The transcrustal magmatic system of a large active monogenetic Mexican volcanic field: A macrocryst-cargo perspective

The Pleistocene-Holocene Serdán-Oriental basin (SOB), located in the eastern sector of the Trans-Mexican Volcanic Belt, hosts a large active monogenetic volcanic field characterized by a multifaceted volcanism including isolated and clustered maars, tuff rings, cinder and lava cones, lava flows, and domes. Recent studies have highlighted its magmatic bimodal nature, characterized by scattered basaltic-to-andesitic eruptive centers and the emplacement of voluminous rhyolitic domes, as well as the presence of mafic melts erupted directly from upper lithospheric mantle sources. In this view, the SOB, with its erupted magmas, represents a unique natural laboratory to investigate the geometry and evolution of a large transcrustal magmatic network beneath active monogenetic volcanic fields. With this aim, we carried out a chemical characterization of the erupted macrocryst-cargo, we applied a suite of inverse thermobarometry models, and integrated the results with a synthesis of published geochemical data and geophysical literature. Our findings indicate the existence of a transcrustal (0–0.9 GPa), vertically distributed, hot (1100–1200 °C) magma plumbing system beneath the volcanic field controlling the ascent, differentiation (through Pl-Cpx fractionation) and eruption of basalt-to-andesite melts, with the presence of two major mafic magma stagnation levels, the first one located in the lower crust above the crust-mantle transition (∼ 30–35 km) and the second one approximatively at depth of the middle crust (∼15 km). Also, the mantle crystal-cargo at the Tecuitlapa maar represents further evidence of a possible pyroxenite mantle source at the local crust-mantle transition zone (0.9–1.2 GPa, 1200 °C). In contrast, the limited mineral-melt equilibrium pairs in rhyolites do not allow a reconstruction of the related feeding system. Moreover, the highly variable bulk compositions of rhyolites, together with their existing Sr-Nd-Pb isotope data, suggest a significant role for the local upper crust in the genesis of the SOB high-silica felsic melts. We conclude that the SOB monogenetic volcanic field evolved through two main stages of volcanic activity: a Pleistocene stage (490–25 ka) and a Holocene stage (11 ka – active), respectively. The proposed magmatic scenario is not intended to be conclusive but wants to stimulate further research on both the evolution of the SOB volcanic field and on a broader scale on the petrological and volcanological processes controlling the evolution of large active monogenetic volcanic fields.