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.

Archean spherule layers, resulting from impacts by large extraterrestrial objects, to date represent the only remnants of the early meteorite, asteroid, and comet bombardment of the Earth. Only few Archean impact debris layers have been documented, all of them embedded in the 3.23 to 3.47 billion year old successions of the Barberton Greenstone Belt (BGB) in South Africa and the Pilbara Craton in Western Australia. Some of them might be correlated with each other. Given the scarcity of Archean spherule deposits, four spherule layer intersections from the recently recovered BARB5 drill core from the central Barberton Greenstone Belt, analyzed in this study, provide an opportunity to gain new insight into the early terrestrial impact bombardment.

Despite being hydrothermally overprinted, siderophile element abundance signatures of spherule-rich samples from the BARB5 drill core, at least in part, retained a meteoritic fingerprint. The impact hypothesis for the generation of the BARB5 spherule layers is supported by correlations between the abundances of moderately (Cr, Co, Ni) and highly siderophile (Re, Os, Ir, Pt, Ru and Pd) elements, whose peak concentrations and interelement ratios are within the range of those for chondrites. Rhenium-Osmium isotope evidence further support the impact hypothesis.

Collectively, this study provides evidence for extraterrestrial admixtures ranging between ∼40 and up to 100% to three of the four analyzed BARB5 spherule layers, and a scenario for their genesis involving (i) impact of a chondritic bolide into a sedimentary target, (ii) varying admixtures of meteoritic components to target materials, (iii) spherule formation via condensation in an impact vapor plume, (iv) transportation of the spherules and sedimentation under submarine conditions, followed by (v) moderate post-impact remobilization of transition metals and highly siderophile elements.

We present 275 new metal-silicate partition coefficients for P, S, V, Cr, Mn, Co, Ni, Ge, Mo, and W obtained at moderate P (1.5 GPa) and high T (1683-1883 K). We investigate the effect of silicate melt composition using four end member silicate melt compositions. We identify possible silicate melt dependencies of the metal-silicate partitioning of lower valence elements Ni, Ge and V, elements that are usually assumed to remain unaffected by changes in silicate melt composition. Results for the other elements are consistent with the dependence of their metal-silicate partition coefficients on the individual major oxide components of the silicate melt composition suggested by recently reported parameterizations and theoretical considerations. Using multiple linear regression, we parameterize compiled metal-silicate partitioning results including our new data and report revised expressions that predict their metal-silicate partitioning behavior as a function of P–T–X–fO₂. We apply these results to constrain the conditions that prevailed during core formation in the angrite parent body (APB). Our results suggest the siderophile element depletions in angrite meteorites are consistent with a CV bulk composition and constrain APB core formation to have occurred at mildly reducing conditions of 1.4±0.5 log units below the iron-wüstite buffer (ΔIW), corresponding to a APB core mass of 18±11%. The core mass range is constrained to 21±8 mass% if light elements (S and/or C) are assumed to reside in the APB core. Incorporation of light elements in the APB core does not yield significantly different redox states for APB core-mantle differentiation. The inferred redox state is in excellent agreement with independent fO₂ estimates recorded by pyroxene and olivine in angrites.

Water contents of the Martian mantle have previously been investigated using Martian meteorites, with several comprehensive studies estimating the water content in the parental melts and mantle source regions of the shergottites and Chassigny. However, no detailed studies have been performed on the Nakhla meteorite. One possible way to determine the water content of a crystallizing melt is to use the water content in nominally anhydrous minerals (NAMs) such as clinopyroxene and olivine. During or after eruption on the surface of a planetary body and during residence in a degassing magma, these minerals may dehydrate. By reversing this process experimentally, original (pre-dehydration) water concentrations can be quantified. In this study, hydrothermal rehydration experiments were performed at 2 kbar and 700 °C on potentially dehydrated Nakhla clinopyroxene crystals. Rehydrated clinopyroxene crystals exhibit water contents of 130 ± 26 (2σ) ppm and are thus similar to values observed in similar phenocrysts from terrestrial basalts. Utilizing clinopyroxene/melt partition coefficients, both the water content of the Nakhla parent melt and mantle source region were estimated. Despite previous assumptions of a relatively dry melt, the basaltic magma crystallizing Nakhla may have had up to 1.42 ±0.28 (2σ) wt.% H₂O. Based on an assumed low degree of partial melting, this estimate can be used to calculate a minimum estimate of the water content for Nakhla’s mantle source region of 72 ±16 ppm. Combining this value with values determined for other SNC mantle sources, by alternative methods, gives an average mantle value of 102 ± 9 (2σ) ppm H₂O for the Martian upper mantle throughout geologic time. This value is lower than the bulk water content of Earth’s upper mantle (∼250 ppm H₂O) but similar to Earth’s MORB source (54-330 ppm, average ∼130 ppm H₂O).

