The origin and evolution of the Mexican Cordillera as registered in modern detrital zircons

Abstract

Continents are thought to be built at convergent margins by mantle-derived mafic inputs, but the processes that transform them into more felsic and long-lasting constituents are still unclear. Here we use U-Pb geochronology, trace elements and Hf isotopic compositions of modern detrital zircons from western Mexico to illustrate how a typical mafic island-arc built on an oceanic basin can be rapidly transformed into a mature intermediate to felsic continent by the combined effects of subduction erosion and rear-arc sediment underthrusting, prompted by the closure of a back-arc basin. In western Mexico, the most significant mass transfer from mantle to crust occurred during the Early Cretaceous in the context of an intra-oceanic island arc, locally dubbed Alisitos-Guerrero. Subsequently, the process of “continentalization” was achieved by the deep reprocessing of the newly formed lithologies once they were dynamically incorporated into the melting source during the development of the Mexican Orogen. The Mexican continental crust did not only grow by arc-related inputs, however, as there was at least one magmatic episode in the Jurassic where extensional-driven mantle upwellings triggered melting of upper-crustal sediments. In this view, mafic island arcs and back-arc basins are ephemeral geologic features that can be easily consumed into trenches, but the geochemical evidence of their existence, and possibly even a significant portion of their mass, can be preserved in younger and more felsic continental igneous rocks.