The Aeolian Island arc, emplaced on continental lithosphere, is composed of seven islands and several seamounts, which have evidence of magmatic activity from 1.3 Ma (Sisifo seamounts) to present time (Vulcano, Stromboli). The rock compositions belong to different magmatic series and show a large silica range (48–76 wt%). Calc-alkaline and high-K calc-alkaline volcanics are present in all the islands, except for Vulcano. Shoshonitic rocks are only lacking at Alicudi, Filicudi, and Salina. Potassic magmas have been erupted at Vulcano and Stromboli. The different parental magmas originated in a heterogeneous mid-ocean-ridge basalt (MORB)–like mantle wedge, variously metasomatized by subduction-related components (oceanic crust + sediments, released as either fluids or sediment melts). Trace-element and Sr-Nd isotopic ratios show clear geographical west-east variations among calc-alkaline rocks. The composition of the mantle source of Stromboli is strongly influenced by the addition of a sedimentary component recycled into the mantle wedge; it shows evidence of a higher amount (∼2%) than in all the other islands (<0.5%). Furthermore, the islands from the central sector of the arc are characterized by a higher proportion of slab-derived fluids, which promotes a higher degree of melting. In this frame, the high Pb isotopic ratios (HIMU-like [high µ–like]) of the rocks of the central and western branch of the arc are explained with the high 206 Pb/ 204 Pb carried from a fluid component derived from the dehydration of the ancient subducting Ionian oceanic crust. On the contrary, the low Pb isotope signature of Stromboli magmas is dictated by the sediment input, as for Sr and Nd isotopes. Parental shoshonitic magmas of Vulcano are generated by low melting degrees of a MORB-like mantle wedge, metasomatized by crustal contaminant with high fluids/sediment values, whereas Vulcano potassic magmas are interpreted as deriving from the shoshonitic magmas by refilling, tapping, fractionation, assimilation (RTFA) processes. At Stromboli, potassic to calc-alkaline magmas are generated by increasing melting degrees of a heterogeneous veined mantle. The involvement of K-micas in the genesis of potassic magmas (during partial melting of mantle wedge and/or subducted sediments) is also suggested. U-Th disequilibria confirm the higher fluid versus melt proportion in the central than in the western islands. At Stromboli, the 238 U excesses measured in calc-alkaline volcanics suggest a consistent addition of slab-derived fluids in the source, also promoting higher degrees of melting. The shift to the consistent 230 Th excesses in shoshonitic and potassic rocks requires dynamic melting processes capable of producing in-growth of 230 Th. Quantitative modeling suggests lower melting rates for shoshonitic and potassic rocks, which are consistent with the lower melting degree proposed for these magmas.

This study focuses on two issues that are still a matter of debate in subduction zones, particularly in western México: (1) the close association within the same volcanic complex of typical amphibole-free andesites to rhyolites and amphibole-bearing andesites to rhyolites, characteristic of the hydrated front of the Mexican arc; and (2) the occurrence of bimodal magmatism without evidence for interaction between mafic and intermediate to silicic magmas, which are in addition characterized by different petrogenetic affinities. Our case study is the San Pedro–Cerro Grande volcanic complex, a Quaternary silicic to intermediate dome complex located in western Mexico. Volcanic activity has been divided into two periods. In the middle Pleistocene, andesitic to dacitic magmas were emplaced along WNW-trending faults in the southern portion of the complex. The Las Cuevas pyroclastic sequence (older than ca. 500 ka) was emplaced during this episode, most likely from a local source. This first period of activity ended before ca. 280 ka with the emplacement of the Cuastecomate Plinian deposit, which is related to the formation of the San Pedro caldera, an ∼4-km-wide subcircular depression that is today partially buried by younger volcanic products. During the second period of activity (ca. 280–30 ka), rhyolitic and dacitic domes were mostly emplaced along the caldera rim and inside the caldera. In addition, hawaiites and mugearites built the Amado Nervo shield volcano on the caldera rim. Intermediate- to high-silica lava and pyroclastic rocks are subalkaline, whereas the Amado Nervo mafic lavas are transitional toward the alkaline series (Na-alkaline). No genetic relationships have been found between subalkaline and transitional Na-alkaline rocks, which are thought to represent different batches of magma from different mantle sources. Petrographic, geochemical, and isotopic variations observed in the transitional Na-alkaline Amado Nervo lavas point to a parental magma from a mantle melt that underwent limited olivine separation during its ascent to the surface. Among subalkaline rocks, two groups showing contrasting petrographical and geochemical features are recognized based on the presence of amphibole. Amphibole-bearing intermediate to silicic rocks are characterized by lower Ce and other incompatible trace element contents and lower 87 Sr/ 86 Sr (0.70382–0.70401) compared to amphibole-free rocks (0.70411–0.70424). On the basis of petrological characteristics, the two groups of magmas are interpreted to have evolved in two different magmatic reservoirs under different pressures and water contents in the mid-upper crust. Both groups of magmas were differentiated by open-system processes. We propose that assimilation and equilibrium crystallization (AEC) processes account for the amphibole-bearing rocks. Hotter and less evolved magmas interacted to a higher degree with the crust than the more evolved and colder magmas. This produced the observed higher 87 Sr/ 86 Sr in the less differentiated rocks of the amphibole-bearing group. On the other hand, amphibole-free rocks have chemical and isotopic characteristics that can be modeled by assimilation and fractional crystallization (AFC) processes. All data suggest that the two groups of subalkaline rocks have been generated by a common parental hydrous magma, but evolved in two different reservoirs. Amphibole-bearing magmas underwent amphibole fractionation in a mid-upper crustal reservoir and show assimilation of two types of basement: one akin to Oaxaquia and another akin to the Guerrero terrane. Amphibole-free magma only shows assimilation of an Oaxaquia-type basement.