The Philippine Basin,surrounded by a series of oceanic trenches,is an independent deep ocean basin in the West Pacific Ocean.Its middle part is divided into three marginal sea sub-basins by the Kyushu-Palau and West Mariana Ridges,namely,the West Philippine Basin,the Shikoku and Parece Vela Basins and the Mariana Trough.This paper,through the analysis of the geomorphologic features and gravity and magnetic characteristics of the basin and identification of striped magnetic anomalies,suggests that the entire Philippine Basin developed magnetic lineation of oceanic nature,and therefore,the entire basin is of the nature of oceanic crust.The basin has developed a series of special geomorphic units with different shapes.The KPR runs through the entire Philippine Basin.From the view of geomorphologic features,the KPR is a discontinuous seamount chain (chain-shaped seamounts) and subduction beneath the Japanese Island arc at the Nankai Trough which is the natural boundary between the basin and the Japanese Island arc.At the positions of 25 N,24 N,23 N and 18 N,obvious discontinuity is shown,which belongs to natural topographic discontinuity.Therefore,the KPR is topographically discontinuous.
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