Geological Strain Analysis in the Murphy Belt,Southern Appalachian Orogen, Georgia, USA

The Great Smokey Group and the Mineral Bluff Group of the southern Appalachians Blue Ridge contain units of metaconglomerate that contain stretched quartz pebbles. Quartz pebbles have been widely used as strain markers in conglomerates. Metaconglomerate strain results of both groups (obtained by using Rf/Ø and Fry methods on two principle strain planes XZ, YZ),show that there are no significant differences between the strain in the Great Smokey Group and the Mineral Bluff Group. The consistent strain results, the unstrained status of the strain markers, the χ2 and Isym tests of Lisle (1985), the symmetrical distribution of the Rf and Ø data along the line of maximum stretching orientation, and the same oblate to almost plane deformation in both Groups (obtained by plotting k values on Flinn diagrams), support that Great Smoky Group and the Mineral Bluff Group were deformed by the same deformation and probably at the same time. This deformation had to be younger than Middle Ordovician (the minimum age of the Mineral Bluff Group); indicating the deformation has to be associated with the Acadian orogeny or younger (neo-Acadian). Therefore, there was no deformation between the Great Smokey Group depositional time (Late Neoproterozoic) and the Mineral Bluff Group depositional time (< Middle Ordovician). During the neo-Acadian deformation the Murphy belt was shortened about 32% in the minimum strain axis direction, Z (N67W 65NW), extended about 6% in the direction of the intermediate strain axis direction, Y (S89E 25SE), and extended about 44% in the direction of the maximum stretching axis, X (S7W 9SW). This study also concluded that the easiest relief for the rocks as a response to the compression (during the neo-Acadian event) in the Z direction was mainly in the direction of X with less flow and extension in the Y direction as the crustal load above the rocks prevented more extension in that direction. There is no difference in the strain values between the northern and middle parts of the Murphy syncline, therefore, the Jasper fold (a later event after Murphy syncline development) was too weak to change or to overprint the earlier deformation that x produced the Murphy syncline and the mineral elongation. The strain results were also correlated across the Murphy syncline (E-W). The two limbs strain results are also consistent with no considerable difference in the results. A component of this study was to correlate the results of the essentially different computational methods used for strain analysis. All the software produces almost the same results for the same sample, indicating that all software used in this study are suitable to be used for similar strain study. The two methods also show no significant difference between their results on two different scales(thin section and bulk sample); indicating that ductility contrast does not significantly affecting the strain values. Therefore, the pebbles represent the whole rock strain. It is concluded by this study that Rf/Ø and Fry methods are suitable to be used for strain analysis on quartz pebbles of conglomerates, if the quartz is abundant on both scales (hand specimens, and thin sections).