Natural calcium isotopic composition of urine as a marker of bone mineral balance.

PubMed

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

2007-06-01

We investigated whether changes in the natural isotopic composition of calcium in human urine track changes in net bone mineral balance, as predicted by a model of calcium isotopic behavior in vertebrates. If so, isotopic analysis of natural urine or blood calcium could be used to monitor short-term changes in bone mineral balance that cannot be detected with other techniques. Calcium isotopic compositions are expressed as delta(44)Ca, or the difference in parts per thousand between the (44)Ca/(40)Ca of a sample and the (44)Ca/(40)Ca of a standard reference material. delta(44)Ca was measured in urine samples from 10 persons who participated in a study of the effectiveness of countermeasures to bone loss in spaceflight, in which 17 weeks of bed rest was used to induce bone loss. Study participants were assigned to 1 of 3 treatment groups: controls received no treatment, one treatment group received alendronate, and another group performed resistive exercise. Measurements were made on urine samples collected before, at 2 or 3 points during, and after bed rest. Urine delta(44)Ca values during bed rest were lower in controls than in individuals treated with alendronate (P <0.05, ANOVA) or exercise (P <0.05), and lower than the control group baseline (P <0.05, t-test). Results were consistent with the model and with biochemical and bone mineral density data. Results confirm the predicted relationship between bone mineral balance and calcium isotopes, suggesting that calcium isotopic analysis of urine might be refined into a clinical and research tool.

Diffusion of multi-isotopic chemical species in molten silicates

NASA Astrophysics Data System (ADS)

Watkins, James M.; Liang, Yan; Richter, Frank; Ryerson, Frederick J.; DePaolo, Donald J.

2014-08-01

Diffusion experiments in a simplified Na2O-CaO-SiO2 liquid system are used to develop a general formulation for the fractionation of Ca isotopes during liquid-phase diffusion. Although chemical diffusion is a well-studied process, the mathematical description of the effects of diffusion on the separate isotopes of a chemical element is surprisingly underdeveloped and uncertain. Kinetic theory predicts a mass dependence on isotopic mobility, but it is unknown how this translates into a mass dependence on effective binary diffusion coefficients, or more generally, the chemical diffusion coefficients that are housed in a multicomponent diffusion matrix. Our experiments are designed to measure Ca mobility, effective binary diffusion coefficients, the multicomponent diffusion matrix, and the effects of chemical diffusion on Ca isotopes in a liquid of single composition. We carried out two chemical diffusion experiments and one self-diffusion experiment, all at 1250 °C and 0.7 GPa and using a bulk composition for which other information is available from the literature. The self-diffusion experiment is used to determine the mobility of Ca in the absence of diffusive fluxes of other liquid components. The chemical diffusion experiments are designed to determine the effect on Ca isotope fractionation of changing the counter-diffusing component from fast-diffusing Na2O to slow-diffusing SiO2. When Na2O is the main counter-diffusing species, CaO diffusion is fast and larger Ca isotopic effects are generated. When SiO2 is the main counter-diffusing species, CaO diffusion is slow and smaller Ca isotopic effects are observed. In both experiments, the liquid is initially isotopically homogeneous, and during the experiment Ca isotopes become fractionated by diffusion. The results are used as a test of a new general expression for the diffusion of isotopes in a multicomponent liquid system that accounts for both self diffusion and the effects of counter-diffusing species. Our results show that (1) diffusive isotopic fractionations depend on the direction of diffusion in composition space, (2) diffusive isotopic fractionations scale with effective binary diffusion coefficient, as previously noted by Watkins et al. (2011), (3) self-diffusion is not decoupled from chemical diffusion, (4) self diffusion can be faster than or slower than chemical diffusion and (5) off-diagonal terms in the chemical diffusion matrix have isotopic mass-dependence. The results imply that relatively large isotopic fractionations can be generated by multicomponent diffusion even in the absence of large concentration gradients of the diffusing element. The new formulations for isotope diffusion can be tested with further experimentation and provide an improved framework for interpreting mass-dependent isotopic variations in natural liquids.

Ca, Sr and Ba stable isotopes reveal the fate of soil nutrients along a tropical climosequence

USGS Publications Warehouse

Bullen, Thomas D.; Chadwick, Oliver A.

2016-01-01

Nutrient biolifting is an important pedogenic process in which plant roots obtain inorganic nutrients such as phosphorus (P) and calcium (Ca) from minerals at depth and concentrate those nutrients at the surface. Here we use soil chemistry and stable isotopes of the alkaline earth elements Ca, strontium (Sr) and barium (Ba) to test the hypothesis that biolifting of P has been an important pedogenic process across a soil climosequence developed on volcanic deposits at Kohala Mountain, Hawaii. The geochemical linkage between these elements is revealed as generally positive site-specific relationships in soil mass gains and losses, particularly for P, Ba and Ca, using the ratio of immobile elements titanium and niobium (Ti/Nb) to link individual soil samples to a restricted compositional range of the chemically and isotopically diverse volcanic parent materials. At sites where P is enriched in surface soils relative to abundances in deeper soils, the isotope compositions of exchangeable Ca, Sr and Ba in the shallowest soil horizons (< 10 cm depth) are lighter than those of the volcanic parent materials and trend toward those of plants growing on fresh volcanic deposits. In contrast the isotope composition of exchangeable Ba in deeper soil horizons (> 10 cm depth) at those sites is consistently heavier than the volcanic parent materials. The isotope compositions of exchangeable Ca and Sr trend toward heavier compositions with depth more gradually, reflecting increasing leakiness from these soils in the order Ba < Sr < Ca and downward transfer of light biocycled Ca and Sr to deeper exchange sites. Given the long-term stability of ecosystem properties at the sites where P is enriched in surface soils, a simple box model demonstrates that persistence of isotopically light exchangeable Ca, Sr and Ba in the shallowest soil horizons requires that the uptake flux to plants from those near-surface layers is less than the recycling flux returned to the surface as litterfall. This observation implicates an uptake flux from an additional source which we attribute to biolifting. We view the heavy exchangeable Ba relative to soil parent values in deeper soils at sites where P is enriched in surface soils, and indeed at all but the wettest site across the climosequence, to represent the complement of an isotopically light Ba fraction removed from these soils by plant roots consistent with the biolifting hypothesis. We further suggest that decreasing heaviness of depth-integrated exchangeable Ba in deeper soils with increasing median annual precipitation across the climosequence reflects greater reliance on shallow nutrient sources as site water balance increases. While the Ca, Sr and Ba isotopes considered together were useful in confirming an important role for nutrient biolifting across the climosequence, the Ba isotopes provided the most robust tracer of biolifting and have the greatest potential to find application as an isotopic proxy for P dynamics in soils.

The calcium isotope evolution of Lake Lisan, the Dead Sea glacial precursor

NASA Astrophysics Data System (ADS)

Bradbury, H. J.; Turchyn, A. V.; Wong, K.; Torfstein, A.

2016-12-01

Calcium is a stoichiometric component of carbonate minerals whose calcium isotopic composition reflects changes in the calcium isotope composition of the water from which it precipitates as well as the calcium isotope fractionation factor during precipitation. The lacustrine deposits of the last glacial Dead Sea (Lisan Formation) are dominated by carbonate minerals (aragonite) that record the geochemical history of the lake. The sediment sequence comprises alternating laminae of aragonite and clay-rich marls, interspersed with primary gypsum beds and disseminated secondary gypsum crystals. The aragonite precipitated annually during high lake stands associated with wet periods, while the primary gypsum precipitated during low lake conditions (arid periods). We report the calcium isotopic composition (δ44Ca in ‰ relative to bulk silicate earth) of primary aragonite laminae, primary gypsum and secondary gypsum at 1-5kyr resolution throughout the Lisan Formation sampled at the Masada section (70 - 14.5 ka). The δ44Ca of the primary gypsum averages +0.29‰, and displays smaller temporal variations than the aragonite, which averages -0.35‰ but ranges between +0.18‰ and -0.68‰. The aragonite δ44Ca changes temporally in sync with the previously reconstructed lake level suggesting the aragonite δ44Ca reflects changes in the lake calcium balance during lake level changes. The secondary gypsum composition (-0.3‰) corresponds to coeval aragonite samples. For the secondary gypsum to have a similar δ44Ca to the aragonite it is likely that the calcium derived from the aragonite in a near quantitative fashion through recrystallization of the aragonite to gypsum. A numerical box model is used to explore the effect of changing lake water levels on the calcium isotope composition of the aragonite and gypsum over the time interval studied.

Natural calcium isotonic composition of urine as a marker of bone mineral balance

USGS Publications Warehouse

Skulan, J.; Bullen, T.; Anbar, A.D.; Puzas, J.E.; Shackelford, L.; LeBlanc, A.; Smith, S.M.

2007-01-01

Background: We investigated whether changes in the natural isotopic composition of calcium in human urine track changes in net bone mineral balance, as predicted by a model of calcium isotopic behavior in vertebrates. If so, isotopic analysis of natural urine or blood calcium could be used to monitor short-term changes in bone mineral balance that cannot be detected with other techniques. Methods: Calcium isotopic compositions are expressed as ??44Ca, or the difference in parts per thousand between the 44Ca/40Ca of a sample and the 44Ca/ 40Ca of a standard reference material. ??44Ca was measured in urine samples from 10 persons who participated in a study of the effectiveness of countermeasures to bone loss in spaceflight, in which 17 weeks of bed rest was used to induce bone loss. Study participants were assigned to 1 of 3 treatment groups: controls received no treatment, one treatment group received alendronate, and another group performed resistive exercise. Measurements were made on urine samples collected before, at 2 or 3 points during, and after bed rest. Results: Urine ??44Ca values during bed rest were lower in controls than in individuals treated with alendronate (P <0.05, ANOVA) or exercise (P <0.05), and lower than the control group baseline (P <0.05, Mest). Results were consistent with the model and with biochemical and bone mineral density data. Conclusion: Results confirm the predicted relationship between bone mineral balance and calcium isotopes, suggesting that calcium isotopic analysis of urine might be refined into a clinical and research tool. ?? 2007 American Association for Clinical Chemistry.

Spatial and mineralogic variation of Na-Ca alteration in Laramide porphyry systems of Arizona

NASA Astrophysics Data System (ADS)

Runyon, S.; Seedorff, E.; Barton, M. D.; Mazdab, F. K.; Lecumberri-Sanchez, P.; Steele-MacInnis, M.

2017-12-01

Na-Ca alteration is characterized by the metasomatic addition of Ca ± Na and the loss of K. Minor volumes of Na-Ca alteration in Laramide porphyry systems develops from 3 to 8 km paleodepth. Mineral assemblages, mineral compositions, hydrogen isotopes, whole-rock analyses, and reconnaissance fluid inclusion characteristics have been documented for Na-Ca alteration in Laramide porphyry systems such as Tea Cup and Sierrita. Volumetrically minor Na-Ca alteration in Laramide porphyry systems documented in this study commonly takes the form of one of three mineral assemblages: albite-epidote-chlorite, Na-plagioclase-actinolite ± epidote, and garnet- or diopside-stable Na-plagioclase-actinolite ± epidote. These different Na-Ca mineral assemblages have broad spatial relationships, from shallow albite-chlorite-epidote to deeper Na-plagioclase-actinolite within a given district. Hydrogen isotope data on Na-Ca alteration minerals shows consistently distinct δD compositions of Na-Ca alteration minerals compared to igneous minerals in a given district. Further, calculated hydrogen isotope composition of fluids in equilibrium with Na-Ca alteration minerals are consistently enriched in δD compared to magmatic-hydrothermal fluids. Whole-rock analyses show consistent losses of K and variable addition of Na and Ca across different Na-Ca alteration assemblages. Na-Ca alteration has been well documented associated with the Jurassic arc. Previous studies demonstrated through mass balance, timing and spatial relationships, isotopic, and fluid inclusion studies that Na-Ca alteration associated with the Jurassic arc likely formed from the circulation of external, highly saline, non-magmatic fluids (e.g., Battles and Barton, 1995; Dilles et al., 1995). Na-Ca alteration documented in Laramide systems is generally similar to Na-Ca alteration documented along the Jurassic arc in mineral assemblages, compositions, and timing, but the volume of Na-Ca alteration in the Laramide systems is small as compared to the voluminous Na-Ca alteration documented in systems associated with the Jurassic arc.

Concentration effect on inter-mineral equilibrium isotope fractionation: insights from Mg and Ca isotopic systems

NASA Astrophysics Data System (ADS)

Huang, F.; Wang, W.; Zhou, C.; Kang, J.; Wu, Z.

2017-12-01

Many naturally occurring minerals, such as carbonate, garnet, pyroxene, and feldspar, are solid solutions with large variations in chemical compositions. Such variations may affect mineral structures and modify the chemical bonding environment around atoms, which further impacts the equilibrium isotope fractionation factors among minerals. Here we investigated the effects of Mg content on equilibrium Mg and Ca isotope fractionation among carbonates and Ca content on equilibrium Ca isotope fractionation between orthopyroxene (opx) and clinopyroxene (cpx) using first-principles calculations. Our results show that the average Mg-O bond length increases with decreasing Mg/(Mg+Ca) in calcite when it is greater than 1/48[1] and the average Ca-O bond length significantly decreases with decreasing Ca/(Ca+Mg+Fe) in opx when it ranges from 2/16 to 1/48[2]. Equilibrium isotope fractionation is mainly controlled by bond strengths, which could be measured by bond lengths. Thus, 103lnα26Mg/24Mg between dolomite and calcite dramatically increases with decreasing Mg/(Mg+Ca) in calcite [1] and it reaches a constant value when it is lower than 1/48. 103lnα44Ca/40Ca between opx and cpx significantly increases with decreasing Ca content in opx when Ca/(Ca+Mg+Fe) ranges from 2/16 to 1/48 [2]. If Ca/(Ca+Mg+Fe) is below 1/48, 103lnα44Ca/40Ca is not sensitive to Ca content. Based on our results, we conclude that the concentration effect on equilibrium isotope fractionation could be significant within a certain range of chemical composition of minerals, which should be a ubiquitous phenomenon in solid solution systems. [1] Wang, W., Qin, T., Zhou, C., Huang, S., Wu, Z., Huang, F., 2017. GCA 208, 185-197. [2] Feng, C., Qin, T., Huang, S., Wu, Z., Huang, F., 2014. GCA 143, 132-142.

The identification of meteorite inclusions with isotope anomalies

NASA Technical Reports Server (NTRS)

Papanastassiou, D. A.; Brigham, C. A.

1989-01-01

Ca-Al refractory inclusions with characteristic chemical and mineralogical compositions show an enhanced occurrence of 20 pct of isotope anomalies reflecting unknown nucleosynthetic effects for O and Mg. The anomalies are characterized by large isotope fractionation in Mg, apparent deficits in Mg-26/Mg-24, and large correlated effects for isotopes of Ca, Ti, and Cr. These isotope patterns define exotic components depleted in the most neutron-rich isotopes of Ca, Ti, and Cr, or components depleted in isotopes produced in explosive O and Si burning. An opaque assemblage within one of the inclusions yields isotope anomalies in Cr similar to the bulk inclusion and must be intrinsically part of the inclusion and not a trapped, foreign grain aggregate.

Calcium Isotopes in Foraminifera Shells: Evaluation for Paleo-temperature Reconstruction

NASA Astrophysics Data System (ADS)

Paytan, A.; Revello, C. A.; Bullen, T. D.

2002-12-01

The Ca stable isotope ratio of foraminifera shells has been suggested as a potential paleo-temperature proxy and has recently been applied in several studies to reconstruct glacial interglacial fluctuations in seawater temperatures. The major advantage of using Ca isotopes for paleo-temperature reconstruction is the relatively long residence time of Ca in the ocean. Thus, no spatial or temporal change in the Ca isotopic composition of seawater is expected over time scales much shorter than a million years. Moreover, since Ca is a major constituent of carbonate, and an isotopic ratio rather than an element concentration or element-element ratio (e.g. Mg/Ca, Sr/Ca) is measured, the Ca isotope proxy is much less likely to be affected by post depositional diagenetic alteration. However, preliminary results indicate that kinetic effects might largely control the Ca isotope fractionation involved in calcite shell formation. Before this new and exciting proxy can be utilized routinely, a better understanding of the parameters controlling Ca isotope fractionation in carbonate minerals in general and in foraminifera and other carbonate-secreting organisms is required. We have measured the Ca stable isotope ratio of several foraminifera species from core top sediments from two well-studied sites to determine the inter-species and within-species variability in Ca isotopes. We assess the effects of water temperature, calcification rate, and vital effects on the Ca stable isotope ratio of modern foraminifera and evaluate the potential of this proxy for paleo-temperature reconstruction.

Natural Ca Isotope Composition of Urine as a Rapid Measure of Bone Mineral Balance

NASA Astrophysics Data System (ADS)

Skulan, J.; Gordon, G. W.; Morgan, J.; Romaniello, S. J.; Smith, S. M.; Anbar, A. D.

2011-12-01

Naturally occurring stable Ca isotope variations in urine are emerging as a powerful tool to detect changes in bone mineral balance. Bone formation depletes soft tissue of light Ca isotopes while bone resorption releases isotopically light Ca into soft tissue. Previously published work found that variations in Ca isotope composition could be detected at 4 weeks of bed rest in a 90-day bed rest study (data collected at 4, 8 and 12 weeks). A new 30-day bed rest study involved 12 patients on a controlled diet, monitored for 7 days prior to bed rest and 7 days post bed rest. Samples of urine, blood and food were collected throughout the study. Four times daily blood samples and per void urine samples were collected to monitor diurnal or high frequency variations. An improved chemical purification protocol, followed by measurement using multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS) allowed accurate and precise determinations of mass-dependent Ca isotope variations in these biological samples to better than ±0.2% (δ44/42Ca) on <25 μg of Ca. Results from this new study show that Ca isotope ratios shift in a direction consistent with net bone loss after just 7 days, long before detectible changes in bone density by X-ray measurements occur. Consistent with this interpretation, the Ca isotope variations track changes observed in N-teleopeptide, a bone resorption biomarker. Bone-specific alkaline phosphatase, a bone formation biomarker, is unchanged over this period. Ca isotopes can in principle be used to quantify net changes in bone mass. Using a mass-balance model, our results indicate an average loss of 0.62 ± 0.16 % in bone mass over the course of this 30-day study. This is consistent with the rate of bone loss in longer-term studies as seen by X-ray measurements. This Ca isotope technique should accelerate the pace of discovery of new treatments for bone disease and provide novel insights into the dynamics of bone metabolism.

Petrographic and C & O isotopic characteristics of the earliest stages of aqueous alteration of CM chondrites

NASA Astrophysics Data System (ADS)

Vacher, Lionel G.; Marrocchi, Yves; Villeneuve, Johan; Verdier-Paoletti, Maximilien J.; Gounelle, Matthieu

2017-09-01

CM chondrites form the largest group of hydrated meteorites and span a wide range of alteration states, with the Paris meteorite being the least altered CM described to date. Ca-Carbonates are powerful proxies for the alteration conditions of CMs because they are direct snapshots of the chemical and isotopic compositions of the parent fluids. Here, we report a petrographic and a C isotope and O isotope survey of Ca-carbonates in Paris in order to better characterize the earliest stages of aqueous alteration. Petrographic observations show that Paris contains two distinct populations of Ca-carbonates: Type 1a Ca-carbonates, which are surrounded by rims of tochilinite/cronstedtite intergrowths (TCIs), and new Type 0 Ca-carbonates, which do not exhibit the TCI rims. The TCI rims of Type 1a Ca-carbonates commonly outline euhedral crystal faces, demonstrating that these Ca-carbonates were (i) partially or totally pseudomorphosed by TCI and (ii) precipitated at the earliest stages of aqueous alteration, before Type 0 Ca-carbonates. Isotopic measurements show that Paris' Ca-carbonates have δ13C values that range from 19 to 80‰ (PDB), δ18O values that range from 29 to 41%, and δ17O values that range from 13 to 24‰ (SMOW). According to the δ13C-δ18O values of Paris' Ca-carbonates, we developed a new alteration model that involves (i) the equilibration of a primordial 17,18O-rich water (PW) with 16O-rich anhydrous silicates and (ii) varying contribution of 12C- and 13C-rich soluble organic matter (SOMs). It also suggests that many parameters control the C and O isotopic composition of Ca-carbonates, the principles being the degree of isotopic equilibration between the PW and the anhydrous silicates, the respective contribution of 12C and 13C-rich SOMs as well as the thermal evolution of CM parent bodies. Consequently, we suggest that CM Ca-carbonates could record both positive and negative δ13C-δ18O relationships, but a systematic correspondence is probably absent in CM chondrites due to the large number of factors involved in generating the isotopic characteristics of Ca-carbonates. From recent reports of the C-isotopic compositions of SOM in CM chondrites, we propose that water-soluble organic compounds were the most probable source of 13C enrichment in the majority of CM carbonates.

Isotopically distinct reservoirs in the solar nebula: Isotope anomalies in Vigarano meteorite inclusions

NASA Technical Reports Server (NTRS)

Loss, R. D.; Lugmair, G. W.; Davis, A. M.; Macpherson, G. J.

1994-01-01

The isotopic compositions of Mg, Ca, Ti, Cr, Zn, Sr, Ba, Nd, and Sm were measured in four relatively unaltered refractory inclusions from the Vigarano carbonaceous chondrite meteorite. Three of the inclusions (USNM 1623-2, 1623-3, and 1623-8) show similar Mg, Ca, Ti, and Cr isotopic compositions to those found in most inclusions in the Allende carbonaceous chondrite. This indicates that these Vigarano inclusions sampled the same isotopic reservoirs as the majority of the Allende inclusions that isotope signatures in the latter were not significantly modified by the secondary alteration that permeates most Allende inclusions. In contrast, inclusion 1623-5 has large deficits in Mg-26, Ca-48, and Ti-50 and small but distinct Cr-54, Zn-66, Sr-84, Ba-135, Ba-137, and Sm-144 anomalies. The magnitudes of these unusual anomalies in the refractory elements are within analytical uncertainty of those found in the Allende 'FUN" inclusion C1, yet 1623-5 has a very different bulk chemical composition from C1. The fact that 1623-5 and C1 have identical isotopic anomalies yet have significantly distinct major and trace element contents provide convincing evidence for the presence of isotopically distinct reservoirs in the early solar system.

Influence of liquid structure on diffusive isotope separation in molten silicates and aqueous solutions

NASA Astrophysics Data System (ADS)

Watkins, James M.; DePaolo, Donald J.; Ryerson, Frederick J.; Peterson, Brook T.

2011-06-01

Molecular diffusion in natural volcanic liquids discriminates between isotopes of major ions (e.g., Fe, Mg, Ca, and Li). Although isotope separation by diffusion is expected on theoretical grounds, the dependence on mass is highly variable for different elements and in different media. Silicate liquid diffusion experiments using simple liquid compositions were carried out to further probe the compositional dependence of diffusive isotopic discrimination and its relationship to liquid structure. Two diffusion couples consisting of the mineral constituents anorthite (CaAl 2Si 2O 8; denoted AN), albite (NaAlSi 3O 8; denoted AB), and diopside (CaMgSi 2O 6; denoted DI) were held at 1450 °C for 2 h and then quenched to ambient pressure and temperature. Major-element as well as Ca and Mg isotope profiles were measured on the recovered quenched glasses. In both experiments, Ca diffuses rapidly with respect to Si. In the AB-AN experiment, D Ca/ D Si ≈ 20 and the efficiency of isotope separation for Ca is much greater than in natural liquid experiments where D Ca/ D Si ≈ 1. In the AB-DI experiment, D Ca/ D Si ≈ 6 and the efficiency of isotope separation is between that of the natural liquid experiments and the AB-AN experiment. In the AB-DI experiment, D Mg/ D Si ≈ 1 and the efficiency of isotope separation for Mg is smaller than it is for Ca yet similar to that observed for Mg in natural liquids. The results from the experiments reported here, in combination with results from natural volcanic liquids, show clearly that the efficiency of diffusive separation of Ca isotopes is systematically related to the solvent-normalized diffusivity - the ratio of the diffusivity of the cation ( D Ca) to the diffusivity of silicon ( D Si). The results on Ca isotopes are consistent with available data on Fe, Li, and Mg isotopes in silicate liquids, when considered in terms of the parameter D cation/ D Si. Cations diffusing in aqueous solutions display a similar relationship between isotopic separation efficiency and Dcation/D, although the efficiencies are smaller than in silicate liquids. Our empirical relationship provides a tool for predicting the magnitude of diffusive isotopic effects in many geologic environments and a basis for a more comprehensive theory of isotope separation in liquid solutions. We present a conceptual model for the relationship between diffusivity and liquid structure that is consistent with available data.

Calcium isotopic fractionation in mantle peridotites by melting and metasomatism and Ca isotope composition of the Bulk Silicate Earth

NASA Astrophysics Data System (ADS)

Kang, Jin-Ting; Ionov, Dmitri A.; Liu, Fang; Zhang, Chen-Lei; Golovin, Alexander V.; Qin, Li-Ping; Zhang, Zhao-Feng; Huang, Fang

2017-09-01

To better constrain the Ca isotopic composition of the Bulk Silicate Earth (BSE) and explore the Ca isotope fractionation in the mantle, we determined the Ca isotopic composition of 28 peridotite xenoliths from Mongolia, southern Siberia and the Siberian craton. The samples are divided in three chemical groups: (1) fertile, unmetasomatized lherzolites (3.7-4.7 wt.% Al2O3); (2) moderately melt-depleted peridotites (1.3-3.0 wt.% Al2O3) with no or very limited metasomatism (LREE-depleted cpx); (3) strongly metasomatized peridotites (LREE-enriched cpx and bulk rock) further divided in subgroups 3a (harzburgites, 0.1-1.0% Al2O3) and 3b (fertile lherzolites, 3.9-4.3% Al2O3). In Group 1, δ44/40Ca of fertile spinel and garnet peridotites, which experienced little or no melting and metasomatism, show a limited variation from 0.90 to 0.99‰ (relative to SRM 915a) and an average of 0.94 ± 0.05‰ (2SD, n = 14), which defines the Ca isotopic composition of the BSE. In Group 2, the δ44/40Ca is the highest for three rocks with the lowest Al2O3, i.e. the greatest melt extraction degrees (average 1.06 ± 0.04 ‰, i.e. ∼0.1‰ heavier than the BSE estimate). Simple modeling of modal melting shows that partial melting of the BSE with 103 ln ⁡αperidotite-melt ranging from 0.10 to 0.25 can explain the Group 2 data. By contrast, δ44/40Ca in eight out of nine metasomatized Group 3 peridotites are lower than the BSE estimate. The Group 3a harzburgites show the greatest δ44/40Ca variation range (0.25-0.96‰), with δ44/40Ca positively correlated with CaO and negatively correlated with Ce/Eu. Chemical evidence suggests that the residual, melt-depleted, low-Ca protoliths of the Group 3a harzburgites were metasomatized, likely by carbonate-rich melts/fluids. We argue that such fluids may have low (≤0.25‰) δ44/40Ca either because they contain recycled crustal components or because Ca isotopes, similar to trace elements and their ratios, may be fractionated by kinetic and/or chromatographic effects of melt percolation in the mantle. The δ44/40Ca in Group 3b lherzolites (0.83-0.89‰) are lower than in the BSE as well, but the effects of metasomatism on δ44/40Ca are smaller, possibly because of the high Ca contents in their protoliths and/or smaller δ44/40Ca differences between the protoliths and metasomatic agents. The BSE estimates based on fertile peridotites in this study fall in the δ44/40Ca ranges for oceanic and continental basalts, various meteorites (achondrites; carbonaceous, ordinary and enstatite chondrites), Mars, and the Moon. These results provide benchmarks for the application of Ca isotopes to planet formation, mantle evolution, and crustal recycling.

Uranium isotope fractionation induced by aqueous speciation: Implications for U isotopes in marine CaCO3 as a paleoredox proxy

NASA Astrophysics Data System (ADS)

Chen, Xinming; Romaniello, Stephen J.; Anbar, Ariel D.

2017-10-01

Natural variations of 238U/235U in marine CaCO3 rocks are being explored as a novel paleoredox proxy to investigate oceanic anoxia events. Although it is generally assumed that U isotopes in CaCO3 directly record 238U/235U of seawater, recently published laboratory experiments demonstrate slight U isotope fractionation during U(VI) incorporation into abiotic calcium carbonates. This fractionation is hypothesized to depend on aqueous U(VI) speciation, which is controlled by pH, ionic strength, pCO2 and Mg2+ and Ca2+ concentrations. Secular variation in seawater chemistry could lead to changes in aqueous U(VI) speciation, and thus, may affect the extent of U isotope fractionation during U(VI) incorporation into CaCO3. In this study, we combine estimates of seawater composition over the Phanerozoic with a model of aqueous U speciation and isotope fractionation to explore variations in the expected offset between the U isotope composition of seawater and primary marine CaCO3 through time. We find that U isotope fractionation between U in primary marine CaCO3 and seawater could have varied between 0.11 and 0.23‰ over the Phanerozoic due to secular variations in seawater chemistry. Such variations would significantly impact estimates of the extent of marine anoxia derived from the U isotope record. For example, at the Permo-Triassic boundary, this effect might imply that the estimated extent of anoxia is ∼32% more extreme than previously inferred. One significant limitation of our model is that the existing experimental database covers only abiotic carbonate precipitation, and does not include a possible range of biological effects which might enhance or suppress the range of isotopic fractionation calculated here. As biotic carbonates dominate the marine carbonate record, more work is need to assess controls on U isotopic fractionation into biotic marine carbonates.

Calcium isotopic composition of mantle xenoliths and minerals from Eastern China

NASA Astrophysics Data System (ADS)

Kang, Jin-Ting; Zhu, Hong-Li; Liu, Yu-Fei; Liu, Fang; Wu, Fei; Hao, Yan-Tao; Zhi, Xia-Chen; Zhang, Zhao-Feng; Huang, Fang

2016-02-01

This study presents calcium isotope data for co-existing clinopyroxenes (cpx), orthopyroxenes (opx), and olivine (ol) in mantle xenoliths to investigate Ca isotopic fractionation in the upper mantle. δ44/40Ca (δ44/40Ca (‰) = (44Ca/40Ca)SAMPLE/(44Ca/40Ca)SRM915a - 1) in opx varies from 0.95 ± 0.05‰ to 1.82 ± 0.01‰ and cpx from 0.71 ± 0.06‰ to 1.03 ± 0.12‰ (2se). δ44/40Ca in ol (P-15) is 1.16 ± 0.08‰, identical to δ44/40Ca of the co-existing opx (1.12 ± 0.09‰, 2se). The Δ44/40Caopx-cpx (Δ44/40Caopx-cpx = δ44/40Caopx-δ44/40Cacpx) shows a large variation ranging from -0.01‰ to 1.11‰ and it dramatically increases with decreasing of Ca/Mg (atomic ratio) in opx. These observations may reflect the effect of opx composition on the inter-mineral equilibrium fractionation of Ca isotopes, consistent with the theoretical prediction by first-principles theory calculations (Feng et al., 2014). Furthermore, Δ44/40Caopx-cpx decreases when temperature slightly increases from 1196 to 1267 K. However, the magnitude of such inter-mineral isotopic fractionation (1.12‰) is not consistent with the value calculated by the well-known correlation between inter-mineral isotope fractionation factors and 1/T2 (Urey, 1947). Instead, it may reflect the temperature control on crystal chemistry of opx (i.e., Ca content), which further affects Δ44/40Caopx-cpx. The calculated δ44/40Ca of bulk peridotites and pyroxenites range from 0.76 ± 0.06‰ to 1.04 ± 0.12‰ (2se). Notably, δ44/40Ca of bulk peridotites are positively correlated with CaO and negatively with MgO content. Such correlations can be explained by mixing between a fertile mantle end-member and a depleted one with low δ44/40Ca, indicating that Ca isotopes could be a useful tool in studying mantle evolution.

High precision calcium isotope analysis using 42Ca-48Ca double-spike TIMS technique

NASA Astrophysics Data System (ADS)

Feng, L.; Zhou, L.; Gao, S.; Tong, S. Y.; Zhou, M. L.

2014-12-01

Double spike techniques are widely used for determining calcium isotopic compositions of natural samples. The most important factor controlling precision of the double spike technique is the choice of appropriate spike isotope pair, the composition of double spikes and the ratio of spike to sample（CSp/CN）. We propose an optimal 42Ca-48Ca double spike protocol which yields the best internal precision for calcium isotopic composition determinations among all kinds of spike pairs and various spike compositions and ratios of spike to sample, as predicted by linear error propagation method. It is suggested to use spike composition of 42Ca/(42Ca+48Ca) = 0.44 mol/mol and CSp/(CN+ CSp)= 0.12mol/mol because it takes both advantages of the largest mass dispersion between 42Ca and 48Ca (14%) and lowest spike cost. Spiked samples were purified by pass through homemade micro-column filled with Ca special resin. K, Ti and other interference elements were completely separated, while 100% calcium was recovered with negligible blank. Data collection includes integration time, idle time, focus and peakcenter frequency, which were all carefully designed for the highest internal precision and lowest analysis time. All beams were automatically measured in a sequence by Triton TIMS so as to eliminate difference of analytical conditions between samples and standards, and also to increase the analytical throughputs. The typical internal precision of 100 duty cycles for one beam is 0.012‒0.015 ‰ (2δSEM), which agrees well with the predicted internal precision of 0.0124 ‰ (2δSEM). Our methods improve internal precisions by a factor of 2‒10 compared to previous methods of determination of calcium isotopic compositions by double spike TIMS. We analyzed NIST SRM 915a, NIST SRM 915b and Pacific Seawater as well as interspersed geological samples during two months. The obtained average δ44/40Ca (all relative to NIST SRM 915a) is 0.02 ± 0.02 ‰ (n=28), 0.72±0.04 ‰ (n=10) and 1.93±0.03 ‰ (n=21) for NIST SRM 915a, NIST SRM 915b and Pacific Seawater, respectively. The long-term reproducibility is 0.10‰ (2 δSD), which is comparable to the best external precision of 0.04 ‰ (2 δSD) of previous methods, but our sample throughputs are doubled with significant reduction in amount of spike used for single samples.

Isotope fractionation by multicomponent diffusion (Invited)

NASA Astrophysics Data System (ADS)

Watkins, J. M.; Liang, Y.; Richter, F. M.; Ryerson, F. J.; DePaolo, D. J.

2013-12-01

Isotope fractionation by multicomponent diffusion The isotopic composition of mineral phases can be used to probe the temperatures and rates of mineral formation as well as the degree of post-mineralization alteration. The ability to interpret stable isotope variations is limited by our knowledge of three key parameters and their relative importance in determining the composition of a mineral grain and its surroundings: (1) thermodynamic (equilibrium) partitioning, (2) mass-dependent diffusivities, and (3) mass-dependent reaction rate coefficients. Understanding the mechanisms of diffusion and reaction in geological liquids, and how these mass transport processes discriminate between isotopes, represents an important problem that is receiving considerable attention in the geosciences. Our focus in this presentation will be isotope fractionation by chemical diffusion. Previous studies have documented that diffusive isotope effects vary depending on the cation as well as the liquid composition, but the ability to predict diffusive isotope effects from theory is limited; for example, it is unclear whether the magnitude of diffusive isotopic fractionations might also vary with the direction of diffusion in composition space. To test this hypothesis and to further guide the theoretical treatment of isotope diffusion, two chemical diffusion experiments and one self diffusion experiment were conducted at 1250°C and 0.7 GPa. In one experiment (A-B), CaO and Na2O counter-diffuse rapidly in the presence of a small SiO2 gradient. In the other experiment (D-E), CaO and SiO2 counter-diffuse more slowly in a small Na2O gradient. In both chemical diffusion experiments, Ca isotopes become fractionated by chemical diffusion but by different amounts, documenting for the first time that the magnitude of isotope fractionation by diffusion depends on the direction of diffusion in composition space. The magnitude of Ca isotope fractionation that develops is positively correlated with the rate of CaO diffusion; in A-B, the total variation is 2.5‰ whereas in D-E it is only 1.3‰. The diffusion of isotopes in a multicomponent system is modeled using a new expression for the isotope-specific diffusive flux that includes self diffusion terms in addition to the multicomponent chemical diffusion matrix. Kinetic theory predicts a mass dependence on isotopic mobility, i.e., self diffusivity, but it is unknown whether or how the mass dependence on self diffusivity translates into a mass dependence on chemical diffusion coefficients. The new experimental results allow us to assess several empirical expressions relating the self diffusivity and its mass dependence to the elements of the diffusion matrix and their mass dependence. Several plausible theoretical treatments can fit the data equally well. We are currently at the stage where experiments are guiding the theoretical treatment of the isotope fractionation by diffusion problem, underscoring the importance of experiments for aiding interpretations of isotopic variations in nature.

Calcium isotope systematics at hydrothermal conditions: Mid-ocean ridge vent fluids and experiments in the CaSO4-NaCl-H2O system

NASA Astrophysics Data System (ADS)

Scheuermann, Peter P.; Syverson, Drew D.; Higgins, John A.; Pester, Nicholas J.; Seyfried, William E.

2018-04-01

Two sets of hydrothermal experiments were performed to explore Ca isotope fractionation and exchange rates at hydrothermal conditions (410-450 °C, 31.0-50.0 MPa). The first set of experiments determined the magnitude of vapor-liquid Ca isotope fractionation and anhydrite solubility in the CaSO4-NaCl-H2O system. The data indicate no statistical difference between the Ca isotopic composition of coexisting vapor and liquid. The second set of experiments utilized an anomalous 43Ca spike to determine the rate of Ca exchange between fluid and anhydrite as a function of total dissolved Ca concentration. Results show that the rate of exchange increases with dissolved Ca concentrations (12-23 mM/kg), but no change in exchange rate is observed when the Ca concentration increases from 23 to 44 mM/kg Ca. 74-142 days are required to achieve 90% anhydrite-fluid Ca isotope exchange at the conditions investigated, while only several hours are necessary for vapor-liquid isotopic equilibrium. The lack of vapor-liquid Ca isotope fractionation in our experiments is consistent with δ44Ca of mid-ocean ridge hydrothermal vent fluids that remain constant, regardless of chlorinity. Moreover, the narrow range of end member fluid δ44Ca, -0.98 to -1.13‰ (SW), is largely indistinguishable from MORB δ44Ca, suggesting that neither phase separation nor fluid-rock interactions at depth significantly fractionate Ca isotopes in modern high-temperature mid-ocean ridge hydrothermal systems.

First-principles Calculations of Equilibrium Calcium Isotope Fractionation among Ca-bearing Minerals

NASA Astrophysics Data System (ADS)

Zhou, C.; Wang, W.; Kang, J.; Wu, Z.; Huang, F.

2016-12-01

Calcium isotope fractionation factors of Ca-bearing minerals are investigated with the first principle calculations based on density functional theory (DFT). The sequence of heavy Ca isotope enrichment is forsterite > grossular > butschliite > lime > fluorite > tremolite diopside > anhydrite dolomite titanite > anorthite > perovskite gehlenite aragonite richterite > akermanite > oldhamite. This order is consistent with variation of Ca-O bond lengths, indicating that Ca-O bond energy plays an overwhelming role on the fractionations of Ca isotopes. Our study provides important insights into the Ca isotopic data of meteorites. Our calculation predicts that oldhamites (CaS) are enriched in light Ca isotopes relative to silicate phase if they are in equilibrium, contrast with the observations in Valdes et al (2014). Therefore, oldhamite and silicate phase in the meteorites should be in disequilibrium for Ca isotopes. Our results can also be used to understand Ca isotopic composition of the Moon. Δ44/40Ca between olivine (with CaO content of 2.48 wt%) and diopside is up to 0.41‰ and Δ44/40Cagrossular-diopside is 0.26‰ at 1500K. Feng et al. (2014) calculated that Δ44/40Ca between opx with CaO content of 1.74 wt% and cpx is about 0.27‰ at 1500 K. According to the Lunar Magma Ocean (LMO) model, the modern Moon is chemically stratified (Snyder et al., 1992; Elardo et al., 2011). Assuming that the lower cumulate and upper residual melt are in isotopic equilibrium during the evolution of Lunar Magma Ocean where the cumulate may be mainly composed of olivine and orthopyroxene or garnet/spinel, δ44/40Ca of the Moon could be underestimated by 0.05‰ to 0.25‰ if the shallow lunar samples are used to represent the bulk Moon.

Evaluation of the Heshang Cave stalagmite calcium isotope composition as a paleohydrologic proxy by comparison with the instrumental precipitation record.

PubMed

Li, Xiuli; Cui, Xueping; He, Dong; Liao, Jin; Hu, Chaoyong

2018-02-08

With their merits of precise dating and sensitivity to climate changes, laminated stalagmites are an important terrestrial archive for reconstructions of paleohydrological changes. In particular, the Ca isotope composition (δ 44/42 Ca) of the Heshang Cave stalagmite has been documented to record a precipitation decrease during the 8.2 ka event in central China. As an extension, this study directly compares near-annual resolution δ 44/42 Ca data with an instrumental precipitation record to evaluate the fidelity of δ 44/42 Ca as a paleohydrologic proxy on annual to decade timescales. Over the period 1881-2001 AD, the δ 44/42 Ca values correlate significantly with both precipitation from a nearby weather station and the dryness/wetness index in the middle Yangtze River, with a stronger correlation on decadal smoothed data. These results clearly show that the δ 44/42 Ca ratio from stalagmites is an effective proxy for paleohydrological changes on a decadal timescale. More study is encouraged to refine understanding of stalagmite Ca isotope ratios and hydrological conditions and their application in paleohydrologic reconstructions.

Ca isotopic geochemistry of an Antarctic aquatic system

USGS Publications Warehouse

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

2017-01-01

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

Characterization of calcium isotopes in natural and synthetic barite

USGS Publications Warehouse

Griffith, E.M.; Schauble, E.A.; Bullen, T.D.; Paytan, A.

2008-01-01

The mineral barite (BaSO4) accommodates calcium in its crystal lattice, providing an archive of Ca-isotopes in the highly stable sulfate mineral. Holocene marine (pelagic) barite samples from the major ocean basins are isotopically indistinguishable from each other (??44/40Ca = -2.01 ?? 0.15???) but are different from hydrothermal and cold seep barite samples (??44/40Ca = -4.13 to -2.72???). Laboratory precipitated (synthetic) barite samples are more depleted in the heavy Ca-isotopes than pelagic marine barite and span a range of Ca-isotope compositions, ??44/40Ca = -3.42 to -2.40???. Temperature, saturation state, a Ba2 + / a SO42 -, and aCa2+/aBa2+ each influence the fractionation of Ca-isotopes in synthetic barite; however, the fractionation in marine barite samples is not strongly related to any measured environmental parameter. First-principles lattice dynamical modeling predicts that at equilibrium Ca-substituted barite will have much lower 44Ca/40Ca than calcite, by -9??? at 0 ??C and -8??? at 25 ??C. Based on this model, none of the measured barite samples appear to be in isotopic equilibrium with their parent solutions, although as predicted they do record lower ??44/40Ca values than seawater and calcite. Kinetic fractionation processes therefore most likely control the extent of isotopic fractionation exhibited in barite. Potential fractionation mechanisms include factors influencing Ca2+ substitution for Ba2+ in barite (e.g. ionic strength and trace element concentration of the solution, competing complexation reactions, precipitation or growth rate, temperature, pressure, and saturation state) as well as nucleation and crystal growth rates. These factors should be considered when investigating controls on isotopic fractionation of Ca2+ and other elements in inorganic and biogenic minerals. ?? 2008 Elsevier Ltd.

Intracellular Cadmium Isotope Fractionation

NASA Astrophysics Data System (ADS)

Horner, T. J.; Lee, R. B.; Henderson, G. M.; Rickaby, R. E.

2011-12-01

Recent stable isotope studies into the biological utilization of transition metals (e.g. Cu, Fe, Zn, Cd) suggest several stepwise cellular processes can fractionate isotopes in both culture and nature. However, the determination of fractionation factors is often unsatisfactory, as significant variability can exist - even between different organisms with the same cellular functions. Thus, it has not been possible to adequately understand the source and mechanisms of metal isotopic fractionation. In order to address this problem, we investigated the biological fractionation of Cd isotopes within genetically-modified bacteria (E. coli). There is currently only one known biological use or requirement of Cd, a Cd/Zn carbonic anhydrase (CdCA, from the marine diatom T. weissfloggii), which we introduce into the E. coli genome. We have also developed a cleaning procedure that allows for the treating of bacteria so as to study the isotopic composition of different cellular components. We find that whole cells always exhibit a preference for uptake of the lighter isotopes of Cd. Notably, whole cells appear to have a similar Cd isotopic composition regardless of the expression of CdCA within the E. coli. However, isotopic fractionation can occur within the genetically modified E. coli during Cd use, such that Cd bound in CdCA can display a distinct isotopic composition compared to the cell as a whole. Thus, the externally observed fractionation is independent of the internal uses of Cd, with the largest Cd isotope fractionation occurring during cross-membrane transport. A general implication of these experiments is that trace metal isotopic fractionation most likely reflects metal transport into biological cells (either actively or passively), rather than relating to expression of specific physiological function and genetic expression of different metalloenzymes.

Calcium isotope constraints on the end-Permian mass extinction

PubMed Central

Payne, Jonathan L.; Turchyn, Alexandra V.; Paytan, Adina; DePaolo, Donald J.; Lehrmann, Daniel J.; Yu, Meiyi; Wei, Jiayong

2010-01-01

The end-Permian mass extinction horizon is marked by an abrupt shift in style of carbonate sedimentation and a negative excursion in the carbon isotope (δ13C) composition of carbonate minerals. Several extinction scenarios consistent with these observations have been put forward. Secular variation in the calcium isotope (δ44/40Ca) composition of marine sediments provides a tool for distinguishing among these possibilities and thereby constraining the causes of mass extinction. Here we report δ44/40Ca across the Permian-Triassic boundary from marine limestone in south China. The δ44/40Ca exhibits a transient negative excursion of ∼0.3‰ over a few hundred thousand years or less, which we interpret to reflect a change in the global δ44/40Ca composition of seawater. CO2-driven ocean acidification best explains the coincidence of the δ44/40Ca excursion with negative excursions in the δ13C of carbonates and organic matter and the preferential extinction of heavily calcified marine animals. Calcium isotope constraints on carbon cycle calculations suggest that the average δ13C of CO2 released was heavier than -28‰ and more likely near -15‰; these values indicate a source containing substantial amounts of mantle- or carbonate-derived carbon. Collectively, the results point toward Siberian Trap volcanism as the trigger of mass extinction. PMID:20421502

The evolution of Carbon isotopes in calcite in the presence of cyanobacteria

NASA Astrophysics Data System (ADS)

Grimm, Christian; Mavromatis, Vasileios; Pokrovsky, Oleg S.; Oelkers, Eric H.

2016-04-01

Stable isotopic compositions in carbonates are widely used as indicators of environmental conditions prevailing during mineral formation. This reconstruction is substantially based on the assumption that there is no change in the mineral composition over geological time. However, recent experimental studies have shown that carbon and magnesium isotopes in hydrous Mg-carbonates undergo continuous re-equilibration with the ambient solution even after mineral precipitation stopped ([1] and [2], respectively). To verify whether this holds true for anhydrous Ca-bearing carbonates which readily form at earth's surface environments, a series of batch system calcite precipitation experiments were performed in the presence of actively growing cyanobacteria Synechococcus sp. The bacteria were grown at ambient temperature in a BG11 culture medium (SIGMA C3061) and continuous stirring, air-bubbling and illumination. Calcite precipitation was initiated by the addition of 8.5mM CaCl2 and 0-50 mM NaHCO3 or NaHCO3-Na2CO3 mixtures. The presence of cyanobacteria is on one hand promoting CaCO3 formation due to increasing pH resulting from photosynthesis. On the other hand, actively growing cyanobacteria drastically change carbon isotope signature of the aqueous fluid phase by preferably incorporating the lighter 12C isotope into biomass [1]. This study explores the effect of continuously changing carbon isotope compositions in dissolved inorganic carbon (DIC) on precipitated calcite which is in chemical equilibrium with the ambient fluid phase. [1] Mavromatis et al. (2015). The continuous re-equilibration of carbon isotope compositions of hydrous Mg-carbonates in the presence of cyanobacteria. Chem. Geol. 404, 41-51 [2] Mavromatis et al. (2012). Magnesium isotope fractionation during hydrous magnesium carbonate precipitation with and without cyanobacteria. Geochim. Cosmochim. Acta 76, 161-174

A pilot study on the use of natural calcium isotope (44Ca/40Ca) fractionation in urine as a proxy for the human body calcium balance.

PubMed

Heuser, Alexander; Eisenhauer, Anton

2010-04-01

We explored the possibility of using natural calcium (Ca) isotope variations in the urine (delta(44/40)Ca(urine)) as a proxy for the Ca balance in the human body. We chose two test persons extremely different in their health status, gender and age (4-year-old healthy boy and a 60-year-old woman known to suffer from osteoporosis). During a 5 day interval the Ca isotope composition of the individual diet (delta(44/40)Ca(diet)) was monitored for both test persons to be in general agreement to the Ca isotope composition of the normal western European diet ( approximately -1.02+/-0.1 per thousand). However, measurements showed that (1) delta(44/40)Ca(urine) of both test persons are approximately 1.37 and approximately 2.49 per thousand, respectively, heavier than delta(44/40)Ca(diet) and that (2) the delta(44/40)Ca(urine-boy) is approximately 1.1 per thousand heavier when compared to the value of the woman. The individual offset between diet and test persons is interpreted to reflect individual Ca reabsorption rates in the kidneys being the result of Rayleigh type Ca isotope fractionation related to the partitioning of Ca between the glomerular filtrate and filtered residue. The relative difference between delta(44/40)Ca(urine-boy) and delta(44/40)Ca(urine-woman) of approximately 1.1 per thousand may reflect individual differences in the balance of bone mineralization and demineralization processes related to age, gender and health status. By arbitrarily defining an equilibrium value for Delta(44/40)Ca(diet-urine) of -1.93 per thousand being the arithmetic mean of delta(44/40)Ca(urine) for both test persons the measured delta(44/40)Ca(urine) values may be applied to model the individual bone mineralization and demineralization processes in a qualitative way. Note, second order influences of intestinal Ca absorption during sequestration of Ca between intestine and blood have to be subject of further studies. Copyright 2009 Elsevier Inc. All rights reserved.

Large Calcium Isotopic Variation in Peridotitic Xenoliths from North China Craton

NASA Astrophysics Data System (ADS)

Huang, S.; Zhao, X.; Zhang, Z.

2016-12-01

Calcium is the fifth most abundant element in the Earth. The Ca isotopic composition of the Earth is important in many aspects, ranging from tracing the Ca cycle on the Earth to comparing the Earth to other terrestrial planets. There is large mass-dependent Ca isotopic variation, measured as δ44/40Ca relative to a standard sample, in terrestrial igneous rocks: about 2 per mil in silicate rocks, compared to 3 per mil in carbonates. Therefore, a good understanding of the Ca isotopic variation in igneous rocks is necessary. Here we report Ca isotopic data on a series of peridotitic xenoliths from North China Craton (NCC). There is about 1 per mil δ44/40Ca variation in these NCC peridotites: The highest δ44/40Ca is close to typical mantle values, and the lowest δ44/40Ca is found in an Fe-rich peridotite, -1.13 relative to normal mantle (or -0.08 on the SRM 915a scale). This represents the lowest δ44/40Ca value ever reported for igneous rocks. Combined with published Fe isotopic data on the same samples, our data show a positive linear correlation between δ44/40Ca and δ57/54Fe in NCC peridotites. This trend is inconsistent with mixing a low-δ44/40Ca and -δ57/54Fe sedimentary component with a normal mantle component. Rather, it is best explained as the result of kinetic isotopic effect caused by melt-peridotite reaction on a time scale of several hundreds of years. In detail, basaltic melt reacts with peridotite, replaces orthopyroxene with clinopyroxene, and increases the Fo number of olivine. Consistent with this interpretation, our on-going Mg isotopic study shows that low-δ44/40Ca and -δ57/54Fe NCC peridotites also have heavier Mg isotopes compared to normal mantle. Our study shows that mantle metasomatism plays an important role generating stable isotopic variations within the Earth's mantle.

Isotopic evolution of the protoplanetary disk and the building blocks of Earth and the Moon.

PubMed

Schiller, Martin; Bizzarro, Martin; Fernandes, Vera Assis

2018-03-21

Nucleosynthetic isotope variability among Solar System objects is often used to probe the genetic relationship between meteorite groups and the rocky planets (Mercury, Venus, Earth and Mars), which, in turn, may provide insights into the building blocks of the Earth-Moon system. Using this approach, it has been inferred that no primitive meteorite matches the terrestrial composition and the protoplanetary disk material from which Earth and the Moon accreted is therefore largely unconstrained. This conclusion, however, is based on the assumption that the observed nucleosynthetic variability of inner-Solar-System objects predominantly reflects spatial heterogeneity. Here we use the isotopic composition of the refractory element calcium to show that the nucleosynthetic variability in the inner Solar System primarily reflects a rapid change in the mass-independent calcium isotope composition of protoplanetary disk solids associated with early mass accretion to the proto-Sun. We measure the mass-independent 48 Ca/ 44 Ca ratios of samples originating from the parent bodies of ureilite and angrite meteorites, as well as from Vesta, Mars and Earth, and find that they are positively correlated with the masses of their parent asteroids and planets, which are a proxy of their accretion timescales. This correlation implies a secular evolution of the bulk calcium isotope composition of the protoplanetary disk in the terrestrial planet-forming region. Individual chondrules from ordinary chondrites formed within one million years of the collapse of the proto-Sun reveal the full range of inner-Solar-System mass-independent 48 Ca/ 44 Ca ratios, indicating a rapid change in the composition of the material of the protoplanetary disk. We infer that this secular evolution reflects admixing of pristine outer-Solar-System material into the thermally processed inner protoplanetary disk associated with the accretion of mass to the proto-Sun. The identical calcium isotope composition of Earth and the Moon reported here is a prediction of our model if the Moon-forming impact involved protoplanets or precursors that completed their accretion near the end of the protoplanetary disk's lifetime.

Isotopic evolution of the protoplanetary disk and the building blocks of Earth and the Moon

NASA Astrophysics Data System (ADS)

Schiller, Martin; Bizzarro, Martin; Fernandes, Vera Assis

2018-03-01

Nucleosynthetic isotope variability among Solar System objects is often used to probe the genetic relationship between meteorite groups and the rocky planets (Mercury, Venus, Earth and Mars), which, in turn, may provide insights into the building blocks of the Earth–Moon system. Using this approach, it has been inferred that no primitive meteorite matches the terrestrial composition and the protoplanetary disk material from which Earth and the Moon accreted is therefore largely unconstrained. This conclusion, however, is based on the assumption that the observed nucleosynthetic variability of inner-Solar-System objects predominantly reflects spatial heterogeneity. Here we use the isotopic composition of the refractory element calcium to show that the nucleosynthetic variability in the inner Solar System primarily reflects a rapid change in the mass-independent calcium isotope composition of protoplanetary disk solids associated with early mass accretion to the proto-Sun. We measure the mass-independent 48Ca/44Ca ratios of samples originating from the parent bodies of ureilite and angrite meteorites, as well as from Vesta, Mars and Earth, and find that they are positively correlated with the masses of their parent asteroids and planets, which are a proxy of their accretion timescales. This correlation implies a secular evolution of the bulk calcium isotope composition of the protoplanetary disk in the terrestrial planet-forming region. Individual chondrules from ordinary chondrites formed within one million years of the collapse of the proto-Sun reveal the full range of inner-Solar-System mass-independent 48Ca/44Ca ratios, indicating a rapid change in the composition of the material of the protoplanetary disk. We infer that this secular evolution reflects admixing of pristine outer-Solar-System material into the thermally processed inner protoplanetary disk associated with the accretion of mass to the proto-Sun. The identical calcium isotope composition of Earth and the Moon reported here is a prediction of our model if the Moon-forming impact involved protoplanets or precursors that completed their accretion near the end of the protoplanetary disk’s lifetime.

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.

Calcium inputs and transport in a base-poor forest ecosystem as interpreted by Sr isotopes

Treesearch

Scott W. Bailey; James W. Hornbeck; Charles T. Driscoll; Henri E. Gaudette

1996-01-01

Depletion of Ca in forests and its effects on forest health are poorly quantified. Depletion has been difficult to document due to limitations in determining rates at which Ca becomes available for ecosystem processes through weathering, and difficulty in determining changes in ecosystem storage. We coupled a detailed analysis of Sr isotopic composition with a mass...

Calcium isotope systematics in small upland catchments affected by spruce dieback in the period of extreme acid rain (1970-1990)

NASA Astrophysics Data System (ADS)

Novak, Martin; Farkas, Juraj; Holmden, Chris; Hruska, Jakub; Curik, Jan; Stepanova, Marketa; Prechova, Eva; Veselovsky, Frantisek; Komarek, Arnost

2017-04-01

Recently, new isotope tools have become available to study the behavior of nutrients in stressed ecosystems. In this study, we focus on changes in the abundance ratio of calcium (Ca) isotopes accompanying biogeochemical processes in small forested catchments. We monitored del44Ca values in ecosystem pools and fluxes in four upland sites situated in the Czech Republic, Central Europe. A heavily acidified site in the Eagle Mts. (northern Czech Republic) experienced 13 times higher atmospheric Ca inputs, compared to the other three sites, which were less affected by forest decline. Industrial dust was responsible for the elevated Ca input. Del44Ca values of individual poos/fluxes were used to identify Ca sources for the bioavailable Ca soil reservoir and for runoff. The bedrock of the study sites differed (leucogranite, orthogneiss vs. serpentinite and amphibolite). Across the sites, mean del44Ca values increased in the order: spruce bark < fine roots < needles < soil < bedrock < canopy throughfall < open-area precipitation < runoff < soil water. Plant preferentially took up isotopically light Ca, while residual isotopically heavy Ca was sorbed to soil particles or exported via runoff. Even at sites with a low del44Ca values of bedrock, runoff had a high del44Ca value. At the base-poor site, most runoff came from atmospheric deposition and residual Ca following plant uptake. It appeared that bedrock weathering did not supply enough Ca to replenish the bioavailable Ca pool in the soil. Currently, we are analyzing Ca isotope composition of individual rock-forming minerals to better assess the effect of different weathering rates of minerals with low/high radiogenic 40Ca contents on runoff del44Ca.

O-16 excesses in Murchison and Murray hibonites - A case against a late supernova injection origin of isotopic anomalies in O, Mg, Ca, and Ti

NASA Technical Reports Server (NTRS)

Fahey, A. J.; Goswami, J. N.; Mckeegan, K. D.; Zinner, E. K.

1987-01-01

Ion probe measurements of the oxygen isotopic composition of seven hibonite samples from the CM chondrites Murchison and Murray are reported. All samples show large O-16 excesses relative to terrestrial oxygen. The data for all samples plot along the carbonaceous chondrite O-16-rich mixing line and show no evidence for isotopic mass fractionation effects characteristic of FUN inclusions. These hibonites have the largest Ca-48 and Ti-50 isotopic anomalies found to date; thus there is no intrinsic relationship between anomalies of a nucleosynthetic origin and isotopic mass fractionation effects. The large O-16 excess seen in the sample with the largest measured Ca-48 and Ti-50 depletions argues against a late injection of exotic material from a nearby supernova as a source for the isotopic anomalies.

Oxygen isotope geochemistry of the amphiboles: isotope effects of cation substitutions in minerals

NASA Astrophysics Data System (ADS)

Kohn, Matthew J.; Valley, John W.

1998-06-01

The occurrence of coexisting amphiboles in rocks and the likelihood of concurrent isotope closure allows equilibrium oxygen isotope fractionations among the amphiboles to be recovered from natural samples. Oxygen isotope analyses of mineral separates using laser fluorination show that coexisting amphiboles increasingly partition 18O in the order: hornblende ≪ gedrite < cummingtonite ≤ anthophyllite. The observed fractionations at ˜575°C are: Δ(Ged-Hbl) = 0.8‰, Δ(Cum-Hbl) = 0.9, Δ(Cum-Ged) = 0.2, Δ(Ath-Ged) = 0.3, and Δ(Ath-Hbl) > 0.9. Previously published data for hornblende, actinolite, glaucophane, and garnet show that Δ(Act-Hbl) ˜ 0.2, Δ(Gln-Grt) ≫ 1, and Δ(Hbl-Grt) ˜ 0. Thus, glaucophane strongly partitions 18O relative to the calcic amphiboles. The fractionation between two amphiboles of arbitrary composition can be predicted from the known fractionations for mica endmembers, pyroxene endmembers, and exchange components such as CaAl(NaSi) -1, NaAl(CaMg) -1, CaMg -1, MgFe -1, FeMn -1, KNa -1, KAl( Si) -1, and Fe 3+Al -1. Applications of the exchange component method reproduce measured amphibole fractionations to within ±0.1 to ±0.2‰, whereas other predictive methods cause misfit for typical metamorphic hornblende of ≥0.5‰ at 575°C. Although the isotope effects of cation exchanges may be small at high-T, they magnify dramatically for minerals formed in surficial, diagenetic, and low-T metamorphic environments. Different composition clays are predicted to have equilibrium δ 18O differences of 2-9‰. If the isotope fractionation can be determined for one mineral endmember, then calibrated exchanges allow accurate prediction of the isotope fractionations for intermediate compositions of most ortho-, ring-, chain-, and sheet-silicates.

Effects of cleaning methods upon preservation of stable isotopes and trace elements in shells of Cyprideis torosa (Crustacea, Ostracoda): Implications for palaeoenvironmental reconstruction

NASA Astrophysics Data System (ADS)

Roberts, L. R.; Holmes, J. A.; Leng, M. J.; Sloane, H. J.; Horne, D. J.

2018-06-01

The trace element (Sr/Ca and Mg/Ca) and stable isotope (δ18O and δ13C) geochemistry of fossil ostracod valves provide valuable information, particularly in lacustrine settings, on palaeo-water composition and palaeotemperature. The removal of sedimentary and organic contamination prior to geochemical analysis is essential to avoid bias of the results. Previous stable isotope and trace element work on ostracod shells has, however, employed different treatments for the removal of contamination beyond simple 'manual' cleaning using a paint brush and methanol under a low-power binocular microscope. For isotopic work pre-treatments include chemical oxidation, vacuum roasting and plasma ashing, and for trace element work sonication, chemical oxidation and reductive cleaning. The impact of different treatments on the geochemical composition of the valve calcite has not been evaluated in full, and a universal protocol has not been established. Here, a systematic investigation of the cleaning methods is undertaken using specimens of the ubiquitous euryhaline species, Cyprideis torosa. Cleaning methods are evaluated by undertaking paired analyses on a single carapace (comprising two valves); in modern ostracods, whose valves are assumed to be unaltered, the two valves should have identical geochemical and isotopic composition. Hence, when one valve is subjected to the chosen treatment and the other to simple manual cleaning any difference in composition can confidently be assigned to the treatment method. We show that certain cleaning methods have the potential to cause alteration to the geochemical signal, particularly Mg/Ca and δ18O, and hence have implications for palaeoenvironmental reconstructions. For trace-element determinations we recommend cleaning by sonication and for stable isotope analysis, oxidation by hydrogen peroxide. These methods remove contamination, yet do not significantly alter the geochemical signal.

Boron incorporation in the foraminifer Amphistegina lessonii under a decoupled carbonate chemistry

NASA Astrophysics Data System (ADS)

Kaczmarek, K.; Langer, G.; Nehrke, G.; Horn, I.; Misra, S.; Janse, M.; Bijma, J.

2014-12-01

A number of studies have shown that the boron isotopic composition (δ11B) and the B/Ca ratio of biogenic carbonates (mostly foraminifers) can serve as proxies for two parameters of the ocean's carbonate chemistry, rendering it possible to calculate the entire carbonate system. However, the B incorporation mechanism into marine carbonates is still not fully understood and analyses of field samples show species specific and hydrographic effects on the B proxies complicating their application. Identifying the carbonate system parameter influencing boron incorporation is difficult due to the co-variation of pH, CO32-, and B(OH)4-. To shed light on the question which parameter of the carbonate system is related to the boron incorporation, we performed culture experiments with the benthic symbiont-bearing foraminifer Amphistegina lessonii using a decoupled pH-CO32- chemistry. The determination of the boron isotopic composition and B/Ca ratios was performed simultaneously by means of a new in situ technique combining optical emission spectroscopy and laser ablation MC-ICP-MS. The boron isotopic composition in the tests gets heavier with increasing pH and B/Ca increases with increasing BOH4-/HCO3- of the culture media. The latter indicates that boron uptake of A. lessonii features a competition between B(OH)4- and HCO3-. Furthermore, the simultaneous determination of B/Ca and δ11B on single specimens allows for assessing the relative variability of these parameters. Among different treatments the B/Ca shows an increasing variability with increasing boron concentration in the test whereas the variability in the isotope distribution is constant.

Isotopic imprints of mountaintop mining contaminants.

PubMed

Vengosh, Avner; Lindberg, T Ty; Merola, Brittany R; Ruhl, Laura; Warner, Nathaniel R; White, Alissa; Dwyer, Gary S; Di Giulio, Richard T

2013-09-03

Mountaintop mining (MTM) is the primary procedure for surface coal exploration within the central Appalachian region of the eastern United States, and it is known to contaminate streams in local watersheds. In this study, we measured the chemical and isotopic compositions of water samples from MTM-impacted tributaries and streams in the Mud River watershed in West Virginia. We systematically document the isotopic compositions of three major constituents: sulfur isotopes in sulfate (δ(34)SSO4), carbon isotopes in dissolved inorganic carbon (δ(13)CDIC), and strontium isotopes ((87)Sr/(86)Sr). The data show that δ(34)SSO4, δ(13)CDIC, Sr/Ca, and (87)Sr/(86)Sr measured in saline- and selenium-rich MTM impacted tributaries are distinguishable from those of the surface water upstream of mining impacts. These tracers can therefore be used to delineate and quantify the impact of MTM in watersheds. High Sr/Ca and low (87)Sr/(86)Sr characterize tributaries that originated from active MTM areas, while tributaries from reclaimed MTM areas had low Sr/Ca and high (87)Sr/(86)Sr. Leaching experiments of rocks from the watershed show that pyrite oxidation and carbonate dissolution control the solute chemistry with distinct (87)Sr/(86)Sr ratios characterizing different rock sources. We propose that MTM operations that access the deeper Kanawha Formation generate residual mined rocks in valley fills from which effluents with distinctive (87)Sr/(86)Sr and Sr/Ca imprints affect the quality of the Appalachian watersheds.

Sr isotopic composition as a tracer of Ca sources in two forest ecosystems in Belgium.

NASA Astrophysics Data System (ADS)

Drouet, T.; Herbauts, J.; Demaiffe, D.

2003-04-01

The two main sources of Ca in forest ecosystem are the mineral weathering release and atmospheric inputs. We use the 87Sr/86Sr isotopic ratio (Sr is a proxy for Ca) to determine the Ca contribution from rain input in two forest ecosystems (beech stands) growing on soils formed from parent materials with distinct total Ca contents and contrasted isotopic ratios: Pleistocene loess in Central Belgium (leached brown soil) with present-day 87Sr/86Sr =0.72788 and Lower Devonian shales and sandstones in Ardennes (ochreous brown earth) with 87Sr/86Sr = 0.76913. The 87Sr/86Sr ratios and the Ca and Sr contents were measured in rainwater, vegetation (beech wood growth rings and leaves) and main soil horizons (total, labile and HCl 0.1 M soluble forms). The relative contributions of atmospheric input and soil mineral weathering to vegetation were calculated using mixing equations. Calculations based on the Sr isotope ratios of rainwater (endmember 1; 87Sr/86Sr close to seawater: 0.7090), labile soil fraction (endmember 2; 87Sr/86Sr: 0.71332 to 0.71785) and beech wood (mixing compartment) indicate that about 50 % (Central Belgium) to 35 % (Ardennes) of Ca uptake originate from atmospheric inputs. The choice of the appropriate 87Sr/86Sr ratio for the weathering endmember is however critical. The isotopic composition of the mineral source is theoretically determined by the mineralogical composition of the soil and the relative weatherability of the Sr-bearing minerals. Due to soil processes (weathering and clay illuviation), the distribution of minerals in both soil profiles is not homogeneous and varies from horizon to horizon. Which horizons are relevant and which kind of soil extract (labile soil fraction, acid soluble fraction, total soil,...) should be selected for isotopic measurement of weathering endmember, is therefore questionable. The different ways of estimation are discussed. Quantitative mineralogical reconstitutions of soil horizons and isotopic data indicate preferential weathering of plagioclase (high Sr content with low 87Sr/86Sr) rather than mica or K-feldspar (high 87Sr/86Sr). Our results emphasize the importance of the Ca atmospheric contribution to the tree mineral nutrition in these forest ecosystems. It is plausible that acid depositions associated with decreasing input of atmospheric cations (“acid rains”) could increase the depletion of soil available cation pool at a short-time scale.

Effect of amino acids on the precipitation kinetics and Ca isotopic composition of gypsum

NASA Astrophysics Data System (ADS)

Harouaka, Khadouja; Kubicki, James D.; Fantle, Matthew S.

2017-12-01

Stirred gypsum (CaSO4 · 2H2O) precipitation experiments (initial Ωgypsum = 2.4 ± 0.14, duration ≈ 1.0-1.5 h) were conducted in the presence of the amino acids glycine (190 μM), L-alanine (190 μM), D- and L-arginine (45 μM), and L-tyrosine (200 μM) to investigate the effect of simple organic compounds on both the precipitation kinetics and Ca isotopic composition of gypsum. Relative to abiotic controls, glycine, tyrosine, and alanine inhibited precipitation rates by ∼22%, 27%, and 29%, respectively, while L- and D-arginine accelerated crystal growth by ∼8% and 48%, respectively. With the exception of tyrosine, amino acid induced inhibition resulted in fractionation factors (αs-f) associated with precipitation that were no more than 0.3‰ lower than amino acid-free controls. In contrast, the tyrosine and D- and L-arginine experiments had αs-f values associated with precipitation that were similar to the controls. Our experimental results indicate that Ca isotopic fractionation associated with gypsum precipitation is impacted by growth inhibition in the presence of amino acids. Specifically, we propose that the surface-specific binding of amino acids to gypsum can change the equilibrium fractionation factor of the bulk mineral. We investigate the hypothesis that amino acids can influence the growth of gypsum at specific crystal faces via adsorption and that different faces have distinct fractionation factors (αface-fluid). Accordingly, preferential sorption of amino acids at particular faces changes the relative, face-specific mass fluxes of Ca during growth, which influences the bulk isotopic composition of the mineral. Density functional theory (DFT) calculations suggest that the energetic favorability of glycine sorption onto gypsum crystal faces occurs in the order: (1 1 0) > (0 1 0) > (1 2 0) > (0 1 1), while glycine sorption onto the (-1 1 1) face was found to be energetically unfavorable. Face-specific fractionation factors constrained by frequency calculations of clusters derived from DFT structures vary by as much as 1.4‰. This suggests that the equilibrium fractionation factor for the bulk crystal can vary substantially, and that surface sorption can induce changes in αeq associated with gypsum precipitation. While we do not rule out the influence of kinetic isotope effects, our results clearly demonstrate that the mode of crystal growth can have a sizeable effect on the bulk fractionation factor (αs-f). Ultimately, our results suggest that the same mechanism by which organic molecules affect the morphology of a mineral can also impact the isotopic composition of the mineral. The results of our study provide valuable insight into the mechanism of Ca isotopic fractionation during gypsum precipitation. Our results are also important for establishing a framework for accurate interpretations of mineral-hosted Ca isotope records of the past, as we demonstrate a mechanistic pathway by which the biological and chemical environment can impact Ca isotopic fractionation during mineral precipitation.

Ca Isotopes Fingerprinting the Earliest Crustal Evolution

NASA Astrophysics Data System (ADS)

Kreissig, K.; Elliott, T. R.

2001-12-01

The mechanisms of continent formation remain unclear and can be explained in two contrasting ways, using either a steady state crustal growth model involving massive crustal recycling or continuous crustal growth models. Recent developments in mass spectrometry manifest in the new Finnigan-Triton allow Ca isotopic measurements precise enough to use the K-Ca isotope system to address the problem of early Archaean crustal evolution. Due to a strong fractionation of 40K and 40Ca during continent formation and a non-linear growth of 40Ca, Archaean continental crust should show radiogenic initial Ca isotopic composition if large volumes of it have already been existed 3.6 Ga ago. Simple 15-step calculations predict a difference in 40Ca /44Ca of 9 epsilon units at 3.6 Ga between the two crustal growth models. To test this, as well as to study the earliest crust formation processes, plagioclase separates from Archaean provinces reflecting the initial Ca isotopic composition and a range of different whole rock samples have been analysed. Preliminary data for ~ 3.6 Ga old TTGs from Zimbabwe show 40Ca /44Ca indistinguishable from the mantle. This is in agreement with rather chondritic initial Sr and Nd data and might reflect a short residence time of the juvenile mafic oceanic crust before partial melting forming the first continental crust. In contrast, the first results for 3.65 Ga old samples from the Itsaq Gneiss Complex of southern West Greenland yield a more evolved radiogenic Ca signature. This can be interpreted in two different ways. Either as partial melting of juvenile mafic crust shortly after its formation but incorporating already existing crust as also suggested by the existence of older inherited zircons in these rocks and negative ɛ Hf values. Partial melting of mafic oceanic crust long after its formation so that 40K and 40Ca had time to evolve would be an alternative explanation. Importantly, there is no evidence so far for high growth and recycling rates prior to 3.6 Ga as required by the most extreme 'big bang' model.

Long-Term Changes in Calcium (Ca) Sources in Base-Poor Forest Ecosystem: Insight from Stable Ca-Isotopes in Tree Rings

NASA Astrophysics Data System (ADS)

Farkas, J.; Dejeant, A.; Orwig, D.; Jacobsen, S. B.

2009-12-01

Calcium (Ca) is an essential nutrient in higher plants and also a major base-cation predicted to be most affected by environmental perturbations such as acid rain deposition and/or excessive biomass harvesting. Therefore, a better understanding of the Ca cycling in terrestrial environment is of primary interest and critical for the sustainable forest management. The aim of this project was to investigate the use of Ca isotopes as a tracer of the forest Ca cycle and its evolution through time. Here we present stable Ca isotope composition (δ44/40Ca and δ44/42Ca) and elemental concentrations of a 260-year record of tree-rings from Red Oak (Quercus rubra). The core sample was collected at an undisturbed old-growth forest site in southern New England (Wachusett Mountain, MA, USA) developed on granitic bedrock. The associated soils (sandy loams) are thus naturally base-poor and sensitive to the loss of Ca due to increased acid rain deposition and/or excessive biological uptake. The δ44/40Ca (NIST) record of decadal tree-ring increments shows a general declining trend from -0.35 to -0.80 ±0.1 per mil (from year 1750 to 2000). Superimposed on this long-term δ44/40Ca trend is a systematic negative excursion with a minimum of -0.95 ±0.1 per mil dated between 1870 and 1950. Overall, the long-term δ44/40Ca record shows statistically significant correlation with Ca/Sr ratios (R2 = 0.87, p < .01) as well as Na/Ca data (R2 = 0.69, p < .01). The fact that δ44/40Ca correlates also with Na/Ca suggest that the observed Ca isotope variations are likely related to changes in soil-Ca sources rather than being a consequence of biological processes within the tree. This is because the sodium budget of trees and forests is primarily controlled by silicate weathering rates derived from the dissolution of Na-rich minerals such as plagioclase and/or K-feldspar. Nevertheless, the role of biological processes on tree-ring δ44/40Ca record will be tested independently via measurements of radiogenic 87Sr/86Sr, as the latter is not discriminated by vital effects. Assuming that the long-term δ44/40Ca and Ca/Sr trends in tree-rings indeed reflect the evolving composition of soil Ca reservoir, the data could be explained by one of the following mechanisms: (i) via selective weathering of apatite (Ca-phosphate) by roots in association with fungus that could provide the source of isotopically light Ca with low Na/Ca ratios (cf. Blum et al. 2002, Nature, 417, 729-731). Alternatively, (ii) the Ca reserves stored in organic matter in the upper soil horizons, as a fairly insoluble Ca-oxalate, were mobilized during times of enhanced acidification (low soil-pH), thus providing the flux of isotopically light Ca to the lower soil nutrient pool. The plausibility of the above scenarios will be tested against new Ca isotope data measured in igneous apatites as well as biological Ca-oxalates.

Cr Isotopes in Allende Ca-Al-rich Inclusions

NASA Technical Reports Server (NTRS)

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

2002-01-01

We have determined Cr isotope compositions in minerals from Allende CAI in order to address the initial 53Mn (half-life 3.7 Ma) abundance in the solar system. Additional information is contained in the original extended abstract.

A novel methodology to investigate isotopic biosignatures

NASA Astrophysics Data System (ADS)

Horner, T. J.; Lee, R. B. Y.; Henderson, G. M.; Rickaby, R. E. M.

2012-04-01

An enduring goal of trace metal isotopic studies of Earth History is to find isotopic 'fingerprints' of life or of life's individual physiochemical processes. Generally, such signatures are sought by relating an isotopic effect observed in controlled laboratory conditions or a well-characterized environment to a more complex system or the geological record. However, such an approach is ultimately limited because life exerts numerous isotopic fractionations on any one element so it is hard to dissect the resultant net fractionation into its individual components. Further, different organisms, often with the same apparent cellular function, can express different isotopic fractionation factors. We have used a novel method to investigate the isotopic fractionation associated with a single physiological process-enzyme specific isotopic fractionation. We selected Cd isotopes since only one biological use of Cd is known, CdCA (a Cd/Zn carbonic anhydrase from the coastal diatom T. Weissflogii). Thus, our investigation can also inform the long standing mystery as to why this generally toxic element appears to have a nutrient-like dissolved isotopic and concentration profile in the oceans. We used the pET-15b plasmid to insert the CdCA gene into the E. coli genome. There is no known biochemical function for Cd in E. coli, making it an ideal vector for studying distinct physiological processes within a single organism. The uptake of Cd and associated isotopic fractionation was determined for both normal cells and those expressing CdCA. It was found that whole cells always exhibited a preference for the light isotopes of Cd, regardless of the expression of CdCA; adsorption of Cd to cell surfaces was not seen to cause isotopic fractionation. However, the cleaning procedure employed exerted a strong control on the observed isotopic composition of cells. Using existing protein purification techniques, we measured the Cd isotopic composition of different subcellular fractions of E. coli (e.g. membranes, cytosol, etc.), including the catalytic metal atoms within CdCA. These experiments allow isotopic exchange reactions to be observed in biological systems at an unparalleled resolution, demonstrating that isotopic fractionation can occur, in vivo, on length scales as small as a few Å. We will explore future applications of this technique using the marine geochemistry of Cd as a case study. This experimental approach has great promise for studying the individual isotopic biosignatures of other biochemical reactions, in particular those which may have been active during early Earth History.

Ca, Sr, O and D isotope approach to defining the chemical evolution of hydrothermal fluids: example from Long Valley, CA, USA

USGS Publications Warehouse

Brown, Shaun T.; Kennedy, B. Mack; DePaolo, Donald J.; Hurwitz, Shaul; Evans, William C.

2013-01-01

We present chemical and isotopic data for fluids, minerals and rocks from the Long Valley meteoric-hydrothermal system. The samples encompass the presumed hydrothermal upwelling zone in the west moat of the caldera, the Casa Diablo geothermal field, and a series of wells defining a nearly linear, ∼16 km long, west-to-east trend along the likely fluid flow path. Fluid samples were analyzed for the isotopes of water, Sr, and Ca, the concentrations of major cations and anions, alkalinity, and total CO2. Water isotope data conform to trends documented in earlier studies, interpreted as indicating a single hydrothermal fluid mixing with local groundwater. Sr isotopes show subtle changes along the flow path, which requires rapid fluid flow and minimal reaction between the channelized fluids and the wallrocks. Sr and O isotopes are used to calculate fracture spacing using a dual porosity model. Calculated fracture spacing and temperature data for hydrothermal fluids indicate the system is (approximately) at steady-state. Correlated variations among total CO2, and the concentration and isotopic composition of Ca suggest progressive fluid degassing (loss of CO2), which drives calcite precipitation as the fluid flows west-to-east and cools. The shifts in Ca isotopes require that calcite precipitated at temperatures of 150–180 °C is fractionated by ca. −0.3‰ to −0.5‰ relative to aqueous species. Our data are the first evidence that Ca isotopes undergo kinetic fractionation at high temperatures (>100 °C) and can be used to trace calcite precipitation along hydrothermal fluid flow paths.

In search of the Earth-forming reservoir: Mineralogical, chemical, and isotopic characterizations of the ungrouped achondrite NWA 5363/NWA 5400 and selected chondrites

NASA Astrophysics Data System (ADS)

Burkhardt, Christoph; Dauphas, Nicolas; Tang, Haolan; Fischer-GöDde, Mario; Qin, Liping; Chen, James H.; Rout, Surya S.; Pack, Andreas; Heck, Philipp R.; Papanastassiou, Dimitri A.

2017-05-01

High-precision isotope data of meteorites show that the long-standing notion of a "chondritic uniform reservoir" is not always applicable for describing the isotopic composition of the bulk Earth and other planetary bodies. To mitigate the effects of this "isotopic crisis" and to better understand the genetic relations of meteorites and the Earth-forming reservoir, we performed a comprehensive petrographic, elemental, and multi-isotopic (O, Ca, Ti, Cr, Ni, Mo, Ru, and W) study of the ungrouped achondrites NWA 5363 and NWA 5400, for both of which terrestrial O isotope signatures were previously reported. Also, we obtained isotope data for the chondrites Pillistfer (EL6), Allegan (H6), and Allende (CV3), and compiled available anomaly data for undifferentiated and differentiated meteorites. The chemical compositions of NWA 5363 and NWA 5400 are strikingly similar, except for fluid mobile elements tracing desert weathering. We show that NWA 5363 and NWA 5400 are paired samples from a primitive achondrite parent-body and interpret these rocks as restite assemblages after silicate melt extraction and siderophile element addition. Hafnium-tungsten chronology yields a model age of 2.2 ± 0.8 Myr after CAI, which probably dates both of these events within uncertainty. We confirm the terrestrial O isotope signature of NWA 5363/NWA 5400; however, the discovery of nucleosynthetic anomalies in Ca, Ti, Cr, Mo, and Ru reveals that the NWA5363/NWA 5400 parent-body is not the "missing link" that could explain the composition of the Earth by the mixing of known meteorites. Until this "missing link" or a direct sample of the terrestrial reservoir is identified, guidelines are provided of how to use chondrites for estimating the isotopic composition of the bulk Earth.

Calcium isotope fractionation in a silicate dominated Cenozoic aquifer system

NASA Astrophysics Data System (ADS)

Li, Junxia; DePaolo, Donald J.; Wang, Yanxin; Xie, Xianjun

2018-04-01

To understand the characteristics of Ca isotope composition and fractionation in silicate-dominated Quaternary aquifer system, hydrochemical and isotope studies (87Sr/86Sr, 13CDIC and 44/40Ca) were conducted on groundwater, sediment and rock samples from the Datong basin, China. Along the groundwater flow path from the basin margin to the center, groundwater hydrochemical type evolves from Ca-HCO3 to Na-HCO3/Na-Cl type, which results from aluminosilicate hydrolysis, vertical mixing, cation exchange between CaX2 and NaX, and calcite/dolomite precipitation. These processes cause the decrease in groundwater Ca concentration and the associated modest fractionation of groundwater Ca isotopes along the flowpath. The groundwater δ44/40Ca value varies from -0.11 to 0.49‰. The elevated δ44/40Ca ratios in shallow groundwater are attributed to vertical mixing involving addition of irrigation water, which had the average δ44/40Ca ratio of 0.595‰. Chemical weathering of silicate minerals and carbonate generates depleted δ44/40Ca signatures in groundwater from Heng Mountain (east area) and Huanghua Uplift (west area), respectively. Along the groundwater flow path from Heng Mountain to central area of east area, cation exchange between CaX2 and NaX on clay mineral results in the enrichment of heavier Ca isotope in groundwater. All groundwater samples are oversaturated with respect to calcite and dolomite. The groundwater environment rich in organic matter promotes the precipitation of carbonate minerals via the biodegradation of organic carbon, thereby further promoting the elevation of groundwater δ44/40Ca ratios.

Lead mobilization during tectonic reactivation of the western Baltic Shield

DOE Office of Scientific and Technical Information (OSTI.GOV)

Romer, R.L.; Wright, J.E.

Lead isotope data from sulfide deposits of the western part of the Baltic Shield define mixing lines in the [sup 206]Pb/[sup 204]Pb-[sup 207]Pb/[sup 204]Pb diagram. Lead from two types of sulfide deposits have been investigated: (1) Exhalative and volcanogenic deposits that are syngenetic with their host rocks; and (2) vein deposits. The syngenetic deposits locally show a very wide range of lead isotopic compositions that reflect a variable addition of highly radiogenic lead, while the vein deposits, although they have radiogenic lead isotopic compositions, exhibit only limited isotopic variations. In different provinces of the shield, both types of deposits fallmore » on the same lead mixing array. The slope of the lead mixing lines varies as a function of the age of basement rocks and the age of the tectonic event which produced the lead mobilization and therefore relates the source rock age with the age of lead mobilization. Calculated mixing ages fall into several short time periods that correspond either to orogenic events or to major phases of continental rifting. The orogenic events are the ca 360--430 Ma Caledonian, ca 900--1100 Ma Sveconorwegian, and the ca 1800--1900 Ma Svecofennian orogenic cycles. The rifting events correspond to the formation of the ca 280 Ma Oslo rift and the Ordovician (ca 450 Ma) graben system in the area of the present Gulf of Bothnia. Each mixing age indicates that lead was mobilized, probably as a consequence of mild thermal disturbances, and that the crust was permeable to lead migration. The data show that the geographic distribution of sulfide deposits with highly radiogenic lead isotopic compositions coincides with old graben systems, orogenic belts, and orogenic forelands on the Baltic Shield. The ages of vein deposits and their geographic distribution demonstrate multiple tectonic reactivation of the interior of the Baltic Shield in response to orogenic events at its margin. 68 refs., 6 refs., 4 tabs.« less

Mineralogy, early marine diagenesis, and the chemistry of shallow-water carbonate sediments

NASA Astrophysics Data System (ADS)

Higgins, J. A.; Blättler, C. L.; Lundstrom, E. A.; Santiago-Ramos, D. P.; Akhtar, A. A.; Crüger Ahm, A.-S.; Bialik, O.; Holmden, C.; Bradbury, H.; Murray, S. T.; Swart, P. K.

2018-01-01

Shallow-water carbonate sediments constitute the bulk of sedimentary carbonates in the geologic record and are widely used archives of Earth's chemical and climatic history. One of the main limitations in interpreting the geochemistry of ancient carbonate sediments is the potential for post-depositional diagenetic alteration. In this study, we use paired measurements of calcium (44Ca/40Ca or δ44Ca) and magnesium (26Mg/24Mg or δ26Mg) isotope ratios in sedimentary carbonates and associated pore-fluids as a tool to understand the mineralogical and diagenetic history of Neogene shallow-water carbonate sediments from the Bahamas and southwest Australia. We find that the Ca and Mg isotopic composition of bulk carbonate sediments at these sites exhibits systematic stratigraphic variability that is related to both mineralogy and early marine diagenesis. The observed variability in bulk sediment Ca isotopes is best explained by changes in the extent and style of early marine diagenesis from one where the composition of the diagenetic carbonate mineral is determined by the chemistry of the fluid (fluid-buffered) to one where the composition of the diagenetic carbonate mineral is determined by the chemistry of the precursor sediment (sediment-buffered). Our results indicate that this process, together with variations in carbonate mineralogy (aragonite, calcite, and dolomite), plays a fundamental and underappreciated role in determining the regional and global stratigraphic expressions of geochemical tracers (δ13C, δ18O, major, minor, and trace elements) in shallow-water carbonate sediments in the geologic record. Our results also provide evidence that a large shallow-water carbonate sink that is enriched in 44Ca can explain the mismatch between the δ44/40Ca value of rivers and deep-sea carbonate sediments and call into question the hypothesis that the δ44/40Ca value of seawater depends on the mineralogy of primary carbonate precipitations (e.g. 'aragonite seas' and 'calcite seas'). Finally, our results for sedimentary dolomites suggest that paired measurements of Ca and Mg isotopes may provide a unique geochemical fingerprint of mass transfer during dolomitization to better understand the paleo-environmental information preserved in these enigmatic but widespread carbonate minerals.

Non-Chondritic Ni Isotope Composition of the Bulk Silicate Earth

NASA Astrophysics Data System (ADS)

Klaver, M.; Elliott, T.

2018-05-01

We present high-precision Ni isotope data of chondritic meteorites and carefully selected mantle peridotites. These data show that the Bulk Silicate Earth is ca. 90 ppm lighter than chondritic meteorites, possibly as the result of core formation.

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 40Ca. On the other hand, 40Ca may desorb more easily, especially if the bond strength is lower as in the case of aragonite. For kinetic oxygen isotopic fractionation, the faster deprotonation of HC16O3- and the faster incorporation of C16O32- at the surfaces causes a smaller enrichment of 18O in all three polymorphs, which will be preserved at higher precipitation rates. In consequence to the different behavior of calcium and oxygen isotopes, they can be useful for multiproxy applications. Thereby calcium isotopes can be used to identify kinetic effects, especially if both aragonite and calcite, can be analyzed in one sample. Oxygen isotopes are more strongly related to temperature. [1]A. Niedermayr, S.J. Köhler and M. Dietzel (2013), Chemical Geology, 340, 105-120.

Origins of GEMS Grains

NASA Technical Reports Server (NTRS)

Messenger, S.; Walker, R. M.

2012-01-01

Interplanetary dust particles (IDPs) collected in the Earth s stratosphere contain high abundances of submicrometer amorphous silicates known as GEMS grains. From their birth as condensates in the outflows of oxygen-rich evolved stars, processing in interstellar space, and incorporation into disks around new stars, amorphous silicates predominate in most astrophysical environments. Amorphous silicates were a major building block of our Solar System and are prominent in infrared spectra of comets. Anhydrous interplanetary dust particles (IDPs) thought to derive from comets contain abundant amorphous silicates known as GEMS (glass with embedded metal and sulfides) grains. GEMS grains have been proposed to be isotopically and chemically homogenized interstellar amorphous silicate dust. We evaluated this hypothesis through coordinated chemical and isotopic analyses of GEMS grains in a suite of IDPs to constrain their origins. GEMS grains show order of magnitude variations in Mg, Fe, Ca, and S abundances. GEMS grains do not match the average element abundances inferred for ISM dust containing on average, too little Mg, Fe, and Ca, and too much S. GEMS grains have complementary compositions to the crystalline components in IDPs suggesting that they formed from the same reservoir. We did not observe any unequivocal microstructural or chemical evidence that GEMS grains experienced prolonged exposure to radiation. We identified four GEMS grains having O isotopic compositions that point to origins in red giant branch or asymptotic giant branch stars and supernovae. Based on their O isotopic compositions, we estimate that 1-6% of GEMS grains are surviving circumstellar grains. The remaining 94-99% of GEMS grains have O isotopic compositions that are indistinguishable from terrestrial materials and carbonaceous chondrites. These isotopically solar GEMS grains either formed in the Solar System or were completely homogenized in the interstellar medium (ISM). However, the chemical compositions of GEMS grains are extremely heterogeneous and seem to rule out this possibility. Based on their solar isotopic compositions and their non-solar elemental compositions we propose that most GEMS grains formed in the nebula as late-stage non-equilibrium condensates.

Biological forcing controls the chemistry of the coral exoskeleton

NASA Astrophysics Data System (ADS)

Meibom, A.; Mostefaoui, S.; Cuif, J.; Yurimoto, H.; Dauphin, Y.; Houlbreque, F.; Dunbar, R.; Constantz, B.

2006-12-01

A multitude of marine organisms produce calcium carbonate skeletons that are used extensively to reconstruct water temperature variability of the tropical and subtropical oceans - a key parameter in global climate-change models. Such paleo-climate reconstructions are based on the notion that skeletal oxygen isotopic composition and certain trace-element abundances (e.g., Sr/Ca and Mg/Ca ratios) vary in response to changes in the water temperature. However, it is a fundamental problem that poorly understood biological processes introduce large compositional deviations from thermodynamic equilibrium and hinder precise calibrations of many paleo-climate proxies. Indeed, the role of water temperature in controlling the composition of the skeleton is far from understood. We have studied trace-element abundances as well as oxygen and carbon isotopic compositions of individual skeletal components in the zooxanthellate and non-zooxanthellate corals at ultra-structural, i.e. micrometer to sub-micrometer length scales. From this body of work we draw the following, generalized conclusions: 1) Centers of calcification (COC) are not in equilibrium with seawater. Notably, the Sr/Ca ratio is higher than expected for aragonite equilibrium with seawater at the temperature at which the skeleton was formed. Furthermore, the COC are further away from equilibrium with seawater than fibrous skeleton in terms of stable isotope composition. 2) COC are dramatically different from the fibrous aragonite skeleton in terms of trace element composition. 3) Neither trace element nor stable isotope variations in the fibrous (bulk) part of the skeleton are directly related to changes in SST. In fact, changes in SST can have very little to do with the observed compositional variations. 4) Trace element variations in the fibrous (bulk) part of the skeleton are not related to the activity of zooxanthellae. These observations are directly relevant to the issue of biological versus non-biological control over skeleton composition and will be discussed.

In situ dating on Mars: A new approach to the K-Ar method utilizing cosmogenic argon

NASA Astrophysics Data System (ADS)

Cassata, William S.

2014-01-01

Cosmogenic argon isotopes are produced in feldspars via nuclear reactions between cosmic rays and Ca and K atoms within the lattice. These cosmogenic isotopes can be used as proxies for K and Ca, much like nuclear reactor-derived 39Ar and 37Ar are used as proxies for K and Ca, respectively, in 40Ar/39Ar geochronology. If Ca and K are uniformly distributed, then the ratio of radiogenic 40Ar (40Ar*) to cosmogenic 38Ar or 36Ar (38Arcos or 36Arcos) is proportional to the difference between the radioisotopic and exposure ages, as well as the K/Ca ratio of the degassing phase. Thus cosmogenic, radiogenic, and trapped Ar isotopes, all of which can be measured remotely and are stable over geologic time, are sufficient to generate an isochron-like diagram from which the isotopic composition of the trapped component may be inferred. Such data also provide a means to assess the extent to which the system has remained closed with respect to 40Ar*, thereby mitigating otherwise unquantifiable uncertainties that complicate the conventional K-Ar dating method.

Determination of chemical purity and isotopic composition of natural and carbon-13-labeled arsenobetaine bromide standards by quantitative(1)H-NMR.

PubMed

Le, Phuong-Mai; Ding, Jianfu; Leek, Donald M; Mester, Zoltan; Robertson, Gilles; Windust, Anthony; Meija, Juris

2016-10-01

In this study, we report the characterization of three arsenobetaine-certified reference materials by quantitative NMR. We have synthesized an arsenobetaine bromide high-purity standard of natural isotopic composition (ABET-1) and two carbon-13-labeled isotopic standards (BBET-1 and CBET-1). Assignments of the chemical purity and isotopic composition are not trivial in the case of arsenobetaine, and in this study we utilized quantitative(1)H-NMR techniques for the determination of the mass fractions (chemical purity). The isotopic purity of all three standards was also assessed by NMR from the carbon-13 satellite signals. The standards are non-hygroscopic, high-purity (ca. 0.99 g/g), and the carbon-13 enrichment for both isotopic standards is x((13)C)≈0.99. These standards are designed for use as primary calibrators for mass spectrometric determination of arsenobetaine in environmental samples.

Petrology of Anomalous Eucrites

NASA Technical Reports Server (NTRS)

Mittlefehldt, D. W.; Peng, Z. X.; Ross, D. K.

2015-01-01

Most mafic achondrites can be broadly categorized as being "eucritic", that is, they are composed of a ferroan low-Ca clinopyroxene, high-Ca plagioclase and a silica phase. They are petrologically distinct from angritic basalts, which are composed of high-Ca, Al-Ti-rich clinopyroxene, Carich olivine, nearly pure anorthite and kirschsteinite, or from what might be called brachinitic basalts, which are composed of ferroan orthopyroxene and high-Ca clinopyroxene, intermediate-Ca plagioclase and ferroan olivine. Because of their similar mineralogy and composition, eucrite-like mafic achondrites formed on compositionally similar asteroids under similar conditions of temperature, pressure and oxygen fugacity. Some of them have distinctive isotopic compositions and petrologic characteristics that demonstrate formation on asteroids different from the parent of the HED clan (e.g., Ibitira, Northwest Africa (NWA) 011). Others show smaller oxygen isotopic distinctions but are otherwise petrologically and compositionally indistinguishable from basaltic eucrites (e.g., Pasamonte, Pecora Escarpment (PCA) 91007). The degree of uniformity in delta O-17 of eucrites and diogenites is one piece of evidence considered to favor of a magma-ocean scenario for their petrogenesis. Given that the O isotopic differences separating Pasamonte and PCA 91007 from other eucrites are small, and that there is an absence of other distinguishing characteristics, a legitimate question is: Did the HED parent asteroid fail to homogenize via a magma-ocean stage, thus explaining outliers like Pasamonte? We are initiating a program of study of anomalous eucrite-like achondrites as one part of our effort to seek a resolution of this issue. Here we present preliminary petrologic information on Asuka (A-) 881394, Elephant Moraine (EET) 87520 and EET 87542. We will have studied several more by conference time.

Carbonic anhydrase distribution across organisms and environments: genomic predictors for soil enzymatic fluxes of carbon cycle tracers δ18O and COS

NASA Astrophysics Data System (ADS)

Meredith, L. K.; Singer, E.

2016-12-01

Carbonyl sulfide (COS) and the oxygen isotope composition (δ18O) of CO2 are potential tools for differentiating the contributions of photosynthesis and respiration to the balance of global carbon cycling. These processes are coupled at the leaf level via the enzyme carbonic anhydrase (CA), which hydrolyzes CO2 in the first biochemical step of the photosynthetic pathway (CO2 + H2O ⇌ HCO3- + H+) and correspondingly structural analogue COS (COS + H2O → CO2 + H2S). CA also accelerates the exchange of oxygen isotopes between CO2 and H2O leading to a distinct isotopic imprint. The biogeochemical cycles of these tracers include significant, yet poorly characterized soil processes that challenge their utility for probing the carbon cycle. In soils, microbial CA also hydrolyze COS and accelerate O isotope exchange between CO2 and soil water. Genomic predictors of microbial CA activity may help account and predict for these soil fluxes. Using a bioinformatics approach, we assess the distribution of the six known CA classes (α, β, γ, δ, η, ζ) in organisms ranging from fungi and plants to archaea and bacteria, and ask whether CA diversity is linked to soil microbial diversity. We survey the diversity and relative abundance of CA in a wide variety of environments and estimate the sensitivity of CA to biome and land use. Finally, we compare the CA distribution in soils to measurements (oxygen isotope and COS fluxes) and models of CA activity to develop genomic predictors for CA activity. This work provides the first survey of CA in soils, a step towards understanding the significant role of CA in microbial ecology and microbe-mediated biogeochemical cycles.

Constraining the mechanisms driving coccolith δ44/40Ca and Sr/Ca variations: new perspectives from cultures, cellular models, and the sediment record

NASA Astrophysics Data System (ADS)

María Mejía, Luz; Paytan, Adina; Eisenhauer, Anton; Kolevica, Ana; Bolton, Clara; Méndez-Vicente, Ana; Abrevaya, Lorena; Isensee, Kirsten; Stoll, Heather

2017-04-01

Coccoliths comprise a major fraction of the calcium carbonate (CaCO3) production, with contributions varying from 95% of the global carbonate sink during the Cenozoic, to 50% in the modern ocean. Therefore, significant changes in coccolith Ca isotopic fractionation could have affected past seawater Ca isotopic composition (δ44/40Ca), with potential important implications for the interpretation of the global Ca cycle and related changes in seawater chemistry. Here we evaluate the mechanisms driving coccolith Ca isotopic fractionation in a quantitative framework, by deriving a steady-state mass balance geochemical model (CaSri-Co), which assumes that fractionation is solely associated with desolvation (i.e. dehydration) of Ca during cellular transport through membranes. The application of the CaSri-Co model to previously published and to our new δ44/40Ca and Sr/Ca results from cultured coccolithophores (Emiliania huxleyi, Gephyrocapsa oceanica and Calcidiscus leptoporus) allowed us to identify calcification rates, Ca retention efficiency and water structure strength as main regulators of the Ca isotopic fractionation and Sr/Ca ratios of cultured coccolith calcite. Higher calcification rates, higher Ca retention efficiencies and higher water structure strength (slower Ca solvation-desolvation reactions) increase both coccolith Sr/Ca and Ca isotopic fractionation. The CaSri-Co model shows that coccolith Ca isotopic fractionation is especially sensitive to changes in water structure strength. On the other hand, Ca retention efficiency appears to be the main driver of the observed Sr/Ca trends, which results from the incomplete usage of the Sr transported to the calcification vesicle and subsequent Sr enrichment of the cytosol, while Ca inside the calcification vesicle is assumed to be completely utilized in the model. In this study we also measured δ44/40Ca and Sr/Ca in two coccolith size fraction from site 925 in the Western Equatorial Atlantic representing the last 11 Ma. We observe an increase of Sr/Ca ratios in both size fractions which may indicate an enhanced Ca retention efficiency during a period of increasing carbon limitation. The rather large changes in Ca isotopic fractionation measured in both cultures (up to 5 ‰ ) and the sedimentary record (up to 0.32 ‰ ), could be in part explained by changes in sea surface temperature (SST) and/or changes in the amount/type of cellular exudates, both of which modify the water structure strength around the cell. Since changes in Ca isotopic fractionation of the magnitude of those observed in this study and in others could potentially affect seawater δ44/40Ca, we would recommend future modeling studies to include coccolith-based studies for a better interpretation of the Ca cycle.

Age and isotopic relationships among the angrites Lewis Cliff 86010 and Angra dos Reis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lugmair, G.W.; Galer, S.J.G.

1992-04-01

Results of a wide-ranging isotopic investigation of the unique Antarctican angrite LEW-86010 (LEW) are presented, together with a reassessment of the type angrite Angra dos Reis (ADOR). The principal objectives of this study are to obtain precise radiometric ages, initial Sr isotopic compositions, and to search for the erstwhile presence of the short-lived nuclei {sup 146}Sm and {sup 26}Al via their daughter products. The isotopic compositions of Sm, U, Ca, and Ti were also measured. This allows a detailed appraisal to be made of the relations between, and the genealogy of, these two angrites.

Spatial and ontogenetic variability in the chemical composition of juvenile common sole ( Solea solea) otoliths

NASA Astrophysics Data System (ADS)

Tanner, S. E.; Vasconcelos, R. P.; Reis-Santos, P.; Cabral, H. N.; Thorrold, S. R.

2011-01-01

A description of variations in the chemical composition of fish otoliths at different spatial scales and life history stages is a prerequisite for their use as natural tags in fish population connectivity and migration studies. Otolith geochemistry of juvenile common sole ( Solea solea), a marine migrant species collected in six Portuguese estuaries was examined. Elemental ratios (Mg:Ca, Mn:Ca, Cu:Ca, Sr:Ca, Ba:Ca, Pb:Ca) were analysed in two zones of the right otolith (corresponding to late larval and juvenile stages) using laser ablation inductively coupled plasma mass spectrometry (ICP-MS). Stable carbon and oxygen isotopes (δ 13C and δ 18O) were determined in left otoliths using isotopic ratio monitoring mass spectrometry (irm-MS). Significant differences in otolith geochemical signatures were found among estuaries, among sites within estuaries and between otolith zones. Several elemental ratios (Mg:Ca, Mn:Ca, Cu:Ca and Sr:Ca) showed consistent patterns between otolith zones and were likely influenced by environmental factors and ontogenetic effects associated with physiological changes during metamorphosis. Assignment of individuals to their collection estuary based on the otolith geochemical signatures was more accurate at the site level (81%) than among estuaries (69%). Site temperature was not correlated with any of the elemental or isotope ratios, but salinity was significantly correlated with Ba:Ca, δ 13C and δ 18O. Observed spatial variations among estuaries and sites within estuaries indicate that geochemical signatures in otoliths are accurate natural tags of estuarine habitat in common sole. Nevertheless, the significant variations observed between otolith zones should be taken into account in the design of population connectivity studies.

Barnacles - recorders of environmental conditions with unique geochemical signatures

NASA Astrophysics Data System (ADS)

Vinzenz Ullmann, Clemens; Gale, Andy; Korte, Christoph; Frei, Robert; Huggett, Jenny; Wray, Dave

2017-04-01

Barnacles are calcite-forming arthropods that occur in a wide range of habitats in modern times and are found in sedimentary successions reaching back to the Paleozoic. Despite potential use of their mostly low-Mg calcite hard parts for palaeoenvironmental reconstructions, their geochemical composition has been little studied. Here, we present the first comprehensive overview of barnacle geochemistry, with C and O isotope, as well as Mg/Ca, Sr/Ca, Mn/Ca and Fe/Ca data for multiple samples of 42 species covering the orders Sessilia, Scalpelliformes, and Lepadiformes. XRD analyses confirm calcite as the only significant carbonate mineral of the studied barnacle shell material. Apart from one species, median Mg/Ca ratios fall below 50 mmol/mol, the approximate limit for low-Mg-calcite. In the order Sessilia, the scuta and terga are on average enriched in Mg by 36 % over the unmoveable plates. Amongst the calcite-forming marine animals, barnacles have very high Sr/Ca ratios of 2.6 to 5.9 mmol/mol, amongst the highest known for calcite secreting animals. Mn/Ca and Fe/Ca ratios are commonly low and compatible with other modern shell calcite, but can be strongly enriched to > 1 mmol/mol in proximal habitats, particularly close to areas strongly affected by human activity. Carbon and oxygen isotope data indicate formation of the calcite in or near isotopic equilibrium with ambient water conditions. Apart from species showing δ18O values below 0 ‰ V-PDB, a negative correlation of oxygen isotope ratios with Sr/Ca ratios is observed, which may be related to metabolic activity. Compositional patterns in barnacle shell material, particularly high Sr concentrations and Mg distribution in shell plates of the Sessilia, point to a great potential of barnacles for high fidelity reconstruction of past seawater chemistry and environmental conditions complementary to other archives.

Magma mixing and the generation of isotopically juvenile silicic magma at Yellowstone caldera inferred from coupling 238U–230Th ages with trace elements and Hf and O isotopes in zircon and Pb isotopes in sanidine

USGS Publications Warehouse

Stelten, Mark E.; Cooper, Kari M.; Vazquez, Jorge A.; Reid, Mary R.; Barfod, Gry H.; Wimpenny, Josh; Yin, Qing-Zhu

2013-01-01

The nature of compositional heterogeneity within large silicic magma bodies has important implications for how silicic reservoirs are assembled and evolve through time. We examine compositional heterogeneity in the youngest (~170 to 70 ka) post-caldera volcanism at Yellowstone caldera, the Central Plateau Member (CPM) rhyolites, as a case study. We compare 238U–230Th age, trace-element, and Hf isotopic data from zircons, and major-element, Ba, and Pb isotopic data from sanidines hosted in two CPM rhyolites (Hayden Valley and Solfatara Plateau flows) and one extracaldera rhyolite (Gibbon River flow), all of which erupted near the caldera margin ca. 100 ka. The Hayden Valley flow hosts two zircon populations and one sanidine population that are consistent with residence in the CPM reservoir. The Gibbon River flow hosts one zircon population that is compositionally distinct from Hayden Valley flow zircons. The Solfatara Plateau flow contains multiple sanidine populations and all three zircon populations found in the Hayden Valley and Gibbon River flows, demonstrating that the Solfatara Plateau flow formed by mixing extracaldera magma with the margin of the CPM reservoir. This process highlights the dynamic nature of magmatic interactions at the margins of large silicic reservoirs. More generally, Hf isotopic data from the CPM zircons provide the first direct evidence for isotopically juvenile magmas contributing mass to the youngest post-caldera magmatic system and demonstrate that the sources contributing magma to the CPM reservoir were heterogeneous in 176Hf/177Hf at ca. 100 ka. Thus, the limited compositional variability of CPM glasses reflects homogenization occurring within the CPM reservoir, not a homogeneous source.

Experimental paleotemperature equation for planktonic foraminifera

NASA Astrophysics Data System (ADS)

Erez, Jonathan; Luz, Boaz

1983-06-01

Small live individuals of Globigerinoides sacculifer which were cultured in the laboratory reached maturity and produced garnets. Fifty to ninety percent of their skeleton weight was deposited under controlled water temperature (14° to 30°C) and water isotopic composition, and a correction was made to account for the isotopic composition of the original skeleton using control groups. Comparison of. the actual growth temperatures with the calculated temperature based on paleotemperature equations for inorganic CaCO 3 indicate that the foraminifera precipitate their CaCO 3 in isotopic equilibrium. Comparison with equations developed for biogenic calcite give a similarly good fit. Linear regression with CRAIG'S (1965) equation yields: t = -0.07 + 1.01 t̂ (r= 0.95) where t is the actual growth temperature and t̂ Is the calculated paleotemperature. The intercept and the slope of this linear equation show that the familiar paleotemperature equation developed originally for mollusca carbonate, is equally applicable for the planktonic foraminifer G. sacculifer. Second order regression of the culture temperature and the delta difference ( δ18Oc - δ18Ow) yield a correlation coefficient of r = 0.95: t̂ = 17.0 - 4.52(δ 18Oc - δ 18Ow) + 0.03(δ 18Oc - δ 18Ow) 2t̂, δ 18Oc and δ18Ow are the estimated temperature, the isotopic composition of the shell carbonate and the sea water respectively. A possible cause for nonequilibnum isotopic compositions reported earlier for living planktonic foraminifera is the improper combustion of the organic matter.

Zinc isotope anomalies in Allende meteorite inclusions

NASA Technical Reports Server (NTRS)

Loss, R. D.; Lugmair, G. W.

1990-01-01

The isotopic compositions of Zn, Cr, Ti, and Ca have been measured in a number of CAIs from the Allende meteorite. The aim was to test astrophysical models which predict large excesses of Zn-66 to accompany excesses in the neutron-rich isotopes of Ca, Ti, Cr, and Ni. Some of the CAIs show clearly resolved but small excesses for Zn-66 which are at least an order of magnitude smaller than predicted. This result may simply reflect the volatility and chemical behavior of Zn as compared to the other (more refractory) anomalous elements found in these samples. Alternatively, revision of parameters and assumptions used for the model calculations may be required.

Calcium Isotope Analysis by Mass Spectrometry

NASA Astrophysics Data System (ADS)

Boulyga, S.; Richter, S.

2010-12-01

The variations in the isotopic composition of calcium caused by fractionation in heterogeneous systems and by nuclear reactions can provide insight into numerous biological, geological, and cosmic processes, and therefore isotopic analysis finds a wide spectrum of applications in cosmo- and geochemistry, paleoclimatic, nutritional, and biomedical studies. The measurement of calcium isotopic abundances in natural samples has challenged the analysts for more than three decades. Practically all Ca isotopes suffer from significant isobaric interferences, whereas low-abundant isotopes can be particularly affected by neighboring major isotopes. The extent of natural variations of stable isotopes appears to be relatively limited, and highly precise techniques are required to resolve isotopic effects. Isotope fractionation during sample preparation and measurements and instrumental mass bias can significantly exceed small isotope abundance variations in samples, which have to be investigated. Not surprisingly, a TIMS procedure developed by Russell et al. (Russell et al., 1978. Geochim Cosmochim Acta 42: 1075-1090) for Ca isotope measurements was considered as revolutionary for isotopic measurements in general, and that approach is used nowadays (with small modifications) for practically all isotopic systems and with different mass spectrometric techniques. Nevertheless, despite several decades of calcium research and corresponding development of mass spectrometers, the available precision and accuracy is still not always sufficient to achieve the challenging goals. This presentation discusses figures of merits of presently used analytical methods and instrumentation, and attempts to critically assess their limitations. Additionally, the availability of Ca isotope reference materials will be discussed.

Crystal growth and disequilibrium distribution of oxygen isotopes in an igneous Ca-Al-rich inclusion from the Allende carbonaceous chondrite

NASA Astrophysics Data System (ADS)

Kawasaki, Noriyuki; Simon, Steven B.; Grossman, Lawrence; Sakamoto, Naoya; Yurimoto, Hisayoshi

2018-01-01

TS34 is a Type B1 Ca-Al-rich inclusion (CAI) from the Allende CV3 chondrite, consisting of spinel, melilite, Ti-Al-rich clinopyroxene (fassaite) and minor anorthite in an igneous texture. Oxygen and magnesium isotopic compositions were measured by secondary ion mass spectrometry in spots of known chemical composition in all major minerals in TS34. Using the sequence of formation from dynamic crystallization experiments and from chemical compositions of melilite and fassaite, the oxygen isotopic evolution of the CAI melt was established. Oxygen isotopic compositions of the constituent minerals plot along the carbonaceous chondrite anhydrous mineral line. The spinel grains are uniformly 16O-rich (Δ17O = -22.7 ± 1.7‰, 2SD), while the melilite grains are uniformly 16O-poor (Δ17O = -2.8 ± 1.8‰) irrespective of their åkermanite content and thus their relative time of crystallization. The fassaite crystals exhibit growth zoning overprinting poorly-developed sector zoning; they generally grow from Ti-rich to Ti-poor compositions. The fassaite crystals also show continuous variations in Δ17O along the inferred directions of crystal growth, from 16O-poor (Δ17O ∼ -3‰) to 16O-rich (Δ17O ∼ -23‰), covering the full range of oxygen isotopic compositions observed in TS34. The early-crystallized 16O-poor fassaite and the melilite are in oxygen isotope equilibrium and formed simultaneously. The correlation of oxygen isotopic compositions with Ti content in the fassaite imply that the oxygen isotopic composition of the CAI melt evolved from 16O-poor to 16O-rich during fassaite crystallization, presumably due to oxygen isotope exchange with a surrounding 16O-rich nebular gas. Formation of spinel, the liquidus phase in melts of this composition, predates crystallization of all other phases, so its 16O-rich composition is a relic of an earlier stage. Anorthite exhibits oxygen isotopic compositions between Δ17O ∼ -2‰ and -9‰, within the range of those of fassaite, indicating co-crystallization of these two minerals during the earliest to intermediate stage of fassaite growth. The melilite and fassaite yield an 26Al-26Mg mineral isochron with an initial value of (26Al/27Al)0 = (5.003 ± 0.075) × 10-5, corresponding to a relative age of 0.05 ± 0.02 Myr from the canonical Al-Mg age of CAIs. These data demonstrate that both 16O-rich and 16O-poor reservoirs existed in the solar nebula at least ∼0.05 Myr after the birth of the Solar System.

