UWA’s Alex Bandini-Maeder (Centre for Energy Geoscience, SEE) and an international group of geoscientists report the unexpected presence of fore-arc basalts (FABs) at the rear-arc side of the Izu-Bonin-Mariana (IBM) arc. This important discovery for the understanding of the tectonic subduction processes was published online in Nature Geoscience on August 24th, 2015.
Subduction initiation and subsequent arc inception are believed to be key mechanisms for the creation of continental crust. On board the JOIDES Resolution, International Ocean Discovery Program (IODP) Expedition 351 led by Richard Arculus (ANU), Osamu Ishizuka (Geological Survey of Japan), and Kara Bogus (IODP) targeted both the sediments and the magmatic crust forming the oceanic basement west of the northern Kyushu-Palau Ridge to unveil the nature of the original crust that existed in the region prior to the beginning of subduction.
A single site was investigated located south of Japan on the Philippine Sea Plate in the Amami Sankaku Basin at about 4,700 m water depth with the deeper core recovered from about 1,600 meters below the sea floor. To recover this deepest core the drill string was about 6,300 m long, which represented a significant technical challenge.
The research team found that the uppermost basement rocks are not mid-ocean ridge basalts (MORBs), but are very similar to FABs commonly found in the adjacent IBM fore-arc region erupted around 52 million years ago, when subduction of the Pacific plate beneath the Philippine Sea plate was initiated. This unexpected widespread distribution of FABs provide significant insights into the process of subduction initiation.