Orogenic andesites and their link to the continental rock cycle

Continents are created and destroyed at convergent margins but understanding the interconnectedness of this system-a complex interplay of subaerial and tectonic erosion, volatile exchange and metamorphism, partial fusion and melt evolution-is far from complete. Here we use geochemical data from the Mexican convergent margin to reveal a strong connectivity between subducted materials and typical orogenic andesites. We find that the along-strike isotopic variations of andesitic stratovolcanoes in Mexico are mirrored by those of riverine sediments sampled along the continental margin, which presumably represent the compositions of tectonically ablated forearc crust entering the subduction zone. Isotopic modelling further indicates that the Mexican andesites represent partial melts of subduction melanges, constituted by mixtures of altered subducted ocean crust, forearc debris and mantle peridotite in similar proportions. Remarkably, the concentrations and ratios of incompatible trace elements in the volcanoes also correlate with the major element compositions of their corresponding forearc sediments. This suggests that the modal contents of key mineral phases in the partially molten melanges control the trace element abundances of the andesitic magmas. These findings demonstrate that a significant proportion of tectonically eroded subducted crust is not lost to the deep mantle, but effectively reincorporated into arc magmas in a closely interlaced continental rock cycle. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

The geochemical data from the Mexican convergent margin shows a strong connection between subducted materials and typical orogenic andesites, indicating a significant proportion of tectonically eroded subducted crust is effectively reincorporated into arc magmas. Isotopic modeling and chemical analysis of volcanic rocks and sediments reveal the mechanisms of interaction between different rocks in the process of tectonic erosion and orogenesis.