Primary and Secondary Diversity Among Enstatite Chondrites and Implications for Their Parent Bodies

The enstatite chondrites (ECs) are noteworthy in having stable isotopic compositions similar to Earth and Moon [1-3], suggesting they were present in Earth’s feeding zone during terrestrial planet formation. To better understand these primitive meteorites, we have been studying their primary and secondary mineralogies and documenting the diversity among the EC groups. Since Keil's landmark paper [4] at least two major groups of ECs have been identified, now known as EH and EL. Lack of EC breccias containing both EH and EL implies at least two separate parent bodies. The ECs are a relatively small meteorite class making up less than 1% of all known meteorites with less than 20 unequilibrated (type 3) individuals known. However, with new samples returned from Antarctica, hot deserts and occasional non-desert meteorites, the diversity of E chondrites has seemed to grow, with potential new groups emerging [e.g., 5]. Based on sulfide compositions, division of EH and EL each into subgroups “a” and “b” has also been proposed and a minimum of four parent bodies for the ECs has been suggested [6]. ECs such as NWA 8785 have secondary minerals not present in other ECs, potentially representing yet another EC parent body [7]. Here we explore the petrologic diversity of EH and EL and anomalous ECs to evaluate their origins, alteration histories and parent bodies.