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冀磊,刘福来,王舫,孙载波. 2018. 滇西哀牢山岩群变沉积岩碎屑锆石LA-ICP-MS U-Pb年龄及其地质意义. 岩石学报, 34(5): 1503-1516
滇西哀牢山岩群变沉积岩碎屑锆石LA-ICP-MS U-Pb年龄及其地质意义
作者单位
冀磊 中国地质科学院地质研究所, 北京 100037 
刘福来 中国地质科学院地质研究所, 北京 100037 
王舫 中国地质科学院地质研究所, 北京 100037 
孙载波 云南省地质调查院, 昆明 650216 
基金项目:本文受国家自然科学基金项目(41372069、41772193)、博士后基金(2017M620853)和国家重点研发计划(2016YFC0600310)联合资助.
摘要:
      出露于扬子板块与印支板块之间的哀牢山岩群中包含大量副片麻岩、大理岩、云母片岩和石英岩等变沉积岩,这些岩石对研究扬子板块西南缘构造演化具有重要意义。但有关哀牢山岩群的沉积时代、物质来源以及形成的构造背景等一系列问题长期以来存在着较大争议。本文选取哀牢山岩群内石榴黑云斜长片麻岩、石榴夕线黑云斜长/二长片麻岩和大理岩4件变沉积岩进行了锆石阴极发光和LA-ICP-MS U-Pb年代学研究。哀牢山岩群碎屑锆石具有明显或弱的振荡环带和较高的Th/U比值,指示其岩浆成因。年代学分析结果表明石榴黑云斜长片麻岩记录始新世末-渐新世(36.3~25.0Ma)哀牢山岩群部分熔融-岩浆活动,其余3件变沉积岩碎屑锆石均得到550~450Ma与900~700Ma两组峰值,其中片麻岩与大理岩中最年轻的碎屑锆石峰值分别为452Ma、461Ma和458Ma,指示哀牢山岩群沉积时代应不早于中奥陶世,而非原先认为的古元古代。碎屑锆石年龄分布特征表明哀牢山岩群物源区包含扬子板块西缘新元古代花岗岩和印支板块内泛非期花岗岩,支持前人提出的哀牢山岩群沉积于古特提斯分支洋盆——金沙江-哀牢山-马江洋拉张过程中沉积的观点。
英文摘要:
      Meta-sedimentary rocks including paragneisses, marble, mica schist and quartzite are widely distributed within the Ailao Shan (ALS) Group, which separated the South China Block (SCB) from the Indochina Block. And it is significantly important to understanding the tectonic evolution of southwest margin of SCB. However, the depositional age, mineral source and tectonic evolution of the ALS Group are still in debate. In this paper, we present LA-ICP-MS zircon U-Pb dating results of garnet-biotite-plagioclase gneiss, garnet-sillimanite-biotite-plagioclase/monzonitic gneisses and dolomitic marble within the ALS Group. Zircons from these samples have high Th/U ratios and exhibit strongly or weakly oscillatory zoning, suggesting their magmatic origin. Zircons from garnet-biotite-plagioclase gneiss recorded intense partial melting-magmatic activity ages in Late-Eocene-Oligocene (36.3~25.0Ma). Inherited zircons from the rest of three samples yield two major age peaks clustered around 550~450Ma and 900~700Ma and the youngest age peaks are~452Ma,~461Ma and~458Ma, respectively. This result indicates that the ALS Group deposited later than Middle Ordovician rather than conventional considered Paleoproterozoic. Age distributions of detrital zircons provide evidence for their provenances derived from the Neoproterozoic granitic rocks in southwest margin of SCB and magmatic rocks of Pan-African event in Indochina Blocks, and support the view that the metasedimentary rocks in ALS Group was deposited during the extension of the Jinshajiang-ALS-Sone Ma Ocean (Paleo-Tethys Ocean branch).
关键词:哀牢山岩群  变沉积岩  碎屑锆石  锆石U-Pb年龄
投稿时间:2017-11-08  修订日期:2018-03-05
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