IS THE MEXICAN SIERRA MADRE ORIENTAL FOLD AND THRUST BELT REALLY A LARAMIDE OROGENIC BELT?
Considering as acceptable the tectonic definitions of Revolution (Billings, 1955) and Orogeny (Glossary of Geology, 1960), by its Structural Style, Timing and Stratigraphy it is not possible to qualify properly as Laramide the Mexican Sierra Madre Oriental and related deformations from Western to Southern Mexico, since 100 to 40 M.y. In fact, after the initial Late Triassic Atlantic Ocean origin, a Late Liassic hot spot appeared at the central region of the present Gulf and a triple junction system was at its origin. Its Middle Jurassic expansion formed the Texas Louisiana and Western México subplates; the Late Paleozoic batholiths, intruded during Appalachian-Ouachita Orogeny, were fragmented and distributed around the Gulf. They became, in the Mexican rim, the most resistant lithospheric pieces which controlled the Jurassic oil basins origin and their stratigraphic sequences and later the Sierra Madre Oriental Orogeny, erroneously considered as a part of the Laramide Orogeny, because compression originated at the southwestern region. As the deformation style is different for each of the 6 segments pertaining to each Mexican tectonic blocks and as it became younger southeastward, it suggests, since Late Albian to Late Eocene, an origin related to the Chortis Block transpressive displacement along these blocks. The collision of the East Pacific Rise and the North American Plate, is at the origin of the triple junction bordering the Jalisco Block and the widening of its Tepic, Colima and the Transmexican Volcanic Belt arms, the final factor of deformation and thrusting of the Sierra Madre Oriental, the Sierra Madre Occidental and the Gulf of California evolution.