5:15 PM - 6:45 PM
[SCG44-P06] Continuous temperature change creep experiments to determine the temperature dependence of olivine grain boundary diffusion creep
Keywords:mantle, rheology, olivine
In the Earth's interior, the change from highly viscous lithosphere to less viscous asthenosphere is largely due to high temperatures. Therefore, in order to understand the temperature dependence of the viscosity of the mantle, we conducted an experiment to obtain the viscosity with high precision for each 1℃ and the activation energy, which is an index of the temperature dependence of the viscosity.
In this experiment, a polycrystalline sample consisting of 95 vol% forsterite and 5 vol% diopside was used as an analog of the upper mantle. A deformation apparatus was used to press the sample at a constant load, during which the temperature was gradually lowered from 1300℃ to 1200℃ and then raised again to 1300℃. The temperature was varied at 9 min/1℃ from 1300℃-1250℃ and 33 min/1℃ from 1250℃-1200℃, and the load of 461N equivalent to 20 MPa was applied from 1300℃-1226℃, and the load of 1062 N, equivalent to 40 MPa, was applied thereafter until the temperature returned to 1300℃. Temperature change and stroke displacement were measured during this period, and a linear fitting of the relationship between time and strain was performed over the range of 1℃ temperature change, and the rate of strain change was considered as the strain rate of the specimen per 1℃. The stress on the sample was determined by considering the load and the deformation of the sample during the test, and the viscosity was calculated from the stress and the strain rate. The inverse of the obtained viscosity was plotted in Arrhenius space, and the activation energy of 602 kJ/mol was obtained from its linear fitted slope.
Comparing this activation energy with previously reported values, we obtained a very large value compared to the activation energy for diffusion creep of olivine, which has been around 350 kJ/mol. Our results obtained this study is consistent with the results of recent studies on the transition of a grain boundary diffusion mechanism with high activation energy at high temperatures [Yabe & Hiraga 2020 JGR].
In this experiment, a polycrystalline sample consisting of 95 vol% forsterite and 5 vol% diopside was used as an analog of the upper mantle. A deformation apparatus was used to press the sample at a constant load, during which the temperature was gradually lowered from 1300℃ to 1200℃ and then raised again to 1300℃. The temperature was varied at 9 min/1℃ from 1300℃-1250℃ and 33 min/1℃ from 1250℃-1200℃, and the load of 461N equivalent to 20 MPa was applied from 1300℃-1226℃, and the load of 1062 N, equivalent to 40 MPa, was applied thereafter until the temperature returned to 1300℃. Temperature change and stroke displacement were measured during this period, and a linear fitting of the relationship between time and strain was performed over the range of 1℃ temperature change, and the rate of strain change was considered as the strain rate of the specimen per 1℃. The stress on the sample was determined by considering the load and the deformation of the sample during the test, and the viscosity was calculated from the stress and the strain rate. The inverse of the obtained viscosity was plotted in Arrhenius space, and the activation energy of 602 kJ/mol was obtained from its linear fitted slope.
Comparing this activation energy with previously reported values, we obtained a very large value compared to the activation energy for diffusion creep of olivine, which has been around 350 kJ/mol. Our results obtained this study is consistent with the results of recent studies on the transition of a grain boundary diffusion mechanism with high activation energy at high temperatures [Yabe & Hiraga 2020 JGR].