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The occurrence of shallow and deep-water sedimentary facies has established the Yangtze Platform in South China as a key site for the study of Neoproterozoic ocean oxidation and Ediacaran animal evolution following the Marinoan glaciation. The Yanwutan section in Hunan Province is one of the few coherent sections on the Yangtze Platform where Ediacaran deep-water carbonate sediments (predominantly dolostones) are preserved together with organic carbon-rich shales. Here we present new major and trace element abundance data as well as Sr-, O- and C-isotope compositions of leachates from carbonates of the Doushantuo Formation. We evaluate the role of diagenetic modification of the carbonate rocks and constrain the redox evolution of Ediacaran seawater in space and time. 87 Sr/ 86 Sr systematically varies with δ 18 O carb , Sr- and Ba abundances, indicating variable but mostly strong modification of fluid-mobile elements by continental basin fluids. In contrast, REE+Y patterns have preserved seawater-like compositions. Cap dolostones (unit I) on top of the Nantuo diamictites differ from cap dolostones at shallow-water sections on the Yangtze Platform in that they show no Ce-anomalies, and little alteration near the top ( 87 Sr/ 86 Sr = 0.7078, δ 18 O = −4.0, δ 13 C carb = 1.1), suggesting that δ 13 C carb and δ 18 O of cap dolostones at many other sections were compromised by hydrothermal alteration. The overlying organic carbon poor micritic dolostone (unit II) shows negative Ce-anomalies that disappear towards the top of the unit. No Ce-anomalies occur in subsequent organic carbon-rich muddy dolostone units (units III to IV). These observations, enrichments in TOC that correlate with variations in redox-sensitive metals in the carbonates, negative δ 13 C carb in units II to IV and the decoupling of δ 13 C carb from δ 13 C org argue for the existence of mostly anoxic deep-water at the Yangtze passive continental margin during the Ediacaran. The negative Ce-anomalies at the base of unit II (with negative δ 13 C carb ) may reflect fluctuations towards suboxic or oxic conditions or an allochthonous origin of this unit. However, trace metal enrichments in carbonates of the same unit argue for reducing conditions in pore-water, whereas the carbonates may have preserved the REE+Y signatures inherited from suboxic- to oxic seawater. The trace element and negative δ 13 C carb values in units II to IV are consistent with a stratified basin model with a large partially remineralised organic matter reservoir in anoxic bottom and pore-waters. [ABSTRACT FROM AUTHOR]

Mass fractions of S, Cu, Se, Mo, Ag, Cd, In, Te, Ba, Sm, W and Tl were determined by isotope dilution sector field ICP- MS in the same sample aliquot of reference materials using HF- HNO3 digestion in PFA beakers in pressure bombs and glassy carbon vessels in a high-pressure asher ( HPA-S) for comparison. Additionally, Bi was determined by internal standardisation relative to Tl. Because isobaric and oxide interferences pose problems for many of these elements, efficient chromatographic separation methods in combination with an Aridus desolvator were employed to minimise interference effects. Repeated digestion and measurement of geological reference materials ( BHVO-1, BHVO-2, SCo-1, MAG-1, MRG-1 and UB-N) gave results with < 5% relative intermediate precision (1 s) for most elements, except Bi. Replicates of NIST SRM 612 glass digested on a hot plate were analysed by the same methods, and the results agree with reference values mostly within 2% relative deviation. Data for the carbonaceous chondrites Allende, Murchison, Orgueil and Ivuna are also reported. Digestion in a HPA-S was as efficient as in pressure bombs, but some elements displayed higher blank levels following HPA-S treatment. Pressure bomb digestion yielded precise data for volatile S, Se and Te, but may result in high blanks for W. [ABSTRACT FROM AUTHOR]

