郑永飞--华南新元古代花岗岩锆石Hf和O同位素

1华南新元古代花岗岩锆石Hf和O同位素地球化学:地幔柱头效应?郑永飞吴元保张少兵赵子福中国科学技术大学地球和空间科学学院徐平吴福元中国科学院地质与地球物理研究所李献华中国科学院广州地球化学研究所李正祥西澳大学地质与地理系构造研究中心2科学问题华南新元古代花岗岩成因?裂谷vs地幔柱vs岛弧地幔柱岩浆与岛弧岩浆的识别?构造vs地球化学vs岩石学板块俯冲是否启动了地幔柱?OIBvsCFB3华南新元古代岩浆岩分布XXXXXXXXXXXXXXXXXXXX4新元古代幕式岩浆活动(LiZXetal.,2003)740~780800~8305新元古代地幔超柱事件LiXHetal.(2003)PrecamResPlumegenesis?6新元古代早期扬子板块周边ZhouMFetal.(2002)EPSLArcgenesis?ZhouJCetal.(2004)WangXLetal.(2004)7EpisodicGrowthofJuvenileCrustSubductionzone:ArcMagmatismMantleplume:OceanicPlateauRiftmagmatism8Upliftofmantleplumeisevidencedbyarapid,pre-volcanicuplift9地幔柱与地幔超柱浅柱深柱White&KcKenzie(1989)Campbell&Griffiths(1990)10HotspotsaroundtheworldRed:core-mantleboundary,yellow:transitionzone,green-lithosphere(Courtillotetal.,2003,EPSL)11PlumevsNon-plumes(Science,2003,May9)DEBATENarrow,verticalseismicstructurestraversingthewholemantleHightemperaturesRelativefixityofhotspotsAgeprogressionofvolcanicchainPredictionsofplumeShallowthermalanomalyatclassichotspotsHotspotisnotsohotHotspotisnotfixed,NotallvolcanicchainhasageprogressionObservations=12Three-dimensionalviewofdeepmantleintomographicalmodelMontellietal.(2004)Science13Three-dimensionalviewoftheshallowmantleandthenewlydiscoveredplumesinverticalmodelMontellietal.(2004)Science14板块构造与地幔柱之间的关系PlumePlate15RelationshipbetweenPlatesubductionandPlumeinitiation16地球系统科学TPXH2O板块构造与地幔柱“阴”与“阳”(Anderson,2004)17在地球科学中的空间尺度微观分析vs.宏观构造18华南新元古代岩浆岩XXXXXX19华南新元古代岩浆岩750~760Ma:I-type810~830Ma:S-type20华南新元古代岩浆岩21华南新元古代花岗岩锆石Hf和O同位素地球化学阴极发光(CL)结构照相MC-ICP-MSLu-Hf同位素分析徐平等(2004)《科学通报》激光氟化氧同位素分析龚冰和郑永飞(2003)《地学前缘》22新元古代岩浆岩锆石CL特点岩浆成因环带结构热液蚀变溶蚀结构23新元古代岩浆岩锆石CL特点24火山喷发InitialHfIsotopeRatioofZirconBimodaldistributionHf(t)=3.3to9.3vs-4.4to-1.225HfModelAgeofZirconBimodaldistributionTDM1=0.95to1.19GavsTDM2=1.79to1.99Ga26ZirconU-Pb&HfIsotopes(1)-8-404812700750800850900U-PbAge(Ma)Hf(t)GuangxiYunnanSichuan(a)27800120016002000700750800850900U-PbAge(Ma)HfModelAge(Ma)GuangxiYunnanSichuan(b)ZirconU-Pb&HfIsotopes(2)28ZirconU-Pb&OIsotopes24681012700750800850900U-PbAge(Ma)d18O(%o)MantlezirconYunnanGuangxiSichuan(c)29ZirconHf-OIsotopes(1)24681012-8-404812Hf(t)d18O(%o)GuangxiYunnanSichuan(a)3024681012800100012001400160018002000HfModelAge(Ma)d18O(%o)GuangxiYunnanSichuan(b)ZirconHf-OIsotopes(2)31MineralOIsotopes(1)-2024624681012d18O()ZirconD18O(%o)Quartz-ZirconGuangxiYunnanSichuanEquilibrium(a)Equilibrium32-4-202424681012d18O(%0)ZirconD18O(%0)Plagioclase-ZirconGuangxiYunnanSichuanEquilibrium(b)MineralOIsotopes(2)Equilibrium33Single-stageHfModelAge800100012001400Mean=1071±92MaMSWD=9.2TDM(Ma)(a)(BimodalIgneousrocksofca.750to760Ma)Anymeaning?1.070.09Ga34Two-stageHfModelage15001700190021002300Mean=1863±69MaMSWD=1.3TcDM(Ma)(b)(Granitoidsofca.825Ma)Paleoproterozoicbasement?1.860.07Ga35Lu-HfIsotopeEvolution(progressivecrust-mantlemixing)-20-10010200500100015002000Age(Ma)Hf(t)CHURDM1.9Ga825MaCrustMantlemixing-2mixing-1Bimodalcompositionsofbothchemistryandisotope36TimingofCrust-MantleInteractionInitialphase:Heat:Crustalremeltingat~820MaPeakphase:Mass:Riftmagmatismat~750MaProgressiveadditionofmantle-derivedmaterialtothecrust37GrowthofJuvenileCrust(外推至亏损地幔线)012360070080090010001100TJC(Ma)NumberMean=797±21MaMSWD=0.56Mean=901±20MaMSWD=0.68AgeofjuvenilecrustinSouthChina797±21Ma901±20MaAgeofjuvenilecrustinSouthChina38AgeofJuvenileCrustGabbroatShabaPlumemagmatism?-8-40481216200400800120016002000HfModelAge(Ma)Hf(t)787±18MaDepletedMantleCHUR98KD11178718Ma39AgeofJuvenileCrustLeucograniteatSanfangArcmagmatism?-8-40481216200400800120016002000HfModelAge(Ma)Hf(t)892±12MaDepletedMantleCHUR98GX9-189212Ma40Masstransferofmantletocrustat~900MabyArcmagmatismXXXXXXXXXX41ca.825Ma花岗岩源区42GrenvilliansubductionMantlesuperplume1.1to0.9Ga0.83to0.74Ga43ca.820Ma花岗岩浆作用Plumeheadeffect?44新元古代扬子板块北缘岩浆活动和热液蚀变RodinianBreakup?Bimodalmagmatism?Meteoric-hydrothermalalterationPaleoproterozoictoArcheanbasements地幔柱45加厚地壳部分熔融物质：~900Ma大陆弧热能：~825Ma地幔柱背景：拉张增生型造山带46破火山口垮塌地幔柱热液蚀变低18O岩浆活动裂谷构造带47大陆边缘岩浆活动物质：~800Ma初生地壳热能：~750Ma地幔超柱背景：主动裂谷构造带48ca.750Ma花岗岩浆作用Plumeheadeffect?49扬子板块北缘新元古代岩浆活动锆石U-Pb年龄主要集中在700~800Ma，岩浆活动峰期约在750Ma。锆石氧同位素比值范围-11‰~+9‰，大多数锆石d18O值低于地幔锆石值，大约一半为负d18O值。新元古代高温热液蚀变，蚀变岩石部分熔融形成低d18O岩浆。与超大陆裂解和地幔超柱事件有关Zhengetal.(2004)GCA50水岩反应Zhengetal.(2003)ESR51地幔超柱活动与花岗岩浆作用(ChemicalGeodynamics)初期：地幔热能为主，在拉张型增生造山带引起表壳物质熔融和中低温热液蚀变，形成S型花岗岩(初生地壳Nd-Sr同位素特点)峰期：地幔物质为主，在大陆边缘裂谷构造带引起初生地壳重熔和高温地表水-岩反应，形成I型花岗岩(M亚型)能量物质52欢迎批评指正！