南祁连党河南山地区拐杖山岩群玄武岩年代学、地球化学及其构造环境  

Zircon U-Pb dating and geochemistry of basalt in Guaizhangshan Group from the Southern Danghe Mountain in South Qilian and its tectonic setting

作　　者：计波[1,2] 李向民 黄博涛[1] 王磊 王国强[1] JI Bo;LI Xiangmin;HUANG Botao;WANG Lei;WANG Guoqiang(MNR Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits,Xi’an Center of Geological Survey,China Geological Survey,Xi’an 710054,Shaanxi,China;State Key Laboratory of Continental Dynamics,Department of Geology,Northwest University,Xi'an 710069,Shaanxi,China)

机构地区：[1]中国地质调查局西安地质调查中心,自然资源部岩浆作用成矿与找矿重点实验室,陕西西安710054 [2]大陆动力学国家重点实验室,西北大学地质学系,陕西西安710069

出　　处：《中国地质》2024年第3期965-977,共13页Geology in China

基　　金：国家自然科学基金项目(41802133);中国地质调查局项目(DD20200208)联合资助。

摘　　要：【研究目的】前人在南祁连志留纪巴龙贡噶尔组中解体出新元古代拐杖山岩群,对该群中玄武岩的年龄、成因与成岩构造环境的研究是厘清南祁连地区构造演化的重要手段。【研究方法】本文基于LA-ICP-MS锆石U-Pb年龄和全岩地球化学分析等方法研究拐杖山岩群火山岩的形成年代、地球化学特征及地质意义。【研究结果】锆石U-Pb定年结果显示,玄武岩喷发年龄为(786.6±5.8)Ma,表明拐杖山岩群形成于新元古代早期。岩石地球化学分析结果表明,玄武岩SiO_(2)含量在48.09%~50.97%,高TiO_(2)(1.34%~2.55%),低MgO(5.78%~7.11%),显示亚碱性拉斑玄武岩特征。岩石轻、重稀土分异明显((La/Yb)_(N)=3.76~4.51),无明显Eu异常(δEu=0.80~1.05),大离子亲石元素Ba、Th、U相对富集,Pb强富集,亏损Nb、Ta、Ti等高场强元素。【结论】岩石地球化学特征暗示拐杖山岩群玄武岩是遭受陆壳物质混染的地幔源区玄武岩,该火山岩形成于大陆裂谷环境,响应了全球新元古代Rodinia超大陆裂解事件。This paper is the result of geological survey engineering.[Objective]The Neoproterozoic Guaizhangshan Group was disintegrated from the Silurian Balonggonggaer Formation.The study of the petrogenesis and tectonic setting of the basalt in Guaizhangshan Group is crucial to clarify the tectonic evolution of South Qilian.[Methods]Based on LA-ICP-MS zircon U-Pb datingand whole-rock geochemistry analysis,the formation age,geochemical characteristics and geological significance of the basalt in Guaizhangshan Group are constrained.[Results]The dating results indicate the eruption age of the basalt is(786.6±5.8)Ma,suggesting that the Guaizhangshan Group formed during Early Neoproterozoic.Geochemical analyses of the basalt show that:SiO_(2)=48.09%-50.97%,TiO_(2)=1.34%-2.55%,MgO=5.78%-7.11%,displaying characteristics of subalkaline tholeiite;Significant differentiation between light rare earth element(LREE)and heavy rare earth elements(HREE)((La/Yb)_(N)=3.76-4.51),and inconspicuous Eu anomalies(δEu=0.80-1.05);Enrichment of Ba,Th,U,Pb,and depletionin Nb,Ta,Ti.[Conclusions]These geochemical characteristics indicate that the basalts were derived from mantle and contaminated by crustal materials.The basalt was formed in continental rift setting,which may be relevant to the break-up of the Rodinia supercontinent.

关 键 词：锆石U-PB定年 玄武岩 拐杖山岩群 构造环境 地质调查工程 南祁连 

分 类 号：P618.51[天文地球—矿床学]