AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Geologic and Geophysical Constraints on Crustal Type and Tectonic Evolution of the Gulf of Mexico
(1) Basin Scanning and Evaluation, Shell Projects and Technology International, Houston, TX.
(2) Gulf of Mexico Regional Team, Shell United Americas Exploration, Houston, TX.
Although one of the most extensively surveyed areas on earth, there remains extensive debate on the origin, nature and evolution of the crust in the deep Gulf of Mexico (GoM). Key reasons include a lack of basement penetration by drilling, and inadequate deep imaging data from refraction, magneto-tellurics, and other geophysical techniques.
The interpretation of potential field data is complicated but can provide important constraints on deep crustal structure. The geometry and the nature of the Mohorovicic Discontinuity (Moho) can be constrained using an integrated and iterative approach that considers lithospheric flexure and isostasy, melt generation as a function of crustal thinning, and dynamic topography while honoring the gravity and the refraction data. A newly developed iterative backstripping work flow was used to generate a crustal thinning factor map that defines Moho geometry and crustal type. Applying a technique to the crustal thinning factor map that restores the volume of the stretched continental crust to its pre-rift configuration produces a map of the pre - rift configuration of the GoM. Using this map and a plate tectonic model tool, we unravel the kinematics of the opening of the GoM and define domains with fundamentally different salt - basement relationships with significant implications for paleogeographic interpretation of the salt and the overlying Jurassic sediment.
The results of this technique supports a two stage opening of the Gulf: an initial Late Triassic rifting along pre-existing NW-SE trending transfer faults followed by the onset of the drift phase with creation of oceanic crust in the Mid - Late Callovian (159 - 160 Ma) as the Yucatan plate underwent counter clock-wise rotation along the East Mexican Transform margin. There is greater uncertainty regarding the end of spreading; earliest estimates range from the Tithonian (144 Ma) to no later than the Valanginian (134 Ma). This implies that the extent of Jurassic oceanic crust is more limited than most previous models. The slow spreading rates and the new integrated modeling suggest that some of what was assumed to be oceanic crust may possibly be exhumed mantle or hyperextended continental crust in some areas of the Eastern GoM.