DI003-03
Revisiting the Effect of Phase Transitions on Layering of Mantle Convection

Monday, 7 December 2020: 17:38
Virtual
Juliane Dannberg, University of Florida, Department of Geological Sciences, Gainesville, FL, United States, Rene Gassmoeller, University of Florida, Department of Geological Sciences, Gainesville, United States, Carolina R Lithgow-Bertelloni, University of California Los Angeles, Los Angeles, CA, United States and Lars P Stixrude, University of California Los Angeles, Department of Earth, Planetary, and Space Sciences, Los Angeles, United States
Recorded Presentation
Abstract:
Phase transitions play an important role for the style of mantle convection. While observations and theory agree that a substantial fraction of subducted slabs and rising plumes can move through the whole mantle at present day conditions, this behavior may have been different throughout Earth’s history. Higher temperatures, such as in the early Earth, cause different phase transitions to be dominant, and also reduce mantle viscosity, favoring a more layered style of convection induced by phase transitions.

Consequently, it is important to accurately model the influence of phase transitions on mantle convection. However, existing numerical methods generally preclude modeling phase transitions that are only present in a particular range of pressures, temperatures or compositions, and they impose an artificial lower limit on the thickness of phase transitions. To overcome these limitations, we have developed a new numerical method. Specifically, we (1) include the full gradient and the time derivative of the density in the mass conservation equation instead of relying on a reference profile, and (2) solve the energy equation for entropy instead of temperature. We find this technique allows for consistent coupling between thermodynamic and geodynamic models and makes it possible to model realistic phase transitions with a wide range of properties and dynamic effects on mantle processes.

Using this new method, we investigate the effects of individual phase transitions in the Earth’s mantle with regard to their potential for layering mantle flow. We demonstrate that the thickness of the phase transition has a bigger influence on the style of convection than previously thought: With all other parameters being the same, a thin phase transition can induce fully layered convection where a broad phase transition would lead to whole-mantle convection. We apply our method to convection in the early Earth and show under which conditions layering could have occurred.

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