Pliocene – Quaternary Extension Across the Volcanic Tableland and Black Mountain Area, Eastern California Shear Zone

Kevin DeLano

Document Type

Oral Presentation

Campus where you would like to present

SURC Ballroom B/C/D

Start Date

21-5-2015

End Date

21-5-2015

Keywords

Tectonics, Normal Faulting, Mapping

Abstract

The San Andreas fault and the Walker Lane Belt (WLB) together form the boundary between the Pacific and North American tectonic plates. A fundamental question in geology is how do faults in the WLB accommodate strike-slip motion between the Pacific and North American tectonic plates over space and time? To document the evolution of faults at a tectonic plate boundary, geologists compare present-day fault slip rates (geodetic studies) with geologic measurements of long-term slip rates (past ~0.1-5.0 million years). At latitude 37.5°N across the WLB, long-term slip rates sum to ~33 percent of the present-day slip rate. Nagorsen-Rinke et al. (2013) proposed that undocumented long-term fault slip explains part of this discrepancy. To test this model, I conducted new field geologic and LiDAR mapping, fault studies, and geochronology (determine the age of a rock) to calculate long-term fault slip rates across two areas: the Black Mountain and the Volcanic Tableland regions, eastern California. To calculate fault slip rates, I divided offset, a measure of the magnitude of displacement across faults, by the age of the displaced rock. In the Black Mountain area, fault slip rates are ≥0.2 mm/yr since 3.5 million years (m. y.). In that time, faulting has horizontally extended the Earth’s crust by ~15 percent. In the Volcanic Tableland area, the fault slip rate is 0.1-0.2 mm/yr since 0.7 m.y. Since 0.7 m.y., faulting has horizontally extended the Earth’s crust ~0.8-1.6 percent. The style of faulting matches our prediction, but our preliminary fault slip rate estimates are slightly lower than hypothesized.

Poster Number

9

Faculty Mentor(s)

Jeffrey Lee

Department/Program

Geological Sciences

Additional Mentoring Department

Geological Sciences

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May 21st, 8:30 AM May 21st, 11:00 AM

Pliocene – Quaternary Extension Across the Volcanic Tableland and Black Mountain Area, Eastern California Shear Zone

SURC Ballroom B/C/D

The San Andreas fault and the Walker Lane Belt (WLB) together form the boundary between the Pacific and North American tectonic plates. A fundamental question in geology is how do faults in the WLB accommodate strike-slip motion between the Pacific and North American tectonic plates over space and time? To document the evolution of faults at a tectonic plate boundary, geologists compare present-day fault slip rates (geodetic studies) with geologic measurements of long-term slip rates (past ~0.1-5.0 million years). At latitude 37.5°N across the WLB, long-term slip rates sum to ~33 percent of the present-day slip rate. Nagorsen-Rinke et al. (2013) proposed that undocumented long-term fault slip explains part of this discrepancy. To test this model, I conducted new field geologic and LiDAR mapping, fault studies, and geochronology (determine the age of a rock) to calculate long-term fault slip rates across two areas: the Black Mountain and the Volcanic Tableland regions, eastern California. To calculate fault slip rates, I divided offset, a measure of the magnitude of displacement across faults, by the age of the displaced rock. In the Black Mountain area, fault slip rates are ≥0.2 mm/yr since 3.5 million years (m. y.). In that time, faulting has horizontally extended the Earth’s crust by ~15 percent. In the Volcanic Tableland area, the fault slip rate is 0.1-0.2 mm/yr since 0.7 m.y. Since 0.7 m.y., faulting has horizontally extended the Earth’s crust ~0.8-1.6 percent. The style of faulting matches our prediction, but our preliminary fault slip rate estimates are slightly lower than hypothesized.