NEW 1:500,000- AND 1:1,000,000-SCALE AEROMAGNETIC MAPS OF ALABAMA

The first aeromagnetic map of Alabama compiling available Alabama Geological Survey (AGS), National Uranium Resource Evaluation (NURE) Program, and U.S. Geological Survey (USGS) data has been published at 1:1M and 1:500,000 scales with 100 nt and 20 nt contours by the AGS (2002). This map was compiled by hand using the original profiles (analogs) rather than conventional electronic methods using a gridded net (computer). As a result, the map shows much more detail and character than previously published magnetic maps. NURE data were collected at 3- and 6-mi N-S spacing (E-W lines), 400 ft above ground; USGS data were collected at 1-mi N-S spacing (E-W), 1000 ft above ground; and an AGS survey was acquired at 1-mi spacing (N-S) 500 ft above ground. Broad, low- to high-amplitude crustal anomalies underlie regions covered by Paleozoic and Coastal Plain sedimentary rocks, and by thinner parts of the Blue Ridge-Piedmont megathrust sheet. The New York-Alabama lineament is traceable from DeKalb and Cherokee Counties in NE AL southwestward into central AL where it apparently bifurcates into several splays. Several large NW-trending magnetic highs (mafic bodies?) appear truncated by one of the splays in NW AL. High-frequency anomalies superposed on the broad, low-amplitude anomalies result from magnetic rocks exposed in the Piedmont NW and SE of the Brevard fault zone (BFZ). The BFZ consists of narrow NE-trending linear anomalies that track the fault zone from the GA border to Elmore and Montgomery Counties, AL, where they turn S to be truncated by or join the Towaliga fault in Lowndes County. Pine Mountain window rocks S of the Inner Piedmont are weakly to nonmagnetic, and the bounding Towaliga (N) and Goat Rock (S) faults produce weak linear anomalies. A narrow zone of high frequency anomalies S of the Goat Rock fault is traceable E into the exposed Carolina terrane in GA. Farther S, all NE-SW Appalachian trends are truncated by the E-W-trending Brunswick terrane of broad, low amplitude, mostly magnetic lows, probably representing the Alleghanian suture partially reactivated as a failed rift system that filled with Triassic-Jurassic sediments. S of this zone are more broad, higher amplitude anomalies, probably representing African crust of the Suwannee terrane.