Paper No. 116-9
Presentation Time: 10:30 AM
NEW PRESSURE-TEMPERATURE-TIME PATHS FROM THE FUNERAL MOUNTAINS, CALIFORNIA, RECORDING LATE JURASSIC BURIAL AND EXHUMATION DURING EARLY SEVIER OROGENESIS
We investigated the pre-detachment history of burial and exhumation in the footwall of the Funeral Mountains metamorphic core complex in Death Valley National Park, California. New metamorphic pressure-temperature (PT) paths from medium grade garnet schists in the Chloride Cliff area were determined from growth zoning on 12 garnet crystals from 6 samples using a G-minimization method. The composite path shows a P increase from 4.2 to 6.5 kbar as T increased from 550 to 575 °C, followed by a P decrease to 5.1 kbar during a further increase in T to 590 °C. Lu-Hf garnet ages from a pelitic schist (172.9 ± 4.9 Ma) and a garnet amphibolite (165.1 ± 9.2 Ma) place these events in the Middle to Late Jurassic. We interpret the P increase part of the path to have developed during thrust-related burial, consistent with a previous interpretation from lower grade rocks at Indian Pass, 8 km to the southeast, where garnet PT paths show a P increase at 158.2 ± 2.6 Ma. Thrust-related burial in the northern Funeral Mountains preceded or was contemporaneous with movement along the oldest known thrusts of the Sevier orogen, specifically in the Clark Mountains, Resting Spring Range and Spring Mountains (160-150 Ma). 40Ar/39Ar muscovite ages in the Chloride Cliff area (86-67 Ma) indicate cooling through the closure T for Ar diffusion (~425 °C) in the Late Cretaceous. The P decrease part of the composite PT path from the Chloride Cliff area may have been coeval with 153-146 Ma cooling recorded in the Indian Pass area by 40Ar/39Ar muscovite ages, or may have just preceded it. The composite PT path and exhumation history can be interpreted within the framework of orogenic cyclicity, which predicts burial due to crustal thickening associated with plate convergence concurrent with high flux magmatism, then lower crustal and upper mantle lithospheric delamination triggering exhumation at the surface and a flare-up of magmatic activity. Magmatism dated 188-140 Ma is represented in the Death Valley area by the Hunter Mountain batholith in the Cottonwood Mountains and by plutons and dikes in the Argus, Inyo and Slate ranges. The Funeral Mountains are located on the eastern flank of the Jurassic arc, where magmatic flux peaked at 150-160 Ma, concurrent with 158 Ma tectonic burial in the Funeral Mountains and the transition to exhumation.