塔里木西南前寒武纪构造演化与地壳增生

发布时间：2018-04-21 12:42

本文选题：塔里木西南 + 锆石年代学　；参考：《中国地质科学院》2016年博士论文

【摘要】：塔里木克拉通是中国最重要的克拉通之一,前寒武纪基底主要出露于塔里木周缘。塔里木西南地区古元古代侵入杂岩、中新元古代火山-沉积地层以及近年来发现的中元古代岩浆岩对塔里木西南地体的构造演化与地壳增生的研究具有非常重要的意义。本文在总结前人成果的基础上,通过详细的野外调查,对塔里木西南地区的前寒武纪岩浆岩、沉积地层进行了系统分析和总结,以探索塔里木西南前寒武纪构造演化及地壳增生。赫罗斯坦杂岩岩性以A型花岗岩和S型花岗岩为主,形成于2.4-2.3 Ga,并在-1.9 Ga遭受了强烈的变质作用。地球化学特征表明,A型花岗岩和S型花岗岩分别来源于太古代的基性地壳岩石和变杂砂岩和/或长英质泥砂岩部分熔融。阿孜拜勒迪岩体岩性主要为二长花岗岩,LA-ICP-MS U-Pb定年结果显示其形成于1.4 Ga左右。地球化学特征指示该岩体为典型的A型花岗岩,其成因可能是由于基性岩浆上涌,导致早元古代基性下地壳部分熔融,并且在此过程中还有不同程度古元古代新生地壳的加入。通过碎屑锆石LA-ICP-MS U-Pb测年,绿片岩相变质和强烈褶皱的塞拉加兹塔格群(SG)火山-沉积地层的沉积时限为860-830Ma之间；相比之下,低绿片岩相变质、强烈变形埃连卡特群(AG)中碎屑岩为820-800 Ma；而未发生变形和变质的上新元古界碳酸盐-碎屑岩-冰碛岩地层恰克马克力克群(QG)沉积时代应不早于760 Ma。其中QG中两次冰期分别可以和塔里木北缘贝义西冰期和特瑞爱肯冰期进行对比。综合年代学、地球化学、碎屑锆石年龄谱、岩石组合以及岩石变质变形特征,塔里木西南地体在2.4-2.3 Ga时处于裂谷构造背景。随后在1.9 Ga左右发生造山事件,使塔里木西南地体汇聚到Columbia超大陆之下,而后在1.4 Ga时该超大陆已经开始发生裂解。直到1.0-0.9Ga,大洋沿着塔里木西南地体南缘和澳大利亚克拉通北缘发生汇聚,形成了以喀拉喀什群(KG)为代表的火山弧。而860-830 Ma之间,由于大洋沿着塔里木西南地体北缘俯冲,形成了弧后盆地,沉积了塞拉加兹塔格群(SG)。之后,弧后盆地闭合,在820-800 Ma时形成了前陆盆地,沉积了埃连卡特群(AG)。直到760 Ma塔里木基底的聚合事件才结束。前寒武纪地质单元锆石的U-Pb年代学及Hf同位素组成显示地壳的增生时间为3.8-3.6Ga、2.4-2.2 Ga、1.0-0.7Ga。塔里木西南地体早前寒武纪地壳增生与塔里木克拉通其他前寒武纪地体完全不同。此外,不同块体之间Columbia超大陆聚合和裂解的时间也并不相同。由此推测塔里木早前寒武纪基底可能来源于不同的大陆块体,直到新元古代才拼合在一起。
[Abstract]:The Tarim craton is one of the most important cratons in China. Gu Yuan's ancient intrusive complex, MesoNeoproterozoic volcanic-sedimentary strata and Mesoproterozoic magmatic rocks discovered in recent years are of great significance to the study of tectonic evolution and crustal accretion in southwest Tarim area. On the basis of summing up the achievements of predecessors, this paper makes a systematic analysis and summary of the Precambrian magmatic rocks and sedimentary strata in southwest Tarim by detailed field investigation. To explore the Precambrian tectonic evolution and crustal accretion in southwest Tarim. The lithology of Herostein complex is mainly A-type granite and S-type granite formed in 2.4-2.3 Ga and suffered strong metamorphism at -1.9 Ga. The geochemical characteristics indicate that the A-type and S-type granites are derived from Archean basic crustal rocks and metamorphic sandstone and / or felsic mudstone, respectively. The lithology of the Azzi Bayerdi body is mainly composed of two feldspar granites, LA-ICP-MS U-Pb dating results show that it was formed at about 1.4 Ga. The geochemical characteristics indicate that the rock body is a typical A-type granite, and its genesis may be caused by the upwelling of the basic rock mass, which leads to the partial melting of the early Proterozoic basic lower crust, and the addition of Gu Yuan's new crust to different degrees in the process. Based on the LA-ICP-MS U-Pb dating of clastic zircon, the sedimentary time between the volcanic and sedimentary strata of greenschist facies metamorphic and strongly folded Seragatag group is between 860-830Ma and low-greenschist facies metamorphism. The strongly deformed Ellenkat Group (AGG) was 820-800 Ma, while the Upper Neoproterozoic carbonate, clastic rock and moraine strata in the Upper Neoproterozoic carbonate, clastic rock and moraine formation should have been deposited no earlier than 760 Ma. The two glacial ages in QG can be compared with the Beyesi glacial and Teriecan glacial periods in the northern margin of Tarim. Combined with geochronology, geochemistry, age spectrum of clastic zircon, rock assemblage and metamorphic deformation, the southwestern Tarim body is in the rift tectonic setting at 2.4-2.3 Ga. Then orogenic events occurred around 1.9 Ga, which led the southwest of Tarim to converge below the Columbia supercontinent, and then the supercontinent began to break up at 1.4 Ga. Up to 1.0-0.9Ga, the ocean converges along the southern margin of the southwest Tarim body and the northern margin of the Australian craton, forming a volcanic arc represented by the Karakash group KG. However, between 860-830 Ma, the ocean subducted along the northern margin of the southwest Tarim body, forming a back-arc basin and depositing the Seragaztag group. After that, the back-arc basin was closed and the Foreland basin was formed at 820-800 Ma, and the Allenkat group was deposited. It was not until 760 Ma that the aggregation of the Tarim basement ended. The U-Pb geochronology and HF isotopic composition of zircon from the Precambrian geological unit indicate that the crustal accretion time is 3.8-3.6 Gaan2.4-2.2 GaS1.0-0.7Ga. The early Precambrian crustal accretion of the southwest Tarim platform is completely different from other Precambrian terraces in the Tarim craton. In addition, the time of Columbia supercontinent polymerization and cracking is different between different blocks. It is inferred that the early Precambrian basement of Tarim may have originated from different continental blocks until the Neoproterozoic.
【学位授予单位】：中国地质科学院
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P542;P313

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