Evidence for Late Devonian movement within the Roberts Mountains allochthon, Roberts Mountains, Nevada

Abstract

New evidence allows better understanding of the sequence of formations and emplacement events during the Antler orogeny in the Roberts Mountains, Nevada. Lower to lower Upper Devonian strata were deformed and unconformably overlain by middle Upper Devonian siliceous shale and chert somewhere west of their present positions in the Roberts Mountains. During a younger episode of deformation, Vinini Group (Ordovician) rocks were thrust over the Devonian rocks that were still west of the present Roberts Mountains at the time of thrusting. Concurrent with this younger thrusting, the ?Webb formation accumulated at the toe of the moving allochthon in the Early Mississippian. As the basal Roberts Mountains thrust stepped eastward, it brought the whole allochthon to its present site above the ?Webb sometime in the Early Mississippian.