Abstract

New geochronologic data from the Clark Mountain area, eastern California, better define the regional development of the Cordilleran magmatic arc and the timing of hinterland and foreland deformation at this latitude. The new ages show that Sevier belt thrusting started in the Clark Mountain thrust complex in Late Jurassic time. This is consistent with other studies that suggest a similar age of initiation of the Sevier belt in areas to the north. The Clark Mountain thrust complex is located at the intersection of the Mesozoic magmatic arc and the east Sierran and Sevier thrust belts. New U-Pb zircon ages for granitic rocks establish the timing of deformation within the thrust complex. The Pachalka thrust, structurally the highest fault in the complex, carries plutonic rocks eastward above Cambrian rocks. Hanging-wall and footwall rocks are mylonitic near the thrust. Hanging-wall plutonic rocks, previously considered Precambrian, are dated at 146 62 Ma and thus are Late Jurassic. Folds kinematically related to thrusting in footwall metasedimentary rocks are overturned eastward and cut by the Pachalka pluton dated at 142 ± 7 Ma. This brackets thrusting and related deformation in structurally high levels of the complex to be latest Jurassic. The Ivanpah and Striped Mountain plutons in the Ivan-pah Mountains have been dated at 147 ± 7 Ma and 141 ± 11 Ma, respectively. These plutons are cut by the Keaney-Mollusk Mine and Morning Star Mine thrusts, which are in turn cut by the middle to late Cretaceous Teutonia batholith. These data indicate that these thrusts are early to middle Cretaceous in age.

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