新疆西天山阿克秋白地区火山岩岩石地球化学特征

Geochemical Characteristics of the Volcanic Rocks in Akeqiubai Area in Western Tianshan Area in Xinjiang

新疆西天山地区进入板块碰撞—板内伸展阶段,由于深源岩浆侵位,在阿克秋白地区形成了由英安斑岩、凝灰熔岩及含角砾晶屑凝灰岩组成的火山机构,并导致铀-钼矿床的形成。在分析西天山阿克秋白地区火山岩分布特征的基础上,结合区内英安斑岩和凝灰熔岩取样分析结果,分析了火山岩岩石地球化学特征及微量元素地球化学特征。研究表明:(1)按照岩石演化顺序,区内所分布的英安斑岩、凝灰熔岩的SiO_2含量由63.39%增加至77.46%,Al_2O_3含量显著下降,K_2O含量由2.63%升高至6.17%,Fe_2O_3、MgO、CaO含量都有不同程度的升高,据此判断,英安斑岩和凝灰熔岩均属于钙碱性系列;(2)英安斑岩、凝灰熔岩的Pb、U、W、Sn、Mo、Bi、As丰度均较高,早期的凝灰熔岩微量元素的丰度值低于相对晚期的英安斑岩,从而表明岩浆的不断分异演化和后期地壳物质的加入,导致相关元素的富集;(3)英安斑岩、凝灰熔岩的源区物质组成较接近,稀土元素的含量变化特征完全符合岩浆演化规律,微量元素、稀土元素的分布特征表明,从凝灰熔岩到英安斑岩,岩石具有较显著的分异演化特征和较好的继承性。分析结果对于该区进一步开展铀矿找矿工作有一定的参考价值。

The western Tianshan area in Xinjiang is entered into plate collision-intraplate extension stage,due to the emplacement of deep source magma,the volcanic mechanism composed of dacite porphyry,tuff lava,chip containing breccia crystal tuff is formed in Akeqiubai area,besides that the uranium-molybdenum deposit is also formed. Based on analyzing the distribution characteristics of volcanic rocks in Akeqiubai area in western Tianshan area in Xinjiang,combing with the analysis results of the samples of dacite porphyry and tuff lava of the area,the rock geochemical characteristics and the geochemical characteristics of the trace elements of volcanic rocks are discussed in depth. The study results show that：（1）according to the rock evolution sequence,the contents the of dacite porphyry and tuff lava are changed obviously,to be specific,contents of SiO_2 is increased from 63. 39% to 77. 46%,contents of Al_2O_3 is lowered significantly,contents of K_2O is increased from 2. 63% to 6. 17%,contents of Fe_2O_3、MgO、CaO are increased in different degree,so,it is indicated that the dacite porphyry and tuff lava are belongs to the calcium alkali series rocks;（2）contents of Pb、U、W、Sn、Mo、Bi、As of dacite porphyry and tuff lava are both high,the rare elements contents of the early stage dacite porphyry are lower than that of the relative later tuff lava,it is indicated that the enrichment of the relative rare elements is conducted under the condition of magmatic differentiation evolution and addition of late crustal materials;（3）the material composition of source areas of dacite porphyry and tuff lava are close with each other,the change characteristics of rare earth elements are completely in conformity with magma evolution regularities,the contents distribution of rare elements and rare earth elements of dacite porphyry and tuff lava show that the differential evolution characteristics and good inheritance of dacite porphyry and tuff lava are significant. The above analysis results in this paper can provide some reference for the further prospecting work of uranium deposit in the area.