DETAILED PETROLOGIC CHARACTERIZATION OF THE WHITESIDES GRANITE, WESTERN NC: RESOLVING ASSIMILATION FROM MAGMATIC VARIABILITY IN AN ANCIENT PLUTON

The Whitesides granite is thought to be a syntectonic pluton that intruded rocks of the olistostromal Ashe Metamorphic Suite (AMS) around ~470 Ma. The unit is strongly deformed, with regional folding and subsequent erosion segregating it into a series of NE-trending lenticular outcrops. The Whitesides Granite is traditionally described as trondhjemitic/tonalitic due to its strongly leucocratic appearance, and is commonly treated as a single coherent body despite its outcrop pattern and indications of variability at both outcrop and handsample scale. Toward understanding this variation, we are examining Whitesides Granite exposures in several different localities (Walnut Creek Road; US 64 near Highlands, NC; US 64 east of Cashiers, NC; US 107 N of Cashiers, NC; the NFS Panthertown Wilderness area), using both field mapping and geochemical analysis techniques.

Detailed geologic mapping of contacts between the Whitesides Granite and surrounding AMS in Panthertown point to extensive migmatite development along its margins, with extensive stoping and incorporation of AMS metapelites and amphibolites. Even far from contacts, petrographic studies indicate significant variation in plagioclase/K-feldspar ratios, in plagioclase compositions, in the presence of muscovite, and in Fe-bearing minerals (variable amounts of biotite (~0-10% modally), occasional appearance of hornblende). This variation suggests a compositional range extending to Qz diorite, monzonite, and granite via IUGS classification. This variation may reflect the effects of assimilation of diverse AMS lithologies, or it may record primary variability in the Whitesides pluton. We are using Whitesides and AMS mineral chemistry data, and bulk compositions of the Whitesides granite from these localities to try to document the extent of its petrologic variability, toward constraining its parental magmatic composition(s) and petrogenetic history.