CAN BACK-ARC PROCESSES IN A SIMPLIFIED MODEL EXPLAIN MUCH OF THE COMPLEXITY OF THE NORTHERN APPALACHIAN OROGEN?

Current tectonic models of the Appalachian orogen invoke multiple subduction zones and terranes, employing comparisons with the complex boundaries between the Pacific, India-Australia, and Asian plates. Here, we explore the possibility that much of the complexity of the New England-Quebec-New Brunswick region can be explained by shredding within back-arc extensional settings of a single peri-Gondwanan (Gander) terrane followed by multi-stage closure. The progression of arcs and back-arcs is largely an areal and temporal expansion of van Staal et al.’s (2016) model. Younger arc rocks are locally superimposed on older arc systems, parts of which were split, now residing in widely separated outcrop belts, due to back-arc extension (remnant arcs). Constrained by published maps and cross sections, paleomagnetic, geochronological and geochemical provenance data, and estimates of shortening, we present a series of 12 paleotectonic maps for the period 515 to 400 Ma and a revised cross section. Vestiges of the Cambrian Penobscot arc occur in coastal ME, in western NH, and in circa 500 Ma rocks of the Shelburne Falls Arc of VT and MA. Back-arc spreading, which accelerated following Early Ordovician collision of the arc with the main Iapetan ridge (possible cause of the Penobscottian orogeny), led to opening of the Tetagouche back arc basin, precursor to the Central Maine Trough. In the model, arc volcanism in southern Quebec marks the final episode of the west-facing peri-Gondwanan arc prior to subduction polarity reversal around 450 Ma. Laurentian signals in these arc rocks and in the Chain Lakes zircon age distribution can be explained, respectively, by subduction of Laurentian sediment and by transport of Laurentian detritus onto the approaching Gander margin and/or from a recently recognized circa-1 billion year old West African source terrane. Remaining peri-Gondwanan elements accreted through the Silurian; following an initial Andean-style regime, the Connecticut Valley trough opened in the back arc region contributing to additional separation of older peri-Gondwanan arc elements. Acadian deformation was dominantly northwest-vergent in the modeled area, with the Central Maine Trough occupying a foredeep position. The model has potential for additional inferences regarding deep structure and rock types.