SNC meteorites: evidence against an asteroidal origin
The 1.3 b.y. crystallization ages and other features of the nine SNC meteorites (shergottites, makhlites, and chassignites) distinguish them from all other meteorites which apparently formed more than 3 b.y. earlier. Proposed models for the origin of the young SNC meteorites include internal melting, either within a large planet such as Mars or within a large asteroid, and impact melting on one or more asteroids. Although an asteroidal source is dynamically more reasonable, we discuss petrologic, geochemical, and isotopic observations that strongly argue against an asteroidal origin for SNC meteorites, either as impact melts or as endogenically derived melts. Cumulate textures, as displayed by the SNC meteorites, have never been observed in terrestrial or lunar impact melts. Even the largest impact melt sheets cooled relatively quickly by thorough mixing with cool clastic debris, and the resulting rocks show obvious lithic and/or mineral clasts derived from the target materials. No clasts or remnants of clasts are present in SNC meteorites. The chemical and isotopic homogeneity of impact melt rocks is not displayed by SNC meteorites. Differences in initial /sup 87/Sr//sup 86/Sr among some of the shergottites, which are otherwise chemically similar, preclude an origin in the same impact melt sheet. These relationships indicate that the SNC meteorites did not form within an impact melt sheet either on an asteroid or anywhere else. Instead, their parental magmas probably formed by internal melting within their parent body.
- Research Organization:
- Lunar and Planetary Institute, 3303 NASA Road 1, Houston, Texas 77058
- OSTI ID:
- 5987751
- Journal Information:
- J. Geophys. Res.; (United States), Journal Name: J. Geophys. Res.; (United States) Vol. 87:S1; ISSN JGREA
- Country of Publication:
- United States
- Language:
- English
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