Beaufort West: New Insight into a Frontier Basin

Stacked lithotectonic units at the south-western end of line BW1-2800 indicate the Belcher antiform may be cored by a hinterland dipping or antiformal stack duplex. The youngest horses are truncated by a large graben (~25 km wide) likely associated with the opening of the Canada Basin (D3), suggesting the duplex may be an Ellesmerian (D2) structure. Shortening produced by the Brooks Range orogeny (D4) was accommodated by inversion along D3 extensional structures, and detachment folding in the Beaufort fold-thrust belt. The position of the lower fold envelope (dark blue) above the duplex, but below an apparent imbricate, suggests D2 structures locally control the geometry of D4 deformation.

Below the fold belt, a conspicuous series of landward-dipping reflections, which we interpret as exhumed subcontinental lithospheric mantle, forms a shallow, structural trough ~30 km wide (extended outer marginal trough). The north-eastern end of the trough steps up ~2 sec/8 km to a package consistent with oceanic crust and Moho, while to the southwest, faults inside the trough sole out and dip under continental crust along a surface we interpret as an outer marginal detachment (e.g. Pindell et al., 2014) associated with the opening of the Canada Basin (D3). If so, anastamosing subhorizontal reflections in the poorly imaged region below the trough may represent layered, mantle peridotite.