A search for ^(70)Zn anomalies in meteorites

No ^(70)Zn isotopic anomalies have been detected in primitive meteorites to a level of precision of less than 40 parts per million (2σ). Any pre-existing nucleosynthetic anomaly on ^(70)Zn was averaged out by mixing in the solar nebula before planetary accretion in the solar system. Because neutron-rich nuclides ^(70)Zn and ^(60)Fe are produced by similar nucleosynthetic processes in core-collapse supernovae, the homogeneity of ^(70)Zn in meteorites limits the possible heterogeneity of extinct 60Fe radioactivity in the early solar system. Assuming that Fe and Zn have not been decoupled during incorporation into the solar system, the homogeneity of the ^(70)Zn/^(64)Zn ratio measured here implies that the ^(60)Fe/^(56)Fe ratio was homogenized to less than 15% dispersion before the formation of planetary bodies. The lack (Zn, Ni, Fe) or presence (Ti, Cr) of neutron-rich isotopic anomalies in the iron mass region may be controlled by the volatility of presolar carriers in the nebula

Nickel and Chromium Stable Isotopic Composition of Ureilites: Implications for the Earth's Core Formation and Differentiation of the Ureilite Parent Body

We report the first Ni and Cr stable isotope data for ureilite meteorites that are the mantle residue of a carbon-rich differentiated planet. Ureilites have similar Ni stable isotope compositions as chondrites, suggesting that the core-mantle differentiation of ureilite parent body (UPB) did not fractionate Ni isotopes. Since the size of Earth is potentially larger than that of UPB; with diameter >690 km), resulting in higher temperatures at the core-mantle boundary of Earth, it can be predicted that the terrestrial core formation may not directly cause Ni stable isotope fractionation. On the other hand, we also report high-precision Cr stable isotope composition of ureilites, including one ureilitic trachyandesite (ALM-A) that is enriched in lighter Cr stable isotopes relative to the main-group ureilites, which suggests that the partial melting occurred on UPB. The globally heavy Cr in the UPB compared to chondrites can be caused by sulfur-rich core formation processes

Late delivery of exotic chromium to the crust of Mars by water-rich carbonaceous asteroids.

The terrestrial planets endured a phase of bombardment following their accretion, but the nature of this late accreted material is debated, preventing a full understanding of the origin of inner solar system volatiles. We report the discovery of nucleosynthetic chromium isotope variability (μ54Cr) in Martian meteorites that represent mantle-derived magmas intruded in the Martian crust. The μ54Cr variability, ranging from -33.1 ± 5.4 to +6.8 ± 1.5 parts per million, correlates with magma chemistry such that samples having assimilated crustal material define a positive μ54Cr endmember. This compositional endmember represents the primordial crust modified by impacting outer solar system bodies of carbonaceous composition. Late delivery of this volatile-rich material to Mars provided an exotic water inventory corresponding to a global water layer >300 meters deep, in addition to the primordial water reservoir from mantle outgassing. This carbonaceous material may also have delivered a source of biologically relevant molecules to early Mars

A partial melting control on the Zn isotope composition of basalts

International audienc

Insights on the origin of oldhamite in enstatite meteorites from Ca stable isotopes

International audienceIn order to understand the origin of oldhamite (CaS) in enstatite meteorites, we report Ca isotopic compositions (δ$^{44}$/$^{40}$Ca) of oldhamite (obtained from water leachate of bulk chondrites and aubrites and mineral separates from the Norton County aubrite) and silicate minerals from different types of enstatite chondrites and aubrite. The δ$^{44}$/$^{40}$Ca of the bulk enstatite chondrites range from 1.05 ‰ to 1.24 ‰, with an average of 1.13 ± 0.12 ‰, higher than that of the estimate of the bulk silicate earth (∼0.94 ‰). Major and trace element analyses show that the water leachates of enstatite chondrites are mainly composed of oldhamite, and they take over 20.6–68.5 % Ca of the bulk meteorite Ca budget. The Ca isotope fractionation between oldhamite and residual silicate (Δ$^{44}$/$^{40}$Ca$_{oldhamite-silicate}$) for the studied enstatite chondrites is minimum (−0.44 ‰) for Abee (impact-melt breccia) and maximum (+0.16) for St.Marks (EH5). The Ca isotope fractionation between oldhamite (individual mineral grains and leachate) and silicates in Norton County varies from −0.47 ‰ to −0.31 ‰ with an average of −0.41 ‰. These Δ$^{44}$/$^{40}$Ca$_{oldhamite-silicate}$ correlate well with previous theoretical calculation and suggests that the oldhamites in Norton County are in isotopic equilibrium with co-existing silicates, and therefore were formed during magmatic processes. However, in enstatite chondrites, the large variation on Δ$^{44}$/$^{40}$Ca$_{oldhamite-silicate}$ and its negative correlation with metamorphic temperature reflects the redistribution and equilibration of Ca isotopes during metamorphism. The variable Δ$^{44}$/$^{40}$Ca$_{oldhamite-silicate}$ found in unequilibrated chondrites reflect kinetic Ca isotope fractionation between oldhamite and nebular gas and therefore is evidence for the formation of oldhamite by condensation in the solar nebula

Rubidium isotopic compositions of angrites controlled by extensive evaporation and partial recondensation

International audienceAngrites have remarkably low abundances of moderately volatile elements, yet the cause of this depletion remains poorly understood. The exceptionally light K isotopic compositions seen in angrites have prompted considerations of a partial recondensation model. However, the chondritic δ87Rb value of Sah99555, the sole reported Rb isotope data for angrites to date, seemingly challenges this recondensation model. Further analyses of Rb isotopic compositions in additional angrites hold the potential to clarify this discrepancy and unveil the origin of volatile depletion. Here, our finding of extremely light Rb isotopic signatures in angrites aligns with a partial recondensation model, emphasizing the substantial influence of condensation, an aspect frequently underestimated in earlier models, on the distribution of volatile elements at planetary scales

Isotope fractionation of Si in protonation/deprotonation reaction of silicic acid: A new pH proxy

International audienceIsotopic fractionation of Si in protonation/deprotonation reactions of monomeric silicic acids was theoretically and experimentally studied. The reduced partition function ratio for Si (as 1000 ln β) complexes was theoretically estimated by ab initio methods. Three permil of isotope fractionation was estimated to be possible for the 28Si-30Si isotope pair. This prediction was experimentally demonstrated by multi-collector inductively coupled plasma mass spectrometer measurements of Si-bearing aqueous solutions, for which equilibrated Si(OH)4 and SiO(OH)3− were separated using an anionic exchange column. The results create a new possibility for the application of Si isotopes as proxies for paleo-pH in the 9 < pH < 12 range