澜沧江杂岩带澜沧群浅变质岩系碎屑锆石LA-ICP-MS U-Pb年代学及其构造意义

发布时间：2018-06-28 11:06

本文选题：锆石U-Pb定年 + 浅变质岩系　；参考：《岩石学报》2017年09期

【摘要】：澜沧群出露于滇西"三江"地区的南段,其主要岩石由遭受低级变质作用改造的泥质岩和基性火山岩组成。这些岩石普遍经历了古特提斯洋的闭合以及随后的洋陆俯冲过程,是研究古特提斯洋俯冲-碰撞过程的重要窗口。但是有关澜沧群的形成时代、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多种争议。本文对澜沧群中3件石英岩和1件绢云母变质石英砂岩样品中分选出的碎屑锆石进行了阴极发光图像分析和LA-ICP-MS U-Pb年代学研究。澜沧群浅变质岩系碎屑锆石具有明显或弱的振荡环带和较高的Th/U比值,表明岩浆成因。年代学分析结果表明,4件浅变质岩石样品均得到了两组主要年龄峰值,分别为530Ma和930Ma、570Ma和915Ma、540Ma和960Ma、570Ma和910Ma。本次研究中碎屑锆石U-Pb年龄主要分布在570~530Ma和960~910Ma。其中,最年轻的碎屑锆石年龄峰值~530Ma,支持了前人认为澜沧群沉积时代为中奥陶纪(462~454Ma)的认识。本研究中澜沧群浅变质岩系碎屑锆石年龄分布特征表明源区可能主要为泛非期和罗迪尼亚超大陆聚合-裂解过程中形成的岩浆岩。碎屑锆石磨圆较好指示其经历了较长距离的搬运。澜沧群浅变质岩系碎屑锆石与羌塘、特提斯喜马拉雅和拉萨地体变沉积岩或地层中碎屑锆石具有相似的年龄分布特征,表明它们可能具有相似的源区。
[Abstract]:Lancang Group is located in the southern section of Sanjiang area in western Yunnan. Its main rocks are composed of shaly rock and basic volcanic rock which were transformed by low grade metamorphism. These rocks generally experienced the closure of the paleoTethys ocean and the subsequent oceanic subduction process, which is an important window to study the subduction-collision process of the paleoTethys ocean. However, there have been many controversies about the formation age, material source and tectonic background of Lancang Group for a long time. The clastic zircon from three quartzite samples and one sericite metamorphic quartz sandstone from Lancang Group have been studied by cathodoluminescence image analysis and LA-ICP-MS U-Pb chronology. The clastic zircon of the shallow metamorphic rock series of Lancang Group has obvious or weak oscillatory ring zone and high Th- / U ratio, which indicates the magma genesis. The results of geochronological analysis show that the four samples of shallow metamorphic rocks have two main age peaks of 530Ma and 930Ma-570Ma and 915Ma-540Ma and 960Ma-570Ma and 910Marespectively. The U-Pb ages of detrital zircon are mainly distributed at 570 Ma and 910 Ma. The youngest detrital zircon age peak value is 530 Ma, which supports the previous understanding that the Lancang Group sedimentary age is the Middle Ordovician (4622 ~ 454 Ma). The age distribution of zircon in the metamorphic rock series of Lancang group indicates that the source area may be mainly composed of magmatic rocks formed during the Pan-African period and during the process of polymerization-pyrolysis of the Lodinia supercontinent. Zircon grinding is a good indicator of its long distance transport. The clastic zircon of the metamorphic rock series of Lancang group has similar age distribution characteristics with that of terrane metamorphic sedimentary rocks or strata in Qiangtang, Tethys Himalayan and Lhasa terrane, indicating that they may have similar source regions.
【作者单位】：中国地质科学院地质研究所;
【基金】：国家重点研发计划项目(2016YFC0600310) 国家自然科学基金项目(41372069、41302039)联合资助
【分类号】：P588.3;P597.3

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