铜陵桂花冲花岗闪长斑岩地球化学特征、锆石U-Pb年龄及其地质意义
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摘要
针对对铜陵桂花冲花岗闪长斑岩进行岩石学、岩石地球化学及锆石U-Pb同位素年代学研究,结果表明该花岗闪长斑岩高硅富碱(w(SiO2)平均为63.60%,w(Na2O+K2O)平均为7.09%,K2O/Na2O为0.51~0.68),属高钾钙碱性系列岩石。岩石稀土总量低(ΣREE在187.43×10-6和209.19×10-6之间),但轻稀土富集而重稀土亏损(ΣLREE/ΣHREE为15.00~16.49,(La/Yb)N为22.37~28.45),且具弱负Eu异常(δEu在0.75~0.83,平均为0.80)。同时,岩石富集大离子亲石元素(Rb,Ba,Th和U),而亏损高场强元素(Nb和Ta)。锆石LA-ICP-MS U-Pb定年测得花岗闪长斑岩年龄为(138.3±1.4)Ma,表明该岩体的形成时代为早白垩世,与铜陵矿集区中生代主要成矿岩体的年龄(137.5 Ma±1.1Ma~151.8Ma±2.6Ma)一致。该花岗闪长斑岩形成于碰撞后构造环境,是由壳幔混合岩浆冷却结晶形成的。
Petrologic and geochemical features and zircon U-Pb isotope age of the Guihuachong granodiorite porphyry in Tongling are studied.It shows that the rock is rich in w(SiO2)(averagely 63.60%)and alkali(averagely 7.09%),with smaller ratios of w(K2O/Na2O)(0.51~0.68),indicating that it belongs to high-K calc-alkaline series.It is characterized by low contents ofΣREE(187.43×10-6~209.19×10-6),high ratios ofΣLREE/ΣHREE(15.00~16.49)and(La/Yb)Nvalues(22.37~28.45),and a little negative Eu anomalies(δEu 0.75~0.83,averagely0.80).The rock is enriched in large iron lithophile elements(Rb,Ba,Th,and U)and depleted in high field strength elements(Nb and Ta).LA-ICP-MS zircon U-Pb age of the granodiorite porphyry is defined to be(138.3±1.4)Ma,suggesting that the rock was formed at the beginning of the Early Cretaceous Period,corresponding to the age(137.5Ma±1.1Ma~151.8Ma±2.6Ma)of main Mesozoic metallogenic plutons in Tongling.It is considered that this granodiorite porphyry was formed by cooling and crystallization of magma with mixing source of mantle and crust in the post-collision tectonic environment.
Petrologic and geochemical features and zircon U-Pb isotope age of the Guihuachong granodiorite porphyry in Tongling are studied.It shows that the rock is rich in w(SiO2)(averagely 63.60%)and alkali(averagely 7.09%),with smaller ratios of w(K2O/Na2O)(0.51~0.68),indicating that it belongs to high-K calc-alkaline series.It is characterized by low contents ofΣREE(187.43×10-6~209.19×10-6),high ratios ofΣLREE/ΣHREE(15.00~16.49)and(La/Yb)Nvalues(22.37~28.45),and a little negative Eu anomalies(δEu 0.75~0.83,averagely0.80).The rock is enriched in large iron lithophile elements(Rb,Ba,Th,and U)and depleted in high field strength elements(Nb and Ta).LA-ICP-MS zircon U-Pb age of the granodiorite porphyry is defined to be(138.3±1.4)Ma,suggesting that the rock was formed at the beginning of the Early Cretaceous Period,corresponding to the age(137.5Ma±1.1Ma~151.8Ma±2.6Ma)of main Mesozoic metallogenic plutons in Tongling.It is considered that this granodiorite porphyry was formed by cooling and crystallization of magma with mixing source of mantle and crust in the post-collision tectonic environment.
引文
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[23]吴淦国,张达,狄永军,等.铜陵矿集区侵入岩SHRIMP锆石U-Pb年龄及其深部动力学背景[J].中国科学(D辑),2008,38(5):630-645.
[24]Whalen J B,Currie K I,Chappell B W.A-type granites:Geochemical characteristics,discrimination and petrogenesis[J].Contrib Mineral Petrol,1987,95(4):407-419.
[25]Pearce J A,Harris N B W,Tindle A G.Trace element discrimination diagrams for the tectonic interpretation of granitic rocks[J].Journal of Petrology,1984,25:956-983.
[2]郭文魁,常印佛,黄崇柯.我国主要类型铜矿成矿和分布的某些问题[J].地质学报,1978,6(3):169-182.
