Deformation of Post‐Spinel Under the Lower Mantle Conditions

To study the viscosity of bridgmanite and ferropericlase aggregate, uniaxial compression deformation experiments on pre-synthesized post-spinel phase and bridgmanite two-layered samples were conducted under top lower mantle pressure and 1773 K utilizing DT-Cup apparatus. Up to the strain of 0.25 ± 0.05, the observed comparable strain of the bridgmanite and post-spinel samples suggests the bridgmanite dominates the bulk viscosity of the post-spinel without strain localization in periclase. The microstructures of the deformed post-spinel samples show evidence of a similar strain of periclase with the bulk strain without strain partitioning. Texture analyses of bridgmanite indicate a dominant slip plane (100), with a steady state fabric strength achieved within the strain of 0.12 ± 0.01. The current experiment has provided no evidence about an onset of strain localization of ∼30 vol.% periclase at 0.25 strain. Our observations provide direct experimental verification of bridgmanite controlled rheology under low strain magnitude, which should be considered in geodynamical models which include mantle compositional and rheological evolution in the lower mantle.