Date of Final Oral Examination (Defense)
Type of Culminating Activity
Master of Science in Geoscience
Matthew Kohn, Ph.D.
Adrian Castro, Ph.D.
C.J. Northrup, Ph.D.
Quartz in garnet (“QuiG”) barometry is a relatively new technique that uses physical properties of minerals to estimate the pressure of garnet nucleation and growth history independent of chemical equilibrium. QuiG barometry was used to determine pressures of garnet growth and compared to thermodynamically calculated P-T conditions for two samples (FH-1M and Z3H) from the Lower Shieferhülle (Formation), Tauern Window, Austria. FH-1M was the first sample for which a P-T path was calculated through inversion of chemical zoning in garnet (Selverstone et al., 1984). Mineral Assemblage Diagrams (MADs) and geothermobarometric techniques were used to determine P-T conditions for garnet nucleation and peak metamorphism. No MAD reproduced either the results of Selvserstone et al. (1984) or petrologic observations such as mineral assemblages and likely P-T conditions as determined using independent thermobarometers. Thermobarometrically calculated rim conditions were consistent between our study and previous work in the Lower Schieferhülle. However, without appropriate inclusion assemblages and compositions, the accuracy of calculated core P-T conditions could not be independently assessed using thermobarometry for either rock. QuiG isomekes from both samples are broadly consistent with growth of garnet during exhumation with heating as originally proposed by Selverstone et al. (1984). However, the QuiG isomekes for Z3H suggest that 90% or more of the Z3H garnet grew over small changes in pressure and temperature or along a QuiG isomeke (heating with a slight increase in pressure). These results support the accuracy of prior P-T paths and their tectonic interpretations. However, inconsistencies between QuiG barometry vs. thermodynamic calculations remain unresolved.
Couch, Sam, "Re-Evaluation of the First Metamorphic P-T Path Using QuiG Barometry and Equilibrium Thermodynamics" (2021). Boise State University Theses and Dissertations. 1859.