广西横县马山晚侏罗世钾玄质侵入岩的年代学和地球化学研究:兼论钦杭成矿带西南段燕山期构造背景
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摘要
广西横县马山杂岩体位于钦杭成矿带西南段,出露于防城—灵山断裂带的西侧,为一套包括辉长岩、玄武(玢)岩、闪长(玢)岩、二长(斑)岩、普通角闪正长岩、石英正长岩、花岗岩在内的从基性到中、酸性的岩浆岩岩系。文中对其中的中性浅成侵入岩进行研究,获得二长闪长玢岩样品的40Ar/39Ar坪年龄为(153.8±0.6)Ma,表明岩石形成于晚侏罗世。所研究的岩石样品富K、富碱、w(K2O+Na2O)=5.73%~8.54%、K2O/Na2O=0.87~1.76,富集大离子亲石元素Rb、Ba、Th、U和轻稀土元素,无明显的Nb-Ta-Ti负异常,为典型板内钾玄质岩石。其(87Sr/86Sr)i变化范围在0.705 11~0.705 47,εNd(t)变化范围在0.6~1.4,206Pb/204Pb为19.019~19.228,207Pb/204Pb为15.720~15.737,208Pb/204Pb为39.372~39.518,元素和同位素地球化学特征指示岩浆来源于亏损的软流圈地幔(DMM)和富集岩石圈地幔(EMⅡ)两个端员的混合。结合前人对南岭西部侏罗纪岩浆岩的研究成果,认为马山杂岩体的岩浆成分和源区特征反映桂东南在晚侏罗世发生了区域软流圈地幔上涌和岩石圈伸展-减薄作用,这是钦杭带西南段燕山期花岗岩和相关矿床形成的重要的地质构造背景。
The Mashan igneous complex,occurring in the southwestern segment of the Qinzhou-Hangzhou metallogenic belt with outcropping in the west side of the Fangcheng-Lingshan fault zone,is composed of alkali shoshonitic rocks in which basic,mediosilicic and acid rocks are included.Geochronology and geochemistry of the mediosilicic intrusive rocks have been studied in detail in this paper.A sample of the rocks have a 40Ar/39 Ar plateau age of 153.8±0.6 Ma,indicating that the rocks were formed in the Late Jurassic.Samples of the rocks are all abundant in alkaline elements of K and Na,with K2O+Na2O being of 5.73%-8.54%,K2O/Na2O=0.87-1.76.They are enriched in the large-ion lithosphile elements of Rb,Ba,Th,U and LREE,and their isotopic compositions are characterized by that the ratios of(87Sr/86Sr)irange from 0.70511 to 0.70547,εNd(t)from 0.6to 1.4,206Pb/204Pb=19.019-19.228,207Pb/204Pb=15.720-15.737,and 208Pb/204Pb=39.372-39.518.These geochemical data show that the magma was derived from the sources mixed by two endmembers of the DMM asthenosphere and the EMⅡ lithosphere.It suggests that upwelling of the asthenosphere and extension of the lithosphere probably took place in southeast Guangxi during the Late Jurassic,which possibly were the tectonic settings of formation for the Yanshanian granites and the related mineral deposits in the southwestern segment of the Qinzhou-Hangzhou metallogenic belt.
The Mashan igneous complex,occurring in the southwestern segment of the Qinzhou-Hangzhou metallogenic belt with outcropping in the west side of the Fangcheng-Lingshan fault zone,is composed of alkali shoshonitic rocks in which basic,mediosilicic and acid rocks are included.Geochronology and geochemistry of the mediosilicic intrusive rocks have been studied in detail in this paper.A sample of the rocks have a 40Ar/39 Ar plateau age of 153.8±0.6 Ma,indicating that the rocks were formed in the Late Jurassic.Samples of the rocks are all abundant in alkaline elements of K and Na,with K2O+Na2O being of 5.73%-8.54%,K2O/Na2O=0.87-1.76.They are enriched in the large-ion lithosphile elements of Rb,Ba,Th,U and LREE,and their isotopic compositions are characterized by that the ratios of(87Sr/86Sr)irange from 0.70511 to 0.70547,εNd(t)from 0.6to 1.4,206Pb/204Pb=19.019-19.228,207Pb/204Pb=15.720-15.737,and 208Pb/204Pb=39.372-39.518.These geochemical data show that the magma was derived from the sources mixed by two endmembers of the DMM asthenosphere and the EMⅡ lithosphere.It suggests that upwelling of the asthenosphere and extension of the lithosphere probably took place in southeast Guangxi during the Late Jurassic,which possibly were the tectonic settings of formation for the Yanshanian granites and the related mineral deposits in the southwestern segment of the Qinzhou-Hangzhou metallogenic belt.
