An upper-crustal fold province in the hinterland of the Sevier orogenic belt, eastern Nevada, U.S.A.: A Cordilleran Valley and Ridge in the Basin and Range

Abstract

Overprinting Cenozoic extension hinders analysis of Cordilleran contractional deformation in the hinterland of the Sevier thrust belt in Nevada. In this study, a 1:250,000 scale paleogeologic map of eastern Nevada, showing spatial distributions of Paleozoic- Mesozoic rocks beneath a Paleogene unconformity, is combined with dip magnitude maps for Paleozoic-Mesozoic and Tertiary rocks, published sedimentary thickness records, and a published reconstruction of extension, in order to define and regionally correlate thrust faults and folds, and estimate the pre-extensional amplitude, wavelength, and limb dips of folds. A new structural province, the Eastern Nevada fold belt, is defined, consisting of a 100-km-wide region containing five first-order folds that can be traced for map distances between 100 and 250 km and have amplitudes of 2-4 km, wavelengths of 20-40 km, pre-extensional limb dips typically between 10° and 30°, and deform rocks as young as Jurassic and Early Cretaceous. No regional-scale thrust faults or décollement horizons breach modern exposure levels in the Eastern Nevada fold belt. Firstorder folds of the Eastern Nevada fold belt are interpreted to have formed above a deep (≥10 km below the Paleogene unconformity), blind décollement or shear zone, perhaps the westward projection of the master décollement of the Sevier thrust belt. Three hinterland structural provinces, the Central Nevada thrust belt, Western Utah thrust belt, and the intervening Eastern Nevada fold belt, collectively record low-magnitude (a few tens of kilometers), upper-crustal shortening that accompanied Cretaceous translation of the Cordilleran passive-margin basin ~220 km eastward during the Sevier orogeny. Low deformation magnitudes in the hinterland are attributed to the rheological competence of this thick basin.