青海南山晚奥陶世花岗复式岩体锆石U-Pb年龄证据及地球化学特征

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英文篇名：Zircon U-Pb Age Evidences and Geochemical Features of Late-Ordovician Granitic Complex in Nanshan Area, Qinghai Province 作者：张世成 ; 姚旭东 ; 李云平 英文作者：ZHANG Shicheng;YAO Xudong;LI Yunping;The Fifth Institute of Geology Exploration in Qinghai Province; 关键词：晚奥陶世 ; 花岗复式岩体 ; 地球化学特征 ; 锆石U-Pb测年 英文关键词：Upper Ordovician;;Granite complex;;Geochemical features;;U-Pb dating of zircon 中文刊名：ZGMM 英文刊名：China's Manganese Industry 机构：青海省第五地质勘查院; 出版日期：2019-02-28 出版单位：中国锰业 年：2019 期：v.37;No.164 基金：中国地质调查局青藏专项地质调查(12120113033020) 语种：中文; 页：ZGMM201901012 页数：6 CN：01 ISSN：43-1128/TD 分类号：50-55

摘要

在青海南山进行野外地质填图过程中,对前人划分的花岗闪长岩系岩相学研究,通过地质特征、地球化学特征和年代学分析,该岩体为一套花岗复式岩体,岩性为石英闪长岩、花岗闪长岩、英云闪长岩及二长花岗岩。侵入古元古代老变质结晶基底中,地球化学特征表明为高硅、中—富钾铝过饱和钙碱性系列,轻稀土富集,Eu中等亏损,微量元素K、Rb、Ba等强烈富集;花岗闪长岩和二长花岗岩LA-ICP-MS锆石U-Pb年龄测定为447.2 Ma±5.3 Ma和446.1 Ma±3.5 Ma。常量和微量元素特征显示形成的构造环境为板块碰撞前的多岛弧及同碰撞,说明了拉脊山小洋盆由北向南俯冲—消减,随后进入陆壳碰撞挤压环境。岩体形成于晚奥陶世,属加里东期I型花岗岩,岩浆物质主要来源于俯冲碰撞,地壳逐渐增厚引发重熔而产生壳源物质,是加里东期多岛小洋盆俯冲消减,碰撞挤压造山的岩浆记录。
        The granitic pluton was mentioned by previous studies to the granitic complex. It covers petrography, geological science, geochemical and chronological studies in field geological mapping in Nanshan area of Qinghai province. The granitic complex includes quartz diorite, granodiorite, tonalite and monzonitic granitite, which is intruded into paleoproterozoic metamorphic basement. Geochemical features show that the granitic complex is high-silicon, medium-high potassium, peraluminouscalc-alkaline series. Meanwhile. The granitic complex also shows enrichment in light and rare earth elements, including K,Rb,Ba, other trace elements and exhibit moderate negative Eu anomalies. LA-ICP-MS U-Pb dating of zircon from granodiorite and monzonitic granitite will indicate magmatic crystallization ages of 447.2 Ma±5.3 Ma and 446.1 Ma±3.5 Ma respectively. Major and trace elements will show that the granitic complex is formed in an island arc or syn-collision setting before plate collision. These suggest small oceanic basin of Lajishan in subduction from north to south, followed by compressional setting to be caused by continental collision. The granitic pluton formed at late-Ordovician is showing I-type granite features. Crust will thicken it to cause the remelting, which produces the magma source material in a subduction-collision setting. These recorded small ocean basin in subduction and magmatic event during collisional orogenesis.

引文

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