Oxide-bearing and FeO-rich clasts in aubrites

Abstract

We report the occurrence of an oxide-bearing clast and an FeO-rich clast from aubrites. The FeO-rich clast in Pesyanoe is dominated by olivine and pyroxene phenocrysts with mineral compositions slightly less FeO-rich than is typical for H chondrites. In Allan Hills (ALH) 84008, the oxide-bearing clast consists of a single forsterite grain rimmed by an array of sulfides, oxides, and phosphides. We consider a number of possible origins. We can exclude formation by melting of oxide-bearing chondrules and CAIs formed in enstatite chondrites. The Pesyanoe clast may have formed in a more oxidized region of the aubrite parent body or, more likely, is a foreign clast from a more oxidized parent body. The ALH 84008 clast likely formed by reaction between sulfides and silicates as a result of cooling, oxidation, or de-sulfidization. This clast appears to be the first oxide-bearing clast from an aubritic breccia that formed on the aubrite parent body. Identification of additional oxide-bearing clasts in aubrites could shed light on whether this was a widespread phenomenon and the origin of these enigmatic objects.