GEOLOGY AND PETROLOGY OF TWO INNER PIEDMONT ULTRAMAFIC BODIES IN THE POOR MOUNTAIN FORMATION FROM THE LANDRUM AND SALEM QUADRANGLES, SOUTH CAROLINA

We have studied two lenticular ultramafic bodies within Poor Mountain Formation amphibolite, from the Salem (Walhalla nappe) and Landrum (Six Mile thrust sheet) quadrangles of the Inner Piedmont, South Carolina. The Salem body is part of a 22 km-long belt of scattered olivine-chlorite-clinoamphibole schist occurrences within amphibolite between Lake Keowee and Table Rock. Exposures are relatively fresh, resistant, and form low ledges and spheroidal boulders. Mesoscopic features include subtle compositional layering, reflected in schistose and more equigranular layers, a discrete crenulation cleavage (a secondary schistosity) locally affected by later chevron folding, and asbestiform veins. The smaller Landrum body forms several prominent exposures and has nematoblastic textures. Warty features (~ 1 cm) may be coronal textures. Contact relationships of the bodies are not exposed, although amphibolite nearby is locally sheared.

Thin section analysis of the Landrum body reveals abundant clinoamphibole and chlorite, as well as scattered opaque minerals (magnetite ± chromite), minor plagioclase, and phlogopite. Optical analysis indicates the amphibole is a magnesio-hornblende, with 2V in the range 80-88° and biaxial (-). It possesses a weak pleochroism from colorless to pale green with first order orange or tan interference colors. Samples of the host rock for the Landrum body consist of hornblende, plagioclase, and epidote, the latter replacing much of the plagioclase throughout the sample. Two samples also contain abundant garnet and veins of quartz, in addition to hornblende. Analysis of the Salem thin sections reveals abundant chlorite and clinoamphibole, which like the Landrum ultramafic appears to be a magnesio-hornblende. Opaque minerals are magnetite and chromite (?). Chlorite exists in schistose zones cutting through the sample and defines a crenulation cleavage (a secondary schistosity). The zones of chlorite schistosity contain small amounts of fresh, relict olivine, as fractured grains cross cut by chlorite. Olivine is colorless, exhibits second order interference colors, 2V=85-88°, and is biaxial positive, indicating that it is forsteritic in composition. Additional information will be gathered using microprobe analysis of polished thin sections.