New Insights Into the Internal Plumbing System of Piton de la Fournaise Volcano: Evidence From Melt Inclusions.
Abstract
Melt inclusions in olivine from the November 2002 eruption of the Piton de la Fournaise volcano, Reunion Island were analysed in order to determine major element and volatile abundances in the magma prior to eruption. The eruption comprised two phases of explosive Strombolian activity, which were accompanied by lava flows, and culminated with the collapse of a small pit crater in the central Dolomieu crater. Primary inclusions are devitrified and consequently, only secondary inclusions were analysed. The latter have an average MgO content of 3.29 wt.% compared to 8.05 wt.% for primary melt inclusions analysed from past major eruptions. This indicates that the magma underwent appreciable (~ 15%) olivine fractionation at low pressure (<< 1 kbar), and represents the first example of the trapping of low pressure melt by olivine phenocrysts at Piton de la Fournaise volcano. The low pressure estimated for fractionation provides evidence for a shallow chamber, which is supplied with magma from the main chamber located at a depth of ~ 4 km. Sulphur and chlorine contents in the secondary melt inclusions vary from below detection limit to 3640 ppm and from 130 ppm to 440 ppm, respectively. The concentrations of both volatiles increase as contents of K2O and P2O5 increase, and reach their maximum values at a K2O content of ~ 1 wt.%. In more differentiated melt inclusions, the contents of sulphur and chlorine are lower, suggesting that sulphur and chlorine degassing occurred in the shallow chamber prior to eruption. This shallow degassing, coupled with the fact that no precursory degassing was evident at the surface, suggests that closed-system conditions may have caused overpressures sufficient to trigger an eruption. The variation in the secondary inclusion volatile content during the November 2002 eruption shows that the second phase of Strombolian activity was probably not caused by the injection of gas-rich magma, but was more likely related to an increased rate of magma discharge due to foundering of wall-rock in the shallow chamber during pit crater collapse.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2004
- Bibcode:
- 2004AGUSM.V21A..08V
- Keywords:
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- 3655 Major element composition;
- 8414 Eruption mechanisms;
- 8434 Magma migration