Effect of Water on Lattice Thermal Conductivity of Ringwoodite and Its Implications for the Thermal Evolution of Descending Slabs

Abstract

The presence of water in minerals generally alters their physical properties. Ringwoodite is the most abundant phase in the lowermost mantle transition zone and can host up to 1.5–2 wt% water. We studied high‐pressure lattice thermal conductivity of dry and hydrous ringwoodite by combining diamond‐anvil cell experiments with ultrafast optics. The incorporation of 1.73 wt% water substantially reduces the ringwoodite thermal conductivity by more than 40% at mantle transition zone pressures. We further parameterized the ringwoodite thermal conductivity as a function of pressure and water content to explore the large‐scale consequences of a reduced thermal conductivity on a slab's thermal evolution. Using a simple 1‐D heat diffusion model, we showed that the presence of hydrous ringwoodite in the slab significantly delays decomposition of dense hydrous magnesium silicates, enabling them to reach the lower mantle. Our results impact the potential route and balance of water cycle in the lower mantle.

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

“…Note that for both Al-phase D and (Al,Fe)-phase D, the thermal conductivity in each measurement run (different crystal orientation) is similar to each other, suggesting that the effect of crystal orientation on their thermal conductivity is negligible. Furthermore, similar to the ferropericlase (W.-P. Hsieh et al, 2018) and δ-(Al,Fe)OOH (W.-P. Hsieh et al, 2020), we observed an enhanced impurity effect of iron in the low-spin Fe-bearing phase D, that is, compared to the high-spin state, the thermal conductivity of low-spin Fe-bearing phase D is much lower than that of the Fe-free phase D.…”

“…TDTR has been a well-established ultrafast optical pump-probe method that enables precise measurement of thermal conductivity at ambient and high pressures, see, for example, (Y.-Y. Chang et al, 2017;W.-P. Hsieh et al, 2018;W. P. Hsieh et al, 2020).…”

“…The thermal conductivity of subducting lithosphere is assumed to be that of dry olivine at 250-410 km (Y.-Y. Chang et al, 2017), dry ringwoodite at 410-660 km (Marzotto et al, 2020), and an aggregate with 80 vol% (Fe,Al)-bearing bridgmanite and 20 vol% ferropericlase at 660-1,250 km (W.-P. Hsieh et al, 2018), see Text S4 in Supporting Information S1 for details. The thermal conductivity of subducting oceanic crust is assumed to be that of an aggregate with 10 vol% pure stishovite that appears after 300 km depth (Text S4 in Supporting Information S1 and (W.-P. Hsieh et al, 2022)) and 90 vol% dry olivine and ringwoodite in the upper mantle and transition zone, respectively; in the lower mantle it is composed of 60 vol% (Fe,Al)-bearing bridgmanite, 20 vol% Fe-bearing new-hexagonalaluminous phase, and 20 vol% stishovite (Text S4 in Supporting Information S1 and (W.-P. Hsieh et al, 2022)).…”

Influence of water on the physical properties of olivine, wadsleyite, and ringwoodite

“…Laboratory measurements of sound wave velocities (compressional (V P ) and shear wave (V S ) velocity) of minerals at high P -T play a central role in enabling scientists to constrain the constitution, composition, and potential hydration state of the Earth's mantle via a comparison with the velocity profiles derived by seismological observations. The elastic properties of olivine, wadsleyite, and ringwoodite have been studied by using various techniques, including Brillouin spectroscopy (e.g., Sinogeikin et al, 2003), ultrasonic interferometry (e.g., Li, 2003;Higo et al, 2008;Li and Liebermann, 2014), resonant sphere technique (Mayama et al, 2005), and theoretical calculations (e.g., Núñez Valdez et al, 2012;Wang et al, 2019). However, most such measurements have been made at high/or room temperature and ambient pressure (Jackson et al, 2000;Jacobsen et al, 2004) or at high pressure and room temperature (Zha et al, 1996;Li et al, 1996;Li and Liebermann, 2000;Li, 2003;Darling et al, 2004;Jacobsen and Smyth, 2006;J.…”

Thermal conductivity of single-crystal brucite at high pressures with implications for thermal anomaly in the shallow lower mantle

“…Lattice thermal conductivity, the ability of a material to conduct heat, of minerals in the mantle and subducting slabs is crucial to control the thermal evolution and geodynamics in Earth's interior (Chang et al, 2017;Dalton et al, 2013;Deschamps and Hsieh, 2019;Hsieh et al, 2017;Hsieh et al, 2018;Hsieh et al, 2020;Marzotto et al, 2020). Recent studies suggested that a temperature anomaly within a subducting slab could be induced by large variations of thermal conductivity in the oceanic crust due to, for instance, the effect of hydration (Chang et al, 2017) or spin transition (Chao and Hsieh, 2019;Hsieh et al, 2020).…”