COLLISIONAL TECTONICS OF THE SOUTHERN APPALACHIAN OROGENIC BELT - REINTERPRETATION OF ADCOH AND COCORP SEISMIC REFLECTION DATA WITH CONSTRAINTS FROM NEW POTENTIAL FIELD DATA

To better constrain the collisional structure of the Southern Appalachian margin, including the Laurentian – Peri-Gondwana suture zone and footwall structures beneath the Blue Ridge/Inner Piedmont allochthon, maps and a 2D regional cross-section model, constrained by seismic reflection and surface geology have been developed by forward and inverse modeling the aeromagnetic and gravity fields. The profile traverses the Southern Appalachians from the Valley and Ridge to the Coastal Plain of South Carolina, and is consistent with the seismic data, as well as the observed gravity and magnetic fields at long and short wavelengths.

The Central Piedmont Suture is the boundary between the Laurentian Inner Piedmont and the Peri-Gondwanan Carolina terrane. The model is consistent with previous interpretations of CPS as a low-angle thrust fault ramping up from an Alleghenian mid-crustal detachment at depths of over 12 km. Unlike previous interpretations, the model explains the Appalachian paired gravity anomaly without a change in lower crustal density. The APGA is explained by the seismically constrained increase in crustal thickness northwest of the CPS and the observed higher densities of the Carolina terrane relative to the Inner Piedmont and Blue Ridge.

Most surprisingly, the seismically imaged low-density rocks in the Piedmont and Blue Ridge allochthon appear to over-thrust high-density footwall duplexes. The gravity anomalies are primarily correlated with the footwall folds, and the high densities suggest that the footwall reflectors may not represent Paleozoic shelf strata as previously interpreted, but may need to be reinterpreted as Grenville basement duplexes. This implies that the eastern edge of Laurentian margin shelf sediments has been displaced westward beyond the Hayesville Fault. Concurrently, the lack of need for a lateral density contrast in the lower crust opens the possibility that Grenville basement may extend as far east as the Coastal Plain.

For this paragraph, maybe we should start with the APGA and put the CPS second – food for thought