Melt inclusions track melt evolution and degassing of Etnean magmas in the last 15 ka
We present major elements compositions and volatiles contents of olivine-hosted melt inclusions from Etna volcano (Italy), which extend the existing database with the aim of interpreting the chemical variability of Etnean magmas over the last 15 ka. Olivine phenocrysts were selected from the most primitive Fall Stratified (FS) eruptive products of picritic composition (Mg# = 67–70, Fo 89–91 ), the Mt. Spagnolo eccentric lavas (Mg# = 52–64, Fo 82–88 ) and among the more recent 2002–2013 eruptive products (Mg# = 33–53, Fo 68–83 ). Crystal fractionation and degassing processes were modeled at temperatures of 1050–1300 °C, pressures <500 MPa, and oxygen fugacity between 1 and 2 log units abo…
Melt inclusions constrain S behaviour and redox conditions in Etnean magmas
Mount Etna is a complex magmatic system characterized by a continuous variability both in terms of eruptive style and composition of erupted products. Currently, its volcanic activity is marked by high gas fluxes (of above all SO2), both during eruptive and non-eruptive periods. In this study, we have studied the volatile contents and Fe speciation of olivine-hosted melt inclusions from 6 eruptions of the last 15 ky, mainly to investigate the behaviour of S during ascent and differentiation of Etnean magmas. Samples selected come from the FS eruption which is the oldest and most primitive (picritic composition, Fo91), the Mt Spagnolo and from more recent eruptions: 2002/3, 2006, 2008, and 2…
Experimental Constraints on the Crystallization of Silica Phases in Silicic Magmas
Abstract Low-pressure silica polymorphs, e.g. quartz (Qtz), tridymite (Trd), and cristobalite (Crs), are common in silicic magmas, but the conditions of their formation are still unclear. The stability fields of these polymorphs have been determined in the SiO2, SiO2–H2O, and haplogranite systems, but these simple systems are not directly applicable to silica polymorph crystallization in natural silicic magmas. The present study compiles an experimental database of new and previously-published data documenting the crystallization of silica phases in natural silicic magmas and simple synthetic systems. Silica polymorphs are identified using Raman spectroscopy and their pressure-temperature d…
Generation of CO2-rich melts during basalt magma ascent and degassing
International audience; To test mechanisms of basaltic ma gma degassing, continuous decompressions of volatile-bearing (2.7-3.8 wt% H2O, 600-1300 ppm CO2) Stromboli melts were performed from 250-200 to 50-25 MPa at 1180-1140°C. Ascent rates were varied from 0.25 to ~ 1.5 m/s. Glasses after decompression show a wide range of textures, from totally bubble-free to bubble-rich, the latter with bubble number densities from 104 to 106/cm3, similar to Stromboli pumices. Vesicularities range from 0 to ~ 20 vol%. Final melt H2O concentrations are homogeneous and always close to solubilities. In contrast, the rate of vesiculation controls the final melt CO2 concentration. High vesicularity charges ha…