北祁连造山带东段老虎山石英闪长岩成因及其地质意义  

Petrogenesis and Tectonic Implications of the Laohushan Quartz Diorite from the Eastern Part of North Qilian Orogen, NW China

作　　者：张海瑞 赵姣龙 于汇洋[1] ZHANG Hairui;ZHAO Jiaolong;YU Huiyang(School of Earth Sciences,Key Laboratory of Western China’s Mineral Resources of Gansu Province,Lanzhou University,Lanzhou 730000,China;State Key Laboratory for Mineral Deposits Research,School of Earth Sciences and Engineering,Nanjing University,Nanjing 210023,China)

机构地区：[1]兰州大学地质科学与矿产资源学院,甘肃省西部矿产资源重点实验室,兰州730000 [2]内生金属矿床成矿机制研究国家重点实验室,南京大学地球科学与工程学院,南京210023

出　　处：《高校地质学报》2019年第5期641-653,共13页Geological Journal of China Universities

基　　金：国家自然科学基金项目（41702048）;内生金属矿床成矿机制研究国家重点实验室开放基金（2017-LAMD-K08）;第二次青藏高原综合科学考察研究（2019QZKK0704）联合资助

摘　　要：以北祁连造山带东段老虎山石英闪长岩体为研究对象,进行了锆石U-Pb年龄及全岩元素与Sr-Nd同位素组成的系统测定,据此探讨了岩石的成因及其对北祁连构造演化的启示。锆石LA-ICP-MSU-Pb定年结果表明,石英闪长岩体的形成年龄为440Ma。岩石具有亚碱、准铝以及贫钙、镁、铁的特征,碱铝指数(AKI值)均低于0.85,铝饱和指数(A/NKC值)多小于1.0,属钙碱性I型花岗岩类岩石。在稀土和微量元素组成上,岩石富集轻稀土和大离子亲石元素(如Rb、Cs、Th和U),亏损高场强元素(如Nb和Ta),显示弧岩浆岩的地球化学特征。岩体具有相对均一的Sr-Nd同位素组成,初始Sr同位素值为0.7058~0.7071,εNd(t)值为-1.06^-0.31。综合分析表明,老虎山石英闪长岩应起源于玄武质下地壳物质的部分熔融,并在成岩过程中有少量幔源物质的混入。对区内火成岩地质地球化学特征与产出背景的全面分析,表明受北祁连洋俯冲及随后岛弧与祁连—柴达木陆块碰撞拼贴影响,弧后盆地的北向俯冲消减作用可能是诱发民乐窑沟和老虎山弧岩浆岩以及导致毛藏寺—老虎山花岗岩带内埃达克质岩石侵位的基本动力机制。This paper presents comprehensive zircon U-Pb ages and whole-rock geochemistry for the Laohushan quartz diorite in the eastern segment of the North Qilian Orogen,with aims to elucidate their petrogenesis and constraints on the early Paleozoic tectonic evolution of North Qilian Orogen.Zircon LA-ICP-MS U-Pb dating of the Laohushan quartz diorite yielded an age of 440 Ma.Rocks from the Laohushan pluton show sub-alkaline and metaluminous signatures,relatively low CaO,MgO and Fe2O3T contents,agpaitic index(AKI)values of less than 0.85,and aluminum saturation index(A/NKC)values of mostly less than 1.0.The Laohushan pluton can thus be grouped into metaluminous calc-alkaline I-type granitoids.All of the rocks are also enriched in LREEs and LILEs(e.g.,Rb,Cs,Th and U)and depleted in HFSEs(e.g.,Nb and Ta),similar to the geochemical characteristics of typical arc magma rocks.They have homogeneous Sr and Nd isotopic compositions with(87Sr/86Sr)i values of 0.7058~0.7071 andεNd(t)values of-1.06^-0.31.Integrated petrological,elemental,and isotopic compositions indicate that the Laohushan quartz diorites were generated by mixing of mantle-derived material with crustal-derived magmas that were formed by dehydration melting of basaltic rocks from the lower crust.By comprehensively synthesizing geochemical compositions and geological setting for magma rocks within the study region,we propose that the northward subduction of back-arc basin induced by the subduction of the North Qilian oceanic plate and the subsequent collision between the Qilian-Qaidam block and magma arc were major dynamic mechanisms responsible for the emplacement of the Minleyaogou and Laohushan granitoids and the adakitic rocks within the Maozangsi-Laohushan granitoid belt.

关 键 词：石英闪长岩体 早古生代 岩石成因 北祁连东段 

分 类 号：P588.12[天文地球—岩石学]