TIMING AND IMPLICATIONS FOR THE EMPLACEMENT OF THE PALEOZOIC VALE (CAT SQUARE) CHARNOCKITE AND WALKER TOP GRANITE, EASTERN INNER PIEDMONT, NORTH CAROLINA

The southern Appalachian eastern Inner Piedmont (eIP) Cat Square terrane (CSt) is bound by the Brindle Creek fault (BCf) to the west and Central Piedmont suture to the east. This terrane is thought to be a remnant ocean basin accreted during the Neoacadian orogeny during collision of Laurentian terranes and the Carolina superterrane (Cs). It consists of metagraywacke, pelitic schist, calc-silicate, minor mafic and ultramafic bodies, and Devonian to Mississippian anatectic granitoids. These granitoids range in age from 407 Ma to 350 Ma, and were emplaced after the terrane was subducted eastward beneath the Cs. Movement on the BCf likely occurred during and after emplacement of the granitoids from 380-330 Ma. The Newton window in the eIP is framed by the BCf and exposes Tugaloo terrane rocks. Within the eastern CSt, just west of the Newton window, are xenoliths of Paleozoic charnockite in the Walker Top Granite (WTG) at Vale, N.C. U-Pb zircon SHRIMP analyses reveal a 367 ± 3 Ma age for charnockite crystallization with metamorphic rims that formed at 359 ± 2 Ma. The enclosing WTG yielded a U-Pb SHRIMP age of 355 ± 5 Ma. Oscillatory zoning in the zircons and REE data collected during zircon analyses indicate an igneous origin for both the Vale charnockite and WTG. Modeling of electron microprobe data from two-pyroxene and two-feldspar assemblages produced a crystallization temperature range of 925-955°C for the charnockite. Based on published estimates for the timing of Neoacadian events, the charnockite likely formed at depth in dry conditions from localized melting after the CSt was subducted beneath Neoacadian Cs. It was then incorporated as a xenolith into the WTG during peak metamorphism and deformation (360-350 Ma, 800-850°C, 5-6 kbar). Outcrop relationships between the two granitoids support this hypothesis, with gradational to sharp contacts and parallel foliations. Because peak metamorphic conditions do not reach charnockite-melting temperatures, it could not have formed as a product of Neoacadian metamorphism.