RIFT TO DRIFT HISTORY OF THE GULF OF MEXICO – THE CASE OF THE MISSING FAULTS

New plate reconstructions are used to outline motions of the major plates during Jurassic rifting and the transition to ocean crust formation in the Gulf of Mexico (GOM). These plate motions resulted in large amounts of crustal thinning and extension before relative plate motions were accommodated by sea floor spreading. Yucatan moved over 300 km relative to North America during rifting. In classic rift models, this motion should have resulted in formation of large rift basins and extreme crustal thinning, yet basement-involved extensional faulting is rarely seen on GOM seismic data. In the onshore basins in particular, seismic data shows an almost conformable section from the surface down to the deepest visible horizons in the Permian. It is likely that extension started earlier than the commonly-invoked middle Jurassic and that it involved large-magnitude low-angle faults that may have resulted in mantle exhumation. Little is known about present-day crustal structure beneath the thick sediment wedge in the northern offshore 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.