Investigation of Olate Subduction Process Based on Continuous Precise Measurement of Fluid Ventings at the Southwestern Japan

深海流体喷口的精确位置位于日本本州西南部南海海槽向陆的趾部，该项目在KAIKO-NANKAI计划的支持下，揭示了其底部表达的详细形态。在1985年的KAIKO计划中已经提出了双壳类的共性。集中在通风口到目前为止，类似的证据已经在世界各地的其他地点发现，例如，在巴巴多斯和俄勒冈州。然而，目前的现场测量的底部温度梯度的结果首次表明，流体排放量达几米，每年只集中在双壳类社区。渗漏水中含有大量的甲烷和一定量的硫，不仅能为蛤类及其共生菌提供食物，而且在表层沉积物中富氧的孔隙水中氧化后还能生成碳酸钙。CaCO_3参与胶结周围沉积物，形成固化物， ...更多信息 在增生棱柱体变形前缘（约3800 m深）的通风带中，软表面沉积物下的艾德砂和粉砂。通过潜水电视和深拖电视确定了一些沉积物“烟囱”，并收集了一个样本并进行了化学分析。在这个流体排放点进行了长期的温度梯度和电位测量，以获得排放速率随时间变化的信息。另一方面，在前缘上方的背冲脊顶部（2000 m深），发现了大量的胶结沉积物（包括蛤壳）暴露在底部，并被海水侵蚀。这里还存在小型的双壳类Calyptogena群落，表明通过高角度逆冲断层发生了小规模的排气，但普遍的现象是在目前之前的某个时候堆积的固化沉积物的抬升。这一地区的原位观测结果可能与通过研究陆上出露的古地质构造推断出的海沟增生棱柱体的形成和发展过程相对应。少

Precise positions of deep-sea fluid ventings was located at the landward toe of the Nankai Trough south off southwestern Honshu, Japan and detailed morphology of its bottom expression was revealed by the effort of this project under aegis of KAIKO-NANKAI Program. t was already suggested by the past KAIKO Project in 1985 that commonity of bivalves Calyptogena. is concentrated upon the vent. So far similar evidences have been found at other sites over the world, for example, at Barbados and off Oregon. However, the present result of in situ measurement of bottom temperature gradient first indicated that the fluid venting amounting to a few meters per year is exclusively focused under the bivalve community. Seeping water contains much methane and some sulphur which not only feed clams and their coexistent bacteria but also generate calcium carbonates after oxidation in O_2-rich pore water in the superficial sediment. The CaCO_3 takes part in cementing surrounding sediment to form solidifi … More ed sand and silt under soft surface sediment in venting zones at the deformation front of the accretionary prism (about 3800m deep). A number of sediment "chimneys" were identified by both submersible and deep-towed TV and a sample was collected and chemically analyzed. At this fluid venting site long-term measurement of temperature gradient and electric potential was conducted to yield information on time variations in venting rates.On the other hand, much cemented sediment including clam shells is found exposed in the bottom and eroded by sea water at the crest of back-thrust ridge above the front (2000m deep). Small community of bivalves Calyptogena is also existent here showing occurrence of small-scale venting through the high-angle thrust fault but prevailing phenomenon is uplifting of solidified sediment accreted some while before present. It seems likely that in situ observation at this area corresponds to the process of origin and development of the trench accretionary prism deduced from study of the ancient geological formation exposed on land. Less