扬子陆块北缘东河铂钯矿化超基性岩脉成岩时代与岩石成因:锆石年代学、地球化学和Sr-Nd-Hf同位素约束  

Geochronology and Petrogenesis of the Donghe Pt-Pd-Bearing Ultramafic Dykesin the Northern Margin of the Yangtze Block:Constraints from Zircon Geochronology,Geochemistry and Sr-Nd-Hf Isotpopes

作　　者：曹亮[1,2] 陈林 段其发[1,2] 周云[1,2] 刘重芃[1,2] 张利国[1,2] Cao Liang;Chen Lin;Duan Qifa;Zhou Yun;Liu Chongpeng;Zhang Liguo(Wuhan Center of Geology Surrey,CGS,Wuhan 430205,China;Research Center of Granitic Diagenesis and Mineralization, China Geological Survey,Wuhan 430205;Second Geological Team o Hubei Geological Bureau,Enshi 445000, China)

机构地区：[1]中国地质调查局武汉地质调查中心,湖北武汉430205 [2]中国地质调查局花岗岩成岩成矿地质研究中心,湖北武汉430205 [3]湖北省地质局第二地质大队,湖北恩施445000

出　　处：《地球科学》2019年第2期366-386,共21页Earth Science

基　　金：中国地质调查局扬子工程湘西-鄂西成矿带神农架-花垣地区地质矿产调查二级项目(No.DD20160029)

摘　　要：东河铂钯矿化超基性岩脉位于扬子陆块北缘房县东河地区,铂钯矿体产于超基性岩辉石岩脉中.LA-ICP-MS锆石U-Pb测年表明该超基性岩脉结晶侵位年龄为433.2±2.9 Ma,属于早志留世.地球化学特征上,岩石具有较低含量的SiO_2(39.73%～47.46%,均值为41.41%)、中等偏低的Mg#(46.98～67.37)和高铝(11.25%～15.46%)的特征,整体上属于高铝质超基性岩类.微量和稀土元素方面,岩石具有较高的稀土总量、轻稀土富集和无明显的Eu正异常特征(ΣREE=59.59×10^(-6)～375.02×10^(-6),(LaN/YbN)=3.94～19.13,δEu=0.93～1.13),所有岩石富集Rb、Ba、Sr、Nb、Ti等元素,亏损K、Hf、P等元素,且具有显著不同于地壳的不相容元素组成.Sr、Nd、Hf同位素研究表明,东河超基性岩具有低的(87 Sr/86 Sr)i(0.703 26～0.704 15),正的εNd(t)(4.37～5.27)和正的εHf(t)(7.29～10.26).综合研究表明:东河超基性岩来自亏损的岩石圈地幔源区,可能有富集岩石圈地幔组分的加入,原始岩浆在上升侵位过程中地壳物质的混染不明显.微量元素构造环境判别显示其形成于板内构造环境,通过分析表明东河地区在早志留世应处于被动大陆边缘,拉张伸展的状态,研究区出露的两期超基性岩床(脉)为岩石圈处于拉张状态下大陆裂谷早期阶段的产物.The Donghe Pt-Pd-bearing ultramafic dykes are located in the northern margin of the Yangtze block in Fangxian,the Pt-Pd ore bodys are present in the ultramafic dykes of pyroxene veins.The LA-ICP-MS zircon U-Pb dating indicates that the ultrabasic dykes were emplaced with age of 433.2±2.9 Ma,belonging to the early Silurian.The rocks are characterized by low SiO2(39.73%-47.46%,mean 41.41%),moderate Mg#(46.98-67.37)and high alumina(11.25%-15.46%),belonging to high-alumina ultrabasic rocks.The rocks have higher total REE,with slightly enriched LREE and without significant Eu positive anomaly(ΣREE=59.59×10^-6 to 375.02×10^-6,(LaN/YbN)=3.94-19.13,δEu=0.93-1.13).All rocks are enriched inRb,Ba,Sr,Nb,Ti,etc.,depleted in Nb,Hf,P,etc.and have significantly different ratios of incompatible elements to that in the crust.Sr,Nd and Hf isotope studies show that the Donghe ultramafic rocks have low initial 87 Sr/86 Sr ratios(0.703 26-0.704 15),positiveεNd(t)(4.37~5.27)and positiveεHf(t)(7.29-10.26).Based on the above discussion,we propose that the studied ultramafic rocks were derived from a depleted lithospheric mantle(garnet-lherzolite)source which may be enriched lithospheric mantle components.Magma in the rising process was not significantly affected by the crust material mixed.The tectonic discrimination of trace elements shows that it formed in intraplate tectonic environment.The analysis shows the Donghe region should be on the passive continental margin during the Early Silurian and should be in extensional state.The twostage ultramafic bedrocks(veins)exposed in the study area were the products of the early stage of the continental rift in the state of extensional of the lithosphere.

关 键 词：超基性岩 锆石年代学 辉石岩 SR-ND-HF同位素 东河地区 扬子陆块 地球化学 

分 类 号：P581[天文地球—岩石学] P597[天文地球—地质学]