Document Type

Thesis

Date of Degree Completion

Winter 2021

Degree Name

Master of Science (MS)

Department

Geological Sciences

Committee Chair

Jeffrey Lee

Second Committee Member

Wendy A. Bohrson

Third Committee Member

Chris G. Mattinson

Abstract

Documenting the spatiotemporal evolution of fault systems along the western margin of North America is a prerequisite for characterizing the forces which drive faulting across the U.S. Cordillera. Within the Cordillera, the Walker Lane, characterized by active intracontinental faults, straddles the western edge of the Basin and Range Province and the eastern edge of the Sierra Nevada. In the Gabbs Valley Range, central Nevada, eastern Central Walker Lane, I combine new mapping, geochronology, and structural studies to document the geometry and timing of dextral fault slip along the Benton Spring fault, an active intracontinental fault. The Benton Spring fault is one of four major dextral faults in the region; my studies provide insight into this fault’s late Oligocene and Miocene fault slip history. Utilizing the walls of a series of inset volcanic rock infilled paleovalleys, which are preserved in the Gabbs Valley Range, I identified five markers dextrally offset across the Benton Spring fault. Previous studies provided ages for three of the volcanic units which infill these paleovalleys, while my new geochronology provides ages for a further two. All five markers record, within error, the same magnitude of dextral offset, indicating that the average dextral offset of 6.9 ± 1.5 km accumulated after the emplacement of the youngest dated volcanic unit at 20.14 ± 0.26 Ma. The adjacent Petrified Spring fault records similar magnitude of dextral offset, and azimuth and timing of fault slip as the Benton Spring fault; I assume that similar forces drove initiation of slip along both faults and thus slip likely initiated at the same time. Initiation of dextral slip along the major dextral faults of the eastern Central Walker Lane is constrained to the Middle Miocene as is initiation of slip along the normal faults bounding the eastern flank of the Sierra Nevada and within the Basin and Range. Given the close spatial-temporal relationship of the two different fault types, I suggest the same forces drove both normal and strike-slip faulting.

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