Magmatic Volatile History

It is well established that the volatile content of magmas (e.g., H₂O, CO₂, SO₂) controls the rate of magma ascent and recharge as well as the styles and intensity of volcanic eruptions. Furthermore, it is also generally accepted that many volcanoes emit much greater amounts of gas than can be dissolved in the erupted volcanic products (including non-eruptive degassing). As such, it is critical to determine the depth at which degassing occurs (e.g., deep vs. shallow), the path the magma and gas have followed (e.g., separate gas phase) to the surface and the processes responsible for this degassing (e.g., intrusion of gas-rich magma, divergent conduits, permeable fluid flow). We are therefore using in situ, remote and microanalytical measurements (glasses) of magmatic volatiles from hot spot volcanoes (e.g., Galapagos, Kilauea) and subduction-related systems (e.g., Kawah Ijen, Masaya, San Cristobal) to accurately constrain these volatile concentrations and magma / degassing pathways. Previous studies have often been limited by the low number of measured gas species and the sporadic nature of the sampling; an "average" concentration is often the only compositional data available for a volcano even though there is significant natural variability from one measurement day to the next. We must thus fully characterise the volatile budget with multi-year repeat measurements to accurately account for processes occurring at the surface (e.g., interaction with crater lake waters) and in the plumbing system (e.g., gas segregation) which modify the primary magmatic concentrations.

In addition to affecting rates of magma ascent, magmatic volatiles also play a role in the formation of metallic mineral deposits. It has been shown that supercritical vapour-like magmatic fluids are capable of transporting economic concentrations of metals, and it has been proposed that they could constitute the principal ore fluids in many magmatic hydrothermal systems. Information on the nature and concentration of volatile components in the source magma is key to the characterisation of these ore fluids, and thus we are currently investigating this via a recently funded NSERC Collaborative Research and Development proposal, linking the degassing hydrothermal system at Kawah Ijen to the Bowone-Binabse high sulphidation epithermal Au deposit in northern Sulawesi, Indonesia.