Abstract

Exotic Tethyan faunas within the Cache Creek terrane contrast markedly with faunas and lithologic associations in the adjacent Quesnel and Stikine terranes. In northern British Columbia and southeast Yukon, all three terranes are enveloped in the north by pericontinental rocks of the Yukon-Tanana terrane, a geometry that imposes severe constraints on terrane assembly models for the northern Canadian Cordillera. Our solution to the problem invokes a northern join between the Stikinia and Quesnellia arcs through the Yukon-Tanana terrane, forming an orocline that encloses the Cache Creek terrane. This model involves (1) collision of a linear oceanic plateau at the cusp between Quesnellia and Stikinia, (2) anticlockwise rotation of Stikinia about an axis in the Yukon-Tanana terrane, (3) simultaneous enclosure of the Cache Creek ocean, and (4) emplacement of Quesnellia onto the margin of ancestral North America and the Cache Creek terrane onto Stikinia during final closure of the orocline. Early Mesozoic Paleomagnetic declinations in Stikinia are permissive of the large anticlockwise rotations predicted by the model. Similar large-scale rotations and ocean-basin enclosure are common features in the southwest Pacific. This model accounts for Paleozoic and younger linkages between Yukon-Tanana and both northern Stikinia and Quesnellia, the striking similarity between Triassic-Jurassic arcs east and west of the Cache Creek terrane, and the profound early Mesozoic deformational event in the Yukon-Tanana terrane.

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