CARBONIFEROUS TO CRETACEOUS EVOLUTION OF THE PALEO-PACIFIC MARGIN OF MEXICO, STRATIGRAPHIC EVIDENCE FOR ALTERNATING STAGES OF SUBDUCTION AND RIFTING

An overview of new stratigraphic and geochronologic data indicates that a number of tectonic events occurred during Late Paleozoic to Late Mesozoic time in the western paleo-continental margin of Mexico. Although it has been suggested that the backbone of Grenville basement of eastern Mexico (Oaxaquia block) was part of Gondwana during Early Paleozoic, and collided with North America by the Permian, its Mississippian faunas of North American affinity suggest that the collision might have occurred earlier. After collision, an east-dipping subduction zone evolved in the paleo-Pacific margin of Oaxaquia from Carboniferous to Early Permian time. Apparently subduction became shallower by the Permo-Triassic, as suggested by the migration of volcanism toward the east. This arc was more felsic than the Carboniferous-Permian arc. By Late Triassic, apparently subduction ceased for a period of time, and a passive margin developed along the paleo-Pacific margin. This is evidenced by a thick successions of continent-derived sediments accumulated on the paleo-continental shelf and slope (Potosi Fan) and in a marginal oceanic basin (Arteaga Basin). Zircon provenance of these rocks shows no evidence of magmatism contemporaneous to the Potosi fan. The passive margin became active again by Late Triassic–Early Jurassic time, and sedimentary rocks of the Potosi fan, with slivers of oceanic crust, were accreted to the continental margin. If this accretion was related to the collision of an oceanic arc (Vizcaíno?) or not is still uncertain. Apparently subduction jumped westward and a continental arc developed onto the accretionary prism by Middle Jurassic time. Subduction roll-back, probably accompanied by strike slip, rifted parts of the Triassic-Jurassic accretionary prism and the Middle Jurassic arc to form the Cretaceous complex arc(s) system that characterized the Guerrero composite terrane of Western Mexico.