大兴安岭中南段下二叠统寿山沟组典型泥岩地球化学特征及其地质意义

TYPICAL MUDSTONE OF THE LOWER PERMIAN SHOUSHANGOU FORMATION IN MIDDLE-SOUTH DAXINGANLING MOUNTAINS:Geochemical Characteristics and Geological Implications

西乌珠穆沁旗地区下二叠统寿山沟组泥岩为大兴安岭中南段发育的较好烃源岩.通过对寿山沟组泥岩中的主量、微量、稀土元素特征的分析,深入剖析了寿山沟组的物源、构造背景及其风化作用.岩石样品ICV值分布于1.15～1.57,平均值为1.33,认为样品基本未受到二次成岩作用影响.通过A-CN-K三角图判断寿山沟组泥岩受到一定的钾交代作用,经过校正得到CIA_(corr)值为54.28～70.06,平均值为65.33,表明物源区经历了初等—中等的化学风化作用.通过主量-微量元素多变量物源区环境分析,认为寿山沟组泥质沉积物主要来源于长英质物源区,且混有少量铁镁质火山岩源区物质,其构造背景为大陆岛弧.综合分析认为,大兴安岭中南段下二叠统寿山沟组泥岩的沉积特征归因于古亚洲洋二叠纪初期洋壳的俯冲作用.

The mudstones of Lower Permian Shoushangou Formation in Xi Ujimqin Qi of Inner Mongolia are well-developed source rocks in middle-south Daxinganling Mountains. With study on the characteristics of major, trace and rare earth elements in the mudstones, the paper analyzes the provenance, tectonic setting and weathering of Shoushangou Formation in depth. The ICV values of rock samples ranging from 1.15 to 1.57(averagely 1.33) show that the samples are basically not affected by secondary diagenesis. According to the A-CN-K triangular diagram, the mudstones are subjected to certain K-metasomatism. The CIAcorr values of 54.28-70.06 (averagely 65.33) are gained after correction, indicating the provenance has experienced primary-moderate weathering. Based on the analysis on the multivariable environment of major and trace elements, it is concluded that the argillaceous sediments of Shoushangou Formation are mainly derived from the felsic provenance, mixed with minus materials from the femic volcanic rock provenance, under the tectonic background of continental island arc. From the above, it is thought that the sedimentary features of the mudstones in the study area are attributed to the subduction of the Paleo-Asian Oceanic crust in early Permian.