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Cache Creek and Nicola Groups near Ashcroft, British Columbia

University of British Columbia

Detailed mapping near the type area of the Cache Creek Group in southern British Columbia has led to significant changes in the distribution of Cache Creek and Nicola rocks. Much of what was called Cache Creek Group is now considered to be part of the Upper Triassic Nicola Group. Several criteria can be used to distinguish the two groups. These include: 1) lithologic differences, 2) fossil information, 3) structural style, and 4) metamorphic history. The Cache Creek Group is subdivided into three mappable, fault-bounded units and appears to be a tectonic melange over much of its extent. A deformational event produced isoclinal folds, a phyllitic foliation in some lithologies, and was accompanied by metamorphism with variable pressure-temperature conditions. Mineral assemblages support conditions from temperatures less than 250°C and pressures of 4 kb or less to transitional blueschist conditions: T = 350° C and P = 6 kb. In contrast, the Nicola Group is characterized by hydrothermal alteration and the lack of a pervasive secondary fabric. It does not have the blocks in a sheared matrix tectonostratigraphic style typical of the Cache Creek Group. The two units were brought together along the Martel Fault, probably a thrust, during late Lower or early Middle Jurassic time. Deformation and melange development in the Cache Creek Group predates this event. Distribution of Cache Creek and Nicola rocks and their relationship to each other during Upper Triassic time are still not clear.

Text

2010-03-02

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http://hdl.handle.net/2429/21359

Geological Sciences

University of British Columbia

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