Abstract

The Central Basin fault in the center of the West Philippine Basin was first discovered ∼50 yr ago. It is a 1000-km-long ridge oriented northwest to southeast and is cut by north-south–trending fracture zones. Hypotheses about the origin and development of the Central Basin fault have remained unresolved until recently. Submersible observations and SeaBeam surveys show that the Central Basin fault is a segmented spreading ridge having a morphology similar to that of a slow spreading ridge, with a nontransform offset, a nodal deep, and an inside corner high. The distance from the ridge versus the depth of the sea floor, the obliqueness of sets of small trough and ridge structures, and heat-flow values both of the crestal and off-axis areas of the Central Basin fault suggest that the fault is not a simple spreading center, but rather underwent multiple spreading episodes. The texture and chemistry of basalts obtained from the ridge suggest that the lavas were formed in a backarc basin setting. These data confirm that the Central Basin fault is a slow backarc spreading center that has a more complicated evolutionary history than previously realized.

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