Tektite Origin in Oblique Impacts: Numerical Modeling of the Initial Stage

Abstract

Numerical modeling of the initial stage of the growth of a Bosumtwi- size crater was performed to reproduce the formation of impact melt from the upper 50 m of the target surface. Such melt, fragmented into em-sized particles, could produce the Ivory Coast tektite strewn field. Melt production from the surface layer of the target due to an asteroidal impact is studied with 3D numerical simulations for various impact angles (15°- 60° to horizon) and velocities (11 - 40 kms-1). For this range in impact angles and velocities, projectile sizes are within the range of 400 to 1100 m, according to the scaling law, and produce the same transient cavity of 9 km in diameter (final crater diameter is 10.5 km). The mass of the near-surface melt (tektite material) is almost constant for all impact velocities, but high velocity impact (>20 kms-1) accelerates the melted ejecta, whereas in the case of low-velocity impact (11 kms-1) all the melt is contained within the crater. The amount of tektite material increases with decreasing impact angle (with a maximum at 15°), but low angle impacts produce melt which is strongly contaminated by projectile material. Pure target melt arises during an impact with an "intermediate" impact angle of 30°- 50°. This melt is ejected from the growing crater with high velocity and may produce tektites after disruption into em-sized particles. The process of disruption is not considered in this paper, but it is shown that solid particles may be transported to distances of hundreds of km in the post- impact atmospheric flow.