Magmatic and tectonic history of the Leech River Complex, Vancouver Island, British Columbia: Evidence for ridge-trench intersection and accretion of the Crescent Terrane

Abstract

The Leech River Complex, part of the Pacifi c Rim Terrane, is a Cretaceous metasedimentary and metaigneous assemblage on southern Vancouver Island. The Leech River Complex is fault-bounded between the Eocene Metchosin Igneous Complex to the south (part of the Crescent Terrane) and the Paleozoic to Jurassic Wrangel Terrane to the north and provides critical information on the evolution of the central part of the western North American forearc in Cretaceous through Eocene time. Single detrital zircons from the metasedimentary component, known as the Leech River Schist, give U-Pb interpreted ages that range from Precambrian to ca. 103 Ma, indicating a varied source region and a probable Early Cretaceous depositional age. U-Pb geochronology and fi eld investigations indicate at least two magmatic-metamorphic events in the Leech River Complex: one during the Late Cretaceous, and the other during the early Middle Eocene. The peraluminous Jordan River metagranodiorite, a fi ne-grained biotitic stock and related dikes intruded the Leech River Complex at ca. 88 Ma, during the older magmatic event. Metamorphic pressure-temperature conditions of 525–550 °C and 2–3 kbar are recorded in the contact aureole. The later event occurred during emplacement of the Walker Creek intrusions, a suite of peraluminous tonalite, trondjhemite, and granodiorite dikes that intruded the Complex at ca. 51 Ma and produced a similar metamorphic aureole. Both intrusive suites have