The Saltville thrust: investigation of a regional thrust fault in a foreland fold and thrust belt

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Virginia Polytechnic Institute and State University


Thin-skinned models of deformation are currently accepted for the southern Appalachians. The mechanics of this type of deformation are not well understood. The Saltville thrust, a major overthrust in the southern Appalachians, was investigated with respect to deformation mechanics. Thrust termination occurs in the overturned, northwest facing Sinking Creek anticline, at the juncture between the southern and central Appalachians . The primary regional displacement transfer mechanism at the thrust terminus is the transition from faulting to folding. Mesoscopic fabrics show variations in deformation intensity across the anticline, with high strains on the northwest limb, and low strains on the upright southeast limb. Strain accommodation on the overturned limb was by folding, faulting, and cleavage development. Knox Dolomite in the core of the anticline is upward facing and unfolded. Strain patterns and facing data indicate that shear thrusting at depth caused passive regional folding. Subsequent movement caused the thrust to act as a break thrust and cut previously folded strata.

Cataclasis is the primary bulk deformation mechanism along the thrust surface. Cataclastic fabrics in dolomites range from protocataclasites to ultracataclasites, and reflect changes in frictional grinding. Foliated cataclasites are described. Fault-rock fabrics indicate that thrust-sheet emplacement occurred through seismic failure, facilitated by transient, abnormally high pore pressures, and aseismic failure accomplished within a layer of cataclastically flowing gouge. Thin fault zones and rapid decreases in deformation intensity away from the fault surface indicate rapid sliding, and a lack of frictional grinding.