Date of Award

Spring 2025

Project Type

Thesis

Program or Major

Earth and Environmental Sciences

Degree Name

Master of Science

First Advisor

Jo Laird

Second Advisor

Joel Johnson

Third Advisor

Ian Honsberger

Abstract

Preservation of high- and ultra-high pressure Taconic metamorphic terranes is enigmatic in the northern Appalachians due to persistent metamorphic overprinting from subsequent orogenies. The Tillotson Peak Complex (TPC) in northern Vermont preserves the highest pressure conditions in the northern Appalachians. Previously, pressure-temperature (P-T) estimates were carried out using albite = jadeite + quartz thermobarometry, which yielded peak conditions of 1.2–1.4 GPa at 520–620ºC. Since these estimates, phase equilibria modeling software has improved, allowing for more accurate estimates of P-T. This study aims to provide new P-T estimates for the TPC by using the phase equilibria modeling software PERPLEX. SEM-EDS obtained mineral chemistry of mafic schist is utilized for phase equilibria (pseudosection) and isopleth calculations to constrain P-T conditions for the Taconic and Acadian orogenies. This thesis integrates results from Laird and Albee (1981) with new data collected in this study. The data are interpreted to reflect prograde conditions of metamorphism as high as 2.10 ± 0.20 GPa and 485 ± 10ºC during the Taconic, and conditions of 0.65 ± 0.25 GPa and 490 ± 20 ºC during the Acadian. Results suggest that the TPC was subducted to ~70 km during the Taconic, then exhumed to depths no greater than ~27 km before the Acadian. These results provide new insight into the variation of pressure and temperature conditions within the TPC, and suggest that the complex may have been multiple, separate slices that were imbricated during exhumation.

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