Morphologic evidence for reorientation of sea-floor spreading in the West Philippine Basin

Abstract

Long-range side-scan sonar mapping (Swathmap) on a track crossing the West Philippine Basin south of the Central Basin fault has shown linear abyssal hills that are parallel and subparallel to the extinct spreading center known as the Central Basin fault zone. Older hills–those farthest from the Central Basin fault–are parallel to the zone, whereas those near the zone are oriented parallel to structures within the zone. Early sea-floor spreading in the Philippine Basin was northeast-southwest. At about 54 m.y. B.P., spreading reoriented nearly north-south, possibly in response to the onset of the northward movement of Australia.