GEOLOGIC MAP OF THE KONNAROCK 7.5–MINUTE QUADRANGLE, VIRGINIA

Geologic mapping on the Konnarock 7.5­–minute quadrangle in southwest Virginia involved the compilation of legacy geologic maps of D.W. Rankin and new geologic mapping. The Konnarock quadrangle straddles parts of the Valley and Ridge and Blue Ridge, and includes part of the northeastern end of the Mountain City window. Rocks of the Blue Ridge include rhyolite and volcaniclastic rocks of the Neoproterozoic Mount Rogers Formation (ca. 760–749 Ma) thrust over the Mountain City window by the Catface and Stone Mountain faults. Exposed in the window is a section of Late Neoproterozoic to Early Cambrian rocks of the Konnarock Formation, Chilhowee Group, Shady Dolomite and Rome Formation; the rocks are overturned in a recumbent fold that plunges 18°/060°. The Iron Mountain fault frames the west side of the Mountain City window, and dips NW beneath the Shady Valley thrust sheet, which carries the Stony Creek syncline. Here, the syncline is an upright, tight syncline that plunges 3°/066° and also exposes a section from the Konnarock Formation through Chilhowee Group on the east limb. Several basalt flows are in the lower part of the Unicoi Formation. The Holston Mountain fault bounds the Shady Valley thrust sheet on the northwest and imbricated and juxtaposed sections of the Chilhowee Group over unmetamorphosed Cambrian to Ordovician rocks of the Pulaski thrust sheet of the Valley and Ridge. The Cambrian to Ordovician section of the Pulaski thrust sheet consists of the Shady Dolomite, Rome Formation, Elbrook Formation, Knox Group, and Knobs formation. Rocks in the footwall of the Holston Mountain fault are overturned in the southeast limb of the Roetown syncline. Part of the of the syncline is excised on the southeast by a thrust fault placing Knox Group dolomite against the Knobs formation in the syncline. Locally, slaty cleavage is well developed in shale units of the Knobs formation and is axial planar to the Roetown syncline, which trends ~070°. Mapped surficial deposits include colluvial fans, alluvium, and terraces above tributaries to the South Fork of the Holston River.