THE STRUCTURAL GEOLOGY OF TWO HIGH STRAIN ZONES ALONG THE NORUMBEGA FAULT SYSTEM, CENTRAL COASTAL MAINE

Strain localization displacement structures such as shear zones and faults occur at any type of tectonic regime and are important manifestations of plate tectonic activity. This study focuses on two northeast striking dextral high strain zones located in central coastal Maine: the 6km long, 100m wide Hill 806 high strain zone which has never been studied in great detail and the 15km long, 1km wide Ray Corner zone high strain zone which was previously undiscovered. The two high strain zones are separated by 2km within the central portion of the Norumbega fault system in Maine (a 450km long and up to 30km wide dextral transcurrent fault system) and this study provides a multipronged approach to comparing the rocks within each of these zones. Understanding and differentiating between the various types of high strain rocks in the Ray Corner and Hill 806 high strain zones provides insight to their relative timing, conditions of deformation and displacement history.

Despite their dextral habit, northeast striking orientation, and proximity to one another, close study at the macroscopic, mesoscopic, and microscopic scales indicate significant differences between these two zones. The Ray Corner high strain zone is characterized by many episodes of deformation and a variety of fault rocks, characteristic of both the ductile and brittle regimes, while the Hill 806 is a high strain zone best described by varying mylonite (from coarse grained to ultramylonitic fabric) with notable similarities to surrounding host rocks but no evidence of reactivation. The Ray Corner high strain zone stands out as a critical piece of the Norumbega fault system, connecting the southwestern region of ductile deformation with the northeastern region of later brittle reactivation. These results can be used to expand the story of the Norumbega fault system and are a useful analog for the processes of active transcurrent faults elsewhere.