引文
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[24]武莉娜,王志畅,汪云亮.微量元素La,Nb,Zr在判别大地构造环境方面的应用[J].华东地质学院学报,2003,26(4):343-348.
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[27]朱金初,李向东,沈渭洲,等.广西花山复式花岗岩体成因的锶、钕和氧同位素研究[J].地质学报,1989(3):225-235.
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[31]Meschede M.A method of discriminating between different type of mid-ocean ridge basalts and continental tholeiites with the Nb-Zr-Y diagram[J].Chemical Geology,1986,56(3/4):207-218.
[32]谢智,李全忠,陈江峰,等.庐枞早白垩世火山岩的地球化学特征及其源区意义[J].高校地质学报,2007,13(2):235-249.
[33]赵崇贺.中基性火山岩成分的ATK图解与构造环境[J].地质科技情报,1989,8(4):1-5.
[34]徐夕生,邱检生.火成岩岩石学[M].北京:科学出版社,2010.
[35]邱家骧,廖群安.中国东部新生代玄武岩中单斜辉石巨晶的主要特征及成因信息[J].岩石矿物学杂志,1987,6(1):56-64.
[36]谢昕,徐夕生,邹海波,等.中国东南沿海中—新生代玄武岩微量元素和Nd-Sr-Pb同位素研究[J].岩石学报,2001,17(4):617-628.
[37]Gilder S A,Gilll J,Coe R S,et al.Isotopic and paleomagnetic constraints on the Mesozoic tectonic evolution of South China[J].Journal of Geophysical Research,1996,101:16137-16154.
[38]洪大卫,谢锡林,张季生.试析杭州—诸广山—花山高εNd值花岗岩带的地质意义[J].地质通报,2002,21(6):348-354.
[2]耿树方,刘平,郑洪伟,等.对中国东部中生代动力学机制的新认识[J].地质通报,2012,31(7):1061-1068.
[3]杨明桂,黄水保,楼法生,等.中国东南陆区岩石圈结构与大规模成矿作用[J].中国地质,2009,36(3):528-543.
[4]毛景文,陈懋弘,袁顺达,等.华南地区钦杭成矿带地质特征和矿床时空分布规律[J].地质学报,2011,85(5):636-658.
[5]Morrison G W.Characteristics and tectonic setting of the shoshonite rock association[J].Lithos,1980,13(1):97-108.
[6]李献华,周汉文,刘颖,等.桂东南钾玄质侵入岩带及其岩石学和地球化学特征[J].科学通报,1999,44(18):1992-1998.
[7]李献华,周汉文,刘颖,等.粤西阳春中生代钾玄质侵入岩及其构造意义:Ⅰ.岩石学和同位素地质年代学[J].地球化学,2000,29(6):513-520.
[8]李献华,周汉文,刘颖,等.粤西阳春中生代钾玄质侵入岩及其构造意义:Ⅱ.微量元素和Sr-Nd同位素地球化学[J].地球化学,2001,30(1):57-65.
[9]李献华,李武显,王选策,等.幔源岩浆在南岭燕山早期花岗岩形成中的作用:锆石原位Hf-O同位素制约[J].中国科学:D辑,2009(7):872-887.
[10]郭新生,陈江峰,张巽,等.桂东南富钾岩浆杂岩的Nd同位素组成:华南中生代地幔物质上涌事件[J].岩石学报,2001,17(1):19-27.
[11]吴根耀,李曰俊.桂东南马山沿灵山断裂出露的印支期洋岛玄武岩及其区域构造意义[J].现代地质,2011,25(4):682-691.
[12]广西壮族自治区区域地质测量队.广西壮族自治区贵县幅1∶20万区域地质图[M].广州:中山大学,1970.
[13]段瑞春,凌文黎,李青,等.桂东南马山杂岩体地球化学与锆石U-Pb同位素年代学特征及其对构造背景的指示意义[J].地质学报,2013,87(9):1221-1232.
