Low Thermal Conductivity of Hydrous Phase D Leads to a Self-Preservation Effect Within a Subducting Slab

Earth's deep water cycle impacts the physical and chemical properties and geodynamics in its deep interior. However, how dense hydrous magnesium silicates (DHMSs) influence the thermal evolution and dynamics of sinking slabs remains poorly understood. We have precisely measured thermal conductivity of phase D, an important DHMS that could carry large amounts of water from the mantle transition zone to the lower mantle, at high pressure-temperature conditions. The thermal conductivity of (Al,Fe)-bearing phase D is lower than those of the pyrolitic mantle and basaltic crust along slab subduction, except for the depth range of similar to 800-1,100 km where a spin transition of iron occurs. Numerical simulations indicate that although the spin transition in phase D has minor effects on slab's temperature due to its small volume fraction, the poorly thermally-conductive hydrous minerals contribute to maintain a cold hydrous layer within a sinking slab, stabilizing slab hydrous minerals and promoting water transportation to the deeper mantle.

Automated summary

The deep water cycle of the Earth has a significant impact on its physical and chemical properties, as well as its geodynamics. This study focuses on the influence of dense hydrous magnesium silicates (DHMSs) on the thermal evolution and dynamics of sinking slabs. The research shows that the thermal conductivity of DHMSs is lower than that of other components along slab subduction, which contributes to the formation of a cold hydrous layer within sinking slabs, stabilizes hydrous minerals, and promotes water transportation to the deeper mantle.