A Nanoscale Analytical STEM Study of the Paris Meteorite

Villalon K. L., Bradley J. P., Ishii H. A., Ohtaki K. K., Davis A. M., Stephan T.

82nd Annual Meeting of The Meteoritical Society 2019

PDF abstract

“Paris is considered to be the least altered CM chondrite [1]. It is a breccia with evidence of
heterogeneous aqueous alteration, containing both metal-rich lithologies with abundant amorphous silicates as well as metal-poor lithologies with abundant phyllosilicates. In the least altered lithologies, Paris has been found to preserve material closely resembling GEMS (glass with embedded metal and sulfides) from interplanetary dust particles (IDPs) [2]. If the GEMS-like material in Paris can be confirmed to be related to IDP GEMS, it may uniquely demonstrate the progression of silicates from the interstellar medium and/or early solar nebula to incorporation into a growing planetesimal and subsequent alteration. If the GEMS-like material in Paris is unrelated to IDP GEMS, it may represent a significant yet altogether unexplored class of objects in primitive meteorites. GEMS grains have yet to be unambiguously identified in meteorites. While the GEMS-like material in Paris has textural similarities to IDP GEMS as well as comparable average chemical compositions as measured by energy-dispersive X-ray spectroscopy (EDS), the ubiquity of nanophase components throughout the GEMS-like material makes comparisons difficult and necessitates more detailed scrutiny before definitive identifications can be asserted. The same is true for GEMS-like material that has recently been observed in the CR chondrite LaPaz Icefield 02342
[3] and whose nanophase components also await definitive mineral identification. Inclusions in GEMS and GEMS-like objects are ~1–30 nm in size, smaller than the thinnest TEM sections. Nanodiffraction [4] is able to obtain diffraction patterns from regions <1 nm. Unlike with EDS, it is more easily discerned when multiple phases are contributing to an electron diffraction pattern, and it is possible to remove the contribution from unwanted phases. Nanodiffraction can therefore provide essential mineralogical information on the often-neglected smallest class of objects in meteorites. “