安徽省岳西县碧溪岭片麻岩地球化学和锆石U-Pb年龄研究
摘要
本文通过对碧溪岭片麻岩综合研究表明,岩石化学成分高硅(SiO_2=73.18%~75.60%)、低铝(Al_2O_3=11.93%~12.79%)、富碱(Na_2O+K_2O=6.11%~7.23%)和高钠(Na_2O/K_2O=1.51~1.94);微量元素富集大离子亲石元素Rb、Ba、Th、U等和Pb,贫Nb、Ta、Zr、Hf、Ti等高场强元素;稀土元素含量范围变化较大(TREE=142.38~308.44×10~(-6)),富集轻稀土(LREE/HREE=5.93~6.01),和铕负异常明显(δEu=0.42~0.64)等。造岩矿物中斜长石聚片双晶常垂直晶体延长方向,以及继承锆石大部分是不同时代的岩浆碎屑锆石等,暗示其寄主岩是沉积岩;锆石LA-ICP-MS定年结果:1)获得超高压变质锆石U-Pb年龄为242 Ma;2)继承锆石U-Pb年龄,除了有比较多的属于元古代(768~639 Ma),还有大量的属于古生代(590~358 Ma)等,表明其寄主岩的时代不会早于古生代。
According to the comprehensive research in this paper,the chemical composition of the gneiss in Bixiling represents high Si(SiO_2=73.18%~75.60%),low Al(A1_2O_3 = 11.93%~12.79%),rich alkali(Na_2O + K_2O = 6.11%~7.23%) and high Na(Na_2O/K_2O = l.51~1.94).And for the trace elements,large-ion lithophile elements such as Rb,Ba,Th,U and Pb are rich,while high field strength elements such as Nb,Ta,Zr,Hf and Ti are poor.For the rare earth elements(TREE = 142.38~308.44×10~(-6) ),the gneiss represents relatively rich LREE (LREE/HREE = 5.93~6.01 ) enrichments and obvious Eu(δ5Eu = 0.42~0.64 ) negative abnormality.The country rock of gneiss is sedimentary because of the polysynthetic twin of plagioclase grew along the vertical direction of crystal extension and most of inherited zircons were magmatic clastic zircons of different times.The date of zircon LA-ICP-MS U-Pb is 242 Ma which belongs to Indo-Chinese epoch and is equal to the Early Triassic.According to the "inheritance zircon" U-Pb different age(Proterozoic eon 768 ~ 639 Ma and Palaeozoic era 590~358 Ma),the country rock of gneiss in Bixiling is felsic sedimentary rock which is rich in Na whose formation age is not earlier than Palaeozoic.
According to the comprehensive research in this paper,the chemical composition of the gneiss in Bixiling represents high Si(SiO_2=73.18%~75.60%),low Al(A1_2O_3 = 11.93%~12.79%),rich alkali(Na_2O + K_2O = 6.11%~7.23%) and high Na(Na_2O/K_2O = l.51~1.94).And for the trace elements,large-ion lithophile elements such as Rb,Ba,Th,U and Pb are rich,while high field strength elements such as Nb,Ta,Zr,Hf and Ti are poor.For the rare earth elements(TREE = 142.38~308.44×10~(-6) ),the gneiss represents relatively rich LREE (LREE/HREE = 5.93~6.01 ) enrichments and obvious Eu(δ5Eu = 0.42~0.64 ) negative abnormality.The country rock of gneiss is sedimentary because of the polysynthetic twin of plagioclase grew along the vertical direction of crystal extension and most of inherited zircons were magmatic clastic zircons of different times.The date of zircon LA-ICP-MS U-Pb is 242 Ma which belongs to Indo-Chinese epoch and is equal to the Early Triassic.According to the "inheritance zircon" U-Pb different age(Proterozoic eon 768 ~ 639 Ma and Palaeozoic era 590~358 Ma),the country rock of gneiss in Bixiling is felsic sedimentary rock which is rich in Na whose formation age is not earlier than Palaeozoic.
