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Genèse et évolution des magmas andésitiques à thyodacitiques récents des volcans Misti et Ubinas (sud du Pérou)

Abstract : The Misti and Ubinas are two active volcanoes in the Central Volcanic Zone of the Andes of southern Peru. The Misti is located in front of the Plio-quaternairee volcanic arc, while the Ubinas is located at the rear of the arc (~ 40 km east). The mineralogical and geochemical study (major, trace and Sr isotopes, Nd and o) Recent products issued by these volcanoes (<112 ka at Misti, <370 ka at Ubinas) shows that the Misti issued mainly andesites and dacites few, while rhyolites were unusually issued between 31 and 34 ka. The Ubinas possesses a greater compositional diversity than the Misti, especially during the last millennium (andesites to dacites basic). Magmas of these volcanoes result from partial melting of mantle metasomatized by aqueous fluids from the dehydration of the subducting plate. Given the location of the buildings from the pit, the amount of fluids from this mechanism would be higher at Misti, located closer to the pit, as the Ubinas; This suggests that the rate of partial melting are slightly stronger than in the Ubinas Misti, which agrees with the production of higher magma of Misti and with the rich in incompatible elements, LILE) magmas of Ubinas. The evolution of magmas of Misti and Ubinas is mainly controlled by processes of assimilation-fractional crystallization (AFC) in reservoirs whose surface contaminant is the Arequipa Massif. And the magmatic evolution of lineages occurs with infection rates <14% at Misti (ACEC major contamination between 31 and 34 ka) and <8% at Ubinas. The rocks of these volcanoes are slightly depleted in HREE and Y relative to calc-alkaline magmas conventional arc. This suggests that the primary magmas have assimilated products derived from partial melting of the base of the continental crust, containing garnet (+ - amphibole residue in their fusion
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Submitted on : Wednesday, July 18, 2012 - 4:14:43 PM
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  • HAL Id : tel-00718983, version 1

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Marco Rivera Porras. Genèse et évolution des magmas andésitiques à thyodacitiques récents des volcans Misti et Ubinas (sud du Pérou). Volcanologie. Université Blaise Pascal - Clermont-Ferrand II, 2006. Français. ⟨NNT : 2010CLF22051⟩. ⟨tel-00718983⟩

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