In the past years the observational evidence that s-process elements from Sr to Pb are produced by stars ascending the so-called Asymptotic Giant Branch (or “ AGB”) could not be explained by self-consistent models, forcing researchers to extensive parameterizations. The crucial point is to understand how protons can be injected from the envelope into the He-rich layers, yielding the formation of presup13C and then the activation of the presup13C(α  ,n)presup16O reaction. Only recently, attempts to solve this problem started to consider quantitatively physically-based mixing mechanisms. Among them, MHD processes in the plasma were suggested to yield mass transport through magnetic buoyancy. In this framework, we compare results of nucleosynthesis models for Low Mass AGB Stars (M≲3M_⊙), developed from the MHD scenario, with the record of isotopic abundance ratios of s-elements in presolar SiC grains, which were shown to offer precise constraints on the presup13C reservoir. We find that n-captures driven by magnetically-induced mixing can indeed account for the SiC data quite well and that this is due to the fact that our presup13C distribution fulfils the above constraints rather accurately. We suggest that similar tests should be now performed using different physical models for mixing. Such comparisons would indeed improve decisively our understanding of the formation of the neutron source.

We report the carbon, silicon, iron, and nickel isotope compositions of twenty-five presolar SiC grains of mostly supernova (SN) origin. The iron and nickel isotope compositions were measured with the new Chicago Instrument for Laser Ionization, CHILI, which allows the analysis of all iron and nickel isotopes without the isobaric interferences that plagued previous measurements with the NanoSIMS. Despite terrestrial iron and nickel contamination, significant isotopic anomalies in ⁵⁴Fe/⁵⁶Fe, ⁵⁷Fe/⁵⁶Fe, ⁶⁰Ni/⁵⁸Ni, ⁶¹Ni/⁵⁸Ni, ⁶²Ni/⁵⁸Ni, and ⁶⁴Ni/⁵⁸Ni were detected in nine SN grains (of type X). Combined multi-isotope data of three grains with the largest nickel isotope anomalies (>100 ‰ or <−100 ‰ in at least one isotope ratio, when expressed as deviation from the solar value) are compared with the predictions of two SN models, one with and one without hydrogen ingestion in the He shell prior to SN explosion. One grain’s carbon-silicon-iron-nickel isotope composition is consistent with the prediction of the model without hydrogen ingestion, whereas the other two grains’ isotope anomalies could not be reproduced using either SN models. The discrepancies between the measured isotope compositions and model predictions may indicate element fractionation in the SN ejecta prior to or during grain condensation, and reiterate the need for three-dimensional SN models.

Individual isotope abundances of Ba, lanthanides of the rare earth element (REE) group, and Hf have been determined in bulk samples of fine-grained silicon carbide (SiC) from the Murchison CM2 chondrite. The analytical protocol involved secondary ion mass spectrometry with combined high mass resolution and energy filtering to exclude REE oxide isobars and Si-C-O clusters from the peaks of interest. Relative sensitivity factors were determined through analysis of NIST SRM reference glasses (610 and 612) as well as a trace-element enriched SiC ceramic. When normalised to chondrite abundances, the presolar SiC REE pattern shows significant deficits at Eu and Yb, which are the most volatile of the REE. The pattern is very similar to that observed for Group III refractory inclusions. The SiC abundances were also normalised to s-process model predictions for the envelope compositions of low-mass (1.5 to 3 fx1) AGB stars with close-to-solar metallicities (Z=0.014 and 0.02). The overall trace element abundances (excluding Eu and Yb) appear consistent with the predicted s-process patterns. The depletions of Eu and Yb suggest that these elements remained in the gas phase during the condensation of SiC. The lack of depletion in some other moderately refractory elements (like Ba), and the presence of volatile elements (e.g. Xe) indicates that these elements were incorporated in to SiC by other mechanisms, most likely ion implantation.