10:45 AM - 12:15 PM
[MGI30-P06] Three-dimensional spherical shell model of mantle convection with stress-history-dependent viscosity; toward a reproduction of plate tectonics
Mantle convection drives plate motion and affects the Earth's surface environment (for example, through water and carbon cycles). Understanding the characteristics and evolution of mantle convection with plate motion is one of the keys for understanding the evolution of the earth's interior and surface environment. We are developing a mantle convection model in three-dimensional spherical shell that can treat plate motion properly.
On the Earth, even if almost the same stress is applied, there are places where the plate is ruptured or is not ruptured. Once a plate has been rifted by strong stress in the past, the pieces of that plate do not immediately stick together and return to their original state even when the stress is reduced. In other words, the mechanical state of a plate is not determined only by instantaneous stress, but depends on stress history.
We have developed a model in a three-dimensional box with stress history dependent viscosity (Ogawa, 2003) and succeeded in capturing the characteristics of plate motion on the Earth, such as plate deformation that concentrates only at plate boundaries and long-term stable rigid body motion(Miyagoshi et al., 2020). The calculated surface heat flow decreases with a distance from a spreading center, or ridge, as observed for the Earth.
The plate motion in a rectangular box is, however, affected by the side walls of the box. Here, we extend the mantle convection model with stress-history-dependent viscosity to a three-dimensional spherical shell mantle. The key free parameters are the strength of the temperature dependence of the viscosity, and the ratio of viscosity at ruptured place compared to intact place.
In the models we have calculated so far, the viscosity ratio due to the temperature difference between the surface and the asthenosphere is up to about O(1E3), which is close to the actual Earth’s value. The lithosphere is divided into several pieces where strain rate is relatively small by shear bands where the low-temperature material in the surface layer subducts. However, in this calculation, the viscosity contrast between the “subduction zones” and the interiors of the lithospheric pieces is O(1E-2), and the pieces are still not “rigid”; the convection is still in a regime called the weak plate regime (Ogawa 2003). In this presentation, we present the progress of the calculation of this model.
On the Earth, even if almost the same stress is applied, there are places where the plate is ruptured or is not ruptured. Once a plate has been rifted by strong stress in the past, the pieces of that plate do not immediately stick together and return to their original state even when the stress is reduced. In other words, the mechanical state of a plate is not determined only by instantaneous stress, but depends on stress history.
We have developed a model in a three-dimensional box with stress history dependent viscosity (Ogawa, 2003) and succeeded in capturing the characteristics of plate motion on the Earth, such as plate deformation that concentrates only at plate boundaries and long-term stable rigid body motion(Miyagoshi et al., 2020). The calculated surface heat flow decreases with a distance from a spreading center, or ridge, as observed for the Earth.
The plate motion in a rectangular box is, however, affected by the side walls of the box. Here, we extend the mantle convection model with stress-history-dependent viscosity to a three-dimensional spherical shell mantle. The key free parameters are the strength of the temperature dependence of the viscosity, and the ratio of viscosity at ruptured place compared to intact place.
In the models we have calculated so far, the viscosity ratio due to the temperature difference between the surface and the asthenosphere is up to about O(1E3), which is close to the actual Earth’s value. The lithosphere is divided into several pieces where strain rate is relatively small by shear bands where the low-temperature material in the surface layer subducts. However, in this calculation, the viscosity contrast between the “subduction zones” and the interiors of the lithospheric pieces is O(1E-2), and the pieces are still not “rigid”; the convection is still in a regime called the weak plate regime (Ogawa 2003). In this presentation, we present the progress of the calculation of this model.