17:15 〜 18:45
[MIS22-P11] KH-23-4航海で採取された西南海トラフおよび琉球海溝北部の泥火山噴出物の空隙率
キーワード：泥火山、間隙率
Mud Volcanoes (MVs) are generally found at convergent plate margins and are one of the important systems that transport fluids and sediments from depths from several to a dozen kilometers below the earth’s surface. The distribution of MVs is uneven, with MVs not well distributed between off-Kumano and Hyuga-nada, whereas MVs are otherwise distributed along the Nankai Trough and Ryukyu Trench. In the case of MVs in the Kumano Basin, sediment is sampled from depths of 2.3-4.3 kilometers below the seafloor(kmbsf), while the original depth of sediment released from the MV off-Tanegashima is estimated to range between 3.2-3.4 kmbsf (Pape et al., 2014; Ijiri et al., 2023). However, there are no reported cases of mud volcanic ejecta in the Hyuga-nada, and only some MVs have been reported off-Tanegashima. In general, sediment porosity decreases with depth by compaction. Therefore, the porosity of the gravel in the erupted MVs deposits was measured, and the depth of origin of the MVs was estimated.
Samples were collected MV ejecta distributed from off-Kikaijima to the Hyuga-nada using piston cores, multiple cores, and okean grabs during the research cruise KH-23-4 by R/V Hakuhomaru in August 2023. The matrix of the samples composed of gray cohesive mud, interspersed with gravels. The gravels were mainly sedimentary rocks, with mudstones and fine-grained sandstones and pumice, and cemented melange-like rocks. The porosity of the gravels varied: sedimentary rocks had porosity ranging from 0.12 to 0.51, pumice showed porosity of 0.65, and melange had a porosity of 0.28, respectively. Due to nearby deep drilling examples such as off Kumano, when compared with IODP Site C0002, depths ranging from approximately 2-3 kmbsf correspond. This depth is consistent with the depth of origin of the sediments from off-Kumano and off-Tanegashima MVs previous results. Since the plate boundary in the Hyuga-nada area is about 10 and 18 kmbsf off-Tanegashima area, the sediments in both cases are anticipated to have originated from shallower areas than the plate boundary.
Samples were collected MV ejecta distributed from off-Kikaijima to the Hyuga-nada using piston cores, multiple cores, and okean grabs during the research cruise KH-23-4 by R/V Hakuhomaru in August 2023. The matrix of the samples composed of gray cohesive mud, interspersed with gravels. The gravels were mainly sedimentary rocks, with mudstones and fine-grained sandstones and pumice, and cemented melange-like rocks. The porosity of the gravels varied: sedimentary rocks had porosity ranging from 0.12 to 0.51, pumice showed porosity of 0.65, and melange had a porosity of 0.28, respectively. Due to nearby deep drilling examples such as off Kumano, when compared with IODP Site C0002, depths ranging from approximately 2-3 kmbsf correspond. This depth is consistent with the depth of origin of the sediments from off-Kumano and off-Tanegashima MVs previous results. Since the plate boundary in the Hyuga-nada area is about 10 and 18 kmbsf off-Tanegashima area, the sediments in both cases are anticipated to have originated from shallower areas than the plate boundary.