Abstract

Newly identified listric thrust faults show eastward translation north of the Lewis and Clark line across all 800 km of Belt terrane from Spokane, Washington, on the west to Glacier National Park on the east. Right-lateral slippage on the line was accompanied by clockwise rotation on the thrusts. These movements were probably in response to the complex plate interactions that began about 200 m.y. ago along the western continental margin. Gravity and magnetic data suggest that basement rock is involved in the thrusting. Reconcentration of strata-bound copper sulfides along bedding-plane shears may help form ore near one thrust. West of the Rocky Mountain Trench, Phanerozoic strata that elsewhere have oil and gas potential may have been stepped up by the thrusting, and eroded, rather than extending beneath most of the thrust belt.

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