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

Abstract

This research investigates the origin and relationship between adakites and non-adakitic magmas found at Los Espinos Volcano (LEV), situated within the Michoacán-Guanajuato Volcanic Field (MGVF) in Mexico. LEV consists of a younger phreatomagmatic tuff cone (LETC) with adakitic features, overlaying two pre-tuff cone units (PTC) made of a lava flow and a scoria cone remnant, both of calc-alkaline composition. The primary objective is to assess whether the shift from calc-alkaline to adakitic compositions results from the development of a crustal magma reservoir beneath the volcano or from broader tectonic processes, such as crustal thickening during the late Miocene to Quaternary periods. The findings indicate that the magmatic source for the PTC and LETC is a metasomatized mantle wedge. High Sr/Y ratios (>40), La/Yb values (7.2–9.9), and Mg# (33–35), along with the isotopic signatures (⁸⁷Sr/⁸⁶Sr: 0.70335–0.70415; ¹⁴³Nd/¹⁴⁴Nd: 0.51278–0.51299; ²⁰⁶Pb/²⁰⁴Pb: 18.508–18.666; ²⁰⁷Pb/²⁰⁴Pb: 15.510–15.559; ²⁰⁸Pb/²⁰⁴Pb: 38.109–38.321) collectively support the interpretation that the adakitic magmas were generated through the mixing between the early calc-alkaline magma and melted lower crust, previously metamorphosed to granulite facies possibly through sustained magmatic underplating and thermal metamorphism from ongoing basaltic magma influx at the base of the crust. The temporal and compositional variations observed in the erupted products indicate that LEV experienced multiple eruptive events, with a significant repose period between the PTC and LETC activities, highlighting the complexity and possible polygenetic nature of this small-volume volcano.