Fluxes of volatiles (H2O, CO2, N2, Cl, F) from arc volcanoes

Abstract

This review gives an overview of the estimates of volatile emissions from arc and mid-ocean ridge volcanoes to the atmosphere and hydrosphere with particular focus on H 2 O, CO 2 , N 2 , Cl and F. The gas compositions of high temperature (>500°C) fumaroles are compiled and used to derive magmatic H 2 O/SO 2 , CO 2 /SO 2 , HCl/SO 2 and HF/SO 2 ratios on an arcby-arc basis to obtain new estimates of major volatile fluxes from arcs globally. The estimate of F flux from arcs is two orders of magnitude smaller than the amount of F released from mid ocean ridges whereas the arc Cl flux exceeds the ridge flux. An important observation is that globally the water budget of subduction zones seems to be balanced and the amount of water degassed through arc volcanism is within the estimates of the amount of water released from the slab below the volcanic front. Recent work that focused on the Central American arc shows that detailed knowledge of the subduction input compositions, coupled with gas emission studies is critical to further constrain the fate of volatiles during the subduction processes.

First volatile inventory for Gorely volcano, Kamchatka

“…When compared with currently available data for high-T volcanic gases in the Kamchatka-Kurile arcs [Fischer, 2008], Gorely's gas is the poorest in water (93.5%), the richest in both CO 2 (2.6%) and SO 2 (2.2%), and moderately rich in HCl (1.1%). The H 2 O content and H 2 O/SO 2 ratio (43 AE 13) are even lower than those of 950 C gases from Kudryavy volcano in the Kuriles [Taran et al, 1995], the most accessible location for magmatic degassing in the entire arc (H 2 O = 94.4-95.3% and H 2 O/SO 2 = 46.5-52.5).…”

“…The calculated fluxes range from 9700 tonsÁday À1 for H 2 O to 0.14 tonsÁday À1 for HI, summing up to 11,000 tonsÁday À1 overall. These emission rates render Gorely as a typical arc emitter, contributing to about 0.6% (H 2 O), 0.3% (CO 2 ), and 1.5-1.6% (SO 2 , HCl) of the global volatile fluxes currently estimated for arc volcanism [Wallace, 2005;Fischer, 2008;Taran, 2009].…”

“…Although we cannot evaluate the temporal stability of this rather large SO 2 release, this degassing rate from Gorely corresponds to a significant fraction (up to 40%) of the current estimated total from the entire K arc segment (≥2000 tÁday À1 [Taran, 2009]) and exceeds the total estimated flux from the Kamchatka arc of $290 t/day, which was based on global extrapolations [Fischer, 2008]. The measured SO 2 flux, combined with the plume composition, allows us to assess Gorely's emission rates for all detected gas species (Table S1).…”

“…The need to better understand the mechanisms and rates of volatile supply to the mantle via subduction, and volatile recycling through arc volcanism has motivated extensive work on the petrology of arc magmas [e.g., Pearce and Peate, 1995] and subducted sediments [Plank and Langmuir, 1998], and on the chemical and isotopic composition of volcanic gases in arc settings [Fischer, 2008]. The Kamchatka (K) peninsula, in the north-west of the Pacific 'Ring of Fire', is one of the most active volcanic arcs on Earth, with 29 historically erupting volcanoes along the $700 km-long Eastern Volcanic Belt (EVB; Figure 1a).…”

Arc volcanism, carbonate platform evolution and palaeo-atmospheric CO<sub>2</sub>: Components and interactions in the deep carbon cycle

“…Both assumptions are problematic. There are several dynamic factors that govern arc CO2 flux such as convergence rates (van der Meer et al, 2014), 20 the composition and volume of subducted sediments (Rea and Ruff, 1996), convergence obliquity (Kerrick and Connolly, 2001), slab volume flux (Fischer, 2008), the relative contribution of metamorphic decarbonation in the crust and in the mantle wedge (Keleman and Manning, 2015) and the efficiency of decarbonation (Johnston et al, 2011). The model does not account for these factors and assumes that the parameters of CO2 flux have remained constant in time.…”