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Deformational history, stratigraphic correlations and geochemistry of eastern Quesnel terrane rocks in the Crooked Lake area, east central British Columbia, Canada

University of British Columbia

The Eureka Peak are lies within the Quesnel terrane of the Intermontane Belt, adjacent to the Omineca Belt - Intermontane Belt tectonic boundary. It represents a convergent zone between the arc related Quesnel terrane and parautochthonous Barkerville terrane. The terrane boundary is defined by the Eureka thrust Underlying the area are middle Triassic to early Jurassic sedimentary and volcanic rocks, represented by the Quesnel River Group and Takla Group, respectively. Petrologic and geochemical studies of the Takla Group volcanics suggest protoliths of island arc and marginal basin affinities. The Quesnel terrane structurally overlies Hadrynian to early Paleozoic metasediments of the Snowshoe Group (Barkerville terrane). The base of the Quesnel terrane is marked by mylonitized mafic and ultramafic rocks of the Crooked Amphibolite. Correlation of features across the plate boundary has established the structural continuity in the region, and recognition of structural phases common to both terranes which developed in response to plate convergence. The deformational history involves two phases of coaxial folding of a mechanically heterogeneous lithologic sequence, accompanied by extensive pressure solution, and later overprinting by NW trending extensional fractures. Synchronous to F₁, detachment surfaces developed along major stratigraphic contacts due to contrasting Theologies of adjacent lithologies. Second phase deformation established the regional map pattern, folding the detachment surfaces and the tectonic boundary. Synchronous to deformation, regional metamorphism is evidenced by the growth of minerals characteristic of amphibolite fades in the Barkerville terrane, and greenschist fades in the Quesnel terrane. Dissipation of heat from the underlying sequences is suggested by the rapid transition in metamorphic grade observed across the boundary. Cleavage surfaces have acted as a locus along which pressure solution has occurred, providing a pathway for the escape of fluids generated during metamorphism. Deposition of material within extensional fractures occurred throughout the deformational history. Fracturing is prominent adjacent to the Quesnel River Group and Takla Group contact, where the viscosity contrast between the two lithologies provided an effective barrier to extensive fluid flow. Concentration of fluids along the contact may have had a buoying effect on the volcanics, allowing furter eastward translation during deformation.

Text

2010-07-07

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http://hdl.handle.net/2429/26170

Geological Sciences

University of British Columbia

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