UNDERSTANDING THE FORMATION AND EMPLACEMENT OF BACK-ARC BASIN ROCKS: FROM THE PACIFIC TO THE SOUTHERN APPALACHIANS

Detailed study of back-arc basins from the Pacific and Indonesia has led to a better understanding of the tectonic conditions under which back-arcs open and close, as well as the conditions under which they are emplaced during subsequent orogenesis. The details of back-arc formation and preservation in modern settings are important for understanding ancient orogenic belts which preserve lithotectonic elements identified as having formed in a back-arc setting. The presence of Early-Middle Ordovician back-arc rocks in the Talladega, Ashland-Wedowee, and Dahlonega Gold belts of the southern Appalachians suggests formation in a tectonic setting analogous to those of the western Pacific and/or Indonesia. The palinspastic position of key lithotectonic terranes in the southern Appalachians provides important constraints on models of Ordovician tectonics at the Iapetus margin of Laurentia. Importantly, the Early Paleozoic position of rocks within the southern Appalachian Blue Ridge and Piedmont suggests the Laurentian continental margin was flanked by a back-arc basin and more outboard volcanic arc and accretionary prism above a B-type subduction zone. The geologic history of these rocks provides a framework for back-arc extension, contraction, and Ordovician accretionary orogenesis with excellent analogues from the Cenozoic record. Key elements linking these modern and ancient back-arcs include the nature of subducting oceanic lithosphere and plate motions during back-arc formation, influence of continental rift architecture on back-arc development, and the relative ages and geometries of lithotectonic belts involved in subsequent orogenesis and obduction of back-arc terranes.