西天山吐拉苏盆地大哈拉军山组火山岩地球化学特征及构造意义

吐拉苏盆地大哈拉军山组由两组火山岩组成,一组为玄武安山岩、安山岩,SiO2含量介于54.8%～59.4%之间,另一组为流纹岩,SiO2含量为70.6% ～74.1%,两组岩石具有相似的稀土和微量元素分配型式,均富集U、Th、K、Pb,而亏损Nb、Ta和Ti,同时两组岩石的一些微量元素对比值基本一致,表明流纹岩是本区玄武...

Geochemical Characteristics of the Dahalajunshan Formation Volcanic Rocks in the Tulasu Basin of Western Tianshan and its Tectonic Implications

The volcanic rocks of the Dahalajunshan Formation in the Tulasu basin are mainly composed of two groups.One group of the volcanic rocks is basaltic andesite and andesite,with SiO2 contents ranging from 54.8% to 59.4%,while the other group is rhyolite,with SiO2 contents between 70.6% and 74.1%.These two group rocks share similar REE patterns,enriched in U,Th,K,Pb,and depleted in Nb,Ta and Ti.Moreover,the two groups have similar Nb/Ta,Th/Ta,Ce/Nb,Zr/Hf ratios,which indicates that the rhyolite was formed through crystallization differentiation of the andesitic magma.The magma might have been derived from partial melting of the metasomatized mantle wedge and contaminated by the overlying crust during ascend.Considering the petrogeochemical characteristics and the regional tectonic evolution when the Dahalajunshan Group was formed,we believe that the Dahalajunshan Group in the Tulasu basin was formed in a back-arc basin.