Volatiles and Fluids in Subduction Zones

Field work

Numerous field campaigns to the CAVA and the SVZ were conducted in the past years to collect a comprehensive set of young, fresh, olivine-bearing mafic pyroclastics and lavas throughout the various sections of the subduction zones. Here are some impressions from our last field work in Chile and Argentina in spring, 2009. 

Volatiles in melts

Volatile studies were conducted to constrain the interplay between the tectonic parameters, resulting pressure-temperature conditions at depth, fluid phases, and melt generation. To determine the initial contents of volatile phases in the magmas, melt inclusions in olivine crystals in mafic tephras are analysed by various analytical techniques. Melt inclusions are small (usually tens of microns) drops of magma that get trapped in a mineral as the mineral grows and precipitates from the magma upon cooling and differentiation. In this way, the melt composition at the time of mineral formation is preserved. For studies of magmatic gases in primitive melts, we investigate melt inclusions in high-Mg olivine crystals, an early crystallising phase, from mafic tephra deposits. Focusing on tephras instead of lavas is necessary to minimise the risk of syn- and post-eruptive gas-loss, which is largely prevented by the instantaneous quenching of the magma during fragmentation process of an explosive eruption, but would be a major problem during slow cooling of a lava flow.

Whole-rock geochemistry

To unravel the subduction input materials and magma source components, major and trace element analyses, and isotopic investigations are carried out on mafic lavas along and across the arc.