Synorogenic extension localized by upper-crustal thickening: An example from the Late Cretaceous Nevadaplano

Title of Publication: 
Synorogenic extension localized by upper-crustal thickening: An example from the Late Cretaceous Nevadaplano
Author: 
Long, Sean P., Thomson, Stuart N., Reiners, Peter W., and Di Fiori, Russell V.
Publication Info: 
Geology, April 2015, v. 43, p. 351-354
Abstract: 

Synconvergent extension within orogenic systems is often interpreted as gravitational spreading of thickened crust or as a response to thrust belt dynamics. However, the processes that spatially localize extension during orogenesis are not fully understood. Here, a case study from the United States Cordillera demonstrates that localized upper-crustal thickening can exert a first-order control on the spatial location of synorogenic extension. The Eureka culmination, a 20-km-wide, north-trending anticline with 4.5 km of structural relief in the hinterland plateau of the Sevier orogenic belt (or “Nevadaplano”) in eastern Nevada was deformed by two sets of north-striking normal faults that pre-date late Eocene volcanism. (U-Th)/He and fission-track thermochronology data collected from Paleozoic quartzite in the footwalls of two normal faults demonstrate rapid (10 °C/m.y.), Late Cretaceous to Paleocene (75–60 Ma) cooling, which we interpret as tectonic exhumation during extension, and which was concurrent with late-stage shortening in the frontal Sevier thrust belt. This example illustrates that structural and topographic relief generated within zones of localized uppercrustal thickening can spatially focus extension during orogenesis, and adds to a growing body of evidence that Late Cretaceous–Paleocene extension in the Nevadaplano occurred at both mid- and upper-crustal levels.

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Figure 2. A: Geologic map of northern Fish Creek Range and southern Diamond Mountains (Nevada, USA), simplified from Long et al. (2014), showing thermochronology samples and ages. B: Geologic map showing locations and ages of Cambrian thermochronology samples. C: Cross-sections A-A′ and B-B′, modified from Long et al. (2014). Quaternary and Tertiary rocks are omitted for simplicity. Cross-sections on left show modern geometry, and on right show retrodeformed, pre-extensional geometry; modern and restored positions of thermochronology samples are shown. Explanation of erosion levels on lower right; translucent areas represent eroded rock. HFS—Hoosac fault system; RBDS—Reese and Berry detachment system; PSF—Pinto Summit fault; DTF—Dugout Tunnel fault.