ISLAND ARC ORIGIN FOR THE GLADESVILLE AND ASSOCIATED BODIES IN THE CAROLINA SUPERTERRANE, CENTRAL GEORGIA

A petrographic, bulk-rock, and mineral composition study has been carried out on the Gladesville, Hillsboro, Juliette, Holly Grove, and Boly Creek bodies in the Carolina superterrane in central Georgia in order to place some constrains on their origin. Rock types in all the bodies are metagabbronorites and olivine metagabbronorites.The mineralogies of these bodies are plagioclase, pyroxene, amphibole, and opaques. MgO contents range from 3.5 to 7.5 wt. % for the Gladesville, Hillsboro, and Boly Creek bodies. The Juliette and Holy Grove bodies have slightly higher MgO concentrations of 11.8 – 12.4 wt. %. The CaO contents from all the bodies range from 6.9 to 18.1 wt. %. Concentrations of trace elements like Ni and Cr in all the bodies range 6-224 and 17-1932 ppm, respectively, broadly comparable to those from magmas. Plagioclase mineral compositions vary widely: the Gladesville body has plagioclase with An_75.1 to An_95.7 whereas the Hillsboro body has plagioclases with anorthite compositions of An_46.2–69.8. Other bodies, such as the Juliette and Holly Grove, are highly calcic with plagioclase contents ranging from An_96.6-99.8 and from An_90.8-96.9, respectively. Amphiboles from these bodies are tschermakites and magnesiohornblendes. Pargasites occur only in the Gladesville body. Calcic pyroxenes vary from body to body: Juliette (Ca_38.5-50.9Mg_54.2-44.9Fe_7.2-4.2), through Holly Grove (Ca_47.1-49.4Mg_43.2-41.2Fe_9.7-9.4), to Gladesville (Ca_48.9-52.5Mg_41.4-42.5Fe_9.7-5.2). Spider diagrams, which show Nb depletions, and tectonic discrimination diagrams, are both consistent with formation of these bodies in island arc settings. The highly calcic nature of most of the plagioclases further support an island arc origin for these bodies.