GROVE MOUNTAINS (GRV) 020043: INSIGHTS INTO ACAPULCOITE-LODRANITE GENESIS FROM THE MOST PRIMITIVE MEMBER

1Timothy J.McCoy,1Catherine M.Corrigan,2Tamara L.Dickinson,3Gretchen K.Benedix,4Devin L.Schrader,4Jemma Davidson
Geochemistry (Chemie der Erde) (in Press) Link to Article [https://doi.org/10.1016/j.chemer.2019.125536https://doi.org/10.1016/j.chemer.2019.125536]
1Dept. of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, DC, 20560-0119, USA
2Science Matters Consulting, LLC, Washington, DC, 20016, USA
3School of Earth and Planetary Sciences, Curtin University, Bentley, WA, 6102, Australia
4Center for Meteorite Studies, School of Earth and Space Exploration, Arizona State University, Tempe, AZ, 85287-1404, USA
Copyright Elsevier

Although acapulcoites and lodranites played a key role in understanding partial differentiation of asteroids, the lack of samples of the chondritic precursor limits our understanding of the processes that formed these meteorites. Grove Mountains (GRV) 020043 is a type 4 chondrite, with abundant, well-delineated, pyroxene-rich chondrules with an average diameter of 690 μm, microcrystalline mesostasis, polysynthetically striated low-Ca pyroxene, and slightly heterogeneous plagioclase compositions. GRV 020043 shows that evidence of partial melting is not an essential feature for classification within the acapulcoite-lodranite clan. GRV 020043 suggests a range of peak temperatures on the acapulcoite-lodranite parent body similar to that of ordinary chondrites, but shifted to higher temperatures, perhaps consistent with earlier accretion. Similarities in mineralogy, mineral composition, and oxygen isotopic composition link GRV 020043 to the acapulcoite-lodranite clan. These features include a high low-Ca pyroxene to olivine ratio, high kamacite to taenite ratio, and relatively FeO-poor mafic silicates (Fa10.3, Fs10.4) relative to ordinary chondrites, as well as the presence of ubiquitous metal and sulfide inclusions in low-Ca pyroxene and ƒO2 typical of acapulcoites. GRV 020043 experienced modest thermal metamorphism similar to type 4 ordinary chondrites. The mineralogy and mineral compositions of GRV 020043, despite modest thermal metamorphism, suggests that most features of acapulcoites previously attributed to reduction were, instead, inherited from the precursor chondrite. Although partial melting was widespread on the acapulcoite-lodranite parent body, ubiquitous Fe,Ni-FeS blebs in the cores of silicates were not implanted by shock or trapped during silicate melting, but were inherited from the precursor chondrite with subsequent overgrowths during metamorphism.

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