POLYDEFORMATION AND INTRUSIVE BRECCIATION OF THE ROPE FERRY GNEISS IN COASTAL OUTCROPS ALONG THE WATERFORD-NIANTIC COASTLINE, EASTERN CONNECTICUT

Detailed mapping in three prominent coastal exposures in the Niantic-Waterford region of eastern Connecticut reveals a complex history of gneiss deformation, intrusive brecciation and pegmatite intrusion. At the Pleasure Beach promontory, Neoproterozoic Rope Ferry Gneiss comprises a mixed felsic-intermediate L-S tectonite that is localy folded, injected by foliation-parallel and cross-cutting pegmatitic dikes and intruded by irregular masses of undeformed granite (Westerly granite equivalent). Locally, the gneiss is strongly brecciated by the intrusive granites creating an agmatite with irregular gneiss blocks occurring in random orientation within the surrounding granite. Six separate deformation and intrusive events are documented. At Camp Harkness, the gneiss is internally isoclinally folded and meso-scale, leucosome-filled, ductile shear zones are widespread. At Waterford State Park, the gneiss is folded into a series of NW striking, WSW-vergent, antiforms and synforms. Folding post-dated development of foliation boudinage and is likely related to a contractional event which caused regional refolding in the New London-Lyme region. Cross-cutting, multi-generational, undeformed pegmatites cut all rock types at all three peninsular study areas. Late-stage NW and NNE striking joints compartmentalize the outcrops and are responsible for the elongate shapes of the bedrock peninsulas. The coastal exposures provide insights into the prolonged tectono-magmatic evolution of the Avalonian basement in SE Connecticut and its local variability in terms of amount of contractional strain, percentage of intrusive material and degree of melt enhanced deformation.