PALEOZOIC PALEOGEOGRAPHY OF THE WESTERN MARGIN OF LAURENTIA AS RECORDED IN THE DISPLACED ROCKS OF FORELAND THRUST AND FOLD BELT OF THE SOUTHEASTERN CANADIAN CORDILLERA

A new palinspastic map of an 850-km segment of the foreland thrust and fold belt between northern Montana (~48⁰ N) and northeastern B.C. (~54⁰ N) is based on restorations of six published balanced regional structure sections. This map shows the hanging-wall traces of the main thrust faults in both their present and their palinspastically restored locations. It provides a framework for reconstructing the 3-D shapes, locations, and mutual relationships among: 1.) the 1500-1400 Ma Belt-Purcell intracontinental rift basin 2.) the 850-600 Ma Windermere intracontinental rift basin, and 3.) the Cordilleran miogeocline (an early Cambrian and younger continental terrace sedimentary wedge), and also for reconstructing the relationships of these basins to the Paleoproterozoic basement that has been outlined by magnetic and gravity anomaly maps and radiometric dates from deep boreholes, and by deep geophysical imaging by the petroleum exploration industry and Lithoprobe. Isopach maps of the estimated total thickness of the palinspastically restored Belt-Purcell Supergroup, the Windermere Supergroup, and the EoCambrian to Middle Devonian strata of the Cordilleran miogeocline illustrate the overlap and truncation relationships among the three basins. In the restoration: 1.) The major negative Bouguer gravity anomaly of the SE Canadian Cordillera coincides with the area of thrust overlap of the displaced miogeocline and underlying Windermere Supergroup relative to the matching autochthonous basin-margin ramp beneath the Cordillera. 2.) South of 50⁰ N, the NE margins of the miogeocline and the Windermere basin are deflected ~220 km SW across the Belt Supergroup, along the Crowsnest Pass cross-strike discontinuity (CPCD), a transverse NE trending fault zone created by reactivation of a tectonic suture in the Paleoproterozoic basement extending under the Cordillera from the Vulcan structure SE of Calgary. 3.) Near the CPCD, the edge of the miogeocline overlaps the Windermere basin to lie directly on the Purcell Supergroup. 4.) The rift margin that severed the Belt-Purcell basin is west of the Okanagan Valley, and in northern Washington it is deflected 80 km SW along the CPCD. The palinspastic map provides a frame of reference for analyzing relationships with displaced Paleozoic terranes from outboard of Laurentia.