PRELIMINARY PETROGRAPHIC AND GEOCHEMICAL DATA ON THE NEWBERRY METAGABBRO IN SOUTH CAROLINA, CAROLINA SUPERTERRANE, SOUTHERN APPALACHIANS

The Newberry metagabbro outcrops as two separate bodies in the Carolina superterrane in western central South Carolina. It is interpreted by previous workers as an intrusive body. Samples were collected from one of the bodies in order to place some constrains on its origin. The mineralogy consists of interlocking fine to medium-grained plagioclase, clinopyroxene, and biotite crystals as major phases, as well as a minor phase of very fine- to fine-grained opaques. SiO₂ content is 48.56 wt. %, whereas MgO content is 5.58 wt. %, comparable to basalts. Normative ilmenite is high (4.01 %), normative plagioclase is 52.62 %, and normative olivine is low (8.44 %). Incompatible trace elements such as Zr and Y have concentrations of 88.5 ppm and 17.6 ppm, respectively, with a Zr/Y ratio comparable to those of within-plate basalts. Plagioclase compositions have anorthite of composition An_45.9-54.0, which plot within the andesine-labradorite range, and K-feldspar of composition Or_1.18-1.57. Clinopyroxene are diopsides and augites, with compositions of Ca_0.83-0.92Mg_0.77-0.84Fe_0.22-0.31. Biotites plot in the pholopite/annite field, with Mg# ranging from 0.52-0.71, and are characterized by higher Al_(total) contents comparable to those in layered intrusions rather than biotites with lower Al_(total) contents from both ophiolites and mafic mantle xenoliths. Tri-octahedral (Y) ions in biotites average 5.88, and range from 5.77 to 6.34. No amphiboles were observed. A spidergram shows enrichments of between 1.2 and 69 times compared to that of N-MORB for all elements except Y. Further, the spidergram also displays trends that closely mimic those of lower crust, suggesting that the Anderson metagabbro was probably contaminated by lower crust during intrusion.