コンビーナ:田村 芳彦(海洋研究開発機構　海域地震火山部門)、石塚 治(産業技術総合研究所活断層火山研究部門)

The western portion of the Pacific Plate, the oldest oceanic plate in the world, has been drilled several times and, based on Ocean Drilling Program (ODP) Site 801, an understanding of its layers, from pelagic clay through chert to alkali basalts and tholeiitic mid-ocean ridge basalts (MORB), has been established. This oldest oceanic plate is experiencing a renaissance and we propose a strategy to drill the most suitable three sites to recover specific parts of the plate to continue its renaissance. This submitted IODP preproposal is entitled The Renaissance of the Oldest Oceanic Plate: REY (Rare Earth elements and Yttrium) rich Mud, Radiolarite of Jurassic-Cretaceous Boundary (JKB), and Jurassic Oceanic Crust without Moho. The drilling sites, MM, MAT, and MINA, target (1) the most complete sedimentary sequence of pelagic clay including REY-rich mud, (2) newly found outcrops of the Jurassic-Cretaceous boundary (JKB), and (3) MORB tholeiites without Moho, respectively. This session invite scientists who are interested in these exciting drillings.
It is common knowledge that the Moho is the boundary between the crust and the Earths mantle, discovered by and named after the Croatian seismologist Andrija Mohorovicic. The oceanic Moho is defined by seismic reflection images, but seismic profiles generally show that Moho reflections are not universal. Where the Moho can be detected clearly the crust is thicker. A good example is the profile from Kaneda et al. (2010) near Minami-Tori Shima, which is the main motivation for drilling at Site MINA. The session also seeks to explore the crust-mantle connections among ophiolites, at divergent and convergent plate boundaries and ocean island settings based on petrology, geochemistry, geophysics, geochronology, and geodynamics studies.