The geodynamics of the Gulf of Mexico and its topographic evolution

Wednesday, 17 December 2014
Daniel J Bower, California Institute of Technology, Pasadena, CA, United States and Michael Gurnis, Caltech, Pasadena, CA, United States
The Gulf of Mexico formed by subsidence due to continental extension and seafloor spreading that accommodated the motion of the Yucatan block during the Late Jurassic-Early Cretaceous. The Yucatan block rotated approximately 45° counterclockwise about an Euler Pole located offshore Florida. It has been proposed that mainly thermal cooling and sediment loading drove subsequent subsidence of the Gulf. However, back-stripping analysis reveals rapid tectonic subsidence (2.5 km) starting around 66 Ma and ending at 40 Ma that remains unexplained. We test the hypothesis that the rapid subsidence can be explained by dynamic topography associated with the Laramide Orogeny.

We develop new kinematic theory to build deforming plate models using a continental stretching factor (or crustal thickness) map and the paleogeographic software GPlates. ``Deforming tectonic blocks’’ are defined along small circles about the opening Euler Pole using neighboring stretching-factor contours. These deforming blocks are palinspastically reconstructed assuming constant true strain which means that deformation occurs more rapidly as the crust is increasingly thinned. The deforming plate model is incorporated in a global plate history model.

We use the combined plate history model to constrain the thermal evolution of the lithosphere and slabs in the upper mantle and plate motions in geodynamic models. This ensures that our geodynamic models are consistent with geological and geophysical observations and thus enables us to investigate the spatial and temporal evolution of subsidence in the Gulf. We compare dynamic and total topography from the models with tectonic subsidence maps and subsidence curves. In addition, we predict mantle structure, notably the distribution of slabs, to compare with seismic tomography and waveform observations.