| 义敦岛弧带晚白垩世海子山二长花岗岩成因及其地质意义 |
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| 引用本文： | 张方毅,赖绍聪,秦江锋.义敦岛弧带晚白垩世海子山二长花岗岩成因及其地质意义[J].高校地质学报,2018,24(3):340. |
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| 作者姓名： | 张方毅 赖绍聪 秦江锋 |
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| 摘 要： | 义敦岛弧是三江特提斯复合造山带的重要组成部分。文章对义敦岛弧海子山花岗岩体进行锆石U-Pb年代学、全岩地球化学及Sr-Nd-Pb同位素地球化学进行分析,探讨其成因与构造意义。海子山花岗岩锆石U-Pb年龄为93.7±1.1 Ma(MSWD=2.1, 2σ),为晚白垩世早期岩浆活动产物,岩石具高硅、富碱的特征,铝饱和指数A/CNK=1.04～1.12,属于弱过铝质岩石。稀土配分曲线呈燕式分布,Eu/Eu~*=0.05～0.32,具有明显的Eu负异常。富集Rb、Th、U、Ta、Pb等元素,明显亏损Ba和Sr,表现出A型花岗岩的特征。岩石的ε_(Nd)(t)=–4.8～-3.4,二阶段模式年龄T_(DM2)=0.91～1.00 Ga,结合岩石的Pb同位素特征及低的CaO/Na_2O比值与高的Al_2O_3/TiO_2比值,说明其应起源于泥质岩石的部分熔融并有少量地幔组分加入。综合地球化学、同位素特征及义敦岛弧地区构造资料,表明海子山花岗岩是造山后伸展背景下形成的A型花岗岩,为地壳拉张、减薄,软流圈地幔上涌引起中上地壳泥质岩部分熔融的产物,具有壳幔物质混合的特征。
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| 关 键 词： | A型花岗岩 地球化学 锆石U-Pb定年 造山后伸展 义敦岛弧带 |
Petrogenesis and Geological Significance of the Late Cretaceous Haizishan Monzogranite from the Yidun Island Arc |
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| ZHANG Fangyi,LAI Shaocong,QIN Jiangfeng.Petrogenesis and Geological Significance of the Late Cretaceous Haizishan Monzogranite from the Yidun Island Arc[J].Geological Journal of China Universities,2018,24(3):340. |
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| Authors: | ZHANG Fangyi LAI Shaocong QIN Jiangfeng |
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| Abstract: | The Yidun island arc is a significant component of Sanjiang Tethys composite orogenic belt. This paper presents zircon
U-Pb age, whole-rock geochemistry and Sr-Nd-Pb isotopic data for the Haizishan granite from the Yidun island arc, aiming to explore
its petrogenesis and geological significance. Zircon U-Pb dating results show that the Haizishan granite pluton was crystallized at 93.7±
1.1 Ma (MSWD=2.1, 2σ), indicating it was produced during early period of Late Cretaceous. The Haizishan granite is characterized by
high SiO2 and alkali, with A/CNK values of 1.04-1.12, showing a weakly peraluminous affinity. REEs of the granites are characterized
by significant negative Eu anomalies with Eu/Eu* values of 0.05-0.32. The granitic rocks are enriched in Rb, Th, U, Ta, Pb but
depleted in Ba, Sr. The εNd(t) values of the granites range from -4.8 to -3.4, with two-stage model age of 0.91-1.00 Ga. In combination
with their Pb isotopic characteristics and the chemical signatures of low CaO/Na2O and high Al2O3/TiO2 ratios, it is suggested that the
Haizishan granite was originated from partial melting of argillaceous rocks with addition of minor mantle component. Based on a
synthesis of their geochemistry, isotope characteristics and geological setting, we suggest that the Haizishan granite can be genetically
grouped into A-type granites which were generated by partial melting of argillaceous rocks with minor involvement of mantle
components in a post-collisional extension tectonic setting induced by upwelling of asthenosphere mantle. |
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| Keywords: | A-type granite geochemistry zircon U-Pb dating post-collisional extension Yidun island arc belt |
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