Award Date
8-1-2022
Degree Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Geoscience
First Committee Member
Michael Wells
Second Committee Member
Thomas Hoisch
Third Committee Member
Oliver Tschauner
Fourth Committee Member
Ashkan Salamat
Fifth Committee Member
Rodney Metcalf
Sixth Committee Member
Pamela Burnley
Number of Pages
340
Abstract
This dissertation investigates and applies different techniques for studying mid-crustal metamorphic rocks including detrital zircon geochronology, monazite petrochronology, thermodynamic pressure-temperature modeling, and elastic geobarometry. The first chapter reconstructs stratigraphy in deformed metamorphic rocks from the Funeral Mountains metamorphic core complex in Death Valley, California, and the Bullfrog Hills, Nevada, using U-Pb detrital zircon (DZ) geochronology. This study documents another successful application of stratigraphic techniques applied to metamorphic rocks and migmatites. DZ geochronology identified Pahrump Group metasediments in rocks that were previously interpreted to be Paleoproterozoic basement gneisses, providing insights into the distribution of Rodinia rift basins. This analysis has shown that the rocks in Monarch Canyon comprise continuous stratigraphy from the Boundary Canyon detachment fault to the deepest level of the core complex, where stratigraphy is repeated by folding and cut by faulting. In the second chapter, monazite petrogenesis is investigated and used to reconstruct the metamorphic history of rocks in the deepest structural levels of the Funeral Mountains, in the Monarch Canyon study area. Petrologic modeling and U-Pb monazite petrochronology provided insights into metamorphic processes and regional tectonics in Monarch Canyon. We reconstructed the pressure-temperature-time (P-T-t) history that comprises Jurassic to Early Cretaceous prograde metamorphism, possible Jurassic decompression, Late Cretaceous (105-88 Ma) peak metamorphism, and Late Cretaceous (88-75 Ma) decompression. This study evaluated the petrogenesis of monazite, which was shown to have crystallized/recrystallized during various prograde and retrograde chemical reactions that produced separate generations with distinct geochemistries and morphologies. Pressure-temperature modeling and petrography document the conditions of mid-crustal Mesozoic metamorphism. The third chapter comprises an analysis of geobarometry by applying quartz-in-garnet (QuiG) geobarometry and thermodynamic P-T modeling in rocks from the Funeral Mountains and the Wood Hills metamorphic core complexes. Spectroscopy, synchrotron X-ray diffraction, and petrology in these rocks gave new insights into the applications and limitations of elastic geobarometry and P-T modeling. We produced an extensive dataset including 260 strains calculated using a hydrostatic Raman calibration, six strains calculated using Grüneisen tensors, and three strains obtained from synchrotron X-ray diffraction data. These data were used to calculate entrapment pressures (analogous to garnet growth pressures in these rocks) and the pressures were compared to pressures obtained using thermodynamic modeling. These comparisons demonstrated that elastic pressures are internally consistent, but several kbar higher than thermodynamic equilibrium-based pressures. The final chapter of this dissertation investigates another aspect of QuiG geobarometry – the Equation of State (EoS) of the garnet host. The compressibility of garnet is used in the elastic calculations, and because natural garnet occurs as a combination of different compositional endmembers, the constitutive properties of a garnet sample must be mixed. This chapter investigates the effect of different approaches to end-member mixing of garnet bulk moduli on QuiG calculations and demonstrated that QuiG pressures in garnet from the Albion Mountains metamorphic core complex were not affected by various mixing approaches, as the mixed values overlapped experimental data. These four studies have contributed to our understanding of regional tectonics and metamorphic processes and provided crucial tests of analytical techniques that are used in petrology and structural geology studies.
Keywords
Funeral Mountains; Metamorphic Core Complex; Monarch Canyon; Monazite petrochronology; QuiG elastic geobarometry; Raman Spectroscopy
Disciplines
Geology | Mineral Physics
File Format
File Size
32700 KB
Degree Grantor
University of Nevada, Las Vegas
Language
English
Repository Citation
Mulligan, Suzanne Renae, "The Application of Detrital Zircon Geochronology, Pressure-Temperature Modeling, Monazite Petrochronology, and Quartz-In-Garnet Elastic Geobarometry to the Tectonic Evolution of the Funeral Mountains and Related Metamorphic Core Complexes" (2022). UNLV Theses, Dissertations, Professional Papers, and Capstones. 4524.
http://dx.doi.org/10.34917/33690300
Rights
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