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Magmatic processes on the asteroid 4-Vesta: implications for differentiation of small rocky bodies
Distel, Andrea
Distel, Andrea
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2021
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2022-09-10
Abstract
As a differentiated asteroid, 4-Vesta is commonly referred to as a protoplanet and is representative of planetary formation processes in the early solar system. The concise petrogenesis, bulk-composition and thermal history of Vesta’s mantle and crust are not clearly understood. Achondritic howardite-eucrite-diogenite (HED) meteorites are igneous crustal rocks derived from various depths within the Vestan crust and provide valuable constraints on the geochemistry and mineralogy of its interior. Using the thermodynamic modeling software alphaMELTS and petrological analysis of eucrite NWA 11455 and diogenite NWA 4664, we compared the modeling results of differing published bulk compositions and model parameters for Vesta’s magmatic and crustal evolution. Our results indicate that a mixed magma ocean bulk composition of 0.7 ordinary (L) chondrite + 0.3 carbonaceous (CV) chondrite on Vesta underwent equilibrium crystallization until it reached a critical melt fraction of 80% solids. Results also confirm that the Vestan magma ocean then underwent separation of melt from solids, resulting in mafic to ultramafic cumulates at depth and a layered fractionated crust that crystallized from the 20% residual liquid. Compositional similarities to the calculated models place diogenite NWA 4664 as a pyroxene-rich cumulate and eucrite NWA 11455 as a cumulate that formed at 1100 °C in the fractional crystallization sequence of the remaining 20% extruded liquid.
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