Abstract
Recent detailed geologic mapping in the Blue Ridge belt of northwestern North Carolina has revealed the first reported eclogite ( sensu stricto) in the southern Appalachian orogen. The eclogite occurs at the base of the Ashe Metamorphic Suite within a shear zone that separates the Spruce Pine thrust sheet from the underlying Grenville-age basement rocks. This contact juxtaposes rocks of apparent oceanic affinities (predominantly metapelite, metabasite, and meta-ultramafic rocks) with rocks of the ancient North American craton. The primary metamorphic assemblage in the eclogite is garnet + omphacite + quartz + rutile. Hornblende and plagioclase occur only as retrograde amphibolite facies phases in the eclogite. Pressure-temperature estimates for the primary eclogite assemblage are consistent with minimum pressures of 13–17 kbar at 625–790°C, while the retrograde amphibolite facies assemblage suggests conditions of 8.5–12 kbar and 650–730°C. Ultramafic blocks also occur within the shear zone containing the eclogite. The presence of high-pressure metamorphic rocks associated with ultramafic rocks and pelitic schists within a shear zone separating continental rocks from oceanic rocks is strong evidence for an ancient subduction event and indicates that at least part of the Ashe Metamorphic Suite is a subduction-related, accretionary mélange.
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