Abstract

Samples of the Soapstone Ridge Complex (SSR) in the Southern Appalachians examined for this study are composed of megacrystic orthopyroxenites, amphibole schists, and talc–chlorite–amphibole schists. The mineralogy of the SSR samples studied consists of varying proportions of amphibole, chlorite, talc, orthopyroxene, and Fe–Ti oxides. Amphibole is the dominant mineral in almost all SSR samples studied. The amphiboles display zoning, whereby cores that are composed of magnesiohornblende and edenite, consistent with amphibolite facies conditions, are rimmed by tremolite/actinolite, consistent with greenschist facies conditions. Oxygen isotope compositions of SSR amphiboles investigated show a wide range in δ18O values, from a low value of 1.8‰ to a high value of 6.1‰. Such wide ranges in δ18Oamphibole values occur in ophiolite complexes and oceanic crustal rocks. Relict orthopyroxene from the SSR has a δ18O value of 3.4‰, a value lower than those from layered intrusions but comparable to some pyroxene δ18O values from ophiolites. Equilibration temperatures calculated for actinolite–chlorite yield a temperature of 227 °C, consistent with greenschist facies conditions. It is proposed that the SSR amphibole cores were metamorphosed probably during terrane–terrane collision under amphibolite facies conditions, with the actinolite rims possibly being formed during thrusting of the SSR rocks onto the continental margin.

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