[Baps] CORRECTION Chicxulub talk Wed Jan 16, 11 AM, Peggy Vermeesch

[Sarah Stewart-Mukhopadhyay]

Correct Date:

EPS Planetary Science Talk
> Wednesday, January 16
> 11:00 - 12:00
> Hoffman Laboratory, Faculty Lounge (4th floor)
> *
> Broad zone of structural uplift beneath the Chicxulub impact structure**
> *Peggy M. Vermeesch and Joanna V. Morgan
>
> 1) University of Texas Institute for Geophysics, Austin, Texas 78758, USA
> 2) Department Earth Science and Engineering, Imperial College London, SW7
> 2AZ, UK
>
>
> Although meteorite impacts are a ubiquitous and fundamental geologic
> process affecting the terrestrial planets, they are relatively poorly
> understood. The Earth has comparatively few pristine craters, and only three
> large (>150 km diameter) impact basins: Chicxulub, Vredefort and Sudbury, of
> which Chicxulub is the best preserved.
>
> Seismic reflection data acquired across the offshore half of the Chicxulub
> crater in 1996 and 2005 reveal clear images of the target rocks and impact
> basin. There is no reflection data across the crater center, and therefore
> central crater structure at Chicxulub, and large impact craters in general,
> is a matter of some debate. Although we know that large craters possess
> particular features (structural uplift, impact melt rocks, impact breccias,
> a peak ring), the precise geometric relationship between these features
> remains uncertain. Models of Chicxulub constructed from geophysical data are
> diverse in part due to the lack of terrestrial examples and the inherent
> ambiguity of geophysical modeling, and also because drill holes within the
> impact basin have penetrated the uppermost crater deposits only.
>
> We have constructed a new model of central crater structure across
> Chicxulub, based upon inversions of geophysical data. Previous
> interpretations of the width of structural uplift beneath Chicxulub vary
> from 50 to 150 km. In 1996 and 2005 we acquired tomographic seismic and
> gravity data, and have performed both 3D travel-time and joint gravity and
> travel-time inversions to produce a well-constrained velocity model across
> the central crater. This model possesses a 15-25 km wide high-velocity-zone
> near the crater center, where rock velocity is >6.3 km/s below 5 km depth
> and, outside this zone, velocity gradually decreases. We 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 mid and upper crust.
>
> The new velocity model across the central crater, which incorporates
> gravity constraints, is a major advance. The resolution of the new 3D
> tomographic velocity model significantly surpasses that of the 1996 model.
> Our interpretation of the velocities from the joint travel-time and gravity
> inversion in terms of lower, mid and upper crustal rocks is supported by
> regional refraction data, general crustal models, the lithology of basement
> clasts in Chicxulub impact breccias, impact scaling laws, observations at
> the similar-sized crater Vredefort, and dynamic models of crater formation.
>
>
>
> --
> Sarah T. Stewart-Mukhopadhyay
> Asst. Professor of Planetary Science
> Dept. of Earth & Planetary Sciences, Harvard University
> Office 617.496.6462 Lab 617.496.5782 Fax 617.384.8249
> sstewart at eps.harvard.edu
> http://www.fas.harvard.edu/~planets/sstewart/
> <http://www.fas.harvard.edu/%7Eplanets/sstewart/>
>
> Assistant: Ben Tobin, tobin at eps.harvard.edu, 617-495-2350
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