Origin and evolution of the West Philippine Basin: A new interpretation

Combined analyses of the magnetic lineations and seafloor structures of the West Philippine Basin show that it was formed by spreading from the Central Basin Spreading Center in two distinctly different spreading phases, before and after subduction was initiated along the Palau-Kyushu trend at ~ 45 Ma B.P. These episodes are recognized by differences in the strike of the magnetic lineations, spreading rates, density and strike of fracture zones, and basement relief. From 60-45 Ma B.P. spreading was NE-SW, relative to present orientations, at a half-rate of 44 mm/a. At about 45 Ma B.P. the spreading direction changed to a more N-S direction with a reconfiguration of the Central Basin Spreading Center into numerous, short E-W segments offset by closely spaced N-S transform faults. Spreading slowed to a half-rate of 18 mm/a, and ceased at 35 Ma B.P. Thus, the West Philippine Basin originated at 45 Ma B.P. by the trapping of normal ocean crust west of the initial subduction along the Palau-Kyushu trend. The 45-35 Ma B.P. period represents the dying phase of spreading on the Central Basin Spreading Center following isolation of the West Philippine Basin from the plate driving forces of the Pacific.