| 构造活动区特征源汇体系及古地理重建:以塔里木块体北缘记录“泛非”事件的碎屑锆石分析为例* |
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| 引用本文： | 李忠,高剑.构造活动区特征源汇体系及古地理重建:以塔里木块体北缘记录“泛非”事件的碎屑锆石分析为例*[J].古地理学报,2016,18(3):424-440. |
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| 作者姓名： | 李忠 高剑 |
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| 作者单位： | 1.中国科学院地质与地球物理研究所,北京 100029;2.北京市地热研究院,北京 100143 |
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| 基金项目： | Financially supported by the National Natural Sciences Foundation of China(Grant No.41372120,41172096,40972085) |
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| 摘 要： | 完整认识盆山沉积系统,这是古地理重建研究的必然趋势,其中从构造稳定区到构造活动区的特征源汇体系解析是重要环节。塔里木块体北缘活动区存在与“泛非”造山事件有关的岩浆和变质记录,但与这一特征构造-热事件有关的碎屑沉积记录以往在塔里木块体北缘及邻区却鲜有报道。主要针对塔里木块体北缘泥盆纪-石炭纪砂岩样品,文中开展了碎屑锆石原位地质年代学分析,结果表明下石炭统野云沟组砂岩碎屑锆石U-Pb年龄以新元古代中-晚期为主体,与“泛非”造山事件的持续时间较为一致,且此类沉积记录在该地区也是首次大量发现。相应的碎屑锆石的εHf(t)值几乎全为负值,是古老陆壳熔融的产物。而野云沟组之下和之上的砂岩碎屑锆石均无“泛非”造山事件的明显信息。研究认为,泥盆纪南天山洋向南俯冲,导致塔里木块体北缘发育岛弧体系;至早石炭世维宪早期南天山洋盆闭合,相关块体拼贴-碰撞作用致使该区构造古地理转变,与“泛非”造山作用有关的结晶基底隆升和剥露,并成为野云沟组主要物源。晚石炭世随海平面上升和沉积超覆,塔里木块体北缘与“泛非”造山事件有关的结晶基底剥露终止。综合对比区域碎屑锆石U-Pb年代学数据发现,研究区其他显生宙地层中(除上奥统桑塔木组外)均未记录到明显的与“泛非”造山事件物源相关的碎屑沉积,可能说明现存的塔里木块体受“泛非”造山构造-热事件影响的范围有限,另一方面也说明相关基底岩石的剥露主要出现在早石炭世以及晚奥陶世。这些信息的揭示对于认识塔里木块体北部古生代古地貌、碎屑源汇体系与构造古地理具有重要意义。
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| 关 键 词： | 构造活动区 构造古地理 塔里木块体 古生代 碎屑物源 “ 泛非” 造山 |
| 收稿时间： | 01 April 2016 |
Characteristic source-sink systems and palaeogeographic reconstruction in active tectonic regions: A case research on detrital zircons recording the Pan-African event in northern Tarim Block |
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| Li Zhong,Gao Jian.Characteristic source-sink systems and palaeogeographic reconstruction in active tectonic regions: A case research on detrital zircons recording the Pan-African event in northern Tarim Block[J].Journal of Palaeogeography,2016,18(3):424-440. |
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| Authors: | Li Zhong Gao Jian |
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| Institution: | 1.Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029;2.Beijing Geotherm Research Institute,Beijing 100143 |
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| Abstract: | Full understanding basin-range system is the inevitable research trend of palaeogeographic reconstruction,in which an analysis of characteristic source-sink systems, both in stable tectonic region and active one,is an key step. Some magmatic and metamorphic records related to the Pan-African orogeny occure in the actively northern Tarim Block,but the characteristic tectonic event is seldom discovered from detrital depositions. For the Devonian-Carboniferous sandstones in the northern Tarim Block,the authors present in situ analysis on geochronology of detrital zircons in the paper. Detrital zircon U-Pb dating of the Lower Carboniferous Yeyungou Formation sandstones dominantly show the middle-late Neoproterozoic ages,corresponding to the duration of the Pan-African orogeny. The depositional records with such zircon ages were firstly and remarkably discovered in the study area. The corresponding εHf(t) values of the detrital zircons are almost negative,reflecting melting origin of the ancient crust. However,there was no obvious information on the Pan-African orogeny revealed by detrital zircons of sandstones from the sedimentary strata underlying or overlying the Yeyungou Formation. In the Devonian,southward subduction of the South Tianshan Ocean led to island arc systems developed in the northern margin of Tarim Block. Up to the early Visean of early Carboniferous,the South Tianshan Ocean gradually closed,which evidently changed tectonic-palaeogeographic framework of the study area due to collage and collision between tectonic blocks. As a result,subsequently magmatic and metamorphic basements related to the Pan-African orogeny rapidly uplifted,which provided primary provenance for the Yeyungou Formation sedimentation. In the Late Carboniferous,the exhumation of the above crystalline basements ceased due to sea level rise and synchronous sedimentary overlap. Based on integrated regional correlation of detrital zircon U-Pb geochronological data,no detrital deposition recording the Pan-African event can be found from the Phanerozoic strata except the Lower Carboniferous mentioned above. In addition, few detrital deposition recording the Pan-African event was also reported from the Upper Ordovician Sangtamu Formation. These evidences probably demonstrate the northern Tarim Block finitely influenced by the Pan-African orogeny and,on the other hand,the associated basement rocks mainly exhumated during the Early Carboniferous and, shortly, the Late Ordovician. The above revealed informations are of important significances to realize the Paleozoic palaeogeomorphology,clastic source-sink system and tectonic paleogeography of the northern Tarim Block. |
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| Keywords: | active tectonic region tectonic palaeogeography Tarim Block Paleozoic detrital provenance Pan-African orogeny |
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