| 航海の目的 | Based on the results of three previous expeditions (206, 309, 312) and the subsequent IODP Proposal 522-Full5, this expedition aims to continue the mission to understand the accretion of oceanic crust formed at a superfast spreading rate at the East Pacific Rise. Previous drilling in Hole 1256D reached a total penetration of 1506 m, including 1250 m into the igneous crust. The hole passed through 345 m of sheeted dikes and continued 100 m into gabbroic rock. This new expedition will deepen Hole 1256D as far as possible into gabbro to complete coring and logging of an entire upper to mid-oceanic crustal section. The primary objectives are to (1) test models of mid-ocean ridge crustal accretion, (2) establish magmatic, hydrothermal, and tectonic processes and interactions, (3) determine the geological nature of layer 3 and the layer 2/3 boundary, and (4) constrain the magnetic contribution of the lower crust to marine magnetic anomalies. |
