AMS PETROFABRICS OF THE CUMBERLAND PLATEAU, TENNESSEE: ALLEGHANIAN DEFORMATION ALONG THE WESTERN MARGIN OF THE APPALACHIAN FOLD-THRUST BELT

The Cumberland Plateau of middle Tennessee is a tableland over 650 m in elevation that spans an area approximately 13,000 km² west of the Valley and Ridge Province. Pennsylvanian foreland-basin clastics shed from the Appalachian highlands cap the plateau, except where older Paleozoic strata are exposed in the core of the Sequatchie Valley anticline--a >300 km long northeast-trending structure located in the middle of the plateau. The Sequatchie Valley thrust is one of several regional Alleghanian faults that underlie the plateau, and previous investigations have suggested that much of the plateau is allochthonous, having been transported to the northwest during the Alleghanian orogeny. To test this hypothesis and to depict the strain gradient and limit of deformation along the western margin of the Appalachian fold-thrust belt in middle Tennessee, we investigated the anisotropy of magnetic susceptibility (AMS) from >30 samples of Pennsylvanian sandstone. AMS was used because the technique is sensitive to low strain and because there are few outcrop-scale structures on the plateau that record deformation. Preliminary Spinner Kappabridge AMS results yield mean susceptibilities between 1-15E-06 with most P-values ranging from 1.005-1.075. Vibrating-sample magnetometer (VSM) analysis indicates the presence of ferrimagnetic minerals in the sandstone samples. Principal-axis orientations of K₁, K₂, and K₃ suggest both diagenetic compaction and layer-parallel shortening deformation. Furthermore, the orientation of the principal axes suggests that Alleghanian deformation affected much of the Cumberland Plateau and that strain is concentrated near large-scale structures such as the Sequatchie Valley anticline.