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西天山特克斯县东南一带的大哈拉军山组中性火山岩具有钙碱性火山岩的地球化学特征,在TAS上多数属于玄武安山岩、安山岩,少数为粗安岩。岩石总体反映高硅低钛、富钠低钾特点,w(SiO2)≥54.18%,w(TiO2)≥0.89%,全碱w(K2O+Na2O)≥4.19%,Na2O/K2O≥1.40%。其地球化学的显著特点是:富集大离子亲石元素(Rb,Th,K等)和轻稀土元素(LREE),亏损高场强元素(Nb,Ti等)和重稀土元素(HREE),Eu负异常明显(δEu=0.39～0.78),与岛弧钙碱性火山岩相似。火山岩具有较高的La/Nb值、Ba/Nb值(1.74～2.77,24.03～59.43)和低La/Ba值(0.038～0.092)。Th/Ta,Nb/Ta和Zr/Hf值分别为2.06～17.38,3.35～13.41和37.94～45.02。元素地球化学特征反映岩浆源区具有富集型地幔岩浆源区的特征。其成因可能是受到地壳物质混染和来自消减残留板片析出流体或熔体交代的双重改造。
The Middle-Halajunshan Formation neutral volcanic rocks in the southeastern part of the western Tianshan Mountains have geochemical characteristics of calc-alkaline volcanic rocks. Most of the TAS belonged to basaltic andesite and andesite, while a few of them are coarse-grained rocks. The rock generally reflects the features of high silicon and low titanium, rich in sodium and low potassium, w (SiO2) ≥54.18%, w (TiO2) ≥0.89%, K2O + Na2O≥4.19% and Na2O / K2O≥1.40%. Its geochemical characteristics are: enrichment of large ion lithophile elements (Rb, Th, K, etc.) and LREE, depleted high field strength elements (Nb, Ti, etc.) and heavy rare earth elements (HREE) Eu negative anomaly (δEu = 0.39 ~ 0.78), similar to the island arc calc-alkaline volcanic rocks. Volcanic rocks have higher La / Nb values, Ba / Nb values (1.74 ~ 2.77, 24.03 ~ 59.43) and low La / Ba values (0.038 ~ 0.092). The values of Th / Ta, Nb / Ta and Zr / Hf were 2.06-17.38, 3.35-13.41 and 37.94-45.02, respectively. The elemental geochemical characteristics reflect the characteristics of the mantle magmatic source area in the magma source area. The cause may be due to the contamination of the crustal material and the dual remodeling of fluid or melt from the elimination of residual plate deposition fluid.