The southwest basin is a key to study the origin and development of the South China Sea（SCS）.We do not know much about its boundaries,geological history,and the formation of its sea floor because it has a complex an...The southwest basin is a key to study the origin and development of the South China Sea（SCS）.We do not know much about its boundaries,geological history,and the formation of its sea floor because it has a complex and highly re-gional structural background,notable sediment activity,and yet few floor rocks.Here a grano-diorite sample was collected from the southern margin of the southwest basin of the South China Sea.The results indicated that the 40Ar-39Ar ages of biotites in the sample are 110.3±0.5 Ma,suggesting that they were prod-ucts of magmatic intrusion during the Early Cretaceous period.The sample＇s geochemistry showed it had high SiO2,K2O,and Al2O3 but low TiO2 levels.Tectonic discriminant diagrams suggested that the sample might represent extrusion-related magmatism,either in an arc or forearc setting in the SCS area and that the sample mainly belonged to the syncollision type,whose formation was related to orogenies.The sample may be part of the main rock that made up the boundaries of rift system.The process of tension cracking was similar to the development of the Red Sea,in which the rifting and sagging occurred in the continental crust.The southwest basin may not be an original ocean,but a rift developed through finite extension on continental crust basement.The oceanic crust came into being when the width and depth of the rift valley reached a certain scale.The granodiorite sample we collected provides a means of determining the boundary of the southwest basin and the clues that may help researchers expand relevant models.It constitutes an important datum regarding the analysis of the formation and development of the SCS.展开更多
基金supported by the National Natural Science Foundation of China(Nos.40972079 and 41172015)the State Key Program of National Natural Science of China(No. 41030853)+3 种基金the National Program on Key Basic Research Project of China(No.2007CB411703)the State Key Laboratory of Biogeology and Environmental Geology of Ministry,China University of Geosciences(No.BGEGF200811)the Ministry of Land and Marine Oil and Gas Resources and Environmental Geology Laboratory Fund(No.MRE200912)the Education Department of Hebei Province(Nos.2009443, 2010248)
文摘The southwest basin is a key to study the origin and development of the South China Sea（SCS）.We do not know much about its boundaries,geological history,and the formation of its sea floor because it has a complex and highly re-gional structural background,notable sediment activity,and yet few floor rocks.Here a grano-diorite sample was collected from the southern margin of the southwest basin of the South China Sea.The results indicated that the 40Ar-39Ar ages of biotites in the sample are 110.3±0.5 Ma,suggesting that they were prod-ucts of magmatic intrusion during the Early Cretaceous period.The sample＇s geochemistry showed it had high SiO2,K2O,and Al2O3 but low TiO2 levels.Tectonic discriminant diagrams suggested that the sample might represent extrusion-related magmatism,either in an arc or forearc setting in the SCS area and that the sample mainly belonged to the syncollision type,whose formation was related to orogenies.The sample may be part of the main rock that made up the boundaries of rift system.The process of tension cracking was similar to the development of the Red Sea,in which the rifting and sagging occurred in the continental crust.The southwest basin may not be an original ocean,but a rift developed through finite extension on continental crust basement.The oceanic crust came into being when the width and depth of the rift valley reached a certain scale.The granodiorite sample we collected provides a means of determining the boundary of the southwest basin and the clues that may help researchers expand relevant models.It constitutes an important datum regarding the analysis of the formation and development of the SCS.
