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Article Dans Une Revue Journal of Volcanology and Geothermal Research Année : 2018

The genetic relationship between andesites and dacites at Tungurahua volcano, Ecuador

F. Nauret
P. Samaniego
Ivan Vlastélic
S. Hidalgo
  • Fonction : Auteur
P. Schiano

Résumé

Volcanic eruptions of intermediary and silica-rich magmas (andesites, dacites and rhyolites) in convergent arc settings generate voluminous and explosive eruptions that can strongly affect human activity and have signi fi - cant environmental impacts. It is therefore crucial to understand how these magmas are generated in order to anticipate their potential impact. At convergent margins, primitive magmas (primitive basalts and/or andesites) are derived from the mantle wedge and they are progressively modi fi ed by physical and chemical processes op- erating between the melting zone and the surface to produce silica-rich magmas. In order to elucidate the relationship between andesites and dacites, we focus on Tungurahua volcano, located in the Ecuadorian Andes. We collected a set of samples comprising such lithologies that were erupted during the last 3000 year BP. This relatively short period of time allows us to assume that the geodynamic parameters re- main constant. Petrology and major-trace element compositions of these lavas have already been examined, and so we performed a complementary Pb-Sr isotope study in order to determine the nature and origin of the components involved in andesite and dacite genesis. Sr isotopes range from 0.70417 to 0.70431, and Pb isotope compositions range from 18.889 to 19.154 for 206 Pb/ 204 Pb, from 15.658 to 15.696 for 207 Pb/ 204 Pb, and from 38.752 to 38.918 for 208 Pb/ 204 Pb. Dacites display a remarkably homogeneous Pb isotopic composition, with higher 206 Pb/ 204 Pb values for a given 207-208 Pb/ 204 Pb compared to andesites. Andesites show notable 207 Pb/ 206 Pb variations for a given SiO 2 content, whereas dacites have lower and homogenous 207 Pb/ 206 Pb values. Andesite and dacite altogether plot in a roughly triangular distribution, with dacitic magmas systematically plot- ting at the high SiO 2 and 87 Sr/ 86 Sr and low 207 Pb/ 206 Pb fi elds. Based on our new dataset, we show that at least 3 different components are required to explain the Tungurahua compositional and isotope variation: one corre- sponds to the mantle, the second has a deep origin (slab component or lower crust), and a mixture between these two components explains andesite heterogeneity. The third component is derived from the underlying upper continental crust. While andesites are derived from deep components, dacites are derived from the andes- itic magmas that underwent an assimilation-fractional crystallization (AFC) process with incorporation of the local metamorphic basement. Finally, we used the geochemical and isotopic data to produce a model of the mag- matic plumbing system beneath Tungurahua, consistent with geophysical and experimental petrology con- straints. We conclude that melt migration and storage in the upper crust appears to be a key parameter for controlling volcanic behavior though time.

Domaines

Géochimie
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Dates et versions

hal-01685451 , version 1 (16-01-2018)

Identifiants

Citer

F. Nauret, P. Samaniego, A. Ancellin, P. Tournigand, J.-L. Le Pennec, et al.. The genetic relationship between andesites and dacites at Tungurahua volcano, Ecuador. Journal of Volcanology and Geothermal Research, 2018, 349, pp.283 - 297. ⟨10.1016/j.jvolgeores.2017.11.012⟩. ⟨hal-01685451⟩
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