大别造山带汤池早白垩世富碱侵入岩成因及地质意义  

Petrogenesis and Geological Implications of the Early Cretaceous Tangchi Alkaline Intrusive Rocks Within the Dabie Orogen

作　　者：朱志鹏 王连训[1] 朱煜翔 李乐广 马昌前[1] ZHU Zhi-Peng;WANG Lian-Xun;ZHU Yu-Xiang;LI Le-Guang;MA Chang-Qian(School of Earth Science,China University of Geosciences,Wuhan 430074,Hubei,China)

机构地区：[1]中国地质大学地球科学学院,湖北武汉430074

出　　处：《华南地质》2024年第1期28-55,共28页South China Geology

基　　金：国家自然科学基金项目(No.42072082);湖北省自然科学基金项目(2022CFB116)。

摘　　要：本文对大别造山带北淮阳东段汤池地区早白垩世富碱侵入岩进行岩石学、锆石U-Pb年代学、岩石地球化学及锆石Lu-Hf同位素分析,揭示其成因及地质意义。该套岩石主要由正长花岗岩、石英正长岩和正长斑岩组成,伴有辉绿玢岩发育。锆石U-Pb定年结果显示,辉绿玢岩、正长花岗岩和正长斑岩分别形成于130.3±1.7 Ma、128.4±1.7 Ma和122.3±1.5 Ma,为早白垩世岩浆活动的产物。汤池辉绿玢岩相对贫硅(SiO_(2)=45.23~56.92 wt.%)和富碱(Na_(2)O+K_(2)O=5.24~8.04 wt.%),Mg#值较高(平均值为48);而其他岩类具有高硅(SiO_(2)=62.44~77.25 wt.%)、高碱(Na_(2)O+K_(2)O=7.97~10.35 wt.%)、低CaO含量以及较高的Ga/Al和FeOT/MgO比值,与典型的A型花岗岩化学特征相似。辉绿玢岩大多数锆石εHf(t)值变化范围为-6.4~-2.9,全岩Nb/Ta比值17.1~22.0(接近地幔Nb/Ta值17.5),表明其为富集地幔部分熔融的产物。汤池A型花岗岩具有更富集的Hf同位素组成,εHf(t)为-23.3~-3.5,以及更低的全岩Nb/Ta比值(11.2~22.7,平均值为16.5),暗示它们是由幔源玄武质岩浆底侵诱发下地壳部分熔融产生的长英质岩浆经历分异演化的产物。结合区域资料分析认为,大别造山带北淮阳地区在早白垩世碰撞挤压作用结束,开始进入后碰撞伸展阶段。An integrated study,involving petrology,zircon U-Pb geochronology,and lithogeochemistry and zircon Lu-Hf isotope,was conducted on the Early Cretaceous alkaline rocks in the Tangchi area of the eastern Beihuaiyang of the Dabie orogen,aiming to constrain its petrogenesis and tectonic implications.The alkaline rock suites consist of syenogranite,quartz syenite,and syenite porphyry,accompanied by dolerite.Zircon U-Pb dating reveals that dolerite,syenogranite,and syenite porphyry were formed at 130.3±1.7 Ma,128.4±1.7 Ma and 122.3±1.5 Ma,respectively,indicating that these rocks were products of Early Cretaceous magmatism.The dolerite exhibits low SiO_(2)(45.23~56.92 wt.%)and high Na_(2)O+K_(2)O contents(5.24~8.04 wt.%)and relatively high Mg#values(average of 48).Other rock types are characterized by high SiO_(2)(62.44~77.25 wt.%)and Na_(2)O+K_(2)O contents(7.97~10.35 wt.%),along with low CaO concentrations,as well as elevated Ga/Al and FeOT/MgO ratios,similar to typical A-type granites.The zirconεHf(t)values of the dolerite range from-6.4 to-2.9,with whole rock Nb/Ta ratio of 17.1~22.0(close to the mantle value of 17.5),indicating that these rocks were formed via partial melting of an enriched mantle.The Tangchi A-type granites yield richer Hf component and much lowerεHf(t)values(-23.3~-3.5)and whole rock Nb/Ta ratio(11.2~22.7,average of 16.5),suggesting that the A-type alkaline magmas have been produced primarily by partial melting of the lower crust caused by the emplacement of the mantle-derived mafic magmas.Together with regional data,it is proposed that the Dabie orogeny was in transition from the collisional extrusion during the Early Cretaceous to subsequent post-collisional extension.

关 键 词：大别造山带 汤池 早白垩世 A型花岗岩 辉绿玢岩 地球化学 

分 类 号：P581[天文地球—岩石学]