Mercury fluxes from volcanic and geothermal sources: an update
E. Bagnato, G. Tamburello, G. Avard, M. Martinez-Cruz, M. Enrico, X. Fu, M. Sprovieri, J. E. Sonke, 2015. "Mercury fluxes from volcanic and geothermal sources: an update", The Role of Volatiles in the Genesis, Evolution and Eruption of Arc Magmas, G. F. Zellmer, M. Edmonds, S. M. Straub
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We review the state of knowledge on global volcanogenic Hg emissions to the atmosphere and present new data from seven active volcanoes (Poás, Rincón de la Vieja, Turrialba, Aso, Mutnovsky, Gorely and Etna) and two geothermal fields (Las Pailas and Las Hornillas). The variability of Hg contents (c. 4–125 ng m−3) measured in gaseous emissions reflects the dynamic nature of volcanic plumes, where the abundances of volatiles are determined by the physical nature of degassing and variable air dilution. Based on our dataset and previous work, we propose that an average Hg/SO2 plume mass ratio of c. 7.8×10−6 (±1.5×10−6; 1 SE, n=13) is best representative of open-conduit quiescent degassing. Taking into account the uncertainty in global SO2 emissions, we infer a global volcanic Hg flux from persistent degassing of c. 76±30 t a−1. Our data are derived from active volcanoes during non-eruptive periods and we do not have any direct constraint on the Hg flux during periods of elevated SO2 flux associated with large-scale effusive or explosive eruptions. This suggests that the time-averaged Hg flux from these volcanoes is even larger if the eruptive contribution is considered. Conversely, closed-conduit degassing and geothermal emissions contribute modest amounts of Hg.
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The subduction zone volatile cycle is key to understanding the petrogenesis, transport, storage and eruption of arc magmas. Volatiles control the flux of slab components into the mantle wedge, are responsible for melt generation through lowering the solidi of mantle materials and influence the crystallizing phase assemblages in the overriding crust. Further, the rates and extents of degassing during magma storage and decompression affect magma rheology, ultimately control eruption style and have consequences for the environmental impact of explosive arc volcanism. This book highlights recent progress in constraining the role of volatiles in magmatic processes.
Individual book sections are devoted to tracing volatiles from the subducting slab to the overriding crust, their role in subvolcanic processes and eruption triggering, as well as magmatic-hydrothermal systems and volcanic degassing. For the first time, all aspects of the overarching theme of volatile cycling are covered in detail within a single volume.