Carbonates in CM chondrites: Complex formational histories and comparison to carbonates in CI chondrites |
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| Authors: | Simone
De LEUW Alan E RUBIN John T WASSON |
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| Institution: | 1. Department of Earth and Space Sciences, University of California, Los Angeles, California 90095–1567, USA;2. Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90095–1567, USA;3. Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095–1567, USA |
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| Abstract: | Abstract– CM chondrites are primitive solar‐system materials that have undergone high degrees of aqueous alteration, resulting in the formation of secondary minerals including carbonates. Two different carbonate minerals (calcite/aragonite and dolomite) together constitute 1.4–2.8 vol% of CM chondrites. In contrast, CI chondrites contain four different carbonate minerals: calcite/aragonite, dolomite, breunnerite, and siderite. CI chondrites have abundant dolomite, a mineral that seems to be absent in the most aqueously altered CM chondrites. In this study, carbonates in seven CM chondrites (Y‐791198, LaPaz Icefield 04796, Cold Bokkeveld, Nogoya, Queen Alexandra Range 93005, Allan Hills 83100, and Meteorite Hills 01070) were studied petrographically and by electron microprobe. The results indicate that carbonate formation in CM chondrites differs from that in CI chondrites and is more complex than previously recognized. Our studies of CM chondrites indicate that (1) carbonates formed on the parent asteroid in an aqueous environment that gradually changed in composition, (2) at some stage, Ca and Mg activities in the environment were high enough to form metastable dolomite, and (3) dolomites disappeared in the most aqueously altered CM chondrites. |
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