青藏高原北部巴颜喀拉山群火山岩锆石U-Pb年龄及其地质意义

应用激光烧蚀多接收器电感耦合等离子体质谱仪(LA-ICP-MS)方法,对青藏高原北部卡巴纽尔多地区巴颜喀拉山群碎屑岩系中酸性火山岩夹层岩样进行了锆石U-Pb年龄测定。结果表明,安山质凝灰熔岩(样品B4989-6)年龄加权平均值为(208.1±0.8)Ma,英安岩(样品B4989-3、B4983-1)年龄加权平均值分别为(206.1±1.2)Ma、(208.2±1.3)Ma,石英粗安岩(样品B4978-1)年龄加权平均值为(207.5±1.1)Ma,流纹岩(样品B4965-1)年龄加权平均值为(203.8±1.9)Ma,英安岩(样品B4959-2)年龄加权平均值为(205.1±1.8)Ma,说明该地区巴颜喀拉山群形成于晚三叠世晚期(瑞替期),而非前人认为的早-中三叠世。该套火山(碎屑)岩的测年结果为巴颜喀拉山群三叠纪复理石岩石地层单元的划分和对比提供了新证据。

Zircon U-Pb Ages for Volcanic Rocks in Bayan Har Group in the Northern Tibetan Plateau and Its Geological Significance

Using laser ablation multiple collector inductively coupled plasma mass spectrometry(LA-ICP-MS)method, the authors determined zircon U-Pb isotopes of the dacitic rock interlayers of Bayan Har Group in Kabaniuerduo area of northern Tibetan Plateau. The authors conducted dating of six samples and obtained ages of (208.1±0.8) Ma, (206.1±1.2) Ma,(208.2±1.3) Ma, (207.5±1.1) Ma, (203.8±1.9) Ma, and (205.1±1.8) Ma, respectively, precisely showing the Early Rhaetian age of the Late Triassic. These dating results of the volcanic rocks would benefit the stratigraphic classification and correlation of the Upper Triassic flysch within the Bayan Har Group and could provide evidence and age constraints for the collision and orogeny between blocks of Baryan Har block and Kunlun block.