Geochemical and petrological insights into the tectonic origin of the Transmexican Volcanic Belt

The Transmexican Volcanic Belt (TMVB) is the magmatic expression of one of the most complex convergent margins on the planet, and as such constitutes a prime location for testing emerging hypotheses on arc magma genesis and its influence on continental crust formation. By coupling an extensive geochemical and petrological database with an improved stratigraphic and geophysical framework, in this contribution we will examine the compositional diversity of the TMVB from the perspective of changes in subduction zone geometry and crustal thickness, as well as within the context of more subtle tectonic processes such as lithospheric foundering, slab detachment, fore-arc subduction erosion, crustal relamination and diapiric exhumation. We will illustrate that the compositional variability of mafic magmas across the region is an inherited characteristic of a geochemically enriched pre-subduction background mantle wedge, which has been variably overprinted by diverse chemical fluxes released from the slab at different thermal conditions. We will argue that the volumetrically dominant intermediate magmas in Mexico - from andesite to dacite and even some rhyolite - represent primary melts from hybrid slab and mantle sources, with no perceptible compositional influences from the overlying continental crust. These interpretations depart from conventional models that invoke intra-crustal differentiation and contamination of basalt to create intermediate magmas, and therefore have important implications to understanding the genesis of global continents.