LITHOSPHERIC DEFORMATION: INSIGHTS FROM SEISMIC IMAGING OF THE GULF OF MEXICO CONTINENTAL MARGINS

Cross-correlation of ambient noise records from the seismic stations in the US, Mexico and Cuba were used to measure Rayleigh wave phase velocity dispersion data. From this, we developed a 3D shear-wave velocity model for the greater Gulf of Mexico region that captures variations in the crustal and lithospheric structures across the continental margins of the US Gulf Coast and Yucatan, Mexico. Our model shows a zone of reduced velocity in the mantle lithosphere underlying the extended continental margin of the northwestern Gulf of Mexico. We attributed this velocity reduction to extensional deformation and melt-induced weakening of the lithosphere during the Triassic rifting that formed the Gulf of Mexico. Melt extraction might have been hindered by the greater lithospheric thickness in the western region along the US Gulf Coast margin that resulted in the progressive increase of rift-related volcanism reported from previous studies. This is also consistent with the observed thinner effective elastic thickness of the lithosphere in the northwestern Gulf of Mexico margin. The clear asymmetry between the US Gulf Coast and its conjugate Yucatan margin suggests extension along a shear zone that focused more deformation to the North American plate prior to breakup. Estimated depths to the lithosphere-asthenosphere (LAB) show the base of the Gulf of Mexico oceanic lithosphere to be 85 km. Un-extended regions north of the Ouachita-Appalachian (O-A) fold belt display the deepest LAB greater than 100 km within our study area. The LAB depth under extended terrains surrounding the GOM ocean ranges from 90-95 km. The difference in the LAB suggests that the oceanic and extended continental lithosphere might have thickened through different mechanisms e.g conductive cooling vs. melt depletion of the asthenosphere. We also incorporated our velocity model into a deformable crustal reconstruction to examine the extensional direction during the Triassic-Jurassic rifting period.