Mineralogy and Petrology of the Northwest Africa 12774 Angrite

H. Hayashi, H. Kim, C. Park, T. Mikouchi, V. H. Hoffmann

51st Lunar and Planetary Science Conference (2020), Abstract #2360


“Angrite is one of the oldest basaltic achondrites showing unusual chemistry enriched in refractory elements and depleted in volatiles [e.g., 1]. Most angrites show two distinct textures, either “quenched” or “slowly-cooled”. Quenched angrites have older crystallization ages (ca. 4564 Ma) compared to slowly-cooled samples (ca. 4558 Ma), and thus quenched angrites can be good time anchors [e.g., 2]. Until now, 10 quenched angrites are known (LEW (Lewis Cliff) 87051, Asuka-881371/12209, D’Orbigny, NWA (Northwest Africa) 1296, NWA 1670, NWA 7203, NWA 7812, NWA 12004, NWA 12320 and Sahara 99555). These quenched angrites show ophitic, dendritic or coarse-grained textures perhaps depended upon slight difference of cooling rates [e.g., 3]. In this study, we performed mineralogical and petrological study of a new quenched angrite NWA 12774 and discuss its relationship to other quenched angrites, especially NWA 1670 and LEW 87051, in order to better understand formation history of quenched angrites.”