HR: 0800h
AN: V21A-0396    [Abstracts]
TI: Distribution and Stratigraphy of Basaltic Lavas in the Southwest Portion of the Quaternary Big Pine Volcanic Field, California
AU: * Woolford, J
EM: jeffrey.woolford@csun.edu
AF: California State University Northridge, 18111 Nordhoff St., Northridge, CA 91330-8266,
AU: Vazquez, J
EM: jvazquez@csun.edu
AF: California State University Northridge, 18111 Nordhoff St., Northridge, CA 91330-8266,
AB: The Pleistocene Big Pine Volcanic Field (BPVF), located in the Owens Valley of eastern California, is dominated by basaltic cinder cones and lavas, and poses a potential volcanic hazard to local infrastructure, in particular Highway 395 and the Los Angeles Aqueduct. However, despite numerous petrologic studies, the volcanic history and distribution of products from individual BPVF eruptions are poorly known. Using detailed field mapping and petrology, we have determined the distribution and stratigraphy of basaltic lavas in the southwest portion of the BPVF, which contains the largest number exposed vents and lava. In the Aberdeen area, individual cinder cones and fissure vents are aligned along N-S trending lineaments, with local clustering of vents and lavas. Approximately 19 cones, and at least 14 lava flows occur in the area. Two cinder cones located near the valley floor are partly buried by younger lavas and alluvium. In most cases, lavas are aa in character and traveled ca. 7 km down alluvial fans (8% gradient) towards the Owens River. On average, individual lavas cover ca. 10-12 km², with average individual volumes of ca. 0.065 km³. Two general groups of basaltic lavas characterize the Aberdeen area: 1) xenocryst-rich and 2) xenolith-poor basalts. Xenolith-rich basalts contain variable amounts of ultramafic, mafic, granitic, and metamorphic lithologies, whereas xenolith-poor lavas are dominated by olivine phenocrysts. Overlapping flow margins define relative ages between adjacent basalts. In both north and south portions of the Aberdeen area, flows composing the base of the volcanic stratigraphy are the xenolith-rich variety, and are typically overlain by xenolith-poor flows. In general, these younger xenolith-poor lavas are approximately 25% larger in volume than the older xenolith-rich lavas. Several vents record changes in lava type during individual eruptions, suggesting transitions in magma discharge rate. At one vent cluster, pahoehoe is restricted to within ca. 1.5 km of its fissure vent and overlies more extensive aa from the same vent, suggesting a decrease in discharge rate of basalt over the course of the eruption. In contrast, lavas from a cinder cone on the eastern portion of BPVF comprise thin (<0.5 m) pahoehoe capped by thicker (1-2 m) aa flows, suggesting increasing discharge rate over the course of this eruption.
DE: 8425 Effusive volcanism
DE: 8429 Lava rheology and morphology
DE: 8486 Field relationships (1090, 3690)
DE: 8488 Volcanic hazards and risks
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting