DIGITAL IMAGES OF AEROMAGNETIC AND GRAVITY DATA SHED NEW LIGHT ON CRUSTAL STRUCTURE OF THE SOUTHEASTERN U.S

Digital compilation, filtering, and innovative map displays of regional aeromagnetic and gravity data reveal the crustal structure of the SE U.S. in ways not possible before, allowing recognition of new structural elements and refining our understanding of previously known structures. The New York-Alabama lineament is the eastern boundary of a buried crustal block with NE-trending magnetic highs and gravity lows that trace into central AL where it ends. Broad, low- to high-amplitude magnetic and gravity anomalies delineate crustal features that underlie near-surface Paleozoic rocks, Coastal Plain sediments, and thinner parts of the Blue Ridge-Piedmont megathrust sheet. Curved magnetic anomalies in the western Inner Piedmont in AL, GA, and SC are truncated to the SE by the Brindle Creek fault. The Central Piedmont suture (CPS) is well defined in both the aeromagnetic and filtered gravity data from AL to VA. Magnetic anomalies over a low-angle segment of the CPS (Abbeville thrust sheet, ATS) in GA, SC, and NC appears truncated by a major fault that may define an overridden ramp of the CPS and delimits the 60-km W displacement on the ATS. The ATS segment may have formed later (early Alleghanian) than the main Neoacadian CPS but could have been coevally active. The Kings Mountain shear zone may be a dextral tear fault bounding the NE end of the ATS. Magnetic anomalies suggest that the dextral Eastern Piedmont fault system (EPFS) is much more extensive than was previously known, with most of it lying beneath the Coastal Plain. The EPFS reaches its greatest width (>100 km) in the Carolinas but narrows abruptly along strike into western GA and southern VA. Aeromagnetic maps indicate that EPFS dextral strike-slip duplexes and the adjacent Brunswick (Charleston) terrane are cut by an ~80-km displacement sinistral strike-slip fault. In southern AL and GA all Appalachian and older crustal anomalies are truncated by the Suwannee-Wiggins suture joining African crust of the Suwannee terrane (ST). Aeromagnetic anomalies within the suture zone are muted by Triassic-Jurassic sediments, but parallel, arcuate, N45°E linear anomalies reflect internal lithologic structure in the ST.