The Florida Magnetic Anomaly and the Alleghenian Suture in Northern Florida

David J. Hall

The 600 nanotesla Florida magnetic anomaly trends north-northeast for more than 300 km across the Suwannee basin in northern Florida. The spatial frequency of the anomaly demonstrates that the source is either shallow and broad or deep and highly magnetic. Subsurface penetrations of undisturbed Paleozoic sedimentary rocks with African affinities eliminate the possibility of a broad shallow source. Detailed modeling constrained by the subsurface information, new COCORP seismic data and regional tectonic considerations suggests that the anomaly is best explained as a deep mafic/ultramafic suture associated with the Alleghenian orogenic closing of the proto-Atlantic. As demonstrated by subsurface penetrations, the Alleghenian suture is not a vertical crustal-penetrating disc ntinuity associated with the Brunswick magnetic anomaly, but is rather a northwest-verging thrust with rocks of the Suwannee basin and their underlying "African" basement in the hanging wall over North American crust. The Florida magnetic anomaly is explained as remnant oceanic crust and mantle in the currently steeply-dipping Alleghenian subduction zone.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995