Crustal structure of an extinct, late Jurassic-to-earliest Cretaceous spreading center and its adjacent oceanic crust in the eastern Gulf of Mexico

Abstract

An extinct, late Jurassic-to-earliest Cretaceous ridge-and-fracture zone geometry in the western Gulf of Mexico (GOM), and extinct seafloor ridge segments in the eastern Gulf of Mexico (EGOM), were previously identified using the vertical gradient of satellite-derived free-air gravity data. Circular gravity anomaly lows, and magnetic anomaly highs, over the center of spreading ridge segments are interpreted as large volcanic centers that erupted within a late Jurassic-to-earliest Cretaceous, slow-spreading center. Detailed mapping of oceanic basement using oil industry seismic data indicates that the EGOM oceanic ridge system is characterized by 30-60-km-long spreading ridge segments, that include 15-km-wide, 2-km-high axial volcanoes in their centers, and nodal basins at their ends. Stratigraphic evidence from seismic reflection data tied to a deepwater well indicates that volcanism along the spreading ridge ended around the same time (Berriasian), or slightly after (Valanginian), the cessation of seafloor spreading in the EGOM. Flowlines of late Jurassic-to-earliest Cretaceous seafloor, based on a pole of rotation from the geometry of GOM spreading ridges and fracture zones, show a good match with gravity and magnetic anomalies along the Florida and Yucatan conjugate margins of the EGOM. Mapping of age-dated, stratigraphic downlaps onto the oceanic crust is consistent with an interpreted ridge jump at the beginning of seafloor spreading (Kimmeridgian) to the southwest, and in the same southwestward direction of a previously inferred mantle plume in the central GOM. Our 3-D gravity structural inversion of the Moho requires 6.4 km thick oceanic crust in the northwestern EGOM, and 5.5 km thick oceanic crust in southeastern EGOM. We interpret this along-ridge, thickness variation to reflect faster spreading and thicker oceanic crust farther from the opening pole located in the southeastern GOM.