CUMBERLAND PLATEAU OVERTHRUST AND PINE MOUNTAIN BLOCKS, TN, KY, VA: SYMMETRICAL FEATURES AROUND THE UNDISTURBED WARTBURG BASIN WITH CONTRASTING KINEMATICS AND MECHANICS

The Pine Mountain (PM) thrust sheet (3.6 km thick) and the Cumberland Plateau overthrust (CPO, ~1.5 km thick) are major Alleghanian structures in the southern Appalachian Cumberland Plateau. This study involves both the northern CPO sheet and the adjacent SW part of the undeformed Wartburg basin, with the dextral Emory River (ER) fault and the CPO separating the tectonic units. PM sheet is bounded on the NE by the dextral Russell Fork fault and to the SW by the sinistral Jacksboro fault, which is subparallel to and symmetrical with the ER fault ~35 km SW. All rock units in the CPO sheet are Pennsylvanian sandstones, shales, coals, and siltstones with Mississippian carbonates and shales exposed to the SW in the breached portions of Sequatchie anticline. The PM fault ramped from the base of the weak Cambrian Rome Formation in the Valley and Ridge (VR) province in to the thick Chattanooga Shale (MDc) beneath the Cumberland Plateau. MDc is much thinner to the SW where the CPO ramped from the Rome and therefore could not act as the higher weak layer, so it ramped to the still higher shale and coal units. Other major regional structures here are the NE plunging Sequatchie anticline that ends at the ER fault and the Powell Valley anticline that ends at the Jacksboro fault. The PM thrust is a nearly straight NE-striking thrust, while the CPO developed in complex short (< 10 km) segments of thrust faults and steeply dipping, short (< 5 km) tear faults.

Detailed geologic mapping of the ER fault and portions of CPO have permitted us to examine the differences between the CPO/ER and PM/Jacksboro faults that were subjected to similar tectonic histories and are mirror images NE and SW of the Wartburg basin. Maximum shortening on the PM block is ~21 km at the SW end, and decreases NE, while minimum shortening on the CPO sheet is ~ 10 km and decreases SW. The Jacksboro fault takes up all of the displacement on the PM block, whereas the CPO is terminated by complex segments of thrust and tear faults.

The Wartburg basin formed almost exactly opposite the point of maximum shortening on the Blue Ridge-Piedmont megathrust sheet indenter, which formed ten major thrusts at this latitude across the VR. The mechanical stratigraphy, mechanics of thin-skin deformation, and the thinner original overburden on the CPO may be responsible for the fundamental differences between the two faults.