GEOCHEMICAL ANALYSIS OF THE ZANA GRANITE AND KOWALIGA GNEISS, EASTERN BLUE RIDGE, ALABAMA

A vast array of Paleozoic pre-, syn- and post-kinematic granitoids intruded the Ashland-Wedowee-Emuckfaw-Dahlonega gold belt of the eastern Blue Ridge of Alabama and Georgia. Three batholith-scale plutons of the belt, the Elkahatchee Quartz Diorite Gneiss, Kowaliga Gneiss, and Zana Granite, have been the subjects of repeated attempts to determine their ages and thereby constrain the structural and magmatic evolution of the southern Appalachians. In the 1980’s, multi-grain zircon analyses coupled with Rb-Sr whole rock analyses were used to establish the crystallization age of the Zana, Kowaliga, and Elkahatchee. These studies suggested crystallization of the Elkahatchee during the latest Cambrian and the Zana and Kowaliga during the Middle Ordovician. Since then, modern techniques that utilize single grain analyses of zircons suggest a Late Devonian age for the Elkahatchee (~370 Ma). These new single grain laser ablation techniques decrease the possibilities of lead-loss, and aid in avoiding high uranium overgrowths and xenocrystic components. Preliminary results from this study indicate Late Ordovician/Early Silurian ages (~430-450 Ma) for both the Zana and Kowaliga. Samples from the Zana and Kowaliga have very similar bulk chemistry, but compared to previous data, our samples show higher average K₂O and lower CaO percentages. A majority of samples from the plutons plot in the granite field of silica vs total alkalis diagrams. Rocks from Zana, Kowaliga, and newly recognized Coley Creek orthogneiss plot in the calc-alkaline magma series in both A-F-M diagrams and SiO₂ vs K₂O diagrams; however, some samples from the Zana and Kowaliga plot in the shoshonitic series in the latter diagram. Trace element data from the Kowaliga, Zana, and Coley Creek all show strong negative europium anomalies. Ta-Yb binary diagrams suggest the Zana is a syn-collisional granite, while the Kowaliga plots largely in the volcanic-arc granite field. Rocks of the Coley Creek largely plot near the boundary of syn-collisional and within-plate granites. Structurally, rocks mapped as Zana intrude both the Timbergut and Josie Leg formations of the Emuckfaw Group and suture the contact between rocks of the Wedowee and Emuckfaw Groups in the southern portion of the Ashland-Wedowee-Emuckfaw-Dahlonega belt.