PRELIMINARY INVESTIGATION OF JOINTS ALONG THE SOUTH-SOUTHEAST PROJECTION OF THE HARPETH RIVER FAULT ZONE, CENTRAL TENNESSEE

One of the investigators (Paladino) measured the orientation of 25 joints at three outcrops within an outcrop-poor area approx. 3.2 km to the south-southeast (SSE) of the Harpeth River fault zone (HRFZ), a largely aseismic cratonic fault and fold zone within the Nashville dome, central Tennessee. At the surface, the HRFZ consists of macroscale and mesoscale folds and minor faults and joints, and these structures define four normal fault zones: Peytonsville (on the west), Arno, McClory Creek, and McDaniel (on the east). Minor faults within the HRFZ are mostly east-side-down normal faults and strike SSE. Published aeromagnetic and subsurface data suggests that the HRFZ coincides with a basement structure that continues to the SSE beneath the Chapel Hill quadrangle. However, most joints measured by Paladino in the Chapel Hill quadrangle do not share the strike of HRFZ fractures. Specifically, most (52%) Chapel Hill joints strike 260°-295°. In contrast, only 1 minor fault out of 45 fractures (0.05%) in the Arno fault zone falls within this range, only 2 joints out of 11 fractures (18%) in the McClory Creek fault zone fall into this range, and no fractures in the Peytonsville and McDaniel fault zones fall into this range. Also, only 2 Chapel Hill joints (8%) share the published 331°-358° strike of macroscale HRFZ fault zones. In contrast, 11 Chapel Hill joints (44%) strike 260°-290°, 7 (28%) strike 290°-315°, 3 (12%) strike 010°-050°, and 2 (8%) strike 050°-060°. These findings are consistent with the interpretation that, at least at the surface, the HRFZ terminates to the north of these Chapel Hill quadrangle outcrops.