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Replacement textures in CAI and implications regarding planetary metamorphism

Meeker, G. P. and Wasserburg, G. J. and Armstrong, J. T. (1983) Replacement textures in CAI and implications regarding planetary metamorphism. Geochimica et Cosmochimica Acta, 47 (4). pp. 707-721. ISSN 0016-7037.

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Textural and chemical features of five coarse-grained, calcium-aluminum-rich inclusions from the Allende meteorite indicate that some of the melilite in these inclusions was formed by a secondary metamorphic event and not by primary crystallization from a melt or by a sequential nebular condensation process. These inclusions contain embayed pyroxene surrounded by melilite. Physically separated pyroxene crystals are often in optical continuity indicating that they were once part of larger single crystals that have been partly replaced by melilite. Other evidences of metamorphism include reaction textures between melilite and spinel, and metamorphic textures such as kink-band-like features, lobate sutured grain boundaries, and 120° triple-points. This type of metamorphic process requires the addition of Ca which we propose came from calcite or by introduction of a fluid phase. We believe that the most likely environment for this metamorphic process is on a small planetary body, and not in the solar nebula. The results of this study are compatible with oxygen isotopic heterogeneities within CAI, and provide a mechanism for producing lower temperature alteration phases and the rim phases found in these inclusions. We conclude that planetary processes must thus be considered in the formation history of CAI, and that it is necessary to reconsider the classification system of these objects in light of the replacement process proposed here.

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Wasserburg, G. J.0000-0002-7957-8029
Additional Information:© 1983 Pergamon Press Ltd. Received August 5, 1982: accepted in revised form January 5, 1983. We are grateful to H. Y. McSween, Jr., D. A. Wark and J. D. Macdougall for their helpful reviews and comments. One of us (G.P.M.) used portions of this work as a partial fulfillment of the requirements for a Master of Science degree at the California State University at Los Angeles. This paper was supported in part by the National Aeronautics and Space Administration grant NGL05-002-188 and the National Science Foundation grant PHY79-23638A2. Contribution No. 3778 (421) of the Division of Geological and Planetary Sciences, the Charles Arms Laboratory of the California Institute of Technology, Pasadena. California.
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Caltech Division of Geological and Planetary Sciences3778
Lunatic Asylum Lab421
Issue or Number:4
Record Number:CaltechAUTHORS:20131021-153014750
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Official Citation:G.P Meeker, G.J Wasserburg, J.T Armstrong, Replacement textures in CAI and implications regarding planetary metamorphism, Geochimica et Cosmochimica Acta, Volume 47, Issue 4, April 1983, Pages 707-721, ISSN 0016-7037, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:41998
Deposited By: Tony Diaz
Deposited On:22 Oct 2013 16:04
Last Modified:09 Mar 2020 13:19

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