, prior to and during the development of the Cordilleran geosyncline and to left-lateral translation along a locus of disturbance identified in the central Mojave Desert. The variations in Rb, Sr, and initial 87Sr/ 86 Sr of the Mesozoic granitic rocks are interpreted as due to variations in composition and age of the source materials of the granitic rocks. The variations of Rb, Sr, and initial 87Sr/ 86 Sr in Mesozoic granitic rocks, the sedimentation history during the late Precambrian and Paleozoic, and the geographic position of loci of Mesozoic magmatism in the western United States are related to the development of the continental margin and different types of lithosphere during rifting.

  5. Comment on "Structural, elastic, electronic, magnetic and optical properties of RbSrX (C, SI, Ge) half-Heusler compounds"

    NASA Astrophysics Data System (ADS)

    Jalilian, Jaafar; Motiepour, Pouria

    2015-12-01

    In a recent article by Ahmad et al. (2015) [1] structural, elastic, electronic, magnetic and optical properties of RbSrX (C, Si, Ge) half-Heusler compounds have been studied by the first principles calculations. After studying this article, we found that there are some physical and computational mistakes in electronic and optical properties sections. In investigating optical properties, they did not consider intraband transitions contribution in complex dielectric function term, while this term has significant effect on optical spectra for half-metallic materials.

  6. Sulfur Isotope Composition of Putative Primary Troilite in Chondrules

    NASA Technical Reports Server (NTRS)

    Tachibana, Shogo; Huss, Gary R.

    2002-01-01

    Sulfur isotope compositions of putative primary troilites in chondrules from Bishunpur were measured by ion probe. These primary troilites have the same S isotope compositions as matrix troilites and thus appear to be isotopically unfractionated. Additional information is contained in the original extended abstract.

  7. The Oxygen Isotopic Composition of the Sun

    NASA Astrophysics Data System (ADS)

    McKeegan, K. D.; Kallio, A.; Heber, V. S.; Jarzebinski, G.; Mao, P.; Coath, C.; Kunihiro, T.; Wiens, R. C.; Judith, A.; Burnett, D. S.

    2010-12-01

    An accurate and precise determination of the oxygen isotopic composition of the Sun is the highest priority scientific goal of the Genesis Mission [1] as such data would provide a baseline from which one could interpret the oxygen isotopic anomalies found at all spatial scales in inner solar system materials. We have measured oxygen isotope compositions of implanted solar wind in 40 spots along a radial traverse of the Genesis SiC target sample 60001 by depth profiling with the UCLA MegaSIMS [2]. Mass-dependent fractionation induced by the solar wind concentrator [3] ion optics was corrected by comparison of the concentrator 22Ne/20Ne with that measured in a bulk solar wind target (diamond-like carbon on Si, [4]). The solar wind captured at L1 has an isotopic composition of (δ18O, δ17O) ≈ (-99, -79)‰, a value which is far removed from the terrestrial mass fractionation line. Profiles from the central portion of the target, where solar concentrations are highest and background corrections minimal, yield a mean Δ17O = -28.3 ± 1.8 ‰ indicating that the Earth and other planetary materials from the inner solar system are highly depleted in 16O relative to the solar wind. A mass-dependent fractionation of ~ -20%/amu in the acceleration of solar wind is required if we hypothesize that the photospheric oxygen isotope value, which represents the bulk starting composition of the solar system, is on the 16O-mixing line characteristic of refractory phase in primitive meteorites [5]. With this assumption, our preferred value for the bulk solar oxygen isotope composition is δ18O ≈ δ17O ≈ -57‰. A mechanism is required to fractionate oxygen isotopes in a non-mass-dependent manner to deplete 16O by ~6 to 7% in the rocky materials of the solar nebula. As oxygen is the third most abundant element in the solar system, and the most abundant in the terrestrial planets, this mechanism must operate on a large scale. Isotope-selective photochemistry, for example as in

  8. Pb and Sr isotopic compositions of snowpack from Quebec, Canada: Inferences on the sources and deposition budgets of atmospheric heavy metals

    SciTech Connect

    Simonetti, A.; Gariepy, C.; Carignan, J.

    2000-01-01

    Elemental concentrations of Al, Ba, Cd, Cu, Mg, Mn, Pb, Rb, Sr, and Zn, as well as Pb and Sr isotopic compositions were determined in samples of snowpack obtained along two main transects from the province of Quebec (Canada); one north-south (between 47 N and 55 N; 1994) and the other within the St. Lawrence Valley (1997). Median enrichment factors (relative to upper crustal abundances) for Cd, Cu, Mn, Pb and Zn for all samples range from {approx}300 to {approx}42,000 and are indicative of an anthropogenic origin. Pb isotopes ratios for snow samples retrieved in 1994 are highly variable ({sup 206}Pb/{sup 207}Pb = 1.148 to 1.193) and are characterized by the most radiogenic Sr isotope values ({sup 87}Sr/{sup 86}Sr {ge} 0.710). In contrast, the Pb and Sr isotope results for 1997 snow samples collected along the St. Lawrence Valley (below latitude 47 N), yield the most radiogenic Pb isotope ratios ({sup 206}Pb/{sup 207}Pb = 1.160 to 1.180) for 1997 samples collected north of latitude 47 N indicate input of an additional anthropogenic component, possibly that of Eurasian pollution being transported over the high Arctic during the winter season. A comparison of the Pb isotope results between lichens and snow samples from identical sample locations indicate that these either overlap (along St. Lawrence Valley), or are significantly different (north-south transect). The latter discrepancy may be attributed to either: (1) different time scales for the integration of the atmospheric signal (months for snow vs. years for lichens); (2) recording of the atmospheric signal at substantially different altitudes; or (3) the presence of an important, local point source of atmospheric pollution. Annual depositional budgets have been estimated for Pb, Cd, Zn, Cu, and Mn, and average values (g/km{sup 2} yr) are 1,500, 130, 196,000, 1,900, and 6,400, respectively. Compared to previous depositional fluxes (1993--1994) estimated from adjacent regions in North America, those reported here

  9. THE NITROGEN ISOTOPIC COMPOSITION OF METEORITIC HCN

    SciTech Connect

    Pizzarello, Sandra

    2014-12-01

    HCN is ubiquitous in extraterrestrial environments and is central to current theories on the origin of early solar system organic compounds such as amino acids. These compounds, observed in carbonaceous meteorites, were likely important in the origin and/or evolution of early life. As part of our attempts to understand the origin(s) of meteoritic CN{sup –}, we have analyzed the {sup 15}N/{sup 14}N isotopic composition of HCN gas released from water extracts of the Murchison meteorite and found its value to be near those of the terrestrial atmosphere. The findings, when evaluated viz-a-viz molecular abundances and isotopic data of meteoritic organic compounds, suggest that HCN formation could have occurred during the protracted water alteration processes known to have affected the mineralogy of many asteroidal bodies during their solar residence. This was an active synthetic stage, which likely involved simple gasses, organic molecules, their presolar precursors, as well as mineral catalysts and would have lead to the formation of molecules of differing isotopic composition, including some with solar values.

  10. An Ldrims Instrument for Portable Rb-Sr Dating with Accuracy of Better than ±150 MA for the MARS-2020 Rover

    NASA Astrophysics Data System (ADS)

    Anderson, F. Scott; Whitaker, Tom; Hamilton, Victoria; Nowicki, Keith

    2013-04-01

    Using a laser desorption resonance ionization mass spectrometer (LDRIMS), we can now demonstrate repeatable dates with portable hardware that could be carried on MER- or MSL-sized rovers. This is important because NASA is developing science requirements for a Mars 2020 rover mission based on MSL hardware, and for Mars, the National Research Council Decadal Survey (NRC DS) specifically supports: "...long-term development of instruments ... focusing on the most important future in situ measurements... [including] ... in situ geochronology experiments". The LDRIMS instrument can produce these science measurements today, and in so doing, triage samples for Mars Sample Return. The LDRIMS technique can be miniaturized and avoids the mass interference issues requiring unwieldy chemical separation for traditional geochronology techniques. With LDRIMS sample is placed in a time-of-flight (TOF) mass spectrometer and surface atoms, molecules, and ions are desorbed with a 213 nm laser. Ions are suppressed by an electric field and the plume of expanding particles is present for many μs, during which it is first illuminated with laser light tuned to ionize only Sr, and then 1-3 μs later, for Rb. This eliminates isobars for Rb and Sr, insures that the measured atoms come from the same ablation event, and hence target materials, and reduces the total number of measurements required. The LDRIMS system has demonstrated a sensitivity of 300 parts-per-trillion, and isotope ratio precisions of ±0.3 to ±0.1% in 3000-5000 ablations of one spot on a sample in 3-5 minutes. The bench top prototype has been tested on the Boulder Creek Granite (BCG) from Elephant Butte, Colorado, comprised primarily of a gneissic quartz monzonite and granodiorite. Whole rock Rb-Sr TIMS measurements of the BCG, and our own preliminary micro-drill TIMS measurements of individual minerals, are consistent with an age of 1700±40 Ma. To obtain a LDRIMS date using the BCG sample, we measured hundreds of spots

  11. Cadmium isotopic composition in the ocean

    NASA Astrophysics Data System (ADS)

    Lacan, Francois; Francois, Roger; Ji, Yongcheng; Sherrell, Robert M.

    2006-10-01

    The oceanic cycle of cadmium is still poorly understood, despite its importance for phytoplankton growth and paleoceanographic applications. As for other elements that are biologically recycled, variations in isotopic composition may bring unique insights. This article presents (i) a protocol for the measurement of cadmium isotopic composition (Cd IC) in seawater and in phytoplankton cells; (ii) the first Cd IC data in seawater, from two full depth stations, in the northwest Pacific and the northwest Mediterranean Sea; (iii) the first Cd IC data in phytoplankton cells, cultured in vitro. The Cd IC variation range in seawater found at these stations is not greater than 1.5 ɛCd/amu units, only slightly larger than the mean uncertainty of measurement (0.8 ɛCd/amu). Nevertheless, systematic variations of the Cd IC and concentration in the upper 300 m of the northwest Pacific suggest the occurrence of Cd isotopic fractionation by phytoplankton uptake, with a fractionation factor of 1.6 ± 1.4 ɛCd/amu units. This result is supported by the culture experiment data suggesting that freshwater phytoplankton ( Chlamydomonas reinhardtii and Chlorella sp.) preferentially take up light Cd isotopes, with a fractionation factor of 3.4 ± 1.4 ɛCd/amu units. Systematic variations of the Cd IC and hydrographic data between 300 and 700 m in the northwest Pacific have been tentatively attributed to the mixing of the mesothermal (temperature maximum) water ( ɛCd/amu = -0.9 ± 0.8) with the North Pacific Intermediate Water ( ɛCd/amu = 0.5 ± 0.8). In contrast, no significant Cd IC variation is found in the northwest Mediterranean Sea. This observation was attributed to the small surface Cd depletion by phytoplankton uptake and the similar Cd IC of the different water masses found at this site. Overall, these data suggest that (i) phytoplankton uptake fractionates Cd isotopic composition to a measurable degree (fractionation factors of 1.6 and 3.4 ɛCd/amu units, for the in situ and

  12. Speculations on nature and extent of Archean basement in Labrador as indicated by SR, ND and PB isotopic systematics of proterozoic intrusives

    NASA Technical Reports Server (NTRS)

    Ashwal, L. D.; Wooden, J. L.; Emslie, R. F.

    1986-01-01

    The Sm-Nd and Rb-Sr isotopic compositions of mid to late Proterozoic (approximately 1.6 to 1.1 Ga) massif-type anorthosites and mafic intrusives in the eastern Canadian shield are correlated with geographic location. Complexes in the Grenville province have positive epsilon sub Nd values and initial Sr-87/Sr-86 (I sub Sr) generally less than 0.703, suggesting derivation from depleted mantle. In Labrador, similar complexes close to or northwest of a line roughly corresponding to the Grenville Front have negative epsilon sub Nd values and I sub Sr 0.703. This contrast was intrepreted as reflecting either enriched mantle under the Nain Province, or contamination of the Nain intrusives with older crustal components. Lead isotopic compositions, however, favor the latter. The possibility of using these Proterozoic intrusives as tracers to characterize the nature and extent of older basement types in Labrador is discussed.

  13. Additional Sr Isotopic Heterogeneity in Zagami Olivine-Rich Lithology

    NASA Astrophysics Data System (ADS)

    Misawa, K.; Niihara, T.; Shih, C.-Y.; Young, Y. D.; Nyquist, L. E.; Yoneda, S.; Yamashita, H.; Hirata, D.

    2012-09-01

    New Rb-Sr data on Zagami demonstrate that the Ol-rich lithology is different from FG, CG, and DML in Sr isotopic signatures, and that highly evolved magma was infiltrated into a nearly solidified body at a final-stage of the Zagami formation.

  14. Oxygen isotope composition of trinitite postdetonation materials.

    PubMed

    Koeman, Elizabeth C; Simonetti, Antonio; Chen, Wei; Burns, Peter C

    2013-12-17

    Trinitite is the melt glass produced subsequent the first nuclear bomb test conducted on July 16, 1945, at White Sands Range (Alamagordo, NM). The geological background of the latter consists of arkosic sand that was fused with radioactive debris and anthropogenic materials at ground zero subsequent detonation of the device. Postdetonation materials from historic nuclear weapon test sites provide ideal samples for development of novel forensic methods for attribution and studying the chemical/isotopic effects of the explosion on the natural geological environment. In particular, the latter effects can be evaluated relative to their spatial distribution from ground zero. We report here δ(18)O(‰) values for nonmelted, precursor minerals phases (quartz, feldspar, calcite), "feldspathic-rich" glass, "average" melt glass, and bulk (natural) unmelted sand from the Trinity site. Prior to oxygen isotope analysis, grains/crystals were examined using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) to determine their corresponding major element composition. δ(18)O values for bulk trinitite samples exhibit a large range (11.2-15.5‰) and do not correlate with activity levels for activation product (152)Eu; the latter levels are a function of their spatial distribution relative to ground zero. Therefore, the slow neutron flux associated with the nuclear explosion did not perturb the (18)O/(16)O isotope systematics. The oxygen isotope values do correlate with the abundances of major elements derived from precursor minerals present within the arkosic sand. Hence, the O isotope ratios documented here for trinitite melt glass can be attributed to a mixture of the respective signatures for precursor minerals at the Trinity site prior to the nuclear explosion. PMID:24304329

  15. Mg Isotopic Compositions of Modern Marine Carbonates

    NASA Astrophysics Data System (ADS)

    Krogstad, E.; Bizzarro, M.; Hemming, N.

    2003-12-01

    We have used a MC-ICP-MS to measure the isotopic composition of magnesium in a number of samples of modern marine carbonate. Due to the large mass difference between 26Mg and 24Mg (similar to that between 13C and 12C), there is potential for mass fractionation during geologic and biologic processes that may make this isotope system useful for geochemical studies. These samples are from the study of Hemming and Hanson (1992, GCA 56: 537-543). The carbonate minerals analyzed include aragonite, low-Mg calcite, and high-Mg calcite. The samples include corals, echinoderms, ooids, etc., from subtropical to Antarctic settings. Mg purification was accomplished by ion-exchange chromatography, using Bio-Rad AG50W-X12 resin on which greater than 99 percent recovery of Mg is achieved. Samples were introduced into the MC-ICP-MS (VG Axiom) using a Cetac MCN-6000 nebuliser. We use a standard-sample-standard bracketing technique, and samples are analysed at least three times. For lab standards we find that the reproducibility on the 26Mg/24Mg to be about ñ 0.12 permil (2 s.d.). We monitored our separated samples for Na and Ca, as we have found that high Ca/Mg and Na/Mg produce variable magnesium isotopic fractionation during mass spectrometry due to as yet unclear matrix effects. We have normalized our results to our measured values for seawater. We observed a d26Mg(s.w.) range of -1.4 to -2.4 permil in our modern carbonate samples relative to present day seawater. Due to the long residence time of Mg in the oceans (ca. 50 my), this must be due to kinetic or biologic effects. Our d25Mg(s.w.) variations as a function of d26Mg(s.w.) plot along the terrestrial fractionation trend. With an average d26Mg(s.w.) of ca. +0.5 permil in all samples of mantle lithologies and mantle-derived igneous rocks (Bizzarro et al., Goldschmidt abs., 2003), we can assume that the Mg isotopic composition of Earth's river water lies between ca. -2.4 and +0.5 permil (relative to seawater). The actual

  16. Internal Rb-Sr Age and Initial Sr-87/Sr-86 of a Silicate Inclusion from the Campo Del Cielo Iron Meteorite

    NASA Technical Reports Server (NTRS)

    Liu, Y.; Nyquist, L.; Wiesmann, H.; Shih, C.; Schwandt, C.; Takeda, H.

    2003-01-01

    The largest group of iron meteorites, IAB, is distinguished by the presence of diverse silicate inclusions. In principle, Rb-Sr and Sm-Nd radiometric dating of these silicate inclusions by internal isochron techniques can determine both the times of melting and parent/daughter ratios in the precursor materials via initial Sr-87/Sr-86 and Nd-143/Nd-144 ratios. The Sr-87/Sr-86 and Nd-143/Nd-144 ratios could distinguish chondritic precursors from already differentiated silicates. We reported Rb-Sr and Sm-Nd internal ischron ages of 4.52+/-0.03 Ga and 4.50+/-0.04 Ga, respectively, for plagioclase-diopside-rich material in the Caddo County IAB iron meteorite. These results are essentially identical to literature values of its Ar-Ar age of 4.520+/-0.005 Ga and its Sm-Nd age of 4.53+/-0.02 Ga. The purpose of this study is to evaluate the formation and evolution of silicate inclusions in IAB iron meteorites by determination of their initial Sr-87/Sr-86 ratios combined with higher-resolution chronology and mineralogical and geochemical studies.

  17. Isotopic composition of Riyadh rainfall, Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Michelsen, Nils; Reshid, Mustefa; Siebert, Christian; Schulz, Stephan; Rausch, Randolf; Knöller, Kay; Weise, Stephan; Al-Saud, Mohammed; Schüth, Christoph

    2015-04-01

    Arid countries like Saudi Arabia often depend on fossil groundwater. Hence, thorough studies of the available resources are crucial. In the course of such investigations, analyses of δ18O and δD are frequently applied to constrain the provenance of the waters and to reconstruct the (paleo)climatic conditions during their recharge. Yet, to be able to evaluate the isotopic signature of the groundwater, one also has to know the isotopic composition of current precipitation. Although a few rain water analyses are available for Central Saudi Arabia in the literature - mostly in unpublished consultant reports - a Local Meteoric Water Line has never been established. To complement the available data, 28 rain events occurring in Riyadh between 2009 and 2013 were studied for their stable isotope composition. Samples were collected as integral samples, i.e., they represent the entire precipitation event. Moreover, one event was sampled several times, aiming at an evaluation of intra-storm variability. During selected storms, a grab sample was taken for 3H analysis. The event samples showed δ18O and δD values scattering between -6.5 and +9.5 and between -30 and +50 ‰ V-SMOW, respectively. In the course of the event that was sequentially sampled, a proceeding isotopic depletion was observed with respect to both isotopes. The relatively large ranges of δ-values for 18O and D of approximately 7 and 38 ‰ V-SMOW highlight the general need for integral sampling. The obtained grab samples are characterized by moderate 3H concentrations of a few Tritium Units. Further results will be presented and discussed in view of associated weather data (e.g. rain amount and temperature) and the probable moisture sources derived from back-trajectories, which were calculated using HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory Model; Draxler & Rolph, 2003). References Draxler, R.R. & Rolph, G.D. (2013): HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory

  18. Molybdenum Isotopic Composition of Iron Meteorites, Chondrites and Refractory Inclusions

    NASA Technical Reports Server (NTRS)

    Becker, H.; Walker, R. J.

    2003-01-01

    Recent Mo isotopic studies of meteorites reported evidence for differences in isotopic compositions for whole rocks of some primitive and differentiated meteorites relative to terrestrial materials. Enrichments of r- and p-process isotopes of up to 3-4 units (e unit = parts in 10(exp 4) over s-process dominated isotopes are the most prominent features. Certain types of presolar grains show large enrichments in s-process isotopes, however, it was concluded on grounds of mass balance that incomplete digestion of such grains cannot explain the enrichments of r- and p-process isotopes in whole rocks of primitive chondrites. If the reported variability in r- and p-process isotope enrichments reflects the true isotopic characteristics of the whole rocks, the implications are quite profound. It would suggest the presence of large scale Mo isotopic heterogeneity within the solar accretion disk with likely collateral effects for other elements. However, such effects were not found for Ru isotopes, nor for Zr isotopes. Another recent Mo isotopic study by multi collector ICP-MS could not confirm the reported deviations in Allende, Murchison or iron meteorites. Here, we present new results for the Mo isotopic composition of iron meteorites, chondrites and CAIs obtained by negative thermal ionization mass spectrometry (NTIMS). We discuss analytical aspects and the homogeneity of Mo isotopic compositions in solar system materials.

  19. Lithium Isotopic Composition of Aleutian Arc Magmas

    NASA Astrophysics Data System (ADS)

    Rudnick, R. L.; Park, Y.; Liu, X.; Kay, S. M.; Kay, R. W.

    2012-12-01

    The lithium isotopic compositions of inputs to subduction zones can be highly variable. For example, altered oceanic crust is isotopically heavy (δ7Li = 4 to 22, Chan et al., 1996; Bouman et al., 2004) due to uptake of seawater Li (32). Sea floor sediments can have highly variable compositions, ranging from isotopically heavy pelagic sediments (6 to 14) to isotopically light terrigneous clays (-1.5 to 5), derived from highly weathered continental crust (Chan et al., 2006). Despite this variability in inputs, arc outputs (magmatic rocks) typically have mantle-like δ7Li (e.g., 2 to 6; Tomascak et al., 2002; Walker et al., 2009). To explore the behavior of lithium and its isotopes in arcs, we have analyzed [Li] and δ7Li in 48 lavas and plutons from the Aleutian island arc, which span the temporal (0 to 38 Ma), geographical (165-184oW) and compositional variations (SiO2 = 46-70 wt.%) seen in this arc. Previous studies have indicated a systematic geographic change in lava chemistry related to changing sediment composition along the arc (terrigneous in the east, pelagic in the west, e.g., Kay and Kay, 1994; Yogodinski et al., 2010), as well as temporal changes that may also reflect changes in sedimentary input (Kay and Kay, 1994), and we wished to determine if Li isotopes also reflect such changes. Lithium concentration [Li] shows a generally positive correlation with SiO2, consistent with the expected incompatible behavior of Li during magmatic differentiation. Intrusive rocks (all from the Adak region) show more scatter than lavas on this plot, suggesting the influence of cumulate processes. The δ7Li of the rocks span an immense range from -1 to +29, well outside the values considered typical for the MORB-source mantle (e.g., 2-6). However, the majority of the samples (28 out of 48) have δ7Li falling within the range of typical mantle values. There is a general tendency for the lavas (all but one are <2 Ma) to have slightly lower δ7Li than intrusions (which range

  20. The Lithium Isotope Composition of Planktonic Foraminifera

    NASA Astrophysics Data System (ADS)

    Hathorne, E. C.; James, R. H.; Harris, N. B.

    2003-12-01

    The temporal record of the lithium isotopic composition of seawater has the potential to provide an important proxy of the relative rates of weathering and hydrothermal processes. One of the most powerful types of evidence for changes in ocean chemistry comes from analyses of foraminiferal calcium carbonate. Here, we explore the utility of foraminifera as recorders of the Li isotopic composition of seawater. The Li isotopic composition of foraminifera tests has been determined by multicollector inductively coupled plasma mass spectrometry (Nu Instruments) using a sample-standard bracketing technique. The external precision of this technique is +/- 0.3 ‰ (2σ ), based on fifteen analyses of seawater over a period of 9 months. Planktonic foraminifera ( ˜10 mg) have been picked from surface sediments of the equatorial Pacific and the North Atlantic. Samples from the equatorial Pacific are Holocene/Pleistocene in age; those from the North Atlantic are from the Holocene. The foraminifera were subject to; cleaning in methanol and water, oxidation (hydrogen peroxide and sodium hydroxide), and leaching in weak acid (0.001M nitric acid). Additional reductive and refractory-phase cleaning steps (respectively, hydrous hydrazine/ammonia and DTPA solutions) had no effect on δ 7Li or Li/Ca. The δ 7Li value of the foraminifera ranges from 27 to 31‰ ; slightly lighter than modern-day seawater (31.1 ‰ ). Different species have consistently different δ 7Li values; O. universa have δ 7Li values within error of seawater, while Gr. truncatulinoides record the lightest δ 7Li (27.1+/- 0.3‰ ). This indicates that there are species specific vital effects on foraminiferal δ 7Li. Samples of the same species from different latitudes in the North Atlantic have the same δ 7Li, suggesting that there is no temperature effect on foraminiferal δ 7Li. Furthermore, with the exception of G. sacculifer, there appears to be no variability in foraminiferal δ 7Li with test size

  1. Measurements of Isotopic Composition of Vapour on the Antarctic Plateau

    NASA Astrophysics Data System (ADS)

    Casado, M.; Landais, A.; Masson-Delmotte, V.; Genthon, C.; Prie, F.; Kerstel, E.; Kassi, S.; Arnaud, L.; Steen-Larsen, H. C.; Vignon, E.

    2015-12-01

    The oldest ice core records are obtained on the East Antarctic plateau. The composition in stable isotopes of water (δ18O, δD, δ17O) permits to reconstruct the past climatic conditions over the ice sheet and also at the evaporation source. Paleothermometer accuracy relies on good knowledge of processes affecting the isotopic composition of surface snow in Polar Regions. Both simple models such as Rayleigh distillation and global atmospheric models with isotopes provide good prediction of precipitation isotopic composition in East Antarctica but post deposition processes can alter isotopic composition on site, in particular exchanges with local vapour. To quantitatively interpret the isotopic composition of water archived in ice cores, it is thus essential to study the continuum water vapour - precipitation - surface snow - buried snow. While precipitation and snow sampling are routinely performed in Antarctica, climatic conditions in Concordia, very cold (-55°C in average) and very dry (less than 1000ppmv), impose difficult conditions to measure the water vapour isotopic composition. New developments in infrared spectroscopy enable now the measurement of isotopic composition in water vapour traces (down to 20ppmv). Here we present the results of a campaign of measurement of isotopic composition in Concordia in 2014/2015. Two infrared spectrometers have been deployed or the first time on top of the East Antarctic Plateau allowing a continuous vapour measurement for a month. Comparison of the results from infrared spectroscopy with cryogenic trapping validates the relevance of the method to measure isotopic composition in dry conditions. Identification of different behaviour of isotopic composition in the water vapour associated to turbulent or stratified regime indicates a strong impact of meteorological processes in local vapour/snow interaction.

  2. Morphology Composition Isotopes: Recent Results from Observations

    NASA Astrophysics Data System (ADS)

    Schulz, R.

    2008-07-01

    This article presents some recent imaging and spectroscopic observations that led to results which are significant for understanding the properties of comet nuclei. The coma morphology and/or composition were investigated for 12 comets belonging to different dynamical classes. The data analysis showed that the coma morphology of three non-periodic comets is not consistent with the general assumption that dynamically new comets still have a relatively uniform nucleus surface and therefore do not exhibit gas and/or dust jets in their coma. The determination of carbon and nitrogen isotopic ratios revealed the same values for all comets investigated at various heliocentric distances. However, the relative abundance of the rare nitrogen isotope 15N is about twice as high as in the Earth’s atmosphere. Observations of comets at splitting events and during outbursts led to indications for differences between material from the nucleus surface and the interior. The monitoring of the induced outburst of 9P/Temple revealed that under non-steady state conditions the fast disintegration of species is detectable.

  3. Magnesium Isotopic Composition of Subducting Marine Sediments

    NASA Astrophysics Data System (ADS)

    Hu, Y.; Teng, F. Z.; Plank, T. A.; Huang, K. J.

    2015-12-01

    Subducted marine sediments have recently been called upon to explain the heterogeneous Mg isotopic composition (δ26Mg, ‰) found in mantle wehrlites (-0.39 to +0.09 [1]) in the context of a homogeneous mantle (-0.25 ± 0.07 [2]). However, no systematic measurements of δ26Mg on marine sediments are currently available to provide direct support to this model. To characterize the Mg inputs to global subduction zones, we measured δ26Mg data for a total of 90 marine sediments collected from 12 drill sites outboard of the world's major subduction zones. These sediments span a 1.73‰ range in δ26Mg. The detritus-dominated sediments have δ26Mg (-0.59 to +0.53) comparable to those of weathered materials on continents (e.g. -0.52 to +0.92 [3]), while the calcareous oozes yield δ26Mg (as light as -1.20) more similar to the seawater value (-0.83 [4]). The negative correlation between δ26Mg and CaO/Al2O3 in these sediments indicates the primary control of mineralogy over the Mg isotopic distribution among different sediment types, as carbonates are enriched in light Mg isotopes (-5.10 to -0.40 [5]) whereas clay-rich weathering residues generally have heavier δ26Mg (e.g. up to +0.65 in saprolite [6]). In addition, chemical weathering and grain-size sorting drive sediments to a heavier δ26Mg, as indicated by the broad positive trends between δ26Mg with CIA (Chemical Index of Alteration [7]) and Al2O3/SiO2, respectively. Collectively, the arc systems sampled in this study represent ~30% of global arc length and the extrapolated global Mg flux of subducting marine sediments accounts for ~9% of the yearly Mg riverine input with a flux-weighted average δ26Mg at -0.26. Subduction of these heterogeneous sediments may not cause significant mantle heterogeneity on a global scale, but the highly variable Mg fluxes and δ26Mg of sediments delivered to different trenches are capable of producing local mantle variations. Volcanic rocks sourced from these mantle domains are thus

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

    USGS Publications Warehouse

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

    1985-01-01

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

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

    PubMed

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

    2010-08-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  7. Lithium isotope fractionation in the southern Cascadia subduction zone

    NASA Astrophysics Data System (ADS)

    Magna, Tomáš; Wiechert, Uwe; Grove, Timothy L.; Halliday, Alex N.

    2006-10-01

    We present lithium (Li) abundances and isotope compositions for a suite of anhydrous olivine tholeiites (HAOTs) and hydrous basalt-andesitic (BA) lavas from the Mt. Shasta and Medicine Lake regions, California. The values of δ7Li vary from + 0.9‰ to + 6.4‰ and correlate inversely with distance from the trench. These data are consistent with continuous isotope fractionation of Li during dehydration of the subducted oceanic lithosphere, an interpretation corroborated by uniformly high pre-eruptive H 2O contents in basaltic andesites accompanied by high Li, Rb, Sr, Ba and Pb abundances. The subduction-derived component that was added to these hydrous magmas is shown to be very similar beneath both Mt. Shasta and Medicine Lake volcanoes despite characteristically distinct Li isotope compositions in the magmas themselves. More evolved andesites and dacites from Mt. Shasta have δ7Li from + 2.8 to + 6.9‰ which is identical with the range obtained for HAOTs and BA lavas from Mt. Shasta. Therefore, Li isotopes do not provide evidence for any other crustal component admixed to Mt. Shasta andesites or dacites during magmatic differentiation and magma mixing in the crust.

  8. The isotopic composition of Nd in different ocean masses

    NASA Technical Reports Server (NTRS)

    Piepgras, D. J.; Wasserburg, G. J.; Dasch, E. J.

    1979-01-01

    The paper examines the isotopic composition of Nd in marine environments. The Sm-Nd data for authigenic ferromanganese sediments indicate that the Atlantic, Pacific, and Indian Oceans have a distinct range in Nd isotopic composition characteristics of each ocean basin and reflect the dissolved load of Nd in the water mass. Measurements of the Nd isotopic seawater composition of seawater indicate that the rare earth elements (REE) in ferromanganese sediments are derived by direct precipitation of these elements out of seawater. It is believed that the Nd isotopic variations in these sediments represent true variations in the dissolved Nd isotopic composition which reflect the age and (Sm-147)/(Nd-144) ratios of the continental masses sampled believed to be the major source of REE in seawater.

  9. Magnesium isotopic composition of the Earth and chondrites

    NASA Astrophysics Data System (ADS)

    Teng, Fang-Zhen; Li, Wang-Ye; Ke, Shan; Marty, Bernard; Dauphas, Nicolas; Huang, Shichun; Wu, Fu-Yuan; Pourmand, Ali

    2010-07-01

    To constrain further the Mg isotopic composition of the Earth and chondrites, and investigate the behavior of Mg isotopes during planetary formation and magmatic processes, we report high-precision (±0.06‰ on δ 25Mg and ±0.07‰ on δ 26Mg, 2SD) analyses of Mg isotopes for (1) 47 mid-ocean ridge basalts covering global major ridge segments and spanning a broad range in latitudes, geochemical and radiogenic isotopic compositions; (2) 63 ocean island basalts from Hawaii (Kilauea, Koolau and Loihi) and French Polynesia (Society Island and Cook-Austral chain); (3) 29 peridotite xenoliths from Australia, China, France, Tanzania and USA; and (4) 38 carbonaceous, ordinary and enstatite chondrites including 9 chondrite groups (CI, CM, CO, CV, L, LL, H, EH and EL). Oceanic basalts and peridotite xenoliths have similar Mg isotopic compositions, with average values of δ 25Mg = -0.13 ± 0.05 (2SD) and δ 26Mg = -0.26 ± 0.07 (2SD) for global oceanic basalts ( n = 110) and δ 25Mg = -0.13 ± 0.03 (2SD) and δ 26Mg = -0.25 ± 0.04 (2SD) for global peridotite xenoliths ( n = 29). The identical Mg isotopic compositions in oceanic basalts and peridotites suggest that equilibrium Mg isotope fractionation during partial melting of peridotite mantle and magmatic differentiation of basaltic magma is negligible. Thirty-eight chondrites have indistinguishable Mg isotopic compositions, with δ 25Mg = -0.15 ± 0.04 (2SD) and δ 26Mg = -0.28 ± 0.06 (2SD). The constancy of Mg isotopic compositions in all major types of chondrites suggest that primary and secondary processes that affected the chemical and oxygen isotopic compositions of chondrites did not significantly fractionate Mg isotopes. Collectively, the Mg isotopic composition of the Earth's mantle, based on oceanic basalts and peridotites, is estimated to be -0.13 ± 0.04 for δ 25Mg and -0.25 ± 0.07 for δ 26Mg (2SD, n = 139). The Mg isotopic composition of the Earth, as represented by the mantle, is similar to chondrites

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  11. Re-Os isotopic ages of pyrite and chemical composition of magnetite from the Cihai magmatic-hydrothermal Fe deposit, NW China

    NASA Astrophysics Data System (ADS)

    Huang, Xiao-Wen; Zhou, Mei-Fu; Qi, Liang; Gao, Jian-Feng; Wang, Yu-Wang

    2013-12-01

    The Eastern Tianshan Orogenic Belt of the Central Asian Orogenic Belt and the Beishan terrane of the Tarim Block, NW China, host numerous Fe deposits. The Cihai Fe deposit (>90 Mt at 45.6 % Fe) in the Beishan terrane is diabase-hosted and consists of the Cihai, Cinan, and Cixi ore clusters. Ore minerals are dominantly magnetite, pyrite, and pyrrhotite, with minor chalcopyrite, galena, and sphalerite. Gangue minerals include pyroxene, garnet, hornblende and minor plagioclase, biotite, chlorite, epidotite, quartz, and calcite. Pyrite from the Cihai and Cixi ore clusters has similar Re-Os isotope compositions, with ˜14 to 62 ppb Re and ≤10 ppt common Os. Pyrrhotite has ˜5 to 39 ppb Re and ˜0.6 ppb common Os. Pyrite has a mean Re-Os model age of 262.3 ± 5.6 Ma ( n = 13), in agreement with the isochron regression of 187Os vs. 187Re. The Re-Os age (˜262 Ma) for the Cihai Fe deposit is within uncertainty in agreement with a previously reported Rb-Sr age (268 ± 25 Ma) of the hosting diabase, indicating a genetic relationship between magmatism and mineralization. Magnetite from the Cihai deposit has Mg, Al, Ti, V, Cr, Co, Ni, Mn, Zn, Ga, and Sn more elevated than that of typical skarn deposits, but both V and Ti contents lower than that of magmatic Fe-Ti-V deposits. Magnetite from these two ore clusters at Cihai has slightly different trace element concentrations. Magnetite from the Cihai ore cluster has relatively constant trace element compositions. Some magnetite grains from the Cixi ore cluster have higher V, Ti, and Cr than those from the Cihai ore cluster. The compositional variations of magnetite between the ore clusters are possibly due to different formation temperatures. Combined with regional tectonic evolution of the Beishan terrane, the Re-Os age of pyrite and the composition of magnetite indicate that the Cihai Fe deposit may have derived from magmatic-hydrothermal fluids related to mafic magmatism, probably in an extensional rift environment.

  12. Sr-Isotope Composition of Feldspar: Implication for age and Evolution of Gabbros from Uralian-Alaskan Type Complexes in the Ural Mountains, Russia

    NASA Astrophysics Data System (ADS)

    Bruegmann, G. E.; Krause, J.; Pushkarev, E.

    2006-12-01

    concentrations (>3000 ppm) than silica undersaturated gabbros (Plag: 800-1000 ppm). These features imply the gabbros are derived from distinct parental magmas. However, no significant differences in Sr isotopic composition could be deciphered. Silica saturated gabbros from different parts of the Kytlym complex have similar 87Sr/86Sr of 0.70406±8 (2SD) and pseudoleucite-bearing rocks have 87Sr/86Sr of 0.70408±5. Interestingly, the Sr isotopic composition of the gabbros from Kytlym and Nizhnii Tagil is also similar. Thus despite their spatial separation and very different magmatic lineage the parental magmas appear to sample a homogenous mantle source. K-Feldspar in the pseudoleucite-bearing gabbros has high 87SRb/86Sr (0.2-0.4) and high 87Sr/86Sr (0.7050-0.7059) due to radiogenic ingrowth. Using the plagioclase and K-feldspar analyses of one polished section and correcting the 87Rb/86Sr for the different analytical sensitivities of Sr and Rb, the data define an isochron giving an age of 348±23 Ma and initial isotopic composition of 0.70406±4 (MSWD=1.14). This result is in very good agreement with Rb-Sr whole rock data of Pushkarev et al. (2003) studying the same rocks at the Kytlym complex.

  13. Lead Abundance In The Martian Mantle Deduced From The Isotopic Data In Snc Meteorites

    NASA Astrophysics Data System (ADS)

    Dreibus, G.; Jagoutz, E.

    Isotopic data are a powerful tool for the study of planetary evolution. Assuming that the SNC meteorites are rocks from Mars their Sm-Nd-, Rb-Sr- and Pb-Pb-isotope systematics reveal the time scale for the chemical evolution of the Martian mantle. From the Rb -Sr isotopic systematic the existence of 3 isotopically distinct reservoirs on Mars was postulated, which remained isolated for a period of 4.3 +/- 0.2 Ga. The basaltic shergottites Shergotty, Zagami and Los Angeles have relatively high radiogenic Sr, which might come from a planetary crust. A second group, characterized by non radiogenic Sr, consists of the two mafic cumulates Nakhla and Chassigny, the olivine rich basaltic shergottites DaG 476, SaU 005, Dhofar 019and the basaltic shergottite QUE 94201, which may represent the depleted mantle. The depletion of this reservoir must have taken place during a very early process. as derived from the primitive Sr isotopes and the existence of Nd-142, the daughter product of the extinct Sm-146, found in Chassigny, the Nakhlites, SaU 005, and DaG476. A third group, with intermediate Sr isotopic composition, represented by the lherzolitic shergottites, could be derived from a primitive, unfractionated mantle. Our observed correlation of Sr-isotopes with Pb-isotopes in SNC's permits to estimate the Pb abundance for the Martian mantle. The Pb isotopes of all measured SNCs show a similar pattern as Sr isotopes. The initial Pb data of Los Angeles, Shergotty, and Zagami from the enriched crustal reservoir and of Nakhla and SaU 005 from the depleted mantle reservoir plot close to the 4.5 Ga Pb -Pb isochron.. We used this correlation to estimate the µ value (238U/204Pb) of 3.1 for the Martian mantle. This corresponds to 366 ppb Pb. Compared to the Earth with a µ = 8.8, Pb is enriched on Mars by at least a fact or of 2.5. The same enrichment was found for all other moderately volatile and volatile elements on Mars. From the high abundance of Pb in the sulfide phases of iron

  14. The Chlorine Isotopic Composition of Lunar urKREEP

    NASA Astrophysics Data System (ADS)

    Barnes, J. J.; Tartese, R.; Anand, M.; McCubbin, F. M.; Neal, C. R.; Franchi, I. A.

    2016-05-01

    We have measured the Cl isotopic composition of apatite in a range of lunar rocks using NanoSIMS. We find a correlation between Cl isotopes and bulk rock chemistry which strongly suggesting urKREEP was characterized by heavy Cl.

  15. Oxygen isotopic composition of hydrous and anhydrous mantle peridotites

    NASA Astrophysics Data System (ADS)

    Chazot, Gilles; Lowry, David; Menzies, Martin; Mattey, David

    1997-01-01

    Oxygen isotope ratios, determined using the laser fluorination technique, are reported for minerals from anhydrous and hydrous (i.e., amphibole-bearing) spinel lherzolites from Yemen, as well as from hydrous spinel lherzolites and amphibole megacrysts from Nunivak Island, Alaska. Oxygen isotopic compositions of olivine vary from 5.1-5.4%c and of pyroxene from 5.5-6.0%c and no systematic difference exists between minerals in hydrous and anhydrous lherzolites. The oxygen isotopic composition of the amphibole in the peridotites and of the amphibole megacrysts is also very homogeneous and varies from δ 18O = 5.3-5.6%o. These results indicate that the metasomatic minerals in the lherzolites are in oxygen isotopic equilibrium with the peridotitic minerals. The only isotopic disequilibria are observed in minerals which have grown in melt-pockets formed by partial melting of amphibole. The homogeneity of the oxygen isotopic ratios of mantle minerals in this study indicate that the fluids circulating in the mantle and precipitating amphibole or mica had the same oxygen isotopic compositions as the mantle protolith or that the fluids had been buffered by the isotopic composition of the olivine, the most abundant mineral, during percolation through the peridotites.

  16. Isotopic Composition of Barium in Single Presolar Silicon Carbide Grains

    NASA Technical Reports Server (NTRS)

    Savina, M. R.; Tripa, C. E.; Pellin, M. J.; Davis, A. M.; Clayton, R. N.; Lewis, R. S.; Amari, S.

    2002-01-01

    We have measured Ba isotope distributions in individual presolar SiC grains. We find that the Ba isotopic composition in mainstream SiC grains is consistent with models of nucleosynthesis in low to intermediate mass asymptotic giant branch (AGB) stars. Additional information is contained in the original extended abstract.

  17. Ruthenium Isotopic Composition of Terrestrial Materials, Iron Meteorites and Chondrites

    NASA Technical Reports Server (NTRS)

    Becker, H.; Walker, R. J.

    2002-01-01

    Ru isotopic compositions of magmatic iron meteorites and chondrites overlap with terrestrial Ru at the 0.3 to 0.9 (epsilon) level. Additional information is contained in the original extended abstract.

  18. Isotopic composition of atmospheric moisture from pan water evaporation measurements.

    PubMed

    Devi, Pooja; Jain, Ashok Kumar; Rao, M Someshwer; Kumar, Bhishm

    2015-01-01

    A continuous and reliable time series data of the stable isotopic composition of atmospheric moisture is an important requirement for the wider applicability of isotope mass balance methods in atmospheric and water balance studies. This requires routine sampling of atmospheric moisture by an appropriate technique and analysis of moisture for its isotopic composition. We have, therefore, used a much simpler method based on an isotope mass balance approach to derive the isotopic composition of atmospheric moisture using a class-A drying evaporation pan. We have carried out the study by collecting water samples from a class-A drying evaporation pan and also by collecting atmospheric moisture using the cryogenic trap method at the National Institute of Hydrology, Roorkee, India, during a pre-monsoon period. We compared the isotopic composition of atmospheric moisture obtained by using the class-A drying evaporation pan method with the cryogenic trap method. The results obtained from the evaporation pan water compare well with the cryogenic based method. Thus, the study establishes a cost-effective means of maintaining time series data of the isotopic composition of atmospheric moisture at meteorological observatories. The conclusions drawn in the present study are based on experiments conducted at Roorkee, India, and may be examined at other regions for its general applicability. PMID:26332982

  19. Macrocrystal phlogopite Rb-Sr dates for the Ekati property kimberlites, Slave Province, Canada: evidence for multiple intrusive episodes in the Paleocene and Eocene

    NASA Astrophysics Data System (ADS)

    Creaser, Robert A.; Grütter, Herman; Carlson, Jon; Crawford, Barbara

    2004-09-01

    New Rb-Sr age determinations using macrocrystal phlogopite are presented for 27 kimberlites from the Ekati property of the Lac de Gras region, Slave Province, Canada. These new data show that kimberlite magmatism at Ekati ranges in age from at least Late Paleocene (˜61 Ma) to Middle Eocene time (˜45 Ma). Older, perovskite-bearing kimberlites from Ekati extend this age range to Late Cretaceous time (˜74 Ma). Within this age range, emplacement episodes at ˜48, 51-53, 55-56 and 59-61 Ma can be recognized. Middle Eocene kimberlite magmatism of the previously dated Mark kimberlite (˜47.5 Ma) is shown to include four other pipes from the east-central Ekati property. A single kimberlite (Aaron) may be younger than the 47.5 Ma Mark kimberlite. The economically important Panda kimberlite is precisely dated in this study to be 53.3±0.6 Ma using the phlogopite isochron method, and up to six additional kimberlites from the central Ekati property have Early Eocene ages indistinguishable from that of Panda, including the Koala and Koala North occurrences. Late Paleocene 55-56 Ma kimberlite magmatism, represented by the Diavik kimberlite pipes adjacent to the southeastern Ekati property, is shown to extend onto the southeastern Ekati property and includes three, and possibly four, kimberlites. A precise eight-point phlogopite isochron for the Cobra South kimberlite yields an emplacement age of 59.7±0.4 Ma; eight other kimberlites from across the Ekati property have similar Late Paleocene Rb-Sr model ages. The addition of 27 new emplacement ages for kimberlites from the Ekati property confirms that kimberlite magmatism from the central Slave Province is geologically young, despite ages ranging back to Cambrian time from elsewhere in the Slave Province. With the available geochronologic database, Lac de Gras kimberlites with the highest diamond potential are currently restricted to the 51-53 and 55-56 Ma periods of kimberlite magmatism.

  20. K, Rb, Sr and 87Sr 86Sr in rocks from the Mid-Indian Oceanic Ridge

    USGS Publications Warehouse

    Subbarao, K.V.; Hedge, C.E.

    1973-01-01

    The 87Sr 86Sr ratios of Mid-Indian Oceanic Ridge (MIOR) basalts are nearly identical (0.7032 to 0.7035), with the exception of one more highly radiogenic sample (0.7043). These values are consistently higher than the strontium isotopic ratios of the ridge basalts from Atlantic and Pacific Oceans, suggesting that the source of the MIOR basalts was depleted in alkalies more recently and/or to a lesser degree than the basalts from other oceans. ?? 1973.

  1. Isotope composition of carbon in amino acids of solid bitumens

    NASA Astrophysics Data System (ADS)

    Shanina, S. N.; Bushnev, D. A.

    2014-06-01

    Primary data are presented on the isotope composition of carbon in individual amino acids from solid bitumens and several biological objects. The amino acids of biological objects are characterized by wide variations of the isotope composition of carbon. This fact occurs owing to the difference in biochemical paths of metabolism resulting in the synthesis of individual amino acids. The δ13C values are somewhat decreased for individual amino acids in asphaltenes, varying from -7.7 to -31.7‰. The carbon of amino acids is weighted in kerits from Bad'el' compared to asphaltenes. All the natural bitumens retain the characteristic trend for natural substances: the isotopically heavy and light amino acids by carbon are glycine and leucine, respectively. The isotope composition of amino-acid carbon is lightened compared to natural bitumens in the samples formed under a pronounced thermal impact (asphalt-like crust and kirishite).

  2. 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).

    USGS Publications Warehouse

    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

  3. The Palladium Isotopic Composition in Iron Meteorites

    NASA Technical Reports Server (NTRS)

    Chen, J. H.; Papanastassiou, D. A.

    2005-01-01

    Ru, Mo and Pd are very useful indicators for the identification of nucleosynthetic components. We have developed techniques for Pd isotopes, in an effort to check the extent of isotopic effects in this mass region and for a Pt-group element which is less refractory than Ru. Stable Pd isotopes are produced by the process only (102Pd), the s-process only (104Pd), the process only (Pd-110) and by both the r- and s-processes (Pd-105, Pd-106, Pd-108). Kelly and Wasserburg reported a hint of a shift in 102Pd (approx. 25(epsilon)u; 1(epsilon)u (triple bonds) 0.01%) in Santa Clara. Earlier searches for Mo and Ru isotopic anomalies were either positive or negative.

  4. Lead isotope systematics of mare basalt 75075

    NASA Technical Reports Server (NTRS)

    Chen, J. H.; Tilton, G. R.; Mattinson, J. M.; Vidal, P.

    1978-01-01

    Uranium, thorium and isotopic lead data are reported for two bulk samples and separated pyroxene, ilmenite and plagioclase from basalt 75075. In a concordia diagram the whole rock, ilmenite and four pyroxene samples define a chord intersecting the concordia curve at approximately 4.25 and 2.8 AE. Three plagioclase samples plot distinctly off the chord. The crystallization age of 75075 is accurately determined at 3.74 AE by Rb-Sr, Sm-Nd and K-Ar measurements from other laboratories. It is not possible to adjust the isotopic composition of initial lead so as to reconcile the U-Pb data with a crystallization age of 3.74 AE. The data therefore indicate some type of post-crystallization disturbance of the U-Pb system that is not detected by the other systems. The 75075 data are one of the few examples of this type of age pattern found on the moon. If the disturbance was a single event, it probably occurred around 2.8 AE ago, the time indicated by the pyroxene, whole rock and ilmenite data.

