Geochronological and geochemical evidence of continental crust ‘relamination’ in the origin of intermediate arc magmas

Abstract

The origin, evolution and long-term preservation of andesitic continents within the context of destructive plate boundaries are still enigmatic for geoscientists. Here we use UPb zircon geochronology and whole-rock geochemical data of arc and forearc lithologies from the Mexican convergent margin to show that subducted trench sediments and eroded forearc debris are being tectonically transported and magmatically reworked into a typical intermediate continental volcanic arc edifice: Malinche volcano. We find that the remarkable variety of inherited zircons carried by the Malinche magmas — with ages ranging from the Early Miocene (~16 Ma) to the Paleoproterozoic (~1.8 Ga) — have not been acquired during ascent through the upper plate crust but incorporated into a subduction mélange constituted by a heterogeneous mixture of tectonically eroded forearc debris, sediments, hydrous mantle and altered ocean floor basalts. We suggest that partial melting of subduction mélanges can form intermediate volcanoes like Malinche without the intervention of parental basalts. These findings imply a fast and efficient connectivity between subduction inputs and magmatic outputs and indicate that a significant proportion of the subducted continental crust is being reincorporated back into continents by primitive intermediate arc magmatism.