Seismic Signatures of Tectonic Lithofacies from Regional Lines, Appalachian Ultradeep Core-Hole Site Area

J. K. Costain, C. Coruh, T. Pratt, R. D. Hatcher, L. Glover, III, R. Phinney, J. Diebold, R. Williams, M. Zoback

A highly reflective upper crust is imaged on regional seismic data between Hayesville, North Carolina, and Fair Play, South Carolina. Above Eocambrian(?) rift basins, reflections originate from probable lower Paleozoic shelf strata at 8-10 km (3 sec). Reflections at 1.2-2.6 sec east of Hayesville also might be from lower Paleozoic rocks, implying a (repeated) thickness of about 5 km of shelf strata. Among the most prominent seismic signatures are wedge-shaped packages of reflections opening to the northwest from depths of 6 km (2 sec) and 9 km (3.2 sec) between Hayesville, North Carolina, and Westminster, South Carolina. These reflections may indicate locations where decollements ramp up to shallower crustal levels, and where local stacking of thin beds has resulted in tu ing of reflections with a two to three fold increase in reflection amplitudes. The horizontal bases of such packages may indicate the crustal levels of decollements that are usually acoustically transparent. By one interpretation, the Blue Ridge master (largest horizontal displacement) decollement lies above these signatures at a depth of 3-5 km. Just northwest of Westminster, reflections from the Brevard zone may be truncated near or at this master decollement at 5.5 km.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.