Studying subduction zone fluid at shallow seismogenic depths is important to understand the nature of fault rocks at the updip limit of the seismogenic zone because fluid-rock interactions affect heat and mass transfer, and fault strength. In this study, we conducted detailed analyses of distribution of shear veins, and estimation of pressuretemperature conditions for shear vein formation for the Yokonami mélange, Shikoku, Southwest Japan, which is tectonic mélange zone in an on-land accretionary complex. We found a seismogenic fault at the upper boundary of the Yokonami mélange, indicating that the Yokonami mélange was active at seismogenic depth. The field-transect distribution of shear veins was examined. The frequency, the total and mean thicknesses of the shear veins were about 3.7 per meter, about 10 mm per meter, and about 3 mm per shear vein, respectively. Quartz within the shear veins shows elongate-blocky textures, suggesting precipitation from advective flow. The pressure and temperature conditions for shear vein formation were examined by fluid inclusion analysis, ranging 175-225°C and 143-215 MPa, respectively. The temperature is almost consistent with the paleotemperature determined from vitrinite reflectance, suggesting that the shear veins were formed at up to the maximum depth. The depth might be consistent with that where the seismogenic fault was formed. On the basis of the pressure and temperature conditions and the distribution of shear veins, we estimated the minimum volumetric ratio of fluid to host rocks, assuming that the shear veins had precipitated from advective flow. The estimated amount of fluid is about 106 m 3 per cubic meter of host rocks. The results suggest that a large amount of fluid migrates through mélange zones at shallow seismogenic depths. This fluid possibly originates from the dehydration of clay minerals from underthrusted sediments and an altered subducting slab.
The ZrC-coated UOz particle is a promising fuel for high-temperature gas-cooled reactors. Particle fuels with multiple layers of pyrolytic carbon and ZrC have been irradiation-tested to a maximum fast-neutron fluence exceeding 2 x 10B/m2 (E > 29 fJ). In-reactor fission-gas release measured at a burnup of 1.5 at.% was minimal. The failure fraction by postirradiation examination was null for all samples. The ZrC-coated particles at 4 at. % burnup were postirradiation heated to 2400"C/min without failure until after 6000 s at the maximum temperature. It was found that the ZrC layer could sustain a large strain at such high temperatures. The behavior is in strong contrast with that of Sic of standard Triso coating, which is brittle to very high temperatures.
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