GEOCHEMICAL CONSTRAINS ON THE ORIGIN OF THE ANDERSON METAGABBRO, TUGALOO TERRANE, SOUTH CAROLINA, SOUTHERN APPALACHIANS

The Anderson metagabbro is exposed for a distance of more than 22 km extending northwards from the city of Anderson, South Carolina, in the Tugaloo terrane, southern Appalachians. Biotite gneiss and schist surround the Anderson metagabbro.

In samples studied, the mineralogy of the Anderson metagabbro is amphibole, plagioclase, garnet, othopyroxene, clinopyroxene, and opaque minerals. The garnet type is mostly almandine and it has an average composition of Gr_22.2Mg_22.8Al_52.6Sp_2.4Al₂O₄. Clinopyroxenes have an average composition of Ca_0.5Mg_0.4Fe_0.1Si₂O₆, orthopyroxenes have an average composition of Mg_0.6Fe_0.4SiO₃, and the plagioclases have an average composition of Na_7.6Ca_92.4AlSi₂O₈.

Bulk-rock compositions in Anderson metagabbroic rocks have SiO₂ contents ranging from 46.9 – 44.0 wt. %, and MgO contents ranging from 8.4 - 9.5 wt. %. Nickel and Cr concentrations range from 41- 68 ppm and 34 - 235 ppm, respectively, whereas Zr concentrations range from 7-22 ppm. Spiderdiagrams show Nd depletions relative to N MORB, and are consistent with contamination of island arc magmas by both upper and lower crust.