THE SOAPSTONE RIDGE COMPLEX, SOUTHERN APPALACHIANS: A PETROGRAPHICAL, MINERAL COMPOSITIONAL, AND OXYGEN ISOTOPE INVESTIGATION

The Soapstone Ridge complex (SSR) is a large metamorphosed body located in the Tugaloo terrane in the southern Appalachians, just southeast of Atlanta, Georgia. The SSR is comprised of dominantly metapyroxenites, chlorite schists, talc chlorite schists, and minor metaultramafic rocks and diablastites. The Soapstone Ridge fault underlies the SSR, which separates it from underlying rocks (Higgins and Crawford, 2007). Amphibole, chlorite, and Fe and FeTi oxides are the dominant minerals comprising rocks of the SSR. Mineral compositional and oxygen isotope data were obtained on amphibole in effort to constrain the origin of rock of the SSR. The amphiboles are typically zoned, with cores of both edenite and magnesiohornblende rimmed by tremolite-actinolite. Edenite and magnesiohornblende cores are consistent with amphibolite facies conditions whereas tremolite-actinolite rims are consistent with greenschist facies conditions. Oxygen isotopes analyses show a wide in δ¹⁸O_amphibole values, from 1.4 to 6.5 ‰. In one thin section, co-existing chlorite and amphibole have δ¹⁸O values of 6.3 and 5.9 ‰. Using a Δ_{chlorite-amphibole} value of 0.4 ‰, an application of the chlorite-H₂O (Cole and Ripley, 1998) and amphibole-H₂O (Zheng, 1993) yields a temperature of 227^oC, consistent with low-temperature formation of chlorite and tremolite-actinolite, possibly during thrusting of the SSR during the final stages of the closing of the Iapetus Ocean (Higgins et al., 1988). The wide range in amphibole δ¹⁸O values mimics amphibole δ¹⁸O values from ocean islands and ophiolite complexes (e.g., Pineau et al., 1976; Stakes and Taylor, 1992; Demény et al., 2008). Layered intrusions are characterized by a more limited range in amphibole δ¹⁸O values of ~7.0 to ~8.0 ‰ (e.g., Taylor, 1968; Kalamarides, 1984), a range which is not comparable to δ¹⁸O_amphibole values from the SSR.