引文
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郑祥身,金成伟,翟明国,石永红.1999.北大别灰色片麻岩的岩石化学特征及大地构造背景.岩石学报,15(3):350-358. Zheng Xiangshen,Jin Chengwei,Zhai Mingguo and Shi Yonghong.1999.Petrochemistry and tectonic background of the gray gneisses in north Dabie terrane.Acta Petrologica Sinica,15(3):350-358.
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程裕淇,刘敦一,Williams I S,简平,庄育勋,高天山.2000.大别山碧溪岭深色榴辉岩和片麻状花岗质岩石SHRIMP分析——晋宁期高压—超高压变质作用的同位素年代学依据地质学报,74(3):193-205. Cheng Yuqi,Liu Dunyi,Williams 1 S,Jia Ping,Zhuang Yuxun and Gao Tianshan.2000.SHRIMP U-Pb dating of zircons of a dark-coloured eclogile and a garnet-bearing gneissic-granitic rock from Bixiling,eastern Dabie area——Isotope chronological evidence of Neoproterozoic HP-UHP metamorphism.Acta Geologica Sinica,74(3):193-205.
高天山,李惠民,汤加福,侯明金.2000.大别山岳西碧溪岭地区片麻状斜长花岗岩锆石U-Ph年龄.安徽地质,10(3): 205-208. Gao Tianshan,Li Huimin,Tang Jiafu and Hou Mingjin.2000.The U-Pb age of zircon from the gneissic plagiogranite in the Bixiling area,Yuexi,the Dabie Mountains.Geology of Anhui,10(3):205-208.
韩宗珠,袁启林,盛上兴.1989.安徽岳西碧溪岭榴辉岩及其伴生石榴石橄榄岩的岩石学和地球化学.岩石学报,5(4): 22-32. Han Zongzhu,Yuan Qilin and Sheng Shixing.1989.Petrology and geochemistry of eclogile and associated garnet peridotite in Bixiling,Yuexi,Anhui Province.Acta Petrologica Sinica,5(4):22-32.
胡世玲,郝杰,李曰俊,戴樟谟,蒲志平.1999.大别山碧溪岭榴辉岩激光探针~(40)Ar~(39)Ar年龄.地质科学,34(4):427-431 Hu Shiling,Hao Jie,Li Yuejun,Dai Tongmo and Pu Zhiping.1999.Laser porobe ~(40)Ar-~(39) Ar isochron age of eclogite from Bixiling,Dabie uhp orogenic belt.Chinese Journal of Geology(Scientia Geologica Sinica),34(4):427-431.
简平,杨巍然,周惠芳.1996.大别山东部含柯石英榴辉岩锆石U-Pb测年——多期超高压变质作用的证据.华南地质与矿产,(4):14-21. Jian Ping,Yang Weiran and Zhou Huifang.1996.U-Pb zircon dating on coesite-bearing eclogues from easterndabie area,central China;The evidence formultiepisode ultrahigh pressure metamorphism.Geology and Mineral Resources of South China, (4):14-21.
李曙光,Jagoutz E,肖益林,葛宁洁,陈移之.1996,大别山—苏鲁地体超高压变质年代学——I.Sm-Nd同位素体系.中国科学(D辑),26(3):251-257 Li Shuguang,Jagoutz E,Xiao Yilin,Ge Ningjie and Chen Yizhi.1996.Chronology of ultrahigh-pressure metamorphism in the Dabie Mountains and Su-Lu terrane:I.Sm-Nd isotope system.Science in China{ Series D),39(6):597-609.
刘福来,许志琴,徐惠芬.1999.东海超高压变质带花岗质片麻岩的岩石学及其成因特征.地质论评,45(增刊):636-644. Liu Fulai,Xu Zhiqin and Xu Huifen.1999.Petrology and genetic mechanism of franitic fneiss in Donghai ultrahigh-pressure metamorphic belt.Geological Review,45(suppl.):636-644.
