BURIED VOLCANIC CENTERS NEAR YUCCA MOUNTAIN, NEVADA: SIGNIFICANCE FOR VOLCANIC HAZARD STUDIES AND THE NEOTECTONICS OF SOUTHERN NEVADA

A high-resolution aeromagnetic survey of the Yucca Mountain (YM) area (O’Leary et al., 2002) revealed 19 dipolar anomalies that most probably represent buried basaltic volcanic centers. Their interpretation as buried centers is strongly supported by the alignment of many of the centers into northeast trending chains and proven by several drill holes that have encountered basalt. The buried centers have implications for the calculation of the recurrence rate of volcanism, models for Quaternary volcanism in the central Great Basin, and earthquake hazard in southern Nevada. Smith et al. (2002) proposed a linkage between Quaternary volcanism near YM and in the Lunar Crater field nearly 100 km to the north. Volcanism was suggested to be episodic and sustained by a common area of hot mantle. Based on this linkage, recurrence rates of 11 to >15 events per m.y. were considered possible for the YM area. This estimate is nearly 4 times higher than previously suggested recurrence rates. The higher recurrence estimate, however, does not agree with the small number of volcanoes exposed at the surface in the YM area. The presence of 19 buried centers significantly affects the values of the recurrence rate and strongly supports the estimates of Smith et al. (2002). Preliminary results suggest that the estimated recurrence rate for volcanism at YM could be as high as 17 events per m.y. (or an estimated annual recurrence rate of 1.69 x 10-5) as determined by an ARIMA-model-based approach. Higher recurrence rates raise the likelihood of magmatic disruption of the proposed YM repository. A criticism of the Smith et al. (2002) model was that it linked one of the largest volume Quaternary volcanic fields in the Great Basin (Lunar Crater) with one of the smallest (Crater Flat-YM). The discovery of the buried centers, however, raises the possibility that the volcanic field near YM could be as large (in number of centers and volume) as Lunar Crater. If this is true, the hypothesis that the two volcanic fields are linked by a common area of hot mantle can be more strongly supported. Because volcanic eruptions are commonly associated with seismic activity, higher recurrence rates imply higher levels of future seismicity in the YM area.