Testing for age correlation among the young shergottites

English Abstract:

Recent investigations have demonstrated that the application of ion and nanoscopic electron beam analysis to highly refractory U-bearing minerals in martian meteorites can reveal the complex petrogenetic history of these rocks, including igneous crystallization and shock ejection. We are evaluating the extent to which the geochemical grouping of the shergottites according to depleted-intermediate-enriched REE compositions and mafic-permafic-ultramafic major element composition axes are reflected in the crystallization ages of shergottites measured by in situ U-Pb dating of igneous Zr-rich minerals and phosphates. We are also evaluating the extent to which martian phosphate minerals record post-crystallization alteration (e.g., by fluids and by impact heating), and searching for launch-generated assemblages (e.g., zircon) that can constrain the timing of the impact events which delivered the shergottites to Earth. Our study encompasses a wide range of shergottites, many of which yield mineral crystallization ages from the last several hundred million years. Phase mapping using SEM-EDS has demonstrated a common association of igneous baddeleyite with ilmenite-dominant oxide assemblages. Primary igneous phosphates, predominantly Mg-merrillite can show partial replacement by chlorapatite in association with pockets of glassy SiO₂-K₂O-rich shock melt. Despite shock effects, all the shergottites in this study exhibit dominantly igneous textures, including core-to-rim zoning of pyroxene and olivine from Mg-rich to Fe-rich and igneous zoning in plagioclase. Isotopic and trace element analyses, spatially correlated with primary and secondary microstructures will test for age correlation and potential comagmatic samples of young martian magmatism.