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Control of magmatic and degassing dynamics on the volcanic activity at Volcan de Colima, Mexico

Final Activity Report Summary - COLIMA (Control of magmatic and degassing dynamics on the volcanic activity at Volcan de Colima, Mexico)

Degassing of volatiles from magmas rising toward the surface of the Earth plays a major control on the style and intensity of volcanic eruptions. Understanding the mechanism and timing of magma degassing is consequently an important task for volcanologists. In order to gain a better understanding of these processes, a study of Volcan de Colima, Mexico was undertaken. The constant activity of this volcano since 1998 provides a unique opportunity to investigate the link between the evolution of the magmas, particularly degassing, beneath the volcano before the eruption and the signal monitored at the surface of the volcano during the same period of time (e.g. gas flux and composition, seismicity). Linking these two distinct records is a fundamental step toward quantitative prediction of volcanic eruptions and one of the major challenges in volcanology.

The main focus of this project was to establish retrospectively the evolution of the magmas collected during or shortly after eruption by studying the chemistry of the crystals and melt inclusions that form in the magma as they crystallise and degases during their ascent trough the continental crust. Melt inclusions are small droplets of quenched silicate liquid caught within the crystals as they grow. They effectively are sealed containers that provide snapshots of the chemical evolution of the melt and importantly of the volatiles (H2O, CO2, F, Cl, S) dissolved in the melt before the eruption. A two step approach was used. First a detailed model for the evolution of the magmas was established on the basis of the melt inclusions and crystal chemistry, then the physical parameters (temperature, pressure of crystallisation, volatile content) of the magma derived form thiese data were compared with the data recorded at the surface of the volcano to establish possible correlations and evaluate the potential of combining the two approaches.

The results obtained demonstrate in the first place the complex evolution of the magmas at Colima. One of the main outcomes of this project was to demonstrate the great ability of melt inclusions to record not only the evolution of the melt before the eruption, but also to fingerprint the processes that affected the magmas during their evolution, processes difficult to identify using standard petrological methods and that have important implications regarding the functioning of the magmatic system feeding Volcan de Colima. On the basis of this information, a detailed model for the evolution of the magmas in the subvolcanic system was developed. The relevance of this model to other subduction zone related volcanoes was subsequently assessed by establishing a global compilation of melt inclusions and experimental petrology data. This showed that most of the conclusions for Volcan de Colima are applicable to similar volcanoes and this led to the elaboration of an innovative model for andesitic volcanism.

Another important outcome of this project was to highlight the potential to integrate melt inclusions studies in the monitoring strategy of active volcanoes. At Volcan de Colima, the depth of crystallisation and the gas chemistry calculated from volatile contents of melt inclusions show good correlations with the location of earthquakes and the gas chemistry recorded at the surface. In addition the inclusions record variations in the volatile contents of the magmas over time. This signifies that, although they can be analysed only after the eruption, the inclusions can provide important information on the location of the magmatic system feeding the eruption, its physical state and its temporal evolution, parameters that can be correlated a posteriori with the surface monitoring record and help to constrain the significance of the future monitoring record.

Overall, the results obtained as part of this project provide a better understanding of the physical characteristics and functioning of the magmatic system feeding the current eruption of Volcan de Colima and led to the development of a genetic model for subduction zone andesite volcanism. In addition, this project demonstrates the potential to integrate melt inclusion studies in the monitoring strategy of persistently active volcanoes, an approach that we believe will significantly improve our understanding of volcanoes.