CORRELLATION OF GARNET GROWTH AND FABRIC DEVELOPMENT AT TYUS, CARROLL COUNTY, WEST-CENTRAL GEORGIA

Interpretations of microstructural fabrics and the timing of garnet growth can be used to correlate multiple periods of deformation with metamorphism. In this study, these relationships were determined for a garnet-bearing schist collected from the Tyus area in west-central Georgia, approximately 10 miles southwest of the city of Carrollton. These samples are part of the Emuckfaw Group (formerly the Roopville Formation of the Heard Group) located in the Piedmont province of the Southern Appalachians. Thin sections were made from two samples collected at this locality; petrographic analysis of minerals and fabrics was used to relate the development of deformational fabrics to metamorphic mineral growth. The rock-forming minerals, in order from most abundant to least abundant, are muscovite-quartz-garnet-biotite-chlorite and opaques. The dominant foliation fabric is defined by alternating quartz-rich and mica-rich layers; this fabric is locally crenulated. These samples contain two distinct populations of garnet: large, subhedral porphyroblasts approximately 4-6 millimeters in diameter, as well as elongated crystals, approximately 3-5 millimeters in length, that grew within the mica-rich layers. The timing relationships between the microstructural fabrics and the porphyroblasts are ambiguous; the degree of alignment between internal fabrics defined by inclusion trails and external foliation fabrics is not consistent. The concentration of crenulated micas wrapping around the large porphyroblasts indicate that these garnets grew prior to the development of this deformational fabric. Continuing research will determine the timing relationships between the two populations of garnet using SEM-EDS chemical analysis, field relationships, and microstructural analysis of additional thin sections. This data will help to better constrain models for the tectonic and metamorphic evolution of this portion of the Southern Appalachians.