中条山地区古元古代变基性岩墙的地球化学特征、LA-ICP-MS U-Pb年龄及其地质意义  

LA-ICP-MS Zircon U-Pb age,geochemical characteristics of the Paleoproterozoic metamorphosed mafic dykes in Zhongtiao Mountains,Shanxi Province,and their geological implications

作　　者：张少华[1,2] 张瑞英[1,3] 周金昱[2] ZHANG Shaohua;ZHANG Ruiying;ZHOU Jinyu(State Key Laboratory of Continental Dynamics,Department of Geology,Northwest University,Xi'an,710069;Research Insititute of Petroleum Exploration&Development,PetroChina Changqing Oilfield Company,Xi'an 710018;College of Geographical Science,Shanxi Normal University,Linfen,Shanxi,041004)

机构地区：[1]大陆动力学国家重点实验室,西北大学地质学系,西安710069 [2]中国石油长庆油田公司勘探开发研究院,西安710018 [3]山西师范大学地理科学学院,山西临汾041004

出　　处：《地质论评》2019年第6期1350-1362,共13页Geological Review

基　　金：国家科技重大专项(编号:2016ZX05050);山西师范大学自然科学基金项目的成果~~

摘　　要：华北克拉通南部中条山地区发育有大量古元古代基性岩墙,它们对于认识华北克拉通古元古代构造演化具有重要意义.本文通过对中条山北段绛县地区变质基性岩墙进行锆石LA-ICP-MS U-Pb测年分析,结果表明该基性岩墙的变质年龄为1847±14 Ma,代表本区一期重要的变质事件,其形成时代大致限定为1.85~2.14 Ga.地球化学数据显示,岩石的SiO2含量为45.94%~51.69%,TiO2(0.93%~1.09%)和K2 O(0.15%~0.46%)含量低,Fe2O3T(11.18%~13.43%)含量高,属于拉斑玄武岩系列;REE总量变化于60.56×10-6~77.26×10-6,LREE、HREE分异明显,大部分样品显示Eu正异常(δEu=0.99~1.29);微量元素总体富集Rb、Ba、La等大离子亲石元素,相对亏损Nb、Ta、Zr、Hf等高场强元素,指示其属于大陆拉斑玄武岩系列,源区具有富集地幔的特征,推测其可能是在拉张环境下被先前俯冲带流体交代的地幔物质部分熔融的结果.综上,中条山地区古元古代基性岩墙可能代表着华北板块在新太古代晚期克拉通化后的一次强烈的伸展事件,随后其经历了18.5 Ga左右强烈的变质作用.Objectives:Mafic dykes mainly formed in intraplate extensional or mantle plume environments,and have important indicative significance of tectonic setting.A large number of mafic dykes occurred in the Zhongtiao Mountains,southern margin of North China Craton(NCC),which had a great bearing on the Paleoproterozoic tectonic evolution of NCC.This paper focuses on the metamorphosed mafic dykes intruded into the Jiangxian Group in Zhongtiao Mountains.Methods:Based on detailed field investigation and systematic petrology,the paper mainly researches its features of the geochemistry and chronology.Here we present new geochemical and high-precision LA-ICP-MS zircon U-Pb data from the metamorphosed mafic dykes,which help to constrain the timing,petrogenesis and tectonic setting.Results:The zircons yielded a upper intercept age of 1847±14 Ma,which is interpreted as the metamorphic age,and its intrusion age should be 1.85?2.14 Ga.Geochemical analysis indicates that the mafic dykes is characterized by low SiO2(45.94%-51.69%),TiO2(0.93%~1.09%),K2O(0.15%~0.46%)and high Fe2O3T(11.18%?13.43%),belonging to tholeiite series.The dykes are slightly rich in LREE,and weakly positive Eu anomalies(δEu=0.99?1.29),enriching in LILE(Rb,Ba La),as well as depleted in HFSE(Nb,Ta,Zr,Hf).The protolith of mafic dykes were possibly tholeiite with a continental affinity,and the magma source mantle shows the E-MORB nature.Conclusions:The Paleoproterozoic metamorphosed mafic dykes in Zhongtiao Mountains was partially melted from enriched mantle source,which was effected by crust materials within the source and it may be effected by fluids in subduction zones.1.85?2.14 Ga magma activity indicated there was an intense extensional event in North China Craton after the cratonization at the end of Archean,and experienced intensive metamorphism at about 18.5 Ga.

关 键 词：古元古代 基性岩墙 锆石U-PB定年 地球化学 中条山地区 华北克拉通 

分 类 号：P58[天文地球—岩石学]