Mantle temperature
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Mantle Temperature: Insights from Recent Research
Adiabatic Temperature Profile in the Mantle
The adiabatic temperature profile of the Earth's mantle has been a subject of extensive research. Recent studies have provided revised estimates for the temperature at various depths. For instance, the temperature at the 410-km discontinuity is estimated to be around 1839 K, with temperatures at other depths such as 50 km, just above and below the 660-km discontinuity, and at 2800 km being 1646 K, 1994 K, 1960 K, and 2587 K, respectively . These findings are consistent with other studies that have recalculated the adiabatic temperature gradient using the thermal expansion coefficients of major mantle minerals, showing a gradual decrease in the gradient with increasing depth .
Temperature in the Lower Mantle
Estimating the temperature in the lower mantle involves utilizing experimental data on rock densities and seismic velocities. One study estimates the temperature at 1300 km depth to be around 2800 K, increasing linearly to 3300 K at 2800 km depth, with an average gradient of about 0.33 K/km . This linear increase is supported by other research, which also highlights the significant uncertainties due to variations in rock density and the equation of state at high pressures .
Mantle Transition Zone Temperature
The temperature distribution across the mantle transition zone, particularly between 350 km and 655 km depth, has been determined using high-pressure phase equilibria. The temperature at the base of the transition zone (655 km depth) is estimated to be about 1600°C, with temperatures increasing from about 1400°C to 1600°C over this depth interval . This steep temperature profile is attributed to phase transitions in mantle minerals such as olivine and wadsleyite.
Upper Mantle and Convective Geotherm
In the upper mantle, numerical computations indicate that the temperature rises rapidly to about 1000°C near a depth of 100 km and remains relatively constant until about 350 km . This is consistent with the convective geotherm determined from sub-mid-ocean ridge mantle potential temperatures, which are estimated to be around 1454°C . These temperatures are crucial for understanding mantle convection and the dynamics of tectonic plates.
Core-Mantle Boundary Temperature
The temperature at the core-mantle boundary (CMB) has been a challenging parameter to estimate accurately. Recent in situ detection methods have determined the anhydrous melting temperature at the CMB to be around 3430 K, which is approximately 700 K lower than previous estimates . This lower temperature suggests faster secular cooling and supports the basal magma ocean hypothesis.
Conclusion
The temperature profile of the Earth's mantle varies significantly with depth, influenced by phase transitions in mantle minerals and the adiabatic temperature gradient. Recent studies provide a more refined understanding of these temperatures, from the upper mantle to the core-mantle boundary. These insights are essential for comprehending the thermal and dynamic processes driving mantle convection and tectonic activity.
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