CIUDAD VICTORIA BLOCK: PRACAMBRIAN AND PALEOZOIC PERI-GONDWANAN CRUSTAL ASSEMBLAGE FROM NE MEXICO

The Mesozoic stratigraphic sequence of the Laramidic Sierra Madre Oriental (SMO) located near Ciudad Victoria (state of Tamaulipas) rests over an intricate Precambrian and Paleozoic metamorphic, igneous, and sedimentary basement. This basement is made up of four contrasting and well-described lithodemic units: (a) Proterozoic Novillo Complex, (b) Ordovician Peregrina Tonalite, (c) Carboniferous Granjeno Complex, and (d) Devonian to Permian Tamatán Group. These make up an assemblage, later covered by Triassic-Jurassic red beds deposited during the opening of the Gulf of Mexico. These units were previously considered as "exotic" blocks or terranes, due to the lack of coherent geological models in time and space.

There are several regional crustal blocks scattered in Mexico, developed on the northwester margin of Gondwana near the collision zone with Laurencia, during the closure of the Rheic Ocean and the Pangea amalgamation. Through the dismemberment of this supercontinent and along with the south-wards migration of the Maya Block and the opening of the Gulf of Mexico during the Jurassic, these blocks were dismembered and drifted forming a discontinuous belt, later buried by Mesozoic and Cenozoic sedimentary and volcanic rocks.

This would imply that the basement, Mexico´s geological backbone, is highly segmented and that it is necessary to review the distribution of the vestiges of the Ouachita-Marathon-Sonora orogen. This since evidence of the late Paleozoic collision has been described in localities now situated in southern Mexico. Additionally, it is proposed to abandon the “Sierra Madre Terrane” concept for the SMO basement and instead use that of the “Ciudad Victoria Block”, to include all its different units.