Shock metamorphism on the ocean floor (numerical simulations)

Impact craters are unknown in deep-ocean basins. Important reasons for this are that the ocean crust is younger than continents and the impacts are weakened by the water column. Laboratory experiments can show specific features of water impacts. However, impact velocities are too small (< 5 km/s) with respect to planetary-scale asteroidal impacts (11.2-40 km/s). Most numerical simulations of impacts deal primarily with continental impacts. We use high-resolution numerical simulations to investigate peak pressures in oceanic-floor rocks for various asteroidal impact velocities (1540 km/s) and for various water-depth/projectile-diameter ratios (1-4). Vertical and oblique impacts are considered. Tracer particles are used to define the amount of shock-modified material. As the shock compression of natural rocks results in shock metamorphic effects, impact events may be identified in the course of oceanic-floor drilling even in the case of total crater degradation. For an Eltanin-like impact into a 4-km deep ocean, the late stage of ejecta evolution is also considered. (C) 2002 Elsevier Science Ltd. All rights reserved.