Calcium isotopic anomalies and the lack of aluminum-26 in an unusual Allende inclusion

NASA Technical Reports Server (NTRS)

Lee, T.; Russell, W. A.; Wasserburg, G. J.

1979-01-01

This letter reports the discovery of an unusual Allende inclusion that is rich in hibonite, Ca(Al, Ti, Mg)12O19, the most refractory and possibly the most primitive major oxide mineral from the solar nebula. The Mg and Ca isotopic compositions of this hibonite-rich inclusion are studied in order to investigate the distribution of Al-26 in the solar system and to extend the search for isotopic anomalies. The Mg results indicate that no Mg isotopic anomalies are present, that the initial Al-26/Al-27 ratio for the inclusion when it crystallized was less than 200 billionths, and that the Mg mass-fractionation effect in the inclusion must be less than about 20 per mil/amu for the hibonite and 10 per mil/amu for other phases. The Ca studies reveal that large Ca mass-fractionation effects of about 7.5 per mil/amu are present and that additional small 'nonlinear' effects of presumably nuclear origin at a level of about 1 to 2 per mil are present in at least Ca-42. A plausible model for the evolution of the hibonite-rich inclusion is outlined.

In situ dating on Mars: A new approach to the K–Ar method utilizing cosmogenic argon

DOE PAGES

Cassata, William S.

2013-08-22

In this paper, cosmogenic argon isotopes are produced in feldspars via nuclear reactions between cosmic rays and Ca and K atoms within the lattice. These cosmogenic isotopes can be used as proxies for K and Ca, much like nuclear reactor-derived 39Ar and 37Ar are used as proxies for K and Ca, respectively, in 40Ar/ 39Ar geochronology. If Ca and K are uniformly distributed, then the ratio of radiogenic 40Ar ( 40Ar*) to cosmogenic 38Ar or 36Ar ( 38Ar cos or 36Ar cos) is proportional to the difference between the radioisotopic and exposure ages, as well as the K/Ca ratio ofmore » the degassing phase. Thus cosmogenic, radiogenic, and trapped Ar isotopes, all of which can be measured remotely and are stable over geologic time, are sufficient to generate an isochron-like diagram from which the isotopic composition of the trapped component may be inferred. Finally, such data also provide a means to assess the extent to which the system has remained closed with respect to 40Ar*, thereby mitigating otherwise unquantifiable uncertainties that complicate the conventional K–Ar dating method.« less

New Proxies for Climate change parameters: Foram Culturing and Pteropod Potentials

NASA Astrophysics Data System (ADS)

Keul, N.; Schneider, R. R.; Langer, G.; Bijma, J.; Peijnenburg, K. T.

2017-12-01

Global climate change is one of the most pressing challenges our society is currently facing and strong efforts are made to simulate future climate conditions. To better validate models that aim at predicting global temperature rise as a consequence of anthropogenic CO2 emissions, accurate atmospheric paleo-CO2 estimates in combination with temperature reconstructions are necessary. Consequently there is a strong need for reliable proxies, allowing reconstruction of climate change. With respect to foraminifera a combination of laboratory experiments and modeling is presented, to show the isolated impact of the different parameters of the carbonate system on trace element composition of their shells. We focus on U/Ca and Sr/Ca ratios, which have recently been established as new proxies reflecting changes in the carbonate system of seawater. While U/Ca correlates with carbonate ion concentration, Sr/Ca is primarily influenced by DIC. The latter is particularly promising since the impact of additional parameters is relatively well constrained and hence, Sr/Ca ratios may allow higher accuracy in carbonate system parameter reconstructions. Furthermore, our results will be discussed on how to advance our knowledge about foraminiferal biomineralization. Pteropods, among the first responders to ocean acidification and warming, are explored as carriers of marine paleoenvironmental signals. In order to characterize the stable isotopic composition of aragonitic pteropod shells and their variation in response to climate change parameters, pteropod shells were collected along a latitudinal transect in the Atlantic Ocean. By comparing shell oxygen isotopic composition to depth changes of the calculated aragonite equilibrium oxygen isotope values, we infer shallow calcification depths for Heliconoides inflatus (75 m), rendering this species a good potential proxy carrier for past variations in surface ocean properties. Furthermore, we demonstrate that indeed, pteropod shells are excellent recorders of climate change, as carbonate ion and temperature in the upper water column have dominant influences on pteropod shell carbon and oxygen isotopic composition. These results, in combination with a wide distribution and high abundance, make H. inflatus, a promising new proxy carrier in paleoceanography.

δ18O and δD of lake waters across the Coast Range and Cascades, central Oregon: Modern insights from hydrologically open lakes into the control of landscape on lake water composition in deep time

NASA Astrophysics Data System (ADS)

Finkelstein, D. B.; Curtin, T.

2016-12-01

Reconstructing the stable isotopic composition of paleolake water normally requires an assumption of paleotemperature. However, hydrologically open paleolakes with short water residence times may have recorded paleoprecipitation along topographic gradients that are independent of lake water temperature. To identify the environmental and geographic controls on the isotopic composition of lake water, we sampled 22 natural lakes and reservoirs along a longitudinal and elevation gradient from the Pacific Ocean up and over the Coast and Cascade Ranges of central Oregon to the High Lava Plains in 2013 and 2015. The transect spans lakes of different origins, 6 geomorphic regions and an elevation range of 2-1942 m absl. The Coast Range lakes are sand hosted whereas the remaining are bedrock (volcanic and sedimentary) hosted. The lakes are hydrologically open and dominated by meteoric recharge. The water residence time ranges from months to decades. Samples were analyzed for temperature, pH, and total dissolved solids (TDS) in the field, and alkalinity and major cations and anions and stable isotopes of D and O in the lab. The pH ranges from 7 to 9.8 and shows no systematic variation based on substrate type or elevation. The lakes are dilute (avg. TDS = 35.8 ppm) and have low alkalinties (18.9 mg/L CaCO3) except for those in the High Lava Plains (avg. TDS = 337 ppm, alk: 291.2 mg/L CaCO3). In the Coast Range, Na is the major cation on an equivalent basis, reflecting proximity to the ocean. The easternmost lakes within the Coast Range are dominated by Ca, reflecting different drainage basins and substrate type. Lakes in the Western and High Cascades are dominated by Ca. The dominant cation and stable isotopic analyses clearly differentiate waters from different geomorphic regions. The δ18O ranges from -5.7 to -9.3 ‰ (VSMOW), and δD ranges from -37.8 to -63.6 ‰ (VSMOW) in the Coast Range whereas the δ18O ranges from -9.7 to -12.1 ‰ (VSMOW) and δD ranges from -71.5 to -86.5‰ (VSMOW) in the Cascades. Stable isotopic differences between mountain ranges reflect distance from the ocean and increasing elevation. Stable isotopes of water show no correlation with air or lake water temperatures. Average annual precipitation and bedrock across this topographic gradient controls the major ions and stable isotopic composition of these lakes.

A calcium isotope test of end-Permian ocean acidification using biogenic apatite

NASA Astrophysics Data System (ADS)

Hinojosa, J.; Brown, S. T.; DePaolo, D. J.; Paytan, A.; Shen, S.; Chen, J.; Payne, J.

2011-12-01

Submarine erosional truncation of uppermost Permian carbonate strata has been interpreted to reflect ocean acidification coincident with the end-Permian mass extinction. Although this scenario is consistent with carbon isotope and paleontological data, several alternative scenarios, such as ocean overturn or collapse of the biological pump, can also account for the carbon isotope and paleontological evidence. Calcium isotopes provide a geochemical proxy to test between acidification and alternative scenarios. Specifically, a negative shift in the calcium isotope composition (δ44/40Ca) of seawater is predicted under the acidification scenario but not the alternatives. The δ44/40Ca of carbonate rocks from south China exhibits a negative excursion of approximately 0.3%, but this shift could result from either a change in the δ44/40Ca of seawater or a change in carbonate mineralogy because calcite and aragonite exhibit substantially different fractionation factors relative to seawater. To test whether the negative shift in δ44/40Ca reflects seawater δ44/40Ca or carbonate mineralogy, we measured the δ44/40Ca of conodont microfossils (calcium hydroxyapatite) from the global stratotype section for the Permian-Triassic boundary at Meishan, China. The conodont δ44/40Ca record shows a negative excursion similar in stratigraphic position and magnitude to that previously observed in carbonate rocks. Parallel negative excursions in the δ44/40Ca of carbonate rocks and conodont microfossils cannot be accounted for by a change in carbonate mineralogy but are consistent with a negative shift in the δ44/40Ca of seawater. These data add further support for the ocean acidification scenario, pointing toward strong similarities between the greatest catastrophe in the history of animal life and anticipated global change during the 21st century.

Foraminiferal Stable Isotope Geochemistry At The Micrometer Scale: Is It A Dream Or Reality?

NASA Astrophysics Data System (ADS)

Misra, S.; Shuttleworth, S.; Lloyd, N. S.; Sadekov, A.; Elderfield, H.

2012-12-01

Over last few decades trace metals and stable isotope compositions of foraminiferal shells became one of the major tools to study past oceans and associated climate change. Empirical calibrations of δ11B, δ18O, Mg/Ca, Cd/Ca, Ba/Ca shells compositions have linked them to various environmental parameters such as seawater pH, temperature, salinity and productivity. Despite their common use as proxies, little is known about mechanisms of trace metals incorporation into foraminiferal calcite. Trace metals partition coefficients for foraminiferal calcite is significantly different from inorganic calcite precipitates underlining strong biological control on metal transport to the calcification sites and their incorporation into the calcite. Microscale distribution of light elements isotopes (e.g. Li, B, Mg) could potentially provide unique inside into these biomineralization processes improving our understanding of foraminiferal geochemistry. In this work we explore potentials of using recent advances in analytical geochemistry by employing laser ablation and multi-collector ICP-MS to study microscale distribution of Mg isotopes across individual foraminiferal shells and δ11B, and δ7Li analyses of individual shell chambers. The analytical setup includes an Analyte.G2 193nm excimer laser ablation system with two volume ablation cell connected to a Thermo Scientific NEPTUNE Plus MC-ICP-MS with Jet Interface option. We will discuss method limitations and advantages for foraminiferal geochemistry as well as our data on Mg isotopes distribution within shells of planktonic foraminifera.

Study of thermochemical sulfate reduction mechanism using compound specific sulfur isotope analysis

USGS Publications Warehouse

Meshoulam, Alexander; Ellis, Geoffrey S.; Ahmad, Ward Said; Deev, Andrei; Sessions, Alex L.; Tang, Yongchun; Adkins, Jess F.; Liu, Jinzhong; Gilhooly, William P.; Aizenshtat, Zeev; Amrani, Alon

2016-01-01

Experiments involving sparingly soluble CaSO4 show that during the second catalytic phase of TSR the rate of sulfate reduction exceeds that of sulfate dissolution. In this case, there is no apparent isotopic fractionation between source sulfate and generated H2S, as all of the available sulfate is effectively reduced at all reaction times. When CaSO4 is replaced with fully soluble Na2SO4, sulfate dissolution is no longer rate limiting and significant S-isotopic fractionation is observed. This supports the notion that CaSO4dissolution can lead to the apparent lack of fractionation between H2S and sulfate produced by TSR in nature. The S-isotopic composition of individual OSCs record information related to geochemical reactions that cannot be discerned from the δ34S values obtained from bulk phases such as H2S, oil, and sulfate minerals, and provide important mechanistic details about the overall TSR process.

Can isotopic variations in structural water of gypsum reveal paleoclimatic changes?

NASA Astrophysics Data System (ADS)

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

2015-12-01

Water of crystallization in gypsum can be used as paleo-environmental proxy to study large scale climatic variability in arid areas. This is because changes in the isotopic composition of water of crystallization are due to isotopic variations in the mother brine from which the mineral precipitated, and the brine isotopic composition is linked to evaporation processes and humidity. This is particularly important when the salts are the only traces left of the original water, i.e. in modern arid areas. This study aims to prove that the 2-D/18-O compositions of the water of crystallization extracted from successive precipitates or even different growth zones of natural gypsum (CaSO4·H2O) can reconstruct the evaporation history and paleo-humidity of the source water basin. The method was tested in a laboratory experiment that evaporated CaSO4 brines under controlled temperature and humidity conditions. The brine was left to evaporate for five days at two different humidities (45 and 75 RH%); subsequently, brines and precipitated gypsum were sampled at 24 hour intervals. In this way we simulated zoned growth of gypsum. The samples were then analyzed for oxygen and hydrogen isotopic composition using a Thermo Scientific TC/EA with modified column, coupled to a MAT 253 Thermo Finnigan mass spectrometer at JPL. If preliminary results validate the novel hypothesis that changes in mineral composition can reveal details of paleo-environmental conditions the theory will be tested on natural gypsum collected from selected areas in White Sands National Monument, New Mexico. The study is currently ongoing but the full dataset will be presented at the conference.

Stable isotopes of pedogenic carbonates from the Somma-Vesuvius area, southern Italy, over the past 18 kyr: palaeoclimatic implications

NASA Astrophysics Data System (ADS)

Zanchetta, G.; di Vito, M.; Fallick, A. E.; Sulpizio, R.

2000-12-01

Stable isotopes were measured in the carbonate and organic matter of palaeosols in the Somma-Vesuvius area, southern Italy in order to test whether they are suitable proxy records for climatic and ecological changes in this area during the past 18000 yr. The ages of the soils span from ca. 18 to ca. 3 kyr BP. Surprisingly, the Last Glacial to Holocene climate transition was not accompanied by significant change in 18O of pedogenic carbonate. This could be explained by changes in evaporation rate and in isotope fractionation between water and precipitated carbonate with temperature, which counterbalanced the expected change in isotope composition of meteoric water. Because of the rise in temperature and humidity and the progressive increase in tree cover during the Holocene, the Holocene soil carbonates closely reflect the isotopic composition of meteoric water. A cooling of about 2°C after the Avellino eruption (3.8 ka) accounts for a sudden decrease of about 1 in 18O of pedogenic carbonate recorded after this eruption. The 13C values of organic matter and pedogenic carbonate covary, indicating an effective isotope equilibrium between the organic matter, as the source of CO2, and the pedogenic carbonate. Carbon isotopes suggest prevailing C3 vegetation and negligible mixing with volcanogenic or atmospheric CO2.

Determination of Sr and Ca sources in small tropical catchments (La Selva, Costa Rica) - A comparison of Sr and Ca isotopes

NASA Astrophysics Data System (ADS)

Wiegand, B. A.; Schwendenmann, L.

2013-04-01

SummaryA comparative study of Sr and Ca isotopes was conducted to assess solute sources and effects of biogeochemical processes on surface water and groundwater in four small tropical catchments located at La Selva Biological Station, Costa Rica. Variable concentrations of dissolved Sr2+ and Ca2+ in the catchments are related to mixing of waters from different origin. Three catchments are influenced by high-solute bedrock groundwater, while another catchment is primarily supplied by local recharge. 87Sr/86Sr ratios were employed to discriminate contributions from mineral weathering and atmospheric sources. Solutes in bedrock groundwater have a predominant geogenic origin, whereas local recharge is characterized by low-solute inputs from rainwater and minor in situ weathering releases from nutrient-depleted soils. Bedrock groundwater contributes more than 60% of dissolved Sr2+ to surface discharge in the Salto, Saltito, and Arboleda catchments, whereas the Taconazo catchment receives more than 95% of dissolved Sr2+ from rainwater. δ44/40Ca values of dissolved Ca2+ vary greatly in the catchments, mainly as a result of heterogeneous Ca isotope compositions of the contributing sources. Based on differences in δ44/40Ca values, two distinct bedrock groundwaters discharging at the Salto and the Arboleda catchments are suggested. Effects of biological processes in the plant-soil system on solute generation in the catchments are indicated by variable Ca/Sr ratios. However, these effects cannot clearly be assessed by Ca isotopes due to the strong heterogeneity of δ44/40Ca values of Ca2+ sources and high Ca2+ concentrations in bedrock groundwater.

Mineralogy and Oxygen Isotope Compositions of an Unusual Hibonite-Perovskite Refractory Inclusion from Allende

NASA Technical Reports Server (NTRS)

Keller, L. P.; Snead, C.; Rahman, Z.; McKeegan, K. D.

2012-01-01

Hibonite-rich Ca- and Al-rich inclusions (CAIs) are among the earliest formed solids that condensed in the early nebula. We discovered an unusual refractory inclusion from the Allende CV3 chondrite (SHAL) containing an approx 500 micron long single crystal of hibonite and co-existing coarse-grained perovskite. The mineralogy and petrography of SHAL show strong similarities to some FUN inclusions, especially HAL. Here we report on the mineralogy, petrography, mineral chemistry and oxygen isotopic compositions in SHAL.

Calcium Isotope Geochemistry: Research Horizons and Nanoscale Fractionation Processes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, W; Simon, J I; DePaolo, D J

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

Oxygen Isotope Measurements of a Rare Murchison Type A CAI and Its Rim

NASA Technical Reports Server (NTRS)

Matzel, J. E. P.; Simon, J. I.; Hutcheon, I. D.; Jacobsen, B.; Simon, S. B.; Grossman, L.

2013-01-01

Ca-, Al-rich inclusions (CAIs) from CV chondrites commonly show oxygen isotope heterogeneity among different mineral phases within individual inclusions reflecting the complex history of CAIs in both the solar nebula and/or parent bodies. The degree of isotopic exchange is typically mineral-specific, yielding O-16-rich spinel, hibonite and pyroxene and O-16-depleted melilite and anorthite. Recent work demonstrated large and systematic variations in oxygen isotope composition within the margin and Wark-Lovering rim of an Allende Type A CAI. These variations suggest that some CV CAIs formed from several oxygen reservoirs and may reflect transport between distinct regions of the solar nebula or varying gas composition near the proto-Sun. Oxygen isotope compositions of CAIs from other, less-altered chondrites show less intra-CAI variability and 16O-rich compositions. The record of intra-CAI oxygen isotope variability in CM chondrites, which commonly show evidence for low-temperature aqueous alteration, is less clear, in part because the most common CAIs found in CM chondrites are mineralogically simple (hibonite +/- spinel or spinel +/- pyroxene) and are composed of minerals less susceptible to O-isotopic exchange. No measurements of the oxygen isotope compositions of rims on CAIs in CM chondrites have been reported. Here, we present oxygen isotope data from a rare, Type A CAI from the Murchison meteorite, MUM-1. The data were collected from melilite, hibonite, perovskite and spinel in a traverse into the interior of the CAI and from pyroxene, melilite, anorthite, and spinel in the Wark-Lovering rim. Our objectives were to (1) document any evidence for intra-CAI oxygen isotope variability; (2) determine the isotopic composition of the rim minerals and compare their composition(s) to the CAI interior; and (3) compare the MUM-1 data to oxygen isotope zoning profiles measured from CAIs in other chondrites.

Geochemical and Sr isotopic variations in groundwaters of the Edwards aquifer, central Texas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oetting, G.C.; Banner, J.L.; Sharp, J.M. Jr.

1992-01-01

The regionally-extensive Edwards aquifer of central Texas lies on the northwestern edge of the Gulf of Mexico Basin. The aquifer system is composed primarily of lower Cretaceous marine limestones and dolostones with minor evaporitic and siliciclastic confining units of the Edwards Group and associated formations. The eastern and southern boundaries of the freshwater aquifer are defined by an abrupt change in groundwater salinity that is known as the badwater line. Variation in the isotopic composition and concentration of Sr in the mineral phases and waters in this aquifer system provide means to examine groundwater evolution processes. Models of simultaneous variationsmore » in Sr isotopes and major and trace ions are used to constrain processes of groundwater-rock interaction and groundwater mixing. Geochemical variations were examined in Edwards carbonate host rocks and groundwaters in Williamson and Bell Counties. Groundwaters were sampled along and across the badwater line, and range in salinity from 320--2,630 mg/l total dissolved solids. Major ion distributions in the water samples demonstrate a hydrochemical facies transition from Ca-HCO[sub 3] freshwaters to Na-Cl-SO[sub 4]-HCO[sub 3] badwaters. Both water types show a wide range of [sup 87]Sr/[sup 86]Sr values: Ca-HCO[sub 3] waters range from values of 0.7078--0.7093, and Na-Cl-SO[sub 4]-HCO[sub 3] waters range from values of 0.7087--0.7097. The Sr isotope compositions for both water groups are significantly greater than their host marine carbonates ([approximately]0.7075). The high Sr isotopic compositions indicate an extraformational source of Sr in both hydrochemical facies. Fluid mixing processes involving a freshwater and at least two badwater endmembers are required to account for variations in elemental and isotopic compositions in the groundwaters. Mineral-solution reactions may operate during and/or subsequent to mixing to produce the compositional variability observed in some intermediate waters.« less

Fossil black smoker yields oxygen isotopic composition of Neoproterozoic seawater.

PubMed

Hodel, F; Macouin, M; Trindade, R I F; Triantafyllou, A; Ganne, J; Chavagnac, V; Berger, J; Rospabé, M; Destrigneville, C; Carlut, J; Ennih, N; Agrinier, P

2018-04-13

The evolution of the seawater oxygen isotopic composition (δ 18 O) through geological time remains controversial. Yet, the past δ 18 O seawater is key to assess past seawater temperatures, providing insights into past climate change and life evolution. Here we provide a new and unprecedentedly precise δ 18 O value of -1.33 ± 0.98‰ for the Neoproterozoic bottom seawater supporting a constant oxygen isotope composition through time. We demonstrate that the Aït Ahmane ultramafic unit of the ca. 760 Ma Bou Azzer ophiolite (Morocco) host a fossil black smoker-type hydrothermal system. In this system we analyzed an untapped archive for the ocean oxygen isotopic composition consisting in pure magnetite veins directly precipitated from a Neoproterozoic seawater-derived fluid. Our results suggest that, while δ 18 O seawater and submarine hydrothermal processes were likely similar to present day, Neoproterozoic oceans were 15-30 °C warmer on the eve of the Sturtian glaciation and the major life diversification that followed.

Calcium isotope analysis by mass spectrometry.

PubMed

Boulyga, Sergei F

2010-01-01

The variations in the isotopic composition of calcium caused by fractionation in heterogeneous systems and by nuclear reactions can provide insight into numerous biological, geological, and cosmic processes, and therefore isotopic analysis finds a wide spectrum of applications in cosmo- and geochemistry, paleoclimatic, nutritional, and biomedical studies. The measurement of calcium isotopic abundances in natural samples has challenged the analysts for more than three decades. Practically all Ca isotopes suffer from significant isobaric interferences, whereas low-abundant isotopes can be particularly affected by neighboring major isotopes. The extent of natural variations of stable isotopes appears to be relatively limited, and highly precise techniques are required to resolve isotopic effects. Isotope fractionation during sample preparation and measurements and instrumental mass bias can significantly exceed small isotope abundance variations in samples, which have to be investigated. Not surprisingly, a TIMS procedure developed by Russell et al. (Russell et al., 1978. Geochim Cosmochim Acta 42: 1075-1090) for Ca isotope measurements was considered as revolutionary for isotopic measurements in general, and that approach is used nowadays (with small modifications) for practically all isotopic systems and with different mass spectrometric techniques. Nevertheless, despite several decades of calcium research and corresponding development of mass spectrometers, the available precision and accuracy is still not always sufficient to achieve the challenging goals. The present article discusses figures of merits of presently used analytical methods and instrumentation, and attempts to critically assess their limitations. In Sections 2 and 3, mass spectrometric methods applied to precise stable isotope analysis and to the determination of (41)Ca are described. Section 4 contains a short summary of selected applications, and includes tracer experiments and the potential use of biological isotope fractionation in medical studies, paleoclimatic and paleoceanographic, and other terrestrial as well as extraterrestrial investigations. 2009 Wiley Periodicals, Inc.

Magnesium stable isotope ecology using mammal tooth enamel

NASA Astrophysics Data System (ADS)

Martin, Jeremy E.; Vance, Derek; Balter, Vincent

2015-01-01

Geochemical inferences on ancient diet using bone and enamel apatite rely mainly on carbon isotope ratios (δ13C) and to a lesser extent on strontium/calcium (Sr/Ca) and barium/calcium (Ba/Ca) elemental ratios. Recent developments in nontraditional stable isotopes provide an unprecedented opportunity to use additional paleodietary proxies to disentangle complex diets such as omnivory. Of particular relevance for paleodietary reconstruction are metals present in large quantity in bone and enamel apatite, providing that biologically mediated fractionation processes are constrained. Calcium isotope ratios (δ44Ca) meet these criteria but exhibit complex ecological patterning. Stable magnesium isotope ratios (δ26Mg) also meet these criteria but a comprehensive understanding of its variability awaits new isotopic data. Here, 11 extant mammal species of known ecology from a single locality in equatorial Africa were sampled for tooth enamel and, together with vegetation and feces, analyzed for δ26Mg, δ13C, Sr/Ca, and Ba/Ca ratios. The results demonstrate that δ26Mg incorporated in tooth enamel becomes heavier from strict herbivores to omnivores/faunivores. Using data from experimentally raised sheep, we suggest that this 26Mg enrichment up the trophic chain is due to a 26Mg enrichment in muscle relative to bone. Notably, it is possible to distinguish omnivores from herbivores, using δ26Mg coupled to Ba/Ca ratios. The potential effects of metabolic and dietary changes on the enamel δ26Mg composition remain to be explored but, in the future, multiproxy approaches would permit a substantial refinement of dietary behaviors or enable accurate trophic reconstruction despite specimen-limited sampling, as is often the case for fossil assemblages.

Ca-rich carbonates associated with ultrabasic-ultramafic melts: Carbonatite or limestone xenoliths? A case study from the late Miocene Morron de Villamayor volcano (Calatrava Volcanic Field, central Spain)

NASA Astrophysics Data System (ADS)

Lustrino, Michele; Prelević, Dejan; Agostini, Samuele; Gaeta, Mario; Di Rocco, Tommaso; Stagno, Vincenzo; Capizzi, Luca Samuele

2016-07-01

The volcanic products of the late Miocene Morron de Villamayor volcano (Calatrava Volcanic Field, central Spain) are known for being one of the few outcrops of leucitites in the entire circum-Mediterranean area. These rocks are important because aragonite of mantle origin has been reported as inclusion in olivine macrocrysts. We use petrographic observations, mineral compositions, as well as oxygen and carbon isotope ratios coupled with experimental petrology to understand the origin of carbonate phase in these olivine-phyric rocks. Groundmass and macrocryst olivines range from δ18OVSMOW of +4.8‰, typical of mantle olivine values, to +7.4‰, indicating contamination by sedimentary carbonate. Carbonates are characterized by heavy oxygen isotope compositions (δ18OVSMOW >+24‰), and relatively light carbon isotopes (δ13CPDB <-11‰), resembling skarn values, and distinct from typical mantle carbonatite compositions. Petrography, mineral compositions such as low Mg# of clinopyroxene and biotite, low Ca# and low incompatible element abundance of the carbonate, and isotopic ratios of O and C, do not support a mantle origin for the carbonate. Rather, the carbonate inclusions found in the olivine macrocrysts are interpreted as basement limestone fragments entrapped by the rising crystallizing magma. Comparison with experimental carbonatitic and silicate-carbonatitic melts indicates that low-degree partial melts of a carbonated peridotite must have a dolomitic rather than the aragonitic/calcitic composition as those found trapped in the Morron de Villamayor olivine macrocrysts.

Evidence for mass-dependent isotopic fractionation of strontium in a glaciated granitic watershed

NASA Astrophysics Data System (ADS)

de Souza, Gregory F.; Reynolds, Ben C.; Kiczka, Mirjam; Bourdon, Bernard

2010-05-01

The stable isotope composition of strontium (expressed as δ 88/86Sr) may provide important constraints on the global exogenic strontium cycle. Here, we present δ 88/86Sr values and 87Sr/ 86Sr ratios for granitoid rocks, a 150 yr soil chronosequence formed from these rocks, surface waters and plants in a small glaciated watershed in the central Swiss Alps. Incipient chemical weathering in this young system, whether of inorganic or biological origin, has no resolvable effect on the 87Sr/ 86Sr ratios and δ 88/86Sr values of bulk soils, which remain indistinguishable from bedrock in terms of Sr isotopic composition. Although due in part to the chemical heterogeneity of the forefield, the lack of a resolvable difference between soil and bedrock isotopic composition indicates that these soils have thus far witnessed minimal net loss of Sr; a low degree of chemical weathering is also implied by bulk soil chemistry. The isotopic composition of Sr in streamwater is more radiogenic than median soil, reflecting the preferential weathering of biotite in the catchment; streamwater δ 88/86Sr values, however, are indistinguishable from bulk soil δ 88/86Sr values, implying that no resolvable fractionation of Sr isotopes takes place during release to the weathering flux in the Damma forefield. Analyses of plant tissue reveal that plants ( Rhododendron and Vaccinium) preferentially assimilate the lighter isotopes of Sr such that their δ 88/86Sr values are significantly lower than those of the soils in which they grow. Additionally, δ 88/86Sr values of foliar and floral tissues are lower than those of roots, contrary to observations for Ca, for which Sr is often used as an analogue in weathering studies. We suggest that processes that discriminate against Sr in favour of Ca, due to the different nutritional requirement of plants for these two elements, are responsible for the observed contrast.

High Resolution Glacial-interglacial Climatic Variations in the South China Sea during the Last 220,000 Years

NASA Astrophysics Data System (ADS)

Huang, K.; You, C.; Li, M.; Shieh, Y.

2002-12-01

The Asian monsoon plays an important role of both regional and global climatic variations. The South China Sea (SCS) located between Southeast Asia continent and Western Pacific Ocean is an ideal place for studying oceanographic responses and changes of monsoon system in the past. Planktonic foraminiferal shells separated from two deep sea cores, ODP Site 1144 and SCS 15B, located near the northeast continental slope and the central ocean basin respectively were used to reconstruct high-resolution climatic records during the last 220 kyrs. Average of 20 individual foraminiferal shells were hand picked and cleaned thoroughly for high precision trace element/calcium ratios (i.e., Mg/Ca, Sr/Ca, and Ba/Ca) determination using a Thermo-Fannigan Element II ICP-MS installed at NCKU. Isotopic compositions of oxygen, carbon, boron and strontium also were measured by stable isotope ratio or Triton TI thermal ionization mass spectrometer. Mg/Ca and Sr/Ca in foraminiferal shells are sensitive proxies for sea surface temperature, chemical weathering and hydrothermal activity on seafloor. The SCS foraminiferal shells Mg/Ca and Sr/Ca show negative correlation with interesting glacial-interglacial variations. The calculated Mg/Ca SSTs varied as large as 6-7 °C with the highest temperature occurred at oxygen stage 5. The Sr/Ca ratios change about 16 % (1.200-1.429 mmole/mole), possibly a result of periodic sea level changes which influencing terrigenous inputs or continental shelves weathering. On the other hand, the Ba/Ca display large variations (0.031-0.117 mmole/mole), possibly reflecting upwelling intensity or SCS bottom water chemistry. The boron isotopic compositions in planktonic foraminiferal shells are used to estimate pH in the surface ocean. Combining these proxies, high-resolution oceanic environmental records in the SCS were reconstructed for the last 220 kyrs. The results obtained from the SCS can be used to gain a better understanding of land-sea interaction in this region.

Archean crustal evolution of the Narryer Gneiss Terrane, Western Australia, as revealed by the U-Pb age and Hf-isotope compositions of zircon from the granitic gneisses

NASA Astrophysics Data System (ADS)

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

2011-12-01

The Narryer Gneiss Terrane of the Yilgarn Craton, Western Australia, is an important area for studies of early crustal evolution because of the preservation of (1) detrital zircons of Hadean to Archean age in the Jack Hills and Mt. Narryer metasedimentary belts, and (2) several widespread units of granitic gneisses emplaced between ca. 3.7 and 2.6 Ga. We have analyzed the U-Pb geochronology and Hf-isotope geochemistry of magmatic zircons from 38 samples of the granitic gneisses using laser ablation - (multicollector) - ICPMS. The sample suite is dominated by the Meeberrie gneiss, a banded quartz-microcline-oligoclase-biotite gneiss of monzogranite to granodiorite composition, and the Dugel gneiss, a leucocratic, pegmatite-layered syenogranite gneiss, but gneisses of dioritic to tonalitic composition, as well as less deformed granite sheets, are also represented. Magmatic zircons were identified on the basis of the preservation of oscillatory zoning in BSE and CL images, igneous Th/U ratios (>0.2), and concordant U-Pb isotopic systematics with low common Pb contents. The results indicate many of the gneisses are composed of the products of multiple magmatic events, as has been reported previously for samples of the Meeberrie gneiss (Kinny & Nutman, 1996, Precambrian Res. 78, 165-178). Major ages of magmatism preserved in the gneisses occurred at ca. 3685-3665 Ma, 3620-3565 Ma, 3495-3440 Ma, 3375-3330 Ma, and 3300-3260 Ma. The late granite sheets crystallized at 2710-2645 Ma. Hf-isotope compositions of the zircons trend to less radiogenic values with decreasing age, with ɛHf values of ca. 0 to -5 for 3.7-3.4 Ga gneisses, ca. -1 to -9 for 3.4-3.2 Ga gneisses and ca. -5 to -20 for the late granite sheets. The array of the Hf isotopic compositions with time for the entire sample set are fit well by a regression indicating a source reservoir with a 176Lu/177Hf of 0.022 extracted from the depleted mantle at 3.9 Ga. This suggests that the Narryer gneisses and late granite sheets were derived by repeated partial melting of an Eoarchean mafic to intermediate crustal source that persisted throughout the Archean. The ɛHf evolution trend for the Narryer gneisses plots distinctly above the ɛHf trend of the Hadean mafic crustal reservoir inferred for the source of the Hadean detrital zircons from the Jack Hills. The implication is that the inferred Hadean crustal reservoir was not an important source of the Narryer gneisses, either because it was largely isolated from zones of melting in the crust of the Narryer Gneiss Terrane during the Archean, or because it was simply of limited volume.

Trace element evidence for a depleted component intrinsic to the Hawaiian plume

NASA Astrophysics Data System (ADS)

DeFelice, C.; Mallick, S.; Saal, A. E.; Huang, S.

2017-12-01

The Hawaii Scientific Drilling Project (HSDP) recovered 3.5 km of Mauna Kea post-shield and shield stage basalts to investigate the geochemical evolution of a Hawaiian shield stage volcano and to constrain the geochemical structure of Hawaiian plume. A group of tholeiitic lavas from 1760-1810 meters below sea level (mbsl) have higher CaO content at given MgO content and are called high-CaO basalts. Isotopes of Pb, Sr, Hf, and Nd of these basalts show they are the most depleted shield basalts ever recovered in Hawaii. Their 206Pb/204Pb-208Pb/204Pb values indicate that they are not related to Pacific MORB. Their Ba/Th values (115-160) are characteristic of Hawaiian plume material and they are isotopically similar to Hawaiian rejuvenated stage lavas. To further investigate this relationship, we compare high-CaO basalts to the Honolulu Volcanics, a set of rejuvenated stage lavas. To determine their possible petrogenetic relation, we calculate their parental melt composition by adding or removing olivine until their geochemical composition is in equilibrium with Fo90. The High-CaO basalt parent magma composition has a much flatter REE pattern and much lower absolute REE contents than that of the Honolulu lavas. Batch melting forward models are calculated to determine potential sources that could contribute to both the Honolulu Volcanics and high-CaO basalts petrogenesis. Both parental magma compositions can be recreated by melting the same rejuvenated-stage source composition to varying degrees. Honolulu Volcanics are the result of a low degree of melting of the rejuvenated source, while higher degrees of melting reproduce the high-CaO basalts. The High-CaO basalts, erupted during shield-stage volcanism, show that the depleted component that rejuvenated stage basalts form from can be sampled during the most voluminous stage of volcanism, and is likely intrinsic to the plume.

Tooth enamel maturation reequilibrates oxygen isotope compositions and supports simple sampling methods

NASA Astrophysics Data System (ADS)

Trayler, Robin B.; Kohn, Matthew J.

2017-02-01

Oxygen isotope and major element zoning patterns of several disparate ungulate teeth were collected to evaluate the timing and geometry of enamel formation, records of isotope zoning, and tooth enamel sampling strategies. Isotopic zoning in mammalian tooth enamel encodes a sub-annual time series of isotopic variation of an animal's body water composition, with a damping factor that depends on the specifics of how enamel mineralizes. Enamel formation comprises two stages: precipitation of appositional enamel with a high CO3:PO4 ratio, followed by precipitation of maturational enamel with a lower CO3:PO4. If appositional and maturational enamel both contribute to isotope compositions (but with different CO3:PO4), and if isotope compositions vary seasonally, paired δ18O values from CO3 and PO4 profiles should show a spatial separation. CO3 isotope patterns should be shifted earlier seasonally than PO4 isotope patterns. Such paired profiles for new and published data show no resolvable shifts, i.e. CO3 and PO4 δ18O profiles show coincident maxima and minima. This coincidence suggests that enamel maturation reequilibrates appositional isotope compositions. If enamel maturation establishes enamel isotope compositions, the geometry of maturation, not apposition, should be considered when devising sampling protocols. X-ray maps of Ca zoning show that the majority of enamel (inner and middle layers) mineralizes heavily at a high angle to the external tooth surface and the enamel-dentine junction over length scales of 2-4 mm, while the outer enamel surface mineralizes more slowly. These data suggest that isotopic sampling strategies should parallel maturational geometry and focus on interior enamel to improve data fidelity. The magnitude of isotopic damping is also smaller than implied in previous studies, so tooth enamel zoning more closely reflects original body water isotopic variations than previously assumed.

Boron Isotopes in Modern and Cenozoic Scleractinian Fossil Corals

NASA Astrophysics Data System (ADS)

Gothmann, A.; Bender, M. L.; Adkins, J. F.

2016-12-01

Recent measurements of boron isotopes in modern coral support the hypothesis that coral biologically up-regulate the pH of the fluid from which they calcify to facilitate skeletal mineralization [1]. While this evidence of biological pH adjustment provides important insight into the mechanism by which coral make their skeletons, it also complicates the use of coral boron isotopes as a paleoseawater pH proxy. We measured boron isotopes in 11 modern and well preserved fossil corals using Secondary Ion Mass Spectrometry to characterize fine-scale ( 30 µm) patterns of δ11B variability. In addition to δ11B, we measured B/Ca, Mg/Ca, Sr/Ca, and Mn/Ca ratios in order to compare isotopes with element/Ca variability and monitor for diagenetic alteration. We find that in different species of modern and well preserved fossil coral, the measured range of δ11B varies from 5 to 15 ‰. Also, while corals of similar geologic age have similar average δ11B compositions, at the scale of our measurements they do not appear to share a consistent pattern of minimum δ11B, maximum δ11B, or range in δ11B. The δ11B of fossil corals increases by 7 ‰ between the Early Cenozoic and today. While the general pattern of coral δ11B change is similar to the pattern found in foraminifera-based δ11B records [e.g., 2], the magnitude of the coral change is approximately 2-3 times as large as changes inferred from foraminifera. Although it is not possible to separate the influence of changing seawater pH and changing δ11Bseawater on fossil coral boron isotope compositions, the record can be explained by a combination of lower seawater pH and lower seawater δ11B during the the Early Cenozoic. Our coral results suggest an Early Cenozoic δ11Bseawater composition that is much lower than inferred from other approaches, and similar to Early Cenozoic δ11Bseawater as inferred from brine inclusions in halite [3]. [1.] McCulloch, M.T., Trotter, J., Montagna, P., Falter, J., Dunbar, R., Freiwald, A., Forsterra, G., Lopez Correa, M., Maier, C., Ruggeberg, A., Taviani, M., 2012. Geochimica et Cosmochimica Acta 87, 21-34. [2.] Pearson, P.N., Palmer, M.R., 2000. Nature 406, 695-699. [3.] Paris, G., Gaillardet, J., Louvat, P. 2010. Geology 38, 1035-1038.

The influence of seawater carbonate chemistry, mineralogy, and diagenesis on calcium isotope variations in Lower-Middle Triassic carbonate rocks

DOE PAGES

Lau, Kimberly V.; Maher, Kate; Brown, Shaun T.; ...

2017-11-01

The geological calcium cycle is linked to the geological carbon cycle through the weathering and burial of carbonate rocks. As a result, calcium (Ca) isotope ratios ( 44 Ca/ 40 Ca, expressed as δ 44/40 Ca) can help to constrain ancient carbon cycle dynamics if Ca cycle behavior can be reconstructed. But, the δ 44/40 Ca of carbonate rocks is influenced not only by the δ 44/40 Ca of seawater but also by diagenetic processes and fractionation associated with carbonate precipitation. In this study, we investigate the dominant controls on carbonate δ 44/40 Ca in Upper Permian to Middle Triassicmore » limestones (ca. 253 to 244 Ma) from south China and Turkey. This time interval is ideal for assessing controls on Ca isotope ratios in carbonate rocks because fluctuations in seawater δ 44/40 Ca may be expected based on several large carbon isotope (δ 13 C) excursions ranging from -2 to + 8‰. Parallel negative δ 13 C and δ 44/40 Ca excursions were previously identified across the end-Permian extinction horizon. Here, we find a second negative excursion in δ 44/40 Ca of ~ 0.2‰ within Lower Triassic strata in both south China and Turkey; however, this excursion is not synchronous between regions and thus cannot be interpreted to reflect secular change in the δ 44/40 Ca of global seawater. Additionally, δ 44/40 Ca values from Turkey are consistently 0.3‰ lower than contemporaneous samples from south China, providing further support for local or regional influences. By measuring δ 44/40 Ca and Sr concentrations ([Sr]) in two stratigraphic sections located at opposite margins of the Paleo-Tethys Ocean, we can determine whether the data represent global conditions (e.g., secular variations in the δ 44/40 Ca of seawater) versus local controls (e.g., original mineralogy or diagenetic alteration). The [Sr] and δ 44/40 Ca data from this study are best described statistically by a log-linear correlation that also exists in many previously published datasets of various geological ages. By using a model of early marine diagenetic water-rock interaction, we illustrate that this general correlation can be explained by the chemical evolution of bulk carbonate sediment samples with different initial mineralogical compositions that subsequently underwent recrystallization. Although early diagenetic resetting and carbonate mineralogy strongly influence the carbonate δ 44/40 Ca values, the relationship between [Sr] and δ 44/40 Ca holds potential for reconstructing first-order secular changes in seawater δ 44/40 Ca composition.« less

The influence of seawater carbonate chemistry, mineralogy, and diagenesis on calcium isotope variations in Lower-Middle Triassic carbonate rocks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lau, Kimberly V.; Maher, Kate; Brown, Shaun T.

The geological calcium cycle is linked to the geological carbon cycle through the weathering and burial of carbonate rocks. As a result, calcium (Ca) isotope ratios ( 44 Ca/ 40 Ca, expressed as δ 44/40 Ca) can help to constrain ancient carbon cycle dynamics if Ca cycle behavior can be reconstructed. But, the δ 44/40 Ca of carbonate rocks is influenced not only by the δ 44/40 Ca of seawater but also by diagenetic processes and fractionation associated with carbonate precipitation. In this study, we investigate the dominant controls on carbonate δ 44/40 Ca in Upper Permian to Middle Triassicmore » limestones (ca. 253 to 244 Ma) from south China and Turkey. This time interval is ideal for assessing controls on Ca isotope ratios in carbonate rocks because fluctuations in seawater δ 44/40 Ca may be expected based on several large carbon isotope (δ 13 C) excursions ranging from -2 to + 8‰. Parallel negative δ 13 C and δ 44/40 Ca excursions were previously identified across the end-Permian extinction horizon. Here, we find a second negative excursion in δ 44/40 Ca of ~ 0.2‰ within Lower Triassic strata in both south China and Turkey; however, this excursion is not synchronous between regions and thus cannot be interpreted to reflect secular change in the δ 44/40 Ca of global seawater. Additionally, δ 44/40 Ca values from Turkey are consistently 0.3‰ lower than contemporaneous samples from south China, providing further support for local or regional influences. By measuring δ 44/40 Ca and Sr concentrations ([Sr]) in two stratigraphic sections located at opposite margins of the Paleo-Tethys Ocean, we can determine whether the data represent global conditions (e.g., secular variations in the δ 44/40 Ca of seawater) versus local controls (e.g., original mineralogy or diagenetic alteration). The [Sr] and δ 44/40 Ca data from this study are best described statistically by a log-linear correlation that also exists in many previously published datasets of various geological ages. By using a model of early marine diagenetic water-rock interaction, we illustrate that this general correlation can be explained by the chemical evolution of bulk carbonate sediment samples with different initial mineralogical compositions that subsequently underwent recrystallization. Although early diagenetic resetting and carbonate mineralogy strongly influence the carbonate δ 44/40 Ca values, the relationship between [Sr] and δ 44/40 Ca holds potential for reconstructing first-order secular changes in seawater δ 44/40 Ca composition.« less

Seasonal variations in the nitrogen isotope composition of Okinotori coral in the tropical western Pacific: A new proxy for marine nitrate dynamics

NASA Astrophysics Data System (ADS)

Yamazaki, Atsuko; Watanabe, Tsuyoshi; Ogawa, Nanako O.; Ohkouchi, Naohiko; Shirai, Kotaro; Toratani, Mitsuhiro; Uematsu, Mitsuo

2011-12-01

To demonstrate the utility of coral skeletons as a recorder of nitrate dynamics in the surface ocean, we collected coral skeletons of Porites lobata and determined their nitrogen isotope composition (δ15Ncoral) from 2002 to 2006. Skeletons were collected at Okinotori Island in southwestern Japan, far from any sources of terrestrial nitrogen. Nitrogen isotope compositions along the growth direction were determined at 800 μm intervals (˜1 month resolution) and compared against the skeletal carbon isotope composition (δ13Ccoral-carb), barium/calcium ratio (Ba/Ca), and Chlorophyll-a concentration (Chl-a). From 2002 to 2004, ratios of the δ15Ncoral varied between +0.8 and +8.3‰ with inverse variation to SST (r = -0.53). Ba/Ca ratios and Chl-a concentrations were also observed to be high during seasons with low SST. These results suggested that the vertical mixing that occurs during periods of low SST carries nutrients from deeper water (δ15NDIN; +5˜+6‰) to the sea surface. In 2005 onward, δ15Ncoral and Ba/Ca ratios also had positive peaks even in high SST during periods of transient upwelling caused by frequent large typhoons (maximum wind speed 30 m/s). In addition, low δ15Ncoral (+0.8˜+2.0‰) four months after the last typhoon implied nitrogen fixation because of the lack of typhoon upwelling through the four years record of δ15Ncoral. Variations in the δ13Ccoral-carb and δ15Ncoral were synchronized, suggesting that nitrate concentration could control zooxanthellae photosynthesis. Our results suggested that δ15Ncoral holds promise as a proxy for reconstructing the transport dynamics of marine nitrate and thus also a tool for estimating nitrate origins in the tropical and subtropical oceans.

Boron incorporation in the foraminifer Amphistegina lessonii under a decoupled carbonate chemistry

NASA Astrophysics Data System (ADS)

Kaczmarek, K.; Langer, G.; Nehrke, G.; Horn, I.; Misra, S.; Janse, M.; Bijma, J.

2015-03-01

A number of studies have shown that the boron isotopic composition (δ11B) and the B / Ca ratio of biogenic carbonates (mostly foraminifers) can serve as proxies for two parameters of the ocean's carbonate chemistry, rendering it possible to calculate the entire carbonate system. However, the B incorporation mechanism into marine carbonates is still not fully understood and analyses of field samples show species-specific and hydrographic effects on the B proxies complicating their application. Identifying the carbonate system parameter influencing boron incorporation is difficult due to the co-variation of pH, CO32- and B(OH)4-. To shed light on the question which parameter of the carbonate system is related to the boron incorporation, we performed culture experiments with the benthic symbiont-bearing foraminifer Amphistegina lessonii using a decoupled pH-CO32- chemistry. The determination of the δ11B and B / Ca ratios was performed simultaneously by means of a new in situ technique combining optical emission spectroscopy and laser ablation MC-ICP-MS. The boron isotopic composition in the tests gets heavier with increasing pH and B / Ca increases with increasing B(OH)4- / HCO3- of the culture media. The latter indicates that boron uptake of A. lessonii features a competition between B(OH)4- and HCO3-. Furthermore, the simultaneous determination of B / Ca and δ11B on single specimens allows for assessing the relative variability of these parameters. Among different treatments the B / Ca shows an increasing variability with increasing boron concentration in the test whereas the variability in the isotope distribution is constant.

Calcium Isotopic Systematics of Peridotite Xenoliths from eastern North China Craton: Implications for Melt-rock Interaction

NASA Astrophysics Data System (ADS)

Zhang, Z.; Zhao, X.; Huang, S.; Xiao, Y.; Li, X.

2017-12-01

In order to better constrain and understand the Ca isotopic variations in the mantle, we report high-precision Ca isotopic data of orthopyroxene (Opx) and clinopyroxene (Cpx) for a set of peridotitic xenoliths from ChangLe, eastern North China craton (NCC). These xenoliths range from lherzolites, Cpx-rich lherzolites to wehrlites, and are variably metasomatised. Lherzolites (Fo≈91) are fertile in mineral composition, and have spoon-shaped to slightly LREE-enriched rare earth element (REE) patterns. They may represent fragments of newly accreted lithospheric mantle that makes up parts of the Late Mesozoic-Cenozoic lithosphere beneath the eastern NCC. Cpx-rich lherzolites and wehrlites formed by reaction of refractory residual peridotites with evolved, Fe-rich silicate melts at high melt/rock ratios, as evidenced by partial to complete replacement of Opx with Cpx, relatively lower Fo contents of Ol (<88) than that from the lherzolites and convex-upward trace element patterns. Our results show that there are large δ44/40Ca variations (1‰) in these peridotitic xenoliths. Lherzolites have δ44/40Ca similar to typical upper mantle value(1.05 ± 0.04). Specifically, lherzolites orthopyroxenes have δ44/40Ca ranging from 1.04 to 1.79, and lherzolites clinopyroxenes have δ44/40Ca from 0.80 to 1.04. In contrast, δ44/40Ca in Cpx-rich lherzolites and wehrlites tend to have lower values reltaive to those of lherzolites. Their clinopyroxenes have δ44/40Ca ranging from 0.42 to 0.92, and their orthopyroxenes have δ44/40Ca ranging from 0.80 to 1.04. Collectively, we identify a positive correlation between clinopyroxene δ44/40Ca and Mg#. Model calculations show that kinetic isotopic fractionation caused by diffusion, probably during mantle melt-rock interaction, is responsible for the positive correlation between clinopyroxene δ44/40Ca and Mg# in these NCC peridotites. Our study shows that melt-rock interaction plays an important role in producing Ca isotopic heterogeneity of the subcontinental mantle.

44Ca/42Ca and 143Nd/144Nd isotope variations in Cretaceous Eocene Tethyan francolites and their bearing on phosphogenesis in the southern Tethys

NASA Astrophysics Data System (ADS)

Soudry, David; Segal, Irena; Nathan, Yaacov; Glenn, Craig R.; Halicz, Ludwik; Lewy, Zeev; Vonderhaar, Denys L.

2004-05-01

Measurements of 44Ca/42Ca and 143Nd/144Nd isotope ratios in carbonate fluorapatite (CFA) through the Aptian Eocene section of the Negev (Israel), together with quantified rates of P and Ca accumulation and bulk sedimentation, permit an examination of the relationships of these five factors to Tethyan phosphogenesis. The data provide an Aptian Eocene (ca. 70 Ma) record of the Ca isotope composition of 35 CFA samples (24 of which were also analyzed for Nd isotopes), representing 11 time-stratigraphic phosphate horizons within the sequence. The δ44Ca values are significantly lower in the Aptian Albian samples (δ44Ca = -0.11‰ to -0.06‰) than in the Campanian Eocene samples (δ44Ca = +0.22‰ to +0.42‰), whereas the ɛNd(T) values increase from continental crust like in the Aptian Albian [ɛNd(T) = -10.9] to more radiogenic, Pacific-like [ɛNd(T) = -6.6 to -6.1] in the Campanian. Both peaks of δ44Ca and ɛNd(T) in the Campanian coincide with the peak of Tethyan phosphogenesis in the Negev, which is marked by a sharp increase of P accumulation rates (from <200 μmol·cm-2·k.y.-1 in pre-Campanian time to ˜1700 μmol·cm-2·k.y.-1 in the Campanian) and a decrease in rates of Ca accumulation and bulk sedimentation. The coincident increases of δ44Ca and ɛNd(T) values and P accumulation rates in the Negev area during the Campanian suggest that they are related in this time interval and were induced by the global Late Cretaceous sea- level rise and increasing circumequatorial Tethyan flow.

Microanalyses of O isotopes and elemental ratios of reef building coral (Montastrea annularis) by ion microprobe

NASA Astrophysics Data System (ADS)

Gabitov, R. I.; Carricart Ganivet, J. P.; Prieto, R. I.

2012-12-01

Our understanding of climate change and oceanographic variability through time is largely derived from knowledge of oxygen isotopes (δ18O) and elemental ratios (X/Ca) signatures in coral reefs. However, the existence of inconsistencies in isotopic composition between different coral specimens suggests that factors other than temperature and seawater composition affect isotopic and chemical records. We conducted in situ Secondary Ion Mass Spectrometry (SIMS) analyses on the reef building coral (Montastraea annularis) from Veracuz Reef in the southern Gulf of Mexico. Coral specimen was sliced in perpendicular and parallel directions of its growth. Therefore, one of the sections exposed simultaneously grown skeletal material; another section represents a time series of continuously extended skeleton. The complex microstructure of the coral yields a few morphologically different zones (architectural elements). There are theca-wall (Th), septa (S), costa (C), exothecal (ExD) and endothecal dissepiments (EnD). Dissepiments formation in Montastraea annularis is linked to moon cycles and there are 12 or 13 ExD formed per year; meanwhile, there are 24 or 26 EnD per year (Dávalos-Dehullu et al. 2008). SIMS analyses were performed on Th, S, C, ExD, and EnD at lateral spatial resolution of ~20 μm. SIMS spot profiles with 100 and 500 μm steps were conducted on Th wall in the direction of coral growth. SIMS analyses demontrate that δ18O in Th, S, C, and ExD that grown at the same time are similar to each other within 1 sigma error. However, δ18O in EnD is isotopically heavier by 1 ‰ than those of simultaneously grown T,S, and ExD. The reverse dependence of δ18O on growth rate of corals and inorganically precipitated aragonite was reported by previous works and potentially could explain the δ18O enrichment in EnD, which grow by 35% slower than ExD (McConnaughey 1989; Dávalos-Dehullu et al. 2008; Gabitov 2012). SIMS spot profiles in the coral growth direction yielded weekly time resolution and demonstrate that factors other than temperature affect elemental and isotopic ratios in corallite aragonite. δ18O positively correlates with Sr/Ca and B/Ca but opposite to Mg/Ca. δ18O-Sr/Ca relationship suggest that they are driven by temperature at least partially. Sr/Ca-Mg/Ca trend is agreed with Raleigh fractionation. Sr/Ca-B/Ca relationship suggests temperature effect on B/Ca. References McConnaughey (1989) 13C and 18O disequilibrium in biological carbonates: I. Patterns. Geochim. Cosmochim. Acta, 53, 151-162. Dávalos-Dehullu, E., Hernández-Arana H., and Carricart-Ganivet J.P. (2008) On the causes of density banding in skeletons of corals of the genus Montastraea. J. Exp. Mar. Biol. Ecol. 365, 142-147. Gabitov R.I. (2012) Growth rate effect on oxygen isotope fractionation between aragonite and fluid at 24°C by in situ analysis. Goldschmidt Conference, Montreal.

Development of routines for simultaneous in situ chemical composition and stable Si isotope ratio analysis by femtosecond laser ablation inductively coupled plasma mass spectrometry.

PubMed

Frick, Daniel A; Schuessler, Jan A; von Blanckenburg, Friedhelm

2016-09-28

Stable metal (e.g. Li, Mg, Ca, Fe, Cu, Zn, and Mo) and metalloid (B, Si, Ge) isotope ratio systems have emerged as geochemical tracers to fingerprint distinct physicochemical reactions. These systems are relevant to many Earth Science questions. The benefit of in situ microscale analysis using laser ablation (LA) over bulk sample analysis is to use the spatial context of different phases in the solid sample to disclose the processes that govern their chemical and isotopic compositions. However, there is a lack of in situ analytical routines to obtain a samples' stable isotope ratio together with its chemical composition. Here, we evaluate two novel analytical routines for the simultaneous determination of the chemical and Si stable isotope composition (δ(30)Si) on the micrometre scale in geological samples. In both routines, multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) is combined with femtosecond-LA, where stable isotope ratios are corrected for mass bias using standard-sample-bracketing with matrix-independent calibration. The first method is based on laser ablation split stream (LASS), where the laser aerosol is split and introduced simultaneously into both the MC-ICP-MS and a quadrupole ICP-MS. The second method is based on optical emission spectroscopy using direct observation of the MC-ICP-MS plasma (LA-MC-ICP-MS|OES). Both methods are evaluated using international geological reference materials. Accurate and precise Si isotope ratios were obtained with an uncertainty typically better than 0.23‰, 2SD, δ(30)Si. With both methods major element concentrations (e.g., Na, Al, Si, Mg, Ca) can be simultaneously determined. However, LASS-ICP-MS is superior over LA-MC-ICP-MS|OES, which is limited by its lower sensitivity. Moreover, LASS-ICP-MS offers trace element analysis down to the μg g(-1)-range for more than 28 elements due to lower limits of detection, and with typical uncertainties better than 15%. For in situ simultaneous stable isotope measurement and chemical composition analysis LASS-ICP-MS in combination with MC-ICP-MS is the method of choice. Copyright © 2016 Elsevier B.V. All rights reserved.

Relationships between water and paddlefish Polyodon spathula dentary elemental and stable-isotopic signatures: potential application for reconstructing environmental history

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bock, Lindsey R.; Whitledge, Gregory W.; Pracheil, Brenda M.

The objectives of this study were to characterize relationships between water and paddlefish Polyodon spathula dentary Sr:Ca, δ 18O and stable hydrogen isotope ratio (δD) to determine the accuracy with which individual P. spathula could be assigned to their collection locations using dentary-edge Sr:Ca, δD and δ 18O. A laboratory experiment was also conducted to determine whether dentary Sr:Ca in age 0 year P. spathula would reflect shifts in water Sr:Ca to which fish were exposed. Significant linear relationships between water and dentary Sr:Ca, δD and δ 18O were observed, although the relationship between water and dentary δ 18O wasmore » weaker than those for Sr:Ca and δD. Classification success for individual fish to collection locations that differed in water Sr:Ca, δD and δ 18O ranged from 86 to 100% based on dentary-edge Sr:Ca, δD and δ18O. Dentary Sr:Ca increased significantly in laboratory-reared age 0 year P. spathula following 4 weeks of exposure to elevated water Sr:Ca; dentary Sr:Ca of fish held in water with elevated Sr:Ca was also significantly higher than that of control fish reared in ambient laboratory water. Results indicated that P. spathula dentaries reflect water signatures for commonly-applied natural chemical markers and strongly suggest that dentary microchemistry and stable-isotopic compositions will be applicable for reconstructing P. spathula environmental history in locations where sufficient spatial differences in water chemistry occur.« less

Relationships between water and paddlefish Polyodon spathula dentary elemental and stable-isotopic signatures: potential application for reconstructing environmental history

DOE PAGES

Bock, Lindsey R.; Whitledge, Gregory W.; Pracheil, Brenda M.; ...

2016-07-26

The objectives of this study were to characterize relationships between water and paddlefish Polyodon spathula dentary Sr:Ca, δ 18O and stable hydrogen isotope ratio (δD) to determine the accuracy with which individual P. spathula could be assigned to their collection locations using dentary-edge Sr:Ca, δD and δ 18O. A laboratory experiment was also conducted to determine whether dentary Sr:Ca in age 0 year P. spathula would reflect shifts in water Sr:Ca to which fish were exposed. Significant linear relationships between water and dentary Sr:Ca, δD and δ 18O were observed, although the relationship between water and dentary δ 18O wasmore » weaker than those for Sr:Ca and δD. Classification success for individual fish to collection locations that differed in water Sr:Ca, δD and δ 18O ranged from 86 to 100% based on dentary-edge Sr:Ca, δD and δ18O. Dentary Sr:Ca increased significantly in laboratory-reared age 0 year P. spathula following 4 weeks of exposure to elevated water Sr:Ca; dentary Sr:Ca of fish held in water with elevated Sr:Ca was also significantly higher than that of control fish reared in ambient laboratory water. Results indicated that P. spathula dentaries reflect water signatures for commonly-applied natural chemical markers and strongly suggest that dentary microchemistry and stable-isotopic compositions will be applicable for reconstructing P. spathula environmental history in locations where sufficient spatial differences in water chemistry occur.« less

The Kramer deposit of southern California--Preliminary insights on the origins of zoned lacustrine evaporite borate deposits

DOE Office of Scientific and Technical Information (OSTI.GOV)

Swihart, G.H.; McBay, E.H.; Smith, D.H.

1992-01-01

Lacustrine evaporite borate deposits span the range from mineralogically unzoned or poorly zoned to concentrically or complexly zoned types. Deposits often contain an inner ulexite or probertite (Na-Ca borates) zone and an outer colemanite (Ca borate) zone. A few deposits contain an innermost borax (Na borate) zone. Boron isotopic analyses of core material from the zoned borax-ulexite-colemanite Kramer deposit have been made with the aim of providing a better understanding of the processes of zone formation. Samples from 6 depths over a 63 foot interval in the borax zone yield a [delta] B-11 range of +0.1 to +2.3 permil. Twomore » samples in the portion of the ulexite zone below the borax zone, vertically separated from one another by 20 feet, yield identical results of [delta]B-11 = [minus]2.1 permit. Three ulexite samples from a 10 foot interval above the borax zone produced results in the range [delta]B-11 = [minus]4.6 to [minus]5.5 permil. A number of possible origins for ulexite at Kramer have been proposed: (1) primary precipitation from the lake brines; (2) postdepositional alteration of the borax zone margin by Ca-rich groundwater; (3) mixing of seeping lake brines and Ca-rich groundwater in muds around the lake. Given the small variation in B isotopic composition exhibited in the borax zone, mechanisms 1 and 2 would produce upper and lower portions of the ulexite zone with similar isotopic compositions. In the third scenario, the difference in composition of the upper and lower ulexites could be due to distance from the lake and relative proportions of seeped lake brine (B-11-rich) and clay adsorbed B (B-10-rich). Furthermore, the cotton ball form of the ulexite in this core is identical to that of ulexite forming today just beneath the surface of dry lakes in NV and CA.« less

Uptake of alkaline earth metals in Alcyonarian spicules (Octocorallia)

NASA Astrophysics Data System (ADS)

Taubner, I.; Böhm, F.; Eisenhauer, A.; Garbe-Schönberg, D.; Erez, J.

2012-05-01

Alcyonarian corals (Octocorallia) living in shallow tropical seas produce spicules of high-Mg calcite with ˜13 mol% MgCO3. We cultured the tropical alcyonarian coral Rhythisma fulvum in experiments varying temperature (19-32 °C) and pH (8.15-8.44). Alkalinity depletion caused by spicule formation systematically varied in the temperature experiments increasing from 19 to 29 °C. Spicules were investigated for their elemental ratios (Mg/Ca, Sr/Ca) using ICP-OES, δ44/40Ca using TIMS, as well as δ18O and δ13C by IRMS. Mg/Ca increased with temperature from 146 to 164 mmol/mol, in good agreement with the range observed for marine inorganic calcite. Mg/Ca increased by 1.0 ± 0.4 mmol/mol/°C, similar to the sensitivity of Miliolid foraminifera. The pH experiments revealed a linear relationship between Mg/Ca and carbonate ion concentration of +0.03 ± 0.02 mmol/mol/μMol. Sr/Ca ranges from 2.5 to 2.9 mmol/mol being in good agreement with other high-Mg calcites. Temperature and pH experiments showed linear dependencies of Sr/Ca matching inorganic calcite trends and pointing to a decoupling of crystal precipitation rate and calcification rate. Ca isotopes range between 0.7‰ and 0.9‰ in good agreement with aragonitic scleractinian corals and calcitic coccoliths. Presumably Ca isotopes are fractionated by a biological mechanism that may be independent of the skeletal mineralogy. We observe no temperature trend, but a significant decrease of δ44/40Ca with increasing pH. This inverse correlation may characterise biologically controlled intracellular calcification. Oxygen isotope ratios are higher than expected for isotopic equilibrium with a temperature sensitivity of -0.15 ± 0.03‰/°C. Carbon isotope ratios are significantly lower than expected for equilibrium and positively correlated with temperature with a slope of 0.20 ± 0.04‰/°C. Many of our observations on trace element incorporation in R. fulvum may be explained by inorganic processes during crystal formation, which do not comply with the intracellular mode of calcification in Alcyonarian corals. The observed elemental and isotopic compositions, however, could be explained if the partitioning caused by biological mechanisms mimics the effects of inorganic processes.

Geochemical Fingerprinting of the World Trade Center Attack in New York Harbor Sediments

NASA Astrophysics Data System (ADS)

Brabander, D. J.; Oktay, S.; Smith, J.; Kada, J.; Bullen, T.; Olsen, C.

2002-12-01

By comparing the textural, chemical, and isotopic composition of World Trade Center (WTC) ash samples (collected near Ground Zero one week after the terrorist attack) with sediment samples from cores taken on October 12, 2001 in known deposition areas in New York Harbor (NYH), we characterized a unique suite of geochemical-textural tracers that allow us to both identify and quantify the input of WTC derived material to adjacent areas in the Hudson River estuary. Scanning electron microscopy coupled with energy dispersive spectroscopy revealed two chemically distinct (Si-rich and Ca-rich) rod-like features (40-200 æm in length) in both ash and sediment samples. The Si-rich rods are consistent with a fiberglass parent material while the Ca-rich rods originate from gypsum. An 87Sr/86Sr ratio for the ash material of 0.7088 (n=2) coupled with Ca/Sr (wt. ratio) ranging from 260-300 suggest that the ash material analyzed is approximately 70% gypsum. As a function of depth within the sediment core, correlations exist between the measured activities of 7Be (a naturally occurring short-lived radionuclide), elemental weight-percent ratios of Ca/Sr, and the isotopic ratios of 87Sr/86Sr ratios. . These combined isotopic approaches allow us to constrain the timing (via 7Be), and the composition and amount (via 87Sr/86Sr and Ca/Sr) of WTC material input into the NYH sediments. These down-core isotope-ratio profiles can be described by a mixing line between background NYH 87Sr/86Sr ratios (>0.724) and the WTC derived ash material. The geochemical-textural tracers associated with the WTC terrorist attack may provide a potential tool for assessing the fate and transport of WTC material in the Lower Hudson River and aid in assessing the environmental and human health impacts of the WTC catastrophe.

Stable Ca Isotopes in Tamarix aphylla Tree Rings, Death Valley, California

NASA Astrophysics Data System (ADS)

Yang, W.; Depaolo, D. J.; Ingram, B. L.; Owens, T. L.

2008-12-01

As a dune stabilizer and windbreak, Tamarix aphylla is an exotic perennial and evergreen tree in Death Valley. Its tap roots can reach down to 30 m depth and sub-superficial side roots may reach 50 m horizontally. The species can store large amounts of water in its roots and undergoes high evapotranspiration. Since Tamarix aphylla is a perennial tree growing in desert environments and its roots reach deep to the water table, it could be a proxy for desert ecological and hydrologic systems through time. We measured Ca isotopes in the soluble fraction of 8 tree ring samples from a 50-year-old specimen growing on an alluvial fan in Death Valley near Furnace Creek. Previous studies (Yang et al, GCA 60, 1996) indicate that this tree's rings contain high sulfur concentrations (4-6% expressed as sulfate) with chemical composition of CaSO4 (0.15-0.62 H2O). The δ34S values of soluble sulfate increase from +13.5 to +18 permil VCDT from the core to the bark, which are interpreted as reflecting deeper sulfate sources as the tree grew. The δ13C variations of the tree-ring cellulose (-27.6 to -24.0 permil VPDB) reflect changes in the local precipitation and show that Tamarix aphylla undergoes C3 photosynthesis. The δ44Ca for the soluble sulfate Ca through the tree-ring section, which covers a time period from 1945 to 1993, have an average value -2.52 permil (-3.4 permil relative to seawater). Only small variations are observed, from -2.69 to -2.28; the highest value (for 1990) occurs near the end of an extended drought. These are the first measurements of tree rings, but the low δ44Ca values are consistent with previous measurements of beech roots and stems from a temperate forest (Page et al., Biogeochem. 88, 2008). In our case, the tree has only one Ca source, which is expected to be isotopically uniform and similar to both local rainfall and limestones (δ44Ca ~ -0.6 permil), and with the minimal vegetation and extensive deep root system it is unlikely that there is a significant depletion of soil Ca due to plant uptake. Thus the Ca isotopic fractionation between trunk and source (ΔCa = -2 permil) is clearly defined by the data. By analogy to the results of Page et al., the Ca fractionation between root and source may be larger (ΔCa ~ -3 permil). This biological Ca isotope fractionation is no doubt due to transport processes during root uptake of Ca, but the magnitude is significantly larger than that observed for inorganic processes such as mineral precipitation or aqueous diffusion. The slight increase in δ44Ca in drought conditions suggests that when the tree is stressed there may be less Ca isotope fractionation, either because the Ca is held more tightly in small pores in the soil, or because the available Ca pool shrinks such that the soil Ca starts to shift to more positive δ44Ca values due to depletion of light Ca by the plant. The slowly accumulating database on Ca isotopes in plants continues to suggest that systematic Ca isotope studies may be fruitful for understanding cation transport in plants, and soil ecological conditions in general.

Two mantle domains and the time scales of fluid transfer beneath the Vanuatu arc

NASA Astrophysics Data System (ADS)

Turner, Simon P.; Peate, David W.; Hawkesworth, Chris J.; Eggins, Stephen M.; Crawford, Anthony J.

1999-11-01

U-Th isotope disequilibria can provide constraints on the time elapsed since fluid addition to the mantle wedge beneath island arcs. The Vanuatu arc offers new insights into these processes because Pb isotopes there are not dominated by components from the subducting plate and so preserve the signatures of the mantle wedge. The Pb isotope data document the presence of separate Pacific and Indian mantle domains beneath the arc volcanoes. The Indian mantle was brought beneath the central part of the arc from the backarc by collision with the D'Entrecasteaux Ridge, resulting in a slowing of subduction there. The distinction in the mantle wedge composition is also uniquely apparent in U-Th isotope data, which define two subparallel arrays on the U-Th equiline diagram, one anchored to high U/Th Pacific mantle and the other to lower U/Th Indian mantle. These data provide clear evidence of the effects of variable mantle composition on U-Th isotope disequilibria. We argue that such arrays faithfully record the time elapsed since fluid release from the subducting plate. The data indicate that this occurred ca. 16 ka in the area of collision and slow subduction, but ca. 60 ka where the rate of subduction is substantially faster. This suggests a link between the rate of subduction and the time elapsed since fluid release.

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

NASA Astrophysics Data System (ADS)

Moynier, Frédéric; Fujii, Toshiyuki

2017-03-01

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

Titanium stable isotope investigation of magmatic processes on the Earth and Moon

NASA Astrophysics Data System (ADS)

Millet, Marc-Alban; Dauphas, Nicolas; Greber, Nicolas D.; Burton, Kevin W.; Dale, Chris W.; Debret, Baptiste; Macpherson, Colin G.; Nowell, Geoffrey M.; Williams, Helen M.

2016-09-01

We present titanium stable isotope measurements of terrestrial magmatic samples and lunar mare basalts with the aims of constraining the composition of the lunar and terrestrial mantles and evaluating the potential of Ti stable isotopes for understanding magmatic processes. Relative to the OL-Ti isotope standard, the δ49Ti values of terrestrial samples vary from -0.05 to +0.55‰, whereas those of lunar mare basalts vary from -0.01 to +0.03‰ (the precisions of the double spike Ti isotope measurements are ca. ±0.02‰ at 95% confidence). The Ti stable isotope compositions of differentiated terrestrial magmas define a well-defined positive correlation with SiO2 content, which appears to result from the fractional crystallisation of Ti-bearing oxides with an inferred isotope fractionation factor of ΔTi49oxide-melt = - 0.23 ‰ ×106 /T2. Primitive terrestrial basalts show no resolvable Ti isotope variations and display similar values to mantle-derived samples (peridotite and serpentinites), indicating that partial melting does not fractionate Ti stable isotopes and that the Earth's mantle has a homogeneous δ49Ti composition of +0.005 ± 0.005 (95% c.i., n = 29). Eclogites also display similar Ti stable isotope compositions, suggesting that Ti is immobile during dehydration of subducted oceanic lithosphere. Lunar basalts have variable δ49Ti values; low-Ti mare basalts have δ49Ti values similar to that of the bulk silicate Earth (BSE) while high-Ti lunar basalts display small enrichment in the heavy Ti isotopes. This is best interpreted in terms of source heterogeneity resulting from Ti stable isotope fractionation associated with ilmenite-melt equilibrium during the generation of the mantle source of high-Ti lunar mare basalts. The similarity in δ49Ti between terrestrial samples and low-Ti lunar basalts provides strong evidence that the Earth and Moon have identical stable Ti isotope compositions.

The role of soil biogeochemistry in wine taste: Soil factors influencing grape elemental composition, photosynthetic biomarkers and Cu/Zn isotopic signature of Vitis vinifera

NASA Astrophysics Data System (ADS)

Blotevogel, Simon; Oliva, Priscia; Darrozes, José; Viers, Jérôme; Audry, Stéphane; Courjault-Radé, Pierre; Orgogozo, Laurent; Le Guedard, Marina; Schreck, Eva

2015-04-01

Understanding the influence of soil composition in wine taste is of great economic and environmental interest in France and around the world. Nevertheless the impact of soil composition on wine taste is still controversially discussed. Since inorganic soil components do not have a proper taste and do not enter the plant anyway, their influence needs to be induced by nutrient absorption and its impact on plant functioning and grape composition. Indeed recent development of geological tracers of origin proof the existence of soil chemical and isotopic signatures in wine. However, type and scale of the impact of soil composition on wine taste are not well understood yet, and little experimental evidence exists due to the complexity of mechanisms involved. Thus, to provide evidence for the impact of soil composition on grape composition and potentially wine taste, we studied soil and plant material from two relevant vineyards (Soave, Italia). On those two directly adjacent vineyards, two different wines are produced with the same plant material and cultivation techniques. The vineyards only differ by their underlying bedrock - limestone versus basaltic rock - and thus present suitable conditions for investigating the impact of soil composition on grapes and wine. Pedological and mineralogical parameters were analyzed for the two vineyards whereas chemical extractions (citrate, CaCl2) were performed to determine nutrient bioavailability in both soils. Elemental compositions were determined by ICP-MS analyses in different compartments (soils, vine leaves and grapes). Isotopic fractionation of Cu and Zn was investigated in various samples as source tracers and in order to better understand fractionation mechanisms involved. Finally, plant health was studied using the Omega-3 biomarker which determines the fatty acid composition in vine leaves, directly involved in photosynthetic processes. Results show that the vineyards are characterized by two different soil types due to the geological difference. These soils differ in elemental compositions and bioavailability of mineral nutrients, preconditions for a potential influence on plants and wine. Elemental ratios of soils are partly transmitted to leaves and grapes of correspondent plants, including nutrients such as Ca. Plant photosynthetic functioning is significantly better on the limestone vineyard due to lower Cu bioavailability: Omega-3 values are negatively linked to Cu bioavailability in corresponding soils. These observations suggest a difference in organic molecule synthesis depending on the vineyard soil, which might include components relevant for taste and fermentation. Cu and Zn isotopic ratios do not differ between both soils. The main fractionation of Cu and Zn isotopes occurs at the soil-plant interface making those isotopes suitable tracers for uptake mechanisms. As a result Zn isotope ratios reveal a strong recycling of Zn in the soil-plant continuum. Our results show a significant influence of soil composition on grape composition, plant biochemistry and potentially wine taste. Determination of organic and sensorial composition of grapes and wine is ongoing and will be discussed in further communications.

Petrography, mineralogy, and Mg isotope composition of VICTA: A vigarano CaAl4O7-bearing type A inclusion

NASA Technical Reports Server (NTRS)

Greenwood, R. C.; Morse, A.; Long, J. V. P.

1993-01-01

Thermodynamic calculations predict that Ca-dialuminate (CaAl4O7) condenses from a cooling gas of solar composition after hibonite and before melilite. Although Ca-dialuminate has now been recorded from Ca Al-rich inclusions (CAI's) in at least 9 meteorites, compared to hibonite it is a relatively rare phase. As pointed out by Michel-Levy et al., the absence of Ca-dialuminate from most hibonite-bearing inclusions poses a serious problem for the condensation model of CAI formation. Here we describe an inclusion which contains abundant CA-dialuminate partially altered to a hercynite-rich (FeAl2O4) assemblage. The evidence from VICTA indicates that compared to all other phases in type A inclusions, Ca-dialuminate is the most susceptible to secondary alteration; a feature which may explain its restricted occurrence. Unaltered Ca-dialuminate and melilite in VICTA display excess Mg-26 indicative of in situ decay of Al-26.

Microbial, Physical and Chemical Drivers of COS and 18O-CO2 Exchange in Soils

NASA Astrophysics Data System (ADS)

Meredith, L. K.; Boye, K.; Whelan, M.; Pang, E.; von Sperber, C.; Brueggemann, N.; Berry, J. A.; Welander, P. V.

2015-12-01

Carbonyl sulfide (COS) and the oxygen isotope composition (δ18O) of CO2 are potential tools for differentiating the contributions of photosynthesis and respiration to the balance of global carbon cycling. These processes are coupled at the leaf level via the enzyme carbonic anhydrase (CA), which hydrolyzes CO2 in the first biochemical step of the photosynthetic pathway (CO2 + H2O ⇌ HCO3- + H+) and correspondingly structural analogue COS (COS + H2O → CO2 + H2S). CA also accelerates the exchange of oxygen isotopes between CO2 and H2O leading to a distinct isotopic imprint [1]. The biogeochemical cycles of these tracers include significant, yet poorly characterized soil processes that challenge their utility for probing the carbon cycle. In soils, microbial CA also hydrolyze COS and accelerate O isotope exchange between CO2 and soil water. Soils have been observed to emit COS by undetermined processes. To account for these soil processes, measurements are needed to identify the key microbial, chemical, and physical factors. In this study, we survey COS and δ18O exchange in twenty different soils spanning a variety of biomes and soil properties. By comparing COS fluxes and δ18O-CO2 values emitted from moist soils we investigate whether the same types of CA catalyze these two processes. Additionally, we seek to identify the potential chemical drivers of COS emissions by measuring COS fluxes in dry soils. These data are compared with soil physical (bulk density, volumetric water content, texture), chemical (pH, elemental analysis, sulfate, sulfur K-edge XANES), and microbial measurements (biomass and phylogeny). Furthermore, we determine the abundance and diversity of CA-encoding genes to directly link CA with measured soil function. This work will define the best predictors for COS fluxes and δ18O-CO2 values from our suite of biogeochemical measurements. The suitability of identified predictor variables can be tested in follow-up studies and applied for modeling purposes. References: [1] Von Sperber, C., Weiler, M. and Brüggemann, N.: The effect of soil moisture, soil particle size, litter layer and carbonic anhydrase on the oxygen isotopic composition of soil-released CO2, Eur. J. Soil Sci., 66(3), doi:10.1111/ejss.12241, 2015.

Ca and Mg isotope constraints on the origin of Earth's deepest δ13 C excursion

NASA Astrophysics Data System (ADS)

Husson, Jon M.; Higgins, John A.; Maloof, Adam C.; Schoene, Blair

2015-07-01

Understanding the extreme carbon isotope excursions found in carbonate rocks of the Ediacaran Period (635-541 Ma), where δ13 C of marine carbonates (δ13 Ccarb) reach their minimum (- 12 ‰) for Earth history, is one of the most vexing problems in Precambrian geology. Known colloquially as the 'Shuram' excursion, the event has been interpreted by many as a product of a profoundly different Ediacaran carbon cycle. More recently, diagenetic processes have been invoked, with the very negative δ13 C values of Ediacaran carbonates explained via meteoric alteration, late-stage burial diagenesis or growth of authigenic carbonates in the sediment column, thus challenging models which rely upon a dramatically changing redox state of the Ediacaran oceans. Here we present 257 δ 44 / 40 Ca and 131 δ26 Mg measurements, along with [Mg], [Mn] and [Sr] data, from carbonates of the Ediacaran-aged Wonoka Formation (Fm.) of South Australia to bring new isotope systems to bear on understanding the 'Shuram' excursion. Data from four measured sections spanning the basin reveal stratigraphically coherent trends, with variability of ∼1.5‰ in δ26 Mg and ∼1.2‰ in δ 44 / 40 Ca. This Ca isotope variability dwarfs the 0.2-0.3 ‰ change seen coeval with the Permian-Triassic mass extinction, the largest recorded in the rock record, and is on par with putative changes in the δ 44 / 40 Ca value of seawater seen over the Phanerozoic Eon. Changes in both isotopic systems are too large to explain with changes in the isotopic composition of Ca and Mg in global seawater given modern budgets and residence times, and thus must be products of alternative processes. Relationships between δ 44 / 40 Ca and [Sr] and δ26 Mg and [Mg] are consistent with mineralogical control (e.g., aragonite vs. calcite, limestone vs. dolostone) on calcium and magnesium isotope variability. The most pristine samples in the Wonoka dataset, preserving Sr concentrations (in the 1000s of ppm range) and δ 44 / 40 Ca values inherited from an originally aragonitic polymorph, have δ13 Ccarb of - 8 ‰ to - 7 ‰ , thereby providing strong geochemical evidence that extremely negative δ13 Ccarb values are primary products of the Ediacaran surface environment.

Calcareous dinoflagellate cysts as recorder of Late Cretaceous paleo-temperature using Sr/Ca thermometry and δ44/40Caseawater

NASA Astrophysics Data System (ADS)

Gussone, N. C.; Friedrich, O.

2017-12-01

We evaluate the potential of calcareous dinoflagellates as archives for Sr/Ca-based paleo-temperature reconstructions and δ44/40Caseawater fluctuations on sediments from Ocean Drilling Program Expedition 113 (Hole 690C, Weddell Sea, Southern Ocean). Between 73 and 68 Ma, Sr/Ca ratios of two Cretaceous dinoflagellate species, Pirumella krasheninnikovii and Orthopithonella globosa show a pronounced decrease, consistent with a significant drop in sea-surface temperature as reflected by the δ18O of planktic foraminifers. The apparent temperature sensitivity of the dinoflagellate cysts' Sr/Ca is 0.06 and 0.08 mmol/mol °C-1, using δ18O-derived paleo sea-surface temperatures, which is significant and large enough to resolve paleoenvironmental temperature changes at current analytical precision. As the chemical composition of the cyst calcite appears to have a good preservability, the Sr/Ca of calcareous dinoflagellates has a high potential to serve as paleo temperature proxy. The Ca isotope composition of the two dinoflagellate species shows identical trends of increasing δ44/40Ca between 73 and 67 Ma. The planktic foraminifer Archaeoglobigerina australis and the benthic foraminifer Nuttallides truempyi reveal the same increase but are offset relative to the dinoflagellates by about +0.5‰, due to species-specific Ca isotope fractionation. Bulk carbonate sediment shows significant scatter, likely caused by changes in faunal composition and does not satisfyingly reproduce the trend revealed by the dinoflagellate and foraminifer records. These observations demonstrate the importance of taxon-specific records and careful determination of fractionation factors of selected archives and highlight complications arising from utilizing less suitable archives, such as bulk sediments, for δ44/40Caseawater reconstructions. Our records indicate strong changes in the oceanic Ca carbonate chemistry associated with the temperature decrease towards the end of the Cretaceous.

Study of thermochemical sulfate reduction mechanism using compound specific sulfur isotope analysis

NASA Astrophysics Data System (ADS)

Meshoulam, Alexander; Ellis, Geoffrey S.; Said Ahmad, Ward; Deev, Andrei; Sessions, Alex L.; Tang, Yongchun; Adkins, Jess F.; Liu, Jinzhong; Gilhooly, William P.; Aizenshtat, Zeev; Amrani, Alon

2016-09-01

The sulfur isotopic fractionation associated with the formation of organic sulfur compounds (OSCs) during thermochemical sulfate reduction (TSR) was studied using gold-tube pyrolysis experiments to simulate TSR. The reactants used included n-hexadecane (n-C16) as a model organic compound with sulfate, sulfite, or elemental sulfur as the sulfur source. At the end of each experiment, the S-isotopic composition and concentration of remaining sulfate, H2S, benzothiophene, dibenzothiophene, and 2-phenylthiophene (PT) were measured. The observed S-isotopic fractionations between sulfate and BT, DBT, and H2S in experimental simulations of TSR correlate well with a multi-stage model of the overall TSR process. Large kinetic isotope fractionations occur during the first, uncatalyzed stage of TSR, 12.4‰ for H2S and as much as 22.2‰ for BT. The fractionations decrease as the H2S concentration increases and the reaction enters the second, catalyzed stage. Once all of the oxidizable hydrocarbons have been consumed, sulfate reduction ceases and equilibrium partitioning then dictates the fractionation between H2S and sulfate (∼17‰). Experiments involving sparingly soluble CaSO4 show that during the second catalytic phase of TSR the rate of sulfate reduction exceeds that of sulfate dissolution. In this case, there is no apparent isotopic fractionation between source sulfate and generated H2S, as all of the available sulfate is effectively reduced at all reaction times. When CaSO4 is replaced with fully soluble Na2SO4, sulfate dissolution is no longer rate limiting and significant S-isotopic fractionation is observed. This supports the notion that CaSO4 dissolution can lead to the apparent lack of fractionation between H2S and sulfate produced by TSR in nature. The S-isotopic composition of individual OSCs record information related to geochemical reactions that cannot be discerned from the δ34S values obtained from bulk phases such as H2S, oil, and sulfate minerals, and provide important mechanistic details about the overall TSR process.

Iron isotope biogeochemistry of Neoproterozoic marine shales

NASA Astrophysics Data System (ADS)

Kunzmann, Marcus; Gibson, Timothy M.; Halverson, Galen P.; Hodgskiss, Malcolm S. W.; Bui, Thi Hao; Carozza, David A.; Sperling, Erik A.; Poirier, André; Cox, Grant M.; Wing, Boswell A.

2017-07-01

Iron isotopes have been widely applied to investigate the redox evolution of Earth's surface environments. However, it is still unclear whether iron cycling in the water column or during diagenesis represents the major control on the iron isotope composition of sediments and sedimentary rocks. Interpretation of isotopic data in terms of oceanic redox conditions is only possible if water column processes dominate the isotopic composition, whereas redox interpretations are less straightforward if diagenetic iron cycling controls the isotopic composition. In the latter scenario, iron isotope data is more directly related to microbial processes such as dissimilatory iron reduction. Here we present bulk rock iron isotope data from late Proterozoic marine shales from Svalbard, northwestern Canada, and Siberia, to better understand the controls on iron isotope fractionation in late Proterozoic marine environments. Bulk shales span a δ 56Fe range from -0.45 ‰ to +1.04 ‰ . Although δ 56Fe values show significant variation within individual stratigraphic units, their mean value is closer to that of bulk crust and hydrothermal iron in samples post-dating the ca. 717-660 Ma Sturtian glaciation compared to older samples. After correcting for the highly reactive iron content in our samples based on iron speciation data, more than 90% of the calculated δ 56Fe compositions of highly reactive iron falls in the range from ca. -0.8 ‰ to +3 ‰ . An isotope mass-balance model indicates that diagenetic iron cycling can only change the isotopic composition of highly reactive iron by < 1 ‰ , suggesting that water column processes, namely the degree of oxidation of the ferrous seawater iron reservoir, control the isotopic composition of highly reactive iron. Considering a long-term decrease in the isotopic composition of the iron source to the dissolved seawater Fe(II) reservoir to be unlikely, we offer two possible explanations for the Neoproterozoic δ 56Fe trend. First, a decreasing supply of Fe(II) to the ferrous seawater iron reservoir could have caused the reservoir to decrease in size, allowing a higher degree of partial oxidation, irrespective of increasing environmental oxygen levels. Alternatively, increasing oxygen levels would have led to a higher proportion of Fe(II) being oxidized, without decreasing the initial size of the ferrous seawater iron pool. We consider the latter explanation as the most likely. According to this hypothesis, the δ 56Fe record reflects the redox evolution of Earth's surface environments. δ 56Fe values in pre-Sturtian samples significantly heavier than bulk crust and hydrothermal iron imply partial oxidation of a ferrous seawater iron reservoir. In contrast, mean δ 56Fe values closer to that of hydrothermal iron in post-Sturtian shales reflects oxidation of a larger proportion of the ferrous seawater iron reservoir, and by inference, higher environmental oxygen levels. Nevertheless, significant iron isotopic variation in post-Sturtian shales suggest redox heterogeneity and possibly a dominantly anoxic deep ocean, consistent with results from recent studies using iron speciation and redox sensitive trace metals. However, the interpretation of generally increasing environmental oxygen levels after the Sturtian glaciation highlights the need to better understand the sensitivity of different redox proxies to incremental changes in oxygen levels to enable us to reconcile results from different paleoredox proxies.

Evidence of subduction and crust-mantle mixing from a single diamond

NASA Astrophysics Data System (ADS)

Schulze, Daniel J.; Harte, Ben; Valley, John W.; Channer, Dominic M. DeR.

2004-09-01

Cathodoluminescence (CL) imaging of polished sections of a diamond from the Guaniamo region of Venezuela suggests a history of the diamond involving two periods of growth separated by a period of resorption and possibly brittle deformation. In situ electron probe analysis of multiple eclogitic garnet inclusions reveals a correlation between garnet composition and location in the stone. An early-formed garnet in the diamond core has higher Ca/(Ca+Mg) and lower Mg/(Mg+Fe) values than later garnets associated with the second period of diamond growth. This variation conforms to an extensive trend of variation in the suite of eclogitic garnets extracted from Venezuelan diamonds. The diamond is zoned in carbon isotope composition (in situ secondary ion mass spectrometry, SIMS, data). The core compositions ( δ13C PDB), corresponding to the first stage of growth, average -17.7‰. The second period of growth is apparently in two sub-sets of CL zones with mean values of -13.0‰ and -7.9‰. Nitrogen contents of diamond are low (30-300 atomic ppm) and do not correlate with carbon isotope composition. Oxygen isotope ratios of the garnet inclusions are elevated substantially above those expected for "common mantle"; δ18O VSMOW of early garnet is approximately +10.5‰ and two late garnets average +8.8‰. The evolutionary trend of magnesium enrichment in garnet is unlikely to represent igneous fractionation. The stable isotope data are consistent with diamond formation in subducted meta-basic rocks that had interacted with sea water at low temperatures at or near the sea floor and contained a substantial biogenic carbon component. During or following subduction, diamonds continued to form in an evolving system that was progressively modified by interaction with mantle material.

Nd Isotope and U-Th-Pb Age Mapping of Single Monazite Grains by Laser Ablation Split Stream Analysis

NASA Astrophysics Data System (ADS)

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

2015-12-01

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

A molecular stable carbon isotope study of organic matter in immature Miocene Monterey sediments, Pismo basin

NASA Astrophysics Data System (ADS)

Schouten, Stefan; Schoell, Martin; Rijpstra, W. Irene C.; Sinninghe Damsté, Jaap S.; de Leeuw, Jan W.

1997-05-01

The 300 m section of the Miocene Monterey Formation outcropping at Shell Beach (Pismo basin; ca. 15-11 Ma) is composed of calcareous phosphatic (15.1-14.5 Ma) and siliceous facies (14.5-11.0 Ma). An objective of this paper is to document lateral paleoenvironmental changes in the Miocene Moneterey Formation by comparing the Shell Beach (SB) profile with the Naples Beach (NB) section in the Santa Barbara-Ventura basin (Schouten et al., 1997) which is ˜80 km to the south. Eight samples (one sample representing, on average, a time period of ca. 2000 y) from this section were analyzed for variations of extractable biomarkers and their carbon isotopic signatures as indicators for paleoenvironmental change during the Miocene. Saturated hydrocarbons present include 28,30-dinorhopane, phytane, n-alkanes (C 17sbnd C 31), lycopane, and 17β,21β(H)-homohopane. The biomarkers released after desulfurization of the polar fractions predominantly consist of phytane, 2,6,10,14-tetramethyl-7-(3-methylpentyl)pentadecane, C 17sbnd C 31n-alkanes, regular 5α- and 5β-steranes, dinosteranes, and (22R)-17β,21β(H)-pentakishomohopane. Steranes have similar carbon isotopic compositions (-25 to -27‰) throughout the section and are isotopically similar at both sites, indicating laterally similar and vertically stable environmental conditions for algae living in the upper part of the photic zone. Free and S-bound n-alkanes at SB mainly originate from marine organisms and not from terrestrial sources as in the NB section. S-bound pentakishomohopane is ca. 1-4‰ depleted compared to the steranes and is thought to be derived from the deeper water dwelling cyanobacteria. These findings are consistent with stable carbon isotopic data obtained for these compounds from Middle Miocene Monterey sediments at Naples Beach and indicates similar environmental conditions in the depositional environments of the Santa Barbara-Ventura and the Pismo basin. S-bound highly branched isoprenoids have, at both sites, different isotopic compositions indicating the presence of different diatom species, special growth conditions, or different bloom periods in the Pismo basin. The carbon isotopic composition of 28,30-dinorhopane shifts to more depleted values up section, suggesting that the dinorhopane-synthesizing organism or organisms live on CO 2, which is isotopically influenced by methane production and oxidation. The C 31 hopane is enriched by 1-4‰ in 13C compared to other hopanes and steranes. Specific bacteria, possibly heterotrophs, may have been the organisms producing this compound.

Calcium and titanium isotopes in refractory inclusions from CM, CO, and CR chondrites

NASA Astrophysics Data System (ADS)

Kööp, Levke; Davis, Andrew M.; Krot, Alexander N.; Nagashima, Kazuhide; Simon, Steven B.

2018-05-01

Previous studies have shown that CV and CM chondrites incorporated Ca, Al-rich inclusions (CAIs) with different isotopic characteristics, which may represent different snapshots in the isotopic evolution of the early Solar System. To better understand how the isotopic characteristics of CAIs vary between different chondrite groups, we have studied calcium and titanium isotopes in CAIs from CM, CO, and CR chondrites. We show that all three chondrite groups contain CAIs with large anomalies in 48Ca and/or 50Ti (10s of ‰ or 100s of ε-units) as well as CAIs with no anomalies resolved beyond measurement uncertainties. Isotopically, the anomalous CO and CR chondrite CAIs resemble the platy hibonite crystals (PLACs) from CM chondrites, but they are more mineralogically complex. The new data are consistent with the well-established mutual exclusivity relationship between incorporation of 26Al and the presence of large anomalies in 48Ca and 50Ti. The two highly anomalous CO chondrite CAIs have correlated anomalies in 46Ti and 50Ti, while most other highly anomalous CAIs do not. This result could indicate that the reservoir with coupled 46Ti and 50Ti that was sampled by bulk meteorites and CV chondrite CAIs already existed before arrival and/or homogeneous distribution of 26Al in the protoplanetary disk. Among the studied CM chondrite CAIs are ten spinel-hibonite inclusions (SHIBs) with known oxygen isotopic compositions. Our results show that these objects sampled a reservoir that was well-mixed in oxygen, calcium, and titanium isotopes. We further show that SHIBs tend to be slightly enriched in the heavy calcium isotopes, suggesting that their formation history was different from CV chondrite CAIs.

Essentials of iron, chromium, and calcium isotope analysis of natural materials by thermal ionization mass spectrometry

USGS Publications Warehouse

Fantle, M.S.; Bullen, T.D.

2009-01-01

The use of isotopes to understand the behavior of metals in geological, hydrological, and biological systems has rapidly expanded in recent years. One of the mass spectrometric techniques used to analyze metal isotopes is thermal ionization mass spectrometry, or TIMS. While TIMS has been a useful analytical technique for the measurement of isotopic composition for decades and TIMS instruments are widely distributed, there are significant difficulties associated with using TIMS to analyze isotopes of the lighter alkaline earth elements and transition metals. Overcoming these difficulties to produce relatively long-lived and stable ion beams from microgram-sized samples is a non-trivial task. We focus here on TIMS analysis of three geologically and environmentally important elements (Fe, Cr, and Ca) and present an in-depth look at several key aspects that we feel have the greatest potential to trouble new users. Our discussion includes accessible descriptions of different analytical approaches and issues, including filament loading procedures, collector cup configurations, peak shapes and interferences, and the use of isotopic double spikes and related error estimation. Building on previous work, we present quantitative simulations, applied specifically in this study to Fe and Ca, that explore the effects of (1) time-variable evaporation of isotopically homogeneous spots from a filament and (2) interferences on the isotope ratios derived from a double spike subtraction routine. We discuss how and to what extent interferences at spike masses, as well as at other measured masses, affect the double spike-subtracted isotope ratio of interest (44Ca/40Ca in the case presented, though a similar analysis can be used to evaluate 56Fe/54Fe and 53Cr/52Cr). The conclusions of these simulations are neither intuitive nor immediately obvious, making this examination useful for those who are developing new methodologies. While all simulations are carried out in the context of a specific isotope system, it should be noted that the same methods can be used to evaluate any isotope system of interest. ?? 2008 Elsevier B.V.

Environmental controls on sulfur isotopic composition of sulfide minerals in seep carbonates from the South China Sea

NASA Astrophysics Data System (ADS)

Gong, S.; Li, N.; Liang, Q.; Chen, D.; Feng, D.

2017-12-01

Authigenic carbonates and pyrite associated with sulfate-driven anaerobic oxidation of methane (AOM) at methane seeps provide archives to explore the biogeochemical processes involved and seepage dynamics over time. The wide range and extremely high δ34Spy value of authigenic sulfide has been used to trace the AOM-related processes. However, the detail mechanism for this is unknown. We proposed the δ34Spy characteristics result from high sulfate reduction rate and its competition with sulfate supply rate. To test this hypothesis, we investigated Mo content, Sr/Ca and Mg/Ca ratios, pyrite content, and its sulfur isotopic compositions in methane-derived carbonates from Site F and Haima in northern South China Sea. Calcite and aragonite were distinguished through the Sr/Ca and Mg/Ca ratios. The data show that aragonites are always associated with relatively low δ34Spy values compared to calcites. The Mo content and pyrite have good linear correlations in both aragonites and calcites, and aragonites have more positive slope than calcites. This indicates that there is more Mo available from seawater during the aragonite precipitation. The data suggest that the low δ34Spy values are formed at higher supply rate of sulfate under relatively open system, and high δ34Spy values result from a deep sulfate methane transition zone where dissolve sulfate near to complete exhausted via AOM. The combination of a detailed elemental study of authigenic carbonate with sulfur isotopes of sulfide minerals in carbonates are promising tools for reconstructing the dynamics of seep intensities in modern and, potentially, geological record.

Isotopic Measurements in CAIs with the Nanosims: Implications to the understanding of the Formation process of Ca, Al-Rich Inclusions

NASA Technical Reports Server (NTRS)

Ito, M.; Messenger, S.; Walker, Robert M.

2007-01-01

Ca, Al-rich Inclusions (CAIs) preserve evidence of thermal events that they experienced during their formation in the early solar system. Most CAIs from CV and CO chondrites are characterized by large variations in O-isotopic compositions of primary minerals, with spinel, hibonite, and pyroxene being more O-16-rich than melilite and anorthite, with delta 17, O-18 = approx. -40%o (DELTA O-17 = delta O-17 - 0.52 x delta O-18 = approx. - 20%o ). These anomalous compositions cannot be accounted for by standard mass dependent fractionation and diffusive process of those minerals. It requires the presence of an anomalous oxygen reservoir of nucleosynthetic origin or mass independent fractionations before the formation of CAIs in the early solar system. The CAMECA NanoSIMS is a new generation ion microprobe that offers high sensitivity isotopic measurements with sub 100 nm spatial resolution. The NanoSIMS has significantly improved abilities in the study of presolar grains in various kind of meteorites and the decay products of extinct nuclides in ancient solar system matter. This instrument promises significant improvements over other conventional ion probes in the precision isotopic characterization of sub-micron scales. We report the results of our first O isotopic measurements of various CAI minerals from EK1-6-3 and 7R19-1(a) utilizing the JSC NanoSIMS 50L ion microprobe. We evaluate the measurement conditions, the instrumental mass fractionation factor (IMF) for O isotopic measurement and the accuracy of the isotopic ratio through the analysis of a San Carlos olivine standard and CAI sample of 7R19-1(a).

Petrogenesis of High-CaO Lavas Recovered from Hawaii Scientific Drilling Project

NASA Astrophysics Data System (ADS)

Huang, S.

2015-12-01

Mauna Kea tholeiitic lavas recovered from Hawaii Scientific Drilling Project (HSDP) can be divided into three groups based on their major element compositions: High-SiO2, Low-SiO2, and High-CaO groups. Detailed geochemical and isotopic studies have been focused on the High- and Low-SiO2 group lavas, and High-CaO lavas were not well studied because they were not included in the original reference suite samples. Here we report trace element compositions determined on a suite of High-CaO glasses, and use these data to constrain the petrogenesis of High-CaO lavas. When normalized to Low-SiO2 lavas, High-CaO lavas form a U-shaped trace element pattern. That is, High-CaO lavas are enriched in both the most (Nb, Th) and the least (Sc, V) incompatible elements. This trace element difference is best explained if High-CaO parental magma represents a mixture of low degree partial melt of the Low-SiO2 mantle source and a mafic cumulate component. This mafic cumulate must be clinopyroxene-rich, and it could be delaminated mafic cumulate formed under arcs during continent formation, lower continental crust, or lower oceanic crust.Mauna Kea tholeiitic lavas recovered from Hawaii Scientific Drilling Project (HSDP) can be divided into three groups based on their major element compositions: High-SiO2, Low-SiO2, and High-CaO groups. Detailed geochemical and isotopic studies have been focused on the High- and Low-SiO2 group lavas, and High-CaO lavas were not well studied because they were not included in the original reference suite samples. Here we report trace element compositions determined on a suite of High-CaO glasses, and use these data to constrain the petrogenesis of High-CaO lavas. When normalized to Low-SiO2 lavas, High-CaO lavas form a U-shaped trace element pattern. That is, High-CaO lavas are enriched in both the most (Nb, Th) and the least (Sc, V) incompatible elements. This trace element difference is best explained if High-CaO parental magma represents a mixture of low degree partial melt of the Low-SiO2 mantle source and a mafic cumulate component. This mafic cumulate must be clinopyroxene-rich, and it could be delaminated mafic cumulate formed under arcs during continent formation, lower continental crust, or lower oceanic crust.

Sulphur and oxygen isotopic composition of sulphates in springs feeding the Wieprz river and other springs of Lublin Upland and Roztocze.

PubMed

Trembaczowski, A; Swieca, A

2002-12-01

Springs on Roztocze and Lublin Upland have been studied. Isotopic data are compared with data of chemical analyses. The results of studies allow us to distinguish five types of groundwaters. The differentiation is based upon different lithology; opokas, gaizes, sandy-silty-clay deposits, sands with shell sandstones, marly opokas, marly limestones and 'soft limestones of chalk type. A correlation can be observed between delta34S and the concentration of Ca or Mg ions also a correlation between HCO3- ion concentration and delta18O in sulphates. Probably these correlations are the result of some simultaneous processes, which occur in groundwater. The seasonal variations of the isotopic composition and sulphate concentration were observed in four springs feeding the upper Wieprz. The variations were simultaneous and often similar in these springs. Probably, these variations are caused by the admixture of sulphates coming from shallow water layers (or leached from soil); however the variations of the groundwater level may also change chemical and isotopic composition in groundwater.

Evidence for distillation in the formation of HAL and related hibonite inclusions. [from Allende, Dhajala, and Murchison chondrites

NASA Technical Reports Server (NTRS)

Ireland, Trevor R.; Zinner, Ernst K.; Fahey, Albert J.; Esat, Tezer M.

1992-01-01

New Ca- and Ti-isotopic analyses of DH-H1, 7-404, and 7-971, and Mg-isotopic analyses on DH-H1 and 7-404 are reported. O-isotopic analyses of HAL, 7-404, 7-971, and a variety of other refractory inclusions from Murchison were made in order to establish the presence or absence of FUN O-isotopic systematics. A higonite-rich residue produced by the evaporation of kaersutite was analyzed for its trace-element and isotopic abundances to see if any of the characteristics of FUN hibonite inclusions can be produced by distillation in the laboratory. These data are then used to evaluate for all four inclusions the HAL-type formation models originally proposed by Allen et al. (1980) and Lee et al. (1980). The four inclusions were found to have very similar chemical and isotopic features. All are characterized by large Ce depletions and very low Mg, Ti, and V concentrations compared to other meteoritic hibonites. All four inclusions have delta(C-48) within error of -5 per mil. Ca-, Ti-, and O-isotopic compositions are fractionated with enrichments of the heavy isotopes, and the Ti-isotopic mass fractionation is inversely correlated with Ti concentration. It is concluded that the inclusions formed primarily as distillation residues in accord with the early conclusions.

Sr - an element shows the way - Applications of Sr isotopes for provenance, tracing and migration (Invited)

NASA Astrophysics Data System (ADS)

Prohaska, T.; Irrgeher, J.; Zitek, A.; Teschler Nicola, M.

2010-12-01

Strontium - named after the small Scottish town Strontian - as such is an element with little popularity. Firstly described by Martin Heinrich Klaproth in 1798, the metal is used in metallurgy to some extent whereas its compounds are interesting in glass industries, electronics and pyrotechnics. The element has chemical similarity to Ca and makes up 1/60 of the earth’s amount of the latter. Nonetheless, it is its isotopic composition which makes Sr so interesting for a large number of scientists. The natural composition of the four naturally occurring isotopes (84Sr, 86Sr 87Sr and 88Sr) varies in nature due to the radioactive decay of 87Rb to 87Sr. Thus, it was early recognized as geochronometer especially in Ca rich matrices. With increasing precision of applied methodology, the natural variation of the 87Sr/86Sr isotope ratio (analyzed at first mainly by thermal ionization mass spectrometry (TIMS)) became more and more popular in provenance studies. The natural variation of the ratio is mainly determined by the geological age and the original composition of the rock and can be used therefore as fingerprint of the local geology. The ratio is transferred with no significant fractionation via the water into plants and finally via the food chain into animal and human tissues (especially bones and teeth). As the element is chemically similar to Ca, it appears in most matrices. The use for provenance studies is supported by the fact that the long half life (4.8 x 1010 years) does not lead to an alteration during the time scales which are investigated (from recent samples to human or animal skeletal remains which date back up to 30.000 BC). The uniqueness of the system besides the natural variation is defined by the ubiquity in nature and the relatively high (and thus measurable) elemental concentration in most tissues. It was finally the advent of multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS) which augmented the number of applications presented for Sr isotope ratios simply supported by the fact that a higher statistical number of samples could be analyzed. Further supported by direct introductions systems such as laser ablation, the popularity of Sr in science has increased steadily. A number of fields of applications make nowadays use of the system so far: anthropology and archaeology as well as food science, chemical technology, forensic science, medicine or biology. The Sr isotope system will be presented along with analytical techniques applied. Selected examples making use of the natural Sr isotopic variation will be reported: Proof of provenance of food, forensic applications and migration studies on prehistoric cultures or modern biological systems. In addition, the application of enriched Sr isotope spikes will be presented. The spikes are administered in order to investigate Sr turnovers (e.g. as proxy for Ca in biomedical studies), marking tissues for tracing and migration experiments and investigating environmental processes.

Variability of 13C-labeling in plant leaves.

PubMed

Nguyen Tu, Thanh Thuy; Biron, Philippe; Maseyk, Kadmiel; Richard, Patricia; Zeller, Bernd; Quénéa, Katell; Alexis, Marie; Bardoux, Gérard; Vaury, Véronique; Girardin, Cyril; Pouteau, Valérie; Billiou, Daniel; Bariac, Thierry

2013-09-15

Plant tissues artificially labeled with (13)C are increasingly used in environmental studies to unravel biogeochemical and ecophysiological processes. However, the variability of (13)C-content in labeled tissues has never been carefully investigated. Hence, this study aimed at documenting the variability of (13)C-content in artificially labeled leaves. European beech and Italian ryegrass were subjected to long-term (13)C-labeling in a controlled-environment growth chamber. The (13)C-content of the leaves obtained after several months labeling was determined by isotope ratio mass spectrometry. The (13)C-content of the labeled leaves exhibited inter- and intra-leaf variability much higher than those naturally occurring in unlabeled plants, which do not exceed a few per mil. This variability was correlated with labeling intensity: the isotope composition of leaves varied in ranges of ca 60‰ and 90‰ for experiments that led to average leaf (13)C-content of ca +15‰ and +450‰, respectively. The reported variability of isotope composition in (13)C-enriched leaves is critical, and should be taken into account in subsequent experimental investigations of environmental processes using (13)C-labeled plant tissues. Copyright © 2013 John Wiley & Sons, Ltd.

Chromium isotope heterogeneity in the mantle

NASA Astrophysics Data System (ADS)

Xia, Jiuxing; Qin, Liping; Shen, Ji; Carlson, Richard W.; Ionov, Dmitri A.; Mock, Timothy D.

2017-04-01

To better constrain the Cr isotopic composition of the silicate Earth and to investigate potential Cr isotopic fractionation during high temperature geological processes, we analyzed the Cr isotopic composition of different types of mantle xenoliths from diverse geologic settings: fertile to refractory off-craton spinel and garnet peridotites, pyroxenite veins, metasomatised spinel lherzolites and associated basalts from central Mongolia, spinel lherzolites and harzburgites from North China, as well as cratonic spinel and garnet peridotites from Siberia and southern Africa. The δ53CrNIST 979 values of the peridotites range from - 0.51 ± 0.04 ‰ (2SD) to + 0.75 ± 0.05 ‰ (2SD). The results show a slight negative correlation between δ53Cr and Al2O3 and CaO contents for most mantle peridotites, which may imply Cr isotopic fractionation during partial melting of mantle peridotites. However, highly variable Cr isotopic compositions measured in Mongolian peridotites cannot be caused by partial melting alone. Instead, the wide range in Cr isotopic composition of these samples most likely reflects kinetic fractionation during melt percolation. Chemical diffusion during melt percolation resulted in light Cr isotopes preferably entering into the melt. Two spinel websterite veins from Mongolia have extremely light δ53Cr values of - 1.36 ± 0.04 ‰ and - 0.77 ± 0.06 ‰, respectively, which are the most negative Cr isotopic compositions yet reported for mantle-derived rocks. These two websterite veins may represent crystallization products from the isotopically light melt that may also metasomatize some peridotites in the area. The δ53Cr values of highly altered garnet peridotites from southern Africa vary from - 0.35 ± 0.04 ‰ (2SD) to + 0.12 ± 0.04 ‰ (2SD) and increase with increasing LOI (Loss on Ignition), reflecting a shift of δ53Cr to more positive values by secondary alteration. The Cr isotopic composition of the pristine, fertile upper mantle is estimated as δ53Cr = - 0.14 ± 0.12 ‰, after corrections for the effects of partial melting and metasomatism. This value is in line with that estimated for the BSE (- 0.12 ± 0.10 ‰) previously.

Disequilibrium δ18O values in microbial carbonates as a tracer of metabolic production of dissolved inorganic carbon

NASA Astrophysics Data System (ADS)

Thaler, Caroline; Millo, Christian; Ader, Magali; Chaduteau, Carine; Guyot, François; Ménez, Bénédicte

2017-02-01

Carbon and oxygen stable isotope compositions of carbonates are widely used to retrieve paleoenvironmental information. However, bias may exist in such reconstructions as carbonate precipitation is often associated with biological activity. Several skeleton-forming eukaryotes have been shown to precipitate carbonates with significant offsets from isotopic equilibrium with water. Although poorly understood, the origin of these biologically-induced isotopic shifts in biogenic carbonates, commonly referred to as "vital effects", could be related to metabolic effects that may not be restricted to mineralizing eukaryotes. The aim of our study was to determine whether microbially-mediated carbonate precipitation can also produce offsets from equilibrium for oxygen isotopes. We present here δ18O values of calcium carbonates formed by the activity of Sporosarcina pasteurii, a carbonatogenic bacterium whose ureolytic activity produces ammonia (thus increasing pH) and dissolved inorganic carbon (DIC) that precipitates as solid carbonates in the presence of Ca2+. We show that the 1000 lnαCaCO3-H2O values for these bacterially-precipitated carbonates are up to 24.7‰ smaller than those expected for precipitation at isotopic equilibrium. A similar experiment run in the presence of carbonic anhydrase (an enzyme able to accelerate oxygen isotope equilibration between DIC and water) resulted in δ18O values of microbial carbonates in line with values expected at isotopic equilibrium with water. These results demonstrate for the first time that bacteria can induce calcium carbonate precipitation in strong oxygen isotope disequilibrium with water, similarly to what is observed for eukaryotes. This disequilibrium effect can be unambiguously ascribed to oxygen isotope disequilibrium between DIC and water inherited from the oxygen isotope composition of the ureolytically produced CO2, probably combined with a kinetic isotope effect during CO2 hydration/hydroxylation. The fact that both disequilibrium effects are triggered by the metabolic production of CO2, which is common in many microbially-mediated carbonation processes, leads us to propose that metabolically-induced offsets from isotopic equilibrium in microbial carbonates may be more common than previously considered. Therefore, precaution should be taken when using the oxygen isotope signature of microbial carbonates for diagenetic and paleoenvironmental reconstructions.

The role of mantle-hybridization and crustal contamination in the petrogenesis of lithospheric mantle-derived alkaline rocks: constraints from Os and Hf isotopes

NASA Astrophysics Data System (ADS)

Mayer, B.; Jung, S.; Brauns, M.; Münker, C.

