THERMAL FOOTPRINT OF AN ERODED THRUST SHEET IN THE SOUTHERN APPALACHIAN BLACK WARRIOR BASIN, ALABAMA, USA
Balanced and restored cross sections in the thrust belt indicate that a 3-km-thick thrust sheet with horizontal dimensions of ~10 x 30 km was emplaced northwestward a distance of ~18 km beyond the present eroded thrust front. This thrust was part of a much larger thrust sheet present in the hinterland. A three-dimensional analytical thermal model of a 3-km-thick thrust sheet that cools both laterally and vertically, reproduces the magnitude and shape of the coal rank anomaly between 500,000 and 800,000 years after thrust emplacement. The geothermal gradient reaches a steady state at 2 m.y., and is never fully re-established because of lateral cooling in the hanging wall of the thrust. It is proposed that the thermal anomaly was caused by the excess tectonic cover of the thrust sheet in a manner analogous to that of a hot clothes iron on a shirt. This hypothesis would indicate the southern Appalachian thrust belt was emplaced farther westward onto the Black Warrior foreland basin than previously recognized and that lateral cooling of thrust sheets may produce oval-shaped isograd patterns in orogenic belts.