AGES OF SAGE HEN FLAT AND REDDING CANYON PLUTONS, WHITE MOUNTAINS, CALIFORNIA

The White Mountains of eastern California expose deformed late Proterozoic to Paleozoic strata that are intruded by several Mesozoic plutons. These plutons can be used to determine the timing of deformation. The Sage Hen Flat and Redding Canyon plutons are undeformed granitic bodies whose ages place younger limits on the deformation that folded the surrounding strata and older limits on the ages of mafic dikes that intrude them. Previous studies indicated an earliest Cretaceous age for Sage Hen Flat pluton (following the 148 Ma Independence dike swarm), during a magmatically quiet period in California.

Uranium-lead analysis of 6 fractions of zircon gave a concordant age of 175 +/- 1.5 Ma for the Sage Hen Flat pluton. This is older than previous ages of 133 and 141 Ma (biotite and hornblende K-Ar) and 144 Ma (zircon U-Pb) and is approximately the same age as the Hunter Mountain batholith of the Inyo Range. Preliminary analysis of four fractions from the Redding Canyon pluton yields a lower-intercept regression age of 164 +/- 5 Ma, pinned by one fraction at 164.

Folds in the White Mountains trend N to NW (attributed to the Permo-Triassic Last Chance thrust system and Middle-Late Jurassic East Sierran thrust system) and NE (attributed to the late Paleozoic Antler orogeny). The Middle Jurassic ages of these plutons indicate that folding cannot be Late Jurassic or younger, but could be related to early deformation in the East Sierran thrust system or to the Last Chance or Antler events. Mafic dikes in both plutons could be part of the Independence dike swarm rather than Cretaceous, as required by the earlier dating.