内蒙乌拉特中旗图古日格二叠纪角闪石岩年龄、岩石成因及构造背景  

Age,Petrogenesis and Tectonic Implications of Permian Hornblendite in Tugurige,Urad Zhongqi,Inner Mongolia

作　　者：王键[1] 孙丰月[1] 李碧乐[1] 王英德[1] 李睿华[1] 

机构地区：[1]吉林大学地球科学学院,吉林长春130061

出　　处：《地球科学（中国地质大学学报）》2016年第5期792-808,共17页Earth Science-Journal of China University of Geosciences

基　　金：国家自然科学基金项目(No.41272093);中国地质调查局项目(No.12120113098300)

摘　　要：为了对古亚洲洋的演化提供新的资料,对内蒙中部乌拉特中旗图古日格角闪石岩进行了角闪石电子探针分析、锆石LAICP-MS U-Pb年代学,锆石Hf同位素和岩石地球化学分析,以确定其岩石成因及其地球动力学背景.两件测年样品加权平均年龄分别为273.5±1.3Ma（MSWD=0.48）和274.4±4.3Ma（MSWD=0.041）,属于早二叠世晚期.角闪石岩贫SiO2、Na2O、K2O,富Al2O3、TFe2O3、MgO和CaO,Mg#值为46.9563.53,M/F比值为0.871.72;稀土元素配分曲线为右倾型,和原始地幔相比明显富集大离子亲石元素（Rb、Ba、K）,而高场强元素Nb、Ta和Ti相对亏损,Th、U同样显示出相对亏损.电子探针分析结果表明角闪石岩中角闪石属于钙质角闪石,具有幔源角闪石的特点.角闪石岩中锆石的εHf（t）值为-0.38.5,锆石Hf单阶段模式年龄（tDM1）为580920Ma.研究表明其源区主要为亏损地幔,上涌过程中与富集岩石圈地幔发生相互作用,形成具有富集地幔特征岩浆.结合区域地质演化,认为角闪石岩形成于古亚洲洋闭合后的伸展环境,可能与俯冲板片的断离有关.Electron microprobe results,zircon U-Pb dating,Hf isotope data and geochemistry of hornblendite at Tugurige,Urad Zhongqi,Inner Mongolia are reported in the paper,which provide constraints on formation time,magma source,and tectonic setting of the intrusions.The dating results indicate that the hornblendite formed in the late Early Permian（273.5±1.3 Ma,MSWD=0.48;274.4±4.3 Ma,MSWD=0.041）,and it contains low Na2O and K2O,high Al2O3,TFe2O3,MgO,CaO,Mg#=46.95-63.53,M/F=0.87-1.72.Chondrite-normalized REE patterns show LREE enrichment.On a trace element spider diagram,large ion lithophile elements（LILEs）such as Rb,Ba and K are enriched,whereas the high field strength elements Ti,P,Th and U are relatively depleted.Electronic Probe analysis results show that hornblende belongs to calcic amphibole and has the characteristics of mantle hornblende.The εHf（t）values of zircons from the hornblendite vary between -0.3 and 8.5,and their Hf one-stage model ages vary from 580 to 920 Ma,implying that their magma source was derived from a depleted mantle and may have been added metasomatic enriched lithospheric mantle components.Combined with regional tectonic evolution,the hornblendite formed in the post-collisional extension setting,perhaps triggered by slab break-off.

关 键 词：内蒙 乌拉特中旗 晶体化学 年代学 地球化学 HF同位素 

分 类 号：P597[天文地球—地球化学]