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Structural geology of part of the Crooked Lake area, Quesnel Highlands, British Columbia

University of British Columbia

The Crooked Lake area, which lies at the boundary of the Omineca Crystalline Belt and the Intermontane Belt of the Canadian Cordillera, has been examined with close attention being paid to the detailed structural relations of the five lithologies that comprise this map area - the late Proterozoic Snowshoe Formation, the late Paleozoic Antler Formation, Upper Triassic to Lower Jurassic phyllites and phyllitic siltstones and a unit of micaceous quartzite, herein named the Crooked Lake Phyllite and the Eureka Quartzite, respectively, and the Upper Triassio to Lower Jurassic Takla Group. These units form a normal stratigraphic succession with respect to each other, though given data suggests far more complicated internal relations for each of the five units. The major contacts, where exposed, were seen to be continuous with internal foliation fabrics, sharply planar (to somewhat gradational in the case of the Takla base), and occasionally associated with mylonitic fabrics. These surfaces may represent faults, though sufficient data is not available for estimates of displacement magnitude and/or direction to be given. Structural features used to develop a relative timing sequence for internal progressive deformation of the Crooked Lake rock units include bedding surfaces and compositional layerings, foliations and cleavages, crenulations and other linear structures, minor fold forms and fold interference patterns, and fracture sets. The five distinct sets of deformation features that represent this timing sequence are the following: isoclinal, intrafolial, rootless folds of compositional layering found exclusively in the Snowshoe and Antler Formations (D1), open to tight folds of bedding, compositional layering, earlier foliations, and major contacts and a pervasive mica/amphibole foliation (D2 relative to Snowshoe and Antler), upright open to medium folds of earlier surfaces and major contacts (D3), gentle to open folds and kink folds of pervasive D2 foliation and compositional layering (D4), and northeasterly directed faults and fracture sets (D5). The metamorphic history of the Crooked Lake rock units has been deduced from extensive microscopic examination of textures and mineral assemblages. Barrovian-type metamorphism accompanied the first three deformational episodes; the first event may have reached amphibolite grade, the second episode reached temperatures of 500-575° at pressures of 4-7 kbars (from equilibria of pelitic and mafic assemblages), and the third approached only the lower to middle greenschist grade. Appendices have been included summarizing rock description data, structural data, fold form data, and stereo-photography of prominent structural features.

Text

2010-06-19

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http://hdl.handle.net/2429/25855

Geological Sciences

University of British Columbia

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