A region of migmatitic felsic paragneiss and pelitic schist containing concordant pods of serpentinite, talc schist, talc-amphibole schist, amphibolite, and metagabbro—here called the Burks Mountain complex—occurs in the southeastern limb of the Kiokee antiform, an Alleghanian D 3 structure in the eastern Piedmont of Georgia and South Carolina. A similar region of migmatitic felsic paragneiss containing small pods of metamorphosed mafic and ultramafic rocks, which occurs in the northwestern limb of the Kiokee antiform, is inferred to be a continuation of the Burks Mountain complex across the crest of the antiform. The composition of the felsic paragneiss and pelitic schist of the Burks Mountain complex suggests derivation from graywacke and shale, respectively. Relict textures preserved in mafic and ultramafic rocks of the complex, along with preliminary whole-rock geochemistry, indicate derivation from ultramafic tectonite (harzburgite), olivine-pyroxene cumulate (wehrlite, olivine pyroxenite), pyroxene-plagioclase cumulate (gabbro, anorthositic gabbro), and mafic volcanic rock. These protoliths suggest an origin as part of a cumulate mafic and ultramafic intrusive and extrusive complex with some associated mantle tectonite. The complex was disrupted prior to or during amphibolite facies regional metamorphism. The mechanism of disruption is not clear. Possible modes of origin include accumulation as an olistostrome, accumulation in a subduction-related accretionary complex, and formation as extreme boudinage during a regional deformation event. The crystalline rocks in the core of the Kiokee belt (including the Burks Mountain complex) are contained in the footwall of a major ductile shear zone (the Modoc zone) that experienced oblique, down to the north-northeast displacement during the early part of the Alleghanian orogeny. Prior to the Alleghanian orogeny, the Burks Mountain complex was located beneath rocks of the Carolina slate belt that are presently exposed north of the Modoc zone. The Burks Mountain complex may have been derived from a unit within the Carolina slate belt or from a Precambrian basement(?) unit beneath the Carolina slate belt. Alternatively, in view of a unique lithostratigraphy, the Burks Mountain complex may be included in a terrane, exotic with respect to both North America and the Carolina slate belt, which was tectonically incorporated into the Appalachians prior to the Alleghanian orogeny.

Abstract Eight stops on a one-day field trip along the Savannah River corridor between Plum Branch, South Carolina, and Augusta, Georgia, review the Ediacaran–Cambrian and Pennsylvanian–Permian history of several terranes that comprise Carolinia in the eastern Piedmont. The foliation of ca. 550 Ma andesitic metatuffs of the Persimmon Fork is isoclinally folded. This event may be related to other recognized events in Carolinia at the Cambrian-Precambrian boundary or the folding of the sub–Asbill Pond angular unconformity before the intrusion of the Clouds Creek pluton. Three stops illustrate features of the Modoc zone in the eastern Piedmont. Variably mylonitized Modoc zone orthogneisses were intruded between 300 and 310 Ma. Mylonitic Modoc zone orthogneisses are parasitically folded around the northwest-vergent Kiokee antiform. Monazites from the core of the Kiokee antiform yield TIMS (thermal ionization mass spectrometry) U-Pb ages of ca. 306–308 Ma, and hornblende yields 40 Ar/ 39 Ar plateaus of ca. 288 and 296 Ma. Favorably oriented near-vertical segments of the steeply dipping to overturned limb of the Kiokee antiform are reactivated with dextral strike-slip sense and locally preserve spectacular composite planar fabric. The serpentinites at Burks Mountain include serpentinized orthopyroxene and chromite. The origin of these ultramafic rocks may have been at the base of an ophiolite or an ultramafic layered intrusion in the lower continental crust. The ca. 294 Ma Appling granite is undeformed and intrudes the trailing limb of the Kiokee antiform. The Augusta fault frames the southeastern margin of the Kiokee belt schists and gneisses. The fault is known from a single quarry exposure that places low-grade metavolcanics and epiclastic rocks in the hanging wall against footwall gneisses and schists of the Kiokee belt. The most distinctive rocks in the quarry are K-silica-metasomatized mylonites interleaved with chlorite schists. The origin of K and Group I cations is thought to be the retrogression of biotite. Furthermore this metasomatism is thought to have accompanied Triassic rifting. These metasomatic effects are heterogeneously developed in the footwall Kiokee belt gneisses, and are well known in the footwall of the Triassic border fault of the Dunbarton basin, underlying the U.S. Department of Energy (DOE) Savannah River Site. It is thought that no differential rotation of the eastern Piedmont in this area occurred after ca. 275 Ma. A final stop is made to observe the low-grade metavolcanic rocks of the Belair belt south of the Augusta fault.