4:15 PM - 4:30 PM
[PPS02-04] Impact processes recorded by high pressure minerals and glass beads in Chang'e-5 regolith
Keywords:Seifertite, stishovite, Chang'e-5 regolith, glass bead, redox condition
Material transport on the lunar surface is predominately controlled by impact processes, which is critical for interpreting the constitution of the target geological units from returned samples. This study presents our progress on high pressure minerals and impact formed glass bead that found in Chang’e-5 regolith. We report a silica fragment consisting of seifertite, stishovite, α-cristobalite, and silica glass and discuss their formation mechanisms. The coexistence of these two high-pressure minerals records different stages of the impact process and their host rock has experienced a peak shock pressure of ~11–40 GPa. Our finding confirms the retention of distant ejecta in Chang’e-5 landing site and emphasizes the significance of studies on lunar high-pressure minerals. The glass bead contains iron metal grains and shows concentration gradients of FeO and K2O (with or without Na2O) from their rims to centers. The compositional profiles exhibit error function-like shapes, which indicates a diffusion-limited mechanism. Our numerical modeling results suggest that the iron metal grains on the surface of the glass beads were generated through the reduction of FeO by elemental K and (or) Na produced during the impact events. Meanwhile, the iron metal grains inside the bead may have formed due to oxygen diffusion driven by redox potential gradients. We suggest that impact processes intensify the local reducing conditions, as evidenced by the presence of calcium sulfide particles within troilite grains that coexist with iron metal grains on the surface of the glass beads. This study provides insights into the oxygen diffusion kinetics during the formation of iron metal spherules and sheds light on the changes in redox conditions of lunar materials caused by impact events.