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The Windermere Supergroup (WSG) is exposed extensively throughout western North America, extending from northwestern Mexico northward through the western United States, along the length of the Canadian cordillera (1), and into the Yukon-Alaska border region (15). The term Windermere Supergroup was coined by Walker (1926) for the mostly sedimentary rocks exposed in the Windermere Valley of southern British Columbia. Subsequent stratigraphic studies, however, have used a variety of terms to describe these rocks, including Miette Group in the western Rocky Mountains, Horsethief Creek Group for exposures in the Purcell Mountains, Kaza and Cariboo Groups in the Cariboo Mountains, and locally Mica Creek assemblage in high grade rocks of the Monashee Complex.

Stewart (1972) was the the first to suggest that the WSG consisted of two parts: A lower sequence comprising laterally discontinuous strata that accumulated synchronous with rifting, and an upper sequence characterized by laterally continuous units interpreted to have accumulated during postrift thermal relaxation. Subsequently, Ross (1991) suggested that the Windermere comprises the sedimentary and volcanic record following the break-up of the supercontinent Rodinia and the formation of the proto-Pacific Ocean >700 Ma. Present-day preservation and exposure of the WSG is the result of Mesozoic deformation during formation of the cordilleran orogenic belt.

In the southern Canadian cordillera, the WSG unconformably overlies Mesoproterozoic sedimentary rocks of the Belt-Purcell Supergroup (1.5–1.4 Ga; 5) or crystalline basement that ranges in age from 2.2–0.73 Ga (4).

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