PETROGRAPHY AND GEOCHEMISTRY OF THE GREENWOOD INTRUSIVE BODY, CAROLINA SUPERTERRANE, CENTRAL SOUTH CAROLINA

Samples of the Greenwood intrusive body utilized in the present study are comprised of medium- to coarse-grained metagabbroic rocks. The mineralogy of the metagabbros is plagioclase, amphibole, olivine, and opaques. From normative compositions, rock types in all the samples investigated are meta-olivine gabbronorites. SiO₂ contents range from 44.3 to 47.1 wt. %, and MgO contents range from 4.6-11.2 wt. %. Concentrations of trace elements like Ni range from 5 to 187 ppm. Amphiboles analyzed are all pargasites. Olivine composition ranges from Fo₈₁ to Fo₈₄. Coronas are developed between olivine and plagioclase grains. Plagioclase An contents range from a low of An₆₂ (further away from coronas) to a high of An₉₂ occurring adjacent to the pargasitic amphiboles (Na ≈ 0.700 and K ≈ 0.040) of the coronas, probably pointing to a metamorphic origin for the highly calcic plagioclases. Calcic pyroxene compositions are (Ca_47.4-53.0Mg_45.7-44.3Fe_6.8-2.7). Olivine and plagioclase compositions are consistent with an intrusive origin. Plagioclase has a δ¹⁸O value of 6.2±0.1 (n=3), and olivine has a δ¹⁸O value of 4.6±0.3 (n=2), yielding an equilibration temperature of 751^oC using the equation of Chiba et al. (1993), and a Δ_{plagioclase-olivine} value of 1.6 ‰ which is consistent with oxygen isotope exchange during slow cooling.

Chiba H., Chacko T., Clayton R.N. & Goldsmith J.R. (1989), Geochimica et Cosmochimica Acta, 53, p. 2985-2995