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Age and geological setting of Gold Creek gneiss, crystalline basement of the Windermere Supergroup, Cariboo Mountains, British Columbia

1991; NRC Research Press; Volume: 28; Issue: 8 Linguagem: Inglês

10.1139/e91-109

1480-3313

Donald C. Murphy, Robert Walker, R. R. Parrish,

Geochemistry and Geologic Mapping

Gold Creek gneiss, the most recently discovered body of crystalline basement in the Canadian Cordillera, is a northwest-trending granitic to dioritic orthogneiss straddling the eastern end of the Canoe River valley, near the southeastern end of the Cariboo Mountains. U–Pb geochronometry of zircons from two samples of quartz diorite orthogneiss from two separate localities yielded similar, nearly linear, discordant arrays with upper intercepts of 2.08 Ga. The patterns of discordance in both samples preclude assigning a precise age, although a date between 2.0 and 2.1 Ga is geologically reasonable.North of Canoe River, Gold Creek gneiss is inferred to be nonconformably overlain by quartzite and marble, which in turn are inferred to be unconformably overlain by a conglomerate- and diamictite-bearing unit at the base of the lower Kaza Group of the Windermere Supergroup. In contrast with other exposures of basement and cover in the area, neither contact is marked by anomalously high strain or mylonitic rocks. Gold Creek gneiss therefore represents the crystalline basement upon which the Windermere Supergroup was deposited.Gold Creek gneiss occurs in a multiply deformed domain bounded on the north by the Purcell thrust and on the east by the North Thompson – Albreda fault (NTAF), an Eocene, down-to-the-west normal fault. Gneiss and overlying Windermere Supergroup are folded by the Canoe River anticline and lie in the hanging wall of a recently identified folded, premetamorphic, southwest-vergent shear zone, the Sir Arthur Meighen thrust. The footwall consists of Mica Creek succession, a sequence of metaclastic rocks, amphibolite, and marble which is in part equivalent to the Windermere Supergroup but may include younger rocks. Hanging wall and footwall rocks and structures are folded by Early Cretaceous, synmetamorphic, northeast-vergent folds.Gold Creek and Malton gneisses are both in the hanging wall of the Purcell thrust but on opposite sides of the NTAF. Strike separation of the Purcell thrust across the NTAF suggests 0.5–4.5 km of normal displacement, affirming earlier estimates of displacement based on geobarometry. This amount of displacement and the consideration that Gold Creek gneiss is thrust over Mica Creek succession, which structurally overlies Malton gneiss along Malton décollement, preclude the interpretation that Gold Creek and Malton gneisses were physically continuous prior to displacement on the NTAF. It is more likely that Gold Creek gneiss lies in the hanging wall of Malton décollement and would restore an unknown distance to the southwest along it. Gold Creek gneiss also lies in the hanging wall of Monashee décollement and would restore at least as far southwest as the western edge of Monashee Complex, or over 100 km.