Structural uplift beneath the Chicxulub impact structure

Abstract

Models of the central structure of large impact craters are poorly constrained, partly because of the lack of well-preserved terrestrial examples, and partly because of the extreme nature of impact events. Even large impact craters take only a few minutes to form, during which time rocks from the deep crust move upward many kilometers, interacting with impact melts and breccias before settling to their final position. We construct a new model of central uplift beneath the Chicxulub crater, based upon a well-constrained 3-D velocity model, obtained by jointly inverting seismic traveltime and gravity data. The input tomographic data set has good resolution, and many rays cross the central uplift in many directions. We use laboratory measurements to convert between velocity and density. Our velocity model possesses a high-velocity zone near the crater center, and velocity gradually decreases outside this zone. We use regional refraction data to interpret these velocities in terms of a broad 80-km-wide zone of structural uplift, in which the central rocks originate from the lower crust, and the surrounding rocks from the midcrust and upper crust. This is in contrast with previous models in which the zone of central uplift is either 40-50 km or 150 km wide. Our interpretation is consistent with scaling laws, Yucatan basement lithology, other velocity data, observations at similar-sized terrestrial craters, and dynamic modeling of peak ring formation. Our model of the uplift at Chicxulub can be used to help distinguish between competing models of effective target strength in numerical models of crater formation.

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