Andean-type granites in a non-Andean post-collisional setting, Central System batholith, Spain

Abstract

The youngest granite suite of the Spanish Central System batholith (CSB) is classically interpreted as a post-collisional magmatic suite emplaced during the final stages of the Variscan orogeny. However, we report here for the first time the presence of discrete Andean-type plutons within the dominant post-collisional batholith. These plutons exhibit petrographic and geochemical signatures consistent with calc-alkaline series, including Ca-rich clinopyroxene and trace element trends that align with experimental cotectic arrays typical of active margin magmatism. MELTS modeling and phase-equilibrium constraints indicate that the parental magmas derived from a mantle-crust hybrid zone likely formed through localized recycling of oceanic-like mafic rocks during continental subduction. U-Pb zircon ages (312–306 Ma) confirm their temporal overlap with post-collisional granites. The low abundance of xenocrystic zircons (<5%) implies limited crustal assimilation, supporting a dominantly mantle-derived origin. We propose that back-arc basin closure and the subduction of hyperextended segments of Gondwana’s margin facilitated the transient involvement of oceanic components, generating conditions favorable for Andean-type magmatism within a nominally post-collisional context. This scenario challenges the conventional spatial and temporal dichotomy between Andean-type and post-collisional granite types and highlights the petrogenetic diversity inherent to late-orogenic magmatism. Our findings underscore the need to reassess current classification schemes for Variscan batholiths and advocate for integrated geochemical, petrographic, and geochronological approaches in unraveling complex source-to-pluton pathways.