Myrmekite and K-feldspar augen in the Ponaganset gneiss, Rhode Island, Connecticut, and Massachusetts, USA

Along the Connecticut and Rhode Island boundary and extending into Massachusetts is the Hope Valley shear zone (Fig.1). On opposite sides are two distinct late-Precambrian Avalonian terranes, the Esmond-Dedham terrane containing the Ponaganset gneiss to the east, and the Hope Valley terrane containing the Hope Valley alaskite to the west (Moore, 1964; Quinn, 1971; Gromet and O`Hara, 1985; O`Hara and Gromet, 1985; Hermes and Zartman, 1985). The Devonian Scituate granite intrudes the Ponaganset gneiss in the southeastern part of the area. The Ponaganset gneiss mostly ranges from granite to tonalite, but small lenticular bodies of diorite and gabbro also occur. Locally, layers of augen gneiss are separated by narrow lenses of amphibolite.