摘要
前人对西藏拉萨地体则弄群的时代仍存在晚侏罗世与早白垩世的争议,且缺乏东西方向上的对比研究.对位于西段的狮泉河则弄群凝灰岩进行了系统的锆石U-Pb年代学、锆石微量元素和Hf同位素研究,完善了则弄群的年代学格架.狮泉河则弄群凝灰岩的锆石多为自形长柱状,发育明显的振荡环带,其微量元素特征显示为岩浆锆石.2件凝灰岩样品LA-ICP-MS锆石U-Pb测年结果显示其成岩年龄分别为157.5±0.9 Ma和159.2±1.3 Ma.结合前人研究成果,确定则弄群时代为晚侏罗-早白垩世.凝灰岩的锆石微量元素与Hf同位素特征表明其形成于大陆弧环境,源区可能由古老的陆壳基底与少量幔源物质混合形成.区域资料表明,Slainajap洋盆在东西延伸方向上俯冲起始时间不同,可能存在西早东晚的特征.
The formation age of the Zenong Group along the Shiquanhe-Yongzhu-Namucuo-Jiani mélange in the middle Lhasa terrane remains controversial between the Late Jurassic and the Early Cretaceous,and there is a lack of comparative study along the east-west direction.In this study,it focuses on the Zenong Group tuff from the Shiquanhe area in the western segment,and systematic analyses of zircon U-Pb age,trace element and Hf isotope for zircon were done for the tuff samples.Zircons from the tuff samples are elongated grains,showing obvious oscillatory zones,and the trace elements also verify the magmatic origin of zircons.Two tuff samples show LA-ICP-MS zircon U-Pb ages as 157.5±0.9 Ma and 159.2±1.3 Ma.Combined with previous research results,the Zenong Group was formed in the Late Jurassic to Early Cretaceous.Zircon trace elements and Hf isotopes of the tuff samples indicate that the Zenong Group were formed in the continental arc setting,and the hybrid of ancient continent crustal basement material and minor mantel material might be the magma source.Combined with the previous studies,the initial time of the subduction might vary from the earlier one in the western part to the later one in the eastern part.
作者
贺娟
王启宇
王保弟
段瑶瑶
He Juan;Wang Qiyu;Wang Baodi;Duan Yaoyao(Chengdu Center of China Geological Survey,Chengdu 610081,China;College of Earth Sciences and Engineering,Shandong University of Science and Technology,Qingdao 266590,China)
出处
《地球科学》
EI
CAS
CSCD
北大核心
2020年第8期2857-2867,共11页
Earth Science
基金
国家自然科学基金项目(No.41603038)
国家重点研究发展计划项目(No.2018YFC0604106)
中国地质调查局项目(No.DD20190053)。
作者简介
贺娟(1986-),女,博士,从事岩石学与岩石地球化学研究.ORCID:0000-0002-8141-711X,E-mail:hejuan7@yeah.net。
