HR: 1340h
AN: OS23A-1051    [Abstracts]
TI: The Microstructure of Nankai Trough Methane hydrate sediments by Scanning Electron Microscope
AU: * Suzuki, K
EM: tade-suzuki@aist.go.jp
AF: National Institute of Advanced Industrial Science and Technology (AIST), 17-2-1, Tsukisamu Higashi 2jyou, Toyohira-ku, Sapporo-city, Japan, 0628517, Japan
AU: NIshimura, O
EM: o-nishimura@aist.go.jp
AF: National Institute of Advanced Industrial Science and Technology (AIST), 17-2-1, Tsukisamu Higashi 2jyou, Toyohira-ku, Sapporo-city, Japan, 0628517, Japan
AU: Narita, H
EM: h.narita@aist.go.jp
AF: National Institute of Advanced Industrial Science and Technology (AIST), 17-2-1, Tsukisamu Higashi 2jyou, Toyohira-ku, Sapporo-city, Japan, 0628517, Japan
AB: The microstructure of Nankai Trough Methane hydrate sediments was observed by Field Emission Scanning Electron Microscope (FE-SEM; JEOL JSM7000F) with an energy dispersive X-ray detector (EDX-detector; JEOL JED2300F). The samples were obtained using Pressure-Temperature Core Sampler (PTCS) that can prevent hydrate dissociation during coring by keeping pressure insitu conditions. Sample that was taken by conventional tools for coring was kept shape by self-prevention nature itself, nevertheless many excellent observations had been reported. Therefore, it was expected that the PTCS core sample was suitable for observing microstructure of methane hydrate occupied in sediments, even though samples were exposed to atmosphere very short time on vessel before storage in liquid nitrogen. In addition, a low-vacuum system and a cryostat sample stage was installed in FE-SEM for observing methane hydrate bearing sediments. The former can make observation until sample chamber pressure is less than 30Pa, and the latter can control temperature from room temperature to 80K. Each sample was trimmed using cryo- system (Gatan Alto2500) at liquid nitrogen temperature and was settled on cryostat sample stage for observation. To compare with images before and after methane hydrate dissociation at the same region, we had made the freezed-dried sample within chamber of FE-SEM under controlling temperature of cryostat sample stage. Sample had been kept observing during drying by a low-vacuum system's work so as to confirm no breakage had been occur. Result of observation, the following were described as microstructural feature of Nankai Trough Methane hydrate bearing sediments, which had been freezed and dried, (1) There are a number of pyrite crystals existing among sand grains, which crystal size are less than 1 micron. (2) Framboidal pyrite can be seen among sand grains. (3) many vacant space can be seen among sand grains ; there are no pyrite and no clay minerals. (4)Pyrite and clay minerals make thin membrane structure around the vacant space. The space occupied by methane hydrate must be blank when hydrate dissociation occur without disturbing microstructure of sediments. This estimation is supported by EDX analysis that carbon detected regions would become vacant spaces by drying. Thus, we concluded that the methane hydrate exists in the vacant space of pore space and is covered with pyrite and clay minerals. These results will become help to understand methane hydrate formation processes in sediments.
DE: 3004 Gas and hydrate systems
DE: 3022 Marine sediments: processes and transport
DE: 3625 Petrography, microstructures, and textures
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting