Simulation experiments for shocked primitive materials in the Solar System

Shock recovery experiments were conducted on porous mixtures (initial porosity 35 ± 5%) in silicate–metal and silicate–metal–sulfide systems in an attempt to simulate impact phenomena of unconsolidated porous materials similar to ordinary chondrites in a wide range of shock pressures from 20 to 70 GPa. The textures and chemical compositions of shocked samples were investigated in detail. Features such as grain deformation, fracture density decrease, and heterogeneous meltings are found. At < 30 GPa, mechanical effects of the shock process, such as silicate fracturing and metal elongation, are dominant. Morphological analysis of metal grains in shocked samples reveals good correlation between the degree of deformation and the shock pressure. The metal grain aspect ratio may be a good indicator of shock pressure. At higher pressures, thermal effects, which are enhanced in the shock compression of porous media, become prominent. Above 30 GPa, silicate grain fractures disappear, and silicate darkening dominates. Shock-induced melting in the shock veins and melt networks is observed and interpreted as localized in situ melting features, the heat source of which is frictional heating between grains. Thin veins and melt pockets of sulfide–metal melt are the principal characteristics in this type of sample. Melting features of metal–sulfide systems alter the spectral property of meteoritic bodies. The initial porosity of a target may have been an important factor in impact processes in the early Solar System.