DIGITAL PROCESSING OF AEROMAGNETIC AND COMPLEMENTARY GRAVITY DATA: KEY TO CRUSTAL STRUCTURE OF THE SOUTHEASTERN U.S. AND UNDERSTANDING TWO COMPLETE WILSON CYCLES AND THE BEGINNINGS OF A THIRD

Aeromagnetic (AM) data for most of the southeastern U.S. were acquired several decades ago at ~1-mi flight-line spacing. Digitization and various filters of these and gravity data have permitted viewing the data at 1:1,000,000 and larger scales in multiple ways. The newly processed data reveal elements of structure not seen before in both the subsurface and exposed Appalachians and adjacent regions. Curved AM anomalies in the western Inner Piedmont in AL, GA, and SC are truncated to the SE by the Brindle Creek fault defined by a linear AM anomaly. The Central Piedmont suture (CPS) is well defined in AM and filtered gravity data from AL to VA, but a low-angle segment (Abbeville thrust sheet, ATS) in GA, SC, and NC appears truncated by a major fault 30-60 km to the SE. This fault may define an overridden segment of the CPS that forms a ramp and delimits the 60-km displacement on the ATS. The ATS segment may have formed later (early Alleghanian) than the main Neoacadian CPS, but both segments could have been coevally active. The Kings Mountain shear zone may have formed a dextral tear fault bounding the NE end of the ATS. The data also reveal that the dextral Eastern Piedmont fault system (EPFS) is much more extensive than previously known, and most of it lies beneath the Coastal Plain. The EPFS reaches its greatest width (>100 km) in the Carolinas, but narrows rapidly into southwestern GA and southern VA. One or more dextral strike-slip duplexes are visible in the AM data, and much of the eastern EPFS, and adjacent Brunswick (Charleston) terrane, are cut by an ~80-km displacement sinistral strike-slip fault. All Appalachian structures, and older Grenvillian crust to the W, are truncated by the Suwannee-Wiggins suture across S AL and GA, which separates Appalachian and older Laurentian crust from African crust of the Suwannee terrane to the S. AM anomalies within the suture zone are muted by Triassic-Jurassic sediments deposited following failed rifting.