POLY-DEFORMATIONAL GEOLOGICAL HISTORY BETWEEN COLCHESTER AND SOUTH SALEM, CONNECTICUT: DOCUMENTING THE MID-CRUSTAL STRUCTURE NORTH AND SOUTH OF THE HONEY HILL FAULT ZONE

The Honey Hill Fault Zone is arguably the most important tectonic boundary in southeastern Connecticut separating the Avalonian and Iapetos basement terranes. However, for most of its length, it is poorly exposed and poorly understood in terms of its internal architecture, nature of fault rocks, kinematics, and record of reactivation. Therefore, in order to understand the deformational history of this key region of Connecticut, a field-based lithological and structural transect was completed during summer 2017 along a 7-mile section of Route 11 in Colchester and Salem that crosses the mapped trace of the fault system.

Outcrops along Route 11, from north to south, comprise rusty quartz-muscovite Brimfield schists, grey biotite-garnet-sillimanite schists, pegmatite boudin-rich quartzite, hornblende-biotite gneiss, feldspar augen-rich granodioritic orthogneiss, and dioritic-gabbroic orthogneiss and amphibolite. The northern half of the transect consists of a major recumbent south-vergent antiform; this interpretation is new and supported by minor fold asymmetries and lithological repetition. Cutting the southern overturned limb of the antiform are top-to-the-north low-angle extensional shear zones with spectacular kinematic indicators including macro-and micro-scale S-C fabrics, extensional shear bands, rotated objects and amphibole fish. Micas from shear zone tectonites are currently being processed for Ar-Ar ages. The core zone of the Honey Hill Fault is not exposed nor is there much outcrop evidence for it. The entire transect is dominated by NW-SE shortening and vertical flattening overprinted by sub-horizontal extensional structures of both a ductile and brittle nature, and younger high-angle brittle normal faults. The highway road cuts reveal world-class examples of boudinage, folds and fabrics typical of mid-crustal polyphase deformation.