新疆西南天山小哈拉军山辉长岩体岩石学及地球化学研究

Petrologic and geochemical research of Xiaohalajunshan gabbro in Southwest Tianshan Mts.,Xinjiang.

出露于西南天山特克斯县东南的小哈拉军山辉长岩体主要由角闪辉长岩和含磁铁矿辉长岩组成。角闪辉长岩主要由单斜辉石、角闪石和斜长石组成;含磁铁矿辉长岩主要由斜长石和磁铁矿组成。这两类岩石都含少量方解石。这些方解石均呈独立矿物出现,且与长石、单斜辉石或黑云母平衡共生。这些方解石是原生碳酸盐矿物(不是后期热液蚀变的产物)。两类岩石属于钙碱性系列,富集轻稀土元素,亏损重稀土元素,轻重稀土之间的分异比较明显,但不显示Eu异常。辉长岩相对富集大离子亲石元素而亏损高场强元素。岩石学和地球化学研究表明,小哈拉军山辉长岩是碳酸盐化地幔极低程度部分熔融的产物,斜长石堆晶过程对岩浆演化起重要作用。

Xiaohalajunshan gabbro,consisting of hornblende gabbro and magnetite-bearing gabbro,intruded into Carboniferous volcanic-sedimentary rocks in southeast Tekesi city.The hornblende gabrro comprises clinopyroxene,hornblende and plagioclase.The magnetite-bearing gabbro mainly comprises plagioclase and magnetite.All these rocks contain magmatic calcite,which is in equilibrium with plagioclase,clinopyroxene and/or biotite.The studied gabbro samples show enrichments of light rare earth elements and depletions of heavy rare earth elements without obvious Eu anomalies.These rocks are also enriched in large ion lithophile elements and depleted in high strength field elements.Petrology and geochemical characteristics suggest that the magma was produced by the partial melting of carbonated mantle in very low degree.