HED Meteorites and Their Relationship to the Geolo

Authors: Harry Y McSween David W Mittlefehldt Andrew W Beck Rhiannon G Mayne Timothy J McCoy

Publish Date: 2010/03/17

Volume: 163, Issue: 1-4, Pages: 141-174

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Abstract

Howarditeeucritediogenite HED meteorites thought to be derived from 4 Vesta provide the best sampling available for any differentiated asteroid However deviations in oxygen isotopic composition from a common massfractionation line suggest that a few eucritelike meteorites are from other bodies or that Vesta was not completely homogenized during differentiation The petrology and geochemistry of HEDs provide insights into igneous processes that produced a crust composed of basalts gabbros and ultramafic cumulate rocks Although most HED magmas were fractionated it is unresolved whether some eucrites may have been primary melts The geochemistry of HEDs indicates that bulk Vesta is depleted in volatile elements and is relatively reduced but has chondritic refractory element abundances The compositions of HEDs may favor a magma ocean model but inconsistencies remain Geochronology indicates that Vesta accreted and differentiated within the first several million years of solar system history that magmatism continued over a span of ∼10 Myr and that its thermal history extended for perhaps 100 Myr The protracted cooling history is probably responsible for thermal metamorphism of most HEDs Impact chronology indicates that Vesta experienced many significant collisions including during the late heavy bombardment The age of the huge south pole crater is controversial but it probably ejected Vestoids and many HEDs Continued impacts produced a regolith composed of eucrite and diogenite fragments containing only minor exotic materials HED meteorites serve as ground truth for orbital spectroscopic and chemical analyses by the Dawn spacecraft and their properties are critical for instrument calibration and interpretation of Vesta’s geologic history

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