No abstract

Howardite-e ucrite-diogenite (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 mass-fractionation line suggest that a few eucrite-like 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 cucrites 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 inconislencies 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 . . . . . \0 Myr, and that its thermal history extended for perhaps 100 Myr. The protracted cooling history is probabl y responsible for thermal metamorphism of most HEDs. Impact chronology indicates that Vesta ex perienced 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 eu-(me and diogenite fragments containing only minor exotic materials. HED meteorites serve ib ground truth for orbital spectroscopic and chemical analyses by the Dawn spacecraft, and H,( \1cSween Jr. (C8J). A

Howardite-e ucrite-diogenite (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 mass-fractionation line suggest that a few eucrite-like 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 cucrites 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 inconislencies 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 . . . . . \0 Myr, and that its thermal history extended for perhaps 100 Myr. The protracted cooling history is probabl y responsible for thermal metamorphism of most HEDs. Impact chronology indicates that Vesta ex perienced 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 eu-(me and diogenite fragments containing only minor exotic materials. HED meteorites serve ib ground truth for orbital spectroscopic and chemical analyses by the Dawn spacecraft, and H,( \1cSween Jr. (C8J). A