A PROPOGATING RIFT MODEL FOR SEAFLOOR SPREADING IN THE GULF OF MEXICO BETWEEN 169-150 MA

Marine magnetic anomalies and satellite gravity data reveal an arcuate concave-south fossil spreading system that accommodated counterclockwise rotation of Yucatan away from North America during Jurassic opening of the Gulf of Mexico. Three sets of lineated positive magnetic anomalies are identified in the central and eastern Gulf, the southernmost of which lies astride a strong satellite Vertical Gravity Gradient interpreted to mark the location of the fossil spreading ridge. The magnetic lineations are interpreted to be isochrons formed by magmatic accretion of new oceanic crust. Synthetic magnetic models show that the magnetic lineations can be correlated with magnetic anomalies M22n (150 Ma), which lies astride the fossil ridge, M33n (161 Ma), which lies between the ridge and the Florida shelf, and M39n (165 Ma), which lies adjacent to the shelf edge in the eastern Gulf. Great circles passing through these isochrons define a North America-Yucatan rotation pole located at 21°N, 78°W. 20° clockwise rotation of Yucatan about this pole places the northeast Yucatan shelf edge tightly against the southwestern Florida shelf edge. The magnetic lineations and paleomagnetic data indicate that an additional ~25° clockwise rotation of Yucatan occurred during opening of the Gulf. This additional rotation places the northern Yucatan shelf against the northwestern Florida shelf. A final ~375 km of northwesterly translation places the northwestern Yucatan shelf adjacent to the basement hinge line beneath the central North American Gulf coastal plain, which is taken to be the pre-rift position of Yucatan. The kinematic and magnetic anomaly age models indicate seafloor spreading initiated in the western Gulf prior to M39n time (165 Ma) and after syn-rift extensional translation had moved Yucatan into a position near the northwestern Florida shelf. Seafloor spreading propagated into the eastern Gulf by anomaly M39n time, and ended synchronously at anomaly M22n time (~150 Ma).