Planetesimal mantles and pyroxentites: Investigating the importance of melt-rock reaction in the early Solar System.

The first formed planetary bodies (planetesimals) underwent melting in the first few million years of Solar System history. These objects rapidly separated into cores and mantles, and crust formation occurred either by extraction of low-degree silicate melts, or by high-degrees of crystallisation from deep silicate magma oceans. These processes are, however, difficult to investigate because of the rarity of mantle samples as meteorites (so-called dunite or harzburgite shortage). Therefore, we are studying rare olivine and spinel mantle xenocrysts in an 'angrite’ meteorite, one of several types of ~basaltic crustal rocks from this earliest period. Additionally, the abundance of pyroxenite meteorites related to basaltic meteorites, including angrites (i.e. the original angrite meteorite, a Ca-pyroxenite), indicates that lower crustal rocks of planetesimals may be similar to the lower oceanic crust of the Earth. Melt-rock reaction during magma flow may therefore be an underestimated process generating planetesimal crust-mantle (Mohorovicic) discontinuities.