EVIDENCE OF SUBDUCTION INITIATION RECORDED IN THE DADEVILLE COMPLEX OF ALABAMA

The Appalachian Mountain range formed from multiple orogen-scale collisional events spanning from the Neoproterozoic to the Devonian. As the Iapetus Ocean began to close, early subduction zone magmatism created forearc lithosphere and volcanic arcs that were subsequently obducted onto Laurentia during the formation of Pangaea. These early magmatic products contain geochemical information that informs our understanding of subduction zone formation and evolution; however multiple collisional events, the emplacement of large (and potentially unrelated) magmatic intrusions, and extreme weathering at the southernmost extent of the Appalachians have made identifying these rocks and reconstructing the history of this portion of the margin notoriously difficult. Fortunately, recent studies of the modern Izu–Bonin–Mariana subduction system have shed new light on the geochemical evolution of subduction initiation and have resulted in the development of new criteria for classifying the first magmatic products of subduction–forearc basalts and boninites. These constraints allow for reassessment of subduction-related rocks throughout the Appalachian margin.

Only one potential volcanic arc has been identified in the Southern Appalachians. This hypothesized arc, the Dadeville Complex of Alabama and Georgia, has geochemical signatures associated with subduction zone influence and is considered to have formed during subduction of Iapetan lithosphere underneath or adjacent to the Laurentian margin; however, the exact nature of the complex and its geologic history remains unclear. We apply the new understanding of subduction zone magmatic evolution derived from the Izu–Bonin–Mariana system to the Dadeville Complex to further elucidate its origin. Using whole rock and mineral major- and trace-element geochemistry coupled with detailed petrographic analyses, we have identified forearc basalts and boninites; therefore, we interpret these data to reflect formation of the Dadeville Complex during initial subduction in the Iapetus Ocean.