A collisional origin to Earth's non-chondritic composition?

Several lines of evidence indicate a non-chondritic composition for bulk Earth. If Earth formed from the accretion of chondritic material, its non-chondritic composition, in particular the super-chondritic Nd-142/Nd-144 and low Mg/Fe ratios, might be explained by the collisional erosion of differentiated plane-tesimals during its formation. In this work we use an N-body code, that includes a state-of-the-art collision model, to follow the formation of protoplanets, similar to proto-Earth, from differentiated plane-tesimals (>100 km) up to isolation mass (>0.16 M-circle dot). Collisions between differentiated bodies have the potential to change the core-mantle ratio of the accreted protoplanets. We show that sufficient mantle material can be stripped from the colliding bodies during runaway and oligarchic growth, such that the final protoplanets could have Mg/Fe and Si/Fe ratios similar to that of bulk Earth, but only if Earth is an extreme case and the core is assumed to contain 10% silicon by mass. This may indicate an important role for collisional differentiation during the giant impact phase if Earth formed from chondritic material. (C) 2014 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY license.