2018-06-01

The Rhön area as part of the Central European Volcanic Province (CEVP) hosts an unusual suite of Tertiary 24-Ma old hornblende-bearing alkaline basalts that provide insights into melting and fractionation processes within the lithospheric mantle. These chemically primitive to slightly evolved and isotopically (Sr, Nd, Pb) depleted basalts have slightly lower Hf isotopic compositions than respective other CEVP basalts and Os isotope compositions more radiogenic than commonly observed for continental intraplate alkaline basalts. These highly radiogenic initial 187Os/188Os ratios (0.268-0.892) together with their respective Sr-Nd-Pb isotopic compositions are unlikely to result from crustal contamination alone, although a lack of Os data for lower crustal rocks from the area and limited data for CEVP basalts or mantle xenoliths preclude a detailed evaluation. Similarly, melting of the same metasomatized subcontinental lithospheric mantle as inferred for other CEVP basalts alone is also unlikely, based on only moderately radiogenic Os isotope compositions obtained for upper mantle xenoliths from elsewhere in the province. Another explanation for the combined Nd, Sr and Os isotope data is that the lavas gained their highly radiogenic Os isotope composition through a mantle "hybridization", metasomatism process. This model involves a mafic lithospheric component, such as an intrusion of a sublithospheric primary alkaline melt or a melt derived from subducted oceanic material, sometime in the past into the lithospheric mantle where it metasomatized the ambient mantle. Later at 24 Ma, thermal perturbations during rifting forced the isotopically evolved parts of the mantle together with the peridotitic ambient mantle to melt. This yielded a package of melts with highly correlated Re/Os ratios and radiogenic Os isotope compositions. Subsequent movement through the crust may have further altered the Os isotope composition although this effect is probably minor for the majority of the samples based on radiogenic Nd and unradiogenic Sr isotope composition of the lavas. If the radiogenic Os isotope composition can be explained by a mantle-hybridization and metasomatism model, the isotopic compositions of the hornblende basalts can be satisfied by ca. 5-25% addition of the mafic lithospheric component to an asthenospheric alkaline magma. Although a lack of isotope data for all required endmembers make this model somewhat speculative, the results show that the Re-Os isotope system in continental basalts is able to distinguish between crustal contamination and derivation of continental alkaline lavas from isotopically evolved peridotitic lithosphere that was contaminated by mafic material in the past and later remelted during rifting. The Hf isotopic compositions are slightly less radiogenic than in other alkaline basalts from the province and indicate the derivation of the lavas from low Lu-Hf parts of the lithospheric mantle. The new Os and Hf isotope data constrain a new light of the nature of such metasomatizing agents, at least for these particular rocks, which represent within the particular volcanic complex the first product of the volcanism.

Calcium and strontium isotope fractionation in aqueous solutions as a function of temperature and reaction rate; I. Calcite

NASA Astrophysics Data System (ADS)

AlKhatib, Mahmoud; Eisenhauer, Anton

2017-07-01

In order to study Strontium (Sr) partitioning and isotope fractionation of Sr and Calcium (Ca) in calcite we performed precipitation (T) experiments decoupling temperature and precipitation rate (R∗). Calcite was precipitated at 12.5, 25.0 and 37.5 °C by diffusing NH3 and CO2 gases into aqueous solutions closely following the experimental setup of Lemarchand et al. (2004). The precipitation rate (R∗) for every sample was determined applying the initial rate method and from the specific surface area of almost all samples for each reaction. The order of reaction with respect to Ca2+ ions was determined to be one and independent of T. However, the order of reaction with respect to HCO3- changed from three to one as temperature increases from 12.5, 25 °C and 37.5 °C. Strontium incorporated into calcite (expressed as DSr = [Sr/Ca]calcite/[Sr/Ca]solution) was found to be R∗ and T dependent. As a function of increasing R∗ the Δ88/86Sr-values become more negative and as temperature increases the Δ88/86Sr values also increase at constant R∗. The DSr and Δ88/86Sr-values are correlated to a high degree and depend only on R∗ being independent of temperature, complexation and varying initial ratios. Latter observation may have important implications for the study of diagenesis, the paleo-sciences and the reconstruction of past environmental conditions. Calcium isotope fractionation (Δ44/40Ca) was also found to be R∗ and T dependent. For 12.5 and 25.0 °C we observe a general increase of the Δ44/40Ca values as a function of R∗ (Lemarchand et al. type behavior, Lemarchand et al. (2004)). Whereas at 37.5 °C a significant decreasing Δ44/40Ca is observed relative to increasing R∗ (Tang et al. type behavior, Tang et al. (2008)). In order to reconcile the discrepant observations we suggest that the temperature triggered change from a Ca2+-NH3-aquacomplex covalent controlled bonding to a Ca2+-H2O-aquacomplex van-der-Waals controlled bonding caused the change in sign of the R∗ - Δ44/40Ca slope due to the switch of an equilibrium type of isotope fractionation related to the covalent bonding during lower temperatures to a kinetic type of isotope fractionation at higher temperatures. This is supported by the observation that the Δ44/40Ca ratios tend to depend on the [Ca]:[DIC] ratio at 12.5 and 25 °C but is highly independent at 37.5 °C. Our observations imply the chemical fluid composition and temperature dependent complexation controls the amount and direction of Ca isotope fractionation in contrast to the Sr isotopes which do not show any change of its fractionation behavior as a function of complexation in the liquid phase.

Petrologic and Oxygen-Isotopic Investigations of Eucritic and Anomalous Mafic Achondrites

NASA Technical Reports Server (NTRS)

Mittlefehldt, D. W.; Greenwood, R. C.; Peng, Z. X.; Ross, D. K.; Berger, E. L.; Barrett, T. J.

2016-01-01

The most common asteroidal igneous meteorites are eucrite-type basalts and gabbros rocks composed of ferroan pigeonite and augite, calcic plagioclase, silica, ilmenite, troilite, Ca-phosphate, chromite and Fe-metal. These rocks are thought to have formed on a single asteroid along with howardites and diogenites (HEDs). However, Northwest Africa (NWA) 011 is mineralogically identical to eucrites, but has an O-isotopic composition distinct from them and was derived from a different asteroid. Modern analyses with higher precision have shown that some eucrites have smaller O-isotopic differences that are nevertheless well-resolved from the group mean.

Zinc isotope anomalies. [in Allende meteorite

NASA Technical Reports Server (NTRS)

Volkening, J.; Papanastassiou, D. A.

1990-01-01

The Zn isotope composition in refractory-element-rich inclusions of the Allende meteorite are determined. Typical inclusions contain normal Zn. A unique inclusion of the Allende meteorite shows an excess for Zn-66 of 16.7 + or - 3.7 eu (1 eu = 0.01 percent) and a deficit for Zn-70 of 21 + or - 13 eu. These results indicate the preservation of exotic components even for volatile elements in this inclusion. The observed excess Zn-66 correlates with excesses for the neutron-rich isotopes of Ca-48, Ti-50, Cr-54, and Fe-58 in the same inclusion.

Ti Isotopes: Echoes of Grain-Scale Heterogenaity in the Protoplanetary Disk

NASA Technical Reports Server (NTRS)

Jordan, M. K.; Kohl, I. E.; McCain, K. A.; Simon, J. I.; Young, E. D.

2017-01-01

Calcium-aluminum-rich inclusions (CAIs) are the oldest surviving solids to have formed in the Solar System. Their chemical and isotopic compositions provide a record of the conditions present in the protoplanetary disk where they formed and can aid our understanding of how solids formed in the solar nebula, an important step in the eventual process of planet building. The isotopic compositions of CAIs are primarily controlled by volatility. Evaporation/sublimation are well understood through both theory and experimental work to produce an enrichment in the heavy isotopes of an element, but less is understood about the effects of condensation. Mass-dependent fractionation can potentially provide a record of nebular condensation. Ti is not likely to experience evaporation due to its refractory nature, making it a useful tool for assessing the effects of condensation. We have undertaken a study of the stable isotope fractionation of Ti isotopes as a tracer of processes that predate the last evaporation events affecting CAIs. We compare the 49Ti/47Ti stable isotope ratio with excess 50Ti common in CAIs. We have collected Ti, Mg, Si, and Ca isotope data for a suite of CAIs in order to search for heterogeneity in each of these isotope systems, and for potential correlations among them. We compare our results to expectations for condensation.

Magnesium Isotopic Compositions of Continental Basalts From Various Tectonic Settings

NASA Astrophysics Data System (ADS)

Yang, W.; Li, S.; Tian, H.; Ke, S.

2016-12-01

Recycled sedimentary carbonate through subduction is the main light Mg isotopic reservoir in Earth's deep interior, thus Mg isotopic variation of mantle-derived melts provides a fresh perspective on investigating deep carbon cycling. Here we investigate Mg isotopic compositions of continental basalts from various tectonic settings: (1) The Cenozoic basalts from eastern China, coinciding with the stagnant Pacific slab in the mantle transition zone revealed by seismic tomography; (2) The Cenozoic basalts from Tengchong area, southwestern China, which comprises a crucial part of the collision zone between the Indian and Eurasian plates; (3) The Permian basalts from Emeishan large igneous province, related to a mantle plume. The Cenozoic basalts from both eastern China and Tengchong area exhibit light Mg isotopic compositions (δ26Mg = -0.60 to -0.30‰ and -0.51 to -0.33‰), suggesting recycled sedimentary carbonates in their mantle sources. This is supported by their low Fe/Mn, high CaO/Al2O3, low Hf/Hf* and low Ti/Ti* ratios, which are typical features of carbonated peridotite-derived melt. The Tengchong basalts also show high 87Sr/86Sr, high radiogenic Pb and upper crustal-like trace element pattern, indicating contribution of recycled continental crustal materials. By contrast, all Emeishan basalts display a mantle-like Mg isotopic composition, with δ26Mg ranging from -0.35 to -0.19‰. Since the Emeishan basalts derived from a mantle plume, their mantle-like Mg isotopic composition may indicate limited sedimentary carbonated recycled into the lower mantle. This is consistent with a recent experimental study which concluded that direct recycling of carbon into the lower mantle may have been highly restricted throughout most of the Earth's history.

Chemical and stable-radiogenic isotope compositions of Polatlı-Haymana thermal waters (Ankara, Turkey)

NASA Astrophysics Data System (ADS)

Akilli, Hafize; Mutlu, Halim

2016-04-01

Complex tectono-magmatic evolution of the Anatolian land resulted in development of numerous geothermal areas through Turkey. The Ankara region in central Anatolia is surrounded by several basins which are filled with upper Cretaceous-Tertiary sediments. Overlying Miocene volcanics and step faulting along the margins of these basins played a significant role in formation of a number of low-enthalpy thermal waters. In this study, chemical and isotopic compositions of Polatlı and Haymana geothermal waters in the Ankara region are investigated. The Polatlı-Haymana waters with a temperature range of 24 to 43 °C are represented by Ca-(Na)-HCO3 composition implying derivation from carbonate type reservoir rocks. Oxygen-hydrogen isotope values of the waters are conformable with the Global Meteoric Water Line and point to a meteoric origin. The carbon isotopic composition in dissolved inorganic carbon (DIC) of the studied waters is between -21.8 and -1.34 permil (vs. VPDB). Marine carbonates and organic rocks are the main sources of carbon. There is a high correlation between oxygen (3.7 to 15.0 permil; VSMOW) and sulfur (-9.2 to 19.5 permil; VCDT) isotope compositions of sulfate in waters. The mixing of sulfate from dissolution of marine carbonates and terrestrial evaporite units is the chief process behind the observed sulfate isotope systematics of the samples. 87Sr/86Sr ratios of waters varying from 0.705883 to 0.707827 are consistent with those of reservoir rocks. The temperatures calculated by SO4-H2O isotope geothermometry are between 81 and 138 °C nearly doubling the estimates from chemical geothermometers.

Geochemical and Nd-Sr-Pb isotope characteristics of synorogenic lower crust-derived granodiorites (Central Damara orogen, Namibia)

NASA Astrophysics Data System (ADS)

Simon, I.; Jung, S.; Romer, R. L.; Garbe-Schönberg, D.; Berndt, J.

2017-03-01

The 547 ± 7 Ma old Achas intrusion (Damara orogen, Namibia) includes magnesian, metaluminous to slightly peraluminous, calcic to calc-alkalic granodiorites and ferroan, metaluminous to slightly peraluminous, calc-alkalic to alkali-calcic leucogranites. For the granodiorites, major and trace element variations show weak if any evidence for fractional crystallization whereas some leucogranites are highly fractionated. Both, granodiorites and leucogranites are isotopically evolved (granodiorites: εNdinit: - 12.4 to - 20.5; TDM: 2.4-1.9; leucogranites: εNdinit: - 12.1 to - 20.6, TDM: 2.5-2.0), show similar Pb isotopic compositions, and may be derived from late Archean to Paleoproterozoic crustal source rocks. Comparison with melting experiments and simple partial melting modeling indicate that the granodiorites may be derived by extensive melting (> 40%) at 900-950 °C under water-undersaturated conditions (< 5 wt.% H2O) of felsic gneisses. Al-Ti and zircon saturation thermometry of the most primitive granodiorite sample yielded temperatures of ca. 930 °C and ca. 800 °C. In contrast to other lower crust-derived granodiorites and granites of the Central Damara orogen, the composition of the magma source is considered the first-order cause of the compositional diversity of the Achas granite. Second-order processes such as fractional crystallization at least for the granodiorites were minor and evidence for coupled assimilation-fractional crystallization processes is lacking. The most likely petrogenetic model involves high temperature partial melting of a Paleoproterozoic felsic source in the lower crust ca. 10-20 Ma before the first peak of regional high-temperature metamorphism. Underplating of the lower crust by magmas derived from the lithospheric mantle may have provided the heat for melting of the basement to produce anhydrous granodioritic melts.

Effects of mother lode-type gold mineralization on 187Os/188Os and platinum group element concentrations in peridotite: Alleghany District, California

USGS Publications Warehouse

Walker, R.J.; Böhlke, J.K.; McDonough, W.F.; Li, Ji

2007-01-01

Osmium isotope compositions and concentrations of Re, platinum group elements (PGE), and Au were determined for host peridotites (serpentinites and barzburgites) and hydrothermally altered ultramafic wall rocks associated with Mother Lode-type hydrothermal gold-quartz vein mineralization in the Alleghany district, California. The host peridotites have Os isotope compositions and Re, PGE, and Au abundances typical of the upper mantle at their presumed formation age during the late Proterozoic or early Paleozoic. The hydrothermally altered rocks have highly variable initial Os isotope compositions with ??os, values (% deviation of 187OS/188OS from the chondritic average calculated for the approx. 120 Ma time of mineralization) ranging from -1.4 to -8.3. The lowest Os isotope compositions are consistent with Re depletion of a chondritic source (e.g., the upper mantle) at ca. 1.6 Ga. Most of the altered samples are enriched in Au and have depleted and fractionated abundances of Re and PGE relative to their precursor peridotites. Geoehemical characteristics of the altered samples suggest that Re and some PGE were variably removed from the ultramafic rocks during the mineralization event. In addition to Re, the Pt and Pd abundances of the most intensely altered rocks appear to have been most affected by mineralization. The 187Os-depleted isotopic compositions of some altered rocks are interpreted to be a result of preferential 187Os loss via destruction of Re-rich phases during the event. For these rocks, Os evidently is not a useful tracer of the mineralizing fluids. The results do, however, provide evidence for differential mobility of these elements, and mobility of 187Os relative to the initial bulk Os isotope composition during hydrothermal metasomatic alteration of ultramafic rocks. ?? 2007 Society of Economic Geologists, Inc.

The isotopic and chemical evolution of Mount St. Helens

USGS Publications Warehouse

Halliday, A.N.; Fallick, A.E.; Dickin, A.P.; Mackenzie, A.B.; Stephens, W.E.; Hildreth, W.

1983-01-01

Isotopic and major and trace element analysis of nine samples of eruptive products spanning the history of the Mt. St. Helens volcano suggest three different episodes; (1) 40,000-2500 years ago: eruptions of dacite with ??{lunate}Nd = +5, ??{lunate}Sr = -10, variable ??18O, 206Pb/204Pb ??? 18.76, Ca/Sr ??? 60, Rb/Ba ??? 0.1, La/Yb ??? 18, (2) 2500-1000 years ago: eruptions of basalt, andesite and dacite with ??{lunate}Nd = +4 to +8, ??{lunate}Sr = -7 to -22, variable ??18O (thought to represent melting of differing mantle-crust reservoirs), 206Pb/204Pb = 18.81-18.87, variable Ca/Sr, Rb/Ba, La/Yb and high Zr, (3) 1000 years ago to present day: eruptions of andesite and dacite with ??{lunate}Nd = +6, ??{lunate}Sr = -13, ??18O ???6???, variable 206Pb/204Pb, Ca/Sr ??? 77, Rb/Ba = 0.1, La/Yb ??? 11. None of the products exhibit Eu anomalies and all are LREE enriched. There is a strong correlation between 87Sr/86Sr and differentiation indices. These data are interpreted in terms of a mantle heat source melting young crust bearing zircon and garnet, but not feldspar, followed by intrusion of this crustal reservoir by mantle-derived magma which caused further crustal melting and contaminated the crustal magma system with mafic components. Since 1000 years ago all the eruptions have been from the same reservoir which has displayed a much more gradual re-equilibration of Pb isotopic compositions than other components suggesting that Pb is being transported via a fluid phase. The Nd and Sr isotopic compositions lie along the mantle array and suggest that the mantle underneath Mt. St. Helens is not as depleted as MORB sources. There is no indication of seawater involvement in the source region. ?? 1983.

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.

Impact of reclaimed water in the watercourse of Huai River on groundwater from Chaobai River basin, Northern China

NASA Astrophysics Data System (ADS)

Yu, Yilei; Song, Xianfang; Zhang, Yinghua; Zheng, Fandong; Liu, Licai

2017-12-01

Reclaimed water is efficient for replenishing the dry rivers in northern China, but regional groundwater may be at risk from pollution. Therefore, samples of reclaimed water, river water, and groundwater were collected at the Huai River in the Chaobai River basin in 2010. The water chemistry and isotopic compositions of the samples were analyzed in the laboratory. The reclaimed water had stable compositions of water chemistry and isotopes, and the Na·Ca-HCO3·Cl water type. The water chemistry of the river water was consistent with that of the reclaimed water. A June peak of total nitrogen was the prominent characteristic in the shallow groundwater, which also had the Na·Ca-HCO3·Cl water type. However, the water chemistry and isotopes in most of the deep groundwater remained stable, and the water type was Ca·Mg-HCO3. The amount of reclaimed water recharging the groundwater was about 2.5 × 107 m3/yr. All of the shallow groundwater was impacted by the reclaimed water, with the mixing proportion of reclaimed water ranging from 42% to 80 % in the dry season and from 20% to 86% in the wet season. Only one deep well, with proportions of 67% (dry season) and 28% (wet season), was impacted. TDS, EC, and major ions (Na, K, Cl, NH4-N, NO2-N, and NO3-N) were increased in the impacted wells.

Understanding the Calcium Isotope and Trace Metal Composition of Elasmobranch Teeth: Implications for Recreating the δ44/40Ca of Seawater

NASA Astrophysics Data System (ADS)

Akhtar, A.; Higgins, J. A.

2017-12-01

Non-traditional stable isotopes in marine fossils have the potential to act as archives of paleo-seawater chemistry, biological evolution, and ancient ecosystems. In particular, bioapatite in elasmobranch enamel has been shown to be a robust proxy for environmental, geochemical and ecological reconstructions through Earth history due to its temporal range (from Devonian to present day) and resistance to diagenetic alteration. Moreover, frequent replacement rates of teeth in individuals, and high species level diversity and global distribution ensure a sample suite that encompasses a wide range of geographies and ecosystems. Here we present δ44/40Ca, δ87/86Sr and trace element (e.g. Sr/Ca, Mg/Ca) data from a suite of 300 teeth spanning the Cretaceous to present day and representing primary, secondary and tertiary piscivores. Modern teeth analyzed as part of this study have an average δ44/40Ca value of -2.07±0.48‰ (2s, n = 80) and Sr/Ca ratio of 2.30±0.24 mmol/mol (2s, n = 40), both offset from present day seawater (0 permil and 8.6 mmol/mol, respectively) due to a combination of inorganic (e.g. mineral precipitation) and biological (e.g. ionic regulation) effects. The total range in δ44/40Ca values in modern teeth is 1.19‰, the same order as that expected for variations in the δ44/40Ca value of ancient seawater. Using results from synthetic apatite synthesis experiments, mathematical modeling, and measurements of shark soft-tissue (e.g. blood and flesh), we explore sources of Ca isotope variability in shark teeth and evaluate their potential as archives of ancient seawater chemistry.

A multidisciplinary approach to define the hydrogeological model of the carbonate aquifer system in the Versilia River basin (Tuscany, Italy)

NASA Astrophysics Data System (ADS)

Menichini, M.; Doveri, M.; Giannecchini, R.; Raco, B.; Rosi, M.

2012-12-01

A hydrogeological study was carried out on important fractured/karst aquifer systems located in the Versilia River basin (Tuscany, Italy), in order to optimize the groundwater resources management. The main aim was the individuation of the feeding areas of the most important springs by means of a multidisciplinary approach using geological, hydrogeological and geochemical-isotopic tools. Some hydrogeological sections were elaborated in order to define the geometry of the main hydrostructures and to individuate possible groundwater divides. The elaboration of geochemical data allowed at identifying 3 main chemical facies: Ca-HCO3, Ca-SO4 and Na-Cl. The first two highlight the interaction of water with limestone/dolostone and carbonate-evaporite rocks for a time sufficient to acquire these chemical compositions and to achieve saturation/supersaturation in calcite and dolomite. The Na-Cl groundwater shows low salinity and a composition similar to rainwater, indicating a circulation in rocks containing minerals not very reactive and/or short interaction time with carbonate rocks. These two main types of water-rock interaction are confirmed by the isotopic ratio δ13C: for the Ca-HCO3 and Ca-SO4 types, δ13C value requires a significant contribution of carbon derived from dissolution of calcite, while for Na-Cl water, δ13C values are consistent with the addition of biogenic CO2 in rainwater. Stable water isotopes (δ18O and δ2H) confirm that groundwaters have a meteoric origin and that the wide range of values essentially depends on the different average altitude of feeding zone. Comparing the geological and hydrogeological features with the results of the geochemical processing, it is reasonable to assume that: the Na-Cl springs are representative of the superficial circuits, with small feeding zones and very low residence times in aquifer; whereas the Ca-HCO3 and Ca-SO4 springs are representative of relatively deep circuits developed in extensive aquifers with high permeability. The first type of springs was used to obtain the relationship between the δ18O ratio and the altitude of rainwater infiltration. Taking into account that they drain a small basin and considering the regulator effect of the aquifers, the isotopic composition of these springs are very similar to the annual average isotopic values of the local meteoric water. This relationship was used to evaluate the average altitude of the feeding area of the second type of springs. All these elements, and some tracer test results available in literature, allowed us to delimit the hydrogeological basins likely drained by the most important springs under study. In addition, for each hydrogeological system, a simplified water balance using meteorological data and the effective infiltration coefficients reported in the literature was performed, verifying that the delimited catchment areas are entirely consistent with the flow rate data of the springs.

Rapidly Assessing Changes in Bone Mineral Balance Using Natural Stable Calcium Isotopes

NASA Technical Reports Server (NTRS)

Morgan, J. L. L.; Gordon, G. W.; Romaniello, S. J.; Skulan, J. L.; Smith, S. M.; Anbar, A. D.

2011-01-01

We demonstrate that variations in the Ca isotope ratios in urine rapidly and quantitatively reflect changes in bone mineral balance. This variation occurs because bone formation depletes soft tissue of light Ca isotopes, while bone resorption releases that isotopically light Ca back into soft tissue. In a study of 12 individuals confined to bed rest, a condition known to induce bone resorption, we show that Ca isotope ratios shift in a direction consistent with net bone loss after just 7 days, long before detectible changes in bone density occur. Consistent with this interpretation, the Ca isotope variations track changes observed in N-teleopeptide, a bone resorption biomarker, while bone-specific alkaline phosphatase, a bone formation biomarker, is unchanged. Ca isotopes can in principle be used to quantify net changes in bone mass. Ca isotopes indicate an average loss of 0.62 +/- 0.16 % in bone mass over the course of this 30-day study. The Ca isotope technique should accelerate the pace of discovery of new treatments for bone disease and provide novel insights into the dynamics of bone metabolism.

Mantle End-Members: The Trace Element Perspective

NASA Astrophysics Data System (ADS)

Willbold, M.; Stracke, A.; Hofmann, A. W.

2004-12-01

On the basis of their isotopic composition, ocean island basalts (OIB) have been classified into three to four end-members; HIMU with the most radiogenic Pb isotope ratios of OIB and Enriched Mantle 1 and 2 (EM1, EM2) with less radiogenic but variable Pb isotope and highly radiogenic Sr isotope signatures. It has also been argued that each of these isotopic families has common trace element characteristics that distinguish them from one another and so substantiated this classification. Here, we present new high-precision trace element data for samples from St. Helena, Tristan da Cunha and Gough in the Atlantic Ocean. The overall data-set is augmented by OIB data from the GEOROC database and includes data from all major isotopic families (HIMU: St. Helena, Mangaia, Tubuai, and Rururtu; EM1: Tristan da Cunha, Gough, Pitcairn; and EM2: Samoa, Marquesas, and Society). For each locality we use only islands defining the most extreme isotopic compositions. The entire data-set has been screened to exclude altered and highly differentiated samples. HIMU basalts have a very uniform trace element composition. Compared to HIMU-type basalts, EM-type basalts are enriched in Rb, Ba, and K, and depleted in U, Nb, and Ta, relative to La. Different EM-type OIBs from the same isotopic family (EM1 or EM2), have distinct trace element characteristics that can ultimately only be caused by different source compositions. For example, Ba/Th ratios in samples from both Tristan da Cunha (EM1) and Samoa (EM2) are similarly high (ca. 110) whereas Ba/Th ratios in samples from Pitcairn (EM1) and Society (EM2) samples are consistently lower (ca. 70). Thus on the basis of their trace element composition, EM-type OIB cannot be classified into EM1 and EM2 type basalts, nor can any other grouping be identified. The remarkably uniform isotopic and trace element composition of HIMU-type basalts suggests derivation from a single common source reservoir, most likely subduction-modified oceanic crust. Although there are some trace element characteristics common to all EM-type basalts, which distinguish them from HIMU-type basalts (e.g. uniformly high Th/U ratios of 4.7 ± 0.3, and enrichment in Cs-U), each suite of EM-type basalts has unique trace element signatures that distinguish them from any other suite of EM-type basalts. This is especially obvious when comparing the trace element composition of EM basalts from one isotopic family, for example EM1-type basalts from Tristan, Gough and Pitcairn. Consequently, the trace element systematics of EM-type basalts suggest that there are many different EM-type sources, whereas the isotopic composition of EM-type basalts suggest derivation from two broadly similar sources, i.e. EM1 and EM2. The large variability in subducting sediments with respect to both parent-daughter (e.g. Rb/Sr, Sm/Nd, U/Pb, Th/Pb,...) and other trace element ratios makes it unlikely that there are reproducible mixtures of sediments leading to two different isotopic evolution paths (EM1 and EM2) while preserving a range of incompatible element contents for each isotopic family, as would be required to reconcile the isotopic and trace element characteristics of EM-type basalts. Although this does not a priori argue against sediments as possible source components for OIB, it does argue against two distinct groups of sediments as EM1 and EM2 sources. Further characterization of sources with the same general origin (e.g. a certain type of crust or lithosphere) or identification of processes leading to reservoirs with similar parent-daughter ratio characteristics but different incompatible trace element contents could resolve the apparent conundrum.

Mass dependence of calcium isotope fractionations in crown-ether resin chromatography.

PubMed

Fujii, Yasuhiko; Nomura, Masao; Kaneshiki, Tositaka; Sakuma, Yoichi; Suzuki, Tatsuya; Umehara, Saori; Kishimoto, Tadahumi

2010-06-01

Benzo 18-crown-6-ether resin was synthesised by the phenol condensation polymerisation process in porous silica beads, of which particle diameter was ca 60micro Calcium adsorption chromatography was performed with the synthesised resin packed in a glass column. The effluent was sampled in fractions, and the isotopic abundance ratios of (42)Ca, (43)Ca, (44)Ca, and (48)Ca against (40)Ca were measured by a thermo-ionisation mass spectrometer. The enrichment of heavier calcium isotopes was observed at the front boundary of calcium adsorption chromatogram. The mass dependence of mutual separation of calcium isotopes was analysed by using the three-isotope-plots method. The slopes of three-isotope-plots indicate the relative values of mutual separation coefficients for concerned isotopic pairs. The results have shown the normal mass dependence; isotope fractionation is proportional to the reduced mass difference, (M - M')/MM', where M and M' are masses of heavy and light isotope, respectively. The mass dependence clarifies that the isotope fractionations are originated from molecular vibration. The observed separation coefficient epsilon is 3.1x10(-3) for the pair of (40)Ca and (48)Ca. Productivity of enriched (48)Ca by crown-ether-resin was discussed as the function of the separation coefficient and the height equivalent to the theoretical plate.

Compositions of HIMU, EM1, and EM2 from Global Trends between Radiogenic Isotopes and Major Elements in Ocean Island Basalts

NASA Astrophysics Data System (ADS)

Jackson, M. G.; Dasgupta, R.

2008-12-01

Sr and Pb isotopes exhibit global trends with the concentrations of major elements (SiO2, TiO2, FeO, Al2O3 and K2O) and major elements ratios (CaO/Al2O3 and K2O/TiO2) in the shield-stage lavas from 18 oceanic hotspots (including Hawaii, Iceland, Galapagos, Cook-Australs, St. Helena, Cape Verde, Cameroon, Canary, Madeira, Comoros, Azores, Samoa, Society, Marquesas, Mascarene, Kerguelen, Pitcairn, and Selvagen). Based on the relationships between major elements and isotopes in ocean island basalts (OIBs), we find that the lavas derived from the mantle end members, HIMU (or high 'ì' = 238U/204Pb), EM1 (enriched mantle 1), EM2 (enriched mantle 2), and DMM (depleted MORB [mid-ocean ridge basalt] mantle) exhibit distinct major element characteristics: When compared to oceanic hotspots globally, the hotspots with a HIMU (radiogenic Pb-isotopes and low 87Sr/86Sr) component, such as St. Helena and Cook-Australs, exhibit high CaO/Al2O3, FeOT, and TiO2 and low SiO2 and Al2O3. EM1 (enriched mantle 1; intermediate 87Sr/86Sr and low 206Pb/204Pb; sampled by hotspots like Pitcairn and Kerguelen) and EM2 (enriched mantle 2; high 87Sr/86Sr and intermediate 206Pb/204Pb; sampled by hotspots like Samoa and Societies) exhibit higher K2O concentrations and K2O/TiO2 weight ratios than HIMU lavas. EM1 lavas exhibit the lowest CaO/Al2O3 in the OIB dataset, and this sets EM1 apart from EM2. A plot of CaO/Al2O3 vs K2O/TiO2 perfectly resolves the four mantle end member lavas. Melting processes (pressure, temperature and degree of melting) fail to provide an explanation for the full spectrum of major element concentrations in OIBs. Such processes also fail to explain the correlations between major elements and radiogenic isotopes. Instead, a long, time integrated history of various parent- daughter elements appears to be coupled to major element and/or volatile heterogeneity in the mantle source. End member lava compositions are compared with experimental partial melt compositions to place constraints on the lithological characteristics of the mantle end members.

Compositions of HIMU, EM1, and EM2 from global trends between radiogenic isotopes and major elements in ocean island basalts

NASA Astrophysics Data System (ADS)

Jackson, Matthew G.; Dasgupta, Rajdeep

2008-11-01

Sr and Pb isotopes exhibit global trends with the concentrations of major elements (SiO 2, TiO 2, FeO, Al 2O 3 and K 2O) and major elements ratios (CaO/Al 2O 3 and K 2O/TiO 2) in the shield-stage lavas from 18 oceanic hotspots (including Hawaii, Iceland, Galapagos, Cook-Australs, St. Helena, Cape Verde, Cameroon, Canary, Madeira, Comoros, Azores, Samoa, Society, Marquesas, Mascarene, Kerguelen, Pitcairn, and Selvagen). Based on the relationships between major elements and isotopes in ocean island basalts (OIBs), we find that the lavas derived from the mantle end members, HIMU (or high 'μ' = 238U/ 204Pb), EM1 (enriched mantle 1), EM2 (enriched mantle 2), and DMM (depleted MORB [mid-ocean ridge basalt] mantle) exhibit distinct major element characteristics: When compared to oceanic hotspots globally, the hotspots with a HIMU (radiogenic Pb-isotopes and low 87Sr/ 86Sr) component, such as St. Helena and Cook-Australs, exhibit high CaO/Al 2O 3, FeO T, and TiO 2 and low SiO 2 and Al 2O 3. EM1 (enriched mantle 1; intermediate 87Sr/ 86Sr and low 206Pb/ 204Pb; sampled by hotspots like Pitcairn and Kerguelen) and EM2 (enriched mantle 2; high 87Sr/ 86Sr and intermediate 206Pb/ 204Pb; sampled by hotspots like Samoa and Societies) exhibit higher K 2O concentrations and K 2O/TiO 2 weight ratios than HIMU lavas. EM1 lavas exhibit the lowest CaO/Al 2O 3 in the OIB dataset, and this sets EM1 apart from EM2. A plot of CaO/Al 2O 3 vs K 2O/TiO 2 perfectly resolves the four mantle end member lavas. Melting processes (pressure, temperature and degree of melting) fail to provide an explanation for the full spectrum of major element concentrations in OIBs. Such processes also fail to explain the correlations between major elements and radiogenic isotopes. Instead, a long, time integrated history of various parent-daughter elements appears to be coupled to major element and/or volatile heterogeneity in the mantle source. End member lava compositions are compared with experimental partial melt compositions to place constraints on the lithological characteristics of the mantle end members.

Evaluating Volatility-controlled Isotope Fractionation During Planet Formation: Kinetics versus Equilibrium

NASA Astrophysics Data System (ADS)

Young, E. D.

2017-12-01

Recent advances in our ability to measure stable isotope ratios of light, rock-forming elements, including those for Zn, K, Fe, Si, and Mg, among others, has resulted in an emerging hypothesis that collisions among rocky planetesimals, planetary embryos, and/or proto-planets caused losses of moderately volatile elements (e.g., K) and "common" or moderately refractory elements (e.g., Mg and Si). The primary evidence is in the form of heavy isotope enrichments in rock-forming elements relative to the chondrite groups that are thought to be representative of planetary precursors. Equilibrium volatility-controlled isotope fractionation for planetesimal magma oceans might have occurred for bodies larger than 0.1% of an Earth mass (½ the mass of Pluto) as these bodies had sufficient gravity to overpower the escape velocities of hot gas at 2000K. Both Jean's escape and viscous drag hydrodynamic escape can obviate the escape velocity limit but will fractionate by mass, not by volatility. Equilibrium vapor/melt fractionation is qualitatively consistent with the greater disparity in 29Si/28Si between Earth and chondrites than in 25Mg/24Mg. However, losses of large masses of vapor are required to record the fractionation in the melts. We consider that if Earth was derived from E chondrite-like materials, the bulk composition of the Earth, assuming refractory Ca was retained, requires > 60% loss of Mg. This is a lot of vapor loss for a process relying on at least intermittent equilibrium, although it comports with the isotopic lever-rule requirements. Paradoxically, the alternative of evaporative loss of rock-forming elements requires less total mass loss. For example, the calculated Mg and Si isotopic compositions of residues resulting from evaporation of chondritic melts can fit the Mg and Si isotopic compositions of Earth, Mars, and angrites with varying background pressures and with total mass losses of near 5% or less. These mass losses are closer to, and even lower than, those suggested by Ca concentrations relative to CI chondrite. Equilibrium models achieve greater Si than Mg isotope fractionation by large mass losses while evaporation models produce this effect for small mass losses. Additional constraints involving other isotope systems as well as models for vapor loss can distinguish between the two scenarios.

Osmium isotopic tracing of atmospheric emissions from an aluminum smelter

NASA Astrophysics Data System (ADS)

Gogot, Julien; Poirier, André; Boullemant, Amiel

2015-09-01

We present for the first time the use of osmium isotopic composition as a tracer of atmospheric emissions from an aluminum smelter, where alumina (extracted from bauxite) is reduced through electrolysis into metallic aluminum using carbonaceous anodes. These anodes are consumed in the process; they are made of petroleum coke and pitch and have high Re/Os elementary ratio. Due to the relatively large geological age of their source material, their osmium shows a high content of radiogenic 187Os produced from in situ187Re radioactive decay. The radiogenic isotopic composition (187Os/188Os ∼ 2.5) of atmospheric particulate emissions from this smelter is different from that of other typical anthropogenic osmium sources (that come from ultramafic geological contexts with unradiogenic Os isotopes, e.g., 187Os/188Os < 0.2) and also different from average eroding continental crust 187Os/188Os ratios (ca. 1.2). This study demonstrates the capacity of osmium measurements to monitor particulate matter emissions from the Al-producing industry.

Hydrogeochemical and isotopic characterisation of groundwater in a sand-dune phreatic aquifer on the northeastern coast of the province of Buenos Aires, Argentina.

PubMed

Carretero, Silvina C; Dapeña, Cristina; Kruse, Eduardo E

2013-01-01

This contribution presents the hydrochemical and isotopic characterisation of the phreatic aquifer located in the Partido de la Costa, province of Buenos Aires, Argentina. In the sand-dune barrier geomorphological environment, groundwater is mainly a low-salinity Ca-HCO3 and Na-HCO3-type, being in general suitable for drinking, whereas in the continental plain (silty clay sediments), groundwater is a Na-Cl type with high salinity and unsuitable for human consumption. The general isotopic composition of the area ranges from-6.8 to-4.3 ‰ for δ(18)O and from-39 to-21 ‰ for δ(2)H, showing that rainwater rapidly infiltrates into the sandy substrate and reaches the water table almost without significant modification in its isotopic composition. These analyses, combined with other chemical parameters, made it possible to corroborate that in the eastern area of the phreatic aquifer, there is no contamination from marine salt water.

The role of soil pH on soil carbonic anhydrase activity

NASA Astrophysics Data System (ADS)

Sauze, Joana; Jones, Sam P.; Wingate, Lisa; Wohl, Steven; Ogée, Jérôme

2018-01-01

Carbonic anhydrases (CAs) are metalloenzymes present in plants and microorganisms that catalyse the interconversion of CO2 and water to bicarbonate and protons. Because oxygen isotopes are also exchanged during this reaction, the presence of CA also modifies the contribution of soil and plant CO18O fluxes to the global budget of atmospheric CO18O. The oxygen isotope signatures (δ18O) of these fluxes differ as leaf water pools are usually more enriched than soil water pools, and this difference is used to partition the net CO2 flux over land into soil respiration and plant photosynthesis. Nonetheless, the use of atmospheric CO18O as a tracer of land surface CO2 fluxes requires a good knowledge of soil CA activity. Previous studies have shown that significant differences in soil CA activity are found in different biomes and seasons, but our understanding of the environmental and ecological drivers responsible for the spatial and temporal patterns observed in soil CA activity is still limited. One factor that has been overlooked so far is pH. Soil pH is known to strongly influence microbial community composition, richness and diversity in addition to governing the speciation of CO2 between the different carbonate forms. In this study we investigated the CO2-H2O isotopic exchange rate (kiso) in six soils with pH varying from 4.5 to 8.5. We also artificially increased the soil CA concentration to test how pH and other soil properties (texture and phosphate content) affected the relationship between kiso and CA concentration. We found that soil pH was the primary driver of kiso after CA addition and that the chemical composition (i.e. phosphate content) played only a secondary role. We also found an offset between the δ18O of the water pool with which CO2 equilibrates and total soil water (i.e. water extracted by vacuum distillation) that varied with soil texture. The reasons for this offset are still unknown.

Does Oxygen Isotopic Heterogeneity in Refractory Inclusions and Their Wark-Lovering Rims Record Nebular Repressing?

NASA Technical Reports Server (NTRS)

Simon, J. I.; Matzel, J. E. P.; Simon, S. B.; Weber, P. K.; Grossman, L.; Ross, D. K.; Hutcheon, I. D.

2013-01-01

Large systematic variations in O-isotopic compositions found within individual mineral layers of rims surrounding Ca-, Al-rich inclusions (CAIs) and at the margins of some CAIs imply formation from distinct environments [e.g., 1-3]. The O-isotope compositions of many CAIs preserve a record of the Solar nebula gas believed to initially be O-16-rich (delta O-17 less than or equal to -25%0) [4-5]. Data from a recent study of the compact Type A Allende CAI, A37, preserve a diffusion profile in the outermost 70 micrometers of the inclusion and show greater than 25%0 variations in delta O-17 within its 100 micrometer-thick Wark-Lovering rim (WL-rim) [3]. This and comparable heterogeneity measured in several other CAIs have been explained by isotopic mixing between the O-16-rich Solar reservoir and a second O-16-poor reservoir (probably nebular gas) with a planetary-like isotopic composition, e.g., [1,2,3,6]. However, there is mineralogical and isotopic evidence from the interiors of CAIs, in particular those from Allende, for parent body alteration. At issue is how to distinguish the record of secondary reprocessing in the nebula from that which occurred on the parent body. We have undertaken the task to study a range of CAI types with varying mineralogies, in part, to address this problem.

Fingerprints for main varieties of argentinean wines: terroir differentiation by inorganic, organic, and stable isotopic analyses coupled to chemometrics.

PubMed

Di Paola-Naranjo, Romina D; Baroni, Maria V; Podio, Natalia S; Rubinstein, Hector R; Fabani, Maria P; Badini, Raul G; Inga, Marcela; Ostera, Hector A; Cagnoni, Mariana; Gallegos, Ernesto; Gautier, Eduardo; Peral-Garcia, Pilar; Hoogewerff, Jurian; Wunderlin, Daniel A

2011-07-27

Our main goal was to investigate if robust chemical fingerprints could be developed for three Argentinean red wines based on organic, inorganic, and isotopic patterns, in relation to the regional soil composition. Soils and wines from three regions (Mendoza, San Juan, and Córdoba) and three varieties (Cabernet Sauvignon, Malbec, and Syrah) were collected. The phenolic profile was determined by HPLC-MS/MS and multielemental composition by ICP-MS; (87)Sr/(86)Sr and δ(13)C were determined by TIMS and IRMS, respectively. Chemometrics allowed robust differentiation between regions, wine varieties, and the same variety from different regions. Among phenolic compounds, resveratrol concentration was the most useful marker for wine differentiation, whereas Mg, K/Rb, Ca/Sr, and (87)Sr/(86)Sr were the main inorganic and isotopic parameters selected. Generalized Procrustes analysis (GPA) using two studied matrices (wine and soil) shows consensus between them and clear differences between studied areas. Finally, we applied a canonical correlation analysis, demonstrating significant correlation (r = 0.99; p < 0.001) between soil and wine composition. To our knowledge this is the first report combining independent variables, constructing a fingerprint including elemental composition, isotopic, and polyphenol patterns to differentiate wines, matching part of this fingerprint with the soil provenance.

Boron isotope systematics during magma-carbonate interaction: an experimental study from Merapi (Indonesia) and Vesuvius (Italy)

NASA Astrophysics Data System (ADS)

Deegan, F. M.; Jolis, E. M.; Troll, V. R.; Freda, C.; Whitehouse, M.

2011-12-01

Carbonate assimilation is increasingly recognized as an important process affecting the compositional evolution of magma and its inherent ability to erupt explosively due to release of carbonate-derived CO2 [e.g., 1, 2, 3]. In order to gain insights into this process, we performed short time-scale carbonate dissolution experiments in silicate melt using natural starting materials from Merapi and Vesuvius volcanoes at magmatic pressure and temperature [2, 4]. The experiments enable us to resolve in detail the timescales, textures and chemical features of carbonate assimilation. Three compositionally distinct glass domains have been defined: i) Ca-normal glass, similar in composition to the starting material; ii) Ca-rich, contaminated glass; and iii) a diffusional glass interface between the Ca-normal and Ca-rich glass, characterized by steady interchange between SiO2 and CaO. Here we present new boron isotope data for the experimental products obtained by SIMS. The glasses show distinct and systematic variation in their δ11B (%) values. The contaminated glasses generally show extremely negative δ11B values (down to -41 %) relative to both the uncontaminated experimental glass and fresh arc volcanics (-7 to +7 % [5]). Considering that carbonates have δ11B values of +9 to +26 [6], the data cannot be explained by simple mixing processes between the end-members alone. This implies that the δ11B of the original contaminant was drastically modified before being incorporated into the melt, which can be explained by B isotope fractionation during breakdown and degassing of the carbonate. Our data represents the first B isotope analyses of experimental products of carbonate assimilation. They provide novel and well constrained insights into the behavior of boron upon degassing of carbonate. This, in turn, has implications for both i) late stage contamination and volatile addition to hazardous volcanic systems located over carbonate basement (cf. [7]) and ii) studies of mass transfer in subduction zones, where B is frequently employed as a tracer of deep crustal recycling [8]. [1] Chadwick et al. (2007) J. Petrol. 48, 1793-1812. [2] Deegan et al. (2010) J. Petrol. 51, 1027-1051. [3] Freda et al. (2010) Bull. Volcanol. 73, 241-256. [4] Jolis et al. (2011) in prep. [5] Leeman & Sisson (1996) Rev. Min. 33, 645-707. [6] Ishikawa & Nakamura (1993) Earth Planet Sci. Lett. 117, 567-580. [7] Deegan et al. (2011) Geology Today 27, 63-64. [8] Rose et al. (2001) Science 293, 281-283.

Geochemical processes controlling groundwater quality under semi arid environment: A case study in central Morocco.

PubMed

Karroum, Morad; Elgettafi, Mohammed; Elmandour, Abdenabi; Wilske, Cornelia; Himi, Mahjoub; Casas, Albert

2017-12-31

Bahira plain is an important area for Morocco due to its agriculture and mining activities. Situated in a sub-arid to arid climate, this plain hosts an aquifer system that represents sequences of carbonates, phosphates, evaporates and alluvial deposits. Groundwater flows from Ganntour plateau (recharge area) to the basin-fill deposits and Zima Lake and Sed Elmejnoun where water evaporates. The objective of this study was to characterize the chemical properties of the groundwater and to assess the processes controlling the groundwater's chemistry. We can divide water samples into three hydrochemical water groups: recharge waters (Ca/Mg-HCO 3 ), transition zone waters (Ca-HCO 3 -SO 4 /Cl) and discharge waters (Na-Cl/SO 4 ). Accordingly, compositions of waters are determined by the availability of easily soluble minerals like calcite (Ca-HCO 3 dominant), halite (Na-Cl dominant) and gypsum (Ca-SO 4 dominant). Cl/Br ratios show that Cl concentration increases from dissolution of natural halite. When groundwater is affected by extreme evaporation Cl/Br ratios may increase up to 1900. High fluoride concentrations are associated with low Ca 2+ concentrations (<100mg/L). That means when recharge waters enter the aquifer, it starts dissolving fluorite since the Ca 2+ concentration is low. Once groundwater becomes saturated with Ca 2+ , the immobilization of fluoride is occurring by precipitation of fluoride-rich minerals like fluoro-apatite. According to the environmental isotope ( 18 O and 2 H) analyses, they are three potential processes affecting groundwater: 1. Evaporation as verified by low slope value, 2. Water-rock interaction, 3. admixture of waters showed different stable isotope compositions and salinities. Copyright © 2017 Elsevier B.V. All rights reserved.

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.

Silicate versus carbonate weathering in Iceland: New insights from Ca isotopes

NASA Astrophysics Data System (ADS)

Jacobson, Andrew D.; Grace Andrews, M.; Lehn, Gregory O.; Holmden, Chris

2015-04-01

Several studies have measured riverine fluxes of Ca and carbonate alkalinity in Iceland with the aim of quantifying the role of basalt weathering in the long-term carbon cycle. A major assumption is that all of the Ca and alkalinity originates from the dissolution of Ca-bearing silicate minerals, such as plagioclase and clinopyroxene. However, hydrothermal calcite occurs throughout Iceland, and even trace levels are expected to impact river geochemistry owing to the mineral's high solubility and fast dissolution rate. To test this hypothesis, we used a new, high-precision Ca isotope MC-TIMS method (δ44/40Ca; 2σSD = ± 0.04 ‰) to trace sources of Ca in Icelandic rivers. We report elemental and Ca isotope data for rivers, high- and low-temperature groundwater, basalt, hydrothermal calcite (including Iceland Spar), and stilbite and heulandite, which are two types of zeolites commonly formed during low-grade metamorphism of basalt. In agreement with previous research, we find that rivers have higher δ44/40Ca values than basalt, with a maximum difference of ∼0.40‰. This difference may reflect isotope fractionation in the weathering zone, i.e., preferential uptake of 40Ca during clay mineral formation, adsorption, and other geochemical processes that cycle Ca. However, calcite δ44/40Ca values are also up to ∼0.40‰ higher than bedrock values, and on a diagram of δ44/40Ca versus Sr/Ca, nearly all waters plot within a plausible mixing domain bounded by the measured compositions of basalt and calcite, with glacial rivers plotting closer to calcite than non-glacial rivers. Calcite and heulandite form during hydrothermal alteration of basalt in the deep lava pile and often occur together in metabasalts now exposed at the surface. Because heulandite δ44/40Ca values are ∼1-2‰ lower than basalt, we suggest that 40Ca uptake by heudlandite explains the relatively high δ44/40Ca values of calcite and that calcite weathering in turn elevates riverine δ44/40Ca values. High mechanical erosion rates are known to facilitate the exposure and weathering of calcite, which explains the isotopic contrast between glacial and non-glacial watersheds. Using a mixing model, we find that calcite weathering provides ∼0-65% of the Ca in non-glacial rivers and ∼25-90% of the Ca in glacial rivers, with silicate weathering providing the remainder. Icelandic hydrothermal calcite contains mantle carbon. Noting that zeolite facies metamorphism and hydrothermal fluid circulation are ubiquitous characteristics of basaltic eruptions and assuming that hydrothermal calcite in other basaltic settings also contains mantle carbon, we suggest that the contribution of basalt weathering to long-term CO2 drawdown and climate regulation may be less significant than previously realized.

Multiple Mechanisms of Transient Heating Events in the Protoplanetary Disk: Evidence from Precursors of Chondrules and Igneous Ca,Al-Rich Inclusions

NASA Astrophysics Data System (ADS)

Krot, A. N.; Nagashima, K.; Libourel, G.; Miller, K. E.

2017-02-01

Here we review the mineralogy, petrography, O-isotope compositions, and trace element abundances of precursors of chondrules and igneous CAIs which provide important constraints on the mechanisms of transient heating events in the protoplanetary disk.

Chemical compositions and precipitation timing of basement carbonate vein from fossil spreading ridge of South China Sea

NASA Astrophysics Data System (ADS)

Ding, W.; Chen, Y.

2016-12-01

Eighteen calcium carbonate veins within the igneous basement recovered close to the fossil spreading ridge of the South China Sea during the Integrated Ocean Drilling Program (IODP) Expedition 349 were investigated. These carbonates are of primarily either calcite or aragonite, or some mixed aragonite and calcite, with rarely ankerite. The chemical (Ca, Mg, Sr, Mn, Fe) contents and isotopic (87Sr/86Sr, δ18O, δ18C) compositions of the veins were determined to study the evolving chemistry of hydrothermal fluids and to constrain the timing of vein formation. The carbonate δ18O values range from -5.0 to -0.2 ‰ PDB, indicating these are typical low temperature basement carbonates. Chemical analyses show distinct Mg/Ca and Sr/Ca ratios for aragonite and calcite. 87Sr/86Sr ratios show negative correlations with both the depth and δ18O-calculated formation temperature, and are independent of mineralogy with both aragonite and calcite, indicating more geochemically evolved carbonated have precipitated from warmer fluids. The hightest 87Sr/86Sr ratios of vein samples at each drill site are believed to reflect the contemporaneous seawater compositions when carbonates precipitated. No unambiguous precipitation ages can be constrained by correlating 87Sr/86Sr ratios with the global seawater Sr isotope evolution. However, based on correlations of vein chemical composition with depth and formation temperature, as well as the Neogene post-spreading magmatism, we hypothesize 10 Ma is a particular time favoring the formation of carbonate veins in our study area.

Isotopic analysis of groundwater and carbonate system in the Surdulica geothermal aquifer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hadzisehovic, M; Miljevic, N.; Sipka, V.

1993-01-01

The authors present here results of their investigation of the isotopic chemical composition of groundwater and carbonates in the Surdulica geothermal aquifer, Serbia. They considered the effects of carbonate dissolution and measured [sup 13]C, [sup 14]C, D, [sup 18]O, [sup 3]H, field pH, temperature, Na[sup +], CA [sup 2+], Mg[sup 2+], HCO[sub 3] and other aqueous species from 30 springs and boreholes. Geothermal waters are supersaturated with calcite. Carbon isotope compositions vary with carbonate mineral dissolution. The [delta]D and [delta][sup 18]O of groundwater samples fit the meteoric water line, and indicate that groundwater is recharged mainly from higher altitudes andmore » the cold season. Different groundwater residence times point out two mechanisms for their formation: fissure flow for young waters and standard diffusion processes for old ones.« less

Coordinated Oxygen Isotopic and Petrologic Studies of CAIS Record Varying Composition of Protosolar

NASA Technical Reports Server (NTRS)

Simon, Justin I.; Matzel, J. E. P.; Simon, S. B.; Weber, P. K.; Grossman, L.; Ross, D. K.; Hutcheon, I. D.

2012-01-01

Ca-, Al-rich inclusions (CAIs) record the O-isotope composition of Solar nebular gas from which they grew [1]. High spatial resolution O-isotope measurements afforded by ion microprobe analysis across the rims and margin of CAIs reveal systematic variations in (Delta)O-17 and suggest formation from a diversity of nebular environments [2-4]. This heterogeneity has been explained by isotopic mixing between the O-16-rich Solar reservoir [6] and a second O-16-poor reservoir (probably nebular gas) with a "planetary-like" isotopic composition [e.g., 1, 6-7], but the mechanism and location(s) where these events occur within the protoplanetary disk remain uncertain. The orientation of large and systematic variations in (Delta)O-17 reported by [3] for a compact Type A CAI from the Efremovka reduced CV3 chondrite differs dramatically from reports by [4] of a similar CAI, A37 from the Allende oxidized CV3 chondrite. Both studies conclude that CAIs were exposed to distinct, nebular O-isotope reservoirs, implying the transfer of CAIs among different settings within the protoplanetary disk [4]. To test this hypothesis further and the extent of intra-CAI O-isotopic variation, a pristine compact Type A CAI, Ef-1 from Efremovka, and a Type B2 CAI, TS4 from Allende were studied. Our new results are equally intriguing because, collectively, O-isotopic zoning patterns in the CAIs indicate a progressive and cyclic record. The results imply that CAIs were commonly exposed to multiple environments of distinct gas during their formation. Numerical models help constrain conditions and duration of these events.

Geochemical characteristics of Cretaceous carbonatites from Angola

NASA Astrophysics Data System (ADS)

Alberti, A.; Castorina, F.; Censi, P.; Comin-Chiaramonti, P.; Gomes, C. B.

1999-12-01

The Early Cretaceous (138-130 Ma) carbonatites and associated alkaline rocks of Angola belong to the Paraná-Angola-Etendeka Province and occur as ring complexes and other central-type intrusions along northeast trending tectonic lineaments, parallel to the trend of coeval Namibian alkaline complexes. Most of the Angolan carbonatite-alkaline bodies are located along the apical part of the Moçamedes Arch, a structure representing the African counterpart of the Ponta Grossa Arch in southern Brazil, where several alkaline-carbonatite complexes were also emplaced in the Early Cretaceous. Geochemical and isotopic (C, 0, Sr and Nd) characteristics determined for five carbonatitic occurrences indicate that: (1) the overall geochemical composition, including the OC isotopes, is within the range of the Early and Late Cretaceous Brazilian occurrences from the Paraná Basin; (2) the La versus {La}/{Yb} relationships are consistent with the exsolution of CO i2-rich melts from trachyphonolitic magmas; and (3) the {143Nd}/{144Nd} and {87Sr}/{86Sr} initial ratios are similar to the initial isotopic ratios (129 Ma) of alkaline complexes in northwest Namibia. In contrast, the Lupongola carbonatites have a distinctly different {143Nd}/{144Nd} initial ratio, suggesting a different source. The Angolan carbonatites have SrNd isotopic compositions ranging from bulk earth to time-integrated depleted sources. Since those from eastern Paraguay (at the western fringe of the Paraná-Angola-Etendeka Province) and Brazil appear to be related to mantle-derived melts with time-integrated enriched or B.E. isotopic characteristics, it is concluded that the carbonatites of the Paraná-Angola-Etendeka Province have compositionally distinct mantle sources. Such mantle heterogeneity is attributed to 'metasomatic processes', which would have occurred at ca 0.6-0.7 Ga (Angola, northwest Namibia and Brazil) and ca 1.8 Ga (eastern Paraguay), as suggested by Nd-model ages.

Oxygen isotope fractionation effects in soil water via interaction with cations (Mg, Ca, K, Na) adsorbed to phyllosilicate clay minerals

NASA Astrophysics Data System (ADS)

Oerter, Erik; Finstad, Kari; Schaefer, Justin; Goldsmith, Gregory R.; Dawson, Todd; Amundson, Ronald

2014-07-01

In isotope-enabled hydrology, soil and vadose zone sediments have been generally considered to be isotopically inert with respect to the water they host. This is inconsistent with knowledge that clay particles possessing an electronegative surface charge and resulting cation exchange capacity (CEC) interact with a wide range of solutes which, in the absence of clays, have been shown to exhibit δ18O isotope effects that vary in relation to the ionic strength of the solutions. To investigate the isotope effects caused by high CEC clays in mineral-water systems, we created a series of monominerallic-water mixtures at gravimetric water contents ranging from 5% to 32%, consisting of pure deionized water of known isotopic composition with homoionic (Mg, Ca, Na, K) montmorillonite. Similar mixtures were also created with quartz to determine the isotope effect of non-, or very minimally-, charged mineral surfaces. The δ18O value of the water in these monominerallic soil analogs was then measured by isotope ratio mass spectrometry (IRMS) after direct headspace CO2 equilibration. Mg- and Ca-exchanged homoionic montmorillonite depleted measured δ18O values up to 1.55‰ relative to pure water at 5% water content, declining to 0.49‰ depletion at 30% water content. K-montmorillonite enriched measured δ18O values up to 0.86‰ at 5% water content, declining to 0.11‰ enrichment at 30% water. Na-montmorillonite produces no measureable isotope effect. The isotope effects observed in these experiments may be present in natural, high-clay soils and sediments. These findings have relevance to the interpretation of results of direct CO2-water equilibration approaches to the measurement of the δ18O value of soil water. The adsorbed cation isotope effect may bear consideration in studies of pedogenic carbonate, plant-soil water use and soil-atmosphere interaction. Finally, the observed isotope effects may prove useful as molecular scale probes of the nature of mineral-water interactions.

Correlated nanoscale characterization of a unique complex oxygen-rich stardust grain: Implications for circumstellar dust formation

NASA Astrophysics Data System (ADS)

Leitner, J.; Hoppe, P.; Floss, C.; Hillion, F.; Henkel, T.

2018-01-01

We report the light to intermediate-mass element abundances as well as the oxygen, magnesium, silicon, and titanium isotope compositions of a unique and unusually large (0.8 μm × 3.75 μm) presolar O-rich grain from the Krymka LL3.2 chondrite. The O-, Al-, and Ti-isotopic compositions are largely compatible with an origin from an asymptotic giant branch (AGB) star of 1.5 solar masses with a metallicity that is 15% higher than the solar metallicity. The grain has an elevated 17O/16O ratio (8.40 ± 0.16 × 10-4) compared to solar, and slightly sub-solar 18O/16O ratio (1.83 ± 0.03 × 10-3). It shows evidence for the presence of initial 26Al, suggesting formation after the first dredge-up, during one of the early third dredge-up (TDU) episodes. Titanium isotopic data indicate condensation of the grain before significant amounts of material from the He-burning shell were admixed to the stellar surface with progressive TDUs. We observed a small excess in 30Si (δ30Si = 41 ± 5‰), which most likely is inherited from the parent star's initial Si-isotopic composition. For such stars stellar models predict a C/O-ratio < 1 even after the onset of TDU, thus allowing the condensation of O-rich dust. The grain is an unusual complex presolar grain, consisting of an Al-Ca-Ti-oxide core, surrounded by an Mg-Ca-silicate mantle, and resembles the condensation sequence for a cooling gas of solar composition at pressures and dust/gas ratios typically observed for circumstellar envelopes around evolved stars. We also report the first observation of phosphorus in a presolar grain, although the origin of the P-bearing phase remains ambiguous.

Distribution of p-process 174Hf in early solar system materials and the origin of nucleosynthetic Hf and W isotope anomalies in Ca-Al rich inclusions

NASA Astrophysics Data System (ADS)

Peters, Stefan T. M.; Münker, Carsten; Pfeifer, Markus; Elfers, Bo-Magnus; Sprung, Peter

2017-02-01

Some nuclides that were produced in supernovae are heterogeneously distributed between different meteoritic materials. In some cases these heterogeneities have been interpreted as the result of interaction between ejecta from a nearby supernova and the nascent solar system. Particularly in the case of the oldest objects that formed in the solar system - Ca-Al rich inclusions (CAIs) - this view is confirm the hypothesis that a nearby supernova event facilitated or even triggered solar system formation. We present Hf isotope data for bulk meteorites, terrestrial materials and CAIs, for the first time including the low-abundance isotope 174Hf (∼0.16%). This rare isotope was likely produced during explosive O/Ne shell burning in massive stars (i.e., the classical "p-process"), and therefore its abundance potentially provides a sensitive tracer for putative heterogeneities within the solar system that were introduced by supernova ejecta. For CAIs and one LL chondrite, also complementary W isotope data are reported for the same sample cuts. Once corrected for small neutron capture effects, different chondrite groups, eucrites, a silicate inclusion of a IAB iron meteorite, and terrestrial materials display homogeneous Hf isotope compositions including 174Hf. Hafnium-174 was thus uniformly distributed in the inner solar system when planetesimals formed at the <50 ppm level. This finding is in good agreement with the evidently homogeneous distributions of p-process isotopes 180W, 184Os and possibly 190Pt between different iron meteorite groups. In contrast to bulk meteorite samples, CAIs show variable depletions in p-process 174Hf with respect to the inner solar system composition, and also variable r-process (or s-process) Hf and W contributions. Based on combined Hf and W isotope compositions, we show that CAIs sampled at least one component in which the proportion of r- and s-process derived Hf and W deviates from that of supernova ejecta. The Hf and W isotope anomalies in CAIs are therefore best explained by selective processing of presolar carrier phases prior to CAI formation, and not by a late injection of supernova materials. Likewise, other isotope anomalies in additional elements in CAIs relative to the bulk solar system may reflect the same process. The isotopic heterogeneities between the first refractory condensates may have been eradicated partially during CAI formation, because W isotope anomalies in CAIs appear to decrease with increasing W concentrations as inferred from time-integrated 182W/184W. Importantly, the 176Lu-176Hf and 182Hf-182W chronometers are not significantly affected by nucleosynthetic heterogeneity of Hf isotopes in bulk meteorites, but may be affected in CAIs.

Mg/Ca, Sr/Ca and Ca isotope ratios in benthonic foraminifers related to test structure, mineralogy and environmental controls

NASA Astrophysics Data System (ADS)

Gussone, Nikolaus; Filipsson, Helena L.; Kuhnert, Henning

2016-01-01

We analysed Mg/Ca, Sr/Ca and Ca isotope ratios of benthonic foraminifers from sediment core tops retrieved during several research cruises in the Atlantic Ocean, in order to improve the understanding of isotope fractionation and element partitioning resulting from biomineralisation processes and changes in ambient conditions. Species include foraminifers secreting tests composed of hyaline low magnesium calcite, porcelaneous high magnesium calcite as well as aragonite. Our results demonstrate systematic isotope fractionation and element partitioning patterns specific for these foraminiferal groups. Calcium isotope fractionation is similar in porcelaneous and hyaline calcite tests and both groups demonstrate the previously described anomaly with enrichment of heavy isotopes around 3-4 °C (Gussone and Filipsson, 2010). Calcium isotope ratios of the aragonitic species Hoeglundina elegans, on the other hand, are about 0.4‰ lighter compared to the calcitic species, which is in general agreement with stronger fractionation in inorganic aragonite compared to calcite. However, the low and strongly variable Sr content suggests additional processes during test formation, and we propose that transmembrane ion transport or a precursor phase to aragonite may be involved. Porcelaneous tests, composed of high Mg calcite, incorporate higher amounts of Sr compared to hyaline low Mg calcite, in agreement with inorganic calcite systematics, but also porcelaneous tests with reduced Mg/Ca show high Sr/Ca. While calcium isotopes, Sr/Ca and Mg/Ca in benthonic foraminifers primarily appear to fractionate and partition with a dominant inorganic control, δ44/40Ca temperature and growth rate dependencies of benthonic foraminifer tests favour a dominant contribution of light Ca by transmembrane transport relative to unfractionated seawater Ca to the calcifying fluid, thus controlling the formation of foraminiferal δ44/40Ca and Sr/Ca proxy signals.

Seasonal dripwater Mg/Ca and Sr/Ca variations driven by cave ventilation: Implications for and modeling of speleothem paleoclimate records

USGS Publications Warehouse

Wong, C.I.; Banner, J.L.; Musgrove, M.

2011-01-01

A 4-year study in a central Texas cave quantifies multiple mechanisms that control dripwater composition and how these mechanisms vary at different drip sites. We monitored cave-air compositions, in situ calcite growth, dripwater composition and drip rate every 4-6weeks. Three groups of drip sites are delineated (Groups 1-3) based on geochemical variations in dripwater composition. Quantitative modeling of mineral-solution reactions within the host carbonate rock and cave environments is used to identify mechanisms that can account for variations in dripwater compositions. The covariation of Mg/Ca (and Sr/Ca) and Sr isotopes is key in delineating whether Mg/Ca and Sr/Ca variations are dictated by water-rock interaction (i.e., calcite or dolomite recrystallization) or prior calcite precipitation (PCP). Group 1 dripwater compositions reflects a narrow range of the extent of water-rock interaction followed by varying amounts of prior calcite precipitation (PCP). Group 2 dripwater compositions are controlled by varying amounts of water-rock interaction with little to no PCP influence. Group 3 dripwater compositions are dictated by variable extents of both water-rock interaction and PCP. Group 1 drip sites show seasonal variations in dripwater Mg/Ca and Sr/Ca, whereas the other drip sites do not. In contrast to the findings of most previous dripwater Mg/Ca-Sr/Ca studies, these seasonal variations (at Group 1 drip sites) are independent of changes in water flux (i.e., rainfall and/or drip rate), and instead significantly correlate with changes in cave-air CO2 concentrations. These results are consistent with lower cave-air CO2, related to cool season ventilation of the cave atmosphere, enhancing calcite precipitation and leading to dripwater geochemical evolution via PCP. Group 1 dripwater Mg/Ca and Sr/Ca seasonality and evidence for PCP as a mechanism that can account for that seasonality, have two implications for many other regions where seasonal ventilation of caves is likely: (1) speleothem trace-element records may provide seasonal signals, and (2) such records may be biased toward recording climate conditions during the season when calcite is depositing. Additionally, we use our results to construct a forward model that illustrates the types of speleothem Mg/Ca and Sr/Ca variations that would result from varying controls on dripwater compositions. The model provides a basis for interpreting paleo-dripwater controls from high frequency Mg/Ca and Sr/Ca variations for speleothems from caves at which long term monitoring studies are not feasible. ?? 2011 Elsevier Ltd.

Geochemical processes leading to the precipitation of subglacial carbonate crusts at Bossons glacier, Mont Blanc Massif (French Alps)

NASA Astrophysics Data System (ADS)

Thomazo, Christophe; Buoncristiani, Jean-Francois; Vennin, Emmanuelle; Pellenard, Pierre; Cocquerez, Theophile; Mugnier, Jean L.; Gérard, Emmanuelle

2017-09-01

Cold climate carbonates can be used as paleoclimatic proxies. The mineralogy and isotopic composition of subglacially precipitated carbonate crusts provide insights into the subglacial conditions and processes occurring at the meltwater-basement rock interface of glaciers. This study documents such crusts discovered on the lee side of a gneissic roche moutonnée at the terminus of the Bossons glacier in the Mont Blanc Massif area (France). The geological context and mineralogical investigations suggest that the Ca used for the precipitation of large crystals of radial fibrous sparite observed in these crusts originated from subglacial chemical weathering of Ca-bearing minerals of the local bedrock (plagioclase and amphibole). Measurements of the carbon and oxygen isotope compositions in the crusts indicate precipitation at, or near to, equilibrium with the basal meltwater under open system conditions during refreezing processes. The homogeneous and low carbonate δ13C values (ca. -11.3‰) imply a large contribution of soil organic carbon to the Bossons subglacial meltwater carbon reservoir at the time of deposition. In addition, organic remains trapped within the subglacially precipitated carbonate crusts give an age of deposition around 6500 years cal BP suggesting that the Mid-Holocene climatic and pedological optima are archived in the Bossons glacier carbonate crusts.

Oxygen isotope constraints on the alteration temperatures of CM chondrites

NASA Astrophysics Data System (ADS)

Verdier-Paoletti, Maximilien J.; Marrocchi, Yves; Avice, Guillaume; Roskosz, Mathieu; Gurenko, Andrey; Gounelle, Matthieu

2017-01-01

We report a systematic oxygen isotopic survey of Ca-carbonates in nine different CM chondrites characterized by different degrees of alteration, from the least altered known to date (Paris, 2.7-2.8) to the most altered (ALH 88045, CM1). Our data define a continuous trend that crosses the Terrestrial Fractionation Line (TFL), with a general relationship that is indistinguishable within errors from the trend defined by both matrix phyllosilicates and bulk O-isotopic compositions of CM chondrites. This bulk-matrix-carbonate (BMC) trend does not correspond to a mass-dependent fractionation (i.e., slope 0.52) as it would be expected during fluid circulation along a temperature gradient. It is instead a direct proxy of the degree of O-isotopic equilibration between 17,18O-rich fluids and 16O-rich anhydrous minerals. Our O-isotopic survey revealed that, for a given CM, no carbonate is in O-isotopic equilibrium with its respective surrounding matrix. This precludes direct calculation of the temperature of carbonate precipitation. However, the O-isotopic compositions of alteration water in different CMs (inferred from isotopic mass-balance calculation and direct measurements) define another trend (CMW for CM Water), parallel to BMC but with a different intercept. The distance between the BMC and CMW trends is directly related to the temperature of CM alteration and corresponds to average carbonates and serpentine formation temperatures of 110 °C and 75 °C, respectively. However, carbonate O-isotopic variations around the BMC trend indicate that they formed at various temperatures ranging between 50 and 300 °C, with 50% of the carbonates studied here showing precipitation temperature higher than 100 °C. The average Δ17O and the average carbonate precipitation temperature per chondrite are correlated, revealing that all CMs underwent similar maximum temperature peaks, but that altered CMs experienced protracted carbonate precipitation event(s) at lower temperatures than the least altered CMs. Our data suggest that the Δ17O value of Ca-carbonates could be a reliable proxy of the degree of alteration experienced by CM chondrites.

Linking Barbados Mineral Dust Aerosols to North African Sources Using Elemental Composition and Radiogenic Sr, Nd, and Pb Isotope Signatures

NASA Astrophysics Data System (ADS)

Bozlaker, Ayse; Prospero, Joseph M.; Price, Jim; Chellam, Shankararaman

2018-01-01

Large quantities of African dust are carried across the Atlantic to the Caribbean Basin and southern United States where it plays an important role in the biogeochemistry of soils and waters and in air quality. Dusts' elemental and isotopic composition was comprehensively characterized in Barbados during the summers of 2013 and 2014, the season of maximum dust transport. Although total suspended insoluble particulate matter (TSIP) mass concentrations varied significantly daily and between the two summers, the abundances (μg element/g TSIP) of 50 elements during "high-dust days" (HDD) were similar. Aerosols were regularly enriched in Na, Cu, Zn, As, Se, Mo, Cd, Sn, Sb, and W relative to the upper continental crust. Enrichment of these elements, many of which are anthropogenically emitted, was significantly reduced during HDD, attributed to mixing and dilution with desert dust over source regions. Generally, Ti/Al, Si/Al, Ca/Al, Ti/Fe, Si/Fe, and Ca/Fe ratios during HDD differed from their respective values in hypothesized North African source regions. Nd isotope composition was relatively invariant for "low-dust days" (LDD) and HDD. In contrast, HDD-aerosols were more radiogenic exhibiting higher 87Sr/86Sr, 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios compared to LDD. Generally, Barbados aerosols' composition ranged within narrow limits and was much more homogeneous than that of hypothesized African source soils. Our results suggest that summertime Barbados aerosols are dominated by a mixture of particles originating from sources in the Sahara-Sahel regions. The Bodélé Depression, long suspected as a major source, appears to be an insignificant contributor of summertime western Atlantic dust.

A IAB-Complex Iron Meteorite Containing Low-Ca Clinopyroxene: Northwest Africa 468 and its Relationship to Iodranites and Formation by Impact Melting

NASA Technical Reports Server (NTRS)

Rubin, Alan E.; Kallemeyn, Gregory W.; Wasson, John T.

2002-01-01

Northwest Africa 468 (NWA 468) is a new ungrouped, silicate-rich member of the IAB complex of nonmagmatic iron meteorites. The silicates contain relatively coarse (approximately 300 micron-size) grains of low-Ca clinopyroxene with polysynthetic twinning and inclined extinction. Low-Ca clinopyroxene is indicative of quenching from high temperatures (either from protoenstatite in a few seconds or high-temperature clinoenstatite in a few hours). It seems likely that NWA 468 formed by impact melting followed by rapid cooling to less than or equal to 660 C. After the loss of a metal-sulfide melt from the silicates, sulfide was reintroduced, either from impact-mobilized FeS or as an S2 vapor that combined with metallic Fe to produce FeS. The O-isotopic composition (delta O-17 = -1.39 %) indicates that the precursor material of NWA 468 was a metal-rich (e.g., CR) carbonaceous chondrite. Lodranites are similar in bulk chemical and O-isotopic composition to the silicates in NWA 468; the MAC 88177 lodranite (which also contains low-Ca clinopyroxene) is close in bulk chemical composition. Both NWA 468 and MAC 88177 have relatively low abundances of REE (rare earth elements) and plagiophile elements. Siderophiles in the metal-rich areas of NWA 468 are similar to those in the MAC 88177 whole rock; both samples contain low Ir and relatively high Fe, Cu and Se. Most unweathered lodranites contain approximately 20 - 38 wt. % metallic Fe-Ni. These rocks may have formed in an analogous manner to NWA 468 (i.e., by impact melting of metal-rich carbonaceous-chondrite precursors) but with less separation of metal-rich melts from silicates.

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

NASA Astrophysics Data System (ADS)

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

2017-12-01

Ca isotope ratio analysis (δ44/40Ca) is a powerful tool to investigate diagenetic reactions in marine sedimentary porewater systems, as it is sensitive to processes such as carbonate dissolution, precipitation, recrystallization, ion exchange and deep fluid sources, due to the isotopic difference between dissolved Ca and solid carbonate minerals (e.g. [1];[2]). We analyzed eight sediment cores of the (paleo-) Pacific equatorial age transect. Two sediment cores show decreasing Ca isotope profiles starting at the sediment/water interface with seawater-like values down to sediment-like values due to recrystallization and an increasing in the bottom part again to seawater-like values. The other studied cores show different degrees of flattening of this middle bulge. We interpret this pattern either as an effect of sediment composition and thickness, decreasing recrystallization rates and/or fluid flux or a combination of all of these factors at the respective sampling sites. Element concentration profiles and Sr-isotope variations on some of these sediment cores show a similar behavior, supporting our findings ([3]; [4]). Seawater influx at (inactive) seamounts is supposed to cause seawater-like values at the bottom of the sediment cores by fluids migrating through the oceanic basement (e.g. [5]). While [6] hypothesizes that two seamounts or bathymetric pits are connected, with a recharge and a discharge site [7] say that uptaken fluids could be released through the surrounding seafloor as well due to diffusive exchange with the underlying oceanic crust. Our Ca isotope results combined with a transport reaction model approach support the latter hypothesis. References: [1] Teichert B. M., Gussone N. and Torres M. E. (2009) [2] Ockert C., Gussone N., Kaufhold S. and Teichert B. (2013) [3] Pälike H., Lyle M., Nishi H., Raffi I., Gamage K. and Klaus A. (eds.) (2010) [4] Voigt J., Hathorne E. C., Frank M., Vollstaedt H. and Eisenhauer A. (2015) [5] Villinger H. W., Pichler T., Kaul N., Stephan S., Pälike H. and Stephan F. (2017) [6] Bekins B. A., Spivack A. J., Davis E. E. and Mayer L. A. (2007) [7] Mewes K., Mogollón J. M., Picard A., Rühlemann C., Eisenhauer A., Kuhn T., Ziebis W. and Kasten S. (2016)

Geochemistry of water and gas discharges from the Mt. Amiata silicic complex and surrounding areas (central Italy)

NASA Astrophysics Data System (ADS)

Minissale, A.; Magro, G.; Vaselli, O.; Verrucchi, C.; Perticone, I.

1997-12-01

The Mt. Amiata volcano in central Italy is intimately related to the post-orogenic magmatic activity which started in Pliocene times. Major, trace elements, and isotopic composition of thermal and cold spring waters and gas manifestations indicate the occurrence of three main reservoir of the thermal and cold waters in the Mt. Amiata region. The deepest one is located in an extensive carbonate reservoir buried by thick sequences of low-permeability allochthonous and neo-autochthonous formations. Thermal spring waters discharging from this aquifer have a neutral Ca-SO 4 composition due to the presence of anhydrite layers at the base of the carbonate series and, possibly, to absorption of deep-derived H 2S with subsequent oxidation to SO 42- in a system where pH is buffered by the calcite-anhydrite pair ( Marini and Chiodini, 1994). Isotopic signature of these springs and N 2-rich composition of associated gas phases suggest a clear local meteoric origin of the feeding waters, and atmospheric O 2 may be responsible for the oxidation of H 2S. The two shallower aquifers have different chemical features. One is Ca-HCO 3 in composition and located in several sedimentary formations above the Mesozoic carbonates. The other one has a Na-Cl composition and is hosted in marine sediments filling many post-orogenic NW-SE-trending basins. Strontium, Ba, F, and Br contents have been used to group waters associated with each aquifer. Although circulating to some extent in the same carbonate reservoir, the deep geothermal fluids at Latera and Mt. Amiata and thermal springs discharging from their outcropping areas have different composition: Na-Cl and Ca-SO 4 type, respectively. Considering the high permeability of the reservoir rock, the meteoric origin of thermal springs and the two different composition of the thermal waters, self-sealed barriers must be present at the boundaries of the geothermal systems. The complex hydrology of the reservoir rocks greatly affects the reliability of geothermometers in liquid phase, which understimate the real temperatures of the discovered geothermal fields. More reliable temperatures are envisaged by using gas composition-based geothermometers. Bulk composition of the 67 gas samples studied seems to be the result of a continuous mixing between a N 2-rich component of meteoric origin related to the Ca-SO 4 aquifer and a deep CO 2-rich component rising largely along the boundaries of the geothermal systems. Nitrogen-rich gas samples have nearly atmospheric N 2/Ar (=83) and 15N/ 14N ( δ=0‰) ratios whereas CO 2-rich samples show anomalously high δ15N values (up to +6.13 ‰), likely related to N 2 from metamorphic schists lying below the carbonate formations. On the basis of average 13C/ 12C isotopic ratio ( δ13C around 0‰), CO 2 seems to originate mainly from thermometamorphic reactions in the carbonate reservoir and/or in carbonate layers embedded in the underlying metamorphic basement. Distribution of 3He/ 4He isotopic ratios indicates a radiogenic origin of helium in a tectonic environment that, in spite of the presence of many post-orogenic basins and mantle-derived magmatics, can presently be considered in a compressive phase.

Hydrogeochemistry and quality of surface water and groundwater in the vicinity of Lake Monoun, West Cameroon: approach from multivariate statistical analysis and stable isotopic characterization.

PubMed

Kamtchueng, Brice T; Fantong, Wilson Y; Wirmvem, Mengnjo J; Tiodjio, Rosine E; Takounjou, Alain F; Ndam Ngoupayou, Jules R; Kusakabe, Minoru; Zhang, Jing; Ohba, Takeshi; Tanyileke, Gregory; Hell, Joseph V; Ueda, Akira

2016-09-01

With the use of conventional hydrogeochemical techniques, multivariate statistical analysis, and stable isotope approaches, this paper investigates for the first time surface water and groundwater from the surrounding areas of Lake Monoun (LM), West Cameroon. The results reveal that waters are generally slightly acidic to neutral. The relative abundance of major dissolved species are Ca(2+) > Mg(2+) > Na(+) > K(+) for cations and HCO3 (-) ≫ NO3 (-) > Cl(-) > SO4 (2-) for anions. The main water type is Ca-Mg-HCO3. Observed salinity is related to water-rock interaction, ion exchange process, and anthropogenic activities. Nitrate and chloride have been identified as the most common pollutants. These pollutants are attributed to the chlorination of wells and leaching from pit latrines and refuse dumps. The stable isotopic compositions in the investigated water sources suggest evidence of evaporation before recharge. Four major groups of waters were identified by salinity and NO3 concentrations using the Q-mode hierarchical cluster analysis (HCA). Consistent with the isotopic results, group 1 represents fresh unpolluted water occurring near the recharge zone in the general flow regime; groups 2 and 3 are mixed water whose composition is controlled by both weathering of rock-forming minerals and anthropogenic activities; group 4 represents water under high vulnerability of anthropogenic pollution. Moreover, the isotopic results and the HCA showed that the CO2-rich bottom water of LM belongs to an isolated hydrological system within the Foumbot plain. Except for some springs, groundwater water in the area is inappropriate for drinking and domestic purposes but good to excellent for irrigation.

The isotopic composition of uranium and lead in Allende inclusions and meteoritic phosphates

NASA Technical Reports Server (NTRS)

Chen, J. H.; Wasserburg, G. J.

1981-01-01

The isotopic compositions of uranium and lead in Ca-Al-rich inclusions from the Allende chondrite and in whitlockite from the St. Severin chondrite and the Angra dos Reis achondrite are reported. Isoptopic analysis of acid soluble fractions of the Allende inclusions and the meteoritic whitlockite, which show isotopic anomalies in other elements, reveals U-235/U-238 ratios from 1/137.6 to 1/138.3, within 20 per mil of normal terrestrial U abundances. The Pb isotopic compositions of five coarse-grained Allende inclusions give a mean Pb-207/Pb-206 model age of 4.559 + or - 0.015 AE, in agreement with the U results. Pb isotope ratios of two fine-grained inclusions and a coarse-grained inclusion with strong mass fractionation and some nonlinear isotopic anomalies indicate that the U-Pb systems of these inclusions have evolved differently from the rest of Allende. Th/U abundance ratios in the Allende inclusions and meteoritic phosphate are found to range from 3.8 to 96, presumably indicating an optimal case for Cm/U fractionation, although the normal U concentrations do not support claims of abundant live Cm-247 or Cm-247/U-238 fractionation at the time of meteorite formation, in contrast to previous results. A limiting Cm-247/U-235 ratio of 0.004 at the time of meteorite formation is calculated which implies that the last major r process contribution at the protosolar nebula was approximately 100 million years prior to Al-26 formation and injection.

Isotopic mass independent signature of black crusts: a proxy for atmospheric aerosols formation in the Paris area (France).

NASA Astrophysics Data System (ADS)

Genot, Isabelle; Martin, Erwan; Yang, David Au; De Rafelis, Marc; Cartigny, Pierre; Wing, Boswell; Le Gendre, Erwann; Bekki, Slimane

2016-04-01

In view of the negative forcing of the sulfate aerosols on climate, a more accurate understanding of the formation of these particles is crucial. Indeed, despite the knowledge of their effects, uncertainties remain regarding the formation of sulfate aerosols, particularly the oxidation processes of S-bearing gases. Since the discovery of oxygen and sulfur mass independent fractionation (O- and S-MIF) processes on Earth, the sulfate isotopic composition became essential to investigate the atmospheric composition evolution and its consequences on the climate and the biosphere. Large amount of S-bearing compounds (SO2 mainly) is released into the atmosphere by anthropogenic and natural sources. Their oxidation in the atmosphere generates sulfate aerosols, H2SO4, which precipitate on the earth surface mainly as acid rain. One consequence of this precipitation is the formation of black crust on buildings made of carbonate stones. Indeed the chemical alteration of CaCO3 by H2SO4 leads to gypsum (CaSO4·2H2O) concretions on building walls. Associated to other particles, gypsum forms black-crusts. Therefore, black crusts acts as 'sulfate aerosol traps', meaning that their isotopic composition reveals the composition and thus the source and formation processes of sulfate aerosols in the atmosphere in a specific region. In this study we collected 37 black crusts on a 300km NW-SE profile centered on Paris (France). In our samples, sulfate represent 40wt.% and other particles 60wt.% of the black crusts. After sulfate extraction from each samples we measured their O- and S-isotopes composition. Variations of about 10‰ in δ18O and δ34S are observed and both O-MIF (Δ17O from 0 to 1.4‰) and S-MIF (Δ33S from 0 to -0.3‰) compositions have been measured. In regards to these compositions we can discuss the source and formation (oxidation pathways) of the sulfate aerosols in troposphere above the Paris region that covers urban, rural and coastal environments. Furthermore, this study shows for the first time O- and S-MIF signature in black crusts. Finally, we demonstrate that black crusts can be considered as a good 'sulfate aerosols traps', which can be widely used to study the sulfate aerosol formation, fate and sink in the troposphere.

Interpreting the Marine Calcium Isotope Record: Influence of Reef Builders

NASA Astrophysics Data System (ADS)

Boehm, F.; Eisenhauer, A.; Farkas, J.; Kiessling, W.; Veizer, J.; Wallmann, K.

2008-12-01

The calcium isotopic composition of seawater as recorded in brachiopod shells varied substantially during the Paleozoic (Farkas et al. 2007, Geochim. Cosmochim. Acta, 71, 5117-5134). The most prominent feature of the record is an excursion to higher 44Ca/40Ca values that started during the Early Carboniferous and lasted until the Permian. The shift occurred shortly after the transition from a calcite-sea to an aragonite-sea (Sandberg 1983, Nature 305, 19-22; Stanley and Hardie 1998, Pal3, 144, 3-19). It therefore has been interpreted to reflect a change in the average calcium isotope fractionation of carbonates produced in the oceans. Aragonite is depleted by about 0.6 permil in 44Ca/40Ca compared to calcite (Gussone et al. 2005, Geochim. Cosmochim. Acta, 69, 4485-4494). Consequently a transient shift from calcite dominated to an aragonite dominated calcium carbonate sedimentation could have caused the observed 0.5 permil isotope shift. We compare the marine calcium isotope record with a new compilation of the Phanerozoic trends in the skeletal mineralogy of marine invertebrates (Kiessling et al. 2008, Nature Geoscience, 1, 527-530). The compilation is based on data collected in the PaleoReef database and the Paleobiology Database, which include information on Phanerozoic reef complexes and taxonomic collection data of Phanerozoic biota, respectively. We find a strong positive correlation between the calcium isotope ratios and the abundance of aragonitic reef builders from the Silurian until the Permian at a sample resolution of about 10 million years. The two records, however, diverge in the Triassic, when reefs were dominated by aragonite but the calcium isotope values remained at a relatively low level. We also find a good correlation between calcium isotopes and the proportion of aragonite in the general record of Phanerozoic biota. However, in this case the records start to diverge already in the latest Carboniferous. The observations suggest that the Paleozoic calcium isotope record was indeed strongly controlled by the skeletal mineralogy of the major carbonate producers. The collapse of the correlation in the late Paleozoic points to the evolution of new biocalcification mechanisms that allowed a more strict biological control of the calcium fluxes in the calcifying biota (sensu Gussone et al. 2006, Geology, 34, 625-628).

Lunar and Planetary Science XXXV: Special Session: Oxygen in the Solar System, II

NASA Technical Reports Server (NTRS)

2004-01-01

The Special Session: Oxygen in the Solar System, II, included the following reports:Evolution of Oxygen Isotopes in the Solar Nebula; Disequilibrium Melting of Refractory Inclusions: A Mechanism for High-Temperature Oxygen; Isotope Exchange in the Solar Nebula; Oxygen Isotopic Compositions of the Al-rich Chondrules in the CR Carbonaceous Chondrites: Evidence for a Genetic Link to Ca-Al-rich Inclusions and for Oxygen Isotope Exchange During Chondrule Melting; Nebular Formation of Fayalitic Olivine: Ineffectiveness of Dust Enrichment; Water in Terrestrial Planets: Always an Oxidant?; Oxygen Barometry of Basaltic Glasses Based on Vanadium Valence Determination Using Synchrotron MicroXANES; A New Oxygen Barometer for Solar System Basaltic Glasses Based on Vanadium Valence; The Relationship Between Clinopyroxene Fe3+ Content and Oxygen Fugacity ; and Olivine-Silicate Melt Partitioning of Iridium.

Laboratory calibration of the calcium carbonate clumped isotope thermometer in the 25-250 °C temperature range

NASA Astrophysics Data System (ADS)

Kluge, Tobias; John, Cédric M.; Jourdan, Anne-Lise; Davis, Simon; Crawshaw, John

2015-05-01

Many fields of Earth sciences benefit from the knowledge of mineral formation temperatures. For example, carbonates are extensively used for reconstruction of the Earth's past climatic variations by determining ocean, lake, and soil paleotemperatures. Furthermore, diagenetic minerals and their formation or alteration temperature may provide information about the burial history of important geological units and can have practical applications, for instance, for reconstructing the geochemical and thermal histories of hydrocarbon reservoirs. Carbonate clumped isotope thermometry is a relatively new technique that can provide the formation temperature of carbonate minerals without requiring a priori knowledge of the isotopic composition of the initial solution. It is based on the temperature-dependent abundance of the rare 13C-18O bonds in carbonate minerals, specified as a Δ47 value. The clumped isotope thermometer has been calibrated experimentally from 1 °C to 70 °C. However, higher temperatures that are relevant to geological processes have so far not been directly calibrated in the laboratory. In order to close this calibration gap and to provide a robust basis for the application of clumped isotopes to high-temperature geological processes we precipitated CaCO3 (mainly calcite) in the laboratory between 23 and 250 °C. We used two different precipitation techniques: first, minerals were precipitated from a CaCO3 supersaturated solution at atmospheric pressure (23-91 °C), and, second, from a solution resulting from the mixing of CaCl2 and NaHCO3 in a pressurized reaction vessel at a pressure of up to 80 bar (25-250 °C).

Structure of liquid tricalcium aluminate

NASA Astrophysics Data System (ADS)

Drewitt, James W. E.; Barnes, Adrian C.; Jahn, Sandro; Kohn, Simon C.; Walter, Michael J.; Novikov, Alexey N.; Neuville, Daniel R.; Fischer, Henry E.; Hennet, Louis

2017-02-01

The atomic-scale structure of aerodynamically levitated and laser-heated liquid tricalcium aluminate (Ca3Al2O6 ) was measured at 2073(30) K by using the method of neutron diffraction with Ca isotope substitution (NDIS). The results enable the detailed resolution of the local coordination environment around calcium and aluminum atoms, including the direct determination of the liquid partial structure factor, SCaCa(Q ) , and partial pair distribution function, gCaCa(r ) . Molecular dynamics (MD) simulation and reverse Monte Carlo (RMC) refinement methods were employed to obtain a detailed atomistic model of the liquid structure. The composition Ca3Al2O6 lies at the CaO-rich limit of the CaO:Al2O3 glass-forming system. Our results show that, although significantly depolymerized, liquid Ca3Al2O6 is largely composed of AlO4 tetrahedra forming an infinite network with a slightly higher fraction of bridging oxygen atoms than expected for the composition. Calcium-centered polyhedra exhibit a wide distribution of four- to sevenfold coordinated sites, with higher coordinated calcium preferentially bonding to bridging oxygens. Analysis of the MD configuration reveals the presence of ˜10 % unconnected AlO4 monomers and Al2O7 dimers in the liquid. As the CaO concentration increases, the number of these isolated units increases, such that the upper value for the glass-forming composition of CaO:Al2O3 liquids could be described in terms of a percolation threshold at which the glass can no longer support the formation of an infinitely connected AlO4 network.

Calcium isotope signature: new proxy for net change in bone volume for chronic kidney disease and diabetic rats.

PubMed

Tanaka, Yu-Ki; Yajima, Nobuyuki; Higuchi, Yusuke; Yamato, Hideyuki; Hirata, Takafumi

2017-12-01

Herein, we measure the Ca isotope ratios ( 44 Ca/ 42 Ca and 43 Ca/ 42 Ca) in serum and bone samples collected from rats with chronic kidney disease (CKD) or diabetes mellitus (DM). For the serum samples, the isotope ratios are lower for the CKD (δ 44 Ca/ 42 Ca serum = 0.16 ± 0.11‰; 2SD, n = 6) and the DM (δ 44 Ca/ 42 Ca serum = -0.11 ± 0.25‰; 2SD, n = 7) rats than that for the control rats (δ 44 Ca/ 42 Ca serum = 0.25 ± 0.04‰; 2SD, n = 7). Bone samples from two distinct positions of 20 rats in total, namely, the center and proximal parts of the tibial diaphysis, are subject to Ca isotope analysis. The resulting δ 44 Ca/ 42 Ca values for the bone of the proximal part are about 0.3‰ lower than that for the serum samples from the same rats. The larger isotope fractionations between the serum and bone are consistent with previously reported data for vertebrate animals (e.g., Skulan and DePaolo, 1999), which suggests the preferential incorporation of lighter Ca isotopes through bone formation. For the bones from the control and CKD rats, there were no differences in the δ 44 Ca/ 42 Ca values between the positions of the bone. In contrast, the δ 44 Ca/ 42 Ca values of the bone for the DM rats were different between the positions of the bone. Due to the lower bone turnover rate for the DM rats, the δ 44 Ca/ 42 Ca for the middle of the diaphysis can reflect the Ca isotopes in the bone formed prior to the progression of DM states. Thus, the resulting δ 44 Ca/ 42 Ca values show a clear correlation with bone mineral density (BMD). This can be due to the release of isotopically lighter Ca from the bone to the serum. In the present study, our data demonstrate that the δ 44 Ca/ 42 Ca value for serum can be used as a new biomarker for evaluating changes in bone turnover rate, followed by changes in bone volume.

Barium isotopes in cold-water corals

NASA Astrophysics Data System (ADS)

Hemsing, Freya; Hsieh, Yu-Te; Bridgestock, Luke; Spooner, Peter T.; Robinson, Laura F.; Frank, Norbert; Henderson, Gideon M.

2018-06-01

Recent studies have introduced stable Ba isotopes (δ 138 / 134Ba) as a novel tracer for ocean processes. Ba isotopes could potentially provide insight into the oceanic Ba cycle, the ocean's biological pump, water-mass provenance in the deep ocean, changes in activity of hydrothermal vents, and land-sea interactions including tracing riverine inputs. Here, we show that aragonite skeletons of various colonial and solitary cold-water coral (CWC) taxa record the seawater (SW) Ba isotope composition. Thirty-six corals of eight different taxa from three oceanic regions were analysed and compared to δ 138 / 134Ba measurements of co-located seawater samples. Sites were chosen to cover a wide range of temperature, salinity, Ba concentrations and Ba isotope compositions. Seawater samples at the three sites exhibit the well-established anti-correlation between Ba concentration and δ 138 / 134Ba. Furthermore, our data set suggests that Ba/Ca values in CWCs are linearly correlated with dissolved [Ba] in ambient seawater, with an average partition coefficient of DCWC/SW = 1.8 ± 0.4 (2SD). The mean isotope fractionation of Ba between seawater and CWCs Δ138/134BaCWC-SW is -0.21 ± 0.08‰ (2SD), indicating that CWC aragonite preferentially incorporates the lighter isotopes. This fractionation likely does not depend on temperature or other environmental variables, suggesting that aragonite CWCs could be used to trace the Ba isotope composition in ambient seawater. Coupled [Ba] and δ 138 / 134Ba analysis on fossil CWCs has the potential to provide new information about past changes in the local and global relationship between [Ba] and δ 138 / 134Ba and hence about the operation of the past global oceanic Ba cycle in different climate regimes.

Assessing the isotopic evolution of S-type granites of the Carlos Chagas Batholith, SE Brazil: Clues from U-Pb, Hf isotopes, Ti geothermometry and trace element composition of zircon

NASA Astrophysics Data System (ADS)

Melo, Marilane G.; Lana, Cristiano; Stevens, Gary; Pedrosa-Soares, Antônio C.; Gerdes, Axel; Alkmin, Leonardo A.; Nalini, Hermínio A.; Alkmim, Fernando F.

2017-07-01

The Carlos Chagas batholith (CCB) is a very large ( 14,000 km2) S-type granitic body formed during the syn-collisional stage of the Araçuaí orogen (southeastern Brazil). Zircons extracted from the CCB record a wide range of U-Pb ages (from 825 to 490 Ma), indicating a complex history of inheritance, magmatic crystallization and partial melting during the evolution of the orogeny. Magmatic zircons (ca. 578-588 Ma) are marked by similar Hf isotope compositions and REE patterns to those of inherited cores (ca. 825-600 Ma), indicating that these aspects of the chemical signature of the magmatic zircons have likely been inherited from the source. The U-Pb ages and initial 176Hf/177Hf ratios from anatectic and metamorphic zircon domains are consistent with a two-stage metamorphic evolution marked by contrasting mechanisms of zircon growth and recrystallization during the orogeny. Ti-in-zircon thermometry is consistent with the findings of previous metamorphic work and indicates that the two metamorphic events in the batholith reached granulite facies conditions (> 800 °C) producing two generations of garnet via fluid-absent partial melting reactions. The oldest metamorphic episode (ca. 570-550 Ma) is recorded by development of thin anatectic overgrowths on older cores and by growth of new anatectic zircon crystals. Both domains have higher initial 176Hf/177Hf values compared to relict cores and display REE patterns typical of zircon that grew contemporaneously with peritectic garnet through biotite-absent fluid partial melting reactions. Hf isotopic and chemical evidences indicate that a second anatectic episode (ca. 535-500 Ma) is only recorded in parts from the CCB. In these rocks, the growth of new anatectic zircon and/or overgrowths is marked by high initial 176Hf/177Hf values and also by formation of second generation of garnet, as indicated by petrographic observations and REE patterns. In addition, some rocks contain zircon crystals formed by solid-state recrystallization of pre-existing zircon, which exhibit similar Hf isotope composition to those of inherited/magmatic core domains. The first anatectic event is interpreted as result of crustal thickening after the intrusion of the batholith. This introduced the batholith to a depth in excess of 30 km and produced widespread anatexis throughout the batholith. The second event was associated with asthenospheric upwelling during extensional thinning and gravitational collapse of the orogen, this produced anatexis in parts from the CCB that had been re-fertilized for anatexis by retrogression along shear zones following the first granulite facies event.

Magnesium Isotopic Composition of Kamchatka Sub-Arc Mantle Peridotites

NASA Astrophysics Data System (ADS)

Hu, Y.; Teng, F. Z.; Ionov, D. A.

2016-12-01

Subduction of the oceanic slab may add a crustal isotopic signal to the mantle wedge. The highly variable Mg isotopic compositions (δ26Mg) of the subducted oceanic crust input[1] and arc lava output[2] imply a distinctive Mg isotopic signature of the mantle wedge. Magnesium isotopic data on samples from the sub-arc mantle are still limited, however. To characterize the Mg isotopic composition of typical sub-arc mantle, 17 large and fresh spinel harzburgite xenoliths from Avacha volcano were analyzed. The harzburgites were formed by 30% melt extraction at ≤ 1 2 GPa and fluid fluxing condition, and underwent possible fluid metasomatism as suggested by distinctively high orthopyroxene mode in some samples, the presence of accessory amphibole and highly variable Ba/La ratios[3]. However, their δ26Mg values display limited variation from -0.32 to -0.21, which are comparable to the mantle average at -0.25 ± 0.07[4]. The overall mantle-like and homogenous δ26Mg of Avacha sub-arc peridotites are consistent with their similar chemical compositions and high MgO contents (> 44 wt%) relative to likely crustal fluids. Furthermore, clinopyroxene (-0.24 ± 0.10, 2SD, n = 5), a late-stage mineral exsolved from high-temperature, Ca-rich residual orthopyroxene, is in broad Mg isotopic equilibrium with olivine (-0.27 ± 0.04, 2SD, n = 17) and orthopyroxene (-0.22 ± 0.06, 2SD, n = 17). Collectively, this study finds that the Kamchatka mantle wedge, as represented by the Avacha peridotites, has a mantle-like δ26Mg, and low-degree fluid-mantle interaction does not cause significant Mg isotope fractionation in sub-arc mantle peridotites. [1] Wang et al., EPSL, 2012 [2] Teng et al., PNAS, 2016 [3] Ionov, J. Petrol., 2010, [4] Teng et al., GCA, 2010.

Experimental identification of mechanisms controlling calcium isotopic fractionations by the vegetation.

NASA Astrophysics Data System (ADS)

Cobert, Florian; Schimtt, Anne-Désirée.; Bourgeade, Pascale; Stille, Peter; Chabaux, François; Badot, Pierre-Marie; Jaegler, Thomas

2010-05-01

This study aims to better understand the role of vegetation on the Ca cycle at the level of the critical zone of the Earth, in order to specify the mechanisms controlling the Ca absorption by plants at the rock/plant interface. To do this, we performed experiments using hydroponic plant cultures in a way that we could control the co-occuring geochemical and physiological process and determine the impact of the nutritive solution on the Ca cycle within plants. A dicotyledon and calcicole plant with rapid growth, the French bean (Phaseolus vulgaris L.), has been chosen to have access to one complete growth cycle. Several experiments have been conducted with two Ca concentrations, 6 (L) and 60 (H) ppm and two pH values (4 and 6) in the nutritive solution, for which the Ca concentration was maintained constant, so its Ca content is considered as infinite. A second experiment (non infinite L6) allowed Ca depletion in the solution through time; therefore, response effects on the Ca isotopic signatures in the plant organs and in the nutritive solution were observed. We determined Ca concentrations and isotopic ratios in the nutritive solution and in different organs (main roots, secondary roots, old and young stems, old and young leaves and fruits) at two different growth stages (10 days and 6 weeks). Preliminary results show that: (1) the roots (main and secondary) were enriched in the light isotope (40Ca) compared to the nutritive solution, and leaves were enriched in the heavy isotope (44Ca) compared to stems. These results are in accord with previously published field studies (Wigand et al., 2005; Page et al., 2008; Cenki-Tok et al., 2009; Holmden and Bélanger, 2010). Leaves and secondary roots were however enriched in the heavy isotope (44Ca) compared to bean pods, stems and main roots. These results could be related to kinetic fractionation processes occurring either during the Ca root uptake, or during the Ca transport within the plant, or physiological mechanisms occurring first at the level of secondary roots, and second at the level of leaves. (2) No Ca isotope difference was observed neither between old and young organs, (except for H6 leaves), nor between the two growth stages (except for H6 roots). This suggest that the mechanisms controlling isotopic fractionations of Ca within common beans do not vary during growth, and that the nutrients stored in the cotyledons have only a minor effect on the Ca isotope fractionations of plants harvested after 10 days. (3) Strongest Ca isotope fractionations were observed at the nutritive solution/root interface. This implies that the mechanisms of light isotope enrichments in the plant are mainly due to transport processes taking place at this interface. (4) The non infinite L6 nutritive solution became enriched in 44Ca during the experiment compared to the infinite L6 nutritive solution and all the other solutions (L4, H4, and H6). This enrichment can be explained by Rayleigh fractionation or isotopic equilibrium. (5) Bean organs, from L4 and non infinite L6 experiment conditions, were enriched in 44Ca compared to stems and roots cultivated under H4, H6 and infinite L6 conditions. This might be due to the limited Ca in the nutritive solutions that cause smallest Ca isotope fractionations in the bean organs. All these results show that there is no simple correlation between Ca isotopic variations, Ca content and pH of the nutrient solution, and that physiological effects have also to be involved. They confirm the potential of the Ca isotopic system for tracing biological fractionations in natural ecosystems.

Evidence for nucleosynthetic enrichment of the protosolar molecular cloud core by multiple supernova events.

PubMed

Schiller, Martin; Paton, Chad; Bizzarro, Martin

2015-01-15

The presence of isotope heterogeneity of nucleosynthetic origin amongst meteorites and their components provides a record of the diverse stars that contributed matter to the protosolar molecular cloud core. Understanding how and when the solar system's nucleosynthetic heterogeneity was established and preserved within the solar protoplanetary disk is critical for unraveling the earliest formative stages of the solar system. Here, we report calcium and magnesium isotope measurements of primitive and differentiated meteorites as well as various types of refractory inclusions, including refractory inclusions (CAIs) formed with the canonical 26 Al/ 27 Al of ~5 × 10 -5 ( 26 Al decays to 26 Mg with a half-life of ~0.73 Ma) and CAIs that show fractionated and unidentified nuclear effects (FUN-CAIs) to understand the origin of the solar system's nucleosynthetic heterogeneity. Bulk analyses of primitive and differentiated meteorites along with canonical and FUN-CAIs define correlated, mass-independent variations in 43 Ca, 46 Ca and 48 Ca. Moreover, sequential dissolution experiments of the Ivuna carbonaceous chondrite aimed at identifying the nature and number of presolar carriers of isotope anomalies within primitive meteorites have detected the presence of multiple carriers of the short-lived 26 Al nuclide as well as carriers of anomalous and uncorrelated 43 Ca, 46 Ca and 48 Ca compositions, which requires input from multiple and recent supernovae sources. We infer that the solar system's correlated nucleosynthetic variability reflects unmixing of old, galactically-inherited homogeneous dust from a new, supernovae-derived dust component formed shortly prior to or during the evolution of the giant molecular cloud parental to the protosolar molecular cloud core. This implies that similarly to 43 Ca, 46 Ca and 48 Ca, the short-lived 26 Al nuclide was heterogeneously distributed in the inner solar system at the time of CAI formation.

O and C stable isotopes in cryogenic cave calcite (CCC) - possible proxy for past climate changes

NASA Astrophysics Data System (ADS)

-Andreea, Badaluta Carmen; Ersek, Vasile; Piotrowska, Natalia; Persoiu, Aurel

2017-04-01

Perennial ice deposits in caves host various proxies of past climate variability, most notable, the isotopic composition of ice, which has been shown to reflect, generally, the temperature outside the cave during the formation of ice (usually, autumn though spring). This ice forms by the freezing of water, water that contains large amounts of dissolved calcium carbonate. The freezing is accompanied by degassing of CO2, and precipitation of cryogenic cave calcite (CCC) under strong kinetic conditions. These kinetic processes could lead to the alteration of the original putative climatic signal carried by the isotopic composition of CCC. Here, we present a possibly climatic explanation of the isotopic composition of CCC from a 1000 years old cave ice deposit from Scărișoara Ice Cave (SIC) in Romania, Eastern Europe. In a 7 m core from the Great Hall of SIC we have analyzed the isotopic composition of the water (oxygen and hydrogen) and CCC (oxygen and carbon) from individual ice layers in the core, as well as that of precipitation , outside the cave. The isotopic composition of precipitation from the cave area varies between -3.6 ‰ for δˡ⁸O and -22 ‰ for δ2H in summer, and -17.8 ‰ for δˡ⁸O and -22 ‰ for δ2H in winter, with mean values of -9.1 ‰ for δˡ⁸O and -62 ‰ for δ2H. A positive correlation between air temperature and the isotopic composition of precipitation, as well as drip water in the cave has been found. The mean values in the ice core during the past 1000 years are -10.3‰ for δ18O and -71 ‰ for δ2H. The water isotopic values in the ice core show low values up to 900 AD, higher values between 900 and 1300 AD (Medieval Warm Period, MWP), and again lower values after 1300 AD (Little Ice Age, LIA), reaching their minimum after 1800 AD. The isotopic composition of CCC shows slightly higher values in the MWP and lower in LIA, possibly suggesting a climatic influence. Modern observations are too short to be able to calibrate this putative signal. Further, clumped isotope thermometry has shown that the kinetic fractionation that dominates during the freezing of water leads to unusual reconstructed formative temperature: +20°C. However, δˡ3C and δˡ⁸O values in CCC have higher values for samples from the MWP than those from the LIA. CCC results from the deposition of CaCO3 from Ca(CO3)2. The main source of CO2 to form carbonic acid is soil CO2, produced by root respiration. Previous studies have shown that δˡ⁸O of this CO2 is in equilibrium with the δˡ⁸O of water, so that the higher (lower) δˡ⁸O values of CCC could reflect warmer (colder) conditions during the MPW (LIA). The interpretation of δˡ3C values of CCC is less straightforward. Higher δˡ3C values in soil CO2 are determined by moisture limitation on plants, either due to low moisture or higher evaporative conditions. While the MWP was warmer in the study area, conflicting data exists on precipitation, with studies suggesting both drier and wetter conditions, so that is difficult to interpret our carbon isotope data. Apart from the direct climatic influence, the depth of soil could have also played a part, as deeper soils, as expected under birch forests that dominated during the MWP, would have had more enrichment in the heavy isotopes with depth, than the thiner soils of the LIA (formed under mostly spruce forests). Further, drought/higher temperatures could also influence the kinetics of the reaction, which can be large enough to overprint any soil signal in δˡ3C.

Lead Isotopic Source Signatures for Rains and River Waters in Taiwan

NASA Astrophysics Data System (ADS)

You, C.; Cheng, M.; Lee, M.; Lin, F.

2002-12-01

Lead isotopic compositions and Pb contents in rains and river waters are sensitive proxies for air-pollutant sources and their transport processes. We have collected more than 100 wet precipitations between 1998 and 2001 at Peng-Chia Yu, an offshore island in northern Taiwan, and two other cities, Taichung and Tainan, located at central and southern Taiwan. Additional 14 river waters collected along the Er-Ren-Shi River, Tainan were investigated for systematic comparison. All collected samples were analyzed for major ions (i.e., Cl, Na, Mg, Ca, SO4, NO3 and NH4) by ion chromatography, trace elements and Pb isotopes by ICP-MS (Element II) installed at NCKU. The Peng-Chia Yu rains show large seasonal variation in major ions where Na and Cl are much higher in the winter season. Significant industrial contributions of SO4, NH4 and nsCa are detected at Taichung and Tainan. Trace element results display a more complicated picture, suggesting mixing among seasalt, Asia continental dust, and atmospheric pollutant. These chemical data can be understood in terms of seasonal wind direction changes due to the Asian monsoon system. In winter, the northerly cold wind blow materials with high concentration of anthropogenic input (i.e., Pb and SO4) and dust source (i.e., Al and Ca) from the Asia continent. In contrast, the intertropical convergence zone (ITCZ) migrates northward and caused southwest monsoon prevail in the summer. The 208Pb/207Pb ratio shows consistent seasonal trends as that of Pb contents, possibly a result of mixing between Asia atmospheric sources and seasalt. For the Er-ren Shi River waters, Pb and Pb isotopic compositions vary systematically downstream. Pb concentrations decrease rapidly from 5200 ppt at upstream stations to a value of less than 50 ppt near the estuary whereas 208Pb/207Pb varied between 2.087 and 2.124. The 208Pb/206Pb vs. 1/Pb plot demonstrates a mixing trend between anthropogenic sources and seawater. These results demonstrate that Pb and Pb isotopes in rains and river waters can be used as useful tools for tracing air-borne pollutant sources and their transportation processes.

Hydrologic, chemical, and isotopic characterization of two small watersheds on Catoctin Mountain, north-central Maryland, U.S.A.

USGS Publications Warehouse

Rice, Karen C.; Bricker, O.P.

1993-01-01

Two small (100 ha) watersheds located on Catoctin Mountain in north-central Maryland were intensively instrumented in 1990 and have been hydrologically, chemically, and isotopically monitored for 3 years. Dissolved concentrations of major ions (Ca2+, Mg2+, Na+, K+, total AI, CI-, NO3-, SO42- , HCO3-, and SiO2) and stable isotopic (D and 18O) values have been analyzed for most types of water (precipitation, throughfall, two depths of soil water, shallow groundwater, and streamwater) that enter, travel through, and exit each watershed. The major objectives of the study were to characterize the chemical and isotopic signatures of all aqueous components of the watersheds and to interpret the causes of the changes in chemical and isotopic compositions of streamwater during storm runoff. This paper describes selected results of the study.

Re-Os isotopic evidence for an enriched-mantle source for the Noril'sk-type, ore-bearing intrusions, Siberia

USGS Publications Warehouse

Walker, R.J.; Morgan, J.W.; Horan, M.F.; Czamanske, G.K.; Krogstad, E.J.; Fedorenko, V.A.; Kunilov, V.E.

1994-01-01

Magmatic Cu-Ni sulfide ores and spatially associated ultramafic and mafic rocks from the Noril'sk I, Talnakh, and Kharaelakh intrusions are examined for Re-Os isotopic systematics. Neodymium and lead isotopic data also are reported for the ultramafic and mafic rocks. The Re-Os data for most samples indicate closed-system behavior since the ca. 250 Ma igneous crystallization age of the intrusions. There are small but significant differences in the initial osmium isotopic compositions of samples from the three intrusions. Ores from the Noril'sk I intrusion have ??Os values that vary from +0.4 to +8.8, but average +5.8. Ores from the Talnakh intrusion have ??Os values that range from +6.7 to +8.2, averaging +7.7. Ores from the Kharaelakh intrusion have ??Os values that range from +7.8 to +12.9, with an average value of +10.4. The osmium isotopic compositions of the ore samples from the Main Kharaelakh orebody exhibit minimal overlap with those for the Noril'sk I and Talnakh intrusions, indicating that these Kharaelakh ores were derived from a more radiogenic source of osmium than the other ores. Combined osmium and lead data for major orebodies in the three intrusions plot in three distinct fields, indicating derivation of osmium and lead from at least three isotopically distinct sources. Some of the variation in lead isotopic compositions may be the result of minor lower-crustal contamination. However, in contrast to most other isotopic and trace element data, Os-Pb variations are generally inconsistent with significant crustal contamination or interaction with the subcontinental lithosphere. Thus, the osmium and lead isotopic compositions of these intrusions probably reflect quite closely the compositions of their mantle source, and suggest that these two isotope systems were insensitive to lithospheric interaction. Ultramafic and mafic rocks have osmium and lead isotopic compositions that range only slightly beyond the compositions of the ores. These rocks also have relatively uniform ??{lunate}Nd values that range only from -0.8 to + 1.1. This limited variation in neodymium isotopic composition may reflect the characteristics of the mantle sources of the rocks, or it may indicate that somehow similar proportions of crust contaminated the parental melts. The osmium, lead, and neodymium isotopic data for these rocks most closely resemble the mantle sources of certain ocean island basalts (OIB), such as some Hawaiian basalts. Hence, these data are consistent with derivation of primary melts from a mantle source similar to that of some types of hotspot activity. The long-term Re/Os enrichment of this and similar mantle sources, relative to chondritic upper mantle, may reflect 1. (1) incorporation of recycled oceanic crust into the source more than 1 Ga ago, 2. (2) derivation from a mantle plume that originated at the outer core-lower mantle interface, or 3. (3) persistence of primordial stratification of rhenium and osmium in the mantle. ?? 1994.

