USING MINERALOGIC VARIATIONS TO RECONSTRUCT STRATIGRAPHIC AND FAULT RELATIONSHIPS IN THE METASEDIMENTARY PINELOG FORMATION NEAR THE CARTERSVILLE FAULT ZONE, GEORGIA

The Blue Ridge – Valley & Ridge Province boundary is especially ill-defined and wide along an area near Cartersville, Georgia. Rocks in the Blue Ridge Province near this boundary include the Paleozoic Pinelog Formation, a unit composed chiefly of quartzite with lesser amounts of metaconglomerate and phyllite. The homogeneity of this quartzite, and similar quartzites in the region, has impeded resolving stratigraphic and fault relationships along the fault zone associated with the Blue Ridge – Valley & Ridge boundary. Detailed field, petrographic and mineralogic characterization of the Pinelog Formation along one stratigraphic section has been undertaken to investigate the possibility of fault-repetition of its stratigraphic units.

X-ray diffractometry and electron microprobe analyses of feldspars within basal metaconglomerates have documented that these feldspars are similar to feldspars in the underlying Precambrian Corbin Metagranite. In contrast, three populations of feldspars with distinct compositions and crystal structures are present in a single quartzite unit interpreted to be higher in the Pinelog Formation. These distinct feldspar populations serve as a marker horizon that has allowed reconstruction of stratigraphic relationships within the Pinelog Formation. This horizon, in conjunction with mapped fault breccia and spatially associated graphitic phyllite, has allowed reconstruction of the original stratigraphy within this area. This reconstruction suggests that units within the formation may have been repeated by faulting, and that the apparent thickness of the formation in this area may have been consequently increased. The stratigraphic reconstruction and observed association between graphitic phyllite and fault breccia may suggest that fault planes have been established preferentially along relatively weak, graphitic horizons within this formation.