Magnetic models of the Moyie anticline, Purcell anticlinorium, southeastern Canadian Cordillera

Abstract

Two-dimensional magnetic models of the Moyie anticline contribute to an independent project targeting development of a regional three-dimensional (3D) model of much of the Purcell anticlinorium by compensating for shortcomings in reflection seismic signatures and distributions of drill holes and surface structural data. Modelling has focused on prominent anomalies related to relatively strong magnetizations within the Creston Formation and Moyie sills. Models of the western flank of the anticline indicate the Creston Formation forms the bulk of a westward-thickening, wedge-shaped sedimentary package whose west-dipping layers are truncated by a steeply west-dipping Moyie fault, truncating also Moyie sills on the opposite side. Near-surface dips of the fault range from 54°to 87°. Stratigraphic comparisons across the fault indicate minimum reverse dip displacements ranging from 5.6 to 8.5 km. The eastern flank of the Moyie anticline is modelled consistently as a monoclinal, eastward-dipping stratigraphic package comprising mainly Lower Aldridge Formation (with intruded Moyie sills) through Kitchener Formation, in general accord with geological models. One magnetic model, however, shows stratigraphy disrupted by shallow thrust faults, above which a series of near-vertical blocks is modelled. The Yahk River syncline is modelled as a symmetrical fold having an axial depth of 4.2 km to the top of the Upper Aldridge Formation. Collectively, the models outline a broad domal pattern of Moyie sills in the core of the anticline to 12 km depth, supporting a proposal that a gravity high correlating with the Moyie anticline relates to high-density Moyie sills at relatively shallow depths, rather than deeper highdensity basement.