Undergraduate Honors Theses

Thesis Defended

Spring 2019

Document Type

Thesis

Type of Thesis

Departmental Honors

Department

Geological Sciences

First Advisor

James Metcalf

Second Advisor

Rebecca Flowers

Third Advisor

Brian Hynek

Fourth Advisor

Douglas Duncan

Creative Commons License

Creative Commons Attribution-Noncommercial 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 4.0 License.

Abstract

Abstract:

The Mesozoic to Cenozoic transition from contraction to extension of the lithosphere in the western U.S. Cordillera is incompletely constrained due to competing interpretations based on low or high temperature thermochronometers. High temperature thermochronometers, petrological relationships, structural field relations, and P-T-t paths signal a long-lived and older period of extension and exhumation starting in the late-Cretaceous to Oligocene; whereas, competing theories from the analysis of low temperature thermochronometers, and analysis of extensional basins, suggest the onset of extension began mid-Miocene. In the following study, we use low temperature thermochronometers consisting of the apatite and zircon (U-Th)/He systems to analyze an extensional, mylonitic shear zone and exhumed metamorphic core complex within the Ruby Mountains, Nevada. Analysis of 28 zircons from the northern Ruby Mountains, NV depict time of rapid exhumation may have occurred ~17 Ma. Apatites and zircons derived over a 6 km east-west transect, from late-Cretaceous to mid-Cenozoic in age leucogranites, provide an age elevation transect that records exhumation and extension. Our data show a late-Oligocene to early Miocene exhumational history with zircon age dates ranging from 23.5 ± 0.7 to 12.1 ± 0.8 Ma while apatite ages span 18.5 ± 1.3 to 14.2 ± 0.7 Ma These dates are complimentary to previous low temperature thermochronometer studies in the southern Ruby Mountains that surmise extension began approximately 17 – 15 Ma. These dates only incorporate low temperature thermochronometers meaning higher temperature thermochronometer systems should record older ages indicative of extension predating the late-Oligocene to early-Miocene ages acquired.

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