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Les intéractions entre magmas calco-alcalins "classiques" et adakitiques [Ressource électronique] : exemple du complexe volcanique Atacazo-Ninahuilca (Equateur)

Abstract : Atacazo-Ninahuilca Volcanic Complex (ANVC) is located in the Western Cordillera of Ecuador, 10 km southward from Quito. Three main edifices have been identified: La Carcacha, Atacazo and the internal domes. 40Ar/39Ar and 14C dating allowed to constrain the detailed emplacement chronology; respectively at 1.29 Ma, 222 to 71 ka and 12 to 2.3 ka. Activity style changed from effusive to explosive form the older to recent edifices. The estimated VEI for the last two eruptions is of 5, indicating the high hazard associated to this complex. Modeling of petrogenetical processes indicates the participation of fractional crystallization and crustal contamination in Carcacha and Atacazo evolution. Ancient magmas seem to be the product of partial melting of an adakite metasomatized mantle, while domes magmas are the products of direct partial melting of a basaltic source. In fact, all ANVC magmas present an adakitic affinity, which increases with time. The same temporal variations have been observed in other Ecuadorian volcanoes. This change in the magmatism nature reflects a progressive change of the magmas source, showing the increasing role of the partial melting of the subducted oceanic crust, interpreted as the result of the arrival of the Carnegie Ridge into the subduction. The presence of the young and hot Carnegie Ridge in the Ecuadorian subduction generates a high geothermal gradient able to produce the partial melting of the subducted oceanic crust. In a first stage, produced adakitic magmas are completely consumed in metasomatic reactions in the mantle wedge, while in a second stage, thanks to successive adakite-mantle interactions and perhaps also to higher partial melting degree, adakitic magmas are able to reach the surface.
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Submitted on : Monday, July 2, 2012 - 1:33:34 PM
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  • HAL Id : tel-00713684, version 1

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Sylvana Hidalgo. Les intéractions entre magmas calco-alcalins "classiques" et adakitiques [Ressource électronique] : exemple du complexe volcanique Atacazo-Ninahuilca (Equateur). Volcanologie. Université Blaise Pascal - Clermont-Ferrand II, 2006. Français. ⟨NNT : 2006CLF21721⟩. ⟨tel-00713684⟩

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