TECTONIC IMPLICATIONS OF NEW GEOLOGICAL MAPPING AND SECTION BALANCING IN THE CENTRAL MACKENZIE MOUNTAINS FORELAND FOLD-THRUST BELT OF NORTHWESTERN CANADA

The central Mackenzie Mountains of NW Canada are underlain by Neoproterozoic and Paleozoic strata deposited along the western ancestral margin of North America that subsequently formed part of the Mesozoic-Tertiary northern Cordilleran foreland fold and thrust belt. Recently completed 1:50,000 scale mapping reveals three unique structural domains based on regional structural elements.

The dominant structure of central Mackenzie Mountains is the east-vergent Plateau Fault (thrust) that developed along a weak regional detachment within gypsum and shale of the Proterozoic Little Dal Group. The hanging-wall of the fault forms the westernmost structural domain. A central domain, in the footwall, is defined by a narrow, complicated zone of folds and thrust faults coined the Ten Stone structural complex. East of the complex, structures are dominated by large-scale, symmetrical, flat-topped, box anticlines and flanking narrow intervening synclines with strike lengths up to several hundred kilometres.

We present the first 1:100,000 scale kinematic restoration (using 2D MOVE) through the central Mackenzie Mountains which transects each of the three structural domains. From the construction of the conceptual and kinematic restorations we have demonstrated that the Plateau Fault, although of great strike-length, is incapable of large overlap above a thick sequence of Paleozoic strata thus has little potential as a hydrocarbon trap. In addition, the cross sections indicate the geometry of the Plateau Fault and location of the westernmost and central structural panels is an artefact of the stratigraphic configuration before deformation. The Mackenzie Arch is a locus of coalescing unconformities and dramatic thinning of late Proterozoic to mid-Paleozoic formations, many of which are incompetent. This favourably-oriented west-dipping “sedimentary ramp” accommodated displacement along a regional detachment (Little Dal gypsum) which later broke through overlying units to be expressed as the Plateau Fault.

In addition, a number of depth-to-detachment calculations were completed for the box anticlines in the easternmost structural panel using the “excess area” method. The result was an estimated depth-of-detachment between 12-7 kilometres below sea level in the north-eastern central Mackenzie Mountains.