HR: 0800h
AN: T11B-0571    [Abstracts]
TI: Seismic Constraints on the Structure and Evolution of the Coast Plutonic Complex in Western British Columbia
AU: * Hansen, S M
EM: shansen1@uwyo.edu
AF: University of Wyoming, 1000 E. University Ave., Laramie, WY 82071,
AU: Peck, J L
EM: jpeck@uwyo.edu
AF: University of Wyoming, 1000 E. University Ave., Laramie, WY 82071,
AU: Stachnik, J C
EM: jstachni@uwyo.edu
AF: University of Wyoming, 1000 E. University Ave., Laramie, WY 82071,
AU: Dueker, K
EM: dueker@uwyo.edu
AF: University of Wyoming, 1000 E. University Ave., Laramie, WY 82071,
AB: The teleseismic component of the Batholith project consisted of 44 broadband seismometers deployed for 15 months in two line arrays in western British Columbia. The arrays traversed the Coast Shear Zone (CSZ) which defines the western extent of the Eocene granitic flare-up that formed the Coast Mountain batholith (CMB). Body wave tomography results show 5% peak to peak p-wave velocity variations and 10% s-wave velocity variations in the crust and upper mantle. The velocity variations in the crust correlate well with the different tectonic terranes. The outboard Wrangellia terrane and the inboard Stikina terrane are generally fast while the CMB is slow, consistent with velocity contrasts between mafic and intermediate composition crust. Receiver function images show significant structural differences along strike of the CSZ. On the south line, the crust thickens from 25km in the outboard Wrangellia terrane to 35km under the CMB. This crustal welt probably formed in the late cretaceous during a period of transpression in which Wrangellia underthrust the inboard terrane. In stark contrast, the north line has a relatively flat moho and the crust is 25-30km thick. We attribute this contrast to the differential exhumation history along the CSZ. Massive exhumation exposed the mid-crustal Central Gneiss Complex at the north line in the early Eocene. Initial s-wave velocity maps from diffusive surface wave inversion correlate well with the receiver function images and show a high velocity anomaly below the batholith.
DE: 7205 Continental crust (1219)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting