Relating strain localization during post-orogenic collapse to inherited crustal structure in the northern Basin and Range extensional province, western United States.

Despite a spatially homogeneous distribution of horsts and grabens in the northern Basin and Range extensional province of the western United States, geologic data indicate that the distribution of finite extensional strain is highly heterogeneous. Apatite and zircon (U-Th)/He cooling ages from the House Range in the eastern Basin and Range are Late Cretaceous, precluding more than 2-3 km of extensional exhumation in the Neogene. In contrast, the adjacent Snake range metamorphic complex and Canyon range exhumed 6 km and 5 km respectively. The cooling histories of these ranges imply an order of magnitude variation in extensional strain over a distance of 140 km. This zone of variable extensional strain is coincident with the Sevier culmination, a structural zone of the Cretaceous Sevier Orogeny that experienced uniquely deep exhumation during contractional deformation, potentially strengthening the upper crust and inhibiting large magnitude Cenozoic extension. From this example, we hypothesize that variations in the depth of exhumation across the structural zones of the Sevier orogeny, including the hinterland, culmination, and fold-thrust belt, may have influenced how later extensional strain localized onto preexisting Mesozoic compressional structures, resulting in a heterogeneous distribution of Neogene extensional strain. To examine this, we present new low temperature thermochronology data in two transects across the northern Basin and Range that constrain the spatial distribution of extensional strain and allow us to assess the role of inherited crustal architecture on extensional strain localization during continental rifting. We circumvent a lack of suitable apatite and zircon bearing host rocks in the carbonate dominated Basin and Range by exploiting an understudied east-west trending suite of Jurassic (pre-extensional) plutons potentially emplaced above a slab tear. We present new apatite and zircon (U-Th)/He and apatite fission track thermochronology data from these plutons to constrain the spatial distribution of Neogene extensional strain across different structural zones of the Sevier orogeny. These data will contribute to our understanding of the tectonic evolution of the northern Basin and Range, and the controls on strain localization during continental rifting.