Geology of the Precambrian Igneous-Metamorphic Complex of the Blue Ridge in the Snowden Quadrangle, Virginia

Abstract

The Snowden 7.5 minute quadrangle is located entirely within the Blue Ridge physiographic province of Virginia. Early Cambrian sediments of the Chilhowee Group occur in the northern half of the quadrangle, while the southern half consists of Precambrian igneous and metamorphic rocks of the Blue Ridge Basement Complex. The basement rocks to the south have been thrust up and over the younger Chilhowee sediments. The fault contact can be traced across the quadrangle. Since the division of the Chilhowee Group north of this fault into the Unicoi, Hampton, and Erwin Formations is widely accepted, this paper will focus on relationships within the basement complex south of the fault. A number of different rock units within the basement can be recognized on the basis of field occurrence and gross lithology. The Pedlar Formation of Bloomer and Werner (1955) occurs as a dark green, garnet-bearing charnockite which appears to grade eastward into a more massive charnockite containing large porphyryoblasts of perthitic feldspar. A third, leucocratic charnockite can be recognized in the vicinity of the thrust fault, but its areal distribution is restricted by the fault itself. Well-foliated granulites occur as large-scale lensoid masses within the younger charnockites. A wide cataclastic zone of protomylonites, mylonites, and mylonite gneisses cuts across the southeastern portion of the map and obscures any original lithologies in that area. Greenstone dikes and isolated granitic intrusions occur locally within the cataclastic zone and, in many cases, have been highly sheared and/or recrystallized.