Magnetic Anomalies and Crustal Structure in Eastern Gulf of Mexico

Abstract

A marine magnetic survey made during 1965 has led to the construction of an anomaly map of the total magnetic field in the eastern Gulf of Mexico. Elongate anomalies with northeast-southwest trend characterize the northern part of the west Florida continental shelf. Anomalies indicative of volcanic-type source rocks lie within a 180-kilometer-wide strip across the central part of the west Florida shelf; it is inferred that a belt of volcanic rocks trends northeast-southwest across Florida, the west Florida shelf, and the abyssal plain to the Campeche Scarp. The eastern Gulf is thus dominated by northeast-southwest (commonly called Appalachian) structural trends in the basement. Depth to the basement in the marine volcanic province is estimated, from the magnetic anomali s and from available seismic refraction evidence, probably to be not much less than 9 kilometers. The west-central part of the map is devoid of large magnetic anomalies and probably corresponds with oceanic-type crust under thick sedimentary cover. North of the eastern part of the Campeche Bank a large negative magnetic anomaly strikes ESE.-WNW. This feature may indicate a synclinal downwarp in the oceanic crust there; it is shown that the theoretical anomaly for a syncline of triangular section fits the observations whereas a graben does not. There is no magnetic expression of the steep escarpment which terminates the west Florida shelf; this suggests that there is no basement faulting at the scarp involving the magnetic source rocks.