TECTONIC EVOLUTION OF MEXICO: A TECTONOSTRATIGRAPHIC UPDATE

Previous tectonic models proposed that most of Mexico was formed by collision of allochthonous terranes. New data indicate allochthony during the Proterozoic-Paleozoic, but lateral translation, rifting, and collision of marginal autochthonous terranes in the Mesozoic. Eastern and northwestern Mexico are formed by Proterozoic basement, but only a small portion of it is autochthonous to the North America craton. The rest of the Proterozoic basement terranes were displaced from their original position, they are: Caborca Terrane, interpreted as a part of the continental margin of North America, and Oaxaquia Block of Gondwanan origin, accreted to North America by the Carboniferous. Paleozoic terranes are: Cortes (related to Caborca Terrane) that is part of the North American continental margin, the Parral Terrane of unknown origin, and the Maya Terrane formed in its northern part by Paleozoic metamorphic rocks associated with the formation of Pangea. Southern Paleozoic geologic entities are the Mixteca Terrane (part of the Appalachian orogen), Juchatengo (Late? Paleozoic possible Pacific origin), and the Chiapas Massif (Permo-Trissic in age, unknown origin). Accretion of these terranes occurred before the Mesozoic. The largest of all the terranes is the Guerrero Composite, characterized by large volumes of Mesozoic mostly submarine arc volcanism. Basement has been identified only in two of the five terranes of the Guerrero Composite; they are fragments of the Paleozoic accreted eugeoclinal rocks of North America (Tahue Terrane) and Triassic-Jurassic accretionary complexes (Zihuatanejo terrane). Basement of the Teloloapan Terrane is unknown, and the Arcelia and Guanajuato terranes apparently lack of old basement and were formed by Cretaceous oceanic arc-back arc assemblages. Tectonic evolution of the western paleo-Pacific margin after the assembling of Pangea was characterized by: 1) a Permo-Triassic continental arc; 2) Late Triassic passive or rifting margin; 3) Early Jurassic accretion of older terranes of the Guerrero Composite; 4) Late Jurassic intra arc rifting and drifting of previously accreted Tahue and Zihuatanejo Terranes; 5) development of a series of marginal arc/back-arc systems during the Cretaceous. Final amalgamation of all the terranes occurred during Late Cretaceous time.