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Published April 1979 | public
Journal Article

A petrogenetic model of the relationships among achondritic meteorites


The basaltic achondrite, shergottite, nakhlite, and chassignite meteorites appear to define a petrological and geochemical sequence. Assuming that they developed from basaltic liquids produced by low pressure partial melting of plagioclase peridotites, their petrological and chemical distinctions can be understood in terms of the compositional differences between their source periodites. The source regions of basaltic achondrite magmas were alkali-poor, metal-bearing peridotites in which pigeonite and/or orthopyroxene was the only pyroxene. By simultaneously increasing the ratio of high-Ca pyroxene to low-Ca pyroxene, the alkali content of the feldspar, the oxidation state, and the overall volatile content of the basaltic achondrite source peridotite, peridotites capable of yielding the parent liquids of the shergottites can be produced. Further increases can produce peridotites capable of yielding the parent liquids of the nakhlites and chassignites. Addition of a volatile-rich component to the volatile-poor type of peridotite required for the source regions of the eucrites appears to be capable of producing the required series of peridotites. Alternatively, progressive volatile-loss from a volatile-rich material, possibly of roughly cosmic composition, could have produced this sequence of peridotites. A simple two-component model of planetary compositions is, to a first approximation, consistent with the petrology and chemistry of these igneous meteorite groups.

Additional Information

© 1979 Elsevier Ltd. Received 10 May 1978. Accepted 28 November 1978. We thank D. Walker and H. Pälme for access to unpublished data and M. Drake, J. Longhi, A. E. Ringwood, R. A. Schmitt, J. V. Smith, D. Walker, and J. T. Wasson for their comments and reviews of the manuscript. This work was supported by NASA grants NGL 22-007-247 (J. F. H.) and NSG 74-13 (H. Y. M.).

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