SULFUR ISOTOPIC COMPOSITIONS OF SUBMICROMETER SiC GRAINS FROM THE MURCHISON METEORITE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Yuchen; Zinner, Ernst; Gallino, Roberto

2015-02-01

We report C, Si, N, S, Mg-Al, and Ca-Ti isotopic compositions of presolar silicon carbide (SiC) grains from the SiC-rich KJE size fraction (0.5-0.8 μm) of the Murchison meteorite. One thousand one hundred thirteen SiC grains were identified based on their C and Si isotopic ratios. Mainstream, AB, C, X, Y, and Z subtypes of SiC, and X-type silicon nitride (Si{sub 3}N{sub 4}) account for 81.4%, 5.7%, 0.1%, 1.5%, 5.8%, 4.9%, and 0.4%, respectively. Twenty-five grains with unusual Si isotopic ratios, including one C grain, 16 X grains, 1 Y grain, 5 Z grains, and 2 X-type Si{sub 3}N{sub 4} grainsmore » were selected for N, S, Mg-Al, and Ca-Ti isotopic analysis. The C grain is highly enriched in {sup 29}Si and {sup 30}Si (δ{sup 29}Si = 1345‰ ± 19‰, δ{sup 30}Si = 1272‰ ± 19‰). It has a huge {sup 32}S excess, larger than any seen before, and larger than that predicted for the Si/S supernova (SN) zone, providing evidence against the elemental fractionation model by Hoppe et al. Two SN models investigated here present a more satisfying explanation in terms of a radiogenic origin of {sup 32}S from the decay of short-lived {sup 32}Si (τ{sub 1/2} = 153 yr). Silicon-32 as well as {sup 29}Si and {sup 30}Si can be produced in SNe by short neutron bursts; evidence for initial {sup 44}Ti (τ{sub 1/2} = 60 yr) in the C grain is additional evidence for an SN origin. The X grains have marginal {sup 32}S excesses, much smaller than expected from their large {sup 28}Si excesses. Similarly, the Y and Z grains do not show the S-isotopic anomalies expected from their large Si isotopic anomalies. Low intrinsic S contents and contamination with isotopically normal S are the most likely explanations.« less

Bonanza: An extremely large dust grain from a supernova

NASA Astrophysics Data System (ADS)

Gyngard, Frank; Jadhav, Manavi; Nittler, Larry R.; Stroud, Rhonda M.; Zinner, Ernst

2018-01-01

We report the morphology, microstructure, and isotopic composition of the largest SiC stardust grain known to have condensed from a supernova. The 25-μm diameter grain, termed Bonanza, was found in an acid-resistant residue of the Murchison meteorite. Grains of such large size have neither been observed around supernovae nor predicted to form in stellar environments. The large size of Bonanza has allowed the measurement of the isotopic composition of more elements in it than any other previous presolar grain, including: Li, B, C, N, Mg, Al, Si, S, Ca, Ti, Fe, and Ni. Bonanza exhibits large isotopic anomalies in the elements C, N, Mg, Si, Ca, Ti, Fe, and Ni typical of an astrophysical origin in ejecta of a Type II core-collapse supernova and comparable to those previously observed for other presolar SiC grains of type X. Additionally, we extracted multiple focused ion beam lift-out sections from different regions of the grain. Our transmission electron microscopy demonstrates that the crystalline order varies at the micrometer scale, and includes rare, higher order polytype domains (e.g., 15 R). Analyses with STEM-EDS show Bonanza contains a heterogeneous distribution of subgrains with sizes ranging from <10 nm to >100 nm of Ti(N, C); Fe, Ni-rich grains with variable Fe:Ni; and (Al, Mg)N. Bonanza also has the highest ever inferred initial 26Al/27Al ratio, consistent with its supernova origin. This unique grain affords us the largest expanse of data, both microstructurally and isotopically, to compare with detailed calculations of nucleosynthesis and dust condensation in supernovae.

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. (Goldschmidt abstract, 2005), but distinctly lower than altered dolostones (δ57Fe = 0.10 - 1.02‰) in a Jurassic, organic-rich mudstone (Matthews et al., GCA, 2004). It is difficult to conclude at this time whether or not the relatively low δ57Fe composition of the cap dolostones is consistent with the Beard et al. (Geology, 2003) hypothesis due to large uncertainties in the solution-mineral fractionation factors for carbonates, the potential effects of diagenesis and biological influences on dolomite precipitation, and the possibility that the Marinoan deep ocean was euxinic.

Hf isotope evidence for effective impact melt homogenisation at the Sudbury impact crater, Ontario, Canada

NASA Astrophysics Data System (ADS)

Kenny, Gavin G.; Petrus, Joseph A.; Whitehouse, Martin J.; Daly, J. Stephen; Kamber, Balz S.

2017-10-01

We report on the first zircon hafnium-oxygen isotope and trace element study of a transect through one of the largest terrestrial impact melt sheets. The differentiated melt sheet at the 1.85 Ga, originally ca. 200 km in diameter Sudbury impact crater, Ontario, Canada, yields a tight range of uniform zircon Hf isotope compositions (εHf(1850) of ca. -9 to -12). This is consistent with its well-established crustal origin and indicates differentiation from a single melt that was initially efficiently homogenised. We propose that the heterogeneity in other isotopic systems, such as Pb, in early-emplaced impact melt at Sudbury is associated with volatility-related depletion during the impact cratering process. This depletion leaves the isotopic systems of more volatile elements more susceptible to contamination during post-impact assimilation of country rock, whereas the systems of more refractory elements preserve initial homogeneities. Zircon oxygen isotope compositions in the melt sheet are also restricted in range relative to those in the impacted target rocks. However, they display a marked offset approximately one-third up the melt sheet stratigraphy that is interpreted to be a result of post-impact assimilation of 18O-enirched rocks into the base of the cooling impact melt. Given that impact cratering was a more dominant process in the early history of the inner Solar System than it is today, and the possibility that impact melt sheets were sources of ex situ Hadean zircon grains, these findings may have significance for the interpretation of the early zircon Hf record. We speculate that apparent εHf-time arrays observed in the oldest terrestrial and lunar zircon datasets may be related to impact melting homogenising previously more diverse crust. We also show that spatially restricted partial melting of rocks buried beneath the superheated impact melt at Sudbury provided a zircon crystallising environment distinct to the impact melt sheet itself.

Modes of planetary-scale Fe isotope fractionation

NASA Astrophysics Data System (ADS)

Schoenberg, Ronny; von Blanckenburg, Friedhelm

2006-12-01

A comprehensive set of high-precision Fe isotope data for the principle meteorite types and silicate reservoirs of the Earth is used to investigate iron isotope fractionation at inter- and intra-planetary scales. 14 chondrite analyses yield a homogeneous Fe isotope composition with an average δ56Fe/ 54Fe value of - 0.015 ± 0.020‰ (2 SE) relative to the international iron standard IRMM-014. Eight non-cumulate and polymict eucrite meteorites that sample the silicate portion of the HED (howardite-eucrite-diogenite) parent body yield an average δ56Fe/ 54Fe value of - 0.001 ± 0.017‰, indistinguishable to the chondritic Fe isotope composition. Fe isotope ratios that are indistinguishable to the chondritic value have also been published for SNC meteorites. This inner-solar system homogeneity in Fe isotopes suggests that planetary accretion itself did not significantly fractionate iron. Nine mantle xenoliths yield a 2 σ envelope of - 0.13‰ to + 0.09‰ in δ56Fe/ 54Fe. Using this range as proxy for the bulk silicate Earth in a mass balance model places the Fe isotope composition of the outer liquid core that contains ca. 83% of Earth's total iron to within ± 0.020‰ of the chondritic δ56Fe/ 54Fe value. These calculations allow to interprete magmatic iron meteorites ( δ56Fe/ 54Fe = + 0.047 ± 0.016‰; N = 8) to be representative for the Earth's inner metallic core. Eight terrestrial basalt samples yield a homogeneous Fe isotope composition with an average δ56Fe/ 54Fe value of + 0.072 ± 0.016‰. The observation that terrestrial basalts appear to be slightly heavier than mantle xenoliths and that thus partial mantle melting preferentially transfers heavy iron into the melt [S. Weyer, A.D. Anbar, G.P. Brey, C. Munker, K. Mezger and A.B. Woodland, Iron isotope fractionation during planetary differentiation, Earth and Planetary Science Letters 240(2), 251-264, 2005.] is intriguing, but also raises some important questions: first it is questionable whether the Fe isotope composition of lithospheric mantle xenoliths are representative for an undisturbed melt source, and second, HED and SNC meteorites, representing melting products of 4Vesta and Mars silicate mantles would be expected to show a similar fractionation towards heavy isotope compositions. This is not observed. Four international granitoid standards with SiO 2 contents between 60 and 70 wt.% yield δ56Fe/ 54Fe values between 0.118‰ and 0.132‰. An investigation of the alpine Bergell igneous rock suite revealed a positive correlation between Fe isotope compositions and SiO 2 contents — from gabbros and tonalites ( δ56Fe/ 54Fe ≈ 0.03 to 0.09‰) to granodiorites and silicic dykes ( δ56Fe/ 54Fe ≈ 0.14 to 0.23‰). Although in this suite δ56Fe/ 54Fe correlates with δ18O values and radiogenic isotopes, open-system behavior to explain the heavy iron is not undisputed. This is because an obvious assimilant with the required heavy Fe isotope composition has so far not been identified. Alternatively, the relatively heavy granite compositions might be obtained by fractional crystallisation of the melt. Ultimately, further detailed studies on natural rocks and the experimental determination of mineral/melt fractionation factors at magmatic conditions are required to unravel whether or not iron isotope fractionation takes place during partial mantle melting and crystal fractionation.

Metasomatism-induced magnesium isotope fractionation in ultramafic rocks: Evidence from the Franciscan Complex, California

NASA Astrophysics Data System (ADS)

Li, W. Y.; Teng, F. Z.; Xiao, Y.

2016-12-01

To investigate the behaviour of Mg isotopes during metasomatic reactions between peridotites and infiltrating fluids along the slab-mantle interface, we analyzed Mg isotopic compositions of a set of well-characterized samples from the ultramafic blocks in the Franciscan Complex of California [1]. The Group 1 and Group 2 samples that were defined by the initial serpentinization and complete serpentinization of peridotites at temperatures of 450-500 ºC, respectively [1], have δ26Mg values (from -0.26 to -0.14‰) clustered around the mantle value. This suggests that Mg isotope fractionation during serpentinization by slab-derived fluids, if any, is small. By contrast, the Group 3 samples that were defined by the replacement of serpentine by talc [1], are enriched in heavy Mg isotopes (δ26Mg of -0.13 to -0.01‰). This may reflect the loss of light Mg isotopes into fluids during the dehydration reaction that produced talc from serpentine, which is consistent with previous observations that secondary clay minerals preferentially incorporate heavy Mg isotopes during water-rock interactions [2, 3]. The Group 4 samples that were defined by the further replacement of talc by tremolite [1], however, have light Mg isotopic compositions (δ26Mg of -0.50 to -0.41‰). Such a shift towards light Mg isotopic compositions likely results from metasomatism by fluids that derived from isotopically light carbonates, which is supported by the remarkably higher CaO content of Group 4 samples (from 6.9 to 9.2 wt%) than Group 3 ones (from 1.1 to 1.4 wt%). Collectively, significant Mg isotopic variations occur during metasomatism of peridotites in the mantle wedge, which would potentially lead to heterogeneous Mg isotopic compositions in arc lavas [4]. Therefore, Mg isotopes can be used as a powerful tracer of crust-mantle interaction at subduction zones. [1] King et al. (2003) Geol. Soc. Am. Bull. 115, 1097-1109. [2] Teng et al. (2010) Earth Planet. Sci. Lett. 300, 63-71. [3] Wimpenny et al. (2014) Geochim. Cosmochim. Acta 128, 178-194. [4] Teng et al. (2016) Proc. Natl. Acad. Sci. 113, 7082-7087. et al. (2016) Proc. Natl. Acad. Sci. 113, 7082-7087.

Measurement of isotope ratio of Ca{sup +} ions in a linear Paul Trap

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hashimoto, Y.; Minamino, K.; Nagamoto, D.

2009-03-17

Measurement of isotope ratios of Calcium is very useful in many fields. So we demonstrated the measurement of isotope ratios of {sup 40}Ca{sup +}(abundance 96.4%) to {sup 44}Ca{sup +}(2.09%) ions in a linear Paul trap with several laser lights tuning to the isotope shifts. And we found that the experimental parameters had large influences on the measurement of the isotope ratios.

Coupling between sulfur recycling and syndepositional carbonate dissolution: evidence from oxygen and sulfur isotope composition of pore water sulfate, South Florida Platform, U.S.A.

NASA Astrophysics Data System (ADS)

Ku, T. C. W.; Walter, L. M.; Coleman, M. L.; Blake, R. E.; Martini, A. M.

1999-10-01

Sulfur cycling in Fe-poor, organic-rich shelf carbonates, known to have rapid rates of SO4-2 reduction, remains poorly studied despite the volumetric significance of shelf deposits in modern and ancient carbon budgets. We investigated sulfur cycling in modern carbonates of the Florida Platform from end-member depositional environments (muddy sands from the Atlantic reef tract and finer-grained mudbank and island flank deposits from Florida Bay). Relations between pore water chemistry (SO4-2, ΣCO2, Ca-2/Cl-) and oxygen and sulfur stable isotope compositions of SO4-2 require direct coupling between sulfur redox cycling and syndepositional carbonate dissolution. Oxygen isotope compositions of pore water sulfate were remarkably shifted away from the established value for marine SO4-2 (+9.5‰), despite near normal SO4-2/Cl- ratios. Chemical evolution was least in reef tract pore waters and greatest in Florida Bay. Relative to overlying seawater, mudbank sediments exhibited sulfate depletion, with δ18OSO4 and δ34SSO4 values both increasing by about 7‰. More bioturbated island flank sediments, colonized by Thalassia grass, had a 5‰ increase in δ18OSO4, variable δ34SSO4 values (+17.7 to +23.3‰) and exceptionally high Ca+2/Cl- ratios. The large excess of Ca+2 (up to 1.7 mM) requires a much larger acid source than the amounts derived from utilization of dissolved O2 (∼0.3 mM) and small degrees of net SO4-2 reduction (<0.5 mM reduced). A conceptual model was constructed using chemical and isotopic data on natural pore waters and on sulfate isotope fractionation factors obtained from sediment incubation experiments. The model outputs show that pore water compositions can be explained by a redox cycle where microbial SO4-2 reduction is followed by very efficient H2S oxidation, thus maintaining virtually invariant SO4-2/Cl- ratios. The enhanced O2 transport may be driven by associated marine grass rhizome systems and microbial communities established in bioturbated sediments. The net result of the cycle is that the rate of sulfide oxidation, which is largely balanced by the rate of microbial sulfate reduction, is stoichiometrically related to the rate of carbonate dissolution. This is consistent with previously reported rates of carbonate dissolution (∼400 μmol/cm2-yr) and average rates of sulfate reduction (∼200 μmol/cm2-yr) from the Florida Platform and a 2:1 stoichiometry.

Titanium stable isotopic variations in chondrites, achondrites and lunar rocks

NASA Astrophysics Data System (ADS)

Greber, Nicolas D.; Dauphas, Nicolas; Puchtel, Igor S.; Hofmann, Beda A.; Arndt, Nicholas T.

2017-09-01

Titanium isotopes are potential tracers of processes of evaporation/condensation in the solar nebula and magmatic differentiation in planetary bodies. To gain new insights into the processes that control Ti isotopic variations in planetary materials, 25 komatiites, 15 chondrites, 11 HED-clan meteorites, 5 angrites, 6 aubrites, a martian shergottite, and a KREEP-rich impact melt breccia have been analyzed for their mass-dependent Ti isotopic compositions, presented using the δ49Ti notation (deviation in permil of the 49Ti/47Ti ratio relative to the OL-Ti standard). No significant variation in δ49Ti is found among ordinary, enstatite, and carbonaceous chondrites, and the average chondritic δ49Ti value of +0.004 ± 0.010‰ is in excellent agreement with the published estimate for the bulk silicate Earth, the Moon, Mars, and the HED and angrite parent-bodies. The average δ49Ti value of komatiites of -0.001 ± 0.019‰ is also identical to that of the bulk silicate Earth and chondrites. OL-Ti has a Ti isotopic composition that is indistinguishable from chondrites and is therefore a suitable material for reporting δ49Ti values. Previously published isotope data on another highly refractory element, Ca, show measurable variations among chondrites. The decoupling between Ca and Ti isotope systematics most likely occurred during condensation in the solar nebula. Aubrites exhibit significant variations in δ49Ti, from -0.07 to +0.24‰. This is likely due to the uniquely reducing conditions under which the aubrite parent-body differentiated, allowing chalcophile Ti3+ and lithophile Ti4+ to co-exist. Consequently, the observed negative correlation between δ49Ti values and MgO concentrations among aubrites is interpreted to be the result of isotope fractionation driven by the different oxidation states of Ti in this environment, such that isotopically heavy Ti4+ was concentrated in the residual liquid during magmatic differentiation. Finally, KREEPy impact melt breccia SaU 169 exhibits a heavy δ49Ti value of +0.330 ± 0.034‰ which is interpreted to result from Ti isotopic fractionation during ilmenite precipitation in the late stages of lunar magma ocean crystallization. A Rayleigh distillation calculation predicts that a δ49Ti value of +0.330‰ is achieved after removal of 94% of Ti in ilmenite.

Uranium Isotopes in Calcium Carbonate: A Possible Proxy for Paleo-pH and Carbonate Ion Concentration?

NASA Astrophysics Data System (ADS)

Chen, X.; Romaniello, S. J.; Herrmann, A. D.; Wasylenki, L. E.; Anbar, A. D.

2015-12-01

Natural variations of 238U/235U in marine carbonates are being explored as a paleoredox proxy. However, in order for this proxy to be robust, it is important to understand how pH and alkalinity affect the fractionation of 238U/235U during coprecipitation with calcite and aragonite. Recent work suggests that the U/Ca ratio of foraminiferal calcite may vary with seawater [CO32-] concentration due to changes in U speciation[1]. Here we explore analogous isotopic consequences in inorganic laboratory co-precipitation experiments. Uranium coprecipitation experiments with calcite and aragonite were performed at pH 8.5 ± 0.1 and 7.5 ± 0.1 using a constant addition method [2]. Dissolved U in the remaining solution was periodically collected throughout the experiments. Samples were purified with UTEVA resin and 238U/235U was determined using a 233U-236U double-spike and MC-ICP-MS, attaining a precision of ± 0.10 ‰ [3]. Small but resolvable U isotope fractionation was observed in aragonite experiments at pH ~8.5, preferentially enriching heavier U isotopes in the solid phase. 238U/235U of the dissolved U in these experiments can be fit by Rayleigh fractionation curves with fractionation factors of 1.00002 - 1.00009. In contrast, no resolvable U isotope fractionation was detected in an aragonite experiment at pH ~7.5 or in calcite experiments at either pH. Equilibrium isotope fractionation among dissolved U species is the most likely mechanism driving these isotope effects. Our quantitative model of this process assumes that charged U species are preferentially incorporated into CaCO3 relative to the neutral U species Ca2UO2(CO3)3(aq), which we hypothesize to have a lighter equilibrium U isotope composition than the charged U species. According to this model, the magnitude of U isotope fractionation should scale with the fraction of the neutral U species in the solution, in agreement with our experimental results. These findings suggest that U isotope variations in abiotic CaCO3 reflect changes in aqueous U(VI) speciation, which are in turn a function of carbonate ion chemistry and pH. Hence, the door is opened to the development of a possible 238U/235U proxy for the carbonate ion system. [1] DeCarlo et al., (2015), GCA, 162,151-165. [2] Reeder et a., (2001), GCA, 65, 3491-3503. [3] Weyer et al., (2008) GCA 72, 345-359.

Ferropericlase inclusions in ultradeep diamonds from Sao Luiz (Brazil): high Li abundances and diverse Li-isotope and trace element compositions suggest an origin from a subduction mélange

NASA Astrophysics Data System (ADS)

Seitz, Hans-Michael; Brey, Gerhard P.; Harris, Jeffrey W.; Durali-Müller, Soodabeh; Ludwig, Thomas; Höfer, Heidi E.

2018-05-01

The most remarkable feature of the inclusion suite in ultradeep alluvial and kimberlitic diamonds from Sao Luiz (Juina area in Brazil) is the enormous range in Mg# [100xMg/(Mg + Fe)] of the ferropericlases (fper). The Mg-richer ferropericlases are from the boundary to the lower mantle or from the lower mantle itself when they coexist with ringwoodite or Mg- perovskite (bridgmanite). This, however, is not an explanation for the more Fe-rich members and a lowermost mantle or a "D" layer origin has been proposed for them. Such a suggested ultra-deep origin separates the Fe-rich fper-bearing diamonds from the rest of the Sao Luiz ultradeep diamond inclusion suite, which also contains Ca-rich phases. These are now thought to have an origin in the uppermost lower mantle and in the transition zone and to belong either to a peridotitic or mafic (subducted oceanic crust) protolith lithology. We analysed a new set of more Fe-rich ferropericlase inclusions from 10 Sao Luiz ultradeep alluvial diamonds for their Li isotope composition by solution MC-ICP-MS (multi collector inductively coupled plasma mass spectrometry), their major and minor elements by EPMA (electron probe micro-analyser) and their Li-contents by SIMS (secondary ion mass spectrometry), with the aim to understand the origin of the ferropericlase protoliths. Our new data confirm the wide range of ferropericlase Mg# that were reported before and augment the known lack of correlation between major and minor elements. Four pooled ferropericlase inclusions from four diamonds provided sufficient material to determine for the first time their Li isotope composition, which ranges from δ7Li + 9.6 ‰ to -3.9 ‰. This wide Li isotopic range encompasses that of serpentinized ocean floor peridotites including rodingites and ophicarbonates, fresh and altered MORB (mid ocean ridge basalt), seafloor sediments and of eclogites. This large range in Li isotopic composition, up to 5 times higher than `primitive upper mantle' Li-abundances, and an extremely large and incoherent range in Mg# and Cr, Ni, Mn, Na contents in the ferropericlase inclusions suggests that their protoliths were members of the above lithologies. This mélange of altered rocks originally contained a variety of carbonates (calcite, magnesite, dolomite, siderite) and brucite as the secondary products in veins and as patches and Ca-rich members like rodingites and ophicarbonates. Dehydration and redox reactions during or after deep subduction into the transition zone and the upper parts of the lower mantle led to the formation of diamond and ferropericlase inclusions with variable compositions and a predominance of the Ca-rich, high-pressure silicate inclusions. We suggest that the latter originated from peridotites, mafic rocks and sedimentary rocks as redox products between calcite and SiO2.

Calcium isotopes in fossil bones and teeth — Diagenetic versus biogenic origin

NASA Astrophysics Data System (ADS)

Heuser, Alexander; Tütken, Thomas; Gussone, Nikolaus; Galer, Stephen J. G.

2011-06-01

We present the first systematic study of Ca isotopes ( δ44/40Ca) in Late Triassic to Late Cretaceous dinosaur bones and teeth (enamel and dentin) from sympatric herbivorous and carnivorous dinosaurs. The samples derive from five different localities, and data from embedding sediments are also presented. Additional δ44/40Ca in skeletal tissues from modern reptiles and birds (avian dinosaurs) were measured for comparison in order to examine whether the original Ca isotopic composition in dinosaur skeletal apatite was preserved or might have changed during the diagenesis and fossilization process. δ44/40Ca of fossil skeletal tissues range from -1.62‰ ( Tyrannosaurus rex enamel) to +1.08‰ ( Brachiosaurus brancai bone), while values in modern archosaur bones and teeth range from -1.63‰ (caiman enamel) to -0.37‰ (ostrich bone). The average δ44/40Ca of the three types of fossil skeletal tissue analyzed - bone, dentin and enamel - show some systematic differences: while δ44/40Ca in bone exhibits the highest values, while δ44/40Ca in enamel has the lowest values, and dentin δ44/40Ca falls in between. Values of δ44/40Ca in the remains of herbivorous dinosaurs (0.1-1.1‰) are generally higher than those of bones of modern mammalian herbivores (-2.6‰ to -0.8‰) and from modern herbivorous archosaurs, which exhibit intermediate δ44/40Ca (-0.8‰ to -0.4‰). These systematic isotopic shifts may reflect physiological differences between dinosaurs, mammals and reptiles representing different taxonomic groups of vertebrates. Systematic offsets in skeletal apatite δ44/40Ca between herbivorous and carnivorous dinosaurs are not obvious, indicating a lack of a clear-cut Trophic Level Effect (TLE) shift between herbivores and carnivores in dinosaurs. This observation can be explained if the carnivorous dinosaurs in this study fed mainly on soft tissues from their prey and did not ingest hard (calcified) tissue to much extent. The most striking indication that the primary δ44/40Ca is actually preserved in most of the fossil teeth is a difference in δ44/40Ca of about 0.35 ± 0.10‰ (1SD) between dentin and enamel, based upon 11 of 16 analyzed dentin-enamel pairs. This difference is close to that found in modern reptiles (0.28 ± 0.05‰), and strongly suggests that this tell-tale signature is a primary feature of the fossilized dinosaur material as well. Furthermore, simple mass balance calculations show that changes of the original δ44/40Ca in bones and teeth by diagenetically-formed calcium-bearing minerals are either small or would require implausible high original δ44/40Ca values in the skeletal apatite.

Delta13C and delta18O isotopic composition of CaCO3 measured by continuous flow isotope ratio mass spectrometry: statistical evaluation and verification by application to Devils Hole core DH-11 calcite.

PubMed

Révész, Kinga M; Landwehr, Jurate M

2002-01-01

A new method was developed to analyze the stable carbon and oxygen isotope ratios of small samples (400 +/- 20 micro g) of calcium carbonate. This new method streamlines the classical phosphoric acid/calcium carbonate (H(3)PO(4)/CaCO(3)) reaction method by making use of a recently available Thermoquest-Finnigan GasBench II preparation device and a Delta Plus XL continuous flow isotope ratio mass spectrometer. Conditions for which the H(3)PO(4)/CaCO(3) reaction produced reproducible and accurate results with minimal error had to be determined. When the acid/carbonate reaction temperature was kept at 26 degrees C and the reaction time was between 24 and 54 h, the precision of the carbon and oxygen isotope ratios for pooled samples from three reference standard materials was

Simulating the Incorporation of Geochemical Proxies into Scleractinian Coral Skeletons: Effects of Different Environmental and Biological Factors and Implications for Paleo-reconstruction

NASA Astrophysics Data System (ADS)

Guo, W.

2017-12-01

Chemical and isotopic compositions of scleractinian coral skeletons reflect the physicochemical condition of the seawater in which corals grow. This makes coral skeleton one of the best archives of ocean climate and biogeochemical changes. A number of coral-based geochemical proxies have been developed and applied to reconstruct past seawater conditions, such as temperature, pH, carbonate chemistry and nutrient concentrations. Detailed laboratory and field-based studies of these proxies, however, indicate interpretation of the geochemistry of coral skeletons is not straightforward, due to the presence of `vital effects' and the variations of empirical proxy calibrations among and within different species. This poses challenges for the broad application of many geochemical proxies in corals, and highlights the need to better understand the fundamental processes governing the incorporation of different proxies. Here I present a numerical model that simulates the incorporation of a suite of geochemical proxies into coral skeletons, including δ11B, Mg/Ca, Sr/Ca, U/Ca, B/Ca and Ba/Ca. This model, building on previous theoretical studies of coral calcification, combines our current understanding of coral calcification mechanism with experimental constraints on the isotope and element partition during carbonate precipitation. It enables quantitative evaluation of the effects of different environmental and biological factors on each proxy. Specifically, this model shows that (1) the incorporation of every proxy is affected by multiple seawater parameters (e.g. temperature, pH, DIC) as opposed to one single parameter, and (2) biological factors, particularly the interplay between enzymatic alkalinity pumping and the exchange of coral calcifying fluid with external seawater, also exert significant controls. Based on these findings, I propose an inverse method for simultaneously reconstructing multiple seawater physicochemical parameters, and compare the performance of this new method with conventional paleo-reconstruction methods that are based on empirical calibrations. In addition, the extension of this model to simulate carbon, oxygen and clumped isotope (δ13C, δ18O, Δ47) composition of coral skeletons will also be discussed at the meeting.

Re — Os isotopic constraints on the origin of volcanic rocks, Gorgona Island, Colombia: Os isotopic evidence for ancient heterogeneities in the mantle

NASA Astrophysics Data System (ADS)

Walker, R. J.; Echeverria, L. M.; Shirey, S. B.; Horan, M. F.

1991-04-01

The Re — Os isotopic systematics of komatiites and spatially associated basalts from Gorgona Island, Colombia, indicate that they were produced at 155±43 Ma. Subsequent episodes of volcanism produced basalts at 88.1±3.8 Ma and picritic and basaltic lavas at ca. 58 Ma. The age for the ultramafic rocks is important because it coincides with the late-Jurassic, early-Cretaceous disassembly of Pangea, when the North- and South-American plates began to pull apart. Deep-seated mantle upwelling possibly precipitated the break-up of these continental plates and caused a tear in the subducting slab west of Gorgona, providing a rare, late-Phanerozoic conduit for the komatiitic melts. Mantle sources for the komatiites were heterogeneous with respect to Os and Pb isotopic compositions, but had homogeneous Nd isotopic compositions (ɛNd+9±1). Initial 187Os/186Os normalized to carbonaceous chondrites at 155 Ma (γOs) ranged from 0 to +22, and model-initial μ values ranged from 8.17 to 8.39. The excess radiogenic Os, compared with an assumed bulk-mantle evolution similar to carbonaceous chondrites, was likely produced in portions of the mantle with long-term elevated Re concentrations. The Os, Pb and Nd isotopic compositions, together with major-element constraints, suggest that the sources of the komatiites were enriched more than 1 Ga ago by low (<20%) and variable amounts of a basalt or komatiite component. This component was added as either subducted oceanic crust or melt derived from greater depths in the mantle. These results suggest that the Re — Os isotope system may be a highly sensitive indicator of the presence of ancient subducted oceanic crust in mantle-source regions.

Re - Os isotopic constraints on the origin of volcanic rocks, Gorgona Island, Colombia: Os isotopic evidence for ancient heterogeneities in the mantle

USGS Publications Warehouse

Walker, R.J.; Echeverria, L.M.; Shirey, S.B.; Horan, M.F.

1991-01-01

The Re - Os isotopic systematics of komatiites and spatially associated basalts from Gorgona Island, Colombia, indicate that they were produced at 155??43 Ma. Subsequent episodes of volcanism produced basalts at 88.1??3.8 Ma and picritic and basaltic lavas at ca. 58 Ma. The age for the ultramafic rocks is important because it coincides with the late-Jurassic, early-Cretaceous disassembly of Pangea, when the North- and South-American plates began to pull apart. Deep-seated mantle upwelling possibly precipitated the break-up of these continental plates and caused a tear in the subducting slab west of Gorgona, providing a rare, late-Phanerozoic conduit for the komatiitic melts. Mantle sources for the komatiites were heterogeneous with respect to Os and Pb isotopic compositions, but had homogeneous Nd isotopic compositions (??Nd+9??1). Initial 187Os/186Os normalized to carbonaceous chondrites at 155 Ma (??Os) ranged from 0 to +22, and model-initial ?? values ranged from 8.17 to 8.39. The excess radiogenic Os, compared with an assumed bulk-mantle evolution similar to carbonaceous chondrites, was likely produced in portions of the mantle with long-term elevated Re concentrations. The Os, Pb and Nd isotopic compositions, together with major-element constraints, suggest that the sources of the komatiites were enriched more than 1 Ga ago by low (<20%) and variable amounts of a basalt or komatiite component. This component was added as either subducted oceanic crust or melt derived from greater depths in the mantle. These results suggest that the Re - Os isotope system may be a highly sensitive indicator of the presence of ancient subducted oceanic crust in mantle-source regions. ?? 1991 Springer-Verlag.

Using Natural Stable Calcium Isotopes to Rapidly Assess Changes in Bone Mineral Balance Using a Bed Rest Model to Induce Bone Loss

NASA Technical Reports Server (NTRS)

Morgan, J. L. L.; Skulan, J. L.; Gordon, G. E.; Smith, Scott M.; Romaniello, S. J.; Anbar, A. D.

2012-01-01

Metabolic bone diseases like osteoporosis result from the disruption of normal bone mineral balance (BMB) resulting in bone loss. During spaceflight astronauts lose substantial bone. Bed rest provides an analog to simulate some of the effects of spaceflight; including bone and calcium loss and provides the opportunity to evaluate new methods to monitor BMB in healthy individuals undergoing environmentally induced-bone loss. Previous research showed that natural variations in the Ca isotope ratio occur because bone formation depletes soft tissue of light Ca isotopes while bone resorption releases that isotopically light Ca back into soft tissue (Skulan et al, 2007). Using a bed rest model, we demonstrate that the Ca isotope ratio of urine shifts in a direction consistent with bone loss after just 7 days of bed rest, long before detectable changes in bone mineral density (BMD) occur. The Ca isotope variations tracks changes observed in urinary N-teleopeptide, a bone resorption biomarker. Bone specific alkaline phosphatase, a bone formation biomarker, is unchanged. The established relationship between Ca isotopes and BMB can be used to quantitatively translate the changes in the Ca isotope ratio to changes in BMD using a simple mathematical model. This model predicts that subjects lost 0.25 0.07% ( SD) of their bone mass from day 7 to day 30 of bed rest. Given the rapid signal observed using Ca isotope measurements and the potential to quantitatively assess bone loss; this technique is well suited to study the short-term dynamics of bone metabolism.

Ca, Sr, Mo and U isotopes evidence ocean acidification and deoxygenation during the Late Permian mass extinction

NASA Astrophysics Data System (ADS)

Silva-Tamayo, Juan Carlos; Payne, Jon; Wignall, Paul; Newton, Rob; Eisenhauer, Anton; Weyer, Stenfan; Neubert, Nadja; Lau, Kim; Maher, Kate; Paytan, Adina; Lehrmann, Dan; Altiner, Demir; Yu, Meiyi

2014-05-01

The most catastrophic extinction event in the history of animal life occurred at the end of the Permian Period, ca. 252 Mya. Ocean acidification and global oceanic euxinia have each been proposed as causes of this biotic crisis, but the magnitude and timing of change in global ocean chemistry remains poorly constrained. Here we use multiple isotope systems - Ca, Sr, Mo and U - measured from well dated Upper Permian- Lower Triassic sedimentary sections to better constrain the magnitude and timing of change in ocean chemistry and the effects of ocean acidification and de-oxygenation through this interval. All the investigated carbonate successions (Turkey, Italy and China) exhibit decreasing δ44/40Ca compositions, from ~-1.4‰ to -2.0‰ in the interval preceding the main extinction. These values remain low during most of the Griesbachian, to finally return to -1.4‰ in the middle Dienerian. The limestone succession from southern Turkey also displays a major decrease in the δ88/86Sr values from 0.45‰ to 0.3‰ before the extinction. These values remain low during the Griesbachian and finally increase to 0.55‰ by the middle Dienerian. The paired negative anomalies on the carbonate δ44/40Ca and δ88/86Sr suggest a decrease in the carbonate precipitation and thus an episode of ocean acidification coincident with the major biotic crisis. The Mo and U isotope records also exhibit significant rapid negative anomalies at the onset of the main extinction interval, suggesting rapid expansion of anoxic and euxinic marine bottom waters during the extinction interval. The rapidity of the isotope excursions in Mo and U suggests substantially reduced residence times of these elements in seawater relative to the modern, consistent with expectations for a time of widespread anoxia. The large C-isotope variability within Lower Triassic rocks, which is similar to that of the Lower-Middle Cambrian, may reflect biologically controlled perturbations of the oceanic carbon cycle. These findings strengthen the evidence for a global ocean acidification event coupled with rapid expansion of anoxic zones as drivers of end-Permian extinction in the oceans.

Stalagmite geochemistry and the timing of the last interglacial-glacial transition in Central Europe (NE Hungary)

NASA Astrophysics Data System (ADS)

Siklosy, Z.; Demeny, A.; Pilet, S.; Leel-Ossy, Sz.; Lin, K.; Shen, C.-C.

2009-04-01

Speleothems can provide accurate chronologies for reconstructions of climate change by combination of U/Th dating and climate-related geochemical compositions. Geochemical studies of speleothems from Central Europe are mostly based on stable C and O isotope analyses, thus, complex geochemical studies combining isotope and trace element measurements are needed for more reliable climate models for this transitional area between oceanic and continental regions. We present stable H-C-O isotope and trace element records obtained on speleothems covering the Last Interglacial (MIS 5e) and the transition to MIS 5d. A stalagmite from Baradla Cave grew from 127.5 to 110 ka. Accelerated growth rates have been detected by U/Th age data in the 127 to 126 ka and 119 to 117 ka parts. Trace element compositions and 230Th/232Th ratios suggest changes in the hydrological regime, whereby early calcite precipitates formed in fissures during the dry and cold glacial period were dissolved by the starting flux of infiltrating meteoric water (producing elevated dissolved ion concentration but low detrital Th component), then the increasing amount of dripwater during the interglacial period resulted in trace element dilution. Temperature and precipitation amount variations are also reflected by the stable isotope compositions. Oxygen isotope composition shows a continuous increase from 127.5 ka until about 118 ka most probably related to temperature rise, whereas C isotope values are shifted in negative direction suggesting increasing humidity in accordance with trace element contents. The presumably warmest period at ca. 118 ka is associated with rather arid climate as indicated by peak d18O values coinciding with the highest dD values of fluid inclusion water. This is followed by a pronounced negative shift in both O and H isotope values, similarly to recent Alpine studies (Meyer et al., 2008), most probably related to cooling. Hydrogen isotope compositions of fluid inclusion water evaluated together with calculated oxygen isotope compositions of water indicate warming and increasing significance of summer precipitation at the latest period of the last interglacial, then increasing importance of winter precipitation and/or changes in oceanic source composition during the cooling phase. The good agreement with other (Alpine and marine) records indicate a synchronous climate change. However, after a negative shift in the wet/warm phase (increasing soil activity), C isotope values start to increase already at about 119 ky BP, warning to the use of the two isotope systems as event correlation tools. In conclusion, our combined isotope and trace element study indicate a complex pattern of temperature and humidity variations during and right after the Last Interglacial. Acknowledgements — This study was financially supported by the Hungarian Scientific Research Fund (OTKA T 049713). Measurements of U-Th isotopic compositions and and 230Th dates were supported by the National Science Council grants (94-2116-M002-012, 97-2752-M002-004-PAE & -005-PAE to C.C.S.). [Meyer, M.; Spötl, C.; Mangini, A. (2008): The demise of the Last Interglacial recorded in isotopically dated speleothems from the Alps. Quaternary Science Reviews, 27, 476-496.

Probing the interface of doped isotopically mixed helium droplets by the directional anisotropy of interatomic Coulombic decay.

PubMed

Kryzhevoi, Nikolai V; Mateo, David; Pi, Martí; Barranco, Manuel; Cederbaum, Lorenz S

2013-11-07

Interatomic Coulombic decay (ICD) represents an efficient electronic relaxation mechanism of an ionized or an excited system embedded in an environment. The type of this environment and its size have a great impact on the ICD performance. It is stressed that ICD is sensitive to the arrangement of neighboring atoms when the initially created vacancy has a polarization direction. This is demonstrated in the present paper for the case of a 3p-ionized Ca surrounded by He atoms. Useful explicit expressions are derived for the ICD widths which show that the neighbors located along the polarization direction of the ionized orbital have the largest contribution to the ICD rate. By comparison with ab initio results for small clusters, we also show that in a helium environment, the pairwise approximation represents a reliable approach for computing ICD widths. Using this approximation and the density distribution of the helium atoms obtained within density functional theory, we explore ICD in large isotopically mixed helium droplets doped with Ca. A special emphasis is given to the difference between the ICD widths for the Ca3p orbitals directed perpendicular and parallel to the droplet surface. Depending on the size and isotopic composition of the droplet, Ca resides in the interfacial layer between the (4)He core and the (3)He outer shell. Hence, ICD studies in these droplets may provide valuable information on the properties of this interface.

Supernova graphite in the NanoSIMS: Carbon, oxygen and titanium isotopic compositions of a spherule and its TiC sub-components

NASA Astrophysics Data System (ADS)

Stadermann, F. J.; Croat, T. K.; Bernatowicz, T. J.; Amari, S.; Messenger, S.; Walker, R. M.; Zinner, E.

2005-01-01

Presolar graphite spherules from the Murchison low-density separate KE3 contain a large number of internal TiC crystals that range in size from 15 to 500 nm. We have studied one such graphite grain in great detail by successive analyses with SEM, ims3f SIMS, TEM and NanoSIMS. Isotopic measurements of the 'bulk' particle in the ims3f indicate a supernova origin for this graphite spherule. The NanoSIMS measurements of C, N, O and Ti isotopes were performed directly on TEM ultramicrotome sections of the spherule, allowing correlated studies of the isotopic and mineralogical properties of the graphite grain and its internal crystals. We found isotopic gradients in 12C/ 13C and 16O/ 18O from the core of the graphite spherule to its perimeter, with the most anomalous compositions being present in the center. These gradients may be the result of isotopic exchange with isotopically normal material, either in the laboratory or during the particle's history. No similar isotopic gradients were found in the 16O/ 17O and 14N/ 15N ratios, which are normal within analytical uncertainty throughout the graphite spherule. Due to an unusually high O signal, internal TiC crystals were easily located during NanoSIMS imaging measurements. It was thus possible to determine isotopic compositions of several internal TiC grains independent of the surrounding graphite matrix. These TiC crystals are significantly more anomalous in their O isotopes than the graphite, with 16O/ 18O ratios ranging from 14 to 250 (compared to a terrestrial value of 499). Even the most centrally located TiC grains show significant variations in their O isotopic compositions from crystal to crystal. Measurement of the Ti isotopes in three TiC grains found no variations among them and no large differences between the compositions of the different crystals and the 'bulk' graphite spherule. However, the same three TiC crystals vary by a factor of 3 in their 16O/ 18O ratios. It is not clear in what form the O is associated with the TiC grains and whether it is cogenetic or the result of surface reactions on the TiC grains before they accreted onto the growing graphite spherule. The presence of 44Ca from short-lived 44Ti (t 1/2 = 60y) in one of the TiC subgrains confirms the identification of this graphite spherule as a supernova condensate.

Chondrites and the Protoplanetary Disk, Part 3

NASA Technical Reports Server (NTRS)

2004-01-01

Contents include the following: Ca-, Al-Rich Inclusions and Ameoboid Olivine Aggregates: What We Know and Don t Know About Their Origin. Aluminium-26 and Oxygen Isotopic Distributions of Ca-Al-rich Inclusions from Acfer 214 CH Chondrite. The Trapping Efficiency of Helium in Fullerene and Its Implicatiion to the Planetary Science. Constraints on the Origin of Chondritic Components from Oxygen Isotopic Compositions. Role of Planetary Impacts in Thermal Processing of Chondrite Materials. Formation of the Melilite Mantle of the Type B1 CAIs: Flash Heating or Transport? The Iodine-Xenon System in Outer and Inner Portions of Chondrules from the Unnamed Antarctic LL3 Chondrite. Nucleosynthesis of Short-lived Radioactivities in Massive Stars. The Two-Fluid Analysis of the Kelvin-Helmholtz Instability in the Dust Layer of a Protoplanetary Disk: A Possible Path to the Planetesimal Formation Through the Gravitational Instability. Shock-Wave Heating Model for Chonodrule Formation: Heating Rate and Cooling Rate Constraints. Glycine Amide Hydrolysis with Water and OH Radical: A Comparative DFT Study. Micron-sized Sample Preparation for AFM and SEM. AFM, FE-SEM and Optical Imaging of a Shocked L/LL Chondrite: Implications for Martensite Formation and Wave Propagation. Infrared Spectroscopy of Chondrites and Their Components: A Link Between Meteoritics and Astronomy? Mid-Infrared Spectroscopy of CAI and Their Mineral Components. The Origin of Iron Isotope Fractionation in Chondrules, CAIs and Matrix from Allende (CV3) and Chainpur (LL3) Chondrites. Protoplanetary Disk Evolution: Early Results from Spitzer. Kinetics of Evaporation-Condensation in a Melt-Solid System and Its Role on the Chemical Composition and Evolution of Chondrules. Oxygen Isotope Exchange Recorded Within Anorthite Single Crystal in Vigarano CAI: Evidence for Remelting by High Temperature Process in the Solar Nebula. Chondrule Forming Shock Waves in Solar Nebula by X-Ray Flares. Organic Globules with Anormalous Nitrogen Isotopic Compositions in the Tagish Lake Meteorite: Products of Primitive Organic Reactions. Yet Another Chondrule Formation Scenario. CAIs are Not Supernova Condensates. Microcrystals and Amorphous Material in Comets and Primitive Meteorites: Keys to Understanding Processes in the Early Solar System. A Nearby Supernova Injected Short-lived Radionuclides into Our Protoplanetary Disk. REE+Y Systematics in CC and UOC Chondrules. Meteoritic Constraints on Temperatures, Pressures, Cooling Rates, Chemical Compositions, and Modes of Condensation in the Solar Nebula. The I-Xe Record of Long Equilibration in Chondrules from the Unnamed Antarctic Meteorite L3/LL3. Early Stellar Evolution.

Variability in magnesium, carbon and oxygen isotope compositions, and trace element contents of brachiopod shells: implications for paleoceanographic studies

NASA Astrophysics Data System (ADS)

Rollion-Bard, Claire; Saulnier, Ségolène; Vigier, Nathalie; Schumacher, Aimryc; Chaussidon, Marc; Lécuyer, Christophe

2016-04-01

Magnesium content in the ocean is ≈ 1290 ppm and is one of the most abundant elements. It is involved in the carbon cycle via the dissolution and precipitation of carbonates, especially Mg-rich carbonates as dolomites. The Mg/Ca ratio of the ocean is believed to have changed through time. The causes of these variations, i.e. hydrothermal activity change or enhanced precipitation of dolomite, could be constrained using the magnesium isotope composition (δ26Mg) of carbonates. Brachiopods, as marine environmental proxies, have the advantage to occur worldwide in a depth range from intertidal to abyssal, and have been found in the geological record since the Cambrian. Moreover, as their shell is in low-Mg calcite, they are quite resistant to diagenetic processes. Here we report δ26Mg, δ18O, δ13C values along with trace element contents of one modern brachiopod specimen (Terebratalia transversa) and one fossil specimen (Terebratula scillae, 2.3 Ma). We combined δ26Mg values with oxygen and carbon isotope compositions and trace element contents to look for possible shell geochemical heterogeneities in order to investigate the processes that control the Mg isotope composition of brachiopod shells. We also evaluate the potential of brachiopods as a proxy of past seawater δ26Mg values. The two investigated brachiopod shells present the same range of δ26Mg variation (up to 2 ‰)). This variation cannot be ascribed to changes in environmental parameters, i.e. temperature or pH. As previously observed, the primary layer of calcite shows the largest degree of oxygen and carbon isotope disequilibrium relative to seawater. In contrast, the δ26Mg value of this layer is comparable to that of the secondary calcite layer value. In both T. scillae and T. transversa, negative trends are observable between magnesium isotopic compositions and oxygen and carbon isotopic compositions. These trends, combined to linear relationships between δ26Mg values and REE contents, are best explained by kinetic effects linked to changes in growth rate during the brachiopod life. The innermost calcite layer of T. transversa is in isotopic equilibrium for both oxygen and magnesium and could therefore be the best target for reconstructing past δ26Mg values of seawater.

Ca cycling and isotopic fluxes in forested ecosystems in Hawaii

USGS Publications Warehouse

Wiegand, B.A.; Chadwick, O.A.; Vitousek, P.M.; Wooden, J.L.

2005-01-01

Biogeochemical processes fractionate Ca isotopes in plants and soils along a 4 million year developmental sequence in the Hawaiian Islands. We observed that plants preferentially take up 40Ca relative to 44Ca, and that biological fractionation and changes in the relative contributions from volcanic and marine sources produce a significant increase in 44Ca in soil exchangeable pools. Our results imply moderate fluxes enriched in 44Ca from strongly nutrient-depleted old soils, in contrast with high 40Ca fluxes in young and little weathered environments. In addition, biological fractionation controls divergent geochemical pathways of Ca and Sr in the plant-soil system. While Ca depletes progressively with increasing soil age, Sr/Ca ratios increase systematically. Sr isotope ratios provide a valuable tracer for provenance studies of alkaline earth elements in forested ecosystems, but its usefulness is limited when deciphering biogeochemical processes involved in the terrestrial Ca cycle. Ca isotopes in combination with Sr/ Ca ratios reveal more complex processes involved in the biogeochemistry of Ca and Sr. Copyright 2005 by the American Geophysical Union.

Site-specific equilibrium isotopic fractionation of oxygen, carbon and calcium in apatite

NASA Astrophysics Data System (ADS)

Aufort, Julie; Ségalen, Loïc; Gervais, Christel; Paulatto, Lorenzo; Blanchard, Marc; Balan, Etienne

2017-12-01

The stable isotope composition of biogenic apatite is an important geochemical marker that can record environmental parameters and is widely used to infer past climates, biomineralization processes, dietary preferences and habitat of vertebrates. In this study, theoretical equilibrium isotopic fractionation of oxygen, carbon and calcium in hydroxyapatite and carbonate-bearing hydroxyapatite is investigated using first-principles methods based on density-functional theory and compared to the theoretical isotopic fractionation properties of calcite, CO2 and H2O. Considering the variability of apatite crystal-chemistry, special attention is given to specific contributions of crystal sites to isotopic fractionation. Significant internal fractionation is calculated for oxygen and carbon isotopes in CO3 between the different structural sites occupied by carbonate groups in apatite (typically 7‰ for both 18O/16O and 13C/12C fractionation at 37 °C). Compared with calcite-water oxygen isotope fractionation, occurrence of A-type substitution in apatite structure, in addition to the main B-type substitution, could explain the larger temperature dependence of oxygen isotope fractionation measured at low temperature between carbonate in apatite and water. Theoretical internal fractionation of oxygen isotopes between carbonate and phosphate in B-type carbonated apatite (∼8‰ at 37 °C) is consistent with experimental values obtained from modern and well-preserved fossil bio-apatites. Concerning calcium, theoretical results suggest a small fractionation between apatite and calcite (-0.17‰ at 37 °C). Internal fractionation reaching 0.8‰ at 37 °C occurs between the two Ca sites in hydroxyapatite. Furthermore, the Ca isotopic fractionation properties of apatite are affected by the occurrence of carbonate groups, which could contribute to the variability observed on natural samples. Owing to the complexity of apatite crystal-chemistry and in light of the theoretical results, measurements of site-specific isotopic fractionation properties could improve our understanding and the interpretation of isotopic records in apatites.

Thermal Diffusion Fractionation of Cr and V Isotope in Silicate Melt

NASA Astrophysics Data System (ADS)

Lin, X.; Lundstrom, C.

2017-12-01

Earth's mantle is isotopically heavy relative to chondrites for V, Cr and some other siderophile elements. A possible solution is that isotopic fractionation by thermal diffusion occurs in a thermal boundary layer between solid mantle and an underlying basal magma ocean (BMO:Labrosse et al.,2007). If so, isotopically light composition might partition into the core, resulting in a complimentary isotopically heavy solid mantle. To verify how much fractionation could happen in this process, piston cylinder experiment were conducted to investigate the fractionation of Cr and V isotope ratios in partially molten silicate under an imposed temperature gradient from 1650 °C to 1350 °C at 1 GPa for 10 to 50 hours to reach a steady state isotopic profile. The temperature profile for experiments was determined by the spinel-growth method at the same pressure and temperature. Experimental runs result in 100% glass at the hot end progressing to nearly 100 % olivine at the cold end. Major and minor element concentrations of run products show systematic changes with temperature. Glass MgO contents increase and Al2O3 and CaO contents decrease by several weight percent as temperature increases across the charge. These are well modeled using IRIDIUM (Boudreau 2003) to simulate the experiments. Isotopic composition measurements of Cr and V at different temperatures are in progress, providing the first determinations of thermal diffusion isotopic sensitivity, Ω (permil isotopic fractionation per temperature offset per mass unit) for these elements. These results will be compared with previously determined Ω for network formers and modifiers and used in a BMO-based thermal diffusion model for formation of Earth's isotopically heavy mantle.

Sm-Nd isotopic compositions of LREE minerals for use as reference materials for in situ analysis by LA-MC-ICPMS

NASA Astrophysics Data System (ADS)

Fisher, C. M.; McFarlane, C. R.; Sylvester, P.; Hanchar, J. M.; Lam, R.; Schmitz, M. D.

2009-12-01

Recent work has demonstrated the possibility of obtaining both accurate and precise in situ Sm-Nd isotopic data in light rare earth enriched (LREE) accessory minerals including apatite, titanite, and monazite, using laser ablation-multicollector-inductively coupled plasma mass spectrometry (LA-MC-ICPMS). A distinct advantage of using LA-MC-ICPMS is that Sm-Nd isotopic data from these minerals can be determined in sub-grain domains potentially avoiding problems of isotopic mixing from inherited or xenocrystic components and allowing both valuable tracer isotope and geochronologic data to be obtained. However, a number of analytical obstacles complicate accurate Sm-Nd determination by LA-MC-ICPMS including mass bias corrections, the 144Sm isobaric interference on 144Nd, and potential offset (ca. 20-40 ppm) from thermal ionization mass spectrometry (TIMS) determination of similar materials. Thus, in order to verify Sm-Nd isotopic determination from unknowns, matrix-matched quality control standards (i.e., reference materials) must be developed to test the data handling protocol. This talk will present new Sm-Nd isotopic data determined by both TIMS as well as LA-MC-ICPMS of a number of natural potential reference minerals including Durango apatite, Fish Canyon titanite, Daibosatsu allanite, Trebilcock monazite, as well as a monazite from the Doi Inthanon core complex in northern Thailand. Our preliminary LA-MC-ICPMS results demonstrate that Durango apatite, Fish Canyon titanite, and Thailand monazite show both inter- and intra-grain homogeneity at current levels of precision (ca. 0.3-0.5 ɛNd) and close agreement with our TIMS data.

Experimental high temperature carbon isotope fractionation involving graphite

NASA Astrophysics Data System (ADS)

Kueter, N.; Schmidt, M. W.; Lilley, M. D.; Bernasconi, S. M.

2016-12-01

Graphite/carbonate carbon isotope fractionation was mainly investigated at 400- 800°C and is based on empirical calibrations, theoretical calculations and few experiments [1,2]. Own work on COH-fluid/graphite isotope fractionation shows that in experiments up to 1000oC a fluid phase is always enriched in 13C compared to coexisting graphitic carbon. The eventual kinetic isotope effect in these experiments is best displayed by the graphitic carbon being at least 3 ‰ lighter than methane. Only few experiments done in the graphite/carbonate pair dealt with higher temperatures reaching 1400°C, indicating a fractionation of up to 2 ‰ at temperatures of the Earth's mantle [2-4]. To better understand carbon isotope fractionation in crustal systems and still overcome kinetic effects, we study the graphite/carbonatite pair with piston cylinder experiments in the Na2CO3-CaCO3-CaO-COH system. Tartaric acid (C4H6O6) supplies reduced carbon, time series are performed at 10 kbar, 1300-1800°C. Initial experiments at 1300°C produce well-ordered, micron-sized graphite flakes growing attached to the capsule walls while the Na-Ca-carbonatite-melt quenches to dendritic textures. No gaseous phase was observed. Conditions well above the liquidus of the Na2CO3-CaCO3-binary lead to dissolution of the H2O from tartaric acid decomposition in the melt, any CO2-component is bound by the excess CaO to CaCO3melt while in the relatively oxidizing capsule environment any CH4-component reacts with CO2 to carbon and H2O. The graphite and the carbonatite quench are measured for their δ13C composition using a GasBench II (carbonate-dissolution in phosphoric acid) and TC/EA (residual graphite combusted in oxygen atmosphere) system coupled to a Thermo Fischer IRMS. Our results expand from the graphite-carbonate system to graphite-fluid system when adding available fluid-carbonate fractionation factors, but are also directly applicable to diamond synthesis as graphite is often found as a precursor phase in diamond-growth experiments in carbonatite systems and natural diamonds. [1] Chacko et al. (2001) Rev Min Geochem; Deines & Eggler (2009) GCA; [3] Scheele & Hoefs (1992) CMP; [4] Chacko et al. (1991) GCA

Stable isotopes, Sr/Ca, and Mg/Ca in biogenic carbonates from Petaluma Marsh, northern California, USA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ingram, B.L.; De Deckker, P.; Chivas, A.R.

2004-10-19

Stable isotope ({sup 18}O/{sup 16}O and {sup 13}C/{sup 12}C) and minor-element compositions (Sr/Ca and Mg/Ca ratios) of ostracodes and gastropods separated from marsh sediments from San Francisco Bay, Northern California, were used to reconstruct paleoenvironmental changes in Petaluma Marsh over the past 700 yr. The value of {delta}{sup 18}O in the marsh carbonates reflects changes in freshwater inflow, evaporation, and temperature. Mg/Ca and Sr/Ca in ostracode calcite reflect changes in both freshwater inflow and temperature, although primarily reflect temperature changes in the salinity range of about 10-35 {per_thousand}. Ostracode {delta}{sup 18}O values show a gradual increase by 5 {per_thousand} betweenmore » 500 yr BR and the present, probably reflecting rising sea level and increased evaporation in the marsh. Superimposed on this trend are higher frequency Mg/Ca and {delta}{sup 18}O variations (3-4 {per_thousand}), probably reflecting changes in freshwater inflow and evaporation. A period of low Mg/Ca occurred between about 100-300 cal yr BP, suggesting wetter and cooler conditions during the Little Ice Age. Higher Mg/Ca ratios occurred 600-700 cal yr BP, indicating drier and warmer conditions during the end of the Medieval Warm Period. Both ostracode and gastropod {delta}{sup 13}C values decrease up-core, reflecting decomposition of marsh vegetation, which changes from C{sub 4} ({delta}{sup 13}C {approx} -12{per_thousand}) to CAM ({delta}{sup 13}C = -26 {per_thousand})-type vegetation over time.« less

Stable isotopes, Sr/Ca, and Mg/Ca in biogenic carbonates from Petaluma Marsh, northern California, USA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ingram, B.L.; Deckker, P. de; Chivas, A.R.

1998-10-01

Stable isotope ({sup 18}O/{sup 16}O and {sup 13}C/{sup 12}C) and minor-element compositions (Sr/Ca and Mg/Ca ratios) of ostracodes and gastropods separated from marsh sediments from San Francisco Bay, Northern California, were used to reconstruct paleoenvironmental changes in Petaluma March over the past 700 yr. The value of {delta}{sup 18}O in the marsh carbonates reflects changes in freshwater inflow, evaporation, and temperature. Mg/Ca and Sr/Ca in ostracode calcite reflect changes in both freshwater inflow and temperature, although primarily reflect temperature changes in the salinity range of about 10--35{per_thousand}. Ostracode {delta}{sup 18}O values show a gradual increase by 5{per_thousand} between 500 yrmore » BP and the present, probably reflecting rising sea level and increased evaporation in the marsh. Superimposed on this trend are higher frequency Mg/Ca and {delta}{sup 18}O variations (3--4{per_thousand}), probably reflecting changes in freshwater inflow and evaporation. A period of low Mg/Ca occurred between about 100--300 cal yr BP, suggesting wetter and cooler conditions during the Little Ice Age. Higher Mg/Ca ratios occurred 600--700 cal yr BP, indicating drier and warmer conditions during the end of the Medieval Warm Period. Both ostracode and gastropod {delta}{sup 13}C values decrease up-core, reflecting decomposition of marsh vegetation, which changes from C{sub 4} ({delta}{sup 13}C {approximately} {minus}12{per_thousand}) to CAM ({delta}{sup 13}C = {minus}26{per_thousand})-type vegetation over time.« less

[Determination of 235U/238U isotope ratios in camphor tree bark samples by MC-ICP-MS after separation of uranium from matrix elements].

PubMed

Wang, Xiao-Ping; Zhang, Ji-Long

2007-07-01

Twelve camphor (cinnamomum camphora) tree bark samples were collected from Hiroshima and Kyoto, and the matrix element composition and morphology of the outer surface of these camphor tree bark samples were studied by EDXS and SEM respectively. After a dry decomposition, DOWEX 1-X8 anion exchange resin was used to separate uranium from matrix elements in these camphor tree bark samples. Finally, 235U/238 U isotope ratios in purified uranium solutions were determined by MC-ICP-MS. It was demonstrated that the outer surface of these camphor tree bark samples is porous and rough, with Al, Ca, Fe, K, Mg, Si, C, O and S as its matrix element composition. Uranium in these camphor tree bark samples can be efficiently separated and quantitatively recovered from the matrix element composition. Compared with those collected from Kyoto, the camphor tree bark samples collected from Hiroshima have significantly higher uranium contents, which may be due to the increased aerosol mass concentration during the city reconstruction. Moreover, the 235 U/23.U isotope ratios in a few camphor tree bark samples collected from Hiroshima are slightly higher than 0.007 25.

Diagenesis of lower Cretaceous pelagic carbonates, North Atlantic: Paleoceanographic signals obscured

USGS Publications Warehouse

Frank, T.D.; Arthur, M.A.; Dean, W.E.

1999-01-01

The stable isotope and minor element geochemistry of Neocomian (Lower Cretaceous) pelagic carbonates of the North Atlantic Basin (Deep Sea Drilling Project Sites 105, 367, 387, 391, and 603) was examined to develop a diagenetic model for pelagic limestones. In particular, we hoped to test the fidelity of whole-rock geochemical records as paleoceanographic indicators for pelagic deposits of pre-Aptian age, in which individual microfossils are not available for analysis. Data indicate that in addition to depth of burial, rhythmic variations in primary carbonate content have strongly controlled diagenetic patterns and associated geochemical signatures in these Neocomian sequences. Samples become increasingly depleted in Sr and 18O with increasing CaCO3 content. Within individual sedimentary sections, substantial decreases in Sr/Ca ratios and ??18O values are evident over a range of 4 to 98% CaCO3. However, even over a relatively narrow range of 50 to 98% CaCO3 a 2.5%c variation in ??18O values and a change of a factor of 1.7 in Sr/Ca ratios are observed. Carbon isotope compositions do not vary as extensively with CaCO3 content, but carbonate-rich intervals tend to be relatively depleted in 13C. Petrographic analysis reveals that these geochemical patterns are related to the transfer of CaCO3 from carbonate-poor intervals (calcareous shales and marlstones) to adjacent carbonate-rich intervals (limestones) during burial compaction and pressure solution. This process results in the addition of diagenetic cement to carbonate-rich intervals to produce a bulk composition that is relatively depleted in Sr and 18O and, at the same time, enables the retention of more-or-less primary carbonate that is relatively enriched in Sr and 18O in adjacent carbonate-poor intervals. Thus, although cyclic variations in CaCO3 content are primary in the Neocomian sequences examined, measured variations in Sr/Ca ratios and ??18O values are not and, as such, do not provide reliable proxies for past variations in climate, oceanographic conditions, or global ice volume.

The origin of volatile element depletion in early solar system material: Clues from Zn isotopes in chondrules

NASA Astrophysics Data System (ADS)

Pringle, Emily A.; Moynier, Frédéric; Beck, Pierre; Paniello, Randal; Hezel, Dominik C.

2017-06-01

Volatile lithophile elements are depleted in the different planetary materials to various degrees, but the origin of these depletions is still debated. Stable isotopes of moderately volatile elements such as Zn can be used to understand the origin of volatile element depletions. Samples with significant volatile element depletions, including the Moon and terrestrial tektites, display heavy Zn isotope compositions (i.e. enrichment of 66Zn vs. 64Zn), consistent with kinetic Zn isotope fractionation during evaporation. However, Luck et al. (2005) found a negative correlation between δ66Zn and 1/[Zn] between CI, CM, CO, and CV chondrites, opposite to what would be expected if evaporation caused the Zn abundance variations among chondrite groups. We have analyzed the Zn isotope composition of multiple samples of the major carbonaceous chondrite classes: CI (1), CM (4), CV (2), CO (4), CB (2), CH (2), CK (4), and CK/CR (1). The bulk chondrites define a negative correlation in a plot of δ66Zn vs 1/[Zn], confirming earlier results that Zn abundance variations among carbonaceous chondrites cannot be explained by evaporation. Exceptions are CB and CH chondrites, which display Zn systematics consistent with a collisional formation mechanism that created enrichment in heavy Zn isotopes relative to the trend defined by CI-CK. We further report Zn isotope analyses of chondrite components, including chondrules from Allende (CV3) and Mokoia (CV3), as well as an aliquot of Allende matrix. All chondrules are enriched in light Zn isotopes (∼500 ppm on 66Zn/64Zn) relative to the bulk, contrary to what would be expected if Zn were depleted during evaporation, on the other hand the matrix has a complementary heavy isotope composition. We report sequential leaching experiments in un-equilibrated ordinary chondrites, which show sulfides are isotopically heavy compared to silicates and the bulk meteorite by ca. +0.65 per mil on 66Zn/64Zn. We suggest isotopically heavy sulfides were removed from either chondrules or their precursors, thereby producing the light Zn isotope enrichments in chondrules.

δ44Ca in N. pachy (left): A Promising Tool for SST-Reconstruction in High-Latitude Oceans

NASA Astrophysics Data System (ADS)

Hippler, D.; Gussone, N.; Darling, K.; Eisenhauer, A.; Nagler, T. F.

2002-12-01

Reconstructions of sea surface temperatures (SSTs) by means of planktonic foraminifera are an essential tool in paleoceanography. Unlike to marine tropical environments where a number of established SST-proxies exist, information on paleo-SST of polar water masses is scarce. In these regions high-resolution records exist mainly for continental environments. Ca isotopes bear a high potential as SST proxies as they are insensitive to changes in global ice volume, evaporation or freshwater input. Here, measurements of the Ca-isotopic composition on calcite shells of Neogloboquadrina pachyderma (left coiling) -a dominant species in subpolar and polar surface waters- are presented. The genotype of individuals tests was determined at the University of Edinburgh. Subsequently the respective calcite shells were analysed for δ44Ca at the University of Bern. The most complete data set is from the polar North Atlantic. All samples are from the same genotype and span a temperature (T) range from 1.9°C to 6.5°C. It was found that T correlates well with δ44Ca. The total δ44Ca-variation results in a δ44Ca-change of 0.2‰ per 1°C defined by a linear regression. In order to test whether the correlation is influenced by hydrographic or genotype differences a second set of a Southern Atlantic genotype of N. pachy (left) has been investigated. Preliminary observations point to T as the main factor controlling δ44Ca variations and a T dependence very similar to that of Arctic specimen. Remarkably, this T dependence (although not the absolute values) is identical within errors to the one of tropical G. sacculifer (Nagler et al., 2000, G3). Thus, even though Ca isotope fractionation is known to be species-dependent, the increase of 0.2‰ δ44Ca per 1°C seems to reflect a particular mode of biocalcification. While more calibration work is needed, it appears that T changes of polar surface waters will be quantitatively resolvable.

Characterisation of methane isotope composition over the Silesian Coal Basin, Poland.

NASA Astrophysics Data System (ADS)

Necki, Jaroslaw; Zimnoch, Miroslaw; Jasek, Alina; Chmura, Lukasz; Galkowski, Michal; Wolkowicz, Wojciech

2017-04-01

Methane emissions from Silesian Coal Basin (SCB), one of European regions associated with coal excavation industry constitute an important component of the continental anthropogenic flux of this gas into the atmosphere. It is estimated by different methodology that SCB is responsible for between 450 - 1350 Gg CH4 of atmospheric methane releases annually, making it one of the most significant sources of this gas in Europe. In this region, active or restructuring coal mining methane emissions may lead to elevated concentrations of this gas in near-ground atmosphere. Observed methane mixing ratio in pbl during nighttime over the specific areas of SCB is elevated by up to 50ppm with carbon isotope source ratio -46‰ to -52‰ with occasionally lighter methane (-58) form particular coal beds. Numbers were derived from direct measurement of samples taken from ventilation shafts (concentration 1.5% to 4% of CH4, subsequently diluted to 2ppm with zero air and measured by Picarro CRDS analyzer). Measurements of CH4 mixing ratios and isotopic composition were performed along latitudinal transects (ca. 50oN), typically extending from ca. 15oE to 20oE, covering the Upper Silesia and bordering regions on the public roads in vicinity of the mine ventilation shafts. Apart from CH4 emissions associated with coal production, other sources of anthropogenic methane are also active over SCB. These include city gas networks leakages that enrich the air by up to 5ppm (in the city centers, carbon isotope ratio on average -52). Most of the numerous landfills, not yet equipped with appropriate CH4 uptake installations, also contribute to substantial anthropogenic flux of this gas to the atmosphere. Values of methane mixing ratio recorded during the in-situ measurements close to the landfill sites reached 15ppm (with carbon isotope ratio -56‰ to -60). The transects of methane concentration over Silesian area, assisted by analysis of its stable isotopic composition has been performed in all of the locations where active and closed mining shafts are positioned, and most of the landfills and cities under the different meteorological and synoptic conditions to provide a base for efficient future verification of methane inventory over SCB. Project will be continued with MEMO2 ITN H2020.

Determination of Mo- and Ca-isotope ratios in Ca100MoO4 crystal for AMoRE-I experiment

NASA Astrophysics Data System (ADS)

Karki, S.; Aryal, P.; Kim, H. J.; Kim, Y. D.; Park, H. K.

2018-01-01

The first phase of the AMoRE (Advanced Mo-based Rare process Experiment) is to search for neutrinoless double-beta decay of 100Mo with calcium molybdate (Ca100MoO4) crystals enriched in 100Mo and depleted in 48Ca using a cryogenic technique at Yangyang underground laboratory in Korea. It is important to know 100Mo- and 48Ca-isotope ratios in Ca100MoO4 crystal to estimate half-life of 100Mo decays and to 2 νββ background from 48Ca. We employed the ICP-MS (Inductive Coupled Plasma Mass Spectrometer) to measure 100Mo- and 48Ca-isotope ratios in Ca100MoO4 crystal. The measured results for 100Mo- and 48Ca-isotope ratios in the crystal are (94 . 6 ± 2 . 8) % and (0 . 00211 ± 0 . 00006) %, respectively, where errors are included both statistical and systematic uncertainties.

Modified ion exchange separation for tungsten isotopic measurements from kimberlite samples using multi-collector inductively coupled plasma mass spectrometry.

PubMed

Sahoo, Yu Vin; Nakai, Shun'ichi; Ali, Arshad

2006-03-01

Tungsten isotope composition of a sample of deep-seated rock can record the influence of core-mantle interaction of the parent magma. Samples of kimberlite, which is known as a carrier of diamond, from the deep mantle might exhibit effects of core-mantle interaction. Although tungsten isotope anomaly was reported for kimberlites from South Africa, a subsequent investigation did not verify the anomaly. The magnesium-rich and calcium-rich chemical composition of kimberlite might engender difficulty during chemical separation of tungsten for isotope analyses. This paper presents a simple, one-step anion exchange technique for precise and accurate determination of tungsten isotopes in kimberlites using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). Large quantities of Ca and Mg in kimberlite samples were precipitated and removed with aqueous H(2)SO(4). Highly pure fractions of tungsten for isotopic measurements were obtained following an anion exchange chromatographic procedure involving mixed acids. That procedure enabled efficient removal of high field strength elements (HFSE), such as Hf, Zr and Ti, which are small ions that carry strong charges and develop intense electrostatic fields. The tungsten yields were 85%-95%. Advantages of this system include less time and less use of reagents. Precise and accurate isotopic measurements are possible using fractions of tungsten that are obtained using this method. The accuracy and precision of these measurements were confirmed using various silicate standard rock samples, JB-2, JB-3 and AGV-1.

Lateglacial and Holocene climatic changes in south-eastern Patagonia inferred from carbonate isotope records of Laguna Potrok Aike (Argentina)

NASA Astrophysics Data System (ADS)

Oehlerich, M.; Mayr, C.; Gussone, N.; Hahn, A.; Hölzl, S.; Lücke, A.; Ohlendorf, C.; Rummel, S.; Teichert, B. M. A.; Zolitschka, B.

2015-04-01

First results of strontium, calcium, carbon and oxygen isotope analyses of bulk carbonates from a 106 m long sediment record of Laguna Potrok Aike, located in southern Patagonia are presented. Morphological and isotopic investigations of μm-sized carbonate crystals in the sediment reveal an endogenic origin for the entire Holocene. During this time period the calcium carbonate record of Laguna Potrok Aike turned out to be most likely ikaite-derived. As ikaite precipitation in nature has only been observed in a narrow temperature window between 0 and 7 °C, the respective carbonate oxygen isotope ratios serve as a proxy of hydrological variations rather than of palaeotemperatures. We suggest that oxygen isotope ratios are sensitive to changes of the lake water balance induced by intensity variations of the Southern Hemisphere Westerlies and discuss the role of this wind belt as a driver for climate change in southern South America. In combination with other proxy records the evolution of westerly wind intensities is reconstructed. Our data suggest that weak SHW prevailed during the Lateglacial and the early Holocene, interrupted by an interval with strengthened Westerlies between 13.4 and 11.3 ka cal BP. Wind strength increased at 9.2 ka cal BP and significantly intensified until 7.0 ka cal BP. Subsequently, the wind intensity diminished and stabilised to conditions similar to present day after a period of reduced evaporation during the "Little Ice Age". Strontium isotopes (87Sr/86Sr ratio) were identified as a potential lake-level indicator and point to a lowering from overflow conditions during the Glacial (∼17 ka cal BP) to lowest lake levels around 8 ka cal BP. Thereafter the strontium isotope curve resembles the lake-level curve which is stepwise rising until the "Little Ice Age". The variability of the Ca isotope composition of the sediment reflects changes in the Ca budget of the lake, indicating higher degrees of Ca utilisation during the period with lowest lake level.

Tracing the distribution of erosion in the Brahmaputra watershed from isotopic compositions of stream sediments

NASA Astrophysics Data System (ADS)

Singh, Sunil K.; France-Lanord, Christian

2002-09-01

Bank sediments and suspended loads of the Brahmaputra River and its important tributaries were collected from the Himalayan front to Bangladesh along with most of the important tributaries. Chemical and isotopic compositions of the sediments are used to trace sediment provenance and to understand erosion patterns in the basin. Overall isotopic compositions range from 0.7053 to 0.8250 for Sr and ɛNd from -20.5 to -6.9. This large range derives from the variable proportions of sediments from Himalayan formations with high Sr isotopic ratios and low ɛNd, and Transhimalayan plutonic belt with lower Sr isotopic ratios and higher ɛNd. The latter are exposed to erosion in the Tsangpo and in the eastern tributary drainages. Overall erosion of the Himalayan rocks is dominant, representing ca 70% of the detrital influx. Compositions of the Brahmaputra main channel are rather stable between 0.7177 and 0.7284 for Sr and between -14.4 and -12.5 for ɛNd throughout its course in the plain from the Siang-Tsangpo at the foot of the Himalayan range down to the delta. This stability, despite the input of large Himalayan rivers suggests that the Siang-Tsangpo River represents the major source of sediment to the whole Brahmaputra. Geochemical budget implies that erosion of the Namche Barwa zone represents about 45% of the total flux at its outflow before confluence with the Ganga from only 20% of the mountain area. Higher erosion rates in the eastern syntaxis compared to the other Himalayan ranges is related to the rapid exhumation rates of this region, possibly triggered by higher precipitation over the far-eastern Himalaya and the high incision potential of the Tsangpo River due to its very high water discharge.

Using the Abitibi Greenstone Belt to Understand Martian Hydrothermal Systems and the Potential for Biosignature Preservation in High Temperature Aqueous Environments

NASA Technical Reports Server (NTRS)

Hurowitz, J.; Abelson, J.; Allwood, A.; Anderson, R.; Atkinson, B.; Beaty, D.; Bristow, T.; Ehlmann, B.; Eigenbrode, J.; Grotzinger, J.;

Determining Solute Sources and Water Flowpaths in a Forested Headwater Catchment: Advances With the Ca-Sr-Ba Multi-tracer

NASA Astrophysics Data System (ADS)

Bullen, T. D.; Bailey, S. W.; McGuire, K. J.; Zimmer, M. A.; Ross, D. S.

2011-12-01

Determining solute sources and water flowpaths in catchments is of critical importance to development of models that effectively describe catchment function. For solutes in soil water and stream water, simple mass balance models that compare precipitation input to catchment outlet compositions can predict average mineral weathering contributions for the catchment as a whole, but fail to provide information about either variability of contributions from different portions of the catchment and different soil depths or processes such as ion exchange and biological cycling. In order to better understand how forested headwater catchments function, we are interpreting concentration and isotope ratios of the alkaline earth elements Ca, Sr and Ba in streamwater, groundwater, the soil ion exchange pool and plants in a hydropedologic context at the 41 hectare hydrologic reference catchment (Watershed 3) at the Hubbard Brook Experimental Forest, New Hampshire, USA. This forested headwater catchment consists of a beech-birch-maple-spruce forest growing on vertically- and laterally-developed Spodosols and Inceptisols formed on granitoid glacial till that mantles Paleozoic metamorphic bedrock. Across the watershed in terms of the soil ion exchange pool, the forest floor has high Sr/Ba and Ca/Sr ratios, mineral soils have intermediate Sr/Ba and low Ca/Sr, and relatively unweathered till in the C horizon has low Sr/Ba and high Ca/Sr. Waters moving through these various compartments will obtain Sr/Ba and Ca/Sr ratios reflecting these characteristics, and thus variations of Sr/Ba and Ca/Sr of streamwater provide evidence of the depth of water flowpaths feeding the streams. 87Sr/86Sr of exchangeable Sr spans a broad range from 0.715 to 0.725, with highest values along the mid-to upper flanks of the catchment and lowest values in a broad zone along the central axis of the catchment associated with numerous groundwater seeps. Thus, variations of 87Sr/86Sr in streamwater provide evidence of the spatial distribution of water flowpaths feeding the streams. In addition, we are exploring the use of Sr and Ba stable isotope ratios (88Sr/86Sr, 138Ba/134Ba) as novel tracers of Sr and Ba sources in catchments. Initial results indicate that both Sr and Ba stable isotopes are fractionated by plants similarly to patterns observed globally for Ca stable isotopes. We hypothesize that while biologically-cycled Ca is efficiently retained in the organic soil-plant system, biologically-cycled Sr and especially Ba will be more easily leached by soil waters and delivered to the streams and thus their stable isotope ratios may provide an additional means to distinguish between shallow and deep water flowpaths in forested catchments.

A change in coral extension rates and stable isotopes after El Niño-induced coral bleaching and regional stress events

NASA Astrophysics Data System (ADS)

Hetzinger, S.; Pfeiffer, M.; Dullo, W.-Chr.; Zinke, J.; Garbe-Schönberg, D.

2016-09-01

Coral reefs are biologically diverse ecosystems threatened with effective collapse under rapid climate change, in particular by recent increases in ocean temperatures. Coral bleaching has occurred during major El Niño warming events, at times leading to the die-off of entire coral reefs. Here we present records of stable isotopic composition, Sr/Ca ratios and extension rate (1940-2004) in coral aragonite from a northern Venezuelan site, where reefs were strongly impacted by bleaching following the 1997-98 El Niño. We assess the impact of past warming events on coral extension rates and geochemical proxies. A marked decrease in coral (Pseudodiploria strigosa) extension rates coincides with a baseline shift to more negative values in oxygen and carbon isotopic composition after 1997-98, while a neighboring coral (Siderastrea siderea) recovered to pre-bleaching extension rates simultaneously. However, other stressors, besides high temperature, might also have influenced coral physiology and geochemistry. Coastal Venezuelan reefs were exposed to a series of extreme environmental fluctuations since the mid-1990s, i.e. upwelling, extreme rainfall and sediment input from landslides. This work provides important new data on the potential impacts of multiple regional stress events on coral isotopic compositions and raises questions about the long-term influence on coral-based paleoclimate reconstructions.

Isotopic composition of atmospheric nitrate in a tropical marine boundary layer.

PubMed

Savarino, Joel; Morin, Samuel; Erbland, Joseph; Grannec, Francis; Patey, Matthew D; Vicars, William; Alexander, Becky; Achterberg, Eric P

2013-10-29

Long-term observations of the reactive chemical composition of the tropical marine boundary layer (MBL) are rare, despite its crucial role for the chemical stability of the atmosphere. Recent observations of reactive bromine species in the tropical MBL showed unexpectedly high levels that could potentially have an impact on the ozone budget. Uncertainties in the ozone budget are amplified by our poor understanding of the fate of NOx (= NO + NO2), particularly the importance of nighttime chemical NOx sinks. Here, we present year-round observations of the multiisotopic composition of atmospheric nitrate in the tropical MBL at the Cape Verde Atmospheric Observatory. We show that the observed oxygen isotope ratios of nitrate are compatible with nitrate formation chemistry, which includes the BrNO3 sink at a level of ca. 20 ± 10% of nitrate formation pathways. The results also suggest that the N2O5 pathway is a negligible NOx sink in this environment. Observations further indicate a possible link between the NO2/NOx ratio and the nitrogen isotopic content of nitrate in this low NOx environment, possibly reflecting the seasonal change in the photochemical equilibrium among NOx species. This study demonstrates the relevance of using the stable isotopes of oxygen and nitrogen of atmospheric nitrate in association with concentration measurements to identify and constrain chemical processes occurring in the MBL.

Isotopic composition of atmospheric nitrate in a tropical marine boundary layer

PubMed Central

Savarino, Joel; Morin, Samuel; Erbland, Joseph; Grannec, Francis; Patey, Matthew D.; Vicars, William; Alexander, Becky; Achterberg, Eric P.

2013-01-01

Long-term observations of the reactive chemical composition of the tropical marine boundary layer (MBL) are rare, despite its crucial role for the chemical stability of the atmosphere. Recent observations of reactive bromine species in the tropical MBL showed unexpectedly high levels that could potentially have an impact on the ozone budget. Uncertainties in the ozone budget are amplified by our poor understanding of the fate of NOx (= NO + NO2), particularly the importance of nighttime chemical NOx sinks. Here, we present year-round observations of the multiisotopic composition of atmospheric nitrate in the tropical MBL at the Cape Verde Atmospheric Observatory. We show that the observed oxygen isotope ratios of nitrate are compatible with nitrate formation chemistry, which includes the BrNO3 sink at a level of ca. 20 ± 10% of nitrate formation pathways. The results also suggest that the N2O5 pathway is a negligible NOx sink in this environment. Observations further indicate a possible link between the NO2/NOx ratio and the nitrogen isotopic content of nitrate in this low NOx environment, possibly reflecting the seasonal change in the photochemical equilibrium among NOx species. This study demonstrates the relevance of using the stable isotopes of oxygen and nitrogen of atmospheric nitrate in association with concentration measurements to identify and constrain chemical processes occurring in the MBL. PMID:23431201

A change in coral extension rates and stable isotopes after El Niño-induced coral bleaching and regional stress events.

PubMed

Hetzinger, S; Pfeiffer, M; Dullo, W-Chr; Zinke, J; Garbe-Schönberg, D

2016-09-13

Coral reefs are biologically diverse ecosystems threatened with effective collapse under rapid climate change, in particular by recent increases in ocean temperatures. Coral bleaching has occurred during major El Niño warming events, at times leading to the die-off of entire coral reefs. Here we present records of stable isotopic composition, Sr/Ca ratios and extension rate (1940-2004) in coral aragonite from a northern Venezuelan site, where reefs were strongly impacted by bleaching following the 1997-98 El Niño. We assess the impact of past warming events on coral extension rates and geochemical proxies. A marked decrease in coral (Pseudodiploria strigosa) extension rates coincides with a baseline shift to more negative values in oxygen and carbon isotopic composition after 1997-98, while a neighboring coral (Siderastrea siderea) recovered to pre-bleaching extension rates simultaneously. However, other stressors, besides high temperature, might also have influenced coral physiology and geochemistry. Coastal Venezuelan reefs were exposed to a series of extreme environmental fluctuations since the mid-1990s, i.e. upwelling, extreme rainfall and sediment input from landslides. This work provides important new data on the potential impacts of multiple regional stress events on coral isotopic compositions and raises questions about the long-term influence on coral-based paleoclimate reconstructions.

Using stable isotopes (δD, δ18O, δ34S and 87Sr/86Sr) to identify sources of water in abandoned mines in the Fengfeng coal mining district, northern China

NASA Astrophysics Data System (ADS)

Qu, Shen; Wang, Guangcai; Shi, Zheming; Xu, Qingyu; Guo, Yuying; Ma, Luan; Sheng, Yizhi

2018-05-01

With depleted coal resources or deteriorating mining geological conditions, some coal mines have been abandoned in the Fengfeng mining district, China. Water that accumulates in an abandoned underground mine (goaf water) may be a hazard to neighboring mines and impact the groundwater environment. Groundwater samples at three abandoned mines (Yi, Er and Quantou mines) in the Fengfeng mining district and the underlying Ordovician limestone aquifer were collected to characterize their chemical and isotopic compositions and identify the sources of the mine water. The water was HCO3·SO4-Ca·Mg type in Er mine and the auxiliary shaft of Yi mine, and HCO3·SO4-Na type in the main shaft of Quantou mine. The isotopic compositions (δD and δ18O) of water in the three abandoned mines were close to that of Ordovician limestone groundwater. Faults in the abandoned mines were developmental, possibly facilitating inflows of groundwater from the underlying Ordovician limestone aquifers into the coal mines. Although the Sr2+ concentrations differed considerably, the ratios of Sr2+/Ca2+ and 87Sr/86Sr and the 34S content of SO4 2- were similar for all three mine waters and Ordovician limestone groundwater, indicating that a close hydraulic connection may exist. Geochemical and isotopic indicators suggest that (1) the mine waters may originate mainly from the Ordovician limestone groundwater inflows, and (2) the upward hydraulic gradient in the limestone aquifer may prevent its contamination by the overlying abandoned mine water. The results of this study could be useful for water resources management in this area and other similar mining areas.

Variations in the chemical and stable isotope composition of carbon and sulfur species during organic-rich sediment alteration: An experimental and theoretical study of hydrothermal activity at guaymas basin, gulf of california

USGS Publications Warehouse

Seewald, Jeffrey S.; Seyfried, W.E.; Shanks, Wayne C.

1994-01-01

Organic-rich diatomaceous ooze was reacted with seawater and a Na-Ca-K-Cl fluid of seawater chlorinity at 325-400??C, 400-500 bars, and fluid/sediment mass ratios of 1.56-2.35 to constrain factors regulating the abundance and stable isotope composition of C and S species during hydrothermal alteration of sediment from Guaymas Basin, Gulf of California. Alteration of inorganic and organic sedimentary components resulted in extensive exchange reactions, the release of abundant H2S, CO2, CH4, and Corganic, to solution, and recrystallization of the sediment to an assemblage containing albitic plagioclase, quartz, pyrrhotite, and calcite. The ??34Scdt values of dissolved H2S varied from -10.9 to +4.3??? during seawater-sediment interaction at 325 and 400??C and from -16.5 to -9.0??? during Na-Ca-K-Cl fluid-sediment interaction at 325 and 375??C. In the absence of seawater SO4, H2S is derived from both the transformation of pyrite to pyrrhotite and S released during the degradation of organic matter. In the presence of seawater SO4, reduction of SO4 contributes directly to H2S production. Sedimentary organic matter acts as the reducing agent during pyrite and SO4 reduction. Requisite acidity for the reduction of SO4 is provided by Mg fixation during early-stage sediment alteration and by albite and calcite formation in Mg-free solutions. Organically derived CH4 was characterized by ??13Cpdb values ranging between -20.8 and -23.1???, whereas ??13Cpdb values for dissolved Corganic ranged between -14.8 and -17.7%. Mass balance calculations indicate that ??13C values for organically derived CO2 were ??? - 14.8%. Residual solid sedimentary organic C showed small (??? 0.7???) depletions in 13C relative to the starting sediment. The experimental results are consistent with the isotopic and chemical composition of natural hydrothermal fluids and minerals at Guaymas Basin and permit us to better constrain sources and sinks for C and S species in subseafloor hydrothermal systems at sediment-covered spreading centers. Our data show that the sulfur isotope composition of hydrothermal Sulfide minerals in Guaymas Basin can be explained by derivation of S from diagenetic sulfide and seawater sulfate. Basaltic S may also contribute to hydrothermal sulfide precipitates but is not required to explain their isotopic composition. Estimates of seawater/ sediment mass ratios based on sulfur isotopic composition of sulfide minerals and the abundance of dissolved NH3 in vent fluids range from 3-29 during hydrothermal circulation. Sources of C in Guaymas Basin hydrothermal fluids include thermal degradation of organic matter, bacteriogenic methane production, and dissolution of diagenetic carbonate. ?? 1994.

Isotopic fractionation of oxygen and carbon in decomposed lower-mantle inclusions in diamond

DOE PAGES

Kaminsky, Felix; Matzel, Jennifer; Jacobsen, Ben; ...

2015-07-25

Two carbonatitic mineral assemblages, calcite + wollastonite and calcite + monticellite, which are encapsulated in two diamond grains from the Rio Soriso basin in the Juina area, Mato Grosso State, Brazil, were studied utilizing the NanoSIMS technique. The assemblages were formed as the result of the decomposition of the lower-mantle assemblage calcite + CaSi-perovskite + volatile during the course of the diamond ascent under pressure conditions from 15 to less than 0.8 GPa. The oxygen and carbon isotopic compositions of the studied minerals are inhomogeneous. They fractionated during the process of the decomposition of primary minerals to very varying values:more » δ 18O from –3.3 to +15.4 ‰ SMOW and δ 13C from –2.8 to +9.3 ‰ VPDB. As a result, these values significantly extend the mantle values for these elements in both isotopically-light and isotopically-heavy areas.« less

High-precision 41K/39K measurements by MC-ICP-MS indicate terrestrial variability of δ41K

USGS Publications Warehouse

Morgan, Leah; Santiago Ramos, Danielle P.; Davidheiser-Kroll, Brett; Faithfull, John; Lloyd, Nicholas S.; Ellam, Rob M.; Higgins, John A.

2018-01-01

Potassium is a major component in continental crust, the fourth-most abundant cation in seawater, and a key element in biological processes. Until recently, difficulties with existing analytical techniques hindered our ability to identify natural isotopic variability of potassium isotopes in terrestrial materials. However, measurement precision has greatly improved and a range of K isotopic compositions has now been demonstrated in natural samples. In this study, we present a new technique for high-precision measurement of K isotopic ratios using high-resolution, cold plasma multi-collector mass spectrometry. We apply this technique to demonstrate natural variability in the ratio of 41K to 39K in a diverse group of geological and biological samples, including silicate and evaporite minerals, seawater, and plant and animal tissues. The total range in 41K/39K ratios is ca. 2.6‰, with a long-term external reproducibility of 0.17‰ (2, N=108). Seawater and seawater-derived evaporite minerals are systematically enriched in 41K compared to silicate minerals by ca. 0.6‰, a result consistent with recent findings1, 2. Although our average bulk-silicate Earth value (-0.54‰) is indistinguishable from previously published values, we find systematic δ41K variability in some high-temperature sample suites, particularly those with evidence for the presence of fluids. The δ41K values of biological samples span a range of ca. 1.2‰ between terrestrial mammals, plants, and marine organisms. Implications of terrestrial K isotope variability for the atomic weight of K and K-based geochronology are discussed. Our results indicate that high-precision measurements of stable K isotopes, made using commercially available mass spectrometers, can provide unique insights into the chemistry of potassium in geological and biological systems. 

Stable isotope analysis of Dacryoconarid carbonate microfossils: a new tool for Devonian oxygen and carbon isotope stratigraphy.

PubMed

Frappier, Amy Benoit; Lindemann, Richard H; Frappier, Brian R

2015-04-30

Dacryoconarids are extinct marine zooplankton known from abundant, globally distributed calcite microfossils in the Devonian, but their shell stable isotope composition has not been previously explored. Devonian stable isotope stratigraphy is currently limited to less common invertebrates or bulk rock analyses of uncertain provenance. As with Cenozoic planktonic foraminifera, isotopic analysis of dacryoconarid shells could facilitate higher-resolution, geographically widespread stable isotope records of paleoenvironmental change, including marine hypoxia events, climate changes, and biocrises. We explored the use of Dacryoconarid isotope stratigraphy as a viable method in interpreting paleoenvironments. We applied an established method for determining stable isotope ratios (δ(13) C, δ(18) O values) of small carbonate microfossils to very well-preserved dacryoconarid shells. We analyzed individual calcite shells representing five common genera using a Kiel carbonate device coupled to a MAT 253 isotope ratio mass spectrometer. Calcite shell δ(13) C and δ(18) O values were compared by taxonomic group, rock unit, and locality. Single dacryoconarid calcite shells are suitable for stable isotope analysis using a Kiel-IRMS setup. The dacryoconarid shell δ(13) C values (-4.7 to 2.3‰) and δ(18) O values (-10.3 to -4.8‰) were consistent across taxa, independent of shell size or part, but varied systematically through time. Lower fossil δ(18) O values were associated with warmer water temperature and more variable δ(13) C values were associated with major bioevents. Dacryoconarid δ(13) C and δ(18) O values differed from bulk rock carbonate values. Dacryoconarid individual microfossil δ(13) C and δ(18) O values are highly sensitive to paleoenvironmental changes, thus providing a promising avenue for stable isotope chemostratigraphy to better resolve regional to global paleoceanographic changes throughout the upper Silurian to the upper Devonian. Our results warrant further exploration of dacryoconarid stable isotope proxy sensitivity, the isotopic contrast among dacryoconarids, other taxa, and bulk rock, as well as other potential dacryoconarid proxies (Mg/Ca, Sr/Ca, (87) Sr/(86) Sr, microlaser and ion microprobe isotope techniques, and clumped isotopes) for stratigraphic research. Copyright © 2015 John Wiley & Sons, Ltd.

Optimization and application of ICPMS with dynamic reaction cell for precise determination of 44Ca/40Ca isotope ratios.

PubMed

Boulyga, Sergei F; Klötzli, Urs; Stingeder, Gerhard; Prohaska, Thomas

2007-10-15

An inductively coupled plasma mass spectrometer with dynamic reaction cell (ICP-DRC-MS) was optimized for determining (44)Ca/(40)Ca isotope ratios in aqueous solutions with respect to (i) repeatability, (ii) robustness, and (iii) stability. Ammonia as reaction gas allowed both the removal of (40)Ar+ interference on (40)Ca+ and collisional damping of ion density fluctuations of an ion beam extracted from an ICP. The effect of laboratory conditions as well as ICP-DRC-MS parameters such a nebulizer gas flow rate, rf power, lens potential, dwell time, or DRC parameters on precision and mass bias was studied. Precision (calculated using the "unbiased" or "n - 1" method) of a single isotope ratio measurement of a 60 ng g(-1) calcium solution (analysis time of 6 min) is routinely achievable in the range of 0.03-0.05%, which corresponded to the standard error of the mean value (n = 6) of 0.012-0.020%. These experimentally observed RSDs were close to theoretical precision values given by counting statistics. Accuracy of measured isotope ratios was assessed by comparative measurements of the same samples by ICP-DRC-MS and thermal ionization mass spectrometry (TIMS) by using isotope dilution with a (43)Ca-(48)Ca double spike. The analysis time in both cases was 1 h per analysis (10 blocks, each 6 min). The delta(44)Ca values measured by TIMS and ICP-DRC-MS with double-spike calibration in two samples (Ca ICP standard solution and digested NIST 1486 bone meal) coincided within the obtained precision. Although the applied isotope dilution with (43)Ca-(48)Ca double-spike compensates for time-dependent deviations of mass bias and allows achieving accurate results, this approach makes it necessary to measure an additional isotope pair, reducing the overall analysis time per isotope or increasing the total analysis time. Further development of external calibration by using a bracketing method would allow a wider use of ICP-DRC-MS for routine calcium isotopic measurements, but it still requires particular software or hardware improvements aimed at reliable control of environmental effects, which might influence signal stability in ICP-DRC-MS and serve as potential uncertainty sources in isotope ratio measurements.

Petrogenesis and origin of the Upper Jurassic-Lower Cretaceous magmatism in Central High Atlas (Morocco): Major, trace element and isotopic (Sr-Nd) constraints

NASA Astrophysics Data System (ADS)

Essaifi, Abderrahim; Zayane, Rachid

2018-01-01

During an uplift phase, which lasted ca. 40 Ma, from the Late Jurassic (165 Ma) to the Early Cretaceous (125 Ma), transitional to moderately alkaline magmatic series were emplaced in the Central High Atlas. The corresponding magmatic products include basaltic lava flows erupted within wide synclines and intrusive complexes composed of layered mafic intrusions and monzonitic to syenitic dykes emplaced along narrow anticlinal ridges. The igneous rock sequence within the intrusive complexes is composed of troctolites, olivine-gabbros, oxide-gabbros, monzonites and syenites. The chemical compositions of the various intrusive rocks can be accounted for by crystal accumulation, fractional crystallization and post-magmatic remobilization. The evolution from the troctolites to the syenites was mainly controlled by a fractional crystallization process marked by early fractionation of olivine, plagioclase and clinopyroxene, followed by separation of biotite, amphibole, apatite, and Ti-magnetite. Hydrothermal activity associated with emplacement of the intrusions within the Jurassic limestones modified the elemental and the Sr isotopic composition of the hydrothermally altered rocks In particular the monzonitic to syenitic dykes underwent an alkali metasomatism marked by depletion in K and Rb and enrichment in Na and Sr. As a result, their Sr isotopic composition was shifted towards higher initial Sr isotopic ratios (0.7067-0.7075) with respect to the associated gabbros (0.7036-0.7046). On the contrary, the Nd isotopic compositions were preserved from isotope exchange with the limestones and vary in a similar range to those of the gabbros (+1.6 < εNdi < +4.1). The isotopic and the trace element ratios of the uncontaminated samples were used to constrain the source characteristics of this magmatism. The Sr-Nd isotopic data and the incompatible element ratios (e.g. La/Nb, Zr/Nb, Th/U, Ce/Pb) are consistent with generation from an enriched upper mantle similar to an ocean island basalt source. Melting of the subcontinental metasomatized lithosphere is tentatively related to small-scale shallow mantle upwelling and asthenospheric uprise at the triple junction between the western High Atlas, the Middle Atlas and the eastern High Atlas domains during a period of relative tectonic quiescence.

Empirical calibration of shell chemistry of Cyprideis torosa (Jones, 1850) (Crustacea: Ostracoda)

NASA Astrophysics Data System (ADS)

Marco-Barba, J.; Ito, E.; Carbonell, E.; Mesquita-Joanes, F.

2012-09-01

Cyprideis torosa is a species of ostracode that inhabits a wide range of aquatic habitats in which its low Alk/Ca requirement is met. Its fossil remains are widely used in palaeoecological studies of coastal environments and inland salt lakes. We collected C. torosa from 20 water bodies near Valencia, Spain. Temperature, chlorophyll a concentration, electrical conductivity, and the concentration of major ions and oxygen isotopes were measured at each site. Between 2 and 20 live individuals of C. torosa were collected per site, their instar stage and sex determined and their shell chemistry (Mg/Ca, Sr/Ca and carbon and oxygen isotope composition) analyzed. Three of these sites were sampled monthly for one year, and ostracode population structure and shell chemistry (20-40 shells) were analyzed. The water chemistry varied widely between sites. TDS (total dissolved solids) ranged from 0.5 to 71.8 g/L but chloride was always the dominant anion. There is a significant positive relationship between ostracode and water δ18O except at high TDS (>20 g/L) when shell δ18O values are lower than expected. No effect of either temperature or water Mg/Ca is observed on the Mg/Ca in the ostracode calcite in waters with Mg/Ca < 6 (molar ratio). Ostracode shell Sr/Ca is strongly and significantly related to water Sr/Ca. δ13C values in C. torosa shells are ˜2‰ lower than observed δ13CDIC. These results provide new and more accurate quantification tools to reconstruct past hydrochemistry from C. torosa shells.

Assessment of hydrogeochemistry and environmental isotopes of surface and groundwaters in the Kütahya Plain, Turkey

NASA Astrophysics Data System (ADS)

Abadi Berhe, Berihu; Erdem Dokuz, Uğur; Çelik, Mehmet

2017-10-01

The aim of the present work is to determine the geochemical processes that control the nature of the groundwater and assess the quality of water for drinking and public health purposes. Surface and groundwater samples of Kütahya plain were analyzed for their physio-chemical and environmental isotope properties. The relative concentrations of the water ions were found to occur in the order of Ca2+>Mg2+>(K+ + Na+) and HCO3->SO42->Cl-. Piper diagram shows that Ca-Mg/Mg-Ca-HCO3 was the dominant water types. Waters in the area were super-saturated with respect to carbonates. However, they were under-saturated with respect to sulphate minerals. The groundwaters had a mean isotopic composition of -67.32 δ2H and -9.72 δ18O and were comparatively lower than surface waters -64.64 δ2H and -9.25 δ18O. Tritium activities in groundwater from the wells ranged from 1.00 to 8.38 TU with a mean value of 4.37 TU. The impact of agricultural practices and poor sanitation conditions is indicated by the positive correlation between K+ - NO3-, K+- NO2- and HCO3- - Cl- ions as well as Na+ and Mg2+ ions with SO42-ion. The groundwater quality of Kütahya plain is influenced by various natural and anthropogenic factors.

Paraná-Etendeka basalts in Misiones, Argentina; characterization and petrogenetic inferences

NASA Astrophysics Data System (ADS)

Rämö, O. T.; Heikkilä, P. A.

2013-12-01

The Early Cretaceous (ca. 130 Ma) Paraná-Etendeka flood basalts constitute one of the major Phanerozoic LIP sequences with an original volume probably in excess of 2.3 Mkm3.The bulk of this volcanic system is preserved in South America (Brazil, Uruguay, Paraguay, Argentina), where it manifests the onset of South Atlantic opening at present 25 degrees Southern Latitude. The sequence is overwhelmingly basaltic (ca. 90%), but also includes contemporaneous silicic volcanic rocks. Known as the Serra Geral Suite (e.g., Bellieni et al., 1984), it fills the Paraná Basin with a northward deepening strata of lavas with a maximum thickness of ca. 1500 m. We have collected and examined basalt samples from the west-central part (western flank) of the Paraná Basin in Misiones State, northeastern Argentina (54-55 degrees Western Longitude), where the estimated thickness of the basalt succession decreases from ca. 700 m in the east to ca. 300 m in the west. The examined samples are massive, aphyric (or microphyric with plagioclase and altered olivine microphenocrysts), and geochemically relatively evolved (Mg number 50-35) basalts and basaltic andesites. Their MgO values are between 6 and 3.7 wt.% and Ni content is relatively low (65-20 ppm). Incompatible trace element values increase with increasing fractionation (decreasing Mg number), e.g., Zr from 135 to 290 ppm, Ce from 45 to 105 ppm, Nd from 20 to 50 ppm, Sm from 5 to 11 ppm, Ba from 280 to 600 ppm, and Y from 25 to 50 ppm. In terms of Ti, the samples fall into two groups (1.9-2.3 and ca. 3.8 wt.% TiO2). These values conform, respectively, to the high-Ti, high-Ti/Y Paranapanema and Pitanga magma types of Peate et al. (1992) that govern the northern half of the Paraná basalt succession. Initial Nd and Sr isotope compositions of the two groups are remarkably uniform. Our analyzed ten samples have an average initial (at 134.6 Ma) epsilon-Nd value of -4.2 × 0.3 (1 SD) and an average initial 87Sr/86Sr of 0.70570 × 0.00015 (1 SD). No change in the initial values is observed with fractionation. This probably renders crustal contamination by the surrounding Precambrian bedrock negligible within the observed fractionation window (Mg number 50-35). The initial Nd and Sr isotope compositions of the basalts from Misiones comply with the isotope composition of the EM1 mantle component. Non-modal equilibrium melting modeling utilizing the Zr/Nb and Ce/Y values implies, for an overall primitive mantle source, a change in the melting regime from garnet lherzolite (Pitanga) to spinel lherzolite (Paranapanema).

Fractionation of 238U/235U by reduction during low temperature uranium mineralisation processes

NASA Astrophysics Data System (ADS)

Murphy, Melissa J.; Stirling, Claudine H.; Kaltenbach, Angela; Turner, Simon P.; Schaefer, Bruce F.

2014-02-01

Investigations of ‘stable’ uranium isotope fractionation during low temperature, redox transformations may provide new insights into the usefulness of the 238U/235U isotope system as a tracer of palaeoredox processes. Sandstone-hosted uranium deposits accumulate at an oxidation/reduction interface within an aquifer from the low temperature reduction of soluble U(VI) complexes in groundwaters, forming insoluble U(IV) minerals. This setting provides an ideal environment in which to investigate the effects of redox transformations on 238U/235U fractionation. Here we present the first coupled measurements of 238U/235U isotopic compositions and U concentrations for groundwaters and mineralised sediment samples from the same redox system in the vicinity of the high-grade Pepegoona sandstone-hosted uranium deposit, Australia. The mineralised sediment samples display extremely variable 238U/235U ratios (herein expressed as δUCRM145238, the per-mil deviation from the international NBL standard CRM145). The majority of mineralised sediment samples have δUCRM145238 values between -1.30±0.05 and 0.55±0.12‰, spanning a ca. 2‰ range. However, one sample has an unusually light isotopic composition of -4.13±0.05‰, which suggests a total range of U isotopic variability of up to ca. 5‰, the largest variation found thus far in a single natural redox system. The 238U/235U isotopic signature of the mineralised sediments becomes progressively heavier (enriched in 238U) along the groundwater flow path. The groundwaters show a greater than 2‰ variation in their 238U/235U ratios, ranging from δUCRM145238 values of -2.39±0.07 to -0.71±0.05‰. The majority of the groundwater data exhibit a clear systematic relationship between 238U/235U isotopic composition and U concentration; samples with the lowest U concentrations have the lowest 238U/235U ratios. The preferential incorporation of 238U during reduction of U(VI) to U(IV) and precipitation of uranium minerals leaves the groundwaters enriched in 235U, resulting in a progressive shift in 238U/235U towards lighter values in the aqueous phase as U is removed. These data can be modelled by a closed system Rayleigh fractionation model, with a fractionation factor (α, representing the 238U/235U composition of the groundwater relative to the solid uranium minerals) ranging from ∼0.9996 to 1.0000, with the majority of datapoints ranging from α values of 0.9998 to 0.9999. The sense and magnitude of the results of this study imply that 238U/235U fractionation is likely to be controlled by volume-dependent nuclear field shift effects during the reduction of U(VI) to U(IV) during mineralisation processes. These findings support the use of the 238U/235U isotopic system as a tracer to constrain the nature and timing of palaeoredox conditions.

Ca-Mg Carbonate Cements in Ophiolite-Hosted Creek Waters of the Del Puerto Ophiolite, CA, and their Potential Significance as a Planetary Biosignature

NASA Astrophysics Data System (ADS)

Blank, J. G.

2015-12-01

Serpentinization, the reaction at moderate pressure and temperature of water with olivine and pyroxene that are common in basalts and ultramafic rocks, results in the formation of alkaline fluids and the precipitation of a variety of secondary minerals. Terrestrial localities where active serpentinization is occurring are ideal Mars analogs for examining the characteristics of an environment that possesses two of the key features that we assume necessary to host life: water and an internally generated energy source. This study focuses on a related but different feature present where active serpentinization is occurring - namely, carbonate cements forming under plain air in the vicinity of Adobe Springs, CA. This site is located in the Del Puerto ophiolite about 150 km ESE of San Francisco, in the Coast Range of California. Two alkaline spring water compositions have been described at the site, a Ca-OH water (which is not currently being emitted by the active springs), and a Mg-CO3 water. Abundant dolomitic and calcitic carbonate cements are found in the creek drainages near the springs, associated with a diverse microbial community. We conducted a systematic study of the carbonate cements using SEM, EMP, XRD, TEM, and SIMS, focusing on sub-mm variations in texture, mineral chemistry and stable isotope (COH) composition. We compared our measurements with thermodynamic modeling results constrained by chemical analysis of water chemistry from the site and known partition coefficients and stable isotope fractionation factors. The wide range of carbonate compositions and textures observed at the Adobe Springs site suggests that more than one process is involved in their precipitation, including the possibility of microbially mediated dolomite mineralization. These carbonate cements could be a mineralogic biomarker of serpentinization and microbiological processes on Mars and other rocky planets and, therefore, prime targets for future astrobiological investigations.

Sr-Nd-Pb Isotope Geochemistry of Melange Formation: Implications for Identification of Fluid Sources in the Mantle Wedge and the Arc

NASA Astrophysics Data System (ADS)

Bebout, G. E.; King, R. L.; Moriguti, T.; Nakamura, E.

2004-12-01

Paramount to our ability to decipher the behavior of fluids and melts within the mantle wedge and the overall subduction system are the chemical compositions of rocks adjacent to the slab-mantle interface. Profound metamorphic and metasomatic alteration of pre-subduction lithologies to form melange along the slab-mantle interface may yield rock types inheriting mixed chemical compositions of diverse pre-subduction lithologies. Early work on melange geochemistry indicates competitive effects between mechanical mixing, metasomatism by fluids or melts, and mineral stabilities imposed by the resulting bulk composition. We have explored the Sr-Nd-Pb isotope geochemistry of low- to high-grade melange zones in the Catalina Schist, CA, to address this crucial missing component in studies of subduction-zone mass flux. The Catalina Schist contains lawsonite-albite (LA), lawsonite-blueschist (LB), and amphibolite (AM) facies melange zones, all with mineralogy dominated by talc, chlorite, and Na-Ca amphiboles, with additional minerals such as micas, rutile, zircon, and apatite stabilized based on bulk sample chemistry. Major element compositions vary, from strongly ultramafic in the AM melange, to more crustal-like compositions (i.e., more reminiscent of basaltic to sedimentary protoliths) for LA and LB melange. However, initial Sr and Nd isotope ratios for all grades of melange are essentially indistinguishable, displaying a wide variation from 87Sr/86Sr=0.703-0.709 and ɛ Nd= +15 to -15. Covariations are generally negative, similar to that of the mantle array, but with some samples extending to higher Sr ratios at constant ɛ Nd that probably reflect inheritance of seawater Sr. No clear mixing relationships between 87Sr/86Sr and 1/Sr exist, suggesting either localized buffering of Sr isotope ratios or that mixing relations are obscured by secondary devolatilization. However, a clear mixing trend for Nd indicates two end-members, one a high-concentration, positive ɛ Nd source (AOC?), the other with low-concentration and negative ɛ Nd (devolatilized sediments?). Likewise, initial Pb isotope ratios for all grades of melange form a single array independent of rock type or inferred protolith. Melange matrix of the Catalina Schist preserves initial 206Pb/204Pb of 18.95-19.59, 207Pb/204Pb of 15.61-15.68, and 208Pb/204Pb of 37.85-39.05. Such elevated Pb ratios are typical of subducting oceanic sediments, but not of MORB-like oceanic crust or peridotites of the depleted mantle. The similarity of these initial ratios suggests pervasive alteration of Pb isotope signatures within diverse rock types by fluids during subduction. As Pb concentrations decline from LA/LB to AM melange, this suggests devolatilization of Pb from the ultramafic AM melange will transfer crustal-like Pb isotope ratios. Sr-Nd-Pb isotope systematics for arc volcanic rocks are commonly used as indicators of fluid sources from the subducting slab to the arc magma source region. Our results suggest such an assumption is extremely dangerous, as hybridization processes common to melange zones are more likely to occur along the slab-mantle interface than is preservation of a pre-subduction section. Such metamorphic mediation and buffering of "slab" compositions is essentially unknown, yet our data support an interpretation where these processes impart a fundamental control on the chemistry of fluids passed to the mantle wedge.

Formation waters from Mississippian-Pennsylvanian reservoirs, Illinois basin, USA: Chemical and isotopic constraints on evolution and migration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stueber, A.M.; Walter, L.M.; Huston, T.J.

1993-02-01

We have analyzed a suite of seventy-four formation-water samples from Mississippian and Pennsylvanian carbonate and siliciclastic strata in the Illinois basin for major, minor, and trace element concentrations and for strontium isotopic composition. A subset of these samples was also analyzed for boron isotopic composition. Data are used to interpret origin of salinity and chemical and Sr isotopic evolution of the brines and in comparison with a similar data set from an earlier study of basin formation waters from Silurian-Devonian reservoirs. Systematics of Cl-Br-Na show that present Mississippian-Pennsylvanian brine salinity can be explained by a combination of subaerial seawater evaporationmore » short of halite saturation and subsurface dissolution of halite from an evaporite zone in the middle Mississippian St. Louis Limestone, along with extensive dilution by mixing with meteoric waters. Additional diagenetic modifications in the subsurface interpreted from cation/Br ratios include K depletion through interaction with clay minerals, Ca enrichment, and Mg depletion by dolomitization, and Sr enrichment through CaCO[sub 3] recrystallization and dolomitization. Ste. Genevieve Limestone (middle Mississippian) formation waters show [sup 87]Sr/[sup 86]Sr ratios in the range 0.70782-0.70900, whereas waters from the siliciclastic reservoirs are in the rante 0.70900-0.71052. Inverse correlations between [sup 87]Sr/[sup 86]Sr and B,Li, and Mg concentrations suggest that the brines acquired radiogenic [sup 87]Sr through interaction with siliciclastic minerals. Completely unsystematic relations between [sup 87]Fr/[sup 86]Sr and 1/Sr are observed; Sr concentrations in Ste. Genevieve and Aux Vases (middle Mississippian) waters appear to be buffered by equilibrium with respect to SrSo[sub 4]. These formation waters are distinguished from Silurian-Devonian brines in the basin by elevated Cl/Br and Na/Br ratios and by unsystematic Sr isotope relationships.« less

Application of laser ablation multicollector inductively coupled plasma mass spectrometry for the measurement of calcium and lead isotope ratios in packaging for discriminatory purposes.

