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UBC Theses and Dissertations

Geology of the Mount Breakenridge area, Harrison Lake, B.C. Reamsbottom, Stanley Baily

Abstract

The metamorphic rocks of the Breakenridge and Cairn Needle Formations are correlated with the Upper Paleozoic and Mesozoic (Jurassic) strata respectively. Those of the Chilliwack Group - Peninsula Formation range in age from Upper Paleozoic to Lower Cretaceous. A gneissic granodiorite on Mount Breakenridge is cored by a younger (Early Tertiary) porphyritic quartz diorite. The Scuzzy granodiorite (Upper Cretaceous) is the main plutonic rock of the area. Between the Jurassic and Mid-Cretaceous the formations were folded into northwest trending antiforms and synforms. Three phases of folding are recognised. Major faults were produced in Mid-Cretaceous time. Contemporaneous with the folding the rocks were migmatized and regionally metamorphosed to form a kyanite-sillimanite facies series in which the metamorphic grade increases rapidly from South to North. The mineral assemblages in pelitic gneisses are considered to have approached equilibrium. The bulk composition of these gneisses may not only have controlled the presence of staurolite but also, through the opaque minerals present, the fs₂,fo₂ of the coexisting fluid phase. Extreme gradients in fluid phase composition (X CO₂) are demonstrated to have existed during the metamorphism of closely associated calc - silicate and dolomitic limestone. An episode of contact metatnorphism, which produced andalusite and sillimanite bearing schists was associated with the emplacement of the Scuzzy fluton. (U. Cretaceous).

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