Tehachapi-San Emigdio intrusive suite
Tehachapi-San Emigdio intrusive suite
Cretaceous, ~100-136 Ma
Occurs in the southern Sierra Nevada, Tehachapi Mountains and San Emigdio Mountains. Chiefly tonalite, diorite, migmatite gneiss, orthogneiss, and gabbro. Intrudes the Kernville and Tehachapi-San Emigdio terranes (units KE and TSS, respectively), and is in turn intruded by the Bear Valley intrusive suite (unit Gbv). Zircon U-Pb ages from this unit range from ~100-136 Ma (James, 1986; Sams, 1986; Saleeby and others, 2007; Chapman and others, 2012; Chapman and Saleeby, 2012). In addition, Kistler and Ross (1990) report whole rock Rb-Sr ages of ~94 Ma and ~117 Ma, and Kellogg and others (2008) report a hornblende Ar-Ar age of ~100 Ma from this unit. Major plutons: garnet-biotite tonalite of Grapevine, gabbroids of Squirrel Spring, San Emigdio quartz diorite orthogneiss, Digier Canyon quartz diorite orthogneiss, quartzofeldspathic gneiss of Pastoria Creek, migmatite gneiss of Cloudburst Canyon, Antimony Peak tonalite, San Emigdio tonalite, and mixed orthogneiss and mafic tonalite. Generally metamorphosed to upper amphibolite facies. Suite interpreted as forming in a deep level of the Early Cretaceous Sierra Nevada batholith during mixing of mantle-derived magma and old metasedimentary continental rocks (Chapman and Saleeby, 2012). Suite structurally underlies the Pastoria terrane (unit PAS) and Pastoria intrusive suite (unit Gps) along the Pastoria Normal fault, and structurally overlies the Pelona Schist terrane (unit PS) along the Rand thrust. Some prior studies (e.g. Kellogg and others, 2008) map the ~91-105 Ma (monzo)granite of Brush Mountain crossing the Pastoria normal fault (and so partially within this unit), which would restrict the timing of offset on that fault, but others (e.g. Chapman and Saleeby, 2012) restrict that pluton to the hanging wall (unit Gpa). Al-in-hornblende emplacement pressures for this unit range from 7.1 to 10.7 kbar (Chapman and others, 2012), indicating uplift from deep crustal levels (~30-35 km).