米仓山新民角闪辉长岩地球化学特征及其构造意义  

Geochemistry of the bojite from the Xinmin area,Micang Mountain

作　　者：甘保平 赖绍聪[1] 秦江锋[1] 

机构地区：[1]西北大学地质学系大陆动力学国家重点实验室,陕西西安710069

出　　处：《岩石矿物学杂志》2016年第2期213-228,共16页Acta Petrologica et Mineralogica

基　　金：国家自然科学基金项目(41372067);国家自然科学基金重大计划项目(41190072);国家自然科学基金委创新群体项目(41421002);教育部创新团队项目(IRT 1281)~~

摘　　要：扬子板块西北缘新元古代岩浆作用的研究对于探讨Rodinia超大陆的构造演化具有重要意义,对米仓山新民地区角闪辉长岩的岩石学和地球化学分析结果表明,岩石Si O2含量较低且变化范围较小,岩石富Al和Ca,低K、Ti、P,Mg^#值中等,属于亚碱性低钾拉斑岩石系列。岩石具有稀土元素总量相对较低、相对富集轻稀土元素和轻重稀土元素分馏程度低的特征,具弱Eu正异常,δEu=1.03~2.36。岩石总体上富集大离子亲石元素（Rb、Ba、Sr）,亏损高场强元素（Nb、Zr、Hf、Th等）,^87Sr/^86Sr=0.703 858,^143Nd/^144Nd=0.512 617,εNd（t）=＋3.1。综合区域地质、地球化学特征,该岩体岩浆起源于亏损地幔的部分熔融,在上升侵位过程中可能受到了地壳物质的混染。在这时期,扬子板块北缘处于汇聚环境,新民角闪辉长岩形成于弧后盆地的构造环境,是Rodinia超大陆在新元古代期间演化过程中岩浆作用的产物。Neoproterozoic igneous rocks on the northwestern margin of the Yangtze block can provide important information about the evolution of Rodinia supercontinent. In this paper,the petrology,geochemistry and isotopic data of the bojite from the Xinmin area of Micang Mountain region are presented. The Xinmin bojite displays low and limited Si O2 content,enrichment of Al and Ca,low K,Ti and P,and medium Mg^#,suggesting typical subalkaline,low-K theolite features. The low REE composition,enriched LREE patterns,and positive Eu anomalies（ δEu = 1. 03 ~ 2. 36） imply the accumulation of plagioclase. The large ion lithophile elements（ Rb,Ba,Sr） show enrichment,whereas the high strength elements（ Nb,Zr,Hf,Th） are relatively depleted.^87 Sr /^86 Sr = 0. 703 858,^143 Nd /^144 Nd = 0. 512 617,and εNd（ t） = ＋ 3. 1. The regional geological and geochemical characteristics reveal that the primary melts were derived from partial melting of depleted mantle rocks and underwent significant crustal contamination in the emplacement process. During this period,the northern margin of the Yangtze block was in a convergence environment and the tectonic environment of the Xinmin bojite was the back arc basin,and hence the Xinmin bojite was the product of the evolution of Rodinia supercontinent in the Neoproterozoic period.

关 键 词：米仓山 角闪辉长岩 地球化学 弧后盆地 RODINIA超大陆 

分 类 号：P588.124[天文地球—岩石学] P59[天文地球—地质学]