Experimental study of thermal conductivity at high pressures: Implications for the deep Earth’s interior

Abstract

Lattice thermal conductivity of ferropericlase and radiative thermal conductivity of iron 18 bearing magnesium silicate perovskite (bridgmanite) -the major mineral of Earth's lower 19 mantle-has been measured at room temperature up to 30 and 46 GPa, respectively, using 20 time domain thermoreflectance and optical spectroscopy techniques in diamond anvil cells. 21 The results provide new constraints for the pressure dependencies of the thermal 22 conductivities of Fe bearing minerals. The lattice thermal conductivity of ferropericlase 23 Mg 0.9 Fe 0.1 O is 5.7(6) W/(m*K) at ambient conditions, which is almost 10 times smaller than 24 that of pure MgO; however, it increases with pressure much faster (6.1(7)%/GPa vs25 3.6(1)%/GPa). The radiative conductivity of Mg 0.94 Fe 0.06 SiO 3 bridgmanite single crystal 26 agrees with previously determined values for powder samples at ambient pressure; it is 27 almost pressure-independent in the investigated pressure range. Our results confirm the 28 reduced radiative conductivity scenario for the Earth's lower mantle, while the assessment 29 of the heat flow through the core-mantle boundary still requires in situ measurements at the 30 relevant pressure-temperature conditions.31

Reduced lattice thermal conductivity of Fe‐bearing bridgmanite in Earth's deep mantle

“…The thermal conductivity of bridgmanite as a function of is calculated using equation , with being given by equation . For the conductivity of ferropericlase, we used the data of Goncharov et al [] for Mg 0.9 Fe 0.1 O extrapolated at 120 GPa and assumed that it does not depend on the iron content, leading to Λ Fp = 76 W m −1 K −1 at room temperature. We further assumed that the temperature dependence of ferropericlase conductivity is similar to that of Fe‐bearing bridgmanite, with n = 0.5 in equation , leading to Λ Fp = 24 W m −1 K −1 at T = 3000 K. Note that variations in the volume fraction of bridgmanite, X Bm , induce changes in the aggregate thermal conductivity, Λ VRH , directly through equation , and indirectly by partially controlling the fractions of iron in bridgmanite and ferropericlase.…”

Reduced radiative conductivity of low spin FeO6-octahedra in FeCO3 at high pressure and temperature

“…2000-25000 cm −1 ) (Clark, 1957a(Clark, , 1957bHofmeister, 2004Hofmeister, , 2005Shankland et al, 1979;Fukao et al, 1968;Goncharov et al, 2008Goncharov et al, , 2009aGoncharov et al, , 2006Goncharov et al, , 2010Goncharov et al, , 2015Keppler and Smyth, 2005;Keppler et al, 2007Keppler et al, , 2008Thomas et al, 2012;Murakami et al, 2014) to allow using the room temperature absorption coefficient in the absence of high-temperature absorption data. Our results are at odds with this assumption because optical properties of Fe-bearing minerals appear sensitive to high temperature.…”

“…In the absence of spectroscopic data at simultaneous conditions of high pressure and temperature a common approach has been to use room temperature absorption coefficients to evaluate k rad values as a function of temperature (Keppler and Smyth, 2005;Goncharov et al, 2006Goncharov et al, , 2015Keppler et al, 2008;Murakami et al, 2014). Experimental measurements of minerals' optical properties at lower mantle pressure-temperature ( P -T ) conditions ( P > 24 GPa, T > 2000 K) are needed to test the validity of this traditional approach and to gain accurate values of thermal conductivity.…”

Synthesis of large and homogeneous single crystals of water-bearing minerals by slow cooling at deep-mantle pressures

“…We finally note that a part of the bridgmanite crystal products in the present study has been successfully applied for in situ radiative thermal conductivity measurements via optical absorption spectroscopy in a high-pressure diamond-anvil cell (Goncharov et al 2015). We are also planning to utilize these crystals for high-pressure studies of electronic spin and valence states of iron in the lower-mantle bridgmanite using synchrotron X-ray emission and Mössbauer spectroscopy, in addition to single-crystal elasticity measurements of iron-bearing bridgmanite in the lower mantle using impulsive stimulated light scattering and Brillion light scattering.…”

“…Finally, lower-mantle bridgmanite (silicate perovskite) crystals 100 to 600 μm in size were synthesized in normal water (H 2 O)-bearing growth environments. Although we were unable to grow these bridgmanite crystals into suitable sizes for TOF single-crystal diffraction, some proved to be ideal for use in advanced high-pressure-high-temperature X-ray and laser experiments (e.g., Goncharov et al 2015).…”