A potential mantle origin for precursor rocks of high-Mg impact glass beads in Chang’e-5 soil

Abstract

The chemical compositions of most lunar impact glass beads reflect mixing of crustal components including mare basalts, highlands rocks, and KREEP [from high concentrations of K, REE (rare earth element), and P]. However, a few glass beads in the soil from the Chang’e-5 mission have unusually high MgO contents that require distinct target compositions. The young age of these high-MgO glass beads suggests an origin through impact melting of ultramafic target rocks with abundant pyroxene and olivine. While such targets might represent cumulates of mare basalts, impact melts, or Mg-suite rocks, they appear unlike any sampled lunar lithologies. Alternatively, these high-Mg beads might be sampling the upper mantle brought to the surface by the Imbrium basin–forming event.