Block Kinematics and Extensional Styles during Gulf of Mexico Evolution

Gulf kinematic history is strongly constrained by Atlantic spreading parameters. Triassic closure defines positions of North/South America (NA, SA) and Yucatan, and constrains pre-Mesozoic central Mexico (represented by Tuxpan) and South Florida/Bahamas (SFB). Yucatan lay between Texas and Venezuela, rotated >32°CW. Tuxpan restores NW along South Burgos transform to avoid Colombia. SFB restores NW into the SE Gulf along trans-Florida transform to avoid Demerara-Guinea. Gulf evolution comprised 2 distinct kinematic stages, each with two sub-stages, during Jurassic inter-American divergence. Stage 1 involved mainly Early Jurassic intra-continental stretching of all margins (1a) followed by Middle Jurassic NW-SE relative motion of Yucatan, SFB, Tuxpan (1b). SFB and Tuxpan probably reached present positions by end Stage 1, when a single salt basin covered the NA and Yucatan margins. In Stage 2, spreading about a migrating pole in Florida Straits carried Yucatan/Campeche salt to their present position; Eastern Mexico is a post-salt Stage 2 transform margin. Stage 1a rifting was of largely low angle, asymmetric detachment character (NA=footwall), continuing between Yucatan and NA during Stage 1b while Tuxpan and SFB moved by transform motion. NA and Yucatan flanks of central Gulf oceanic crust are marked by a 1-2sec gradual structural step-up (over tens of km) from top rifted continent to top ocean crust that mimics the edge of mother salt. A favoured model suggests that oceanic plate accretion began at/landward of the base of the step-ups beneath 5-6km of continuing salt deposition, and that, when salt deposition stopped, the isostatically-controlled accretion depth rose basinward as salt collapsed and thinned under gravity. Where salt reached zero thickness, ocean crust spread normally at 2.6 km paleo-depth. A contrasting model of two salt basins separated by an Icelandic oceanic high is refuted by backstripping, which clearly shows the oceanic crust was emplaced at 2.5-3 km paleodepth.