5:15 PM - 6:30 PM
[SIT16-P02] High-temperature deformation properties of Li-doped polycrystalline olivine
Keywords:mantle rheology, diffusion creep, upper mantle, olivine, water weakening
In order to understand the upper mantle flow, it is important to determine high-temperature deformation properties of major constituent minerals of the upper mantle such as olivine. Olivine is considered to contain water (H2O) up to 0.1 wt.% in the upper mantle. The deformation properties of hydrous olivine have been experimentally investigated, which have revealed that the viscosity is greatly reduced by the presence of water (Mei and Kohlstedt, 2000). At the same time, one study questions the existence of water weakening or proposes very small effect of water on olivine rheology based on Si self-diffusion experiments (Fei et al., 2013). Recently, Yabe and Hiraga (2020) showed significant weakening of polycrystalline olivine due to grain-boundary-disordering which begins from a certain temperature near solidus. They proposed the water weakening as a result of grain-boundary-disordering in which the starting temperature is lowered by the water.
In this study, we compare high-temperature deformation properties of lithium-doped and undoped olivine. We expected Lithium (Li+) to behave like water (H+), which helps to elucidate the mechanism of water weakening, even under 1 atm creep tests. Li-doped polycrystalline olivine (Mg2SiO4) with an average grain size of ~1 μm and porosity of <3.5 vol% was synthesized using vacuum sintering technique. This polycrystalline material was deformed at atmospheric pressure, temperatures of 843~996 ℃, and stresses of 5 ~200 MPa. We found that the material deformed with the same strain rate at the same stress and grain size but nearly 200°C lower temperature for the undoped olivine, which showed a dramatic effect of Li on olivine diffusion creep. We discuss the mechanism of Li effect on olivine rheology, which is expected to provide insight into water weakening.
In this study, we compare high-temperature deformation properties of lithium-doped and undoped olivine. We expected Lithium (Li+) to behave like water (H+), which helps to elucidate the mechanism of water weakening, even under 1 atm creep tests. Li-doped polycrystalline olivine (Mg2SiO4) with an average grain size of ~1 μm and porosity of <3.5 vol% was synthesized using vacuum sintering technique. This polycrystalline material was deformed at atmospheric pressure, temperatures of 843~996 ℃, and stresses of 5 ~200 MPa. We found that the material deformed with the same strain rate at the same stress and grain size but nearly 200°C lower temperature for the undoped olivine, which showed a dramatic effect of Li on olivine diffusion creep. We discuss the mechanism of Li effect on olivine rheology, which is expected to provide insight into water weakening.