SOUTHWESTERN NORTHAMERICAN IMPLICATIONS OF THE TRIPLE JUNCTION MODEL FOR THE GULF OF MEXICO

During Late Triassic at least three blocks existed at the present Gulf of Mexico region: Tlaxiaco, Huayacocotla and Huizachal-Peregrina.

During Late Liassic, Tlaxiaco and Huayacocotla blocks moved southwestward just before the RRR triple junction originated, formed by the SE-NW Texas-Boquillas-Sabinas, the SW-NE Campeche Escarpement and the N-S Nautla-Pico de Orizaba arms, bordering the Texas-Louisiana, Western Region of Mexico, and Chiapas-Yucatán subplates. As this one remained joined to South American Plate up to Early Cretaceous time, only Texas-Louisiana and Western Region of Mexico subplates were displaced northwestward. So,the original RRR triple junction formed two land masses with a predominantly ridge boundary, and a failed arm of a ridge forming a trough. Texas-Louisiana subplate displacement was possible because it was bordered by the Texas-Boquillas-Sabinas and Vancouver-Bahamas megashears, and because the Farallon subduction zone existed in the Pacific border of North-America. This fact displaced northwestward the Ouachita System 800 km, and produced the western orogenic zone during Jurassic-Eocene time, which deformed the Western Mesozoic Geosyncline (Sevier, 130-80 M.y., and Laramide, 80-50 M.y. orogenies. This motion allowed the Campeche Escarpement and Nautla-Pico de Orizaba arms became wider ridges and seafloor spreading zones, and Gulf of Mexico formed.

The Gulf triple junction expansion divided batholits, originated during Permo-Carboniferous Appalachian-Oachita Orogeny, in pieces. These fractions were distributed around the Gulf and became, in the Mexican rim, the resistant lithospheric pieces that controlled the Jurassic oil basins origin and the Sierra Madre Oriental deformation (100-40 M.y.), considered as a part of the Laramide Orogeny. As this deformation became younger southeastward, an origin related to the Chortis Block displacement is possible, before the collision between East Pacific Rise and Northamerica, during Oligocene; this is the beginning of the Transmexican Volcanic Belt, Sierra Madre Occidental and Gulf of California evolution. Another important tectonic fact was the development of a new triple junction which is bordering the Jalisco Block by its Tepic and Colima arms. The widening of the Tepic arm is considered as the cause of deformation and thrusting of the Sierra Madre Occidental at its Monterrey- Victoria portion.