THE ZANA GRANITE AND KOWALIGA GNEISS: MAP RELATIONSHIPS AND GEOCHEMICAL CHARACTERISTICS OF ORDOVICIAN AND SILURIAN PLUTONS IN THE EASTERN BLUE RIDGE OF ALABAMA

The Zana Granite and Kowaliga Gneiss of the southern Appalachian, Alabama eastern Blue Ridge terrane are two of the largest plutons in the Ashland-Wedowee-Emuckfaw belt, exposed collectively over >350 square kilometers. These plutons were mapped at the regional, as well as 1:24000 scales, and span thirteen 7.5” quadrangles northwest of the Brevard fault zone and northeast of the Gulf-Coastal Plain onlap. In conjunction with existing geologic maps the spatial boundaries of the Zana and Kowaliga, as well as that of the surrounding country rock, have been revised. Map relationships indicate the Zana and Kowaliga are sill-like intrusions, with contacts oriented parallel to primary layering in the surrounding metasedimentary and metavolcanic units. The Zana and Kowaliga plutons intruded the Middle Ordovician Emuckfaw Group and have been isotopically dated at ca. 455 Ma and ca. 430 Ma, respectively. A Middle Ordovician age for the Zana Granite is consistent with formation during the Taconic orogeny as part of the Wedowee-Emuckfaw-Dahlonega back-arc basin. Volcanic components of this silicic center may have provided zircons of this age to the upper Wedowee and/or lower Emuckfaw Groups (Josie Leg Formation). A Silurian age for the Kowaliga Gneiss is more enigmatic, but indicates continued magmatism in the region for >20 m.y. following the end of back-arc volcanism in the preserved Wedowee-Emuckfaw-Dahlonega basin. Protoliths of the Zana and Kowaliga orthogneisses range from alkali feldspar granites to tonalites. Geochemistry of these rocks suggests a predominantly S-type character for the Zana Granite, whilst the Kowaliga has predominantly I-type characteristics; however, both possess characteristics suggesting a mixed I-type/S-type source. Although both plutons are peraluminous, the Zana generally has higher alumina saturation indices than the Kowaliga. Additionally, while the Zana is typically magnesian in nature, the Kowaliga sometimes displays mixed ferroan/magnesian characteristics. These new data and isotopic analyses in progress are improving our understanding the tectonic setting and genesis of these plutons.