THE NEWTON ANTIFORM, NC: A PREVIOUSLY UNRECOGNIZED WINDOW THROUGH THE ALLOCHTHONOUS INNER PIEDMONT THRUST STACK

The southern Appalachian Inner Piedmont (IP) is a migmatitic, polydeformed, composite terrane that consists of a gently dipping stack of SW-directed ductile Type F thrust sheets. The Brindle Creek fault separates Laurentian affinity paragneisses and Ordovician to Silurian orthogneisses of the eastern Tugaloo terrane from mixed Laurentian and Gondwanan affinity, Siluro-Devonian paragneisses and Devonian to Mississippian granitoids of the Cat Square terrane. The Newton antiform (NA), recognized by Goldsmith et al., is a broad NE-SW-trending, doubly plunging antiform in the eastern IP between Hickory and Statesville, NC. It exposes a unique assemblage of biotite gneiss, biotite–hornblende gneiss, amphibolite, and ultramafic rocks that dip gently to steeply NW beneath the typical Cat Square terrane rocks. Truncations of Siluro-Devonian paragneisses and bodies of ~366 Ma Walker Top Granite occur along the NW boundary of the NA. On the southeast flank of the NA the rocks dip southeast beneath the central Piedmont suture. Biotite gneiss with amphibolite interlayers and boudins dominate and surround larger bodies of amphibolite and altered ultramafic rocks. Lesser amounts of pelitic schist and metagraywacke occur locally. Amphibolite geochemistry varies from MORB, to calc-alkali basalt, and island-arc tholeiite. Detrital zircons were separated from two paragneisses from the NA, and SHRIMP U-Pb ages reveal peaks at 1.0, 1.15, 1.2 Ga (Grenvillian), and 1.4 Ga (Granite-Rhyolite Province?) implying a Laurentian provenance. A sample interpreted as a biotite orthogneiss yielded a U-Pb age of 1050±18 Ma with metamorphic rims of ~350 Ma and may be a fragment of Grenville crust. Similar lithostratigraphies, detrital zircon populations, and possible Grenville basement permit correlation of NA rocks with the Tugaloo terrane. The NA thus is a window through the Brindle Creek thrust sheet, supporting the allochthonous nature of the Cat Square terrane restoring to a position ~40 km east of the NA.