AmericanChemicalSociety.com

A finite element model simulating extension on the North American Gulf of Mexico continental margin demonstrates that the fundamental controls on the style of rifting were inherited from preexisting tectonic events. The southern North American continental margin underwent formation of a rift/transform margin during the Late Precambrian, which was followed by accretion of a volcanic arc terrane during the Late Paleozoic Ouachita orogeny. Mesozoic extension was distributed in regions south of the Ouachita orogeny, initially in a very broad region encompassing the accreted arc terrane, and later by more focused rifting further south that ultimately led to seafloor spreading adjacent to the modern continental rise.  The finite element models show that the structure of the North American central Gulf of Mexico continental margin results from inheritance of pre-existing tectonic features created during Paleozoic assembly of Pangea.  The models confirm that the Ouachita orogen behaved as a strong zone during Mesozoic extension, rather than as a zone of weakness as is typically inferred in Wilson cycle models of continental rifting.  The strength of the Ouachita orogen is responsible for the abrupt northward termination of extensional deformation on the southern flank of the orogenic belt, broadly distributed extension in throughout the coastal plain, shelf, and rise between Late Triassic and Callovian time, and the rapid deepening of the distal shelf and rise and onset of seafloor spreading in late Callovian or early Oxfordian time. The results are in marked contrast to similar dynamic models of rifting on the U.S. Atlantic margin (e.g., Harry and Sawyer, 1992) that depict orogens as zones of weakness due to the presence of a thick crustal root beneath the interior of the orogen.  In contrast, the Ouachita orogen is underlain by a relatively undeformed subduction system that results in a shallow mantle and strong lithosphere. Behavior of the rift system is robust over a range of assumptions regarding the strength of the lithosphere, variations in crustal thickness, and thermal regimes, demonstrating that tectonic structures inherited from Precambrian rifting and the Paleozoic Ouachita orogeny are the dominant controls on the style of rifting on the North American Gulf of Mexico continental margin.