Abstract

The Shuswap Metamorphic Complex consists of three parts, each with unique stratigraphy and orogenic evolution, separated by major faults of diverse nature and having in common only a post-late Mesozoic tectonic history. The first part, the Monashee Complex, is a possible extension of the Precambrian Shield that contains limited evidence of Mesozoic orogenesis and that was rapidly uplifted during the Cretaceous to Paleogene. The Monashee Décollement, a warped mylonite zone interpreted as a regional thrust fault active through the Middle Jurassic, separates this complex from the second part, which contains rocks correlative with Hadrynian to late Paleozoic strata of the pericratonic prism. The third part, the Okanagan Complex, straddling the 49th Parallel from the Okanagan Valley to Kootenay Lake, contains the probable exhumed roots of a Mesozoic magmatic arc built upon possible North American continental and transitional crust and includes late Paleozoic and early Mesozoic suspect terranes.The Columbian Orogen formed during westward drift of the craton into a continent of accreted elements. Response of the craton, attenuated during at least two episodes of Proterozoic rifting, and its overlying sedimentary prism to underthrusting from the east and simultaneous collision with an accreting collage from the west took place in two stages. First, attenuated crust was telescoped and thickened to its approximate original configuration while westernmost parts of the bordering prism were deformed and metamorphosed (the Jura-Cretaceous Columbian Orogeny that affected the Okanagan Complex and strata above the Monashee Décollement). Second, the thickened crust, the deformed prism, and platformal strata were thrust eastward (the Late Cretaceous – Paleocene Laramide Orogeny that formed the Rocky Mountains Thrust Belt). Waning convergent tectonism led to ascendancy of crustal extension (primarily in the Okanagan Complex) and final uplift of cratonic massifs.

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