北阿尔金早古生代同碰撞花岗质岩浆记录及其对增生造山过程的启示  

Early Palaeozoic syn-collisional granitic magmatism in the North Altun and its implication for accretionary orogenic processes

作　　者：吴玉[1,2] 陈正乐[2,3] 陈柏林[2] 王永[2] 孙岳[3] 孟令通 何江涛 王斌[2] WU Yu;CHEN ZhengLe;CHEN BaiLin;WANG Yong;SUN Yue;MENG Ling Tong;HE JiangTao;WANG Bin(Beijing Research Institute of Uranium Geology,CNNC,Beijing 100029,China;Institute of Geomechanics,Chinese Academy of Geological Sciences,Bejing 100081,China;East China Institute of Technology,Nanchang 330013 China;Institute of Geology and Geophysics,Chinese Academy of Sciences,Bejing 100029,China;Tianjin Center,China Geological Surey,Tianjin 300170,China)

机构地区：[1]核工业北京地质研究院地质矿产研究所,北京100029 [2]中国地质科学院地质力学研究所,北京100081 [3]东华理工大学,南昌330013 [4]中国科学院地质与地球物理研究所,北京100029 [5]中国地质调查局天津地质调查中心,天津300170

出　　处：《岩石学报》2021年第5期1321-1346,共26页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41802218、41502086);“十二·五”国家科技支撑计划重点项目(2011BAB06B08-04);中国核工业地质局铀矿地质科研项目(地D1902)联合资助。

摘　　要：本文对出露在北阿尔金的喀腊大湾似斑状花岗岩、沟口泉似斑状二长花岗岩、卓尔布拉克花岗岩和木孜萨依白云母花岗岩进行了详细的岩相学、岩石地球化学、锆石U-Pb年代学和Hf同位素研究。地球化学特征显示喀腊大湾似斑状花岗岩具有高硅和钠,低铁、镁和钙的特征,铝饱和指数(A/CNK)为1.03~1.04,属弱过铝质I-S过渡型花岗岩;沟口泉似斑状二长花岗岩和卓尔布拉克花岗岩具有相对高的钠含量和准铝质-弱过铝质特征,表现为I型花岗岩;木孜萨依白云母花岗岩具有高硅、富碱、富集Rb、Th和LREE,亏损Ba、Sr、Ti和Eu特征,铝饱和指数大于1.1,属过铝质S型花岗岩。锆石U-Pb定年结果显示4个岩体的年龄分别为432.4±4.9Ma、432.8±4.1Ma、439.6±3.5Ma和437.3±2.4Ma。结合区域地质资料和构造判别图解,揭示这4个岩体均形成于同碰撞构造背景下,表明北阿尔金洋最终关闭以及洋陆转换的时间节点应为445~440Ma。锆石Hf同位素结果显示沟口泉似斑状二长花岗岩和卓尔布拉克花岗岩岩浆起源于新生地壳物质的部分熔融;喀腊大湾似斑状花岗岩起源于变杂砂岩部分熔融,木孜萨依白云母花岗岩起源于变泥质岩石的低程度部分熔融;但喀腊大湾似斑状花岗岩和木孜萨依白云母花岗岩ε_(Hf)(t)值分别为+0.18~+5.88和-6.47~+4.52,反映二者的岩浆源区也均有新生地壳物质的加入。上述这些特征与北祁连早古生代同碰撞花岗岩体具有良好的可对比性,进一步支持二者曾作为统一的整体经历了洋盆裂解-扩张-俯冲-闭合造山等构造演化过程。This paper present a set of new petrography,major and trace element geochemistry,zircon U-Pb geochronology and insitu Hf isotopic compositions for Kaladawan porphyritc granite,Goukouquan porphyritc monzogranite,Zhuoerbulake granodiorite and Muzisayi muscovite granite in North Altun.The Kaladawan porphyritc granite are characterized by relatively high contents of silicon and sodium,but low contents of iron,magnesium and calcium,with moderate alumina saturation index(A/CNK=1.03~1.04),belonging to slightly peraluminous I-S transition type granite.Goukouquan porphyritc monzogranite and Zhuoerbulake granodiorite exhibit relatively high sodium contents and metaluminous to slightly peraluminous calc-alkaline I-type granitoids features.Muzisayi muscovite granite show relatively high SiO2,ALK(Na2O+K2O),enrichment Rb,Th and LREE,depletion Ba,Sr,Ti,Eu,and yields alumina saturation index values of>1.1,showing S-type granite features.Zircon U-Pb dating suggest that four granitic plutons were emplaced during Early Silurian(439~432 Ma).Integrating the regional tectonic evolution and discrimination diagrams,we propose the closure time of North Altun Ocean occurred during ca.445~440 Ma.Goukouquan porphyritc monzogranite and Zhuoerbulake granodiorite exhibit relatively high zirconεHf(t)values(+4.72~+7.55 and+6.33~+9.96,respectively),suggest that they were generated by partial melting of the pre-existing juvenile crustal rocks.Geochemical characteristics show that the Kaladawan porphyritc granite was derived from partial melting of metagreywackes rocks,whereas the Muzisayi muscovite granite was derived from low degree partial melting of metapelitic rocks.However,the relatively positiveεHf(t)values(+0.18~+5.88 and-6.47~+4.52,respectively)strongly suggest that the involvement of some juvenile crust components in different proportions.Above these features are similar to the Early Palaeozoic syn-collision granitoids from the North Qilian,which further support that two orogenic belts have undergone similar geological and tectonic proc

关 键 词：同碰撞花岗岩 增生造山 洋陆转化 早古生代 北阿尔金 

分 类 号：P534.4[天文地球—古生物学与地层学] P588.11[天文地球—地质学] P542