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Igneous Graphite in Enstatite ChondritesIgneous graphite. a rare constituent in terrestrial mafic and ultramafic rocks. occurs in three EH and one EL enstatite chondrite impact-melt breccias as 2-150 Ilm long euhedrallaths. some with pyramidal terminations. In contrast. graphite in most enstatite chondrites exsolved from metallic Fe-Ni as polygonal. rounded or irregular aggregates. Literature data for five EH chondrites on C combusting at high temperatures show that Abee contains the most homogeneous C isotopes (i.e. delta(sup 13)C = -8.1+/-2.1%); in addition. Abee's mean delta(sup l3)C value is the same as the average high-temperature C value for the set of five EH chondrites. This suggests that Abee scavenged C from a plurality of sources on its parent body and homogenized the C during a large-scale melting event. Whereas igneous graphite in terrestrial rocks typically forms at relatively high pressure and only moderately low oxygen fugacity (e.g., approx. 5 kbar. logfO2, approx. -10 at 1200 C ). igneous graphite in asteroidal meteorites formed at much lower pressures and oxygen fugacities.
Document ID
20130010125
Acquisition Source
Headquarters
Document Type
Reprint (Version printed in journal)
Authors
Rubin, Alan E.
(California Univ. Los Angeles, CA, United States)
Date Acquired
August 27, 2013
Publication Date
October 1, 1997
Publication Information
Publication: Mineralogical Magazine
Volume: 61
Subject Category
Geophysics
Funding Number(s)
CONTRACT_GRANT: NAGW-3535
Distribution Limits
Public
Copyright
Other

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