鄭永飛--華南新元古代花崗巖鋯石hf和o同位素

1、1,華南新元古代花崗巖鋯石Hf和O 同位素地球化學: 地幔柱頭效應?,鄭永飛 吳元保 張少兵 趙子福中國科學技術大學地球和空間科學學院徐平 吳福元中國科學院地質與地球物理研究所李獻華中國科學院廣州地球化學研究所李正祥西澳大學地質與地理系構造研究中心,2,科學問題,華南新元古代花崗巖成因?裂谷 vs 地幔柱 vs 島弧地幔柱巖漿與島弧巖漿的識別?構造 vs 地球化學 vs 巖石學 板塊俯沖是否啟動了地幔柱?

2、OIB vs CFB,3,華南新元古代巖漿巖分布,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,4,新元古代幕式巖漿活動,(Li ZX et al., 2003),740~780,800~830,5,新元古代地幔超柱事件,Li XH et al. (2003) Precam Res,Plume genesis?,6,新元古代早期揚子板塊周邊,Zhou MF et al. (2002) EPSL,Arc

3、 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, pr

4、e-volcanic uplift,9,地幔柱與地幔超柱,淺柱,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,

5、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 pl

6、ume,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,Mont

7、elli 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,板塊構造與地幔柱之間的關系,Plume,Plate,15,Relationship between Plate sub

8、duction and Plume initiation,16,地球系統(tǒng)科學,TPXH2O,板塊構造與地幔柱,“陰”與“陽”,(Anderson, 2004),17,在地球科學中的空間尺度,微觀分析 vs. 宏觀構造,18,華南新元古代巖漿巖,,X,X,X,X,X,X,19,華南新元古代巖漿巖,750~760 Ma: I-type,810~830 Ma: S-type,,20,華南新元古代巖漿巖,,,21,華南新元古代花崗巖

9、鋯石Hf和O同位素地球化學,陰極發(fā)光(CL)結構照相MC-ICP-MS Lu-Hf同位素分析徐平等(2004)《科學通報》激光氟化氧同位素分析龔冰和鄭永飛(2003)《地學前緣》,22,新元古代巖漿巖鋯石CL特點巖漿成因環(huán)帶結構熱液蝕變溶蝕結構,23,新元古代巖漿巖鋯石CL特點,24,火山噴發(fā),Initial Hf Isotope Ratio of Zircon,Bimodal distribution,?Hf(t) = 3

10、.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-P

11、b & 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

12、 to 760 Ma),Any meaning?,1.07? 0.09 Ga,34,Two-stage Hf Model age,(Granitoids of ca.825 Ma),Paleoproterozoic basement?,1.86?0.07 Ga,35,Lu-Hf Isotope Evolution(progressive crust-mantle mixing),Bimodal compositions of both

13、 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,3

14、7,Growth of Juvenile Crust,(外推至虧損地幔線),797±21 Ma,901±20 Ma,Age of juvenile crust in South China,38,Age of Juvenile Crust,,Gabbro at Shaba,Plume magmatism?,787?18 Ma,39,Age of Juvenile Crust,,Leucogranite at Sanf

15、ang,Arc magmatism?,892?12 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花崗巖源區(qū),42,Grenvillian subduction ? Mantle superplume,1.1 to 0.9 Ga,0.83 to 0.74 Ga,43,ca.820Ma花崗巖

16、漿作用,Plume head effect ?,44,新元古代揚子板塊北緣巖漿活動和熱液蝕變,Rodinian Breakup? Bimodal magmatism?,Meteoric-hydrothermal alteration,Paleoproterozoic to Archean basements,地幔柱,45,加厚地殼部分熔融物質： ~900 Ma 大陸弧熱能： ~825 Ma

17、地幔柱背景： 拉張增生 型造山帶,46,破火山口垮塌,地幔柱,熱液蝕變,低18O巖漿活動,,,,,,,裂谷構造帶,,,47,大陸邊緣巖漿活動物質： ~800 Ma 初生地殼熱能： ~750 Ma 地幔超柱背景： 主動裂谷 構造帶,48,ca.750Ma花崗巖漿作用,Plume head effect ?,49,揚子板塊北緣新元古代巖漿活動,鋯石U-Pb年齡主要集中在700~800M

18、a，巖漿活動峰期約在750Ma。鋯石氧同位素比值范圍-11‰ ~ +9‰，大多數(shù)鋯石?18O 值低于地幔鋯石值，大約一半為負?18O 值。 新元古代高溫熱液蝕變，蝕變巖石部分熔融形成低?18O 巖漿。與超大陸裂解和地幔超柱事件有關,Zheng et al. (2004) GCA,50,水巖反應,Zheng et al. (2003) ESR,51,地幔超柱活動與花崗巖漿作用(Chemical Geodynamics),初期：地