MINERALOGIC AND TEXTURAL COMPARISON OF TWO SAMPLES OF AMPHIBOLITE FROM CARROLL COUNTY, WESTERN GEORGIA

Petrographic and chemical analytical techniques were applied to two samples of amphibolite gneiss collected from exposures of the Ropes Creek Metabasalt in Carroll County, western Georgia, in order to examine the mineralogic and textural changes in these rocks produced by Paleozoic metamorphism. Sample CG07-5 was collected one mile east of Carrollton and sample CG07-13 was collected on The University of West Georgia campus one mile west of Carrollton. Both samples contain similar overall mineralogy: calcic amphibole, plagioclase, quartz, and epidote with accessory minerals titanite, zircon and ilmenite. Texturally, these rocks have several distinct differences. Sample CG07-5 contains mm- to cm-scale compositional layering with amphibole-rich layers alternating with layers consisting mainly of epidote and quartz. The foliation defined by mm-scale layering in CG07-13 is less well-developed; this sample is also finer-grained and epidote is less-abundant. Both samples contain small-scale crenulations that modify the dominant foliation fabrics. Epidote-quartz symplectites are developed in both samples, although the distribution and abundance of this texture are different: in CG07-5 the symplectites are found most commonly at the boundaries between the amphibole-rich layers and the epidote-quartz layers; the epidote-quartz symplectites in sample CG07-13 are more abundant and more evenly distributed throughout the rock. SEM-EDS and EPMA analyses collected on amphibole, epidote, and plagioclase crystals from multiple layers from each sample, together with bulk compositions for each layer and combination of layers, will be used as input for equilibrium thermodynamic models to evaluate the changes in pressure and temperature conditions recorded in these rocks and to test hypotheses for formation of the epidote-quartz symplectites found in these samples.