CAT SQUARE TERRANE OF THE SOUTHERN APPALACHIAN PIEDMONT: CORRELATION WITH NORTHERN APPALACHIAN SALINIC BASINS AND MAGMATISM

Structural analysis requires the Southern Appalachian Inner Piedmont and Eastern Blue Ridge be restored to their position along the Laurentian margin at the Devonian-Mississippian boundary (ca. 360 Ma), inboard of the exposed PA-NY App, after removing more than 500 km of Miss (and Dev?) dextral slip preserved within these terranes. Restored to this (present day) latitude, the relationship between the Inner Piedmont Wenlock-Ludlow Cat Square basin and more “classic” late Silurian Salinic basins – Connecticut Valley-Gaspé, central Maine, Fredericton Trough, La Poile Group of southwestern Newfoundland – becomes more clear. These basins formed following accretion of Carolina or Ganderia to Laurentia as Iapetus closed in the Late Ordovician. In the southern Appalachians, earliest basin sedimentation (post 430 Ma) is coeval with extensive plutonic activity (partial melting of crust?) and followed by (mantle-derived?) bimodal plutonism (Concord-Mecklenburg and Salisury-Southmont suites). These patterns are also recognized in the New England and Maritime App, where bimodal volcanism of the Tobique, Piscataquis, and Coastal Maine belts is observed. The simultaneity of these events along strike is remarkable. Subcrustal lithospheric delamination has been suggested by several authors as a means to generate the post-accretion continental rift. Delamination has the benefits of removing the “strong” part of the lithosphere: kinematically disconnecting Caro-Gand from Laur and aiding post-accretionary terrane dispersal (including the Laur Goochland fragment), and ultimately major crustal shortening across the width of the basin. Additionally delamination yields isostatic effects lowering average elevation and promoting basinal sedimentation. Thus stratigraphic and igneous expressions of the Salinic event are interpreted to be responses to changes in the thickness of the sub-crustal lithosphere.