Investigating the generation of transport-parallel gradients in ductile strain and kinematic vorticity in the footwalls of metamorphic core complexes: Insights from the Northern Snake Range, Nevada, USA

Several metamorphic core complexes exhibit structural asymmetry in their exhumed footwalls, with ductile strain, crystallographic preferred orientation (CPO) intensity, and/or mean kinematic vorticity (W m ) increasing in the direction of detachment fault displacement. Here, we investigate the Northern Snake Range metamorphic core complex in Nevada, to explore the processes that are the most influential for generating transport-parallel strain gradients in detachment fault footwalls. Eocene-Oligocene tectonic strain (Rs), lineation-parallel extension, and foliation-normal thinning in the Northern Snake Range increase eastward from 1.5-1.6 to 240-820, 25-30% to 1,400-2,400%, and 15-21% to 93-95%, respectively (assuming no volume change). CPO intensity parameters (cylindricity and J PF index) increase eastward from 0.45 to 0.90-0.95 and 1.40 to 2.64-6.40, respectively, and average W m increases eastward from 0.26-0.40 (72-82% pure shear) to 0.77-0.83 (56-63% simple shear). Restoration of a strain model supported by a range-wide cross-section defines 17.9 km (470%) of Eocene-Oligocene ductile extension. Published footwall cooling histories demonstrate an eastward progression of exhumation-related cooling, driven by unroofing via top-down-to-ESE displacement on the master detachment. This progressive unroofing resulted in an eastward increase in the residence time of quartz-rich footwall rocks at temperatures above ∼300 °C (and thus a longer ductile strain history on the eastern side of the range), which we interpret was a 1 st -order factor for generating the eastward increases in strain, CPO intensity, and W m . The Northern Snake Range is an excellent case study that demonstrates the potential for generation of pronounced transport-parallel structural asymmetry in metamorphic core complexes that are exhumed by high-displacement detachment faults.