Abstract
The competing contributions of tectonic and magmatic processes in accommodating continental extension are commonly obscured by a lack of on-fault paleoseismic information. This is especially true of the Sevier Desert, located at the eastern margin of the Basin and Range in central Utah (USA), where surface-rupturing faults are spatially associated with both regional detachment faults and Quaternary volcanism. Here, we use high-resolution topographic surveys (terrestrial lidar scans and real-time kinematic GPS), terrestrial cosmogenic nuclide (10Be and 3He) exposure dating, 40Ar/39Ar geochronology, and new neotectonic mapping to distinguish between modes of faulting and extension in a transect across the Sevier Desert. In the western Sevier Desert, the House Range and Cricket Mountains faults each have evidence of a single surface-rupturing earthquake in the last 20–30 k.y. and have time-integrated slip and extension rates of <0.1 and ∼0.05 mm yr−1, respectively, since ca. 15–30 ka. These rates are similar to near-negligible modern geodetic extension estimates. Despite relatively low geologic, paleoseismic, and modern extension rates, both faults show evidence of contributing to the long-term growth of topographic relief and the structural development of the region. In the eastern Sevier Desert, the intrabasin Tabernacle, Pavant, and Deseret fault systems show markedly different surface expressions and behavior from the range-bounding normal faults farther west. Pleistocene to Holocene extension rates on faults in the eastern Sevier Desert are >10× higher than those on their western counterparts. Faults here are co-located with Late Pleistocene to Holocene volcanic centers, have events temporally clustered around the timing of Pleistocene volcanism in at least one instance, and have accommodated extension ∼2×–10× above geodetic and long-term geologic rates. We propose a model whereby Pliocene to recent extension in the Sevier Desert is spatially partitioned into an eastern magma-assisted rifting domain, characterized by transient episodes of higher extension rates during volcanism, and a western tectonic-dominated domain, characterized by slower-paced faulting in the Cricket Mountains and House Range and more typical of the “Basin and Range style” that continues westward into Nevada. The Sevier Desert, with near-complete exposure and the opportunity to utilize a range of geophysical instrumentation, provides a globally significant laboratory for understanding the different modes of faulting in regions of continental extension.
Paleoseismic patterns of Quaternary tectonic and magmatic surface deformation in the eastern Basin and Range, USA
