Horizon 1 1 17 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES Lithos 240-259 El Misti Central Andes Arc magmatism Magmatic evolution Geochemistry Assimilation-fractional crystallisation PEROU ANDES EL MISTI VOLCAN 2017 fdi:010068904 ENG Lithos 0024-4937 ISI:000392680400016 10.1016/j.lithos.2016.11.009 https://www.documentation.ird.fr/hor/fdi:010068904 https://www.documentation.ird.fr/intranet/publi/2017/02/010068904.pdf 268 Horizon (IRD) El Misti volcano, a large and hazardous edifice of the Andean Central Volcanic Zone (CVZ) of southern Peru, consists of four main growth stages. Misti 1 (>112 ka) is an old stratovolcano partly concealed by two younger stratocones (Misti 2, 112-40 ka; Misti 3, 38-11 ka), capped in turn by a recent summit cone (Misti 4, <11 ka). In order to gain insights into magma composition controls on eruptive behaviour through time at El Misti, we have conducted a petrological and geochemical study of selected rock samples from the main growth stages of the volcano. Whole rock compositions range from andesite to rhyolite and belong to a medium to high-K calk alkaline magmatic suite. El Misti samples are characterised by high large-ion lithophile elements, but low concentrations of high field strength elements, and heavy rare earth elements, consistent with a subduction zone setting. The Sr-87/Sr-86 (0.70715-0.70882) and Nd-143/Nd-144 (0.511983-0.512277) isotope ratios suggest that magma composition is significantly affected by contamination and/or assimilation processes during their evolution, likely due to the presence of thick (65-70 km) continental crust beneath the CVZ in southern Peru. Geochemical evidence indicates that magmatic evolution is mostly controlled by Assimilation-Fractional Crystallisation (AFC) mechanisms. Modelling reveals a mass-assimilated/mass-fractionated ratio (p) <= 2.2, which suggests an assimilated crust fraction below 14 wt.% on average. Our isotopic data clearly identify the Proterozoic "Charcani gneiss" basement as the main contaminant. Both contamination and assimilation processes peaked at similar to 30 wt.%, during the Misti 3 stage when rhyolites were generated. We ascribe the general depletion in HREE and Y and elevated La/Yb and Sr/Y ratios in El Misti samples to the enrichment of the mantle wedge source of the parental magmas by a felsic melt of adakitic composition and hydrous fluids. Our work highlights that El Misti's magmatic system has remained relatively homogeneous since at least 0.12 Ma, with a marked influence of the contaminating crust in the Late Pleistocene Misti 3 stage, which resulted in highly explosive eruptions. Andesitic-dacitic compositions are dominant in the Holocene and historical Misti 4 stage, and are expected for future volcanic events at El Misti. 066 ; 064 UR163 Pérou