C. Caillet

Petrologic and AlMg isotopic clues to the accretion of two refractory inclusions onto the Leoville parent body: One was hot, the other wasn't

Abstract Two type B refractory inclusions found within several centimeters of each other in the foliated Leoville meteorite differ greatly in their styles of deformation, textures, and Mg-Al isotopic characteristics. One is a subspheroidal type B1 with textures similar to those observed previously in many type B1s from other CV3 meteorites, and whose deformation (fracturing, some granulation) has been almost entirely brittle in nature. Its isotopic composition shows 26 Mg 24 Mg correlated with 27 Al 24 Mg which, although disturbed, indicates a lower limit for initial 26 Al 27 Al of ~4.9 × 10 −5 . The other inclusion is a highly elongate ( L W ~6 ) object whose long axis lies in the plane of foliation of the Leoville meteorite. It has a predominantly metamorphic texture, but relict islands of an earlier and more “normal” type B precursor are preserved in its core. The isotopic compositions of the two textural variants in this inclusion are different, anorthite in the metamorphic region mostly showing little or no excess 26 Mg [( 26 Al 27 Al ) 0 −6 ] that would be attributable to in situ decay of 26 Al whereas anorthite in the relict islands shows well-resolved excess 26 Mg that gives a lower limit for initial 26 Al 27 Al of ~4.6 × 10 −5 . The effects of shock metamorphism on the Leoville meteorite are clearly seen in both inclusions, including brittle deformation and local shock melting, but are not responsible for the major textural differences between the two inclusions. The most likely origin for the deformed and recrystallized features of the elongate inclusion is that it accreted onto the Leoville parent body while still very hot, and deformed into its present shape at the instant it impacted. If the resetting of the Al-Mg system occurred during this event, it must have taken place at least ~3.3 million years after formation of the precursor inclusion. The possibility that other deformed Leoville components accreted while hot should not be discounted.