摘要
长城系是华北克拉通统一结晶基底形成后的首套沉积盖层,其碎屑锆石U-Pb年代学及其Hf同位素特征分析对探讨地层形成时代、源区特征以及基底演化均具重要研究意义。本文对华北克拉通中部黎城地区长城系下部地层的碎屑锆石进行了U-Pb年龄和Hf同位素分析。结果表明,该区长城系碎屑锆石U-Pb年龄呈现了2.55~2.45Ga、2.15~2.0Ga和~1.92Ga等三个主峰期,同时存在3.5~3.1Ga和2.9~2.7Ga的年龄次峰期。最年轻碎屑锆石的207 Pb/206 Pb加权平均年龄限定了该区长城系沉积发生于1.76Ga之后。碎屑锆石的年龄分布和Hf同位素特征与华北克拉通中、南部基底物质记录的地质事件高度相似,区内长城系地层与南部熊耳地区长城系地层可对比性强,证明太行山南段在1.76Ga后已与南部熊耳裂谷盆地相连,其沉积物质均主要来自华北克拉通中、南部地区。其中,3.5~3.4Ga的古老碎屑锆石εHf(t)=-8.6~-4.6,揭示中、南部地区存在古太古代地壳物质。新太古代早期2.9~2.7Ga的锆石εHf(t)以正值为主(占比85%),它们的t C DM=3190~2774Ma,与其结晶年龄相同或接近,证明华北克拉通南部在新太古代早期以新生地壳生长为主。新太古代晚期2.55~2.45Ga峰期的锆石也以正的εHf(t)值为主(占比69%),而2.15~2.0Ga峰期锆石的εHf(t)值大多偏负(占比56%),说明华北克拉通南部地区从新太古代末期的新生地壳增生为主伴有陆壳再造转变为古元古代中期以古老陆壳物质再造为主,并有少量新生陆壳增生;古元古代晚期~1.92Ga年龄峰期的碎屑锆石εHf(t)=-11.9~+2.0,揭示至古元古代末期华北克拉通中南部进入到以古老陆壳物质再造为主的演化阶段。
The Changcheng System is the oldest sedimentary cover after the formation of the unified crystalline basement in the North China Craton(NCC).The analysis for the U-Pb geochronology and Hf isotopes of the detrital zircons from the Changcheng System is of great significance for exploring the formation age and source characteristics of this strata as well as the basement evolution.This study conducted a detailed analysis upon the U-Pb ages and Hf isotopes of the detrital zircons from the lower segment of the Changcheng System in the Licheng area of the central part of NCC.The results demonstrate the U-Pb ages of detrital zircons exhibit three main age peaks of 2.55~2.45Ga,2.15~2.0Ga and~1.92Ga,as well as two minor ones of 3.5~3.1Ga and 2.9~2.7Ga,respectively.The 207 Pb/206 Pb weighted average age of the youngest detrital zircons constrain the Changcheng System to be deposited after 1.76Ga in this area.The age distributions and Hf isotope characteristics from the detrital zircons are highly similar to the geological events recorded by the basements in the central and southern parts of the NCC.In addition,the strong comparability of the Changcheng System between the Licheng and the southern Xiong er areas suggests that the extension of the southern Xiong er rift basin should reach the southern areas of Taihang Mountains after 1.76Ga,and their sedimentary materials were mainly derived from the central and southern parts of NCC.The 3.5~3.4Ga old detrital zircons yieldedεHf(t)values from-8.6 to-4.6,likely indicating the presence of Paleoarchean crustal material in the central and southern NCC.TheεHf(t)values of 2.9~2.7Ga zircons in the Early Neoarchaean period are mainly positive(accounting for 85%),and their t C DM ranges from 3190Ma to 2774Ma,which are the same or close to their crystallization ages,indicating there was an important juvenile crustal growth at the Early Neoarchean in the southern NCC.The zircons within the 2.55~2.45Ga peak in the Late Neoarchean period are also dominated by positiveεHf(t)values(69%of
作者
胡漾
祝禧艳
张瑞英
赵太平
张成立
HU Yang;ZHU XiYan;ZHANG RuiYing;ZHAO TaiPing;ZHANG ChengLi(Precambrian Research Center,State Key Laboratory of Continental Dynamics,Northwest University,Xi'an 710069,China;Key Laboratory of Mineral Resources,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;Key Laboratory of Mineralogy and Metallogeny,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,China)
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2024年第1期295-312,共18页
Acta Petrologica Sinica
基金
国家自然科学基金重大项目(41890831、92062103)
国家重点研发计划项目(2020YFA0714803)
自然科学基金创新群体(41421002)
大陆动力学国家重点实验室科技部专项(201210133)联合资助.
关键词
中元古代早期
碎屑岩
物源分析
地壳演化
太行山南段
Early Mesoproterozoic
Clastic rocks
Source analysis
Crustal evolution
Southern Taihang Mountains
