GRAVITY AND MAGNETIC MODELING OF THE BASEMENT BENEATH ALABAMA GULF COASTAL PLAIN

The southeastern United States has experienced two complete successions of Wilson cycles: (1) assembly and break up of Rodinia and the opening of the Iapetus Ocean; and (2) closing of Iapetus ocean, assembly of supercontinent Pangaea and its subsequent break up, and opening of modern Atlantic Ocean. The evidence of these supercontinent cycles are recorded in the rocks of Alabama and adjacent areas, but in the southern portion of the state, these rocks are covered by as much as 7 km of Coastal Plain sediments. In this study, we use airborne gridded gravity and magnetic data to develop crustal models along transects that cross major tectonic structures and the ancient North American (Laurentian) margin. Models derived from gravity and magnetic data are constrained by well-log information and by geologic mapping. Preliminary results show that a pronounced gravity lows can be interpreted as the suture between relict Gondwanan crust and volcanic arcs accreted to the Laurentian margin. The denser crystalline rocks of Piedmont and Valley and Ridge correspond to the minor gravity highs. The Alexander City fault zone has a strong expression both in the gravity and magnetic data, suggesting it is a major, crust-penetrating structure, whereas other features, such as the NY-AL magnetic lineament appear to reflect shallower properties.