TRANSPRESSION OR COMPRESSION: AN EARLY EVENT IN THE TECTONIC HISTORY OF THE ROME TROUGH

The Rome Trough is a northeast-trending, asymmetric, extensional rift basin of Middle to Late Cambrian age. Grenville basement underlies the trough, and both the Rome and Conasauga Formations are syn-rift units within the trough. Single-fold, reflection-seismic data have revealed a series of small, imbricate thrust faults within the deepest section of the trough in eastern Kentucky. These faults lie between the Irvine-Paint Creek and Rockcastle River Fault Zones and occur in a region approximately 10 miles wide. The thrust faults primarily cut the basement and the lower Rome sequence and have an approximate apparent dip of 6o to the northwest. This is significant because the northwest dip is the opposite of the usual east-dipping fabric of the Grenville Province. Because these faults have affected the lower Rome reflectors, they cannot be entirely the result of pre-rift tectonics. Furthermore, because the upper Conasauga reflectors have not been affected, the faults apparently were not initiated or reactivated by later Paleozoic movement. Consequently, we conclude that these faults formed during early stages of trough development. Although we cannot determine conclusively the origin of the thrust faults, we propose the following explanations for their occurrence: (1) transpression due to early strike-slip faulting, (2) deformation due to compression within a confined subsiding graben block, or (3) a combination of these two mechanisms.