西藏班戈县蓬错地区富铌玄武岩地球化学特征及地质意义  

Geochemical Characteristics and Geological Implications of the Nb-enriched Basalt in Pengcuo Aera,Bange County of Tibet

作　　者：李振江[1] 张宽忠[1] 游水生 谢晓文 赵波 张家毅 LI Zhen-jiang;ZHANG Kuan-zhong;YOU Shui-sheng;XIE Xiao-wen;ZHAO Bo;ZHANG Jia-yi(Regional Geological Survey Team,Sichuan Geology and Mineral Bureau,Chengdu 610213,China;No.6 Geological Party,Tibet Bureau of Geological Exploration and Exploitation of Mineral Resources,Duilongdeqing 8751400,China)

机构地区：[1]四川省地质矿产勘查开发局区域地质调查队,成都610213 [2]西藏自治区地质矿产勘查开发局第六地质大队,堆龙德庆851400

出　　处：《科学技术与工程》2018年第24期9-15,共7页Science Technology and Engineering

基　　金：中国地质调查局项目(12120114062501)资助

摘　　要：系统的岩石化学与地球化学研究表明西藏蓬错地区存在富铌玄武岩。SiO_2含量为45.84%~55.88%,TiO_2含量为1.05%~3.25%,与加拿大Superior省太古代Wawa绿岩带的富铌玄武岩相当。Na_2O含量为0.92%~5.10%,P_2O_5含量为0.23%~1.19%,与新生代富铌玄武岩相同。稀土分布模式为无明显铕异常或弱负铕异常的右倾曲线,轻重稀土分馏较强烈。虽然铌含量很高,但Th与轻稀土元素的强烈富集,在微量元素蛛网图中铌依然显示亏损,高场强元素Ta、Ti也呈弱负异常。微量元素地球化学特征显示,蓬错富铌玄武岩形成于班公湖—怒江结合带中段的洋内弧,是adakite熔体交代的地幔楔橄榄岩部分熔融的产物,其源区处于石榴石—尖晶石稳定域,作用深度60~100 km。蓬错富铌玄武岩的发现和厘定,表明班公湖—怒江带中段在中—晚侏罗世经历了洋内俯冲消减过程,揭示了自北向南的洋内俯冲极性,也暗示了班公湖—怒江结合带多次俯冲改造的复杂性。The systematical study of petrochemistry and geochemistry indicates the occurrence of Nb-enriched basalt in the area of Pengcuo,Tibet.With SiO 2 contents of 45.84%~55.88%,TiO 2 contents of 1.05%~3.25%,are similar to Nb-enriched basalts from Archaen Wawa greenstone belt in Superior Province,Canada.and Na 2O contents of 0.92%~5.10%,P 2O 5 contents of 0.23%~1.19%,are similar to Nb-enriched basalt in the Cenozoic era.The REE patterns are of LREE enrichment with weak Eu anomalies,suggesting obvious fractionation.Moreover,they are characterized by obviously negative Nb anomalies and negative Ta and Ti anomalies.The geochemical characteristics of trace elements showed that the Nb-enriched basalt in Pengcuo formed within the intra-oceanic arc in the central part of the Bangong Co-Nujiang River suture zon,were probably derived from partial melting of mantle peridotie.The source region is in the stable field of garnet-spinel,reaching the depth of 60~100 km.The discovery and confirmation of the Nb-enriched basalt in Pengcuo revealed that the central part of the Bangong Co-Nujiang River suture zon had experienced the intra oceanic subduction with the polarity from north to south,and imply the complexity of the multiple subduction transformation.

关 键 词：富铌玄武岩 地球化学 班公湖-怒江带中段 洋内俯冲 蓬错 班戈县 西藏 

分 类 号：P581[天文地球—岩石学] P591[天文地球—地质学]