THE “WOODBURY STRUCTURE” OF THE PINE MOUNTAIN BELT IN MERIWETHER COUNTY, GEORGIA: IMPACT CRATER VS. STRUCTURAL DOME INTERPRETATION

The Pine Mountain belt (PMB) of Georgia consists of metasedimentary rocks overlying Grenville basement (e.g. Woodland Gneiss). Metamorphosed cover sequences of the Pine Mountain Group (PMG) include the Sparks-Halawaka Schist, Hollis Quartzite, Chewacla Marble, and Manchester Schist. These cover sequences are interpreted as stratigraphic equivalents of Paleozoic, Laurentian margin, rift-drift facies rocks (e.g. Ocoee Supergroup and Chilhowee Group) lying unconformably above granulite facies, Grenville-aged charnockites and other basement units. Rocks of the PMB have been folded into a large, recumbent fold nappe which exposes the Hollis Quartzite in the east-west trending Pine Mountain and Oak Mountain ridges. North of Pine Mountain, near Woodbury, GA, the Hollis Quartzite is exposed in a circular ridge, 6km in diameter, referred to by some workers as the “Cove dome”. Although traditionally interpreted as a structural dome resulting from complex folding of the PMG, recent workers have suggested the Cove is the topographic expression of an impact crater (“Woodbury structure”). Although modeled as a late Proterozoic-Early Paleozoic astrobleme, evidence presented in support of the impact model (e.g. rocks interpreted as pseudotachylite, microfabrics interpreted as planar deformation features, breccia dike, shatter cone) is not consistent with formation prior to middle-upper amphibolite facies metamorphism and deformation, which would have obliterated these inferred impact features. However, a model wherein the Cove formed following Alleghenian deformation and uplift of the PMB could accommodate the purported impact features. Complicating the impact interpretation, however, are granulite facies units and a proximal brittle fault zone, which could also explain some of the features attributed to impact. An impact origin for the Cove should be associated with younger structural features distinct from the Paleozoic PMB fold nappe. Detailed structural analysis of joint patterns within and outside the Cove has the potential to identify a distinct fracture pattern unique to the Cove and would support the impact model. Preliminary research, however, suggests joint patterns within the Cove are similar to those observed in other regions of the PMB.