New Insights about How Mesozoic Rifting Formed the Texas Continent-Ocean Boundary

The Gulf of Mexico began to develop in early Mesozoic times, when westernmost Pangea ruptured along the trend of the Late Paleozoic Ouachita Orogen. Late Triassic rifting was associated with a significant domal and/or rift-flank uplift precursory to the development of a volcanic rifted margin (VRM), similar to the Vøring margin of Norway. Detrital zircon chronology from Triassic sandstones across the SW USA indicate that a flood (>600,000 km2) of Chinle/Dockum clastic sediments flowed WNW from central Texas during the late Triassic (Carnian-Norian, 225-204 Ma) and equivalent sediments poured SW into Mexico. Chinle/Dockum sediment source was likely Texas-Oklahoma crust, dominated by Late Mesoproterozoic and Ouachita facies zircons. Drainage integration revealed by detrital zircon ages changed rapidly; we infer that up to 2km relief existed on the uplift. A magnetic high along the Texas-Louisiana coast indicates a deeply buried VRM. This magnetic high disappears in coastal Mexico, which evolved as a sheared margin (Tehuantepec Transform). Uplift combined with the evidence for a VRM indicates a mantle plume/thermal anomaly during early Gulf development. Evolution of the Texas passive margin was protracted, beginning with uplift ~225 Ma ago and continuing until true seafloor spreading began ~170 Ma ago. Reactivation of the Texas craton-transitional crust boundary coincides with 85 Ma alkaline volcanic rocks of the Balcones Igneous Province (BIP), which represent low degree melts of the uppermost asthenosphere. More alkaline lavas erupted through transitional lithosphere during the Late Cretaceous but are now deeply buried. The westward extension of BIP indicates that transitional crust underlies the Rio Grande Embayment. This Embayment marks the mouth of the Mexican Borderland aulacogen, a Jurassic-Cretaceous trough that extends 1500 km NW from the Gulf to California. The junction of these tectonic elements defines a RRF triple junction that is key for understanding Gulf of Mexico evolution.