Extracting Metamorphic Conditions from Mineral Compositions: Quantitative Assessment of Peak Metamorphic Conditions in the Southern Appalachians of Western Georgia

The tectonic and metamorphic history of the Southern Appalachians of western Georgia is quite poorly understood, relative to the Central and Northern portions of the orogenic belt. The conditions of peak metamorphism in the Southern Appalachians are poorly constrained; prior work in this region has largely been focused on mapping and large-scale structural analysis, with very little modern study of the petrology or geochemistry of the metamorphic rocks at the core of the orogenic belt. This study seeks to quantify pressure and temperature conditions for the peak of Appalachian metamorphism in the Piedmont province of western Georgia, in order to develop a better understanding of the tectonic processes in this portion of the Appalachian chain.

Fresh samples of layered amphibolites (amphibole + epidote + quartz + plagioclase + titanite) have been collected from two localities in the vicinity of Carrollton, GA. These rocks have been mapped as part of the Ashland Group, a sequence of metamorphosed basalts and volcaniclastics. Most samples contain very thin (less than one centimeter thick) layers of alternating amphibole-rich, epidote-rich, or quartz-rich bands. Mineral compositions as determined by SEM-EDS and EPMA analyses will be applied to a suite of mineral thermometers and barometers, including Al-in-hornblende, Ti-in-hornblende, and hornblende-plagioclase exchange, to produce the first quantitative assessment of metamorphic conditions in this region of the Southern Appalachians. Preliminary data indicate that the amphibolites equilibrated at temperatures of approximately 600 deg-C.