THE TECTONIC IMPLICATIONS OF 460 MA ECLOGITE ALONG THE TACONIAN SUTURE IN THE EASTERN BLUE RIDGE OF NORTH CAROLINA

The presence of ca. 460 Ma eclogite near the base of the Ashe Metamorphic Suite (AMS) at the contact between the eastern and western Blue Ridge in North Carolina supports the idea that the AMS is part of an accretionary complex that was sutured to the Laurentian margin during the Taconian orogeny. At this time we do not know if the eclogites were formed by subduction of an oceanic slab and then emplaced as blocks into a lower grade matrix, similar to the Franciscan eclogites in California, or if the eclogite is the product of deep underthrusting of the margin following the Taconian collision. In this latter mechanism, both the eclogite and the surrounding rocks would have undergone eclogite facies metamorphism. In the Franciscan model, eclogite metamorphism predates collisional metamorphism. In the collisional model, peak metamorphism of all of the rocks involved should be roughly synchronous. Existing ages for peak Taconian metamorphism in the southern Appalachians range from about 460 to 495 Ma. The 460 Ma age of the Blue Ridge eclogite is either the same age as, or post-dates Taconian collisional metamorphism. This could indicate that eclogite metamorphism in the Blue Ridge was associated with the Taconian collision and would imply that large segments of the margin were buried to eclogite facies depths during the collision. If the eclogite facies metamorphism is restricted to the blocks of eclogite then a Franciscan-type scenario for the generation of the eclogite may be more appropriate. The 460 Ma age of eclogite formation, however, creates a problem because it should be older than the collisional metamorphism. One solution to this problem is that the eclogite was generated in a subduction zone farther north, in the central or northern Appalachians where the Taconian collision occurred much later than in the southern Appalachians. Later dextral strike-slip motion, perhaps along the Acadian Burnsville fault, could have moved the AMS eclogite to its present position.