GEOLOGY OF THE DADEVILLE COMPLEX IN THE CAMP HILL 7.5′ QUADRANGLE, APPALACHIAN INNER PIEDMONT OF ALABAMA

The Dadeville Complex (DC) is located in the Alabama Inner Piedmont of the southern Appalachians immediately SE of the Brevard Zone, in the core of the Tallassee synform (TS). Geologic mapping in the Camp Hill 7.5’ quadrangle has revealed the following relationships and characteristics of this region. The DC consists of predominantly metavolcanic and metaplutonic rocks and minor sedimentary rocks. It experienced multi-stage deformation and kyanite-silliminite grade metamorphism and intensive plutonism, and was lastly folded by the TS. Felsic rocks like those found in the DC commonly erupt in the early stages of back-arc basin opening, forming a bimodal volcanic suite with more voluminous basalts. The Camp Hill quadrangle consists of three lithostratigraphic sequences from SE to NW: Ropes Creek amphibolite (RCA) at the base, overlain by Waverly gneiss (WG), overlain by Agricola schist (AS). These sequences are intruded by felsic plutonic rocks, with the Chattasofka Creek gneiss (CCG) (granite) intrusive into the AS, and the Camp Hill gneiss (CHGG) (tonalite) intrusive into the WG and RCA. Also intrusive into the AS is a ultramafic-mafic complex (UMC) consisting of the Doss Mountain suite (DMS) and the Slaughters Gabbro suite (SGS). The DMS is characterized by having an abundance of interlayered metaorthopyroxenite and metanorite, as well as their foliated equivalents. SGS is a metagabbro unit consisting of both olivine and non-olivine bearing gabbro. Within the UMC, there are various felsic dikes cutting through metagabbro and amphibolite, which suggest intrusions of felsic and mafic rocks could have occurred simultaneously. Distinct geochemical signatures of the DMS and SGS suggest two episodes of mafic intrusion related to an arc environment. The DMS rocks are tholeiitic and probably formed in an arc environment by partial melting of an undepleted source. The SGS rocks are calc-alkaline in nature and also indicate an arc tectonic setting. Structural field data outline the overall nature of the TS in the Camp Hill quadrangle. In the SE section of the quadrangle planar fabrics dip NW and the rocks in the NW section of the quadrangle dip SE, representing the limbs of the TS.