The formation of Type B CAIs: Evolution from Type A CAIs

Five Type A CAIs from three CV3 chondrites (Vigarano, Northwest Africa 3118, Allende), which differ in age by no more than ?105 years, show mineralogical and textural evidence of gradual transition into Bs, indicating that B inclusions formed evolution the solar nebula. This model differs conventional condensation aggregates condensate grains form different kinds depending on relative populations grains. In our pyroxene forms nearly isochemically reaction perovskite with melilite under highly reducing conditions. Anorthite requires addition silica gas, originally as veins rims gehlenitic within Fluffy As. Later partial re-melting these assemblages results formation poikilitic anorthite enclose rounded (partially melted) tablets melilite. Oxygen isotopes four support Ti-rich 16O-depleted perovskite, but not fifth CAI. An alternative possibility is result later solid-state exchange preferentially affects most pyroxene. Regardless origin pyroxene, we give a for nebular reservoir based sporadic FU-Orionis flare-ups 16O-rich region near proto-Sun fluctuated size whether was flare-up stage or quiescent.