Retrograde metamorphism of eclogite in the southern Appalachian Mountains,USA - A case involving seamount subduction?

This work supports a growing body of evidence that the Ashe Metamorphic Sui te (AMS) of the eastern Blue Ridge province in North Carolina has an ensima tic origin and is part of a subduction-related accretionary melange, markin g the Taconic suture between the North American craton and the Inner Piedmo nt. In a palinspastic reconstruction, the thrust fault at the base of the A MS appears to have intercepted the greatest depths (i.e. highest-P metamorp hic rocks) beneath parts of the AMS now exposed adjacent to the Grandfather Mountain window. The greatest volume of mafic rock is found in these same areas. We suggest that the nascent, subduction-related, basal thrust fault was deflected downward by an obstacle in the form of an isolated, mafic vol canic edifice on the oceanic crust-a sea mount. Pelitic and mafic rocks dom inate the AMS. North of the Grandfather Mountain window, retrograded eclogi te occurs in the amphibolite near the base of the AMS. Textures and mineral ogy indicate that an original eclogite assemblage was subjected to the foll owing sequence of parageneses: (a) Eclogite(I) facies: omphacite + garnet + quartz, (b) Eclogite (II) facies: omphacite + garnet + epidote + quartz, (c) Symplectic (diopside + plagioclase) + garnet + epidote + quartz, (d) Amphibolite facies: (diopside + plagioclase) + garnet + epidote + hornb lende + quartz, (e) Amphibolite facies: plagioclase + garnet + epidote + hornblende + quart z. P-T conditions, estimated from geothermobarometry applied to relevant miner al compositions, are c.720 degreesC and c. 16 kbar for (b) eclogite(II) fac ies; c.655 degreesC and c.8.5 kbar for (e) amphibolite facies.