A new type of decollement thrusting

Abstract

One of the fundamental rules of decollement tectonics is that decollement horizons form in mechanically weak layers. Here we document two examples of decollement-style thrust faults that detach within thick platformal dolostones in preference to apparently weaker layers of shale, siltstone and limestone underlying the dolostones. The thrusts are the Keystone–Muddy Mountain–Glendale thrust system (the KMG thrust system), , and the underlying Contact–Red Spring–North Buffiington–Mormon thrust system (the CRM thrust system), both of southern Nevada. They form part of the Sevier orogenic belt, and extend for roughly 250km along strike, together showing at least 65 km tectonic overlap (Fig. 1). Although the thrust systems are closely related spatially, the higher KMG system is younger than the underlying CRM thrust system, and the two developed essentially independently. Three points are important: first, that both the KMG and the CRM thrust systems are decollement style thrusts; second, that the decollement horizon is primarily restricted to a narrow stratigraphical interval within a bedded sequence of essentially homogeneous dolostones of the Middle Cambrian Bonanza King Formation; the third, that the thrust faults formed at a very shallow crustal level (<5 km).