Geology and tectonics of the Nootka Island region, British Columbia

Nootka Island represents a portion of an accreted volcanoplutonic arc, on the western coast of Vancouver Island, British Columbia, of the Canadian Cordillera Insular Belt . This work provides a 1:110,000 scale geologic map and synthesises the regional tectonics. Two main protolith groups are evident on Nootka Island. Group 1 contains tholeiitic basalts that have within-plate / E-MORB element signatures. Limestones and siltstones comprise the intervening sedimentary strata. Group 2 comprises the youngest and consists of calc-alkaline, arc-like basalts, a plutonic suite, and minor hypabyssal bodies. Groups 1 and 2 resemble the Triassic Karmutsen and Jurassic Bonanza Formations. Plagioclase-hornblende thermometry and aluminium-in-hornblende barometry indicate metamorphism at up to 710o Celsius and 3.2 kbar of early Jurassic and older rocks. Whole rock argon dating of a basalt dyke post-deformation reveals crystallization ages of 168 Ma, and metamorphism at 158 Ma from an older Group 1 hyaloclastite