HALF A CENTURY OF MODERN APPALACHIAN TECTONICS—ARE WE HALFWAY THERE YET? (Invited Presentation)

The fossiliferous Appalachian (AP) foreland yielded a basic stratigraphic framework before the 20^th century; since 1970, strides were made in resolving the interior APs producing the first plate tectonics models (PTM): formulation of PTM for the central APs, Newfoundland (NFL) geology, and Williams’ formulation of the “NFL model.” Pre-1970s Billings’ and Thompson’s students produced quality geologic maps in New England, and a basic stratigraphic framework. They resolved major boundaries, geometries of plutons, and metamorphic zonation. A conceptual framework evolved earlier than in other parts of the APs. The central APs benefitted from quality work by the Stoses, Cloos, et al. before 1970, producing a stratigraphic-structural framework. Interior southern APs, however, remained the least known with huge areas known only by recon, and only a few small islands of DGM sufficient to construct rudimentary stratigraphic frameworks during the 1960s. Recent detailed geologic mapping (DGM) in interior Canadian Maritimes yielded new tectonic models. Conventional wisdom said the Blue Ridge and Piedmont (BRP) are so poorly exposed it was not worth venturing off of the roads, leaving ~70% of the BRP unknown today, but islands of DGM, incorporating shear-sense indicators that resolved many disputes about kinematics of major faults, grew in the interior APs in the late 20^th and early 21^st centuries. These data enabled use of TIMS, SIMS, and ICP-MS techniques since the 1990s, yielding quality ages of plutons and basement, detrital zircon provenance, timing of metamorphism, and discovered new exotic and suspect terranes.

New data-driven problems and tectonic models will emerge when DGM islands grow and are delimited by better geochronologic-geochemical, structural, and petrologic data. Addressing the remaining the Mesozoic-Cenozoic uplift of the APs problem requires better mantle structure geophysical data, and new geomorphic, modern geochronologic, and stratigraphic data.