滇西洱海北部北衙地区富碱斑岩的地球化学、锆石SHRIMPU-Pb定年及成因  

Geochemistry, zircon SHRIMP U-Pb dating and origin of alkali-rich porphyries in Beiya area,north Erhai Lake,western Yunnan,China

作　　者：肖晓牛[1] 喻学惠[1] 莫宣学[1] 杨贵来[1,2] 李勇[1] 黄行凯[1] 

机构地区：[1]中国地质大学北京/地质过程与矿产资源国家重点实验室/岩石圈构造、深部过程及探测技术教育部重点实验室,100083 [2]云南省地矿资源股份有限公司,云南昆明650215

出　　处：《地质通报》2009年第12期1786-1803,共18页Geological Bulletin of China

基　　金：国家重点基础研发发展规划项目(编号:2004CB412603)资助

摘　　要：用SHRIMP锆石U-Pb测年法获得滇西北衙地区炭窑石英正长斑岩的年龄TY-1为31.5 Ma±1.1Ma,TY-3为31.34Ma±0.73Ma,证明该斑岩形成于新生代。北衙富碱斑岩具有富碱、高钾的特点,总体属于钾玄岩系列的岩石。岩石富轻稀土和Rb、Ba等大离子亲石元素而亏损Nd、Ta等高场强元素。岩石的∑LREE/∑HREE比值和(La/Yb)N比值高,Eu异常不明显。综合北衙地区富碱侵入岩的常量、微量、稀土元素和同位素地球化学特征发现,富碱斑岩具有许多与埃达克岩(adakite)相似的岩石地球化学特征,但又与Defant等定义的典型埃达克岩有明显的差别,而与中国可可西里钾质埃达克岩更为接近。通过对北衙地区富碱斑岩的Sr、Nd、Pb同位素的系统研究发现,富碱斑岩的源区具有EMⅡ富集地幔的地球化学特征。In this paper SHRIMP U-Pb ages,TY-1 （31.5±1.1Ma）,TY-3 （31.34±0.73 Ma） of Tanyao quartz syenite porphyries in Beiya are published for the first time, which suggest that the intrusions are formed in Cenozoic. The results show that alkali-rich porphyries in Beiya are characterized by enrichment in alkaline and potassium. They are high in LREE and LILE （such as Rb,Ba etc.）, with depletion of HFSE（such as Nd、Ta etc.）, high ∑ LREE/∑ HREE and （La/Yb）N ratios, and lack of apparent Eu anomalies. Based on the characteristics of major elements, trace elements, REE, and isotope geochemistry of alkali-rich intrusion in Beiya area, we＇ve concluded that they have many similar petrological and geochemical characteristics to adakites, but are quite different from those of typical features of adakite defined by Defant and Drummond （1990）, which are more close to those adakites in Hoh Xil Area. Systematical studies on Sr、Nd、Pb isotopic characteristics in this paper found out that the source region of the alkali-rich porphyries have the typical geochemical characteristics of EM Ⅱ enriched mande.

关 键 词：锆石SHRIMPU-PB年龄 钾玄岩 埃达克岩 Sr、Nd、Pb同位素 起源和成因 

分 类 号：P588.13[天文地球—岩石学] P595[天文地球—地质学]