Origin of boundary clinopyroxenes between spinel and melilite in type B1 CAIs

Abstract

Small (<5 μm) boundary clinopyroxenes (b-cpx) on spinel (sp) inclusions in melilite (mel) are ubiquitous in the type B1 CAIs. B-cpx on sp in high-Åk mel in the core of the inclusion could be explained by crystallization, either initial or during remelting. However, b-cpx on sp inclusions in low-Åk mantle mel are not readily explained in this way because mantle mel crystallized and incorporated b-cpx long before the appearance of clinopyroxene (cpx) in the crystallization sequence. To further constrain the crystallization and/or alteration processes, and to test the hypothesis that b-cpx were formed from melt inclusions, we examined the sp/mel interface of four sp in Leoville and Allende CAIs using FIB/TEM.

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