Systematics of water isotopic composition and chlorine content in arc-volcanic gases
Published:January 01, 2015
Yuri Taran, Mikhail Zelenski, 2015. "Systematics of water isotopic composition and chlorine content in arc-volcanic gases", 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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In this review paper a set of chemical (H2O, CO2, S, HCl, HF) and water isotopic (δD, δ18O) data is compiled for 26 subduction zone volcanoes and 3 volcanoes of other tectonic settings. To the arc-volcano dataset we added new data on high-temperature gas vents from three Kamchatkan volcanoes (Gorely, Bezymianny and Tolbachik) and also published data on the chemical composition of volcanic plumes obtained by remote instrumental techniques (Open-Path Fourier Transform Infrared Spectroscopy (OP-FTIR), Differential Optical Absorption Spectroscopy (DOAS) MultiGas) for volcanoes of different tectonic settings. Three typical cases of the persistent volcanic degassing in terms of δD, δ18O of the volcanic vapour and its HCl content are discussed in detail: (1) Kudryavy type with a clear two-end-member mixing behaviour; (2) degassing of active or cooling lava domes with fractionation of both water isotopes and Cl content; and (3) degassing of small volcanic islands with a complex admixing of meteorics and seawater. We show that independently of the complexity of the shallow processes which affect volcano degassing, the highest temperature volcanic gases are characterized by δD values and HCl concentrations close to −25‰ V-SMOW and 0.5–1.0 mol%, respectively. These values are the same for any volcanic arc (except maybe Mediterranean volcanoes) and are the result of seawater recycling at subduction zones on the global scale. In contrast to volcanic fluids of non-arc settings, the arc-magmatic fluid has uniformity not only in water isotopic composition and Cl content but also in the total composition (H–C–O–S–Cl–F).
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The Role of Volatiles in the Genesis, Evolution and Eruption of Arc Magmas
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.