东昆仑东段青海战红山地区早三叠世火山岩的发现及其地质意义

The discovery of Early Triassic volcanic rocks in Zhanhongshan area of Qinghai Province in the eastern section of East Kunlun Mountain and its geological significance

在东昆仑东段都兰县沟里乡战红山地区开展1∶2.5万区域地质矿产调查工作时,新填绘出一套早三叠世火山岩地层,主要为一套酸性火山岩局部夹灰岩组合,具海相喷发特点。火山岩主量元素显示为弱过铝质中钾-高钾钙碱性系列岩石,轻稀土元素富集、重稀土元素亏损,Eu中等负异常。大离子亲石元素K、Rb、Ba、Th富集,高场强元素Ti、Nb、Ta等亏损,构造环境显示具有岛弧火山岩特征。通过LA-ICP-MS方法获得流纹岩锆石U-Pb年龄为244.1±1.8 Ma,认为该套火山岩形成于早三叠世。结合东昆仑区域构造演化,认为战红山地区酸性火山岩地层是与东昆仑东段同时期大规模岛弧型花岗岩配套的弧火山岩,为早三叠世阿尼玛卿古特提斯洋向北俯冲阶段岩浆活动的产物,是继东昆仑中段晚二叠世大灶火沟组的发现与建组之后,在东昆仑地区晚二叠世—早三叠世存在火山活动的又一力证。

During 1∶25000 regional geological and mineral resources survey in Zhanhongshan area of Gouli Township,Dulan Country,Eastern Kunlun Mountain,conducted by the authors,a set of Early Triassic volcanic rocks was mapped.The rocks consist mainly of a set of acidic volcanic rocks with local limestone assemblage,characterized by marine eruption.The main elements of volcanic rocks suggest weakly peraluminous rocks such as medium-K to high-K calc-alkaline series,assuming LREE-enriched pattern.The REE distribution pattern shows medium Eu anomaly,enrichment of LILE K,Rb,Ba and Th and depletion of HFSE Ti,Nb and Ta.The tectonic environment shows characteristics of island arc volcanic rocks.The zircon LA-ICP-MS U-Pb age of rhyolite is 244.1±1.8 Ma.It is believed that the volcanic rocks were formed in the Early Triassic.Combined with regional tectonic evolution of East Kunlun,it is considered that the acidic volcanic rocks in the Zhanhongshan area were associated with large-scale island-arc granites in the eastern part of East Kunlun,and they were formed by magmatic activity during the northward subduction of the Early Triassic in Animaqin of Paleo-Tethys Ocean.It seems to be a fine example of volcanic activity during the Late Permian to Early Triassic in the East Kunlun area after the discovery and establishment of the Late Permian Dazaohuo Formation in the middle part of the East Kunlun Mountain.