HRTEM and EFTEM Studies of Phyllosilicate-Organic Matter Assocations in Matrix and Dark Inclusions in the EET 92042 CR2 Carbonaceous Chondrite

摘要

Based on petrologic and isotopic observations, the CR chondrites represent one of the most primitive carbonaceous chondrite groups. The organic matter in CR chondrite matrices is considered to be among the most ancient carbonaceous matter known, potentially providing a link between organic matter in the interstellar medium and our solar system. However, the organic chemistry of CR chondrites may be complicated by the fact that these meteorites have undergone moderate secondary alteration, which potentially overprints primordial features. Although the general effects of this alteration have been documented, the details of the fine-grained mineralogy and alteration styles of CR matrices are not fully understood. Here we present TEM observations of matrix in EET 92042, a CR chondrite that contains particularly primitive insoluble organic matter. Preliminary studies determined that EET 92042 matrix is heterogeneous in terms of mineralogy, texture, and petrographic fabric on the micron scale. EET 92042 contains magnetite-rich regions, foliated matrix and dark inclusions (DIs).