Implications of continental crust extension for plate reconstruction: An example from the Gulf of Mexico

Abstract

The prerift reconstruction of continental plates bounded by rifted margins requires the closure of relative motion accomplished both by seafloor spreading and by the extension of continental crust during the rift phase of continental breakup. Continental extension is not expected to be pervasive throughout the plate, but to be confined to a zone of up to several hundred kilometers in width. The direction of particle motion in this zone is expected to be parallel to flow lines followed by the rigid portions of the plates. The “best fit” between rifted continental margins is then described by the rotation angle about an Euler pole which best closes both the oceanic crust and the extension within the continental crust, along small circles about the Euler pole. As an example application of these concepts, the pattern of Late Mesozoic crust extension within the Gulf of Mexico basin is used to constrain the location of the Euler pole and angle of rotation of the Yucatan block with respect to North America. Both crust type and the degree of extension within the transitional crust surrounding the basin are estimated on a point‐by‐point basis from bathymetry and basement depth. The root‐mean‐square (rms) misfit in the apparent total closure of both oceanic crust and extension within the continental crust is computed for a range of possible poles of opening. A contour map of misfit versus pole location reveals a global minimum rms misfit of ±47 km for a 45° counterclockwise opening of the Gulf of Mexico basin about an Euler pole at 25°N, 79°W. An elongate trend of poles, for which the misfit is less than 100 km, extends from the Bahama Islands eastward across the Atlantic and through North Africa. The reconstruction of the Gulf of Mexico for the best fit pole places the palinspastically restored Yucatan block in contact with North America along the Texas and Louisiana shelf. The resulting restored southern margin of North America fits against the the northern margin of South America in its prerift position to within the uncertainty in the North America‐Africa‐South America plate circuit. We conclude that the prerift placement of the Yucatan block between North and South America along the Texas‐Louisiana shelf is consistent with both the pattern of extension within the Gulf of Mexico basin and seafloor spreading history of the central Atlantic basin.