17:15 〜 18:45
[SGL17-P04] Noble gas release and age resetting or rejuvenating during coseismic faulting: Insights from high-velocity friction experiments on granite
キーワード：脱ガス、断層ガス、年代のリセット／年代若返り、摩擦溶融実験、アルゴン
Noble gases react very little with other elements because of their inert nature. Therefore, the isotope ratios of noble gases in certain minerals are believed to reflect well those of their ambient reservoirs when the temperatures of the minerals containing them increase to their closure temperatures or higher.
We have reported the resetting of isotope signatures (changing from the original rock ratio descending to atmospheric ratio) of noble gases released during rotary-shear high-velocity friction experiments. In the experiment, a pair of cylindrical granite samples from the Aji area of Kagawa prefecture were pressed together and sheared at a slip velocity of 1.6 m/s (corresponding to coseismic slip velocity) and a constant normal stress of 1.4 MPa. Friction increased with slip and reached a maximum value at <1 second ("first fuse" event; Hirose et al, 2005) after the beginning of the slip. Completely melted glass formed by frictional heat was found on the sliding surface. Most of the post-experiment specimens were little or not melted, possibly due to the very short time duration of the experiment. A rejuvenated age or age-resetting age of gabbroid was previously reported by Sato et al., 2009.
Under the controlled gas environment of the experiments on granite, limited first fusion occurred due to flash temperature at asperity contacts. Then, friction suddenly dropped and decreased gradually in several seconds associated with moderate melting. Compared to the experiments on gabbro, the experiment required special caution due to the fragile nature under shear stress in the experimental condition: because granitoids have over 60% silica, containing quartz minerals that undergo the phase transition to high-pressure phase under pressure conditions in the experiment.
Compared with the experiment’s gabbro, much Argon gas degassed at the "first fuse" of the granitoid experiment. It was caused by the abundant radiogenic 40Ar contained granite used, with an age of 77.2~ 87.1 Ma (Yuhara, 2008). All Argon was emitted after only 5 seconds of sliding. Also, the timing of melting depended on the atmospheric conditions of the experiment (e.g. moist air, dry air, dry Helium, or Argon), regardless of abundant hydrous minerals, such as biotite and muscovite. These results suggest that the dissipation of friction-induced heat depends on the mass numbers of the ambient gases controlled by the humidity of the experimental atmosphere contributed by water content in the specimen. Furthermore, if a sedimentary rock containing much higher potassium is in contact with the wall rock of a fault, the emission of 40Ar may be faster and much more intense during the fault motion. Thus, the liberation of volatiles believed to be detected in some large earthquakes (even if the 2024 Noto Earthquake) may be controlled by the atmospheric condition of the fault and rejuvenated original rock age.
We have reported the resetting of isotope signatures (changing from the original rock ratio descending to atmospheric ratio) of noble gases released during rotary-shear high-velocity friction experiments. In the experiment, a pair of cylindrical granite samples from the Aji area of Kagawa prefecture were pressed together and sheared at a slip velocity of 1.6 m/s (corresponding to coseismic slip velocity) and a constant normal stress of 1.4 MPa. Friction increased with slip and reached a maximum value at <1 second ("first fuse" event; Hirose et al, 2005) after the beginning of the slip. Completely melted glass formed by frictional heat was found on the sliding surface. Most of the post-experiment specimens were little or not melted, possibly due to the very short time duration of the experiment. A rejuvenated age or age-resetting age of gabbroid was previously reported by Sato et al., 2009.
Under the controlled gas environment of the experiments on granite, limited first fusion occurred due to flash temperature at asperity contacts. Then, friction suddenly dropped and decreased gradually in several seconds associated with moderate melting. Compared to the experiments on gabbro, the experiment required special caution due to the fragile nature under shear stress in the experimental condition: because granitoids have over 60% silica, containing quartz minerals that undergo the phase transition to high-pressure phase under pressure conditions in the experiment.
Compared with the experiment’s gabbro, much Argon gas degassed at the "first fuse" of the granitoid experiment. It was caused by the abundant radiogenic 40Ar contained granite used, with an age of 77.2~ 87.1 Ma (Yuhara, 2008). All Argon was emitted after only 5 seconds of sliding. Also, the timing of melting depended on the atmospheric conditions of the experiment (e.g. moist air, dry air, dry Helium, or Argon), regardless of abundant hydrous minerals, such as biotite and muscovite. These results suggest that the dissipation of friction-induced heat depends on the mass numbers of the ambient gases controlled by the humidity of the experimental atmosphere contributed by water content in the specimen. Furthermore, if a sedimentary rock containing much higher potassium is in contact with the wall rock of a fault, the emission of 40Ar may be faster and much more intense during the fault motion. Thus, the liberation of volatiles believed to be detected in some large earthquakes (even if the 2024 Noto Earthquake) may be controlled by the atmospheric condition of the fault and rejuvenated original rock age.