MICROSTRUCTURAL AND ISOTOPIC ANALYSIS OF THE RUBY-HUMBOLDT SHEAR ZONE AT LAMOILLE CANYON, NV

The brittle-ductile transition zone (BDT) marks the tectonic and thermal boundary where deformation shifts from seismogenic, frictional sliding and granular flow to largely aseismic crystal-plastic processes. Below the BDT, rocks deform predominantly by dynamic recrystallization and movement is accomplished via viscous flow. When strain localizes into a discrete shear zone, recrystallization forms mylonites, which records the strain history as fabrics at a high angle to the shear direction. The Basin and Range extensional province of the western USA contains a series of exhumed metamorphic core complexes (MMCs), which preserve deformation in the crystal-plastic regime. The Ruby Mountains-East Humboldt Range, NV contains a MMC exhumed along a low-angle detachment fault. Whereas previous work has investigated the shear zone in the Secret Pass region, we apply microstructural analysis to samples collected 25 km to the south in the Lamoille Canyon area. Lamoille Canyon is located closer to the center of the detachment and near a large constraining bend, allowing for exploration of along-strike heterogeneity in strain history, which has recently been documented as an important control on the strength and morphology of detachment faults. Petrographic assessment identifies fabric variation that correlates with protolith, local strain gradients, and hypothesized interaction with meteoric water during deformation. Ongoing work includes electron backscatter diffraction to obtain grain size measurements, determine slip systems, and assess fabric strength of key phases. Microstructural analysis will be paired with stable isotope analysis of garnet, quartz, and micas to determine sources of fluids in that aid in deformation and whether the surface-derived fluids identified at Secret Pass were pervasive along strike. Comparing our findings to those extrapolated from Secret Pass informs along-strike compatibility of tectonic models and constructs a wider image of the Ruby Mountains-East Humboldt Range.