西秦岭印支早期铁堂峡石英正长斑岩的地球化学特征及其地质意义  

Geochemistry and Its Geological Significance of the Quartz Syenites in the Early Indosinian from the Tietang Gorge, West Qinling

作　　者：赵东辉 平先权[2] 郑建平[2] 艾磊 邓昊 Zhao Donghui;Ping Xianquan;Zheng Jianping;Ai Lei;Deng Hao(School of Lisiguang,China University of Geosciences,Wuhan 430074,China;School of Earth Sciences,China University of Geosciences,Wuhan 430074,China)

机构地区：[1]中国地质大学李四光学院,湖北武汉430074 [2]中国地质大学地球科学学院,湖北武汉430074

出　　处：《地球科学》2019年第12期4203-4221,共19页Earth Science

基　　金：国家自然科学基金项目(Nos.41503018,41873038);国家重点研发计划“深地资源勘查开采”重点专项资助项目(No.2016YFC0600403);中国地质大学中央高校基本科研业务费专项资金资助项目(Nos.CUGCJ1814,1810491A29)

摘　　要：西秦岭东部发育大量小规模中酸性脉岩,但对这些脉岩的研究相对缺乏.在详细的野外观察和岩相学研究的基础上,对西秦岭天水铁堂峡石英正长斑岩进行了地球化学、锆石U-Pb年代学和Lu-Hf同位素研究.石英正长斑岩的锆石U-Pb定年结果表明它们的形成时代为~250 Ma,属印支早期岩浆产物.地球化学研究显示它们属于弱过铝质的高钾钙碱性岩系列,高Mg#,以富集Ba、Sr、K,强烈亏损Nb、Ta,且Eu异常不明显为特征.这些特征与埃达克岩的性质相似.铁堂峡石英正长斑岩的锆石εHf(t)值介于-1.44^+3.17,一阶段Hf模式年龄(tDM1)在765~945 Ma之间.铁堂峡石英正长斑岩形成于阿尼玛卿洋北向俯冲的大陆边缘弧环境,是俯冲洋壳及大洋沉积物熔体与上覆地幔楔作用的产物,并在浅部岩浆房中经历了轻微的分离结晶作用.A large number of small-scale dykes are located in the eastern part of the West Qinling,but they are lack of detailed study.Based on the detailed field work and petrological research,zircon U-Pb geochronology,geochemistry and zircon Lu-Hf isotope studies were carried out for the quartz syenites in the Tietang Gorge from Tianshui,West Qinling.The zircon U-Pb dating shows the crystallization ages of the quartz syenites are^250 Ma,indicating that they were formed in the Early Indosinian.Geochemistry research shows that the Tietang Gorge quartz syenites belong to the series of high-alkaline calc-alkaline rocks with weakly peraluminous.They have some adakitic characteristics with high Mg#,enrichment in Ba,Sr,K and strong depletion in Nb and Ta,and no significant Eu anomalies.The zirconεHf(t)for the quartz syenites ranges from-1.44 to+3.17,and the one-stage Hf model ages(tDM1)vary from 765 to 945 Ma.The Tietang Gorge quartz syenites formed in the continental marginal arc environment of the northward subduction of the Animaqing Ocean.They derived from the partial melting of the subduction oceanic crust with its overlying sediment interacted with the mantle wedge,and a slight fractional crystallization occurred in their shallow magma chamber.

关 键 词：石英正长斑岩 错石U-Pb定年 皓石Lu-Hf同位素 印支早期 西秦岭 岩石学 

分 类 号：P581[天文地球—岩石学]