Paleotectonic setting of the Takla Group volcano-sedimentary assemblage, Stikine Terrane, McConnell Creek map area, north central British Columbia
Gale, Vanessa G.
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The Upper Triassic Takla Group volcano-sedimentary assemblage is located within the Stikine Terrane of the Intermontane Belt in the Canadian Cordillera. In the McConnell Creek area, the assemblage consists of clinopyroxene and plagioclase porphyritic basaltic to andesitic effusive and pyroclastic rocks that are interlayered with sandstones, siltstones, argillites and conglomerates. Relatively immobile trace element analysis indicates that rocks are subalkaline and compositionally intermediate between tholeiitic and calc-alkaline. Chondrite normalized rare earth element (REE) plots show minor light REE enrichment consistent with subalkaline tholeiitic to calc-alkaline magmas. Mantle normalized trace element patterns display a pronounced Nb depletion and large ion lithophile element enrichment that suggest magmatism was subduction-related. A coeval volcano-sedimentary assemblage occurs in fault contact with the Takla Group of the Stikine Terrane. This group, also named Takla, occurs in the adjacent Quesnel terrane and is also subduction related. In the past, the two have been interpreted as a single cogenetic unit as well as two separate, non-related units. Similarities in relatively immobile trace element abundances indicate that the eastern and western Takla Groups are broadly geochemically alike and may have similar source compositions and melt histories. However, field relations preclude genetic association, The chemical resemblance between the two groups emphasizes larger scale similarities noted between the Stikine and Quesnel terranes. Keywords: Takla Group, Stikine Terrane, arc-magmatism, REE, Nb-depletion, Quesnel Terrane Pages: 158 Supervisors: Jarda Dostal and Marcos Zentilli