吉林中部靠山地区早侏罗世正长花岗岩锆石U-Pb年代学、地球化学特征及其动力学意义  

Zircon U-Pb Geochronology,Geochemical Characteristics and Geodynamic Significance of the Early Jurassic Syenogranite in Kaoshan Area of Central Jilin Province

作　　者：叶希青 孙立影 徐智涛 闫东晗 冯靖乔[2] 曹戎机 Ye Xiqing;Sun Liying;Xu Zhitao;Yan Donghan;Feng Jingqiao;Cao Rongji(Institute of Volcanology,China Earthquake Administration,Changchun 130117,China;Jilin Earthquake Agency,Changchun 130117,China)

机构地区：[1]中国地震局火山研究所,长春130117 [2]吉林省地震局,长春130117

出　　处：《吉林大学学报（地球科学版）》2023年第3期964-983,共20页Journal of Jilin University：Earth Science Edition

基　　金：中国地震局地质研究所国家野外科学观测研究站项目(NORSCBS22-06);吉林省地震局青年科技发展课题(JZQ-202310);中国工程院院地合作项目(JL2021-03-01)

摘　　要：吉林省中部靠山地区的早侏罗世中粒正长花岗岩出露于张广才岭山脉南段,侵位接触于中三叠世花岗岩类和泥盆纪—石炭纪侵入岩类,主要造岩矿物由钾长石、石英、斜长石和黑云母组成。为了对靠山地区花岗岩的成岩时代、地球化学特征和地球动力学背景进行探讨,我们对研究区出露的早侏罗世非造山A型中粒正长花岗岩进行了岩相学、年代学、地球化学和Hf同位素研究。锆石U-Pb年代学和地球化学研究表明:研究区中粒正长花岗岩的谐和年龄为(193.2±0.9)Ma,成岩时间应归属为早侏罗世;其具有高的SiO_(2)(75.49%~75.82%)和全碱(8.28%~9.17%)质量分数,高A/CNK(1.08~1.13)、LREE(20.89×10^(-6)~46.38×10^(-6))和FeO/MgO(3.29~5.83)值,富集Rb、K、Pb等大离子亲石元素(LILE)和Th、U、Hf、Nb、Zr等高场强元素(HFSE);此外,其具有低的MgO(0.06%~0.14%)、TiO_(2)(0.05%~0.12%)、P2O5(0.02%~0.04%)、Sr(24.20×10^(-6)~62.59×10^(-6))、HREE(5.14×10^(-6)~11.80×10^(-6))质量分数和中等δEu值(0.41~0.56),类似于非造山A型花岗岩的岩石地球化学特征。锆石的Hf同位素分析结果显示,εHf(t)值范围为9.7~15.7,二阶段Hf同位素模式年龄(TDM2)为612~225 Ma。结合区域研究资料认为,靠山地区中粒正长花岗岩的成岩母岩浆可能来自伸展环境下的年轻下地壳。早期古太平洋板块俯冲造成的软流圈地幔上涌和弧后伸展的构造环境,可能是研究区早侏罗世非造山A型花岗质岩浆活动的重要地球动力学因素。The Early Jurassic medium-grained syenogranite in Kaoshan area of central Jilin Province is exposed in the southern part of Zhangguangcai range,and emplaced in contact with the Middle Triassic granitoids and Devonian-Carboniferous intrusive rocks.Its main rock-forming minerals are composed of K-feldspar,quartz,plagioclase and biotite.In order to explore the diagenetic age,geochemical characteristics and geodynamic background of the granites in Kaoshan area,we carried out petrographic,chronological,geochemical and Hf isotope studies on the Early Jurassic non-orogenic A-type medium-grained syenogranite exposed in the study area.Zircon U-Pb geochronology and geochemical studies show that:The concordant age of the medium-grained syenogranite in the study area is(193.2±0.9)Ma,and the diagenetic time should be attributed to the Early Jurassic.It has a high SiO_(2)(75.49%-75.82%)and total alkali(8.28%-9.17%)mass fraction,together with high A/CNK(1.08-1.13),LREE(20.89×10^(-6)-46.38×10^(-6))and FeO/MgO(3.29-5.83)values.It is also enriched in large ionic lithophile elements(LILE,such as Rb,K and Pb)and high-field strength elements(HFSE,such as Th,U,Hf,Nb and Zr).It has low MgO(0.06%-0.14%),TiO_(2)(0.05%-0.12%),P2O5(0.02%-0.04%),Sr(24.20×10^(-6)-62.59×10^(-6)),HREE(5.14×10^(-6)-11.80×10^(-6))mass fraction and mediumδEu(0.41-0.56)value,which is similar to the lithogeochemical characteristics of non-orogenic A-type granite.Hf isotopic analysis results of zircons show that theεHf(t)values range from 9.7 to 15.7,and the two-stage Hf-isotope model ages(TDM2)range from 612 to 225 Ma.Combined with the regional research data,we think the diagenetic parent magma of the medium-grained syenogranite in the Kaoshan area was probably derived from the juvenile lower crust in an extensional environment.The tectonic environment of asthenosphere mantle upwelling and back-arc extension caused by the subduction of the early paleo-Pacific plate,may be an important geodynamic factor for the Early Jurassic non-orogenic A-type granitic ma

关 键 词：A型花岗岩 锆石U-Pb年龄 地球化学特征 Hf同位素 吉林中部靠山地区 

分 类 号：P59[天文地球—地球化学]