DECIPHERING DEFORMATION CONDITIONS ALONG THE CARTHAGE-COLTON MYLONITE ZONE, NW ADIRONDACKS, BASED ON FELDSPAR MICROSTRUCTURES

The Adirondack Mountains, located in northern New York State, constitutes the southeastern extension of the Grenville Province and consists of two tectonic domains; The Adirondack Highlands and Adirondack Lowlands. The Adirondack Highlands is characterised by granulite-facies metamorphic rocks, whereas upper amphibolite-facies metamorphic rocks form the Lowlands. The Carthage-Colton Mylonite Zone (CCMZ), a northeast trending, ductile shear zone, represents the boundary between the two domains. While the importance of the CCMZ is well-recognised, the timing and style of deformation have not been clearly documented. Previous research has variably interpreted this shear zone as a normal, thrust, or strike-slip fault active during either the Ottawan (ca. 1090-1020 Ma) or Shawinigan (ca. 1190-1140 Ma) orogenies. In order to better understand the sense of motion along the CCMZ and deformation conditions, we focused on feldspar microstructures in the mylonitic rocks exposed along the Raquette River area. Kinematic indicators within the mylonites, including asymmetric porphyroclasts, C-C’ fabrics, core-mantle structures dominantly suggest top-to-north sense of shear. Microstructures in feldspars, such as the presence of serrated core-mantle boundaries, non-polygonal subgrains, and shear bands within individual feldspar grains, flame perthites at grain boundaries, intragrain fractures, restrict the conditions of deformation between 400 to >500°C. Our results match well with the temperature ranges obtained from the southern part of the CCMZ.