  5. Magnesium isotopic compositions of the Mesoproterozoic dolostones: Implications for Mg isotopic systematics of marine carbonates

    NASA Astrophysics Data System (ADS)

    Huang, Kang-Jun; Shen, Bing; Lang, Xian-Guo; Tang, Wen-Bo; Peng, Yang; Ke, Shan; Kaufman, Alan J.; Ma, Hao-Ran; Li, Fang-Bing

    2015-09-01

    Available Mg isotope data indicate that dolostones of different ages have overlapping range of Mg isotopic composition (δ26Mg) and there is no systematic difference among different types of dolomites. To further explore the Mg isotopic systematics of dolomite formation, we measured Mg isotopic compositions of Mesoproterozoic dolostones from the Wumishan Formation in North China Block, because dolomite formation in Mesoproterozoic might have been fundamentally different from the younger counterparts. Based on petrographic observations, three texturally-different dolomite phases (dolomicrite, subhedral dolomite and anhedral dolomite) are recognized in the Wumishan dolostones. Nevertheless, these three types of dolomites have similar δ26Mg values, ranging from -1.35‰ to -1.72‰, which are indistinguishable from Neoproterozoic and Phanerozoic dolostones. To explain δ26Mg values of dolostones, we simulate the Mg isotopic system during dolomite formation by applying the one-dimensional Diffusion-Advection-Reaction (1D-DAR) model, assuming that the contemporaneous seawater is the Mg source of dolostone. The 1D-DAR modeling results indicate that the degree of dolomitization is controlled by sedimentation rate, seawater Mg concentration, temperature, and reaction rate of dolomite formation, whereas Mg isotopic composition of dolostone is not only dependent on these factors, but also affected by δ26Mg of seawater and isotope fractionation during dolomite formation. Moreover, the 1D-DAR model predicts that dolomite formation within sediments has limited range of variation in δ26Mg with respect to limestones. Furthermore, the modeling results demonstrate that dolostone is always isotopically heavier than Ca-carbonate precipitated from seawater, explaining the systematic isotopic difference between dolostones and limestones. Finally, we can infer from the 1D-DAR model that early-formed dolostone at shallower depth of sediments is always isotopically lighter than that

  6. What does the oxygen isotope composition of rodent teeth record?

    NASA Astrophysics Data System (ADS)

    Royer, Aurélien; Lécuyer, Christophe; Montuire, Sophie; Amiot, Romain; Legendre, Serge; Cuenca-Bescós, Gloria; Jeannet, Marcel; Martineau, François

    2013-01-01

    Oxygen isotope compositions of tooth phosphate (δ18Op) were measured in 107 samples defined on the basis of teeth obtained from 375 specimens of extant rodents. These rodents were sampled from pellets collected in Europe from 38°N (Portugal) to 65°N (Finland) with most samples coming from sites located in France and Spain. Large oxygen isotopic variability in δ18Op is observed both at the intra- and inter-species scale within pellets from a given location. This isotopic variability is partly explained by heterochrony in tooth formation related to the short time of mineralization for all rodent species as well as the duration of mineralization that is species-dependent. Consequently, tooth phosphate of rodents records a short seasonal interval in the oxygen isotope compositions of meteoric waters (δ18Omw). In addition, inter-species isotopic variability observed in the same pellets suggests behavioural differences implying distinct isotopic compositions for species living in the same location. At the scale of Europe, a robust linear oxygen isotope fractionation equation was determined for Muroidea between the midrange δ18Op values and δ18Omw values: δ18Op=1.21(±0.20)δ18Omw+24.76(±2.70) with R2=0.79 (n=9; p<0.0001).

  7. Calcium isotopic compositions of mid-ocean ridge basalts

    NASA Astrophysics Data System (ADS)

    Zhu, H.; Zhang, Z.; Sun, W.; Wang, G. Q.

    2015-12-01

    Previous studies have demonstrated that Earth's mantle has heterogeneous calcium isotopic compositions. But the reason why mantle has its heterogeneity remains uncertain. In general, δ44/40Ca values of mantle xenolith samples have a variation of >0.45‰. While ultramafic rocks, especially dunites, have higher δ44/40Ca values than volcanic rocks, and there is a positive correlation between δ44/40Ca and Ca/Mg. These phenomena imply that the heterogeneity of Ca isotopic compositions of mantle xenolith samples might result from different degrees of melt extraction, as indicated by large Ca isotopic fractionation between co-existing clinopyroxene and orthopyroxene. However, because ancient marine carbonate has its own unique calcium isotopic characteristics, recycling of even a small amount of ancient marine carbonates into the mantle could also cause the heterogeneity of Ca isotopes in Earth's mantle. This could be the reason why oceanic island basalts (OIB) have lighter Ca isotopic compositions than the mantle xenolith. Thus, the lighter Ca isotopic compositions in the mantle source cannot only be ascribed to magmatic processes. Therefore, it is more important to know calcium isotopic characteristics during partial melting and oceanic crust contamination.Mid-ocean ridge basalts (MORB) are formed from the partial melts of the upper mantle and are rarely affected by crustal contamination. Different types of MORB, including D-MORB, N-MORB and E-MORB, have experienced different degrees of partial melting and contamination of enriched end-members. Here we report calcium isotopic characteristic of different types of MORB, we believe it will be very helpful to understand the behaviors of Ca isotopes during partial melting and it is possible to provide further information to discover the reason why calcium isotopic compositions is heterogeneous in Earth's mantle. This work was supported by Natural Science Foundation of China (No. 41373007, No. 41490632 and No. 91328204

  8. Monitoring the water vapor isotopic composition in the North Atlantic

    NASA Astrophysics Data System (ADS)

    Sveinbjornsdottir, A. E.; Steen-Larsen, H.; Jonsson, T.; Johnsen, S. J.

    2011-12-01

    Water stable isotopes have during many decades been used as climate proxies and indicators for variations in the hydrological cycle. However we are to a great extent still using simple empirical relationships without any deeper theoretical understanding. In order to properly relate changes in the climate and hydrological cycle to changes in the observed stable water isotopic signal we must understand the underlying physical processes. Furthermore it is a challenge for General Climate Models to adequately represent the isotopes in the hydrological cycle because of lack of in-situ measurements of the atmospheric water-vapor composition in the source regions. During the fall of 2010 we installed an autonomous water vapor spectroscopy laser (from Los Gatos Research) in a lighthouse on the South Coast of Iceland (63.83 N 21.47W) with the plan to be operational for several years. The purpose of this installation was through monitoring of the water vapor isotopic composition to understand the physical processes governing the isotopic composition of the water vapor evaporated from the ocean as well as the processes of mixing between the free troposphere and marine boundary layer. Because of the remoteness of the monitoring site and simple topography we are able to isolate the 'fingerprint' on the isotopic signal in the water vapor from respectively the ocean and the interior highland leading to a near perfect case-study area. Using back-trajectories we find a strong influence of the origin of the air masses on the measured isotopic composition. The mixing of the marine-boundary layer is found to strongly influence the measured isotopic composition. The second order isotopic parameter, d-excess, is found to depend on both the isotopic composition as well as the relative humidity as prescribed by theories for evaporation from an ocean. The site likely represents a major source region for the moisture that later falls as snow on parts of the Greenland Ice Sheet. This leads to

  9. Isotopic compositions of cometary matter returned by Stardust.

    PubMed

    McKeegan, Kevin D; Aléon, Jerome; Bradley, John; Brownlee, Donald; Busemann, Henner; Butterworth, Anna; Chaussidon, Marc; Fallon, Stewart; Floss, Christine; Gilmour, Jamie; Gounelle, Matthieu; Graham, Giles; Guan, Yunbin; Heck, Philipp R; Hoppe, Peter; Hutcheon, Ian D; Huth, Joachim; Ishii, Hope; Ito, Motoo; Jacobsen, Stein B; Kearsley, Anton; Leshin, Laurie A; Liu, Ming-Chang; Lyon, Ian; Marhas, Kuljeet; Marty, Bernard; Matrajt, Graciela; Meibom, Anders; Messenger, Scott; Mostefaoui, Smail; Mukhopadhyay, Sujoy; Nakamura-Messenger, Keiko; Nittler, Larry; Palma, Russ; Pepin, Robert O; Papanastassiou, Dimitri A; Robert, François; Schlutter, Dennis; Snead, Christopher J; Stadermann, Frank J; Stroud, Rhonda; Tsou, Peter; Westphal, Andrew; Young, Edward D; Ziegler, Karen; Zimmermann, Laurent; Zinner, Ernst

    2006-12-15

    Hydrogen, carbon, nitrogen, and oxygen isotopic compositions are heterogeneous among comet 81P/Wild 2 particle fragments; however, extreme isotopic anomalies are rare, indicating that the comet is not a pristine aggregate of presolar materials. Nonterrestrial nitrogen and neon isotope ratios suggest that indigenous organic matter and highly volatile materials were successfully collected. Except for a single (17)O-enriched circumstellar stardust grain, silicate and oxide minerals have oxygen isotopic compositions consistent with solar system origin. One refractory grain is (16)O-enriched, like refractory inclusions in meteorites, suggesting that Wild 2 contains material formed at high temperature in the inner solar system and transported to the Kuiper belt before comet accretion. PMID:17170292

  10. Determination of plutonium isotopic composition by gamma-ray spectroscopy

    SciTech Connect

    Sampson, T.E.; Hsue, S.T.; Parker, J.L.; Johnson, S.S.; Bowersox, D.F.

    1981-01-01

    We discuss the general approach, computerized data analysis methods, and results of measurements used to determine the isotopic composition of plutonium by gamma-ray spectroscopy. The simple techniques are designed to be applicable to samples of arbitrary size, geometry, age, chemical, and isotopic composition. The combination of the gamma spectroscopic measurement of isotopic composition coupled with calorimetric measurement of total sample power is shown to give a totally nondestructive determination of sample plutonium mass with a precision of 0.6% for 1000-g samples of PuO/sub 2/ with 12% /sup 240/Pu content. The precision of isotopic measurements depends upon many factors, including sample size, sample geometry, and isotopic content. Typical ranges are found to be /sup 238/Pu, 1 to 10%; /sup 239/Pu, 0.1 to 0.5%; /sup 240/Pu, 2 to 5%; /sup 241/Pu, 0.3 to 0.7%; /sup 242/Pu (determined by isotopic correlation); and /sup 241/Am, 0.2 to 10%.

  11. Zinc isotope fractionation during magmatic differentiation and the isotopic composition of the bulk Earth

    USGS Publications Warehouse

    Chen, Heng; Savage, Paul S.; Teng, Fang-Zehn; Helz, Rosalind T.; Moynier, Frédéric

    2013-01-01

    he zinc stable isotope system has been successfully applied to many and varied fields in geochemistry, but to date it is still not completely clear how this isotope system is affected by igneous processes. In order to evaluate the potential application of Zn isotopes as a proxy for planetary differentiation and volatile history, it is important to constrain the magnitude of Zn isotopic fractionation induced by magmatic differentiation. In this study we present high-precision Zn isotope analyses of two sets of chemically diverse, cogenetic samples from Kilauea Iki lava lake, Hawaii, and Hekla volcano, Iceland, which both show clear evidence of having undergone variable and significant degrees of magmatic differentiation. The Kilauea Iki samples display small but resolvable variations in Zn isotope composition (0.26‰66Zn66Zn defined as the per mille deviation of a sample's 66Zn/64Zn compositional ratio from the JMC-Lyon standard), with the most differentiated lithologies exhibiting more positive δ66Zn values. This fractionation is likely a result of the crystallization of olivine and/or Fe–Ti oxides, which can both host Zn in their crystal structures. Samples from Hekla have a similar range of isotopic variation (0.22‰66Zn66Zn=0.28±0.05‰ (2s.d.).

  12. Zinc isotope fractionation during magmatic differentiation and the isotopic composition of the bulk Earth

    NASA Astrophysics Data System (ADS)

    Chen, Heng; Savage, Paul S.; Teng, Fang-Zhen; Helz, Rosalind T.; Moynier, Frédéric

    2013-05-01

    The zinc stable isotope system has been successfully applied to many and varied fields in geochemistry, but to date it is still not completely clear how this isotope system is affected by igneous processes. In order to evaluate the potential application of Zn isotopes as a proxy for planetary differentiation and volatile history, it is important to constrain the magnitude of Zn isotopic fractionation induced by magmatic differentiation. In this study we present high-precision Zn isotope analyses of two sets of chemically diverse, cogenetic samples from Kilauea Iki lava lake, Hawaii, and Hekla volcano, Iceland, which both show clear evidence of having undergone variable and significant degrees of magmatic differentiation. The Kilauea Iki samples display small but resolvable variations in Zn isotope composition (0.26‰<δ66Zn<0.36‰; δ66Zn defined as the per mille deviation of a sample's 66Zn/64Zn compositional ratio from the JMC-Lyon standard), with the most differentiated lithologies exhibiting more positive δ66Zn values. This fractionation is likely a result of the crystallization of olivine and/or Fe-Ti oxides, which can both host Zn in their crystal structures. Samples from Hekla have a similar range of isotopic variation (0.22‰<δ66Zn<0.33‰), however, the degree of fractionation caused by magmatic differentiation is less significant (only 0.07‰) and no correlation between isotope composition and degree of differentiation is seen. We conclude that high temperature magmatic differentiation can cause Zn isotope fractionation that is resolvable at current levels of precision, but only in compositionally-evolved lithologies. With regards to primitive (ultramafic and basaltic) material, this signifies that the terrestrial mantle is essentially homogeneous with respect to Zn isotopes. Utilizing basaltic and ultramafic sample analyses, from different geologic settings, we estimate that the average Zn isotopic composition of Bulk Silicate Earth is δ66Zn=0.28

  13. Anomalous isotopic composition of cosmic rays

    SciTech Connect

    Woosley, S.E.; Weaver, T.A.

    1980-06-20

    Recent measurements of nonsolar isotopic patterns for the elements neon and (perhaps) magnesium in cosmic rays are interpreted within current models of stellar nucleosynthesis. One possible explanation is that the stars currently responsible for cosmic-ray synthesis in the Galaxy are typically super-metal-rich by a factor of two to three. Other possibilities include the selective acceleration of certain zones or masses of supernovas or the enhancement of /sup 22/Ne in the interstellar medium by mass loss from red giant stars and planetary nebulas. Measurements of critical isotopic ratios are suggested to aid in distinguishing among the various possibilities. Some of these explanations place significant constraints on the fraction of cosmic ray nuclei that must be fresh supernova debris and the masses of the supernovas involved. 1 figure, 3 tables.

  14. Chemical and isotopic compositions in acid residues from various meteorites

    NASA Technical Reports Server (NTRS)

    Kano, N.; Yamakoshi, K.; Matsuzaki, H.; Nogami, K.

    1993-01-01

    We are planning to carry out systematic isotopic investigations of Ru, Mg, etc., in primordial samples. The investigations will be pursued in the context of a study of the pre-history of the solar system. It is hoped that the study will yield direct evidence for processes of nucleosynthesis in the pre-solar stage and detection of extinct radioactive nuclides. In this paper, we present the results of chemical compositions of acid residues obtained from three types of meteorites: Canyon Diablo (IA), Allende (CV3), and Nuevo Mercuro (H5); and the preliminary results of Ru isotopic compositions.

  15. Carbon isotopic composition of individual Precambrian microfossils

    NASA Astrophysics Data System (ADS)

    House, Christopher H.; Schopf, J. William; McKeegan, Kevin D.; Coath, Christopher D.; Harrison, T. Mark; Stetter, Karl O.

    2000-08-01

    Ion microprobe measurements of carbon isotope ratios were made in 30 specimens representing six fossil genera of microorganisms petrified in stromatolitic chert from the ˜850 Ma Bitter Springs Formation, Australia, and the ˜2100 Ma Gunflint Formation, Canada. The δ13CPDB values from individual microfossils of the Bitter Springs Formation ranged from -21.3 ± 1.7‰ to -31.9 ± 1.2‰, and the δ13CPDB values from microfossils of the Gunflint Formation ranged from -32.4 ± 0.7‰ to -45.4 ± 1.2‰. With the exception of two highly 13C-depleted Gunflint microfossils, the results generally yield values consistent with carbon fixation via either the Calvin cycle or the acetyl-CoA pathway. However, the isotopic results are not consistent with the degree of fractionation expected from either the 3-hydroxypropionate cycle or the reductive tricarboxylic acid cycle, suggesting that the microfossils studied did not use either of these pathways for carbon fixation. The morphologies of the microfossils suggest an affinity to the cyanobacteria, and our carbon isotopic data are consistent with this assignment.

  16. Stable isotopic compositions in Australian precipitation

    NASA Astrophysics Data System (ADS)

    Liu, Jianrong; Fu, Guobin; Song, Xianfang; Charles, Stephen P.; Zhang, Yinghua; Han, Dongmei; Wang, Shiqin

    2010-12-01

    Stable deuterium (δD) and oxygen-18 (δ18O) isotopes in 1962 to 2002 precipitation from the seven Australian stations of the Global Network of Isotopes in Precipitation (GNIP) were used to investigate isotope characteristics including temporal and spatial distributions across different regions of Australia. On the basis of 1534 samples, the local meteoric water line (LMWL) was established as δD = 7.10δ18O + 8.21. δ18O showed a depletion trend from north and south to central Australia (a continental effect) and from west to east. Precipitation amount effects were generally greater than temperature effects, with quadratic or logarithmic correlations describing δ/T and δ/P better than linear relationships. Nonlinear stepwise regression was used to determine the significant meteorological control factors for each station, explaining about 50% or more of the δ18O variations. Geographical control factors for δ18O were given by the relationship δ18O (‰) = -0.005 longitude (°) - 0.034 latitude (°)-0.003 altitude (m) - 4.753. Four different types of d-excess patterns demonstrated particular precipitation formation conditions for four major seasonal rainfall zones. Finally, wavelet coherence (WTC) between δ18O and SOI confirmed that the influence of ENSO decreased from east and north to west Australia.

  17. Carbon isotopic composition of individual Precambrian microfossils

    NASA Technical Reports Server (NTRS)

    House, C. H.; Schopf, J. W.; McKeegan, K. D.; Coath, C. D.; Harrison, T. M.; Stetter, K. O.

    2000-01-01

    Ion microprobe measurements of carbon isotope ratios were made in 30 specimens representing six fossil genera of microorganisms petrified in stromatolitic chert from the approximately 850 Ma Bitter Springs Formation, Australia, and the approximately 2100 Ma Gunflint Formation, Canada. The delta 13C(PDB) values from individual microfossils of the Bitter Springs Formation ranged from -21.3 +/- 1.7% to -31.9 +/- 1.2% and the delta 13C(PDB) values from microfossils of the Gunflint Formation ranged from -32.4 +/- 0.7% to -45.4 +/- 1.2%. With the exception of two highly 13C-depleted Gunflint microfossils, the results generally yield values consistent with carbon fixation via either the Calvin cycle or the acetyl-CoA pathway. However, the isotopic results are not consistent with the degree of fractionation expected from either the 3-hydroxypropionate cycle or the reductive tricarboxylic acid cycle, suggesting that the microfossils studied did not use either of these pathways for carbon fixation. The morphologies of the microfossils suggest an affinity to the cyanobacteria, and our carbon isotopic data are consistent with this assignment.

  18. Mercury isotope compositions in North American forest soils and litters

    NASA Astrophysics Data System (ADS)

    Zheng, W.; Obrist, D.; Bergquist, B. A.

    2013-12-01

    Soils represent one of the largest reservoirs of mercury on Earth, playing a critical role in the natural cycle of mercury by acting as both a sink and source. However, it is not well understood how soils sequestrate and remobilize Hg. Natural variations in stable Hg isotopes are being explored as a promising tool in studying the transformation and transport of Hg. However, Hg isotopic data in soils is scarce. In addition, the limited isotopic data that exists is significantly different from those of atmospheric Hg, which is one of the major sources of Hg to soils. For example, Hg mass independent fractionation (MIF, typically reported as Δ199Hg) is positive in atmospheric wet deposition, but most soils display negative Δ199Hg. MIF on 200Hg (Δ200Hg) is also observed in atmospheric wet deposition, but not in soils. The discrepancy between soils and atmospheric samples is still unexplained. In this study, we surveyed the Hg isotope compositions in soil profiles, litters and fresh vegetation from four different forest sites across United States (Thompson forest, WA, Truckee, CA, Niwot Ridge, CO and Howland, MA). The current results from the WA site show that soils primarily display negative mass dependent fractionation for the even isotopes (MDF, reported as δ202Hg) with values for δ202Hg of up to -2.0‰. Significant MIF for both odd isotopes is also observed in all WA soil samples and Δ199Hg is mostly negative (up to -0.4‰). No MIF on 200Hg is observed in these soils. The negative Δ199Hg in soils is inconsistent with the positive Δ199Hg reported in atmospheric wet deposition, suggesting that either Hg transformations within or on the surface of soils and/or plants alter its isotope composition after deposition or other types of Hg deposition (e.g., Hg(0) or Hg(II) dry deposition) is more predominant. The Δ199Hg/Δ201Hg ratio is close to 1 in the soils, which is consistent with the results of laboratory photochemical reduction of inorganic Hg

  19. The Stable Isotopic Composition of Atmospheric CO2

    NASA Astrophysics Data System (ADS)

    Yakir, D.

    2003-12-01

    When a bean leaf was sealed in a closed chamber under a lamp (Rooney, 1988), in two hours the atmospheric CO2 in the microcosm reached an isotopic steady state with a 13C abundance astonishingly similar to the global mean value of atmospheric CO2 at that time (-7.5‰ in the δ13C notation introduced below). Almost concurrently, another research group sealed a suspension of asparagus cells in a different type of microcosm in which within about two hours the atmospheric O2 reached an isotopic steady state with 18O enrichment relative to water in the microcosm that was, too, remarkably similar to the global-scale offset between atmospheric O2 and mean ocean water (21‰ versus 23.5‰ in the δ18O notation introduced below; Guy et al., 1987). These classic experiments capture some of the foundations underlying the isotopic composition of atmospheric CO2 and O2. First, in both cases the biological system rapidly imposed a unique isotopic value on the microcosms' atmosphere via their massive photosynthetic and respiratory exchange of CO2 and O2. Second, in both cases the biological system acted on materials with isotopic signals previously formed by the global carbon and hydrological cycles. That is, the bean leaf introduced its previously formed organic matter (the source of the CO2 respired into microcosm's atmosphere), and the asparagus cells were introduced complete with local tap water (from which photosynthesis released molecular oxygen). Therefore, while the isotopic composition of the biological system used was slave to long-term processes, intense metabolic processes centered on few specific enzymes (Yakir, 2002) dictated the short-term atmospheric composition.In a similar vein, on geological timescales of millions of years, the atmosphere and its isotopic composition are integral parts of essentially a single dynamic ocean-atmosphere-biosphere system. This dynamic system exchanges material, such as carbon and oxygen, with the sediments and the lithosphere via

  20. The Clumped Isotope Composition of Biogenic Methane.

    NASA Astrophysics Data System (ADS)

    Sessions, A. L.; Douglas, P. M.; Eiler, J. M.; Stolper, D. A.

    2015-12-01

    The excess or lack of 13CH3D, a doubly substituted ("clumped") isotopologue of methane, relative to that expected for a random distribution of isotopes across molecules, is a function of the processes that generated the methane. For high-temperature thermogenic methane, which typically achieves internal equilibrium, an excess of 13CH3D is expected and the amount of excess can serve as a thermometer. In contrast, biogenic methane often - though not always - has a smaller excess of clumped isotopologues, and sometimes even a deficit of clumped species ("anti-clumped"). The effect presumably arises from kinetic isotope effects accompanying enzymatic reactions in the methanogenic pathway, though the particular reaction(s) has not yet been positively identified. The decrease in clumping is also known to correlate with both the reversibility of the pathway and the methane flux. In this talk, we will present recent data bearing on the origin and utility of biologic fractionations of clumped isotopologues in methane. Preliminary data suggest that methane deriving from the fermentative pathway is enriched in D-bearing isotopologues, at the same level of clumping, relative to that derived from the CO2-reductive pathway. This property offers another potential means to distinguish biogenic methane sources in the environment. Recently, we have also begun to measure the 12CH2D2 isotopologue, for which equilibrium and kinetic isotope effects are predicted to be distinct from 13CH3D. Preliminary data suggest that the combination of both doubly-substituted isotopologues will be especially useful for disentangling mixtures containing biogenic gas.

  1. H-Isotopic Composition of Apatite in Northwest Africa 7034

    NASA Technical Reports Server (NTRS)

    McCubbin, F. M.; Barnes, J. J.; Santos, A. R.; Boyce, J. W.; Anand, M.; Franchi, I. A.; Agee, C. B.

    2016-01-01

    Northwest Africa (NWA) 7034 and its pairings comprise a regolith breccia with a basaltic bulk composition [1] that yields a better match than any other martian meteorite to estimates of Mars' bulk crust composition [1]. Given the similarities between NWA 7034 and the martian crust, NWA 7034 may represent an important sample for constraining the crustal composition of components that cannot be measured directly by remote sensing. In the present study, we seek to constrain the H isotopic composition of the martian crust using Cl-rich apatite in NWA 7034.

  2. Measurement of Plutonium Isotopic Composition - MGA

    SciTech Connect

    Vo, Duc Ta

    2015-08-21

    In this module, we will use the Canberra InSpector-2000 Multichannel Analyzer with a high-purity germanium detector (HPGe) and the MGA isotopic anlysis software to assay a variety of plutonium samples. The module provides an understanding of the MGA method, its attributes and limitations. You will assess the system performance by measuring a range of materials similar to those you may assay in your work. During the final verification exercise, the results from MGA will be combined with the 240Pueff results from neutron coincidence or multiplicity counters so that measurements of the plutonium mass can be compared with the operator-declared (certified) values.

  3. Heavy nickel isotope compositions in rivers and the oceans

    NASA Astrophysics Data System (ADS)

    Cameron, V.; Vance, D.

    2014-03-01

    Nickel is a biologically-active trace metal whose dissolved concentration depth profiles in the ocean show nutrient-like behaviour. If the pronounced removal of nickel from the dissolved phase in the surface ocean, and its return in the deep, is associated with an isotopic fractionation nickel isotopes may be able to yield constraints on the precise biogeochemical processes involved. Here we present the first nickel isotope data for seawater along with data for the dissolved phase of rivers, one of the principal sources of nickel to the oceans. The dissolved phase of rivers exhibits substantial variability in both Ni concentration and δ60Ni: from 2.2 to 35 nmol kg-1 and +0.29 to +1.34‰, respectively. The most striking result from the nickel isotope analyses of rivers is that they are substantially heavier (by up to 1‰ for δ60Ni) than the range for silicate rocks on the continents, a finding that is analogous to that for other transition metal isotope systems. If the data presented here are close to representative of the global riverine flux, they suggest an annual input of Ni to the oceans of 3.6 × 108moles, and a discharge- and concentration-weighted δ60Ni average of +0.80‰. The relationship between Ni isotopes and concentrations shows similarities with those for other transition metal isotope systems, where the main control has been suggested to be isotopic partitioning between the dissolved phase and particulates, either in the weathering environment or during transport. In stark contrast to the rivers, the dataset for seawater is very homogeneous, with 2SD of the entire dataset being only twice the analytical reproducibility. The second main feature is that seawater is distinctly heavier in Ni isotopes than rivers. The average δ60Ni is 1.44 ± 0.15‰ (2SD), and only 2 of the 29 seawater analyses have a Ni isotopic composition that is lighter than the heaviest river. The lack of an isotopic shift associated with the drawdown of nickel concentrations

  4. What controls the isotopic composition of Greenland surface snow?

    NASA Astrophysics Data System (ADS)

    Steen-Larsen, H. C.; Masson-Delmotte, V.; Hirabayashi, M.; Winkler, R.; Satow, K.; Prié, F.; Bayou, N.; Brun, E.; Cuffey, K. M.; Dahl-Jensen, D.; Dumont, M.; Guillevic, M.; Kipfstuhl, J.; Landais, A.; Popp, T.; Risi, C.; Steffen, K.; Stenni, B.; Sveinbjörnsdottír, A.

    2013-10-01

    Water stable isotopes in Greenland ice core data provide key paleoclimatic information, and have been compared with precipitation isotopic composition simulated by isotopically-enabled atmospheric models. However, post-deposition processes linked with snow metamorphism remain poorly documented. For this purpose, a monitoring of the isotopic composition (δ18O, δD) of surface water vapor, precipitation and samples of top (0.5 cm) snow surface has been conducted during two summers (2011-2012) at NEEM, NW Greenland. The measurements also include a subset of 17O-excess measurements over 4 days, and the measurements span the 2012 Greenland heat wave. Our observations are consistent with calculations assuming isotopic equilibrium between surface snow and water vapor. We observe a strong correlation between surface vapor δ18O and air temperature (0.85 ± 0.11 ‰ °C-1 (R = 0.76) for 2012). The correlation with air temperature is not observed in precipitation data or surface snow data. Deuterium excess (d-excess) is strongly anti-correlated with δ18O with a stronger slope for vapor than for precipitation and snow surface data. During nine 1-5 days periods between precipitation events, our data demonstrate parallel changes of δ18O and d-excess in surface snow and surface vapor. The changes in δ18O of the vapor are similar or larger than those of the snow δ18O. It is estimated that 6 to 20% of the surface snow mass is exchanged with the atmosphere using the CROCUS snow model. In our data, the sign of surface snow isotopic changes is not related to the sign or magnitude of sublimation or condensation. Comparisons with atmospheric models show that day-to-day variations in surface vapor isotopic composition are driven by synoptic weather and changes in air mass trajectories and distillation histories. We suggest that, in-between precipitation events, changes in the surface snow isotopic composition are driven by these changes in surface vapor isotopic composition. This

  5. What controls the isotopic composition of Greenland surface snow?

    NASA Astrophysics Data System (ADS)

    Steen-Larsen, H. C.; Masson-Delmotte, V.; Hirabayashi, M.; Winkler, R.; Satow, K.; Prié, F.; Bayou, N.; Brun, E.; Cuffey, K. M.; Dahl-Jensen, D.; Dumont, M.; Guillevic, M.; Kipfstuhl, S.; Landais, A.; Popp, T.; Risi, C.; Steffen, K.; Stenni, B.; Sveinbjörnsdottír, A. E.

    2014-02-01

    Water stable isotopes in Greenland ice core data provide key paleoclimatic information, and have been compared with precipitation isotopic composition simulated by isotopically enabled atmospheric models. However, post-depositional processes linked with snow metamorphism remain poorly documented. For this purpose, monitoring of the isotopic composition (δ18O, δD) of near-surface water vapor, precipitation and samples of the top (0.5 cm) snow surface has been conducted during two summers (2011-2012) at NEEM, NW Greenland. The samples also include a subset of 17O-excess measurements over 4 days, and the measurements span the 2012 Greenland heat wave. Our observations are consistent with calculations assuming isotopic equilibrium between surface snow and water vapor. We observe a strong correlation between near-surface vapor δ18O and air temperature (0.85 ± 0.11‰ °C-1 (R = 0.76) for 2012). The correlation with air temperature is not observed in precipitation data or surface snow data. Deuterium excess (d-excess) is strongly anti-correlated with δ18O with a stronger slope for vapor than for precipitation and snow surface data. During nine 1-5-day periods between precipitation events, our data demonstrate parallel changes of δ18O and d-excess in surface snow and near-surface vapor. The changes in δ18O of the vapor are similar or larger than those of the snow δ18O. It is estimated using the CROCUS snow model that 6 to 20% of the surface snow mass is exchanged with the atmosphere. In our data, the sign of surface snow isotopic changes is not related to the sign or magnitude of sublimation or deposition. Comparisons with atmospheric models show that day-to-day variations in near-surface vapor isotopic composition are driven by synoptic variations and changes in air mass trajectories and distillation histories. We suggest that, in between precipitation events, changes in the surface snow isotopic composition are driven by these changes in near-surface vapor

  6. Oxygen isotopic constraints on the composition of the moon

    NASA Technical Reports Server (NTRS)

    Grossman, L.; Clayton, R. N.; Mayeda, T. K.

    1974-01-01

    The mean oxygen isotopic composition of 5 Apollo 17 soils, one Apollo 17 breccia and one Apollo 12 soil is delta O-18 = 5.63 + or - .05 and delta O-17 = 3.8 + or - .2%. These values are within several tenths of a part permil of the composition of a large fraction of the lunar interior. High-temperature condensate aggregates from Allende and other C2 and C3 chondrites are vastly enriched in O-16 compared to this composition. The moon cannot be a mixture of ordinary chondrites and Allende inclusions, nor can it be derived from such a mixture by chemical fractionation processes. The moon's isotopic composition is consistent with a mixture of high- and low-temperature condensates but the refractory fraction would have to be free of the O-16-rich component so prevalent in the meteoritic aggregates, a fact which makes such models less attractive than they once seemed.

  7. Pressure-dependent isotopic composition of iron alloys.

    PubMed

    Shahar, A; Schauble, E A; Caracas, R; Gleason, A E; Reagan, M M; Xiao, Y; Shu, J; Mao, W

    2016-04-29

    Our current understanding of Earth's core formation is limited by the fact that this profound event is far removed from us physically and temporally. The composition of the iron metal in the core was a result of the conditions of its formation, which has important implications for our planet's geochemical evolution and physical history. We present experimental and theoretical evidence for the effect of pressure on iron isotopic composition, which we found to vary according to the alloy tested (FeO, FeH(x), or Fe3C versus pure Fe). These results suggest that hydrogen or carbon is not the major light-element component in the core. The pressure dependence of iron isotopic composition provides an independent constraint on Earth's core composition. PMID:27126042

  8. Pressure-dependent isotopic composition of iron alloys

    NASA Astrophysics Data System (ADS)

    Shahar, A.; Schauble, E. A.; Caracas, R.; Gleason, A. E.; Reagan, M. M.; Xiao, Y.; Shu, J.; Mao, W.

    2016-04-01

    Our current understanding of Earth’s core formation is limited by the fact that this profound event is far removed from us physically and temporally. The composition of the iron metal in the core was a result of the conditions of its formation, which has important implications for our planet’s geochemical evolution and physical history. We present experimental and theoretical evidence for the effect of pressure on iron isotopic composition, which we found to vary according to the alloy tested (FeO, FeHx, or Fe3C versus pure Fe). These results suggest that hydrogen or carbon is not the major light-element component in the core. The pressure dependence of iron isotopic composition provides an independent constraint on Earth’s core composition.

  9. Fe Isotope Composition of Neoproterozoic Post-Glacial "Cap Dolostones"

    NASA Astrophysics Data System (ADS)

    Halverson, G. P.

    2005-12-01

    The largest variations in the Fe isotope composition in the geological record are found in sedimentary rocks, presumably as the result of redox transformations of iron during mineral precipitation, microbial processing, and diagenesis (Johnson et al., Cont. Min. Petrol., 2003). Systematic trends in the variability of the Fe isotope composition of sulfide minerals formed in ancient marine black shales broadly mirror patterns in sulfur isotope data (Δ33S, Δ34S), which are consistent with geological and other geochemical evidence for the progressive oxidation of the earth's surface during the Precambrian (Rouxel et al., Science, 2005). Therefore, the record of the Fe isotope composition of minerals formed in the marine environment appears to be a promising proxy for the redox evolution of the ocean. We have developed a method to extract the marine Fe isotope composition from carbonates in an attempt to establish higher resolution records of changes in marine redox changes than permitted by black shale geochemistry. We have applied this method to the study of ca. 635 Ma iron-rich dolostones, which are found in Neoproterozoic successions worldwide and immediately post-date a purported snowball (Marinoan) glaciation during which time the deep ocean is thought to have become anoxic (Hoffman et al., Science, 1998), allowing its Fe isotopic composition to evolve towards the composition of relatively light (δ57Fe vs. IRMM-14 ~ -0.6‰) hydrothermal iron (Beard et al., Geology, 2003). Fe isotope compositions were measured relative to IRMM-14 in medium-resolution mode on a Neptune MC-ICP-MS with a long-term external (2σ) reproducibility of < 0.04‰/amu. Preliminary data on dolomite samples from Svalbard, northern Namibia and northwest Canada show a range in δ57Fe values from -0.65 to 0.04‰, similar to the range found in siderite and Fe-rich dolomite in ancient BIFs (Johsnon et al., 2003) and to values for the Namibian cap dolostone reported by Leighton et al

  10. Heavy nickel isotope compositions in rivers and the oceans

    NASA Astrophysics Data System (ADS)

    Cameron, V.; Vance, D.

    2014-03-01

    Nickel is a biologically-active trace metal whose dissolved concentration depth profiles in the ocean show nutrient-like behaviour. If the pronounced removal of nickel from the dissolved phase in the surface ocean, and its return in the deep, is associated with an isotopic fractionation nickel isotopes may be able to yield constraints on the precise biogeochemical processes involved. Here we present the first nickel isotope data for seawater along with data for the dissolved phase of rivers, one of the principal sources of nickel to the oceans. The dissolved phase of rivers exhibits substantial variability in both Ni concentration and δ60Ni: from 2.2 to 35 nmol kg-1 and +0.29 to +1.34‰, respectively. The most striking result from the nickel isotope analyses of rivers is that they are substantially heavier (by up to 1‰ for δ60Ni) than the range for silicate rocks on the continents, a finding that is analogous to that for other transition metal isotope systems. If the data presented here are close to representative of the global riverine flux, they suggest an annual input of Ni to the oceans of 3.6 × 108moles, and a discharge- and concentration-weighted δ60Ni average of +0.80‰. The relationship between Ni isotopes and concentrations shows similarities with those for other transition metal isotope systems, where the main control has been suggested to be isotopic partitioning between the dissolved phase and particulates, either in the weathering environment or during transport. In stark contrast to the rivers, the dataset for seawater is very homogeneous, with 2SD of the entire dataset being only twice the analytical reproducibility. The second main feature is that seawater is distinctly heavier in Ni isotopes than rivers. The average δ60Ni is 1.44 ± 0.15‰ (2SD), and only 2 of the 29 seawater analyses have a Ni isotopic composition that is lighter than the heaviest river. The lack of an isotopic shift associated with the drawdown of nickel concentrations

  11. A reconnaissance of the boron isotopic composition of tourmaline

    SciTech Connect

    Swihart, G.H.; Moore, P.B. )

    1989-04-01

    A preliminary investigation of the boron isotopic composition of tourmaline from some boron-rich associations has been made. The results for tourmaline from metasedimentary paragneisses (n = 12) range from {delta}{sup 11}B = {minus}22 to +22 per mil. These data mainly fall between the boron isotopic compositions of normal marine sediments with {delta}{sup 11}B = {minus}2 to +5 per mil and seawater with {delta}{sup 11}B = +39.5 per mil. Tourmaline samples from granitic pegmatites (n = 6), on the other hand, range from {delta}{sup 11}B = {minus}12 to {minus}5 per mil. The data provide a rudimentary indication of the range of boron isotopic variation in tourmaline, some of the processes leading to this range, and some possible geochemical tracer applications.

  12. Identification of Marchfeld asparagus using Sr isotope ratio measurements by MC-ICP-MS.

    PubMed

    Swoboda, S; Brunner, M; Boulyga, S F; Galler, P; Horacek, M; Prohaska, T

    2008-01-01

    This work focuses on testing and application of Sr isotope signatures for the fast and reliable authentication and traceability of Asparagus officinalis originating from Marchfeld, Austria, using multicollector inductively coupled plasma mass spectrometry after optimised Rb/Sr separation. The major sample pool comprises freeze-dried and microwave-digested asparagus samples from Hungary and Slovakia which are compared with Austrian asparagus originating from the Marchfeld region, which is a protected geographical indication. Additional samples from Peru, The Netherlands and Germany were limited in number and allowed therefore only restricted statistical evaluation. Asparagus samples from Marchfeld were harvested within two subsequent years in order to investigate the annual variation. The results show that the Sr isotope ratio is consistent within these 2 years of investigation. Moreover, the Sr isotope ratio of total Sr in soil was found to be significantly higher than in an NH4NO3 extract, reflecting the mobile (bioavailable) phase. The isotope composition in the latter extract corresponds well to the range found in the asparagus samples in Marchfeld, even though the concentration of Sr in asparagus shows no direct correlation to the concentration of Sr in the mobile phase of the soil. The major question was whether the 'Marchfelder Spargel' can be distinguished from samples from the neighbouring countries of Hungary and Slovakia. According to our findings, they can be clearly (100%) singled out from the Hungarian samples and can be distinguished from the Slovakian asparagus samples with a probability of more than 80%. PMID:17874075

  13. Sr-Nd-Pb isotope systematics of the Banda Arc, Indonesia: Combined subduction and assimilation of continental material

    NASA Astrophysics Data System (ADS)

    Vroon, P. Z.; van Bergen, M. J.; White, W. M.; Varekamp, J. C.

    1993-12-01

    We present Sr, Nd, and Pb isotope results and SiO2, Rb, Sr, Sm, Nd, U, Th, and Pb data for six active volcanoes and one extinct volcanic island distributed over the whole length of the Banda Arc. Rock types range from low-K tholeiitic in the NE to high-K calc-alkaline in the SW. The volcanoes in the NE have 'normal' arc signatures, whereas those in the SW have extreme values. Serua, situated in the central part, is the most anomalous volcano with regard to its Sr and Nd isotopic composition but not with regard to Pb isotopes. The inactive island of Romang in the SW overlaps the Serua trends. The volcanoes display variable within-suite ranges in Sr-87/Sr-86 and Nd-143/Nd-144. Large ranges (e.g., at Nila) are consistent with assimilation (10-20%) of carbonate-bearing sediments from the arc crust. Despite the evidence for assimilation, it cannot explain all of the Sr-Nd isotopic trends found, and Banda Arc magmas must have already obtained a 'continental' signature at depth before they reached the arc crust. Within-suit trends of Pb isotopes are virtually absent. We found an extreme range in the volcanics along the arc which coincide with a similar trend in sediments in front of the arc and consider this as strong evidence for the contribution of subducted continent-derived material to magma sources.

  14. Converting isotope ratios to diet composition - the use of mixing models - June 2010

    EPA Science Inventory

    One application of stable isotope analysis is to reconstruct diet composition based on isotopic mass balance. The isotopic value of a consumer’s tissue reflects the isotopic values of its food sources proportional to their dietary contributions. Isotopic mixing models are used ...

  15. Effects of interaction between ultramafic tectonite and mafic magma on Nd-Pb-Sr isotopic systems in the Neoproterozoic Chaya Massif, Baikal-Muya ophiolite belt

    USGS Publications Warehouse

    Amelin, Y.V.; Ritsk, E. Yu; Neymark, L.A.

    1997-01-01

    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 with ??Nd = +6.6 to +7.1 and ??Sr = -11 to -16; and (2) websterite of the lower unit and gabbronorites of the upper mafic unit: ??Nd = + 4.6 to + 6.1 and ??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 basaltic

  16. Authentication of bell peppers using boron and strontium isotope compositions

    NASA Astrophysics Data System (ADS)

    Rosner, Martin; Pritzkow, Wolfgang; Vogl, Jochen; Voerkelius, Susanne

    2010-05-01

    The wrong declaration of food in terms of geographical origin and production method is a major problem for the individual consumer and public regulatory authorities. The authentication of food matrices using H-C-N-O-S isotopic compositions is already well established. However, specific questions require additional isotopic systems, which are more diagonstic for the source reservoires involved or production methods used. Here we present B and Sr isotopic compositions of bell peppers from Europe (Germany, Austria, Netherlands, Spain) and Israel to verfiy their origin. The bell peppers' B isotopic compositions between different locations are highly variable (d11BNISTSRM951 -8 to +35 ‰), whereas the 87Sr/86Sr ratios are all close to modern seawater Sr isotopic composition of about 0.7092 (0.7078 to 0.7107), but still can reliably be distinguished. Distinct isotopically heavy and light B isotopic fingerprints are obtained for bell peppers from Israel and the Netherlands. Samples from Germany, Austria, and Spain display overlapping d11B values between 0 and +12 ‰. Bell peppers from Israel show high d11B values (+28 to +35 ‰) combined with 87Sr/86Sr ratios slightly more unradiogenic than modern seawater (ca 0.7079). Bell peppers from the Netherlands, however, show low d11B values (-8 ‰) combinded with 87Sr/86Sr ratios of modern seawater (approx. 0.7085). Mainly based on diagnostic B isotopic compositions bell peppers from Israel and the Netherlands can be related to a specific geographical growing environment (Israel) or production method (Netherlands). The isotope fingerprints of bell peppers from the Netherlands are consistent with growing conditions in greenhouses typical for the Netherlands vegetable farming. Using optimized production methods crops in greenhouses were supplied with nutritients by liquid fertilizers on artificial substrates. As most fertilizers derive from non-marine salt deposits, fertilization typically imprints invariant d11B values close

  17. Sm-Nd isotopic systematics of lherzolitic shergottite Yamato-793605

    USGS Publications Warehouse

    Misawa, K.; Yamada, K.; Nakamura, N.; Morikawa, N.; Yamashita, K.; Premo, W.R.

    2006-01-01

    We have undertaken Sm-Nd isotopic studies on Yamato-793605 lherzolitic shergottite. The Sm-Nd internal isochron obtained for acid leachates and residues of whole-rock and separated mineral fractions yields an age of 185 ??16 Ma with an initial ??Nd value of +9.7??0.2. The obtained Sm-Nd age is, within analytical errors, identical to the Rb-Sr age of this meteorite as well as to the previous Rb-Sr and Sm-Nd ages of Allan Hills-77005 and Lewis Cliff 88516, although the ??Nd values are not identical to each other. Elemental abundances of lithophile trace elements remain nearly unaffected by aqueous alteration on the Martian surface. The isotopic systems of lherzolitic shergottites, thus, are considered to be indigenous, although disturbances by shock metamorphism are clearly observed. "Young ages of ??? 180 Ma" have been consistently obtained from this and previous Rb-Sr, Sm-Nd and U-Pb isotopic studies and appear to represent crystallization events. ?? 2006 National Institute of Polar Research.

  18. Boron isotopic compositions of some boron minerals

    NASA Astrophysics Data System (ADS)

    Oi, Takao; Nomura, Masao; Musashi, Masaaki; Ossaka, Tomoko; Okamoto, Makoto; Kakihana, Hidetake

    1989-12-01

    Boron minerals that have different structural formulae but are supposed to have the same geologic origin have been collected and analyzed for the 11B /10B isotopic ratio. It has been reconfirmed that minerals of marine origin have higher 11B /10B ratios than those of nonmarine origin. It has been found that the sequence of decreasing 11B /10B values among the minerals with the same geologic origin is; borax, tincal, kernite (Na borates) > ulexite ( Na/Ca borate) > colemanite, iyoite, meyerhofferite (Ca borates). This sequence is explainable on the basis of the difference in crystal structure among the minerals. That is, minerals with higher BO 3/BO 4 ratios, (the ratio of the number of the BO 3 triangle units to the number of the BO 4 tetrahedron units in the structural formula of a mineral) have higher 11B /10B ratios.

  19. Controls over the strontium isotope composition of river water

    SciTech Connect

    Palmer, M.R. ); Edmond, J.M. )

    1992-05-01

    Strontium concentrations and isotope ratios have been measured in river and ground waters from the Granges, Orinoco, and Amazon river basins. When compared with major element concentrations, the data set has allowed a detailed examination of the controls over the strontium isotope systematics of riverine input to the oceans in the following environments: (1) typical drainage basins containing limestones, evaporites, shales, and alumino-silicate metamorphic and igneous rocks; (2) shield terrains containing no chemical or biogenic sediments; and (3) the flood plains that constitute the largest areas of many large rivers. The strontium concentration and isotope compositions of river waters are largely defined by mixing of strontium derived from limestones and evaporites with strontium derived from silicate rocks. The strontium isotope composition of the limestone end member generally lies within the Phanerozoic seawater range, which buffers the [sup 87]Sr/[sup 86]Sr ratios of major rivers. A major exception is provided by the rivers draining the Himalayas, where widescale regional metamorphism appears to have led to an enrichment in limestones of radiogenic strontium derived from coexisting silicate rocks. The strontium isotope systematics of rivers draining shield areas are controlled by the intense, transport-limited, nature of the weathering reactions, and thereby limits variations in the strontium flux from these terrains. Flood plains are only a minor source of dissolved strontium to river waters, and precipitation of soil salts in some flood plains can reduce the riverine flux of dissolved strontium to the oceans.

  20. CALCIUM ISOTOPE COMPOSITION OF METEORITES, EARTH, AND MARS

    SciTech Connect

    Simon, Justin I.; DePaolo, Donald J.; Moynier, Frederic

    2009-09-01

    The relative abundances of calcium isotopes in the mass range 40-44 were measured in primitive and differentiated meteorites and igneous rocks from Earth and Mars in search of non-mass-dependent variations that could provide clues about early solar system processes. Most bulk samples of planetary materials have calcium isotopic compositions identical with Earth's within the current resolution of about 0.01% in {sup 40}Ca/{sup 44}Ca. Possible exceptions include carbonaceous chondrites, some ordinary chondrites, and two samples of calcium-aluminum-rich inclusions, which have small excesses of {sup 40}Ca. The samples with {sup 40}Ca excesses are also known to have {sup 50}Ti and {sup 135}Ba excesses and {sup 142}Nd and {sup 144}Sm deficits. Collectively these data from refractory elements suggest that the planetary embryos represented by chondrites preserve isotopic heterogeneity that reflects different nucleosynthetic sources. No late admixture from a single nucleosynthetic source can explain all observations. The results are most compatible with variable proportions of material derived from Type II supernovae. The initial calcium isotope compositions of Earth and Mars are indistinguishable and similar to the {sup 40}Ca abundance found in some chondrites and all differentiated meteorites studied. It appears that isotopic heterogeneity in calcium was still present at the completion of disk formation but was homogenized during planetary accretion.

  1. Isotope composition and volume of Earth’s early oceans

    PubMed Central

    Pope, Emily C.; Bird, Dennis K.; Rosing, Minik T.

