Stokes Mountain intrusive suite
Stokes Mountain intrusive suite
Early Cretaceous, ~110-130 Ma
Occurs in foothills along western slopes of central Sierra Nevada. Chiefly cumulate gabbro, norite, tonalite, and granodiorite with lesser granite. Zircon U-Pb ages are ~110-130 Ma (Saleeby and Sharp, 1980; Chen and Moore, 1982; Clemens-Knott and Saleeby, 1999). This unit has also yielded amphibole K-Ar ages of 123, 142, and 176 Ma, but the older two ages are anomalously old and may represent remnants within the plutons of the older Late Jurassic mafic dikes that intrude the adjacent Merced River terrane wall rock (Saleeby and Sharp, 1980). Hildebrand and Whalen (2021) report relatively low Nb/Y, La/Yb, and Sr/Y for this unit. Lackey and others (2008) report low zircon d18O (~5.5o/oo VSMOW) and whole-rock d18O (~6-7o/oo VSMOW) and 87Sr/86Sri values between ~.703-.706. Major plutons: the eastern and western ring complexes in the Stokes Mountain area north of the Kaweah River, and the ring-like Academy Pluton located farther north (Mack and others, 1979; Clemens-Knott and Saleeby, 1999). In the Stokes Mountain area, low-pressure contact metamorphism and coeval volcanic xenoliths indicate that the ring dike complexes are shallow, subvolcanic structures. The primitive geochemical and isotopic signatures of these Early Cretaceous plutonic rocks reveal the role of a depleted-mantle–derived parental magma for the westernmost and earliest phases of the Cretaceous Sierra Nevada batholith (Clemens-Knott and Saleeby, 1999). Saleeby and Sharp (1980) attributed a distinctive, elongate gravity and aeromagnetic high to dense and magnetically susceptible magnetite-rich cumulate rocks of this unit in the subsurface, although small outcrops of the unit extend southward beyond the main geophysical anomaly (perhaps the small volumes of the plutonic bodies of this unit there minimize its geophysical expression).