第七届青年地学论坛

Redox input by subducting slab into deep mantle is of vital importance for deep cycle and isotopic evolution of volatile elements, whose chemically stable forms are controlled by redox state. Lithospheric mantle is crucial in redefining redox state of the Earth’s deep mantle. To investigate how much oxygen is supplied from subducted slab, we investigate redox kinetics of olivine adopting diffusion couple methods at 1 GPa, 1373-1573 K using piston cylinder apparatus. It is found that redox process in olivine is diffusion-controlled, and diffusing on the order of 10^-12 m²/s at 1473 K. For oxidation process it is oxygen fugacity (fO₂)-independent and controlled by oxygen grain boundary diffusion with activation enthalpy of 235±56 kJ/mol. For reduction process, it is fO₂-dependent with an exponent of 2/5 and controlled by hydrogen diffusion related with Mg vacancy. The slow rate restricts homogenization of slab and results in rarely changed redox state of the upper mantle over past 3.5 Ga. A highly underestimated oxygen reservoir could have formed in the lower mantle.

redox kinetics, olivine, subducting slab, redox budget, the deep Earth