内蒙古宝音图隆起地区早白垩世玄武质火山岩地球化学特征及其意义  

Geochemical Characteristics of Early Cretaceous Akali-Basalt in the Buyant Area,Inner Mongolia

作　　者：何付兵[1] 孙永华[1] 张磊[1] 张慧军[2] 徐吉祥[1] 崔一龙[3] 

机构地区：[1]北京市地质调查研究院,北京100193 [2]中国地质调查局发展研究中心,北京100037 [3]中国地质大学(北京)地球科学与资源学院,北京100083

出　　处：《矿物岩石地球化学通报》2013年第4期436-444,455,共10页Bulletin of Mineralogy, Petrology and Geochemistry

基　　金：中国地质调查局地质调查项目(2005-(2-13)-KD71)

摘　　要：野外路线地质调查和剖面测量发现,内蒙古宝音图隆起地区中新生代凹陷早白垩世白女洋盘组地层中发育多层玄武质火山岩,其呈夹层或脉状产出,主要岩性为玄武质粗面安山岩和粗面安山岩。岩石的SiO2、Al2O3含量分别为45.75%～55.88%和16%～17%,全碱含量(K2O+Na2O)>6.48,MgO和Mg#含量为3.08%～5.3%和51.53～61.35;富集Rb、Ba、K等大离子亲石元素(LILE),亏损Ta、Nb、Hf、Ti高场强元素(HFSE),稀土元素球粒陨石标准化图表现为轻稀土弱富集、铕弱负异常右倾型。火山岩主、微量特征显示其属于大陆碱性玄武岩系列,岩浆演化表现为橄榄石和斜长石的同时分离结晶作用,未经历岩浆混染和岩浆混合作用。而其形成的大地构造背景为大陆板内环境,火山岩是华北板块北缘早白垩世岩石圈减薄减压、地幔上涌并引起其下部软流圈地幔低程度部分熔融后沿构造脆弱带喷发的产物。According to field geological surveys and profile measurements,the abundant basaltic volcanic rocks,whose occurrences are mainly veins or clips,in the Bainvyangpan depression formation in the Buyant area,Inner Mongolia,were formed in the Mesozoic,and the main types of these rocks are basaltic trachyandesite and trachandesite.The geochemical studies on these rocks revealed that： their contents of SiO2,Al2O3,MgO,Mg# range from 45.75% to 55.88%,16% to 17%,3.08% to 5.3%,and 51.53 to 61.35,respectively,and their total alkali（K2O＋Na2O） contents exceed 6.48.Their trace elements contents are characterized by enriching large-ion lithophile elements（LILE）,such as K,Rb and Ba,and depleting high field strength elements（HFSE）,such as Ta,Nb,Hf and Ti.The chondrite-normalized rare earth elements diagrams show right inclined smooth lines,slight enrichment of light REE and slight anomaly of Eu.The characteristics of the major and trace elements show these rocks belong to the typical continental alkalic basalt series.These above characteristics indicate that the most important magma evolution type of the early Cretaceous basalts in the Buyant area is fractional crystallization between olivine and plagioclase,with no effect of magma contamination and magma mixing.The basaltic volcanics were formed under the circumstance of continental intra-plate tectonic,and were the result of lithosphere thinning and pressure reducing,mantle upwelling and subsequently low degree partial melting of asthenosphere mantle.

关 键 词：内蒙古宝音图 白女洋盘组 岩石地球化学 岩浆演化 

分 类 号：P588.14[天文地球—岩石学]