Pressure of postspinel transition

A revised adiabatic temperature profile for the mantle

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This study reevaluates the adiabatic temperature profile of the Earth's mantle. The global average temperature at the 410-km discontinuity is estimated to be 1839 (38) K by comparing the globally averaged depths of the 410-km discontinuity with the previously determined phase diagram of the olivine-wadsleyite transition in the system (Mg,Fe)2SiO4 at two temperatures. The temperature at the 410-km discontinuity is extrapolated to shallower and deeper regions using the adiabatic temperature gradient, which is estimated from the pressure-volume-temperature relations and heat capacities of the major mantle minerals, namely, olivine, wadselyite, ringwoodite, and bridgmanite. The experimental temperatures and pressures in the original studies used in these evaluations are recalculated using the recently proposed pressure correction on EMF of the W97Re3-W75Re25 thermocouple. The uncertainties are evaluated by the Monte Carlo simulation. The temperatures on the adiabatic temperature profile are found to be 1646 (35), 1994 (40), 1960 (40), and 2587 (60) K, respectively, at a 50-km depth, just above the 660-km discontinuity, just below the 660-km discontinuity, and at 2,800-km depth. The lower mantle temperatures in the current estimation are lower than those given by Katsura et al. (2010), https://doi.org/10.1016/j.pepi.2010.07.001. The 50-km depth temperature is slightly higher but generally agrees to that estimated from the melting of depleted peridotite.

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Adiabatic temperature profiles in the mantle. Red: The current study; violet: Katsura et al. (2010); blue: MgSiO₃ bridgmanite lower mantle by Wolf et al. (2015); green: Mg_0.87Fe_0.13SiO₃ bridgmanite lower mantle by Wolf et al. (2015); gray: Brown and Shankland (1981). The solid and dashed curves show the most probably and 68% confidence intervals, respectively.