CORRELATION OF MICROSTRUCTURAL FABRICS AND REGIONAL METAMORPHISM: AN EXAMPLE FROM GARNET HILL, NORTHWESTERN GEORGIA

Patterns of microstructures and the development of deformational fabrics within garnet-bearing schists at Garnet Hill, Paulding County, northwestern Georgia, contain clues to the tectonic and metamorphic evolution of this portion of the Appalachian orogen. Correlation of internal microstructural fabrics within the large (up to 2cm) garnet porphyroblasts and the external fabrics within the chlorite- and quartz-rich matrix help to constrain timing relationships between deformation and metamorphism. A combination of field relationships, thin-section petrography, and back-scattered electron (BSE) image analysis were used to identify textural fabrics and evaluate their spatial and temporal relationships. Preliminary results indicate that there are multiple phases of deformation associated with garnet-grade metamorphism at this locality. Garnet cores overgrow an internal foliation defined by elongate quartz inclusions that is discontinuous with and oriented at a high angle to the external foliation. Outside garnet cores, ilmenite inclusions define a second foliation within the porphyroblast that wraps around the garnet cores. This internal fabric is continuous with the external matrix foliation, implying a post-kinematic growth of garnet. A narrow zone within the outer margin of garnet cores shows evidence of curvature in the quartz inclusion trails, evidence for a brief interval of syn-deformational garnet growth. Quartz strain shadows adjacent to the garnet porphyroblasts and crenulations within the chlorite-rich matrix indicate that pulses of deformation continued after garnet growth was completed. These relationships between microstructural fabrics and metamorphic mineral growth will be used to develop better constraints on the P-T-D-t evolution of this part of the Southern Appalachians.