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Carbon in howardite, eucrite and diogenite basaltic achondrites

Abstract— The C contents and isotopic compositions of four eucrites, four diogenites and two howardites have been determined. Stepped heating in an O atmosphere was employed to convert selectively different carbonaceous materials to CO2 gas at various temperatures. This technique successfully distinguishes between terrestrial contaminants and indigenous C. With the exception of the Kapoeta howardite, the howardite, eucrite, and diogenite (HED) meteorites contain ∼10–30 ppm indigenous C with δ13C between −29% and −19%. Kapoeta (a regolith breccia) has an elevated C content and δ13C, due to the presence of 13C‐enriched carbonate minerals (δ13C ∼ +20%) in CM2‐ or CR2‐like clasts. The range in δ13C displayed by HED samples is similar to that of other solar system basalts, such as lunar rocks and Martian meteorites but distinctly different from that of the terrestrial mantle.