Creep behavior during the eutectoid transformation of albite: Implications for the slab deformation in the lower mantle

•We report changes of creep behavior during eutectoid transformation at high pressure.•Deformation and transformation processes were examined by in-situ X-ray observations.•EBSD analysis indicates that eutectoid colonies deform by dislocation creep at first.•Further deformation causes degeneration of the colonies and weakening by GSS creep.•Slab deformation in the lower mantle is possibly affected by these creep behaviors.

In order to investigate effects of the post-spinel transformation on rheological behavior of descending slabs, we conducted simultaneous deformation and eutectoid reaction experiments using an analogue reaction from albite to jadeite and quartz by a deformation-DIA apparatus. Flow stress and transformed fraction were quantitatively obtained by in-situ X-ray observations during the constant strain rate deformation. The microstructures of recovered samples as well as the flow and kinetic data suggest sequential variation of the creep mechanism from dislocation creep of the transformed eutectoid colony followed by the grain-size sensitive creep in the degenerated eutectoid structure. Our study demonstrated that the creep behavior during the eutectoid transformation involves various processes than previously thought. The slabs may not be weaken promptly after entering into the lower mantle when the size of eutectoid colony is enough large, and keep their strength (or harden) over a period of time depending on the degeneration kinetics of the colony.