Partial melting of the Indarch (EH4) meteorite: A textural, chemical, and phase relations view of melting and melt migration

To test whether aubrites can be formed by melting of enstatite chondrites and to understand igneous processes at very low O fugacities, we have conducted partial melting experiments on the Indarch (EH4) chondrite at 1000-1500 C. Silicate melting begins at 1000 C, and Indarch is completely melted by 1500 C. The metal-sulfide component melts completely at 1000 degrees C. Substantial melt migration occurs at 1300-1400 C, and metal migrates out of the silicate charge at 1450 C and similar to 50% silicate partial melting. As a group, our experiments contain three immiscible metallic melts (Si-, P-, and C-rich), two immiscible sulfide melts (Fe- and FeMgMnCa-rich), and silicate melt. Our partial melting experiments on the Indarch (EH4) enstatite chondrite suggest that igneousprocesses at low fO(2) exhibit several unique features. The complete melting of sulfides at 1000 C suggests that aubritic sulfides are not relics. Aubritic oldhamite may have crystallized from Ca and S complexed in the silicate melt. Significant metal-sulfide melt migration might occur at relatively low degrees of silicate partial melting. Substantial elemental exchange occurredbetween different melts (e.g., S between sulfide and silicate, Si between silicate and metal), a feature not observed during experiments at higher fO(2). This exchange may help explain the formation of aubrites from known enstatite chondrites.