Sierra Nevada Aquatic Research Laboratory

25 Sep, 10 AM - 28 Sep, 03 AM

The Hilton Creek fault, adjacent to the Sierra Nevada Aquatic Research Laboratory in eastern California, is a prominent range-front normal fault bounding Long Valley caldera to the mountains of the southern Sierra Block (fig. 1). This fault is within the Eastern California Shear Zone (a diffuse zone of deformation between the Pacific and North American plates), and is hypothesized to be the eruptive epicenter of the 760 ka Long Valley caldera eruption, which ejected ~ 600 km3 of rhyolitic magma and blanketed a large portion of the southwest United States in the Bishop tuff (Hildreth and Mahood, 1986). Recent seismicity in the caldera coincident with the growth of Long Valley’s resurgent dome since 1980 has prompted renewed interest in studying the tectonics and magmatism of the area to better mitigate geologic hazards (e.g., Hill et al., 2002, 2003). Though we know the Hilton Creek fault has been active since the Last Glacial Maximum (Berry, 1997), little is known about the long-term evolution of the Hilton Creek fault and its relationship to the magmatic evolution of Long Valley caldera. Furthermore, recent work by the author and collaborators shows through an analysis of pleistocene lake-shoreline deformation that post-caldera extensional tilting did not begin until about 175 ka, revealing a ~500 kyr gap in normal faulting in Long Valley Caldera during a period of prolonged regional extension (Perkins et al., 2010 AGU Fall Meeting abstract). This suggests a dynamic relationship between regional tectonics, magma chamber evolution, and crustal rheology in Long Valley caldera that is at present poorly understood. To better understand the relationship between the magmatic evolution of Long Valley and the rheology of the Hilton Creek fault, however, we must first understand how this structure behaved before the eruption of the Bishop tuff. Here we propose to study the long-term evolution of the Hilton Creek fault using (U-Th)/He and apatite fission track thermochronology. Establishing constraints on motion of the Hilton Creek fault over million-year timescales will: 1)provide a baseline for determining the initial boundary conditions of Long Valley before the eruption of the Bishop Tuff and formation of its caldera; 2) provide a long-term, integrated slip rate that can be compared to other primary faults in the Eastern California Shear Zone; 3) allow comparison with slip rates measured over much shorter timescales (e.g., Berry, 1997); and 4)paired with geomorphic observations, help toward understanding the influence of magma intrusion on the rheology of the fault and the associated tectonic evolution of Long Valley caldera.

Visit #29721 @Sierra Nevada Aquatic Research Laboratory

Approved

Under Project # 21625 | Research

Late Pleistocene Surface Deformation at Long Valley Caldera

faculty - University of California, Santa Cruz

Reservation Members(s)

Group of 1 Graduate Student Sep 25 - 28, 2012 (4 days)
Group of 1 Research Assistant (non-student/faculty/postdoc) Sep 25 - 28, 2012 (4 days)

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Dorm 2 Sep 25 - 28, 2012