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Abstract. Understanding the anatomy of magma plumbing systems of active volcanoes is
essential not only for unraveling magma dynamics and eruptive behaviors but
also to define the geometry, depth, and temperature of the heat sources for
geothermal exploration. The Pleistocene–Holocene Los Humeros volcanic
complex is part of the eastern Trans-Mexican Volcanic Belt (central Mexico),
and it constitutes one of the most important exploited geothermal fields in
Mexico with ca. 90 MW of produced electricity. With the aim to decipher the
anatomy (geometry and structure) of the magmatic plumbing system feeding the
geothermal field at Los Humeros, we carried out a field-based petrological
and thermobarometric study of the exposed Holocene lavas. Textural analysis,
whole-rock major-element data, and mineral chemistry are integrated with a
suite of mineral-liquid thermobarometric models. Our results support a
scenario characterized by a heterogeneous multilayered system, comprising a
deep (depth of ca. 30 km) basaltic reservoir feeding progressively shallower
and smaller discrete magma stagnation layers and batches, up to
shallow-crust conditions (depth of ca. 3 km). The evolution of melts in the feeding
system is mainly controlled by differentiation processes through fractional
crystallization (plagioclase + clinopyroxene + olivine + spinel). We
demonstrate the inadequacy of the existing conceptual models, where a single
voluminous melt-controlled magma chamber (or “Standard Model”) at
shallow depths was proposed for the magmatic plumbing system at Los Humeros.
We instead propose a magmatic plumbing system made of multiple, more or less
interconnected, magma transport and storage layers within the crust, feeding
small (ephemeral) magma chambers at shallow-crustal conditions. This revised
scenario provides a new configuration of the heat source feeding the
geothermal reservoir at Los Humeros, and it should be taken into account to
drive future exploration and exploitation strategies.
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