江西省金溪—南城混合岩和花岗岩的岩石地球化学及同位素地球化学研究
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摘要
在研究金溪—南城变质混合岩带中混合岩、花岗岩的矿物岩石学基础上 ,详细研究了它们的Nd、Sr、Pb、O同位素组成。混合岩、花岗岩初始钕同位素组成 (14 3Nd/14 4 Nd) i=0 .5116 89~0 .511853,在εNd -T图中位于该地区结晶基底变粒岩、片岩Nd同位素演化域上方 ,褶皱基底绢云千枚岩Nd同位素演化线下方 ;初始锶同位素组成 (87Sr/86 Sr) i=0 .74 86 4~ 0 .752 57;氧同位素组成δ18O为 10 .2 3‰~ 14.89‰ ,相当于高氧花岗岩的氧同位素变化范围 (>10‰ ) ;放射性成因铅较低 ,μ =10 .0 7~ 10 .4 ,变化范围小 ,铅同位素组成位于上部地壳演化线上方。这表明混合岩、花岗岩是由成熟度高、富氧的变粒岩及片岩等变质沉积岩经部分重熔形成的。
Jinxi-Nancheng metamorphic migmatite zone composed mainly of Jinxi igneous mass amd controlled by various ductile shear zones is a multi-facies, multi-type and progressive metamorphic zone. On the basis of a comprehensive petrological and mineralogical study of Jinxi-Nancheng metamorphic migmatite zones, their Nd-Sr-Pb-O isotopic geochemistry has been investigated in detail. The initial Nd and Sr isotopic compositions of migmatites and granites are 0.511689~0.511853 and 0.74864~0.75257 respectively. δ 18O values of migmatites and granites are 10.23‰~14.89‰, similar to the δ 18O values of high O granites(>10‰). Below the evolution line of sericite schist of folded-basement in the εNd-T evolution diagram, initial Nd isotopic composition of migmatites and granites is apparently located in the evolution area of granulitite and schist of crystalline-basement. Their contents of radiogenic Pb are relatively low, with μ being 10.07~10.4, and their Pb isotopic compositions are above the evolution line of the upper crust. The above features show that migmatites and granites in Jinxi-Nancheng migmatite zone are formed by partial remelting of O-rich and highly-matured granulitite and schist.
Jinxi-Nancheng metamorphic migmatite zone composed mainly of Jinxi igneous mass amd controlled by various ductile shear zones is a multi-facies, multi-type and progressive metamorphic zone. On the basis of a comprehensive petrological and mineralogical study of Jinxi-Nancheng metamorphic migmatite zones, their Nd-Sr-Pb-O isotopic geochemistry has been investigated in detail. The initial Nd and Sr isotopic compositions of migmatites and granites are 0.511689~0.511853 and 0.74864~0.75257 respectively. δ 18O values of migmatites and granites are 10.23‰~14.89‰, similar to the δ 18O values of high O granites(>10‰). Below the evolution line of sericite schist of folded-basement in the εNd-T evolution diagram, initial Nd isotopic composition of migmatites and granites is apparently located in the evolution area of granulitite and schist of crystalline-basement. Their contents of radiogenic Pb are relatively low, with μ being 10.07~10.4, and their Pb isotopic compositions are above the evolution line of the upper crust. The above features show that migmatites and granites in Jinxi-Nancheng migmatite zone are formed by partial remelting of O-rich and highly-matured granulitite and schist.
引文
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[5 ] 章邦桐 ,胡恭任 ,王湘云 .相山地区变质基底新认识及其原岩归属的对比研究 [J].铀矿地质 ,1997,13(1) :1~ 7.
[6 ] HuGongren ,ZhangBangtong ,YuRuilian .Petrology ,ageandgeochemistryoftheproterozoicamphibolitesfromXiang shan ,centralJiangxiProvince[J].ChineseJournalofGeochemistry ,1999,18(2 ) :139~ 149.
[7] 胡恭任 ,刘丛强 ,章邦桐 ,等 .赣中变质岩带的组成及构造变质变形特征 [J].中国区域地质 ,2 0 0 0 ,19(4 ) :375~381.
[8] 刘昌实 .华南陆壳改造系列花岗岩类型划分和成岩物质来源 [J].地质学报 ,1990 (1) :43~ 6 2 .
[9] 章邦桐 .花岗岩物理化学与铀金属矿床成矿机制研究 [M ].北京 :原子能出版社 ,1992 .
[10 ] FaureG .PrinciplesofIsotopicGeology[M ].JohnWiley&Sons ,1986 .
[11] 胡恭任 ,章邦桐 ,于瑞莲 .赣中变质岩带的Sm -Nd、Rb -Sr同位素年代研究 [J].地质论评 ,1999,45 (2 ) :12 9~134 .
[12 ] JohannesW .Ontheoriginoflayeredmigmatites[A].GribbleCD .Migmatitesmelting[C].ShiraPublishingLimited ,198 3.
[13] 胡恭任 ,章邦桐 .赣中变质基底的Nd同位素组成和物质来源 [J].岩石矿物学杂志 ,1998,17(1) :35~ 40 .
[14] O’NionsRK .ANd_isotopicinvestigationofsedimentsrelatedtocrustaldevelopmentinBritishIsles[J].EarthPlanet .Sci.Lett.,1983,6 3:2 2 9~ 2 40 .
[15 ] AllegreCJandOthmanDB .Nd_Srisotopicrelationshipingranitoidrocksandcontinentalcrustdevelopment:achemicalapproachtoorogenesis[J].Nature,1980 ,2 86 :335~ 34 2 .
[16 ] 徐克勤 ,王德滋 ,胡受奚 ,等 .华南花岗岩的成因及其成矿关系 [A].徐克勤 ,涂光炽 .花岗岩地质及成矿关系[C].南京 :江苏科技出版社 ,1984,1~ 2 0 .
[17] 张理刚 .稳定同位素在地质科学中的应用 [M ].西安 :陕西科学技术出版社 ,1985 .
[18] ZartmanRE .LeadisotopicprovincesintheCordilleraofthewesternUnitedStateandtheirgeologicalsignificance[J].Econ .Geol.,1974,6 9:792 .
[19] AshworthJR .PetrogenesisofmigmatitesintheHuntly -Portsoyarea ,north_eastscottland[J],Mineral.40 (3) :6 6 1~ 6 82 .
[2 0 ] YardleyBW .GenesisofsksgitgensismigmatitesWashingtonandtheColoadoFrontRange[J].Contrib .Miner .Petrol.,1984,85 :30~ 44 .
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