    2012-01-01

    Oxygen and hydrogen isotope compositions of Earth’s seawater are controlled by volatile fluxes among mantle, lithospheric (oceanic and continental crust), and atmospheric reservoirs. Throughout geologic time the oxygen mass budget was likely conserved within these Earth system reservoirs, but hydrogen’s was not, as it can escape to space. Isotopic properties of serpentine from the approximately 3.8 Ga Isua Supracrustal Belt in West Greenland are used to characterize hydrogen and oxygen isotope compositions of ancient seawater. Archaean oceans were depleted in deuterium [expressed as δD relative to Vienna standard mean ocean water (VSMOW)] by at most 25 ± 5‰, but oxygen isotope ratios were comparable to modern oceans. Mass balance of the global hydrogen budget constrains the contribution of continental growth and planetary hydrogen loss to the secular evolution of hydrogen isotope ratios in Earth’s oceans. Our calculations predict that the oceans of early Earth were up to 26% more voluminous, and atmospheric CH4 and CO2 concentrations determined from limits on hydrogen escape to space are consistent with clement conditions on Archaean Earth. PMID:22392985

  2. The chromium isotopic composition of seawater and marine carbonates

    NASA Astrophysics Data System (ADS)

    Bonnand, P.; James, R. H.; Parkinson, I. J.; Connelly, D. P.; Fairchild, I. J.

    2013-11-01

    Chromium isotopes are fractionated during redox reactions and have the potential to provide a record of changes in the oxygenation levels of the oceans in the geological past. However, Cr is a trace metal in seawater and its low concentrations make isotopic measurements challenging. Here we report the first determinations of δCr53 for seawater from open ocean (Argentine Basin) and coastal (Southampton Water) settings, using a double-spike technique. The total chromium concentration in seawater from Southampton Water is 1.85 nM, whereas the Cr content of Argentine Basin samples is 5.8-6.6 nM. The δCr53 value of seawater from the Argentine Basin is 0.491-0.556‰ in intermediate and deep waters, and varies between 0.412 and 0.664‰ in surface waters (<150 m). The δCr53 value of Southampton Water seawater is 1.505‰, which may reflect in situ reduction of Cr(VI) to Cr(III). All of our seawater samples have higher δCr53 than crustal and mantle silicates, and mass balance modelling demonstrates that river water must also be enriched in heavy Cr isotopes, indicating that Cr isotopes are fractionated during weathering and/or during transport to the oceans. We also show that the Cr isotopic composition of modern non-skeletal marine carbonates (0.640- 0.745‰) encompasses the range that we measure for Argentine Basin seawater. Thus, fractionation of Cr isotopes during precipitation of these marine carbonates is likely to be small (<0.2‰), and they have the potential to provide a record of the Cr isotopic composition of ancient seawater. Phanerozoic carbonates are also characterised by heavy δCr53 and a correlation between δCr53 and Ce/Ce* suggests that the Cr and Ce cycles in the ocean are linked.

  3. Lithium concentration and Li isotopic compositions of carbonatitic complexes

    NASA Astrophysics Data System (ADS)

    Halama, R.; McDonough, W. F.; Rudnick, R. L.; Ash, R. D.; Keller, J.; Klaudius, J.; Trumbull, R.

    2005-12-01

    To evaluate the Li isotopic signatures of the mantle sources of carbonatites and the influence of magmatic differentiation and post-magmatic processes on δ7Li, we determined the Li concentrations and isotopic compositions of carbonatites and spatially associated silicate rocks, spanning a wide range in composition and age. Natrocarbonatites from Oldoinyo Lengai (1995 and 2000 eruptions) have high Li concentrations (211-292 ppm) and uniform Li isotopic signatures (δ7Li = +4.4 to +5.1 per mil). Associated silicate rocks (melilitite, nephelinite and phonolite) have lower Li concentrations (16-47 ppm) and trend towards lighter Li isotopic values (δ7Li = 0 to +3.5 per mil). Clinopyroxenes from these lavas are significantly lighter than the whole rocks by 1 to 6 per mil. Since the lavas appear to be fresh, this suggests fractionation of Li isotopes between minerals and whole rocks. In comparison to the modern natrocarbonatites, Proterozoic calciocarbonatites from Greenland (Grønnedal-Ika) and Cretaceous calciocarbonatites from Namibia (Kalkfeld) are poor in Li (< 2 ppm) and have more scattered Li isotopic compositions (δ7Li = -1 to +4 and -0.5 to +5 per mil, respectively). The lower δ7Li values may reflect contamination by crustal Li, since the low Li contents in the carbonatites make them susceptible to this. Silicate lavas from Kalkfeld have higher Li concentrations (11-12 ppm) than their associated carbonatites, but overlapping isotopic compositions (δ7Li = +4 to +6 per mil). At Grønnedal-Ika, clinopyroxene separates from nepheline syenites vary considerably in δ7Li from -6 to +5. Since Li is preferentially partitioned into fenitizing fluids [1] and an enrichment of light 6Li in fluids during degassing can be anticipated [2], the trend towards negative δ7Li can be interpreted as a result of variable interaction with metasomatizing fluids. However, fractionation of Li isotopes between minerals and melts may also have played a role. Our preliminary data

  4. The elemental and isotopic composition of galactic cosmic rays

    NASA Technical Reports Server (NTRS)

    Mewaldt, R. A.

    1982-01-01

    Galactic cosmic rays represent samples of matter from areas outside the solar system. New information regarding the elemental composition of cosmic rays has been obtained in connection with the French-Danish experiment on HEA0-3 and recent balloon experiments. The energy dependence of the source composition is considered along with a comparison of cosmic ray and solar system abundances, and the N-14 source abundance. Attention is given to cosmic ray clocks and the Mn-54 problem, advances concerning cross section measurements, and cosmic ray isotopes. The considered new observations suggest that cosmic ray elemental abundance differences from the solar system continue to be ordered by atomic parameters such as first ionization potential, at least up through Z equals 40. The isotopic composition of the cosmic ray source is found to be unlike that of the solar system.

  5. Multi-Isotopic evidence from West Eifel Xenoliths

    NASA Astrophysics Data System (ADS)

    Thiemens, M. M.; Sprung, P.

    2015-12-01

    Mantle Xenoliths from the West Eifel intraplate volcanic field of Germany provide insights into the nature and evolution of the regional continental lithospheric mantle. Previous isotope studies have suggested a primary Paleoproterozoic depletion age, a second partial melting event in the early Cambrian, and a Variscan metasomatic overprint. Textural and Sr-Nd isotopic observations further suggest two episodes of melt infiltration of early Cretaceous and Quaternary age. We have investigated anhydrous, vein-free lherzolites from this region, focusing on the Dreiser Weiher and Meerfelder Maar localities. Hand separated spinel, olivine, ortho- and clinopryoxene, along with host and bulk rocks were dissolved and purified for Rb-Sr, Sm-Nd, and Lu-Hf analysis on the Cologne/Bonn Neptune MC-ICP-MS. We find an unexpected discontinuity between mineral separates and whole rocks. While the latter have significantly more radiogenic ɛNd and ɛHf, mineral separates imply close-to chondritic compositions. Our Lu-Hf data imply resetting of the Lu-Hf systematic after 200 Ma. Given the vein-free nature of the lherzolites, this appears to date to the second youngest metasomatic episode. We suggest that markedly radiogenic Nd and Hf were introduced during the Quarternary metasomatic episode and most likely reside on grain boundaries.

  6. The abundance and isotopic composition of water in eucrites

    NASA Astrophysics Data System (ADS)

    Barrett, T. J.; Barnes, J. J.; TartèSe, R.; Anand, M.; Franchi, I. A.; Greenwood, R. C.; Charlier, B. L. A.; Grady, M. M.

    2016-05-01

    Volatile elements play a key role in the dynamics of planetary evolution. Extensive work has been carried out to determine the abundance, distribution, and source(s) of volatiles in planetary bodies such as the Earth, Moon, and Mars. A recent study showed that the water in apatite from eucrites has similar hydrogen isotopic compositions compared to water in terrestrial rocks and carbonaceous chondrites, suggesting that water accreted very early in the inner solar system given the ancient crystallization ages (~4.5 Ga) of eucrites. Here, the measurements of water (reported as equivalent H2O abundances) and the hydrogen isotopic composition (δD) of apatite from five basaltic eucrites and one cumulate eucrite are reported. Apatite H2O abundances range from ~30 to ~3500 ppm and are associated with a weighted average δD value of -34 ± 67‰. No systematic variations or correlations are observed in H2O abundance or δD value with eucrite geochemical trend or metamorphic grade. These results extend the range of previously published hydrogen isotope data for eucrites and confirm the striking homogeneity in the H-isotopic composition of water in eucrites, which is consistent with a common source for water in the inner solar system.

  7. The abundance and isotopic composition of water in eucrites

    NASA Astrophysics Data System (ADS)

    Barrett, T. J.; Barnes, J. J.; TartèSe, R.; Anand, M.; Franchi, I. A.; Greenwood, R. C.; Charlier, B. L. A.; Grady, M. M.

    2016-06-01

    Volatile elements play a key role in the dynamics of planetary evolution. Extensive work has been carried out to determine the abundance, distribution, and source(s) of volatiles in planetary bodies such as the Earth, Moon, and Mars. A recent study showed that the water in apatite from eucrites has similar hydrogen isotopic compositions compared to water in terrestrial rocks and carbonaceous chondrites, suggesting that water accreted very early in the inner solar system given the ancient crystallization ages (~4.5 Ga) of eucrites. Here, the measurements of water (reported as equivalent H2O abundances) and the hydrogen isotopic composition (δD) of apatite from five basaltic eucrites and one cumulate eucrite are reported. Apatite H2O abundances range from ~30 to ~3500 ppm and are associated with a weighted average δD value of -34 ± 67‰. No systematic variations or correlations are observed in H2O abundance or δD value with eucrite geochemical trend or metamorphic grade. These results extend the range of previously published hydrogen isotope data for eucrites and confirm the striking homogeneity in the H-isotopic composition of water in eucrites, which is consistent with a common source for water in the inner solar system.

  8. The Chlorine Isotopic Composition Of Lunar UrKREEP

    NASA Technical Reports Server (NTRS)

    Barnes, J. J.; Tartese, R.; Anand, M.; McCubbin, F. M.; Neal, C. R.; Franchi, I. A.

    2016-01-01

    Since the long standing paradigm of an anhydrous Moon was challenged there has been a renewed focus on investigating volatiles in a variety of lunar samples. However, the current models for the Moon’s formation have yet to fully account for its thermal evolution in the presence of H2O and other volatiles. When compared to chondritic meteorites and terrestrial rocks, lunar samples have exotic chlorine isotope compositions, which are difficult to explain in light of the abundance and isotopic composition of other volatile species, especially H, and the current estimates for chlorine and H2O in the bulk silicate Moon. In order to better understand the processes involved in giving rise to the heavy chlorine isotope compositions of lunar samples, we have performed a comprehensive in situ high precision study of chlorine isotopes, using NanoSIMS (Nanoscale Secondary Ion Mass Spectrometry) of lunar apatite from a suite of Apollo samples covering a range of geochemical characteristics and petrologic types.

  9. Isotopic composition of hydrogen in insoluble organic matter from cherts

    NASA Technical Reports Server (NTRS)

    Krishnamurthy, R. V.; Epstein, S.

    1991-01-01

    Robert (1989) reported the presence of unusually enriched hydrogen in the insoluble HF-HCl residue extracted from two chert samples of Eocene and Pliocene ages. Since the presence of heavy hydrogen might be due to the incorporation of extraterrestrial materials, we desired to reexamine the same samples to isolate the D-rich components. Our experiments did not reveal any D-rich components, but the hydrogen isotope composition of the insoluble residue of the two chert samples was well within the range expected for terrestrial organic matter. We also describe a protocol that needs to be followed in the hydrogen isotope analysis of any insoluble organic matter.

  10. The isotopic composition of solar flare accelerated neon

    NASA Technical Reports Server (NTRS)

    Mewaldt, R. A.; Spalding, J. D.; Stone, E. C.; Vogt, R. E.

    1979-01-01

    The individual isotopes of neon in energetic solar-flare particles have been clearly resolved with a rms mass resolution of 0.20 amu. The ratios found are Ne-20/Ne-22 = 7.6 (+2.0, -1.8) and Ne-21/Ne-22 of no more than about 0.11 in the 11-26 MeV per nucleon interval. This isotopic composition is essentially the same as that of meteoritic planetary neon-A and is significantly different from that of the solar wind.

  11. Tracing anthropogenic thallium in soil using stable isotope compositions.

    PubMed

    Kersten, Michael; Xiao, Tangfu; Kreissig, Katharina; Brett, Alex; Coles, Barry J; Rehkämper, Mark

    2014-08-19

    Thallium stable isotope data are used in this study, for the first time, to apportion Tl contamination in soils. In the late 1970s, a cement plant near Lengerich, Germany, emitted cement kiln dust (CKD) with high Tl contents, due to cocombustion of Tl-enriched pyrite roasting waste. Locally contaminated soil profiles were obtained down to 1 m depth and the samples are in accord with a binary mixing relationship in a diagram of Tl isotope compositions (expressed as ε(205)Tl, the deviation of the (205)Tl/(203)Tl ratio of a sample from the NIST SRM 997 Tl isotope standard in parts per 10(4)) versus 1/[Tl]. The inferred mixing endmembers are the geogenic background, as defined by isotopically light soils at depth (ε(205)Tl ≈ -4), and the Tl emissions, which produce Tl-enriched topsoils with ε(205)Tl as high as ±0. The latter interpretation is supported by analyses of the CKD, which is also characterized by ε(205)Tl ≈ ± 0, and the same ε(205)Tl value was found for a pyrite from the deposit that produced the cocombusted pyrite roasting waste. Additional measurements for samples from a locality in China, with outcrops of Tl sulfide mineralization and associated high natural Tl backgrounds, reveal significant isotope fractionation between soils (ε(205)Tl ≈ +0.4) and locally grown green cabbage (ε(205)Tl between -2.5 and -5.4). This demonstrates that biological isotope fractionation cannot explain the isotopically heavy Tl in the Lengerich topsoils and the latter are therefore clearly due to anthropogenic Tl emissions from cement processing. Our results thus establish that isotopic data can reinforce receptor modeling for the toxic trace metal Tl. PMID:25055714

  12. Boron isotopic compositions of some boron minerals

    SciTech Connect

    Oi, Takao; Musashi, Masaaki; Ossaka, Tomoko; Kakihana, Hidetake ); Nomura, Masao; Okamoto, Makoto )

    1989-12-01

    Boron minerals that have different structural formulae but are supposed to have the same geologic origin have been collected and analyzed for the {sup 11}B/{sup 10}B isotopic ratio. It has been reconfirmed that minerals of marine origin have higher {sup 11}B/{sup 10}B ratios than those of nonmarine origin. It has been found that the sequence of decreasing {sup 11}B/{sup 10}B values among the minerals with the same geologic origin is; borax, tincal, kernite (Na borates) > ulexite (Na/Ca borate) > colemanite, iyoite, meyerhofferite (Ca borates). This sequence is explainable on the basis of the difference in crystal structure among the minerals. That is, minerals with high BO{sub 3}/BO{sub 4} ratios, (the ratio of the number of the BO{sub 3} triangle units to the number of the BO{sub 4} tetrahedron units in the structural formula of a mineral) have higher {sup 11}B/{sup 10}B ratios.

  13. Unnatural Isotopic Composition of Lithium Reagents

    USGS Publications Warehouse

    Qi, H.P.; Coplen, T.B.; Wang, Q. Zh; Wang, Y.-H.

    1997-01-01

    Isotopic analysis of 39 lithium reagents from several manufacturers indicates that seven were artificially depleted in 6Li significantly in excess of the variation found in terrestrial materials. The atomic weight of lithium in analyzed reagents ranged from 6.939 to 6.996, and ??7-Li, reported relative to L-SVEC lithium carbonate, ranged from -11 to +3013???. This investigation indicates that 6Li-depleted reagents are now found on chemists' shelves, and the labels of these 6Li-depleted reagents do not accurately reflect the atomic and (or) molecular weights of these reagents. In 1993, IUPAC issued the following statement: "Commercially available Li materials have atomic weights that range between 6.94 and 6.99; if a more accurate value is required, it must be determined for the specific material." This statement has been found to be incorrect In two of the 39 samples analyzed, the atomic weight of Li was in excess of 6.99.

  14. The Chlorine Isotopic Composition Of Lunar UrKREEP

    NASA Technical Reports Server (NTRS)

    Barnes, J. J.; Tartese, R.; Anand, M.; McCubbin, F. M.; Neal, C. R.; Franchi, I. A.

    2016-01-01

    Since the long standing paradigm of an anhydrous Moon was challenged there has been a renewed focus on investigating volatiles in a variety of lunar samples. Numerous studies have examined the abundances and isotopic compositions of volatiles in lunar apatite, Ca5(PO4)3(F,Cl,OH). In particular, apatite has been used as a tool for assessing the sources of H2O in the lunar interior. However, current models for the Moon's formation have yet to fully account for its thermal evolution in the presence of H2O and other volatiles. For ex-ample, in the context of the lunar magma ocean (LMO) model, it is anticipated that chlorine (and other volatiles) should have been concentrated in the late-stage LMO residual melts (i.e., the dregs enriched in incompatible elements such as K, REEs (Rare Earth Elements), and P, collectively called KREEP, and in its primitive form - urKREEP, given its incompatibility in mafic minerals like olivine and pyroxene, which were the dominant phases that crystallized early in the cumulate pile of the LMO. When compared to chondritic meteorites and terrestrial rocks, lunar samples have exotic chlorine isotope compositions, which are difficult to explain in light of the abundance and isotopic composition of other volatile species, especially H, and the current estimates for chlorine and H2O in the bulk silicate Moon (BSM). In order to better understand the processes involved in giving rise to the heavy chlorine isotope compositions of lunar samples, we have performed a comprehensive in situ high precision study of chlorine isotopes in lunar apatite from a suite of Apollo samples covering a range of geochemical characteristics and petrologic types.

  15. The Li isotope composition of modern biogenic carbonates

    NASA Astrophysics Data System (ADS)

    Dellinger, M.; West, A. J.; Adkins, J. F.; Paris, G.; Eagle, R.; Freitas, P. S.; Bagard, M. L.; Ries, J. B.; Corsetti, F. A.; Pogge von Strandmann, P.; Ullmann, C. V.

    2015-12-01

    The lithium stable isotope composition (δ7Li) of sedimentary carbonates has great potential to unravel weathering rates and intensity in the past, with implications for understanding the carbon cycle over geologic time. However, so far very little is known about the potential influence of fractionation of the stable Li isotope composition of biogenic carbonates. Here, we investigate the δ7Li of various organisms (particularly mollusks, echinoderms and brachiopods) abundant in the Phanerozoic record, in order to understand which geologic archives might provide the best targets for reconstructing past seawater composition. The range of measured samples includes (i) modern calcite and aragonite shells from variable natural environments, (ii) shells from organisms grown under controlled conditions (temperature, salinity, pCO2), and (iii) fossil shells from a range of species collected from Miocene deposits. When possible, both the inner and outer layers of bivalves were micro-sampled to assess the intra-shell heterogeneity. For calcitic shells, the measured δ7Li of bivalve species range from +32 to +41‰ and is systematically enriched in the heavy isotope relative to seawater (31 ‰) and to inorganic calcite, which is characterized by Δ7Licalcite-seawater = -2 to -5‰ [1]. The Li isotope composition of aragonitic bivalves, ranging from +16 to +22‰, is slightly fractionated to both high and low δ7Li relative to inorganic aragonite. The largest intra-shell Li isotope variability is observed for mixed calcite-aragonite shells (more than 20‰) whereas in single mineralogy shells, intra-shell δ7Li variability is generally less than 3‰. Overall, these results suggest a strong influence of vital effects on Li isotopes during bio-calcification of bivalve shells. On the contrary, measured brachiopods systematically exhibit fractionation that is very similar to inorganic calcite, with a mean δ7Li of 27.0±1.5‰, suggesting that brachiopods may provide good

  16. Effect of Plant Uptake on Perchlorate Isotopic Composition

    NASA Astrophysics Data System (ADS)

    Estrada, N. L.; Jackson, W. A.; Bohlke, J. K.; Sturchio, N. C.; Gu, B.; Rao, B.; Hatzinger, P. B.; Harvey, G.; Burkey, K.; McGrath, M. T.; Sevanthi, R.

    2013-12-01

    The occurrence of perchlorate (ClO4-) in the environment is attributed to both synthetic and natural sources. Unlike anthropogenic ClO4-, natural ClO4- exhibits a wide range in isotopic compositions, suggesting that natural ClO4- is formed through more than one pathway and/or undergoes post-depositional isotopic fractionation processes. One of these processes could be plant uptake and metabolism. Plants are known to reversibly accumulate ClO4-. However, there is little information available regarding the ability for plants to isotopically fractionate ClO4-. Plants could alter ClO4-isotopic composition either by mass dependent fractionation via transport carriers in the root, diffusion limitations through the root, translocation within the plant, reduction of ClO4- by plant enzymes, or non-specific exchange of oxygen in ClO4- catalyzed by plant compounds/processes. We examined the potential for plants to alter the isotopic composition of ClO4- (δ37Cl, δ18O, and Δ17O) in both hydroponic and field scale experiments. Hydroponically grown snap bean plants were exposed to variable ClO4-concentrations (2mg/L and 10mg/L) in solutions prepared from ClO4- with both normal and anomalous O isotopic abundances. At maturity, we evaluated the uptake of ClO4-relative to other anions and the isotopic compositions of ClO4- in both plants and growth solutions. Additional experiments involved field scale exposures of snap beans to irrigation water containing low levels (< 10 ug/L) of ClO4-. The majority of the initial mass of ClO4- for both the low and high exposure hydroponic treatments was recovered in the growth solutions (20-40%) or plant compartments (40-60%), while some mass was not recovered (~20%). ClO4- isotopic compositions were essentially identical between recovered ClO4- in the plant tissues and hydroponic solutions. Anion ratios indicate that ClO4-was accumulated similarly to NO3- but preferentially to Cl- (~4X). In field experiments, the isotopic composition of ClO4

  17. Do foraminifera accurately record seawater neodymium isotope composition?

    NASA Astrophysics Data System (ADS)

    Scrivner, Adam; Skinner, Luke; Vance, Derek

    2010-05-01

    Palaeoclimate studies involving the reconstruction of past Atlantic meridional overturning circulation increasingly employ isotopes of neodymium (Nd), measured on a variety of sample media (Frank, 2002). In the open ocean, Nd isotopes are a conservative tracer of water mass mixing and are unaffected by biological and low-temperature fractionation processes (Piepgras and Wasserburg, 1987; Lacan and Jeandel, 2005). For decades, benthic foraminifera have been widely utilised in stable isotope and geochemical studies, but have only recently begun to be exploited as a widely distributed, high-resolution Nd isotope archive (Klevenz et al., 2008), potentially circumventing the difficulties associated with other methods used to recover past deep-water Nd isotopes (Klevenz et al., 2008; Rutberg et al., 2000; Tachikawa et al., 2004). Thus far, a single pilot study (Klevenz et al., 2008) has indicated that core-top sedimentary benthic foraminifera record a Nd isotope composition in agreement with the nearest available bottom seawater data, and has suggested that this archive is potentially useful on both millennial and million-year timescales. Here we present seawater and proximal core-top foraminifer Nd isotope data for samples recovered during the 2008 "RETRO" cruise of the Marion Dufresne. The foraminifer samples comprise a depth-transect spanning 3000m of the water column in the Angola Basin and permit a direct comparison between high-resolution water column and core-top foraminiferal Nd isotope data. We use these data to assess the reliability of both planktonic and benthic foraminifera as recorders of water column neodymium isotope composition. Frank, M., 2002. Radiogenic isotopes: Tracers of past ocean circulation and erosional input, Rev. Geophys., 40 (1), 1001, doi:10.1029/2000RG000094. Klevenz, V., Vance, D., Schmidt, D.N., and Mezger, K., 2008. Neodymium isotopes in benthic foraminifera: Core-top systematics and a down-core record from the Neogene south Atlantic

  18. Elemental and strontium isotopic geochemistry of the soil profiles developed on limestone and sandstone in karstic terrain on Yunnan-Guizhou Plateau, China: Implications for chemical weathering and parent materials

    NASA Astrophysics Data System (ADS)

    Liu, Wen-Jing; Liu, Cong-Qiang; Zhao, Zhi-Qi; Xu, Zhi-Fang; Liang, Chong-Shan; Li, Long-bo; Feng, Jia-Yi

    2013-05-01

    The limestone and yellow sandstone soil profiles from SW China were measured for chemical and Sr isotope compositions of the bulk soils and their sequential leachates (labile, carbonate, and residue or silicate fraction), aiming to characterize the parent materials of the soils, to understand the soil weathering and formation processes, and to discuss the origin of the red residua (terra rossa). The studied yellow sandstone soil, yellow limestone soil, and black limestone soil show different pH values, SiO2 contents, Rb/Sr abundance ratios, and 87Sr/86Sr ratios. The sequential leachates of different soil types also have different 87Sr/86Sr and Ca/Sr ratios. The major chemical compositions of the studied soil profiles suggest that all the sandstone and limestone soils are developing at a stage that feldspar is exhausting and the clay minerals are changing from smectite to kaolinite and gibbsite. As compared with the red residua distributed in the karst region, the soils studied here show lower CIA values (58-84), but both higher Na2O/K2O (0.9-2.7) and Na2O/Al2O3 concentration ratios (0.07-0.26) on average, suggesting a lower weathering intensity than that of the red residua. The depth profiles of soil CIA values, Na2O/K2O and Rb/Sr ratios, and 87Sr/86Sr ratios indicate that the weathering intensity is slightly lower for the upper and higher for the deeper soils, which suggest that the sandstone and limestone soil profiles were formed through both accumulation and weathering of in situ weathering residue and input of external detritus or soil from upper land. During weathering of the soils, preferential release of Ca and retention of Sr in soil result in higher Ca/Sr ratios in both labile and carbonate fractions than those in the residue fractions of all soil profiles. The co-variations of Hf/Nb and Zr/Nb ratios, together with those Rb/Sr and 87Sr/86Sr ratios of limestone soils, sandstone soils, and the red residua, demonstrate that their parent materials are

  19. Stable isotopic composition of bottled mineral waters from Romania

    NASA Astrophysics Data System (ADS)

    Bădăluţă, Carmen; Nagavciuc, Viorica; Perșoiu, Aurel

    2015-04-01

    Romania has a high potential of mineral waters resources, featuring one of the largest mineral resources at European and global level. In the last decade, due to increased in consumption of bottled water, numerous brands have appeared on the market, with equally numerous and variable sources of provenance. In this study we have analyzed the isotopic composition of bottled mineral waters from Romania in order to determine their source and authenticity. We have analysed 32 carbonated and 24 non-carbonated mineral waters from Romania. and the results were analysed in comparison with stable isotope data from precipitation and river waters. Generally, the isotopic values of the mineral waters follow those in precipitation; however, differences occur in former volcanic regions (due to deep circulation of meteoric waters and increased exchange with host rock and volcanic CO2), as well as in mountainous regions, where high-altitude recharge occurs.

  20. The chromium isotope composition of reducing and oxic marine sediments

    NASA Astrophysics Data System (ADS)

    Gueguen, Bleuenn; Reinhard, Christopher T.; Algeo, Thomas J.; Peterson, Larry C.; Nielsen, Sune G.; Wang, Xiangli; Rowe, Harry; Planavsky, Noah J.

    2016-07-01

    The chromium (Cr) isotope composition of marine sediments has the potential to provide new insights into the evolution of Earth-surface redox conditions. There are significant but poorly constrained isotope fractionations associated with oxidative subaerial weathering and riverine transport, the major source of seawater Cr, and with partial Cr reduction during burial in marine sediments, the major sink for seawater Cr. A more comprehensive understanding of these processes is needed to establish global Cr isotope mass balance and to gauge the utility of Cr isotopes as a paleoredox proxy. For these purposes, we investigated the Cr isotope composition of reducing sediments from the upwelling zone of the Peru Margin and the deep Cariaco Basin. Chromium is present in marine sediments in both detrital and authigenic phases, and to estimate the isotopic composition of the authigenic fraction, we measured δ53Cr on a weakly acid-leached fraction in addition to the bulk sediment. In an effort to examine potential variability in the Cr isotope composition of the detrital fraction, we also measured δ53Cr on a variety of oxic marine sediments that contain minimal authigenic Cr. The average δ53Cr value of the oxic sediments examined here is -0.05 ± 0.10‰ (2σ, n = 25), which is within the range of δ53Cr values characteristic of the bulk silicate Earth. This implies that uncertainty in estimates of authigenic δ53Cr values based on bulk sediment analyses is mainly linked to estimation of the ratio of Cr in detrital versus authigenic phases, rather than to the Cr-isotopic composition of the detrital pool. Leaches of Cariaco Basin sediments have an average δ53Cr value of +0.38 ± 0.10‰ (2σ, n = 7), which shows no dependency on sample location within the basin and is close to that of Atlantic deepwater Cr (∼+0.5‰). This suggests that authigenic Cr in anoxic sediments may reliably reflect the first-order Cr isotope composition of deepwaters. For Peru Margin samples

  1. Controls over the strontium isotope composition of river water

    NASA Astrophysics Data System (ADS)

    Palmer, M. R.; Edmond, J. M.

    1992-05-01

    Strontium concentrations and isotope ratios have been measured in river and ground waters from the Ganges, Orinoco, and Amazon river basins. When compared with major element concentrations, the data set has allowed a detailed examination of the controls over the strontium isotope systematics of riverine input to the oceans in the following environments: (1) "typical" drainage basins containing limestones, evaporites, shales, and alumino-silicate metamorphic and igneous rocks; (2) shield terrains containing no chemical or biogenic sediments; and (3) the floodplains that constitute the largest areas of many large rivers. The strontium concentration and isotope composition of river waters are largely defined by mixing of strontium derived from limestones and evaporites with strontium derived from silicate rocks. The strontium isotope composition of the limestone endmember generally lies within the Phanerozoic seawater range, which buffers the 87Sr /86Sr ratios of major rivers. A major exception is provided by the rivers draining the Himalayas, where widescale regional metamorphism appears to have led to an enrichment in limestones of radiogenic strontium derived from coexisting silicate rocks. The strontium isotope systematics of rivers draining shield areas are controlled by the intense, transportlimited, nature of the weathering reactions, and thereby limits variations in the strontium flux from these terrains. Floodplains are only a minor source of dissolved strontium to river waters, and precipitation of soil salts in some floodplains can reduce the riverine flux of dissolved strontium to the oceans. The most effective mechanisms for altering the isotope ratio and flux of riverine strontium to the oceans are increased glaciation and large-scale regional metamorphism of the type produced during continental collision. Both mechanisms provide a means for increasing the 87Sr /86Sr ratio of the global riverine flux.

  2. Groundwater changes in evaporating basins using gypsum crystals' isotopic compositions

    NASA Astrophysics Data System (ADS)

    Gatti, E.; Bustos, D.; Allwood, A.; Coleman, M. L.

    2014-12-01

    While the dynamics of groundwater evaporation are well known, it is still challenging to reconstruct the water patterns in areas where water is not available anymore. We selected a specific location in White Sands National Monument (WSNM), New Mexico, to validate a method to extract information from hydrated minerals regarding past groundwater evaporation patterns in evaporitic basins. WSNM has gypsum (CaSO4.2H2O) dunes and crystals precipitated from the evaporation of an ancient lake. Our approach aims to extract the water of crystallization of gypsum and measure its oxygen and hydrogen isotopic compositions, in order to reconstruct the groundwater history of the area. The idea is that as the mother brine evaporates its isotopic composition changes continuously, recorded as water of crystallization in successive growth zones of gypsum. To check if the isotopic composition of the salt could effectively differentiate between distinctive humidity conditions, the methodology was tested first on synthetic gypsum grown under controlled humidity and temperature conditions. T and RH% were maintained constant in a glove box and precipitated gypsum was harvested every 24 hours. d2H and d18O of water of crystallization from the synthetic gypsum was extracted using a specially developed technique on a TC/EA. The brine was measured using a Gas Bench II for d18O and an H-Device for d2H on a Thermo Finnigan MAT 253 mass spectrometer. With the method tested, we measured natural gypsum. In order to identify the growth zones we mapped the surface of the crystals using an experimental space flight XRF instrument. Crystals were then sampled for isotopic analyses. Preliminary results suggest that site-specific groundwater changes can be described by the isotopic variations. We will show that the methodology is a reliable and fast method to quantify hydrological changes in a targeted environment. The study is currently ongoing but the full dataset will be presented at the conference.

  3. The Stable Isotopic Composition of Atmospheric CO2

    NASA Astrophysics Data System (ADS)

    Yakir, D.

    2003-12-01

    When a bean leaf was sealed in a closed chamber under a lamp (Rooney, 1988), in two hours the atmospheric CO2 in the microcosm reached an isotopic steady state with a 13C abundance astonishingly similar to the global mean value of atmospheric CO2 at that time (-7.5‰ in the δ13C notation introduced below). Almost concurrently, another research group sealed a suspension of asparagus cells in a different type of microcosm in which within about two hours the atmospheric O2 reached an isotopic steady state with 18O enrichment relative to water in the microcosm that was, too, remarkably similar to the global-scale offset between atmospheric O2 and mean ocean water (21‰ versus 23.5‰ in the δ18O notation introduced below; Guy et al., 1987). These classic experiments capture some of the foundations underlying the isotopic composition of atmospheric CO2 and O2. First, in both cases the biological system rapidly imposed a unique isotopic value on the microcosms' atmosphere via their massive photosynthetic and respiratory exchange of CO2 and O2. Second, in both cases the biological system acted on materials with isotopic signals previously formed by the global carbon and hydrological cycles. That is, the bean leaf introduced its previously formed organic matter (the source of the CO2 respired into microcosm's atmosphere), and the asparagus cells were introduced complete with local tap water (from which photosynthesis released molecular oxygen). Therefore, while the isotopic composition of the biological system used was slave to long-term processes, intense metabolic processes centered on few specific enzymes (Yakir, 2002) dictated the short-term atmospheric composition.In a similar vein, on geological timescales of millions of years, the atmosphere and its isotopic composition are integral parts of essentially a single dynamic ocean-atmosphere-biosphere system. This dynamic system exchanges material, such as carbon and oxygen, with the sediments and the lithosphere via

  4. The mercury isotope composition of Arctic coastal seawater

    NASA Astrophysics Data System (ADS)

    Štrok, Marko; Baya, Pascale Anabelle; Hintelmann, Holger

    2015-11-01

    For the first time, Hg isotope composition of seawater in the Canadian Arctic Archipelago is reported. Hg was pre-concentrated from large volumes of seawater sampling using anion exchange resins onboard the research vessel immediately after collection. Elution of Hg was performed in laboratory followed by isotope composition determination by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). For comparison, seawater from two stations was shipped to the laboratory and processed within it. Results showed negative mass-dependent fractionation in the range from -2.85 to -1.10‰ for δ202Hg, as well as slightly positive mass-independent fractionation of odd Hg isotopes. Positive mass-independent fractionation of 200Hg was also observed. Samples that were pre-concentrated in the laboratory showed different Hg isotope signatures and this is most probably due to the abiotic reduction of Hg in the dark by organic matter during storage and shipment after sampling. This emphasizes the need for immediate onboard pre-concentration.

  5. Isotopic composition of lithium, potassium, rubidium, and strontium in lunar surface material

    NASA Technical Reports Server (NTRS)

    Zaslavskiy, V. G.; Levskiy, L. K.; Murin, A. N.

    1974-01-01

    The isotopic composition of alkali and alkaline earth elements in the Luna 16 regolith was investigated by the method of thermionic emission, without chemical separation. The isotopic composition of the lithium in two regolith samples did not differ (within the limits 0.5 percent) from the mean of the terrestrial reference standard. At the same time, the observed difference (1 percent) in the isotopic composition of lithium between the samples requires further investigation and confirmation. The isotopic compositions of K and Rb did not differ within the limits of experimental error from the isotopic composition of the reference standard.

  6. Neodymium and strontium isotopic study of Australasian tektites - New constraints on the provenance and age of target materials

    NASA Technical Reports Server (NTRS)

    Blum, Joel D.; Papanastassiou, D. A.; Wasserburg, G. J.; Koeberl, C.

    1992-01-01

    The Nd and Sr isotopic compositions of Australasian tectites (including two flanged Australian tectites, two low-SiO2 Muong Nong-type tectites, and three high-SiO2 Muong Nong-type tectites) and the Nd, Sm, Sr, and Rb concentrations were investigated by isotope-dilution thermal ionization mass spectrometry, and the Sm-Nd and Rb-Sr isotope systematics were used to study the characteristics of the parental material. It is shown that the Nd and Sr isotopic data provide evidence that all Australasian tektites were derived from a single sedimentary formation with a narrow range of stratigraphic ages close to 170 Ma. It is suggested that all of the Australasian tektites were derived from a single impact event and that the australites represent the upper part of a melt sheet ejected at high velocity, whereas the indochinites represent melts formed at a lower level in the target material distributed closer to the area of the impact.

  7. Mass Independent Isotopic Compositions of Aerosol Sulfate and Nitrates

    NASA Astrophysics Data System (ADS)

    Thiemens, M. H.

    2001-12-01

    For nearly a half-century stable isotope ratio measurements have been utilized as a tool to understand sources, fates, and transformation mechanisms of atmospheric molecules. Carbon and oxygen (δ 13C and δ 18O) measurements of CO2 have been instrumental in providing specific details of the carbon cycle. Without these measurements, understanding of the carbon cycle and transfer rates between reservoirs would be considerably diminished. Deuterium and oxygen isotopic measurements of atmospheric water has similarly enhanced the ability to model the atmospheric and geochemical recycling of the hydrologic cycle. Other molecules investigated include, for example, CO, CH4, N2O, SO4, NH, and Cl. The ability to interpret these high precision isotope ratio measurements relies upon a fundamental understanding of the basic physical-chemical processes which produce the alteration of the stable isotope ratio. Such processes typically include thermodynamics (viz a viz isotope exchange), kinetics, and evaporation-condensation. Though the mechanism by which these alterations occur, they all depend in some fashion upon mass differences in the isotopically substituted atoms. In 1983, Thiemens and Heidenreich (1) demonstrated that a chemical process is capable of producing an alteration of stable isotopes which was independent of mass. Subsequent to that time, it has been shown that measurements of mass independent isotopic compositions provide a new view of atmospheric process which may not be derived from single isotope ratio measurements (reviews by (2), (3)). In the past few years, mass independent isotopic compositions have been utilized to understand ancient atmospheres on both Earth and Mars (review by (4)). It has been known for decades that atmospheric sulfate is an extraordinary species. It participates in climate change in its capacity as a cloud condensation nuclei and it is a human and environmental health hazard. By the same token, aerosol nitrate is an environmental

  8. The Nd-, Sr- and Pb-isotopic character of lavas from Taal, Laguna de Bay and Arayat volcanoes, southwestern Luzon, Philippines: Implications for arc magma petrogenesis

    NASA Astrophysics Data System (ADS)

    Mukasa, Samuel B.; Flower, Martin F. J.; Miklius, Asta

    1994-07-01

    Following the amalgamation of a collage of pre-Neogene terranes largely by strike-slip and convergence mechanisms to form the Philippine islands, volcanic chains, related to oppositely dipping subduction zones, developed along the eastern and western margins of the archipelago. There is ample field evidence that this volcanic activity, predominantly calc-alkaline in chemical character, had commenced by the Oligocene. Volcanoes resulting from subduction along the Manila-Negros trench in the west (e.g. Taal, Laguna de Bay and Arayat) form a high-angle linear array, trending away from the MORE field on Pb-isotopic covariation diagrams; have the highest Sr- and lowest Nd-isotopic compositions, of the two chains (but nevertheless plotting above bulk earth on the 87Sr/ 86Sr versus 143Nd/ 144Nd covariation diagram); and exhibit Sm/Nd and Rb/Sr values that are lower and higher, respectively, than the estimated values for bulk earth. While the Sm/Nd and Rb/Sr characteristics are common to both chains, volcanoes associated with the Philippine-East Luzon trench have Pb-isotopic compositions that fall in the Indian Ocean MORB field and that require time-integrated evolution in a high Th/U environment. They also have higher Nd- and lower Sr-isotopic ratios. The source materials of Philippine volcanoes, therefore, have undergone varied recent enrichments in LILE, as indicated by the decoupling of isotopic and elemental ratios. These enrichments, particularly for the western volcanoes, cannot be entirely due to small degrees of partial melting in the mantle wedge, considering that they were accompanied by elevations in radiogenic Pb. Elevated Pb ratios are best explained by the introduction of subducted, continentally derived sediments. The sedimentary component in the western volcanoes is probably the South China Sea sediments derived largely from Eurasia. That this component is not available in the Philippine-East Luzon trench is reflected by the fact that the eastern volcanoes

  9. The Nd-, Sr- and Pb-isotopic character of lavas from Taal, Laguna de Bay and Arayat volcanoes, southwestern Luzon, Philippines: Implications for arc magma petrogenesis

    USGS Publications Warehouse

    Mukasa, S.B.; Flower, M.F.J.; Miklius, Asta

    1994-01-01

    Following the amalgamation of a collage of pre-Neogene terranes largely by strike-slip and convergence mechanisms to form the Philippine islands, volcanic chains, related to oppositely dipping subduction zones, developed along the eastern and western margins of the archipelago. There is ample field evidence that this volcanic activity, predominantly calc-alkaline in chemical character, had commenced by the Oligocene. Volcanoes resulting from subduction along the Manila-Negros trench in the west (e.g. Taal, Laguna de Bay and Arayat) form a high-angle linear array, trending away from the MORE field on Pb-isotopic covariation diagrams; have the highest Sr- and lowest Nd-isotopic compositions, of the two chains (but nevertheless plotting above bulk earth on the 87Sr/86Sr versus 143Nd/144Nd covariation diagram); and exhibit Sm/Nd and Rb/Sr values that are lower and higher, respectively, than the estimated values for bulk earth. While the Sm/Nd and Rb/Sr characteristics are common to both chains, volcanoes associated with the Philippine-East Luzon trench have Pb-isotopic compositions that fall in the Indian Ocean MORB field and that require time-integrated evolution in a high Th/U environment. They also have higher Nd- and lower Sr-isotopic ratios. The source materials of Philippine volcanoes, therefore, have undergone varied recent enrichments in LILE, as indicated by the decoupling of isotopic and elemental ratios. These enrichments, particularly for the western volcanoes, cannot be entirely due to small degrees of partial melting in the mantle wedge, considering that they were accompanied by elevations in radiogenic Pb. Elevated Pb ratios are best explained by the introduction of subducted, continentally derived sediments. The sedimentary component in the western volcanoes is probably the South China Sea sediments derived largely from Eurasia. That this component is not available in the Philippine-East Luzon trench is reflected by the fact that the eastern volcanoes

  10. Oxygen isotopic composition of opaline phytoliths: Potential for terrestrial climatic reconstruction

    SciTech Connect

    Shahack-Gross, R.; Weiner, S.; Shemesh, A.; Yakir, D.

    1996-10-01

    Opaline mineralized bodies are produced by many terrestrial plants and accumulate in certain soils and archaeological sites. Analyses of the oxygen isotopic compositions of these so-called phytoliths from stems and leaves of wheat plants grown in a greenhouse showed a linear relationship with stem and leaf water isotopic compositions and hence, indirectly, rain water isotopic composition. Analyses of wheat plants grown in fields showed that stem phytoliths isotopic composition directly reflects the seasonal air temperature change, whereas leaf phytoliths isotopic composition reflects both temperature and relative humidity. Temperature and the oxygen isotopic composition of stem phytoliths were related by an equation similar to that proposed for marine opal. Oxygen isotopic compositions of fossil phytoliths, and in particular those from stems, could be valuable for reconstructing past terrestrial climate change.

  11. The Abundance and Isotopic Composition of Hg in Extraterrestrial Materials

    NASA Technical Reports Server (NTRS)

    Lauretta, D. S.

    2004-01-01

    During the past three year grant period we made excellent progress in our study of the abundances and isotopic compositions of Hg and other volatile trace elements in extraterrestrial materials. As part of my startup package I received funds to construct a state-of-the-art experimental facility to study gas-solid reaction kinetics. Much of our effort was spent developing the methodology to measure the abundance and isotopic composition of Hg at ultratrace levels in solid materials. In our first study, the abundance and isotopic composition of Hg was determined in bulk samples of the Murchison (CM) and Allende (CV) carbonaceous chondrites. We have continued our study of mercury in primitive meteorites and expanded the suite of meteorites to include other members of the CM and CV chondrite group as well as CI and CO chondrites. Samples of the CI chondrite Orgueil, the CM chondrites Murray, Nogoya, and Cold Bokkeveld, the CO chondrites Kainsaz, Omans, and Isna, and the CV chondrites Vigarano, Mokoia, and Grosnaja were tested. We have developed a thermal analysis ICP-MS technique and applied it to the study of a suite of thermally labile elements (Zn, As, Se, Cd, In, Sn, Sb, Te, Hg, Au, Tl, Pb, and Bi) in geologic materials as well.

  12. Alkali elemental and potassium isotopic compositions of Semarkona chondrules

    USGS Publications Warehouse

    Alexander, C.M. O'D.; Grossman, J.N.

    2005-01-01

    We report measurements of K isotope ratios in 28 Semarkona chondrules with a wide range of petrologic types and bulk compositions as well as the compositions of CPX-mesostasis pairs in 17 type I Semarkona chondrules, including two chondrules with radial alkali zonation and 19 type II chondrules. Despite the wide range in K/Al ratios, no systematic variations in K isotopic compositions were found. Semarkona chondrules do not record a simple history of Rayleigh-type loss of K. Experimentally determined evaporation rates suggest that considerable alkali evaporation would have occurred during chondrule formation. Nevertheless, based on Na CPX-mesostasis distribution coefficients, the alkali contents of the cores of most chondrules in Semarkona were probably established at the time of final crystallization. However, Na CPX-mesostasis distribution coefficients also show that alkali zonation in type I Semarkona chondrules was produced by entry of alkalis after solidification, probably during parent body alteration. This alkali metasomatism may have gone to completion in some chondrules. Our preferred explanation for the lack of systematic isotopic enrichments, even in alkali depleted type I chondrule cores, is that they exchanged with the ambient gas as they cooled. ?? The Meteoritical Society, 2005.

  13. Isotopic composition of precipitation during different atmospheric circulation patterns

    NASA Astrophysics Data System (ADS)

    Brenčič, Mihael; Kononova, Nina; Vreča, Polona

    2016-04-01

    Precipitation generating processes depend on atmospheric circulation patterns and consequently it is expected that its water stable isotopic composition of hydrogen and oxygen is related to them. Precipitation generated at similar atmospheric circulation patterns should have similar empirical distribution of δ2H and δ18O values. There are several approaches in which atmospheric circulation patterns are classified as elementary air circulation mechanisms - ECM; in our approach we have applied Dzerdzeevskii classification. Two types of models of relation between ECM and isotopic composition of precipitation are proposed; first is based on the linear combination of δ2H and δ18O values with precipitation amount weighted average (Brenčič et al., 2015) and the second new one is based on the multiple regression approach. Both approaches make possible also to estimate empirical distributions' dispersion parameters. Application of the models is illustrated on the precipitation records from Ljubljana and Portorož GNIP stations, Slovenia. Estimated values of the parameters for empirical distributions of δ2H and δ18O of each ECM subtype have shown that calculated estimates are reasonable. Brenčič, M., Kononova, N.K., Vreča, P., 2015: Relation between isotopic composition of precipitation and atmospheric circulation patterns. Journal of Hydrology 529, 1422-1432: doi: 10.1016/j.jhydrol.2015.08.040

  14. NBL CRM 112-A: A new certified isotopic composition

    NASA Astrophysics Data System (ADS)

    Thomas, R. B.; Essex, R. M.; Mason, P.

    2007-12-01

    NBL CRM 112-A Uranium Metal Assay Standard is commonly used as a natural uranium isotopic reference material within the earth science mass spectrometry community. The metal is from the same parent material as NBS SRM 960, the uranyl nitrate solution, CRM 145, and the high-purity uranyl nitrate solution CRM 145-B. Because CRM 112-A has not yet been certified for isotopic composition, it has been assumed that this material has a natural 235U/238U (0.0072527), and the δ234U has been determined by measurement (e.g. -37.1‰; Cheng et al., 2000). These values have been widely used to calibrate the concentration of spikes and standards, and to correct measurements for instrument or mass bias. New, preliminary, isotopic measurements on CRM 145 and CRM 112-A performed at New Brunswick Laboratory suggest that these reference materials have a slightly lower 235U/238U and δ234U than have been commonly used. If this is the case, then data using the accepted values may be slightly biased. The significance of this bias will depend on the uncertainty of the measurement, how the CRM 112-A data is used to correct measurement data, the cited values that were used to correct the data, and the final certified values of the CRM. This fall, New Brunswick Laboratory is certifying the isotopic composition of the CRM 112-A metal using high precision thermal ionization mass spectrometry techniques. Upon completion of certification, the new CRM 112- A standard with certified isotopic ratios will provide the earth science community with a well characterized and traceable reference for calibrating and correcting their mass spectrometry measurement systems.

  15. Stable isotope composition of the meteoric precipitation in Croatia.

    PubMed

    Hunjak, Tamara; Lutz, Hans O; Roller-Lutz, Zvjezdana

    2013-01-01

    The precipitation is the input into the water system. Its stable isotope composition has to be known for the proper use and management of water resources. Croatia is not well represented in the Global Network of Isotopes in Precipitation (GNIP) database, and the geomorphology of the country causes specific local conditions. Therefore, at the Stable Isotope Laboratory (SILab), Rijeka, we monitor the stable isotope composition (δ(18)O, δ(2)H) of precipitation. Since δ(18)O and δ(2)H are well correlated, we concentrate the discussion on the δ(18)O distribution. Together with GNIP, our database contains 40 stations in Croatia and in the neighbouring countries. Their different latitudes, longitudes and altitudes give information of great detail, including the influence of the topographic structure on the precipitation in the south-eastern part of Europe, as well as the complex interplay of the different climate conditions in the area. Within a few hundred kilometres, the stable isotope values display a significant change from the maritime character in the south (mean δ(18)O around-6 to-8‰) to the continental behaviour in the north (mean δ(18)O around-8 to-11‰). Depending on the location, the mean δ(18)O values vary with altitude at a rate of approximately-0.2‰/100 m and-0.4‰/100 m, respectively. Also the deuterium excess has been found to depend on location and altitude. The data are being used to construct a δ(18)O map for the entire area. PMID:23937110

  16. Magnesium stable isotope composition of Earth's upper mantle

    NASA Astrophysics Data System (ADS)

    Handler, Monica R.; Baker, Joel A.; Schiller, Martin; Bennett, Vickie C.; Yaxley, Gregory M.

