THE STRUCTURAL EVOLUTION AND REGIONAL TECTONIC IMPORTANCE OF THE HONEY HILL FAULT ZONE, SE, CONNECTICUT – A KEY TO UNDERSTANDING THE OROGENIC COLLAPSE OF THE SOUTHERN NEW ENGLAND APPALACHIANS

The Honey Hill Fault system (HHF) is one of the most significant fault systems in southern New England because it forms a boundary between two major terranes (`Avalonia' and `Ganderia'). It also links with the Lake Char Fault further north which has experienced repeated low-level historical seismicity, including a notable earthquake swarm in Plainfield in 2015. The fault system is poorly understood in terms of its motion history and timing. However, understanding the structural evolution of the HHF system is essential for determining: 1) how the crust of southern New England was assembled, 2) how the Appalachian Mountains were created, and 3) how the mountain belt was later disassembled by orogenic collapse. All models of the tectonic evolution of southern New England have remained incomplete until now, because of uncertainty regarding the HHF system's history. In this study, detailed field investigations of the HHF along its E-W segment between Bozrah and Preston, CT were carried out during summer-fall, 2019 to document the rock types that the fault passes through and separates, structural evidence for brittle and ductile deformation, and outcrop-scale kinematic indicators. In addition, samples were collected for thin-section analysis of micro-structures that reveal mineral-scale deformation mechanisms and shear sense. Preliminary results indicate that the fault zone contains spectacular mylonites and ultramylonites with high-temperature ductile shearing indicative of top-to-the-northwest extensional displacement with left-lateral components of strike-slip displacement, followed by brittle normal faulting. Evidence for earlier top-to-the-south thrusting was also identified. Our results provide further evidence for deep-seated and regional orogenic collapse in the southeastern New England Appalachians following Pennsylvanian-Permian crustal thickening during Pangea assembly.