Magnetic Anomalies in the Philippine Sea: Implications for Regional Tectonics

Marine magnetic anomalies are used to date the seafloor, characterize the oceanic crust, and reconstruct the evolutionary process of ocean basins. The Japanese continental shelf survey has collected high-quality, dense magnetic data from around Japan, which have increased our understanding of the tectonic history of the area. The Philippine Sea consists of volcanic arcs, paleoarcs, active, and inactive backarc basins and fragments of older arc and oceanic crusts. Clear magnetic lineation patterns in the basins reveal the seafloor spreading process of the backarc region. Magnetic anomalies associated with paleo-arcs provide us with information on the paleolatitude and/or rotation of the Philippine Sea Plate, as well as magmatism in the transitional phase from arc volcanism to backarc volcanism. Magnetic anomaly data are compiled for the Philippine Sea north of 15 degrees N collected during the continental shelf survey, and the tectonic interpretation is summarized on the basis of a new magnetic anomaly map reduced to the pole.