A Microanalytical (TEM) Study of Fine-grained Chondrule Rims in NWA 5717

Northwest Africa (NWA) 5717 is a highly primitive ordinary chondrite of petrologic type 3.05 with ubiquitous fine-grained chondrule rims [1, 2]. Rims appear around approximately 60% of chondrules and are comprised of micron-sized mineral and lithic fragments and microchondrules that are embdedded in an FeO-rich submicron groundmass that compositionally resembles fayalitic olivine. Some rim clasts appear overprinted with FeO-rich material, suggesting secondary alteration that postdates rim formation. Here we present a microanalytical (TEM) study of the submicron component (i.e. the groundmass) of the rims in order to determine the crystal structures and compositions of their constituent phases and decipher the accretion and alteration history recorded in rims.