Publication Date

8-2024

Date of Final Oral Examination (Defense)

5-3-2024

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Geoscience

Department

Geosciences

Supervisory Committee Chair

Matt Kohn, Ph.D.

Supervisory Committee Member

Karen Viskupic, Ph.D.

Supervisory Committee Member

C.J. Northrup, Ph.D.

Abstract

Constructing and interpreting pressure-temperature (P-T) paths in metamorphic rocks is crucial to understanding tectonic processes occurring at mid- to deep-crustal levels. Conventional methods for obtaining P-T paths rely on mineral chemistry, such as chemical zoning in garnets, which assumes growth at chemical equilibrium. However, studies show that garnet growth can occur with disequilibrium nucleation, which can result in a biased or potentially incorrect P-T path. An alternative, physics-based approach using Raman spectroscopy can also be used to determine P-T paths. This method involves using elastic thermobarometry of quartz inclusions within garnet. In this study, I tested the hypothesis that P-T paths calculated using Raman microspectroscopy yield values for pressure that are comparable to those previously calculated from chemical zoning in garnets. This hypothesis was tested by calculating the entrapment pressure of quartz in garnets from the Hardscrabble Synclinorium, west-central New Hampshire, which can be used to interpret the nucleation pressure of garnet. Two samples were analyzed, K87-21C and D84-1C. I also recalculated these paths using thermodynamic inversion of chemical zoning in garnets. Both Raman results and newly calculated P-T paths were compared to previously calculated P-T paths. Raman spectroscopy isomekes for both samples show a scatter of pressures that do not allow for a robust comparison of Raman methods and thermodynamic modeling, suggesting Raman spectroscopy may not be applicable for calculating P-T paths with low- to moderate- variations in pressure.

DOI

https://doi.org/10.18122/td.2316.boisestate

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