    2009-05-01

    The mantle is Earth's largest reservoir of Mg containing > 99% of Earth's Mg inventory. However, no consensus exists on the stable Mg isotope composition of the Earth's mantle or how variable it is and, in particular, whether the mantle has the same stable Mg isotope composition as chondrite meteorites. We have determined the Mg isotope composition of olivine from 22 mantle peridotites from eastern Australia, west Antarctica, Jordan, Yemen and southwest Greenland by pseudo-high-resolution MC-ICP-MS on Mg purified to > 99%. The samples include fertile lherzolites, depleted harzburgites and dunites, cryptically metasomatised ('dry') peridotites and modally metasomatised apatite ± amphibole-bearing harzburgites and wehrlites. Olivine from these samples of early Archaean through to Permian lithospheric mantle have δ25Mg DSM-3 = - 0.22 to - 0.08‰. These data indicate the bulk upper mantle as represented by peridotite olivine is homogeneous within current analytical uncertainties (external reproducibility ≤ ± 0.07‰ [2 sd]). We find no systematic δ25Mg variations with location, lithospheric age, peridotite fertility, or degree or nature of mantle metasomatism. Although pyroxene may have slightly heavier δ25Mg than coexisting olivine, any fractionation between mantle pyroxene and olivine is also within current analytical uncertainties with a mean Δ25Mg pyr-ol = +0.06 ± 0.10‰ (2 sd; n = 5). Our average mantle olivine δ25Mg DSM-3 = - 0.14 ± 0.07‰ and δ26Mg DSM-3 = - 0.27 ± 0.14‰ (2 sd) are indistinguishable from the average of data previously reported for terrestrial basalts, confirming that basalts have stable Mg isotope compositions representative of the mantle. Olivine from five pallasite meteorites have δ25Mg DSM-3 = - 0.16 to - 0.11‰ that are identical to terrestrial olivine and indistinguishable from the average δ25Mg previously reported for chondrites. These data provide no evidence for measurable heterogeneity in the stable Mg isotope

  17. Probing the Isotopic Composition of Surface Waters Across Isotopic Extremes of Cryogenian Carbonates

    NASA Astrophysics Data System (ADS)

    Bosak, T.; Matys, E. D.; Bird, L. R.; Macdonald, F. A.; Freeman, K. H.

    2012-12-01

    Neoproterozoic carbonate strata record unusually large and positive carbon isotope values (δ13Ccarb from 4 to 10 per mil), and stratigraphically extensive large negative carbon isotope excursions (δ13Ccarb < -5 per mil). Mechanisms that account for the magnitude, the facies distribution and the global abundance of these isotopically extreme carbonates in Neoproterozoic successions remain poorly understood. Little is also known about organisms and metabolisms that cycled carbon in these carbonate strata, because they rarely contain well-preserved organic-rich fossils. To better understand the cycling of carbon during the deposition of the 715-635 Ma Tayshir member of the Tsagaan Oloom Formation, Mongolia, we analyzed δ13Cfossil of two types of organic fossils that occur in 13C- enriched carbonates (+ 5 to 9.9 per mil) and within 13C-depleted carbonates of the Tayshir anomaly (-3 to -6 per mil). Because these organic microfossils are remarkably similar to the tests of modern planktonic, herbivorous tintinnid ciliates and benthic macroscopic red algae, respectively, they can be used as tracers of organic matter production in surface waters. Fossil tests were extracted by acid maceration, cleaned and analyzed morphologically and microscopically. Their carbon isotopic composition was measured using a nano-scaled elemental analyzer inlet (nano-EA-IRMS), with ±1 per mil analytical precision. To date, we analyzed 12 samples of 100-150 organic tests, representing 3 different fossiliferous parts of the Tayshir anomaly (δ13Ccarb < -3 per mil) and 3 different strata predating the Tayshir anomaly (δ13Ccarb > +5 per mil), respectively. More samples, including those of fossil algae and tests from the carbonate strata overlying the Tayshir anomaly, are currently being analyzed. Initial data reveal a rather constant isotopic composition of organic carbon in fossil tests (δ13Cfossil), with values of -23 ±1 per mil both within 13C-enriched and 13C-depleted carbonates. The

  18. The triple isotopic composition of oxygen in leaf water

    NASA Astrophysics Data System (ADS)

    Landais, A.; Barkan, E.; Yakir, D.; Luz, B.

    2006-08-01

    The isotopic composition of atmospheric O 2 depends on the rates of oxygen cycling in photosynthesis, respiration, photochemical reactions in the stratosphere and on δ17O and δ18O of ocean and leaf water. While most of the factors affecting δ17O and δ18O of air O 2 have been studied extensively in recent years, δ17O of leaf water—the substrate for all terrestrial photosynthesis—remained unknown. In order to understand the isotopic composition of atmospheric O 2 at present and in fossil air in ice cores, we studied leaf water in field experiments in Israel and in a European survey. We measured the difference in δ17O and δ18O between stem and leaf water, which is the result of isotope enrichment during transpiration. We calculated the slopes of the lines linking the isotopic compositions of stem and leaf water. The obtained slopes in ln( δ17O + 1) vs. ln( δ18O + 1) plots are characterized by very high precision (˜0.001) despite of relatively large differences between duplicates in both δ17O and δ18O (0.02-0.05‰). This is so because the errors in δ18O and δ17O are mass-dependent. The slope of the leaf transpiration process varied between 0.5111 ± 0.0013 and 0.5204 ± 0.0005, which is considerably smaller than the slope linking liquid water and vapor at equilibrium (0.529). We further found that the slope of the transpiration process decreases with atmospheric relative humidity ( h) as 0.522-0.008 × h, for h in the range 0.3-1. This slope is neither influenced by the plant species, nor by the environmental conditions where plants grow nor does it show strong variations along long leaves.

  19. Light and heavy element isotopic compositions of mainstream SiC grains.

    SciTech Connect

    Amari, S.; Clayton, R. N.; Davis, A. M.; Lewis, R. S.; Pellin, M. J.

    1999-02-03

    Although a variety of types of pre-solar SiC grains have been classified by their C, N, and Si isotopic composition, the majority of such grains are so-called mainstream grains and are believed to have come from asymptotic giant branch stars [1]. We have previously reported the Mo isotopic compositions of presolar SiC grains whose C, N, and Si isotopic compositions were not known [2]. Since most presolar SiC grains fall in the mainstream group, we assumed that these grains were mainstream. The excellent match of the Mo isotopic data with expectations for nucleosynthesis in AGB stars was consistent with this identification. In order to better understand the distribution of isotopic compositions in presolar grains, we have begun to measure heavy element isotopic compositions of presolar SiC grains of known C, N and Si isotopic composition.

  20. Silicon isotopes in granulite xenoliths: Insights into isotopic fractionation during igneous processes and the composition of the deep continental crust

    NASA Astrophysics Data System (ADS)

    Savage, Paul S.; Georg, R. Bastian; Williams, Helen M.; Halliday, Alex N.

    2013-03-01

    The silicon (Si) cycle is of great current interest but the isotopic composition of the continental crust has not been determined. Magmatic differentiation generates liquids with heavier Si and the lower crust, thought to be dominated by cumulates and restites, is predicted to have a light isotopic composition. This is borne out by the composition of many types of granite, which appear to have relative light Si for their silica content. Here we report the Si isotopic compositions of two granulite facies xenolith suites, from the Chudleigh and McBride volcanic provinces, Australia, providing new constraints on deep crustal processes and the average composition of the deep continental crust. The xenoliths display a range of isotopic compositions (δ30Si=-0.43‰ to -0.15‰) comparable to that measured previously for igneous rocks. The isotopic compositions of the McBride xenoliths reflect assimilation and fractional crystallisation (AFC) and/or partial melting processes. Silicon and O isotopes are correlated in the McBride suite and can be explained by AFC of various evolved parent melts. In contrast, the Chudleigh xenoliths have Si isotope compositions predominantly controlled by the specific mineralogy of individual cumulates. Using the xenolith data and a number of weighting methods, the Si isotope compositions of the lower and middle crust are calculated to be δ30Si=-0.29±0.04‰ (95% s.e.) and -0.23±0.04‰ (95% s.e.) respectively. These values are almost identical to the composition of the Bulk Silicate Earth, implying minimal isotope fractionation associated with continent formation and no light lower crustal reservoir.

  1. Determination of the combined isotopic composition of atmospheric methane

    NASA Astrophysics Data System (ADS)

    Butterworth, Anna Lucy

    Methane is an important global warming gas, present in the atmosphere at a concentration of 1.714 ppmv. Its concentration has more than doubled since the start of the industrial revolution and the increase is generally acknowledged to be due to human activities. The continued rise in concentration of methane is believed to be contributing to an increase in mean global temperature. Recently, the global budget of methane has been constrained by balancing the magnitude and isotopic signature of the sources and sinks with the measured tropospheric abundance and isotopic composition. The dual element stable isotopic composition (δ13C and /delta D) of methane may be used to characterise different sources of methane. Traditional methods of determining the δ13C value and the /delta D value of methane require large sample sizes. An alternative approach to investigating the stable isotopic composition of methane was to determine the combined ratio of 13CH4 and 12CH3D (mass 17) relative to 12CH4 (mass 16) and quote the results on a δ17M scale. A static-vacuum mass spectrometer has been developed specifically for the determination of the 17M/16M ratio of sub- nanomole quantities of methane with a δ17M precision of [/pm]0.2/ /perthous. An on-line sample preparation technique has also been developed to separate the methane from 10 ml of air and provide a pure, dry, ~300 picomole methane sample for isotope ratio determination. The overall δ17M precision of the analysis of the methane in air samples was [<][/pm]0.5/ /perthous. A number of sources of atmospheric methane have been investigated, demonstrating that sources may be distinguished from each other on the δ17M scale. The very small sample requirements for the instrument permitted a simple air sampling procedure to be employed, which was particularly useful for collecting air samples in remote locations. Air samples, containing methane emitted by termites, were collected from a tropical rainforest. The methane produced

  2. BOREAS TE-5 CO2 Concentration and Stable Isotope Composition

    NASA Technical Reports Server (NTRS)

    Hall, Forrest G. (Editor); Curd, Shelaine (Editor); Ehleriinger, Jim; Brooks, J. Renee; Flanagan, Larry

    2000-01-01

    The BOREAS TE-5 team collected measurements in the NSA and SSA on gas exchange, gas composition, and tree growth. This data set contains measurements of the concentration and stable carbon (C-13/C-12 and oxygen (O-18/O-16) isotope ratios of atmospheric CO2 in air samples collected at different heights within forest canopies. The data were collected to determine the influence of photosynthesis and respiration by the forest ecosystems on the concentration and stable isotope ratio of atmospheric CO2 These measurements were collected at the SSA during each 1994 IFC at OJP, OBS, and OA sites. Measurements were also collected at the NSA during each 1994 IFC at the OJP, T6R5S TE UBS, and T2Q6A TE OA sites. The stable isotope ratios are expressed using standard delta notation and in units of per mil. The isotope ratios are expressed relative to the international standard, PDB, for both carbon and oxygen samples. The data are stored in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Activity Archive Center (DAAC).

  3. Isotopic composition of strontium in sea water throughout Phanerozoic time

    USGS Publications Warehouse

    Peterman, Z.E.; Hedge, C.E.; Tourtelot, H.A.

    1970-01-01

    Isotopic analyses of strontium in primary fossil carbonate reveal significant variations in Sr87 Sr86 of sea water during the Phanerozoic. The strontium isotopic composition may have been uniform from the Ordovician through the Mississippian, with an average Sr87 Sr86 of 0.7078. A subsequent decrease in this value into the Mesozoic is interrupted by two provisionally documented positive pulses in Sr87 Sr86-one in the Early Pennsylvanian and one in the Early Triassic. The lowest observed value (0.7068) occurred in Late Jurassic time, and this was followed by a gradual increase to 0.7075 in the Late Cretaceous and a more rapid increase through the Tertiary to 0.7090 for modern sea water. These variations are thought to be the result of a complex interplay of periods of intense volcanism and epeirogenic movements of the continents on a worldwide scale. ?? 1970.

  4. On the mean oxygen isotope composition of the Solar System

    NASA Astrophysics Data System (ADS)

    Ozima, M.; Podosek, F. A.; Higuchi, T.; Yin, Q.-Z.; Yamada, A.

    2007-02-01

    Since the first discovery of extraordinary oxygen isotope compositions in carbonaceous meteorites by Clayton et al. [Clayton, R.N., Grossman, L., Mayeda, T.K., 1973. Science 182, 485-488], numerous studies have been done to explain the unusual mass-independent isotope fractionation, but the problem is still unresolved to this day. Clayton's latest interpretation [Clayton, R.N., 2002. Nature 415, 860-861] sheds new light on the problem, and possible hypotheses now seem to be fairly well defined. A key issue is to resolve whether the oxygen isotopes in the Solar System represented by the Sun (solar oxygen) are the same as oxygen isotopes in planetary objects such as bulk meteorites, Mars, Earth, and Moon, or whether the solar oxygen is more similar to the lightest oxygen isotopes observed in CAIs (Calcium Aluminum-rich Inclusions) in primitive meteorites. Here, we examined the problem using oxygen isotope analytical data of about 400 bulk meteorite samples of various classes or types (data compiled by K. Lodders). We used in our discussion exclusively the parameter Δ 17O, a direct measure of the degree of mass-independent isotope fractionation of oxygen isotopes. When Δ 17O is arranged according to a characteristic size of their host planetary object, it shows a systematic trend: (1) Δ 17O values scatter around zero; (2) the scatter from the mean (Δ 17O=0) decreases with increasing representative size of the respective host planetary object. This systematic trend is easily understood on the basis of a hierarchical scenario of planetary formation, that is, larger planetary objects have formed by progressive accretion of planetesimals by random sampling over a wide spectrum of proto-solar materials. If this progressive random sampling of planetesimals were the essential process of planetary formation, the isotopic composition of planetary oxygen should approach that of the solar oxygen. To test this random sampling hypothesis, we applied a multiscale, multistep

  5. Perchlorate in the Great Lakes: isotopic composition and origin.

    PubMed

    Poghosyan, Armen; Sturchio, Neil C; Morrison, Candice G; Beloso, Abelardo D; Guan, Yunbin; Eiler, John M; Jackson, W Andrew; Hatzinger, Paul B

    2014-10-01

    Perchlorate is a persistent and mobile contaminant in the environment with both natural and anthropogenic sources. Stable isotope ratios of oxygen (δ(18)O, Δ(17)O) and chlorine (δ(37)Cl) along with the abundance of the radioactive isotope (36)Cl were used to trace perchlorate sources and behavior in the Laurentian Great Lakes. These lakes were selected for study as a likely repository of recent atmospheric perchlorate deposition. Perchlorate concentrations in the Great Lakes range from 0.05 to 0.13 μg per liter. δ(37)Cl values of perchlorate from the Great Lakes range from +3.0‰ (Lake Ontario) to +4.0‰ (Lake Superior), whereas δ(18)O values range from -4.1‰ (Lake Superior) to +4.0‰ (Lake Erie). Great Lakes perchlorate has mass-independent oxygen isotopic variations with positive Δ(17)O values (+1.6‰ to +2.7‰) divided into two distinct groups: Lake Superior (+2.7‰) and the other four lakes (∼+1.7‰). The stable isotopic results indicate that perchlorate in the Great Lakes is dominantly of natural origin, having isotopic composition resembling that measured for indigenous perchlorate from preindustrial groundwaters of the western USA. The (36)Cl/Cl ratio of perchlorate varies widely from 7.4 × 10(-12) (Lake Ontario) to 6.7 × 10(-11) (Lake Superior). These (36)ClO4(-) abundances are consistent with an atmospheric origin of perchlorate in the Great Lakes. The relatively high (36)ClO4(-) abundances in the larger lakes (Lakes Superior and Michigan) could be explained by the presence of (36)Cl-enriched perchlorate deposited during the period of elevated atmospheric (36)Cl activity following thermonuclear bomb tests in the Pacific Ocean. PMID:25171443

  6. Stable isotope composition of precipitation over southeast Asia

    NASA Astrophysics Data System (ADS)

    AraguáS-AraguáS, Luis; Froehlich, Klaus; Rozanski, Kazimierz

    1998-11-01

    Spatial and temporal variability of the stable isotope composition of precipitation in the southeast Asia and western Pacific region is discussed, with emphasis on the China territory, based on the database of the International Atomic Energy Agency/World Meteorological Organization Global Network "Isotopes in Precipitation" and the available information on the regional climatology and atmospheric circulation patterns. The meteorological and pluviometric regime of southeast Asia is controlled by five different air masses: (1) polar air mass originating in the Arctic, (2) continental air mass originating over central Asia, (3) tropical-maritime air mass originating in the northern Pacific, (4) equatorial-maritime air mass originating in the western equatorial Pacific, and (5) equatorial-maritime air mass originating in the Indian Ocean. The relative importance of different air masses in the course of a given year is modulated by the monsoon activity and the seasonal displacement of the Intertropical Convergence Zone (ITCZ). Gradual rain-out of moist, oceanic air masses moving inland, associated with monsoon circulation, constitutes a powerful mechanism capable of producing large isotopic depletions in rainfall, often completely overshadowing the dependence of δ18O and δ2H on temperature. For instance, precipitation at Lhasa station (Tibetan Plateau) during rainy period (June-September) is depleted in 18O by more than 6‰ with respect to winter rainfall, despite of 10°C higher surface air temperature in summer. This characteristic isotopic imprint of monsoon activity is seen over large areas of the region. The oceanic air masses forming the two monsoon systems, Pacific and Indian monsoon, differ in their isotope signatures, as demonstrated by the average δ18O of rainfall, which in the south of China (Haikou. Hong Kong) is about 2.5‰ more negative than in the Bay of Bengal (Yangoon). Strong seasonal variations of the deuterium excess values in precipitation

  7. Isotope Fractionation During N Mineralization and the N Isotope Composition of Terrestrial Ecosystem N Pools

    NASA Astrophysics Data System (ADS)

    Dijkstra, P.; Schwartz, E.; Hungate, B. A.; Hart, S. C.

    2008-12-01

    It has been an open question for several decades whether N mineralization is a fractionating process. This question is important for N cycling in terrestrial ecosystems because even a small fractionation during N mineralization could potentially have a large influence on the N isotope composition of other ecosystem N pools. Fractionation during N mineralization should result in a difference between the N isotope composition of the soil microorganisms, that of its substrates, and products. We analyzed the N isotope composition of the soil microbial biomass in a variety of ecosystems, and found that it was 15N enriched compared to that of other soil N pools, such as soil soluble, organic and inorganic N (Dijkstra et al. 2006a,b). We observed a negative correlation between the 15N enrichment of the microorganisms and the relative C and N availability for soil from ecosystems in Hawaii and Arizona, across a broad range of climates, grasslands and forests, and more than four million years of ecosystem development. This suggests that during N dissimilation (and associated transaminations) and N export, the lighter 14N N isotope is preferentially removed in a manner similar to that proposed for animals and ectomycorrhizae. This was further confirmed by the positive correlation between microbial 15N enrichment and net N mineralization rate (Dijkstra et al. 2008, Ecology Letters 11: 389-397) and by culture experiments with Escherichia coli (Collins et al. 2008). Since mineralization is the largest flux of N in ecosystems, fractionation during N mineralization has the potential to influence the N isotope composition of other N pools, such as inorganic N, plant N and soil organic matter N. We demonstrate that the N isotope compositions of these ecosystem N pools exhibit differences that are consistent with fractionation during N mineralization. Our results show that the N isotope composition can be used as a measure to trace N mineralization and decomposition in ecosystems

  8. The concentration and isotopic composition of osmium in the oceans

    SciTech Connect

    Sharma, M.; Papanastassiou, D.A.; Wasserburg, G.J.

    1997-08-01

    Osmium is one of the rarer elements in seawater. Analytical difficulties have previously prevented the direct measurement of the osmium concentration and isotopic composition in seawater. We report a chemical separation procedure that yields quantitative extraction of osmium standard and of osmium tracer by iron hydroxide precipitation from seawater doped with osmium standard, osmium tracer, and FeCl{sub 3}. The iron hydroxide precipitate is processed to extract osmium, using techniques developed for iron meteorites. Utilizing this procedure, water samples from the Pacific and Atlantic oceans were analyzed for osmium concentration and isotopic composition. Direct determination of the osmium concentration of seawater gives between 15 and 19 fM kg{sup -1}. Detailed experiments on different aliquots of one seawater sample from the North Atlantic Ocean, keeping the amounts of reagents constant, yield concentrations from 16 to 19 fM kg{sup -1}. The variability in concentration is outside the uncertainty introduced because of blanks and indicates a lack of full equilibration between the osmium tracer and seawater osmium. The most reliable osmium concentration of the North Atlantic deep ocean water is 19 fM kg {sup -1} with the {sup 187}Os/{sup 186}Os ratio being 8.7{+-}2 (2{sigma}). Detailed experiments on one seawater sample from the Central Pacific Ocean indicate that the most reliable osmium concentration of the deep ocean water from the Central Pacific is 19 fM kg{sup -1} with the {sup 187}Os/{sup 186}Os ratio being 8.7{+-}0.3 (2{sigma}). The directly measured osmium isotopic composition of the oceans is in good agreement with that obtained from the analysis of some rapidly accumulating organic rich sediments. A sample of ambient seawater around the Juan de Fuca Ridge gave {sup 187}Os/{sup 186}Os = 6.9{+-} 0.4. 42 refs., 6 figs., 4 tabs.

  9. Modeling the carbon isotope composition of bivalve shells (Invited)

    NASA Astrophysics Data System (ADS)

    Romanek, C.

    2010-12-01

    The stable carbon isotope composition of bivalve shells is a valuable archive of paleobiological and paleoenvironmental information. Previous work has shown that the carbon isotope composition of the shell is related to the carbon isotope composition of dissolved inorganic carbon (DIC) in the ambient water in which a bivalve lives, as well as metabolic carbon derived from bivalve respiration. The contribution of metabolic carbon varies among organisms, but it is generally thought to be relatively low (e.g., <10%) in shells from aquatic organism and high (>90%) in the shells from terrestrial organisms. Because metabolic carbon contains significantly more C-12 than DIC, negative excursions from the expected environmental (DIC) signal are interpreted to reflect an increased contribution of metabolic carbon in the shell. This observation contrasts sharply with modeled carbon isotope compositions for shell layers deposited from the inner extrapallial fluid (EPF). Previous studies have shown that growth lines within the inner shell layer of bivalves are produced during periods of anaerobiosis when acidic metabolic byproducts (e.g., succinic acid) are neutralized (or buffered) by shell dissolution. This requires the pH of EPF to decrease below ambient levels (~7.5) until a state of undersaturation is achieved that promotes shell dissolution. This condition may occur when aquatic bivalves are subjected to external stressors originating from ecological (predation) or environmental (exposure to atm; low dissolved oxygen; contaminant release) pressures; normal physiological processes will restore the pH of EPF when the pressure is removed. As a consequence of this process, a temporal window should also exist in EPF at relatively low pH where shell carbonate is deposited at a reduced saturation state and precipitation rate. For example, EPF chemistry should remain slightly supersaturated with respect to aragonite given a drop of one pH unit (6.5), but under closed conditions

  10. The carbon isotopic composition of Novo Urei diamonds

    NASA Technical Reports Server (NTRS)

    Fisenko, A. V.; Semjenova, L. F.; Verchovsky, A. B.; Russell, S. S.; Pillinger, C. T.

    1993-01-01

    The carbon isotopic composition of diamond grains isolated from the Novo Urei meteorite are discussed. A diamond separate was obtained from 2g of whole rock using the chemical treatments described aimed at obtaining very pure diamond. X ray diffraction of the residue, which represented 5000 ppm of the parent mass, indicated only the presence of the desired mineral. The diamond crystals were 1-30 microns in diameter, and some grains had a yellow color. The chemical treatments were followed by a size separation to give a 1-10 microns and a 5-30 microns fraction, which were named DNU-1 and DNU-2, respectively.

  11. Isotopic composition of cosmic-ray boron and nitrogen

    NASA Technical Reports Server (NTRS)

    Krombel, K. E.; Wiedenbeck, M. E.

    1988-01-01

    New measurements of the cosmic-ray boron and nitrogen isotopes at earth and of the elemental abundances of boron, carbon, nitrogen, and oxygen are presented. A region of mutually allowed values for the cosmic-ray nitrogen source ratios is determined, and the cosmic-ray escape mean free path is determined as a function of energy using a leaky box model for cosmic-ray propagation in the Galaxy. Relative to O-16, a N-15 source abundance consistent with solar system composition and a N-14 source abundance which is a factor of about three underabundant relative to the solar value are found.

  12. Isotope and trace element geochemistry of lamprophyres and syenites from different areas of South-Chuya complex, SE Altai.

    NASA Astrophysics Data System (ADS)

    Vasyukova, Elena

    2016-04-01

    Major and trace elements and radiogenic isotope data are reported for lamprophyres and syenites of South-Chuya complex associated with ore districts in South East of Gornyi Altai, Russia. Dikes of lamprophyres form big area, elongated from north-west to south-east. Within the area of complex dikes distribute irregularly accompanied the fault zones. Lamprophyres of three largest areas, named Aktash, South Chuya and Yustyd were characterized in terms of geology, petro- and geochemistry, isotopic composition. Some of the lamprophyres judging by the high mg'>60 reveal mantle signatures. They reveal round TRE patterns typical of the primitive low degree partial melts but with the negative Nb- Ta anomalies. The others with the lower mg' suggest their differentiation and contamination in crust material. They reveal slightly lower level of TRE and lower troughs of all HFSE. All dikes had intruded in the period of 250-235 Ma, have similar mineralogical, petro- and geochemistry characteristics which were the reasons for unite all of them in one complex. On the most of geochemistry diagrams dikes from 3 areas form their own, but intersected clusters. But on the isotopic diagrams (Sm/Nd and Rb/Sr systems) they show the principle dissimilarity between dikes from various areas. Yustyd lamprophyres initial isotopic characteristics are close to the BSE. The south-chuya rocks isotopic compositions are more enriched by 87Sr/86Sr and have negative ɛNd (-2.84..-4.05). Contamination by the lower crust material suggested at the early stage during the formation of the lamprophyres. Bu the Yustyd lamprophyres were contaminated also during the ascend by the upper crust. Two competitive hypotheses n the isotopic composition are dicussed: 1) different sources or 2) different proportions between the material from the same sources, which ensemble generate the parental magma for the rocks.

  13. On the isotopic composition of magmatic carbon in SNC meteorites

    NASA Technical Reports Server (NTRS)

    Wright, I. P.; Grady, M. M.; Pillinger, C. T.

    1992-01-01

    SNC meteorites are thought, from many lines of evidence, to come from Mars. A line of investigation which has been pursued in our laboratory over the years involves measurement of the stable isotopic composition of carbon, in its various forms, in SNC meteorites. In order to establish a firm basis for studying the isotopic systematics of carbon in the martian surface environment, it is first necessary to try and constrain the delta C-13 of bulk Mars. Taking all of the available information, it would seem that the delta C-13 of the Earth's mantle lies somewhere in the range of -5 to -7 percent. Preliminary assessment of magnetic carbon in SNC meteorites, would tend to suggest a delta C-13 of 20 to 30 percent, which is conspicuously different from that of the terrestrial mantle. It is not obvious why there should be such a difference between the two planets, although many explanations are possible. One of these possibilities, that previous delta C-13 measurements for magnetic carbon in SNC meteorites are in error to some degree, is being actively investigated. The most recent results seem to constrain the theta C-13 of the magnetic carbon in SNC meteorites to about -20 percent, which is not at odds with previous estimates. As such, it is considered that a detailed investigation of the carbon isotopic systematics of martian surface materials does have the necessary information with which to proceed.

  14. Chemical and isotopic study of extraterrestrial particles from the ocean floor

    NASA Technical Reports Server (NTRS)

    Papanastassiou, D. A.; Wasserburg, G. J.; Brownlee, D. E.

    1983-01-01

    An Rb-Sr isotopic analysis of deep-sea spherules (DSS) from the Pacific, vesicular iridium-rich glassy objects (VIRGO) from an Antarctic-Ocean diatomaceous-ooze core, and equigranular objects (EGO) associated with or included in VIRGO, is reported. The techniques of sample collection, preparation, chemical analysis, and isotopic analysis (by mass spectrometry) are described in detail, and the results are presented in tables. The Sr-87/Sr-86 determination has a precision of 1-2 percent in microsamples of 2-8 x 10 to the 11th Sr atoms. The DSS are found to have Sr concentrations and Sr-87/Sr-86 (0.730-0.757) typical of chondritic meteorites. Extreme Rb depletion is attributed to volatization during meteoroid atmospheric heating. The VIRGO, while having major-element compositions like that of meteorites and high Ir levels suggesting extraterrestrial origin, have Sr-87/Sr-86 = 0.703-0.705; and the associated EGO has Sr-87/Sr-86 = 0.701 + or - 0.001, typical of MORB or basaltic achondrites. Hence their extraterrestrial origin is not proved, and some lithic component other than the EGO must be the source of the high Ir concentration.

  15. Chemical and isotopic study of extraterrestrial particles from the ocean floor

    NASA Astrophysics Data System (ADS)

    Papanastassiou, D. A.; Wasserburg, G. J.; Brownlee, D. E.

    1983-09-01

    An Rb-Sr isotopic analysis of deep-sea spherules (DSS) from the Pacific, vesicular iridium-rich glassy objects (VIRGO) from an Antarctic-Ocean diatomaceous-ooze core, and equigranular objects (EGO) associated with or included in VIRGO, is reported. The techniques of sample collection, preparation, chemical analysis, and isotopic analysis (by mass spectrometry) are described in detail, and the results are presented in tables. The Sr-87/Sr-86 determination has a precision of 1-2 percent in microsamples of 2-8 x 10 to the 11th Sr atoms. The DSS are found to have Sr concentrations and Sr-87/Sr-86 (0.730-0.757) typical of chondritic meteorites. Extreme Rb depletion is attributed to volatization during meteoroid atmospheric heating. The VIRGO, while having major-element compositions like that of meteorites and high Ir levels suggesting extraterrestrial origin, have Sr-87/Sr-86 = 0.703-0.705; and the associated EGO has Sr-87/Sr-86 = 0.701 + or - 0.001, typical of MORB or basaltic achondrites. Hence their extraterrestrial origin is not proved, and some lithic component other than the EGO must be the source of the high Ir concentration.

  16. Microphysical controls on the isotopic composition of wintertime orographic precipitation

    NASA Astrophysics Data System (ADS)

    Moore, M.; Blossey, P. N.; Muhlbauer, A.; Kuang, Z.

    2016-06-01

    The sensitivity of mixed-phase orographic clouds, precipitation, and their isotopic content to changes in dynamics, thermodynamics, and microphysics is explored in idealized two-dimensional flow over a mountain barrier. These simulations use the Weather Research and Forecasting (WRF) model with stable water isotopologues (HDO and H218O), which have been integrated into the Thompson microphysics scheme within WRF as part of the present project. In order to understand how the isotopic composition of precipitation (δ18Oprecip) is fixed, the mountain height, temperature, and the prescribed cloud droplet number concentration (CDNC) have been varied in a series of simulations. For the given range of values explored in this work, changes in mountain height and temperature induce stronger responses in domain-averaged δ18Oprecip than do changes in CDNC by a factor of approximately 10. The strongest response to changing CDNC leads to local variations of δ18Oprecip of about 3‰, though those occur in regions of weak precipitation (<0.1 mm h-1). Changes in δ18Oprecip can be understood through the microphysical pathways by which precipitable hydrometeors are formed and by the isotopic signature associated with each pathway. The decrease in δ18Oprecip with increasing mountain height is not just a function of decreasing temperature but also reflects the changing contributions and distinct isotopic signatures of riming of cloud liquid and vapor deposition onto snow, the leading sources of precipitation in these simulations. The changes in δ18Oprecip with mountain height, temperature, and CDNC are governed in part by the microphysical pathways through which precipitating hydrometeors are formed and grow.

  17. The Li isotopic composition of Oldoinyo Lengai: Nature of the mantle sources and lack of isotopic fractionation during carbonatite petrogenesis

    NASA Astrophysics Data System (ADS)

    Halama, Ralf; McDonough, William F.; Rudnick, Roberta L.; Keller, Jörg; Klaudius, Jurgis

    2007-02-01

    Lithium concentrations and Li isotope compositions are reported for natrocarbonatites and silicate lavas from Oldoinyo Lengai, Tanzania. Natrocarbonatites are characterized by very high Li contents (211-294 ppm) and a narrow range of δ7Li values between + 3.3 and + 5.1. These Li isotope compositions overlap with those reported for MORB and OIB and suggest that the natrocarbonatites reflect the Li isotopic composition of their mantle source. Co-genetic silicate lavas, covering a wide compositional spectrum, show no obvious isotopic fractionation as a function of igneous differentiation or liquid immiscibility. Primitive olivine melilitites (Mg# = 58-70), considered to be parental magmas, contain 14-23 ppm Li and have δ7Li values of + 2.4 to + 4.4. A highly differentiated, peralkaline nephelinite (Mg# = 12), likely to be related to the natrocarbonatites by liquid immiscibility, has about twice as much Li as the melilitite (57 ppm), but a similar isotopic composition (δ7Li = + 3). In contrast, a phonolite with 15 ppm Li has a lighter Li isotope composition (δ7Li = - 0.4), which may reflect assimilation of isotopically light lower crustal mafic granulites, a conclusion supported by radiogenic isotope data. Clinopyroxene and olivine separates from the silicate lavas have uniformly lower Li concentrations (3-15 ppm) and lower δ7Li values (δ7Li = - 2.9 to - 0.5) than the respective whole-rocks, with Δ7Liwhole-rock-mineral between 1.4 and 6.3. This difference between whole-rock and mineral data is interpreted to reflect diffusion-driven isotopic fractionation.

  18. The Abundance and Isotopic Composition of Hg in Extraterrestrial Materials

    NASA Technical Reports Server (NTRS)

    Blum, J. D.; Klaue, Bjorn

    2005-01-01

    During the three year grant period we made excellent progress in our study of the abundances and isotopic compositions of Hg and other volatile trace elements in extraterrestrial materials. At the time the grant started, our collaborating PI, Dante Lauretts, was a postdoctoral research associate working with Peter Buseck at Arizona State University. The work on chondritic Hg was done in collaboration with Dante Lauretta and Peter Buseck and this study was published in Lauretta et a1 (2001a). In July, 2001 Dante Lauretta accepted a position as an Assistant Professor in the Lunar and Planetary Laboratory at the University of Arizona. His funding was transferred and this grant has supported much of his research activities during his first two years at the U of A. Several other papers are in preparation and will be published soon. We presented papers on this topic at Goldschmidt Conferences, the Lunar and Planetary Science Conferences, and the Annual Meetings of the Meteoritical Society. The work done under this grant has spurred several new directions of inquiry, which we are still pursuing. Included in this paper are the studies of bulk abundances and isotopic compositions of metreoritic Mercury, and the development of a thermal analysis ICP-MS technique applied to thermally liable elements.

  19. Genetic Effect on Carbon-Isotope Composition of a Plant

    NASA Astrophysics Data System (ADS)

    Yeh, H.

    2005-05-01

    Stable carbon isotopes of organic sediments are potential tools in investigating a wide spectrum of geological problems. These include paleoclimate, paleoecology, and the origin of life. The quality of the information the tools provides depends largely on our knowledge on the factors determining the isotopic composition of a plant. This is because most biogenic organic sediments are derived from plants. The factors can be grouped into internal and external. The internal factors are ultimately attributable to the genetic make-up of a plant. The most well known internal factor is the photosynthetic pathway. Others include structure of the leave tissue and metabolic characteristics of a plant. External factors are concentration and the isotopic composition of the source CO2 and the physical and chemical conditions of the plant's growth environments. This study addresses primarily the genetic effect, the internal factors. Based on the results of two suites of natural plant samples, it is concluded that the difference in photosynthetic pathway entails about 20.0 % of spread in terms of ä13CPDB values. Genetic effect is also accountable for up to 7.0 to 8.0 % spread in ä13CPDB values within a single category of photosynthetic pathway (i.e. the Calvin cycle). With constrains from the relevant known knowledge, it is concluded that the ä13CPDB values of terrestrial plants are probably ranging from - 8.0 to equal or less than -44.9 %. This range of ä13CPDB values may also be considered the bio-signature of organic sediments of great antiquity.

  20. Lithium Isotopic Composition of the Deep Continental Crust

    NASA Astrophysics Data System (ADS)

    Teng, F.; McDonough, W. F.; Rudnick, R. L.; Gao, S.

    2004-12-01

    We have investigated the Li isotopic composition of the deep continental crust by measuring composite samples from Archean high-grade metamorphic terranes in East China and granulite-facies xenoliths from East China (Hannuoba suite) and Queensland, Australia (Chudleigh and McBride suites). The 30 composite samples, including TTG gneiss, amphibolites and felsic to mafic granulites, have a narrow range of δ 7Li values from +1.7 to +7.5‰ , with an average of +4 ± 1.4‰ (1σ ), which is indistinguishable from the upper mantle. In contrast, the three granulite xenolith suites display a much larger range in δ 7Li, from +15.7 to -17.9‰ with average values decreasing in the order: Hannuoba (-0.7 ± 4.9‰ (1σ , 18 samples)), Chudleigh (-2.5 ± 5.5‰ (1σ , 14 samples)) and McBride (-3.8 ± 7.6‰ (1σ , 12 samples)). The xenoliths are, on average, lighter than the high-grade metamorphic terrane composites. The Li concentrations are also variable with xenoliths having lower Li concentration than high-grade metamorphic terrane composites (5 ± 4 ppm vs. 13 ± 6 ppm, 1σ ). δ 7Li correlates positively with H2O for 12 granulite composites; mafic samples have the highest H2O contents and δ 7Li values while felsic ones have the lowest. This, together with an excellent positive correlation between Li concentration and Mg# for 13 TTG gneiss composites, suggests that both metamorphic dehydration and protolith lithology play important roles in determining the Li isotopic composition of metamorphic rocks. For the Hannuoba xenoliths, δ 7Li correlates positively with Al2O3/CaO and negatively with Li, FeO, MgO, CaO and Co, suggesting that the protolith composition primarily controls the δ 7Li values. No such correlations are found for the other granulite xenoliths. The difference in δ 7Li between terranes and granulite xenoliths may reflect evolving lighter δ 7Li with depth in the crust, since the former equilibrated at middle to upper lower crustal depths, while the

  1. The chlorine isotopic composition of Martian meteorites 1: Chlorine isotope composition of Martian mantle and crustal reservoirs and their interactions

    NASA Astrophysics Data System (ADS)

    Williams, J. T.; Shearer, C. K.; Sharp, Z. D.; Burger, P. V.; McCubbin, F. M.; Santos, A. R.; Agee, C. B.; McKeegan, K. D.

    2016-05-01

    The Martian meteorites record a wide diversity of environments, processes, and ages. Much work has been done to decipher potential mantle sources for Martian magmas and their interactions with crustal and surface environments. Chlorine isotopes provide a unique opportunity to assess interactions between Martian mantle-derived magmas and the crust. We have measured the Cl-isotopic composition of 17 samples that span the range of known ages, Martian environments, and mantle reservoirs. The 37Cl of the Martian mantle, as represented by the olivine-phyric shergottites, NWA 2737 (chassignite), and Shergotty (basaltic shergottite), has a low value of approximately -3.8‰. This value is lower than that of all other planetary bodies measured thus far. The Martian crust, as represented by regolith breccia NWA 7034, is variably enriched in the heavy isotope of Cl. This enrichment is reflective of preferential loss of 35Cl to space. Most basaltic shergottites (less Shergotty), nakhlites, Chassigny, and Allan Hills 84001 lie on a continuum between the Martian mantle and crust. This intermediate range is explained by mechanical mixing through impact, fluid interaction, and assimilation-fractional crystallization.

  2. Perchlorate in The Great Lakes: Distribution, Isotopic Composition and Origin

    NASA Astrophysics Data System (ADS)

    Poghosyan, A.; Sturchio, N. C.; Jackson, W. A.; Guan, Y.; Eiler, J. M.; Hatzinger, P. B.

    2013-12-01

    Concentrations, stable chlorine and oxygen isotopic compositions, and 36Cl abundances of perchlorate were investigated in the five Laurentian Great Lakes. Samples were collected during monitoring cruises in 2007 and 2008 of the U.S. EPA's RV Lake Guardian and in 2010 at the water supply intake of Marquette, MI on the southern shore of Lake Superior. Concentrations of perchlorate were measured by IC/MS/MS at 24 locations, including one or two depth profiles in each lake. Mean concentrations (μg/L) are: Superior, 0.06 × 0.01; Michigan, 0.10 × 0.01; Huron, 0.11 × 0.01; Erie, 0.08 × 0.01, and Ontario, 0.09 × 0.01. Concentration vs. depth is nearly constant in each lake, indicating well-mixed conditions. Perchlorate was extracted from near-surface water by passing 15,000 to 80,000 L of water through 1-L cartridges containing Purolite A530E bifunctional anion-exchange resin. In the laboratory, perchlorate was eluted from the resin, purified, and precipitated as a >99% pure crystalline phase. Milligram amounts were recovered from each lake. Chlorine and oxygen isotopic analyses were performed at Caltech using the Cameca 7f-GEO SIMS instrument, following validation of the SIMS method with analyses of USGS-37 and USGS-38 isotopic reference materials. Results indicate a relatively narrow range in δ37Cl values (+2.9 to +3.9 ‰) and a wider range in δ18O values (-4.0 to +4.1 ‰), with a general geographic trend of increasing δ18O from west to east. Oxygen-17 was measured at UIC using dual-inlet IRMS of O2 produced by decomposition of KClO4. Great Lakes perchlorate has mass-independent oxygen isotopic variations with positive Δ17O values (+1.6 ‰ to +2.7 ‰) divided into two distinct groups: Lake Superior (+2.7 ‰) and the other four lakes (~ +1.7 ‰). The isotopic data indicate that perchlorate is dominantly of natural origin, having stable isotopic compositions resembling those of perchlorate from pre-industrial groundwaters in the western USA. The 36Cl

  3. Continuous measurements of isotopic composition of water vapour on the East Antarctic Plateau

    NASA Astrophysics Data System (ADS)

    Casado, Mathieu; Landais, Amaelle; Masson-Delmotte, Valérie; Genthon, Christophe; Kerstel, Erik; Kassi, Samir; Arnaud, Laurent; Picard, Ghislain; Prie, Frederic; Cattani, Olivier; Steen-Larsen, Hans-Christian; Vignon, Etienne; Cermak, Peter

    2016-07-01

    Water stable isotopes in central Antarctic ice cores are critical to quantify past temperature changes. Accurate temperature reconstructions require one to understand the processes controlling surface snow isotopic composition. Isotopic fractionation processes occurring in the atmosphere and controlling snowfall isotopic composition are well understood theoretically and implemented in atmospheric models. However, post-deposition processes are poorly documented and understood. To quantitatively interpret the isotopic composition of water archived in ice cores, it is thus essential to study the continuum between surface water vapour, precipitation, surface snow and buried snow. Here, we target the isotopic composition of water vapour at Concordia Station, where the oldest EPICA Dome C ice cores have been retrieved. While snowfall and surface snow sampling is routinely performed, accurate measurements of surface water vapour are challenging in such cold and dry conditions. New developments in infrared spectroscopy enable now the measurement of isotopic composition in water vapour traces. Two infrared spectrometers have been deployed at Concordia, allowing continuous, in situ measurements for 1 month in December 2014-January 2015. Comparison of the results from infrared spectroscopy with laboratory measurements of discrete samples trapped using cryogenic sampling validates the relevance of the method to measure isotopic composition in dry conditions. We observe very large diurnal cycles in isotopic composition well correlated with temperature diurnal cycles. Identification of different behaviours of isotopic composition in the water vapour associated with turbulent or stratified regime indicates a strong impact of meteorological processes in local vapour/snow interaction. Even if the vapour isotopic composition seems to be, at least part of the time, at equilibrium with the local snow, the slope of δD against δ18O prevents us from identifying a unique origin leading

  4. Investigation of magnesium isotope fractionation during granite differentiation: Implication for Mg isotopic composition of the continental crust

    NASA Astrophysics Data System (ADS)

    Liu, Sheng-Ao; Teng, Fang-Zhen; He, Yongsheng; Ke, Shan; Li, Shuguang

    2010-09-01

    High-precision Mg isotopic analysis was performed on a suite of well-characterized I-type granitoids and associated hornblende and biotite minerals from the Dabie Orogen in central China, to address the behavior of Mg isotopes during granite differentiation. Although these granitoids formed through different degrees of partial melting and fractional crystallization, with large variations in elemental and mineral compositions, their δ26Mg values vary from -0.26 to -0.14 and are indistinguishable within our analytical precision (± 0.07‰; 2 SD). Coexisting hornblendes and biotites in these granitoids display similar Mg isotopic composition, with δ26Mg ranging from -0.31 to -0.14 in hornblendes and -0.23 to -0.12 in biotites. The inter-mineral fractionation factors (Δ 26Mg Hbl-Bt = δ26Mg Hbl - δ26Mg Bt) vary from -0.10 to -0.02, with an average = -0.06 ± 0.08 (2 SD). The limited inter-mineral fractionation agrees with the theoretic prediction that Mg cations in both hornblende and biotite are octahedrally coordinated with oxygen, which restricts the magnitude of equilibrium isotope fractionation. Overall, data from both bulk granitoids and associated mineral separates suggest that Mg isotope fractionation during I-type granite differentiation is limited. Collectively, granitoids studied here have Mg isotopic composition similar to that of terrestrial basalts and peridotites ( δ26Mg = -0.21 ± 0.07 vs. -0.25 ± 0.07; 2 SD), confirming that magmatic processes do not significantly fractionate Mg isotopes. The continental crust in the Dabie Orogen, as sampled by these I-type granitoids, has a mantle-like Mg isotopic composition. Given that significant Mg isotope fractionation occurs during chemical weathering processes, Mg isotopes may potentially be used for tracing granite genesis, in particular, if sedimentary materials are involved in granite sources.

  5. Geochronological and isotopic evidence for early Proterozoic crust in the eastern Arabian Shield.

    USGS Publications Warehouse

    Stacey, J.S.; Hedge, C.E.

    1984-01-01

    Zircon U/Pb, feldspar common Pb, whole-rock Sm/Nd, and Rb/Sr data indicate that the fine-grained granodiorite (Z103) has yielded conclusive evidence for rocks of early Proterozoic age in the eastern Arabian Shield (21o19' N, 44o50' W). Z103 may have been emplaced approx 1630 m.y. ago and subsequently was severely deformed or perhaps even remobilized at approx 660 m.y. Furthermore, lead isotope data, along with other evidence, show that the 1630 m.y. crustal rocks inherited material from an older, probably Archaean, source at the time of their formation. At that time addition of mantle material considerably modified the Rb-Sr and Sm-Nd systems so that they now yield similar, or only slightly older apparent ages (1600-1800 m.y.).-L.diH.

  6. Evaluating Foraminifera as an Archive for Seawater Chromium Isotopic Composition

    NASA Astrophysics Data System (ADS)

    Wang, X.; Planavsky, N.; Hull, P. M.; Tripati, A.; Reinhard, C.; Zou, H.; Elder, L. E.; Henehan, M. J.

    2015-12-01

    In recent years there has been growing interest in using chromium isotopes (δ53Cr) as a proxy to investigate the redox evolution of Earth's ocean-atmosphere system throughout geological history. Potential archives for seawater δ53Cr that have been identified to date include iron formations and organic-rich siliciclastic sediments. However, these types of sediments are not common and they are discontinuous over geologic time. As a result, alternative types of archives are needed. Here we evaluate the utility of foraminifera tests as a recorder of seawater δ53Cr. Core-tops used were from different ocean basins. Mono-specific samples of Globigerinoides sacculifer, Orbulina universa, Pulleniatina obliquiloculata, Globoratalia crassula-crassaformis, Globoratalia truncatulinoides, and Globigerinella siphonifera were isolated to investigate inter-species isotope fractionation. Chromium concentrations were measured by isotope dilution method to be 0.1-0.3 μg/g. The δ53Cr values of these species range from 0.2‰ to 2.4‰, with an analytical uncertainty of 0.3‰ (95% confidence). Despite the high analytical uncertainty due to the extremely low levels of Cr present, there is still large detectable variation in foraminiferal δ53Cr values, which overlap presently available seawater values (Bonnand et al., 2013; Scheiderich et al., 2015). Possible explanations for such variations in foraminiferal δ53Cr values include heterogeneity of seawater δ53Cr in the modern oceans, and/or photobiochemical redox cycling of Cr in the surface oceans. Therefore, care should be taken when using foraminifera to reconstruct past seawater δ53Cr values. ReferencesBonnand, P., James, R., Parkinson, I., Connelly, D., Fairchild, I., 2013. The chromium isotopic composition of seawater and marine carbonates. Earth and Planetary Science Letters, 382: 10-20. Scheiderich, K., Amini, M., Holmden, C., Francois, R., 2015. Global variability of chromium isotopes in seawater demonstrated by Pacific

  7. Amino acid nitrogen isotopic composition patterns in lacustrine sedimenting matter

    NASA Astrophysics Data System (ADS)

    Carstens, Dörte; Lehmann, Moritz F.; Hofstetter, Thomas B.; Schubert, Carsten J.

