Subduction zone between the paleo-american and the paleo-african plates in New England

Abstract

Cambrian and Tremadocian faunas of the Acado-Baltic Province have remarkable similarities on both sides of the Atlantic (Fig. I). Lower and Middle Cambrian representatives of this province are present in eastern Massachusetts, whereas Pacific Province faunas are present in nearby western New England and eastern New York. The Boston Border Fault and its presumed continuation to the south marks the western margin of the Palco-African Plate which contains the Acado-Baltic fauna localities (Fig. 2). Immediately west of the Acado-Baltic localities in Massachusetts is a sequence of rocks interpreted as an ophiolite suite (Figs. 3, 4 and 5), marking a subduction zone whose western margin is marked by the Clinton-Newbury Fault Zone (Fig. 3). The trace of this fault is marked by the most conspicuous magnetic lineament in southeastern New England (Fig. 6) and is interpreted as the eastern margin of the Paleo-American Plate. The Marlboro and Nashoba Formations and younger Unnamed Formations (Figs. 3 and 4) whose protoliths consist of sea floor metavolcanics and metasediments of the ophiolite suite, represent ensimatic crust, squeezed and in tensely deformed between the two paleo-plates. Thus a collision boundary between two continental plates (Fig. 7) is hypothesized for the northern Appalachians. I infer that plate tectonic mechanisms have been operative since at least the end of Precambrian time.