Date of Graduation

5-2015

Level of Access

Restricted Access Thesis

Department or Program

Earth and Oceanographic Science

First Advisor

Emily M. Peterman

Abstract

Although the Appalachians formed one of the largest mountain belts on Earth, their early history remains elusive in large part because this early history has been overprinted. Garnet-kyanite-cordierite schist units cropping out on the western margin of the Goshen Dome of western Massachusetts provide a valuable window into these earliest phases of Appalachian mountain building. Laser ablation split-stream inductively coupled plasma-mass spectrometry (LASS-ICP-MS) and electron probe micro-analyzer (EPMA) wavelength-dispersive x-ray spectrometry (WDS) data from monazite included in two garnet-kyanite-cordierite schists yield a ~395 to 355 Ma metamorphic history constructed via the integration of U-Pb ages, rare earth element (REE) distributions, Gd/Yb ratios, Y compositional maps, and host phase population distributions.

This metamorphic history is characterized by a period of relic ultrahigh-pressure (UHP) garnet breakdown from ~396 to 383 Ma, a period of garnet growth from ~383 to 369 Ma concomitant with fluid pulsing/anatexis likely related to the high-T Acadian thermal event, and a second period of garnet breakdown from ~369 to 355 Ma. The schists share similar histories of exhumation, however the timing of early (pre-380 Ma) retrograde reactions is offset between the two samples by ~5 Myr. This suggests that the schist units came together at ~383 Ma during exhumation from UHP conditions to the mid-crust.

This study presents the first nearly continuous record of metamorphism during the early phases of mountain building in the Appalachians and provides valuable insight into exhumation processes of UHP terranes.

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