5:15 PM - 7:15 PM
[SCG54-P10] High-pressure deformation experiments on chlorite-actinolite schist using a modified Griggs-type solid-medium apparatus
Keywords:Slow slip event, Subduction zone, Nomo metamorphic rocks, Chlorite-actinolite schist, deformation experiments
High-pressure deformation experiments on chlorite-actinolite schist using a modified Griggs-type solid-medium apparatus
Miyano Kusumoto, ken-ichi Hirauchi, and Keishi Okazaki
In warm subduction zones such as Nankai and Cascadia, deep slow earthquakes are known to occur along the shallow slab-mantle wedge interface (Obara, 2002). One of the key candidate lithologies constituting the slab-mantle wedge interface zone is serpentinite (antigoritized) mantle peridotites, and high-pressure deformation experiments on antigorite-rich rocks have been conducted (e.g., Burdette and Hirth, 2022). On the other hand, Nishiyama et al. (2023) conducted structural and geochemical analyses of a tectonic mélange (Mie mélange) in the Nishisonogi metamorphic rocks, revealing that the mélange consists of lenticular blocks derived from both the mantle wedge and subducting slab, enclosed in a metasomatically formed chlorite-actinolite schist (CAS) matrix. Since CAS is occasionally intensely schistosed, it may have acted as a localized shear zone within slab-mantle wedge interface zone. Therefore, understanding the frictional and viscous properties of CAS is essential for elucidating the physical mechanisms governing deep slow earthquakes. We therefore conducted high-pressure deformation experiments on CAS samples using a modified Griggs-type solid-medium apparatus.
The starting material was a CAS block collected from the Nomo metamorphic rocks in Kyusyu, southwestern Japan. The CAS block was crushed and sieved to a grain size of <53 μm. For the experiment, shear deformation was imposed on a thin layer (ca. 1 mm thick) of powdered CAS, which was sandwiched between two alumina pistons with oblique surfaces oriented 45° from the maximum compression axis. The deformation experiments were conducted at a temperature of 500°C, a confining pressure of 1 GPa, and axial displacement rates ranging from 0.05 to 1.5 μm/s. A preliminary experiment showed that the shear stress increased linearly prior to apparent yielding. After yielding, the sample reached a peak stress (μ = 0.40) at a shear strain (γ) of 1, and then strain weakened towards μ = 0.33 until the end of the experiment (γ = 4). The values for the velocity dependence (a − b) of μ, obtained from axial displacement rate steps from 0.15 μm/s to 0.05 μm/s, 0.15 μm/s, and 1.5 μm/s, were all positive, suggesting that CAS exhibits stable sliding at the shallow slab-mantle interface.
References: Obara, 2002, Science, 296, 1679-1681. Burdette and Hirth, 2022, J. Geophys. Res. Solid Earth, 127, 2022JB024260. Nishiyama et al., 2023, Lithos, 446-447, 107115.
Miyano Kusumoto, ken-ichi Hirauchi, and Keishi Okazaki
In warm subduction zones such as Nankai and Cascadia, deep slow earthquakes are known to occur along the shallow slab-mantle wedge interface (Obara, 2002). One of the key candidate lithologies constituting the slab-mantle wedge interface zone is serpentinite (antigoritized) mantle peridotites, and high-pressure deformation experiments on antigorite-rich rocks have been conducted (e.g., Burdette and Hirth, 2022). On the other hand, Nishiyama et al. (2023) conducted structural and geochemical analyses of a tectonic mélange (Mie mélange) in the Nishisonogi metamorphic rocks, revealing that the mélange consists of lenticular blocks derived from both the mantle wedge and subducting slab, enclosed in a metasomatically formed chlorite-actinolite schist (CAS) matrix. Since CAS is occasionally intensely schistosed, it may have acted as a localized shear zone within slab-mantle wedge interface zone. Therefore, understanding the frictional and viscous properties of CAS is essential for elucidating the physical mechanisms governing deep slow earthquakes. We therefore conducted high-pressure deformation experiments on CAS samples using a modified Griggs-type solid-medium apparatus.
The starting material was a CAS block collected from the Nomo metamorphic rocks in Kyusyu, southwestern Japan. The CAS block was crushed and sieved to a grain size of <53 μm. For the experiment, shear deformation was imposed on a thin layer (ca. 1 mm thick) of powdered CAS, which was sandwiched between two alumina pistons with oblique surfaces oriented 45° from the maximum compression axis. The deformation experiments were conducted at a temperature of 500°C, a confining pressure of 1 GPa, and axial displacement rates ranging from 0.05 to 1.5 μm/s. A preliminary experiment showed that the shear stress increased linearly prior to apparent yielding. After yielding, the sample reached a peak stress (μ = 0.40) at a shear strain (γ) of 1, and then strain weakened towards μ = 0.33 until the end of the experiment (γ = 4). The values for the velocity dependence (a − b) of μ, obtained from axial displacement rate steps from 0.15 μm/s to 0.05 μm/s, 0.15 μm/s, and 1.5 μm/s, were all positive, suggesting that CAS exhibits stable sliding at the shallow slab-mantle interface.
References: Obara, 2002, Science, 296, 1679-1681. Burdette and Hirth, 2022, J. Geophys. Res. Solid Earth, 127, 2022JB024260. Nishiyama et al., 2023, Lithos, 446-447, 107115.