CONSTRAINTS ON THE DEVELOPMENT OF MULTIPHASE CORONAS IN JULIETTE MAFIC SUITE METAGABBROS, CENTRAL GEORGIA, SOUTHERN APPALACHIANS

The Juliette Mafic Suite, located within the larger Gladesville Complex at the southwestern tip of the Charlotte terrane, part of the Carolina superterrane, consists of a series of outcrop-scale, lens-shaped bodies entrained within felsic gneisses. Recent work by Chaumba (2014) assigned these mafic and ultramafic bodies to an island arc origin on the basis of bulk-rock chemistry and compositions of relict igneous minerals. This study focuses on the development of complex textures and mineral assemblages that document post-emplacement metamorphism and partial hydration of these bodies. Most samples collected at this locality contain clear metamorphic overprints, with amphibole, epidote, and Ca-rich plagioclase partially replacing gabbroic assemblages. In the northernmost exposure of the Juliette Mafic Suite complex multi-phase coronas are developed around relict olivine (Fo₇₄) phenocrysts in contact with anorthitic plagioclase (An₉₈), producing the following sequence of minerals moving outward from olivine: (1) orthopyroxene (En₇₈); (2) discontinuous layer of tremolite; (3) tschermakitic amphibole; and (4) tschermakitic amphibole + spinel symplectite. Where relict clinopyroxene (Wo₄₉En₄₅Fs₀₆) is adjacent to relict olivine, the corona consists of layers of (1) orthopyroxene and (2) tschermakitic amphibole. Spinel grains preserved as inclusions within olivine and clinopyroxene are compositionally distinct from the spinel within the symplectitic coronas. The incomplete replacement of relict olivine and plagioclase by hydrous corona minerals provides a constraint on the availability of water during corona formation. P-T, T-M_H2O, and P-M_H2O equilibrium assemblage diagrams constructed using Theriak-Domino are compared to the observed mineral assemblages, mineral chemistries, mineral modes, and modelled balanced reactions to evaluate the extant conditions during corona formation.