Decompression experiments as an insight into ascent rates of silicic magmas

Discussion on ‘Magma storage region processes of the Soufrière Hills Volcano, Montserrat’, Geological Society, London, Memoirs , 39, 361-381

“…However, the same trend of (2003) and Couch et al (2003), and the matrix glass and melt inclusion data of Buckley et al (2006). increasing K 2 O and decreasing CaO is also observed, more clearly, in the experimental studies of Couch et al (2003), Martel & Schmidt (2003) and Brugger & Hammer (2010). The experiments of Martel & Schmidt (2003) are particularly appropriate because their starting material was chosen to have the composition of the most evolved (i.e.…”

“…increasing K 2 O and decreasing CaO is also observed, more clearly, in the experimental studies of Couch et al (2003), Martel & Schmidt (2003) and Brugger & Hammer (2010). The experiments of Martel & Schmidt (2003) are particularly appropriate because their starting material was chosen to have the composition of the most evolved (i.e. highest SiO 2 on an anhydrous basis) plagioclase-hosted melt inclusions from Devine et al (1998), equivalent to melts in equilibrium with phenocryst rims during decompression crystallization (Martel & Schmidt 2003).…”

“…The experiments of Martel & Schmidt (2003) are particularly appropriate because their starting material was chosen to have the composition of the most evolved (i.e. highest SiO 2 on an anhydrous basis) plagioclase-hosted melt inclusions from Devine et al (1998), equivalent to melts in equilibrium with phenocryst rims during decompression crystallization (Martel & Schmidt 2003). In all sets of experiments, the very high-K compositions are achieved only at very low final pressures (e.g.…”

Textures of plagioclase microlite and vesicles within volcanic products of the 1914-1915 eruption of Sakurajima Volcano, Kyushu, Japan

“…This indicates that the crystallization process during emplacement mainly involves renewed growth of pre nucleated microlite. Previous decompression experiments indicate that crystallization is induced by decompression and that modal content and number density of microlite change in response to the amount of decompression (∆P) and decompression rate (∆P/∆t) (Hammer and Rutherford, 2002;Couch et al, 2003;Couch, 2003;Martel and Schmidt, 2003). Figure 13 shows the logarithm of ∆P/∆t against the logarithm of number density plot for the MSD (Multi Step Decompression) experiment.…”

“…The vesicularity of volcanic products changes in response to the degassing process, i.e., closed system gas expansion or escape of gas from the system (Martel et al, 2000). Furthermore, volatile exsolution from melt increases the liquidus temperatures of melt and consequently can induce the crystallization of microlite (Hammer and Rutherford, 2002;Couch et al, 2003;Martel and Schmidt, 2003). According to previous decompression experiments, the number density and modal content of microlite change markedly in response to decompression rate, which in turn is related to magma ascent rate.…”