MOHO UPWARPING BENEATH THE CHICXULUB IMPACT CRATER

In 1996 and 2005 we conducted onshore-offshore seismic experiments to constrain the structure of the Chicxulub impact crater; these datasets can provide constraints on both the crustal and mantle structure of the crater. We inverted more than 50,000 PmP reflection picks recorded on 191 ocean bottom and land seismometers for Moho structure beneath the crater. The Moho is associated with a velocity discontinuity to velocities ~8.0 km/s and it typically follows the crust-mantle boundary. There are two primary features in the Moho map: 1) a regional deepening of the Moho from ~33 km in the west to ~35-37 km in the east, and 2) upwarping of the Moho by ~1.5 km near the center of the crater. The Moho depths also show a downwarping of the Moho of ~0.5 km at a radius of 25-30 km from the crater center.

Moho upwarping has also been observed beneath lunar craters, and has been attributed to rapid mantle uplift following impact (e.g., Taylor, 1982; Neumann et al., 1996). These craters are not in isostatic equilibrium, implying that the lithosphere is strong enough to maintain these stress states. The Chicxulub crater is also not in isostatic equilibrium. Scaling laws place the depth of the transient cavity at 35-40 km below the transient crater rim for the Chicxulub impact crater (Morgan et al., 1997). This depth suggests that deformation from the impact may have reached the base of the crust, although it should be noted that transient cavity depth is measured from the transient crater rim which could have had a maximum uplift of ~8 km (Morgan et al., 1997). Asthenospheric flow is a component of the ring tectonic theory of multiring crater formation (Melosh and McKinnon, 1978); this flow may result in the Moho topography constrained by our data. The relationships between ring locations, crustal faulting, and Moho topography should provide new insights into the mechanics of multiring crater formation.

References: Melosh, H.J. and W.B. McKinnon (1978), Geophys. Res. Lett. 5, 985-988. Morgan, J. et al. (1997), Nature 390, 472-476. Neumann et al. (1996), J. Geophys. Res., 101, 16,841-16,843. Taylor (1982), Planetary Science: A Lunar Perspective.