Thermochronology and geobarometry of the Granite Mountains, southeast California: Exhumation of a plutonic complex during collapse of the Sevier orogen

Thermochronologic data and geobarometry from the Granite Mountains indicate exhumation of mid-crustal plutons during Late Cretaceous extensional tectonics. U/Pb zircon and 40Ar/39Ar ornblende ages indicate intrusion, crystallization, and geologically instantaneous cooling through 500°C at ∼75 Ma. K-feldspar multi-diffusion domain modeling indicates a cooling rate gradient from SW to NE of 63, 32, and 16°C/Ma for three samples spanning a transect across the range. NE K-feldspar cooled through ∼252°C by 73 Ma while other samples remained >375°C suggesting a short lived down-to-the-east normal faulting event at ∼75 to 74 Ma. Faster cooling rates with later initial K-feldspar recording (∼71 Ma) suggest extension continued along a shallow down-to-the-southwest detachment active from ∼73 to 69 Ma. U-Th/He apatite ages suggest the Late Cretaceous extensional event juxtaposed the deeper-seated Granite Mountains plutons with the shallow-level southern Providence Mountains plutons and the two cooled through 70°C as a single block.