西秦岭临潭地区隆务河组碎屑锆石U-Pb年龄、地球化学特征及沉积环境分析

以西秦岭造山带临潭地区早三叠世隆务河组碎屑岩为研究对象,进行LA-ICP-MS锆石UPb年代学研究,探讨其形成时代和源区,推断其沉积环境。所获得碎屑锆石年龄可划分为259~418Ma(16.8%)、448~474Ma(2.9%)、848~1115 Ma(2.9%)和1701~2672 Ma(77.4%)四组,最小年龄为259Ma,说明隆务河组沉积时代不早于晚二叠世。综合区域资料限定隆务河组沉积时代为早三叠世,物源总体来自隆务河盆地北侧新太古代-古元古代火山岩基底,包括华北板块、西秦岭造山带北缘、祁连造山带东段。结合地球化学及沉积相特征推断隆务河组砂岩主体形成于活动大陆边缘,为扩张阶段的弧后裂陷盆地。

U-Pb Age,Geochemical Characteristics and Sedimentary Environment Analysis of Detrital Zircons from the Longwuhe Formation in Lintan area,West Qinling

Taking the clastic rocks of the early Triassic Longwuhe Formation in Lintan area,West Qinling orogenic belt,as the research object,the LA-ICP-MS zircon U-Pb geochronology was carried out to explore its formation age and source,and to infer its sedimentary environment.The ages of the obtained detrital zircon can be divided into 4 groups:259—418 Ma(16.8%),448—474 Ma(2.9%),848—1115 Ma(2.9%)and 1701—2672 Ma(77.4%).The minimum age is 259 Ma,indicating that the sedimentary age of the Longwuhe Formation is not earlier than the Late Permian.The comprehensive regional data define the sedimentary age of the Longwuhe Formation as early Triassic.Sediment source is generally from Neo-archean-Paleoproterozoic volcanic basement in the northern side of the Longwuhe basin,including the North China Plate,the northern margin of the Western Qinling orogenic belt,and the eastern section of the Qilian orogenic belt.Combined with geochemical and sedimentary facies characteristics,it is concluded that the main body of the Longwuhe Formation sandstone formed in the active continental margin.The prototype of the basin should be the post-arc rift basin in the expansion stage.