An experimental study of partial melting and fractional crystallization on the HED parent body

TL;DR

This study combines experimental and modeling approaches to understand partial melting and fractional crystallization processes in the HED parent body, shedding light on its mantle composition and meteorite formation.

Contribution

It provides new experimental data and modeling insights into the melting behavior and crystallization sequences of the HED parent body's mantle.

Findings

Melt crystallizes olivine until orthopyroxene joins at 1350°C

Fractional crystallization produces diogenite-like compositions below 1250°C

MELTS predictions align reasonably with experimental results

Abstract

We have performed an experimental and modeling study of the partial melting behavior of the HED parent body and of the fractional crystallization of liquids derived from its mantle. We estimated the mantle composition by assuming chondritic ratios of refractory lithophile elements, adjusting the Mg# and core size to match the density and moment of inertia of Vesta, and the compositions of Mg-rich olivines found in diogenites. The liquidus of a mantle with Mg# (=100*(Mg/(Mg+Fe))) 80 is ~1625oC and, under equilibrium conditions the melt crystallises olivine alone until it is joined by orthopyroxene at 1350oC. We synthesized melt from our 1350oC experiment and simulated its fractional crystallization path. Orthopyroxene crystallizes until it is replaced by pigeonite at 1200oC. Liquids become eucritic and crystal assemblages resemble diogenites below 1250oC. MELTS correctly predicts the olivine liquidus but overestimates the orthopyroxene liquidus by ~70oC. Predicted melt compositions are in reasonable agreement with those generated experimentally. We used MELTS to determine that the range of mantle compositions that can produce eucritic liquids and diogenitic solids in a magma ocean model is Mg# 75-80 (with chondritic ratios of refractory elements). A mantle with Mg# ~ 70 can produce eucrites and diogenites through sequential partial melting.