DILLON CUTOFF - BASEMENT-INVOLVED TECTONIC LINK BETWEEN THE DISTURBED BELT OF WEST-CENTRAL MONTANA AND THE OVERTHRUST BELT OF EXTREME SOUTHWESTERN MONTANA

The front of the Cordilleran fold and thrust belt in western Montana follows the disturbed belt in the N, merges with the SW Montana transverse zone in the W-central part of the region, and in S-western Montana is marked by a broad zone characterized by complex interaction between thrust belt structures and basement uplifts. The front margin of the thrust belt in Montana reflects mainly thin-skinned tectonic features in the N, an E-trending lateral ramp that curves SW in the central part into the Dillon cutoff, an oblique-slip, thick-skinned displacement transfer zone that cuts through basement rocks of the Lima recess, and a zone of overlap between thin- and thick-skinned thrusts in extreme S-western Montana. The transverse ramp and basement-involved thrust faults are controlled by Proterozoic structures. -Authors