Ophiolite Complexes are fragments of oceanic lithosphere emplaced on land. They are important because they provide evidence for the age and distribution of past oceans, information needed for making past plate reconstructions and understanding Earth evolution. In his talk, Julian Pearce will demonstrate the use of geochemical fingerprinting for identifying the type of ocean basin in which a given ophiolite complex originated. He will also present new results from the recent IODP Expedition (352) to the Bonin Trench, in which he was Co-Chief Scientist. This expedition drilled oceanic crust formed in the Eocene at the start of subduction in the Western Pacific. Drilling, for the first time, in situ oceanic crust from this subduction initiation setting provides the opportunity to resolve one of the major controversies surrounding the origin of many of the world’s major ophiolites, including the Troodos Massif of Cyprus and the Semail Nappe in Oman.