DIRECTLY DATING COMPLEX DEFORMATION VIA STRUCTURALLY INTEGRATED MULTI-MINERAL U-PB PETROCHRONOLOGY AND (U-TH)/HE THERMOCHRONOLOGY (SE CALIFORNIA AND WEST-CENTRAL ARIZONA, USA)
Structural petrography and electron backscatter diffraction (EBSD) analyses of quartz and feldspar in these shear zones, coupled with upper greenschist-amphibolite facies mineral assemblages, are indicative of deformation conditions > 500°C. The apatite U-Pb system has a closure temperature ~450°C, making it an ideal thermochronometer to constrain shear zone deformation and formation of amphibolite- to upper greenschist-facies mylonitic fabrics. Apatite U-Pb cooling ages within Jurassic and Mesoproterozoic gneisses range from ~155-145 and ~125-105 Ma in the Riverside Mountains, ~75-58 Ma in the Big Maria Mountains, and ~85 Ma in the Dome Rock/Moon Mountains, indicating variable and distinct phases of mid-crustal cooling in different parts of the MFTB. Further, in-situ EBSD analyses and U-Pb petrochronology of pre-kinematic (magmatic) titanite also indicate the potential to constrain Late Cretaceous greenschist-amphibolite facies deformation. Zircon and apatite (U-Th)/He low-temperature thermochronology indicate shallow-crustal exhumation via a series of temporally and structurally distinct detachment systems in the Big Maria and Riverside Mountains in the Late Cretaceous-Paleocene and the Miocene.