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Carbon in howardite, eucrite and diogenite basaltic achondrites
Author(s) -
GRADY M. M.,
WRIGHT I. P.,
PILLINGER C. T.
Publication year - 1997
Publication title -
meteoritics and planetary science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.09
H-Index - 100
eISSN - 1945-5100
pISSN - 1086-9379
DOI - 10.1111/j.1945-5100.1997.tb01576.x
Subject(s) - achondrite , meteorite , geochemistry , astrobiology , regolith , geology , basalt , parent body , chondrite , physics
— 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 CO 2 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 δ 13 C between −29% and −19%. Kapoeta (a regolith breccia) has an elevated C content and δ 13 C, due to the presence of 13 C‐enriched carbonate minerals (δ 13 C ∼ +20%) in CM2‐ or CR2‐like clasts. The range in δ 13 C 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. The diogenites have a slightly lower total C yield and higher δ 13 C than the eucrites, which is a result of degassing of trapped CO/CC 2 /CO 2– 3 from the silicate lattice during metamorphism or annealing. However, three out of the four diogenites studied appear to contain a discrete component, possibly of graphitic C coating silicate grains, that is seemingly unaffected by the extended annealing period experienced by the diogenites. It is possible that this component might host the indigenous primitive Xe recently identified in diogenites.