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Structural and stratigraphic relationships within the Tchaikazan River area, southwestern British Columbia : implications for the tectonic evolution of the southern Coast Belt Israel, Steve A.


New stratigraphic and structural data combined with U-Pb ages from the Tchaikazan River area requires the re-assignment of Early Cretaceous volcanic, volcaniclastic and sedimentary rocks from the Taylor Creek Group to three new informal successions, the Twin Creek, the Tchaikazan River and the Falls River successions. The Twin Creek succession is composed of marine sedimentary rocks that have been intruded by an aplitic/dacitic dyke which yielded a U-Pb age of 251 ± 16 Ma. The Tchaikazan River succession which is divided into a lower sedimentary facies and an upper volcanic facies, yields fossil ages indicating a Hauterivian or older age for the succession. The Falls River succession is dominated by volcanic breccias and bedded crystal tuffs and volcaniclastic sandstones of intermediate to felsic composition in the lower most portions and marine turbidites and shales in the upper parts. The age of the Falls River succession is not well constrained but is interpreted to be between Hauterivian and Albian. Previously unrecognized latest Paleozoic rocks of the Twin Creek succession are correlated with rocks located to the east and are interpreted as basement to the Cadwallader Terrane, and thus intimately associated with the southeast Coast Belt. The Early Cretaceous Tchaikazan River succession is correlated with rocks of the Eastern Waddington Belt which is correlated with the Early Cretaceous Gambier Group of the southwest Coast Belt. The study area represents the transition between volcanic dominated deposits of the southwest Coast Belt and sedimentary deposits of the Tyaughton Basin of the southeast Coast Belt. Early Cretaceous volcanic rocks of the study area are the source for mid-Cretaceous Taylor Creek Group sedimentary rocks of the Tyaughton Basin. Identification of high strain, sinistral shear zones supports the hypothesis that large scale, orogen parallel sinistral movement occurred from Hauterivian to mid-Cretaceous times. Ar-Ar dating of high strain sinistral shear zone records sinistral movement ca. 90 Ma. The relationships between rocks of the southeast Coast Belt with those of the southwest Coast Belt suggests that the two belts, and thus accretion of the Insular superterrane to the western margin of the Intermontane superterrane occurred in at least Hauterivian times.

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