AN ANNULAR DRAINAGE PATTERN IN TRANSYLVANIA AND HENDERSON COUNTIES, NC: EVIDENCE OF AN IMPACT STRUCTURE IN THE BLUE RIDGE MOUNTAINS?
The first phase of our investigation is to collect structural data around the perimeter of the circle. Joint orientations are generally tangential to the two rings but some joints parallel preexisting regional trends. Samples have been collected from the centers of both rings and are being prepared for petrographic analysis.
Rocks exposed within the circle are mostly early Paleozoic gneisses, granites, amphibolites, and schists. In our working hypothesis, we speculate that the origin of the annular pattern occurred when a roughly 1.5 km diameter bolide collided with the planet in the heart of a relatively high mountain range during late Permian or early Triassic time. All vestiges of the surface expression of this feature were lost to erosion but the deep fractures that could result from such an event preserve the circular pattern.