Abstract

Amphibolites occur in three distinct localities (Hudson Rapids, Davis Mill, and Lindsey Creek) in the west-central Georgia part of the Uchee belt, southern Appalachian Piedmont. Epidote-amphibolite facies assemblage (plagioclase [An24-36] + hornblende + epidote + sphene + quartz) at the Davis Mill occurrence gives way to the amphibolite assemblage (calcic plagio-clase [An33-88] + hornblende + garnet + epidote + ilmenite + quartz) at Hudson Rapids. Mineral chemistries indicate that the transition was controlled by increasing pressure and unusual bulk compositions.

Equilibrium mineral assemblages record temperatures ranging from 610 to 780 °C at the garnet isograd, and from 570 to 634 °C close to the calc-silicate isograd. Estimated pressures range from 7 to 9.25 ±2 kbar. These P-T conditions are consistent with a thickened crustal section caused by emplacement of the Piedmont allochthon, followed by isobaric cooling (or isothermal compression), and the formation of symplectites of epidote + amphibole around plagioclase + clinopyroxene.

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