Tectonostratigraphy and Tectonic Inheritance: The Cordilleran Foreland Thrust and Fold Belt, Southern Canada and Adjacent U.S.A

Raymond A. Price
Geological Sciences & Geological Engineering, Queen's Univeristy, Kingston, ON, Canada

This segment of the Cordilleran foreland thrust and fold belt is a critical-taper accretionary wedge comprising imbricate slices of supracustal rock that were scraped off the under-riding Paleoproterozoic basement of Laurentia by Intermontane terrane, an over-riding tectonic collage of oceanic, mainly volcanic-arc rocks. It formed during Late Jurassic to late Paleocene convergence between Laurentia and subduction zones farther west, while Intermontane terrane was being detached from its underlying lithosphere and asthenosphere and displaced over Laurentia. Large culminations within the thrust-and-fold belt were inherited by tectonic inversion of three pre-existing, superimposed deep basins. The Mesoproterozoic (1.5-1.4 Ga) Belt-Purcell intracontinental rift basin, up to 20 km deep, was overlapped discordantly near the Crowsnest Pass cross-strike discontinuity (CPCD) by the late Neoproterozoic (850-600 Ma) Windermere intracontinental rift basin. The Cordilleran miogeocline, a Phanerozoic continental shelf terrace wedge, up to 15 km deep, overlapped the Belt-Purcell basin along the CPCD and the Windermere basin. The CPCD, which includes a 230 km right-hand deflection of the margin of the miogeocline southwestward from the central Canadian Rockies to the Columbia River in NE Washington, was inherited by reactivation of a Paleoproterozoic crustal suture that extends into the subsurface SE of Calgary. The basins were inverted as basin-fill strata were detached and displaced over the flat surface of Laurentia. Basin-margin ramps became hanging-wall thrust ramps that defined margins of major culminations. A deflection of the thrust-and-fold belt between the NW-trending Belt-Purcell basin and the north-trending miogeocline is a result of critical-taper wedge profiles that were aligned with the resulting high topography, as is SE-verging thrusting and folding along the CPCD.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas