Sinking Event of the Gagua Ridge in the West Philippine Basin and the Formation Time of the Southwest Ryukyu Subduction Zone
Although the Gagua Ridge has a water depth of 1506-2880 m at present,a large number of coral and shallow-water microfossils revealed that it had been in a shallow water environment for a long time and has undergone a sinking event.The topographic map and seismic profiles show that,(1)the northern Gagua Ridge subducted into the Ryukyu tectonic zone,(2)the reef sediments developed on the northern ridge were subsequently buried under the Ryukyu Trench.According to a comprehensive analysis of the drilling core data from the Deep Sea Drilling Program(DSDP)in the West Philippine Sea,the sedimentary sequences above the buried reef in the trench probably developed in the Early Miocene to Quaternary period.This indicates that,(1)the Gagua Ridge began to sink from the Early Miocene and gradually moved away from the shallow water environment,(2)the growth of the organic reefs stopped after the Early Middle Miocene,(3)the organic reefs in the northern part of the ridge were covered by trench sediments.The above evidence shows that the Gagua Ridge,as a part of the Philippine Sea plate,participated in subduction of the Southwest Ryukyu Trench resulting in subsidence.Therefore,the sinking of the Gagua Ridge may have resulted from the subduction of the West Philippine Sea plate to the southwest Ryukyu tectonic belt.It is inferred that in the Early Miocene,the Gagua Ridge began to subduct into the Southwest Ryukyu tectonic belt and the Southwest Ryukyu subduction zone began to form simultaneously.The formation of the northern forearc basin of the Southwest Ryukyu subduction zone was influenced by the Gagua ridge subduction,and the forearc basin can be divided into two parts:the Nanao Basin and the Dongnanao Basin.The forearc basin was formed in the Early Middle Miocene.These geological processes revealed the sequential formation and interaction of tectonic units in the plate convergence zone.
Philippine Sea plateGagua RidgeSouthwest Ryukyu subduction beltformation time
万方数据
维普
