Partial melting of the Allende (CV3) meteorite: Implications for origins of basaltic meteorites

Eucrites and angrites are distinct types of basaltic meteorites whose origins are poorly known. Experiments in which samples of the Allende (CV3) carbonaceous chondrite were partially melted indicate that partial melts can resemble either eucrites or angrites, depending only on the oxygen fugacity (f_O2). Melts are eucritic if the f_O2 is below that of the iron-wüstite buffer or angritic if above the f_O2 of that buffer. With changing pressure, the graphite-oxygen redox reaction can produce oxygen fugacities that are above or below those of the iron-wüstite buffer. Therefore, a single, homogeneous, carbonaceous planetoid > 110 kilometers in radius could produce melts of drastically different composition, depending on the depth of melting.