[3]毛景文,邵拥军,谢桂青,等.长江中下游成矿带铜陵矿集区铜多金属矿床模型[J].矿床地质,2009,28(2):109-119.
[4]蒋其胜,赵自宏,黄建满.安徽南陵姚家岭铜铅锌矿床的发现及意义[J].中国地质,2008,35(2):314-321.
[5]Liu Y S,Hu Z C,Gao S,et al.In situ analysis of major and trace elements of anhydrous minerals by LA-ICP-MS without applying an internal standard[J].Chemical Geology,2008,257:34-43.
[6]Liu Y,Gao S,Hu Z,et al.Continental and oceanic crust recycling-induced melt-peridotite interactions in the Trans-North China Orogen:U-Pb dating,Hf isotopes and trace elements in zircons of mantle xenoliths[J].Journal of Petrology,2010,51:537-571.
[7]Ludwig K R.3.0.A Geochronological Toolkit for Micro-soft Excel[M].Berkeley Geochronology Center,Special Publication,2003,(4):1-70.
[8]Maniar P D and Piccolli P M.Tectonic discrimination of granitoids[J].Geol Soc Am Bull,1989,101(5):635-643.
[9]Rickwood P c.Boundary lines within petrologic diagrams which use oxides of major and minorelements[J].lithos,1989,22(4):247-263.
[10]Boynton W V.Cosmochemistry of the rare earth element:Meteorite studies[C]//Henderson P(ed.).Rare Earth Element Geochemistry.Amsterdam:Elsevier,1984,63-114.
[11]Sun S S,McDonough W F.Chemical and isotopic systematics of oceanic basalts:Implications for mantle composition and processes[J].Geol Soc London Spec Pub,1989,42:313-345.
[12]Vavran G,Schmid R,GEBAUER,D.Internal Morphol-ogy,Habit and U-Th-Pb Microanalysis of Amphibolite-to-Granulite Facies Zircons:Geochronology of the Ivrea Zone(Southern Alps)[J].Mineral Petrol,1999,134(4):380-404.
[13]Hanchar J M,Miller C F.Zircon zonation patterns as revealed by cathodolum and backscattered electron images:Implications for interpretation of complex crustalhistories[J].Chem Geol,1993,110:1-13.
[14]杜杨松,李顺庭,曹毅,等.安徽铜陵铜官山矿区中生代侵入岩的形成过程-岩浆底侵、同化混染和分离结晶[J].现代地质,2007,21(1):71-77.
[15]谢建成,杨晓勇,杜建国.铜陵地区中生代侵入岩LA-ICP-MS锆石U-Pb年代学及Cu-Au成矿指示意义[J].岩石学报,2008,24(8):1 782-1 800.
[16]刘绍峰,杜杨松,付水兴,等.安徽姚家岭锌金多金属矿区花岗闪长斑岩锆石U-Pb年龄和Hf同位素特征及其地质意义[J].地球科学——中国地质大学学报,2013,38(增刊1):91-102.
[17]Green T H.Significanca of Nb/Ta as an indicator of geochemical processes in the crust-mantle system[J].Chemical Geology,1995,120:347-359.
[18]Hofinann A W.Chemical differentiation of the earth:The relationship between large crust,and oceanic,crust earth planet[J].Sci Lett,1988,90:297-314.
[19]岳元珍,史鸿歧,王小平,等.铜陵地区中酸性侵入岩的矿物特征及成岩条件初析[J].矿物岩石,1986,6(2):132-148.
[20]谢建成,杨晓勇,Insung Lee.安徽沿江地区燕山期含铜岩体稀土、微量地球化学特征[J].矿物岩石,2008,28(1):72-78.
[21]Andersson U B,Eklund O.Cellular plagioclase intergrowths as a result of crystal-magma mixing in the Proterozoic and rapakivi batholiths,SW Finland[J].Contributions to Mineralog and Petrology,1994,117:124-136.
[22]杜杨松,秦新龙,李炫具.安徽铜陵地区中生代幔源岩浆底侵作用-来自矿物巨晶和岩石包体的证据[J].岩石矿物学杂志,2004,6(2):109-116.
[23]吴淦国,张达,狄永军,等.铜陵矿集区侵入岩SHRIMP锆石U-Pb年龄及其深部动力学背景[J].中国科学(D辑),2008,38(5):630-645.
[24]Whalen J B,Currie K I,Chappell B W.A-type granites:Geochemical characteristics,discrimination and petrogenesis[J].Contrib Mineral Petrol,1987,95(4):407-419.
[25]Pearce J A,Harris N B W,Tindle A G.Trace element discrimination diagrams for the tectonic interpretation of granitic rocks[J].Journal of Petrology,1984,25:956-983.
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