Hornitos pluton
Hornitos pluton
Late Jurassic, ~150 Ma
Hornblende tonalite, diorite, and gabbro with numerous mafic to felsic dikes. Exposed in two small bodies just east of the Bear Mountains fault near the old town of Hornitos, west of Mariposa. Intrudes the Mariposa Formation of the Cosumnes terrane (unit CMMS). Mylonitic deformation is widespread throughout the pluton. This unit has a zircon U-Pb age of ~150 Ma, and a hornblende Ar-Ar age of ~140 Ma from the sheared rock along the Bear Mountains fault zone at the western margin of the pluton (Saleeby and others, 1989a).