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- Title
A Revised Adiabatic Temperature Profile for the Mantle.
- Abstract
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. Plain Language Summary: This study estimates the temperature profile of the Earth's mantle by generally following the approach described in Katsura et al. (2010), https://doi.org/10.1016/j.pepi.2010.07.001. The estimation consists of two steps. First, the temperature at the 410‐km seismic discontinuity (D410), at which the seismic wave velocities abruptly increase almost everywhere in the mantle, is evaluated. The D410 is usually attributed to the olivine‐wadsleyite transition in peridotite. Comparing the globally averaged D410 depth with the phase diagram of the olivine‐wadsleyite transition yields a D410 temperature of 1839 (38) K. Second, this temperature is extrapolated to shallower and deeper regions by assuming that the heat is mainly transferred by convection in the mantle. The temperature gradient in such cases is the product of the thermal expansion coefficient and the temperature divided by the density and the heat capacity. The thermal expansion coefficients of the major mantle mineral are obtained by recalculating our previous experimental data. We found that the temperatures at 50‐km depth, the bottom of the mantle transition zone, the top of the lower mantle, and 2,800‐km depth are found to be 1646 (35), 1994 (40), 1960 (40), and 2587 (60) K, respectively. The 50‐km depth temperature is slightly higher but generally agrees to that estimated from the melting of depleted peridotite. Key Points: The previous olivine‐wadsleyite phase relations and P‐V‐T relations of mantle minerals are corrected using the pressure effect on electromotive forceComparing the 410‐km discontinuity depth with the olivine‐wadsleyite phase relations suggests 1839 (38) K at the discontinuityThe adiabatic temperatures are 1646 (35) at 50‐km depth and 2587 (60) K at 2,800‐km depth
- Subjects
EARTH'S mantle; INTERNAL structure of the Earth; EARTH temperature; TERRESTRIAL heat flow; HEAT transfer
- Publication
Journal of Geophysical Research. Solid Earth, 2022, Vol 127, Issue 2, p1
- ISSN
2169-9313
- Publication type
Article
- DOI
10.1029/2021JB023562