SYN-CONTRACTIONAL DEPOSITION OF THE CRETACEOUS NEWARK CANYON FORMATION, DIAMOND MOUNTAINS, NEVADA: IMPLICATIONS FOR STRAIN PARTITIONING WITHIN THE NORTH AMERICAN CORDILLERA

The timing of deformation and deposition within syn-tectonic basins provides critical information for understanding the space-time evolution of strain within mountain belts. In the Western U.S. portion of the North American Cordilleran orogen, contractional deformation was partitioned between the frontal Sevier thrust belt in Utah and several structural provinces within the hinterland in Nevada. One hinterland province, the Central Nevada thrust belt (CNTB), accommodated up to ~15 km of shortening. However, in most places this deformation can only be bracketed between Permian and Eocene. Cretaceous deposits of the Newark Canyon Formation (NCF), which are sparsely exposed in the northern part of the CNTB, offer the opportunity to constrain deformation timing. Here, we present new geologic mapping and U-Pb zircon geochronology from the NCF in the southern Diamond Mountains, which demonstrate deposition, thrust faulting, and folding of the NCF during proximal CNTB deformation. Our new geochronology indicates that deposition of the basal NCF member was underway no earlier than ~107 Ma, a waterlain tuff in the middle part of the NCF section was deposited at ~103 Ma, and the youngest NCF member was deposited no earlier than ~94 Ma. Clast compositions from NCF conglomerates define unroofing of locally sourced Devonian-Permian sedimentary rocks, which we interpret as the progressive erosion of a regional-scale CNTB anticline ~10 km to the west. Intraformational angular unconformities and abrupt along- and across-strike thickness changes observed in the NCF indicate that deposition and deformation were controlled by the growth of an east-vergent CNTB fault-propagation fold. CNTB deformation was contemporaneous with shortening in the Sevier thrust belt to the east, which defines out-of-sequence folding and thrusting. We interpret that the CNTB deformation observed in the Diamond Mountains records partitioning of contractional strain between the Sevier thrust belt and interior components of the Sevier hinterland during the middle Cretaceous. Strain partitioning may have been promoted by renewed westward underthrusting of the North American craton, which was coincident with a period of high-flux magmatism in the Sierra Nevada magmatic arc between ~105-90 Ma.