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The Nature of the Crust Beneath the Deep Gulf of Mexico and Development of the Syn-Rift and Early Post-Rift Gulf Basin Dennis L. Harry, Geosciences, Colorado State University, Colorado State University, Department of Geosciences, Fort Collins, CO 80523-1482 Ordovician Mesozoic opening of the Gulf of Mexico was strongly influenced by pre-existing tectonic structures associated with assembly of Pangea during the Paleozoic Era. The figure at right illustrates the key sequence of events. From top to bottom, formation of the Wiggins volcanic arc by south-directed subduction; collision of the Wiggins arc with North America, forming the Ouachita suture with a transition to north-directed subduction further south; final suturing of Gondwana with Laurentia, creating an orogen underlain by shallow mantle; Triassic rifting south of the Ouachita orogen. Key findings to date are derived from finite element modeling and are schematically illustrated in the figure: The interaction of inherited crust and mantle weaknesses exerted a primary control on the locus of extension and shifts in depocenters in the rift. The shallow mantle beneath the Ouachita orogen served as a strong zone, forcing extension to occur in regions further southward. Early extension of the Wiggins terrain formed the Interior Salt Basin, but the suture between South America and the Wiggins arc proved weaker in the long run, causing extension to shift further south to form the modern Gulf of Mexico. The model predicts very little rift-related magmatism, consistent with observations on the Gulf continental margins. By comparison with International Ocean Drilling Program results on the non-volcanic Iberia margin, the model raises the question of whether the deep water central Gulf region might not be underlain by oceanic crust, and may instead potentially contain syn-rift hydrocarbon source rocks. North America Ouachita Trough Wiggins Arc South America Mississippi (early Ouachita orogeny) Ouachita Suture Pennsylvanian (late Ouachita orogeny) Black Warrior Basin Alleghanian Suture Triassic (rifting) Ouachita Orogen Salt Basin Wiggins Gulf of Arch Mexico South America