PubMed

Santamaria-Fernandez, Rebeca; Wolff, Jean-Claude

2010-07-30

The potential of high-precision calcium and lead isotope ratio measurements using laser ablation coupled to multicollector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) to aid distinction between four genuine and five counterfeit pharmaceutical packaging samples and further classification of counterfeit packaging samples has been evaluated. We highlight the lack of reference materials for LA-MC-ICP-MS isotope ratio measurements in solids. In this case the problem is minimised by using National Institute of Standards and Technology Standard Reference Material (NIST SRM) 915a calcium carbonate (as solid pellets) and NIST SRM610 glass disc for sample bracketing external standardisation. In addition, a new reference material, NIST SRM915b calcium carbonate, has been characterised in-house for Ca isotope ratios and is used as a reference sample. Significant differences have been found between genuine and counterfeit samples; the method allows detection of counterfeits and aids further classification of packaging samples. Typical expanded uncertainties for measured-corrected Ca isotope ratio values ((43)Ca/(44)Ca and (42)Ca/(44)Ca) were found to be below 0.06% (k = 2, 95% confidence) and below 0.2% for measured-corrected Pb isotope ratios ((207)Pb/(206)Pb and (208)Pb/(206)Pb). This is the first time that Ca isotope ratios have been measured in packaging materials using LA coupled to a multicollector (MC)-ICP-MS instrument. The use of LA-MC-ICP-MS for direct measurement of Ca and Pb isotopic variations in cardboard/ink in packaging has definitive potential to aid counterfeit detection and classification. Copyright 2010 John Wiley & Sons, Ltd.

The ungrouped chondrite El Médano 301 and its comparison with other reduced ordinary chondrites

NASA Astrophysics Data System (ADS)

Pourkhorsandi, Hamed; Gattacceca, Jérôme; Devouard, Bertrand; D'Orazio, Massimo; Rochette, Pierre; Beck, Pierre; Sonzogni, Corinne; Valenzuela, Millarca

2017-12-01

El Médano 301 (EM 301) is an ungrouped chondrite with overall texture and trace-element distribution similar to those of ordinary chondrites (OCs), but with silicate (olivine and low-Ca pyroxene) compositions that are more reduced than those in OCs, with average olivine and low-Ca pyroxene of Fa3.9±0.3 and Fs12.8±4.9, respectively. These values are far lower than the values for OCs and even for chondrites designed as ;reduced; chondrites. Low-Ca pyroxene is the dominant mineral phase and shows zoning with higher MgO contents along the crystal rims and cracks (reverse zoning). The Co content of kamacite is also much lower than the concentrations observed in OCs (below detection limit of 0.18 wt% versus 0.44-37 wt%). Oxygen isotopic composition is Δ17O = +0.79,+0.78‰ and slightly different from that of OCs. The lower modal olivine/pyroxene ratio, different Infrared (IR) spectra, lower Co content of kamacite, lower mean FeO contents of olivine and pyroxene, different kamacite texture, and different oxygen-isotopic composition show that EM 301 does not belong to a known OC group. EM 301 shows similarities with chondritic clasts in Cumberland Falls aubrite, and with Northwest Africa 7135 (NWA 7135) and Acfer 370 ungrouped chondrites. However, dissimilar to NWA 7135 and the clasts, it does not contain highly reduced mineral phases like daubréelite. Our observations suggest the formation of EM 301 in a nebular region compositionally similar to OCs but with a different redox state, with oxygen fugacity (ƒO2) in this region lower than that of OCs and higher than that of enstatite chondrites condensation region. A second, possibly nebular, phase of reduction by the production of reducing gas phases (e.g., C-rich) could be responsible for the subsequent reduction of the primary material and the occurrence of reverse zoning in the low-Ca pyroxene and lower average Fa/Fs ratio. Based on the IR spectra of EM 301 we suggest the possibility that the parent body of this chondrite was a V-type asteroid.

Calcium Isotope Analysis with "Peak Cut" Method on Column Chemistry

NASA Astrophysics Data System (ADS)

Zhu, H.; Zhang, Z.; Liu, F.; Li, X.

2017-12-01

To eliminate isobaric interferences from elemental and molecular isobars (e.g., 40K+, 48Ti+, 88Sr2+, 24Mg16O+, 27Al16O+) on Ca isotopes during mass determination, samples should be purified through ion-exchange column chemistry before analysis. However, large Ca isotopic fractionation has been observed during column chemistry (Russell and Papanastassiou, 1978; Zhu et al., 2016). Therefore, full recovery during column chemistry is greatly needed, otherwise uncertainties would be caused by poor recovery (Zhu et al., 2016). Generally, matrix effects could be enhanced by full recovery, as other elements might overlap with Ca cut during column chemistry. Matrix effects and full recovery are difficult to balance and both need to be considered for high-precision analysis of stable Ca isotopes. Here, we investigate the influence of poor recovery on δ44/40Ca using TIMS with the double spike technique. The δ44/40Ca values of IAPSO seawater, ML3B-G and BHVO-2 in different Ca subcats (e.g., 0-20, 20-40, 40-60, 60-80, 80-100%) with 20% Ca recovery on column chemistry display limited variation after correction by the 42Ca-43Ca double spike technique with the exponential law. Notably, δ44/40Ca of each Ca subcut is quite consistent with δ44/40Ca of Ca cut with full recovery within error. Our results indicate that the 42Ca-43Ca double spike technique can simultaneously correct both of the Ca isotopic fractionation that occurred during column chemistry and thermal ionization mass spectrometry (TIMS) determination properly, because both of the isotopic fractionation occurred during analysis follow the exponential law well. Therefore, we propose the "peak cut" method on Ca column chemistry for samples with complex matrix effects. Briefly, for samples with low Ca contents, we can add the double spike before column chemistry, and only collect the middle of the Ca eluate and abandon the both sides of Ca eluate that might overlap with other elements (e.g., K, Sr). This method would eliminate matrix effects and improve efficiency for the column chemistry.

Growth Rates and Mechanisms of Magmatic Orbicule Formation: Insights from Calcium Isotopes

NASA Astrophysics Data System (ADS)

Antonelli, M. A.; Watkins, J. M.; DePaolo, D. J.

2017-12-01

Orbicular diorites and granites are rare plutonic rock textures that remain enigmatic despite a century of study. Orbicules consist of a rounded core (xenolith, xenocryst, or autolith) surrounded by a variable number of concentric rings defined by different modal mineralogies and textures. Recent work suggests that the alternating layers of mineral growth are a consequence of either changes in external conditions of the magma (e.g. temperature, magma composition due to mixing, changes in volatile abundances), or rapid growth of one mineral phase (e.g plagioclase) creating a depleted boundary layer that then promotes precipitation of an alternative mineral phase (e.g. pyroxene). This process can be repeated to produce multiple layers. The rates at which orbicules grow is also of interest and relates to the mechanisms. Studies of orbicular diorites from the northern Sierra Nevada suggest exceptionally high growth rates (McCarthy et al., 2016). Ca isotopes can offer a unique perspective on orbicule formation, as diffusive isotope fractionation should be substantial when growth rates are high, and they are also sensitive to the nature of the growth medium (silicate liquid or supercritical fluid phase). We present δ44Ca measurements and chemistry for a transect of a dioritic orbicule collected from Emerald Lake, California (Sierra Nevada), where the growth layers are defined by variations in plagioclase/pyroxene ratio, grain size, and texture. Ca concentration varies from 5-13 wt%, and d44Ca values oscillate between -0.5 to 0.0‰ relative to BSE, correlating with changes in mineralogy and texture. Zones of plagioclase comb texture are associated with negative δ44Ca excursions of -0.2 to -0.4‰, consistent with diffusive isotope fractionation during rapid mineral growth. Assuming a 10‰ difference in diffusivity for 44Ca vs. 40Ca in dioritic liquids (Watson et al., 2016), and using the models of Watson and Muller (2009) as a guide, these small fractionations indicate relatively fast plagioclase growth rates, of order 10 cm/yr, or growth from an aqueous medium where diffusive fractionation would be smaller. The growth rates suggested by our models imply that the mineralogical layering is likely to represent changes in external conditions of the host magma.

Calcium induced ATP synthesis: Isotope effect, magnetic parameters and mechanism

NASA Astrophysics Data System (ADS)

Buchachenko, A. L.; Kuznetsov, D. A.; Breslavskaya, N. N.; Shchegoleva, L. N.; Arkhangelsky, S. E.

2011-03-01

ATP synthesis by creatine kinase with calcium ions is accompanied by 43Ca/ 40Ca isotope effect: the enzyme with 43Ca 2+ was found to be 2.0 ± 0.3 times more active than enzymes, in which Ca 2+ ions have nonmagnetic nuclei 40Ca. The effect demonstrates that primary reaction in ATP synthesis is electron transfer between reaction partners, Сa( HO)n2+ ( n ⩽ 3) and Ca 2+(ADP) 3-. It generates ion-radical pair, in which spin conversion results in the isotope effect. Magnetic parameters (g-factors and HFC constants a( 43Ca) and a( 31P)) confirm that namely terminal oxygen atom of the ADP ligand in the complex Ca 2+(ADP) 3- donates electron to the Ca( HO)n2+ ion.

Planktic foraminifera shell chemistry response to seawater chemistry: Pliocene-Pleistocene seawater Mg/Ca, temperature and sea level change

NASA Astrophysics Data System (ADS)

Evans, David; Brierley, Chris; Raymo, Maureen E.; Erez, Jonathan; Müller, Wolfgang

2016-03-01

Foraminifera Mg/Ca paleothermometry forms the basis of a substantial portion of ocean temperature reconstruction over the last 5 Ma. Furthermore, coupled Mg/Ca-oxygen isotope (δ18O) measurements of benthic foraminifera can constrain eustatic sea level (ESL) independent of paleo-shoreline derived approaches. However, this technique suffers from uncertainty regarding the secular variation of the Mg/Ca seawater ratio (Mg/Casw) on timescales of millions of years. Here we present coupled seawater-test Mg/Ca-temperature laboratory calibrations of Globigerinoides ruber in order to test the widely held assumptions that (1) seawater-test Mg/Ca co-vary linearly, and (2) the Mg/Ca-temperature sensitivity remains constant with changing Mg/Casw. We find a nonlinear Mg/Catest-Mg/Casw relationship and a lowering of the Mg/Ca-temperature sensitivity at lower than modern Mg/Casw from 9.0% °C-1 at Mg/Casw = 5.2 mol mol-1 to 7.5 ± 0.9% °C-1 at 3.4 mol mol-1. Using our calibrations to more accurately calculate the offset between Mg/Ca and biomarker-derived paleotemperatures for four sites, we derive a Pliocene Mg/Casw ratio of ∼4.3 mol mol-1. This Mg/Casw implies Pliocene ocean temperature 0.9-1.9 °C higher than previously reported and, by extension, ESL ∼30 m lower compared to when one assumes that Pliocene Mg/Casw is the same as at present. Correcting existing benthic foraminifera datasets for Mg/Casw indicates that deep water source composition must have changed through time, therefore seawater oxygen isotope reconstructions relative to present day cannot be used to directly reconstruct Pliocene ESL.

Short-Term Coral Bleaching Is Not Recorded by Skeletal Boron Isotopes

PubMed Central

Schoepf, Verena; McCulloch, Malcolm T.; Warner, Mark E.; Levas, Stephen J.; Matsui, Yohei; Aschaffenburg, Matthew D.; Grottoli, Andréa G.

2014-01-01

Coral skeletal boron isotopes have been established as a proxy for seawater pH, yet it remains unclear if and how this proxy is affected by seawater temperature. Specifically, it has never been directly tested whether coral bleaching caused by high water temperatures influences coral boron isotopes. Here we report the results from a controlled bleaching experiment conducted on the Caribbean corals Porites divaricata, Porites astreoides, and Orbicella faveolata. Stable boron (δ11B), carbon (δ13C), oxygen (δ18O) isotopes, Sr/Ca, Mg/Ca, U/Ca, and Ba/Ca ratios, as well as chlorophyll a concentrations and calcification rates were measured on coral skeletal material corresponding to the period during and immediately after the elevated temperature treatment and again after 6 weeks of recovery on the reef. We show that under these conditions, coral bleaching did not affect the boron isotopic signature in any coral species tested, despite significant changes in coral physiology. This contradicts published findings from coral cores, where significant decreases in boron isotopes were interpreted as corresponding to times of known mass bleaching events. In contrast, δ13C and δ18O exhibited major enrichment corresponding to decreases in calcification rates associated with bleaching. Sr/Ca of bleached corals did not consistently record the 1.2°C difference in seawater temperature during the bleaching treatment, or alternatively show a consistent increase due to impaired photosynthesis and calcification. Mg/Ca, U/Ca, and Ba/Ca were affected by coral bleaching in some of the coral species, but the observed patterns could not be satisfactorily explained by temperature dependence or changes in coral physiology. This demonstrates that coral boron isotopes do not record short-term bleaching events, and therefore cannot be used as a proxy for past bleaching events. The robustness of coral boron isotopes to changes in coral physiology, however, suggests that reconstruction of seawater pH using boron isotopes should be uncompromised by short-term bleaching events. PMID:25396422

Short-term coral bleaching is not recorded by skeletal boron isotopes.

PubMed

Schoepf, Verena; McCulloch, Malcolm T; Warner, Mark E; Levas, Stephen J; Matsui, Yohei; Aschaffenburg, Matthew D; Grottoli, Andréa G

2014-01-01

Coral skeletal boron isotopes have been established as a proxy for seawater pH, yet it remains unclear if and how this proxy is affected by seawater temperature. Specifically, it has never been directly tested whether coral bleaching caused by high water temperatures influences coral boron isotopes. Here we report the results from a controlled bleaching experiment conducted on the Caribbean corals Porites divaricata, Porites astreoides, and Orbicella faveolata. Stable boron (δ11B), carbon (δ13C), oxygen (δ18O) isotopes, Sr/Ca, Mg/Ca, U/Ca, and Ba/Ca ratios, as well as chlorophyll a concentrations and calcification rates were measured on coral skeletal material corresponding to the period during and immediately after the elevated temperature treatment and again after 6 weeks of recovery on the reef. We show that under these conditions, coral bleaching did not affect the boron isotopic signature in any coral species tested, despite significant changes in coral physiology. This contradicts published findings from coral cores, where significant decreases in boron isotopes were interpreted as corresponding to times of known mass bleaching events. In contrast, δ13C and δ18O exhibited major enrichment corresponding to decreases in calcification rates associated with bleaching. Sr/Ca of bleached corals did not consistently record the 1.2°C difference in seawater temperature during the bleaching treatment, or alternatively show a consistent increase due to impaired photosynthesis and calcification. Mg/Ca, U/Ca, and Ba/Ca were affected by coral bleaching in some of the coral species, but the observed patterns could not be satisfactorily explained by temperature dependence or changes in coral physiology. This demonstrates that coral boron isotopes do not record short-term bleaching events, and therefore cannot be used as a proxy for past bleaching events. The robustness of coral boron isotopes to changes in coral physiology, however, suggests that reconstruction of seawater pH using boron isotopes should be uncompromised by short-term bleaching events.

δ13C and δ18O isotopic composition of CaCO3 measured by continuous flow isotope ratio mass spectrometry: statistical evaluation and verification by application to Devils Hole core DH-11 calcite

USGS Publications Warehouse

Revesz, Kinga M.; Landwehr, Jurate M.

2002-01-01

A new method was developed to analyze the stable carbon and oxygen isotope ratios of small samples (400 ± 20 µg) of calcium carbonate. This new method streamlines the classical phosphoric acid/calcium carbonate (H3PO4/CaCO3) reaction method by making use of a recently available Thermoquest-Finnigan GasBench II preparation device and a Delta Plus XL continuous flow isotope ratio mass spectrometer. Conditions for which the H3PO4/CaCO3 reaction produced reproducible and accurate results with minimal error had to be determined. When the acid/carbonate reaction temperature was kept at 26 °C and the reaction time was between 24 and 54 h, the precision of the carbon and oxygen isotope ratios for pooled samples from three reference standard materials was ≤0.1 and ≤0.2 per mill or ‰, respectively, although later analysis showed that materials from one specific standard required reaction time between 34 and 54 h for δ18O to achieve this level of precision. Aliquot screening methods were shown to further minimize the total error. The accuracy and precision of the new method were analyzed and confirmed by statistical analysis. The utility of the method was verified by analyzing calcite from Devils Hole, Nevada, for which isotope-ratio values had previously been obtained by the classical method. Devils Hole core DH-11 recently had been re-cut and re-sampled, and isotope-ratio values were obtained using the new method. The results were comparable with those obtained by the classical method with correlation = +0.96 for both isotope ratios. The consistency of the isotopic results is such that an alignment offset could be identified in the re-sampled core material, and two cutting errors that occurred during re-sampling then were confirmed independently. This result indicates that the new method is a viable alternative to the classical reaction method. In particular, the new method requires less sample material permitting finer resolution and allows automation of some processes resulting in considerable time savings. 

In-situ Sr isotopic measurement of scheelite using fs-LA-MC-ICPMS

NASA Astrophysics Data System (ADS)

Li, Chao; Zhou, Limin; Zhao, Zheng; Zhang, Zhiyuan; Zhao, Hong; Li, Xinwei; Qu, Wenjun

2018-07-01

Scheelite is one of the main ore minerals in tungsten deposits, and Sr isotopic compositions of scheelite can be used to examine the petrogenesis of igneous rocks and fluid metasomatism in mineralization processes. Both thermal ionization mass spectrometer (TIMS) and femsecond laser ablation multi-collector inductively coupled plasma mass spectrometer (fs-LA-MC-ICP-MS) have been applied to analyze Sr isotopic compositions in scheelite. Here we describe a LA-MC-ICP-MS technique which can obtain in-situ, accurate, high precision 87Sr/86Sr ratios from 20 to 50 μm scheelite in line mode without requiring time-consuming mineral separation and pre-chemical procedures. We found that Ca dimers and Ca argides do not detectably affect the obtained 87Sr/86Sr ratios, and the adopted protocol overcomes interferences from Kr+, Rb+, Er2+ and Yb2+. The results of three MPI-DING reference glasses (KL2-G, ML3B-G and StHs6/80-G) are consistent with the recommended values. Here we show that the values of 87Sr/86Sr are relatively homogeneous for two scheelites from quartz veins, and are comparable to the values determined by a traditional solution method. Hence, these two scheelite samples have the potential to be reference materials for Sr isotopic determination by LA-MC-ICP-MS. To illustrate the utility of the technique, Sr isotopes of scheelites from three different types of tungsten deposits of South China are documented. The 87Sr/86Sr of scheelite from granite-related veinlet-disseminated and porphyry tungsten deposits varies systematically, showing a positive correlation between Sr content and 87Sr/86Sr ratios. These micrometer scale inhomogeneities could be explained by mixing of two components, reflecting intense fluid metasomatism during mineralization processes. High 87Sr/86Sr ratios were obtained for the scheelite samples from a quartz vein type tungsten deposit, indicating that the late stage ore-forming fluid was mainly derived from the surrounding strata. These examples show that in-situ Sr isotopic measurement of scheelite is a powerful tool to decipher the degree of fluid-rock interaction in ore-forming processes.

A Multi-Proxy Investigation into the Biomineralization Pathways of Benthic Invertebrate Taxa

NASA Astrophysics Data System (ADS)

DeCorte, I. A.; Liu, Y. W.; Doss, W. C.; Ries, J. B.; Eagle, R.

2016-12-01

Ocean acidification is the result of surface ocean absorption of anthropogenic carbon dioxide emissions and endangers many marine organisms. Decreases in pH and a coupled reduction in CaCO3 saturation state have been shown to disrupt the process of biomineralization within many species of marine calcifiers. Recent studies, however, demonstrate that calcifying organisms respond in diverse ways to changes in pH and CaCO3 saturation state. We examine element ratios (including Sr/Ca, Mg/Ca, Li/Ca, and B/Ca) and boron isotope ratios (δ11B) in 7 macro-invertebrate species (blue crab, shrimp, coralline red algae, pencil urchin, purple urchin, temperate coral, and serpulid worm) and compare results to net calcification rates and experimental seawater carbonate system parameters. Correlations between seawater carbonate chemistry and the elemental compositions of biogenic calcite and aragonite vary widely and are highly taxon-specific, ranging from strongly correlated to no significant response—a finding that is consistent with mounting evidence that many marine calcifying organisms regulate the chemistry of the fluid at their site of calcification. A Rayleigh framework is used to interpret the elemental data. We then analyze δ11B of the same samples as a proxy for pH at their site of calcification. Preliminary results suggest that coralline red algae, shrimp, urchin, serpulid worm and temperate coral taxa elevate pH at the site of calcification relative to the organism's ambient seawater. We plan to utilize a multi-proxy approach to examine the biomineralization pathways that influence elemental and boron isotope fractionation during calcification and precipitation of biogenic aragonite and calcite. A better understanding of these biomineralization pathways will help us to predict the responses of benthic invertebrate taxa to ocean acidification, as well as provide insights into drivers of so-called vital effects on elemental and stable boron isotope fractionation within biogenic carbonates—thereby assessing the fidelity of these proxies for reconstructing paleo-environmental change within a diverse range of marine calcifiers.

Evaluation of the Impacts of Marine Salts and Asian Dust on the Forested Yakushima Island Ecosystem, a World Natural Heritage Site in Japan.

PubMed

Nakano, Takanori; Yokoo, Yoriko; Okumura, Masao; Jean, Seo-Ryong; Satake, Kenichi

2012-11-01

To elucidate the influence of airborne materials on the ecosystem of Japan's Yakushima Island, we determined the elemental compositions and Sr and Nd isotope ratios in streamwater, soils, vegetation, and rocks. Streamwater had high Na and Cl contents, low Ca and HCO(3) contents, and Na/Cl and Mg/Cl ratios close to those of seawater, but it had low pH (5.4 to 7.1), a higher Ca/Cl ratio than seawater, and distinct (87)Sr/(86)Sr ratios that depended on the bedrock type. The proportions of rain-derived cations in streamwater, estimated by assuming that Cl was derived from sea salt aerosols, averaged 81 % for Na, 83 % for Mg, 36 % for K, 32 % for Ca, and 33 % for Sr. The Sr value was comparable to the 28 % estimated by comparing Sr isotope ratios between rain and granite bedrock. The soils are depleted in Ca, Na, P, and Sr compared with the parent materials. At Yotsuse in the northwestern side, plants and the soil pool have (87)Sr/(86)Sr ratios similar to that of rainwater with a high sea salt component. In contrast, the Sr and Nd isotope ratios of soil minerals in the A and B horizons approach those of silicate minerals in northern China's loess soils. The soil Ca and P depletion results largely from chemical weathering of plagioclase and of small amounts of apatite and calcite in granitic rocks. This suggests that Yakushima's ecosystem is affected by large amounts of acidic precipitation with a high sea salt component, which leaches Ca and its proxy (Sr) from bedrock into streams, and by Asian dust-derived apatite, which is an important source of P in base cation-depleted soils.

Rapidly assessing changes in bone mineral balance using natural stable calcium isotopes

PubMed Central

Morgan, Jennifer L. L.; Skulan, Joseph L.; Gordon, Gwyneth W.; Romaniello, Stephen J.; Smith, Scott M.; Anbar, Ariel D.

2012-01-01

The ability to rapidly detect changes in bone mineral balance (BMB) would be of great value in the early diagnosis and evaluation of therapies for metabolic bone diseases such as osteoporosis and some cancers. However, measurements of BMB are hampered by difficulties with using biochemical markers to quantify the relative rates of bone resorption and formation and the need to wait months to years for altered BMB to produce changes in bone mineral density large enough to resolve by X-ray densitometry. We show here that, in humans, the natural abundances of Ca isotopes in urine change rapidly in response to changes in BMB. In a bed rest experiment, use of high-precision isotope ratio MS allowed the onset of bone loss to be detected in Ca isotope data after about 1 wk, long before bone mineral density has changed enough to be detectable with densitometry. The physiological basis of the relationship between Ca isotopes and BMB is sufficiently understood to allow quantitative translation of changes in Ca isotope abundances to changes in bone mineral density using a simple model. The rate of change of bone mineral density inferred from Ca isotopes is consistent with the rate observed by densitometry in long-term bed rest studies. Ca isotopic analysis provides a powerful way to monitor bone loss, potentially making it possible to diagnose metabolic bone disease and track the impact of treatments more effectively than is currently possible. PMID:22652567

A link between oxygen, calcium and titanium isotopes in 26Al-poor hibonite-rich CAIs from Murchison and implications for the heterogeneity of dust reservoirs in the solar nebula

NASA Astrophysics Data System (ADS)

Kööp, Levke; Davis, Andrew M.; Nakashima, Daisuke; Park, Changkun; Krot, Alexander N.; Nagashima, Kazuhide; Tenner, Travis J.; Heck, Philipp R.; Kita, Noriko T.

2016-09-01

PLACs (platy hibonite crystals) and related hibonite-rich calcium-, aluminum-rich inclusions (CAIs; hereafter collectively referred to as PLAC-like CAIs) have the largest nucleosynthetic isotope anomalies of all materials believed to have formed in the solar system. Most PLAC-like CAIs have low inferred initial 26Al/27Al ratios and could have formed prior to injection or widespread distribution of 26Al in the solar nebula. In this study, we report 26Al-26Mg systematics combined with oxygen, calcium, and titanium isotopic compositions for a large number of newly separated PLAC-like CAIs from the Murchison CM2 chondrite (32 CAIs studied for oxygen, 26 of these also for 26Al-26Mg, calcium and titanium). Our results confirm (1) the large range of nucleosynthetic anomalies in 50Ti and 48Ca (our data range from -70‰ to +170‰ and -60‰ to +80‰, respectively), (2) the substantial range of Δ17O values (-28‰ to -17‰, with Δ17O = δ17O - 0.52 × δ18O), and (3) general 26Al-depletion in PLAC-like CAIs. The multielement approach reveals a relationship between Δ17O and the degree of variability in 50Ti and 48Ca: PLAC-like CAIs with the highest Δ17O (∼-17‰) show large positive and negative 50Ti and 48Ca anomalies, while those with the lowest Δ17O (∼-28‰) have small to no anomalies in 50Ti and 48Ca. These observations could suggest a physical link between anomalous 48Ca and 50Ti carriers and an 16O-poor reservoir. We suggest that the solar nebula was isotopically heterogeneous shortly after collapse of the protosolar molecular cloud, and that the primordial dust reservoir, in which anomalous carrier phases were heterogeneously distributed, was 16O-poor (Δ17O ⩾ -17‰) relative to the primordial gaseous (CO + H2O) reservoir (Δ17O < -35‰). However, other models such as CO self-shielding in the protoplanetary disk are also considered to explain the link between oxygen and calcium and titanium isotopes in PLAC-like CAIs.

Iron isotope effect in the iron arsenide superconductor (Ca0.4Na0.6)Fe2As2

NASA Astrophysics Data System (ADS)

Tsuge, Y.; Nishio, T.; Iyo, A.; Tanaka, Y.; Eisaki, H.

2014-05-01

We report a new sample synthesis technique for polycrystalline (Ca1-xNax)Fe2As2 (0

Lu-Hf and Sm-Nd isotope systematics of Korean spinel peridotites: A case for metasomatically induced Nd-Hf decoupling

NASA Astrophysics Data System (ADS)

Choi, Sung Hi; Mukasa, Samuel B.

2012-12-01

We determined the Lu-Hf and Sm-Nd isotope compositions of spinel peridotite xenoliths in alkali basalts from Baengnyeong and Jeju islands, South Korea, to constrain the timing of melt-depletion events and stabilization of the lithospheric mantle beneath the region. Equilibration temperatures estimated by two-pyroxene thermometry range from 780 to 950 °C, and from 960 to 1010 °C for Baengnyeong and Jeju peridotites, respectively. The Baengnyeong peridotite clinopyroxenes are characterized by extremely radiogenic Hf in association with isotopically less extreme Nd, resulting in strong Nd-Hf decoupling referenced to the mantle array. This is in stark contrast to the well-correlated isotopic compositions of Hf and Nd in the Jeju peridotite clinopyroxenes, which plot along the Nd-Hf mantle array. The Hf abundances and isotopic compositions of the Baengnyeong clinopyroxenes were less affected by relatively recent secondary enrichments that overprinted the light rare earth element abundances and Nd isotopes, causing the decoupling of the Nd-Hf isotopes. The Nd-Hf isotopic compositions of the Jeju peridotites appear to have been re-equilibrated, probably as a result of efficient diffusion at the relatively higher temperatures of the Jeju peridotites. Lu-Hf tie lines for clinopyroxene and orthopyroxene from four of the Korean peridotites have negative slopes on a Lu-Hf isochron diagram, yielding negative ages. This is interpreted to indicate recent isotopic exchange in orthopyroxene by reaction with metasomatic agents having low 176Hf/177Hf components. Secondary overprinting in orthopyroxene was facilitated by the considerably lower Hf concentrations than in co-located clinopyroxene. Baengnyeong lherzolite clinopyroxenes yield a Lu-Hf errorchron age of 1.9 ± 0.1 Ga, which is independently supported by a model Os age (based on Re depletion or TRD) of 1.8 Ga on a refractory Baengnyeong peridotite. We interpret this age range to mark the time of stabilization of the mantle section beneath this area by major melt extraction. This Proterozoic melt removal coincided in time with widespread ca. 2.1 to 1.8 Ga tectonothermal events documented throughout the Korean Peninsula. These observations indicate that the Lu-Hf system can be used to date mantle melting events recorded in lherzolite xenoliths.

Lu-Hf and Sm-Nd isotope systematics of Korean spinel peridotites: A case for metasomatically induced Nd-Hf decoupling

NASA Astrophysics Data System (ADS)

Choi, S.; Mukasa, S. B.

2012-12-01

We determined the Lu-Hf and Sm-Nd isotope compositions of spinel peridotite xenoliths in alkali basalts from Baengnyeong and Jeju islands, South Korea, to constrain the timing of melt-depletion events and stabilization of the lithospheric mantle beneath the region. Equilibration temperatures estimated by two-pyroxene thermometry range from 780 to 950°C, and from 960 to 1010°C for Baengnyeong and Jeju peridotites, respectively. The Baengnyeong peridotite clinopyroxenes are characterized by extremely radiogenic Hf in association with isotopically less extreme Nd, resulting in strong Nd-Hf decoupling referenced to the mantle array. This is in stark contrast to the well-correlated isotopic compositions of Hf and Nd in the Jeju peridotite clinopyroxenes, which plot along the Nd-Hf mantle array. The Hf abundances and isotopic compositions of the Baengnyeong clinopyroxenes were less affected by relatively recent secondary enrichments that overprinted the light rare earth element abundances and Nd isotopes, causing the decoupling of the Nd-Hf isotopes. The Nd-Hf isotopic compositions of the Jeju peridotites appear to have been re-equilibrated, probably as a result of efficient diffusion at the relatively higher temperatures of the Jeju peridotites. Lu-Hf tie lines for clinopyroxene and orthopyroxene from four of the Korean peridotites have negative slopes on a Lu-Hf isochron diagram, yielding negative ages. This is interpreted to indicate recent isotopic exchange in orthopyroxene by reaction with metasomatic agents having low 176Hf/177Hf components. Secondary overprinting in orthopyroxene was facilitated by the considerably lower Hf concentrations than in co-located clinopyroxene. Baengnyeong lherzolite clinopyroxenes yield a Lu-Hf errorchron age of 1.9 ± 0.1 Ga, which is independently supported by a model Os age (based on Re depletion or TRD) of 1.8 Ga on a refractory Baengnyeong peridotite. We interpret this age range to mark the time of stabilization of the mantle section beneath this area by major melt extraction. This Proterozoic melt removal coincided in time with widespread ca. 2.1 to 1.8 Ga tectonothermal events documented throughout the Korean Peninsula. These observations indicate that the Lu-Hf system can be used to date mantle melting events recorded in lherzolite xenoliths.

Neodymium Isotopic Compositions of the Titanite Reference Materials Used in U-Pb Geochronology

NASA Astrophysics Data System (ADS)

Ma, Q.; Yang, Y.; Zhao, Z.

2017-12-01

Titanite (CaTiSiO5) is a widespread mineral and preferentially incorporates considerable uranium and significant light rare earth elements (LREEs) in its structure. Geochronology based upon U-Pb and Pb-Pb analyses of titanite has proven to be useful for understanding the P-T-t evolution of many igneous, metamorphic and hydrothermally altered rock samples (Scott and St-Onge, 1995). In the meantime, Sm-Nd isotopic composition in single titanite can be used to obtain initial Nd isotope composition at the time of titanite crystallization when combined with its U-Pb age, making titanite the most versatile mineral for dating metamorphism and tracing hydrothermal source (Amelin et al., 2009). The widely utilized in situ analyses by SIMS and LA-(MC)-ICP-MS have emphasized the significance for uniform and homogeneous reference materials for external correction (Liu et al., 2012, Sun et al., 2012, Yang et al., 2014). Here, we present U-Pb ages and Sm-Nd isotope analyses of twelve natural titanite crystals (12YQ82, T004, Ontario, BLR-1, OLT1, Khan, Qinghu, TLS-36, NW-IOA, C253, Pakistan and MKED1) acquired by Agilent 7500a Q-ICP-MS and Neptune MC-ICP-MS, respectively, combined a 193 nm ArF excimer laser ablation system. For U-Pb dating, elemental fractionation and instrumental drift were externally corrected using MKED1 titanite standard, showing results of U-Pb analyses all within error of those recommended values. With respect to Sm-Nd isotopes, we employed the interference-free 147Sm/149Sm to deduct 144Sm isobaric interference on 144Nd, and the fractionation between 147Sm and 144Nd was calibrated using BLR-1 titanite, which is proved homogenous in Sm-Nd isotopic system. The obtained Sm-Nd isotopic compositions for natural titanite samples are all consistent with those values determined by isotope dilution (ID) MC-ICP-MS, demonstrating the precision and accuracy currently available for in situ Sm-Nd analyses. Our results demonstrate that BLR-1, OLT1 and Ontario titanites are relatively uniform and homogeneous in Sm-Nd isotopic system and thus can serve as ideal reference materials for external calibration during in situ Sm-Nd analysis.

A LOWER INITIAL ABUNDANCE OF SHORT-LIVED {sup 41}Ca IN THE EARLY SOLAR SYSTEM AND ITS IMPLICATIONS FOR SOLAR SYSTEM FORMATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Ming-Chang; Chaussidon, Marc; Srinivasan, Gopalan

The short-lived radionuclide {sup 41}Ca plays an important role in constraining the immediate astrophysical environment and the formation timescale of the nascent solar system due to its extremely short half-life (0.1 Myr). Nearly 20 years ago, the initial ratio of {sup 41}Ca/{sup 40}Ca in the solar system was determined to be (1.41 {+-} 0.14) Multiplication-Sign 10{sup -8}, primarily based on two Ca-Al-rich Inclusions (CAIs) from the CV chondrite Efremovka. With an advanced analytical technique for isotopic measurements, we reanalyzed the potassium isotopic compositions of the two Efremovka CAIs and inferred the initial ratios of {sup 41}Ca/{sup 40}Ca to be (2.6more » {+-} 0.9) Multiplication-Sign 10{sup -9} and (1.4 {+-} 0.6) Multiplication-Sign 10{sup -9} (2{sigma}), a factor of 7-10 lower than the previously inferred value. Considering possible thermal processing that led to lower {sup 26}Al/{sup 27}Al ratios in the two CAIs, we propose that the true solar system initial value of {sup 41}Ca/{sup 40}Ca should have been {approx}4.2 Multiplication-Sign 10{sup -9}. Synchronicity could have existed between {sup 26}Al and {sup 41}Ca, indicating a uniform distribution of the two radionuclides at the time of CAI formation. The new initial {sup 41}Ca abundance is 4-16 times lower than the calculated value for steady-state galactic nucleosynthesis. Therefore, {sup 41}Ca could have originated as part of molecular cloud materials with a free decay time of 0.2-0.4 Myr. Alternative possibilities, such as a last-minute input from a stellar source and early solar system irradiation, could not be definitively ruled out. This underscores the need for more data from diverse CAIs to determine the true astrophysical origin of {sup 41}Ca.« less

Surface area dependence of calcium isotopic reequilibration in carbonates: Implications for isotopic signatures in the weathering zone

NASA Astrophysics Data System (ADS)

Fernandez, N. M.; Druhan, J. L.; Potrel, A.; Jacobson, A. D.

2016-12-01

The concept of dynamic equilibrium carries the implicit assumption of continued isotopic exchange between a mineral and the surrounding fluid. While this effect has received much attention in the marine paleoproxy literature, it has been relatively overlooked in application to the terrestrial environment. In weathering systems, a potential consequence is that rapid reequilibration may alter or erase isotopic signatures generated during secondary mineral formation. The extent and timescale over which isotopic signatures are reset in these hydrologic systems is unknown. Using reactive transport modeling, we show isotopic reequilibration under conditions reflecting terrestrial hydrologic settings to be significant and dependent on the reactive surface area of the solid. In particular, we suggest that the non-traditional stable isotopes commonly used in application to carbonates (e.g., Ca, Mg, Sr) are sensitive to these effects due to their rapid reaction rates. We aim to characterize the dependence of Ca isotopic reequilibration on surface area during calcite precipitation via batch experiments conducted at ambient temperature over 48-hour time periods. Calcite precipitation was performed in a closed batch reactor utilizing a controlled free-drift method. The batch reactors contained mixed supersaturated solutions of CaCl2 and NaHCO3 at an initial pH of 8.54. Precipitation was initiated by seed inoculation of calcite crystals with two distinct, pre-constrained surface areas. All experiments achieved the same final state of chemical equilibrium, but as expected, the fastest approach to equilibrium occurred for experiments employing calcite seeds with the highest surface area. This implies that differences in equilibrated Ca isotope ratios (δ44/40Ca) should reflect differences in surface area. This prediction is upheld by models of the experiments, indicating a measureable difference in δ44Ca during calcite precipitation where the higher surface area corresponds to lower δ44Ca values and a faster approach to isotopic equilibrium. The dependence of δ44Ca resetting on calcite surface areas has broad ramifications for tracing carbonate weathering in the Critical Zone.

Actualistic models of mantle metasomatism documented in a composite xenolith from Dish Hill, California

USGS Publications Warehouse

Nielson, J.E.; Budahn, J.R.; Unruh, D.M.; Wilshire, H.G.

1993-01-01

Major and trace-element whole rock and mineral variations in composite hornblendite-peridotite xenolith Ba-2-1, from Dish Hill, CA, are due to a single event of metasomatism in the mantle. The hornblendite is the crystallized selvage of a dike conduit charged with incompatible-element-enriched hydrous mafic magma. The magma infiltrated the refractory peridotite wallrock, reacted with its constituent minerals, and simultaneously deposited amphibole. The systematic data from this study show considerable variation in isotopic values and trace elements. These data provide insight into a mantle process that was defined previously from samples without context, lacking evidence about the number or source of metasomatic events. In the contact zone of Ba-2-1, peridotite is enriched in Fe, Ti, CO2) and H2O; clinopyroxene and amphibole also are enriched in Fe and Ti, but clinopyroxene appears slightly depleted in CaO. Compared to chondrites, peridotite, clinopyroxene, and probably amphibole are enriched in light rare earth (LREEcn) and other incompatible trace elements. Values of 87Sr 86Sr and 143Nd 144Nd in the contact zone are close to isotopic equilibrium with the dike. Whole rock and constituent clinopyroxene compositions change to those of refractory peridotite with distance from the contact. These compositional variations were modelled using Gresens' equation for whole-rock major and minor elements, and calculations for isotopic ratios and REEs, which emulate the effects of Chromatographic fractionation. The choice of endmembers was restricted to compositions actually present in mantle samples from Dish Hill. Model results indicate that: 1. (1) the variations can be explained as the result of a single metasomatic event, probably a single pulse of previously fractionated liquid; 2. (2) the ratio of total interacting liquid to peridotite was at least 1:3 by weight in the contact zone; and 3. (3) the composition of the metasomatic liquid changed progressively as it infiltrated beyond that zone. The small distance over which variations occur is due to the small amount of liquid that infiltrated. Only in the contact zone was peridotite wallrock saturated by a liquid composition similar to the dike. Comparison of the Ba-2-1 data with those of another xenolith from Dish Hill suggests that the compositional variations of mantle metasomatism result from both the compositional contrast between the metasomatizing liquid and wallrock and the relative abundances of each. Compositional and volumetric variations of mantle partial melts and their fractionates, and repeated events of melting and reaction in contiguous mantle, can create broad ranges of metasomatic "signatures" from the same process. ?? 1993.

The oxygen isotope composition of Karoo and Etendeka picrites: High δ18O mantle or crustal contamination?

NASA Astrophysics Data System (ADS)

Harris, Chris; le Roux, Petrus; Cochrane, Ryan; Martin, Laure; Duncan, Andrew R.; Marsh, Julian S.; le Roex, Anton P.; Class, Cornelia

2015-07-01

Oxygen isotope compositions of Karoo and Etendeka large igneous province (LIP) picrites and picrite basalts are presented to constrain the effects of crustal contamination versus mantle source variation. Olivine and orthopyroxene phenocrysts from lavas and dykes (Mg# 64-80) from the Tuli and Mwenezi (Nuanetsi) regions of the ca 180 Ma Karoo LIP have δ18O values that range from 6.0 to 6.7 ‰. They appear to have crystallized from magmas having δ18O values about 1-1.5 ‰ higher than expected in an entirely mantle-derived magma. Olivines from picrite and picrite basalt dykes from the ca 135 Ma Etendeka LIP of Namibia and Karoo-age picrite dykes from Dronning Maud Land, Antarctica, do not have such elevated δ18O values. A range of δ18O values from 4.9 to 6.0 ‰, and good correlations between δ18O value and Sr, Nd and Pb isotope ratios for the Etendeka picrites are consistent with previously proposed models of crustal contamination. Explanations for the high δ18O values in Tuli/Mwenezi picrites are limited to (1) alteration, (2) crustal contamination, and (3) derivation from mantle with an abnormally high δ18O. Previously, a variety of models that range from crustal contamination to derivation from the `enriched' mantle lithosphere have been suggested to explain high concentrations of incompatible elements such as K, and average ɛNd and ɛSr values of -8 and +16 in Mwenezi (Nuanetsi) picrites. However, the primitive character of the magmas (Mg# 73), combined with the lack of correlation between δ18O values and radiogenic isotopic compositions, MgO content, or Mg# is inconsistent with crustal contamination. Thus, an 18O-enriched mantle source having high incompatible trace element concentration and enriched radiogenic isotope composition is indicated. High δ18O values are accompanied by negative Nb and Ta anomalies, consistent with the involvement of the mantle lithosphere, whereas the high δ18O themselves are consistent with an eclogitic source. Magma δ18O values about 1 ‰ higher than expected for mantle-derived magma are also a feature of the Bushveld mafic and ultramafic magmas, and the possibility exists that a long-lived 18O-enriched mantle source has existed beneath southern Africa. A mixed eclogite peridotite source could have developed by emplacement of oceanic lithosphere into the cratonic keel during Archaean subduction.

Diagnosis and assessment of skeletal related disease using calcium 41

DOEpatents

Hillegonds, Darren J [Oakland, CA; Vogel, John S [San Jose, CA; Fitzgerald, Robert L [Encinitas, CA; Deftos, Leonard J [Del Mar, CA; Herold, David [Del Mar, CA; Burton, Douglas W [San Diego, CA

2012-05-15

A method of determining calcium metabolism in a patient comprises the steps of administering radioactive calcium isotope .sup.41Ca to the patient, allowing a period of time to elapse sufficient for dissemination and reaction of the radioactive calcium isotope .sup.41Ca by the patient, obtaining a sample of the radioactive calcium isotope .sup.41Ca from the patient, isolating the calcium content of the sample in a form suitable for precise measurement of isotopic calcium concentrations, and measuring the calcium content to determine parameters of calcium metabolism in the patient.

Diagnosis and assessment of skeletal related disease using calcium 41

DOEpatents

Hillegonds, Darren J.; Vogel, John S.; Fitzgerald, Robert L.; Deftos, Leonard J.; Herold, David; Burton, Douglas W.

2013-03-05

A method of determining calcium metabolism in a patient comprises the steps of administering radioactive calcium isotope .sup.41Ca to the patient, allowing a period of time to elapse sufficient for dissemination and reaction of the radioactive calcium isotope .sup.41Ca by the patient, obtaining a sample of the radioactive calcium isotope .sup.41Ca from the patient, isolating the calcium content of the sample in a form suitable for precise measurement of isotopic calcium concentrations, and measuring the calcium content to determine parameters of calcium metabolism in the patient.

Experimental and Analytical Studies of Solar System Chemistry

NASA Technical Reports Server (NTRS)

Burnett, Donald S.

2003-01-01

The cosmochemistry research funded by this grant resulted in the publications given in the attached Publication List. The research focused in three areas: (1) Experimental studies of trace element partitioning. (2) Studies of the minor element chemistry and O isotopic compositions of MgAlO4 spinels from Ca-Al-Rich Inclusions in carbonaceous chondrite meteorites, and (3) The abundances and chemical fractionations of Th and U in chondritic meteorites.

Growth rates, stable oxygen isotopes (δ18O), and strontium (Sr/Ca) composition in two species of Pacific sclerosponges (Acanthocheatetes wellsi and Astrosclera willeyana) with δ18O calibration and application to paleoceanography

NASA Astrophysics Data System (ADS)

Grottoli, AndréA. G.; Adkins, Jess F.; Panero, Wendy R.; Reaman, Daniel M.; Moots, Kate

2010-06-01

The isotopic and elemental composition of sclerosponge skeletons is used to reconstruct paleoceanographic records. Yet few studies have systematically examined the natural variability in sclerosponge skeletal δ18O, growth, and Sr/Ca, and how that may influence the interpretation of sclerosponge proxy records. Here, we analyzed short records in seven specimens of Acanthocheatetes wellsi (high-Mg calcite, 21 mol% Mg) from Palau, four A. wellsi (high-Mg calcite, 21 mol% Mg) from Saipan, and three Astrosclera willeyana (aragonite) sclerosponges from Saipan, as well as one long record in an A. wellsi specimen from Palau spanning 1945-2001.5. In Saipan, species-specific and mineralogical effects appear to have a negligible effect on sclerosponge δ18O, facilitating the direct comparison of δ18O records between species at a given location. At both sites, A. wellsi δ18O and growth rates were sensitive to environmental conditions, but Sr/Ca was not sensitive to the same conditions. High-resolution δ18O analyses confirmed this finding as both A. wellsi and A. willeyana deposited their skeleton in accordance with the trends in isotopic equilibrium with seawater, though with a 0.27‰ offset in the case of A. willeyana. In the high-Mg-calcite species A. wellsi, Mg may be interfering with Sr incorporation into the skeleton. On multidecadal timescales, A. wellsi sclerosponge δ18O in Palau tracked the Southern Oscillation Index variability post-1977, but not pre-1977, coincident with the switch in the Pacific Decadal Oscillation (PDO) at ˜1976. This suggests that water mass circulation in the region is influenced by El Niño— Southern Oscillation variability during positive PDO phases, but not during negative ones.

Growth Rates, Stable Oxygen Isotopes (18O), and Strontium (Sr/Ca) Composition in Two Species of Pacific Sclerosponges (Acanthocheatetes wellsi and Astrosclera willeyana) with 18O Calibration and Application to Paleoceanography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grottoli, A.; Adkins, J; Panero, W

2010-01-01

The isotopic and elemental composition of sclerosponge skeletons is used to reconstruct paleoceanographic records. Yet few studies have systematically examined the natural variability in sclerosponge skeletal {delta}{sup 18}O, growth, and Sr/Ca, and how that may influence the interpretation of sclerosponge proxy records. Here, we analyzed short records in seven specimens of Acanthocheatetes wellsi (high-Mg calcite, 21 mol% Mg) from Palau, four A. wellsi (high-Mg calcite, 21 mol% Mg) from Saipan, and three Astrosclera willeyana (aragonite) sclerosponges from Saipan, as well as one long record in an A. wellsi specimen from Palau spanning 1945-2001.5. In Saipan, species-specific and mineralogical effects appearmore » to have a negligible effect on sclerosponge {delta}{sup 18}O, facilitating the direct comparison of {delta}{sup 18}O records between species at a given location. At both sites, A. wellsi {delta}{sup 18}O and growth rates were sensitive to environmental conditions, but Sr/Ca was not sensitive to the same conditions. High-resolution {delta}{sup 18}O analyses confirmed this finding as both A. wellsi and A. willeyana deposited their skeleton in accordance with the trends in isotopic equilibrium with seawater, though with a 0.27{per_thousand} offset in the case of A. willeyana. In the high-Mg-calcite species A. wellsi, Mg may be interfering with Sr incorporation into the skeleton. On multidecadal timescales, A. wellsi sclerosponge {delta}{sup 18}O in Palau tracked the Southern Oscillation Index variability post-1977, but not pre-1977, coincident with the switch in the Pacific Decadal Oscillation (PDO) at {approx}1976. This suggests that water mass circulation in the region is influenced by El Nino-Southern Oscillation variability during positive PDO phases, but not during negative ones.« less

The 3.66 Ga Nuvvuagittuq Tonalite-Trondhjemite-Granodiorite Suite: A Case of Hadean Anatexis

NASA Astrophysics Data System (ADS)

Stevenson, R. K.; Bizzarro, M.

2011-12-01

The ca 3.8-4.3 Ga Nuvvuagittuq supracrustal sequence in northern Quebec, Canada, ranks as one of the most exciting early Earth terrain discoveries of the past fifteen years. The supracrustal sequence consists of mafic amphibolite rocks with rare felsic schists along with ultramafic sills and oxide-rich and quartz-rich iron formation. The supracrustal sequence is semi-oval in form and is folded around a core of foliated tonalite-trondhjemite-granodiorite (TTG) suite. A similar TTG suite forms a sheath around the exterior margin of the Nuvvuagittuq supracrustal sequence. Zircons from a felsic volcanic unit within the sequence yielded a minimum age of 3.8 Ga (U-Pb) for volcanic rocks of the sequence (David et al. 2009). A study of the Nd142 isotope systematics of the sequence found evidence for a Nd142 deficit in the sequence and a Nd142-Sm147 isochron yielded an age of 4.28 Ga (O'Neil et al. 2008). Dating of zircons from the tonalite sheath (U-Pb TIMS; David et al., 2009) and from the inner core (U-Pb SHRIMP; this study) yield similar ages (3.66 Ga). Zircons from this sequence undoubtedly contributed to the Hf isotopic composition of Archean sedimentary sequences of the Canadian Shield (Stevenson and Patchett 1990).The zircons from the TTG suite are very homogeneous and only have rare thin metamorphic rims that yield an age of 2.7 Ga (U-Pb Shrimp; this study). Radiogenic isotope studies (Sm-Nd and Lu-Hf) indicate that the TTG suite is an anatectic product of the melting of the Nuvvuagittuq supracrustal suite. The geochemical compositions of the Nuvvuagittuq TTG suite are compared with the compositions of ca 3.6 TTG suites from other localities around the world. David, J. Godin, L., Stevenson, R., O'Neil, J. and Francis, D. 2009. U-Pb ages (3.8-2.7 Ga) and Nd isotope data from the newly- identified Eoarchean Nuvvuagittuq supracrustal sequence, Superior Craton, Canada. GSA Bulletin 121; 150-163. O'Neil, J., Carlson, R.W., Francis, D., and Stevenson, R.K. 2008. Neodymium-142 Evidence Hadean Mafic Crust. Science 321 (Sept. 26), 1828-1831. Stevenson, R.K. and Patchett, P.J. (1990): Implications for the evolution of continental crust from Hf isotope systematics of Archean detrital zircons. Geochimica et Cosmochimica Acta 54, 1683-1697.

Calcium isotope ratios in animal and human bone

NASA Astrophysics Data System (ADS)

Reynard, L. M.; Henderson, G. M.; Hedges, R. E. M.

2010-07-01

Calcium isotopes in tissues are thought to be influenced by an individual's diet, reflecting parameters such as trophic level and dairy consumption, but this has not been carefully assessed. We report the calcium isotope ratios (δ 44/42Ca) of modern and archaeological animal and human bone ( n = 216). Modern sheep raised at the same location show 0.14 ± 0.08‰ higher δ 44/42Ca in females than in males, which we attribute to lactation by the ewes. In the archaeological bone samples the calcium isotope ratios of the herbivorous fauna vary by location. At a single site, the archaeological fauna do not show a trophic level effect. Humans have lower δ 44/42Ca than the mean site fauna by 0.22 ± 0.22‰, and the humans have a greater δ 44/42Ca range than the animals. No effect of sex or age on the calcium isotope ratios was found, and intra-individual skeletal δ 44/42Ca variability is negligible. We rule out dairy consumption as the main cause of the lower human δ 44/42Ca, based on results from sites pre-dating animal domestication and dairy availability, and suggest instead that individual physiology and calcium intake may be important in determining bone calcium isotope ratios.

Self diffusion of alkaline-Earth in Ca-Mg-aluminosilicate melts: Experimental improvements on the determination of the self-diffusion coefficients

NASA Technical Reports Server (NTRS)

Paillat, O.; Wasserburg, G. J.

1993-01-01

Experimental studies of self-diffusion isotopes in silicate melts often have quite large uncertainties when comparing one study to another. We designed an experiment in order to improve the precision of the results by simultaneously studying several elements (Mg, Ca, Sr, Ba) during the same experiment thereby greatly reducing the relative experimental uncertainties. Results show that the uncertainties on the diffusion coefficients can be reduced to 10 percent, allowing a more reliable comparison of differences of self-diffusion coefficients of the elements. This type of experiment permits us to study precisely and simultaneously several elements with no restriction on any element. We also designed an experiment to investigate the possible effects of multicomponent diffusion during Mg self-diffusion experiments by comparing cases where the concentrations of the elements and the isotopic compositions are different. The results suggest that there are differences between the effective means of transport. This approach should allow us to investigate the importance of multicomponent diffusion in silicate melts.

Rare gases and Ca, Sr, and Ba in Apollo 17 drill-core fines

NASA Technical Reports Server (NTRS)

Pepin, R. O.; Dragon, J. C.; Johnson, N. L.; Bates, A.; Coscio, M. R., Jr.; Murthy, V. R.

1975-01-01

Trapped gas isotopic compositions and spallation gas concentrations as functions of depth in the Apollo 17 drill core were determined from mass spectrometer studies by means of correlation techniques. The distribution of He, Ne, Ar, Kr, and Xe as well as Ca, Sr, and Ba was investigated, and rare-gas spallation and neutron capture profiles are compared with attention to proposed depositional models for the Taurus-Littrow regolith. The data exclude a sedimentation pattern similar to that found at the Apollo 15 site but are possibly compatible with long-term continuous accretion models or models of very recent rapid accumulation of regolith.

Diamonds from the Machado River alluvial deposit, Rondônia, Brazil, derived from both lithospheric and sublithospheric mantle

NASA Astrophysics Data System (ADS)

Burnham, A. D.; Bulanova, G. P.; Smith, C. B.; Whitehead, S. C.; Kohn, S. C.; Gobbo, L.; Walter, M. J.

2016-11-01

Diamonds from the Machado River alluvial deposit have been characterised on the basis of external morphology, internal textures, carbon isotopic composition, nitrogen concentration and aggregation state and mineral inclusion chemistry. Variations in morphology and features of abrasion suggest some diamonds have been derived directly from local kimberlites, whereas others have been through extensive sedimentary recycling. On the basis of mineral inclusion compositions, both lithospheric and sublithospheric diamonds are present at the deposit. The lithospheric diamonds have clear layer-by-layer octahedral and/or cuboid internal growth zonation, contain measurable nitrogen and indicate a heterogeneous lithospheric mantle beneath the region. The sublithospheric diamonds show a lack of regular sharp zonation, do not contain detectable nitrogen, are isotopically heavy (δ13CPDB predominantly - 0.7 to - 5.5) and contain inclusions of ferropericlase, former bridgmanite, majoritic garnet and former CaSiO3-perovskite. This suggests source lithologies that are Mg- and Ca-rich, probably including carbonates and serpentinites, subducted to lower mantle depths. The studied suite of sublithospheric diamonds has many similarities to the alluvial diamonds from Kankan, Guinea, but has more extreme variations in mineral inclusion chemistry. Of all superdeep diamond suites yet discovered, Machado River represents an end-member in terms of either the compositional range of materials being subducted to Transition Zone and lower mantle or the process by which materials are transferred from the subducted slab to the diamond-forming region.

First-principles investigations of equilibrium Ca, Mg, Si and O isotope fractionations between silicate melts and minerals

NASA Astrophysics Data System (ADS)

Qi, Y.; Liu, X.; Kang, J.; He, L.

2017-12-01

Equilibrium isotope fractionation factors are essential for using stable isotope data to study many geosciences processes such as planetary differentiation and mantle evolution. The mass-dependent equilibrium isotope fractionation is primarily controlled by the difference in bond energies triggered by the isotope substitution. With the recent advances in computational capabilities, first-principles calculation has become a reliable tool to investigate equilibrium isotopic fractionations, greatly improving our understanding of the factors controlling isotope fractionations. It is important to understand the isotope fractionation between melts and minerals because magmatism is critical for creating and shaping the Earth. However, because isotope fractionation between melts and minerals is small at high temperature, it is difficult to experimentally calibrate such small signature. Due to the disordered and dynamic character of melts, calculations of equilibrium isotope fractionation of melts are more challenging than that for gaseous molecules or minerals. Here, we apply first-principles molecular dynamics method to calculate equilibrium Ca, Mg, Si, and O isotope fractionations between silicate melts and minerals. Our results show that equilibrium Mg, Si, and O isotope fractionations between olivine and pure Mg2SiO4 melt are close to zero at high temperature (e.g. δ26Mgmelt-ol = 0.03 ± 0.04‰, δ30Simelt-ol = -0.06 ± 0.07‰, δ18Omelt-ol = 0.07‰ ± 0.08 at 1500 K). Equilibrium Ca, Mg, Si, and O isotope fractionations between diopside and basalt melt (67% CaMgSi2O6 + 33% CaAl2Si2O8) are also negligible at high temperature (e.g. δ44/40Camelt-cpx = -0.01 ± 0.02‰, δ26Mgmelt-cpx = -0.05 ± 0.14‰, δ30Simelt-cpx = 0.04 ± 0.04‰, δ18Omelt-cpx = 0.03 ± 0.07‰ at 1500 K). These results are consistent with the observations in natural samples that there is no significant Ca, Mg, Si, and O isotope fractionation during mantle partial melting, demonstrating the reliability of our methods. Thus, our results can be used to understand stable isotope fractionation during partial melting of mantle peridotite or fractional crystallization during magmatic differentiation. The first-principles molecular dynamics method is a promising tool to obtain equilibrium fractionation of more isotope systems for complicate liquids.

Carbonate mineralization via an amorphous calcium carbonate (ACC) pathway: Tuning polymorph selection by Mg, pH, and mixing environment

NASA Astrophysics Data System (ADS)

Dove, P. M.; Blue, C.; Mergelsberg, S. T.; Giuffre, A. J.; Han, N.; De Yoreo, J. J.

2017-12-01

Mineral formation by nonclassical processes is widespread with many pathways that include aggregation of nanoparticles, oriented attachment of fully formed crystals, and sequential nucleation/transformation of amorphous phases (De Yoreo et al., 2015, Science). Field observations indicate amorphous calcium carbonate (ACC) can be the initial precipitate when local conditions promote high supersaturations for short time periods. Examples include microbial mats, marine porewaters that undergo pulses of increased alkalinity, closed basin lakes, and sabkhas. The crystalline products exhibit diverse morphologies and complex elemental and isotopic signatures. This study quantifies relationships between solution composition and the crystalline polymorphs that transform from ACC (Blue et al., GCA, 2017). Our experimental design synthesized ACC under controlled conditions for a suite of compositions by tuning input pH, Mg/Ca, and total carbonate concentration. ACC products were allowed to transform within output suspensions under stirred or quiescent mixing while characterizing the polymorph and composition of evolving solutions and solids. We find that ACC transforms to crystalline polymorphs with a systematic relationship to solution composition to give a quantitative framework based upon solution aMg2+/aCa2+ and aCO32-/aCa2+. We also measure a polymorph-specific evolution of pH and Mg/Ca during the transformation that indicates the initial polymorph to form. Pathway is further modulated by stirring versus quiescent conditions. The findings reconcile discrepancies among previous studies of ACC to crystalline products and supports claims that monohydrocalcite may be an overlooked, transient phase during formation of some aragonite and calcite deposits. Organic additives and extreme pH are not required to tune composition and polymorph. Insights from this study reiterate the need to revisit long-standing dogmas regarding controls on CaCO3 polymorph selection. Classical models assume thermodynamic equilibria but cannot provide a reliable predictor of compositions when kinetic factors are driving mineralization. Nonclassical pathways to mineralization may be the missing link to interpreting unusual CaCO3 polymorphs, compositions and textures in modern and ancient carbonates.

Generation of syntectonic calc-alkaline, magnesian granites through remelting of pre-tectonic igneous sources - U-Pb zircon ages and Sr, Nd and Pb isotope data from the Donkerhoek granite (southern Damara orogen, Namibia)

NASA Astrophysics Data System (ADS)

Schwark, L.; Jung, S.; Hauff, F.; Garbe-Schönberg, D.; Berndt, J.

2018-06-01

The 541 ± 4 Ma-old magnesian, weakly peraluminous, calc-alkalic Donkerhoek Onanis granite is part of the ca. 6000 km2 large Donkerhoek batholith in the Southern Zone of the Damara orogen of Namibia. Linear major and trace element variations and decreasing MgO, FeO, Al2O3, CaO, K2O, Na2O, Ba and Sr concentrations with increasing SiO2 indicate that this part of the batholith represent a coherent mass and underwent fractional crystallization processes. The Donkerhoek Onanis granites are isotopically evolved (initial εNd: -4.7 to -12.3, initial 87Sr/86Sr: 0.7099-0.7157) with moderately radiogenic Pb isotope ratios (206Pb/204Pb: 17.26-18.22; 207Pb/204Pb: 15.59-15.67; 208Pb/204Pb: 37.60-38.06). Beside heterogeneities imparted by the sources, an evaluation of LREE fractionation and Nd isotope data suggests that AFC processes also modified some samples. Based on the chemical and isotope data, the Donkerhoek Onanis granites cannot be derived by partial melting of Al- and Fe-rich metasedimentary rocks of the Kuiseb formation in which they intruded. Instead, melting of meta-igneous crustal sources with Proterozoic crustal residence ages is more likely. Three igneous to meta-igneous rock suites from the area (Matchless amphibolites, Proterozoic mafic to felsic gneisses from the southern Kalahari craton basement, syn-tectonic Salem granodiorites to granites) are potential sources. An evaluation of chemical and isotope data suggests that remelting of early syn-orogenic Salem-type granites is the most likely process which would also explain the existence of ca. 563 ± 4 Ma-old zircon in the Donkerhoek Onanis granites. Comparison of the Donkerhoek Onanis granites with experimentally derived melt compositions from an intermediate igneous parent indicates temperatures between 800 and 850 °C. It is suggested that the Pan-African igneous activity in this part of the Damara Belt was a moderate-temperature intra-crustal event. Although there are some compositional similarities with juvenile granites generated in subduction zones, unradiogenic Pb isotope ratios and moderately radiogenic Sr and unradiogenic Nd isotopes suggest that reprocessed crustal rocks are more likely sources. Previously obtained high δ18O values of the Donkerhoek Onanis granites ranging from 11.8 to 13.6‰, covering the range of δ18O values obtained on Salem-type granites from the area (12.5-13.3‰) confirm this view. In contrast to igneous processes along active continental margins that produce juvenile batholiths with calc-alkaline affinities, this igneous event was not a major crust-forming episode and the Donkerhoek Onanis granites represent reprocessed crustal material.

Evolution of the carbon cycle and seawater temperature from the Triassic-Jurassic boundary to the Early Toarcian based on brachiopod geochemistry

NASA Astrophysics Data System (ADS)

Müller, Tamás; Tomašových, Adam

2017-04-01

The ecological crisis and extinction at the end of the Triassic coincides with several environmental perturbations such as global temperature rise, ocean acidification and carbon isotope anomalies, with a large observed negative carbon isotope excursion (CIE) in the Late Rhaetian as well. Followed by the ETE, the Early Jurassic was characterized by marked fluctuations of the global seawater temperature and carbon cycle. Carbon isotope records are showing positive and remarkable negative excursions. A particular example of these phenomena is connected to the Toarcian Oceanic Anoxic Event (TOAE). The δ13C record of the TOAE is showing a negative excursion of a high magnitude, suggesting the injection of large amount of light carbon into the ocean-atmosphere system, coinciding with rapid global warming and widespread anoxia. Beside the TOAE there are many other, smaller scale carbon isotope anomalies and environmental perturbations at the Sinemurian-Pliensbachian transition or at the Pliensbachian-Toarcian boundary. In our study, we provide new brachiopod δ13C, δ18O, and Mg/Ca data from the time interval starting in the Rhaetian till the end of the Early Toarcian. Considering the strong resistance of brachiopod shells against diagenesis, our aim is to reconstruct seawater temperature, seawater Mg/Ca, and carbon cycle evolution based on a reliable geochemical proxy database of the studied time interval. The samples have been collected from various localities across Europe achieving a good, at least ammonite subzone scale resolution for the Rhaetian stage and for the Lower Jurassic. The geochemical preservation of the shell material have been tested by several approaches. Thin-sections were made from the shells and analyzed by electron microprobe and ICP-OES to evaluate their preservation by assessing concentrations of Fe, Mn, Sr, and their ratios (Mn/Ca, Sr/Ca). Considering the various elemental composition data of fossil and recent brachiopods published by several authors, we established thresholds as Sr/Ca > 0,46 ( 400 ppm Sr) and Mn/Ca < 0,37 ( 200 ppm Mn) for samples with good preservation and Sr/Ca > 0,34 ( 300 ppm Sr) and Mn/Ca < 1 ( 460 ppm Mn) for moderate preservation. Samples not fitting to this criteria were excluded from the data sets used in our interpretations. We find that average values of Mg/Ca measured on different species collected in the same stratigraphic level show low variability, suggesting minor species-specific effects on this ratio. High-resolution transects through shells of some species detect cyclic fluctuations in Mg/Ca that coincide with growth lines, suggesting that this ratio captures changes in temperature seasonality.

CaSiO3 perovskite in diamond indicates the recycling of oceanic crust into the lower mantle

NASA Astrophysics Data System (ADS)

Nestola, F.; Korolev, N.; Kopylova, M.; Rotiroti, N.; Pearson, D. G.; Pamato, M. G.; Alvaro, M.; Peruzzo, L.; Gurney, J. J.; Moore, A. E.; Davidson, J.

2018-03-01

Laboratory experiments and seismology data have created a clear theoretical picture of the most abundant minerals that comprise the deeper parts of the Earth’s mantle. Discoveries of some of these minerals in ‘super-deep’ diamonds—formed between two hundred and about one thousand kilometres into the lower mantle—have confirmed part of this picture. A notable exception is the high-pressure perovskite-structured polymorph of calcium silicate (CaSiO3). This mineral—expected to be the fourth most abundant in the Earth—has not previously been found in nature. Being the dominant host for calcium and, owing to its accommodating crystal structure, the major sink for heat-producing elements (potassium, uranium and thorium) in the transition zone and lower mantle, it is critical to establish its presence. Here we report the discovery of the perovskite-structured polymorph of CaSiO3 in a diamond from South African Cullinan kimberlite. The mineral is intergrown with about six per cent calcium titanate (CaTiO3). The titanium-rich composition of this inclusion indicates a bulk composition consistent with derivation from basaltic oceanic crust subducted to pressures equivalent to those present at the depths of the uppermost lower mantle. The relatively ‘heavy’ carbon isotopic composition of the surrounding diamond, together with the pristine high-pressure CaSiO3 structure, provides evidence for the recycling of oceanic crust and surficial carbon to lower-mantle depths.

Hf isotope compositions In detrital zircons as a new tool for provenance studies

NASA Astrophysics Data System (ADS)

Jacobsen, Y. J.; Münker, C.; Mezger, K.

2003-04-01

Identifying the provenance of continental sediments is a major issue in palaeo-tectonic studies, providing important information for paleogeographic reconstructions. Isotope studies, e.g. those of whole rock Sm-Nd or detrital zircon U-Pb dating, have widely been used for this purpose. Here we assess the potential of combined Lu-Hf data and U-Pb ages determined on the same single detrital zircons as a new tool for provenance studies. Due to the low Lu/Hf ratios in zircons the Hf isotope composition of a zircon changes insignificantly after its crystallization. Thus each particular grain preserves information on the Hf-siotpe composition of its source and the age of this source. Provided that both the U-Pb and Lu-Hf isotope systems have not been disturbed, this information can be used to constrain the sources of each individual zircon. In order to demonstrate the capability of Hf isotope studies on detrital zircons for provenance studies, we obtained combined U-Pb ages and Lu-Hf isotope data for zircons from the Cambrian Junction Formation in New Zealand. The Junction Formation was deposited on the (present) SE margin of Gondwana near the Australian continent and consists of turbidites, siltstones and conglomerates [1]. Typical continent derived Paleozoic sediments in SE Gondwana generally show characteristic age maxima at 500-600 Ma, 1000-1200 Ma (Grenvillian) and additional older peaks (early Proterozoic to Archean) [2]. We focused on two groups of detrital zircons with Grenvillian and Proterozoic to Late Archean ages. The initial ɛHf values for these zircons range from 0.7 to -15.5 for the Grenvillian and from -5.2 to -14.1 for the Proterozoic/Archean zircons. Corresponding two stage Hf model ages range from ca. 1500 to 2500 Ma for the Grenvillian and from ca. 3200 to 3600 Ma for the Proterozoic/Archean zircons. Furthermore it can be shown that the Grenvillian zircons must have been derived from recycled Grenvillian provinces. Comparison of these Hf model ages with Nd crustal residence ages from the possible sources in Australia, Antarctica and Laurentia reveals the possible sources of the zircons. Based on the paleogeographic setting in Cambrian time the Grenville-age zircons were most likely derived from Drauning Maud Land (Antarctica), thus confirming earlier models by [1] and [3]. The Archean zircons were most likely derived from W-Australia (Yilgarn or Pilbara Kraton) or E-Antarctica (Miller Range). [1] Wombacher and Münker 2000: J. Geol. 108, [2] Ireland et al. 1998: Geology 26, [3] Flöttmann et al. 1998: J. Geol. Soc. 155.

Hydrochemical effects on the life cycle, shell size, thickness, and chemistry of ostracode Cyprideis torosa

NASA Astrophysics Data System (ADS)

Marco-Barba, J.; Ito, E.; Mezquita, F.; Carbonell, E.

2006-12-01

Cyprideis torosa is a species of ostracode that inhabits and reproduces in wide range of ionic concentrations as long as (carbonate alkalinity)/Ca ratio is low. It is found in inland springs, lakes, estuaries, wetlands and seawater evaporation ponds as long as its Alk/Ca requirement is met. We collected C. torosa from 20 sites near Valencia, Spain in early spring 2004. Main environmental variables were analyzed in situ or in the lab, including temperature and concentration of major ions and oxygen isotopes. Several (2-20) live individuals were sorted out, their growth instar, sex and size measured and their shell chemistry (Mg/Ca, Sr/Ca and oxygen isotopes) analyzed. Three of these 20 sites were sampled monthly for an entire year, and its population structure, juvenile and adult shell chemistry (between 20 and 40 shells) analyzed. The chemistry of the single-visit sites varied widely with TDS from 9 to 2200 meq/L. Generally, Cl was the most dominant anion, with an averaged value of 76% (16% - 94%). CO3 plus HCO3 varied between 0.4 and 64% and SO4 between 4 and 26%. Principal Components Analysis showed that all waters follow a similar solute evolution trend of increasing Cl and SO4 and decreasing carbonate alkalinity with increasing TDS. Water δ18O also increase with TDS suggesting evaporation is the dominant driver of solute evolution. Among the sites sampled monthly, U1 is a HCO3>Ca>Mg>SO4 spring with the TDS of 9 meq/L. Sites P5 and P7 are part of a coastal wetland system of Cl>Na>Mg~SO4>Ca>HCO3 composition with TDS of 1700meq/L and 270meq/L, respectively. Water temperature varies from 12 to 30°C in P5, 13 to 33°C in P7 and 16 to 30°C in U1. At all 3 sites, the highest temperature occurred in July. The longest animals have the highest shell Ca content, and size is related to water chemistry. Both males and females are smaller in high TDS waters, and in particular, in high SO4 waters. The shell-water oxygen isotope fractionation decreases drastically at higher TDS. Cation composition of the shells show a trend of decreasing values of Mg/Cashell/Mg/Cawater with TDS as might be expected since ostracodes form low-Mg calcite shells. This trend is also observed between Sr/Cashell/Sr/ Cawater and TDS albeit with a large scatter. The changes in the population structure suggest that in U1, moulting from A-1 to A occur throughout the year whereas in P5 and P7, this moulting process is restricted to spring and fall months. This is corroborated by oxygen isotope values and Mg/Ca and Sr/Ca of adult and juvenile shells from all 3 sites: observed changes in U1 shells parallel the changes in U1 water; for P5 and P7, no such parallel is observed probably because A-1 juveniles live longer and do not moult until favorable conditions occur, and all the adults collected over the course of the year had calcified during a narrower time window. This is in agreement with the trend observed in the whole dataset.

Impact of moisture source regions on the isotopic composition of precipitation events at high-mountain continental site Kasprowy Wierch, southern Poland

NASA Astrophysics Data System (ADS)

Rozanski, Kazimierz; Chmura, Lukasz; Dulinski, Marek

2016-04-01

Five-year record of deuterium and oxygen-18 isotope composition of precipitation events collected on top of the Kasprowy Wierch mountain (49° 14'N, 19° 59'E, 1989 m a.s.l.) located in north-western High Tatra mountain ridge, southern Poland, is presented and discussed. In total 670 precipitation samples have been collected and analysed. Stable isotope composition of the analysed precipitation events varied in a wide range, from -2.9 to -26.6‰ for δ18O and from -7 to -195 ‰ for δ2H. The local meteoric water line (LMWL) defined by single events data (δ2H=(7.86±0.05)δ18O+(12.9±0.6) deviate significantly from the analogous line defined by monthly composite precipitation data available for IAEA/GNIP station Krakow-Balice (50o04'N, 19o55'E, 220 m a.s.l.), located ca. 100 km north of Kasprowy Wierch ((δ2H=(7.82±0.11)δ18O+(6.9±1.1). While slopes of those two LMWLs are statistically indistinguishable, the intercept of Kasprowy Wierch line is almost two times higher that that characterizing Krakow monthly precipitation. This is well-documented effect associated with much higher elevation of Kasprowy Wierch sampling site when compared to Krakow. The isotope data for Kasprowy Wierch correlate significantly with air temperature, with the slope of the regression line being equal 0.35±0.02 ‰oC for δ18O, whereas no significant correlation with precipitation amount could be established. The impact of moisture source regions on the isotopic composition of precipitation events collected at Kasprowy Wierch site was analysed using HYSPLITE back trajectory model. Five-days back trajectories were calculated for all analysed precipitation events and seasonal maps of trajectory distribution were produced. They illustrate changes in the prevailing transport patterns of air masses bringing precipitation to the sampling site. Back trajectories for the events yielding extreme isotopic composition of precipitation collected at Kasprowy Wierch were analyzed in detail. Acknowledgements. Financial support of this work through Ministry of Science and Higher Education (statutory funds of AGH University od Science and Technology, project No.11.11.220.01) is kindly acknowledged.

Middle-Upper Permian carbon isotope stratigraphy at Chaotian, South China: Pre-extinction multiple upwelling of oxygen-depleted water onto continental shelf

NASA Astrophysics Data System (ADS)

Saitoh, Masafumi; Isozaki, Yukio; Ueno, Yuichiro; Yoshida, Naohiro; Yao, Jianxin; Ji, Zhansheng

2013-05-01

In order to examine the causal relationships between the carbon cycle in a shallow euphotic zone and the environmental changes in a relatively deep disphotic zone at the end-Guadalupian (Middle Permian), isotopic compositions of carbonate carbon (δ13Ccarb) of the Guadalupian-Lopingian (Upper Permian) rocks were analyzed in the Chaotian section in northern Sichuan, South China. By analyzing exceptionally fresh drill core samples, a continuous chemostratigraphic record was newly obtained. The ca. 65 m-thick analyzed carbonate rocks at Chaotian comprise three stratigraphic units, i.e., the Limestone Unit of the Guadalupian Maokou Formation, the Mudstone Unit of the Maokou Formation, and the lower part of the Wuchiapingian (Lower Lopingian) Wujiaping Formation, in ascending order. The Limestone Unit of the Maokou Formation is characterized by almost constant δ13Ccarb values of ca. +4‰ followed by an abrupt drop for 7‰ to -3‰ in the topmost part of the unit. In the Mudstone Unit of the Maokou Formation, the δ13Ccarb values are rather constant around +2‰, although distinct three isotopic negative excursions for 3‰ from ca. +2 to -1‰ occurred in the upper part of the unit. In the lower part of the Wujiaping Formation, the δ13Ccarb values monotonously increase for 5‰ from ca. 0 to +5‰. The present data newly demonstrated four isotopic negative excursions in the topmost part of the Maokou Formation in the Capitanian (Late Guadalupian) at Chaotian. It is noteworthy that these negative excursions are in accordance with the emergence of an oxygen-depleted condition on the relatively deep disphotic slope/basin on the basis of litho- and bio-facies characteristics. They suggest multiple upwelling of oxygen-depleted waters with dissolved inorganic carbon of relatively low carbon isotope values along the continental margin, from the deeper disphotic slope/basin to the shallower euphotic shelf, slightly before the end-Guadalupian extinction. Although the negative excursions at Chaotian are apparently correlated with the previously proposed large negative excursion in the middle Capitanian in South China, the age difference according to the biostratigraphic constraints clearly exclude this interpretation. The isotopic negative excursions at Chaotian are unique and no similar isotopic signal in the same period has been reported elsewhere. The multiple upwelling of oxygen-depleted waters onto the euphotic shelf may have represented local phenomena that occurred solely around northwestern South China.

Cumulate xenoliths from St. Vincent, Lesser Antilles Island Arc: a window into upper crustal differentiation of mantle-derived basalts

NASA Astrophysics Data System (ADS)

Tollan, P. M. E.; Bindeman, I.; Blundy, J. D.

2012-02-01

In order to shed light on upper crustal differentiation of mantle-derived basaltic magmas in a subduction zone setting, we have determined the mineral chemistry and oxygen and hydrogen isotope composition of individual cumulus minerals in plutonic blocks from St. Vincent, Lesser Antilles. Plutonic rock types display great variation in mineralogy, from olivine-gabbros to troctolites and hornblendites, with a corresponding variety of cumulate textures. Mineral compositions differ from those in erupted basaltic lavas from St. Vincent and in published high-pressure (4-10 kb) experimental run products of a St. Vincent high-Mg basalt in having higher An plagioclase coexisting with lower Fo olivine. The oxygen isotope compositions (δ18O) of cumulus olivine (4.89-5.18‰), plagioclase (5.84-6.28‰), clinopyroxene (5.17-5.47‰) and hornblende (5.48-5.61‰) and hydrogen isotope composition of hornblende (δD = -35.5 to -49.9‰) are all consistent with closed system magmatic differentiation of a mantle-derived basaltic melt. We employed a number of modelling exercises to constrain the origin of the chemical and isotopic compositions reported. δ18OOlivine is up to 0.2‰ higher than modelled values for closed system fractional crystallisation of a primary melt. We attribute this to isotopic disequilibria between cumulus minerals crystallising at different temperatures, with equilibration retarded by slow oxygen diffusion in olivine during prolonged crustal storage. We used melt inclusion and plagioclase compositions to determine parental magmatic water contents (water saturated, 4.6 ± 0.5 wt% H2O) and crystallisation pressures (173 ± 50 MPa). Applying these values to previously reported basaltic and basaltic andesite lava compositions, we can reproduce the cumulus plagioclase and olivine compositions and their associated trend. We conclude that differentiation of primitive hydrous basalts on St. Vincent involves crystallisation of olivine and Cr-rich spinel at depth within the crust, lowering MgO and Cr2O3 and raising Al2O3 and CaO of residual melt due to suppression of plagioclase. Low density, hydrous basaltic and basaltic andesite melts then ascend rapidly through the crust, stalling at shallow depth upon water saturation where crystallisation of the chemically distinct cumulus phases observed in this study can occur. Deposited crystals armour the shallow magma chamber where oxygen isotope equilibration between minerals is slowly approached, before remobilisation and entrainment by later injections of magma.

Isotopically exchangeable organic hydrogen in coal relates to thermal maturity and maceral composition

USGS Publications Warehouse

Mastalerz, Maria; Schimmelmann, A.

2002-01-01

Hydrogen isotopic exchangeability (Hex) and ??Dn values of non-exchangeable organic hydrogen were investigated in coal kerogens ranging in rank from lignite to graphite. The relative abundance of Hex is highest in lignite with about 18% of total hydrogen being exchangeable, and decreases to around 2.5% in coals with Ro of 1.7 to ca. 5.7%. At Still higher rank (Ro > 6%), Hex increases slightly, although the abundance of total hydrogen decreases. ??Dn is influenced by original biochemical D/H ratios and by thermal maturation in contact with water. Therefore, ??Dn does not show an overall consistent trend with maturity. ?? 2002 Elsevier Science Ltd. All rights reserved.

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.

Calcium Isotope Fractionation during Carbonate Weathering in the Northern Guangdong, South China

NASA Astrophysics Data System (ADS)

Liu, F.; Mao, G.; Wei, G.; Zhang, Z.

2017-12-01

CO2 is consumed during the weathering of carbonates, whereas carbonates are precipitated rapidly in the oceans, which are pivotal to modulate atmospheric CO2, oceanic pH and climate. Calcium carbonate in limestone is one of the largest reservoirs of carbon at the Earth's surface, so calcium is an important element that links the lithosphere, hydrosphere, biosphere, and the atmosphere. Compared with silicate rocks, carbonate rocks have more rapid rates of physical and chemical erosions, so the carbonate weathering will respond more quickly to the climatic changes. In the southeast of China, enormous of carbonate rocks are widely distributed. Due to the influence of the subtropical monsoon climate, the rocks experienced strong chemical weathering and pedogenic process, resulting in red weathering crust of carbonate rocks. This type of weathering crust is geochemistry-sensitive and ecology-vulnerable, which can provide important insights into the recycle of supergene geochemistry in the karst areas. In this study, we report calcium isotopic compositions of saprolites from a weathering profile developed on argillaceous carbonate rocks in northern Guangdong, South China. The acid-leachable fraction, which was extracted by 1N hydrochloride acid, showed limited variation of δ44/40Ca(NIST 915a) spanning from 0.55 ± 0.06‰ (2SD) to 0.72 ± 0.05‰ (2SD) despite CaO content ranging from 0.01 wt.% to 45.7 wt.%, implying that Ca isotope didn't fractionate much which may due to the congruent dissolution of limestone minerals. In contrast, radiogenic 87Sr/86Sr ratios of the whole rocks changed with depth from 0.710086 ± 6 (2SE) at the base rock to 0.722164± 8 (2SE) at the top-soil, which are possibly attributed to the mixing effect between carbonate and silicate fractions. Sr is an analogue for Ca due to its similar ionic size and charge; however, these two systems can differ in certain respects. The coupled study of Ca and Sr will be helpful to verify sources of Ca and the global Ca and C cycles.

Geochronological, geochemical and Sr-Nd-Hf isotopic constraints on the petrogenesis of Late Cretaceous A-type granites from the Sibumasu Block, Southern Myanmar, SE Asia

NASA Astrophysics Data System (ADS)

Jiang, Hai; Li, Wen-Qian; Jiang, Shao-Yong; Wang, He; Wei, Xiao-Peng

2017-01-01

The Late Cretaceous to Paleogene granitoids occur widespread in the Sibumasu block within Myanmar (SE Asia), which show a close association with tin-tungsten mineralization. However, the precise timing, petrogenesis and tectonic significance of these granitoids are poorly constrained so far. In this study, we present a detailed study on geochronology, elemental and Sr-Nd-Hf isotopic geochemistry for the Hermyingyi and Taungphila granites in southern Myanmar, with the aim of determining their petrogenesis and tectonic implications. LA-ICP-MS U-Pb dating of zircon grains from the two granites yield ages of 69-70 Ma, indicating a Late Cretaceous magmatic event. These granitic rocks are weakly peraluminous and belong to the high-K calc-alkaline series. They are both characterized by high SiO2, K2O + Na2O, FeOT/(FeOT + MgO) and Ga/Al ratios and low Al2O3, CaO, MgO, P2O5 and TiO2 contents, enriched in Rb, Th, U and Y, but depleted in Ba, Sr, P, and Eu, suggesting an A-type granite affinity. Moreover, they display prominent tetrad REE patterns and non-CHARAC trace element behavior, which are common in late magmatic differentiates with strong hydrothermal interaction or deuteric alteration. The granites belong to A2-type and probably formed at a high temperature and anhydrous condition. They have zircon εHf(t) values from - 12.4 to - 10.0 and whole-rock εNd(t) values from - 11.3 to - 10.6, with Paleoproterozoic TDM2 ages (1741-1922 Ma) for both Hf and Nd isotopes. Geochemical and isotopic data suggest that these A-type granites were derived from partial melting of the Paleoproterozoic continental crust dominated by metaigneous rocks with tonalitic to granodioritic compositions, without significant input of mantle-derived magma and followed by subsequent fractional crystallization. By integrating all available data for the regional tectonic evolution in SE Asia and adjacent regions, we attribute the formation of the Late Cretaceous A-type granites to a back-arc extension in the hinterland behind the subduction zone, which is induced by the rollback of the flat Neo-Tethyan subducting slab around ca. 70 Ma. Table 2 Major (wt.%) and trace element (ppm) compositions from the Hermyingyi and Taungphila granites. LOI is loss on ignition; A/CNK = Al2O3/(CaO + Na2O + K2O) (molar ratio); FeOT = FeO + Fe2O3 × 0.8998. Eu/Eu* is a measure of the Eu anomaly when compare to Sm and Gd. Eu/Eu* = EuN/[(SmN) × (GdN)]0.5. Table 3 Sr-Nd isotopic compositions of the Hermyingyi and Taungphila granites. Table 4 Hf isotopic compositions of zircons from the Hermyingyi and Taungphila granites. (176Lu/177Hf)CHUR = 0.0032, (176Hf/177Hf)CHUR,0 = 0.282772 (Blichert-Toft and Albarède, 1997); (176Lu/177Hf)DM = 0.0384, (176Hf/177Hf)DM,0 = 0.28325 (Griffin et al., 2000); λ = 1.867 × 10- 11/year (Soderlund et al., 2004).

Dissolution of barite for the analysis of strontium isotopes and other chemical and isotopic variations using aqueous sodium carbonate

USGS Publications Warehouse

Breit, G.N.; Simmons, E.C.; Goldhaber, M.B.

1985-01-01

A simple procedure for preparing barite samples for chemical and isotopic analysis is described. Sulfate ion, in barite, in the presence of high concentrations of aqueous sodium carbonate, is replaced by carbonate. This replacement forms insoluble carbonates with the cations commonly in barite: Ba, Sr, Ca and Pb. Sulfate is released into the solution by the carbonate replacement and is separated by filtration. The aqueous sulfate can then be reprecipitated for analysis of the sulfur and oxygen isotopes. The cations in the carbonate phase can be dissolved by acidifying the solid residue. Sr can be separated from the solution for Sr isotope analysis by ion-exchange chromatography. The sodium carbonate used contains amounts of Sr which will affect almost all barite 87Sr 86Sr ratios by less than 0.00001 at 1.95?? of the mean. The procedure is preferred over other techniques used for preparing barite samples for the determination of 87Sr 86Sr ratios because it is simple, rapid and enables simultaneous determination of many compositional parameters on the same material. ?? 1985.

High Precision Low-blank Lithium Isotope Ratios in Forams.

NASA Astrophysics Data System (ADS)

Misra, S.; Froelich, P. N.

2007-12-01

We present a high precision (±1‰, 2σ) low blank (<500 fg/ml) method for Li isotope measurements of forams using <2 ng of Li by single collector Quad ICP-MS (Agilent 7500cs). The Li isotope ratio of seawater (δ7Li) recorded in planktonic forams has the potential to constrain the evolution of seawater chemistry and elucidate the factors driving variations of oceanic mass balances linked to the continental and sea floor/hydrothermal silica cycles. In addition a δ7Li record of seawater will complement other long-term recorders of seawater chemistry such as Sr, Os and S isotopes. Li isotope measurements of forams are limited by several factors: low Li concentrations in forams (1-2 ppm), instrument-induced fractionation and mass bias effects, matrix effects, high Li blanks and incomplete recovery of Li during column separation. Modest concentrations of alkali and alkaline earth elements in the matrix result in variable mass bias in measured Li isotope ratios. Even worse, Li strongly fractionates during chromatographic clean-up to remove Na+, Ca2+ and Mg2+, from +100‰ in the leading edge to - 100‰ in the trailing edge of elution peaks (Urey 1938). Consequently, miniscule incomplete recoveries of Li during chromatographic separations can result in large unrecognized isotope fractionation of eluents. Large mass-dependent fractionation caused by a difference of 17% in mass between 6Li and 7Li, makes Li a powerful tracer of geochemical processes, but also promotes large and difficult-to-fix isotope fractionations during laboratory chemical processing. Matrix effects of Na & Ca and of column chromatography on Li isotope ratios were investigated using artificial Li solutions representative of foram compositions (matrix matching). Li/Ca and Li/Na ratios in cleaned forams are 10 μmol/mol and 3 mmol/mol respectively. An ICP-MS tolerance limit of 20 ppb for Na and 20 μM for Ca was established, much higher tolerances than by TIMS. A single step chromatographic method to quantitatively separate Li from matrix elements using both small volume resin (3.4 meq/2ml AG50W-X8) and acid (6 ml of 0.5N HCl) was developed. Our low blank (<0.5 pg/ml) and high yield (>99.99%) column method minimizes errors in measured Li isotope ratios associated with incomplete column recovery and presence of matrix elements. High sensitivity and precision achieved with a 7500cs using cold plasma (600W), soft extraction and peak jumping coupled with very low sample to blank ratios enables high precision (±1‰, 2σ) statistically significant Li isotope measurements using very small mass of Li (0.8 ng). The development of this technique makes possible good quality Li isotope measurements from samples that are mass limited for Li, i.e., reasonable number of picked forams. This will enable us to test interferences regarding chemical cleaning and species effects in planktonic forams along the road toward creating a δ7Li record of seawater for the Cenozoic.

A young Moon-forming giant impact at 70-110 million years accompanied by late-stage mixing, core formation and degassing of the Earth.

PubMed

Halliday, Alex N

2008-11-28

New W isotope data for lunar metals demonstrate that the Moon formed late in isotopic equilibrium with the bulk silicate Earth (BSE). On this basis, lunar Sr isotope data are used to define the former composition of the Earth and hence the Rb-Sr age of the Moon, which is 4.48+/-0.02Ga, or 70-110Ma (million years) after the start of the Solar System. This age is significantly later than had been deduced from W isotopes based on model assumptions or isotopic effects now known to be cosmogenic. The Sr age is in excellent agreement with earlier estimates based on the time of lunar Pb loss and the age of the early lunar crust (4.46+/-0.04Ga). Similar ages for the BSE are recorded by xenon and lead-lead, providing evidence of catastrophic terrestrial degassing, atmospheric blow-off and significant late core formation accompanying the ca 100Ma giant impact. Agreement between the age of the Moon based on the Earth's Rb/Sr and the lead-lead age of the Moon is consistent with no major losses of moderately volatile elements from the Earth during the giant impact. The W isotopic composition of the BSE can be explained by end member models of (i) gradual accretion with a mean life of roughly 35Ma or (ii) rapid growth with a mean life of roughly 10Ma, followed by a significant hiatus prior to the giant impact. The former assumes that approximately 60 per cent of the incoming metal from impactors is added directly to the core during accretion. The latter includes complete mixing of all the impactor material into the BSE during accretion. The identical W isotopic composition of the Moon and the BSE limits the amount of material that can be added as a late veneer to the Earth after the giant impact to less than 0.3+/-0.3 per cent of ordinary chondrite or less than 0.5+/-0.6 per cent CI carbonaceous chondrite based on their known W isotopic compositions. Neither of these on their own is sufficient to explain the inventories of both refractory siderophiles such as platinum group elements and rhenium, and volatiles such as sulphur, carbon and water.

Segregation of Calcium Isotopes in the Atmospheres of CP Stars as a Consequence of Light-Induced Drift

NASA Astrophysics Data System (ADS)

Parkhomenko, A. I.; Shalagin, A. M.

2018-06-01

A mechanism for the segregation of calcium isotopes in the atmospheres of chemically peculiar (CP) stars due to light-induced drift (LID) of singly charged 48Ca+ ions is discussed. One peculiarity of Ca+ is that an adequate description of the effect of LID requires taking into account several energy levels of Ca+, and thus several pairs of relative differences ( ν i - ν k )/ ν i for the transport frequencies for collisions of levels i and k with neutral atoms (hydrogen, helium). The known real (calculated ab initio) interaction potentials are used to numerically calculate the factors ( ν i - ν k )/ ν i for several states of Ca+ for collisions with H and He atoms. These computations show that, at the temperatures characteristic of the atmospheres of CP stars, T = 6600-12 000 K, fairly high values are obtained for Ca+ ions, ( ν i - ν k )/ ν i ≈ 0.4-0.6. Simple, transparent computations demonstrate that the LID rates of Ca+ ions in the atmospheres of cool CP stars ( T eff = 6600 K) exceed the drift rate due to light pressure by two orders of magnitude. The LID is directed upward in the stellar atmosphere, and the heavy isotope 48Ca is pushed into upper layers of the atmosphere. This can explain the observed predominance of the heavy isotope 48Ca in the upper atmospheric layers of CP stars; according to the radiative-diffusion theory, the action of light pressure alone (in the absence of LID) would lead to sinking of the isotope 48Ca deeper into stellar atmosphere, following the lighter main isotope 40Ca. The 48Ca+ LIDrate decreases and its drift rate due to light pressure increases with growth of the effective temperatures in the atmospheres of CP stars. The manifestations of LID and light pressure are roughly comparable in the atmospheres of CP stars with effective temperatures near T eff = 9500 K.

Preparative chromatography for specific δ13C isotopic analysis of individual carbohydrates in environmental samples

NASA Astrophysics Data System (ADS)

Nouara, Amel; Panagiotopoulos, Christos; Balesdent, Jérôme; Sempéré, Richard

2017-04-01

Carbohydrates are among the most abundant organic molecules on the Earth and are present in all geochemical systems. Despite their high abundance in the environment, very few studies assessed their origin using molecular carbohydrate isotopic analyses. In contrast with bulk stable isotope analysis (BSIA), which gives the isotopic signature of the entire sample without any specification about its chemical composition, compound specific 13C isotopic analysis of individual sugars (CSIA) offers valuable information about the origin of single molecules. Previous investigations used gas or liquid chromatography coupled with isotope ratio mass spectroscopy (GC-IRMS; HPLC-IRMS) for CSIA of sugars however the former requires δ13C corrections due to the carbon added to the sugar (derivatization) while the later does not provide always adequate separations among monosaccharides. Here we used cation preparative chromatography (Ca2+, Pb2+ and Na+) with refractive index detection in order to produce pure monosaccharide targets for subsequent EA-IRMS analyses. Milli-Q water was used as eluant at a flow rate 0.6 ml min-1. In general, three successive purifications (Ca2+, Pb2+, Ca2+) were sufficient to produce pure compounds. Pure monosaccharides were compared with authentic monosaccharide standards using 1H NMR and/or mass spectroscopy. The detection limit of our technique was about 1µM/sugar with a precision of 10% (n=6). Blanks run with Milli-Q water after three successive purifications resulted in carbon content of 0.13 to 2.77 µgC per collected sugar. These values are much lower than the minimum required amount (5 µgC) of the EA-IRSMS system with a precision of ± 0.35 ‰. Application of our method to environmental samples resulted in δ13C values of glucose, fructose, and levoglucosan in the range of -24 to -26 ‰ (PM10 atmospheric particles), and -15‰ to -22 ‰ for arabinose, glucose, and xylose (marine high molecular dissolved organic matter). These results fall in the range of previous reported values for terrestrial and aquatic ecosystems.

Shell architecture, element composition, and stable isotope signature of the giant deep-sea oyster Neopycnodonte zibrowii sp. n. from the NE Atlantic

NASA Astrophysics Data System (ADS)

Wisshak, Max; López Correa, Matthias; Gofas, Serge; Salas, Carmen; Taviani, Marco; Jakobsen, Joachim; Freiwald, André

2009-03-01

A conspicuous new deep-sea oyster, Neopycnodonte zibrowii sp. n., is described from the Azores Archipelago, where it thrives in 420 to >500 m water depth in high densities concealed underneath overhangs. The new species reaches a relatively large size, which may exceed 20 cm, and is characterised by a very unusual hinge line morphology, straight without a bulge of the resilium. It is compared to the extant Indo-Pacific Empressostrea kostini Huber and Lorenz, 2007 and to the cosmopolitan Neopycnodonte cochlear (Poli, 1791), which has a broadly sympatric distribution at shallower depths in the Azores and Bay of Biscay. Radiocarbon dating reveals that individuals reach an impressive lifespan of one to more than five centuries, placing them among the longest-lived molluscs known to date. They often grow on top of each other, forming stacks that resemble dish piles—an effective measure to optimise shell stability with minimal biomineralisation effort, but with the drawback of increased bioerosion ultimately leading to detachment. Three microstructure types are developed in N. zibrowii: (1) the cross-foliated, calcitic, dorsal to central endostracum and aragonitic ligostracum, (2) the porous vesicular structure of the calcitic ventral endostracum, and (3) the simple prismatic aragonitic myostracum. Foliated and vesicular shell portions show sub-millimetre-scale first-order increments delineated by conchiolin-rich growth breaks (interpreted as reproductive cyclicity), and less distinct second-order increments (interpreted as annual in nature). This pattern is clearly reflected by the elemental composition with the primary growth breaks lacking Ca and Sr but including Mg and S as organic matrix constituents. The second-order increments within the calcite are mirrored by moderately co-varying Mg/Ca and S/Ca fluctuations at stable Sr concentrations, reflecting varying proportions of organic matrix. Dorsal and central endostracum transects reveal a low inter-valve, but considerable inter-specimen variability with high Mg/Ca molar ratios and fluctuations (22.5±17.6 mmol/mol), low Sr/Ca values (0.2±0.1 mmol/mol), and a typical to high S/Ca content (6.9±2.2 mmol/mol), when compared to other calcitic bivalves. Unlike short-lived, shallow-water oysters, N. zibrowii thrives under very stable environmental conditions. Minimal temperature fluctuations and stable open marine salinity provide an optimal basis to recognise biological fractionation processes. Strong Mg/Ca fluctuations indicate a physiological control related to metabolism and biomineralisation, prohibiting the use of this ratio as a temperature or ocean chemistry proxy. Low Sr/Ca ratios indicate rather constant and low long-term accretion rates, while short-scale fluctuations may be attributed to short-term variations in growth rate and Mg incorporation. Oxygen isotopes yield a considerable spread of 1.8‰ with a mean of 2.0±0.3‰ δ18O V-PDB, and low correlation between different contemporaneous parts of the shell and between specimens. These values surprisingly exceed expected equilibrium conditions, calculated from in situ temperature data (annual mean 12.3±0.3 °C) and seawater isotopic composition (0.5±0.1‰ δ18O SMOW), by 0.5‰ on average. Such positively shifting vital effects, previously reported for limpets and barnacles, are often overlooked in high-temperature and high-amplitude settings and may be more common than is currently believed. Carbon isotopes range from 0.2 to 3.5‰ δ13C V-PDB (mean 1.8±0.7‰) and show an ontogenetic decrease, but may incorporate an environmental signal in adult portions, indicated by a strong correspondence of peaks between specimens. This signal is likely driven by a complex interplay of different factors, such as primary production, current-based food supply and metabolism.

Osmium Isotopic Evolution of the Mantle Sources of Precambrian Ultramafic Rocks

NASA Astrophysics Data System (ADS)

Gangopadhyay, A.; Walker, R. J.

2006-12-01

The Os isotopic composition of the modern mantle, as recorded collectively by ocean island basalts, mid- oceanic ridge basalts (MORB) and abyssal peridotites, is evidently highly heterogeneous (γ Os(I) ranging from <-10 to >+25). One important question, therefore, is how and when the Earth's mantle developed such large-scale Os isotopic heterogeneities. Previous Os isotopic studies of ancient ultramafic systems, including komatiites and picrites, have shown that the Os isotopic heterogeneity of the terrestrial mantle can be traced as far back as the late-Archean (~ 2.7-2.8 Ga). This observation is based on the initial Os isotopic ratios obtained for the mantle sources of some of the ancient ultramafic rocks determined through analyses of numerous Os-rich whole-rock and/or mineral samples. In some cases, the closed-system behavior of these ancient ultramafic rocks was demonstrated via the generation of isochrons of precise ages, consistent with those obtained from other radiogenic isotopic systems. Thus, a compilation of the published initial ^{187}Os/^{188}Os ratios reported for the mantle sources of komatiitic and picritic rocks is now possible that covers a large range of geologic time spanning from the Mesozoic (ca. 89 Ma Gorgona komatiites) to the Mid-Archean (e.g., ca. 3.3 Ga Commondale komatiites), which provides a comprehensive picture of the Os isotopic evolution of their mantle sources through geologic time. Several Precambrian komatiite/picrite systems are characterized by suprachondritic initial ^{187}Os/^{188}Os ratios (e.g., Belingwe, Kostomuksha, Pechenga). Such long-term enrichments in ^{187}Os of the mantle sources for these rocks may be explained via recycling of old mafic oceanic crust or incorporation of putative suprachondritic outer core materials entrained into their mantle sources. The relative importance of the two processes for some modern mantle-derived systems (e.g., Hawaiian picrites) is an issue of substantial debate. Importantly, however, the high-precision initial Os isotopic compositions of the majority of ultramafic systems show strikingly uniform initial ^{187}Os/^{188}Os ratios, consistent with their derivation from sources that had Os isotopic evolution trajectory very similar to that of carbonaceous chondrites. In addition, the Os isotopic evolution trajectories of the mantle sources for most komatiites show resolvably lower average Re/Os than that estimated for the Primitive Upper Mantle (PUM), yet significantly higher than that obtained in some estimates for the modern convecting upper mantle, as determined via analyses of abyssal peridotites. One possibility is that most of the komatiites sample mantle sources that are unique relative to the sources of abyssal peridotites and MORB. Previous arguments that komatiites originate via large extents of partial melting of relatively deep upper mantle, or even lower mantle materials could, therefore, implicate a source that is different from the convecting upper mantle. If so, this source is remarkably uniform in its long-term Re/Os, and it shows moderate depletion in Re relative to the PUM. Alternatively, if the komatiites are generated within the convective upper mantle through relatively large extents of partial melting, they may provide a better estimate of the Os isotopic composition of the convective upper mantle than that obtained via analyses of MORB, abyssal peridotites and ophiolites.

Oxygen-18 isotope of breath CO2 linking to erythrocytes carbonic anhydrase activity: a biomarker for pre-diabetes and type 2 diabetes

PubMed Central

Ghosh, Chiranjit; Banik, Gourab D.; Maity, Abhijit; Som, Suman; Chakraborty, Arpita; Selvan, Chitra; Ghosh, Shibendu; Chowdhury, Subhankar; Pradhan, Manik

2015-01-01

Carbonic anhydrase (CA), a well-characterized metalloenzyme, is associated with oxygen-18 ( 18O)-isotopic fractionations of CO2. To investigate how CA activity links the 18O of breath CO2 to pre-diabetes (PD) and type 2 diabetes (T2D) during metabolism, we studied pre- and post-dose CA activities in erythrocytes with simultaneous monitoring of 18O/ 16O-isotope ratios of breath CO2 and thereafter elucidated potential metabolic pathways underlying CA alteration in the pathogenesis of T2D. Here we show that the post-dose CA activity in both T2D and PD was markedly enhanced, whereas the non-diabetic controls (NDC) exhibited a considerable reduction in post-dose CA activity when compared with their basal CA activities. However, T2D and PD exhibited isotopic enrichments of 18O in breath CO2, while a marked depletion of 18O in CO2 was manifested in NDC. Thus, the isotopic enrichments and depletions of 18O in breath CO2 were well correlated with the changes in CA activities for controls, PD and T2D. Our findings suggest the changes in CA activities in erythrocytes may contribute to the pathogenesis of T2D and the breath C 18O 16O regulated by the CA activity as a potential biomarker for non-invasive assessment of T2D, and thus may open a new method for treating T2D. PMID:25633556

Isotopic and Trace Element Compositions of Antarctic Micrometeorites and Comparison with IDPs

NASA Astrophysics Data System (ADS)

Stadermann, F. J.; Olinger, C. T.

1992-07-01

Antarctic micrometeorites (AMMs) show resemblances and differences to both stratospheric interplanetary dust particles (IDPs) and chondritic meteorites, but the exact nature of this relationship has yet to be established. We measured Ne, H, C, and N isotopic compositions, as well as trace element abundances in several AMMs in order to compare the results to similar measurements of IDPs (Stadermann, 1991). AMMs for this study were collected near Cap-Prudhomme (Maurette et al., 1989), and optically selected (Olinger et al., 1990). Noble gases of 23 selected AMMs were extracted through laser vaporization. Nine of these particles contained implanted solar Ne and one showed a clear signature from spallogenic Ne, confirming their extraterrestrial origin. We selected fragments from 6 of these particles, plus 2 containing apparent Ne excess and one with a roughly chondritic bulk chemistry but immeasurably low Ne, for further analyses. Secondary ion mass spectrometry (SIMS) was used to measure the H, C, and N isotopic compositions. These measurements turned out to be difficult, since the concentrations of H and C in the analyzed samples were significantly lower than in IDPs. The low concentration of C also affected the N isotopic measurements because N could only be measured as CN-. We were able to measure H in 9, as well as C and N in 3 AMMs. All measurements yielded isotopically normal results. Previous determinations of the O isotopic compositions of the same samples (Virag, pers. comm.) also gave no indication of isotopic anomalies. These results are significantly different from measurements of IDPs, where isotopic anomalies in H and N were found in roughly 1/2 and 1/3 of the particles, respectively. SIMS was also used to measure the rare earth and trace element abundances in up to 4 different fragments of 6 AMMs. Although most particles had roughly chondritic abundances, anomalous concentrations were found for Ca, Li, Co, Ni, and Ba. Significant Ca depletions up to 0.03 x C1 were observed in 5 out of 6 particles. This effect is well known from IDPs but nonetheless little understood. Enrichments up to 10 x C1 in Li and up to 100 x C1 in Ba were detected in 4 particles each. The Ba enrichment in AMMs has been observed before and can most likely be attributed to terrestrial contamination (Maurette et al., 1992). The origin of the unusual Li enrichment is unknown. Ni was depleted in all analyzed particles and was strongly correlated with Co, whose depletions relative to C1 were always smaller than for Ni. In the particle with the largest Ni-Co depletion, a melted sphere, this effect was accompanied by an Fe depletion. The Fe/Si, Co/Si and Ni/Si ratios relative to C1 were (0.4, 0.06, 0.02). Similar correlated depletions of Fe, Co, and Ni were also found in 2 out of 13 IDPs with otherwise chondritic abundances (Stadermann, 1991). The ratios of their Fe, Co, Ni depletions were (0.2, 0.07, 0.01) and (0.3, 0.03, 0.01), respectively. Interestingly, these 2 IDPs also contained H with isotopically normal composition and C concentrations that were too low for C and N isotopic measurements. One of these particles was a melted spherule. All these similarities suggest that some AMMs and some IDPs may have close relationships, although AMMs and IDPs in general do not represent the same class of extraterrestrial material. Maurette M. et al. (1989) Lunar Planet. Sci. 20, 644-645. Maurette M. et al. (1992) Lunar Planet. Sci. 23, 859-860. Olinger C.T. et al. (1990) Earth Planet. Sci. Lett. 100, 77-93. Stadermann F.J. (1991) Lunar Planet. Sci. 22, 1311-1312.

Deciphering the Boron Proxy Records of the Paleocene-Eocene Thermal Maximum

NASA Astrophysics Data System (ADS)

Hoenisch, B.; Haynes, L.; Harper, D. T.; Penman, D. E.; Holland, K.; Rosenthal, Y.; Zachos, J. C.

2016-12-01

Rapid surface ocean acidification at the PETM has been documented by pronounced decreases in the boron isotope and B/Ca proxies measured in surface dwelling planktic foraminifera (Babila et al., 2016; Penman et al., 2014). However, translating these geochemical signatures to past seawater carbonate chemistry is challenging due to the different-from-modern elemental and isotopic composition of seawater, in addition to the lack of constraints on vital effects in foraminifer species that are now extinct. While the pH decrease can be reasonably quantified from boron isotopes, the application of modern laboratory calibrations to translate the B/Ca signal yields unfeasible estimates, thus raising questions about how well we understand fundamental proxy systematics. Here we present a possible solution to this conundrum from laboratory culture experiments performed under simulated Paleocene seawater conditions, with lower [B] and [Mg], higher [Ca] and across a range of dissolved inorganic carbon and pH. These experiments suggest that raising DIC in addition to acidification amplifies the B/Ca decrease recorded in planktic foraminifera shells, thus providing an opportunity to deconvolve the B/Ca record into pH and DIC signals. Using the boron proxy records in ODP 1209 from Shatsky Rise in the Pacific Ocean as a case study, we will perform a series of sensitivity studies to better constrain the carbon perturbation at the PETM, and the long-term evolution of surface ocean chemistry from the Paleocene into the Eocene. Our results will be compared to LOSCAR model estimates of different carbon input scenarios at the PETM. Babila, T.L., Rosenthal, Y., Wright, J.D. and Miller, K.G. (2016) A continental shelf perspective of ocean acidification and temperature evolution during the Paleocene-Eocene Thermal Maximum. Geology 44, 275-278. Penman, D.E., Hönisch, B., Zeebe, R.E., Thomas, E. and Zachos, J.C. (2014) Rapid and sustained surface ocean acidification during the Paleocene-Eocene Thermal Maximum. Paleoceanography 29, 2014PA002621.

North Pacific barium isotope distributions illustrate importance of ocean mixing in controlling barium distributions despite weak regional circulation

NASA Astrophysics Data System (ADS)

Geyman, B.; Auro, M. E. E.; LaVigne, M.; Ptacek, J. L.; Horner, T. J.

2016-12-01

The dissolved behavior of barium in the ocean exhibits a `refractory' nutrient-type profile similar to that of silicon, which has led to the use of Ba as a proxy for paleo-productivity and carbon cycling. Marine barium cycling appears to be controlled by the precipitation of micron-scale barite crystals in the mesopelagic and their subsequent dissolution throughout the water column, which has been shown to impart an isotopic signature that may itself harbor information about ocean circulation and export production. However, the utility of Ba-based proxies in chemical and paleoceanography relies on a sound understanding of the processes governing marine barium distributions, which remain unresolved. Here, we report the first full oceanographic depth profile of barium isotopes from the North Pacific Ocean (30 N, 140 W), which offers the ability to resolve biogeochemical cycling from mixing processes in a given water mass. Our data confirm findings from other oceanographic regions showing a close coupling between increasing [Ba] and decreasing Ba-isotope compositions with depth. Unlike other profiles however, this coupling is restricted to the upper 1,000 m of the North Pacific water column, with samples from between 1,000 m and 4,500 m showing a roughly 60 % increase in [Ba] but essentially no changes in their Ba-isotope compositions (within measurement uncertainty of 15 ppm/AMU). As with Atlantic data, samples spanning the entire profile define a linear trend (R2 > 0.9) when plotted as Ba-isotope compositions against 1/[Ba], indicating that conservative mixing can account for much of the Ba-isotope variation in the North Pacific water column. Overall, these findings highlight the utility of stable isotope measurements to illuminate the processes governing nutrient cycling, and support the critical role of large-scale ocean circulation in setting `refractory' nutrient distributions. These results have particular relevance to regions with relatively weak overturning circulation, such as the North Pacific, because they elucidate the mechanistic basis that underpins Ba/Ca and other Ba-based tracers of the marine carbon cycle in paleoceanography.

Impact of contamination and pre-treatment on stable carbon and nitrogen isotopic composition of charred plant remains

PubMed Central

Vaiglova, Petra; Snoeck, Christophe; Nitsch, Erika; Bogaard, Amy; Lee-Thorp, Julia

2014-01-01

Rationale Stable isotope analysis of archaeological charred plants has become a useful tool for interpreting past agricultural practices and refining ancient dietary reconstruction. Charred material that lay buried in soil for millennia, however, is susceptible to various kinds of contamination, whose impact on the grain/seed isotopic composition is poorly understood. Pre-treatment protocols have been adapted in distinct forms from radiocarbon dating, but insufficient research has been carried out on evaluating their effectiveness and necessity for stable carbon and nitrogen isotope analysis. Methods The effects of previously used pre-treatment protocols on the isotopic composition of archaeological and modern sets of samples were investigated. An archaeological sample was also artificially contaminated with carbonates, nitrates and humic acid and subjected to treatment aimed at removing the introduced contamination. The presence and removal of the contamination were investigated using Fourier transform infrared spectroscopy (FTIR) and δ13C and δ15N values. Results The results show a ca 1‰ decrease in the δ15N values of archaeological charred plant material caused by harsh acid treatments and ultra-sonication. This change is interpreted as being caused by mechanical distortion of the grains/seeds rather than by the removal of contamination. Furthermore, specific infrared peaks have been identified that can be used to detect the three types of contaminants studied. We argue that it is not necessary to try to remove humic acid contamination for stable isotope analysis. The advantages and disadvantages of crushing the grains/seeds before pre-treatment are discussed. Conclusions We recommend the use of an acid-only procedure (0.5 M HCl for 30 min at 80°C followed by three rinses in distilled water) for cleaning charred plant remains. This study fills an important gap in plant stable isotope research that will enable future researchers to evaluate potential sources of isotopic change and pre-treat their samples with methods that have been demonstrated to be effective. © 2014 The Authors. Rapid Communications in Mass Spectrometry published by John Wiley & Sons Ltd. PMID:25366397

Volatile composition of microinclusions in diamonds from the Panda kimberlite, Canada: Implications for chemical and isotopic heterogeneity in the mantle

NASA Astrophysics Data System (ADS)

Burgess, Ray; Cartigny, Pierre; Harrison, Darrell; Hobson, Emily; Harris, Jeff

2009-03-01

In order to better investigate the compositions and the origins of fluids associated with diamond growth, we have carried-out combined noble gas (He and Ar), C and N isotope, K, Ca and halogen (Cl, Br, I) determinations on fragments of individual microinclusion-bearing diamonds from the Panda kimberlite, North West Territories, Canada. The fluid concentrations of halogens and noble gases in Panda diamonds are enriched by several orders of magnitude over typical upper mantle abundances. However, noble gas, C and N isotopic ratios ( 3He/ 4He = 4-6 Ra, 40Ar/ 36Ar = 20,000-30,000, δ 13C = -4.5‰ to -6.9‰ and δ 15N = -1.2‰ to -8.8‰) are within the worldwide range determined for fibrous diamonds and similar to the mid ocean ridge basalt (MORB) source value. The high 36Ar content of the diamonds (>1 × 10 -9 cm 3/g) is at least an order of magnitude higher than any previously reported mantle sample and enables the 36Ar content of the subcontinental lithospheric mantle to be estimated at ˜0.6 × 10 -12 cm 3/g, again similar to estimates for the MORB source. Three fluid types distinguished on the basis of Ca-K-Cl compositions are consistent with carbonatitic, silicic and saline end-members identified in previous studies of diamonds from worldwide sources. These fluid end-members also have distinct halogen ratios (Br/Cl and I/Cl). The role of subducted seawater-derived halogens, originally invoked to explain some of the halogen ratio variations in diamonds, is not considered an essential component in the formation of the fluids. In contrast, it is considered that large halogen fractionation of a primitive mantle ratio occurs during fluid-melt partitioning in forming silicic fluids, and during separation of an immiscible saline fluid.

