郑永飞--华南新元古代花岗岩锆石Hf和O同位素

Montelli et al. (2004) Science
13
Plume
Plate
板 块 构 造 与 地 幔 柱 之 间 的 关 系
14
Relationship between Plate subduction and Plume initiation
15
ቤተ መጻሕፍቲ ባይዱ
地球系统科学
板块构造与地幔柱
T P
XH2O
Predictions of plume Narrow, vertical seismic structures traversing the whole mantle High temperatures Relative fixity of hotspots Age progression of volcanic chain
=
Observations
Shallow thermal anomaly at classic hotspots Hotspot is not so hot Hotspot is not fixed, Not all volcanic chain has age progression
2 800 1000 1200 1400 1600 1800 2000
Hf Model Age (Ma)
30
Mineral O Isotopes (1)
6
18 D O (%o) Quartz-Zircon
(a)
4
Equilibrium
2
Equilibrium
0
Guangxi Yunnan Sichuan
“阴”与“阳”
(Anderson, 2004)
16
在地球科学中的空间尺度
微观分析 vs. 宏观构造
17
华南新元古代岩浆岩
X X X XX X
18
810~830 Ma: S-type
华南 新元古代 岩浆岩
750~760 Ma: I-type
19
华南新元古代岩浆岩
20
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
Hf(t) = 3.3 to 9.3 vs -4.4 to -1.2
24
Hf Model Age of Zircon
Bimodal distribution
TDM1 = 0.95 to 1.19 Ga vs TDM2 = 1.79 to 1.99 Ga
25
Zircon U-Pb & Hf Isotopes (1)
800
33
Two-stage Hf Model age
(Granitoids of ca.825 Ma)
2300
Paleoproterozoic basement? (b)
2100
(Ma) T
c DM
1900
1.860.07 Ga
1700
Mean = 1863±69 Ma MSWD = 1.3
1500
Bimodal compositions of both chemistry and isotope
35
Timing of Crust-Mantle Interaction
Initial phase:
Heat: Crustal remelting at ~820 Ma
Peak phase:
Mass: Rift magmatism at ~750 Ma Progressive addition of mantle-derived material to the crust
7
Uplift of mantle plume is evidenced by a rapid, pre-volcanic uplift
8
地幔柱与地幔超柱
浅柱 White & KcKenzie (1989)
Campbell & Griffiths (1990)
深柱
9
Hotspots around the world
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》
21
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
22
新元古代岩浆岩锆石CL特点
23
Initial Hf Isotope Ratio of Zircon
火山喷发
Bimodal distribution
12
(a)
8
Hf(t)
4
0
Guangxi
-4
Yunnan Sichuan
-8 700 750 800 850 900
U-Pb Age (Ma)
26
Zircon U-Pb & Hf Isotopes (2)
2000
Guangxi
(b)
Hf Model Age (Ma)
Yunnan Sichuan
1600
11
Three-dimensional view of deep mantle in tomographical model
Montelli et al. (2004) Science 12
Three-dimensional view of the shallow mantle and the newly discovered plumes in vertical model
X X X X X X X X XX
40
ca.825Ma花岗岩源区
41
1.1 to 0.9 Ga
0.83 to 0.74 Ga
Grenvillian subduction Mantle superplume
42
ca.820Ma花岗岩浆作用
Plume head effect ?
43
Rodinian Breakup? Bimodal magmatism?
892±12 Ma Depleted Mantle
Hf(t)
8 4 0 -4 -8 0
89212 Ma
CHUR
400
800
1200
1600
2000
39
Hf Model Age (Ma)
Mass transfer of mantle to crust at ~900 Ma by Arc magmatism
-2 2 4 6 8 10 12
d18O ( ) Zircon
31
Mineral O Isotopes (2)
4
18 D O (%0) Plagioclase-Zircon
(b)
2
Equilibrium Equilibrium
0
-2
Guangxi Yunnan Sichuan
-4 2 4 6 8 10 12
36
Growth of Juvenile Crust
(外推至亏损地幔线)
3
Age of juvenile crust in South China
Age of juvenile crust in South China
797±21 Ma
2
Number
Mean = 797±21 Ma MSWD = 0.56
Red: core-mantle boundary, yellow: transition zone, green-lithosphere 10 (Courtillot et al., 2003, EPSL)
DEBATE Plume vs Non-plumes
(Science, 2003, May 9)
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
1
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
Paleoproterozoic to Archean basements
Meteoric-hydrothermal alteration
地 幔 柱
新元古代
扬子板块北缘岩浆活动和热液蚀变
44
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
5
新元古代早期扬子板块周边
Zhou MF et al. (2002) EPSL
Zhou JC et al. (2004) Wang XL et al. (2004)
Arc genesis?
6
Episodic Growth of Juvenile Crust
Subduction zone: Arc Magmatism Mantle plume: Oceanic Plateau Rift magmatism
2
华南新元古代岩浆岩分布
XX X X X XX X X X X X X X X X X X
X
X
3
新元古代幕式岩浆活动
740~780
800~830
(Li ZX et al., 2003)
4
Li XH et al. (2003) Precam Res
Plume genesis?
新 元 古 代 地 幔 超 柱 事 件
901±20 Ma
Mean = 901±20 Ma MSWD = 0.68
1
0 600 700 800 900 1000 1100
TJC (Ma)
37
Age of Juvenile Crust
Gabbro at Shaba
20
98KD111
16 12
Plume magmatism?
Depleted Mantle
45
裂谷构造带
破火山口 垮塌
热液蚀变
低18O岩浆活动
地幔柱
46
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
47
ca.750Ma花岗岩浆作用
Plume head effect ?
48
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
787±18 Ma
Hf(t)
8 4 0 -4 -8 0
78718 Ma
CHUR
400
800
1200
1600
2000
38
Hf Model Age (Ma)
Age of Juvenile Crust
Leucogranite at Sanfang
20
98GX9-1
16 12
Arc magmatism?
1200
800 700 750 800 850 900
U-Pb Age (Ma)
27
Zircon U-Pb & O Isotopes
12
(c)
10
18 d O (%o)
Guangxi
8
Sichuan
Yunnan Mantle zircon
6
4
2 700 750 800 850 900
U-Pb Age (Ma)
Zheng et al. (2004) GCA
49
水岩反应
Zheng et al. (2003) ESR
50
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)
d18O (%0) Zircon
32
Single-stage Hf Model Age
(Bimodal Igneous rocks of ca.750 to 760 Ma)
1400
Any meaning?
1200
(a)
TDM (Ma)
1.07 0.09 Ga
1000
Mean = 1071±92 Ma MSWD = 9.2
28
Zircon Hf-O Isotopes (1)
12
(a)
10
18 d O (%o)
8
6
Guangxi
4
Yunnan Sichuan
2 -8 -4 0 4 8 12
Hf(t)
29
Zircon Hf-O Isotopes (2)
12
(b)
10
18 d O (%o)
8
6
Guangxi
4
Yunnan Sichuan
34
Lu-Hf Isotope Evolution
(progressive crust-mantle mixing)
20
825 Ma
Mantle
mixing-2
10
DM
mixing-1
1.9 Ga
Hf(t)
0
CHUR
-10
Crust
-20 0 500 1000 1500 2000
Age (Ma)