GEOCHEMISTRY OF DADEVILLE COMPLEX MAFIC-ULTRAMAFIC ROCKS

Seventeen mafic-ultramafic samples are from the Dadeville Complex in northeastern Alabama. The Dadeville Complex is located in the southern part of the Appalachian belt with abundant amphibolite facies mafic rocks, as well as well-preserved-ultramafic rocks. Currently, data provided from igneous protoliths (456 ± 9 Ma to 446 ± 2 Ma) represent Ordovician formation of the Dadeville back-arc during the late Taconic orogeny. No in-depth research has been previously conducted on the Dadeville Complex mafic-ultramafic rocks (Doss Mountain ultramafics and Slaughters gabbro). The goal of this research effort is to determine whether these rocks formed during the proposed Dadeville back-arc, felsic magmatism or if they represent an intrusion that occurred after arc magmatism ceased. Ongoing research on these 17 samples show SiO2 contents ranging from 45%-55% and MgO content from 20%-30%. Observations of samples in thin sections indicate a gabbroic and pyroxenitic protoliths for most, with many samples containing grains of unaltered pyroxene (sizes varying from 1mm-5mm) as well as olivine (~1mm in size). Whole-rock samples were crushed and powdered in order to obtain elemental analyses and age determinations. Major element data were collected using XRF, HR-ICP-MS was employed for trace element data, and Sm-Nd isotopic dating for determining age constraints for the samples by multi-collector ICP-MS. These data will provide historical context for these mafic-ultramafic rocks and their emplacement in and the evolution of the Dadeville Complex.