Low Thermal Conductivity of Hydrous Phase D Leads to a Self‐Preservation Effect Within a Subducting Slab. Issue 6 (26th June 2022)

• Record Type: Journal Article
• Authors: Hsieh, Wen‐Pin; Marzotto, Enrico; Ishii, Takayuki; Dubrovinsky, Leonid; Aslandukova, Alena A.; Criniti, Giacomo; Tsao, Yi‐Chi; Lin, Chun‐Hung; Tsuchiya, Jun; Ohtani, Eiji
• Is Part Of: Journal of geophysical research. Volume 127:Issue 6(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-06-26
• Subjects: water cycle -- dense hydrous magnesium silicates -- thermal conductivity -- thermal evolution; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2022JB024556
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: 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 ∼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. Plain Language Summary: Subduction of the oceanic lithosphere brings water‐bearing (hydrous) minerals into the Earth's interior, which could critically influence the thermal evolution and geodynamics of a sinking slab and ambient mantle. Among the hydrous minerals, Phase D is a key phase that could carry large amounts of water from the mantle transition zone (MTZ) to the shallow lower mantle (∼1, 250 km depth). Here we showed that, compared to the subducting lithosphere and crustal materials, the (Al, Fe)‐bearing phase D has a relatively low thermal conductivity at the depths of the MTZ and shallow lower mantle. This might be due to the large amounts of water contained in Phase D (∼18 wt.%). The low thermal conductivity of Phase D hinders heat transport through a sinking slab, and thus protects the lithosphere from excessive dehydration. Such effect promotes the survival of hydrous phases to greater depth than previously expected. Key Points: We precisely measured the thermal conductivity of Al‐ and (Al, Fe)‐phase D at high pressure and wide range of temperature Thermal conductivity of (Al, Fe)‐phase D is relatively low, except across the spin transition where it suddenly peaks and varies by four folds Low thermal conductivity of hydrous minerals maintains cold temperatures in a sinking slab, deepening the stability fields of slab minerals