Subduction zone fluxes of halogens and noble gases in seafloor and forearc serpentinites

Abstract

Kendrick-11Dec'12.docx Click here to view linked References serpentinites trap noble gases and halogens that originate from seawater, diverse crustal lithologies and organic matter. Combined with previous analyses of metamorphosed serpentinites, the new data suggest that approximately 60-70% of the 36 Ar entering subduction zones in serpentinites is lost from chrysotile and/or antigorite and could potentially escape through the forearc. An additional, ~20-30 % of the 36 Ar entering subduction zones in serpentinites is lost during antigorite breakdown and may be cycled through the arc or back-arc, and ~1-10 % of the 36 Ar entering subduction zones in serpentinites may be subducted into the deeper mantle. The data demonstrate decoupling of noble gases, halogens and water during subduction and suggest that subduction-zone fluid fluxes may concentrate noble gases and iodine in newly formed forearc serpentinites. The distinctive I/Cl enrichment of forearc serpentinites suggest that halogen abundance ratios provide a plausible means for inferring the geotectonic setting of serpentinisation in ophiolite samples. The exceptional Cl, Br, I and noble gas concentrations of serpentinites, the potential subduction of the forearc serpentinites and the stability of serpentine minerals to mantle depths of >200 km, imply that serpentinites could dominate the deep recycling budgets of both the heavy halogens and atmospheric noble gases.

Fluid-related inclusions in Alpine high-pressure peridotite reveal trace element recycling during subduction-zone dehydration of serpentinized mantle (Cima di Gagnone, Swiss Alps)

“…It has been proposed that element extraction from such rocks is boosted by fluids released by serpentinite dehydration Kessel et al, 2005b;Spandler and Pirard, 2013). However, it is increasingly shown that serpentinites have the capacity to store volatiles and fluid-mobile elements sequestered during oceanic alteration, or during interaction with slab-fluids circulating in subduction-zone environments (Hattori and Guillot, 2003;Scambelluri et al, 2004a;Sharp and Barnes, 2004;Savov et al, 2005;Deschamps et al, 2011Deschamps et al, , 2013Kendrick et al, 2011Kendrick et al, , 2013John et al, 2011;Spandler et al, 2011;Alt et al, 2013;Evans et al, 2014;Bebout, 2014). Once stored in serpentinite, these elements are progressively released by the prograde dehydration reactions chrysotile ± lizardite + SiO 2,aq = antigorite + fluid,…”

Bromine and chlorine emissions from Plinian eruptions along the Central American Volcanic Arc: From source to atmosphere

“…Kendrick et al, 2014Kendrick et al, , 2013. However, the heterogeneity of subducted rocks requires the use of geochemical proxies for source identification prior to determination of regional mass budgets (e.g.…”

Origin of sub-lithospheric diamonds from the Juina-5 kimberlite (Brazil): constraints from carbon isotopes and inclusion compositions

“…Subduction of crustal material is responsible for providing the return flow of volatile species to the mantle from the Earth's surface environment (Hilton et al 2002;Dasgupta and Hirschmann 2010;Kendrick et al 2013). Experiments have demonstrated that hydrous materials undergo deserpentinisation and melting at sub-arc depths (2-6 GPa) causing the loss of the majority of the water stored in subducted material (e.g.…”