Magmatic dynamics in the plumbing system of Mt. Etna from 1995 to 2000 as inferred by petrologic investigations

Abstract

The studies performed during last decades evidenced that the feeding system of Mt. Etna is quite complex. It consists of a shallow zone, about less than 5 km deep, where a porphyritic, plagioclase-rich trachybasaltic magma is stored. This magma is the most frequently erupted at Mt. Etna during both summit and flank eruptions. A deep portion of the plumbing system also exists. Here, a sub-aphyric, plagioclase-poor basaltic magma resides and is rarely erupted during “eccentric” (Rittmann, 1973) eruptions. The study of 2001 and 2002-2003 Etna eruptions, involving both the shallow and the deep portion of the plumbing system, showed that a relationship occurs between the eruptive activity and the movements of the volcano eastern flank. In the framework of INGV-DPC 2007-2009 project, we proposed to investigate if a link exists between magma dynamics and the tectonic of the eastern flank, also before the onset of 2001 eruption. More in detail we study the period 1995-2000, when the eruptive activity occurred exclusively from the summit craters. We present the results obtained during the first stage of the project, whose goal was to investigate the magmatic processes occurring in the plumbing system of Mt. Etna from 1995 to 2000 using a petrologic approach. To this purpose we selected 25 samples of lavas and pyroclastites archived at INGV-CT and erupted from the four summit craters (Voragine, Bocca Nuova, South-East Crater and North-East Crater) during the investigated period. The study of mineralogical, petrographic, compositional (major and trace elements) and isotopic features preliminarly suggest that: i) Bocca Nuova and Voragine products show quite similar compositions throughout the investigated period. This suggests that both craters were fed by a magma stored in a common reservoir, with a buffered composition; ii) North-East Crater products are slightly more evolved than Bocca Nuova and Voragine and maintain homogeneous throughout the investigated period; iii) South-East Crater products show compositional patterns which significantly vary in time. From South-East Crater reactivation in 1996 up to September 1998, the erupted magma is different from Bocca Nuova, Voragine and North-East Crater. It results more evolved, probably due to the crystallization of plagioclase at shallow depth. From September 1998 to 4 February 1999, when a sub-terminal eruption from the South-East Crater started, the sharp variation of compositional parameters suggests the progressive arrival in the South-East Crater plumbing system of a new more primitive magma, which progressively mixed with the earlier residing one. Another recharge of the South-East Crater reservoir is evident before the onset of 2000 fire fountains at South-East Crater. In a second stage of the project we will investigate if the magmatic processes someway influenced the dynamics of the volcano eastern flank. To this purpose petrologic data will be correlated with other time-related sequence of volcanological, geophysical and geochemical parameters available in literature.