DECIPHERING PALEOZOIC DEFORMATIONAL HISTORY OF THE MORETOWN FORMATION, WESTERN MASSACHUSETTS

The Rowe-Moretown-Hawley Belt of western Massachusetts contains rocks that are interpreted to mark the Taconic arc-continent suture zone. The fabrics within this zone record the tectonic history of the Taconic collision and/or reactivation by later events such as the Salinic, Acadian, and Alleghenian orogenies. However, resolving the structural fabrics and tectonic events, particularly in southern New England, is hindered by the degree of transposition of earlier fabrics into the dominant N-S striking fabric. One significant area that may assist in separating and interpreting the structural fabrics is located within the Moretown Formation in the vicinity of the Hallockville Pond gneiss. The Ordovician Moretown Fm is believed to represent metamorphosed turbidite sediments associated with the Taconic forearc. The alternating schists and impure quartzites contain several generations of well-developed fabrics and microstructures. The Hallockville Pond gneiss is an isolated tonalitic body (3.8km x 1.7km) within the Moretown Fm. It is interpreted to be related to the Shelbourne Falls Arc (Karabinos et. Al 1998). The 479 ± 8 Ma age of the gneiss (Karabinos et al. 1998) suggests that it predates most or all of the deformational fabrics in the adjacent Moretown Fm. The fabrics wrap around the gneiss both on the east and west, but the region to the north is characterized by a complex set of folds and intersecting fabrics. This area is interpreted as a “low strain zone” where earlier structural relationships are preserved due to the competency of the adjacent gneiss. Field mapping and sample collection were conducted around and within the area of the low strain zone. On-going investigation includes detailed petrography, microstructural analysis, compositional mapping, monazite dating, and thermodynamic modeling. The acquired information will be used to constrain P-T-t-D path(s) and tectonic history of the Moretown Fm and provide new constraints on Paleozoic deformational history of the region.