HR: 1340h
AN: T13B-0467    [Abstracts]
TI: Distribution of Fluid Conduit and Estimation of Fluid Volume Along Subduction Interface, the Yokonami Melange, the Cretaceous Shimanto Belt, Shikoku, Southwest Japan
AU: Kikuchi, T
EM: kikuchi@geo.kankyo.tohoku.ac.jp
AF: Tohoku University, AzaAoba 6-6-20, Aramaki, Aobaku, Sendai, 9808579 Japan
AU: Yoshimitsu, T
EM: tossy_bikenotabi@ybb.ne.jp
AF: Kochi University, Akebonocyo 2-5-1, kochi, 7808520 Japan
AU: * Hashimoto, Y
EM: hassy@cc.kochi-u.ac.jp
AF: Kochi University, Akebonocyo 2-5-1, kochi, 7808520 Japan
AB: The rapid deformation and fluid expulsion occur along subduction interface. We examined distribution of fluid conduit and fluid volume along subduction interface in the Yokonami melange, the northern Shimanto Belt, the Cretaceous accretionary complex on land. The Yokonami melange is the tectonic melange zone in the northern Shimanto Belt, Shikoku, Southwest Japan, which is the Cretaceous accretionary complex on land. This area is considered to be a fossil rocks of subduction interface around seismic front on the basis of systematic deformation and P-T conditions. In Yokonami melange, lithology is composed mainly of sandstone and shale with minor hemiperagic shale, limestone, chert and basalt. Those rocks represent ocean floor stratigraphy repeated twice in the study area. In each ocean floor stratigraphy, two overturned facing of sediment are recognized, which suggest that the study area represents fold and thrust zone. Mineral veins are observed almost parallel to the foliations. Mineral veins are comprised by quartz and calcite. We investigated the vein thickness and frequency in each 1m and examined the distribution of mineral veins. Mineral veins concentrate in the overturned axes of facing, not in the thrust boundary. The mean of thickness of total outcrops was 13.33mm/m. Under the assumption that the mineral veins are as a board in 1 m³, the volume of mineral veins is 0.00137 m³ within each 1 m³ of host rocks. The P-T condition of the mineral veins formation represents about 200°C and about 160MPa estimated from fluid inclusion analysis corresponding with about 5-6km depth below sea floor. Using the vein volume and the P-T condition of mineral vein formation, we can estimate the minimum fluid volume to dissolve the quartz and calcite. The estimated volume is 150 times as much volume as host rock volume. This result suggests that the so large amount of fluid concentrate in this zone may be from outside of subduction plate boundary or more deeper portion along subduction interface. This volume is, however, integrated by time in the complex history of fluid migration in the study area.
DE: 1043 Fluid and melt inclusion geochemistry
DE: 3652 Pressure-temperature-time paths
DE: 3653 Fluid flow
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: Fall Meeting 2005