Microfaults: Abundant shear deformation and frictional melting in chondrites

Abstract

The majority of ordinary chondrite (OC) meteorites record some amount of textural evidence for impact-induced deformation. Melt veins in some shocked samples have been compared to terrestrial impact-related pseudotachylites, which form by frictional melting of host rock. However, lacking in situ context, the role of friction in driving impact-related melting in meteorites remains unclear. Here, we present evidence for an important role for shear deformation and friction in complementing shock melting of OC material. We find microfaults directly associated with textural evidence for quenched frictional shock melt in samples of a broad range of bulk shock stages and across all three classes studied (LL, L, or H). Microfaults occur in 20% of our studied samples. We identify examples of both individual microfaults and, in rare cases, microfault networks, complete with subsidiary shear structures. Our observations indicate that friction plays an important role in melt generation in weakly to moderately shocked samples and may also be relevant for strongly shocked meteorites. Microfault structures may be of underestimated significance in chondrites in general—both with regard to their general abundance and their possible utility for elucidating the geological settings sampled by meteoritic impactites.