    2013-11-01

    Amino acids (AAs) comprise a large fraction of organic nitrogen (N) in plankton and sedimenting matter. Aquatic studies of organic N compounds in general and of AAs in particular, mostly concentrate on marine environments. In order to study the cycling and fate of organic N and AAs in lakes, we measured the N isotopic composition (δ15N) of bulk organic matter (OM) and of single hydrolysable AAs in sediment trap and sediment samples from two Swiss lakes with contrasting trophic state: Lake Brienz, an oligotrophic lake with an oxic water column, and Lake Zug a eutrophic, meromictic lake. We also measured the N isotopic composition of water column nitrate, the likely inorganic N source during biosynthesis in both lakes. The δ15N-AA patterns found for the sediment trap material were consistent with published δ15N-AA data for marine plankton. The AA composition and primary δ15N-AA signatures are preserved until burial in the sediments. During early sedimentary diagenesis, the δ15N values of single AAs appear to increase, exceeding those of the bulk OM. This increase in δ15N-AA is paralleled by a decreased contribution of AAs to the total OM pool with progressed degradation, suggesting preferential AA degradation associated with a significant N isotope fractionation. Indicators for trophic level based on δ15N-AAs were determined, for the first time in lacustrine systems. In our samples, the trophic AAs were generally enriched in 15N compared to source AAs and higher trophic δ15N-AA values in Lake Zug were consistent with a higher trophic level of the bulk biomass compared to Lake Brienz. Especially the difference between average trophic δ15N-AAs and average source δ15N-AAs was sensitive to the trophic states of the two lakes. A proxy for total heterotrophic AA re-synthesis (ΣV), which is strongly associated with heterotrophic microbial reworking of the OM, was calculated based on δ15N values of trophic AAs. Higher ΣV in Lake Brienz indicate enhanced

  8. Triple sulfur isotope composition of Late Archean seawater sulfate

    NASA Astrophysics Data System (ADS)

    Paris, G.; Fischer, W. W.; Sessions, A. L.; Adkins, J. F.

    2013-12-01

    Multiple sulfur isotope ratios in Archean sedimentary rocks have provided powerful insights into the behavior of the ancient sulfur cycle, the redox state of fluid Earth, and the timing of the rise of atmospheric oxygen [1]. Most processes fractionate sulfur isotopes in proportion to their mass differences, but the Archean sulfur isotope record is marked by pronounced mass-independent fractionation (MIF, Δ33S≠0). The origin of these signatures has been traditionally interpreted as the result of photolysis of SO2 from short wavelength UV light, with positive Δ33S values recorded in pyrite and negative Δ33S values in sulfate-bearing phases [2]. This long-held hypothesis rests on observations of negative Δ33S from enigmatic barite occurrences from mixed volcanic sedimentary strata in Mesoarchean greenstone terrains. Despite forming the framework for understanding Archean sulfur cycle processes [3], it is largely untested [3]. It is largely untested. Consequently, the biggest challenge to our current understanding of the early sulfur cycle is a poor understanding of the isotopic composition of seawater sulfate. Sulfate evaporite minerals are absent from Archean strata and the sulfur isotope record is written entirely by measurements of pyrite. Carbonate associated sulfate (CAS) provides an important archive for assaying the isotopic composition of ancient seawater sulfate It has been exploited in many studies of Phanerozoic and Proterozoic sulfate but have been only marginally used thus far for Archean samples because of the extremely low concentration of CAS in limestones and dolomites from this era. We have developed a novel MC-ICP-MS approach to solve this problem [4]. This new method lowers the detection limit by up to three orders of magnitude for δ34S and Δ33S measurements, enabling to work on a few nmols of sulfate which represent only tens of mg of sample powders micromilled from specific carbonate textures. Two stratigraphic sections from the 2

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

  10. Variations in Urine Calcium Isotope: Composition Reflect Changes in Bone Mineral Balance in Humans

    NASA Technical Reports Server (NTRS)

    Skulan, Joseph; Anbar, Ariel; Bullen, Thomas; Puzas, J. Edward; Shackelford, Linda; Smith, Scott M.

    2004-01-01

    Changes in bone mineral balance cause rapid and systematic changes in the calcium isotope composition of human urine. Urine from subjects in a 17 week bed rest study was analyzed for calcium isotopic composition. Comparison of isotopic data with measurements of bone mineral density and metabolic markers of bone metabolism indicates the calcium isotope composition of urine reflects changes in bone mineral balance. Urine calcium isotope composition probably is affected by both bone metabolism and renal processes. Calcium isotope. analysis of urine and other tissues may provide information on bone mineral balance that is in important respects better than that available from other techniques, and illustrates the usefulness of applying geochemical techniques to biomedical problems.

  11. Chemistry and isotopic composition of fumarole discharges of Furnas caldera

    NASA Astrophysics Data System (ADS)

    Ferreira, Teresa; Oskarsson, Niels

    1999-09-01

    Two fumarole grounds at Lagoa das Furnas and Furnas village and a fumarole on the bank of Ribeira dos Tambores are located on a west-east tectonic lineament across the topographic low of the Furnas caldera. The discharge of the fumaroles derives from steam separation from shallow (100-200 m) aquifers at temperatures of about 180°C. As inferred from nitrogen/argon relations and deuterium-oxygen isotope relations the hydrothermal fluid is derived from local precipitation after some 10% steam fractionation in the fumarole conduits. Sulphur isotope ratios of the discharge, being close to those of juvenile rock sulphur, indicate extensive rock-leaching within the aquifers. The carbon isotope composition of the fumarole discharge and carbon dioxide saturated waters encountered across the caldera floor suggests that the source of carbon is regional outgassing of mantle derived juvenile carbon dioxide. Chemistry of the acid gases, carbon dioxide and hydrogen sulphide in the discharge indicates a slight fractionation induced by different boiling in the shallow hydrothermal aquifers. Traces of hydrogen and methane contained in the discharge bear no relation to the low temperature water-steam equilibria of the Furnas fumaroles. Assuming a deeper origin of these gases, a simple model for binary mixtures of methane and hydrogen indicates that these gases are derived from supercritical conditions, presumably equilibrated within hot rocks below the hydrothermal system. The remarkably stable ratios of hydrogen and methane, also considering their inferred deep origin, suggest that these gases might be considered for future chemical monitoring of the fumarole discharge in Furnas.

  12. Isotopic composition of sulfate accumulations, Northern Calcareous Alps, Austria

    NASA Astrophysics Data System (ADS)

    Bojar, Ana-Voica; Halas, Stanislaw; Bojar, Hans-Peter; Trembaczowski, Andrzej

    2015-04-01

    The Eastern Alps are characterised by the presence of three main tectonic units, such as the Lower, Middle and Upper Austroalpine, which overlie the Penninicum (Tollmann, 1977). The Upper Austroalpine unit consists of the Northern Calcareous Alps (NCA) overlying the Greywacke zone and corresponding to the Graz Paleozoic, Murau Paleozoic and the Gurktal Nappe. Evaporitic rocks are lacking in the later ones. The Northern Calcareous Alps are a detached fold and thrust belt. The sedimentation started in the Late Carboniferous or Early Permian, the age of the youngest sediments being Eocene. The NCA are divided into the Bajuvaric, Tirolic and Juvavic nappe complexes. The evaporitic Haselgebirge Formation occurs in connection with the Juvavic nappe complex at the base of the Tirolic units (Leitner et al., 2013). The Haselgebirge Formation consists mainly of salt, shales, gypsum and anhydrite and includes the oldest sediments of the NCA. The age of the Haselgebirge Formation, established by using spors and geochronological data, is Permian to Lower Triassic. For the Northern Calcareous Alps, the mineralogy of sulphate accumulations consists mainly of gypsum and anhydrite and subordonates of carbonates. The carbonates as magnesite, dolomite and calcite can be found either as singular crystals or as small accumulations within the hosting gypsum. Sulfides (sphalerite, galena, pyrite), sulfarsenides (enargite, baumhauerite) and native sulphur enrichments are known from several deposits (Kirchner, 1987; Postl, 1990). The investigated samples were selected from various gypsum and halite rich deposits of the Northern Calcareous Alps. A total of over 20 samples were investigated, and both oxygen and sulfur isotopic composition were determined for anhydrite, gyps, polyhalite, blödite and langbeinite. The sulfur isotopic values vary between 10.1 to 14 ‰ (CDT), with three values higher than 14 ‰. The Oxygen isotopic values show a range from 9 to 23 ‰ (SMOW). The sulfur

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

    USGS Publications Warehouse

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

    1991-01-01

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

  14. Morphology-Composition-Isotopes: Recent Results from Observations

    NASA Astrophysics Data System (ADS)

    Schulz, R.

    This article presents some recent imaging and spectroscopic observations that led to results which are significant for understanding the properties of comet nuclei. The coma morphology and/or composition were investigated for 12 comets belonging to different dynamical classes. The data analysis showed that the coma morphology of three non-periodic comets is not consistent with the general assumption that dynamically new comets still have a relatively uniform nucleus surface and therefore do not exhibit gas and/or dust jets in their coma. The determination of carbon and nitrogen isotopic ratios revealed the same values for all comets investigated at various heliocentric distances. However, the relative abundance of the rare nitrogen isotope 15N is about twice as high as in the Earth's atmosphere. Observations of comets at splitting events and during outbursts led to indications for differences between material from the nucleus surface and the interior. The monitoring of the induced outburst of 9P/Temple revealed that under non-steady state conditions the fast disintegration of species is detectable.

  15. Lithium isotope fractionation in the Ganges-Brahmaputra floodplain and implications for groundwater impact on seawater isotopic composition

    NASA Astrophysics Data System (ADS)

    Bagard, Marie-Laure; West, A. Joshua; Newman, Karla; Basu, Asish R.

    2015-12-01

    Lithium isotopes are a promising proxy for reconstructing past weathering processes, but unraveling the seawater record requires a comprehensive understanding of the magnitude and isotopic composition of Li fluxes to the oceans, and of how these change over time. Little information is available on the role of floodplain sediments and groundwater systems in setting the Li isotope signature of the dissolved flux delivered from the continents to the oceans. Here we investigate the Li dissolved fluxes of river waters and groundwaters in the Ganges-Brahmaputra floodplain. The data suggest that a maximum of 3.1 ×108 and 1.5 ×108 moles Li/yr are carried to the Bay of Bengal by Ganges-Brahmaputra rivers and groundwaters, respectively. The riverine flux has a significantly heavier Li isotope composition (average δ7Li: 26‰) than the groundwater flux (average δ7Li: 16‰) and increases downstream across the floodplain. δ7Li in both river waters and shallow groundwater can be explained by Li scavenging by Quaternary floodplain sediments following a Rayleigh fractionation process, with preferential removal of 6Li. On the other hand, deep groundwaters (>40 m) contributing to submarine groundwater discharge to the Bay of Bengal are enriched in 6Li at depth, likely due to the dissolution of floodplain sediments releasing Li with a light isotope composition. Similarly low δ7Li has been reported in other large sedimentary aquifers. The deep groundwater values are close to the average isotope composition of the global Li inputs to the ocean (∼15‰), so groundwater submarine discharge has only a minor influence on the assessment of the modern Li isotope budget of the ocean. Our analysis further suggests that groundwater discharge of Li has probably played at most a small and secondary role in past changes in the isotope composition of the total continental flux of Li to the ocean.

  16. Carbon and hydrogen isotopic compositions of stratospheric methane: 2. Two-dimensional model results and implications for kinetic isotope effects

    NASA Astrophysics Data System (ADS)

    McCarthy, M. C.; Boering, K. A.; Rice, A. L.; Tyler, S. C.; Connell, P.; Atlas, E.

    2003-08-01

    New high-precision measurements of the carbon and hydrogen isotopic compositions of stratospheric CH4 made on whole air samples collected aboard the NASA ER-2 aircraft are compared with results from the Lawrence Livermore National Laboratory 2-D model. Model runs incorporating sets of experimentally determined kinetic isotope effects (KIEs) for the reactions of CH4 with each of the oxidants OH, O(1D), and Cl are examined with the goals of determining (1) how well the 2-D model can reproduce the observations for both the carbon and hydrogen isotopic compositions, (2) what factors are responsible for the observed increase in the apparent isotopic fractionation factors with decreasing methane mixing ratios, and (3) how sensitive the modeled isotopic compositions are to various experimentally determined KIEs. Bound by estimates of the effects of uncertainties in model chemistry and transport on isotopic compositions, we then examine the constraints the ER-2 observations place on values for the KIEs. For the carbon KIE for reaction of CH4 with O(1D), for example, the analysis of model results and observations favors the larger of the experimental values, 1.013, over a value of 1.001. These analyses also suggest that intercomparisons of results from different models using a given set of KIEs may be useful as a new diagnostic of model-model differences in integrated chemistry and transport.

  17. Chemical composition of HAL, an isotopically-unusual Allende inclusion

    NASA Technical Reports Server (NTRS)

    Davis, A. M.; Tanaka, T.; Grossman, L.; Lee, T.; Wasserburg, G. J.

    1982-01-01

    Samples of hibonite, black rim, and portions of friable rim from an unusual Allende inclusion, named HAL, were analyzed by INAA and RNAA for 37 major, minor, and trace elements. An unusually low amount of Ce was found in HAL, although it otherwise was highly enriched in REE compared to C1 chondrites. HAL is also depleted in Sr, Ba, U, V, Ru, Os, and Ir relative to other refractory elements. It is concluded that the distribution of REE between hibonite and rims was established when hibonite and other refractory minerals were removed at slightly different temperatures from a hot, oxidizing gas in which they previously coexisted as separate grains. Possible locations for the chemical and mass dependent isotopic fractionation are considered to be in ejecta from the low temperature helium-burning zone of a supernova and in the locally oxidizing environment generated by evaporation of interstellar grains of near-chondritic chemical composition.

  18. The elemental and isotopic composition of galactic cosmic ray nuclei

    NASA Technical Reports Server (NTRS)

    Mewaldt, R. A.

    1983-01-01

    A directly accessible sample of matter which originates outside the solar system is provided by galactic cosmic rays. The present investigation is primarily concerned with progress related to questions raised regarding the similarity or difference between solar system matter and matter coming from outside the solar system. The investigation takes into account U.S. contributions to this topic over the period from 1979 to 1982. The cosmic ray (CR) abundances of all the elements from H to Ni (atomic number Z=1 to 28) have now been measured. Cosmic ray source (CRS) and solar system (SS) elemental compositions are listed in a table, and the ratio of CRS to SS abundance for 21 elements is shown in a graph. There is now clear evidence from CR isotope studies that the nucleosynthesis of CRS material has differed from that of SS material.

  19. Neodymium isotope evidence for a chondritic composition of the Moon.

    PubMed

    Rankenburg, K; Brandon, A D; Neal, C R

    2006-06-01

    Samarium-neodymium isotope data for six lunar basalts show that the bulk Moon has a 142Nd/144Nd ratio that is indistinguishable from that of chondritic meteorites but is 20 parts per million less than most samples from Earth. The Sm/Nd formation interval of the lunar mantle from these data is 215(-21)(+23) million years after the onset of solar system condensation. Because both Earth and the Moon likely formed in the same region of the solar nebula, Earth should also have a chondritic bulk composition. In order to mass balance the Nd budget, these constraints require that a complementary reservoir with a lower 142Nd/144Nd value resides in Earth's mantle. PMID:16741118

  20. The silicon isotopic composition of the Ganges and its tributaries

    NASA Astrophysics Data System (ADS)

    Fontorbe, Guillaume; De La Rocha, Christina L.; Chapman, Hazel J.; Bickle, Michael J.

    2013-11-01

    The silicon isotopic composition (δSi30) of the headwaters of the Ganges River, in the Himalaya, ranged from +0.49±0.01‰ to +2.17±0.04‰ at dissolved silicon (DSi) concentrations of 38 to 239 μM. Both the concentration and isotopic composition of DSi in the tributaries increased between the highest elevations to where the Ganges leaves the Himalayas at Rishikesh. The tributaries exhibit a linear correlation between δSi30 and DSi that may represent mixing between a low DSi, low δSi30 (e.g., 40 μM, +0.5‰) component potentially reflecting fractionation during adsorption of a small fraction of silicon onto iron oxides and a high DSi, high δSi30 component (e.g., 240 μM, +1.7‰) produced during higher intensity weathering with a greater proportional sequestration of weathered silicon into secondary minerals or biogenic silica. On the Ganges alluvial plain, in the Ganges and the Yamuna, Gomati, and their tributaries, DSi ranged from 122 to 218 μM while δSi30 ranged from +1.03±0.03‰ to +2.46±0.06‰. Highest values of δSi30 occurred in the Gomati and its tributaries. In general, the lower DSi and higher δSi30 of DSi in these rivers suggests control of both by removal of DSi by secondary mineral formation and/or biogenic silica production. A simple 1-dimensional model with flow through a porous medium is introduced and provides a useful framework for understanding these results.

  1. Trace elemental and Nd-Sr-Pb isotopic compositional variation in 37 lava flows of the Mandla lobe and their chemical relation to the western Deccan stratigraphic succession, India

    NASA Astrophysics Data System (ADS)

    Shrivastava, J. P.; Mahoney, J. J.; Kashyap, M. R.

    2014-12-01

    The Mandla lobe is a 900 m thick lava pile that forms a 29,400 km2 northeastern extension of the Deccan Traps. Earlier, combined field, petrographic, and major element studies have shown that this lobe comprises 37 lava flows. Using a combination of trace elements (Ba, Ti, Zr, Rb, Sr) and Nb/Zr values, we group the flows into six chemical types (A-F) that are separated stratigraphically. Combined trace element and Nd-Pb-Sr isotopic data, document the presence of lavas resembling those of the Poladpur Formation and less abundantly, the Ambenali Formation of the southwestern Deccan are in conformity with the earlier reconnaissance work. In addition, our data reveal several flows similar to those of the Mahabaleshwar Formation, the type sections of which are located ~ 900 km to the southwest. Based on the isotopic data the superposition of Mahabaleshwar-like flows over flows with Ambenali- and Poladpur-like characteristics is in the same stratigraphic order seen in the southwestern Deccan type section. However, from the stratigraphy indicated by the Discriminant Function Analysis (DFA) results and the serious discrepancy between the DFA and isotopic data, it seems that few Mandla lobe flows are different and not in the same stratigraphic order as in the southwestern part of the province. To some extent the differences may be explained by faulting along four large post-Deccan normal faults near Nagapahar, Kundam, Deori, and Dindori areas across which offsets of ~150 m have been measured. This post-emplacement faulting accounts for the presence of several chemically Mahabaleshwar-like lavas at the base of the ~900 m thick Mandla lobe pile, at a lower elevation than a thick sequence dominated by chemically Poladpur-like flows. However, presence of common signature lavas (similar to that in the northeastern Deccan) cannot be ruled out in this area. They are similar to Poladpur-type lavas both chemically and isotopically. They appear in different formations and erupted at

  2. Baseline shifts in coral skeletal oxygen isotopic composition: a signature of symbiont shuffling?

    NASA Astrophysics Data System (ADS)

    Carilli, J. E.; Charles, C. D.; Garren, M.; McField, M.; Norris, R. D.

    2013-06-01

    Decades-long records of the stable isotopic composition of coral skeletal cores were analyzed from four sites on the Mesoamerican Reef. Two of the sites exhibited baseline shifts in oxygen isotopic composition after known coral bleaching events. Changes in pH at the calcification site caused by a change in the associated symbiont community are invoked to explain the observed shift in the isotopic composition. To test the hypothesis that changes in symbiont clade could affect skeletal chemistry, additional coral samples were collected from Belize for paired Symbiodinium identification and skeletal stable isotopic analysis. We found some evidence that skeletal stable isotopic composition may be affected by symbiont clade and suggest this is an important topic for future investigation. If different Symbiodinium clades leave consistent signatures in skeletal geochemical composition, the signature will provide a method to quantify past symbiont shuffling events, important for understanding how corals are likely to respond to climate change.

  3. Geochemical and Isotopic Composition of Aerosols in Tucson

    NASA Astrophysics Data System (ADS)

    Riha, K. M.; Michalski, G. M.; Lohse, K. A.; Gallo, E. L.; Brooks, P. D.; Meixner, T.

    2010-12-01

    isotopic analyses have been conducted on these samples using the denitrifier method (Casciotti et al., 2002). Observed elevated δ18O values correspond to atmospheric oxidation processes and varying δ15N are possibly linked to different N sources. These isotopic values will be used as a proxy for deposition in a mass balance mixing model for nitrogen in arid streams. References: Casciotti, K. L., D. M. Sigman, M. G. Hastings, J. K. Böhlke and A. Hilkert, Measurement of the oxygen isotopic composition of nitrate in seawater and freshwater using the denitrifier method, Anal. Chem., 74(19), 4905-4912, 2002. Michalski, G., Z. Scott, M. Kabiling and M. Thiemens, First Measurements and Modeling of Δ17O in Atmospheric Nitrate, Geophys. Res. Lett., 30(16), (1870), 2003.

  4. Isotopic fractionation of methane in the stratosphere and its effect on free tropospheric isotopic compositions

    NASA Astrophysics Data System (ADS)

    McCarthy, M. C.; Connell, P.; Boering, K. A.

    Kinetic isotope effects (KIEs) for the oxidation of CH4 by OH, Cl, and O(¹D) were incorporated into a 2D model of the atmosphere to examine how sensitive the carbon isotopic composition of CH4 in the free troposphere is to three influences: realistic stratospheric chemistry and transport, tropospheric Cl chemistry, and use of new, experimentally-determined KIEs for the OH and O(¹D) sinks. At steady-state, our results indicate that stratospheric chemistry and transport enrich tropospheric δ13CH4 by 0.5 to 0.6‰, tropospheric Cl chemistry as modeled enriches δ13CH4 by ∼0.3‰, and the new KIE for the OH sink depletes modeled global δ13CH4 by >1‰. Ignoring the stratosphere (and Cl chemistry in general) in models therefore happens to partially compensate for use of the previously accepted KIE for OH when comparisons with observations of free tropospheric δ13CH4 are made. In contrast, including only one of these influences increases the error relative to including none. Thus, all 3 effects are of sufficient magnitude to warrant their inclusion in inverse models in order to reduce uncertainties in the CH4 budget.

  5. Geochemical Investigation of Chemical Weathering in Taiwan: River water chemistry and Sr Isotopes

    NASA Astrophysics Data System (ADS)

    You, C.; Chung, S.; Lin, P.; Wang, B.; Wang, R.; Hsieh, Y.; Lin, H.; Lee, H.

    2003-12-01

    Taiwan is an active tectonic island and has the highest physical denudation rate in the world. In this study, we investigate the state of chemical weathering in various river systems distributed all around the island. More than 200 water samples were collected from eight major rivers and their tributaries, including Choshui, Kaopin, Erhjen, Wu, Houlung, Hsiukuluan and Pachang. Among them, the Erhjen was visited nine times at 19 stations in two consecutive years for a detailed study of impacts due to seasonal variation. These water samples were centrifuged and analyzed for major ions (i.e., Na, K, Mg, Ca, Cl, bicarbonate and sulfate) and trace elements (Li, B, Si, Rb, Sr, Ba, and REE), as well as Sr, Pb and U isotopes. Applying factor analysis method, the most dominant factors controlling the chemical compositions are: (1) sea-salt contribution and tidal effect; (2) degree of water-ambient rock interaction; and (3) anthropogenic pollutant. Other effects including regional and seasonal variability are also detected. For instance, Sr isotopes indicate significant seasonal variation in river waters possibly reflecting source changes in ambient soils due to monsoon rain in summer. The Sr concentration and Sr isotope plot show interesting mixing among four sources. The near estuary stations display strong seawater isotopic signature. Stations at mid-stream were influenced by chemical erosion of bed-rock or ambient soils. The upstream samples were affected largely by the characteristics of tributary waters. Uranium isotopes vary largely in the Taiwanese river samples, a range of 1.14 to 2.5, possibly due to alpha recoils.

  6. Lead Isotopes in Olivine-Phyric Shergottite Tissint: Implications for the Geochemical Evolution of the Shergottite Source Mantle

    NASA Technical Reports Server (NTRS)

    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

  7. Influence of water-flow on skeletal isotopic compositions of branching coral Pocilopora damicornis

    NASA Astrophysics Data System (ADS)

    Suzuki, A.; Nakamura, T.; Yamasaki, H.; Minoshima, K.; Kawahata, H.

    2006-12-01

    Oxygen and carbon isotope compositions of coral skeleton appear to be more influenced by skeletal growth rate than physical conditions such as temperature in a particular setting. We examined the influence of water motion on the isotopic composition of branching coral Pocilopora damicornis grown in experimental flumes. Colony size and buoyant weight became significantly greater in the flow condition than the still condition, indicating water-flow was favorable for coral growth. Despite of the evident difference in skeletal growth rate, the skeletal oxygen isotope, carbon isotope as well, of the outer tips were almost identical between the flow- and still-treated colonies, indicating the limited influence of water-flow on the isotopic composition of active calcification site. The result suggested the potential role of light level, which was relatively high in the present experiment, for suppressing the growth-rate-related kinetic isotopic fractionation.

  8. Zinc isotopic composition of iron meteorites: Absence of isotopic anomalies and origin of the volatile element depletion

    NASA Astrophysics Data System (ADS)

    Chen, Heng; Nguyen, Bach Mai; Moynier, Frédéric

    2013-12-01

    High-precision Zn isotopic compositions measured by MC-ICP-MS are documented for 32 iron meteorites from various fractionally crystallized and silicate-bearing groups. The δ66Zn values range from -0.59‰ up to +5.61‰ with most samples being slightly enriched in the heavier isotopes compared with carbonaceous chondrites (0 < δ66Zn < 0.5). The δ66Zn versus δ68Zn plot of all samples defines a common linear fractionation line, which supports the hypothesis that Zn was derived from a single reservoir or from multiple reservoirs linked by mass-dependent fractionation processes. Our data for Redfields fall on a mass fractionation line and therefore refute a previous claim of it having an anomalous isotopic composition due to nonmixing of nucleosynthetic products. The negative correlation between δ66Zn and the Zn concentration of IAB and IIE is consistent with mass-dependent isotopic fractionation due to evaporation with preferential loss of lighter isotopes in the vapor phase. Data for the Zn concentrations and isotopic compositions of two IVA samples demonstrate that volatile depletion in the IVA parent body is not likely the result of evaporation. This is important evidence that favors the incomplete condensation origin for the volatile depletion of the IVA parent body.

  9. NEW INSIGHTS ON SATURN'S FORMATION FROM ITS NITROGEN ISOTOPIC COMPOSITION

    SciTech Connect

    Mousis, Olivier; Lunine, Jonathan I.; Fletcher, Leigh N.; Mandt, Kathleen E.; Ali-Dib, Mohamad; Atreya, Sushil

    2014-12-01

    The recent derivation of a lower limit for the {sup 14}N/{sup 15}N ratio in Saturn's ammonia, which is found to be consistent with the Jovian value, prompted us to revise models of Saturn's formation using as constraints the supersolar abundances of heavy elements measured in its atmosphere. Here we find that it is possible to account for both Saturn's chemical and isotopic compositions if one assumes the formation of its building blocks at ∼45 K in the protosolar nebula, provided that the O abundance was ∼2.6 times protosolar in its feeding zone. To do so, we used a statistical thermodynamic model to investigate the composition of the clathrate phase that formed during the cooling of the protosolar nebula and from which the building blocks of Saturn were agglomerated. We find that Saturn's O/H is at least ∼34.9 times protosolar and that the corresponding mass of heavy elements (∼43.1 M {sub ⊕}) is within the range predicted by semi-convective interior models.

  10. New Insights on Saturn's Formation from its Nitrogen Isotopic Composition

    NASA Astrophysics Data System (ADS)

    Mousis, Olivier; Lunine, Jonathan I.; Fletcher, Leigh N.; Mandt, Kathleen E.; Ali-Dib, Mohamad; Gautier, Daniel; Atreya, Sushil

    2014-12-01

    The recent derivation of a lower limit for the 14N/15N ratio in Saturn's ammonia, which is found to be consistent with the Jovian value, prompted us to revise models of Saturn's formation using as constraints the supersolar abundances of heavy elements measured in its atmosphere. Here we find that it is possible to account for both Saturn's chemical and isotopic compositions if one assumes the formation of its building blocks at ~45 K in the protosolar nebula, provided that the O abundance was ~2.6 times protosolar in its feeding zone. To do so, we used a statistical thermodynamic model to investigate the composition of the clathrate phase that formed during the cooling of the protosolar nebula and from which the building blocks of Saturn were agglomerated. We find that Saturn's O/H is at least ~34.9 times protosolar and that the corresponding mass of heavy elements (~43.1 M ⊕) is within the range predicted by semi-convective interior models.

  11. Herbivore tooth oxygen isotope compositions: Effects of diet and physiology

    NASA Astrophysics Data System (ADS)

    Kohn, Matthew J.; Schoeninger, Margaret J.; Valley, John W.

    1996-10-01

    The applicability of rapid and precise laser probe analysis of tooth enamel for δ18O has been verified, and the method has been applied to different modern herbivores in East Africa. Sampling and pretreatment procedures involve initial bleaching and grinding of enamel to <75 μm, and elimination of adsorbed water and organic compounds with BrF 5. Typical analytical reproducibilities for 0.5-2 mg samples are ±0.08‰ (± 1σ). Chemical and spectroscopic characterization of pretreated but unanalyzed samples show no alteration compared to fresh enamel. Solid reaction products are nearly pure CaF 2 with little evidence for residual O 2. Because laser probe fluorination extracts oxygen from all sites in the apatite structure (phosphate, structural carbonate, and hydroxyl), only unaltered tooth enamel (>95% apatite) can be analyzed reliably. Different East African herbivores exhibit previously unsuspected compositional differences. Average enamel δ18O values (V-SMOW) are approximately: 25‰ (goat), 27‰ (oryx), 28‰ (dikdik and zebra), 29‰ (topi), 30‰ (gerenuk), and 32‰ (gazelle). These compositions differ from generalized theoretical models, but are broadly consistent with expected isotope effects associated with differences in how much each animal (a) drinks, (b) eats C3 vs. C4 plants, and (c) pants vs. sweats. Consideration of diet, water turnover, and animal physiology will allow the most accurate interpretation of ancient teeth and targeting of environmentally-sensitive animals in paleoclimate studies.

  12. Light element isotopic compositions of cometary matter returned by the STARDUST mission

    SciTech Connect

    McKeegan, K D; Aleon, J; Bradley, J; Brownlee, D; Busemann, H; Butterworth, A; Chaussidon, M; Fallon, S; Floss, C; Gilmour, J; Gounelle, M; Graham, G; Guan, Y; Heck, P R; Hoppe, P; Hutcheon, I D; Huth, J; Ishii, H; Ito, M; Jacobsen, S B; Kearsley, A; Leshin, L A; Liu, M; Lyon, I; Marhas, K; Marty, B; Matrajt, G; Meibom, A; Messenger, S; Mostefaoui, S; Nakamura-Messenger, K; Nittler, L; Palma, R; Pepin, R O; Papanastassiou, D A; Robert, F; Schlutter, D; Snead, C J; Stadermann, F J; Stroud, R; Tsou, P; Westphal, A; Young, E D; Ziegler, K; Zimmermann, L; Zinner, E

    2006-10-10

    Hydrogen, carbon, nitrogen, and oxygen isotopic compositions are heterogeneous among comet 81P/Wild2 particle fragments, however extreme isotopic anomalies are rare, indicating that the comet is not a pristine aggregate of presolar materials. Non-terrestrial nitrogen and neon isotope ratios suggest that indigenous organic matter and highly volatile materials were successfully collected. Except for a single circumstellar stardust grain, silicate and oxide minerals have oxygen isotopic compositions consistent with solar system origin. One refractory grain is {sup 16}O-enriched like refractory inclusions in meteorites, suggesting formation in the hot inner solar nebula and large-scale radial transport prior to comet accretion in the outer solar system.

  13. Evaluation of the sulfur isotopic composition and homogeneity of the Soufre de Lacq reference material

    USGS Publications Warehouse

    Carmody, R.W.; Seal, R.R., II

    1999-01-01

    Sulfur isotopic analysis of the elemental sulfur reference material Soufre de Lacq, prepared as silver sulfide by chromous chloride reduction and as copper sulfide by sealed-tube synthesis, indicates that Soufre de Lacq is isotopically homogeneous across different size fractions to within analytical uncertainty (??0.15???). The sulfur isotopic composition of aliquots of Soufre de Lacq prepared by these two techniques are identical to within analytical uncertainty. The mean sulfur isotopic composition for Soufre de Lacq prepared as silver sulfide and copper sulfide (relative to VCDT) is +16.20 ?? 0.15??? (1??).

  14. Uranium isotopic composition and absolute ages of Allende chondrules

    NASA Astrophysics Data System (ADS)

    Brennecka, G. A.; Budde, G.; Kleine, T.

    2015-11-01

    A handful of events, such as the condensation of refractory inclusions and the formation of chondrules, represent important stages in the formation and evolution of the early solar system and thus are critical to understanding its development. Compared to the refractory inclusions, chondrules appear to have a protracted period of formation that spans millions of years. As such, understanding chondrule formation requires a catalog of reliable ages, free from as many assumptions as possible. The Pb-Pb chronometer has this potential; however, because common individual chondrules have extremely low uranium contents, obtaining U-corrected Pb-Pb ages of individual chondrules is unrealistic in the vast majority of cases at this time. Thus, in order to obtain the most accurate 238U/235U ratio possible for chondrules, we separated and pooled thousands of individual chondrules from the Allende meteorite. In this work, we demonstrate that no discernible differences exist in the 238U/235U compositions between chondrule groups when separated by size and magnetic susceptibility, suggesting that no systematic U-isotope variation exists between groups of chondrules. Consequently, chondrules are likely to have a common 238U/235U ratio for any given meteorite. A weighted average of the six groups of chondrule separates from Allende results in a 238U/235U ratio of 137.786 ± 0.004 (±0.016 including propagated uncertainty on the U standard [Richter et al. 2010]). Although it is still possible that individual chondrules have significant U isotope variation within a given meteorite, this value represents our best estimate of the 238U/235U ratio for Allende chondrules and should be used for absolute dating of these objects, unless such chondrules can be measured individually.

  15. Nutritional assessment by isotope dilution analysis of body composition

    SciTech Connect

    Szeluga, D.J.; Stuart, R.K.; Utermohlen, V.; Santos, G.W.

    1984-10-01

    The three components of body mass, body cell mass (BCM), extracellular fluid (ECF), and fat + extracellular solids (ECS: bone, tendon, etc) can be quantified using established isotope dilution techniques. With these techniques, total body water (TBW) and ECF are measured using 3H/sub 2/O and /sup 82/Bromine, respectively, as tracers. BCM is calculated from intracellular fluid (ICF) where ICF . TBW - ECF. Fat + ECS is estimated as: body weight - (BCM + ECF). TBW and ECF can be determined by either of two calculation methods, one requiring several timed plasma samples (extrapolation method) and one requiring a single plasma sample and a 4-h urine collection (urine-corrected method). The comparability of the two calculation methods was evaluated in 20 studies in 12 bone marrow transplant recipients. We found that for determination of TBW and ECF there was a very strong linear relationship (r2 greater than 0.98) between the calculation methods. Further comparisons (by t test, 2-sided) indicated that for the determination of ECF, the methods were not significantly (p greater than 0.90) different; however, TBW determined by the urine-corrected method was slightly (0.1 to 6%), but significantly (p less than 0.01) greater than that determined by the extrapolation method. Therefore, relative to the extrapolation method, the urine-corrected method ''over-estimates'' BCM and ''under-estimates'' fat + ECS since determination of these compartment sizes depends on measurement of TBW. We currently use serial isotope dilution studies to monitor the body composition changes of patients receiving therapeutic nutritional support.

  16. Reassessing the stable isotope composition assigned to methane flux from natural wetlands in isotope-constrained budgets

    NASA Astrophysics Data System (ADS)

    Hornibrook, Edward; Maxfield, Peter; Gauci, Vincent; Stott, Andrew

    2013-04-01

    Stable isotope ratios in CH4 preserve information about its origin and history, and are commonly used to constrain global CH4 budgets. Wetlands are key contributors to the atmospheric burden of CH4 and typically are assigned a stable carbon isotope composition of ~-60 permil in isotope-weighted stable isotope models despite the considerable range of δ13C(CH4) values (~ -100 to -40 permil) known to occur in these diverse ecosystems. Kinetic isotope effects (KIEs) associated with the metabolism of CH4-producing microorganisms generate much of the natural variation but highly negative and positive δ13C(CH4) values generally result from secondary processes (e.g., diffusive transport or oxidation by soil methanotrophs). Despite these complexities, consistent patterns exist in the isotope composition of wetland CH4 that can be linked conclusively to trophic status and consequently, natural succession or human perturbations that impact nutrient levels. Another challenge for accurate representation of wetlands in carbon cycle models is parameterisation of sporadic CH4 emission events. Abrupt release of large volumes of CH4-rich bubbles in short periods of time can account for a significant proportion of the annual CH4 flux from a wetland but such events are difficult to detect using conventional methods. New infrared spectroscopy techniques capable of high temporal resolution measurements of CH4 concentration and stable isotope composition can readily quantify short-lived CH4 pulses. Moreover, the isotope data can be used conclusively to determine shifts in the mode of CH4 transport and provide the potential to link initiation of abrupt emission events to forcing by internal or external factors.

  17. Investigating Tungsten Concentrations and Isotopic Compositions of Natural Water Samples from the Carson River Basin

    NASA Astrophysics Data System (ADS)

    Wasserman, N. L.; Williams, R. W.; Kayzar, T. M.; Schorzman, K. C.

    2012-12-01

    Recent studies have shown that W-isotopes may fractionate in nature1; however, the magnitude and cause of the isotopic variations are largely unknown and unconstrained. In this study, the isotopic compositions of the NIST 3163 W standard, W ore minerals, and 15 natural surface waters from Nevada's Carson River Basin were analyzed by MC-ICP-MS using external bracketing with NIST 3163 and the IUPAC 184W/183W for mass bias correction. Chemical separation procedures were developed to purify W from natural matrices and tested to assure fractionation was not introduced during column chemistry. The W isotopic compositions of these samples were measured and compared to the accepted IUPAC composition of natural W. Samples of wolframite (Fe, MnWO4) and hubnerite (MnWO4) have compositions similar to the IUPAC value but vary from the isotopic composition of NIST 3163 - particularly in 182W/183W. The isotopic compositions of the natural waters, except for an extremely evaporated sample from Soda Lake, are similar to the NIST standard. This evaporative lake, formed by a maar, has a unique chemical composition compared to other surface waters with high W (800 ± 20 ng/g) and As (1665 ± 17 ng/g) concentrations; and relatively low Fe (5.00 ± 0.13 ng/g) and Mn (0.52 ± 0.07 ng/g). These results support recent observations of natural W isotopic variation and imply that W-isotope compositions may be useful for environmental applications of stable isotope geochemistry. 1. Irisawa, K. and Hirata, T. (2006) Tungsten isotopic analysis on six geochemical reference materials using multiple collector-ICP-mass spectrometry coupled with a rhenium-external correction technique. Journal of Analytical Atomic Spectrometry 21, 1387-1395.

  18. Climatic influences on the oxygen isotopic composition of biogenic silica in prairie grass

    NASA Astrophysics Data System (ADS)

    Webb, Elizabeth A.; Longstaffe, Fred J.

    2002-06-01

    Samples of Calamovilfa longifolia were collected from across the North American prairies to investigate the relationship between the oxygen-isotope composition of biogenic silica (phytoliths) deposited in this grass and relative humidity, temperature, and the oxygen-18 enrichment of soil water relative to local precipitation. The δ 18O values of silica in nontranspiring tissues were controlled by soil-water composition and temperature, whereas the oxygen-18 content of silica formed in leaf and inflorescence tissues was enriched further by transpiration. Accurate calculation of growing temperature was possible only when the oxygen-isotope compositions of both stem silica and soil water were known. However, the oxygen-isotope values of stem phytoliths can be used to calculate the variation in the isotopic composition of soil water across a North American temperature gradient. As plant organic matter decays and phytoliths are transferred to the soil, the temperature and soil-water signals carried by the oxygen-isotope composition of silica from nontranspiring tissues can be masked by the oxygen-18 enrichment of phytoliths from transpiring tissues. However, the overall oxygen-isotope composition of a soil-phytolith assemblage can be related to temperature using an empirical relationship based on temperature and the difference between soil-phytolith and estimated soil-water oxygen-isotope compositions.

  19. An Early Paleozoic orogenic gold belt along the Jiang-Shao Fault, South China: Evidence from fluid inclusions and Rb-Sr dating of quartz in the Huangshan and Pingshui deposits

    NASA Astrophysics Data System (ADS)

    Ni, Pei; Wang, Guo-Guang; Chen, Hui; Xu, Ying-Feng; Guan, Shen-Jin; Pan, Jun-Yi; Li, Lin

    2015-05-01

    There are several gold deposits in the eastern section of the regional Jiang-Shao Fault between the Yangtze and Cathaysia Blocks in South China. Auriferous quartz veins in these deposits are strictly hosted in second-order NE-trending ductile shear zones. The ores generally contain low amounts of sulfide minerals (<5%), with pyrite as the most common sulfide mineral hosting native gold. Detailed fluid inclusion work and Rb-Sr dating were conducted on the auriferous quartz veins from the Pingshui and Huangshan deposits. H2O-CO2 inclusions (type I) and aqueous inclusions (type II) ubiquitously coexist in the main mineralization stage veins in the Huangshan and Pingshui deposits. Type I and II inclusions in the Huangshan deposit have similar homogenization temperatures at 214-282 °C, but different salinities with 1.2-6.0 and 2.7-8.7 wt.% NaCl equivalent, respectively. In the gold orebodies from the Pingshui deposit, type I and II inclusions also have similar homogenization temperatures ranging from 236 to 304 °C, but different salinities ranging from 1.2 to 6.4 and from 3.2 to 9.8 wt.% NaCl equivalent, respectively. Fluid inclusion observations and microthermometric results show that the ore fluids are low salinity and CO2-rich. Petrography and microthermometric results of fluid inclusions suggest that extensive fluid immiscibility occurred during the gold mineralization stage. Rb-Sr dating of quartz-hosted fluid inclusions (ca. 450 Ma) for the gold mineralization at Pingshui, combined with previous radiometric age data (ca. 397 Ma) of gold mineralization at Huangshan, suggest that the regional gold mineralization was formed in the Early Paleozoic. This study suggests that there is an Early Paleozoic orogenic gold belt in the eastern section of the Jiang-Shao Fault, formed in response to the coeval northward underthrusting of the Cathaysia Block beneath the Yangtze Block during the Caledonian Orogeny in South China.

  20. Heterogeneous magnesium isotopic composition of the lower continental crust: A xenolith perspective

    NASA Astrophysics Data System (ADS)

    Teng, Fang-Zhen; Yang, Wei; Rudnick, Roberta L.; Hu, Yan

    2013-09-01

    We report 26 high-precision whole-rock Mg isotopic analyses for two suites of well-characterized granulite xenoliths from Chudleigh and McBride, North Queensland, Australia, in order to constrain the behavior of Mg isotopes during deep crustal processes and the Mg isotopic composition of the lower continental crust. Previous studies suggest that the Chudleigh granulites are a suite of cogenetic cumulates crystallized from mafic magmas that intruded into and assimilated the preexisting lower crust via combined assimilation and fractional crystallization (AFC). The δ26Mg values of the xenoliths range from -0.31 to -0.21‰ and correlate with radiogenic isotopes, reflecting mixing of mantle-derived mafic magma (δ26Mg = -0.31‰) with preexisting isotopically heavy crustal materials (δ26Mg = ˜ +0.5‰) through the AFC process. The McBride granulites range compositionally from mafic to felsic, and originated as cumulates, solidified mafic/felsic melts, and restites that formed during basaltic underplating and reworking of preexisting lower crust. Their δ26Mg values vary widely from -0.72 to +0.19‰. The large Mg isotopic variation in the McBride xenoliths reflects both distinct source compositions and metamorphic enrichment of garnet, which is isotopically light. Based on these results, the lower continental crust has a heterogeneous Mg isotopic composition, with a weighted average δ26Mg of -0.18‰. The bulk continental crust, based on available data, has an average Mg isotopic composition of -0.19‰, and is slightly heavier than the mantle. The highly heterogeneous Mg isotopic distribution in the crust indicates that chemical weathering not only modifies the upper crust compositions but also significantly influences lower crust compositions through emplacement of upper crustal materials into the deep crust.

  1. Sr-Nd isotope and geochemical characterisation of the Paleoproterozoic Västervik formation (Baltic Shield, SE-Sweden): a southerly exposure of Svecofennian metasiliciclastic sediments

    NASA Astrophysics Data System (ADS)

    Kleinhanns, I. C.; Fischer-Gödde, M.; Hansen, B. T.

    2012-01-01

    The Paleoproterozoic Västervik formation represents the southernmost exposure of Svecofennian metasediments and comprises a large psammitic succession of up to 5,000 m thickness dominated by quartzite with minor pelite and arkose. The Västervik formation was deposited in a time interval of ~30 m.y. from 1.88 until 1.85 Ga. Whole-rock geochemical data and Rb-Sr-Sm-Nd analyses in combination with bulk zircon U-Pb ID-TIMS studies help to gain insight into the depositional and geodynamic history of the metasiliciclastic units of the Västervik formation. Discrimination function diagrams show good agreement of major element composition with petrographic characterisation pointing towards a quartzose sedimentary provenance area with a tendency towards felsic igneous provenance. Trace element characteristics show typical upper crustal composition and remarkably similar patterns despite the respective petrographic differences. Sm-Nd isotope systematics reveal a restricted range of TDM with 2.3 ± 0.1 Ga and initial Nd (1.80 Ga) values from -4 to -2. These values are in agreement with known values from other Svecofennian sedimentary basins and support the interpretation of the Västervik formation as a typical Svecofennian metasedimentary sequence. Three samples were analysed with the zircon U-Pb ID-TIMS technique, and resulting mixing ages of ~2.1 Ga are typical for Svecofennian metasediments. The final stage of the geodynamic history of the Västervik area was a HT/LP overprint that caused intense migmatisation and anatectic production of in situ granite melts. This was accompanied by large-scale metasomatism, which led to a regional disturbance of the Rb-Sr isotope system indicating an age of ~1,750 Ma for this event. This age overlaps with timing of the tectonic activity of the Loftahammar-Linköping deformation zone (LLDZ), a large-scale deformation zone, lying directly to the north of the study area, presumably linking these two events.

  2. Rare earth abundances and Rb-Sr systematics of basalts, gabbro, anorthosite and minor granitic rocks from the Indian Ocean Ridge System, Western Indian Ocean

    USGS Publications Warehouse

    Hedge, C.E.; Futa, K.; Engel, C.G.; Fisher, R.L.

    1979-01-01

    Basalts dredged from the Mid-Indian Ocean Ridge System have rare earth, Rb, and Sr concentrations like those from other mid-ocean ridges, but have slightly higher Sr87/Sr86 ratios. Underlying gabbroic complexes are similar to the basalts in Sr87/Sr86, but are poorer K, Rb, and in rare earths. The chemical and isotopic data, as well as the geologic relations suggest a cumulate origin for the bulk of the gabbroic complexes. ?? 1979 Springer-Verlag.

  3. Herbivore tooth oxygen isotope compositions: Effects of diet and physiology

    SciTech Connect

    Kohn, M.J.; Valley, J.W.; Schoeninger, M.J.

    1996-10-01

    The applicability of rapid and precise laser probe analysis of tooth enamel for {delta}{sup 18}O has been verified, and the method has been applied to different modern herbivores in East Africa. Sampling and pretreatment procedures involve initial bleaching and grinding of enamel to <75 {mu}m, and elimination of adsorbed water and organic compounds with BrF{sub 5}. Typical analytical reproducibilities for 0.5-2 mg samples are {+-}0.08{per_thousand} ({+-} 1{sigma}). Chemical and spectroscopic characterization of pretreated but unanalyzed samples show no alteration compared to fresh enamel. Solid reaction products are nearly pure CaF{sub 2} with little evidence for residual O{sub 2}. Because laser probe fluorination extracts oxygen from all sites in the apatite structure (phosphate, structural carbonate, and hydroxyl), only unaltered tooth enamel ( >95% apatite) can be analyzed reliably. Different East African herbivores exhibit previously unsuspected compositional differences. Average enamel {delta}{sup 18}O values (V-SMOW) are approximately: 25{per_thousand} (goat). 27{per_thousand} (oryx), 28{per_thousand} (dikdik and zebra), 29{per_thousand} (topi), 30{per_thousand} (gerenuk), and 32{per_thousand} (gazelle). These compositions differ from generalized theoretical models, but are broadly consistent with expected isotope effects associated with differences in how much each animal (a) drinks, (b) eats C3 vs. C4 plants, and (c) pants vs. sweats. Consideration of diet, water turnover. and animal physiology will allow the most accurate interpretation of ancient teeth and targeting of environmentally-sensitive animals in paleoclimate studies. 66 refs., 2 figs., 2 tabs.

  4. Factors affecting the hydrogen isotopic composition of dissolved organic matter along a salinity gradient

    NASA Astrophysics Data System (ADS)

    Debond, A. A.; Ziegler, S. E.; Fogel, M. L.; Morrill, P. L.; Bowden, R.

