[M-IS18] Drilling Earth Science

[MIS18-15] Understanding of Oceanic Plate Hydration by drillings into plate bending-induced normal fault in incoming plate at off-Tohoku and the Horoman Peridotite complex

★Invited Papers

*Tomoaki Morishita¹ (1.School of Geoscience and Civil Engineering, College of Science and Technology, Kanazawa University)

Keywords:Hydration of Oceanic Plate, Drilling project into plate bending-induced fault at outerrise region, The first touch of water with the uppermost mantle in incoming plate

The oceanic plate has played an essential role in Earth’s water circulation. In the last two decades, it has generally accepted that hydration due to plate bending-induced normal faults (bend-faults) occurs in the region between trench and outer-rise region. The northwest Pacific (NW Pacific) region is one of the world oldest, thus coldest, and most studied oceanic plates, and is therefore a high priority region to study bend-fault hydration. Water circulation (deep penetration and deep upwelling) and hydration through bend-faults in the NW Pacific region is supported by results from extensive recent geophysical surveys. In order to deepen our understanding of bend-fault hydration processes and their effects on changing in physical properties in incoming oceanic plate in many subduction zones, such as the young-hot middle America and the old-cold northwest Pacific region. An International Oceanic Drilling proposal named Bending fault hydrology of the Old Incoming Plate (H-ODIN) for the northwest Pacific region is developed. Hydration of oceanic plate prior to subduction is also key to describing and quantifying water flux into the deep Earth. Mantle drilling project is aimed at obtaining the pristine material of the oceanic plate and can provide a reference for the less-altered oceanic plate. It should be emphasized that little is known about the onset of hydration of the uppermost mantle. In order to address this fundamental question, we are also developing a new on-land drilling project into a fresh peridotite body, the Horoman peridotite body, Hokkaido, Japan. In the presentation, we will introduce the main scientific objectives and drilling strategies of these drilling projects.