Durations Of Magma Storage And Mixing: The Record In Compositional Zoning Of Minerals And Its Connection To Surface Monitoring Data From Mt. Etna

Understanding the magmatic processes that occur within the plumbing systems of active volcanoes and the duration of magma storage beneath these are some of the main objectives of igneous petrology and volcanology. Over the past years, detailed petrological (e.g. thermobarometry) and geophysical (seismicity, ground deformation, microgravity etc.) work has considerably advanced our knowledge of the depth, size and shape of magma storage systems beneath volcanoes. Continuous monitoring provides time series data from the surface, but the actual processes involved in the dynamic evolution of the storage systems and their connection to the surface observations remain elusive. Temperature-dependent partitioning of elements, on which element exchange thermometry is based, combined with our knowledge of diffusion rates of the relevant elements allow us to model the continuous record stored in the compositional variations of minerals to access the dynamic evolution of plumbing systems. We have modeled the compositional zoning in olivine crystals from the eruptive products at Mt. Etna to study the time gap between intrusion of magma and their mixing at depth, and their eventual eruption at the surface. We consider data from the 1991/1993 eruptions, the two major flank eruptions in 2001 and 2002 and the very recent eruptive episodes in 2006 and 2007. We find that the time scales of magma mixing in this highly active and continually erupting system range between a few days and 2 years and that this interval has not varied significantly over the past two decades. Eruptive products fed by different plumbing systems (e.g. some 2001 and 2002 eruptions) are characterized by different time scales. This may provide a means of identifying different plumbing systems in historic eruptive products. Our inferences on timing of magma intrusion and movement at depth for the 1991/1993 period correlate well with real time monitoring data from the surface (seismicity, ground deformation, gas geochemistry and microgravity). Work is in progress to assess the correlation between monitoring data and time scales obtained from studying the more recent eruptive products.