INFERRED REACTIVATION OF BASEMENT STRUCTURES WITHIN THE NASHVILLE DOME, CENTRAL TENNESSEE

The Nashville dome, central Tennessee, is an approx. 12,000 km² north-northeast-trending, elliptical cratonic uplift. A published crustal density model shows that a previously-undescribed Precambrian or Cambrian rift, the Nashville rift, probably runs north-northeast from northwestern Alabama through the Nashville dome to southern Kentucky. Within the Nashville dome, macroscale folds and mesoscale structures of the Stones River and Harpeth River fault zones have been interpreted previously as the surface manifestation of sub-surface normal faults. New research reveals two previously-undescribed inferred sub-surface fault zones: the Marshall Knobs fault zone (MKFZ) and the Northern Highland Rim fault zone (NHRFZ). The MKFZ is inferred to lie in the sub-surface beneath the southern edge of the Marshall Knobs syncline (MKS). The MKS is near the center of the Nashville dome, is ~16.3 km long, is associated with ~35 m of structural relief, and trends east-southeast. The inferred fault zone is down on the north side. The NHRFZ is on the northern periphery of the dome and consists of east-northeast-striking minor normal and reverse faults and a minor strike-slip fault. The authors hypothesize that the NHRFZ may be related to the sub-surface continuation of a macroscale fault previously-mapped at the surface 25 km to the southwest. All of the inferred faults fit into a tectonic model in which they originally formed within a rift and later reactivated, accommodating extension of the uppermost crust during uplift of the Nashville dome.