17:15 〜 18:30
[SGL22-P02] Noble gas release and model fault experiment degassing during coseismic sliding: gabbroid vs granitoid for future comparison between oceanic and continental lithospheres
★招待講演
キーワード：アルゴン、断層、希ガス、地殻起源、ヘリウム
Noble gases very limitedly react with other elements because of their inert nature. Therefore, 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 went up to their closure temperat ures or higher.
We have reported the resetting of isotope signatures (changing from original rock ratio to atmospheric ratio) of noble gases released during rotary-shear high velocity friction experiment. In the experiment, on a granite samples from Aji area shikoku Iskand were shaped as cylinders and rotated at 1.6 m/s at a constant normal stress of 1.4 MPa. Friction increased with slip and reached maxim um value at 5 seconds ("first fuse"; Hirose et al, 2005) after the beginning of the slip. Completely melted glass formed by frictional heat was found only on the sliding surface. The most part of the post experiment specimen were little or not melted, which is possibly due to very short duration of the experiment. A rejuvinated age or age resetting of gabbroid was previously reported in Sato et al. (2009).
Under controlled gas environment of granitoid experiment, limited first fusion occurred at the first temperature maxima (correspond ing to th e displacement of M agnitude 2 ~ 3). Then, friction suddenly dropped down, and decreased gradually further in several seconds associated with moderate melting ("second fuse", corresponding to the displacement of the M agnitude 5 or larger; e.g. Kanamori et al ., 2005). Compared to the gabbroid, the experiment required special caution due to the fragile nature under shear stress in the experimental condition: because granitoid have over the 60% of silica, containing quartz minerals that undergo the phase transition to high pressure phase under pressure condition in the experiment.
Compared with gabbroid experiments, much Ar gas degassed at the "first fusion" of 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 Ar was clearly emitted after only 5 seconds sliding. Also the timing of melting depended on the atmospheres of the experiment; whether moist-air, dry-air, dry-He or Ar was used in the experiment regardless of abundantof hydrous minerals, such as biotite and/or 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 atmosatmosphere contributed from water content in the specimen. Furthermore, in the case that a sedimentary rock containing much higher potassium is in contact with a fault, emission of 40Ar may be faster and much intense during the fault motion. Thus, the liberation of volatiles believed to be detected in some large earthquakes may be controlled by ambient condition of the fault.
We have reported the resetting of isotope signatures (changing from original rock ratio to atmospheric ratio) of noble gases released during rotary-shear high velocity friction experiment. In the experiment, on a granite samples from Aji area shikoku Iskand were shaped as cylinders and rotated at 1.6 m/s at a constant normal stress of 1.4 MPa. Friction increased with slip and reached maxim um value at 5 seconds ("first fuse"; Hirose et al, 2005) after the beginning of the slip. Completely melted glass formed by frictional heat was found only on the sliding surface. The most part of the post experiment specimen were little or not melted, which is possibly due to very short duration of the experiment. A rejuvinated age or age resetting of gabbroid was previously reported in Sato et al. (2009).
Under controlled gas environment of granitoid experiment, limited first fusion occurred at the first temperature maxima (correspond ing to th e displacement of M agnitude 2 ~ 3). Then, friction suddenly dropped down, and decreased gradually further in several seconds associated with moderate melting ("second fuse", corresponding to the displacement of the M agnitude 5 or larger; e.g. Kanamori et al ., 2005). Compared to the gabbroid, the experiment required special caution due to the fragile nature under shear stress in the experimental condition: because granitoid have over the 60% of silica, containing quartz minerals that undergo the phase transition to high pressure phase under pressure condition in the experiment.
Compared with gabbroid experiments, much Ar gas degassed at the "first fusion" of 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 Ar was clearly emitted after only 5 seconds sliding. Also the timing of melting depended on the atmospheres of the experiment; whether moist-air, dry-air, dry-He or Ar was used in the experiment regardless of abundantof hydrous minerals, such as biotite and/or 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 atmosatmosphere contributed from water content in the specimen. Furthermore, in the case that a sedimentary rock containing much higher potassium is in contact with a fault, emission of 40Ar may be faster and much intense during the fault motion. Thus, the liberation of volatiles believed to be detected in some large earthquakes may be controlled by ambient condition of the fault.