Metamorphosed hypabyssal intrusive bodies and metagranitic rocks
Metamorphosed hypabyssal intrusive bodies and metagranitic rocks
middle Cretaceous, ~98-110 Ma
Occurs in the Boyden Cave, Strawberry Mine, Goddard, and Saddlebag Lake/Mount Dana roof pendants in central and southern Sierra Nevada. Predominantly small granitic plutons, in places intruding coeval metavolcanic rocks (unit SHKOV). In the western Boyden Cave roof pendant, this unit is ~108 Ma (zircon U-Pb) schistose hypabyssal hornblende-biotite dacite porphyry (Saleeby and others, 1990; Moore and Nokleberg, 1992). In the Strawberry Mine roof pendant, the unit is chiefly metamorphosed hypabyssal intrusive bodies of quartzofeldspathic gneiss and dikes of quartzofeldspathic hornfels, which have yielded a whole-rock Rb-Sr isochron age of ~98 Ma (Nokleberg, 1981). In these areas, the unit intrudes the metavolcanic member of the Kings terrane (unit KSV). In the eastern Boyden Cave pendant, this unit is a subvolcanic intrusion of massive hypersthene-bearing metadacite and a stock of metagranodiorite. These have a zircon U-Pb age of ~102-103 Ma (Saleeby and others, 1990). In that area, the unit intrudes the roughly coeval metavolcanic rocks (unit SHKOV) and is roughly the same age as the surrounding granitic units. In the Saddlebag Lake and Mount Dana roof pendants, chiefly shallow intrusive dacite porphyry and quartz monzodiorite. This part of the unit has yielded a whole rock Rb-Sr age of ~118 Ma (Kistler and Swanson, 1981), but Nokleberg and Kistler (1980) shows a Rb-Sr isochron age of ~100 Ma and Ardill and others (2020) report zircon U-Pb ages of ~100-101 Ma. In this area the unit intrudes and overlies the High Sierra terrane (units HSS and HSV). Saleeby and others (1990) report zircon U-Pb ages of ~105-110 Ma for bodies too small to show of similar rocks in the Oak Creek roof pendant, where they intrude rocks of the Sierra Crest terrane (unit SCGV). Unit intrusively linked to Merced Peak and Washburn Lake intrusive suite (unit Gmw) and to Buena Vista Crest intrusive suite (unit Gbvc). Along with the two intrusive suites and associated metavolcanic rocks (unit SHKOV), this unit forms the Monarch arc, a major volcanic arc overlap assemblage.