BASEMENT ARCHITECTURE AND TECTONIC EVOLUTION OF THE EASTERN GULF OF MEXICO

In the Gulf of Mexico (GoM), current kinematic analyses, basement maps and paleogeographic reconstructions are a source of ongoing scientific debate. Issues such as the initial geometry of the basement rocks, the style of initial breakup and rifting, and how spreading occurred are contentious subjects. These issues are particularly unclear in the Eastern GoM where a drilling moratorium has been in place since 1988. Therefore, the evolution of the Eastern GoM is primarily based on inferred deep basement faults. Most of these near-vertical normal and transfer faults cannot be resolved using industry seismic data.

Along the Florida shelf edge, alternating basement highs and lows are apparent when the top of the basement is contoured. Models that explain these highs and lows and their relationship to the opening of the Eastern GoM include: (1) extensional oblique-shear led to the development of horst and graben structures bounded by two NW-SE trending, regionally extensive transfer faults; (2) the thinning or subsidence of regions of less competent Paleozoic rock bordering relatively unaffected crystalline basement blocks during a period of early extension; and (3) relatively unaltered structural paleohighs that predate the breakup of Pangea. This study proposes a new model to explain the trend of structural highs and lows by postulating a NW-SE extensional stress regime during the opening of the GoM, allowing for the development of a series of horst and graben structures with NE-SW trending normal faults. These faults may have aligned themselves along older structural weakness parallel to the trend of the Appalachian front (NE-SW) and other suture zones developed during the formation of Pangea or Rodinia. In this new model, the major NW-SE trending transfer faults proposed in model 1 are of minor structural importance and do not control the lateral extent of the horst and graben structures.

By analyzing a combination of gravity data, magnetic anomalies, and recent high resolution two-dimensional seismic lines across and along strike of the basement highs and lows, it may be possible to resolve the orientation of the deep basement structures. This is essential in deciphering the tectonic history of the Eastern GoM, as well as the origin and development of the entire GoM.