Shock re-equilibration of fluid inclusions in crystalline basement rocks from the Ries crater, Germany

Abstract

This study examines the effects of shock metamorphism on fluid inclusions in crystalline basement target rocks from the Ries crater, Germany. The occurrence of two-phase fluid inclusions decreases from shock stage 0 to shock stage 1, while single-phase inclusions increase, likely as a result of re-equilibration. In shock stages 2 and 3, both two-phase and single-phase inclusions decrease with increasing shock stage, indicating that fluid inclusion vesicles are destroyed due to plastic deformation and phase changes in the host minerals. However, quartz clasts entrained in shock stage 4 melts contain both single-phase and two-phase inclusions, demonstrating the rapid quenching of the melt and the heterogeneous nature of impact deformation. Inclusions in naturally shocked polycrystalline samples survive at higher shock pressures than those in single crystal shock experiments. However, fluid inclusions in both experimental and natural samples follow a similar trend in re-equilibration at low to moderate shock pressures leading to destruction of inclusion vesicles in higher shock stages. This suggests that shock processing may lead to the destruction of fluid inclusions in many planetary materials and likely contributed to shock devolatilization of early planetesimals. © The Meteoritical Society, 2006.