地学前缘 ›› 2018, Vol. 25 ›› Issue (1): 80-94.DOI: 10.13745/j.esf.yx.2017-5-14

• 物质成分改造与构造年代学 • 上一篇    下一篇

扬子板块西北缘碧口地块中—新生代变质、变形与年代限定

许晨光，颜丹平，古术航，孟祥坤，邱亮，Michael L.WELLS   

  1. 1. 中国地质大学(北京) 地球科学与资源学院, 北京 100083
    2. Department of Geoscience, University of Nevada, Las Vegas, Nevada, USA
    3. 北京大学 地球与空间科学学院; 造山带与地壳演化教育部重点实验室, 北京 100871
  • 收稿日期:2016-12-01 修回日期:2017-02-24 出版日期:2018-01-15 发布日期:2018-01-15
  • 作者简介:许晨光（1989—），男，博士研究生，构造地质学专业，主要从事区域构造解析及构造年代学研究。E-mail:cgxu@cugb.edu.cn
  • 基金资助:
    高等学校博士学科点专项科研基金（20120022110013）；国家自然科学基金项目（41372212）；国家重点基础研究发展计划“973”项目（2014CB440903）

Deformation sequence and geochronological constraints on the metamorphism of the Bikou terrane, northwestern margin of the Yangtze Block

XU Chenguang,YAN Danping,GU Shuhang,MENG Xiangkun,QIU Liang，Michael L.WELLS,WANG Jibin,MA Fang   

  1. 1. School of Earth Sciences and Resources, China University of Geosciences(Beijing), Beijing 100083, China
    2. Department of Geoscience, University of Nevada, Las Vegas, Nevada, USA
    3. School of Earth and Space Sciences, Peking University; Key Laboratory of Orogenic Belts and Crustal Evolution (Ministry of Education), Beijing 100871, China
  • Received:2016-12-01 Revised:2017-02-24 Online:2018-01-15 Published:2018-01-15

PDF (PC)

535

摘要： 碧口地块位于扬子板块西北缘，由北部变质沉积岩系及南部变质中基性火山岩组成。碧口地块北部岩石变质为千枚岩、云母石英片岩，南部岩石经历绿片岩蓝片岩相变质。由于对碧口地块变形特征及区域变质作用分析深度不够，缺少精确的变质时间限定，碧口地块变质杂岩系性质、区域变质年代及其大地构造属性始终处于争议之中，导致对西秦岭和龙门山造山过程的认识产生分歧。通过详细区域构造解析，将碧口地块划分为3期变形：D1期以紧闭褶皱、面理S1及矿物线理L1为特征；D2期形成于由北向南的正断拆离作用，显示韧性变形特征，D2期变形改造先期逆断层并形成半地堑盆地；D3期形成于喜山期逆冲走滑运动，以脆性变形为主要特征。本研究获得碧口变质岩中变形脉锆石UPb年龄（227.2±6.2） Ma，碧口地块已报道的D1期变形后期侵入体年龄为226~215 Ma，从而限定D1期碧口区域变质变形年龄为约220 Ma。因此推测D1期形成于三叠纪末华南、华北板块碰撞，碧口地块区域变质主要形成于这一时期的俯冲碰撞作用；D2与D3期则与青藏高原的东向扩张有关。

关键词: 碧口地块, 区域变质, 扬子板块, 三叠纪

Abstract: The Bikou terrane lies on the northwestern margin of the Yangtze Block. It comprises pelitic rocks in the north and maficintermediate volcanic rocks in the south. Rocks in the north metamorphosed into phyllite and mica schist, while rocks in the south experienced greenschistblueschist facies metamorphism. Presently, there are no detailed analyses on the deformation sequence and regional metamorphism of the Bikou terrane; geochronological constraints for regional metamorphism are also lacking. As a result, nature of the Bikou terrane and age of regional metamorphism and tectonic settings are not known, causing controversy over the orogenies of West Qinling and Longmen Mountain. Here, after detailed field study and structural analysis, we divided the Bikou terrane deformation sequence into three stages, D1, D2 and D3. D1 is marked by tight fold, foliation S1 and mineral lineation L1; D2 is normal ductile shear dipping to the south, transforming thrust faults and resulting in formation of Jurassic halfgraben basins; and D3, formed in the sinistral strikeslip thrust in the Himalayan, is characterized by brittle deformation. In this study, we obtained UPb zircon age of 227.2±6.2 Ma from deformed felsic veins in the Bikou terrane. Since the undeformed intrusive plutons after D1 deformation yielded age of 226215 Ma in previous studies, the age of regional metamorphism in the Bikou terrane is constrained at ca. 220 Ma. Therefore we infer that, D1 formed during subduction and collision between the North and South China blocks in the Late Triassic, when regional metamorphism of the Bikou terrane occurred, and D2 and D3 were related to eastward expansion of the Tibetan Plateau.

Key words:  Bikou terrane, regional metamorphism, Yangtze Block, Triassic

中图分类号: