TIMING OF PLUTONISM AND DEFORMATION IN THE WHITE MOUNTAINS, CALIFORNIA

U-Pb geochronology and 1:10,000 scale mapping in the White Mountains establish the timing of contractional deformation and magmatism in eastern California. New U-Pb zircon ages of the weakly deformed to undeformed Beer Creek (179 ± 3 Ma), Sage Hen Flat (175.4 ± 0.3 Ma), and Redding Canyon (163.8 ± 0.5 Ma) plutons indicate that most ductile deformation occurred before 164 Ma. In the west-central portion of the range near Poleta and Redding Canyons, Mesozoic deformation characterized by east-vergent reverse faulting and recumbent folding was followed by upright folding with axes that plunge moderately to the north. The latter folding event, characterized by penetrative, vertical, N-striking axial planar cleavage of Cambrian sedimentary units, folded and boudinaged dikes, including a diorite dike in Poleta Canyon (ca. 164.5 ± 0.6 Ma; single concordant U-Pb zircon). The Redding Canyon pluton cuts this cleavage, signifying that a significant portion of the deformation in this area was Middle Jurassic and related to the widespread East Sierran thrust system. The older ages of the undeformed Beer Creek and Sage Hen Flat plutons indicate that the effects of the East Sierran event did not propagate as far eastward as those plutons at this level of exposure. The ages of the dike in Poleta Canyon and another dike 6 km north in Silver canyon (ca. 163, U-Pb zircon) indicate they are not part of the 148 Ma Independence dike swarm, although they are “Independence-type” dikes. However, mafic dikes cutting the Sage Hen Flat and Redding Canyon plutons may be part of the Independence dike swarm. The new pluton ages, along with other high-precision geochronology in the east-central Sierra Nevada and White Mountains, indicate a wide temporal gap in magmatism between two pulses of activity at ca. 180-165 Ma and 102-86 Ma.