Hydrocode modeling of Chicxulub as an oblique impact event

Since the confirmation that the buried Chicxulub structure is the long-soug ht K/T boundary crater, numerous efforts have been devoted to modeling the impact event and estimating the amount of target material that underwent me lting and vaporization. Previous hydrocode simulations modeled the Chicxulu b event as a vertical impact. We carried out a series of three-dimensional (3D) hydrocode simulations of the Chicxulub impact event to study how the i mpact angle affects the results of impact events. The simulations model an asteroid, 10 km in diameter, impacting at 20 km/s on a target resembling th e lithology of the Chicxulub site. The angles of impact modeled are 90 degr ees (vertical), 60 degrees, 45 degrees, 30 degrees, and 15 degrees. We find that the amount of sediments (surface layer) vaporized in the impact reach es a maximum for an impact angle of 30 degrees from the surface, correspond ing to less than two times the amount of vaporization for the vertical case . The degassing of the sedimentary layer, however, drops abruptly for a 15 degrees impact angle. The amount of continental crust melted in the impact decreases monotonically (a consequence of the decrease in the maximum depth of melting) from the vertical impact case to the 15 degrees impact. Meltin g and vaporization occur primarily in the downrange direction for oblique i mpacts, due to asymmetries in the strength of the shock wave with respect t o the point of impact. The results can be used to scale the information fro m the available vertical simulations to correct for the angle of impact. A comparison of a 3D vertical impact simulation with a similar two-dimensiona l (2D) simulation shows good agreement between vertical 3D and 2D simulatio ns. (C) 1999 Elsevier Science B.V. All rights reserved.