Document Type

Thesis

Date of Degree Completion

Summer 2018

Degree Name

Master of Science (MS)

Department

Geological Sciences

Committee Chair

Jeffrey Lee

Second Committee Member

Wendy A. Bohrson

Third Committee Member

Andrew Calvert

Fourth Committee Member

Chris Mattinson

Abstract

The Central Walker Lane, NV is an active dextral shear zone superimposed on the western boundary of the Basin and Range extensional province. Approximately 25% of dextral shear along the Pacific-North American plate boundary accommodated in the Walker Lane, a NW-striking, intracontinental dextral fault system in eastern California- western Nevada. In the Central Walker Lane, shear is accommodated on five major NW- striking faults, one of which is the Petrified Springs fault, with poorly constrained slip magnitudes, slip rates, and initiation ages. We completed new detailed geologic mapping, combined with structural studies, and 40Ar/39Ar geochronology document offset markers across the Petrified Springs fault and form the first dataset to constrain its geometry and pre-Pleistocene slip history. The Petrified Springs field area is predominantly Mesozoic metasedimentary and intrusive rocks that are overlain unconformably by Oligocene and Miocene tuffs and lavas offset by the Petrified Springs fault, a northwest-southeast striking, ~65 km long, dextral fault. Four Cenozoic offset markers, three paleovalleys and one truncated normal fault, constrain the slip history of the Petrified Springs fault. The three volcanic-filled paleovalleys yield ages of 27.11 ± 0.07 Ma (Henry and Faulds, 2010), 16.1 ± 0.1 Ma (40Ar/39Ar age, this study), 15.71 ± 0.03 Ma (40Ar/39Ar age, this study). The absence of measurable differential offset between the two oldest markers constrains the Petrified Springs fault’s initiation age to after 16.1 ± 0.1 Ma. The dextral offset of the two oldest markers yields an averaged dextral offset magnitude of 9.5 ± 1.8 km since ~16 Ma, indicating a minimum long-term dextral slip rate of 0.5 ± 0.2 mm/yr since the middle Miocene. This calculated long-term slip rate is equivalent, within error, to dextral offset rates calculated for the west adjacent dextral Benton Springs and Gumdrop Hills faults in the Central Walker Lane (Dubyoski et al., 2016; Mayberry and Lee, 2017) and to GPS data constrained estimates for current slip on the Petrified Springs fault (Bormann et al., 2016). Kinematic and structural data do not indicate a significant magnitude of vertical offset on the Petrified Springs fault.

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