Tectonic significance of the pass fault, central Bridger Range, southwest Montana

TL;DRAbstract

The Pass fault of the Ross Pass fault zone in the central Bridger Range of southwest Montana is significant in that it marks the tectonic boundary between Archean metamorphic rocks of the basement or foreland province to the south and Proterozoic Belt Supergroup rocks of the batholithic province to the north.As such, it represents the juncture of two major rock types and styles of deformation within one range: "thick-skinned" basement-involved deformation to the south and "thin-skinned" deformation without significant basement involvement to the north.The Pass fault formed during the Paleocene Epoch at the southeast comer of the Helena salient.At the time of its formation, the Pass fault had a strike of approximately N21E with a net slip of roughly 1.3 miles (2.2 km).It was an oblique slip thrust fault with predominantly dip slip movement and represented an oblique footwall ramp at the leading edge of the Helena salient.In this context, it was the structural link between the Jefferson

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