title: Hydration-reduced lattice thermal conductivity of olivine in Earth's upper mantle.
abstract: Earth's water cycle enables the incorporation of water (hydration) in mantle minerals that can influence the physical properties of the mantle. Lattice thermal conductivity of mantle minerals is critical for controlling the temperature profile and dynamics of the mantle and subducting slabs. However, the effect of hydration on lattice thermal conductivity remains poorly understood and has often been assumed to be negligible. Here we have precisely measured the lattice thermal conductivity of hydrous San Carlos olivine (Mg0.9Fe0.1)2SiO4(Fo90) up to 15 gigapascals using an ultrafast optical pump-probe technique. The thermal conductivity of hydrous Fo90 with ∼7,000 wt ppm water is significantly suppressed at pressures above ∼5 gigapascals, and is approximately 2 times smaller than the nominally anhydrous Fo90 at mantle transition zone pressures, demonstrating the critical influence of hydration on the lattice thermal conductivity of olivine in this region. Modeling the thermal structure of a subducting slab with our results shows that the hydration-reduced thermal conductivity in hydrated oceanic crust further decreases the temperature at the cold, dry center of the subducting slab. Therefore, the olivine-wadsleyite transformation rate in the slab with hydrated oceanic crust is much slower than that with dry oceanic crust after the slab sinks into the transition zone, extending the metastable olivine to a greater depth. The hydration-reduced thermal conductivity could enable hydrous minerals to survive in deeper mantle and enhance water transportation to the transition zone.
authors.affiliation: Institute of Earth Sciences, Academia Sinica, Taipei 11529, Taiwan.
authors.forename: Yun-Yuan
authors.initials: YY
authors.lastname: Chang
authors.affiliation: Institute of Earth Sciences, Academia Sinica, Taipei 11529, Taiwan; wphsieh@earth.sinica.edu.tw.
authors.forename: Wen-Pin
authors.initials: WP
authors.lastname: Hsieh
authors.affiliation: Institute of Earth Sciences, Academia Sinica, Taipei 11529, Taiwan.
authors.forename: Eh
authors.initials: E
authors.lastname: Tan
authors.affiliation: Center for High Pressure Science and Technology Advanced Research, Changchun 130012, China.|Center for the Study of Matter at Extreme Conditions, Florida International University, Miami, FL 33911.
authors.forename: Jiuhua
authors.initials: J
authors.lastname: Chen
keywords: geodynamics; hydration; metastable olivine; subducting slab; thermal conductivity