WALKER TOP GRANITOID, EASTERN INNER PIEDMONT CAT SQUARE TERRANE, NORTH CAROLINA: ENIGMATIC PLUTONS AT BEST

The southern Appalachian Inner Piedmont (IP) Cat Square terrane, in the Devonian Acadian/Neoacadian deformational/metamorphic core, contains numerous Devonian-Mississippian high-K, peraluminous, catazonal granitic incompatible trace element-enriched plutons, with negative Eu anomalies. They intruded metasedimentary sequences containing mixed Laurentian and peri-Gondwanan affinity detrital zircons suggesting remnant-ocean deposition, identical to that in the Putnam-Nashoba terrane in New England, and that both were proximal when the ocean was open. In central-western NC, the garnet-bearing, megacrystic, catazonal Walker Top Granite/Granodiorite (WT) preserves blocky K-spar megacrysts 1–10 cm long in a groundmass of Ms-Bt-Qz-Pl-Afs. It was emplaced into the Appalachian eastern IP Cat Square terrane during the Acadian-Neoacadian orogeny. Several bodies were intruded from NE to SW from 407 to 357 Ma as this part of the Acadian-Neoacadian metamorphic core reached peak second sillimanite zone conditions. Major and trace-element, and isotopic chemistry indicate high-K, peraluminous, deep-seated I-type plutons that plot as volcanic arc or syn-collisional in standard diagrams. Kinematics suggest a transpressional-oblique, zippered N-to-S closure as Cat Square was subducted beneath Carolina-Avalon.

Deformed WT plutons occupy the upper plates of linear, SW-directed sheath folds enveloped by partially melted pelitic and quartzofeldspathic rocks. Less deformed, more elliptical WT bodies occur SE of the leading edge of the Brindle Creek thrust sheet. The 406 to 372 Ma megacrystic High Falls Granite in the central GA IP has a similar volcanic-arc and syncollisional geochemistry. Collectively, WT and other plutons helped weaken the crust and lubricated the IP lateral flow channel during the Acadian-Neoacadian event. Far-field connections may exist with the 413 ± 5 Ma megacrystic Kinsman Granodiorite in New England, and to the 397-386 Ma Devonian ash beds in the southern-central Appalachian foreland. Although uncommon for mid-crustal plutons like the WT to erupt, they may have provided conduits for magma to form magma chambers for volcanoes.