北大别南部存在巨量隐伏燕山期岩浆作用:岩浆岩锆石U-Pb年龄、元素及Sr-Nd-Hf同位素证据  

Giant Unexposed Yanshanian Magmatism in Southern North Dabie Terrane: Evidence from Zircon U-Pb Age,Elemental and Sr-Nd-Hf Isotope Geochemistry of Magmatic Rocks

作　　者：刘锐[1] 吴昌雄 祝莉玲 赵新福[1] LIU Rui;WU Changxiong;ZHU Liling;ZHAO Xinfu(Faculty of Earth Resources,China University of Geosciences(Wuhan),Wuhan 430074,Hubei,China;The Sixth Geological Party of Hubei Province,Xiaogan 432000,Hubei,China;Hubei Geological Survey,Wuhan 430034,Hubei,China)

机构地区：[1]中国地质大学(武汉)资源学院,湖北武汉430074 [2]湖北省地质局第六地质大队,湖北孝感432000 [3]湖北省地质调查院,湖北武汉430034

出　　处：《大地构造与成矿学》2020年第1期119-140,共22页Geotectonica et Metallogenia

基　　金：国家自然科学基金项目(41002025);中央高校基本科研业务费专项资金(CUGL140406)联合资助

摘　　要：大别造山带广泛分布着与造山作用有关的中生代花岗岩类,这些花岗岩类是研究造山带深部地壳物质组成、结构以及壳‒幔相互作用机制的重要窗口。目前对北大别晚中生代花岗岩类的研究主要集中于其北部,其南部晚中生代岩浆作用的研究相对薄弱。本研究对北大别南部两路口钨(钼)矿区的岩脉(株)进行了系统的岩石学、锆石U-Pb年代学、元素及Sr-Nd-Hf同位素地球化学研究,以反演北大别造山带深部物质组成、燕山期岩浆作用时限及背景、岩浆物质来源及演化过程。锆石U-Pb定年表明,所有岩浆岩(辉绿岩、闪长岩、闪长玢岩、花岗闪长斑岩、黑云母花岗岩和花岗斑岩)的侵位年龄值集中于133~129 Ma,在误差范围内基本一致,表明这些岩浆岩几乎同时侵位。地球化学研究表明,黑云母花岗岩和闪长(玢)岩类的主量元素Fe2O3 T、MgO、TiO2、CaO和P2O5,以及微量元素V、Sm+Eu和Eu/Eu*与SiO2均呈较好的负相关关系。结合黑云母花岗岩与闪长(玢)岩类较为一致的Sr-Nd同位素(分别为(87Sr/86Sr)i=0.706492~0.707426,εNd(t)=−15.2~−16.0;(87Sr/86Sr)i=0.706520~0.707916,εNd(t)=−19.9~−13.0)特征,说明它们可能具有相似的源区。另外,Hf同位素研究表明,辉绿岩、闪长玢岩和黑云母花岗岩具有几乎一致的Hf同位素组成(εHf(t)值分别为−23.1~−20.8、−22.6~−19.4和−21.6~−17.1;tDM2范围分别为2.5~2.6 Ga、2.4~2.6 Ga和2.3~2.5 Ga)。这进一步表明,两路口钨(钼)矿区的岩浆岩为同源岩浆演化的产物,其源区很可能来自于受俯冲熔体/流体交代形成的富集地幔的熔融。两路口钨(钼)矿区广泛出露的约130 Ma的基‒中‒酸性岩浆岩表明北大别南部存在隐伏燕山期岩浆作用,为壳‒幔相互作用的产物。壳‒幔相互作用机制可能与晚中生代古太平洋板块向东亚大陆边缘俯冲有关。Mesozoic granitoids are widespread in the Dabie orogenic belt,which provide an important window to probe the deep crustal structure,crustal composition,and crust-mantle interaction mechanism for orogenic belts.At present,studies on the late Mesozoic granitoids in the North Dabie terrane are mainly focused on outcrops in the northern part,whereas few are available for their counterparts in the south part.In this paper,an integrated petrological,zircon LA-ICP-MS U-Pb geochronological,elemental and Sr-Nd-Hf isotopic study has been conducted on magmatic rocks distributed in the Lianglukou W(Mo)mining area in the North Dabie terrane.Zircon U-Pb dating shows that the dolerite,diorite,dioritic porphyrite,granodiorite-porphyry,biotite granite and granite porphyry have consistent ages of 133 to 129 Ma.All these intrusions of diverse lithologies are nearly contemporaneous.The biotite granite and dioritic porphyrite display significant negative correlations between Fe2O3 T,MgO,TiO2,CaO,P2O5,V,Sm+Eu,Eu/Eu*and SiO2.Combined with their similar Sr-Nd isotopic compositions(with(87Sr/86Sr)i ratios of 0.706492 to 0.707426 and 0.706520 to 0.707916,εNd(t)values of−15.2 to−16.0 and−19.9 to−13.0,respectively),they were likely derived from the same magmatic source.In addition,the dolerite,dioritic porphyrite and biotite granites have consistent Hf isotopic compositions,withεHf(t)values of−23.1 to−20.8,−22.6 to−19.4 and−21.6 to−17.1,respectively.This further suggests that these magmatic rocks were likely derived from a similar source,which may be generated by reaction between the mantle-wedge peridotite and felsic melts from the subducting continental crust.The widespread ca.130 Ma magmatic rocks(basic,intermediate,acid)in the area may indicate there are abundant unexposed Yanshanian intrusions in the southern North Dabie terrane,which may have resulted from the westward subduction of the Pacific plate beneath the East Asian continental margin during the late Mesozoic.

关 键 词：锆石U-PB年龄 SR-ND-HF同位素 燕山期 两路口 北大别 

分 类 号：P597[天文地球—地球化学] P595[天文地球—地质学]