LITHOSPHERIC PROCESSES AND THE LATE CENOZOIC ORIGIN OF THE APPALACHIAN MOUNTAINS

Appalachian (AP) lithosphere is a composite of: (1) Grenville crust/lithosphere (CL) beneath the AP foreland, Blue Ridge, and W Piedmont; (2) early to late Paleozoic (PZ) crust; (3) Peri-Gondwanan CL E of the central Piedmont suture; and (4) Gondwanan CL in FL, S GA, and S AL and possibly other places. CL beneath the E Piedmont underwent extension during the early Mesozoic (MZ) to break up Pangea and open the Atlantic. ~40% of AP crust is buried beneath the Atlantic and Gulf Coastal Plains and continental shelf (AGCP), with knowledge restricted to geophysical and drillhole data. Stresses along the Laurentian margin inverted from tensional to compressional and ridge push from the Late Jurassic to the Early Cretaceous (K), remaining to today. The AP likely eroded to low hills with a few monadnocks by the early Paleocene. Late K and Eocene-Paleocene sedimentation rates (SR) are dwarfed by late Miocene-Pliocene (LMP) SR in AGCP sediments that likely record the late Mesozoic (MZ)-Tertiary (T) AP uplift. Present-day topography (TP) and major drainages in the non-glaciated AP reveal anomalous patterns that alone indicate PZ-early MZ tectonics and rock types play a minor role in today’s topography: major drainages that drain the W AP head in the E Blue Ridge (BR) and Piedmont. The 1,500->2000 m maximum AP height shifts from the S AP BR to the central AP foreland. Thick LMP sediments occur at anomalously high elevations (>200 m) in southern MS, and Cretaceous-T non-marine sediments are trapped in the AP at 285-685 m. The late Miocene Gray fossil site inverted lake in NE TN further documents TP inversion. Deep CL rather than surficial processes had to produce these data; a residual PZ isostatic uplift component was largely exhausted in the MZ. Proposed continental shelf loading is an effect of uplift, not a cause. Lithospheric upwelling with incremental surface strain in the early T and LMP are probably responsible for TP uplift, and the LMP event for present high TP in the AP from S U.S. to NFLD.