CONSTRAINING THE TIMING AND KINEMATICS OF DEFORMATION IN THE ADIRONDACKS: MICROSTRUCTURAL ANALYSIS OF THE COLTON-CARTHAGE SHEAR ZONE, NORTHWEST ADIRONDACKS

The Adirondack Mountains exposes poly-deformed deep crustal rocks dissected by numerous ductile shear zones, therefore, provides a unique opportunity to better understand the conditions, timing, and mechanisms of metamorphism and deformation during the Greenville Orogeny. Forming one of the major tectonic boundaries in the Adirondacks, the Colton-Carthage Shear Zone (CCSZ) separates the upper amphibolite facies rocks of the Adirondack Lowlands from the granulite facies units in the Adirondack Highlands. Although it is widely accepted that the CCSZ has a prolonged history with variable movements, the timing, kinematics, and conditions of different deformation phases are highly debated. In this study, we focus on the northern end of the CCSZ within the Stone Valley area, where various lithologies of both the Highlands and Lowlands are exposed over 3.5 km long transect along the Raquette River. Macro and micro kinematic indicators in mylonites show dominant top-to-north shear of sense. Quartz and feldspar microstructures indicate medium to high deformation temperatures (400 to >500°C) during mylonitization in the shear zone as sub-grain rotation and grain boundary migration are the dominant deformation mechanisms. EBSD analysis indicate prism and rhomb <a> slip in quartz. Overall, combined with previous geo/thermochrometry, our results suggest that the CCSZ acted as a normal fault during the Ottawan Orogeny.