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The origin of type C inclusions from carbonaceous chondrites

Beckett, John R. and Grossman, Lawrence (1988) The origin of type C inclusions from carbonaceous chondrites. Earth and Planetary Science Letters, 89 (1). pp. 1-14. ISSN 0012-821X. doi:10.1016/0012-821X(88)90028-3.

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Type C inclusions are plagioclase-rich, Ca-, Al-rich inclusions found in carbonaceous chondrites. They formed as solid condensates which were later melted in an event that destroyed the original condensate grains. Neither the melting event nor secondary alteration had a significant effect on bulk composition. Two stages in the condensation history can be discerned on the basis of major element bulk compositions. As in type A inclusions, the condensate phase assemblage originally consisted of melilite + spinel + perovskite ± hibonite. Type C's were, however, significantly enriched in spinel relative to unaltered portions of most type A's. In contrast to type A's, condensate grains of spinel and melilite in type C's reacted partially with a coexisting gas to produce anorthite + diopside. One-half to two-thirds of the silica now in type C inclusions was introduced by this process. The reactions involving melilite and spinel that are predicted by equilibrium condensation calculations for a cooling gas of solar composition did not occur, probably due to kinetic constraints. Type C's may be related to Al-rich chondrules in ordinary chondrites by the addition of olivine and albite. Bulk compositions of Al-rich chondrules in enstatite chondrites are consistent with the addition of orthopyroxene and albite to type C inclusions. Thus, types A and C inclusions and Al-rich chondrules could represent sequences of condensates removed from interaction with the primitive solar nebula at progressively lower temperatures. If Al-rich chondrules represent the high-temperature component in chondritic material, then type C inclusions rather than the more common subgroups of CAIs could be the true parents of chondrites.

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Additional Information:© 1988 Elsevier Science Publishers B.V. Received December 1, 1987; revised version received March 2, 1988. V. Ekambaram, A. Hashimoto and R. Hinton are acknowledged for stimulating discussions. Comments of and reviews by M. Johnson, G.J. MacPherson, K.M. Nolan, J.M. Paque and an anonymous reviewer are also appreciated. Initial stages of this work were conducted by the first author as part of his Ph.D. dissertation at the University of Chicago. This work was supported by NASA grant NAG 9-54 to L.G.
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Official Citation:John R. Beckett, Lawrence Grossman, The origin of type C inclusions from carbonaceous chondrites, Earth and Planetary Science Letters, Volume 89, Issue 1, June 1988, Pages 1-14, ISSN 0012-821X, 10.1016/0012-821X(88)90028-3.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:37280
Deposited By: Tony Diaz
Deposited On:04 Mar 2013 22:53
Last Modified:09 Nov 2021 23:28

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