西秦岭党川地区花岗岩的成因及其构造意义

王婧; 张宏飞; 徐旺春; 蔡宏明

西秦岭党川地区花岗岩的成因及其构造意义

王婧^{1, 2},
张宏飞^{1, 2, ,},
徐旺春^{1, 2},
蔡宏明^{1, 2}

1.
中国地质大学地质过程与矿产资源国家重点实验室, 湖北武汉 430074
2.
中国地质大学地球科学学院, 湖北武汉 430074

基金项目:

国家自然科学基金 40521001

国家自然科学基金 40773019

教育部长江学者和创新团队发展计划 IRT0441

详细信息

作者简介:
王婧(1983-), 女, 硕士研究生, 地球化学专业

通讯作者:
张宏飞, E-mail: hfzhang@cug.edu.cn

中图分类号: P588.12
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出版历程
- 收稿日期: 2007-08-15
- 刊出日期: 2008-07-25

Petrogenesis of Granites from Dangchuan Area in West Qinling Orogenic Belt and Its Tectonic Implication

WANG Jing^{1, 2},
ZHANG Hong-fei^{1, 2
, ,},
XU Wang-chun^{1, 2},
CAI Hong-ming^{1, 2}

1.
State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China
2.
Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, China

摘要

摘要: 对西秦岭造山带党川地区的党川花岗岩和石门花岗岩进行了LA-ICP-MS锆石U-Pb定年、元素地球化学和Sr-Nd-Pb同位素组成的研究.结果表明, 党川花岗岩和石门花岗岩的岩浆结晶年龄分别为438±3Ma和220±2Ma.在岩石地球化学特征上, 党川花岗岩类似于C-型埃达克质岩石, 岩浆产生于增厚地壳物质的部分熔融, 而石门花岗岩类似于普通的地壳深熔型花岗岩.党川花岗岩的I_Sr=0.70660~0.70929, ε_Nd (t) =-2.24~-4.48;石门花岗岩的I_Sr=0.70581~0.70804, ε_Nd (t) =-3.73~-4.72.Sr-Nd同位素组成进一步指示它们的岩浆派生于地壳物质.然而, 在Pb同位素组成上, 党川花岗岩和石门花岗岩存在着明显的差异.党川花岗岩以相对富放射成因Pb同位素组成为特征, 初始Pb同位素比值为: ²⁰⁶Pb/²⁰⁴Pb=18.288~18.484, ²⁰⁷Pb/²⁰⁴Pb=15.677~15.693, ²⁰⁸Pb/²⁰⁴Pb=38.182~38.283;而石门花岗岩以相对低的放射成因Pb同位素组成为特征, 初始Pb同位素比值为: ²⁰⁶Pb/²⁰⁴Pb=17.989~18.189, ²⁰⁷Pb/²⁰⁴Pb=15.560~15.567, ²⁰⁸Pb/²⁰⁴Pb=37.982~38.000.这表明党川花岗岩和石门花岗岩的岩浆来自于不同地壳物质的部分熔融.区域分析表明, 西秦岭党川地区中古生代和早中生代的岩浆事件、岩石成因机制及岩浆源区均可与东秦岭地区北秦岭构造单元相对比, 由此说明西秦岭党川地区是东秦岭地区北秦岭构造单元的西延, 并且东秦岭地区早中生代南秦岭块体向北秦岭块体的大陆俯冲作用向西一直延至到西秦岭地区.
- 西秦岭造山带 /
- 花岗岩 /
- U-Pb锆石定年 /
- Sr-Nd-Pb同位素 /
- 岩石成因
Abstract: This paper carries out a study of U-Pb zircon dating using LA-ICP-MS method, geochemical and Sr-Nd-Pb isotopic compositions of the Dangchuan and Shimen granites in Dangchuan area of the West Qinling orogenic belt.The results show that the Dangchuan and Shimen granites have magma crystallization ages of 438±3Ma and 220±2Ma, respectively.Geochemical signatures indicate that the Dangchuan granite is similar to C-type adakitic rock that resulted from partial melting of thickened crustal material and the Shimen granite is similar to common anatexis-type granite.The Dangchuan granite has initial Sr isotopic ratios (I_Sr) of 0.70660-0.70929 and ε_Nd (t) values of-2.24 to-4.48, and the Shimen granite has I_Sr of 0.70581-0.70804 and ε_Nd (t) values of-3.73 to-4.72.The Sr-Nd isotopic composition of the Dangchuan and Shimen granites provides an additional eveidence that both the granites were derived from crustal source.However, Pb isotopic composition of the Dangchuan granite is distinct from that of the Shimen granite.The Dangchuan granite is characterized by more radiogenic Pb isotopic composition with initial Pb isotopic ratios of ²⁰⁶Pb/²⁰⁴Pb=18.288-18.484, ²⁰⁷Pb/²⁰⁴Pb=15.677-15.693 and ²⁰⁸Pb/²⁰⁴Pb=38.182-38.283, whereas the Shimen granite is characterized by relatively less radiogenic Pb isotopic composition with initial Pb isotopic ratios of ²⁰⁶Pb/²⁰⁴Pb=17.989-18.189, ²⁰⁷Pb/²⁰⁴Pb=15.560-15.567 and ²⁰⁸Pb/²⁰⁴Pb=37.982-38.000.It is strongly suggested that the magmas of the Dangchuan and Shimen granites were derived from different crustal sources.The Early Paleozoic and Early Mesozoic tectono-magma events, their petrogenesis and magma sources of Dangchuan area in the West Qinling orogenic belt can be comparable with those of the North Qinling tectonic unit in the East Qinling orogenic belt, indicating that the North Qinling tectonic unit can be extended to Dangchuan area in the West Qinling orogenic belt.In the East Qinling orogenic belt, the South Qinling continental crust was subducted beneath the North Qinling crust due to Early Mesozoic continental collision between the Yangtze and North China blocks.This continental subduction also occurred in the West Qinling orogenic belt.
- West Qinling orogenic belt /
- granite /
- U-Pb zircon dating /
- Sr-Nd-Pb isotopes /
- petrogenesi

