BEDROCK GEOLOGIC MAP AND STRUCTURAL ANALYSIS OF THE HONEY HILL FAULT AND ADJACENT TERRANES IN SOUTHEASTERN CONNECTICUT, 1:50,000 SCALE

The Honey Hill Fault (HHF) is a north-dipping ductile mylonite zone located in southeastern Connecticut. The fault separates rocks of the Ganderian Putnam terrane (PT) in the northeast and overlying metasedimentary rocks of the Merrimack belt (MB) in the northwest from the Avalon terrane (AT) to the south. Geologic mapping was carried out as part of a USGS EDMAP project and partly supported by a GSA Graduate Student Research Grant to understand the structural history of the HHF and adjacent domains. Within the field area, the PT is composed of Cambrian-Silurian rocks that include gabbro, gneiss, schist, amphibolite, granofels, pegmatite and marble. The MB is composed of Silurian to Early Devonian rocks that include gneiss, schist, granofels and metamorphosed calcareous turbidite. The AT is composed of Neoproterozoic to Devonian rocks that include granite, gneiss, schist, pegmatite and quartzite. The HHF zone shows mylonitic and cataclastic rocks.

In the AT, southeast of the line between Stoddard State Park and North Stonington, CT, foliations generally dip NNE to NW and lineations plunge N or NE. Northwest of this line in the AT, foliations dip to the NNE to NW and lineations plunge to the N to NW. In the Preston Gabbro of the eastern PT, flow foliation orientations vary. In the PT, west of the Preston Gabbro, foliations are folded by shallowly NNW-plunging folds. Lineations are parallel to the fold axis. To the west, in the PT and MB, foliations dip N along the HHF and ENE to the NE indicating the presence of a NE-dipping, N-plunging synform. Lineations and S-folds here plunge to the north. Along the HHF, S-C fabrics and asymmetric folds indicate north-side-down movement. Joints in the AT, PT and MB are typically orthogonal to foliation. In the Preston Gabbro, and in a north-trending exposure of quartzite along a north-trending fault system in the AT at Lantern Hill, south of the Preston Gabbro, joints and veins strike north and west.

These structures represent deformation as a result of late Silurian accretion of the AT culminating in the Acadian orogeny (most structures in the PT) followed by the formation of Pangea resulting in the Alleghanian orogeny (most structures in the AT, based on published work). The normal movement along the HHF may have occurred during Mesozoic breakup of Pangea.