New constraints on the timing and character of the Laramide Orogeny and associated gold mineralization in SE California, USA

Abstract The timing of deformation and associated gold mineralization in SE California, USA, is contentious, partly due to the challenges involved with dating ductile deformation. We therefore combine modern geo- thermochronology field microscopic observations show that Cargo Muchacho Mountains preserve evidence northward thrusting a kilometer-scale shear zone during Late Cretaceous Laramide Orogeny, accompanied by hydrothermal fluid flow, mineralization, pegmatite emplacement. Penetrative strain was largely accommodated within Jurassic metavolcaniclastic Tumco Formation, whereas intrusive granitoids behaved as competent bodies. Quartz microstructures suggest at ~500 °C, which consistent fabrics defined amphibolite facies minerals. constrained dynamically recrystallized titanite U-Pb age 68 ± 1 Ma late syn-kinematic pegmatites yield zircon ages 65.0 4.2–63.2 4.8 Ma. Syn-kinematic flow focused into lateral thrust ramp where foliation deflected around relatively rigid pluton, creating zones rich magnetite-quartz veins epidote, precipitating pyrite chalcopyrite. Dating these sulfides via Re-Os yields an 64.7 0.8 Ma, confirms for mineralization. Together, apatite from nearby granite 60.4 3.5 reflecting cooling below 530–450 °C. Comparison published studies suggests thick-skinned driven flat-slab subduction conjugate Hess Plateau, occurred several million years after south Shatsky Rise. This Plateau may have been subducted up hundred kilometers farther north than previously thought. Metamorphic devolatilization underplated Orocopia Schist likely generated gold-bearing fluids, anatexis schist formed peraluminous pegmatites, highlights importance underplating along much Californian Mexican cordillera.