ORIGIN OF THE “S”-CURVE IN THE MURPHY BELT, GEORGIA BLUE RIDGE

The Murphy synclinorium (MS), a 1st generation, NW-overturned, doubly-plunging, large amplitude and wavelength isoclinal fold, extends ~linearly (S35°-S45°W) for ~120 km in the Blue Ridge (BR) from North Carolina into Georgia, before being folded into a regional “S” pattern by a NE-trending synform-antiform pair (Johnson Mountain synform-JMS and Jasper antiform-JA). These open F4 structures displace the MS ~28 km SE from its main SW linear trend. Superposition of the upright F4 JA on a NW-trending, upright regional F3 antiform, produces the Salem Church Grenville basement culmination (SCC), a ~symmetrical interference dome (Ramsay Type 1 interference pattern) in the MS and underlying rocks. These F3 and F4 structures are superposed on a basement-cored, F1 recumbent anticlinorium, a MS companion fold. The axial trace of the JA extends SW from the SCC across the Talladega-Cartersville-Great Smoky thrust (TCGS), folding it into a NE-plunging antiform. Embedded beneath the TCGS here is the Johnson Mountain thrust sheet (JMT), a west-dipping-to-overturned panel of Lower Cambrian rocks forming the west flank and hinge of a hanging-wall ramp anticline-the JA. The JA crosses the TCGS and extends ~30 km S along the E flank of the JMT, until it again intersects and folds the TCGS into a south-plunging antiform, producing the concave NW inflection in the TCGS and the mountain front (Cartersville syntaxis). Thus, the axial trace of the doubly-plunging JA intersects the TCGS in two places-the N and S terminations of the JMT, where it folds the TCGS and metamorphic fabrics in the W. Blue Ridge-Talladega allochthon (WBRT). The TCGS cuts in the direction of displacement up section to the NW across the JMT, merging with the JMT thrust at that fault’s N and S terminations, making the JMT a large horse embedded at the base of the WBRT. The JA initiated in the JMT beneath the previously emplaced WBRT, deforming the latter allocthon into the JMS and JA as the JMT moved up and over its foot-wall ramp. Thus, displacement of the JMT and overlying WBRT arched the MS into its distinctive “S” shape.