STRIKE-SLIP FAULTS AND FABRIC VARIATION: IMPLICATIONS FOR STRUCTURAL AND TECTONIC DEVELOPMENT, NORTHERN IRON MOUNTAINS, SOUTHWEST VIRGINIA

Neoproterozoic to Early Cambrian Chilhowee Group sedimentary rocks in the northern Iron Mountains, southwest Virginia, record structural imbrication and deformation of the Late Paleozoic Alleghanian Orogeny. Mapping along a transect through the Dry Run Gap area, located in Mt. Rogers National Recreation Area, gives detail on the structural development of the area during orogenesis. Outcrop-scale strike-slip faults—with both dextral and sinistral sense and some strike-slip slickenside surfaces overprinting dip-slip surfaces—are present at several locations along the mapped transect. Many of the strike-slip faults trend NNE-SSW, suggesting a component of orogen-parallel motion, while some strike-slip faults trend NW-SE, suggesting the convergent tectonic transport direction. At least one generation of cleavage is present in the region with a dominant NE-SW trend. However, in some domains, more than one cleavage orientation is present, varying from NW-SE to E-W trends, with steep to intermediate dips. Presence of numerous strike-slip faults, and varying cleavage orientation suggest that deformation in the northern Iron Mountains may be due to: 1) multiple phases of deformation; 2) accommodation of a component of orogen-parallel motion by strain partitioning during oblique convergence; or 3) progressive structural change during continued imbrication and interaction with pre-existing continental margin shape during Alleghanian convergence. Further analysis is required to re-evaluate and interpret the role of strike-slip faults and development of varying cleavage orientations during the structural and tectonic progression of the northern Iron Mountains.