Strontium and neodymium isotopic evidence for the heterogeneous nature and development of the mantle beneath Afar (Ethiopia)

NASA Astrophysics Data System (ADS)

Betton, P. J.; Civetta, L.

1984-11-01

Neodymium isotope and REE analyses of recent volcanic rocks and spinel lherzolite nodules from the Afar area are reported. The 143Nd/ 144Nd ratios of the volcanic rocks range from 0.51286 to 0.51304, similar to the range recorded from Iceland. However, the 87Sr/ 86Sr ratios display a distinctly greater range (0.70328-0.70410) than those reported from the primitive rocks of Iceland. Whole rock samples and mineral separates from the spinel lherzolite nodules exhibit uniform 143Nd/ 144Nd ratios (ca. 0.5129) but varied 87Sr/ 86Sr ratios in the range 0.70427-0.70528. The Sr sbnd Nd isotope variations suggest that the volcanic rocks may have been produced by mixing between two reservoirs with distinct isotopic compositions. Two possible magma reservoirs in this area are the source which produced the "MORB-type" volcanics in the Red Sea and Gulf of Aden and the anomalous source represented by the nodule suite. The isotopic composition of the volcanics is compatible with mixing between these two reservoirs. It is shown that the anomalous source with a high 87Sr/ 86Sr ratio cannot have been produced by simple processes of partial melting and mixing within normal mantle. Instead the high 87Sr/ 86Sr is equated with a fluid phase. A primitive cognate fluid, subducted seawater or altered oceanic lithosphere may have been responsible for the generation of the source with a high 87Sr/ 86Sr ratio.

Decoupled carbonate chemistry controls on the incorporation of boron into Orbulina universa

NASA Astrophysics Data System (ADS)

Howes, Ella L.; Kaczmarek, Karina; Raitzsch, Markus; Mewes, Antje; Bijma, Nienke; Horn, Ingo; Misra, Sambuddha; Gattuso, Jean-Pierre; Bijma, Jelle

2017-01-01

In order to fully constrain paleo-carbonate systems, proxies for two out of seven parameters, plus temperature and salinity, are required. The boron isotopic composition (δ11B) of planktonic foraminifera shells is a powerful tool for reconstructing changes in past surface ocean pH. As B(OH)4- is substituted into the biogenic calcite lattice in place of CO32-, and both borate and carbonate ions are more abundant at higher pH, it was suggested early on that B / Ca ratios in biogenic calcite may serve as a proxy for [CO32-]. Although several recent studies have shown that a direct connection of B / Ca to carbonate system parameters may be masked by other environmental factors in the field, there is ample evidence for a mechanistic relationship between B / Ca and carbonate system parameters. Here, we focus on investigating the primary relationship to develop a mechanistic understanding of boron uptake. Differentiating between the effects of pH and [CO32-] is problematic, as they co-vary closely in natural systems, so the major control on boron incorporation remains unclear. To deconvolve the effects of pH and [CO32-] and to investigate their impact on the B / Ca ratio and δ11B, we conducted culture experiments with the planktonic foraminifer Orbulina universa in manipulated culture media: constant pH (8.05), but changing [CO32-] (238, 286 and 534 µmol kg-1 CO32-) and at constant [CO32-] (276 ± 19.5 µmol kg-1) and varying pH (7.7, 7.9 and 8.05). Measurements of the isotopic composition of boron and the B / Ca ratio were performed simultaneously using a femtosecond laser ablation system coupled to a MC-ICP-MS (multiple-collector inductively coupled plasma mass spectrometer). Our results show that, as expected, δ11B is controlled by pH but it is also modulated by [CO32-]. On the other hand, the B / Ca ratio is driven by [HCO3-], independently of pH. This suggests that B / Ca ratios in foraminiferal calcite can possibly be used as a second, independent, proxy for complete paleo-carbonate system reconstructions. This is discussed in light of recent literature demonstrating that the primary relationship between B / Ca and [HCO3-] can be obscured by other environmental parameters.

Non-destructive estimates of soil carbonic anhydrase activity and associated soil water oxygen isotope composition

NASA Astrophysics Data System (ADS)

Jones, Sam P.; Ogée, Jérôme; Sauze, Joana; Wohl, Steven; Saavedra, Noelia; Fernández-Prado, Noelia; Maire, Juliette; Launois, Thomas; Bosc, Alexandre; Wingate, Lisa

2017-12-01

The contribution of photosynthesis and soil respiration to net land-atmosphere carbon dioxide (CO2) exchange can be estimated based on the differential influence of leaves and soils on budgets of the oxygen isotope composition (δ18O) of atmospheric CO2. To do so, the activity of carbonic anhydrases (CAs), a group of enzymes that catalyse the hydration of CO2 in soils and plants, needs to be understood. Measurements of soil CA activity typically involve the inversion of models describing the δ18O of CO2 fluxes to solve for the apparent, potentially catalysed, rate of CO2 hydration. This requires information about the δ18O of CO2 in isotopic equilibrium with soil water, typically obtained from destructive, depth-resolved sampling and extraction of soil water. In doing so, an assumption is made about the soil water pool that CO2 interacts with, which may bias estimates of CA activity if incorrect. Furthermore, this can represent a significant challenge in data collection given the potential for spatial and temporal variability in the δ18O 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 inferring the rate of CO2 hydration and the δ18O of soil water from the relationship between the δ18O of CO2 fluxes and the δ18O of CO2 at the soil surface measured at different ambient CO2 conditions. This approach was tested through laboratory incubations of air-dried soils that were re-wetted with three waters of different δ18O. Gas exchange measurements were made on these soils to estimate the rate of hydration and the δ18O of soil water, followed by soil water extraction to allow for comparison. Estimated rates of CO2 hydration were 6.8-14.6 times greater than the theoretical uncatalysed rate of hydration, indicating that CA were active in these soils. Importantly, these estimates were not significantly different among water treatments, suggesting that this represents a robust approach to assay the activity of CA in soil. As expected, estimates of the δ18O of the soil water that equilibrates with CO2 varied in response to alteration to the δ18O of soil water. However, these estimates were consistently more negative than the composition of the soil water extracted by cryogenic vacuum distillation at the end of the gas measurements with differences of up to -3.94 ‰ VSMOW-SLAP. These offsets suggest that, at least at lower water contents, CO2-H2O isotope equilibration primarily occurs with water pools that are bound to particle surfaces and are depleted in 18O compared to bulk soil water.

Radiogenic Ingrowth of 40CA from Decay of 40K Provides a Powerful Tracer for Understanding the Origins of Felsic Magmas

NASA Technical Reports Server (NTRS)

Mills, Ryan D.; Simon, Justin I.; Depaolo, Donald J.; Bachmann, Olivier

2013-01-01

Over time high K/Ca continental crust produces a unique Ca isotopic reservoir, with measurable 40Ca excesses compared to Earth's mantle (?Ca=0). Thus, values of ?Cai > 1 indicate a significant crustal contribution to a magma. Values of ?Cai (<1) indistinguishable from mantle Ca indicate that the Ca in those magmas is either directly from the mantle, or is from partial melting of newly formed crust. So, whereas 40Ca excesses clearly define crustal contributions, mantle-like 40Ca/44Ca ratios are not as definitive. Here we present Ca isotopic measurements of intermediate to felsic igneous rocks from the western United States, and two crustal xenoliths found within the Fish Canyon Tuff (FCT). The two crustal xenoliths found within the 28.2 Ma FCT of the southern Rocky Mountain volcanic field (SRMVF) yield ?Ca values of 4 and 7.5, respectively. The 40Ca excesses of these possible source rocks are due to long-term in situ 40K decay and suggest that they are Precambrian in age. However, the FCT (?Cai 0.3) is within uncertainty of the mantle 40Ca/44Ca. Together, these data indicate that little Precambrian crust was involved in the petrogenesis of the FCT. Nd isotopic analyses of the FCT imply that it was generated from 10- 75% of an enriched component, and the Ca isotopic data appear to restrict that component to newly formed lower crust, or enriched mantle. However, the Ca isotopic data do permit assimilation of some crust with low Ca/Nd; decreasing the 143Nd/144Nd without adding much excess 40Ca to the FCT. Several other large tuffs from the SRMVF and from Yellowstone have ?Cai indistinguishable from the mantle. However, a few large tuffs from the SRMVF show significant 40Ca excesses. These tuffs (Wall Mountain, Blue Mesa, and Grizzly Peak) are likely sourced from near, or within the Colorado Mineral Belt. New isotopic measurements of Mesozoic and Tertiary granites from across the northern Great Basin show a range of ?Cai from 0 to 3. In these samples ?Cai is generally correlated with ?Sri and is broadly negatively correlated with ?Ndi. However, for granites with similar ?Ndi at a given general location ?Cai can vary significantly (1 to 2 epsilon units). In rocks where low ?Ndi could also be due to melting from enriched reservoirs in the mantle lithosphere, the combination of high ?Cai with low ?Ndi clearly identifies crustal melts.

Effect of Wood Aging on Wine Mineral Composition and 87Sr/86Sr Isotopic Ratio.

PubMed

Kaya, Ayse D; Bruno de Sousa, Raúl; Curvelo-Garcia, António S; Ricardo-da-Silva, Jorge M; Catarino, Sofia

2017-06-14

The evolution of mineral composition and wine strontium isotopic ratio 87 Sr/ 86 Sr (Sr IR) during wood aging were investigated. A red wine was aged in stainless steel tanks with French oak staves (Quercus sessiliflora Salisb.), with three industrial scale replicates. Sampling was carried out after 30, 60, and 90 days of aging, and the wines were evaluated in terms of general analysis, phenolic composition, total polysaccharides, multielement composition, and Sr IR. Li, Be, Mg, Al, Sc, Ti, V, Mn, Co, Ni, Cu, Zn, Ga, Ge, As, Rb, Sr, Y, Zr, Mo, Sb, Cs, Ba, Pr, Nd, Sm, Eu, Dy, Ho, Er, Yb, Lu, Tl, and Pb elements and 87 Sr/ 86 Sr were determined by quadrupole inductively coupled plasma mass spectrometry (Q-ICP-MS) and Na, K, Ca, and Fe by flame atomic absorption spectrometry (FAAS). Two-way ANOVA was applied to assess wood aging and time effect on Sr IR and mineral composition. Wood aging resulted in significantly higher concentrations of Mg, V, Co, Ni, and Sr. At the end of the aging period, wine exhibited statistically identical Sr IR compared to control. Study suggests that wood aging does not affect 87 Sr/ 86 Sr, not precluding the use of this parameter for wine traceability purposes.

Shallow stratification prevailed for ∼1700 to ∼1300 Ma ocean: Evidence from organic carbon isotopes in the North China Craton

NASA Astrophysics Data System (ADS)

Luo, Genming; Junium, Christopher K.; Kump, Lee R.; Huang, Junhua; Li, Chao; Feng, Qinglai; Shi, Xiaoying; Bai, Xiao; Xie, Shucheng

2014-08-01

The Late Paleoproterozoic to Early Mesoproterozoic (from ∼1700 Ma to ∼1300 Ma) was highlighted by the assembly of the Nuna supercontinent, expansion of euxinic marine environments and apparent stasis in the diversity of eukaryotes. The isotopic composition of carbonate carbon (δ13Ccarb) was surprisingly constant during this interval, but little is known about the secular variation in the organic carbon isotopic composition (δ13Corg). Here we report δ13Corg data from the latest Paleoproterozoic (>1650 Ma) to Early Mesoproterozoic (∼1300 Ma) succession in North China. The δ13Corg values range from -25‰ to -34‰, and are dependent on sedimentary facies. In subtidal and deeper environments δ13Corg values are low and constant, ca. -32‰, but relatively enriched and more variable in shallower intertidal and supratidal environments. We attribute the facies-dependent variation in δ13Corg to the presence of a shallow chemocline. A probable result of a shallow chemocline is that it supported significant contributions of organic matter produced by chemoautotrophic and/or anaerobic photoautotrophic microbes in relatively deep environments from the latest Paleoproterozoic to Early Mesoproterozoic continental shelf of North China.

Mo isotope record of shales points to deep ocean oxygenation in the early Paleoproterozoic

NASA Astrophysics Data System (ADS)

Asael, Dan; Scott, Clint; Rouxel, Olivier; Poulton, Simon; Lyons, Timothy; Javaux, Emmanuelle; Bekker, Andrey

2014-05-01

Two steps in Earth's surface oxidation lie at either end of the Proterozoic Eon. The first step, known as the Great Oxidation Event (GOE), occurred at ca. 2.32 Ga (1), when atmospheric oxygen first exceeded 0.001% of present atmospheric levels (2). The second step, occurred at ca. 0.58 Ga, resulting in the pervasive oxygenation of the deep oceans, a feature that persisted through most of the Phanerozoic (3). The conventional model envisions two progressive and unidirectional increases in free oxygen. However, recent studies have challenged this simplistic view of the GOE (4, 5). A dramatic increase and decline in Earth oxidation state between 2.3 and 2.0 Ga is now well supported (6-9) and raises the question of how well-oxygenated the Earth surface was in the immediate aftermath of the GOE. In order to constrain the response of the deep oceans to the GOE, we present a study of Mo isotope composition and Mo concentration from three key early Paleoproterozoic black shale units with ages ranging from 2.32 to 2.06 Ga. Our results suggest high and unstable surface oxygen levels at 2.32 Ga, leading to an abrupt increase in Mo supply to the still globally anoxic ocean, and producing extreme seawater Mo isotopic enrichments in these black shales. We thus infer a period of significant Mo isotopic Rayleigh effects and non-steady state behaviour of the Mo oceanic system at the beginning of the GOE. Between 2.2-2.1 Ga, we observe smaller Mo isotopic variations and estimate the δ98Mo of seawater to be 1.42 ± 0.27 ‰W conclude that oxygen levels must have stabilized at a relatively high level and that the deep oceans were oxygenated for the first time in Earth's history. By ca. 2.06 Ga, immediately after the Lomagundi Event, the Mo isotopic composition decreased dramatically to δ98MoSW = 0.80 ± 0.21 o reflecting the end of deep ocean oxygenation and the return of largely anoxic deep oceans. References: [1] A. Bekker et al., 2004, Nature 427, 117-20. [2] A. Pavlov and J. Kasting, 2002, Astrobiology 2, 27-41. [3] C. Scott et al., 2008, Nature 452, 456-9. [4] C. Goldblatt et al., 2006, Nature 443, 683-6. [5] L. Kump et al., 2011, Science 334, 1694-6. [6] A. Bekker and D. Holland, 2012, Earth Planet. Sci. Lett. 317-318, 295-304. [7] N. Planavsky et al., 2012, Proc. Natl. Acad. Sci. U. S. A. 109, 18300-5. [8] C. Partin et al., 2013, Chem. Geol. 362, 82-90. [9] C. Scott et al., 2014, Earth Planet. Sci. Lett. 389, 95-104.

Origins and evolution of rhyolitic magmas in the central Snake River Plain: insights from coupled high-precision geochronology, oxygen isotope, and hafnium isotope analyses of zircon

NASA Astrophysics Data System (ADS)

Colón, Dylan P.; Bindeman, Ilya N.; Wotzlaw, Jörn-Frederik; Christiansen, Eric H.; Stern, Richard A.

2018-02-01

We present new high-precision CA-ID-TIMS and in situ U-Pb ages together with Hf and O isotopic analyses (analyses performed all on the same grains) from four tuffs from the 15-10 Ma Bruneau-Jarbidge center of the Snake River Plain and from three rhyolitic units from the Kimberly borehole in the neighboring 10-6 Ma Twin Falls volcanic center. We find significant intrasample diversity in zircon ages (ranges of up to 3 Myr) and in δ18O (ranges of up to 6‰) and ɛHf (ranges of up to 24 ɛ units) values. Zircon rims are also more homogeneous than the associated cores, and we show that zircon rim growth occurs faster than the resolution of in situ dating techniques. CA-ID-TIMS dating of a subset of zircon grains from the Twin Falls samples reveals complex crystallization histories spanning 104-106 years prior to some eruptions, suggesting that magma genesis was characterized by the cyclic remelting of buried volcanic rocks and intrusions associated with previous magmatic episodes. Age-dependent trends in zircon isotopic compositions show that rhyolite production in the Yellowstone hotspot track is driven by the mixing of mantle-derived melts (normal δ18O and ɛHf) and a combination of Precambrian basement rock (normal δ18O and ɛHf down to - 60) and shallow Mesozoic and Cenozoic age rocks, some of which are hydrothermally altered (to low δ18O values) by earlier stages of Snake River Plain magmatism. These crustal melts hybridize with juvenile basalts and rhyolites to produce the erupted rhyolites. We also observe that the Precambrian basement rock is only an important component in the erupted magmas in the first eruption at each caldera center, suggesting that the accumulation of new intrusions quickly builds an upper crustal intrusive body which is isolated from the Precambrian basement and evolves towards more isotopically juvenile and lower-δ18O compositions over time.

The origin of Neoproterozoic Cap Carbonates: a view from Mg and Sr Isotopes

NASA Astrophysics Data System (ADS)

Liu, C.; Raub, T. D.; Evans, D. A.; Wang, Z.

2010-12-01

Neoproterozoic cap carbonates are suggested to document Earth’s transition from a ‘snowball earth’ to an ‘extreme greenhouse’ environment. Geochemistry of these rocks is essential for its paleo-environment reconstruction, and Mg and Sr isotopes can help to understand its origin and constrain geochemical evolution of the contemporary ocean. In this study, we studied Mg and Sr isotope composition of 18 cap dolostone samples from Nuccaleena formation carbonate and one from the the mixed siliciclastic transition at its base at Elatina Creek in Adelaide Geosyncline of South Australia. We established a step-leaching procedure using ammonium acetate, various concentrations of acetic acid, and HCl on four of these cap carbonate samples to untangle the isotopic signatures of its various constituent phases. 87Sr/86Sr values of the leachates in each sample decrease continuously as leaching process proceeds and sometimes rebound as silicates are dissolved. The lowest leachate 87Sr/86Sr values, down to 0.7084, are lower than the reported dolostone(~0.7096) but still higher than those of limestones overlying the dolostone in other basins(~0.7079), indicating an input of increasing level of weathering to the ocean over the course of cap-carbonate precipitation. In contrast, δ26MgDSM3 variation with progressing leaching steps exhibits a wave pattern (variation up to 0.4~0.5‰) during the leaching processes, due to different chemical affinity of Mg in various mineral phases. More importantly, Mg isotope composition of the portion that is associated with stratigraphically low, minimum Sr isotope composition is similar to those of contemporary corals (or inorganic aragonite precipitation), but up to ca. 0.6 per mil lower than stratigraphically-higher values, suggesting a warmer weather and/or more significant silicate weathering than contemporary Earth’s climate, and a transition from physical weathering to chemical weather during deglaciation.

Tracing Tethyan Phosphogenesis From Temporal Variations of 44Ca/42Ca and 143Nd/144Nd Isotope Ratios in Francolites and P Accumulation

NASA Astrophysics Data System (ADS)

Soudry, D.; Glenn, C.; Nathan, Y.; Segal, I.; Vonderhaar, D.

2004-12-01

Measurements of 44Ca/42Ca and 143Nd/144 isotope ratios in carbonate fluorapatite (CFA) through the Cretaceous-Eocene of the Negev (Israel) and of other sites in the Tethys margins, together with quantified rates of P and Ca accumulation and bulk sedimentation, allow us to understand variations of Tethyan phosphogenesis in time and space. The data provide a ˜ 90 m.y. (Hauterivian-Eocene) record of the Ca and Nd isotopic composition in 72 CFA samples representing 25 time-stratigraphic phosphate levels. Similar temporal changes are displayed by δ 44Ca and ɛ NdT. δ 44Ca is much lighter in the Hauterivian-Albian (δ 44Ca = - 0. 19 to - 0.06 ‰ ; n = 9) than in the Campanian-Eocene (δ 44Ca = + 0.29 to + 0.40 ‰ ; n = 41), whereas ɛ NdT increases from continental crust-like values in the Hauterivian-Albian (ɛ NdT = -12.8 to - 10.9; n = 8) to more radiogenic Pacific-like values (ɛ NdT = - 7.5 to - 6.2; n = 27) in the Campanian. Both δ 44Ca and ɛ NdT peaks in the Campanian coincide with the peak of Tethyan phosphogenesis in the Negev, marked by a sharp rise in P accumulation rates (from < 200 μ mole.cm-2 kyr-1 in pre-Campanian times to ˜ 1700 < 200 μ mole.cm-2 kyr-1 in the Campanian) and by a decrease in the rates of Ca accumulation and bulk sedimentation. The coincident increases of δ 44Ca, ɛ NdT, and P accumulation in the Negev during the Campanian is interpreted as the combined effect of the Late Cretaceous global sea level rise, the development of a long-transit, westward-flowing circumglobal Tethyan current enhanced by widening of the Caribbean threshold at those times, and a favorable paleolatitude (8° -15° ) of the south Tethys shelf in the path of easterly winds. Extensive flooding of continental platforms, induced by the Late Cretaceous global sea level rise, probably reduced the influx of riverine Ca to oceans and increased carbonate deposition on shelves both causing seawater enrichment with heavy Ca. Similarly, intensification of ocean circulation, causing more incursion of Pacific water masses into the Tethys, probably also led to increase both the input of radiogenic Nd into the Tethys and the availability of dissolved P in photic waters. The much lower ɛ NdT values recorded in N. Africa CFA during Eocene times (ɛ NdT = - 10.0 to - 9.4) suggests Atlantic waters as main source of dissolved P for fuelling phosphate deposition in this area.

Perspectives on geochemical proxies: The impact of model and parameter selection on the quantification of carbonate recrystallization rates

NASA Astrophysics Data System (ADS)

Huber, Christian; Druhan, Jennifer L.; Fantle, Matthew S.

2017-11-01

Diagenetic reactions in marine sediments, such as the recrystallization of carbonates, can impact the accuracy of paleo-environmental and paleo-climatic reconstructions by geochemical proxies. The extent to which the recrystallization of carbonates affects the chemistry of sedimentary archives depends on the reaction rate, extent of isotopic disequilibrium, and duration of reaction. The reaction rate, which is obviously critical, can be constrained by the elemental and isotopic compositions of pore fluids. Such constraints are affected by assumptions regarding the temperature in the sedimentary column relative to the temperature of formation, the burial rate, pore fluid advection, the composition of the sediments (carbonate-rich versus siliciclastic), and the porosity of the sediment column. In this study, we use a steady-state analytical solution to the diagenetic equations to constrain depth-dependent reaction rates (and extents of recrystallization) based on the Ca isotopic compositions of pore fluids in sedimentary columns at multiple ocean drilling sites (Sites 807, 984, 1170, and 1171), which encompass a diverse range of sedimentary compositions and conditions. We find that carbonates in siliciclastic sediments are generally less altered by diagenesis than their carbonate-rich counterparts. The discrepancy in recrystallization rates between siliciclastic and carbonate-rich sedimentary sections is, however, significantly smaller than previously estimated, suggesting that siliciclastic archives are not immune to diagenetic effects. While we find that diagenesis can decouple contemporaneous proxies of sea surface temperature (Mg/Ca and δ18O), our calculations also reveal that δ18O-based temperature estimates are more robust in siliciclastic sections relative to carbonate-rich sections. Sensitivity tests of the calculated extent of recrystallization suggest that uncertainties in porosity and burial rate are generally the greatest sources of error to proxy reconstruction from diagenetically altered sediments. The conclusions drawn using the analytical solution are benchmarked against a depth-dependent, forward numerical model using the CrunchFlow software (Steefel et al., 2015); ultimately, this comparison demonstrates that the assumptions necessary in deriving the analytical solutions have a relatively minor impact on the resulting conclusions.

Apportionment of carbon dioxide over central Europe: insights from combined measurements of atmospheric CO2 mixing ratios and carbon isotope composition

NASA Astrophysics Data System (ADS)

Zimnoch, M.; Jelen, D.; Galkowski, M.; Kuc, T.; Necki, J.; Chmura, L.; Gorczyca, Z.; Jasek, A.; Rozanski, K.

2012-04-01

The European continent, due to high population density and numerous sources of anthropogenic CO2 emissions, plays an important role in the global carbon budget. Nowadays, precise measurements of CO2 mixing ratios performed by both global and regional monitoring networks, combined with appropriate models of carbon cycle, allow quantification of the European input to the global atmospheric CO2 load. However, measurements of CO2 mixing ratios alone cannot provide the information necessary for the apportionment of fossil-fuel related and biogenic contributions to the total CO2 burden of the regional atmosphere. Additional information is required, for instance obtained through measurements of radiocarbon content in atmospheric carbon dioxide. Radiocarbon is a particularly useful tracer for detecting fossil carbon in the atmosphere on different spatial and temporal scales. Regular observations of atmospheric CO2mixing ratios and their isotope compositions have been performed during the period of 2005-2009 at two sites located in central Europe (southern Poland). The sites, only ca. 100 km apart, represent two extreme environments with respect to the extent of anthropogenic pressure: (i) the city of Krakow, representing typical urban environment with numerous sources of anthropogenic CO2, and (ii) remote mountain site Kasprowy Wierch, relatively free of local influences. Regular, quasi-continuous measurements of CO2 mixing ratios have been performed at both sites. In addition, cumulative samples of atmospheric CO2 have been collected (weekly sampling regime for Krakow and monthly for Kasprowy Wierch) to obtain mean carbon isotope signature (14C/12C and 13C/12C ratios) of atmospheric CO2 at both sampling locations. Partitioning of the local atmospheric CO2 load at both locations has been performed using isotope- and mass balance approach. In Krakow, the average fossil-fuel related contribution to the local atmospheric CO2 load was equal to approximately 3.4%. The biogenic component turned out to be of the same magnitude. Both components revealed a distinct seasonality, with the fossil-fuel related component reaching maximum values during winter months and the biogenic component shifted in phase by ca. 6 months. Seasonality of fossil-fuel related CO2 load in the local atmosphere is linked with seasonality of local CO2sources, mostly burning of fossil fuels for heating purposes. Positive values of biogenic component indicate prevalence of the local respiration and biomass burning processes over local photosynthesis. Summer maxima of biogenic CO2 component represent mostly local respiration activity. Direct measurements of soil CO2 fluxes in the Krakow region showed an approximately 10-fold increase of those fluxes during the summer months. Partitioning of the local CO2 budget for Kasprowy Wierch site revealed large differences in the derived components when compared to urban atmosphere of Krakow: the fossil-fuel related component was ca. 5 times lower whereas the biogenic component was negative in summer, pointing to the importance of photosynthetic sink associated with extensive forests in the neighborhood of the station. The isotope- and mass balance approach was also used to derive mean monthly 13C isotope signature of fossil-fuel related CO2 emissions in Krakow. Although the derived δ13CO2 values revealed large variability, they are confined in the range of 13C isotope composition being reported for various sources of CO2 emissions in the city (burning of coal and oil, burning of methane gas, traffic).

Assessing Precipitation Isotope Variations during Atmospheric River Events to Reveal Dominant Atmospheric/Hydrologic Processes

NASA Astrophysics Data System (ADS)

McCabe-Glynn, S. E.; Johnson, K. R.; Yoshimura, K.; Buenning, N. H.; Welker, J. M.

2015-12-01

Extreme precipitation events across the Western US commonly associated with atmospheric rivers (ARs), whereby extensive fluxes of moisture are transported from the subtropics, can result in major damage and are projected by most climate models to increase in frequency and severity. However, they are difficult to project beyond ~ten days and the location of landfall and topographically induced precipitation is even more uncertain. Water isotopes, often used to reconstruct past rainfall variability, are useful natural tracers of atmospheric hydrologic processes. Because of the typical tropical and sub-tropical origins, ARs can carry unique water isotope (δ18O and δ2H, d-excess) signatures that can be utilized to provide source and process information that can lead to improving AR predictions. Recent analysis of the top 10 weekly precipitation total samples from Sequoia National Park, CA, of which 9 contained AR events, shows a high variability in the isotopic values. NOAA Hysplit back trajectory analyses reveals a variety of trajectories and varying latitudinal source regions contributed to moisture delivered to this site, which may explain part of the high variability (δ2H = -150.03 to -49.52 ‰, δ18O = -19.27 to -7.20 ‰, d-excess = 4.1 to 25.8). Here we examine the top precipitation totals occurring during AR events and the associated isotopic composition of precipitation samples from several sites across the Western US. We utilize IsoGSM, an isotope-enabled atmospheric general circulation model, to characterize the hydrologic processes and physical dynamics contributing to the observed isotopic variations. We investigate isotopic influences from moisture source location, AR speed, condensation height, and associated temperature. We explore the dominant controls on spatial and temporal variations of the isotopic composition of AR precipitation which highlights different physical processes for different AR events.

Springwater geochemistry at Honey Creek State Natural Area, central Texas: Implications for surface water and groundwater interaction in a karst aquifer

NASA Astrophysics Data System (ADS)

Musgrove, M.; Stern, L. A.; Banner, J. L.

2010-06-01

SummaryA two and a half year study of two adjacent watersheds at the Honey Creek State Natural Area (HCSNA) in central Texas was undertaken to evaluate spatial and temporal variations in springwater geochemistry, geochemical evolution processes, and potential effects of brush control on karst watershed hydrology. The watersheds are geologically and geomorphologically similar, and each has springs discharging into Honey Creek, a tributary to the Guadalupe River. Springwater geochemistry is considered in a regional context of aquifer components including soil water, cave dripwater, springwater, and phreatic groundwater. Isotopic and trace element variability allows us to identify both vadose and phreatic groundwater contributions to surface water in Honey Creek. Spatial and temporal geochemical data for six springs reveal systematic differences between the two watersheds. Springwater Sr isotope values lie between values for the limestone bedrock and soils at HCSNA, reflecting a balance between these two primary sources of Sr. Sr isotope values for springs within each watershed are consistent with differences between soil compositions. At some of the springs, consistent temporal variability in springwater geochemistry (Sr isotopes, Mg/Ca, and Sr/Ca values) appears to reflect changes in climatic and hydrologic parameters (rainfall/recharge) that affect watershed processes. Springwater geochemistry was unaffected by brush removal at the scale of the HCSNA study. Results of this study build on previous regional studies to provide insight into watershed hydrology and regional hydrologic processes, including connections between surface water, vadose groundwater, and phreatic groundwater.

The Central Atlantic Magmatic Province (CAMP)

NASA Astrophysics Data System (ADS)

Marzoli, A.; Callegaro, S.; Davies, J.; Chiaradia, M.; Reisberg, L. C.; Merle, R.; Jourdan, F.; Bertrand, H.; Youbi, N.

2017-12-01

Basaltic lava flows, dykes, sills, and layered intrusion of the CAMP (Central Atlantic magmatic province) crop out in Europe, Africa, North and South America over > 10 million square km, making this one of Earth's largest igneous provinces. CAMP is characterized by 100-400 m thick preserved lava piles and by huge shallow intrusions (e.g., > 1.5 million cubic km sills). Magmatism occurred mainly between 201.6 and 201.1 Ma (according to U-Pb and Ar/Ar ages) during the end-Triassic extinction event and a few Ma before break-up of Pangea. Pulsed emplacement seems consistent with high-precision geochronology, but needs further confirmation. All over the province, basalts with quite similar composition reflect a common mantle source. These basalts have low Ti contents (TiO2 ca. 1.0-1.3 wt.%), moderately enriched Sr-Nd-Pb isotopic compositions close to the EM-II mantle end-member, and 187Os/188Os close to 0.130. We attribute these characteristics to a dominant shallow asthenospheric mantle source that was enriched by subduction-related components. Assimilation of crustal rocks generally played a minor role and rarely exceed 5-10%. Instead, assimilation of the sub-continental lithospheric mantle (SCLM) was instead recognized in the high-Ti basalts (TiO2> 2.0 wt.%) that were emplaced in a restricted area around the Man and Amazonian cratons (Sierra Leone, Liberia, Brazil, Guyana). The SCLM-like signature of these basalts suggests assimilation of metasomatically enriched parts of the SCLM. Also early basalts emplaced north of the West African craton (Morocco, Mali) are contaminated by enriched SCLM components even if to a lesser degree, while later basalts from the same African regions have low 187Os/188Os (ca. 0.120) and probably tapped a more depleted cratonic SCLM. Calculated mantle potential temperatures are low (ca. 1450 °C) and geochemical data do not support a significant contribution from mantle-plume material. The only available He isotopic data are just slightly higher than those of MORB. This argues against a substantial contribution from mantle-plume material. The only basalts trending to isotopic compositions similar to those of present-day Atlantic island basalts are quite limited in volume and restricted to a small area of Morocco.

Hercynian Pb-Zn mineralization types in the Alcudia Valley mining district (Spain) and their reflect in Pb isotopic signatures

NASA Astrophysics Data System (ADS)

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

2003-04-01

More than 450 ore deposits indexed within the Alcudia Valley of the Central-Iberian Zone (Spain) may be grouped by their tectonic and lithologic characteristics (1,2) as follows: type A of rare stratabound mineralizations, and types B, C, D and E represented by abundant Hercynian veins (post-Namurian). 86 new Pb isotope analyses of galenas from the four vein types reveal that types B and C have similar isotopic ratios with values of μ_2 = 10.07, ω_2 = 40.6 and a mean model age of 564 Ma. Types D and E have μ_2 and ω_2 values of 9.79 and 38.5, respectively, but differ each other with respect to their model ages, 600 Ma (type D) and 335 Ma (type E). The observed variations appear to be related to the geochemical features of the metasedimentary host-rocks of the mineralizations where two distinct types of Pb isotopic ratios have been reported (3): one with μ_2 and ω_2 comparable to those of the D and E types and another with a more radiogenic composition, close to those of the B and C types of galenas. Nägler et al. have suggested partial rehomogeneization of Pb isotopic composition within the metasediments at ca. 330 Ma, that is, prior to the mineralization events, but the extent of this process and its effects on the ore bodies isotopic features is not evident. The origin of the more abundant E type ore bodies has been related to the Hercynian granitic rocks in the area (2, and references therein). Other plutons within this sector of the Central Iberian Zone (e.g., Linares, etc.; cf. accompanying Abstract) associate ore bodies whose Pb isotopic composition is very similar to that of the E type galenas from the Alcudia Valley. The isotopic data obtained thus point to a related or common source material for the various types of granites within the area studied. Yet, the Pb isotopic composition of other mineralizations (B, C, D), likewise located in Hercynian veins, allow to consider different types of Pb-Zn ore bodies and point therefore to different sources of Pb at a regional scale. (1) Palero, F.J. Ph. D., University of Salamanca, Spain (1991). (2) Palero, F.; Both, R.A.; Arribas, A.; Boyce, A.J.; Mangas, J. &Martín-Izard, A. Economic Geology (in press). (3) Nägler, T. Ph. D., Diss ETH, Zurich N^o 9245 (1990).

Compilation of minimum and maximum isotope ratios of selected elements in naturally occurring terrestrial materials and reagents

USGS Publications Warehouse

Coplen, T.B.; Hopple, J.A.; Böhlke, J.K.; Peiser, H.S.; Rieder, S.E.; Krouse, H.R.; Rosman, K.J.R.; Ding, T.; Vocke, R.D.; Revesz, K.M.; Lamberty, A.; Taylor, P.; De Bievre, P.

2002-01-01

Documented variations in the isotopic compositions of some chemical elements are responsible for expanded uncertainties in the standard atomic weights published by the Commission on Atomic Weights and Isotopic Abundances of the International Union of Pure and Applied Chemistry. This report summarizes reported variations in the isotopic compositions of 20 elements that are due to physical and chemical fractionation processes (not due to radioactive decay) and their effects on the standard atomic weight uncertainties. For 11 of those elements (hydrogen, lithium, boron, carbon, nitrogen, oxygen, silicon, sulfur, chlorine, copper, and selenium), standard atomic weight uncertainties have been assigned values that are substantially larger than analytical uncertainties because of common isotope abundance variations in materials of natural terrestrial origin. For 2 elements (chromium and thallium), recently reported isotope abundance variations potentially are large enough to result in future expansion of their atomic weight uncertainties. For 7 elements (magnesium, calcium, iron, zinc, molybdenum, palladium, and tellurium), documented isotope-abundance variations in materials of natural terrestrial origin are too small to have a significant effect on their standard atomic weight uncertainties. This compilation indicates the extent to which the atomic weight of an element in a given material may differ from the standard atomic weight of the element. For most elements given above, data are graphically illustrated by a diagram in which the materials are specified in the ordinate and the compositional ranges are plotted along the abscissa in scales of (1) atomic weight, (2) mole fraction of a selected isotope, and (3) delta value of a selected isotope ratio. There are no internationally distributed isotopic reference materials for the elements zinc, selenium, molybdenum, palladium, and tellurium. Preparation of such materials will help to make isotope ratio measurements among laboratories comparable. The minimum and maximum concentrations of a selected isotope in naturally occurring terrestrial materials for selected chemical elements reviewed in this report are given below: Isotope Minimum mole fraction Maximum mole fraction -------------------------------------------------------------------------------- 2H 0 .000 0255 0 .000 1838 7Li 0 .9227 0 .9278 11B 0 .7961 0 .8107 13C 0 .009 629 0 .011 466 15N 0 .003 462 0 .004 210 18O 0 .001 875 0 .002 218 26Mg 0 .1099 0 .1103 30Si 0 .030 816 0 .031 023 34S 0 .0398 0 .0473 37Cl 0 .240 77 0 .243 56 44Ca 0 .020 82 0 .020 92 53Cr 0 .095 01 0 .095 53 56Fe 0 .917 42 0 .917 60 65Cu 0 .3066 0 .3102 205Tl 0 .704 72 0 .705 06 The numerical values above have uncertainties that depend upon the uncertainties of the determinations of the absolute isotope-abundance variations of reference materials of the elements. Because reference materials used for absolute isotope-abundance measurements have not been included in relative isotope abundance investigations of zinc, selenium, molybdenum, palladium, and tellurium, ranges in isotopic composition are not listed for these elements, although such ranges may be measurable with state-of-the-art mass spectrometry. This report is available at the url: http://pubs.water.usgs.gov/wri014222.

Ground- and Surface-Water Chemistry of Handcart Gulch, Park County, Colorado, 2003-2006

USGS Publications Warehouse

Verplanck, Philip L.; Manning, Andrew H.; Kimball, Briant A.; McCleskey, R. Blaine; Runkel, Robert L.; Caine, Jonathan S.; Adams, Monique; Gemery-Hill, Pamela A.; Fey, David L.

2008-01-01

As part of a multidisciplinary project to determine the processes that control ground-water chemistry and flow in mineralized alpine environments, ground- and surface-water samples from Handcart Gulch, Colorado were collected for analysis of inorganic solutes and water and dissolved sulfate stable isotopes in selected samples. The primary aim of this study was to document variations in ground-water chemistry in Handcart Gulch and to identify changes in water chemistry along the receiving stream of Handcart Gulch. Water analyses are reported for ground-water samples collected from 12 wells in Handcart Gulch, Colorado. Samples were collected between August 2003 and October 2005. Water analyses for surface-water samples are reported for 50 samples collected from Handcart Gulch and its inflows during a low-flow tracer injection on August 6, 2003. In addition, water analyses are reported for three other Handcart Gulch stream samples collected in September 2005 and March 2006. Reported analyses include field parameters (pH, specific conductance, temperature, dissolved oxygen, and Eh), major and trace constituents, oxygen and hydrogen isotopic composition of water and oxygen and sulfur isotopic composition of dissolved sulfate. Ground-water samples from this study are Ca-SO4 type and range in pH from 2.5 to 6.8. Most of the samples (75 percent) have pH values between 3.3 and 4.3. Surface water samples are also Ca-SO4 type and have a narrower range in pH (2.7?4.0). Ground- and surface-water samples vary from relatively dilute (specific conductance of 68 ?S/cm) to concentrated (specific conductance of 2,000 ?S/cm).

Potassium Stable Isotopic Compositions Measured by High-Resolution MC-ICP-MS

NASA Technical Reports Server (NTRS)

Morgan, Leah E.; Lloyd, Nicholas S.; Ellam, Robert M.; Simon, Justin I.

2012-01-01

Potassium isotopic (K-41/K-39) compositions are notoriously difficult to measure. TIMS measurements are hindered by variable fractionation patterns throughout individual runs and too few isotopes to apply an internal spike method for instrumental mass fractionation corrections. Internal fractionation corrections via the K-40/K-39 ratio can provide precise values but assume identical K-40/K-39 ratios (e.g. 0.05% (1sigma) in [1]); this is appropriate in some cases (e.g. identifying excess K-41) but not others (e.g., determining mass fractionation effects and metrologically traceable isotopic abundances). SIMS analyses have yielded measurements with 0.25% precisions (1sigma) [2]. ICP-MS analyses are significantly affected by interferences from molecular species such as Ar-38H(+) and Ar-40H(+) and instrument mass bias. Single collector ICP-MS instruments in "cold plasma" mode have yielded uncertainties as low as 2% (1sigma, e.g. [3]). Although these precisions may be acceptable for some concentration determinations, they do not resolve isotopic variation in terrestrial materials. Here we present data from a series of measurements made on the Thermo Scientific NEPTUNE Plus multi-collector ICP-MS that demonstrate the ability to make K-41/K-39 ratio measurements with 0.07% precisions (1sigma). These data, collected on NIST K standards, indicate the potential for MC-ICP-MS measurements to look for K isotopic variations at the sub-permil level. The NEPTUNE Plus can sufficiently resolve 39K and 41K from the interfering 38ArH+ and 40ArH+ peaks in wet cold plasma and high-resolution mode. Measurements were made on small but flat, interference-free, plateaus (ca. 50 ppm by mass width for K-41). Although ICP-MS does not yield accurate K-41/K-39 values due to significant instrumental mass fractionation (ca. 6%), this bias can be sufficiently stable over the time required for several measurements so that relative K-41/K-39 values can be precisely determined via sample-standard bracketing. As cold plasma conditions can amplify matrix effects, experiments were conducted to test the matrix tolerance of measurements; the use of clean, matrix-matched samples and standards is critical. Limitations of the cold-plasma high-resolution MC-ICP-MS methodology with respect to matrix tolerance are discussed and compared with the limitations of TIMS methodologies.

Geochemical constraints on the spatial distribution of recycled oceanic crust in the mantle source of late Cenozoic basalts, Vietnam

NASA Astrophysics Data System (ADS)

Hoang, Thi Hong Anh; Choi, Sung Hi; Yu, Yongjae; Pham, Trung Hieu; Nguyen, Kim Hoang; Ryu, Jong-Sik

2018-01-01

This study presents a comprehensive analysis of the major and trace element, mineral, and Sr, Nd, Pb and Mg isotopic compositions of late Cenozoic intraplate basaltic rocks from central and southern Vietnam. The Sr, Nd, and Pb isotopic compositions of these basalts define a tight linear array between Indian mid-ocean-ridge basalt (MORB)-like mantle and enriched mantle type 2 (EM2) components. These basaltic rocks contain low concentrations of CaO (6.4-9.7 wt%) and have high Fe/Mn ratios (> 60) and FeO/CaO-3MgO/SiO2 values (> 0.54), similar to partial melts derived from pyroxenite/eclogite sources. This similarity is also supported by the composition of olivine within these samples, which contains low concentration of Ca and high concentrations of Ni, and shows high Fe/Mn ratios. The basaltic rocks have elevated Dy/Yb ratios that fall within the range of melts derived from garnet lherzolite material, although their Yb contents are much higher than those of modeled melts derived from only garnet lherzolite material and instead plot near the modeled composition of eclogite-derived melts. The Vietnamese basaltic rocks have lighter δ26Mg values (- 0.38 ± 0.06‰) than is expected for the normal mantle (- 0.25 ± 0.07‰), and these values decrease with decreasing Hf/Hf* and Ti/Ti* ratios, indicating that these basalts were derived from a source containing carbonate material. On primitive mantle-normalized multi-element variation diagrams, the central Vietnamese basalts are characterized by positive Sr, Eu, and Ba anomalies. These basalts also plot within the pelagic sediment field in Pbsbnd Pb isotopic space. This suggests that the mantle source of the basalts contained both garnet peridotite and recycled oceanic crust. A systematic analysis of variations in geochemical composition in basalts from southern to central Vietnam indicates that the recycled oceanic crust (possibly the paleo-Pacific slab) source material contains varying proportions of gabbro, basalt, and sediment. The basalts from south-central Vietnam (12°N-14°N) may be dominated by the lowest portion of the residual slab that contains rutile-bearing plagioclase-rich gabbroic eclogite, whereas the uppermost portion of the recycled slab, including sediment and basaltic material with small amounts of gabbro, may be a major constituent of the source for the basalts within the central region of Vietnam (14°N-16°N). Finally, the southern region (10°N-12°N) contains basalts sourced mainly from recycled upper oceanic crust that is basalt-rich and contains little or no sediment.

Cross sections for He and Ne isotopes in natural Mg, Al, and Si, He isotopes in CaF2, Ar isotopes in natural Ca, and radionuclides in natural Al, Si, Ti, Cr, and stainless steel induced by 12- to 45-MeV protons

NASA Technical Reports Server (NTRS)

Walton, J. R.; Heymann, D.; Yaniv, A.; Edgerley, D.; Rowe, M. W.

1976-01-01

Stacks of thin Mg, Al, Si, Ca, CaF2, Ti, and stainless steel foils were bombarded in twelve irradiations by a variable energy cyclotron. Cross sections are reported for He and Ne in natural Mg, Al, and Si, and for He in CaF2, and for Ar in natural Ca, as determined from mass spectrometer analysis of the inert gases. In addition, cross sections of Na-22 in natural Al and Si, of V-48 in natural Ti, and of Cr-51, Mn-52, and Co-57 in stainless steel are reported. From these were deduced Cr-51 and Mn-52 cross sections in natural Cr.

Ca biogeochemical cycle at the beech tree - soil solution interface from the Strengbach CZO (NE France): a clue from stable Ca and radiogenic Sr isotopes

NASA Astrophysics Data System (ADS)

Schmitt, Anne-Désirée; Gangloff, Sophie; Labolle, François; Chabaux, François; Stille, Peter

2017-04-01

Stable calcium and radiogenic Sr are analysed in several organs from two beech trees that were collected in June and September in the Strengbach CZO (NE France) and in corresponding soil solutions. The combination of these two isotopic systems shows that the isotopic signatures of roots are dominated by Ca fractionation mechanisms and Sr, and thus Ca, source variations. In contrast, translocation mechanisms are only governed by Ca fractionation processes. This study also confirms in the field that the Ca uptake mechanisms from nutritive solutions are controlled by adsorption processes in small roots because of physico-chemical mechanisms. Similarly, a study of surface soil solutions suggests that recent soil waters are less affected by vegetation uptake than in the past, probably because of a decline in the growth of the vegetation that is linked to climate warming, which causes drought episodes. Thus, soil solutions reflect the role of soil components in addition to nutrient uptake by vegetation. This isotopic Ca-Sr study also helps to identify one-time events that are caused by snow cover melting and/or dry episodes that release cations.

Geochemical and Isotopic Evidences of the Magmatic Sources in the Eastern Sector of the Trans-Mexican Volcanic Belt: Xihuingo-Chichicuautla Volcanic Field

NASA Astrophysics Data System (ADS)

Valadez, S.; Martinez-serrano, R.; Juarez-Lopez, K.; Solis-Pichardo, G.; Perez-Arvizu, O.

2011-12-01

The study of magmatism in the Trans-Mexican Volcanic Belt (TMVB) has great importance due to several features such as its obliquity with respect to the Middle American Trench and its petrological and geochemical variability, which are not common in most typical volcanic arcs. Although several papers have contributed significantly to the understanding of most important magmatic processes in this province, there are still several questions such as the characterization of magmatic sources. In the present work, we provide new stratigraphic, petrographic, geochemical and Sr, Nd and Pb isotopic data as well as some K-Ar age determinations from the Xihuingo-Chichicuautla volcanic field (XCVF), located at the eastern part of the TMVB, with the aim to identify the magmatic sources that produced the main volcanic rocks. The volcanic structures in the XCVF are divided in two main groups according to the petrographic and geochemical compositions: 1) dacitic domes, andesitic lava flows and some dacitic-rhyolitic ignimbrites and 2) scoria cones, shield volcanoes and associated lava flows of basalt to basaltic-andesite composition. Distribution of most volcanic structures is probably controlled by NE-SW fault and fractures system. This fault system was studied by other authors who established that volcanic activity started ca. 13.5 Ma ago, followed by a volcanic hiatus of ca. 10 Ma, and the late volcanic activity began ca. 3 to 1 Ma. In this work we dated 2 rock samples by K-Ar method, which yielded ages of 402 and 871 Ka, which correspond to the most recent volcanic activity in this study area. The volcanic rocks of the XCVF display compositions from basalts to rhyolites but in general all rocks show trace element patterns typical of magmatic arcs. However, we can identify two main magmatic sources: a depleted magmatic source represented by dacitic-andesitic rocks which present a LILE enrichment with respect to HFSE indicating that a magmatic source was modified by fluids derived from the subduction processes. These magmas probably suffered fractional crystallization and minor assimilation in the continental crust. Sr, Nd isotopic compositions for this first group display the most radiogenic values (87Sr/86Sr from 0.7046 to 0.7047 and ɛNd from 2.2 to 2.8). The second source for the basaltic-andesite and basalt could be associated with an enriched mantle. These rocks present a minor LILE enrichment with respect to HSFE, and Sr and Nd isotopic values less radiogenic than the felsic rocks of the first group (87Sr/86Sr from 0.7040 to 0.7045 and ɛNd from 3.1 to 4.8). According to these evidences we can establish that the magmas emplaced in the study area were produced from a heterogeneous mantle source with complex magmatic processes combined with different interaction degrees between the magmas and continental crust.

Microcrystalline dolomite within massive Japan Sea methane hydrate: origin and development ascertained by inclusions within inclusions.

NASA Astrophysics Data System (ADS)

Snyder, G. T.; Kakizaki, Y.; Matsumoto, R.; Suzuki, Y.; Takahata, N.; Sano, Y.; Tanaka, K.; Tomaru, H.; Imajo, T.; Iguchi, A.

2017-12-01

Microcrystalline dolomite grains were recently discovered as inclusions within relatively pure massive gas hydrate recovered from the Joetsu Basin area of the Japan Sea. These grains presumably formed as a consequence of the highly saline conditions in fluid inclusions which developed between coalescing grain boundaries within the growing hydrate. Stable carbon and oxygen isotopic composition of the dolomite is consistent with crystal growth occurring within such fluids. In addition to stable isotopes, we investigate trends in Mg/Ca ratios of the grains as well as the composition of inclusions which exist within the dolomites. Preliminary research shows that these inclusions retain valuable information as to the conditions which existed at the time of formation, as well as the dynamics of these extensive hydrate deposits over time. This study was conducted under the commission from AIST as a part of the methane hydrate research project funded by METI (the Ministry of Economy, Trade and Industry, Japan).

Chlorine Isotope Evidence for Syn-Subduction Modification of Serpentinites by Interaction with Sediment-Derived Fluid

NASA Astrophysics Data System (ADS)

Selverstone, J.; Sharp, Z. D.

2012-12-01

High-pressure serpentinites and rodingites and high- to ultrahigh-pressure metasedimentary rocks from the Aosta region, Italy, preserve strikingly different chlorine isotope compositions that can be used to constrain the nature of fluid-rock interactions during subduction. Serpentinites and rodingitized gabbroic dikes subducted to 70-80 km have bulk δ37Cl values between -1.6 and +0.9‰ (median= -0.5‰, n=26 plus 5 replicates; one amphibole-vein outlier at -2.9‰). Serpentinite δ37Cl values are positively correlated with Cr ± Cl contents (r2= 0.97 and 0.58) and negatively correlated with CaO (r2=0.72). BSE imaging and X-ray mapping reveal up to three generations of compositionally distinct serpentine and chlorite in single samples. The youngest generation, which is most abundant, has the lowest chlorine content. Three rodingite samples contain abundant texturally early fluid inclusions. These samples were finely crushed and leached in 18 MΩ H2O to extract water-soluble chlorides. The leachates, which are assumed to record the compositions of the fluid inclusions, have δ37Cl values that are 0.7-1.5‰ lower than the corresponding bulk rock values. Leachate from the outlier amph-magnesite vein is indistinguishable from the bulk value at -2.7‰. There is almost no overlap between the Cl isotope compositions of HP serp/rod samples and associated HP/UHP metasedimentary rocks. Calcmica schists, diamond-bearing Mn nodules, and impure marbles subducted to >130 km and calcmica schists and Mn crusts transported to 70-80 km have δ37Cl values between -4.5 and -1.5‰ (median= -2.7‰, n=25 plus 7 replicates; two outlier points at -0.5‰). Primary fluid inclusions in the diamondiferous samples contain carbonate- and silicate-bearing aqueous fluids with very low chloride contents (Frezzotti et al., 2011, Nature Geosci). Taken together, these data record a history of progressive modification of serpentinites and rodingites by mixing with low-δ37Cl, low-Cl, high-Ca fluids during subduction and metamorphism. Serpentinites with the highest Cr contents have Cl isotopic compositions identical to those of modern seafloor serpentinites (δ37Cl=0.2-0.6‰), consistent with primary serpentinization by seawater (e.g., Barnes et al. 2009, Lithos). Low-Cr serpentinites record significant interaction with a Ca-rich fluid that shifted the rocks to lower δ37Cl values and diluted the original Cr and Cl contents. The fluid was likely derived from continuous devolatilization reactions in associated low-δ37Cl, calcareous metasedimentary rocks. These data have important implications for models of subduction mass transfer associated with antigorite breakdown. If serpentinites are commonly modified by interaction with metasedimentary fluids prior to antigorite dehydration, chemical signatures imparted during deserpentinization will reflect the integrated history of fluid-rock interaction in the subduction channel rather than an endmember "serpentinite signature". The data further suggest that Cl may be hydrophobic in HP/UHP carbonate-bearing aqueous fluids, resulting in generation of low-Cl fluid during metamorphic devolatilization.

Potential of calcium isotopes to identify fractionations in vegetation: experimental approach

NASA Astrophysics Data System (ADS)

Cobert, F.; Schmitt, A.; Bourgade, P.; Stille, P.; Chabaux, F. J.; Badot, P.; Jaegler, T.

2010-12-01

This study aims to better understand the role of vegetation on the Ca cycle at the level of the critical zone of the Earth, in order to specify the mechanisms controlling the Ca absorption by plants at the rock/plant interface. To do this, we performed experiments using hydroponic plant cultures in a way that we could control the cooccuring geochemical and biological processes and determine the impact of the nutritive solution on the Ca cycle within plants. A dicotyledon and calcicole plant with rapid growth, the French bean (Phaseolus vulgaris L.), has been chosen to have access to one complete growth cycle. Several experiments have been conducted with two Ca concentrations, 5 (L) and 60 (H) ppm and two pH values (4 and 6) in the nutritive solution, for which the Ca concentration was maintained constant, so its Ca content is considered to be infinite. We determined Ca concentrations and isotopic ratios in the nutritive solution and in different organs (main roots, secondary roots, old and young stems, old and young leaves and fruits) at two different growth stages (10 days and 6 weeks). Our results show, in accord with previously published field studies, that the bean organs are all enriched in the light 40Ca isotope compared to the nutritive solution (e.g. Wigand et al., 2005; Page et al., 2008; Cenki-Tok et al., 2009; Holmden and Bélanger, 2010). We identify two fractionation levels. The first occurs during the uptake of the nutrient elements by the lateral roots. This implies that the main mechanisms of light isotope enrichments in the plant are due to electrochemical gradient transport processes taking place at this interface. The second fractionation can be observed within the plant itself and is due to the nature of the considered organ itself. Indeed structural reservoirs (primary roots, stem, reproductive organs) incorporate more the light 40Ca isotope compared to the transfer reservoirs (lateral roots, xylem sap, leaves). This could be linked to ion-exchange reactions with the pectins in the cell walls of the conducting xylem. However, we also observe that bean organs from L4 experiment growing in nutrient solutions with lower Ca concentrations and low pH behave slightly differently and show reduced Ca isotopic fractionations compared with beans from the other experiments. All these results indicate that there is no simple correlation between Ca isotopic variations, Ca content and pH of the nutrient solution, and that also biological effects have to be involved. The data confirm the potential of the Ca isotopic system for tracing biological fractionations in natural ecosystems. Wiegand et al., (2005). Geophys. Res. Lett., 32, L11404 Page et al., (2008). Biogeochemistry, 88, 1-13 Cenki-Tok et al,. (2009). Geochim. Cosmochim. Acta, 73, 2215-2228 Holmden and Bélanger(2010). Geochim. Cosmochim. Acta, 74, 995-1015

Isotopic constraints on the formation of carbonates during low-temperature hydrothermal oceanic crust alteration

NASA Astrophysics Data System (ADS)

Stolper, D. A.; Antonelli, M. A.; Ramos, D. S.; Bender, M. L.; Schrag, D. P.; DePaolo, D. J.; Higgins, J. A.

2016-12-01

Low temperature (<100°C) water-rock reactions in oceanic crust have a potentially large influence on seawater chemical compositions and atmospheric pCO2. Quantification of the conditions (e.g., temperature) of oceanic crust alteration is needed to evaluate its importance for global silicate weathering fluxes. The isotopic and chemical compositions of secondary carbonates in oceanic crust reflect the temperature and chemistry of the circulating fluid and thus are used to reconstruct past conditions of crustal alteration. For example, temperatures are calculated via carbonate δ18O thermometry using measured δ18Ocarb vs. assumed δ18Ofluid. δ18Ofluid is usually assumed to be the seawater value at the time of carbonate formation. We present measured clumped-isotope temperatures (Tclump) and δ18O, δ13C, δ44Ca, and 87Sr/86Sr values of Jurassic carbonates from altered oceanic crust (ODP Site 801). Tclump measured at Caltech ranges from 24-51°C. Calculated δ18Ofluid (based on Tclump and δ18Ocarb) ranges from -0.4‰ (±0.4, 1σ) to -3.5‰ (±0.6). Higher temperatures correlate with lower δ18Ofluid (R2 = 0.75). This suggests that at elevated temperatures, δ18Ofluid was modified away from seawater values, likely via the preferential incorporation of 18O vs. 16O into secondary minerals relative to water. This indicates that δ18Ofluid values of circulating fluids are not necessarily identical to seawater δ18O. Tclump measurements are being replicated at Harvard for further verification. Carbonates with δ13C indicating a seawater C source (δ13C > 0‰) have average δ44Ca (relative to modern seawater) of -0.84‰ (±0.08). This is indistinguishable from igneous rock δ44Ca and suggests that carbonate Ca is derived from igneous Ca released during crustal alteration. Carbonates with δ13C indicating an organic C source (δ13C < -2.5‰) have lower δ44Cacarb (< -1‰). Carbonate 87Sr/86Sr ranges from 0.70742 to 0.70656. Based on the seawater 87Sr/86Sr curve, this range requires the release of low 87Sr/86Sr strontium from igneous rocks (87Sr/86Sr ≈ 0.7025) during alteration. Together these results support the presence of substantial water-rock interactions and fluid modification during alteration and carbonate precipitation. They will be discussed in the context of models of fluid flow coupled to alteration reaction kinetics.

Up-scaling mineral-aqueous interfacial processes that govern isotope and trace element partitioning during calcite growth

NASA Astrophysics Data System (ADS)

Lammers, L. N.

2014-12-01

The dependence of the isotopic and trace element composition of calcium carbonate minerals on growth conditions including temperature, pH, and salinity is widely used to infer paleoclimate conditions. These inferences rely heavily on phenomenological observations of biogenic and inorganic precipitation both in and ex situ, where only limited variability in solution conditions can be explored. Ionic fluxes between the mineral surface and aqueous growth solution govern the net uptake of both stoichiometric and trace species during calcification, so developing a mechanistic understanding of the reactions governing these fluxes is critical to refine existing proxies and to develop new ones. The micro-scale mechanisms of calcite precipitation from aqueous solution have been extensively studied, and net ionic uptake post-nucleation is known to occur primarily at monomolecular kink sites along step edges at the mineral surface. In this talk, I will present a theoretical framework that uses the quasi-elementary ion attachment and detachment reactions governing ion uptake at kink sites to simultaneously model bulk mineral growth kinetics and tracer partitioning during calcite precipitation. Several distinct processes occur during ion uptake at kink sites that can influence the distribution of trace species, directly impacting the composition of various carbonate paleoproxies including δ44Ca, δ18O, Sr/Ca and Mg/Ca. The distribution of these trace species will be shown to depend on (1) the relative rates of ion desolvation during attachment to kink sites, (2) the relative rates of bond breaking during detachment from kink sites, and (3) the equilibrium partitioning of trace aqueous species. This model accounts for the impact of solution conditions on net ion fluxes and surface speciation, which in turn controls the population of kink sites available for direct ion exchange with the aqueous phase. The impacts of solution variables including pH, temperature and salinity can be treated independently, which unlike traditional partitioning studies allows the impacts of these parameters to be deconvolved. The type of theoretical framework discussed here can be readily extended to explicitly account for each of the major solution composition variables that are implicated in paleoproxy composition.

Linking Carbonic Anhydrase Abundance and Diversity in Soils to Ecological Function

NASA Astrophysics Data System (ADS)

Pang, E.; Meredith, L. K.; Welander, P. V.

2015-12-01

Carbonic anhydrase (CA) is an ancient enzyme widespread among bacteria, archaea, and eukarya that catalyzes the following reaction: CO2 + H2O ⇌ HCO3- + H+. Its functions are critical for key cellular processes such as concentrating CO2 for autotrophic growth, pH regulation, and pathogen survival in hosts. Currently, there are six known CA classes (α, β, γ, δ, η, ζ) arising from several distinct evolutionary lineages. CA are widespread in sequenced genomes, with many organisms containing multiple classes of CA or multiple CA of the same class. Soils host rich microbial communities with diverse and important ecological functions, but the diversity and abundance of CA in soils has not been explored. CA appears to play an important, but poorly understood, role in some biogeochemical cycles such as those of CO2 and its oxygen isotope composition and also carbonyl sulfide (COS), which are potential tracers in predictive carbon cycle models. Recognizing the prevalence and functional significance of CA in soils, we used a combined bioinformatics and molecular biology approach to address fundamental questions regarding the abundance, diversity, and function of CA in soils. To characterize the abundance and diversity of the different CA classes in soils, we analyzed existing soil metagenomic and metatranscriptomic data from the DOE Joint Genome Institute databases. Out of the six classes of CA, we only found the α, β, and γ classes to be present in soils, with the β class being the most abundant. We also looked at genomes of sequenced soil microorganisms to learn what combination of CA classes they contain, from which we can begin to predict the physiological role of CA. To characterize the functional roles of the different CA classes in soils, we collected soil samples from a variety of biomes with diverse chemical and physical properties and quantified the rate of two CA-mediated processes: soil uptake of COS and acceleration of the oxygen isotope exchange between CO2 and H2O. We employed PCR-based methods to quantify the abundance and diversity of CA encoding genes and their expression in our samples to link CA classes to the gas flux data. These studies provide the first survey of CA in soils, a step towards understanding CA's potentially significant role in microbial survival and microbe-mediated biogeochemical cycles.

Documenting the diet in ancient human populations through stable isotope analysis of hair.

PubMed

Macko, S A; Engel, M H; Andrusevich, V; Lubec, G; O'Connell, T C; Hedges, R E

1999-01-29

Fundamental to the understanding of human history is the ability to make interpretations based on artefacts and other remains which are used to gather information about an ancient population. Sequestered in the organic matrices of these remains can be information, for example, concerning incidence of disease, genetic defects and diet. Stable isotopic compositions, especially those made on isolates of collagen from bones, have been used to help suggest principal dietary components. A significant problem in the use of collagen is its long-term stability, and the possibility of isotopic alteration during early diagenesis, or through contaminating condensation reactions. In this study, we suggest that a commonly overlooked material, human hair, may represent an ideal material to be used in addressing human diets of ancient civilizations. Through the analysis of the amino-acid composition of modern hair, as well as samples that were subjected to radiation (thus simulating ageing of the hair) and hair from humans that is up to 5200 years old, we have observed little in the way of chemical change. The principal amino acids observed in all of these samples are essentially identical in relative abundances and content. Dominating the compositions are serine, glutamic acid, threonine, glycine and leucine, respectively accounting for approximately 15%, 17%, 10%, 8% and 8% of the total hydrolysable amino acids. Even minor components (for example, alanine, valine, isoleucine) show similar constancy between the samples of different ages. This constancy clearly indicates minimal alteration of the amino-acid composition of the hair. Further, it would indicate that hair is well preserved and is amenable to isotopic analysis as a tool for distinguishing sources of nutrition. Based on this observation, we have isotopically characterized modern individuals for whom the diet has been documented. Both stable nitrogen and carbon isotope compositions were assessed, and together provide an indication of trophic status, and principal type (C3 or C4) of vegetation consumed. True vegans have nitrogen isotope compositions of about 7/1000 whereas humans consuming larger amounts of meat, eggs, or milk are more enriched in the heavy nitrogen isotope. We have also analysed large cross-sections of modern humans from North America and Europe to provide an indication of the variability seen in a population (the supermarket diet). There is a wide diversity in both carbon and nitrogen isotope values based at least partially on the levels of seafood, corn-fed beef and grains in the diets. Following analysis of the ancient hair, we have observed similar trends in certain ancient populations. For example, the Coptics of Egypt (1000 BP) and Chinchorro of Chile (5000-800 BP) have diets of similar diversity to those observed in the modern group but were isotopically influenced by local nutritional sources. In other ancient hair (Egyptian Late Middle Kingdom mummies, ca. 4000 BP), we have observed a much more uniform isotopic signature, indicating a more constant diet. We have also recognized a primary vegetarian component in the diet of the Neolithic Ice Man of the Oetztaler Alps (5200 BP). In certain cases, it appears that sulphur isotopes may help to further constrain dietary interpretations, owing to the good preservation and sulphur content of hair. It appears that analysis of the often-overlooked hair in archaeological sites may represent a significant new approach for understanding ancient human communities.

Documenting the diet in ancient human populations through stable isotope analysis of hair.

PubMed Central

Macko, S A; Engel, M H; Andrusevich, V; Lubec, G; O'Connell, T C; Hedges, R E

1999-01-01

Fundamental to the understanding of human history is the ability to make interpretations based on artefacts and other remains which are used to gather information about an ancient population. Sequestered in the organic matrices of these remains can be information, for example, concerning incidence of disease, genetic defects and diet. Stable isotopic compositions, especially those made on isolates of collagen from bones, have been used to help suggest principal dietary components. A significant problem in the use of collagen is its long-term stability, and the possibility of isotopic alteration during early diagenesis, or through contaminating condensation reactions. In this study, we suggest that a commonly overlooked material, human hair, may represent an ideal material to be used in addressing human diets of ancient civilizations. Through the analysis of the amino-acid composition of modern hair, as well as samples that were subjected to radiation (thus simulating ageing of the hair) and hair from humans that is up to 5200 years old, we have observed little in the way of chemical change. The principal amino acids observed in all of these samples are essentially identical in relative abundances and content. Dominating the compositions are serine, glutamic acid, threonine, glycine and leucine, respectively accounting for approximately 15%, 17%, 10%, 8% and 8% of the total hydrolysable amino acids. Even minor components (for example, alanine, valine, isoleucine) show similar constancy between the samples of different ages. This constancy clearly indicates minimal alteration of the amino-acid composition of the hair. Further, it would indicate that hair is well preserved and is amenable to isotopic analysis as a tool for distinguishing sources of nutrition. Based on this observation, we have isotopically characterized modern individuals for whom the diet has been documented. Both stable nitrogen and carbon isotope compositions were assessed, and together provide an indication of trophic status, and principal type (C3 or C4) of vegetation consumed. True vegans have nitrogen isotope compositions of about 7/1000 whereas humans consuming larger amounts of meat, eggs, or milk are more enriched in the heavy nitrogen isotope. We have also analysed large cross-sections of modern humans from North America and Europe to provide an indication of the variability seen in a population (the supermarket diet). There is a wide diversity in both carbon and nitrogen isotope values based at least partially on the levels of seafood, corn-fed beef and grains in the diets. Following analysis of the ancient hair, we have observed similar trends in certain ancient populations. For example, the Coptics of Egypt (1000 BP) and Chinchorro of Chile (5000-800 BP) have diets of similar diversity to those observed in the modern group but were isotopically influenced by local nutritional sources. In other ancient hair (Egyptian Late Middle Kingdom mummies, ca. 4000 BP), we have observed a much more uniform isotopic signature, indicating a more constant diet. We have also recognized a primary vegetarian component in the diet of the Neolithic Ice Man of the Oetztaler Alps (5200 BP). In certain cases, it appears that sulphur isotopes may help to further constrain dietary interpretations, owing to the good preservation and sulphur content of hair. It appears that analysis of the often-overlooked hair in archaeological sites may represent a significant new approach for understanding ancient human communities. PMID:10091248

High-temperature rims around calcium-aluminum-rich inclusions from the CR, CB and CH carbonaceous chondrites

NASA Astrophysics Data System (ADS)

Krot, Alexander N.; Nagashima, Kazuhide; van Kooten, Elishevah M. M.; Bizzarro, Martin

2017-03-01

We describe the mineralogy, petrology and oxygen isotopic compositions of high-temperature rims around mineralogically pristine calcium-aluminum-rich inclusions (CAIs) from the CR, CB and CH carbonaceous chondrites. In CR chondrites, nearly all CAIs are surrounded by single- or multi-layered rims composed of CAI-like minerals; relict CAIs inside chondrules in which the rims were resorbed by the host chondrule melt (Aléon et al., 2002; Makide et al., 2009) are the only exception. A complete multi-layered rim sequence (from inside outward: spinel + hibonite + perovskite → melilite → anorthite replacing melilite → Al-diopside → forsterite) is rarely observed; Al-diopside ± forsterite rims are more common. The CR CAIs and all rim layers are uniformly 16O-rich (Δ17O ∼-24‰), indicating formation in a 16O-rich gaseous reservoir. The mineralogy, petrology and 16O-rich compositions of these rims suggest formation by evaporation/condensation, melting (?), and thermal annealing in the formation region of the host CAIs. We define such rims as the primordial Wark-Lovering (WL) rims. In CH chondrites, most CAIs are uniformly 16O-rich and surrounded by the primordial WL rims. One of the 16O-rich CAIs is surrounded by an anorthite-Al-diopside WL rim showing a range of Δ17O values, from ∼-24‰ to ∼-6‰; Δ17O decreases towards the CAI core. We infer that this rim experienced incomplete melting and O-isotope exchange in an 16O-poor nebular gas, most likely during chondrule formation. Most CAIs in CB chondrites and about 10% of CAIs in CH chondrites are uniformly 16O-depleted igneous inclusions; Δ17O values between individual CAIs vary from ∼-12‰ to ∼-5‰. These CAIs have diverse mineralogies (grossite-rich, hibonite-rich, melilite-rich, spinel-rich, and Al,Ti-diopside ± forsterite-rich), but are surrounded by the mineralogically similar igneous rims composed of ±melilite, Al-diopside and Ca-rich forsterite (0.5-1.4 wt% CaO). The igneous rims and the host igneous CAIs have identical (within uncertainties of our SIMS measurements) O-isotope compositions, suggesting that they crystallized from isotopically similar, but chemically distinct melts. We suggest that the uniformly 16O-depleted igneous rims around the uniformly 16O-depleted igneous CAIs in CB and CH chondrites formed during melting of pre-existing CAIs in an impact-generated plume invoked for the origin of CB chondrites (Krot et al., 2005), followed by O-isotope exchange with an 16O-poor plume gas (Δ17O ∼-2‰), condensation of gaseous SiO and Mg into CAI melt, and its subsequent crystallization. We conclude that high-temperature rims around CAIs from CR, CH and CB chondrites recorded thermal processing in gaseous reservoirs with different oxygen isotopic compositions. In contrast to the isotopically heterogeneous WL rims around CV CAIs, our data provide no evidence that CAIs were transported between 16O-rich and 16O-poor gaseous reservoirs multiple times. We suggest instead that oxygen-isotope heterogeneity in the CV WL rims resulted from a fluid-rock interaction on the CV parent asteroid.

Assessing human weaning practices with calcium isotopes in tooth enamel

PubMed Central

Tacail, Théo; Thivichon-Prince, Béatrice; Martin, Jeremy E.; Charles, Cyril; Viriot, Laurent

2017-01-01

Weaning practices differ among great apes and likely diverged during the course of human evolution, but behavioral inference from the fossil record is hampered by a lack of unambiguous biomarkers. Here, we show that early-life dietary transitions are recorded in human deciduous tooth enamel as marked variations in Ca isotope ratios (δ44/42Ca). Using a sequential microsampling method along the enamel growth axis, we collected more than 150 enamel microsamples from 51 deciduous teeth of 12 different modern human individuals of known dietary histories, as well as nine enamel samples from permanent third molars. We measured and reconstructed the evolution of 44Ca/42Ca ratios in enamel from in utero development to first months of postnatal development. We show that the observed variations of δ44/42Ca record a transition from placental nutrition to an adult-like diet and that Ca isotopes reflect the duration of the breastfeeding period experienced by each infant. Typically, the δ44/42Ca values of individuals briefly or not breastfed show a systematic increase during the first 5–10 mo, whereas individuals with long breastfeeding histories display no measurable variation in δ44/42Ca of enamel formed during this time. The use of Ca isotope analysis in tooth enamel allows microsampling and offers an independent approach to tackle challenging questions related to past population dynamics and evolution of weaning practices in hominins. PMID:28559355

Hydrogeological and hydrochemical investigation of groundwater using environmental isotopes (18O, 2H, 3H, 14C) and chemical tracers: a case study of the intermediate aquifer, Sfax, southeastern Tunisia

NASA Astrophysics Data System (ADS)

Ayadi, Rahma; Trabelsi, Rim; Zouari, Kamel; Saibi, Hakim; Itoi, Ryuichi; Khanfir, Hafedh

2018-06-01

Major element concentrations and stable (δ18O and δ2H) and radiogenic (3H and 14C) isotopes in groundwater have proved useful tracers for understanding the geochemical processes that control groundwater mineralization and for identifying recharge sources in the semi-arid region of Sfax (southeastern Tunisia). Major-ion chemical data indicate that the origins of the salinity in the groundwater are the water-rock interactions, mainly the dissolution of evaporitic minerals, as well as the cation exchange with clay minerals. The δ18O and δ2H relationships suggest variations in groundwater recharge mechanisms. Strong evaporation during recharge with limited rapid water infiltration is evident in the groundwater of the intermediate aquifer. The mixing with old groundwater in some areas explains the low stable isotope values of some groundwater samples. Groundwaters from the intermediate aquifer are classified into two main water types: Ca-Na-SO4 and Ca-Na-Cl-SO4. The high nitrate concentrations suggest an anthropogenic source of nitrogen contamination caused by intensive agricultural activities in the area. The stable isotopic signatures reveal three water groups: non-evaporated waters that indicate recharge by recent infiltrated water; evaporated waters that are characterized by relatively enriched δ18O and δ2H contents; and mixed groundwater (old/recent) or ancient groundwater, characterized by their depleted isotopic composition. Tritium data support the existence of recent limited recharge; however, other low tritium values are indicative of pre-nuclear recharge and/or mixing between pre-nuclear and contemporaneous recharge. The carbon-14 activities indicate that the groundwaters were mostly recharged under different climatic conditions during the cooler periods of the late Pleistocene and Holocene.

Hydrogeological and hydrochemical investigation of groundwater using environmental isotopes (18O, 2H, 3H, 14C) and chemical tracers: a case study of the intermediate aquifer, Sfax, southeastern Tunisia

NASA Astrophysics Data System (ADS)

Ayadi, Rahma; Trabelsi, Rim; Zouari, Kamel; Saibi, Hakim; Itoi, Ryuichi; Khanfir, Hafedh

2017-12-01

Major element concentrations and stable (δ18O and δ2H) and radiogenic (3H and 14C) isotopes in groundwater have proved useful tracers for understanding the geochemical processes that control groundwater mineralization and for identifying recharge sources in the semi-arid region of Sfax (southeastern Tunisia). Major-ion chemical data indicate that the origins of the salinity in the groundwater are the water-rock interactions, mainly the dissolution of evaporitic minerals, as well as the cation exchange with clay minerals. The δ18O and δ2H relationships suggest variations in groundwater recharge mechanisms. Strong evaporation during recharge with limited rapid water infiltration is evident in the groundwater of the intermediate aquifer. The mixing with old groundwater in some areas explains the low stable isotope values of some groundwater samples. Groundwaters from the intermediate aquifer are classified into two main water types: Ca-Na-SO4 and Ca-Na-Cl-SO4. The high nitrate concentrations suggest an anthropogenic source of nitrogen contamination caused by intensive agricultural activities in the area. The stable isotopic signatures reveal three water groups: non-evaporated waters that indicate recharge by recent infiltrated water; evaporated waters that are characterized by relatively enriched δ18O and δ2H contents; and mixed groundwater (old/recent) or ancient groundwater, characterized by their depleted isotopic composition. Tritium data support the existence of recent limited recharge; however, other low tritium values are indicative of pre-nuclear recharge and/or mixing between pre-nuclear and contemporaneous recharge. The carbon-14 activities indicate that the groundwaters were mostly recharged under different climatic conditions during the cooler periods of the late Pleistocene and Holocene.

D/H Exchange Reactions in Salts Extracted from LEW 85320

NASA Astrophysics Data System (ADS)

Socki, R. A.; Romanek, C. S.; Gibson, E. K., Jr.

1993-07-01

Understanding the effects of terrestrial weathering on meteorites has been shown to be critical in distinguishing primary chemical and isotopic features from secondary alterations [1]. To further constrain weathering effects we report here the D/H composition of water thermally extracted from three distinct generations of efflorescence (,98, ,99, and ,102) occurring on the Antarctic H-5 chondrite LEW85320. To better understand the hydrogen isotope exchange systematics of these precipitates, an experiment was performed to characterize the rate of isotope exchange between a synthetic analog to the predominant weathering product, nesquehonite (Mg(HCO3)(OH).2H2O), found on the exterior of LEW85320 [2], and water. Synthetic nesquehonite, produced following the procedure of Ming and Franklin [3], a dehydrated CaSO4 standard, and deuterium-spiked water (deltaD = +701 permil SMOW) were placed together in a closed box and allowed to exchange hydrogen isotopes at constant temperature and humidity (30 degrees +- 2 degrees C and 75% +- 5%). Samples of each solid phase were taken initially and at 1, 3, 20, and 30 days. These samples along with three generations of efflorescence on LEW85320 (,98, ,99, and ,102) were weighed and loaded into separate high-purity, prebaked, 9-mm (O.D) quartz tubes. After degassing for two hours under high vacuum, samples were heated to 625 degrees C for 4 hr while all condensable gases were collected in a trap immersed in liquid nitrogen. CO2 was separated from water by exchanging the LN2 trap with a dry ice/alcohol mixture. All evolved water was frozen into a tube containing Zn turnings, which was then heated to 450 degrees C for 30 min, producing hydrogen gas for isotopic analysis. Results of our exchange experiment show that the CaSO4 standard quickly assumes the deltaD composition of the water (from -29 permil to +581 permil in 30 days). On the other hand, nesquehonite becomes only slightly enriched in deltaD (from -29 permil to +51 permil). Mass balance calculations reveal that absorption of the spiked water is stoichiometric with respect to the formation of CaSO4.2H2O, while within limits of sampling error no net change of weight was observed for the nesquehonite. Assuming that the change in deltaDnesq. is due entirely to exchange (i.e., no absorption), mass balance constraints dictate that less than 5 wt% of water exchanged. These data suggest that nesquehonite retains its original deltaD composition even under conditions of relatively high temperature and humidity. Hydrogen isotope data of water extracted from three generations of nesquehonite on LEW85320 are plotted as a function of the theoretical delta18O composition of water in equilibrium with the carbonate at 0 degrees C (where delta18Onesq. is derived by phosphoric acid digestion of the carbonate, assuming a calcite-CO2 fractionation factor of 1.01012). Our data plot very near the meteoric water line indicating formation from slightly enriched Antarctic meltwater. Water extracted from generations II (,99), salts consisting mostly of hydromagnesite (Mg5(CO3)4(OH)2.4H2O) (Gooding, 1993, personal communication), and III (,102), with mineralogy as yet unknown, is enriched in D (deltaD = -55 and -75 permil, respectively) and plot above the meteoric water line. Both generations precipitated in the Houston curatorial facility. Data suggest either that hydrogen isotopes have exchanged at least partially with local (i.e., Houston) water, or that the exchange reactions differ between structural sites within or among the various generations of efflorescent salts. Hydrogen isotopes extracted from hydrous weathering products can reveal information about the environment of crystal growth. However, hydrogen isotope exchange systematics could be complicated if water within the crystal structure of the mineral is located in multiple sites. Furthermore, these results could have profound implications for curation and long-term storage strategies in curatorial facilities. References: [1] Socki R. A. et al., (1991) Meteoritics, 26, 396-397. [2] Gooding J. L. et al., (1988) LPSC XIX, 397-398. [3] Ming D. W. and Franklin W. T. (1985) Soil Sci. Soc. Am. J., 49, 1303-1308.

A novel procedure for Rubidium separation and its isotope measurements on geological samples by MC-ICP-MS

NASA Astrophysics Data System (ADS)

Ma, J.; Zhang, Z.; Wei, G.; Zhang, L.

2017-12-01

A method including a novel column Rb separation procedure and high-precision Rb isotope measurement in geological materials by using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) in standard-sample-bracketing (SSB) mode has been developed. Sr-Spec resin was employed, in which the distribution coefficients for Rb, K, Ba and Sr are different in nitric acid, to sequentially separate them from the matrix. The dissolved samples were loaded on the column in 3 M HNO3, the main matrix such as Al, Ca, Fe, Mg, Mn and Na were removed by rinsing with 4.5 mL HNO3, Rb and K were then sequentially eluted by 3 M HNO3 in different volumes. After that, Ba was eluted by 8 M HNO3, and Sr was finally eluted by Milli-Q water. This enable us to collect the pure Rb, K, Ba and Sr one by one with recovery close to 100% for their isotopic compositions measurement on MC-ICP-MS. We here focus on Rb isotope measurement. The measurement using MC-ICP-MS yielded an internal precision for δ87Rb of < ± 0.03‰ (2SE), and the external precision was generally better than ± 0.06‰ (2SD) based on the long-term results of the Rb standard solutions NIST SRM 984. A series of geological rock standards, were analyzed using this method, and the results indicate significant Rb isotope differences in different geologic materials. This will provide a powerful tool to investigate Rb isotope fractionation during geological processes.Based on this method, Rb isotope compositions from a basaltic weathering profile were carried out. The data show the lighter Rb (85Rb) isotope is preferentially leached from the weathering profile and remains heavy Rb isotope (87Rb) in the weathered residues during the incipient weathering stage. From the moderate to advanced weathering stage, the significant variations of Rb isotope were observed and multiple factors, such as leaching, adsorption, desorption, and precipitation, should play important role in fractionating Rb isotope.

Analytical pyrolysis and stable isotope analyses reveal past environmental changes in coralloid speleothems from Easter Island (Chile).

PubMed

Miller, Ana Z; De la Rosa, José M; Jiménez-Morillo, Nicasio T; Pereira, Manuel F C; González-Pérez, José A; Calaforra, José M; Saiz-Jimenez, Cesareo

2016-08-26

This study comprises an innovative approach based on the combination of chromatography (analytical pyrolysis and pyrolysis compound-specific isotope analysis (Py-CSIA)), light stable isotopes, microscopy and mineralogy analyses to characterize the internal layering of coralloid speleothems from the Ana Heva lava tube in Easter Island (Chile). This multidisciplinary proxy showed that the speleothems consist of banded siliceous materials of low crystallinity with different mineralogical compositions and a significant contribution of organic carbon. Opal-A constitutes the outermost grey layer of the coralloids, whereas calcite and amorphous Mg hydrate silicate are the major components of the inner whitish and honey-brown layers, respectively. The differences found in the mineralogical, elemental, molecular and isotopic composition of these distinct coloured layers are related to environmental changes during speleothem development. Stable isotopes and analytical pyrolysis suggested alterations in the water regime, pointing to wetter conditions during the formation of the Ca-rich layer and a possible increase in the amount of water dripping into the cave. The trend observed for δ(15)N values suggested an increase in the average temperature over time, which is consistent with the so-called climate warming during the Holocene. The pyrolysis compound-specific isotope analysis of each speleothem layer showed a similar trend with the bulk δ(13)C values pointing to the appropriateness of direct Py-CSIA in paleoenvironmental studies. The δ(13)C values for n-alkanes reinforced the occurrence of a drastic environmental change, indicating that the outermost Opal layer was developed under drier and more arid environmental conditions. Copyright © 2016 Elsevier B.V. All rights reserved.

Evaluating the cave carbonate chemical signal as a proxy for rain patterns in Mallorca Island

NASA Astrophysics Data System (ADS)

Cacho, Isabel; Cisneros, Mercé; Torner, Judit; Català, Albert; Moreno, Ana; Stoll, Heather; Iglesias, Miguel; Bladé, Ileana; Fornos, Joan

2017-04-01

Mallorca's climate is marked by a strong seasonal cycle in both temperatures and precipitations which is likely to be recorded in the carbonate precipitates formed in its extended karst systems. Here we present isotopes and trace elements measured in dripwaters collected at weakly and/or seasonal bases since spring 2013 in three caves from Mallorca that represent the eastern and S-eastern sector of the island. This information is complemented with isotopic composition of rain events in the same region, other cave environmental parameters and chemistry of seasonal farmed carbonates in the same caves. Drip water results are very consistent between the different studied caves and indicate an important attenuation of the rainfall isotopic signal in the epikarst and only extreme climate conditions such as the severe dry conditions in summer 2015. Farmed carbonates present a clear seasonal cycle with low values, in both carbon and oxygen isotopes, in summer and autumn and high values in winter and spring. This cyclicity can not be attributed to amount effect or rain composition and we propose a close relation to cave environmental conditions. High CO2 concentrations in summer and autumn would avoid degasification reducing the PCP process and resulting in more negative isotopic relationships in both oxygen and carbon isotopes. Coherently, this CO2 cycles are in phase with those of temperature since both reflect ventilation rates in the cave. Nevertheless, ultra-high resolution profiles of Mg/Ca ratios measured by laser ablation on last century carbonate precipitates in the same caves, reveal a inter-annual variability with a persistent cyclicity which show coherent patterns with the instrumental rain records from Mallorca. This comparison reveals the potential of the Mallorca carbonates to reveal the long-term precipitation evolution of the island.

Role of deep-Earth water cycling in the growth and evolution of continental crust: Constraints from Cretaceous magmatism in southeast China

NASA Astrophysics Data System (ADS)

Li, Zhen; Wang, Xuan-Ce; Wilde, Simon A.; Liu, Liang; Li, Wu-Xian; Yang, Xuemei

2018-03-01

The late Mesozoic igneous province in southeast China provides an excellent opportunity to understand the processes that controlled the growth and evolution of Phanerozoic continental crust. Here we report petrological, whole-rock geochemical and isotopic data, and in situ zircon U-Pb-Lu-Hf isotopic data from granitoids and associated gabbros in the Pingtan and Tong'an complexes, southeast China. Through combining the new results with published datasets in southeast China, we show that the Early Cretaceous magmatic rocks are dominated by juvenile Nd-Hf isotopic compositions, whereas the Late Cretaceous ones display less radiogenic Nd-Hf isotope signatures. Furthermore, Nd-Hf isotope systematics are coupled with decreasing abundance of hydrous minerals and an increase of zircon saturation temperatures. Compiled zircon Hf-O data indicates that the 117-116 Ma granites have zircon δ18O values ranging from mantle values (close to 5.3‰) to as low as 3.9‰, but with dominantly positive initial epsilon Hf (εHf(t)) values. Zircon grains from 105 to 98 Ma rocks have δ18O values plotting within the mantle-like range (6.5‰ - 4.5‰), but mainly with negative εHf(t) values. Zircon grains from ca. 87 Ma rocks have positive εHf(t) values (+ 9.8 to + 0.7) and a large range of δ18O values (6.3‰ - 3.5‰). The variations in Hf-Nd-O isotopic compositions are correlated with decreasing abundance of magma water contents, presenting a case that water-fluxed melting generated large-scale granitic magmatism. Deep-Earth water cycling provides an alternative or additional mechanism to supply volatiles (e.g., H2O) for hydrous basaltic underplating, continental crustal melting, and magmatic differentiation.

Understanding the mechanisms of Si-K-Ca glass alteration using silicon isotopes

NASA Astrophysics Data System (ADS)

Verney-Carron, Aurélie; Sessegolo, Loryelle; Saheb, Mandana; Valle, Nathalie; Ausset, Patrick; Losno, Rémi; Mangin, Denis; Lombardo, Tiziana; Chabas, Anne; Loisel, Claudine

2017-04-01

It is important to understand glass alteration mechanisms and to determine their associated kinetics in order to develop models able to predict the alteration of nuclear, basaltic or archaeological glasses. Recent studies revealed that the respective contributions of diffusion, dissolution, condensation and precipitation processes in alteration are still a matter for debate. In this work, the alteration of a medieval-type glass (Si-K-Ca) was investigated as it presents a specific composition (without B and with low Al). Experiments were performed using a dynamic device, at 30 °C, at pH 8 and 9 and during 1 month in order to simulate alteration in contact with water (rainfall or condensation). The solution was doped in 29Si to discriminate between the silicon from glass (mainly 28Si) and from solution. The results showed that the external region of the alteration layer is devoid of modifier cations (K, Ca) and presents a 29Si/28Si ratio close to the solution one. This excludes that the alteration layer is a glass skeleton and highlights a progressive hydrolysis/condensation process, even if non-hydrolyzed silica tetrahedra could remain when the Si isotopic equilibrium is not reached. The internal zone appears to be gradually depleted in modifier cations and partly enriched in 29Si, but the thickness of this zone is overestimated using SEM-EDS and SIMS techniques. Even if in these experiments the dissolution mechanism is favored, the contribution of interdiffusion cannot be neglected to explain the weathering of ancient stained glassed windows in the atmosphere. The respective contribution of diffusion and dissolution are also discussed as a function of glass composition and surface texture, as well as of experimental conditions (alkaline pH, renewal of the solution).

Oxygen isotope systematics in the aragonite-CO2-H2O-NaCl system up to 0.7 mol/kg ionic strength at 25 °C

USGS Publications Warehouse

Kim, Sang-Tae; Gebbinck, Christa Klein; Mucci, Alfonso; Coplen, Tyler B.

2014-01-01

To investigate the oxygen isotope systematics in the aragonite-CO2-H2O-NaCl system, witherite (BaCO3) was precipitated quasi-instantaneously and quantitatively from Na-Cl-Ba-CO2 solutions of seawater-like ionic strength (I = 0.7 mol/kg) at two pH values (~7.9 and ~10.6) at 25 °C. The oxygen isotope composition of the witherite and the dissolved inorganic carbon speciation in the starting solution were used to estimate the oxygen isotope fractionations between HCO3¯ and H2O as well as between CO3 2 and H2O. Given the analytical error on the oxygen isotope composition of the witherite and uncertainties of the parent solution pH and speciation, oxygen isotope fractionation between NaHCO3° and HCO3¯, as well as between NaCO3¯ and CO3 2, is negligible under the experimental conditions investigated. The influence of dissolved NaCl concentration on the oxygen isotope fractionation in the aragonite-CO2-H2O-NaCl system also was investigated at 25 °C. Aragonite was precipitated from Na-Cl-Ca-Mg-(B)-CO2 solutions of seawater-like ionic strength using passive CO2 degassing or constant addition methods. Based upon our new experimental observations and published experimental data from lower ionic strength solutions by Kim et al. (2007b), the equilibrium aragonite-water oxygen isotope fractionation factor is independent of the ionic strength of the parent solution up to 0.7 mol/kg. Hence, our study also suggests that the aragonite precipitation mechanism is not affected by the presence of sodium and chloride ions in the parent solution over the range of concentrations investigated.

Assessing modern climatic controls on southern Sierra Nevada precipitation and speleothem δ18O

NASA Astrophysics Data System (ADS)

McCabe-Glynn, S. E.; Johnson, K. R.; Berkelhammer, M. B.

2012-12-01

Precipitation in the southwestern United States (SW US) is highly seasonal and exhibits inter-annual to inter-decadal variability. A 1154-year δ18O time series obtained from a southwestern Sierra Nevada Mountain stalagmite from Crystal Cave, CRC-3, (36.58°N; 118.56°W; 1540 m) reveals substantial decadal to multi-decadal variability closely linked to the Pacific Decadal Oscillation (PDO), and more specifically, to sea surface temperatures (SSTs) in the Kuroshio Extension region, which impact the atmospheric trajectory and isotopic composition of moisture reaching the study site. The instrumental portion of the CRC-3 δ18O time series suggests that more negative precipitation δ18O values are delivered from higher latitudes during positive phases of the PDO and/or when SSTs in the Kuroshio Extension region are anomalously cool, such as during La Niña events. In order to improve our understanding of the controls on speleothem δ18O in this region, we have conducted a detailed modern study of the climate, hydrology, and stable isotopic composition of meteoric waters (precipitation and drip water) at the cave. Here we present Crystal Cave drip logger results from 2010 to 2012, the isotopic composition of North American Deposition Program precipitation samples collected from 2001 to 2012 from several locations near our site including Ash Mountain (ASM), Sequoia National Park-Giant Forest (Ca75), and Yosemite National Park (Ca99), and isotopic composition of cave drip water and glass plate calcite. We also compare the δ18O values in the precipitation to satellite imagery, NCAR/NCEP data, and NOAA Hysplit Model backward trajectories between the sites. Results indicate that this site is particularly sensitive to "Pineapple Express" type storms, a persistent flow of atmospheric moisture and heavy rainfall extending from near the Hawaiian Islands to the coast of North America, which average about twice as much precipitation as other storms in the Sierra Nevada during winter. Crystal Cave drip logger results indicate a low drip rate variability in the cave between July 2010 and July 2011, averaging between ~25 drips/hour but we observe a significant increase during three "Pineapple Express" type storms (PE) during the 2010-2011 winter. Analysis of the δ18O of precipitation samples collected during these storms events exhibit significantly more negative values which could complicate the interpretation of speleothem δ18O if the relative contribution of PE moisture varies on interannual to multi-decadal timescales.

Calcium and strontium isotope fractionation during precipitation from aqueous solutions as a function of temperature and reaction rate; II. Aragonite

NASA Astrophysics Data System (ADS)

AlKhatib, Mahmoud; Eisenhauer, Anton

2017-07-01

In order to study Strontium (Sr) partitioning and isotope fractionation of Sr and Calcium (Ca) in aragonite we performed precipitation experiments decoupling temperature and precipitation rates (R∗, μmol/m2 h) in the interval of about 2.3-4.5 μmol/m2 h. Aragonite is the only pure solid phase precipitated from a stirred solutions exposed to an atmosphere of NH3 and CO2 gases throughout the spontaneous decomposition of (NH4)2CO3. The order of reaction with respect to Ca ions is one and independent of temperature. However, the order of reaction with respect to the dissolved inorganic carbon (DIC) is temperature dependent and decreases from three via two to one as temperature increases from 12.5 and 25.0 to 37.5 °C, respectively. Strontium distribution coefficient (DSr) increases with decreasing temperature. However, R∗ responds differently depending on the initial Sr/Ca concentration and temperature: at 37.5 °C DSr increase as a function of increasing R∗ but decrease for 12.5 and 25 °C. Not seen at 12.5 and 37.5 °C but at 25 °C the DSr-R∗ gradient is also changing sign depending on the initial Sr/Ca ratio. Magnesium (Mg) adsorption coefficient between aragonite and aqueous solution (DMg) decreases with temperature but increases with R∗ in the range of 2.4-3.8 μmol/m2 h. Strontium isotope fractionation (Δ88/86Sraragonite-aq) follows the kinetic type of fractionation and become increasingly negative as a function of R∗ for all temperatures. In contrast Ca isotope fractionation (Δ44/40Caaragonite-aq) shows a different behavior than the Sr isotopes. At low temperatures (12.5 and 25 °C) Ca isotope fractionation (Δ44/40Caaragonite-aq) becomes positive as a function of R∗. In contrast, at 37.5 °C and as a function of increasing R∗ the Δ44/40Caaragonite-aq show a Sr type like behavior and becomes increasingly negative. Concerning both the discrepant behavior of DSr as a function of temperature as well as for the Ca isotope fractionation as a function of temperature we infer that the switch of sign in the trace element partitioning as well as in the direction of the Ca isotope fractionation is probably due to the switch of complexation from a Ca2+-NH3 complexation at and below 25 °C to an Ca2+-H2O aquacomplex at 37.5 °C. The DSr-Δ88/86Srcalcite-aq correlation for calcite is independent of temperature in contrast to aragonite. We interpreted the strong DSr-temperature dependency of aragonite, the smaller range of Sr isotope fractionation as well as the shallower Δ88/86Srcalcite-aq-R∗ gradients to be a consequence of the increased aragonite solubility and the "Mg blocking effect". In contrast to Sr the Ca isotope fractionation values in calcite and aragonite depend both on the complexation in solution and independent on polymorphism.

P-T Path and Nd-isotopes of Garnet Pyroxenite Xenoliths From Salt Lake Crater, Oahu

NASA Astrophysics Data System (ADS)

Ichitsubo, N.; Takahashi, E.; Clague, D. A.

2001-12-01

Abundant garnet pyroxenite and spinel lherzolite xenoliths are found in Salt Lake Crater (SLC) in Oahu, Hawaii [Jackson and Wright, 1970]. The SLC pyroxenite suite xenoliths (olivine-poor type) have complex exsolution textures that were probably formed during a slow cooling. In this study, we used digital image software to obtain modal data of exsolved phases in the host pyroxene using backscattered electron images (BEIs). The abundances of the exsolved phases were multiplied by the phase compositions determined by electron probe micro-analyzer (EPMA) to reconstruct pyroxene compositions prior to exsolution. In order to evaluate the error in this calculation, we recalculated the reconstructed pyroxene compositions using the different pyroxene pairs. Reconstructed clinopyroxenes in each sample have almost no variations (MgO, CaO +/-1wt %, FeO +/-0.5wt % and the other oxides ~+/-0.1wt %). Reconstructed orthopyroxenes are more variable in MgO, CaO (+/-2wt %) and FeO (+/-1wt %) than reconstructed clinopyroxenes, but the other oxides have only limited variations ( ~+/-0.5wt %). These compositions were used to calculate igneous stage (magmatic) P-T conditions based on the geothermometers and geobarometers of Wells [1977] and Brey and Kohler [1990] Following assumptions are made: (1) the reconstructed pyroxene compositions are the final record in the primary igneous stage, and (2) cores of the largest garnet grains in each sample record the primary igneous stage composition.. The recalculation using the different pairs of reconstructed pyroxenes show the uncertainty to be +/- 30° C and 0.1 GPa. These appear to be small compared to the large intrinsic errors of geothermometer and geobarometers (+/-20° -35° C and +/- 0.3-0.5 GPa). Estimated P-T conditions for garnet pyroxenites are 1.5-2.2 GPa, 1000° -1100° C in the final reequilibration stage and 2.2-2.6 GPa (at maximum), 1150° -1300° C (at minimum) in the igneous stage. The all samples show ca. 200° C cooling and 0.5 GPa decompression. This implies that the garnet pyroxenites cooled ca. 200° C to develop the observed complex exsolution and may have risen from about 70-80 km to 50-65 km depth. Glass pockets and fine minerals (olivine, pyroxene, spinel) occur in the SLC garnet pyroxenite xenoliths. Amphibole and phlogopite, which may have crystallized by metasomatism, are common accessory minerals in them. In order to study the nature of metasomatism as revealed by the glass pockets and fine aggregate of spinel and pyroxene, Nd-isotope study on the SLC xenoliths is under way.

Calcium biogeochemical cycle at the beech tree-soil solution interface from the Strengbach CZO (NE France): insights from stable Ca and radiogenic Sr isotopes

NASA Astrophysics Data System (ADS)

Schmitt, Anne-Désirée; Gangloff, Sophie; Labolle, François; Chabaux, François; Stille, Peter

2017-09-01

Calcium (Ca) is the fourth most abundant element in mineral nutrition and plays key physiological and structural roles in plant metabolism. At the soil-water-plant scale, stable Ca isotopes are a powerful tool for the identification of plant-mineral interactions and recycling via vegetation. Radiogenic Sr isotopes are often used as tracers of Ca sources and mixtures of different reservoirs. In this study, stable Ca and radiogenic Sr are combined and analysed in several organs from two beech trees that were collected in June and September in the Strengbach critical zone observatory (CZO) (NE France) and in corresponding soil solutions. At the beech-tree scale, this study confirms the field Ca adsorption (i.e., physico-chemical mechanism and not vital effects) on carboxyl acid groups of pectin in the apoplasm of small roots. The analysis of the xylem sap and corresponding organs shows that although the Strengbach CZO is nutrient-poor, Ca seems to be non-limiting for tree-growth. Different viscosities of xylem sap between the stemwood and branches or leaves can explain δ44/40Ca values in different tree-organs. The bark and phloem 40Ca-enrichments could be due to Ca-oxalate precipitation in the bark tissues and in the phloem. The results from this study regarding the combination of these two isotopic systems show that the isotopic signatures of the roots are dominated by Ca fractionation mechanisms and Sr, and thus Ca, source variations. In contrast, translocation mechanisms are only governed by Ca fractionation processes. This study showed that at the root-soil solution interface, litter degradation was not the main source of Ca and Sr and that the soil solutions are not the complement of uptake by roots for samples from the 2011/2013 period. The opposite is observed for older samples. These observations indicate the decreasing contribution of low radiogenic Sr fluxes, such as recycling, alimenting the soil solutions. Such reduced importance of nutrient uptake and biomass production by the trees could be because the Strengbach trees are ageing and probably weakened by repeated storm events and drought episodes.

Conditions of Mytilus edulis extracellular body fluids and shell composition in a pH-treatment experiment: Acid-base status, trace elements and δ11B

NASA Astrophysics Data System (ADS)

Heinemann, Agnes; Fietzke, Jan; Melzner, Frank; BöHm, Florian; Thomsen, JöRn; Garbe-SchöNberg, Dieter; Eisenhauer, Anton

2012-01-01

Mytilus edulis were cultured for 3 months under six different seawater pCO2 levels ranging from 380 to 4000 μatm. Specimen were taken from Kiel Fjord (Western Baltic Sea, Germany) which is a habitat with high and variable seawater pCO2 and related shifts in carbonate system speciation (e.g., low pH and low CaCO3 saturation state). Hemolymph (HL) and extrapallial fluid (EPF) samples were analyzed for pH and total dissolved inorganic carbon (CT) to calculate pCO2 and [HCO3-]. A second experiment was conducted for 2 months with three different pCO2 levels (380, 1400 and 4000 μatm). Boron isotopes (δ11B) were investigated by LA-MC-ICP-MS (Laser Ablation-Multicollector-Inductively Coupled Plasma-Mass Spectrometry) in shell portions precipitated during experimental treatment time. Additionally, elemental ratios (B/Ca, Mg/Ca and Sr/Ca) in the EPF of specimen from the second experiment were measured via ICP-OES (Inductively Coupled Plasma-Optical Emission Spectrometry). Extracellular pH was not significantly different in HL and EPF but systematically lower than ambient water pH. This is due to high extracellular pCO2 values, a prerequisite for metabolic CO2 excretion. No accumulation of extracellular [HCO3-] was measured. Elemental ratios (B/Ca, Mg/Ca and Sr/Ca) in the EPF increased slightly with pH which is in accordance with increasing growth and calcification rates at higher seawater pH values. Boron isotope ratios were highly variable between different individuals but also within single shells. This corresponds to a high individual variability in fluid B/Ca ratios and may be due to high boron concentrations in the organic parts of the shell. The mean δ11B value shows no trend with pH but appears to represent internal pH (EPF) rather than ambient water pH.

Tracking Transport and Transformation of Aerosols using C and O-triple Isotopic Composition of Carbonates: CSI La Jolla

NASA Astrophysics Data System (ADS)

Thiemens, M. H.; Shaheen, R.; Chong, K.; Hill, A.; Wong, J.; Zhang, Z.; Dominguez, G.

2012-12-01

Aerosols affect climate in numerous ways, including change in the earth's energy balance by absorbing and scattering solar radiations, alteration of the hydrological cycle by serving as cloud condensation nuclei, change in biogeochemical cycles by providing nutrients. Another significant process is the effect on the chemical composition of the atmosphere by providing surfaces for heterogeneous chemical reactions. Fine particles of aerodynamic diameter less than 2.5μm (PM2.5) also impinge upon human health by admission to the respiratory system causing a range of cardiopulmonary diseases. Both climate and public health aspects depend on their physical and chemical properties, therefore, understanding physico-chemical and photochemical transformations on aerosol surfaces is important for predicting their effects on climate change, atmospheric chemistry and human health. Here we present initial findings on the processes occurring on aerosol surfaces using isotopes to delineate day and night time chemistry, thus resolving photochemistry effects, and to identify their sources by way of the carbon isotopes. Aerosols were collected on filter papers for 12h during the day and at night time from June-Dec. 2011in La Jolla, CA., using high volume, multi stage cascade impactors. CO2 released after treating these filter papers with 100% phosphoric acid at 27oC was collected, purified chromatographically and analyzed for both C and O isotopes. Our data indicate that both C and O isotopes can be used to distinguish between heterogeneous and photochemical transformations. Aerosol carbonates collected during the day time were depleted in δ13Cday = -23 to -28‰ and δ18Oday = +3 to +10‰ and were isotopically distinct from the carbonates collected at night time δ13Cnight = 0 to -12‰, δ18Onightnight = +23 to +32‰. Higher chloride concentration in the samples collected at night time indicated the transport of marine air masses whereas higher nitrate and sulfate concentration indicated urban air pollution in the samples collected during the day time. To further constraint the origin of air masses being collected at La Jolla, Ca, NOAA Hysplit back trajectories were analyzed for 24 and 48h at three different altitudes (500m, 1000m, <1500m). Our analysis found dominance of urban air masses from Los Angeles and San Diego area during the day time whereas aerosols collected at night time had a significant component of marine air masses and some contribution from San Diego areas at our sampling site, as expected. To further understand the role of ozone in heterogeneous and photochemical transformation, oxygen triple isotopic composition of the carbonates will be measured. Scanning electron microscopy will also be used to characterize the physical and chemical features of the aerosols. The comprehensive approach will facilitate to define changes in surface chemistry of the aerosols occuring during their transport and aging.

Calcium isotope fractionation between soft and mineralized tissues as a monitor of calcium use in vertebrates.

PubMed

Skulan, J; DePaolo, D J

1999-11-23

Calcium from bone and shell is isotopically lighter than calcium of soft tissue from the same organism and isotopically lighter than source (dietary) calcium. When measured as the (44)Ca/(40)Ca isotopic ratio, the total range of variation observed is 5.5 per thousand, and as much as 4 per thousand variation is found in a single organism. The observed intraorganismal calcium isotopic variations and the isotopic differences between tissues and diet indicate that isotopic fractionation occurs mainly as a result of mineralization. Soft tissue calcium becomes heavier or lighter than source calcium during periods when there is net gain or loss of mineral mass, respectively. These results suggest that variations of natural calcium isotope ratios in tissues may be useful for assessing the calcium and mineral balance of organisms without introducing isotopic tracers.

Calcium isotope fractionation between soft and mineralized tissues as a monitor of calcium use in vertebrates

PubMed Central

Skulan, Joseph; DePaolo, Donald J.

1999-01-01

Calcium from bone and shell is isotopically lighter than calcium of soft tissue from the same organism and isotopically lighter than source (dietary) calcium. When measured as the 44Ca/40Ca isotopic ratio, the total range of variation observed is 5.5‰, and as much as 4‰ variation is found in a single organism. The observed intraorganismal calcium isotopic variations and the isotopic differences between tissues and diet indicate that isotopic fractionation occurs mainly as a result of mineralization. Soft tissue calcium becomes heavier or lighter than source calcium during periods when there is net gain or loss of mineral mass, respectively. These results suggest that variations of natural calcium isotope ratios in tissues may be useful for assessing the calcium and mineral balance of organisms without introducing isotopic tracers. PMID:10570137

Silicon and Zinc Isotopes in Ocean Island Basalts

NASA Astrophysics Data System (ADS)

Pringle, E. A.; Savage, P. S.; Jackson, M. G.; Moreira, M. A.; Day, J. M.; Moynier, F.

2013-12-01

Analyses of Ocean Island Basalts (OIB) have shown that the Earth's mantle contains isotopically distinct components, but current debate about the degree and scale of compositional variability persists. Isotopic heterogeneities in OIB for both radiogenic (e.g. Sr, Nd, Pb) and stable (e.g. Li, O, Ca) isotope systems have been attributed to the presence of recycled materials in different mantle reservoirs [1]. The study of both silicon and zinc isotopes in OIB form a complimentary approach to investigate potential heterogeneities in the mantle. Both isotope systems show limited fractionation during igneous process [2,3]. However, both Si and Zn exhibit larger (>1‰) variability in low-temperature environments (e.g. as a result of chemical weathering and biological utilization). Therefore, Si and Zn isotopes may be useful as tracers for the presence of crustal material (derived from low-T surface processes) in OIB source regions. Furthermore, characterizing the isotopic composition of the mantle is of central importance to the use of these isotopic systems as a basis for interplanetary comparisons. Here we present high-precision Si and Zn isotopic data obtained by MC-ICPMS for a diverse suite of OIB representing the EM-1, EM-2, and HIMU mantle components. Samples represent locations in the Pacific, Atlantic, and Indian Oceans. Data are reported as the permil deviation (×2 sd) from NBS28 for Si (δ30Si) and JMC-Lyon for Zn (δ66Zn). Average δ30Si values for OIB from EM-1 (-0.32×0.09‰), EM-2 (-0.30×0.03‰), and HIMU (-0.34×0.12‰) are all in general agreement with previous estimates for the δ30Si value of Bulk Silicate Earth (BSE) [4]. Similarly, the δ66Zn average values for OIB from the EM-1, EM-2, and HIMU components (0.31×0.06‰, 0.31×0.04‰, 0.31×0.05‰, respectively) agree well with previously published data for the δ66Zn value of BSE [3]. At the current levels of precision, both Si and Zn isotopes exhibit little variation in OIB, confirming the large-scale homogeneity of the mantle for these isotopic systems. Furthermore, when averaged according to surface location, neither Si nor Zn shows any variation in isotopic composition according to oceanic basin. However, some small variations in the data may be present; many HIMU samples (Mangaia, Cape Verde) are enriched in the lighter isotopes of Si (δ30Si tending toward chondritic values), which might reflect preservation of isotopic heterogeneity within the mantle, an incorporation of an isotopically light component in the source of these lavas, or isotopic fractionation during magmatic differentiation. References: [1] Hofmann, RiMG 2007 [2] Savage et al., GCA 2011 [3] Chen et al., EPSL 2013 [4] Savage et al., EPSL 2010

Petrogenesis of Late Triassic ultramafic rocks from the Andong Ultramafic Complex, South Korea

NASA Astrophysics Data System (ADS)

Kim, Nak Kyu; Choi, Sung Hi

2016-11-01

To constrain the source and tectonomagmatic processes that gave rise to the Andong Ultramafic Complex (AUC) in South Korea, we determined the clinopyroxene Sr-Nd-Hf-Pb isotope and trace element compositions as well as the whole-rock and mineral compositions for the Late Triassic (ca. 222 Ma) ultramafic rocks from the complex. They are composed of dunites, wehrlites, pyroxene/hornblende peridotites, and pyroxenites. The constituent minerals are olivines, diopsides/augites, bronzites, calcic-amphiboles, and spinels. Clinopyroxenes exhibit a convex-upward rare earth element (REE) pattern, with an apex at Sm. The whole-rock compositions plot away from the residual mantle peridotite trends, with variable but lower Al2O3 and SiO2 contents, and higher CaO, FeO*, and TiO2 contents at a given value of MgO. Estimated equilibrium temperatures for the AUC rocks range from 420 to 780 °C. These observations, together with the absence of reaction or melt impregnation textures, indicate that the AUC ultramafic rocks are magmatic cumulates emplaced within the crust rather than residual mantle or mantle-melt reaction products. The AUC clinopyroxenes have compositions intermediate between the oceanic island basalt- and arc basalt-related cumulate clinopyroxenes. The AUC spinels have lower Cr#s than the arc-related magmatic cumulate spinels. They plot within the field for spinels from mid-ocean ridge basalts (MORB) on a TiO2 vs. Cr# diagram. However, the AUC clinopyroxenes have much more radiogenic Sr ([87Sr/86Sr]i = 0.70554 to 0.70596), unradiogenic Nd ([εNd]i = - 1.0 to - 0.3), and Hf ([εHf]i = + 4.4 to + 6.6) isotopic compositions than those of the MORB or fore-arc basalts (FAB). In the Sr-Nd isotopic correlation diagram, the AUC clinopyroxenes plot in the enriched extension of the "mantle array". They also have more elevated 207Pb/204Pb ratios at a given 206Pb/204Pb than those of the MORB or FAB. In the Nd-Hf isotope space, the AUC clinopyroxenes have somewhat elevated 176Hf/177Hf ratios at a given 143Nd/144Nd compared to the "mantle-crust" array. These observations indicate that the sub-continental lithospheric mantle (SCLM) overprinted by secondary volatile-rich silicate melts might be the principal source of the AUC magmatism. Heat from the upwelling asthenosphere, through the slab window produced by detachment of the oceanic slab from the buoyant continental lithosphere during continental collision between the North and South China Cratons, might lead to partial melting of the overlying metasomatized SCLM, resulting in the post-collisional Triassic magmatism in South Korea.

