An Integrated Geophysical Study of the Northern Gulf of Mexico

The end members of passive continental margins are characterized as non-volcanic or volcanic depending on the nature of the transition zone. Differences between these two types are usually reflected by the differences of the physical properties of the Ocean-Continent Transition (OCT). Gravity, magnetic, and seismic data used to investigate the crustal structure of a portion of the northern Gulf of Mexico. Six 800-km long, crustal cross sections have been constructed across the study area with 70 km spacing. Two-dimensional crustal models, comprising 7 layers have been developed to simulate the observed Free-air gravity anomalies. The density of each layer has been kept constant and the geometry of the individual layers modified to obtain a good match to the gravity data. Where possible the gravity models have been constrained by available seismic and magnetic data. Interpretations for the boundaries between different crustal types are delineated by modeling. The magnetic anomalies were used to define the extent of the transitional crust and interpreted as the effects of subaerial flood basalts. For this study OCT was defined as the region where the crustal thickness is greater than 9 km and less than 25 km. The average width of the OCT in the models is 250 km which is greater than that found in previous studies at other volcanic margins. To satisfy concerns that some magnetic anomalies may be due to sea-floor spreading, an alternative model with a narrower transition was constructed which matched the data equally well. In order to reconstruct the pre-extension position of Yucatan the stretched continental crust and transitional zone (restored back to 32 km thickness) across the northern margin, 15° of rotation about a pole south of Florida and 9° further rotation for southern Gulf of Mexico is required. Results from previous studies suggest that the Yucatan Block underwent an additional 20° of rotation due to sea-floor spreading along the restoration arc (total amount of 44° counterclockwise rotation). The results of this thesis supports some previous studies that concluded: (1) the nature of the margin can be classified as being volcanic passive margin and (2) plate reconstructions require counterclockwise rotation for the opening of Gulf of Mexico.