Petrography,stable isotope compositions,microRaman spectroscopy,and presolar components of Roberts Massif 04133: A reduced CV3 carbonaceous chondrite |
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| Authors: | Jemma Davidson Devin L Schrader Conel M O'D Alexander Dante S Lauretta Henner Busemann Ian A Franchi Richard C Greenwood Harold C Connolly Jr Kenneth J Domanik Alexander Verchovsky |
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| Institution: | 1. Lunar and Planetary Laboratory, University of Arizona, , Tucson, Arizona, 85721–0092 USA;2. Planetary and Space Sciences, The Open University, , Milton Keynes, Buckinghamshire, MK7 6AA UK;3. Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, 10th & Constitution NW, , Washington, District of Columbia, 20560–0119 USA;4. Department of Terrestrial Magnetism, Carnegie Institution of Washington, , Washington, District of Columbia, 20015–1305 USA;5. School of Earth, Atmospheric and Environmental Sciences, The University of Manchester, , Manchester, M13 9PL UK;6. Department of Physical Sciences, Kingsborough Community College of the City University of New York, , Brooklyn, New York, 100235 USA;7. Earth and Environmental Sciences, The Graduate Center of the City University of New York, , New York City, New York, 10016 USA |
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| Abstract: | Here, we report the mineralogy, petrography, C‐N‐O‐stable isotope compositions, degree of disorder of organic matter, and abundances of presolar components of the chondrite Roberts Massif (RBT) 04133 using a coordinated, multitechnique approach. The results of this study are inconsistent with its initial classification as a Renazzo‐like carbonaceous chondrite, and strongly support RBT 04133 being a brecciated, reduced petrologic type >3.3 Vigarano‐like carbonaceous (CV) chondrite. RBT 04133 shows no evidence for aqueous alteration. However, it is mildly thermally altered (up to approximately 440 °C); which is apparent in its whole‐rock C and N isotopic compositions, the degree of disorder of C in insoluble organic matter, low presolar grain abundances, minor element compositions of Fe,Ni metal, chromite compositions and morphologies, and the presence of unequilibrated silicates. Sulfides within type I chondrules from RBT 04133 appear to be pre‐accretionary (i.e., did not form via aqueous alteration), providing further evidence that some sulfide minerals formed prior to accretion of the CV chondrite parent body. The thin section studied contains two reduced CV3 lithologies, one of which appears to be more thermally metamorphosed, indicating that RBT 04133, like several other CV chondrites, is a breccia and thus experienced impact processing. Linear foliation of chondrules was not observed implying that RBT 04133 did not experience high velocity impacts that could lead to extensive thermal metamorphism. Presolar silicates are still present in RBT 04133, although presolar SiC grain abundances are very low, indicating that the progressive destruction or modification of presolar SiC grains begins before presolar silicate grains are completely unidentifiable. |
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