南秦岭长角坝群低庄沟组的锆石U-Pb年龄及其构造意义  

Zircon U-Pb dating of the Dizhuanggou Formation,Changjiaoba Group in the South Qinling Belt and its tectonic significance

作　　者：刘志慧 刘晓春[1,2] 陈龙耀 郑光高[1,2] 胡娟 LIU Zhihui;LIU Xiaochun;CHEN Longyao;ZHENG Guanggao;HU Juan(Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing 100081,China;Key Laboratory of Paleomagnetism and Tectonic Reconstruction,Ministry of Natural Resources,Beijing 100081,China)

机构地区：[1]中国地质科学院地质力学研究所,北京100081 [2]自然资源部古地磁与古构造重建重点实验室,北京100081

出　　处：《地质力学学报》2024年第6期1012-1027,共16页Journal of Geomechanics

基　　金：国家自然科学基金项目(42202057,41872059);中国地质调查局地质调查项目(DD20240031)。

摘　　要：长角坝群出露于南秦岭佛坪地区,是该构造带内残留的少数研究程度较低的地层之一,其物质组成、形成时代一直缺乏准确的限定,进而制约了对南秦岭的构造归属和构造演化的深入研究。文章对长角坝群内低庄沟组变质沉积岩开展了岩石学和锆石U-Pb年代学研究,结果显示所取2个样品的碎屑锆石年龄主要峰值为810~835 Ma,最年轻的年龄区间为600~700 Ma,最大沉积时代为新元古代。这与同为长角坝群、出露最广泛的泥盆纪黑龙潭组具有明显的时代差异,显示了长角坝群物质组成的复杂性。此外,低庄沟组的碎屑锆石年龄谱系特征与用于对比测试的另一个碎屑锆石最小年龄峰值为718 Ma、主要峰值为810 Ma的佛坪群样品高度相似,结合二者的岩石学及野外地质特征,认为二者共同构成了南秦岭西部的过渡性基底,与南秦岭带内宁陕断裂以东的过渡性基底-武当群、耀岭河群具有明显的可对比性。长角坝群新元古代物质的识别还为佛坪地区变质单元的划分提供了新的依据,进而梳理出成层性、变质程度不同的3个单元,为南秦岭中生代造山演化过程的恢复提供了佐证。[Objective]The Changjiaoba Group,located in the Foping area of the South Qinling Belt,is one of the few poorly-studied strata in the belt.The lack of an accurate composition and formation age of these strata has restricted research on the tectonic affinity and evolution of the South Qinling Belt.[Method]This paper investigates the petrological characteristics and zircon U-Pb chronology of two metasedimentary rocks from the Dizhuanggou Formation of the Changjiaoba Group.[Results]The results show that the dominant peak detrital zircon dates of the two samples were approximately 810–835 Ma,with the youngest date range being approximately 600–700 Ma,indicating that the maximum depositional age was Neoproterozoic.This age spectrum differs significantly from that of the most exposed Devonian Heilongtan Formation of the Changjiaoba Group,but is highly similar to that of another sample from the Foping Group,which has a minimum age peak of 718 Ma and a major peak at 810 Ma.In addition,metamorphic zircons from the Dizhuanggou Formation and the Foping Group yielded ages of 207 Ma and 193 Ma,respectively.[Conclusion]The distinct depositional age of the Changjiaoba Group indicate the complexity of its composition.Combined with the petrological and field geological features,the Dizhuanggou Formation and a Neoproterozoic strata of the Foping Group are considered to form the transitional basement of the western South Qinling Belt.This is comparable to the transitional basement of the Wudang and Yaolinghe Groups east of the Ningshan Fault in the South Qinling Belt.[Significance]The identification of Neoproterozoic and Mesozoic materials in the Changjiaoba Group provides a new basis for the division of metamorphic units in the Foping area,identifying three units with different degrees of layering and metamorphism,which,in turn,facilitates understanding of the Mesozoic orogenic process in the South Qinling Belt.

关 键 词：南秦岭 长角坝群 碎屑锆石 新元古代 单元划分 

分 类 号：P534[天文地球—古生物学与地层学] P597[天文地球—地质学]