BIRTH OF THE SIERRA NEVADA BATHOLITH: AGE AND COMPOSITION OF THE SCHEELITE INTRUSIVE SUITE AND COEVAL VOLCANIC ROCKS IN THE SADDLEBAG LAKE PENDANT, EASTERN CALIFORNIA

Granitic and volcanic rocks in the east central Sierra Nevada record the earliest stages of magmatism in the Sierra Nevada batholith, allowing us to examine magma sources and connections between plutonic and volcanic processes in the initial stages of batholith construction. Scheelite Intrusive Suite (SIS) is composed of the Wheeler Crest Granodiorite, Lee Vining Canyon Granite, granite of Mount Olsen, and (informal) granite of upper Pine Creek. SIMS ages of multiple zircons from each unit suggest SIS ranges in age from 226 to as young as 215 Ma, older than previously indicated by conventional bulk fraction zircon TIMS ages. SIS is a calc-alkalic suite compositionally broadly similar to the nearby Late Cretaceous Tuolumne and John Muir intrusive suites, though SIS plutons are Fe-rich and consistently lower in Sr/Y and La/Yb and higher Rb/Sr and Ba/Zr. SIS exhibits a trend toward lower ISr and higher εNd with increasing silica, in contrast to the constant or more radiogenic whole rock ISr trends observed in nearby Late Cretaceous intrusive suites. Along the western margin of the SIS, the basal Mesozoic volcanic section in the Saddlebag Lake pendant (SLP) includes volcanic rocks that are coeval and potentially comagmatic with components of the SIS. Widespread quartz-phyric welded tuffs of Black Mountain, Saddlebag Lake, and Greenstone Lake yield SIMS zircon ages of 232, 224, and 219 Ma, indicating that felsic ignimbrite volcanism continued during assembly of the SIS. SLP welded tuffs have high field strength element abundances and εNd values suggesting compositional affinity to the relatively felsic parts of the Wheeler Crest Granodiorite and the granite of Mount Olsen. SLP welded tuffs are interlayered with mafic flows and flow breccias, suggesting that felsic volcanism and perhaps caldera formation were spatially associated with construction of andesitic(?) stratovolcanoes. Mafic volcanism was coeval with 222 Ma monzodiorite intrusions in SLP Paleozoic basement.