Geochemistry and Sr-Nd-Pb isotope systematics of Pleistocene adakites at Los Espinos Volcano (Mexico) and implications for the volcanic plumbing system of a small-volume volcano

Los Espinos Volcano, located within the Michoacán-Guanajuato Volcanic Field (MGVF) in Mexico, presents a unique opportunity to investigate the transition from calc-alkaline to adakitic-like magmatism in small-volume volcanoes (SVVs). This study aims to understand the origin of adakitic magmas at Los Espinos Volcano (LEV) and determine if the observed transition is related to the evolution of a shallow magma pond or chamber beneath the volcano. The research evaluates if this compositional transition is linked to regional tectonic evolution, especially the crust thickening from the late Miocene to the Quaternary. The findings suggest that the magmas were derived from a metasomatized mantle wedge, with the adakitic characteristics of the tuff cone lavas resulting from the partial melting of a thickened lower crust. High Sr/Y (>40), La/Yb (7.2–9.9), and Mg# (33–35), along with the isotopic signatures ( ⁸⁷ Sr/ ⁸⁶ Sr: 0.70335–0.70415; ¹⁴³ Nd/ ¹⁴⁴ Nd: 0.51278–0.51299; ²⁰⁶ Pb/ ²⁰⁴ Pb: 18.508 -18.666; ²⁰⁷ Pb/ ²⁰⁴ Pb: 15.510 - 15.559; ²⁰⁸ Pb/ ²⁰⁴ Pb: 38.109 - 38.321) supports the hypothesis that the adakitic magmas were generated through the interaction of mantle-derived melts with the lower crust. The temporal and compositional variations observed in the erupted products indicate that Los Espinos Volcano experienced multiple eruptive episodes, with a significant repose period between the pre-tuff cone and tuff cone activities. This polygenetic nature of the volcano underscores the complexity of SVVs and challenges the traditional view of these systems as being monogenetic. Overall, this research contributes to a better understanding of the magmatic and tectonic processes that drive the evolution of SVVs in the MGVF, providing a framework for interpreting the geochemical and isotopic data of SVVs worldwide.