The nature of volatiles on 4-Vesta: clues from apatite in eucrites

Eucrites are basaltic and gabbroic meteorites that are paired with howardites and diogenites, all of which are thought to be from the asteroid 4-Vesta. Because eucrites are volatile-depleted, and this volatile-depletion is poorly understood, I studied the volatiles fluorine, chlorine and water in eucritic apatite. Partition coefficients were used to estimate the ratio of the volatiles (hydroxyl vs. fluorine vs. chlorine) in the coexisting melt and textures of apatite and mineral associations were used to determine the conditions of apatite crystallization. The majority of the apatite is nearly pure fluorapatite, occurs in mesostasis, and probably crystallized from a degassed magma, similar to lunar mare basalt magma. Chlorine-rich apatites in the GRA 98098 meteorite and vein apatites associated with pyroxene and troilite in the Juvinas meteorite may have crystallized from a high temperature fluid.