Abstract

Faults at low angles to bedding that emplace younger over older rocks are widespread in the hinterland of the Sevier orogenic belt near the border between Nevada and Utah and are attributed to horizontal extension during latest Jurassic, Cretaceous, or mid-Tertiary time. At Carlin Canyon, approximately 150 km west of the border, we document a low-angle fault of probable Mesozoic age between Upper Pennsylvanian rocks and Lower Pennsylvanian strata, a contact that previously was mapped as a locally angular segment of a regional Middle Pennsylvanian unconformity and was considered evidence for Upper Pennsylvanian orogeny (Humboldt orogeny). Loss of section in Carlin Canyon was in response to top-northwest layer-parallel shear along a backthrust during northwest/southeast regional contraction. Deformation is later than Permian and earlier than Miocene but is probably latest Jurassic to Cretaceous. Structures in the upper Paleozoic rocks of Carlin Canyon may record shallow, thin-skinned contraction in the hinterland of the Sevier orogenic belt above deep-seated metamorphism and deformation exposed nearby in the Ruby Mountains-East Humboldt Range. The fault at Carlin Canyon indicates that the Humboldt orogeny reflected primarily vertical, not horizontal, displacements.

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