VARIATIONS IN GARNET CHEMISTRY, INCLUSION ASSEMBLAGE, AND MICROSTRUCTURAL DEVELOPMENT AT GARNET HILL, WEST-CENTRAL GEORGIA

The spatial distribution of mineral assemblages, compositional zoning patterns, and relationships between porphyroblast growth and microstructural fabrics development have been the subject of ongoing study at the Garnet Hill locality in Paulding County, west-central Georgia. The examination of these characteristics produces better constraints on the evolution of P-T-D-X conditions during Paleozoic orogenesis in this region of the Southern Appalachians. The dominant rock-forming mineral assemblage includes extremely coarse-grained (> 1 cm) porphyroblastic garnets in a very fine-grained matrix of chlorite, magnetite, ilmenite and quartz. Garnet cores are iron and manganese-rich, and have a poikiloblastic texture due to abundant quartz inclusions. This is followed by a calcium spike and a textural break in the inclusion fabric at the core-rim interface where inclusions of ilmenite ± chlorotoid wrap around the garnet cores. Garnet rims overprint the matrix fabric; garnet growth in quartz-rich layers is poikiloblastic, while garnets in chlorite-rich layers are inclusion-poor. Garnet-chlorite Fe-Mg exchange thermometry of two samples shows metamorphic temperatures of 500-550 deg-C during growth of garnet rims. A second suite of samples collected at Garnet Hill have noticeable differences in grain size and textures as compared to those seen in the previously studied samples: garnets are much smaller and more numerous. The results of microstructural and SEM-EDS chemical analyses on these samples will be used to further constrain the metamorphic and deformational conditions experienced by rocks at this locality.