Microstructure of calcite in the CM2 carbonaceous chondrite LON 94101: Implications for deformation history during and/or after aqueous alteration

Abstract

The microstructure of calcite in the CM2 carbonaceous chondrite LON 94101 has been characterized using electron backscatter diffraction (EBSD) analysis, to reconstruct the parent body deformation history during and/or after aqueous alteration. The results suggest that at least two events of calcite crystallization have taken place during aqueous alteration, and at least three episodes of deformation are recorded by the calcite. The first event of calcite crystallization produced calcite grains scattered throughout the matrix, and the second event formed a calcite vein via localized fluid flow. The first episode of deformation is recorded in the crystallographic preferred orientations of the calcite grains and occurred via a directed stress probably induced by compaction in shallow crustal levels of the parent body. The second episode of deformation is recorded in an e-twin microstructure and it suggests a deformation induced via directed stress by impact processing, also in shallow crustal levels. The third episode of deformation generated subgrains in the calcite vein and in some calcite grains, and fragmented and disrupted the calcite vein. This could have been a result of a relatively forceful deformation event, perhaps when the meteorite was released from its parent body. This study shows that carbonate microstructures in carbonaceous chondrites is a powerful and versatile tool for reconstructing the history of deformation during and/or after aqueous alteration.