PETROLOGY OF THE NINE TIMES AMPHIBOLITE-ULTRAMAFIC BODY FROM THE SUNSET 7.5-MINUTE QUADRANGLE, WESTERN INNER PIEDMONT OF SOUTH CAROLINA
Petrographic analysis of 10 ultramafic samples reveals the major mineralogy is about 60% clinoamphibole and 40% chlorite, with minor oxide minerals. Garnet is a minor accessory mineral in two samples but was not observed in thin section. All samples show a well-developed foliation defined by aligned chlorites and amphibole crystals in alternating bands, with a crosscutting schistosity. Two of the ultramafic samples show large relict olivine crystals with embayed margins, surrounded by chlorite and amphibole. The olivine is biaxial (+) with a high 2V, indicating a Mg-rich composition. Relict olivine grains are fractured and show extensive oxide exsolution. Chlorite is also Mg-rich, with pale green pleochroism and abnormal brown interference colors. Metamorphic amphiboles occur in magnesio-hornblende and edentic-hornblende compositional varieties. Magnesio-hornblende grains are pleochroic (colorless to pale green) with maximum lower 2nd order interference colors, display high 2V (~60-70°), and are biaxial (-). Edentic-hornblende grains form longer prisms, have pale blue-green pleochroism, middle 2nd order interference colors, a high 2V (~60-70°), and are biaxial (-). Edentic-hornblende grains have reacted margins and abundant oxide exsolution. Further petrography and microprobe analysis will examine mineral chemistry and reaction relations in conjunction with bulk rock chemical analysis.