Northeastern Section (39th Annual) and Southeastern Section (53rd Annual) Joint Meeting (March 25–27, 2004)

Paper No. 7
Presentation Time: 8:00 AM-12:00 PM

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


HATCHER Jr, Robert D., Earth and Planetary Sciences, Univ of Tennessee, 306 E & PS Building, Knoxville, TN 37996-1410, THOMAS, William A., Department of Geological Sciences, Univ of Kentucky, Lexington, KY 40506-0053, ZIETZ, Isidore, 8340 Greensboro Dr Apt 414, Mc Lean, VA 22102-3544, WILSON, Gary V., 2812 4th Street NW, Birmingham, AL 35215 and STELTENPOHL, Mark G., Department of Geology and Geography, Auburn Univ, Petrie Hall, Auburn, AL 36849, dianashatcher@aol.com

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.