赣南铅厂岩体锆石U-Pb年代学与地球化学特征
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摘要
本文报道了江西省赣州市铅厂闪长质岩体的锆石LA-ICP-MS U-Pb年龄、全岩主量元素和微量元素地球化学特征资料,以确定其形成时代、源区性质、岩石成因及其地质意义。闪长岩中的锆石均呈半自形-自形晶,震荡环带发育,Th/U比值=0.69～1.17,指示其岩浆成因。对岩浆锆石的定年结果显示,铅厂闪长岩形成于(463.5±5.0)Ma。铅厂闪长岩SiO_2含量介于54%～56%之间,显示高钾(K_2O>Na_2O)的特征,里特曼指数介于2.28～2.55之间小于3.3,A/CNK平均值为0.69,属于高钾钙碱性偏铝质系列岩石。铅厂岩体稀土总量均值为182.04×10~(-6)。该区闪长岩富集轻稀土元素(LREEs)和大离子亲石元素(LILEs),亏损重稀土元素(HREEs)和高场强元素(HFSEs),样品具微弱铕负异常(dEu=0.71～0.75),表明其源区有斜长石的残留。岩体相对亏损高场强元素(Nb,Ta和Ti),显著富集大离子亲石元素(Pb和K),岩石地球化学分析表明,赣南铅厂闪长岩的岩浆源区可能受俯冲流体交代作用的地幔楔,其形成应与大洋板片俯冲有关,形成于活动大陆边缘环境。
This paper presents LA-ICP-MS zircon U-Pb ages, whole-rock major and trace elements geochemical data of the Qianchang dioritic intrusion in Ganzhou City, Jiangxi Province, in order to constrain the emplacement age, property of magmatic source, petrogenesis of the intrusion, and geological significances of those geochemical data. Zircon grains from those diorite samples are euhedral-subhedral crystals, with obvious oscillatory growth zoning and Th/U ratios of 0.69-1.17, indicating a magmatic origin. Zircon U-Pb dating results show that the emplacement age of Qianchang diorite is 463.5±5.0 Ma. The Qianchang diorite samples are characterized with stable SiO_2 concentrations of 54-56% and high potassium(K_2O > Na_2O) features, with Rittmann indexes of 2.28-2.55(< 3.3) and the mean A/CNK value of 0.69. The diorite belongs to the high potassium calc-alkaline metaluminous rock series. The diorite samples have average REE content of 182.04 ug/g, with enriched light rare earth elements(LREEs) and large ion lithophile elements(LILEs),depleted heavy rare earth elements(HREEs) and high field strength elements(HFSEs), and weak negative Eu anomalies(dEu = 0.71-0.75), suggesting the existence of residual plagioclase in the source area. These rocks are obviously enriched in LILE(such as Pb and K), but relatively depleted in HFSE(such as Nb, Ta, and Ti). Petro-geochemical results show that the magma of Qianchang diorite could be sourced from the subduction fluid metasomatized mantle wedge which was formed in association with the subduction of oceanic slab in the active continental margin setting.
This paper presents LA-ICP-MS zircon U-Pb ages, whole-rock major and trace elements geochemical data of the Qianchang dioritic intrusion in Ganzhou City, Jiangxi Province, in order to constrain the emplacement age, property of magmatic source, petrogenesis of the intrusion, and geological significances of those geochemical data. Zircon grains from those diorite samples are euhedral-subhedral crystals, with obvious oscillatory growth zoning and Th/U ratios of 0.69-1.17, indicating a magmatic origin. Zircon U-Pb dating results show that the emplacement age of Qianchang diorite is 463.5±5.0 Ma. The Qianchang diorite samples are characterized with stable SiO_2 concentrations of 54-56% and high potassium(K_2O > Na_2O) features, with Rittmann indexes of 2.28-2.55(< 3.3) and the mean A/CNK value of 0.69. The diorite belongs to the high potassium calc-alkaline metaluminous rock series. The diorite samples have average REE content of 182.04 ug/g, with enriched light rare earth elements(LREEs) and large ion lithophile elements(LILEs),depleted heavy rare earth elements(HREEs) and high field strength elements(HFSEs), and weak negative Eu anomalies(dEu = 0.71-0.75), suggesting the existence of residual plagioclase in the source area. These rocks are obviously enriched in LILE(such as Pb and K), but relatively depleted in HFSE(such as Nb, Ta, and Ti). Petro-geochemical results show that the magma of Qianchang diorite could be sourced from the subduction fluid metasomatized mantle wedge which was formed in association with the subduction of oceanic slab in the active continental margin setting.
