STRUCTURE OF THE CENTRAL CANADIAN CORDILLERAN THRUST-AND-FOLD BELT, ATHABASCA-BRAZEAU AREA, ALBERTA - A LARGE, COMPLEX INTERCUTANEOUS WEDGE

In the central Canadian Cordilleran foreland thrust-and-fold belt, thr ee types of first order decollements are identified within or along th e border of the present orogenic wedge: one basal decollement, three i nternal decollements and one upper decollement. These decollements out line three major structural compartments in the orogenic prism termed Upper Panel, Middle Wedge and Lower Wedge. The Upper Panel is an exten sive SW-directed fault (backthrust) panel, gliding on the upper decoll ement within the Wapiabi Formation. It is imbricated and forms several fault panels separated by NE-dipping backthrusts. Within the orogenic wedge, at least three internal decollements are recognized. Each corr esponds to an extensive flat between two ramps which link it to other internal decollements, the basal decollement or the upper decollement. Many fault imbricates emanate from the basal and internal decollement s to form duplexes within the orogenic prism. The most extensive of th ese duplexes (Middle Wedge) occurs between the Upper Panel. and the Lo wer Wedge. It extends for more than 60 km across the strike of the Foo thills within the Upper Cretaceous Alberta Group. During deformation, the Middle Wedge appears to have formed at the leading edge of the Foo thills with the Lower Wedge developing farther toward the hinterland. The Middle Wedge propagated progressively eastward across the foreland basin, at the same stratigraphic level (Alberta Group), beneath the u pper decollement. At the same time the Lower Wedge propagated eastward forming a duplex in Paleozoic to Lower Cretaceous strata beneath the Middle Wedge.