郑永飞华南新元古代花岗岩锆石Hf和O同位素ppt课件.ppt
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?OIB vs CFB,3,华南新元古代岩浆岩分布,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,4,新元古代幕式岩浆活动,(Li ZX et al., 2003),740780,800830,5,新元古代地幔超柱事件,Li XH et al. (2003) Precam Res,Plume genesis?,6,新元古代早期扬子板块周边,Zhou MF et al. (2002) EPSL,Arc genesis?,Zhou JC et al. (2004)Wang XL et al. (2004),7,Episodic Growth of Juvenile Crust,Subduction zone: Arc MagmatismMantle plume: Oceanic PlateauRift magmatism,8,Uplift of mantle plume is evidenced by a rapid, pre-volcanic uplift,9,地幔柱与地幔超柱,浅柱,深柱,White & KcKenzie(1989),Campbell & Griffiths(1990),10,Hotspots around the world,Red: core-mantle boundary, yellow: transition zone, green-lithosphere(Courtillot et al., 2003, EPSL),11,Plume vs Non-plumes(Science, 2003, May 9),DEBATE,Narrow, vertical seismic structures traversing the whole mantleHigh temperaturesRelative fixity of hotspotsAge progression of volcanic chain,Predictions of plume,Shallow thermal anomaly at classic hotspotsHotspot is not so hotHotspot is not fixed, Not all volcanic chain has age progression,Observations,=,12,Three-dimensional view of deep mantle in tomographical model,Montelli et al. (2004) Science,13,Three-dimensional view of the shallow mantle and the newly discovered plumes in vertical model,Montelli et al. (2004) Science,14,板块构造与地幔柱之间的关系,Plume,Plate,15,Relationship between Plate subduction and Plume initiation,16,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,X,X,X,X,X,X,19,华南新元古代岩浆岩,750760 Ma: I-type,810830 Ma: S-type,20,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-MS Lu-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,Initial Hf Isotope Ratio of Zircon,Bimodal distribution,Hf(t) = 3.3 to 9.3 vs -4.4 to -1.2,25,Hf Model Age of Zircon,Bimodal distribution,TDM1 = 0.95 to 1.19 Ga vs TDM2 = 1.79 to 1.99 Ga,26,Zircon U-Pb & Hf Isotopes (1),27,Zircon U-Pb & Hf Isotopes (2),28,Zircon U-Pb & O Isotopes,29,Zircon Hf-O Isotopes (1),30,Zircon Hf-O Isotopes (2),31,Mineral O Isotopes (1),Equilibrium,32,Mineral O Isotopes (2),Equilibrium,33,Single-stage Hf Model Age,(Bimodal Igneous rocks of ca.750 to 760 Ma),Any meaning?,1.07 0.09 Ga,34,Two-stage Hf Model age,(Granitoids of ca.825 Ma),Paleoproterozoic basement?,1.860.07 Ga,35,Lu-Hf Isotope Evolution(progressive crust-mantle mixing),Bimodal compositions of both chemistry and isotope,36,Timing of Crust-Mantle Interaction,Initial phase: Heat: Crustal remelting at 820 MaPeak phase: Mass: Rift magmatism at 750 Ma Progressive addition of mantle-derived material to the crust,37,Growth of Juvenile Crust,(外推至亏损地幔线),79721 Ma,90120 Ma,Age of juvenile crust in South China,38,Age of Juvenile Crust,Gabbro at Shaba,Plume magmatism?,78718 Ma,39,Age of Juvenile Crust,Leucogranite at Sanfang,Arc magmatism?,89212 Ma,40,Mass transfer of mantle to crust at 900 Ma by Arc magmatism,X,X,X,X,X,X,X,X,X,X,41,ca.825Ma花岗岩源区,42,Grenvillian subduction Mantle superplume,1.1 to 0.9 Ga,0.83 to 0.74 Ga,43,ca.820Ma花岗岩浆作用,Plume head effect ?,44,新元古代扬子板块北缘岩浆活动和热液蚀变,Rodinian Breakup? Bimodal magmatism?,Meteoric-hydrothermal alteration,Paleoproterozoic to Archean basements,地幔柱,45,加厚地壳部分熔融物质： 900 Ma 大陆弧热能： 825 Ma 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： 800 Ma 初生地壳热能： 750 Ma 地幔超柱背景： 主动裂谷 构造带,48,ca.750Ma花岗岩浆作用,Plume head effect ?,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700800Ma，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18O 值低于地幔锆石值，大约一半为负18O 值。 新元古代高温热液蚀变，蚀变岩石部分熔融形成低18O 岩浆。与超大陆裂解和地幔超柱事件有关,Zheng et al. (2004) GCA,50,水岩反应,Zheng et al. (2003) ESR,51,地幔超柱活动与花岗岩浆作用(Chemical Geodynamics),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,谢谢光临！,Thanks for your attention,欢迎批评指正！,
