Earth and Planetary Sciences ETDs

Publication Date

Fall 10-25-2018

Abstract

Metamorphic core complexes (MCC) are distinctive uplifts that expose deeply exhumed and deformed crustal rocks due to localized extensional deformation. Consequently, their detailed structure provide a window into deep crustal mechanics. The North American Cordillera contains numerous MCC, one of which is the Ruby Mountains core complex (RMCC) located in the highly extended northern Basin and Range. To constrain the extent to which anisotropy below the RMCC deviates from the regional Basin and Range average and test the depth dependence of crustal anisotropy we conduct a radial anisotropy investigation below the RMCC and surrounding northern Basin and Range. Data from the Ruby Mountains Seismic Experiment (RMSE) and surrounding networks are used to cross correlate ambient noise and obtain Rayleigh and Love wave signals. Using the frequency-time analysis (FTAN) method we compute inter-station Rayleigh and Love wave dispersion curves and invert for phase velocity maps for periods 5-40 s. A Bayesian Markov chain Monte Carlo (BMMC) inversion technique is used to obtain 3D Vs structure and estimate radial anisotropy as a function of depth and geographic location. Results show a relatively simple but pervasive, ~6%, positive (VSH > VSV) signal distributed throughout the middle crust (~5-20 km) of the study region required at 95% confidence. In contrast, there is an absence of similarly strong and significant lower crustal radial anisotropy. Interestingly, the volume directly below the RMCC does not uniformly deviate from the regional trend. Middle crustal radial anisotropy is stronger than average beneath the southern RMCC and weaker than the regional average beneath the northern RMCC. The lack of clear correlation between the RMCC and radial anisotropy in the crust suggests mechanisms of core complex exhumation either never produced a resolvable radial anisotropy pattern or that anisotropy associated with RMCC exhumation has subsequently been overprinted. Multiple mechanisms have the potential to explain the regional depth distribution of anisotropy, including decreasing prevalence of mica from the middle-to-lower crust and a temperature-controlled rheological transition from localized ductile deformation in the middle crust to distributed ductile deformation in the lower crust.

Degree Name

Earth and Planetary Sciences

Level of Degree

Masters

Department Name

Department of Earth and Planetary Sciences

First Committee Member (Chair)

Dr. Brandon Schmandt

Second Committee Member

Dr. Karl Karlstrom

Third Committee Member

Dr. Lindsay Lowe Worthington

Language

English

Keywords

ambient noise, surface waves, inversion, tomography, brittle ductile transition, Nevada, metamorphic core complex, tectonics, geology, Bayesian statistics

Document Type

Thesis

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