引文
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[23]许德如,陈广浩,夏斌,等.湘东地区板杉铺加里东期埃达克质花岗闪长岩的成因及地质意义[J].高校地质学报,2006,12(4):507-521.
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[37]Winchester J.A.and Floyd P.A.Geochemical discrimination of different magma series their differentiation products using immobile elements[J].Chem Geol,1977,20:325-345.
[38]Sun S S,McDonough W F.Chemical and isotopic systematics of oceanic basalts:Implication for mantle composition and process[J].Saunders A D,Norry M J.Magmatism in the Ocean Basins[J].Geological Society,London,Special Publications,1989,42(1):313-345.
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[2]黄萱,孙世华,DePaolo D J,等.福建省白垩纪岩浆岩Nd、Sr同位素研究[J].岩石学报,1986,2(2):50-63.
[3]汪屹华,卢华夏,贾东,等.闽西南里田推覆构造带的特征与围埔花岗岩的成因联系[G]//东南大陆岩石圈结构域地质演化[C].北京:冶金工业出版社,1993:190-198.
[4]谢振东,杨永革.江西信丰安西岩体同位素年龄及其地质意义[J].江西地质,2000,14(3):172-175.
[5]舒良树,王德滋,沈渭洲.江西武功山中生代变质核杂岩的花岗岩类Nd-Sr同位素研究[J].南京大学学报(自然科学版),2000,36(3):306-311.
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[7]彭松柏,金振民,刘云华,等.云开造山带强过铝深熔花岗岩地球化学、年代学及构造背景[J].地球科学,2006,31(1):110-120.
[8]张芳荣,舒良树,王德滋,等.华南东段加里东期花岗岩类形成构造背景探讨[J].地学前缘,2009,8(1):248-260.
[9]张家菁,赵正,陈振宇,等.赣南-粤北油山-猫头寨岩体的成岩时代及其地质意义[J].岩矿测试,2012,9(3):554-558.
[10]程顺波,付建明,马丽艳,等.桂东北越城岭岩体加里东期成岩作用:锆石U-Pb年代学、地球化学和Nd-Hf同位素制约[J].大地构造与成矿学,2016,(04):853-872.
[11]刘善宝,李鹏,陈振宇,等.赣南于都万田花岗岩锆石铀-铅定年及启示[J].岩矿测试,2012,31(4):724-729.
[12]毛建仁,厉子龙,赵希林,等.赣南上犹岩体的锆石SHRIMP定年和地球化学特征及其构造意义[G]//中国矿物岩石地球化学学会.中国矿物岩石地球化学学会第11届学术年会论文集.中国矿物岩石地球化学学会,2007:29-31.
[13]吴富江,张芳荣.华南板块北缘东段武功山加里东期花岗岩的特征及成因探讨[J].中国地质,2003,30(2):166-172.
[14]赵芝,陈振宇,陈郑辉,等.赣南加里东期阳埠(垇子下)岩体的锆石年龄、构造背景及含矿性评价[J].岩矿测试,2012,31(3):530-535.
[15]苏晓云,郭春丽,陈振宇,等.赣南加里东期陡水岩体的锆石U-Pb年龄、地球化学特征及其稀土含矿性探讨[J].大地构造与成矿学,2014,(02):334-346.
[16]孙涛.新编华南花岗岩分布图及其说明[J].地质通报,2006,25(3):332-335.
