Paper No. 7
Presentation Time: 1:30 PM-5:00 PM
A COMPARATIVE ANALYSIS OF THE MINERALOGY AND GEOCHEMISTRY OF TWO AMPHIBOLITES, CARROLL COUNTY, WEST-CENTRAL GEORGIA
The Southern Appalachians of west-central Georgia are characterized by greenschist to amphibolite facies Paleozoic regional metamorphism. A comparative analysis of two amphibolites from this region was conducted in this study in order to better constrain the thermobarometric evolution, and the influence of bulk compositional variations on the thermodynamic models used to evaluate them. Two samples were collected in Carroll County, Georgia: the first, CG07-5, was collected approximately one mile east of the city of Carrollton; the second, CG07-13, was collected from the University of West Georgia campus located approximately one mile west of Carrollton. Mineralogically the amphibolites are very similar: each sample contains layers of amphibole + plagioclase alternating with layers of epidote + quartz. However, CG07-5 is a fine-grained banded amphibolite gneiss with centimeter-scale layering consisting of amphibole rich layers alternating with epidote-rich layers while CG07-13 is a medium-grained amphibolite gneiss containing a weak foliation defined by the amphibole-rich and epidote-rich layers. CG07-13 also lacks the mineralogic banding present in CG07-5. Petrographic and scanning electron microscope (SEM) analysis show inclusions such as titanite, ilmenite, and zircon are present in both samples, though CG07-5 contains a higher concentration of these inclusions than CG07-13. Texturally, each sample contains crenulations within the fabric; crenulations appear to be more abundant in CG07-5. Quartz symplectites have been seen in epidote from both amphibolites; however, symplectites from CG07-5 are seen mainly at the interface between the amphibole-rich and episode-rich layers, and are not as abundant as those in CG07-13. As research continues, bulk compositional data will be obtained through the crushing and dissolution of portions of the samples. Whole rock compositional data will be obtained on both samples, as well as bulk compositions from individual centimeter-scale layers of CG07-5 selected due to obvious differences in mineralogy. Differences in bulk composition affect the mineralogy and prograde reactions; this data will allow an assessment of the influence of bulk chemistry on the patterns of mineralogic layering and metamorphic fabric development observed in these samples.