EXHUMATION MECHANISMS IN THE CHESTER DOME, SOUTHEAST VERMONT: COLLABORATIVE UNDERGRADUATE RESEARCH

The Chester dome is a large north-south trending gneiss dome of the New England Appalachians located in southeastern Vermont that has a complex geological history. The Chester quadrangle has been mapped in detail and actively studied for decades, yet questions regarding the Chester-Athens Dome origin remain unanswered. As part of an undergraduate research class at Wayne State University, we focused on questions surrounding the exhumation mechanisms of gneiss domes, the Chester dome as an example. Specifically, we set out to test whether the Chester dome exhumed due to extensional unroofing or diapiric rise. Four teams of three students each developed hypotheses, planned and conducted field work, and performed analyses. Field work included making strike and dip measurements, as well as collecting rock samples to be analyzed via Scanning Electron Microscopy (SEM), and petrographic analysis.

The dome contains several bounding faults with two different kinematic histories visible at the microscopic scale throughout the Chester dome. Petrographic analyses reveal numerous S-C fabrics within muscovite/biotite mica foliation indicating dextral shear, while pyrope-grossular spiral garnets suggest sinistral motion, possibly indicating two episodes of deformation.

SEM analyses suggest that there are at least two different compositions of garnets, and alteration textures surrounding the garnets, which is consistent with multiple episodes of garnet growth. Field data collected indicate extreme deformation along the outsides of the gneiss dome with chevron and zed folds visible throughout the outer portion of the dome.

Our results contribute to understanding the exhumation mechanisms of gneiss domes, but are unable to distinguish between extensional unroofing versus diapiric rise mechanisms.

Understanding the complex nature of exhumation processes in mountain belts will improve our understanding of how crustal material is cycled through orogens, and how to ultimately use exhumed material to better understand the lower continental crust.