Distribution and stratigraphy of basalts in the Southwest (Aberdeen) Portion of the Big Pine Volcanic Field, Owens Valley, California

The Pleistocene Big Pine Volcanic Field (BPVF), located in the Owens Valley of eastern California, is dominated by basaltic cinder cones and lavas, and should the field reactivate 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, I have determined the distribution and stratigraphy of basaltic lavas in the southwest portion of the BPVF, which contains the largest number of 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 13 cones, and at least 10 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 ~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 0.065 km3. Two general groups of basaltic lavas characterize the Aberdeen area: 1) xenocryst-rich and 2) xenolith-poor basalts. Xenolithrich basalts contain variable amounts ofultramafic, mafic, granitic, and metamorphic lithologies, whereas xenolith-poor lavas are dominated by olivine phenocrysts. In the xenolith rich lavas, Cr-spinel inclusions occur in olivine phenocrysts. Overlapping flow margins define relative ages between adjacent basalts. In both the North and South portions of the Aberdeen area, flows composing the base of the volcanic stratigraphy are from the xenolith-rich group, and are typically overlain by xenolith-poor flows. These xenolith-poor lavas are ~25% larger in volume than the relatively older xenolith-rich lavas. The relative stratigraphy of the vents and flows in the Aberdeen area is consistent with published isotopic ages for the mapped lava flows.