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The southern Canoe River area (lat 52° N, long 118°W), situated adjacent to the northeast flank of the Shuswap complex of British Columbia, was mapped in detail in conjunction with mineralogic and petrologic studies. This work is the basis for a section some 50 km long which illustrates the transition from the Rocky Mountain fold and thrust belt on the east to the metamorphic core zone of the Columbian orogen on the west.

A 5-km-thick succession of Proterozoic and Cambrian clastic rocks have been metamorphosed from biotite to sillimanite grade. Three sets of major structures are superimposed in the core zone, although only one major set of buckle folds and thrusts (which formed during the last two deformation phases) is predominant in the Rockies. The Malton Gneiss, a sheet of reworked basement, emerges in the northern part of the area. Mylonite marks the cover-basement decollement that was active early in the orogeny. Southwest-verging isoclinal recumbent nappes sheared off from the Malton Gneiss are refolded by two sets of northeast-verging folds. Isogradic surfaces were imposed late in the second deformation phase with a morphology related to heat flow. These surfaces were subsequently deformed and folded in a third deformation phase. In the core zone, staurolite disappears within the kyanite zone, and trondhjemite migmatite appears concommitantly. In the Rocky Mountains, stauro-lite persists to the appearance of fibrolite, and no migmatite is found. Geobarometric studies suggest metamorphic pressures in the core zone some 2-kb higher than in the western part of the Rockies and indicate that the vertical motion on the Purcell thrust was about 7 km. Contrasting stratigraphic thicknesses and facies as well as contrasting structural styles and histories across the fault suggest substantial horizontal shortening.

Temperatures and pressures estimated from element fractionation between coexisting minerals are consistent with the structural and isograd pattern.

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