Quantification of shock in enstatite chondrites using micro-X-ray diffraction

Enstatite chondrite meteorites are chemically and isotopically related to the precursors of inner Solar System planetesimals, and bear evidence of shock metamorphism which reflects events in enstatite chondrite evolution. Here, we build upon a micro-X-ray diffraction (micro-XRD)-based method to relate strain-related mosaicity (SRM) to petrographic shock stage. Making use of the peak pressure ranges estimated for the petrographic shock stages, we are able to provide quantitative constraints on the peak shock pressures recorded in enstatite (MgSiO3). Full-width at half-maximum measurement of X-ray diffraction maxima distributed along the Debye rings (ΣFWHMχ) are a proxy for SRM in enstatite grains. Eleven Antarctic enstatite chondrites spanning all documented shock stages (S1−S5), petrologic types, and metamorphic grades, are used to establish a linear correlation P (GPa) = 4.62 × ΣFWHMχ + 0.57; with R2 = 0.92 between estimated peak shock pressure and ΣFWHMχ. Enstatite lattice planes (020), (610) and (131) show similar ΣFWHMχ values where meaningful comparisons can be made, suggesting that enstatite has, within measurement error, an isotropic response to shock deformation along its three crystal axes. The (610) reflection is particularly productive at all shock stages and could be used exclusively for future peak pressure studies, under the assumption that enstatite is isotropic to shock deformation. This 2D XRD method enables the estimation of peak shock pressures up to at least 30 GPa in enstatite chondrites and for other enstatite-rich meteorites.