    2010-12-01

    The role of terrestrial dissolved organic matter (DOM) in regulating estuarine ecosystem processes is poorly understood, in part due to difficulties in tracking terrestrial DOM in marine environments. Analysis of multiple stable isotopes (C, N, S) is often required due to poor separation of the carbon isotope signatures of marine and terrestrial sources. However, hydrogen isotopes exhibit greater fractionation. Marine DOM sources have a hydrogen isotope signature of 0‰ while terrestrial DOM can have signatures of up to -270‰ at the poles. Some challenges must be addressed before hydrogen isotopes can be used to track terrestrial DOM in aquatic environments. Hydrogen isotopes may undergo exchange between water and organic matter, obscuring terrestrial signatures. Riverine discharge into marine environments introduces terrestrial DOM to water of different chemical and isotopic compositions which could influence the isotopic composition of the terrestrial DOM. We investigate the effects of changes in water isotopic composition on DOM by introducing terrestrial DOM to freshwaters of isotopic compositions up to +1000‰ for up to two months. We also use surface water samples along a salinity transect at the Salmonier Arm, Newfoundland, Canada to investigate the effects of changes in water mass conditions (pH, salinity and water isotopes) on terrestrial DOM. In addition to changes in water mass conditions, methods for isolating estuarine DOM may regulate affect its isotopic composition. Ultrafiltration (UF), a size-exclusion technique, has been shown to isolate and concentrate the largest proportion of DOM in estuarine environments. UF separates DOM into low molecular weight (LMW, <1kDa) and high molecular weight (HMW, >1kDa) fractions. However, under certain processing conditions, some LMW DOM can be retained. During desalting (diafiltration), LMW DOM continues to be removed from the concentrate, whereas HMW DOM is retained. The proportion of LMW DOM retained

  5. Investigating the Source, Transport, and Isotope Composition of Water in the Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Griffis, T. J.; Schultz, N. M.; Lee, X.

    2011-12-01

    The isotope composition of water (liquid and vapor phases) can provide important insights regarding the source of water used by plants, the origins of atmospheric water vapor, and the sources of carbon dioxide. In recent years there have been significant advances in the ability to quantify the isotope composition of water and water vapor using optical isotope techniques. We have used and helped develop some of these techniques to determine the isotope composition of soil and plant waters, to measure the isoflux of water vapor between the land surface and atmosphere, and to examine the isotope composition of water vapor and deuterium excess in the atmospheric boundary layer. In this presentation we will discuss three related issues: 1) Identification and correction of spectral contamination in soil and plant water samples using optical techniques; 2) The benefits and practical limitations of quantifying the isotope composition of evapotranspiration using the eddy covariance approach; and 3) The scientific value and feasibility of tracking the long-term (seasonal and interannual) behavior of the isotope composition of water vapor and deuterium excess in the atmospheric boundary layer. A few short stories will be provided from experiments conducted in the lab, at the field scale, and from a very tall tower at the University of Minnesota from 2008 to 2011.

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

    USGS Publications Warehouse

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

    2005-01-01

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

  7. Correlated Os-Pb-Nd-Sr isotopes in the Austral-Cook chain basalts: the nature of mantle components in plume sources

    NASA Astrophysics Data System (ADS)

    Schiano, P.; Burton, K. W.; Dupré, B.; Birck, J.-L.; Guille, G.; Allègre, C. J.

    2001-04-01

    Osmium (Os), strontium (Sr), neodymium (Nd) and lead (Pb) isotopes have been measured on a suite of aphyric basalts from 12 islands of the Austral-Cook island archipelago, an area which exhibits a range in Pb isotope compositions that encompasses almost the entire range displayed by ocean island basalts (OIB). Although the samples have Os concentrations (1.69-34.80 ppt) at the lower end of the range measured for OIB, they display a range of initial 187Os/ 188Os ratios (between 0.1279 and 0.1594) similar to that defined by olivine-phyric, Os-rich OIB. Positive Os-Nd, Os-Pb and negative Os-Sr isotope correlations are documented, indicating that the isotopic arrays represent various proportions of mixing between a HIMU-type end-member represented by Mangaia and Tubuai islands and characterized by radiogenic Os and Pb isotopic compositions, and an end-member represented by Rarotonga island which is characterized by unradiogenic Os and intermediate Sr, Nd and Pb isotopic compositions. The HIMU signature of the mantle component involved in Tubuai-Mangaia mantle sources requires long-term enrichments of U and Th relative to Pb and Re relative to Os, without associated increase in Rb/Sr, that are consistent with recycled oceanic crust. The end-member represented by Rarotonga basalts shows Os, Sr, Nd, and Pb isotopic signatures similar to those presumed for the 'bulk silicate earth' (BSE), which cannot be obtained by mixing the four mantle components (DMM, HIMU and EM1 and 2) generally used to circumscribe the Sr-Nd-Pb isotopic data of OIB. The primitive-like isotopic characters of this end-member might be ascribed to the presence of undepleted material from a lower segment of the mantle in the source of the Austral-Cook island basalts (and more specifically Rarotonga basalts); however, such a hypothesis is challenged by both the absence of a primordial 3He signature and the non-primitive Ce/Pb and Nb/U values for the Austral-Cook island basalts. Alternatively, assuming

  8. Hydrogen and oxygen in brine shrimp chitin reflect environmental water and dietary isotopic composition

    NASA Astrophysics Data System (ADS)

    Nielson, Kristine E.; Bowen, Gabriel J.

    2010-03-01

    Hydrogen and oxygen isotope ratios of the common structural biopolymer chitin are a potential recorder of ecological and environmental information, but our understanding of the mechanisms of incorporation of H and O from environmental substrates into chitin is limited. We report the results of a set of experiments in which the isotopic compositions of environmental water and diet were varied independently in order to assess the contribution of these variables to the H and O isotopic composition of Artemia franciscana chitin. Hydrogen isotope ratios of chitin were strongly linearly correlated with both food and water, with approximately 26% of the hydrogen signal reflecting food and approximately 38% reflecting water. Oxygen isotopes were also strongly correlated with the isotopic composition of water and food, but whereas 69% of oxygen in chitin exchanged with environmental water, only 10% was derived from food. We propose that these observations reflect the position-specific, partial exchange of H and O atoms with brine shrimp body water during the processes of digestion and chitin biosynthesis. Comparison of culture experiments with a set of natural samples collected from the Great Salt Lake, UT in 2006 shows that, with some exceptions, oxygen isotope compositions of chitin track those of water, whereas hydrogen isotopes vary inversely with those of lake water. The different behavior of the two isotopic systems can be explained in terms of a dietary shift from allochthonous particulate matter with relatively higher δ 2H values in the early spring to autochthonous particulate matter with significantly lower δ 2H values in the late summer to autumn. These results suggest oxygen in chitin may be a valuable proxy for the oxygen isotopic composition of environmental water, whereas hydrogen isotope values from the same molecule may reveal ecological and biogeochemical changes within lakes.

  9. Ages and Nd, Sr isotopic systematics in the Sierran foothills ophiolite belt, CA: the Smartville and Feather River complexes

    SciTech Connect

    Shaw, H.F.; Niemeyer, S.

    1985-01-01

    Sm-Nd dating has shown the Kings-Kaweah ophiolite to be approx. 480 My old. Its Nd, Sr, and Pb isotopic compositions require an unusually old depleted mantle source. Samples from the Smartville and Feather River complexes have been analyzed in a search for similar highly depleted, early Paleozoic ophiolites in the northern foothills ophiolite belt. Six whole rocks from Smartville, encompassing representative lithologies, plus plagioclase and pyroxene mineral separates define a 183 +/- 22 My Sm-Nd isochron. This age, interpreted as the igneous age, is older than, but within error of, approx. 160 My U-Pb ages previously obtained from plagiogranite zircon analyses. One diabase with unusually high Rb/Sr yields a depleted mantle Sr model age of 200 +/- 25 My, consistent with the Sm-ND age. These compositions are clearly oceanic in character but do not discriminate among possible tectonic settings for the formation of the Smartville complex. Sm-Nd data for flaser gabbros and related rocks from Feather River scatter about an approx. 230 My errorchron with element of/sub Nd/(T) = +6.3 to +8.7. Initial /sup 87/Sr//sup 86/Sr ranges from 0.7028 to 0.7031. These results indicate a complex history with initial isotopic heterogeneities and/or disturbances of the isotopic systems. If primary, the element of/sub Nd/ (T) values are somewhat low, suggesting a possible arc origin for these rocks. Neither the Smartville nor Feather R. complexes appear to be related to the Kings-Kaweah ophiolite which, so far, is unique among foothill ophiolites in having an early Paleozoic age and a clear MORB, as opposed to arc or marginal basin, isotopic signature.

  10. The iron isotope composition of enstatite meteorites: Implications for their origin and the metal/sulfide Fe isotopic fractionation factor

    NASA Astrophysics Data System (ADS)

    Wang, Kun; Savage, Paul S.; Moynier, Frédéric

    2014-10-01

    Despite their unusual chemical composition, it is often proposed that the enstatite chondrites represent a significant component of Earth’s building materials, based on their terrestrial similarity for numerous isotope systems. In order to investigate a possible genetic relationship between the Fe isotope composition of enstatite chondrites and the Earth, we have analyzed 22 samples from different subgroups of the enstatite meteorites, including EH and EL chondrites, aubrites (main group and Shallowater) and the Happy Canyon impact melt. We have also analyzed the Fe isotopic compositions of separated (magnetic and non-magnetic) phases from both enstatite chondrites and achondrites. On average, EH3-5 chondrites (δ56Fe = 0.003 ± 0.042‰; 2 standard deviation; n = 9; including previous literature data) as well as EL3 chondrites (δ56Fe = 0.030 ± 0.038‰; 2 SD; n = 2) have identical and homogeneous Fe isotopic compositions, indistinguishable from those of the carbonaceous chondrites and average terrestrial peridotite. In contrast, EL6 chondrites display a larger range of isotopic compositions (-0.180‰ < δ56Fe < 0.181‰; n = 11), a result of mixing between isotopically distinct mineral phases (metal, sulfide and silicate). The large Fe isotopic heterogeneity of EL6 is best explained by chemical/mineralogical fragmentation and brecciation during the complex impact history of the EL parent body. Enstatite achondrites (aubrites) also exhibit a relatively large range of Fe isotope compositions: all main group aubrites are enriched in the light Fe isotopes (δ56Fe = -0.170 ± 0.189‰; 2 SD; n = 6), while Shallowater is, isotopically, relatively heavy (δ56Fe = 0.045 ± 0.101‰; 2 SD; n = 4; number of chips). We take this variation to suggest that the main group aubrite parent body formed a discreet heavy Fe isotope-enriched core, whilst the Shallowater meteorite is most likely from a different parent body where core and silicate material remixed. This could be

  11. Soil drying effects on the carbon isotope composition of soil respiration

    EPA Science Inventory

    Stable isotopes are used widely as a tool for determining sources of carbon (C) fluxes in ecosystem C studies. Environmental factors that change over time, such as moisture, can create dynamic changes in the isotopic composition of C assimilated by plants, and offers a unique opp...

  12. Non-chondritic sulphur isotope composition of the terrestrial mantle.

    PubMed

    Labidi, J; Cartigny, P; Moreira, M

    2013-09-12

    Core-mantle differentiation is the largest event experienced by a growing planet during its early history. Terrestrial core segregation imprinted the residual mantle composition by scavenging siderophile (iron-loving) elements such as tungsten, cobalt and sulphur. Cosmochemical constraints suggest that about 97% of Earth's sulphur should at present reside in the core, which implies that the residual silicate mantle should exhibit fractionated (34)S/(32)S ratios according to the relevant metal-silicate partition coefficients, together with fractionated siderophile element abundances. However, Earth's mantle has long been thought to be both homogeneous and chondritic for (34)S/(32)S, similar to Canyon Diablo troilite, as it is for most siderophile elements. This belief was consistent with a mantle sulphur budget dominated by late-accreted chondritic components. Here we show that the mantle, as sampled by mid-ocean ridge basalts from the south Atlantic ridge, displays heterogeneous (34)S/(32)S ratios, directly correlated to the strontium and neodymium isotope ratios (87)Sr/(86)Sr and (143)Nd/(144)Nd. These isotope trends are compatible with binary mixing between a low-(34)S/(32)S ambient mantle and a high-(34)S/(32)S recycled component that we infer to be subducted sediments. The depleted end-member is characterized by a significantly negative δ(34)S of -1.28 ± 0.33‰ that cannot reach a chondritic value even when surface sulphur (from continents, altered oceanic crust, sediments and oceans) is added. Such a non-chondritic (34)S/(32)S ratio for the silicate Earth could be accounted for by a core-mantle differentiation record in which the core has a (34)S/(32)S ratio slightly higher than that of chondrites (δ(34)S = +0.07‰). Despite evidence for late-veneer addition of siderophile elements (and therefore sulphur) after core formation, our results imply that the mantle sulphur budget retains fingerprints of core-mantle differentiation. PMID:24005324

  13. Isotope composition (C, H, O) and gas potential assessment in the South Caspian depression (Azerbaijan)

    NASA Astrophysics Data System (ADS)

    Poletayev, A. V.

    2009-04-01

    The large amount of HC isotope composition material of over 330 samples allows to study gas potential assessment within the South Caspian depression. Maps of isotope composition changes according to area extent, as well as graphs of HC distribution depending upon stratigraphic age including rocks, graphs of isotope composition change on sampling depth were compiled for HC study and oil-gas deposits formation. Comparison of mud volcanoes gases, oil and gas fields, gas-hydrates and bottom sediments was conducted. Gases genesis according to M. Shoelle and A. James methodic was studied. Model of area paleoconstruction was studied. Comparison of mud volcanoes gases with gases of oil fields within South Caspian depression shows that their isotope composition varies within the same ranges. Their difference is observed in chemical composition. Mud volcanoes gases are sharply impoverished by amount of heavy hydrocarbons. Study of isotope gases composition distribution in extent area allowed to distinguish zones and areas with different composition of heavy isotope. For example, in the deep-seated areas of the South Caspian depression toward flank zones of Low Kura depression as well some areas of Baku archipelago and Absheron peninsula gradually one can observe zones with a low content of heavy carbon isotope etc. Isotope gases composition depending upon stratigraphic age of including rocks has a certain peculiarities. From low to the upper section of PS as well as deposits of Cretaceous system toward chokrak regiostage (underlying PS deposits) one can observe increase of light carbon isotope. This fact allows to suppose that there exits two stages of HC formation. Comparison of HC gases isotope composition with sampling depth allowed to conclude that in the near-flank zones oil-gas deposits were re-formed by a large gas volumes the source of which was there same deposits within new thermobaric conditions. Gases of biochemical, diagenetic and thermocatalytic genesis etc

  14. Triple-Point Temperature and the Isotopic Composition of Three Commercial Neon Gases

    NASA Astrophysics Data System (ADS)

    Yang, I.; Gam, K. S.; Joung, W.; Kim, Y.-G.

    2015-08-01

    The triple-point temperature of neon, , is known to have dependence on the isotopic composition. Recently, the Technical Annex for the International Temperature Scale of 1990 was updated to specify the method of correction for the isotopic reference ratio of neon. In this study, to confirm this correction in the Technical Annex independently, the effects of the isotopic composition of neon on for three commercial neon gas sources were studied. For the measurement of the isotopic composition, a gas mass spectrometer was used to compare the sample gases with a reference neon gas whose isotopic composition was known with high precision by a gravimetric method. For the measurement of , an open-cell type cryostat for the realization of low-temperature fixed points was used. The physical cell and the thermal environment around it remained very similar for all measurements with the neon gases due to the nature of the open-cell type system. Therefore, the difference in among different samples could be measured with a relatively low uncertainty, canceling many systematic effects that are common to all measurements. Our result was consistent with the correction in the Technical Annex. Furthermore, because one of the commercial neon gases was the bottle that was used for KRISS measurements in the international comparison CCT-K2, it is now possible to correct the measurement for the reference isotopic ratio and compare it with other measurements for which isotopic composition data are available.

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

    NASA Astrophysics Data System (ADS)

    Rudnick, Roberta L.; Goldstein, Steven L.

    1990-05-01

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

  16. Monitoring the water vapor isotopic composition in the temperate North Atlantic

    NASA Astrophysics Data System (ADS)

    Sveinbjörnsdottir, Arny E.; Steen-Larsen, Hans Christian; Jonsson, Thorsteinn; Johnsen, Sigfus J.

    2013-04-01

    Water stable isotopes have during many decades been used as climate proxies and indicators for variations in the hydrological cycle. However we are to a great extent still using simple empirical relationships without any deeper theoretical understanding. In order to properly relate changes in the climate and hydrological cycle to changes in the observed stable water isotopic signal we must understand the underlying physical processes. Furthermore it is a challenge for General Climate Models to adequately represent the isotopes in the hydrological cycle because of lack of in-situ measurements of the atmospheric water-vapor composition in the source regions. During the fall of 2010 we installed an autonomous water vapor spectroscopy laser (from Los Gatos Research) in a lighthouse on the South Coast of Iceland (63.83 N 21.47W) with the plan to be operational for several years. The purpose of this installation was through monitoring of the water vapor isotopic composition to understand the physical processes governing the isotopic composition of the water vapor evaporated from the ocean as well as the processes of mixing between the free troposphere and marine boundary layer. Because of the remoteness of the monitoring site and simple topography we are able to isolate the 'fingerprint' on the isotopic signal in the water vapor from respectively the ocean and the interior highland leading to a near perfect case-study area. Using back-trajectories we find a strong influence of the origin of the air masses on the measured isotopic composition. The mixing of the marine-boundary layer is found to strongly influence the measured isotopic composition. The second order isotopic parameter, d-excess, is contrary to theory and previous observations found not to depend on the relative humidity. However we do find a good correlation between the d-excess and the measured isotopic composition. We speculate that the lack of correlation between d-excess and relative humidity can be

  17. Monitoring the water vapor isotopic composition in the temperate North Atlantic

    NASA Astrophysics Data System (ADS)

    Steen-Larsen, H. C.; Sveinbjörnsdottir, A. E.; Jónsson, T. H.; Johnsen, S. J.

    2012-04-01

    Water stable isotopes have during many decades been used as climate proxies and indicators for variations in the hydrological cycle. However we are to a great extent still using simple empirical relationships without any deeper theoretical understanding. In order to properly relate changes in the climate and hydrological cycle to changes in the observed stable water isotopic signal we must understand the underlying physical processes. Furthermore it is a challenge for General Climate Models to adequately represent the isotopes in the hydrological cycle because of lack of in-situ measurements of the atmospheric water-vapor composition in the source regions. During the fall of 2010 we installed an autonomous water vapor spectroscopy laser (from Los Gatos Research) in a lighthouse on the South Coast of Iceland (63.83 N 21.47W) with the plan to be operational for several years. The purpose of this installation was through monitoring of the water vapor isotopic composition to understand the physical processes governing the isotopic composition of the water vapor evaporated from the ocean as well as the processes of mixing between the free troposphere and marine boundary layer. Because of the remoteness of the monitoring site and simple topography we are able to isolate the 'fingerprint' on the isotopic signal in the water vapor from respectively the ocean and the interior highland leading to a near perfect case-study area. Using back-trajectories we find a strong influence of the origin of the air masses on the measured isotopic composition. The mixing of the marine-boundary layer is found to strongly influence the measured isotopic composition. The second order isotopic parameter, d-excess, is contrary to theory and previous observations found not to depend on the relative humidity. However we do find a good correlation between the d-excess and the measured isotopic composition. We speculate that the lack of correlation between d-excess and relative humidity can be

  18. Non-destructive measurement of carbonic anhydrase activity and the oxygen isotope composition of soil water

    NASA Astrophysics Data System (ADS)

    Jones, Sam; Sauze, Joana; Ogée, Jérôme; Wohl, Steven; Bosc, Alexandre; Wingate, Lisa

    2016-04-01

    Carbonic anhydrases are a group of metalloenzymes that catalyse the hydration of aqueous carbon dioxide (CO2). The expression of carbonic anhydrase by bacteria, archaea and eukarya has been linked to a variety of important biological processes including pH regulation, substrate supply and biomineralisation. As oxygen isotopes are exchanged between CO2 and water during hydration, the presence of carbonic anhydrase in plants and soil organisms also influences the oxygen isotope budget of atmospheric CO2. Leaf and soil water pools have distinct oxygen isotope compositions, owing to differences in pool sizes and evaporation rates, which are imparted on CO2during hydration. These differences in the isotopic signature of CO2 interacting with leaves and soil can be used to partition the contribution of photosynthesis and soil respiration to net terrestrial CO2 exchange. However, this relies on our knowledge of soil carbonic anhydrase activity and currently, the prevalence and function of these enzymes in soils is poorly understood. Isotopic approaches used to estimate soil carbonic anhydrase activity typically involve the inversion of models describing the oxygen isotope composition of CO2 fluxes to solve for the apparent, potentially catalysed, rate of oxygen exchange during hydration. This requires information about the composition of CO2 in isotopic equilibrium with soil water obtained from destructive, depth-resolved soil water sampling. This can represent a significant challenge in data collection given the considerable potential for spatial and temporal variability in the isotopic composition of soil water and limited a priori information with respect to the appropriate sampling resolution and depth. We investigated whether we could circumvent this requirement by constraining carbonic anhydrase activity and the composition of soil water in isotopic equilibrium with CO2 by solving simultaneously the mass balance for two soil CO2 steady states differing only in the

  19. Isotopic Composition of Presolar Silicon Carbide Grains Analyzed with CHILI

    NASA Astrophysics Data System (ADS)

    Stephan, T.; Trappitsch, R.; Davis, A. M.; Pellin, M. J.; Rost, D.; Savina, M. R.; Jadhav, M.; Kelly, C. H.

    2015-07-01

    Twenty-two presolar SiC grains were analyzed for Sr, Zr, and Ba isotopes with the Chicago Instrument for Laser Ionization. Most grains showed isotope patterns consistent with formation in AGB star like observed previously. One grain is a supernova grain.

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

    USGS Publications Warehouse

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

    2004-01-01

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

  1. Enstatite Chondrites, their Origin and the Composition of the Earth

    NASA Astrophysics Data System (ADS)

    Jacobsen, S. B.; Petaev, M. I.; Huang, S.

    2012-12-01

    The nearly identical O isotopic compositions of the enstatite chondrites (EC), Earth's mantle, and Moon have been used to argue that the EC provide the best Solar System material for estimating the chemical composition of the Earth. A possible link between the EC and Earth is further supported by recent observations that EC and Earth have the same isotopic compositions for both major and minor elements (O, Ca, Ti, Cr) which exhibit substantial variations among different chondrite groups, with Si being the only exception. However, there is a huge mismatch in chemical compositions between the EC and Earth. For example, the EC have much too high Rb/Sr and K/U ratios and are depleted in FeO and refractory lithophile elements compared to the composition of Earth's mantle deduced from terrestrial rocks. This discrepancy could be resolved by assuming that the Earth and EC had a common nebular precursor but they have experienced different chemical evolution. Such an assumption is supported by the mineralogy and O isotopic data for the most primitive EH3 chondrites. The abundant FeO-bearing silicates, compositionally similar to those in other classes of chondrites, are well documented in ECs, with most silicates having O isotopic compositions of the bulk EC values. Recent studies showed that the chalcophile behaviour of Ca, Mg, Na, and other elements in EC is due to secondary processing of FeO-bearing silicates in an H-poor environment with high fS2 (Fe-FeS buffer) and fO2 close to the CO-CO2 buffer. We suggest that a nebular reservoir that produced the precursor material for EC has also produced the building blocks for the Earth, chemically similar to the widely accepted Earth's composition derived from mantle peridotites. It is possible that the EC precursors initially formed in an isotopically homogeneous inner terrestrial planet region (Mercury, Venus, Earth) by the disruption of a planetesimal and then were scattered to an isotopically heterogeneous outer terrestrial

  2. The effect of small scale variablity in isotopic composition of precipitation on hydrograph separation results

    NASA Astrophysics Data System (ADS)

    Fischer, Benjamin; van Meerveld, Ilja; Seibert, Jan

    2016-04-01

    Understanding runoff processes is important for predictions of streamflow quantity and quality. The two-component isotope hydrograph separation (IHS) method is a valuable tool to study how catchments transform rainfall into runoff. IHS allows the stormflow hydrograph to be separated into rainfall (event water) and water that was stored in the catchment before the event (pre-event water). To be able to perform an IHS, water samples of baseflow (pre-event water) and stormflow are collected at the stream outlet. Rainfall is usually collected at one location by hand as an event total or sampled sequentially during the event. It is usually assumed that the spatial variability in rainfall and the isotopic composition of rainfall are negligible for small (<10km2) catchments. However, different studies have shown that precipitation can vary within short distances. Subsequently it remains unclear how the spatio-temproal variability of rainfall and the stable isotope composition of rainfall affect the results of an IHS. In this study, we investigated the effects of the spatio-temporal variability in the isotopic composition of rainfall across a small headwater catchment in Switzerland. Rainfall was measured at eight locations and three streams (catchment area of 0.15, 0.23, and 0.7 km2). The isotopic composition of rainfall and streamflow were sampled for 10 different rain events (P: 5 mm intervals, Q: 12 to 51 samples per events). This dataset was used to perform a two-component isotope hydrograph separation. The results show that for some events the spatial variability in total rainfall, mean and maximum rainfall intensity and stable isotope composition of rainfall was high. There was no relation between the stable isotope composition of rainfall and the rainfall sum, rainfall intensity or altitude. The spatial variability of the isotopic composition of rainfall was for 4 out of the 10 events as large as the temporal variability in the isotopic composition. Different

  3. A comparative Rb-Sr, Sm-Nd, and K-Ar study of shocked norite 78236 - Evidence of slow cooling in the lunar crust

    NASA Technical Reports Server (NTRS)

    Nyquist, L. E.; Bogard, D. D.; Wooden, J. L.; Bansal, B. M.; Wiesmann, H.; Shih, C.-Y.; Reimold, W. U.

    1982-01-01

    The sample 78236 was chipped from the top of a norite boulder at Station 8 by the Apollo 17 landing team. Jackson et al. (1975) concluded that this rock formed at a depth of 8-30 km in the lunar crust and suggested that it was excavated by a large basin-forming impact event. A petrographic description of the boulder is provided, and isotopic analyses are discussed. Attention is given to a chronology for 78236 which seems to be most consistent with radiometric and other evidence. It is proposed that cumulate norite 78236 formed deep in the lunar crust approximately 4.4 AE ago. The rock cooled slowly in the crust until it was excavated by a major basin-forming event. Excavation may have occurred about 4.2 AE ago, but the time of this event is not well constrained.

  4. Rb-Sr age and content of potassium, rubidium strontium, barium, and rare earths in surface material from the Sea of Fertility

    NASA Technical Reports Server (NTRS)

    Allegre, C. J.; Birck, J. L.; Loubet, M.; Provost, A.

    1974-01-01

    The Luna 16 automatic station returned from the Sea of Fertility a 35 cm long column of lunar surface material. 1 g of the Luna 16 lunar surface material, taken at a depth of 22 cm, consists of fine material: surface material and fine fragments of rocks from 1 to 4 mm in diameter. Analyses made on 17 mg of the fine lunar surface material are presented. The results obtained for the Luna 16 surface material are plotted on the diagram of the isotopic evolution of strontium and show that this surface material is most depleted of radiogenic Sr-87 of all the known lunar surface materials and that the point characterizing Lunar 16 lies somewhat to the right of the line corresponding to an age of 4.6 billion years.

  5. Origin and time-space distribution of hydrothermal systems in east-central Australian sedimentary basins: Constraints from illite geochronology and isotope geochemistry.

    NASA Astrophysics Data System (ADS)

    Uysal, I. Tonguç

    2016-04-01

    Some well-known precious mineral deposits and hydrocarbon resources occur extensively in east-central Australian sedimentary Basins. The metal occurrences are abundant in northwestern and eastern part of Queensland, whereas no significant deposits are known in large areas further south, which may, however, be hidden beneath the Jurassic-Cretaceous sedimentary basins. Important hydrocarbon resources exist within the Jurassic-Cretaceous sedimentary rocks at relatively shallow depths, of which the distribution represent zones of high paleo-geothermal gradients. This study examines the time-space distribution in relation to the regional tectonic history of concealed metal deposits and areas of high paleo-geothermal gradient leading to hydrocarbon maturation. To this end, authigenic illitic clay minerals representing various locations and stratigraphic depths in east-central Australia were investigated, of which the Rb-Sr and Ar-Ar geochronology and stable isotope geochemistry assist in delineating zones of hydrothermal systems responsible for hydro-carbon maturation/migration and potentially ore deposition. The Late Carboniferous - Early Permian crustal extension that affected large areas of eastern Australia and led to the epithermal mineralisations (e.g., the Drummond Basin) is also recorded in northern South Australia and southwest Queensland. A Late Triassic - Early Jurassic tectonic event being responsible for coal maturation and gas generation in the Bowen Basin and the epithermal mineralisation in the North Arm goldfield in SE Queensland likewise affected the areas much further west in Queensland. Some illites from the basement in outback Queensland and fault gouges from the Demon Fault in NE New South Wales yield younger Rb-Sr and Ar-Ar ages indicating the effect of hydrothermal processes as a result of a Middle-Upper Jurassic tectonic event. The majority of illite samples from the crystalline basement rocks, Permian Cooper Basin, and Jurassic

  6. Changes in Oxygen Isotopes Composition of Precipitation over Tibetan Plateau during Cenozoic

    NASA Astrophysics Data System (ADS)

    Botsyun, S.; Sepulchre, P.; Donnadieu, Y.; Risi, C. M.; Fluteau, F.

    2014-12-01

    Despite the increasing role of the stable oxygen isotopes measurements for reconstructing mountains belts paleoelevation, some issues remain that lead to a large uncertainty in paleoelevation estimationes. Among them, the use of modern isotopic lapse rate with no account of climate change linked to lower topography can lead to misinterpretation of uplift rates. In this study, we use the atmospheric general circulation model LMDZ-iso to simulate changes in isotopic composition of precipitation due to uplift of the Himalayas and Tibetan plateau. Various scenarios of TP growth have been applied together with Paleocene, Eocene, Oligocene and Miocene boundary conditions. Our simulations allow us to estimate the magnitude of precipitation, temperature and wind field changes related to the spatial and temporal evolution of the Tibetan Plateau and Himalayas. Such changes affected the isotopic composition of precipitation during the Cenozoic.We investigate the impact of these changes on the isotopic lapse rate and the implications for paleoelevation estimates.

  7. Calcium and Oxygen Isotopic Composition of Calcium Carbonates

    NASA Astrophysics Data System (ADS)

    Niedermayr, Andrea; Eisenhauer, Anton; Böhm, Florian; Kisakürek, Basak; Balzer, Isabelle; Immenhauser, Adrian; Jürgen Köhler, Stephan; Dietzel, Martin

    2016-04-01

    Different isotopic systems are influenced in multiple ways corresponding to the crystal structure, dehydration, deprotonation, adsorption, desorption, isotope exchange and diffusion processes. In this study we investigated the structural and kinetic effects on fractionation of stable Ca- and O-isotopes during CaCO3 precipitation. Calcite, aragonite and vaterite were precipitated using the CO2 diffusion technique[1]at a constant pH of 8.3, but various temperatures (6, 10, 25 and 40° C) and precipitation rates R (101.5 to 105 μmol h‑1 m‑2). The calcium isotopic fractionation between solution and vaterite is lower (Δ44/40Ca= -0.10 to -0.55 ‰) compared to calcite (-0.69 to -2.04 ‰) and aragonite (-0.91 to -1.55 ‰). In contrast the fractionation of oxygen isotopes is highest for vaterite (32.1 ‰), followed by aragonite (29.2 ‰) and calcite (27.6 ‰) at 25° C and equilibrium. The enrichment of 18O vs. 16O in all polymorphs decreases with increasing precipitation rate by around -0.7 ‰ per log(R). The calcium isotopic fractionation between calcite/ vaterite and aqueous Ca2+ increases with increasing precipitation rate by ˜0.45 ‰ per log(R) and ˜0.1 ‰ per log(R) at 25° C and 40° C, respectively. In contrast the fractionation of Ca-isotopes between aragonite and aqueous Ca2+ decreases with increasing precipitation rates. The large enrichment of 18O vs. 16O isotopes in carbonates is related to the strong bond of oxygen to the small and highly charged C4+-ion. In contrast equilibrium isotopic fractionation between solution and calcite or vaterite is nearly zero as the Ca-O bond length is similar for calcite, vaterite and the hydrated Ca. Aragonite incorporates preferentially the lighter 40Ca isotope as it has very large Ca-O bonds in comparison to the hydrated Ca. At the crystal surface the lighter 40Ca isotopes are preferentially incorporated as dehydration and diffusion of lighter isotopes are faster. Consequently, the surface becomes enriched in

  8. The Isotopic Composition of Cosmic-Ray Iron and Nickel

    NASA Technical Reports Server (NTRS)

    Wiedenbeck, M.; Binns, W.; Christian, E.; Cummings, A.; George, J.; Hink, P.; Klarmann, J.; Leske, R.; Lijowski, M.; Mewaldt, R.; Stone, E.; Rosenvinge, T. von

    2000-01-01

    Observations from the Cosmic Ray Isotope Spectrometer (CRIS) on ACE have been used to derive contraints on the locations, physical conditions, and time scales for cosmic-ray acceleration and transport.

  9. Isotopic composition of Lake Agassiz-Ojibway water just prior to final drainage

    NASA Astrophysics Data System (ADS)

    Hillaire-Marcel, C.; Helie, J.; McKay, J.; Lalonde, A.

    2006-12-01

    Controversies persist with respect to the impact of the final drainage of Lake Agassiz-Ojibway on the thermohaline circulation of the North Atlantic, some 8.4 ka ago. The lack of response of planktic foraminifer isotope records, off Hudson Strait (i.e., at the outlet of the drainage channel) constitutes one of the most puzzling elements in this debate. However, data on the isotopic composition of drainage waters are needed to estimate the response of the 18-O-salinity relationship in NW Atlantic surface waters. In the literature, a large array of isotopic compositions have been suggested, notably for modeling experiment purposes. Scattered information about the isotopic composition of Lake Agassiz water does exist. It includes isotopic measurements of pore waters of lacustrine sediments [1], analyses of oxygen isotopes in cellulose from algal or plant remains [2], and stable isotope compositions of concretions from varves [3]. Whereas, relatively low oxygen isotope values (apx. -25 per mil vs. VSMOW) are inferred for Lake Agassiz waters during cold pulses of the deglaciation, most data suggest much higher values during the final stages of Lake Agassiz-Ojiway, just prior to its drainage. Calcareous concretions from Lake Ojibway varves (not necessarily contemporaneous to the lacustrine stage) yielded oxygen isotope compositions of about -10 per mil (vs. VPDB), suggesting values as high as -14 per mil (vs. VSMOW) for pore waters (assuming a 0-4 degrees C temperature range). Similar high values (as high as -8 per mil vs. VSMOW [1]) were also estimated from pore water analyses of contemporaneous Lake Agassiz sediments. Here, we used a core raised from Eastern Hudson Bay, off Great Whale River, to further document isotopic compositions of the lake waters prior to their drainage into the North Atlantic. The 7.40 m long core has an apx. 1.3 m-thick lacustrine layer at its base, including the drainage sub- layer. It is overlain by Tyrrell Sea clays. Scarce valves of Candona

  10. The isotopic composition of cosmic-ray calcium

    NASA Technical Reports Server (NTRS)

    Wiedenbeck, M. E.; George, J. S.; Binns, W. R.; Christian, E. R.; Cummings, A. C.; Davis, A. J.; Israel, M. H.; Leske, R. A.; Mewaldt, R. A.; Stone, E. C.; Rosenvinge, T. T. von

    2001-01-01

    We find that the relative abundance of cosmic ray calcium isotopes in the cosmic-ray source are very similar to those found in solar-system material, in spite of the fact that different types of stars are thought to be responsible for producing these two isotopes. This observation is consistent with the view that cosmic rays are derived from a mixed sample of interstellar matter.

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

    NASA Astrophysics Data System (ADS)

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

    2011-11-01

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

  12. Analysis of the site-specific carbon isotope composition of propane by gas source isotope ratio mass spectrometer

    NASA Astrophysics Data System (ADS)

    Piasecki, Alison; Sessions, Alex; Lawson, Michael; Ferreira, A. A.; Neto, E. V. Santos; Eiler, John M.

    2016-09-01

    Site-specific isotope ratio measurements potentially provide valuable information about the formation and degradation of complex molecules-information that is lost in conventional bulk isotopic measurements. Here we discuss the background and possible applications of such measurements, and present a technique for studying the site-specific carbon isotope composition of propane at natural abundance based on mass spectrometric analysis of the intact propane molecule and its fragment ions. We demonstrate the feasibility of this approach through measurements of mixtures of natural propane and propane synthesized with site-specific 13C enrichment, and we document the limits of precision of our technique. We show that mass balance calculations of the bulk δ13C of propane based on our site-specific measurements is generally consistent with independent constraints on bulk δ13C. We further demonstrate the accuracy of the technique, and illustrate one of its simpler applications by documenting the site-specific carbon isotope signature associated with gas phase diffusion of propane, confirming that our measurements conform to the predictions of the kinetic theory of gases. This method can be applied to propane samples of moderate size (tens of micromoles) isolated from natural gases. Thus, it provides a means of studying the site-specific stable isotope systematics of propane at natural isotope abundances on sample sizes that are readily recovered from many natural environments. This method may also serve as a model for future techniques that apply high-resolution mass spectrometry to study the site-specific isotopic distributions of larger organic molecules, with potential applications to biosynthesis, forensics and other geochemical subjects.

  13. The Sr isotope composition of the world ocean, marginal and inland seas: Implications for the Sr isotope stratigraphy

    NASA Astrophysics Data System (ADS)

    Kuznetsov, A. B.; Semikhatov, M. A.; Gorokhov, I. M.

    2012-11-01

    We studied the Sr isotope composition of shells of modern shallow-water mollusks and coral fragments. Twenty five of the studied samples were collected in beach zones of open oceans and marginal seas; twelve and eight additional samples are from saline and freshened inland seas respectively. The 87Sr/86Sr ratio in samples from the Atlantic, Indian, and Pacific oceans and their marginal seas corresponds on average to 0.709202 ± 0.000003 and coincides with the average ratio in the standard USGS EN-1 sample. The average 87Sr/86Sr ratio in inner parts of evaporite subbasins of the Mediterranean and Red seas is identical to that of the oceanic water. In shells of shallow-water mollusks from the Black Sea and Sea of Azov, where the degree of seawater dilution by riverine runoff is as high as 50 to 70%, the 87Sr/86Sr ratio is lower than that in the oceans by only a value of 0.00002 on average. As oceanic waters penetrated into these freshwater basins no earlier than in the Holocene, we conclude that the Sr isotopic equilibration with the oceanic water is realized very rapidly in the epicontinental seas even under conditions of restricted water exchange with the World Ocean. The established uniformity of the Sr isotope composition in all geographic types of currently existing sea basins open to the World Ocean proves the efficiency of the Sr isotope stratigraphy in correlation of contemporaneous chemogenic sediments.

  14. Oxygen isotopic composition of relict olivine grains in cosmic spherules: Links to chondrules from carbonaceous chondrites

    NASA Astrophysics Data System (ADS)

    Rudraswami, N. G.; Prasad, M. Shyam; Nagashima, K.; Jones, R. H.

    2015-09-01

    Most olivine relict grains in cosmic spherules selected for the present study are pristine and have not been disturbed during their atmospheric entry, thereby preserving their chemical, mineralogical and isotopic compositions. In order to understand the origin of the particles, oxygen isotope compositions of relict olivine grains in twelve cosmic spherules collected from deep sea sediments of the Indian Ocean were studied using secondary ion mass spectrometry. Most of the data lie close to the CCAM (Carbonaceous Chondrite Anhydrous Mineral) line, with Δ17O ranging from -5‰ to 0‰. The data overlap oxygen isotopic compositions of chondrules from carbonaceous chondrites such as CV, CK, CR and CM, which suggests that chondrules from carbonaceous chondrites are the source of relict grains in cosmic spherules. Chemical compositions of olivine in cosmic spherules are also very similar to chondrule olivine from carbonaceous chondrites. Several olivine relict grains in three cosmic spherules are 16O-rich (Δ17O -21.9‰ to -18.7‰), similar to oxygen isotopic compositions observed in calcium aluminum rich inclusions (CAIs), amoeboid olivine aggregates (AOAs), and some porphyritic chondrules from carbonaceous chondrites. These grains appear to have recorded the initial oxygen isotopic composition of the inner solar nebula. Three olivine grains from two cosmic spherules have δ18O values >+20‰, which could be interpreted as mixing with stratospheric oxygen during atmospheric entry.

  15. Trihalomethanes formed from natural organic matter isolates: Using isotopic and compositional data to help understand sources

    USGS Publications Warehouse

    Bergamaschi, B.A.; Fram, M.S.; Fujii, R.; Aiken, G.R.; Kendall, C.; Silva, S.R.

    2000-01-01

    Over 20 million people drink water from the Sacramento-San Joaquin Delta despite problematic levels of natural organic matter (NOM) and bromide in Delta water, which can form trihalomethanes (THMs) during the treatment process. It is widely believed that NOM released from Delta peat islands is a substantial contributor to the pool of THM precursors present in Delta waters. Dissolved NOM was isolated from samples collected at five channel sites within the Sacramento-San Joaquin Rivers and Delta, California, USA, and from a peat island agricultural drain. To help understand the sources of THM precursors, samples were analyzed to determine their chemical and isotopic composition, their propensity to form THMs, and the isotopic composition of the THMs. The chemical composition of the isolates was quite variable, as indicated by significant differences in carbon-13 nuclear magnetic resonance spectra and carbon-to-nitrogen concentration ratios. The lowest propensity to form THMs per unit of dissolved organic carbon was observed in the peat island agricultural drain isolate, even though it possessed the highest fraction of aromatic material and the highest specific ultraviolet absorbance. Changes in the chemical and isotopic composition of the isolates and the isotopic composition of the THMs suggest that the source of the THMs precursors was different between samples and between isolates. The pattern of variability in compositional and isotopic data for these samples was not consistent with simple mixing of river- and peat-derived organic material.

  16. Measurements of the isotopic composition of ice and vapor above a tropical convective system

    NASA Astrophysics Data System (ADS)

    O'Brien, A.; Hanisco, T. F.; Sayres, D. S.; St Clair, J.; Smith, J. B.; Weinstock, E. M.; Anderson, J.

    2011-12-01

    We present observations of the isotopic composition of condensed and vapor water in the lower tropical tropopause layer (TTL) above a large summertime tropical convective system obtained by the Hoxotope and ICOS isotope instruments flown on the NASA WB-57 during TC4. A simple ice isotopic physics model is used in conjunction with our observational data to determine the origin of the condensed phase encountered above the cloud top. Regions of ice that are characteristic of both convective lofting, where the ice is isotopically heavier than the surroundings, and in situ condensation, where the ice shows little difference in isotopic composition with respect to the vapor, are encountered above the convective cell with convective lofting being the dominant mechanism by which water is transported to this altitude. While ice lofting is an important component of water transport models in the TTL, the isotopic composition of ice has been a relatively unconstrained parameter. Observations of condensed isotopes coupled with the vertical profile of vapor in the summertime TTL suggests that there is a seasonal variation in convective timescales that needs to be accounted for in convectively-influenced trajectory models describing the transport of water in the TTL.

  17. Normal variations in the isotopic composition of metabolically relevant transition metals in human blood

    NASA Astrophysics Data System (ADS)

    Van Heghe, L.; Cloquet, C.; Vanhaecke, F.

    2012-04-01

    Cu, Fe and Zn are transition metals with great catalytic, structural and regulating importance in the human body. Hence, an aberrant metabolism of these elements can have serious implications on the health of a person. It is assumed that, due to differences in isotope fractionation, the isotopic composition of these elements in whole blood of patients can be different from that in blood of healthy subjects. Therefore, isotopic analysis of the element affected by the disease can be a promising approach for early diagnosis. A method for isotopic analysis of Cu, Fe and Zn in human whole blood was developed. The simultaneous chromatographic isolation of these elements and the conditions for isotope ratio measurement via multi-collector ICP - mass spectrometry (MC-ICP-MS) were optimized. So far, only whole blood of supposedly healthy volunteers (reference population) was analyzed. Results for Fe confirmed the known differences in isotopic composition between male and female blood. It is also shown that other parameters can have influence as well, e.g., the isotopic composition of Zn seems to be governed by the diet.

  18. Antimony isotopic composition in river waters affected by ancient mining activity.

    PubMed

    Resongles, Eléonore; Freydier, Rémi; Casiot, Corinne; Viers, Jérôme; Chmeleff, Jérôme; Elbaz-Poulichet, Françoise

    2015-11-01

    In this study, antimony (Sb) isotopic composition was determined in natural water samples collected along two hydrosystems impacted by historical mining activities: the upper Orb River and the Gardon River watershed (SE, France). Antimony isotope ratio was measured by HG-MC-ICP-MS (Hydride Generation Multi-Collector Inductively Coupled Plasma Mass Spectrometer) after a preconcentration and purification step using a new thiol-cellulose powder (TCP) procedure. The external reproducibility obtained for δ(123)Sb measurements of our in-house Sb isotopic standard solution and a certified reference freshwater was 0.06‰ (2σ). Significant isotopic variations were evident in surface waters from the upper Orb River (-0.06‰≤δ(123)Sb≤+0.11‰) and from the Gardon River watershed (+0.27‰≤δ(123)Sb≤+0.83‰). In particular, streams that drained different former mining sites exploited for Sb or Pb-Zn exhibited contrasted Sb isotopic signature, that may be related to various biogeochemical processes occurring during Sb transfer from rocks, mine wastes and sediments to the water compartment. Nevertheless, Sb isotopic composition appeared to be stable along the Gardon River, which might be attributed to the conservative transport of Sb at distance from mine-impacted streams, due to the relative mobile behavior of Sb(V) in natural oxic waters. This study suggests that Sb isotopic composition could be a useful tool to track pollution sources and/or biogeochemical processes in hydrologic systems. PMID:26452900

  19. Application of Sr and O isotope relations to the petrogenesis of the alkaline rocks of the Red Hill complex, New Hampshire, USA

    USGS Publications Warehouse

    Foland, K.A.; Friedman, I.

    1977-01-01

    The Red Hill ring complex in central New Hampshire is composed of apparently cogenetic syenites, nepheline-sodalite syenite, and granite. The ages and petrogenetic relations among five of the six recognized units have been investigated by rubidiumstrontium and oxygen isotope analysis of whole rocks and separated minerals. Whole-rock samples from three syenite units are consistent with a single Rb-Sr isochron which gives an age of 198??3 m.y. and an initial (87Sr/86Sr)o ratio of 0.70330??0.00016 (??2 sigma; ??=1.42?? 10-11y-1). However, Sr isotope data for two other units, nepheline syenite and granite, are not consistent with this isochron but rather indicate higher initial ratios which range from 0.7033 to about 0.707. Whole-rock O isotope analyses give ??18O values which range from+6.2 to+9.3??? Sr and O isotope analyses on mineral separates indicate that observed whole-rock variations in (87Sr/86Sr)o are primary and are not due to any secondary process. The fact that the isotope systematics correlate with rock type, suggests that crustal interaction is likely to have played a significant role in the development of this over-and undersaturated association. Such process(es), while still not fully delineated, could be of fundamental importance to the genesis of associations of critically undersaturated and oversaturated intrusives. The data support the idea that interaction between magmas and crustal materials strongly influenced the compositional relations of similar complexes elsewhere including those of the White Mountain magma series. ?? 1977 Springer-Verlag.

  20. The stable Cr isotopic compositions of chondrites and silicate planetary reservoirs

    NASA Astrophysics Data System (ADS)

    Schoenberg, Ronny; Merdian, Alexandra; Holmden, Chris; Kleinhanns, Ilka C.; Haßler, Kathrin; Wille, Martin; Reitter, Elmar

    2016-06-01

    The depletion of chromium in Earth's mantle (∼2700 ppm) in comparison to chondrites (∼4400 ppm) indicates significant incorporation of chromium into the core during our planet's metal-silicate differentiation, assuming that there was no significant escape of the moderately volatile element chromium during the accretionary phase of Earth. Stable Cr isotope compositions - expressed as the ‰-difference in 53Cr/52Cr from the terrestrial reference material SRM979 (δ53/52CrSRM979 values) - of planetary silicate reservoirs might thus yield information about the conditions of planetary metal segregation processes when compared to chondrites. The stable Cr isotopic compositions of 7 carbonaceous chondrites, 11 ordinary chondrites, 5 HED achondrites and 2 martian meteorites determined by a double spike MC-ICP-MS method are within uncertainties indistinguishable from each other and from the previously determined δ53/52CrSRM979 value of -0.124 ± 0.101‰ for the igneous silicate Earth. Extensive quality tests support the accuracy of the stable Cr isotope determinations of various meteorites and terrestrial silicates reported here. The uniformity in stable Cr isotope compositions of samples from planetary silicate mantles and undifferentiated meteorites indicates that metal-silicate differentiation of Earth, Mars and the HED parent body did not cause measurable stable Cr isotope fractionation between these two reservoirs. Our results also imply that the accretionary disc, at least in the inner solar system, was homogeneous in its stable Cr isotopic composition and that potential volatility loss of chromium during accretion of the terrestrial planets was not accompanied by measurable stable isotopic fractionation. Small but reproducible variations in δ53/52CrSRM979 values of terrestrial magmatic rocks point to natural stable Cr isotope variations within Earth's silicate reservoirs. Further and more detailed studies are required to investigate whether silicate

  1. Isotope composition of iron delivered to the oceans by intertropical rivers: The Amazon River Basin case

    NASA Astrophysics Data System (ADS)

    Poitrasson, F.; Vieira, L. C.; Seyler, P.; dos Santos Pinheiro, G. M.; Mulholland, D. S.; Ferreira Lima, B. A.; Bonnet, M.; Martinez, J.; Prunier, J.

