阿尔泰造山带南缘岩浆混合作用:阿克布拉克岩体岩石学、地球化学和年代学证据  

LA-ICP-MS U-Pb Geochronology,Geochemistry and Petrography of Akebulake Pluton in Southern Altay Orogenic Belt:An Example for Magma Mixing

作　　者：蔺新望 张亚峰 陈国超[2,3] 郭岐明 王星 赵端昌 Lin Xinwang;Zhang Yafeng;Chen Guochao;Guo Qiming;Wang Xing;Zhao Duanchang(Shaanxi Mineral Resources and Geological Survey,Xi’an 710068,China;School of Civil Engineering,Nanyang Institute of Technology,Nanyang 473000,China;Key Laboratory of Western China’s Mineral Resources and Geological Engineering,Ministry of Education,Chang’an University,Xi’an 710054,China)

机构地区：[1]陕西省矿产地质调查中心,陕西西安710068 [2]南阳理工学院土木工程学院,河南南阳473000 [3]长安大学西部矿产资源与地质工程教育部重点实验室,陕西西安710054

出　　处：《地球科学》2023年第10期3597-3612,共16页Earth Science

基　　金：中国地质调查局区域地质调查项目(Nos.1212011120503,1212011120509,DD20160006);新疆维吾尔自治区地质勘查基金项目(No.A16-1-LQ01);中央高校基本科研业务费专项资金项目(No.300102261505).

摘　　要：阿尔泰造山带南缘阿克布拉克英云闪长岩体由寄主岩石、微细粒闪长质暗色包体和基性辉长岩脉组成,具有明显的岩浆混合作用特征:如暗色包体中发育长石斑晶、针状磷灰石,寄主岩中的黑云母包裹石英、斜长石等.寄主岩石、暗色包体和基性岩脉代表了岩浆混合演化过程中不同端元比例混合的产物.LA-ICP-MS锆石U-Pb定年结果表明寄主岩石、暗色包体和基性岩脉岩浆结晶年龄分别为396.3±3.3 Ma、392.2±3.7 Ma和402.3±3.3 Ma,说明三者是早泥盆世同一岩浆事件的产物,为阿克布拉克岩体岩浆混合成因提供了重要的年代学证据.岩石地球化学特征方面,包体、寄主岩石和基性岩脉主要氧化物之间存在良好的线性关系,且三者的稀土元素配分曲线、微量元素蛛网形态相近,暗示寄主岩石与包体在岩石形成过程中发生过物质成分交换并达到均一化.锆石Hf同位素组成不均一,寄主岩石、包体和基性岩脉ε_(Hf)(t)分别变化于1.22~4.70、-3.49~7.41和3.65~9.02之间,Hf同位素模式年龄(t_(DM2))分别介于962~1131 Ma、816~1375 Ma和740~1015 Ma.综合区域资料分析认为,岩体中发育的暗色闪长质包体是在活动大陆边缘的陆缘弧挤压构造背景下,幔源基性岩浆与其诱发熔融的壳源长英质岩浆混合作用的产物.阿克布拉克岩体的岩浆混合成因的确立进一步证实了早泥盆世时期阿尔泰造山带南缘地壳深部发生过强烈的壳幔岩浆混合作用,并导致了该区重要的俯冲增生地壳水平生长事件.The Akebulake pluton in the southern margin of the Altay orogenic belt is composed of tonalite,dioritic microgranular enclaves and mafic dikes.The pluton exhibits excellent evidence for magma mixing and mingling,such as the feldspathic phenocryst,long prisms of apatite in enclaves and quartz,plagioclase wrapped in biotite in the host rock.Host rocks,dioritic microgranular enclaves and mafic dikes of the Akebulake pluton are products of mixing with different end element ratios in the process of magma mixing evolution.LA-ICP-MS zircon U-Pb dating from three samples yielded weighted mean 206Pb/238U ages of 396.3±3.3 Ma,392.2±3.7 Ma and 402.3±3.3 Ma,respectively.It indicates that they were formed in the same magmatic event,which provides important chronological evidence for the genesis of magma mixing of Akebulake pluton.Geochemically,the major oxide content of the mafic dikes,dioritic enclaves and their host rocks all have a good linear relationship in the plot,and the patterns of REE,spidergrams of trace elements of the dioritic enclaves and mafic dikes are similar to those of the host granites,suggesting that component exchange and homogenization occurred between the enclaves and the host rocks in the process of rock formation.Hf isotopic composition of zircon is not uniform.The host rocks,enclaves and mafic dikesε_(Hf)(t)vary from 1.22 to 4.70,-3.49 to 7.41 and 3.65 to 9.02,respectively.The Hf isotopic model ages(t_(DM2))range from 962 to 1131 Ma,816 to 1375 Ma and 740 to 1015 Ma,respectively.Based on a comprehensive analysis with the data of southern margin of Altay,the authors hold that the dioritic enclaves in the Akebulake pluton were generated by mixing of mantle-derived mafic magma and its induced crustal felsic magma in an island-arc setting of active continental margin.The formation of magma mixing of the Akebulake pluton further confirms that strong crust-mantle magmatic mixing occurred in the deep crust of the southern margin of the Altay orogenic belt during the Early Devonian,which resulted in an

关 键 词：LA-ICP-MS锆石U-Pb年龄 岩浆混合 微细粒镁铁质包体 阿克布拉克岩体 阿尔泰 地球化学 岩石学 

分 类 号：P588.115[天文地球—岩石学] P597.3[天文地球—地质学]