HR: 08:30h
AN: V31E-03    [Abstracts]
TI: Defining the Boundaries of the Volcanic Field about Yucca Mountain, Nevada: Implications for Volcanic Hazard Studies
AU: * Smith, E
EM: gsmith@ccmail.nevada.edu
AF: Department of Geoscience University of Nevada, Las Vegas, 4505 S. Maryland Parkway, Las Vegas, NV 89154-4010
AU: Keenan, D
EM: avertagus@cox.net
AF: Geoscience Consultants, 543 British CT, Henderson, NV 89014
AB: Knowledge of the size and shape of a volcanic field and the recurrence rate of volcanism are important components of a volcanic hazard study. The extent of the Pliocene-Quaternary basalt field about Yucca Mountain (YM) is controversial. Proposed volcanic field geometries include all Pliocene and Quaternary volcanoes, just Quaternary centers, all volcanoes about the Timber Mountain Caldera, volcanoes related to the Amargosa Valley Isotope Province, and volcanoes within the Amargosa trough. We suggest an alternative volcanic-field geometry that includes all Pliocene and Quaternary volcanoes in a belt extending from YM northeastward to the Reveille and Lunar Crater areas (RLC)in central Nevada. The following observations support this alternative volcanic field geometry: (1) Volcanoes near YM lie near the southern end of a belt of Pliocene-Quaternary basalt that stretches from Death Valley, California to the RLC. The belt rarely exceeds a width of 20 km and is completely isolated from similar aged basaltic volcanic fields in the Basin Range-Colorado Plateau transition zone to the east and the eastern front of the Sierra Nevada Range to the west. (2) Basaltic magmas along the length of the belt were produced by deep partial melting of asthenospheric mantle (133 to 115 km at YM and 162 to 110 km beneath the RLC). (3) Basaltic volcanism near YM and in the RLC is episodic with peaks of activity occurring at about 4 and 1 m.y. Most of these observations can be explained by an understanding of how the lithosphere interacts with the mantle. Mantle flow caused by a buttress produced by lithospheric thickening and delamination resulted in eddies or rolls that stir up areas of mantle close to the melting temperature. Mantle caught in upward flow melts due to pressure reduction and produces basaltic magma. A mantle eddy travels with the lithosphere and results in long-lived, geographically restricted magmatism. The shape and spacing of areas of hot mantle and the geometry of the buttress control the geographic extent and episodic nature of volcanism. An implication of this model is that a future peak of magmatism may occur when the next area of hot mantle is intersected by a mantle eddy caused by the lithospheric buttress. An implication of linking YM to the RLC is that higher RLC recurrence rates of volcanism may apply to YM. Recurrence rates for the RLC are as high as 12 events per million years; 4 times the rate calculated for the YM area.
DE: 8450 Planetary volcanism (5480, 6063, 8148)
DE: 8488 Volcanic hazards and risks
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005