Permo-Triassic continental arc in eastern Mexico: Tectonic implications for reconstructions of southern North America

A series of granitoids yielding Permo-Triassic ages (287-232 Ma) extend northwest-southeast along the entire length of Mexico and across various terrane boundaries. The intrusives range from diorites to granodiorites and their major and trace element geochemistry is typical of magmas produced in magmatic arcs. Initial eNd values of the granitoids vary from -4.4 to +2.5, indicating that they were emplaced through evolved continental crust. The Permo-Triassic granitoids constrain the time of amalgamation of the older eastward terranes of Mexico to pre-Permian times, and support interpretations that terranes to the west are a collage of juvenile Triassic or Cretaceous arcs. Paleogeographic reconstructions of the previously unrecognized Permo-Triassic arc in Mexico suggest that the subduction was east-dipping along the western margin of Pangea. This Permo-Triassic arc marks a change in the tectonics of Mexico from domination by circum-Atlantic collisions to accretionary tectonics of circum-Pacific terranes.