[14]刘颖,刘海臣,李献华.用ICP-MS准确测定岩石样品中的40余种微量元素[J].地球化学,1996,25(6):552-558.
[15]Samson S D,Alexander E C.Calibration of the interlaboratory 40Ar/39Ar dating standard,Mmhb-1[J].Chemical Geology,1987,66(1/2):27-34.
[16]Hall C M,Farrell J W.Laser 40Ar/39Ar ages of tephra from Indian Ocean deep-sea sediments:Tie points for the astronomical and geomagnetic polarity time scales[J].Earth and Planetary Science Letters,1995,133:327-338.
[17]Middlemost E A K.Naming materials in the magma/igneous rock system[J].Earth-Science Reviews.1994,37(3/4):215-224.
[18]路远发.GeoKit:一个用VBA构建的地球化学工具软件包[J].地球化学,2004(5):459-464.
[19]邱家骧,林景仟.岩石化学[M].北京:地质出版社,1991.
[20]Peccerillo A,Taylor S R.Geochemistry of eocene calc-alkaline volcanic rokcs from the Kastamonu area,northern Turkey[J].Contributions to Mineralogy and Petrology,1976,58:63-81.
[21]Middlemost E A K.Magmas and Magmatic Rocks:An Introduction to Igneous Petrology[M].London:Longman,1985.
[22]李昌年.火成岩微量元素岩石学[M].武汉:中国地质大学出版社,1992.
[23]Sun S S,McDonugh W F.Chemical and isotopic systematics of oceanic basalts:Implications for mantle composition and processes[M]∥Saunders A D,Norry M J.Magmatism in the Ocean Basins.London:Geological Society of London,Special Publication,1989,42:313-345.
[24]武莉娜,王志畅,汪云亮.微量元素La,Nb,Zr在判别大地构造环境方面的应用[J].华东地质学院学报,2003,26(4):343-348.
[25]Goldstein S L,ONions R K,Hamilton P J.A Sm-Nd isotopic study of atmospheric dusts and particulates from major river systems[J].Earth and Planetary Science Letters,1984,70(2):221-236.
[26]Peucat J J,Vidal P,Bernard-Griffiths J,et al.Sr,Nd,and Pb isotopic systematics in the archean low-to high-grade transition zone of Southern India syn-accretion vs.post-accretion granulites[J].The Journal of Geology,1989,97(5):537-549.
[27]朱金初,李向东,沈渭洲,等.广西花山复式花岗岩体成因的锶、钕和氧同位素研究[J].地质学报,1989(3):225-235.
[28]Zindler A,Hart S.Chemical Geodynamics[J].Annual Review on Earth and Planetary Science,1986(14):493-571.
[29]郑海飞,郝瑞霞.普通地球化学[M].北京:北京大学出版社,2007.
[30]Mullen E D.MnO/TiO2/P2O5:A minor element dicriminatfor basaltic rocks of oceanic environments and its implications for petrogenesis[J].Earth and Planetary Science Letters,1983,62:53-62.
[31]Meschede M.A method of discriminating between different type of mid-ocean ridge basalts and continental tholeiites with the Nb-Zr-Y diagram[J].Chemical Geology,1986,56(3/4):207-218.
[32]谢智,李全忠,陈江峰,等.庐枞早白垩世火山岩的地球化学特征及其源区意义[J].高校地质学报,2007,13(2):235-249.
[33]赵崇贺.中基性火山岩成分的ATK图解与构造环境[J].地质科技情报,1989,8(4):1-5.
[34]徐夕生,邱检生.火成岩岩石学[M].北京:科学出版社,2010.
[35]邱家骧,廖群安.中国东部新生代玄武岩中单斜辉石巨晶的主要特征及成因信息[J].岩石矿物学杂志,1987,6(1):56-64.
[36]谢昕,徐夕生,邹海波,等.中国东南沿海中—新生代玄武岩微量元素和Nd-Sr-Pb同位素研究[J].岩石学报,2001,17(4):617-628.
[37]Gilder S A,Gilll J,Coe R S,et al.Isotopic and paleomagnetic constraints on the Mesozoic tectonic evolution of South China[J].Journal of Geophysical Research,1996,101:16137-16154.
[38]洪大卫,谢锡林,张季生.试析杭州—诸广山—花山高εNd值花岗岩带的地质意义[J].地质通报,2002,21(6):348-354.
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