刘福来,许志琴,张泽明,杨经绥.2001.中国大陆科学钻探工程预先导孔中片麻岩—花岗质片麻岩的岩石学和地球化学研究.地质学报,75(1):70-81. Liu Fulai,Xu Zhiqin,Zhang Zeming and Yang Jingsui.2001.Petrology and geochemistry of gneiss and granitic gneiss from prepilot drillhole(CCSD-PP1),Chinese Continental Scientific Drilling Project.Acta Geologica Sinica,75(1):70-81.
刘若新,樊祺诚,李惠民.1995.大别山碧溪岭石榴橄榄岩—榴辉岩体的原岩性质及同位素年代学的启示.岩石学报, 11(3):234-256. Liu Ruoxin,Fan Qicheng and Li Huimin.1995.The nature of protolith of Bixiling garnet peridotite-eclogite massif in Dabie Mountains and the implication of its isotopic geochronology.Acta Petrologica Sinica,11(3):234-256.
刘文元,刘景波,柳小明.2009.大别山高压—超高压片麻岩核—边结构锆石成因探讨,44(3):966-982. Liu Wenyuan,Liu Jingbo and Liu Xiaoming.2009.Genesis of zircons with core-rim structure from HP-UHP gneisses of the Dabie Mountains.Chinese Journal of Geology,44(3):966-982.
涂湘林,张红,邓文峰,凌明星,梁华英,刘颖,孙卫东.2011 RESOlution激光剥蚀系统在微量元素原位微区分析中的应用.地球化学,40(1):83-98. Tu Xianglin,Zhang Hong,Deng Wenfeng,Ling Mingxing,Liang Huaying,Liu Ying and Sun Weidong.2011.Application of RESOlution in-situ laser ablation ICP-MS in trace element analyses.Geochimica,40(1):83-98.
王松山,葛宁洁,桑海清,裘冀.1999.多硅白云母过剩Ar成因及绿辉石Ar-Ar年龄谱意义:以南大别超高压榴辉岩为例.科学通报,44(24):2607-2613. Wang Songshan,Ge Ningjie,Sang Haiqing and Qiu Ji.1999.The cause of excess Ar in white mica and the implication of doleritic Ar-Ar date.Chinese Science Bulletin,44(24):2607-2613.
夏斌,王敏,张玉泉,李建峰,黄强太,王洪,刘立文,李贺,董春艳.2011.江苏东海片麻状碱性花岗岩地质地球化学及其年代学研究——以驼峰、牛山岩体为例.地质学报,85(9):1464-1476. Xia Bin,Wang Min,Zhang Yuquan,Li Jianfeng,Huang Qiangtai,Wang Hong,Liu Liwen,Li He and Dong Chunyan.2011. Geological and geochemical characteristics of the gneissic alkali granite in Donghai,Jiangsu Province,and chronology research;Two examples from the Tuofeng and Niushan regions.Acta Geologica Smica,85(9):1464-1476.
鄢全树,钟增球,周汉文.2005.大别超高压变质地体四道河地区岩石学研究.岩石矿物学杂志,24(3):186-196. Yan Quanshu,Zhong Zengqiu and Zhou Hanwen.2005.Petrology of Sidaohe area in UHP metamorphic terrane,the Dabie Mountains.Acta Petrologica et Mineralogica,24(3):186-196. (11):1013—1015.
翟明国,从柏林,赵中岩,王清晨,李家驹.1991.大别山榴辉岩带的高压硬玉石英岩块体及其地质意义.科学通报,37 (11):1013-1015. Zhai Mingguo,Cong Bailin,Zhao Zhongyan,Wang Qingchen and Li Jiaju.1991.High pressure jadeitic quartzite from Dabie eclogite belt and its geological implication.Chinese Science Bulletin,37(11):1013-1015.
张旗,赵大升,刘若新,马宝林,樊祺诚,李齐.1993.安徽省岳西碧溪岭—五河地区石榴石橄榄岩—榴辉岩组合的原岩性质,科学通报,38(18):1694-1697. Zhang Qi,Zhao Dasheng,Liu Ruoxin,Ma Baolin,Fan Qicheng and Li Qi.1993.The protolith character of garnetperidotite and eclogite from Bixiling and Wuhe,Anhui Province.Chinese Science Bulletin,38(18):1694-1697.
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