HR: 0800h
AN: T11B-0569    [Abstracts]
TI: Whole crustal response to Late Tertiary extension near Prince Rupert, British Columbia
AU: * Hollister, L S
EM: linc@princeton.edu
AF: Princeton University, Dept. of Geosciences, Princeton, NJ 08544, United States
AU: Diebold, J
EM: johnd@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory, P.O. Box 1000, Rte 9W, Palisades, NY 10964, United States
AU: Das, T
EM: triparna.das@conocophillips.com
AF: Princeton University, Dept. of Geosciences, Princeton, NJ 08544, United States
AB: The 1994 wide angle offshore-onshore seismic component of ACCRETE (funded by NSF-Continental Dynamics program) led to exceptional Vp and Vs images of the crust under the Coast Mountains of British Columbia (Morozov et al. 2003). As part of this experiment, some 1700 km of crust penetrating multichannel seismic (MCS) data were collected, and a portion of these data imaged features attributable to Late Tertiary extension in east Dixon Entrance, British Columbia. The data show grabens up to 3 km deep, arches of the Moho with relief up to 3 km (Moho depths 24.8 to 27.5 km), mid to lower crustal sub horizontal reflecting horizons, mid crustal west- dipping reflecting packages interpreted as shear zones, and a highly reflective Moho above the arches. We conclude these features formed during east-west directed extension. Based on dated extension-related features reported for the region, this extension occurred between 40 and 20 Ma and may have been concentrated between 25 and 20 Ma (Dehler et al. 1997). We estimate a minimum amount of thinning due to the extension in east Dixon Entrance to be 30% if the Early Tertiary crustal thickness had been 34 km, which was the thickness of the adjacent crust to the east during the Late Tertiary. The grabens, reflective Moho, lower crustal reflectivity, west dipping lower crustal reflective packages, and arches in Moho imply flow of the whole crust above a stronger mantle lithosphere during the extension. Our data thus confirm and extend the interpretation of crustal extension by Lowe and Dehler (1995) and Dehler et al. (1997) for Hecate Strait and Queen Charlotte Sound. During the Late Tertiary extension, pre-existing zones of structural weakness appear to have controlled the pattern of crustal thinning and of relief on Moho. The offshore-onshore and MCS data of ACCRETE may be the last such data collected by an academic group in coastal British Columbia, using airguns as a sound source, according to the notice of termination of the Batholiths marine seismic experiment (see Public Affairs abstract by Hollister for this meeting).
DE: 3025 Marine seismics (0935, 7294)
DE: 7205 Continental crust (1219)
DE: 8011 Kinematics of crustal and mantle deformation
DE: 8031 Rheology: crust and lithosphere (8159)
DE: 8109 Continental tectonics: extensional (0905)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting