Abstract

New mapping and U-Pb zircon geochronology help establish the timing of contractional deformation and magmatism in the White Mountains of California. In the Redding Canyon area of the west-central White Mountains, Mesozoic deformation characterized by east-directed movement along reverse faults as well as recumbent folding was followed by development of upright folds with axes that plunge moderately to the north. This later folding event produced penetrative, vertical, north-striking axial-planar cleavage that is present along much of the western flank of the range. Deformed units include folded and/or boudinaged diorite dikes (ca. 165 Ma; U-Pb zircon) that contain the later penetrative cleavage. The cleavage is clearly cut by the Redding Canyon pluton (ca. 164 Ma; U-Pb zircon), demonstrating that at least some of the intense deformation preserved in the area is Middle Jurassic and correlative with the East Sierran thrust system identified elsewhere in California. Dates for the Beer Creek pluton (ca. 179 Ma; U-Pb zircon) and the Sage Hen Flat pluton (ca. 175 Ma; U-Pb zircon), which cut deformation in their wall rocks, suggest that East Sierran thrust deformation did not propagate as far eastward as these plutons at the present level of exposure. The new dates also cast doubt on the presence of any Late Jurassic–Early Cretaceous plutonism in the White Mountains. Throughout the east-central Sierra Nevada and White Mountains, high-precision U-Pb zircon geochronology is resolving significant plutonism into two short-lived events that occurred at ca. 180–165 Ma and 102–86 Ma.

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