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Article Dans Une Revue Bulletin of Volcanology Année : 2017

Eruption and emplacement dynamics of a thick trachytic lava flow of the Sancy volcano (France)

Andrew J.L. J.L. Harris
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Etienne Médard
Lucia Gurioli

Résumé

A 70-m-thick, 2200-m-long (51 × 106 m3) trachytic lava flow unit underlies the Puy de Cliergue (Mt. Dore, France). Excellent exposure along a 400-m-long and 60- to 85-m-high section allows the flow interior to be accessed on two sides of a glacial valley that cuts through the unit. We completed an integrated morphological, structural, textural, and chemical analysis of the unit to gain insights into eruption and flow processes during emplacement of this thick silicic lava flow, so as to elucidate the chamber and flow dynamic processed that operate during the emplacement of such systems. The unit is characterized by an inverse chemical stratification, where there is primitive lava beneath the evolved lava. The interior is plug dominated with a thin basal shear zone overlying a thick basal breccia, with ramping affecting the entire flow thickness. To understand these characteristics, we propose an eruption model that first involves processes operating in the magma chamber whereby a primitive melt is injected into an evolved magma to create a mixed zone at the chamber base. The eruption triggered by this event first emplaced a trachytic dome, into which banded lava from the chamber base was injected. Subsequent endogenous dome growth led to flow down the shallow slope to the east on which the highly viscous (1012 Pa s) coulée was emplaced. The flow likely moved extremely slowly, being emplaced over a period of 4–10 years in a glacial manner, where a thick (>60-m) plug slid over a thin (5-m-thick) basal shear zone. Excellent exposure means that the Puy de Cliergue complex can be viewed as a case type location for understanding and defining the eruption and emplacement of thick, high-viscosity, silicic lava flow systems.
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Dates et versions

hal-01426407 , version 1 (04-01-2017)

Identifiants

Citer

Benjamin Latutrie, Andrew J.L. J.L. Harris, Etienne Médard, Lucia Gurioli. Eruption and emplacement dynamics of a thick trachytic lava flow of the Sancy volcano (France). Bulletin of Volcanology, 2017, 79, ⟨10.1007/s00445-016-1084-6⟩. ⟨hal-01426407⟩
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