Volatiles in subduction zone magmatism

Abstract

Abstract:The volatile cycle at subduction zones is key to 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. Globally, magma ponding depths may be partially controlled by melt volatile contents. Volatiles also affect the rate and extent of degassing during magma storage and decompression, influence magma rheology and therefore control eruption style. The style of eruptions in turn determines the injection height of environmentally sensitive gases into the atmosphere and the impact of explosive arc volcanism. In this overview we summarize recent advances regarding the role of volatiles during slab dehydration, melt generation in the mantle wedge, magmatic evolution in the overriding crust, eruption triggering, and the release of some magmatic volatiles from volcanic edifices into the Earth's atmosphere.In contrast to mid-ocean ridge magmatism, where upwelling and adiabatic decompression of the mantle is the primary cause of melt generation, subduction zone magmatism is triggered by the depression of the mantle solidus due to influx of volatiles (dominantly There is ongoing debate about the processes that form extractable melts of the hydrated mantle wedge. One model suggests that efficient melt extraction requires a degree of melting of the wedge so large that melts are generally extracted at or above the 1300 8C isotherm, that is, close to the anhydrous solidus (Kushiro 1987;Schmidt & Poli 1998). The advective flux of heat carried by this melt then perturbs the location of the anhydrous solidus upwards (England & Katz 2010b), and melts eventually penetrate the lithosphere and enter the crust by hydrofracture and dyking. Alternatively, melting is dominated by decompression in slab and mantle diapirs that may rise upwards through the wedge (Behn et al. 2011).Here, we address volatile cycling from the dehydration of the subducting slab to arc volcanic degassing into the atmosphere (Fig. 1). A product of subduction is the output of volatiles as volcanic gases; another is the sinking of the slab containing 'residual' volatiles into the deep mantle. Volcanic gases in arcs are rich in H 2 O, chlorine, bromine and iodine compared to gases at rift and ocean island settings, which directly reflects the influence of slab-derived fluids on primary melt compositions by guest on May 10, 2018 http://sp.lyellcollection.org/ Downloaded from (Pyle & Mather 2009;Kutterolf et al. 2013; Kendrick et al. 2014a, b). Arc magmas are in general far richer in sulphur than their oceanic counterparts, reflecting the higher oxygen fugacity characteristic of arc melts and their enhanced capacity to carry dissolved sulphate (Wallace & Edmonds 2011). There is little direct evidence that primary arc melts are inherently richer in CO 2 than ocean island basalts, although it has been suggested that deep and pe...

Magma-derived CO 2 emissions in the Tengchong volcanic field, SE Tibet: Implications for deep carbon cycle at intra-continent subduction zone

“…Mo et al, 2008;Niu et al, 2013;Zhu et al, 2015), post-collisional volcanism (Guo et al, 2006(Guo et al, , 2007(Guo et al, , 2013(Guo et al, , 2014a(Guo et al, , 2015a, subduction zone metamorphism (Kerrick and Connolly, 2001;Cook-Kollars et al, 2014) and modern hydrothermal activities (Guo et al, 2014b;Zhang et al, 2014Zhang et al, , 2016 release carbon. Additionally, chemical geodynamics of volatile recycling at mid-ocean ridge (MOR; Graham, 2002;Stagno et al, 2013;Burley and Katz, 2015;Kagoshima et al, 2015) and oceanic subduction zone (OSZ; Sano and Williams, 1996;Lee and Lackey, 2015;Kelemen and Manning, 2015;Zellmer et al, 2015) have been well established, while little attention has been paid to volatile recycling at continental subduction zone (CSZ) and continental collision zone (CCZ), which highlights the importance of investigating flux and origin of volatiles (e.g., CO 2 ) from continental subduction zone.…”

Discharge of deeply rooted fluids from submarine mud volcanism in the Taiwan accretionary prism

“…Such fluid circulation in the deep crustal region also leads to increasing the pore pressure and reactivity of minerals, modifying the rheological property and weakening the rock strength [1][2][3] . The discharge of deeply generated fluids into the bottom ocean further influences the distribution of biological communities and seawater chemistry 4,5 . Therefore, a systematic assessment of fluid origins and its intrinsic characteristics in subduction systems would facilitate the implementation of a quantitative framework for fluid cycling and budget.…”

Origin and evolution of volatiles in the Central Europe late Variscan granitoids, using the example of the Strzegom-Sobótka Massif, SW Poland

“…Some studies have been performed on concentrations of volatiles that depend on the composition of the magma (e.g., Shabani et al 2003;De De Vivo et al 2005;Wallace 2005;Teiber et al 2014;Zellmer et al 2015;Bao et al 2016). Unfortunately, this information is lacking in the Variscan granitoids.…”

“…Since previous researchers have proposed that limited magma mixing occurred in the SSM (Domańska-Siuda and Słaby 2003Słaby , 2004Słaby , 2005Domańska-Siuda 2007), the influence of volatiles from mafic melt is expected to be limited. Unfortunately, most research related to volatiles in magmatic systems have focused on volatiles in subduction zones (e.g., De De Vivo et al 2005, Wallace 2005, Zellmer et al 2015. The concentrations of halogens vary widely in mafic and intermediate melts.…”