Grain-size-sensitive creep of olivine induced by oxidation of olivine in the Earth's deep upper mantle: Implications for weakening of the subduction interface

• Published in: Physics of the earth and planetary interiors Vol. 326; p. 106865
• Main Author: Ohuchi, T.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.05.2022
• Subjects: Decoupling; Grain boundary sliding; Olivine; Oxidation; Subduction zone; Trench-parallel flow; Olivine; Grain boundary sliding; Oxidation; Subduction zone; Decoupling; Trench-parallel flow
• ISSN: 0031-9201; 1872-7395
• DOI: 10.1016/j.pepi.2022.106865

Creep behavior of olivine has been studied at pressures of 9–16 GPa and temperatures of 960–1450 K, which is equivalent to the conditions in/around the slab subducted into the deep upper mantle, using a combination of synchrotron radiation and a deformation-DIA apparatus. At pressures above 12 GPa, the creep strength of olivine was primarily controlled by Peierls creep, and nucleation of wadsleyite caused softening by a contribution of grain-size-sensitive creep to deformation. Similarly, oxidation of deforming olivine caused a significant softening due to another grain-size-sensitive creep presumed to be dislocation-accommodated grain boundary sliding (dislGBS) of olivine with a low activation enthalpy (~260 kJ/mol) at pressures of 9–12 GPa. Extrapolation of the obtained flow law of dislGBS to mantle conditions predicts a formation of a weak layer along the slab-asthenosphere interface in the deep upper mantle. The viscosity contrast between the weak layer and the surrounding asthenosphere is estimated to be up to 3 orders of magnitude, resulting in a partial slab-asthenosphere decoupling in the deeper part of the subduction zones. The weak layer would allow for the occurrence of trench-parallel flow above/beneath the slab. [Display omitted] •Oxidation of olivine induced softening at pressures of 9–12 GPa.•This may result in a formation of a weak layer along the slab-asthenosphere interface in the deep upper mantle.•The weak layer may cause a partial slab-asthenosphere decoupling.•Olivine-wadsleyite transition induced softening at pressures of >12 GPa.•Deflection of cold slabs could be due to the softening induced by the olivine-wadsleyite transition.