Northernmost Mojave intrusive suite
Northernmost Mojave intrusive suite
Cretaceous and Jurassic, ~82-96 Ma; ~147 Ma
Occurs in the northernmost Mojave block south of the Garlock fault, intruding the Bean Canyon terrane (units BCB and BCT). Chiefly granodiorite, tonalite, and granite. Includes Tejon Lookout Granite of Swanson and Olson (2016) and Olson and Swanson (2017; 2019); the granite of Tejon Lookout, the granodiorite of Gato Montes, granite of Bean Canyon, and granodiorite of Cameron of Ross (1989); the granite of Bean Canyon, granite of Tejon Lookout, and granodiorite of Gato Montes of Chapman and others (2012), and various unnamed plutonic units of Dibblee (1963; 1967) [each work defines and maps the units somewhat differently]. This unit has yielded Rb-Sr ages of ~96 Ma (Kistler and Ross, 1990) and zircon U-Pb ages of ~82-90, 92, and 96 Ma (James and others, 1986; Chapman and others, 2012; Nourse and others, 2020). Evernden and Kistler (1970) reported a biotite K-Ar age (representing cooling through ~300 degrees C) of ~80-81 Ma. Kistler and Ross (1990) stated that their granodiorite of Gato Montes in this unit is the same as their granodiorite of Lebec (part of unit Gps), offset along the Garlock fault. This unit has aluminum in hornblende emplacement pressure of about 2.4-2.8 kbar (Chapman and others, 2012), somewhat less than the possibly correlated Pastoria intrusive suite (unit Gps). This unit as mapped also incorporates the granodiorite of Gamblespring Canyon of Chapman and others (2012) [not mapped in detail], which has a zircon U-Pb age of ~147 Ma. The Gamblespring Canyon granodiorite is probably the same as the unnamed hornblende diorite unit of Dibblee (1963) which crops out in lenses adjacent to the schist of Tylerhorse Canyon (part of unit BC) and pods in the Cretaceous granitics too small to show on the map, and probably is part of the wall rock for the later Cretaceous plutons. Chapman and others (2012) note the similarity in age and lithology between the Gamblespring Canyon granodiorite and the Independence Dike Swarm (unit Gid), but in their model they do not restore the block to the area of the dike swarm, so correlation is unclear. This unit is apparently in the upper plate of the Pastoria Normal fault based on depth of emplacement, although that fault does not bound this block.