Tectonic Evolution of the Appalachian Inner Piedmont from a New Detailed Geologic Map from the Brevard Fault into the Newton Window

The Appalachian Inner Piedmont (IP) contains the Acadian-Neoacadian metamorphic core of the Southern Appalachians and is bound by the Brevard fault zone (Bfz) to the W and Central Piedmont suture to the E. It consists of the Tugaloo (W) and Cat Square (E) terranes: both polydeformed, migmatitic terranes separated by the Brindle Creek fault (BCf). The Neoproterozoic, Laurentian provenance, deep-water Tugaloo terrane (Tt) sedimentary and volcanic rocks were deposited on oceanic crust and local Grenville basement massifs, intruded by Ordovician and younger plutons. The Siluro-Devonian, Laurentian and Peri-Gondwanan sourced, deep-water Cat Square terrane (CSt) sediments were deposited on oceanic crust, intruded by Devonian to Mississippian plutons. CSt amphibolite bodies may represent vestiges of remnant Rheic oceanic crust. Four ductile thrusts have been mapped in detail across ~3400km2 of the IP: the Tumblebug Creek fault (TCf), Sugarloaf Mountain-Six Mile fault (SMf), Mill Spring fault (MSf), and the BCf. The TCf, SMf, and MSf are SW-directed thrusts within the Tt. The BCf is a low-angle, E-dipping, SW-directed thrust in the South and Brushy Mountains and moderate to steeply W-dipping, NW-directed thrust framing the Newton Window (NtW). The BCf is strongly mylonitic containing ~1km of mylonite in the Brushy Mountains and is recognized by the truncation of CSt metasedimentary units and Walker Top Granite (WTG) against Tt rocks in the NtW. The WTG yielded U-Pb zircon SHRIMP ages of ~407 and ~355 Ma, which provide a minimum age for emplacement of the BCf. Metamorphic rim ages of 345-340 Ma were recorded during peak Neoacadian metamorphism. Metamorphic grade increases from staurolite-kyanite near the Bfz to sillimanite and higher across the core of the IP. The dominant mineral (transport) lineation, formed during peak deformation conditions, forms a curved pattern across the IP as large, plastic thrust sheets were deflected SW against the Bfz buttress.