阿尔金山前东坪花岗岩成因及其构造环境研究

The Petrogenesis and Tectonic Environment of the Dongping Granite in South Frontier of the Altyn Mountains

为探讨阿尔金山前东坪基岩花岗岩的岩石成因类型和构造演化背景,对东坪花岗岩进行了岩石学和元素地球化学研究。结果表明,东坪花岗岩体富硅（SiO2均值为71.4%）、富铝（Al2O3均值为13.57%）,其碱度率A.R.值为2.23~3.19,铝饱和指数A/CNK大于1.44,属于过铝质的高钾钙碱性花岗岩;其富集大离子亲石元素、亏损高场强元素,稀土配分模式属于中等右倾型,铕负异常（δEu为0.44~0.61）,轻稀土富集。其岩石成因类型为S型花岗岩,源自地壳杂砂岩重熔,没有地幔物质参与或参与较少。东坪花岗质岩浆侵入活动发育在加里东晚期的岛弧环境,指示南阿尔金山前地区存在大陆边缘的沟-弧-盆体系,其原岩形成于塔里木向柴达木地块的俯冲及碰撞演化背景。

In order to probe the petrogenesis and tectonic setting of the Dongping granite batholith in south frontier of the Altyn Mountains,studies on petrological and elemental geochemical characteristics of the Dongping granite have been carried out in this paper. The results show that the Dongping granite is characterized with rich silica（ average Si O2 content of71. 4%） and aluminum（ average Al2 O3 content of 13. 57%）,AR（ alkalinity rate） values of 2. 23-3. 19,and high aluminum saturation indexes（ A/CNK values〉1. 44）,indicating that it belongs to peraluminous and high potassium calc-alkaline granite. It is enriched in LILEs and depleted in HFSEs,with moderate right-declined REE patterns,negative Eu anomalies（ δEu of 0. 44-0. 61）,and the characteristic of LREEs enrichment. The Dongping granite belongs to the S-type granite,which was derived from the re-melting of greywacke in crust,with involvement of none or little mantle material.It is assumed that the magmatic intrusion of the Dongping granite occurred in the island-arc setting in Late Caledonian period,indicating the existence of trench-arc-basin system in south frontier of the Altyn mountains. It is believed that the Dongping granite was formed in the evolution background of the subduction and collision of the Tarim terrain to the Qaidam terrain.