Pastoria intrusive suite
Pastoria intrusive suite
Cretaceous, ~80-105 Ma
Occurs in the western Tehachapi Mountains and easternmost San Emigdio Mountains north of the Garlock fault south branch and south of the Pastoria fault, intruding the Pastoria terrane (unit PAS). Chiefly granodiorite, tonalite, and granite. Includes the Lebec granodiorite and monzogranite of Brush Mountain of Kellogg and others (2008); Lebec granodiorite, granite of Brush Mountain, and tonalite of San Emigdio Creek of Chapman and Saleeby (2012); granodiorite of Lebec and granite of Brush Mountain of Kistler and Ross (1990) [each work defines and maps the units somewhat differently]. The granite of Brush Mountain of Kistler and Ross has yielded a Rb-Sr age of ~91 Ma, whereas the granite of Brush Mountain of Chapman and Saleeby (2012) has yielded a zircon U-Pb age of ~105 Ma, and James (1986) assigned it a U-Pb age of ~98 Ma. The granodiorite of Lebec has yielded zircon U-Pb ages of ~80-92 Ma (Chapman and others, 2012; Kellogg and others, 2008, Nourse and others, 2020). However, the only age in this unit less than 88 Ma is the 80 Ma age of Nourse and others (2020), which is from rock within the Garlock fault zone at the intersection with the San Andreas fault, so that anomalous age may indicate lead loss near the San Andreas fault or may indicate that the sample is actually from a fault sliver of a younger part of the Northernmost Mojave intrusive suite (unit Gnm) which crops out just south of the Garlock fault south branch. On the other hand, Kistler and Ross (1990) correlate the granodiorite of Lebec with the granodiorite of Gato Montes (in unit Gnm), offset by the Garlock fault, so differentiation between units Gps and Gnm may be moot. Local pervasive alteration to sausserite and sericite. Discrete secondary muscovite and chlorite. Widespread, disseminated hornblende phenocrysts. Aluminum in hornblende indicates igneous pressure of 3.1-5.8 kbar (Chapman and others, 2012). This suite is in the upper block of the Pastoria normal (detachment) fault.