Abstract
The scientific research results of the Geological Survey of Japan (GSJ) from the five-year project of the Cross-ministerial Strategic Innovation Promotion Program (SIP), “Next-generation technology for ocean resources exploration” are summarized. GSJ has been involved in one of the four R&D themes, namely“ Scientific research on formation processes of ocean resources” in collaboration with the Japan Agency for Marine-earth Science and Technology (JAMSTEC) and Kyushu University. GSJ’s research focused mainly on (1) tectono-magmatic evolution of basement geology, petrogenesis of igneous rocks and the relationship between magmatism and ore-formation, and (2) determination of scientific indices for marine surveys, narrowing down the potential areas based on investigations of geochemical and physical properties of igneous rocks, sediments and sulfides, as part of the research on genesis of seafloor massive sulfide deposits in Okinawa Trough. For (1), it was observed that, based on petrological and geochemical investigations of igneous rocks, mantle-derived mafic magma ascended to shallower portions of the crust and extruded on the seafloor due to thinning by back-arc rifting. These magmatic products were hydrothermally altered while the periodical ascent of mafic magma induced hydrous partial melting of altered basaltic rocks and production of felsic magma. These processes reasonably explain composition of extrusive rocks and formation of ore-fluid. In (2), new geochemical survey method for detecting the ore-related features were proposed, based on studies of felsic igneous rocks (pumices) widely distributed in the hydrothermal field, and electrical properties of subsea rocks, including sulfides, which contribute to the upgrading of the electromagnetic survey method, were disclosed from recovered cores by D/V Chikyu cruises. These results would save the effort for the first stage of surveys by narrowing down the potential areas and contribute towards developing more efficient surveys by determining optimal spec and acquisition data for next-generation technology for ocean resources exploration.
