GONDWANAN - SOUTH AMERICAN CONNECTIONS IN TACONIAN, ACADIAN-CALEDONIAN, AND YOUNGER OROGENIC RECORDS IN THE NORTHERN APPALACHIANS AND NORWEGIAN CALEDONIDES (I)

Discovery of an E Laurentian terrane in the Argentine pre-Cordillera led to thoughts that subduction beneath, and continental collision with, W South America was active in the Taconian of E Laurentia. Recent work in Argentina suggests separate arrival to South America, but similar timing. However, relationships in 'medial New England', incl. crust contamination in igneous rocks of the 480-442 Ma Shelburne Falls - Bronson Hill arc(s?) above the Taconian subduction zone(s?), indicate Late Ordovician arrival of a quasi-continental mass and subsequent extension/flooding. Further, the Early- to Mid-Silurian is a thin shelf sequence unconformably on ruins of the Taconian orogen grading SE into a thick continentally derived sedimentary wedge fronting on a deep basin or ocean. Complicating this 'simple' view in New Brunswick are early Silurian NW subduction and blueschists, on the NW margin of the Miramichi terrane, with broad evidence of phengite metamorphism. Miramichi has good Gondwanan connections and correlation with 'medial New England', though the trace of the high-P zones is obscured in high-T zones of W and S New England.

The Acadian orogen (423-380 Ma) involved Avalon arrival, with NW-spreading clastic facies, volcanism, plutonism, fold/thrust tectonics, and metamorphism across the Silurian, and the deformed medial New England, igneous arcs and Laurentian margin. The heart of deformation/metamorphism in S New England is not Acadian, but a new Quaboagian ('Neo-Acadian') cycle 370-350 Ma (Late Dev. - Early Miss.) with mantle-related magmatism, crustal melting, granulite-facies metamorphism, and tectonics, first with SE-directed thrusting, then a large dextral shear regime. Quaboagian, especially dextral shear, could relate to a plate reconstruction with NW South America near Newfoundland at 370 Ma with an ocean to SW, and near Florida at 340 with 'Paleotethys' to NE; thus an image of 'side-swipe tectonics' for this episode. Gondwana influence continued. A narrow belt of Late Pennsylvanian ('Northfieldian') kyanite-grade metamorphism formed near the Connecticut Valley at 310-285 Ma, while Westphalian-Stephanian coals were deposited in SE New England, themselves overtaken by up to sillimanite-grade metamorphism during final Alleghanian deformation (270-250 Ma), equating with arrival of W. Africa.