TACONIC BASIN FORMATION AND MAGMATISM IN NEW ENGLAND AND NEWFOUNDLAND

Previous models have suggested the Taconic orogeny was diachronous along the Appalachian margin. Here we present new CA-TIMS ages on Middle Ordovician ashes in foreland deposits of the Table Head Group of Newfoundland. These ages are indistinguishable from ages on ashes in the Indian River Formation of New York and biostratigraphic constraints on the Saint Daniel mélange in Quebec. Thus, we suggest that this Middle Orodvician Taconic foreland is a feature that is ubiquitous along the margin of the northern Appalachians. In Newfoundland, Middle Ordovician foreland deposition is due to the emplacement of Dashwoods onto the Humber margin. In New York and Quebec, loading may be due to the thrusting of Moretown onto the platform margin. We also present new detrital zircon data to test if Dashwoods is North American or Gondwanan and represents a continuation of the Moretown Terrane. A later, Katian, successor retro-arc foreland basin is preserved in the Long Point Group of Newfoundland, which is superimposed on the underlying Middle Ordovician foreland deposits of the Table Head and Goose Tickle groups. Similarly, the Katian Utica Shale represents a second, distinct, basin-forming event in New York. These two, distinct subsidence events are borne out in subsidence analyses in both New England and Newfoundland.