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Paper No. 14
Presentation Time: 8:00 AM-6:00 PM


BROWN, Sarah, Earth Sciences, Simon Fraser Universitty, 8888 University Drive, Burnaby, BC V5A 1S6, Canada, ANDREWS, Graham D.M., Department of Geology, California State University Bakersfield, 9001 Stockdale Highway, Bakersfield, CA 93311 and GIBSON, H. Daniel, Earth Sciences, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada,

The distribution of metamorphic rocks along the western margin of the Shuswap metamorphic complex (SMC) in southern British Columbia has encouraged recent debate about the importance of detachment faults as controls on SMC exhumation. Most of the western margin the SMC is bounded by a line of Eocene, en echelon, west-dipping detachment faults, including the Okanagan Valley fault (OVF). The existence of the OVF is supported by many structural, geochronological, and thermochronological studies. However, locally there are belts of semi-continuous upper plate stratigraphy found east of the fault trace within the footwall domain which have been interpreted to demonstrate the absence of the OVF in several places. This implies that exhumation of some parts of the SMC from the mid-crust occurred before the Cenozoic, which has significant implications for Cordilleran stratigraphy, geochronology, and tectonic models. This study provides a viable model to explain such occurrences using the morphology of non-planar detachment faults; the semi-continuous nature of upper plate units is, in part, controlled by synformal WNW-trending corrugations of the detachment surface.

New mapping of the OVF in the south reveals that it is strongly non-planar and forms major salients and embayments. The detachment surface dips between 0-30° parallel to the extension direction, and is deformed by open, upright, km-scale folds with axes both parallel and perpendicular to the extension direction. Gneisses within the shear zone and upper plate rocks occur in structural depressions and granitic rocks of the lower plate occur in highs, sometimes leaving gneissic carapaces. Erosion of salients and embayments created antiformal fensters and synformal klippe, respectively; many structural lows are associated with syn-extensional basins in the upper plate.

E-W trending synformal corrugations of the OVF preserve semi-continuous belts of upper plate stratigraphy that are demonstrably allochthonous in the study area. These synformal structures are parallel and similar scale to major belts of semi-continuous upper plate stratigraphy that have been inferred to be autochthonous to the north and south. We propose that such belts are significantly allochthonous, and that the OVF is present along the entire southwestern margin of the SMC.

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