What caused rifting in the Gulf of Mexico and why it matters: Stratigraphic and thermal implications

Abstract

This study explores the challenges that confront proposals to explain the rift opening of the Gulf of Mexico and the implications of different solutions. In recent years, evidence has increased to support the view that latest stage rifting in the Gulf of Mexico accommodated counter-clockwise relative rotations of the Yucatan Block away from southern North America (Sandwell et al., 2014). Counter-clockwise kinematics present a challenge to explain because, in the context of global plate motions, they appear to be inconsistent with most (all?) models previously proposed to explain the geodynamic formation of the Gulf of Mexico. Previous literature contains at least the following ideas to explain the rift opening of the Gulf of Mexico during the Mesozoic: I. the Gulf of Mexico as a central Atlantic rift that ceased following a late Jurassic ridge jump into the proto-Caribbean seaway (Keller and Cebull, 1973) — the cause of rifting is thus indirectly implied to be the cause of central Atlantic rifting generally, II. the Gulf of Mexico as a back-arc basin related to east-dipping subduction under the western margin of paleo-Mexico (Stern and Dickinson, 2010) — the cause of rifting is thus implied to be tensional stress caused by subduction trench rollback, or some other unidentified mechanism, arising due to subduction along western Mexico, III. the Gulf of Mexico as a local response to a vertical forcing — the cause of rifting is thus implied to be a mantle plume impinging on the overlying lithosphere from below (Burke and Dewey, 1973), or perhaps, the Gulf is an impact crater produced from a large collision of an extraterrestrial body with Earth (Stanton, 2002), and IV. the Gulf of Mexico formed because the Yucatan Block remained coupled only at its southeastern corner to northern South America during the breakup of Pangaea— the cause of rifting is thus implied to be the motion of South America away from North America while South America’s coupling to the Yucatan Block was only retained temporarily at its southeast corner (Carey, 1958). The central Atlantic ridge jump hypothesis does not explain the counter-clockwise phase of Gulf of Mexico opening because central Atlantic opening between North America and South America had distinct kinematics. The back-arc basin model does not explain why the Gulf of Mexico opened perpendicular to the Pacific margin in a location distal from a trench which experienced little (no?) rollback relative to its upper plate. The back-arc basin and vertical forcing hypotheses require an independent basin-localized process to have acted independently from, but in concert with, whatever process governed central Atlantic rifting — critically, without imposing any change on central Atlantic rifting itself. This requires a high degree of coincidence between two distinct causal processes and, while possible, may not be plausible. Finally, while the South America-Yucatan partial coupling hypothesis can explain the counter-clockwise opening of the Gulf of Mexico, the hypothesis was proposed in the context of the expanding earth theory. Partial coupling at the southeast end of the Yucatan Block does not work to explain Gulf of Mexico opening if South America remained relatively stationary in a mantle reference frame as has been generally deduced in subsequent studies. Counter-clockwise Gulf of Mexico opening that was distinct from central Atlantic opening is difficult to explain in any of the above models given modern plate motion constraints. The evolution of the literature on Gulf of Mexico opening can be evaluated as a connected entity. From this perspective, one observation that stands out is that when the central Atlantic ridge jump hypothesis was lowered in potential significance on the strength of inconsistent kinematics — the idea that the timing of Gulf of Mexico opening was nonetheless synchronous with central Atlantic rifting appears to have been retained. If the assumption of synchronous timing is relaxed, an additional category of model can be proposed for the opening of the Gulf of Mexico. Subduction in the Caribbean region to the south of the Yucatan Block could have taken place after initial formation of the proto-Caribbean region, but prior to the start of counter-clockwise rifting in the Gulf of Mexico. Subduction in the proto-Caribbean domain could have caused, or at least balanced, counter-clockwise opening of the Gulf of Mexico. Such a model would be simple and plate tectonic and warrants further testing. The timing of Gulf of Mexico formation in relation to Caribbean-localized subduction could impact all models of paleo-climate, paleo-ocean circulation, sedimentation, as well as thermal and petroleum systems evolution. This study revisits the evidence for the timing of Gulf of Mexico formation and the potential evidence for or against the idea of linking Gulf of Mexico opening to subduction in the ancient Caribbean domain. Tentative, main conclusions are that: (1) evidence in support of a central Atlantic-synchronous age for Gulf of Mexico opening may only be robust for early phases of rifting; the same evidence may not apply as constraints for younger phases of rifting where counter-clockwise kinematics appear most likely, and (2) whereas conventional models subduct most (all?) proto-Caribbean lithosphere from the late Cretaceous onward and thus plausibly remove all record of hypothetical prior subduction zones, the modern record may retain some important observables that support a tectonic connection between the Gulf of Mexico and the proto-Caribbean region during their mutual formation. In the first sixty years of literature on plate tectonics, most studies of Pangaea breakup appear to have overlooked the fact that central Atlantic opening was balanced by shortening across Tethyan subduction zones (Keppie, 2015). Mistaken senses that Atlantic and Tethyan rifting were extensions of one another or that shortening across Pacific subduction zones balanced Mesozoic rifting in the central Atlantic have been and continue to be widespread. In similar fashion, I suggest here that in the first seventy years of literature on plate tectonics, most studies of Middle America during the Mesozoic appear to have overlooked the possibility that counter-clockwise opening in the Gulf of Mexico may have been balanced by, and causally related to, shortening across Caribbean-located subduction zones.

AAPG Datapages/Search and Discovery Article #90330©2018 AAPG Hedberg: Geology of Middle America – the Gulf of Mexico, Yucatan, Caribbean, Grenada and Tobago Basins and Their Margins “Integration of the geology of the area from the southern onshore of North America to the northern onshore of South America”, Siguenza, Guadalajara, Spain, July 2-5, 2018