Younger metavolcanic rocks
Younger metavolcanic rocks
middle Cretaceous, ~95-106 Ma
Occurs in the Strawberry Mine, eastern Boyden Cave, western Ritter Range, southwestern Goddard, and associated smaller roof pendants in central Sierra Nevada. Chiefly metamorphosed rhyolite to dacite ash-flow tuff, andesite, and basalt volcaniclastic rocks and flows. Local metaandesite and metabasalt flows. In Merced Peak Quadrangle, chiefly metarhyolite to metadacite ash flows, which have yielded a zircon U-Pb age of ~100 Ma (Peck, 1980). The Strawberry Mine roof pendant is chiefly metamorphosed and deformed, shallow-level, andesite to rhyolite flows, tuff, and breccia. The closely spaced Merced Peak and Strawberry Mine roof pendants have yielded whole rock Rb-Sr ages of ~95-98 Ma (Peck, 1980; Nokleberg, 1981). In these areas, the unit overlies the Kings terrane (unit KSV). In the eastern Boyden roof pendant, metavolcanic units are chiefly metarhyolite and metadacite tuff and airfall ash, with lesser rhyolite lava and metavolcanic sedimentary rocks. These rocks have zircon U-Pb ages of ~104 and ~106 Ma (Saleeby and others, 1990). The western Ritter Range roof pendant, contains highly varied units of metamorphosed tuff breccia, crystal tuff, flows, hypabyssal intrusives, and bedded tuff ranging in composition from rhyolite to basalt, but with an average composition of dacite to rhyodacite. The unit is weakly schistose with dominant primary textures. The unit here has a zircon U-Pb age of ~100 Ma (Bateman, 1992), as well as a detrital zircon maximum depositional age (MDA) of ~101 Ma (Attia and others, 2022). In the Ritter Range area, the unit stratigraphically overlaps the metavolcanic member of the Goddard terrane of Nokleberg (1983; herein part of the Sierra Crest terrane, unit SCGV). Unit intrusively linked to Merced Peak and Washburn Lake intrusive suite (unit Gmw; Peck, 1980). This unit forms part of the Monarch arc, along with units SHKOG, Gmw, and Gbvc.