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图 1 西秦岭党川地区地质简图(Zhang et al., 2006a)

DC.党川花岗岩; SM.石门花岗岩

Fig. 1. Simplified geological map of Dangchuan area in West Qinling

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图 2 样品0588和0593锆石阴极发光(CL) 图像

图中圆圈代表激光束斑的剥蚀范围; 数字为该点的²⁰⁶Pb/²³⁸U年龄, 单位为Ma.短白线为标尺, 长度100μm; a.样品0588代表性锆石; b.样品0593代表性锆石

Fig. 2. CL images of representative zircons of samples 0588 and 0593

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图 3 锆石U-Pb谐和图

Fig. 3. U-Pb zircon concordia diagram of samples 0588 and 0593

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图 4 稀土元素组成模式(球粒陨石标准化值据Taylor and McLennan, 1985)

Fig. 4. Chondrite normalized REE patterns

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图 5 党川和石门花岗岩的ε_Nd (t) -I_Sr图

Fig. 5. ε_Nd (t) vs. I_Sr diagram of Dangchuan and Shimen granites

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图 6 (a) (La/Yb) _N-Yb_N图(Matin, 1999); (b) Sr/Y-Y图(Defant and Drummond, 1990)

Fig. 6. (a) (La/Yb) _N vs. Yb_N diagram; (b) Sr/Y vs. Y diagram

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图 7 (a) ²⁰⁶Pb/²⁰⁴Pb-²⁰⁷Pb/²⁰⁴Pb图; (b)²⁰⁶Pb/²⁰⁴Pb-²⁰⁸Pb/²⁰⁴Pb图

北秦岭早古生代花岗岩的Pb同位素组成范围据Zhang et al. (1997a); 北秦岭和南秦岭早中生代花岗岩类的Pb同位素组成范围据Zhang et al. (1997a, 2007) 和张宏飞等(1997b)

Fig. 7. (a)²⁰⁶Pb/²⁰⁴Pb vs.²⁰⁷Pb/²⁰⁴Pb diagram; (b)²⁰⁶Pb/²⁰⁴Pb vs.²⁰⁸Pb/²⁰⁴Pb diagram

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表 1 党川花岗岩和石门花岗岩锆石LA-ICP-MS U-Pb同位素分析数据

Table 1. U-Pb zircon LA-ICP MS chronological data of Dangchuan granite and Shimen granite

表 2 党川花岗岩和石门花岗岩主量元素(%) 和微量元素(10^-6) 数据

Table 2. Major element (%) and trace element (10^-6) data of Dangchuan granite and Shimen granite

表 3 党川花岗岩和石门花岗岩Sr-Nd同位素组成

Table 3. Sr and Nd isotopic compositions for Dangchuan granite and Shimen granite

表 4 党川花岗岩和石门花岗岩全岩Pb同位素组成

Table 4. Whole-rock Pb isotopic compositions for Dangchuan granite and Shimen granite

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