At the Mount Etna volcano (Italy) the massive release of magmatic gases (especially H2O, CO2 and SO2) during explosive eruptions and through the persistent gas plume, raises important issues: i) the volume of magma erupted at given periods is insufficient to feed the gas plume of the related periods; ii) gas-dominated, explosive eruptions do not emit differentiated products, but relatively Mg-rich magmas; iii) H2O measured in melt inclusions (~3.5 wt.% at about 0.4 GPa) exceeds what is expected from intraplate mantle-derived melts (<1.4 wt%). Literature data on melt inclusions (MI) along with textural and compositional analyses of plagioclase and phase stability constrained by MELTs calculations, enabled us to build a model that reconciles the above mentioned discrepancies with the high variability of the water content along the Etnean feeding system. We propose that along an open magma conduit, continuous gas loss from the free surface of magma at depth promotes an almost steady stream of H2O-rich fluid extending well below the gas saturation depth. The velocity of volatiles migration might be enhanced by the huge amount of CO2 present at Mount Etna, because the CO2 exsolved at high-pressure conditions may act as carrier for other volatile ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT species. In this way the H2O-undersaturated primitive magma present in the plumbing system, may undergo a volatile “flushing” proportional to the residing time. This process is fundamental to increase the originally low H2O content of primitive magma (<1.4 wt%) allowing it to overcome the saturation threshold, to exsolve as gas and to promote the eruption of Mg-rich lavas. Such mechanism would also account for the unexpectedly high amount of magmatic water released during non-eruptive periods.
The volatiles flushing triggers eruptions at open conduit volcanoes: evidences from Mount Etna volcano (Italy)
COLTORTI, Massimo;GIACOMONI, Pier Paolo
2014
Abstract
At the Mount Etna volcano (Italy) the massive release of magmatic gases (especially H2O, CO2 and SO2) during explosive eruptions and through the persistent gas plume, raises important issues: i) the volume of magma erupted at given periods is insufficient to feed the gas plume of the related periods; ii) gas-dominated, explosive eruptions do not emit differentiated products, but relatively Mg-rich magmas; iii) H2O measured in melt inclusions (~3.5 wt.% at about 0.4 GPa) exceeds what is expected from intraplate mantle-derived melts (<1.4 wt%). Literature data on melt inclusions (MI) along with textural and compositional analyses of plagioclase and phase stability constrained by MELTs calculations, enabled us to build a model that reconciles the above mentioned discrepancies with the high variability of the water content along the Etnean feeding system. We propose that along an open magma conduit, continuous gas loss from the free surface of magma at depth promotes an almost steady stream of H2O-rich fluid extending well below the gas saturation depth. The velocity of volatiles migration might be enhanced by the huge amount of CO2 present at Mount Etna, because the CO2 exsolved at high-pressure conditions may act as carrier for other volatile ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT species. In this way the H2O-undersaturated primitive magma present in the plumbing system, may undergo a volatile “flushing” proportional to the residing time. This process is fundamental to increase the originally low H2O content of primitive magma (<1.4 wt%) allowing it to overcome the saturation threshold, to exsolve as gas and to promote the eruption of Mg-rich lavas. Such mechanism would also account for the unexpectedly high amount of magmatic water released during non-eruptive periods.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
