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

The Blue Ridge – Valley & Ridge Province boundary is especially ill-defined and wide along an area near Cartersville, Georgia. 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.

Part I: X-ray diffractometry and electron microprobe analyses of feldspars within basal metaconglomerates indicate 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 were utilized as a marker horizon to facilitate reconstruction of stratigraphic relationships within the Pinelog Formation. This horizon, in conjunction with mapped fault breccia and spatially associated graphitic phyllite, was used to reconstruct the original stratigraphy within the area. This reconstruction suggested that units within the formation may have been repeated by faulting, increasing the apparent thickness of the formation.

Part II: The presence of orthoclase within the Corbin Metagranite eliminates its use as a “simple” marker horizon in the stratigraphically higher/younger Pinelog Formation. The specific transverse investigated within this study, and namely this specific area of the Corbin Metagranite, does not appear to display identifiable amounts of orthoclase as verified through the use of x-ray diffractometry. Continuous stratigraphic mapping of the Pinelog Formation shows an increasing percentage of orthoclase as rocks become younger. These orthoclase differ both structurally, and compositionally, to those orthoclase typically identified within the Corbin. The presence of orthoclase as a “simple” marker horizon may be null due to the presence of orthoclase in the much older Corbin basement. However, due to the distinct structure and composition, the orthoclase in the Pinelog may have been derived from a separate granitic source. An increasing percentage of orthoclase in stratigraphically younger Pinelog may argue against repetition of the Pinelog within the study area, as previously suggested.