[17]程顺波,付建明,马丽艳,等.桂东北越城岭-苗儿山地区印支期成矿作用:油麻岭和界牌矿区成矿花岗岩锆石U-Pb年龄和Hf同位素制约[J].中国地质,2013,40(4):1189-1201.
[18]付建明,马昌前,谢才富,等.湖南金鸡岭铝质A型花岗岩的厘定及构造环境分析[J].地球化学,2005,34(4):215-226.
[19]郭娜欣,赵正,陈振宇,等.赣南鹅婆岩体的年代学和岩石地球化学特征及其地质意义[J].岩矿测试,2014,33(4):589-597.
[20]孙明志,徐克勤.华南加里东花岗岩及其形成地质环境浅析[J].南京大学学报:地球科学,1990,2(4):10-22.
[21]刘宝珺,周名奎,王汝植.中国南方早古生代古地理轮廓及构造演化[J].中国地质科学院院报,1990(1):97-98.
[22]周新民.对华南花岗岩研究的若干思考[J].高校地质学报,2003,9(4):556-565.
[23]许德如,陈广浩,夏斌,等.湘东地区板杉铺加里东期埃达克质花岗闪长岩的成因及地质意义[J].高校地质学报,2006,12(4):507-521.
[24]Pupin J P.Zircon and granite petrology[J].Contributions to Mineralogy&Petrology,1980,73(3):207-220.
[25]徐夕生.华南花岗岩-火山岩成因研究的几个问题[J].高校地质学报,2008,14(3):283-294.
[26]赵磊.江西崇-余-犹成矿带钨多金属矿地质特征和资源评价[D].南京:南京大学,2013:10-80.
[27]Koschek G.Origin and significance of the SEM cathodoluminescence from zircon[J].Journal of Microscopy,1993,171:223-232.
[28]Wilson B M.Igneous Petrogenesis:A Global Tectonic Approach[M].Springer,1989:82.
[29]Peccerillo R,Taylor SR.Geochemistry of Eocene Calc-Alkaline Volcanice Rocks from the Kastamonu Area,Northern Turkey[J].Contributions to Mineralogy and Petrology,1976,58:63-81.
[30]Maniar P D,Piccoli P M.Tectonic discrimination of granitoids[J].Geological society of America bulletin,1989,101(5):635-643.
[31]Sun S S,Mcdonough W F.Chemical and Isotopic Systematics of Oceanic Basalts:Implications for Mantle Composition and Processes[J].Geological Society,London,Special Publications,1989,42(1):313-345.
[32]Hofmann A W.Chem ical differentiation of the earth:the relationship between mantle,continental crust,and oceanic crust[J].Earth Planet Sci Lett,1988,90(3):297-314.
[33]Rudnick RL,Gao S.Composition of the continental crust[G]//Rudnick RL.The Crust,Treatise in Geochemistry,2003:1-64.
[34]Taylor S R,Mclennan S M.The geochemical evolution of the continental curst[J].Reviews of Geophysics,1995,33(2):241-265.
[35]Kepezhinskas P,McDermott F,Defant M J,et al.Trace element and Sr Nd Pb isotop ic constraints on a three2component model of Kamchatka arc petrogenesis[J].Geochim ica et Cosmochimica Acta,1997,61(3):577-600.
[36]Pearce J A,Cann J R.Tectonic Setting of Basic Volcanic Rocks Determined Using Trace Element Analyses[J].Earth and Planetary Science Letters,1973,19:290-300.
[37]Winchester J.A.and Floyd P.A.Geochemical discrimination of different magma series their differentiation products using immobile elements[J].Chem Geol,1977,20:325-345.
[38]Sun S S,McDonough W F.Chemical and isotopic systematics of oceanic basalts:Implication for mantle composition and process[J].Saunders A D,Norry M J.Magmatism in the Ocean Basins[J].Geological Society,London,Special Publications,1989,42(1):313-345.
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