IODP Drilling at the Godzilla Megamullion: The Nature of the Backarc Basin Lower Crust and Upper Mantle

A significant fraction of the ocean floor is created in back-arc basins, where water plays a major role generating basin basalts, contrasting strikingly with magmatic processes at mid-oceanic ridges. Furthermore, much our understanding all oceanic crust comes from ophiolites, which are largely attributed to supra-subduction zone environments. Therefore, studying lower and uppermost mantle arguably important, contributing overall geology crust. The Godzilla Megamullion, located extinct Parece Vela Basin Philippine Sea, largest known core complex. It an elongated massif distinct corrugated surface consisting several individual domal highs. records secular evolution melting beneath dying spreading ridge along length megamullion surface. strong heterogeneity P-wave velocity structure observed megamullion, normal crust-like distal (i.e., near breakaway) medial parts, shallow high-velocity body proximal termination) part. Megamullion should be best place world study architecture mantle, actual crust/mantle boundary through International Ocean Discovery Program (IODP). By locating three 400- 800 m-deep drill holes its length, key data obtained better understand constrain composition as well complexes. environment provides further unique opportunity explore life after extinction hydrothermal activity.