Tectonics of the Gulf of Mexico at the Transition from Rift to Drift: Crustal Structure of the Basin during Salt Deposition

New plate reconstructions of the Gulf of Mexico (GOM) are used to outline motions of the major plates during Jurassic rifting and the transition to ocean crust formation. These plate motions resulted in large amounts of crustal thinning and extension before relative plate motions were accommodated by sea floor spreading. We use plate motions to estimate crustal stretching factors. Yucatan moved over 300 km relative to North America during rifting. This motion must have resulted in formation of large rift basins and extreme crustal thinning, yet no basement-involved extensional faulting has ever been seen on GOM seismic data. It is likely that extension involved large-magnitude low-angle faults and may also have involved mantle exhumation. Little is known about present-day crustal structure beneath the thick sediment wedge in the northern GOM. By making some assumptions about initial crustal thickness, we use plate motions to estimate crustal stretching factors and hence crustal structure at the end of rifting. Sedimentation during the final rifting phase, before initiation of sea floor spreading, consisted of a very thick salt section. The basin in which this salt was deposited was floored by extremely thin continental crust or, if mantle exhumation did take place, salt was deposited directly on exposed continental mantle. When sea floor spreading commenced, salt deposition stopped and, as the basin continued to open, salt flowed out onto new oceanic crust forming the deep allochthonous salt beneath the present-day Sigsbee Escarpment.