The origin and tectonic history of the Southwest Philippine Sea

Abstract

This thesis is a collection and analysis of seafloor magnetic anomalies, bathymetry, and the paleomagnetism of DSDP sediments and basalt in the West Philippine Basin, in an attempt to resolve questions about its origin as a marginal basin. Our results suggest that this basin was formed in an Eocene pulse of rapid spreading (v1/2 = 41-44 mm/yr) in a direction (N 21°E) significantly different from later pulses which opened the more eastern basins of the Philippine Sea. The Central Basin Fault appears to be intimately associated with this spreading by nature of its structure and trend, and it may be a remanent of a former ridge system. Our preliminary calculation of paleopole positions also suggests that there was a large amount (60°) of clockwise rotation between this basin and the magnetic pole. This is consistent with rotations of the Pacific plate with respect to the magnetic pole and current directions of Philippine- Pacific'relative rotations. Basement depths of 6 km in the West philippine Basin imply that its crustal and/or lithospheric structure is different from Pacific structure of the same age.