Tectogenesis and metamorphism of the Piedmont from Columbia to Westview, Virginia along the James River.

Abstract

During Late Precambrian or Early Cambrian (~550 m.y.) a sequence of interlayered graywackes and shales was intruded by the Columbia granite. At approximately 340 m.y. the granite and sediments were metamorphosed to at least amphibolite facies. During the peak and waning stages of metamorphism, these lighologies experienced 3 or possibly 4 deformational events which occurred while faulting was initiated along the Lakeside fault zone. Retrogressive mineral assemblages in fractures along the Lakeside fault and Central Piedmont Lineament indicate that reactivations along these zones occurred during regional cooling and continued after 221 m.y. During Late Triassic or Early Jurassic, the region was intruded by diabase dikes. An erosional unconformity separates alluvium and colluvium from the layered and intrusive rocks.