5:15 PM - 7:15 PM
[SMP28-P08] Phase mixing experiments for understanding physical processes at plate boundaries
Keywords:Phase mixing, Plate boundaries, Polycrestal, Deformation
The local softening of macroscopically hard lithospheres at plate boundaries is thought to be a key to understanding why plate tectonics occurs only on the Earth. To understand this, we conducted an experiment to determine the mixing process of different phases that leads to the formation of the soft structure.
In this experiment, two polycrystalline samples were used to simulate the upper mantle: one with 95 vol% forsterite and 5 vol% enstatite, and the other with 90.4 vol% forsterite and 9.6 vol% enstatite. Using a deformation tester, these two samples were stacked and pressed with a constant load of 1580 N, which corresponds to 90 MPa in the initial sample, against the sample at 1300°C to become Pure Shear. Electron microscopic observation of the area near the boundary of the samples after the experiment showed that enstatite accumulated along the grain boundary. This could be seen as a process of mixing of different phases.
Whereas the mixing already confirmed in the Simple Shear experiment with rotary shear tests showed olivine entering the pyroxene layer [Tasaka et al. 2017 JGR], the process in the present study is the opposite. The migration of Mg,O, which diffuses faster than Si, as considered in the previous study, can not explain the formation of enstatite near the grain boundary. I plan to present the discussion by adding considerations from the observation.
In this experiment, two polycrystalline samples were used to simulate the upper mantle: one with 95 vol% forsterite and 5 vol% enstatite, and the other with 90.4 vol% forsterite and 9.6 vol% enstatite. Using a deformation tester, these two samples were stacked and pressed with a constant load of 1580 N, which corresponds to 90 MPa in the initial sample, against the sample at 1300°C to become Pure Shear. Electron microscopic observation of the area near the boundary of the samples after the experiment showed that enstatite accumulated along the grain boundary. This could be seen as a process of mixing of different phases.
Whereas the mixing already confirmed in the Simple Shear experiment with rotary shear tests showed olivine entering the pyroxene layer [Tasaka et al. 2017 JGR], the process in the present study is the opposite. The migration of Mg,O, which diffuses faster than Si, as considered in the previous study, can not explain the formation of enstatite near the grain boundary. I plan to present the discussion by adding considerations from the observation.