嫩江河漫滩沉积物碎屑锆石U-Pb年龄、Hf同位素组成及其地质意义  

Detrital Zircon U-Pb Age and Hf Isotopes and Their Geological Significance of the Nenjiang River Floodplain Sediments

作　　者：梁乾坤 陈岳龙[1] 王善辉 于洋 杨帆[1] LIANG Qiankun;CHEN Yuelong;WANG Shanhui;YU Yang;YANG Fan(School of Earth Sciences and Resources,China University of Geosciences(Beijing),Beijing 100083,China;No.3 Exploration Institute of Geology and Mineral Resources,Yantai,Shandong 264000,China)

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083 [2]山东省第三地质矿产勘查院,山东烟台264000

出　　处：《现代地质》2023年第3期529-546,共18页Geoscience

基　　金：国家自然科学基金项目(40973010)。

摘　　要：利用LA-(MC)-ICP-MS技术,对嫩江河漫滩沉积物碎屑锆石进行了U-Pb定年和Hf同位素组成分析研究。结果显示,293颗碎屑锆石多为岩浆成因锆石,其U-Pb年龄主要分为4组:2300~1746 Ma、363~331 Ma、316~260 Ma和252~86 Ma。中生代碎屑锆石占到全部数量的80.9%,说明该时期源区岩浆活动强烈。嫩江流域不同时代地层的相对出露面积不同:侏罗系—白垩系约占72%,石炭系—二叠系约占13%,三叠系约占8%,前寒武系约占5%,寒武系—志留系约占1%。结合Lu-Hf同位素分析结果进一步分析嫩江流域大陆地壳的形成与演化历史。嫩江流域大陆地壳主要以新生地壳的产生为主,1200~400 Ma时期是嫩江流域地壳强烈增生阶段,构成了现今地壳的98.8%,可能与古亚洲洋的发展与关闭等过程有关;400~100 Ma时期嫩江流域发生了壳内再循环的岩浆作用。依据前人公式计算了嫩江河漫滩沉积物源区不同时期大陆地壳的重熔/增生比例。中生代锆石重熔比例较低,含有约70%的新生物质。该现象与蒙古—鄂霍次克洋和古太平洋俯冲引起地幔物质的部分熔融有关。In this study,we conducted LA-(MC)-ICP-MS U-Pb dating and Hf isotope analysis on detrital zircons from the Nenjiang River floodplain sediments.The results show that the U-Pb ages of 293 detrital zircons can be divided into four major groups,i.e.,2,300-1,746 Ma,363-331 Ma,316-260 Ma,and 252-86 Ma.Mesozoic detrital zircons account for 80.9%of the total amount,indicating strong magmatism in the source region during this period.The relative outcrop size of strata(of different ages)is different in the basin:Jurassic-Cretaceous(~72%),Carboniferous-Permian(~13%),Triassic(~8%),Precambrian(~5%),and Cambrian-Silurian(~1%).The Hf isotope composition may reflect the formation and evolution of continental crust in the Nenjiang River catchment.Continental crust in the Nenjiang River basin is mainly produced by juvenile crust formation.The ca.1,200-400 Ma period likely represents a major continental growth event in NE China,which formed 98.8%crustal components of the present crust,which may be related to the Paleo-Asian Ocean development and subduction.During ca.400-100 Ma,the Nenjiang Basin may have experienced intense intra-continental crustal recycling.Furthermore,using the formula of recycling ratio,the remelting vs.juvenile crust ratios have been calculated.The Mesozoic zircon have a low remelting ratio and contain about 70%juvenile crust.This phenomenon is related to the partial melting of mantle material caused by subduction of the Mongol-Okhotsk Ocean and Paleo-Pacific Ocean.

关 键 词：嫩江 碎屑锆石 U-PB年龄 HF同位素 

分 类 号：P512.2[天文地球—地质学] P597