DEVELOPMENT OF THE APPALACHIANS FROM PALEOZOIC OROGENIES TO THE ANTHROPOCENE

Supercontinent Rodinia rifted apart in the Neoproterozoic. The Appalachians (AP) were built via a series of Paleozoic (PZ) accretionary and collisional events forming supercontinent Pangea (PG). The Ordovician Taconic orogeny involved arc generation and obduction above E- and W-dipping subduction zones. The Devonian-early Mississippian Acadian-Neoacadian orogeny was produced by collision of Peri-Gondwanan Gander, Avalon, Meguma, and Carolina superterranes with Laurentia (LW) and Taconian crust. The AP Wilson cycle was completed via zippered collision of Gondwana with LW and new PZ crust in the Alleghanian orogeny, doubling the crust in the southern-central APs forming supercontinent PG. All orogenies produced diachronous clastic wedges from exhumation of the internides of the AP. Rifting of PG began during the Mid-Triassic (TR, ~230 Ma), with early dextral then sinistral motion that reactivated many older faults, formed new ones, and formed S- to N-opening stepover basins. Brief compression formed brittle faults and stepovers containing siliceous cataclasite and zeolites that share mutually overprinting crosscutting relationships with 200 Ma CAMP diabase dikes. Spreading began in the Middle Jurassic and conjugate margins developed around the central Atlantic. Stresses along the LW margin inverted from tensional to compressional from the Late TR to the Early Cretaceous (K), remaining to the present, related to nearby cooled, dense ocean crust, and ridge push. The entire AP likely eroded to low hills with scattered monadnocks by the early Tertiary (T). Modern APs were uplifted to >2000 m in the late T, indicated by Coastal Plain (CP) marine strata at anomalous elevations, K and T trapped sediment at 250-685 m in the AP, changes in geomorphology, the late M inverted lake Gray fossil site in NE TN, anomalous drainages, and thick late Miocene (M)-Pliocene CP sediments. These data invalidate the long-held idea that “the APs are the oldest mountain chain in the world.”