Laramide Shortening in the Clark Mountain Thrust Complex: Reinterpretation of the Timing of the Winters Pass Thrust, Mojave Desert, SE California

Author

Hayden M. KombrinkFollow

Award Date

5-1-2024

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Geoscience

First Committee Member

Michael Wells

Second Committee Member

Andrew Martin

Third Committee Member

Kevin Konrad

Fourth Committee Member

George Rhee

Number of Pages

131

Abstract

The transition to flat slab subduction, around ~90-80 Ma during the Laramide orogeny, marks a pivotal shift in the style of deformation for the North American Cordillera. Late Cretaceous deformation associated with the change in subduction angle is observed throughout the Mojave, paradoxically manifesting as extensional strain deforming the thickened crust formed during the Sevier orogeny. The Winters Pass thrust, located in the Mesquite Mountains of southeastern California, has long been regarded to be the southern continuation of the Wheeler Pass thrust of the NW Spring Mountains, 50 km to the north, and the northern continuation of the Pachalka thrust, 20 km to the south in the Clark Mountains. This study uses ⁴⁰Ar/³⁹Ar geochronology on synkinematic muscovite to provide direct geochronologic constraints on mylonitic deformation for the Winters Pass, Powerline Road and Pachalka thrusts. Structural data paired with kinematic and microstructural data from petrographic and SEM observations, and data collected with electron backscatter diffraction on recrystallized quartz allows for temperatures of deformation, the geometry of the thrust complex and transport direction of the upper-plate(s) to be determined. This study provides deformation timing constraints of ~73 Ma for the Winters Pass thrust, ~81 Ma for the Powerline Road thrust, and looser constraints on the Pachalka thrust of ~70-85 Ma. Structural data shows an overall NE-E direction of transport for the upper plate. These data suggest that these faults record a Laramide thrust complex with a backwards-breaking thrust sequence and are not correlative to any thrusts of the southern Sevier fold-thrust-belt in the Spring Mountains. We discuss possible drivers of contractional strain in the Mojave during this time and suggest that subduction of the conjugate Shatsky Rise paired with the proximity of the paleo rift-margin played a critical role in the unique style and age of deformation that is reported herein for this portion of the eastern Mojave Desert.

Keywords

Laramide; Mesquite Mountains; Mojave; Structural Geology; Tectonics; Thrust

Disciplines

Geology

File Format

pdf

File Size

14000 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

Repository Citation

Kombrink, Hayden M., "Laramide Shortening in the Clark Mountain Thrust Complex: Reinterpretation of the Timing of the Winters Pass Thrust, Mojave Desert, SE California" (2024). UNLV Theses, Dissertations, Professional Papers, and Capstones. 5024.
http://dx.doi.org/10.34917/37650848

Rights

IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/