Oblique impacts into volatile sediments: ejection distribution patterns

Category Tectonic & Seismotectonic
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Gisler, Galen۱; Weaver, Robert P.۲; Gittings, Michael L.۳
Holding Date 11 October 2008

We have performed a series of three-dimensional calculations of the impact of large meteors into volatile sediments, and study the patterns of volatilisation, ejection, and expulsion as a function of impact angle and kinetic energy. The motivation was supplied by the Chicxulub crater at the K/T extinction boundary, but the results may be more generally applicable to impacts in other locations rich in volatiles. The target is conceived as a granite continental crust overlain by a carbonate platform and a thin layer of water, and the projectile a sphere of 10-12 km diameter. Impact angles of 15, 30, 45, 50, 60, and 90 degrees (to the horizontal) have been calculated for stony objects with velocities of 15 and 20 km/s, and 50 degrees for an icy object with a velocity of 60 km/s. For a given kinetic energy, steeper impacts produce larger craters, deeper excavation, and more symmetrical ejecta distributions, though butterfly ejecta patterns persist up to 60 degree inclinations. Acceleration of ejected material to above earth escape velocity frequently occurs in high-angle impacts, and an appreciable quantity of material can be moved great distances without suffering high pressures or temperatures. These calculations have been done with the Los Alamos/SAIC adaptive grid hydrocode Sage, on clusters at Los Alamos.