2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 1
Presentation Time: 8:10 AM

Block Kinematics and Extensional Styles during Gulf of Mexico Evolution


PINDELL, James, Tectonic Analysis Ltd, Chestnut House, Burton Park, Duncton, West Sussex, GU28 0LH, United Kingdom, jim@tectonicanalysis.com

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.