Adiabatic temperature profile in the mantle, revisited

Temperature (T) is one of the essential parameters to understand the dynamics and evolution of the Earths interior. For this reason, Katsura et al. [2010] proposed an adiabatic T- profile in the mantle, which was obtained from a T-estimation at the 410-km discontinuity (D410) by comparing the D410 depth and the olivine-wadsleyite (Ol-Wd) transition pressure (POl-Wd) and the adiabatic T gradients calculated using P-V-T relations of major mantle minerals measured by multianvil in situ X-ray experiments. However, this profile was too steep due to miscalculation. Furthermore, since Nishihara et al. [2020] determined pressure effects on EMF of the W-Re thermocouple, T and P values obtained by multianvil in situ X-ray experiments have to be re-evaluated. For these reasons, this study recalculated the POl-Wd and adiabatic T gradients to propose a corrected adiabatic T-profile in the mantle. The errors in the current calculations were obtained using the bootstrap method. The corrected experimental Ts for determining the POl-Wd by Katsura et al. [2004] were 1962 and 1644 K instead of 1900 and 1600 K, respectively, which increase the POl-Wd by 0.3 and 0.2 GPa. The D410 depths were taken from Chambers et al. [2005] and Houser [2016], 409 and 410 km, respectively. These data lead to T at the D410 of 180518 K based on Stixrudes [1997] formalism. The P-V-T data of Ol, Wd, ringwoodite (Rw), and bridgmanite were recalculated from Katsura et al. [2004; 2009a; 2009b; 2009c] and Tange et al. [2012]. Fitting these data to the Mie-Gruneisen-Debye equation of state yielded the Gruneisen parameters () of 1.00(2), 1.36(6) 1.12(6), 1.34(6), and 1.57(4) and their volume exponents (q) of 2.6(4), 1.5(11), 2.9(7), and 1.6(4), respectively, for these minerals. Note that the q values of Wd and Rw cannot be obtained precisely due to their narrow stability fields. The T gradient in the lower mantle decreases from 9.0 to 4.3 K/GPa from 670 to 2400 km depth in this study, essentially identical to Wolf et al. [2015] (4.7 to 8.0 K/GPa). The obtained T profile gives the T at 50 km depth of 1617(16) K, generally agreeing with that given by a petrological study [Sarafian et al., 2017], 1593(10) K. That at 2400 km depth is 2440(30) K, which is 120 K lower and 60 K higher than those given by Katsura et al. [2010] and Wolf et al. [2015].