Gamet-bearing high-temperature peridotite massifs in lower Austria were exhumed during Carboniferous plate convergence in the Bohemian massif. The peridotite massifs contain garnet pyroxenite layers, most of which are high-pressure cumulates that crystallized in the deep lithosphere during ascent and cooling of hot asthenospheric melts. Many of the pyroxenites have negative Eu anomalies and high LREE abundances in pyroxenes and bulk rocks, 87Sr/86Sr (335 Ma) as high as 0.7089, and εNd (335 Ma) as low as −4.8 (leached clinopyroxenes and garnets). These pyroxenites also show strong depletions in Rb, K, Ta, P and Ti compared with the REE Equilibrium melt compositions calculated from the cumulate compositions have very high LREE abundances (Lan = 300–600) and show strong LREEfractionation [(La/Sm)n = 7–47)]. Trace element abundances, the Ca–Al-rich composition of the cumulates and possible Ti saturation in the melts suggest that these melts were of primitive carbonatitic–melilitic or lamprophyrt-like composition. Other garnet pyroxenites such as Al-rich garnet-kyanite clinopyroxemtes with positive Eu anomalies probably represent metamorphosed crustal rocks which were subducted and accreted to the lithospheric mantle. The high 87Sr/86Sr, low εNd (335 Ma) and negative Eu anomalies of the high-pressure cumulates can be explained if their equilibrium melts contained a component derived from subducted upper-crustal rocks. The high equilibration pressures of the host peridotites (3–3.5 GPa) and the high equilibration temperatures of the pyroxenites (1100–1400°C) indicate that these melts are likely to be derived from the sub-lithospheric mantle. There, melting may have been triggered by small amounts of melt or fluids derived from a subducting slab at greater depth. [ABSTRACT FROM AUTHOR]

The geodynamic reorganization of major cratonic blocks during the assembly of Gondwana in the late Neoproterozoic caused a (bio)geochemical evolution of marine habitats that witnessed fluctuating seawater oxygenation and nutrient fluxes. Previous studies of carbonates deposited on the Yangtze Platform (South China) have shown their use as reliable archives of paleo-redox and bio-productivity changes intrinsically linked to continental weathering fluxes and water mass cycling. Despite its complex submarine morphology, only a few carbonate-bearing sections comprising deeper depositional environments of the Yangtze Platform have been evaluated. Here we report temporal, lateral, and vertical variations of stable C and radiogenic Sr, Nd, and Os isotopic compositions together with trace element and rare earth and yttrium (REY) systematics in carbonates from the Doushantuo Formation representing different paleo-marine environments of the Yangtze Platform, including I) inner shelf, II) restricted intra-shelf basin, III) slope and IV) deep-water basin sections to trace the extent and evolution of paleo water masses. Variations in shale-normalized (subscript SN) Ce anomalies argue for variably oxidizing atmosphere/ocean conditions. The combination of REY SN systematics with carbonate associated P enrichments defines three distinct local water masses from which the carbonates precipitated: i) fully oxidized shallow-water, ii) nutrient-poor intra-shelf basin waters, and iii) organic carbon-rich slope and deep-waters with temporal evolution to higher dissolved p O 2. Negative carbon isotope excursions in the carbonates such as during the putative Shuram equivalent Doushantuo Negative Carbon Excursion (DOUNCE) correlate with less negative Ce SN anomalies and ambient seawater shifts to more radiogenic initial 87 Sr/ 86 Sr and 187 Os/ 188 Os, but unradiogenic 143 Nd/ 144 Nd compositions, arguing for coupling of redox and weathering trends. Our comprehensive geochemical study highlights the vertical and temporal variations of physicochemical water mass properties recorded in late Neoproterozoic Yangtze Platform carbonates until the emergence of the first metazoans. • Intensive geochemical study spanning four paleo-depths on the Yangtze Platform • First carbonate Osmium isotopic compositions from the Late Neoproterozoic • Os, Nd and Sr isotope variations in concert with influx of terrigenous solutions towards the end of the Doushantuo Fm • REY systematics and P enrichments reveal significantly different water masses along the passive margin of the Yangtze craton • Changes in C-P cycles during Shuram anomaly linked to intensified terrigenous solution flux [ABSTRACT FROM AUTHOR]

