HR: 0830h
AN: V51G-0356    [PDF]
TI: Tertiary Paleogeography and Paleotectonic Evolution of the Sierra Nevada in the Carson Pass-Kirkwood Area, California
AU: * DeOreo, S
EM: deoreo@lsit.ucsb.edu
AF: Department of Geological Sciences, University of California, Santa Barbara,, CA 93106 United States
AU: Busby, C
EM: busby@geol.ucsb.edu
AF: Department of Geological Sciences, University of California, Santa Barbara,, CA 93106 United States
AU: Skilling, I
EM: skilling@pitt.edu
AF: Department of Geology and Planetary Science, 200 SRCC, University of Pittsburgh, Pittsburg, PA 15260 United States
AB: Volcanic and sedimentary rocks of the Miocene Mehrten Formation in the Carson Pass- Kirkwood Valley-Silver Lake area of Sierra Nevada (California) occupy a paleocanyon cut into Mesozoic granitic rocks. Nine unconformities were recognized within the sequence during recent fieldwork, demonstrating that the canyon was repeatedly incised. The lowest 5 units are dominantly braided stream and minor debris flow deposits with silicic to intermediate-composition volcanic clasts. These clasts, together with interstratified ignimbrites, were probably derived from volcanic centers to the east in Nevada, prior to the Sierra Nevada range front faulting. The upper 4 units are dominated by andesitic volcanic debris flow and debris avalanche deposits, interstratified with andesitic to dacitic lava domes, flow breccias, block-and-ash-flow tuffs and peperite intrusions. These units record the westward sweep of the arc from Nevada into the present-day Sierran crest, and development of high-relief centers that probably blocked sediment supply from the east. No significant faults were recognized in the region, although a N-S trending paleocanyon wall on the north side of Carson Pass was mistaken as a fault by previous workers. Ar/Ar dating in progress on volcanic rocks of units 2, 4, 6 and 8 will constrain the timing of the eight canyon incision events. The origin of the incision events is not yet clear.
DE: 1749 Volcanology, geochemistry, and petrology
DE: 8400 VOLCANOLOGY
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting