Don Pedro intrusive suite
Don Pedro intrusive suite
Middle and Early Jurassic, ~162-177 Ma
Chiefly metamorphosed granodiorite and diorite in the west-central Sierra Nevada. Typical description: light-gray granodiorite, approximately equal proportions of fine- to medium-grained quartz and plagioclase feldspar, with 5 to 10% mafic minerals (primarily biotite and hornblende). This unit has zircon U-Pb ages of ~162-177 Ma (Sharp and Saleeby, 1979; Stern and others, 1981; Wooden and others, 1999; Bedrossian and Saucedo, 1981; Irwin and Wooden, 2001; Rotberg, 2008), excluding one age of ~133 Ma (Irwin and Wooden, 2001), which is anomalously young and is probably a western outlier of younger plutonic units to the east. This unit also has biotite K-Ar ages of ~138-152 Ma and hornblende K-Ar and Ar-Ar ages of ~136-168 Ma (Evernden and Kistler, 1970; Herzig and Sharp, 1992). Unit occurs in small to large plutons intruding the Merced River and Northern Sierra terranes and is itself intruded by younger plutonic units on the east. On the west, two plutons of this unit are truncated by the Melones fault zone. This unit, along with units of phyllite (MRDPH) and greenschist (MRDGS), is interpreted as an Early and Middle Jurassic Don Pedro island arc overlap assemblage deposited on and intruded into the western margin of the marine sedimentary member of the Calaveras Complex (MRCS) and associated carbonate lenses (MRCC) and across the Calaveras-Shoo Fly thrust into the Shoo Fly complex (units NSSA and NSSF).