Boron isotopes in brachiopods during the end-Permian mass extinction: constraints on pH evolution and seawater chemistry

NASA Astrophysics Data System (ADS)

Jurikova, Hana; Gutjahr, Marcus; Liebetrau, Volker; Brand, Uwe; Posenato, Renato; Garbelli, Claudio; Angiolini, Lucia; Eisenhauer, Anton

2017-04-01

The global biogeochemical cycling of carbon is fundamental for life on Earth with the ocean playing a key role as the largest and dynamically evolving CO2 reservoir. The boron isotope composition (commonly expressed in δ11B) of marine calcium carbonate is considered to be one of the most reliable paleo-pH proxies, potentially enabling us to reconstruct past ocean pH changes and understand carbon cycle perturbations along Earth's geological record (e.g. Foster et al., 2008; Clarkson et al., 2015). Brachiopods present an advantageous and largely underutilised archive for Phanerozoic carbon cycle reconstructions considering their high abundance in the geological record and its origin dating back to the early Cambrian. Moreover, their shell made of low-magnesium calcite makes these marine calcifiers more resistant to post-depositional diagenetic alteration of primary chemical signals. We have investigated the δ11B using MC-ICP-MS (Neptune Plus) and B/Ca and other elemental ratios (Mg/Ca, Sr/Ca, Al/Ca, Li/Ca, Ba/Ca, Na/Ca and Fe/Ca) using ICP-MS-Quadrupole (Agilent 7500cx) from the same specimens in pristine brachiopod shells from two sections from northern Italy during the Late Permian. These sections cover the δ13C excursion in excess of ˜4 ‰ (Brand et al., 2012) and are associated with major climate and environmental perturbations that lead to the mass extinction event at the Permian-Triassic boundary. Particular emphasis will be placed on the implications of our new paleo-pH estimates on the seawater chemistry during the Late Permian. Brand, U., Posenato, R., Came, R., Affek, H., Angiolini, L., Azmy, K. and Farabegoli, E.: The end-Permian mass extinction: A rapid volcanic CO2 and CH4-climatic catastrophe, Chemical Geology 323, 121-144, doi:10.1016/j.chemgeo.2012.06.015, 2012. Clarkson, M.O., Kasemann, S.A., Wood, R.A., Lenton, T.M., Daines, S.J., Richoz, S., Ohnemueller, F., Meixner, A., Poulton, S.W. and Tipper, E.T.: Ocean acidification and the Permo-Triassic mass extinction. Science 348, 229-232, doi: 10.1126/science.aaa0193, 2015. Foster, G.L.: Seawater pH, pCO2 and [CO32-] variations in the Caribbean Sea over the last 130 kyr: A boron isotope and B/Ca study of planktic foraminifera. Earth and Planetary Science Letters 271, 254-266. doi:10.1016/j.epsl.2008.04.015, 2008.

The spatial geochemical characteristics of groundwater and surface in the Tuul River basin, Ulaanbatar, Mongolia

NASA Astrophysics Data System (ADS)

Batdelger, Odsuren; Tsujimura, Maki; Zorigt, Byambasuren; Togtokh, Enkhjargal

2017-04-01

The capital city, Ulaanbaatar, is located along the Tuul River and its water supply totally dependent on the groundwater, which comes from the aquifer of the Tuul River. Due to the rapid growth of the population and the increasing human pressures in this basin, water quality has been deteriorating and has become a crucial issue for sustainable environmental and socio-economic development. Hydro-chemical and stable isotope tracing approaches were applied into the groundwater and surface water in order to study geochemical characteristics and groundwater and surface water interaction. The Tuul River water was mostly characterized by the Ca-HCO3 type, spatially variable and it changed into Ca-Na-HCO3 type in the downstream of the city after wastewater (WW) meets the river. Also, electrical conductivity (EC) values of Tuul River are increasing gradually with distance and it increased more than 2 times after WW meets the stream, therefore anthropogenic activities influence to the downstream of the river. The dominant hydro-chemical facies of groundwater were the Ca-HCO3 type, which represents 83% of the total analyzed samples, while Ca- HCO3-Cl-NO3, Na-HCO3, Ca-HCO3-SO4 each represent 4%, and Ca-mixed and Ca-Mg-HCO3 each represent 2% of the total samples. This suggests that groundwater chemistry is controlled by rock-water interaction and anthropogenic pollution. The floodplain groundwater chemical characteristics were similar to Tuul River water and showing lowest EC values. Groundwater far from floodplain showed higher EC (mean value of 498 μs/cm) values than river waters and floodplain groundwater. Also, different kinds of hydro-chemical facies were observed. The stable isotopic compositions revealed less evaporation effect on the groundwater and surface water, as well as an altitude effect in the river water. The similarity of stable isotopes and chemical characteristics of floodplain groundwater and river water suggests that alluvial groundwater is recharged by Tuul River water in the study area. The cluster analysis (CA) clearly indicated a connection between floodplain groundwater and river water, and also the effect of anthropogenic activities (such as canal and WW) in the system. The analysis results show that CA is a useful approach for future spatial sampling strategy in an optimal manner and offers a reliable classification of sampling stations in the region, especially along Tuul River. Therefore, the number of sampling stations in the monitoring network could be optimized without losing any significant information and saving cost.

A MIS 9/MIS 8 speleothem record of hydrological variability from Macedonia (F.Y.R.O.M.)

NASA Astrophysics Data System (ADS)

Regattieri, Eleonora; Zanchetta, Giovanni; Isola, Ilaria; Bajo, Petra; Perchiazzi, Natale; Drysdale, Russell N.; Boschi, Chiara; Hellstrom, John C.; Francke, Alexander; Wagner, Bernd

2018-03-01

The period corresponding to Marine Isotope Stages 9 (MIS 9) offers the opportunity to study orbital and sub-orbital scale climate variability under boundary conditions different from those of better studied intervals such as the Holocene and the Last Interglacial. Yet, it is poorly represented in independently-dated continental archives around the Mediterranean Region. Here, we present a speleothem stable isotope record (δ18O and δ13C) from the Former Yugoslavian Republic of Macedonia (F.Y.R.O.M., southern Balkans), which consists of two periods of growth broadly covering the ca. 332 to 292 ka and the ca. 264 to 248 ka intervals (MIS 9e-b and late MIS 8). We interpret the speleothem δ18O as mostly related to regional hydrology, with variations that can be interpreted as due to changes in rainfall amount, with higher/lower values associated to drier/wetter condition. This interpretation is corroborated by a change in mineralogical composition between aragonite and calcite at ca. 328 ka, which marks increasing precipitation at the onset of MIS 9 and occurs within a trend of decreasing δ18O values. Also the comparison with the multiproxy climate record available from the nearby Lake Ohrid seems to support the proposed interpretation. The MIS 9e interglacial appears to be characterized by wettest conditions between ca. 326 and 321 ka, i.e. lasting ca. 5 kyr. Decreasing precipitation and enhanced millennial scale variability matches the glacial inception (MIS9 d to b), with drier events at ca. 319 ka (ca. 2 kyr long) and 310 ka (ca. 1 kyr long), and a major rainfall reduction between 306 and 298 ka. The latter is followed by a prominent wetter period between 298 and 295 ka, for which carbon data values suggest high infiltration rate. Rainfall decreases again after 295 ka, and remain low until the growth interruption at ca. 292 ka. Resumption of the growth and progressive soil development, expressed by the carbon isotope record, occurred during the late part of MIS 8. Despite the rather high temporal uncertainty (average 6 ka), the speleothem hydrological record complements the environmental information provided by the Lake Ohrid record and also fits well to the framework of regional and extra-regional variability, showing similarities with pollen records from southern and western Europe, both at orbital and at sub-orbital time scale.

Earth's Coming of Age: Isotopically Tracking the Global Transformation from the Hadean to the Geologically Modern Earth

NASA Astrophysics Data System (ADS)

Bennett, V. C.; Nutman, A. P.

2017-12-01

Some of the strongest direct evidence that documents fundamental changes in the chemistry and organisation of Earth's interior derives from radiogenic isotopic compositions that include both long-lived (particularly 176Lu-176Hf and 147Sm-143Nd) and short-lived, i.e., now extinct parent isotope, systems (182Hf-182W, 146Sm-142Nd). Changes in patterns of isotopic evolution are linked to changes in mantle dynamics such that tracking these signatures in geologically well-characterised rocks can be used to discover the the nature and evolution of tectonic processes. Over the past decade, intensive geochemical investigations by various groups focussing on the oldest (> 4.0 Ga to 3.6 Ga) rock record, as preserved in several localities, have revealed isotopic distinctions in the early Earth compared with those in Proterozoic and younger rocks. For example, whilst the major and trace element compositions of Eoarchean gneisses have analogs in younger rocks in accord with a continuum of crust formation processes, radiogenic isotopic signatures from both long and short half-life decay schemes record an image of the Earth in transition from early differentiation processes, likely associated with planetary accretion and formation, to more modern style characterised by plate tectonics. The emerging image is that many Eoarchean rocks possess extinct nuclide anomalies in the form of 142Nd and 182Hf isotopic signatures that are absent in modern terrestrial samples; these signatures are evidence of chemical fractionation processes occuring within the first ca. 10-300 million years of Solar System history. In addition, viewing the global database, patterns of long-half life isotope signatures i.e., 143Nd and 176Hf differ from those seen in younger (<3.6 Ga) rocks, again providing a tracer of mantle dynamics and reflecting the influence of early processes. It is becoming increasingly apparent that the well demonstrated "coupled" 176Hf-143Nd isotopic evolution generated by plate tectonic processes and characterizing Phanerozoic and Proterozoic mantle derived rocks is absent in the Eoarchean record. Here, we track this isotopic transition in key regions and demonstrate how this places limits on the timing and style of transition from early to modern Earth.

Triple oxygen isotope analysis of tropospheric CO2 on the two sides of the Pacific Ocean

NASA Astrophysics Data System (ADS)

Liang, M. C.; Newman, S.; Laskar, A. H.

2017-12-01

The abundance variations of near surface atmospheric CO2 isotopologues (primarily 16O12C16O, 16O13C16O, 17O12C16O, and 18O12C16O) represent an integrated signal from anthropogenic/biogeochemical processes, including fossil fuel burning, biospheric photosynthesis and respiration, hydrospheric isotope exchange with water, stratospheric photochemistry, cross-tropopause exchange, and subsequent vertical mixing between the free troposphere and planetary boundary. Oxygen isotopes, in particular, are affected by both the carbon and water cycles. Being a useful tracer that directly probes governing processes in CO2 biogeochemical cycles, D17O (= ln(1+d17O) - 0.516 ln(1+d18O)) provides a powerful constraint on the strengths of the associated cycles involving CO2. Here, we report and compare summer to winter seasons CO2 isotopic composition from Taiwan (Taipei) and USA (Palos Verdes, CA). On average, the D17O values from Taiwan are significantly higher than those in USA. Analysis shows that the impact of 2014-2016 El Nino event on the observed D17O values is not visible, in contrast to what was reported for the 1997-1998 El Nino from the CO2 data collected from La Jolla, CA. Attempts are made to understand the elevated D17O values in the eastern Pacific compared to those in the western Pacific. Implications for utilizing the new tracer D17O along with the conventional d18O for carbon cycling studies are also discussed.

Petrology of Anomalous Mafic Achondrite Polymict Breccia Pasamonte

NASA Technical Reports Server (NTRS)

Mittlefehldt, D. W.; Berger, E. L.; Le, L.

2017-01-01

The most common asteroidal igneous meteorites are eucrite-type basalts and gabbros - rocks composed of ferroan pigeonite and augite, calcic plagioclase, silica, ilmenite, troilite, Ca-phosphate, chromite and Fe-metal [1]. These rocks are thought to have formed on a single asteroid, widely considered to be 4 Vesta, along with howardites and diogenites [1, 2]. High precision O-isotopic analyses have shown that some eucrites have small, well-resolved O-isotopic differences from the group mean [3-5]. These Oanomalous eucrites are thought to hail from asteroidal parents that are distinct from that of eucrites [5]. Three O-anomalous eucrites are PCA 82502, PCA 91007 (paired) and Pasamonte, all of which have the same O-isotopic composition [5, 6]. Our petrologic studies have shown that PCA 82502 and PCA 91007 have well-resolved anomalies in low-Ca pyroxene Fe/Mn compared to eucrites [6]. Divalent Mn and Fe are homologous species that do not greatly fractionate during igneous processes; mafic mineral Fe/Mn can be used to fingerprint parent object sources [7]. Previous petrological studies of Pasamonte [8-10] have not yielded sufficiently precise Fe/Mn ratios to allow distinction of anomalies of the scale of those found for the PCA basalts. We have begun petrological study of Pasamonte for comparison with our results on normal and anomalous eucrites [6], and to constrain its origin.

Uranium Isotope Compositions of Mid-Proterozoic Organic-rich Mudrocks: Evidence for an Episode of Increased Ocean Oxygenation at ca. 1.36 Ga and Evaluation of the Effect of Post-Depositional Hydrothermal Fluid Flow

NASA Astrophysics Data System (ADS)

Kendall, B.; Yang, S.; Lu, X.; Zhang, F.; Zheng, W.

2016-12-01

The U isotope system represents a relatively new paleoredox proxy that can help trace the evolution of global ocean redox chemistry, but has rarely been applied to the Mid-Proterozoic. We report U isotope data for marine black shales of the early Mesoproterozoic Velkerri Formation (Roper Group) and late Paleoproterozoic Wollogorang Formation (Tawallah Group) from the McArthur Basin, Northern Australia. An average authigenic δ238U of 0.13 ± 0.04‰ (1SD; relative to standard CRM145) was obtained for six euxinic shales from a 1 m interval that previously yielded a precise Re-Os depositional age of 1361 ± 21 Ma. After correcting for a U isotope fractionation of 0.60-0.85‰ between seawater and open-ocean euxinic sediments, we infer that coeval global seawater had a δ238U of -0.47‰ to -0.72‰, which is 0.1-0.3‰ lighter than modern seawater (-0.40 ± 0.03‰). A U isotope mass-balance model suggests that anoxic marine environments accounted for 25-50% of the global oceanic U sink at 1.36 Ga, which is 3-7 times greater than today. The model suggests that a significant proportion, potentially even a majority, of the seafloor was not covered by anoxic waters. Hence, we infer that a significant extent of the ocean floor was covered by O2-bearing waters at 1.36 Ga. The O2 concentrations of those waters were not necessarily high, and a large expanse of weakly to mildly oxygenated deep waters is consistent with the U isotope data. Uranium isotope data from a 1 m interval in the lower Velkerri Formation, deposited at 1417 ± 29 Ma based on Re-Os geochronology, yield a greater estimate for the extent of ocean anoxia. Hence, the upper Velkerri Formation may capture a transient episode of increased ocean oxygenation. Previous Re-Os isotope data from black shales of the ca. 1.73 Ga Paleoproterozoic Wollogorang Formation yielded an erroneously young date of 1359 ± 150 Ma because hydrothermal fluids percolated through the Tawallah Group rocks at ca. 1640 Ma. Higher δ238U is observed in samples closer to the base of the black shale unit where the greatest extent of open-system Re-Os isotope behavior was observed. Hence, post-depositional hydrothermal fluid flow can overprint the depositional δ238U of black shales and lead to erroneous interpretations of global ocean paleoredox conditions.

Relationships between the stable isotopic signatures of living and fossil foraminifera in Monterey Bay, California

NASA Astrophysics Data System (ADS)

Martin, Jonathan B.; Day, Shelley A.; Rathburn, Anthony E.; Perez, M. Elena; Mahn, Chris; Gieskes, Joris

2004-04-01

Fossil foraminifera are critical to paleoceanographic reconstructions including estimates of past episodes of methane venting. These reconstructions rely on benthic foraminifera incorporating and retaining unaltered the ambient isotopic compositions of pore fluids and bottom waters. Comparisons are made here of isotopic compositions of abundant live and fossil foraminifera (Uvigerina peregrina, Epistominella pacifica, Bulimina mexicana, and Globobulimina pacifica) collected in Monterey Bay, CA from two cold seeps (Clam Flats and Extrovert Cliffs) and from sediments ˜5 m outside of the Clam Flats seep. Clam Flats has steep δ13CDIC gradients (to <-45‰), but DIC at Extrovert Cliffs is less enriched in 12C (to approximately -22‰). Oxygen isotope values of fossil foraminifera at Clam Flats are ˜1.5‰ enriched in 18O over the living foraminifera, as well as those of both live and fossil foraminifera at Extrovert Cliffs, suggesting they may have lived during the last glacial maximum. Statistical comparisons (Student's t and Kolmogorov-Smirnov tests) of δ13C and δ18O values indicate that live and fossil foraminifera come from different populations at both Clam Flats and Extrovert Cliffs. At Clam Flats, the difference appears to result from alteration enriching some fossil foraminifera in 12C over live foraminifera. At Extrovert Cliffs, the fossil foraminifera are enriched in 13C over the live foraminifera, suggesting they lived prior to the onset of venting and thus that venting began recently. The short time of venting at Extrovert Cliffs may be responsible for the less alteration there compared with Clam Flats. These results indicate that preservation of foraminifera is likely to be poor within long-lived cold seeps, but that foraminifera living in the surrounding sediment may incorporate and preserve broad basin-wide changes in isotopic compositions of the ambient water.

The role of sedimentology, oceanography, and alteration on the δ56Fe value of the Sokoman Iron Formation, Labrador Trough, Canada

NASA Astrophysics Data System (ADS)

Raye, Urmidola; Pufahl, Peir K.; Kyser, T. Kurtis; Ricard, Estelle; Hiatt, Eric E.

2015-09-01

The Sokoman Formation is a ca. 100-m-thick succession of interbedded iron formation and fine-grained siliciclastics deposited at 1.88 Ga. Accumulation occurred on a dynamic paleoshelf where oxygen stratification, coastal upwelling of hydrothermally derived Fe and Si, microbial processes, tide and storm currents, diagenesis, and low-grade prehnite-pumpellyite metamorphism controlled lithofacies character and produced complex associations of multigenerational chert, hematite, magnetite, greenalite, stilpnomelane and Fe carbonate. Hematite-rich facies were deposited along suboxic segments of the coastline where photosynthetic oxygen oases impinged on the seafloor. Hematitic, cross-stratified grainstones were formed by winnowing and reworking of freshly precipitated Fe-(oxyhydr)oxide and opal-A by waves and currents into subaqueous dunes. Magnetite-rich facies contain varying proportions of greenalite and stilpnomelane and record deposition in anoxic middle shelf environments beneath an oxygen chemocline. Minor negative Ce anomalies in hematitic facies, but prominent positive Ce and Eu anomalies and high LREE/HREE ratios in magnetite-rich facies imply the existence of a weakly oxygenated surface ocean above anoxic bottom waters. The Fe isotopic composition of 31 whole rock (-0.46 ⩽ δ56Fe ⩽ 0.47‰) and 21 magnetite samples (-0.29 ⩽ δ56Fe ⩽ 0.22‰) from suboxic and anoxic lithofacies was controlled primarily by the physical oceanography of the paleoshelf. Despite low-grade metamorphism recorded by the δ18O values of paragenetically related quartz and magnetite, the Sokoman Formation preserves a robust primary Fe isotopic signal. Coastal upwelling is interpreted to have affected the isotopic equilibria between Fe2+aq and Fe-(oxyhydr)oxide in open marine versus coastal environments, which controlled the Fe isotopic composition of lithofacies. Unlike previous work that focuses on microbial and abiotic fractionation processes with little regard for paleoenvironment, our work demonstrates that depositional setting is paramount in governing the Fe isotopic composition of iron formations irrespective of what Fe-bearing minerals precipitated.

Sr-Nd-Hf-O isotope geochemistry of the Ertaibei pluton, East Junggar, NW China: Implications for development of a crustal-scale granitoid pluton and crustal growth

NASA Astrophysics Data System (ADS)

Tang, Gong-Jian; Wang, Qiang; Zhang, Chunfu; Wyman, Derek A.; Dan, Wei; Xia, Xiao-Ping; Chen, Hong-Yi; Zhao, Zhen-Hua

2017-09-01

To better understand the compositional diversity of plutonic complexes and crustal growth of the Central Asian Orogenic Belt (CAOB), we conducted an integrated study of the Ertaibei pluton, which obtained geochronological, petrological, geochemical, and isotopic (including whole rock Sr-Nd, in situ zircon Hf-O) data. The pluton (ca. 300 Ma) is composed of granodiorites that contain mafic microgranular enclaves (MMEs), dolerite dikes, and granite dikes containing quartz-tourmaline orbicules. The dolerite dikes were possibly generated by melting of an asthenospheric mantle source, with discrete assimilation of lower crustal components in the MASH (melting, assimilation, storage, and homogenization) zone. The MMEs originated from hybridization between mantle and crust-derived magmas, which spanned a range of melting depths (˜25-30 km) in the MASH zone and were episodically tapped. Melting of the basaltic lower crust in the core of the MASH zone generated magmas to form the granodiorites. The granite dikes originated from melting of an arc-derived volcanogenic sedimentary source with a minor underplated basaltic source in the roof of the MASH zone (˜25 km). The compositional diversity reflects both the magma sources and the degree of maturation of the MASH zone. Although having mantle-like radiogenic isotope compositions, the Ertaibei and other postcollisional granitoids show high zircon δ18O values (mostly between +6 and +9‰), indicating a negligible contribution to the CAOB crustal growth during the postcollisional period.

Lack of Correlated Isotopic and Compositional Variations in Mauna Loa Lavas: A Serious Problem for Pyroxenite/Eclogite Plume Source Models

NASA Astrophysics Data System (ADS)

Rhodes, J. M.; Weis, D.; Norman, M. D.; Garcia, M. O.

2007-12-01

The long held notion that basaltic magmas are produced by decompressional melting of peridotite is under challenge. Recent models for the Hawaiian and other plumes argue that they consist of a heterogeneous mix of peridotite and discrete eclogite blobs, the latter derived from recycled subducted crust. Eclogite melting produces relatively siliceous magmas (dacite to andesite) which either mix with picritic melts from the peridotite, or, more plausibly, react with the peridotite to produce pyroxenite. Melting of varying proportions of the peridotite/pyroxenite mix is thought to produce the correlated compositional and isotopic characteristics of Hawaiian volcanoes. Magmas from Mauna Loa and Koolau volcanoes are thought to contain more of the recycled component; those from Loihi and Kilauea volcanoes contain less. A simple test of these mixed source models examines whether isotopic changes within the long magmatic history of a single volcano are accompanied by corresponding changes in major and trace element characteristics. Mauna Loa, where we have sampled around 400 - 500 ka of the volcano's eruptive history, provides an excellent opportunity for such a test. During this time, Mauna Loa will have traversed almost half the Hawaiian plume. According to the models, it should have erupted magmas produced from a range of pyroxenite/peridotite mixes with corresponding differences in both isotopic ratios and major and trace elements. Our data show that there is only minor isotopic (Sr, Pb, Nd, Hf) diversity in young lavas (<100 ka), but older lavas are highly diverse, ranging from modern values to those that are close to, and overlap with, those of Loihi volcano. If this isotopic diversity is a consequence of different proportions of pyroxenite and peridotite in the plume source, as the new models predict, we should expect to see correlated changes in bulk composition, particularly. in normalized SiO2, CaO/Al2O3, FeO/MgO and Ni - MgO relationships, as well as changes in Ni - Sc - V relationships. We do not. These parameters remain remarkably uniform over the 400 to 500 ka magmatic history of the volcano, with no correlated variation with isotopic ratios. We conclude that the isotopic heterogeneity within the Hawaiian plume is intrinsic to the peridotite plume source and not dependent on variable contributions from entrained, lithologically-discrete units.

A FIB/TEM Study of a Complex Wark-Lovering Rim on a Vigarano CAI

NASA Technical Reports Server (NTRS)

Keller, L. P.; Needham, A. W.; Messenger, S.

2013-01-01

Wark-Lovering (WL) rims are thin multilayered mineral sequences that surround most Ca, Al-rich inclusions (CAIs). Several processes have been proposed for WL rim formation, including condensation, flash-heating or reaction with a nebular reservoir, or combinations of these [e.g. 1-7], but no consensus exists. Our previous coordinated transmission electron microscope (TEM) and NanoSIMS O isotopic measurements showed that a WL rim experienced flash heating events in a nebular environment with planetary O isotopic composition, distinct from the (16)O-rich formation environment [6]. Our efforts have focused on CAIs from the CV(sub red) chondrites, especially Vigarano, because these have escaped much of the parent body alteration effects that are common in CAIs from CV(sub ox) group.

Using Calcium Isotopic Composition of Calcium Carbonate Veins to Assess the Roles of Vein Formation and Seafloor Alteration in Regulation of the Carbon Cycle

NASA Astrophysics Data System (ADS)

Chen, F.; Coggon, R. M.; Teagle, D. A. H.; Turchyn, A. V.

2016-12-01

Calcium carbonate vein formation in the oceanic crust has been proposed as a climate-sensitive feedback mechanism that regulates the carbon cycle on million-year timescales. The suggestion has been that higher pCO2 levels may drive changes in ocean temperature and pH that increase seafloor alteration, releasing more calcium from oceanic basalt. This results in more removal of carbon from Earth's surface through calcium carbonate formation, which includes calcium carbonate vein formation in oceanic crust. The importance of this feedback mechanism remains enigmatic. Measurements of the δ44Ca of calcium carbonate veins in the oceanic crust may constrain the sources of calcium and timing of vein formation. Seawater and basalt are the only sources present shortly after crustal formation, whereas other sources, such as anhydrite dissolution and sedimentary carbonates become available when the crust ages, at which point carbonate veins may form far from the ridge axis. We report the calcium isotopic composition of 65 calcium carbonate veins, ranging from 108 to 1.2 million years old, in hydrothermally altered basalt from the Mid-Atlantic and Juan de Fuca ridges. We also present 43 δ44Ca measurements of 5.9 million year old basalts and dikes from the Costa Rica Rift that have undergone hydrothermal alteration over a range of conditions in upper crust. The δ44Ca of the calcium carbonate veins ranges from -1.59 to 1.01‰ (versus Bulk Silicate Earth), whereas the δ44Ca of altered basalts ranges from -0.18 to 0.28‰. Depth and temperature of formation seem to be major influences on calcium carbonate vein δ44Ca, with veins formed at cool, shallower depths having higher δ44Ca, closer to seawater. In contrast, we note no temporal variation in δ44Ca of calcium carbonate veins when comparing samples from older and younger crust. The majority of veins (54 out of 65) have δ44Ca between that of seawater and basalt, which implies that they may have formed quite soon after crustal formation before other sources of calcium became available. We conclude that calcium carbonate vein formation may derive a significant fraction of calcium from seafloor alteration of basalts. This may cause rates of carbonate vein formation to be sensitive to aspects of ocean chemistry that vary due to changing climate conditions.

Processes affecting the stable isotope composition of calcite during precipitation on the surface of stalagmites: Laboratory experiments investigating the isotope exchange between DIC in the solution layer on top of a speleothem and the CO2 of the cave atmosphere

NASA Astrophysics Data System (ADS)

Dreybrodt, Wolfgang; Hansen, Maximilian; Scholz, Denis

2016-02-01

We present a theoretical derivation of the exchange time, τex, needed to establish isotopic equilibrium between atmospheric CO2 in a cave and HCO3- dissolved in a thin water film covering the surface of a speleothem. The result is τex = τredex · [HCO3-]/ (KH · pCO2cave) , where τredex depends on the depth, a, of the water film and on temperature. [HCO3-] is the concentration of bicarbonate, pCO2cave the partial pressure of CO2, and KH is Henry's constant. To test the theory we prepared stagnant or flowing thin films of a NaHCO3 solution and exposed them at 20 °C to an CO2 containing atmosphere of pCO2 500, 12,500, or 25,000 ppmV and defined isotope composition. The δ13C and δ18O values of the DIC in the solution were measured as a function of the exposure time. For stagnant films with depths between 0.06 and 0.2 cm the δ13C values exhibit an exponential approach towards isotope equilibrium with the atmospheric CO2 with exchange time, τex. The δ18O values first evolve towards isotopic equilibrium with atmospheric CO2, reach a minimum value and then drift away from the isotopic equilibrium with atmospheric CO2 approaching a steady state caused by isotopic exchange of oxygen with water. The experimental findings are in satisfactory agreement with the theoretical predictions. To further investigate isotope evolution in cave analogue conditions, a water film containing 5 mmol/L of NaHCO3 with a depth of 0.013 cm flowing down an inclined borosilicate glass plate was exposed to an atmosphere with pCO2 = 500 ppmV at a temperature of 20 °C. The δ13C and δ18O values were measured as a function of flow (exposure) time, t. The isotope compositions in the DIC of the water film decrease linear in time by δDIC (t) =δDIC (0) - (δDIC (0) -δDIC (∞)) · t /τex where δDIC (0) is the initial isotope composition of dissolved inorganic carbon (DIC) in the water film and δDIC (∞) its final value. From these data an exchange time τex of ca. 7000 s was obtained, in satisfactory agreement with the theoretical predictions. The exchange times can be calculated by τex = τredex · [HCO3-]/ (KH · pCO2cave), where τredex is given by the theory as function of temperature and the depth, a, of the water film. This way it is possible to obtain exchange times for various conditions of stalagmite growth as they occur in caves.

Indian Summer Monsoon dynamics during Termination II and MIS 5e

NASA Astrophysics Data System (ADS)

Magiera, Matthias; Erhardt, Andrea M.; Hartland, Adam; Kwiecien, Ola; Cheng, Hai; Immenhauser, Adrian; Turchyn, Alexandra; Breitenbach, Sebastian F. M.

2017-04-01

The interpretation of speleothem oxygen isotope ratios (δ18O) as proxy for Indian Summer Monsoon (ISM) dynamics is ambiguous, due to multiple influencing factors. Here we combine δ18O and calcium isotope δ44Ca analyses with elemental data to delineate regional shifts in moisture source, local rainfall amount, and changes in ISM intensity and length during Termination II and MIS 5e. Oxygen isotope ratios reflect a mixed signal of moisture source dynamics and rainfall amount; δ44Ca and Mg/Ca ratios are interpreted as proxies for local effective moisture and prior calcite precipitation (PCP) in the epikarst. The age of stalagmite MAW-3 from Mawmluh Cave, NE India, is constraint by six U-series dates. 108 samples, obtained at 0.4 mm resolution from the 70 mm long speleothem sample, have been analysed for δ18O, δ44Ca and Mg/Ca. Oxygen isotope ratios were measured on a ThermoFisher Scientific MAT 253 at Ruhr-University Bochum. Elemental ratios were measured on a quadrupole ICP-MS at Waikato University. Calcium isotope ratios were analyzed on a ThermoFisher Scientific Triton at University of Cambridge. MAW-3 grew from 136 kyrs BP to 96 kyrs BP, covering Termination II and MIS 5e. Oxygen isotope values are high (ca. +0.91 ‰) during Termination II, reach a minimum during MIS 5e (-3.5 ‰), and rise again to -0.2 ‰ at the end of MIS 5e. Calcium isotope ratios range from -0.32 ‰ to -0.70 ‰ and show a positive correlation (R2= 0.7) with δ18O. High δ18O values during Termination II reflect reduced atmospheric circulation and/or a proximal moisture source (Bay of Bengal), implying lowered ISM intensity. A positive correlation of δ18O with δ44Ca suggests concurrent changes of moisture source location and local rainfall amount, with a proximal moisture source and reduced effective rainfall during periods of weak ISM. Elevated Mg/Ca ratios at such intervals corroborate PCP occurrence, which reflects dry conditions. The beginning of MIS 5e (ca. 132 kyrs BP) is marked by a rapid change to lower δ18O and δ44Ca, suggesting increased local infiltration with increasing ISM rainfall, and a concurrent change to a more distal moisture source. The MAW-3 multi-proxy record compares well with reconstructions from China and northern India, the latter being more depleted, due to Rayleigh fractionation. We suggest that multi-proxy analyses of δ18O, δ44Ca and Mg/Ca greatly help to delineate regional circulation pattern and local effective moisture dynamics in monsoonal settings.

Mineralogy and petrography of HAL, an isotopically-unusual Allende inclusion

NASA Technical Reports Server (NTRS)

Allen, J. M.; Grossman, L.; Lee, T.; Wasserburg, G. J.

1980-01-01

Results of a detailed mineralogical and textural study of the HAL (Hibonite ALlende) inclusion of the Allende meteorite, which has been found to exhibit no Mg-26 excesses despite very high Al-27/Mg-24 ratios and large fractionation effects with small nuclear effects in its Ca, are reported. The inclusion is found to consist of three up to 1-mm diameter hibonite crystals partially surrounded by a black rim resembling a devitrified glass and containing an anisotropic Al-Fe oxide, which is in turn surrounded by a 2-mm thick friable rim sequence consisting of five layers distinguishable by mineral composition. From the available evidence, it is concluded that each of the layers of the friable rim formed by the accretion of an assemblage of condensate grains rather than by the complete reaction of a HAL precursor with a nebular gas, thus explaining its unusual isotopic characteristics and supporting the conclusion that the solar nebular contained isotopically-distinct reservoirs.

Coordinated mineralogical and isotopic analyses of a cosmic symplectite discovered in a comet 81P/Wild 2 sample

NASA Astrophysics Data System (ADS)

Nguyen, Ann N.; Berger, Eve L.; Nakamura-Messenger, Keiko; Messenger, Scott; Keller, Lindsay P.

2017-09-01

We have discovered in a Stardust mission terminal particle a unique mineralogical assemblage of symplectically intergrown pentlandite ((Fe,Ni)9S8) and nanocrystalline maghemite (γ-Fe2O3). Mineralogically similar cosmic symplectites (COS) have only been found in the primitive carbonaceous chondrite Acfer 094 and are believed to have formed by aqueous alteration. The O and S isotopic compositions of the Wild 2 COS are indistinguishable from terrestrial values. The metal and sulfide precursors were thus oxidized by an isotopically equilibrated aqueous reservoir either inside the snow line, in the Wild 2 comet, or in a larger Kuiper Belt object. Close association of the Stardust COS with a Kool mineral assemblage (kosmochloric Ca-rich pyroxene, FeO-rich olivine, and albite) that likely originated in the solar nebula suggests the COS precursors also had a nebular origin and were transported from the inner solar system to the comet-forming region after they were altered.

Marine Carbonate Component in the Mantle Beneath the Southeastern Tibetan Plateau: Evidence From Magnesium and Calcium Isotopes

NASA Astrophysics Data System (ADS)

Liu, Fang; Li, Xin; Wang, Guiqin; Liu, Yufei; Zhu, Hongli; Kang, Jinting; Huang, Fang; Sun, Weidong; Xia, Xiaoping; Zhang, Zhaofeng

2017-12-01

Tracing and identifying recycled carbonates is a key issue to reconstruct the deep carbon cycle. To better understand carbonate subduction and recycling beneath the southeastern Tibetan Plateau, high-K cal-alkaline volcanic rocks including trachy-basalts and trachy-andesites from Tengchong were studied using Mg and Ca isotopes. The low δ26Mg (-0.31 ± 0.03‰ to -0.38 ± 0.03‰) and δ44/40Ca (0.67 ± 0.07‰ to 0.80 ± 0.04‰) values of these volcanic rocks compared to those of the mantle (-0.25 ± 0.07‰ and 0.94 ± 0.05‰, respectively) indicate the incorporation of isotopically light materials into the mantle source, which may be carbonate-bearing sediments with low δ26Mg and δ44/40Ca values. In addition, no correlations of δ26Mg and δ44/40Ca with either SiO2 contents or trace element abundance ratios (e.g., Sm/Yb and Ba/Y) were observed, suggesting that limited Mg and Ca isotopic fractionation occurred during cal-alkaline magmatic differentiation. A binary mixing model using Mg-Ca isotopes shows that 5-8% carbonates dominated primarily by dolostone were recycled back into the mantle. Since Tengchong volcanism is still active and probably related to ongoing plate tectonic movement, we propose that the recycled carbonates are derived from oceanic crust related to the ongoing subduction of the Indian plate.

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

NASA Astrophysics Data System (ADS)

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

2014-12-01

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

Unexpectedly large charge radii of neutron-rich calcium isotopes

DOE PAGES

Garcia Ruiz, R. F.; Bissell, M. L.; Blaum, K.; ...

2016-02-08

Here, despite being a complex many-body system, the atomic nucleus exhibits simple structures for certain ‘magic’ numbers of protons and neutrons. The calcium chain in particular is both unique and puzzling: evidence of doubly magic features are known in 40,48Ca, and recently suggested in two radioactive isotopes, 52,54Ca. Although many properties of experimentally known calcium isotopes have been successfully described by nuclear theory, it is still a challenge to predict the evolution of their charge radii. Here we present the first measurements of the charge radii of 49,51,52Ca, obtained from laser spectroscopy experiments at ISOLDE, CERN. The experimental results aremore » complemented by state-of-the-art theoretical calculations. The large and unexpected increase of the size of the neutron-rich calcium isotopes beyond N = 28 challenges the doubly magic nature of 52Ca and opens new intriguing questions on the evolution of nuclear sizes away from stability, which are of importance for our understanding of neutron-rich atomic nuclei.« less

Separation of Isotopes by Electromigration in Fused Salts; SEPARATION DES ISOTOPES PAR ELECTROMIGRATION EN SELS FONDUS (in French)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Menes, F.

1961-12-01

A process is given for the separation of isotopes by reflux electromigration of fused salts. The process is carried out in a countercurrent manner on a fused mixture of a salt containing the isotopic cations with a salt having the same anion and a cation with a mobility as near as possible to that of the isotopic cations. An electrolytic cell for carrying out the process is described. Examples are presented of the process in which lithium-6 and lithium-7 are separated in a LiBr-KBr mixture, and calcium isotopes are separated in CaBr/sub 2/-KBr and CaBr/sub 2/- LiBr systems. (N.W.R.)

Variability of Fe isotope compositions of hydrothermal sulfides and oxidation products at mid-ocean ridges

NASA Astrophysics Data System (ADS)

Li, Xiaohu; Wang, Jianqiang; Chu, Fengyou; Wang, Hao; Li, Zhenggang; Yu, Xing; Bi, Dongwei; He, Yongsheng

2018-04-01

Significant Fe isotopic fractionation occurs during the precipitation and oxidative weathering of modern seafloor hydrothermal sulfides, which has an important impact on the cycling of Fe isotopes in the ocean. This study reports the Fe-isotope compositions of whole-rock sulfides and single-mineral pyrite collected from hydrothermal fields at the South Mid-Atlantic Ridge (SMAR) and the East Pacific Rise (EPR) and discusses the impacts of precipitation and late-stage oxidative weathering of sulfide minerals on Fe isotopic fractionation. The results show large variation in the Fe-isotope compositions of the sulfides from the different hydrothermal fields on the mid-oceanic ridges, indicating that relatively significant isotope fractionation occurs during the sulfide precipitation and oxidative weathering processes. The Fe-isotope compositions of the sulfides from the study area at the SMAR vary across a relatively small range, with an average value of 0.01‰. This Fe-isotope composition is similar to the Fe-isotope composition of mid-oceanic ridge basalt, which suggests that Fe was mainly leached from basalt. In contrast, the Fe-isotope composition of the sulfides from the study area at the EPR are significantly enriched in light Fe isotopes (average value - 1.63‰), mainly due to the kinetic fractionation during the rapid precipitation process of hydrothermal sulfide. In addition, the pyrite from different hydrothermal fields is enriched in light Fe isotopes, which is consistent with the phenomenon in which light Fe isotopes are preferentially enriched during the precipitation of pyrite. The red oxides have the heaviest Fe-isotope compositions (up to 0.80‰), indicating that heavy Fe isotopes are preferentially enriched in the oxidation product during the late-stage oxidation process. The data obtained from this study and previous studies show a significant difference between the Fe-isotope compositions of the sulfides from the SMAR and EPR. The relatively heavy Fe isotopes compositions of the sulfides from the SMAR may suggest the equilibrium fractionation process under high temperature conditions. The red Fe oxides are enriched in heavy Fe isotopes, indicating that the oxidative weathering processes result in the occurrence of significant Fe-isotope fractionation and the preferential enrichment of heavy Fe isotopes in the oxidation product.

Constraining seasonal active layer dynamics and chemical weathering reactions occurring in North Slope Alaskan watersheds with major ion and isotope (δ34SSO4, δ13CDIC, 87Sr/86Sr, δ44/40Ca, and δ44/42Ca) measurements

NASA Astrophysics Data System (ADS)

Lehn, Gregory O.; Jacobson, A. D.; Douglas, T. A.; McClelland, J. W.; Barker, A. J.; Khosh, M. S.

2017-11-01

Rising air temperatures in the Arctic may destabilize a large pool of organic carbon stored in permafrost, thereby causing a positive feedback to global climate warming. Permafrost thaw could also deepen hydrologic flow paths and expose previously frozen rock and mineral fragments to chemical weathering. Future shifts in the inorganic solute geochemistry of Arctic rivers may signal changes in soil processes that also affect organic carbon storage. Tracing permafrost thaw with dissolved riverine loads requires understanding the spatial and seasonal variation of chemical weathering reactions and other biogeochemical phenomena that affect elemental mass-transport. To help identify connections between mineral weathering and active layer processes, we studied the major ion and isotope (δ34SSO4, δ13CDIC, 87Sr/86Sr, δ44/40Ca, and δ44/42Ca) geochemistry of five streams draining the North Slope of Alaska. Continuous permafrost underlies all streams, but the Atigun River, Roche Moutonnée Creek, and Trevor Creek primarily drain bare bedrock outcrops in the Brooks Range, while the Upper Kuparuk River and Imnavait Creek primarily drain tundra. In total, we collected 546 water samples spanning the spring freshet through fall freeze-up in 2009 and 2010. We also analyzed snow, rock, sediment, soil, and plant samples. Major ion ratios and δ13CDIC values point to the overall dominance of carbonate weathering by carbonic and sulfuric acids, with additional influences from atmospheric deposition, plant decay, sulfate salt dissolution, and silicate weathering by carbonic acid. δ13CDIC values may also reflect partial equilibration with soil and atmospheric CO2. All streams display large seasonal variations in major ion ratios and δ13CDIC values that are consistent with progressive deepening of the seasonally thawed zone over the summer. In the mountain watersheds, carbonate weathering dominates during the spring and summer, while sulfate salt (primarily CaSO4 and MgSO4) dissolution dominates during the fall. Riverine δ34SSO4 values reveal that the sulfate salts are secondary precipitates. We propose a conceptual model where cryoconcentration in soils during the late fall and winter causes secondary mineral formation at depth and re-exposure during subsequent thaw seasons produces the observed geochemical signals in rivers. The tundra streams lack definitive evidence for sulfate salt dissolution, presumably because thick peat soils limit the exposure and weathering of underlying glacial sediment where the salts are expected to form and dissolve. Appearance of a sulfate salt dissolution signal in tundra streams may correlate with future permafrost degradation. Carbonate weathering dominates riverine 87Sr/86Sr ratios, but the compositional heterogeneity of bedrock limits interpretation of the data. All rivers have higher δ44/40Ca values compared to bedrock, likely due to plant uptake of lighter Ca isotopes. In the tundra watersheds, freshet δ44/40Ca values were 0.10-0.20‰ lower than summer and fall values. These trends likely reflect contributions from plant decay, as comparison between δ44/40Ca and δ44/42Ca values suggests that all isotopic variation is mass-dependent with minimal radiogenic 40Ca inputs from the weathering of old silicate minerals with high K/Ca ratios.

Isotopy of the hydrosphere

NASA Astrophysics Data System (ADS)

Ferronskii, V. I.; Poliakov, V. A.

This book is concerned with the natural relations regarding the distribution of the stable isotopes of hydrogen and oxygen in the hydrosphere, taking into account the most important problems with respect to the dynamics and the origin of waters. The solution of these problems on an isotopic basis is considered. The physicochemical principles of isotope separation are discussed along with the isotopic composition of atmospheric moisture, the isotopic composition of surface continental waters, the hydrogen and oxygen isotopic composition of minerals of magmatic and metamorphic rocks and fluid inclusions, the isotopic composition of groundwaters of modern volcanic regions, and the origin of the earth's hydrosphere in the light of isotopic, cosmochemical, and theoretical studies. Attention is also given to the separation of hydrogen and oxygen isotopes of waters in the underground cycle, the isotopic composition of the deep-formation waters of sedimentary basins, the relationship between surface and ground waters, and the groundwater residence time in an aquifer.

The influence of authigenic clay formation on the mineralogy and stable isotopic record of lacustrine carbonates

NASA Astrophysics Data System (ADS)

Bristow, Thomas F.; Kennedy, Martin J.; Morrison, Keith D.; Mrofka, David D.

2012-08-01

The mineralogical, compositional and stable isotopic variability of lacustrine carbonates are frequently used as proxies for ancient paleoenvironmental change in continental settings, under the assumption that precipitated carbonates reflect conditions and chemistry of ancient lake waters. In some saline and alkaline lake systems, however, authigenic clay minerals, forming at or near the sediment water interface, are a major sedimentary component. Often these clays are rich in Mg, influencing the geochemical budget of lake waters, and are therefore expected to influence the properties of contemporaneous authigenic carbonate precipitates (which may also contain Mg). This paper documents evidence for a systematic feedback between clay mineral and carbonate authigenesis through multiple precessionally driven, m-scale sedimentary cycles in lacustrine oil-shale deposits of the Eocene Green River Formation from the Uinta Basin (NE Utah). In the studied section, authigenic, Mg-rich, trioctahedral smectite content varies cyclically between 9 and 39 wt.%. The highest concentrations occur in oil-shales and calcareous mudstones deposited during high lake level intervals that favored sedimentary condensation, lengthening the time available for clay diagenesis and reducing dilution by other siliciclastic phases. An inverse relation between dolomite percentage of carbonate and trioctahedral smectite abundance suggests the Mg uptake during clay authigenesis provides a first order control on carbonate mineralogy that better explains carbonate mineralogical trends than the possible alternative controls of (1) variable Mg/Ca ratios in lake water and (2) degree of microbial activity in sediments. We also observe that cyclical change in carbonate mineralogy, believed to be induced by clay authigenesis, also causes isotopic covariation between δ13CPDB and δ18OPDB of bulk sediments because of differences in the equilibrium fractionation factors of dolomite and calcite (˜2‰ and ˜2.6%, respectively). This provides an alternative mechanism for the common pattern of isotopic covariation, which is typically attributed to the effect of simultaneous changes in water balance and biological activity on the carbon and oxygen isotopic composition of lake waters. These findings may help improve paleoenvironmental reconstructions based on lacustrine carbonate records by adding to the factors known to influence the mineralogical, compositional and stable isotopic signals recorded by lacustrine carbonates.

Geology, geochemistry and genesis of the Eocene Lailishan Sn deposit in the Sanjiang region, SW China

NASA Astrophysics Data System (ADS)

Cao, Hua-Wen; Pei, Qiu-Ming; Zhang, Shou-Ting; Zhang, Lin-Kui; Tang, Li; Lin, Jin-Zhan; Zheng, Luo

2017-04-01

The Lailishan deposit is an important tin deposit that is genetically associated with an Early Eocene biotite granite in the western Yunnan metallogenic belt in the Sanjiang region, SW China. This study reports new zircon U-Pb ages and Hf isotopic data, whole-rock elements, mica Ar-Ar age and C-H-O-S-Pb isotope for the Lailishan Sn deposit. The mineralization-related biotite granite crystallized during the Early Eocene (50.5 Ma), with its zircon εHf(t) values ranging from -11.5 to -7.6 and two-stage Hf model ages (TDM2) ranging from 1.60 to 1.85 Ga. The rocks are peraluminous with A/CNK values of 0.99-1.08. The granites display high Si, Al and K contents but low Mg, Fe and Ca contents. The rocks show flat chondrite-normalized REE patterns with strong Eu negative anomalies. These characteristics indicate that the magma originated from a continental crustal source. The hydrothermal muscovite exhibits an Ar-Ar plateau age of 50.4 ± 0.2 Ma. The δ18O and δD values of hydrothermal quartz from the deposit range from -7.32‰ to 4.01‰ and from -124.9‰ to -87.1‰, respectively. The δ13CPDB and δ18OSMOW values of calcite range from -11.3‰ to -3.7‰ and from +2.2‰ to +12.7‰, respectively. The sulfur isotopic compositions (δ34SV-CDT) range from +3.3‰ to +8.6‰ for sulfide separates, and the lead isotopic ratios 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb range from 18.668 to 18.746, from 15.710 to 15.743 and from 39.202 to 39.295, respectively. These isotopic compositions are similar to those of magma-derived fluids, indicating that the ore-forming fluids and materials mainly originated from magmatic rocks with some input from meteoric water. This evidence suggests that the tin mineralization is closely linked to the Lailishan I-type granites. In combination with previous data, it is proposed in this study that widespread early Eocene magmatism resulted from the slab breakoff of the subducting Neo-Tethyan slab at ca. 55 Ma.

Microscale Variations in the 13C Content of the Murchison Meteorite

NASA Astrophysics Data System (ADS)

Romanek, C.; Gibson, E.; Socki, R.; Burkett, P. J.

1993-07-01

Heretofore unresolved micrometer-scale carbon isotopic zonation in the Murchison meteorite (CM3) is documented using a laser microprobe mass spectrometer. High-resolution isotopic gradients and heterogeneities between high- and low-temperature textural components help to constrain the processes that have shaped the physiochemical character of this carbonaceous chondrite. Previous bulk samples of Murchison yield an average delta ^13C value of - 5.7 +/- 4.3 per mil [1] while individual components such as micrometer-sized mineral separates (e.g., C(sub)graphite , C(sub)diamond, and SiC), acid- soluble extracts (e.g., CaCO3 and polar hydrocarbons), and insoluble residues (e.g., polycyclic aromatic hydrocarbons) are isotopically diverse (delta ^13C of -1000 to 29,000 per mil). While these studies shed light on the origin and occurrence of C-bearing phases, they fail to constrain intrinsic spatial isotopic heterogeneities. The power of the laser microprobe lies in the fact that in situ chemical and isotopic compositions are measured simultaneously for volatiles extracted from extremely small sample volumes (i.e., 0.025 mm^3 for 5 wt% C). Nd-YAG laser irradiation (1.06 micrometers) is directed onto texturally defined targets (>=50 micrometers wide) from which solid material is volatilized. Condensible gaseous phases are collected in a variable-temperature cold trap while the more volatile species (CH4 and CO) are quantified using an ion trap mass spectrometer. All gases are then converted to CO2 in a CuO furnace (containing Pt) held at 600 degrees C and analyzed for carbon and oxygen isotope ratios. The concentration and isotopic composition of condensed species are determined by stepped sublimation of unstable components and conversion to CO2. Preliminary isotopic analyses of the total volatile C content (i.e., bulk microanalysis) from distinct textural components at least 0.05 mm^3 in volume are described below. The most ^13C-depleted components within Murchison reside within the cores of chondrules and/or aggregates. Three typical cores were analyzed, with an average bulk composition of -21.0 +/- 0.5 per mil (n = 7). The bulk ^13C content of C-bearing phases increases monotonically outward in all directions within 100 to 200 micrometers of each core (i.e., within dust mantles) to a constant matrix value of -12.5 +/- 0.5 per mil (n = 40). The most isotopically enriched textural component found in Murchison is a regolith breccia clast without chondrules that has an average bulk delta ^13C value of -10 +/-0.5 per mil (n = 5). The clast was originally detectable only under cathodoluminescence, but with the aid of the laser microprobe it is now characterized by an unusually low volatile content and enriched ^13C composition. In general, the most isotopically enriched components also produce the lowest yield of gas (normalized to sampling volume). This trend of isotopic enrichment from chondrule to matrix has been documented previously for oxygen isotopes in carbonaceous chondrites [2]. Carbon isotopic gradients and heterogeneities within Murchison reflect fundamental changes in the chemical speciation and/or isotopic content of the main C-bearing components (i.e., acid-soluble and insoluble hydrocarbon fractions) within the meteorite. Perhaps core interiors and dust mantles are responding to environmental changes reflected in the speciation of C-bearing species distributed within the solar nebula or the parent body. Inverse correlations between hydrocarbon atomic mass number and ^13C abundance in the acid-soluble [3] and insoluble residues [4] of Murchison have been documented. Alternatively, micrometer-scale isotopic gradients may reflect fundamental changes in the isotopic composition of individual C-bearing species through time. Enrichments may represent kinetically controlled processes related to hydrocarbon formation. In contrast, assuming an equilibrium fractionation mechanism, isotopic enrichments may record a temperature-dependent component to hydrocarbon delta ^13C values. These opposing alternatives will be discussed in light of the isotopic composition of individual C-bearing components volatilized from tightly constrained sample volumes within Murchison. References: [1] Kerridge J. F. (1985) GCA, 49, 1707-1714. [2] Clayton R. N. and Mayeda T. K. (1984) EPSL, 67, 151-161. [3] Yuen G. et al. (1984) Nature, 307, 254. [4] Gilmour I. et al. (1991) Meteoritics, 26, 337-338.

Paleoclimatic and paleoceanographic records through Marine Isotope Stage 19 at the Chiba composite section, central Japan: A key reference for the Early-Middle Pleistocene Subseries boundary

NASA Astrophysics Data System (ADS)

Suganuma, Yusuke; Haneda, Yuki; Kameo, Koji; Kubota, Yoshimi; Hayashi, Hiroki; Itaki, Takuya; Okuda, Masaaki; Head, Martin, J.; Sugaya, Manami; Nakazato, Hiroomi; Igarashi, Atsuo; Shikoku, Kizuku; Hongo, Misao; Watanabe, Masami; Satoguchi, Yasufumi; Takeshita, Yoshihiro; Nishida, Naohisa; Izumi, Kentaro; Kawamura, Kenji; Kawamata, Moto; Okuno, Jun'ichi; Yoshida, Takeshi; Ogitsu, Itaru; Yabusaki, Hisashi; Okada, Makoto

2018-07-01

Marine Isotope Stage (MIS) 19 is an important analogue for the present interglacial because of its similar orbital configuration, especially the phasing of the obliquity maximum to precession minimum. However, sedimentary records suitable for capturing both terrestrial and marine environmental changes are limited, and thus the climatic forcing mechanisms for MIS 19 are still largely unknown. The Chiba composite section, east-central Japanese archipelago, is a continuous and expanded marine sedimentary succession well suited to capture terrestrial and marine environmental changes through MIS 19. In this study, a detailed oxygen isotope chronology is established from late MIS 20 to early MIS 18, supported by a U-Pb zircon age and the presence of the Matuyama-Brunhes boundary. New pollen, marine microfossil, and planktonic foraminiferal δ18O and Mg/Ca paleotemperature records reveal the complex interplay of climatic influences. Our pollen data suggest that the duration of full interglacial conditions during MIS 19 extends from 785.0 to 775.1 ka (9.9 kyr), which offers an important natural baseline in predicting the duration of the present interglacial. A Younger Dryas-type cooling event is present during Termination IX, suggesting that such events are linked to this orbital configuration. Millennial- to multi-millennial-scale variations in our δ18O and Mg/Ca records imply that the Subarctic Front fluctuated in the northwestern Pacific Ocean during late MIS 19, probably in response to East Asian winter monsoon variability. The climatic setting at this time appears to be related to less severe summer insolation minima at 65˚N and/or high winter insolation at 50˚N. Our records do not support a recently hypothesized direct coupling between variations in the geomagnetic field intensity and global/regional climate change. Our highly resolved paleoclimatic and paleoceanographic records, coupled with a well-defined Matuyama-Brunhes boundary (772.9 ka; duration 1.9 kyr), establish the Chiba composite section as an exceptional climatic and chronological reference section for the Early-Middle Pleistocene boundary.

Holocene environmental changes in northern Lebanon as inferred from a multiproxy study on lacustrine-palustrine sediment

NASA Astrophysics Data System (ADS)

Vidal, Laurence; Jenna, Hage-Hassen; Demory, François; Develle, Anne-Lise; van Campo, Elise; Elias, Ata

2016-04-01

The reconstruction of the Levantine post-glacial environmental evolution is essential to understand the interactions between variability of regional water cycle, dynamics of the global climate, and cultural evolution. We present a paleolacustrine record from the karstic Yammouneh basin (34.06N-34.09N; 36.0E-36.03E, 1360 m a.s.l.), located on the eastern flank of Mount Lebanon (northern Levant). Holocene sediments (retrieved from gully and a trenbch) (1.5 to 3.6 m thick) consist of pale lacustrine chalk interrupted by an ash layer and remarkable centimetric beds of ocher to dark brown silty clays used, in addition to 14C ages, as stratigraphical markers. Lacustrine biogenic remains are diversified and abundant (ostracods, gastropods, charophytes, chlorophyceae, plant debris…) all reflecting a freswater, generally shallow waterbody. We analysed the sediment mineralogy and geochemistry, TOM contents, magnetic properties, pollen and calcite oxygen isotope composition derived from ostracod shells. These sequences are compared to former data from 2 trenches and 1 core collected in different points of the basin (Daeron et al., 2007; Develle et al., 2009, 2010). A total of 42 AMS 14C dating (partly carbonized wood) provide a solid chronology from the YD to present. Results reveal the following main features : 1- intervals dominated by authigenic calcite suggest that the major water supply was the karstic springs, which still deliver Ca-rich water and low surface runoff; 2- the lake oxygen isotope composition has been impacted by the source isotope composition throughout the Holocene and by increased inland rainfall during the early Holocene; 3- a decideous oak forest, implying much more soil water availability than today, was developed around the lake from ca. 11.5 to 9.5 kyr (the very bad pollen preservation after 8.3 kyr reflects oxidation or frequent oscillations of the water level); 4- four paleosols evidenced from lithofacies and magnetic properties are identified, during the YD, and around 8 kyr, 6 kyr and 2 kyr. Our data are compared with other Holocene paleohydrological (lake and speleothem) records from the northern and southern Levant.

Calcium and magnesium isotope systematics in rivers draining the Himalaya-Tibetan-Plateau region: Lithological or fractionation control?

NASA Astrophysics Data System (ADS)

Tipper, Edward T.; Galy, Albert; Bickle, Mike J.

2008-02-01

In rivers draining the Himalaya-Tibetan-Plateau region, the 26Mg/ 24Mg ratio has a range of 2‰ and the 44Ca/ 42Ca ratio has a range of 0.6‰. The average δ26Mg values of tributaries from each of the main lithotectonic units (Tethyan Sedimentary Series (TSS), High Himalayan Crystalline Series (HHCS) and Lesser Himalayan Series (LHS)) are within 2 standard deviation analytical uncertainty (0.14‰). The consistency of average riverine δ26Mg values is in contrast to the main rock types (limestone, dolostone and silicate) which range in their average δ26Mg values by more than 2‰. Tributaries draining the dolostones of the LHS differ in their δ44Ca values compared to tributaries from the TSS and HHCS. The chemistry of these river waters is strongly influenced by dolostone (solute Mg/Ca close to unity) and both δ26Mg (-1.31‰) and δ44Ca (0.64‰) values are within analytical uncertainty of the LHS dolostone. These are the most elevated δ44Ca values in rivers and rock reported so far demonstrating that both riverine and bedrock δ44Ca values may show greater variability than previously thought. Although rivers draining TSS limestone have the lowest δ26Mgandδ44Ca values at -1.41 and 0.42‰, respectively, both are offset to higher values compared to bedrock TSS limestone. The average δ26Mg value of rivers draining mainly silicate rock of the HHCS is -1.25‰, lower by 0.63‰ than the average silicate rock. These differences are consistent with a fractionation of δ26Mg values during silicate weathering. Given that the proportion of Mg exported from the Himalaya as solute Mg is small, the difference in 26Mg/ 24Mg ratios between silicate rock and solute Mg reflects the 26Mg/ 24Mg isotopic fractionation factor ( αsilicate-dissolvedMg) between silicate and dissolved Mg during incongruent silicate weathering. The value of αsilicate-dissolvedMg of 0.99937 implies that in the TSS, solute Mg is primarily derived from silicate weathering, whereas the source of Ca is overwhelmingly derived from carbonate weathering. The average δ44Ca value in HHCS rivers is within uncertainty of silicate rock at 0.39‰. The widespread hot springs of the High Himalaya have an average δ26Mg value of -0.46‰ and an average δ44Ca value of 0.5‰, distinct from riverine values for δ26Mg but similar to riverine δ44Ca values. Although rivers draining each major rock type have δ44Ca and δ26Mg values in part inherited from bedrock, there is no correlation with proxies for carbonate or silicate lithology such as Na/Ca ratios, suggesting that Ca and Mg are in part recycled. However, in spite of the vast contrast in vegetation density between the arid Tibetan Plateau and the tropical Lesser Himalaya, the isotopic fractionation factor for Ca and Mg between solute and rocks are not systematically different suggesting that vegetation may only recycle a small amount of Ca and Mg in these catchments. The discrepancy between solute and solid Ca and Mg isotope ratios in these rivers from diverse weathering environments highlight our lack of understanding concerning the origin and subsequent path of Ca and Mg, bound as minerals in rock, and released as cations in rivers. The fractionation of Ca and Mg isotope ratios may prove useful for tracing mechanisms of chemical alteration. Ca isotope ratios of solute riverine Ca show a greater variability than previously acknowledged. The variability of Ca isotope ratios in modern rivers will need to be better quantified and accounted for in future models of global Ca cycling, if past variations in oceanic Ca isotope ratios are to be of use in constraining the past carbon cycle.

A reference time scale for Site U1385 (Shackleton Site) on the SW Iberian Margin

NASA Astrophysics Data System (ADS)

Hodell, D.; Lourens, L.; Crowhurst, S.; Konijnendijk, T.; Tjallingii, R.; Jiménez-Espejo, F.; Skinner, L.; Tzedakis, P. C.; Abrantes, Fatima; Acton, Gary D.; Alvarez Zarikian, Carlos A.; Bahr, André; Balestra, Barbara; Barranco, Estefanìa Llave; Carrara, Gabriela; Ducassou, Emmanuelle; Flood, Roger D.; Flores, José-Abel; Furota, Satoshi; Grimalt, Joan; Grunert, Patrick; Hernández-Molina, Javier; Kim, Jin Kyoung; Krissek, Lawrence A.; Kuroda, Junichiro; Li, Baohua; Lofi, Johanna; Margari, Vasiliki; Martrat, Belen; Miller, Madeline D.; Nanayama, Futoshi; Nishida, Naohisa; Richter, Carl; Rodrigues, Teresa; Rodríguez-Tovar, Francisco J.; Roque, Ana Cristina Freixo; Sanchez Goñi, Maria F.; Sierro Sánchez, Francisco J.; Singh, Arun D.; Sloss, Craig R.; Stow, Dorrik A. V.; Takashimizu, Yasuhiro; Tzanova, Alexandrina; Voelker, Antje; Xuan, Chuang; Williams, Trevor

2015-10-01

We produced a composite depth scale and chronology for Site U1385 on the SW Iberian Margin. Using log(Ca/Ti) measured by core scanning XRF at 1-cm resolution in all holes, a composite section was constructed to 166.5 meter composite depth (mcd) that corrects for stretching and squeezing in each core. Oxygen isotopes of benthic foraminifera were correlated to a stacked δ18O reference signal (LR04) to produce an oxygen isotope stratigraphy and age model. Variations in sediment color contain very strong precession signals at Site U1385, and the amplitude modulation of these cycles provides a powerful tool for developing an orbitally-tuned age model. We tuned the U1385 record by correlating peaks in L* to the local summer insolation maxima at 37°N. The benthic δ18O record of Site U1385, when placed on the tuned age model, generally agrees with other time scales within their respective chronologic uncertainties. The age model is transferred to down-core data to produce a continuous time series of log(Ca/Ti) that reflect relative changes of biogenic carbonate and detrital sediment. Biogenic carbonate increases during interglacial and interstadial climate states and decreases during glacial and stadial periods. Much of the variance in the log(Ca/Ti) is explained by a linear combination of orbital frequencies (precession, tilt and eccentricity), whereas the residual signal reflects suborbital climate variability. The strong correlation between suborbital log(Ca/Ti) variability and Greenland temperature over the last glacial cycle at Site U1385 suggests that this signal can be used as a proxy for millennial-scale climate variability over the past 1.5 Ma. Millennial climate variability, as expressed by log(Ca/Ti) at Site U1385, was a persistent feature of glacial climates over the past 1.5 Ma, including glacial periods of the early Pleistocene ('41-kyr world') when boundary conditions differed significantly from those of the late Pleistocene ('100-kyr world'). Suborbital variability was suppressed during interglacial stages and enhanced during glacial periods, especially when benthic δ18O surpassed 3.3-3.5‰. Each glacial inception was marked by appearance of strong millennial variability and each deglaciation was preceded by a terminal stadial event. Suborbital variability may be a symptomatic feature of glacial climate or, alternatively, may play a more active role in the inception and/or termination of glacial cycles.

Kinetically Controlled Alteration of the Chemical Record During Diagenesis: An Experimental Study on Hydrothermal Carbonate Replacement

NASA Astrophysics Data System (ADS)

Mueller, T.; Dohmen, R.; Jonas, L.; Immenhauser, A.

2016-12-01

The geological record stored in the geochemical composition of carbonates provides a direct source of information on the Earth systems. However, the robustness and accuracy of these key records can be compromised by post-depositional alteration of sediments, such as dolomitization during diagenesis or low temperature metamorphism. Hence, knowledge on the mechanisms and rates of these processes hold the key to evaluate the robustness of proxies or to evaluate the extent of geochemical alteration. Previously, we presented experimental results of hydrothermal alteration of single calcite crystals and aragonitic coral fragments leading to replacement of the original carbonate by a Ca-Mg carbonate phase of variable composition. The experiments revealed the formation of a multiphase reaction rim with multiple replacement fronts [1]. Here, the reaction rate as well as composition of the reaction products is controlled by element transport in the pore fluid. In this study we focus on the reaction path of the replacement reaction and its effect on the recorded Mg-isotope composition. XRD diffraction patterns suggest the initial precipitation of non-ordered protodolomite that is subsequently continuously recrystallizing over the duration of the experiments to form an ordered, albeit non-stoichiometric dolomite. These observations are in agreement with Mg-isotope composition measured of the bulk reaction rim showing a systematic evolution over time that cannot be explained by simple Rayleigh or equilibrium fractionation. We interpret these findings as additional, but delayed reaction fronts affecting the microstructure and chemical composition of the newly formed carbonate rim that are essentially decoupled from the initial replacement front. Our results highlight the need to quantitatively understand alteration processes during diagenesis in order to accurately interpret the preserved geochemical record stored in element and isotope ratios of carbonates. [1] Jonas L., Mueller T., Dohmen R., Baumgartner L., and Putlitz B. (2015): Transport-controlled hydrothermal replacement of calcite by Mg-carbonates, Geology, 43, 779-782.

Lead isotopic evidence for mixed sources of Proterozoic granites and pegmatites, Black Hills, South Dakota, USA

NASA Astrophysics Data System (ADS)

Krogstad, Eirik J.; Walker, Richard J.; Nabelek, Peter I.; Russ-Nabelek, Carol

1993-10-01

The lead isotopic compositions of K-feldspars separated from the ca. 1700 Ma Harney Peak Granite complex and spatially associated granitic pegmatites indicate that these rocks were derived from at least two sources. It has been reported previously that the core of the Harney Peak Granite complex is dominated by relatively lower/ gd18O (avg. 11.5 %.) granites, whereas higher / gd18O (avg. 13.2%.) granites occur around the periphery of the complex. The higher δ 18O granites and one simple pegmatite have low values of 207Pb /204Pb for their 206Pb /204Pb Thus, they likely were derived from a source with a short crustal residence time. This source may have been the pelitic schists into which the Harney Peak Granite complex and pegmatites were intruded. Feldspars from granites with lower / gd18O values have significantly higher 207Pb /204Pb for their 206Pb /204Pb . The data define a linear array with a slope equivalent to an age of ca. 2.6 Ga with t 2 defined to be 1.7 Ga. Such a slope could represent a mixing array or a secondary isochron for the source. These low δ18O granites could have been derived from a source with a high U/ Pb and with a crustal residence beginning before the Proterozoic. The source (s) of these granites may have been a sediment derived from late Archean continental crust. The highly evolved Tin Mountain pegmatite has lead isotopic systematics intermediate between those of the two granite groups, suggesting either a mixed source or contamination. Two late Archean granites, the Little Elk Granite and the Bear Mountain Granite, had precursors with high U/Pb and low Th/U histories. The Th/U history of the Bear Mountain Granite is too low for this rock to have been an important component of the source of the Proterozoic granites. However, crustal rocks with lead isotopic compositions similar to those of the Little Elk Granite were an important source of lead for some of the Proterozoic granitic rocks.

Origin of temporal compositional trends in monogenetic vent eruptions: Insights from the crystal cargo in the Papoose Canyon sequence, Big Pine Volcanic Field, CA

NASA Astrophysics Data System (ADS)

Gao, Ruohan; Lassiter, John C.; Ramirez, Gabrielle

2017-01-01

Many monogenetic vents display systematic temporal-compositional variations over the course of eruption. Previous studies have proposed that these trends may reflect variable degrees of crustal assimilation, or melting and mixing of heterogeneous mantle source(s). Discrimination between these two endmember hypotheses is critical for understanding the plumbing systems of monogenetic volcanoes, which pose a significant volcanic hazard in many areas. In this study, we examine the Papoose Canyon (PC) monogenetic vent in the Big Pine Volcanic Field (BPVF), which had been well characterized for temporal-compositional variations in erupted basalts. We present new major and trace element and Sr-Nd-Pb-O isotopic data from the PC "crystal cargo" (phenocrysts and xenoliths). Comparison of "crystal cargo" and host basalt provides new constraints on the history of magma storage, fractionation, and crustal contamination that are obscured in the bulk basalts due to pre- and syn-eruptive magma mixing processes. The abundances of phenocrysts and ultramafic xenoliths in the PC sequence decrease up-section. Olivine and clinopyroxene phenocrysts span a wide range of Mg# (77-89). The majority of phenocrysts are more evolved than olivine or clinopyroxene in equilibrium with their host basalts (Mg# = 68- 71, equilibrium Fo ≈ 85- 89). In addition, the ultramafic xenoliths display cumulate textures. Olivine and clinopyroxene from ultramafic xenoliths have Mg# (73-87) similar to the phenocrysts, and lower than typical mantle peridotites. Sr-Nd-Pb isotope compositions of the xenoliths are similar to early PC basalts. Finally, many clinopyroxene phenocrysts and clinopyroxene in xenoliths have trace element abundances in equilibrium with melts that are more enriched than the erupted basalts. These features suggest that the phenocrysts and xenoliths derive from melt that is more fractionated and enriched than erupted PC basalts. Pressure constraints suggest phenocrysts and ultramafic xenoliths crystallized at ∼5-7 kbar, corresponding to mid-crust depths. Correlations between HFSE depletion and Sr-Nd-Pb isotopic compositions, high δ18 O values in olivines, and radiogenic Os isotopic compositions in whole rocks also suggest incorporation of a crustally contaminated component. We propose that the phenocrysts and ultramafic xenoliths derive from melts that ponded and fractionated and assimilated continental crust, possibly in mid-crustal sills. These melts were drained and mixed with more primitive melts as the eruption began, and the temporal-compositional trends and decreasing crystal phase abundances reflect gradual deflation and exhaustion of these sills as the eruption progressed. The isotopic variations in the PC sequence span much of the compositional range observed in the BPVF. Evidence for variable crustal contamination of PC basalts suggests that much of the isotopic variation observed in the BPVF may also reflect crustal contamination rather than mantle source heterogeneity as previously proposed. In addition, evidence of pre-eruptive magma ponding and fractionation, if applicable to other monogenetic vents, may have significant implications for monitoring and hazard assessment of monogenetic volcano fields.

Re-Os systematics of komatiites and komatiitic basalts at Dundonald Beach, Ontario, Canada: Evidence for a complex alteration history and implications of a late-Archean chondritic mantle source

NASA Astrophysics Data System (ADS)

Gangopadhyay, Amitava; Sproule, Rebecca A.; Walker, Richard J.; Lesher, C. Michael

2005-11-01

Osmium isotopic compositions, and Re and Os concentrations have been examined in one komatiite unit and two komatiitic basalt units at Dundonald Beach, part of the 2.7 Ga Kidd-Munro volcanic assemblage in the Abitibi greenstone belt, Ontario, Canada. The komatiitic rocks in this locality record at least three episodes of alteration of Re-Os elemental and isotope systematics. First, an average of 40% and as much as 75% Re may have been lost due to shallow degassing during eruption and/or hydrothermal leaching during or immediately after emplacement. Second, the Re-Os isotope systematics of whole rock samples with 187Re/ 188Os ratios >1 were reset at ˜2.5 Ga, possibly due to a regional metamorphic event. Third, there is evidence for relatively recent gain and loss of Re in some rocks. Despite the open-system behavior, some aspects of the Re-Os systematics of these rocks can be deciphered. The bulk distribution coefficient for Os (D Ossolid/liquid) for the Dundonald rocks is ˜3 ± 1 and is well within the estimated D values obtained for komatiites from the nearby Alexo area and stratigraphically-equivalent komatiites from Munro Township. This suggests that Os was moderately compatible during crystal-liquid fractionation of the magmas parental to the Kidd-Munro komatiitic rocks. Whole-rock samples and chromite separates with low 187Re/ 188Os ratios (<1) yield a precise chondritic average initial 187Os/ 188Os ratio of 0.1083 ± 0.0006 (γ Os = 0.0 ± 0.6) for their well-constrained ˜2715 Ma crystallization age. The chondritic initial Os isotopic composition of the mantle source for the Dundonald rocks is consistent with that determined for komatiites in the Alexo area and in Munro Township, suggesting that the mantle source region for the Kidd-Munro volcanic assemblage had evolved with a long-term chondritic Re/Os before eruption. The chondritic initial Os isotopic composition of the Kidd-Munro komatiites is indistinguishable from that of the projected contemporaneous convective upper mantle. The uniform chondritic Os isotopic composition of the Kidd-Munro komatiites contrasts with the typical large-scale Os isotopic heterogeneity in the mantle sources for ca. 89 Ma komatiites from the Gorgona Island, arc-related rocks and present-day ocean island basalts. This suggests that the Kidd-Munro komatiites sampled a late-Archean mantle source region that was significantly more homogeneous with respect to Re/Os relative to most modern mantle-derived rocks.

A comparative study on effects of heterotrophic microbial activity on the stability of bivalve and coral carbonate during early diagenesis.

NASA Astrophysics Data System (ADS)

Lange, Skadi M.; Krause, Stefan; Immenhauser, Adrian; Ritter, Ann-Christin; Gorb, Stanislav N.; Kleinteich, Thomas; Treude, Tina

2016-04-01

Following deposition and shallow burial, marine biogenic carbonates are exposed to an environment that is geochemically affected by a manifold of bacterial metabolic redox processes. To allow for comparison of potential microbe-mediated alteration effects on carbonates, we used aragonitic bivalve shell samples and porous aragonitic coral fragments for incubation experiments in oxic- and anoxic seawater media. The media contained marine sediment slurries or bacterial cultures to mimic the natural processes in vitro. The results for anoxic experimental media containing bivalve shell samples or coral fragments displayed considerable changes in carbonate-system parameters (pH, AT, CA, DIC) and divalent-cation ratios (Mg/Ca, Mg/Sr, Sr/Ca) over time. Furthermore, incubated bivalve shell samples were altered in morphology, elemental composition and isotopic signature. Coral-fragment bearing oxic incubations were run at two temperature regimes and divalent-cation ratios of the high-temperature bacterial medium displayed withdrawal of Ca2+ and Sr2+ from the medium, thus indicating microbe-induced secondary aragonite precipitation. Analyses of coral fragments include electron-microprobe mapping and X-ray microtomography to resolve elemental sample composition and pore-space alteration features, respectively. Up to this point our results indicate that heterotrophic bacterial activity has the potential to affect surficial or open pore space in carbonate archives by increasing rates of alteration relative to sterile environments.

Tracking natural and anthropogenic origins of dissolved arsenic during surface and groundwater interaction in a post-closure mining context: Isotopic constraints.

PubMed

Khaska, Mahmoud; Le Gal La Salle, Corinne; Verdoux, Patrick; Boutin, René

2015-01-01

Arsenic contamination of stream waters and groundwater is a real issue in Au-As mine environments. At the Salsigne Au-As mine, southern France, arsenic contamination persists after closure and remediation of the site. In this study, natural and anthropogenic arsenic inputs in surface water and groundwater are identified based on (87)Sr/(86)Sr, and δ(18)O and δ(2)H isotopic composition of water. In the wet season, downstream of the remediated zone, the arsenic contents in stream water and alluvial aquifer groundwater are high, with values in the order of 36 μg/L and 40 μg/L respectively, while upstream natural background average concentrations are around 4 μg/L. Locally down-gradient of the reclaimed area, arsenic concentrations in stream water showed 2 peaks, one during an important rainy event (101 mm) in the wet season in May, and a longer one over the dry period, reaching 120 and 110 μg/L respectively. The temporal variations in arsenic content in stream water can be explained i) during the dry season, by release of arsenic stored in the alluvial sediments through increased contribution from base flow and decreased stream flow and ii) during major rainy events, by mobilization of arsenic associated with important surface runoff. The (87)Sr/(86)Sr ratios associated with increasing arsenic content in stream waters downstream of the reclaimed area are significantly lower than that of the natural Sr inherited from Variscan formations. These low (87)Sr/(86)Sr ratios are likely to be associated with the decontaminating water treatment processes, used in the past and still at present, where CaO, produced from marine limestone and therefore showing a low (87)Sr/(86)Sr ratios, is used to precipitate Ca3(AsO4)2. The low Sr isotope signatures will then impact on the Sr isotope ratio of (1) the Ca-arsenate stored in tailing dams, (2) effluent currently produced by water treatment process and (3) groundwater draining from the overall site. Furthermore, Δ(2)H shows that the low (87)Sr/(86)Sr ratio, arsenic rich water is characterized by an evaporated signature suggesting a potential influence of water impacted by evaporation during storage in decantation lagoons. This study shows the suitability of Sr and stable isotopes of water as tracers to differentiate natural and anthropogenic sources of arsenic release or other trace elements from mining context where CaO is used for water treatment. Copyright © 2015 Elsevier B.V. All rights reserved.

Tracking natural and anthropogenic origins of dissolved arsenic during surface and groundwater interaction in a post-closure mining context: Isotopic constraints

NASA Astrophysics Data System (ADS)

Khaska, Mahmoud; Le Gal La Salle, Corinne; Verdoux, Patrick; Boutin, René

2015-06-01

Arsenic contamination of stream waters and groundwater is a real issue in Au-As mine environments. At the Salsigne Au-As mine, southern France, arsenic contamination persists after closure and remediation of the site. In this study, natural and anthropogenic arsenic inputs in surface water and groundwater are identified based on 87Sr/86Sr, and δ18O and δ2H isotopic composition of water. In the wet season, downstream of the remediated zone, the arsenic contents in stream water and alluvial aquifer groundwater are high, with values in the order of 36 μg/L and 40 μg/L respectively, while upstream natural background average concentrations are around 4 μg/L. Locally down-gradient of the reclaimed area, arsenic concentrations in stream water showed 2 peaks, one during an important rainy event (101 mm) in the wet season in May, and a longer one over the dry period, reaching 120 and 110 μg/L respectively. The temporal variations in arsenic content in stream water can be explained i) during the dry season, by release of arsenic stored in the alluvial sediments through increased contribution from base flow and decreased stream flow and ii) during major rainy events, by mobilization of arsenic associated with important surface runoff. The 87Sr/86Sr ratios associated with increasing arsenic content in stream waters downstream of the reclaimed area are significantly lower than that of the natural Sr inherited from Variscan formations. These low 87Sr/86Sr ratios are likely to be associated with the decontaminating water treatment processes, used in the past and still at present, where CaO, produced from marine limestone and therefore showing a low 87Sr/86Sr ratios, is used to precipitate Ca3(AsO4)2. The low Sr isotope signatures will then impact on the Sr isotope ratio of (1) the Ca-arsenate stored in tailing dams, (2) effluent currently produced by water treatment process and (3) groundwater draining from the overall site. Furthermore, Δ2H shows that the low 87Sr/86Sr ratio, arsenic rich water is characterized by an evaporated signature suggesting a potential influence of water impacted by evaporation during storage in decantation lagoons. This study shows the suitability of Sr and stable isotopes of water as tracers to differentiate natural and anthropogenic sources of arsenic release or other trace elements from mining context where CaO is used for water treatment.

Using MASHA+TIMEPIX Setup for Registration Beta Decay Isotopes Produced in Heavy Ion Induced Reactions

NASA Astrophysics Data System (ADS)

Rodin, A. M.; Belozerov, A. V.; Chernysheva, E. V.; Dmitriev, S. N.; Gulyaev, A. V.; Gulyaeva, A. V.; Itkis, M. G.; Novoselov, A. S.; Oganessian, Yu. Ts.; Salamatin, V. S.; Stepantsov, S. V.; Vedeneev, V. Yu.; Yukhimchuk, S. A.; Krupa, L.; Granja, C.; Pospisil, S.; Kliman, J.; Motycak, S.; Sivacek, I.

2015-06-01

Radon and mercury isotopes were produced in multi nucleon transfer (48Ca + 232Th) and complete fusion (48Ca + naturalNd) reactions, respectively. The isotopes with given masses were detected using two detectors: a multi-strip detector of the well-type (made in CANBERRA) and a position-sensitive quantum counting hybrid pixel detector of the TIMEPIX type. The isotopes implanted into the detectors then emit alpha- and betaparticles until reaching the long lived isotopes. The position of the isotopes, the tracks, the time and energy of beta-particles were measured and analyzed. A new software for the particle recognition and data analysis of experimental results was developed and used. It was shown that MASHA+ TIMEPIX setup is a powerful instrument for investigation of neutron-rich isotopes far from stability limits.

Ages and Nd, Sr isotopic systematics in the Sierran foothills ophiolite belt, CA: the Smartville and Feather River complexes

DOE Office of Scientific and Technical Information (OSTI.GOV)

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 zirconmore » 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.« less

Ca ISOTOPE EFFECTS IN ORGUEIL LEACHATES AND THE IMPLICATIONS FOR THE CARRIER PHASES OF {sup 54}Cr ANOMALIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moynier, Frederic; Podosek, Frank A.; Brannon, Joyce

Primitive meteorites contain small {sup 40}Ca excesses, in addition to rare anomalies in {sup 48}Ca. Refractory inclusions from Vigarano and Allende have larger {sup 40}Ca and resolvable {sup 48}Ca anomalies. These results imply that Ca isotopic heterogeneities were still present in the early solar system at both the mineral and whole-rock scale. The absence of correlated Ca isotope anomalies in leachates from the CI1 chondrite Orgueil containing large {sup 54}Cr anomalies has implications on the origin of the Cr anomalies. {sup 54}Cr has to be produced either in massive stars during s-process nucleosynthesis without accompanying {sup 48}Ca or in particularmore » zones in the rare Type Ia supernovae. In the latter case, {sup 54}Cr has been produced in a zone predominantly enriched in Cr and {sup 54}Cr and not mixed with other zones, or {sup 54}Cr has been produced together with other neutron-rich nuclides and there has been subsequent decoupling of this material in the star, in the solar system, or in the laboratory.« less

Interstellar and Solar Nebula Materials in Cometary Dust

NASA Technical Reports Server (NTRS)

Messenger, Scott; Nakamura-Messenger, Keiko; Keller, Lindsay; Nguyen, Ann; Clemett, Simon

2017-01-01

Laboratory studies of cometary dust collected in the stratosphere and returned from comet 81P/Wild 2 by the Stardust spacecraft have revealed ancient interstellar grains and molecular cloud organic matter that record a range of astrophysical processes and the first steps of planetary formation. Presolar materials are rarer meteorites owing to high temperature processing in the solar nebula and hydrothermal alteration on their asteroidal parent bodies. The greater preservation of presolar materials in comets is attributed to their low accretion temperatures and limited planetary processing. Yet, comets also contain a large complement of high temperature materials from the inner Solar System. Owing to the limited and biased sampling of comets to date, the proportions of interstellar and Solar System materials within them remains highly uncertain. Interstellar materials are identified by coordinated isotopic, mineralogical, and chemical measurements at the scale of individual grains. Chondritic porous interplanetary dust particles (CP IDPs) that likely derive from comets are made up of 0.1 - 10 micron-sized silicates, Fe-Ni-sulfides, oxides, and other phases bound by organic material. As much as 1% of the silicates are interstellar grains that have exotic isotopic compositions imparted by nucleosynthetic processes in their parent stars. Crystalline silicates in CP IDPs dominantly have normal isotopic compositions and probably formed in the Solar System. 81P samples include isotopically normal refractory minerals that resemble Ca-Al rich inclusions and chondrules common in meteorites. The origins of sub-micron amorphous silicates in IDPs are not certain, but at least a few % of them are interstellar grains. The remainder have isotopic compositions consistent with Solar System origins and elemental compositions that are inconsistent with interstellar grain properties, thus favoring formation in the solar nebula [4]. The organic component in comets and primitive meteorites has large enrichments in D/H and N-15/N-14 relative to terrestrial materials. These isotopic signatures are probably due to low temperature chemical processes in cold molecular clouds or the outermost reaches of the protoplanetary disk. The greatest isotopic anomalies are found in sub-micron organic nanoglobules that show chemical signatures of interstellar chemistry. The observation that cometary dust is mostly composed of isotopically normal minerals within isotopically anomalous organic matter is difficult to reconcile with the formation models of each component. The mineral component likely formed in high temperature processes in the inner Solar System, while the organic fraction shows isotopic and chemical signatures of formation near 10 K. Studying more primitive remnants of the Solar System starting materials would help in resolving this paradox. Comets formed across a vast expanse of the outer disk under differing thermal and collisional regimes, and some are likely to be better preserved than others. Finding truly pristine aggregates of presolar materials may require return of a pristine sample of comet nucleus material.

In situ study at high pressure and temperature of the environment of water in hydrous Na and Ca aluminosilicate melts and coexisting aqueous fluids

NASA Astrophysics Data System (ADS)

Le Losq, Charles; Dalou, Célia; Mysen, Bjorn O.

2017-07-01

The bonding and speciation of water dissolved in Na silicate and Na and Ca aluminosilicate melts were inferred from in situ Raman spectroscopy of the samples, in hydrothermal diamond anvil cells, while at crustal temperature and pressure conditions. Raman data were also acquired on Na silicate and Na and Ca aluminosilicate glasses, quenched from hydrous melts equilibrated at high temperature and pressure in a piston cylinder apparatus. In the hydrous melts, temperature strongly influences O-H stretching ν(O-H) signals, reflecting its control on the bonding of protons between different molecular complexes. Pressure and melt composition effects are much smaller and difficult to discriminate with the present data. However, the chemical composition of the melt + fluid system influences the differences between the ν(O-H) signals from the melts and the fluids and, hence, between their hydrogen partition functions. Quenching modifies the O-H stretching signals: strong hydrogen bonds form in the glasses below the glass transition temperature Tg, and this phenomenon depends on glass composition. Therefore, glasses do not necessarily record the O-H stretching signal shape in melts near Tg. The melt hydrogen partition function thus cannot be assessed with certainty using O-H stretching vibration data from glasses. From the present results, the ratio of the hydrogen partition functions of hydrous silicate melts and aqueous fluids mostly depends on temperature and the bulk melt + fluid system chemical composition. This implies that the fractionation of hydrogen isotopes between magmas and aqueous fluids in water-saturated magmatic systems with differences in temperature and bulk chemical composition will be different.

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

USGS Publications Warehouse

Truesdell, A.H.

1974-01-01

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

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.

Investigations of Methane Production in Hypersaline Environments

NASA Technical Reports Server (NTRS)

Bebout, Brad M.

2015-01-01

The recent reports of methane in the atmosphere of Mars, as well as the findings of hypersaline paleo-environments on that planet, have underscored the need to evaluate the importance of biological (as opposed to geological) trace gas production and consumption. Methane in the atmosphere of Mars may be an indication of life but might also be a consequence of geologic activity and/or the thermal alteration of ancient organic matter. Hypersaline environments have now been reported to be extremely likely in several locations in our solar system, including: Mars, Europa, and Enceladus. Modern hypersaline microbial mat communities, (thought to be analogous to those present on the early Earth at a period of time when Mars was experiencing very similar environmental conditions), have been shown to produce methane. However, very little is known about the physical and/or biological controls imposed upon the rates at which methane, and other important trace gases, are produced and consumed in these environments. We describe here the results of our investigations of methane production in hypersaline environments, including field sites in Chile, Baja California Mexico, California, USA and the United Arab Emirates. We have measured high concentrations of methane in bubbles of gas produced both in the sediments underlying microbial mats, as well as in areas not colonized by microbial mats in the Guerrero Negro hypersaline ecosystem, Baja California Mexico, in Chile, and in salt ponds on the San Francisco Bay. The carbon isotopic (d13C) composition of the methane in the bubbles exhibited an extremely wide range of values, (ca. -75 per mille ca. -25 per mille). The hydrogen isotopic composition of the methane (d2H) ranged from -60 to -30per mille and -450 to -350per mille. These isotopic values are outside of the range of values normally considered to be biogenic, however incubations of the sediments in contact with these gas bubbles reveals that the methane is indeed being produced by these sediments. Substrate limitation of methanogenesis in these environments, and not methane oxidation, would explain the isotopic values of the methane in these environments. Incubations with both isotopically labeled and unlabeled putative substrates for methanogenesis have shown that the substrates most important for methanogenesis in these environments are the so-called non-competitive substrates, e.g., methylamines, dimethylsulfide, and methanol. Acetate and bicarbonate appear not to be important substrates for methanogens in these environments. Extraction of DNA and analysis of a gene used for methane production (mcrA) has revealed that the community composition of methanogens is consistent with organisms known to use non-competitive substrates. Our work has shown that hypersaline environments have the potential to both produce and preserve methane for analysis, e.g., by capable rovers. Our work expends the range of methane isotopic values now known to be produced by active methanogenesis

Old groundwater influence on stream hydrochemistry and catchment response times in a small Sierra Nevada catchment: Sagehen Creek, California

USGS Publications Warehouse

Rademacher, Laura K.; Clark, Jordan F.; Clow, David W.; Bryant, Hudson G.

2005-01-01

The relationship between the chemical and isotopic composition of groundwater and residence times was used to understand the temporal variability in stream hydrochemistry in Sagehen basin, California. On the basis of the relationship between groundwater age and [Ca2+], the mean residence time of groundwater feeding Sagehen Creek during base flow is approximately 28 years. [Cl−]:[Ca2+] ratios in Sagehen Creek can be used to distinguish between two important processes: changes in the apparent age of groundwater discharging into the creek and dilution with snowmelt. The mean residence time of groundwater discharging into the creek is approximately 15 years during snowmelt periods. The results from this study have implications for hydrograph separation studies as groundwater is not a single, well‐mixed chemical component but rather is a variable parameter that predictably depends on groundwater residence time. Most current models of catchment hydrochemistry do not account for chemical and isotopic variability found within the groundwater reservoir. In addition, this study provides valuable insight into the long‐term hydrochemical response of a catchment to perturbations as catchment‐flushing times are related to the mean residence time of water in a basin.

Coeval Formation of Zircon Megacrysts and Host Magmas in the Eifel Volcanic Field (Germany) Based on High Spatial Resolution Petrochronology

NASA Astrophysics Data System (ADS)

Schmitt, Axel; Klitzke, Malte; Gerdes, Axel; Ludwig, Thomas; Schäfer, Christof

2017-04-01

Zircon megacrysts (approx. 0.5-6 mm in diameter) from the Quaternary West and East Eifel volcanic fields, Germany, occur as euhedral crystals in porous K-spar rich plutonic ejecta clasts, and as partially resorbed xenocrysts in tephrite lava. Their relation to the host volcanic rocks has remained contentious because the dominantly basanitic to phonolitic magma compositions in the Eifel are typically zircon undersaturated. We carried out a detailed microanalytical study of zircon megacrysts from seven locations (Emmelberg and Rockeskyll in the West Eifel; Bellerberg, Laacher See, Mendig, Rieden, and Wehr in the East Eifel). Crystals were embedded in epoxy, sectioned to expose interiors through grinding with abrasives, diamond-polished, and mapped by optical microscopy, backscattered electron, and cathodoluminescence imaging. Subsequently, isotope-specific analysis using secondary ionization mass spectrometry (SIMS) and laser ablation inductively coupled mass spectrometry (LA-ICP-MS) was carried out placing 100 correlated spots on 20 selected crystals. Concordant U-Th disequilibrium and U-Pb ages determined by SIMS are between ca. 430 ka (Rieden) and 170 ka (Mendig) and indicate that the megacryst zircons crystallized almost always briefly before eruption. A significant gap between zircon megacryst crystallization (ca. 230 ka) and eruption (ca. 45 ka) ages was only detected for the Emmelberg location. SIMS trace element abundances (e.g., rare earth elements) vary by orders-of-magnitude and correlate with domain boundaries visible in cathodoluminescence; trace element patterns match those reported for zircon from syenitic origins. Isotopic compositions are homogeneous within individual crystals, but show some heterogeneity between different crystals from the same locality. Average isotopic values (δ18O SMOW = +5.3±0.6 ‰ by SIMS; present-day ɛHf = +1.7±2.5 ‰ by LA-ICP-MS; 1 standard deviation), however, are consistent with source magmas being dominantly mantle-derived. The porous structure and relatively small grain size of the host enclaves suggests that they originated from subvolcanic intrusions. Moreover, the preservation of zircon in hot, zircon undersaturated magmas requires brief residence times. Zircon megacrysts thus appear to have crystallized in highly differentiated magmas or nearly solidified intrusions from which crystals or rock aggregates were incorporated into more primitive magmas en route to surface. This implies that chemical signatures of apparently primitive magmas in basaltic volcanic fields can be modified by interaction with evolved melts that differentiated prior to eruption, mostly within an interval less than the ca. 10-25 ka uncertainty range of the radiometric ages.

Oxygen Isotopic Compositions of Solar Corundum Grains

NASA Astrophysics Data System (ADS)

Makide, Kentaro; Nagashima, Kazuhide; Krot, Alexander N.; Huss, Gary R.

2009-11-01

Oxygen is one of the major rock-forming elements in the solar system and the third most abundant element of the Sun. Oxygen isotopic composition of the Sun, however, is not known due to a poor resolution of astronomical spectroscopic measurements. Several Δ17O values have been proposed for the composition of the Sun based on (1) the oxygen isotopic measurements of the solar wind implanted into metallic particles in lunar soil (< -20‰ by Hashizume & Chaussidon and ~ +26‰ by Ireland et al.), (2) the solar wind returned by the Genesis spacecraft (-27‰ ± 6‰ by McKeegan et al.), and (3) the mineralogically pristine calcium-aluminum-rich inclusions (CAIs) (-23.3‰ ± 1.9‰ by Makide et al. and -35‰ by Gounelle et al.). CAIs are the oldest solar system solids, and are believed to have formed by evaporation, condensation, and melting processes in hot nebular region(s) when the Sun was infalling (Class 0) or evolved (Class 1) protostar. Corundum (Al2O3) is thermodynamically the first condensate from a cooling gas of solar composition. Corundum-bearing CAIs, however, are exceptionally rare, suggesting either continuous reaction of the corundum condensates with a cooling nebular gas and their replacement by hibonite (CaAl12O19) or their destruction by melting together with less refractory condensates during formation of igneous CAIs. In contrast to the corundum-bearing CAIs, isolated micrometer-sized corundum grains are common in the acid-resistant residues from unmetamorphosed chondrites. These grains could have avoided multistage reprocessing during CAI formation and, therefore, can potentially provide constraints on the initial oxygen isotopic composition of the solar nebula, and, hence, of the Sun. Here we report oxygen isotopic compositions of ~60 micrometer-sized corundum grains in the acid-resistant residues from unequilibrated ordinary chondrites (Semarkona (LL3.0), Bishunpur (LL3.1), Roosevelt County 075 (H3.2)) and unmetamorphosed carbonaceous chondrites (Orgueil (CI1), Murray (CM2), and Alan Hills A77307 (CO3.0)) measured with a Cameca ims-1280 ion microprobe. All corundum grains, except two, are 16O-rich (Δ17O = -22.7‰ ± 8.5‰, 2σ), and compositionally similar to the mineralogically pristine CAIs from the CR carbonaceous chondrites (-23.3‰ ± 1.9‰, 2σ), and solar wind returned by the Genesis spacecraft (-27‰ ± 6‰, 2σ). One corundum grain is highly 17O-enriched (δ17O ~ +60‰, δ18O ~ -40‰) and is probably of the presolar origin; the origin of another 17O-rich grain (δ17O ~ -15‰, δ18O ~ -35‰) is unclear. We conclude that the 16O-rich corundum grains in the acid-resistant residues from unequilibrated ordinary and unmetamorphosed carbonaceous chondrites recorded initial oxygen isotopic composition of the solar nebula, and, hence, of the Sun. Our inferred oxygen isotopic composition of the Sun is inconsistent with the more extreme 16O-rich value (Δ17O ~ -35‰) proposed by Gounelle et al. on the basis of two extremely 16O-rich CAIs from the CH/CB-like chondrite Isheyevo and with the 16O-poor value observed as a component of the solar wind implanted into the metallic particles in lunar soil (Ireland et al.).

B and Mg isotopic variations in Leoville mrs-06 type B1 cai:origin of 10Be and 26Al

NASA Astrophysics Data System (ADS)

Chaussidon, M.; Robert, F.; Russel, S. S.; Gounelle, M.; Ash, R. D.

2003-04-01

The finding [1-3] in Ca-Al-rich refractory inclusions (CAI) of primitive chondrites of traces of the in situ decay of radioactive 10Be (half-life 1.5Myr) indicates that irradiation of the protosolar nebula by the young Sun in its T-Tauri phase has produced significant amounts of the Li-Be-B elements. This irradiation may have produced also some or all of the short-lived 26Al (half-life 0.7Myr) and 41Ca (half-life 0.1Myr) previously detected in CAIs. To constrain the origin of 10Be and 10Al it is important to look for coupled variations in the 10Be/9Be and 26Al/27Al ratios in CAIs and to understand the processes responsible for these variations (e.g. variations in the fluences of irradiation, secondary perturbations of the CAIs, ...) We have thus studied the Li and B isotopic compositions and the Be/Li and Be/B concentration ratios in one CAI (MRS-06) from the Leoville CV3 chondrite in which large variations of the Mg isotopic compositions showing both the in situ decay of 26Al and the secondary redistribution of Mg isotopes have been observed [4]. The results show large variations for the Li and B isotopic compositions (^7Li/^6Li ranging from 11.02±0.21 to 11.82±0.07, and 10B/11B ratios ranging from 0.2457±0.0053 to 0.2980±0.0085). The ^7Li/^6Li ratio tend to decrease towards the rim of the inclusion. The 10B/11B ratios are positively correlated with the ^9Be/11B ratios indicating the in situ decay of 10Be. However perturbations of the 10Be/B system are observed. They would correspond to an event which occurred approximately 2Myr after the formation of the CAI and the irradiation of the CAI precursors which is responsible for the 10Be observed in the core of the CAI. These perturbations seem compatible with those observed for the 26Al/Mg system but they might be due to an irradiation of the already-formed, isolated CAI which would have resulted in increased 10Be/^9Be ratios and low ^7Li/^6Li ratios in the margin of the CAI. [1] McKeegan K. D. et al. (2000) Science, 90, 1334-1337. [2] Sugiura N. et al. et al. (2001) Meteoritics &Planet. Sci., 36, 1397-1408. [3] McPherson G. J. and Huss G. R. (2001) LPS XXXII, Abstract #1882. [4] Ash R. D. et al. (2002) LPS XXXIII, Abstract #2063.

Extreme 13C depletions in seawater-derived brines and their implications for the past geochemical carbon cycle

NASA Astrophysics Data System (ADS)

Lazar, Boaz; Erez, Jonathan

1990-12-01

Extreme depletions in the 13C content of the total dissolved inorganic carbon (CT) were found in brines overlying microbial mat communities. Total alkalinity (AT) and CT in the brines suggest that intense photosynthetic activity of the microbial mat communities depletes the CT from the brine. We suggest that this depletion drives a large, kinetic, negative fractionation of carbon isotopes similar to that observed in highly alkaline solutions. In brines of extreme salinity where microbial mat communities no longer exist, the 13C content of the CT increases, probably because photosynthesis no longer dominates the gas-exchange processes. This mechanism explains light carbon-isotope compositions of carbonate rocks from evaporitic sections and bears on the interpretation of δ13C values in bedded stromatolitic limestones that are ca. 3.5 b.y. old.

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

USGS Publications Warehouse

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

2015-01-01

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

Climate variability during the Medieval Climate Anomaly and Little Ice Age based on ostracod faunas and shell geochemistry from Biscayne Bay, Florida: Chapter 14

USGS Publications Warehouse

Cronin, Thomas M.; Wingard, G. Lynn; Dwyer, Gary S.; Swart, Peter K.; Willard, Debra A.; Albietz, Jessica

2012-01-01

An 800-year-long environmental history of Biscayne Bay, Florida, is reconstructed from ostracod faunal and shell geochemical (oxygen, carbon isotopes, Mg/Ca ratios) studies of sediment cores from three mudbanks in the central and southern parts of the bay. Using calibrations derived from analyses of modern Biscayne and Florida Bay ostracods, palaeosalinity oscillations associated with changes in precipitation were identified. These oscillations reflect multidecadal- and centennial-scale climate variability associated with the Atlantic Multidecadal Oscillation during the late Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). Evidence suggests wetter regional climate during the MCA and drier conditions during the LIA. In addition, twentieth century anthropogenic modifications to Everglades hydrology influenced bay circulation and/or processes controlling carbon isotopic composition.

Asian dust input in the western Philippine Sea: Evidence from radiogenic Sr and Nd isotopes

NASA Astrophysics Data System (ADS)

Jiang, Fuqing; Frank, Martin; Li, Tiegang; Chen, Tian-Yu; Xu, Zhaokai; Li, Anchun

2013-05-01

The radiogenic strontium (Sr) and neodymium (Nd) isotope compositions of the detrital fraction of surface and subsurface sediments have been determined to trace sediment provenance and contributions from Asian dust off the east coast of Luzon Islands in the western Philippine Sea. The Sr and Nd isotope compositions have been very homogenous near the east coast of the Luzon Islands during the latest Quaternary yielding relatively least radiogenic Sr (87Sr/86Sr = 0.70453 to 0.70491) and more radiogenic Nd isotope compositions (ɛNd(0) = +5.3 to +5.5). These isotope compositions are similar to Luzon rocks and show that these sediments were mainly derived from the Luzon Islands. In contrast, the Sr and Nd isotope compositions of sediments on the Benham Rise and in the Philippine Basin are markedly different in that they are characterized by overall more variable and more radiogenic Sr isotope compositions (87Sr/86Sr = 0.70452 to 0.70723) and less radiogenic Nd isotope compositions (ɛNd(0) = -5.3 to +2.4). The Sr isotope composition in the Huatung Basin is intermediate between those of the east coast of Luzon and Benham Rise, but shows the least radiogenic Nd isotope compositions. The data are consistent with a two end-member mixing relationship between Luzon volcanic rocks and eolian dust from the Asian continent, which is characterized by highly radiogenic Sr and unradiogenic Nd isotope compositions. The results show that Asian continental dust contributes about 10-50% of the detrital fraction of the sediments on Benham Rise in the western Philippine Sea, which offers the potentials to reconstruct the climatic evolution of eastern Asia from these sediments and compare this information to the records from the central and northern Pacific.

Numerical Modelling of Speleothem and Dripwater Chemistry: Interpreting Coupled Trace Element and Isotope Proxies for Climate Reconstructions

NASA Astrophysics Data System (ADS)

Owen, R.; Day, C. C.; Henderson, G. M.

2016-12-01

Speleothem palaeoclimate records are widely used but are often difficult to interpret due to the geochemical complexity of the soil-karst-cave system. Commonly analysed proxies (e.g. δ18O, δ13C and Mg/Ca) may be affected by multiple processes along the water flow path from atmospheric moisture source through to the cave drip site. Controls on speleothem chemistry include rainfall and aerosol chemistry, bedrock chemistry, temperature, soil pCO2, the degree of open-system dissolution and prior calcite precipitation. Disentangling the effects of these controls is necessary to fully interpret speleothem palaeoclimate records. To quantify the effects of these processes, we have developed an isotope-enabled numerical model based on the geochemical modelling software PHREEQC. The model calculates dripwater chemistry and isotopes through equilibrium bedrock dissolution and subsequent iterative CO2 degassing and calcite precipitation. This approach allows forward modelling of dripwater and speleothem proxies, both chemical (e.g. Ca concentration, pH, Mg/Ca and Sr/Ca ratios) and isotopic (e.g. δ18O, δ13C, δ44Ca and radiocarbon content), in a unified framework. Potential applications of this model are varied and the model may be readily expanded to include new isotope systems or processes. Here we focus on calculated proxy co-variation due to changes in model parameters. Examples include: - The increase in Ca concentration, decrease in δ13C and increase in radiocarbon content as bedrock dissolution becomes more open-system. - Covariation between δ13C, δ44Ca and trace metal proxies (e.g. Mg/Ca) predicted by changing prior calcite precipitation. - The effect of temperature change on all proxies through the soil-karst-cave system. Separating the impact of soil and karst processes on geochemical proxies allows more quantitative reconstruction of the past environment, and greater understanding in modern cave monitoring studies.

Habitat Use and Trophic Structure in a Highly Migratory Predatory Fish Identified with Geochemical Proxies in Scales

NASA Astrophysics Data System (ADS)

Seeley, M.; Walther, B. D.

2016-02-01

Atlantic tarpon, Megalops atlanticus, are highly migratory euryhaline predators that occupy different habitats throughout ontogeny. Specifically, Atlantic tarpon are known to inhabit oligohaline waters, although the frequency and duration of movements across estuarine gradients into these waters are relatively unknown. This species supports over a two billion dollar industry within the Gulf of Mexico and is currently listed as vulnerable under the International Union for the Conservation of Nature (IUCN). A new non-lethal method for reconstructing migrations across estuaries relies on trace element and stable isotope compositions of growth increments in scales. We analyzed Atlantic tarpon scales from the Texas coast to validate this method using inductively coupled plasma mass spectrometry (ICP-MS) for trace elements and isotope ratio mass spectrometry (IR-MS) for stable isotope ratios. Multiple scales were also taken from the same individual to confirm the consistency of elemental uptake within the same individual. Results show that scale Ba:Ca, Sr:Ca and δ13C are effective proxies for salinity, while enrichments in δ15N are consistent with known ontogenetic trophic shifts. In addition, chemical transects across multiple scales from the same individual were highly consistent, suggesting that any non-regenerated scale removed from a fish can provide equivalent time series. Continuous life history profiles of scales were obtained via laser ablation transects of scale cross-sections to quantify trace element concentrations from the core (youngest increments) to the edge (oldest increments). Stable isotope and trace element results together indicate that behavior is highly variable between individuals, with some but not all fish transiting estuarine gradients into oligohaline waters. Our findings will provide novel opportunities to investigate alternative non-lethal methods to monitor fish migrations across chemical gradients.

LA-MC-ICPMS Determination of Copper Isotope Ratios in Turquoise from the Southwestern United States.

NASA Astrophysics Data System (ADS)

Evans, M. J.; Fayek, M.; Riciputi, L.; Anovitz, L.; Hull, S.; Mathien, F. J.; Milford, H.

2004-12-01

Hydrothermal circulation driven by igneous intrusion led to the deposition of turquoise throughout the southwestern United States and Mesoamerica. The genesis of these copper-ore deposits is unclear; conflicting hypotheses call on ascent of magmatic waters (hypogene) or descent and recirculation of meteroric waters (supergene). Copper isotope analyses were performed by laser-ablation multi-collector ICPMS to survey turquoise deposits from AZ, NV, CA, NM, and CO. The turquoise have [Cu] from 0.1 to 10 wt% and are all found in near-surface alteration zones. Analyses of individual turquoise grains are reproducible to better than 0.4\\permil \\delta65Cu (1\\sigma) (relative to NBS-976). \\delta65Cu values show significant variation (ca. 10\\permil) between the deposits, equal to the total range reported for continental ores and both hypogene and supergene deposits. The variability between deposits may reflect differences in source Cu isotopic composition or more likely, hydrothermal processes during leaching and deposition. The mining and trade of turquoise played an important role in early social and economic development between Mesoamerica and N. America. Copper isotopes will improve differentiation between turquoise source areas, aiding archaeological and cultural studies of trade between and within Mesoamerica and the SW USA. Research sponsored by NSF-BCS (Archaeology) grant #0312088 to Fayek and the Office of Basic Energy Sciences, U.S. Department of Energy, under contract with Oak Ridge National Laboratory, managed by UT-Battelle, LLC. The submitted manuscript has been authored by a contractor of the U.S. Government under contract No. DE-AC05-00OR22725. Accordingly, the U.S. Government retains a nonexclusive, royalty-free license to publish or reproduce the published form of this contribution, or allow others to do so, for U.S. Government purposes.

MG Isotopic Measurement of FIB-Isolated Presolar Silicate Grains

NASA Technical Reports Server (NTRS)

Messenger, Scott R.; Nguyen, A.; Ito, M.; Rahman, Z.

2010-01-01

The majority of presolar oxide and silicate grains are ascribed to origins in low-mass red giant and asymptotic giant branch (AGB) stars based on their O isotopic ratios. However, a minor population of these grains (< 10%) has O isotopic ratios incompatible with these sources. Two principle alternative sources are higher-than-solar metallicity (Z) stars or, more likely, supernovae (SN) [1-3]. These rare (Group 4) grains [3] are characterized by enrichments in O-18, and typically also enrichments in O-17. An even rarer subset of grains with extremely large enrichments in O-17 and smaller depletions in O-18 were suggested to come from binary star systems [2]. To establish the origins of these isotopically unusual grains, it is necessary to examine isotopic systems in addition to O. Presolar silicates offer several elements diagnostic of their stellar sources and nuclear processes, including O, Si, Mg, Fe and Ca. However, the database for minor element isotopic compositions in silicates is seriously lacking. To date only two silicate grains have been analyzed for Mg [4] or Fe [5]. One major complicating factor is their small size (average 230 nm), which greatly limits the number of measurements that can be performed on any one grain and makes it more difficult to obtain statistically relevant data. This problem is compounded because the grains are identified among isotopically solar silicates, which contribute a diluting signal in isotopic measurements [1]. Thus, relatively small isotopic anomalies are missed due to this dilution effect. By applying focused ion beam (FIB) milling, we obtain undiluted Mg isotopic ratios of isolated rare presolar silicate grains to investigate their sources.

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.

Reverse weathering in marine sediments and the geochemical cycle of potassium in seawater: Insights from the K isotopic composition (41K/39K) of deep-sea pore-fluids

USGS Publications Warehouse

Santiago Ramos, Danielle P.; Morgan, Leah; Lloyd, Nicholas S.; Higgins, John A.

2018-01-01

In situ Al-silicate formation, also known as “reverse weathering,” is an important sink of many of the major and minor cations in seawater (e.g. Mg, K, and Li). However, the importance of this sink in global geochemical cycles and isotopic budgets of these elements remains poorly constrained. Here, we report on the potassium isotopic composition (41">41K/39">39K) of deep-sea sediment pore-fluids from four (Integrated) Ocean Drilling Program sites (1052, U1378, U1395 and U1403) to characterize potassium isotopic fractionation associated with the formation of authigenic Al-silicate minerals in marine sediments and its role in elevating the 41">41K/39">39K of seawater relative to bulk silicate Earth. Isotopic ratios are obtained by high-resolution multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) in cold plasma conditions with a long-term external reproducibility of ca. 0.17‰. We find that, although all sites are characterized by pore-fluid K concentrations that decline with increasing depth, their K isotopic profiles vary systematically from site-to-site; at sites characterized by rapid sedimentation rates, pore-fluid profiles of 41">41K/39">39K are relatively invariant whereas at sites characterized by slow sedimentation rates, 41">41K/39">39K declines with depth by up to 1.8‰. Results from 1-D diffusion-advection-reaction models suggest that these differences may result from a complex interplay between sedimentation rate and fractionation of K isotopes during diffusion, Al-silicate authigenesis, and ion exchange. Model simulations suggest fractionation factors between 0.9980 and 1.0000 for reverse weathering reactions in deep-sea sediments. Although deep-sea sites do not constitute major sinks of K in seawater, some of the processes responsible for K isotopic fractionation at these sites (diffusion and Al-silicate authigenesis) likely play a role in determining the 41">41K/39">39K of seawater.

Compositions of Normal and Anomalous Eucrite-Type Mafic Achondrites

NASA Technical Reports Server (NTRS)

Mittlefehldt, D. W.; Peng, Z. X.; Mertzman, S. A.

2016-01-01

The most common asteroidal igneous meteorites are eucrite-type mafic achondrites - basalts and gabbros composed of ferroan pigeonite, ferroan augite, calcic plagioclase, silica, ilmenite, troilite, Ca-phosphate, chromite and Fe-metal. These rocks are thought to have formed on a single asteroid along with howardites and diogenites. However, high precision O-isotopic analyses have shown that some mafic achondrites have small, well-resolved, non-mass-dependent differences that have been interpreted as indicating derivation from different asteroids. Some of these O-anomalous mafic achondrites also have anomalous petrologic characteristics, strengthening the case that they hail from distinct parent asteroids. We present the results of bulk compositional studies of a suite of normal and anomalous eucrite-type basalts and cumulate gabbros.

Study of the 249-251Cf + 48Ca reactions: recent results and outlook

NASA Astrophysics Data System (ADS)

Voinov, A. A.; Oganessian, Yu Ts; Abdullin, F. Sh; Brewer, N. T.; Dmitriev, S. N.; Grzywacz, R. K.; Hamilton, J. H.; Itkis, M. G.; Miernik, K.; Polyakov, A. N.; Roberto, J. B.; Rykaczewski, K. P.; Sabelnikov, A. V.; Sagaidak, R. N.; Shirokovsky, I. V.; Shumeiko, M. V.; Stoyer, M. A.; Subbotin, V. G.; Sukhov, A. M.; Tsyganov, Yu S.; Utyonkov, V. K.; Vostokin, G. K.

2018-02-01

Experiment aiming at the synthesis of heavy isotopes of Z=118 (Og) using beam of 48Ca and a target of 249-251Cf was undertaken in October 2015 - April 2016 employing the Dubna Gas-Filled Recoil Separator (FLNR JINR). The target of mixed isotopes of 249-251Cf (50.7% of 249Cf, 12.9% of 250Cf, and 36.4% of 251Cf) was irradiated by 48Ca ions at two beam energies of 252 and 258 MeV with the corresponding accumulated beam doses of 1.6×1019 and 1.1×1019. A single event observed at lower beam energy was assigned to the isotope 294Og, the product of the reaction 249Cf(48Ca, 3n); its decay pattern and the observed radioactive properties of the nuclides in the decay chain reproduce in full those observed for 294Og in our earlier experiments of 2002-2005 and 2012. At higher beam energy we observed no decay chains that could be attributed to the isotopes of Og. The possibility of renewal of this experiment in the future is discussed.

