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Constraining the Timing and Magnitude of Extension along the Southern Okanagan Valley Fault, Southern BC

Sarah Brown
Simon Fraser University, Earth Sciences Burnaby, B.C. Canada [email protected]

Within the southern Okanagan Valley, medium- to high-grade metamorphic rocks are juxtaposed against nearly pristine volcanic and sedimentary rocks. Previous work has demonstrated that the nature of the boundary between these two disparate packages of rock is predominantly a <1 km-thick ductile shear zone, termed the Okanagan Valley fault (OVF). The shear zone grades abruptly from cataclasite to mylonite in amphibolite-grade gneiss, which, along with younger granitic intrusions, has undergone polyphase deformation and shows evidence of significant flattening. Linear fabric elements and kinematic criteria strongly indicate extensional motion through which the hanging wall has moved to the west.

Farther to the north, within the central portion of the OVF, recent work has attributed minimal displacement to the OVF and brought into question previous estimates for the magnitude of extensional displacement as determined to the south (~45-90 km) and north (~32 km. In order to better understand the nature of the OVF and constrain motion along the southern portion of the shear zone, we intend to conduct a comprehensive thermo-structural analysis. This work will comprise 1:50 000 scale mapping and strain analysis to constrain the dimensions and geometry of the shear zone. This study will be complemented by petrography, geothermobarometry, U-Pb geochronology (e.g., in situ dating of metamorphic and fabric-forming minerals) and Ar-Ar and fission track thermochronology to constrain the P-T-t-d path and rate of exhumation related to extension. Lastly, geochemistry of the gneissic rocks within the footwall will be used in an attempt to identify their protolith.


AAPG Search and Discovery Article #90070 © 2007 AAPG Foundation Grants in Aid