Day 4: South Fork Big Pine Creek
Published:January 01, 2005
2005. "Day 4: South Fork Big Pine Creek", Incremental assembly and emplacement of Mesozoic plutons in the Sierra Nevada and White and Inyo ranges, California, Drew S. Coleman, John M. Bartley, Allen F. Glazner, Richard D. Law
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Today we spend time in the central portion of the Sierra Nevada batholith, mapped here in detail by Moore (1963) and Bateman (1965). Plutons exposed along the eastern escarpment of the Sierra Nevada typically have U-Pb zircon ages between either 180-165 Ma or 96-88 Ma (Stern et al., 1981; Chen and Moore, 1982; Saleeby et al., 1990; Coleman et al., 1995; Coleman and Glazner, 1997). Both Jurassic and Cretaceous plutons are dominated by granodiorites with subordinate leucogranite. Cretaceous rocks also include an unusually high number of basaltic and dioritic rocks at this latitude (Moore, 1963; Frost and Mahood, 1987; Coleman et al., 1995; Sisson et al., 1996). Most Jurassic plutons are easily recognizable because they are cut by the 148 Ma Independence dike swarm which crops out nearly continuously between the central Sierra Nevada and the southern Mojave Desert (Moore and Hopson, 1961; James, 1989; Carl and Glazner, 2002). However, at least some such dikes in the region are Cretaceous (Coleman et al., 2000).
Today's route takes us south down Owens Valley. Owens Valley is the westernmost basin of the Basin and Range, and for much of its length it separates predominantly plutonic rocks of the Sierra Nevada from predominantly sedimentary rocks of the White and Inyo Mountains. Geologic offsets indicate ∼65 km of right-lateral displacement across Owens Valley (Bartley et al., 2003; Kylander-Clark et al., 2005; Glazner et al., 2005).
Driving south out of Bishop, a few miles south of town at M11, the White Mountains to the east (left) are composed predominantly of late Proterozoic and early Paleozoic metasedimentary rocks. Black Mountain, the peak at 11 o'clock, contains a thick sequence of dark brown Campito Formation quartzite, which we will see trapped between plutons in the Sierra Nevada at the next stop. At M104 radio telescopes of the Owens Valley Radio Observatory are visible at 9 o'clock. Entering Big Pine, Birch Mountain is the dominant peak at 2:45, and Crater Mountain, a tall basalt cinder cone of the Pleistocene Big Pine volcanic field, is at 1 o'clock.
Figures & Tables
Incremental assembly and emplacement of Mesozoic plutons in the Sierra Nevada and White and Inyo ranges, California
This field guide was created in coordination with the Geological Society of America Field Forum “Rethinking the Assembly and Evolution of Plutons: Field Tests and Perspectives,” held 7-14 October 2005 in the Sierra Nevada and White and Inyo ranges, California. The goal of this five-day field trip was to examine field relations and characteristics of plutons in the central Sierra Nevada and in the White and Inyo ranges as they relate to processes of pluton growth and emplacement and, more particularly, as they relate to the hypothesis that plutons are assembled slowly and incrementally.