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Isotopic composition of carbon and nitrogen in ureilitic fragments of the Almahata Sitta meteorite
Author(s) -
Downes H.,
Abernethy F. A. J.,
Smith C. L.,
Ross A. J.,
Verchovsky A. B.,
Grady M. M.,
Jenniskens P.,
Shaddad M. H.
Publication year - 2015
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/maps.12413
Subject(s) - enstatite , chondrite , meteorite , carbon fibers , breccia , nitrogen , isotopes of nitrogen , parent body , chemistry , geology , mineralogy , astrobiology , analytical chemistry (journal) , geochemistry , environmental chemistry , materials science , physics , organic chemistry , composite material , composite number
This study characterizes carbon and nitrogen abundances and isotopic compositions in ureilitic fragments of Almahata Sitta. Ureilites are carbon‐rich (containing up to 7 wt% C) and were formed early in solar system history, thus the origin of carbon in ureilites has significance for the origin of solar system carbon. These samples were collected soon after they fell, so they are among the freshest ureilite samples available and were analyzed using stepped combustion mass spectrometry. They contained 1.2–2.3 wt% carbon; most showed the major carbon release at temperatures of 600–700 °C with peak values of δ 13 C from −7.3 to +0.4‰, similar to literature values for unbrecciated (“monomict”) ureilites. They also contained a minor low temperature (≤500 °C) component (δ 13 C = ca −25‰). Bulk nitrogen contents (9.4–27 ppm) resemble those of unbrecciated ureilites, with major releases mostly occurring at 600–750 °C. A significant lower temperature release of nitrogen occurred in all samples. Main release δ 15 N values of −53 to −94‰ fall within the range reported for diamond separates and acid residues from ureilites, and identify an isotopically primordial nitrogen component. However, they differ from common polymict ureilites which are more nitrogen‐rich and isotopically heavier. Thus, although the parent asteroid 2008 TC 3 was undoubtedly a polymict ureilite breccia, this cannot be deduced from an isotopic study of individual ureilite fragments. The combined main release δ 13 C and δ 15 N values do not overlap the fields for carbonaceous or enstatite chondrites, suggesting that carbon in ureilites was not derived from these sources.