ASSESSMENT OF POST-EMPLACEMENT METAMORPHISM IN METAGABBROIC ROCKS OF THE JULIETTE MAFIC SUITE, CENTRAL GEORGIA

The Juliette Mafic Suite in central Georgia, part of the Carolina superterrane in the southern Appalachians, is one of several small bodies of metagabbroic rocks emplaced within the Piedmont. Recent work on these rocks provided insight into their igneous petrogenesis, however little modern work has been done to determine constraints on metamorphism preserved within these rocks. For this work, samples were collected from three distinct lens-shaped bodies of mafic rocks near Juliette, Georgia. Previously-published geochemical analyses concluded that these igneous protoliths were of island arc origin and were emplaced along the Laurentian margin during the closure of the Iapetus ocean.

Petrographically, the rocks contain relict igneous minerals, including olivine, plagioclase, and pyroxene phenocrysts, and relict ophitic textures with subhedral crystals of plagioclase included within pyroxene. These rocks also contain distinct metamorphic replacement textures; in the northern body, these include the development of complex coronas, in which igneous olivine phenocrysts are rimmed by orthopyroxene, tremolitic amphibole, and a amphibole-spinel symplectite. Preliminary investigation of rocks from the central and southern bodies (Berry Creek and Holly Grove) also document evidence of a metamorphic overprint and partial replacement of the original igneous mineral assemblages. In samples from the Holly Grove body, infiltrating fluids reacted with the igneous clinopyroxene and Ca-plagioclase phenocrysts to produce abundant amphibole-spinel symplectite. In samples from the Berry Creek lens, textural relationships suggest the metamorphic overprint is represented by reactions between calcic amphibole and plagioclase to produce epidote and a second amphibole phase at the interface between epidote and the reactant amphibole. Additional whole-rock and mineral chemical analyses will be used to develop equilibrium assemblage diagrams to model constraints on their metamorphic evolution, including the temperature range over which these reactions occurred and the availability of infiltrating fluids.