Lunar soil is a fine mixture of local rocks and exotic components. The bulk-rock chemical composition of the newly returned Chang'E-5 (CE-5) lunar soil was studied to understand its chemical homogeneity, exotic additions, and origin of landing site basalts. Concentrations of 48 major and trace elements, including many low-concentration volatile and siderophile elements, of two batches of the scooped CE-5 soil samples were simultaneously obtained by inductively coupled plasma mass spectrometry (ICP-MS) with minimal sample consumption. Their major and trace elemental compositions (except for Ni) are uniform at milligram levels (2–4 mg), matching measured compositions of basaltic glasses and estimates based on mineral modal abundances of basaltic fragments. This result indicates that the exotic highland and KREEP (K, rare earth elements, and P-rich) materials are very low (<5%) and the bulk chemical composition (except for Ni) of the CE-5 soil can be used to represent the underlying mare basalt. The elevated Ni concentrations reflect the addition of about 1 wt% meteoritic materials, which would not influence the other bulk composition except for some highly siderophile trace elements such as Ir. The CE-5 soil, which is overall the same as the underlying basalt in composition, displays low Mg# (34), high FeO (22.7 wt%), intermediate TiO 2 (5.12 wt%), and high Th (5.14 µg/g) concentrations. The composition is distinct from basalts and soils returned by the Apollo and Luna missions, however, the depletion of volatile or siderophile elements such as K, Rb, Mo, and W in their mantle sources is comparable. The incompatible lithophile trace element concentrations (e.g., Ba, Rb, Th, U, Nb, Ta, Zr, Hf, and REE) of the CE-5 basalts are moderately high and their pattern mimics high-K KREEP. The pattern of these trace elements with K, Th, U, Nb, and Ta anomalies of the CE-5 basalts cannot be explained by the partial melting and crystallization of olivine, pyroxene, and plagioclase. Thus, the mantle source of the CE-5 landing site mare basalt could have contained KREEP components, likely as trapped interstitial melts. To reconcile these observations with the initial unradiogenic Sr and radiogenic Nd isotopic compositions of the CE-5 basalts, clinopyroxene characterized by low Rb/Sr and high Sm/Nd ratios could be one of the main minerals in the KREEP-bearing mantle source. Consequently, we propose that the CE-5 landing site mare basalts very likely originated from partial melting of a shallow and clinopyroxene-rich (relative to olivine and orthopyroxene) upper mantle cumulate with a small fraction (about 1–1.5 %) of KREEP-like materials. [ABSTRACT FROM AUTHOR]

Various lines of evidence suggest that material isotopically similar to enstatite chondrites may have accreted to the terrestrial planets. However, the enrichment of light Si isotopes in bulk enstatite chondrites is not easy to reconcile with the heavy Si isotopic composition of the Bulk Silicate Earth (BSE). To investigate the origin of the light Si isotopic composition of enstatite chondrites, we have obtained in situ Si isotope data and simultaneously major- and trace element data in silicate and metal phases of chondrules, a metal-troilite spherule, and matrix from the enstatite chondrites Sahara 97072 (EH3) and Indarch (EH4) using laser ablation split stream-ICP-MS, which combines femto-second LA-MC-ICP-MS and Quadrupole-ICP-MS. Silicates in chondrules show variations in δ 30Si (‰ variations of 30Si/28Si relative to NBS-28) ranges from −1.06 ± 0.13‰ (2 S.E.) to −0.38 ± 0.11‰. δ 30Si in matrix silicates ranges from −0.96 ± 0.18‰ to −0.22 ± 0.12‰. The δ 30Si-value of silicate phases varies independently of Mg/Si, ruling out simple equilibrium condensation from nebular gas. Some silicates in both enstatite chondrites have δ 30Si-values like CI chondrites, whereas Si in other silicates is isotopically lighter, suggesting that the precursor materials of EH chondrites were already depleted in heavy Si isotopes. The metal phases in the matrix show average δ 30Si of −6.0 ± 0.6‰. In spite of different metamorphic grades, the fractionation of Si isotopes between matrix metal and silicates in Sahara 97072 and Indarch shows no systematic differences, and thus no re-equilibration of Si isotopes occurred between silicates and metal at metamorphic temperatures below 900 K. The δ 30Si-value of metal from a metal-troilite spherule from Sahara 97072 (−8.24 ± 0.12‰) is lower than that of matrix metals. These differences were likely inherited from different formation environments of matrix- and spherule metal. If metal