Mount Etna basaltic plumbing system: the magma storage capacity tracked from four decades of lava compositional change and degassing
Abstract
Deciphering the magma plumbing systems of basaltic volcanoes is crucial to improved understanding and forecasting of their eruptive behavior. Mount Etna is one of the most active basaltic volcanoes on Earth, built upon a 20-km thick continental crust at the collision boundary between the African and Eurasian continental plates. Seismic imaging indicates the presence a huge plutonic body in its sedimentary basement, as well as molten magma bodies ponding at main lithological discontinuities in the upper 10 km of the crust. However, limitations in seismic spatial resolution still hamper accurate size estimate of these molten magma bodies. Here we present an updated estimate of the magma storage capacity of Mt. Etna plumbing system based on both a remarkable compositional change of Etna lavas over the last four decades (progressive enrichment of alkalis and 87Sr since the early seventies), erupted magma volumes and sulfur-related magma degassing rates. Temporal trends in K2O/Th, Rb/Th and 87Sr/86Sr ratios - insensitive to magma differentiation processes - track the replenishment of Etna's plumbing system by a new, more alkaline and more radiogenic basaltic magma that has gradually mixed with and replaced the former resident magma, while promoting a sharp increase in the mean lava extrusion rate. On some occasions (e.g. 1974, 1998, 2001-2003) this new magma was able to reach the surface without pre-eruptive mixing in the main storage cell, leading to the most violent eruptive events. Such variations indicate a complex storage system, made of sills and dykes, in which some magma batches can either remain preserved for a significant time span or propagate independently of the central volcano conduits. Results obtained until late 2015 demonstrate that the influx of new magma has definitely ended after the 2002-2003 flank eruptions. Combining these geochemical changes with the cumulative volumes of degassed and erupted magma, we quantify an overall magma storage capacity of ca. 1.5 km3 in the 10-km deep crustal magma feeding system of Etna. This figure is larger than previous estimates and could be usefully compared to results from a recent seismic tomography realized within the framework of MED-SUV European project.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.V12A..02A
- Keywords:
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- 8414 Eruption mechanisms and flow emplacement;
- VOLCANOLOGYDE: 8419 Volcano monitoring;
- VOLCANOLOGYDE: 8425 Effusive volcanism;
- VOLCANOLOGYDE: 8488 Volcanic hazards and risks;
- VOLCANOLOGY