Crustal structure and along-strike variations in the Gulf of Mexico conjugate margins: From early rifting to oceanic spreading

<p>The&#160;Gulf of Mexico&#160;opened as a Late Triassic-Mid Jurassic continental rift that was first largely covered by the Mid-Jurassic Louann Salt and later split apart by a triangular-shaped&#160;oceanic crust. Salt in the Gulf of Mexico largely hampers the imaging and interpretation of underlying pre-salt and crustal geometries, which are fundamental for assessing the early kinematic evolution of the margin. To better define these deep geometries and their lateral variations, we built three seismic-based crustal-scale cross-sections across the Florida-Yucatan conjugate margins, in the areas where the Mid-Jurassic salt unit is thinner.</p><p>Seismic-based cross-sections image the architecture of rifting and the geometries of the continental and oceanic crusts and the transition between them (ocean-continent transition, OCT). They show a meaningful along-strike variation: the South Florida-East Yucatan area is characterized by a narrower rifted&#160;continental crust&#160;that evolves sharply to oceanic crust whereas in the North Florida and central-western Yucatan areas, the rifted continental crust is wider and the transition to the oceanic crust corresponds to a narrow magmatic or exhumed mantle domain. In the rifted continental crust, seismic profiles image doubly-verging basement faults organized into decoupled and coupled rift domains. The geometrical and cross-cutting relationships between these basement faults, the Louann Salt and the underlying pre-salt sequence indicates a progressive migration of rifting from proximal to distal domains and from the central and north-eastern to the south-eastern Gulf of Mexico. &#160;</p><p>Bulk continental crust extension was determined using the area balancing method. Estimated horizontal extension values vary from a minimum of &#8764;120 km in the South Florida-East Yucatan conjugate to a minimum of &#8764;240 km in the North Florida-Central Yucatan conjugate, being systematically larger in the northern margin. Crustal domains identified in the cross-sections were laterally correlated and westwards extended considering gravity and magnetic anomalies data to build a regional-scale, crustal domains map of the Gulf of Mexico. This map, together with the crustal extension estimates, has been used as the reference to carry out a plate-scale reconstruction of the Gulf of Mexico from the early rifting stages to the end of oceanic spreading.</p><p>Based on our observations and considering previous models, we propose that the study area evolved from an early rift involving&#160;magmatism, to a magma-poor margin, with continental break-up (OCT formation) being characterized by mantle exhumation and associated magmatism along the North Florida and central-western Yucatan areas.</p>