formation occurred under equilibrium conditions, then matrix metal may have formed at higher temperatures than the MTS metal. or at similar temperatures but slightly lower oxygen fugacities, or the MTS metal equilibrated with gas or silicates which were not incorporated into EH chondrites because they were lost from the EH chondrite formation region. Alternatively, the differences in δ 30Si of different metals could also reflect variable kinetic isotope fractionation during the formation of metal and exsolution of perryite. The considerably lower δ 30Si-values of bulk EH chondrites compared to CI- and other chondrites partly reflects the presence of Si bearing metal and partly silicates with isotopically light Si. The latter indicate loss of a heavy Si-rich silicate component from the EH3 formation region, presumably together with refractory elements. Although the Si isotopic composition of bulk EH chondrites precludes that these represent major building material of the Earth, the combination of complementary heavy Si isotope- and refractory element-enriched reduced materials and carbonaceous or ordinary chondrites could provide a match for the heavy Si isotopic composition of Earth. [ABSTRACT FROM AUTHOR]

Abstract: The apparent overabundance of the highly siderophile elements (HSEs: Pt-group elements, Re and Au) in the mantles of Earth, Moon and Mars has not been satisfactorily explained. Although late accretion of a chondritic component seems to provide the most plausible explanation, metal–silicate equilibration in a magma ocean cannot be ruled out due to a lack of HSE partitioning data suitable for extrapolations to the relevant high pressure and high temperature conditions. We provide a new data set of partition coefficients simultaneously determined for Ru, Rh, Pd, Re, Ir and Pt over a range of 3.5–18GPa and 2423–2773K. In multianvil experiments, molten peridotite was equilibrated in MgO single crystal capsules with liquid Fe-alloy that contained bulk HSE concentrations of 53.2–98.9 wt% (XFe =0.03–0.67) such that oxygen fugacities of IW−1.5 to IW+1.6 (i.e. logarithmic units relative to the iron-wüstite buffer) were established at run conditions. To analyse trace concentrations of the HSEs in the silicate melt with LA-ICP-MS, two silicate glass standards (1–119ppm Ru, Rh, Pd, Re, Ir, Pt) were produced and evaluated for this study. Using an asymmetric regular solution model we have corrected experimental partition coefficients to account for the differences between HSE metal activities in the multicomponent Fe-alloys and infinite dilution. Based on the experimental data, the P and T dependence of the partition coefficients (D) was parameterized. The partition coefficients of all HSEs studied decrease with increasing pressure and to a greater extent with increasing temperature. Except for Pt, the decrease with pressure is stronger below ∼6GPa and much weaker in the range 6–18GPa. This change might result from pressure induced coordination changes in the silicate liquid. Extrapolating the D values over a large range of potential P–T conditions in a terrestrial magma ocean (peridotite liquidus at P ⩽60–80GPa) we conclude that the P–T-induced decrease of D would not have been sufficient to explain HSE mantle abundances by metal–silicate equilibration at a common set of P–T-oxygen fugacity conditions. Therefore, the mantle concentrations of most HSEs cannot have been established during core formation. The comparatively less siderophile Pd might have been partly retained in the magma ocean if effective equilibration pressures reached 35–50GPa. To a much smaller extent this could also apply to Pt and Rh providing that equilibration pressures reached ⩾60GPa in the late stage of accretion. With most of the HSE partition coefficients at 60GPa still differing by 0.5–3 orders of magnitude, metal–silicate equilibration alone cannot have produced the observed near-chondritic HSE abundances of the mantles of the Earth as well as of the Moon or Mars. Our results show that an additional process, such as the accretion of a late veneer composed of some type of chondritic material, was required. The results, therefore, support recent hybrid models, which propose that the observed HSE signatures are a combined result of both metal–silicate partitioning as well as an overprint by late accretion. [Copyright &y& Elsevier]