The role of the Shuswap Metamorphic Complex in Cordilleran tectonism: a review

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.

Density, temperature, and rheological models for the southeastern Canadian Cordillera: implications for its geodynamic evolution

“…Continuity between basement rocks exposed in the Monashee Terrane and the cratonic rocks beneath the Foreland Belt is assumed. Such continuity has been suggested by previous workers on the basis of structural and isotopic similarities (see Okulitch 1984 for a review) and interpretations of recently collected Lithoprobe seismic reflection data (Cook et al 1992).…”

Formation of the Shuswap metamorphic core complex during late-orogenic collapse of the Canadian Cordillera: Role of ductile thinning and partial melting of the mid-to lower crust

“…Based on tratigraphic correlation and recognition of major tectonic contacts, the Shuswap MCC has been divided into three crustal units (Ree or & Moore, 1971;Okulitch, 1984;Brown & Journeay, 1987;Carr, 1991bCarr, , 1992. The high-grade metamorphic core of the complex comprises parautochthonous basement gneisses overlain by allochthonou amphibolite-facie unit above the Monashee decollement.…”

“…Petrographic analysis of the high-grade rocks of the Shu wap MCC indicate widespread occurrence of synkinematic sillimanite after kyanite and roughly concentric distribution of isograds around the domes cored by the basement gneisses (Reesor & Moore, 197 I;Read & Brown, 198 J;Okulitch, 1984;Carr, 1992 thermore, REE pattern of the peraluminous granite suggest that they could have been generated by partial melting of the metapelites found in the Selkirk allochthon and in the basement gneis es (Sevigny et al, 1989). (Parkinson, 1991), and yielding ages from 1.87 Ga to 2.10 Ga for orthogneisse (Wanles & Reesor, 1975;Parkinson, 1991;Armstrong el al., 1991).…”

“…In the northern part of the Cordillera, most authors attributed the ductile fabric and the formation of the Cordilleran metamorphic core complexes to Mesozoic to Paleogene contraction associated with crustal thickening (Brown & Read, 1983;Mattauer el ai., 1983;Okulitch, 1984;Brown & Journeay, 1987) whereas the importance of Tertiary extension overprint was emphasised in the southern part (Armstrong, 1972;Davis & Coney, 1979;Wernicke, 1985). We Mathews, 1981;Parrish et al, 1988).…”

Westerly derived Early Cretaceous gold paleoplacers in the Western Canada foreland basin, southwestern Alberta: tectonic and economic implications

“…11) (Panteleyev 1991;Dawson et al 1991). The age of these veins is unknown, but many cut across the fabric associated with Middle Jurassic metamorphism (Fyles 1984;Dawson et al 1991 ;Okulitch 1984). The metamorphic rocks were progressively uplifted over the following 50-60 Ma, as shown by the spread of KIAr uplift ages (Fig.…”