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Integration of Deep Image Seismic Reflection Surveys and A New Reflection Refraction Profile To Clarify Basin-Wide Gulf of Mexico Interpretation: Part 1, Crustal Framework


Reprocessed pre-stack depth migrated seismic data from Mexican water and a regional refraction profile (E Texas to abyssal plain) are integrated with other deep penetration seismic data and used to evaluate basement structure and type around the Gulf of Mexico in relation to models for passive margin formation. We interpret 3 stages of tectonic development: 1) Triassic-Callovian NW-SE rifting; 2) Callovian-Early Oxfordian amagmatic “outer marginal collapse”, resulting in rapid creation of accommodation space for salt deposition on pre-stretched outer continental margins, basinward tilting and slumping of salt on base-salt unconformities, establishment of abyssal depths where salt is thin/absent, possible exhumation of mantle from beneath thinned continental crust, and formation of basement step-ups to the future oceanic plateau; and 3) Late Oxfordian-Berriasian CCW rotational seafloor spreading. The SW Florida-NE Yucatan conjugate and the Tuxpan-Veracruz transcurrent margins have no salt, as they post-date salt deposition. Basinward shoulders of outer marginal troughs, or basement step-ups, define the limits of ocean crust. Merged reflection-refraction data constrain the step-up in offshore East Texas, and a planar base salt unconformity and several sub-salt rift basins occur landward. In SW Florida, lower crust pinches out and upper crust lies on mantle that likely is exhumed in the adjacent outer marginal trough; brittle faults cross this crust and enter elevated Moho. NW Florida has been considered as magmatic but is here interpreted as amagmatic, because syn-rift magmatism pre-dated our stage-2 outer marginal collapse when SDRs are normally formed. The western GoM margin is narrow due to its transform nature. Along Yucatan the outer marginal trough and basement step-up shows no magmatism during outer marginal collapse. We deduce that rapid outer marginal collapse is a distinct stage between rifting and drifting, achieved by low-angle shear of pre-stretched continental crust off rising sub-continental mantle at outer marginal detachments. The rapid creation of accommodation space leading to deep water or thick salt (or a combination) is a post-rift tectonic process, where outer margins act as hanging walls on outer marginal detachments, belts of exhumed mantle are the footwalls, and the straddling outer marginal troughs are large half grabens. This marginal architecture can be used to predict initial heat flow patterns around the GoM.