Northern Cordilleran Volcanic Province - Geology - Terranes and Boundaries

Terranes and Boundaries

The bedrock of the Northern Cordilleran Volcanic Province consists of four large terranes, known as Stikinia, Cache Creek, Yukon-Tanana and Cassiar. Stikinia is a sequence of late Paleozoic and Mesozoic aged volcanic, plutonic and sedimentary rocks interpreted to have been created in an island arc environment that were later placed along a pre-existing continental margin. The Cache Creek Terrane is believed to have formed widely in a pre-existing oceanic basin. It comprises late Paleozoic to Mesozoic aged oceanic melange and abyssal peridotites intruded by younger granitic intrusions. The Yukon-Tanana and Cassiar terranes consist of shifted sedimentary and metamorphic rocks that were derived from the North American continent.

The southern boundary of the Northern Cordilleran Volcanic Province is parallel with southwestern Stikinia and is characterized by separate volcanic vents and erosional remains of lavas south of the small community of Stewart. The southern boundary of the Northern Cordilleran Volcanic Province also parallels with a gap in modern volcanism and the supposed northern boundary of the Cascadia subduction zone, defined by the eastward extension of the northern edge of the subducting Juan de Fuca Plate. These two zones divide the Northern Cordilleran Volcanic Province from modern volcanic zones further south, including the broad Chilcotin Plateau, the east-west trending Anahim Volcanic Belt and the monogenetic Wells Gray-Clearwater volcanic field in the British Columbia Interior. The eastern boundary of the Northern Cordilleran Volcanic Province is bounded by the Cassiar Terrane and is adjoined by a cluster of volcanic plugs in central British Columbia. The northern and western boundaries are adjoined by the Yukon-Tanana and Cache Creek terranes where there lies volcanics in eastern Alaska and weathered remains of lava flows just north and west of Dawson City in west-central Yukon.