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The Nieve monogenetic volcanic cluster is located in the central–eastern region of the Michoacán–Guanajuato volcanic field, along the Huiramba fault zone, a relay ramp in the Morelia–Acambay fault system produced by oblique north-northwest transtension. This volcanic cluster includes at least 17 middle Pliocene to late Pleistocene lava domes, two small shield volcanoes, and two scoria cones. Between 4 and 3.8 Ma, two effusive eruptions built two small shield volcanoes overlying one another, with a magma volume of 3.93 km3. Between 2.9 Ma and 21.4 ka, 17 lava domes and two scoria cones were emplaced on the flanks of these volcanoes. The entire cluster resulted in a total erupted volume of 17 km3, covering an area of 326 km2 and reaching a thickness of emplaced volcanic material of 1200 m, resulting in a magma eruption rate equivalent to 0.004 km3/ka. All the rocks associated with this cluster are within a relatively restricted range in composition, between 53.9 and 64.2 wt% SiO₂, from andesite enriched in silica to basaltic andesite. The presence of intrusive-rock xenoliths and xenocrysts with dissolution textures reveals that assimilation processes modified the magmas. Based on the regional geological record, we suggest that the establishment of the Nieve volcanic cluster has been controlled by tectonic structures and the basement of the region, which has allowed the chemical evolution of these magma batches that probably had sources in at least two deep reservoirs as reflected by the Nb/Th versus Ta/U ratio. • The Nieve cluster includes 21 Pliocene-Pleistocene monogenetic volcanoes in México. • 19 self-similar volcanoes share distribution, mineral assemblage and composition. • Two deep reservoirs feed the independent and spatially coalescent volcanoes. [ABSTRACT FROM AUTHOR]

In the Central Andes, large (> 500 km2) and long-lived (1–5 Ma) volcanic clusters (LVCs) are less explored and their eruptive history and magmatic regimes less understood than smaller, short-lived (<0.5 Ma), individual stratocones. The Chachani-large volcanic cluster (C-LVC) sizeable volume (c. 290 km3) consists of twelve edifices forming the 1.06–0.64 Ma group of stratovolcanoes and the 0.46–0.05 Ma group of domes coulees and block-lava flow fields. Both groups overlie pre-Chachani lavas and tuffs 1.02–1.27 Ma, and together they have buried large nested craters or a caldera associated with the c. 1.62–1.66 Ma Arequipa Airport ignimbrite. The C-LVC evolved from: (i) homogeneous compositions of the pre-Chachani and Chachani basal eruptive units to (ii) relatively wide compositional variations (53–67 wt% SiO 2) between mafic andesite and dacite at moderate eruptive rates (0.27–0.41 km3/ka) for the 'Old Edifice' group, and finally to (iii) narrower (57–64 wt% SiO 2) andesitic compositions coinciding with extrusive activity at 2.5 times lower eruptive rates (0.12–0.15 km3/ka) for the 'Young Edifice' group. The large compositional variations in the Old Edifice group are related to strongly contrasting resident and recharge magma compositions of hybridized lavas. In contrast, the narrow compositional range and lower eruption rate during the second half of the C-LVC eruptive history represent a trend towards more homogeneous, andesitic magma composition with time. Mineral texture and compositional studies provide evidence for disequilibrium and magma mixing in the C-LVC shallow (5–20 km depth range) magma reservoirs. These temporal changes in magma composition document that the transcrustal magma systems of the C-LVC evolved and matured with time by a combination of processes: fractional crystallization, crustal contamination and magma mixing/mingling with variable rates of mafic recharge. This resulted in a shift in time to a steady state, monotonous (andesite) regime as a result of coupling between compositional parameters and thermal conditions, density constraints, and the viscosity/crystallinity of erupted magmas. • Long-lived volcanic clusters are less explored than stratocones in the Central Andes. • The Chachani LVC eruptive history shows narrowing SiO 2 compositional ranges over time. • Mineral composition changes support frequent recharge events along the C-LVC lifetime. • Eruptive rates have slowed in time at C-LVC, coinciding with magmatic compositions. • C-LVC represents post-caldera activity after the 1.66 Ma Arequipa Airport ignimbrite. [ABSTRACT FROM AUTHOR]

Volcanic arc clusters are groups of adjacent volcanic edifices that allow the investigation of geochemical changes occurring through time within a limited area (< few hundreds of km2). As such they may increase our understanding of processes that lead to magma differentiation in arcs. Geochemical changes over time in volcanic clusters can be related to source or intracrustal processes. Here, we show that magmatic rocks of 9 edifices of the Chachimbiro-Pulumbura-Pilavo-Yanaurcu volcanic cluster, in the frontal arc of Ecuador, display temporal changes of major and trace elements as well as Pb isotopes during their ~13 Ma long life history (13 Ma to 6 ka). Additionally, geochemical compositions of magmatic rocks of these edifices also become more homogeneous through time. Fractionation, assimilation and recharge models suggest that the changes in geochemical composition and in the compositional spread of erupted materials of the cluster are controlled by an increased depth of magma evolution since ~300–400 ka ago. We propose two speculative scenarios to explain the deepening of magmatic evolutionary processes since ~300–400 ka in the studied cluster. Nonetheless, a higher geochronological and geochemical resolution is needed to determine the cause and exact timing of such a switch as well as its synchronicity or diachroneity with respect to the geochemical changes observed in other volcanic centers along and across the Ecuadorian arc. [Display omitted] [ABSTRACT FROM AUTHOR]