河北风化店中生代火山岩的地球化学特征及其成因探讨  

Discussion on the Origin and Geochemical Characteristics of the Mesozoic Volcanic Sequences in Fenghuadian Area,Hebei Province

作　　者：罗静兰[1] 高知云[1] 

机构地区：[1]西北大学地质系

出　　处：《岩石学报》1998年第1期108-116,共9页Acta Petrologica Sinica

摘　　要：河北风化店中生代火山岩主要为钙碱性到偏碱性的流纹英安岩－流纹岩－碱流岩及少量碱性粗面岩和石英粗面岩。岩石全碱含量高，平均９．２５％，大部分岩石的Ｋ２Ｏ／Ｎａ２Ｏ＞１，Ｆｅ２Ｏ３／ＦｅＯ比值大，ＴｉＯ２含量低，以富集大离子亲石元素（ＬＩＬＥ）和贫高场强元素（ＨＦＳＥ）及贫亲铁元素为特征。稀土元素配分型式表现为轻稀土富集并具Ｅｕ弱负异常。（８７Ｓｒ／８６Ｓｒ）初始比和（１４３Ｎｄ／１４４Ｎｄ）初始比分别为０．７０５４和０．５１１５，εＮｄ（ｔ）为－１８．２。所有这些特征均表明该区火山岩的物源来自地壳硅铝层的重熔并有消减带物质及幔源物质的加入。该火山岩形成于中生代时期中国东部活动大陆边缘挤压作用向引张作用转变前的挤压应力环境，是较成熟火山孤后拉张前的产物。An intensive volcanic activity took place in Fenghuadian area during Mesozoic era. The volcanic activity can be divided into three to four eruption cycles and each with the begining of intensive eruption (with the characterisitics of pyroclastic breccias), followed by effusive eruption (mainly lava) and ended with the volcanic sedimentary facies (tuff and sedimentary tuff rocks). The volcanic rocks mainly consist of calc alkaline rocks such as rhyodacite rhyolites、 alkaline rhyolites as well as a small amount of alkaline rocks of quartz trachytes. The characteristics of this volcanic sequence are : low TiO 2 and silica saturation, high alkalis with 9 25% on the average, high K 2O/Na 2O value and Fe 2O 3/FeO value, enrichment in large ion lithophile elements (K、Ba、Rb、Th and LREE) and lean in high field strength elements (Ti、Y、Ta、Yb、Nb and HREE) as well as siderophile elements (Co、Ni、V、Cr). The REE pattern is characterized by rightward declined V shaped curves with slight negative Eu anomalies. The initial ( 87 Sr/ 86 Sr) and( 143 Nd/ 144 Nd) ratios are 0 7054 and 0 5115,respectively, ε Nd(t) =-18 2. All these features indicate that the primary magmas of this volcanic sequence were mainly derived from remelting of the silic crust with some materials from the mantle and subduction zone.According to the analyses of geochemical features and geodynamic situation it is considered that they were produced in the compressional stress setting in the active continental margin of East China before the transition stage from compresssion to extension during Mesozoic Period when Pacific plate subducted toward the Eurasian plate. They were products in a mature volcanic arc before extension.

关 键 词：火山岩 地球化学 构造环境 风化店 

分 类 号：P588.14[天文地球—岩石学]