THE NEOACADIAN OROGENY IN THE SOUTHERN AND CENTRAL APPALACHIANS: A KINEMATIC MODEL LINKING MIDDLE DEVONIAN–EARLY MISSISSIPPIAN ACCRETION OF THE CAROLINA SUPERTERRANE, OROGENIC CHANNEL FLOW, AND FORELAND SEDIMENTATION

The Neoacadian orogeny in the southern and central Appalachians (SCA) is characterized by 380-340 Ma metamorphism, deformation, and plutonism in the Blue Ridge and Inner Piedmont (IP). The IP is the core of the Neoacadian orogen in the SCA and records Late Dev.-Miss. closure of the Rheic remnant ocean basin, and high-grade metamorphism (sillimanite I and II) of Siluro-Dev. pelite and psammite. The IP is a large, composite, sillimanite-grade terrane that extends from near the VA-NC border, to central AL and consists of the eastern Tugaloo, Milton, and Cat Square (CSt) terranes. The IP is bounded to the west by the Brevard fault zone and the east by the central Piedmont suture. The CSt is bounded by the younger-over-older Brindle Creek fault to the west and the central Piedmont suture to the east. It consists of a unique sequence of Siluro-Dev. metapsammite and pelitic schist intruded by Dev. anatectic granitoids (Toluca Granite, ~378 Ma, and Walker Top Granite, ~366 and ~407 Ma). Rare mafic and ultramafic rocks occur in the eastern CSt and may represent relict oceanic lithosphere on which CSt sediments were deposited. Minimum sediment thickness is estimated at 4 km (13,000 ft). Detrital zircons indicate CSt rocks have a maximum age of ~430 Ma, with both Laurentian (1.1, 1.4, 1.8, 2.8 Ga) and peri-Gondwanan Carolina superterrane (Ct) (500, 600 Ma) provenance. Intrusion of the Concord and Salisbury plutonic suites into the Ct and position of the Smith River allochthon above the IP support Dev. subduction of the CSt and Tugaloo terranes beneath the Ct. Thus, the CSt was a Siluro-Devonian remnant ocean basin between Laurentia and the approaching Ct. Net estimates of SW-directed dextral strike-slip displacements of the Brevard fault zone range from 250 to 450 km. Palinspastic restoration of the IP delimits the location of the CSt basin to the Pennsylvania embayment, and links the mid-Dev. to Miss. deformation in the Neoacadian core with SW-migrating pulses of the diachronous Acadian-Neoacadian clastic wedge. Location and SW-migration of the clastic wedge in concert with structural patterns in the IP support transpressive NW-directed collision of the Ct with the New York promontory and zippered closing of the basin from NE to SW. Subduction of the CSt and parts of the Tugaloo terranes beneath the Ct resulted in a SW-directed orogenic channel.