32 research outputs found
A Thermodynamic Model of the Water–Rock Interaction under Hydrothermal Exposure of the Bazhenov Formation
Geochemical structure of base-metal filling veins and parameters of hydrothermal ore formation
HCh: New potentialities for the thermodynamic simulation of geochemical systems offered by windows
Equilibriums between Cu, Fe, and Zn sulfides and oxides in chloride solution: A thermodynamic study
Hydrolysis and Complex Formation of Zr and Hf in Aqueous Solutions of HClO4, HCl, and NaOH in Equilibrium with Baddeleyite (Zr and Hf)O2(cr) at 250°C
Redox dynamics of subduction revealed by arsenic in serpentinite
International audienceRedox dynamics of subduction processes remain poorly constrained owing to the lack of direct geochemical tracers. We studied, using X-ray absorption spectroscopy, the chemical and redox state of arsenic in the Tso Morari serpentinites that are witnesses of the Himalayan subduction. Our measurements reveal remarkably contrasting redox speciation, from arsenide (As-III) to arsenite (As III) and arsenate (As V). Combined with physical-chemical constraints, these data enable reconstruction of the 'redox travel' of arsenic in the subduction process. Upon early serpentinisation of mantle peridotite, arsenic was scavenged from the fluid and dragged down as insoluble nickel arsenide. Partial deserpentinisation close to the peak metamorphism (550-650 °C) resulted in oxidative dissolution of arsenide to aqueous As III and As V and their non-specific intake by antigorite. The As V /As III ratios (∼0.1-10) analysed in the mineral are ∼10 4 times higher on average than predicted assuming bulk system thermodynamic equilibrium. These findings reflect a transient out-of-equilibrium release of highly oxidised fluids, with f O 2 reaching ∼10 log units above the fayalite-magnetite-quartz buffer (FMQþ10). Arsenic in serpentinite is thus a sensitive record of subduction redox dynamics inaccessible when using traditional equilibrium approaches applied to bulk fluid-mineral systems