    2011-12-01

    Riverborne iron is a notable source for this biogeochemically key element to the oceans. Recent investigations have shown that its isotopic composition may vary significantly in oceanic waters. Hence, a proper understanding of the Fe cycle at the surface of the Earth requires a good characterization of the isotopic composition of its various reservoirs. However, as the database growths, it appears that the isotope composition of the riverborne Fe delivered to the oceans may be more varied than initially thought, in agreement with inferences from soil studies from different climatic contexts. It is therefore important to compare major rivers from different latitudes. We focused our attention on the Amazon River and its tributaries that represent ca. 20% of the freshwater delivered to the oceans by world rivers. Preliminary experiments suggest that water filtration may induce biases in stable Fe isotope composition. Therefore, we worked first on bulk waters, sampled during multidisciplinary field campaigns on the Amazon River and its tributaries, including the Solimoes, Negro, Madeira and Tapajos Rivers. Besides a complete sample physical-chemical characterization, Fe isotope determinations were conduced after water sample mineralization, iron purification and MC-ICP-MS analysis. Our first results reveal that most bulk water samples cluster close to the continental crust value (0.1% δ57FeIRMM-14) with an overall range of 0.2%. This is consistent with the restricted range found in lateritic soils elsewhere that represent 80% of the Amazon basin surface. Only black water rivers flowing over the podzols of the northern portion of the Amazon basin tend to show lighter isotopic compositions, down to -0.18%. However, sediment analyses suggest that this light Fe isotopic is lost through sedimentation on the river bed, thereby leading the waters to have Fe isotope compositions remaining close to that of the continental crust. This constant isotopic signature holds whatever

  2. The carbon isotope composition of ancient CO2 based on higher-plant organic matter.

    PubMed

    Gröcke, Darren R

    2002-04-15

    Carbon isotope ratios in higher-plant organic matter (delta(13)C(plant)) have been shown in several studies to be closely related to the carbon isotope composition of the ocean-atmosphere carbon reservoir, and, in particular, the isotopic composition of CO(2). These studies have primarily been focused on geological intervals in which major perturbations occur in the oceanic carbon reservoir, as documented in organic carbon and carbonates phases (e.g. Permian-Triassic and Triassic-Jurassic boundary, Early Toarcian, Early Aptian, Cenomanian-Turonian boundary, Palaeocene-Eocene Thermal Maximum (PETM)). All of these events, excluding the Cenomanian-Turonian boundary, record negative carbon isotope excursions, and many authors have postulated that the cause of such excursions is the massive release of continental-margin marine gas-hydrate reservoirs (clathrates). Methane has a very negative carbon isotope composition (delta(13)C, ca. 60 per thousand ) in comparison with higher-plant and marine organic matter, and carbonate. The residence time of methane in the ocean-atmosphere reservoir is short (ca. 10 yr) and is rapidly oxidized to CO(2), causing the isotopic composition of CO(2) to become more negative from its assumed background value (delta(13)C, ca. -7 per thousand ). However, to date, only the Early Toarcian, Early Aptian and PETM are well-constrained chronometric sequences that could attribute clathrate release as a viable cause to create such rapid negative delta(13)C excursions. Notwithstanding this, the isotopic analysis of higher-plant organic matter (e.g. charcoal, wood, leaves, pollen) has the ability to (i) record the isotopic composition of palaeoatmospheric CO(2) in the geological record, (ii) correlate marine and non-marine stratigraphic successions, and (iii) confirm that oceanic carbon perturbations are not purely oceanographic in their extent and affect the entire ocean-atmosphere system. A case study from the Isle of Wight, UK, indicates that the

  3. One year observation of water vapour isotopic composition at Ivittuut, Southern Greenland

    NASA Astrophysics Data System (ADS)

    Bonne, Jean-Louis; Masson-Delmotte, Valérie; Delmotte, Marc; Cattani, Olivier; Sodemann, Harald; Risi, Camille

    2013-04-01

    In September 2011, an automatic continuous water vapour isotopic composition monitoring instrument has been installed in the atmospheric station of Ivittuut (61.21° N, 48.17° W), southern Greenland. Precipitation has been regularly sampled on site at event to weekly scales and analysed in our laboratory for isotopic composition. Meteorological parameters (temperature, pressure, relative humidity, wind speed and direction) and atmospheric composition (CO2, CH4, Atmospheric Potential Oxygen) are also continuously monitored at Ivittuut. The meteorological context of our observation period will be assessed by comparison with the local climatology. The water vapour analyser is a Picarro Wavelength Scanned Cavity Ring-Down Spectrometer (WS-CRDS, model L2120i). It is automatically and regularly calibrated on the VSMOW scale using measurements of the isotopic composition of vaporized reference water standards using the Picarro Syringe Delivery Module (SDM). As measurements are sensitive to humidity level, an experimentally estimated calibration response function is used to correct our isotopic measurements. After data treatment, successive isotopic measurements of reference waters have a standard deviation of around 0.35 per mil for δ18O and 2.3 per mil for δD. Our instrumentation protocol and data quality control method will be presented, together with our one year δ18O, δD and d-excess measurements in water vapour and precipitation. The relationship between surface water vapour isotopic composition and precipitation isotopic composition will be investigated based on a distillation model. Specific difficulties linked to our low maintenance remote station will also be discussed. The processes responsible for the synoptic variability of Ivittuut water vapour isotopic composition will be investigated by comparing our observational dataset with (i) atmospheric back-trajectories and (ii) results from an isotopically-enabled atmospheric general circulation model (AGCM

  4. The influence of oxygen exchange between sulfite and water on the oxygen isotope composition of sulfate

    NASA Astrophysics Data System (ADS)

    Müller, I. A.; Brunner, B.

    2012-12-01

    Sulfate does not exchange oxygen with the water under most environmental conditions. Therefore, its oxygen isotope composition serves as an archive of past oxidative sulfur cycling. Studies on the oxygen isotope signature of sulfate produced from reduced sulfur compounds show varying relative contributions of two possible oxygen sources; molecular oxygen and water, and variable isotope fractionations relative to these two compounds. These discrepancies could be due to differences in the production and consumption of sulfuroxy intermediates which exchange oxygen with water. Thereby, the rate of oxygen exchange as well as the rate of oxidation depends on the pH. Studies on the oxygen isotope exchange effects between sulfuroxy intermediates and water and on the oxygen isotope effects during the oxidation of sulfuroxy intermediates are scarce, severely limiting the interpretability of oxygen isotope signatures in sulfate. Sulfite is often considered to be the last/final sulfuroxy intermediate in the oxidation of reduced sulfur compounds to sulfate and may, therefore, be pivotal in shaping the oxygen isotope signature of sulfate. We determined the oxygen isotope equilibrium fractionation between sulfite and water and used the obtained equilibrium value to determine the oxygen isotope effects in abiotic sulfite oxidation experiments. Our results demonstrate that natural variations in the oxygen isotope composition of sulfate produced by oxidative processes can be explained by differences in the interplay of the sulfite oxidation rate and oxygen isotope exchange rate between sulfite and water which both depend on pH conditions and availability of oxidizing agents (e.g. molecular oxygen or ferric iron). Our findings contribute to a more detailed mechanistic understanding of the oxidation of reduced sulfur compounds and underline the importance of sulfite as the final sulfuroxy intermediate in oxidative sulfur cycling.

  5. Genetic relations among basic lavas and ultramafic nodules: Evidence from oxygen isotope compositions

    USGS Publications Warehouse

    Kyser, T.K.; O'Neil, J.R.; Carmichael, I.S.E.

    1982-01-01

    ??18O values of unaltered basic lavas range from 4.9 to 8.3 but different types of basalts are usually restricted to narrow and distinct ranges of isotopic composition. The average ??18O values for Hawaiian tholeiites, mid-ocean ridge tholeiites, and alkali basalts are 5.4, 5.7, and 6.2 permil, respectively. Potassic lavas and andesites tend to be more 18O rich with ??18O values between 6.0 and 8.0 permil. The differences among the oxygen isotopic compositions of most of these lavas can be attributed to partial melting of isotopically distinct sources. The oxygen isotope compositions of the sources may be a function of prior melting events which produce 18O-depleted partial melts and 18O-enriched residues as a consequence of relatively large isotopic fractionations that exist at high temperatures. It is proposed that lavas with relatively low ??18O values are derived from primitive, 18O-depleted sources whereas 18O-rich basalts are produced from refractory sources that have already produced partial melts. High temperature fractionations among silicate liquids and coexisting minerals can be used in conjunction with the oxygen isotope compositions of ultramafic nodules to place constraints on the genetic relations between some nodules and different types of basic lavas. ?? 1982 Springer-Verlag.

  6. Heterogeneous Os isotope compositions in the Kalatongke sulfide deposit, NW China: the role of crustal contamination

    NASA Astrophysics Data System (ADS)

    Gao, Jian-Feng; Zhou, Mei-Fu; Lightfoot, Peter C.; Qu, Wenjun

    2012-10-01

    Re-Os isotope compositions of mantle-derived magmas are highly sensitive to crustal contamination because the crust and mantle have very different Os isotope compositions. Crustal contamination may trigger S saturation and thus the formation of magmatic Ni-Cu-(PGE) sulfide deposits. The ˜287-Ma Kalatongke norite intrusion of NW China are hosted in carboniferous tuffaceous rocks and contain both disseminated and massive sulfide mineralization. The Re-Os isotope compositions in the intrusion are highly variable. Norite and massive sulfide ores have γ Os values ranging from +59 to +160 and a Re-Os isochron age of 239 ± 51 Ma, whereas disseminated sulfide ores have γ Os values from +117 to +198 and a Re-Os isochron age of 349 ± 34 Ma. The variability of Os isotope compositions can be explained as the emplacement of two distinct magma pulses. Massive sulfide ores and barren norite in the intrusion formed from the same magma pulse, whereas the disseminated sulfide ores with more radiogenic Os isotopes formed from another magma pulse which underwent different degrees of crustal contamination. Re-Os isotopes may not be suitable for dating sulfide-bearing intrusions that underwent variable degrees of crustal contamination to form magmatic sulfide deposits.

  7. Coupled isotopes of plant wax and hemicellulose markers record information on relative humidity and isotopic composition of precipitation

    NASA Astrophysics Data System (ADS)

    Tuthorn, M.; Zech, R.; Ruppenthal, M.; Oelmann, Y.; Kahmen, A.; del Valle, H. F.; Eglinton, T.; Zech, M.

    2015-02-01

    The δ2H isotopic composition of leaf waxes is used increasingly for paleohydrological and -climate reconstructions. However, it is challenging to disentangle past changes in the isotopic composition of precipitation and changes in evapotranspirative enrichment of leaf water. We analyzed δ2H on n-alkanes and fatty acids in topsoils along a climate transect in Argentina, for which we had previously measured δ18O on plant-derived sugars. Our results indicate that leaf wax biomarker δ2H values (δ2Hlipids) primarily reflect δ2Hsource water (precipitation), but are modulated by evapotranspirative enrichment. A mechanistic model is able to produce the main trends in δ2Hlipids along the transect, but seems to slightly underestimate evapotranspirative enrichment in arid regions and overestimate it in grass-dominated ecosystems. Furthermore, the (i) coupling of the δ2Hlipid and δ18Osugar biomarker results and (ii) application of biosynthetic fractionation factors allows calculating the δ2H-δ18O isotopic composition of leaf water along the transect. This also yields the deuterium excess (d excess) of leaf water, which mainly reflects evapotranspirative enrichment, and can be used to model relative air humidity (RH). The high correlation of modeled (reconstructed based on biomarker results) and measured RH, as well as the good agreement between modeled and actual δ2H and δ18O of precipitation along the transect lends support to the coupled δ2Hlipid and δ18Osugar biomarker approach for future paleoclimate research.

  8. The influence of kinetics on the oxygen isotope composition of calcium carbonate

    NASA Astrophysics Data System (ADS)

    Watkins, James M.; Nielsen, Laura C.; Ryerson, Frederick J.; DePaolo, Donald J.

    2013-08-01

    Paleotemperature reconstructions rely on knowledge of the equilibrium separation of oxygen isotopes between aqueous solution and calcium carbonate. Although oxygen isotope separation is expected on theoretical grounds, the temperature-dependence remains uncertain because other factors, such as slow exchange of isotopes between dissolved CO2-species and water, can obscure the temperature signal. This is problematic for crystal growth experiments on laboratory timescales and for interpreting the oxygen isotope composition of crystals formed in natural settings. We present results from experiments in which inorganic calcite is precipitated in the presence of 0.25 μM dissolved bovine carbonic anhydrase (CA). The presence of dissolved CA accelerates oxygen isotope equilibration between the dissolved carbon species CO2, H2CO3, HCO3-, CO32- and water, thereby eliminating this source of isotopic disequilibrium during calcite growth. The experimental results allow us to isolate, for the first time, kinetic oxygen isotope effects occurring at the calcite-water interface. We present a framework of ion-by-ion growth of calcite that reconciles our new measurements with measurements of natural cave calcites that are the best candidate for having precipitated under near-equilibrium conditions. Our findings suggest that isotopic equilibrium between calcite and water is unlikely to have been established in laboratory experiments or in many natural settings. The use of CA in carbonate precipitation experiments offers new opportunities to refine oxygen isotope-based geothermometers and to interrogate environmental variables other than temperature that influence calcite growth rates.

  9. Assessment of shock effects on amphibole water contents and hydrogen isotope compositions: 1. Amphibolite experiments

    NASA Astrophysics Data System (ADS)

    Minitti, Michelle E.; Rutherford, Malcolm J.; Taylor, Bruce E.; Dyar, M. Darby; Schultz, Peter H.

    2008-02-01

    Kaersutitic amphiboles found within a subset of the Martian meteorites have low water contents and variably heavy hydrogen isotope compositions. In order to assess if impact shock-induced devolatilization and hydrogen isotope fractionation were determining factors in these water and isotopic characteristics of the Martian kaersutites, we conducted impact shock experiments on samples of Gore Mountain amphibolite in the Ames Vertical Gun Range (AVGR). A parallel shock experiment conducted on an anorthosite sample indicated that contamination of shocked samples by the AVGR hydrogen propellant was unlikely. Petrographic study of the experimental amphibolite shock products indicates that only ˜ 10% of the shock products experienced levels of damage equivalent to those found in the most highly shocked kaersutite-bearing Martian meteorites (30-35 GPa). Ion microprobe studies of highly shocked hornblende from the amphibolite exhibited elevated water contents (ΔH 2O ˜ 0.1 wt.%) and enriched hydrogen isotope compositions (Δ D ˜ + 10‰) relative to unshocked hornblende. Water and hydrogen isotope analyses of tens of milligrams of unshocked, moderately shocked, and highly shocked hornblende samples by vacuum extraction/uranium reduction and isotope ratio mass spectrometry (IRMS), respectively, are largely consistent with analyses of single grains from the ion microprobe. The mechanisms thought to have produced the excess water in most of the shocked hornblendes are shock-induced reduction of hornblende Fe and/or irreversible adsorption of hydrogen. Addition of the isotopically enriched Martian atmosphere to the Martian meteorite kaersutites via these mechanisms could explain their enriched and variable isotopic compositions. Alternatively, regrouping the water extraction and IRMS analyses on the basis of isotopic composition reveals a small, but consistent, degree of impact-induced devolatilization (˜ 0.1 wt.% H 2O) and H isotope enrichment (Δ D ˜ + 10

  10. Chromium isotope composition of reducing and anoxic sediments from the Peru Margin and Cariaco Basin

    NASA Astrophysics Data System (ADS)

    Gueguen, B.; Planavsky, N.; Wang, X.; Algeo, T. J.; Peterson, L. C.; Reinhard, C. T.

    2014-12-01

    Chromium isotope systematics in marine sediments are now being used as a new redox proxy of the modern and ancient Earth's surface. Chromium is primarily delivered to the oceans by riverine inputs through weathering of Cr(III)-rich minerals present in the continental crust and oxidation of insoluble Cr(III) to soluble Cr(VI) species. Since oxidation-reduction reactions fractionate Cr isotopes whereby oxidized Cr(VI) species are preferentially enriched in heavy Cr isotopes, the Cr isotope composition of marine sediments may be useful tracers of redox conditions at the Earth's surface through geological time. Chromium is quantitatively removed in organic-rich sediments where reducing conditions prevail and promote reduction of Cr(VI) to Cr(III), and thus, these sediments should capture the ambient seawater Cr isotope composition. However, the isotopic composition of modern organic-rich sediments is poorly documented so far, and this step is essential for further modeling the global oceanic Cr isotope mass balance and assessing the effects of sedimentation and post-depositional processes on the marine Cr isotopes archive. In this study, we have characterized modern marine organic-rich sediments for their Cr isotope composition (δ53/52Cr) from two different settings, the Peru margin upwelling zone and the anoxic Cariaco Basin (Venezuela). Chromium isotopes were measured on a MC-ICP-MS (Nu Plasma) using a double-spike correction method. The authigenic fraction of shallow samples from the Peru margin sedimentary sequence with a high Total Organic Carbon (TOC) content (>10 wt%) yield an average δ53/52Crauthigenic value of +0.67 ±0.05 ‰ (2sd). However, although this value is close to the seawater value (Atlantic Ocean) and to Cariaco basin sediments (~ +0.6 ‰), reducing sediments from the Peru margin are on average isotopically slightly heavier, especially in samples having a low authigenic fraction and a low TOC content (δ53/52Crauthigenic values up to +1.30

  11. Natural variations in calcium isotope composition as a monitor of bone mineral balance in humans.

    NASA Astrophysics Data System (ADS)

    Skulan, J.; Anbar, A.; Thomas, B.; Smith, S.

    2004-12-01

    The skeleton is the largest reservoir of calcium in the human body and is responsible for the short term control of blood levels of this element. Accurate measurement of changes in bone calcium balance is critical to understanding how calcium metabolism responds to physiological and environmental changes and, more specifically, to diagnosing and evaluating the effectiveness of treatments for osteoporosis and other serious calcium-related disorders. It is very difficult to measure bone calcium balance using current techniques, however, because these techniques rely either on separate estimates of bone resorption and formation that are not quantitatively comparable, or on complex and expensive studies of calcium kinetics using administered isotopic tracers. This difficulty is even more apparent and more severe for measurements of short-term changes in bone calcium balance that do not produce detectable changes in bone mineral density. Calcium isotopes may provide a novel means of addressing this problem. The foundation of this isotope application is the ca. 1.3 per mil fractionation of calcium during bone formation, favoring light calcium in the bone. This fractionation results in a steady-state isotopic offset between calcium in bone and calcium in soft tissues, blood and urine. Perturbations to this steady state due to changes in the net formation or resorption of bone should be reflected in changes in the isotopic composition of soft tissues and fluids. Here we present evidence that easily detectable shifts in the natural calcium isotope composition of human urine rapidly reflect changes in bone calcium balance. Urine from subjects in a 17-week bed rest study was analyzed for calcium isotopic composition. Bed rest promotes net resorption of bone, shifting calcium from bone to soft tissues, blood and urine. The calcium isotope composition of patients in this study shifted toward lighter values during bed rest, consistent with net resorption of isotopically

  12. Hafnium and neodymium isotope composition of seawater and filtered particles from the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Stichel, T.; Frank, M.; Haley, B. A.; Rickli, J.; Venchiarutti, C.

    2009-12-01

    Radiogenic hafnium (Hf) and neodymium (Nd) isotopes have been used as tracers for past continental weathering regimes and ocean circulation. To date, however, there are only very few data available on dissolved Hf isotope compositions in present-day seawater and there is a complete lack of particulate data. During expedition ANTXXIV/3 (February to April 2008) we collected particulate samples (> 0.8 µm), which were obtained by filtrations of 270-700 liters of water. The samples were separated from the filters, completely dissolved, and purified for Nd and Hf isotope determination by TIMS and MC-ICPMS, respectively. In addition, we collected filtered (0.45 µm) seawater samples (20-120 liters) to determine the dissolved isotopic composition of Hf and Nd. The Hf isotope composition of the particulate fraction in the Drake Passage ranged from 0 to -28 ɛHf and is thus similar to that observed in core top sediments from the entire Southern Ocean in a previous study. The most unradiogenic and isotopically homogenous Hf isotope compositions in our study were found near the Antarctic Peninsula. Most of the stations north of the Southern Antarctic Circumpolar Front (SACC) show a large variation in ɛHf between 0 and -23 within the water column of one station and between the stations. The locations at which these Hf isotope compositions were measured are mostly far away from the potential source areas. Nd, in contrast, was nearly absent throughout the entire sample set and the only measurable ɛNd data ranged from 0 to -7, which is in good agreement with the sediment data in that area. The dissolved seawater isotopic compositions of both Hf and Nd show only minor variance (ɛHf = 4.2 to 4.7 and ɛNd = -8.8 to -7.6, respectively). These patterns in Hf isotopes and the nearly complete absence of Nd indicates that the particulate fraction does not contain a lot of terrigeneous material but is almost entirely dominated by biogenic opal. The homogenous and relatively radiogenic

  13. Isotopic composition of water of crystallisation of sulfates of Permian-Triassic age, Eastern Alps, Austria

    NASA Astrophysics Data System (ADS)

    Bojar, Ana-Voica; Halas, Stanislaw; Trembaczowski, Andrzej; Bojar, Hans-Peter

    2016-04-01

    The investigated sulfates as gypsum and polyhalite were selected from various gypsum and halite rich deposits of the Northern Calcareous Alps and the Central Alpine Mesozoic. The two units of the Eastern Alps are characterised by the presence of Permian-Triassic evaporitic deposits. Crystallisation water of mineral phases was extracted by heating the samples under vacuum. The cryogenically trapped water was subsequently analysed for delta 18O and delta D on a Picarro L2120-i Analyzer. The isotopic compositions were synchronously measured, with a standard deviation better than 0.1 permil. The fractionation factors for both oxygen and hydrogen between brine where the sulfates formed and crystallisation water of sulfates are not temperature dependent. Using the appropriate relationships, we conclude from the calculations that, for gypsum, oxygen and hydrogen isotopic composition of fluid in equilibrium with crystallisation water varied between -16 to -6 permil and between -90 to -25 permil, respectively. The crystallization water of gypsum associated with halite type deposits has heavier isotopic compositions. The isotopic composition of crystallisation water of gypsum points towards reequilibration with a younger meteoric fluid. In contrast, polyhalite crystallisation water show much heavier values between +10 to +11 permil for oxygen and +16 to +19 permil for hydrogen. These values suggest the fact that this water of crystallisation indicates the isotopic composition of brines. The origin of these brines, diagenetic versus later thermal overprint is subject of further investigations. All the measured values plot along a regression line.

  14. Lead content and isotopic composition in submound and recent soils of the Volga Upland

    NASA Astrophysics Data System (ADS)

    Pampura, T. V.; Probst, A.; Ladonin, D. V.; Demkin, V. A.

    2013-11-01

    Literature data on the historical reconstructions of the atmospheric lead deposition in Europe and the isotopic composition of the ores that are potential sources of the anthropogenic lead in the atmospheric deposition in the lower Volga steppes during different time periods have been compiled. The effect of the increasing anthropogenic lead deposition recorded since the Bronze Age on the level of soil contamination has been investigated. For the first time paleosol buried under a burial mound of the Bronze Age has been used as a reference point to assess of the current contamination level. The contents and isotopic compositions of the mobile and total lead have been determined in submound paleosols of different ages and their recent remote and roadside analogues. An increase in the content and fraction of the mobile lead and a shift of its isotopic composition toward less radiogenic values (typical for lead from the recent anthropogenic sources) has been revealed when going from a Bronze-Age paleosol to a recent soil. In the Bronze-Age soil, the isotopic composition of the mobile lead is inherited from the parent rock to a greater extent than in the modern soils, where the lead is enriched with the less radiogenic component. The effect of the anthropogenic component is traced in the analysis of the mobile lead, but it is barely visible for the total lead. An exception is provided by the recent roadside soils characterized by increased contents and the significantly less radiogenic isotopic composition of the mobile and total lead.

  15. The minor sulfur isotope composition of Cretaceous and Cenozoic seawater sulfate

    NASA Astrophysics Data System (ADS)

    Masterson, A. L.; Wing, Boswell A.; Paytan, Adina; Farquhar, James; Johnston, David T.

    2016-06-01

    The last 125 Myr capture major changes in the chemical composition of the ocean and associated geochemical and biogeochemical cycling. The sulfur isotopic composition of seawater sulfate, as proxied in marine barite, is one of the more perplexing geochemical records through this interval. Numerous analytical and geochemical modeling approaches have targeted this record. In this study we extend the empirical isotope record of seawater sulfate to therefore include the two minor sulfur isotopes, 33S and 36S. These data record a distribution of values around means of Δ33S and Δ36S of 0.043 ± 0.016‰ and -0.39 ± 0.15‰, which regardless of δ34S-based binning strategy is consistent with a signal population of values throughout this interval. We demonstrate with simple box modeling that substantial changes in pyrite burial and evaporite sulfate weathering can be accommodated within the range of our observed isotopic values.

  16. Ca-,Al-rich inclusions in the unique chondrite ALH85085 - Petrology, chemistry, and isotopic compositions

    NASA Technical Reports Server (NTRS)

    Kimura, Makoto; El-Goresy, Ahmed; Palme, Herbert; Zinner, Ernst

    1993-01-01

    A comprehensive study is performed for the Ca-,Al-rich inclusions (CAIs) in the unique chondrite ALH85085. The ALH85085 inclusions are smaller (5-80 microns) and more refractory than their counterparts in carbonaceous chondrites. The study includes 42 inclusions for petrography and mineralogy, 15 for bulk major and minor element chemical composition, six for Mg-Al isotopic systematics, 10 for Ca isotopes, nine for Ti isotopes, and six for trace element abundances. In addition, oxygen-isotopic compositions were determined in minerals from a single inclusion. No correlation is found between mineralogy, major element chemistry, and trace element abundances. It is further shown that the high-temperature geochemical behavior of ultrarefractory trace elements is decoupled from that of the major elements Ca and Ti (Ti is correlated with the relatively volatile elements Nb and Yb) implying that perovskite is of only minor importance as carrier of ultrarefractories.

  17. Ca-,Al-rich inclusions in the unique chondrite ALH85085 - Petrology, chemistry, and isotopic compositions

    NASA Astrophysics Data System (ADS)

    Kimura, M.; El Goresy, A.; Palme, H.; Zinner, E.

    1993-05-01

    A comprehensive study is performed for the Ca-,Al-rich inclusions (CAIs) in the unique chondrite ALH85085. The ALH85085 inclusions are smaller (5-80 microns) and more refractory than their counterparts in carbonaceous chondrites. The study includes 42 inclusions for petrography and mineralogy, 15 for bulk major and minor element chemical composition, six for Mg-Al isotopic systematics, 10 for Ca isotopes, nine for Ti isotopes, and six for trace element abundances. In addition, oxygen-isotopic compositions were determined in minerals from a single inclusion. No correlation is found between mineralogy, major element chemistry, and trace element abundances. It is further shown that the high-temperature geochemical behavior of ultrarefractory trace elements is decoupled from that of the major elements Ca and Ti (Ti is correlated with the relatively volatile elements Nb and Yb) implying that perovskite is of only minor importance as carrier of ultrarefractories.

  18. Determination of the hydrogen isotopic compositions of organic materials and hydrous minerals using thermal combustion laser spectroscopy.

    PubMed

    Koehler, Geoff; Wassenaar, Leonard I

    2012-04-17

    Hydrogen isotopic compositions of hydrous minerals and organic materials were measured by combustion to water, followed by optical isotopic analysis of the water vapor by off-axis integrated cavity output spectroscopy. Hydrogen and oxygen isotopic compositions were calculated by numerical integration of the individual isotopologue concentrations measured by the optical spectrometer. Rapid oxygen isotope exchange occurs within the combustion reactor between water vapor and molecular oxygen so that only hydrogen isotope compositions may be determined. Over a wide range in sample sizes, precisions were ±3-4 per mil. This is comparable but worse than continuous flow-isotope ratio mass spectroscopy (CF-IRMS) methods owing to memory effects inherent in water vapor transfer. Nevertheless, the simplicity and reduced cost of this analysis compared to classical IRMS or CF-IRMS methods make this an attractive option to determine the hydrogen isotopic composition of organic materials where the utmost precision or small sample sizes are not needed. PMID:22432837

  19. Clumped Isotope Composition of Cold-Water Corals: A Role for Vital Effects?

    NASA Astrophysics Data System (ADS)

    Spooner, P.; Guo, W.; Robinson, L. F.

    2014-12-01

    Measurements on a set of cold-water corals (mainly Desmophyllum dianthus) have suggested that their clumped isotope composition could serve as a promising proxy for reconstructing paleocean temperatures. Such measurements have also offered support for certain isotope models of coral calcification. However, there are differences in the clumped isotope compositions between warm-water and cold-water corals, suggesting that different kinds of corals could have differences in their biocalcification processes. In order to understand the systematics of clumped isotope variations in cold-water corals more fully, we present clumped isotope data from a range of cold-water coral species from the tropical Atlantic and the Southern Ocean.Our samples were either collected live or recently dead (14C ages < 1,000 yrs) with associated temperature data. They include a total of 11 solitary corals and 1 colonial coral from the Atlantic, and 8 solitary corals from the Southern Ocean. The data indicate that coral clumped isotope systematics may be more complicated than previously thought. For example, for the genus Caryophyllia we observe significant variations in clumped isotope compositions for corals which grew at the same temperature with an apparent negative correlation between Δ47 and δ18O, different to patterns previously observed in Desmophyllum. These results indicate that existing isotope models of biocalcification may not apply equally well to all corals. Clumped isotope vital effects may be present in certain cold-water corals as they are in warm-water corals, complicating the use of this paleoclimate proxy.

  20. Potassium Isotopic Compositions of NIST Potassium Standards and 40Ar/39Ar Mineral Standards

    NASA Technical Reports Server (NTRS)

    Morgan, Leah; Tappa, Mike; Ellam, Rob; Mark, Darren; Higgins, John; Simon, Justin I.

    2013-01-01

    Knowledge of the isotopic ratios of standards, spikes, and reference materials is fundamental to the accuracy of many geochronological methods. For example, the 238U/235U ratio relevant to U-Pb geochronology was recently re-determined [1] and shown to differ significantly from the previously accepted value employed during age determinations. These underlying values are fundamental to accurate age calculations in many isotopic systems, and uncertainty in these values can represent a significant (and often unrecognized) portion of the uncertainty budget for determined ages. The potassium isotopic composition of mineral standards, or neutron flux monitors, is a critical, but often overlooked component in the calculation of K-Ar and 40Ar/39Ar ages. It is currently assumed that all terrestrial materials have abundances indistinguishable from that of NIST SRM 985 [2]; this is apparently a reasonable assumption at the 0.25per mille level (1s) [3]. The 40Ar/39Ar method further relies on the assumption that standards and samples (including primary and secondary standards) have indistinguishable 40K/39K values. We will present data establishing the potassium isotopic compositions of NIST isotopic K SRM 985, elemental K SRM 999b, and 40Ar/39Ar biotite mineral standard GA1550 (sample MD-2). Stable isotopic compositions (41K/39K) were measured by the peak shoulder method with high resolution MC-ICP-MS (Thermo Scientific NEPTUNE Plus), using the accepted value of NIST isotopic SRM 985 [2] for fractionation [4] corrections [5]. 40K abundances were measured by TIMS (Thermo Scientific TRITON), using 41K/39K values from ICP-MS measurements (or, for SRM 985, values from [2]) for internal fractionation corrections. Collectively these data represent an important step towards a metrologically traceable calibration of 40K concentrations in primary 40Ar/39Ar mineral standards and improve uncertainties by ca. an order of magnitude in the potassium isotopic compositions of standards.

  1. Factors that control the stable carbon isotopic composition of methane produced in an anoxic marine sediment

    NASA Technical Reports Server (NTRS)

    Alperin, M. J.; Blair, Neal E.; Albert, D. B.; Hoehler, T. M.; Martens, C. S.

    1993-01-01

    The carbon isotopic composition of methane produced in anoxic marine sediment is controlled by four factors: (1) the pathway of methane formation, (2) the isotopic composition of the methanogenic precursors, (3) the isotope fractionation factors for methane production, and (4) the isotope fractionation associated with methane oxidation. The importance of each factor was evaluated by monitoring stable carbon isotope ratios in methane produced by a sediment microcosm. Methane did not accumulate during the initial 42-day period when sediment contained sulfate, indicating little methane production from 'noncompetitive' substrates. Following sulfate depletion, methane accumulation proceeded in three distinct phases. First, CO2 reduction was the dominant methanogenic pathway and the isotopic composition of the methane produced ranged from -80 to -94 per thousand. The acetate concentration increased during this phase, suggesting that acetoclastic methanogenic bacteria were unable to keep pace with acetate production. Second, acetate fermentation became the dominant methanogenic pathway as bacteria responded to elevated acetate concentrations. The methane produced during this phase was progressively enriched in C-13, reaching a maximum delta(C-13) value of -42 per thousand. Third, the acetate pool experienced a precipitous decline from greater than 5 mM to less than 20 micro-M and methane production was again dominated by CO2 reduction. The delta(C-13) of methane produced during this final phase ranged from -46 to -58 per thousand. Methane oxidation concurrent with methane production was detected throughout the period of methane accumulation, at rates equivalent to 1 to 8 percent of the gross methane production rate. Thus methane oxidation was too slow to have significantly modified the isotopic signature of methane. A comparison of microcosm and field data suggests that similar microbial interactions may control seasonal variability in the isotopic composition of methane

  2. Variation in the terrestrial isotopic composition and atomic weight of argon

    USGS Publications Warehouse

    Böhlke, John Karl

    2014-01-01

    The isotopic composition and atomic weight of argon (Ar) are variable in terrestrial materials. Those variations are a source of uncertainty in the assignment of standard properties for Ar, but they provide useful information in many areas of science. Variations in the stable isotopic composition and atomic weight of Ar are caused by several different processes, including (1) isotope production from other elements by radioactive decay (radiogenic isotopes) or other nuclear transformations (e.g., nucleogenic isotopes), and (2) isotopic fractionation by physical-chemical processes such as diffusion or phase equilibria. Physical-chemical processes cause correlated mass-dependent variations in the Ar isotope-amount ratios (40Ar/36Ar, 38Ar/36Ar), whereas nuclear transformation processes cause non-mass-dependent variations. While atmospheric Ar can serve as an abundant and homogeneous isotopic reference, deviations from the atmospheric isotopic ratios in other Ar occurrences limit the precision with which a standard atomic weight can be given for Ar. Published data indicate variation of Ar atomic weights in normal terrestrial materials between about 39.7931 and 39.9624. The upper bound of this interval is given by the atomic mass of 40Ar, as some samples contain almost pure radiogenic 40Ar. The lower bound is derived from analyses of pitchblende (uranium mineral) containing large amounts of nucleogenic 36Ar and 38Ar. Within this interval, measurements of different isotope ratios (40Ar/36Ar or 38Ar/36Ar) at various levels of precision are widely used for studies in geochronology, water–rock interaction, atmospheric evolution, and other fields.

  3. Clumped isotope composition of cold-water corals: A role for vital effects?

    NASA Astrophysics Data System (ADS)

    Spooner, Peter T.; Guo, Weifu; Robinson, Laura F.; Thiagarajan, Nivedita; Hendry, Katharine R.; Rosenheim, Brad E.; Leng, Melanie J.

    2016-04-01

    The carbonate clumped isotope thermometer is a promising tool for determining past ocean temperatures. It is based on the temperature dependence of rare isotopes 'clumping' into the same carbonate ion group in the carbonate mineral lattice. The extent of this clumping effect is independent of the isotope composition of the water from which carbonate precipitates, providing unique advantages over many other paleotemperature proxies. Existing calibrations of this thermometer in cold-water and warm-water corals suggest clumped isotope 'vital effects' are negligible in cold-water corals but may be significant in warm-water corals. Here, we test the calibration of the carbonate clumped isotope thermometer in cold-water corals with a recently collected and well characterised sample set spanning a range of coral genera (Balanophyllia, Caryophyllia, Dasmosmilia, Desmophyllum, Enallopsammia and Javania). The clumped isotope compositions (Δ47) of these corals exhibit systematic dependences on their growth temperatures, confirming the basis of the carbonate clumped isotope thermometer. However, some cold-water coral genera show Δ47 values that are higher than the expected equilibrium values by up to 0.05‰ (equivalent to underestimating temperature by ∼9 °C) similar to previous findings for some warm-water corals. This finding suggests that the vital effects affecting corals Δ47 are common to both warm- and cold-water corals. By comparison with models of the coral calcification process we suggest that the clumped isotope offsets in these genera are related to the kinetic isotope effects associated with CO2 hydration/hydroxylation reactions in the corals' calcifying fluid. Our findings complicate the use of the carbonate clumped isotope thermometer in corals, but suggest that species- or genus-specific calibrations could be useful for the future application of this paleotemperature proxy.

  4. Elemental composition, isotopes, electrons and positrons in cosmic rays

    NASA Technical Reports Server (NTRS)

    Balasubrahmanyan, V. K.

    1979-01-01

    Papers presented at the 16th International Cosmic Ray Conference, Kyoto, Japan, dealing with the composition of cosmic rays are reviewed. Particular interest is given to data having bearing on nucleosynthesis sites, supernovae, gamma-process, comparison with solar system composition, multiplicity of sources, and the energy dependence of composition.

  5. Fe Isotopic Composition of Presolar SiC Mainstream Grains

    NASA Technical Reports Server (NTRS)

    Tripa, C. E.; Pellin, M. J.; Savina, M. R.; Davis, A. M.; Lewis, R. S.; Clayton, R. N.

    2002-01-01

    Iron isotopic distribution was measured in SiC mainstream grains from the Murchison meteorite by time-of-flight resonance ionization mass spectrometry. All grains exhibit 54Fe depletions of 50 to 200, lower than what are predicted by calculations of s-process nucleosynthesis in AGB stars. Additional information is contained in the original extended abstract.

  6. Magnesium Isotopic Composition of CAIs and Chondrules from CBb Chondrites

    NASA Astrophysics Data System (ADS)

    Gounelle, M.; Young, E. D.; Shahar, A.; Kearsley, A.

    2006-03-01

    We measured magnesium isotope ratios in 17 chondrules and 3 CAIs from the CBb chondrites HH 237 and QUE 94411 by LA-MC-ICPMS. We find no detectable 26Al excesses in the three CAIs and approximately normal (chondritic) d25Mg in CAIs and chondrules.

  7. Determining the oxygen isotope composition of evapotranspiration with eddy covariance

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The oxygen isotope componsition of evapotranspiration (dF) represents an important tracer in the study of biosphere-atmosphere interactions, hydrology, paleoclimate, and carbon cycling. Here we demonstrate direct measurement of dF based on eddy covariance (EC) and tunable diode laser (EC-TDL) techni...

  8. Zirconium isotope constraints on the composition of Theia and current Moon-forming theories

    NASA Astrophysics Data System (ADS)

    Akram, W.; Schönbächler, M.

    2016-09-01

    The giant impact theory is the most widely recognized formation scenario of the Earth's Moon. Giant impact models based on dynamical simulations predict that the Moon acquired a significant amount of impactor (Theia) material, which is challenging to reconcile with geochemical data for O, Si, Cr, Ti and W isotopes in the Earth and Moon. Three new giant impact scenarios have been proposed to account for this discrepancy - hit-and-run impact, impact with a fast-spinning protoEarth and massive impactors - each one reducing the proportion of the impactor in the Moon compared to the original canonical giant impact model. The validity of each theory and their different dynamical varieties are evaluated here using an integrated approach that considers new high-precision Zr isotope measurements of lunar rocks, and quantitative geochemical modelling of the isotopic composition of the impactor Theia. All analysed lunar samples (whole-rock, ilmenite and pyroxene separates) display identical Zr isotope compositions to that of the Earth within the uncertainty of 13 ppm for 96Zr/90Zr (2σ weighted average). This 13 ppm upper limit is used to infer the most extreme isotopic composition that Theia could have possessed, relative to the Earth, for each of the proposed giant impact theories. The calculated Theian composition is compared with the Zr isotope compositions of different solar system materials in order to constrain the source region of the impactor. As a first order approximation, we show that all considered models (including the canonical) are plausible, alleviating the initial requirement for the new giant impact models. Albeit, the canonical and hit-and-run models are the most restrictive, suggesting that the impactor originated from a region close to the Earth. The fast-spinning protoEarth and massive impactor models are more relaxed and increase the allowed impactor distance from the Earth. Similar calculations carried out for O, Cr, Ti and Si isotope data support

  9. Isotopic composition of high-activity particles released in the Chernobyl accident

    SciTech Connect

    Osuch, S.; Dabrowska, M.; Jaracz, P.; Kaczanowski, J.; Le Van Kho; Mirowski, S.; Piasecki, E.; Szeflinska, G.; Szeflinski, Z.; Tropilo, J.; )

    1989-11-01

    Gamma spectra were measured and activities of the detected isotopes were analyzed for 206 high-activity particles (hot particles, HPs) found in northeastern Poland after the Chernobyl accident. The isotopic composition of HPs observed in gamma-activity is compared with that of the general fallout and core inventory calculations. Particle formation and a process of depletion in Ru and Cs isotopes are discussed. On the basis of a search performed a year later, some comments on the behavior of HPs in the soil are made.

  10. A large area multi-element telescope for measuring the cosmic ray isotope composition

    NASA Technical Reports Server (NTRS)

    Fisher, A. J.; Ormes, J. F.; Hagen, F. A.

    1974-01-01

    To measure the isotopic composition of cosmic rays up to Fe an instrument is needed with good isotopic resolution and a large exposure. The large geometry needed for a balloon-borne detector has been obtained with large mapped detectors and a trajectory determining spark chamber. The instrument achieves isotopic resolution only for stopping particles. For low charge particles where there is no Cerenkov response the detector works as a multiple dE/dx-Range-Energy detector. For higher charges where scintillator saturation becomes important it becomes a Cerenkov-range measurement.

  11. Copper and Zinc isotope composition of CR, CB and CH-like meteorites.

    NASA Astrophysics Data System (ADS)

    Russell, S.; Zhu, X.; Guo, Y.; Mullane, E.; Gounelle, M.; Mason, T.; Coles, B.

    2003-04-01

    Copper and zinc isotopes have recently been shown to be variable in isotopic composi-tion among terrestrial and extraterrestrial materials [1-3]. For this study, we have se-lected samples (bulk meteorite and chondrule separates) from the CR meteorite clan: Bencubbin (CB), Renazzo (CR2), NWA 801 (CR2), and HaH237 (CH-like). These meteorites were selected because meteorites from this clan have experienced very little alteration since their initial formation [4] and for their extremely high refrac-tory/volatile element ratios. The latter characteristic may allow a test of the correlation observed by [2] between element ratios and Cu isotope composition. Measurements were performed on NHM/IC Micromass Isoprobe and Oxford Nu MC-ICP-MS using techniques described elsewhere [1,5]. Each of the meteorites measured so far for Cu and Zn are isotopically light compared to the terrestrial mantle. This suggests that the terrestrial value may have been altered from the pristine solar system value, or else there were multiple early solar system components. Zinc isotopic com-positions lie on a fractionation line and range from δ66ZnNIST = -1.4±0.1ppm (bulk NWA801) to -1.9±0.1ppm (separated chondrule, NWA 801). Copper isotope compositions vary from δ65CuNIST976 = -1.5±0.1ppm (bulk Renazzo) to -3.1±0.1ppm (separated chondrule, NWA 801). Two chondrules from NWA 801 have differing Cu isotope values (-3.1±0.1 and -2.0±0.1ppm) and both are lighter than the bulk meteorite (-1.9±0.1ppm), suggesting a lack of equilibration with respect to Cu in this meteorite. The light values for the two separated chondrules, compared the bulk meteorite, hints that chondrules may be isotopically lighter than co-existing matrix, metal and sulphides with respect to Cu. The copper isotope compositions are not as isotopically light as expected for the high refractory/volatile element ratio observed in these chondrites. Thus a model to account for the Cu isotopes in chondrites may require greater com

  12. The elemental and isotopic composition of cosmic rays - Silicon to nickel

    NASA Technical Reports Server (NTRS)

    Young, J. S.; Freier, P. S.; Waddington, C. J.; Brewster, N. R.; Fickle, R. K.

    1981-01-01

    The reported observations were made with the aid of the Cosmic Ray Isotope Instrument System (CRISIS) which had been designed to detect and resolve the isotopes of cosmic ray nuclei with atomic numbers equal to or greater than 10. The CRISIS detector was flown on a balloon launched from Aberdeen, South Dakota on 1977 May 20. The period 1977 May 19-22 has been classified by Mason et al. (1979) as one of 'superquiet' solar activity, characterized by the lowest fluxes of low-energy solar particles ever observed. The obtained results are presented in a number of graphs and tables. It was found that the elemental and isotopic abundances of Si are solar-like. Elemental S is underabundant in the cosmic rays by a factor of approximately 3 relative to the solar system, but its isotopic composition resembles the solar composition with S-32 being the dominant isotope. Elemental Ar is virtually absent in the source, and the observed isotopic composition is consistent with a secondary origin. Elemental Ni has a solar-like abundance.

  13. Oxygen isotope composition of sulfate produced during microbial sulfur oxidation: A pathway-specific fingerprint?

    NASA Astrophysics Data System (ADS)

    Pjevac, P.; Brunner, B.; Mußmann, M.

    2012-04-01

    The oxidation of zero-valent sulfur such as elemental sulfur (S0) is an important energy source in many marine habitats including deep-sea vents, pelagic redox-clines and coastal surface sediments. Many microorganisms oxidize elemental sulfur to sulfate to gain reducing power. This transformation is catalyzed by a few known enzymatic pathways such as the reverse dissimilatory sulfite reductase (rDSR)-aprAB/Sor pathway or the Sox multienzyme pathway. The isotopic composition of oxygen and sulfur in produced sulfate (δ34S and δ18O) is determined by the isotope composition of the reactants, the ratio between forward and backward fluxes of enzymatically catalyzed reaction steps, and by kinetic and equilibrium isotopic fractionation. We hypothesize that the activity of distinct oxidation pathways is reflected in different δ34S and particularly, in unique δ18O isotopic fingerprints in the produced sulfate. To test our hypothesis we grew pure cultures of photo- and chemoautotrophic sulfur-oxidizing microorganisms of different phylogenetic origin with S0 as sole source of reducing power and determined the sulfur and oxygen isotope composition of the produced sulfate. The identification of characteristic isotope fingerprints for each sulfur oxidation pathway could serve as a tool to estimate and deduce the importance of certain enzymatic pathways and sulfur-oxidizing microorganisms in the environment.

  14. Measurement of natural carbon isotopic composition of acetone in human urine.

    PubMed

    Yamada, Keita; Ohishi, Kazuki; Gilbert, Alexis; Akasaka, Mai; Yoshida, Naohiro; Yoshimura, Ryoko

    2016-02-01

    The natural carbon isotopic composition of acetone in urine was measured in healthy subjects using gas chromatography-combustion-isotope ratio mass spectrometry combined with headspace solid-phase microextraction (HS-SPME-GC-C-IRMS). Before applying the technique to a urine sample, we optimized the measurement conditions of HS-SPME-GC-C-IRMS using aqueous solutions of commercial acetone reagents. The optimization enabled us to determine the carbon isotopic compositions within ±0.2 ‰ of precision and ±0.3‰ of error using 0.05 or 0.2 mL of aqueous solutions with acetone concentrations of 0.3-121 mg/L. For several days, we monitored the carbon isotopic compositions and concentrations of acetone in urine from three subjects who lived a daily life with no restrictions. We also monitored one subject for 3 days including a fasting period of 24 h. These results suggest that changes in the availability of glucose in the liver are reflected in changes in the carbon isotopic compositions of urine acetone. Results demonstrate that carbon isotopic measurement of metabolites in human biological samples at natural abundance levels has great potential as a tool for detecting metabolic changes caused by changes in physiological states and disease. Graphical abstract The natural carbon isotopic composition of acetone in urine can be determined using HS-SPME-GCC-IRMS and can provide information on changes in the availability of glucose in the liver. PMID:26718914

  15. Is my C isotope excursion global, local, or both? Insights from the Mg and Ca isotopic composition of primary, diagenetic, and authigenic carbonates

    NASA Astrophysics Data System (ADS)

    Higgins, J. A.; Blättler, C. L.; Husson, J. M.

    2014-12-01

    The C isotopic composition of ancient limestones and dolomites is a widely used proxy for the global geochemical cycles of carbon and oxygen in the ocean-atmosphere system and a critical tool for chemostratigraphy in Precambrian rocks. Although relatively robust to diagenesis, the C isotopic composition of bulk carbonates can be reset when conditions favor high water-to-rock ratios or fluids with high C concentrations and distinct isotopic compositions. Authigenic carbonates and different pools of primary carbonate (e.g. calcite vs. aragonite) may also bias the C isotopic composition of bulk carbonates if they are both abundant and isotopically distinct. New approaches to quantifying contributions from diagenesis, authigenesis, and mixing of primary carbonates to the C isotopic composition of bulk sedimentary carbonates are needed. Here we present preliminary Mg and Ca isotope data sets of primary, diagenetic, and authigenic carbonates, both modern and ancient. We show that recrystallization, dolomitization, and authigenesis produce Mg and Ca isotope fingerprints that may be used to identify and characterize these processes in ancient carbonate sediments.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  17. Nd, Sr, Pb, Ar, and O isotopic systematics of Sturgeon Lake kimberlite, Saskatchewan, Canada: constraints on emplacement age, alteration, and source composition

    NASA Astrophysics Data System (ADS)

    Hegner, E.; Roddick, J. C.; Fortier, S. M.; Hulbert, L.

    1995-06-01

    Rb-Sr isotopic dating of phlogopite megacryst samples separated from Sturgeon Lake kimberlite, Saskatchewan, yields a crystallization age of 98±1 Ma (2 σ, MSWD=1.2; 87Sr/86Sr( t)=0.7059). The 40Ar/39Ar analyses of a phlogopite megacryst sample indicate the presence of large amounts of excess 40Ar and yield an excessively old age of ˜410 Ma. Assessment of the Ar data using isotope correlation plots indicates clustering of the data points about a mixing line between the radiogenic 40Ar component at 98 Ma and a trapped component with uniform 36Ar/40Ar and Cl/40Ar. Values of δ 18O as high as +20‰ (VSMOW) for calcite from the groundmass and a whole-rock sample indicate pervasive low-temperature alteration. The δ 13C of matrix carbonate is -11.3‰ (PDB), slightly lighter than typical values from the literature. The δ 18O values of about +5‰ (VSMOW) for brown phlogopite megacrysts may be primary, green phlogopites are interpreted to be an alteration product of the brown variety and are 2‰ heavier. Initial Nd-Sr-Pb isotopic ratios for a whole-rock sample ( ɛ Nd=+0.8; 87Sr/86Sr=0.7063, 206Pb/204Pb=18.67, 207Pb/204Pb=15.54, 208Pb/204Pb=38.97) suggest an affinity with group I kimberlites. Initial ɛ Nd values of +1.7 and +0.5 (87Sr/86Sr( t)=0.7053 and 0.7050) for eclogitic and lherzolitic garnet megacryst samples, and values of 0.0 for two phlogopite megacryst samples reflect an origin from an isotopically evolving melt due to assimilation of heterogeneous mantle. Lilac high-Cr lherzolitic garnet megacrysts give an unusually high ɛ Nd(98. Ma) of +28.6 (87Sr/86Sr=0.7046) indicating a xenocrystic origin probably from the lithospheric mantle. The very radiogenic 87Sr/86Sr and 206Pb/204Pb ratios of the kimberlite are consistent with melting of EM II (enriched) mantle components.

