Geophysical Studies of Large Blind Thrust, Valley and Ridge Province, Central Appalachians

Abstract

Possible thrust-sheet geometries in the unexposed Cambrian-Ordovician lithotectonic unit in the Nittany anticlinorium of the Valley and Ridge province in West Virginia are defined through analysis of geophysical data. Calculated gravity for different subsurface interpretations is compared with observed gravity. Comparisons of model calculations to terrain-corrected Bouguer gravity indicate that a large blind thrust of the Cambrian-Ordovician lithotectonic unit, extending across the entire width of the anticlinorium, is an acceptable subsurface interpretation. A seismic line across the anticlinorium is also presented. The seismic line reveals that a large part of the area is underlain by a double thickness of the Cambrian-Ordovician lithotectonic unit. Data can be interpreted many ways. However, the gravity data require that an acceptable model have only minor lateral density contrasts across the anticlinorium so that effectively, a double thickness of the Cambrian-Ordovician lithotectonic unit exists across it. Both the gravity and seismic data indicate that the presence of separate horses beneath the major Silurian-Devonian structures exposed at the surface is unlikely.