Geology of the Dadeville Complex in the Camp Hill 7.5’ Quadrangle, Appalachian Inner Piedmont of Alabama

The Dadeville Complex is a large klippe located in the Alabama Inner Piedmont of the southern Appalachian orogen lying immediately above rocks of the eastern Blue Ridge and Brevard Zone, in the core of the Tallassee synform. Structural field data outline the overall nature of the Tallassee synform in the Dadeville Complex. The Camp Hill 7.5' quadrangle contains the two major Dadeville Complex lithostratigraphic sequences, from southeast to northwest: the Ropes Creek Amphibolite, a bimodal metabasalt/metatuff, metadacite at the base, overlain by the Agricola Schist, a metaturbidite consisting of metapelitic, metagreywacke, and minor metabasalt. These sequences are intruded by felsic plutonic rocks, with the Chattasofka Creek Gneiss (granite) intrusive into the Agricola Schist, and the Camp Hill Granite (tonalite) intrusive into the Ropes Creek Amphibolite. Also intrusive into the Agricola Schist is a mafic complex consisting of the Doss Mountain suite and the Slaughters Gabbro suite. The Doss Mountain suite is characterized by having an abundance of interlayered metaorthopyroxenite and metanorite, and their metamorphosed equivalents. The Slaughters Gabbro suite consists of both olivine and non-olivine bearing gabbro. Within the mafic complex, there are various felsic dikes cutting through metagabbro and amphibolite, which suggest that intrusions of felsic and mafic rocks could have overlapped temporarily. Distinctive major and trace element geochemical signatures of the Chattasofka Creek Gneiss, Camp Hill Granite, Ropes Creek Amphibolite, Doss Mountain suite, and Slaughters Gabbro suite on tectonic discrimination diagrams all suggest formation within a volcanic arc environment. Preliminary U/Pb dating of detrital zircons in the Agricola Schist and igneous zircons in the Chattasofka Creek Gneiss yield Middle Ordovician ages, with the Agricola Schist also containing a subordinate fraction of Grenville ages. These relationships suggest that the Dadeville Complex arc resulted from subduction of Iapetus lithosphere beneath the distended Laurentian plate, and that the Dadeville Complex could potentially be a key fragment of the missing Taconic arc in the southern Appalachians. A supplementary file of a detailed geologic map of the Camp Hill 7.5' quadrangle is included with this document.