  18. The multiple sulfur isotopic composition of iron meteorites: Implications for nebular evolution

    NASA Astrophysics Data System (ADS)

    Antonelli, Michael Ariel

    2013-12-01

    Multiple sulfur isotopic measurements of troilite from 61 different iron meteorites were undertaken in order to test for sulfur isotopic homogeneity within (and between) 8 different iron meteorite groups. It was found that different members within a given group of iron meteorites have homogeneous Delta 33S compositions, but that these Delta33S compositions differ between groups. This thesis shows that iron meteorites from the groups IC, IIAB, IIIAB, IIIF, and IVA have small yet resolvable enrichments or depletions in Delta33S relative to Canyon Diablo Troilite (CDT) and troilite from other non-magmatic (IAB and IIE) iron meteorites. The observed anomalous sulfur isotopic compositions in magmatic iron meteorites are most consistent with Lyman-alpha photolysis of H2S, pointing towards inheritance of an unexpected photolytically-derived sulfur component in magmatic iron meteorite groups which is absent in non-magmatic iron meteorites, chondrites, and the Earth-Moon System.

  19. The oxygen isotopic composition of the Sun inferred from captured solar wind.

    PubMed

    McKeegan, K D; Kallio, A P A; Heber, V S; Jarzebinski, G; Mao, P H; Coath, C D; Kunihiro, T; Wiens, R C; Nordholt, J E; Moses, R W; Reisenfeld, D B; Jurewicz, A J G; Burnett, D S

    2011-06-24

    All planetary materials sampled thus far vary in their relative abundance of the major isotope of oxygen, (16)O, such that it has not been possible to define a primordial solar system composition. We measured the oxygen isotopic composition of solar wind captured and returned to Earth by NASA's Genesis mission. Our results demonstrate that the Sun is highly enriched in (16)O relative to the Earth, Moon, Mars, and bulk meteorites. Because the solar photosphere preserves the average isotopic composition of the solar system for elements heavier than lithium, we conclude that essentially all rocky materials in the inner solar system were enriched in (17)O and (18)O, relative to (16)O, by ~7%, probably via non-mass-dependent chemistry before accretion of the first planetesimals. PMID:21700868

  20. Isotopic and Elemental Composition of Roasted Coffee as a Guide to Authenticity and Origin.

    PubMed

    Carter, James F; Yates, Hans S A; Tinggi, Ujang

    2015-06-24

    This study presents the stable isotopic and elemental compositions of single-origin, roasted coffees available to retail consumers. The δ(13)C, δ(15)N, and δ(18)O compositions were in agreement with those previously reported for green coffee beans. The δ(15)N composition was seen to be related to organic cultivation, reflected in both δ(2)H and δ(18)O compositions. The δ(13)C composition of extracted caffeine differed little from that of the bulk coffee. Stepwise discriminant analysis with jackknife tests, using isotopic and elemental data, provided up to 77% correct classification of regions of production. Samples from Africa and India were readily classified. The wide range in both isotopic and elemental compositions of samples from other regions, specifically Central/South America, resulted in poor discrimination between or within these regions. Simpler X-Y and geo-spatial plots of the isotopic data provided effective visual means to distinguish between coffees from different regions. PMID:26001050

  1. High Temporal Resolution Measurements and Modeling of the Isotopic Composition of Methane in Europe

    NASA Astrophysics Data System (ADS)

    Popa, E.; Röckmann, T.; Eyer, S.; van der Veen, C.; Tuzson, B.; Monteil, G.; Houweling, S.; Harris, E. J.; Brunner, D.; Fischer, H.; Fisher, R. E.; Lowry, D.; Nisbet, E. G.; Emmenegger, L.; Mohn, J.

    2015-12-01

    Isotope measurements can help constraining the atmospheric budget of methane because different sources emit methane with slightly different isotopic composition. In the past, high precision isotope measurements have primarily been carried out by isotope ratio mass spectrometry on flask samples that are usually collected at relatively low temporal resolution. During the EU project INGOS, we have deployed a fully automated gas chromatography - isotope ratio mass spectrometry system (GC-IRMS), together with two laser instruments, during a 4-months campaign in the field at the Cabauw Experimental Site for Atmospheric Research (CESAR). More than 1600 measurements for δ13C and δD were obtained with IRMS during this period. Measurements show clear isotope signals associated with methane elevations both on the diurnal as well as the synoptic scale. In order to assess the added value of such measurements for constraining the CH4 budget, we performed coupled simulations of CH4 and δ13C-CH4 using the chemistry transport model TM5. We specifically assessed the relative impact of uncertainties in i) CH4 emissions, ii) CH4 isotope source signatures and iii) methane transport and chemistry throughout the atmosphere. By randomly perturbing CH4 emissions and δ13C source signatures, we identified areas where simulated variations are dominated by uncertainties in the emission strength and areas where uncertainties in the isotope signatures dominate. At observation sites where the uncertainties in CH4 emissions dominate the other sources of uncertainty, isotope observations should provide useful additional constraints on CH4 emissions. At locations where uncertainties in the isotope signatures dominate, the isotope measurements will be useful to better constrain the source signatures themselves.

  2. Isotopic composition of trace elements in presolar silicon carbide A+B grains

    NASA Astrophysics Data System (ADS)

    Savina, M.; Tripa, C.; Pellin, M.; Davis, A.; Clayton, R.; Lewis, R.; Amari, S.

    2003-04-01

    Presolar SiC are classified into several types based on C, N, and Si isotopic compositions. Most are mainstream, which are generally believed to derive from low-mass asymptotic giant branch (AGB) stars. Among the less common grains, A+B grains, which comprise ˜3-4% of presolar SiC, are perhaps the least well understood. Recent measurements of trace element concentration patterns in individual grains suggest that A+B grains can be divided into at least 4 groups, and thus have multiple astrophysical sites of origin^1. We report here our Resonant Ionization Mass Spectrometry (RIMS) measurements of Zr, Mo, Ba, and Fe isotopic compositions in individual mainstream and type A+B presolar SiC. While the mainstream grains show isotopic compositions compatible with condensation around low-mass AGB stars, most A+B grains have near-solar isotopic compositions, though some show Zr, Mo, and Fe isotope patterns that have not been observed in other types of presolar SiC grains. We discuss these results in terms of possible astrophysical sites for the production of these unusual grains. This work was supported in part by the Department of Energy, BES-Materials Sciences through Contract No. W-31-109-ENG-38. ^1 Amari S., Nittler L. R., Zinner E., Lodders K., and Lewis R. S. (2001) Astrophys. J. 559, 463-483.

  3. Oxygen and Sulfur Isotope Composition of Dissolved Sulfate in Interstitial Waters of the Great Australian Bight, ODP Leg 182.

    NASA Astrophysics Data System (ADS)

    Bernasconi, S. M.; Böttcher, M. E.; Wormann, U. G.

    2005-12-01

    We measured the sulfur and oxygen isotope composition of dissolved sulfides and sulfate at ODP Sites 1129, 1130, 1131 and 1132 in the Great Australian Bight (GAB). At all Sites, a saline brine is present in the subsurface as indicated by increasing chloride concentrations with depth to reach contents up to 3 times seawater. Sulfate also increases with depth but the concentrations are reduced by intense microbial sulfate reduction. The sulfur isotope fractionation between coexisting dissolved sulfate and sulfide is very large and reaches up to 70 ‰ at all studied Sites. Due to the high sulfide concentrations and the lack of a significant source of oxidants we consider that the large sulfur isotope fractionations are induced by sulfate reducing bacteria alone without a significant contribution of elemental sulfur disproportionation and sulfide oxidation processes. The oxygen isotope composition of dissolved sulfate reaches maximum values of approximately +27 ‰ vs. VSMOW at all sites, close to the equilibrium isotope fractionation between sulfate and water. The oxygen isotope composition of dissolved sulfate positively correlates with the sulfur isotope fractionation between sulfate and sulfide. These oxygen isotope data thus support the hypothesis that that the high sulfur isotope fractionation are related to a single step fractionation by sulfate reducing bacteria and do not involve significant sulfide oxidation reactions and/or elemental sulfur disproportionation. Sulfide oxidation processes would lead to a lowering of the oxygen isotope composition of residual sulfate. Elemental sulfur disproportionation has been shown to increase the oxygen isotope composition of sulfate but to a smaller extent than that that observed in the GAB. The patterns of the oxygen isotope increase with progressive sulfate reduction indicate a predominant influence of isotope exchange rather than a kinetic isotope fractionation controlling the oxygen isotope composition of sulfate

  4. Vanadium isotopic composition of the sea squirt (Ciona savignyi).

    PubMed

    Nomura, Masao; Nakamura, Mana; Soeda, Ryosuke; Kikawada, Yoshikazu; Fukushima, Michiko; Oi, Takao

    2012-09-01

    Vanadium (V) in the sea squirt (Ciona savignyi) from Onagawa Bay, Miyagi, Japan, was isolated and purified through adsorption on a diamine resin and anion and cation exchanges after the dissolution of sea squirt samples with nitric acid and hydrogen peroxide. The (50)V/(51)V isotope ratio of V thus obtained was mass-spectrometrically determined to be from 2.51×10(-3) to 2.55×10(-3) with the average of 2.53×10(-3) by the thermal ionisation technique. This value agreed with those of vanadyl chloride and vanadyl nitrate both prepared from vanadyl sulphate (Wako Pure Chemical Industries, Ltd., Japan) and of V in coastal seawater (Shimokita Peninsula, Aomori, Japan) within experimental uncertainties (standard deviation of±0.04), which suggested that no appreciable V isotope fractionation occurs accompanying V uptake by the sea squirt from sea water. PMID:22462478

  5. [Carbon Isotope Composition in Landscape Components and Its Changes under Different Ecological Conditions].

    PubMed

    Kovda, I V; Morgun, E G; Gongalskii, K B; Balandin, S A; Erokhina, A I

    2016-01-01

    The composition of stable carbon isotopes in plants, plant litter, leaf litter, and soil organic matter was studied experimentally in the western part of the northern foothills of the Caucasus and mountainsides. It was found that the changes in carbon isotope composition depending on the vertical zonation do not exceed 8 per thousand and depend on the type of C3 plant communities, its presence in biogeocenosis components (living matter, plant litter, soil organic matter), and the degree of moistening of the plot studied. PMID:27396183

  6. Pb and Sr isotopic constraints on lithospheric magma sources during Mesozoic continental margin arc initiation, southern California

    SciTech Connect

    Barth, A.P. . Dept. of Geology); Tosdal, R.M.; Wooden, J.L. )

    1993-04-01

    Initiation of the Mesozoic Cordilleran arc in the southwestern US is marked by plutonism from about 241--213 Ma, exposed in the Granite Mountains in the southwestern Mojave Desert, through the Transverse Ranges to the Colorado River trough in southeastern California and southwestern Arizona. Plutons range in composition from diorite to granite, but quartz monzonite and monzodiorite predominate. Plutons intruded 1,700 to 1,100 Ma rocks of the Mojave crustal province [as defined isotopically by Wooden and Miller (1990) and Bennett and DePaolo (1987)], and episomal plutons locally intruded its deformed cratonal/miogeoclinal cover. Plutons emplaced during arc initiation overlap isotopically with local Proterozoic basement rocks, but typically have less radiogenic [sup 207]Pb/[sup 204]Pb, [sup 208]Pb/[sup 204]Pb and [sup 87]Sr/[sup 86]Sr than adjacent, more voluminous Middle-Late Jurassic and Late Cretaceous arc plutons. Among early arc plutons, an inter-suite trend toward more radiogenic Pb and [sup 87]Sr/[sup 86]Sr at similar silica contents reflects regional basement isotopic variability. Generally high Sr contents, low Rb/Sr and limited REE data suggest this inter-suite variations records heterogeneity in eclogite/garnet amphibolite facies mafic lithospheric magma sources, corresponding to mafic lower crust and/or upper mantle formed during 1,700 Ma orogenesis or rift-related magmatism at 1,100 Ma. Intra-suite trends toward less radiogenic Pb at constant or more radiogenic Sr reflect involvement of a U and Th depleted, silicic intracrustal contaminant. Distinctive magma sources and limited crustal interaction during emplacement probably reflects the relatively cool thermal structure of the nascent Cordilleran continental margin arc.

  7. Composition dependence of the interaction parameter in isotopic polymer blends

    SciTech Connect

    Londono, J.D.; Narten, A.H.; Wignall, G.D. ); Honnell, K.G.; Hsieh, E.T.; Johnson, T.W. . Research and Development); Bates, F.S. . Dept. of Chemical Engineering)

    1994-05-09

    Isotopic polymer mixtures lack the structural asymmetries and specific interactions encountered in blends of chemically distinct species. In this respect, they form ideal model systems for exploring the limitations of the widely-used Flory-Huggins (FH) lattice model and for testing and improving new theories of polymer thermodynamics. The FH interaction parameter between deuterium-labeled and unlabeled segments of the same species ([sub [chi]HD]) should in principle be independent of concentration ([phi]), through previous small-angle neutron scattering (SANS) experiments have shown that it exhibits a minimum at [phi] [approximately] 0.5 for poly(vinylethylene) (PVE) and poly(ethylethylene) (PEE). The authors report new data on polyethylene (PE) as a function of molecular weight, temperature (T), and [phi], which show qualitatively similar behavior. However, measurements on [sub [chi]HD]([phi]) for polystyrene (PS) show a maximum at [phi] [approximately]0.5, in contrast to PVE, PEE, and PE. Reproducing the concentration dependence of [phi] in different model isotopic systems should serve as a sensitive test of the way in which theories of polymer thermodynamics can account for the details of the local packing and also the effects of noncombinatorial entropy, which appear to be the main cause of the variation of [sub [chi]HD]([phi]) for PE. These data also serve to quantify the effects of isotopic substitution in SANS experiments on polyolefin blends and thus lay the ground work for definitive studies of the compatibility of branched and linear polyethylenes.

  8. Long-term monitoring of stable isotopic compositions of precipitation over volcanic island, Jeju, Korea

    NASA Astrophysics Data System (ADS)

    Kim, Young-Hee; Koh, Dong-Chan; Park, Won-Bae; Bong, Yeon-Sik; Lee, Kwang-Sik; Lee, Jeonghoon

    2015-04-01

    Stable isotopic compositions of precipitation can be widely used to understand moisture transport in the atmosphere, proxies for paleoclimate and interactions between groundwater and precipitation. Over Jeju volcanic island, located southwest of the Korean Peninsula, precipitation penetrated directly into the highly permeable aquifer is the main source of groundwater. In this study, long-term stable isotopic compositions of precipitation over Jeju Island are characterized to describe spatial and temporal patterns for hydrology and paleoclimate. At fifteen sites from September 2000 to December 2003, precipitation samples were collected and analyzed by Isotope Ratio Mass Spectrometer at the Korea Basic Science Institute. Compared to Lee et al. (2003), the two seasonal local meteoric water lines widen, which may change the relative contributions of winter and summer season precipitation to the groundwater recharge. The precipitation isotopes are inversely correlated with precipitation amount in summer, whereas they do not show a strong correlation with surface air temperature. The precipitation isotopes monthly averaged relatively show a periodic function (R2=0.63 and 0.40 for hydrogen and oxygen, respectively), and deuterium excess (d-excess=δD-8×δ18O) shows a strong pattern of quadratic function (R2=0.97), which is related to a seasonal change of air masses. Altitude effect of precipitation isotopes, which can be a clue to reveal sources of groundwater, can be observed in every aspect of the volcanic island (for the oxygen isotope, -0.14‰ for east and west, -0.18‰ for north and -0.085‰ for south per 100 m). Our analysis of precipitation isotopes will be helpful to provide limitations and opportunities for paleoclimate reconstruction using isotopic proxies and water movement from atmosphere to subsurface.

  9. Anomalous sulfur isotope compositions of volcanic sulfate over the last millennium in Antarctic ice cores

    NASA Astrophysics Data System (ADS)

    Baroni, MéLanie; Savarino, JoëL.; Cole-Dai, Jihong; Rai, Vinai K.; Thiemens, Mark H.

    2008-10-01

    The reconstruction of past volcanism from glaciological archives is based on the measurement of sulfate concentrations in ice. This method does not allow a proper evaluation of the climatic impact of an eruption owing to the uncertainty in classifying an event between stratospheric or tropospheric. This work develops a new method, using anomalous sulfur isotope composition of volcanic sulfate in order to identify stratospheric eruptions over the last millennium. The advantages and limits of this new method are established with the examination of the 10 largest volcanic signals in ice cores from Dome C and South Pole, Antarctica. Of the 10, seven are identified as stratospheric eruptions. Among them, three have been known to be stratospheric (Tambora, Kuwae, the 1259 Unknown Event) and they exhibit anomalous sulfur isotope compositions. Three unknown events (circa 1277, 1230, 1170 A.D.) and the Serua eruption have been identified as stratospheric eruptions, which suggests for the first time that they could have had significant climatic impact. However, the Kuwae and the 1259 Unknown Event stratospheric eruptions exhibit different anomalous sulfur isotope compositions between South Pole and Dome C samples. Differences in sulfate deposition and preservation patterns between the two sites can help explain these discrepancies. This study shows that the presence of an anomalous sulfur isotope composition of volcanic sulfate in ice core indicates a stratospheric eruption, but the absence of such composition does not necessarily lead to the conclusion of a tropospheric process because of differences in the sulfate deposition on the ice sheet.

  10. Molybdenum Isotopic Composition of the Archean Mantle As Inferred from Studies of Komatiites

    NASA Astrophysics Data System (ADS)

    Greber, N. D.; Puchtel, I. S.; Nagler, T. F.; Mezger, K.

    2014-12-01

    Molybdenum isotopic composition has been shown to be a powerful tool in studies of planetary processes, e.g. estimating core formation temperatures [1,2]. However, Mo isotope compositions of terrestrial reservoirs are not well constrained. In order to better constrain the Mo isotopic composition of the early Earth's mantle, komatiites from four locations were analyzed for their Mo concentrations and isotopic compositions. Komatiites are particularly appropriate for this type of study because they formed by high degrees of partial melting of the mantle leading to a complete base metal sulfide removal from the residual mantle and the production of sulfur-undersaturated melts and thus a quantitative removal of Mo from the source into the melt. All samples, except for two strongly altered specimens specifically chosen to study the effects of secondary alteration, are very fresh having preserved most of their primary mineralogy. The Mo concentrations in komatiites range from 10 to 120 ng/g. Fresh komatiites have lighter δ98Mo (NIST SRM 3134 = 0.25‰, [3]) than altered samples. The estimated primary Mo isotope compositions of the studied komatiite melts range from 0.02 ± 0.16‰ to 0.19 ± 0.14‰ and are therefore indistinguishable within analytical uncertainty (2SD) from published values for chondritic meteorites (0.09 ± 0.04 ‰; 2SD; [2]) and lighter than the proposed average for Earth's continental crust (0.3 to 0.4‰ [4]). All data combined, although overlapping in errors, show a consistent trend of lighter δ98Mo and lower Mo concentrations in more melt-depleted mantle sources, indicating incompatible behaviour of Mo and preferential mobilization of heavy Mo isotopes during mantle melting. [1] Hin et al. (2013) EPSL, 379 [2] Burkhardt et al. (2014) EPSL, 391 [3] Nägler, et al. (2014) GGR, 38. [4] Voegelin et al. (2014) Lithos, 190-191.

  11. Moisture sources of precipitation over Postojna (Slovenia) and implication of its oxygen isotope composition

    NASA Astrophysics Data System (ADS)

    Krklec, Kristina; Domínguez-Villar, David; Lojen, Sonja

    2016-04-01

    The source of moisture is an important part of the hydrological cycle that affects climate system. Potentially, moisture sources are important controls of the isotope composition of precipitation, but their studies in the continental mid- and low-latitudes are still scarce due to the complexity of general circulation models with integrated isotope modules. We identify moisture uptake locations of precipitation over Postojna (Slovenia) for period from 2009 to 2013. By using HYSPLIT trajectory model of NOAA we did 5-day reconstruction of air mass history for the days with precipitation and determination of moisture uptake locations along back trajectories. Moisture uptake locations were identified along each trajectory using HYSPLIT output data and standard equations for saturation humidity mixing ratio, saturation vapour pressure and specific humidity. Although NNE winds were prevailing during the period 2001-2014, our analysis showed that during this period around 45% of the precipitation over Postojna originated from Mediterranean and south Atlantic area, with majority of locations originated in the Adriatic Sea. On the other hand, 41% of precipitation originated from moisture recycled over continents, predominantly from Pannonian basin. The comparison of monthly oxygen isotope composition of precipitation with the percentage of precipitation originated in different source regions shows a significant correlation only for the north Atlantic region. However, less than 7% of the variability of oxygen isotope composition of precipitation is associated with this moisture source. Multivariable analyses of source regions do not explain any additional variability of the oxygen isotope composition of precipitation over Postojna. This research shows that at this location, although significant, moisture sources are not important controls of the oxygen isotope composition of precipitation.

  12. Geochronologic and isotopic evidence for early Proterozoic crust in the eastern Arabian Shield

    SciTech Connect

    Stacey, J.S.; Hedge, C.E.

    1984-05-01

    The authors report zircon U-Pb, feldspar common Pb, whole-rock Sm-Nd, and Rb-Sr data from sample Z-103, a fine-grained granodiorite from the Jabal Khida region of the Saudi Arabian Shield (lat 21/sup 0/19'N; long 44/sup 0/50'W). The measurements yield conclusive evidence for continental crust of early Proterozoic age (approx.1630 Ma) at that locality. Furthermore, lead-isotope data indicate an even earlier, perhaps Archean, crustal history for the source of the lower Proterozoic rocks. 17 references, 4 figures, 1 table.

  13. The effect of phosphomonoesterases on the oxygen isotope composition of phosphate

    NASA Astrophysics Data System (ADS)

    von Sperber, Christian; Kries, Hajo; Tamburini, Federica; Bernasconi, Stefano M.; Frossard, Emmanuel

    2014-01-01

    Plants and microorganisms under phosphorus (P) stress release extracellular phosphatases as a strategy to acquire inorganic phosphate (Pi). These enzymes catalyze the hydrolysis of phosphoesters leading to a release of Pi. During the enzymatic hydrolysis an isotopic fractionation (ε) occurs leaving an imprint on the oxygen isotope composition of the released Pi which might be used to trace phosphorus in the environment. Therefore, enzymatic assays with acid phosphatases from wheat germ and potato tuber and alkaline phosphatase from Escherichia coli were prepared in order to determine the oxygen isotope fractionation caused by these enzymes. Adenosine 5‧ monophosphate and glycerol phosphate were used as substrates. The oxygen isotope fractionation caused by acid phosphatases is 20-30‰ smaller than for alkaline phosphatases, resulting in a difference of 5-7.5‰ in δ18O of Pi depending on the enzyme. We attribute the enzyme dependence of the isotopic fractionation to distinct reaction mechanisms of the two types of phosphatases. The observed difference is large enough to distinguish between the two enzymatic processes in environmental samples. These findings show that the oxygen isotope composition of Pi can be used to trace different enzymatic processes, offering an analytical tool that might contribute to a better understanding of the P-cycle in the environment.

  14. H, C, and N isotopic compositions of Hayabusa category 3 organic samples

    NASA Astrophysics Data System (ADS)

    Ito, Motoo; Uesugi, Masayuki; Naraoka, Hiroshi; Yabuta, Hikaru; Kitajima, Fumio; Mita, Hajime; Takano, Yoshinori; Karouji, Yuzuru; Yada, Toru; Ishibashi, Yukihiro; Okada, Tatsuaki; Abe, Masanao

    2014-08-01

    Since isotopic ratios of H, C, and N are sensitive indicators for determining extraterrestrial organics, we have measured these isotopes of Hayabusa category 3 organic samples of RB-QD04-0047-02, RA-QD02-0120, and RB-QD04-0001 with ion imaging using a NanoSIMS ion microprobe. All samples have H, C, and N isotopic compositions that are terrestrial within errors (approximately ±50‰ for H, approximately ±9‰ for C, and approximately ±2‰ for N). None of these samples contain micrometer-sized hot spots with anomalous H, C, and N isotopic compositions, unlike previous isotope data for extraterrestrial organic materials, i.e., insoluble organic matters (IOMs) and nano-globules in chondrites, interplanetary dust particles (IDPs), and cometary dust particles. We, therefore, cannot conclude whether these Hayabusa category 3 samples are terrestrial contaminants or extraterrestrial materials because of the H, C, and N isotopic data. A coordinated study using microanalysis techniques including Fourier transform infrared spectrometry (FT-IR), time-of-flight secondary ion mass spectrometry (ToF-SIMS), NanoSIMS ion microprobe, Raman spectroscopy, X-ray absorption near edge spectroscopy (XANES), and transmission electron microscopy/scanning transmission electron microscopy (TEM/STEM) is required to characterize Hayabusa category 3 samples in more detail for exploring their origin and nature.

  15. Plutonium isotopes in the atmosphere of Central Europe: Isotopic composition and time evolution vs. circulation factors.

    PubMed

    Kierepko, Renata; Mietelski, Jerzy W; Ustrnul, Zbigniew; Anczkiewicz, Robert; Wershofen, Herbert; Holgye, Zoltan; Kapała, Jacek; Isajenko, Krzysztof

    2016-11-01

    This paper reports evidence of Pu isotopes in the lower part of the troposphere of Central Europe. The data were obtained based on atmospheric aerosol fraction samples collected from four places in three countries (participating in the informal European network known as the Ring of Five (Ro5)) forming a cell with a surface area of about 200,000km(2). We compared our original data sets from Krakow (Poland, 1990-2007) and Bialystok (Poland, 1991-2007) with the results from two other locations, Prague (Czech Republic; 1997-2004) and Braunschweig (Germany; 1990-2003) to find time evolution of the Pu isotopes. The levels of the activity concentration for (238)Pu and for ((239+240))Pu were estimated to be a few and some tens of nBqm(-3), respectively. However, we also noted some results were much higher (even about 70 times higher) than the average concentration of (238)Pu in the atmosphere. The achieved complex data sets were used to test a new approach to the problem of solving mixing isotopic traces from various sources (here up to three) in one sample. Results of our model, supported by mesoscale atmospheric circulation parameters, suggest that Pu from nuclear weapon accidents or tests and nuclear burnt-up fuel are present in the air. PMID:27450248

  16. Carbon isotope composition of latex does not reflect temporal variations of photosynthetic carbon isotope discrimination in rubber trees (Hevea brasiliensis).

    PubMed

    Kanpanon, Nicha; Kasemsap, Poonpipope; Thaler, Philippe; Kositsup, Boonthida; Gay, Frédéric; Lacote, Régis; Epron, Daniel

    2015-11-01

    Latex, the cytoplasm of laticiferous cells localized in the inner bark of rubber trees (Hevea brasiliensis Müll. Arg.), is collected by tapping the bark. Following tapping, latex flows out of the trunk and is regenerated, whereas in untapped trees, there is no natural exudation. It is still unknown whether the carbohydrates used for latex regeneration in tapped trees is coming from recent photosynthates or from stored carbohydrates, and in the former case, it is expected that latex carbon isotope composition of tapped trees will vary seasonally, whereas latex isotope composition of untapped trees will be more stable. Temporal variations of carbon isotope composition of trunk latex (δ(13)C-L), leaf soluble compounds (δ(13)C-S) and bulk leaf material (δ(13)C-B) collected from tapped and untapped 20-year-old trees were compared. A marked difference in δ(13)C-L was observed between tapped and untapped trees whatever the season. Trunk latex from tapped trees was more depleted (1.6‰ on average) with more variable δ(13)C values than those of untapped trees. δ(13)C-L was higher and more stable across seasons than δ(13)C-S and δ(13)C-B, with a maximum seasonal difference of 0.7‰ for tapped trees and 0.3‰ for untapped trees. δ(13)C-B was lower in tapped than in untapped trees, increasing from August (middle of the rainy season) to April (end of the dry season). Differences in δ(13)C-L and δ(13)C-B between tapped and untapped trees indicated that tapping affects the metabolism of both laticiferous cells and leaves. The lack of correlation between δ(13)C-L and δ(13)C-S suggests that recent photosynthates are mixed in the large pool of stored carbohydrates that are involved in latex regeneration after tapping. PMID:26358051

  17. Determining terrestrial paleotemperatures using the oxygen isotopic composition of pedogenic carbonate

    NASA Astrophysics Data System (ADS)

    Dworkin, S. I.; Nordt, L.; Atchley, S.

    2005-08-01

    Quantifying terrestrial paleotemperatures has proven to be a challenging endeavor. This paper explores the use of the oxygen isotopic composition of pedogenic calcite for terrestrial paleotemperature reconstructions. We generate three paleotemperature equations, two of them derived by simultaneous solution of equations that describe the fractionation of oxygen isotopes in the exogenic cycle, while the third equation is derived using a linear regression through modern δ18Occ / MAT (oxygen isotopic composition of pedogenic calcite versus mean annual temperature) data. We use the paleotemperature equations to evaluate climate change across the K-T boundary by analyzing the oxygen isotopic composition of pedogenic carbonates from a series of stacked paleosols in west Texas. The fabrics in the calcite nodules were evaluated in order to identify soil carbonate components that have the best chance of containing isotopic information that represents ancient pedogenic conditions. The average temperature for West Texas during the time period studied is 18+ / - 0.5 °C. Two temperature excursions are recognized prior to the K-T boundary in which terrestrial temperatures increase by about 4 °C for relatively short periods of time. These short greenhouse events documented in west Texas correlate with changes in marine temperatures as well as terrestrial temperatures in North Dakota during the same time period. Latitudinal temperature gradients generated using the West Texas and North Dakota data indicate that the spatial simultaneous solution yields the most reliable temperature reconstructions of the three equations considered in this study.

  18. Oxygen and carbon isotopic compositions of gases respired by humans

    SciTech Connect

    Epstein, S.; Zeiri, L. )

    1988-03-01

    Oxygen-isotope fractionation associated with respiration in human individuals at rest is linearly related to the fraction of the O{sub 2} utilized in the respiration process. The slope of this relationship is affected by a history of smoking, by vigorous exercise, and by the N{sub 2}/O{sub 2} ratio of the inhaled gas. For patients who suffer anemia-related diseases, the slope of this relationship is directly proportional to their level of hemoglobin. These results introduce a new approach for studying the mechanisms of O{sub 2} consumption in human respiration and how they are affected by related diseases.

  19. Satellite measurements of the isotopic composition of galactic cosmic rays

    NASA Technical Reports Server (NTRS)

    Mewaldt, R. A.; Spalding, J. D.; Stone, E. C.; Vogt, R. E.

    1979-01-01

    The individual isotopes of galactic cosmic ray Ne, Mg, and Si at 100 MeV/nucleon were clearly resolved with an rms mass resolution of 0.20 amu. The results suggest the cosmic ray source is enriched in Ne-22, Mg-25, and Mg-26 when compared to the solar system. The ratio of (Mg-25)+(Mg-26) to Mg-24, which is approximately 0.49 compared to the solar system value of 0.27, suggest that the cosmic ray source and solar system material were synthesized under different conditions.

  20. Unexpected variations in the triple oxygen isotope composition of stratospheric carbon dioxide

    PubMed Central

    Wiegel, Aaron A.; Cole, Amanda S.; Hoag, Katherine J.; Atlas, Elliot L.; Schauffler, Sue M.; Boering, Kristie A.

    2013-01-01

    We report observations of stratospheric CO2 that reveal surprisingly large anomalous enrichments in 17O that vary systematically with latitude, altitude, and season. The triple isotope slopes reached 1.95 ± 0.05(1σ) in the middle stratosphere and 2.22 ± 0.07 in the Arctic vortex versus 1.71 ± 0.03 from previous observations and a remarkable factor of 4 larger than the mass-dependent value of 0.52. Kinetics modeling of laboratory measurements of photochemical ozone–CO2 isotope exchange demonstrates that non–mass-dependent isotope effects in ozone formation alone quantitatively account for the 17O anomaly in CO2 in the laboratory, resolving long-standing discrepancies between models and laboratory measurements. Model sensitivities to hypothetical mass-dependent isotope effects in reactions involving O3, O(1D), or CO2 and to an empirically derived temperature dependence of the anomalous kinetic isotope effects in ozone formation then provide a conceptual framework for understanding the differences in the isotopic composition and the triple isotope slopes between the laboratory and the stratosphere and between different regions of the stratosphere. This understanding in turn provides a firmer foundation for the diverse biogeochemical and paleoclimate applications of 17O anomalies in tropospheric CO2, O2, mineral sulfates, and fossil bones and teeth, which all derive from stratospheric CO2. PMID:23940331

  1. Unexpected variations in the triple oxygen isotope composition of stratospheric carbon dioxide.

    PubMed

    Wiegel, Aaron A; Cole, Amanda S; Hoag, Katherine J; Atlas, Elliot L; Schauffler, Sue M; Boering, Kristie A

    2013-10-29

    We report observations of stratospheric CO2 that reveal surprisingly large anomalous enrichments in (17)O that vary systematically with latitude, altitude, and season. The triple isotope slopes reached 1.95 ± 0.05(1σ) in the middle stratosphere and 2.22 ± 0.07 in the Arctic vortex versus 1.71 ± 0.03 from previous observations and a remarkable factor of 4 larger than the mass-dependent value of 0.52. Kinetics modeling of laboratory measurements of photochemical ozone-CO2 isotope exchange demonstrates that non-mass-dependent isotope effects in ozone formation alone quantitatively account for the (17)O anomaly in CO2 in the laboratory, resolving long-standing discrepancies between models and laboratory measurements. Model sensitivities to hypothetical mass-dependent isotope effects in reactions involving O3, O((1)D), or CO2 and to an empirically derived temperature dependence of the anomalous kinetic isotope effects in ozone formation then provide a conceptual framework for understanding the differences in the isotopic composition and the triple isotope slopes between the laboratory and the stratosphere and between different regions of the stratosphere. This understanding in turn provides a firmer foundation for the diverse biogeochemical and paleoclimate applications of (17)O anomalies in tropospheric CO2, O2, mineral sulfates, and fossil bones and teeth, which all derive from stratospheric CO2. PMID:23940331

  2. Stable sulfur and nitrogen isotopic compositions of crude oil fractions from Southern Germany

    NASA Astrophysics Data System (ADS)

    Hirner, A. V.; Graf, W.; Treibs, R.; Melzer, A. N.; Hahn-Weinheimer, P.

    1984-11-01

    Eleven samples of crude oil from the Molasse Basin of Southern Germany were fractionated and their contents of sulfur and nitrogen as well as the stable isotope compositions of these elements ( 34S /32S and 15N /14N , resp.) investigated. According to the δ34S determinations, all crude oils from the Tertiary base of the Western and Eastern Molasse belong to one oil family and differ significantly from the Triassic and Liassic oils in the Western Molasse. An enrichment of 34S was observed with increasing polarity of crude oil fractions. The isotope distributions of sulfur in the polar constituents of the biodegraded oils from the sandstones of Ampfing, however, approach a homogeneous distribution. The nitrogen isotope distribution is rather uniform in Southern German oils. A regional differentiation can be recognized, although the overall isotopic variation is small. The δ15N values of the crudes and asphaltenes do not correlate.

  3. Isotope composition of sulphate in acid mine drainage as measure of bacterial oxidation

    USGS Publications Warehouse

    Taylor, B.E.; Wheeler, M.C.; Nordstrom, D.K.

    1984-01-01

    The formation of acid waters by oxidation of pyrite-bearing ore deposits, mine tailing piles, and coal measures is a complex biogeochemical process and is a serious environmental problem. We have studied the oxygen and sulphur isotope geochemistry of sulphides, sulphur, sulphate and water in the field and in experiments to identify sources of oxygen and reaction mechanisms of sulphate formation. Here we report that the oxygen isotope composition of sulphate in acid mine drainage shows a large variation due to differing proportions of atmospheric- and water-derived oxygen from both chemical and bacterially-mediated oxidation. 18O-enrichment of sulphate results from pyrite oxidation facilitated by Thiobacillus ferrooxidans in aerated environments. Oxygen isotope analysis may therefore be useful in monitoring the effectiveness of abatement programmes designed to inhibit bacterial oxidation. Sulphur isotopes show no significant fractionation between pyrite and sulphate, indicating the quantitative insignificance of intermediate oxidation states of sulphur under acid conditions. ?? 1984 Nature Publishing Group.

  4. First Measurements of Osmium Concentration and Isotopic Composition in a Summit, Greenland Ice Core

    NASA Astrophysics Data System (ADS)

    Osterberg, E. C.; Sharma, M.; Hawley, R. L.; Courville, Z.

    2010-12-01

    Osmium (Os) is one of the rarer elements in the environment and therefore one of the most difficult to accurately measure, but its isotopically distinctive crustal, mantle-derived, and extra-terrestrial sources make it a valuable geochemical tracer. Recent state-of-the-art analyses of precipitation, river water, and ocean water samples from around the world have revealed elevated concentrations of Os with a characteristically low (unradiogenic) Os isotopic signature (187Os/188Os). This unusual low Os isotopic signal has been interpreted as evidence for widespread Os pollution due to the smelting of Platinum Group Element (PGE) sulfide ores for use in automobile catalytic converters. However, an environmental time series of Os concentrations and isotopic composition spanning the pre-industrial to modern era has not previously been developed to evaluate changes in atmospheric Os sources through time. Here we present the first measurements of Os concentration and isotopic composition (to our knowledge) in a 100 m-long ice core collected from Summit, Greenland, spanning from ca. 1700 to 2010 AD. Due to the extremely low Os concentrations in snow (10-15 g/g), these analyses have only recently become possible with advances in Thermal Ionization Mass Spectrometry (TIMS) and ultra-clean analytical procedures. Initial results indicate that the 187Os/188Os of Greenland snow was unradiogenic (187Os/188Os = 0.13-0.15) for at least several periods over the past 300 years, including both pre-anthropogenic and modern times. Os concentrations in the Summit ice core are relatively high (11-52 pg/kg) compared to previously measured precipitation in North America, Europe, Asia and Antarctic sea ice (0.35-23 pg/kg). The low (unradiogenic) isotopic composition are consistent with extraterrestrial (cosmic dust and meteorites; 187Os/188Os = 0.13) and possibly volcanic (187Os/188Os = 0.15-0.6) Os sources, although the Os isotopic composition of volcanic emissions is poorly constrained

  5. Isotopic composition of Murchison organic compounds: Intramolecular carbon isotope fractionation of acetic acid. Simulation studies of cosmochemical organic syntheses

    NASA Technical Reports Server (NTRS)

    Yuen, G. U.; Cronin, J. R.; Blair, N. E.; Desmarais, D. J.; Chang, S.

    1991-01-01

    Recently, in our laboratories, samples of Murchison acetic acid were decarboxylated successfully and the carbon isotopic composition was measured for the methane released by this procedure. These analyses showed significant differences in C-13/C-12 ratios for the methyl and carboxyl carbons of the acetic acid molecule, strongly suggesting that more than one carbon source may be involved in the synthesis of the Murchison organic compounds. On the basis of this finding, laboratory model systems simulating cosmochemical synthesis are being studied, especially those processes capable of involving two or more starting carbon sources.

  6. Lithium contents and isotopic compositions of ferromanganese deposits from the global ocean

    USGS Publications Warehouse

    Chan, L.-H.; Hein, J.R.

    2007-01-01

    To test the feasibility of using lithium isotopes in marine ferromanganese deposits as an indicator of paleoceanographic conditions and seawater composition, we analyzed samples from a variety of tectonic environments in the global ocean. Hydrogenetic, hydrothermal, mixed hydrogenetic–hydrothermal, and hydrogenetic–diagenetic samples were subjected to a two-step leaching and dissolution procedure to extract first the loosely bound Li and then the more tightly bound Li in the Mn oxide and Fe oxyhydroxide. Total leachable Li contents vary from 2 by coulombic force. Hence, the abundant Li in hydrothermal deposits is mainly associated with the dominant phase, MnO2. The surface of amorphous FeOOH holds a slightly positive charge and attracts little Li, as demonstrated by data for hydrothermal Fe oxyhydroxide. Loosely sorbed Li in both hydrogenetic crusts and hydrothermal deposits exhibit Li isotopic compositions that resemble that of modern seawater. We infer that the hydrothermally derived Li scavenged onto the surface of MnO2 freely exchanged with ambient seawater, thereby losing its original isotopic signature. Li in the tightly bound sites is always isotopically lighter than that in the loosely bound fraction, suggesting that the isotopic fractionation occurred during formation of chemical bonds in the oxide and oxyhydroxide structures. Sr isotopes also show evidence of re-equilibration with seawater after deposition. Because of their mobility, Li and Sr in the ferromanganese crusts do not faithfully record secular variations in the isotopic compositions of seawater. However, Li content can be a useful proxy for the hydrothermal history of ocean basins. Based on the Li concentrations of the globally distributed hydrogenetic and hydrothermal samples, we estimate a scavenging flux of Li that is insignificant compared to the hydrothermal flux and river input to the ocean.

  7. Variation of lithium isotope composition in the marine environment: A preliminary report

    SciTech Connect

    Chan, Luiheung; Edmond, J.M. )

    1988-06-01

    The Li isotopic compositions of ocean waters, lake water, hydrothermal solutions, altered and unaltered basalts have been determined using the technique of thermal ionization mass spectrometry of lithium tetraborate. Seawater appears to be homogeneous in Li isotopic composition. The mean {delta}{sup 6}Li value is {minus}32.3 {plus minus} 0.5{per thousand}, relative to an isotopic standard. Three lakes studied (Lake Tanganyika, Caspian Sea and Dead Sea) yield {delta}{sup 6}Li similar to the seawater isotopic composition. A fresh basalt glass from 21{degree}N, East Pacific Rise displays a {delta}{sup 6}Li value of {minus}4.7{per thousand}. A hydrothermal solution from a 21{degree}N vent field has {delta}{sup 6}Li of {minus}10{per thousand}, indicating incomplete extraction of Li from the igneous minerals or partial retention in secondary phases. The alteration margin of a basalt from the Mid-Atlantic Ridge has {delta}{sup 6}Li of {minus}8.4{per thousand}. The isotope data of submarine basalts suggest preferential removal of {sup 6}Li from seawater into alteration minerals during low temperature weathering. The {delta}{sup 6}Li values of two hydrothermal solutions from Guaymas Basin were found to be {minus}5{per thousand} and {minus}10{per thousand}. The results can be interpreted as the net effect of Li addition from basalt and sediments and incorporation in hydrothermal precipitates as the hydrothermal fluids interact with basin sediments. The observed enrichment of {sup 7}Li in seawater relative to submarine hydrothermal solutions, its principal Li input, is tentatively attributed to isotopic fractionation associated with low temperature alteration of sea floor basalt and incorporation in authigenic sediments. It appears that the Li isotope system may have characteristics that can resolve the mass balance of Li in the ocean.

  8. The carbon and nitrogen isotopic composition of ureilites Implications for their genesis

    NASA Astrophysics Data System (ADS)

    Grady, M. M.; Wright, I. P.; Swart, P. K.; Pillinger, C. T.

    1985-04-01

    Stepped combustion is used to determine C and N isotopic compositions in 14 and 5 ureilites, respectively. The results are presented in tables and graphs and characterized in detail. Relatively constant values of delta-(C-13) are found at 500-1000 C in each meteorite, indicating that the diamond components formed from the graphite components under conditions such as impact which did not cause isotopic fractionation. Among the ureilites, two groups with delta-(C-13) near -10 and -2 per mil are identified and found to correspond to the groups identified by Berkley et al. (1980) on the basis of the Fe content of their olivine components; this finding suggests formation from more than one ureilite parent body. Wide variations are found in the N isotopic compositions, with N abundances ranging from 25 to 150 ppm and much lower C/N ratios than in carbonaceous chondrites.

  9. Controls on the distribution and isotopic composition of helium in deep ground-water flows

    USGS Publications Warehouse

    Zhao, X.; Fritzel, T.L.B.; Quinodoz, H.A.M.; Bethke, C.M.; Torgersen, T.

    1998-01-01

    The distribution and isotopic composition of helium in sedimentary basins can be used to interpret the ages of very old ground waters. The piston-flow model commonly used in such interpretation, how ever, does not account for several important factors and as such works well only in very simple flow regimes. In this study of helium transport in a hypothetical sedimentary basin, we develop a numerical model that accounts for the magnitude and distribution of the basal helium flux, hydrodynamic dispersion, and complexities in flow regimes such as subregional flow cells. The modeling shows that these factors exert strong controls on the helium distribution and isotopic composition. The simulations may provide a basis for more accurate interpretations of observed helium concentrations and isotopic ratios in sedimentary basins.

  10. Isotopic composition analysis and age dating of uranium samples by high resolution gamma ray spectrometry

    NASA Astrophysics Data System (ADS)

    Apostol, A. I.; Pantelica, A.; Sima, O.; Fugaru, V.

    2016-09-01

    Non-destructive methods were applied to determine the isotopic composition and the time elapsed since last chemical purification of nine uranium samples. The applied methods are based on measuring gamma and X radiations of uranium samples by high resolution low energy gamma spectrometric system with planar high purity germanium detector and low background gamma spectrometric system with coaxial high purity germanium detector. The "Multigroup γ-ray Analysis Method for Uranium" (MGAU) code was used for the precise determination of samples' isotopic composition. The age of the samples was determined from the isotopic ratio 214Bi/234U. This ratio was calculated from the analyzed spectra of each uranium sample, using relative detection efficiency. Special attention is paid to the coincidence summing corrections that have to be taken into account when performing this type of analysis. In addition, an alternative approach for the age determination using full energy peak efficiencies obtained by Monte Carlo simulations with the GESPECOR code is described.

  11. Isotopic composition of lead and strontium from Ascension and Gough Islands

    USGS Publications Warehouse

    Gast, P.W.; Tilton, G.R.; Hedge, C.

    1964-01-01

    Isotopic composition of lead and strontium has been determined in a series of rock samples from two islands on the Mid-Atlantic Ridge. Both inter-and intra-island variations exist in the abundance of radiogenic isotopes of both elements. Lead from basalt of Ascension Island has a Pb206-Pb 204 ratio of 19.5, while the corresponding ratio at Gough Island is only 18.4. The Pb208-Pb204 ratios from the two islands do not differ. Conversely, strontium from basalt of Ascension Island is less radiogenic than that from Gough Island basalts. The trachytes of both islands have lead and strontium that is more radiogenic than that found in the basalts. The inter-island differences indicate the existence of regional variations in the uranium-lead and rubidium-strontium ratios of the upper mantle source of these rocks and show that isotope compositions are a means for investigating chemical heterogeneities in the mantle.

  12. Constraints on Galactic Cosmic-Ray Origins from Elemental and Isotopic Composition Measurements

    NASA Technical Reports Server (NTRS)

    Binns, W. R.; Christian, E. R.; Cummings, A. C.; deNolfo, G. A.; Israel, M. H.; Leske, R. A.; Mewaldt, R. A,; Stone, E. C.; vonRosevinge, T. T.; Wiedenbeck, M. E.

    2013-01-01

    The most recent measurements by the Cosmic Ray Isotope Spectrometer (CRIS) aboard the Advanced Composition Explorer (ACE) satellite of ultra-heavy cosmic ray isotopic and elemental abundances will be presented. A range of isotope and element ratios, most importantly Ne-22/Ne-20, Fe-58/Fe-56, and Ga-31/Ge -32 show that the composition is consistent with source material that is a mix of approx 80% ISM (with Solar System abundances) and 20% outflow/ejecta from massive stars. In addition, our data show that the ordering of refractory and volatile elements with atomic mass is greatly improved when compared to an approx 80%/20% mix rather than pure ISM, that the refractory and volatile elements have similar slopes, and that refractory elements are preferentially accelerated by a factor of approx 4. We conclude that these data are consistent with an OB association origin of GCRs.

  13. Sulphur isotopic compositions of deep-sea hydrothermal vent animals

    NASA Technical Reports Server (NTRS)

    Fry, B.; Gest, H.; Hayes, J. M.

    1983-01-01

    The S-34/S-32 ratios of tissues from vestimentiferan worms, brachyuran crabs, and giant clams living around deep hydrothermal vents are reported. Clean tissues were dried, ground, suspended in 0.1 M LiCl, shaken twice at 37 C to remove seawater sulfates, dried at 60 C, combusted in O2 in a Parr bomb. Sulfur was recovered as BaSO4, and the isotopic abundances in SO2 generated by thermal decomposition of 5-30-mg samples were determined using an isotope-ratio mass spectrometer. The results are expressed as delta S-34 and compared with values measured in seawater sulfates and in normal marine fauna. The values ranged from -4.7 to 4.7 per thousand, comparable to vent sulfide minerals (1.3-4.1 per thousand) and distinct from seawater sulfates (20.1 per thousand) and normal marine fauna (about 13-20 per thousand). These results indicate that vent sulfur rather than seawater sulfur is utilized by these animals, a process probably mediated by chemoautotrophic bacteria which can use inorganic sulfur compounds as energy sources.

  14. The isotopic composition of methane in polar ice cores

    NASA Technical Reports Server (NTRS)

    Craig, H.; Chou, C. C.; Welhan, J. A.; Stevens, C. M.; Engelkemeir, A.

    1988-01-01

    Air bubbles in polar ice cores indicate that about 300 years ago the atmospheric mixing ratio of methane began to increase rapidly. Today the mixing ratio is about 1.7 parts per million by volume, and, having doubled once in the past several hundred years, it will double again in the next 60 years if current rates continue. Carbon