华北克拉通辽宁兴城玄武岩脉LA-ICP-MS U-Pb年龄及其地质意义

LA-ICP-MS ZIRCON U-Pb AGE OF BASALT DIKES IN XINGCHENG OF LIAONING,NORTH CHINA CRATON:Geologic Implications

华北克拉通中生代期间受古太平洋板块俯冲作用的影响,岩石圈发生大规模的减薄,导致其物理化学性质明显改变.揭示克拉通减薄的机制并约束克拉通破坏时限是地学界的重大科学问题.华北克拉通广泛发育中生代玄武岩,玄武岩作为岩浆作用的产物,所蕴含的年代学信息可以为岩石圈演化过程提供重要的时间约束.辽宁兴城地区位于华北克拉通的北缘,其内发育的太古宙—中新生代岩浆岩是研究华北克拉通破坏的理想对象.尽管前人对这些玄武岩做了大量的研究,但是对其结束时间仍然存在争论.本文选取兴城地区出露的玄武岩脉为研究对象,采用LA-ICP-MS锆石U-Pb年代学和金红石U-Pb年代学方法,探讨成岩年代学及其地质意义.锆石U-Pb定年结果表明,辽宁兴城玄武岩脉年龄为104.8±6.5Ma,而华北克拉通中生代岩石圈减薄的结束年龄也可推到105Ma左右.此年代学信息为早白垩世晚期华北克拉通大规模岩石圈减薄过程的时限提供了约束.

Affected by the subduction of Paleo-Pacific plate in Mesozoic,large-scale lithosphere thinning took place in North China Craton,leading to the significant changes of its physical and chemical properties.To reveal the mechanism of craton thinning and constrain the timing of craton destruction becomes a major scientific problem for geologists.The Mesozoic basalts are widely developed in North China Craton.As the product of magmatism,basalt contains geochronological information that can provide important timing constraint for lithosphere evolution.The Archean-Meso-Cenozoic magmatic rocks developed in Xingcheng area of Liaoning Province in the northern margin of North China Craton are ideal objects for studying the destruction of North China Craton.Although lots of research has been done on these basalts,their end time is still disputed.The Xingcheng basalt dike is selected as the research object,and LA-ICP-MS zircon U-Pb chronology and rutile U-Pb chronology are studied to discuss the diagenetic chronology and its geological significance.The zircon U-Pb dating results show that the age of Xingcheng basalt dike is 104.8±6.5 Ma,and the end age of Mesozoic lithosphere thinning in North China Craton can be inferred to about 105 Ma.The chronological information provides constraint on the timing of large-scale lithosphere thinning process in North China Craton in the late Early Cretaceous.