GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 240-11
Presentation Time: 10:45 AM


HEWETT, Kelsey, MURRAY, Breauna and BROWNLEE, Sarah J., Department of Geology, Wayne State University, 0224 Old Main, Detroit, MI 48208

Deformation in continental orogens occur at multiple scales from outcrop-scale folds down to folds within thin sections. The Chester Gneiss Dome, located in southeastern Vermont, is a ~50 x 20 km scalefold composed of gneiss and schist and contains various smaller scales of folding. This study will focus on how these rocks are deformed using electron backscatter diffraction (EBSD) to measure how the crystallographic preferred orientation (CPO) varies throughout the Chester Dome as a function of location within dome structure, magnitude of strain, and the mineralogic composition of the rock. We expect that rocks rich in quartz and feldspar will have weaker CPO’s than those rich in mica and amphibole, and rocks with higher strain, i.e. from boundary shear zones, will have stronger CPO’s than rocks from the interior of the dome. Preliminary results from 16 samples suggests that there is a wide variation in the CPO patterns and magnitude of CPO strength throughout Chester Dome for all minerals. Generally, quartz and feldspar display weaker and less well-defined patterns. Micas display consistent CPO’s suggesting slip on the basal plane with variability in the strength of the CPO. Amphibole displays strong CPO’s with variable patterns from those consistent with slip on (100)[001] to those displaying distinct girdles of (100) and [010], suggesting varying styles of deformation. Samples with significant clinozoisite have surprisingly strong CPOs generally consistent with slip on the (001) cleavage plane in the [010] direction. We will present further analysis of CPO patterns in Chester Dome from an additional ~40 samples.