14:00 〜 14:15
[MGI31-07] IODP Exp.399 生命の構成要素： 蛇紋岩掘削における記録更新とその要因
キーワード：国際深海掘削計画、第399次航海、アトランティス岩体、蛇紋岩、海洋コアコンプレックス、ジョイデス・レゾリューション号
The Atlantis Massif, located 30 degrees North in the Central Atlantic Ridge, is an ocean core complex where gabbroic rocks and serpentinized peridotite from the lower oceanic crust to the uppermost mantle are exposed on the seafloor. Four previous expeditions (Exps. 304, 305, 340T, and 357) by the International Ocean Drilling Program (IODP) were conducted this massif. IODP Exp. 399 was (from April 12 to June 12, 2023) by D/V JOIDES Resolution at the Atlantis Massif with the scientific objectives of elucidating the formation process of the marine core complex, exploring the reaction process between the oceanic crust and upper mantle and seawater, to explore non-biological reactions between water and rock that may represent ancient systems that predate life on Earth, and to evaluate sub-seafloor life activity, and to recover rock core samples and fluid samples. The results of this study showed that the existing hole U13009D.
As a result, the existing hole U1309D was extended by 83m to reach 1498 mbsf, and gabbros recovered similar to that of cores from Exps. 304 and 305. Fluid was also successfully sampled from the hole. The temperature near the bottom of the hole is about 140 degrees C, which is almost consistent with the results of Exp. 340T measurements. At the serpentine site in the south part of the massif, a new hole (Hole U1601C) was drilled to 1267.8 mbsf, and it became the fifth deepest hard rock hole drilled in the IODP. Hole U1601C is composed of serpentinized peridotite with small amounts of gabbroic intrusions. Continuous borehole measurements of temperature, density, porosity, and seismic velocity were taken, and fluid samples were collected from multiple depths within the hole.
Future analysis of the core samples and data obtained from this drilling is expected to elucidate the structure of the oceanic lithosphere, the formation process of oceanic core complexes, the alteration process of oceanic crust, and the generation system of hydrogen and methane, which are essential energy sources for the subsurface biosphere. In addition, these two boreholes, both over 1000m in length, are expected to be used to observe changes in borehole temperature and fluid composition in the Atlantis Massif.
As a result, the existing hole U1309D was extended by 83m to reach 1498 mbsf, and gabbros recovered similar to that of cores from Exps. 304 and 305. Fluid was also successfully sampled from the hole. The temperature near the bottom of the hole is about 140 degrees C, which is almost consistent with the results of Exp. 340T measurements. At the serpentine site in the south part of the massif, a new hole (Hole U1601C) was drilled to 1267.8 mbsf, and it became the fifth deepest hard rock hole drilled in the IODP. Hole U1601C is composed of serpentinized peridotite with small amounts of gabbroic intrusions. Continuous borehole measurements of temperature, density, porosity, and seismic velocity were taken, and fluid samples were collected from multiple depths within the hole.
Future analysis of the core samples and data obtained from this drilling is expected to elucidate the structure of the oceanic lithosphere, the formation process of oceanic core complexes, the alteration process of oceanic crust, and the generation system of hydrogen and methane, which are essential energy sources for the subsurface biosphere. In addition, these two boreholes, both over 1000m in length, are expected to be used to observe changes in borehole temperature and fluid composition in the Atlantis Massif.