CONTRASTING MODES OF STRAIN ACCOMMODATION AND INTRABLOCK DEFORMATION ZONES (IDZs) IN THE MARION—SALTVILLE REGION OF THE VALLEY AND RIDGE STRUCTURAL BELT, SW VIRGINIA, USA

The Saltville Block, overlying the Saltville Fault and bounded above by the Pulaski Fault (and Block) in the Marion—Saltville region of SW Virginia, contrasts in its mode of strain accommodation with the overlying and underlying fault blocks. Immediately above the bounding Pulaski Thrust Fault, the structuraly overlying Pulaski Block contains a distinctive zone of block-in-matrix rock that contains distinct subunits of melange and broken formation and in part resembles the type Max Meadows Breccia. Within the block, there are both folds and some ancillary faults that locally connect with the Pulaski Fault (Whitlock and Derby, 2005; Webb et al., 2008). In the underlying Copper Creek--Narrows Block, strain is almost entirely accommodated by folding of rocks into regional, typically open, macroscopic folds. In the Saltville-Broadford region, on the Saltville Block, strain accommodation occurs via three modes. Strain is accommodated (1) by a few mesoscopic to macroscopic folds; (2) by faulting yielding fault blocks or “horses” along the Saltville Fault zone, and (3) in narrow, intrablock deformation zones (IDZs) containing both folds and faults. The IDZs are characterized by high angle shears and spaced disjunctive cleavages and by mesoscopic, meter-scale folds. In the Broadford Quadrangle, the Saltville block contains three IDZs. One – characterized by high angle shear planes (cleavages) and by mesoscopic, meter-scale folds – increased the map width and apparent thickness of the Honaker Formation via diachronous faulting and folding, followed by extension. The second, marked by folds localized in the Nolichucky Formation, locally increases the map width of that unit. The third IDZ is a complex zone of folding with bedding plane thrust faults in the Witten and overlying Moccasin formations, cut by a later high angle cleavage zone that trends oblique to unit contacts. The fold-thrust zone locally results in an increase in the mapped width of the Moccasin Formation.