LATE-STAGE ALLEGHANIAN WRENCHING OF THE SOUTHWESTERN NARRAGANSETT BASIN, RHODE-ISLAND

Late-stage Alleghanian deformation is broadly distributed over the western portion of the Narragansett Basin, Rhode Island, and overprints several generations of collision-related, synmetamorphic, nappe-like folds. The geometries of all structural generations are profoundly influenced by the curved western basin margin, indicating that the shape of the margin is not just an erosional feature. The late phase structures are best explained by two independent transcurrent shear zones: (1) sinistral transcurrent motion on (and between) north-northeast-striking zones in the western passage of the Narragansett Bay and along the western basin margin, and (2) dextral transcurrent motion along a wide northeast-striking zone from the Beaverhead shear zone to the western basin margin. Deformation within the high-grade metamorphic rocks in the western portion of the basin is expressed much differently than that in the lower grade rocks of the southeastern and south-central portions of the basin.