大兴安岭哈达陶勒盖组火山岩年龄、地球化学特征及其陆缘弧构造背景

根据野外调查,将大兴安岭北段新巴尔虎右旗地区的一套火山岩归属为哈达陶勒盖组。通过SHRIMP锆石U-Pb测年,获得哈达陶勒盖组绿帘石化安山岩的年龄加权平均值为(254.3±7.9)Ma(MSWD=4.7),结合区域地层对比,将该组的形成时代置于早三叠世。根据元素地球化学分析,可将哈达陶勒盖组火山岩划分为中基性和酸性火山岩两类。其中,中基性火山岩岩浆可能来源于受俯冲作用影响的岩石圈地幔,并遭受到地壳物质的混染;而酸性火山岩岩浆则形成于地壳。结合区域地质特征,通过构造环境判别,该组火山岩的形成可能与蒙古—鄂霍茨克板块向南俯冲引起的陆缘弧背景密切相关。哈达陶勒盖组的厘定丰富了大兴安岭北段地层层序,也为大兴安岭地区区域构造演化和岩浆活动提供了证据。

Zircon age and geochemical characteristics of Hadataolegai Formation volcanic rocks in Da Hinggan Mountains and its continental marginal arc setting

A series of volcanic rocks, such as basalt, andesite and rhyolite, were determined in Xin Barag Right Banner of northern Da Hinggan Mountains. Geological survey reveals that these volcanic rocks should be assigned to Hadataolegai Formation. SHRIMP zircon U-Pb dating indicates that the epidotized andesite from Hadataolegai Formation was formed at(254.3±7.9)Ma(MSWD=4.7). According to geochemical researches, these volcanic rocks of Hadataolegai Formation can be divided into two types, i.e., intermediate-basic rocks and acidic rocks. The magma of intermediate-basic rocks was derived from the lithospheric mantle affected by the southward subduction of Mongolia-Okhotsk plate. The acidic volcanic rocks have a crustal-derived magma source features. Based on tectonic setting analysis, the authors hold that the Hadataolegai Formation volcanic rocks were formed under the continental marginal arc environment and related to southward subduction of Mongolia-Okhotsk plate. The determination of Hadataolgegai Formation improves the stratigraphic sequence of northern Da Hinggan Mountains and provides a favorable evidence for regional tectonic evolution of Da Hinggan Mountains.