Trans-Hudson orogen and Williston basin in Montana and North Dakota: New COCORP deep-profiling results

Abstract

COCORP (Consortium for Continental Reflection Profiling) deep reflection profiling across the Williston basin and underlying Trans-Hudson orogen shows the following. (1)There is no evidence for a precursor rift basin beneath the axis of the Williston basin. With the exception of small-scale structures (e.g., Nesson and Cedar Creek anticlines), the basement surface beneath the Williston basin is smooth and has a dish-shaped geometry. (2) Crustal penetrating reflections within the eastern Trans-Hudson orogen dip eastward, in apparent contradiction to the conventional that the Superior province underthrusts the eastern side of the orogen. (3) Basement reflections beneath the center of the orogen define a broad crustal-scale antiform, the axis of which coincides approximately with the depocenter of the overlying Williston basin. Midcrustal reflections defining the crest and western flank of this antiform also coincide generally with the location and shape of the source of the North American Central Plains conductivity anomaly. (4) Crustal penetrating reflections beneath the western side of the orogen dip westward, supporting the current view that subduction polarity was to the west beneath the Wyoming province. (5) The eastern edge of the Wyoming province is marked by east-dipping upper-crustal reflections and subhorizontal lower-crustal reflections that are truncated by the west-dipping reflectivity of the Trans-Hudson orogen.