Topographic and geomorphological features and tectogenesis of the southern section of the Kyushu-Palau Ridge(KPR)and its adjacent areas

摘要

The Philippine Sea is the largest marginal sea in the Western Pacific Ocean and is divided into two parts by the Kyushu-Palau Ridge(KPR).The western part is the West Philippine Basin,and the eastern part consists of the Shikoku and Parece Vela basins.Based on surveyed data of massive high-resolution multibeam bathymetric data and sub-bottom profiles data collected from the southern section of the KPR from 2018 to 2021,this paper analyzes the topographic and geomorphological features,shallow sedimentary features,and tectonic genesis of the southern section of the KPR,obtaining the following conclusions.The southern section of the KPR has complex and rugged topography,with positive and negative topography alternatingly distributed and a maximum height difference of 4086 m.The slope of seamounts in this section generally exceeds 10°and is up to a maximum of 59°.All these contribute noticeably discontinuous topography.There are primarily nine geomorphological types in the southern section of the KPR,including seamounts,ridges,and intermontane valleys,etc.Among them,seven independent seamount groups are divided by five large troughs,forming an overall geomorphological pattern of seven abyssal seamount groups and five troughs.This reflects the geomorphological features of a deep oceanic ridge.Intramontane basins and intermontane valleys in the southern section of the KPR are covered by evenly thick sediments.In contrast,sediments in ridges and seamounts in this section are thin or even missing,with slumps developing locally.Therefore,the sediments are discontinuous and unevenly developed.The KPR formed under the control of tectonism such as volcanic activities and plate movements.In addition,exogenic forces such as underflow scouring and sedimentation also play a certain role in shaping seafloor landforms in the KPR.