西天山伊犁地块早古生代拼贴:来自碎屑锆石U-Pb年代学和Hf同位素的制约  

Early Paleozoic Amalgamation of the Yili Block(Chinese West Tianshan):Insight from Detrital Zircon U-Pb Geochronology and Hf Isotopes

作　　者：黄惠明 李鹏飞 胡万万[1,2,3] 令佳琪 HUANG Huiming;LI Pengfei;HU Wanwan;LING Jiaqi(State Key Laboratory of Isotope Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,Guangdong,China;Center for Excellence in Deep Earth Science,Chinese Academy of Sciences,Guangzhou 510640,Guangdong,China;University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院广州地球化学研究所,同位素地球化学国家重点实验室,广东广州510640 [2]中国科学院深地科学卓越创新中心,广东广州510640 [3]中国科学院大学,北京100049

出　　处：《大地构造与成矿学》2021年第4期786-804,共19页Geotectonica et Metallogenia

基　　金：中国科学院国际合作项目(132744KYSB20200001);国家自然科学基金(41872222);广东省项目(2019QN01H101)联合资助。

摘　　要：西天山伊犁地块记录着中亚造山带构造演化方面的关键信息,前人多认为伊犁地块是一个单独块体,但其西延境外部分对应着多个块体。这些块体在奥陶纪末期完成拼贴,它们之间的缝合带在西天山的延伸部分被晚古生代‒中新生代地层覆盖,但通过境内外地质对比,认为其很可能沿着伊犁地块中部向东延伸,并将伊犁地块划分为南、北伊犁两个块体。目前,对于南、北伊犁地块的拼贴时限缺少精确限定,其是否类似于境外部分于奥陶纪末期完成拼贴仍不清楚。为此,本项研究选取北伊犁地块志留系库茹尔组为研究对象,通过开展碎屑锆石U-Pb年代学和Hf同位素分析,约束南、北伊犁两个块体的拼贴时限。结果显示,库茹尔组碎屑锆石U-Pb年龄主要集中在早古生代(422~519 Ma),其最年轻峰值432 Ma约束了库茹尔组的最大沉积时代。在对比南北伊犁地块岩浆活动的基础上,发现库茹尔组沉积地层同时接收到了南北伊犁地块的物源供给,表明南北伊犁地块已在库茹尔组沉积前完成拼贴。通过综合解析碎屑锆石及区域岩浆岩锆石Hf同位素数据,发现其在奥陶纪末期同时向富集和亏损的方向演化,与显生宙以来东亚多块体拼贴过程中的Hf同位素演化趋势相似,因而我们将这种ε_(Hf)(t)值扇形演化样式归因于南北伊犁地块的碰撞拼贴,进而约束伊犁地块的拼贴时限在奥陶纪末期。The Yili Block in the Chinese West Tianshan records key information for the tectonic evolution of the southwestern Central Asian Orogenic Belt(CAOB).Traditionally,the Yili Block is considered as a discrete block.It extends farther west into Kazakhstan/Kyrgyzstan,and is correlated to multiple blocks bounded by a series of sutures.The spatial extension of these sutures within the Yili Block in the Chinese West Tianshan is concealed by late Paleozoic to Cenozoic sedimentary and volcanic rocks.Based on the regional geological correlation,these sutures are considered to merge in the China/Kazakhstan border,and extend eastward along the central Yili Block,and separate the Yili Block into two subunits of northern and southern Yili blocks.In this contribution,we report detrital zircon U-Pb and Hf isotope results of sedimentary rocks of the Silurian Kuru’er Formation within the northern Yili block,with an aim to constrain the amalgamation time of the Yili Block.51 detrital zircon grains yield early Paleozoic ages of 422 to 519 Ma,and the rest of 12 detrital zircon grains have ages of 903 to 1755 Ma.The youngest age peak of 432 Ma provides a maximum age constraint for the deposition of the Kuru’er Formation,which together with available fossils suggest a Silurian deposition age for this formation.Compared with the early Paleozoic magmatism in the Yili Block,we conclude that the Kuru’er Formation receives detrital zircon from both northern and southern Yili blocks,suggesting that the amalgamation of the Yili Block occurred prior to the deposition of the Kuru’er Formation in the Silurian.Furthermore,a compilation of Hf isotope data of new detrital and magmatic zircon grains from the early Paleozoic igneous rocks shows a fanning array for the ε_(Hf)(t)values in the late Ordovician to Silurian,which was interpreted to result from the amalgamation of the Yili Block.Altogether,we consider that the Yili Block may have been amalgamated since the late Ordovician,which is consistent with the amalgamation of the Kazakhstan m

关 键 词：中亚造山带 哈萨克斯坦微陆块 西天山 伊犁地块 碎屑锆石 

分 类 号：P597[天文地球—地球化学] P542[天文地球—地质学]