SEAFLOOR SPREADING IN THE EASTERN GULF OF MEXICO: NEW EVIDENCE OF MARINE MAGNETIC ANOMALIES

The timing and history of opening of the Gulf of Mexico has been complicated by a lack of seafloor spreading magnetic anomalies in the basin. The lack of clear magnetic anomalies associated with seafloor spreading has previously been attributed to opening during a period of Earth history lacking magnetic pole reversals (the Late Cretaceous), the near-equatorial position of the Gulf at the time of opening (a location of low magnetic field strength), and most recently, the suggestion that the Gulf is underlain not by typical mafic oceanic crust but is instead underlain by ultramafic mantle material exhumed along a low angle fault during opening of the Gulf.

Re-examination of seagoing magnetic surveys, drawing not on the gridded magnetic data but instead on the original shipborne records, identifies a pattern of symmetric magnetic anomalies that can be correlated with the geomagnetic time scale using previously proposed opening histories for the Gulf of Mexico basin. The models are consistent with NE-SW directed seafloor spreading off the west coast of Florida beginning 160 Ma and ending 140 Ma. The inferred direction of opening is consistent with a counter-clockwise rotation of Yucatan away from Laurentia, as has been previously proposed. The magnetic models, to date, do not distinguish between a mafic oceanic crust or ultramafic mantle exhumed during rifting as the source of the anomalies.