Assumptions on the early evolution of the Asteroid Vesta include a combined (i) ordinary plus carbonaceous chondritic bulk composition, (ii) complete melting of the silicate fraction within tens of Ma after CAI, (iii) equilibration of silicate material and FeNiS-core, as well as (iv) formation of an ultramafic (peridotitic/pyroxenetic) lower crust and upper mantle plus a basaltic crust. There is, however, little consensus about the volume proportions within the silicate components. Estimates of the thickness of the basaltic crust depend on crystallization models of the bulk silicate composition. The diogenitic component of DAG 779 (believed to originate from Vesta) reveals temperatures of orthopyroxene (opx) formation from 1450 and 1200 °C measured for bulk exsolved opx and for host regions between exolution lamellae , respectively. This range coincides with calculated temperatures of opx formation by equilibrium and fractional crystallization sequences for Vestas silicate shell. Calculations of the thickness of the remaining basaltic (eucritic) crust and the onset of the ultramafic interior suggest depths of 20 to 40 km. The early large impacts that produced the Veneneia and Reasilvia basins most probably excavated rocks from this depth but did not produce large amounts of olivine-rich rocks on Vestas surface. In the light of the above mentioned crystallization models, an orthopyroxenite-rich layer can be assumed to depth of up to 80 km; olivine-dominated rocks are probably restricted to Vestas deeper mantle.
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