准噶尔盆地腹部陆西地区二叠系-石炭系火山岩地球化学特征及构造背景分析

GEOCHEMICAL CHARACTERISTICS AND TECTONIC SETTING OF THE PERMIAN-CARBONIFEROUS VOLCANIC ROCKS IN LUXI AREA OF JUNGGAR BASIN

通过对准噶尔盆地腹部陆西地区基底二叠系佳木河组—石炭系107个火山岩样品的全岩元素分析表明,其中38.7%属钙碱性系列,碱性系和强碱性系列占61.3%。该区火山岩不仅在纵向上分异、演化特征明显,在平面上也存在明显的分区分带性。研究表明,陆西地区火山岩喷发的构造环境具有岛弧体系特征,同时由于火山岩的主量元素和微量元素均具有明显的大陆稳定构造区派生的碱性火山岩特征,说明其岩浆源深度较大,可能为上地幔或洋壳物质在高等选择性熔融条件下形成。因此盆地腹部陆西地区火山岩的喷发环境应该是在岛弧发展后期,属于岛弧近大陆一侧、在地壳增厚的环境下喷发。

The testing and analysis of 107 volcanic rock samples from Jiamuhe Formation of Permian-Carboniferous in the Luxi area in the central Junggar basin revealed that calc-alkaline series accounted for 38.7% and alkaline series made up of 61. 3%. The volcanic rocks in this region were not only characteristic of vertical partition and evolution, but also of horizontal zoning. It was suggested that the tectonic setting of these volcanic rock samples in the Luxi area belonged to island arc system. Moreover, major elements and trace elements of these samples were obviously characteristic of tectonic features of alkaline volcanic rocks on a steady continent, suggesting the magma formed at great depth where the uppermost mantle or oceanic crust matter was melted through high selectivity. Therefore, the tectonic environment of the volcanic rocks in the Luxi area occurred in the late stage development of island arc system near to the side of continent with a thickening crust condition.