福建湄州岛镁铁质岩墙群与寄主花岗岩的形成时差、地球化学及成因  

The Age Difference,Geochemistry and Petrogenesis of Mafic Dikes and Host Granites from Meizhou Island in Fujian Province

作　　者：董传万[1] 周超[1] 顾虹艳[1] 马骁雄[1] 吕青[1] 

机构地区：[1]浙江大学地球科学系,杭州310027

出　　处：《吉林大学学报（地球科学版）》2011年第3期735-744,共10页Journal of Jilin University：Earth Science Edition

基　　金：国家自然科学基金项目(40872051;40372035);国家'973'计划项目(2007CB411706)

摘　　要：福建湄洲岛的镁铁质岩墙群侵入于花岗岩中。镁铁质岩墙主要由斜长石（An=45~55,中-拉长石）、普通角闪石及少量辉石和石英等组成,锆石SHRIMP U-Pb年龄为（95±2）Ma。寄主花岗岩主要由石英、钾长石、斜长石（An=22~25,更长石）及少量的黑云母组成,锆石SHRIMP U-Pb年龄为（105±3）Ma。它们的形成时差约10 Ma。在岩石地球化学上,镁铁质岩墙群具有低CaO、MgO、TiO2而高Al2O3、轻稀土元素和大离子亲石元素富集、高场强元素亏损等特点,（87Sr/86Sr）i=0.705 2~0.705 4,εNd（t）=-0.03~1.57,与福建沿海同时代镁铁质岩墙群相似。寄主花岗岩与沿海高钾钙碱性花岗岩基本相同,都具有高硅、富碱的特点,它们的w（SiO2）〉75%,A/CNK=1.05~1.12,w（K2O＋Na2O）=7.68%~8.12%,w（K2O）〉w（Na2O）,（87Sr/86Sr）i=0.705 5,εNd（t）=-3.92。综合研究表明：湄洲岛寄主花岗岩是由受消减作用影响的岩石圈地幔部分熔融而产生的玄武岩浆底侵,并熔融中下地壳所产生的花岗岩浆形成;而镁铁质岩墙是底侵、滞留并经过结晶分异的玄武质岩浆,因地壳再次伸展,而沿花岗岩体中节理侵入形成。湄洲岛花岗岩与镁铁质岩墙群形成于伸展构造环境,对应福建沿海2次地壳伸展事件。湄洲岛花岗岩和镁铁质岩墙群的研究为沿海晚中生代构造-岩浆活动提供了一个新例证,同时为福建沿海晚中生代岩石圈伸展时限提供了制约。Mafic dikes in Meizhou Island,Fujian Province,intrude along joints of the granite.They are mainly hornblende diabase and composed of plagioclase（An=45-55）,hornblende and minority of augite and/or quartz.The SHRIMP U-Pb age of zircons from mafic dikes is（90±2） Ma.The host granite,with zircon SHRIMP U-Pb age of（105±3） Ma,is composed of quartz（25%-30%）,perthite（50%-60%）,plagioclase（An=22-25,10%-15%） and minority of biotite（5%）.The age difference between the mafic dikes and their host granite is approximately 10 Ma.Geochemically,the mafic dikes are of low CaO,MgO,TiO2,high Al2O3,with LREE and LILE enriched,Ta-Nb depleted,（87Sr/86Sr）i=0.705 2-0.705 4,εNd（t） =-0.03-1.57.The overall elemental and Sr-Nd isotopic characteristics of the Meizhou Island mafic dikes are similar to those of mafic dikes from the coastal area of Fujian Province.The host granite is rich in silicon,alkalis,w（SiO2）75%,A/CNK=1.05-1.12,w（K2O＋Na2O）=7.68%-8.12%,（87Sr/86Sr）i=0.705 5,εNd（t） =-3.92,which is consistent with that of the late Mesozoic high-K calc-alkaline granitoid in the coastal region of Fujian Province.It＇s suggested that the host granites in Meizhou Island be formed by partial melting in middle-lower crustal rocks by underplating and heating of basaltic magma produced from partial melting of enriched lithospheric mantle.The mafic dikes were probably derived from the detained basaltic magma experienced fractional crystallization process.The granite and mafic dikes from Meizhou Island formed in the extensional setting and responded to two extension events.The study on the Meizhou Island granite and mafic dikes provides a new case for Late Mesozoic tectonic-magmatic activities and constraint to the time of lithosphere extensional events in the coastal area of Fujian Province.

关 键 词：形成时差 锆石SHRIMP U-PB定年 镁铁质岩墙群 寄主花岗岩 地球化学 福建湄洲岛 

分 类 号：P588.13[天文地球—岩石学]