A mutli-technique search for the most primitive CO chondrites

As part of a study to identify the most primitive COs and to look for weakly altered CMs amongst the COs, we have conducted a multi-technique study of 16 Antarctic meteorites that had been classified as primitive COs. For this study, we have determined: (1) the bulk H, C and N abundances and isotopes, (2) bulk O isotopic compositions, (3) bulk modal mineralogies, and (4) for some selected samples the abundances and compositions of their insoluble organic matter (IOM). Two of the 16 meteorites do appear to be CMs – BUC 10943 seems to be a fairly typical CM, while MIL 090073 has probably been heated. Of the COs, DOM 08006 appears to be the most primitive CO identified to date and is quite distinct from the other members of its pairing group. The other COs fall into two groups that are less primitive than DOM 08006 and ALH 77307, the previously most primitive CO. The first group is composed of members of the DOM 08004 pairing group, except DOM 08006. The second group is composed of meteorites belonging to the MIL 03377 and MIL 07099 pairing groups. These two pairing groups should probably be combined. There is a dichotomy in the bulk O isotopes between the primitive (all Antarctic finds) and the more metamorphosed COs (mostly falls). This dichotomy can only partly be explained by the terrestrial weathering experienced by the primitive Antarctic samples. It seems that the more equilibrated samples interacted to a greater extent with 16O-poor material, probably water, than the more primitive meteorites

Corrigendum to “Volatiles in lunar felsite clasts: Impact-related delivery of hydrous material to an ancient dry lunar crust” [Geochim. Cosmochim. Acta 276 (2020) 299–326]

Corrigendum to “Volatiles in lunar felsite clasts: Impact-related delivery of hydrous material to an ancient dry lunar crust

Isotopic composition of presolar spinel grain OC2: Constraining intermediate-mass asymptotic giant branch models

We analyze the O, Mg, Al, Cr and Fe compositions predicted by detailed models of AGB stars of different masses and metallicities and discuss them in the light of the precise measurements of the composition of a single extraordinary presolar spinel grain, named OC2. Large excesses of the heavy Mg isotopes are present in this grain and thus an origin from an intermediate-mass (IM) asymptotic giant branch (AGB) star was previously proposed for it. Our IM-AGB models with temperatures at the base of the convective envelope ≃ 80 - 85 million degrees produce a good match to the composition of OC2 within the uncertainties related to reaction rates. This solution is possible if, in particular, we take the lower limit and the upper limit for the 16O(p,γ )17F and the 17O(p,α) 14N reaction rates, respectively

The matrices and rims of unequilibrated chondrites Origins, metamorphism and alteration

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