Age and tectonic evolution of the northwest corner of the West Philippine Basin

To understand the tectonic characteristics and age of the northwestern part of the West Philippine Basin (WPB), multi-beam bathymetry and geomagnetic data have been collected and analyzed. The seafloor morphology obviously shows NW–SE trending seafloor fabrics and NE–SW trending fracture zones, indicating a NE–SW seafloor spreading direction. An overlapping spreading center near 22°20′N and 125°E is identified. Besides, numerous seamounts indicate an excess supply of magma during or after the oceanic crust formation. A V-shaped seamount chain near 21°52′N and 124°26′E indicates a southeastward magma propagation and also indicates the location of the seafloor spreading ridge. On the basis of the newly collected geomagnetic data, the magnetic anomaly shows NW–SE trending magnetic lineations. Both bathymetry and geomagnetic data reveal NE–SW seafloor spreading features between the Gagua Ridge and the Luzon Okinawa fracture zone (LOFZ). Our magnetic age modeling indicates that the age of the northwestern corner of the WPB west of the LOFZ is between 47.5 to 54 Ma (without including overlapping spreading center), which is linked to the first spreading phase of the WPB to the east of the LOFZ. In addition, the age of the Huatung Basin is identified to be between 33 to 42 Ma, which is similar to the second spreading phase of the WPB.