Silverthrone Caldera - Geology

Geology

Silverthrone is part of the Pemberton Volcanic Belt, which is circumscribed by a group of epizonal intrusions. At another deeply eroded caldera complex called Franklin Glacier Volcano, the Pemberton Volcanic Belt merges with the Garibaldi Volcanic Belt, a northwest-trending belt of volcanic cones and fields extending from near the Canada–United States border east of Vancouver on the British Columbia Coast. The intrusions are thought to be subvolcanic bodies associated with a volcanic front that was active in the Miocene, during early stages of subduction of the Juan de Fuca Plate. With the notable exception of King Island, all the intrusive and eruptive rocks are calc-alkaline, mainly granodioritic bodies and dacite ejecta.

On a broader scale, the intrusive and eruptive rocks are part of the Coast Plutonic Complex, which is the single largest contiguous granite outcropping in North America. The intrusive and metamorphic rocks extend approximately 1,800 kilometres (1,100 mi) along the coast of British Columbia, the Alaska Panhandle and southwestern Yukon. This is a remnant of a once vast volcanic arc called the Coast Range Arc that formed as a result of subduction of the Farallon and Kula Plates during the Jurassic-to-Eocene periods. In contrast, Garibaldi, Mount Meager, Mount Cayley and Silverthrone areas are of recent volcanic origin.