Award Date

12-1-2017

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Geoscience

First Committee Member

Wanda J. Taylor

Second Committee Member

Arya Udry

Third Committee Member

Rodney Metcalf

Fourth Committee Member

Luke Barbara

Number of Pages

66

Abstract

Strike-slip faults play an important role in the development and evolution of extensional regimes including in the intraplate extension in the Basin and Range province. The Basin and Range province is divided into the Northwestern, Northern, Central and Southern Basin and

Range subprovinces. The boundary zone between the Northern and Central subprovinces is marked by several left-lateral fault zones, including the Pahranagat Shear Zone (PSZ), Caliente-Enterprise Zone and Rock Valley Fault Zone. The PSZ has a close spatial and kinematic relationship with the left-lateral Caliente-Enterprise Zone, which lies to the NE, and a slightly more distal relationship to the left-lateral Rock Valley Fault Zone off to the southwest. Understanding the internal deformation within these left-lateral zones is

fundamental to understanding how these zones, in part or as a whole, accommodate deformation and interact with other structures. The PSZ consists of three ENE-striking left lateral strike-slip faults: the Arrowhead Mine Fault, Buckhorn Fault (BF), and Maynard Lake Fault, from north to south, respectively, with intervening normal to oblique slip faults and folds. Understanding the internal deformation is critical to understanding the PSZ as a whole, and thus, development of the sub-province boundary.

The BF, the largest structure internal to the PSZ, along with surrounding structures provides insight into the internal deformation history of the PSZ. Important surrounding structures include the Buckhorn Syncline and Anticline, which are located between the Arrowhead Mine

Fault and the BF. Both of these structures formed from stresses internal to the PSZ. This study focuses on formation of strike-slip faults, timing of deformation, kinematic history, and geometry of structures using data from a new 1:12,000 scale map of the western BF and a new 40Ar/39Ar date.

Exposed structures near the BF display three ages of deformation: (1) an episode of early Miocene normal faulting between 22.56 and 18.51 Ma, (2) mid-Miocene normal faulting between 18.51 Ma and 15.3 Ma, and (3) faulting and folding after deposition of the Kane

Wash Tuff at15.3 Ma. The 15.3 Ma age was acquired from 40Ar/39Ar dating of sanidine crystals from the Kane Wash Tuff, subunit 3. The third deformation is the best preserved and exposed in the area. In addition, paleohills can be identified by a buttress unconformity

between the Paleozoic strata and Tertiary ash-flow tuffs. Retrodeforming these paleohills by removing the three episodes of post 22.56 Ma deformations steepens the dip of bedding in the hills to >50° before deposition of the tuffs. The paleohill located just south of the BF is relatively internally undeformed and is here suggested to belong to the footwall of the Gass Peak Thrust, which is a part of the ~Cretaceous Sevier fold-and-thrust belt.

Overall, the boundary zone between the NBR and CBR is defined by a series of left-lateral zones including the PSZ. The folds and faults define a zone of3D (triaxial strain) within the PSZ. The PSZ acts as part of the modern, and developing, transfer zone between the Eastern California Shear Zone and/or Walker Lane Belt and the Wasatch Fault Zone/Intermountain Seismic Belt.

Keywords

Buckhorn; Geoscience; Pahranagat; Structure

Disciplines

Geology

Language

English

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