DIFFERENTIATING KINEMATICALLY SIMILAR DEFORMATION BY APPLYING STRUCTURALLY INTEGRATED U-PB GEO-THERMOCHRONOLOGY ALONG THE SOUTHWESTERN MARGIN OF THE COLORADO RIVER EXTENSIONAL CORRIDOR (SE CALIFORNIA, USA)

Long-lived continental margins preserve often preserve multiple generations of deformation with similar direction, conditions, and kinematics. In the Sonoran Basin and Range province, Miocene-aged metamorphic core complexes and normal faults along the southwestern margin of the Colorado River extensional corridor have exhumed rocks previously deformed in Jurassic, Cretaceous, and Paleocene-Eocene events associated with Central Cordilleran tectonics. We build upon previous low-temperature thermochronology in the Big Maria Mountains and Riverside Mountains (SE California) by utilizing a combination of grain mount and in-situ U-Pb geo-thermochronology of apatite and titanite to temporally constrain greenschist-amphibolite facies shear zones and gneissic fabrics. Electron backscatter diffraction (EBSD) analyses and structural petrography of quartz and feldspar in discrete, top-NE shear zones show quartz C-slip and feldspar bulge nucleation and subgrain rotation textures and are indicative of deformation conditions > 500°C, while quartz fringe textures overprinting distributed gneissic fabrics record later, < 300°C strain. Apatite U-Pb ages (closure temperature ~450°C) from top-NE, S-C mylonitic shear zones in the Big Maria Mountains are Late Cretaceous to Eocene (~75-58 Ma), while distributed gneissic fabrics in Mesoproterozoic and Jurassic-aged rocks in the Riverside Mountains yield two different apatite U-Pb age populations in the Jurassic (~155-145 Ma) and Cretaceous (~125-105 Ma). In-situ EBSD analyses and U-Pb petrochronology of pre-kinematic (magmatic) titanite from shear zones within the Big Maria Mountains also partially preserve Late Cretaceous U-Pb ages (~75-65 Ma) and greenschist-amphibolite facies deformation.