Structural and Metamorphic History of the Leech River Shear Zone, Vancouver Island, British Columbia

The Leech River Shear Zone (LRSZ) on southern Vancouver Island separates the metasedimentary schists of Complex (LRC) from accreted oceanic plateau Siletz-Crescent terrane. juxtaposition these rock units suggests a possible origin as subduction plate boundary but tectonic context LRSZ has yet to be fully established. We present field, microstructural, petrological, and geochronological observations that constrain structural metamorphic history LRSZ. mylonite zone straddles lithologic contact between LRC basalts Foliation orientations, steeply plunging stretching lineation, kinematic indicators all suggest reverse-sinistral motion. Compositions garnet in schist amphibole metabasalt record synkinematic growth at temperature pressure conditions 550°C–570°C 450–490 MPa. These require elevated geotherms are consistent with models position Kula-Farallon Ridge Yellowstone Hotspot region Eocene (∼50 Ma). Detrital zircon U-Pb age distributions for Schist have Paleocene maximum depositional ages similar Upper Nanaimo Group unconformably overlies Wrangellia Our support early deposition trench/slope environment followed by underthrusting underplating. results establish exhumed paleo-plate interface was active during subduction.