Condensation and mixing in supernova ejecta

NASA Astrophysics Data System (ADS)

Fedkin, A. V.; Meyer, B. S.; Grossman, L.

2010-06-01

Low-density graphite spherules from the Murchison carbonaceous chondrite contain TiC grains and possess excess 28Si and 44Ca (from decay of short-lived 44Ti). These and other isotopic anomalies indicate that such grains formed by condensation from mixtures of ejecta from the interior of a core-collapse supernova with those from the exterior. Using homogenized chemical and isotopic model compositions of the eight main burning zones as end-members, Travaglio et al. (1999) attempted to find mixtures whose isotopic compositions match those observed in the graphite spherules, subject to the condition that the atomic C/O ratio = 1. They were partially successful, but this chemical condition does not guarantee condensation of TiC at a higher temperature than graphite, which is indicated by the spherule textures. In the present work, model compositions of relatively thin layers of ejecta within the main burning zones computed by Rauscher et al. (2002) for Type II supernovae of 15, 21 and 25 M ʘ are used to construct mixtures whose chemical compositions cause equilibrium condensation of TiC at a higher temperature than graphite in an attempt to match the textures and isotopic compositions of the spherules simultaneously. The variation of pressure with temperature and the change in elemental abundances with time due to radioactive decay were taken into account in the condensation calculations. Layers were found within the main Ni, O/Ne, He/C and He/N zones that, when mixed together, simultaneously match the carbon, nitrogen and oxygen isotopic compositions, 44Ti/ 48Ti ratios and inferred initial 26Al/ 27Al ratios of the low-density graphite spherules, even at subsolar 12C/ 13C ratios. Due to the relatively large proportion of material from the Ni zone and the relative amounts of the two layers of the Ni zone required to meet these conditions, predicted 28Si excesses are larger than observed in the low-density graphite spherules, and large negative δ46Ti/ 48Ti, δ47Ti/ 48Ti, δ49Ti/ 48Ti and δ50Ti/ 48Ti are produced, in contrast to the observed normal δ46Ti/ 48Ti and δ47Ti/ 48Ti, large positive δ49Ti/ 48Ti and smaller positive δ50Ti/ 48Ti. Although better matches to the observed δ46Ti/ 48Ti, δ47Ti/ 48Ti and 28Si excesses can be found using much smaller amounts of Ni zone material and some Si/S zone material, it is very difficult to match simultaneously the Ti and Si isotopic compositions in any mixtures of material from these deep layers with He/C and He/N zone material, regardless of the condensation sequence. The occurrence of Fe-rich, Si-poor metal grains inside the graphite spherules does not have a satisfactory explanation.

Petrogenesis and provenance of ungrouped achondrite Northwest Africa 7325 from petrology, trace elements, oxygen, chromium and titanium isotopes, and mid-IR spectroscopy

NASA Astrophysics Data System (ADS)

Goodrich, Cyrena A.; Kita, Noriko T.; Yin, Qing-Zhu; Sanborn, Matthew E.; Williams, Curtis D.; Nakashima, Daisuke; Lane, Melissa D.; Boyle, Shannon

2017-04-01

Northwest Africa (NWA) 7325 is an ungrouped achondrite that has recently been recognized as a sample of ancient differentiated crust from either Mercury or a previously unknown asteroid. In this work we augment data from previous investigations on petrography and mineral compositions, mid-IR spectroscopy, and oxygen isotope compositions of NWA 7325, and add constraints from Cr and Ti isotope compositions on the provenance of its parent body. In addition, we identify and discuss notable similarities between NWA 7325 and clasts of a rare xenolithic lithology found in polymict ureilites. NWA 7325 has a medium grained, protogranular to poikilitic texture, and consists of 10-15 vol.% Mg-rich olivine (Fo 98), 25-30 vol.% diopside (Wo 45, Mg# 98), 55-60 vol.% Ca-rich plagioclase (An 90), and trace Cr-rich sulfide and Fe,Ni metal. We interpret this meteorite to be a cumulate that crystallized at ⩾1200 °C and very low oxygen fugacity (similar to the most reduced ureilites) from a refractory, incompatible element-depleted melt. Modeling of trace elements in plagioclase suggests that this melt formed by fractional melting or multi-stage igneous evolution. A subsequent event (likely impact) resulted in plagioclase being substantially remelted, reacting with a small amount of pyroxene, and recrystallizing with a distinctive texture. The bulk oxygen isotope composition of NWA 7325 plots in the range of ureilites on the CCAM line, and also on a mass-dependent fractionation line extended from acapulcoites. The ε54Cr and ε50Ti values of NWA 7325 exhibit deficits relative to terrestrial composition, as do ordinary chondrites and most achondrites. Its ε54Cr value is distinct from that of any analyzed ureilite, but is not resolved from that of acapulcoites (as represented by Acapulco). In terms of all these properties, NWA 7325 is unlike any known achondrite. However, a rare population of clasts found in polymict ureilites ("the magnesian anorthitic lithology") are strikingly similar to NWA 7325 in mineralogy and mineral compositions, oxygen isotope compositions, and internal textures in plagioclase. These clasts are probably xenolithic in polymict ureilites, and could be pieces of NWA 7325-like meteorites. Using constraints from chromium, titanium and oxygen isotopes, we discuss two possible models for the provenance of the NWA 7325 parent body: (1) accretion in the inner solar system from a reservoir similar to that of acapulcoites in Δ17O, ε54Cr and ε50Ti; or (2) early (<1 Ma after CAI formation) accretion in the outer solar system (beyond the snow line), before 54Cr and 50Ti anomalies were introduced to this region of the solar system. The mid-IR emission spectrum of NWA 7325 obtained in this work matches its modal mineralogy, and so can be compared with spectra of new meteorites or asteroids/planets to help identify similar materials and/or the parent body of NWA 7325.

Zircon U-Pb, O, and Hf isotopic constraints on Mesozoic magmatism in the Cyclades, Aegean Sea, Greece

NASA Astrophysics Data System (ADS)

Fu, Bin; Bröcker, Michael; Ireland, Trevor; Holden, Peter; Kinsley, Leslie P. J.

2015-01-01

Compared to the well-documented Cenozoic magmatic and metamorphic rocks of the Cyclades, Aegean Sea, Greece, the geodynamic context of older meta-igneous rocks occurring in the marble-schist sequences and mélanges of the Cycladic Blueschist Unit is as yet not fully understood. Here, we report O-Hf isotopic compositions of zircons ranging in age from ca. 320 Ma to ca. 80 Ma from metamorphic rocks exposed on the islands of Andros, Ios, Sifnos, and Syros with special emphasis on Triassic source rocks. Ion microprobe (SHRIMP II) single spot oxygen isotope analysis of pre-Cretaceous zircons from various felsic gneisses and meta-gabbros representing both the marble-schist sequences and the mélanges of the study area yielded a large range in δ18O values, varying from 2.7 ‰ to 10.1 ‰ VSMOW, with one outlier at -0.4 %. Initial ɛHf values (-12.5 to +15.7) suggest diverse sources for melts formed between Late Carboniferous to Late Cretaceous time that record derivation from mantle and reworked older continental crust. In particular, variable δ18O and ɛHf( t) values for Triassic igneous zircons suggest that magmatism of this age is more likely rift- than subduction-related. The significant crustal component in 160 Ma meta-gabbros from Andros implies that some Jurassic gabbroic rocks of the Hellenides are not part of SSZ-type (supra-subduction zone) ophiolites that are common elsewhere along the margin of the Pelagonian zone.

1.8 billion years of fluid-crust interaction: A zircon oxygen isotope record for the lower crust, western Churchill Province, Canadian Shield

NASA Astrophysics Data System (ADS)

Petts, Duane C.; Moser, Desmond E.; Longstaffe, Frederick J.; Davis, William J.; Stern, Richard A.

2014-04-01

The western Churchill Province of the Canadian Shield experienced a prolonged and complex formation history (ca. 4.04 to 1.70 Ga), with evidence for multiple episodes of orogenesis and regional magmatic activity. Here we report on the oxygen isotopic compositions of garnet and zircon recovered from lower crustal xenoliths, which have U-Pb ages between ca. 3.5 and 1.7 Ga. Overall, zircon from four metabasite xenoliths from the Rankin Inlet sample suite have δ18O values ranging from + 5.5 to + 8.6‰. Zircon from three metatonalite/anorthosite xenoliths and five metabasite xenoliths from the Repulse Bay sample suite have δ18O values of + 5.6 to + 8.3‰. High δ18O values (> + 6.0‰) for the oldest igneous zircon cores (ca. 3.5 Ga and 3.0-2.6 Ga) indicate that their metatonalite/anorthosite protolith magmas were generated from, or had assimilated, supracrustal rocks that interacted previously with surface-derived fluids. Igneous zircon cores (ca. 2.9-2.6 Ga) from one metabasite xenolith have δ18O values of + 5.6 to + 6.4‰, which suggests a formation from a mantle-derived basaltic/gabbroic magma. Metamorphic zircon cores (ca. 2.0-1.9 Ga) from one metabasite xenolith commonly have δ18O values between + 6.0 and + 6.3‰, which is indicative of a basalt/gabbro protolith and localized reworking of the lower crust caused by regional-scale plate convergence. The wide range of δ18O values (+ 5.5 to + 8.3‰) for ca. 1.75-1.70 Ga metamorphic zircon rims (identified in all xenoliths) indicates regional transient heating and reworking of mantle- and supracrustal-derived crust, induced by magmatic underplating along the crust-mantle boundary.

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.

Changes in Lava Compositions and With Time From the Eocene Through the Miocene for the Mariana Forearc

NASA Astrophysics Data System (ADS)

Reagan, M. K.; Mohler, D.; Brian, H.; Hickey-Vargas, R.; Hanan, B.

2003-12-01

We are investigating the evolution of volcanism in the Mariana arc from the initiation of subduction of the Pacific plate beneath the Philippine plate in the Eocene through the Miocene. The oldest lavas in the Mariana fore-arc region are a ca 49 Ma tholeiite to boninite sequence from DSDP sites 458 and 459. These tholeiites have NMORB-like REE, HFSE, and Th concentrations, but are enriched in LIL elements, Pb, and U. The capping boninite-series glasses have similar slab-derived trace element abundance patterns, but lower and flatter REE contents (1-2 x PUM). 40Ar/39Ar ages obtained on boninite series lavas from Guam stretch back to 44Ma. These lavas have U-shaped REE patterns and HREE concentrations about 3-8 x PUM. La/Nb decrease and Hf/Sm increase with increasing Ba/La for both the DSDP and Guam lavas. Pb isotope values plot within fields defined by Pacific plate lavas and volcanogenic sediments (Meijer, 1976, GSA Bull., v. 87; Pearce et al., 1999, J. Petrol., v. 40). Hf and Pb isotopic compositions change consistently with Hf/Sm and Ba/La ratios for lavas from the DSDP sites, but not for those from Guam. The data suggest either that little of the Pb in these lavas was derived from subducting sediments, or that the contrast in Pb isotopes between lavas from Guam and slab fluids was inconsequential. The source of the DSDP site lavas was similar to a Pacific or transitional Pacific-Indian Ocean MORB-source. Fluxed melting at high-P generated the tholeiites. Boninites were generated at low-P by continued fluxed melting. The mantle source for the boninite-series lavas from Guam was less depleted. Progressive fluxed melting here apparently occurred with less mantle upwelling. In both locations, the variations in La/Nb and perhaps the Hf/Sm ratios appear to be related to changes in the residual mantle source mineralogy with progressive melting. Rhyolites erupted on Saipan at 45- 46 Ma are unusually high in silica for an oceanic island arc setting. These lavas are enigmatic in that they have trace element and isotopic compositions similar to those of Oligocene (36-32 Ma) mature arc andesites and dacites from forearc sites. Pb isotope values for all of these lavas plot along a trend that stretches from the NHRL toward Pacific siliceous sediments, with the rhyolites plotting at the least radiogenic end of the array. Basalt dikes with ages of ca. 41 Ma cut the boninite series lavas in Guam. These basalts have trace element patterns of typical arc tholeiites, and mark the first appearance of relatively normal mafic arc lavas in this system. Pb isotope compositions for these samples indicate that siliceous sediment also makes its first appearance at this time. A second stage of normal arc volcanism began on Guam and Saipan at about 14 Ma, after spreading in the Parece Vela Basin ceased. These lavas have incompatible trace element and isotopic ratios that are remarkably similar to those of the modern Mariana arc. In conclusion: lavas from DSDP sites 458 and 459 were apparently generated from upwelling mantle that rushed in behind the newly subducting Pacific lithosphere (see Stern and Bloomer, 1992, GSA Bull. v. 104; Hall et al., 2003, EPSL, v. 212). The transition from an upwelling mantle wedge to relatively normal mantle counterflow and P-T distributions in the mantle wedge apparently required several million years of subduction and cooling of the corner of the mantle wedge. The compositions of the mantle (Pacific to Indian) and the subducted components (basaltic to silicic sediment) both changed with the mantle convection regime.

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. The chondritic composition of the Earth implies that Mg isotopes were well mixed during accretion of the inner solar system.

Hydrogeochemical and isotopic evidences of groundwater salinization in coastal aquifers: A case study in Jeju volcanic island, Korea

NASA Astrophysics Data System (ADS)

Kim, Y.; Lee, D.; Lee, K.; Koh, D.; Lee, S.; Park, W.; Koh, G.; Woo, N.

2001-12-01

In order to clearly identify the origin of saline groundwaters in the eastern part of Jeju volcanic island, Korea the hydrogeochemical and isotopic studies have been carried out for 18 observation wells located in east and southeast coastal regions. The total dissolved solid (TDS) contents of groundwater samples are highly variable (77 to 21,782 mg/L). Most of the groundwaters in the study area are classified into Na-Cl type except a few samples showing Ca-Cl type. Hydrochemical characteristics based on bivariate and triangular diagrams of major ions show that the changes of chemical compositions of groundwaters were mainly controlled by the salinization process linked to cation-exchange reactions. The oxygen, hydrogen, sulfur, and strontium isotopic data explicitly show a simple mixing trend of groundwater and seawater. Using two-components fractional mixing model on the basis of 18O contents as well as Br and Cl contents, the proportion of seawater in fresh groundwater was quantitatively determined as high as 60 %. Sr isotopic compositions and Br/Cl ratios strongly suggest that the source of groundwater salinization is present-day seawater intrusion rather than paleoseawater or formation water, which can also be supported by the I/Cl ratios. The highly permeable aquifers in the east coastal region characterized by low hydraulic gradient and recharge rate and high hydraulic conductivity comparing with other regions are advantageous to the groundwater salinization. Based on the Cl, ¥ä18O, and 87Sr/86Sr it was determined that seawater has intruded into inland 2.5 km from coastline.

Variation in the carbon and oxygen isotope composition of plant biomass and its relationship to water-use efficiency at the leaf- and ecosystem-scales in a northern Great Plains grassland.

PubMed

Flanagan, Lawrence B; Farquhar, Graham D

2014-02-01

Measurements of the carbon (δ(13) Cm ) and oxygen (δ(18) Om ) isotope composition of C3 plant tissue provide important insights into controls on water-use efficiency. We investigated the causes of seasonal and inter-annual variability in water-use efficiency in a grassland near Lethbridge, Canada using stable isotope (leaf-scale) and eddy covariance measurements (ecosystem-scale). The positive relationship between δ(13) Cm and δ(18) Om values for samples collected during 1998-2001 indicated that variation in stomatal conductance and water stress-induced changes in the degree of stomatal limitation of net photosynthesis were the major controls on variation in δ(13) Cm and biomass production during this time. By comparison, the lack of a significant relationship between δ(13) Cm and δ(18) Om values during 2002, 2003 and 2006 demonstrated that water stress was not a significant limitation on photosynthesis and biomass production in these years. Water-use efficiency was higher in 2000 than 1999, consistent with expectations because of greater stomatal limitation of photosynthesis and lower leaf ci /ca during the drier conditions of 2000. Calculated values of leaf-scale water-use efficiency were 2-3 times higher than ecosystem-scale water-use efficiency, a difference that was likely due to carbon lost in root respiration and water lost during soil evaporation that was not accounted for by the stable isotope measurements. © 2013 John Wiley & Sons Ltd.

Isotopic and elemental analysis of fish tissues for provenance determination

NASA Astrophysics Data System (ADS)

Zannella, Carmela; Adamo, Paola; Opper, Christine; Schwendinger, Susanne; Knezevic, Sara; Van den Oever, Sabrina; Tchaikovsky, Anastassiya; Zitek, Andreas; Prohaska, Thomas

2017-04-01

The reliable tracing of the productions flows of food products through the entire supply chain is an essential requirement for all types of food commodities qualified by origin, composition and quality. This is a minimum requirement to implement safety for the consumer, enhance consumer confidence and countervail fraudulent practices. One important food commodity is fish and fish products. Reliable methods to trace the origin of fish have become of high importance. The investigation focused on the identification of adequate geochemical marker in fish meat and the corresponding linkage to the ambient water. The Sr/Ca ratio along with the 87Sr/86Sr isotope ratio analyzed by (multi collector) inductively coupled plasma mass spectrometry (MC ICP-MS) proved to be the most potential tools in this respect. For the first time, a direct link of fish meat to water could be accomplished.In addition, fish hard parts (otoliths, fin rays, fish bones) were under investigation to reconstruct the habitat changes during the lifespan of a fishes life. Fish hard parts have the potential to serve as "life time recorder". Thus the spatial investigation of the elemental and isotopic composition can be used to monitor habitat changes with time. The spatially resolved data of hard tissues was collected by means of Laser Ablation Split Stream ICP-MS/MC ICP-MS. This work is accomplished within the scope of the project "CSI: TRACE YOUR FOOD".

Experimental and geochemical evidence for derivation of the El Capitan Granite, California, by partial melting of hydrous gabbroic lower crust

USGS Publications Warehouse

Ratajeski, K.; Sisson, T.W.; Glazner, A.F.

2005-01-01

Partial melting of mafic intrusions recently emplaced into the lower crust can produce voluminous silicic magmas with isotopic ratios similar to their mafic sources. Low-temperature (825 and 850??C) partial melts synthesized at 700 MPa in biotite-hornblende gabbros from the central Sierra Nevada batholith (Sisson et al. in Contrib Mineral Petrol 148:635-661, 2005) have major-element and modeled trace-element (REE, Rb, Ba, Sr, Th, U) compositions matching those of the Cretaceous El Capitan Granite, a prominent granite and silicic granodiorite pluton in the central part of the Sierra Nevada batholith (Yosemite, CA, USA) locally mingled with coeval, isotopically similar quartz diorite through gabbro intrusions (Ratajeski et al. in Geol Soc Am Bull 113:1486-1502, 2001). These results are evidence that the El Capitan Granite, and perhaps similar intrusions in the Sierra Nevada batholith with lithospheric-mantle-like isotopic values, were extracted from LILE-enriched, hydrous (hornblende-bearing) gabbroic rocks in the Sierran lower crust. Granitic partial melts derived by this process may also be silicic end members for mixing events leading to large-volume intermediate composition Sierran plutons such as the Cretaceous Lamarck Granodiorite. Voluminous gabbroic residues of partial melting may be lost to the mantle by their conversion to garnet-pyroxene assemblages during batholithic magmatic crustal thickening. ?? Springer-Verlag 2005.

A non-zircon Hf isotope record in Archean black shales from the Pilbara craton confirms changing crustal dynamics ca. 3 Ga ago.

PubMed

Nebel-Jacobsen, Yona; Nebel, Oliver; Wille, Martin; Cawood, Peter A

2018-01-17

Plate tectonics and associated subduction are unique to the Earth. Studies of Archean rocks show significant changes in composition and structural style around 3.0 to 2.5 Ga that are related to changing tectonic regime, possibly associated with the onset of subduction. Whole rock Hf isotope systematics of black shales from the Australian Pilbara craton, selected to exclude detrital zircon components, are employed to evaluate the evolution of the Archean crust. This approach avoids limitations of Hf-in-zircon analyses, which only provide input from rocks of sufficient Zr-concentration, and therefore usually represent domains that already underwent a degree of differentiation. In this study, we demonstrate the applicability of this method through analysis of shales that range in age from 3.5 to 2.8 Ga, and serve as representatives of their crustal sources through time. Their Hf isotopic compositions show a trend from strongly positive εHf initial values for the oldest samples, to strongly negative values for the younger samples, indicating a shift from juvenile to differentiated material. These results confirm a significant change in the character of the source region of the black shales by 3 Ga, consistent with models invoking a change in global dynamics from crustal growth towards crustal reworking around this time.

Understanding key drivers controlling daily stable isotope variations in precipitation of Costa Rica, Central America

NASA Astrophysics Data System (ADS)

Sanchez-Murillo, Ricardo; Welsh, Kristin; Birkel, Christian; Esquivel-Hernández, Germain; Corrales-Salazar, Jose; Boll, Jan; Brooks, Erin; Roupsard, Olivier; Katchan, Irina; Arce-Mesén, Rafael; Soulsby, Chris; Araguás-Araguás, Luis

2015-04-01

Costa Rica is located on the Central American Isthmus, which receives direct moisture inputs from the Caribbean Sea and the Pacific Ocean. The relatively narrow, but high relief Central American land bridge is characterized by unique mountainous and lowland microclimates. However, only limited knowledge exists about the impact of relief and regional atmospheric circulation patterns on precipitation origin, transport, and isotopic composition in this tropical region. Therefore, the main scope of this study is to identify the key drivers controlling variations in meteoric waters of Costa Rica using stable isotopes based on daily sample collection for the year 2013. The monitoring sites comprise three strategic locations across Costa Rica: Heredia (Central Valley), Turrialba (Caribbean slope), and Caño Seco (South Pacific slope). Sporadic dry season rain is mostly related to isolated enriched events ranging from -5.8‰ d18O up to -0.9‰ d18O. By mid-May, the Intertropical Convergence Zone reaches Costa Rica resulting in a notable depletion in isotope ratios (up to -18.5‰ d18O). HYSPLIT back air mass trajectories indicate the strong influence on the origin and transport of precipitation of two main moisture transport mechanisms, the Caribbean Low Level Jet and the Colombian Low Level Jet as well as localized convection events. Multiple linear regression models constructed based on Random Forests of surface meteorological information and atmospheric sounding profiles suggest that Lifted Condensation Level and surface relative humidity are the main factors controlling isotopic variations. These findings diverge from the recognized 'amount effect' in monthly composite samples across the tropics. Understanding of stable isotope dynamics in tropical precipitation can be used to enhance catchment and groundwater modeling efforts in ungauged basins where scarcity of long-term monitoring data drastically limit current and future water resources management.

Multivariate statistical analysis of the hydrogeochemical and isotopic composition of the groundwater resources in northeastern Peloponnesus (Greece).

PubMed

Matiatos, Ioannis; Alexopoulos, Apostolos; Godelitsas, Athanasios

2014-04-01

The present study involves an integration of the hydrogeological, hydrochemical and isotopic (both stable and radiogenic) data of the groundwater samples taken from aquifers occurring in the region of northeastern Peloponnesus. Special emphasis has been given to health-related ions and isotopes in relation to the WHO and USEPA guidelines, to highlight the concentrations of compounds (e.g., As and Ba) exceeding the drinking water thresholds. Multivariate statistical analyses, i.e. two principal component analyses (PCA) and one discriminant analysis (DA), combined with conventional hydrochemical methodologies, were applied, with the aim to interpret the spatial variations in the groundwater quality and to identify the main hydrogeochemical factors and human activities responsible for the high ion concentrations and isotopic content in the groundwater analysed. The first PCA resulted in a three component model, which explained approximately 82% of the total variance of the data sets and enabled the identification of the hydrogeological processes responsible for the isotopic content i.e., δ(18)Ο, tritium and (222)Rn. The second PCA, involving the trace element presence in the water samples, revealed a four component model, which explained approximately 89% of the total variance of the data sets, giving more insight into the geochemical and anthropogenic controls on the groundwater composition (e.g., water-rock interaction, hydrothermal activity and agricultural activities). Using discriminant analysis, a four parameter (δ(18)O, (Ca+Mg)/(HCO3+SO4), EC and Cl) discriminant function concerning the (222)Rn content was derived, which favoured a classification of the samples according to the concentration of (222)Rn as (222)Rn-safe (<11 Bq·L(-1)) and (222)Rn-contaminated (>11 Bq·L(-1)). The selection of radon builds on the fact that this radiogenic isotope has been generally related to increased health risk when consumed. Copyright © 2014 Elsevier B.V. All rights reserved.

Multiple sulfur isotope records at the end-Guadalupian (Permian) at Chaotian, China: Implications for a role of bioturbation in the Phanerozoic sulfur cycle

NASA Astrophysics Data System (ADS)

Saitoh, Masafumi; Ueno, Yuichiro; Matsu'ura, Fumihiro; Kawamura, Tetsuya; Isozaki, Yukio; Yao, Jianxin; Ji, Zhansheng; Yoshida, Naohiro

2017-03-01

A recent study on quadruple sulfur isotopes (32S, 33S, 34S, and 36S) of sedimentary pyrite suggested that the end-Guadalupian extinction was caused by shoaling of the sulfidic deep-water. This scenario is based on the assumption that sulfur isotopic compositions of pyrite from hosting sediments were controlled by benthos activities, thus by the redox conditions of the sedimentary environments. Nonetheless, the relationship between the sulfur isotope records and redox conditions, reconstructed from litho- and bio-facies, are poorly known. In order to examine the effect of bioturbation in sediments, quadruple sulfur isotopic compositions of sedimentary pyrite from the end-Guadalupian succession in Chaotian, South China, were analyzed. Black mudstones of deep-water facies immediately below the extinction horizon have consistently high Δ33S values of ca. +0.079‰, clearly suggesting a sulfate reduction in the anoxic water column. Our new data are consistent with the emergence of a sulfidic deep-water mass prior to the end-Guadalupian extinction; the upwelling of the toxic deep-water may have contributed to the extinction. In contrast, shallow-marine bioclastic limestones with burrows deposited under oxic conditions have negative Δ33S values. This anomalous isotopic signal indicates the mixing of two distinct types of pyrite; one generated during the sulfate reduction in an open system and the other in a closed system. We interpret that bioturbation supplied sulfate in the sediments and promoted sulfate reduction and in-situ sulfide precipitation within the sediments. The negative Δ33S values of oxic sediments in Chaotian are inconsistent with the previous model and demonstrate that the sedimentary sulfur cycle associated with bioturbation was more complicated than previously thought. Our study also implies that, more generally, the role of bioturbation in increasing seawater sulfate concentration in the Phanerozoic may have been overestimated in the previous studies, because bioturbation may have enhanced sulfide burial or sulfur output from the oceans.

High-precision isotopic characterization of USGS reference materials by TIMS and MC-ICP-MS

NASA Astrophysics Data System (ADS)

Weis, Dominique; Kieffer, Bruno; Maerschalk, Claude; Barling, Jane; de Jong, Jeroen; Williams, Gwen A.; Hanano, Diane; Pretorius, Wilma; Mattielli, Nadine; Scoates, James S.; Goolaerts, Arnaud; Friedman, Richard M.; Mahoney, J. Brian

2006-08-01

The Pacific Centre for Isotopic and Geochemical Research (PCIGR) at the University of British Columbia has undertaken a systematic analysis of the isotopic (Sr, Nd, and Pb) compositions and concentrations of a broad compositional range of U.S. Geological Survey (USGS) reference materials, including basalt (BCR-1, 2; BHVO-1, 2), andesite (AGV-1, 2), rhyolite (RGM-1, 2), syenite (STM-1, 2), granodiorite (GSP-2), and granite (G-2, 3). USGS rock reference materials are geochemically well characterized, but there is neither a systematic methodology nor a database for radiogenic isotopic compositions, even for the widely used BCR-1. This investigation represents the first comprehensive, systematic analysis of the isotopic composition and concentration of USGS reference materials and provides an important database for the isotopic community. In addition, the range of equipment at the PCIGR, including a Nu Instruments Plasma MC-ICP-MS, a Thermo Finnigan Triton TIMS, and a Thermo Finnigan Element2 HR-ICP-MS, permits an assessment and comparison of the precision and accuracy of isotopic analyses determined by both the TIMS and MC-ICP-MS methods (e.g., Nd isotopic compositions). For each of the reference materials, 5 to 10 complete replicate analyses provide coherent isotopic results, all with external precision below 30 ppm (2 SD) for Sr and Nd isotopic compositions (27 and 24 ppm for TIMS and MC-ICP-MS, respectively). Our results also show that the first- and second-generation USGS reference materials have homogeneous Sr and Nd isotopic compositions. Nd isotopic compositions by MC-ICP-MS and TIMS agree to within 15 ppm for all reference materials. Interlaboratory MC-ICP-MS comparisons show excellent agreement for Pb isotopic compositions; however, the reproducibility is not as good as for Sr and Nd. A careful, sequential leaching experiment of three first- and second-generation reference materials (BCR, BHVO, AGV) indicates that the heterogeneity in Pb isotopic compositions, and concentrations, could be directly related to contamination by the steel (mortar/pestle) used to process the materials. Contamination also accounts for the high concentrations of certain other trace elements (e.g., Li, Mo, Cd, Sn, Sb, W) in various USGS reference materials.

Reconstruction of Holocene Climate Variability within the Central Mediterranean Using Lake Sediments from the Akrotiri Peninsula, Crete

NASA Astrophysics Data System (ADS)

Magill, C. R.; Rosenmeier, M. F.; Cavallari, B. J.; Curtis, J. H.; Weiss, H.

2005-12-01

Middle and late Holocene geochemical records from the Limnes depression, a small sinkhole located within the Akrotiri Peninsula, Crete, document centennial and millennial-scale climate variability within the central Mediterranean region. The oldest sediments of the basin consist largely of fibrous plant macrofossils and organic matter and likely indicate lake filling and expansion of wetland vegetation beginning ~5700 radiocarbon years before present (14C-yrs B.P.) (4550 B.C.). The basal peat layers grade into predominantly open water and less shallow lacustrine deposits by 4500 14C-yrs B.P (3200 B.C.). Continuous open water sedimentation within the Limnes core is interrupted by a number of distinct lag deposits and peaty deposits centered at 3700, 1600, and 350 14C-yrs B.P (2100 B.C., 500 A.D., and 1500 A.D.) indicating periods of significantly lowered lake level or perhaps lake desiccation. These ages coincide roughly with oxygen isotope (δ18O) minima measured in biogenic carbonates (ostracod shells) and support the inference for low lake stage. Trace element (Ca, Mg, and Sr) concentrations in ostracod shells from the Limnes core parallel the oxygen isotope record, suggesting that the data reflect basin hydrology rather than changes in the isotopic composition of rainfall. Furthermore, covariance in both δ18O and Mg concentrations eliminate temperature as a control on the oxygen isotope record. Sediments from the basin also contain aragonite remains of the green alga Chara and isotope analysis of the calcite may record additional paleoenvironmental information. The paleoclimate history inferred from the Limnes record correlates temporally (albeit tenuously) to previous paleoenvironmental data that document abrupt onset of arid conditions in the eastern Mediterranean and western Asia ca. 2200 B.C. Moreover, stratigraphic and geochemical evidence of low lake level (drying) within the Limnes basin at 2100 B.C. may correspond to the termination of the Early Minoan II (Early Bronze Age) culture.

Selected isotope ratio measurements of light metallic elements (Li, Mg, Ca, and Cu) by multiple collector ICP-MS

PubMed Central

Platzner, Thomas I.; Segal, Irina

2007-01-01

The unique capabilities of multiple collector inductively coupled mass spectrometry (MC-ICP-MS) for high precision isotope ratio measurements in light elements as Li, Mg, Ca, and Cu are reviewed in this paper. These elements have been intensively studied at the Geological Survey of Israel (GSI) and other laboratories over the past few years, and the methods used to obtain high precision isotope analyses are discussed in detail. The scientific study of isotopic fractionation of these elements is significant for achieving a better understanding of geochemical and biochemical processes in nature and the environment. PMID:17962922

The Influence of Non-spectral Matrix Effects on the Accuracy of Isotope Ratio Measurement by MC-ICP-MS

NASA Astrophysics Data System (ADS)

Barling, J.; Shiel, A.; Weis, D.

2006-12-01

Non-spectral interferences in ICP-MS are caused by matrix elements effecting the ionisation and transmission of analyte elements. They are difficult to identify in MC-ICP-MS isotopic data because affected analyses exhibit normal mass dependent isotope fractionation. We have therefore investigated a wide range of matrix elements for both stable and radiogenic isotope systems using a Nu Plasma MC-ICP-MS. Matrix elements commonly enhance analyte sensitivity and change the instrumental mass bias experienced by analyte elements. These responses vary with element and therefore have important ramifications for the correction of data for instrumental mass bias by use of an external element (e.g. Pb and many non-traditional stable isotope systems). For Pb isotope measurements (Tl as mass bias element), Mg, Al, Ca, and Fe were investigated as matrix elements. All produced signal enhancement in Pb and Tl. Signal enhancement varied from session to session but for Ca and Al enhancement in Pb was less than for Tl while for Mg and Fe enhancement levels for Pb and Tl were similar. After correction for instrumental mass fractionation using Tl, Mg effected Pb isotope ratios were heavy (e.g. ^{208}Pb/204Pbmatrix > ^{208}Pb/204Pbtrue) for both moderate and high [Mg] while Ca effected Pb showed little change at moderate [Ca] but were light at high [Ca]. ^{208}Pb/204Pbmatrix - ^{208}Pb/204Pbtrue for all elements ranged from +0.0122 to - 0.0177. Isotopic shifts of similar magnitude are observed between Pb analyses of samples that have seen either one or two passes through chemistry (Nobre Silva et al, 2005). The double pass purified aliquots always show better reproducibility. These studies show that the presence of matrix can have a significant effect on the accuracy and reproducibility of replicate Pb isotope analyses. For non-traditional stable isotope systems (e.g. Mo(Zr), Cd(Ag)), the different responses of analyte and mass bias elements to the presence of matrix can result in del/amu for measured & mass bias corrected data that disagree outside of error. Either or both values can be incorrect. For samples, unlike experiments, the correct del/amu is not known in advance. Therefore, for sample analyses to be considered accurate, both measured and exponentially corrected del/amu should agree.

Lithology of the basement underlying the Campi Flegrei caldera: Volcanological and petrological constraints

NASA Astrophysics Data System (ADS)

D'Antonio, Massimo

2011-02-01

A geologically reasonable working hypothesis is proposed for the lithology of the basement underlying the Campi Flegrei caldera in the ca. 4-8 km depth range. In most current geophysical modeling, this portion of crust is interpreted as composed of Meso-Cenozoic carbonate rocks, underlain by a ca. 1 km thick sill of partially molten rock, thought to be a main magma reservoir. Shallower magma reservoirs likely occur in the 3-4 km depth range. However, the lack of carbonate lithics in any Campi Flegrei caldera volcanic rocks does not support the hypothesis of a limestone basement. Considering the major caldera-forming eruptions, which generated widespread and voluminous ignimbrites during late Quaternary times, including the Campanian Ignimbrite and Neapolitan Yellow Tuff eruptions, the total volume of trachytic to phonolitic ejected magma is conservatively estimated at not less than 350 km 3. Results of least-squared mass-balance calculations suggest that this evolved magma formed through fractional crystallization from at least 2500 km 3 of parent shoshonitic magma, in turn derived from even more voluminous, more mafic, K-basaltic magma. Calculations suggest that shoshonitic magma, likely emplaced at ca. 8 km depth, must have crystallized about 2100 km 3 of solid material, dominated by alkali-feldspar and plagioclase, with a slightly lower amount of mafic minerals, during its route toward shallower magma reservoirs, before feeding the Campi Flegrei large-volume eruptions. The calculated volume of cumulate material, likely syenitic in composition at least in its upper portions, is more than enough to completely fill the basement volume in the 4-8 km depth range beneath the Campi Flegrei caldera, estimated at ca. 1250 km 3. Thus, it is proposed that the basement underlying the Campi Flegrei caldera below 4 km is composed mostly of crystalline igneous rocks, as for many large calderas worldwide. Syenite sensu lato would meet physical properties requirements for geophysical data interpretations, explain some geochemical and isotopic features of the past 15 ka volcanics, and justify the carbon isotopic composition of fumaroles at the Campi Flegrei caldera. This implies that Meso-Cenozoic limestones, if still present today beneath the Campi Flegrei caldera, no longer constitute significant portions of its basement.

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 ...

Osmium isotopic homogeneity in the CK carbonaceous chondrites

NASA Astrophysics Data System (ADS)

Goderis, Steven; Brandon, Alan D.; Mayer, Bernhard; Humayun, Munir

2017-11-01

Variable proportions of isotopically diverse presolar components are known to account for nucleosynthetic isotopic anomalies for a variety of elements (e.g., Ca, Ti, Cr, Ni, Sr, Zr, Mo, Ru, Pd, Ba, Nd, and Sm) in both bulk chondrites and achondrites. However, although large Os isotopic anomalies have been measured in acid leachates and residues of unequilibrated chondrites, bulk chondrites of various groups, iron meteorites, and pallasites exhibit Os isotopic compositions that are indistinguishable from terrestrial or bulk solar isotopic abundances. Since the magnitude of nucleosynthetic anomalies is typically largest in the carbonaceous chondrites, this study reports high-precision Os isotopic compositions and highly siderophile element (HSE) concentrations for ten CK chondrites. The isotope dilution concentration data for HSE and high-precision Os isotope ratios were determined on the same digestion aliquots, to precisely correct for radiogenic contributions to 186Os and 187Os. While acid leached bulk unequilibrated carbonaceous chondrites show deficits of s-process Os components to the same extent as revealed by unequilibrated enstatite, ordinary, and Rumuruti chondrites, equilibrated bulk CK chondrites exhibit no resolvable Os isotopic anomalies. These observations support the idea that acid-resistant, carbon-rich presolar grains, such as silicon carbide (SiC) or graphite, are major carriers for nucleosynthetic isotopic anomalies of Os. The destruction of these presolar grains, which are omnipresent in unequilibrated meteorites, must have occurred during aqueous alteration and thermal metamorphism, early in the CK chondrite parent body history. The dispersal of CK chondrites along the IIIAB iron meteorite isochron on a 187Os/188Os versus 187Re/188Os diagram, with Re/Os ratios from 0.032 to 0.083, in combination with the observed redistribution of other HSE (e.g., Pt, Pd), highlights the influence of parent body processes, overprinted by effects of recent terrestrial alteration. Under the oxidizing conditions prevalent on the CK parent body, evident from high abundances of magnetite and limited Fe-Ni metal in CK chondrites, these parent body processes made all isotopically anomalous Os, originally hosted in reduced presolar grains, accessible. The absence of Os isotopic anomalies in ordinary, enstatite, and now also carbonaceous chondrites, implies that the carriers of s- and r-process Os must have been effectively homogenized across the region of chondrite formation, and possibly even the entire solar protoplanetary nebula, as suggested by the Os isotopic compositions of iron meteorites and non-anomalous ureilites. Except for a limited number of ureilites, the relative proportions of presolar s- and r-process carriers of Os (and other elements such as W) in chondrites, and most other planetary bodies, must have remained constant during all subsequent nebular and planetary processes, which appears not to have been the case for other siderophile elements, including Mo, Ru, and Pd. The existence of Mo, Ru, Pd and other siderophile element isotopic anomalies thus appears to be in part controlled by the chemical properties of these elements (e.g., volatility), their host phase(s) (e.g., SiC, graphite, metal, sulfides), and the nature of the nebular or planetary processes experienced in the early solar system.

A multielement isotopic study of refractory FUN and F CAIs: Mass-dependent and mass-independent isotope effects

NASA Astrophysics Data System (ADS)

Kööp, Levke; Nakashima, Daisuke; Heck, Philipp R.; Kita, Noriko T.; Tenner, Travis J.; Krot, Alexander N.; Nagashima, Kazuhide; Park, Changkun; Davis, Andrew M.

2018-01-01

Calcium-aluminum-rich inclusions (CAIs) are the oldest dated objects that formed inside the Solar System. Among these are rare, enigmatic objects with large mass-dependent fractionation effects (F CAIs), which sometimes also have large nucleosynthetic anomalies and a low initial abundance of the short-lived radionuclide 26Al (FUN CAIs). We have studied seven refractory hibonite-rich CAIs and one grossite-rich CAI from the Murchison (CM2) meteorite for their oxygen, calcium, and titanium isotopic compositions. The 26Al-26Mg system was also studied in seven of these CAIs. We found mass-dependent heavy isotope enrichment in all measured elements, but never simultaneously in the same CAI. The data are hard to reconcile with a single-stage melt evaporation origin and may require reintroduction or reequilibration for magnesium, oxygen and titanium after evaporation for some of the studied CAIs. The initial 26Al/27Al ratios inferred from model isochrons span a range from <1 × 10-6 to canonical (∼5 × 10-5). The CAIs show a mutual exclusivity relationship between inferred incorporation of live 26Al and the presence of resolvable anomalies in 48Ca and 50Ti. Furthermore, a relationship exists between 26Al incorporation and Δ17O in the hibonite-rich CAIs (i.e., 26Al-free CAIs have resolved variations in Δ17O, while CAIs with resolved 26Mg excesses have Δ17O values close to -23‰). Only the grossite-rich CAI has a relatively enhanced Δ17O value (∼-17‰) in spite of a near-canonical 26Al/27Al. We interpret these data as indicating that fractionated hibonite-rich CAIs formed over an extended time period and sampled multiple stages in the isotopic evolution of the solar nebula, including: (1) an 26Al-poor nebula with large positive and negative anomalies in 48Ca and 50Ti and variable Δ17O; (2) a stage of 26Al-admixture, during which anomalies in 48Ca and 50Ti had been largely diluted and a Δ17O value of ∼-23‰ had been achieved in the CAI formation region; and (3) a nebula with an approximately canonical level of 26Al and a Δ17O value of ∼-23‰ in the CAI formation region.

Significance of nodule formation for the interpretation of matrix micrite C and O isotope ratios in Upper Jurassic Ammonitico Rosso limestones (Betic Cordillera, SE Spain)

NASA Astrophysics Data System (ADS)

Coimbra, R.; Immenhauser, A.; Olóriz, F.

2009-04-01

Three Ammonitico Rosso (AR) sections from the Betic Cordillera in SE Spain were analysed to obtain stable isotope records and access paleoenvironmental information. The study area corresponded to a Late Jurassic distal epioceanic setting and is characterized by the occurrence of more or less calcareous AR horizons ranging from greyish to redish colour. The carbonate materials under scope where retrieved from the Cardador, Salcedo and Cañada del Hornillo sections and consist on matrix micrite, carbonate cements and skeletals and were analysed for their carbon and oxygen isotope signature. At least one bulk sample per ammonite biozone was retrieved under a strict biochronostratigraphic control. The degree of diagenetic imprint was acessed by cathodoluminiscence analysis and carbonate ultrastructure was analysed by scanning electron microscope. Micrite matrix showed dull luminiscence, revealing a low degree of diagenetic overprint, as oposite to carbonate cements and skekeltal materials, that presented bright orange luminiscence. The identification of coccoliths and filaments under SEM attested for the good degree of preservation of the carbonate ultrastructure. The carbon isotope chemostratigraphy resembles the known trends for Jurassic northern Tethyan margins and absolute values (from 1.1 to 3.3 permil) are within the range usually reported for well preserved material. Oxygen isotopes of matrix micrite samples present higher values than those expected for Upper Jurassic materials (ranging from -0.3 to 0.9 permil for the Cardador and Salcedo sections and from -2.1 to 0.4 permil at the Cañada del Hornillo section), whilts commonly well preserved low-Mg calcite skeletal materials, such as belemenite rostra present lower values than matrix micrite, acompanied by a very bright orange luminiscence. In contrast to what is usually reported, matrix micrite presents values closer to what would be the original isotopic composition and skeletal material is more affected by latter diagenesis. In this context, paleoenvironmental considerations are available, and the oxygen curve is interpreted as reasonable approximation of seawater paleo-temperatures and relative depth. Very early marine nodule formation is thought to be determinant for the high isotope values found at these locations. It is proposed that early diagenetic nodule formation preserved near-seawater isotopic signals and inhibited subsequent diagenetic overprint as revealed by several proxies retrieved from intra-nodule samples.

Calcium isotopes in wine

NASA Astrophysics Data System (ADS)

Holmden, C. E.

2011-12-01

The δ 44/40Ca values of bottled wine vary between -0.76% to -1.55% on the seawater scale and correlate weakly with inverse Ca concentration and Mg/Ca ratio, such that the lowest δ 44/40Ca values have the highest Ca concentrations and lowest Mg/Ca ratios. The correlation is notable in the sense that the measured wines include both whites and reds sampled from different wine growing regions of the world, and cover a wide range of quality. Trends among the data yield clues regarding the cause of the observed isotopic fractionation. White wines, and wines generally perceived to be of lower quality, have lower δ 44/40Ca values compared to red wines and wines of generally perceived higher quality. Quality was assessed qualitatively through sensory evaluation, price, and scores assigned by critics. The relationship between δ 44/40Ca and wine quality was most apparent when comparing wines of one varietal from one producer from the same growing region. In the vineyard, wine quality is related to factors such as the tonnage of the crop and the ripeness of the grapes at the time of harvesting, the thickness of the skins for reds, the age of the vines, as well as the place where the grapes were grown (terroir). Quality is also influenced by winemaking practices such as fermentation temperature, duration of skin contact, and barrel ageing. Accordingly, the relationship between δ 44/40Ca and wine quality may originate during grape ripening in the vineyard or during winemaking in the cellar. We tested the grape ripening hypothesis using Merlot grapes sampled from a vineyard in the Okanagan, British Columbia, using sugar content (degrees Brix) as an indicator of ripeness. The grapes were separated into pulp, skin, and pip fractions and were analyzed separately. Thus far, there is no clear evidence for a systematic change in δ 44/40Ca values associated with progressive ripening of grapes in the vineyard. On the day of harvesting, the δ 44/40Ca value of juice squeezed from Merlot grapes was -1.94%, which is lower than any of the bottled wines measured, thus far, whether white or red. The wine made from this juice yielded -1.16%, which points to fermentation being the principal source of isotopic variability found in bottled wine. The working hypothesis is that light isotopes of Ca are preferentially stripped from the juice during maceration, fermentation, and lees contact, by ion exchange sites on solid organic-matter comprising the skins and yeast and/or by Ca-tartrate precipitation. High quality wines (especially reds) tend to involve longer contact times between juice and skins in order to increase the extraction of color and phenolic compounds (tannins) from the grape skins, a practice that might also result in greater losses of light isotopes of Ca from the juice, thus explaining the isotopic pattern in bottled wine.

A reduced order model to analytically infer atmospheric CO2 concentration from stomatal and climate data

NASA Astrophysics Data System (ADS)

Konrad, Wilfried; Katul, Gabriel; Roth-Nebelsick, Anita; Grein, Michaela

2017-06-01

To address questions related to the acceleration or deceleration of the global hydrological cycle or links between the carbon and water cycles over land, reliable data for past climatic conditions based on proxies are required. In particular, the reconstruction of palaeoatmospheric CO2 content (Ca) is needed to assist the separation of natural from anthropogenic Ca variability and to explore phase relations between Ca and air temperature Ta time series. Both Ta and Ca are needed to fingerprint anthropogenic signatures in vapor pressure deficit, a major driver used to explain acceleration or deceleration phases in the global hydrological cycle. Current approaches to Ca reconstruction rely on a robust inverse correlation between measured stomatal density in leaves (ν) of many plant taxa and Ca. There are two methods that exploit this correlation: The first uses calibration curves obtained from extant species assumed to represent the fossil taxa, thereby restricting the suitable taxa to those existing today. The second is a hybrid eco-hydrological/physiological approach that determines Ca with the aid of systems of equations based on quasi-instantaneous leaf-gas exchange theories and fossil stomatal data collected along with other measured leaf anatomical traits and parameters. In this contribution, a reduced order model (ROM) is proposed that derives Ca from a single equation incorporating the aforementioned stomatal data, basic climate (e.g. temperature), estimated biochemical parameters of assimilation and isotope data. The usage of the ROM is then illustrated by applying it to isotopic and anatomical measurements from three extant species. The ROM derivation is based on a balance between the biochemical demand and atmospheric supply of CO2 that leads to an explicit expression linking stomatal conductance to internal CO2 concentration (Ci) and Ca. The resulting expression of stomatal conductance from the carbon economy of the leaf is then equated to another expression derived from water vapor gas diffusion that includes anatomical traits. When combined with isotopic measurements for long-term Ci/Ca, Ca can be analytically determined and is interpreted as the time-averaged Ca that existed over the life-span of the leaf. Key advantages of the proposed ROM are: 1) the usage of isotopic data provides constraints on the reconstructed atmospheric CO2 concentration from ν, 2) the analytical form of this approach permits direct links between parameter uncertainties and reconstructed Ca, and 3) the time-scale mismatch between the application of instantaneous leaf-gas exchange expressions constrained with longer-term isotopic data is reconciled through averaging rules and sensitivity analysis. The latter point was rarely considered in prior reconstruction studies that combined models of leaf-gas exchange and isotopic data to reconstruct Ca from ν. The proposed ROM is not without its limitations given the need to a priori assume a parameter related to the control on photosynthetic rate. The work here further explores immanent constraints for the aforementioned photosynthetic parameter.

Widespread refertilization of cratonic and circum-cratonic lithospheric mantle

NASA Astrophysics Data System (ADS)

Tang, Yan-Jie; Zhang, Hong-Fu; Ying, Ji-Feng; Su, Ben-Xun

2013-03-01

Studies of mantle xenoliths have confirmed that Archean subcontinental lithospheric mantle (SCLM) is highly depleted in basaltic components (such as Al, Ca and Na) due to high-degree extraction of mafic and ultramafic melts and thus is refractory and buoyant, which made it chronically stable as tectonically independent units. However, increasing studies show that ancient SCLM can be refertilized by episodic rejuvenation events like infiltration of upwelling fertile material. The North China Craton is one of the most typical cases for relatively complete destruction of its Archean keel since the eruption of Paleozoic kimberlites, as is evidenced by a dramatic change in the compositions of mantle xenoliths sampled by Paleozoic to Cenozoic magmas, reflecting significant lithospheric thinning and the change in the character of the SCLM. The compositional change has been interpreted as the result of refertilization of Archean SCLM via multiple-stage peridotite-melt reactions, suggested by linear correlations between MgO and indices of fertility, covariations of Al2O3 with CaO, La/Yb, 87Sr/86Sr, 143Nd/144Nd, 187Os/188Os and Re-depletion ages (TRD), high Re abundances, scatter in Re-Os isotopic plot, variable in situ TRD ages of sulfides, and correlation between TRD ages and olivine Fo of peridotite xenoliths in Paleozoic kimberlites and Cenozoic basalts on the craton. By integrating major and trace element, Sr, Nd and Os isotopic compositions of peridotite xenoliths and orogenic massif peridotites from the continents of Europe, Asia, America, Africa and Australia, together with previous studies of petrology and geochemistry of global peridotites, we suggest that (1) refertilization of cratonic and circum-cratonic lithospheric mantle is widespread; (2) Archean SCLM worldwide has experienced a multi-stage history of melt depletion and refertilization since segregation from the convecting mantle; (3) cratonic SCLM may be more susceptible to compositional change caused by refertilization than is generally assumed; (4) the original character of much Archean cratonic mantle has been partly overprinted, or even erased by varying degrees of refertilization, which may play a key role in the rejuvenation and erosion of the SCLM beneath the Archean cratons. Due to the refertilization of ancient SCLM, (1) many published whole-rock Re-depletion ages cannot represent the formation ages of peridotites, but the mixtures of different generations of sulfides. Thus, the chronological significance of the Re-Os isotopic composition in individual peridotite should be cautiously interpreted; (2) many kimberlite- and intraplate basalt-borne lherzolite xenoliths, with major element compositions close to primitive mantle, may be the fragments of the ancient SCLM, strongly refertilized by infiltration of asthenosphere-derived melts, rather than newly-accreted SCLM. Consequently, new accretion of SCLM beneath ancient cratons such as the North China Craton may be less than was previously assumed.

An internally consistent inverse model to calculate ridge-axis hydrothermal fluxes

NASA Astrophysics Data System (ADS)

Coogan, L. A.; Dosso, S.

2010-12-01

Fluid and chemical fluxes from high-temperature, on-axis, hydrothermal systems at mid-ocean ridges have been estimated in a number of ways. These generally use simple mass balances based on either vent fluid compositions or the compositions of altered sheeted dikes. Here we combine these approaches in an internally consistent model. Seawater is assumed to enter the crust and react with the sheeted dike complex at high temperatures. Major element fluxes for both the rock and fluid are calculated from balanced stoichiometric reactions. These reactions include end-member components of the minerals plagioclase, pyroxene, amphibole, chlorite and epidote along with pure anhydrite, quartz, pyrite, pyrrhotite, titanite, magnetite, ilmenite and ulvospinel and the fluid species H2O, Mg2+, Ca2+, Fe2+, Na+, Si4+, H2S, H+ and H2. Trace element abundances (Li, B, K, Rb, Cs, Sr, Ba, U, Tl, Mn, Cu, Zn, Co, Ni, Pb and Os) and isotopic ratios (Li, B, O, Sr, Tl, Os) are calculated from simple mass balance of a fluid-rock reaction. A fraction of the Cu, Zn, Pb, Co, Ni, Os and Mn in the fluid after fluid-rock reaction is allowed to precipitate during discharge before the fluid reaches the seafloor. S-isotopes are tied to mineralogical reactions involving S-bearing phases. The free parameters in the model are the amounts of each mineralogical reaction that occurs, the amounts of the metals precipitated during discharge, and the water-to-rock ratio. These model parameters, and their uncertainties, are constrained by: (i) mineral abundances and mineral major element compositions in altered dikes from ODP Hole 504B and the Pito and Hess Deep tectonic windows (EPR crust); (ii) changes in dike bulk-rock trace element and isotopic compositions from these locations relative to fresh MORB glass compositions; and (iii) published vent fluid compositions from basalt-hosted high-temperature ridge axis hydrothermal systems. Using a numerical inversion algorithm, the probability density of different model parameter sets has been computed and thus the probability of different fluid and chemical fluxes. Most data can be fit by the model within their uncertainty. The entire dataset is best-fit with a water-to-rock mass ratio between 1.3 and 2.1 (~1 to 1.5 x10**13 kg yr-1) implying a substantial fraction of the magmatic (latent) heat available to drive the axial hydrothermal system is extracted by these systems. Many element fluxes are better constrained than in previous studies (e.g., Sr: 2 to 7 x10**8 moles yr-1; Ca: 2 to 7 x10**11 moles yr-1). Future developments will use experimental data to further constrain the model.

Effect of paleoseawater composition on hydrothermal exchange in midocean ridges

NASA Astrophysics Data System (ADS)

Antonelli, Michael A.; Pester, Nicholas J.; Brown, Shaun T.; DePaolo, Donald J.

2017-11-01

Variations in the Mg, Ca, Sr, and SO4 concentrations of paleoseawater can affect the chemical exchange between seawater and oceanic basalt in hydrothermal systems at midocean ridges (MOR). We present a model for evaluating the nature and magnitude of these previously unappreciated effects, using available estimates of paleoseawater composition over Phanerozoic time as inputs and 87Sr/86Sr of ophiolite epidosites and epidote-quartz veins as constraints. The results suggest that modern hydrothermal fluids are not typical due to low Ca and Sr relative to Mg and SO4 in modern seawater. At other times during the last 500 million years, particularly during the Cretaceous and Ordovician, hydrothermal fluids had more seawater-derived Sr and Ca, a prediction that is supported by Sr isotope data. The predicted 87Sr/86Sr of vent fluids varies cyclically in concert with ocean chemistry, with some values much higher than the modern value of ˜0.7037. The seawater chemistry effects can be expressed in terms of the transfer efficiency of basaltic Ca and Sr to seawater in hydrothermal systems, which varies by a factor of ˜1.6 over the Phanerozoic, with minima when seawater Mg and SO4 are low. This effect provides a modest negative feedback on seawater composition and 87Sr/86Sr changes. For the mid-Cretaceous, the low 87Sr/86Sr of seawater requires either exceptionally large amounts of low-temperature exchange with oceanic crust or that the weathering flux of continentally derived Sr was especially small. The model also has implications for MOR hydrothermal systems in the Precambrian, when low-seawater SO4 could help explain low seawater 87Sr/86Sr.

Effect of paleoseawater composition on hydrothermal exchange in midocean ridges

DOE Office of Scientific and Technical Information (OSTI.GOV)

Antonelli, Michael A.; Pester, Nicholas J.; Brown, Shaun T.

Variations in the Mg, Ca, Sr, and SO 4 concentrations of paleoseawater can affect the chemical exchange between seawater and oceanic basalt in hydrothermal systems at midocean ridges (MOR). Here, we present a model for evaluating the nature and magnitude of these previously unappreciated effects, using available estimates of paleoseawater composition over Phanerozoic time as inputs and 87Sr/ 86Sr of ophiolite epidosites and epidote-quartz veins as constraints. The results suggest that modern hydrothermal fluids are not typical due to low Ca and Sr relative to Mg and SO 4 in modern seawater. At other times during the last 500 millionmore » years, particularly during the Cretaceous and Ordovician, hydrothermal fluids had more seawater-derived Sr and Ca, a prediction that is supported by Sr isotope data. The predicted 87Sr/ 86Sr of vent fluids varies cyclically in concert with ocean chemistry, with some values much higher than the modern value of ~0.7037. The seawater chemistry effects can be expressed in terms of the transfer efficiency of basaltic Ca and Sr to seawater in hydrothermal systems, which varies by a factor of ~1.6 over the Phanerozoic, with minima when seawater Mg and SO 4 are low. This effect provides a modest negative feedback on seawater composition and 87Sr/ 86Sr changes. For the mid-Cretaceous, the low 87Sr/ 86Sr of seawater requires either exceptionally large amounts of low-temperature exchange with oceanic crust or that the weathering flux of continentally derived Sr was especially small. Lastly, the model also has implications for MOR hydrothermal systems in the Precambrian, when low-seawater SO 4 could help explain low seawater 87Sr/ 86Sr.« less

Effect of paleoseawater composition on hydrothermal exchange in midocean ridges

DOE PAGES

Antonelli, Michael A.; Pester, Nicholas J.; Brown, Shaun T.; ...

2017-11-06

Variations in the Mg, Ca, Sr, and SO 4 concentrations of paleoseawater can affect the chemical exchange between seawater and oceanic basalt in hydrothermal systems at midocean ridges (MOR). Here, we present a model for evaluating the nature and magnitude of these previously unappreciated effects, using available estimates of paleoseawater composition over Phanerozoic time as inputs and 87Sr/ 86Sr of ophiolite epidosites and epidote-quartz veins as constraints. The results suggest that modern hydrothermal fluids are not typical due to low Ca and Sr relative to Mg and SO 4 in modern seawater. At other times during the last 500 millionmore » years, particularly during the Cretaceous and Ordovician, hydrothermal fluids had more seawater-derived Sr and Ca, a prediction that is supported by Sr isotope data. The predicted 87Sr/ 86Sr of vent fluids varies cyclically in concert with ocean chemistry, with some values much higher than the modern value of ~0.7037. The seawater chemistry effects can be expressed in terms of the transfer efficiency of basaltic Ca and Sr to seawater in hydrothermal systems, which varies by a factor of ~1.6 over the Phanerozoic, with minima when seawater Mg and SO 4 are low. This effect provides a modest negative feedback on seawater composition and 87Sr/ 86Sr changes. For the mid-Cretaceous, the low 87Sr/ 86Sr of seawater requires either exceptionally large amounts of low-temperature exchange with oceanic crust or that the weathering flux of continentally derived Sr was especially small. Lastly, the model also has implications for MOR hydrothermal systems in the Precambrian, when low-seawater SO 4 could help explain low seawater 87Sr/ 86Sr.« less

Sulfur and Oxygen Isotopic Analysis of a Cosmic Symplectite from a Comet Wild 2 Stardust Terminal Particle

NASA Technical Reports Server (NTRS)

Nguyen, A. N.; Berger, E. L.; Nakamura-Messenger, K.; Messenger, S.

2015-01-01

Introduction: Analyses of comet 81P/Wild 2 samples re-turned from the Stardust mission have uncovered surprising simi-larities to meteoritic material, including the identification of inner solar system grains [1-3]. The TEM characterization of terminal particle (TP) 4 from Stardust track #147 revealed an assemblage consisting of symplectically intergrown pentlandite and nanocrys-talline maghemite coexisting with high-Ca pyroxene [4]. Mineral-ogically similar cosmic symplectites (COS) containing pentlandite and magnetite in the primitive Acfer 094 meteorite are highly de-pleted in 16O (?17O, ?18O 180 per mille) [5-7]. This isotopic signature is proposed to record alteration with primordial solar nebula water. Conversely, the normal O isotopic composition of the Stardust COS indicates alteration by a different aqueous reservoir, perhaps on the comet [8]. In this study, we analyzed the Wild 2 COS for S isotopes to further constrain its origin. Experimental: Thin sections of TP4 (12 ?m) were produced and their mineralogy was thoroughly characterized by TEM. Two of the sections were analyzed for O isotopes by isotopic imaging in the JSC NanoSIMS 50L. The sample in one of the slices was completely consumed. The remaining material in the adjacent slice was analyzed simultaneously for 16O, 32S, 33S, 34S, and 56Fe16O in electron multipliers using a Cs+ primary ion beam. Quasi-simulta-neous arrival (QSA) can have a significant effect on S isotopic ra-tios when using electron multipliers, resulting in undercounting of 32S [9]. Canyon Diablo troilite (CDT) was measured numerous times to deduce a correction factor for QSA and ensure measure-ment reproducibility. Isotopic ratios are reported relative to CDT. Results and Discussion: The Wild 2 COS is enriched in the heavy S isotopes relative to CDT (?33S = 6.5 +/- 1.6 per mille; ?34S = 5.1 +/- 0.7 per mille; 1?). The degree of 33S enrichment indicates mass-inde-pendent fractionation (MIF) with ?33S = 3.9 +/- 1.7 per mille. MIF of S has been observed in some chondrules (?33S up to 0.11per mille) [10], but this effect has not been identified in sulfides from carbonaceous chondrites [11] or IDPs [12]. S isotopic analysis of Stardust impact craters also did not reveal MIF or anomalies, save for one potential 32S-rich presolar sulfide [13]. Measurement errors on these impact craters were much larger than those in this study, however. MIF of S has been proposed to result from heterogeneities in the solar neb-ula from nucleosynthetic components [14] or photochemical irra-diation of solar nebula gas [10]. Presolar SiC grains are observed to have 32S enrichments [15, 16] contrary to the S isotopic compo-sition of the cometary COS. The S isotopic composition more likely reflects irradiation of nebular gas.

The general description of major ion concentrations in groundwater of Latvia

NASA Astrophysics Data System (ADS)

Kalvāns, A.; Delina, A.

2012-04-01

Latvia is situated at the North central part of the Baltic sedimentary basin where the crystalline basement is found in depth between 0.6 to 2 km. Three large aquifer complexes with distinct chemical composition of groundwater are identified: the stagnant water exchange zone where Na-Ca-Cl brine is found; the slow water exchange zone where Na-Ca-Cl-SO4 brackish water is found and active water exchange zone where the freshwater resides. These are separated by distinct regional aquicludes. The composition of the Cl- dominated brines at the base of sedimentary basin is characterised by shift from Na+ towards Ca++ as dominant cation, partially associated with depth of the aquifer and the strength of the brine. The concentration of SO4-- here is inversely linked to the concentration of Ca++ and, according to geochemical modelling, often is close to the solubility limit of the gypsum. The major ion concentrations in the E and W part of the territory are rather different. Therefore two different initial sources of the formation brine were suggested. Alternatively the observations can be explained by different thermal histories of different parts of the basin, affecting the rate of albitization - exchange of the Na for Ca in the solution due to water-rock interaction. The groundwater composition in the slow exchange zone can be nicely explained by the mixing of freshwater and brine residing deeper in the presence of gypsum during some but no all stages of mixing. In some shallow parts of the zone still bound by the Narva regional aquiclude freshwater is found. The question is posted - could this be a paleogroundwater originating from the extensive continental glaciations that override the territory several times during the Pleistocene? Initial isotope studies presented elsewhere seems to give negative answer to this question. The active water exchange zone is characterised by fresh Ca-Mg-HCO3 water with exceptions in cases where gypsum are abundant in sedimentary rocks and sulphate ion prevails. The freshwater composition seems to be mostly controlled by three minerals - calcite, dolomite and gypsum. It is suggested that clay minerals can play a significant role in controlling the relative concentrations of cations, but this is not strictly proven jet. Well documented modern seawater intrusion induced by water abstraction is found in the territory of Liepāja city. The upwelling of slat water from below can be spotted across the territory as well. These zones are usually associated with tectonic faults, enabling the upwelling of salty water across regional aquicludes. Particularly prominent is the saltwater body in the vicinity of the Riga city. Three major rives are discharging in the sea there making it a natural confluence zone of groundwater as well. The intensive groundwater abstraction in the city probably enhanced the upwelling of saltwater here, but primary it is a natural phenomenon. The interesting question is if there is any paleogroundwater trapped in the active or slow water exchange zone of the sedimentary basin that could be distinguished from modern infiltration water due to particular isotope signal originating in the quaternary cold stages or chemical composition - remains of relict sea water or sedimentation water. This study is supported by the ESF project No. 2009/0212/1DP/1.1.1.2.0/09/APIA/VIAA/060.

Mesozoic high-Mg andesites from the Daohugou area, Inner Mongolia: Upper-crustal fractional crystallization of parental melt derived from metasomatized lithospheric mantle wedge

NASA Astrophysics Data System (ADS)

Meng, Fanxue; Gao, Shan; Song, Zhaojun; Niu, Yaoling; Li, Xuping

2018-03-01

Mineral chemistry, major- and trace-element data, zircon U-Pb ages, and Sr-Nd isotopic data are presented for a suite of volcanic rocks from the Daohugou area, Ningcheng City, Inner Mongolia, on the northern margin of the North China Craton. Samples from the suite are of basaltic andesite to rhyolite in composition, with the rocks containing <60 wt% SiO2 have high MgO, Cr, and Ni contents, and classify as high-Mg andesites (HMAs). Zircons from a rhyolite yielded weighted mean 206Pb/238U age of 164 ± 1 Ma, indicating that the Daohugou volcanic suite is coeval with the Tiaojishan Formation of northern Hebei and western Liaoning Province. The HMAs have similar enriched-mantle I (EMI)-type isotopic compositions to each other, with low εNd (t) values, moderate (87Sr/86Sr) i ratios, enrichment in LREEs relative to LILEs, and depletion in HFSEs (e.g., Nb, Ta, Ti), indicating formation through protracted fractional crystallization of a common parental magma. The unusually low CaO contents and CaO/FeO ratios of olivine phenocrysts in the HMAs suggest that the parental melt was subduction-related. The results of Rhyolite-MELTS modelling indicates that HMAs may form through upper-crustal fractional crystallization from arc basalts. Therefore, the Daohugou HMAs were most likely formed through fractional crystallization of a parental melt derived from metasomatized lithospheric mantle at crustal depths. The addition of "water" to the cratonic keel may have played a key role in the destruction of the North China Craton.

Rapid Shifts in Oxygen and Hydrogen Isotopes, and Chemical Components in Pore Waters During mid-Oligocene in Sediments from IODP 351drilling

NASA Astrophysics Data System (ADS)

Zhang, Z.

2017-12-01

A total of 65 pore water samples were obtained from a sediment sequence in the Amami-Sankaku Basin during the IODP 351 Expedition, which consists of a 160 m thick section of terrestrial origin and underlying 1.3 km thick volcaniclastic section sampled at site U1438. Downcore variations of chemical compositions are characterized by increasing salinity/pH, increasing concentrations of Cl and Ca, and decreasing concentrations of Mg, K and Na, as well as decreasing d18O and dD. The rapid changes in those chemical components and isotopic composition occurred deeper than the lithology boundary between Unit III and Unit II, most likely as a result of substantial difference in extent of alteration above and below this boundary. The strong alterations of volcanicalstic minerals below the boundary not only result in diminishment of K, Mg, Si, and Mn, and an increase of Ca and Cl, but also depleted d18O in pore water. However, hydrogen fractionation factors between pore water and secondary minerals are less 1, and depleted dD values in pore water most likely reflect the signal of paleo-seawater. As a result, samples below the boundary are all plotted on the left side of the meteorite water line (MWL) on the dD vs. d18O plot. Above the boundary, they are placed to the right side of MWL due to substantially weakened alteration, reflecting an evolving trend in sediment setting from the predominance of alterated volcaniclasts to terrestrial pelagic sediments.

Formation and Evolution of the Continental Lithospheric Mantle: Perspectives From Radiogenic Isotopes of Silicate and Sulfide Inclusions in Macrodiamonds

NASA Astrophysics Data System (ADS)

Shirey, S. B.; Richardson, S. H.

2007-12-01

Silicate and sulfide inclusions that occur in diamonds comprise the oldest (>3 Ga), deepest (>140 km) samples of mantle-derived minerals available for study. Their relevance to the evolution of the continental lithosphere is clear because terrestrial macrodiamonds are confined to regions of the Earth with continental lithospheric mantle keels. The goals of analytical work on inclusions in diamond are to obtain paragenesis constraints, radiogenic ages, and initial isotopic compositions. The purpose is to place diamond formation episodes into the broader framework of the geological processes that create and modify the continental lithosphere and to relate the source of the C and N in diamond-forming fluids to understanding the Earth's C and N cycles in the Archean. Although sulfide and silicate inclusions rarely occur in the same diamond, they both can be grouped according to their geochemical similarity with the chief rock types that comprise the mantle keel: peridotite and eclogite. Silicate inclusions are classified as harzburgitic (depleted; olivine > Fo91, garnet Cr2O3 > 3 wt% and CaO from 0 to 5 wt%), lherzolitic (fertile), or eclogitic (basaltic; garnet Cr2O3 < 2 wt% and CaO from 3 to 15 wt%, clinopyroxene with higher Na2O, Al2O3, and FeO); they are amenable for trace element study by SIMS and for Sm-Nd and Rb-Sr analysis by conventional P-TIMS after grouping by mineralogical similarity. Sulfide inclusions (chiefly FeS with lesser Ni, Cu, and Co) are classified as peridotitic (Ni > 14 wt%; Os > 2 ppm) versus eclogitic (Ni < 10 wt%; Os < 200 ppb); single sulfides are amenable for S isotopic study by SIMS or TIMS, and Re-Os analysis by N-TIMS. Work on inclusions in diamonds depends on the distribution of mined, diamond-bearing kimberlites, and the generosity of mining companies because of the extreme rarity of inclusions in suites of mostly gem-quality diamonds. Most isotopic work has been on the Kaapvaal-Zimbabwe craton with lesser work on the Slave, Siberian, and Australian cratons. Sm-Nd ages on silicate suites and Re-Os ages on sulfide suites confirm diamond formation from the Mesoarchean though the Neoproterozoic. Most important are the systematics across cratons in the context of crustal geology that lead to generalities about craton evolution. Inclusion suites date mantle keels as Mesoarchean and clearly point to subduction as the major process to form the earliest continental nuclei and to amalgamate the cratons in their present form. This is evident from the elevated initial Os isotopic compositions in 3.5 Ga Slave (Panda) and 2.9 Ga Kaapvaal (Kimberley) sulfides, the low Sm/Nd and elevated initial Sr isotopic compositions of 3.4 Ga Kaapvaal (Kimberley) harzburgitic garnets, the preponderance of 2.9 Ga eclogitic sulfides in every western Kaapvaal craton locality, and the occurrence of surficial, volcanogenic S in Kaapvaal (Orapa) sulfides. The continental lithosphere was accessible to melts and fluids from the asthenosphere throughout the Proterozoic as evident from silicate and sulfide inclusion suites of 0.9 to 2.0 Ga age in every locality studied in the Kaapvaal craton. The correspondence of silicate inclusion type with current seismic velocity structure of the Kaapvaal mantle keel shows that its structure is at least Bushveld age (2 Ga) and due to compositional differences. Seismic velocity structures of continental mantle keels may be more a function of their geologic history than current temperature distribution.

The origin of groundwater composition in the Pampeano Aquifer underlying the Del Azul Creek basin, Argentina.

PubMed

Zabala, M E; Manzano, M; Vives, L

2015-06-15

The Pampean plain is the most productive region in Argentina. The Pampeano Aquifer beneath the Pampean plain is used mostly for drinking water. The study area is the sector of the Pampeano Aquifer underlying the Del Azul Creek basin, in Buenos Aires province. The main objective is to characterize the chemical and isotopic compositions of groundwater and their origin on a regional scale. The methodology used involved the identification and characterization of potential sources of solutes, the study of rain water and groundwater chemical and isotopic characteristics to deduce processes, the development of a hydrogeochemical conceptual model, and its validation by hydrogeochemical modelling with PHREEQC. Groundwater samples come mostly from a two-depth monitoring network of the "Dr. Eduardo J. Usunoff" Large Plains Hydrology Institute (IHLLA). Groundwater salinity increases from SW to NE, where groundwater is saline. In the upper basin groundwater is of the HCO3-Ca type, in the middle basin it is HCO3-Na, and in the lower basin it is ClSO4-NaCa and Cl-Na. The main processes incorporating solutes to groundwater during recharge in the upper basin are rain water evaporation, dissolution of CO2, calcite, dolomite, silica, and anorthite; cationic exchange with Na release and Ca and Mg uptake, and clay precipitation. The main processes modifying groundwater chemistry along horizontal flow at 30 m depth from the upper to the lower basin are cationic exchange, dissolution of silica and anorthite, and clay precipitation. The origin of salinity in the middle and lower basin is secular evaporation in a naturally endorheic area. In the upper and middle basins there is agricultural pollution. In the lower basin the main pollution source is human liquid and solid wastes. Vertical infiltration through the boreholes annular space during the yearly flooding stages is probably the pollution mechanism of the samples at 30 m depth. Copyright © 2015 Elsevier B.V. All rights reserved.

Filling the gap in Ca input-output budgets in base-poor forest ecosystems: The contribution of non-crystalline phases evidenced by stable isotopic dilution

NASA Astrophysics Data System (ADS)

van der Heijden, Gregory; Legout, Arnaud; Mareschal, Louis; Ranger, Jacques; Dambrine, Etienne

2017-07-01

In terrestrial ecosystems, plant-available pools of magnesium and calcium are assumed to be stored in the soil as exchangeable cations adsorbed on the surface of mineral and/or organic particles. The pools of exchangeable magnesium and calcium are measured by ion-exchange soil extractions. These pools are sustained in the long term by the weathering of primary minerals in the soil and atmospheric inputs. This conceptual model is the base of input-output budgets from which soil acidification and the sustainability of soil chemical fertility is inferred. However, this model has been questioned by data from long-term forest ecosystem monitoring sites, particularly for calcium. Quantifying the contribution of atmospheric inputs, ion exchange and weathering of both primary, secondary and non-crystalline phases to tree nutrition in the short term is challenging. In this study, we developed and applied a novel isotopic dilution technique using the stable isotopes of magnesium and calcium to study the contribution of the different soil phases to soil solution chemistry in a very acidic soil. The labile pools of Mg and Ca in the soil (pools in equilibrium with the soil solution) were isotopically labeled by spraying a solution enriched in 26Mg and 44Ca on the soil. Labeled soil columns were then percolated with a dilute acid solution during a 3-month period and the isotopic dilution of the tracers was monitored in the leaching solution, in the exchangeable (2 sequential 1 mol L-1 ammonium acetate extractions) and non-crystalline (2 sequential soil digestions: oxalic acid followed by nitric acid) phases. Significant amounts of Mg and Ca isotope tracer were recovered in the non-crystalline soil phases. These phases represented from 5% to 25% and from 24% to 50%, respectively, of the Mg and Ca labile pools during the experiment. Our results show that non-crystalline phases act as both a source and a sink of calcium and magnesium in the soil, and contribute directly to soil solution chemistry on very short-term time scales. These phases are very abundant in acid soils and, in the present study, represent a substantial calcium pool (equivalent in size to the Ca exchangeable pool). The gradual isotopic dilution of Mg and Ca isotope ratios in the leaching solution during the experiment evidenced an input flux of Mg and Ca originating from a pool other than the labile pool. While the Mg input flux originated primarily from the weathering of primary minerals and secondarily from the non-crystalline phases, the Ca input flux originated primarily from the non-crystalline phases. Our results also show that the net calcium release flux from these phases may represent a significant source of calcium in forest ecosystems and actively contribute to compensating the depletion of Ca exchangeable pools in the soil. Non-crystalline phases therefore should be taken into account when computing input-output nutrient budgets and soil acid neutralizing capacity.

Variations of the Indian summer monsoon over the Mio-Pliocene recorded in the Bengal Fan (IODP Exp354): implications for the evolution of the terrestrial biosphere.

NASA Astrophysics Data System (ADS)

Galy, Valier; Feakins, Sarah; Karkabi, Elias; Ponton, Camilo; Galy, Albert; France-Lanord, Christian

2017-04-01

A pressing challenge in climate research is understanding the temporal evolution of the Indian monsoon system; its response to global and regional climatic controls (including warming); as well as implications in terms of vegetation (C4 expansion), erosion of the Himalaya and carbon sequestration in the Bengal Fan. Studies on climate dynamics have recently offered new insights into the mechanistic controls on the monsoon: the tectonic boundary of the Himalaya is implicated as the major control on Indian summer monsoon dynamics today. Since this region has been uplifted since at least the late Oligocene, it is possible to test the response of monsoon precipitation to global and regional climate change, and also understand feedbacks on the climate system via carbon sequestration in the Bengal Fan. The evidence for monsoon intensity changes across the Miocene and Pliocene is currently incomplete given temporal uncertainty and diagenesis in terrestrial records; biases in the records reconstructed from the distal fan; and conflicting evidence from wind speed and aridity metrics for a stronger or weaker monsoon. Our alternative approach is therefore to study the basin-wide hydrological changes recorded in a multi-proxy, multi-site study of the marine sediments of the Bengal Fan recovered during IODP expedition 354. In turbiditic sediments of Himalayan origin, the late Miocene C4 expansion was found in all three long records recovered during expedition 354 (i.e. at sites U1451, U1450 and U1455, from East to West) based on stable carbon isotope composition of terrestrial leaf-wax compounds. Cores from sites U1455 (a reoccupation of DSDP Leg 22 Site 218) provide the highest resolution record of the C4 transition, which appears to occur abruptly within a relatively continuous series of turbiditic sequences. Bio- and magneto-stratigraphic dating of these records by members of Expedition 354 science party is underway and will provide the best stratigraphic constraint of the C4 expansion in the Himalayan system. Hemipelagic sediments generally carry 13C enriched signatures indicative of C4-dominated source areas, and based on a combination of the wind field climatology and the wetness and ecosystems of source regions today, we suggest that these would likely represent wind transport, likely from peninsular India. Interestingly we found hemipelagic horizons carrying this enriched 13C character prior to the C4 expansion recorded in turbiditic sediments, likely revealing an earlier C4 colonization of peninsular India. Based on our preliminary data we thus propose that C4 plants colonized peninsular India around 9-10 Ma. The hydrogen isotopic composition of the same leaf-wax compounds reveals a surprisingly small (on the order of 10 ‰) isotopic shift associated with the late Miocene C4 expansion. In contrast, the hydrogen isotope composition shift observed across the last deglaciation is far greater (ca. 40‰; Hein et al., in prep.). Cores from site U1451, provide a low resolution record across at least the last 26 Myr and appear to indicate a long term hydrological change from ca. 11Ma to ca. 7Ma, as inferred from progressive D enrichment in the biomarker records. These compound specific hydrogen isotope data will be discussed in the context of changing erosion patterns and attendant variations in the strength of the Indian summer monsoon as well as with respect to the mechanisms that led to the C4 expansion.

Thallium as a tracer of fluid-rock interaction in the shallow Mariana forearc

NASA Astrophysics Data System (ADS)

Nielsen, Sune G.; Klein, Frieder; Kading, Tristan; Blusztajn, Jerzy; Wickham, Katie

2015-11-01

Fluids driven off the subducting Pacific plate infiltrate the shallow Mariana forearc and lead to extensive serpentinization of mantle peridotite. However, the sources, pathways, and chemical modifications of ascending, slab-derived fluids remain poorly constrained and controversial. In this study, we use thallium (Tl) concentrations and isotopic ratios of serpentinized peridotite and rodingitized diabase from the South Chamorro and Conical Seamounts to discriminate between potential fluid sources with distinct Tl isotope compositions. Serpentinite samples from the Mariana forearc all display ε205 Tl > - 0.5 (where ε205 Tl = 10 , 000 × (205Tl /Tl203sample -205Tl /SRM 997 203Tl ) / (205Tl / SRM 997 203Tl )), which is significantly enriched in 205Tl compared to the normal mantle (ε205 Tl = - 2). Given that high temperature hydrothermal processes do not impart significant Tl isotope fractionation, the isotope compositions of the serpentinites must reflect that of the serpentinizing fluid. Pelagic sediments are the only known slab component that consistently displays ε205 Tl > - 0.5 and, therefore, we interpret the heavy Tl isotope signatures as signifying that the serpentinizing fluids were derived from subducting pelagic sediments. A rodingitized diabase from Conical Seamount was found to have an ε205 Tl of 0.8, suggesting that sediment-sourced serpentinization fluids could also affect diabase and other mafic lithologies in the shallow Mariana forearc. Forearc rodingitization of diabase led to a strong depletion in Tl content and a virtually complete loss of K, Na and Rb. The chemical composition of hybrid fluids resulting from serpentinization of harzburgite with concomitant rodingitization of diabase can be highly alkaline, depleted in Si, yet enriched in Ca, Na, K, and Rb, which is consistent with the composition of fluids emanating from mud volcanoes in the Mariana forearc. Our study suggests that fluid-rock interactions between sedimentary, mafic, and ultramafic lithologies are strongly interconnected even in the shallowest parts of subduction zones. We conclude that transfer of fluids and dissolved elements at temperatures and pressures below 400 °C and 1 GPa, respectively, must be taken into account when elemental budgets and mass transfer between the subducting plate, the forearc, the deep mantle and the ocean are evaluated.

Osmium Isotope Compositions of Komatiite Sources Through Time

NASA Astrophysics Data System (ADS)

Walker, R. J.

2001-12-01

Extending Os isotopic measurements to ancient plume sources may help to constrain how and when the well-documented isotopic heterogeneities in modern systems were created. Komatiites and picrites associated with plume-related volcanism are valuable tracers of the Os isotopic composition of plumes because of their typically high Os concentrations and relatively low Re/Os. Re-Os data are now available for a variety of Phanerozoic, Proterozoic and Archean komatiites and picrites. As with modern plumes, the sources of Archean and Proterozoic komatiites exhibit a large range of initial 187Os/188Os ratios. Most komatiites are dominated by sources with chondritic Os isotopic compositions (e.g. Song La; Norseman-Wiluna; Pyke Hill; Alexo), though some (e.g. Gorgona) derive from heterogeneous sources. Of note, however, two ca. 2.7 Ga systems, Kostomuksha (Russia) and Belingwe (Zimbabwe), have initial ratios enriched by 2-3% relative to the contemporary convecting upper mantle. These results suggest that if the 187Os enrichment was due to the incorporation of minor amounts of recycled crust into the mantle source of the rocks, the crust formed very early in Earth history. Thus, the Os results could reflect derivation of melt from hybrid mantle whose composition was modified by the addition of mafic crustal material that would most likely have formed between 4.2 and 4.5 Ga. Alternately, the mantle sources of these komatiites may have derived a portion of their Os from the putative 187Os - and 186Os -enriched outer core. For this hypothesis to be applicable to Archean rocks, an inner core of sufficient mass would have to have crystallized sufficiently early in Earth history to generate an outer core with 187Os enriched by at least 3% relative to the chondritic average. Using the Pt-Re-Os partition coefficients espoused by our earlier work, and assuming linear growth of the inner core started at 4.5 Ga and continued to present, would yield an outer core at 2.7 Ga with a gamma Os value of only +1.2 and a 186Os/188Os enrichment relative to the contemporary upper mantle of only +13 ppm. Greater isotopic enrichments could have been achieved by 2.7 Ga if either the inner core comprised >2.8% of the mass of the core by 2.7 Ga, or if Re and Os solid metal-liquid metal D's for core crystallization were greater that those applied in the initial calculation.

Charge radii of neutron-deficient Ca isotopes

NASA Astrophysics Data System (ADS)

Miller, A. J.; Minamisono, K.; Klose, A.; Everett, N.; Kalman, C.; Powel, R. C.; Watkins, J.; Garand, D.; Sumithrarachchi, C.; Krämer, J.; Maa, B.; Nörtershäuser, W.; Rossi, D. M.; Kujawa, C.; Pineda, S.; Lantis, J.; Liu, Y.; Mantica, P. F.; Pearson, M. R.

2017-09-01

Nucleon shell closures are generally associated with a local minimum in mean-square charge radii, 〈r2 〉 , along an isotopic chain. The 〈r2 〉 of 18Ar and 19K isotopes, however, do not show this signature at the N = 20 neutron shell closure. To gain a microscopic understanding of this abnormal behavior, measurements of 〈r2 〉 of neutron-deficient Ca isotopes below N = 20 have been proposed at the BEam COoling and LAser spectroscopy (BECOLA) facility at NSCL/MSU. Preliminary results will be presented and the deduced charge radii will be compared to theoretical calculations and the trends in the nearby isotopic chains. Work supported in part by NSF Grant PHY-15-65546, U.S. DOE Grant DE-NA0002924 and by the Deutsche Forschungsgemeinschaft through Grant SFB 1245.

Impact of Climate Variability on the Hydrogeochemistry of Ecologically Important Prairie Wetlands and Lakes

NASA Astrophysics Data System (ADS)

Goldhaber, M. B.; Mills, C. T.; Mushet, D. M.; Stricker, C. A.; Rover, J.

2015-12-01

The Prairie Pothole region encompasses 715,000 km2 of the north central US and south central Canada and contains millions of small wetlands and lakes. It sustains large populations of shore birds and migratory waterfowl. PPR ecology is influenced by wetland geochemistry, which can range dramatically over short distances (≤ 200m) from dilute Ca2+-HCO3- to saline Na+-Mg2+-SO42- compositions. These compositional differences result, in part, from long-term critical zone processes in upland areas coupled to groundwater inflow, but they are also influenced by climate. Climate impacts on the geochemistry of 167 wetlands/lakes from a 9700 km2 area of North Dakota (USA) were studied. The chemical composition of these wetlands was determined in the early 1970's during slightly dry climatic conditions and again in 2012-2013, a period of exceptional precipitation. Dilution dominated wetland geochemical trends. Concentrations of Cl-, Na+, K+, and Mg2+ generally decreased in 2012-2013 compared to earlier data. In contrast Ca2+ increased, and SO42- change was variable. The processes driving these modifications were evaluated using inverse (mass balance based) geochemical modeling. The decrease in the largely inert ion, Na+ by rainwater addition was used to approximate the net dilution factor of the wetlands which ranged to >9. This volume increase was associated with large expansions of wetland area determined from time-series Landsat data. Introducing dissolution of authigenic CaCO3, a known constituent of wetland sediments, matched the observed Ca2+ increase. Addition of SO42--enriched groundwater (composition determined from well analyses) was required to model wetlands with increased SO42-. Those wetlands with increased SO42- had more negative δ34SSO4 values, a result consistent with a previously established isotopically light marine pyrite source for groundwater SO42-. Understanding the evolution of wetland chemistry may aid in assessing future climatic impacts to the PPR.

Predominant floodplain over mountain weathering of Himalayan sediments (Ganga basin)

NASA Astrophysics Data System (ADS)

Lupker, Maarten; France-Lanord, Christian; Galy, Valier; Lavé, Jérôme; Gaillardet, Jérôme; Gajurel, Ananta Prasad; Guilmette, Caroline; Rahman, Mustafizur; Singh, Sunil Kumar; Sinha, Rajiv

2012-05-01

We present an extensive river sediment dataset covering the Ganga basin from the Himalayan front downstream to the Ganga mainstream in Bangladesh. These sediments were mainly collected over several monsoon seasons and include depth profiles of suspended particles in the river water column. Mineral sorting is the first order control on the chemical composition of river sediments. Taking into account this variability we show that sediments become significantly depleted in mobile elements during their transit through the floodplain. By comparing sediments sampled at the Himalayan front with sediments from the Ganga mainstream in Bangladesh it is possible to budget weathering in the floodplain. Assuming a steady state weathering regime in the floodplain, the weathering of Himalayan sediments in the Gangetic floodplain releases ca. (189 ± 92) × 109 and (69 ± 22) × 109 mol/yr of carbonate bound Ca and Mg to the dissolved load, respectively. Silicate weathering releases (53 ± 18) × 109 and (42 ± 13) × 109 mol/yr of Na and K while the release of silicate Mg and Ca is substantially lower, between ca. 0 and 20 × 109 mol/yr. Additionally, we show that sediment hydration, [H2O+], is a sensitive tracer of silicate weathering that can be used in continental detrital environments, such as the Ganga basin. Both [H2O+] content and the D/H isotopic composition of sediments increases during floodplain transfer in response to mineral hydrolysis and neoformations associated to weathering reactions. By comparing the chemical composition of river sediments across the floodplain with the composition of the eroded Himalayan source rocks, we suggest that the floodplain is the dominant location of silicate weathering for Na, K and [H2O+]. Overall this work emphasizes the role of the Gangetic floodplain in weathering Himalayan sediments. It also demonstrates how detrital sediments can be used as weathering tracers if mineralogical and chemical sorting effects are properly taken into account.

Cryogenic Carbonate Formation on Mars: Clues from Stable Isotope Variations Seen in Experimental Studies

NASA Technical Reports Server (NTRS)

Socki, Richard A.; Niles, Paul B.; Fu, Qi; Gibson, Everett K., Jr.

2010-01-01

Discoveries of large deposits of sedimentary materials on the planet Mars by landers and orbiters have confirmed the widely held hypothesis that water has played a crucial role in the development of the martian surface. Recent studies have indicated that both water ice and liquid water may have been present and in the case of water ice perhaps is still present on or near the surface of Mars. However, there remains much controversy about the prevailing atmospheric conditions and climate of Mars during its history and whether liquid water existed on the martian surface simply during discrete geological events or whether this water was present over relatively much longer geologic time periods. The recent identification of Ca-rich carbonate by the Phoenix lander as well as its measurement of the isotopic composition of atmospheric CO2 has shown the importance of understanding the carbonates on Mars as an important sink of atmospheric carbon. This work compliments that of our past experiments where we produced cryogenic calcite in open containers, as analogs for terrestrial aufeis formation, and as a means for evaluating the fractionation of C-13 in CO2 during bicarbonate freezing [13]. Unlike our previous experiments in which carbonates were grown in ambient laboratory condition in open containers (atmospheric pressure and composition), this work attempts to quantify the amount of delta C-13 enrichment possible in both fluids and secondary carbonates formed from freezing of bicarbonate fluids under martian-like atmospheric conditions. Morphologic textures of produced carbonates in these experiments are also examined under SEM in order to identify the effect that the cryogenic freezing process has on the mineral's mineralogy. Understanding the role of kinetic isotope fractionation during formation of carbonates under martian-like conditions will aid in our ability to quantify the isotopic composition of the carbonate sink furthering our ability to model the climate history of Mars.

History of crustal recycling recorded in transition zone diamonds

NASA Astrophysics Data System (ADS)

Pearson, D. G.; Stachel, T.; Palot, M.; Ickert, R. B.

2015-12-01

The Earth's transition zone (TZ) is a key region within the Earth that, from seismology, may be composed of a mixture of relatively primitive material together with the products of crustal recycling throughout the history of plate tectonics. The only samples of the TZ come in the form of inclusions in diamonds, that, for the most-part are retrogressed lower pressure equivalents of their precursor phases that formed at depth. Recent work by our group and others [1] on transition zone diamonds indicate that both peridotite and eclogitic paragenesis diamonds may record the products of crustal recycling. In-situ ion probe nitrogen and carbon isotopic measurements indicate the crystallisation of TZ diamonds from fluids bearing crustal signatures, of both oxidised and reduced forms. At the same time, majoritic garnets record extreme oxygen isotope compositions that track the interaction of oceanic crust with seawater at low temperature [2]. Such an origin is consistent with the few measured Sr-Nd isotope compositions of majorite garnet inclusions which resemble depleted MORB [3]. We have found considerably more enriched Sr isotope compositions (87Sr/86S ranging to > 0.8) in CaSiO3 inclusions that are from deep asthenosphere to TZ depths, supporting an origin that includes incorporation of recycled crustal sediment, in addition to the basaltic oceanic crust required to explain the phase equilibria [4]. Lastly, the discovery of hydrous ringwoodite in a diamond [5] containing more water than is soluble at the lower TZ adiabat indicates the possible role of recycling in transporting water as well as carbon into the TZ via a cool thermally unequilibrated slab. [1] Thomson et al (2014) CMP, 168, 1081. [2] Ickert et al (2015) Geochemical perspectives Letters, 1, 65-74. [3] Harte & Richardson (2011) Gondwana Research, 21, 236-235. [4] Walter et al. (2011) Science, 334, 54-57.[Pearson et al. (2014) Nature, 507, 221-224.

Diagenetic overprinting of the sphaerosiderite palaeoclimate proxy: are records of pedogenic groundwater δ18O values preserved?

USGS Publications Warehouse

Ufnar, David F.; Gonzalez, Luis A.; Ludvigson, Greg A.; Brenner, Richard L.; Witzkes, Brian J.

2004-01-01

Meteoric sphaerosiderite lines (MSLs), defined by invariant ??18O and variable ??13C values, are obtained from ancient wetland palaeosol sphaerosiderites (millimetre-scale FeCO3 nodules), and are a stable isotope proxy record of terrestrial meteoric isotopic compositions. The palaeoclimatic utility of sphaerosiderite has been well tested; however, diagenetically altered horizons that do not yield simple MSLs have been encountered. Well-preserved sphaerosiderites typically exhibit smooth exteriors, spherulitic crystalline microstructures and relatively pure (> 95 mol% FeCO3) compositions. Diagenetically altered sphaerosiderites typically exhibit corroded margins, replacement textures and increased crystal lattice substitution of Ca2+, Mg2+ and Mn2+ for Fe2+. Examples of diagenetically altered Cretaceous sphaerosiderite-bearing palaeosols from the Dakota Formation (Kansas), the Swan River Formation (Saskatchewan) and the Success S2 Formation (Saskatchewan) were examined in this study to determine the extent to which original, early diagenetic ??18O and ??13C values are preserved. All three units contain poikilotopic calcite cements with significantly different ??18O and ??13C values from the co-occurring sphaerosiderites. The complete isolation of all carbonate phases is necessary to ensure that inadvertent physical mixing does not affect the isotopic analyses. The Dakota and Swan River samples ultimately yield distinct MSLs for the sphaerosiderites, and MCLs (meteoric calcite lines) for the calcite cements. The Success S2 sample yields a covariant ??18O vs. ??13C trend resulting from precipitation in pore fluids that were mixtures between meteoric and modified marine phreatic waters. The calcite cements in the Success S2 Formation yield meteoric ??18O and ??13C values. A stable isotope mass balance model was used to produce hyperbolic fluid mixing trends between meteoric and modified marine end-member compositions. Modelled hyperbolic fluid mixing curves for the Success S2 Formation suggest precipitation from fluids that were < 25% sea water. ?? 2004 International Association of Sedimentologists.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Motyka, R.J.; Hawkins, D.B.; Poreda, R.J.

Two compositionally different groups of mud volcanoes exist in the Copper River Basin: the Tolsona group which discharges Na-Ca rich, HCO/sub 3/-SO/sub 4/ poor saline waters accompanied by small amounts of gas, composed predominately of CH/sub 4/ and N/sub 2/; and the Klawasi group which discharges Ca poor, Na-HCO/sub 3/ rich saline waters accompanied by enormous amounts of CO/sub 2/. The Tolsona-type water chemistry and isotopic composition could have been produced through the following processes: dilution of original interstitial seawaters with paleo-meteoric waters, possibly during a period of uplift in the mid-Cretaceous; loss of HCO/sub 3/ and SO/sub 4/ andmore » modification of other constituent concentrations by shale-membrane filtration; further depletion of Mg, K, HCO/sub 3/, and SO/sub 4/, and enrichment in Ca and Sr through dolomitization, hydrolysis, and clay-forming processes; and leaching of B, I, Li, and SiO/sub 2/ from marine sediments. Compared to the Tolsona waters, the Klawasi waters are strongly enriched in Li, Na, K, Mg, HCO/sub 3/, SO/sub 4/, B, SiO/sub 2/ and delta/sup 18/O and strongly depleted in Ca, Sr and D. The Klawasi wates also contain high concentrations of arsenic (10 to 48 ppM). The differences in fluid chemistry between Klawasi and Tolsona can be explained as the result of the interaction of fluids derived from a magmatic intrusion and contact decarbonation of limestone beds underlying the Klawasi area with overlying Tolsona-type formation waters.« less

Effects of climatic seasonality on the isotopic composition of evaporating soil waters

NASA Astrophysics Data System (ADS)

Benettin, Paolo; Volkmann, Till H. M.; von Freyberg, Jana; Frentress, Jay; Penna, Daniele; Dawson, Todd E.; Kirchner, James W.

2018-05-01

Stable water isotopes are widely used in ecohydrology to trace the transport, storage, and mixing of water on its journey through landscapes and ecosystems. Evaporation leaves a characteristic signature on the isotopic composition of the water that is left behind, such that in dual-isotope space, evaporated waters plot below the local meteoric water line (LMWL) that characterizes precipitation. Soil and xylem water samples can often plot below the LMWL as well, suggesting that they have also been influenced by evaporation. These soil and xylem water samples frequently plot along linear trends in dual-isotope space. These trend lines are often termed "evaporation lines" and their intersection with the LMWL is often interpreted as the isotopic composition of the precipitation source water. Here we use numerical experiments based on established isotope fractionation theory to show that these trend lines are often by-products of the seasonality in evaporative fractionation and in the isotopic composition of precipitation. Thus, they are often not true evaporation lines, and, if interpreted as such, can yield highly biased estimates of the isotopic composition of the source water.

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.

Fluid sources and metallogenesis in the Blackbird Co-Cu-Au-Bi-Y-REE district, Idaho, U.S.A.: Insights from major-element and boron isotopic compositions of tourmaline

USGS Publications Warehouse

Trumbull, Robert B.; Slack, John F.; Krienitz, M.-S.; Belkin, Harvey E.; Wiedenbeck, M.

2011-01-01

Tourmaline is a widespread mineral in the Mesoproterozoic Blackbird Co–Cu–Au–Bi–Y–REE district, Idaho, where it occurs in both mineralized zones and wallrocks. We report here major-element and B-isotope compositions of tourmaline from stratabound sulfide deposits and their metasedimentary wallrocks, from mineralized and barren pipes of tourmaline breccia, from late barren quartz veins, and from Mesoproterozoic granite. The tourmalines are aluminous, intermediate in the schorl–dravite series, with Fe/(Fe + Mg) values of 0.30 to 0.85, and 10 to 50% X-site vacancies. Compositional zoning is prominent only in tourmaline from breccias and quartz veins; crystal rims are enriched in Mg, Ca and Ti, and depleted in Fe and Al relative to cores. The chemical composition of tourmaline does not correlate with the presence or absence of mineralization. The δ11B values fall into two groups. Isotopically light tourmaline (−21.7 to −7.6‰) occurs in unmineralized samples from wallrocks, late quartz veins and Mesoproterozoic granite, whereas heavy tourmaline (−6.9 to +3.2‰) is spatially associated with mineralization (stratabound and breccia-hosted), and is also found in barren breccia. At an inferred temperature of 300°C, boron in the hydrothermal fluid associated with mineralization had δ11B values of −3 to +7‰. The high end of this range indicates a marine source of the boron. A likely scenario involves leaching of boron principally from marine carbonate beds or B-bearing evaporites in Mesoproterozoic strata of the region. The δ11B values of the isotopically light tourmaline in the sulfide deposits are attributed to recrystallization during Cretaceous metamorphism, superimposed on a light boron component derived from footwall siliciclastic sediments (e.g., marine clays) during Mesoproterozoic mineralization, and possibly a minor component of light boron from a magmatic–hydrothermal fluid. The metal association of Bi–Be–Y–REE in the Blackbird ores suggests some magmatic input, but involvement of granite-derived fluids cannot be conclusively established from the present database.

Quaternary bimodal volcanism in the Niğde Volcanic Complex (Cappadocia, central Anatolia, Turkey): age, petrogenesis and geodynamic implications

NASA Astrophysics Data System (ADS)

Aydin, Faruk; Schmitt, Axel K.; Siebel, Wolfgang; Sönmez, Mustafa; Ersoy, Yalçın; Lermi, Abdurrahman; Dirik, Kadir; Duncan, Robert

2014-11-01

The late Neogene to Quaternary Cappadocian Volcanic Province (CVP) in central Anatolia is one of the most impressive volcanic fields of Turkey because of its extent and spectacular erosionally sculptured landscape. The late Neogene evolution of the CVP started with the eruption of extensive andesitic-dacitic lavas and ignimbrites with minor basaltic lavas. This stage was followed by Quaternary bimodal volcanism. Here, we present geochemical, isotopic (Sr-Nd-Pb and δ18O isotopes) and geochronological (U-Pb zircon and Ar-Ar amphibole and whole-rock ages) data for bimodal volcanic rocks of the Niğde Volcanic Complex (NVC) in the western part of the CVP to determine mantle melting dynamics and magmatic processes within the overlying continental crust during the Quaternary. Geochronological data suggest that the bimodal volcanic activity in the study area occurred between ca. 1.1 and ca. 0.2 Ma (Pleistocene) and comprises (1) mafic lavas consisting of basalts, trachybasalts, basaltic andesites and scoria lapilli fallout deposits with mainly basaltic composition, (2) felsic lavas consisting of mostly rhyolites and pumice lapilli fall-out and surge deposits with dacitic to rhyolitic composition. The most mafic sample is basalt from a monogenetic cone, which is characterized by 87Sr/86Sr = 0.7038, 143Nd/144Nd = 0.5128, 206Pb/204Pb = 18.80, 207Pb/204Pb = 15.60 and 208Pb/204Pb = 38.68, suggesting a moderately depleted signature of the mantle source. Felsic volcanic rocks define a narrow range of 143Nd/144Nd isotope ratios (0.5126-0.5128) and are homogeneous in Pb isotope composition (206Pb/204Pb = 18.84-18.87, 207Pb/204Pb = 15.64-15.67 and 208Pb/204Pb = 38.93-38.99). 87Sr/86Sr isotopic compositions of mafic (0.7038-0.7053) and felsic (0.7040-0.7052) samples are similar, reflecting a common mantle source. The felsic rocks have relatively low zircon δ18O values (5.6 ± 0.6 ‰) overlapping mantle values (5.3 ± 0.3 %), consistent with an origin by fractional crystallization from a mafic melt with very minor continental crustal contamination. The geochronological and geochemical data suggest that mafic and felsic volcanic rocks of the NVC are genetically closely related to each other. Mafic rocks show a positive trend between 87Sr/86Sr and Th, suggesting simultaneous assimilation and fractional crystallization, whereas the felsic rocks are characterized by a flat or slightly negative variation. High 87Sr/86Sr gneisses are a potential crustal contaminant of the mafic magmas, but the comparatively low and invariant 87Sr/86Sr in the felsic volcanics suggests that these evolved dominantly by fractional crystallization. Mantle-derived basaltic melts, which experienced low degree of crustal assimilation, are proposed to be the parent melt of the felsic volcanics. Geochronological and geochemical results combined with regional geological and geophysical data suggest that bimodal volcanism of the NVC and the CVP, in general, developed in a post-collisional extensional tectonic regime that is caused by ascending asthenosphere, which played a key role during magma genesis.

Archival processes of the water stable isotope signal in East Antarctic ice cores

NASA Astrophysics Data System (ADS)

Casado, Mathieu; Landais, Amaelle; Picard, Ghislain; Münch, Thomas; Laepple, Thomas; Stenni, Barbara; Dreossi, Giuliano; Ekaykin, Alexey; Arnaud, Laurent; Genthon, Christophe; Touzeau, Alexandra; Masson-Delmotte, Valerie; Jouzel, Jean

2018-05-01

The oldest ice core records are obtained from the East Antarctic Plateau. Water isotopes are key proxies to reconstructing past climatic conditions over the ice sheet and at the evaporation source. The accuracy of climate reconstructions depends on knowledge of all processes affecting water vapour, precipitation and snow isotopic compositions. Fractionation processes are well understood and can be integrated in trajectory-based Rayleigh distillation and isotope-enabled climate models. However, a quantitative understanding of processes potentially altering snow isotopic composition after deposition is still missing. In low-accumulation sites, such as those found in East Antarctica, these poorly constrained processes are likely to play a significant role and limit the interpretability of an ice core's isotopic composition. By combining observations of isotopic composition in vapour, precipitation, surface snow and buried snow from Dome C, a deep ice core site on the East Antarctic Plateau, we found indications of a seasonal impact of metamorphism on the surface snow isotopic signal when compared to the initial precipitation. Particularly in summer, exchanges of water molecules between vapour and snow are driven by the diurnal sublimation-condensation cycles. Overall, we observe in between precipitation events modification of the surface snow isotopic composition. Using high-resolution water isotopic composition profiles from snow pits at five Antarctic sites with different accumulation rates, we identified common patterns which cannot be attributed to the seasonal variability of precipitation. These differences in the precipitation, surface snow and buried snow isotopic composition provide evidence of post-deposition processes affecting ice core records in low-accumulation areas.

Compound-specific isotopic analyses: a novel tool for reconstruction of ancient biogeochemical processes

NASA Technical Reports Server (NTRS)

Hayes, J. M.; Freeman, K. H.; Popp, B. N.; Hoham, C. H.

1990-01-01

Patterns of isotopic fractionation in biogeochemical processes are reviewed and it is suggested that isotopic fractionations will be small when substrates are large. If so, isotopic compositions of biomarkers will reflect those of their biosynthetic precursors. This prediction is tested by consideration of results of analyses of geoporphyrins and geolipids from the Greenhorn Formation (Cretaceous, Western Interior Seaway of North America) and the Messel Shale (Eocene, lacustrine, southern Germany). It is shown (i) that isotopic compositions of porphyrins that are related to a common source, but which have been altered structurally, cluster tightly and (ii) that isotopic differences between geolipids and porphyrins related to a common source are equal to those observed in modern biosynthetic products. Both of these observations are consistent with preservation of biologically controlled isotopic compositions during diagenesis. Isotopic compositions of individual compounds can thus be interpreted in terms of biogeochemical processes in ancient depositional environments. In the Cretaceous samples, isotopic compositions of n-alkanes are covariant with those of total organic carbon, while delta values for pristane and phytane are covariant with those of porphyrins. In this unit representing an open marine environment, the preserved acyclic polyisoprenoids apparently derive mainly from primary material, while the extractable, n-alkanes derive mainly from lower levels of the food chain. In the Messel Shale, isotopic compositions of individual biomarkers range from -20.9 to -73.4% vs PDB. Isotopic compositions of specific compounds can be interpreted in terms of origin from methylotrophic, chemautotrophic, and chemolithotrophic microorganisms as well as from primary producers that lived in the water column and sediments of this ancient lake.

Seasonality of Oxygen isotope composition in cow (Bos taurus) hair and its model interpretation

NASA Astrophysics Data System (ADS)

Chen, Guo; Schnyder, Hans; Auerswald, Karl

2017-04-01

Oxygen isotopes in animal and human tissues are expected to be good recorders of geographical origin and migration histories based on the isotopic relationship between hair oxygen and annual precipitation and the well-known spatial pattern of oxygen isotope composition in meteoric water. However, seasonal variation of oxygen isotope composition may diminish the origin information in the tissues. Here the seasonality of oxygen isotope composition in tail hair was investigated in a domestic suckler cow (Bos taurus) that underwent different ambient conditions, physiological states, and keeping and feeding strategies during five years. A detailed mechanistic model involving in ambient conditions, soil properties and animal physiology was built to explain this variation. The measured oxygen isotope composition in hair was significantly related (p<0.05) to the isotope composition in meteoric water in a regression analysis. Modelling suggested that this relation was only partly derived from the direct influence of feed moisture. Ambient conditions (temperature, moisture) did not only influence the isotopic signal of precipitation but also affected the animal itself (drinking water demand, transcutaneous vapor etc.). The clear temporal variation thus resulted from complex interactions with multiple influences. The twofold influence of ambient conditions via the feed and via the animal itself is advantageous for tracing the geographic origin because the oxygen isotope composition is then less influenced by variations in moisture uptake; however, it is unfavorable for indicating the production system, e.g. to distinguish between milk produced from fresh grass or from silage.

Major and Trace Element Geochemistry and Os Isotopic Compositions of Komatiites From Dundonald Beach, Abitibi Greenstone Belt, Canada

NASA Astrophysics Data System (ADS)

Gangopadhyay, A.; Walker, R. J.; Sproule, R. A.; Lesher, C.

2003-12-01

We have examined the major and trace elements, and Os isotopic compositions of a suite of cumulate and spinifex textured komatiitic rocks from the Dundonald Beach area, part of the ˜2.7 Ga Abitibi greenstone Belt, Ontario, Canada. This suite of rocks forms a series from peridotitic komatiites (MgO ˜ 42 wt.% on a volatile-free basis) to komatiitic basalts (MgO ˜8 wt.%). Based on major element oxide ratios (e.g. Al2O3/TiO2 ˜21-26 and CaO/Al2O3 typically <= 1) and unfractionated HREE characteristics (e.g. (Gd/Yb)N ˜0.9-1.1), these rocks are similar to the spatially associated Al-undepleted komatiites from Alexo and Munro Townships. Also, these rocks are strongly LREE-depleted ((La/Sm)N = 0.41-0.67; (Ce/Yb)N = 0.41-0.70)) and have variable total REE (4-22 ppm). A strong negative correlation between Mg# and total REEs suggests that the REE patterns of these rocks are primary features of their mantle source. The Re-Os isotope results for whole-rock komatiites and chromite separates from a single flow yield a model 3 isochron age of 2606 +/- 55 Ma. This age is slightly younger ( ˜50 Ma) compared to the U-Pb zircon ages of the associated volcanics reported from the presumed extension of the same Kidd-Munro assemblage in Alexo and Munro Townships. The initial 187Os/188Os ratio (0.1090 +/- 0.0019) obtained from the regression is essentially chondritic (γ Os(T) = -0.2 +/- 1.7). The peridotitic komatiites have the highest Os concentrations and low 187Re/188Os ratios (up to ˜4.2 ppb and < 0.5, respectively) among the whole rocks, whereas the komatiitic basalts have relatively low Os concentrations ( ˜0.3 ppb) and high 187Re/188Os ratios ( ˜3.1-11.9). For these komatiites, Os was compatible with the mantle residue (DOsmantle-melt ˜7.6), whereas Re was moderately incompatible (DRe ˜0.6), typical of most komatiitic magmas. The absence of a strong correlation between Os and Ni concentrations in the whole-rocks suggests that the distribution of Os in these rocks is not primarily controlled by fractionation of olivine. The apparent DReol+chmt/liq. ( ˜0.7), on the other hand, suggests that Re was moderately incompatible in olivine and/or chromite during the differentiation of komatiitic magmas. A chondritic initial Os isotopic composition for the mantle source for these komatiites is consistent with that previously reported for the komatiites from Alexo and Munro Townships. Our Os isotopic results for Dundonald komatiites, combined with those reported for Alexo and Pyke Hill komatiites, therefore, suggest that a major portion of the ˜2.7 Ga mantle source for the komatiites in the Abitibi greenstone belt was dominated by Os with chondritic isotopic compositions. Also, the LREE-depleted, yet chondritic Os isotopic composition for the mantle source of these komatiites is indistinguishable from the projected chondritic composition of the contemporaneous depleted convective upper mantle.

Tracing of ca 800 yr old mining activity in peat bog using Pb elemental concentrations and isotope compositions.

NASA Astrophysics Data System (ADS)

Baron, S.; Carignan, J.; Ploquin, A.

2003-04-01

Sixty sites of slags have been documented on the Mont-Lozère in southern France. The petrographic analysis shows that slags are metallurgical wastes (800 to 850 yr BP) which certainly result from smelting activity for lead and silver extraction (Ploquin et al., 2001). The aims of this study are: 1) to trace the source of Pb ores which supplied the smelting sites, by using the Pb isotopic composition of several surrounding Pb deposits, 2) to evaluate the actual pollution caused by these slags, by using elemental and isotopic compositions of soils, water and vegetation, and 3) to document the pollution history of the region, by using elemental and isotopic compositions of peat bog cores collected in the neighbourhood of the historical smelting sites. The lead isotopic composition of galena collected in most surrounding ores is very similar to that of different slag samples. On the other hand, the high precision of the results allowed us to select the mineralised areas which were probably the ore sources. The Pb isotopic composition of slags is even more homogeneous: 208/206 Pb: 2.092±0.002; 206/207 Pb: 1.179±0.001; 208/204 Pb: 38.663±0.025; 207/204 Pb: 15.665±0.006; 206/204 Pb: 18.476±0.023, and will allow source tracing in the environment. The "Narses Mortes" peat bog, around which two smelting sites have been reported, is strongly minerotrophic and contains 8 to 60% ash. A 1.40 m core have been retrieved and divided into 58 individual samples. Minerotrophic peat bog records both atmospheric deposition, soils leaching and the grounwater influence. The measured metal concentrations are normalised to Al contents of peat bog samples and the metal/Al ratios are compared to that of the Mont-Lozère granite: relative excess in metal concentrations are found in peat bog samples. An increasing excess of most metals (Pb, Zn, Cd...) was measured for surface samples, from 55 cm depth to the top of the core (23 cm depth). This profil might be attributed to atmospheric input during the last centuries. Pb and As alone are also enriched in some deeper samples (between 120--90 cm depth). At the moment, no sedimentation rates are available for this section of the peat bog. However, according to palynological data (de Beaulieu, in progress), the bottom of the core might be as old as 5000 years BP. This would place the medieval activities at the base of the surface metal enrichment (˜55 cm depth), having no large effect in Pb concentrations measured in peat bog. The older Pb-As enrichment remain enigmatic and may correspond to earlier anthropogenic activities (2000--2500 BP), a period for which very few traces of metallurgical activities are found in Occidental Europe. 14C dating and Pb isotope works are going on peat bog samples trying to discriminate metals sources.

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-aluminum-rich inclusions in the proto planetary disc is thus not required to explain the Mg isotopic composition of the Earth.