Deserpentinization in Subduction Zones as a Source of Oxidation in Arcs: a Reality Check

Abstract Previous studies have concluded that dehydration of serpentinites in subduction zones produces oxidizing fluids are the cause oxidized arc magmas. Here, observations natural samples and settings combined with thermodynamic models to explore some factors complicate interpretation form basis this conclusion. These include variability serpentinite protoliths, roles carbon sulfur evolution, serpentinization different tectonic settings, changes bulk compositions ultramafic rocks during serpentinization, fundamental differences between deserpentinization, absence precise geothermobarometers for rocks. The capacity serpentinite-derived oxidize sub-arc magma is also examined. can transport redox budget as carbon-, sulfur-, iron-bearing species. Iron- carbon-bearing species might be present sufficient concentrations deep within zones, but not viable transporters at temperatures antigorite breakdown, which largest proportion fluid released by dehydration. Sulfur-bearing carry significant budget, calculations using Deep Earth Water (DEW) model show these stable breakdown. However, oxygen fugacities ??FMQ + 3 (where FMQ refers fayalite–magnetite–quartz buffer, ?FMQ log fO2 – fO2, FMQ), close to, or above, hematite–magnetite buffer conditions interest, required stabilize sulfur-bearing Pseudosection indicate attained breakdown if starting sufficiently oxidized, further work assess metamorphic pressures temperatures, confirm relative positions mineral buffers relation speciation.