UPLIFT OF THE NASHVILLE DOME, CENTRAL TENNESSEE BY INVERSION OF THE PREVIOUSLY-UNDESCRIBED NASHVILLE RIFT

The Nashville dome, central Tennessee, is a north-northeast-trending, elliptical cratonic uplift spanning more than 12,000 km² and located 50-125 km northwest of the edge of the Appalachian foreland thrust belt. We seek to shed new light on the mechanisms and structures responsible for uplift of the dome by investigating spatial relationships among structural geology, Paleozoic sedimentary geology, and middle and upper crustal structure. The Nashville dome roughly coincides with a north-northeast-trending Bouguer gravity high that extends from northwestern Alabama through the Nashville dome to southern Kentucky. We combine seismic velocity, gravity and topography to map crustal density structure, finding that this anomaly is the result of a contiguous belt of high-density material in the middle/upper crust (0–30 km depth) varying in width from ~25-100 km. The belt shares the north-northeast orientation of many cratonic extensional structures in the central and eastern United States, suggesting that it comprises mafic units associated with a previously-undescribed Proterozoic or Cambrian rift, here dubbed the Nashville rift. At its southern end, the rift terminates against the New York-Alabama lineament, and its northern terminus is ~35 km south of the Rough Creek graben. The Nashville rift fills what would otherwise be a ~375 km gap in the belt of extensional structures found west of the Appalachians between Pennsylvania and Alabama. Comparisons of the location and trend of the rift with maps of post-Ordovician faults and probable fault-propagation folds, middle and upper Ordovician facies and isopach maps, and a structure contour map of the base of the upper Devonian Chattanooga shale show that rift inversion almost certainly contributed to uplift of the Nashville dome. This hypothesis is consistent with the common observation that intracratonic structures reactivate repeatedly over geologic time, focusing intraplate deformation.