CHARACTERIZATION OF EASTERN BLUE RIDGE ARC TERRANE(S) IMMEDIATELY ADJACENT TO THE TERRANE BOUNDING ALLATOONA FAULT OF THE GEORGIA APPALACHIANS

The Allatoona fault is the terrane boundary between native Laurentian rocks (western Blue Ridge/Talladega belt) and an accreted arc terrane(s) (eastern Blue Ridge). Recently, detailed geologic mapping (1:24,000) of the Draketown, New Georgia, Yorkville and Dallas 7.5’ quadrangles in Georgia, and petrographic and geochemical studies have been employed to elucidate the nature and timing of the origin and accretion onto Laurentia of eastern Blue Ridge terranes immediately adjacent to the Allatoona fault. Northeast of the Mulberry Rock Gneiss structural recess, a bimodal meta-volcanic arc sequence (Ordovician Pumpkinvine Creek Formation) occurs along the northwest bounding Allatoona fault (and trends northeast into the Dahlonega Gold belt), and is bordered to the southeast by lithologically dissimilar, but dominantly meta-plutonic and meta-volcanic rocks (Sandy Springs Group). Major and trace-element studies place the Pumpkinvine Creek Formation in the volcanic arc field and petrographic and textural studies display characteristics leading towards an extrusive origin for this meta-basalt/rhyolite sequence. The Sandy Springs Group, southeast of the Pumpkinvine Creek Formation, though structurally above the latter, displays a more deeply rooted meta-plutonic (primary granitoid and gabbro now felsic gneiss and course-grained amphibolite) and meta-volcanic sequence. While the Sandy Springs Group may be genetically related (though structurally out of sequence) to the Pumpkinvine Creek Formation, it is likely a structurally deeper portion of a volcanic arc, as evidenced by the multiple intrusions of granitic rocks into the gabbroic sequences and the course textural characteristics. Established field relationships and petrographic/geochemical samples are used to help compare and contrast the Sandy Springs Group and Pumpkinvine Creek Formation as well as help understand the timing of generation of the arc terranes and the accretion to native Laurentia during the Paleozoic, southern Appalachian Orogeny.